Cavity optomechanical liquid level meter using a twin-microbottle resonator

TL;DR

This paper introduces a novel cavity optomechanical liquid level meter using a twin-microbottle resonator, capable of high-resolution measurements of water levels with potential applications in detecting tiny interface fluctuations.

Contribution

The work presents the first cavity optomechanical architecture specifically designed for sensing liquid levels, demonstrating high sensitivity and resolution in a fiber-based microresonator system.

Findings

Achieved water level measurement resolution of 2.6±0.9 pm.

Maintained high optical quality factor during water immersion.

Demonstrated sensitive detection of tiny interface fluctuations.

Abstract

Cavity optomechanical devices can be made to have good compatibility with optical fiber technology by utilizing fiber-based waveguides and cavities and can be used in high-performance optical sensor applications. Such optomechanical microsensors have a great potential for exploring the properties of liquids, such as density, viscosity, and masses of included nanoparticles. However, as yet, there is no cavity optomechanical architecture that can be used to sense the liquid's shape, e.g., liquid level. In this paper, we report a demonstration of a liquid-level meter using a twin-microbottle resonator that can make measurements at arbitrary positions and depths in the liquid. The twin-microbottle resonator has a maximum diameter of 68 $\mu$m and length of 800 $\mu$m. By immersing one part of it in water and keeping the other part in air, the mechanical radial breathing mode can be read out sensitively while maintaining a high optical quality factor of the optical whispering gallery mode regardless of the water immersion. This high mechanical displacement sensitivity provides a frequency resolution that is high enough to measure the mechanical frequency shift due to the water immersion and resolves the water level to 2.6$\pm$0.9 pm. This unique liquid-level meter based on a highly sensitive cavity optomechanical setup can be used to detect tiny fluctuations of various air-liquid and liquid-liquid interfaces.