Bae Systems Information and Electronic Systems Integration Inc.

Wesley H Halstead

Thomas V Gunn

Michael Schmidt

Richmond F Hicks

A system is provided for increasing the brightness and color saturation of a liquid crystal display to permit direct sunlight viewing which includes the utilization of an array of diffractive color separation microlenses which serve both to spatially separate incoming white light into red, green and blue bands which do not overlap and to focus the bands onto a subpixel matrix such that each of the sub-pixels is illuminated with only one color. The diffractive color separation is made possible through the utilization of the iterative genetic algorithm which specifies the stepped surface of the lens that provide for exceptionally fine color separation. In one embodiment the genetic algorithm is applied iteratively to define the optimal stepped surfaces which are utilized to focus the various colors at different positions at the focal plane of the lens. The subject system improves the overall transmission efficiency of 5% for a standard liquid crystal display to in excess of 30% overall efficiency. This results in lower power requirements or alternatively a brighter display such that the displays are sunlight viewable and have application in lap top computers, cockpit displays, automobile instrument displays, ATM displays, projection displays, equipment displays, and in general any display of a color LCD nature which is to be viewed in direct sunlight.

Color liquid crystal display having diffractive color separation microlenses

A trimodal microlens configuration is provided for the lenses in a microlens array utilized as a diffraction separator for generating separated bands of different color when the microlens array is provided with a collimated light source. To provide the trimodal functionality, each microlens is divided up into three segments, with the center segment providing a red, green, blue diffraction pattern, with the left segment providing a blue, red, green diffraction pattern, and with the right segment providing a green, blue, red diffraction pattern. This pattern is directed towards an adjacent liquid crystal color display in which its sub-pixels are arranged red, green, blue, with the green sub-pixel aligned with the center segment of the corresponding lens. The result of the trimodal lens is an overlapping of illumination for each of the sub-pixels in that the lens segment aligned with the particular colored sub-pixel provides one third of the light, with the other two thirds of the light being provided by adjacent segments of the lenses in the microlens array. The result of the overlapping illumination of the sub-pixels is that the viewing direction is symmetric about a normal to the array which makes the design of the diffuser used with liquid crystal displays quite simple and eliminates off-axis dead zones. The trimodal structure of the microlens also permits fabrication of a thin lens which minimizes the number of steps for a diffraction line and thus limits the number of etching steps required as well as making the etching process easier to control.

Trimodal microlens

A collimator is provided to collimate light from a lambertian light source in which light from a fluorescent lamp is reflected towards an exit slit and in which light which leaves the slit at 180 degrees and is collimated in one direction to &plus;/&minus;1/2 degree. The collimator is utilized in one application to maximize the diffraction efficiency of a diffractive color separator microlens array to increase the brightness of a color liquid crystal display and to increase color saturation. In order to provide collimation, the light exiting the exit slit is collimated by parabolic surfaces of an optical waveguide to provide a beam which has a collimation of &plus;/&minus;3 degrees in one direction. This light in one embodiment is spread out by a reflective array and is further collimated by a cylindrical lens array so that it exits a panel with the required &plus;/&minus;1/2 degree collimation.

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Sammamish, WA, United States of America

Wesley H Halstead