Systematic design and fabrication of high-Q single-mode pulley-coupled planar silicon nitride microdisk resonators at visible wavelengths

Abstract

High quality (Q ≈ 6 × 10⁵) microdisk resonators are demonstrated in a Si₃N₄ on SiO₂platform at 652–660 nm with integrated in-plane wrap-around coupling waveguides to enable critical coupling to specific microdisk radial modes. Selective coupling to the first three radial modes with >20dB suppression of the other radial modes is achieved by controlling the wrap-around waveguide width. Advantages of such pulley-coupled microdisk resonators include single mode operation, ease of fabrication due to larger waveguide-resonator gaps, the possibility of resist reflow during the lithography phase to improve microdisk etched surface quality, and the ability to realize highly over-coupled microdisks suitable for low-loss delay lines and add-drop filters.