Semiconductor quantum dots can be used for an optical gain-chip in an external cavity to construct a stable two- or few-mode laser. In this study, we demonstrate wide-range mode separation control of a few-mode laser by using a multistep etalon filter. Since the precise control of multistep thickness in one etalon plate was achieved, the frequency separation of the few-mode laser can be changed by choosing the etalon position. We can change the frequency separation from 83 to 104 GHz by using this method.

We present a 100-GHz integrated photoreceiver using an optical-to-radio converter and an enhancement-mode PHEMT amplifier driven by all optical resources without an external electric power supply. Technology for the simultaneous generation of radio and power was developed using a zero-bias operational uni-travelling carrier (UTC) high-speed photodetector. To improve the optical-to-electrical conversion efficiency, a 110-GHz enhancement-mode InP-PHEMT amplifier was also newly developed, which operates using an internal electric power supply in an optical-to-radio converter. Using a hybrid integration based on all optical resources, a +5.5 dBm RF output at 97 GHz was successfully achieved through the optical-to-radio conversion process. Herein, the two key devices and the integrated photoreceiver are discussed.

This paper describes the concept of sensor over fibres (SoF), consisting of many sensor heads connected by fibre networks. SoF transfer waveforms from the sensor heads and performs joint signal processing to achieve high-resolution and agile imaging, while wireless sensor networks are digital networks to collect measured data at small sensors. SoF can compile information from sensor heads coherently at central signal processing units. We will also show applications of SoF technologies, such as high resolution millimetre-wave radar for airport runway surveillance.

This paper reviews our recent research activities on seamless fiber-wireless systems for future mobile networks, including: radio-on-radio-over-fiber
signal processing-aided multiple signal transmission
high-capacity seamless system
and simultaneous power- and radio-over-fiber.

This presentation reviews radar systems with many antenna units connected by optical networks, which distribute waveforms of wideband frequency modulated millimeter-wave signals, where the range resolution can be a few centimeters.

We have developed a 100-GHz fiber-fed optical-to-radio converter for radio-and power-over-fiber transmission. A zero-bias operational high-speed photodetector (3-dB bandwidth >100 GHz) could be applied for the optical-to-radio converter, taking significant advantage of no-bias feed 100-GHz operation. We have successfully demonstrated simultaneous radio and power generation from one device through a bias-T circuit. A 100-GHz pseudomorphic high electron mobility transistor amplifier allowed a hybrid integrated photoreceiver to enhance the O/E conversion gain. Using the generated electric power, a gate bias in the 100-GHz amplifier was driven. The performance of each device and the integrated photoreceiver is described. High data rate photonic wireless transmission based on photonic power supply without external electric power supply is demonstrated.

We have developed a 100-GHz fiber-fed optical-to-radio converter for radio-and power-over-fiber transmission. A zero-bias operational high-speed photodetector (3-dB bandwidth >100 GHz) could be applied for the optical-to-radio converter, taking significant advantage of no-bias feed 100-GHz operation. We have successfully demonstrated simultaneous radio and power generation from one device through a bias-T circuit. A 100-GHz pseudomorphic high electron mobility transistor amplifier allowed a hybrid integrated photoreceiver to enhance the O/E conversion gain. Using the generated electric power, a gate bias in the 100-GHz amplifier was driven. The performance of each device and the integrated photoreceiver is described. High data rate photonic wireless transmission based on photonic power supply without external electric power supply is demonstrated.

© 2017 Optical Society of America. We developed a 100 GHz optical-to-radio converter module integrated with a 100 GHz amplifier, which was applied in radio (12-Gbps, OFDM, 16-QAM, IF = 92-GHz) and power over fiber transmission through a multi-core fiber.

© 2017 Optical Society of America. We propose and demonstrate a simultaneous transmission of LTE-A, 25-GHz OFDM/FBMC radio access, and 96-GHz filtered-OFDM mobile fronthaul signals over a simple and low cost intermediate-frequency-over-fiber system. We confirm the successful transmission of all signals.

© 2017 COPYRIGHT SPIE.In this paper, we present efficient solutions for simultaneous transmission of multiple radio signals over seamless fiber wireless systems, including radio signals in legacy microwave bands and in high frequency bands. At central stations, radio signals can be mapped onto the same optical transport channel using data mapping algorithms and/or subcarrier multiplexing technique. After the fiber transmission, the received signals can be down-converted, digitized, and de-mapped to recover the originally transmitted signals. We present and compare two different methods, including a radio-over-fiber system and optical up-conversion at remote sites and an intermediate-frequency-over-fiber system and an electrical up-conversion at remote sites. We experimentally confirm the suitability of both the transmission methods, and achieve satisfactory performance for all signals, including LTE-advanced, orthogonal frequency-division multiplexing, and filtered-orthogonal frequency-division multiplexing signals. In particular, the latter method can provide a high optical spectral efficiency and low fiber dispersion effect and is suitable for ultra-dense small cell deployment in future mobile networks.

We present a double cladding, high-mesa-type waveguide UTC photodetector with an improved the responsivity. In this device structure, an InGaAs thin core layer was sandwiched by p-InP/InGaAsP and n-InP/InGaAsP cladding layers, including a UTC structure, in order to obtain a good optical coupling between the waveguide and the fiber. By comparing the resulting mode field with that obtained with a single cladding layer structure, we confirmed that the vertical mode field was enlarged. Without a spot size converter, the measured responsivity was as high as 0.6 A/W at 1550 nm, which suggests a responsivity three times higher than that of back-illuminated structures, and higher responsivity than that of previous reports. A high frequency performance (f(3dB) = 100 GHz) was also measured. The device structure, including the layer, doping level conditions, and optical fiber coupling results are discussed, and its performance is characterized in detail.

© 2016 EuMA.We successfully designed and fabricated a high-conversion-gain 100-GHz photoreceiver integrated with a UTC-PD and a PHEMT amplifier for 92-GHz carrier photonic wireless communication. Then, in a demonstration of 92-GHz carrier, OFDM, 16-QAM photonic wireless communication, we confirmed that high data rate of 11.03-Gbps (bit error rate of 1× 10-3) could be achieved at a low optical input power, without post amplifiers for the photoreceiver. The designs and the results are discussed.

