Double resonant enhancement of optical second harmonic susceptibility in the compositionally asymmetric coupled quantum well

The dependence of the second harmonic susceptibility on the quantum well width and the composition of the AlyGa1-yAs quantum well was theoretically investigated. Subband envelope wave functions and eigenenergies were calculated self-consistently by simultaneously solving the Schrodinger equation and the Poisson equation. The Schrodinger equation was solved by the transfer matrix method and the Poisson equation by numerical integration. The energy-dependent effective mass due to energy-band nonparabolicity was also considered. This analysis was then used to determine the energy-band nonparabolicity induced lowering of the subband eigenenergy. Based on the theoretical calculation, the compositionally asymmetric coupled quantum well (CACQW) gave a very strong nonlinear optical effect. Second harmonic susceptibility as high as 220 nm/V can be achieved for the CACQW structure. Variation of the second harmonic susceptibility under the applied electric field showed a very interesting phenomenon of the electric field quenching effect.