Security monitoring system based on a line structure Sagnac interferometer with 3 × 3 coupler

Abstract

Damage action, such as human disruption, is one of the major threats to pipeline operation. It is essential to monitor perturbation behavior and locate the position in real time. A pipeline security monitoring system is proposed using a line structure Sagnac distributed optic fiber interferometer with a 3 × 3 coupler that can modulate the optic signal phase without special modulation and demodulation. The optic structure of the system is simplified, signal processing accuracy improved, and the effect of polarization reduced. The working principle of the monitoring in ideal conditions and phase demodulation are analyzed and the location of the possible damage point is formulated. Simulation and validation tests confirm the feasibility of the proposed monitoring system and indicate that the low frequency signals <1 kHz can be detected effectively. A disturbance can be accurately located over long monitoring distances. Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 06/27/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Optical Engineering 064108-6 June 2016 • Vol. 55(6) Ruan, He, and Wu: Security monitoring system based on a line structure Sagnac interferometer with 3 × 3 coupler Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 06/27/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Li Ruan received his PhD degree from Beijing University of Technology. His research interests include optic fiber detection and signal processing. Cunfu He is now a professor. He received his PhD degree from the Department of Engineering Mechanics, Tsinghua University. His research interests include modern NDT method and signal processing. Bin Wu is currently a professor. He received his PhD degree from Taiyuan University of Technology. His research interests include elastodynamics, modern NDT method, and signal processing. Optical Engineering 064108-8 June 2016 • Vol. 55(6) Ruan, He, and Wu: Security monitoring system based on a line structure Sagnac interferometer with 3 × 3 coupler Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 06/27/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

Distributed Acoustic Sensor Using a Double Sagnac Interferometer Based on Wavelength Division Multiplexing

“…This requires a scheme with two loops that differ from each other by an fixed length amount L D . The scheme includes a MZI at one end of the loop [ 11 , 12 , 13 ], as shown in Figure 2 , or a linear section with a mirror at the opposite edge [ 14 , 15 ], formed using couplers or WDM modules. The formed MZIs have a length difference L D between the arms that exceeds the coherence length of a laser source.…”

A Method to Eliminate the Influence of Frequency-Modulating-Induced Auxiliary Amplitude Modulation on the Calibration of 3 × 3 Coupler Asymmetric Parameters

“…The 3 × 3 demodulation algorithm is a common methods to demodulate the phase signal of the interferometric optical fiber sensing system [1][2][3][4][5], owning a great deal of advantages such as possessing a high dynamic range and a simple structure compared with the phase generated carrier (PGC) method. However, an effective 3 × 3 demodulation algorithm relies greatly on the strictly symmetric splitting ratio of the 3 × 3 coupler, which can hardly be guaranteed that can lead to the distortion of the retrieved phase signals and the deterioration of the demodulation algorithm [6], limiting the further application of it as a result.…”