© 2016 EuMA.Multi-layered stacked patch-antennas on an electro-optic (EO) material are proposed for optical modulation. By using multi-layered structures, larger antenna gain can be obtained to induce stronger millimeter-wave electric fields. The induced millimeter-wave electric field can be used for optical modulation through the Pockels effects of the EO crystal. Since the antenna gain is enhanced by using multi-layered stacked patch-antennas, the modulation index improvement can be obtained.

The generation of high-frequency signals including those in the terahertz region has become indispensable in state-of-the-art communication systems. A synthesizer as a measurement device generates signals of desired frequencies with high-frequency resolution. Electric signals (microwaves or millimeter waves) can be generated by a photomixer performing optical-electrical energy conversion based on the phase difference between two coherent optical signals. Recently, the frequency bandwidth for photomixers has reached the terahertz region and photomixers are now more readily available. The main purpose of this letter is to provide an optical synthesizer with a high-frequency resolution (better than 1 Hz) and with seamless frequency coverage from the microwave to the terahertz-wave regions using one apparatus. The system is designed in such a way that the mean of the resolution frequency includes the frequency instability of the generated signal.

© 2016 IEICE-ES.We investigated fundamental characteristics of a hybrid integrated photoreceiver module with a 1.5 μm-band quantum dot semiconductor optical amplifier (QD-SOA) and conventional pin-photodiode (pin-PD) as a first stage. The results indicated the photoreceiver integrated with a QD-SOA and QD-PD has the potential to be operated for signals over 100 Gb/s.

© 2016 IEICE-ES.A ridge-waveguide laser with highly stacked InAs quantum dot structure based on strain compensation technique was fabricated. The threshold current of this laser was decreased to approximately 75 mA without coating the facet mirror. A high characteristic temperature of over 100 K was obtained using this laser.

© 2016 OSA.We clarify that fiber nonlinearity cancellation in the conjugated-paired radio-on-fiber system is a phase sensitive process. The best nonlinearity tolerance is achieved if the dual sidebands are constructively superposed during photonic down conversion.

© 2016 OSA.We report a recent progress for performance of 90GHz electro-optic modulator with patch-antennas in high-power wireless radio irradiation. Optical sidebands to carrier ratio of -40dB can be achieved by wireless radio irradiation power of 33dBm.

© 2016 OSA.We demonstrate 100-GHz optical-to-radio converter without electric power supplies by combination of a newly developed bias-free-operational UTC-PD and an integrated bias-tee for effective regeneration of the supplied power to a 100-GHz amplifier.

© 2016 OSA.We fabricated 1.5 μm quantum dot waveguide photodetector, and characterized the electrical and optical properties. It was found that the avalanche photocurrent strongly depends on TE/TM polarization.

In this paper, the application of the ultraprecision ductile-mode cutting method to the fabrication of microring waveguides in lithium niobate crystal was investigated. Although it was difficult to apply a mechanical cutting method to the fabrication of microring waveguides with smooth sidewalls, it was confirmed that no harmful cutting traces on the machined surface occur with the appropriate movement of the cutting tool. The root-mean-square surface roughness of the resulting sidewall was 6.1 nm, which is sufficiently small to suppress the scattering loss of the circulating light. In addition, the conditions for the ductile-mode cutting of lithium niobate crystal were investigated. (C) 2016 The Japan Society of Applied Physics

In this paper, the application of the ultraprecision ductile-mode cutting method to the fabrication of microring waveguides in lithium niobate crystal was investigated. Although it was difficult to apply a mechanical cutting method to the fabrication of microring waveguides with smooth sidewalls, it was confirmed that no harmful cutting traces on the machined surface occur with the appropriate movement of the cutting tool. The root-mean-square surface roughness of the resulting sidewall was 6.1 nm, which is sufficiently small to suppress the scattering loss of the circulating light. In addition, the conditions for the ductile-mode cutting of lithium niobate crystal were investigated. (C) 2016 The Japan Society of Applied Physics

© 2016 IEEE.We have developed a stable two-mode laser by using a quantum dot optical gain chip in an external cavity. In this study, we demonstrate continuous change of frequency separation of a two-mode laser by using a birefringent etalon filter. Since the polarization of the quantum dot optical gain chip is TE-dominant, the frequency separation of the two-mode laser is controlled by rotating the birefringent etalon filter. We can change the frequency separation from 84 to 93 GHz by using this method.

© 2016 IEEE.We have demonstrated an orthogonal frequency division multiplexing (OFDM) radar experiment combined with millimeter-wave radio over fiber (RoF). In result, high flame rate and high space resolution of 30 cm in 5 m distance (theoretical space resolution of 1.52 cm) was successfully achieved.

Fiber-wireless transmission in the terahertz-wave band as well as in the millimeter-wave band is the key for a seamless integration of radio and optical networks in a physical layer. Advanced optical fiber communication technology enables a high precision direct waveform transfer between optical and radio domains. For realization of a seamless conversion, an optical-terahertz converter is configured with optical heterodyning for an optical-to-terahertz conversion. Analog optical modulation techniques by an input millimeter-wave signal and an intermediate frequency component after a frequency downconversion are utilized for a terahertz-to-optical conversion. A quadrature phase-shift keying signal transmission in an optical-fiber-to-radio-to-optical-fiber link (fiber-wireless bridge) is successfully demonstrated with the 90 and 300-GHz signals, simultaneously, using an optical frequency comb source. The possible transmission distance in severe weather conditions in these frequency bands is also discussed.

