Time-resolved nonlinear absorption modulation in GaAs/AlGaAsmultiple-quantum-well waveguides at 1.06 μm

Time-resolved nonlinear absorption modulation due to two-photon absorption (TPA) and free carrier absorption (FCA) was demonstrated in GaAs/AlGaAs waveguides at 1.06 μm. For a peak input intensity of 4.5×10¹¹ Wm^-2, there was a maximum absorption modulation of 35%. This was caused by TPA, so that the recovery time was limited by the laser pulsewidth alone. At a peak input intensity of 1.5×10¹² Wm^-2, a 65% absorption modulation was observed. This consisted of two components: an instantaneous effect due to TPA and also a slower component, attributed to FCA, whose recovery time was limited by the carrier lifetime. A theoretical model was also derived which provided a good fit to the experimental data