Optimized second-harmonic generation in asymmetric double quantum wells

We present a theoretical analysis of surface-incidence and waveguide-mode second harmonic generation with detuned intersubband transitions in GaAs-AlGaAs, InGaAs-InAlAs and GaSb-InGaSb-AlGaSb asymmetric double quantum wells, The analysis includes the effects of absorption, saturation, pump depletion, optical carrier heating, mode confinement and competition, and the loss of phase coherence due to waveguide, bulk and resonant intersubband contributions to the refractive index mismatch, Optimal structures have been determined for each material system in both surface-incidence and waveguide-mode geometries, A scheme for maintaining phase matching by incorporation of a separate region with an intersubband transition tuned midway between the first and second harmonic frequencies is analyzed, At 10.6 mu m, the maximum conversion efficiency for the optimized InGaAs-InAlAs waveguide-mode device is approximate to 16% at a pump-beam intensity of 40 MW/cm(2). Furthermore, the same device can be modulated to vanishing second harmonic output power when an electric field of -32 kV/cm is applied.