JPH0572417A - Polarized light converting element - Google Patents

Abstract

PURPOSE:To efficiently converts indeterminate polarized light emitted by a light source into linear polarized light and to obtain the polarized light converting element which is effective for an increase in the brightness of a projection image without deterioration of a polarizing plate and a liquid crystal display element, deterioration in the picture quality of the projection image, or an increase in the size of, specially, a projection type liquid crystal display device when this projection type liquid crystal display device is used. CONSTITUTION:A luminous flux width converting element 1 reduces the luminous flux width of incident light 10 to half only in one direction and its projection light 11 is split by a polarization beam splitter 2 into two linear polarized light beams which are (p)-polarized light 12 and (s)-polarized light 13. The (p)-polarized light 12 is projected as it is and the (s)-polarized light 13 is reflected by a luminous flux reflecting element 3 to travel in parallel to the (p)-polarized light 12. Further, the reflected light is transmitted through a 1/2-wavelength plate 4 and then its polarizing direction is rotated by 90. Consequently, projection light beams 14 and 16 travel in the same direction with the incident light 10 and are equal in luminous flux width to the incident light and thus the linear polarized light beams which are uniformly in the specific polarizing direction are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization conversion element,
In particular, it relates to a polarization conversion element capable of efficiently converting indefinite polarized light emitted from a light source into linearly polarized light.

[0002]

2. Description of the Related Art Some devices and other devices that use polarized light utilize linearly polarized light. An example of a device that uses linearly polarized light is a projection type liquid crystal display device that magnifies and projects a display image of a TN (twisted nematic) liquid crystal display element on a screen by using a light source and a projection lens.

Conventionally, when a halogen lamp, a xenon lamp, a metal halide lamp or the like is used as a light source in such a device, the light generated from these light sources is indefinite polarized light, and therefore, to obtain linearly polarized light. , A polarizing element is used.

As an example of such a polarizing element, a polarizing film is prepared by orienting and adsorbing iodine or the like on a polyvinyl alcohol film, and a plastic sheet or glass plate is adhered on both sides for protection. A polarizing plate is used. In addition, one of the two right-angle prisms is coated with a semi-permeable membrane on one slope, and the slopes are joined together.
There is also used a polarization beam splitter that extracts transmitted light and reflected light as linearly polarized light whose polarization directions are orthogonal to each other.

However, when such a polarizing element such as a polarizing plate or a polarizing beam splitter is used for a light source such as a halogen lamp, it absorbs or reflects light of an unnecessary polarization component, so that a light flux from the light source is emitted. Light utilization efficiency is 50%
Since it had to be lower than the following, there was a problem that the loss of light was large. For example, when the device used is a projection type liquid crystal display device, this requires a more accurate light source to be used as a light source when a projection screen having a required brightness is to be secured.

That is, as described above, as an example of a device using linearly polarized light, a display image of a TN (twisted nematic) liquid crystal display device is enlarged and projected on a screen by using a light source and a projection lens. Although there is a projection type liquid crystal display device, when a configuration in which a polarizing plate is arranged on the light incident / exiting surface of the liquid crystal display element is adopted, the transmittance of the light flux from the light source is 40% or less even with the polarizing plate alone. Further, in the liquid crystal display element, the transmittance of the entire element including the polarizing plate has to be a considerably low value due to absorption of liquid crystal, transparent electrodes, etc., reflection at the boundary surface, aperture ratio and the like. Therefore, in order to obtain a bright projection screen, a light source with high brightness must be used.

If a light source with high brightness is required, the problem of low light utilization efficiency in the case of using a polarizing plate to obtain linearly polarized light is not limited to the above problem. This will affect the temperature rise, the deterioration and deterioration of the performance of the polarizing plate and the liquid crystal display element, and the noise generation from the air-cooling fan used to suppress the temperature rise.

