JPH11305167A - Polarized light converting element and picture projecting device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to make an incident luminous flux to exit with the directions of polarization made the same by tilting a polarized light separating plane at a specific angle to incident light. SOLUTION: A polarized light converting element is formed out of a polarized light separating plane M11 for separating incident light into mutually straight-going reflected light and transmitted light by a plane of polarization, a reflecting plane M21 for reflecting either of the reflected light and the transmitted light and directing it almost in the same traveling direction of the other light, and a 1/2-wave plate F1 for matching both planes of polarization with each other by varying at least one of the planes of polarization of the reflected light and the transmitted light. In such a composition, the polarized light separating plane M11 is tilted at an angle of 47-53 degrees to the incident light. Incident light La on a glass block G11 is separated into P- and S-polarized light via the polarized light separating plane M11. The P-wave is transmitted through the polarized light separating plane M11 and made to exit from a light exit surface GE. The S-wave is reflected thereby and further reflected by the reflecting plane M21, and then, it is directed in the same direction of the P-wave. After the S-wave has been made to exit from the glass block G11, the plane of polarization of the S-wave is rotated by 90 degrees, and it becomes P-wave to be made to exit from the light exit surface GE.

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 and an image projection apparatus using the same, and more particularly, to a liquid crystal display element (liquid crystal panel) as an image display element, and to effectively use an image displayed on the liquid crystal panel with a light beam. This is suitable for a liquid crystal projector that illuminates and projects the image on a predetermined surface, for example, a screen, with a projection lens.

[0002]

2. Description of the Related Art Conventionally, an image is displayed using a liquid crystal panel, the liquid crystal panel is illuminated by a light beam from a light source, and an image based on transmitted light or reflected light from the liquid crystal panel is enlarged and projected on a screen by a projection lens. Various liquid crystal projectors have been proposed.

A TN type liquid crystal panel from which a high-contrast image can be obtained relatively easily utilizes the polarization characteristics of liquid crystal. For this purpose, a polarizing filter such as a polarizer or an analyzer is usually provided before and after the liquid crystal panel. The polarizing filter has a characteristic of transmitting a specific polarization direction of incident light and blocking a polarization direction orthogonal thereto. Therefore, at least half of the light used in the liquid crystal projector is blocked by the polarizing filter, and the brightness of the projected image tends to decrease.

As a lighting device for a liquid crystal projector,
Efficient use of luminous flux from the light source using a polarization conversion element that converts incident light into a luminous flux having a polarization plane in a specific direction and emits it, and a uniform illuminating means (optical integrator) for uniformly illuminating the illuminated slope For example, Japanese Patent Laid-Open Publication No. Hei 8-
No. 304739 proposes. FIG. 6 is a schematic view of a main part of a polarized light illuminating device proposed in the publication.

[0005] In the polarized light illumination device shown in FIG.
Is a polarization conversion element, which is arranged near the condenser lens array 304. The polarization separation prism array (polarization conversion element) 310 is formed of a plate-like element in which a plurality of polarization beam splitters 305 and a total reflection prism unit 306 are arranged as one unit (optical unit). Reference numeral 303 denotes a first lens plate, of which one array lens 3
Reference numeral 07 condenses the image of the light source 301 on the corresponding array lens 308 of the condensing lens array 304, and thereafter, makes it incident on the optical unit of the polarizing beam splitter 305. The polarization beam splitter 305 splits the incident light into two linearly polarized lights (P-polarized light and S-polarized light) whose polarization planes are orthogonal to each other.
Among them, the linearly polarized light (for example, P-polarized light) transmitted through the polarization beam splitter 305 is converted into the plate-shaped polarization conversion element 31.
The phase is 9 with the half-wave plate 309 arranged on the exit surface
The light is inverted by 0 degrees and becomes linearly polarized light (S-polarized light) having a different polarization plane from the transmitted light.

