Electro-optical backplane demonstrator with multimode polymer waveguides for board-to-board interconnects

In this paper, we report developments of electro-optical PCBs (EO-PCB) with embedded polymer waveguide layers. The paper focuses on results for fabricating and characterizing the first multimode demonstrator designed in the PhoxTrot project. Our results shows successful fabrication of complex waveguide structures and integration of optical layer part of hybrid optical / electrical PCBs utilizing production scale process and PCB panels. The optical layer comprise of multiple waveguides exhibiting a full range of geometric configurations required to meet practical optical routing functions. Test patterns include varied cross-sectional sizes, 90° bends of varying radii (40mm-2mm), cascaded bends with varying radii, waveguide crossings with varied crossing angles (90°-20°), splitters, tapered waveguides and waveguide interconnect to midboard interface slots. Moreover, we show results for fabricating electrical interconnect structures (e.g. tracing layers, vias, plated vias) top/bottom and through optical layers in OE-PCB stack. The purpose of the complex routed copper layers is to enable the crucial demonstration of the fabrication and thermal robustness challenges inherent to electro-optical PCBs with optical layers. Process compatibility with accepted practices and challenges in production scale up for high volumes are key concerns to meet the yield target and cost efficiency. Characterization results include waveguide characterization, waveguide transmission loss, misalignment tolerance, and effect of lamination. Moreover, we report development conducted for implementing waveguide interfaces in inner layer buried polymer waveguides to support 12-ch MT compliant optical couplers (Fig 3). Results on waveguide termination by in-plane edge connector and with 90° out-of-plane couplers are reviewed.