Optimal Coupling for the Reduction of bimodality in 850nm-VCSEL-based Radio-over-G.652-Fiber

A promising reduction of costs, consumption and environmental impact for infrastructures exploiting Radio-over-Fiber systems can be given by the use of Vertical Cavity Surface Emitting Lasers operating in the first optical transmission window (i.e., 850nm) and by the re-use of already installed G.652 fiber. However, the effectiveness of this combination of elements is strongly dependent on the presence of intermodal dispersion, produced mainly by the bi-modal propagation in the G.652 when operating in the first window. However, in principle, the excitation of each mode strictly depends on the coupling conditions, such as relative alignment and tilting between fiber and VCSEL, and the input field of the latter. The numerical and experimental analysis performed in this work shows the impact of different coupling conditions on the two-mode excitation focusing on its impact on multimode effects such as intermodal dispersion and modal noise.