Optical humidity sensor based on a liquid whispering-gallery mode resonator

TL;DR

This paper presents a highly sensitive optical humidity sensor using a glycerol droplet whispering-gallery-mode resonator doped with rhodamine 6G, capable of detecting minute humidity changes through wavelength shifts.

Contribution

It introduces a novel liquid whispering-gallery-mode resonator sensor with unprecedented sensitivity for humidity measurement.

Findings

Sensitivity of 10^-3 per RH percent

Effective detection of ambient humidity changes

Utilization of glycerol droplet as a resonator

Abstract

We experimentally demonstrate the use of a novel liquid state, whispering-gallery-mode optical resonator as a highly sensitive humidity sensor. The optical resonator used consists of a droplet made of glycerol, a transparent liquid that enables high optical quality factor, doped with rhodamine 6G, which acts as fluorescent emitter. As glycerol is highly hygroscopic, the refractive index and radius of the droplet change with ambient humidity. This produces a shift on the whispering gallery modes wavelengths, which modulates the emission of rhodamine 6G. This easily-made device has an unpreceded sensitivity of 10-3 per relative humidity percent.