高橋 浩

We developed an 8×8 wavelength router incorporating two AWGs and multiple 4×4 matrix switches to allocate WDM channels for each route flexibly. We describe the design principles of the router and its basic transmission characteristics. © 2007 Optical Society of America.

We present an DQPSK demodulator with a silica-based PLC type MZI, where a half-wave plate is asymmetrically allocated to reduce polarization dependent frequency shifts, and demonstrate an error-free 43-Gbit/s demodulation for any incident SOP. (C) 2008 Optical Society of America.

We successfully demonstrate the polarization-insensitive operation of an MZI-based LN switch with PLC-integrated polarization beam splitter/combiners. The switch functions for both polarizations with a PDL of 0.1 dB and a switching speed of 40 ps. (C) 2008 Optical Society of America.

Silica waveguide planar lightwave circuit (PLC) technology is very useful for fabricating the compact and high performance optical devices used in transparent and flexible networks. Wavelength multiplexers and optical switches for ROADM and OXC are still being developed to achieve higher performance and they are integrated to provide the compactness required for future applications. New devices for the advanced modulation format can also be made with PLC technology.

We propose a new PLC design for a 43 Gb/s DQPSK demodulator. The design reduces both the module size and the power consumption without degrading any of the module characteristics.

We propose a novel waveband-selective switch that uses cyclic Arrayed-Waveguide Gratings. The device is fabricated on one chip using Planer Lightwave Circuit technologies. Tests demonstrate that the designed performance is successfully realized.

A 43 Gbit/s DQPSK demodulator is demonstrated with a wide operational bandwidth enhanced by birefringence control achieved using stress release grooves. The demodulator exhibits a sufficiently low PDf over the C and L bands. ©2008 IEEE.

We have studied the wavefront matching (WFM) method, which synthesizes optimum waveguide patterns from the desired characteristics, and demonstrated its feasibility. In this paper, we expand this method to create optimum waveguide shapes with low-loss and low-wavelength dependence in waveguide lenses, Y-branches, and waveguide crossings. We describe the design procedures for each waveguide element and report the experimental results as proof of concept. The measured results agree well with our design requirements, and the waveguide patterns designed by the WFM method exhibit better characteristics than the reference patterns.

We have developed an arrayed-waveguide-grating-based wavelength router with a loop-back structure for a system with nonuniformly distributed traffic. We describe the design principle with particular regard to the loop-back waveguide connections, and discuss its optical routing functions with some experimental results.

We propose a novel integrated photonic decoder for two-dimensional (time spreading, wavelength hopping) optical code division multiple access. The decoder is composed of multiplexers-demultiplexers, variable delay lines, and a coupler, which processes complementary codes and utilizes balanced detection to reduce unwanted cross-correlation interference. We successfully carried out a 10 Gbit/s transmission that demonstrated its effectiveness. (c) 2007 Optical Society of America.

A compact and low-loss Y-branch splitter is designed made with a high refractive-index difference waveguide and using the authors' wavefront matching method. The splitter was then fabricated using silica-based planar lightwave circuit technology. Excess loss was less than 0.2 dB per branch over a wide wavelength range of 1250 to 1650 nm.

We developed an AWG-based wavelength router with a loop-back structure for a system with non-uniformly distributed traffic. We describe the design of the loop-back waveguides and the transmission characteristics of the developed device. © 2006 Optical Society of America.

We propose a novel integrated-photonic decoder for two-dimensional (time/wavelength) OCDMA, which processes complementary codes and utilizes balanced detection to reduce unwanted cross-correlation interference. We successfully carried out a 10 Gbit/s transmission that demonstrated its effectiveness. © 2006 Optical Society of America.

We designed waveguide crossings with small angles by the wavefront matching method to reduce excess loss and crosstalk. The designed waveguide crossings were fabricated using silica-based planar lightwave circuit (PLC) technology. We experimentally obtained excess loss and crosstalk values of less than 0.3 and 30 dB, respectively, for a crossing angle of 5°, and of less than 0.1 and 38 dB, respectively, for an angle of 20°, in the 1530-1565-nm wavelength range. The designed waveguide crossings are promising as basic circuit elements for realizing more compact PLC devices. © 2006 IEEE.

Mode converters have been designed that reduce mode transition losses in arrayed waveguide grating (AWG) multi/demultiplexers using the authors' recently proposed wavefiront matching method. The designed mode converters are very compact and easy to fabricate AWGs were fabricated equipped with the authors' mode converters. The loss reduction principle was confirmed experimentally.

