A. Sugita

Very low insertion loss arrayed-waveguide grating with vertically tapered waveguides

We propose and demonstrate a very low insertion loss silica-based arrayed-waveguide grating (AWG) achieved using a novel structure, which has vertically tapered waveguides between arrayed-waveguides to reduce the slab-to-arrayed-waveguide transition loss. A spot-size converter is also incorporated in the AWG to reduce the fiber-to-waveguide coupling loss. The structure can be formed by a process involving the conventional photolithography and reactive ion etching. The structure provided a loss reduction of 1.5 dB. Moreover, we have successfully obtained a minimum insertion loss of 0.75 dB with a crosstalk of -40 dB and polarization-independent operation.

Estimation of waveguide phase error in silica-based waveguides

A new estimation method is proposed in order to clarify waveguide phase error factors. Using the proposed method, it is possible to analyze such factors as core size error and refractive index error, which cause optical phase error in waveguides. This method is applied to silica-based waveguides to estimate the waveguide phase error. This revealed an average core size error of 2.1/spl times/10/sup -3/ /spl mu/m and an average refractive index error of 1.9/spl times/10/sup -6/. Finally, based on the measured phase error values, the optimum arrayed-waveguide grating (AWG) configuration is considered with a view to achieving low crosstalk.

Birefringence control of silica waveguides on Si and its application to a polarization-beam splitter/switch

A novel polarization-beam splitter/switch with a Mach-Zehnder interferometer configuration was fabricated using a silica-based planar lightwave circuit (PLC) on a silicon substrate. The polarization-beam splitter/switch was realized by accurately controlling the waveguide birefringence and the phase state by laser trimming two kinds of stress-applying amorphous silicon film with widths of 50 /spl mu/m and 95 /spl mu/m. Fiber-waveguide-fiber insertion loss of 0.5 dB and crosstalk attenuations of over 25.6 dB were attained. >

Generation of high-repetition-rate WDM pulse trains from an arrayed-waveguide grating

We present what we believe to be the first demonstration of femtosecond pulse train generation from an arrayed-waveguide grating. Terahertz-rate bursts of femtosecond pulses are produced with the rate determined by the arrayed-waveguide delay spacing.

Silica-based waveguide-type 16 x 16 optical switch module incorporating driving circuits

We developed a 16/spl times/16 optical matrix switch module in which we incorporated a silica-based thermooptic switch chip and driving circuits. The module exhibited excellent levels of performance, namely a low insertion loss and a high extinction ratio. This is the largest scale waveguide-type matrix switch module yet reported. Driving circuits with a serial-to-parallel control signal conversion function enabled us to realize a new module structure that is both simple and flexible for use with larger scale switches.

1.5%-/spl Delta/ athermal arrayed-waveguide grating multi/demultiplexer with very low loss groove design

We describe a compact 1.5%-/spl Delta/ athermal silica-based 100-GHz-spacing 16-channel arrayed-waveguide grating (AWG) multi/demultiplexer with a modified groove design for a very low excess loss. We propose new approaches for modifying the shape of the grooves and the arrayed waveguides and optimize the shape modifications for 1.5%-/spl Delta/ waveguides. By employing this modified groove design, we greatly reduced the groove excess loss from 1.9 to 0.4 dB in the 1.5%-/spl Delta/ athermal AWG.

128-channel polarization-insensitive frequency-selection-switch using high-silica waveguides on Si

A 128-channel polarization-insensitive frequency-selection-switch (FS-SW) with 10-GHz frequency spacing is discussed. The FS-SW was fabricated on Si using low-loss GeO/sub 2/-doped high-silica waveguides, and its frequency-insensitive operation was attained by the laser trimming adjustment of a-Si film which controls waveguide birefringence. The fiber-to-fiber loss of the transmitted channel was 6.7 dB in the pigtailed FS-SW and the total crosstalk level was less than -13 dB. By using this FS-SW, a 100-channel optical frequency division multiplexing (FDM) transmission-distribution experiment at 622 M b/s over a 50-km fiber length was achieved.<<ETX>>

Generation of flat-topped 500-GHz pulse bursts using loss engineered arrayed waveguide gratings

A specially engineered arrayed waveguide grating is demonstrated. The 500-GHz repetition rate bursts of femtosecond pulses with a flat-topped temporal intensity profile window are shown here for what we believe is the first time.

400-channel 25-GHz spacing arrayed-waveguide grating covering a full range of C- and L-bands

We realized a 400-channel 25-GHz spacing arrayed-waveguide (AWG) on a 6-inch Si wafer using 1.5%-/spl Delta/ silica-based waveguides. This AWG covers the full C- and L-bands and exhibits an on-chip loss of 3.8-6.4 dB.

Fabrication of silica-on-Si waveguide with higher index difference and its application to 256 channel arrayed waveguide multi/demultiplexer

Improved techniques were used to fabricate a silica-on-Si waveguide with a higher core-to-cladding index difference and a 2 mm bending radius. A 256 channel and 25 GHz spacing arrayed-waveguide multiplexer with low loss and low crosstalk was successfully fabricated for the first time using the waveguides.