JP2001117087A - Liquid crystal display device and liquid crystal projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which displays a picture with a high contrast ratio and a liquid crystal projector utilizing it by ensuring an excellent black display with a simple construction. SOLUTION: The liquid crystal display device is constructed with an incident light side polarizing plate P1, a transmissive liquid crystal panel LP, a quarter- wave plate WP and a light emitting side polarizing plate P2 equipped along the optical path in a state that turn enables the rotation of the quarter-wave plate WP and the light emitting side polarizing plate P2 around the center line AX which is vertical to the respective light incident or emitting plane. Elliptically polarized light is transformed into linearly polarized light by controlling the optical rotation with the quarter-wave plate WP and the linearly polarized light is completely extinguished by controlling the optical rotation with the light emitting side polarizing plate P2.

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 and a liquid crystal projector using the same.

[0002]

2. Description of the Related Art FIG. 5 shows a liquid crystal display device using a TN (Twisted Nematic) type liquid crystal. The main components of this device are two polarizers (P1, P1) whose transmission axes (TX, polarization axes) are orthogonal.
2) and a transmissive liquid crystal panel (LP) disposed therebetween. The liquid crystal panel (LP) has liquid crystal (L) sealed between a pair of glass substrates (G1, G2), and applies a voltage to the liquid crystal (L) on the inner surface of each glass substrate (G1, G2). Transparent electrodes (not shown) are provided. The orientation state of the liquid crystal molecules (M) and the polarization state at each position in the optical path are as shown in FIG. 5A when the voltage is off, and as shown in FIG. 5B when the voltage is on.

[0003] As shown in FIG.
Although the major axis direction of (M) is parallel to the glass substrates (G1, G2), the liquid crystal molecules (M) near one glass substrate (G1) and the liquid crystal molecules near the other glass substrate (G2) In the molecule (M), the major axis directions are orthogonal to each other. That is, liquid crystal panel (LP)
When no voltage is applied to the two glass substrates (G
1, G2), the liquid crystal molecules (M) take a twisted arrangement. The linearly polarized light transmitted through the entrance-side polarizing plate (P1) has a polarization direction of 90 degrees in the liquid crystal panel (LP), similar to the twist of the liquid crystal molecules (M).
Rotate the liquid crystal panel (LP). LCD panel
The linearly polarized light that has exited (LP) can pass through the exit-side polarizing plate (P2), so that white light is displayed by the transmitted light (normally white type).

When a voltage is applied to the liquid crystal panel (LP), the liquid crystal molecules (M) are oriented vertically to the glass substrates (G1, G2). As a result, a change occurs in birefringence (that is, phase difference), and light emitted from the liquid crystal panel (LP) changes from linearly polarized light to elliptically polarized light. Accordingly, the output side polarizing plate (P
The light transmittance for 2) decreases, and the display turns black. The relationship between the voltage and the transmittance is shown by the solid line in FIG. As can be seen from FIG. 4, the larger the applied voltage, the more the liquid crystal panel
(LP) has a low transmittance. When a sufficiently large voltage is applied to the liquid crystal panel (LP), almost all of the liquid crystal molecules (M) are oriented perpendicular to the glass substrates (G1, G2), so that the liquid crystal molecules (M) show isotropic properties, Almost all light is absorbed by the exit-side polarizing plate (P2).

However, it is actually impossible to sufficiently increase the applied voltage because of the relationship with the corresponding drive circuit. In addition, a sufficiently large voltage is applied to the LCD panel.
Even when subjected to (LP), the liquid crystal molecules (M) cannot be oriented perpendicularly to the glass substrates (G1, G2) at the interface of the glass substrates (G1, G2), so that they are shown in FIG. Thus, the light emitted from the liquid crystal panel (LP) is slightly elliptically polarized light. Since the exit-side polarizing plate (P2) cannot completely cut the elliptically polarized light, the transmittance does not become zero as shown by the solid line in FIG. 4, and black floating occurs.

[0006]

The brightness of a liquid crystal projector has been dramatically improved in recent years, but the black floating when displaying black on a screen has become a problem. If the illuminance ratio between white and black (contrast ratio) is the same as before, the illuminance of black increases as the illuminance increases,
Black cannot be recognized as black. As one method of increasing the contrast ratio, a method of adjusting the inclination angle of the transmission axis of the incident side polarizing plate or the exit side polarizing plate so as to make the darkest is proposed in Japanese Patent Application Laid-Open No. 5-188344. I have. However, since elliptically polarized light is emitted from the liquid crystal panel (LP), it cannot be completely extinguished as described above.

