Liquid crystal cells – elements and systems – Liquid crystal optical element – Liquid crystal diffraction element
Reexamination Certificate
2003-07-08
2004-12-28
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal optical element
Liquid crystal diffraction element
C349S063000, C349S086000, C349S113000
Reexamination Certificate
active
06836314
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Filed of the Invention
The present invention relates to an optical device for electrically controlling retrieval of light in a light guide and a display apparatus using the optical device. The present invention further relates to a thin-structured, lightweight and large-screen display apparatus which is capable of preventing degradation of image and providing high-contrast display.
2. Description of the Prior Art
Recently, in research and development of a flat panel display to be display means of image information, demand is increasing for a large-area display apparatus which is ready for set-up and transportation. As prior art display apparatus, for example, a plasma display, a liquid-crystal display, and the like are known.
The plasma display is a display utilizing a light emission phenomenon in association with gas discharge, which is at present limited to about 50 inches in screen size. Further, since problems such as in weight, cost, productivity and the like occur with increasing screen size, there are still problems to be solved in general application as a large-screen display apparatus.
As to the liquid-crystal display, since its tin film transistor(TFT) drive board as a main component makes use of an advanced and fine semiconductor process, it is difficult to be large-sized. Further, the liquid-crystal display is driven from an end of the panel, there occurs a substantive problem of delaying signal propagation time in association with increasing screen size, that is, in construction of a large-area screen.
Further, there is known a projector using a liquid-crystal light bulb. An example thereof is shown in
FIGS. 1A and 1B
.
FIG. 1A
is a schematic sectional diagram showing a projector as a display apparatus using a liquid-crystal light bulb as an example of a prior art display apparatus, and
FIG. 1B
is a schematic sectional diagram showing the construction of the liquid-light bulb applied to the display apparatus.
The projector is constructed by arranging the light bulbs in an array to from a liquid crystal panel
10
, illuminating the liquid-crystal panel
10
driven by a matrix electrode from the backside by an illumination
11
, and focusing on a screen
13
by a lens
12
.
Incident light from a light source(i.e., illumination
11
) to the liquid-crystal panel
10
is linearly polarized by a polarizing plate
14
, and applied to a twisted nematic(TN) liquid crystal cell
15
.
When no electric field is applied to the liquid-crystal cell
15
, the polarization direction is rotated by 90 degrees, but when applied with an electric field, the polarization direction is unchanged, and the light transmits, as is. Therefore, by selecting a polarization in a specific direction by a polarizing plate
16
, light transmission or blocking can be electrically selected, thus providing a light bulb.
However, the projector of such a construction requires a depth for illuminating from the backside, which inevitably results in a large-sized apparatus.
As an alternative to the above-described plasma display, liquid-crystal display, and projector, the present invention proposes a display apparatus capable of providing a large screen, which uses a light guide and a liquid crystal. In this display apparatus, using a lightweight and inexpensive material as the light guide, and light propagating in the light guide can be retrieved to achieve a large-area screen which is lightweight, inexpensive, and thin-structured.
Here, as an example of prior art display apparatus using a light guide and a liquid crystal, a display apparatus disclosed in Japanese Patent Application Laying-open No. 6-308543(1994) will be described with reference to FIG.
2
. This display apparatus comprises a light guide
21
having on the side surface thereof a light source
22
and a reflecting plate
23
for the light source, an electrode
25
a
provided on the lower surface of the light guide
21
through an electrode support substrate
26
a
, a ferroelectric liquid-crystal layer
24
provided on the lower surface of the electrode, an electrode
25
b
provided on the lower surface of the liquid-crystal layer
24
, and a reflecting plate
27
provided under the electrode
25
b
through an electrode support substrate
26
b
. In this case, furthermore, a light-diffusing plate
28
is provided on the light guide
21
.
With this construction, by light scattering of a disclination line appearing when applied with an AC electrical field in the vicinity of relaxation frequency of Goldstone mode of the liquid crystal, output light from the upper surface of the light guide can be adjusted to display an image. However, in the above invention, differing from a TN crystal or the like, application of an electric field by AC drive is essential. For this reason, there has been a disadvantage that passive matrix drive and active matrix drive such as TFT drive are difficult and bit-map display cannot be performed. Further, since directivity of scattering cannot be controlled, light intensity in the display direction (in general, normal direction to the display surface) is not enhanced. Still further, the invention does not describe ease of fabrication in large-screen construction nor signal delay.
Yet further, as examples of other prior art display apparatus, there are known display apparatuses disclosed in Japanese Patent Application Laying-open No. 6-347790(1994), U.S. Pat. No. 4,626,074, Japanese Patent Application Laying-open No. 6-258640(1994)(U.S. Pat. No. 5,452,385) and the like.
Specifically, in the display apparatus disclosed in Japanese Patent Application Laying-open No. 6-347790(1994), light is guided in a display part and scattering and transmission state of the display part is controlled to make display, in which the display part uses a phase transition-type liquid crystal (not described in detail) or a conventional polymer dispersed liquid crystal. Here, the conventional polymer dispersed liquid crystal becomes a scattering state when no electric field is applied, and a transmission state when an electric field is applied. Since the conventional polymer dispersed liquid crystal has no directivity in its scattering state, light intensity in the display direction cannot be enhanced. Further, in its transmission state, it has a high transmissivity when viewed from the front direction, however, scattering is high when viewed from a small angle with respect to the display surface. Similarly, contrast is low when viewed from the side surface, as a result, scattering state and transmission state may reverse. Still further, when matrix drive is performed, since the spacing between electrodes always shows scattering, display of black is difficult, resulting in a very low contrast display screen. In the specification of the above invention, any of ease of fabrication of large-area construction and signal delay is not described.
The specification of U.S. Pat. No. 4,626,074 discloses a display screen using light scattering by liquid-crystal layer. However, in this case, since diffraction is not used, the output direction cannot be controlled. Still further, in the display apparatus according to the invention, a gap is required on the backside surface, and problems of divisional drive in the large-area construction, ease of fabrication, signal delay and the like are still unsolved, which makes it difficult to achieve a large-area construction.
Since any of the above-described technologies on prior art display apparatus controls display by scattering and transmission, the display screen is illuminated by an illumination at the side of a person looking the display apparatus. As a result, scattered light overlaps with the display image, the display image is affected not only by the color of the light source but also by ambient illumination light, which degrades the display image and makes color display difficult.
Yet further, Japanese Patent Application Laying-open No. 6-258640(1994) (corresponding to U.S. Pat. No. 5,452,385) discloses a display apparatus in which light propagating in the light guide is
Date Munekazu
Kato Kinya
Suyama Shiro
Uehira Kazutake
Alston & Bird LLP
Nippon Telegraph and Telephone Corporation
Schechter Andrew
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