Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-03-14
2003-05-27
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S290000
Reexamination Certificate
active
06570700
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
None.
BACKGROUND OF THE INVENTION
The present invention relates to microfabricated structures to interact with electromagnetic waves and, more particularly to addressable, reusable visual displays. Still more particularly, an embodiment of the invention relates to preformed microstructured substrates containing assisting optical elements to enhance the visual effect of visual displays, such as gyricon displays using rotatable particles (e.g., rotary balls).
For purpose of illustration, the present application uses structures of gyricon displays to demonstrate the concepts and the benefits of the inventive structure.
A gyricon display, also called a twisting-particle display, rotary ball display, particle display, dipolar particle light valve, etc., is a type of addressable visual displays. A gyricon display offers a technology for making a form of electric paper and other reflective 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. The rotary particle can be of various shapes, such as spherical or cylindrical. For convenience, balls, rather than cylinders, are used in this description for illustrations.
Addressable visual displays typically have multiple display units such as pixels or subpixels. A separate assisting optical element is sometimes used in connection with each display to enhance or create certain visual effect. U.S. Pat. No. 5,777,782 to Sheridon, for example, discloses a gyricon or rotating-particle display having an auxiliary optical structure which is a pre-formed array of lenses indexed to gyricon particles. Although the Sheridon patent relates to gyricon displays only, in principle the use of an auxiliary optical structure is not limited to the gyricon displays. A properly designed auxiliary optical structure may be used to enhance or create certain visual effects in other types of visual displays containing multiple display units, such as displays using electronic ink based on the electrophoretic principle made by E Ink Corp. For purpose of illustration, however, the present application uses structures of gyricon displays to demonstrate the concepts and the benefits of the inventive structure.
A gyricon display, also called a twisting-particle display, rotary ball display, particle display, dipolar particle light valve, etc., offers a technology for making a form of electric paper and other reflective 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. The rotary particle can be of various shapes, such as spherical or cylindrical. For convenience, balls, rather than cylinders, are used in this description for illustrations.
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 still images and text. Thus, it is particularly useful for bistable displays where real-time imagery is not essential, but also adaptable for use in real-time imaging such as a computer display screen or a television.
A gyricon display, also called a twisting-particle display, rotary ball display, particle display, dipolar particle light valve, etc., offers a technology for making a form of electric paper and other reflective 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. The rotary particle can be of various shapes, such as spherical or cylindrical. For convenience, balls, rather than cylinders, are used in this description for illustrations.
In the prior art, the black-and-white balls (particles) are embedded in a sheet of optically transparent material, such as an elastomer sheet. The elastomer sheet is then cured. After curing, the elastomer sheet is placed in a plasticizer liquid, such as a dielectric fluid. The dielectric plasticizer swells the elastomer sheet containing the particles creating cavities larger than the particles around the particles. The cavities are also filled with the absorbed dielectric fluid. The fluid-filled cavities accommodate the particles, one particle per cavity, so as to prevent the particles from migrating within the sheet.
Besides being optically anisotropic, the particles are electrically dipolar in the presence of the fluid. This may be accomplished by simply including in one or both hemispheres materials that impart an electrical anisotropy, or by coating one or both sides of hemispheres with materials that impart electrical anisotropy. The above charge activation agents may impart an electrical anisotropy and an optical anisotropy at the same time. For example, when each hemisphere of a gyricon particle is coated with a material of a distinct electrical characteristic (e.g., Zeta potential with respect to a dielectric fluid) corresponding to a distinct optical characteristic the particles will have an electrical anisotropy in addition to their optical anisotropy when dispersed in a dielectric liquid. It is so because when dispersed in a dielectric liquid the particles acquire an electric charge related to the Zeta potential of their surface coating.
An optically anisotropic particle 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. Under the action of an addressing electric field, such as provided by a conventional matrix addressing scheme, selected ones of the optically and electrically anisotropic particles are made to rotate or otherwise shift their orientation within their cavities to provide a display by the selective absorption and reflection of ambient light. Since the particles need only rotate, not translate, to provide an image, much faster imaging response is achieved than with the display of U.S. Pat. No. 3,612,758.
When the electric field is applied to the sheet, the adhesion of each particle to the cavity is overcome and the particles are rotated to point either their black or white hemispheres towards the transparent surface. Even after the electric field is removed, the structures (particles in specific orientations) will stay in position and thus create a bistable display until the particles are dislodged by another electric field. An image is formed by the pattern collectively created by each individual black and white hemisphere. Thus, by the application of an electric field addressable in two dimensions (as by a matrix addressing scheme), the black and white sides of the particles can be caused to appear as the image elements (e.g., pixels or subpixels) of a displayed image. These bistable displays are particularly useful for remotely addressable displays that require little power to switch and no power to maintain display image for a long period of time (e.g., months).
Gyricon display technology is described further in U.S. Pat. No. 4,126,854 (Sheridon, “Twisting Ball Panel Display”) and U.S. Pat. No. 5,389,945 (Sheridon, “Writing System Including Paper-Like Digitally Addressed Media and Addressing Device Therefor”). Further advances in black and white gyricon displays have been described in U.S. Pat. No. 6,055,091 (Sheridon, “Twisti
Biernath Rolf W.
Engler David A.
Nelson John C.
3M Innovative Properties Company
Abutayeh M.
Buckingham Stephen W.
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