Takahashi Hiroshi

We propose a compact polarization diversity circuit for a silicon waveguide device. It consists of silica waveguides and photonic crystal waveplates, and can convert input light with various polarization states into two output light signals with the same polarization. Setting these circuits at the front and rear of two silicon optical switches, the polarization dependence in the switch can be dramatically suppressed. We fabricated polarization diversity circuits for a 4x4 silicon optical switch and realized a polarization insensitive 4x4 optical switch. The polarization dependent loss was reduced to 1.1 dB and the polarization dependent crosstalk was less than - 17 dB.

We propose a compact polarization diversity optical circuit using silica waveguides and photonic crystal waveplates. By setting these circuits at the front and rear of the silicon optical devices, the polarization dependence of the silicon devices can be suppressed. Photonic crystals can be produced artificially using nanolithography, so that the retardation and orientation of the photonic crystal waveplate can be locally varied on a single chip. This enables to dramatically reduce the size of the polarization diversity circuit, which consists of a 1x2 multimode interference (MMI) coupler, two arm waveguides with quarter-waveplates (QWPs), a 2x2 MMI coupler, and output waveguides with half-waveplates (HWPs). The input light, including the transverse electric (TE) and transverse magnetic (TM) modes, is split by the 1x2 MMI coupler. The optical axes of the two QWPs, spaced 125 lam apart, are set to be orthogonal to each other, so that the phases of the TE modes in the two arm waveguides differ by 90 degrees, and those of the TM modes differ by -90 degrees. The TE mode and the TM mode are separated at the outputs of the 2x2 MMI coupler, and the polarization of the light at one of the outputs is aligned to that at the other output by the HWP. In this paper, we designed a 4x8 polarization diversity circuit for a 4x4 silicon optical switch.

Processing ultra-fast optical signals without optical/electronic conversion is in demand and time-to-space conversion has been proposed as an effective solution. We have designed and fabricated an arrayed-waveguide grating (AWG) based optical spectrum control circuit (OSCC) using silica planar lightwave circuit (PLC) technology. This device is composed of an AWG, tunable phase shifters and a mirror. The principle of signal processing is to spatially decompose the signal's frequency components by using the AWG. Then, the phase of each frequency component is controlled by the tunable phase shifters. Finally, the light is reflected back to the AWG by the mirror and synthesized. Amplitude of each frequency component can be controlled by distributing the power to high diffraction order light. The spectral controlling range of the OSCC is 100 GHz and its resolution is 1.67 GHz. This paper describes equipping the OSCC with optical coded division multiplex (OCDM) encoder/decoder functionality. The encoding principle is to apply certain phase patterns to the signal's frequency components and intentionally disperse the signal. The decoding principle is also to apply certain phase patterns to the frequency components at the receiving side. If the applied phase pattern compensates the intentional dispersion, the waveform is regenerated, but if the pattern is not appropriate, the waveform remains dispersed. We also propose an arbitrary filter function by exploiting the OSCC's amplitude and phase control attributes. For example, a filtered optical signal transmitted through multiple optical nodes that use the wavelength multiplexer/demultiplexer can be equalized.

We designed and fabricated an integrated 1 x 4 wavelength selective switch using a silica planar lightwave circuit. The channel spacing is 100 GHz and the number of channels is 40. Signal switching experiments show the switch to be error-free and have low power penalty bit-error rate performance.

We introduce and demonstrate an ultra-compact 5x5 waveband cross-connect module that can process 80 channels (50-GHz spacing) per fiber; it combines 50-100-GHz interleavers and two 5 x 5 waveband cross-connect (WBXC) modules with 100-GHz channel spacing that are staggered by 50 GHz. The interleavers have a nearly rectangular spectral shape so that this scheme minimizes the spectrum narrowing effect. Our proposed 50-GHz spaced waveband cross-connect holds the 3 dB bandwidth of 86% of the component WBXC module that is designed for 100-GHz spaced channels. This architecture yields very small size WBXCs that provide wide passband and sharp cutoff. Its routing capability and transmission characteristics are also confirmed.

We propose a novel large-scale OXC architecture that utilizes WSSs for dynamic wavelength grouping and 1xn switches for fiber selection. We also develop a network design algorithm that can make the best use of the routing capability of the proposed nodes. Numerical experiments on several topologies show that the architecture attains substantial hardware scale reduction. A prototype demonstrates good transmission performance and confirms the technical feasibility of the proposed OXC architecture. (C)2013 Optical Society of America

A compact integrated 1×2 wavelength-selective switch (WSS) is demonstrated for which the structure is designed such that the WSS has no waveguide crossings. By employing a loopback configuration, only one arrayed-waveguide grating is needed in the WSS. The channel spacing is 100 GHz and the number of channels is 40. The measured transmission loss of the selected wavelength was &lt 8.1 dB, and the average crosstalk from two output ports were 23.0 and 40.7 dB. © 2012 IEEE.

