Simplification of data extraction and measurements from tilted FBG surface plasmon resonance sensors

It is shown here that measurements of a tilted fiber Bragg grating with a single-sided gold coating using an unpolarized light source and no polarization control in the interrogation path can be used instead, thereby considerably facilitating both the fabrication of the grating sensor and simplifying the interrogation system requirements. A 10 degree tilt, 1 cm-long grating with Bragg wavelength near 1610 nm and a single-sided deposition of a 50 nm gold layer results in well-separated TE-HE and TM-EH mode groups with minimum and maximum sensitivity to surrounding refractive index changes, respectively. In these conditions, a well-defined SPR resonance is observed in the transmission spectrum as well as the position of the cladding mode cutoff. The differential sensitivities of mode group resonances in spectrum slice provide clear signatures of surrounding index change, both from surface effects on the gold layer and from cutoff wavelength shifts, thereby providing multi-resonant data and more accurate sensing results.