Published papers

Silica-based polarization diversity circuit for QD-SOA operating in T-band was fabricated. By connecting polarization diversity circuits to QD-SOA chip, the polarization dependent gain of less than 0.8 dB and the optical gain of 3.2 dB were achieved.

The design of a novel 1 × M fold-back type wavelength selective switch (WSS), which has fewer waveguide crossings than a conventional integrated WSS, is reported. The WSS is composed of interleavers, 1 × M optical switches, and arrayed waveguide gratings (AWGs). Switches are combined with AWGs by fold-back waveguides, and each AWG works as both a demultiplexer and multiplexer thus avoiding center wavelength mismatch caused by fabrication errors. Waveguide crossings cause excess crosstalk and loss in lightwave circuits. By using a fold-back architecture the number of crossings can be reduced to less than half that of a conventional design. We discuss the operating principle, the design method, and the scalability of the fold-back type WSS. Furthermore, the switching operation of a 200-GHz spacing, 20-channel, 1 × 2 silicon WSS in a fold-back configuration on a 5 mm × 10 mm SOI chip is demonstrated. This has 15 waveguide crossings in a path, of which six are additional crossings with monitor waveguides. The average insertion loss and average extinction ratio are 29.6 dB and 10.9 dB, respectively.

© 2018 Optical Society of America A wavelength selective switch (WSS) can route optical signals into any of output ports by wavelength, and is a key component of the reconfigurable optical add/drop multiplexer. We propose a wavefront control type WSS using silicon photonics technology. This consists of several arrayed waveguide gratings sharing a large slab waveguide, wavefront control waveguides and distributed Bragg reflectors. The structure, design method, operating principle, and scalability of the WSS are described and discussed. We designed and fabricated a 1 × 2 wavefront control type WSS using silicon waveguides. This has 16 channels with a channel spacing of 200 GHz. The chip size is 5 mm × 10 mm. The switching operation was achieved by shifting the phase of the light propagating in each wavefront control waveguide, and by controlling the propagation direction in the shared large slab waveguide. Our WSS has no crossing waveguide, so the loss and the variation in loss between channels were small compared to conventional waveguide type WSSs. The heater power required for switching was 183 mW per channel, and the average extinction ratios routed to Output#1 and Output#2 were 9.8 dB and 10.2 dB, respectively.

© IEICE 2018. The wavelength range of 1000–1260 nm, known as T-band, where T denotes “thousand”, is one of the promising wavebands suitable for the future moderate-range optical networks. We have developed T-band specific semiconductor devices based on quantum-dot technology. However, the cut-off wavelength of optical fiber cables currently utilized in access networks, i.e., G.652 fibers, is specified to be less than 1260 nm. Therefore, the fibers do not fully support the T-band. This letter presents a demonstration of the feasibility of 10-Gbit/s transmission over G.652 fibers in the T-band by experiments.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. For further improvement of phase change material switches, relationships between optical characteristics of phase change materials(PCM) and the performance of optical switches were investigated. PCM optical switch is optimized for the both states of the insertion loss to be balanced. With optimized three-channel directional coupler switch, the refractive index difference between amorphous and crystalline state was inversely proportional to the insertion loss.

© 2020, The Author(s). Sapphirinid copepods, which are marine zooplankton, exhibit tunable structural colors originating from a layered structure of guanine crystal plates. In the present study, the coloring portion of adult male of a sapphirinid copepod, Sapphirina nigromaculata, under the dorsal body surface was characterized to clarify the regulation and actuation mechanism of the layered guanine crystals for spectral control. The coloring portions are separated into small domains 70–100 µm wide consisting of an ordered array of stacked hexagonal plates ~1.5 µm wide and ~80 nm thick. We found the presence of chitin-based honeycomb frameworks that are composed of flat compartments regulating the guanine crystal plates. The structural color is deduced to be tuned from blue to achromatic via yellow and purple by changing the interplate distance according to vital observation and optical simulation using a photonic array model. The framework structures are essential for the organization and actuation of the particular photonic arrays for the exhibition of the tunable structural color.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement Optical switching techniques featuring the fast and large capacity have the potential to enable low latency and high throughput optical data center networks (DCN) to afford the rapid increasing of traffic-boosted applications. Flexibility of the DCN is of key importance to provide adaptive and dynamic bandwidth to handle the variable traffic patterns generated by the heterogeneous applications while optimizing the network resources. Aiming at providing the flexible bandwidth for optical DCNs, we propose and experimentally investigate a software-defined networking (SDN) enabled reconfigurable optical DCN architecture based on novel optical top of rack (OToR) switch exploiting photonic-integrated wavelength selective switch. Experimental results show that the optical bandwidth per link can be automatically reallocated under the management of the deployed SDN control plane according to the variable traffic patterns. With respect to the network with inflexible interconnections, the average packet loss of the reconfigurable DCN decreases 1 order of magnitude and the server-to-server latency performance improves of 42.2%. Scalability investigation illustrates limited (11.7%) performance degradation as the reconfigurable network scale from 2560 to 40960 servers. Both the numerical and experimental assessments validate the proposed DCN with reconfigurable bandwidth feature and lower latency variations with respect to the inflexible DCNs.

© 2018, Institute of Electronics Information Communication Engineers. All rights reserved. We report on a novel design of a wavelength selective switch (WSS) using silicon photonics technology. It comprises of 1 × 4 interleavers, arrayed-waveguide gratings (AWGs) connected to fold-back waveguides, and 1 × 2 optical Mach-Zehnder interferometer switches. In the proposed WSS, fold-back waveguides enable the AWGs to be used for both demulti-plexing and multiplexing. Therefore the WSS has less waveguide crossings than a conventional configuration. Moreover, a 20-channel, 200-GHz spacing, 1 × 2 fold-back type WSS was fabricated on 5 mm × 10 mm SOI chip using CMOS technology.

A photonic integrated 1×2 Wavelength Selective Switch (WSS) based on a loopback configuration is shown to operate on the C and L-Bands due to the cyclic nature of the employed arrayed-waveguide gratings (AWGs). An average of -22.59 dB and -20.40 dB were observed in the C and L-band channels respectively. Crosstalk levels are kept below -40 dB on the output port A and below -30 dB on output port B. Experimental results on NRZ OOK data indicate a bit-error-rate (BER) below 1×10-11 with very limited penalty at both bands up to a bit rate of 30 Gbps.

A photonic integrated WSS operating on the S-, C- and L-Band is presented with an average extinction-ratio of -20.40 dB. Crosstalk levels were kept below -20 dB for all bands and experimental results on NRZ OOK data indicate error-free operation for up to 35 Gb/s.

This paper reviews recent progress in silicon photonics and compares it with other optical device platforms. The key components for optical communication systems, including arrayed waveguide gratings, optical switches, modulators and optical functional devices fabricated on silicon photonics platforms are explained. The integration of III-V compounds, lithium niobate, polymers, phase change and other functional materials are necessary to strengthen silicon photonics platforms. These are also reviewed, and the feasibilities are discussed. Finally, I express my personal view as to the best research direction for silicon photonics.

© 2018 OSA. We demonstrate a wavelength routing system that covers a broad wavelength range of 1000-1360 nm, i.e., T/O-band. The system includes our developed T/O-band-specific quantum dot semiconductor devices and 1081-channel arrayed waveguide grating (AWG) router.

© OSA 2018. We demonstrate a wavelength routing system that covers a broad wavelength range of 1000-1360 nm, i.e., T/O-band. The system includes our developed T/O-band-specific quantum dot semiconductor devices and 1081-channel arrayed waveguide grating (AWG) router.