Hybrid 2D/3D photonic integration for non-planar circuit topologies

TL;DR

This paper introduces a 3D-printed waveguide overpass technique to eliminate waveguide crossings in complex photonic circuits, demonstrated on a silicon-based switch matrix, reducing crossings significantly as circuit complexity grows.

Contribution

The paper presents a novel 3D-printed waveguide overpass method for non-planar PICs, enabling WGX-free designs and providing a graph-theoretical analysis of circuit topologies.

Findings

Waveguide overpasses reduce crossings from n^4 to n^2 for large circuits.

Experimental demonstration on a 4x4 switch circuit validates the approach.

WOPs significantly decrease circuit complexity and crossings.

Abstract

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 rely on 3D-printed freeform waveguide overpasses (WOP). We experimentally demonstrate the viability of our approach using the example of a $4 \times 4$ switch-and-select (SAS) circuit realized on the silicon photonic platform. We further present a comprehensive graph-theoretical analysis of different $n \times n$ 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 $n^2$.