Fiber Bragg grating (FBG) acoustic emission (AE) sensors have been used in many applications. In this paper, based on an FBG AE sensor, the sensing principle of the interaction between the AE wave and the sensor is introduced. Then, the directionality of the FBG AE sensor on the surface of a thin polymer-bonded explosive (PBX) material is studied. Finally, the time coefficient location method is proposed to correct the AE time detected by the FBG AE sensor, thereby improving the accuracy of location experiments.

Fiber Bragg grating acoustic emission sensors have been used in many applications. In this paper, based on four fiber Bragg grating acoustic emission sensors, an acoustic emission location experiment is carried out on the surface of a cylindrical polymer-bonded explosive specimen. Due to the difference in the strain sensitivity of fiber Bragg grating in different directions, the traditional time-difference location method is not fit for fiber Bragg grating acoustic emission sensors. A 4-layer dense neural network for fiber Bragg grating acoustic emission sensors, together with a Bayesian regularization method is used to calculate the coordinates of the acoustic emission wave source. The experimental results show that the neural network location method is suitable for fiber Bragg grating acoustic emission sensors.

A heatsink is a large experimental device which is used to simulate the outer space environment. In this paper, a Raman-based distributed temperature sensor was used for real-time and continuous heatsink temperature monitoring, and a special Raman-based distributed temperature sensing method and system have been proposed. This method takes advantage of three calibration parameters ( $\Delta \alpha ,$ $\gamma ,C$ ) to calculate the temperature. These three parameters are related to the attenuation of the optical fiber, the Raman translation, and the difference of optoelectronic conversion, respectively. Optical time domain reflectometry was used to calculate the location. A series of heatsink temperature measurement experiments were performed in a vacuum and −173 °C environment. When the temperature dropped to −100 °C, the parameter $\Delta \alpha$ was found to vary. A method was proposed to recalculate $\Delta \alpha$ and modify the traditional Raman fiber temperature equation. The results of the experiments confirmed the validity of this modified Raman fiber temperature equation. Based on this modified equation, the temperature field in the heatsink was calculated. The Raman-based distributed temperature sensor has potential applications in temperature measurement and judging the occurrence of faults in space exploration.

The whispering-gallery mode microresonator self-injection locking lasers for atomic comagnetometers have excellent characteristics, and their stability needs to be improved. In this study, through the analysis and simulations of optical injection rate equations with thermal dynamics of the microresonator, a frequency adjustment strategy is presented that ensures the stability of the self-injection locking laser output wavelength over time. The normalized Allan deviation of the output wavelength is 1.7 × 10⁻¹⁰, and both the 20.6 Hz / Hz laser frequency noise and the 375 Hz linewidth are maintained within one hour. These results demonstrate exceptional self-injection locking stability with the 10⁹ quality factor microresonator.

A high-sensitivity spin exchange relaxation free (SERF) atomic magnetometer based on a noise-suppressed master oscillator power amplifier (MOPA) system is demonstrated. The spectrum and frequency noise of the laser are measured and it is proved that the frequency noise in the MOPA system is affected by the amplified spontaneous emission (ASE) stimulated from the power amplifier. The frequency noise of the MOPA system is decreased by filtering out the ASE background in the spectrum through a bandpass filter. The sensitivity of the SERF atomic magnetometer is improved by using the frequency noise-suppressed MOPA system as a pumping laser. This method can also be applied to other precision measurement fields based on MOPA systems that have high requirements for frequency noise of lasers.