Waveguide coupled air-slot photonic crystal nanocavity for optomechanics

We investigate a structure consisting of two parallel GaAs thin membranes with an air-slot type photonic crystal (PhC) nanocavity, which is designed to achieve highly efficient optomechanical coupling. The structure shows a large theoretical optomechanical coupling factor of ~990 GHz/nm. We designed, fabricated, and performed optical characterization of a system consisting of a grating coupler, a PhC waveguide, and a PhC nanocavity, which achieves highly efficient vertical emission using the band folding technique. The experimentally obtained overall efficiency is about 0.3% for a microscope objective lens with a moderate numerical aperture of 0.65. This waveguide coupled air-slot PhC nanocavity with efficient vertical light coupling can be useful for on-chip cavity optomechanical systems.