Study of Straight-Line-Type Sagnac Optical Fiber Acoustic Sensing System

Abstract

A straight-line-type Sagnac optic fiber acoustic sensing system is proposed in this paper to adopt the application needs of no man’s plateau borderline for monitoring mechanical invasion. The Sagnac interference fiber loop is replaced by a straight-line fiber and a 1 × 2 coupler, and the length of the Sagnac interference fiber loop is shortened by close to 50%. The influences of delay fiber and sensing fiber on the sensing system are analyzed by theory calculation and simulation and the optimal lengths of delay fiber and sensing fiber were decided. The experiment system was set, and the sensing fiber was wound into titanium alloy cylinder to compose the sensing element. Experimental results show that the sensing system has a good response to 50−8000 Hz and 70 dB sinusoidal acoustical signals and can well distinguish the signals of different frequencies. Using a small-scale helicopter audio signal as the acoustical signal, the test results show that the response curve is consistent with the simulation results and the sensitivity reaches 30.67 mV/Pa.

Research on Multi-Source Simultaneous Recognition Technology Based on Sagnac Fiber Optic Sound Sensing System

“…Eventually, the two beams interfere at C1, and the interfering light is output to the PD (photoelectric detector) via the 3rd port of C1. When the sound field is applied to the pickup L2 of the linear Sagnac fiber optic sound sensing system, the light from the different optical paths entering the sensing system all pass through the pickup twice; therefore, the phase sensitivity of the system can be expressed as follows [10]:…”

“…where ∆φ denotes the phase difference between the two beams of coherent light under the action of the sound field, n denotes the refractive index of the optical fiber, f denotes the frequency of the sound, k is a constant influenced by the refractive index of the fiber, the modulus of elasticity of the pick-up structure and the optical fiber bounce coefficient, L1 is When the sound field is applied to the pickup L 2 of the linear Sagnac fiber optic sound sensing system, the light from the different optical paths entering the sensing system all pass through the pickup twice; therefore, the phase sensitivity of the system can be expressed as follows [10]:…”

“…In the linear Sagnac fiber optic sound sensing system, the interferometric light intensity obtained from the detector can be expressed as follows [10]:…”

“…However, research on multi-target identification for Sagnac fiber optic sensing systems deployed in harsh environments such as plateaus border security has not been reported. Therefore, in this paper, a multi-target online recognition algorithm study is carried out for the linear Sagnac fiber optic sound sensing system [10,11].…”

A study on the improvement of sensitivity consistency in Sagnac photoacoustic sensing system

“…In 2015, Ma et al [7] proposed to replace the acoustic sensitive structure with a special material graphite probe to greatly improve the sensitivity and stability of Sagnac fiber optic based acoustic sensors. In 2023, Wang Jiang et al [8] proposed a linear Sagnac fiber-optic acoustic sensing system, and analyzed the effects of the delay fiber and sensing fiber on the sensing system through theoretical calculations and simulations, and determined the optimal lengths of the delay fiber and the sensing fiber.…”