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Method and apparatus for optical data storage using non-linear heating by excited state absorption for the alteration of pre-formatted holographic gratings
| Details |
Inventors: Cumpston, Brian H.; Perry, Joseph W.; Marder, Seth R.;
Assignee: Siros Technologies, Inc. (San Jose, CA)
Primary Examiner: Angebranndt; Martin
Assistant Examiner:
Attorney, Agent or Firm: Sierra Patent Group, Ltd., Smith; Andrew V.
The present invention comprises an optical data storage system utilizing a host material and molecules that exhibit non-linear absorption dissolved therein. The non-linear absorbing molecules allow for energy in the form of heat to be generated during the optical data storage process. This heat provides for localized alterations to occur in the pre-formatted holographic grating. The non-linear feature of these molecules allow for alterations to occur at specific depths and locations within the storage medium while limiting the secondary effects on other locations within the storage medium. The molecules exhibiting non-linear absorption may be selected from the group of molecules exhibiting two-photon absorption or reverse saturable absorption. The invention also comprises a method for preparing the optical storage medium, an optical data storage device comprising the optical data storage medium and having a format hologram stored within the medium. Additionally, the invention comprises an optical data storage system and method for use thereof wherein the storage system uses the optical data storage medium described above when altering a pre-formatted holographic grating in a localized region by non-linear thermal disruption of the grating. Another embodiment of the present invention comprises an optical data retrieval system embodying the optical data storage device described above and a method for retrieving the format hologram stored on the optical data storage device of the present invention. |
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DETAILED DESCRIPTION OF THE INVENTION In a presently preferred embodiment of the present invention, by way of example and not necessarily by way of limitation, an optical data storage medium, that includes molecules which exhibit non-linear absorption, is used in an optical data storage process in which a pre-formatted holographic grating is altered in a localized region by thermal disruption of the grating.
These non-linear absorbing molecules remain transparent at low intensities of light and, thus, allow for light to penetrate to greater depths within the storage medium when recording data, at a plurality of depths in the material.
Furthermore, non-linear absorption provides for strong absorption at an accessed data point, and proportionally less absorption at data points above and below the accessed data point and through which lower intensity light passes.
It is shown in this disclosure that excitation of a weakly absorbing ground state of such a non-linear absorbing molecule leads to a strong excited state absorption in that molecule on a nanosecond time scale.
The initial ground state absorption may occur by a linear or nonlinear (multiphoton) absorption process.
Once an upper excited state is achieved, rapid non-radiative relaxation by internal conversion occurs and this process releases energy in the form of heat.
The heat produced by this process is sufficient to cause melting or relaxation of polymer chains leading to an inelastic deformation of the pre-formatted holographic grating.
This melting or relaxation of the polymer chains is seen as an alteration of the pre-formatted holographic grating that manifests itself as a recording of data within the storage medium.
Alteration of a pre-formatted holographic grating in this manner is also described in the co-ending U.
S.
Patent Application entitled "METHOD AND APPARATUS FOR OPTICAL DATA STORAGE AND/OR RETRIEVAL BY SELECTIVE ALTERATION OF A HOLOGRAPHIC STORAGE MEDIUM", to inventors Sergei Sochava, Sergei Orlov, Tokuyuki Honda, Brian H
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Optical Systems 
