Pulse-Width Multiplexing ϕ-OTDR for Nuisance-Alarm Rate Reduction.

Area of Science:

• Photonics and Optical Sensing
• Signal Processing
• Security Systems

Background:

• Phase-sensitive optical time-domain reflectometry (ϕ-OTDR) is crucial for detecting physical disturbances.
• High nuisance-alarm rates can limit the practical application of ϕ-OTDR systems, especially in perimeter protection.
• Optimizing signal-to-noise ratio (SNR) is key to improving the reliability of optical sensing.

Purpose of the Study:

• To develop and validate a novel pulse-width multiplexing method for reducing nuisance alarms in ϕ-OTDR.
• To investigate the impact of varying pulse widths on the SNR of ϕ-OTDR signals.
• To enhance the performance of ϕ-OTDR systems for reliable perimeter security.

Main Methods:

• A pulse-width multiplexing technique was implemented, injecting light pulses of varying widths into a sensing fiber.
• Data from different pulse widths were treated as outputs from multiple sensors and processed using a multisensor data fusion algorithm.
• A feature-layer algorithm based on Dempster-Shafer evidential theory utilized SNR as a key feature.

Main Results:

• Laboratory tests demonstrated a clear correlation between pulse width and the SNR of ϕ-OTDR data.
• A four-pulse-width multiplexing ϕ-OTDR system was constructed and tested.
• The proposed method achieved a significant reduction in the nuisance-alarm rate by approximately 70%.

Conclusions:

• The pulse-width multiplexing method effectively reduces nuisance alarms in ϕ-OTDR systems.
• The technique offers a simple yet powerful approach to enhance the reliability of optical sensing for perimeter protection.
• This method shows great potential for practical deployment in security applications.