In this study, we propose a novel silicon-core optical fiber with a bowtie shaped slot core structure for ultrasmall light-spot transmission. Our simulations show that this dielectric structure creates a nanosized optical spot with the high intensity and transmits it
with the low loss. As an example, we obtained an optical spot with the full width at half maximum of 5 nm × 5 nm and a peak power density 167 times higher than that of the surrounding areas. The optical loss because of the scattering in the waveguides and the material absorption was estimated to be 0.58 dB/cm, which is a thousand times less than the optical losses in typical plasmonic waveguides. We believe our proposed structure will
contribute to research studies in the field of near-field sensing systems. It also has application potential in nanolithography with high-power lasers.

We have demonstrated crosstalk mitigation in single-mode MCFs using optical space coding. Four types of single-mode multicore fiber (MCF) models were evaluated by our scheme with the modified prime code and di erential detection. Typically, intercore crosstalk was improved by 7–20 dB in 9-core fibers with an original crosstalk of 10–20 dB.

We numerically analyzed the performance of a T-shaped combiner with metal-insulator-metal plasmonic waveguides. We showed that an extremely low combining loss can be realized over a wide infrared wavelength region. Moreover, the combining efficiency can be controlled between 0 and 1 by changing the phase difference between two input light sources, and it appears to be insensitive toward unequal powers of input light sources. Finally, we proposed a novel, optical 90 degrees hybrid coupler with a modified T-shaped structure.

This paper proposes a novel optical fibre probe containing a scattering layer that is capable of sensing the surrounding light through the lateral surface of the fibre. The performance of the probe in sensing various target objects in free space and water environment has been evaluated by ray-trace simulation. For the probe of diameter 1 mm and length 50 mm, the normalised power, which is defined as the ratio of the signal power to the source power, was obtained within 0.1–0.01 % for the target object over a surrounding space with a radius of ~20 mm. Besides, the probe exhibits sharp directional property with an angular diameter of ~10° in the radial direction. Utilizing this functionality, the probe with the spiral-shaped scattering part will enable the sensing of target objects that are spatially distributed along a fibre axis with a minimum detectable gap of less than 2 mm.

© Copyright 2016 by SCITEPRESS-Science and Technology Publications, Lda. All rights reserved.We analysed the space coding scheme applied to the space division multiplexing transmission in two types of multicore fibres with different intercore crosstalk. Rather than the usual optical multiple-input and multipleoutput processing, simple space coding based on optical code division multiplexing was used to achieve separate detection of the desired signals. The signal to interference-and-noise ratio has a positive value when the relative phase drift between the optical signals in different cores is suppressed to values typically less than ∼π/10. Although a complete solution of the phase drift control problem was not achieved, this scheme suggests that real-time MCF transmissions are possible.

We numerically analyzed the power-coupling characteristics between a high-index-contrast dielectric slot waveguide and a metal-insulator-metal (MIM) plasmonic slot waveguide as functions of structural parameters. Couplings due mainly to the transfer of evanescent components in two waveguides generated high transmission efficiencies of 62% when the slot widths of the two waveguides were the same and 73% when the waveguides were optimized by slightly different widths. The maximum transmission efficiency in the slot-to-slot coupling was about 10% higher than that in the coupling between a normal slab waveguide and an MIM waveguide. Large alignment tolerance of the slot-to-slot coupling was also proved. Moreover, a small gap inserted into the interface between two waveguides effectively enhances the transmission efficiency, as in the case of couplings between a normal slab waveguide and an MIM waveguide. In addition, couplings with very wideband transmissions over a wavelength region of a few hundred nanometers were validated. (C) 2015 Optical Society of America

In this study, we present a new design for an optical near-field probe with a slot-waveguide structure and evaluate it using a finite-difference time-domain simulation. Our model, with a 50-nm slot core, enables illumination around the tip of the probe using a small optical spot 50-250 nm wide with 20%-30% transmission efficiency. Based on the high-index-contrast structure in a slot waveguide, a nanosized optical spot is easily generated, which is impossible with a normal slab waveguide. Similar properties of optical spot and transmission efficiency are obtained for different geometric configurations of flat-faced and tapered dielectric slot waveguides in illumination mode. The transmission efficiency of our models is the same or higher than that in conventional metallic tapered optical probes. When operating in illumination and collection modes, a near-field light reflected at 50-200-nm-wide measured objects is clearly observed, and a spatial resolution of similar to 50 nm is obtained. These findings suggest the potential for slot-waveguide structures to expand the versatility of nanosized optical probes. (C) 2014 Optical Society of America

A 1-mm-diameter fiber-optic photoreceiver with a sidesurface interface is proposed. By controlling the scattering part embedded in the fiber, the receiving sensitivity along the fiber's axis is successfully flattened over a 5-m-length. The simulation results suggest a potential for a large-area photo-detector of ~3-m-spherical diameter.