Fiber-wireless transmission in the terahertz-wave band as well as in the millimeter-wave band is the key for a seamless integration of radio and optical networks in a physical layer. Advanced optical fiber communication technology enables a high precision direct waveform transfer between optical and radio domains. For realization of a seamless conversion, an optical-terahertz converter is configured with optical heterodyning for an optical-to-terahertz conversion. Analog optical modulation techniques by an input millimeter-wave signal and an intermediate frequency component after a frequency downconversion are utilized for a terahertz-to-optical conversion. A quadrature phase-shift keying signal transmission in an optical-fiber-to-radio-to-optical-fiber link (fiber-wireless bridge) is successfully demonstrated with the 90 and 300-GHz signals, simultaneously, using an optical frequency comb source. The possible transmission distance in severe weather conditions in these frequency bands is also discussed.

© 2016 IEICE.We present an efficient mobile fronthaul system for co-transmission of radio signals in the microwave and millimeter-wave bands. We successfully transmit a WLAN and an LTE-A signal at 2.6 GHz and 33.6 GHz, respectively, over the system.

© 2016 IEICE.A 100 GHz photoreceiver was designed, fabricated, and integrated with a pHEMT amplifier, based on a photonic power supply. In this paper, a high data rate photonic wireless communication over 11 Gbps is demonstrated.

© 2016 IEICE.We propose a new measurement method of modulator response in phasor domain for Mach-Zehnder modulators embedded in IQ modulator using simple equipments. The modulation curve with extinction ratio of 14.7 and 22 dB were measured.

© 2016 IEICE.We designed and fabricated a LiNbO3 integrated optical modulator for mode-division multiplexing, where optical signals in two modes can be independently controlled and combined together. Mode crosstalk was smaller than -20dB in C-band.

© 2016 IEICE.We propose new electro-optic modulators using gap-embedded patch antennas with stacked structure. Utilizing stacked structure, the antenna gain, electric field for modulation, and interaction length increase, then modulation efficiency increases 3.65 dB at 60 GHz.

© 1979-2012 IEEE.Mobile transport networks will play a vital role in future 5G and beyond networks. In particular, access transport networks connecting radio access with core networks are of critical importance. They will be required to support massive connectivity, super high data rates, and real-time services in a ubiquitous environment. To attain these targets, transport networks should be constructed on the basis of a variety of technologies and methods, depending on application scenarios, geographic areas, and deployment models. In this article, we present several technologies, including analog radio-over-fiber transmission, intermediate-frequency- over-fiber technology, radio-on-radio transmission, and the convergence of fiber and millimeter-wave systems, that can facilitate building such effective transport networks in many use cases. For each technology, we present the system concept, possible application cases, and demonstration results. We also discuss potential standardization and development directions so the proposed technologies can be widely used.

This paper proposes a high-speed multiband filtered-orthogonal frequency division multiplexing (F-OFDM) signal transmission over a seamless fiber-millimeter-wave (MMW) system at 92.5 GHz. The system employs a frequency and phase stabilized optical MMW signal generation at the transmitter and a simple direct detection at the receiver. We confirm a successful transmission of multiband F-OFDM signal over a seamless 20-km single mode fiber (SMF) and 1-m 92.5-GHz wireless system. Compared to the single-band and multiband OFDM signal transmission, the proposed system can provide a much better performance, particularly at the edges of each band.

© 2016 OSA.Single-carrier photonic wireless transmission at 31 GHz and 8.0 Gbaud with 64QAM is successfully achieved with error-free operation. A newly developed wide bandwidth high power photodetector and a pre-equalizing subsystem are presented.

© 2016 OSA.This paper presents the simultaneous transmission of millimeter-wave and terahertz-wave radio signals over an optical fiber and air by a single optical frequency comb source with several types of receiver configurations.

© 2016 OSA.To avoid the modal crosstalk-induced power fading, a mode assignment technique has been proposed and experimentally demonstrated for mode division multiplexed W-band radio-over-fiber links.

© 2016 OSA.We propose a dual-hop network to high-speed trains by using a seamless fiber-millimeter-wave system for backhaul transmission and a high-speed in-train network. Transmission of a 64-QAM OFDM signal over the cascaded system is successfully confirmed.

© 2016 IEEE.This paper reviews train communication networks (TCNs) based on radio-over-fibre (RoF) technology. TCNs connect base stations (BSs) in trains to world wide networks through trackside links consisting of optical fibres and many radio access units (RAUs). Waveform for radio communications can be effectively delivered to each RAU by RoF. The TCN can be controlled by train location information to reduce overhead due to hand-over in mobile communication systems.

© 2016 IEEE.The rat-race (RR) circuit, which operates as a 180-degree hybrid, with an asymmetric power split ratio was integrated with the dual electrode type electro-optic modulator on the same substrate. Thereby, frequency chirp modulation with a compact configuration was realized. The RR circuit was designed with 4.5 1 power split ratio on a z-cut LiNbO3 substrate. The operation of the modulator was confirmed by observing the output light spectra. Moreover, the chirp parameter was directly measured by using the chromic dispersion of the optical fiber, where the power penalty of detected modulation signals transmitted through optical fiber was observed as a function of the fiber distance. The chirp parameter of the modulated light at 10 GHz was confirmed to be 0.47 by the measurement.

© 2016 IEEE.A closed-form capacity expression for polarization-multiplexed coherent MIMO radio-over-fiber (RoF) links at millimeter-wave bands is derived and the impact of the fiber's polarization rotation and the wireless antenna misalignment on the MIMO channel capacity is revealed. The analytical results are validated via an indoor W-band (75-110 GHz) 10-Gbaud MIMO-RoF transmission experiment.

An array of patch-antennas with meandering-gaps on an optical modulator is proposed for wireless millimeter-wave beam-steering through high-speed radio-over-fiber systems. Wireless millimeter-wave can be received by the array of patch-antennas and directly modulated to lightwave by the optical modulator. The wireless millimeter-wave can be steered using the meandering-gaps at the patch-antennas by controlling interaction between millimeter-wave and lightwave electric fields in electro-optic modulation. The basic operation and analysis of the proposed device are discussed. In the experiment, 5 x 5 antenna array in 40 GHz millimeter-wave bands was designed and realized for device characterization and demonstration to wireless millimeter-wave beam-steering. There were five variations of wireless millimeter-wave beam-steering for one-dimensional in xz- or yz-planes that can be obtained with wireless millimeter-wave steerable beams of about +/- 30 degrees. Additionally, 25 variations of wireless beam-steering can be obtained for two dimension in xyz-space through orthogonal optical modulation. The proposed device is promising to be applied in millimeter-wave/tera-hertz bands for future directional wireless communication and sensing with high-speed and high-resolution operation.