A theoretical and experimental study of an optical interferometer circuit with a uniform wavelength spacing is presented. The operating principle of the filter and a phase-generating coupler (PGC) that can transform a conventional filter into a uniform-wavelength-spaced optical filter is described. As an example, a transformation method is applied to a conventional Mach-Zehnder interferometer (MZI), and the PGC variables are optimized to obtain an MZI with a constant channel spacing of 20 nm. Furthermore, the designed MZI is fabricated using 1.5%-Delta silica-based planar lightwave circuit technology and a 20-nm-spaced MZI is realized with a wavelength displacement that was less than 1.2% of the wavelength period. The fabrication tolerance of the MZI in relation to the PGC design variables is discussed. It is shown that a certain PGC design can increase the fabrication tolerance.

We demonstrate an eight-channel coarse wavelength-division-multiplexing interleave filter that employs a silica-based lattice-form filter. The filter incorporates phase-generating couplers to convert a conventional frequency interleave filter into a wavelength interleave filter with a constant channel spacing with respect to wavelength. We fabricated the designed interleave filter on a 1.5%-Δ silica-based waveguide and realized a constant channel spacing of 20 nm with a wavelength displacement of within ±0.5 nm and an insertion loss of less than 1.7 dB over eight channels. © 2006 IEEE.

Quantum key distribution (QKD) is being studied as a way to provide unconditionally secure communications. Several experiments have shown its feasibility. However, most experiments have used a point-to-point occupied optical link. In order to use QKD for secure communications on a real network, it is preferable to be able to change parties on demand and to have quantum transmission and ordinary optical transmission share the optical network. In this work, QKD, through a silica-based planar lightwave circuit (PLC) 8 x 8 nonblocking matrix switch was investigated. We found that an interferometer type switch can work even for a single-photon-level light and that a multi-user QKD network can be constructed using a silica-based PLC 8 x 8 non-blocking matrix switch. In addition, single-photon-level transmission and ordinary optical transmission can share the same 8 x 8 non-blocking matrix switch, so which shows the possibility of sending quantum signals through current optical networks. (c) 2006 Elsevier B.V. All rights reserved.

In this paper, ultradense wavelength-division multiplexing (WDM) transmission technologies are discussed, and a field demonstration of over-1000-channel ultradense WDM transmission is reported. The generation of an ultradense WDM signal using a supercontinuum multicarrier source that generates more than 1000 carriers and uniform precise channel spacing of 6.25 GHz is presented. The influence of four-wave-mixing generated in the transmission fiber and the requirements placed on the WDM multiplexer and demultiplexer is described. An over-1000-channel ultradense WDM transmission experiment is reported. A 1046 x 2.67-Gbit/s 6.25-GHz-spaced ultradense WDM signal is successfully. transmitted over 126 km of field-installed fibers in the test bed of JGN II.

スーパーコンティニウム光源を用いて2.5GHz間隔の10000波長を超える高確度の光キャリア発生を実現した。周波数安定化光の外部変調で得た2つの基準光を用いて2系統の5GHz間隔SC光を発生し、これらを多重することで、1460〜1665nmの波長域において2.5GHz間隔の10000波長・高確度の光キャリアを発生した。発生した光キャリアの光周波数確度は±30MHz以内であり、SNRは18dB以上であった。また、光キャリアを外部変調した時の信号品質を評価したところ3100チャネルがギガビットイーサ等のデータ転送に適用できることを確認した。

Over-10 000-channel multi-carriers with uniform channel spacing of 2.5 GHz are generated from a supercontinuum (SC) multi-carrier source. which uses two parallel SC conversion sections. More than 3100 channels in the C divided by L-bands are confirmed to offer Q-factors sufficient for GbE transport.

A novel wideband planar lighwave circuit type variable optical attenuator (VOA) that incorporates a phase-generating coupler is proposed. The proposed VOA was fabricated on a 1.5%-Delta silica-based waveguide, and obtained a low insertion loss of less than 1.2 dB and a low wavelength dependent loss of less than 0.8 dB at attenuation levels of 0 to 25 dB over the C- and L-band wavelength range.

We propose and demonstrate a new method for adjusting the center wavelength of a silica-based planar lightwave circuit interferometer via the densification of silica glass. We applied the proposed method to an arrayed waveguide grating multiplexer using a hot isostatic press, and observed a large center wavelength shift of more than 1 nm. We confirmed that the wavelength shift was stable for more than 100 h at 120 degrees C and 90% RH.

We designed optical Y-branch waveguides with a stabilized splitting ratio by using a new design approach based on the wavefront matching method. The designed Y-branches were fabricated using silica-based planar lightwave circuit technology. We suppressed any variation in the splitting ratio of the Y-branch experimentally and obtained excess losses of &lt 0.35 dB over a wide wavelength range of 1.3 μm. © 2006 IEEE.