We have designed a novel fiber-optic light concentrator with scattering layers and evaluated the light concentration characteristics by ray-trace simulations as functions of the parameters of the incident light angle and wavelength, as well as the waveguide structure. Unlike well-known luminescent solar concentrators, in our models, illuminating light is directly captured through the proposed waveguide structure. The optical efficiency in our fiber-optic models is remarkably improved in long-length regions compared with that in simple slab waveguides. In addition, the waveguide length required to effectively collect light is extended to 300 mm and 1.5 m for optical fibers with 1- and 10-mm core diameters, respectively, which are ten times longer than those in slab waveguides with an equivalent scale. Because of the cylindrical structure of optical fibers, we have also evaluated the sensitivity of our models to surrounding light. Consequently, an obvious directional property containing single or three peaks of the sensitivity is clarified, and their widths can be tuned by changing the width of the scattering parts. These results suggest that our models are suited for sensor devices such as optical receiving antennas, rather than simple light concentrators. Finally, we model a fiber-optic probe as an application and evaluate the light concentration characteristics when the concentrator is serially concatenated with a normal optical fiber.

This study describes resilient access network structures in time-division multiplexing passive optical networks (TDM-PONs) and wave-division multiplexing (WDM)/TDM-PONs, and compares their network unavailability versus outage scale. In addition, this study discusses the unavailability for media networks with simple ladder and more realistic ring-to-tree topologies for cases with simplex and full/partial duplex configurations between drop points and central offices. In large-scale networks, the unavailability in duplex networks is drastically improved by 4-5 orders of magnitude compared with that in simplex networks for large outage scales. Cable failure significantly affects the unavailability, especially in feeder sections, whereas failures due to optical fiber or optical add-drop multiplexers are mostly masked by cable failure in WDM/TDM-PONs. Consequently, there is little difference in the unavailability of the two PON schemes, except for the difference due to PON splitters. A comparison of the unavailability for fully and partially duplicated networks shows that the latter with a ring-to-tree topology has the advantage of lower unavailability in large-scale regions. These results imply that a realistic duplication scheme successfully enhances the network reliability regardless of imperfect duplex structure.

We address emerging threats to the security of photonic networks as these networks become heterogeneous being opened to the upper layers, other operators, and end users. We review the potential threats, mainly loss of the confidentiality of user data transmitted through optical fibers and disturbances of network control, both of which could seriously damage the entire network. We then propose a novel conceptual model of a secure photonic network by introducing a quantum key distribution (QKD) network to its legacy structure. Secure keys generated by the QKD network are managed by key management agents (KMAs) and used to encrypt not only user data but also control signals. The KMAs cooperate with the generalized multiprotocol label-switching controller for secure path provisioning and drive photonic and modern crypto engines in appropriate combinations. Finally, we present a roadmap of a deployment scenario, starting from niche applications such as mission critical and business applications and the next. Digital cinema distribution through a photonic network is presented as an example of a niche application.

This paper proposes a resilient access network architecture with a cable-route protection function based on hybrid wavelength division multiplexing and time division multiplexing passive optical network (WDM/TDM-PON) systems. The reuse of existing optical cable networks allows our ladder and grid networks to introduce duplicate routes for the shared portions of PONs by using a few optical fibers with simple structures. It automatically builds alternative optical paths in response to the wavelengths of optical line terminal and optical network units (ONUs) at both ends of the network. Our simulation achieved network capacities of 1.25 Gb/s x 500 ONUs and 10 Gb/s x 64 ONUs by applying 48 and 16 WDMs, respectively, to the networks. We think that these results show sufficient scalability; in particular, the ladder network composed of simple WDM components is a promising architecture for resilient access networks.

We propose a new photonic crystal fiber design with a W-shaped effective index profile to achieve the largest effective area (A(eff)) for telecommunication use. We realized a 220-mu m(2) A(eff) while achieving both a cable cutoff wavelength of less than 1300 nm and a bending loss compatible with ITU-T recommendations G.655 and G.656.