On the other hand, the linearly polarized light (S-polarized light) reflected by the polarization beam splitter 305 is further transmitted to a total reflection section 306.
And is emitted in the same direction as the transmitted light. However,
Since the half-wave plate 309 is not applied to the reflected light emitting portion, the transmitted light (P-polarized light) has the same polarization plane as the phase-converted light (S-polarized light). The array lenses 307 and the like of the first lens plate 303 are eccentric and have a positive refractive power as a whole. Thus, the light beam from the first lens plate 303 is emitted in parallel and guided to the polarization conversion element 310. Here, the reason why the light is guided to the polarization conversion element 310 with substantially parallel light is to reduce the angle dependence of the polarization beam splitter 305 as much as possible. The linearly polarized light having the same polarization plane is configured to illuminate the liquid crystal panel surface 312 in a rectangular shape by the condenser lens 311 on the emission side.

[0007]

In the polarized light illuminating device shown in FIG. 11, a light beam emitted from a light source 301 passes through a first lens plate 303 in which a plurality of rectangular lenses are arranged in a matrix, and then a condensing lens is formed. The polarization state is made uniform by the polarization splitting prism array 310 and the λ / 2 plate 309 via the array 304 to make oblique light, and then the light is condensed by the emission side lens 311 to illuminate the illumination area 312.

Then, the polarization conversion element 310 in FIG.
The polarization beam splitter 305 is arranged at an inclination of 45 degrees with respect to the incident light. Since the angle (45 degrees) at this time is apart from the Brewster angle, the polarization beam splitter 305 is used to obtain predetermined polarization characteristics as described later.
Has a tendency to be very difficult to manufacture due to the multilayer structure.

According to the present invention, by appropriately setting the shapes of the polarization separation surface and the reflection surface, the film configuration of the polarization separation surface can be simplified, and the incident light beam can be emitted in the same polarization direction. It is an object of the present invention to provide a polarization conversion element suitable as a lighting device for a liquid crystal display element and a liquid crystal projector, and an image projection apparatus using the same.

[0010]

According to the present invention, there is provided a polarization conversion element comprising: (1-1) a polarization separation surface for dividing incident light into reflected light and transmitted light whose polarization planes are perpendicular to each other; It has a reflecting surface that reflects one of the lights and directs the light in the same direction as the other traveling direction, and a wave plate that changes at least one polarizing surface of the reflected light and the transmitted light to match both polarizing surfaces. The polarization conversion element is characterized in that the polarization splitting surface is inclined at 47 to 53 degrees with respect to the incident light.

The plate-like polarization conversion element of the present invention is characterized in that (2-1) a plurality of the polarization conversion elements having the constitution (1-1) are arranged.

An image projection apparatus according to the present invention is: (3-1) An image projection apparatus which guides a light beam from a light source to a liquid crystal display element and projects a display image of the liquid crystal display element onto a predetermined surface by a projection lens. And the liquid crystal display element is characterized in that the polarization conversion element having the configuration (1-1) or the plate-shaped polarization conversion element having the configuration (2-1) is used between the light source and the liquid crystal display element.

(3-2) The light beam from the light source is separated into a plurality of color lights by a color separation optical system via a light amount equalizing means, and the separated light beams are guided to liquid crystal display elements of the corresponding color lights. In an image projection apparatus that synthesizes a display image of the liquid crystal display element of the above with a color synthesizing optical system and projects a predetermined surface with a projection lens, a configuration (1-1) is provided between the light source and the liquid crystal display element. It is characterized by using a polarization conversion element or a plate-like polarization conversion element having the configuration (2-1).

[0014]

FIG. 1 shows a polarization conversion element 10 according to the present invention.
FIG. 2 is a sectional view of a main part of the first embodiment. In the present embodiment, the polarization separation surface M11 is set in a range of 47 ° to 53 ° with respect to the incident light. In the figure, the polarization separation plane M11 is set at 50 degrees with respect to the reference plane LP. That is, the polarization separation surface M11
Is 50 degrees with respect to the incident light La. G11 in the figure
G31 denotes prism blocks 1 to 3, M11 denotes a polarization separation surface, M21 denotes a reflection surface, and F1 denotes a half-wave plate.

