The development of a theory of four-wave mixing in photo-refractive crystals is described. This theory is solved in the undepleted pumps approximation with linear absorption and without using the undepleted pumps approximation for negligible absorption. Both the transmission and reflection gratings are treated individually. The results are used to analyze several photorefractive phase conjugate mirrors, yielding reflectivities and thresholds. The use of photorefractive crystals as optical distortion correction elements and experimental demonstrations of several of the passive phase conjugate mirrors are described.

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Theory and applications of four-wave mixing in photorefractive media

The polarization properties of diffraction from volume phase gratings in photorefractive sillenite crystals such as bismuth silicon oxide (Bi12SiO20), bismuth germanium oxide (Bi12GeO20), and bismuth titanium oxide (Bi12TiO20) are strongly modified by the presence of concomitant natural optical activity and electric-field-induced linear birefringence. A set of coupled-wave equations that characterize the Bragg regime has been derived for the 〈110〉 and the 〈001〉 crystallographic orientations typically employed in volume holographic storage and multiwave-mixing applications. The predicted anisotropic behavior of the grating diffraction is experimentally confirmed, and a significant efficiency improvement is shown to occur for proper choice of the operating mode and the probe beam polarization in a given configuration.

Polarization properties of photorefractive diffraction in electrooptic and optically active sillenite crystals (Bragg regime)

A new type of holographic recording in photorefractive crystals is disclosed, termed orthogonal data storage, in which counterpropagating, reflection mode holograms are wavelength multiplexed to form gratings lying along a common axis. It is shown that this configuration provides substantial improvements in data storage capacity in comparison to prior art systems and that higher coupling coefficients are achieved. In consequence, not only storage of data but a wide range of other devices including wavelength selective filters, lenses and optical correlation systems are disclosed. Further, methods of writing and processing metastable images are disclosed which substantially improve the strength of the gratings that are permanently developed in the medium. These methods include advantageous use of electrical potentials and photovoltaic properties, together with different interrelationships during processing.

Photorefractive systems and methods

This chapter reviews different suggestions for applications of PRCs. Due to the high sensitivity, high diffraction efficiency, reversibility, and the ease of handling, these dynamic photosensitive media attracted the attention of researchers working in different areas of coherent optics. Early proposals on the use of photorefractive crystals and SLMs for holographic interferometry and 2D image processing are still interesting. Recently, a number of new ideas on PRC applications based on various phase-conjugate geometries have appeared, too.

http://iopscience.iop.org/article/10.1088/0034-4885/57/1/002/pdf

Applications of photorefractive crystals

We consider holographic optical data storage systems implemented with photorefractive media. Our viewpoint emphasizes the close interaction between materials and device issues. First we discuss our current understanding of photorefractive physics as it pertains to the holographic data storage problem. Then we consider architecture issues, including angular, phase-encoded, and wavelength-multiplexing techniques, and several approaches to increasing the signal-to-noise ratio of the recordings. Finally, we discuss materials issues related to crystal growth and how crystal quality impacts the performance of data storage systems. Both bulk and fibre crystal growth techniques are reviewed.

Optical memories implemented with photorefractive media

Efficient unstationary holographic recording in photorefractive crystals under an external alternating electric field

Degenerate four-wave mixing via shifted phase holograms in cubic photorefractive crystals

Using birefringent crystals such as LiNbO3: Fe, reading and writing of holograms at different wavelengths and so nondestructive readout of information may be accomplished.

Holographic storage of information and peculiarities of light diffraction in birefringent electro-optic crystals

Light diffraction from the volume holograms in electrooptic birefringent crystals

The theory of the volume phase holograms in the birefringent electrooptic crystals has been developed. On the basis of this theory some phenomena experimentally observed in LiNbO3 are analysed, and specifically: electrically controlled light diffraction and pattern reconstruction at a read wavelength different from that of the writing beams.

S.I. Stepanov

Papers

Efficient unstationary holographic recording in photorefractive crystals under an external alternating electric field

Degenerate four-wave mixing via shifted phase holograms in cubic photorefractive crystals

Holographic storage of information and peculiarities of light diffraction in birefringent electro-optic crystals

Light diffraction from the volume holograms in electrooptic birefringent crystals

Light diffraction in photorefractive ferroelectrics