JPH06265890A - Polarized light selecting element and image display device - Google Patents

Abstract

PURPOSE:To provide the polarized light selecting element which is small in size and lightweight and easily obtain linear polarized light in a necessary direction from a white light source for natural polarized light. CONSTITUTION:This polarized light selecting element 3 has plural polarized light separating surfaces 3b whose normals are at 45 deg. to the travel direction of incident light, so 50% of the incident light is transmitted as P-polarized light through the polarized light selecting element 3. Adjacent polarized light separating surfaces 3b cross each other at right angles, so S-polarized light is reflected by a polarized light separating surface 3b on which the light is made incident and then reflected again by a polarized light separating surface 3b on which its reflected light is made incident. Consequently, the S-polarized light is reflected to the light incidence side. Thus, a polarized light component in a necessary direction can be extracted from natural polarized light (unpolarized light).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization selecting element which is thin and can withstand strong light. Further, linear polarized light of a required direction is extracted from natural polarized light emitted from a light source, and an image is displayed by light modulation of the linear polarized light. The present invention relates to an image display device.

[0002]

2. Description of the Related Art A projection type liquid crystal projector using a twisted nematic liquid crystal display element, which is a typical light modulator, irradiates a liquid crystal display element with linearly polarized light to perform light modulation, and then displays the liquid crystal display. The emitted light from the device is enlarged and displayed on the screen by the projection lens.

In the display element used in such a liquid crystal projector, two polarizing plates called a polarizer and an analyzer are provided on the light incident side and the light emitting side, respectively, and their polarization directions are parallel or orthogonal to each other. Is provided. In the liquid crystal projector, linearly polarized light is extracted from the light (illumination light) with which the display element is irradiated by this polarizer to perform light modulation. Of the illumination light, the liquid crystal display element can utilize only the component that has passed through the polarizer. Therefore, effective components of the illumination light are limited to those along the polarization direction of the polarizer, and unnecessary components that cannot pass through the polarizer are absorbed by the polarizer and converted into heat. When the polarizer is attached to the surface of the liquid crystal display element, the temperature rise in the polarizer causes a phase change in the liquid crystal in the liquid crystal display element, which deteriorates the display characteristics of the display element. Further, when the illumination light is too strong, there is a problem in that the polarizing ability is lowered due to the temperature rise of the polarizer itself.

FIG. 6 shows a front view of an example of a conventional optical system proposed as a measure against the above problem. This optical system includes a light source 1, a UV-IR filter 2 for removing ultraviolet rays and infrared rays from the light from the light source 1, and a UV-IR filter.
It is provided with a cube-type broadband polarization beam splitter 11 on which the light emitted from the IR filter 2 is incident, and a liquid crystal display element 8 arranged on the opposite side of the UV-IR filter 2 with the broadband polarization beam splitter 11 interposed therebetween. . The broadband polarization beam splitter 11 converts white natural polarization into P polarization and S polarization.
Separated into polarized light. Broadband polarization beam splitter 11
May be replaced with an optical element having an equivalent function.

In the conventional optical system having the above structure,
The broadband polarization beam splitter 11 transmits a specific polarization component (P-polarized light in the drawing) of the light incident from the light source 1 via the UV-IR filter 2, and a polarization component orthogonal to this polarization component (FIG. The S-polarized light is split into side surfaces, and the liquid crystal display element 8 is illuminated only with a specific polarization component. Therefore, if the polarization direction of the polarizer provided on the light incident side of the liquid crystal display element 8 is made to coincide with the direction of the specific polarization component that illuminates the liquid crystal display element, light absorption and temperature rise in this polarizer are suppressed. be able to.

[0006]

However, in the above-mentioned conventional method, when the display area of the liquid crystal display element 8 is increased, the volume of the broadband polarization beam splitter 11 is increased accordingly. Therefore, in a liquid crystal projector using a liquid crystal display element having a large display area, the size of the optical system becomes large and the weight of the liquid crystal projector becomes heavy due to the large volume of the broadband polarization beam splitter.

