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Attractive Features of Butt Coupling between Single/Multi Mode GaAs-VCSELs and SSMF for Green, Low-cost Radio-over-Fiber Systems

Optical transmitters based on Vertical Cavity Surface Emitting Lasers operating in the first optical window (FW-VCSELs) constitute an attractive option to realize Green Radio over Fiber (RoF) systems, due to their low energy consumption. In addition, these devices can take advantage of the widespread existing infrastructures realized on G.652 Standard Single Mode Fibers (SSMF) to develop low-cost RoF connections while remaining transparent for the presently transmitted Fiber-To-The-Home services, which exploit the second and third optical windows. Within this context, the use of simple butt-coupling between FW-VCSELs and SSMF should be a desirable feature, which however is theoretically exposed to possible drawbacks of poor efficiency and two-mode propagation effects. Through a detailed experimental activity referred to commercial high-performance multi- and single-mode FW-VCSELs, it is shown how to optimize their butt-coupling configuration to SSMF reducing the mentioned drawbacks and consider this solution suitable for 5G-and-beyond low-cost Green RoF applications.