Abstract

The second-order nonlinear susceptibility χ⁽²⁾of asymmetric or electrically biased quantum wells in the frequency region near the bandgap has recently been the object of intensive theoretical^1-3 and experimental⁴ investigation. Applications for frequency conversion and signal processing in semiconductor waveguides are envisaged. Theoretical estimations, however, are complicated by the necessity to evaluate cumbersome triple sums over levels.¹ On the other hand, truncation of the sum can lead to overestimation of the ξ⁽²⁾ due to neglect of cancellation effects.¹ We derive a compact expression, that permits evaluation of the contribution of levels in the continuum above the barriers, and we show that the χ⁽²⁾ value is subsequently less than previous estimates.

© 1995 Optical Society of America