© 2015 The Institute of Electronics, Information and Comm.We report current research progress on a metamaterial antenna integrated to an optical modulator for millimeter-wave-photonic links. The metamaterial antenna is composed by an array of electric-LC resonators on a LiNbO3 optical crystal. Large millimeter-wave electric field is induced across the capacitive gaps of the resonators due to free-space millimeter-wave irradiation. Optical modulation through Pockels effects can be obtained when light propagates along the capacitive gaps. The integrated device is operated effectively by considering interaction between millimeter-wave and lightwave electric fields along the capacitive gaps. Basic operations of the integrated device for 90GHz millimeter-wave bands are reported and discussed. Optical sidebands with carrier-to-sideband ratio of about ™60dB by millimeter-wave irradiation power of ∼20mW can be experimentally measured using optical spectrum analyzer.

A monolithically integrated quantum dot (QD) optical gain modulator (OGM) with a QD semiconductor optical amplifier (SOA) was successfully developed with T-band (1.0 mu m waveband) and O-band (1.3 mu m waveband) QD optical gain materials for Gbps-order, high-speed optical data generation. The insertion loss due to coupling between the device and the optical fiber was effectively compensated for by the SOA section. It was also confirmed that the monolithic QD-OGM/SOA device enabled >4.8 Gbps optical data generation with a clear eye opening in the T-band. Furthermore, we successfully demonstrated error-free 4.8 Gbps optical data transmissions in each of the six wavelength channels over a 10-km-long photonic crystal fiber using the monolithic QD-OGM/SOA device in multiple O-band wavelength channels, which were generated by the single QD gain chip. These results suggest that the monolithic QD-OGM/SOA device will be advantageous in ultra-broadband optical frequency systems that utilize the T+O-band for short-and medium-range optical communications. (C) 2016 The Japan Society of Applied Physics

A heterogeneous wavelength-tunable laser diode combining quantum dot and silicon photonics technologies is proposed. A compact wavelength-tunable filter with two ring resonators was carefully designed and fabricated using silicon photonics technology. The tunable laser combining the wavelength-tunable filter and an optical amplifier, which includes InAs quantum dots, achieved a 44.0 nm wavelength-tuning range at around 1250 nm. The broadband optical gain of the quantum dot optical amplifier was effectively used by the optimized wavelength-tunable filter. This heterogeneous wavelength-tunable laser diode could become a breakthrough technology for high-capacity data transmission systems. (C) 2016 The Japan Society of Applied Physics

We fabricate broad-area laser diodes consisting of 30-layer stacks of InAs quantum dots by using a strain-compensation technique on a vicinal (001)InP substrate. These laser diodes exhibit ground-state lasing at 1576 nm in the pulsed mode with a high characteristic temperature of 111K at around room temperature (20-80 degrees C). (C) 2016 The Japan Society of Applied Physics

© 2015 IEEE.A government-funded R and D program aiming at a resilient optical and millimeter-wave wireless link for a novel span protection scheme in a disaster recovery is presented. We also describe the key enabling technologies of both optical and wireless sub- systems and devices, including MIMO radio-over- fiber system, optical two-tone generation, and the transceiver and power amplifier in W-band.

<p>This paper proposes a high-speed multiband filtered-orthogonal frequency division multiplexing (F-OFDM) signal transmission over a seamless fiber-millimeter-wave (MMW) system at 92.5 GHz. The system employs a frequency and phase stabilized optical MMW signal generation at the transmitter and a simple direct detection at the receiver. We confirm a successful transmission of multiband F-OFDM signal over a seamless 20-km single mode fiber (SMF) and 1-m 92.5-GHz wireless system. Compared to the single-band and multiband OFDM signal transmission, the proposed system can provide a much better performance, particularly at the edges of each band.</p>

© 2016 SPIE.A seamless combination of fiber and millimeter-wave (MMW) systems can be very attractive for future heterogeneous mobile networks such as 5G because of its flexibility and high bandwidth. Analog mobile signal transmission over seamless fiber-MMW systems is very promising to reduce the latency and the required band-width, and to simplify the systems. However, stable and high-performance seamless systems are indispensable to conserve the quality of the analog signal transmission. In this paper, we present several technologies to develop such seamless fiber-MMW systems. In the downlink direction, a high-performance system can be realized using a high-quality optical MMW signal generator and a self-homodyne MMW signal detector. In the uplink direction, a cascade of radio-on-radio and radio-over-fiber systems using a burst-mode optical amplifier can support bursty radio signal transmission. A full-duplex transmission with negligible interference effects can be realized using frequency multiplexing in the radio link and wavelength-division multiplexing in the optical link. A high-spectral efficiency MMW-over-fiber system using an intermediate frequency-over-fiber system and a high-quality remote delivery of a local oscillator signal is highly desirable to reduce the costs.

© 2016 SPIE.A 100-GHz narrowband photoreceiver module integrated with a zero-bias operational uni-traveling-carrier photodiode (UTC-PD) and a GaAs-based pseudomorphic high-electron-mobility transistor (pHEMT) amplifier was fabricated and characterized. Both devices exhibited flat frequency response and outstanding overall performance. The UTC-PD showed a 3-dB bandwidth beyond 110 GHz while the pHEMT amplifier featured low power consumption and a gain of 24 dB over the 85-100 GHz range. A butterfly metal package equipped with a 1.0 mm (W) coaxial connector and a microstrip-coplanar waveguide conversion substrate was designed for low insertion loss and low return loss. The fabricated photoreceiver module demonstrated high conversion gain, a maximum output power of +9.5 dBm at 96 GHz, and DC-power consumption of 0.21 W.

