Coating influence on the refractometric sensitivity of plasmonic optical fiber grating spectral combs

Abstract

Gold-coated tilted fiber Bragg gratings (TFBGs) can now be considered as a mature technology for lab-on-fiber sensing based on surface plasmon resonance (SPR) excitation. This sensing architecture brings considerable assets such as easy light injection, temperature fluctuations immunity and remote operation in very small volumes of analytes. Different metal configurations have been used so far, without considerations about their relative performances in terms of surrounding refractive index (SRI) sensing. In this work, we study the impact of the coating on the cladding mode distribution in the TFBG transmitted amplitude spectrum and subsequently on its SRI sensitivity. Different configurations of gold coating are produced and tested, relying on both the sputtering and electroless deposition processes. Interesting spectral features are reported, confirming that the coating thickness and its relative disparity are important design parameters that drive the overall sensing performances.