02-03-2011, 12:48 PM
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1. INTRODUCTION
An HVD (Holographic Versatile Disc), a holographic storage media, is an advanced optical disk 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 in 1960. An HVD would be a successor to today's Blue-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 disk will store up to 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. The strengths and weaknesses of available write-once and read-writeable storage media are discussed, including the development issues of achieving non-volatile readout from read-write media. Systems issues such as the major noise sources and avenues for defeating or finessing them are detailed, including the potentials and pitfalls of phase- conjugate readout and holographic storage on spinning media. I conclude by describing the current state of holographic storage research and development efforts in the context of on going improvements to established storage technology.
1.1 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/ A3 where A, is the wave-length of the light beam used.
Since each data page is retrieved by an array of photo detectors in parallel, rather than bit-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. Despite this attractive potential and fairly impressive early progress research into holographic data storage died out in the mid-1970s because suitable devices for the input and output of large pixilated 2-D data pages were just not available.
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 hand-held camcorders, digital cameras, and video projectors. With these components in hand, holographic-storage 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 aerial 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.
1.2 LONGEVITY
Holographic data storage can provide companies a method to preserve and archive information. The write-once, read many (WORM) approach to data storage would ensure content security, preventing the information from being overwritten or modified. Manufacturers believe this technology can provide safe storage for content without degradation for more than 50 years, far exceeding current data storage options. Counterpoints to this claim point out the evolution of data reader technology changes every ten years; therefore, being able to store data for 50-100 years would not matter if you could not read or access it.
1.3 FEATURES
Data transfer rate: l gbps.
The technology permits over 10 kilobits of data to be written and read in
parallel with a single flash.
Most optical storage devices, such as a standard CD saves one bit per pulse.
HVDs manage to store 60,000 bits per pulse in the same place.
1 HVD = 5800 CDs = 830 DVD =160 BLU-RAY Discs.
2. UNDERLYING TECHNOLOGY
2.1 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 wave 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. Figure 2.1 shows this process.
1. INTRODUCTION
An HVD (Holographic Versatile Disc), a holographic storage media, is an advanced optical disk 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 in 1960. An HVD would be a successor to today's Blue-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 disk will store up to 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. The strengths and weaknesses of available write-once and read-writeable storage media are discussed, including the development issues of achieving non-volatile readout from read-write media. Systems issues such as the major noise sources and avenues for defeating or finessing them are detailed, including the potentials and pitfalls of phase- conjugate readout and holographic storage on spinning media. I conclude by describing the current state of holographic storage research and development efforts in the context of on going improvements to established storage technology.
1.1 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/ A3 where A, is the wave-length of the light beam used.
Since each data page is retrieved by an array of photo detectors in parallel, rather than bit-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. Despite this attractive potential and fairly impressive early progress research into holographic data storage died out in the mid-1970s because suitable devices for the input and output of large pixilated 2-D data pages were just not available.
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 hand-held camcorders, digital cameras, and video projectors. With these components in hand, holographic-storage 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 aerial 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.
1.2 LONGEVITY
Holographic data storage can provide companies a method to preserve and archive information. The write-once, read many (WORM) approach to data storage would ensure content security, preventing the information from being overwritten or modified. Manufacturers believe this technology can provide safe storage for content without degradation for more than 50 years, far exceeding current data storage options. Counterpoints to this claim point out the evolution of data reader technology changes every ten years; therefore, being able to store data for 50-100 years would not matter if you could not read or access it.
1.3 FEATURES
Data transfer rate: l gbps.
The technology permits over 10 kilobits of data to be written and read in
parallel with a single flash.
Most optical storage devices, such as a standard CD saves one bit per pulse.
HVDs manage to store 60,000 bits per pulse in the same place.
1 HVD = 5800 CDs = 830 DVD =160 BLU-RAY Discs.
2. UNDERLYING TECHNOLOGY
2.1 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 wave 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. Figure 2.1 shows this process.
