Data at the Speed of Light
By Ali Diallo
The University of Maryland
IBM has invested heavily in research and development for holographic storage systems. The following paper investigates this research to determine the nature of holographic storage, its applicability to primary and secondary storage, and the likelihood of seeing products based on holographic technology in the near future.
Holographic storage is an innovative technology that uses the properties of light to store massive amount of data onto a single plate. The technology in itself dates back to 1976 (Quan 1999). In the past, the development of holographic data storage has been impeded by the absence of adequate storage materials. However, the advent of optical data storage has reawakened interest in this technology. IBM has been one of the strongest advocates of holographic storage, investing millions in the development of low-cost holographic devices. In the mid-nineties, the IBM Almaden Research Center launched an ambitious research program called Holographic Data Storage System (HDSS). This program has been highly successful, with the realization of many successful test platforms. A couple of other computer firms have also started developing their own holographic technologies, with varying degrees of success. The constant need for higher storage capacity and the enormous storage possibilities holographic drives provide represent the two main reasons why holographic technology is poised to become the next standard in data storage.
HDDS differs from traditional optical mass storage technology in the way data is stored onto the recording media. Optical and magnetic storage record bits of information on the surface of a recording medium. One of the main drawbacks of such a recording technique is the physical limit of the medium's recording capabilities. On the other hand, holographic technology stores information throughout the volume of a medium. This technique allows for massive storage capacity, as millions of bits of information can be stored at once inside the medium. In theory, one terabyte (TB) of data may be stored in a sugar-cube-sized crystal. The capture of data is done by intersecting two laser beams within a photosensitive optical material. The two laser beams create an interference pattern that holds key physical properties. These properties represent the most important and amazing aspects of holographic data storage. In order to better understand how holographic storage works, it is necessary to be acquainted with some of the properties of light. Therefore, let us quickly review how light interference works.
When two light waves collide, they produce an interference pattern that contains a set of combined information about the two waves. This interference pattern, which may be stored in an optical medium, is in fact a coded version of the previous waves. In order to decode the information that was contained in either one of the two waves, one needs to reconstruct that particular wave. The only way to achieve this reconstruction is to illuminate the medium with the other wave at exactly the same angle of incidence. In summary, when two waves A and B interfere at a specific angle, they generate a pattern of interference AB that is stored on a medium and that contains coded information about both A and B. Whenever one wants to retrieve the information wave A was carrying, one illuminates the medium with wave B at the same angle at which this wave interfered with wave A. This illumination produces a perfect reconstruction of wave A. In holographic storage, wave A, which carries the data to be stored is called the object beam while wave B, which is used to reproduce the object beam, is called the reference beam. These two beams are in fact two split parts of a single laser. Below is a picture from IBM's official Web site (www.IBM.com) that highlights the physics of holography.
Figure 1 - Copyright IBM.com
Besides a laser, there are other components one needs to have in order to develop a holographic storage device system. These components are a beam splitter, a set of mirrors, an LCD panel, a couple of lenses, a lithium-niobate crystal and a detector. The beam splitter is used to split the laser beam while the mirrors assist in directing the beams. The LCD panel is called a spatial light modulator (SLM). The SLM is a screen that shows pages of binary information encoded as dark and clear boxes. The crystal is the recording medium. The laser beam is initially split in two distinct beams. The object beam passes through the SLM and is therefore encoded with the data page. The object beam then intersects with the reference beam through the volume of the crystal, creating an interference pattern that stores the data it was carrying. When it is time to retrieve the data stored in the crystal, the reference beam is fired into the crystal at the exact same angle at which it overlapped with the object beam. Because of this sudden illumination, the object beam is recreated and projected onto a detector array that captures and decodes the binary information the beam is carrying. Here are two pictures from InPhase Technologies that highlights this process.
