Advancing VCSEL integration with femtosecond laser microstructuring and 3D nanoprinting

Abstract

With increasing demands on data processing speeds and the correspondingly high requirements for data transfer bandwidth, research is focusing on replacing pluggable optical transceivers with co-packaged optics architectures. Vertical-cavity surface-emitting lasers (VCSELs) have been considered a promising candidate in such configurations, but traditional optoelectronic packaging approaches—such as flip-chip and wire-bonding—fall short of meeting the low-cost and high-speed requirements. In this paper, we present the integration of bare-die VCSEL arrays into femtosecond laser-fabricated fused silica microwells, combined with direct on-VCSEL fabrication of micro-optics using two-photon polymerization-based direct laser writing. The $1\times 4$ VCSEL arrays, operating at a wavelength of 850 nm, are aligned in a face-up configuration and are electrically interconnected within a 5.5 µm passivation layer with photolithographically defined copper tracks. Efficient beam shaping is demonstrated by 3D nanoprinting 200 µm tall refractive and diffractive focusing microlenses directly onto the integrated VCSELs with an in-plane pitch of 250 µm. The emitted beams are focused into a 5 µm diameter Gaussian spot and are efficiently coupled into a single-mode fiber. This scalable packaging approach highlights the potential for compact, high-density solutions for co-packaged optics architectures with glass interposers.