KR100354798B1 - System and method for holographic storage using a holographic optical element - Google Patents

Abstract

Embodiments of the present invention provide a holographic memory system (HMS) that advantageously uses a holographic optical element (HOE) in a holographic memory system, such as a phase correlation multiplexing (PCM) holographic memory system, to reproduce a reference beam arm, Apparatus and methods. Holographic memory systems include a data storage device such as a holographic memory cell (HMC), a holographic optical element (HOE) for generating an HMC reference beam (HOE object beam), and a HOE reference for irradiating the HOE to generate an HMC reference beam A beam and an HMC object beam containing information to be stored in the HMS. The present holographic optical element (HOE) is formed of a holographic storage material such as a photopolymer, photoresist, thermoplastic, photorefractive material or photochromic material. The holographic optical element (HOE) reproduces the HOE object beam stored through illumination of the HOE reference beam. In this case, the reproduced HOE object beam is used as a reference beam for storing the information in the data-coded HMC object beam as a hologram. The data storage device is placed in a common volume for holographic storage to intersect them in the path of the HMC reference beam (HOE object beam) and the HMC object beam, thereby forming an interference pattern. The holographic optical element (HOE) is generated or formed in the holographic storage material such that the HOE object beam interferes with the HOE reference beam so that the interference pattern can be stored in the holographic storage material. The holographic optical element (HOE) device, once generated, replaces the reference arm optical arrangement in the holographic memory system, and thus, is complex, fragile, required in many holographic memory systems for generating a reference beam, Expensive reference masks, lenses, and filter arrangements are eliminated.

Description

FIELD OF METHOD FOR HOLOGRAPHIC STORAGE USING A HOLOGRAPHIC OPTICAL ELEMENT

The present invention relates to holographic storage. More specifically, the present invention relates to an apparatus and method for generating light beams in a holographic memory system, such as a phase correlation multiplexing (PCM) holographic memory system.

Holographic memory systems record three-dimensional recording of holographic representations (holograms) of data components as patterns of varying refractive and / or absorptivity stamped within the volume of the storage medium, such as crystals of lithium niobate. Include. Holographic memory systems are characterized by high density storage and possible speeds in which stored data is randomly accessed and transmitted.

In general, holographic storage memory systems combine data-coded object beams with reference beams to provide interference patterns across photosensitive recording media, such as holographic memory cells (HMCs). It works by creating This interference pattern causes material variation that causes holograms in the HMC. Holograms in the storage medium are formed as a function of the relative amplitudes and polarization states of the object and reference beams and the phase difference between these beams. In addition, the formation of the hologram is highly dependent on the wavelength and angle of the incident beam when the object beam and the reference beam are projected into the storage medium.

The data stored in the hologram is reproduced by projecting a reference beam similar to the reference beam used to store the data in the HMC at the same angle, wavelength, phase and position as used to generate the hologram. The hologram and the reference beam interact to reproduce the stored object beam. At this time, the reproduced object beam is detected using, for example, a photodetector array. The recovered data is then post-processed for the purpose of transfer to the output device.

Typically, the dynamic range of holographic storage media is larger than necessary to store a single hologram with an acceptable signal to noise ratio. Therefore, it is often desirable to multiplex multiple holograms at one point to obtain greater storage densities. One technique for multiplexing is phase correlation multiplexing, which uses correlation selectivity and Bragg selectivity to distinguish overlapping holograms within a storage medium. Correlation selectivity depends on the difference in amplitude, phase, and angular amount of the reference beam generated by the relative change (in either direction) of the storage medium relative to the reference beam.

However, multiplexing techniques such as phase correlation multiplexing (PCM) require relatively complex reference beams, the formation of which is, for example, complex phase masks, high performance lenses and Fourier plane spatial filtering. plane spatial filtering). Unfortunately, phase masks are structurally fragile, lenses are expensive and bulky, and the essential Fourier plane spatial filters block the majority of the optical energy, thus significantly increasing the power consumption of the system. In addition, for systems such as phase-correlated multiplexing (PCM) holographic memory systems, the alignment of these components is accurate to sub-micron (μm) levels and typically must match between systems. This level of consistency is usually difficult, although not impossible to achieve using conventional components and techniques.

The present invention provides a relatively inexpensive, simple, and reproducibly consistent alternative to a plurality of components of a reference arm of a holographic system, such as a phase correlation multiplexing (PCM) holographic memory system.

