This paper presents an experimental evaluation of network protocols for control and management of optical networks and optical network equipment as seen in current trends. This paper presents the YANG data modeling language and its associated RESTCONF/NETCONF protocols. Later, it details multiple data models used in optical networks, such as IETF TEAS, ONF Transport API, OpenROADM, and OpenConfig. It also presents multiple protocols for telemetry (i.e., YANG PUSH, gRPC, and gNMI). Later, a zero-touch SDN controller architecture for multiple standard-defining organizations (SDOs) is presented, to support the usage of multiple protocols in a zero-touch optical network. Finally, the presented protocol implementations are experimentally evaluated and compared in terms of latency and overhead. The paper explores the use of these protocols (e.g., in research, demonstrations, and open-source optical networking projects) and provides results and recommendations for their integration in equipment and networks. (C) 2021 Optical Society of America

We report the first experimental demonstration of transoceanic distance real-time transmission over coupled multicore fibers. The WDM DP-QPSK signals were transmitted over 7, 200-km coupled-core four-core fibers by a recirculating loop and demodulated by real-time MIMO DSP.

We implement an FPGA-based real-time MIMO-DSP for equalizing spatial modes and polarizations. With MIMO-DSP, we demonstrate real-time transmission over weakly coupled 10-mode fibers and strongly coupled 4-core fibers using WDM DP-QPSK signals.

Network operators are facing a critical issue on their optical transport networks to deploy 5G$+$+ and Internet of Things services. They need to address the capacity increase by a factor of 10, while keeping a similar cost per user. Over the past years, network operators have been working on the optical disaggregated approach with great interest for achieving the required efficiency and cost reduction. In particular, partially disaggregated optical networks make it possible to decouple the transponders from the transport system (known as an open line system) that are provided by different vendors. On the other hand, space division multiplexing (SDM) has been proposed as the key technology to overcome the capacity crunch that the optical standard single-mode fibers are facing to support the forecasted $10 \times$10× growth. Spatial core switching is gaining interest because it makes it possible to deploy SDM networks to bypass the overloaded wavelength division multiplexing (WDM) networks, by provisioning spatial media channels between WDM nodes. This paper presents, to the best of our knowledge, the first experimental demonstration of transport-application-programming-interface-enabled software defined networking control architecture for partially disaggregated multi-domain and multi-layer (WDM over SDM) optical networks.

We adopted probabilistic shaping (PS) to couple multicore fiber transmission to maximize the transmission capacity for the first time. By utilizing 152-WDM 24-Gbaud DP-PS-16QAM signals, 85.2-Tbit/s coupled four-core fiber transmission over 3,120 km was demonstrated.

We provide an overview of SDN control architectures for WDM over SDM (WDMoSDM) optical networks. We address dynamic management of end-to-end connectivity services and WDM virtual network topologies (VNTs) for partially disaggregated multi-domain WDMoSDM networks.

We present the dynamic deployment of logical WDM VNTs by deploying virtual links between ROADM/OXC nodes using spatial channels provided by SDM networks. We propose a cloud-native WDM over SDM (WDMoSDM) SDN orchestrator that is responsible for the lifecycle management of the SDN-enabled WDM VNTs.

We present a cloud-native architecture with a machine learning QoT predictor that enables cognitive functions in transport SDN controllers. We evaluate the QoT predictor training and auto-scaling capabilities in a real WDM/SDM testbed. (c) 2021 The Author(s)

50.47-Tbit/s transpacific coupled multi-core fiber transmission has been experimentally demonstrated using standard cladding ultra-low-loss coupled 4-core fibers. The Q-factors of all SDM/WDM channels modulated with 24-Gbaud DP-QPSK exceeded the assumed FEC limits after 9,150-km transmission. (C) 2021 The Author(s)

This paper presents novel extensions for Cloud-native SDN controller for partially disaggregated optical networks that allow real-time monitoring of optical transponders. New SDN controller components are presented, as well as overall architecture. Evaluation is performed with gNMI enabled OpenConfig transceivers.

This paper presents an overview of current trends in network protocols for control and management of optical networks and optical network equipment. The paper explores the usage of these protocols in open source optical networking projects.

For weakly coupled mode-division multiplexed (MDM) transmission systems, we design and implement optical coherent receiver prototypes with real-time multiple-input multiple-output (MIMO) digital signal processing to equalize two degenerate linearly polarized modes with dual polarization. Using field programmable gate array circuits, we implement real-value 8 x 2 MIMO adaptive equalization with externally separated phase compensators based on the least mean square algorithm, which enables not only training equalization but also fast carrier-phase tracking. With the optical coherent MIMO receiver prototype, we demonstrate real-time weakly coupled 10 x MDM wavelength-division multiplexed dual-polarization quadrature phase shift keying transmission over 48-km few-mode fibers. This report shows a record number of multiplexed spatial modes, namely, 10 modes with dual polarization, in real-time MDM transmission experiments. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

The mode-division-multiplexing (MDM) transmission technique using a few-mode fiber (FMF) has been investigated to overcome the theoretical limitation of the transmission capacity of a single-mode fiber. In MDM transmission, multiple-input multiple-output (MIMO) digital signal processing (DSP) is generally required on the receiver side to compensate for the modal crosstalk (XT) between the spatial modes. However, the computational cost is high, especially for high-order MDM systems that use many spatial modes. To reduce the MIMO matrix size, MDM transmission with partial MIMO-based DSP has been proposed using weakly coupled FMFs. The modal XT in such fibers can be suppressed by a special fiber design; however, the modal XT still remains and strongly limits the signal-to-noise-ratio (SNR) and capacity. To further increase the capacity for a given SNR, an optimization of the modulation format is significant. Recently, probabilistic shaping (PS) has received attention since it can gradually change the entropy of a modulation format and maximize the capacity for a given SNR. In this article, we demonstrate weakly coupled 10-mode-multiplexed transmission with four 4 x 4 MIMOs and two 2 x 2 MIMOs using rate-adaptive PS-16QAM signals over 48-km FMF, achieving a record transmission capacity of 402.7 Tb/s in 125-mu m cladding single-core fiber transmission experiments. Furthermore, we also show the possibility of a further capacity increase by adjusting the entropies of the PS-16QAM signals depending on the spatial mode.

We show a real-time optical coherent MIMO receiver for 4-mode division multiplexed transmission. With the receiver, we demonstrate real-time strongly-coupled 4-core fiber transmission of WDM DP-QPSK signals over 60 km.

We experimentally verify the nonlinear compensation gain of digital back propagation in ultra long-haul 4-core fibre transmissions over 6020 km. The gain was 1.1 dB in the uncoupled core transmission. By contrast, this gain was not observed in the coupled core transmission with spatial modal dispersion.

We present the first SDN-enabled multi-domain multi-layer (WDM/SDM) control architecture for partially disaggregated optical networks with multiple WDM and SDM OLS domains and transponders to provision end-to-end TAPI connectivity services involving spatial and optical channels. (C) 2020 The Author(s)

We compared the ultra-long-haul multi-core fibre (MCF) transmission performance of standard cladding ultra-low-loss uncoupled and coupled 4-core fibres. From the results obtained, 15,652-km transmission in uncoupled MCF and 16,856-km transmission in coupled MCF was demonstrated using a centre channel of 16-WDM 24-Gbaud DP-QPSK signals.

Recent progress on ultra-high capacity, space division multiplexed optical transmission is reviewed. The highest capacity of 10.16 Pbit/s has been achieved by using 19 core 6 mode fiber, and the highest capacity of 402.7 Tbit/s for multimode single core fiber has been demonstrated by using weakly-coupled 10 mode fiber with a standard cladding diameter.

Space division multiplexing (SDM) super-channels are the only way to guarantee a sustainable scaling of the optical line interface rate. High-capacity terabit interfaces can be deployed by logically associating several optical sub-channels transmitted in parallel in different spatial cores or modes in order to create an (logical) optical channel with the desired interface rate. This paper is focused on the use of spatial modes for SDM super-channels. First, we present a software defined networking (SDN)-controlled disaggregated SDM network architecture that deploys the proposed sliceable-mode transceivers with multiple-input multiple-output equalization. Then, we present the adaptive SDN workflow and heuristics for the provisioning, scaling up/down, and soft-failure restoration of SDM super-channels using spatial modes. Two proofs of concept are deployed in the joint testbed between KDDI Research and CTTC.

We present an SDM network and node architecture based on sliceable spatial-mode, spatial-core and spectral transceivers, and a centralized SDN controller with NETCONF and TAPI for the management of SDM super-channels by multiple NFVorchestrators.

We present an IoT-aware cloud and network orchestration architecture for multi-domain transport SDN networks and cloud/edge computing that deploys an IoT-traffic control and congestion avoidance mechanism for dynamic distribution of IoT analytics to the edge.

We propose a heuristic and experimentally demonstrate dynamic scaling up/down of SDM super-channels to increase/decrease the capacity by exploiting the spatial modes. We deploy mode-adaptive MIMO equalization and modulation format assignment controlled by SDN.

This paper presents the first experimental demonstration of gRPC-based SDN control and telemetry architecture for spectral/spatial super-channels with SDM/WDM transceivers that monitor the BER to detect soft-failures over an 11-km 6-mode 19-core fiber. An evaluation of possible SDN protocols is provided for the discussed scenario.

We demonstrate a weakly-coupled 10-mode-multiplexed transmission with four 4u4 and two 2u2 MIMOs using rate-adaptive probabilistically-shaped (PS) PDM-16QAM signals over 48-km step-index few-mode fibre, achieving a record transmission capacity of 402.7 Tb/s in 125-Pm cladding single-core fibre transmission experiments.

A field trial of high-density 0.92-km 200-fiber cable with 5-core fibers (5CFs) was conducted for reliability tests. No degradation of cable attenuation of 5CFs was observed even after installation into underground conduits and aerial area.

We implemented a two-hidden-layer dynamic complex deep neural network nonlinear equalizer which outperforms the linear equalizer, static and dynamic single hidden layer CDNN-NLE by 1.38-dB, 1.01-dB and 0.62-dB for a 34-GBaud/s, 64-QAM signal over 1200-km.

The combination of spatial division multiplexing (SDM) with flexi-grid wavelength division multiplexing (WDM) enables optical transceivers to provide super-channels that exploit the spectral and spatial dimensions. For the first time to the best of our knowledge, in this paper we extend SDM-WDM transceivers to support sliceability and make effective use of spatial and spectral resources. The proposed architecture provides multiple independent spectral-spatial super-channels (i.e., slices) sharing the same transceiver and exploiting different spectrum/core/mode resources. The proposed architecture also enables us to monitor the bit error rate of the provisioned slices in order to detect any signal-quality degradation due to the provisioning of additional slices. On the other hand, there is a general trend toward the disaggregation of optical networks. In this paper, we also propose the first open application program interface based on a YANG data model and NETCONF protocol for software-defined-networking-enabled sliceable SDM-WDM transceivers. The proposed transceiver is experimentally validated in a joint test bed between CTTC and KDDI research.

First experimental demonstration of an SDN monitoring and restoration architecture for spectral/spatial superchannels with SDM/WDM transceivers that monitor the BER/OSNR to detect soft failures and restore the degraded channels by reconfiguring the transmission formats over an 11-km 6-mode 19-core fiber.

This paper presents optical (SDM/WDM) and packet transport solutions for 5G fronthaul/backhaul and the hierarchical Transport SDN control and monitoring architecture. It dynamically provides multiple spectral-spatial super-channels and packet flows, and monitors the signal quality degradation of the optical super-channels and the aggregated packet traffic.

We demonstrate the first SDN-enabled sliceable SDM-WDM transceiver providing multiple spectral-spatial super-channels spanning different cores and modes over a 11-km 6-mode 19-core fiber. We define an open API based on YANG/NETCONF for disaggregated optical networks.

We show all-fiber-based six-mode multiplexer and demultiplexer. The OSNR penalty due to six-mode multiplexing is suppressed to be 2 dB in DP-16QAM with 12 12MIMO and 3 dB in DP-QPSK even with 4 4/2 2MIMO over C-band.

Space-division-multiplexing is a promising technology to increase a system capacity drastically and the highest capacity in a single optical fiber has reached to 10 Pbit/s recently. In this paper, we review 10.16 Pbit/s transmission experiment using 6-mode 19-core fiber.

Space-division multiplexing is a promising technology enabling significant growth of a fiber capacity. By using a combination of SDM and DWDM in C+L bands, the fiber capacity has recently reached to 10.16 Pbit/s.

This paper reviews recent progress on research of space division multiplexing (SDM) technology in Japan. Three multi-vendor SDM transmission trials, which have been conducted based on the four national projects since 2010, are summarized.

This paper reports our recent demonstrations of ultra-dense SDM transmission using C+L-band 739-WDM 12-Gbaud dual polarization- 64-quadrature amplitude modulation (QAM) / 16-QAM signals over 11.3-km 6-mode 19-core fiber. We achieve a record fiber capacity of 10.16 Pbit/s with an aggregate spectral efficiency of 1099.9 bit/s/Hz.

Partial multiple-input multiple-output (MIMO)based weakly coupled mode-division multiplexing (MDM) transmission is proposed to reduce the MIMO matrix size in MDM. This technique can mitigate the burden of MIMO processing for high-order few-mode fiber (FMF) transmission. In this paper, we first show that modal XT can be sufficiently suppressed over the C+L band using a weakly coupled FMF and a highly mode-selective multiplexer/demultiplexer. Next, 10-mode-multiplexed 336-WDM transmission of dual-carrier 12-Gbaud dual-polarization-quadrature phase-shift keying signals over a 48-km weakly coupled FMF using only 2 x 2 or 4 x 4 partial MIMOs is demonstrated. To the best of our knowledge, in this experiment, we achieved a record fiber capacity of 257 Tbps with an aggregate spectral efficiency of 30.5 bit/s/Hz in single-core fiber transmission.

We show all-fiber-based selective mode multiplexers and demultiplexers for weakly-coupled mode-division multiplexed systems. We fabricate a set of six-mode multiplexer and demultiplexer based on fiber mode selective couplers, and experimentally evaluate the performance for the six-mode dual-polarization (DP) quadrature phase shift keying (QPSK) optical signals. In the mode multiplexer and demultiplexer, the mode couplings between the lower three modes and the higher three modes are suppressed to be less than -20 dB, which enables us to apply partial 6x6 MIMO equalizers even for the six-mode demultiplexing. For the six-mode DP-QPSK signals, the penalty of optical signal-to-noise ratio by replacing the full 12x12MIMO to the partial 6x6 MIMO is suppressed by less than 1 dB. (C) 2017 Elsevier B.V. All rights reserved.

Space-division multiplexing (SDM) is an attractive technique for dramatically enhancing the transmission capacity in a single optical fiber. Recently, ultradense SDM transmission experiments with a spatial multiplicity of over 100 have been reported by using few mode multicore fibers (FM-MCFs). Considering the maximum capacity of around 100 Tb/s reported in single-mode single-core fiber transmission experiments, the capacity in FM-MCF transmission with more than 100 spatial channels is expected to reach 10 peta-b/s; however, the maximum capacity has been limited to 2 peta-b/s. In this paper, we demonstrate ultradense SDM transmission of 739 WDM 12-Gbd dual polarization-64-quadrature amplitude modulation (QAM)/16-QAM signals over 11.3-km 6-mode 19-core fiber using the C+L band, achieving a record fiber capacity of 10.16 peta-b/s with an aggregate spectral efficiency of 1099.9 b/s/Hz.

The metro-embedded datacenter (ME-DC) architecture which is based on micro-DCs (mDC) is introduced and implemented to deliver more flexible services with less access latency. Hierarchical SDN control is employed to adaptively interconnect the distributed mDCs and the metro network slices into re-configurable virtual DC (VDC). Such an approach improves the overall resource mobility, especially for traveling users that need to dynamically access the service. In this paper, the VDC re-configuration and pre-configuration mechanisms for dynamic user access are proposed and demonstrated for the first time. In specific, by re-configuring the VDC with the most accessible resources with user location tracking, fast and flexible service is provided with consistent service access. Furthermore, by pre-configuring the VDC with user prediction, mDC and metro network resources are reserved in advance for users in order to provide seamless service. Demonstration based on the implemented ME-DC prototype shows that VDC is adaptively constructed for dynamic user access with fast and flexible service provisioning.

Internet of Things (IoT) requires cloud infrastructures for data analysis (e.g., temperature monitoring, energy consumption measurement, etc.). Traditionally, cloud services have been implemented in large datacenters in the core network. Core cloud offers high-computational capacity with moderate response time, meeting the requirements of centralized services with low-delay demands. However, collecting information and bringing it into one core cloud infrastructure is not a long-term scalable solution, particularly as the volume of IoT devices and data is forecasted to explode. A scalable and efficient solution, both at the network and cloud level, is to distribute the IoT analytics between the core cloud and the edge of the network (e.g., first analytics on the edge cloud and the big data analytics on the core cloud). For an efficient distribution of IoT analytics and use of network resources, it requires to integrate the control of the transport networks (packet and optical) with the distributed edge and cloud resources in order to deploy dynamic and efficient IoT services. This paper presents and experimentally validates the first IoT-aware multilayer (packet/optical) transport software defined networking and edge/cloud orchestration architecture that deploys an IoT-traffic control and congestion avoidance mechanism for dynamic distribution of IoT processing to the edge of the network (i.e., edge computing) based on the actual network resource state.

