Optical: systems and elements – Lens – With reflecting element
Reexamination Certificate
2002-02-20
2004-11-16
Dunn, Drew A. (Department: 2872)
Optical: systems and elements
Lens
With reflecting element
C359S730000, C359S529000
Reexamination Certificate
active
06819507
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical element having a reflective function and to a reflective display device including such an optical element.
2. Description of the Related Art
In recent years, a micro lens having an extremely small lens diameter and an array of such micro lenses have been developed and more and more extensively applied to the fields of optical communications and display devices. Along with those micro lenses and micro lens arrays, various other micro optical elements, including micro mirrors and micro prisms, have also been developed day after day. And it is expected that the optical technology and display technology will be further developed and advanced by realizing those micro optical elements.
A reflective liquid crystal display device, including a retroreflector as such a micro optical element, is disclosed in Japanese Laid-Open Publication Nos. 11-7008 and 2000-19490, for example. Using a retroreflector, an incoming light ray may be retro-reflected, or reflected along a path parallel to that of the incoming light ray. Accordingly, in the reflective liquid crystal display device, reflected part of light that has been emitted from a light source located near the user selectively reaches the user's eyes but reflected part of other external light sources (e.g., illuminator or sun) does not reach his or her eyes. In this manner, unwanted back reflection (i.e., glare) is minimizable and the visibility is improvable. Also, since the reflective liquid crystal display device reduces the unwanted back reflection by using such a retroreflector, there is no need to reduce the intensity of the reflected light by intentionally decreasing the reflectance of the reflector, for example. As a result, display of a bright, high-contrast image is realized.
A retroreflector for use in the reflective liquid crystal display device, for example, may be formed as a micro optical element such as a corner cube array. A corner cube typically has three perpendicularly opposed reflective planes. The corner cube is an optical element for reflecting an incoming light ray back to its source by getting the light ray reflected by each one of those reflective planes after another The corner cube can always reflect the incoming light back to its source irrespective of its angle of incidence Hereinafter, a conventional reflective liquid crystal display device
80
, including a retroreflector that has been formed as a corner cube array, will be described with reference to FIG.
1
.
The reflective liquid crystal display device
80
includes: a substrate
82
on which a corner cube array
83
has been formed; a transparent substrate
81
located closer to an observer; and a polymer-dispersed liquid crystal layer
84
interposed between these substrates
81
and
82
. A metallic reflective film
85
has been formed on the corner cube array
83
. When color black should be displayed, incoming light, which has been transmitted through the transparent substrate
81
and the polymer-dispersed liquid crystal layer
84
controlled to a light transmitting state, can be reflected back toward its origin. The concave portions of the corner cube array
83
are filled with a transparent flattening member
86
, on which a transparent electrode
87
has been formed. A color filter layer
88
and another transparent electrode
89
are provided on the surface of the transparent substrate
81
that is opposed to the liquid crystal layer
84
. By regulating the voltage applied between the transparent electrodes
87
and
89
, the reflective liquid crystal display device
80
controls the light transmittance (or scattering state) of the polymer-dispersed liquid crystal layer
84
, thereby displaying an image thereon.
The size L1 of each corner cube included in the display device
80
is preferably equal to or smaller than the size L2 of each pixel. Accordingly, if the pixel size L2 of a display device is about 100 &mgr;m, the corner cube size L1 is preferably several tens &mgr;m or less. For example, Japanese Laid-Open Publication No. 11-7008 describes that when an array of quadrangular pyramidal concave portions is formed, the upper square of each quadrangular pyramidal concave portion should have a minimum size of about 5 &mgr;m each side.
In the conventional reflective liquid crystal display devices, the retroreflector thereof often has triangular pyramidal, quadrangular pyramidal or spherical concave portions. However, there are only a limited number of optical element shapes that can be formed precisely enough at that small size of several tens &mgr;m or less. An optical element including only concave or convex portions is relatively easy to shape. As for a display device that is currently having its pixel size reduced as much as possible to realize a high resolution, a micro corner cube should be formed at a very small size and with sufficiently high shape precision. Nevertheless, it is difficult to form such a micro corner cube in a complex shape.
On the other hand, it is known that a retroreflector of a relatively large size for use in a road sign, for example, includes corner cubes of a more complex shape. Hereinafter, a corner cube of such a complex shape will be described with reference to
FIGS. 2A through 2C
.
As shown in
FIGS. 2A through 2C
, the corner cube
90
has a structure including three substantially square reflective planes S
1
, S
2
and S
3
that are opposed almost perpendicularly to each other. As shown in
FIG. 2C
, an incoming light ray, which has been incident onto the corner cube
90
, is reflected by one of these three planes S
2
, S
3
and S
1
after another, for example, so as to be reflected back to the direction from which it comes. In the corner cube
90
, the substantially square reflective planes S
1
, S
2
and S
3
correspond to three of the six planes of a cube, which share one vertex of the cube. As shown in
FIG. 2A
, the corner cube
90
is made up of convex portions
92
, each having a highest point indicated by an open circle ∘ (which is higher in level than intermediate points indicated by crosses X), and concave portions
94
, each having a lowest point indicated by a solid circle &Circlesolid; (which is lower in level than the intermediate points indicated by the crosses X).
Such a corner cube
90
(which will be herein referred to as a “cubic corner cube”) has a shape including both the convex portions
92
and concave portions
94
. Accordingly, compared to an optical element including only concave or convex portions (e.g., triangular pyramidal portions) as disclosed in Japanese Laid-Open Publication No. 11-7008, for example, it is more difficult to make this cubic corner cube
90
. Hereinafter, a conventional method of making the cubic corner cube array shown in
FIGS. 2A through 2C
will be described.
Pin Bundling Method
In a pin bundling method, the end of a hexagonal columnar metal pin is provided with a prism having three square facets that are opposed perpendicularly to each other, and a number of such pins are bundled together to make a collection of prisms. In this manner, a cubic corner cube is made up of three facets of three prisms that are formed at the respective ends of three adjacent pins.
According to this method, however, a corner cube array should be made by collecting a plurality of prisms that have been separately formed for mutually different pins. Thus, it is actually difficult to make a corner cube of a small size. The minimum possible size of a corner cube (as indicated by L3 in
FIG. 2B
) that can be formed by this method is 1 mm. That is to say, a cubic corner cube having a size of several tens &mgr;m is hard to make by this method.
Plate Method
In a plate method, a number of flat plates, each having two mutually parallel planes, are stacked one upon the other. At the side end face of these flat plates stacked, V-grooves are cut vertically to the parallel planes at an equal pitch, thereby forming a series of roof-shaped protrusions each having an apical angle of ap
Minoura Kiyoshi
Tomikawa Masahiko
Ueki Shun
Dunn Drew A.
Nixon & Vanderhye P.C.
Pritchett Joshua L
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