JP3452843B2 - Image display device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a projection type image display device for displaying an image by magnifying and projecting an image of the liquid crystal display device by a projection lens or the like.

[0002]

2. Description of the Related Art A projection type image display device uses an image display element as an optical switching element and enlarges and projects an image on the image display element onto a screen by a projection optical system. The image display device includes a transmissive image display device that transmits and projects light and a reflective image display device that reflects and projects light.

In a projection type image display device using a transmissive image display element, a path of illumination light to the image display element and a path through which the transmitted light modulated by the image display element is projected on a screen through a projection lens. And are placed in different areas. On the other hand, in the projection type image display device using the reflection type image display element, the path of the illumination light and the path of the reflected light modulated by the image display element are partially or mostly arranged in the same region. Therefore, the projection type image display device using the reflection type image display device can reduce the space occupied by the device itself.

Further, a transmissive image display device is generally provided with a driving transistor in each pixel. A light shielding layer is provided on the signal line to the drive transistor and the pixel in order to prevent the drive transistor from being irradiated with light and changing the transistor characteristics. This light-shielding layer necessarily reduces the aperture ratio of the pixel. On the other hand, in the reflection type image display element, generally, as shown in FIG. 4, the reflection type pixel electrode 42 can be formed on the TFT 41 as a switching element, so that the reflection electrode surface also serves as a light shielding layer. The aperture ratio of the pixel is larger than that of the transmissive type.

As a projection type image display device using a reflection type image display element, for example, Japanese Patent Laid-Open No. 63-39294 discloses a video image display device having an optical system for separating and combining polarized light from a light source. A projection device is disclosed. Further, for example, from the same inventor of the present invention, Japanese Patent Application No. 10-318749 discloses a projection-type image display device having an optical system that divides a pupil region of a projection lens group to separate incident light and emitted light. It is disclosed.

First, the video projection apparatus disclosed in the above Japanese Patent Laid-Open No. 63-39294 will be described below.

FIG. 5 is a schematic diagram showing a schematic configuration of the video projection device. The video projection device includes a light source 21, a collimating lens 22 that collimates light from the light source, and a polarizing beam splitter (hereinafter, referred to as PBS) 2
3, a color separation prism 24, liquid crystal display elements 25, 26 and 27 for displaying images of respective color components of blue, red and green, and a reflecting mirror 28 provided on each of the liquid crystal display elements 25, 26 and 27.
29.30 and a projection lens 32.

The light emitted from the light source 21 passes through the collimator lens 22 to become substantially parallel light, enters the PBS 23, and is separated into two linearly polarized light components orthogonal to each other. Of the separated light, the light reflected by the PBS 23 enters the color separation prism 24.

The color separation prism 24 is the first prism 24.
A, a second prism 24B, and a third prism 24C. The light that has entered the color separation prism 24 first enters the first prism 24A, the blue component is separated by the dichroic interference thin film, and is guided to the liquid crystal display element 25 that displays an image of the blue component. Light other than the blue component is incident on the second prism 24B, the red component is separated by the dichroic interference thin film, and is guided to the liquid crystal display element 26 that displays an image of the red component. The remaining green component light enters the third prism 24C and then enters the liquid crystal display element 27 that displays a green component image.

The light of each color component incident on each of the liquid crystal display elements 25, 26 and 27 is reflected by the reflecting mirrors 28, 29 and 30 and transmitted through each of the liquid crystal display elements 25, 26 and 27 again. At this time, the light of each color component transmitted through each liquid crystal display element 25, 26, 27 again becomes
The polarization direction is modulated according to the 27 image signal.

The light of each color component which has been modulated in the polarization direction is
It again enters the color separation prisms 24 and is combined. The combined light is incident on the PBS 23, and only the polarization component of the light whose polarization direction has been modulated passes through the PBS 23,
The image is projected onto a screen (not shown) by the projection lens 32.

Next, the projection type image display device disclosed in the above-mentioned Japanese Patent Application No. 10-318749 will be described below.