A world record capacity 118.5 Tbit/s transmission through optical fiber with a 125 micron cladding diameter was achieved using a low loss and 316 km-long full space division multiplexing link incorporating multiple vendor technologies.

In super-Nyquist wavelength division multiplexed (WDM) systems with frequency spacing smaller than the signal baudrate, the maximum-likelihood (ML) decoder in the receiver is usually introduced to compensate for intersymbol interference due to tight spectral filtering, such as polybinary shaping. After the ML decoder, symbol errors tend to propagate, causing excess continuous errors. Considering that forward error correction (FEC) is commonly introduced, the excess continuous errors degrade bit-error ratio (BER) performance after FEC, so-called post-FEC BER. In order to suppress the performance degradation, we introduce iterative decoding between the first ML decoder for polybinary shaping and the second FEC decoder in the receiver. First, we calculate BER characteristics of polybinary-shaped super-Nyquist WDM quadrature phase-shift keying (QPSK) signals. The results show that iterative decoding is effective for improving post-FEC BER performance. A lager pre-FEC BER threshold for post-FEC BER < 10(-5) is obtained in super-Nyquist WDM case than in the Nyquist WDM case, although a higher signal-to-noise ratio (SNR) is required. Next, we measure the BER characteristics of three-channel duobinary-shaped super-Nyquist WDM 12.5-Gbaud dual-polarization QPSK signals. The iterative decoding reduces the optical SNR penalty by 0.8 dB. A larger pre-FEC BER threshold of 3.1 x 10(-2) is obtained in the duobinary-shaped super-Nyquist WDM case, compared with the threshold of 2.2 x 10(-2) in the Nyquist WDM case.

We present and experimentally assess the first IoT-aware SDN and cloud architecture that deploys IoT flow monitoring and traffic-congestion avoidance techniques in order to dynamically and efficiently distribute the processing of IoT analytics from core datacentres to the network edge.

Over 10 peta-bit/s transmission has been experimentally demonstrated for the first time using 11.3-km-length low-DMD 6-mode 19-core fibre across C+L band. Q-factors of all 84,246 SDM/WDM channels modulated with 12-Gbaud DP-64QAM/16QAM exceeded the assumed FEC limits.

Recent progress on space division multiplexed optical transmission is reviewed. 2.05 peta bit/s transmission with 114 spatial multiplecity, ultra-high aggregate spectral efficiency of 947 bit/s/Hz and long haul transmission over 6160km with 200 Gbit/s channel bit rate have been achieved.

This paper proposes the introduction of SDN-enabled containers to support the deployment of SDN/NEV applications located at the network edge, which are able to trigger on demand connectivity services. A video analytics use case is demonstrated.

This paper reviews recent progress on space-division multiplexed (SDM) transmission with focusing on aggregate spectral efficiency (SE) and discusses current issues with SDM transmission toward ultra-high SE.

Traditional data centers (DCs) that are located in distant areas usually lack flexibility and also have long service latency for metro users. On the other hand, the recently introduced and implemented metro-embedded data center (ME-DC) architecture, based on micro-data centers (mDCs), delivers more flexible services with less access latency. Hierarchical software-defined network control is employed to virtualize and holistically coordinate the distributed mDCs and metro network slices into a reconfigurable virtual data center. Such an approach improves the overall resource mobility and access to the service; however, the impact on the metro network traffic profile induced by user/mDC and inter-mDC connections due to the dispersion of mDCs has not been evaluated. In this paper, we develop a mixed integer linear programming model that optimizes the total DC traffic, taking into consideration the intra-, inter-, and external DC communications. Furthermore, we numerically assess the changes in the metro network traffic induced by ME-DC architecture, considering different types of DCs and their corresponding traffic profile. Simulation shows that the distribution of the mDCs has a beneficial effect, leading to a fourfold reduction in the total traffic load.

In the context of the fifth generation of mobile technology (5G), multiple technologies will converge into a unified end-to-end system. For this purpose, software defined networking (SDN) is proposed, as the control paradigm will integrate all network segments and heterogeneous optical and wireless network technologies together with massive storage and computing infrastructures. The control orchestration protocol is presented as a unified transport application programming interface solution for joint cloud/network orchestration, allowing interworking of heterogeneous control planes to provide provisioning and recovery of quality of service (QoS)-aware end-to-end services. End-to-end QoS is guaranteed by provisioning and restoration schemes, which are proposed for optical circuit/packet switching restoration bymeans of signalmonitoring and adaptivemodulation and adaptive route control, respectively. The proposed solution is experimentally demonstrated in an international multi-partner test bed, which consists of a multi-domain transport network comprising optical circuit switching and optical packet switching domains controlled by SDN/OpenFlow and Generalized Multiprotocol Label Switching (GMPLS) control planes and a distributed cloud infrastructure. The results show the dynamic provisioning of IT and network resources and recovery capabilities of the architecture.

The combination of software-defined networking (SDN) and optics, i.e., a software-defined optical network (SDON), offers combined benefits that include flexible SDN control and large optical transport capacity. In this paper, we introduce the unified SDN as a common control solution for end-to-end OCS/OPS networks, with the introduction of an additional network element, namely the OpenFlow agent. The SDN control plane is implemented in the OPS network for simplified data plane design, optimal network organization, and contention alleviation, as well as improved control flexibility and advanced handling of network dynamics. The SDON demonstration is conducted in the nationwide transport networks constructed with different technologies via various internetworking testbeds. Based on the SDON platform, we further introduce the service design concept for advanced network abstraction. The general network architecture based on a service design concept offering flexible, reconfigurable, and economical end-to-end (FREE) service features is described. This service design aims to provide customized service and maximum network freedom with virtualized and flexibly selected functionalities, while maintaining a moderate network configuration cost and promoting network innovation at the same time. Moreover, the service design concept could easily be extended to any layers and any network domains, thus providing the unified network abstraction ability and the end-to-end control solution. Based on the service design, control, coordinated, and orchestrated optical transmission is demonstrated by reconfiguring the virtualized optical functions. This type of approach to network abstraction is further exploited in the heterogeneous multidomain networks, where differentiated and featured service provisioning is demonstrated.

Conventional mega datacenter (DC) lacks flexibility and has poor service connectivity for users faraway. Therefore, the metro-embeded DC architecture has been introduced to deliver more reliable and flexible services with less access latency. For fine-grained all-optical switching ability and high bandwidth connection, optical burst switching (OBS) ring is deployed inside the micro-DCs (mDC) and OBS over wavelength switched optical network paradigm is used for inter-mDC communication. Meanwhile, hierarchical SDN control is employed to virtualize and holistically coordinate the distributed mDCs and the metro network slices into reconfigurable virtual DC (VDC). Optimal VDC provisioning based on an integer linear programming (ILP) formulation is also developed in the SDN control plane to provide services With minimum latency and traffic load. A dynamic VDC provisioning algorithm based on partial ILP is further Proposed to reconfigure the VDC with reduced complexity considering the user and resource dynamics. Experimental demonstrations conducted on the implemented metro-embedded DC prototype testbed show that optimal and fast VDC provisioning is realized based on the proposed ILP, while dynamic VDC reconfiguration makes sure that VDC is adjusted accordingly with the change of user location and resource requirement.

In this Paper, we experimentally demonstrate highly flexible and intelligent interdomain coordinated actions based on adaptive software-defined networking (SDN) orchestration. An advanced multidomain multitechnology testbed is implemented, which consists of a 400-Gb/s variable capacity optical packet switching domain and a Tb/s-class flexi-grid wavelength division multiplexed optical circuit switching domain. The SDN-controllable transponders and the extended transport applications programming interface enable the congestion-aware provisioning of end-to-end real-time services. At the data plane level, different transponders based on orthogonal frequency division multiplexing are employed for inter/intradomain links in order to adaptively provision services with fine granularity. For adaptation, SDN-capable domain-specific optical performance monitors are also introduced. In the control plane, the applications based network operations architecture has been extended and addressed as an adaptive SDN orchestrator.

A common Transport API is proposed for joint cloud/network orchestration, allowing interworking of heterogeneous control planes to provide provisioning/recovery of QoS-aware E2E services. We present its first demonstration in a multi-partner testbed including data-plane monitoring.

Cognitive SDN orchestration over 400-Gbps OPS and Tbps-class Flexi-WDM networks is demonstrated, where the SDN-controllable OFDM transponders and the extended transport API enable the congestion-aware provisioning of end-to-end real-time services.

This papers proposes the usage of Control Orchestration Protocol (COP) as an East-West interface in order to interconnect different SDN controllers (peer model) through multiple administrative domains. An experimental validation of network connectivity provisioning is presented in an international testbed.

In Super-Nyquist WDM systems, maximum likelihood decoder for duobinary shaping degrades the post-FEC BER performance. We experimentally confirm that degradation of post-FEC BER characteristics can be remarkably suppressed by introducing turbo equalization.

The unified SDN-enabled OCS/OPS network infrastructure is presented. Moreover, with function abstraction and virtualization based on the service design concept, orchestrated optical system control and customized service provisioning are realized in the software-defined optical networks.

We investigate turbo equalization with 20%-overhead turbo code for duobinary-shaped signals introduced in Super-Nyquist WDM systems. The turbo equalization can efficiently suppress the degradation of BER performance due to duobinary shaping.

Software-defined optical network has the combined benefit of both control flexibility and large transport capacity, thus having the potential of realizing a new ground-breaking optical network framework. In this paper, we introduce our recent efforts that have been devoted to the research supported by the STRAUSS project on SDN/Openflow controlled optical networks. The unified SDN control plane is able to configure the optical nodes/devices and thus the optical network through the cooperation of Openflow agents with more flexibility and optimization, thanks to its global knowledge of network resource and centralized controllability. Furthermore, we are able to interconnect our network with other heterogeneous multidomain networks, while demonstrating the end-to-end flexible service provisioning over both nationwide and international testbeds with SDN orchestration via unified interface based on control orchestration protocol.

A "service design" paradigm is presented to flexibly accommodate customized services by applying and chaining reconfigurable virtual network functions. Functional and featured service provisioning is demonstrated across heterogeneous IP/OPS/OCS domain networks with end-to-end SDN orchestration.

A service design concept is introduced into the optical transport network. Customized and orchestrated optical transmission is realized by coordinating and reconfiguring the sharable virtualized optical functions, while better flexibility is provided for optical networking.

We propose an ILP-based model and a time-efficient heuristic algorithm for multicast scheduling in optical burst ring network. Simulation results verify the proposed methods could improve latency and throughput performance significantly compared to unicast transmission.

We experimentally evaluate the bit-error rate performance of six-mode-multiplexed DP-QAM signals in back-to-back configuration. In Nyquist WDM and 64QAM format cases, BERs of less than 2x10(-2) for all modes are achieved.

We present ultra-dense-SDM Super-Nyquist-WDM transmission over 9.8-km six-mode nineteen-core fibers with a spatial multiplicity of 114, achieving a transmission capacity of 2.05 Pbit/s with a record aggregate spectral efficiency of 456 bit/s/Hz in C band.

In this paper, recent progress on ultra-dense, space division multiplexed (SDM) optical transmission towards multi-Peta bit/s are reviewed. By using 6-mode 19-core fiber, we have demonstrated 2.05 Pbit/s transmission over 9.8 km just using C-band. High spatial multiplicity of 114 and ultra-high aggregate spectral efficiency of 456 bit/s/Hz/fiber have been achieved.

Traditional datacenters are typically deployed with highly clustered resources and built-in remote areas far away from users, requiring huge floor space and power consumption. The proposed metro-embedded datacenter architecture with distributed resources spreading across the metro area close to users could be a promising solution, which exhibits lower access latency and more flexibility for service orchestration. Based on metro-embedded datacenter, we propose the conception of "follow the user" with user access location aware dynamic hotspots adjustments. By enabling service hotspots adjustment according to user access frequency statistics, the quality of service can be significantly improved in terms of reduced latency. Finally, we experimentally demonstrate low-latency service provisioning based on the proposed principle. (C) 2016 Elsevier B.V. All rights reserved.

In Super-Nyquist wavelength-division multiplexed (WDM) systems, in which WDM channel spacing is smaller than a signal baudrate, there is a tradeoff relationship between the WDM crosstalk and inter-symbol interference due to the tight spectral shaping. For optimizing the tradeoff relationship, polybinary shaping with maximum likelihood sequence estimation is introduced. In this paper, we numerically and experimentally investigate the bit-error rate characteristics of the Super-Nyquist WDM quadrature amplitude modulated signals with polybinary shaping in order to clarify the relationship between the spectral efficiency and required signal-to-noise ratio (SNR). These results indicate that the Super-Nyquist WDM technique based on polybinary shaping is effective to optimize the spectral efficiency for the target required SNR equivalent to the target transmission distance.

Ultra-dense spatial-division multiplexing (SDM) is achieved by mode multiplexed technique with multiple cores in a single fiber, namely few-mode multi-core fiber. Using a 9.8-km six-mode nineteen-core fiber, we demonstrate an ultra-dense SDM transmission of 16-channels wavelength-division-multiplexed (WDM) dual-polarization quadrature phase shift keying signals, achieving a record spatial multiplicity of 114. With the help of ultra-dense Super-Nyquist WDM techniques in the 4.5-THz bandwidth of the full C-band, we demonstrate 2.05 Pbit/s transmission over 9.8-km six-mode nineteen-core fibers. In this experiment, the highest aggregate spectral efficiency of 456 bit/s/Hz is achieved. (C) 2016 Optical Society of America

Multicore erbium-doped fiber amplifiers (MCEDFAs) are essential components to achieve long-haul multicore fiber (MCF) transmission. An attractive technique for reducing the number of components and power consumption is the cladding-pumping scheme in MC-EDFAs in which all cores are simultaneously pumped using a single high-power multimode laser diode. In this paper, we experimentally demonstrate long-haul MCF transmission using cladding-pumped seven-core EDFAs. We confirm that 73 x 128-Gbit/s Nyquist-pulse-shaped dual-polarization quadrature phase-shift keying signals are successfully transmitted over 2520-km seven-core fiber.

We demonstrate ultra-dense SDM transmission of 360-channel Super-Nyquist-WDM DP-QPSK signals over 9.8-km 6-mode 19-core fiber, achieving the record fiber capacity of 2.05 Pbit/s (360WDM×114SDM×50Gbit/s) with the highest aggregate spectral efficiency of 456 bit/s/Hz.

We experimentally demonstrate ultra-long-haul multi-core fiber transmission using a cladding pumped 7-core erbium-doped fiber amplifier. We confirm 76 × 128-Gbit/s Nyquist-pulse-shaped DP-QPSK signals are successfully transmitted over 4,200-km 7-core fiber.

We experimentally demonstrate dynamic congestion control in an optical packet switching network employing an optical packet counter for traffic flow diagnosis and a rate-adaptive transmitter and receiver to reduce packet loss ratio while preserving the transmission capacity.

The Control Orchestration Protocol (COP) abstracts a common set of control plane functions used by an various SDN controllers, allowing the interworking of heterogeneous control plane paradigms (i.e., OpenFlow, GMPLS/PCE). COP has been defined using YANG model language and can be transported using RESTconf, which is being incorporated by industry. COP has been defined in the scope of STRAUSS due to the need for an overarching control plane protocol for network orchestration. In this paper, several research projects describe how the COP could fit in their architecture and propose a use case for COP usage. The proposed COP use cases cover the following research projects: STRAUSS, IDEALIST, DISCUS, COMBO, INSPACE.

A network hypervisor is introduced to dynamically deploy multi-tenant virtual networks on top of multi-technology optical networks. It provides an abstract view of each virtual network and enables its control through an independent SDN controller.

Hierarchical network virtualization is demonstrated on a heterogeneous multi-domain network testbed, based on SDN/Openflow and two-level Flowvisor. Differentiated services with various sets of QoS requirements are provisioned in the end-to-end optimally organized virtual networks.

The dynamic optical packet switching network based on advanced SDN/Openflow control is introduced in this paper. Promoted resource allocation and prompt network adjustment is achieved under dynamic network environment with real-time optical packet monitoring.

We demonstrated a novel metro-embedded datacenter architecture with intra-datacenter optical burst switching ring and inter-datacenter optical burst switching over wavelength switched optical network interconnections, and virtual datacenter provisioning under the coordination of SDN control plane.

We show transmission experiments of 16-Nyquist-WDM 6-mode-multiplexed DP-QPSK signals over 9.8-km 6-mode 19-core fibers. The record spatial multiplicity of 114 and the aggregate spectral efficiency over 345 bit/s/Hz have been achieved.

We experimentally evaluate bit-error rate performance of polybinary-pulse-shaped QAM signals in Super-Nyquist-WDM conditions, and clarify the relationship between spectral efficiency and SNR compared with conventional Nyquist-pulse-shaped signals.

We review Super-Nyquist WDM techniques for ultra-long-haul high-capacity transmission. In Super-Nyquist WDM systems, optical signals are multiplexed with the frequency spacing of less than baud rate. With the help of multi-core fibers with multi-core EDFA, 140.7-Tbit/s, 7 x 326-km transmission of 201-channel 25-GHz-spaced Super-Nyquist-WDM 100-Gbit/s DP-QPSK signals has been demonstrated, achieving the capacity-distance product over 1 Exabit/s. km.

