JP2000180794A - Illuminator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide illuminator for a liquid crystal projector, etc., combining a polarized light conversion means and lens arrays with optical performance at a low cost. SOLUTION: This illuminator is comprised of a lamp 11, a parabolic mirror 12, 1st and 2nd lens arrays 13, 14, a polarized light-separating prism array 15 (PBS array), a phase plate 16, and a condenser lens 17. Since the 1st and 2nd lens arrays 13, 14 are of the same lens surface form but formed out of different materials, tooling can be shared at the time of manufacture, and moreover, selection of the materials makes it possible to independently make a focal distance f1 of the 1st lens array 13 longer than a focal distance f2 of the 2nd lens array 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device, and more particularly to a lighting device used as a light source for a liquid crystal projector or the like.

[0002]

2. Description of the Related Art In a screen display device such as a liquid crystal projector, a bright and clear image must generally be projected to every corner of the screen, and an illuminating device with extremely low illuminance unevenness is required. As a technique for realizing such an illumination device, an illumination system using a lens array having the function of an optical integrator is known.

FIG. 3 shows an example of such a system.
1 shows a polarized light illuminating device described in Japanese Patent No. 4739. The lighting device includes a lamp 31, a parabolic mirror 32, and a lens array (hereinafter, referred to as a “first lens array”) 3 on the light source side.
3, a lens array (hereinafter, referred to as a "second lens array") 34 on a surface to be illuminated,
It comprises a “PBS array” 35, a phase difference plate 36, a condenser lens 37, and a surface to be illuminated 38, and these optical elements operate as described below.

[0004] The parabolic mirror 32 converts the light emitted from the lamp 31 into a parallel light and makes it incident on the first lens array 33. The first lens array 33 has a configuration in which a plurality of minute rectangular lenses similar in shape to the surface to be illuminated 38 are arranged vertically and horizontally, and the focal point of each lens coincides with the center of the PBS array 35. As a result, a minute secondary light source image is formed near the polarization separation surface 35a, and the light beam is efficiently guided to the PBS array 35.

[0005] The PBS array 35 and the phase difference plate 36, which are polarization conversion means, operate as follows. PBS array 35
Has a function of separating an incident light beam into two polarization components of an S-wave and a P-wave. The S-wave component is reflected on the polarization splitting surface 35a and is reflected again on the reflecting surface 35b.
On the other hand, the P-wave component passes through the polarization splitting surface 35a and is converted by the phase difference plate 36 into an S-wave component. In this way, all the illumination light is converted into the S wave component.

[0006] The second lens array 34 is the same as the first lens array 33 turned upside down, and each lens has the function of imaging the corresponding lens shape of the first lens array 33. I have. Each lens image corresponds to the illuminance distribution of each lens in the first lens array 33, and the plurality of illuminance distributions are superimposed and imaged on the illumination target surface 38 by the condenser lens 37. By such an operation of the integrator, the illuminance distribution on the illuminated surface 38 becomes very uniform.

[0007]

In the illumination device according to the prior art described above, the focal point of the first lens array 33 is set to coincide with the center of the PBS array 35. Means that the focal length of each minute rectangular lens is slightly longer than the distance between the two lens arrays. Therefore, the first lens array 33
The focus of the second lens array 34 having the same specification as that of FIG.
As shown in the figure, it is located closer to the light source than the first lens array 33 is. Since the lens image of the first lens array 33 superimposed and formed on the illuminated surface 38 is formed by the second lens array 34, this shift of the focal position is caused by blurring of the contour of the illumination light, that is, image formation. This will result in poor performance.

Of course, if the first lens 33 and the second lens 34 have different shapes, such a problem can be solved. However, in this case, it is necessary to separately prepare jigs and tools to be used for molding the lens surface, which leads to an increase in cost, which is not a preferable method.

As another method, it is conceivable to change the focal length of the first lens array 33 while giving importance to the focal length of the second lens array 34. But with this method,
The secondary light source image formed by the first lens array 33 is not formed inside the PBS array 35, causing a light-condensing loss.

