Optical waveguides – Miscellaneous
Reexamination Certificate
1999-07-26
2003-11-18
Cherrry, Euncha (Department: 2872)
Optical waveguides
Miscellaneous
C385S016000
Reexamination Certificate
active
06650822
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical devices, specifically, panel display, with interactive capabilities, which utilizes optical waveguides, mechanical light-switches, and linear-array light sources.
DESCRIPTION OF THE RELATED ART
Conventional television (TV) sets and computer monitors use cathode ray tubes (CRTs) as display devices. The CRTs are undesirably large, heavy, and utilize power inefficiently. Therefore, there is a genuine need to replace CRTs with thin, light weight and energy efficient flat-panel displays (FPDs).
Commercial FPD technologies include liquid crystal displays (LCDs), thin-film electroluminescence (TFEL) displays, plasma display panels (PDPs), field emission displays (FEDs), and light-emitting-diode (LED) matrix displays.
Transmissive matrix-LCDs dominate the current FPD market. This type of displays uses a backlight for illumination. These LCD devices are very inefficient. Before reaching a viewer, a light beam must pass through polarizer layers, liquid crystal layers, color filters, and some electronic component films. In the process, about 95% of the light energy is lost. Moreover, the fabrication processes, especially for active matrix LCDs (AMLCDs), are very complex and expensive. A high resolution AMLCD requires thousands of addressing lines and millions of transistors on a large substrate, therefore manufacturing is expensive. The production of AMLCDs relies on the use of sophisticated semiconductor processes. Particularly, expensive photolithography has to be used. As a result, the diagonal of an affordable display is limited.
Other FPD also suffer limitations. TFEL displays lack efficient blue phosphors and thus have low overall energy efficiency. PDP technology has been used for commercial production, however manufacturing cost is high and high energy-efficiency displays have yet to be demonstrated. FED technology potentially is more energy efficient than liquid crystal based displays, however, this potential has not yet been demonstrated. In addition, manufacturing cost of FEDs currently exceeds that of AMLCDs.
LED matrix displays are composed of pluralities of individual LEDs arranged in a matrix. Recent commercial availability of high-efficiency InGaN-based blue and green LEDs coupled with the existence of high performance AlGaAs- and AlInGaP-based red LEDs has made it possible to form high-brightness, full color LED panel displays. This type of display is presently limited to very large displays such as those used for stadium and outdoor advertisement applications. The main limitations of matrix LED technology include high cost and impractical manufacture of regular sized displays. The high cost is due to the necessity of using a large number of LEDs to make the displays. For example, a 1024×768 full-color display requires the use of 1024×768×3=2,359,296 LEDs. Such a display is made by assembling individual LEDs that are usually larger than a couple of millimeters in diameter. It is difficult and costly to make and assemble smaller LEDs. A new approach must be sought if the high performance LEDs are to be used in low-cost flat-panel displays. The present invention provides such an approach.
A less known but viable display technology uses optical waveguides to convey light from a small light source onto a large display screen. Optical fiber projectors (Awai et al., U.S. Pat. No. 4,763,984, (1988)) and stacked planar waveguide projectors (Veligdan, U.S. Pat. No. 5,381,502 (1995) and U.S. Pat. No. 5,455,882 (1995)) are magnifying projectors that channel light images from a small but intense light-image source to a large screen. The construction of an optical fiber projector is fairly complex, due to a huge number of fibers to be assembled. A stacked planar waveguide projector requires an expensive laser scanner or digital micromirror array combined with a sophisticated focusing system as the video source and is, therefore, high cost. In addition, while these two displays can be made relatively compact, neither of them is a true flat-panel display.
Waveguide-based flat-panel displays use planar and channel waveguides (Andrews in U.S. Pat. No. 3,871,747 (1975)). Most of the display devices of this category involve parallel channel waveguides assembled on a flat substrate to form a display screen. Light switches are placed on top or inside the channel waveguides and are distributed across the display screen. Light beams are first injected into the channel waveguides from the side and are then extracted by the light switches at appropriate locations on the display screen to form an image. The main differences among various approaches are the underlying light-extraction mechanisms and the constructions of the light switches. Rockwell (U.S. Pat. No. 5,106,181 (1992) and U.S. Pat. No. 5,009,483 (1991)) described methods of using electro-optical effect, thermal-optical effect, and acoustic effect to alter the optical confinement property of waveguides so as to extract light. Staelin et al. (U.S. Pat. No. 4,822,145 (1989)), disclosed a waveguide display using liquid crystals as the cladding materials of waveguides. By applying an electrical field, one may increase the refractive index of the liquid-crystal cladding layer and, therefore, permit light to escape in a controlled fashion from the waveguides. Nishimura, (U.S. Pat. No. 4,640,592 (1987)), describes a liquid-channel waveguide display. Heat is applied to local regions of the waveguide channels and bubbles are produced in the liquid. These bubbles cause light scattering out of the waveguides. While all these methods can, in principle, extract light out of waveguides, they suffer from low extraction coefficient, high-energy consumption, sluggishness, and/or high manufacturing cost.
Recently, a micromechanical flat-panel display was proposed by Stern (“Large-area micromechanical flat-panel display,” Conf. Record 1997 Int. Display Res. Conf. (Soc. For Inf. Display, Toronto, Canada, Sept. 15-19, 1997), pp. 230-233). The display screen consists of a planar waveguide, on which a matrix of electrostatically driven micromechanical light switches are placed. Fluorescent light tubes are used as the light source of the display. The light extraction from the planar waveguide is achieved by light tunneling from the waveguide into the light switches due to a close proximity the light switches to the waveguide surface (Kim et al. “Micromechanically based integrated optic modulators and switches,” Proc. Integrated Optics and Microstructures, SPIE 1793, 183 (1992) and Piska et al. “Electrostatically actuated optical nanomechanical devices,” Proc. Integrated Optics and Microstructures, SPIE 1793, 259-272 (1992)). There are several inherent limitations in the proposed embodiment that will prevent the production of high-quality, full color, and energy efficient displays.
First, shadow and ghost images will be inevitable because along each light propagation direction several light switches could be activated at same time and shadows of upper stream pixels would be cast onto down stream pixels.
Second, optical efficiency is inherently low. In order to achieve an acceptable uniformity or to minimize shadow images light extraction at each light switch has to be very low so that the light flux throughout the waveguide is not significantly attenuated. Consequently, only a small portion of the light inside a waveguide can be utilized.
Third, full-color and gray-scale displays will be difficult. Colors are achieved by using multilayer band-pass filters coated on the waveguide. The complexity and cost of depositing such filters on closely spaced areas is high. Gray scales are achieved by using area weighting and temporal weighting methods. The area weighting control uses a plurality of light switches of varied sizes on each pixel. A gray scale is obtained by turning on a number of light switches that add up to a total area proportional to the gray scale. A large number of light switches must be used on each pixel in order to achieve decent gray scales. Temporal weighting
Cherrry Euncha
Smith G. Keneth
Xeotion Corp.
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