Characterization of coupling efficiency of silicon microring resonator using add-drop filter model

This paper presents a way of accurate characterization of the coupling efficiency of silicon microring resonator through curve fitting approach using an add-drop filter model which considers not only the waveguide propagation loss but also the backscattering effect due to sidewall roughness. The effective coupling efficiencies for different coupling angles from five differently positioned chips of two wafers are measured by comparing the experimental curve with the theoretical fit obtained from the developed model. The comparison of the results from this model with the Finite-Difference Time-Domain (FDTD) simulation results shows that the discrepancies increase with larger coupling angle i.e. larger coupling length, since longer couplers are more sensitive to the fabrication inaccuracies. The results found in this paper can serve as a good design tool in future to streamline the design of microring based structures on the same technological process.