Objective Chaotic Raman distributed fiber optic sensing technology replaces the traditional pulsed laser as the detection signal with chaotic laser, breaking the technical bottleneck of the traditional Raman distributed fiber optic sensing system where the spatial resolution is limited by the pulse width, which can be applied in the field of safety monitoring such as transportation infrastructure, pipeline leakage, coal mine and so on. Since the incoming power of chaotic single pulse is limited by the nonlinear scattering threshold in the fiber can’t be infinitely improved, limiting the coupled optical flux of the system, resulting in the system signal-to-noise ratio decreases with the increase of the sensing distance, thus failing to achieve a longer distance of high spatial resolution temperature sensing. Therefore, this paper proposes a Raman distributed fiber optic sensing scheme with chaotic pulse cluster correlation compression, which suppresses the correlation between the noise and the sensing signal and the nonlinear effect in the optical fiber, improves the system signal-to-noise ratio, and realizes the high-performance Raman distributed fiber optic sensing technology.

Methods A simulation system of chaotic pulse-cluster Raman distributed fiber-optic sensing is established (Fig.1), the position and length information of the temperature mutation region is obtained by the time-delayed self-differential reconstruction and correlation compression scheme (Fig.3), and the theoretical spatial resolution of the chaotic pulse-cluster Raman sensing system is determined (Fig.5), and the temperature demodulation scheme is utilized to obtain the temperature information of the temperature mutation region and analyze the temperature sensitivity of the system (Fig.6).

Results and Discussions The effect of the number of pulses on the sensing performance of the Raman distributed fiber optic sensing system with chaotic pulse clusters is investigated by numerical simulation experiments. With the increase of the number of pulses in the chaotic pulse cluster, the optical flux that can be coupled to the system increases, and the dynamic range of the system gradually improves, and the dynamic range of the sensing system is 5.35 times higher than that of the chaotic single-pulse system when the number of pulses in the pulse cluster is 5 (Fig.2); the system can achieve a high spatial resolution of 10 cm at different sensing distances (Fig.3), and as the number of pulses in the chaotic pulse cluster increases, the positive correlation obtained by the correlation compression scheme increases the spatial resolution of the system. With the increase of the number of pulses in the chaotic pulse cluster, the peak value of the positive correlation peak obtained by the correlation compression scheme also shows a certain nonlinear increase (Fig.4); the theoretical spatial resolution of the Raman distributed fiber optic sensing system with chaotic pulse clusters is investigated, and the theoretical spatial resolution does not change with the change of chaotic pulse clusters (Fig.5); the analysis reveals that with the increase of the number of pulses in the chaotic pulse clusters, the system's sensitivity to the temperature increases, and the optimal value is reached at the time when the number of pulses is 5 (Fig.6).

Conclusions A Raman distributed fiber optic sensing scheme with chaotic pulse cluster correlation compression is designed to achieve high spatial resolution, long sensing distance, and strong temperature sensitivity, and it is proved that the chaotic pulse cluster correlation compression Raman distributed fiber optic sensing scheme can greatly improve the dynamic range, signal-to-noise ratio, and temperature sensitivity under the premise of guaranteeing the high spatial resolution of the system, which provides a new scheme for the high-performance Raman distributed fiber optic sensing system. It provides a new solution for high-performance Raman distributed fiber optic sensing system.