Abstract

Nonlinear optical properties of quantum wells (QW’s) and superlattices (SL’s) have recently become an object of intense studies ^1,2. Quantum confinement of carriers leads to existence of strong resonances in the absorption spectra attributed to both conduction-to-valence band ³ and intersubband ⁴ transition. That, in turn, leads to large optical nonlinearities. Third order nonlinearity in symmetrical QW’s and SL’s have been studied by numerous authors ^5-8. More recently, calculations of second order nonlinear coefficients of asymmetric QW structures were made for interband ^9,10 and intersubband ^10,11 transitions. Second -order nonlinear properties based on interband processes in various asymmetric QW structures were evaluated in Ref ¹⁰ for wide range of materials and QW geometries. It was snown that although both second harmonic generation (SHG) and linear electro-optic (LEO) coefficient are large (on the order of 10⁻¹⁰m /V) they are at least an order of magnitude smaller than what could be expected from a two-level asymmetric system with comparable transition strength. The reason for that is compensation of second-order susceptibilities associated with various ground and excited states and having opposite signs.

© 1989 Optical Society of America