The Investigation of All-Sapphire Fabry–Perot Fiber Acoustic Sensor Operating Up to 800 °C
Zonghao Li, Yan Cao, Jiamin Chen, Yongqiu Zheng, Jiandong Bai, Junping Zhang, Xinyu Zhao, Yonghua Wang, Zhen‐Nan Tian, Chenyang Xue
Abstract
Acoustic sensors for ultrahigh temperature environments are urgently demanded in the aerospace field. An all-sapphire Fabry–Perot (F-P) cavity acoustic sensor has been proposed, which acquires acoustic signals by detecting changes in the refractive index of the air. Based on high-temperature direct bonding technology, the sensor with a rigid structure is fabricated in three layers on a whole 4-in wafer. A 3/4-period length gradient index optical fiber (GIOF) is employed as a mode-field adapter, reducing heterogeneous fiber fusion losses between sapphire and silica fiber. It is clearly demonstrated that the sensor has superior spectrum quality at a wide range of temperatures (25 °C–1000 °C). The fringe visibility of the sensor is 40.68% and 24.58% at 25 °C and 1000 °C, respectively. At 800 °C, the sensor achieves a frequency response flatness of less than ±2 dB, a sensitivity of 0.15 mV/Pa, and a maximum measurable sound pressure level of 171.16 dB. The proposed F-P fiber acoustic sensor has the advantages of a compact structure and tolerance to high temperature. This work provides a feasible strategy for achieving the acoustic performance of F-P fiber acoustic sensors in ultrahigh temperature and high sound pressure level environments.