Analysis of giant forward Brillouin gain enhancement in double-disk microcavities by tailoring optical forces

Abstract

Stimulated Brillouin scattering in whispering gallery resonators has numerous potential applications. However, previously reported approaches are difficult to integrate and the Brillouin gain coefficient is small. We propose here a new approach to achieve giant forward stimulated Brillouin scattering (FSBS) and lasing on chip with double-disk microcavities made of silica glass. By considering the thickness of air gap to tailor optical forces especially radiation pressure in these double-disk microcavities, giant Brillouin gain enhancement can be realized in the intermode FSBS. The numerical simulation results indicate that for double-disk microcavity within the radius range of 50 μm, stimulated Brillouin scattering gain is ten times larger than that of single-disk microcavity up to 74.3 m−1W−1 with Rayleigh acoustic mode and 102 to 103 times larger up to 6361.19 m−1W−1 with symmetric Lamb acoustic mode. Correspondingly, the on-chip pump power threshold of Brillouin lasing can be reduced to 55 μW with the slope efficiency of 8.0%. Our proposed double-disk microcavities offer an effective and simple method to implement Brillouin lasing and can find versatile applications of acousto-optic interaction on all-integrated CMOS compatible chip.