The past few decades have seen rapid growth in global information traffic, driven by the increasing amount of data processed in large data centers for Artificial Intelligence applications. Short-range optical interconnects have become the backbone of this infrastructure, and Vertical-Cavity Surface-Emitting Lasers (VCSELs) are the main light source, owing to their energy efficiency and high-speed performance. VCSELs are complex semiconductor lasers, able to provide optical power in the range of a few to tens of milliwatts. They are composed of hundreds of layers, some of which feature lateral variations, with multiple quantum wells as the active material. They constitute an entangled electrical, optical, and thermal problem that poses significant challenges from the simulation and modeling standpoint.