Phononically shielded multi-wavelength photonic-crystal membrane for cavity quantum optomechanics

We propose and design a stoichiometric silicon-nitride membrane resonator featuring high reflectivity at multi-wavelengths and high mechanical quality factors. The membrane resonator has a thickness of 100 nm and 2D-photonic and phononic crystal patterns. By designing concentric holes of suitable radius on both sides of the membrane, high reflectivity at multi-wavelengths can be achieved. In particular, the simulation shows that high reflectivity can be realized at telecommunications wavelengths and alkaline atomic absorption lines, achieving reflectivity of 99.76% at 852 nm, 99.98% at 1054 nm, and 99.96% at 1566 nm, respectively. The designed device can find useful applications in cavity optomechanical systems to realize quantum frequency conversion and precise quantum measurements, and other quantum information processing tasks.