In this embodiment, light La enters from the left side as viewed in the drawing. The light incident on the prism block G11 is separated into P-wave and S-wave polarized light by the polarization splitting film on the polarization splitting surface M11. The separated P-wave passes through the polarization separation surface M11 and exits from the exit surface GE. On the other hand, the S wave is reflected, further reflected by the reflection surface M21, and directed in the same direction as the P wave. And the prism block G1
After the light is emitted from No. 1, the polarization plane is rotated by 90 degrees by the half-wave plate F1 to become a P-wave, and emitted from the emission surface GE. As a result, a polarization conversion element that doubles the amount of P-wave is achieved.

Here, the light ray La1 passing from the upper end of the entrance surface GI of the prism block G11 to the center lower part behaves as described above, but the light ray La2 passing through the lower end is not as described above. Specifically, the glass block G11
Ray La2 entering the lower end portion of P
The P wave is separated into a wave and an S wave, and the P wave is transmitted through the polarization separation surface M11 and reflected by the S wave. The reflected S wave is a reflection surface M2
1, the light is emitted from the glass block G11 as it is and emitted in a direction different from the P wave. However, the amount of light at this time does not cause a large loss. The reason is that the light beam incident on the polarization conversion element of the present invention is not necessarily a light beam having a uniform intensity, but a light beam having an intensity peak at a central portion having a Gaussian distribution to some extent. is there. Therefore, the conversion efficiency when the polarization separation film is multilayered in order to obtain a predetermined polarization characteristic is much more affected than the loss. In this embodiment, in order to increase the efficiency of the polarization action of the polarization conversion element, the polarization separation surface M11 is set at the above-described angle to simplify the film configuration of the polarization separation film.

In particular, in the present embodiment, the inclination of the polarized light separating surface with respect to the incident light is set to 47 ° to 53 °, which is larger than 45 °, so that even if the film configuration of the polarized light separating film is 5 to 9 layers, it is good. Polarization characteristics are obtained.

FIG. 2 is a cross-sectional view of a principal part of Embodiment 2 of the polarization conversion element 101 of the present invention. In this embodiment, the polarization separation plane M11 is set at 50 degrees with respect to the reference plane LP.
In the figure, G12 to G32 are prism blocks 1 to 3, M12
Denotes a polarization separation surface, M22 denotes a reflection surface, and F2 denotes a half-wave plate.

In this embodiment, the polarization separation surface M of the first embodiment is used.
11 and the reflection surface M21 are lengthened to further increase the efficiency. Specifically, the light La2 incident on the lower end of the incident surface GI is separated into a P wave and an S wave by the polarization separating surface M12, and the reflected S wave is reflected by the reflecting surface M22 to be 1
The light is converted into a P-wave through the half-wave plate F1, and is emitted from the emission surface GE in the same direction as the P-wave that has passed through the polarization separation surface M12. Although the length is longer in the optical axis direction, the conversion efficiency is improved compared to the first embodiment.

FIG. 3 shows a plate-like polarization conversion element 101 of the present invention.
It is principal part sectional drawing of Embodiment 3 of FIG. In the present embodiment, the polarization conversion element of the first embodiment is formed in an array shape (plate shape), and substantially the same effects as in the first embodiment can be obtained.

FIG. 4 shows a plate-like polarization conversion element 101 of the present invention.
It is principal part sectional drawing of Embodiment 4 of FIG. In the present embodiment, the polarization conversion element of the second embodiment is formed in an array shape (plate shape), and substantially the same effects as in the second embodiment can be obtained.

In each of the embodiments described above, the incident light is converted into a P wave after the polarization conversion by the polarization conversion element.
By changing the position where the wave plate is disposed, the wave plate may be aligned with the S wave after the polarization conversion.

The form of the polarization conversion element of the present invention preferably satisfies at least one of the following conditions in terms of optical performance.

