3D-printed Beam Expanding Lens for Chip to Fiber Vertical Coupling

To achieve scalable manufacturing and improve the performance of Co-Packaged Optics (CPO) technology, there is an expectation for vertical coupling techniques with wide bandwidth and large alignment tolerances. We have devised a Vertically-Coupled Beam Expanding Lens (VCBEL), which is composed of a freeform mirror and lens, and is directly attached to the end face of a Photonics Integrated Circuit (PIC). We achieved an increased output beam size by incorporating a convex mirror, enabling highly efficient coupling with wide alignment tolerance. Prototypes of the VCBEL were fabricated using nano-scale 3D printing technology based on two-photon polymerization. We demonstrated a coupling efficiency of -1.2 dB over an ultra-wide bandwidth of 1260 to 1575 nm, and an in-plane alignment tolerance of ±10 μm. Furthermore, we demonstrated the compatibility of the VCBEL with reflow. Based on these results, inspection of the PIC can be conducted in a wafer state, followed by singulation and reflow implementation.