Polarization discrimination in a phase-sensitive optical time-domain reflectometer intrusion-sensor system.

Area of Science:

• Optoelectronics
• Fiber Optic Sensing
• Security Systems

Background:

• Traditional perimeter security systems often have limitations in detection range and environmental adaptability.
• Phase-sensitive optical time-domain reflectometry (phi-OTDR) offers a promising method for distributed fiber optic sensing.
• Polarization discrimination can enhance the sensitivity and accuracy of phi-OTDR systems.

Purpose of the Study:

• To develop and evaluate a distributed intruder detection and location system using a polarization-discriminating phi-OTDR.
• To assess the performance of the system in detecting foot traffic at a distance from a buried fiber optic cable.
• To demonstrate the feasibility of using standard telecommunications fiber for perimeter security.

Main Methods:

• A single-mode telecommunications fiber, housed in a 3 mm cable, was buried in a trench within clay soil.
• Light pulses from a narrow-linewidth, low-frequency-drift Er fiber Fabry-Perot laser were injected into the fiber.
• Orthogonal polarizations of backscattered light were monitored using separate receivers, with phase changes detected by trace subtraction.

Main Results:

• The system successfully detected intruders on foot up to 4.5 meters away from the buried sensing cable.
• Consistent detection was achieved over a monitored perimeter length of 12 km.
• The use of polarization discrimination in the phi-OTDR system proved effective for intruder detection.

Conclusions:

• The described polarization-discriminating phi-OTDR system provides a robust and effective solution for distributed intruder detection.
• The system demonstrates high sensitivity, capable of detecting subtle disturbances caused by human movement at a significant distance from the sensing fiber.
• This technology holds potential for enhancing perimeter security in various environments.