Conversion devices between free-space microwave/millimeter-wave and lightwave signals are required in Fiber-Wireless (Fi-Wi) links. In this paper, we propose a free-space millimeter-wave Electro-Optic (EO) modulator using Quasi-Phase-Matching (QPM) gap-embedded-patch-antennas on a low dielectric constant substrate. Free-space millimeter-wave signals can be received and converted directly to lightwave signals using the proposed device. It can be operated passively with no external power supply and operated with extremely low millimeter-wave losses. The QPM array structure can be adopted for improving modulation efficiency by considering the transit-time effects. The proposed device is easy connected to optical fiber, therefore Fi-Wi can be realized using the proposed device. Basic structure, analysis, and experimental results of the proposed device are discussed and reported for 40 GHz operational millimeter-wave bands.

© 2015 International Telecommunication Union.In addition to new radio technologies, end-to-end transport networks will play a vital role in future 5G (and beyond) networks. In particular, access transport networks connecting radio access with core networks are of critical importance. They should be able to support massive connectivity, super high data rates, and real time services in a ubiquitous environment. To attain these targets, transport networks should be constructed on the basis of a variety of technologies and methods, depending on application scenarios, geographical areas, and deployment models. In this paper, we present several technologies, including analog radioover-fiber transmission, intermediate-frequency-over-fiber technology, radio-on-radio transmission, and the convergence of fiber and millimeter-wave systems, that can facilitate building such effective transport networks in many use cases. For each technology, we present the system concept, possible application cases, and some demonstration results. We also discuss potential standardization and development directions so that the proposed technologies can be widely used.

We propose a flexible and high-performance fronthaul system for future mobile networks using a seamless combination of fiber-optic and millimeter-wave (MMW) systems. The proposed system employs a high-quality optical MMW signal generation at the transmitter and a stable and high-performance MMW self-homodyne detection at the receiver. In the downlink direction, successful transmission of intraband and interband carrier aggregation (CA) long-term evolution-advanced (LTE-A) signals over the system is experimentally confirmed. We also confirm satisfactory performance for the transmission over a fiber-wireless bridge using a cascade of the seamless system and a conventional radio-over-fiber (RoF) link. In the uplink direction, we successfully demonstrate the transmission of an intraband CA LTE-A signal over a cascade of a radio-on-radio and a RoF system. In addition, we confirm that the full-duplex transmission of LTE-A signals over the proposed bidirectional system does not experience performance degradation compared to the case with half-duplex transmission. The proposed system is a potential solution for mobile-signal transmission in future networks.

A laser-phase-fluctuation-insensitive optical coherent transmission of a 10-Gbaud 16-quadrture-amplitude-modulation radio-over-fiber signal with an offset-frequency-spaced two-tone local light and an digital-signal-processing technique is experimentally demonstrated. Error-free symbol recovery after the 20-km-long fiber-optic transmission is shown and the transmission quality is evaluated.

We report a 30-110 GHz, high conversion gain, and high output photodetector consisting of a hybrid integration of a high-speed photodetector and an RF amplifier with an additional gain emphasis circuit. High data-rate photonic wireless communication over 44 Gbps was demonstrated with a predistortion technique. The minimum optical input power level for an error free operation was also discussed.

This paper reviews seamless networks based on radio-over-fiber (RoF) technology. We focus on train communication networks (TCNs) consisting of optical networks and many radio access units (RAUs). Waveform for radio communications can be effectively delivered to each RAU by RoF. The TCN can be controlled by train location information to reduce overhead due to hand-over in mobile communication systems.

A photonic terahertz synthesizer is configured and demonstrated by100-GH, 300-GHz and 600-GHz signal generation. An optical frequency shifter in an amplified optical fiber loop technique configures an optical frequency comb generator with a resultant optical bandwidth up to 2 THz. An observed phase noise characteristic by the photonic synthesizer is considerable for application to the complex modulation formats even in the terahertz bands.

We propose an architecture of the radio-over-fiber systems for train communication networks. Prediction-based dynamic optical routing can track the train cars by train location information. High spectral-efficient millimeter-wave signal modulation and demodulation are also discussed with the modulation format and its configuration of the frequency conversions in the paper.

We present efficient mobile fronthaul systems for simultaneous transmission of radio signals in the microwave and millimeter-wave hands over fiber links. We compare the performance for signal transmission over intermediate frequency over fiber systems using an electrical and optical up-conversion to the MEW hand at remote sites. We experimentally confirm the successful transmission of an LTE-A signal at 2.6 GHz and a wideband OFDM signal at 35.4 GHz over the systems.

We experimentally demonstrate fiber-nonlinearity-tolerant conjugated-paired radio-on-fiber (C-RoF) system for the first time. A C-RoF signal is simply generated by dual-sideband modulation and fiber nonlinearity is cancelled through asymmetric photonic heterodyne down-conversion. A QPSK-CRoF signal is transferred over 20-km SMF fiber.

New communication system for high-speed train passengers is required to provide broadband services in the train. Radio over fiber in millimeter wave band is considered to provide a high throughput of the system. As a proof of concept, we generate 92 GHz 200 M symbol/sec 64QAM signals by optical frequency doubler. EVM of the signal is 7.14%. The result shows 1.2Gbps transmission is available in MMW band by radio over fiber.

We successfully designed and fabricated a highconversion-gain 100-GHz photoreceiver integrated with a UTC-PD and a PHEMT amplifier for 92-GHz carrier photonic wireless communication. Then, in a demonstration of 92-GHz carrier, OFDM, 16-QAM photonic wireless communication, we confirmed that high data rate of 11.03-Gbps (bit error rate of 1 x 10(-3)) could be achieved at a low optical input power, without post amplifiers for the photoreceiver. The designs and the results are discussed.

