JPH11167105A - Projection image display - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In a projection type image display device using a liquid crystal light valve, a black matrix is conspicuous, and the image quality cannot be improved. A light source unit that emits white light in one direction,
A modulation unit having a dot matrix type liquid crystal light valve that modulates a light beam and performs image display according to an input signal;
A projection lens for enlarging and projecting the modulated light beam onto a screen, and a λ / 4 plate on the modulation means side between the modulation means and the projection lens, and a non-polarized incident light beam on the projection lens side. It has a birefringent optical element that splits into an ordinary ray and an extraordinary ray having polarization planes perpendicular to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type image display apparatus which uses a dot matrix type liquid crystal light valve and enlarges and projects the image on a screen via a projection lens.

[0002]

2. Description of the Related Art In recent years, small televisions, laptop OA
With the remarkable commercialization of devices using a liquid crystal panel as a display device, such as devices, a liquid crystal projector has attracted attention as a large-screen display device. The liquid crystal projector has advantages over a conventional CRT projector in that it can be reduced in size and weight, is not affected by geomagnetism, and can ensure convergence accuracy uniformly over the entire display. On the other hand, liquid crystal projectors require a liquid crystal panel with a large number of pixels compared to a direct-view type liquid crystal display device, because the roughness of pixels is noticeable because the image is enlarged and projected on the screen. A liquid crystal panel is required.

FIG. 4 is a conceptual diagram showing a basic configuration of a conventional projection display device. This projection type image display device includes a light source lamp 1, a concave reflecting mirror 2, an integrator lens 3,
A field lens 4, a liquid crystal light valve 5, a projection lens 8, and a screen (not shown) are sequentially arranged in series. Light from the light source 1 is condensed by a concave reflecting mirror 2 and illuminates a liquid crystal light valve 5 via an integrator lens 3 for illumination optical system composed of two lens arrays and a field lens 4. The liquid crystal light valve 5 controls the transmittance of the pixel according to the video signal, and the image is displayed on the projection lens 8.
Is magnified and projected on the screen.

[0004] Among the projection type image display devices using a liquid crystal panel as a liquid crystal light valve, the mainstream at present is a dot matrix type, and an active matrix type using a TFT is often used. In a TFT active matrix type liquid crystal panel, transmittance cannot be controlled in a liquid crystal layer other than a display electrode of each pixel. Further, when light is applied to the channel portion of the TFT, a leakage current when the TFT is off increases due to a photoexcitation current, and the voltage holding ratio when the TFT is off becomes insufficient. In particular, in a normally white mode liquid crystal panel, portions other than the display electrodes are in a light transmitting state, so that the contrast is reduced unless the light is sufficiently shielded. Therefore, in order to obtain sufficient contrast, the TFT
A black matrix is formed on the counter electrode substrate to shield light from sneaking into the TFT and light leakage from other than the display electrode.

[0005]

However, in such a projection type image display apparatus using a dot matrix type liquid crystal panel as a liquid crystal light valve, an image composed of pixels of the liquid crystal panel is enlarged and projected on a screen by a projection lens. Therefore, when the number of pixels is small and the width of the black matrix is relatively wide, or as the magnification is increased, the pixel structure itself looks like a mosaic, and the impression when an image is viewed deteriorates.

Further, the size of the liquid crystal panel has been reduced in order to reduce the size and weight of the device itself, and the aperture ratio indicating the ratio of the aperture through which light is transmitted to the black matrix decreases. Therefore, the pixel structure itself looks clearly like a mosaic, and the impression when the image is viewed deteriorates.

As a simple method of making the pixel structure inconspicuous, it is conceivable to project the image by defocusing the projection lens so that the black matrix becomes inconspicuous, but the projected image itself becomes blurred. Furthermore, in a projection lens, since the defocus characteristics of the MTF are different between on-axis and off-axis of the optical axis, it is difficult to make the black matrix uniformly inconspicuous over the entire screen. For example, there may be a case where the black matrix is hardly seen in the periphery but the vicinity on the axis is clearly seen. Alternatively, the black matrix near the on-axis is difficult to see, but off-axis, the image itself may be too blurry to see.

There is also a method in which a diffraction grating is provided between the projection lens and the liquid crystal panel, and the black matrix is blurred by diffracted light. However, the MTF characteristic is reduced, and as a result, the sharpness of the image is reduced. The image becomes blurred and the impression worsens.

[0009]

According to a first aspect of the present invention, a projection type image display apparatus is provided.
A light source unit that emits white light in one direction, a modulation unit that includes a dot matrix type liquid crystal light valve that modulates the light beam and displays an image according to an input signal, and enlarges the modulated light beam on the screen A projection lens for projecting, and λ is provided on the modulation means side between the modulation means and the projection lens.
On the side of the projection lens, there is provided a birefringent optical element for splitting an unpolarized incident light into an ordinary ray and an extraordinary ray having polarization planes orthogonal to each other.

