Holographic Data Storage

Holographic versatile disc (hvd)

Holographic recording technology records data on discs in the form of laser interference fringes, enabling discs the same size as today's DVDs to store more than one terabyte of data (200 times the capacity of a single layer DVD), with a transfer rate of over one gigabit per second (40 times the speed of DVD). This approach is rapidly gaining attention as a high-capacity, high-speed data storage technology for the age of broadband.

Holography

A hologram is a block or sheet of photosensitive material which records the interference of two light sources.  To create a hologram, laser  light  is  first  split  into  two  beams,  a  source  beam  and  a reference beam.  The source beam is then manipulated and sent into the photosensitive material. Once  inside  this  material,  it intersects the reference beam and the resulting interference of laser light  is  recorded  on  the  photosensitive  material,  resulting  in  a hologram.   Once a hologram is recorded, it can be viewed with only the reference beam. 

Recording Errors

When data is recorded in a holographic medium, certain factors can lead to erroneously recorded data.  One major factor is the electronic noise generated by laser beams.  When a laser beam is  split  up  (  for  example,  through a  SLM  ),  the  generated  light bleeds into places where light was meant to be blocked out.  Areas where zero light is desired might have minuscule amounts of laser light present which mutates its bit representation. 

Retrieval Of Data

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.

Abstract

Currently data access times are extremely slow for magnetic disks when compared to the speed of execution of CPUs so that any improvement in data access speeds will greatly increase the capabilities of computers, especially with large data and multimedia files. Holographic data storage is a technology that uses a three dimensional medium to store data and it can access such data a page at a time instead of sequentially, which leads to increases in storage density and access speed. Holographic data storage systems are very close to becoming economically feasible.

Challenges

During the retrieval of data the reference beam has to be focused at exactly the same angle at which it was projected during recording. A slight error can cause a wrong data page to be accessed.  It is difficult to obtain that much of accuracy. The crystal used as the photographic filament must have exact optical characteristics such as high diffraction efficiency, storage of data safely without any erasure and fast erasure on application of external stimulus light ultra violet rays. 

Conclusion

The future of holographic data storage is very promising.   The page access  of  data  that  holographic data storage creates will provide a window  into  next  generation  computing  by  adding  another dimension  to  stored  data. Finding holograms in personal computers might be a bit longer off, however.  The large cost of high-tech optical equipment would make small-scale systems implemented with holographic data storage impractical.