We present space-division multiplexed transmission with spatial multiplicity over 100 using weakly-coupled-6-mode uncoupled-19-core fiber. Suppressing mode coupling and core-to core crosstalk, MIMO complexity can be reduced. The record aggregate spectral efficiency over 345 bit/s/Hz is achieved.

Network virtualization is a promising technology to reduce CAPEX and OPEX of telecommunication networks together with providing new service agility. This paper reviews recent research activities on network virtualization to enhance its benefits.

A multidomain and multitechnology optical network orchestration is demonstrated in an international testbed located in Japan, the U.K., and Spain. The application-based network operations architecture is proposed as a carrier software-defined network solution for provisioning end-to-end optical transport services through a multidomain multitechnology network scenario, consisting of a 46-108 Gb/s variable-capacity Open-Flow-capable optical packet switching network and a programmable, flexi-grid elastic optical path network.

This paper describes promising techniques for approaching the capacity-distance product over 1 Exabit/sxkm in the transoceanic-class optical fiber transmission. One is the Super-Nyquist wavelength-division multiplexing (WDM) technique based on poly-binary-pulse shaping with maximum likelihood sequence estimation, in which it is possible to multiplex optical signals with WDM spacing of less than the signal baudrate. Another technique is the space-division multiplexing technique based on multi-core fibers (MCFs) with multi-core Erbium-doped fiber amplifiers (ED-FAs), in which the fiber capacity can be increased when the number of cores of MCF is increased. Finally, we present a demonstration of 140.7-Tbit/s, 7 326-km transmission of 201-channel 25-GHz-spaced Super-Nyquist-WDM 100-Gbit/s optical signals using seven-core fibers and full C-band seven-core EDFAs.

A virtualization architecture is presented for deploying multitenant virtual networks on top of multi-technology optical networks. A multidomain network hypervisor (MNH) and a multidomain SDN orchestrator (MSO) are introduced with this purpose. The MNH provides an abstract view of each virtual network and gives control of it to each independent customer SDN controller. The MNH is able to provide virtual networks across heterogeneous control domains (i.e., generalized multiprotocol label switching and OpenFlow) and transport technologies (i.e., optical packet switching and elastic optical networks). The MSO is responsible for providing the necessary end-to-end connectivity. We have designed, implemented, and experimentally evaluated the MNH and MSO in an international testbed across Spain, UK, Germany, and Japan.

New and emerging use cases, such as the interconnection of geographically remote data centers, are drawing attention to the need for provisioning end-to-end connectivity services spanning multiple and heterogeneous network domains. This heterogeneity is due not only to the data transmission and switching technology (the so-called data plane) but also to the deployed control plane, which may be used within each domain to automate the setup and recovery of such services, dynamically. The choice of a control plane is affected by factors such as availability, maturity, operator's preference, and the ability to satisfy a list of functional requirements. Given the current developments around OpenFlow and software-defined networking (SDN) along with the need to account for existing deployments based on GMPLS, the problem of heterogeneous control plane interworking needs to be solved. The retained solution must equally address the specific issues of multidomain networks, such as limited domain topology visibility, given the scalability and confidentiality constraints that characterize them. In this setting, we propose a functional and protocol architecture for such interworking, based on the key concepts of network abstraction and overarching control, implemented in terms of a hierarchical stateful path computation element (PCE), which provides the orchestration and coordination layer. In the proposed architecture, the PCEP and BGP-LS protocols are extended to support OpenFlow addresses and datapath identifiers, unifying both GMPLS and OpenFlow domains. The solution is deployed in an experimental testbed and validated. Although the main scope of the approach is the interworking of OpenFlow and GMPLS, the same approach can be directly applied to a wide range of multidomain scenarios, with either homogeneous or heterogeneous control technologies.

Optical transport networks provide transport, multiplexing, routing, management, supervision, and survivability of optical channels. Within a flexible dense wavelength division multiplexing grid, the optical spectrum can be allocated in multiples of a width granularity, depending on the client signal rate and modulation format. A control plane (CP) can be used for efficient and dynamic provisioning and recovery of flexi-grid connections. Two main CP architectures coexist, with common functions like addressing, automatic topology discovery, network abstraction, path computation, and connection provisioning: a distributed generalized multiprotocol label switching CP (with optional path computation element, PCE path computation and instantiation/modification) and a CP based on software-defined networking, with a logically centralized controller and an open protocol, such as the OpenFlow protocol. Both architectures have their own strengths and weaknesses, and are being extended to address the new requirements associated with the aforementioned emerging optical technologies, such as flexible spectrum allocation, efficient corouted connection setup, and configuration of related optical parameters. However, new use cases such as remote data center interconnection highlight the need for multidomain service provisioning, and heterogeneous CP interworking, potentially requiring an overarching control. Different alternatives, with varying degrees of integration and flexibility, are available: straightforward approaches characterized by the adaptation of one control model to the other or more advanced interworking requiring the definition of common models (e.g., a subset of attributes for network elements) and of coordination and orchestration functions. This paper discusses the main relevant interworking architectures and presents a selected set of use cases and proof-of-concepts.

Elastic optical networking (EON), with its flexible use of the optical spectrum, is a promising solution for future metro/core optical networking. For the deployment of EON in a real-operational scenario, the dynamic lightpath restoration, driven by an intelligent control plane, is a necessary network function. Dynamic restoration can restore network services automatically and, thus, greatly reduce the operational cost, compared with traditional manual or semistatic lightpath restoration strategies enabled by network operators via a network management system. To this end, in this paper, we present an OpenFlow-enabled dynamic lightpath restoration in elastic optical networks, detailing the restoration framework and algorithm, the failure isolation mechanism, and the proposed OpenFlow protocol extensions. We quantitatively present the restoration performance via control plane experimental tests on the Global Environment for Network Innovations testbed.

We propose a multi-domain resource broker to dynamically provision multi-domain virtual optical networks across heterogeneous control domains (i.e., GMPLS and OpenFlow) and transport (i.e., optical packet switching and elastic optical networks) technologies. We have designed, implemented, and experimentally evaluated the multi-domain resource broker in an international test-bed across Spain, the UK, and Japan.

This paper presents and experimentally demonstrates the generalized architecture of Openflow-controlled optical packet switching (OPS) network. Openflow control is enabled by introducing the Openflow/OPS agent into the OPS network, which realizes the Openflow protocol translation and message exchange between the Openflow control plane and the underlying OPS nodes. With software-defined networking (SDN) and Openflow technique, the complex control functions of the conventional OPS network can be offloaded into a centralized and flexible control plane, while promoted control and operations can be provided due to centralized coordination of network resources. Furthermore, a contention-aware routing/rerouting strategy as well as a fast network adjustment mechanism is proposed and demonstrated for the first time as advanced Openflow control to route traffic and handle the network dynamics. With centralized SDN/Openflow control, the OPS network has the potential to have better resource utilization and enhanced network resilience at lower cost and less node complexity. Our work will accelerate the development of both OPS and SDN evolution.

Both GMPLS and OpenFlow are positioned to become the pillars of a dynamic control plane for optical transport networks, each with its own strengths and weaknesses. This paper summarizes both approaches and discusses potential SDN interworking architectures.

Seven-core MC-EDFA pumped with single MM-LD optimized for L-band is developed. Output power of 19 dBm for each core is realized between 1576-1603nm with 33% reduced power consumption.

We report the experimental testbed evaluation of connectivity provisioning in which OpenFlow and GMPLS control planes interwork by means of an orchestrating stateful PCE. The hierarchical nature of the PCE allows seamless multi-domain operation. © 2014 OSA.

The first experimental demonstrator of 46-108Gb/s discrete-multi-tone (DMT) fixedlength variable capacity OPS over programmable, flexi-grid elastic optical path network (EON), orchestrated via multiple OpenFlow controllers in the framework of SDN is presented. © 2014 OSA.

We have experimentally demonstrated Openflow-controlled optical packet switching network, while also proposed and demonstrated an advanced Openflow control mechanism to handle the network dynamics with prompt response.

We experimentally investigate crosstalk characteristics of Super-Nyquist-WDM DP-QPSK signals with duobinary-pulse shaping. The bit-error rate performance of 100-Gbit/s-class duobinary-pulse shaped DP-QPSK WDM signals with frequency spacing of 25 GHz is evaluated experimentally.

We review recent experimental demonstration of transoceanic multi-core-fiber transmission with multi-core EDFAs. With the help of Super-Nyquist WDM techniques, the product of the transmission capacity and distance of 1 Exabit/sxkm has been achieved.

We review trans-oceanic-class multi-core fiber transmission systems with Super-Nyquist-WDM technique, in which optical signals are multiplexed with frequency spacing of less than baudrate. The capacity-distance product over 1 Exabit/s.km has been achieved.

We present OpenFlow-enabled dynamic restoration in elastic optical networks, detailing the restoration framework and algorithm, failure isolation mechanism, OpenFlow protocol extensions, and quantitatively presenting the restoration performance via the experimental validation on the Global Environment for Network Innovations (GENI) testbed.

Space-division multiplexing with multi-core fiber is a promising technology to increase a system capacity drastically. By using a combination of MCF and spectral efficient modulation format, trans-oceanic transmission with a capacity-distance product of 1.03 Ebit/s.km has been achieved.

Optical Orthogonal Frequency Division Multiplexing (O-OFDM), which transmits high speed optical signals using multiple spectrally overlapped lower-speed subcarriers, is a promising candidate for supporting future elastic optical networks. In contrast to previous works which focus on Coherent Optical OFDM (CO-OFDM), in this paper, we consider the direct-detection optical OFDM (DDO-OFDM) as the transport technique, which leads to simpler hardware and software realizations, potentially offering a low-cost solution for elastic optical networks, especially in metro networks, and short or medium distance core networks. Based on this network scenario, we design and deploy a software-defined networking (SDN) control plane enabled by extending OpenFlow, detailing the network architecture, the routing and spectrum assignment algorithm, OpenFlow protocol extensions and the experimental validation. To the best of our knowledge, it is the first time that an OpenFlow-based control plane is reported and its performance is quantitatively measured in an elastic optical network with DDO-OFDM transmission. (C) 2013 Optical Society of America

We show super-Nyquist-WDM transmission technique, where optical signals with duobinary-pulse shaping can be wavelength-multiplexed with frequency spacing of below baudrate. Duobinary-pulse shaping can reduce the signal bandwidth to be a half of baudrate while controlling inter-symbol interference can be compensated by the maximum likelihood sequence estimation in a receiver. First, we experimentally evaluate crosstalk characteristics as a function of channel spacing between the dual-channel DP-QPSK signals with duobinary-pulse shaping. As a result, the crosstalk penalty can be almost negligible as far as the ratio of baudrate to frequency spacing is maintained to be less than 1.20. Next, we demonstrate 140.7-Tbit/s, 7,326-km transmission of 7 x 201-channel 25-GHz-spaced super-Nyquist-WDM 100-Gbit/s optical signals using seven-core fiber and full C-band seven-core EDFAs. To the best of our knowledge, this is one of the first reports of high-capacity transmission experiments with capacity-distance product in excess of 1 Exabit/s.km. (C) 2014 Optical Society of America

We numerically and experimentally evaluate the performance of higher-order mode conversion based on phase plates for 10-mode fibers (10MFs). The phase plates have the phase jump of pi between multiple planes, which match the phase patterns of linearly polarized (LP) modes of 10MF. First, we numerically investigate the effects of the fabrication errors such as the phase-difference error and the slope in the phase jump of the phase plate. The simulation results for the mode conversion to LP11 indicate that such errors make the spatial pattern of the converted beam asymmetric. In order to maintain the symmetric pattern, the phase-difference error is required to be less than +/- 2%, and the ratio of the slope width to the input beam waist should be suppressed to be less than 0.05. Next, we calculate the coupling power efficiencies of the excitation of LP modes in 10MF when the converted beams after the phase plate are launched into 10MF using a lens. As the calculation results, highly accurate adjustment of the input beam waist is required to suppress the crosstalk due to coupling of undesirable LP modes by less than -20 dB. For mode excitation of LP11 or LP12, crosstalk of more than -20 dB is not avoidable even if the input beam waist is carefully adjusted. In contrast, the crosstalk for the mode excitation of LP21 or LP31 is easily suppressed to be less than -20 dB without careful adjustment of the input beam waist. These results suggest that phase plates are not applicable to mode conversion to LP11 and LP12 in 10MF while they are suitable for conversion to LP02, LP21 and LP31. Finally, we experimentally demonstrate conversion from LP01 to LP21 and LP31 modes in 10MF using phase plates. We obtain nearly ideal LP21 and LP31 modes with the small crosstalk due to the coupling of the other undesirable LP modes. (C) 2014 Optical Society of America

Space-division multiplexing with uncoupled multi-core fiber is a promising technology to drastically increase a fiber capacity in optical communication systems. Trans-oceanic class ultra-long-haul transmission was successfully achieved by using 7-core MCF with suppressed inter-core crosstalk. By using a combination of MCF and spectral efficient modulation format, the fiber capacity could be increased from 28.8 Tbit/s to 140 Tbit/s and a capacity-distance product exceeding 1 Exabit/s.km was obtained in 7 cores x 201 lambda x 100 Gbit/s transmission over 7326 km. These results indicate that the MCF transmission will be one of promising candidates for future ultra-high capacity optical communication systems. (C) 2014 Optical Society of America

OpenFlow, which allows operators to control the network using software running on a network operating system within an external controller, has recently been proposed and experimentally validated as a promising intelligent control plane technique. To mitigate the potential scalability issue of an OpenFlow-based centralized control plane and to leverage the mature, well-defined, and feature-complete path computation element (PCE) communication protocol, the complex path computation function required in optical networks can be formally decoupled from the OpenFlow controller so the controller can off-load the task to one or more dedicated PCEs. In addition to the control plane intelligence, future optical networks also feature data plane intelligence such as the introduction of flexible transmitters and receivers, which can dynamically change the modulation format and transmission rate of the optical signal without hardware modifications. In this paper, for the first time, we successfully demonstrate a dynamic transparent wavelength-switched optical network employing flexible transmitters and receivers controlled by an OpenFlow-stateless PCE integrated control plane. Our designed flexible transmitter is implemented by a cascade of a dual-drive Mach-Zehnder modulator (MZM) and a dual-parallel MZM. By adjusting the electrical binary drive signals, the flexible transmitter is able to flexibly switch the symbol rate and the modulation format, including binary phase shift keying, quadrature phase shift keying, 8-ary quadrature amplitude modulation (8QAM), and 16QAM. The flexible receiver is able to automatically detect different modulation formats and symbol rates and measure the bit-error rate. All the network elements, including optical switching nodes and flexible transmitters and receivers, are extended with OpenFlow interfaces, which can be intelligently controlled by the OpenFlow-stateless PCE integrated control plane with significant protocol extensions. On an actual network testbed with real hardware, we successfully validate dynamic and seamless interworking operations between the OpenFlow controller, a stateless PCE, and all the data plane hardware. The overall feasibility and efficiency of the proposed solutions are verified, and dynamic end-to-end path provisioning and lightpath restoration in such a new network scenario are quantitatively evaluated. We also tested the scalability of the proposed control plane; the experiment results indicated that dynamic path provisioning and restoration can be achieved within hundreds of milliseconds by using the proposed approach, and the overall architecture scales well with a batch of requests.

For RF-pilot-assisted PDM-CO-OFDM systems, we propose and demonstrate a carrier recovery method applying a simple moving average filter (MAF) to extract the central RF-pilot for phase noise compensation. Because only two additions per output sample would be required to implement such a MAF, its computational complexity is rather simple compared to any other direct-form finite impulse response (FIR) filter. To handle its weak side-lobe attenuation, which would cause the spectrally nearby OFDM signal to interfere with the extracted pilot signal, we further propose using multiple MAFs in cascade to enhance the side-lobe attenuation. We evaluate the performance of a 16-QAM and 40-Gbps PDM-CO-OFDM signal, in terms of the bandwidth tolerance, optical signal to noise ratio (OSNR) tolerance, nonlinear tolerance, linewidth tolerance, and residual carrier frequency offset (RFO) tolerance, with different filters including the simple MAF, cascaded MAFs, and the previously-demonstrated multi-stage decimation and interpolation filter (MDIF). We've found that 1) all the filters exhibit similar performance to the ideal brick-wall filter in terms of noise and nonlinear tolerances, 2) the MAF1 exhibits the worse tolerances against linewidth and RFO, and 3) the MDIF has to be carefully designed to enhance its tolerances against both the linewidth and RFO.

A control plane is a key enabling technique for dynamic and intelligent end-to-end path provisioning in optical networks. In this paper, we present an OpenFlow-based control plane for spectrum sliced elastic optical path networks, called OpenSlice, for dynamic end-to-end path provisioning and IP traffic offloading. Experimental demonstration and numerical evaluation show its overall feasibility and efficiency. (C)2013 Optical Society of America

To mitigate the potential scalability issues of an OpenFlow-based control plane, a seamless OpenFlow and Path Computation Element (PCE) integrated control plane is proposed, by means of an architecture in which the path computation function is formally decoupled from the controller so the controller can off-load the task to one or more dedicated PCEs using an open and standard interface and protocol, and where the PCE obtains its topology database by means of a dedicated dynamic topology server, which is accessed by the PCE on a per-request basis. The overall feasibility and performance metrics of this integrated control plane are experimentally verified and quantitatively evaluated on a real IP over translucent Wavelength Switched Optical Network (WSON) testbed. (C)2013 Optical Society of America

We report the design, implementation and experimental evaluation of a centralized control plane based on a stateful PCE, acting as an OpenFlow controller. We detail the protocol extensions for elastic optical networks and the performance. © 2013 OSA.

