Micropascal-sensitivity ultrasound sensors based on optical microcavities

TL;DR

This paper investigates the thermal-noise-limited sensitivity of whispering gallery mode microcavity ultrasound sensors, optimizing their design to achieve record sensitivity levels for air-coupled ultrasound detection.

Contribution

It provides a theoretical and experimental analysis of sensitivity limits and demonstrates optimized microdisk designs with record sensitivity for ultrasound sensing.

Findings

Achieved a peak sensitivity of 1.18 uPa Hz^{-1/2} at 82.6 kHz

Optimized microdisk parameters enhance sensitivity beyond previous records

Design modifications like trench structures improve sensor performance

Abstract

Whispering gallery mode (WGM) microcavities have been widely used for high-sensitivity ultrasound detection, due to their optical and mechanical resonances enhanced sensitivity. The ultrasound sensitivity of the cavity optomechanical system is fundamentally limited by the thermal noise. In this work, we theoretically and experimentally investigate the thermal-noise-limited sensitivity of a WGM microdisk ultrasound sensor, and optimize the sensitivity by varying the radius and thickness of the microdisk, as well as using a trench structure around the disk. Using a microdisk with a radius of 300 um and thickness of 2 um, a peak sensitivity of 1.18 uPa Hz^{-1/2} is achieved at 82.6 kHz, which is to our knowledge the record sensitivity among the cavity optomechanical ultrasound sensors. Such high sensitivity can improve the detection range of air-coupled ultrasound sensing technology.