Pulse Intensity Coding Phase-Sensitive OTDR With Mismatched Filtering

Optical pulse coding phase-sensitive optical time-domain reflectometry ( <tex-math notation="LaTeX">Φ</tex-math> -OTDR) sends a series of pulses into the sensing fiber to enhance signal-to-noise ratio (SNR). And the spatial resolution is determined by the subpulse duration. The current challenges in optical pulse coding <tex-math notation="LaTeX">Φ</tex-math> -OTDR include long measurement time, complex coding design, and intricate modulation process. In this paper, pulse intensity coding and mismatched filtering is introduced, which could reach the theoretical measurement time determined by the fiber length. Additionally, it also simplifies coding design and modulation process. In order to obtain satisfactory decoding results, the least-squares criterion is used to design the mismatched filter. Experimental result demonstrates a 6.6 dB improvement in the SNR of the demodulated signal using a 10-bit coding pulse.