JPH05273404A - Dichroic prism - Google Patents

Abstract

PURPOSE:To eliminate the doubling of an image and to improve the image contrast by slanting a prism incidence surface and a prism projection surface at the angles where light reflected by the incidence surface or projection surface is guided out of the optical path. CONSTITUTION:The dichroic prism 1 is constituted by integrally coupling prisms 2-5 and its base body is cubic, but the incidence surface 2a of the prism 2 which faces the chart surface 6a of a liquid crystal display panel 6 for R(red), the incidence surface 3a of the prism 3 which faces the chart surface 7a of a liquid crystal display panel 6 for G(green), the incidence surface 4a of the prism 4 which faces the chart surface 8a of a liquid crystal display panel 8 for B(blue), and the projection surface 5a of the prism 5 which faces the incidence surface 9a of a projection lens are slanted at the specific angles to the optical axis. In this case, the incidence surfaces 2a-4a of the prisms 2-4 face up forward and the projection surface 5a of the prism 5 faces down backward.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dichroic prism used for image synthesizing means of a liquid crystal projector.

[0002]

2. Description of the Related Art In a liquid crystal projector for irradiating a chart surface of a transmissive liquid crystal display panel with light from a light source and enlarging and projecting an image of a television or the like displayed on the liquid crystal display panel onto a screen, as shown in FIG. , Three liquid crystal display panels 100, 101, 102 for RGB (red green blue)
There is known a system (so-called three-panel liquid crystal projector) provided with. In such a system, each liquid crystal display panel 1
After the RGB images of 00, 101, and 102 are combined by the image combining unit composed of the dichroic prism 103, they are enlarged and projected on the screen 105 by the projection lens 104. Each liquid crystal display panel 100, 101, 1
The dichroic prism 103 for synthesizing the RGB image of No. 02 is conventionally four rectangular prisms 106 to 109.
Has a cube shape integrally connected (by bonding) so that the shape in the figure becomes a square. In the illustrated case, the image of the R (red) component of the R liquid crystal display panel 100 arranged above the right-angle prism 106 is the right-angle prism 1.
06 and 109 and their R component reflecting surfaces 106
The light is reflected by a and 109a toward the projection lens 104. Further, the image of the G (green) component of the G liquid crystal display panel 101 arranged in front of the right-angle prism 107 is transmitted through the right-angle prisms 106 to 109 toward the projection lens 104. Further, the B (blue) component image of the B liquid crystal display panel 102 arranged below the right-angled prism 108 is incident on the right-angled prisms 108 and 109 and is reflected by the B (blue) component reflection surfaces 108a and 109b. Toward the projection lens 4, and the RGB images of the liquid crystal display panels 100, 101 and 102 are combined on the screen 105 after these steps. In FIG. 4, reference numeral 110 indicates the lamp 1.
A light source device 11 including a reflector 10b and a reflector 10b.
Reference numeral 1 is a condenser lens, 112 is a dichroic mirror that distributes the light from the light source device 110 to the R, G, and B liquid crystal display panels 100, 101, and 102 into R (red component), G (green component), and B (blue component). Reference numerals 113 and 114 are mirrors that convey the light reflected by the dichroic mirror 112 to the liquid crystal display panels 100 and 102 for RB.

[0003]

2. Description of the Related Art However, in the case of a conventional three-panel liquid crystal projector in which the cube-shaped dichroic prism 103 is adopted as an image synthesizing means for synthesizing RGB images of each liquid crystal display panel 100, 101, 102, There is a problem that the image contrast is low and good image quality cannot be obtained. This is because a part of the light (a few% of the light) that passes through the dichroic prism 103 is reflected by both the incident surface and the exit surface that are perpendicular to the liquid crystal display panel 100, 1.
The main cause is that the light is further reflected by the chart surfaces of 01 and 102 and returns to the optical path (that is, image dubbing occurs). In addition, part of the light (several% of light) transmitted through the projection lens 104 is reflected by the incident surface thereof and further reflected by the exit surface of the dichroic prism 103 to return to the optical path. .. FIG. 5 is a schematic diagram showing the reflection of light generated on the incident surface and the emission surface of the dichroic prism 103 and the reflection of light generated on the incident surface of the projection lens 104. In addition, here, the liquid crystal display panel 101 for G is used.
The image of the G (green) component is shown. Light (G component image) a from the G liquid crystal display panel 101 is sequentially transmitted through the dichroic prism 103 and the projection lens 104. When the light a is transmitted through the dichroic prism 103, a part of the light a ₁ is reflected by the vertical incident surface 107a, further reflected by the chart surface 101a of the G liquid crystal display panel 101, and returned to the optical path. Further, a part of the light a ₂ is reflected by the vertical exit surface 109c and is reflected by the dichroic prism 103.
Through the chart surface 10 of the G liquid crystal display panel 101.
It is further reflected by 1a and returns to the optical path. The light a is the projection lens 10
When passing through 4, part of the light a ₃ is reflected by the convex incident surface 104a and further reflected by the exit surface 109c of the dichroic prism 103 to return to the optical path.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to significantly reduce the generation of reflected light returning to the optical path at the prism entrance surface and the prism exit surface. To provide.