We address emerging threats to the security of photonic networks as these networks become heterogeneous being opened to the upper layers, multi-operator, and end users. We review the potential threats, mainly loss of the confidentiality of user data transmitted through optical fibres and disturbances of network control, both of which could seriously damage the entire network. We then propose a novel conceptual model of a secure photonic network by introducing a quantum key distribution (QKD) network to its legacy structure. Secure keys generated by the QKD network are managed by key management agents (KMAs) and used to encrypt not only user data but also control signals. The KMAs cooperate with the Generalized Multi-Protocol Label Switching (GMPLS) controller for secure path provisioning and drive photonic and modern crypto engines in appropriate combinations. Finally, we present a roadmap of a deployment scenario, starting from niche applications such as mission critical and business applications.

The macro-bending based fiber identification technique is widely used to identify optical fibers at the worksite. Bending-loss insensitive fibers have been receiving increasing attention, however it is difficult to apply the macro-bending based fiber identification technique to these fibers. In this paper, we propose a new fiber identification technique based on a mechanically induced long-period grating (LPG), and show that the proposed technique can be utilized for a hole-assisted fiber with an extremely low bending loss. We also propose combining the chirped LPG technique with our fiber identification method to simultaneously specify fibers with different structures.

We show that any optical pulse train recovers its original waveform after passing through a group velocity dispersion (GVD) device when the total GVD value of the device is equal to an integral multiple of 1/(2 pi f(rep)(2)), where f(rep) is the repetition rate of the optical pulse train. In addition, we detail our proposed GVD measurement method, or optical phase-modulation (PM) method, which utilizes a sinusoidally PM continuous wave (CW) light as a probe light. The total GVD B-2 of a device under test (DUT) is derived by using a very simple equation, vertical bar B-2 vertical bar = 1/(2 pi f(null)(2)), where f(null) is the smallest modulation frequency at which the sinusoidally PM light becomes CW light again after passing through the DUT. (c) 2010 Optical Society of America OCIS codes: 060.0060, 060.2300, 060.5060, 260.2030.

We suppressed fiber fuse propagation in hole-assisted fiber (HAF) and photonic crystal fiber (PCF) with input powers above 14 W at 1480 and 1550 nm. This result indicates that the threshold power of fiber fuse propagation in HAF and PCF can be at least 10 times larger than that in conventional single-mode fiber (SMF) in the optical communication band. We also observed the dynamics of fiber fuse termination at a splice point between a test fiber (HAF or PCF) and a conventional fiber (SMF or dispersion-shifted fiber (DSF)). Our experimental results show that air holes in HAF and PCF play an important role in suppressing fiber fuse propagation.

A novel technology for simultaneous WDM signal monitoring is presented based on ultrafast field sampling. Its flexibility regarding channel allocation and/or channel bandwidth is unique and attractive, as is its ultrafast nature. Two- and four-channel WDM signals, with the total bandwidth of 800 GHz, are successfully discriminated and observed with the proposed scheme. (C) 2010 Optical Society of America

We demonstrate, for the first time, a 10-Gbit/s burst-mode optical receiver with an automatic level controlled burst-mode optical fiber amplifier (ALC-burst-OFA). We receive burst signals with 198.5-ns guard-time and 496.4-ns preamble, and achieve the wide dynamic-range of over 16.6-dB and -22.5-dBm sensitivity at BER=10(-10) using our proposed ALC-burst-OFA and a DC-coupled continuous-mode optical receiver. (C) 2008 Optical Society of America

We propose and demonstrate an ac-coupled burst-mode transmitter with a differential interface for 10-Gbit/s-class passive optical network (PON) systems by using a novel baseline-wander common-mode-rejection (BLW-CMR) technique. This technique can cancel the transient responses of capacitors at the ac-coupled differential interface, and produce an optical burst-mode signal with a fast response. We confirmed the feasibility of this technique experimentally with the prototype we developed. The response time of the optical burst-mode signal was 500 ps, which is the fastest response time reported for a burst-mode transmitter. Good temperature dependences were also observed. Moreover, we conducted a burst-mode upstream experiment using a burst-mode avalanche photodiode (APD) receiver that we developed for 10 G-EPON systems. We obtained a large loss budget of 33 dB and a wide dynamic range of 25.5 dB at a bit error rate (BER) of 10(-3).

