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Holographic Memory for High density data storage & High speed pattern recognition
PRESENTED BY-:
Name: PINKI SINGH, HAPPY BHATT
Roll no: 08BK1A1239, 08BK1A1216
Year & Group: B-TECH IIyr (IT)
College: St Peters Engineering College.
ABSTRACT:
As computers and the internet become faster and faster, more and more information is transmitted, received, and stored everyday. The demand for high density and fast access time data storage is pushing scientists and engineers to explore all possible approaches including magnetic, mechanical, optical, etc. Optical data storage has already demonstrated its potential in the competition against other storage technologies. CD and DVD are showing their advantages in the computer and entertainment market. What motivated the use of optical waves to store and access information is the same as the motivation for optical communication. Light or an optical wave has an enormous capacity (or bandwidth) to carry information because of its short wavelength and parallel nature. In optical storage, there are two types of mechanism, namely localized and holographic memories. What gives the holographic data storage an advantage over localized bit storage is the natural ability to read the stored information in parallel, therefore, meeting the demand for fast access. Another unique feature that makes the holographic data storage attractive is that it is capable of performing associative recall at an incomparable speed. Therefore, volume holographic memory is particularly suitable for high-density data storage and high-speed pattern recognition. In this paper, we review previous works on volume holographic memories and discuss the challenges for this technology to become a reality.
INTRODUCTION
With its omnipresent computer all connected via internet information age has lead an explosion of information available to users. With the decreasing cost of storing data and increasing storage capacity with a same small device footprint have been key enablers of this revolution. While the current storage need is being met, the storage technologies must continue in order to keep pace with a rapidly increasing demand.
However, both magnetic and conventional optical data storage technologies, where individual bits are stored as distinct magnetic or optical changes in the surface of recording medium, are approaching physical limits beyond which individual bits are too small or too difficult to store. Storing information through the volume of the medium not on, its surface offers an intriguing high capacity alternative. Holographic data storage is a volumetric approach, which has made recent progress towards practicality with the appearance of lower cost enabling technologies. Hence, the holographic memory has become a great white whale of technology research.
CONCEPT OF HOLOGRAPHIC MEMORY
Holography is a technique, which allows recording and playback of 3-dimensional images. This is called a hologram unlike other 3-dimenssional picture hologram provide hologram provide what is called parallax. Parallax allows the viewer to move back and forth up and down and see different perspective “ as if the object were actually there.
In Holography, the aim is to record complete wave field (both amplitude and phase) as it is intercepted by recording medium the record in plane may not even be an image plane. The scattered or reflected light by object is intercepted by the recording medium and recorded completely in spite of the fact that the detector is insensitive to the phase difference among the various part of the optical field
In holography, interference between the object wave and reference wave is formed and recorded on a holographic material. The record known as hologram (whole record) captures the complete wave, which can be viewed at the later time by illuminating the hologram with an appropriate light beam.
To this day holography continues to provide the most accurate depiction of 3-D image in the world.
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.
HISTORICAL ROOTS
Dr.Dennis Gabor is known as the father of holography. In year 1947, Dr.Gabor a Hungarian Physicist gave the idea of holography at the Imperial College of London. In 1971, Dr.Gabor received a noble prize in physics for holography. His theory was originally meant to increase the resolving power of electronic microscope and towards that he used light of beam instead of electronic beam and this resulted in the first hologram ever made.
In 1960s, two engineers from the university of Michigan, Emmit Lerth and Juris Upatlipks, developed a new device that produce a 3-D image of an object Polaroid scientist Peter J.Vann Heerdern proposed the idea of holographic storage in the early 1960s and decade later scientist at RCA laboratories demonstrated the holographic storage technology by recording 500 holograms in an iron doped lithium niobate crystal and 550 holograms of high resolution images in a light sensitive polymer. However, the development of holographic data storage was put on holed for several years because of the absence of cheap parts of the advancement in magnetic and semiconductor memories.
In recent years, IBM and lucent Bell labs are actively involved in creating a successful holographic storage medium because of which it has become possible to store 1000 GB of data in a small cube.
WHAT IS HOLOGRAM?
The word Hologram is derived from Greek word Holosmeaning ËœWholeâ„¢ and GRAM meaning ËœMessageâ„¢. Older English dictionaries define a hologram as a document (such as a last will and testament) hand written by the person whose signature is attached. A hologram is often described as a 3-D picture.
While a photograph has an actual physical image, a hologram contains information about size, shape, brightness and contrast of object being recorded .This information is stored in a very microscopic and complex pattern of interference. The interference pattern is made possible by the properties of light generated by a LASER. In order to record the whole pattern, the light used must be highly directional and must be one of one color. Such light is called coherent. Because the light from a LASER is one color and leaves the LASER with one wave in perfect one-step with all others, it is perfect for making hologram.
When we shine a light on the hologram the information that is stored as an interference pattern takes the incoming light and re-creates the original optical wave front that was reflected off the object hence the eyes and brain now perceives the object as being in front of us once again.
HOLOGRAPHIC MEMORY
Holographic Memory is a simple optical imaging technique that stores digital information throughout the depth of storage medium as opposed to surface storage through conventional means .This enables massive increase in storage capacities over existing technologies and at the same time reduces the cost of storing massive amount of data in a randomly accessible digital format. Most holographic storage systems contain some components basic to the setup.
These are-
i. Laser Beam
ii. Beam Splitters to Split the Laser Beam
iii. Mirrors to direct the Laser Beam
iv. A liquid Crystal Display Panel
Lenses to Focus The Laser Beam
v. Recording Material
vi. CCD Cameras
Technique of storing data on a holographic material
To record on the hologram, a page composer converts the data in the form of electric signals to optical signal the controller generate the address to access the desired page. This results in the exposure of a small area of the recording medium through an aperture. The optical output signal is directed to the exposed area by the deflector.
When the Blue-Argon laser is focused, a beam splitter splits it into two, a reference beam and a signal beam. The signal beam passes through spatial light modulators (SLM) where digital information organized in a page like format of ones and zeros, is modulated onto the signal beam as a two-dimensional pattern of brightness and darkness. This signal beam is then purified using different crystals. When the signal beam and reference beam meets the interference pattern created stores the data that is carried by the Different data pages are recorded over the surface depending on the angle at which the reference beam meet the signal beam a holographic data storage system is fundamentally page oriented with each block of data defined by the no. of data bits that can be spatially impressed onto the object the total storage capacity of the system is then equal to the product of the paper size (in bits) and the no. of pages that can be recorded.
The above diagram shows how data is stored from a holographic data storage system.
Spatial Light Modulator (SLM)
Spatial light modulator is used for creating binary information out of laser light. The SLM is a 2-D plane, consisting of pixels, which can be turned on and off to create 1â„¢s and 0â„¢s. An illustration of this is a window and a window shade. It is possible to pull the shade down over window to block incoming sunlight. If sunlight is desired again, the shade can be raised. A spatial light modulator contains a two dimensional array of windows which are only microns wide. These windows block some parts of the incoming laser light and let other parts go through. The resulting cross section of the laser beam is a two dimensional array of binary data, the same as what was represented in SLM. After the laser beam is manipulated, it is sent into hologram to be recorded. This data is written into the hologram as page form. It is called this due to its representation in
Two“dimensional plane or page of data. Holographic memory reads data in the form of pages instead. For example, if a stream 0f 32 bit is sent to a processing unit by a conventional read head, a holographic memory system would in turn send 32*32 bits, or 1024 bits due to its added dimension this provides very fast access times in volumes for greater than serial access methods. The volume could be one Megabit per page using a SLM resolution of 1024*1024 bits at 15-20 microns per pixel.
Multiplexing
Once one can store a page of bits in a hologram, an interface to a computer can be made. The problem arises, however, that storing only one page of bits is not beneficial. Fortunately, the properties of hologram provide a unique solution to this dilemma. Unlike magnetic storage mechanisms, which store data on their surface, holographic memories store information throughout their whole volume. After a page of data is recorded in a hologram, a small modification to the source beam before it reenters the hologram will record another page of data in the same volume. This method of storing multiple pages of data in the hologram is called multiplexing. The thicker the volume becomes, the smaller the modifications to the source beam can be.
Angular multiplexing
When a reference beam recreates the source beam, it needs to be at the same angle it was during recording. A very small alteration in this angle will make the regenerated source beam disappear. Harnessing this property, angular multiplexing changes the angle of source beam by very minuscule amount after each page of data is recorded. Depending on the sensitivity of recording material, thousands of pages of data can be stored in the same hologram, at the same point of laser beam entry. Staying away from conventional data access system that move mechanical matter to obtain data, the angle of entry of source beam can be deflected by high frequency sound waves in solids. The elimination of mechanical access methods reduces access time from milliseconds to microseconds.
Wavelength multiplexing
Used mainly in conjunction with other multiplexing methods, wavelength multiplexing alters the wavelength of source and reference beams between recordings. Sending beams to the same point of origin in the recording medium at different wavelengths allows multiple pages of data to be recorded. Due to the small tuning range of lasers, however, this form of multiplexing is limited on its own.
Spatial multiplexing
Spatial multiplexing is the method of changing the point of entry of source and reference beams into the recording medium. This form tends to break away from the non-mechanical paradigm because either the medium or recording beams must be physically moved. Like wavelength multiplexing, this is combined with other forms of multiplexing to maximize the amount of data stored in the holographic volume. To commonly used forms of spatial multiplexing are peristrophic multiplexing and shift multiplexing.
