Improvement of silicon microdisk resonators with movable waveguides by hydrogen annealing treatment

In silicon photonics, silicon microdisk resonators with movable waveguides driven by electrostatic comb-drive actuators have been used as wavelength-selective switches. However, the sidewall roughness of silicon waveguides formed by the etching process is the main cause of optical loss in such devices, which leads to the deterioration of the wavelength selectivity. In this study, we fabricated a silicon microdisk resonator with a movable waveguide and performed a hydrogen annealing treatment as a postprocessing step to remove the sidewall roughness. By using scanning electron microscopy, a reduction in sidewall roughness was confirmed following the hydrogen annealing treatment. Then, the extinction ratio at the through port was evaluated while changing the gap between the microdisk and the movable waveguide. A dip in the extinction ratio was observed at the resonant wavelength while decreasing the gap, which indicated that the fabricated device successfully functioned as a wavelength-selective switch. Due to the hydrogen annealing treatment, the quality factor of the dip increased from 7102 to 37 402. These results show that the hydrogen annealing treatment can be used as a postprocessing step and is helpful for improving the wavelength selectivity of silicon photonic wavelength-selective switches.