1 is a simplified schematic diagram of a reference beam optical path and related components conventional in a holographic system such as a phase correlation multiplexing (PCM) holographic memory system;

2 is a schematic diagram briefly illustrating generation or formation of a transmission mode holographic optical element in accordance with an embodiment of the present invention;

3 is a schematic diagram briefly illustrating generation or formation of a reflection mode holographic optical element in accordance with an embodiment of the present invention;

4 is a simplified block diagram of a method of manufacturing a holographic optical element in accordance with an embodiment of the present invention;

5A and 5B are schematic diagrams schematically illustrating the use of the holographic optical element of FIG. 2 in accordance with an embodiment of the present invention;

6A and 6B are schematic diagrams schematically illustrating the use of the holographic optical element of FIG. 3 in accordance with an embodiment of the present invention;

7 is a simplified block diagram of a method of using a holographic optical element in accordance with an embodiment of the present invention;

8A is a schematic diagram schematically illustrating the generation or formation of a holographic optical element according to another embodiment of the present invention;

8B is a schematic diagram schematically illustrating the use of the holographic optical element of FIG. 8A;

9A is a schematic diagram schematically illustrating the generation or formation of a holographic optical element according to another embodiment of the present invention;

FIG. 9B is a simplified schematic diagram using the holographic optical element of FIG. 9A;

10A and 10B are schematic diagrams schematically illustrating the use of holographic optical elements using various Bragg multiplexing techniques;

11A and 11B are schematic diagrams schematically illustrating the use of holographic optical elements using various spatial multiplexing techniques;

12A-12C are schematic diagrams schematically illustrating the use of holographic optical elements using the parallel effect of a reproduced beam;

FIG. 13A shows the integrated diffraction efficiency of holograms recorded as a function of the shift of the holographic memory cell (HMC) or HMC reference beams with respect to each other using conventional optics, FIG.

FIG. 13B illustrates the integrated diffraction efficiency of holograms recorded as a function of the shift of the holographic memory cell (HMC) or HMC reference beams with respect to each other using the holographic optical element (HOE) according to one embodiment of the invention.

Explanation of symbols for the main parts of the drawings

100: reference beam path

105: interference beam

110, 210, 310: reference mask

115, 215, 315: first lens

120, 220, 320: low pass filter

125, 225, 325: second lens

130, 575, 675, 875, 975: image plane

140, 240, 340. 540, 640, 840, 940, 1140: HOE object beam

200, 250, 350, 550, 650, 850, 950, 1050, 1150, 1250: HOE

264, 564, 664, 864, 964: light source

360, 560, 660, 860, 960, 1160, 1260: HOE reference beam

680, 880, 980, 1280: HMC

885, 985, 1285: HMC object beam

990: alignment beam

The invention is as defined by the claims. Embodiments of the present invention utilize a holographic memory system (HMS) and a holographic optical element (HOE) to incorporate a reference beam arm in a holographic memory system such as a phase correlation multiplexing (PCM) holographic memory system. It includes a device to play. The holographic memory system includes a data storage device such as a holographic memory cell (HMC), a holographic optical element (HOE) for generating an HMC reference beam (HOE object beam), and a HOE for irradiating the HOE for generating an HMC reference beam An HMC object beam containing the reference beam and ultimately the information to be stored in the HMS. Holographic optical elements (HOEs) are incorporated into holographic storage materials such as photopolymers, photoresists, thermoplastics, photorefractive materials, or photochromatic materials. Is formed. The holographic optical element HOE reproduces the stored HOE object beam upon irradiation with the HOE reference beam. The reproduced HOE object beam is then used as a reference beam for storing the information in the data coded HMC object beam as a hologram. The holographic memory cell (HMC) is disposed in a common volume to intersect in the path of the HMC reference beam (HOE object beam) and the HMC object beam, whereby the interference pattern formed is stored as a hologram in the common volume.

The holographic optical element (HOE) is generated or formed in the holographic storage material in such a way that the HOE object beam interferes with the HOE reference beam so that its interference pattern is capable of being stored in the holographic storage material. The azimuth angle of the interference beam is comparable to whether the holographic optical element (HOE) is a transmissive device or a reflective device and to the focal length of the final lens in the optical device used to generate the holographic optical element (HOE). It depends on the distance D between the optical element HOE and the optical device used to generate this holographic optical element HOE. Once generated, the holographic optical element (HOE) replaces the reference arm optical configuration in the holographic memory system, eliminating the complex reference mask, lens and filter configuration required by many holographic memory systems to generate a reference beam. do. This removal significantly improves the throughput of the reference arm because there is no light loss due to the filtering operation during reading from the holographic optical element (HOE). Thus, the system according to embodiments of the present invention consumes less power and operates at high speed.

In the following description, like elements are referred to by the same reference numerals to simplify the sequential aspects of the drawings and to better understand the present invention through the description of the drawings.

DETAILED DESCRIPTION In the following specification, specific features, configurations, and arrangements are described, but it will be understood that this is described for illustrative purposes only. Those skilled in the art will appreciate that other steps, configurations and arrangements may be used without departing from the spirit and scope of the invention.

