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  Thermoplastic holographic mediaUSPTO Application #: 20080102378Title: Thermoplastic holographic media Abstract: The present invention provides an article comprising: a binder component, a polymerizable component; and a photoinitiator component comprising at least one photoinitiator that causes the polymerizable component to form a polymer or co-polymer when a portion of the polymerizable component is exposed to a light source. The present invention also provides a method for making such an article, and a method and a system for holographically recording a spatial light distribution to such an article. The present invention also provides an article comprising: a binder component and a photoactive component, a method of making such an article, a method of recording to such an article and a system for recording to such an article. (end of abstract) Agent: Jagtiani + Guttag - Fairfax, VA, US Inventors: Michael C. COLE, Timothy J. Trentler USPTO Applicaton #: 20080102378 - Class: 430002000 (USPTO) Related Patent Categories: Radiation Imagery Chemistry: Process, Composition, Or Product Thereof, Holographic Process, Composition, Or Product, Composition Or Product Or Process Of Making The Same The Patent Description & Claims data below is from USPTO Patent Application 20080102378. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001] 1. Field of the Invention [0002] The present invention relates to optical articles including holographic recording media, in particular media useful either with holographic storage systems or as components such as optical filters or beam steerers. [0003] 2. Related Art [0004] Developers of information storage devices and methods continue to seek increased storage capacity. As part of this development, so-called page-wise memory systems, in particular holographic systems, have been suggested as alternatives to conventional memory devices. Page-wise systems involve the storage and readout of an entire two-dimensional representation, e.g., a page, of data. Typically, recording light passes through a two-dimensional array of dark and transparent areas representing data, and the holographic system stores, in three dimensions, holographic representations of the pages as patterns of varying refractive index imprinted into a storage medium. Holographic systems are discussed generally in D. Psaltis et al., "Holographic Memories," Scientific American, November 1995, the disclosure of which is hereby incorporated by reference. One method of holographic storage is phase correlation multiplex holography, which is described in U.S. Pat. No. 5,719,691, issued Feb. 17, 1998, the disclosure of which is hereby incorporated by reference. In one embodiment of phase correlation multiplex holography, a reference light beam is passed through a phase mask, and intersected in the recording medium with a signal beam that has passed through an array representing data, thereby forming a hologram in the medium. The spatial relation of the phase mask and the reference beam is adjusted for each successive page of data, thereby modulating the phase of the reference beam and allowing the data to be stored at overlapping areas in the medium. The data is later reconstructed by passing a reference beam through the original storage location with the same phase modulation used during data storage. It is also possible to use volume holograms as passive optical components to control or modify light directed at the medium, e.g., filters or beam steerers. Writing processes that provide refractive index changes are also capable of forming articles such as waveguides. [0005] The capabilities of typical holographic storage systems are limited in part by the storage media. Iron-doped lithium niobate has been used as a storage medium for research purposes for many years. However, lithium niobate is expensive, exhibits poor sensitivity (1 J/cm.sup.2), has low index contrast (.DELTA.n of about 10.sup.-4), and exhibits destructive read-out (i.e., images are destroyed upon reading). Alternatives have therefore been sought, particularly in the area of photosensitive polymer films. See, e.g., W. K. Smothers et al., "Photopolymers for Holography," SPIE OE/Laser Conference, 1212-03, Los Angeles, Calif., 1990, the disclosure of which is hereby incorporated by reference. The material described in this article contains a photoimageable system containing a liquid monomer material (the photoactive monomer) and a photoinitiator (which promotes the polymerization of the monomer upon exposure to light), where the photoimageable system is in an organic polymer host matrix that is substantially inert to the exposure light. During writing of information into the material (by passing recording light through an array representing data), the monomer polymerizes in the exposed regions. Due to the lowering of the monomer concentration caused by the polymerization, monomer from the dark, unexposed regions of the material diffuses to the exposed regions. The polymerization and resulting concentration gradient create a refractive index change, forming the hologram representing the data. Unfortunately, deposition onto a substrate of the pre-formed matrix material containing the photoimageable system requires use of solvent and the necessity of using a solvent deposition process for forming the holographic storage medium. For example, it is difficult to use a solvent-based deposition method to form a data storage media having thicknesses greater than 150 .mu.m, or to form a holographic recording medium that does not include a substrate onto which the holographic recording medium is deposited. Also, only a limited number of types of plastic may be used in an article formed using a solvent-based deposition method, and only a limited amount of post-processing may be performed on an article formed using a solvent-based deposition method. SUMMARY [0006] According to a first broad aspect of the present invention, there is provided an article comprising: a binder component comprising at least one thermoplastic; a polymerizable component comprising at least one photoactive monomer that is soluble in the binder component; and a photoinitiator component comprising at least one photoinitiator that causes the polymerizable component to form a polymer or co-polymer when a portion of the polymerizable component is exposed