Current modulation of multi-transverse mode vertical-cavity surface-emitting lasers

A theoretical analysis of both, small and large signal modulation of vertical-cavity surface-emitting lasers emitting in several transverse modes is presented. For the case of the small signal current modulation response, analytical expressions for that response, including spatial effects, are obtained. Current modulation response of the power of individual modes and total power present a multipeaked structure. Very simple expressions for the frequencies at which those peaks appear are presented in such a way that the dependence of those frequencies on the spatial overlap between transverse modes is clearly elucidated. For the case of the large signal current modulation response the phenomenon of turn-off transients is numerically analysed. This phenomenon consists in the generation of pulses with appreciable optical power during the switch-off of VCSELs. The dependence of turn-off transients on the turn-off current and their impact on the bit error rate in high-frequency optical communication systems using VCSELs is discussed.