Patent Application
20050180300
The present invention generally relates to photonics data memory devices. In particular, the present invention relates to parallel recording and reading of photonics data memory.
There is a strong interest in high-capacity data storage systems with fast data access due to an ever-increasing demand for data storage. Limitations in the storage density of conventional magnetic memory devices have led to considerable research in the field of optical memories. Holographic memories have been proposed to supersede the optical disc (compact disc read only memories, or CD-ROMs, and digital video data, or DVDs) as a high-capacity digital storage medium. The high density and speed of holographic memory results from the use of three-dimensional light modulation of the recording material and from the ability to simultaneously read out an entire page of data. The principal advantages of holographic memory are a higher information density, a short random-access time, and a high information transmission rate.
In holographic recording, a light beam from a coherent monochromatic source (e.g., a laser) is split into a reference beam and an object beam. The object beam is passed through a spatial light modulator (SLM) and then into a storage medium. The SLM forms a matrix of cells that modulate light intensity with grey levels. The SLM forms a matrix of shutters that represents a page of binary or grey-level data. The object beam passes through the SLM, which acts to modulate the object beam with binary information being displayed on the SLM. The modulated object beam is directed to one point, after an appropriate beam processing, where it intersects with the reference beam after being routed by an addressing mechanism. It is also contemplated that for multispectral holography, the multispectral hologram may be recorded with more than one wavelength from different lasers or from the same multiline laser at the same time. In other words, the recording can be operating with several wavelengths in the holographic multiplexing process.
An optical system consisting of lenses and mirrors is used to precisely direct the optical beam encoded with the packet of data to the particular addressed area of the storage medium. Optimum use of the capacity of a thick storage medium is realized by spatial and angular multiplexing that can be enhanced by adding frequency polarization, phase multiplexing, etc. In spatial multiplexing, a set of packets is stored in the storage medium and shaped into a plane as an array of spatially separated and regularly arranged subholograms by varying the beam direction in the X-axis and Y-axis of the plane. Each subhologram is formed at a point in the storage medium with the rectangular coordinates representing the respective packet address as recorded in the storage medium. In angular multiplexing, recording is carried out by keeping the X- and Y-coordinates the same while changing the irradiation angle of the reference beam in the storage medium. By repeatedly incrementing the irradiation angle, a plurality of packets of information is recorded as a set of subholograms at the same X- and Y-spatial location.
A volume (thick) hologram requires a thick storage medium, made up of a material sensitive to a spatial distribution of light energy produced by interference of a coherent object light beam and a reference coherent light beam. A hologram may be recorded in a medium as a variation of absorption or phase or both. The storage material responds to incident light patterns causing a change in its optical properties. In a volume hologram, a large number of packets of data can be superimposed, so that every packet of data can be reconstructed without distortion. A volume (thick) hologram may be regarded as a superposition of three-dimensional gratings recorded in the depth of the recording photosensitive material, each satisfying the Bragg law (i.e., a volume phase grating). The grating structures in a volume hologram produce changes in refraction and/or absorption.
While holographic storage systems have not yet replaced current compact disc (CD) and digital video data (DVD) systems, many advances continue to be made which further increase the potential of storage capacity of holographic memories. This includes the use of various multiplexing techniques such as angle, wavelength, phase-code, fractal, peristrophic, and shift. However, methods for recording information in highly multiplexed volume holographic elements, and for reading them out, have not proved satisfactory in terms of throughput, crosstalk, and capacity.
Currently, the recording and reading of the holographic memory is done on one point of the recording plate at a time (i.e., sequentially). For fast recording and reading processes, parallel recording and reading of multiple points (e.g., a matrix of points) is provided.
In order to facilitate a fuller understanding of the present invention, reference is now made to the appended drawings. These drawings should not be construed as limiting the present invention, but are intended to be exemplary only.
A recording system in the present invention comprises a laser, a storage layer, a matrix of SLMs and a matrix of focusing lenses. A reading system, which is assembled to read data from the diffractive optics memory by emitting a read (e.g., reference) beam onto the memory, comprises the diffractive optics memory and a matrix of CCDs. The diffractive optics memory has information stored therein, located at a plurality of points on the memory. At one angle, a plurality of packets of information is formed on a matrix of points on the diffractive optics memory. At another angle, another plurality of packets is formed at a different matrix of points on the memory. The present invention introduces the use of a matrix of SLMs in a recording system and a matrix of CCDs in a reading system to simultaneously store and read information on a matrix of points of a recording plate respectively. Furthermore, the present invention uses a large collimated object beam and a large reference beam, in the recording system, that can cover the matrix of points of the recording plate (i.e., the diffractive optics memory). In the reading system, a large read beam (e.g., reference beam) is used for reading the information from the matrix of points of the recording plate.