As mentioned above, one technique of multiplexing a large number of holograms at one point to obtain greater storage density is a phase correlation multiplexing (PCM) technique. In phase correlation multiplexing, correlation selectivity and Bragg selectivity are used to distinguish superimposed holograms in a storage medium. For purposes of explanation, the term "phase correlation multiplexing" includes the use of unidirectional and / or bidirectional phase selectivity. It should also be noted that phase correlation multiplexing is available alone or in combination with other Bragg techniques, ie in combination with other methods of shift multiplexing in the orthogonal direction.

Referring now to FIG. 1, a typical reference beam path 100 for a conventional phase correlation multiplexing (PCM) holographic memory system is shown. For example, an interference beam 105 of laser light, which is a plane wave, is a highly structured reference mask (e.g., a phase mask and / or that encodes the light beam 105, for example by inducing high spatial bandwidth generation on a plane wave). Or amplitude mask 110).

The encoded beam propagates the distance f1 to the first lens 115 having the focal length f1. The beam passes through the first lens 115 and is then Fourier transformed by the reference phase mask 110 at another distance f1 past the first lens 115. A high pass spatial filter 120 is provided in the plane of this Fourier transform. Typically, filter 120 blocks a large amount of low spatial frequency components emitted from reference mask 110.

After passing through the high pass filter 120, the encoded beam propagates up to a distance f2 to the second lens 125 having a focal length f2. The encoded beam passes through the second lens 125, propagates another distance f2 and reaches its image plane 130. The encoded beam 140 passing through the image plane 130 is a reference beam of the holographic memory system (HMS).

Typically, image plane 130 is one possible location where a holographic memory cell (HMC) or other suitable data storage device may be provided for digital hologram storage, eg, in a PCM holographic memory system. However, as will be apparent from the following description, according to embodiments of the present invention, any plane of interest, even if the holographic memory cell (HMC) or other suitable data storage devices, is not necessarily the image plane 130. Can be placed for storage.

2, the generation or formation of a holographic optical element (HOE) 200 in accordance with one embodiment of the present invention is shown. In particular, FIG. 2 illustrates the generation of a transmission mode holographic optical element (HOE). The optical path arrangement consisting of the mask 210, the first lens 215, the filter 220, the second lens 225, and the respective distance therebetween is similar to that shown in FIG. 1 and described above. The first beam 240 penetrates the second lens 225. Beam 240 propagates or is directed towards distance holographic storage material 250 by distance D. For the purposes of this specification and as will be apparent from the following description, the beam 240 is an object beam used for the generation or formation of a HOE object beam (beam A), ie a holographic optical element (HOE).

The HOE object beam 240 passes through the holographic storage material 250, where it intersects the second beam 260, which is the reference beam of the HOE. The beam 260 that interferes with the HOE object beam 240 is generated from the light source 264 and appropriately directed to irradiate the holographic storage material 250, and the HOE object beam at the desired location within the holographic storage material 250. Intersect with As a result, an interference pattern between the beam 260 and the HOE object beam 240 is obtained as a hologram in the holographic storage material 250, thus holographically storing the holographic storage material 250 in accordance with an embodiment of the present invention. Convert to Graphic Optical Element (HOE).

Therefore, in the method, beam 260 is a HOE reference beam, ie, a "reference" beam for hologram generation of HOE object beam 240 in holographic storage material 250. HOE reference beam 260 is any suitable beam, but is typically a plane wave or other beam that can be easily reproduced. As known to those skilled in the holography art, the HOE object beam 240 and the HOE reference beam 260 are typically generated by light interference from the same or similar laser source.

Holographic storage material 250 is any suitable material or composition or arrangement of materials capable of recording face or stereoscopic holograms or generating diffracted light. For example, the holographic storage material 250 is a photopolymer, a photoresist, a thermoplastic material, a photorefractive material or a photochromatic material. The holographic storage material 250 has a first surface 265 and a second surface 270 opposite it, and has a comprehensive feature that is sufficiently flat or reproduces up to approximately two light wavelengths per centimeter (cm).

FIG. 3 illustrates the generation of a reflection mode holographic optical element (HOE) 300 according to an embodiment of the invention, which holographic optical element (HOE) is shown in FIG. 2 above. It has a different geometry than the optical element HOE. The mask 310, the first lens 315, the filter 320 and the second lens 325, and their respective distances between them are similar to those shown in FIGS. 1 and 2 described above. As shown, the HOE object beam 340 propagates through the second lens 325 or travels a distance D toward the holographic storage material 350.

