The filtering characteristic of double-waveguide parallel-coupled microring resonators is theoretically investigated in this paper. Transfer matrix of the structure consisting of arbitrary number of rings is deduced. Number of very narrow symmetrical transparent channels within each stop-band can increase to any integer by extending rings of the structure, and any one or more channels can be continuously tuned and switched on/off selectively by adjusting the additional phase shift between adjacent rings. The structure is compact, reliable, flexible and tunable, and has potential vital applications for optical switches in dense wave division multiplexing (DWDM) systems.
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