A visibility enhanced broadband phase-sensitive OTDR based on the UWFBG array and frequency-division-multiplexing

Abstract

Abstract The phase-sensitive optical time domain reflectometers (Φ-OTDR), which can realize distributed acoustic sensing, has been widely applied in health monitoring of civil structures. To break through the limit of the frequency response bandwidth (FRB) and to reduce the fading positions of traditional Φ-OTDR systems, we propose an Φ-OTDR system based on the ultra-weak fiber Bragg grating (UWFBG) array and the frequency-division-multiplexing (FDM) scheme. Taking advantage of UWFBGs, the probability of fading positions occurred on the Rayleigh backscattering (RBS) waveforms can be dramatically reduced, which means the visibility of the system can be enhanced. The FDM structure can enhance the sampling rate by interleaving algorithm, which helps the Φ-OTDR system to expand its FRB. The experimental results show that the frequency of vibration up to 440 kHz can be detected along 330 m UWFBGs, which is approximately three times higher than the upper limit of the FRB of traditional systems. When compared with the traditional scheme that adopts ordinary single-mode fiber as the sensing part, the probability of fading occurrence in the proposed system has been reduced from 10−2 to 10−10. The proposed sensing system in this paper reveals a promising option for the performance enhancement of the Φ-OTDR system, which can offer wider FRB as well as the enhanced visibility characteristic.