Figure 2 - Holographic Recording of Data - Copyright InPhase Technologies
Figure 3 - Holographic Recording of Data - Copyright InPhase Technologies
The advantage of holographic data storage lies in the medium's ability to store and to allow for retrieval of multiple pages of data at the same time. The smallest change in the wavelength of the reference beam produces a different interference pattern. Therefore, by varying the angle of incidence of the reference beam, scientists are able to record many different pages of data in the same volume of material. The overlapping page formats also allow for a fast transfer rate, which can be as high as 1GB per second. The multiplexing property of holographic data storage is what has experts and scientists feel optimist about holographic technologies. In 2001, Lucent's InPhase Technologies have collaborated with Imation Enterprise to develop holographic plates "with the potential to store 125GB of data in a removable 5.25 inch disk, with read rates greater than 30M bps (Lelii, 2001). Currently, IBM is focusing on two promising holographic projects called PRISM and DEMON. The international community has also demonstrated a genuine interest in the development of HDDS technology. In august 2004, a Japanese firm by the name of Optware announced that it would start selling 200GB HVDs (Holographic Versatile Discs) in the first quarter of 2006 (Kallender, 2004).
However, HDSS is not free from problems. One of the major problems associated with this technology is noise propagation. According to members of the IBM Holographic Storage Team, noise can arise in a holographic storage system from a number of sources, among which are poor imaging of the encoded data pattern, cross-talk between multiplexed holograms, and optical scatter (Burr, 2000). The electronic detector that is used to interpret the reconstructed object wave may also generate noise. IBM built a series of special testers to combat noise in HDDS and to evaluate the coding and signal-processing techniques of the technology. These testers were named DEMON I and DEVON II. The testers proved to be very successful at reducing the level of noise in HDDS. When too many data pages are read from the storage medium, the diffracted pattern of information becomes blurred. Consequently, the quality of the signal decreases. IBM's DEVON tester uses powerful algorithm and signal-processing techniques to re-modulate the codes and to produce regenerated signals, thus decreasing the number of incorrect bits. IBM also used the DEMON testers to store data at an areal density of 390 bits per square micron. In comparison, DVD disks have an areal density of 20 bits µm-2 (Burr, 2000).
Another major problem holographic storage faces is the lack of adequate holographic data storage materials. In order to achieve high quality, the imaging of the interference pattern must be perfect. The optical quality of the recording medium plays a vital role in the perfection of this imaging. Indeed, the medium must not deteriorate when the reference beam hits it in different directions. Low scattered light, high sensitivity, high dynamic range, and excellent optical quality are among the most important properties a holographic storage material must exhibit. The material must also have a high recording fidelity in order to accurately record the reference beam's amplitude for future reconstruction of the object beam. Furthermore, the storage material should be able to retain the holographic pattern of interference for a considerable time.
In an attempt to evaluate the recording media that is most suitable for HDDS technology, IBM has developed a tester called PRISM (Photorefractive Information Storage Materials). The PRISM tester was built as part of the DARPA PhotoRefractive Information Storage Materials consortium. This evaluation tester has helped identify materials that exhibit minimal light scattering properties. Intrinsic light scattering of the recording material is indeed what causes noise in the detector. IBM's PRISM tester has shown that, in general, "the best organic media have a higher scattering level than inorganic crystals, by about a factor of 100 or more" (Ashley, 1999). PRISM has also helped IBM evaluate the necessary optical quality for both inorganic photorefractive crystals and organic photopolymer media. The PRISM tester was so successful that IBM decided to share its technology with other development firms such as Aprilis and Bayer "to evaluate and markedly improve their materials and fabrication processes" (Burr, 2000).
While IBM continues to focus on holographic research, a couple of companies committed themselves to producing commercially-viable holographic data storage drives. With its proven dedication and genuine enthusiasm, Lucent Technologies has emerged as the leader in this particular field. Through its Bell Laboratories and in partnership with Imation Corporation, the firm is currently developing a photopolymer material that is suited for holographic storage. According to Brad Rubin, director of R&D at Imation, Lucent Technologies has solved the key industry problems in holographic storage, thanks to its photopolymers (Quan, 1999). Lucent scientists have indeed discovered a photopolymer that has more sensivity and better dynamic range than the traditional lithium niobate that had been used for the last decades.
