We examine theoretically the contribution from different transition channels to optical absorption in an InAs/GaSb-based type II and
broken-gap quantum well in which both electron and hole subbands in different layers are occupied by carriers. We find that in such a
system, due to a weak overlap of the electron and hole wavefunction at the interface, optical absorption is mainly achieved via intersubband
transition within the same material layer. As a result, two sharp absorption peaks can be observed and the intensity of this
two-colour absorption depends rather weakly on temperature up to room-temperature.