Photonic-integrated circuits with non-planar topologies realized by 3D-printed waveguide overpasses.

Complex photonic-integrated circuits (PIC) may have strongly non-planar topologies that require waveguide crossings (WGX) when realized in single-layer integration platforms. The number of WGX increases rapidly with the complexity of the circuit, in particular when it comes to highly interconnected optical switch topologies. Here, we present a concept for WGX-free PIC that relies on 3D-printed freeform waveguide overpasses (WOP). We experimentally demonstrate the viability of our approach using the example of a 4 x 4 switch-and-select (SAS) circuit realized on the silicon photonic platform. We further present a comprehensive graph-theoretical analysis of different n x n SAS circuit topologies. We find that for increasing port counts n of the SAS circuit, the number of WGX increases with n(4), whereas the number of WOP increases only in proportion to n(2). (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement