Introduction to how holographic memory devices will work:
Devices that use light to store and read data have been the backbone of data storage for nearly two decades. Compact discs revolutionized data storage in the early 1980s, allowing multi-megabytes of data to be stored on a disc that has a diameter of a mere 12 centimeters and a thickness of about 1.2 millimeters. In 1997, an improved version of the CD, called a digital versatile disc (DVD), was released, which enabled the storage of full-length movies on a single disc.
Holographic Memory Image(above mentioned diagram explanation):
In a holographic memory device, a laser beam is split in two, and the two resulting beams interact in a crystal medium to store a holographic recreation of a page of data.
CDs and DVDs are the primary data storage methods for music, software, personal computing and video. A CD can hold 783 megabytes of data, which is equivalent to about one hour and 15 minutes of music, but Sony has plans to release a 1.3-gigabyte (GB) high-capacity CD. A double-sided, double-layer DVD can hold 15.9 GB of data, which is about eight hours of movies. These conventional storage mediums meet today's storage needs, but storage technologies have to evolve to keep pace with increasing consumer demand. CDs, DVDs and magnetic storage all store bits of information on the surface of a recording medium. In order to increase storage capabilities, scientists are now working on a new optical storage method, called holographic memory, that will go beneath the surface and use the volume of the recording medium for storage, instead of only the surface area.
Three-dimensional data storage will be able to store more information in a smaller space and offer faster data transfer times. Now i will explain you how a holographic storage system might be built , and what it will take to make a desktop version of such a high-density storage system. Holography enables storage densities that can far surpass the superparamagnetic and diffraction limits of traditional magnetic and optical recording. Holography can break through these density limits because it goes beyond the two-dimensional approaches of conventional storage technologies to write data in three dimensions.
Holography working principle:
Holography was invented in 1947 with the advancement of laser technology. It is a photographic process which does not capture an image of the object being photographed, as is the case with the conventional technique, but rather records the phases and amplitudes of light waves reflected from the object. The wave amplitudes are readily encoded on an ordinary
photographic film. The phases are recorded as interference patterns produced by the reflected light and a reference coherent light (from the same laser). Each point on the hologram received light reflected from every part of the illuminated object and, therefore, contains the complete visual record of the object as a whole. When the hologram obtained from the development
of a film exposed in this way is placed in a beam of coherent light, two sets of strong diffracted waves are produced - each an exact replica of the original signal bearing waves that impinged on the plate when the hologram was made. One set of diffracted waves produces a virtual image, which can be seen by looking through the hologram. It appears in a complete three-dimensional form with highly realistic perspective effects. In fact, the reconstructed picture has all the visual properties of the original object.
Why so we need holographic technology:
Have you ever watched an old movie on TV? Perhaps it was in black and white. Perhaps looking at it was slow and booorrrring. When you see something new on TV, it is usually made with the help of computers and is very fast and exciting. But everything gets old. Even those big-screen TV's that seem so hi-tech will one day be very boring. Why?
Well, someday everything that we look at will be holographic images. In fact, all of those "really cool" special effects that you love in the movies today . . . would you believe that someday you will actually LAUGH at them? One day in the future, 3-D holographic images will be sent into our homes and we will see all the action as if it is taking place right in our own living rooms.
Why don't we have that now?
We do not have it now because we are not as advanced in science and technology as we sometimes like to think we are. If you have an antenna, cable TV, or a sattelite dish, you know that what you watch on TV has to get there somehow. It's OK for us to send regular pictures to a TV, but we cannot send a hologram. In fact, we are not even close to being at the point where we can send a hologram and have it show up in someone's house. It's going to take a lot of clever minds (like your own) to make this happen. But it will happen. And maybe, yes maybe, you'll be part of it.
A Little Background:
Holographic memory offers the possibility of storing 1 terabyte (TB) of data in a sugar-cube-sized crystal. A terabyte of data equals 1,000 gigabytes, 1 million megabytes or 1 trillion bytes. Data from more than 1,000 CDs could fit on a holographic memory system. Most computer hard drives only hold 10 to 40 GB of data, a small fraction of what a holographic memory system might hold.
Polaroid scientist Pieter J. van Heerden first proposed the idea of holographic (three-dimensional) storage in the early 1960s. A decade later, scientists at RCA Laboratories demonstrated the technology by recording 500 holograms in an iron-doped lithium-niobate crystal, and 550 holograms of high-resolution images in a light-sensitive polymer material. The lack of cheap parts and the advancement of magnetic and semiconductor memories placed the development of holographic data storage on hold.
Over the past decade, the Defense Advanced Research Projects Agency (DARPA) and high-tech giants IBM and Lucent's Bell Labs have led the resurgence of holographic memory development.
The Basics:
Prototypes developed by Lucent and IBM differ slightly, but most holographic data storage systems (HDSS) are based on the same concept. Here are the basic components that are needed to construct an HDSS:
· Blue-green argon laser
· Beam splitters to spilt the laser beam
· Mirrors to direct the laser beams
· LCD panel (spatial light modulator)
· Lenses to focus the laser beams
· Lithium-niobate crystal or photopolymer
· Charge-coupled device (CCD) camera
When the blue-green argon laser is fired, a beam splitter creates two beams. One beam, called the object or signal beam, will go straight, bounce off one mirror and travel through a spatial-light modulator (SLM). An SLM is a liquid crystal display (LCD) that shows pages of raw binary data as clear and dark boxes. The information from the page of binary code is carried by the signal beam around to the light-sensitive lithium-niobate crystal. Some systems use a photopolymer in place of the crystal. A second beam, called the reference beam, shoots out the side of the beam splitter and takes a separate path to the crystal. When the two beams meet, the interference pattern that is created stores the data carried by the signal beam in a specific area in the crystal -- the data is stored as a hologram.
