Modes trimming and clustering in a weakly perturbed high-Q whispering gallery microresonator

TL;DR

This paper demonstrates a controllable method for trimming and clustering whispering gallery modes in high-Q microresonators, enabling precise mode selection and organization for advanced photonic applications.

Contribution

It introduces a novel mode trimming and clustering mechanism in weakly perturbed microresonators, supported by experimental observations and theoretical modeling.

Findings

Observation of polygon and star modes in microresonators

Mode control achieved by tuning excitation wavelength and coupling position

Theoretical model accurately reproduces experimental results

Abstract

In general, a high-Q microresonator can accommodate abundant whispering gallery modes (WGMs) with the mode number increasing with the dimensional sizes of the microresonator. Removing the unnecessary modes while reorganizing the remaining modes is of vital importance, which, however, has been proved challenging and usually results in a tradeoff with the Q of the microresonator. Here, we reveal an effective and controllable mode trimming and clustering mechanism underlying the generation of polygon and star modes in weakly perturbed tapered fiber-coupled lithium niobate whispering gallery microresonators. Experimentally, various polygon and star modes are observed in sequence within a single microresonator by tuning the excitation wavelength or varying the coupling position between a tapered fiber and the circular microresonator, which can be well reproduced with our theoretical model. The finding offers a ubiquitous solution for a broad range of applications requiring elaborate selection and organization of the high-Q WGMs.