We proposed an ultra high-speed automatic level controlled optical amplifier with wide dynamic range and 110-ns guard time and 20-dB dynamic range for input power is achieved for the first time. (C) 2008 Optical Society of America

We demonstrate, for the first time, a 10-Gbit/s burst-mode optical receiver with an automatic level controlled burst-mode optical fiber amplifier (ALC-burst-OFA). We receive burst signals with 198.5-ns guard-time and 496.4-ns preamble, and achieve the wide dynamic-range of over 16.6-dB and -22.5-dBm sensitivity at BER=10(-10) using our proposed ALC-burst-OFA and a DC-coupled continuous-mode optical receiver. (C) 2008 Optical Society of America

Proposed is an easy technique for overlaying multiple wavelength division multiplexing (WDM) signals on optical code division multiplexing (OCDM) signals. The approach results in a broad coding spectrum for OCDM signals, and thus provides highly secure services in WDM-based networks. The technique is validated experimentally using an OCDM signal and two WDM signals.

An advanced dense wavelength division multiplexing small form factor pluggable (DWDM-SFP) transceiver for the L-band, which features a wavelength tunability of 3 nm, is proposed and developed. By using the developed wavelength-tunable DWDM-SFP transceiver, a colorless optical network unit (ONU) prototype for coexistence-type wavelength division multiplexing passive optical networks (WDM-PONs) that enable coexistence with existing PONs is achieved. Both wavelength and temperature dependencies of the colorless ONU prototype are evaluated and the applicability to the existing Class B+ optical distribution network that has a 28 dB loss is discussed.

A three-level-control electronic dispersion compensation (EDC) technique using a simple eye monitor detecting the duty ratios of the received signal is proposed and demonstrated. The EDC prototype can compensate for the chromatic dispersion of 40 km singlemode fibre and realise a cost-effective 10 Gbit/s transceiver utilising a directly modulated laser diode for access networks.

A multi-wavelength optical transmitter that employs time-domain modulation of directly modulated wavelength-swept light is proposed. This scheme offers the simplicity and. exibility needed for future optical access networks based on high spectral density wavelength division multiplexing. A proof-of-concept demonstration of the generation and selective detection of four-channel 1.25 Gbit/s signals is shown.

In order to relax the limitation of the number of multiplexed signal lights caused by beat noise between signal lights, we investigate the applicability of a heterodyne detection technique to a spectral amplitude coding optical code division multiple access scheme. In this investigation, for the first time, we found analytically that the optical frequency chips that form parts of the signal and local lights require uniform phase differences even for envelope detection. We also confirm this requirement and our theoretical analysis experimentally. © 2008 IEEE.

In order to realize flexible bandwidth allocation in access networks with bit rates of 10 Gb/s or more, transmitting data by parallel streams with different wavelengths is an attractive approach. In such systems, the timing skew induced by fiber dispersion is the critical problem. This paper proposes a skew compensation LSI for an optical access system based on power splitter based wavelength division multiplexing passive optical network (PS-WDM-PON). The LSI can compensate timing skew of more than 9.6 ns with 82 ps resolution; experiments show that transmission distance of 24 km are possible if the bit rate of each wavelength is 2.5Gbit/s and all wavelengths lie within 20 nm.

A frequency monitoring/stabilisation technique for dense wavelength division multiplexing access networks is proposed. To achieve more precise frequency stabilisation, the bias current used to drive each directly modulated LD is dithered. The key techniques are adding an offset bias to the detected error signal and offsetting the centre frequency of the arrayed waveguide grating port against the grid frequency to achieve effective frequency stabilisation. Experiments show that the relative frequency deviation of +/- 30 GHz can be suppressed to less than +/- 1 GHz without any BER degradation.

The loss budget of a 12.5 GHz-spaced wide-area carrier-distributed wavelength division multiplexed passive optical networks (WDM-PON) using an semiconductor optical amplifier (SOA) modulator is reported. Based on a loss budget estimation approach that takes the excess spectral broadening caused by SOA modulation into consideration, it is shown that achievable loss budget is more than 26 dB over a 45 nm wavelength range at a bit rate of 1.25 Gbit/s.

A DWDM-PON is proposed that realizes a spectral efficiency of I bit/s/Hz by using homodyne detection based on digital signal processing. The feasibility is confirmed with a transmission experiment, and the application area is discussed. (C) 2007 Optical Society of America.

A novel gain-clamping technique that controls the amplifier output power of the gain-clamp light by the ALC mechanism is proposed and experimentally confirmed. It yields signal-light gain controllability and stability in burst-mode PON signal amplification. (c) 2008 Optical Society of America.