FIG. 6 is a schematic diagram showing a schematic configuration of the projection type image display device. The projection-type image display device includes a light source unit including a light source 61 and a parabolic mirror 62, a lens 63 that collects light from the light source unit, an illumination light incident mirror (illumination light introducing unit) 64, and a dichroic mirror. 66R / 6
6B, polarizing plates 67R / 67G / 67B, and λ / 4 plate
(Retardation plate) 68R / 68G / 68B and liquid crystal display elements 69R / 69G / that display images of red, green and blue color components
69B, a projection lens group 65, and a screen (not shown).

The substantially parallel light L1 emitted from the light source section is converted into a condensed light L2 by the condensing lens 63, and the projection lens group 6
The light enters from the side surface of the projection lens group 65 toward the illumination light incident mirror 64 arranged at the pupil position of 5. Projection lens group 6
5 is a liquid crystal display element 69R / 69G /
The panel side lens group 65P on the 69B side and the screen side lens group 65S on the screen side of the pupil position.
It consists of and. The light reflected by the illumination light incident mirror 64 passes through the panel side lens group 65P,
It is incident on the dichroic mirrors 66R and 66B.

The focal length of the condenser lens 63 is
The light after passing through the panel side lens group 65P is designed to be substantially parallel light L3. Further, the illumination light incident mirror 64 is disposed in one of the divided pupil areas obtained by dividing the pupil area of the projection lens group 65 into two, and the panel side lens group 65P.
The light emitted after passing through is adjusted so as to reach the liquid crystal display element 69G arranged on the center line of the projection lens group 65.

The light incident on the dichroic mirror 66R is reflected only by the red component. Reflected red light LR
After passing through the polarizing plate 67R and the λ / 4 plate 68R,
It is incident on the liquid crystal display element 69R.

Of the light transmitted through the dichroic mirror 66R, the blue component light is the dichroic mirror 66B.
Reflected by. The reflected blue light LB passes through the polarizing plate 67B and the λ / 4 plate 68B and then enters the liquid crystal display element 69B.

The green light LG transmitted through the dichroic mirror 66B is incident on the liquid crystal display element 69G after passing through the polarizing plate 67G and the λ / 4 plate 68G.

The color lights LR, LG, and LB incident on the liquid crystal display elements 69R, 69G, and 69B are modulated in the polarization direction according to image information and reflected. The respective color lights LR, LG, and LB reflected thereafter are respectively λ / 4 plate 68R.
The light passes through 68G / 68B and polarizing plates 67R / 67G / 67B and is combined by the dichroic mirrors 66R / 66B to become projection light L4. The projection light L4 passes through the panel-side lens group 65P and once converges in the divided pupil area of the projection lens group 65 where the illumination light entrance mirror 64 is not arranged, and then the projection-side light group The light passes through 65S and is projected on a screen (not shown).

A method of constructing the λ / 4 plate 68R / 68G / 68B in a multi-layer structure is also shown in order to make the band wide.

[0021]

In the above video projection apparatus, PBS which switches the optical path depending on the polarization direction is essential as a constituent element. Generally, PB
S is composed of a glass block, and such a PBS has a large volume and weight and is expensive. Further, due to the birefringence of the glass that constitutes the PBS, the polarization direction of the incident light is disturbed, and it is difficult to switch the optical path accurately, and the quality of the projected image and the contrast ratio are degraded. Was there.

On the other hand, in the above projection type image display device, PBS is used.
Although the above problem due to the PBS is solved by not using, the λ / 4 plate is necessary in order to prevent the surface reflected light of each liquid crystal display element from reaching the screen and lowering the contrast ratio. . However, since the PBS is not used, it is necessary to make light incident on the liquid crystal display element in an oblique direction in order to switch the optical paths of incident light and reflected light in the liquid crystal display element. Since the performance of the λ / 4 plate greatly affects the quality of black display, that is, the performance of the contrast ratio, it is essential to widen the band of the λ / 4 plate. Therefore, in the above-mentioned projection type image display device, the λ / 4 plate has a wide viewing angle and a wide band due to the multi-layered retardation plate.