[0005]

In order to achieve the above object, the dichroic prism of the present invention has a prism entrance surface and a prism exit surface each having an inclined surface having an angle at which light reflected by the entrance surface or exit surface is guided outside the optical path. That is the main point.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below in detail with reference to the drawings. Here, the case where the present invention is applied to a dichroic prism used as an image synthesizing means of a three-plate type liquid crystal projector is shown.

<First Embodiment> FIGS. 1 (a), 1 (b),
(C) shows a dichroic prism according to the first embodiment of the present invention. FIG. 1 (a) is a plan view thereof,
1B is a side view in the G liquid crystal display panel direction, and FIG. 1C is a side view in the B liquid crystal display panel direction.

This dichroic prism 1 is constructed by integrally connecting (by bonding) four prisms 2-5. Although the basic shape of such a dichroic prism 1 is a cubic shape, the incident surface 2a of the prism 2 facing the chart surface 6a of the R liquid crystal display panel 6 and the chart surface 7a of the G liquid crystal display panel 7 are opposed to each other. The incident surface 3a of the prism 3, the incident surface 4a of the prism 4 facing the chart surface 8a of the liquid crystal display panel 8 for B, and the exit surface 5a of the prism 5 facing the incident surface 9a of the projection lens 9, respectively. It is an inclined surface that is inclined at a predetermined angle (here, 70 degrees) with respect to the optical axis. In this case, the incident surfaces 2a, 3a, 4 of the prisms 2, 3, 4 are
Reference character a is a frontwardly inclined surface, and the exit surface 5a of the prism 5 is a rearwardly downward inclined surface.

In such a dichroic prism 1, the image of the R (red) component of the R liquid crystal display panel 6 is incident on the prisms 2 and 5 and their R component reflecting surfaces 2b and 5 are formed.
It is reflected by b and goes toward the projection lens 9. The image of the G (green) component of the G liquid crystal display panel 7 is the prisms 2-5.
To the projection lens 9. Further, the image of the B (blue) component of the B liquid crystal display panel 8 is incident on the prisms 4 and 5, is reflected by the B (blue) component reflecting surfaces 4b and 5c, and is directed to the projection lens 9, where these processes are performed. After that, the R of each liquid crystal display panel 6, 7, 8 is displayed on a screen not shown.
GB images are combined. In this case, the R component image of the R liquid crystal display panel 6, the G component image of the G liquid crystal display panel 7, and the B component image of the B liquid crystal display panel 8 are transmitted through the dichroic prism 1 in the same state. Then, the light passes through the projection lens 9. That is, each incident surface 2a of the dichroic prism 1 (image of the R component of the R liquid crystal display panel 6), 3a (image of the G component of the G liquid crystal display panel 7), 4a (B component of the B liquid crystal display panel 8) Of light), and the exit surface 5a of the dichroic prism 1 (the image of the R component of the R liquid crystal display panel 6, the image of the G component of the G liquid crystal display panel 7, and the B liquid crystal display panel 8). The state of emission of the B component image) and the state of incidence on the incident surface 9a of the projection lens 9 are the same.

FIG. 2 shows an image of the G component of the G liquid crystal display panel 7 as an example. The incident state of the light on the incident surface 3a and the emitted state of the light on the exit surface 5a of the dichroic prism 1 according to the present invention, In addition, the incident state of light on the incident surface 9a of the projection lens 9 is shown.

Light a from the G liquid crystal display panel 7 is incident on the incident surface 3a of the dichroic prism 1, refracted and transmitted there, and further refracted on the exit surface 5a (here, with respect to the optical axis).
It is refracted at 11.8 degrees) and enters the incident surface 9a of the projection lens 9. Here, the optical axes of the light a are displaced from each other before and after the dichroic prism 1, but are in parallel with each other. In general, the upper surface 1a and the lower surface 1b of the dichroic prism 1 are sanded and then black-painted.