Further, in the liquid crystal display device, in order to obtain the visual characteristic in the upward direction of the image, the horizontal and vertical axes are set to four.
It is known that the liquid crystal may be oriented in the direction of 5 degrees and the orientation of the polarizer may be tilted in the same direction. In a normal liquid crystal display device, in order to improve the light utilization efficiency, the orientation of the polarizer is matched with either P-polarized light transmitted through the broadband polarization beam splitter or S-polarized light reflected.
Since an ordinary broadband polarization beam splitter is a cube type, in order to illuminate the liquid crystal display element by extracting the polarized component tilted with respect to the horizontal axis of the liquid crystal display element, the liquid crystal screen of the liquid crystal display element needs to be inclined 45 degrees. There is a need for a square size broadband polarization beam splitter that circumscribes in degrees. Therefore, when incorporating a cube-type wideband polarization beam splitter into a general optical system, the orientation of the polarizer is horizontal or vertical due to the limitation due to the shape and size of the wideband polarization beam splitter. On the other hand, it is difficult to tilt it in the direction of 45 degrees. As a result, a high-contrast area of the image is obliquely upward and the visual characteristics are insufficient.

The present invention solves the above-mentioned problems of the prior art, and is a small-sized and light-weight polarization selection element capable of easily obtaining linearly polarized light of a desired direction from a naturally polarized white light source. The purpose is to provide.

Further, according to the present invention, by using the above-mentioned polarization selection element, the size and weight of the entire device can be reduced, and the display element can be illuminated with strong light, and the display characteristics due to heat can be improved. An object of the present invention is to provide an image display device capable of preventing deterioration and providing a bright and high-contrast image.

[0010]

The polarization selection element of the present invention has a plurality of polarization splitting surfaces whose normals form an angle of 45 degrees with respect to the traveling direction of incident light, and the adjacent polarization splitting surfaces are adjacent to each other. They are orthogonal to each other, which achieves the above objectives.

The image display device of the present invention has a light source and a plurality of polarization splitting surfaces whose normals form an angle of 45 degrees with respect to the traveling direction of incident light from the light source, and the adjacent polarization splitting surfaces. Polarization selecting elements which are orthogonal to each other, and by performing light modulation on the linearly polarized light separated by the polarization selecting element, a display element for visualizing an image is provided.
The above object is achieved.

[0012]

Since the polarization selection element of the present invention has a plurality of polarization splitting planes whose normal is at an angle of 45 degrees with respect to the traveling direction of the incident light, 50% of the incident light is polarized as P-polarized light. Permeate the selection element. With regard to S-polarized light, since the adjacent polarization separation surfaces are orthogonal to each other, first, the incident polarization separation surfaces are reflected, and the reflected light is reflected again by the incident adjacent polarization separation surfaces. As a result, the S-polarized light is reflected on the light incident side. In this way, it is possible to extract the polarized component of the desired orientation from the naturally polarized light (non-polarized light). In addition, by using this polarization selection element in an image display device that displays an image by light modulation of linearly polarized light, only the linearly polarized light of the polarization component necessary for display illuminates the display element, so that the display characteristics Deterioration can be prevented.

[0013]

EXAMPLES Examples of the present invention will be described below.

<First Embodiment> FIG. 1A shows a perspective view of a polarization selection element 3 according to a first embodiment of the present invention.
FIG. 1B is a perspective view of a broadband polarization beam splitter 3a which is one unit of the polarization selection element 3 shown in FIG.

A broadband polarization beam splitter 3a shown in FIG. 1 (b) has a thin prism shape, and its polarization splitting surface 3
The normal line of b forms an angle of 45 degrees with the traveling direction of the incident light. In the broadband polarization beam splitter 3a, as shown in the figure, P polarized light of the incident natural polarized light is transmitted through the polarized light separating surface 3b, and S polarized light is reflected by the polarized light separating surface 3b. Therefore, by adjusting the arrangement direction of the broadband polarization beam splitter 3a, it is possible to take out the polarization component of the necessary orientation from the natural polarization.

