Temperature-compensated fiber-optic Fabry-Perot interferometric gas refractive-index sensor based on hollow silica tube for high-temperature application

- A temperature-compensated Fabry-Perot interferometric gas refractive index sensor is firstly described and experimentally demonstrated for high-temperature application.
- The temperature-compensated structure can realize an approximately zero temperature coefficient in theory.
- The experimental results showed that the refractive index and temperature is basically decoupled.

A temperature-compensated Fabry-Perot (FP) interferometric gas refractive-index (RI) sensor, fabricated by inserting a single-mode fiber (SMF) and a hollow silica tube (HST) with an inner diameter of 5 μm, from opposite ends, into a silica casing, is described and experimentally demonstrated for high-temperature application. The thermal expansion of the silica casing and that of the SMF and HST offset each other when the SMF and HST are fixed far from their end facets. The lights are reflected and refracted multiple times between the end facets of the SMF and HST, and the RI changes in the open-cavity FP interferometric sensor can be detected by determining the wavelength shift of the interference spectrum. Experimental results show that the gas RI sensor has a linear sensitivity of approximately 1546 nm/RIU from room temperature to 800 °C. The gas RI sensor also has a temperature coefficient of approximately zero owing to its temperature-compensated structure.