Abstract
Short-Time Fourier Transform-Brillouin Optical Time-Domain Reflectometry (STFT-BOTDR) implements STFT over the full frequency spectrum to measure the distributed temperature and strain along the optic fiber, providing new research advances in dynamic distributed sensing. The spatial and frequency resolution of the dynamic sensing are limited by the Signal to Noise Ratio (SNR) and the Time-Frequency (T-F) localization of the input pulse shape.T-Flocalization is fundamentally important for the communication system, which suppresses interchannel interference (ICI) and intersymbol interference (ISI) to improve the transmission quality in multicarrier modulation (MCM). This paper demonstrates that theT-Flocalized input pulse shape can enhance the SNR and the spatial and frequency resolution in STFT-BOTDR. Simulation and experiments ofT-Flocalized different pulses shapes are conducted to compare the limitation of the system resolution. The result indicates that rectangular pulse should be selected to optimize the spatial resolution and Lorentzian pulse could be chosen to optimize the frequency resolution, while Gaussian shape pulse can be used in general applications for its balanced performance in both spatial and frequency resolution. Meanwhile,T-Flocalization is proved to be useful in the pulse shape selection for system resolution optimization.
Highlights
Dynamic strain measurement in distributed fiber optic sensing (DFOS) is essential for structural health monitoring (SHM) of the strain changes induced by aging material and seismic or man-made activities [1]
This paper demonstrates the importance for T-F localized input pulses to improve the Signal to Noise Ratio (SNR) of the Brillouin scattering signal, which leads to a narrower frequency bandwidth and an efficient pulse length to enhance the spatial and frequency resolution
In branch A, after passing a coupler, a part of the continuous light was modulated by an electrooptic modulator (EOM) with a 20 μs period and 50 ns pulse width signal generated by an Agilent 33600 arbitrary waveform generator (AWG)
Summary
Dynamic strain measurement in distributed fiber optic sensing (DFOS) is essential for structural health monitoring (SHM) of the strain changes induced by aging material and seismic or man-made activities [1]. Among the different DFOS systems, BOTDR launches pulsed light into one end of the fiber and detects the scattered spontaneous Brillouin signal at the same end [3, 4]. This paper demonstrates the importance for T-F localized input pulses to improve the SNR of the Brillouin scattering signal, which leads to a narrower frequency bandwidth and an efficient pulse length to enhance the spatial and frequency resolution. The pulse localization model, based on the physical description of BOTDR and time-frequency analysis of the pulses with the definition of TEW and FEL, has been built to investigate the performance of various pulse shapes, such as Lorentzian, rectangular, Gaussian, and triangular pulses, which are compared theoretically and experimentally according to their performances in the timedomain (spatial resolution) and the frequency-domain (pulse modulated Brillouin spectrum linewidth). T-F localization should be considered in general to evaluate the power, averaging number settings in DFOS development
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