Refractive index sensor based on a D-shaped resonator and a stub resonator and its slow light characteristics

In this paper, a metal-insulator-metal waveguide structure is proposed based on a D-shaped resonator and a stub resonator, and it can generate multiple Fano resonances. The magnetic field (Z-direction) distribution and transmission spectrum of the structure are analyzed by the finite element method (FEM). The theory results are performed with the multimode interference coupled mode theory (MICMT), and they show high agreement with the simulation outcomes. The calculations also discuss the effect of structural parameters on the transmission spectrum. Moreover, the structure's sensing characteristics are analyzed in detail, achieving a maximum sensitivity and FOM* of 1300 nm/RIU and 181.44, respectively. In addition, the slow light properties of the structure are also investigated, whose group delay and group index can reach 0.24 ps and 48.93, respectively. The group delay time is dynamically regulated by controlling the number of D-shaped resonators to achieve the effect of a delay line. It can provide some reference value for multifunctional on-chip optical integrated devices based on MIM waveguide structure. (c) 2023 Optica Publishing Group