© 2016 IEEE. In wireless communications, the data traffic increases rapidly every year, as well as in fixed optical fiber communications, where the trend for data traffic is not saturated yet. In the next generation of advanced wireless communication services, a high data rate, high capacity, low latency, and low cost are desired. The large radio cover area for present macro-cell should be divided into plenty of small-cells in order to mitigate heavy data traffic in the one macro-cell [1]. Here, radio over fiber (RoF) is a promising technology for access networks such as mobile back-haul and front-haul in wireless communication. High data rate transmission through optical fibers should be introduced near end-user points and be converted to radio signals from simple antennas in small-cells. Here, a high speed photoreceiver is one of key components in RoF communications. On the other hand, power over fiber (PoF) technology, which provides electric power supply through optical fibers, is a compatible technology with a good affinity to RoF technology. The 90 to 110 GHz band is a very attractive frequency band, which involves not only low atmospheric attenuation [2] but also a wider bandwidth compared to that in the microwave region.

We discuss key device technologies for realization of an optical-fiber-network-connected distributed radar system in the millimeter-wave band using radio over fiber techniques. The radio over fiber technique is useful for precise signal generation and distribution over the fiber network. In the scenario, each millimeter-wave radar head is not necessary to be equipped with aprecision radar signal source; low cost and low energy consumption radar head will be realized. For connection to the optical network, advanced high-speed optical/electrical converters are developed for signal conversion from/to optical signals in 90-GHz band directly in a central office and each radar head. A signal-to-noise power ratio of generated 90-GHz optical signal was achieved larger than 30 dB: enough quality to use in the radar system. An optical switching technique is useful not only for routing the optical signal to the radar heads but also for filtering unnecessary optical components. These device technologies are applicable for distributed millimeter-wave radar systems.

We have proposed a new electro-optic signal converter which enables us to convert wireless millimeter-wave signals to Iightwave signals. This is based on a LiNbO3 guided-wave optical modulator combined with vertically-stacked planar patch antennas embedded with a narrow (similar to 5 mu m) gap. Utilizing the stacked structure, the antenna gain, antenna area, and electric field for optical modulation are increased, so that the signal conversion efficiency is increased by 3.65 dB at 60 GHz.

© 2015 IEEE.An optical frequency-interleaving full-duplex multi-channel transmission of W-band frequency-modulated continuous-wave downlink and 10-Gb/s on-off-keying uplink signals is investigated. Two-channel transmission with a flexible wavelength channel selector over 10-km-class fiber-optic network is experimentally demonstrated.

Quantum-dot nanotechnology is attractive for use in advanced photonic devices that will augment the available optical-frequency resources and will increase the number of wavelength channels usable by wired and wireless networks in short/middle-range communication systems. © 2015 OSA.

We discussed crosstalk issues on parallel photonics assuming high-density integration. RF crosstalk has become a more serious problem than optical crosstalk, and it is affected by the operating frequency (baud rate). A bias free UTC-PD was designed and fabricated. © 2015 OSA.

© 2015 IEEE.In this paper, we investigate the optical power fluctuation of the output in optical comb generator using an optical single sideband (SSB) modulator with a fiber loop. This fluctuation is caused by undesired sidebands of the SSB modulator. We show that the fluctuation can be suppressed by stabilizing the fiber loop length. In experiment, the averaged peak-to-peak power fluctuation of 23 comb outputs was suppressed from 0.86 dB to 0.13 dB.

© 2015 IEEE.300-GHz multilevel signal transmission over optical fibers and air is demonstrated using advanced optical communication technology including optical frequency comb generation. Local oscillator signal transport over optical fibers to optical-terahertz converters removes the need for setting any terahertz-capable oscillators in the converters. This fiber-remoted configuration with seamless conversion between the optical and terahertz signals is compatible with high-speed terahertz backhaul and fronthaul links.

© 2015 IEEE.In this study, we successfully fabricated a W-band high-power photoreceiver with high output power and low power consumption. This W-band photoreceiver was integrated with a bias-free uni-travelling carrier photodetector (UTC-PD) and an InP high electron mobility transistor (PHEMT) amplifier for the first time. An ultrabroad 3 dB bandwidth beyond 110 GHz in an UTC-PD and maximum oscillation frequency of 320 GHz in a PHEMT low-noise amplifier were used for this hybrid integration. At 109 GHz, a high radio frequency output power of +10 dBm, high transimpedance gain of 828 □, and low power consumption of 67 mW was achieved in an optical-electrical converting process.

© 2015 EuMA.We propose a flexible and low-latency cascaded fiber-wireless system for future mobile fronthauling using seamless combination of fiber-optic and millimeter-wave links. Successful transmission of intraband and interband carrier aggregation LTE-A signals over the system is experimentally confirmed. Satisfactory performance is achieved owing to the use of a high-quality optical millimeter-wave signal generation technique at the transmitter and a proposed high-performance self-homodyne detection at the receiver.

© 2015 IEEE.Envelope-detector-based transceiver configurations are useful for both digital signal transmission and radar systems in the terahertz band. A dual-purpose transceiver is demonstrated using a 1-Gb/s on-off keying signal and 12.5-GHz-bandwidth frequency-modulated continuous-wave radar.

© 2015 IEEE.We present a pseudo-delta-sigma modulator and demonstrate transmission using an advanced modulation. This digitally implemented transmitter helps in reducing the complexity at the receiver and realizing waveform transport over a digital optical network.

© 2015 IEEE.An optical frequency-interleaving full-duplex transmission of 96-GHz-band frequency-modulated continuous-wave downlink signal and 10-Gb/s on-off-keying uplink signals is investigated. The proposed full-duplexing transmission with a flexible wavelength channel selector over 10-km fiber-optic link is experimentally demonstrated.

© 2015 Viajes el Corte Ingles, VECISA.We experimentally demonstrate generation of polarization-multiplexed phase-conjugated twin signals by using oppositely-biased dual-polarization IQ modulators, compensating for nonlinear signal distortion in fiber transmission. Bias condition is optimized investigating nonlinearity tolerance of the generated signals transmitted over SMF.

