Compensation of laser source frequency drift in Φ-OTDR system using inter-pulse difference

Area of Science:

• Optoelectronics
• Signal Processing
• Sensing Technology

Background:

• Distributed acoustic sensing (DAS) systems using coherent optical time-domain reflectometry (COTDR) offer advantages but suffer from phase drift caused by narrow-linewidth lasers.
• This frequency drift degrades detection performance, particularly in the sub-hertz frequency band.

Purpose of the Study:

• To propose and validate a novel method for eliminating phase drift in COTDR-based DAS systems.
• To enhance the detection performance of DAS systems in low-frequency bands.

Main Methods:

• Implementation of an inter-pulse differencing technique utilizing multiple pulses with different central frequencies.
• Exploitation of the spatial difference in beat signals to isolate vibration information and suppress frequency drift.

Main Results:

• Noise near zero frequency reduced by over 20 dB.
• Signal-to-noise ratio (SNR) for 1.0 Hz vibration signals improved by approximately 10 dB.
• Successful recovery of 0.1 Hz vibration signal waveforms with an SNR above 30 dB.

Conclusions:

• The proposed multi-frequency inter-pulse differencing method effectively eliminates phase drift in DAS systems.
• The technique significantly enhances low-frequency vibration detection reliability and performance.
• This method offers a reliable solution for improving DAS system accuracy in sensitive applications.