Intersubband absorption saturation in InGaAs-AlAs-AlAsSb coupled quantum wells

This paper gives saturation (switching) energy (I_S) estimates in an all-optic switch material based on absorption saturation in InGaAs-AlAs-AlAsSb coupled-double quantum wells (cDQWs). A model based on density matrix theory for a 4-level system is used to simulate the pulsed excitation conditions of the experiment in the communication wavelength region. The theoretical estimates are compared with experimentally determined values. A comparison of the I_S in two different cDQWs (one with an indium composition in the well of about 53% and without an AlAs stopping layer at the well-barrier interface and another with 72% indium and an AlAs stopping layer) clearly shows that the samples with high indium content are of a better quality compared to those with lattice-matched indium composition (53%). An order-of-magnitude reduction in the I_S in an all-optic switch based on cDQWs with high indium content is reported.