However, in reality, since the incident light is obliquely incident on the liquid crystal display element, the phase difference of the liquid crystal display element between the light incident from the front and the light incident from the oblique direction. Due to the difference in size, the contrast ratio decreases for oblique light. Further, even when a voltage is not applied to the liquid crystal molecules in which no phase difference occurs, the liquid crystal molecules slightly tilt and have a tilt angle, so that a slight phase difference occurs even for light from the front. Therefore, a liquid crystal display element actually requires a retardation plate for compensating for those retardations. That is, in order to prevent the contrast ratio from being lowered by the λ / 4 plate with respect to oblique light, the λ / 4 plate is multi-layered and the phase difference plate for compensating the phase difference for the oblique light of the liquid crystal display element is inserted. There is a need to.

On the other hand, in the above-mentioned multi-layered retardation plate, when the retardation value of each layer and the angle of the optical axis change, the overall contrast ratio is greatly affected. At the time of mass production, manufacturing errors occur in the retardation value of each layer and the angle of the optical axis. Therefore, as the number of layers increases, the variation in the overall performance increases, which leads to an increase in cost.

An object of the present invention is to provide an image display device having a low contrast ratio and a good contrast ratio and image quality.

[0026]

In order to solve the above problems, an image display device of the present invention is provided with a polarization regulating means for regulating the polarization direction of light from a light source, a birefringent element, and light from the light source. and a reflection type liquid crystal display device that modulates the said reflection
The principal ray of the incident light is inclined with respect to the normal direction of the liquid crystal display device.
The light reflected by the reflective liquid crystal display element at the time of white or black display in the image display device that is incident on the same direction is the same or orthogonal to the polarization direction of the light incident on the polarization control unit in the polarization control unit. Control the birefringence of the reflective liquid crystal display element and the birefringent element , and
The refraction element is composed of a plurality of birefringence elements,
Of the refraction elements, the one closest to the reflection type liquid crystal display element
The optical axis direction of the birefringent element and the liquid crystal of the reflective liquid crystal display element.
It is characterized in that the crystal orientation directions are substantially the same .

Further, the image display device of the present invention includes the plurality of
The birefringent element is the closest to the reflective liquid crystal display element.
Optical axis direction of folding element and optical axis direction of other birefringent elements
Is characterized by different .

The operation of the above configuration will be described below.

According to the structure of the present invention, the light reflected by the image display element is made to be the same or orthogonal to the polarization direction of the light passing through the polarization regulating means during the white or black display as described above. Since the birefringence of the image display element and the birefringence element is designed, the contrast ratio of the liquid crystal image display device is improved.

Further, as described above, by aligning the alignment direction of the liquid crystal of the liquid crystal display element with the optical axis direction of the birefringent element closest to the image display element among the plurality of birefringent elements, The phase difference compensation of the liquid crystal panel can also be performed by the birefringent element closest to the image display element among the plurality of birefringent elements. Therefore, the phase difference plate for compensating the phase difference for the oblique light of the liquid crystal panel becomes unnecessary. for that reason,
Since the number of retarders can be reduced as a whole,
Factors of variation during manufacturing are reduced. Therefore, variations in the contrast ratio of the system at the time of manufacturing are also reduced, leading to cost reduction.

Furthermore, by irradiating the liquid crystal display element with the incident light obliquely as described above, the incident light and the reflected light can be separated without using the PBS. Therefore, PBS
It is possible to provide a high-contrast liquid crystal image display device with good display quality by using the liquid crystal image display device configured to prevent the deterioration of the contrast ratio against oblique light. it can.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a schematic diagram showing a schematic configuration of a liquid crystal image display device according to an embodiment of the present invention. The liquid crystal image display device includes a light source section including a light source 1 and a parabolic mirror 2, a condenser lens 3 for condensing light from the light source section, a polarizing plate 4, a multilayer retardation plate 5, and a reflection type. A liquid crystal panel 6, a projection lens 7, and a screen (not shown) are provided.

