Volume 58, Nº 10 (2016)

Special features of spatial self-action of light fields in nonlinear optical photonic waveguide structures formed in strontium barium niobate and lithium niobate electro-optic crystals are discussed. The main methods of forming such structures including photorefractive waveguide elements and systems are briefly considered. The formation of spatial optical solitons in planar waveguides based on lithium niobate and strontium barium niobate crystals as well as in one-dimensional photonic lattices in lithium niobate is demonstrated experimentally for light beams of microwatt power. In regimes of spatial optical solitons, channel optical waveguides are formed not only in the planar waveguides, but also in the volume of photorefractive lithium niobate.

Optical encryption of arrays of binary digits in spatially incoherent light is experimentally implemented. Successful optical encryption and numerical decryption of images of binary arrays using a developed setup is demonstrated. Faultless decryption of arrays with normalized average energies (NAEs) up to 0.3 inclusive has been implemented. It is demonstrated that a decrease in the NAE of arrays to be encrypted leads to a decrease in the encryption error rate.

The work is devoted to investigation of noise in reconstructed holographic images in the form of a system of fringes parallel to the hologram frame boundaries. Mathematical and physical interpretation is proposed together with an algorithm for reduction of this effect by extrapolation of digital holograms using bicubic splines. The efficiency of the algorithm is estimated and examples of its application are presented.

Basic patterns of interaction of Gaussian and singular light beams (optical vortices) in media with resonant and thermal nonlinearity are experimentally investigated. It is demonstrated that interference of the Gaussian and singular beams in a nonlinear medium leads to the formation of dynamic volume holograms characterized by a singular structure. Under conditions of nonlinear holographic recording and Bragg diffraction on singular volume holograms, multiplexing of a topological charge and frequency conversion of optical vortices (transition from the IR to the visible range of the spectrum) is observed. Polarization recording of singular holograms that allows dynamic control to be performed over polarization of singular light beams including rotation of the polarization plane and conversion of linearly polarized radiation into circularly or elliptically polarized radiation.

The problem of recognition of the common fragments in a series of images in the absence of a priori criteria relating any one fragment to the common fragments, apart from the frequency of its appearance, is considered with application to recording of superimposed Fourier holograms with spatially modulated reference images. An analysis of the dependence of the variance of the reconstructed images on the number of superimposed holograms and the characteristics of the recorded images is given. It is shown that the problem can be solved for correlated reference images. Theoretical conclusions are confirmed by numerical modeling for presentation images by realizations of a stationary random process.

The procedures and algorithms providing a numerical implementation of the physical process of image reconstruction from in-line particle holograms are discussed. The methods are proposed which allow functioning of this process in an automatic mode and ensure data processing and extraction from digital particle holograms in a form convenient for subsequent physical interpretation. The experimental results on realization of these methods are presented, using digital holograms of plankton particles, air bubbles in water, and sand particles, obtained under laboratory conditions as examples.

A technique for automatic calculation of concentrations of particles in a volume and determination of their size distribution from the data reconstructed from digital holograms is proposed. The experimental results of implementation of this technique, using settling particles as an example, are presented.