Wavelength-scanning coherent OTDR for dynamic high strain resolution sensing

Area of Science:

• Photonics and Optical Sensing
• Materials Science and Engineering
• Geophysics

Background:

• Distributed vibration sensing using optical fibers offers broad applications in security and seismic monitoring.
• Existing phase demodulation techniques often struggle to determine the algebraic sign of strain changes.

Purpose of the Study:

• To demonstrate a simple and robust approach for dynamic strain measurement.
• To enable accurate strain change sign retrieval for structural health monitoring and modal analysis.

Main Methods:

• Utilizing wavelength-scanning coherent optical time domain reflectometry (C-OTDR).
• Employing laser current modulation and Rayleigh backscatter shift correlation for signal processing.

Main Results:

• Achieved a linear strain response down to 47.5 picoepsilon (pε).
• Demonstrated a strain noise level of 100 pε/√Hz at kHz repetition rates.
• Successfully retrieved the algebraic sign of strain changes, a key advantage over existing methods.

Conclusions:

• The developed C-OTDR method offers a cost-effective, high-resolution solution for structural vibration analysis.
• This technique is well-suited for geophysical applications requiring precise dynamic strain measurements.
• The ability to determine strain change direction enhances its utility in structural health monitoring.