Modeling and simulation of an identical double micro-ring resonator

An identical double micro-ring resonator is investigated using finite-difference time-domain algorithm of the full-wave Maxwell's equations (FullWAVE/FDTD). The exploration shows that at wavelength of 1.55 μm the resonance is only achieved when the ring radius is 1 μm, the gap between waveguides is 0.1 μm, the waveguide width is 0.2 μm, and the core-cladding refractive index difference is equal to 2. A general rule is then concluded for an optimal design of an identical double micro-ring resonator at a given wavelength: the waveguide width needs be larger than the gap between waveguides and the ring radius bigger than two times of the summation of the waveguide width and the gap between waveguides. Moreover, a compromise must be made between the ring radius and the core-cladding refractive index difference because bending loss decreases with the ring radius and the core-cladding refractive index difference increasing but the higher refractive index difference requires the smaller ring radius.