However, according to this alternative embodiment, the HOE reference beam 360 (beam B) is generated from the light source 364 and proceeds towards the second surface 370 of the holographic storage material 350, then the holographic Intersect with HOE objectbeam 340 (beam A) at a desired location within storage material 350. As a result, the resulting interference pattern is obtained holographically in holographic storage material 350, thereby forming a holographic optical element (HOE). Reflective mode holographic optical elements, in particular, are generated using beams in which the transmissive mode holographic optical element is irradiated on the same surface of the holographic storage material, whereas the reflective mode holographic optical element is the opposite surface of the holographic storage material It is different from the transmission mode holographic optical element in that it is generated by the beam irradiated to the field.

As shown generally in FIG. 4, a method 400 for generating or forming a holographic optical element in a holographic memory system (HMC) firstly comprises a distance from an optical path arrangement as shown in FIGS. 2 and 3. Providing 410 a holographic storage material, irradiating the first beam (HOE object beam) through the light path towards the holographic storage material (420), and simultaneously with the step 420, the second beam Irradiating (HOE reference beam) towards the holographic storage material to interfere with the HOE object beam at a desired location within the holographic storage material (430). As shown in Figures 2 and 3, the HOE reference beam is irradiated at an appropriate angle on both sides of the holographic storage material. The interference pattern is obtained at the desired location in the holographic storage material, thus forming the holographic optical element (HOE).

The transmission mode and reflection mode holographic optical element (HOE) can store a plurality of HOE object beams by multiplexing. For example, when the holographic optical element (HOE) is relatively thick, for example 1 mm, for example, by changing the angle, wavelength or position of the HOE reference beam while changing the characteristics of the HOE object beam, for example, Object beams can be multiplexed into holographic optical elements. Changing the HOE object beam includes, for example, the use of different masks, filters or lens combinations.

5A and 5B, a transmission mode holographic optical element (HOE) 550 in use is shown. In order to reproduce the HOE object beam (beam A) stored in the holographic optical element (HOE) 550, a beam 560, which is the same as or similar to the HOE reference beam (beam B), is generated from the light source 564, so that the holographic Irradiation toward the optical element (HOE) 550. By this irradiation the beam emitted from the holographic optical element (HOE) 550 is reproduced by the HOE object beam 540 (beam A), which is described above. As is the beam A which was originally captured on the holographic optical element (HOE) 550. The amount and direction of the HOE reference beam 560 relative to the holographic optical element HOE is, for example, comparable to the focal length f2 of the second lens during the generation of the holographic optical element 550. It depends on the distance D between the storage materials (for example described above with reference to FIG. 2).

As shown in FIG. 5A, when the distance D is shorter than the focal length f2 of the second lens (see FIG. 2), for the holographic information stored in the holographic optical element (HOE) 550, the HOE object beam 540 Image plane 575 is formed beyond holographic optical element (HOE) 550. In this case, the holographic optical element (HOE) 550 is irradiated by the HOE reference beam 560 at the same surface side 565 that was used to generate it. At this time, the HOE object beam 540 is reproduced by the intersection of the HOE reference beam 560 and the holographic optical element (HOE) 550, and the HOE object beam 540 beyond the holographic optical element (HOE) 550. An image plane (or other major plane) 575 is formed.

A suitable storage device, such as holographic memory cell 580 (HMC), is disposed relative to main plane P 575 for proper data retrieval. In many applications, this main plane is, but is not necessarily the plane with the image plane of the light beam or the focal point of the HOE reference beam. For example, if the optical system of FIG. 1 has to produce a Fourier plane as its output, plane P may be this Fourier plane. Thus, plane P can be any major plane for the associated holographic memory system (HMC).

As shown in FIG. 5B, when the distance D is longer than the focal length f2 of the second lens, for the holographic information stored in the holographic optical element (HOE) 550, the image plane of the HOE object beam 540 is It is formed in front of the holographic optical element (HOE) 550. In this case, the complex conjugate beam B ^* 562 of the HOE reference beam 560 generated from the light source 563 is from the second surface side 570, i.e., the holographic optical element HOE ( 550 is used to irradiate the holographic optical element (HOE) 550 from the opposite surface side of the surface that was used to generate 550. Thereafter, the complex conjugate beam A ^* 542 of the HOE object beam 540 is reproduced by the interaction of the beam 562 (B ^* ) and the holographic optical element (HOE) 550, so that the holographic optical element ( A major plane 575 of beam A ^* is formed in front of HOE) 550. Suitable data storage devices are arranged in this main plane for proper data retrieval. For example, in a PCM holographic memory system, the HMC is placed in the main plane.