to a light source, wherein the article is capable of recording spatial light distribution via a spatial refractive index change. [0007] According to a second broad aspect of the invention, there is provided a method for making a solid article comprising the following steps: (a) mixing together a binder component, a polymerizable component and a photoinitiator component to form a mixture; (b) heating the mixture to form a substantially homogeneous liquid; and (c) cooling the liquid to form the solid article, wherein the binder component comprises at least one thermoplastic, wherein the polymerizable component comprises at least one photoactive monomer that is soluble in the binder component, wherein the photoinitiator component comprises at least one photoinitiator that causes the polymerizable component to form a polymer or co-polymer when a portion of the polymerizable component is exposed to a light source, and wherein the article is capable of recording spatial light distribution via a spatial refractive index change. [0008] According to a third broad aspect of the invention, there is provided a method for holographically recording a spatial light distribution via a spatial refractive index change to a holographic recording medium comprising: providing the holographic recording medium; and forming holographic gratings in the holographic recording medium by holographically recording the spatial light distribution via the spatial refractive index change to the holographic recording medium, wherein the holographic recording medium comprises: a binder component comprising at least one thermoplastic; a polymerizable component comprising at least one photoactive monomer that is soluble in the binder component; and a photoinitiator component comprising at least one photoinitiator that causes the polymerizable component to form a polymer or co-polymer when a portion of the polymerizable component is exposed to a light source. [0009] According to a fourth broad aspect of the invention, there is provided a system for holographically recording a spatial light distribution via a spatial refractive index change to a holographic recording medium comprising: the holographic recording medium; and means for forming holographic gratings in the holographic recording medium by recording the spatial light distribution via the spatial refractive index change to the holographic recording medium, wherein the holographic recording medium comprises: a binder component comprising at least one thermoplastic; a polymerizable component comprising at least one photoactive monomer that is soluble in the binder component; and a photoinitiator component comprising at least one photoinitiator that causes the polymerizable component to form a polymer or co-polymer when a portion of the polymerizable component is exposed to a light source. [0010] According to a fifth broad aspect of the invention, there is provided a solid article comprising: a binder component comprising at least one thermoplastic; and a photoactive component comprising at least one photoactive molecule, wherein the article is capable of recording spatial light distribution via a spatial refractive index. [0011] According to a sixth broad aspect of the invention, there is provided a method for making a solid article comprising the following steps: (a) mixing a binder component with a photoactive component; (b) heating the mixture to form a substantially homogeneous liquid; and (c) cooling the liquid to form the solid article, wherein the binder component comprises at least one thermoplastic, wherein the photoactive component comprises at least one photoactive molecule, and wherein the solid article is capable of recording spatial light distribution via a spatial refractive index change. [0012] According to a seventh broad aspect of the invention, there is provided a method for holographically recording a spatial light distribution via a spatial refractive index change to a holographic recording medium comprising the following steps: (a) providing the holographic recording medium; and (b) forming holographic gratings in the holographic recording medium by holographically recording the spatial light distribution via the spatial refractive index change to the holographic recording medium, wherein the holographic recording medium comprises: a binder component comprising at least one thermoplastic; and a photoactive component comprising at least one photoactive molecule. [0013] According to an eighth broad aspect of the invention, there is provided a system for holographically recording a spatial light distribution via a spatial refractive index change to a holographic recording medium comprising: (a) the holographic recording medium; and (b) means for forming holographic gratings in the holographic recording medium by recording the spatial light distribution via the spatial refractive index change to the holographic recording medium, wherein the holographic recording medium comprises: a binder component comprising at least one thermoplastic; and a photoactive component comprising at least one photoactive molecule. BRIEF DESCRIPTION OF THE DRAWING [0014] The invention will be described in conjunction with the accompanying drawings, in which: [0015] The sole drawing FIGURE shows a basic holographic storage system according to an embodiment of the present invention. DETAILED DESCRIPTION [0016] It is advantageous to define several terms before describing the invention. It should be appreciated that the following definitions are used throughout this application. DEFINITIONS [0017] Where the definition of terms departs from the commonly used meaning of the term, applicant intends to utilize the definitions provided below, unless specifically indicated. [0018] For the purposes of the present invention, the term "light source" refers to any source of electromagnetic radiation of any wavelength. In one embodiment, the light source of the present invention is a laser of a particular wavelength. [0019] For the purposes of the present invention, the term "capable of being used as a holographic storage medium" refers to an article that is capable of storing, in three dimensions, holographic representations of one or more pages as patterns of varying refractive index imprinted into an article of the present invention. Continue reading... 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