10-08-2012, 03:26 PM
Holographic Versatile Disc
HVD-report.doc (Size: 1.19 MB / Downloads: 37)
INTRODUCION
An HVD (holographic Versatile Disc), a holographic storage media, is an advanced optical disc that’s presently in the development stage. Polaroid scientist J. van Heerden was the first to come up with the idea for holographic three-dimensional storage media in 1960. An HVD would be a successor to today’s Blu-ray and HD-DVD technologies. It can transfer data at the rate of 1 Gigabit per second. The technology permits over 10 kilobits of data to be written and read in parallel with a single flash. The disc will store upto 3.9 terabyte (TB) of data on a single optical disk.
Holographic data storage, a potential next generation storage technology, offers both high storage density and fast readout rate. In this article, I discuss the physical origin of these attractive technology features and the components and engineering required to realize them. I conclude by describing the current state of holographic storage research and development efforts in the context of ongoing improvement to established storage technologies.
BRIEF HISTORY
Although holography was conceived in the late 1940s, it was not considered a potential storage technology until the development of the laser in the 1960s. The resulting rapid development of holography for displaying 3-D images led researchers to realize that holograms could also store data at a volumetric density of as much as 1/ where is the wave-length of the light beam used.
Since each data page is retrieved by an array of photo detectors, rather than bi-by-bit, the holographic scheme promises fast readout rates as well as high density. If a thousand holograms, each containing a million pixels, could be retrieved every second, for instance, then the output data rate would reach 1 Gigabit per second.
In the early 1990s, interest in volume-holographic data storage was rekindled by the availability of devices that could display and detect 2-D pages, including charge coupled devices (CCD), complementary metal-oxide semiconductor (CMOS) detector chips and small liquid-crystal panels. The wide availability of these devices was made possible by the commercial success of digital camera and video projectors. With these components in hand, holographic-storages researchers have begun to demonstrate the potential of their technology in the laboratory. By using the volume of the media, researchers have experimentally demonstrated that data can be stored at equivalent area densities of nearly 400 bits/sq. micron. (For comparison, a single layer of a DVD disk stores data at ~ 4.7 bits/sq. micron) A readout rate of 10 gigabit per second has also been achieved in the laboratory.
UNDERLYING ECHNOLOGY
HOLOGRAPHY
Holographic data storage refers specifically to the use of holography to store and retrieve digital data. To do this, digital data must be imposed onto an optical wave front, stored holographically with high volumetric density, and then extracted from the retrieved optical wav front with excellent data fidelity.
A hologram preserves both the phase and amplitude of an optical wave front of interest called the object beam – by recording the optical interference pattern between it and a second coherent optical beam – the reference beam. Fig 2.1 shows this process.
COLLINEAR HOLOGRAPHY
HVD uses a technology called ‘collinear holography’, in which two laser rays, one blue-green and one red, are collimated into a single beam. The role of the blue-green laser is to read the data encoded in the form of laser interference fringes from the holographic layer on the top, while the red laser serves the purpose of a reference beam and also to read the servo info from the aluminum layer – like in normal CDs – near the bottom of the disk. The servo info is meant to monitor the coordinates of the read head above the disk (this is similar to the track, head and sector information on a normal hard disk drive).
STORAGE DATA
RECORDING DATA
A simplified HVD system consists of the following main components:
Blue or green laser (532-nm wavelength in the test system)
Beam splitter/merger
Mirrors
Spatial light modulator (SLM)
CMOS sensor
Polymer recording medium
The process of writing information onto an HVD begins with encoding the information into binary data to be stored in the SLM. These data are turned into ones and zeroes represented as opaque or translucent areas on a "page" -- this page is the image that the information beam is going to pass through.
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.
READING DATA
To read the data from an HVD, you need to retrieve the light pattern stored in the hologram.
In the HVD read system, the laser projects a light beam onto the hologram -- a light beam -- a light beam that is identical to the reference beam.
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.
HARDWARE
SPATIAL LIGHT MODULATOR
To use volume holography as a storage technology, digital data must be imprinted onto the object beam for recording and then retrieved from the reconstructed object beam during readout. The device for putting data into the system is called a spatial light modulator (SLM) – a planner array consisting of thousand of pixels. Each pixel is independent microscopic shutters that can either block or pass light using liquid-crystal or micro-mirror technology. Liquid crystal panels and micro-mirror arrays with 1280 X 1024 pixels are commercially available due to the success of computer-driven projection displays. The pixels in both types of devices can be refreshed over 1000 times per second, allowing the holographic storage system to reach an input data rate of 1 gigabit per second – assuming that laser power and material sensitivities would permit. The data are read using an array of detector pixels, such as a CCD camera or CMOS sensor array.
CONCLUSION
The Information Age has led to an explosion of information available to users. While current storage needs are being me, storage technology must continue to improve in order to keep pace with the rapidly increasing demand. However, conventional data storage technologies, where individual bits are stored as distinct magnetic or optical changes on the surface of a recording medium are approaching physical limits. Storing information throughout the volume of a medium—not just on its surface—offers an intriguing high-capacity alternative. Holographic data storage is a volumetric approach which, although conserved decades ago, has made recent progress towards practicality with the appearance of lower-cost enabling technologies, significant results from longstanding research efforts and progress in holographic recording material.
