JPH0229777A - Liquid crystal light valve device - Google Patents

Abstract

PURPOSE:To display an image high in picture quality and excellent in reproducibility of black and a high contrast ratio by providing a means which changes a direction of polarization by 90 deg. on one surface of a panel part. CONSTITUTION:Liquid crystal 13 is sandwiched between transparent plates 12 and 14 and liquid crystal 15 is sandwiched between transparent plates 14 and 15. The transparent plate 14 is provided with a transistor (TR) for electric field supply and a transparent electrode 18 is formed on the transparent plate 16 so as to apply a voltage to the liquid crystal 15. When S-polarized light is inputted to this light valve, the direction of polarization is changed by 90 deg. by the liquid crystal 13 to generate P-polarized light, which is incident on the liquid crystal 15 from the transparent plate 14. An S-polarizing plate 19 is provided on the output side of this panel part and the panel part enters a P polarization-S polarization normally white state. Consequently, white is reproduced when the level of the input voltage is low and black is reproduced when the level is high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a liquid crystal light valve device that applies voltage to a liquid crystal panel in which a liquid crystal is sandwiched between transparent plates to control the brightness of transmitted light.

(Prior Art) Liquid crystals used in liquid crystal panels and the like have a twisted liquid crystal molecular arrangement, and have the property of converting the polarization direction of light by 90 degrees and transmitting light. Furthermore, it has the property that when a voltage is applied to it, its polarization direction changes. Therefore, if you create a panel with a liquid crystal sandwiched between transparent plates, place polarizing plates on both sides of the panel, and apply a voltage to the liquid crystal,
The amount of transmitted light can be controlled. Can be used for Zunawara light bulbs.

Generally, there are two types of polarized light: S-polarized light and P-polarized light, which has a 90-degree polarization angle different from S-polarized light. Polarizing plates include S-polarized light that transmits S-polarized light, and P-polarized light that transmits P-polarized light. be. Depending on the combination of polarizing plates provided on both sides of the panel, two types of liquid crystal light valves, normally black and normally white, can be obtained. Normally black blocks light without applying an electric field to the liquid crystal, and normally white allows light to pass through without applying an electric field to the liquid crystal. When both sides of the panel have the same polarizing plate, it is normally black, and when different polarizing plates are used, it is normally white. These are shown in FIGS. 2(a) and (b).

In both cases, the input-side polarizing plate 41 is an S-polarizing plate, but the output-side polarizing plate 43 is an S-polarizing plate and II is a P-polarizing plate. Therefore, when the relationship between the brightness and the applied voltage is shown in FIGS. 3(a) and 3(b), as shown in (a), in the case of normally black, the polarization shifts by 90 degrees when no voltage is applied to the liquid crystal 42. Light does not pass through the S polarizing plate 43, and the amount of transmitted light increases as the applied voltage increases.On the other hand, as shown in (b), in the normally white case, light can pass through the P polarizing plate 43 when no voltage is applied. The amount of transmitted light decreases as the applied voltage increases. As a result, the transmitted light becomes S-polarized light, which is the same as the incident light in the case of normally black, and the P polarized light is perpendicular to the incident light in the case of normally white.
It becomes polarized light.

To briefly explain the projection Hffi using this liquid crystal light valve, there are conventionally two types: a single-panel type shown in FIG. 4 and a three-panel type shown in FIG. 5.

The single-plate type shown in FIG. 4 uses one liquid crystal light valve, in which light from a light source 21 is incident on a liquid crystal light valve 24 through a condensing lens 23, and the light transmitted through the liquid crystal light valve 24 by a projection lens 25. It is configured to project the image onto the screen 26. 22 is a reflecting mirror for efficiently utilizing the light [21].

On the other hand, the three-plate type shown in FIG. 5 uses three of the above-mentioned liquid crystal light valves, and the light emitted from the light source device consisting of the light [31 and the reflecting mirror 32] is passed through the condensing lens 33, and the light is passed through the resolving mirror ( prism) 34, R (red) component, G (green) component, B
(Blue) Separates the light into its components and sends each decomposed light to the mirror 35.
LCD light valve 3 for each light reflected by
7 and are combined by a combining mirror 36, and the combined light is projected onto a screen 39 through a projection lens 38.

