Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-08-30
2004-03-09
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S267000, C430S035000, C345S107000, C345S084000, C204S478000, C204S485000
Reexamination Certificate
active
06704133
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electro-optic displays and systems for addressing such displays and, in particular, to electro-optic display overlays.
BACKGROUND OF THE INVENTION
Many types of emissive displays exist and there are many methods of fabricating emissive displays. However, most emissive displays suffer from poor contrast, viewing angle restrictions, and constant power requirements. For example, liquid crystal displays (LCD's), which are commonly used in screens for laptop computers and other consumer electronic devices, suffer from both viewing angle restrictions, meaning that these displays can only be viewed from a few physical positions constrained by the viewing axis of the display, and limited favorable light conditions. Thus, the usefulness of emissive LCD displays is typically limited. For example, use of emissive LCD displays in high light situations (such as outdoor use) is generally impractical.
Further, nearly all emissive display require a constant supply of power to operate. This power requirement makes emissive displays challenging to incorporate in devices that do not have a connection to a constant supply of power or that have a connection only to a limited power supply such as batteries.
It is desirable to provide a display overlay that improves contrast and viewing angle for an emissive display while, at the same time, reducing power consumption.
SUMMARY OF THE INVENTION
The display overlays described later improve the contrast and remedy the viewing angle restrictions present in emissive displays as they exist today. Such display overlays will increase the usefulness of current day emissive displays and enable them to be used in more numerous situations, including high light situations. It is desirable that such display overlays improve the life and power efficiency of emissive displays. The display overlays may be added to existing emissive displays or, in other embodiments, may be designed as an integral part of emissive displays. Display overlays of the invention may be flexible. The display overlay materials may, for example, be printed onto thin, flexible substrates. Such substrates may include pliable, plastics, polymeric films, metal foils, and thin glass, for example.
Reflective electro-optic display overlays, especially encapsulated electro-optic display overlays, and systems including modules for addressing such display overlays may improve the usefulness and lifetime of present day emissive displays. Preferable systems of the invention avoid the high costs associated with using direct drive and active matrix drive addressing schemes by allowing for the addressing of display media that have poor threshold behavior. The display overlay of the invention improves the viewing angle restrictions and performance of the display in bright conditions by converting the emissive display to a reflective display. An emissive display includes emissive material (i.e., a light system that generates a pattern of light).
There are a number of interesting reflective display media which provide good optical appearance and the ability to be easily constructed in large areas or on flexible substrates at low cost. Such display media may be employed in displays and display overlays in accordance with the present invention. Suitable display media include microencapsulated electro-optic displays, electrochromic displays, rotating bichromal ball displays, suspended particle displays, and composites of liquid crystals with polymers, including polymer dispersed liquid crystals, polymer stabilized liquid crystals, and liquid crystal gels.
In one aspect of the invention, a display overlay is a reflective electro-optic display in optical communication with an emissive display. The display overlay also includes a photoconductive layer that is adjacent an electro-optic layer and a means for applying an electric field across the electro-optic layer (which may hereinafter be referred to as the “contrast media” layer). An electro-optic layer may be a reflective electrophoretic layer. In one embodiment, the means for applying an electric field includes an electrostatic charge deposited on at least one of the electro-optic layer or the photoconductive layer. In a second embodiment, the means for applying an electric field includes a first electrode and a second electrode. The display overlay includes a synchronization module that receives signals indicative of an emissive display output and controls the application of an electric field to the display overlay in response to the signals received by the synchronization module. In one embodiment, the synchronization module controls application of light to the display overlay.
In some embodiments, the first electrode is adjacent the first side of the photoconductive layer, and the second electrode is adjacent the contrast media layer. One or more electrode of the display overlay may be light-transmissive, transparent, or translucent. The electrodes may be formed from indium tin oxide (ITO). In a particular embodiment, the electrode on the rear side of the display overlay is translucent. In another embodiment, the electrode on the rear side of the display overlay is light-transmissive. In yet another embodiment, the electrode on the rear side of the display overlay is transparent. Light from the light source travels through the rear electrode to strike the photoconductive layer. When the display overlay is exposed to an emission, such as light generated from a light source, the pattern of light reduces impedance in the photoconductive layer. The reduced impedance permits an applied electric field to address the contrast media layer. In one embodiment, the electro-optic display visual appearance is substantially similar to the visual appearance of the emissive display. In another particular embodiment, the electrode on the front side of the display overlay is translucent; a translucent front electrode may enhance viewability of the electro-optic display visual appearance. In one embodiment, the electrode on the front side of the display overlay is transparent; a transparent front electrode may also enhance viewability of the electro-optic display visual appearance. In another embodiment, the electrode on the front side of the display overlay is light-transmissive; a light-transmissive front electrode may similarly enhance viewability of the electro-optic display visual appearance. The display may include, for example, a first protective layer adjacent the first electrode and a second protective layer adjacent the second electrode.
The display overlay may be placed adjacent, or overlay, an emissive display. The emissive display may include, for example, a cathode ray tube, LCD or other emissive display such as an electroluminescent display. Alternatively, the display overlay may be integral with the emissive display.
In some embodiments the display overlay synchronization module receives signals indicative of emissive display output. Responsive to the received signals, the synchronization module controls the first and second electrodes to apply an electric field to the contrast media layer. In a first embodiment, the synchronization module controls the first and second electrode via a universal serial bus (USB). In a second embodiment, the synchronization module controls the first and second electrodes via a serial cable. In another embodiment, the synchronization module controls the first and second electrodes via an optical interface. The synchronization module may include, for example, a device driver, a thread, or WINDOWS sub-system. In other embodiments the synchronization module may be special-purpose hardware such as appropriately configured programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), or application-specific integrated circuits (ASICs).
In other embodiments, the display overlay has one or more optical barrier layers. The optical barrier layers may be placed between a second side of the photoconductive layer and the contrast media layer. Such an optical barrier laye
Albert Jonathan D.
Davis Benjamin M.
Gates Holly G.
Morrison Ian
Ozier Owen W.
Ben Loha
E-Ink Corporation
Testa Hurwitz & Thibeault LLP
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