Breaking the Bandwidth Limit of Vertical‐Cavity Surface‐Emitting Lasers by Selective Spatial‐Mode Outcoupling

ABSTRACT The rapid development of computation‐heavy applications, including artificial intelligence (AI), has driven exponentially growing demand for high‐speed optical modules, where 850 nm vertical‐cavity surface‐emitting lasers (VCSELs) play an important role. However, its transmission speed has long been limited to ≤100 Gb/s per lane (or bandwidth below 30 GHz) due to intrinsic physical processes. To overcome this bottleneck, coupled VCSELs are proposed as a mechanism to significantly exceed the bandwidth limit when light is partially selected to avoid spatial averaging. In this paper, we make the first attempt to experimentally verify this strategy by fabricating two coupled‐mesa VCSELs. While varying the distance between two coupled VCSELs, we compare the modulation bandwidth between two output collection approaches: entire collection and selective collection through a 5‐micron aperture. We observe a 37% improvement in modulation bandwidth from 27 GHz in the first case and 37.2 GHz in the second. This improved bandwidth represents the highest performance of 850 nm VCSELs so far and does not require complicated design or fabrication. This research offers a cost‐effective solution for next‐generation AI and data center applications and may also pave the way for a systematic exploration of out‐coupling strategies in ultra‐high‐speed VCSELs.