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Simulating the effect of spatial hole burning on the modulation responses of VCSELs

This work focuses on the effects of spatial hole-burning (SHB) on the modulation response of oxide-confined vertical-cavity surface-emitting lasers. The comprehensive laser diode simulator, Minilase, as well as a simple 1-D rate equation models are used as simulation tools in the studies. We demonstrate that, due to the non-uniform transverse optical intensity, carriers at different locations of the quantum well (QW) have different stimulated recombination rates, and therefore exhibit different dynamic responses under direct modulation. This non-uniformity is revealed to be responsible for an over-damping of the relaxation oscillation and the reduction of the modulation bandwidth. Due to the limit of this nonlinear effect, VCSELs with small oxide apertures show lower intrinsic maximum bandwidth compared with that of large aperture structures. Further simulations demonstrate that this damping effect can be greatly reduced by making the electrical aperture smaller than the optical aperture, thereby significantly improving the modulation response.