Holographic Data Storage System

                                          A Revolution in 21st Century

                                                                                         By Rizwan Ahmad

Introduction

“Image/signal processing is a wide research area of analysis, transformation, compression, and reconstruction of visual information with application to different fields of Science and Technology, such as Biomedicine, Industrial inspection, Control and security systems, Robotic vision, etc. Essentially, detection and localization of objects is reduced to the performance of correlation operation of the given object with the observed picture and subsequent comparison of the result with a threshold”1.

 

The use of lens to image an object is one of the oldest principles in optics and photography. Surprisingly, little is known about the history of the early development of lenses and especially the early utilization of spectacle lenses and magnifiers. However, in 1948 two-step imaging processs was introduced by Gabor in which he used a combination of lenses in order to produce a record containing the information necessary to create an image. Although, the technique has advanced considerably since then but Gabor’s two step method did provide the necessary groundwork for the recent technological innovations 2. A few years later, LASER came into existence and became known in particularly every branch of science and technology. LASER stands for Light Amplification by Stimulated Emission of Radiation and is a very pure and intense beam of light formed within a crystal, or the device that creates the light 3.This approach is a record in the history of technological advancement because its arrival signaled the expansion of an era that seemed to revolutionize the application of LASER and its potential as a new tool. Holography, in which a combination of lenses are used to produce an image, is one of the earliest applications of LASER and “enjoyed a period of exciting exposition in the early to middle 1960s followed by a short period of pessimism about its future, and it is now firmly established as a viable application which are likely to show steady growth in future”4. Holographic data storage is a volumetric approach which, although conceived decades ago, has made recent progress toward practicality with the appearance of lower-cost enabling technologies, significant results from longstanding research efforts, and progress in holographic recording materials 5.

 

“Holography” also known as “Wavefront Reconstruction”  is a way to retrieve the likeness of a subject from a record of its unfocussed diffraction pattern. In other words, it is a practical means for storing wavefronts in a record from which the wavefronts may later be reconstructed. The record, formed in photosensitive material is called a hologram 6. The quality and ease with which the holograms  may be produced have considerable bearing on their utility. The main factors which influence this, are the  available recording materials and versatility of optical components. With the exception of the LASER, it is shown that useful holographic work can be carried out with a minimum of capital equipment 7. Here, photosensitive materials may be defined as those materials which change its chemical and physical properties when exposed to light.

 

The idea of holographic storage was first proposed in 1963 by Pieter J. Van Heerden at Polaroid who predicted that a volume V of holographic recording medium can store about V/(l3) bits of information (where l is the wavelength of light used in the holographic storage device). This yields 6 terabits (Unit to measure storage of data) of information in a cube-of-sugar-like, 1 cm3 storage volume, using green light of wavelength 550 nanometers (A unit used to measure wavelength). This impressive storage capacity can be further increased several orders of magnitude by sophisticated spectral hole-burning techniques that can overlap as much as 108 different data pages in a single spot of the storage medium (each data page being recorded by a slightly different light frequency) 8. Here, wavelength may be defined as the distance between one peak or crest of a wave of light and the next corresponding peak or crest. It determines the nature of the various forms of radiant energy that comprise the electromagnetic spectrum and is equal to waveform velocity (the velocity with which the light wave travels) divided by frequency (number of oscillations per second) of a wave 9.

After decades of research and development, holographic storage system  is close at hand. This paper would focus on the following topics concerning Holographic Data Storage System:

(i)                  To provide a brief history of the development of the technology itself and how it works.

(ii)                How this technology has been used in various fields so far.

(iii)               Its advantages and disadvantages as opposed to the other conventional mechanical and optical storage devices and then drawing the conclusion objectively to determine the suitability and practicality of the technology for both current and future use  in United States.

Brief Historical Background

After the invention of LASER which revitalized the ancient science of optics and enthused a new hope for the study of coherent light and combination of lenses that aroused the method of reconstruction of an object known as “holography”. Albeit, the principal of “holography” had been in existence for a while when “Wavefront Construction” was invented by Dennis Gabor of Imperial College of Science and Technology in London in 1947.He used the wave nature of electrons to create electron interference patterns from which he could reconstruct magnified images by optical rather than electrical means 10. In his first step which is called the formation or recording, he allowed the background wave to interfere with the diffracted object field. The second step which is called reconstruction, consisted of placing the photographic transparency into a coherent beam of light thereby, producing an image of the original object. The resulting interference pattern was called a hologram after the Greek word holos, which means “the whole” because the photographic record contains information concerning both the amplitude and phase of the original object 11.At that time he could not get the desired coherence  in the electron beam but with the arrival of coherent LASER beam, light could be constructed millions of times brighter than its source. Holography was indeed on his way 12.

