Conduction-band nonparabolicity effect on refractive index and phase match in asymmetric quantum wells pumped by two infrared beams

Abstract

An asymmetric quantum well (AQW) system that is pumped by two infrared beams is designed to generate terahertz (THz) waves. The refractive index and phase mismatch associated with the intersubband transition of the AQW structure are calculated and analyzed for both present and absent conduction band nonparabolicity. The calculated results reveal that, for increasing wavelengths, the refractive index of the AQW for the short-wavelength pump beam varies more than 0.83 and undergoes a 0.204 [Formula: see text]m redshift, when the conduction band nonparabolicity is considered. The variation of the refractive index of the AQW with the long-wavelength pump beam, changes from 0.225 to 0.316 after considering the conduction-band nonparabolicity. In addition, no redshift is observed. Whether the refractive index of one pump beam with its specific wavelength increases is determined mainly by the linear terms. However, for increasing the other pump wavelengths, the refractive index of one pump beam mainly depends on the nonlinear terms. Subband energy-levels and dipole transition matrix elements show noticeable changes due to conduction-band nonparabolicity, which change the refractive index. Phase matching can be achieved by adjusting the wavelength of the two pump beams. However, both phase mismatch and coverage increase when the conduction band nonparabolicity is considered.