Large optical Kerr signal of GaAs/AlAs multilayer cavity with InAs quantum dots embedded in strain-relaxed barriers

A strong and ultrafast optical Kerr signal at ∼1.5μm has been demonstrated in a GaAs/AlAs multilayer cavity containing self-assembled InAs quantum dots (QDs) embedded in strain-relaxed In0.35Ga0.65As barriers. Time-resolved optical measurements using 100 fs pulses with 100 kHz repetition rate were carried out in the various excitation powers at room temperature. Although only 2 layers of the InAs QDs were inserted in the half-wavelength (λ/2) cavity layer, the strongly enhanced optical Kerr signal was observed compared to that of a GaAs λ/2 cavity which had no QDs, in the whole range of excitation power (1-10 mW). The signal enhancement becomes more significant with decreasing excitation power because two-photon absorption is suppressed in the λ/2 cavity consisting of the 2 QD layers and strain-relaxed In0.35Ga0.65As barrier. In the low-excitation power regime of 1-2 mW, the optical Kerr signal was about 2 orders of magnitude larger than that of the GaAs λ/2 cavity due to the large nonlinearity of the resonant InAs QDs.