Optical data storage polymer-dispersed liquid crystals

To overcome volatility problems, two-photon absorption (TPA) is the most promising long-term data storage technique to date. TPA can be observed in all materials and lacks the noncentrosymmetric symmetry requirements of even-order nonlinear optical effects. Nevertheless, in centrosymmetric polymers two-photon absorption is allowed between states that have the same parity according to parity selection rules (112). Such a system has been demonstrated with nondestructive readout (113). Additionally, use of two-photon absorption on photorefractive polymer dispersed liquid crystals has been used to record a high 3D data density of 204.8 Gbits/cm (158). 

Lin Q, Jho JY, Yee AF (1993) Effect of drawing on structure and properties of a liquid crystalline polymer and polycarbonate in situ composite. Polym Eng Sci 33 789-798 Liu YJ, Sun XW (2008) Holographic polymer-dispersed liquid crystals materials, formation, and applications. Adv Optoelectron. 2008. Article ID 684349, 52 pages Matharu AS, Jeeva S, Ramanujam PS (2007) Liquid crystals for holographic optical data storage. Chem Soc Rev 36 1868-1880... 

Several methods of optical data storage using LCPs are known."" " The preferred thermo-optical system uses a thin (5 to 7 pm) film of a high (60 to 80°C) polymer which has a subsequent liquid crystal phase (either nematic or smectic) up to 20 to 30°C above the Tg. Either bonded to the polymer backbone or simply dispersed in the polymer is a dye, chosen to absorb the laser light used to write on the film. 

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