Lucent's InPhase Technologies is one of the most dynamic data storage companies of the United States. The InPhase Technologies researchers have developed innovative multiplexing techniques for holographic data storage systems. These techniques increase the capacity and performance of the medium. InPhase Technologies have already successfully tested these techniques on small PCMCIA drives. InPhase Technologies has also formed key alliances with strategic partners both on a national level and on an international level. The firm is currently receiving financial assistance from Signal Lake Venture, Yasuda Enterprise Development, and Japan Asia Investment Company (Wheeler, 2004). Moreover, in April 2004, the firm teamed with Pegasus Disk Technologies, a software management firm, to provide holographic storage solution.
Holographic data storage technology has now passed the stage of hypothetic assumption and is being currently marketed and developed throughout the world. Although availability is still a major issue, commercial holographic devices are being distributed throughout the Asian and American continents at a gradual rate. Since 2001, InPhase Technologies has been providing holographic media to holographic device manufacturers. In addition, in February 2004, the Colorado-based firm announced that it was ready to ship "the first blue laser holographic media that enables greater amounts of information to be stored on a single disc" (InPhase, 2004). InPhase has planned to commercialize the first-generation recordable holographic drive in 2006. This drive, which is called Tapestry HDS-200R, has a 200GB storage capacity and a 20 megabyte per second transfer rate. According to InPhase, a single disc can hold "100 million pages of text, 200,000 photos, over 1,500 hours of audio, or 14 hours of high definition video" (InPhase, 2004).
InPhase's holographic drive is similar to Optware's Holographic Versatile Disc in many regards: both discs are believed to have storage capacities of 200 gigabytes. Both drives are also scheduled for a 2006 release date. Optware has developed a Collinear Holographic Data Storage System that enables accurate tracking of the drive. Like InPhase's Bell technology, Optware's holographic technology has been recognized as one of the most promising ones. An increasing number of international firms are forming alliances with Optware to research holographic storage technology. In July 2004, Sony ordered collinear holographic equipment from Optware. According to Yasuhide Kageyama, manager of business development and marketing at Yokohama-based Optware, ""Sony and some major Japanese electronics companies are studying holographic storage to replace HD-DVDs and Blu-ray Discs" (Kallender, 2004). Kageyama further adds, "Sony wants to develop next-next generation storage technologies and we can say that our collinear solution is getting very popular" (Kallender, 2004).
The holographic technology's major problem has always been the lack of adequate storage media. IBM's long and constant dedication to holographic research has been decisive in sharpening the HDSS technology. Indeed, by developing three successful testers, the firm has favored the emergence of noise-resistant and high-sensitive media. With the rapid progress in optical storage technology and the emergence of better quality-driven recording materials, it is only a matter of time before the HDSS technology become widely available. Many companies such as Lucent Technologies and Optware have already promised to commercialize holographic drives in less than two years. In France, the Louis-Pasteur University recently announced that it has successfully captured holographic data through animal proteins. The only unanswered question of HDSS technology is the future price of the commercial drive. Current enterprise drive cost about $20,000. Such a prohibitive price is guaranteed to impede the popularization of holographic technology. Storage developers will have to keep the price of the media at a reasonable level if they want to turn HDSS into a mass-consumption product.
Official Academic Bio (The University of Maryland):
Ali Diallo (link), an alumnus of the University of Maryland and business entrepreneur, is the author of the upcoming management book The Corporate Phoenix and of an inspirational book called Road Less Traveled. Diallo has written various articles on Einstein's Relativity Theory and on the nature of Light and quantum matter. He also wrote a 300 page book on modern science and spirituality and co-wrote a 52 page handbook to reform the curriculum of the University of Maryland's Introduction to Engineering Design course. The proposal was presented at the James Clark School of Engineering in November 2003.
In addition to his scientific work, Diallo has written a book of spiritual poetry called Le Soleil des Mendiants (Poor Men's Paradise).
Diallo holds an interdisciplinary Bachelor of Science in Computer Studies, and four degrees in Project Management, Information Management, Computer Engineering and Web Design. As the founder of the Investments group Unity One Investments LLC, he is affiliated with various international businesses and currently sserves as Advertising Operations Manager at Detroit Media Partnership, a Company owned by Gannett, Co. He may be reached at firstname.lastname@example.org.
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