JPH01116527A - Optical writing liquid crystal display element and its driving method - Google Patents

Abstract

PURPOSE:To execute a display of a color image and a negative - positive inversion of the color image by providing a color filter on both sides of a photoconductive film of an optical write liquid crystal display element. CONSTITUTION:On a write side, an array 100 of color filters is provided, and on a projecting light side, the same color filter array 101 which is aligned with the color filter array of the write side is provided. As for the array 100 and 101 of color filters, three color filters of R (red), G (green) and B (blue) are provided by the same pattern. By making only information of specific wavelength of a write light incident on a photoconductive film 2, the information of specific wavelength is displayed by a liquid crystal, and by displaying the display of the liquid crystal concerned as information of light of specific wavelength again, a color image is displayed. Also, by setting a voltage applied between two sheets of transparent conductive films higher than a voltage which is used up to this time, a negative - positive inversion display of the color image can be executed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optically written field-effect color liquid crystal display device and a method for driving the same, and particularly relates to a field-effect color liquid crystal display device capable of displaying a negative/positive color image in reverse. The present invention relates to display elements and methods for driving the same.

[Prior Art] An optically written field-effect liquid crystal display element called a light valve is an element used for converting image intensity, etc., and has the features of being simple and compact.

The operating principle of the optically written field effect liquid crystal display element will be explained below.

A photoconductive film is provided on one of the two electrodes of a field-effect liquid crystal display element, and an optical image is formed on the photoconductive film to spatially modulate the resistance within the film plane. Furthermore, attempts have been made to transfer an image into a liquid crystal layer by applying an electric field between the photoconductive film and the transparent conductive film, and to use this for visible light modulation in a projection type device. An example of a cross section of a liquid crystal display element used in this projection type device is shown in Fig. 5. - In this element, a photoconductive film 2 and a liquid crystal layer Nia are laminated, and the photoconductive film 2 and a liquid crystal layer are sandwiched between them. Transparent electrodes = 4 and 41 are attached to the outside of the layer nearer. Normally, an AC voltage = 9 is applied between these electrodes, and photoconductive film = 2 and liquid crystal layer = 7.
A visible light blocking film (CdTe film) 3 and a dielectric light reflecting film (mirror layer) 5 are inserted at the boundary between the two to form a mirror surface for visible light incident from the right side (projection side) of the element. .

In general, photoconductivity M: 2 is about 2 to 20 μ-(DC
dS[lI is used. When no image writing light is incident from the left side of the element, the electrical conductivity of this photoconductive film 2 is sufficiently higher than that near the liquid crystal layer, and when light is incident, the electrical resistance of the photoconductive film 2 increases. is adjusted so that it is sufficiently lower than that of liquid crystal layer=7.

In this way, when an image is drawn on the photoconductive film 2 by the image writing light incident from the left side of the element, the internal resistance of the photoconductive film 2 changes locally according to the density of the image. For this purpose, the above-mentioned AC voltage: 9 is applied to the near liquid crystal layer corresponding to these portions while being spatially modulated according to the density of the image.

In this liquid crystal layer near, a smectic liquid crystal with positive dielectric anisotropy is initially oriented in HFE (45 degrees twist).If an AC voltage of 9 is applied between the electrodes, the light will be absorbed more and more. Since the resistance value of the photoconductive film 2 is high in the area where the photoconductive film 2 is not present, the AC voltage 9 is not applied to the liquid crystal and the orientation of the liquid crystal is not disturbed. Therefore, the polarization plane of the projected light incident through the polarizing plate follows the twist of the liquid crystal. Rotate 45 degrees and reach dielectric light reflection film (mirror layer)=5. The reflected light is rotated 45 degrees in the opposite direction and exits with the same polarization direction as when it was incident. In the part where the image is drawn on the zero-order photoconductive film: 2, an AC voltage is applied to the liquid crystal. =9 is applied, so the liquid crystal molecules change direction in the direction of the electric field (perpendicular to the electrodes). As a result, the above-mentioned conditions for rotation of the polarization plane change, and the reflected light of the projection light includes a polarization direction component perpendicular to the polarization direction of the projection light. Therefore, by detecting the component perpendicular to the polarization direction of this projection light, projection output light having the same pattern as the writing light can be obtained.

