JPH11271682A - Polarized light converter and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize the color and brightness of light for illumination by a short optical path by eliminating irregularities thereof and to convert all incident light into polarized light having the same polarization plane. SOLUTION: In this polarized light converter, the plural pieces of the combination of a luminous flux conversion element 4 composed of a first prism 2 for refracting an incident luminous flux 1 in a specified direction and a second prism 3 for refracting the refracted luminous flux to the propagation direction of the incident luminous flux 1 again and arranged so as to make the incident angle of the light on the incident surface of the light smaller than the emission angle of the light on the emission surface of the light in the first prism 2 and the second prism 3 and a polarized light conversion element 8 composed of a polarized light separation means 5 for separating the light from the luminous flux conversion element 4 into two linearly polarized light components orthogonal to each other, a reflection means 6 for matching the advancing directions of the light of the respective linearly polarized light components separated by the polarized light separation means 5 in the same direction and a 1/2 wavelength plate 7 for matching the polarization direction of the separated light are arranged in parallel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization conversion device and a liquid crystal display device, and more particularly, to a light source in a display device or the like which projects a light whose intensity is modulated by a light valve using a liquid crystal element onto a screen by a projection lens. TECHNICAL FIELD The present invention relates to a polarization conversion device characterized by a configuration for increasing the utilization of a liquid crystal display, and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Hitherto, a liquid crystal display panel, a liquid crystal television, or a display for enlarging and projecting an image on a screen by a projection lens by combining with a polarizer utilizing the dependency of the polarization direction of transmitted light on the applied voltage in a liquid crystal element. It is used as a light valve for equipment. Here, a conventional light valve using a liquid crystal element will be described with reference to FIG.

As shown in FIG. 6, incident light 31 from a light source (not shown), which is substantially parallel light, is transmitted through a first polarizer 32 so that a specific straight line corresponding to the direction of the polarization axis of the polarizer 32 is obtained. After aligning the incident light 31 only with the polarization component, the light enters the liquid crystal element 33. The incident light is incident on the second polarizer 35 after the polarization direction is rotated by a specific angle due to the voltage locally applied to the liquid crystal 34, and is again specified according to the direction of the polarization axis of the polarizer 35. Is obtained as the output light 36.

In this case, by adjusting the rotation angle of the polarization for each pixel by the voltage applied to the liquid crystal 34, characters, images, and the like can be arbitrarily generated. For example, as shown in FIG. When the polarization axes of the polarizer 32 and the second polarizer 35 are orthogonal to each other, the light whose polarization plane is rotated by 90 ° by the liquid crystal 34 is transmitted through the polarizer 35 and emitted as output light 36. As a result, a white display section is formed. On the other hand, light that has not been rotated by the liquid crystal 34 cannot pass through the second polarizer 35, and thus becomes a black display section.

However, the incident light 3 illuminating the light valve 3
1 is that the polarization is usually random, so that when passing through the first polarizer 32, the amount of light is attenuated by about half, and the light removed here has no effect on the display. Was wasted.

In order to eliminate such useless light, all the randomly polarized light is converted into linearly polarized light having the same polarization plane, and the linearly polarized light having all the same polarization plane is incident on the liquid crystal element 33. Therefore, such a conventional polarization conversion device will be described with reference to FIG.

FIG. 7A is a cross-sectional view showing a basic structure of a polarization conversion device, in which a polarizing prism 42 having a multilayer film 43 provided between two prisms, and a reflecting film 45 on an inclined surface. And a prism 44 provided with a λ / 2 plate (波長 wavelength plate) 46 on the light exit surface side. The multilayer film 43 reflects S-polarized light and transmits P-polarized light. Because of the nature,
When the incident light 41 in which the P-polarized light and the S-polarized light are mixed at random enters the polarizing prism 42, the multilayer film 43 forms the S-polarized light.
Polarized light is reflected, and P-polarized light is transmitted as it is.

