Dynamic BOTDA Based on Spectrally Efficient Frequency-Division Multiplexing

The tradeoff between the spatial resolution and estimation accuracy of the Brillouin frequency shift (BFS) sets a technical hurdle for Brillouin optical time-domain analyzers (BOTDAs) based on orthogonal frequency division multiplexing (OFDM), due to orthogonality between the OFDM subcarriers. To solve this problem, a novel BOTDA using spectrally efficient frequency-division multiplexing (SEFDM) is proposed. A partial Zadoff-Chu sequence that generates a centralized pulse after inverse discrete Fourier transform (IDFT) is used. SEFDM signaling is done by discarding the sidelobe of the time domain pulse before being sent as the probe wave. As such, the symbol period is dramatically reduced compared with OFDM signals, leading to a much higher spatial resolution. Meanwhile, the subcarrier spacing of the SEFDM signals remains the same as that of the OFDM signals, which ensures a high estimation accuracy of the BFS if a small subcarrier spacing is used. We experimentally demonstrate a 3.1 m spatial resolution with a 1.294 MHz measurement accuracy in a SEFDM based BOTDA over a 10 km sensing range. Moreover, by using SEFDM signals with very short symbol periods as the probe wave, the time-consuming frequency sweeping process is eliminated, which makes dynamic sensing possible. We successfully demonstrate a dynamic measurement with a vibration frequency of 26 Hz. The introduction of SEFDM provides the desirable flexibility for BOTDAs to be used in both static and dynamic distributed fiber sensing areas with a large dynamic range.