Effects of side-coupling on the phase response of cascaded microring all-pass filters

All-pass filters are useful devices that allow phase correction or equalization of signal without introducing any amplitude distortion. We present a new design scheme in which a grating is introduced in the interaction region of the two adjacent microrings in a cascaded multiring structure. The analysis accounts for the counter-directional coupling between the two waveguides. Theoretical analysis shows that this side-coupling can effectively double the filter order thus either give better performance with the same filter order or decrease the filter dimensions with the same performance. 2003 Elsevier B.V. All rights reserved. PACS: 42.79.Gn; 42.82.Et