Optimization, bandwidth and the effect of loss on the characteristics of the coupled ring reflector

Reflection and group delay characteristics of the coupled ring reflector (CRR), consisting of two identical microrings coupled to each other and to a bus waveguide providing feedback, is analytically and numerically investigated under loss-free and lossy conditions and subject to arbitrary (asymmetric) positioning of the couplers. Allowing for a variable coupling strength, the spectral locations where the extreme values of the reflectivity occur as well as its bandwidth are determined and their sensitivity to loss evaluated. Critical coupling conditions that determine the shape and the turning points of the reflectance spectrum, and their sensitivity to loss are obtained. Attention is paid to the bandwidth maximization satisfying a prescribed ripple tolerance within the passband. Group delay in the presence of loss and circuit parameter variations is also treated.