High-accuracy dual-slope-assisted chaotic Brillouin fiber dynamic strain measurement

Nowadays, distributed dynamic sensing technology based on stimulated Brillouin scattering has been widely employed in civil structure health monitoring, disaster warning, national defense, etc. In this paper, we propose and experimentally demonstrate a novel Brillouin optical correlation-domain analysis based-on gain-switch modulation and dual-slope assisted method for achieving high-accuracy large-range dynamic strain measurement. In single-slope assisted chaotic Brillouin sensing, the measurement accuracy of dynamic strain is deteriorated by the inherent characteristics of time delay signature and power stochastic fluctuations. First, the mechanism behind the acoustic field deterioration and principle of background noise suppression are analyzed theoretically. Then, the chaotic continuous pump light is modulated into pulsed light with a higher extinct ratio of 48.6 dB, where the electro-optical modulator is replaced by a gain switch. And thus, the noise peaks, induced by the secondary peaks and irregular basal oscillations of chaotic auto-correlation curve, are greatly restrained. Comparing with the electro-optical modulator-based system, the signal-to-noise ratio of stimulated Brillouin acoustic field is increased by 3.31 dB in simulation and the signal-to-background ratio of Brillouin gain spectrum is doubled in experiment. Consequently, the measurement accuracy of dynamic strain is improved from ± 40.2 με to ± 23.1 με and the relative error decreases from ± 5.0% to ± 2.9% in single-slope assisted system based-on gain switch modulation. In addition, a dual-slope assisted method is inspired to eliminate the detrimental effect caused by the intrinsic power fluctuations of chaotic laser. A verification experiment is pre-conducted that the dynamic strain could be correctly interrogated although a wide range pump power variation has been manually applied. The measurement accuracy is ultimately enhanced to ± 8.1 με and the relative error is ± 1% correspondingly, implying a higher stability. The dynamic range of this proposed system is retained at 800 με, which is approximately 5 times as large as the dynamic range of the traditional dual-slope assisted configurations. The 4-cm spatial resolution along 30-m FUT is also investigated and consistent with the result obtained previously. A larger measurement range and a higher vibration frequency would be further explored by using the multi-slope assisted method and piezoelectric ceramic oscillator respectively. The superior slope-assisted chaotic Brillouin optical correlation-domain analysis will provide a new solution for the accurate positioning and real-time monitoring of dynamic parameters in modern industry.