Remote phase-sensitive optical frequency domain reflectometry.

Area of Science:

• Optics and Photonics
• Fiber Optic Sensing
• Metrology

Background:

• Traditional phase-sensitive optical frequency domain reflectometry (φ-OFDR) systems face limitations due to laser phase noise and transmission distance in long-haul fiber sensing.
• Accurate remote sensing in ultra-long fibers is crucial for applications like geophysical exploration and structural health monitoring.

Purpose of the Study:

• To develop a common-path, self-referenced φ-OFDR system capable of high-precision sensing at a remote location on an ultra-long fiber.
• To overcome the limitations imposed by lead fiber length and laser phase noise on sensing performance.
• To enhance system robustness against polarization fading.

Main Methods:

• A common-path, self-referenced φ-OFDR architecture utilizing the fiber's far-end reflection as the local oscillator.
• Implementation of a novel single-ended polarization diversity receiving scheme to mitigate polarization fading.
• Experimental validation using a 75-km single-mode fiber with a 1-m sensing window containing femtosecond laser-inscribed weak reflectors.

Main Results:

• Successful compensation for laser phase noise accumulated over the 75-km lead fiber.
• Demonstration of a 2 cm spatial resolution within the remote sensing window.
• Achieved vibration frequency response up to 2 kHz in the remote sensing window.

Conclusions:

• The proposed system provides a practical and cost-effective solution for localized, high-precision quasi-distributed sensing over ultra-long lead fibers.
• This methodology is suitable for challenging environments such as deep-well geophysical exploration and structural health monitoring.
• The system effectively decouples sensing performance from transmission distance constraints.