 

A decade later, holography seemed to be a certainty. In 1962, Leith and Upatneiks, published a series of reports demonstrating a new approach to optical holography based on Communication theory technique. By 1964, there was an ample proof how eminent was the use of LASER light in holography. The three dimensional images that they generated by illuminating a photographic plate with light from a LASER “excited the imagination of all who saw them and stimulated many to initiate their own investigations into the potential of holography. Today holography is widely known as practical means for storing wavefronts in a record form which the wavefronts may later be constructed 13. Finally, the idea of holographic data storage was postulated by Pieter J. Van Heerden at Polaroid in 1963 who predicted that a very large information of data  can be stored in holographic recording medium and how its storage capacity can be increased considerably 14. After years of research and development, researchers are on the verge of using holograms to store data in memories that are both fast and vast.

 

Principle (Working of holographic data storage system)

Holography is a three-dimensional imaging technique in which laser light records the patterns of light waves reflected from an object onto the emulsion of light sensitive film (or glass plates). After the film is developed, and re-exposed to laser light (or normal incandescent light like most holograms today), it re-creates, in space,  all the points of light that originally came from the object. The resulting image, either behind or in front of the holographic film, has all the dimensions of the original object and looks so real that if one is tempted to reach out and touch it, nothing is found there except focused light 15.

Holographic data-storage works by recording the differences between two beams of laser light. In holographic data storage, an entire page of information is stored at once as an optical interference pattern within a thick, photosensitive optical material. The first is a reference beam that contains no information. The second carries data that it has picked up by being passed through a liquid-crystal panel known as a spatial light modulator.The resulting optical interference pattern causes chemical and/or physical changes in the photosensitive medium. This is done by intersecting two coherent laser beams within the storage material.  A replica of the interference pattern is stored as a change in the absorption or thickness of the photosensitive medium. When the stored interference grating is illuminated with one of the two waves that was used during recording, some of this incident light is diffracted by the stored grating in such a fashion that the other wave is reconstructed. Illuminating the stored grating with the reference wave reconstructs the object wave and vice versa. Interestingly, a backward-propagating  reference wave, illuminating the stored grating from the “back” side, reconstructs an object wave that also propagates backward toward its original source. A large number of these interference gratings or patterns can be superimposed in the same thick piece of media and can be accessed independently, as long as they are distinguishable by the direction or the spacing of the gratings. Such separation can be accomplished by changing the angle between the object and reference wave or by changing the laser wavelength. Any particular data page can then be read out independently by illuminating the stored gratings with the reference wave that was used to store that page  16.

There are two types of holograms and can be distinguished the way they are illuminated. One is “Reflection” and the other one is “Transmission”. Reflection holograms are lit from the front, reflecting the light to us as we view it, like a painting or photograph hung on a wall whereas, Transmission holograms are lit from the rear (like a photographic transparency) and bend light as it passes through the hologram to our eyes to form the image 17.

Because of holography being a volume storage method, the capacity of a holographic storage system increases with the thickness of the medium, since greater the thickness, the more “independent diffraction gratings with higher selectivity” it stores so that individual data pages can be read out “without crosstalk from other pages stored in the same volume” 18.The thicker the holographic material, the more sensitive is the reconstruction to the particular angle of incidence of the reference beam due to which multiple objects are recorded in the same volume in order to access independently by using an appropriate set of associated reference beams 19.

A Significant Development

Unlike photography or painting, holography can render a subject with complete dimensional fidelity. A hologram creates everything the eyes see - depth, size, shape, texture, and relative position from many points of view 20. With three-dimensional recording and parallel data readout, holographic memories can outperform existing optical storage techniques.The angularly selective property of holograms recorded in thick materials enables a unique form of high-capacity data storage distinguished by its parallel data access capability. A holographic data storage system is fundamentally page-oriented, with each block of data defined by the number of data bits that can be spatially impressed onto the object beam. The total storage capacity of the system is then equal to the product of the page size (in bits) and the number of pages that can be recorded 21. In addition to high storage density, holographic data storage promises fast access times, because the laser beams can be moved rapidly unlike in disk drives. With the inherent parallelism of its page-wise storage and retrieval, a very large compound data rate can be reached by having a large number of relatively slow, and therefore low-cost, parallel channels 22.