Japanese Patent Application Laid-Open No. Hei 5-323331 proposes a liquid crystal display device provided with a phase difference correction plate between a polarizing plate and a liquid crystal panel for correcting the optical anisotropy of liquid crystal with respect to incident light. ing. However, in this device, the phase difference to be corrected must be known,
Further, it cannot cope with variations in liquid crystal panels. Further, if the relative angle between the phase difference correction plate and the liquid crystal panel or the polarizing plate is not accurate, the effect cannot be sufficiently exhibited.

The present invention has been made in view of such circumstances, and a liquid crystal display device capable of displaying an image with a high contrast ratio by realizing good black display with a simple configuration and a liquid crystal display device having the same. An object of the present invention is to provide a liquid crystal projector using the same.

[0009]

In order to achieve the above object, a liquid crystal display device according to a first aspect of the present invention comprises, in order of an optical path, an incident side polarizing plate, a transmission type liquid crystal panel, a quarter wavelength plate, A light-emitting side polarizing plate, wherein the １ ／ wavelength plate and the light-emitting side polarizing plate are configured to be rotatable about a perpendicular to an incident surface or a light emitting surface, respectively. It is characterized by.

A liquid crystal projector according to a second aspect of the present invention provides a liquid crystal display device according to the first aspect of the present invention, a light source for emitting light incident on the incident side polarizing plate, and an image projection using the light emitted from the exit side polarizing plate. And a projection lens for performing the operation.

A liquid crystal projector according to a third aspect of the present invention is the liquid crystal projector according to the second aspect of the present invention, further comprising an optical path between the light source and the incident side polarizing plate, the incident light being converted into three color lights of three primary colors RGB. A color separation system for performing color separation, wherein three primary colors RGB are provided in an optical path between the emission-side polarizing plate and the projection lens;
A color combining system for combining the three color lights.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid crystal display device and a liquid crystal projector embodying the present invention will be described with reference to the drawings. In the above-described conventional example (FIG. 5) and the embodiments, the same portions or corresponding portions are denoted by the same reference numerals, and redundant description will be appropriately omitted.

FIG. 1 shows an embodiment of the liquid crystal display device according to the present invention. This liquid crystal display device includes, in the order of optical paths, an incident-side polarizing plate (P1), a transmission-type liquid crystal panel (LP), a quarter-wave plate (WP), and an output-side polarizing plate (P2). I have. 1 /
The four-wavelength plate (WP) and the outgoing side polarizing plate (P2) have the optical axis (AX)
It is configured to be rotatable around. Since a projection type liquid crystal display device is assumed here, the optical axis (AX) serving as the center of rotation corresponds to the optical axis of an optical system including a projection lens and the like. However, since it can be used as a direct-view type liquid crystal display device, the center of rotation may be a perpendicular line to the entrance surface or exit surface of the quarter-wave plate (WP) or the exit-side polarizing plate (P2). .

Horizontal axis (HX) and vertical axis centered on optical axis (AX)
(VX) is set as shown in FIG. Incident side polarizing plate (P1)
Since the transmission axis (TX) is parallel to the horizontal axis (HX), the light transmitted through the incident-side polarizing plate (P1) enters the liquid crystal panel (LP) as horizontal linearly polarized light. Liquid crystal panel (LP)
When the voltage applied to the liquid crystal panel is 0, the light transmitted through the liquid crystal panel (LP) becomes linearly polarized light parallel to the vertical axis (VX). LCD panel
As the voltage applied to the (LP) increases, the light emitted from the liquid crystal panel (LP) changes from vertical linear polarization to elliptically polarized light, and the elliptically polarized light further approaches horizontal linearly polarized light. To go. However, as shown in FIG. 1, the elliptically polarized light is not completely linearly polarized light.

FIG. 2 shows the elliptically polarized light as viewed from the exit surface side of the liquid crystal panel (LP). The angle between the major axis (C1) of the elliptically polarized light and the horizontal axis (HX) is ψ, and the ellipticity angle of the elliptically polarized light is χ. The quarter-wave plate (WP) has its fast axis coincident with the long axis (C1) of the elliptically polarized light (in other words, the slow axis (LX, FIG. 1) is aligned with the short axis (C2) of the elliptically polarized light. The rotation has been adjusted to match}. The quarter-wave plate (W
P) converts the elliptically polarized light into linearly polarized light whose polarization direction (PX) is tilted by ψ + χ counterclockwise with respect to the horizontal axis (HX).
The transmission axis (TX) of the output side polarizing plate (P2) has a horizontal axis (HX).
The rotation is adjusted so that it is at an angle of 90 ° + ψ + 反 counterclockwise from. The output-side polarizing plate (P2) rotated and adjusted in this way completely cuts the linearly polarized light output from the quarter-wave plate (WP). Therefore, the light transmitted through the exit-side polarizing plate (P2) becomes 0, and a complete black display is realized.

