Distributed dynamic strain sensing in coherent Φ-OTDR with a pulse conversion algorithm

Area of Science:

• Photonics and Optical Sensing
• Fiber Optic Sensing Technology
• Signal Processing in Optics

Background:

• Coherent phase-sensitive optical time-domain reflectometry (Φ-OTDR) is crucial for distributed strain sensing.
• Traditional Φ-OTDR systems often require complex chirp modulation hardware for dynamic strain quantification.
• Rayleigh interference pattern (RIP) demodulation is a key technique for strain measurement in Φ-OTDR.

Purpose of the Study:

• To propose a novel chirped-pulse conversion algorithm (CPCA) for Φ-OTDR systems.
• To enable dynamic strain quantification in traditional coherent Φ-OTDR without requiring chirp modulation.
• To enhance the capabilities of existing Φ-OTDR infrastructure through digital signal processing.

Main Methods:

• A chirped-pulse conversion algorithm (CPCA) is developed to digitally generate an equivalent chirped probe pulse.
• The algorithm convolves a chirp factor onto the received signal in coherent Φ-OTDR.
• Rayleigh interference pattern (RIP) demodulation is applied to the processed signal.

Main Results:

• The CPCA successfully converts a normal probe pulse into an equivalent chirped probe pulse.
• The method allows for the quantification of dynamic strain using RIP demodulation in traditional coherent Φ-OTDR.
• The system achieves a spatial resolution of 4 m, a sensing range of 8 km, and a frequency response of 5 kHz.
• A strain resolution of 56 pε/√Hz is demonstrated.

Conclusions:

• The proposed CPCA offers a cost-effective and hardware-independent solution for dynamic strain sensing in Φ-OTDR.
• Digital generation of chirped pulses eliminates the need for complex and expensive modulation hardware.
• The technique significantly enhances the strain quantification capabilities of conventional coherent Φ-OTDR systems.