Hybrid Fabry–Perot interferometer: polymer-induced microcavity for temperature and gas pressure measurement

Developing new Fabry–Perot interferometer (FPI) with high sensitivity has always been a focus in the field of optical fiber sensing. This work proposed and experimentally demonstrated a novel hybrid-structured FPI based on harmonic Vernier effect and traditional Vernier effect, utilizing a polydimethylsiloxane (PDMS) microcavity. The reference FPI is formed by the hollow core fiber, which is insensitive to temperature and gas pressure change. The sensing element is formed by two parts including a short single-mode fiber (SMF) and a PDMS microcavity. Due to the similar refractive index between the SMF and PDMS microcavity, there is very weak reflection at the interface. Only reflection at the interface between the PDMS microcavity and the air is observed. Additionally, five hybrid FPIs consisting of PDMS microcavity were fabricated and applied for temperature and gas pressure measurement, which exhibited high temperature and gas pressure sensitivities with maximal values of 5.49 nm/°C, and 22.97 nm/MPa, respectively.