Spatial investigation of transverse mode turn-on dynamics in VCSELs

Data transmission experiments with single-mode as well as multimode 850-nm vertical-cavity surface-emitting lasers (VCSELs) are carried out from a near-field point of view. Special attention is paid to important quantities like on/off-ratio and bit error rate (BER). A single-mode VCSEL oscillating on the fundamental LP₀₁ mode shows no change in eye opening, on/off-ratio, and BER at different lateral fiber coupling positions. In the case of a multimode VCSEL oscillating both on the LP₀₁ mode and LP₁₁ donut mode, we observe a significant lateral change in the on/off-ratio, which plays an important role in BER measurements