Temperature-Decoupled Single-Crystal MgO Fiber-Optic Fabry-Perot Vibration Sensor Based on MEMS Technology for Harsh Environments.

A high-temperature-resistance single-crystal magnesium oxide (MgO) extrinsic Fabry-Perot (FP) interferometer (EFPI) fiber-optic vibration sensor is proposed and experimentally demonstrated at 1000 °C. Due to the excellent thermal properties (melting point > 2800 °C) and optical properties (transmittance ≥ 90%), MgO is chosen as the ideal material to be placed in the high-temperature testing area. The combination of wet chemical etching and direct bonding is used to construct an all-MgO sensor head, which is favorable to reduce the temperature gradient inside the sensor structure and avoid sensor failure. A temperature decoupling method is proposed to eliminate the cross-sensitivity between temperature and vibration, improving the accuracy of vibration detection. The experimental results show that the sensor is stable at 20-1000 °C and 2-20 g, with a sensitivity of 0.0073 rad (20 °C). The maximum nonlinearity error of the vibration sensor measurement after temperature decoupling is 1.17%. The sensor with a high temperature resistance and outstanding dynamic performance has the potential for applications in testing aero-engines and gas turbine engines.

Extensible multi-wavelength interrogation method for arbitrary cavities in low-fineness multi-cavity Fabry-Pérot interferometric sensors.

To the best of our knowledge, a novel extensible multi-wavelength (EMW) method to interrogate arbitrary cavities in low-fineness fiber-optic multi-cavity Fabry-Pérot interferometric (LFMFPI) sensors is proposed and experimentally demonstrated. Based on the derived model of the LFMFPI sensor with any amount of cascaded cavities, theoretically, variation in each cavity of a LFMFPI sensor can be extracted simultaneously once the necessary parameters are acquired in advance. The feasibility of this method is successfully demonstrated in simulations and experiments utilizing LFMFPI sensors. In experiments with the LFMFPI sensor, optical path differences (OPD) of 78 nm and 2.95 µm introduced by temperature variation in two cavities, and the OPD induced by vibration with the amplitude from 5.891 nm to 38.116 nm were extracted, respectively. The EMW method is potential in multi-parameter sensing for pressure, vibration, and temperature.

High-Temperature Fiber-Optic Fabry-Perot Vibration Sensor Based on Single-Crystal Sapphire.

In this paper, a fiber-optic Fabry-Perot (F-P) vibration sensor that can work at 800 °C is proposed. The F-P interferometer is composed of an upper surface of inertial mass placed parallel to the end face of the optical fiber. The sensor was prepared by ultraviolet-laser ablation and three-layer direct-bonding technology. Theoretically, the sensor has a sensitivity of 0.883 nm/g and a resonant frequency of 20.911 kHz. The experimental results show that the sensitivity of the sensor is 0.876 nm/g in the range of 2 g to 20 g at an operating frequency of 200 Hz at 20 °C. The nonlinearity was evaluated from 20 °C to 800 °C with a nonlinear error of 0.87%. In addition, the z-axis sensitivity of the sensor was 25 times higher than that of the x-axis and y-axis. The vibration sensor will have wide high-temperature engineering-application prospects.