Large-scale strain sensor based on a distance reposition method by permanent scatters in an OFDR system

Area of Science:

• Optoelectronics
• Fiber Optics Sensing

Background:

• Large-scale strain in optical fibers causes significant distance referencing errors in spectrum-based optical frequency-domain reflectometry (OFDR).
• These errors lead to position segment mismatches and reduced measurement accuracy, limiting applications in structural health monitoring and other fields.

Purpose of the Study:

• To develop and demonstrate a novel method for correcting strain-induced spatial mismatches in OFDR systems.
• To enhance the accuracy and reliability of distributed large-scale strain sensing using OFDR.

Main Methods:

• A distance reposition method (DRM) was proposed, utilizing a femtosecond-laser-inscribed permanent scatter (PS) array as an in-fiber reference marker.
• The DRM realigns adjacent fiber segments to repositioned PS locations, enabling self-correction of strain-induced spatial mismatches during local demodulation.
• PSs were inscribed at 12 cm intervals in a 2.29 m region, providing approximately 25 dB enhancement with negligible insertion loss.

Main Results:

• The DRM effectively corrects spatial mismatches caused by large-scale strain in OFDR systems.
• Enhanced correlation and accuracy of Rayleigh backscattering spectra were achieved between reference and measurement signals.
• Distributed strain sensing up to 5000 µε over a 1 m segment with 6.4 mm spatial resolution was demonstrated.

Conclusions:

• The proposed DRM offers a simple and practical solution for real-time distributed large-scale strain sensing in OFDR systems.
• This method significantly improves the performance and accuracy of strain measurements in challenging environments with substantial strain variations.