© 2015 Viajes el Corte Ingles, VECISA.We present a high-spectral efficiency fronthaul system for the transmission of millimeter-wave and multiple-input multiple-output (MIMO) signals in future mobile networks. The transmission of an interband carrier aggregation and a 2 × 2 MIMO LTE-A signal over the system is successfully demonstrated.

A combination of fiber and radio links would be attractive for efficient fronthauling to small cells and moving cells. However, achieving connectivity by using wired-wireless media converters significantly increases system complexity, power consumption, and latency. A seamless combination of fiber and radio links in which photonics-based technologies are used to generate and transmit radiowave signals is more suitable. In this article, we present an overview of fiber-radio link combination for mobile signal transmission. We propose an efficient solution for future mobile fronthauling based on the analog transmission of mobile signals over a bidirectional seamless system. We discuss the potential as well as the challenges and perspectives of the systems applied for mobile fronthauling in small-cell-and moving-cell-based networks. We also present a proof-of-concept demonstration of the transmission of mobile signals over the system. Satisfactory performance is obtained for different high-speed advanced signals. The transmission range over fiber links and the estimated range of the radio links are sufficiently long to facilitate the practical implementation of the system. The system is scalable to include new deployments of small cells and wireless services using wavelength-division and subcarrier multiplexing techniques. It can provide a high-speed, low-latency, and flexible solution for fronthauling in new emerging wireless systems such as 5G networks.

A millimeter-wave radar receiver using a z-cut LiNbO3 optical modulator with orthogonal-gap-embedded patch-antennas on a low-k dielectric material is proposed. A millimeter-wave from a reflected radar signal can be received by the patch-antennas and converted directly to a lightwave through electro-optic modulation. A low-k dielectric material is used as a substrate for improving antenna gain. Additionally, an interaction length between millimeter-wave and lightwave electric fields becomes long. As a result, large modulation efficiency can be obtained, which is proportional to sensitivity of the millimeter-wave radar receiver. Optical millimeter-wave radar beam-forming can be obtained using the proposed device with meandering-gaps for controlling interaction between millimeter-wave and lightwave electric fields in electro-optic modulation. Analysis and experimentally demonstration of the proposed device are discussed and reported for 40GHz millimeter-wave bands. Optical millimeter-wave radar beam-forming in 2-D is also discussed.

© 2015 OSA. We demonstrate high spurious suppression ratio single-sideband modulation by a high extinction-ratio parallel Mach-Zehnder modulator. An electrical third-order nonlinearity suppression technique can enhance the suppression ratio as high as 47 dB.

This paper describes photonic technologies for millimeter-wave generation and distribution. External modulation would be useful for stable and high-quality radio-over-fiber signal generation, where frequency stability and spurious suppression are very important for radio services such as mobile communications, radio locations etc. This paper provides outline of radio-over-fiber signal generation techniques. Precise and high-speed lightwave optical modulation would play important roles for suppression of undesired spectrum components. Photonic harmonic generation would be useful for very high-frequency signals. Reciprocating optical modulators consisting of optical modulators and fiber Bragg gratings can provide optical modulation by sub-THz signals.

We propose a flexible and low-latency cascaded fiber-wireless system for future mobile fronthauling using seamless combination of fiber-optic and millimeter-wave links. Successful transmission of intraband and interband carrier aggregation LTE-A signals over the system is experimentally confirmed. Satisfactory performance is achieved owing to the use of a high-quality optical millimeter-wave signal generation technique at the transmitter and a proposed high-performance self-homodyne detection at the receiver.

In this paper, we demonstrate a 300-GHz FM-CW radar using optical modulation technology. An optical frequency comb based on the optical modulation is utilized as a broadband frequency multiplier with a factor of 12. At a central frequency of 300 GHz, we generate a 12-GHz-bandwidth FM-CW signal with a pulse duration of 10 mu s, realizing a precise ranging with a resolution of several centimeters. We show that the optical frequency comb generator is capable of generating larger bandwidth FM-CW signals.

© 2015 IEEE.High-precision imaging technology and its application are highly demanded for the enhancement of civil security. They are used to help prevent major incidents in railways or airports. In these applications, both small object detection and high-range resolution are key features. As far as the detectable target size is concerned, a high-frequency carrier is indispensable in radar systems. However, a radio signal with millimeter-wave (high frequency) suffers from large atmospheric attenuation. For example, the attenuation coefficient at 90 GHz is estimated to be 1 dB/km, while it is less than 0.1 dB/km in microwave bands [1]. Thus, the radar signal will have to originate from an area close to the target. Setting up a radar system with a synthesizer close to the target might not be desirable because a high-precision electrical synthesizer is generally large and consumes high energy. Radio-over-fiber (RoF) technology, used to transport the signal over optical fibers, is a promising candidate to deliver the millimeter-wave signal to the suitable point over a low-loss optical fiber cable. Radars utilizing the RoF technology have already been reported; however, digital signal processing in remote radar heads was required to reduce large transmission data [2, 3].

We discuss the performance of Mach-Zehnder modulators with asymmetric power-splitting Y-branches theoretically and confirmed it experimentally. The output characteristics of the modulator depend on the relationship between the power splitting ratios of the front and the back Y-branches. Even if the modulator consists of two asymmetric Y-branches, we can achieve high-extinction-ratio operation, with an additional loss as compared with the ideal case, by tuning the splitting ratio of only one of the two Y-branches. The additional loss, however, is small in many cases because the asymmetry considered here is caused by fabrication errors. (C) 2014 The Japan Society of Applied Physics

本稿では、高周波信号により駆動された干渉型光スイッチのクロストークを評価する手法について述べる。光スイッチのドロップポートの出力に含まれるキャリア成分を利用するもので、時間領域測定における光検出器の利得帯域幅積の制約を回避することが可能である。この手法を用いて、干渉型光スイッチの各アームにマッハツェンダー構造を入れ子にした2x2光スイッチのクロストークを実験的に評価した結果も報告する。

