The requirement for diverse applications such as digital video, interactive media etc. demands high storage densities, rapid data transfer rates, random access to data and removability of the storage media. The complete technology involves suitable recording medium and the processes for recording, post treatment and reading. The challenge in the development of holographic storage system is the availability of appropriate recording medium which shows maximum refractive index change on irradiation. In this article, attempt has been made to discuss the important disclosure of patents made during rapid development of the holographic recording medium. Silver halide emulsions to variety of photopolymers are developed to achieve minimum polymer film shrinkage, minimum post processing and multiple writing. All types of polymer based mediums are incorporated in this article. Few discussions are divided into subsections. It has generally been observed that acrylates, acrylamide, carbazolyl-, fluorenyl-, anthracenyl- containing monomers are common monomers and polymethyl methacrylates, polyvinyl alcohols, epoxy resin, sol-gel to polyelectrolytes are the common matrix resin. A recent addition is the nanoparticles in the composition to improve the diffraction efficiency and hologram stability. A different class of photopolymer called photorefractive polymer is also reported. Liquid crystalline polymer is photopolymer which provides erasable holographic media. Claims chosen are mostly from US patents. Some other literatures are also included as demanded by the discussion. The important features of the medium used in patents are highlighted. The details about performance, as claimed in certain patents, are incorporated. Rapid developments are observed in the subject.
Holography, holographic recording medium, optical storage, reference beam, diffraction efficiency, optical, polymer, monomer, photochromism, nanocomposite
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