[0010] Such a problem arises because the original focal length differs between the two lens arrays, and is not limited to the illuminating device using the PBS array. This can generally occur also in other lighting devices in which is inserted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an illumination device combining a polarization conversion means and a lens array at low cost while maintaining optical performance. It is what it was.

[0012]

According to a first aspect of the present invention, there is provided a light source unit for emitting irregularly polarized light, a polarization conversion unit for converting the irregularly polarized light into a specific polarization direction, the light source unit and the polarization conversion unit. And a condenser lens for condensing the polarized light by the polarization conversion means, wherein the first and second lens arrays are the same lens. The present invention relates to a lighting device characterized by being made of different materials while having a planar shape.

According to a second aspect of the present invention, the polarization conversion means includes:
The illumination device according to claim 1, comprising a polarization separation prism array and a retardation plate.

According to a third aspect of the present invention, the first lens array of the first and second lens arrays is arranged on the light source section side, and the second lens array is arranged on the illuminated surface side. 3. The lighting device according to claim 1, wherein a refractive index of the two-lens array is larger than a refractive index of the first lens array.

According to a fourth aspect of the present invention, the material of the first and second lens arrays is such that the first lens array is heat-resistant glass and the second lens array is crown or borosilicate crown glass. A lighting device according to any one of claims 1 to 3.

According to a fifth aspect of the present invention, the focal position of the first lens array is set near the polarization separation plane of the polarization separation prism array, and the focal position of the second lens array is set to the first position.
The lighting device according to any one of claims 1 to 4, wherein the lighting device is set near the lens surface of the lens array.

According to a sixth aspect of the present invention, there is provided a light source unit that emits indefinitely polarized light, a first lens array disposed on the light source unit side acting as an integrator, and a second lens array disposed on the illuminated surface side. Two lens arrays, polarization separating means arranged between the light source unit and the first lens array, a phase difference plate closely or closely arranged to the second lens array, and condensed polarized light And a condenser lens, wherein the first and second lens arrays have the same lens surface shape and are made of different materials.

According to a seventh aspect of the present invention, the focal position of the first lens array is set near the phase difference plate surface, and the focal position of the second lens array is set near the lens surface of the first lens array. A lighting device according to claim 6, wherein

[0019]

FIG. 1 shows an embodiment of a lighting device according to the present invention. This illumination device comprises a lamp 11 and a parabolic mirror 12 constituting a light source section, a first lens array 13 and a second lens array 14 acting as an optical integrator, a PBS array 15 as a polarization conversion means, and a phase difference plate 16. , A condenser lens 17 for condensing illumination light on the surface to be illuminated, and a surface 18 to be illuminated.

The basic functions of the illumination device shown in FIG. 1, such as the integrator and polarization conversion, are based on the same principle as described in the prior art. For this reason, the description of the general contents overlapping with those of the related art will be omitted below, and the description will focus on the contents related to the lens array that is the key of the present invention.

The two lens arrays of the present illuminating device, that is, the first lens array 13 and the second lens array 14 are formed by arranging a plurality of minute rectangular lenses having a shape similar to the surface 18 to be illuminated vertically and horizontally. The lens surfaces of the first lens array 13 and the second lens array 14 have the same specifications. This is to reduce the cost by sharing the jig and tool for producing the first and second lens arrays. However, different materials are used for the lenses, so that the focal length of each lens array can be set independently.

In the illumination device as shown in FIG. 1 in which the polarization conversion means is disposed immediately after the second lens array, the focus of the first lens array 13 is changed to the polarization separation surface 1 in consideration of the efficiency of the polarization conversion and the like.
It is preferable to adjust to the vicinity of 5a. On the other hand, it is preferable that the focal point of the second lens array 14 be adjusted to the lens surface of the first lens array 13 irrespective of the presence or absence of the polarization conversion means from the viewpoint of imaging performance. For this reason, the focal length f1 of the first lens array needs to be slightly longer than the focal length f2 of the second lens array.

