Synthesis of ideal window filter response in grating-assisted couplers

Abstract
Synthesizing ideal windowlike spectral response in codirectional grating-assisted couplers is considered. The method of variational optimization is used to design couplers theoretically with near 100% power transfer efficiency over the passband width and with sidelobes suppressed to −40 dB. The physical role of the π-phase-reversal sections for passband flattening is explained.