We propose the OSNR monitoring technique for m-ary QAM formats in the presence of fiber nonlinearities, which is based on the analysis of the power spectral density of amplitude noises in a digital coherent receiver. © 2013 IEICE.

This paper presents an extended OpenFlow-based control plane for labeled optical burst switching networks to achieve application-aware burst assembly and scheduling, and experimental demonstration verifies its overall feasibility. © 2013 IEICE.

We propose a technique for higher-order mode conversion based on cascade multiple phase plates with simple phase patterns. Using our scheme, the mode conversion to LP11 and LP21 has been demonstrated. © 2013 IEICE.

The multicore fiber transmission technologies is promising candidate to increase the capacity per fiber. In this paper, ultra-long-haul transmission using multicore fiber and multicore EDFA is explained. © 2013 IEICE.

In this paper, we review OpenFlow-based control and management technology for optical networks including multi-layer optical networks, multi-domain optical networks and elastic optical networks. We also present the interworking between OpenFlow and PCE/GMPLS control planes. © 2013 IEICE.

We propose a modified Walsh-Hadamard transform (MWHT) that reduces the PDL penalty by equalizing the performance of both polarization tributaries. The realization of MWHT requires just one piece of PMF and therefore exhibits a very low-cost PDL solution.

We propose a practically-implementable nonlinear noise cancellation (NLNC) method that effectively removes the "1st-order" fiber nonlinearities. After 6720-km (84x80-km) SSMF transmission, the signal performance in terms of Q-factor is improved by ∼1.4 dB with the proposed NLNC method.

We report the implementation and performance evaluation of an active stateful PCE that relies on a GMPLS control plane for the actual provisioning of elastic connections in a flexi-grid DWDM network. It is based on experimental extensions to the PCEP protocol and enables more advanced and concurrent path computations.

We report fabrication of a 45.5-km seven-core fiber with enlarged Aeff and a high-power seven-core EDFA with 5-THz bandwidth. Using them, we confirmed the feasibility of 100-Tbit/s-class transoceanic transmission.

We design and deploy an extended OpenFlow-based control plane for elastic optical networks with DDO-OFDM transmission, detailing the network architecture, the two-phase routing and spectrum assignment algorithm, OpenFlow protocol extensions and the experimental validation.

We present a versatile optical transmitter composed of tandem I/Q modulators driven by electrical binary signals. This transmitter is able to simply generate higher-order QAM formats (from BPSK up to 64QAM) without hardware modification.

We demonstrate the feasibility of spectrum defragmentation in a flexible-grid optical network utilizing the flexible transmitter and receiver. According to the defragmentation controller, the flexible transmitter dynamically switches the modulation format/symbol rate/wavelength without hardware modification.

We propose a technique for stabilizing frequencies of multiple semiconductor lasers, which can reduce the fluctuation of the frequency spacing to below 3MHz. Using our scheme, we demonstrate 10-GBaud Nyquist-WDM PDM 16QAM transmission over 1,000km.

GPU-accelerated high performance switching design using hybrid flow tables allocated in host and GPU memories is proposed based on LightFlow architecture. In this work, careful placement of hash and wildcard tables is proposed considering overhead of data copy during lookup process, in order to tackle massive flow entries using commodity hardware. Experimental results show that the proposal achieves 14.6 Mpps which is the fastest record of the software flow switch operated under a large scale reaching 4 million flow entries. With this proposal, it is also demonstrated that the average processing delay is about one forth compared with Open vSwitch.

Space-division-multiplexing is an attractive approach to increase the capacity of submarine cable systems. The feasibility of transoceanic class transmission with multicore fiber was confirmed in 7 x 40 x 128 Gbit/s transmission over 6160 km.

Space-division multiplexing with multi-core fiber is an attractive technology to increase a system capacity drastically. In this paper, the feasibility of trans-oceanic transmission using multi-core fibers is discussed.

Space-division multiplexing (SDM) with multi-core/multi-mode fibers has potential to increase the transmission capacity drastically. In this paper, we investigate the feasibility of trans-oceanic transmission towards beyond 100 Tbit/s using multi-core fibers. Experimental results using 7-core fibers/EDFAs are also presented.

Core-pumped 7-core EDFA with two stage amplification is realized. Combination of its higher gain and GFF enables wide bandwidth operation. NF of Less than 5.5 dB is achieved with improved fan-in device.

A novel scheme capable of dynamic wavelength assignment and burst contention mitigation is proposed to achieve efficient optical burst flow grooming in the OpenFlow controlled LOBS-over-WSON network. Simulation and experiment verified its feasibility.

In this paper, we verify the effectiveness of the last-stage long memory filter (LMF) in mitigating the long-memory response (LMR) of hardware, i.e. the transmitter and receiver. Based on the experimental results, we draw the following conclusions: 1) LMF can effectively mitigate the LMR impact, such as transmitter reflections, and its efficiency is more significant for high-order QAM signals. 2) Using LMF, a partially-correlated pattern exhibits similar performance to that of an uncorrelated pattern both in back-to-back and after 320-km standard single mode fiber (SSMF) transmission. Moreover, a simple solution to the computational complexity of LMF, effective-tap (ET) LMF, is proposed and demonstrated. (C) 2013 Optical Society of America

For polarization-division-multiplexing coherent optical orthogonal frequency division multiplexing (PDM-CO-OFDM) systems, we propose a per-symbol-based digital back-propagation (DBP) approach which, after cyclic prefix removal, conducts DBP for each OFDM symbol. Compared with previous DBP, this new proposal avoids the use of inefficient overlap-and-add operation and saves one fast Fourier transform (FFT) module, therefore simplifying the hardware implementation. Transmitting a 16-QAM, 42.8-Gb/s PDM-CO-OFDM signal over 960-km standard single mode fiber (SSMF), we compare the previous and the proposed DBP approaches with different receiver's sampling rates and different step lengths in each DBP iteration, and found that the proposed DBP can achieve a similar performance as that of the previous DBP while enjoying a simpler implementation. We have also specifically introduced a small self-phase modulation (SPM) model for DBP and demonstrated its feasibility with the same experimental setup. (C) 2013 Optical Society of America

A translucent wavelength switched optical network (WSON), with sparse 3R regenerators to guarantee the signal quality of an optical connection, is a promising paradigm for a metro/core network. This is because a translucent WSON can achieve performance comparable to that of an all-electronic switching (i.e., opaque) network with far lower network cost and a great reduction in power consumption. Because of its advantages, many recent research and standardization efforts have focused on translucent WSONs. However, most of them study the intradomain case, and issues related to multidomain translucent WSONs are largely open at present. In light of this, in this article, we present two possible strategies to improve interdomain path computation and lightpath establishment in a multidomain translucent WSON. Both approaches are experimentally demonstrated and quantitatively evaluated. Our aim is to provide feasible and efficient solutions for supporting a multidomain translucent WSON, as well as to obtain valuable insight into the proposed strategies through experiments, which will be beneficial for the potential industrial deployment of translucent optical networks.

In this paper we demonstrate high-baud generation and transmission of PDM-64QAM signals. The 64QAM signal is generated using one single in-phase/quadrature (I/Q) modulator driven with eight-level signals synthesized by all binary electrical inputs. With hard-decision forward error correction (HD-FEC), we first demonstrate 11.2-GBd and 22.4-GBd PDM-64QAM transmissions over 320-km standard single mode fiber (SSMF). Then we specifically introduce a long memory filter (LMF) and prove its effectiveness in reflection compensation both theoretically and experimentally. With the aid of soft-decision FEC (SD-FEC), optical pre-shaping, and LMF, we transmit a 41.4-GBd PDM-64QAM signal over 1200-km SSMF. Finally, using per-channel 41.6-GBd PDM-64QAM with SD-FEC, we successfully demonstrate 50-GHz-spaced, 8 499-Gb/s transmission over 720-km SSMF. This is the first demonstration of 400-Gb/s/ch WDM transmission on the 50-GHz ITU grid that uses a per-channel single-carrier scheme.

We demonstrate the first 7-core multicore erbium-doped fiber amplified (MC-EDFA) transmission of 40 × 128-Gbit/s PDM-QPSK signals over 6,160-km 7-core multicore fiber (MCF). The crosstalk (XT) from all of the other 6 cores of a MC-EDFA and a 55-km length MCF are about -46.5 dB and -45.6 dB at center core, respectively. The core-to-core rotation approach at every amplified span is used to average the XT of all cores. The averaged optical signal-to-noise ratio (OSNR) after 6,160-km transmission is 15.6 dB with 0.1 nm resolution bandwidth. The Q-factor of all 40 channels surpasses the threshold of the forward-error-correction of 6.4 dB with 1 dB margin after 6,160 km. The total net capacity is 28.8 Tbit/s per fiber and achieved capacity-distance product is 177 Pbit/s·km per fiber. We confirmed the feasibility of MC-EDFA repeatered systems for trans-oceanic transmission. © 2013 Optical Society of America.

We present an OpenFlow-based control plane for spectrum sliced elastic optical path networks, called OpenSlice, for dynamic end-to-end path provisioning and IP traffic offloading. Experimental demonstration and numerical evaluation show its overall feasibility and efficiency.

The control plane techniques based on the Generalized Multi-Protocol Label Switching (GMPLS) and Path Computation Element (PCE) architectures are promising candidates for potential industrial deployment in Wavelength Switched Optical Networks (WSON), because they can greatly reduce operational expenses and improve the network intelligence. Moreover, link failures have a critical effect on WSON, since a single failure may result in the loss of a huge amount of data. In light of this, in this paper, we detail the design and implementation of a GMPLS control plane, with PCE-based, impairment-aware, full restoration capability for translucent WSON. We investigate the enabling techniques for such a PCE/GMPLS control plane by surveying a series of solutions, and, based on these enabling techniques, we present an experimental demonstration of service recovery for uncompressed video stream in a GMPLS controlled WSON with PCE-based full lightpath restoration. We also quantitatively evaluate the performance of the PCE-based full restoration, and compare it with the PCE-based pre-planned restoration and the PCE-based pre-computed dynamic restoration in terms of signaling latency and restorability. To the best of our knowledge, it is the first time that the PCE-based full restoration is experimentally investigated on an actual GMPLS controlled WSON testbed, which is beneficial for verifying the overall feasibility and efficiency of the proposed solutions, obtaining valuable insights for its future deployment in a real operational scenario, and providing active contribution in support of the on-going Internet Engineering Task Force (IETF) standardization activities. © 2012 Elsevier B.V.

A seamless OpenFlow/PCE integrated control plane for IP over translucent WSON is presented via a per-request-based dynamic topology server. The overall feasibility and performance metrics of this integrated control plane are experimentally verified and quantitatively evaluated.

Software defined networking (SDN) and flexible grid optical transport technology are two key technologies that allow network operators to customize their infrastructure based on application requirements and therefore minimizing the extra capital and operational costs required for hosting new applications. In this paper, for the first time we report on design, implementation & demonstration of a novel OpenFlow based SDN unified control plane allowing seamless operation across heterogeneous state-of-the-art optical and packet transport domains. We verify and experimentally evaluate OpenFlow protocol extensions for flexible DWDM grid transport technology along with its integration with fixed DWDM grid and layer-2 packet switching. © 2013 Optical Society of America.

ITU-T Recommendation G.694.1 [1] defines normative DWDM frequency grids, each being a reference set of values that correspond to allowed nominal central frequencies, obtained using a fixed channel spacing (e.g., 12.5 GHz, 25 GHz, 50 GHz or 100 GHz). This rigid, grid-based approach does not seem well adapted for data rates beyond 100 Gb/s, is particularly inefficient when a whole wavelength is assigned to a lower rate optical path, and is not flexible enough for multi-rate systems [2]. Consequently, the next generation of optical networks will require a flexible, highly efficient and adaptive management of the optical spectrum, along with advanced optical modulation schemes that efficiently use allocated spectrum slots, and recent progress on optical network technology justifies research on both new optical transmission systems as well as the applicability of control and management frameworks to such networks.We design and deploy a GMPLS control plane for flexible optical networks with coherent optical orthogonal frequency-division multiplexing (O-OFDM) transmission; we detail its functional architecture, which combines a centralized entity that performs path routing and modulation assignment, with a distributed spectrum allocation. The centralized entity (i.e., a path computation element) uses pre-configured static path characterizations, based on exhaustive OFDM transmission simulations, when performing dynamic path computation in line with GMPLS constrained shortest path mechanisms. The distributed spectrum allocation assigns frequency ranges (slots) to connection requests, by using dynamic signaling procedures and applying slot assignment policies. We summarize the control plane protocol extensions involved in the main functional aspects: routing and topology dissemination, path computation, signaling and resource reservation.We experimentally validate and evaluate the integrated centralized PCE and GMPLS control plane in a control plane testbed, obtaining key performance indicators such as path setup latency and blocking probability for different frequency slot assignment policies.

The feasibility of spectrum defragmentation is demonstrated in a flexigrid optical network employing the multi-format and multi-rate transmitter and receiver. For efficient defragmentation, the push-pull defragmentation technique is improved with additional functionality, which tunes the occupied frequency slots as well as the centre frequency. © The Institution of Engineering and Technology 2013.

Software defined networking and OpenFlow, which allow operators to control the network using software running on a network operating system within an external controller, provide the maximum flexibility for the operator to control a network, and match the carrier's preferences given its centralized architecture, simplicity, and manageability. In this paper, we report a field trial of an OpenFlow-based unified control plane (UCP) for multilayer multigranularity optical switching networks, verifying its overall feasibility and efficiency, and quantitatively evaluating the latencies for end-to-end path creation and restoration. To the best of our knowledge, the field trial of an OpenFlow-based UCP for optical networks is a world first.

We confirm the feasibility of 100-Tbit/s-class trans-oceanic SDM transmission. Using seven-core fiber spans with seven-core full C-band EDFAs, 7 x 264-channel quasi-Nyquist-WDM 60-Gbit/s PDM-QPSK signals are transmitted over 6,370 km. (C) 2013 Optical Society of America

A bit-error rate (BER)-adaptive wavelength-switched optical network (WSON) employing the multiformat and multirate transmitter/receiver is experimentally demonstrated. The flexible transmitter is capable of generating binary phase-shift-keying, quadrature phase-shift-keying, eight-ary quadrature amplitude modulation, 8QAM, and 16QAM, as well as changing the symbol rate. On the other hand, the flexible receiver based on a coherent detection scheme is utilized not only to detect the optical signal with any modulation format/rate, but also to send the BER information to an OpenFlow controller via extended OpenFlow protocols. Since the measured BER is a reliable barometer of the optical path conditions, an extended OpenFlow-based control plane with the OpenFlow controller intelligently determines and assigns either appropriate modulation format/rate or a backup path in WSON in accordance with BER information.

A path computation element (PCE) is briefly defined as a control plane functional component (physical or logical) that is able to perform constrained path computation on a graph representing (a subset of) a network. A stateful PCE is a PCE that is able to consider the set of active connections, and its development is motivated by the fact that such knowledge enables the deployment of improved, more efficient algorithms. Additionally, a stateful PCE is said to be active if it is also able to affect (modify or suggest the modification of) the state of such connections. A stateful active PCE is thus able not only to use the knowledge of the active connections as available information during the computation, but also to reroute existing ones, resulting in a more efficient use of resources and the ability to dynamically arrange and reoptimize the network. An OpenFlow controller is a logically centralized entity that implements a control plane and configures the forwarding plane of the underlying network devices using the OpenFlow protocol. From a control plane perspective, an OpenFlow controller and the aforementioned stateful PCE have several functions in common, for example, in what concerns network topology or connection management. That said, both entities also complement each other, since a PCE is responsible mainly for path computation accessible via an open, standard, and flexible protocol, and the OpenFlow controller assumes the task of the actual data plane forwarding provisioning. In other words, the stateful PCE becomes active by virtue of relying on an OpenFlow controller for the establishment of connections. In this framework, the integration of both entities presents an opportunity allowing a return on investment, reduction of operational expenses, and reduction of time to market, resulting in an efficient approach to operate transport networks. In this paper, we detail the design, implementation, and experimental evaluation of a centralized control plane based on a stateful PCE, acting as an OpenFlow controller, targeting the control and management of optical networks. We detail the extensions to both the OpenFlow and the PCE communication protocol (PCEP), addressing the requirements of elastic optical networks as well as the system performance, obtained when deployed in a laboratory trial.

By using an OpenFlow/stateless PCE integrated control plane with significant protocol extensions, we successfully demonstrate and quantitatively evaluate dynamic end-to-end path provisioning and lightpath restoration in a transparent WSON employing flexible transmitters/receivers.

This paper presents and experimentally evaluates efficient strategies for dynamic source/Path Computation Element (PCE) routing with aggregated resource information and advanced distributed spectrum allocation algorithms in Generalized Multi-Protocol Label Switching (GMPLS)-controlled elastic optical networks. (C)2012 Optical Society of America

We demonstrate the world's first single-carrier-based, 400-Gb/s-class and 50-GHzspaced WDM system using 41.6-GBd PDM-64QAM per channel. Eight channels are successfully transmitted over 720-km SSMF with hybrid Raman and EDF amplification. © OSA 2012.

