Distributed Fiber optical sensor has been widely used in communication cables and pipelines defense. Among them, Fiber Sagnac Interferometer shows several merits such as low noise, low requirement and high reliability. While the loop-based configurations are difficult in practical application for two aspects: the inconvenience to install Sagnac loop along a line (such as communication cables) and the isolation of the unused half of the Sagnac loop. Though some linear structures with delay loops or dual-loop were developed to satisfy reality requirements, they usually make a sacrifice of sensitivity and have complex circuits. To acquire high sensitivity with simple circuits, we propose a structure in which the two sides of Sagnac loop are in one cable. When a disturbance applies to the cable, one fiber is compressed and another is stretched, and vice versa. The phases of clockwise (CW) light and the counter clockwise (CCW) light are affected by the disturbance at the same time but with different direction. It means that the phase affection acting on the two fibers by the intrusion are synchronous but differ with half period. Besides the advantages of linear laying and high sensitivity, the high order of null frequencies are integer multiple of the fundamental null frequency. Closer null frequencies make more accuracy on peaks location on the Fourier transform. Experiments on simulating the intrusion in lab have been launched. A 50m resolution has been achieved when the intrusion distance is 100km. This structure is proved simple and accurate.

Date Published: 18 August 2014
PDF: 6 pages
Proc. SPIE 9203, Interferometry XVII: Techniques and Analysis, 92030Y (18 August 2014); doi: 10.1117/12.2059925

Published in SPIE Proceedings Vol. 9203:
Interferometry XVII: Techniques and Analysis
Katherine Creath; Jan Burke; Joanna Schmit, Editor(s)