Concept of miniature optical pressure sensor based on coupled WGMs in a dielectric microsphere

TL;DR

This paper introduces a novel miniature optical pressure sensor utilizing coupled whispering gallery modes in a dielectric microsphere, which detects pressure changes via interference effects without mechanical contact.

Contribution

It proposes a new sensor design that uses double excitation of WGMs and free-space coupling, enhancing sensitivity and miniaturization compared to existing sensors.

Findings

Sensor sensitivity depends on quality factor and membrane parameters

Design achieves miniaturization with no mechanical contact

Interference of WGMs encodes pressure information

Abstract

We present the physical concept and sample engineering design of a new miniature pressure sensor based on the whispering gallery modes (WGMs) optically excited in a dielectric microsphere placed near a flexible reflective membrane which acts as an ambient pressure sensing element. WGMs excitation is carried out by free-space coupling of optical radiation to a microsphere. The distinctive feature of proposed sensor design is double excitation of optical eigenmodes by forward and backward propagating radiation reflected from a membrane that causes WGMs interference in particle volume. The optical intensity of resulting resonant field established in the microsphere carries information about the exact position of the pressure-loaded reflecting membrane. The sensitivity of the proposed sensor strongly depends on the quality factor of the excited resonant mode, as well as geometrical and mechanical parameters of the flexible membrane. Important advantages of the proposed sensor are miniature design (linear sensor dimensions depends only on the membrane diameter) and the absence of a mechanical contact of pressure-sensitive element with WGM resonator.