by December 5, 2002 0 comments

In Minority Report, you will find Tom Cruise watching the video of his lost child from some kind of palm-sized transparent glass plates. A huge video in such thin a medium? Difficult as it may sound, even that is in the realm of the possible. Welcome to the world of holographic storage, which can accommodate terabytes of data in small spaces. It is also much faster than conventional storage media. Holographic storage uses laser beams to read and write data. 

Prototypes of this technology have been demonstrated, and useable products are expected soon. Holographic storage traces its roots to way back in 1947 when Dennis Gobor theorised that two beams of light crossing each other could produce a 3D image called a hologram. Holography has come a long way since then as a way of producing 3D pictures. But it was only in 1995 that effort were
initiated to use Gobor’s theory to develop stor-age systems. 


Holographic storage system

How it writes 
Holographic storage technology uses two laser beams, split out from the same source; one is the signal beam for carrying data, and the other is the reference beam. The signal beam is passed through the SLM (Spatial Light Modulator), which is a small LCD display. The SLM presents the data to the beam as pages of 0’s and 1’s . The signal beam gets imprinted with this data before reaching the recording media. Simultaneously, the reference beam is also focused on to the recording media. Both the beams (reference and imprinted signal beam) intersect on recording media, creating a pattern, which gets embossed on the photosensitive recording media.

Once you have the image for writing, you can multiplex it. That is, you overlap multiple such holograms to increase capacity and performance of the storage device. The DEMON (holographic storage DEMONstrator) from IBM, for example, stored 6.7 MB of data using 1200 superimposed holograms. 

And reads
Reading is the reverse. While reading the data from the holographic storage, the reference beam passes through the holographic media, to reconstruct the stored array of bits. This is then projected on to a detector that reads the data in parallel.

The basic technology is already available. However, research is still going on to make it more compact and durable. Major players in the area, like IBM and Inphase Technologies, have either come out with prototypes, or are in the verge of doing so. Inphase has designed a prototype for holographic drives, using a new type of media code-name 

Tapestry, which is expected to be in the market by mid 2003. Currently, Tapestry can store 2 gigabytes on a postage stamp size, 
20 gigabytes on a credit-card size and 100’s of gigabytes on a disk. 

Sanjay Majumder

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