Mode Selection for a Whispering Gallery Mode Resonator

An original mode selection technique for whispering gallery mode sapphire resonator (WGMR) is presented. A set of metallic screws, inserted in the cavity, allows to improve the frequency isolation of the WGEm,0,0 modes, with little Q-factor degradation. The design has been performed using a 3-D Finite Element Method (FEM) software to check the validity of the technique, and experimental results are in good agreement with theoretical ones.