Increasing bandwidth demands for cloud computing and autonomous applications push the need for system scaling instead of transistor scaling as predicted by Moore’s Law. Optoelectronic interconnections have the potential to enable system scaling at higher bandwidth, power efficiency, and lower cost than copper wiring. The objective of this research is to demonstrate polymer-based optical waveguides with integrated optical turning structures in ultra-thin glass interposers, for fiber-to-chip or chip-to-chip optical interconnections. The fundamental material and process challenges associated with achieving this objective are encompassed in: (1) polymer-glass interfaces and adhesion, (2) lithographically-defined polymer waveguides, and (3) integrated turning structures by inclined lithography. Process guidelines for substrate preparation, adhesion enhancement, and lithographic precision of siloxane-based polymer waveguides in glass were established by fundamentally breaking down and optimizing each process step. In addition, a new process was demonstrated to achieve, for the first time, waveguides with integrated turning structures with self-alignment and symmetry in a single exposure. The new process was enabled by fabricating pre-existing, direct-coated, metallic masks before the inclined exposure step. The demonstrated structures were imaged by polished cross-sectioning and Scanning Electronic Microscopy (SEM).