Abstract
We have performed an analysis of the conversion efficiency for waveguide-mode second-harmonic generation (SHG) with detuned intersubband transitions in asymmetric double quantum wells (ADQW). The modeling includes the effects of absorption, saturation of the absorption and SHG, pump depletion, carrier heating, mode confinement, and the loss of phase coherence due to waveguide, bulk and resonant intersubband contributions to the mismatch of the refractive indices at the pump and second-harmonic frequencies. ADQW designs with the optimum detuning of intersubband transition energies from resonance with the pump and second-harmonic photon energies have been derived from a balance between low absorption losses, sufficient nonlinear susceptibility, and adequate compensation of the refractive index mismatch to maintain phase coherence. These have been determined for structures employing the GaAs/AlGaAs, InGaAs/InAlAs and GaSb/InGaSb/AlGaSb material systems, all subject to the constraint that the epitaxial growth thickness should not exceed 10 μm. In the best GaAs/AlGaAs ADQWs, the maximum attainable conversion efficiency at high intensities is limited by the electron transfer to X-valley states whenever the Γ-valley offsets are large enough to permit optimal detuning. Since GaAs-based waveguides also require a thick bottom cladding to isolate the active region from the substrate, the large waveguide dispersion limits the peak conversion efficiency to 2.6%.
© 1996 Optical Society of America
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