Illumination – Light fiber – rod – or pipe – Illuminating or display apparatus
Reexamination Certificate
2001-12-28
2003-12-02
O'Shea, Sandra (Department: 2875)
Illumination
Light fiber, rod, or pipe
Illuminating or display apparatus
C362S035000, C362S555000
Reexamination Certificate
active
06655825
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to backlighting of a liquid crystal display (LCD), and more particularly to generating white light for LCD backlighting by mixing red green and blue (RGB) light produced by light emitting diodes (LED) to form white light, and coupling the white light to the LCD display.
BACKGROUND OF THE INVENTION
In many modern electronic devices, such as flat-screen televisions and computer monitors, the images viewed by the user are produced on a liquid crystal display (LCD). An LCD generally requires some form of backlighting for the images to be visible in normal or reduced ambient light environments. The backlighting is provided by placing a light guide structure behind the LCD panel, and illuminating one or more edges of the light guide.
In recent years, the edges of the light guide have been illuminated by red green and blue (RGB) light emitting diodes (LED)s, arranged in linear arrays and distributed along the edges of the light guide or mounted in a light distributing structure attached to an edge of the light guide. The light emitted from the RGB LED arrays is then mixed in the light guide or the distributing structure, to form white light for backlighting the LCD.
Providing white light in this manner has several drawbacks. It is often necessary to make the light guide and/or the distributing structure larger or more complex than would otherwise be required to provide sufficient “mixing distance,” or to include reflective features in the light guide or distributing structure, to ensure that a white light of acceptable quality is produced. The actual color of light produced by an LED varies from one production lot of LEDs to another. The wavelength of the light produced in a given LED changes over time and as a function of operating temperature. Developing an optimal spacing and arrangement of RGB LEDs to provide acceptable white light, and dealing with the inherent variability of wavelength produced in the LEDs has required in the past that the LEDs be matched and stored according to the wavelength of light actually produced and the operating idiosyncrasies of each LED. Such constraints on matching performance significantly drive up the complexity and cost of manufacturing a backlighting system giving repetitively consistent light quality.
Another problem with prior backlighting approaches has been dealing with removal of the heat generated by the LEDs from the LCD. Incorporating effective and efficient heat sinks in close proximity to the LCD is often very difficult, without undesirably increasing the size and cost of the LCD and backlighting system. Newer generations of LEDs having higher light emitting efficiencies and operating at higher driving currents have allowed the number of LEDs in a typical array to be reduced, but the problem of heat removal still exists. Reducing the number of LEDs, and spreading them farther apart in the arrays, to facilitate incorporation of heat sinks, can make the problem of achieving proper mixing more difficult, however, than in prior backlighting approaches using a larger number of the older, less efficient LEDs spaced more closely together.
What is needed, therefore, is an improved method and apparatus for backlighting an LCD, in a manner overcoming one or more of the problems described above.
SUMMARY OF THE INVENTION
Our invention provides such an improved method and apparatus for backlighting a liquid crystal display by directing red green and blue light into the first end of a color mixing optical fiber, mixing the red green and blue light in the color mixing fiber to produce white light, and conducting the white light out of the second end of the color mixing fiber to the liquid crystal display. The color mixing optical fiber and the sources for generating the red green and blue light may be located remotely from the LCD, and the white light produced in the color mixing optical fiber coupled to the LCD by coupling optical fibers, thus simplifying and facilitating construction of the backlighting system, and allowing for more convenient removal of heat remotely from the LCD.
In one form of our invention an apparatus for backlighting a liquid crystal display includes a color mixing optical fiber for mixing red green and blue light in the color mixing fiber to produce white light, the color mixing optical fiber having a first end adapted for receiving red green and blue light and a second end adapted for delivering the white light. The apparatus also includes means for directing red green and blue light into the first end of the color mixing optical fiber, and means for conducting the white light out of the second end of the color mixing fiber to the liquid crystal display.
The means for directing the red green and blue light to the first end of the color mixing fiber may include means for generating the red green and blue light in individual light sources. The means for directing the red green and blue light to the first end of the color mixing fiber may also include means for collecting and coupling the light generated by each of the individual red green and blue light sources to the first end of the color mixing fiber as unmixed red green and blue light. The means for collecting and coupling the red green and blue light from the red green and blue light sources to the first end of the of the color mixing fiber may include in-coupling optics, and monochromatic light coupling fibers for coupling the light of the red green and blue light from the red green and blue light sources to the first end of the of the color mixing fiber as unmixed red green and blue light.
Where monochromatic light fibers are included, the monochromatic light coupling fibers each have an output end joined to the first end of the color mixing optical fiber. Where the output ends of the coupling fibers have a combined area smaller than the area of the first end of the color mixing optical fiber, the area of the first end of the color mixing optical fiber extending beyond the area of the output ends of the coupling fiber may include a mirrored surface for reflecting light back into the color mixing optical fiber.
Where multiple fibers are coupled into one fiber, a non-circular (i.e. rectangular or semi-circular) fiber cross section may provide most efficient coupling. Any internal angles in the cross section must be large enough, however, that total internal reflection occurs inside the fiber.
The apparatus may also include additional structures such as a light guide for guiding the white light through the liquid crystal display, a reflector for reflecting the white light out of the liquid crystal display, and a light distributor rod for distributing the white light into the liquid crystal display.
In some forms of our invention, the second end of the color mixing optical fiber is attached directly to the light distributor rod. In other forms of our invention, a light coupling fiber may be operably attached between the second face of the color mixing optical fiber and the light distributor rod for coupling the white light from the color mixing optical fiber to the light distributor rod. Where the coupling fiber has an input end joined to the second end of the color mixing optical fiber, with the second end of the color mixing optical fiber having an area smaller than the area of the input end of the coupling fiber, the area of the input end of the coupling fiber extending beyond the area of the second end of the color mixing optical fiber may include a mirrored surface for reflecting light back into the coupling fiber.
At each junction/coupling between optical elements, care must be taken to match the etendue of the two elements. (The etendue of the element that the light is going into should be equal to or greater than the etendue of the element that the light is coming from). As a general rule, this can be accomplished by making the total incoupling area in the piece(s) that the light is going into equal to or larger than the total outcoupling area that the light came from, and making any area of the incoupling ar
Frank J. P. Schuurmans
Gaines James M.
Muthu Subramanian
Koninklijke Philips Electronics , N.V.
O'Shea Sandra
Ward John Anthony
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