The relationship between the voltage and the transmittance in the present embodiment is shown by a broken line in FIG. As can be seen from FIG. 4, the transmittance becomes 0% at an applied voltage of 4.3 V. Therefore, voltage ON
If the applied voltage is sometimes controlled to be 4.3 V or more, it is possible to realize good black display. Further, the linearly polarized light emitted from the liquid crystal panel (LP) when the applied voltage is 0 V is also used for the rotation-adjusted quarter-wave plate (WP) and the emission-side polarizing plate (P).
Although it is affected by 2), the rate of decrease in transmittance relative to the conventional transmittance is negligible. Therefore, when the voltage is OFF
Since white display (for example, an applied voltage of 0 to 2 V) is also good, a beautiful image with a high contrast ratio can be displayed. In addition, the conversion from the elliptically polarized light to the linearly polarized light is performed by adjusting the rotation of the quarter-wave plate (WP), and the complete extinction of the linearly polarized light is performed by adjusting the rotation of the output side polarizing plate (P2). Therefore, it is also effective in achieving a reduction in cost, weight, and size of the device.

1/4 wavelength plate (WP) rotatable as described above
When the light-emitting side polarizing plate (P2) is used, light shielding (that is, black display) for arbitrary elliptically polarized light (that is, arbitrary ψ and χ) can be performed. This means that black display (transmittance 0%) at an arbitrary voltage
Is feasible. For example, when a voltage of 3.5 V is applied only to the liquid crystal panel (LP) having the voltage-transmittance characteristics shown in FIG.
Black display is possible by the rotation adjustment of (P2). This characteristic configuration is applicable not only to an image display device but also to an optical shutter used for optical information processing and optical communication. If applied to an optical shutter, a higher extinction ratio than before can be realized with low voltage driving.

Next, a liquid crystal projector using the liquid crystal display device (FIG. 1) will be described with reference to FIG. In general, there are a direct-view type and a projection type as a display method of a liquid crystal display. The liquid crystal display described here is a projection type liquid crystal display device, that is, a liquid crystal projector. The main components of this LCD projector are the light source lamp (1);
A reflector (2); an integrator optical system comprising first and second lens arrays (4, 5) and a superimposing lens (6); a dichroic mirror (8, 10) for RGB color separation; ), Three incident-side polarizers (16R, 16G, 16B);
Three liquid crystal panels (17R, 1R) corresponding to the liquid crystal panel (LP)
7G, 17B); three rotatable quarter-wave plates (18R, 18G, 18B) corresponding to the quarter-wave plate (WP);
(P2), three rotatable exit-side polarizing plates (19R, 19R)
G, 19B); a cross dichroic prism (20); and a projection lens (21).

The light source lamp (1) is, for example, an ultra-high pressure mercury lamp or a metal halide lamp, and its light emission point is located at the focal position of the reflector (2) whose reflecting surface is a paraboloid of revolution. The light emitted from the light source lamp (1) is
(2) becomes almost parallel light, UV-IR cut filter
After unnecessary light is removed in (3), the light enters the integrator optical system including the first and second lens arrays (4, 5) and the superimposing lens (6). The first lens array (4) is a liquid crystal panel
(17R, 17G, 17B) is formed by arranging rectangular lens cells substantially similar to each other in a two-dimensional array. Second lens array
In (5), the same number of cells as the cells of the first lens array (4) are arranged in an array. Second lens array (5)
The cells of the first lens array (4) are superimposed and formed on the liquid crystal panels (17R, 17G, 17B) by the cells of (1) and the superimposing lens (6). Thereby, the liquid crystal panels (17R, 17G, 17B) are uniformly illuminated.

The light emitted from the integrator optical system has its optical path bent by a total reflection mirror (7), and is then subjected to color separation by dichroic mirrors (8, 10). The dichroic mirror (8, 10) is a color separation system that separates incident light into three color lights of three primary colors RGB. That is, the color separation is performed by the dichroic mirror (8) transmitting the R light and reflecting the BG light, and the dichroic mirror (10) transmitting the B light and reflecting the G light. The G light is reflected by the dichroic mirror (10) and then enters the field lens (15G), while the R light is reflected by the mirror (9) and the B light is reflected by the mirrors (12 and 14). Thereafter, the light enters each of the field lenses (15R, 15B). Since the color light B has a different optical path length from the color light RG, the correction is performed by the first and second relay lenses (11, 13).