The plug-and-play function for coexistence-type colorless WDM-PONs, which remotely and automatically assigns dedicated wavelengths, is demonstrated using tunable DWDM-SFP transceivers. Prototypes of the tunable ONU controller are developed and its dynamic performance is evaluated. (C) 2007 Optical society of America.

A novel technique is proposed for suppressing light interference caused by the connection of noncompliant equipment. In this technique, the detected optical frequency is synchronized with the chirped frequency of a directly modulated laser diode. (C) 2008 Optical Society of America.

The burst-mode 311 receiver using monolithic ICs for 10-Gbit/s-class optical access networks is reported. In a point-to-multipoint access system like a passive optical network (PON), the receiver at the optical line terminal (OLT) must be able to handle burst-mode optical packets with significantly different powers and phases. An OLT receiver with high sensitivity with instantaneous response to burst inputs is desired for widening the accommodation area and for high efficiency in PON uplinks. Currently, the diffusion of high-speed Internet connection services represented by fiber to the home services at 1.25 Gbit/s is remarkable and the standardization of the next-generation system operating at 10 Gbit/s has started in IEEE. We first discuss the issues in the implementation of 10-Gbit/s-class PON systems, focusing on securing the accommodation area and the quality of the service comparable with those of the deployed system. Against that background, we propose target specifications for sensitivity, a dynamic range and response speed of the 10-Gbit/s-class burst-mode receiver so as to secure the power budget and the upstream efficiency comparable with those of the already-installed systems. Our burst-mode 311 receiver was designed to meet the above requirements and developed using monolithic ICs of transimpedance amplifier, limiting amplifier, and clock and data recovery circuit fabricated by using SiGe BiCMOS technologies along with a p-i-n photodiode. High sensitivity of - 18.0 dBm, a wide dynamic range of over 16.5 dB, and quick response time of 75 ns were confirmed for burst inputs with extremely different powers.

We propose and demonstrate a 1.25/10.3-Gbi/s dual-rate burst-mode receiver with two gate circuits to separate the signals according to the bit rate of the input signals. This receiver is cost effective because it employs devices with an ac-coupled interface and no reset signals.

We propose an error signal transfer method for remote frequency stabilization in DWDM-PON. The error signal is embedded in a downlink signal using a supervisory frame; the effectiveness of this method is experimentally confirmed.

Wavelength resource scalable heterodyne detection based WDM access employing time-domain modulation of wavelength-swept light is proposed. We experimentally demonstrate 1ch similar to 5ch 12.5 GHz-spaced 1.0 Gb/s WDM transmission.

The effectiveness of installing fast AGC in a PDFA for amplifying burst mode PON upstream signals is reported for the first time. The technique has the potential to realize high-gain/high-power burst-mode PON repeaters.

We propose and demonstrate phase-matched OCDM transmission based on multi-frequency self-homodyne detection. The feasibility is verified based on experiments using a developed PLC-LN module at the bit rate of 1.5 Gbit/s.

We demonstrate the burst-mode optical amplifier for 1310 nm. Even when the input burst length varies rapidly from 500 ns to 50 mu s, the gain error within +/- 0.5 dB is achieved.

A multi-wavelength stabilization technique is proposed based on a local minimum search. Experiments confirm that the estimated frequency stability is 3GHz even for 100 downstream wavelengths with 50GHz spacing.

We propose and demonstrate a 1.25/10.3-Gbi/s dual-rate burst-mode receiver with two gate circuits to separate the signals according to the bit rate of the input signals. This receiver is cost effective because it employs devices with an ac-coupled interface and no reset signals.

This letter proposes a centralized frequency stabilization technique for uplink signals in dense wavelength-multiplexed passive optical networks
it is based on dithering the transmission spectra of the demultiplexer. To ensure that the proposed technique achieves a wide capture range, a planar lightwave circuit is developed that incorporates a Mach-Zehnder interferometer and two arrayed waveguide gratings. Experimental results show that the wide capture range of ±25 GHz is established without any significant power penalty. © 2008 IEEE.

We propose a multilevel transmission technique using stacked optical binary signals without any loss budget reduction when receiving multilevel signals. The principle is described and the validity of the technique is verified by numerical calculation.

We propose an inexpensive multilevel transmission system that uses several laser diodes (LDs) of different wavelengths and receives each stream as a block. To compensate for the skew induced by group velocity dispersion (GVD), we propose a dynamic skew compensation method and fabricate a prototype LSI. Experiments show that 5 Gbps transmission can be achieved in a network (NW) with a loss budget only 0.73 dB lower than that of a 2.5 Gbps binary transmission.

