High Spatial-Resolved φ-OTDR System Based on Differential Pulse Width Sequence Technique

The spatial-resolved capacity of a phase-sensitive optical time-domain reflectometry (
$\varphi $
-OTDR) is limited by the optical pulse width, which increases the localization errors when measuring vibrations with range shorter than that determined by the pulse width. To overcome this problem, a high spatial-resolved
$\varphi $
-OTDR with a differential pulse width sequence is proposed. The centimeter spatial resolution sensing can be realized by using meter equivalent pulses. This scheme utilizes the time-domain waveform subtraction obtained from the same pulse repetition rate and different pulse widths to form the differential vibration information at each fiber location. First, we provide a comprehensive treatment to prove that the proposed scheme can improve the spatial-resolved capacity of the
$\varphi $
-OTDR system. The spatial resolution of 1.08m for 60/50ns pulse sequence is realized with a 30cm vibration source. Second, in a further proof-of-concept experiment, the spatial resolution is achieved up to 0.55m with a 55/50ns pulse sequence. It is demonstrated that the ability of spatial-resolved is enhanced greatly without any hardware modifications, compared to that required in the conventional method. This method holds great significance in accurately locating vibration signals within the narrow range of the distributed vibration sensor.