Fast thermo-optical switch based on SOI waveguides

Thermo-optical silicon-on-insulator (SOI) waveguide switch has been fabricated and characterized. The switch is based on a 2x2 Mach-Zehnder interferometer and 9 microns thick ridge waveguides. The extinction ratio of the switch is 17 dB with ultra-slow modulation and it is limited by the unoptimized directional coupler lengths. Thermo-optical switching with conventional on/off modulation was demonstrated up to 10 kHz. The average power consumption was 150 mW and the extinction ratio was 15 dB in 10 kHz square wave modulation. By using a novel modulation principle the maximum frequency was rised up to 167 kHz, while still maintaining the 15 dB extinction ratio in square wave modulation. With random binary modulation at 167 kHz frequency (3 mus per bit) the extinction ratio remained above 13 dB and the average power consumption was 590 mW. The obtained frequency limits for square wave modulation correspond to a maximum of 1% deviation from the attainable extinction ratio limits. With less strict extinction ratio requirements the maximum frequencies can be much higher. The new modulation method can be used to radically speed up interferometric switches with a tolerable increase in the power consumption.