Parallel-cascaded semiconductor microring resonators for high-order and wide-FSR filters

We demonstrate an optical channel dropping filter (OCDF) using three parallel-cascaded vertically coupled microrings with improved rolloff, bandpass flattening, and wide free spectral range (FSR) compared to a single-ring OCDF using single-mode tightly confined waveguides in both GaAs-AlGaAs and GaInAsP-InP. We achieve FSRs of 30 nm for GaAs-AlGaAs and 40 nm for GaInAsP-InP devices, which are three and four times greater, respectively, than those for single rings. The rolloff is 2.8 times faster than that for a single ring.