Conventionally, as a technique for reducing the light amount loss due to such a polarizing plate and improving the light utilization efficiency of the light source, as disclosed in, for example, Japanese Patent Application Laid-Open No. 59-127019, an optical element such as a liquid crystal shutter is used. In a printer head using a modulator, a polarization beam splitter, a reflection mirror,
An illumination method using a half-wave plate has been proposed. According to this illumination method, an illumination light beam is made incident on a polarization beam splitter, separated into two linearly polarized light beams whose polarization directions are orthogonal to each other, one light beam is made incident on a liquid crystal shutter as it is, and the other light beam is 1 / By rotating the polarization direction by 90 degrees with the two-wave plate to make it equal to the polarization direction of one light flux, and by making the light flux enter the liquid crystal shutter using the reflection mirror, the light utilization efficiency of the illumination light is improved. There is.

[0009]

However, when the conventional illuminating method is applied to the projection type liquid crystal display device, since the luminous flux diameter of the illuminating light is large, it is required to use a large polarization beam splitter. This not only affects the weight and manufacturing cost, but also causes a problem that the combining angle becomes large when the two light beams separated by the polarization beam splitter are combined again. The problem that the combined angle of the two light fluxes becomes large is that the image quality of the projected image is deteriorated in the projection type liquid crystal display device because the liquid crystal display element or the optical element having the incident angle dependency on the light transmission and reflection characteristics is used. Or the vignetting of the projection lens causes the projected image to become dark. In order to prevent vignetting in the projection lens, a projection lens with a large aperture is required, which causes an increase in the size of the projection device and an increase in manufacturing cost. Also, in order to reduce the combined angle of the two light fluxes, the optical path of the illumination light must be lengthened, the device becomes large, and the illumination light flux diverges, so that the light utilization efficiency is not improved. Become.

An object of the present invention is to efficiently convert indefinitely polarized light emitted from a light source into linearly polarized light, and particularly when it is used for a projection type liquid crystal display device, deterioration of a polarizing plate or a liquid crystal display element is caused. Another object of the present invention is to provide a polarization conversion element effective for increasing the brightness of a projected image without degrading the image quality of the projected image, increasing the size of the apparatus, and significantly increasing the manufacturing cost.

[0011]

In order to achieve the above object, a polarization conversion element of the present invention comprises a light flux width conversion element for reducing the width of a light flux to half in one direction and an output from the light flux width conversion element. A polarization splitting surface that splits the emitted light into two linearly polarized light beams of p-polarized light and s-polarized light whose polarization directions are orthogonal to each other is provided with a direction for reducing the luminous flux width of the luminous flux width conversion element and a reflection direction for the s-polarized light. A polarization beam splitter formed to be parallel to each other, and a light beam reflection element having a light beam reflection surface parallel to the polarization splitting surface and arranged adjacent to the polarization beam splitter in a reflection direction of the s-polarized light. , A half-wave plate disposed in the optical path of either p-polarized light, s-polarized light, or s-polarized light separated by the polarization beam splitter is used as a constituent element, and the constituent elements are used alone or in two sets. Place the above in parallel It is characterized by being made.

[0012]

According to the above configuration of the present invention, when the outgoing light flux which is the indefinite polarized light from the light source is incident on the polarization conversion element, the incident light flux is halved in only one direction by the light flux width conversion element. It is reduced. The reduced light beam enters the polarization beam splitter, and the p-polarized component light is transmitted as it is on the polarization separation surface thereof, and the s-polarized component light is reflected, so that two linearly polarized light beams whose polarization directions are orthogonal to each other. Is separated into The reflected s-polarized light is reflected by the light flux reflecting surface of the adjacent light flux reflecting element. Since the light flux reflecting surface of the light flux reflecting element is arranged in parallel to the polarization splitting surface of the polarization beam splitter, the s-polarized light is emitted in parallel in the same direction as the traveling direction of the p-polarized light. The incident light flux reduced to half by the conversion element becomes equal to the original light flux width again. Furthermore, since the half-wave plate has the function of rotating the polarization direction of the incident linearly polarized light by 90 degrees and outputting it,
Of the p-polarized light and the s-polarized light, the polarization direction of the one linearly polarized light having the half-wave plate arranged in the optical path is the same as the polarization direction of the other linearly polarized light by passing through the half-wave plate. Will be equal. Therefore, when indefinite polarized light from the light source is incident on the polarization conversion element, the output light from the polarization conversion element is linearly polarized light in which the incident light has the same traveling direction and the same luminous flux width, and the polarization direction is aligned in a specific direction. It will be converted into light efficiently.

