Optical EngineeringOptimal excitation of the Bloch modes of coupled resonator optical waveguides
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When light is injected into a microring-based coupled resonator optical waveguide (CROW), it usually excites one of the whispering gallery modes (WGMs) in each microring. Because the WGMs are not, in fact, the actual eigenmodes of the structure, the modal dispersion accompanied by such excitation schemes is expected to limit the device performance, especially for wide bandwidth and large time delay applications. To overcome this problem, an alternative method of exciting the CROW, via a Y power splitter exciting the symmetric eigenmode rather than a WGM, is proposed and studied in detail. The impact of fabrication tolerances and errors for silicon-on-insulator(SOI) are explored and analyzed. It is shown that this approach can significantly improve the performance of a CROW delay line in terms of eye-closure penalty and delay-bandwidth product.