Flip-Chip Photonic-Electronic Integration Platform for Co-Packaged Optics Using a Glass Substrate with Vertically-Coupled Beam Expanding Lens

A glass substrate is promising for large-scale integration of multiple dies because of its minimal warpage and compatibility of CTE with Si. It is also a promising candidate for a photonic-electronic integration platform because electrical wiring and optical waveguides can coexist on glass. One of the challenges for photonic-electronic integration on glass is how to achieve an optical connection between a PIC and a glass waveguide. When PICs are mounted using a typical flip-chip bonder, a positional misalignment of $\pm 3 \mu ~\mathrm{m}$ occurs, leading to a catastrophic optical coupling loss. We have devised a method to establish electrical and optical connections simultaneously through flip-chip bonding. We introduce a Vertically-Coupled Beam Expanding Lens (VCBEL) to relax alignment tolerance, so the optical coupling loss due to positional misalignments is significantly reduced. Through 3D-printed prototypes, we demonstrated optical coupling between the PIC and the glass waveguide with a typical loss of 1.6 dB, and excess loss of less than 0.1 dB with misalignment of $\pm 3 \mu ~\mathrm{m}$. In addition, while roughness on a glass trench causes substantial optical loss in the air, we showed that the optical loss can be drastically reduced by using a resin lens. As a proof of concept, we successfully mounted the PIC onto the glass substrate, demonstrating simultaneous electrical and optical connections through flip chip bonding, as well as its operation as an optical circuit switch module. This technology will facilitate the integration of PICs on glass substrates, enabling optical fan-out on the substrate. This is expected to improve beachfront density and enable detachable connections with fibers for CPO.