We experimentally present the seamless interworking between OpenFlow and PCE for dynamic wavelength path control in multi-domain WSON, assessing the overall feasibility and quantitatively evaluating both the path computation and lightpath provisioning latencies. © 2012 OSA.

We have successfully demonstrated the first terabit-class WDM transmission (7 × 1.12 Tb/s PDM-16QAM) over all-EDFA 400-km standard single mode fiber (SSMF) and 2 ROADMs. Q factors larger than 9.4 dB are found for all channels. © 2012 OSA.

In the current IP/optical multi-layer networks, the control approaches for IP and optical domains are separated, which is inconvenient for the end-to-end service provisioning. Therefore, the investigation of a unified control plane for multi-layer networks is a very important issue for network carriers, since it can simplify the network manageability, improve the network agility and reduce the operational expenditure (OPEX) and capital expenditure (CAPEX). The OpenFlow protocol, which has been proposed recently, provides a potential solution to address such an issue. On the other hand, the multi-layer optical burst switching (OBS) /wavelength switched optical network (WSON) has been proposed as one of the promising paradigms for future optical Internet, and the respective control plane for OBS and WSON layers under an overlay model has been intensively investigated in our previous works. In light of this, in this paper, we experimentally present an OpenFlow-based unified control plane for OBS/WSON multi-layer optical switched networks. The protocol extensions and design details of the OpenFlow-controlled OBS/WSON are discussed. By using two different signaling approaches (with and without confirmation mechanism during the lightpath provisioning period), we successfully demonstrate the overall feasibility of a unified control plane for OBS/WSON networks, and the performance of two signaling solutions is quantitatively evaluated in terms of end-to-end signaling latency and packet loss rate. © 2012 IEEE.

We investigate the effects of LiNbO 3 modulator chirp on the performances of optical multilevel signals detected by a digital coherent receiver and evaluate the optical filtering tolerances of multilevel signals. The results show that return-to-zero (RZ) pulse carving is useful to prevent the performance deterioration caused by the modulator chirp. © 2012 IEICE Institute of Electronics Informati.

In this paper, for the first time, we experimentally investigate OpenFlow-based reliable service provisioning and dynamic service differentiation in IP/DWDM multi-layer optical networks. All the solutions are experimentally demonstrated on a real testbed with both control and data planes, verifying their overall feasibility and efficiency, and quantitatively evaluating their performance. © 2012 IEICE Institute of Electronics Informati.

We propose a novel optical transmitter which can change flexibly the modulation format and/or bit rate of the optical signal. This transmitter can be used to generate BPSK, QPSK, 6PSK/6QAM, and 8PSK/8QAM formats. © 2012 IEEE.

In this paper we numerically investigate the impacts of 1) pulse width, 2) pulse chirp, 3) power imbalance, and 4) timing offset, for a 16-QAM, 448-Gb/s signal that uses optical time-division-multiplexing and electronic time-division-demultiplexing (OMED) scheme. © 2012 IEEE.

We compare the transmission performance of 413-Gb/s multi-band OFDM with 32-QAM (7%FEC) and 64-QAM (20%FEC) by simulations. The reachable distance with 64-QAM is longer than 32-QAM due to the filtering effects of 50-GHz-grid ROADMs. © 2012 IEEE.

Optical OFDM is a promising technology for increasing the bit-rate per WDM channel. The transmission experiments of 400 Gbit/s OFDM signal per WDM channel with 4bit/s/Hz and 8bit/s/Hz spectral efficiency are explained. © 2012 IEEE.

This paper shows the architecture of a router offloading method utilizing a superchannel signal technology that shows significant savings in energy consumption, compared to a router offloading method utilizing a sub-wavelength switching technology. © 2012 OSA.

We demonstrate a differential 6-ary PSK-based transmission system with 10-Gb/s NRZOOK neighboring channels over 320-km long SMF with in-line dispersion compensation and DSF links and compare its performances with that of a classical PDM-DQPSK-based system. ©2012 Optical Society of America.

We propose a polarization demultiplexing using linearly-estimated channel matrix for faster polarization tracking. Through experiments, we confirm that the proposed method can enhance tolerance of SOP change compared with demultiplexing using an identical channel matrix. ©2012 Optical Society of America.

We demonstrate for the first time an extended OpenFlow based control plane allowing seamless operation across heterogeneous state-of-the-art optical and packet domains. We also demonstrate for the first time multi-domain network slicing and verified results on a global scale trial involving test-beds in UK, Spain and Japan. © 2012 OSA.

We have successfully demonstrated 3 x 458-Gbit/s Optical Multi-band OFDM transmission over 160 km of SSMF with EDFA-only amplification at 50 GHz WDM spacing by utilizing narrowband optical filter. © 2012 OSA.

We have successfully demonstrated the first terabit-class WDM transmission (7 x 1.12 Tb/s PDM-16QAM) over all-EDFA 400-km standard single mode fiber (SSMF) and 2 ROADMs. Q factors larger than 9.4 dB are found for all channels. © 2011 OSA.

In this paper we introduced two power-efficient CO-OFDM systems and showed that both systems can have ~1-dB gain in receiving sensitivity (BER = 1e-3) and exhibit ~1.1-dB benefit in Q factor after 9360-km transmission when compared with the regular PDM-CO-OFDM. © 2012 OSA.

We design and deploy a GMPLS control plane for elastic CO-OFDM optical networks, detailing its functional architecture combining PCE routing and modulation assignment (RMA) with distributed spectrum allocation, the protocol extensions and the experimental validation. © 2012 OSA.

We propose a new method of generating 64QAM using electrical binary drive signals. The proposed technique has a potential to achieve the high symbol rate since it does not require the multilevel drive signals.

We propose a new transmitter for 16QAM generation based on a combination of a dual-drive Mach-Zehnder modulator (DD-MZM) and a dual-parallel Mach-Zehnder modulator (DP-MZM) with electrical binary drive signals. By using the proposed transmitter, we successfully evaluated the performances of 224-Gb/s and 320-Gb/s PDM-RZ-16QAM signals.

Elastic Optical Networks (EON), which are able to allocate an appropriate optical spectrum range and modulation format to an optical path according to the client (e.g. IP) traffic demand and path attributes (e.g., physical length or optical impairments), have been proposed to more efficiently utilize network spectrum resources. A control plane is a key enabling technique for dynamic and intelligent end-to-end path provisioning and recovery in such networks. In this paper, we design and deploy two different control planes for EON. One is based on the Generalized Multi-Protocol Label Switching (GMPLS) / Path Computation Element (PCE) architecture and protocols, and the other one is based on a centralized model extending OpenFlow. We detail the protocol extensions involved in the main functional aspects, and we experimentally validate both control plane approaches in a control plane testbed and compare them in terms of path provisioning latency.

Control plane techniques are very important for optical networks since they can enable dynamic lightpath provisioning and restoration, improve the network intelligence, and greatly reduce the processing latency and operational expenditure. In recent years, there have been great progresses in this area, ranged from the traditional generalized multi-protocol label switching (GMPLS) to a path computation element (PCE)/GMPLS-based architecture. The latest studies have focused on an OpenFlow-based control plane for optical networks, which is also known as software-defined networking. In this paper, we review our recent research activities related to the GMPLS-based, PCE/GMPLS-based, and OpenFlow-based control planes for a translucent wavelength switched optical network (WSON). We present enabling techniques for each control plane, and we summarize their advantages and disadvantages.

A unified control plane (UCP) for IP/Dense Wavelength Division Multiplexing (DWDM) multi-layer optical networks is a very important issue for network carriers. Generalized Multi-Protocol Label Switching (GMPLS), with a decade of development and standardization work, is a mature control plane technique for optical transport networks. But GMPLS-based UCP for IP/DWDM multi-layer networks is overly complex for deployment in a real operational scenario. On the other hand, OpenFlow has been verified as a promising solution for a UCP, but it is not mature enough to control optical switching nodes so far. Therefore, as an intermediate step towards a fully OpenFlow-based UCP, a logical choice at present is to introduce an OpenFlow/GMPLS interworking control plane which is able to use GMPLS to control the optical layer and use OpenFlow to dynamically coordinate between IP and optical layers. In light of this, in this paper, we experimentally present three interworking solutions (parallel, overlay and integrated) between OpenFlow and GMPLS for intelligent wavelength path control in IP/DWDM multi-layer optical networks. The overall feasibility of these solutions is assessed and their performance is quantitatively evaluated and compared on an actual network testbed.

The lightpaths within a wavelength switched optical network (WSON) are usually bi-directional, with a same route and a same wavelength which are allocated for both directions from the viewpoint of optical network operation. On the other hand, the introduction of generalized multi-protocol label switching (GMPLS) as a network control plane is expected to bring more intelligence and to provision the end-to-end lightpath in a cost-efficient manner. In this paper, we experimentally demonstrate and evaluate dynamic provisioning of bidirectional lightpaths in GMPLS controlled optical networks, considering the wavelength continuity constraint and the physical impairment constraint on both directions.

OpenFlow, which allows operators to control the network using software running on an external controller, provides the maximum flexibility for operators, and matches the carrier's preferences given its centralized architecture, simplicity and manageability. In this paper, we present an OpenFlow-based approach for dynamic wavelength path control in future photonic networks, assessing its overall feasibility and efficiency through a field trial.

This paper gives an overview of recent high capacity WDM transmission experiments using superchannels, in which multiple optical carriers are utilized to generate terabit-class channels.

In this paper we will review our recent works on DAC-free-generated 41-GBd PDM-64QAM (similar to 497 Gb/s) using one single I/Q modulator. Reaches from 720 to 1200 km on SSMF can be achieved by different receiving algorithms.

For PDM-CO-OFDM we propose and experimentally demonstrate a per-symbol-based digital back-propagation method which avoids the use of inefficient overlap-add method, saves one FFT circuit, and exhibits a similar performance when compared with the previous proposal

With optical time-division-multiplexing and electronic time-division-demultiplexing (OMED), we experimentally demonstrate the generation and detection of 22.4-GBd/s (2xOTDM) 64QAM and investigate the system sensitivities against both the power imbalance and timing offset between OTDM tributaries.

We successfully generate 11.2-GBd PDM-64QAM using one I/Q modulator driven with eightlevel signals synthesized by all binary electrical inputs. The signal quality is verified with similar to 1-dB Q margin (from 7% FEC threshold) after 320-km SSMF transmission.

In this paper we review our previously-proposed direct-detection optical OFDM superchannel and the corresponding optical-multi band receiving. With this technique we have successfully demonstrated the transmissions of no-and 1200-km SSMF, respectively, at 214- and 117-Gb/s data rates.

Optimization of the joint 32/64-QAM subcarrier modulation is investigated using 3x515-Gbit/s multi-band OFDM transmission over 320-km SSMF with 50-GHz frequency grid. It is confirmed that the optimized joint 32/64-QAM with 20%-overhead FEC enables to increase OSNR sensitivity compared to 32-QAM with 7%-overhead FEC and 64-QAM with 20%-overhead FEC.

Optical OFDM is a promising technology for highly spectrally efficient (SE) wavelength-division-multiplexing (WDM) system. Furthermore, the bit-rate 400 Gbit/s per WDM channel with SE of 8 bit/s/Hz is expected to be adopted for the next generation WDM system. For the application, optical OFDM is one of promising candidates because of the scalability for higher SE and higher bit-rate using multi-band OFDM technique. In this paper, the SE of multi-band OFDM is explained first, and WDM transmission experiments of multi-band OFDM signals with SE of over 8bit/s/Hz are introduced.

We present and experimentally evaluate efficient strategies in GMPLS-controlled elastic optical networks for dynamic source/PCE routing algorithms. These operate with aggregated optical spectrum information in combination with advanced distributed spectrum allocation algorithms which collect the status of all basic spectrum slots on each link.

We propose a new 16QAM optical transmitter based on a combination of a dual-drive Mach-Zehnder modulator (DD-MZM) and a dual-parallel Mach-Zehnder modulator (DP-MZM) with electrical binary drive signals. For 16QAM generation, two arms of DD-MZM are independently driven by two different binary data, and consequently, the DD-MZM produces an offset square 4QAM of the 16QAM constellation. This 4QAM signal is then switched over other quadrants through a typical QPSK modulation scheme by the following DP-MZM, and resulting in 16QAM. By using the proposed transmitter together with a digital coherent receiver, we successfully demonstrate the 224-Gb/s and 320-Gb/s PDM-RZ-16QAM systems. Their OSNR sensitivities at 3.8x10(-3) BER are observed to be 19.8 dB and 23 dB, respectively. (C) 2012 Optical Society of America

We present the implementation and validation of an Inter-layer Traffic Engineering (TE) architecture based on a hierarchical path computation element (PCE), where the parent PCE is notified of established optical layer Label Switched Paths that induce packet traffic engineering (TE) links, thus not requiring full topology visibility. We summarize the architecture, the control plane extensions and its experimental evaluation in a control plane testbed. © 2012 Optical Society of America.

We present new generation and detection methods for high symbol-rate 64-ary quadrature amplitude modulation (64QAM). The 64QAM signal is created by tandem in-phase/quadrature (I/Q) modulators driven by electrical binary signals. The first I/Q modulator, which has four drive arms (i.e. a dual-drive I/Q modulator), yields 16QAM with an offset at the 1st quadrant of the complex plane. Subsequently, the second modulator switches this 16QAM signal over four quadrants via the typical quadrature phase-shift-keying (QPSK) modulation scheme, hence the desired 64QAM is generated. To mitigate the impacts of transmitter imperfections, we also propose a phase-folded decision-directed (PF-DD) linear equalizer at the receiver. Using these new techniques, we experimentally demonstrate the 120- and 240-Gb/s polarization-division-multiplexed (PDM) return-to-zero (RZ) 64QAM systems. The required optical signal-to-noise ratio (OSNR) for a bit-error rate (BER) of 2.4x10(-2) is measured at 20.2 or 23 dB, respectively, which is similar to 3.5 dB off the theoretical limit. (C)2012 Optical Society of America

Proposed is a new method to synthesise the 8-ary quadrature amplitude modulation (8QAM) signal and demonstrate the 112Gbit/s polarisation-multiplexed 8QAM system. The proposed transmitter consists of a dual-drive Mach-Zehnder modulator (DD-MZM) and phase modulators in tandem. The DD-MZM is utilised to manipulate the amplitude and phase of the optical signal by adjusting its chirp. The optical signal-to-noise ratio sensitivity of the 112Gbit/s polarisation-multiplexed 8QAM signal to achieve the bit error rate of 10 -3 is measured to be 18.8dB (in 0.1nm resolution bandwidth). © 2012 The Institution of Engineering and Technology.

Current optical transport networks use optical channel carriers (wavelengths) that are defined and constrained by a fixed ITU-T dense wavelength division multiplexing (DWDM) grid. Such a grid is not adapted to high data rates (beyond 100 Gb/s) and is inefficient when a wavelength is assigned to a low-rate optical signal. Consequently, the ITU-T is updating the set of DWDM reference frequencies with the inclusion of a smaller channel spacing (e. g., 6.25 GHz) while allowing the allocation of frequency slots, that is, variable-sized frequency ranges composed of a number of slices. In this paper, we propose the design, implementation, and experimental validation of a Generalized Multi-Protocol Label Switching/path computation element (GMPLS/PCE) control plane for such flexible optical networks, using optical orthogonal frequency division multiplexing transmission technology, given its unique flexibility, bit-rate/bandwidth scalability, and subwavelength granularity. The control plane uses a distance-adaptive and PCE-based routing and modulation assignment, combined with distributed frequency slot (spectrum) selection. A comparative analysis of path computation algorithms is carried out, highlighting the benefits of extending the path computation function with the knowledge of the status of the slices and the spectral efficiency of the modulation formats.

We demonstrate an optical transmission system based on a 53.5-Gb/s differential 6-ary phase-shift-keying (D6PSK) signal with copropagating 10.7-Gb/s nonreturn-to-zero (NRZ) on-off keying (OOK) channels over either 320-km-long single-mode fiber link with in-line dispersion compensation or 320-km-long dispersion-shifted fiber link, and compare its performances with that of a classical polarization-division-multiplexing differential quadrature phase-shift-keying (DQPSK)-based system. The results show that the nonlinear tolerance of the D6PSK signal outperforms that of the PDM-DQPSK signal in terms of the cross-phase modulation effect induced by the 10.7-Gb/s NRZ-OOK neighboring channels.

In this paper, we propose and experimentally demonstrate the direct-detection optical orthogonal-frequency-division-multiplexing superchannel (DDO-OFDM-S) and optical multiband receiving method (OMBR) to support >100-Gb/s data rate and a longer distance for direct-detection systems. For the new OMBR, we discuss the optimum carrier-to-sideband power ratio (CSPR) both in the cases of back-to-back and after transmission, and derive the analytical form for CSPR which is verified with numerical results. An overhead-efficient training method for in-phase/quadrature-phase imbalance estimation is also introduced in order to obtain a better performance while maintaining the high throughput of the system. With experimental setups, we evaluate the two systems with 1) 16-QAM, 214-Gb/s (190 Gb/s without overhead) and 2) 4-QAM, 117-Gb/s (100 Gb/s without overhead) systems. The new proposals enable the record data rate per wavelength (214 Gb/s) and record distance of 720-km standard single-mode fiber (SSMF) for the >100-Gb/s DDO-OFDM systems, and achieve the record optical signal-to-noise ratio sensitivity of 21.2 dB and record distance of 1200-km SSMF (similar to 1 dB penalty) for the 100-Gb/s class DDO-OFDM systems.

