From the get downing coevals of computing machine, velocity of the processors has been increasing enormously about twice the capacity for every 3 old ages. Today, we can entree big sum of informations with in few seconds utilizing CPU and informations storage. While the computing machine evolves many applications for big binary files like sound or image informations for high capacity storage and informations entree. But, there is no high capacity signifier of informations storage to manage these big files rapidly and expeditiously. So, Holographic memory is a hopeful engineering in the following coevals over conventional storage system because it is a 3-dimensional information storage system that can hive away information at high denseness inside the crystal or photopolymer which has a capacity to Storage system, the informations of full page can be accessed at a clip alternatively of consecutive method and there are really few traveling parts so the restrictions of the mechanical gesture can be minimized. Holographic memory uses a light-sensitive stuff to enter intervention forms of a mention beam and a signal beam of coherent visible radiation, where the signal beam is reflected away and an object or which contains the information in the signifier of light and dark countries. The natural history of the light-sensitive stuff is to enter the intervention form which reproduces it after using a beam of visible radiation to the stuff that is indistinguishable to the mention beam. The attendant visible radiation that is transmitted through the medium will take on the recorded intervention form and will be collected on a optical maser sensor array that encompasses the full surface of the holographic medium. Lots of holographs are recorded in the same infinite by altering the angle or the wavelength of the incident visible radiation. The whole page of informations can be accessed in this manner. Hence holographic storage system has the possible to became the following storage coevals over conventional storage
2. Definition of Holographic Memory
It is a storage device that records binary information in the signifier of holographs, which are produced ( as interfering forms ) on photographic or photo chromic media by the manner of optical maser beams, and can be read by agencies of low-power optical maser beams. It is a technique that can hive away information at high denseness inside the crystals or photopolymers. The advantage of a holograph is the manner in which the image is dispersed over the recording surface so that dust or abrasions do non wholly vague informations though they may cut down the contrast. Several undertakings have attempted to use this engineering but none have yet been commercially successful.
3. What is HVD?
HVD known as Holographic Versatile Disc is an optical phonograph record engineering still in the research phase which would keep up to 4 TB ( TB ) of information. It employs a technique known as collinear holography, whereby two optical masers, one red and one blue-green, are collimated in a individual beam. It employs a technique known as collinear holography, whereby two optical masers, one red and one blue-green, are collimated in a individual beam. The bluish green optical maser reads informations encoded as optical maser intervention peripheries from a holographic bed near the top of the phonograph record while the ruddy optical maser is used as the mention beam and to read servo information from a regular CD-style aluminum bed near the underside.
These phonograph records have the capacity to lade up to 4 TB of information, which is about 6,000 times the capacity of a CD-ROM, 830 times the capacity of DVD, 160 times the capacity of single-layer Blu-ray-Discs and about 8 times the capacity of standard computing machine difficult drives as of 2007. These phonograph record besides had a transportation rate of 1GB/S.
4. Structure of HVD
The construction of HVD is shown in the above figure and constituents with regard to figure are shown below:
1. Green writing/reading optical maser ( 532 nanometer )
2. Red positioning/addressing optical maser ( 650nm )
3. Hologram ( informations )
4. Polycarbon bed
5. Photo polymeric bed ( informations incorporating bed )
6. Distance beds
7. Diachronic bed ( reflecting green visible radiation )
8. Aluminium brooding bed ( reflecting red visible radiation )
9. Crystalline base
( I ) . Working of HVD
A holographic information storage system consists of a recording medium, an optical recording system, and a exposure sensor array. A beam of coherent visible radiation is split into a mention beam and a signal beam which are used to enter a holograph into the recording medium. The entering medium is normally a photorefractive crystal such as LiNbO3 or BaTiO3 that has certain optical features. These features are high diffraction efficiency, high declaration, and lasting storage until erasure, and fast erasure on the application of external stimulation such as UV visible radiation. A ‘hologram ‘ is merely the 3-dimensional intervention form of the intersection of the mention and signal beams at 90 grades to each other. This intervention form is imprinted into the crystal as parts of positive and negative charge. To recover the stored holograph, a beam of visible radiation that has the same wavelength and angle of incidence as the mention beam is sent into the crystal and the resulting diffraction form is used to retrace the form of the signal beam. Many different holographs may be stored in the same crystal volume by altering the angle of incidence of the mention beam. One feature of the entering medium that limits the utility of holographic storage is the belongings that every clip the crystal is read with the mention beam, the stored holograph at that “ location ” is disturbed by the mention beam and some of the information unity is lost. With current engineering, recorded holographs in Fe- and Tb-doped LiNbO3 that usage UV visible radiation to trip the Tb atoms can be preserved without important decay for two old ages.
( two ) . Writing Datas
The procedure of composing information onto an HVD begins with encoding the information into double star to be stored in the SLM. These informations are turned into 1s and nothings represented as opaque or semitransparent countries on a “ page ” . The below is the image that the information beam is traveling to go through through.
When the bluish green Ar optical maser is fired, a beam splitter creates two beams. One beam, called the object or signal beam, will travel directly, resile off one mirror and travel through a Spatial- Light Modulator ( SLM ) . An SLM is a Liquid crystal show ( LCD ) that shows pages of natural binary informations as clear and dark boxes. The information from the page of binary codification is carried by the signal beam around to the photosensitive lithium-niobate crystal. Some systems use a photopolymer in topographic point of the crystal. A 2nd beam, called the mention beam, shoots out the side of the beam splitter and takes a separate way to the crystal. When the two beams meet, the intervention form that is created shops the informations carried by the signal beam in a specific country in the crystal. Thus the information is stored as a holograph.