Hence, we have seen that Holographic Data Storage system is a promising digital storage technology because of its potential for high data storage density, high data rate and short access time. The ability to multiplex several pages into a given volume of the medium leads to potentially high volumetric storage densities.

Applications

Since the discovery of the Holography, its use as a storage device has accelerated the ongoing research as to how this technology can be used in many different areas.“The limit of hard drive storage is expected to be reached within the next ten to fifteen years. By then magnetic bit sizes will be so small that phenomenon such as the super paramagnetic effect (SPE) and shot noise will cause the polarity of the magnetic fields to flip randomly. Likewise, optical disks such as DVDs may reach their maximum capacity due to the diffraction limit of the laser light used” 23. So it can be assumed that Holographic Data Storage System can save us from this overload of storage capacity because of its high storage capacity, high data rate and short access time.

 Optware Corp., the developer of Collinear Holographic Data Storage System,  has already produced world's first recording and play back of digital movies on a holographic recording disc with a reflective layer using Optware's revolutionary Collinear Holography. This is a major milestone for commercializing holographic data storage system  24. JPL, under current sponsorships from NASA Space Science and Earth Science Programs, is developing a “high-density, nonvolatile and advanced Compact Holographic Data Storage (CHDS) system to enable large-capacity, high-speed, low power consumption, and read/write of data for potential commercial and NASA space applications” 25. Similarly, Stanford team is all set to build first digital holographic video, data and sound storage system. With this, they believe it will be possible to store “hundreds of billions of bytes of digital data and retrieve them at a rate of billions of bits per second with a high degree of accuracy”. Holographic storage could also be a solution for “high-speed parallel computing and for storing large databases, like the constant stream of photographs from LANDSAT (Land Remote Sensing Satellite System) satellites”. Because of a quick retrieval time, a holographic video archive could be set up and consumers could dial in to order movies on demand from a central source, via “fiber-optic cables”.A rich variety of images can be easily pulled up in seconds by multimedia and video-game inventors 26. Having seen its potential use in so many areas, it may be assumed that The Air Force or any such highly secured organization can also make use of Holographic Data Storage System to store different information per cubic volume in order to access memory having highly secured information which can be accessed by their unique different frequencies. Hence these unique frequencies and the difference in wavelength of the various frequencies would keep these information separate as well as confidential since these information can only be accessed by eligible and trained individuals.

 

 

ADVANTAGES

Devices which use light to store data have been in use for many years. But Holographic Data Storage System has revolutionized the technology for storing data not only because of its high storage capacity but also due to its high data rate and low access time. Holographic memory offers the possibility of storing 1 terabyte (TB) of data in a sugar-cube-sized crystal (200 times the capacity of a single layer DVD), with a transfer speed of one gigabyte per second (40 times the speed of DVD). This approach is rapidly gaining attention as a high-capacity, high-speed data storage technology for the age of broadband.CDs and DVDs are the primary data storage mediums. A CD can hold 783 megabytes of data. A double-sided, double-layer DVD can hold 15.9 GB of data. These conventional storage mediums meet today's storage needs, but storage technologies have  to keep pace with increasing consumer demand. Data from more than 1,000 CDs could fit on a holographic memory system. Most computer hard drives only hold less than 100 GBs of data, a small fraction of what a holographic memory system might hold 27. Holographic Data Storage System has many advantages over other conventional storage methods.  

Recording

First, millions of data are read and written out simultaneously in hologram unlike data being recorded and written out by bit by bit like other conventional devices.  By varying the reference beam angle between reference beam and data carrying signal beam, multiple holograms are recorded in the same volume of the medium, vastly increasing the data density 28. All three dimensions of the material are used to store data and not just the surface. This three dimension of storage allows for a phenomenon where many information-laden holograms can be superimposed or multiplexed in the same volume of medium. Since all the information in the hologram is recorded as a complex interference pattern in the bulk of the material, so the effects of scratches, dust etc. can be completely eliminated as could be the case with other conventional devices such as CDs or DVDs, thereby reducing the “bit rate error” 29.

Reading

 

A reference beam with characteristics identical to the object used to store the data reconstructs the stored data page in order to read the data. The reconstructed data page is imaged onto a detector that reads all of the one million bits on the data in parallel. This parallel recording and read out of data provides holography with its very fast transfer rates 30. It is also because data is read out or written as two dimensions digital in a three dimension volume rather than a bit stream unlike many other conventional storage devices 31.

 

Holographic data storage has shown the capability of rapid parallel search through the stored data via “associative retrieval: Imprinting a partial or search data pattern on the object beam and illuminating the stored holograms reconstructs all of the reference beams that were used to store data. The intensity that is diffracted by each of the stored interference gratings into the corresponding reconstructed reference beam is proportional to the similarity between the search pattern and the content of that particular data page. By determining, for example, which reference beam has the highest intensity and then reading the corresponding data page with this reference beam, the closest match to the search pattern can be found without initially knowing its address” 32.

The first holographic drive prototype developed by InPhase, with a 50-year life records 1.3 million bits of data in one page and 80 to 130 pages of data in a single location in the disk. Each data page is recorded at an unique angular address separated by 1 degree 33.

Disadvantages

Although, Holographic Data Storage System has brought innovation in its fold as far as data storage capabilities in the 21st century are concerned but still is suffering from some technical difficulties that needs to be addressed. For example, if we sore too many pages  in one crystal, the strength of each hologram is diminished. If  too many holograms are stored on a crystal, and the reference laser used to retrieve a hologram is not shined at the precise angle, a hologram will pick up a lot of background from the other holograms stored around it. It is also a challenge to align all of these components in a low-cost system 34. However, researchers are confident that they would find a way out of this situation in the next few years. Holographic data storage also suffers from the relatively high component and integration costs faced by any emerging technology as opposed to magnetic hard  drives which are well established, with a broad knowledge base, infrastructure, and market acceptance 35.

Recording Material

The connections between materials properties and system performance are complex, and many tradeoffs are possible in adapting a given material to yield the best results. Lithium Niobate Crystal or photopolymer is the recording material which are normally used in implementing the holographic data storage system 36. Their properties can be broadly characterized as “optical quality,” “recording properties,” and “stability”. These are the factors which directly affect the “data density” and “capacity”, “the data rates for input and output”, and the “Bit Error Ratio” 37. In some cases, it was found difficult to maintain the necessary optical quality while scaling up the thickness of the material in order to improve the storage capacity, while in other cases thickness is limited by the physics and chemistry of the recording process 38.  Dynamic range has a strong impact on the data storage density that is barely achievable with known recording materials under exposure conditions appropriate for recording high-fidelity data holograms. In the case of holographic storage, the response of the recording medium, which converts the optical interference pattern to the hologram is generally linear in light intensity and lacks the response threshold found in bi-stable storage media such as magnetic films. Stability in the dark over long periods is also an issue; “organic photopolymer materials” are often subject to aging processes caused by residual reactive species left in the material after recording or by stresses built up in the material during recording. Erasure may occur because of residual thermal diffusion of the molecules which record the hologram thereby, causing destructive read-outs and degrading previous writes 39. In case of photopolymers being used as recording materials, they might cause “shrinkage of the material with polymerization and the possibility of nonlinear response” thereby distorting the “reconstructed holograms” and thus causing “errors in decoding the digital data” 40.

Conclusion & Prediction

 

With computers and internet flooding around us, the information age has provided an explosion of information that can be stored and transferred from one part of the world to the other within a fraction of second. The decreasing cost of storing data and increasing storage capacity have brought forth this revolution which led to a demand of more and more research on improving the storage capacity both in terms of its capacity and stability.

 

Despite certain drawbacks in the Holographic Data Storage System such as destructive read-outs and degraded writes, distortion of the reconstructed holograms etc., it has emerged as a revolutionary storage technology in the 21st century for its extremely high capacity, very high data rate and low access time free of any scratches or dust as opposed to other conventional mechanical and optical storage devices. Both magnetic and conventional optical data storage technologies, where individual bits are stored as distinct magnetic or optical changes on the surface of a recording medium seem to be approaching physical limits beyond which individual bits may be too small or too difficult to store. Storing information in all the dimension of a medium (3D)—not just on its surface—offers an intriguing high-capacity alternative. For the longer term and significant gain in market share, removable volumetric parallel accessible holographic storage systems approach appear attractive. The parallel recording and extremely fast transfer rates make the holographic data storage system a very viable alternative to other optical and mechanical conventional storage devices.

