Displacement sensing based on thermo-optic effect of whispering-gallery mode microcavity with spectrum area

High-precision displacement sensing is essential for diverse applications, ranging from precision manufacturing to micro-nanotechnology. Among various sensing technologies, optical microcavity-based displacement sensors have received significant attention due to their high quality (Q) factors, compact structure, and immunity to electromagnetic interference. In this paper, we propose and demonstrate a displacement sensing scheme based on the thermo-optic effect in a fiber-coupled whispering-gallery mode (WGM) microsphere. Unlike conventional methods that monitor a single spectral parameter through complex Lorentzian fitting, our approach utilizes the thermo-optic spectral area as the primary sensing parameter. This parameter integrates multiple spectral features and can be obtained through simple numerical integration, which significantly simplifies the demodulation process and enhances sensing sensitivity. Experimental results show that the proposed scheme can accurately detect displacement variations with high sensitivity, offering a robust and efficient alternative for high-precision displacement metrology.