Fading-suppressed Φ-OTDR with high spatial-resolution based on a chirped electro-optic frequency comb.

Area of Science:

• Optoelectronics
• Fiber Optic Sensing
• Signal Processing

Background:

• Phase-sensitive optical time-domain reflectometer (φ-OTDR) systems are crucial for distributed acoustic sensing.
• Signal fading and limited spatial resolution hinder the performance of conventional φ-OTDR systems, especially for long-distance applications.

Purpose of the Study:

• To propose and demonstrate a fading-suppressed φ-OTDR system with high spatial resolution.
• To enhance the potential for long-distance distributed acoustic sensing applications.

Main Methods:

• A chirped electro-optic frequency comb (CEOFC) was generated using a dual-parallel Mach-Zehnder modulator and a phase modulator.
• Multiple parallel chirped probe channels were created for simultaneous wideband interrogation.
• Matched filtering and multi-channel Rayleigh trace combination were employed to suppress fading and preserve spatial resolution.

Main Results:

• The proposed CEOFC-based φ-OTDR achieved a spatial resolution of 50 cm over a 10.84-km sensing distance.
• The system demonstrated a 12.92 dB improvement in average normalized intensity signal-to-noise ratio (SNR).
• A 54% reduction in fading rate and a 22.36 dB enhancement in phase SNR were observed compared to conventional chirped-pulse φ-OTDR.

Conclusions:

• The CEOFC-based φ-OTDR system effectively suppresses fading and achieves high spatial resolution.
• The technology shows significant potential for robust, long-distance distributed acoustic sensing.
• Accurate recovery of remote vibration events with high fidelity was demonstrated.