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Liquid crystal information storage and retrieval system
| Details |
Inventors: Kahn, Frederic J.; Birecki, Henryk; Burmeister, Robert A.;
Assignee: Hewlett-Packard Company (Palo Alto, CA)
Primary Examiner: Hecker; Stuart M.
Assistant Examiner:
Attorney, Agent or Firm: Smith; Joseph H., Grubman; Ronald E.
An optical erasable thermally addressed, liquid crystal information storage and retrieval system is disclosed having an information density and the order of 10.sup.7 bits/cm.sup.2 while using liquid crystal cell thickness of relatively standard dimensions (.about.10 .mu.m). The system includes two substrates containing a smectic-A phase liquid crystal medium, and several thin filing attached to the substrates for establishing the proper conditions within the liquid crystal medium for creating a radiation scattering defect which is small in size (<1.0 .mu.m), and for performing erase functions in conjunction with an optical beam. A device according to the invention has an array of such defects in the liquid crystal medium representing information bits, with the array having a ratio of the shortest distance between individual defects to the thickness of the liquid crystal medium of less than 0.4, for a liquid crystal medium having thickness larger than 5 microns. |
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DETAILED DESCRIPTION In accordance with the illustrated preferred embodiments, the present invention provides an optical, erasable, liquid crystal information storage and retrieval system.
The system includes two substrates containing the liquid crystal medium, preferrably a smectic-A material, and several thin films attached to the substrates for establishing the proper conditions within the liquid crystal medium for achieving the desired small "spot" (or defect) size and for performing erase functions in conjunction with an optical beam.
Writing onto the cell is accomplished by locally heating the liquid crystal with a pulsed, optical beam or array of beams to create radiation scattering defects forming the desired bit pattern.
Despite all indications to the contrary from the prior art described in the Background, a system according to the preferred embodiments can achieve spot diameters of less than 1.
0 microns, essentially independently of the thickness of the liquid crystal medium.
In addition, the system is capable of consistently providing a ratio of spot spacing to liquid crystal thickness of less than 0.
4 for crystal thickness over 5 microns.
For practical reasons, however, crystals thicker than about 15 microns are seldom used.
Hence, for liquid crystals with thicknesses of the order of 10 microns (an easily constructed production size), stable center-to-center spot spacings of less than 4 microns can be readily achieved.
This corresponds to an information density of approximately 10.
sup.
7 bits/cm.
sup.
2 for an array of square domains.
Furthermore, limitations in this regard are not presently inherent in the liquid crystal medium, but are a function of the absorbing materials and beam focusing.
In contrast to the prior art, these information densities do not require tight control over cell thickness, so that substrate thickness can be reduced.
A reduction in substrate thickness results in shorter working distances in the optical systems; hence, smaller lenses and less massive systems can be used
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LCD 
