Ultra-Thin silver-coated tilted fiber grating for surface and bulk refractive index measurement

An ultra-thin silver-coated tilted fiber Bragg grating (TFBG) sensor with clear surface plasmon resonance (SPR) together with strong evanescent wave in transmission for "surface" and "bulk" surrounding refractive index (SRI) measurement is proposed and experimentally demonstrated. The thickness of the silver coating over the fiber surface is precisely controlled at 1216 nm (much thinner than 4050 nm for traditional SPR excitation). The transmission spectrum of the sensor provides a fine comb of narrowband resonances that overlap with the broader absorption of the surface plasmon and thus provide a unique tool