Small-Signal Analysis of Ultra-High-Speed Multi-Mode VCSELs

In this paper, we show that the dynamic performance of multi-mode vertical-cavity surface-emitting lasers (VCSELs) can be modeled by single-mode rate equations developed for edge emitters as long as the lasing modes share a common carrier reservoir. However, this assumption does not hold for ultra-high performing VCSEL devices. Due to the high photon densities inside these optimized VCSELs, the common carrier reservoir splits up as a result of the spatial hole burning effect. This is caused by the high intensity of the multiple transverse modes. In this case, a small-signal modulation response with a different shape is expected. We derive an easy-to-apply fitting function, which allows the extraction of consistently expanded figures of merit. This novel function works for all VCSELs, particularly, including devices with carrier reservoir splitting. Furthermore, we use this new model to perform a detailed analysis of our latest VCSEL generation with a modulation bandwidth of up to 32.7 GHz.