Golay Coding Φ-OTDR With Distributed Frequency-Drift Compensation

The performance of optical-pulse-coding (OPC) phase-sensitive optical time-domain reflectometry ( $\boldsymbol {\Phi }$ -OTDR) has been improved significantly in recent years. However, laser frequency drift is still a crucial issue, as it reduces the peak to side-lobe ratio (PSR) in Golay coding $\boldsymbol {\Phi }$ -OTDR. In this paper, a novel and simple distributed frequency-drift compensation method is proposed. As the phase accumulations of the reference fiber and the sensing fiber are consistent through theoretical analysis and experimental verification, the frequency drift can be compensated by injecting the modulated Golay coding pulses into two fibers at the same time, and subtracting the phase drift of the sensing fiber and the reference fiber. In order to verify the distributed compensation effect, a two-point perturbation measurement experiment is carried out in 9.7 km sensing range. As a result, the far-end signal-to-noise ratio (SNR) is enhanced and the demodulation perturbation SNRs are increased by 2.8 dB and 18.9 dB separately compared with the case without frequency drift compensation. Furthermore, this scheme can also be used in other complex coding systems, providing more possibilities for system designs.