Hollow Core Bragg Fiber-based Gas Pressure Sensor Using Parallel Fabry-Perot Interferometers

An ultra-high sensitivity parallel-connected Fabry-Perot interferometers (FPIs) pressure sensor based on hollow core Bragg fiber (HCBF) and harmonic Vernier effect is proposed and demonstrated. One FPI (FPI-1) acts as the sensing unit while the other FPI (FPI-2) is used as the reference unit to generate the Vernier effect. The FPI-1 was prepared by fusion splicing a section of HCBF between a single-mode fiber (SMF) and a hollow silica tube (HST), and the FPI-2 was fabricated by sandwiching a piece of HCBF between two SMFs. Two FPIs with very different free spectral ranges (FSR) in the fringe pattern were connected to the 3-dB coupler parallelly, which realizes the harmonic Vernier effect and ensures the stability of the interference fringe. Both measurements of the air pressure in the range of 0-0.24 MPa and the temperature in the range of 25-55 °C were conducted using the dual FPIs sensor. Experimental results exhibited that high sensitivity of 124.35 nm/MPa with excellent linearity of 0.9967 was achieved by the sensing probe. Moreover, the calculated temperature crosstalk was as low as ~0.072 kPa/°C. The proposed sensor can be a promising candidate for real-time and high-precision gas pressure monitoring.