A Spectral Cleaning Method of Whispering Gallery Modes Resonance in the Microsphere Resonator

The applicability of whispering gallery mode (WGM) microsphere resonators is limited due to the intricate modes and dense spectrum they exhibit. This article investigates the spectral cleaning approach of WGM microsphere resonators through simulation and experiments. Additionally, a method is proposed to suppress the excitation of higher-order azimuthal modes in WGM microsphere resonators by etching double-grooved micro-nanostructures on the surface of the microspheres. This approach achieves resonance mode selection and spectral cleaning, and leads to an enhancement of the extinction ratio of resonance peaks (from 1.068 dB to 1.8 dB, representing an improvement of approximately 0.732 dB). Consequently, this advancement establishes the necessary conditions for achieving long-range tracking of a single resonance peak. Meanwhile, a double T-grooved structure has been proposed based on the mode distribution characteristics of the spherical microcavity. Experimental results indicate a significant enhancement in the quality factor (Q-value) of the microsphere cavity, with an improvement of one order of magnitude (from ∼10⁴ to ∼10⁵) observed following the etching process, as compared to the double rectangular grooves configuration. The process presented in this research article demonstrates an efficient approach to suppressing the excitation of higher-order azimuthal modes in microsphere resonators. This method achieves resonance mode selection and simplifies the spectra, addressing the challenge of applying mode densities in large-sized spherical microcavities.