( three ) . Reading Datas
An advantage of a holographic memory system is that an full page of informations can be retrieved rapidly and at one clip. In order to recover and retrace the holographic page of informations stored in the crystal, the mention beam is shined into the crystal at precisely the same angle at which it entered to hive away that page of informations. Each page of informations is stored in a different country of the crystal, based on the angle at which the mention beam strikes it. During Reconstruction, the beam will be diffracted by the crystal to let the diversion of the original page that was stored. This reconstructed page is so projected onto the charge-coupled device ( CCD ) camera, which interprets and forwards the digital information to a computing machine.
CCD is a 2-D array of 1000s or 1000000s of bantam solar cells, each of which transforms the visible radiation from one little part of the image into negatrons. Following measure is to read the value ( accrued charge ) of each cell in the image. In a CCD device, the charge is really transported across the bit and read at one corner of the array. An analog-to-digital convertor turns each pel ‘s value into a digital value. CCDs use a particular fabrication procedure to make the ability to transport charge across the bit without deformation. This procedure leads to really high-quality detectors in footings of fidelity and light sensitiveness. CCD detectors have been mass produced for a longer period of clip, so they are more mature. They tend to hold higher quality and more pels.
The cardinal constituent of any holographic informations storage system is the angle at which the 2nd mention beam is fired at the crystal to recover a page of informations. It must fit the original mention beam angle precisely. A difference of merely a thousandth of a millimeter will ensue in failure to recover that page of informations.
5. Advantages of Holographic Memory
Holographic memory offers storage capacity of about 1 Terbium. Speed of retrieval of informations in 10s of microseconds compared to data entree clip of about 10ms offered by the fastest difficult disc today. By the clip they are available they can reassign an full DVD film in 30 seconds. Information hunt is besides faster in holographic memory. See the instance of big databases that are stored on difficult disc today. To recover any piece of information you foremost supply some mention informations. The information is so searched by its reference, path, sector and so on after which it is compared with the mention informations. In holographic storage full pages can be retrieved where contents of two or more pages can be compared optically without holding to recover the information contained in them. Besides HDSS has no traveling parts. So the restrictions of mechanical gesture such as clash can be removed.
It besides had the undermentioned advantages:
Resistance to damage – If some parts of the medium are damaged, all information can still be obtained from other parts.
Efficient retrieval – All information can be retrieved from any portion of the medium.
These phonograph records have the capacity to keep up to 3.9 TB ( TB ) of information, which is about 6,000 times the capacity of a CDROM, 830 times the capacity of a DVD, 160 times the capacity of single-layer Blu-ray-Discs, and approximately 48 times the capacity of standard computing machine difficult thrusts.
The HVD besides has a transportation rate of 1 Gigabit/s
6. Applications of Holographic Memory
There are many possible applications of holographic memory. Holographic memory systems can potentially supply the high-velocity transportations and big volumes of future computing machine systems. One possible application is data excavation. Data excavation is the procedure of happening forms in big sums of informations. Data excavation is used greatly in big databases which hold possible forms which ca n’t be distinguished by human eyes due to the huge sum of informations. Some current computing machine systems implement informations excavation, but the mass sum of storage required is forcing the bounds of current informations storage systems. The many progresss in entree times and informations storage capacity that holographic memory provides could transcend conventional storage and rush up informations excavation well. This would ensue in more placed forms in a shorter sum of clip.
Another possible application of holographic memory is in petaflop computer science. A Petaflop is a 1000 trillion drifting point operations per second. The fast entree in highly big sums of informations provided by holographic memory systems could be utilized in petaflop architecture. Clearly progresss are needed in more than memory systems, but the theoretical schematics do be for such a machine. Optical storage such as holographic memory provides a feasible solution to the utmost sum of informations which is required for petaflop computer science.
Holographic memory can be used as drawn-out DRAM with 10ns entree clip, Hard disc thrusts, CD ROMs of big storage capacity and stone mounted of PBs storage capacity.
The research on holographic memory is taking topographic point in good guarded and rich companies like IBM, ROCKWELL and InPhase. InPhase claims to hold developed a holographic memory of size somewhat larger than a DVD. It has a capacity of about 100GB. They are seeking to force it upto 1TB.
IBM and ROCKWELL claims to hold developed a entering medium less sensitive than lithium niobate crystals.
7. Comparison with Other Storage Devicess
Data Transfer Rate
Main Memory ( RAM )
10 – 40 N
5 – 20 MB/s
Comparing the entree times holographic memory lies halfway between that of chief memory and magnetic disc. Data transportation rate is 10GB/s which is higher than that of other storage devices and, and a storage capacity that is higher than both chief memory and magnetic disc. Surely if the issues of holograph decay and intervention are resolved, so holographic memory could go a portion of the memory hierarchy, or take the topographic point of magnetic disc much as magnetic disc has displaced magnetic tape for most applications.
The hereafter of holographic memory is really promising. The page entree of informations that holographic memory creates will supply a window into following coevals computer science by adding another dimension to stored informations. Finding holograph in personal computing machines might be a spot longer off, nevertheless. The big cost of hi-tech optical equipment would do small-scale systems implemented with holographic memory impractical. Holographic memory will most probably be used in following coevals super computing machines where cost is non every bit much of an issue. Current magnetic storage devices remain far more cost effectual than any other medium on the market. As computing machine systems evolve, it is non unreasonable to believe that magnetic storage will go on to make so. As mentioned earlier, nevertheless, these betterments are non made on the conceptual degree. The current storage in a personal computing machine operates on the same rules used in the first magnetic informations storage devices. The parallel nature of holographic memory has many possible additions on consecutive storage methods. However, many progresss in optical engineering and light-sensitive stuffs need to be made before we find holographs in computing machine systems.