Deployment strategy of access systems is described toward next generation access (NGA). Considering service requirements and consecutive evolution to NGA, we think that 10 Gbit TDM-PON will be the most promising system among several technologies. The other systems like WDM-PON, for which we have not yet found a suitable segment of users, can be contribute to high-end access services with scalability and reliability.

This paper proposes a novel lambda/Bit conversion technique that improves the efficiency of wavelength utilization; it allows multiple optical wavelengths to transfer both optical power and signal information of wavelength combinations, and simultaneous multi optical wavelength reception by a single Pin-PD. The proposal can increase the optical received power with highly efficient wavelength utilization; it can both extend the FTTH introduction area and network service bandwidth easily and economically.

In order to replace existing TDM-PON (TDM-Passive Optical Network) systems by new PON (10G-PON) systems providing 10 Gbit/s access in a flexible manner, it is necessary to realize loss budgets that are not less than those of existing PON systems. In this paper, we propose a new 10Gbit/s APD burst-mode receiver, which attains the sensitivity of -24.8 dBm and the dynamic range of 17.8 dB. When forward error correction (FEC) is employed, the corresponding values are -29.8 dBm and 22.8 dB; the resulting loss budget of 29 dB satisfies the requirement for new PON systems.

We propose the M-switching technique to realize a high sensitivity and wide dynamic range 10Gbit/s APD burst receiver. Experiments show that the combination of M-switching and FEC realizes high sensitivity (-31.4dBm) and wide dynamic range (24.4dB).

We propose a flexible optical receiver module for an optical access system that offers not only user/service-multiplexing but also rate-extendibility. Proposed module compensates delays of over 9.6nsec, caused by G VD, and provides physical rate flexibility.

We have analyzed polarization dispersion determined from the Stokes parameter measurement for a single-mode fiber. The polarization state changes has been considered for a discrete, tandem fiber model using Poincare sphere representation. As a result, it is newly found that the differential delay time estimated from the Stokes vectors of output light is not given as the cumulation of zero-mean random values but as positive random values, when random mode conversion exists along a fiber axis. It thus can be estimated that polarization dispersion increases in proportion to square root of distance.

This paper theoretically determines the optimum fiber parameters for an Er3+-doped fiber amplifier pumped by a 1.48-mu-m laser diode using the rate equation for a three-level laser system. The signal gain depends on the cutoff wavelength and the Er3+-doped area radius.

Optical heterodyne FSK system experiment with Brillouin amplifier is demonstrated using a CW pump of a DFB-LD operating at the 1.54µm wavelength. The 30 Mbit/s coherent FSK signal is amplified by 4 dB through 52 km single-mode fiber when the pump power of 2.5 mW is injected into the fiber. To obtain the flat gain profile ranging over the signal bandwidth, Brillouin gain bandwidth is broadened by means of modulating the pump frequency. Bit-error-rate performance is improved to reduce the rate by a factor of ten with the amplifier. Brillouin amplifier is useful for transmission systems at a bit-rate of less than 1 Gbit/s, as opposed to a fiber Raman amplifier. © 1989, De Gruyter. All Rights Reserved.

Tightness of fiber ribbons in a slot-type cable is estimated by measuring temperature dependence of fiber strain due to temperature change for free fiber ribbons and those assembled in the cable. Fiber-strain measurements were carried out by means of an optical heterodyne detection technique for free nylon-jacketed and LCP-jack-eted fiber-ribbons, and for the cabled fiber ribbons. By making a comparison between thermal behavior of fiber strain for the both states of jacketed fibers, it is clearly understood that the fiber ribbons are tightly accommodated in the slot-type cable in temperature regions over -15°C for nylon-jacketed fiber ribbons and 0°C for LCP-jacketed fiber ribbons under additional fiber-strain value of 0.015 percent through the cabling process. The fiber ribbons, which are tightly accommodated with suitable tension level through the process at room temperature, show reasonable thermal-strain behavior in comparison with the initially introduced fiber strain during the cabling process. © 1988 IEEE

微細な光集積回路における隣接導波路間結合特性評価の一環として、今年度はナノサイズスラブ導波路間で生じる結合に依存した光波長合分岐デバイスを検討した。具体的には、並行配置のスラブ導波路間で生じる光結合量／損失とその波長特性について、主に2次元FDTD法に基づいたシミュレーション評価を実施した。評価事例として、導波路に複数導波路を並行配置させることで、希望波長成分を抽出可能であること、多段の並行配置の組み合わせで同時に空間分岐が可能となる構造を提案した。さらに、波長合分岐特性に大きく関与せずに分岐効率を向上させる策として、結合部の一部にスタブ部を挿入させる構造が有効なことを提案した。これら成果は、学内修士論文に反映された。