 

The key issue for holographic storage is the development of an inexpensive, reliable write-once storage material. An interrupted research for the last few years in order to improve the performance of the holographic storage has produced excellent results both in terms of its stability and efficiency. Most of the drawbacks and limitations associated with the stability, dynamic range and thickness of the recording material of holographic storage device have been controlled to a greater extent. For example, InPhase developed a highly efficient and commercially viable photopolymer material that “offers high dynamic range, high photosensitivity, dimensional stability, optical clarity, manufacturability, nondestructive readout, thickness, and environmental and thermal stability” what it calls two-chemistry system which is intended to solve the distortion problem by using a material in which the chemical processes that hold it together are separate from those that make it photosensitive 41. Similarly, IBM has claimed to have solved another longstanding problem associated with parallel recording of holography, as it is known “cross-talk noise” , responsible to cause faint images of all the files recorded to be  called up even when only one is being accessed 42.

 

The ongoing research and technological development to improve the performance and efficiency of holographic data storage system while making it cost-effective at the same time, makes it an extremely viable alternative to all the previously existed storage devices and it seems the product is all set to flood the market in the next few years.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Footnotes

1.        T. Alieva, and M. L. Calvo, "Fractionalization of the linear cyclic transforms," J. Opt. Soc. Am. A Vol.17, P.2330. (2000). P.1

2.        Develis, John B. & Reynolds, George O.  Theory And Applications of Holography. Addison-Wesley Publishing Company: Reading, Massachusetts, Menlo Park, California. P.1

3.        Available[Online]. http://www.google.com/search?hl=en&lr=&ie=UTF-8&oi=defmore&q=define:LASER

4.        Butters, John N. Holography and its Technology. University Printing House, Cambridge, p. I

5.        Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology. P.1Volume 44, Number 3, 200

6.        Collier, Robert J. & Burckhardt, Christoph B. & Lin, Lawrence H. Optical   Holography. Academic Press: New York, London. P. 1-2

7.        Butters, John N. Holography and its Technology. University Printing House,  Cambridge, p. 2.

8.        P. Cheben and M. L. Calvo "A Photopolymerizable Glass with Diffraction Efficiency near 100% for Holographic storage," Appl. Phys. Lett., Vol. 78, P. 1490-1491 (2001).

9.         Available[Online]. http://www.answers.com/topic/wavelength

10.     Kiley, Leo A. United States Air Force, Office of Aerospace Research. Holography. S.P.I.E Seminar Proceedings. Volume 15, P. 4

11.     Develis, John B. & Reynolds, George O.  Theory And Applications of Holography. Addison-Wesley Publishing Company: Reading, Massachusetts, Menlo Park, California. P.1

12.     Develis, John B. & Reynolds, George O.  Theory And Applications of Holography. Addison-Wesley Publishing Company: Reading, Massachusetts, Menlo Park, California. P.1

13.     Collier, Robert J. & Burckhardt, Christoph B. & Lin, Lawrence H. Optical   Holography. Academic Press: New York, London. P. 2

14.     P. Cheben and M. L. Calvo "A Photopolymerizable Glass with Diffraction Efficiency near 100% for Holographic Storage," Appl. Phys. Lett., Vol. 78, P. 1490-1491(2001).

15.     Outwater, Chris & Hamersyeld, Van. The Guide To Practical Holography. P.1 Available[Online]. http://www.holophile.com/html/about.htm

16.     Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology. P.1

17.     Outwater, Chris & Hamersyeld, Van. The Guide To Practical Holography. P.1-2. Available[Online]. http://www.holophile.com/html/about.htm

18.     Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology. P. 17.

19.     Hong, John H. & Psaltis Demetri. Dense Holographic Storage Promises Fast Access. Adapted from Laser Focus World (April 1996, p. 119), P.1 Available[Online].Vhttp://silver.neep.wisc.edu/~lakes/hoStorage.html

20.     Outwater, Chris & Hamersyeld, Van. The Guide To Practical Holography. P.1 Available[Online]. http://www.holophile.com/html/about.htm

21.     Hong, John H. & Psaltis Demetri. Dense Holographic Storage Promises Fast Access. Adapted from Laser Focus World (April 1996, p. 119), P.1 Available[Online].Vhttp://silver.neep.wisc.edu/~lakes/hoStorage.html

22.     Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology. P.2

23.     Sherif, Hosam. Optimisation of a Novel Photopolymer for use in Holographic Data Storage. P.1 Available[Online]. res://C:\WINDOWS\System32\shdoclc.dll/navcancl.htm#https://tumail.temple.edu/wm/mail/login.html

24.     Kageyama, Yasuhide. Optware Corporation. P. 1 Available[Online].http://www.optware.co.jp/english/what_040823.htm

25.     Eighteenth IEEE Symposium on Mass Storage Systems and Technologies(MSS’01). Compact Holographic Data Storage System. P 237.

