Enhanced Sensitivity of Gas Pressure Sensor Based on FPIs With Harmonic Vernier Effect

This article presents a high-sensitivity fiber optic gas pressure sensor based on the first-order harmonic Vernier effect (FHVE). The sensor comprises two parallel Fabry-Perot interferometer (FPI): a sensing cavity and a reference cavity. The sensing cavity, formed by a single-mode fiber (SMF) and a capillary tube filled with polyvinylidene fluoride (PVDF) film, creates a closed-air microcavity ( $214~\mu $ m in length) that also reflects light. The reference cavity, constructed by fusing an SMF at both ends of a capillary tube, ensures high stability. By matching the free spectral ranges (FSRs) of the sensing cavity (FPI1) and reference cavity (FPI2), the traditional Vernier effect achieves a gas pressure sensitivity of −58.8 nm/MPa, 19.73 times higher than that of FPI1 alone. Furthermore, by setting the FSR of FPI1 to approximately half that of a modified reference cavity (FPI3), the FHVE enhances sensitivity to −83.03 nm/MPa, 27.86 times greater than FPI1. The sensor demonstrates minimal temperature cross-sensitivity, with gas pressure variations of only 2.44 kPa/°C. Key advantages include high sensitivity, robust mechanical strength, compact size, ease of fabrication, and cost-effectiveness, making it ideal for pressure monitoring in harsh environments such as offshore oil drilling and underwater operations.