Enhanced second-order optical nonlinearity using inter- and intra-band transitions in low-dimensional semiconductors

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Abstract
We propose a novel scheme of enhancing χ(2)(ω3;−ω1,ω2) in asymmetric quasi‐low‐ dimensional (QLD) semiconductors. The ω1 and ω2 are tuned to exciton levels, while ω3=ω2−ω1 is tuned to an intersubband transition energy. Fairly large χ(2) is obtained when a certain asymmetry is introduced in the QLD structure by, e.g., an external electric field F. A possible application is the efficient down conversion of coherent light emitted from a laser diode(s) into an intersubband frequency ω3 via a parametric process or difference‐frequency generation. It is also possible to modulate the intensity of the down‐converted, long‐wavelength light by modulating F at a very high frequency of several tens of GHz.