Origin of optical losses in gallium arsenide disk whispering gallery resonators

TL;DR

This paper investigates the residual optical losses in high-Q GaAs disk resonators, identifying scattering from surface roughness and waviness as key factors, and suggests pathways for performance improvement.

Contribution

It combines TEM analysis with an improved Volume Current Method to quantify and analyze various optical loss mechanisms in GaAs disk resonators.

Findings

Surface roughness and waviness significantly contribute to scattering losses.

Surface reconstruction layer causes optical absorption detectable via spectroscopy.

Routes for reducing losses and enhancing resonator performance are proposed.

Abstract

Whispering gallery modes in GaAs disk resonators reach half a million of optical quality factor. These high Qs remain still well below the ultimate design limit set by bending losses. Here we investigate the origin of residual optical dissipation in these devices. A Transmission Electron Microscope analysis is combined with an improved Volume Current Method to precisely quantify optical scattering losses by roughness and waviness of the structures, and gauge their importance relative to intrinsic material and radiation losses. The analysis also provides a qualitative description of the surface reconstruction layer, whose optical absorption is then revealed by comparing spectroscopy experiments in air and in different liquids. Other linear and nonlinear optical loss channels in the disks are evaluated likewise. Routes are given to further improve the performances of these miniature GaAs cavities.