In this embodiment, the light source 1 is 250
A metal halide lamp with W and an arc length of 3 mm is used.
Besides, a halogen lamp, a xenon lamp, or the like can be used as the light source 1. On the back of the light source 1,
A parabolic mirror 2 for emitting light from a light source as substantially parallel light is arranged.

The substantially parallel light L1 emitted from the light source unit becomes a condensed light L2 by the condenser lens 3, passes through the polarizing plate 4 and the multilayer retardation plate 5, and then enters the reflection type liquid crystal panel 6 from an oblique direction. The condensed light L2 that has entered the reflective liquid crystal panel 6 has its polarization direction modulated according to image information and is reflected. After that, the light specularly reflected by the reflective liquid crystal panel 6 again passes through the multilayer retardation plate 5 and the polarizing plate 4, and also passes through the projection lens 7 to reach a screen (not shown).
In the present embodiment, the condenser lens 3 is designed to be condensed light, but it may be configured to be substantially parallel light.

As the reflection type liquid crystal panel 6, 1.3
Type S-VGA (800 x 600 dots, pixel pitch 33
× 33 μm), and the display mode is a birefringence mode in which an image is displayed by controlling the polarization direction of incident light by utilizing the birefringence of liquid crystal.

The birefringence mode includes a vertical alignment type in which liquid crystal molecules are aligned perpendicularly to the panel surface and a horizontal alignment type in which liquid crystal molecules are aligned parallel to the panel surface. Although a birefringence mode liquid crystal panel is used in the present embodiment, a twisting mode liquid crystal panel utilizing the optical rotatory power of liquid crystal may be used.

The horizontal alignment type exhibits a birefringence even in a no-voltage state and is used in a normally black state in which the alignment axis of liquid crystal molecules and the transmission axis of a polarizing plate are set to an appropriate angle to obtain a black state. However, if the thickness of the liquid crystal layer is non-uniform during this black display, the polarization state of the reflected light will fluctuate accordingly, resulting in uneven contrast.

On the other hand, the vertical alignment type does not exhibit birefringence in a no-voltage state, but when a voltage is applied, it exhibits birefringence according to the applied voltage. That is, it is used in a normally white state in which white display is performed in the no-voltage state. So in this case,
If the thickness of the liquid crystal layer is not uniform, the polarization state of the reflected light of white display will vary accordingly, so that the effect of the nonuniformity of the thickness of the liquid crystal layer on the contrast ratio is relatively small.

In this embodiment, the liquid crystal image display device is
The above vertical alignment type is used as the reflection type liquid crystal panel 6.

FIG. 2 is an enlarged view of a portion in which the polarizing plate 4, the multilayer retardation plate 5 and the reflective liquid crystal panel 6 are arranged.

The design of the multilayer retardation plate 5 will be described below.

First, in black display, when the condensed light L2 is reflected by the reflective liquid crystal panel 6, its polarization direction is not modulated. Therefore, when the condensed light L2 enters the multilayer retardation plate 5, is reflected by the reflective liquid crystal panel 6, and is transmitted through the multilayer retardation plate 5 again, the polarization plane of the condensed light is rotated by 90 degrees. Design a multilayer retarder.

Further, a specific method of designing the multilayer retardation plate will be described.

In this embodiment, first, "" The Proceed
ings of the Indian Academy of Sciences ", Vol.XLI,
No. 4, Sec. A, (1955) '', "ACHROMATIC COMBINATIONS
According to the calculation method described in "OF BIREFRINGENT PLATES", a wide band, wide viewing angle λ / 4 plate was designed with three layers. In FIG. 2, the retardation values and the directions of the fast axes of the retardation plates of the respective layers are such that the transmission axis of the polarizing plate 4 is arranged at 90 degrees, and the retardation plate 51 is 225 nm at 225 nm in order from the polarizing plate side.
, The phase difference plate 52 is 225 nm at 35 degrees, and the phase difference plate 53
Became 113 degrees at 102 degrees. Arranging the transmission axis of the polarizing plate 4 at 90 degrees means that it is perpendicular to the plane containing the principal rays of the incident light and the emitted light. Also,
The retardation value of each retardation plate is such that the best characteristics are obtained at the center wavelength of 550 nm in order to obtain good characteristics in the visible light region.