The polarization selection element 3 shown in FIG. 1 (a) has a structure in which a plurality (four in this embodiment) of the wide band polarization beam splitters 3a are arranged adjacent to each other in one direction. Here, adjacent broadband polarization beam splitters 3a
The broadband polarization beam splitters 3a are arranged so that the respective polarization separation surfaces 3b of 2 are orthogonal to each other. Examples of the method of manufacturing the polarization selection element 3 include a method of joining the broadband polarization beam splitters 3a to each other with an adhesive, a method of holding the broadband polarization beam splitter 3a with an appropriate member, and the like.

FIG. 2 shows a front view of an optical system including the polarization selection element 3 of this embodiment. This optical system is configured such that the light from the white light source 1 is incident on the polarization selection element 3 via the UV-IR filter 2.

The operation principle of the polarization selection element 3 will be described with reference to FIG. As shown in the figure, unpolarized white light from the light source 1 passes through the UV-IR filter 2 and the polarization selection element 3
When it is incident on, 50% of the incident light is transmitted through the polarization selection element 3 as P-polarized light by the action of the broadband polarization beam splitter 3a. Regarding the S-polarized light, since the polarization splitting surfaces 3b of the adjacent broadband polarization beam splitters 3a are orthogonal to each other, first, the polarization splitting surfaces 3b of the incident broadband polarization beam splitter 3a are reflected and the reflected light is incident. It is reflected again by the polarization splitting surface 3b of the adjacent broadband polarization beam splitter 3a. As a result, the S-polarized light is totally reflected on the light source 1 side. When all the S-polarized light is reflected to the light source 1 side, it is possible to prevent the S-polarized light from being scattered around. S
In order to reflect all the polarized light to the light source 1 side, an even number of broadband polarization beam splitters 3a forming the polarization selection element 3 may be used.

When the polarization selecting element 3 of this embodiment is used in an image display device, a display element for forming an image by light modulation is arranged on the side opposite to the light source 1 with the polarization selecting element 3 interposed therebetween, The P-polarized light transmitted through the selection element 3 illuminates this display element. At this time, the arrangement direction of the polarization selection elements 3 is adjusted so that the P-polarized light is along the azimuth of the polarizer provided on the incident side of the display element.

As described above, the polarization selection element 3 of this embodiment
Has a plate-like thin shape as compared with the conventional wide band polarization beam splitter, and therefore has a small volume and is light. Therefore, the distance between the display element and the light source 1 can be shortened, and the size and weight of the image display device can be reduced.

Further, in order to obtain good image characteristics, when the azimuth of the polarizer provided on the display element is inclined at an arbitrary angle with respect to the horizontal direction of the screen of the display element, as shown in FIG. In addition, the polarization selection element is configured such that the wide band polarization beam splitters 3a are arranged so as to be inclined with respect to the horizontal direction of the screen according to the azimuth of the polarizer so as to cover the entire display area of the display element. With such a configuration, the polarization selection element can extract only the necessary polarization component that passes through the polarizer from the light from the light source.
Light absorption and heat generation in the polarizer can be suppressed. This means that the display element is illuminated with almost all P-polarized light transmitted through the polarization selection element. That is, it is possible to obtain a bright display image by increasing the emission brightness of the light source.

<Second Embodiment> FIG. 4 shows a front view of a liquid crystal projector which is a second embodiment of the present invention. This liquid crystal projector includes a light source 1 that emits unpolarized white light, and a U for removing ultraviolet rays and infrared rays of the light from the light source 1.
The V-IR filter 2, the polarization selecting element 3 shown in the first embodiment, the image forming section 40 that forms an image by receiving the illumination light from the polarization selecting element 3, and the image formed by the image forming section 40 A projection lens 10 for projecting on a screen (not shown).

