We present a study of photoelectrical properties of the Stranski-Krastanow InAs quantum dots embedded in an InGaAs matrix with low In content, emitting at about 1.3μm. The ground-state electron-hole transition of the dots was investigated as a function of the temperature in presence of electric fields parallel and perpendicular to the plane of the dots by photocurrent spectroscopy. Microphotoluminescence measurements were also carried out, allowing us to evidence carrier capture from the GaAs matrix into the dots.
Quadratic spatial solitons exist in media with second order nonlinearities near the phase-matching condition for frequency mixing processes involving two or three waves of different frequency. Discussed here are a number of properties of these special solitons which are different from those of other spatial solitons which rely on optically induced index changes for guiding. First, the self-guiding properties of quadratic solitons are shown to have completely different origins than solitons which rely on index changes. Second, it is shown that there exists a large variety of quadratic solitons which contain two or three distinct spectral components with relative amplitudes depending on the phase mismatch, dimensionality of the propagation geometry, the soliton power and the launching conditions. Third, under appropriate conditions, solitons can be formed even when the group velocity directions for the spectral components lead to walk-off under normal circumstances. Fourth, for type II phase-matching in bulk crystals, seeded interactions lead to saturating amplifier characteristics.
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