In-Cavity Suspended Probe for Fiber-Optic Microforce Sensing Based on Harmonic Vernier Effect

This study presents an optical microforce fiber sensor leveraging the harmonic vernier effect (HVE) through a Fabry-Perot interferometer (FPI) architecture. The sensor comprises a precisely aligned thin fiber (TF) nested within a section of hollow-core fiber (HCF), with UV-curable adhesive providing both structural fixation and force transduction. Unlike conventional vernier effect (CVE) configurations requiring high fabrication precision, the proposed HVE-based design demonstrates relaxed structural tolerances while maintaining superior performance metrics. The sensor achieves exceptional microforce sensitivity of 11.7 pm/μN through optimized cavity length modulation, enabling first-order harmonic Vernier amplification. Advanced signal processing through inner envelope intersection tracking produces a high measurement resolution of 16.41 μN, with temperature cross-sensitivity minimized to 7.85 pm/°C. Experimental validation confirms the robust performance of the sensor in practical microforce measurement scenarios, offering significant advantages in fabrication simplicity, stable measurement, and high repeatability compared to existing optical microforce sensors.