Similarly, FIGS. 6A and 6B illustrate the use of reflective mode holographic optical element (HOE) 650. In general, the HOE object beam (beam A) is reproduced by directing the HOE reference beam 660 (or similar beam) from the light source 664 toward the holographic optical element (HOE) 650. The amount and direction of the HOE reference beam 660 (beam B) relative to the holographic optical element HOE is, for example, the focal length f2 of the second lens during generation of the holographic optical element HOE (eg, described above). Comparable to the description of FIG. 3), depends on the distance D between the second lens 625 and the holographic storage material.

As shown in FIG. 6A, when the distance D is shorter than the focal length f2 of the second lens during generation of the holographic optical element (HOE) 650, the image plane P 675 of the HOE object beam 640 becomes It is formed beyond the holographic optical element (HOE) 650. In this case, the holographic optical element (HOE) 650 is irradiated from the second surface side 670 by the HOE reference beam 660. Then, similarly as described above, the HOE object beam 640 is reproduced by the interaction of the HOE reference beam 660 and the holographic optical element (HOE) 650, thereby producing a holographic optical element (HOE) 650. Beyond) forms an image plane 675 (or other major plane) of the HOE object beam 640. Suitable storage devices, such as holographic memory cells (HMC) 680, are placed in this major plane for proper data retrieval. As described above with reference to FIGS. 5A and 5B, plane P may be any major plane for the associated holographic memory cell HMC.

As shown in FIG. 6B, when the distance D is longer than the focal length f2 of the second lens during generation of the holographic optical element (HOE) 650, the image plane P of the complex conjugate beam of the HOE object beam 642 675 is formed in front of the holographic optical element (HOE) 650. In this case, the holographic optical element (HOE) 650 is irradiated by the complex conjugate beam B ^* 662 of the HOE reference beam generated from the light source 663. Beam B ^* illuminates the holographic optical element with a first surface 665 opposite the surface that was used while writing data in the holographic optical element (HOE) 650. The complex conjugate A ^* 642 of the HOE object beam is reproduced by the interaction of the beam 662 (B ^* ) with the holographic optical element (HOE) 650, so that the holographic optical element (HOE) 650 It forms in front of the image plane 675 or another major plane of the beam A ^* . Data storage devices such as holographic memory cells (HMC) are typically placed in the main plane for proper data retrieval.

Thus, as shown generally in FIG. 7, a method 700 using a holographic optical element in accordance with an embodiment of the present invention is a holographic with a holographic representation of a coded data beam (eg, a HOE object beam). Providing 710 an optical element and directing a beam (eg, a HOE object beam) towards the holographic optical element to irradiate the holographic optical element to interact with the holographic information stored therein (720). And storing 730 the reproduced beam (eg, the HOE object beam) in the major plane of the reproduced beam. As described above with reference to FIGS. 5A and 5B and FIGS. 6A and 6B, the complex conjugate beams of the HOE reference beam (eg, beam B) and the HOE reference beam (eg, beam B ^* ) are suitable for the holographic optical element. Irradiated at an appropriate angle from the side.

For example, from the foregoing, it can be seen that the holographic optical element (HOE) is very suitable for replicating on a mass production scale. For example, once a master holographic optical element (HOE) has been generated, it is possible for its replication to be generated using conventional techniques such as stamping and embossing. It should also be understood that mass reproduction of holographic optical elements (HOEs) is possible. That is, a second identical holographic optical element HOE can be generated using the initially generated holographic optical element HOE. More specifically, data from the initially generated holographic optical element HOE is read and used to generate the second holographic optical element HOE. In this way, continuous reproduction of the holographic optical element HOE containing the same information is possible.

According to an embodiment of the invention, it is also possible to store the HOE object beam in its proximal region, as opposed to the holographic optical element beam storing in its central or Fresnel region as described previously herein. As shown in FIGS. 8A and 8B, the main plane (eg, image plane) of the HOE object beam is in front of or beyond the holographic storage material (eg, in the case of a typical holographic memory system) during the formation of the holographic optical element. , Less than approximately 2 millimeters or within a few pixels). In this way, when the reproduced HOE object beam is placed in the vicinity of a storage device such as an HMC, the reproduced HOE object beam is projected into the HMC or other data storage device.

Referring now to FIG. 8A, HOE object beam 840 (beam A) is stored in holographic storage material 850 to form a holographic optical element HOE, for example, in the manner described above. do. More specifically, the HOE object beam 840 and the HOE reference beam 860 (beam B) generated from the light source 864 propagate toward the holographic storage material 850 such that the interference pattern of the two beams is holographic. Stored in the photosensitive portion of storage material 850. The figure shows that the major plane P 875 of the HOE object beam 840 is formed just beyond the holographic storage material.

