Interaction and fusion of light pulses at the dynamical four-wave mixing in photorefractive media
All-optical control of impulse parameters is realized via a dynamical transmission four-wave mixing. We show that the nonlinear system, which includes both coupled wave equations and an evolution equation for the dynamical grating amplitude, contains soliton-like solution for the intensity pattern formed in the medium. The nonlocality of the nonlinear response is the main important requirement to the soliton-like solution is established during the wave-mixing process. On some determined conditions the convergence of input pulses into one pulse takes place (i.e. the merge of the solitons) that lead to the dramatic changes of the output pulse shapes and intensities. The precise conditions, when the impulse output can be driven by another guiding pulse are obtained and discussed.
Soliton Profile of the Dynamic Grating Amplitude and its Alteration by Photorefractive Wave Mixing
The wave-mixing problem is considered with respect to the amplitude of the dynamic grating forming in photorefractive crystals. For non-local response and transmission geometry the grating amplitude dynamics is described by a sine-Gordon equation. Hence the grating amplitude has a soliton form. For an experimental verification the spatial distribution of the grating amplitude was imaged within a LiNbO3 sample by a topographic set-up. The results on changes of the profile of the grating amplitude versus input intensity ratio were in good qualitative agreement with the theoretical prediction. Such alterations of the grating amplitude profile can possibly be applied to signal processing.
Two-wave mixing in nonlinear media
The physics of the photorefractive effect is briefly discussed. A coupled-mode theory is then developed to analyze the coupling of two coherent electromagnetic waves inside a photorefractive medium. Both codirectional and contradirectional coupling are considered. The coupled-mode theory is then extended to consider the case of nondegenerate two-wave mixing. A discussion of the fundamental limit of the speed of photorefractive effect is then introduced. The coupling of two polarized beams inside photorefractive cubic crystals is considered. The formulation is focused on the cross-polarization two-beam coupling in semiconductors such as GaAs. The coupling of two electromagnetic waves inside a Kerr medium and the electrostrictive Kerr effect are discussed. A new concept of nonlinear Bragg scattering is introduced. The similarity among various kinds of two-wave mixing, including stimulated Brillouin scattering and stimulated Raman scattering are pointed out. Several applications of two-wave mixing are discussed. These include photorefractive resonators, optical nonreciprocity, resonator model of self-pumped phase conjugators, real-time holography, and nonlinear optical information processing. >