1.研究及び結果の概要光ファイバの側面を入出射のインターフェースとした新たな細径光ファイバプローブ構造を考案し、光線追跡シミュレーションを用いて、その有効性を確認した。医療の内視鏡などに用いられる通常の光ファイバプローブは主に光ファイバ端点が送受光の点インターフェースとなっており、そのために結合レンズ系や長さ方向のスイープ制御など微細で複雑な機構が必須であったが、本提案では側面送受光を利用することでレンズレスの簡易な機構で広範囲かつ高速な計測が期待できる。本提案の光ファイバプローブは、外径約1mmφで長さ50mmの形状を持ち、クラッドの一部にMie散乱層を設け、片側端面内に発光素子及び面受光素子を備えることで送受光一体の構造をとる。光源からの光は光ファイバに沿って伝搬しながら散乱を受け、側面から外部へ指向性を持って発光される。プローブ周囲に物体が分布している場合は、その物体面で反射された一部の光が再びプローブ側面を通じて入射し、散乱過程を経て受光器にまで到達する。この受光パワーをモニタすることで周囲に分布する物体の計測が可能となる。シミュレーション結果によれば、光ファイバプローブ周囲20mm程度までに位置する被測定物体に対して0.01％–10％の受光効率での光検出が認められた。プローブ下側側面に反射コーティングを施すことで効率は半桁程度まで改善された。さらに、空間的に分布する物体を測定するため、光ファイバ内の散乱層をスパイラル形状に構成することにより、長さ方向の物体分布の測定が～2mmの空間分解能で達成できることが検証された。今後はS/Nの改善及び長さ方向に対する受光効率平坦化などが主な課題となる。本研究はJSPS科研費　25420346の助成及び本特定課題A6338の助成を受け、実施されたものである。2.決算内訳以下の通り、支出した。予算　270,000円、使用額 269923円。（内訳概要：ソフトウェアライセンス　185,850円、学会参加出張費　24,300円、その他消耗品　

１．概要説明　光ファイバなどの光導波路は端面から入力した光については低損失な伝搬が可能であるが、側面からの入射光は透過してしまい殆ど導波できない。一方、側面からの光を取り込むことが出来れば、太陽光の集光器や照明ガイド、センサなど数多くの利用が考えられるため、この導波光への変換の効率（集光率）を向上させるための研究がなされている。本研究では平板型導波路と光ファイバに新たに散乱層を付与することで集光率を改善させる構造を提案し、シミュレーション評価を行った。Ｍｉｅ散乱を生じさせる散乱層構造を有するスラブ型導波路では5mm程度の短い導波路で40%を超える集光率が得られるものの10mm以上で長さに対し逆比例関係になり、集光に寄与する有効長が10mm程度と短く、長尺な導波路への拡張が困難なことが分かった。同時に光波長と入射角度への依存性は低いことが判明した。これに対し円柱形の特性を活かし散乱層を設けた光ファイバでは、スラブ導波路に比べ、有効長が100mm程度と約1桁改善され、同時に最大集効率も１０%程度上昇した。しかしながら、まだ数十cmを超える長さでは逆比例の特性が現れるため、実用的な用途には更なる改良策が望まれる。光ファイバ型の特徴として一方向だけではなく周囲からの光を同時に取り込める利点がある。これに関して３６０度の入射角に対する周効効率の評価も実施した。その結果、提案の構造では60度間隔の３方向に対して指向性を有した受光が可能なことが分かった。また、別なアプローチとして、光ファイバや導波路の形状を変形させることにより外部光の取り込みを改善する方法がある。簡単な変形モデルを作成し、変形が集光率に与える影響も分析した。その結果、集光率の改善度合いは散乱層をも散る手法に比べ１桁程度低く、変形単独では効果が小さいことが確認された。変形の利用に関しては、多様な形状やスケールに対する依存性が強いため、今後多様なモデルを構築しシミュレーション評価を継続していく予定である。上記に関して得られた成果は、電子通信学会全国大会にて発表を行い、併行して現在学術論文に投稿中である。２．決算内訳　予算　400000円、使用額　400000円　【内訳】　計算用PC　一式　209508円　コピー機トナー、文具類　68892円　会議出張旅費及び宿泊費　107600円（2名分）　会議参加・資料費　14000円(2名分）

