In extreme environments such as abysmal sea and deep space, the characteristics of low-temperature, vacuum, electromagnetic interference will significantly affect the performance of measuring instruments. With merits of anti-electromagnetic interference, corrosion resistance, compact size and so on, optical fiber sensing systems can accurately measure the pressure, the temperature, the strain and the acoustic vibration in their working environments. This article reviews the measurement methods and the characteristics of optical fiber multi-parameter sensing, and summarizes the technologies and the instrumentation of the fiber mechanical and thermal multi-parameter measurement instrument.

The thermal cycling process experienced by spacecraft during orbital operation would lead to deterioration of the demodulation performance of fiber Bragg grating (FBG). A new demodulation method based on Fabry-Perot (F-P) filter and hydrogen cyanide (HCN) gas is proposed to improve the performance. The method skillfully utilizes the self-marked HCN absorption lines as absolute wavelength references. In the thermal cycling environment whose temperature ranging from 5°Cto 65°C,the fluctuation of demodulation wavelength reduces to ± 2.6 pm, which is improved by 3.1 times compared with traditional method. The proposed method also shows a good robustness in the cases of weak light source intensity and poor signal-to-noise ratio (SNR) of HCN spectrum.

A compact fiber optic Fabry-Perot (F-P) sensor for simultaneous acoustic and temperature measurement has been proposed in the research. The sensor consists of silicon-glass-silicon sandwich structure by anodic bonding. The air F-P cavity with a circular hole and slots utilizes the deformation of the silicon membrane to realize acoustic measurement, and the silicon F-P cavity utilizes the temperature sensitivity of the refractive index of silicon to realize temperature measurement. The acoustic signal and temperature information could be recovered by acoustic and temperature demodulation method, respectively. The experimental results demonstrate that the sensor has a signal-to-noise ratio (SNR) of 53 dB and the acoustic sensitivity of 4.65 mV/Pa at 21 kHz, and the temperature sensitivity of 123.10 nm/°C at 20 °C~120 °C. The proposed fiber optic F-P sensor has great potential for simultaneous acoustic and temperature measurement in aviation, due to its compact structure, mass production and immunity to electromagnetic interference.

A fiber optical anemometer using dual Fabry-Perot sensors with sealed cavity is proposed for high-speed airflow measurement. The airflow velocity is measured based on principle of differential pressure, and temperature compensation is realized by reference F-P sensor to improve measurement accuracy and environmental adaptability. The location of dual F-P sensors in the airflow field and quadratic functional relation between differential pressure and airflow velocity are obtained by the simulation of turbulence model. F-P sensors in this experiment can be employed to measure pressure from 100kPa to 107kPa and temperature from 5°C to 50°C. The full-scale error of F-P sensors is less than 0.53% by calibration. It is demonstrated experimentally this fiber optical anemometer is qualified for measuring air velocity in the range of 7.9-81m/s with velocity error less than 0.69%. The device has the potential to measure high speed airflow in various applications.

This paper reports a torsion sensor based on the multimode interference theory. The sensor is fabricated by sandwiching a section of perfluorinated polymer optical fiber (POF) between two silica single mode fibers to construct a single-mode-multimode-single-mode (SMS) structure. The perfluorinated POF is easily connected to the optical fiber via the precise alignment of ceramic ferrules and ceramic mating sleeve. With the considerable flexibility and deformability of the perfluorinated POF, the proposed sensor is especially suitable for torsion measurement. Experimental results show that a wavelength sensitivity of 106.762 pm/(rad/m) and an intensity sensitivity of 0.165 dBm/(rad/m) are obtained within a large torsion rate of −100∼100 rad/m.

In this paper, a structural damage identification algorithm based on a single fiber Bragg grating (FBG) sensor is proposed. The signal detected by the FBG can be analyzed by the wavelet packet decomposition and back propagation neural network to obtain the damage location information. A high-speed FBG demodulation system based on a tunable Fabry–Perot filter and unbalanced Mach–Zehnder (M-Z) interferometer is designed to respond to a signal with a frequency range from 0 to 4 kHz, which will increase the sensing accuracy. This algorithm is verified by the aluminum plate model, which can simulate the generation of damage in reality. The experimental results show that a single FBG sensor is enough to realize accurate damage location identification according to this algorithm, and identification accuracy can reach 90.0%.