Silicon photonic-wire waveguide devices

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 × 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 × N optical switches were Mach-Zehnder interferometer types and were also thermally controlled. The 1 × 2 switch was compact with a footprint of 85 × 30 μm². Its maximum extinction ratio exceeded 30 dB. The switching power and switching time was about 90 m W and 100 μsec, respectively. The 1 × 4 optical switch was constructed based on the 1 × 2 switch. Its operation was successfully demonstrated. The 1 × 4 optical switch was believed to be the smallest switch in the world. A 1 × 8 optical switch was also demonstrated with its switching operations. Further, we are fabricating a compact packaged switch module with a size of 15 × 8 × 5 (height) mm³, which includes a 1 × 4 optical switch and the input and output fiber couplers assembly.