Highly efficient prism coupling to whispering gallery modes of a square μ cavity

By using prism coupling to a square μ cavity, over 75% energy transfer to the whispering gallery modes ${\text{(Q>10}}^6)$ by frustrated total internal reflection was observed. A good comparison was found between measured data and theoretical model (based on a Fabry–Perot resonator), for the dependence of the coupling and linewidth of the whispering gallery modes (WGMs) as a function of relative separation between the prism and the μ cavity. By selecting the incident angle at the prism interface, the coupling to all four different sets of WGMs can be changed to coupling to only one set of WGMs.