Fiber-optic Fabry-Perot sensor based on spectral quality-enhanced microsphere lens for high-temperature strain measurement

This paper proposes a fiber-optic Fabry-Perot sensor based on a microsphere lens to overcome the limited measurement range and accuracy in high-temperature strain sensing. The sensor consists of an external-cavity Fabry-Perot interferometer (EFPI) with a microsphere lens and a gold-coated fiber Bragg grating (GFBG) in cascade, enabling simultaneous measurement of strain and temperature. The microsphere lens enhances the EFPI spectral quality through optical focusing, maintaining a fringe contrast above 8 dB at a cavity length of 800 μm and mitigating the measurement range limitation caused by spectral degradation at high temperatures. The GFBG provides precise temperature sensing to eliminate thermal strain interference and improve measurement accuracy. A split-type bonding process is introduced to address the mechanical constraints of connection materials and minimize the risk of sensor failure. Experimental results demonstrate that the sensor measures mechanical strain exceeding 4000 με at a high temperature of 800 ℃, with post-compensation measurement error below 2.17% F.S. These features demonstrate that the sensor possesses high precision and stability, making it well-suited for structural health monitoring in extreme environments.