An optical device includes a waveguide and a microdisk that is optically coupled to the waveguide. The gap between the microdisk and the waveguide is between 0.3 microns and 0.7 microns. The diameter of the microdisk is between 15 microns and 50 microns. The quality factor of the microdisk is at least 105. The microdisk is tuned optoelectrically or piezoelectrically.