We devised an optical modulator with a high field-response linearity, which is suitable for a DAC-based multilevel coherent transmitter. An advantage over a conventional MZM in terms of the linearity-loss tradeoff was demonstrated.

The wavelength tunable filter will play a key role in realizing C/D/C add/drop functions in ROADMs. We fabricate a novel tunable filter for 192 optical channels on a PLC chip. Transmission experiments verify its optical characteristics.

We report a compact receiver optical sub-assembly (ROSA) for 100GbE CFP4 transceivers. All the four channels of fabricated module exhibits wide wavelength passband and high receiver sensitivity enough for 10-km-reach transmission.

Digital homodyne OTDR with dual polarization optical hybrid using M-sequence correlation was demonstrated for PMD distribution measurement without averaging. The relative phase fluctuation of Rayleigh backscattered field were successfully compensated, for the first time.

An ultra-compact 3x12 mm(2) DPOH on a 1.5 %-Delta silica-based PLC employing a novel coupler is reported. The excess loss is <2 dB and the CMRR is <-27 dBe over the C- and L-bands.

We developed a reflection-type 4x1 transversal filter (TF) on an InP substrate as a compact and low-loss wavelength multiplexer (MUX) for monolithically integrated light source arrays. The filter has a satisfactory MUX function and is very compact of about 900 mu m x 50 mu m which is one twentieth of a size of a conventional 4x1 TF. It is suitable for a MUX of a monolithically integrated light source array thanks to its compactness and input/output-port arrangement.

We have proposed an optical spectrum control circuit that realizes various kinds of signal processing in the optical domain using a silica-based planar lightwave circuit including arrayed-waveguide gratings. In order to obtain a flat transmission spectrum required for processing an optical signal that has a continuous spectrum, the number of the spectral output waveguides is set more than the number of waveguides in the waveguide array. In this study, we demonstrated a phase error compensation and obtained the flat transmission spectrum with ripples below 0.9 dB. We also demonstrated a tunable bandwidth operation as an example of the spectral amplitude control and a variable pulse delay operation as an example of the spectral phase control, respectively. In the tunable bandwidth operation, the pass-band characteristic of the minimum bandwidth of 5-GHz and tunable pass-band characteristics with different center frequencies with about 20-dB extinction ratio were obtained. In the variable delay operation, pulse delays equal to calculated values could be observed with some phase settings.

We propose a cyclic NxN AWG router that can multi/demultiplex upstream and downstream signals with different channel spacings in different wavelength regions. We fabricated a 4x4 AWG router for our novel lambda-tunable WDM/TDM-PON using silica-based PLC technology and showed that it can cyclically multi/demultiplex both 20 nm-spaced and 200 GHz-spaced signals at 1.3 and 1.5 mu m, respectively. (c) 2012 Optical Society of America

We demonstrate an integrated 100GbE receiver optical sub-assembly (ROSA) that incorporates a monolithic four-channel avalanche photodiode (APD) array and a planer lightwave circuit (PLC) based LAN-WDM demultiplexer. A record minimum receiver sensitivity of -20 dBm and 50-km error-free SMF transmission without an optical amplifier have been achieved. (C)2012 Optical Society of America

We propose a highly scalable switch architecture suitable for client-side cross-connect switches in reconfigurable optical add/drop multiplexers and optical switching in data centers. It consists of cascaded cyclic arrayed waveguide gratings (AWGs). We develop a 270 x 270 prototype switch consisting of an assembly of arrayed small switches and couplers and AWGs that are fabricated on planar lightwave circuit chips. Transmission experiments verify its technical feasibility.

We demonstrate a Colorless, Directionless, and Contentionless add/drop that is made possible by newly proposed multi-stage tunable filters; it will be effective in the creation of flexible and dynamic optical path networks. The filters consist of small-scale switches and AWGs (Arrayed Waveguide Gratings) and so are cost effective. The technical feasibility of the drop configuration using proposed tunable filters is experimentally verified.

A low-loss integrated 1x2 gridless wavelength selective switch (WSS) is reported. The WSS has a fewer waveguide crossings than a conventional device and only one multiplexer is needed. The bandwidth can be controlled from 200 GHz to 4000 GHz. The transmission loss and the crosstalk are less than 5.9 dB and -25.1 dB, respectively.

This paper proposes a 40Gbit/s-class-lambda-tunable WDM/TDM-PON for flexible photonic aggregation networks that achieves the aggregation of a large number of users using the DWBA algorithm without an L2-SW. A lambda-switching transmission experiment was conducted using a newly developed 40Gbit/s-class fast-switching tunable B-Tx and 4 x 4 cyclic AWG router.