In the above description, when the light a from the G liquid crystal display panel 7 is incident on the incident surface 3a of the dichroic prism 1, a part (several%) of the light a ₁ is reflected by the incident surface 3a. The reflected light a ₁ is guided to the outside of the optical path directly or after being further reflected by the chart surface 7 a of the G liquid crystal display panel 7. Further, when the light a is emitted from the emission surface 5a of the dichroic prism 1, a part (several%) of the light a ₂ is emitted.
Is reflected by the exit surface, and the reflected light a ₂ travels to the upper surface 1a of the dichroic prism 1 and is absorbed there (when the upper surface 1a is sanded and is not blackened, it is guided to the outside). Further, the light a is the incident surface 9a of the projection lens 9.
When incident on the incident surface 9, a part (several%) of the light a ₃ is incident on the incident surface 9
Although reflected by a, it lights a ₃ that this reflected in the case of a generally convex as illustrated is guided to the outside of the optical path after further reflection at the exit surface 5a of the light a ₃ near the convex lens directly or dichroic prism 1. There is an exit surface 5 in the light a _3.
Some of them enter the convex lens after being reflected by a,
Since the light is incident after being reflected twice, the amount of light is extremely small (about 0.01% when reflected by the incident surface 9a), and therefore, even if it returns to the optical path, it hardly appears as a double image in the image.

As described above, in the dichroic prism 1 of this embodiment, the lights a ₁ and a ₂ reflected on the incident surfaces 2a, 3a, 4a and the exit surface 5a can be guided out of the optical path, and thus reflected. The light beams a ₁ and a ₂ do not return to the optical path, so that the image does not become dull.
Good image quality with high image contrast can be obtained.

<Second Embodiment> FIGS. 3 (a), 3 (b),
(C) shows a dichroic prism according to the second embodiment of the present invention. FIG. 3A is a plan view thereof,
FIG. 3B is a side view in the direction of the G liquid crystal display panel,
FIG. 3C is a side view in the direction of the B liquid crystal display panel.

The dichroic prism 1'is also constructed by integrally connecting (by bonding) the four prisms 2'-5 ', and its basic shape is a cubic shape. Also in the case of this dichroic prism 1, the chart surface 6 of the R liquid crystal display panel 6'is also provided.
a chart surface 2a 'of the prism 2'opposed to a', and G
Incidence surface 3a 'of the prism 3'opposed to the chart surface 7a' of the liquid crystal display panel 7'for B and the liquid crystal display panel 8'for B
Incidence surface 4 of prism 4'opposed to chart surface 8a 'of
a 'and the exit surface 5a' of the prism 5'opposed to the entrance surface 9a 'of the projection lens 9'are inclined surfaces inclined at a predetermined angle (here, 70 degrees) with respect to the optical axis.
In the case of this dichroic prism 1 ', the respective incident surfaces 2a', 4a 'of the prisms 2', 4'are right downward inclined surfaces, and the incident surface 3a 'of the prism 3'and the exit surface 5a of the prism 5'. ′ Is a slope descending to the left.

Also in the dichroic prism 1'having such a structure, the light reflected on the incident surfaces 2a ', 3a', 4a 'and the exit surface 5a' is out of the optical path like the dichroic prism 1 of the first embodiment. It is possible to guide it to the optical path and not return to the optical path.

Although each of the above embodiments has been applied to the dichroic prism used in the image synthesizing means of the three-plate type liquid crystal projector, the present invention is similarly applied to the dichroic prism forming the optical system of other equipment. It is possible to apply.

[0018]

As explained above, according to the dichroic prism of the present invention, the prism entrance surface and the prism exit surface each have an inclined surface at which the light reflected by the entrance surface or the exit surface is guided outside the optical path. Because,
It is possible to guide the light reflected by the prism entrance surface and the prism exit surface to the outside of the optical path so as not to return to the optical path.
For this reason, image dull does not occur, the image contrast is enhanced, and a good image can be obtained.

[Brief description of drawings]

1A is a plan view of a dichroic prism according to a first embodiment of the present invention, FIG. 1B is a side view of the dichroic prism for a G liquid crystal display panel, and FIG. 1C is a B view of the dichroic prism. It is a side view of a liquid crystal display panel direction.

FIG. 2 is a cross-sectional view showing a light incident state and a light emitting state on an entrance surface and an exit surface of a dichroic prism.

3A is a plan view of the dichroic prism according to the second embodiment, FIG. 3B is a side view of the dichroic prism in the direction of a G liquid crystal display panel, and FIG. 3C is a B liquid crystal display of the dichroic prism. It is a side view of a panel direction.

FIG. 4 is a schematic configuration diagram of a conventional three-panel liquid crystal projector.

5A and 5B are schematic diagrams showing a light incident state on the incident surface of the dichroic prism, a light outgoing state on the outgoing surface, and a light incident state on the incident surface of the projection lens in the three-plate liquid crystal projector.

[Description of Hogo]

1,1 dichroic prism 2a, 2a ', 3a, 3a ', 4a, 4a ' entrance surface 5a, 5a' exit surface a ₁ ~a ₂ reflected light

Claims (1)

[Claims] 1. A dichroic prism, wherein the prism entrance surface and the prism exit surface are inclined surfaces having an angle at which the light reflected by the entrance surface or the exit surface is guided outside the optical path.