High-Sensitivity Simultaneous Temperature and Gas Pressure Monitoring via DSP-Empowered Multi-Vernier Effect Demodulation

In this article, an in-line interferometer-based sensor is proposed and experimentally demonstrated for the simultaneous measurement of gas pressure and high temperature. The optical sensing system is composed of two sensing probes. One probe is formed by sandwiching a segment of hollow core Bragg fiber (HCBF) between the lead-in single-mode fiber (SMF) and the hollow core capillary (HCC). The other is fabricated by fusion splicing the HCBF with two pieces of SMFs. By incorporating the optimized lengths of the HCBF and HCC in our probes, the Vernier effect (VE) can be employed to improve the sensitivity. Meanwhile, a digital signal processing (DSP) algorithm is applied to deal with and demodulate the required VE-based envelopes from the complex superimposed reflected spectrum. Both parameters of gas pressure and temperature can be obtained at the same time in a single test. The sensitivities of gas pressure and temperature reach 55.31 nm/MPa and 119.11 pm/°C with the high linearity of 0.99768 and 0.99743, respectively. This work can benefit industrial applications and safety monitoring in the harsh environment of narrow spaces and high temperatures.