Modeling and enhancing the sensing performance of silicon nitride slotted-ring-resonator-based refractive index...

In this work, a silicon nitride-based slotted ring resonator refractive index (RI) sensor is modeled using a coupled-mode theory approach. An analytical model for the bent slot waveguide is derived by solving fields with Hankel and Bessel functions. The continuity of H_y across interfaces yields a system of eight equations forming an 8×8 matrix (Z₁). Solving det(Z₁)=0 for a given frequency (ω) allows us to determine the bent slot propagation constant (γ) for the transverse magnetic mode. The scattering matrix is constructed to accurately model the 2D slotted ring resonator and is validated using both 2D and 3D finite-difference time-domain methods, demonstrating superior computational efficiency in terms of simulation time. The device exhibits high sensitivity of 750 nm/RIU and a maximum quality factor of 7536. The impact of key parameters, including bent waveguide width, slot width, bent radius, and slot position, on sensing performance is analyzed to optimize the device dimensions. A comparative analysis with coupled-mode-theory-based disk and ring resonator RI sensors, along with other similar devices, underscores the efficacy and advancement of the proposed sensor.