Compensating for influence of laser-frequency-drift in phase-sensitive OTDR with twice differential method

Area of Science:

• Optoelectronics and Photonics
• Fiber Optic Sensing Technologies
• Signal Processing for Measurement Systems

Background:

• Laser frequency drift is a critical limitation in phase-sensitive optical time domain reflectometry (Φ-OTDR), causing signal fluctuations.
• These fluctuations severely restrict the measurement capabilities of Φ-OTDR systems, particularly for low-frequency signals.
• Accurate detection of low-frequency phenomena is essential in various industrial and scientific fields.

Purpose of the Study:

• To develop and validate a novel method for compensating laser frequency drift in Φ-OTDR systems.
• To improve the sensitivity and low-frequency response of Φ-OTDR measurements.
• To expand the application scope of Φ-OTDR in demanding measurement scenarios.

Main Methods:

• A twice differential method was proposed to mitigate the effects of laser frequency drift.
• The method utilizes a differential signal between two points on the sensing fiber as a reference.
• This reference signal is subtracted from the main signal to isolate the true measurement.

Main Results:

• Experimental results demonstrated a reduction in signal fluctuation caused by laser frequency drift by over 95%.
• A 0.1 Hz vibration on a 6 km fiber was successfully detected with 10 m spatial resolution.
• The system achieved a sensitivity of 5.9 nε and accurately measured fiber stretching by a stepper motor.

Conclusions:

• The twice differential method effectively compensates for laser frequency drift in Φ-OTDR.
• This technique significantly enhances the system's ability to detect low-frequency vibrations with high sensitivity.
• The proposed method broadens the applicability of Φ-OTDR for high-precision, low-frequency sensing applications.