Holographic storage technologies

The theory of holography was developed by Dennis Gabor, a Hungarian physicist, in the year 1947. His theory was originally intended to increase the resolving power of electron microscopes. Gabor proved his theory not with an electron beam, but with a light beam. The result was the first hologram ever made. The early holograms were legible but plagued with many imperfections because Gabor did not have the correct light to make



crisp clear holograms as we can today . Gabor needed laser Light. In the 1960s two engineers from the University of Michigan: Emmett Leith and Juris Upatnieks, developed a new device which produced a three dimensional image of an object. Building on the discoveries of Gabor, they produced the diffuse light hologram. Today, we can see holograms, or 3D images, on credit cards, magazine covers and in art galleries. Yet this unique method of capturing information with lasers has many more applications in the industrial world and is on the verge of revolutionizing data storage technology as we know it.



A project at Lucent Technologies Bell Laboratories could result in the first commercially viable holographic storage system. Leveraging advances across a number of technologies from micromirror arrays to new non linear polymer recording media, the team hopes to spin the project off into a startup. This technology not only offers very high storage densities, it could access that data at very high rates, due to the fact that holographic methods read an entire page of data in one operation. While conventional optical storage techniques read and write data by altering an optical medium on a per bit basis, holographic storage records an entire interference pattern in a single operation. This technique makes
Unique demands on both the light source and the recording medium. While a conventional optical disk system can get by with a relatively low power laser diode and a single detector, holographic techniques require high quality laser sources and detector arrays. However, these types of components have been getting cheaper. For example, CMOS pixel sensors offer the potential for the low cost detection of data arrays, while digital micromirrors can be used for data input from electronic systems. The biggest challenge has been devising a suitable optical medium for storing the interference patterns. The team turned to none



Linear polymers in its search for that key component. What is needed is a medium that can support the overlap of megabyte data pages, each with a high enough diffraction efficiency to enable high transfer rates. These two demands sound reasonably simple, but it really leads to a very long list of pretty stringent criteria for what a material has to do. The researchers have found what they believe is a suitable candidate, an acrylic polymer compound that polymerises in response to light. In addition to having the required optical performance properties, the new material, being a polymer, is easy to form into thick films. Film thickness directly relates to storage capacity and inorganic nonlinear materials, which are crystalline, are difficult to build in thick films. The researchers have built a prototype system using off the shelf components such as camera lenses and digital micromirrors from Texas Instruments.