Influence of Initial Phase Modulation on the Sensitivity of the Optical Fiber Sagnac Acoustic Emission Sensor

Abstract

Improving the phase sensitivity of the optical fiber Sagnac sensor is very important for accurately detecting weak signals of acoustic emission. Theoretical analysis shows that the initial phase of the sensor is π under ideal conditions, and the maximum phase sensitivity is obtained when the bias phase is π/2. In this work, an experimental system was built with an aluminum alloy plate as the experimental object. The initial phase of the sensor was modulated by a Y-branch waveguide, and the fitting curve of the experimental data was in good agreement with the curve of the numerical simulation. Moreover, our experiments show there was a single value for the bias phase of π/2, which significantly deviated from the theoretical value. The results show that the greatest phase sensitivity of the sensor not only could be increased by nearly nine times through modulating the initial phase, but also could suppress the harmonic interferences in the sensing system. This study can provide a useful reference for improving the phase sensitivity of the optical fiber Sagnac AE sensor in practical applications.

Low Acoustic Frequency Sensing Based on Ghost Mode of Small Angle Tilted Fiber Bragg Grating

“…In recent decades, fiber-optic acoustic sensors (FOAS) have attracted wide attention for obvious advantages of high sensitivity, antielectromagnetic interference, long-distance detection, low cost and small size in comparison with traditional capacitive and piezoelectric-based electric-type acoustic sensors [4,5]. Various FOAS techniques are widely investigated including fiber laser [6][7][8][9], no-diaphragm interferometer based on Mach Zehnder(MZ) [10], Michelson [11], Sagnac [12]; diaphragmbased fiber acoustic systems such as Fabry Perot (FP) structures [13], fiber coupler [14], tapered fiber [15,16] and fiber gratings [17][18][19]. Among these acoustic detection schemes, Jing Tian, Yi-Wu Zuo, Qing Yang, Xiao Hu and Yang Jiang are with the College of Physics, Guizhou University, Huaxi Road, Huaxi District, Guiyang, China (e-mail: jtian1@gzu.edu.cn; 941061337@qq.com; 2631609229@qq.cm; huxiao0410@qq.com; jiangyang415@163.com) Kai-Ming Zhou is with the Electronic Engineering Department, Aston University, Aston Triangle, Birmingham, B4 7ET , United Kingdom (e-mail: k.zhou@aston.ac.uk) those based on optical fiber lasers are mainly used for detection of high acoustic frequencies, and they show large noises for low frequencies [6][7][8][9], making them ineffective for detection of low acoustic frequencies.…”

High-Performance Extrinsic Fabry-Perot Fiber Optic Acoustic Sensor Based on Au/PI Composite Film

“…According to different modulated optical parameters, fiber optic acoustic sensors could be classified into intensity type, phase type, wavelength type, etc. Among them, phase type fiber optic acoustic sensors are developed based on different interference structures, including Michelson [5], [6], Fabry-Perot [3], [7], Mach-Zehnder [8], [9], and Sagnac structures [10], [11]. In contrast, acoustic sensors with F-P structure only require one fiber, forming an F-P cavity between the fiber end face and the vibrating diaphragm.…”