As a second means, the projection type image display apparatus of the present invention separates the light from the light source into three color lights of red, blue and green by emitting a white light in one direction. A color light separating unit; a modulating unit including a liquid crystal light valve for modulating polarized light included in a light beam from the color light separating unit to display an image according to an input signal; and a modulation after being modulated by the modulating unit. A color light synthesizing means for synthesizing the light flux, a projection lens for enlarging and projecting the modulated light flux on a screen, and a λ / 4 plate on a modulation means side between the modulation means and the projection lens; On the side, there is provided a birefringent optical element for splitting an unpolarized incident light beam into an ordinary light beam and a extraordinary light beam having polarization planes perpendicular to each other.

In the second means, a dichroic prism is used for the color light synthesizing means, and the polarization direction of the color light traveling from the dichroic prism toward the λ / 4 plate is the same in red, blue and green. They may be regulated and placed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A projection type image display device according to the present invention comprises a light source section for emitting white light in one direction, and a dot matrix type liquid crystal light for modulating a light beam to display an image in accordance with an input signal. A modulating means having a valve; a projection lens for enlarging and projecting the modulated light beam onto a screen; and a λ / 4 plate on the modulating means side between the modulating means and the projection lens; By having a birefringent optical element that splits unpolarized incident light into ordinary light and extraordinary light having polarization planes that intersect at right angles to each other,
Due to the optical action of the λ / 4 plate, the output light directed to the birefringent optical element as circularly polarized light or elliptically polarized light is split into an ordinary ray and an extraordinary ray by the birefringent optical element, and is projected onto a screen via a projection lens. As a result, the extraordinary ray is projected at a position shifted vertically, horizontally, or obliquely from the ordinary ray. In other words, the extraordinary ray is projected at a position shifted in the direction regulated from the projection position of the ordinary ray,
Since the extraordinary ray is superimposed on the black matrix of the image projected by the ordinary ray, the black matrix becomes inconspicuous and the impression of the image projected on the screen is significantly improved. However, whether the direction is vertical, horizontal, or oblique is determined by the direction of the optical axis of the birefringent optical element.
Needless to say, the light emitted from the liquid crystal light valve 5 is linearly polarized light.

Hereinafter, the embodiment will be described with reference to the drawings. However, since the configuration from the light source to the modulation means is not limited in any way, both the first and second embodiments are conventional. It may have the same configuration as the example, or may have a different configuration.

(Embodiment 1) FIG. 1 is a schematic configuration diagram of Embodiment 1 and shows a light source lamp 1 shown in FIG.
The optical path from the liquid crystal light valve 5 to the liquid crystal light valve 5 is the same as that of the conventional example.
And a birefringent optical element 7 for splitting an unpolarized incident light beam into an ordinary light beam and an extraordinary light beam having polarization planes orthogonal to each other on the projection lens 8 side. Liquid crystal light valve 5
Is converted by the λ / 4 plate 6 into elliptically polarized light or circularly polarized light, and enters the birefringent optical element 7. The incident light beam is split into an ordinary light beam and an extraordinary light beam by the function of the birefringent optical element 7 to split into an ordinary light beam and an extraordinary light beam having polarization planes that intersect at right angles to each other. More specifically, the birefringent optical element 7 is made of a birefringent crystal such as calcite, and has the property of splitting a monochromatic incident light beam into two light beams having polarization planes that cross each other. The two split light beams normally propagate in mutually different directions and have different propagation speeds. Depending on whether the birefringent crystal is uniaxial or biaxial,
There are one or two optical axes along the crystal plane in which the light rays maintain the same propagation velocity and are co-propagating. If both surfaces of the birefringent crystal are parallel as in this embodiment,
If the incident direction of the light beam does not coincide with the direction of the optical axis, the light beam emitted from the crystal is split into two polarized lights whose polarization planes are orthogonal to each other.

That is, the ordinary ray is projected on a screen (not shown) in the same manner as the conventionally projected polarized light, but the pixel opening of the extraordinary ray is vertically overlapped on the black matrix of the ordinary ray. It is projected at a position shifted in the horizontal, horizontal, or oblique direction. However, the direction is regulated by the direction of the optical axis of the birefringent optical element, and the amount of displacement is regulated by the thickness of the birefringent optical element.
As a result, when the black matrix 9 which is the projection image of the ordinary ray shown in FIG. 2A overlaps with the extraordinary ray, it becomes an image diagram of the projection image as shown in FIG. 2B and as shown in FIG. It becomes an image graph with a great screen brightness. In the first embodiment, as shown in (b) and (c) of FIG. 2, the light is regulated so as to be shifted in the vertical direction. Since the pixel openings of the extraordinary ray are projected on top of each other, the black matrix 9 in the vertical direction is almost invisible, and the image quality is markedly improved. In addition, although the black matrix of the projected image of the extraordinary ray overlaps the pixel opening of the adjacent ordinary ray, no problem occurs because the pixel matrix is basically a portion where there is no light.

