An Absolute Displacement Sensor Based on SNAP Microresonator and Similarity Matching Method

We propose and demonstrate an absolute displacement sensor based on a surface nanoscale axial photonics (SNAP) microresonator and similarity matching method. To obtain a direct readout of the absolute displacement from the spectrum, we calculate the correlation coefficient between the detected spectrum and the spectrum in the reference spectrum library. The feasibility of this method is first verified by simulation, and further, the influence of signal-to-noise ratio (SNR), sampling points, coupling parameters, and resonant wavelengths on displacement sensing accuracy is studied. Simulation results show that this method is highly resistant to noise interference and low sampling points. Importantly, we experimentally implemented SNAP's absolute displacement sensing with an error of <tex-math notation="LaTeX">± 2 μ m </tex-math> after optimizing the reference library. This work lays the foundation for the development of high-performance probe absolute position sensors based on the whispering gallery mode (WGM) resonators.