Highly sensitive gas pressure sensor utilizing the harmonic vernier effect in parallel FPIs with femtosecond laser processing

Abstract

This work proposes and prepares a high-sensitive fiber optic gas pressure sensor based on the first harmonic vernier effect (FHVE). It has two parallel Fabry-Perot interferometers (FPI), each made of a single-mode fiber and a small segment of capillary tube fused as a sensing cavity and a reference cavity, and the end face of the sensing cavity is cut into a thin slice with a femtosecond laser pulse to make it sensitive to gas pressure. When the sensing cavity's (FPI1) and reference cavity's (FPI2) free spectral ranges are close to each other, a traditional vernier effect occurs, and the gas pressure sensitivity approaches 58.49 nm/MPa, which is approximately 14.64 times that of the single sensing cavity (FPI1). When the free spectral range of the sensing cavity (FPI1) is roughly twice that of the reference cavity (FPI3), the first harmonic vernier effect is observed. This leads to a significant increase in gas pressure sensitivity, up to 141.80 nm/MPa, which is about 35.45 times higher than what a single sensing cavity (FPI1) would achieve. Furthermore, testing results reveal that the sensor is temperature insensitive, with a low cross-sensitivity of 3.1 × 10−5 MPa/°C for gas pressure to temperature. This device is made of pure quartz glass, has high mechanical strength, a sealed construction, is easy to fabricate, has a high sensitivity of gas pressure, and may be used to monitor pressure in extreme conditions such as offshore oil or underwater operations.