Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-06-29
2001-09-04
Malinowski, Walter J. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06285425
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 that is capable of yielding preferential viewing cones with selectable shapes for enhanced viewing of 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 diffusive 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 an angle of reflection. Diffusive reflectors typically have a roughened surface which is predominately coated with a metallic reflective coating. Diffusive 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 an incident angle approximately equals the magnitude of a reflection angle. 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 display device has a preferential viewing cone, which defines the relationship between a viewer and a display device, where the viewer has the best vantage of the display based upon observational factors, such as glare, legibility, contrast, and display brightness. The display device typically has a symmetrical viewing cone with a generally circular cross section about an axis normally extending from the display device. The display device has a physical viewing interface, such as a lens or screen.
The preferential viewing cone may not coincide with viewing proclivities of viewers in various circumstances. The viewing proclivities are influenced by human factors which may differ from device to device, incorporating optical displays. For example, cellular phone users may prefer displays which may be brightly viewed by both the driver and the passenger of an automobile. Yet, most commercially available cellular phones do not offer a preferential viewing cone of sufficient horizontal breadth for simultaneously bright viewing by both the driver and the passenger. In another example, seated users of personal digital assistants (PDA's) may prefer displays which may be brightly viewed regardless of the height of the user relative to display, which will further vary with attendant circumstances such as chair heights, table heights, ambient light directivity, and the like. Many commercially available personal digital assistants do not offer sufficient vertical breadth to accommodate seated users of various heights with equally bright displays. As a result, seated users may find PDA's awkward and uncomfortable to use.
Thus, a need exists for a display device which has a viewing cone with a selectable shape corresponding to the viewing proclivities of users, as impacted by human factors and the intended use of an electronic device incorporating the display device. In addition, a need exists for a reflector which reduces perceived glare in display devices.
SUMMARY OF THE PRESENT INVENTION
The present invention relates to a ridged reflector permitting operation of an optical display device in ambient light. A ridged reflector for use in an optical display includes a polymeric 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 intersecting the first face. A reflective layer predominately or entirely overlies at least the first face of the ridged surface. The ridged reflector has an opposite surface opposite the ridged surface. The first face is preferably oriented at a first angle relative to a plane lying parallel to the opposite surface. The first angle is selected to reflect and biasedly focus light obliquely intercepting the first face into a radiation pattern about a normal axis extending orthogonally from the opposite surface.
The ridged reflector may be incorporated into an optical display device. For example, the optical display device may include 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 within an exiting angle range distinct in magnitude from the incident angle range and within a preferential viewing cone. The incident angle range and the exiting angle range may be described with reference to their peak intensities, which may be defined by a peak incident angle and a peak exiting angle. Accordingly, the peak incident angle and the peak exiting angle have different magnitudes so that the peak exiting angle differs from a glare angle associated with 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. Thus, the ridged reflector may reduce the perceived glare of a viewer.
The ridged reflector feature
Akins Robert Benjamin
Jelley Kevin William
Valliath George Thomas
Fekete Douglas D.
Malinowski Walter J.
Motorola Inc.
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