An integrated-optic encoder/decoder with a spread factor of 48 has been fabricated for time-spreading/wavelength-hopping optical CDMA (the largest number reported for this CDMA). A 2.5 Gbit/s transmission, With plural users using the devices, has been carried out.

An integrated-optic encoder/decoder with a spread factor of 48 has been fabricated for time-spreading/wavelength-hopping optical CDMA (the largest number reported for this CDMA). A 2.5 Gbit/s transmission, With plural users using the devices, has been carried out.

We fabricated an integrated-optic encoder/decoder with a spread factor of 48 for time-spreading/wavelength-hopping optical CDMA (the largest number reported for this CDMA). We successfully carried out a 2.5 Gbit/s transmission with plural users using the devices. (C) 2005 Optical Society of America.

We propose a new Mach-Zehnder interferometer (MZI) that can align passband/rejection-band centers exactly with an arbitrary frequency grid. The proposed MZI incorporates pliase-generating couplers, which generate a nonlinear frequency-dependent phase to control the absolute frequency and the dispersion of the waveguide refractive index simultaneously. As an example, we present an MZI that is exactly aligned with the 50-GHz spaced International Telecommunication Union grid. We fabricated the proposed MZI using silica-based planar lightwave circuit technology and demonstrated an MZI with a frequency error of less than +/- 0.3 GRz over a wide frequency range of 10 THz.

The wavefront matching method provides us with a new way to obtain the optimum shape for waveguides used in planar lightwave circuit devices. This presentation reviews the principle behind the method and shows its usefulness with some experimental results. (C)2006 Optical Society of America.

We propose a novel mode converter designed with the wavefront matching method for suppressing the mode transition loss in an arrayed waveguide grating multiplexer. We fabricated and examined the multiplexer, and confirmed the loss reduction principle. (C)2004 Optical Society of America.

This paper describes recent progress on circuit design, fabrication and integration technologies for silica based planar lightwave circuit devices for the next generation optical networks, which require high functionality, reliability and compactness.

We have developed the first silica-based PLC type 32 × 32 optical matrix switch. The switch is the largest scale waveguide type switch yet reported, which has excellent optical characteristics with an average insertion loss of 6.6 dB.

We propose an optical circuit design method for coherent waves as a boundary value problem. The method produces a very compact circuit in which the refractive index pattern is automatically synthesized for given input and output fields with a numerical calculation. We employ the method to design a 1.3/1.55 mu m wave-length demultiplexer and also describe the features of a circuit generated by use of the method. (c) 2005 Optical Society of America.

We propose a large-scale variable delay line based on planar light-wave circuit technology and its application as a reference arm in an optical low-coherence reflectometer. This variable delay line is composed of 16 asymmetrical delay arm pairs sandwiched between 2 optical switches, which select the path for a needed delay. This configuration enables us to eliminate the need for a moving part in the reflectometer. We can scan the reference arm over a length of 262.1 mm with a step of less than 1.0 mu m in air and achieve reflectometer sensitivity of about -47 dB. (c) 2005 Optical Society of America

We propose a novel method for reducing the diffraction loss in an arrayed-waveguide grating. Our method introduces an interference fringe at the interface between slab and arrayed waveguides to relax the mode mismatch between them. We achieved a loss reduction of more than 0.42 dB with this method. Moreover, we provide an explanation of the loss-reduction mechanism of our method in terms of the point of imaging property of light. (c) 2005 Optical Society of America.

We propose an arrayed-waveguide grating with a built-in interferometer that enables us to evaluate the amplitude and phase distribution in the arrayed waveguides easily and precisely. We fabricated the proposed optical circuit with silica waveguides, and successfully confirmed its operational principle in experiments.

We present a low-phase-noise and frequency-tunable photonic millimeter-wave (MMW) generator based on two-mode beating. The generator consists of a single-mode laser, an external optical intensity modulator, and a planar lightwave circuit (PLC) on which an arrayed-waveguide grating (AWG) and 3-dB optical combiners are integrated. Because the AWG and the optical combiners are connected with optical waveguides and the optical path length difference between the two modes filtered by the AWG is kept constant, the phase fluctuation of the generated MMW signal is suppressed. The generator can generate MMWs with a phase noise of less than -75 dBc/Hz at 100 Hz and has a frequency tunability in a range of 90 to 125 GHz. The generator can be applied for the local oscillator (LO) in 10-Gbit/s wireless links that use heterodyne detection.