45 Degree polymer micro-mirror integration for board-level three-dimensional optical interconnects

We introduced here a novel method to fabricate polymer optical waveguides with integrated 45deg total internal reflection (TIR) micro-mirrors by contact photolithography on printed circuit boards (PCBs) to achieve fully embedded optical interconnects. The 45deg TIR mirrors were shaped at the ends of the waveguides in one step to provide surface normal light coupling between waveguides and optoelectronic devices. A tank of de-ionized (D.I.) water is used to couple the ultraviolet (UV) exposure beam through the core polymer layer at 45deg angle during the contact photolithography process, and then the 45 mirror facet will be formed after the post-process. Compared to the conventional glass prism-polymer coupling interface, this novel water-polymer interface provides a simple, convenient, and cost efficient solution. This technique is not only compatible with PCB manufacturing facility and technology, but also suitable to large panel board-level manufacturing for optical interconnects. The 45deg angle can be controlled with an accuracy of plusmn1deg and has a high reproducibility. The average insertion loss of the 45deg TIR uncoated mirrors is around 1.6 dB.