The difference between the two is whether the light from the light source is used as is or whether it is used after being separated into three colors. In other words, with a single panel type, RGB
Using a liquid crystal light bulb with 3 color filters, 3
The plate type uses a liquid crystal light valve without a filter.

In this way, the three-plate type uses a liquid crystal light valve without a filter, so it has excellent brightness and resolution. Therefore, the current mainstream liquid crystal projection device is this three-panel type projection device.

By the way, in the case of the three-plate type shown in FIG.
It is divided into an R component, a G component, and a B component. Since the R and B components of the light are reflected by the prism 34, most of them are S-polarized light. On the other hand, since the same applies to the combining mirror 36, the polarization direction must be S-polarized light. Therefore, for at least the R component and the 8 component, a normally black liquid crystal light valve must be used as the liquid crystal light valve 37 in which both the incident polarization direction and the output polarization direction are S polarization.

For this reason, normally black liquid crystal light valves have been used in conventional three-panel liquid crystal projection devices.

The light transmission characteristics of normally black and normally white are as explained in FIGS. 3(a) and 3(b). Next, we will discuss the reproducibility of black and white when these are used.

When reproducing white, the former increases the applied voltage and the latter decreases the applied voltage. As is clear from both graphs, normally
In the case of black, the curve is smooth where the signal level (applied voltage) is high, so the reproducibility is good, but with normally white, there are peaks where the signal level is low, so the reproducibility is good. do not have. However, since the human eye is insensitive to changes in high brightness areas, this difference in reproducibility does not pose a problem.

On the other hand, the reproducibility of black is good in normally white because the brightness gradually decreases as the No. 15 level increases, and in normally black, when the signal level is lowered, the brightness decreases once and then increases again. do.

Since humans react sensitively to low luminance, the poor reproducibility of normally black black becomes a problem. In addition, normally black also has a problem in that the contrast ratio, which is calculated by dividing the maximum brightness by the minimum brightness, also becomes low.

Roughly speaking, LCD panels have wavelength-dependent characteristics in that the characteristics at the area where the applied pressure is low (when the liquid crystal is twisted) differ depending on the wavelength of the light. This is due to the correlation between the lobes length (thickness).In other words, a liquid crystal made with a specific thickness for green light cannot completely narrow down the red and blue waves, causing black to turn purple. In other words, the moth, which is supposed to be black, turns purple. This phenomenon is quite noticeable and degrades the quality of the projection. As a means to solve this inconvenience, it is disclosed in Japanese Patent Application Laid-Open No. 60-202423. There is a multi-gap method that can be used.
This is a method of optimizing the gap length of the liquid crystal for red, green, and front, respectively. However, with the current level of technology, it is difficult to control the thickness with an accuracy of 1 to 2 .mu.m, and it is even more difficult to achieve a uniform thickness over the entire screen. If this thickness control is not successful, the peripheral area of the screen! , the black is typical of L black, but the center part tends to be reddish, causing color unevenness, and there is a problem of poor black reproducibility.

Therefore, when configuring a three-panel liquid crystal projection device, problems tend to occur in the reproducibility of -Ei1 black because normally black is used.

(Problems to be Solved by the Invention) Conventionally, when configuring a three-panel type liquid crystal projection device, it is necessary to use six normally black liquid crystal panels, which improves black reproducibility and contrast between one and last. It was unfavorable due to its characteristics.

The present invention has been made to solve these problems, and an object of the present invention is to provide a liquid crystal display device that can display high-quality images with good black reproducibility and a high contrast l-ratio. This is what it says.

[Structure of the Invention] (Means for Solving the Problems) Therefore, the present invention provides a transparent substrate in which a liquid crystal is sandwiched between a transparent plate on which a transparent electrode is formed and a transparent plate on which an electric field supply transistor is formed. A means for changing the polarization direction of the transmitted light by 90 degrees is provided on either side of the panel section that changes the polarization direction of the transmitted light of the liquid crystal between them by applying a voltage to the pole and the electric field supply transistor. It is characterized by:

It goes without saying that a liquid crystal may be used as a specific example of a means for changing the polarization direction by 90 degrees.

In the light valve of the present invention, a polarizing plate is provided at least on the output side, but this is generally provided on the output side of the panel section. A polarizing plate may be placed on the output side.

(Function) As described above, in the present invention, means for changing the polarization direction by 90 degrees is provided on one surface of the panel portion that changes the polarization direction by applying a voltage. If the means is provided on the input side of this panel section, the input light to the means is si light, so the output side, that is, the input to the panel section is P.
It becomes polarized light.

