FBG bandwidth impact on dual-comb interrogation for high fidelity strain sensing

Dual Optical Frequency Comb (DOFC) interrogation has emerged as a promising approach for high-resolution Fiber Bragg Grating (FBG) sensing, yet its robustness across gratings of differing spectral bandwidths remains insufficiently explored. Two key gaps persist: first, the lack of systematic evaluation of a single DOFC platform applied consistently to both narrow- and broadband FBGs; and second, the absence of a unified signal-processing strategy that maintains accuracy under variable spectral sampling conditions. Here, we address these challenges by developing a bandwidth-adaptive DOFC interrogation framework that unifies optical and algorithmic optimization across diverse FBG bandwidths. To the best of our knowledge, this is the first systematic assessment of a mutually coherent dual-comb system applied to multiple FBG bandwidth regimes within a single interrogation platform. The system employs Externally-Injected Gain-Switched Lasers (EI-GSLs) to generate two mutually coherent combs and a custom ADC-FFT module enabling real-time spectral acquisition. A spectral-envelopeassisted inverted Gaussian fitting (IGF) algorithm is implemented to reconstruct sparsely sampled FBG notches and extract precise Bragg wavelength shifts. Experiments on FBGs with 0.1 nm and 0.3 nm bandwidths demonstrate consistent high-fidelity strain tracking, achieving effective detection limits of ~ 375–380 nε, dynamic ranges up to 1300 µε, and linearity of R2 ≈ 0.98. Compared with a state-of-the-art swept-laser interrogator, which fails to resolve at the finest nano-strain increments, the proposed DOFC-IGF approach delivers superior stability and resolution across all tested bandwidths. These findings establish a practical framework for bandwidth-adaptive DOFC interrogation, enabling scalable and cost-effective deployment of mixed-bandwidth FBG arrays in high-resolution sensing networks.