Further, in the case of a configuration in which two or more sets of the above-mentioned components are arranged in parallel, the thickness of the light beam width conversion element and the polarization beam splitter can be made thin, and the polarization conversion element can be made small and lightweight. become.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a polarization conversion element showing a first embodiment of the present invention. As shown in FIG. 1, the polarization conversion element of this embodiment includes a light flux width conversion element 1, a polarization beam splitter 2, a light flux reflection element 3, and a ½ wavelength plate 4. The light flux width conversion element 1 and the polarization beam splitter 2 have the same optical axis, and are arranged so that the emitted light 11 from the light flux width conversion element 1 enters the polarization beam splitter 2. The polarization beam splitter 2 is arranged such that the reflection direction of the s-polarized light 13 reflected by the polarization splitting surface 7 is parallel to the direction in which the light flux width is reduced in the light flux width conversion element 1. The light flux reflecting element 3 is configured to reflect the s-polarized light 13
Is arranged so as to be adjacent to the polarization beam splitter 2 in the reflection direction of and the light flux reflecting surface 8 is parallel to the polarization splitting surface 7. The half-wave plate 4 is arranged in the optical path of the s-polarized light 13.

Next, the principle of the polarization conversion element according to the present invention having the configuration shown in FIG. 1 will be described. For example, the emitted light from a white light source such as a xenon lamp or a halogen lamp is indefinite polarized light, and such emitted light is incident on the polarization conversion element.
And Incident light 10 has its luminous flux width reduced to half in one direction by a luminous flux width conversion element 1 including cylindrical lenses 5 and 6 having a refractive power in only one direction. The outgoing light 11 having the reduced luminous flux width is incident on the polarization beam splitter 2, and the polarization splitting surface 7 formed on the polarization beam splitter 2
In, the p-polarized light is transmitted as it is, and the s-polarized light 13 is reflected to be separated into two linearly polarized lights whose polarization directions are orthogonal to each other. Here, the polarization direction of the p-polarized light 12 is parallel to the paper surface, and the polarization direction of the s-polarized light 13 is perpendicular to the paper surface. The reflected s-polarized light 13 is reflected by the light flux reflecting surface 8 of the adjacent light flux reflecting element 3. Since the light flux reflecting surface 8 is arranged in parallel with the polarization splitting surface 7 of the polarization beam splitter 2, the traveling direction of the s-polarized light 13 reflected by the light flux reflecting element 3 is the same as that of the p-polarized light 12. Become parallel. Therefore, the outgoing light 14 from the polarization conversion element,
The light beams 16 are emitted in parallel in parallel, and the width of the light beam once reduced to half by the light beam width conversion element 1 becomes equal to the light beam width of the incident light 10 again. Furthermore, 1/2 wavelength plate 4
Has a function of rotating the polarization direction of the incident linearly polarized light by 90 degrees and emitting the same, the polarization direction of the s-polarized light 13 having the half-wave plate 4 arranged in the optical path is transmitted through the half-wave plate 4. By doing so, it becomes equal to the polarization direction of the p-polarized light 12. As a result, when the indefinite polarized light from the light source is incident on the polarization conversion element, the outgoing lights 14 and 16 from the polarization conversion element have the same traveling direction and the same luminous flux width as the incident light 10, and the polarization direction is a specific direction. Therefore, according to the configuration of the present invention, it is possible to obtain a polarization conversion element that efficiently converts indefinite polarized light emitted from a light source into linearly polarized light. become.

The configuration shown in FIG. 1 uses two cylindrical lenses 5 and 6 as the light beam width conversion element 1, and
1 shows an example of a mode in which the / 2 wavelength plate 4 is arranged in the optical path of the s-polarized light 13, which will be described more specifically below.

The light flux width conversion element 1, the polarization beam splitter 2, the light flux reflection element 3, 1 / used in the configuration of FIG.
The two wave plates 4 are specifically as follows.

