Modeling of ultrafast recovery times and saturation intensities of the intersubband absorption in InGaAs/AlAs/AlAsSb coupled double quantum wells

Ultrafast optical switches are one of the crucial components in next generation all-optical communication networks. One promising candidate is the optical switch based on saturable intersubband (ISB) absorption in doped InGaAs/AlAs/AlAsSb coupled double quantum wells (CDQW). We employ the density matrix theory and modified optical Bloch equations with the relaxation-time approximation to simulate the time evolution of optical nonlinearities in quantum well (QW) structures. The absorption saturation characteristics are derived afterwards. The theoretical estimates are used to interpret the corresponding experimental results. Furthermore, several impact factors related to dynamic and saturation characteristics of the materials are discussed theoretically. The studies provide useful clues to optimize the QW material and device design.