Ryoichi Kasahara

New structure of silica-based planar lightwave circuits for low-power thermooptic switch and its application to 8 /spl times/ 8 optical matrix switch

We propose a novel structure that reduces the switching power of a silica-based thermooptic switch (TOSW). The structure consists of silicon trenches and heat insulating grooves, which are formed beneath and beside the arms of a Mach-Zehnder interferometer, respectively. We optimize the structure using the differential-element method (DEM) and fabricate a 2 /spl times/ 2 TOSW with a switching power of only 90 mW, namely, 75% less than that of a conventional TOSW. We also obtain an insertion loss of about 1 dB and an extinction ratio of over 30 dB with a response time from 0% to 90% of 4.9 ms. We then use the structure to fabricate an 8 /spl times/ 8 matrix switch and confirm a total power consumption of 1.4 W with an average insertion loss of 7.4 dB and an extinction ratio of 50.4 dB for 64 possible optical paths.

Low-power consumption silica-based 2 x 2 thermooptic switch using trenched silicon substrate

We propose a silica-based 2/spl times/2 thermooptic switch using heat insulating grooves and trenches on a Si substrate to reduce electric power consumption. The switching power of a fabricated switch was successfully reduced to 135 mW, less than 1/3 that of a conventional switch. No detrimental effect on optical characteristics was observed: we obtained the insertion loss of 1 dB, the extinction ratio of better than 30 dB and no polarization dependency.

Silica-based, compact and variable-optical-attenuator integrated coherent receiver with stable optoelectronic coupling system

We demonstrate a compact and variable-optical-attenuator (VOA) integrated coherent receiver with a silica-based planar lightwave circuit (PLC). To realize the compact receiver, we integrate a VOA in a single PLC chip with polarization beam splitters and optical 90-degree hybrids, and employ a stable optoelectronic coupling system consisting of micro lens arrays and photodiode (PD) subcarriers with high-speed right-angled signal lines. We integrate a VOA and a coherent receiver in a 27x40x6 mm package, and successfully demodulate a 128-Gbit/s polarization division multiplexed (PDM) quadrature phase shift keying (QPSK) signal with a VOA-assisted wide dynamic range of more than 30 dB.

100-GHz spacing 8-channel light source integrated with external cavity lasers on planar lightwave circuit platform

We have successfully fabricated a 100-GHz spacing 8-channel light source using hybrid integration technologies based on planar lightwave circuits (PLCs). The light source was composed of UV-written Bragg gratings and laser diode (LDs) on PLC platforms. To adjust the Bragg wavelength to the ITU-T grid, we used a precise phasemask with eight different pitches. Moreover, to suppress temperature-dependent mode hopping, we tuned the longitudinal mode wavelength so that it became stable by photosensitively modifying the waveguide refractive index in the cavity, which we achieved using an ArF excimer laser, in addition to inserting silicone in the cavity. As a result, we obtained eight lasing wavelengths controlled to those of the ITU-T grids and optical powers of more than 1.5 mW at an injection current of 80 mA without any temperature dependent mode hopping in the 8-channel light source. We also confirmed direct modulation at 2.5 Gb/s in every channel and we showed that we could modulate two adjacent channels simultaneously without any interference effect. These results show that the compact PLC-type integrated light source is promising for use in WDM systems.

Extremely low power consumption thermooptic switch (0.6 mW) with suspended ridge and silicon-silica hybrid waveguide structures

We demonstrated an extremely low power consumption thermooptic switch using suspended ridge and silicon-silica hybrid waveguide structures. The switching power was successfully reduced to only 0.6 mW.

Temperature insensitive and ultra wideband silica-based dual polarization optical hybrid for coherent receiver with highly symmetrical interferometer design.

We designed temperature-insensitive dual-polarization optical hybrids for the coherent receivers, and firstly demonstrated temperature-insensitive performance with a polarization extinction ratio over 25 dB and phase errors within 3 degrees over fully C-and L-bands.

Silica-based PLC with heterogeneously-integrated PDs for one-chip DP-QPSK receiver.

We fabricated a DP-QPSK receiver PLC by the heterogeneous integration of eight high-speed PDs on a compact silica-based PLC platform with a PBS, 90-degree optical hybrids and a VOA. 32 Gbaud DP-QPSK signal demodulation was successfully demonstrated.

Ultrasmall 100 GHz 40-Channel VMUX/DEMUX Based on Single-Chip 2.5%-

The extension of optical add/drop multiplexing (OADM) systems to metro-core and metro-access networks has led to the need for economical and compact OADM devices. In this paper, we demonstrate a 1-in.2 100 GHz spacing 40-channel (ch) single-chip variable attenuator multiplexer/demultiplexer based on a monolithic 2.5%-Delta silica planar lightwave circuit (PLC) and stacked photodiode arrays. We also investigate the particular issues raised by monolithic integration with such high Delta waveguides. One is the loss increase caused by high index contrast of the waveguides. Performance fluctuation and thermal interference between the integrated circuits are also inherent issues. By utilizing effective solutions, we have successfully overcome such problems and confirmed that a 2.5%-Delta silica PLC is effective for use in monolithic integration.

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We developed a compact 16-ch optical wavelength selector (OWS). Our OWS is composed of two arrayed-waveguide gratings (AWGs) and an optical gate array (OGA) integrated on a single PLC platform by using the hybrid integration technique. We successfully obtained lossless operation with an extinction ratio of better than -45 dB for all wavelength channels. We also obtained a switching time of less than 1 ns. These excellent characteristics are the same as those of a previously reported OWS fabricated using PLC-PLC direct attachment.

PLC

We propose a new hybrid integrated optical front-end module for a 100-Gb/s-class coherent receiver using silica-based planar lightwave circuit (PLC) technology. We have developed an integrated structure composed of multichannel microcollimator optics between PLC waveguides and photodiodes (PDs), and compact hermetically sealed optical-to-electrical converters with a PD array and a transimpedance amplifier array to maintain reliability. We used the technology to fabricate an all-in-one optical front-end module for a dual polarization quadrature phase-shift-keying (DP-QPSK) coherent receiver, and confirmed that the module operated successfully for 112-Gb/s DP-QPSK signal detection.