Abstract
We have proposed and demonstrated a vertically coupled microring resonator (VCMRR) filter. This configuration has many features, such as the independent optimum design of lower waveguide and upper ring, and the possibility of dense integration resulting from the cross-grid configuration. In addition, the coupling strength between the ring and bus waveguides can be controlled more precisely than the lateral coupling, because the vertical separation is obtained by the well controlled deposition rather than etching fine gaps. In this review, the recent progress in the development of compact integrated photonic functional devices using micro-ring resonator is reported. The key features of the vertically coupled micro-ring resonator filters are summarized and the potential applications of the filters leading to the development of ultra-dense integrated photonic circuits are described.
