We have markedly improved the optical properties of extremely thin quantum wells (QWs) required for ISBT devices operating at optical communication wavelengths using novel InGaAs/AlAs/AlAsSb QW structures with 4–7 monolayers (MLs) of AlAs. The intersubband saturation intensity (Is) was reduced to 3 fJ/µm2. This represented an IS reduction of nearly 3 orders of magnitude relative to that of the previous samples, whether or not the sample had a 1-ML AlAs interface. In this paper, we report the properties of novel InGaAs/AlAs/AlAsSb quantum wells grown by molecular beam epitaxy, and discuss the linear and nonlinear optical responses of ISBT.