Enabling quasi-Single-Mode Operation in Low-Cost 850nm VCSEL-over-SSMF Optical Links

VCSELs sources at 850 nm, are attractive for shortreach links due to their low cost and power consumption. While using them with standard single-mode fibers (SSMFs) could provide higher bandwidth, cost effectiveness, and increase in transmission capacity, it is necessary to take into consideration that SSMFs support higher-order modes at this wavelength. This multi-mode behavior can indeed cause modal dispersion and modal noise, limiting the practical advantages of this approach. In this work, we investigate theoretically and experimentally the modal behavior of SSMFs at 850 nm using VCSEL-based excitation. By properly controlling the launch conditions, we ensure selective excitation of the fundamental LP01 mode, and we show that this quasi-single-mode regime remains stable under fiber bending, with no observable LP11 mode generation. Attenuation remains the only major limitation to transmission distance, so these results demonstrate the feasibility of highbandwidth short-reach transmission over SSMFs at 850 nm.