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 re solving the spontaneous emission near field above threshold and show t hat 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 wi th increasing output power, exacerbating the spatial hole burning prob lem and inducing a transition to multimode operation at relatively low powers.