Synthesis of ideal window filter response in grating-assisted couplers

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 pi-phase-reversal sections for passband f lattening is explained.