We propose a new optical transmitter which is capable of changing flexibly the modulation format of the optical signal. By using this transmitter, we can handle and assign various modulation formats: binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-ary quadrature amplitude modulation (8QAM), and 16QAM. The proposed transmitter is based on a combination of a dual-drive Mach-Zehnder modulator (DD-MZM) and a dual-parallel MZM (DP-MZM) with electrical binary drive signals. DD-MZM is a key element to produce the 8QAM and 16QAM formats where each arm of DD-MZM is driven by independent binary data. This is because we can modulate the amplitude and phase of the optical signal by using a frequency chirp of the modulator when we adjust properly the amplitudes of the electrical drive signals. In addition, we show an algorithm by which the proposed transmitter can intelligently select the modulation format in accordance with the signal quality. (C)2012 Optical Society of America

Our Terabit LAN initiatives attempt to enhance the scalability and utilization of lambda resources. This paper describes bandwidth-on-demand virtualized 100GE access to WDM networks on a field fiber test-bed using multi-domain optical-path provisioning. (C)2011 Optical Society of America

Dynamic lightpath restoration is a key issue in wavelength switched optical networks (WSON). On the other hand, the introduction of the path computation element (PCE) and the generalized multi-protocol label switching (GMPLS) architectures into WSON as control plane technologies is expected to bring more intelligence and to enable the dynamic computation and control of end-to-end lightpaths in a cost-efficient manner. In this paper, for the first time and through a lab trial with four domains and a field trial located in Japan and Spain, we experimentally present PCE-based optical signal to noise ratio (OSNR)-aware dynamic restoration in multi-domain GMPLS-enabled translucent WSON, assessing the overall feasibility of the proposed techniques and quantitatively evaluating the service disruption time and path computation latency during end-to-end lightpath restoration. (C) 2011 Optical Society of America

Network architecture and transmission technologies to increase an overall efficiency in transport networks are discussed. Traffic grooming in a flexible grid with rate-tunable transponders by optical OFDM is an attractive solution. © 2011 IEEE.

Optical OFDM is one of promising technology to increase spectral efficiency. We explain the modulation scheme and WDM transmission experiments of 458 Gbit/s OFDM signal per WDM channel with 8 bit/s/Hz spectral efficiency. © 2011 National Sun Yat-Sen Univ.

We demonstrate a hybrid QAM transmission technique for single-carrier ultra-dense wavelength division multiplexing (UD-WDM) systems. With 112-Gb/s per channel on 25-GHz grid, we found the hybrid 4 and 8QAM technique shows a much better performance than the pure 4QAM and exhibits an ∼0.9-dB OSNR benefit over the pure 8QAM. © 2011 National Sun Yat-Sen Univ.

We will review our recent works on the transmission of a high-speed (> 100Gb/s) direct-detection optical OFDM super-channel (DDO-OFDM-S) over the dispersion-unmanaged standard-single-mode-fiber (SSMF) link. © 2011 National Sun Yat-Sen Univ.

We propose a polarization demultiplexing scheme using linearly interpolated channel matrix in PDM systems with MIMO processing. We confirm that the proposed scheme can double a tolerance for polarization changes compared to the conventional scheme. © 2011 National Sun Yat-Sen Univ.

Effectiveness of the MPLS-TP based router off-loading method is studied from power consumption and node cost perspectives. We compare power consumption and node cost between a conventional network and a router-off loading network utilizing a reference network. © 2011 National Sun Yat-Sen Univ.

We will review the transmissions of a high-speed (> 100Gb/s) direct-detection superchannel using optical OFDM over an all- EDFA-based standard-single-mode-fiber (SSMF) link.

We demonstrate an optical transmission system based on a 6-level PSK modulation format and differential detection with a partial symbol delay. The 6-level PSK signal is simply generated by using a chirp-free Mach-Zehnder modulator followed by a phase modulator. In order to convert the phase information of the 6-level PSK signal into the intensity, we utilize a pair of two Mach-Zehnder delay-line interferometers with having a differential delay less than the symbol duration of the signal unlike a conventional differential detection scheme. We evaluate the performances of the differential 6-level PSK signal and compare them with that of a conventional DQPSK signal. In addition, the transmission performance of the 21.4-Gb/s 6-level PSK signal is experimentally verified in a 240-km long dispersionmanaged fiber link. Furthermore, additional simulation results show that the tolerance to optical filtering and chromatic dispersion of the 107-Gb/s differential 6-level PSK signal is improved significantly by adopting the partial demodulation scheme. © 2011 SPIE-OSA-IEEE.

The lightpaths within a wavelength switched optical network (WSON) are usually bi-directional, with a same route and a same wavelength which are allocated for both directions from the viewpoint of optical network operation. On the other hand, the introduction of generalized multi-protocol label switching (GMPLS) as a network control plane is expected to bring more intelligence and to provision the end-to-end lightpath in a cost-efficient manner. In this paper, we experimentally demonstrate and evaluate dynamic provisioning of bidirectional lightpaths in GMPLS controlled optical networks, considering the wavelength continuity constraint and the physical impairment constraint on both directions.

We experimentally present a proof-of-concept demonstration of OpenFlow-based wavelength path control for lightpath provisioning in transparent optical networks, assessing its overall feasibility and quantitatively evaluating the network performances.

To provide end-to-end wide-bandwidth data transfer over lambda and Ethernet networks, we demonstrate dynamic circuit provisioning by web services interface proxy which enables interoperability among different network provisioning systems.

With EDFA-only amplification, we successfully demonstrate the transmission of a 4-QAM, 117-Gb/s (100 Gb/s without overhead) DDO-OFDM super-channel over 1200-km SSMF with only 1-dB OSNR penalty. We also discuss the impact of PMD on the transmission link. (C)2011 Optical Society of America

We have demonstrated an efficient scattered pilot channel tracking approach with a new polar-based intra-symbol frequency domain average (ISFA) for 16-QAM, 40-Gb/s PDM-CO-OFDM systems. This proposal could promise an relatively stable performance even under an rapidly time-varying environment. (C)2011 Optical Society of America

We will review the transmission and signal processing techniques (phase noise & IQ imbalance compensation) of our previously-proposed direct-detection optical OFDM super-channel (DDO-OFDM-S) over dispersion-unmanaged standard single mode fiber (SSMF) link.

For carrier-assisted PDM-CO-OFDM systems, we propose and demonstrate a practical carrier recovery method applying a very-simple moving average filter (MAF). Besides simplicity, we confirm its excellent performance from the results of a 16-QAM, 40-Gbps OFDM transmission experiment.

We investigated the optimized signal condition of the combined 8-QAM and QPSK subcarrier modulation for optical OFDM. The performance improvement was confirmed by WDM transmission experiments with the optimized power difference and subcarrier number.

We have demonstrated 7 x 463-Gbit/s Optical OFDM transmission over 960 km of SSMF with EDFA-only amplification at 100-GHz WDM spacing. It is confirmed that the intra-channel penalty is dominant compared to inter-channel penalty.

We design and fabricate an optical wireless USB 2.0 system with a wireless power transfer. A coverage of the optical wireless transceiver is expanded by more than 30 % at the optimum distance for the power transfer, which can maximize the coverage of the system with the commercially available power transfer module. Wireless data and power transfer are successfully demonstrated between a portable music/video player and a PC using the fabricated system.

Our Terabit LAN challenges are to enhance the scalability and utilization of lambda resources. Bandwidth-on-demand virtualized 100GE access to WDM networks on a field fiber test-bed using multi-domain optical-path provisioning is described.

The required bit resolution of digital-analog-converter (DAC) for optical OFDM was evaluated through simulation and experiment. We found that the signal degradation caused by quantization depends on the number of subcarriers theoretically, but the other noise generated in experiment suppresses the dependency. Additionally, signal degradation caused by quantization is independent of subcarrier modulation, and the performance improvement saturates with increasing bit resolution. With the criteria for the BER of 1 x 10(-3), the required DAC resolution by simulation with ideal analog-digital-converter at receiver is 3 bits for QPSK, 4 bits for 8-QAM and 5 bits for 16-QAM and 32-QAM. From the experimental result, the required bit resolution is increased as 6 bits for 32-QAM.

The design of an energy-efficient wavelength division multiplexing (WDM) transponder is proposed and effectiveness of the proposed WDM transponder is experimentally studied. The proposed WDM transponder interworking with the link-aggregation technique possessed by a layer 2 switch can achieve power saving depending on traffic volume variations by utilizing an adaptive interface control. Monitoring methods for the link connectivity of a sleep link are also discussed.

OpenFlow, as an open-source protocol for network virtualization, is also widely regarded as a promising control plane technique for heterogeneous networks. But the utilization of the OpenFlow protocol to control a wavelength switched optical network has not been investigated. In this paper, for the first time, we experimentally present a proof-of-concept demonstration of OpenFlow-based wavelength path control for lightpath provisioning in transparent optical networks. We propose two different approaches (sequential and delayed approaches) for lightpath setup and two different approaches (active and passive approaches) for lightpath release by using the OpenFlow protocol. The overall feasibility of these approaches is experimentally validated and the network performances are quantitatively evaluated. More importantly, all the proposed methodologies are demonstrated and evaluated on a real transparent optical network testbed with both OpenFlow-based control plane and data plane, which allows their feasibility and effectiveness to be verified, and valuable insights of the proposed solutions to be obtained for deploying into real OpenFlow controlled optical networks. (C) 2011 Optical Society of America

We experimentally present a lab trial of PCE-based OSNR-aware dynamic restoration in multi-domain GMPLS-enabled translucent WSON, assessing the overall feasibility and quantitatively evaluating the service disruption time and path computation latency during end-toend lightpath restoration.

A translucent wavelength switched optical network (WSON) is a cost-efficient infrastructure between opaque networks and transparent optical networks, which aims at seeking a graceful balance between network cost and service provisioning performance. In this paper, we experimentally present a resilient translucent WSON with the control of an enhanced path computation element (PCE) and extended generalized multi-protocol label switching (GMPLS) controllers. An adaptive routing and wavelength assignment scheme with the consideration of accumulated physical impairments, wavelength availabilities and regenerator allocation is experimentally demonstrated and evaluated for dynamic provisioning of lightpaths. By using two different network scenarios, we experimentally verify the feasibility of the proposed solutions in support of translucent WSON, and quantitatively evaluate the path computation latency, network blocking probability and service disruption time during end-to-end light-path restoration. We also deeply analyze the experimental results and discuss the synchronization between the PCE and the network status. To the best of our knowledge, the most significant progress and contribution of this paper is that, for the first time, all the proposed methodologies in support of PCE/GMPLS controlled translucent WSON, including protocol extensions and related algorithms, are implemented in a network testbed and experimentally evaluated in detail, which allows verifying their feasibility and effectiveness when being potentially deployed into real translucent WSON.

We present a lab-trial of the designed and implemented path computation architecture for multi-domain translucent wavelength switched optical networks (WSON), using hierarchical Path Computation Elements (H-PCE). The approach is based on the dynamic aggregation of the domain topologies, represented as a virtual link meshes at a higher level, in order to perform dynamic domain sequence selection. We detail the extended path computation procedures, involving both domain selections considering inter domain links and segment expansions which are impairment-aware, along with the proposed control plane protocol extensions. We validate the approach with the overall performance of the end to end path computation latency, highlighting the benefits of parallelization. (C) 2011 Optical Society of America

We propose a low-overhead method of polarization-multiplexed direct detection optical orthogonal frequency-division-multiplexing transmission that requires no digital multiple-input and multiple-output processing at the receiver. Optical filtering of carrier components allows a simple polarization separation. Using 16-quadrature amplitude modulation and only 31-GHz bandwidth, 100-Gb/s transmission over 80 km of standard single-mode fiber is successfully demonstrated. The crosstalk penalty was only 1.2 dB. We also investigated the laser frequency offset tolerance for the proposed 100-Gb/s transmission method.

The inter-channel crosstalk in high spectral efficient coherent PDM-OFDM transmission is experimentally studied. We confirm that the inter-channel nonlinear penalty is 0.1dB in 8x66.8-Gbit/s transmission over 640 km with up to 5.6bit/s/Hz spectral efficiency.

Key technologies for manageable and controllable translucent optical networks are reviewed. The overall demonstrations on PCE-based and fully distributed translucent optical network are also presented. ©2010 Optical Society of America.

In order to determine the optimal training symbol interval, we have experimentally evaluated the tolerable polarization change in PDM-OFDM systems. It was confirmed that the allowable polarization change is 0.17 radians in a TS interval of 20.88 μs. ©2010 IEEE.

A translucent optical network is a cost-efficient infrastructure between-opaque networks and transparent optical networks, which aims at seeking a graceful balance between network cost and service provisioning performance. This paper addresses the dynamic provisioning of lightpath within a GMPLS-enabled translucent optical network. The GMPLS extensions are implemented, and dynamic lightpath establishment with explicit 3R regeneration control is experimentally demonstrated and evaluated. All the proposed methodologies are evaluated on a real network testbed with both control plane and data plane, which allows verifying their feasibility and effectiveness when being potentially deployed into real translucent optical networks.

This paper overviews the recent technologies in the optical submarine cable systems and discusses technical challenges in order to raise the capacity-distance product to the order of 'exa' in Trans-Pacific systems.

We propose and demonstrate the optical multiband receiving method which supports transmission of a 16-QAM, 213.7-Gb/s (189.7-Gb/s) DDO-OFDM super-channel over 720-km SSMF. After transmission all the 9 OFDM bands exhibit BERs lower than the FEC threshold (BER = 3.8e-3).

We demonstrate a simple beat interference cancellation approach enabling higher spectral efficiency and better sensitivity (>2 dB) for DDO-OFDM. The associated benefits of enhanced phase noise and PMD tolerances, as well as the impacts of diverse filter parameters, are also discussed.

We demonstrate the first digital laser-phase-noise (PN) mitigation approach for DDO-OFDM which applies a simple Wiener filter for adaptively estimating the statistical-unknown PN. The PN tolerance, in terms of the achievable fibre length, is about tripled with this PN mitigation technique.

The required resolution of digital-analog-converter for optical OFDM was evaluated through simulation and experiment. Signal degradation caused by quantization was independent of subcarrier modulation, and the performance improvement saturates with increasing bit resolution. (C) 2010 Optical Society of America

400-Gbit/s coherent PDM-OFDM transmission over 80 km has been successfully demonstrated in 50-GHz frequency grid. The use of multiband OFDM with 32-QAM subcarrier modulation enables to increase a spectral efficiency to 8.0 bit/s/Hz at 400 Gbit/s.

We newly design and fabricate an optical wireless USB 2.0 system with a 1 Gbit/s optical transceiver. A performance of the 1 Gbit/s optical transceiver is evaluated, and a wireless music/video data transfer is successfully demonstrated using the system.

We propose an optical wireless USB 2.0 system with a 1 Gbit/s optical wireless interface and a new protocol which does not require any change of existing USB peripherals. A wireless video transmission and a data transmission are successfully demonstrated using the proposed system.

Design of an energy efficient wavelength division multiplexing (WDM) transponder is proposed and demonstrated. The WDM transponder interworking with the link-aggregation (LAG) technique possessed by a layer 2 switch (L2SW) can achieve power saving depending on traffic variations by utilizing an adaptive interface control.

Transmitter and receiver IQ imbalance causes image interference that degrades performance in high capacity and high spectral efficiency optical orthogonal frequency division multiplexing (OFDM) schemes. Digital compensation is an attractive method to relax component specifications. In this paper we report the details of a hybrid compensation method for IQ imbalance compensation, comprising of orthogonal training symbol-based method for transmitter-side compensation and an iterative image reduction-based method for receiver-side imbalance compensation. We demonstrate performance improvement using the hybrid method in presence of frequency dependent imbalance by both simulation and back-to-back direct detection optical OFDM experiment. We report on the tolerable limit of transmitter IQ imbalance under presence of carrier frequency offset. (C) 2010 Optical Society of America

In this paper, we discuss the realization of wavelength-division multiplexing (WDM) transmission at high spectral efficiency. For this experiment, coherent polarization-division multiplexing--orthogonal frequency-division multiplexing (PDM-OFDM) is used as a modulation format. PDM-OFDM uses training symbols for channel estimation. This makes OFDM easily scalable to higher level modulation formats as channel estimation is realized with training symbols that are independent of the constellation size. Furthermore, because of its well-defined spectrum OFDM requires only a small guard band between WDM channels. The dependence of the number of OFDM subcarriers is investigated with respect to the interchannel linear crosstalk. At a constant data rate the number of OFDM subcarriers is estimated to achieve lower linear crosstalk in order to achieve higher spectral efficiency. We then experimentally demonstrate dense WDM (DWDM) transmission with 7.0-b/s/Hz net spectral efficiency using 8 x 65.1-Gb/s coherent PDM-OFDM signals with 8-GHz WDM channel spacing utilizing 32-quadrature-amplitude-modulation subcarrier modulation. Successful transmission is achieved over 240 km standard single-mode fiber (SSMF) spans with hybrid erbium-doped fiber amplifiers/Raman amplification.

