Mathematical modelling of a ring resonator based refractive index sensor for cancer detection

A silicon microring resonator-based refractive index sensor is proposed using the coupled mode theory (CMT). The ring resonator is decomposed into two bent-straight waveguide coupling regions to obtain a mathematical model. To derive coupled mode equations for the interaction between bent and straight waveguides, the bent mode fields are converted from cylindrical coordinate systems to cartesian coordinates and are solved by using numerical integration. Coupled mode equations between bent and straight waveguides are derived, describing the input and output amplitude related by the scattering matrix. For the fixed dimensions and parameters, the resonant wavelength of the silicon micro-ring resonator structure is computed. The proposed CMT-based ring resonator results are validated with high accuracy with simulation results of FDTD and 2D FEM methods. Compared to FDTD and 2D FEM methods, the CMT-based ring resonator shows a significant reduction in computer resource requirements (time, speed, and memory). The ring resonator-based refractive index sensor for cancer detection applications is proposed with a high sensitivity of 146 nm/Refractive index unit and a Q factor of 3459. Finally, various parameters of the ring resonator are varied to improve sensitivity and Q factor.