Here, the multi-layer retardation plate 5 is the retardation plate 5
1, the phase difference plate 52 and the phase difference plate 53. For each retardation plate, a birefringent element such as a crystal or a liquid crystal element can be used, and any phase difference plate may be used. The phase difference plate 51 and the phase difference plate 52 are each λ /
These are two plates, and when these are combined with the phase difference plate 53, the band is broadened, that is, the phase difference of approximately λ / 4 is approximated even for wavelengths deviated to some extent from the central wavelengths of red, green, and blue. Can be provided, and the display contrast can be improved.

Next, although the reflective liquid crystal panel 6 used in the present embodiment is vertically aligned, there is slight retardation even when no voltage is applied because the liquid crystal molecules are slightly inclined. Therefore, the retardation value of the retardation plate 53 is subtracted from the retardation value due to the liquid crystal molecules in the reflective liquid crystal panel 6 having a slight inclination. Therefore, the multilayer retardation film 5 is transmitted through the polarizing plate 4.
When the light transmitted through the liquid crystal layer 43 of the reflection type liquid crystal panel in FIG. 4 reaches the reflection electrode surface 42, the phase difference of the liquid crystal layer 43 of the multilayer retardation plate 5 and the reflection type liquid crystal panel 6 is combined. Is λ / 4, which means that it is in a completely circularly polarized state.

Incidentally, in an optical system using a reflection type liquid crystal panel having a polarizing plate, generally, in order to make a crossed Nicol state between incident light and emitted light at the time of black display, a transmission axis or an absorption axis of the polarizing plate is used. Are arranged at 0 degrees or 90 degrees. Therefore, when the phase difference plate is not provided, light in the polarization direction of 0 degree direction or 90 degree direction is incident on the reflection type liquid crystal panel, so that the alignment direction of liquid crystal molecules is generally 45 degrees. Will be placed. However, in the case of the structure having the retardation plate, since the circularly polarized light is incident on the reflection type liquid crystal panel, the alignment direction of the liquid crystal molecules can be freely arranged at any angle.

Therefore, in the present embodiment, the retardation plate 53
By making the fast axis of and the alignment direction of the liquid crystal molecules coincide with each other, the polarization state on the reflection electrode surface 42 of the reflection type liquid crystal panel can be made completely circularly polarized. As a result, when the reflected light is transmitted through the multilayer retardation plate 5 again, the reflected light can be completely set to 90 degrees with respect to the plane of polarization of the incident light.

On the other hand, in the present embodiment, in the reflection type liquid crystal panel 6, only the retardation value is compensated by the tilt of the liquid crystal molecules, but the reflection type liquid crystal panel 6 compensates the phase difference with respect to the oblique light. When the retardation plate of 1 is arranged, it is preferable to arrange so that the fast axis of the retardation plate coincides with the fast axis of the retardation plate 53. In this case, the retardation value of the retardation plate for compensating the phase difference with respect to the light from the oblique direction of the reflective liquid crystal panel 6 is added to the retardation plate 53 to design the oblique angle of the reflective liquid crystal panel 6. The phase difference plate for compensating for the phase difference with respect to the light from is unnecessary.

In this embodiment, an example in which only one reflective liquid crystal panel 6 is used has been described, but a plurality of reflective liquid crystal panels are formed by inserting an optical system for color separation / synthesis in front of the reflective liquid crystal panel. It goes without saying that it can be configured by using a panel.

As described above, in the liquid crystal image display device according to the present embodiment, in the same optical system, when the retardation plate is not provided, when the retardation plate is a single layer, the retardation plate is the present embodiment. As shown in FIG. 3, the contrast ratio according to the present embodiment is about 5 times that in the case without the retardation plate, compared with the case where the retardation plate is a single layer, as shown in FIG. It's about four times.

