Backward degenerate four-wave mixing (F W M) of coherent light beams in ferroelectric crystals LiNb0₃ and LiTa0₃ has been studied. The theory of F W M is developed taking into account the specific nonlinear response of electrooptic crystals. The results of calculation have been compared with the experimental data for continuous wave excitation of these crystals by He-Cd laser light. The possibility of phase conjugation and compensa-tion for static and time dependent phase inhomogeneitis via F W Min LiTa0₃ is demonstrated.

The paper is devoted to the analysis and demonstration of a noiograpnic coupler or single-mode fibres and cables. It consists of hologram output windows for each cable end. Coupling between the two terminations proceeds by means of pseudo plane waves. This desensi-tizes the tolerances to some critical coupler parameters, namely transverse alignment. Assembly in the field is relatively undemanding. Precision work in the factory production is comparatively simple.

Backward wave degenerate four-wave mixing in solid nonlinear materials CdTe and LiTaO₃ is investigated. Amplified reflection of the fourth wave with wavefront complex conjugate to the signal wave is first observed in solid state medium. The theory of four-wave mixing for the case of strong coupling of the signal and pump beams is developed. It is shown that total intensity of each pump wave may be transfered into one of the signal waves for equal intensities of the pump beams.

Trapping of electromagnetic energy in an optical waveguide is a good condition for second harmonic generation, owing to the energy confinement along the guided beam. However, this advantage is drastically reduced by the difficulties for phase-matching obtention, and by the small overlap between non linear polarization and harmonic wave. For the case of Ga As infrared waveguides (fundamental vacuum wavelength = 10.6 μm), we study a solution based on an extension of Ito and Inaba's suggestion for waveguides in the visible range. Basically the deposition of an amorphous Silicon film upon the Ga As guide breaks harmonic guided wave and non linear induced polarization orthogonality allowing thus an overlapping integral enhancement of two orders of magnitude.

An experimental procedure to determine the optical anisotropy of optical fibers is proposed. The index differences n_z -n_r and n_z-n_e , where (r,e,z) is a cylindrical coordinate system associated to the cylindrical preform, are determined by measuring the change of state of polarisation when a laser beam (reduced in diameter) crosses the preform perpendicular to the axis and at different distances from it. The internal stresses which give rise to this anisotropy may influence the quality of the fiber obtained from the preform, and these stresses could then be modified by thermal treatment. If this is the case, our procedure could be used to control preforms before ftbering.

An exact optical theorem for the scattering of TM waves by optical fibers is established. For optical wavelengths, the interpretation of the scattering in eikonal approximation as a diffraction phenomenon is explored. Some numerical estimates for a cladded optical fiber with quartic dielectric permeability profile are presented.

Planar optical waveguides can be used for self-imaging. The formation of one-dimensional self-images in solid waveguide slabs of homogeneous refractive index is reported. The location of the self-images along the guide are shown to be dependant on the optical path of the signal wave. Reflective means are used to shorten the device size and to provide focussing so that a two-dimensional imaging device can be fabricated. The integration of a dispersive element such as a grating is proposed to permit the design of angularly dis-persive devices to the multiplexing of several optical signals at different wavelengths. Possible applications in multimode optics include branching couplers, frequency multiplexers for multimode transmission systems, fail-safe multimode switching and electro -optical modulators.

Spatial frequency mixing or combinational hologram writing by means of nonlirearity of photorefractive crystals in stationary regime of holographic writing is discussed as a new promising technique of volume holography. In particular, two important problems of Bi₁₂Si0₂₀ crystals: nondestructive readout at the wavelength different from that of the writing beams and correlation analysis of complex 2D pictures can be solved by this method.

The article is concerned with the utilization of the Mach-Zehnder twin-wave interferometer in the system of correlational processing of spatial optical information using the photoelectric detection. In the first channel of the interferometer an information Transparency, containing an image to be analysed, is placed. In the second channel the another one is placed. The transmittance of the latter characterizes the structure of the filter, conforming directly to the definite image. The use of the scheme of the twin-wave interferometer permits to decrease coherence light requirements, allowes the information processing in continuous mode, increases the flexibility of the scheme, because various transformations of light fields can be performed in each channel.

The Bare code system will be used, in every market and supermarket. The code, which is normalised in US and Europe (code EAN) gives informations on price, storage, nature and allows in real time the gestion of theshop.

The methods of increasing the resolution of phase volume holographic gratings and their efficiency are reported; effective selectors (total-internal-reflection selector and selector-telescope) containing a holographic volume phase gratings are proposed. Experimental results are presented for selectors with volume holographic gratings recorded in dichro-mated gelatin which were used in dye and solid state lasers for linewidth narrowing and wide range spectrum tuning.

Consider the light propagation in a weak-inhomogeneous medium ( 1/2p An/n << 1 for distances on the order of ?, where n is the refractive index of the mediumn and ? is the light wavelength). It is known that for the conditions of this problem, the Maxwell equa-tions for monochromatic electric field component in Fock-Leontovich paraxial (parabolic) approximation can be reduced to the equivalent Schrodinger equation (1-3). Thus, if Z-axis of a rectangular coordinate system X, Z is chosen in the direction of light propagation, then for the reduced field ?(X, Z) = no1/2E (X,Z) exp {-i K oz nodZ}