Ultra long distance distributed fiber-optic system for intrusion detection

Abstract

This paper research an ultra long distance distributed fiber-optic intrusion detects system. Laser source is amplified and modulated before input to the dual Mach-Zehnder interferometers. This ensures the system can detect longer distance with less loss and nonlinearity than continuous laser input. The cross correlation algorithm is considered to locate the vibration event after the polarization controlled of the optical source, and the locate precision is also discussed. Finally, an experiment result is given as the sensing fiber length is 112km with the location precision about 160m.

Distributed Fiber-Optic Sensors for Vibration Detection

“…Finally, the signals are received by PD 1 and PD 2 from the CCW and CW light wave. Consequently, the vibration point where the external vibration occurs can be obtained by [ 31 ]: x = L 2 − c ∆ t/ (2 n ) where x is the distance from the point to Coupler 2, L 2 is the length of the interference region, and ∆t is the time delay, which can be obtained by means of the correlation operation [ 58 ]. Since the CW and CCW lights are emitted from the same laser and affected by the same vibration, the two interfering signals detected by PD1 and PD2 are of strong correlativity.…”

“…Compared with point and quasi-distributed vibration sensors, which can only be used individually on a small scale and often have poor concealment, distributed fiber-optic vibration sensors inherit the advantages of general fiber sensors and offer clear advantages such as light weight, large-scale monitoring, good concealment, excellent flexibility, geometric versatility of optical fibers, quick response, system simplicity, immunity to EM interference, high sensitivity, accurate location, etc. [ 30 , 31 , 32 ].…”

Influence of stimulated Brillouin scattering on positioning accuracy of long-range dual Mach–Zehnder interferometric vibration sensors

“…Then both fibers A and B were connected and their interference signals were measured (labeled as dualarm). Since the frequency of the intrusion event is often lower than tens of kHz in practical applications, 9 the bandwidth we measured is 1 MHz. 12 who found that the transmitted noise bandwidth of Brillouin scattering was ∼90 kHz while the backward noise bandwidth was about tens of MHz.…”

“…Tu et al 9 reported a DMZI system with 160 m positioning precision on a 112-km-long sensing fiber. In this system, four single mode fibers (SMFs) in an optical cable were used.…”

“…9,10 On the other hand, a nonlinear effect (e.g., stimulated Brillouin scattering, SBS) starts to appear when its threshold P th is reached 11 E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 2 ; 3 2 6 ; 3 8 5…”