High-density optical RDL on photonic interposers using out-of-plane coupling structures

High-density optical redistribution layers (RDL) on photonic interposers—combining polymer waveguides (PWG) with organic RDL, or silicon nitride (SiN) on silicon/glass platforms—require robust solutions for system-level integration onto printed circuit boards (PCBs). A key challenge lies in assembling the interposer onto a substrate while maintaining efficient optical connectivity. This requires the development of a reliable optical interface between the interposer and the PCB, enabling low-loss signal transfer across different material platforms and packaging levels.

To address this, out-of-plane coupling elements such as micro-mirrors and micro-lenses become essential building blocks. These structures facilitate vertical light redirection from the interposer waveguides towards optical interfaces integrated on the PCB. From there, optical signals can be coupled into board-level connectors, such as fiber array connectors or pluggable modules, enabling scalable and high-bandwidth system interconnects.

The research focus therefore lies in designing and integrating low-loss, high-bandwidth passive photonic components—such as mirrors, lenses, and coupling structures—that enable seamless optical interfacing between interposers and PCBs. This includes ensuring precise alignment tolerances, high reliability under assembly conditions, and compatibility with heterogeneous integration schemes. Such advancements are critical to support emerging applications in AI/ML hardware, optical I/O architectures, and next-generation photonic packaging technologies.