High-SNR Φ-OTDR based on the 1440-level diversity merging technique

In this paper, a high signal-to-noise ratio (SNR) phase-sensitive optical time-domain reflectometer (Φ-OTDR) system based on the 1440-level diversity merging technique is proposed, aiming to solve the problem of SNR degradation in long-distance detection of the conventional Φ-OTDR. The 1440-level diversity merging scheme is realized by combining 4-level wavelength diversity, 3-level frequency diversity, 30-level space diversity, and 4-level time diversity techniques, which can significantly improve the detection capability and the system SNR without triggering the nonlinear effect of the fiber. The experimental results show that the system achieves the fading suppression over the whole-line 20 km fiber, the mean noise floor reaches -77.4 dB (re 1rad²/Hz)@500 Hz, and the SNR is improved by 28.5 dB compared with the conventional Φ-OTDR system, and the external disturbance signal is successfully reconstructed. Furthermore, the system is verified to achieve the long-distance detection up to 70 km, which noise performance rivals that of commercial long-distance system. This study provides effective technical support for the application of Φ-OTDR in long-distance and high-SNR detection scenarios such as geophysical prospecting and marine acoustics.