Observation of bistability in GaAs quantum-well vertical-cavity surface-emitting lasers

Two different types of bistability in proton-implanted GaAs quantum-well (QW) vertical-cavity surface-emitting lasers (VCSELs) have been observed. The first type of bistability has a small hysteresis width (~50 μA) in the light versus current and voltage versus current characteristics. Light-induced large negative differential resistance, random fluctuations, and self-pulsations are observed at the switching point. The emission patterns show that the bistability occurs at a spatially localized area under the output facet that covers only a small fraction of the N1S-μm-diameter aperture. The bistability stems from spatially localized saturable absorption. The second type of bistability has a large hysteresis width (~1 μA) in the L-1 characteristics and is observed well above the threshold current. In this case, no observable bistable loop exists in the voltage versus current characteristics, and the bistability is associated with transverse mode-hopping