Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-06-14
2001-02-27
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S005000, C349S011000, C353S034000
Reexamination Certificate
active
06195143
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal device that modulates light in accordance with supplied image information, and to a projection display apparatus that uses the liquid crystal device.
2. Description of the Related Art
Liquid crystal apparatuses (liquid crystal panels) that modulate light in accordance with supplied image information are widely utilized as direct view display apparatuses and as light valves (light modulators) of projection display apparatuses.
FIG. 14
is an exploded view showing the general configuration of a conventional liquid crystal device
1000
. The liquid crystal device
1000
is equipped with a liquid crystal cell
1020
, a micro-lens array
1030
and two polarizers
1040
and
1050
. The liquid crystal cell
1020
has a transparent substrate
1021
, an opposed (transparent) substrate
1025
and a liquid crystal layer
1027
set between the transparent substrate
1021
and the opposed substrate
1025
. A thin-film transistor
1022
and pixel electrode
1023
are provided on the transparent substrate
1021
for each pixel. A common electrode
1024
is provided on the opposed substrate
1025
. A light shield layer
1026
is provided between the opposed substrate
1025
and the common electrode
1024
. The light shield layer
1026
has a corresponding opening
1026
W for each pixel electrode
1023
.
The micro-lens array
1030
is provided on the opposite side of the opposed substrate
1025
to the liquid crystal layer
1027
. The micro-lens array
1030
is constituted of a plurality of concentrically shaped micro-lenses
1030
M. As shown by
FIG. 15
, the micro-lenses
1030
M are arranged so that the optical axis of each of the micro-lenses
1030
M is substantially in alignment with the center axis of the corresponding opening
1026
W.
The first polarizer
1040
is provided on the opposite side of the micro-lens array
1030
to the opposed substrate
1025
, and the second polarizer
1050
is provided on the opposite side of the liquid crystal cell
1020
to the liquid crystal layer
1027
.
In this liquid crystal device
1000
, light enters the liquid crystal layer
1027
via the opposed substrate
1025
and exits via the transparent substrate
1021
(the exit surface being the display surface).
The passage of incident light through the liquid crystal device
1000
is illustrated by FIG.
15
. The incident light is split into a plurality of beams and is converged by its passage through each of the micro-lenses
1030
M of the micro-lens array
1030
, and then enters the opening
1026
W of the corresponding pixel, from which it passes through the common electrode
1024
and pixel electrode
1023
and exits from the display surface. The light is caused to form an image on the display surface by using the application of a voltage (determined by the image information) between the common electrode
1024
and each pixel electrode
1023
to control (modulate) the light transmissivity of each pixel. In a projection display apparatus that uses this type of liquid crystal device, the image displayed on the liquid crystal device is projected by an optical projection system (such as a projection lens) to be displayed on a screen.
A characteristic of a liquid crystal device is that it changes the contrast of the image displayed on the display surface in the direction in which the image is viewed. Here, the direction in which the image is viewed is termed the viewing angle or viewing angle direction, and is expressed as the angle from the normal of the display surface and the plane angle. Each type of liquid crystal device also has a viewing angle direction (hereinafter referred to as “clear viewing direction”) at which contrast is at a maximum (hereinafter referred to as “optimum contrast”). The arrow in
FIG. 15
indicates the clear viewing direction VD of the liquid crystal device
1000
. Thus, the contrast of the viewed image is best when the light from the display surface of the liquid crystal device exits in a direction that is substantially parallel to the clear viewing direction VD, and when the light exits in a direction that is not parallel to the clear viewing direction VD the contrast is degraded by an amount that is dependent on the direction of the light and increases with the increase in the angle by which the light departs from being parallel with the clear viewing direction VD.
For illumination liquid crystal devices generally employ divergent or substantially parallel light, and light emitted by the display surface includes light with the various directional components. Although it is termed substantially parallel light, the fact is that it includes quite a high proportion of non-parallel components. Therefore, since the contrast of a liquid crystal device is determined by light thus comprised of these various directional components, the contrast of the liquid crystal device is degraded compared to the optimum contrast in the clear viewing direction.
In order for a viewer to obtain a good understanding of images displayed on a liquid crystal device, it is preferable to have good image contrast, a large brightness differential between light display (white screen display) and dark display (black screen display). That is, it is preferable for there to be a large difference between light transmissivity during light display and light transmissivity during dark display. However, the problem with conventional liquid crystal devices is that, as described, owing to the fact that the light consists of various directional components images can be viewed only at a contrast that is degraded compared to the optimum contrast.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a liquid crystal device having improved contrast of displayed images compared to that of a conventional liquid crystal device.
At least part of the above and the other related object are attained by a first liquid crystal device that modulates light in accordance with supplied image information, comprising: a plurality of pixels arranged in a matrix, each pixel having an opening to allow passage of light; and a micro-lens array that has a plurality of micro-lenses arranged in a matrix that divides illumination light into a plurality of partial light beams and converges the light to a light incidence plane of the pixels. Characteristics of micro-lenses are adjusted to increase a proportion of light exiting from the opening of each pixel substantially parallel to a clear viewing direction of the liquid crystal device compared to a proportion of light parallel to other directions.
Here, “clear viewing direction” refers to the viewing angle direction at which contrast is at a maximum (optimum contrast). Also, “adjusting micro-lens characteristics” refers to modification of the shape, refractive index or position of micro-lenses.
In accordance with the above configuration, the proportion of light emitted from the pixel openings that is comprised of light that is substantially parallel to the clear viewing direction of the liquid crystal device can be increased, improving the contrast compared to that of a conventional liquid crystal device.
In accordance with one preferable structure of the first liquid crystal device, the micro-lenses are formed as concentric lenses and are each positioned so that an optical center thereof is offset from a center axis of each pixel to increase a proportion of light exiting from the opening of each pixel substantially parallel to the clear viewing direction of the liquid crystal device compared to the proportion of light parallel to the other directions.
Here, “optical center” corresponds to the optical axis of concentric lenses, a position along which incident light proceeds without refraction.
In accordance with the above configuration, of the light exiting the micro-lenses, light that is substantially parallel to the clear viewing direction passes through the pixels and is emitted in a direction substantially parallel to the clear viewing direction. On the other hand, part of th
Chowdhury Tarifur R.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
Sikes William L.
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