The image forming section 40 includes dichroic mirrors 4a and 4b for separating the illumination light from the polarization selection element 3 into red light, green light and blue light, and a reflecting mirror for changing the traveling direction of the light. 5a and 5b, liquid crystal display elements 8a, 8b and 8c corresponding to each color light, and light provided on the light incident side of each liquid crystal display element 8a, 8b and 8c, respectively, for converging light to the projection lens 10 without waste. Condenser lenses 6a, 6b and 6c, and correction polarizers 7a, 7b and 7c respectively disposed between the respective liquid crystal display elements 8a, 8b and 8c and the corresponding condenser lenses 6a, 6b and 6c, Each liquid crystal display element 8
A dichroic mirror for combining the analyzers 9a, 9b and 9c respectively provided on the light emitting sides of a, 8b and 8c and the light transmitted through the respective liquid crystal display elements 8a, 8b and 8c and making them enter the projection lens 10. 4c and 4d. The liquid crystal display elements 8a, 8b, and 8c are transmissive liquid crystal display elements for forming red, green, and blue images, respectively, and each modulate the illumination light based on a video signal. This modulation rotates the polarization direction of outgoing light by 90 degrees with respect to incident light. Each correction polarizer 7
The azimuths of a, 7b, and 7c correspond to the respective analyzers 9
It is orthogonal to the azimuths of a, 9b and 9c.

In the liquid crystal projector having such a configuration, linearly polarized light having a uniform polarization direction is extracted from the parallel white light from the light source 1 by the polarization selection element 3 and is emitted to the image forming section 40 as illumination light. This illumination light is separated by reflection by the dichroic mirror 4a into the first color light that is any one of the red light, the green light and the blue light, and is separated via the condenser lens 6a and the correction polarizer 7a. The display element 8a is illuminated. The light transmitted through the dichroic mirror 4a is one of the two colored lights obtained by removing the first colored light from the red, green and blue lights by the dichroic mirror 4b.
The colored light of is separated by reflection and is illuminated on the liquid crystal display element 8b through the condenser lens 6b and the correction polarizer 7b. The third color light, which is the other color light of the two color lights transmitted through the dichroic mirror 4b, illuminates the liquid crystal display element 8c via the condenser lens 6c and the correcting polarizer 7c.

The principle of image formation will be described by taking the liquid crystal display element 8a as an example. The light that passes through the correcting polarizer 7a and illuminates the liquid crystal display element 8a is linearly polarized light in the direction of the correcting polarizer 7. When no electric field is applied to the liquid crystal portion of the liquid crystal display element 8a, this linearly polarized light is rotated by 90 degrees and can pass through the analyzer 9a having an azimuth orthogonal to the azimuth of the correction polarizer 7a. Therefore, a portion of the display area where no electric field is applied to the liquid crystal is visually recognized as a bright state. On the other hand, when an electric field is applied to the liquid crystal portion of the liquid crystal display element 8a, no modulation is caused by the liquid crystal portion, and linearly polarized light having the same polarization direction as the incident light is emitted from the liquid crystal display element 8a. The emitted linearly polarized light is blocked by the analyzer 9a. Therefore, the portion of the display area where the electric field is applied to the liquid crystal is in a dark state. In the liquid crystal display element 8a, an image is formed by applying an electric field to the liquid crystal portion based on a video signal to control the transmission of the illumination light as described above.

In this way, light having image information corresponding to each color is formed by the liquid crystal display elements 8a, 8b and 8c, and the light is reflected by the reflecting mirror 5b and the dichroic mirror 4.
Color combination is performed with c and 4d. The color-combined light is enlarged and projected by a projection lens 10 onto a screen (not shown).

FIG. 5 (a) shows the azimuths of the analyzer and the polarizer in the improved liquid crystal projector in order to increase the contrast of the displayed image, and FIG. 5 (b) shows a partial front view of the liquid crystal projector. The figure is shown. In FIG. 5B, the polarizer 7, the liquid crystal display element 8 and the analyzer 9 are shown.