26.     Defense Department's Advanced Research Projects Agency Report. Stanford University. P.1 Available[Online]. http://www.stanford.edu/dept/news/relaged/940804Arc4171.html

27.     Bonsor, Kevin. How Holographic Memory will work. P.1 Available[Online]. http://computer.howstuffworks.com/holographic-memory.htm

28.     Murphy, Liz. Holography Data Storage: New Technology Meets Exponential Growth Needs. InPhase Technologies. P.1 Available [Online]. www.inphase-tech.com

29.     Sherif, Hosam. Optimisation of a novel photopolymer for use in holographic data storage. P.1 Available[Online]. res://C:\WINDOWS\System32\shdoclc.dll/navcancl.htm#https://tumail.temple.edu/wm/mail/login.html

30.     Murphy, Liz. Holography Data Storage: New Technology Meets Exponential Growth Needs. InPhase Technologies. P.2 Available [Online]. www.inphase-tech.com

31.     Sherif, Hosam. Optimisation of a novel photopolymer for use in holographic data storage. P.1 Available[Online]. res://C:\WINDOWS\System32\shdoclc.dll/navcancl.htm#https://tumail.temple.edu/wm/mail/login.html

32.     Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology, P. 2

33.     Murphy, Liz. Holography Data Storage: New Technology Meets Exponential Growth Needs. InPhase Technologies. P. 3 Available [Online]. www.inphase-tech.com

34.     Bonsor, Kevin. How Holographic Memory will work. P. 4 Available[Online]. http://computer.howstuffworks.com/holographic-memory.htm

35.     Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology, P. 23

36.     Bonsor, Kevin. How Holographic Memory will work. P. 3 Available[Online]. http://computer.howstuffworks.com/holographic-memory.htm

37.     Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology P. 16

38.     Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology P.17

39.     Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology P.18

40.     Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology P.19

41.     Murphy, Liz. Holography Data Storage: New Technology Meets Exponential Growth Needs. InPhase Technologies. P.2Available [Online]. www.inphase-tech.com

42.     Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, 2000, Directions In Information Technology P.12

 

Bibliography

Ashley, Bernal, Burr, Coufal, Guenther, Hoffnagle, Jefferson, Marcus, Macfarlane, Shelby & Sincerbox. IBM Journal of Research and Development, Volume 44, Number 3, (2000) Directions In Information Technology.

Bonsor, Kevin. How Holographic Memory will work. Available[Online]. http://computer.howstuffworks.com/holographic-memory.htm

      Butters, John N. Holography and its Technology. University Printing House,  Cambridge.

Collier, Robert J. & Burckhardt, Christoph B. & Lin, Lawrence H. Optical   Holography. Academic Press: New York, London.

Defense Department's Advanced Research Projects Agency Report. Stanford University. Available[Online]. http://www.stanford.edu/dept/news/relaged/940804Arc4171.html

Develis, John B. & Reynolds, George O.  Theory And Applications of Holography. Addison-Wesley Publishing Company: Reading, Massachusetts, Menlo Park, California.

Eighteenth IEEE Symposium on Mass Storage Systems and Technologies(MSS’01). Compact Holographic Data Storage System.

Hong, John H. & Psaltis Demetri. Dense Holographic Storage Promises Fast Access. Adapted from Laser Focus World (April 1996, p. 119).

Kageyama, Yasuhide. Optware Corporation. Available[Online].http://www.optware.co.jp/english/what_040823.htm

Kiley, Leo A. United States Air Force, Office of Aerospace Research. Holography. S.P.I.E Seminar Proceedings. Volume 15.

Murphy, Liz. Holography Data Storage: New Technology Meets Exponential Growth Needs. InPhase Technologies. Available [Online]. www.inphase-tech.com

Outwater, Chris & Hamersyeld, Van. The Guide To Practical Holography. Available[Online]. http://www.holophile.com/html/about.htm

P. Cheben and M. L. Calvo "A Photopolymerizable Glass with Diffraction Efficiency near 100% for Holographic storage," Appl. Phys. Lett., Vol. 78 (2001).  

Sherif, Hosam. Optimisation of a novel photopolymer for use in holographic data storage. Available[Online]. res://C:\WINDOWS\System32\shdoclc.dll/navcancl.htm#https://tumail.temple.edu/wm/mail/login.html

T. Alieva, and M. L. Calvo, "Fractionalization of the linear cyclic transforms," J. Opt. Soc. Am. A Vol.17 (2000).