Spin-orbit interaction in coupled quantum wells

We theoretically investigate the spin-orbit interaction in GaAs/AlxGal_xAs coupled quantum wells. We consider the contribution of the interface-related Rashba term as well as the linear and cubic Dresselhaus terms to the spin splitting. For the coupled quantum wells which bear an inherent structure inversion asymmetry, the same probability density distribution of electrons in the two step quantum wells results in a large spin splitting from the interface term. If the widths of the two step quantum wells are different, the electron probability density in the wider step quantum well is considerably higher than that in the narrower one, resulting in the decrease of the spin splitting from the interface term. The results also show that the spin splitting of the coupled quantum well is not significantly larger than that of a step quantum well.

Kuznetsov-Ma Soliton in Coupled Quantum Wells

We show the possibility to generate Kuznetsov-Ma solitons based on bound-to-bound intersubband transitions in an asymmetric two-coupled well structure. By presenting the modulation instability of the nonlinear system provided by the interaction between light fields and quantum wells, we show that the plane wave with small perturbation can evolve into periodic trains of pulses at high while controllable repetition rates. It is found that the formation of Kuznetsov-Ma solitons as well as their period is determined by the combination of group velocity dispersion, Kerr nonlinearity and the initial amplitude of the background wave. The present research may be useful for generating subpicosecond and femtosecond pulses.

Studies on Linear and Nonlinear Intersubband Optical Absorptions in a Wurtzite AlGaN/GaN Coupling Quantum Well

Based on the density matrix approach and iterative procedure, a detailed procedure for the calculation of the linear and nonlinear intersubband optical absorption coefficients is given in wurtzite GaN-based coupling quantum wells （CQWs）. The simple analytical formulas for electronic eigenstates and the linear and nonlinear optical absorption coefficients in the systems are also deduced. Numerical result on a typical A1GaN/GaN CQW shows that, the linear and nonlinear optical absorption coefficients sensitively depend on the structural parameters of the CQW system as well as the incident optics beam intensity.

Strain effects on performance of electroabsorption optical modulators

This paper reports a detailed theoretical investigation of strain effects on the performance of electroabsorption optical modulators based on the asym- metric intra-step-barrier coupled double strained quantum wells （AICD-SQWs） active layer. For this purpose, the electroabsorption coefficient was calculated over a range of AICD-SQWs strain from compressive to tensile strain. Then, the extinction ratio （ER） and insertion loss parameters were evaluated from calculated electroabsorp- tion coefficient for transverse electric （TE） input light polarization. The results of the simulation suggest that the tensile strain from 0.05% to 0.2% strain in the wide quantum well has a significant impact on the ER and insertion loss as compared with compressive strain, whereas the compressive strain of the narrow quantum well from -0.5% to -0.7% strain has a more pronounced impact on the improvement of the ER and insertion loss as compared with tensile strain.