H23年度は、ソフトウェアツールを用いた導波路形状の作成と基本特性の分析に取り組んだ。また、実際の光ファイバを用いた場合の微小部分の変形による光の取り込み効果の検討を実施した。設計及び計算用のPCと導波路断面等を観察するための簡易顕微鏡等を購入し、情報収集の一環として国際会議、展示会参加費用の一部を支出した。初めに、自然光集光に関する参考文献等を調査分析し、多様な方式の原理理解、現行の性能、課題等について情報収集した。太陽光の集光器に関しては、mm以下のミクロな構造をもつ特殊レンズ加工を施したものが主流で研究されているが、価格面、技術面の困難さが課題である。新たな方式として直接光ではなく蛍光を介することで特殊形状の加工が不要かつ、集光効率を向上させる有望な方式が提案されている。この方式は有望であるが、蛍光材料等が特定され、権利化もされているため、本研究では、集光効率の最大化ではなく、簡易さと経済性を追求し、特殊材料・高精度加工を必要としない比較的簡易な集光器の設計を当面の目標とした。具体的には、通常の２層、３層のガラス導波路をベースとし、コア・クラッド境界面を鋸歯状、正弦波状などに変化させた場合の構造モデルを作成し、外部側面方向からの照射光がどの程度取り込まれ、伝搬するかについて机上計算を行い、レイトレースのシミュレーションツールを用いて評価した。実際には修士学生がソフトウェアツールの使用方法の習得から、光学特性の条件設定までを学びながらモデル作成と評価を行った。残念ながら、現時点では、集光効率はまだまだ不十分であり、新たなモデル構築が最大の課題である。候補技術としては、境界面形状変化ではなく、空気等の散乱体を境界付近に付与した構造等を想定し、継続検討中である。検討途上において、別な要求や派生技術の話題がいくつか生じた。一例として、通常の通信用途において細径の光ファイバへの側方からの光入射技術の課題が持ち上がり、現在平行して方式を検討中。主に２通りの方式が考えられ、現在はミクロな光ファイバ変形を利用する集光技術、ファイバグレーティングなど伝搬モード変換を利用した集光技術について机上検討を行っている。研究成果は現在、研究室内での議論のレベルにあり、今後シミュレーションや実験を通じて具体化し、発表等を行う予定。

今年度は、主に関連するセンシング技術のサーベイと測定原理の基本検討を実施した。研究費は実験を実施していくための光ファイバ等、基本ツールの一部の購入、分析用のPC及び情報収集の一環として国内の関連会議への参加費を支出した。検討内容を整理すると、１）関連技術（特に周波数領域リフレクトメトリ（OFDR)、低コヒーレンストモグラフィー、光ファイバブラッググレーティング（FBG)技術）に関し、文献調査・分析を行い、ゼミ等にて議論、検討を行った。２）低コヒーレンス干渉法をベースとした計測原理を発案し、数式による確認、基本特性を評価した。例えば分布的に局在する光ファイバ曲がり角度を温度や応力と分離して評価する原理、曲げ形状に依存しない角度検出法などの計算による確認を行った。３．センサの適用領域拡大に向け、例えば内視鏡などへの適用性の検討も行った。項目１については、センサの全体の設計において必要となる技術の洗い出しを行い、片端での多点の同時計測を可能とするOTDR、OFDRを調査し、数m程度の比較的短尺な対象で数mm程度の分解能を得るためにはOFDRをベースとした。既存の方法ではいくつかの異なる刺激が加わった際にデータが重なって検出されてしまうため、例えば、空間位置が異なる多点の情報を分離し、かつ曲がりの影響だけを温度や歪から分離検出する必要がある。これを解決するための検出手段として、低コヒーレンス干渉技術を応用し、参照光の設定を工夫した新しい干渉計構成を組むことで必要情報だけを雑音から抽出する原理を数式レベルで確認した。オルタナティブ技術として検討例の多いFBGについても情報収集を行い、センサヘッド部にFBGを用いた場合の干渉性構成と分解能等についても合わせて特性の確認を行った。また、原理の応用範囲を拡げる意図から、他分野のアプリケーションの検討を行い、医療分野における内視鏡などへの適用の可能性を調査中である。現段階では、いずれも研究室内部での初期検討に留まっているが、今後、実験等による確認を行うことで外部発表していく予定である。