Vertically stacked microring waveguides for coupling between multiple photonic planes.

We present a design for a low-footprint optical interconnect that efficiently couples between two photonic planes with significant vertical separation up to 10 μm and a footprint less than 10 μm × 10 μm. The device may be used to connect between deposited passive waveguide devices in the upper plane and active devices on a substrate. The design is based on a vertical stack of coupled ring resonators. We demonstrate basic feasibility of the design and estimates of device performance based on numerical simulation. A matrix model is presented to estimate spectral performance as a function of several design parameters.