Digital and holographic optical storage systems are compared. Requirements for the improvement of current storage systems are defined. Techniques to study storage properties of polymer liquid crystals (PLCs) are described; they include diffraction grating, polarization holography, spectroscopic methods, refractive index determination (interferometry, birefringence), methods of surface characterization, and testing reversibility and the number of write-read cycles. Results are reported for several PLCs and interpreted in terms of the effects of the choice of the main chain, the spacer, the chromophore, the LC components, the molecular weight, photoorientation and the surface morphology.
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