Maro Publications

Holographic Memory



Maro Topics


Patents with Abstracts


Memory Devices



“Volume of distribution of digital data contents is increasing by leaps and bounds as a result of recent spreading of internet system and starting of ground wave digital broadcasting service mainly offering high vision image programs. Volume of digital data has reached 1,644 peta-byte in 2006 on a worldwide scale and are increasing at a rate of 30% per annum, and 92% thereof is accumulated in digital devices. In the optical disc industry, "heat assist", "pattern media" and "vertical magnet recording system" are proposed in addition to "holographic system" as technology for data storage exceeding 100 tera-byte/cm.sup.2. However, since an important point for practical use is "height of transfer rate", holographic optical memory is expected as a candidate of a next-generation optical disk.

In the next-generation recording media, page type memory system, especially holographic recording has been proposed as a system replacing conventional memory devices and recently the spotlight of attention is focused upon it since it is a system having high memory capacity and enabling random access and high speed transfer. This holographic recording is explained in detail in some references (for example, refer to Hans J. Coufal, et al. "Holographic Data Storage (Springer Series in Optical Sciences, Vol. 76" Springer-Verlag GmbH & Co. KG, August (2000)).

In this holographic recording system, for example, there are proposed a recording method using a holographic recording medium having transparent substrates arranged at both sides of a holographic recording layer (for example, refer to U.S. Pat. No. 5,719,691) and a recording method using a holographic recording medium having a holographic recording layer provided with a reflection surface at one side thereof (for example, refer to JP2002-123949A).

The basic theory of such holographic recording media is to record data by holographic exposure to change a refractive index of the inside of a holographic recording layer of the media and to reconstruct a change in refractive index in the media, thus reconstructing the data For this holographic recording layer, there are proposed various materials such as a material using an inorganic material (for example, refer to G.B Patent No. 9,929,953), a compound undergoing structural isomerization by means of light (for example, refer to JP10-340479A) and a material utilizing diffusion polymerization of a photo-polymer (for example, refer to U.S. Pat. No. 4,942,112).

In volume holographic material generally using a photo-polymer undergoing photo-polymerization, its holographic recording mechanism is such that upon incidence of interference light in a material, a polymerization initiator is activated in an area receiving high intensity of light, thereby initiating photo-polymerization. In the area receiving high intensity of light, monomers are consumed by the polymerization, and on the contrary, monomers in an area receiving low intensity of light are diffused and transferred toward the area receiving high intensity of light. As a result, a difference in monomer density is said to be generated by a difference in intensity of light, thus resulting in a difference in refractive index and forming a hologram (for example, refer to W. S. Colburn, K. H. Hains: Appl. Opt., 10, 1636 (1971)”

[Satou, Hanazawa and Aoki, US Patent 8,192,898 (6/5/2012)]


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(RDC 6/5/2012)


Roger D. Corneliussen

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Copyright 2012 by Roger D. Corneliussen.
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* Date of latest addition; date of first entry is 6/25/2012.