On the other hand, the S-polarized light reflected by the multilayer film 43 is reflected again by the reflection film 45, and then becomes λ / 2
Since the plane of polarization is rotated by 90 ° by the plate 46 and converted into P-polarized light and emitted as outgoing light 47, all the incident light 41 incident on the polarization converter is converted into the same P-polarized light.

However, in such a polarization conversion method, the distribution of the wavelength spectrum is slightly different between the light transmitted through the polarizing prism 42 and the light reflected by the polarizing prism 42. The emitted light 47 emitted and the emitted light 4 emitted via the λ / 2 plate 46
7 differs slightly in color and brightness. Therefore, when light generated by such a polarization conversion device is used as illumination light for a liquid crystal light valve, color and brightness unevenness occurs in a displayed image.

In order to eliminate such unevenness in color and brightness, it is necessary to dispose the polarization conversion device at a position appropriately distant from the liquid crystal element and to eliminate unevenness by mixing light at a distant position. However, increasing the optical path length of the illumination light is not realistic because it corresponds to increasing the size of the liquid crystal light valve device.

The optical path length at which such unevenness in color and brightness is uniform depends on the size of the polarizing prism 42, and the smaller the polarizing prism 42, the shorter the optical path length. By arranging a plurality of such polarizing prisms 42 in a small size, it becomes possible to make light and brightness unevenness uniform with a short optical path length. This situation will be described with reference to FIG.

FIG. 7B shows a plurality of microscopic polarizing prisms 42 arranged in parallel in an array.
Incident light 41 incident on the liquid crystal element is converted into P-polarized light 47, which is emitted from the polarization prism 42 and the λ / 2 plate 46. Since they are mixed at the position, the color and brightness are not uneven, and are uniformed.

[0013]

However, when a plurality of minute polarizing prisms are arranged in parallel in an array as described above, all of the light incident on the polarizing prism is converted into P-polarized light. However, light that has not entered the polarizing prism is wasted or becomes S-polarized light. In either case, there is a problem that the light is wasted and is lost, so this situation will be described with reference to FIG.

FIG. 8 is an enlarged view of the array of polarizing prisms shown in FIG. 7B. As is apparent from FIG. The incident light is
The S-polarized light component is reflected by the back surface of the reflection film 45 and enters the adjacent polarizing prism 42 deflected by 90 °. The S-polarized light component is reflected by the multilayer film 43 and exits from the polarizing prism 42 as it is.

On the other hand, the P-polarized light component passes through the multilayer film 43 and is reflected by the reflection film 45, then the polarization plane is rotated by 90 ° by the λ / 2 plate 46, converted into S-polarized light, and emitted light 47. Therefore, the incident light 41 incident on the reflective film 45 side is converted into the same S-polarized light. Therefore, the incident light 41 incident on the reflective film 45 side is provided in a stage before the liquid crystal element. Since the light is removed by the polarizer, the light does not become effective light for the liquid crystal element, half of the entire incident light 41 is wasted, and the waste of the conventional incident light is not improved as a result. The reflection film 45
Is covered with a non-reflective film, S-polarized light is not emitted, but is lost when the light enters the reflective film 45.
Again, the waste of incident light is not improved.

Accordingly, the present invention eliminates unevenness in the color and brightness of the irradiation light with a short optical path length and makes it uniform.
An object of the present invention is to provide a polarization conversion device that converts all incident light into polarized light having the same polarization plane.

[0017]

FIG. 1 is an explanatory view of the principle configuration of the present invention. Referring to FIG. 1, means for solving the problems in the present invention will be described. See FIG. 1. (1) In the polarization conversion device, the first prism 2 for refracting the incident light beam 1 in a specific direction and the second prism for refracting the refracted light beam in the propagation direction of the incident light beam 1 again in the polarization conversion device. Of the first prism 2 and the second prism 3 are arranged such that the angle of incidence of light on the light incident surface is smaller than the angle of light emission on the light exit surface. A conversion element 4; polarization separation means 5 for separating the light from the light flux conversion element 4 into two linearly polarized light components orthogonal to each other; and a traveling direction of the light of each linearly polarized light component separated by the polarization separation means 5 And a polarization conversion element 8 comprising a half-wave plate 7 for aligning the polarization direction of the separated light. The light flux conversion element 4 and the polarization conversion element Combination with 8 It is characterized in that several are arranged in parallel.

