Fundamental mode selection in spherical microresonator using a thin metal film with a gap

Using numerical simulation in COMSOL Multiphysics software we demonstrate for the first time the possibility of selecting a fundamental whispering gallery mode in a spherical microresonator with a radius of 80 μm based on the absorption effect in a thin metal film with a gap located at some distance from the resonator surface. Q-factors of radial and azimuthal modes were calculated for modes with the azimuthal index m = 455. The results showed a high Q-factor ≈10⁹ of the fundamental mode including to internal loss and the possibility of ∼100-times and 10-times suppression with a 5-nm layer of the Q-factor of higher radial and azimuthal modes, respectively. In addition, the paper shows the possibility of using this method for selecting the fundamental mode in a wide range of index m values while maintaining high Q-factor and suppression factor of higher modes.