Monolithic Whispering-Gallery Mode Resonators With Vertically Coupled Integrated Bus Waveguides

We report on the realization of a silicon-based microresonator/waveguide coupled system, fully integrated on a silicon chip. The device uses a vertical coupling scheme of the resonator and a buried strip waveguide. We demonstrate that its high optical quality follows from the accurate planarization of the waveguide topography, which is achieved by multiple depositions-and-reflows of a borophosphosilicate glass over strip waveguides. More importantly, we demonstrate wafer-scale mass fabrication of freestanding planar resonators suspended in air and coupled to integrated bus waveguides, as well as controlled selective excitation of different mode families of the resonator. This opens the door for the realization of stable all-integrated complex resonator systems for optomechanical and metrological applications, with the potential to substitute today's intensive use of complicated fiber-taper coupling schemes.