Tunable Multi-Channel Filters Based On Double-Waveguide Parallel-Coupled Microring Resonators

Optical micro-ring resonators have brought many significant research progresses in many areas of optics. In terms of optical filters, micro-ring resonators possess high Q value, as well as the advantages of traveling wave resonators, thus play an important role in the field of optical filters today. However, number of channels in these conventional structures is usually fixed, and channels cannot be tuned both individually, partial simultaneously, and simultaneously, which makes optical channel switching inflexible. Fortunately, parallel-coupled microring structure, first experimentally verified by Michal Lipson’s group, could make up for these deficiencies. In this paper, we theoretically discuss the double-waveguide parallel-coupled microring resonator.To begin with, an overview of the research progress and status of micro-ring resonators in recent years is given, and parallel cascade coupled microring resonators are briefly introduced. The basic theory of micro-ring resonator is analyzed, and parameters characterizing micro-ring resonators are presented.Moreover, the normalized transmission response of the double-waveguide parallel-coupled microring resonator with arbitrary number of rings are deduced using transfer matrix method, mechanism of CRIT(coupled resonator induced transparency) phenomenon in the structure is analyzed, and its CRIT condition is deduced.Furthermore, the transmission spectrum of the double-waveguide parallel-coupled microring resonator is simulated based on the normalized transmission response, and features of the spectrum are analyzed. The influence of different structure parameters on the transmission spectrum is analyzed, which demonstrates that performance of the structure remains stable when parameter tolerances generated during the manufacturing process exist. We focus on detailed discussion of continuous tuning of the transmission intensity of arbitrary channel: imposing continuously tunable additional phase shifts between adjacent rings via thermo-optic tuning, we can continuously adjust transmission intensities of arbitrary number of any channels, while the other channels will not be significantly affected.Finally, applications of the double-waveguide parallel-coupled microring resonator in optical communications are listed, and multiplexer / demultiplexer and routers are realized using the structure.