In this display element, the dielectric reflective film 5 is used to completely reflect the strong projected visible light that enters from the right side of the element, and is made of high and low dielectric constant dielectrics such as ZnS and Na5AIFe. It is made by stacking about 15 layers of membranes alternately. Furthermore, the light blocking film 3 is designed to block visible light for projection that enters from the right side of the element.

The above is an explanation of the structure and operation of a conventionally known optical writing field effect liquid crystal display element called light pulp.

[Problems to be Solved by the Invention] However, the conventional optically written field-effect liquid crystal display device described above projects a black and white gray pattern as it is, and has the problem of not being able to display a color image. Ta. Another problem was that it was not possible to convert a negative image into a positive image.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems. In an optical writing liquid crystal display element in which a conductive film and a liquid crystal layer are sandwiched, color filters are provided on both sides of the photoconductive film.

It is preferable that a plurality of sets of color filters are provided on both sides, and that at least one transparent conductive film is formed as a divided electrode corresponding to the plurality of sets of color filters, so that white balance can be maintained. desirable for obtaining a clear image.

The above-mentioned optical writing liquid crystal display element is a method for driving an optical writing liquid crystal display element in which a photoconductive film and a liquid crystal layer are sandwiched between opposing transparent conductive films of two transparent substrates with transparent conductive films. While providing a means to disturb the alignment of the liquid crystal when there is no information, the written information is incident on the photoconductive film through a first color filter provided on one side of the photoconductive film as light, and the light is inversely proportional to the written information. The liquid crystal display information can be driven by a method of displaying the information using light that has passed through a second color filter that is provided in pair with the first color filter with a photoconductive film in between.

As a means to disturb the liquid crystal alignment when there is no written information, for example, (1) the material of the photoconductive film of the light valve,
Converts to a material with higher conductivity in the dark than conventional materials. ■
The thickness of the photoconductive film of the light valve is changed to be thinner than before. In addition, ■ a method using a voltage applied between two transparent conductive films such as 0, which increases the AC voltage value applied to the light valve higher than conventional methods, and ■ a method of applying a constant amount of light to the photoconductive film. incident. The following methods can be exemplified.

[Function] The present invention is a conventional optically written liquid crystal display device in which color filters are provided on both sides of the photoconductive film. Information of a specific wavelength is displayed on the liquid crystal by inputting it,
The liquid crystal display is again displayed as information of light of a specific wavelength using a color filter.

Since it is possible to display color image information as finely divided photosynthesis of specific wavelengths, according to the present invention, it is possible to display color images, which was previously impossible.

Further, according to the method for driving an optically written liquid crystal display element of the present invention, it is possible to perform negative-positive reversal of a color image. Below, a method of driving the optically written liquid crystal display element for negative/positive reversal will be explained.

FIG. 4 shows the writing light intensity: L of the optically written field-effect liquid crystal display element (light valve) described above as a conventional example.
FIG. 3 is a diagram showing the relationship between the output light intensity of the projection light and the output light intensity of the projection light.

When the writing light intensity L=O, no AC voltage is applied to the liquid crystal layer as described in the conventional example, and the component perpendicular to the polarization direction of the projection light, that is, the projection light output is zero. However, as the writing light intensity is gradually increased, a voltage is applied to the liquid crystal and a projection light output is generated.

Furthermore, if the writing light intensity is made sufficiently large, the alignment of the liquid crystal is completely disrupted, the optical rotation of the liquid crystal disappears, and the projection light is completely unaffected by the polarization direction of the dielectric mirror layer: 5
It comes out reflected by. In other words, no projection light output is generated (C in the figure). Therefore, the projection light output and writing light intensity are:
As shown in FIG. 4, the gradient of the writing and projection light output is reversed at the writing light intensity Lp that gives the maximum projection light output light intensity. That is, the writing light intensity that gives the maximum projection light output intensity: 1. There are a region A where the projection light output intensity increases as the writing light intensity increases, and a region B where the projection light output intensity decreases as the writing light intensity increases.

In the conventional light valve, the light valve is driven using the region A where the projection light output intensity increases as the writing light intensity increases.

