Distributed Brillouin optical fiber sensors assisted by first‐order Raman amplification with window functions

Abstract

Raman amplification can extend the sensing distance of distributed Brillouin optical fiber sensor, and there is a corresponding relationship between the optimal Raman pump, the sensing distance, and the lanched probe power. We propose a scheme of co-directional Raman pumping Brillouin optical time-domain reflectometer (BOTDR) with window functions to make a better tradeoff between sensing distance and signal-to-noise ratio (SNR). The mathematical model of window functions is designed based on the relationship between the sensing distance and Raman pump power. Both simulations and experiments analyze the distributions of Brillouin scattering power, which are detected under the fixed Raman pump and processed by the window functions. We then obtain the Brillouin frequency shift (BFS) distribution curve by Lorentzian curve fitting. The experimental results show that the system SNR is increased by 3.3 dB at the near-end of the 78.8 km long sensing fiber. Moreover, the accuracy of temperature and strain at the far-end is enhanced by 2.75 °C and 389 με by using window functions, respectively.