As described above, since the light beam converting element 4 for reducing the size of the incident light beam 1 and entering the polarization converting element 8 is provided in front of the polarization converting element 8 for aligning the polarization direction of the incident light beam 1, Can be effectively incident on the polarization conversion element 8, whereby the loss of light can be greatly reduced. In addition, a plurality of such combinations of the light flux conversion element 4 and the polarization conversion element 8 can be used. Since they are arranged in parallel, it is possible to eliminate unevenness in the color and brightness of the emitted light beam 9 and make it uniform.

(2) According to the present invention, in the above (1), the apex angle of the first prism 2 and the second prism 3 is
The width of the converted light beam emitted from the second prism 3 is an angle that is equal to or less than の of the width of the incident light beam 1.

As described above, the apex angle θ of the first prism 2 and the second prism 3 is set such that the width W ″ of the converted light beam emitted from the second prism 3 is one of the width W of the incident light beam 1. By setting the angle to be equal to or less than / 2, all of the incident light beam 1 can be converted into light of one linearly polarized light component, and the incident light beam 1 can be used completely effectively, for example, the first prism 2 When the refractive index of the second prism 3 is n and the incident light beam 1 is perpendicularly incident on the incident surface of each prism, that is, when the incident angle is 0 °, the outgoing light beam 9 with respect to the width W of the incident light beam 1 W ″ / W = ｛cos [sin ⁻¹ (n · sin θ)] / c
osθ｝ ² , and when n ≒ 1.52, W ″ / W ≦ 1 /
In order to set it to 2, the apex angle θ is set to θ ≦ 31.6 ° ≒ 32 °
It is necessary to

(3) Further, according to the present invention, in the above (1) or (2), the first prism 2 and the second prism 3 are arranged so that light is incident perpendicularly on the incident surface. And the second prism 3 is disposed.

As described above, by arranging the first prism 2 and the second prism 3 so that the incident angle of light to the first prism 2 and the second prism 3 is 0 °, the width of the incident light beam 1 can be reduced most efficiently. .

(4) Further, according to the present invention, in any one of the above (1) to (3), the first prism 2 and the second prism 2
Is characterized in that each of the prisms 3 has an integral structure.

As described above, by forming the first prism 2 and the second prism 3 into an integral structure, that is, by integrally molding them by injection molding or die molding, the individual first prism 2 and second prism 3 are formed. 2 prisms 3
Is unnecessary, and thus the assembly of the polarization conversion device is facilitated.

(5) Further, according to the present invention, in a liquid crystal display device provided with a polarization conversion device in front of a liquid crystal element, any one of the above-mentioned polarization conversion devices (1) to (4) is used as the polarization conversion device. It is characterized by the following.

As described above, by using the above-described polarization conversion device of the present invention, a liquid crystal display device having no display unevenness or unevenness in brightness and having high display luminance by increasing light use efficiency can be provided. Can be.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A polarization converter according to a first embodiment of the present invention will now be described with reference to FIGS. FIG. 2 shows a polarization converter 1 according to the first embodiment of the present invention.
FIG. 3 is a conceptual configuration diagram of elements, including a light flux conversion element including a first prism 12 and a second prism 13, a polarizing prism 14 having a multilayer film 15 provided between two prisms, and a reflection provided on an oblique side of the prism 16. It is constituted by a polarization conversion element comprising a film 17 and a λ / 2 plate 18 provided on the exit end face of the prism 16.

The incident light 11 having a width W of a substantially parallel light beam emitted from a light source (not shown) enters the first prism 12 and is refracted to be converted into light having a width W '. And is converted into light having a width W ″ by refraction by the second prism 13. In order for the light having the width W ″ to completely enter the polarizing prism 14, the width W ″ of the light flux is required. Must be equal to or smaller than the width of the incident surface of the polarizing prism 14.
Are arranged in parallel in order to eliminate unevenness in color and brightness as described later, and the width of the polarizing prism 14 needs to be W / 2 if the size occupied by the reflective film 17 is taken into consideration. Therefore, it is necessary to satisfy the relationship of W ″ / W ≦ 1/2.