(Embodiment 2) FIG. 3 is a schematic configuration diagram of Embodiment 2, which is different from the configuration of FIG.
Total reflection mirror 10 between lens arrays of integrator lens 3 comprising two lens arrays as an illumination optical system
A dichroic mirror 11 as a color separating means between the integrator 3 and the liquid crystal light valve 5; a dichroic prism 12 as a color synthesizing means between the liquid crystal light valve 5 and the λ / 4 plate 6; A relay lens 13 and a total reflection mirror 10 are provided as necessary so that light separated into each color is guided to an optical path having a different optical path length to the lens to each liquid crystal light valve 5.

However, the λ / 4 plate 6 and the birefringent optical element 7 are provided between the projection lens and the dichroic prism 12 which is a color synthesizing means. This is because, in the optical characteristics of the dichroic prism 12, the polarization directions of the red and blue lights that are reflected and combined are limited to only one direction. Therefore, the dichroic prism 12 used in the color combining unit and the liquid crystal light valve are used. 5 and λ / 4, respectively.
A configuration including the plate 6 and the birefringent optical element 7 in a series order cannot be used. That is, a configuration in which the projection image is overlaid on the black matrix 9 using the extraordinary light cannot be taken.

Further, only green light, which is color-combined as transmitted light, can use both polarization directions. However, only the extraordinary ray of green light overlaps the black matrix projected and synthesized on the screen, and as a result, the black matrix 9 looks green and the projected image has a poor impression.

Therefore, in the second embodiment using three liquid crystal light valves 5 of red, blue and green and having a color separating means and a color synthesizing means, the color synthesizing means is changed to the λ / 4 plate 6. The incoming linearly polarized light has a configuration limited to the same direction.
Further, it is also possible to use a dichroic mirror for the color synthesizing means. The ordinary ray and the extraordinary ray having different colors overlap each other, resulting in color unevenness.
That is, similarly to the second embodiment, a configuration is provided in which the λ / 4 plate 6 and the birefringent optical element 7 are provided between the projection lens 8 and the color combining means.

With the above configuration, in the second embodiment,
A projection image having three times the pixel density of the first embodiment is obtained on the screen, and the pixel opening of the extraordinary ray overlaps on the black matrix 9 which looks clearly mosaic only with ordinary rays. Therefore, the black matrix 9 in the vertical direction is almost invisible, and the image quality is significantly improved. However, in the second embodiment, the λ / 4 plate 6 is regulated so that the optical axis of the birefringent optical element 7 is shifted in the vertical direction. Further, in principle, the black matrix of the extraordinary ray sometimes overlaps with the pixel opening of the adjacent ordinary ray. However, since there is basically no light, no problem occurs.

[0021]

As described above, according to the present invention, it is possible to provide a projection type image display apparatus in which a black matrix which clearly looks like a mosaic is almost invisible and the image quality is significantly improved. it can. Further, by using an inexpensive liquid crystal panel with a small number of pixels, it is possible to provide a projection-type image display device in which the black matrix is made inconspicuous and the image quality is improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment.

FIG. 2 is a screen image diagram of the first embodiment.

FIG. 3 is a configuration diagram of a second embodiment.

FIG. 4 is a conceptual diagram showing a basic configuration of a conventional projection display device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light source lamp 2 concave reflecting mirror 3 integrator lens 4 field lens 5 liquid crystal light valve 6 λ / 4 plate 7 birefringent optical element 8 projection lens 9 black matrix 10 total reflection mirror 11 dichroic mirror 12 dichroic prism 13 relay lens

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G03B 33/12 G03B 33/12 H04N 5/74 H04N 5/74 K

Claims (3)

[Claims] A light source unit that emits white light in one direction;
A modulation unit having a dot matrix type liquid crystal light valve that modulates a light beam and performs image display according to an input signal;
A projection lens for enlarging and projecting the modulated light beam onto a screen, and a λ / 4 plate on the modulation means side between the modulation means and the projection lens, and a non-polarized incident light beam on the projection lens side. A projection-type image display device, comprising: a birefringent optical element that splits an ordinary ray and an extraordinary ray having polarization planes perpendicular to each other. 2. A light source unit for emitting white light in one direction;
Color light separating means for separating light from the light source into three color lights of red, blue and green, and a liquid crystal for modulating polarized light contained in a light beam from the color light separating means to display an image according to an input signal A modulating means having a light valve, a color light synthesizing means for synthesizing a modulated light beam modulated by the modulating means, a projection lens for enlarging and projecting the modulated light beam onto a screen, and the color light synthesizing means A λ / 4 plate on the side of the color light combining means between the lens and the projection lens, and a birefringent optic on the projection lens side for splitting unpolarized incident light into an ordinary ray and an extraordinary ray having polarization planes perpendicular to each other. A projection-type image display device comprising: an element; 3. A dichroic prism is used for a color light combining means, and a λ / 4 is provided from the dichroic prism.
3. The projection type image display device according to claim 2, wherein the polarization direction of the color light traveling toward the plate is regulated so as to be the same for red, blue and green.