Therefore, as shown in FIG. 8B, upon reproduction of the HOE object beam 840 (beam A) from the holographic optical element (HOE) 850, the holographic optical element (HOE) 850 is the HMC 880. ), If placed within about 2 mm, for example, the major plane 875 is projected into the HMC 880 (or other suitable data storage device). The relatively narrow space between the holographic optical element (HOE) 850 and the HMC 880 is advantageous in that it is practical to pack them together as a portable pair for use in one or more holographic memory systems. . Thus, in fact, the "read head" (HOE) 850 and the "storage medium" (HMC) 880 of the holographic memory system are movable together.

Also, the embodiments shown in FIGS. 8A and 8B are advantageous because when the holographic optical element (HOE) 850 is being used to reproduce the HOE object beam 840, the HMC object beam C 885. ) Can penetrate the holographic optical element (HOE) 850 without being disturbed. The HMC object beam 885 passes through the holographic optical element (HOE) 850 undisturbed, which causes the holographic optical element (HOE) 850 to mismatch the HMC object beam 885 (played HOE object). The Bragg match diffraction) of the beam 840.

It should be noted that for purposes of explanation herein, the HMC object beam 885 (beam C) represents the object beam used to store holographic information within the HMC 880. As noted above in describing the HOE object beam 840 (beam A), during generation or formation of the holographic optical element (HOE) 850, the HOE object beam 840 acts as an object beam. . However, while storing holographic information in the HMC 880, the HMC object beam 885 acts as an object beam for the HMC 880, while the HOE object beam 840 is a reference beam for the HMC 880. Act as.

As described above, holographic optical elements (HOEs) can store multiple object beams (in this case, HMC reference beams) through multiplexing. That is, multiple HMC reference beams are multiplexed in the holographic optical element (HOE), for example by changing the angle, wavelength or position of the HOE reference beam while changing the HMC reference beam characteristics. HMC reference beam changes include, for example, the use of different masks, filters or lens combinations.

Referring now to FIGS. 9A and 9B, another embodiment of the present invention in which alignment information to assist in aligning the holographic optical element is provided as part of the information stored in the holographic storage material and then reproduced from the holographic optical element. Shown. As shown in FIG. 9A, while storing information in the near field of holographic storage material 950 (during the generation of holographic optical element), HOE object beam 940 is, for example, in the manner described above. Stored as. That is, the HOE object beam 940 and the HOE reference beam 960 (generated from the light source 964) propagate toward the holographic storage material 950, so that the interference patterns of the two beams of the holographic storage material 950 It will be stored in the light sensitive portion. The figure shows that the major plane P 975 of the HOE object beam 940 is formed just beyond the holographic storage material.

However, in this embodiment, alignment beam E 990 containing alignment information propagates towards holographic storage material 950 and is stored therein by HOE object beam 940. Alignment beam 990 may or may not be set to propagate with HMC object beam 985 (beam C) within the optical system.

As shown in FIG. 9B, while using the holographic optical element (HOE) 950, the alignment beam 990 and the HMC reference beam 940 are simultaneously reproduced by the HOE reference beam 960, which is the HOE reference. Beam 960 is similar or identical to the HOE reference beam of FIG. 9A. By using the HMC reference beam 940, the HMC object beam 985 and the reproduced alignment beam 990 are stored in and passed through the HMC 980 or other suitable storage device. After passing through the HMC 980, the alignment beam 990 impinges on a photodetector (not shown), for example, and the response of the photodetector is related to the alignment state of the holographic optical element (HOE) 950. Is provided as information. This information is provided for the dynamic alignment of the holographic optical element (HOE) 950. In addition, the alignment beam 990 is stored in the HMC 980 along with the HMC object beam 985 so that upon reproduction of the HMC object beam 985, the alignment beam 990 can also be reproduced.

The reproduced alignment beam provides information about the alignment of the HMC 980 in a manner similar to that for the holographic optical element (HOE) 950. Furthermore, according to this embodiment, the interference effect between the alignment beam 990 reproduced from the holographic optical element (HOE) 950 and the alignment beams reproduced from the HMC 980 is allowed, which effect the holographic optics. Provides information about the relative alignment between element (HOE) 950 and HMC 980.

As discussed above, there are a number of multiplexing techniques for storing and reproducing multiple HOE object beams within a single holographic optical element (HOE). Such techniques include, for example, Bragg angle, wavelength or phase multiplexing (overlapping holograms), or spatial multiplexing (non-overlapping) storing holograms at different locations within the HOE.

For example, FIGS. 10A and 10B show two general Bragg multiplexing examples of HOE object beam reproduction. 10A shows two HOE object beams A ₁ and A in the same radial direction from the same location of the holographic optical element (HOE) 1050, using their respective HOE reference beams B ₁ and B ₂ 1060. Reproducing ₂ 1040 is shown overall. In this way, the HOE object beams A1 and A2 are directed to the same position in the HMC (not shown). However, the HOE object beams A ₁ and A ₂ have different wavelength and / or phase structures so that they can be distinguished from each other.