Orthogonal frequency division multiplexing (OFDM) is an attractive modulation format that recently

A hybrid compensation method for transmitter and receiver IQ imbalance in high capacity OFDM is investigated. Effectiveness is confirmed by simulation and a 16QAM 27.3-Gbit/s transmission experiment. After 320km SSMF, 3.5dB OSNR improvement is achieved. © 2009 OSA.

We investigate the effect of reflection-generated coherent crosstalk on the performance of optical OFDM transmission. From simulation, allowable total crosstalk at a given OSNR was found to be independent of the number of subcarriers. Experimental comparison is provided, showing a similar crosstalk-generated variance for optical OFDM and NRZ-OOK format. ©2009 Optical Society of America.

We propose a low-overhead method of polarization multiplexing in direct detection OFDM that requires no digital MIMO processing. Using 16QAM and only 31GHz bandwidth, 100 Gbps transmission over 80 km of SSMF is successfully demonstrated.

Optical orthogonal frequency division multiplexing for high-speed, long-haul optical transmission systems is reviewed. Some important aspects of the systems are discussed and demonstrations of high-speed transmission up to 122 Gbit/s are presented.

Spectral efficient transmission of 8x65.1-Gbit/s PDM-OFDM is reported over 240 km. Using coherent detection and 32-QAM subcarrier modulation the channel spacing is reduced to 8 GHz, allowing a net spectral efficiency of 7.0 bit/s/Hz. (C) 2009 Optical Society of America

Higher bit-rate transmission is attractive for improving network resource efficiency and reducing the complexity of network management in future transmission systems. However, chromatic dispersion and polarization mode dispersion (PMD) are one of the most serious impairments. In particular, PMD should be compensated for dynamically because it changes rapidly according to environmental variations such as temperature change and mechanical vibration. Therefore, an adaptive PMD compensator is indispensable for higher bit-rate transmission systems. In this paper, we employed a simple and bit-rate independent PMD compensator based on a polarizer with an optical power monitoring scheme in 160 Gb/s-based field experiments. By using the PMD compensator, the single channel transmission of a 160 Gb/s return-to-zero differential phase-shift-keying modulation signal over an installed fiber link with buried and aerial cable routes was successfully achieved. Approximately 1 dB of Q-factor was improved by using the PMD compensator when PMD impairment was maximized. Through these experiments, the effectiveness of the PMD compensator in the higher bit-rate transmission systems was confirmed in the field environment. Furthermore, single-polarization 8 x 160 Gb/s wavelength division multiplexing transmission over the installed 200 km standard single mode fiber without polarization demultiplexing was successfully achieved by using the simple PMD compensator.

In this letter, we investigate 132.2-Gb/s polarization-division-multiplexed orthogonal frequency-division-multiplexing (PDM-OFDM) transmission at 25-GHz channel spacing. We show that the nonlinear tolerance is dependent on the OFDM symbol length. By using 14.4-ns-long OFDM symbols, 7 x 132.2-Gb/s transmission of PDM-OFDM at 4-b/s/Hz spectral efficiency is reported over 1300-km standard single-mode fiber.

We discuss optical multi-band orthogonal frequency division multiplexing (OFDM) and show that by using multiple parallel OFDM bands, the required bandwidth of the digital-to-analogue/ analogue-to-digital converters and the required cyclic prefix can significantly be reduced. With the help of four OFDM hands and polarization division multiplexing (PDM) we report continuously detectable transmission of 10 x 121.9-Gb/s (112.6-Gb/s without OFDM overhead) at 50-GHz channel spacing over 1,000-km standard single mode fiber (SSMF) without any inline dispersion compensation. In this experiment 8 QAM subcarrier modulation is used which confines the spectrum of the 121.9 Gb/s PDM-OFDM signal within a 22.8 GHz optical bandwidth. Moreover, we propose a digital signal processing method to reduce the matching requirements for the wideband transmitter IQ mixer structures required for PDM-OFDM.

In this paper the optical performance and complexity of polarization division multiplexed quadrature phase shift keying (PDM-QPSK) is compared to that of PDM orthogonal frequency division multiplexing (PDM-OFDM). The benefits and drawbacks of each modulation format are discussed with respect to the implementation, complexity and transmission performance. (C) 2009 Elsevier Inc. All rights reserved.

Optical orthogonal frequency division multiplexing for long-haul optical transmission systems is reviewed. We discuss some important aspects of the systems and present a demonstration of long-haul transmission at 122 Gb/s without dispersion compensation. © 2008 Optical Society of America.

We have shown that a capacity of the transpacific system designed to support 8 × 2.5 Gbit/s can be increased to a factor of eight by using 16 × 10 Gbit/s RZ-DPSK in transmission experiments using a deployed submarine cable. © 2008 IEEE.

The influence of the dispersion map is studied on the nonlinear tolerance of OFDM transmission systems. We show that the nonlinear tolerance is severely degraded when inline dispersion compensation is employed in the transmission line.

During the last two years, numerous researchers have dedicated their work in optical OFDM and, consequently, the number of papers has grown exponentially. In this paper we evaluate the suitability of OFDM for long-haul 100GbE applications.

We show that the tolerance of 100GbE PDM-OFDM with respect to narrowband optical filtering is comparable to that of its single-carrier counterpart. This translates into a comparable spectral efficiency of OFDM and single-carrier modulated signals.

The automatic PMD compensator using polarization filtering with a polarizer was evaluated in 40Gbit/s and 160Gbit/s WDM transmission over installed fiber cables. The performance and long-term stability were enhanced with the simple PMD mitigation scheme.

We discuss the use of multi-band OFDM for 120-Gb/s polarization division multiplexed orthogonal frequency division multiplexing (PDM-OFDM). Compared to single-band OFDM we show that a significant reduction in required DAC/ADC bandwidth is obtained at comparable computational complexity.

8x66.8-Gbit/s DWDM transmission is demonstrated over 640-km SSMF with 9-GHz channel spacing. Employing coherent detected polarization-division-multiplexing OFDM with 16-QAM subcarrier modulation, a record spectral efficiency of 5.6 bit/s/Hz is achieved.

We discuss coherent optical orthogonal frequency division multiplexing (CO-OFDM) as a suitable modulation technique for long-haul transmission systems. Several design and implementation aspects of a CO-OFDM system are reviewed, but we especially focus on phase noise compensation. As conventional CO-OFDM transmission systems are very sensitive to laser phase noise a novel method to compensate for phase noise is introduced. With the help of this phase noise compensation method we show continuously detectable OFDM transmission at 25.8 Gb/s data rate (20 Gb/s after coding) over 4160-km SSMF without dispersion compensation.

We discuss the realization and performance of polarization-division-multiplexed orthogonal frequency division multiplexing (PDM-OFDM) for long-haul transmission systems. Polarization demultiplexing of the PDM signal at the receiver is realized by employing a multiple-input multiple-output (MIMO) detector. Using a recirculating loop a long-haul transmission experiment is reported of 52.5 Gbits/s PDM-OFDM (40 Gbits/s after coding) over 4160 km of standard single-mode fiber (SSMF). In this transmission experiment, 16 wavelength-division-multiplexed (WDM) channels are transmitted at 50 GHz channel spacing, and we show that MIMO processing in the receiver enables both polarization demultiplexing and a large PMD tolerance. (c) 2008 Optical Society of America.

In order to realize a future 100-Gb Ethernet (100 GbE) transport, 100-Gb/s transmission without 100-GHz-class electronics and optical time-division-multiplexing technique was demonstrated. By using a differential quadrature phase-shift-keying (DQPSK) modulation format and commercially available electronics, 2- and 50-km transmissions of 100-Gb/s signal were successfully achieved over a standard single mode fiber. The receiver sensitivity, chromatic dispersion, and differential group delay tolerances of 100-Gb/s DQPSK signal were also evaluated. Through these evaluations, the possibility of DQPSK modulation for future 100-GbE transport is verified.

We experimentally assess the nonlinear tolerance of 10-Gb/s NRZ in a precompensated dispersion map. It is observed that even for relatively wide 100-GHz channelspacing, XPM further reduces the nonlinear tolerance in contrast to periodically-compensated maps. © 2006 Optical Society of America.

We introduce a novel method to compensate for local oscillator offset and phase-noise in coherent-OFDM systems and report continuously detectable transmission at 20-Gb/s data rate (25.8 Gb/s before coding) over 4,160-km SSMF without dispersion compensation. © 2007 Optical Society of America.

We show that using RF-pilot tone phase noise compensation optical coherent 10-Gb/s OFDM (12.5 Gb/s before coding) can be realized with conventional DFB lasers.

This paper gives an overview of recent 100-Gbitls transmission experiments and reviews enabling technologies for the realization of single-channel 100 Gbit/s Ethernet.

This paper discusses advanced modulation formats for the realization of single-channel 100-Gbit/s transmission in optical fiber communication systems.

We demonstrate 100Gbit/s DQPSK transmission experiment over 50km SMF. Without resorting OTDM, 100Gbit/s transmission was enabled with DQPSK format and commercially available electronics. Possibility of DQPSK modulation for future 100G Ethernet transport is verified. (C) 2006 Optical Society of America.

The performance of various modulation formats, namely OOK, DPSK and DQPSK with and without RZ carving, were experimentally compared to clarify the optimum modulation formats for 40 Gbit/s DWDM transmission systems with 50 GHz channel spacing. © 2004 Optical Society of America.

The optimum 42.7 Gbit/s modulation format to upgrade 10.7 Gbit/s transmission systems with 50 GHz channel spacing was studied. RZ-DQPSK was more suitable than duobinary, since 1600 km transmission was achievable with a wider tolerance to PMD.

We demonstrate 100Gbit/s DQPSK transmission experiment over 50km SMF. Without resorting OTDM, 100Gbit/s transmission was enabled with DQPSK format and commercially available electronics. Possibility of DQPSK modulation for future 100G Ethernet transport is verified. © 2006 Optical Society of America.

Single-polarization 160-Gb/s-based wavelength-division-multiplexing (WDM) field transmission has been successfully demonstrated. By using a return-to-zero differential phase-shiftkeying modulation format and a simple polarization-mode dispersion compensator, we have successfully demonstrated single-polarization 8 × 160 Gb/s WDM transmission without the polarization demultiplexing. © 2005 IEEE.

Single-polarization 160 Gbit/s-based field transmission experiments have been successfully conducted. By utilizing 160 Gbit/s RZ-DPSK signals and a simple PMD compensator, single-channel transmission and 8 WDM transmission with 300 GHz channel spacing have been achieved over the inter-city 200 km SMF.

We have performed numerical and experimental optimization of dispersion-managed Wavelength Division Multiplexed (WDM) Return-to-Zero (RZ) transmission without in-line control at 40 Gbit/s per channel in symmetric dispersion maps using effective area enlarged positive dispersion fiber and reverse dispersion fiber. Our results show the feasibility of transmission over 2800 km without Forward Error Correction (FEC) and over 4500 km with 8 % FEC overhead. The results of numerical modeling are in good agreement with experimental data. © by Fachverlag Schiele & Schön 2005.

1.14 b/s/Hz spectrally efficient 50 × 85.4-Gb/s copolarized return-to-zero differential quarternary phase-shift keying (RZ-DQPSK) signals have been transmitted over 300 km of nonzero dispersion-shifted fiber (NZ-DSF), using optical prefiltering and conventional C-band erbium-doped fiber amplifier (EDFA) repeaters. In this study, in order to enhance the spectral efficiency, the impact of optical prefiltering on the RZ-DQPSK signal was experimentally investigated in comparison to the DQPSK signal, and we found that the RZ-DQPSK signal had better sensitivity with almost the same nonlinear tolerance than the DQPSK signal even with 65-GHz bandwidth optical prefiltering. © 2005 IEEE.

1.14 b/s/Hz spectrally-efficient 50 × 85.4 Gb/s transmission over 300 km (75 km × 4 spans) of NZ-DSF has been successfully demonstrated with copolarized CS-RZ DQPSK signals. 42.7 Gsymbol/s-based 4 Tb/s DQPSK transmission has been achieved for the first time without polarization multiplexing. © 2004 Optical Society of America.

High spectral efficiency is the key to achieve ultra DWDM transmission with a finite bandwidth. This paper reviews highly spectral efficient transmission experiments using bandlimited signals for terrestrial systems and ultra long-haul systems.

High spectral efficiency is a key to cost-effective capacity expansion in WDM systems. This paper discusses the characteristics of optically filtered CS-RZ OOK and DPSK signals for higher spectral efficiency. © 2004 IEEE.

The impact of asymmetric pre-filtering for 42.7Gbit/s CS-RZ DPSK signals were investigated experimentally and numerically, including 9000km WDM transmission experiments. We have found that asymmetric pre-filtering is effective for quasi-linear system applications. © 2003 Optical Society of America.

Ultra-long-haul 42.7-Gbit/s-based dense wavelength-division multiplexing (DWDM) transmission using optically prefiltered carrier-suppressed return-to-zero (CS-RZ) signal has been experimentally investigated. First, we have numerically and experimentally evaluated the impact of 3-dB bandwidth and filter detuning of bandlimiting filters on the 42.7-Gbit/s CS-RZ signal in back-to-back condition. We found that the asymmetrically filtered CS-RZ signal had a great potential for ultra-DWDM applications. Next, we have numerically and experimentally investigated the basic transmission characteristics of a 45-GHz-wide prefiltered CS-RZ signal, such as the robustness against residual dispersion, nonlinear effects, and PMD, and have confirmed that the prefiltered CS-RZ signal had less tolerance against fiber nonlinearity than an unfiltered CS-RZ signal. Finally, we have experimentally investigated the optimum filtering condition for 65- or 45-GHz-wide prefiltered CS-RZ signals in the ultra-long-haul DWDM transmission and have conducted the 70- and 50-GHz spaced 32 × 42.7 Gbit/s transmission using prefiltered CS-RZ signals. Through these experiments, we have confirmed the effectiveness of prefiltered CS-RZ signal ultra-long-haul DWDM transmission.

The effectiveness of a self-phase modulation (SPM)-based all-optical reshaper with optically time-division-demultiplexing receiver was experimentally investigated using 42.7-Gb/s carrier-suppressed return-to-zero (CS-RZ) signals. We have confirmed that this scheme is quite effective to suppress the waveform degradation due to optical signal bandlimitation. We have demonstrated 80% spectral efficiency without using polarization demultiplexing by using the all-optical reshaper. We have also demonstrated 50-GHz-spaced 55 × 42.7 Gb/s signals transmission over 2500 km, using an optically bandlimited CS-RZ signal and the SPM-based all-optical reshaper in receiver without using polarization demultiplexing. A Q-factor improvement of about 1.5 dB was obtained by using the all-optical reshaper.

70-GHz-spaced 40 × 42.7 Gb/s prefiltered carrier-suppressed return-to-zero differential phase-shift keying (CSRZ-DPSK) signals have been transmitted over transpacific distances for the first time, using all-Raman repeaters with two pump-wavelengths, dispersion-managed fiber commercially available in volume, and an ETDM receiver. In this paper, first, in order to enhance the spectral efficiency, the impact of bandlimitation to a CSRZ-DPSK signal was experimentally investigated in comparison to a conventional CSRZ-on-off-keying (OOK) signal, and we found that the bandlimitation tolerance of CSRZ-DPSK signal was smaller than that of CSRZ-OOK signal in back-to-back condition. We also confirmed that the prefiltering CSRZ-DPSK signal with up to 65 GHz bandlimitation potentially had better transmission performance than the prefiltered CSRZ-OOK signal. In addition, we found that, although the nonlinear transmission penalty was increased by bandlimitation, this penalty for CSRZ-DPSK signal was smaller than that for CSRZ-OOK signal. Through this study, long-term stability of the transmission performance was also evaluated with low-speed signal polarization scrambling without using any polarization mode dispersion (PMD) compensation.

We numerically and experimentally investigated the upgradability of the longest and the typical segments of the JIH system. Through these studies, we confirmed that a 100 GHz-spaced 25×42.7 Gbit/s transmission with the total capacity of 1 Tbit/s can be attainable even by using NRZ signal and standard FEC for the typical segments. We also found that RZ signal format was desirable for the longest segment and a further wide system margin could be expected by using adjacent channel polarization control and advanced FEC technologies.

We have studied the transmission characteristics of optically pre-filtered 32× 42.7Gbit/s CS-RZ signals in 57% and 80% spectral-efficient all-Raman repeatered transmission over > 4000km under various pre-filtering conditions. We found that the advantage of asymmetrical pre-filtering reduced with transmission distance.

We have studied the gain modulation characteristics of 80nm-band high-power backward-pumped Raman amplifier. We found that flat gain modulation response was obtained over the entire signal bandwidth by intensity-modulating the longest-wavelength pump light source at a frequency higher than 10kHz.

We have numerically and experimentally studied the benefit of asymmetrically filtered 40Gbit/s CS-RZ signals, We also evaluated their tolerance to chromatic dispersion, fiber nonlinearity and polarization mode dispersion in comparison with symmetrically filtered and unfiltered CS-RZ signals.

