A novel broadband and high sensitivity fiber Bragg grating (FBG) accelerometer is designed and analyzed. The accelerometer is based on a compact structure consisting of double diaphragms and h-shaped hinges. The h-shaped hinge structure is used to break through the restriction between sensitivity and resonance frequency. The FBG accelerometer is demodulated by an interferometric method and test results show that the acceleration sensitivity is 32 dB re pm/g between 1 Hz and 1 kHz, with a fluctuation less than ±3 dB, and the resonant frequency is above 1.6 kHz. The cross-sensitivity is less than -26 dB in the flat frequency range. The sensor shows a high acceleration resolution of 15 μg /√Hz in a wide frequency range, making it promising for cross-well seismic, micro-seismic monitoring and electromechanical equipment vibration monitoring, etc.

In this paper, we propose a new scheme that combines a capillary tube with an elastic cavity to develop a thin fiber laser hydrophone (FLH) with static pressure equalization, enhanced dynamic pressure sensitivity and broadband flat response. We demonstrate the improvement on the hydrophone response characteristics by introducing the compensation structure into a diaphragm-based FLH. A hydrophone prototype with a diameter of 7.2 mm was packaged and the hydrophone has a flat pressure sensitivity of 9×10-3 pm/Pa (120 dB re Hz/Pa) over a bandwidth from 40 Hz to 4 kHz. The static pressure sensitivity is -11×10-6 pm/Pa in the measurement range of 0 to 3 MPa.

A fiber-optic extrinsic Fabry–Perot interferometric (EFPI) temperature sensor with extremely high resolution and large dynamic range is proposed and demonstrated. The sensor uses a thermally expanded core (TEC) fiber as the first reflective surface of the interference cavity to focus the beam to improve the finesse of the interference fringes, which enables extremely high cavity length resolution and large dynamic range with a multi-valley averaging method based on dynamic estimation of the fringe order. Using a borosilicate capillary as the temperature-sensitizing material, a cavity length sensitivity of 79.25 nm/°C as well as a good linearity was obtained in the temperature range of 10-100 °C. A temperature resolution of 7.5×10 ^-5 °C was demonstrated. The extremely high temperature resolution with a large dynamic range has important application value in the monitoring of weak temperature changes in deep sea and underground fluids.

We propose a distributed optical fiber sensing event recognition scheme based on Markov Transition Field (MTF) and knowledge distillation. The event recognition algorithm has the advantages of being lightweight, fast, and high accuracy. The event data are converted into images by the MTF algorithm, which keeps the event signals correlated in the time domain while highlighting the visual differences between different events. A two-stage knowledge distillation model compression method is proposed, which effectively compresses the large-scale model into a lightweight model with optimal learning capability, ensuring the lightweight and efficient recognition of events by the compressed model (student model). The experimental results show that the student model improves the recognition rate of six events by 5.2% and achieves 96.6% event recognition accuracy by the two-stage knowledge distillation method. The size of the student model is only 1.4 MB, the number of parameters is only 0.35 M, and the FLOPs are only 0.17 G. The student model recognizes a single event in 0.129s on a low configuration device, which can meet the requirements of deployment and real-time monitoring of resource-limited devices.

The trade-off between sensitivity and frequency band is problematic for FBG accelerometer, synchronous enhancement is an urgent technical problem. We report a novel fiber-optic accelerometer with high figure of merit based on double short gratings, which are inscribed by a femtosecond laser and symmetrically fixed to a M-shaped hinge to increase the sensitivity and reduce the temperature interference. Experiments show that the sensor possesses a resonant frequency of 400 Hz, a high acceleration sensitivity of 729.24 pm/g (1.5 dB), and a high figure of merit of 116678400 pm·g ^-1 ·Hz ² , which is higher than the level (5000000 pm·g ^-1 ·Hz ² ) of conventional FBG sensors. The sensor has great potential in low-frequency (as low as 0.1Hz) micro-vibration measurement.