Diiusive Turn-oo Transients in Current Modulated Multitransverse Mode Vcsels

Secondary pulsations are an example of di usive turn-o transients that can limit the performance of VCSELs in optical communication systems. Secondary pulsations are rstly analysed by using a model where a modal expansion of the electric eld is performed. The maximum power of the secondary pulsations and the time at which they appear uctuate when the spontaneous emission noise is present. A linear relation between the two previous quantities for each individual turn-o event is found. In the single-mode regime, the averaged maximum power during turn-o transients increases when increasing the injection current. However, in the multi-mode regime, the strength of secondary pulsations decreases when increasing the current. Secondary pulsations are also analysed by using a spatio-temporal description of the VCSEL dynamics, where the modal pro les are determined from the distribution of injected carriers and the thermal lens. This model also incorporates polarization e ects and a frequency-dependent susceptibility. In this model, the carrier-induced refractive index changes increase the strength of secondary pulsations as compared to that obtained with the modal expansion. It is also shown that the use of ring-shaped electrical contact enhances the strength of secondary pulsations, while it decreases when multi-transverse mode operation is present.