Frequency-Multiplexed Barker-Coded Φ-OTDR for High-Speed Distributed Acoustic Sensing

Abstract

Pulse pre-coding Φ-OTDR has been widely employed to enhance the signal-to-noise ratio (SNR) of recovery perturbation while with the compromising of interrogation frequency. In this paper, a novel frequency-multiplexed Barker-coded Φ-OTDR is proposed to improve interrogation speed and phase-demodulation fidelity with reduced system complexity. In this scheme, dual acousto-optic modulators (AOM) with distinct radio-frequency shifts driven by unipolar Barker sequences are utilized to achieve parallel interrogation, enabling with heterodyne coherent detection and eliminating the need for IQ modulation. Compared with conventional Golay complementary coding, the proposed scheme achieves a fourfold increase in interrogation repetition rate at the same clock frequency. Broadband linear-chirp simulations from 10 Hz to 5 kHz confirm an extended usable dynamic frequency range, with the Barker-coded response exhibiting improved phase fidelity and producing sharper, more uniform short-time Fourier transform (STFT) ridges than the Golay-coded benchmark. The decoding performance is subsequently evaluated using the phase-recovery SNR as the primary metric. For a 1 kHz sinusoidal phase perturbation with a peak excursion of approximately 1 rad over a 2 km fiber, averaging over repeated simulation runs yields an SNR enhancement of about 4.1 dB relative to the Golay-coded case. Moreover, a parametric study over different Barker code lengths shows that increasing the code length improves phase stability and results in a larger recovered phase excursion at the perturbation location, confirming the role of correlation gain in enhancing phase-recovery fidelity. In a 10 km fiber scenario, repeated simulation results further indicate an approximately 4 dB SNR improvement of the Barker-coded scheme over single-pulse interrogation for a 1 kHz sinusoidal phase perturbation. The proposed approach is fully compatible with existing fading-suppression and noise-reduction techniques, making it well suited for high-speed and large-scale Φ-OTDR applications.