Ultra-wide sensing range plasmonic refractive index sensor based on a two-dimensional circular-hole grating engraved on a gold film

We propose a simple structure with a two-dimensional (2D) circular-hole grating engraved on a gold film for ultra-wide range plasmonic refractive index (RI) sensing. The electromagnetic field distributions and reflection spectra of the structure are obtained using the finite-difference time-domain approach for resonance mode analysis and sensing capability characterization. The simulation results show that a high-quality surface plasmon resonance with a narrow spectral bandwidth and strong dip strength can be excited using a 2D grating after compensating for a suitable optical momentum. The structure exhibits a high sensitivity of 1131 nm/RIU and stable sensing performance over an ultra-wide RI range of 1.0-2.0. An improved figure of merit is used to more comprehensively characterize the structural sensing performance. This sensor has the potential to be widely used in the field of biochemistry because of its simple preparation, high sensitivity, and ultra-wide sensing range.