Further advantages and novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description, as well as by practice of the invention. While the invention is described below with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the invention as disclosed and claimed herein, and with respect to which the invention could be of significant utility.
Storing/Recording Phase
The collimated beam expander 103 expands the object beam 115 and produces an expanded object beam 125. The expanded object beam 125 is expanded to fit the matrix of SLMs. The reference beam expander 104 expands the reference beam 110 and produces an expanded reference beam 120. The expanded object beam 125 passes through a matrix of SLMs (e.g., displays), which acts to modulate the expanded object beam 125 to produce a plurality of object beams, which carry binary information. In one embodiment, the number of SLMs in the matrix of SLMs corresponds to the number of object beams, which also corresponds to the number of matrix of points on the recording plate (see
It is contemplated that the memory device 205 has a plurality of cells to hold the recorded information. The memory device 205 is a holographic memory device that contains information stored during a phase of storing information. The memory device 205 is typically a three-dimensional body made up of a material sensitive to a spatial distribution of light energy produced by interference of the matrix of object beams 203 and the expanded reference light beam 120. Holograms may be recorded in the medium 205 as a variation of absorption or phase or both. The storage material responds to incident light patterns, causing the change in its optical properties. In a volume (thick) hologram, a large number of packets of data can be superimposed, so that every packet of data can be reconstructed without distortion. The volume hologram may be regarded as a superposition of three-dimensional gratings recorded in the depth of the layer of the recording material, each satisfying the Bragg law (i.e., a volume phase grating). The grating structures in a volume hologram produce changes in refraction and/or absorption. Each of a plurality of points on the matrix of points is defined by its rectilinear coordinates (X,Y). An image-forming system (not shown) reduces the matrix of object beams 203 to a plurality of sub-holograms each having a minimum size at one of the X,Y points of the matrix of points. A point in physical space, defined by its rectilinear coordinates, contains a plurality of packets.
In one embodiment, the memory device 205 is constructed of organic material, such as a polypeptide material, and made in accordance with the techniques described in the co-pending patent application entitled “Photonics Data Storage System Using a Polypeptide Material and Method for Making Same,” Serial No. PCT/FR01/02386, which is herein incorporated by reference.
A display in the matrix of displays 201 may be any device for displaying data packets in a system, such as spatial light modulators (SLMs) or liquid crystal light valves (LCLVs). The plurality of bits represented on the display screen of the display is presented as a two-dimensional pattern of transparent and opaque pixels (i.e., data packet). The data packet displayed is derived from any source such as a computer program, the Internet, and so forth. In an Internet storage application, the packets displayed may be formatted similarly to the packets of the Internet.
When the matrix of object beams 203 passes through the matrix of displays 201, the display acts to modulate the matrix of object beams 203 with the binary information. The matrix of object beams 203 is then directed to a defined matrix of points on the recording medium 205 where these object beams intersect with the expanded reference beam 120 to create a plurality of interference patterns loaded with data packets. The matrix of lenses 202 may be used to converge the modulated matrix of object beams 203 and to focus the beams to the recording medium 205. In other words, the modulated object beams become reduced by means of the lenses in the matrix of lenses 202 so that the matrix of points of convergence of the modulated object beams lie slightly beyond the recording medium 205. The expanded reference beam 120 is positioned at different angles by the angular multiplexing method so that a plurality of data packets is recorded at the matrix of points of the recording medium 205.
