JPH03249616A - Liquid crystal projector - Google Patents

Abstract

PURPOSE:To attain excellent color separation by a dichroic mirror without increasing the size of a device and to increase the brightness of a projection image with small loss by converting luminous flux outputted by a light source into elliptically sectioned luminous flux by an optical means. CONSTITUTION:The luminous flux which is outputted by the light source 12 is used to generate a light image on a liquid crystal panel 20. A cylindrical lens 50 which converts the sectional shape of the luminous flux into a nearly elliptic shape corresponding to the photodetection surface shape of the liquid crystal panel 20 is arranged between the light source 12 and liquid crystal panel 20. Namely, the quantity of light incident on the photodetection surface of the liquid crystal panel 20 increases as compared with the case of the section of the luminous flux is circular and the section conversion by a lens means 50 is possible. Consequently, the color separation by the dichroic mirror is performed excellently without increasing the size of the device and the brightness of the projection image can be increased with small light loss.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid crystal projector, and particularly relates to an improvement in a light guiding system that projects light from a light source onto a liquid crystal panel or a liquid crystal light valve. .

[Prior Art] An example of a liquid crystal projector using a liquid crystal panel is shown in FIG. In the same figure, reflector 1
Light emitted from a light source 12, such as a halogen having zero, first enters a cold filter 14. This cuts infrared rays, making it difficult for heat from the light source 12 to be transmitted to the front.

The light transmitted through the cold filter 14 enters the blue reflective mirror 16, where the blue (B) light is separated.The separated B light is reflected by the reflective mirror 18, and the blue (B) light is separated. incident on the panel 20. A B image signal is input to the liquid crystal panel 20, and a B image is formed based on this signal.

Next, the light that has passed through the blue-reflecting guichroic mirror 16 enters the green-reflecting guichroic mirror 22, where the G
The six separated G lights enter the G liquid crystal panel 24. A G image signal is manually applied to the liquid crystal panel 24, and a G image is formed based on this signal.

Next, the red (R) light that has passed through the green reflective mirror 22 is sequentially reflected by the reflective mirrors 26 and 28 and enters the R liquid fixture panel 30. An R image signal is input to the liquid crystal panel 30, and based on this, R
image is formed.

Next, the B, G, and H images respectively formed by the B, G, and H liquid crystal panels 20.24° 30 are combined by the color compositing gicroic prism 32, and the combined color image is Screen 36 by projection lens 34
is shown in the image.

Incidentally, in such a liquid crystal projector, the shape of the light beam output from the light source side in a plane perpendicular to the optical axis is approximately circular as shown by a broken line 38 in FIG. On the other hand, the light-receiving surface of the liquid crystal panel 20°24.30 is rectangular, corresponding to the reproduced image, as shown by the solid line 40, and light is guided to this (the light guide system or light pipe also has a rectangular cross section). It has a prismatic shape.

For this reason, when the substantially circular light beam is larger than the circumscribed circle of the sunset rectangle of the light pipe, the space between the light beams is eclipsed. For example, when the circular shape of the light beam coincides with the circumscribed circle of the sunset rectangle of the light pipe, the light in the hatched area in FIG. 7 is eclipsed, resulting in light loss.

To improve this point, Japanese Patent Application Laid-Open No. 64-490
There is a light pipe disclosed in Publication No. 17. As shown in FIG. 8, this light pipe has a circular part 100 and a rectangular part 102, which are joined so that the shape changes smoothly. The light entrance 104 is approximately circular, and the light exit 106 is rectangular. In addition, a light reflecting film is formed on the inner walls thereof.

According to such a light pipe, a light beam having a substantially circular cross section is output as a rectangular light beam. Further, the light incident on the inner wall of the light pipe is reflected by the reflective film and output, thereby making effective use of the light.

[Problems to be Solved by the Invention] However, the above conventional techniques have the following disadvantages.

(1) Since a circular light beam is gradually transformed into a rectangular light beam, the light pipe needs to be longer than a certain length. Therefore, the optical path from the light source to the liquid crystal panel becomes long, resulting in an increase in the size of the device body.

(2) Also, since the light is reflected many times by the reflective film formed on the inner wall of the light pipe and output, the amount of light increases, but there is also light traveling diagonally with the optical axis shifted. Become. This light whose optical axis is shifted causes the following problems in relation to the action of the guichroic mirror that performs color separation.

In other words, a guichroic mirror is designed to selectively reflect light of a certain wavelength of incident light, and the incident light is usually designed to enter the guichroic mirror at an angle of 45 degrees. has been done. However, when the traveling direction of the light deviates from the optical axis, the light enters the guichroic mirror at an angle different from 45 degrees. Then, in the gicroic mirror, the cutoff frequency (or wavelength) of selective reflection changes.