The incident-side polarizing plates (16R, 16G, 16
B) Each field lens (15R, 15R
(G, 15B) has a power determined so that the illumination light illuminates the entire area of the liquid crystal panel (17R, 17G, 17B) at a uniform angle, and can efficiently guide the light to the projection lens (21). ing. The 1/4 wavelength plates (18R, 18G, 18B) and the output side polarizing plates (19R, 19G, 19B) of each of the RGB colors are rotatable about the optical axis (AX). That is, as described above, the 波長 wavelength plate (18R, 18G, 18B) and the output side polarizing plate (19R, 19R) are set so that the transmittance becomes 0 when a voltage is applied to the liquid crystal panel (LP).
G, 19B) are each configured to be rotationally adjustable. As a matter of course, quarter-wave plates (18R, 18G, 18B) having a wavelength corresponding to the light of each color of RGB are used.
Furthermore, the incident side polarizing plates (16R, 16G, 16B) are also adjusted so that the transmission axis (TX, FIG. 1) matches the orientation direction of the liquid crystal molecules (M, FIG. 5).
You may comprise so that rotation is possible with respect to an optical axis (AX).

The light modulated by the liquid crystal panels (17R, 17G, 17B) of each color of RGB is combined by the cross dichroic prism (20) so that the three colors are aligned on the same optical axis (AX).
The cross dichroic prism (20) is formed by joining four right-angle prisms, and is a color combining system for combining three primary colors of RGB light. The reflecting surface (20R) is coated with a dichroic film that reflects R light and transmits G light. The reflecting surface (20B) is coated with a dichroic film that reflects B light and transmits G light. Thus, the three colors of light are combined, and a color image is projected and displayed on a screen (not shown) by the projection lens (21).

[0023]

As described above, according to the present invention, an excellent black display is realized with a simple structure, which is lower than that of the prior art, so that an image with a high contrast ratio can be displayed.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing one embodiment of a liquid crystal display device.

FIG. 2 is a view for explaining elliptically polarized light formed in an optical path of the liquid crystal display device of FIG.

FIG. 3 is a plan view showing an optical configuration of a liquid crystal projector using the liquid crystal display device of FIG.

4 is a graph showing voltage-transmittance characteristics in the embodiment of FIG. 1 and the conventional example of FIG. 5;

FIG. 5 is a perspective view schematically showing the operation principle of a conventional liquid crystal display device.

[Explanation of symbols]

 LP… Liquid crystal panel P1… Incoming side polarizing plate P2… Outgoing side polarizing plate WP… 1/4 wavelength plate AX… Optical axis HX… Horizontal axis VX… Vertical axis LX… Slow axis C1… Long axis (fast axis) C2 … Short axis PX… Polarization direction TX… Transmission axis 1… Light source lamp (light source) 2… Reflector 3… UV-IR cut filter 4… First lens array 5… Second lens array 6… Superimposed lens 7… Total reflection mirror 8 … A dichroic mirror for R transmission (color separation system) 9… a mirror for R reflection 10… a dichroic mirror for B transmission (color separation system) 11… first relay lens 12… mirror for B reflection 13… second relay Lens 14: Mirror for B reflection 15R: Field lens for R 16R: Incident-side polarizing plate for R 17R: Liquid crystal panel for R 18R: 1/4 wavelength plate for R 19R: Exit-side polarizing plate for R 15G… Field lens for G 16G… Incoming side polarizing plate for G 17G… Liquid crystal panel for G 18G… G 1/4 wavelength plate 19G ... Emission side polarizing plate for G 15B ... Field lens for B 16B ... Incoming side polarizing plate for B 17B ... Liquid crystal panel for B 18B ... 1/4 wavelength plate for B 19B ... B Outgoing side polarizing plate 20… Cross dichroic prism (color combining system) 20R… Reflecting surface for R 20B… Reflecting surface for B 21… Projection lens

Claims (3)

[Claims] 1. A liquid crystal display device comprising at least an incident side polarizing plate, a transmission type liquid crystal panel, a 波長 wavelength plate, and an emission side polarizing plate in the order of optical paths, wherein the 波長 wavelength A liquid crystal display device, wherein the plate and the emission-side polarizing plate are configured to be rotatable about a perpendicular line of an incidence surface or an emission surface, respectively. 2. The liquid crystal display device according to claim 1, further comprising: a light source for emitting light to be incident on the incident-side polarizing plate; and a projection lens for projecting an image with the light emitted from the emitting-side polarizing plate. A liquid crystal projector characterized by the following. 3. An optical path between the light source and the incident-side polarizing plate, further comprising a color separation system that separates incident light into three color lights of three primary colors RGB. 3. The liquid crystal projector according to claim 2, further comprising a color synthesizing system for synthesizing three color lights of three primary colors RGB in an optical path between the projection lens and the projection lens.