In this liquid crystal projector, in order to obtain the visual characteristic in the upper direction of the image, as described above, the liquid crystal molecules in the liquid crystal display element 8 are oriented in the direction of 45 degrees with respect to the horizontal axis X and the vertical axis Y. is doing. As shown in FIG. 5A, the orientation of the polarizer 7 and the orientation of the analyzer 9 are 4 with respect to the horizontal axis X and the vertical axis Y in accordance with the orientation direction of the liquid crystal.
It is tilted 5 degrees. In this liquid crystal projector, a wide band polarization beam splitter 3a as shown in FIG. 3 is arranged with an inclination of 45 degrees with respect to the horizontal direction of the screen.
Is used.

In the liquid crystal projector having the above-mentioned structure, FIG.
As indicated by an arrow L in (b), the illumination light is made to enter from a slightly oblique lower side of the front surface of the liquid crystal display element so that the best visual characteristics can be obtained in the slightly upper half on the emission side of the panel. In this case, since light is emitted upward from the projection lens 10 to form an image above the liquid crystal projector main body, there is also an advantage that the image light beam does not hit the floor in normal use.

The alignment direction of the liquid crystal molecules in the liquid crystal projector of this embodiment is not limited to 45 degrees obliquely, and any alignment direction is possible. In that case, the polarization direction of the wide band polarization beam splitter in the polarization selection element may be obliquely matched with the alignment direction of the liquid crystal molecules, and the polarization selection element may cover the entire display area. As a result, the required polarization component can be extracted by the polarization selection element, and the liquid crystal display element can be illuminated with strong light. Therefore, there is no fear of deterioration of the polarizer due to heat due to unnecessary polarization components, and it is possible to obtain a good image with high brightness and high contrast.

[0031]

As is apparent from the above description, according to the polarization selection element of the present invention, it is possible to reduce the size and weight of the element, and to easily obtain a straight line of a desired direction from a naturally polarized white light source. Polarized light is obtained. Further, according to the image display device of the present invention, since the polarization selection element is used, the size and weight of the entire device can be reduced, and the display element can be illuminated with strong light. Furthermore, since the direction of linearly polarized light obtained by the polarization selection element can be easily matched with the direction of the polarizer, unnecessary linearly polarized light does not enter the polarizer,
It is possible to prevent deterioration of display characteristics due to heat, and it is possible to provide a bright and high-contrast image.

[Brief description of drawings]

FIG. 1A is a perspective view of a polarization selection element that is a first embodiment of the present invention, and FIG. 1B is a perspective view of a broadband polarization beam splitter that constitutes the polarization selection element shown in FIG. Is.

FIG. 2 is a front view showing the operation of the polarization selection element of the first embodiment.

FIG. 3 is a perspective view of another polarization selection element of the present invention.

FIG. 4 is a front view of a liquid crystal projector that is a second embodiment of the present invention.

FIG. 5A is a diagram showing an orientation of an analyzer and an orientation of a polarizer in an improved liquid crystal projector,
(B) is a partial front view of the liquid crystal projector.

FIG. 6 is a front view of an optical system using a conventional cube-type broadband polarization beam splitter.

[Explanation of symbols]

 1 Light source 2 UV-IR filter 3 Polarization selection element 3a Broadband polarization beam splitter 3b Polarization separation surface 4a, 4b, 4c, 4d Dichroic mirror 5a, 5b Reflection mirror 6a, 6b, 6c Condenser lens 7, 7a, 7b, 7c Polarizer 8, 8a, 8b, 8c Liquid crystal display element 9, 9a, 9b, 9c Analyzer 10 Projection lens 40 Image forming unit

Claims (2)

[Claims] 1. A polarization selection element having a plurality of polarization splitting planes whose normal line forms an angle of 45 degrees with respect to the traveling direction of incident light, and adjacent polarization splitting surfaces are orthogonal to each other. 2. A polarization selection device having a light source and a plurality of polarization splitting surfaces having a normal line at an angle of 45 degrees with respect to a traveling direction of incident light from the light source, and adjacent polarization splitting surfaces being orthogonal to each other. An image display device comprising: an element; and a display element for visualizing an image by optically modulating linearly polarized light separated by the polarization selection element.