That is, the vertex angle of the first prism 12 and the second prism 13 is θ, the refractive index is n, the incident angle of the first prism 12 with respect to the incident surface is ι, and the output angle of the first prism 12 is ρ. In the case of ι = 0 °, that is, in the case of normal incidence, the light beam conversion efficiency is maximized.
When the first prism 12 is arranged with respect to the incident light 11 so that = 0 °, the width W ′ of the light flux emitted from the first prism 12 is W ′ = W · cos ρ / cos θ, and according to the law of refraction, , N = sin ρ / sin θ, ρ = sin ⁻¹ (n · sin θ), and by substituting this ρ, W ′ = W · cos [sin ⁻¹ (n · sin θ)] / co
sθ.

Next, in order to maximize the light beam conversion efficiency, light having a width W 'is perpendicularly incident on the second prism 13, and
In addition, by arranging the propagation direction of the incident light 11 so as to return to the original direction, light having a width W ″ is emitted from the second prism 13.
In order to be emitted substantially parallel to the incident light 11 and to make the incident light 11 completely enter the polarizing prism 14, the width W ″ of the light flux needs to satisfy the relationship of W ″ / W ≦ １ ／.

On the other hand, the light beam width W ″ is calculated as follows: W ″ = W ′ · cos [sin ⁻¹ (n · sin θ)] / cos θ = W × ｛cos [sin ⁻¹ (n · sin [theta]) / cos [theta] >> ² , so that the incident light 11 is completely incident on the polarizing prism 14, W "/ W = {cos [sin ^-1 (n.sin [theta])] / c
It is necessary to set the apex angle θ so that os θ｝ ² ≦ 1/2, and when this is calculated, θ ≦ 31.6 ° ≒ 32 °.

More simply, the width W ″ of the light beam is represented by W ″ / W = {cosρ / cosθ} ² and n = sinρ / sinθ, so that cos ² ρ = 1−sin ² ρ = 1−n ² sin ² θ = (1−n ² ) + n ² cos ² θ Therefore, W ″ / W = [(1−n ² ) + n ² cos ² θ] / cos
By solving ² θ ≦ 1/2, θ ≦ 31.6 ° ≒ 32 ° is obtained.

Next, the light flux converted to the width W ″ is all incident on the polarizing prism 14 and is converted into P-polarized light of the linearly polarized light component of the incident light 11 by the multilayer film 15 provided between the two prisms. Is transmitted as it is and emitted as emission light 19.

On the other hand, the S-polarized light whose polarization plane is orthogonal to the P-polarized light is reflected by the multilayer film 15 and is reflected again by the reflection film 17 provided on the oblique side of the prism 16 so that the traveling direction is aligned with the P-polarized light. By transmitting through the λ / 2 plate 18, the light is emitted as P-polarized light 19 whose polarization plane is rotated by 90 °.

In this manner, the incident light 11 having a light beam width of W
Is converted into light having a width of W ″ by the light beam conversion means, then enters the polarization conversion means, and is emitted as outgoing light 19 in a state where all the light is P-polarized.

It is conceivable to use a lens or the like as the light beam converting means. In this case, depending on the wavelength dependence of the refractive index, the light condensing state and the parallelism differ for each wavelength. In the first embodiment of the present invention,
Since two prisms are used as the light beam converting means, that is, the first prism 12 and the second prism 13, the chromatic dispersion generated in the first prism 12 based on the wavelength dependence of the refractive index is canceled by the second prism 13. It is possible,
The problem of wavelength dispersion can be improved as compared with the case where a lens or the like is used as the light beam converting means.

