Optical fibre refractive index sensor modified with ultra-thin gold nanodisc metasurface

The sensitivity of the localized surface plasmon resonance (LSPR) of the periodical structure of ultra-thin gold nanodisc metasurfaces was studied for two deposition cases: (i) nanodiscs embedded into the polymer and (ii) nanodiscs directly deposited on the tip of an optical fibre sensor (OFS). The reflected spectra were simulated using Lumerical FDTD to calculate the refractive index (RI) sensitivity of the OFS. The effects of metasurface parameters, such as radius, thickness, and distance, on the LSPR peak shift were also analyzed. It was shown that for the range of 1.3 – 1.4 RI, the sensitivity of 500 nm/RI for case (i) and 510 nm/RI for case (ii) can be reached for nanodiscs array with 200 nm radius and 50 nm thickness due to the appearance of an additional reflection peak. Optical fibre sensors modified with an ultra-thin gold nanodisc metasurface were fabricated using a transfer process, and a sensitivity of 396 nm/RIU was experimentally confirmed for the case (i).