Optical: systems and elements – Polarization without modulation – By relatively adjustable superimposed or in series polarizers
Reexamination Certificate
1999-04-05
2003-09-23
Chang, Audrey (Department: 2872)
Optical: systems and elements
Polarization without modulation
By relatively adjustable superimposed or in series polarizers
C359S443000, C359S452000, C359S453000, C359S492010, C359S599000, C349S057000, C349S062000, C349S065000
Reexamination Certificate
active
06624937
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarization splitting sheet that passes light of one polarization and reflects light of another polarization, an optical sheet laminate of the aforementioned polarization splitting sheet and a prism sheet, a transmission-type liquid-crystal display apparatus, a planar light source apparatus that is used in illuminating a light transmission-type display element such as used in an advertising panel and which makes use of the aforementioned polarization splitting sheet or optical sheet laminate, and a transmission type display apparatus, such as a liquid-crystal display, which uses this planar light source apparatus.
2. Description of the Related Art
A liquid-crystal display apparatus that is used as a display in, for example, computers and television receivers modulates passes light through a polarizer and uses a liquid-crystal layer to modulate the polarized light obtained in doing so. For example, a typical liquid-crystal display
1
in the prior art is shown in
FIG. 12
, this being configured so that light that is emitted from a light source
3
of a backlighting apparatus
2
is incident to one end-surface
4
A of an approximately planar light guide
4
, this light exiting from the light exiting surface
4
B, which is the upper surface as shown in this drawing, this light then being diffused by a diffusion sheet
5
, after which it is collected by a prism sheet
6
, so that it illuminates a liquid-crystal display panel
7
from the rear surface thereof.
In the above-noted backlighting apparatus
2
, the light of the light source that is incident at the above-noted one end-surface of
4
A is subjected to repeated total reflections within the light guide
4
, and part of this light is reflected by the light exiting surface
4
B and the light-diffusing element
4
D that is disposed at the rear surface
4
C, this light passing from the light exiting surface
4
B through the diffusion sheet
5
and being shone in the direction of the liquid-crystal display panel
7
. Light that is output from the above-noted rear surface
4
C of the light guide
4
, this being light directed downward in the drawing, is reflected by a reflecting sheet
8
that is disposed therebelow, so that this light is returned once again to the light guide
4
.
The above-noted prism sheet is provided with a plurality of unit prisms
6
A, these being triangular prisms (having a cross-sectional shape of a triangle or a triangle with a rounded top vertex) or unit lenses having a cross-section shape that is semicircular or semi-elliptical (not shown in the drawing), arranged so that the ridge lines thereof are mutually parallel.
The above-noted liquid-crystal display panel
7
is formed by a liquid-crystal cell
7
A and polarizers
7
B and
7
C, the liquid-crystal cell
7
A being configured as a liquid-crystal layer (such as a TN liquid crystal, STN liquid crystal, or a liquid crystal for an IPS or VA), this layer being held between two glass substrates or plastic substrates (neither shown in the drawing), and the above-noted polarizers
7
B and
7
C hold these substrates between them from the outsides (top and bottom in FIG.
12
).
The above-noted liquid-crystal display panel
7
, by means of an electric field that is applied to the liquid-crystal layer in the liquid-crystal cell
7
A, modulates the condition of the light that passes therethrough, so that, by controlling the relationship of the light-transmitting axes of the polarizers
7
B and
7
C and the polarized light that passes through the liquid-crystal layer, the amount of light that passes through the liquid-crystal cell
7
A is changed, so that information is displayed.
Another prior art liquid-crystal display apparatus
1
A, which is shown in
FIG. 13
, is different from the liquid-crystal display apparatus
1
that is shown in
FIG. 12
in that the direction of the prism sheet
6
in the backlighting apparatus
2
A is reversed, so that, in contrast to the unit prisms
6
A of
FIG. 12
which face upward, the unit prisms face downward, and in that a light-scattering light guide
9
is used instead of the light guide
4
.
The above-noted light-scattering light guide
9
is made, for example, of a light-transmitting resin which has a substance having a different refractive index at a minute interval therein, so that this itself acts so as to scatter light, thereby making the light-diffusing element
4
D that is used in the liquid-crystal display apparatus
1
unnecessary.
Because other elements of the configuration of the above-noted liquid-crystal display apparatus
1
A are the same as in the liquid-crystal display apparatus
1
, they are assigned the same reference numerals and will not be explicitly described herein.
FIG. 14
shows yet another liquid-crystal display apparatus
1
B, in which the backlighting apparatus
2
B differs from the backlighting apparatus
2
A in that it uses a light guide
9
A that has an uneven surface height instead of the light-scattering light guide
9
. The light guide
9
A with the uneven surface height has the effect of providing minute height variations in the light exiting surface
4
B of the transparent light guide
4
, so that the light exiting surface
4
C itself has the action of diffusing light, thereby changing the direction of travel of light within the light guide
4
, and making the light-diffusing element
4
D as described above unnecessary. It is also possible to provide the minute height variations in the surface that is on the opposite side of the light exiting surface
4
B.
Because other elements of the configuration of the above-noted liquid-crystal display apparatus are the same as in the liquid-crystal display apparatus
1
A of
FIG. 13
, they are assigned the same reference numerals and will not be explicitly described herein.
In all of the liquid-crystal display apparatuses
1
,
1
A, and
1
B, the liquid-crystal cell
7
A is held between the polarizers
7
B and
7
C and, because the polarizers
7
B and
7
C absorb approximately 50% of the incident light, the efficiency of light usage (transmissivity) is low, thereby making it necessary to shine more light from a light source onto the polarizer
7
B, in order to achieve sufficient brightness at the surface of the liquid-crystal display panel
7
.
If this is done, however, not only is there an increase in the power consumption of the light source
3
of the backlighting apparatus, but also heat from the light source
3
has an adverse affect on the liquid-crystal layer in the liquid-crystal cell
7
A, this leading to such problems as an unclear display on the liquid-crystal display panel
7
.
In contrast to the above situation, as disclosed in the Japanese Unexamined Patent Application publications H7-49496 and H8-146416, and in PCT (WO) H9-506985, and as shown in
FIG. 15
, there is an arrangement in which unpolarized light from a backlighting apparatus
2
(
2
A,
2
B) is splitted into two circularly polarized lights which exhibit rotation directions that are mutually opposite, after which these are either converted to linear polarization, or wherein a polarization splitting sheet
9
B is used to split light into two linearly polarized lights which are mutually perpendicular, one of the splitted polarized light components being caused to strike the liquid-crystal display panel
7
, and the other polarized light component being returned to the backlighting apparatus
2
(
2
A,
2
B), a reflective sheet (not shown in the drawing) or the like within the backlighting apparatus guiding the light once again to the polarization splitting sheet
9
B side for re-use, thereby improving the efficiency of light usage.
In the disclosure in Japanese Unexamined Patent Application publication H7-49496, a polarization splitting sheet that is formed as a laminate of adjacent layers that having mutually different refractive indices is provided at the light exiting surface side of a planar light guide, unpolarized light from the light exiting surface being splitted into two pola
Chang Audrey
Curtis Craig
Dai Nippon Printing Co. Ltd.
Oliff & Berridg,e PLC
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