Multi-planar amorphous silicon photonics with compact interplanar couplers, cross talk mitigation, and low crossing loss

We propose and experimentally demonstrate a photonic routing architecture that can efficiently utilize the space of multi-plane (3D) photonic integration. A wafer with three planes of amorphous silicon waveguides was fabricated and characterized, demonstrating $<3\times 10^{-4}$ dB loss per out-of-plane waveguide crossing, $0.05\pm 0.02$ dB per interplane coupler, and microring resonators on three planes with a quality factors up to $8.2\times 10^4$ . We also explore a phase velocity mapping strategy to mitigate the cross talk between co-propagating waveguides on different planes. These results expand the utility of 3D photonic integration for applications such as optical interconnects, neuromorphic computing and optical phased arrays.