Looking for optimal materials for whispering gallery modes applications at the 2 $\mu$m window

TL;DR

This paper analytically evaluates the quality factor and free spectral range of whispering gallery mode resonators at 2 μm wavelength, comparing materials to identify optimal choices for enhanced optical sensing and communication applications.

Contribution

It introduces a methodology for selecting optimal materials for WGM resonators at the 2 μm window, focusing on key parameters like quality factor and free spectral range.

Findings

Fused silica, AsSe chalcogenide glass, and calcium fluoride compared

Identified optimal parameter regions in wavelength and radius space

Provided guidelines for material selection at 2 μm

Abstract

The diverse applications of whispering gallery modes in spherical microresonators are strongly related to the sphere size and material composition. Their design should therefore be optimized to ensure that parameters such as the quality factor and the free spectral range are maximized. Because of the imminent capacity crisis of the optical communication systems operating at the 1550 nm wavelength regime, it is time to explore optical communications at the 2 $\mu\mbox{m}$ wavelength window. In this work, we analytically investigate key resonator parameters - quality factor and free spectral range - as a function of wavelength, aiming to establish a methodology to help identify optimal materials for whispering gallery mode sensors, with special attention at the 2 $\mu\mbox{m}$ wavelength window. Specifically, we examine three materials: fused silica, AsSe chalcogenide glass and calcium fluoride, and we perform a comparison between them in order to identify the region in the parameter space of resonant wavelengths and sphere radius, $(\lambda_R,R$), where the WGM resonators are optimal at wavelengths $1.8 \mu\mbox{m}<\lambda<2.1 \mu\mbox{m}$.