Silicon photonic-wire waveguide is one of the most promising platforms in constructing compact optical devices, since
the waveguide can be bent with a radius of less then several microns. Recently, we have demonstrated various optical
devices based on silicon photonic-wire waveguides, which include a directional coupler, a tunable optical add-drop
multiplexer, and some ultra-compact 1 x N optical switches. The optical coupling length of the directional coupler was
just around 10 microns, due to its high coupling efficiency. The tunable optical add-drop multiplexer was constructed
with Bragg grating waveguides. It was about 700-μm-long, and was controlled through thermo-optic effect. The
maximum center-wavelength shift of the tunable optical add-drop multiplexer was 6.6 nm, which was obtained at a
tuning power of 0.82 W. The 1 x N optical switches were Mach-Zehnder interferometer types and were also thermally
controlled. The 1 x 2 switch was compact with a footprint of 85 x 30 µm2. Its maximum extinction ratio exceeded 30 dB.
The switching power and switching time was about 90 mW and 100 μsec, respectively. The 1 x 4 optical switch was
constructed based on the 1 x 2 switch. Its operation was successfully demonstrated. The 1 x 4 optical switch was
believed to be the smallest switch in the world. A 1 x 8 optical switch was also demonstrated with its switching
operations. Further, we are fabricating a compact packaged switch module with a size of 15 x 8 x 5 (height) mm3, which
includes a 1 x 4 optical switch and the input and output fiber couplers assembly.