Referring to FIG. 3, FIG. 3 shows a light beam converting means comprising the first prism 12 and the second prism 1 as described above, and a polarization converting means comprising the polarizing prism 14, the reflection film 15, and the λ / 2 plate 18. Is a conceptual configuration diagram of a polarization converter in which a plurality of combinations (6 in the figure) are arranged in parallel. By arranging a plurality of combinations in parallel in this manner, all the incident light Outgoing light 1 composed of P-polarized light having the same polarization plane
9 and the light beam conversion means and the polarization conversion means are very small, so that the color and brightness unevenness generated in one element can be eliminated by uniformizing with a short optical path length. it can.

FIG. 4 is a conceptual overall configuration diagram of the polarization conversion device according to the first embodiment of the present invention, which comprises an arc tube such as a metal halide lamp or an ultra-high pressure mercury lamp, and a parabolic mirror. Light mixed with various kinds of polarized light emitted from the light emitting tube of the light source 20 is converted into substantially parallel incident light 11 by a parabolic mirror, and is converted into a light flux converting means including a first prism 12 and a second prism 13 having a triangular prism shape. The light is converted into a strip-shaped light beam whose width is narrower than the width of the incident light beam, ideally narrowed by half by the light beam converting means.

The luminous flux converted into a strip shape is supplied to a polarizing prism 14 having a multilayer film, a reflection film 17, and a λ /
The outgoing light 19 of linearly polarized light having the same width as the incident light 11 is polarized into P-polarized light by the polarization conversion means comprising the two plates 18.
The emitted light 19 is used as illumination light for a liquid crystal element constituting a liquid crystal light valve.

As described above, in the first embodiment of the present invention, since the light beam converting means including the first prism 12 and the second prism 13 is used, incident light can be reduced without causing a problem of chromatic dispersion. Since the light can be incident on the effective area of the polarizing prism 14 and the light loss is greatly reduced, the light use efficiency of the liquid crystal light valve is improved, and accordingly, the brightness of the projected display is improved. be able to.

Also, one element of the polarization conversion means consisting of the polarizing prism 14 having the individual multilayer films 15, the reflection film 17, and the λ / 2 plate 18 is minutely formed, and a plurality of these elements are arrayed in parallel. Since the light is arranged in the shape, it is possible to eliminate unevenness in color and brightness of the outgoing light 19 converted into P-polarized light by a short optical path length and obtain uniform illumination light.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a conceptual configuration diagram of a polarization conversion device according to a second embodiment of the present invention, in which a first prism and a second prism are integrated, and other configurations are as described above. This is exactly the same as the first embodiment.

That is, the first prism and the second prism in the polarization conversion device of the second embodiment are integrally formed by injection molding or die molding.
It is composed of the prism 21 and the integrally formed second prism 22, and the use of such an integrally formed prism makes it unnecessary to align the individual prisms, thereby facilitating the assembly of the polarization conversion device.

The embodiments of the present invention have been described above. However, the present invention is not limited to the configuration described in the embodiments, and various modifications are possible. The reflection film 17 and the λ / 2 plate 18 use a prism 16 having a cross section of an isosceles triangle, and a reflection film is formed on the slope of the prism 16 to serve as a reflection means. Is provided as a polarization conversion element, but the prism 16 is used as a space, and a reflector and λ /
The two plates may be fixed and arranged by another means.

In the description of the above-described embodiment, the incident angle ι of the incident light 11 incident on the first prism 12 is set to the vertical incidence of ι = 0 in order to enhance the conversion efficiency of the light flux. It is not limited to this, and may be set to ι ≠ 0 if necessary.

Further, in the above description of the embodiment, the first prism 12 and the second prism 1 are used to convert the width W of the incident light beam to a light beam having a width W ″ which is に or less.
3 according to the refractive index n, and n = 1.52,
θ ≦ 31.6 °, but not necessarily W ″ / W ≦ 1
/ 2 need not be satisfied, and accordingly, θ> 3
1.6 °, and the apex angles θ of the first prism 12 and the second prism 13 may be different from each other.

Further, in the above description of the embodiment, in order to separate the light for each polarization, the polarization conversion comprising the polarizing prism 14 having the multilayer film 15, the reflection film 17, and the λ / 2 plate 18 is performed. Although means is used, an optical element having anisotropy with respect to polarization components orthogonal to each other, for example, calcite or liquid crystal may be used.