Technique of retrieving data from holographic material
To retrieve the data, the reference beam is focused on hologram at a particular Angle, this will retrieve the modulated data page stored at the same angle of interference to read the page, reference beam is passed through a detector and then through a CCD camera which will project the data on the display panel. The laser (reference beam) is focused on the appropriate page according to the address generated. A photo detector array on the other side of hologram record the image of that sub hologram.
When the stored interference pattern is illuminated with either of the two original beams, it diffracts the light to reconstruct the other beam used to produce the pattern originally. Thus, illuminating the material with the reference beam recreate the object beam, with its imprinted page of data. It is then a relatively simple matter to detect the data pattern with a solid-state camera chips. The data from the chip are interpreted and forwarded to the computer as stream of digital information. The page can be separated either by varying the angle between the object and the reference beam or by changing the laser wavelength.
The above diagram shows how data is retrieved from a holographic data storage system.
Recording material
The recording material over which a holographic pattern is stored can be made of either organic or inorganic material. The most common inorganic material are ones that exhibit photo refractivity such as lithium niobate(LiNBO3). Lithium niobate has been around for many decades can be fabricated in a large crystal of high optical quality.
Holographic recording in organic photo polymer system has been around for a decade and most of the early attention was directed towards fabrication of holographic optical elements and scanners. Such data recorded could not be erased. This was particularly suited for ËœWrite once run many timesâ„¢ applications. The organic materials currently suffer from two major drawbacks as they cannot be fabricated to a thickness greater than 100 microns enhance the no of holograms that can be multiplexed is very much reduced. They also undergo some degree of shrinkage with exposure, which complicates retrieval of multiplexed hologram and leads to a situation of cross talk.
However, research continues because of their inherent advantages over grown and polished inorganic crystals.
TECHNICAL SPECIFICATIONS
i. Latency : 40 m seconds
ii. Potential Transfer Rate : 1 Gigabit per second
iii. Minimum Sector Size : 128 KB
iv. Potential capacity : 1 Terabit( 128 GB in a 1 Cubic centimeter
Crystal)
v. Power : 1 Watt per Square mm of hologram size
ADVANTAGE
1) The very first advantage of holographic memory system is that an entire page of data can be retrieved quickly and at one time.
2) It provides the very high storage density amount in the order of terabytes and be stored in small cubic devices.
3) High data transfer rates can be achieved with a perfect holographic setup with data transfer rate b/w 1-10 GB per second. Since this memory is not serially or sequentially operated like most memory that is why a page of data can be read out in parallel.
LIMITATIONS
1) In any holographic data storage system, the angle at which the second reference beam is focused on the crystal to a page of data is the crucial component. It must match the original reference beam exactly without deviation. A difference of even a thousandth of a millimeter will result in failure to retrieve that page of data.
2) Also, if too many pages are stored in one crystal, the strength of each hologram gets diminished.
3) If there are too many holograms stored on a crystal and a reference crystal used to retrieve a hologram is not focused at the precise angle, it will pick up a lot of background from the other holograms stored around it.
CONCLUSION
The future of holographic memory is very promising. The holographic storage provides high data density. It can easily store 1000GB of data in a small cubic centimeter crystal reducing the cost on the other hand. It may offer high data transfer rate.
Even then, the holographic way of storing data is still at the toddler stage and it may take another couple of years for this technique to hit desktop with a real life data storage solution.
However, this technology itself is dazzling and aims to light up the desktop experience.
Truly the best things in life come small!!!!
REFERENCES
1) CHIP magazine, pp- 26-32, April 2001
2) www.almaden.com
3) www.eik.bme.hu
4) www.vision.caltech.edu
5) Mansi, Mark the hard disk survival guide, BPB publications, 1993
CONTENTS
1) INTRODUCTION
2) A) CONCEPT OF HOLOGRAPHY
B) HISTORICAL ROOT
C) WHAT IS HOLOGRAM
3) HOLOGRAPHIC MEMORY
4) TECHNIQUE FOR STORING DATA ON A HOLOGRAPHIC MATERIAL
5) SPATIAL LIGHT MODULATOR
6) MULTIPLEXING
7) TECHNIQUE FOR RETREIVING DATA FROM A HOLOGRAOHIC
MATERIAL
8) A) ADVANTAGES
B) LIMITATIONS
9) CONCLUSION
10) REFERENCES
please read https://seminarproject.net/Thread-hologr...ull-report
https://seminarproject.net/Thread-hologr...mory--5241
https://seminarproject.net/Thread-hologr...nar-report
https://seminarproject.net/Thread-hologr...ull-report
for getting more information about Holographic memory and related devices