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Holographic Data Storage System (HDSS) program was a US Federal government-funded consortium on holographic data storage by Teledyne Technologies, IBM and Stanford University, created in 1995. [1] Work on the program began in 1994 and it was funded by DARPA. [2]
Proposed in the 1960s, holographic storage records data by capturing the interference patterns between a modulated optical field and a reference field within a storage medium. The data is retrieved by diffracting the reference field off the hologram, reconstructing the original optical field containing the data. [3] The holographic data storage system was created with the initial goals of developing several key components for the system, including a high-capacity, high-bandwidth spatial light modulator used for data input, optimized sensor arrays for data output, and a high-power red semiconductor laser. At the same time, the HDSS researchers were to explore issues relating to the optical systems architecture (such as multiplexing schemes and access modes), data encoding and decoding methods, signal processing techniques, and the requirements of target applications. Into the program's final year, progress has been such that consortium member, IBM Research Division, believed that holograms could hold the key to high-capacity data storage in the next millennium.
Large amounts of data can be stored holographically because lasers are able to store pages of electronic patterns. [4] Holographic storage is sometimes referred to as 3D storage within special optical materials as opposed to just on the surface. In traditional holography, each viewing angle gives a different aspect of the same object. With holographic storage, however, a different 'page' of information is accessed.
Holographic storage uses two laser beams, a reference and a data beam, to create an interference pattern at a medium where the two beams intersect. This intersection causes a stable physical or chemical change which is stored in the medium.
During the reading sequence, the action of the reference beam and the stored interference pattern in the medium recreates this data beam which may be sensed by a detector array. The medium may be a rotating disk containing a polymeric material, or an optically sensitive single crystal. The key to making the holographic data storage system work is the second laser beam which is fired at the crystal to retrieve a page of data. It must exactly match the original reference beam angle. A difference of a thousandth of a millimeter will fail to retrieve the data. Holography is expected to be of value in archival or library storage applications where large quantities of data need to be retained at the lowest costs possible.
Since it involves no moving parts, holographic data storage has the potential for higher reliability compared to traditional hard disk technologies. Research conducted by IBM has demonstrated the potential for storing up to 1 TB of data within a crystal approximately the size of a sugar cube, with data transfer rates reaching one trillion bits per second. A significant hurdle remains in the development of a rewritable form of holographic storage.
At the Consumer Electronics Show (CES) in 2006, a prototype holographic drive was demonstrated, which achieved a storage capacity of 300 GB, in contrast to the 100 GB capacity of Blu-ray discs at the time. It has been suggested that holographic disks could serve as a successor to Blu-ray.
An optical disc is a flat, usually disc-shaped object that stores information in the form of physical variations on its surface that can be read with the aid of a beam of light. Optical discs can be reflective, where the light source and detector are on the same side of the disc, or transmissive, where light shines through the disc to be detected on the other side.
Holography is a technique that enables a wavefront to be recorded and later reconstructed. It is best known as a method of generating three-dimensional images, and has a wide range of other uses, including data storage, microscopy, and interferometry. In principle, it is possible to make a hologram for any type of wave.
Interferometry is a technique which uses the interference of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber optics, engineering metrology, optical metrology, oceanography, seismology, spectroscopy, quantum mechanics, nuclear and particle physics, plasma physics, biomolecular interactions, surface profiling, microfluidics, mechanical stress/strain measurement, velocimetry, optometry, and making holograms.
A spatial light modulator (SLM) is a device that can control the intensity, phase, or polarization of light in a spatially varying manner. A simple example is an overhead projector transparency. Usually when the term SLM is used, it means that the transparency can be controlled by a computer.
The photorefractive effect is a nonlinear optical effect seen in certain crystals and other materials that respond to light by altering their refractive index. The effect can be used to store temporary, erasable holograms and is useful for holographic data storage. It can also be used to create a phase-conjugate mirror or an optical spatial soliton.
Density is a measure of the quantity of information bits that can be stored on a given length of track, area of the surface, or in a given volume of a computer storage medium. Generally, higher density is more desirable, for it allows more data to be stored in the same physical space. Density therefore has a direct relationship to storage capacity of a given medium. Density also generally affects the performance within a particular medium, as well as price.
The Holographic Versatile Disc (HVD) is an optical disc technology that was expected to store up to several terabytes of data on an optical disc 10 cm or 12 cm in diameter. Its development commenced in April 2004, but it never arrived due to lack of funding. The company responsible for HVD went bankrupt in 2010.
