Democratizing high-Q plasmonic optical fiber biosensing with low-resolution interrogation and Fourier demodulation

Gold-coated tilted fiber Bragg gratings have established themselves as powerful plasmonic biosensors, but their widespread deployment remains hindered by the need for costly, high-resolution interrogators and complex signal processing. Here, we demonstrate that tilted fiber Bragg gratings sensors can be effectively interrogated using a low-cost, coarsely resolved fiber Bragg grating interrogator with only 256 pixels spanning 45 nm, corresponding to a low resolution (~180 pm, 10 times coarser than standard interrogators). By applying a fast Fourier transform-based demodulation technique to the dense, comb-like cladding mode spectrum, we extract robust sensing information using only a narrow spectral window of a few tens of nanometers. This dramatically reduces hardware and computational requirements while preserving high sensitivity. We validate our approach in both refractometry and biosensing, targeting the clinically relevant biomarker Proteinase 3. Furthermore, we show that temperature cross-sensitivity can be compensated directly within this narrow spectral range by tracking a dedicated cladding mode resonance, eliminating the need to reference the Bragg mode. These advances pave the way for compact, cost-effective, and user-friendly plasmonic fiber sensor systems deployable in real-world biomedical environments.