Fading suppression in the Ф-OTDR system based on a phase-modulated optical frequency comb

Area of Science:

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

Background:

• Phase-sensitive optical time domain reflectometry (Ф-OTDR) is susceptible to fading effects.
• Fading in Ф-OTDR arises from variations in Rayleigh backscattering (RBS) intensity distributions with probe light frequency.
• Existing methods for fading suppression have limitations in modulation bandwidth and frequency flexibility.

Purpose of the Study:

• To propose and experimentally validate a novel method for suppressing fading effects in Ф-OTDR.
• To leverage phase-modulated optical frequency combs for enhanced fading mitigation.
• To demonstrate a significant reduction in fading probability density compared to conventional techniques.

Main Methods:

• Generation of a continuous light in the form of a phase-modulated optical frequency comb.
• Modulation of the frequency comb into pulsed probe light for injection into the sensing fiber.
• Extraction and processing of phase information using an amplitude evaluation method to eliminate distortion.
• Utilizing frequency division multiplexing based on differing RBS intensity distributions for various frequencies.

Main Results:

• The proposed method dramatically reduced fading probability density from 5.49%-9.83% to 0.08% using an equal-amplitude optical frequency comb with seven frequency components.
• The method offers a larger modulation bandwidth and more flexible frequency combination schemes than conventional systems.
• The response bandwidth of the system is preserved, and phase delay is precisely controlled for effective fading suppression.

Conclusions:

• The phase-modulated optical frequency comb method is a highly effective technique for suppressing fading in Ф-OTDR systems.
• This approach provides superior performance compared to conventional methods, particularly in terms of fading reduction and operational flexibility.
• The technique holds promise for improving the reliability and accuracy of Ф-OTDR sensing applications.