50-km-Long distributed vibration fiber sensor based on phase-sensitive OTDR using coherent detection

We have demonstrated a long distance distributed vibration fiber-optic sensing system based on phase-sensitive optical time-domain reflectometer (φ-OTDR). Without any additional components, vibration detection utilizing heterodyne detection and digital coherent detection is successfully demonstrated over a 50-km-long optical fiber and the external disturbance signal simulated by PZT is well restored with signal-to-noise ratio (SNR) of ∼32.8 dB through phase difference method. For the first time, the distributed vibration sensing based on phase-extraction is realized in optical fiber over such a long distance. This measuring technique is ideal for applications in fields of oil and gas pipeline monitoring, national borders and can be further optimized to realize the longer sensing distance.