MgO Single Crystals MEMS-Based Fiber-Optic Fabry–Perot Pressure Sensor for Harsh Monitoring

A single crystalline magnesium oxide (MgO) MEMS-based fiber-optic Fabry-Perot (FP) pressure sensor was designed, fabricated and tested for 800 °C high-temperature environmental applications. In this article, MgO was selected as the sensitive materials of the optical sensor owing to its high melting point, and excellent mechanical and optical properties at elevated temperatures. The sensor head was constructed by combining wet chemical etching with direct bonding. This MEMS process technique realized all-MgO sensor head structure, which is beneficial to reduce the temperature gradient within the sensor structure, and avoid sensor failures. In addition, a non-scanning cross-correlated interrogation method is used to realize the demodulation of FP pressure cavity length having multiple reflectors. The experimental tests demonstrate that the proposed sensor can stably operate at an ambient environment of 22-800 °C and 0-0.6 MPa with a pressure sensitivity of 5.21 μm/MPa (room temperature), a repeatability error of 1.67% and a zero drift of 0.00353 μm/°C. In addition, the high-temperature testing proves that the adhesive-free well-sealed pressure cavity is conducive to improve the operating temperature and the performance of the sensor. To our best knowledge, this is the first research to realize fabrication of high-temperature pressure sensor by developing MgO micromachining technology. Our work is of fundamental importance in realization of pressure detecting in harsh environments.