70GHz-spaced 40×42.7Gbit/s pre-filtered CS-RZ DPSK signals have been successfully transmitted over 8700km for the first time, using all-Raman repeaters, "ABA" dispersion map and an ETDM receiver. Long-term stability was also confirmed with low-speed polarization scrambling and without using PMD compensation. © 2003 Optical Society of America.

40 Gbit/s-based transoceanic transmission was achieved by introducing various kinds of technologies to suppress the nonlinear effects in the transmission fiber, including fiber dispersion management, distributed Raman amplified, modified modulation format and powerful FEC codes. The possibility of enhancing the practicality and commercial viability of 40 Gbit/s-based transoceanic systems further was emphasized.

Dispersion tolerance improvement through self-phase modulation-based all-optical reshaping in receiver was experimentally investigated using 10-Gb/s return-to-zero signal. We have confirmed that this scheme is quite effective to restore the optical signal deformed due to chromatic dispersion.

The authors have successfully demonstrated 40 Gbit/s-based terabit-capacity unrepeatered transmission over 306 km. They transmitted 100 GHz-spaced 25 × 40 Gbit/s RZ signals with Q-factors all better than 15.6 dB using a hybrid transmission line configuration of 175 μm2-Aeff (effective core area) fibres and NZ-DSF and using a remote EDFA that requires no dedicated pump light transmission fibre. The attained transmission distance was over 306 km for 40 Gbit/s-based unrepeatered transmission.

The pattern dependency in bit error characteristics of asymmetrically filtered CS-RZ signals has been experimentally and numerically studied. It was found that the bit error intensively occurs just after the end of a long sequence of 1s or 0s for strong asymmetrical filtering.

The optimum signal format and forward error correction (FEC) code rate for 40 Gbit/s-based WDM signals was investigated. The impact of optical filtering for 40 Gbits/s signals was studied. Results showed that the symmetrically filtered signals had more tolerance for dispersion compensation for fiber nonlinearity.

The impact of the inter-pulse relative optical phase in optical time division multiplexing (OTDM) signals on long-distance 40 Gbit/s transmission performance was investigated. The transmission performance between OTDM and conventional 40 Gbit/s carrier-suppressed (CS)-RZ signals was compared. It was found that the OTDM CS-RZ signals had superb large tolerance in pulse generation process.

Bit error rate performance improvement using an SPM-based all-optical reshaper with OTDM receiver was demonstrated. We have achieved 80% spectral efficiency without using polarisation demultiplexing at the receiver for 42.7 Gb/s-based DWDM CS-RZ signals.

40 GHz-spaced 25 × 42.7Gbit/s transmission was successfully conducted over 320km by using EDFA repeaters, asymmetrically filtered CS-RZ signal, an OTDM receiver and a novel spectral crosstalk suppressor based on the optical gating of dispersively stretched signal.

Bit error rate performance improvement by using self-phase modulation-based all-optical reshaping in a receiver was experimentally investigated using 10 Gbit/s return-to-zero (RZ) signals. We have confirmed this scheme quite effective in restoring the degraded pulse shape due to optical bandlimitation.

40 Gbit/s-based unrepeatered wavelength division multiplexed transmission over 362 km has been demonstrated for the first time. The obtained bit error rate was better than 1 × 10-9 for all 25 channels despite the highly dispersive transmission line (∼8000 ps/nm).

The impact of optical filtering on 40-Gb/s return-to-zero (RZ) signals was experimentally investigated with an optically time-division multiplexing (OTDM) receiver. Through the evaluation of the signal performance by changing the interpulse-phase conditions of the symmetrically band-limited 40-Gb/s signals, we have confirmed that the similar performance was obtained regardless of the interpulse-phase condition, owing to the pulse-reshaping capability of an OTDM receiver. The performance comparison was also conducted between the symmetrically and asymmetrically filtered 40-Gb/s RZ signals. It was found that the symmetrically filtered signal was more tolerant for the dispersion-compensation error, while the asymmetrically filtered signal was more tolerant for the fiber nonlinearity with optical filters that have a 3-dB bandwidth of 45 GHz.

The Raman gain shape of several types of dispersion-flattened fibre span was evaluated under different operating conditions in backward pumping. It was found that the overall gain shape depends on the fibre span configuration. It was also found that the Raman gain shape has little dependence on the operating conditions in the fibre span configurations.

The effectiveness of Aeff enlarged positive dispersion fiber (EE-PDF) and hybrid amplification configuration with erbium-doped fiber amplifier (EDFA) and fiber Raman amplifier for reducing the fiber nonlinearity and improving the transmission performance in long distance 40 Gbit/s-based WDM transmission was investigated. We have confirmed that the use of EE-PDF in modified dispersion map for 40 Gbit/s transmission is quite effective to increase the transmissible distance and have successfully demonstrated 16 × 40 Gbit/s WDM transmission over 2000 km with proper dispersion management. We have also confirmed that the use of distributed Raman amplification is quite effective to extend the repeated spacing. By adding the optimum Raman amplification, almost the same transmission performance was obtained with a doubled repeater spacing in long distance 40 Gbit/s-based WDM transmission.

The transmission of 20 Gbit/s-based terabit wavelength division multiplexing (WDM) signals over 9170 km was demonstrated. A 23-nm bandwidth C-band erbium doped fiber amplifier (EDFA) and symmetrically dispersion-managed fibre span were used for the purpose. The use of enhanced forward error correction (FEC) with 7% redundancy resulted in the enhancement of the FEC gain for the transpacific transmission.

Optimum configuration for hybrid Raman/EDFA amplification in ultra-long-distance 40 Gbit/s WDM transmission was investigated. By optimizing the Raman gain, 16 × 40 Gbit/s WDM transmission over 2000 km was achieved with 80 km amplifier spacing.

Transmission performance of DSB and VSB signals was compared for the first time in 20Gbit/s-based ultra-long-haul WDM transmission systems. Impact of channel spacing, repeater output power variation and terminal dispersion compensation error was investigated.

We have demonstrated 50GHz-spaced 40Gbit/s × 64WDM unrepeated transmission over 230km using a low-noise Raman amplifier, 170μm2-Aeff fiber and bandlimited RZ signals without polarization-demultiplexing at the receiver. 2.56Tbit/s capacity was transmitted with only 25.8nm bandwidth.

The possible key technologies for the ultra long-haul multi-terabit transmission systems were studied. The effectiveness of VSB-RZ transmission for high spectral efficiency and the need for further nonlinearity suppression in the transmission line for 40Gbit/s based WDM system applications was shown. The reconstruction of the suppressed sideband was found to be very small, thus the overall signal spectrum was kept narrow after 4260 km transmission. The Q-factor after 1935 km and 4260 km transmission was found to be 15.7dB and 12.6dB.

The study of polarization mode dispersion (PMD) and dispersion tolerance of 20 Gbit/s vestigial-sideband (VSB)-RZ optical signal was presented. The performance degradation of 20 Gbit/s double-sideband (DSB)-RZ and VSB-RZ signals were compared against PMD/PDL and dispersion compensation error. Results showed that the VSB-RZ signal had similar tolerance for first-order PMD with better tolerance for dispersion.

The transmission of 20 Gbit/s-based terabit wavelength division multiplexing (WDM) signals over transpacific distances was reported. The transmission was done using a 23 nm-bandwidth C-band erbium-doped fibre amplifiers (EDFA) and symmetrically dispersion-managed fibre span. The average Q-factor and averaged optical signal-to-noise ratio (OSNR) of all channels against transmission distance was presented. Results showed that both Q-factor and OSNR degrade almost linearly with transmission distance in the 6500 to 9200 km range.

50 GHz spaced 40 Gbit/s×25WDM transmission over 480 km has been successfully demonstrated using bandlimited RZ signals and an SMF-based dispersion-flattened transmission line. What the authors believe is the longest distance transmission for a spectral efficiency of 0.8 bit/s/Hz was achieved without using polarisation demultiplexing.

The optimum configuration for hybrid Raman/EDFA amplification in ultra-long-distance 40Gbit/s WDM transmission using a dispersion-flattened fibre span is investigated. By optimising the Raman gain, 16 × 40Gbit/s WDM transmission over 2000km was achieved with 80km repeater spacing.

The unrepeatered transmission of 40 Gbit/s-based teracapacity 306 km wavelength division multiplexed (WDM) signals using 175 μm2-Aeff fibre was demonstrated. The system used remote-erbium doped fiber amplifiers (EDFA) and Raman amplification without using a separate fibre for pump power transmission. The development of ultra-large-Aeff positive dispersion fibre (PDF) cables was stated to be necessary for the realization of ultra-long-distance unrepeatered systems.

40 Gbit/s-based WDM transmission using the dispersion flattened transmission span, which consisted of positive and negative dispersion fiber, was experimentally investigated. In the SMF-based transmission line, which has large dispersion, the penalty due to nonlinear crosstalk between WDM channels was found to be small. The effectiveness of distributed Raman amplification and low-nonlinear fiber to suppress the intra-channel nonlinear crosstalk was also investigated. By using optimum dispersion map on low-nonlinear fiber span, transmission distance over 2000 km was achieved in 16 x 40 Gbit/s WDM transmission experiment.

A 40 Gbit/s single-channel transmission experiment over standard single mode fiber was conducted using distributed Raman amplification (DRA). A transmission distance of over 10000 km was achieved using dispersion management on dispersion shifted fiber (DSF). It was found that DRA reduced the effect of pulse interactions and improved the transmission performance.

Dispersion-flattened fiber spans with a single mode fiber (SMF) and a slope-compensating dispersion compensation fiber (SCDCF) have been demonstrated as fiber link for 40 Gbit/s wavelength division multiplexed (WDM) transmission. However, massive dense WDM (DWDM) transmission may cause significant interchannel crosstalk due to fiber nonlinearities. The impact of nonlinear penalty due to increase of the channel count in a 0.8 nm-spaced SMF/SCDCF-based 40-Gbit/s DWDM system is investigated. It is shown that the performance degradation for the increase of WDM channel count is not so large and that the penalty due to nonlinear crosstalk was <1 dB even in 16-channel transmission over 1500 km.

The impact of the dispersion map on 10-Gbit/s single-channel transmission was experimentally investigated. The transmission performance was significantly varied with the dispersion map. By using the optimum dispersion map, 40-Gbit/s transmission over 10,200 km has been achieved.

A 20 Gb/s-based soliton wavelength division multiplexed (WDM) transmission experiments using periodic dispersion compensation and dispersion slope compensation were demonstrated. Accumulated dispersion slope was compensated with two methods. The first method was periodical individual dispersion compensation. By using this technique, 60 Gb/s (20 Gb/s × 3 WDM) transmission over 8000 km was demonstrated. The second method was the use of a dispersion-flattened transmission fiber. 160 Gb/s (20 Gb/s × 8 WDM) transmission over 4000 km using periodically dispersion compensated dispersion-flattened fiber was also demonstrated. © 1999 IEEE.

1 Tbit/s (10×10.7 Gbit/s) transmission over 6200 km is obtained using 30 nm wide single-stage C-band optical repeaters (gain flatness <+/-10.1 dB), Aeff-enlarged positive dispersion fiber (Aeff>110 μm2) and slope-compensating dispersion-compensating fiber with a channel spacing of 0.3 nm. This transmission is investigated to study the possibility of terabit/s submarine systems.

Forty Gb/s single-channel soliton transmission experiments using periodic dispersion compensation were conducted. The impact of the dispersion map on the transmission performance was experimentally investigated. The transmission performance was significantly varied with the dispersion map. The improvement of the transmission performance by the polarization division multiplexing, which reduced soliton-soliton interaction furthermore, was also confirmed. By using the polarization division multiplexing in the optimum dispersion map, 40 Gb/s single-channel transmission over 10 200 km has been successfully demonstrated without any active inline transmission control.

400 Gbit/s (20×20 Gbit/s) wavelength division multiplexing (WDM) transmission over 2000 km with a channel spacing of 0.8 nm using pre- and periodic dispersion compensation scheme and dispersion flattened fiber (DFF) is demonstrated. A bit error rate of less than 10-9 is obtained for all the channels after over 2000 km transmission. The transmission scheme is quite effective to increase the number of channels keeping higher channel bit rate in ultra large capacity transmission. Transmission distance seems to be limited by the signal-to-noise ratio after the transmission. Small effective area of around 35·m2 of DFF prevents increasing the signal power level.

By reducing the timing jitter and soliton-soliton interaction effectively, 40 Gbit/s transmission over 10200 km has been successfully demonstrated for the first time without any active components in the transmission line.

400Gbit/s (20 × 20Gbit/s) soliton-based return-to-zero signals were successfully transmitted over 2000km of dispersion flattened fibre with a channel spacing of 0.8nm by using a pre- and periodical dispersion compensation scheme.

A 40Gbit/s single-channel soliton transmission experiment using periodic dispersion compensation is described. By applying dispersion management and optimum initial phase modulation, single-channel 40Gbit/s transmission over 8600km has been successfully demonstrated, for the first time, without any active transmission control in the transmission line.

160Gbit/s (8 × 20 Gbit/s) soliton WDM signals were successfully transmitted over 4000km with a BER of < 10-9, by using periodically dispersion-compensated dispersion-flattened fibre with an average dispersion slope of 0.0005 ps/km/nm2.

The effectiveness of periodic dispersion compensation on single-channel 40 Gbit/s soliton transmission system was experimentally investigated. This technique requires just the dispersion compensation fibers and wideband optical filters in the transmission line, which has no difficulty to be used in the practical system. By using polarization-division-multiplexing together with periodic dispersion compensation, single-channel 40 Gbit/s transmission over 4700 km was demonstrated. Single-polarization 40 Gbit/s transmission experiments, which are more suitable for system implementation and compatible with WDM were also conducted. We investigated the transmission characteristics and pulse dynamics in different dispersion maps and in the optimized dispersion map, single-channel, single-polarization 40 Gbit/s transmission over 6300 km was successfully demonstrated.

160 Gbit/s (8×20 Gbit/s) soliton WDM signals were successfully transmitted over 4000 km with BER of less than 10-9, by using periodically dispersion-compensated dispersion flattened fibre with average dispersion slope of 0.0005 ps/km/nm2.

The influence of initial pulse overlapping conditions on the transmission performance in soliton wavelength division multiplexing (WDM) transmission scheme was investigated using periodic dispersion and dispersion slope compensation. The effect of the initial pulse overlap on the transmission performance was small in the 2-channel 20 Gbit/s soliton WDM system. A transmission over 10000 km was possible regardless of the initial pulse overlap conditions indicating the applicability of the optical add-drop multiplexing to soliton WDM systems.

The accumulation of Gordon-Haus jitter can be effectively suppressed by the use of periodic dispersion compensation and in-line optical filters. The feasibility of 20-Gbit/s soliton-based transoceanic systems has been confirmed through 1000-km loop transmission experiments and 8100-km straight-line transmission experiments that employed periodic dispersion compensation. For a 20-Gbit/s, 9000-km transmission system, a Q2 of 19 dB, a sufficient power window of 2.5 dB, and robustness to repeater output power reduction have been demonstrated, as has compatibility with the conventional supervision scheme. A dramatic increase in system capacity can be expected from soliton wavelength-division multiplexing with periodic compensation of dispersion and its slope. © 1997 Optical Society of America.

Soliton WDM transmission of two and three-channel 20Gbit/s signals over transoceanic distances has been demonstrated, for the first time, using periodic compensation of dispersion and its slope of the transmission fibre without any active soliton control, sliding frequency guiding filters, or dispersion tapering fibre.

The authors have demonstrated the effectiveness of periodic dispersion compensation and polarisation-division-multiplexing for timing jitter reduction in 40Gbit/s single-channel soliton transmission, and have succeeded in 5000km straight-line transmission experiments at 40Gbit/s for the first time.

Transmission performance has been greatly improved by employing bit-synchronous phase modulation to source pulses in 20Gbit/s soliton-based RZ transmission experiments. The tolerable window for both repeater output power and signal wavelength, for 9000km transmission, was doubled with phase modulation.

We have demonstrated the effectiveness of the periodic dispersion compensation and polarization-division-multiplexing for timing jitter reduction in 40 Gbit/s single-channel soliton transmission, and have succeeded in 5000 km straight-line transmission experiments at 40 Gbit/s for the first time.

20 Gb/s single-channel soliton signal has been successfully transmitted over 9000 km without inline filters, for the first time, using periodic dispersion compensation. The Gordon-Haus timing jitter at 9000 km was reduced by a factor of more than 3 just with the dispersion management.

Straight-line single-channel 20 Gbit/s transmission experiments were conducted over 8100 km for the first time. The obtained Q2 was 19 dB. Superimposed-tone transmission capability and robustness to repeater output power reduction were also confirmed.

Novel techniques for data-coded dark pulse generation and detection using bright-dark conversion have been proposed. 10 Gbit/s data-coded dark pulse generation using a nonlinear optical loop mirror and dark pulse detection using an electroabsorption modulator were demonstrated.

A novel soliton transmission scheme to suppress the accumulation of the Gordon-Haus jitter using periodic dispersion compensation and inline optical filters has been proposed. With 90% dispersion compensation rate and optimum optical filters, a Q2 of 19dB and a large power window of 2dB were confirmed for a 20Gbit/s, 9000 km transmission system by using a 1000km-long recirculating loop. © 1995, IEE. All rights reserved.