Brillouin Frequency Estimation in Distributed Brillouin Optical Fiber Sensors Based on Instantaneous Frequency

Short-time Fourier transform (STFT) algorithm with Lorentzian fitting is popular in distributed Brillouin optical fiber sensors to acquire Brillouin frequency. However, STFT often suffers from the tradeoff between Brillouin frequency measurement resolution and computation complexity. To lower the complexity of Brillouin frequency analysis and speedup measurement, a novel method based on instantaneous frequency (IF) analysis is proposed. The instantaneous Brillouin frequency can be obtained through the instantaneous phase change between two adjacent samples in the time domain. The requirement on the spectral resolution is, therefore, greatly relaxed, significantly reducing computation complexity and lowering measurement time cost. A Brillouin optical time-domain reflectometry (BOTDR) scheme is demonstrated with a spatial resolution of 1.2 m over a 5-km sensing fiber. For an average count of 4096 over measurements, experiments show that the IF algorithm can reduce computation complexity by 122 times at a standard deviation (STD) of 0.5065 MHz for BFS estimation which is comparable to the STD obtained through STFT in conjunction with Lorentzian fitting.