Optics: image projectors – Composite projected image
Reexamination Certificate
1999-01-19
2002-04-23
Metjahic, Safet (Department: 2858)
Optics: image projectors
Composite projected image
Reexamination Certificate
active
06375328
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical modulation element and a projection display device. More particularly, the present invention relates to a layout structure of optical elements on the periphery of an optical modulation element that modulates a light flux according to image information.
2. Description of Related Art
A projection display device basically consists of a light source lamp unit, an optical unit for optically processing a light flux emitted from the light source lamp unit so as to synthesize a color image corresponding to image information, a projection lens unit for enlarging and projecting the synthesized light flux onto a screen, a power supply unit, and a circuit substrate on which a control circuit and the like are mounted.
FIGS.
17
(A)-(C) schematically show the construction of the optical unit and the projection lens unit of the above-mentioned components. As shown in this drawing, an optical system of an optical unit
9
a
includes a lamp body
81
serving as a light source, a color separation optical system
924
for separating a light flux W emitted from the lamp body
81
into respective color light fluxes R, G and B of the primary colors of red (R), green (G) and blue (B), three sheets of liquid crystal modulation elements
925
R,
925
G and
925
B for modulating the separated respective color light fluxes according to image information, and a color synthesizing prism
910
in the shape of a prism with a square cross section to synthesize the modulated color light fluxes. The light flux W emitted from the lamp body
81
is separated into respective color light fluxes R, G and B by the color separation optical system
924
including various types of dichroic mirrors, and the red and green light fluxes R and G of the respective color light fluxes are emitted from outgoing sections provided in the color separation optical system
924
towards corresponding liquid crystal modulation elements
925
R and
925
G. The blue light flux B is guided to the corresponding liquid crystal modulation element
925
B via a light guide system
927
, and is emitted from an outgoing section provided in the light guide system
927
towards the corresponding liquid crystal modulation element
925
B.
As shown in FIGS.
17
(B) and
17
(C) in enlargement, in the optical unit
9
a
, polarizers
960
R,
960
G and
960
B are respectively arranged on the side of incident surfaces of the liquid crystal modulation elements
925
R,
925
G and
925
B so that they unify the planes of polarization of the respective color light fluxes to be incident on the liquid crystal modulation elements
925
R,
925
G and
925
B. In addition, polarizers
961
R,
961
G and
961
B are respectively arranged on the side of outgoing surfaces of the liquid crystal modulation elements
925
R,
925
G and
925
B so that they unify the planes of polarization of the modulated color fluxes to be incident on the color synthesizing prism
910
. The actions of these polarizers allow an enlarged image excellent in contrast to be projected onto the surface of a screen
10
. Of the two polarizers that sandwich the liquid crystal modulation elements
925
R,
925
G and
925
B, the polarizers
961
R,
961
G and
961
B positioned on the side of the outgoing surfaces of the liquid crystal modulation elements
925
R,
925
G and
925
B are bonded to the light outgoing surfaces of the liquid crystal modulation elements.
Incidentally, as the liquid crystal modulation elements
925
R,
925
G and
925
B, an active matrix-type liquid crystal device is generally used, in which pixels arranged in the form of a matrix are controlled by a switching element.
Here, in order to improve the contrast of an image enlarged and projected onto the screen
10
, it is effective to bond a polarizer, which has high selection properties with respect to polarized light, to the light outgoing surface of each of the liquid crystal modulation elements
925
R,
925
G and
925
B. However, such a polarizer having high selection properties absorbs much light and therefore, generates much heat. Inside the projection display device mentioned above, an air flow is formed as shown in FIG.
17
(C) and cools the polarizer. However, since the polarizer is directly attached to the light outgoing surface of the liquid crystal modulation element, heat is apt to be transmitted to the liquid crystal modulation element, and to thereby increase the temperature of the liquid crystal modulation element. This increase in temperature deteriorates the optical properties of a liquid crystal panel, and the image contrast.
Thus, it may be possible to arrange the polarizer apart from the light outgoing surface of the liquid crystal modulation element. However, if the polarizer is simply arranged apart from the light outgoing surface, there is a fear that the switching element in the liquid crystal modulation element may malfunction due to a light beam reflected by the light outgoing surface of the liquid crystal modulation element. In addition, there is a fear that dust or the like may be caused by an air flow formed inside the projection display device to adhere to the light outgoing surface of the liquid crystal modulation element, and it may make high-quality image projection impossible.
SUMMARY OF THE INVENTION
In view of the above-described points, an object of the present invention is to provide an optical modulation element and a projection display device that achieve high-quality image projection by preventing dust from adhering to the light outgoing surface of the optical modulation element without deteriorating the switching characteristic of the optical modulation element.
In order to achieve the above-described object, there is provided an optical modulation element for modulating a light flux emitted from a light source according to image information, wherein a transparent plate is provided on at least one surface thereof, and the space between the transparent plate and the optical modulation element is shielded from the outside by a dust-preventing member.
In such an optical modulation element, heat generated by a polarizer to be transmitted to the optical modulation element can be further reduced. In addition, since the space between the transparent plate and the optical modulation element is shielded from the outside by the dust-preventing member, dust does not enter the space. For this reason, negative effects, such as the light flux emitted from the optical modulation element being scattered by dust, can be solved.
The dust-preventing member may preferably be formed of resin containing glass fiber. In this case, it is possible to restrict linear expansion, to prevent movement of the optical modulation element, and to maintain a constant temperature and a uniform in-plane temperature distribution of the optical modulation element.
On the other hand, the dust-preventing member may be made of metal. This makes it possible to improve the heat dissipation effect. In particular, when a polarizer is bonded to the transparent plate, it is preferable that the dust-preventing member be made of metal because heat is generated with the absorption of light by the polarizer.
In the optical modulation element of the present invention, it is also possible to bond the polarizer to the transparent plate. This prevents dust from entering between the polarizer and the transparent plate. For this reason, negative effects, such as the light flux emitted from the optical modulation element being scattered by dust, can be prevented more effectively.
In addition, in the optical modulation element of the present invention, at least one surface of the transparent plate may preferably be coated with a surface-active agent, or treated for electrostatic protection. This makes it possible to prevent dust from adhering to the transparent plate.
A projection display device of the present invention may be constructed in which a transparent plate is provided on the side of a light outgoing surface of the optical modulation element, an
Fujimori Motoyuki
Haba Shinji
Hashizume Toshiaki
LeRoux E P
Metjahic Safet
Oliff & Berridg,e PLC
Seiko Epson Corporation
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