Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-07-06
2001-09-04
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S067000, C349S113000
Reexamination Certificate
active
06285426
ABSTRACT:
BACKGROUND ART
The present invention relates generally to a ridged reflector for use in optical displays and an optical display device incorporating the reflector. More particularly, the present invention relates to a ridged reflector having optically transmissive properties for use in back-lighted and reflective liquid crystal displays.
Reflectors are often used in optical displays, such as liquid crystal displays, to permit viewing of the displays in ambient light alone. Prior art reflectors include planar specular reflectors and planar diffuse reflectors. Specular reflectors include a substantially planar surface that is covered with a reflective metallic coating. Specular reflectors are characterized by an angle of incidence being substantially equal to the angle of reflection. Diffuse reflectors typically have a roughened surface which is predominately coated with a metallic reflective coating. Diffuse reflectors are characterized by reflecting and scattering incident light. However, neither prior art specular reflectors, nor diffuse reflectors adequately compensate for the effects of glare in optical displays.
Glare represents an unwanted reflection of incident light off any refractive interface associated with a display device. In practice, the refractive interfaces are generally planar with smooth surfaces that are substantially parallel to one another so that the glare from multiple refractive interfaces may be additive. In general, as the difference between refractive indexes increases at the refractive interface, the amount of reflection also increases from the impedance mismatch at the refractive interface. Glare is characterized in that angle of incidence approximately equals the magnitude of the angle of reflection. Glare typically occurs at both glancing incident angles and nonglancing incident angles relative to any refractive interface above the liquid crystal material of the display device. Perceived glare is glare which is coincident with or lies within a preferential viewing cone of an optical display. Perceived glare may be perceived by a viewer and may detract from the usable brightness and the legibility of the display. Actual glare may exist regardless of whether or not, it is actually perceived by a viewer.
Glare may be categorized as primary glare and secondary glare. Primary glare occurs as ambient light is reflected from an exterior face of an optical display. Primary glare is typically more prevalent and bothersome to a viewer than secondary glare. Secondary glare occurs as ambient light is reflected from other refractive interfaces within the display without first reaching the reflector. For example, in a twisted nematic display secondary glare occurs when light entering the display is reflected from indium-tin oxide electrodes.
Commercially available glare-reducing films have been used in optical displays to match different impedances at the refractive interfaces so as to reduce glare reflections. The glare-reducing film generally has a thicknesses which is an integer multiple of a quarter wavelength within the visible light frequency range. However, glare reducing films tend to increase manufacturing costs in a manner which discourages their wide-spread commercial use.
Specular and diffusive reflectors may be further characterized as single-mode or dual-mode reflectors. Single-mode reflectors merely reflect light. Dual-mode reflectors have both a reflective mode and a transmissive mode. Dual-mode reflectors are sometimes referred to as transflectors. The reflective operational mode is desired when using the device in ambient light. The transmissive mode is desired when using the device in the dark or when inadequate ambient light is present. A severe limitation of dual-mode reflectors is that the percentage of transmissiveness of the transmissive mode usually may only be increased at the expense of decreasing the percentage of reflectivity of the reflective mode, and vice versa. For example, typical commercially available dual-mode reflectors may offer 70 percent reflectivity and 30 percent transmissiveness, or 60 percent reflectivity and 40 percent transmissiveness.
Thus, a need exists for a reflector which reduces perceived glare in display devices. In addition, a need exists for a dual-mode reflector which reduces perceived glare, while permitting efficient use and improved legibility of displays with back-lighting, ambient light, or both.
SUMMARY OF THE INVENTION
The invention relates to a ridged reflector permitting operation of an optical device in ambient light. The ridged reflector for use in an optical display includes an optically transmissive layer having a ridged surface. The ridged surface includes a series of ridges. Each of the ridges has a first face and a second face preferably intersecting the first face. A reflective layer overlies the first face of each of the ridges, while the second face is light-transmissive and substantially free of the reflective layer. The ridged surface has an opposite surface opposite the ridged surface. The second face of each of said ridges allows optical communication with the opposite surface.
The ridged film may be incorporated into an optical display device. For example, the optical display device includes an optical cell having a cell front with at least one cell region being capable of an optically transmissive mode and an optically nontransmissive mode with reference to the cell front. The optical cell contains an optically active material responsive to an applied electrical field or thermal input such that optical properties of the material are controllably changeable. The ridged reflector is optically coupled to the optical cell. The ridged reflector and the cell optically cooperate such that light entering the display within a nonglancing incident angle range is emitted from the display at an exiting angle range distinct in angular magnitude from the incident angle range and within a preferential viewing cone. The ridged reflector is capable of asymmetrically reflecting incident light such that the preferential viewing cone is angularly offset from glare. The incident angle range and the exiting angle range are measured relative to a normal axis orthogonally extending from a viewing plane substantially parallel to the cell front.
The ridged reflector is adapted to enhance a viewer's perception of the preferential viewing cone by directing (i.e. beam-steering) exiting light into the preferential viewing cone, which is angularly displaced from a glare angle range for enhanced brightness and legibility of the display device. In general, corresponding incident angles differ in angular magnitude from their associated exiting angles such that the exiting angles are angularly displaced from glare by an asynmnetrical reflection of the ridged reflector. An incident angle is associated with a corresponding glare angle of equal magnitude, but of a different direction with reference to the normal axis in accordance with a basic optical law of reflection.
A resultant difference in magnitude between a peak incident angle within the incident angle range and a peak exiting angle within the exiting angle range may result in the reduction of perceived glare; and, hence improved brightness of the display. The peak incident angle represents an incident angle within the incident angle range which has a peak intensity or highest amplitude within the incident angle range. The peak exiting angle represents an exiting angle within the exiting angle range which has a peak intensity or the highest amplitude within the exiting angle range.
The ridged reflector is capable of producing a symmetrical preferential viewing cone or skewed preferential viewing cones. The symmetrical preferential viewing cone is characterized by a generally circular cross section about a normal axis to the viewing plane. In contrast, the skewed viewing cones typically are characterized by generally oval (i.e. elliptical) cross sections about a normal axis to the viewing plane. The skewed preferential viewing cones have selectable shape
Akins Robert Benjamin
Jelley Kevin William
Valliath George Thomas
Fekete Douglas D.
Motorola Inc.
Parker Kenneth
Qi Mike
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