Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-07-21
2003-09-09
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06618106
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to liquid crystal displays and more particularly to a high brightness and high color saturation color liquid crystal display which is sunlight viewable.
BACKGROUND OF THE INVENTION
Liquid crystal displays have long been utilized for the display of information which is computer generated and which is to be viewable in direct sunlight, if possible. Such displays originated with the marine fishing industry in which so called super twist pixels were utilized to make a black and white display viewable in direct sunlight. This technology was extended for use in cockpit displays and indeed in other black and white displays in which the display was to have been used outdoors.
The problem with super twist crystals and the back and white displays was the amount of information that could be conveniently presented to the viewer. Many attempts have been made to adopt the super twist liquid crystal display technology for color liquid crystal displays in order to make them sunlight viewable.
The most recent attempts at such displays have been in the field of lap top commuters in which the lap top is provided with a liquid crystal display panel viewable from plus or minus 60 degrees for ease of usage. However, these displays wash out in bright sunlight primarily due to the reflection of the sunlight towards the viewer and lack of an ability to compensate for the reflection.
In the past, attempts to compensate for the reflection have centered around the utilization of so called anti-reflective coatings. However, the anti-reflective coating alone is insufficient to overcome the problem of daylight viewing given a limited power source. It will be appreciated that current liquid display stacks have an optical efficiency of only 5% when viewed from the point of view of the power in to the illuminator lamp verses illuminated power out. What this means is that while it may be possible to provide suitable daylight viewing liquid crystal displays, it is only at the cost of power consumption which in a portable application is not acceptable.
While in some applications power consumption is not the problem that it is portable applications, it is nonetheless important to be able to achieve the brightest, most highly visible color display possible to be able to counter the effects of direct sunlight and its reflection.
As illustrated in U.S. Pat. No. 5,600,486 issued to George Gal and Bruce Herman on Feb. 4, 1997 and assigned to the assignee thereof, color separation microlenses are described in which a single micro optical element is made up of a color separation grating integrated with a refractive lens. The color separation micro lens separates the spectrum into distinct color spots and focuses these spots into a common plain. These spots fall at the locations of different diffraction orders of the grating, with the color separation accomplished by the grating and the focusing being done by the lens. As mentioned in this patent, the color separation microlens can be fabricated as a monolithically integrated element or as a dual sided thin wafer.
While the color separation microlens described in U.S. Pat. No. 5,600,486 serves adequately for some applications, it has been found that the degree of color separation achievable with the stepped structure illustrated in this patent is insufficient to provide the necessary fineness of color separation required, for instance, for a 256×256 liquid crystal display. It will be appreciated that there are only a limited number of steps in the micro lens shown in the above identified patent with the steps being insufficient to provide sufficient color separation because the diffraction efficiency is determined by a number of factors including the number of steps. It can be demonstrated that the larger the number of steps the more fine will be the color separation and the more saturated will be each of the colors at the focal plane of the lens. Note that the fewer the number of steps in the microlens, the more the light spreads out which degrades the overall performance of the microlens.
It will also be appreciated that in this patent the color separation is in terms of spots or circles. With the step structure shown and the focusing properties of the lens it will be appreciated that what this patent describes is a means for providing focused spots of color as opposed to bands. However, as is common in color liquid displays the pixels are made up of three side by side rectangles which are separated by a mask. Thus the stepped structure and focusing described in this patent do not provide a pattern of colored bands which match to a rectilinear subpixel on the display.
Moreover, nowhere in the above mentioned patent is addressed the question of overall brightness of a display. It was sufficient for the Gal et al patent to be able to achieve color separation utilizing a microlens display. However, how a sunlight readable device is achievable using the Gal et al system it is not discussed within the patent.
However, as illustrated in U.S. Pat. No. 5,781,257 some of these issues are addressed, albeit with the same type of micro lens structure. In this patent it is pointed out that because of the color separation microlenses no color filters are required in the display which eliminates the light losses due to transmitting light through a color filter. It is however noted that the amount of brilliance of the display is directly proportional to the degree of color separation achievable and color saturation achievable by the microlens. The Gal et al device as described does not achieve maximal brightness or color saturation. More particularly, in a CIE color diagram while CRT displays in general conform to the best possible color saturation to generate the colors, and whereas color liquid crystal displays provide sufficient color saturation to permit portrayal of colored on-screen objects, the Gal et al patents and the microlens used therein do not permit depiction of a large number of colors, and more importantly, those colors normally utilized to portray colored on-screen objects.
By way of further background, it will be appreciated that in addition to the above mentioned patents which describe microlens structures, there are several methods in the prior art for fabricating microlenses. As can be seen in U.S. Pat. Nos. 5,310,623 and 5,482,800, photolithographic methods are described which permit the fabrication of microlenses utilizing a photoresist process, with a photoresist material replica used to reproduce the replica directly in a substrate material. Finally, a dispersive microlens is shown in U.S. Pat. No. 5,497,269 in which the dispersive microlens apparatus is used for detecting multiple different wavelengths or for combining a plurality of different emitted wavelengths into a bandwave of wavelengths.
SUMMARY OF THE INVENTION
A high brightness, high color saturation liquid crystal display permits direct sunlight viewing. The display includes a collimated light source, an array of diffractive color separation microlenses, in one embodiment, trimodal, generated from a genetic algorithm, 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, a polarizer, an addressable color liquid crystal panel, a crossed polarizer and a gradient index diffuser with an anti-reflective coating. The diffractive color separation is 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
Gunn Thomas V.
Schmidt Michael P.
BAE Systems Information and Electronics Systems Integration, Inc
Maine & Asmus
Schechter Andrew
Ton Toan
LandOfFree
Sunlight viewable color liquid crystal display using... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sunlight viewable color liquid crystal display using..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sunlight viewable color liquid crystal display using... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3092232