An OTDR and Gratings Assisted Multifunctional Fiber Sensing System

Abstract

Abstract-We report a distributed multifunction fiber sensing network based on weak-fiber Bragg gratings (WFBGs) and long period fiber grating (LPG) assisted OTDR system. The WFBGs are applied for temperature, strain and vibration monitoring at key-positions, and the LPG is used as a linear filter in the system to convert the wavelength shift of WFBGs caused by environmental change into the power change. The simulation results show that it is possible to integrate more than 4472 WFBGs in the system when the reflectivity of WFBGs is less than − . Besides, the reflected light of weak FBGs and the back-Rayleigh scattering along the whole fiber can also be detected which makes distributed bend sensing possible. As an experimental demonstration, we have used 3 WFBGs UV-inscribed with 50 m interval at the end of a 2.6 km long fiber, which part was subjected for temperature, strain and vibration sensing, respectively. The results show strain and temperature sensitivities are . × − / and . × − /℃, respectively. Detection of multiple vibrations and single vibration with the broad frequency band up to 500 Hz are also achieved. In addition, distributed bend sensing which could be simultaneously realized in this system has been proposed.

Untitled

“…In addition, by improving the reflectivity of the fiber, the SNR of the OTDR system can also be improved. The SNR of the OTDR system is improved by 11 dB using the ultra-weak fiber Bragg grating (FBG)-based fiber whose reflectivity is about one order higher than the Rayleigh scattering [18] . Besides the traditional OTDR techniques, the Brillouin optical time domain analysis (BOTDA) is another hot topic in this area, which employs a pump light and a pulsed light simultaneously to improve the SNR of the system.…”