(A-1) When the refractive index of the material of the polarization conversion element is Nd, it satisfies 1.48 <Nd <1.58 (1).

This conditional expression (1) is a factor that is greatly related to the above-mentioned Brewster angle. If the refractive index is smaller than the lower limit, the angle θ of the prism block becomes large, and the light amount loss as described in the first embodiment becomes so large that it cannot be ignored, which undesirably lowers the polarization conversion efficiency. Conversely, if the refractive index exceeds the upper limit and becomes too large, the material of the glass becomes physically and chemically unstable, which is not good.

(A-2) The polarized light separating surface is formed by laminating five to nine thin films.

This is because the refractive index of the material of the polarization conversion element satisfies the conditional expression (1), and the angle θ of the polarization conversion element is brought close to the Brewster's angle. Is easily composed of five to nine layers, thereby facilitating manufacture.

(A-3) The refractive index of the material of the uppermost film and the lowermost film of the laminated film of the polarization separation film is NU, NS, and the film thickness is DU, DS.
(Nm), 2.0 <NU <2.4 (2) 2.0 <Ns <2.4 (3) 170 <DU <340 (4) 170 <DS <340 ... (5) is satisfied.

By satisfying these conditional expressions (2) to (4), a high transmittance is achieved for visible light having a wavelength of 400 nm to 700 nm.

(A-4) Assuming that the thickness of the intermediate layer of the laminated film of the polarized light separating film is DM, the following condition is satisfied: 150 <DM <210 (6).

Thus, the wavelength of 400 nm to 700 nm
And a good transmittance with little ripple in visible light.

(A-5) Assuming that the refractive indices of the high refractive index film and the low refractive index film of the polarization separation film are NH and NL, 0.55 <NH−NL <0.95... 7) is satisfied.

As a result, high transmittance is achieved with a small number of thin films.

FIG. 5 is a functional diagram showing the configuration of the polarization conversion element of the present invention and a liquid crystal projector (image projection apparatus) using the same, and is a schematic view of the liquid crystal projector main body as viewed from above.

In the figure, reference numeral 51 denotes a projection lens.
It consists of a zoom lens and a single focal length lens.
52 is a lens holder for connecting the projection lens to the main body,
53 is an exterior part of the main body of the liquid crystal projector, 54 is an optical engine box containing various optical components, 55
Is a lamp reflector, 56 is a glass book of a color combining prism and a color filter, 57 to 59 are liquid crystal display elements for displaying images corresponding to R, G, and B colors, and 60 to 62.
Is a condenser lens for shaping light incident on the liquid crystal display element, 63, 65, 68 are dichroic mirrors (color separation mirrors) or total reflection mirrors, 64, 66 are condenser lenses, 67, 69 are dichroic mirrors,
Numerals 70 and 72 are light quantity equalizing means for making the light quantity on the screen substantially uniform and having an afocal function, and include, for example, a fly-eye lens, a rod lens, a rectangular lens array, and the like. Numeral 80 denotes the polarization conversion element of the present invention shown in FIGS. 1 to 4, which has a function of aligning the polarization directions of the light in order to effectively use the light from the light source 73 and increase the amount of light on the screen.
71 is a total reflection mirror and 73 is a light source.

In the present embodiment, the polarization conversion element 80 is disposed between the light source 73 and the liquid crystal display elements 57 to 59 to increase the efficiency of using light from the light source 73.

In the figure, white light emitted from a light source 73 is reflected forward by a reflector 55, reflected by a total reflection mirror 71 via a fly-eye lens 72, and then reflected by a polarization conversion element 80 via a fly-eye lens 70. The polarization planes are aligned and the light becomes substantially uniform, and enters the first dichroic mirror 69. The first dichroic mirror 69 decomposes the light into, for example, two colors (R) and (G, B), and one of the lights (R) is transmitted and reflected by a third dichroic mirror or a total reflection mirror 68 so as to be condensed. The light enters the lens 60.