As the light flux width conversion element 1, two cylindrical lenses 5 and 6 were used. The cylindrical lens 5 is a plano-convex lens and the cylindrical lens 6 is a plano-concave lens. The focal length ratio is 2: 1, and the luminous flux width of the outgoing light 11 is reduced to half the luminous flux width of the incident light 10 by the Galileo type arrangement. .. That is, the luminous flux diameter of the incident light 10 is 50 mmφ
On the other hand, the size of the incident surface of the cylindrical lens 5 is 5
0 × 50 mm, the focal length is 150 mm, the size of the entrance surface of the cylindrical lens 6 is 25 × 50 mm, the focal length is −75 mm, and the principal point distance between the cylindrical lenses 5 and 6 is set to 75 mm Width 25
Output light 11 of mm was obtained.

The polarization beam splitter 2 has a structure in which a polarization separating surface 7 is formed by coating a semi-permeable film made of a dielectric multilayer film on one slope of two right-angle prisms, and the slopes are joined together. In particular, the one having the ability to sufficiently separate the p-polarized light 12 and the s-polarized light 13 with respect to the indefinite polarized light having the wavelength in the visible light region was used. The extinction ratio, that is, the intensity ratio of the p-polarized component and the s-polarized component of the transmitted light is
It was 100: 1 or more. The size of the entrance surface is 25 x 50
The thickness was 25 mm, the thickness was 25 mm, and an antireflection film made of a dielectric multilayer film was applied to the entrance surface and the exit surface.

As the light flux reflecting element 3, an aluminum surface mirror was used in which aluminum was vapor-deposited on a glass substrate and the surface was subjected to an increased reflection coating made of a dielectric multilayer film.

The half-wave plate 4 is formed by stretching a polyvinyl alcohol film so as to have a desired birefringence and sandwiching it between protective glasses so as to effectively act on light in the visible light range. did. An antireflection film made of a dielectric multilayer film is applied to the light incident / emission surface of the half-wave plate 4.

Now, in the polarization conversion element of FIG. 1, if indefinite polarized light from the light source enters the polarization conversion element,
As described in the above description of the principle, the incident light 10 has its luminous flux width reduced to half in only one direction by the luminous flux width conversion element 1 including the cylindrical lenses 5 and 6. The outgoing light 11 having the reduced luminous flux width is polarized by the polarization beam splitter 2 and the polarization directions of the p-polarized light 12 and the s-polarized light 13 are orthogonal to each other.
It is split into two linearly polarized lights. Here, the polarization direction of the p-polarized light 12 is parallel to the paper surface, and the polarization direction of the s-polarized light 13 is perpendicular to the paper surface. The p-polarized light 12 is emitted from the polarization conversion element as it is, and emitted light 14 is obtained. The s-polarized light 13 is reflected by the adjacent light beam reflection element 3, and the traveling direction of the reflected light 15 is parallel to the traveling direction of the p-polarized light 12. Furthermore, the polarization direction of the reflected light 15 becomes equal to the polarization direction of the p-polarized light 12 by passing through the half-wave plate 4, and the emitted light 16 from the polarization conversion element is obtained.

As a result, the output light 1 from the polarization conversion element 1
4 and 16 are converted into linearly polarized light whose traveling direction is the same as that of the incident light 10 and whose luminous flux width is the same, and whose polarization direction is aligned in a specific direction, which is a direction parallel to the paper surface here. In the above process, the light loss is a slight amount caused by absorption and scattering of the medium. Thus, by using the polarization conversion element of FIG. 1 according to the present invention to obtain linearly polarized light, it is possible to efficiently obtain linearly polarized light.

FIG. 2 is a plan view of a polarization conversion element showing the second embodiment of the present invention. As shown in FIG. 2, the polarization conversion element of the present embodiment has a light flux width conversion element 21, a polarization beam splitter 22, a light flux reflection element 23, and a ½ wavelength plate 24 as constituent elements 20, and its configuration. It is configured by arranging four sets of the elements 20 in parallel. Arrangement of each component is 1/2
The wave plate 24 is separated by the polarization beam splitter 22 from p
It is similar to the first embodiment except that it is arranged in the optical path of polarized light.

The configuration shown in FIG. 2 shows an example of a mode in which a right-angle prism is used as the light flux reflecting element 23 and a ½ wavelength plate 24 is arranged in the optical path of p-polarized light. Hereinafter, this will be described more specifically.

A light flux width conversion element 21, a polarization beam splitter 22, and a light flux reflection element 2 used in the constituent element 20 of FIG.
The 3, 1/2 wave plate 24 is specifically as follows.

