Characteristics of the ultrafast all-optical cross-phase modulation in InGaAs/AlAs/AlAsSb coupled double-quantum-well optical waveguides

The effect of intersubband (ISB) pump-wavelength detuning, spatial ISB absorption, and optical confinement on the characteristics of the ultrafast all-optical cross-phase modulation (XPM) in InGaAs/AlAs/AlAsSb coupled double-quantum-well (CDQW) ISB transition optical waveguides are studied. For pump energies below the saturation point of ISB absorption, experimental and theoretical results show that all the photons confined to the absorption layers are absorbed. Consequently, higher ISB absorption coefficients do not lead to improved XPM efficiency. Increasing ISB absorption may be effective in raising the saturation point of ISB absorption so that higher induced phase shift may be achieved at higher pump energies. Nevertheless, it is found that the pump energy of these devices should be limited to below approximately 10 pJ at the input facet of these devices. Otherwise, the effects of two-photon absorption become considerable and this leads to reduced throughput of these devices. Hence, it becomes apparent that the approach to enhance the XPM efficiency for any given absorption-layer volume of any CDQW design of these devices is to increase the optical confinement to the absorption layers. (C) 2010 American Institute of Physics. [doi:10.1063/1.3428456]