Development of CaF₂-brass hybrid WGM microcavity by using ultra-precision machining

Abstract

Optical microcavities, which can confine light spatially, are important devices in the field of optics. Singlecrystal calcium fluoride (CaF2) is one of the most suitable materials for optical microcavities. To manufacture a cavity made from CaF2, ultra-precision machining is an appropriate process. In the previous study, we have investigated the machinability of CaF2 and successfully manufactured a whispering gallery mode (WGM) CaF2 cavity. Although the manufactured cavity can confine light for a certain amount of time, it was found that the cavity performance could be unstable due to its negative thermo-optic coefficient. In this study, a novel CaF2brass hybrid WGM microcavity was proposed and manufactured, which could stabilize the cavity performance. By using finite element method (FEM) simulations, it was shown that the proposed microcavity structure facilitates rapid heat diffusion from the cavity. A hybrid microcavity without a large brittle fracture was successfully manufactured by ultra-precision machining. Thermo-optic (TO) effects that cause an instability of the cavity performance are assumed to be suppressed during resonance.