An optical disc system has been proposed that stores data holographically in three dimensions as microholograms combining different multiplexing techniques. Such microholograms can be stored overlapping in the same volume by using angle multiplexing, wavelength multiplexing or the combination of both. Storage of several information bits in one single position on the disc increases the data rate so that the total storage capacity could reach more than 100 GBytes on a DVD sized disc. In contrast to photorefractive memory systems, the storage media are made of cheap and massproducible photopolymer layers instead of expensive crystals. Furthermore, the microholographic storage method can be downward compatible with today's CompactDisk (CD)-and Digital-Versatile-Disk (DVD)-systems. In this paper we report on wavelength multiplexing of microscopic reflection holograms and on thermal processing of the photopolymer.
We report on the holographic recording and read-out of microscopic Bragg-reflectors in DuPont Omnidex HRF-800 photopolymer films with 20 jim thickness. A Helium-Neon laser operating at x = 632.8 nm was employed as light source. Lenses from Digital Versatile Disk (DVD) pick-ups were used to realize a beam waist with submicron diameter. The local distribution of the diffraction efficiency was investigated by applying a confocal scanning microscope setup. Holograms with a lie2-radius of 1 .8 im and 12 im depth (FWHM) have been recorded. Due to shrinkage, the maximum diffraction efficiency was 0.4 %, which can be improved by adjusting the read-out wavelength.Storage systems with high capacity and fast data access are essential for high resolution image processing and future multimedia services. The dominant storage technology of today is magnetic recording, where storage densities still continue to advance. However, the superparametric limit is a fundamental physical problem that is expected to restrict the achievable storage densities. Holographic data storage allows data densities well beyond the superparamagnetic limit. For more than 30 years holographic data storage attracts much attention as a promising way to the next generation of high density memories il-3/. Recent development of digital holographic data storage shows its potential advantages such as high storage capacity, fast transfer rate and short access time compared with currently available technologies. Although high storage densities of more than 100 bits4im2 have been proposed and demonstrated 14,51, no successful commercialization of a holographic memory has been appeared so far. This indicates the amount of problems connected with the transition from 118 SPIE Vol. 3401 • 0277-786X/981$1O.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
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