Enhanced sensitivity and wide refractive index detection range of D-shaped SPR fiber sensor based on Au/ZnO nanostructures

We propose and numerically investigate a D-shaped SPR fiber sensor based on Au nanowire grating-zinc oxide (ZnO) nanofilm hybrid structure. Plasmonic mode couplings are investigated by birefringence analysis. The resonance peak can be found by searching the wavelength where birefringence is zero. It proves that in visible and near-infrared (NIR) region, ZnO nanofilm can greatly improve the refractive index sensitivity (RIS) of the sensor, which is the result of the promoted photon interaction and enhanced electric field intensity at the metal-semiconductor junction. The calculated maximum RIS is 15,433 nm/RIU within a wide refractive index detection range of 1.29-1.42, which is better than most reported D-shaped SPR fiber sensors to the best of our knowledge. In addition, it's found ZnO nanofilm inhibits the coupled intensity of degenerate mode in x direction to some extent, and the degree of inhibition is related to the film thickness, which might be due to its large dielectric constant.