Spatial hole burning and self-focusing in vertical-cavity surface-emitting laser diodes

We measure spatial hole burning in weakly index guided vertical-cavity surface-emitting laser diodes (VCSELs) by spatially and spectrally resolving the spontaneous emission near field above threshold and show that spatial holes produce a significant lensing effect. We demonstrate experimentally, and with a simple model, that in weakly index guided VCSELs, self-focusing causes the fundamental mode width to decrease with increasing output power, exacerbating the spatial hole burning problem and inducing a transition to multimode operation at relatively low powers.