The HOE object beams A ₁ and A ₂ are irradiated at the same general angle toward the same general position of the HOE 1050, so that the same position of the HOE 1050 (relative to each other, not necessarily beam A ₁ and / or A ₂₎ . Are stored at the same location by interfering with the HOE reference beams B ₁ and B ₂ which have also been irradiated. Reference beams B ₁ and B ₂ are irradiated toward the location of HOE 1050 at the same or different angles with respect to each other.

10B shows HOE object beams from the same location of holographic optical element (HOE) 1050 in different radial directions (generally toward different locations in the HMC) using their respective HOE reference beams B ₁ and B ₂ . Overall reproduction of A ₁ and A ₂ is shown. Thus, the HOE object beams A ₁ and A ₂ are stored (and reproduced) in the HOE 1050 at the same location in the HOE 1050 at different radiation angles. In addition, the beams A ₁ and A ₂ do not necessarily have the same wavelength and / or phase structure.

11A and 11B, another embodiment is shown that illustrates two spatial multiplexing examples of HOE object beam reproduction. FIG. 11A generally illustrates reproduction of two HOE object beams A ₁ and A ₂ in the same radial direction from different locations of holographic optical element (HOE) 1150. In this example, the regenerated beams A ₁ and A ₂ are generally directed toward different locations within the HMC (not shown) and may or may not have the same wavelength and / or phase structure. As shown, the HOE reference beams B ₁ and B ₂ are irradiated toward different positions of the HOE 1150 at the same angle or alternatively at different angles.

FIG. 11B generally illustrates reproduction of two HOE object beams A ₁ and A ₂ 1140 in different radial directions from the same location of holographic optical element (HOE) 1150. In this way, the regenerated beams A ₁ and A ₂ are generally directed toward the same position in the HMC (not shown) but do not have the same angle of incidence. The regenerated beams A ₁ and A ₂ may or may not have the same wavelength and / or phase structure. As shown, the HOE reference beams B ₁ and B ₂ 1160 are directed toward different locations of the HOE 1150 at the same angle or alternatively at different angles.

Another consideration in using the HOE object beam (HMC reference beam) emitted from the holographic optical element (HOE) is whether the beams are reproduced sequentially in time, simultaneously, or in various combinations of each. . Sequential use of HMC reference beams, such as beams A ₁ and A ₂ , reproduced from a single HOE, allows multiple readouts of the HMC during each HMC multiplexing step. Thus, one of the respective HMC reference beams irradiates the HMC at a predetermined time to reproduce its respective data page, such as the HMC object beam (beam C), from the HMC. This is implemented, for example, when one of the HMC reference beam regeneration techniques described above is used (FIGS. 10A and 10B, 11A and 11B).

Using HMC reference beams, such as beams A ₁ and A ₂ , reproduced from a single HOE simultaneously, enables multiple readouts of the HMC during each HMC multiplexing step. In this way, the plurality of HMC reference beams irradiate the HMC at a predetermined time to reproduce a plurality of data pages from the HMC, such as a single data page from the HMC object beam (beam C) or the HMC. This is implemented, for example, when one of the HMC reference beam regeneration techniques described above is used (FIGS. 10A and 10B, 11A and 11B).

When playing back a plurality of data pages (HMC object beams) at any given time, a single data page is directed, for example, to its own detector array, thereby increasing the concurrent throughput of the data. When reproducing a single data page (HMC object beam) at a given time, a plurality of HOE object beams work together to reproduce a single data page, thereby increasing the multiplex density of the HMC. This is implemented, for example, by partially combining the HMC object beam (beam C) from the same spatial location within the HMC, or by partially combining the HMC object beam (beam C) (all pointing to the same detector array) from different spatial locations within the HMC. do. In this way, for example using three HOE object beams (each "ON" or "OFF" state), eight (2 ³ ) different HMC object beams are reproduced, whereas in the prior art only Three HMC object beams are played.

For example, FIGS. 12A-12C illustrate various exemplary uses of parallel beam reproduction. Overall, FIG. 12A shows that the holographic optical element (HOE) 1250 is irradiated with HOE reference beams B ₁ and B ₃ 1260 to generate HOE object beams and HMC reference beams A ₁ and A ₃ . These beams interrogate into the HMC 1280 or other suitable data storage device at a single spatial location, whereby at least one HMC object beam 1285 (beam C _j ) is generated. This means that HOE reference beams B ₂ and B ₃ irradiate the holographic optical element (HOE) 1250 to generate HOE objects / HMC reference beams A ₂ and A ₃ , and enter the HMC 1280 at a single spatial location. This is compared with the example shown in FIG. 12B where at least one HMC object beam 1285 (beam C _k ) is generated by this incidence. Thus, it is possible for different combinations of the same beam to generate different data page beams.

