Direct detection based φOTDR using the Kramers-Kronig receiver

Area of Science:

• Optoelectronics
• Optical Sensing
• Signal Processing

Background:

• Phase-sensitive optical time domain reflectometry (phi-OTDR) is crucial for distributed sensing.
• Direct detection methods in phi-OTDR often face limitations in phase retrieval accuracy.
• Accurate phase retrieval is essential for high-resolution sensing applications.

Purpose of the Study:

• To implement and validate a Kramers-Kronig receiver for phase-sensitive optical time domain reflectometry.
• To encode phase information into optical intensity using an imbalanced Mach-Zehnder interferometer.
• To retrieve the optical phase by combining direct detection with Hilbert transform-based quadrature component estimation.

Main Methods:

• Utilizing an imbalanced Mach-Zehnder interferometer with a 2x2 coupler to encode phase into intensity.
• Employing direct detection to obtain the in-phase component of the optical signal.
• Applying a Kramers-Kronig receiver, which uses Hilbert transform to derive the quadrature component.
• Performing IQ demodulation for optical phase retrieval.

Main Results:

• Successfully demonstrated the functionality of the Kramers-Kronig receiver in a phase-sensitive OTDR system.
• Validated the theoretical analysis of the obtained phase variance.
• Achieved accurate optical phase retrieval through IQ demodulation.

Conclusions:

• The Kramers-Kronig receiver is effectively applied to phase-sensitive OTDR based on direct detection.
• The proposed method enables robust optical phase retrieval by combining direct detection with Hilbert transform.
• The experimental results confirm the theoretical predictions and the sensor's reliable performance.