As stated above, the recording system 100 includes the expanded reference beam 120, the matrix of object beams 203, and the recording medium 205. The expanded reference beam 120 and the object beams in the matrix of object beams 203 intersect to form patterns to be recorded on the recording medium 205 at a matrix of X,Y locations. The expanded reference beam 120 is angularly modified sequentially so that different data can be recorded on a different matrix of points with different angles on the recording medium 205. The expanded reference beam 120 is also spatially changed so that data can be recorded on a different matrix of points of the recording medium 101. This is the spatial multiplexing that is carried out by sequentially changing the rectilinear coordinates. Angular multiplexing is achieved by varying the angle of the expanded reference beam 120 with respect to the surface plane of the storage medium 205. In other words, angular multiplexing is carried out by sequentially changing the angle of the expanded reference beam 120. Multiple packets of information are recorded in the storage medium 205 as a matrix of diffraction patterns (e.g., matrix of sub-holograms) for each selected angle and spatial location. Spatial multiplexing is achieved by shifting the expanded reference beam 120 with respect to the surface of the storage medium 205 so that a matrix of points shifts to another spatial location. A matrix of data packets may be reconstructed by shining the expanded reference beam 120 at the same angle and spatial location at which the matrix of data packets was recorded. The portion of the expanded reference beam 120 diffracted by the storage medium material forms the reconstruction, which is typically detected by a detector array. The storage medium 205 may be mechanically shifted in order to store data packets at a different matrix of points by their coordinates (X,Y).
The storage medium 205 is arranged in matrices. Each of a plurality of points on the matrix is defined by its rectilinear coordinate's signals involved in recording a diffraction pattern (i.e., a hologram) in a storage medium using angular and spatial multiplexing. Various diffractive recording processes have been developed in the art, and further details can be found in the book Holographic Data Storage by H. J. Coufal, D. Psaltis, and G. T. Sincerbox (Springer 2000). It is contemplated that a storage diffractive patterns matrix, in some cases, can also be implemented by using techniques other than the interference of a reference and object beam, such as using an e-beam and a microlithography process for etching materials to generate diffractive structures.
Reading Phase
Retrieving the recorded/stored information from the recording medium 205 requires the use of a reference beam (i.e., read beam) whose characteristics correspond to those employed for writing or for storage. The reference beam induces diffraction due to perturbation in the refractive index modulation corresponding to the characteristics of the recording beams, thereby creating a data loaded modulated beam. The reading angle values in the reading procedure are similar to those of the writing procedure in that they both use the same principles of nodal points. The reading procedure may be carried out with a greater degree of tolerance than the recording procedure. However, the laser source used for reading may not be as powerful as the laser source used for recording.
The reference beam is positioned in order to access a plurality of data packets contained at a defined matrix of points (XM, YN, where M and N are positive integers) in the recorded medium 205. In one embodiment, M equals N. The reading procedure is similar in the addressing angle values to the writing or recording procedure. However, the reading procedure may be carried out with a greater degree of tolerance than the recording procedure. It is possible to use a very compact laser source of a solid-state type for the reading process because the laser power necessary for reading is much lower than the one for recording.
Data packets are reconstructed by shining the expanded reading beam 301 (i.e. reference beam) at the same angle and spatial location in which the data packets were recorded. The expanded reading beam 301 may be the same as the expanded reference beam 120 as shown in
The reading apparatus 300 may also include dynamic devices (e.g., actuators, micromirrors, etc.) that shape and direct the expanded reading beam 301 generated by the laser 101 at a position and angle onto the matrix of points of the recording plate 205. A computer (not shown) may be used to control the dynamic devices.
Each of the sensing devices in the matrix of sensing devices 305 may be any sensor that can sense the images from a matrix of output beams 302. The sensing device may be made of CCD or CMOS (complementary metal-oxide-semiconductor) active pixel sensors (APS). In one embodiment, the sensing device is a charge-coupled diode.
The matrix of output of beams 302, which contains a plurality of output pages carrying data/information in the memory device, is created by the expanded reading beam 302. The plurality of data packets from the matrix of points in the recording medium 205 are reconstructed simultaneously by shining the expanded reference beam (i.e., read beam) 301 at the same location in which the data packets were recorded. The expanded reference beam 301 diffracted by the recording medium 205 forms the reconstruction of the matrix of stored data packets, which are detected by the matrix of sensing devices 305. The expanded reference beam 301 is configured to address the plurality of packets at different locations in the recording medium 205. The digital output of the matrix of image sensors 305 is further processed by a computer (not shown).
The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, this application is intended to cover any modifications of the present invention, in addition to those described hereih, and the present invention is not confined to the details which have been set forth. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP02/05449 | 4/26/2002 | WO |