The other light (G, B) is reflected by the first dichroic mirror 69 and enters the second dichroic mirror 67. The dichroic mirror 67 further separates the light into two colors G and B, and one light G is reflected and enters the condenser lens 61.

The other light B is transmitted and transmitted through the first condenser lens 66, further reflected by the fourth dichroic mirror or the total reflection mirror 65, transmitted through the second condenser lens 64, and transmitted through the fifth condenser lens 64. Condenser lens 6 reflected by dichroic mirror or total reflection mirror 63
2 is incident.

The light incident on each of the condenser lenses 60 to 62 irradiates the liquid crystal display elements 57 to 59 corresponding to each color, and becomes light having image information.
Eject from 7-59. These three lights are combined into one light by each combining prism 56, and the projection lens 51
Is projected on the screen.

In some cases, a polarizing filter is disposed between the liquid crystal display element and the condenser lens.

FIG. 6 is a side view of the liquid crystal projector. In the figure, reference numeral 81 denotes an optical axis of the zoom lens, and reference numeral 82 denotes an axis perpendicularly passing through the center of the screen of the liquid crystal display device.

In the figure, it can be seen that 81 and 82 do not match and are shifted. This is because when the image displayed on the liquid crystal display element is projected on a screen (not shown) by the zoom lens, the image is projected above the liquid crystal projector main body. Accordingly, when observing an image on the screen behind the liquid crystal projector with respect to the screen, the portion where the liquid crystal projector main body overlaps with the image projected on the screen is reduced, and an image which is easy to observe is provided. It becomes possible.

Next, Numerical Examples 1 to 4 of the film configuration of the polarization splitting surface of the polarization conversion element of the present invention will be shown. The film number is a number counted from one glass block sandwiched between two glass blocks (G11 and G31). Numerical example 1,
The film numbers 0 (G11) and 8 (G31) of 2 and the film numbers 0 (G11) and 10 (G31) of Numerical Examples 3 and 4 indicate a glass block or an adhesive. Numerical Example 1
7 to 10 show the color light transmittances of No. 4 to No. 4.

[0045]

[Outside 1]

[0046]

[Outside 2] Table 1 shows the relationship between the above-mentioned conditional expressions and the numerical examples 1-4.

[0047]

[Table 1]

[0048]

As described above, according to the present invention, by appropriately setting the shapes of the polarization separation surface and the reflection surface, the film configuration of the polarization separation surface can be simplified, and the polarization direction of the incident light beam can be changed. The light can be emitted in a line, and for example, a polarization conversion element suitable as a lighting device for a liquid crystal display device and a liquid crystal projector and an image projection device using the same can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a first embodiment of a polarization conversion element of the present invention.

FIG. 2 is a sectional view of a principal part of a polarization conversion element according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a main part of a third embodiment of the plate-like polarization conversion element of the present invention.

FIG. 4 is a sectional view of a main part of a fourth embodiment of the plate-like polarization conversion element of the present invention.

FIG. 5 is a schematic view of a main part of an embodiment of the image projection apparatus of the present invention.

FIG. 6 is a schematic diagram of a main part of an embodiment of the image projection apparatus of the present invention.

FIG. 7 is an explanatory diagram of the spectral transmittance of Numerical Example 1 of the polarization conversion element of the present invention.

FIG. 8 is an explanatory diagram of the spectral transmittance of Numerical Example 1 of the polarization conversion element of the present invention.

FIG. 9 is an explanatory diagram of the spectral transmittance of Numerical Example 1 of the polarization conversion element of the present invention.

FIG. 10 is an explanatory diagram of the spectral transmittance of Numerical Example 1 of the polarization conversion element of the present invention.

FIG. 11 is a schematic view of a main part of a conventional polarized lighting device.

