Photorefractive quantum wells are nonlinear materials characterised by high sensitivity and a fairly fast response (≈ μs) at relatively low densities of optical power (μW/cm2). For structures working in the Franz-Keldysh geometry (with the electric field parallel to quantum wells) observed phenomena are related to the nonlinearity of electrons transport, i.e. the dependence of electron mobility on electric field intensity. This phenomenon plays an important role in photorefractive two-wave mixing, causing the shift of the space-charge field relative to the interference pattern, which allows obtaining high photorefractive gain, reaching 1000 cm-1 for E=10 kV/cm. One of the parameters of SI-MQW structures that affects nonlinear transport is the electron and hole trapping coefficient. In the literature describing the processes taking place in GaAs/AlGaAs quantum wells that value is presented as constant. In article, the authors describe experiments testing the effect of strong electric field on the electron and hole trapping coefficients for bulk GaAs. An analysis of how the electric field-dependent trapping coefficient affects the process of two-wave mixing in MQW structures is discussed in. The results presented therein relate only to the stationary interference pattern. However in some studies the shift of the electric field distribution relative to the distribution of light intensity is obtained by using a moving interference pattern. We present the results of a numerical analysis of the impact of the electric field-dependent carriers trapping coefficients on the space-charge field formation under a moving grating.
The photorefractive response of semi-insulating multiple quantum well structure operating with an external electric field applied along the quantum well planes to a localized illumination is investigated. An approximate steady-state relation between space-charge electric field and light intensity is found. To confirm used approximations, band transport model is numerically solved. The time evolution of the space-charge field is also analyzed.
We investigate nonlinear propagation of light in 1D array of optically induced waveguides. The array is generated by two plane waves interfering in slab waveguide core made of photorefractive material with a quadratic electrooptic effect. The influence of the guided wave on the refractive index distribution of the array and the possibility of discrete solitons generation is considered.
Stationary and transient behaviour of photorefractive multiple quantum well structure illuminated by interfering plane waves of near resonant frequency was investigated in frames of photogeneration, diffusion, drift and trapping (PDDT) model. The influence of high intensity electric field applied along the quantum wells planes was considered and an effect of a nonlinear transport of electrons, characteristic for GaAs/AlGaAs samples, was included. An analytical expression for the fundamental amplitude of space-charge field in the sample and the dependence of the photorefractive grating response time on material parameters in the case of low interference pattern contrast is presented and compared with the earlier results.
A new type of directional coupler with a diffraction grating formed by two external beams interfering in nonlinear material is analyzed. The parameters of the grating depend on the external waves properties and thus can vary during the work of the coupler. As a result an external power controlled coupling of a chosen pair of normally mismatched couplers modes can be realized.
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