Passive photonic alignment with submicrometer repeatability and accuracy

In this paper, we report on passive alignment with submicrometer accuracy of two photonic chips on a silicon optical bench. An effective design principle to minimize the tolerance chain is presented and applied to a case study. The chips have been successfully manufactured and an experimental setup has been made that can precisely assemble the chips and evaluate the alignment performance based on the camera images and coupling efficiency. It was demonstrated that passive alignment features defined in the waveguiding layers are robust enough to function as mechanical endstops. Subpixel image analysis of assembled chips showed that a 3s chip-to-chip repeatability better than 500 nm can be achieved. Finally, based on optical coupling measurements, an absolute alignment accuracy of 670 nm has been concluded.