Optical packaging of photonic integrated circuits: bottlenecks and potential solutions

Photonic integrated circuits (PICs) are revolutionizing telecommunications, quantum computing, and sensing applications by manipulating light instead of electrical signals, bringing unprecedented improvements in speed, bandwidth, efficiency and integration density. However, optical packaging remains a critical bottleneck for mass deployment of PIC-based products and components, primarily due to mode field diameter (MFD) mismatch between fibers and PIC waveguides and its sub-micron alignment tolerances, hindering efficient optical coupling, as well as rapid and reproducible PIC assembly processes. Key challenges also include thermal management through coefficient of thermal expansion (CTE) matching, optical adhesive selection, and standardized design rules for scalable packaging. This paper reviews current optical coupling approaches, comparing surface and edge coupling methods, while evaluating emerging solutions including two-photon polymerization (TPP) for 3D micro-optical structures and self-written waveguides (SWWs) with self-aligning capabilities. Novel alignment strategies, from active feedback systems to AI-driven algorithms and passive techniques are also investigated. Future prospects highlight inverse-designed structures, silicon nitride integration for high-power applications and nanoimprint lithography for mass production, paving the way for wafer-level optical packaging solutions.