High sensitivity all-sapphire fiber diaphragm-based extrinsic Fabry-Perot interferometric pressure sensor for ultra-high temperature environments.

A high sensitivity all-sapphire fiber diaphragm-based extrinsic Fabry-Perot interferometer (EFPI) is proposed for pressure measurement in ultra-high temperature environments. The sensor is fabricated by directly bonding three polished sapphire wafers, forming the composite Fabry-Perot (FP) structure to simultaneously measure pressure and temperature. The demodulation accuracy is improved due to the polished sapphire wafers with low surface roughness. The sapphire fiber is adopted to pick up the sensing signals, effectively increasing the operating temperature of the sensing structure. Experimental results show that the sensing structure can work stably within the pressure range of 0 kPa to 300 kPa and the temperature range of 20 °C to 1415 °C. The optical cavity length (OCL) of the air cavity varies linear with pressure, and the pressure sensitivity increases from 17.02 nm/kPa at room temperature to 22.34 nm/kPa at 1415 °C. Based on its excellent performance, the proposed sensing structure is prospective for accurate pressure measurement in harsh environments.