This panel section inputs P polarized light and outputs S polarized light during JUG with no voltage applied, so if an S polarizing plate is placed on the output side of the panel section, this section will be used as the normally white state. On the other hand, when viewed as a whole, there is an S polarized light input and an SG light output.

When the means is provided on the output side of the panel section, the output of the panel section must be PG light or the like in order to make the output S-polarized light. Since the human power applied to this panel section is S-polarized light, the human power output in this part becomes S-polarized light and P-polarized light when no voltage is applied.

In this case as well, the panel section is in the same state as the normally white state, and the entire light valve has S-polarized light input and S-polarized light output.

(Embodiment) FIG. 1 is a sectional view showing a liquid crystal light valve device according to an embodiment of the present invention, in which a liquid crystal 13 is sandwiched between transparent plates 12 and 14, and a liquid crystal 15 is sandwiched between transparent plates 14 and 16. It's in between.

In order to apply a voltage to this liquid crystal 15, an electric field supply transistor (TPT) 17 is provided on the transparent plate 14.
A transparent electrode 18 is formed thereon. That is, this portion forms a panel portion that controls the polarization direction of transmitted light, similar to a conventional liquid crystal light valve. That is, liquid crystal 1
A voltage is applied to the liquid crystal 5, but no voltage is applied to the liquid crystal 13. In this embodiment, a polarizing plate 11 is further provided on the input side of the transparent plate 12, and a polarizing plate 19 is provided on the output side of the transparent plate 16. Both of these polarizing plates 11 and 19 are S
It is a polarizing plate.

When S-polarized light is input manually to this light valve from the input side,
The polarization direction of the light is changed by 90 degrees by the liquid crystal 13 and the light is converted into Pgl light, which is incident on the liquid crystal 15 from the transparent plate 14 . Since the S polarizing plate 19 is installed on the output side of this panel section, the S polarizing plate 19 allows this panel section to convert the P8 light into
The polarized light is in a normally white state (light is transmitted when no voltage is applied). Therefore, in this embodiment, white is reproduced when the input voltage level is low, and black is reproduced when the input voltage level is high. However, since the entire panel can input S-polarized light and output S-polarized light, it can be used as is in a conventional liquid crystal light valve projection device.

Note that if all of the incident light is S-polarized light, the polarizing plate 11 on the incident side may be omitted.

Further, the layer of the liquid crystal 13 is provided on the output side of the transparent plate 16 by a transparent plate 12.
It is also possible to set the

In the above embodiment, the light valve is constructed using two layers of liquid crystal, but instead of this structure, it is also possible to have a structure in which two liquid crystal panels are arranged side by side.

[Effects of the Invention] As described above, according to the present invention, it is possible to output S-polarized light in response to input of S-polarized light, and to control the amount of transmitted light, a normally white liquid crystal light valve is used. be able to.

That is, when the liquid crystal light valve of the present invention is used in a three-panel liquid crystal projection device, it is possible to obtain a high-quality display with good black reproducibility and good contrast.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a liquid crystal light valve device according to an embodiment of the present invention, FIG. 2 is a sectional view showing the structure of a conventional liquid crystal light valve device, and FIG. 3 is a graph showing the operating characteristics of FIG. 2. , FIG. 4 is an explanatory diagram of a single-panel type liquid crystal projection device, and FIG. 5 is an explanatory diagram of a three-panel type liquid crystal projection device. 11.19...Polarizing plate, 12.14.16...Transparent plate, 13.15...Liquid crystal, 17...Electric field supply transistor, 18...Transparent electrode. Figure 1 (a) Normally ゛゛゛゛　　　　　　　　　　　　　　　　　　　　　　Figure 3　(b) Normally/IN1''7. Figure 5

Claims (1)

[Scope of Claims] A liquid crystal is interposed between a transparent plate on which a transparent electrode is formed and a transparent plate on which an electric field supply transistor is formed, and a voltage is applied to the liquid crystal by the electric field supply transistor and the transparent electrode. a panel section that changes the polarization direction of the transmitted light; a polarizing plate disposed at least on the light output side of the panel section; and a polarizing plate provided on either side of the panel section to change the polarization direction of the transmitted light by 90 degrees. A liquid crystal light valve device comprising means for: and.