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.