Interposer registration elements

A substrate comprises multiple interposers. Each interposer includes interposer elements, where an optical device is coupled to at least some of the interposer elements; two passages formed through the interposer, where each passage is registered with respect to the interposer elements; two blind holes formed in a surface of the interposer, where each blind hole is concentric with a different passage; two annular troughs formed in the surface, each concentric with a different passage, and an annular area separates the annular troughs from an outer diameter of the corresponding concentric passage; and two spherical registration elements, where each registration element is positioned on uncured adhesive on one of the annular areas, where the passages enable a vacuum to be drawn through such that the registration elements are pulled toward the surface of the interposer to self-align to the inner diameter of the blind holes.