# US 4,396,997 A · Liquid crystal information storage and retrieval system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,396,997 A - Document ID: US4396997A - Status: Granted - Kind: A - Application number: 06/267,275 - Filed: 1981-05-26 - Granted: 1983-08-02 - Earliest claimed: 1981-05-26 - Assignees: Hewlett-Packard Company - Inventors: Frederic J. Kahn; Henryk Birecki; Robert A. Burmeister - Web page: https://patentgrep.com/patent/US4396997A ## CPC - G11B 7/00555: {involving liquid crystal media} - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract 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. ## Claims ### Claim 1 An information storage device comprising: confinement means for confining a liquid crystal medium; a liquid crystal medium confined by said confinement means, said liquid cystal medium being in the smectic-A phase and having an approximately uniform thickness of more than 5 microns; and an array of defects in said liquid crystal medium representing information bits, the ratio of the shortest distance between individual defects to the thickness of the liquid crystal medium being less than 0.4, with said defects having a maximum size of 6 microns. ### Claim 2 (depends on 1) A device as in claim 1 further comprising: at least two electrodes on said device; alignment means for aligning said liquid crystal medium; and absorber means for absorbing a portion of radiation incident thereon. ### Claim 3 (depends on 2) A device as in claim 2 further comprising heat control means for controlling the relative distribution of energy conducted from said absorber means to said liquid crystal medium and from said absorber means to said confinement means. ### Claim 4 (depends on 3) A device as in claim 3 further comprising reflector means for reflecting a portion of radiation incident thereon. ### Claim 5 (depends on 4) A device as in claim 4 wherein said confinement means further comprises two substrates between which said liquid crystal medium is sandwiched. ### Claim 6 (depends on 5) A device as in claim 5 wherein: said electrodes are located opposite each other with said liquid crystal medium therebetween; and said alignment means and absorber means, are comprised of at least one film located between said substrates. ### Claim 7 (depends on 6) A device as in claim 6 wherein said heat control means comprises at least one film located between said liquid crystal medium and at least one of said substrates. ### Claim 8 (depends on 7) A device as in claim 7 wherein said reflector means comprises at least one film located between said liquid crystal medium and at least one of said substrates. ### Claim 9 (depends on 1, 3, 7) A device as in claim 1, 3, 7, or 8 further comprising a first means for at least one of writing information bits onto said liquid crystal medium, reading information bits which are stored on said liquid crystal medium, and erasing individual bits of information which are stored on said liquid crystal medium. ### Claim 10 (depends on 9) A device as in claim 9 wherein said first means further comprises a radiation source and a focusing means for focusing radiation from said radiation source onto said absorber means. ### Claim 11 (depends on 10) A device as in claim 10 wherein said first means is further comprised of an imaging means for imaging radiation scattered from said liquid crystal medium. ### Claim 12 (depends on 11) A device as in claim 11 wherein said imaging means is further comprised of a dark field optical system. ### Claim 13 (depends on 11) A device as in claim 11 wherein said imaging means is further comprised of an inverted dark field optical system.