Coherence-length-gated distributed optical fiber sensing based on microwave-photonic interferometry

Area of Science:

• Photonics
• Optical Sensing
• Fiber Optics

Background:

• Distributed sensing requires precise measurement of physical parameters along optical fibers.
• Existing methods face challenges in resolution and accuracy for strain measurements.
• Coherent microwave-photonics interferometry (CMPI) offers a new approach for enhanced sensing capabilities.

Purpose of the Study:

• To introduce and demonstrate a novel optical fiber distributed sensing concept using CMPI.
• To investigate the strain measurement resolution achievable with cascaded fiber Fabry-Perot interferometers (FPIs).
• To analyze the trade-offs between sensitivity and dynamic range in the proposed sensing system.

Main Methods:

• Utilizing a microwave modulated coherent light source to interrogate cascaded interferometers.
• Employing microwave frequency scanning to obtain a complex microwave spectrum.
• Applying complex Fourier transform to convert spectral data into time-domain signals for location-specific measurements.
• Fabricating cascaded FPIs using femtosecond laser micromachining.

Main Results:

• Demonstrated a strain measurement resolution better than 0.6 µε with a 1.5 cm FPI cavity length.
• Indicated potential for nε-level strain resolution by increasing FPI cavity length to over 1m.
• Analyzed the sensitivity-versus-dynamic range trade-off.
• Implemented an optical power reference using a single reflector to compensate for power instability.

Conclusions:

• The CMPI concept provides a viable and high-resolution method for distributed optical fiber sensing.
• Femtosecond laser-fabricated FPIs are effective interrogation elements for this sensing technique.
• The system shows promise for advanced applications requiring precise distributed strain monitoring.