Large-Scale Glass Waveguide Circuit for Board-Level Optical Interconnects Between Faceplate and Co-Packaged Optical Transceivers

By co-packaging of optical transceivers and highperformance electrical integrated circuits into a single module, board-level optical interconnects are required inside network rack chassis for switches and servers. Currently, optical fibers are deployed to provide the interconnection between the faceplate and the co-packaged optics module. While these optical fiber interconnects are low loss, they require extra space for routing and slack management over the electrical printed circuit board (PCB). As the bandwidth demands of next-generation solutions increase, an increasing number of fibers must be managed within a rack chassis. The introduction of optical circuit boards for faceplate to co-packaged optics (CPO) module connectivity could simplify this process, reduce the required space, and increase the interconnect density. For the first time, a board-level fan-out optical circuit, measuring an area of $420 ~\text{mm} \times 255 ~\text{mm}$ and a thickness of 0.7 mm, has been fabricated as an alternative to fibers between CPO transceivers and optical connectors at the faceplate. This optical circuit routes 1024 waveguides from one edge to the CPO area, with a measured propagation loss of $0.1 ~\text{dB} / \text{cm}$. Further improvements are being discussed, aiming for less than $0.04 ~\text{dB} / \text{cm}$ at $\lambda=1310 ~\text{nm}$.