The focal length f of the first and second lens arrays
1, f2 is calculated using the refractive indices n1, n2 of the material forming the first and second lens arrays and the radius of curvature r of the lens surface.
f1 = r / (n1-1) and f2 = r / (n2-1). For this reason, in order to make the focal length f1 of the first lens array 13 longer than the focal length f2 of the second lens array 14, the refractive index n1 of the first lens array 13 is made larger than the refractive index n2 of the second lens array 14. What is necessary is just to make it small.

As a combination of materials satisfying such conditions, for example, the first lens array 13 is made of heat-resistant glass (refractive index n1 = 1.47), and the second lens array 14 is made of crown glass (refractive index n2 = 1. 52). These materials are easily available and advantageous in terms of cost, and also have the effect of increasing reliability by using heat-resistant glass for the first lens array 13 immediately after the reflecting mirror.

The material of the lens array is not limited to the above-mentioned heat-resistant glass and crown glass, but may be any glass material or a plastic material if there is no problem in heat resistance and transmittance. Thereby, the choice of the refractive index increases, and the focal length of the two lens arrays can be set more freely.

When the ratio of the focal length of the lens array is calculated from the refractive indexes of the heat-resistant glass and the crown glass, f1 / f
2 = (n2-1) / (n1-1) = 1.11 That is, the focal length f1 of the first lens array 13 can be made about 10% longer than the focal length f2 of the second lens array 14. This is because the second lens array 14 and the PBS
Considering the thickness of the array 15, it can be said that the value is appropriate for achieving both the light-collecting performance and the imaging performance.

A situation in which the optimum focal length differs between the two lens arrays can generally occur even in other illumination devices in which polarization conversion means are inserted near the lens arrays. As the polarization conversion means that can be used together with the lens array, for example, those that perform polarization separation using a dielectric multilayer film, those that use birefringence or optical rotation of calcite or a polymer material, and the like are known, and these were used. Various polarized lighting devices have been invented. The present invention is applicable to all of these illuminating devices. FIG. 2 shows an illuminating device in which polarization separation means is disposed closer to the light source than the first lens array. Is shown.

The illumination device shown in FIG. 2 has a lamp 21 and a parabolic mirror 22, which constitute a light source section, a PBS prism 25 which performs polarization separation, a first lens array 23 and a second lens array 24 which function as optical integrators, Phase difference plate 26 for converting polarization direction, condenser lens 27, illuminated surface 28
It is composed of

The basic principle of the polarization conversion in the present lighting device is as follows. In the parallel light emitted from the parabolic mirror 22, one of the polarization components is reflected by the polarization separation surface 25a, and the other polarization component is reflected by the reflection surface 25b. Each knitting light component enters the first lens array 23 at a different angle,
Light is collected at different positions on the lens array 24. By arranging a phase difference plate at one of the light condensing positions and aligning it with the other polarized light component, polarized illumination is realized.

In the case of the lighting device of the embodiment shown in FIG.
It is preferable that the focal point of the lens array 23 be set near the plane side of the second lens array 24 on which the phase difference plate is disposed, in consideration of the light-collecting performance. On the other hand, it is preferable that the focal point of the second lens array 24 be adjusted to the lens surface of the first lens array 23 as before. That is, it is necessary to make the focal length f1 of the first lens array shorter than the focal length f2 of the second lens array.

In order to realize this, the first lens array 23 has the same lens surface shape, for example, a crown glass (refractive index n1 = 1.52), a second lens array 2
A material such as an acrylic resin (refractive index n2 = 1.49) may be used for 4. When the ratio of the focal lengths is calculated, f1 / f2
= (N2-1) / (n1-1) = 0.94. That is, the focal length of the first lens array 23 can be shortened by about 6% compared to the second lens array 24. In this way, it is possible to achieve both light focusing performance and imaging performance.

In the above two embodiments, it has been assumed that the lens surface shape of each lens array uses a spherical lens when calculating the focal length. However, as the shape of the lens surface, it is conceivable to use not only a spherical surface but also an arbitrary aspherical shape for the purpose of improving optical characteristics and the like. Further, the light source unit of the lighting device is configured by combining a light source and a parabolic mirror, but as means for generating parallel light,
It is also conceivable to use a combination of an elliptical mirror and a collimator lens as the light source.

