Phase-Shifted Fiber Bragg Grating for Simultaneous Measurement of Pressure and Temperature

A microcavity sensor based on phase-shifted fiber Bragg grating (PS-FBG) is presented for the simultaneous measurement of gas pressure and temperature. The sensing structure comprises two segments of single-mode fiber (SMF) fused with a hollow-core fiber (HCF) that features a notch. The fiber Bragg grating (FBG) is inscribed using femtosecond (Fs) lase and is located exclusively at the ends of the SMF, separated by the HCF. This configuration introduces a phase discontinuity at the center of the FBG, effectively forming a PS-FBG. Gas can enter and exit the microcavity through the notch in the HCF. Variations in external gas pressure lead to corresponding changes in the refractive index of the gas within the microcavity. The microcavity is sensitive only to gas pressure, whereas the FBG responds solely to temperature. This complementary sensitivity enables simultaneous measurement of both parameters. To eliminate temperature crosstalk in gas pressure measurement, we derived a simple sensitivity matrix based on the wavelength shifts observed at points A and B. We fabricated a sensor with an HCF cavity length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$80~\mu $ </tex-math></inline-formula>m and an FBG length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1000~\mu $ </tex-math></inline-formula>m. The experimental results show that this sensor offers a pressure sensitivity of 0.63 nm/MPa and a temperature sensitivity of 0.0088 nm/°C. The sensor’s straightforward structure, compact size, and strong linearity, and repeatability make it an effective solution for dual-parameter sensing of pressure and temperature in invasive medical procedures and oil and gas pipeline monitoring.