Hereinafter, referring to another example of FIG. 12C, HOE reference beams B ₂ and B ₃ 1260 irradiate a holographic optical element (HOE) 1250, whereby the HOE object beam and the HMC reference beam A _2. And A ₃ are generated, and these beams enter the HMC 1280 at different spatial locations within the HMC 1280 to collectively generate the HMC object beam 1285 (beam C _m ).

13A and 13B show an exemplary comparison between a conventional holographic memory system and a holographic memory system using a holographic optical element (HOE) in accordance with the present invention. In general, recording holograms with complex reference arms is important for PCM holography, and typically extremely narrow selectivity functions are obtained. Thus, phase correlation multiplexing (PCM) holography allows for significant densities (eg, much greater than approximately 300 channel bits / μm ² ). For example, at half of the maximum correlation between the hologram and the reference beam, the overall width does not exceed about 5 μm. The peak represents the diffraction intensity of the stored hologram as a function of HMC position.

FIG. 13A shows the total diffraction efficiency of the recorded hologram as a function of the holographic memory cell (HMC) or HMC reference beam shifting with respect to each other when using a complex optical train. In this configuration, the reference arm used was a chirped phase mask with a randomly selected phase of 0 or π, with the x-coordinate changing linearly on one side from approximately 15 μm to 5 μm in the center. And rectangular pixel columns that change on the opposite side and vice versa (ie, 15-5-15 μm). The mask is Fourier filtered (high pass filter is placed in the Fourier plane) and imaged onto a holographic memory cell (HMC), for example using a 4f optical system as shown in FIG. Holograms whose diameter is approximately 5 millimeters (mm) are shifted in microns, and the total diffraction intensity is measured as a function of relative position. This result is shown in FIG. 13A.

FIG. 13B illustrates the overall diffraction efficiency of the recorded holograms as a shift function of the holographic memory cell (HMC) or HMC reference beam when using the holographic optical element (HOE) according to an embodiment of the present invention. have. As shown, according to an embodiment of the invention, the overall width at half of the maximum correlation shown in FIG. 13B is similar to that recorded by conventional optics (4f optical system), i.e., the total diffraction intensity is It is shown in Figure 13a. Repeating the same experiments, the holograms had the same physical size (5 mm). The HOE object beam in this case is the same as generating the data shown in FIG. 13A.

As described above, numerous embodiments of the holographic memory system, apparatus and method disclosed herein without departing from the spirit and scope of the invention as defined by the appended claims and their full scope of equivalents. It will be apparent to those skilled in the art that modifications and substitutions may be made.

The present invention provides a relatively inexpensive, simple, and reproducibly consistent alternative to a plurality of components of a reference arm of a holographic system, such as a phase correlation multiplexing (PCM) holographic memory system.

Claims (3)

In a phase correlation multiplexing (PCM) holographic memory system, A holographic optical element (HOE) having stored therein at least one hologram of at least one HMC reference beam, the hologram having optical information corresponding to a phase correlation multiplexed reference arm lens array; A reference beam generating source for generating at least one HOE reference beam, An object beam generator for generating at least one HMC object beam, Include at least one data storage device, Upon irradiation of the holographic optical element HOE by the HOE reference beam, the holographic optical element HOE reproduces the HMC reference beam to project the HMC reference beam, and the HMC reference beam is Storing at least one hologram of the data coded HMC object beam in the data storage device in accordance with a phase correlation multiplexing technique upon interference with the HMC object beam data encoded at a location within the data storage device. Phase-correlated multiplexed holographic memory system. The method of claim 1, The holographic optical element (HOE) is selected from the group comprising photopolymers, photoresists, thermoplastics, photorefractive materials or photochromatic materials. Phase correlation multiplexed holographic memory system consisting of at least one material. A device used in a phase correlation multiplexing (PCM) holographic memory system, At least one hologram of at least one HMC reference beam, wherein the hologram has optical information corresponding to a phase correlation multiplexed reference arm lens array; a holographic optical element (HOE) stored therein—the holographic optical element by a HOE reference beam Upon irradiation of HOE, the holographic optical element HOE reproduces the HMC reference beam and projects the HMC reference beam toward at least one holographic data storage device, wherein the HMC reference beam is the data. Storing at least one hologram of the data encoded HMC object beam in the data storage device in accordance with a phase correlation multiplexing technique upon interference with the at least one HMC object beam data encoded at a location in the storage device. Device.