As is clear from the above characteristics, the condition is set such that L=Lp as the zero point of the writing light intensity: L, and the light valve is operated in region B where the projection light output intensity decreases as the writing light intensity increases. If this is possible, the writing light intensity and the projection light output will be reversed, and a negative/positive image reversal function will be provided.

Writing light intensity: Conditions such that L≧I, p as the zero point of L (
As mentioned above, the conditions for operating in area B are as follows:
The material of the photoconductive film of the light valve is changed to one that has higher conductivity in the dark than conventional materials. ■Light bulb,
The thickness of the photoconductive film is changed to be thinner than before. Furthermore, (1) the AC voltage value applied to the light valve is made higher than before;

Examples include a method using a voltage applied between two transparent conductive films, and a method in which a constant amount of light is incident on the photoconductive film.

[Example] Example-1 Fig. 1 shows an embodiment of the present invention.The difference from the conventional example Fig. 5 is that a color filter array 100 is provided on the writing side, and a writing side color is provided on the projection light side. This is because the same color filter array 101 is provided which is aligned with the filter array.

Color filter arrays 100 and 101 are R (red)
, G (green), and B (blue) are provided in the same pattern.

For the above optical writing liquid crystal display element (light valve),
By setting the voltage applied between the two transparent conductive films higher than the voltage used in the conventional example, it was possible to perform negative-positive reversal display of color images. The mechanism of negative-positive inversion display of a color image is considered to be as follows.

Now, if the light on the writing side is R (red), the light passes only to the R pixel, and the other G and B filters cut the light and do not enter it. Since the light valve is inverted from negative to positive, the R pixels into which light enters are not extracted as projection light. However, since the G and B pixels where no light enters are taken out as projection light, the projection output light is G,
It becomes a cyan color mixed with B. This is a complementary color to R. Similarly, for incident light of 0% B, magenta and yellow light, which are complementary colors, are output. Further, when there is no writing light, white light is output, and conversely, when white light is input, nothing is output, so that the complementary color of the writing light is extracted as projection light. That is, this function corresponds to negative-positive reversal, and it is possible to invert and view an image on a negative film used for ordinary photography. Even if you directly view a negative film with the naked eye, you cannot get a good sense of the atmosphere of the image, but if you use the liquid crystal display element according to the present invention, you can see the original image without having to print it on photographic paper or the like.

Note that the arrangement of the color filters can be in any shape such as a stripe arrangement, a triangular arrangement, or a checkered arrangement, and in this embodiment, the color filters 100 and 101 are provided outside the transparent electrodes 4 and 40. However, it works without any problems even if it is inside.

Although the liquid crystal operation mode is the HFE mode according to the previous invention, other modes may be used as long as the operation is the same.

In this embodiment, both the light shielding film 3 and the dielectric reflective film 5 are provided, but the light shielding film 3 may not be necessary if the intensity of the projection light is weak.

Furthermore, in this invention, as a method for driving a light valve,
Although a driving method for black-and-white negative-positive reversal using a voltage applied between two transparent conductive films is mentioned, it does not necessarily have to be this method, and other operations that have a black-and-white negative-positive reversal function can be used. It may be a mode.

Further, although R, G, and B are given as examples as color filters, it is not necessary to use these colors, and a complementary color filter or other background color may be used.

Example 2 FIG. 2 shows another example of the present invention. The difference from FIG. 1 of Example 1 is that the color filter R%G.

A separate transparent electrode is provided for each of B, and separate AC voltages VR, VG, and VB are applied to each electrode, and an optically written field-effect liquid crystal display element (light valve): 200 For writing light: 30
1. Bias light: 303 to half mirror = 400
The point is that the negative-positive image is inverted.

According to this embodiment as well, it was possible to perform negative-positive reversal display of a color image.

Here, although the light valve of Example 1 has the advantage of being able to display color images, which could not be done conventionally, the photoelectric conversion characteristics of the photoconductive film used for detecting optical images are wavelength dependent. Therefore, this wavelength dependence is also reflected in the projection output, resulting in the problem that the projected light output deviates from white even when writing with white light (the problem that the color of the written image and the color of the projected light image deviate, ) That is, there was a problem in that it was difficult to maintain white balance.

