Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-06-07
2003-10-14
Tarifur, Chowdhury (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S087000, C349S088000, C349S098000, C349S176000
Reexamination Certificate
active
06633354
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to single-layer broadband reflective polarizers having electrically controllable polarization efficiencies and reflection bandwidths, and more particularly to single-layer reflective polarizers which can be electrically switched from broadband operation to narrow band operation over the visible and infra-red (IR) bands, as well as single-layer reflective polarizers which can be electrically switched from narrow band operation to broadband operation over the visible and IR bands.
2. Brief Description of the Prior Art
Humans have a natural affinity for pictures. Dramatic improvements in modern display devices are possible with the advent of novel polarizer technologies. In many advanced display techniques, a polarizing device having electrically controllable transmission characteristics such as polarization, transmittance, and spectra is desired in order to actively control the display brightness as well as color balance, for example.
Electrically controllable polarizers can also serve as an enabling technology for other applications such as smart window, wherein the window transmission is electrically switchable from a totally reflective state to a totally transparent state by incorporating two switchable polarizers with opposite polarization states. Such a window can provide lighting control and can additionally provide energy conservation benefits if externally mounted.
Since early attempts at utilizing cholesteric film as optical filters and polymer encapsulated nematic liquid crystals for display devices, there has been great attention focused on trying to bring polymeric liquid crystals and cholesteric liquid crystals together to make devices or light control application.
U.S. Pat. No. 5,691,789 discloses a single-layer reflective super broadband circular polarizer and method of fabricating the same by producing a single layer having cholesteric liquid crystal (CLC) order where the pitch of the liquid crystal order varies in a non linear fashion across the layer.
European Patent Application 0 643 121 A published Mar. 15, 1995 discloses a narrow band, switchable polarizing single layer reflector.
PCT application WO 97/2358, published Jul. 3, 1997, discloses a switchable polarizing single-layer reflector having a broader bandwidth.
General references on polymer dispersed liquid crystals may be found: “Polymer Dispersed Liquid Crystal Displays”, by J. W. Doane; a chapter in “Liquid Crystals”, Ed. B. Bahadur, World Scientific Publishing, Singapore; and “CLC/Polymer Dispersion For Haze-Free Light Shutters”, by D. Yang et al. Appl. Phys. Lett. 60, 3102 (1992).
Smart Window Design is described in “Electrochromism And Smart Window Design”, by C. Granqvist, Solid State Ionics 53-56 (1992) and “Large Scale Electochromic Devices For Smart Windows And Absorbers”, by T. Meisel and R. Baraun, SPIE 1728, 200 (1992).
The above identified U.S. patents and other prior art references are hereby incorporated by reference.
While there is a great need in the art for an improved single-layer electrically controllable broad-band reflective polarizer for use in diverse applications, prior art methods and technology have clearly failed to teach how to how to practice the same in a feasible manner.
OBJECTS OF THE PRESENT INVENTION
Accordingly, a primary object of the present invention is to provide a single layer polarizing film having a very wide bandwidth which is switchable.
Another object of the invention is to provide a switchable reflecting polarizing filter having a very wide bandwidth which is controllable by an electric field.
Another object of the invention is to provide a switchable reflective film having little variation in the reflectivity outside of the reflective bandwidth of the film.
Another object of the invention is to provide a “smart window” using a polarizing reflective film having a very wide bandwidth.
Another object of the invention is to provide a “smart window” using a polarizing reflective film having a very wide bandwidth combined with a reflective multilayer polymer film having a very wide bandwidth.
Another object of the invention to provide a “smart window” using a polarizing reflective film having a very wide bandwidth combined with a reflective multilayer polymer film having little variation in the reflectivity outside of the reflective bandwidth of the film.
Another object of the invention to provide a “smart window” using a polarizing reflective multilayer polymer film having a very wide bandwidth combined with a light scattering layer for further control of transmitted light.
Another object of the invention to provide a reflective polarizing film having a bandwidth which is controllable by an electric field.
Another object of the invention to provide a “smart window” using a polarizing reflective film having a very wide bandwidth which is controllable by an electric field.
Another object of the present invention is to provide an electrically-switchable family of infrared reflective polarizers and filters, based on the remarkable properties of cholesteric liquid crystals (CLCs), having far-reaching dual-use aerospace and window-glazing applications.
Another object of the present invention is to provide electrically controllable polarizers and filters that can be remotely controlled and involve no moving parts, to active-solar-control window glazings having the unheard-of property of infrared switchability while maintaining total visible transparency.
Another object of the present invention is to provide novel near-infrared switchable polarizers, filters, and reflectors, which fulfill a market need for remote-controlled, robust, thin-film, multiple-use optical components.
Another object of the present invention is to provide fast electrically-switchable infrared reflective polarizers capable of switching from broad-to-narrow band reflective operation over the IR band.
Another object of the present invention is to provide such a fast electrically-switchable infrared reflective polarizers, wherein its rise time is about 14.5 ms and its fall time about 8.5 ms.
Another object of the present invention is to provide fast electrically-switchable infrared reflective polarizers capable of switching from narrow-to-broad band reflective operation over the IR band.
Another object of the present invention is to provide a full understanding and comprehensive model of the chemical and physical switching mechanisms, verified through computer simulations.
Another object of the present invention is to provide an electrically-tunable infrared reflective polarizer.
Another object of the present invention is to provide an electrically switchable IR reflector based on an electrically switchable broadband reflective polarizer that operates in the IR region from 780 nm to 4 microns.
Another object of the present invention is to provide left- and right-handed CLC based switchable broadband polarizers that operate in the IR region from 780 nm to 4 microns.
Another object of the present invention is to provide a field-switchable broadband reflective polarizer operable in the NIR spectral region.
Another object of the present invention is to provide a field-switchable broadband reflective polarizer operable in the spectral region from 700 to >1000 nm, and having a polarizing bandwidth and extinction ratio which are changeable via an applied electric field. Another object of the present invention is to provide a novel method of optimizing the performance of such electro-optical structures in terms of extinction ratio, overall reflectivity, and reflection spectral cutting-off edge.
Another object of the present invention is to provide novel material recipes for making the switchable, broadband-to-narrow-band polarizers of the present invention, which enable further expansion of the polarizer bandwidth, shift to longer wavelengths, and increase the extinction ratio to the desired level.
Another object of the present invention is to provide a method of making such electrically-switchable IR reflective po
Fan Bunsen
Faris Sadeg M.
Jiang Yingqiu
Li Jian-Feng
Li Le
Crispino Ralph J.
Perkowski Esq., PC Thomas J.
Reveo Inc.
Schechter Andrew
Tarifur Chowdhury
LandOfFree
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