Independently tunable refractive index sensor based on metal-insulator-metal waveguide with key-shaped resonator and application in human blood plasma detection

In this paper, a metal-insulator-metal waveguide structure based on a key-shaped resonator is proposed. Firstly, the structure is simulated using the finite difference in time domain (FDTD) method, revealing the generation of three resonant peaks. And the theoretical results are then analyzed using multimode interference coupled mode theory (MICMT), demonstrating a high level of agreement with the simulation results. Then the parameters of the structure are adjusted, so that the resonant peaks can be tuned independently. Notably, the structure exhibits a maximum sensitivity of 1520 nm RIU-1 with a figure of merit (FOM*) of 195.89, highlighting its exceptional sensing capabilities. Additionally, an analysis of the asymmetric structure reveals the emergence of a new Fano resonance. Due to its outstanding sensing performance, the structure holds potential for applications blood plasma concentration testing. Feasibility is assessed in terms of blood plasma concentration detection, achiveing a maximum sensitivity of 3.07 nm l g(-1). As a result, this structure offers promising opportunities in the field of on-chip optical integration and the biomedical field, among others.