To realize the potential of co-packaged optics, we have been working on efficiently coupling light from chip-to-chip in a package. Our design uses a 15-layer stack of varying stoichiometry SixOxNz to achieve a parabolic refractive-index profile. This parabolic profile has a focusing effect: light incident on all 15 layers is focused into the highest index layer, the waveguide. We call this the GRIN (GRaded-INdex) Coupler. By aligning two GRINs opposite each other, one on a top chip and one on a bottom chip, light can efficiently be coupled between them. The GRIN improves on prior architectures with lower loss, greater alignment tolerances, and better manufacturing compatibility, and we believe it is an effective solution toward realizing the potential gains of co-packaged optics. A publication is in preparation, so images are coming soon to this page.