Generally, the spectral characteristics vary considerably depending on the type of photoconductive film. For example, even though they are the same silicon, amorphous silicon and polycrystalline silicon are completely different. Since polycrystalline silicon has the same bandgap as silicon, it has strong red sensitivity and weak blue sensitivity, which obviously disrupts the white balance.

By using the structure of this embodiment, it becomes possible to adjust the alternating current voltage applied to each color filter, and it becomes possible to freely set the white balance.

Although we have explained here that separate transparent electrodes are provided for each of the three primary color filters, if it is not necessary to adjust the three primary colors separately, a combination of two transparent electrodes, one color and the other two colors, may be used. .

Application Examples Possible applications of the present invention include a projector that can directly project from a photographic negative film instead of a conventional dedicated positive film, and a negative/positive inversion V& . A specific example of its application is shown in FIG.

The image of the negative film 505 is formed using the lens 506 onto the optical writing field effect liquid crystal display element (light valve) 200 prepared in Example-2.

On the other hand, the projection light is light! :500 light refracting mirror: 5
It changes direction at 01 and enters a polarizing beam splitting prism: 503 through a condenser lens: 502.

Then, only the specific polarized light component enters the projection light side of the optically written field effect liquid crystal display element (light valve) 200 of the present invention. Then, the reflected light enters the polarizing beam splitting prism = 503 again, and only the polarized component perpendicular to the incident polarization direction of the previous light valve passes through, and the projection lens: 60
Projected onto screen: 600 at 4.

In this application example, if the half mirror 400 is not fixed between the lens 506 and the light bulb 200, but is detachable, it can be used as a negative-positive, negative-negative, positive-negative, positive-positive, etc. depending on the type of film image. It is possible to create a slide projection device that allows selective photography on the spot.

[Effects of the Invention] As described above, according to the present invention, color display can be performed using an optically written field effect liquid crystal display element (light valve). Further, according to the method for driving an optically written liquid crystal display element of the present invention, color negative-positive inversion display can be performed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing the optical writing liquid crystal display element prepared in Example-1, FIG. 2 is a cross-sectional view schematically showing the optical writing liquid crystal display element prepared in Example-2, and FIG. FIG. 4 is a cross-sectional view schematically showing a projector that can directly project a positive image from a photographic negative film explained in the application example, and FIG. 4 is a diagram showing the relationship between the writing light intensity and projection output intensity of a conventional optical writing liquid crystal display element. FIG. 5 is a cross-sectional view schematically showing a conventional optically written liquid crystal display element. 9 AC voltage Figure 1 Figure 4 tJS diagram

Claims (6)

[Claims] (1) In an optical writing liquid crystal display element in which a photoconductive film and a liquid crystal layer are sandwiched between two opposing transparent conductive films of transparent substrates with transparent conductive films, color filters are provided on both sides of the photoconductive film. An optically written liquid crystal display element characterized in that: (2) The optical writing liquid crystal display element according to claim 1, wherein a plurality of sets of color filters on both sides are provided. (3) At least one of the transparent conductive films is
3. The optically written liquid crystal display element according to claim 2, wherein divided electrodes are provided corresponding to the plurality of color filter sets. (4) In a method of driving an optical writing liquid crystal display element in which a photoconductive film and a liquid crystal layer are sandwiched between two transparent conductive substrates with transparent conductive films facing each other, when there is no written information, the liquid crystal display While providing means to disturb the orientation, the written information is incident on the photoconductive film through a first color filter provided on one side of the photoconductive film as light, and liquid crystal display information that is inversely proportional to the written information is displayed. A method for driving an optically written liquid crystal display device, characterized in that display is performed using light that has passed through a second color filter that is provided in pair with the first color filter with a photoconductive film in between. (5) Driving the optically written liquid crystal display element according to claim 4, wherein the means for disturbing the liquid crystal alignment when there is no written information is a voltage applied between two transparent conductive films. Method. (6) The method for driving an optically written liquid crystal display element according to claim 4, wherein the means for disturbing the liquid crystal alignment when there is no written information is the incidence of a constant amount of light on the photoconductive film.