HVD-report.doc (Size: 1.19 MB / Downloads: 37)
INTRODUCION
An HVD (holographic Versatile Disc), a holographic storage media, is an advanced optical disc that’s presently in the development stage. Polaroid scientist J. van Heerden was the first to come up with the idea for holographic three-dimensional storage media in 1960. An HVD would be a successor to today’s Blu-ray and HD-DVD technologies. It can transfer data at the rate of 1 Gigabit per second. The technology permits over 10 kilobits of data to be written and read in parallel with a single flash. The disc will store upto 3.9 terabyte (TB) of data on a single optical disk.
Holographic data storage, a potential next generation storage technology, offers both high storage density and fast readout rate. In this article, I discuss the physical origin of these attractive technology features and the components and engineering required to realize them. I conclude by describing the current state of holographic storage research and development efforts in the context of ongoing improvement to established storage technologies.
BRIEF HISTORY
Although holography was conceived in the late 1940s, it was not considered a potential storage technology until the development of the laser in the 1960s. The resulting rapid development of holography for displaying 3-D images led researchers to realize that holograms could also store data at a volumetric density of as much as 1/ where is the wave-length of the light beam used.
Since each data page is retrieved by an array of photo detectors, rather than bi-by-bit, the holographic scheme promises fast readout rates as well as high density. If a thousand holograms, each containing a million pixels, could be retrieved every second, for instance, then the output data rate would reach 1 Gigabit per second.
In the early 1990s, interest in volume-holographic data storage was rekindled by the availability of devices that could display and detect 2-D pages, including charge coupled devices (CCD), complementary metal-oxide semiconductor (CMOS) detector chips and small liquid-crystal panels. The wide availability of these devices was made possible by the commercial success of digital camera and video projectors. With these components in hand, holographic-storages researchers have begun to demonstrate the potential of their technology in the laboratory. By using the volume of the media, researchers have experimentally demonstrated that data can be stored at equivalent area densities of nearly 400 bits/sq. micron. (For comparison, a single layer of a DVD disk stores data at ~ 4.7 bits/sq. micron) A readout rate of 10 gigabit per second has also been achieved in the laboratory.
UNDERLYING ECHNOLOGY
HOLOGRAPHY
Holographic data storage refers specifically to the use of holography to store and retrieve digital data. To do this, digital data must be imposed onto an optical wave front, stored holographically with high volumetric density, and then extracted from the retrieved optical wav front with excellent data fidelity.
A hologram preserves both the phase and amplitude of an optical wave front of interest called the object beam – by recording the optical interference pattern between it and a second coherent optical beam – the reference beam. Fig 2.1 shows this process.
COLLINEAR HOLOGRAPHY
HVD uses a technology called ‘collinear holography’, in which two laser rays, one blue-green and one red, are collimated into a single beam. The role of the blue-green laser is to read the data encoded in the form of laser interference fringes from the holographic layer on the top, while the red laser serves the purpose of a reference beam and also to read the servo info from the aluminum layer – like in normal CDs – near the bottom of the disk. The servo info is meant to monitor the coordinates of the read head above the disk (this is similar to the track, head and sector information on a normal hard disk drive).
STORAGE DATA
RECORDING DATA
A simplified HVD system consists of the following main components:
Blue or green laser (532-nm wavelength in the test system)
Beam splitter/merger
Mirrors
Spatial light modulator (SLM)
CMOS sensor
Polymer recording medium
The process of writing information onto an HVD begins with encoding the information into binary data to be stored in the SLM. These data are turned into ones and zeroes represented as opaque or translucent areas on a "page" -- this page is the image that the information beam is going to pass through.
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.
READING DATA
To read the data from an HVD, you need to retrieve the light pattern stored in the hologram.
In the HVD read system, the laser projects a light beam onto the hologram -- a light beam -- a light beam that is identical to the reference beam.
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.
HARDWARE
SPATIAL LIGHT MODULATOR
To use volume holography as a storage technology, digital data must be imprinted onto the object beam for recording and then retrieved from the reconstructed object beam during readout. The device for putting data into the system is called a spatial light modulator (SLM) – a planner array consisting of thousand of pixels. Each pixel is independent microscopic shutters that can either block or pass light using liquid-crystal or micro-mirror technology. Liquid crystal panels and micro-mirror arrays with 1280 X 1024 pixels are commercially available due to the success of computer-driven projection displays. The pixels in both types of devices can be refreshed over 1000 times per second, allowing the holographic storage system to reach an input data rate of 1 gigabit per second – assuming that laser power and material sensitivities would permit. The data are read using an array of detector pixels, such as a CCD camera or CMOS sensor array.
CONCLUSION
The Information Age has led to an explosion of information available to users. While current storage needs are being me, storage technology must continue to improve in order to keep pace with the rapidly increasing demand. However, conventional data storage technologies, where individual bits are stored as distinct magnetic or optical changes on the surface of a recording medium are approaching physical limits. Storing information throughout the volume of a medium—not just on its surface—offers an intriguing high-capacity alternative. Holographic data storage is a volumetric approach which, although conserved decades ago, has made recent progress towards practicality with the appearance of lower-cost enabling technologies, significant results from longstanding research efforts and progress in holographic recording material.