An example of such angular dependence is shown in FIG.
The relationship between and the incident light transmittance (vertical axis) is shown. As shown in this figure, when the incident angle changes by ±5 degrees from 45 degrees, the graph LA changes as shown by LB and LC. Therefore, the cutoff frequency changes by ±12 nm in terms of wavelength. Therefore, the color separation by the guichroic mirror cannot be performed satisfactorily.

The present invention has been made in view of these points, and it is possible to achieve high brightness of a projected image with less light loss by performing good color separation using a gicroic mirror without increasing the size of the device. The purpose is to provide a liquid crystal projector.

[Means for Solving the Problems] The present invention provides a liquid crystal projector that uses a light beam output from a light source to generate an optical image on a liquid crystal panel. The present invention is characterized in that a lens means for converting the image into a substantially elliptical shape is disposed in the optical path between the light source and the liquid crystal panel.

[Function] According to the present invention, the lens means 1 makes the cross section of the light beam approximately elliptical.
For example, a cylindrical lens is placed between the light source and the liquid crystal panel. Therefore, the amount of light incident on the light receiving surface of the liquid crystal panel increases compared to the case where the cross section of the light beam is circular. Furthermore, since the cross-section is transformed by lens means, the device can be constructed in a compact size, and light can be properly incident on the dichroic mirror.

[Example] Hereinafter, an example of a liquid crystal projector according to the present invention will be described with reference to the accompanying drawings.

Note that the same reference numerals are used for the same components as in the conventional example described above.

First Embodiment First, a first embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 shows the main structure of the first embodiment. This embodiment is an application of the present invention to the conventional example shown in FIG. 6, and has almost the same structure.

In the figure, a cylindrical lens 50 is arranged between the light output side of the cold filter 14 and the light input side of the blue reflective dichroic mirror 16. As is well known, the cylindrical lens 50 is a lens that acts as a lens only in one direction and does not act in any other direction orthogonal to this.

Fig. 2 fAl shows the cylindrical lens 5 when a light source equipped with a parabolic reflector 10A is used.
An example of the effect of 0 is shown.

In the arrangement state shown in FIG. 1, the light beam with a circular cross section outputted from the light source 12 directly enters the cylindrical lens 50.
Arrow F1. The cylindrical lens 50 acts as a lens in the vertical direction of the drawing indicated by F2. Therefore, by appropriately selecting the curvature of the cylindrical lens 50 and the optical distance thereto, it is possible to irradiate the liquid crystal panel 20, 24, 30 with a light beam having a circular cross section as an elliptical cross section.

The same figure (B) shows the case where a light source equipped with a spheroidal reflector 10B is used. In this case, a condenser lens 52 is arranged on the output side of the light source 12, and the light outputted from the light source 12, once focused, and then spread, is made to enter the condenser lens 52. and,
The light that has been parallelized by the condenser lens 52 is incident on the cylindrical lens 50, and the circular cross section of the light beam is made into an elliptical cross section.

Next, the operation of the first embodiment configured as above will be explained. The light emitted from the light source 12 has infrared rays cut off by the cold filter 14 and then enters the cylindrical lens 50 . The cylindrical lens 50 performs the lens action as shown in FIG. 2 described above, and the condensed light enters the blue reflective dichroic mirror 16, where the B light is separated. The separated B light is reflected by the reflection mirror 18, and the B light
The light enters the liquid crystal panel 20 of.

Incidentally, when reproducing a normal television image, the incident screen 20F of the liquid crystal panel 20 has a rectangular shape with a length x width ratio of 3=4 as shown in FIG. On the other hand, the cross-sectional shape of the irradiated B light is
By appropriately setting the optical distance between the cylindrical lens 50 and the liquid crystal panel 20 and the curvature of the cylindrical lens 50, a substantially elliptical shape as shown by a broken line 54 in the figure is obtained. Therefore, as is clear from a comparison with FIG. 7, waste is reduced and light is effectively incident on the liquid crystal panel 20. A B image signal is input to the liquid crystal panel 20, and a B image is formed based on this signal.

Similarly, G and H light fluxes each having an elliptical cross section are incident on the liquid crystal panel 24, 30, and G and R images are respectively formed. The B, G, and R images respectively formed by the liquid crystal panels 20°, 24, and 30 are combined by a color compositing gicroic prism 32, and the combined color image is projected onto a screen 36 by a projection lens 34. .

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. In the first embodiment described above, a prism was used to synthesize R, G, and B images, but in this second embodiment, a mirror was used to synthesize images.

In the figure, a cylindrical lens 64 is disposed on the output side of a light source 60 via a condenser lens 62, and a red reflective guicroic mirror 66 is disposed on the output side. This red reflective guichroic mirror 66
An R liquid crystal panel 70 is arranged on the reflection output side of the mirror 68 with a mirror 68 interposed therebetween.

On the other hand, a blue reflective dichroic mirror 72 is arranged on the transmission output side of the red reflective dichroic mirror 66. A G liquid crystal panel 76 is arranged on the transmission output side of the blue reflective dichroic mirror 72 with a mirror 74 in between. Further, a B liquid crystal panel 78 is arranged on the reflection output side of the blue reflection dichroic mirror 72. Each liquid crystal panel 70, 76, 78 is provided with a polarizing plate.