As the luminous flux width conversion element 21, two cylindrical lenses 25 and 26 are used as in the first embodiment. In this embodiment, the luminous flux diameter of the incident light is 80 mmφ.
On the other hand, a light flux with a width of 20 mm is incident on each of the four sets of constituent elements. Cylindrical lens 25
The size of the entrance surface is 20 x 80 mm, and the focal length is 60 m
m, the size of the incident surface of the cylindrical lens 26 is 10
By setting the distance between the principal points of the cylindrical lenses 25 and 26 to be 30 mm, the emitted light having a luminous flux width of 10 mm was obtained.

The polarization beam splitter 22 used has the same performance as that of the first embodiment. The incident surface has a size of 10 × 80 mm and a thickness of 10 mm. An antireflection film made of a dielectric multilayer film was applied to the incident surface.

As the light flux reflecting element 23, a rectangular prism is used. The light flux reflecting surface is an inclined surface of a right angle prism and was used in a form utilizing total internal reflection. An antireflection film was applied to the emission surface. The polarizing beam splitter 22 and the polarizing beam splitter 22 are adhered to each other while matching the refractive index, but the present invention is not limited to this method, and one prism of the polarizing beam splitter 22 can be integrally manufactured in the shape shown in the figure for polishing.

As the half-wave plate 24, one having the same performance as that of the first embodiment was used. An antireflection film made of a dielectric multilayer film was applied to the emission surface. The half-wave plate 24 and the polarization beam splitter 22 are adhered to each other with matching refractive indexes.

The polarization conversion element of the present embodiment includes a constituent element 20 composed of the light flux width conversion element 21, the polarization beam splitter 22, the light flux reflection element 23, and the ½ wavelength plate 24 described above.
Four sets were arranged in parallel. Therefore, the size of the incident surface of the polarization conversion element was 80 × 80 mm, and the length in the optical axis direction was 50 mm with respect to the luminous flux diameter of 80 mmφ of the incident light.

Now, in the polarization conversion element of FIG. 2, when indefinite polarized light from the light source enters the polarization conversion element, the light beam is divided into light beams having the incident surface of each component as a cross section. In order to achieve the above, attention is paid to the luminous flux that has entered the constituent element 20, and the optical path thereof will be used in the following description.

The luminous flux incident on the constituent element 20 is, as described in the first embodiment, cylindrical lenses 25 and 26.
The beam width conversion element 21 made of reduces the beam width by half in only one direction. The emitted light with the reduced luminous flux width is separated by the polarization beam splitter 22 into two linearly polarized lights of p-polarized light and s-polarized light whose polarization directions are orthogonal to each other. Here, the polarization direction of the p-polarized light is parallel to the paper surface, and the polarization direction of the s-polarized light is perpendicular to the paper surface. The s-polarized light is reflected by the adjacent light flux reflecting element 23, the traveling direction of the reflected light becomes parallel to the traveling direction of the p-polarized light, and exits the constituent element 20. The p-polarized light is transmitted through the half-wave plate 24 so that its polarization direction becomes equal to that of the s-polarized light,
Emitted from the component 20.

As a result, the light emitted from the constituent element 20 is converted into linearly polarized light whose traveling direction is the same as that of the incident light, and whose luminous flux width is equal, and whose polarization direction is aligned in a specific direction, here, the direction perpendicular to the paper surface. To be done.

With respect to the luminous flux incident on the other components,
Similar to the luminous flux incident on the constituent element 20, the emitted light thereof is a linearly polarized light whose traveling direction is equal to that of the incident light, and the luminous flux width is equal, and the polarization direction is aligned in a specific direction, here, a direction perpendicular to the paper surface. Is converted to.

In the above process, the light loss is a slight amount caused by absorption and scattering of the medium. As described above, by using the polarization conversion element of FIG. 2 according to the present invention to obtain linearly polarized light, it is possible to efficiently obtain linearly polarized light. Further, according to the configuration of the second embodiment, the length of the polarization conversion element in the optical axis direction can be made shorter than the diameter of the incident light beam, and the thickness of the light beam width conversion element and the polarization beam splitter can be reduced. Therefore, it is possible to reduce the size, weight and cost of the polarization conversion element.

