Enhanced Coherent BOTDA System Without Trace Averaging

Abstract

We propose and experimentally demonstrate a scheme of a coherent Brillouin time domain analysis (BOTDA) system without any trace averaging. Assisted by a commercial integrated coherent receiver with a local oscillator generated through single sideband modulation from the same laser source, the Brillouin signals carried on a stable intermediate frequency (IF) are extracted by electrical/digital filters and then recovered to baseband by digital signal processing. This increases the signal-to-noise ratio and avoids the need of trace averaging and enables real-time signal acquisition. To eliminate the Brillouin gain fluctuation, two adjacent Brillouin time-domain traces stimulated by two sequential orthogonal pump pulses are recovered after the IF signals are detected in a real-time manner. Based on this configuration, a spatial resolution of 4 m and Brillouin frequency shift uncertainty of 1.473 MHz are realized in distributed temperature sensing over 40.63 km range. With the nonlocal means algorithm and distributed Raman amplification integrated into the system, the BFS uncertainty is enhanced to 0.843 MHz and better spatial resolution of 2 m over the same sensing fiber is achieved.