Images courtesy Lucent TechnologiesThese two diagrams show how information is stored and retrieved in a holographic data storage system.
An advantage of a holographic memory system is that an entire page of data can be retrieved quickly and at one time. In order to retrieve and reconstruct the holographic page of data stored in the crystal, the reference beam is shined into the crystal at exactly the same angle at which it entered to store that page of data. Each page of data is stored in a different area of the crystal, based on the angle at which the reference beam strikes it. During reconstruction, the beam will be diffracted by the crystal to allow the recreation of the original page that was stored. This reconstructed page is then projected onto the charge-coupled device (CCD) camera, which interprets and forwards the digital information to a computer.
The key component of any holographic data storage system is the angle at which the second reference beam is fired at the crystal to retrieve a page of data. It must match the original reference beam angle exactly. A difference of just a thousandth of a millimeter will result in failure to retrieve that page of data.
Why only laser light is required:
Right now, we still need lasers to MAKE holograms -- because only a laser can provide the special light that's needed. But we do not need a laser to VIEW a hologram.
Desktop Holographic Data Storage:
After more than 30 years of research and development, a desktop holographic storage system (HDSS) is close at hand. Early holographic data storage devices will have capacities of 125 GB and transfer rates of about 40 MB per second. Eventually, these devices could have storage capacities of 1 TB and data rates of more than 1 GB per second -- fast enough to transfer an entire DVD movie in 30 seconds. So why has it taken so long to develop an HDSS, and what is there left to do?
When the idea of an HDSS was first proposed, the components for constructing such a device were much larger and more expensive. For example, a laser for such a system in the 1960s would have been 6 feet long. Now, with the development of consumer electronics, a laser similar to those used in CD players could be used for the HDSS. LCDs weren't even developed until 1968, and the first ones were very expensive. Today, LCDs are much cheaper and more complex than those developed 30 years ago. Additionally, a CCD sensor wasn't available until the last decade. Almost the entire HDSS device can now be made from off-the-shelf components, which means that it could be mass-produced.
Although HDSS components are easier to come by today than they were in the 1960s, there are still some technical problems that need to be worked out. For example, if too many pages are stored in one crystal, the strength of each hologram is diminished. If there are too many holograms 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.
Researchers are confident that technologies will be developed in the next two or three years to meet these challenges. With such technologies on the market, you will be able to purchase the first holographic memory players. This DVD-like disc would have a capacity 27 times greater than the 4.7-GB DVDs available today, and the playing device would have data rates 25 times faster than today's fastest DVD players.
Various fields where an holographic technique is used:
1. With holography, we can test all kinds of things . . . from automobile engines, to aircraft tires, to artificial bones and joints. This type of holography is called "interferometry", and the resulting hologram is called an "interferogram".
2. Holography is also used in medical imaging where doctors can look at a 3-dimensional cat scan and actually go in and take measurements within the holographic image.
3. Very simple (and colorful) holograms are used on consumer packaging materials such as cereal and toothpaste boxes, and a host of other items.
4. Holograms are used for security for credit cards and for identifying manufactured objects such as clothing to help cut down on conterfeiting.
5. Holographic Optica Elements (HOE's) are used by airplane pilots for navigation. It allows them to keep their eyes on the sky or runway, while still being able to read their instrumentation . . . which appears to float in front of their cockpit window. This feature is already available as an option on several automobiles.
6. Holographic lenses and contacts can make one lens provide several different functions, such as correcting regular vision and also act as magnifiers for reading -- all in the same lens, and throughout the entire lens at the same time.
7. Holograms can be made into portraits of people, pets, etc.
8. Artists use holography to express their creativity and are shown in galleries around the world.
9. They are used in printing for magazine and book covers. National Geographic as well as Sports Illustrated (Michael Jordon) have been famous examples.
10. They can be used for point-of-purchase advertising, taking the place of a photograph of a product or service in a store or supermarket.
11. Holograms can be used for data storage such as holographic hard drives. The entire contents of the library of congress can be stored in the area the size of a sugar cube.
12. As the technology grows and develops we will see holographic television and motion pictures as mentioned earlier.
Conculsion:
An Interactive Future for Imaging:
In future Three-dimensional holographic video images will be generated by a computer rather than being fixed in a static medium; they will be shown in full-motion color and, with input from a user, changed on the fly. What’s more, viewers who move around a holographic video image will be able to see it moving from every side -- a phenomenon important to realism and one that many conventional eyeglass-based systems cannot replicate.
Because the new video holograms produce fully 3-D images that float in space near the viewing screen, they can be examined from different angles by multiple viewers.
And sony which is one of the leading companies in electronics field has made there lastest research in developing a holographic storage device with 7 layers and they are further continuing there venture to reach a new heights with a device which has 500GB of storage capacity and with 20layer, this is far better and 100 times faster and reliable than the ordinary DVD that we use now. But this is still underconstruction stage which may be completed in year 2010, on seeing this finally we come to a conculsion that the future which we are going to step into will be completely overtaken by holographic technology.