Next, a blue reflective dichroic mirror 80 is arranged on each output side of the liquid crystal panel 70, 76, 78. A green reflective dichroic mirror 82 is provided on each output side of the blue reflective dichroic mirror 80 and the liquid crystal panel 76.
is located.

On the output side of this green reflective dichroic mirror 82, a projection lens 84. Screens 86 are arranged one after the other.

Next, the operation of the second embodiment configured as above will be explained. The light output from the light source 60 is condensed by a condenser lens 62 and enters a cylindrical lens 64 . As shown in FIG. 2, the cylindrical lens 64 condenses the light beam having a circular cross section in one direction and turns it into a light beam having an elliptical cross section.

This light beam first enters the red reflective mirror 66 , where the R light is reflected and separated, further reflected by the mirror 68 , and enters the liquid crystal panel 70 . The light transmitted through the red reflecting dichroic mirror 66 enters the blue reflecting dichroic mirror 72, where the B light is reflected and separated and enters the liquid crystal panel 78. The G light transmitted through the blue reflective dichroic mirror 72 is reflected by the mirror 74 and enters the liquid crystal panel 76.

As shown in FIG. 3, light beams are incident on the liquid crystal panels 70, 76, and 78, and R, B, and G optical images are generated, respectively. These light images are captured by the blue reflective gear clock mirror 80.
The green reflecting dichroic mirror 82 combines the images, and the combined images are projected onto the screen 86 by the projection lens 84.
It will be projected on.

According to this embodiment, the optical distance between the cylindrical lens 64 and the liquid crystal panels 70, 76, 7'B can be made the same, so the optical design is easy.

Other Examples> Note that the present invention is not limited to the above embodiments. For example, in the example shown in FIG. 2, the cylindrical lens 50 has a rectangular shape, but it may also have a circular shape with the same size as the aperture shape of the parabolic reflector IOA or the shape of the condenser lens 52. .

Furthermore, the cross-sectional shape of the light pipe that guides the light from the light source to each liquid crystal panel or projection lens may be of any shape as long as it is larger than the cross-sectional shape of the light flux output from the cylindrical lens.

As mentioned above, the current size ratio of television images is 3:4, but in high-definition, for example, as shown in FIG. 5, the ratio is 9=16, resulting in a horizontally long screen. When a liquid crystal panel has such a light-receiving surface and a light beam having a circular cross section is used, the loss becomes even greater. In such cases, the present invention works particularly effectively.

In addition, although only a cylindrical lens was used in the above embodiment, other lens elements may be combined to obtain the desired cross-sectional shape of the light beam.The optical path length from the cylindrical lens to each liquid crystal panel for R, G, and B. If the values are different, an appropriate optical element for modifying the beam cross section may be used.

In the above embodiment, the present invention is applied to a color display projector, but it is also applicable to a black and white projector.

[Effects of the Invention] As explained above, according to the liquid crystal projector according to the present invention, the luminous flux output from the light source is converted into a luminous flux having a substantially elliptical cross section by the optical means. This has the effect that the color separation by the guichroic mirror can be performed well and the projected image can be made to have high brightness with little light loss.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a liquid crystal projector according to the present invention, FIG. 2 is an explanatory diagram showing the action of a cylindrical lens, and FIG. 3 is a diagram showing the relationship between the cross-sectional shape of a light beam and the light receiving surface of a liquid crystal panel FIG. 4 is a configuration diagram showing a second embodiment of the present invention. FIG.
Figure 7 is a configuration diagram showing an example of a liquid crystal projector, Figure 7 is an explanatory diagram showing the relationship between the cross-sectional shape of the luminous flux output from the light source and the light receiving surface of the liquid crystal panel, Figure 8 is a perspective view showing the prior art, and Figure 8 is a perspective view showing the prior art. FIG. 9 is a graph showing the dependence of light transmittance on the angle of incidence of a diagonal mirror. 10...Reflector, 12.60...Light source, 16°72.80...Blue reflective guichroic mirror 18,2
6,2B, 68.74...Mirror, 20°24.30
．． 70.76.78...LCD panel, 22.82...
・Green reflective chromic mirror 32...Color synthesis dichroic prism, 34°84...Projection lens,
36.86...Screen, 50.64...Cylindrical lens, 52°62...Condenser lens,
66...Red reflective mirror

Claims (1)

[Claims] In a liquid crystal projector that generates an optical image on a liquid crystal panel using a luminous flux output from a light source, a lens means for converting a cross-sectional shape of the luminous flux into a substantially elliptical shape corresponding to the shape of a light receiving surface of the liquid crystal panel is connected to the light source. A liquid crystal projector characterized in that it is placed in an optical path between it and a liquid crystal panel.