Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-03-14
2004-03-02
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S254000, C345S107000, C430S032000
Reexamination Certificate
active
06700695
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to visual displays, and more particularly to addressable, reusable, paper-like visual displays, such as “gyricon” (or twisting particle) displays or other forms of electronic paper, such as particulate electrophoretic displays, which are available from E-ink Corporation. Specifically, the invention relates to substrates usable as a writing surface for gyricon displays or electronic paper.
A gyricon display, also called a twisting-ball display, rotary ball display, particle display, dipolar particle light valve, etc., offers a technology for making a form of electric paper and other electronically controlled displays. Briefly, a gyricon display is an addressable display made up of a multiplicity of optically anisotropic particles, with each particle being selectively rotatable to present a desired face to an observer. For example, a gyricon display can incorporate “balls” where each ball has two distinct hemispheres, one black and the other white, with each hemisphere having a distinct electrical characteristic (e.g., zeta potential with respect to a dielectric fluid) so that the ball is electrically as well as optically anisotropic. The balls are electrically dipolar in the presence of the fluid and are subject to rotation. A ball can be selectively rotated within its respective fluid-filled cavity, for example, by application of an electric field, so as to present either its black or white hemisphere to an observer viewing the surface of the sheet.
A reflective image is formed by the pattern collectively created by individual black and white hemispheres. By the application of an electric field addressable in two dimensions (as by a matrix addressing scheme), the black and white sides of the balls are controlled as the image elements (e.g., pixels or subpixels) of a displayed image. Alternatively, the display may be controlled by shaped electrodes to form one or more fixed images.
The balls are typically embedded in a sheet of optically transparent material, such as an elastomer sheet. A dielectric fluid, such as a dielectric plasticizer, is used to swell the elastomer sheet containing the balls. Through this swelling, the dielectric fluid effectively creates a fluid-filled cavity around each ball. The fluid-filled cavity accommodates the ball and allows the ball to rotate within its respective fluid-filled cavity, yet prevents the ball from migrating within the sheet.
When an electric field is applied to the sheet over a bead, the electrical force on the bead overcomes the frictional adhesion of the bead to the cavity wall and causes the bead to rotate. Once rotation is complete, each bead will remain in a fixed rotational position within its cavity. Thus, even after the electric field is removed, the structures (balls) will stay fixed in position until they are dislodged by another electric field. This bistability of the beads enables the gyricon display to maintain a fixed image without power. The bistability of a gyricon display is beneficial over other types of displays such as a liquid crystal display (LCD) or a light emitting diode (LED) display which consume energy to maintain an image. Gyricon displays are thus particularly useful for displays which will show an image for a prolonged period of time and only periodically have the image changed.
Gyricon displays are not limited to black and white images, as gyricon and other display mediums are known in the art to have incorporated color. Gyricon displays have been developed incorporating either bichromal color, trichromol color, or four quadrant colored balls. Also developed are three or four segmented colored balls, as disclosed in U.S. Pat. No. 6,128,124 ( Silverman, ADDITIVE COLOR ELECTRIC PAPER WITHOUT REGISTRATION OR ALIGNMENT OF INDIVIDUAL ELEMENTS), incorporated by reference herein.
The colored balls can be charged by adsorption of ions from a liquid onto the ball surface. Alternatively, colored balls can be charged by electret formation by injection of an external charge into the surface region of a colored ball, as is disclosed in U.S. Pat. No. 6,072,621 (Kishi, COLOR BALL DISPLAY SYSTEM), incorporated by reference herein.
Like ordinary paper, electric paper preferably can be written on and erased, can be read in ambient light, and can retain imposed information in the absence of an electric field or other external retaining force. Also like ordinary paper, electric paper preferably can be made in the form of a lightweight, flexible, durable sheet that can be folded or rolled into tubular form about any axis and can be conveniently placed into a shirt or coat pocket and then later retrieved, restraightened, and read substantially without loss of information. Yet unlike ordinary paper, electric paper preferably can be used to display full-motion and changing images as well as text. While gyricon displays are particularly useful for displays where real-time imagery is not essential, gyricon displays are adaptable for use in a computer system display screen or a television.
Gyricon display arrangements have typically taken one of three forms: (1) a slurry coat with balls randomly dispersed in a relatively thick film, (2) a monolayer where balls are closely packed in a layer; or (3) a dual layer, where balls are closely packed in a first layer and a second layer of balls is provided to fill in the voids. To create displays which appear brighter with sharper images, gyricon displays should have high light reflectance. One way to improve the reflectance of a monolayer gyricon display is to closely pack the bichromal balls. However, in dual or multiple layer displays, the packing density of the balls may be of little consequence insofar as overall display reflectance is concerned, because balls located farther from the viewing surface of the gyricon display will “fill in the gaps” between balls located nearer the viewing surface. So long as the two-dimensional projection of the balls onto the viewing surface at all distances from the viewing surface substantially covers the viewing surface, a high-quality display will be obtained.
In the context of gyricon displays, the “balls” are not necessarily perfectly round or hemispherical. Instead of balls, a gyricon display can use substantially cylindrical bichromal particles rotatably disposed in a substrate. The twisting cylinder display has certain advantages over the rotating ball gyricon display because the bichromal elements can achieve a higher packing density. The higher packing density leads to improvements in the brightness of the twisting cylinder display as compared to the rotating ball gyricon display.
One drawback to twisting particle displays (using balls, cylinders, etc.) is that the quality of the image viewed is dependent on the rotatability of the structures within the fluid. In practice, a particle may not rotate completely or not at all, thus only partially exposing the white or black color or a mix therebetween. Incomplete rotation or non-rotation causes a loss in image contrast and color purity. It is therefore desirable to improve the resolution of the image on the display by improving the rotatability of the structures within the fluid.
To achieve still higher packing density, a gyricon display can be constructed without elastomer and without cavities. In such a display, the bichromal balls are placed directly in the dielectric fluid. The balls and the dielectric fluid are then sandwiched between two retaining members (e.g., between the addressing electrodes) with no elastomer substrate.
Substrates usable as a writing surface for Gyricon displays are known in the prior art. EPO 942,405 A2 (Howard et al., “CHARGE RETENTION ISLANDS FOR ELECTRIC PAPER AND APPLICATIONS THEREOF”) discloses a pattern of conductive charge retaining islands on the surface of a Gyricon sheet.
In addition to using the present invention with Gyricon displays, the invention can also be used in combination with particulate electrophoretic displays, such as available from E-Ink Corporation, or other electronic paper. A pa
Biernath Rolf W.
Engler David A.
Buckingham Stephen W.
Dang Hung Xuan
Tra Tuyen
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