Small and scalable laser source for AR glasses by flip-chipping of bare laser diode in silicon nitride PIC technology

A small laser engine for AR glasses is demonstrated based on a Silicon Nitride PIC using a flip-chip assembly process. By etching recesses in the silicon nitride PIC, and flip-chipping of bare Red, Green and Blue laser diodes, a passive alignment method is provided. The improved design of this device has a footprint of only 4×4.5×1.5mm. The optical output is optimized in performance for use in AR systems: Circular output modes (1:1) and low dispersion (NA~0.06) over wavelength. Optical output powers of >10mW are measured and depend on the laser diodes used. The devices are sealed with a top cap of silicon providing, next to wafer level laser integration, wafer level hermetic packaging for scalable volume manufacturing. In this paper we describe the flip-chip assembly process used to create the laser engine with small footprint of 4×4.5mm. As the alignment of the laser diodes to the photonic IC platform is critical for highly efficient systems, the process we propose is a passive flip-chip approach, were two directions are controlled by state-of-the art vision systems for submicron alignment. For the 3rd and most critical direction, a passive alignment is used based on accurately controlled landing pads (<100nm accuracy). Fixation and the electrical bottom contact are achieved using laser-assisted reflow of solder. The results show that this is a viable way to produce laser engines for AR on waferscale into large volumes.