High-Precision and Large-Scale Identical Ultra-Weak FBG Sensors With OFDR

To achieve the large-multiplexing capability, identical weak fiber Bragg grating (WFBG) sensors typically adopt a short grating length to reduce the reflectivity. However, the corresponding broadband reflection spectrum compromises the attainable wavelength-shift measurement precision. In this work, to overcome this limitation, an array of identical weak FBGs with extended grating lengths is employed, which facilitates the narrower bandwidth and improved spectral precision. Weaker refractive-index modulation is required in the FBGs with a longer grating length, which makes it harder to locate the individual FBG. A correlation-based algorithm is proposed for accurate WFBG localization, while the reflection signal is extracted using a window length precisely matched to the physical grating length for the suppression of the system noise. Experimental results using an array with 4000 identical WFBGs, each WFBG with a 10 mm grating length, demonstrate the strain measurement precision of 3.92 με. The proposed approach effectively balances the requirements for the high sensor density and high measurement precision, enabling practical applications for real-time structural health monitoring and high-precision sensing systems.