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.