[0033]

According to the first to seventh aspects of the present invention, there is provided an illuminating device made of different materials while having the same lens surface shape of the first and second lens arrays acting as integrators. Because the shape is the same, the jigs and tools used for molding the lens array are shared and cost is reduced, while the focal length of each lens is set independently,
Optical performance can be ensured.

According to the third to fifth aspects of the present invention, in a lighting apparatus using a polarization separating prism array (PBS array) and a retardation plate as polarization conversion means, the refractive indices of the first and second lens arrays are changed to a light source section. The second lens array on the illuminated surface side is larger than the first lens array on the side,
The focal length of the second lens array on the illuminated surface side is shorter than that of the first lens array on the light source unit side, and it is possible to achieve both light focusing performance and imaging performance.

According to the invention of claim 4, claims 1 to 3 are provided.
The lighting device according to claim 1, wherein heat-resistant glass is used for the first lens array on the light source surface side and crown or borosilicate crown glass is used for the second lens array on the illuminated surface side as a material of the lens array. Since an appropriate focal length difference is given between the second lens arrays, and the heat-resistant glass is used for the first lens array on the lamp side where the temperature rises sharply, reliability is improved, and the cost is improved because the material is easily available. It is possible to go down.

According to a seventh aspect of the present invention, the polarization conversion means includes PBS.
In an illumination device using a polarization separation unit such as a prism and a retardation plate, the focal position of the first lens array is set to the retardation plate surface, and the focal position of the second lens array is set to the lens surface of the first lens array. Thus, it is possible to achieve both light focusing performance and imaging performance.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a lighting device according to the present invention.

FIG. 2 is a view showing another embodiment of the lighting device of the present invention.

FIG. 3 is a diagram showing an example of a lighting device according to the related art.

FIG. 4 is a diagram for explaining a problem of the lighting device of FIG. 3;

[Explanation of symbols]

11, 21, 31 ... lamp, 12, 22, 32 ... parabolic mirror, 13, 23, 33 ... first lens array, 14, 2
4, 34: second lens array, 15, 35: PBS array, 15a, 25a, 35a: polarization splitting surface, 15b, 2
5b, 35b: reflection surface, 16, 26, 36: retardation plate,
17, 27, 37 ... condenser lens, 18, 28, 3
8: Illuminated surface, 25: PBS prism.

Claims (7)

[Claims] A light source unit that emits irregularly polarized light; and a polarization conversion unit that converts the irregularly polarized light into a specific polarization direction.
First and second lens arrays disposed between the light source unit and the polarization conversion unit and functioning as integrators;
A condenser lens for condensing the polarized light by the polarization conversion means, wherein the first and second lens arrays have the same lens surface shape and are made of different materials. Lighting equipment. 2. The illumination device according to claim 1, wherein said polarization conversion means comprises a polarization separation prism array and a phase difference plate. 3. The first and second lens arrays, wherein the first lens array is disposed on the light source unit side, the second lens array is disposed on an illuminated surface side, and the second lens array is refracted. The lighting device according to claim 1, wherein a refractive index is higher than a refractive index of the first lens array. 4. The first lens array is made of heat-resistant glass,
4. The lighting device according to claim 1, wherein the second lens array is a crown or borosilicate crown glass. 5. The apparatus according to claim 1, wherein a focal position of said first lens array is set near a polarization separating surface of said polarization separating prism array, and a focal position of said second lens array is set near a lens surface of said first lens array. Claims 1 to 4
The lighting device according to any one of the above. 6. A two-lens array comprising: a light source for emitting indefinitely polarized light; a first lens array disposed on the light source side acting as an integrator; and a second lens array disposed on the illuminated surface side. And a polarization separation unit disposed between the light source unit and the first lens array; a phase difference plate closely or closely disposed to the second lens array; and a condenser lens for condensing polarized light. Wherein the first and second lens arrays have the same lens surface shape,
A lighting device characterized by being made of different materials. 7. The apparatus according to claim 1, wherein a focal position of said first lens array is set near a phase difference plate surface, and a focal position of said second lens array is set near a lens surface of said first lens array. 7. The lighting device according to 6.