Switchable volume hologram materials and devices
First Claim
1. A reflection hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure:
- (a) a polymerizable monomer;
(b) a liquid crystal;
(c) a cross-linking monomer;
(d) a coinitiator; and
(e) a photoinitiator dye;
whereby the polymer-dispersed liquid crystal material is adapted to reflect radiation after exposure.
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Accused Products
Abstract
A new photopolymerizable material allows single-step, fast recording of volume holograms with properties that can be electrically controlled. Polymer-dispersed liquid crystals (PDLCs) in accordance with the invention preferably comprise a homogeneous mixture of a nematic liquid crystal and a multifunctional pentaacrylate monomer, in combination with photoinitiator, coinitiator and cross-linking agent. Optionally, a surfactant such as octanoic acid may also be added. The PDLC material is exposed to coherent light to produce an interference pattern inside the material. Photopolymerization of the new PDLC material produces a hologram of clearly separated liquid crystal domains and cured polymer domains. Volume transmission gratings made with the new PDLC material can be electrically switched between nearly 100% diffraction efficiency and nearly 0% diffraction efficiency. By increasing the frequency of the switching voltage, switching voltages in the range of 50 Vrms can be achieved. The optional use of surfactant allows low switching voltages at lower frequencies than without surfactant. In an alternative embodiment, a PDLC material in accordance with the invention can be utilized to form reflection gratings, including switchable reflection gratings. In still further embodiments, a PDLC material in accordance with the invention can be used to form switchable subwavelength gratings. By further processing, static transmission reflection, and subwavelength PDLC materials can be formed.
291 Citations
28 Claims
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1. A reflection hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure:
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(a) a polymerizable monomer; (b) a liquid crystal; (c) a cross-linking monomer; (d) a coinitiator; and (e) a photoinitiator dye; whereby the polymer-dispersed liquid crystal material is adapted to reflect radiation after exposure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A reflection hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure:
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(a) a polymerizable monomer; (b) more than about 20% by weight of liquid crustal; (c) a cross-linking monomer; (d) a coinitiator; and (e) a photoinitiator dye; whereby the polymer-dispersed liquid crystal material is adapted to reflect radiation after exposure. - View Dependent Claims (23)
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24. A reflection hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure:
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(a) a polymerizable monomer; (b) from about 20% by weight to 35% by weight of liquid crystal; (c) a cross-linking monomer; (d) a coinitiator; and (e) a photoinitiator dye; whereby the polymer-dispersed liquid crystal material is adapted to reflect radiation after exposure.
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25. A reflection hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure:
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(a) a polymerizable monomer; (b) a liquid crystal comprising 10-40% by total weight of the material; (c) a cross-linking monomer comprising 5-15% by total weight of the material; (d) 10-3 to 10-4 gram moles of a coinitiator; and (e) 10-5 to 10-6 gram moles of a photoinitiator dye; whereby the polymer-dispersed liquid crystal material is adapted to reflect radiation after exposure. - View Dependent Claims (26)
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27. A reflection hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure:
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(a) a polymerizable monomer; (b) a liquid crystal comprising 10-40% by total weight of the material; (c) a cross-linking monomer comprising 10-18% by total weight of the material; (d) a coinitiator comprising 2-3% by total weight of the material; and (e) a photoinitiator dye comprising 0.2-0.4% by total weight of the material; whereby the polymer-dispersed liquid crystal material is adapted to reflect radiation after exposure. - View Dependent Claims (28)
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Specification