Therefore, it is possible to provide a high-contrast image having better image quality than that of the conventional projection type image display device, and since the number of retardation plates can be reduced, the variation in performance at the time of manufacture is reduced, It leads to cost reduction.

[0054]

As described above, the liquid crystal image display device according to the present invention includes a polarization regulating means for regulating the polarization direction of the light from the light source, a birefringent element, and a reflection type liquid crystal for modulating the light from the light source. A reflective liquid crystal display device, comprising:
In an image display device in which a chief ray of incident light is inclined with respect to the line direction, the light reflected by the reflective liquid crystal display element during white or black display, in the polarization control means, the polarization control means, The birefringence of the reflective liquid crystal display element and the birefringent element is controlled so as to be the same or orthogonal to the polarization direction of the incident light , and a plurality of the birefringent elements are provided.
Of the plurality of birefringent elements
Optical axis of the birefringent element closest to the reflective liquid crystal display element
Direction and the alignment direction of the liquid crystal of the reflective liquid crystal display element are roughly
It has the same structure.

As a result, the contrast ratio of the liquid crystal image display device is improved, so that the image quality of the image can be improved.

Further , for example, there is an effect that a retardation plate for compensating a retardation for oblique light of the liquid crystal panel becomes unnecessary. In addition, since the number of retardation plates can be reduced as a whole, variations in the contrast ratio of the system at the time of manufacturing are also reduced, leading to cost reduction.

[0057] Further, by irradiating the incident light from oblique to the liquid crystal display device, no longer a decrease in display quality due PBS, further despite the use of oblique light, good display quality, high-contrast liquid crystal image There is an effect that a display device can be provided.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of a liquid crystal image display device according to an embodiment of the present invention.

FIG. 2 is an enlarged view showing a portion where a reflective liquid crystal panel, a multilayer retardation plate, and a polarizing plate are arranged in the liquid crystal image display device.

FIG. 3 is an explanatory diagram showing an effect of the liquid crystal image display device when a multilayer retardation plate is used.

FIG. 4 is a cross-sectional view showing a configuration of a reflective liquid crystal panel.

FIG. 5 is a schematic diagram showing a schematic configuration of a conventional video projection device.

FIG. 6 is a schematic configuration diagram showing a conventional projection-type image display device.

[Explanation of symbols]

1 light source 2 parabolic mirror 3 condenser lens 4 Polarizer 5 Multi-layer retarder 6 Reflective liquid crystal panel (reflective image display device) 7 Projection lens 51 ・ 52 ・ 53 Retardation plate constituting multi-layer retardation plate

Continuation of front page (56) Reference JP-A-3-276122 (JP, A) JP-A-9-292610 (JP, A) JP-A-8-262435 (JP, A) JP-A-10-232390 (JP , A) JP-A-11-142836 (JP, A) JP-A-10-206842 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/1335

Claims (2)

(57) [Claims] Comprising a polarization regulating means for regulating the polarization direction of light from 1. A light source, a birefringent element, a reflection type liquid crystal display device for modulating light from a light source, a normal of the reflection type liquid crystal display device Direction of incident light
In an image display device in which light rays are obliquely incident, the light reflected by the reflective liquid crystal display element at the time of white or black display is the same as the polarization direction of the light incident on the polarization regulating means in the polarization regulating means. Alternatively, the birefringence of the reflective liquid crystal display element and the birefringent element is controlled to be orthogonal to each other , and the birefringent element is composed of a plurality of birefringent elements,
Of the multiple birefringent elements, the reflective liquid crystal display element is the most
Close to the optical axis direction of the birefringent element and the reflective liquid crystal surface.
An image display device , wherein the liquid crystal of the display element has substantially the same alignment direction . 2. A reflective liquid crystal display device comprising a plurality of the birefringent elements.
The optical axis direction of the birefringent element closest to the
The image display device according to claim 1, wherein the birefringent elements have different optical axis directions .