Holonomic brain theory is a branch of neuroscience investigating the idea that human consciousness is formed by quantum effects in or between brain cells. Holonomic refers to representations in a Hilbert phase space defined by both spectral and space-time coordinates. Holonomic brain theory is opposed by traditional neuroscience, which investigates the brain's behavior by looking at patterns of neurons and the surrounding chemistry.
Professional Disc (PFD) is a digital recording optical disc format introduced by Sony in 2003 primarily for XDCAM, its tapeless camcorder system. It was one of the first optical formats to utilize a blue laser, which allowed for a higher density of data to be stored on optical media compared to infrared laser technology used in the CD and red laser technology used in the DVD format.
Optical storage refers to a class of data storage systems that use light to read or write data to an underlying optical media. Although a number of optical formats have been used over time, the most common examples are optical disks like the compact disc (CD) and DVD. Reading and writing methods have also varied over time, but most modern systems as of 2023 use lasers as the light source and use it both for reading and writing to the discs. Britannica notes that it "uses low-power laser beams to record and retrieve digital (binary) data."
In computing, external storage refers to non-volatile (secondary) data storage outside a computer's own internal hardware, and thus can be readily disconnected and accessed elsewhere. Such storage devices may refer to removable media, compact flash drives, portable storage devices, or network-attached storage. Web-based cloud storage is the latest technology for external storage.
Holographic data storage is a potential technology in the area of high-capacity data storage. While magnetic and optical data storage devices rely on individual bits being stored as distinct magnetic or optical changes on the surface of the recording medium, holographic data storage records information throughout the volume of the medium and is capable of recording multiple images in the same area utilizing light at different angles.
Ultra Density Optical (UDO) is an optical disc format designed for high-density storage of high-definition video and data. The format was introduced by Sony to replace the Magneto-optical disc format.
For holographic data storage, holographic associative memory (HAM) is an information storage and retrieval system based on the principles of holography. Holograms are made by using two beams of light, called a "reference beam" and an "object beam". They produce a pattern on the film that contains them both. Afterwards, by reproducing the reference beam, the hologram recreates a visual image of the original object. In theory, one could use the object beam to do the same thing: reproduce the original reference beam. In HAM, the pieces of information act like the two beams. Each can be used to retrieve the other from the pattern. It can be thought of as an artificial neural network which mimics the way the brain uses information. The information is presented in abstract form by a complex vector which may be expressed directly by a waveform possessing frequency and magnitude. This waveform is analogous to electrochemical impulses believed to transmit information between biological neuron cells.
Holographic interferometry (HI) is a technique which enables the measurements of static and dynamic displacements of objects with optically rough surfaces at optical interferometric precision. These measurements can be applied to stress, strain and vibration analysis, as well as to non-destructive testing and radiation dosimetry. It can also be used to detect optical path length variations in transparent media, which enables, for example, fluid flow to be visualised and analyzed. It can also be used to generate contours representing the form of the surface.
Digital holography is the acquisition and processing of holograms with a digital sensor array, typically a CCD camera or a similar device. Image rendering, or reconstruction of object data is performed numerically from digitized interferograms. Digital holography offers a means of measuring optical phase data and typically delivers three-dimensional surface or optical thickness images. Several recording and processing schemes have been developed to assess optical wave characteristics such as amplitude, phase, and polarization state, which make digital holography a very powerful method for metrology applications .
Computer-generated holography (CGH) is a technique that uses computer algorithms to generate holograms. It involves generating holographic interference patterns. A computer-generated hologram can be displayed on a dynamic holographic display, or it can be printed onto a mask or film using lithography. When a hologram is printed onto a mask or film, it is then illuminated by a coherent light source to display the holographic images.
3D optical data storage is any form of optical data storage in which information can be recorded or read with three-dimensional resolution.
A holographic display is a type of 3D display that utilizes light diffraction to display a three-dimensional image to the viewer. Holographic displays are distinguished from other forms of 3D displays in that they do not require the viewer to wear any special glasses or use external equipment to be able to see the image, and do not cause the vergence-accommodation conflict.
Optical holography is a technique which enables an optical wavefront to be recorded and later re-constructed. Holography is best known as a method of generating three-dimensional images but it also has a wide range of other applications.