In this case, in the optical element, one linearly polarized light goes straight, and the other linearly polarized light is emitted from a position different from the one linearly polarized light by a distance Δd.
By arranging λ / 2 plates of width Δd at intervals of width Δd on the emission end face of the optical element and arranging light flux conversion elements for converting a light flux of width 2Δd into a light flux of width Δd in an array, all the incident light Can be converted into light of only one type of linearly polarized light component.

Further, in the description of each of the above embodiments, when the light whose light flux is narrowed by the light flux conversion means is incident on the polarization conversion means, the light is aligned so as to be incident on the polarizing prism 14. And, in some cases, reflective film 1
7 may be made to be incident on the back surface, in which case, as described with reference to FIG. 8, all light is obtained as S-polarized light.

[0050]

According to the present invention, since the light beam conversion means is provided in front of the polarization conversion means, the incident light can be used effectively, and the combination of the light beam conversion means and the polarization conversion means can be reduced. And a plurality of these minute combinations are arranged in parallel, so that there is no unevenness in color and brightness, whereby a projection display device using a bright liquid crystal light valve without display unevenness can be configured. .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 shows the polarization converter 1 according to the first embodiment of the present invention.
It is a conceptual block diagram of an element.

FIG. 3 is a conceptual configuration diagram of a polarization conversion device according to the first embodiment of the present invention.

FIG. 4 is a schematic overall configuration diagram of the polarization conversion device according to the first embodiment of the present invention.

FIG. 5 is a conceptual configuration diagram of a polarization conversion device according to a second embodiment of the present invention.

FIG. 6 is an explanatory view of a light valve using a conventional liquid crystal element.

FIG. 7 is an explanatory diagram of a polarization conversion device used for a conventional light valve.

FIG. 8 is an explanatory diagram of a problem of a conventional polarization conversion device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incident light beam 2 Prism 3 Prism 4 Light beam conversion element 5 Polarization separation means 6 Reflection means 7 1/2 wavelength plate 8 Polarization conversion element 9 Outgoing light beam 11 Incident light 12 First prism 13 Second prism 14 Polarizing prism 15 Multilayer film 16 Prism Reference Signs List 17 reflective film 18 λ / 2 plate 19 outgoing light 20 light source 21 integrally formed first prism 22 integrally formed second prism 31 incident light 32 polarizer 33 liquid crystal element 34 liquid crystal 35 polarizer 36 emitted light 41 incident light 42 polarizing prism 43 multilayer Film 44 prism 45 reflective film 46 λ / 2 plate 47 outgoing light

Claims (5)

[Claims] 1. A first method for refracting an incident light beam in a specific direction.
And a second prism for refracting the refracted light beam again in the propagation direction of the incident light beam.
A light beam converting element disposed so that an incident angle of light on a light incident surface of the prism and the second prism is smaller than a light emitting angle of light on a light emitting surface; Polarization splitting means for splitting light into two linearly polarized light components orthogonal to each other; reflecting means for aligning the traveling directions of light of the respective linearly polarized light components separated by the polarization splitting means in the same direction; And a polarization conversion element comprising a half-wave plate for aligning the polarization direction of the divided light, wherein a plurality of combinations of the light flux conversion element and the polarization conversion element are arranged in parallel. Polarization conversion device. 2. A vertex angle of the first prism and the second prism is an angle at which a width of a converted light beam emitted from the second prism is equal to or less than の of a width of the incident light beam. The polarization conversion device according to claim 1, wherein the polarization conversion device is provided. 3. The first prism and the second prism, wherein the first prism and the second prism are arranged so that light is incident perpendicularly on an incident surface in the first prism and the second prism. 3. The polarization conversion device according to item 1. 4. The apparatus according to claim 1, wherein the first prism and the second prism have an integral structure.
The polarization converter according to any one of claims 1 to 4. 5. A liquid crystal display device provided with a polarization conversion device in front of a liquid crystal element, wherein the polarization conversion device according to claim 1 is used as the polarization conversion device. Display device.