High-spatial-resolution quasi-distributed acoustic sensing with phase noise suppression based on φ-OFDR

A quasi-distributed acoustic sensor with high-spatial-resolution based on phase-sensitive optical frequency domain reflectometry (φ-OFDR) was demonstrated. The source of noise that affects the accuracy of phase demodulation was analyzed. Two low noise linear frequency sweeps (LFSs) with different sweep ranges obtained by injection-locking method were used to achieve high-spatial-resolution and long-distance sensing. The phase noise caused by laser, intensity and fading noises was effectively suppressed by further combining a femtosecond-laser-inscribed weak reflector array (WRA) and a phase index method (PIM). Vibration signals located a long distance of over 1 km were successfully demodulated with a spatial resolution of 2 cm through the use of 12 GHz LFS and a WRA with an interval of 2 cm. In addition, the 5 mm ultra-high spatial resolution capability of the system had been demonstrated through the use of 52 GHz LFS and a WRA with an interval of 5 mm.