Plasmonic sensor with self-reference capability based on functional layer film composed of Au/Si gratings

We propose a simple one-dimensional grating coupling system that can excite multiple surface plasmon resonances for refractive index (RI) sensing with self-reference characteristics in the near-infrared band. Using theoretical analysis and the finite-difference time-domain method, the plasmonic mechanism of the structure is discussed in detail. The results show that the excited resonances are independent of each other and have different fields of action. The mode involving extensive interaction with the analyte environment achieves a high sensitivity of 1236 nm/RIU, and the figure of merit (FOM) can reach 145 RIU^-1. Importantly, the mode that is insensitive to the analyte environment exhibits good self-reference characteristics. Moreover, we discuss the case of exchanging the substrate material with the analyte environment. Promising simulation results show that this RI sensor can be widely deployed in unstable and complicated environments.