Carriers' spatial separation nonlinearity in quantum wells

We present theoretical analysis and simulation of optical nonlinearity in asymmetric quantum well (QW) that explicitly include the effect of carriers' spatial separation. Carriers' spatial separation nonlinearity (CSSNL) has two additional significant contributions to the induced polarization beside the transition dipole moment; namely, the permanent dipole moment (PDM) and the time-varying internally induced electrical potential. These effects are included by modifying the interaction Hamiltonian. We focus mainly on the polarization at the frequency of the applied field, from which the nonlinear change of refractive index can be obtained. The results show that the CSSNL largely enhances the refractive index change when compared with the Kerr effect. Also, the inclusion of the induced electric potential effect adds a second-order interaction contribution to the refractive index change.