High-Resolution FBG Strain Sensing With Dual-Comb Interrogation and Optimized Signal Processing

In this work, we present a high-resolution strain sensing system based on Dual Optical Frequency Comb (DOFC) interrogation of Fiber Bragg Gratings (FBGs), employing optimized signal processing methods for both reflection and transmission spectra. Femtosecond (fs) written FBGs with non-uniform profiles with bandwidths of ∼0.5 nm were interrogated using a mutually coherent DOFC generated by externally injected gain-switched lasers (EI-GSL). Different algorithms were used to process the DOFC signal to extract the FBG frequency shifts caused by the various strain increments. Using these approaches, we could detect strains with a sub-μϵ resolution (0.32 μϵ), sensitivities ranging from 0.7 - 1 pm/μϵ, and a dynamic range of 422 μϵ. These methods increased low-strain sensitivity typical of DOFC interrogation systems, enabling precise monitoring of standard off-the-shelf fs-written FBGs. The DOFC system showed enhanced linearity (R2 ∼0.98) and Figure of Merit (FoM - 2.58/μϵ) at lower strains than a standard commercial interrogator (R2 ∼0.82 and FoM – 0.88/μϵ). Our findings highlight the potential of the DOFC-FBG interrogation as a powerful tool for real-time high-resolution sensing applications, ranging from structural health monitoring to biomedical diagnostics.