In the above description of the first and second embodiments, as the light beam width converting element, two plano-convex cylindrical lenses having a focal length ratio of 2: 1 are arranged in a Kepler-type arrangement, or a prism. It is also possible to use a structure in which the width of the light flux is halved by utilizing the refraction of. As the cylindrical lens, one having one surface or both surfaces processed into a spherical surface or an aspherical surface, a gradient index lens, or the like can be used, and the light flux width conversion element may be configured by a combination thereof.
As the light flux reflecting element, a surface mirror having a metal such as silver or a dielectric multilayer film deposited thereon, a polarization beam splitter, or the like can be used in addition to the aluminum surface mirror and the rectangular prism. 1
In addition to this, as the / 2 wavelength plate, a structure in which two or more retardation plates are stacked, an optical crystal having birefringence, or a structure in which a liquid crystal is sandwiched between two glass substrates that have been subjected to an alignment treatment A liquid crystal cell or the like can also be used. Further, in order to further improve the polarization degree of the emitted light, a polarizing plate may be inserted in the optical path of the emitted light. In this case, since the light incident on the polarizing plate is linearly polarized in advance, the light absorption by the polarizing plate is small, and the light utilization efficiency is reduced, heat is generated, and the performance is not deteriorated.

[0039]

As described above, according to the present invention,
A polarization conversion element capable of efficiently converting indefinite polarized light emitted from a light source into linearly polarized light can be obtained.

Particularly when used in a projection type liquid crystal display device, the size of the polarization beam splitter, which has been a problem in the conventional example due to the large luminous flux diameter of the illumination light, can be made small, and the size of the entire element is also reduced. Comparing with the second embodiment of the present invention, for example, when the incident light beam diameter is 80 mmφ, the length in the optical axis direction is 62.5%, the outer shape deposition is 42.0%, and the weight is 18.1%. Therefore, it was possible to realize smaller size and lighter weight. Further, in the present invention, since it is not necessary to combine the light beams separated by the polarization beam splitter again, even if a liquid crystal display element or an optical element having an incident angle dependency is used, the image quality of the projected image is not deteriorated, and the projection image is projected. There was no problem due to vignetting of the lens. Furthermore, since it is possible to efficiently obtain linearly polarized light, it is possible to reduce the power consumption of the device, and it is possible to avoid the adverse effect of heat generation. That is, according to the present invention, in the projection type liquid crystal display device, the projection image can be displayed at a high image quality without deterioration of the polarizing plate or the liquid crystal display element, deterioration of the image quality of the projection image, increase in size of the device, and significant increase in manufacturing cost. It was possible to obtain a polarization conversion element that is effective for increasing the brightness.

The polarization conversion element according to the present invention is effective not only for projection type liquid crystal display devices but also for devices and devices that use polarized light.

[Brief description of drawings]

FIG. 1 is a plan view of a polarization conversion element showing a first embodiment of the present invention.

FIG. 2 is a plan view of a polarization conversion element showing a second embodiment of the present invention.

[Explanation of symbols]

 1, 21 Light flux width conversion element 2, 22 Polarization beam splitter 3, 23 Light flux reflection element 4, 24 1/2 wavelength plate 5, 6, 25, 26 Cylindrical lens 7 Polarization separation surface 8 Light flux reflection surface 10 Incident light 11, 14 , 16 Emitted light 12 p-polarized light 13 s-polarized light 15 reflected light 20 components

Claims (1)

[Claims] 1. A light flux width conversion element for reducing the width of a light flux to half in one direction, and two linearly polarized light beams, p-polarized light and s-polarized light, whose polarization directions are orthogonal to each other. A polarization beam splitting surface for splitting light into light is formed so that a direction in which the light flux width of the light flux width conversion element is reduced and a reflection direction of the s-polarized light are parallel to each other; Light-reflecting element having a light-reflecting surface that is adjacent to the polarization beam splitter in the reflection direction of the s-polarized light, and one of p-polarized light and s-polarized light separated by the polarization beam splitter. And a half-wave plate arranged in the optical path of 1. as a constituent element, and the constituent element is configured alone or by arranging two or more sets in parallel.