We propose a cyclic NxN AWG router with which to realize a novel lambda-tunable WDM/TDM-PON with bandwidth allocation flexibility for inhomogeneous user distribution. We fabricated the router with silica-based PLC technology, and demonstrate that it can cyclically multi/demultiplex both 20 nm- and 200 GHz-spaced signals at 1.3 and 1.5 mu m, respectively.

We propose a novel large-scale OXC architecture that utilizes WSSs for dynamic wavelength grouping and 1xn switches for fiber selection. Our network design algorithm shows that the architecture attains significant hardware scale reduction. A prototype demonstrates good transmission performance and confirms the architecture's technical feasibility.

We present a novel wavelength routing switch configuration that consists of interconnected small arrayed waveguide gratings (AWGs). We introduce an optimization method for A WG interconnection and fabricate a prototype. Transmission experiments verify its practical applicability.

We propose a cyclic NxN AWG router with which to realize a novel lambda-tunable WDM/TDM-PON with bandwidth allocation flexibility for inhomogeneous user distribution. We fabricated the router with silica-based PLC technology, and demonstrate that it can cyclically multi/demultiplex both 20 nm- and 200 GHz-spaced signals at 1.3 and 1.5 mu m, respectively.

This paper proposes a 40Gbit/s-class-lambda-tunable WDM/TDM-PON for flexible photonic aggregation networks that achieves the aggregation of a large number of users using the DWBA algorithm without an L2-SW. A lambda-switching transmission experiment was conducted using a newly developed 40Gbit/s-class fast-switching tunable B-Tx and 4 x 4 cyclic AWG router.

Both high-density multiplexing and high-speed transmission are required for large capacity networks supporting broadband service penetration. Silica waveguide optical circuit technology can provide key optical devices for such systems because it has high controllability as regards optical amplitude and sufficient phase for realizing sophisticated optical interferometric circuits. This paper reviews recent progress on this technology, and reports experimental results for an ultra wideband AWG, an optical OFDM filter, a demodulator for a coherent receiver and a highly functional modulator. (C) 2011 Optical Society of America

A wavefront matching design method is successfully applied to a high-index-contrast InP waveguide for the first time. Fabricated 2 x 2 MMI coupler exhibits a 1.6 times wider operation wavelength range than a conventional MMI coupler. This coupler has less waveguide-width sensitivity and is suitable for InP-based large-scale photonic integrated circuits.

A tunable optical dispersion compensator (TODC) that uses a high-resolution arrayed-waveguide grating and integrated resin lenses is reported. The dispersion tuning range is 1426 ps/nm, three times larger than that in our previous report for the same type of TODC. A transmission experiment using a 43-Gbps carrier-suppressed return-to-zero differential quadrature phase shift keying (CSRZ-DQPSK) signal is also reported.

A tunable optical dispersion compensator that uses cascaded arrayed-waveguide gratings and an integrated phase shifter is reported. It is a catoptric circuit but does not require a circulator. The dispersion is successfully controlled from 142 to + 1148 ps/nm. Error-free transmission is confirmed after dispersion compensation in a transmission experiment using 43 Gbps CSRZ-DQPSK modulation.

We demonstrate an optical orthogonal frequency division multiplexing (OFDM) demultiplexer with an optical discrete Fourier transform circuit fabricated using silica planar lightwave circuit technology. This compact device can process an arbitrary number of subcarriers. The operation of a ten-channel device is demonstrated by demultiplexing a 100 Gbit/s (10 subcarrier x 10 Gbits/s) OFDM signal. We also discuss a main factor affecting characteristics degradation of the device. (C) 2011 Optical Society of America

We proposed and fabricated an optical spectrum control circuit using an arrayed-waveguide grating (AWG) and an array of channel waveguides with tunable phase shifters. We found that the spectral phase and amplitude of a modulated optical signal could be arbitrarily controlled if the number of channel waveguides was set to be more than twice the number of waveguides in the AWG. As a first demonstration, we successfully obtained a flat band-pass filter function with the fabricated device by controlling the tunable phase shifters to control the interference between the light propagating through them.

The first practical terabit-scale hierarchical optical cross-connect system is realized by employing silica-based planar lightwave circuit devices. The system is scalable to 320 line cross connects +160 client cross connects, and fully implemented equipment would require a 16-U-high chassis and only a 350-W power consumption. The potential of node cascadability is discussed and experimentally confirmed using partially implemented equipment that has four wavelength-division-multiplexed ports and one waveband switching capability. Stable operation was also confirmed using field-installed fibers.

Compact and practical 4-degree optical cross-connect equipment with add/drop ports is realized for use in connecting ROADM ring networks. Eight 40-channel AWGs and forty 4x4 matrix switches are integrated in a 2-U high chassis. (C)2011 Optical Society of America