Highly Sensitive Fiber Gas Pressure Sensor Based on Two Diaphragm-Type Fabry–Pérot Interferometers in Parallel Forming the Enhanced Vernier Effect

An innovative in-line fiber gas pressure sensor with high sensitivity, based on the enhanced Vernier effect achieved through the parallel connection of two diaphragm-type Fabry–Pérot interferometers (FPIs), is proposed and demonstrated. FPI1 is a conventional diaphragm-type FPI, whereas FPI2 is a novel two-parameter diaphragm-type FPI, which is capable of utilizing both the gas refractive index (RI) and the geometrical length of the FPI cavity to detect gas pressure. The proposed new structure of FPI2 exhibits an inverse wavelength response compared to the FPI1 in response to changes in gas pressure, thereby the enhanced Vernier effect can be generated by connecting the two FPIs in parallel, leading to a greater sensitivity magnification compared with the conventional Vernier effect. The proposed fiber gas pressure sensor exhibits an ultrahigh sensitivity of 905.91 nm/kPa over a gas pressure range of 0–0.25 kPa, which further amplifies the sensitivity by 2.58 times (350.47 nm/kPa) and 1.54 times (578.79 nm/kPa), respectively, as compared with the conventional Vernier effect. Furthermore, the sensor shows good repeatability and stability, with a gas pressure-temperature crosstalk of approximately 0.7 kPa/°C. The sensor structure offers a novel insight and solution for investigating high-sensitivity fiber optic gas pressure sensors.