All-Optical Switching of Silicon Nanobeam Cavities with an Ultra-compact Heater Utilizing the Photothermal Effect

Strong light absorption by a metal-on-silicon hybrid waveguide structure can realize efficient photothermal conversion at a microscale. Based on the photothermal effect, an all-optical switch with an ultra-high tuning efficiency is experimentally demonstrated based on a suspended photonic crystal nanobeam cavity integrated with an ultra-compact metal optical heater. The measurement results exhibit a high photothermal efficiency of 15.52 nm/mW. The rising and falling times of all-optical switching are ∼6.8 and ∼1.6 μs, respectively. Moreover, the heater has only an ultra-compact footprint of only 2 μm × 0.8 μm. Since no conventional electrically driven elements are required to supply power for heating, this device is rather easy to fabricate and has a compact structure. These results show that the device can potentially provide a functionally integrated component for many kinds of efficient all-optical control applications.