Phase-Sensitive Optical Time-Domain Reflectometric System Based on Optical Synchronous Heterodyne

Aiming at the frequency drift of the laser and acousto-optic modulator in the traditional phase-sensitive optical time domain reflectometric (Φ-OTDR), a Φ-OTDR system based on optical synchronous heterodyne is proposed and demonstrated. The method of optical synchronization heterodyne is used to follow the beat frequency signal to eliminate the interference of frequency shift fluctuation in the phase information and the ubiquitous residual frequency before the optical path heterodyne. The signal-to-noise ratio (SNR) is more than 31.4 dB on a 10 km sensing optical fiber with a probe light pulses of 5 kHz repetition rate and 100 ns pulse width. The error between the demodulated signal amplitude and the actual signal amplitude is less than 1%, and the maximum harmonic amplitude is about 28.3 dB less than the actual signal amplitude. While improving the real-time performance, this research greatly improves the demodulation characteristics of the system, which is of great significance to the advancement of the practical process of the phase-sensitive optical time domain reflectometric system.