Comparison of simulation and measurement of dynamic fiber-coupling effects for high-speed multimode VCSELs

Static and dynamic measurements are performed with GaAs oxide-confined vertical-cavity surface-emitting lasers (VCSELs), using multimode fibers with a core diameter of 50 and 62.5 /spl mu/m and different numerical apertures (NAs). They show that a small NA can have a severe impact on the eye opening and thus also on the bit-error rate. The measurements are analyzed with a spatiotemporal two-dimensional (2-D) multimode VCSEL model. The required parameter extraction for the model is verified with small- and large-signal measurements. The analysis shows that the change of the eye opening can be explained by the interaction between the mode- and the current-injection profile, carrier diffusion, and intermodal gain compression (IGC). IGC increases differences in the modal power distribution caused by the interaction between the mode profiles and the current-injection profile. Carrier diffusion is able to compensate these increased differences of the modal power distribution. Its impact, however, on dynamic changes caused by IGC is moderate.

I. Introduction

Vertical-Cavity Surface-Emitting Lasers (VCSELs) [1]–[3] show a large potential for the use in short-distance optical links. There are three main reasons for this: first, their moderate power consumption at high data rates [1]; second, the possibility to scale them spatially, such as in two-dimensional (2-D) arrays; and third, their low-cost due to the possibility of on-wafer testing and batch processing. On the other hand, their multimode behavior severely aggravates the VCSEL-to-fiber coupling. Thus, building optical links requires a detailed understanding of these effects.