[Explanation of symbols]

G11, G21, G31 Glass block M11, M12 Polarized light separation surface M21, M22 reflection surface F1, F21 / 2 wave plate PP wave S S wave 51 Projection lens 53 Exterior part of image projection device 54 Various optical components are included. Optical engine box 55 Lamp reflector 56 Glass block of color combining prism and color filter 57, 58, 59 Liquid crystal display elements 60, 61, 62 for displaying images corresponding to the respective colors of light 60, 61, 62 Light incident on the liquid crystal display elements Lenses 63, 65, 68 dichroic mirrors (color separation mirrors) or total reflection mirrors 64, 66 condenser lenses 67, 69 dichroic mirrors 70, 72 Fly-eye lenses 80 for making the amount of light on the screen substantially uniform Polarization conversion element of the invention 71 Total reflection mirror 73 Light Axis passing through the vertical center of the screen of the optical axis 82 the liquid crystal display device of 81 the projection lens

Claims (13)

[Claims] 1. A polarization splitting surface for splitting incident light into reflected light and transmitted light whose polarization planes are orthogonal to each other, and reflects one of the reflected light and the transmitted light and directs the reflected light and the transmitted light in substantially the same direction as the other traveling direction. In a polarization conversion element having a reflection surface and a wave plate for changing at least one of the reflected light and the transmitted light so as to match both polarization planes, the polarization splitting surface has a wavelength of 47 to the incident light. A polarization conversion element characterized by being inclined at an angle of 53 degrees to 53 degrees. 2. The refractive index of the material of the polarization conversion element is Nd.
2. The polarization conversion device according to claim 1, wherein: 1.48 <Nd <1.58 is satisfied. 3. The polarization conversion element according to claim 1, wherein the polarization separation surface is formed by laminating five to nine thin films. 4. The refractive index of the material of the uppermost film and the lowermost film of the laminated film of the polarized light separating film is NU, NS, and the film thickness is DU, DS (n
4. The polarization conversion element according to claim 3, wherein, when m), 2.0 <NU <2.4 2.0 <NS <2.4 170 <DU <340 170 <DS <340. 5. The polarization conversion device according to claim 3, wherein, when the thickness of the intermediate layer of the laminated film of the polarization separation film is DM, 150 <DM <210 is satisfied. 6. When the refractive indices of the high refractive index film and the low refractive index film in the laminated film of the polarization separating film are NH and NL, the following relationship is satisfied: 0.55 <NH−NL <0.95. The polarization conversion element according to claim 3. 7. A plate-like polarization conversion element comprising a plurality of the polarization conversion elements according to claim 1 arranged therein. 8. An image projection apparatus for guiding a light beam from a light source to a liquid crystal display element and projecting a display image of the liquid crystal display element on a predetermined surface by a projection lens, wherein a light beam is transmitted between the light source and the liquid crystal display element. An image projection apparatus comprising the polarization conversion element according to claim 1 or the plate-like polarization conversion element according to claim 7. 9. A luminous flux from a light source is separated into a plurality of color lights by a color separation optical system via a light amount equalizing means, and the light is guided to a liquid crystal display element of each corresponding color light, and the liquid crystal display of each color light is performed. 7. An image projection apparatus which synthesizes a display image of an element by a color synthesizing optical system and projects the image on a predetermined surface by a projection lens, between the light source and the liquid crystal display element. An image projection apparatus, comprising: the polarization conversion element according to any one of claims 1 to 7, or the plate-shaped polarization conversion element according to claim 7. 10. The light amount equalizing means includes at least one of a rectangular lens array in which a plurality of minute rectangular lenses are arranged, a fly-eye lens in which a plurality of minute lenses are arranged, or a rod lens. The image projection device according to claim 9, wherein: 11. The polarization conversion element according to claim 1, or the plate-like polarization conversion element according to claim 7 is arranged on the light exit surface side of the light quantity equalizing means. The image projection device according to claim 9, wherein: 12. The image projection apparatus according to claim 9, wherein a condenser lens is disposed on a light incident surface side of the liquid crystal display element for each color light. 13. An image projection apparatus according to claim 9, wherein said light amount equalizing means has an afocal function of emitting an incident light beam as a substantially afocal light beam.