本稿では、高周波信号により駆動された干渉型光スイッチのクロストークを評価する手法について述べる。光スイッチのドロップポートの出力に含まれるキャリア成分を利用するもので、時間領域測定における光検出器の利得帯域幅積の制約を回避することが可能である。この手法を用いて、干渉型光スイッチの各アームにマッハツェンダー構造を入れ子にした2x2光スイッチのクロストークを実験的に評価した結果も報告する。

本稿では、高周波信号により駆動された干渉型光スイッチのクロストークを評価する手法について述べる。光スイッチのドロップポートの出力に含まれるキャリア成分を利用するもので、時間領域測定における光検出器の利得帯域幅積の制約を回避することが可能である。この手法を用いて、干渉型光スイッチの各アームにマッハツェンダー構造を入れ子にした2x2光スイッチのクロストークを実験的に評価した結果も報告する。

本稿では、高周波信号により駆動された干渉型光スイッチのクロストークを評価する手法について述べる。光スイッチのドロップポートの出力に含まれるキャリア成分を利用するもので、時間領域測定における光検出器の利得帯域幅積の制約を回避することが可能である。この手法を用いて、干渉型光スイッチの各アームにマッハツェンダー構造を入れ子にした2x2光スイッチのクロストークを実験的に評価した結果も報告する。

本稿では、高周波信号により駆動された干渉型光スイッチのクロストークを評価する手法について述べる。光スイッチのドロップポートの出力に含まれるキャリア成分を利用するもので、時間領域測定における光検出器の利得帯域幅積の制約を回避することが可能である。この手法を用いて、干渉型光スイッチの各アームにマッハツェンダー構造を入れ子にした2x2光スイッチのクロストークを実験的に評価した結果も報告する。

Crosstalk is one of the significant measures of an optical cross-bar switch. In this paper, we describe a configuration for crosstalk suppression of a balanced-bridge interferometric type optical switch and its application to an optical-signal routing device. Since crosstalk of the optical switch originates from imbalance in the amplitude of a lightwave propagating within the arm of the interferometer, additional Mach-Zehnder structures were embedded for trimming the amplitude of the light. By adjusting the transmittance of the trimmers, crosstalk of less than -56 dB is achieved for dc voltage. Also, for high-frequency voltages, a crosstalk estimation procedure was developed, and crosstalk at 10-GHz sinusoidal voltage was evaluated to be -48 dB. Furthermore, based on the transient response measurement, its switching time was evaluated to be 26 ps. For a demonstration utilizing extremely low crosstalk and quick response, a guard-time-free optical signal routing experiment is also described. © 2013 IEEE.

For precise chirp parameter control, we investigated x-cut LiNbO3 single-drive asymmetric Mach-Zehnder modulators with extinction-ratio adjustable active Y-branch structures, which can enhance on-off extinction ratio. The chirp parameter of the modulated output was precisely measured by using high extinction ratio operation. Experimental results show that it is possible to fabricate modulators with desired chirp parameters.

We fabricated a diode-pumped mode-locked Ti-diffused Er-doped LiNbO3 (Ti:Er:LN) laser with a SiO2/TiO2 dielectric multilayered mirror. The lasing threshold power was 70mW at 1484 nm, and the slope efficiency was 1.48%. Stable optical pulses with a width of 10.86 ps were measured by driving the phase modulator at 13.575 GHz.

本研究では,光通信システムにおいて広く用いられているLiNbO_3光変調器の高効率・小型化を図ることを目的とする.その手法として,進行波型光変調器と比ペて小型であり狭帯域において高効率変調が可能である共振型LiNbO_3光変調器を用い,Auミラーによって光波を反射させ再び変調をかけることで高効率・小型化を図るものとする.今回,実際に作製し評価を行った結果,Auミラー反射を用いることによる高効率・小型化を確認した.

本研究では,光通信システムにおいて広く用いられているLiNbO_3光変調器の高効率・小型化を図ることを目的とする.その手法として,進行波型光変調器と比ペて小型であり狭帯域において高効率変調が可能である共振型LiNbO_3光変調器を用い,Auミラーによって光波を反射させ再び変調をかけることで高効率・小型化を図るものとする.今回,実際に作製し評価を行った結果,Auミラー反射を用いることによる高効率・小型化を確認した.

We propose a high extinction-ratio (ER) Mach-Zehnder modulator (MZM) with an active Y-branch optical intensity trimmer. In addition, we investigate a high ER integrated MZM for optical single-sideband (SSB) signal generation, where the active Y-branch trimmers are embedded in a dual-parallel MZM. Optical SSB generation with high suppression ratio of main carrier (47 dB) and undesired sidebands (&gt;42 dB) is achieved by optimizing the optical amplitude imbalances corresponding to the ER.

我々のグループでは,LiNbO_3光変調器の基本構造となるマッハツェンダ型干渉構造の光入射側のY分岐部分に新たな電極を設置することで,光変調器の消光比を改善する報告を行った.今回これらの方法を多値変調技術に応用することを考え,並列型マッハツェンダ構造を有するLiNbO_3光変調器でのバイアス制御方法についてシミュレーションを行い確認した.また新たな電極構造を設置すると,その電極から発生する電界により光の位相変化が生じるため,その位相変化を考慮したバイアス制御方法が必要となる.本研究では実際にその位相変化の影響を実験によって確認し,その構造を並列型LiNbO_3光変調器の構造に導入するためのバイアス制御方法について検討した.

我々のグループでは,LiNbO_3光変調器の基本構造となるマッハツェンダ型干渉構造の光入射側のY分岐部分に新たな電極を設置することで,光変調器の消光比を改善する報告を行った.今回これらの方法を多値変調技術に応用することを考え,並列型マッハツェンダ構造を有するLiNbO_3光変調器でのバイアス制御方法についてシミュレーションを行い確認した.また新たな電極構造を設置すると,その電極から発生する電界により光の位相変化が生じるため,その位相変化を考慮したバイアス制御方法が必要となる.本研究では実際にその位相変化の影響を実験によって確認し,その構造を並列型LiNbO_3光変調器の構造に導入するためのバイアス制御方法について検討した.