Distributed optical fiber sensing in coherent Φ-OTDR with a broadband chirped-pulse conversion algorithm

Area of Science:

• Optoelectronics
• Fiber Optic Sensing
• Signal Processing

Background:

• Coherent phase-sensitive optical time domain reflectometry (Φ-OTDR) is crucial for distributed fiber optic sensing.
• Chirped-pulse Φ-OTDR (CP-ΦOTDR) systems enable quantitative measurement of environmental perturbations like strain and temperature.
• Existing methods may have limitations in measurable perturbation range.

Purpose of the Study:

• To introduce a novel broadband chirped-pulse conversion algorithm (BCPCA) for enhancing Φ-OTDR systems.
• To enable the conversion of finite-step scanning probe pulses into equivalent broadband chirped probe pulses.
• To expand the measurable perturbation range in distributed fiber optic sensing.

Main Methods:

• A broadband chirped-pulse conversion algorithm (BCPCA) was proposed.
• The algorithm convolved a chirp factor onto the received signal in coherent Φ-OTDR.
• Combined with Rayleigh interference pattern (RIP) demodulation in CP-ΦOTDR for quantitative measurements.

Main Results:

• A proof-of-concept experiment demonstrated high-performance distributed strain measurement over a 10 km fiber.
• The system achieved a frequency response of 5 kHz, limited only by fiber length.
• A strain resolution of 8.04 με/√Hz was obtained.

Conclusions:

• The proposed digital method for generating equivalent broadband chirped pulses effectively supplements CP-ΦOTDR.
• This technique expands the measurable perturbation range by increasing the bandwidth of the chirped pulse.
• The BCPCA offers a flexible and powerful approach for advanced fiber optic sensing applications.