JP2004085981A - Polarization splitter, polarization converter, and projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compensate intensity differences between primary colors included in a light source in a projector. <P>SOLUTION: A liquid crystal projector is provided with lens arrays 140 and 150 which generate partial luminous fluxes from light radiated from the light source and a polarization converter 160 which converts partial luminous fluxes into polarized light which should be supplied to a liquid crystal light valve. The polarization converter 160 is provided with a polarization splitter film 64a for splitting s-polarized light and p-polarized light and a reflecting film 64b for reflecting the s-polarized light in an exit direction. The p-polarized light is converted into s-polarized light by a selective retarder 66 and is emitted. A reflecting film 64c in the outermost part is a dichroic mirror which selectively reflects only R. Thus intensities of G and B in a part of a luminous flux can be reduced to compensate intensity differences between primary colors. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a projector that projects and displays an image, and a polarization separation element and a polarization conversion element used in the projector.
[0002]
[Prior art]
The projector modulates light with a liquid crystal panel and projects an image on a screen. In a projector, a high-pressure mercury lamp is often used as a light source that can secure sufficient brightness at a reasonable cost.
[0003]
In order to make effective use of the irradiation light from the light source, the projector is provided with a polarization conversion unit that adjusts the irradiation light to s-polarized light or p-polarized light and enters the liquid crystal panel. For example, a polarization conversion unit that converts irradiation light into s-polarized light includes a polarization separation film that separates irradiation light into s-polarized light and p-polarized light, and a retardation layer that converts the separated p-polarized light into s-polarized light. You.
[0004]
The light that has been aligned to s-polarized light or p-polarized light in the polarization conversion unit is separated into red (R), green (G), and blue (B) three-color light. The luminous flux of the color light is modulated for each color by the three liquid crystal panels, then combined and projected.
[0005]
In order to project an image with a good color balance, it is preferable that the intensity of the three-color light included in the light emitted from the light source is uniform, but the high-pressure mercury lamp has weaker R than G and B. There is a characteristic that. As a method for adjusting the color balance caused by such an intensity difference, there is known a method of lowering the overall intensity of G and B by a filter, and a method of adjusting the modulation in the liquid crystal panel so that G and B are darkened. Has been.
[0006]
[Problems to be solved by the invention]
In general, the intensity of a light beam from a light source is higher near the center, and is high-quality light close to parallel light. In the conventional method, the intensity of such high-quality light is also reduced for G and B, so that the energy efficiency in projection is low. In addition, there are problems that heat is easily generated and the whole is easily darkened.
[0007]
Poor color balance caused by a light source has been a common problem in projectors in general. SUMMARY An advantage of some aspects of the invention is to provide a technique for efficiently compensating for a color balance defect caused by a light source in a projector.
[0008]
[Means for Solving the Problems and Their Functions and Effects]
In order to solve at least a part of the above problems, the present invention provides a projector for projecting an image, from a light source to a projection lens, on a light path through which a light beam passes, for a part of the light beam, while separating the light beam into color light. And an intensity adjusting unit for guiding color light having relatively low intensity into the optical path. It is assumed that the light source has a characteristic having a relative intensity difference between the color lights.
[0009]
ADVANTAGE OF THE INVENTION According to this invention, it can guide | induce the color light whose intensity | strength is relatively weak about a part of light beam in an optical path. Colored light having relatively high intensity can be prevented from reaching the projection lens by absorption, reflection, transmission, or the like. By performing such intensity adjustment for a part of the light beam, a part of the light having relatively high intensity can be directly used for projection. Therefore, it is possible to efficiently compensate for the intensity difference between the color lights.
[0010]
In the present invention, it is preferable to provide a lens array that divides a light beam into a plurality of partial light beams, and to provide an intensity adjustment unit on any optical path through which the partial light beams pass. By adjusting the intensity with a part of the partial light beam, it is possible to suppress the influence on other partial light beams.
[0011]
In the present invention, the intensity adjustment can be realized, for example, by a color separation unit that selectively transmits or reflects color light having a relatively low intensity.
[0012]
In the present invention, it is preferable that the intensity adjusting section is provided so as to separate the light around the light beam. By doing so, it is possible to compensate for the difference in intensity while using the high-quality light near the center for projection as it is.
[0013]
In the case of a liquid crystal projector that performs modulation using a liquid crystal panel, there is also an advantage that the contrast characteristics can be improved as described below by adjusting the intensity at the peripheral portion. In general, it is known that the contrast characteristic of a liquid crystal panel changes depending on the incident angle, and the contrast characteristic decreases as the position deviates from the normal direction of the liquid crystal panel. Of the luminous flux incident on the liquid crystal panel, the light in the peripheral portion is often shifted from the normal direction, so that the contrast characteristic may be reduced. In the present invention, when the intensity adjusting unit is provided so as to separate the light in the peripheral part, it is possible to suppress the light of the incident angle that lowers the contrast characteristic of the color light having relatively strong intensity. Therefore, the contrast characteristics can be improved.
[0014]
The present invention is applicable to various projectors such as a projector using DMD (registered trademark) and a liquid crystal projector. When applied to a liquid crystal projector, for example, it is preferable to provide an intensity adjustment unit in a polarization conversion element for aligning a light beam to a predetermined s-polarized light or p-polarized light. In the polarization conversion element, a polarization separation film for separating s-polarized light and p-polarized light, and a reflection film that reflects the polarized light separated by the polarization separation film in the emission direction are laminated via a light-transmitting member. I have. In such a polarization conversion element, by configuring at least a part of the reflection film to selectively reflect color light having relatively low intensity, an intensity adjustment unit can be realized.
[0015]
For example, in the case of a polarization conversion element in which a plurality of polarization separation films and reflection films are alternately laminated via a translucent member, at least one of the reflection films selectively reflects color light having relatively weak intensity. (Hereinafter, referred to as a selective reflection area). A partial area of the reflection film may be a selective reflection area. Considering the effect of improving the contrast described above, the selective reflection region preferably includes the outermost layer.
[0016]
There is also a type of polarization conversion device that includes a polarization separation film and a reflection film one by one. In such a type, a partial area of the reflection film may be used as a selective reflection area.
[0017]
The invention is applicable to various types of light sources. When a high-pressure mercury lamp is used as a light source, colored light having relatively low intensity is red.
[0018]
The present invention can be configured in various modes other than the configuration as the projector described above. For example, it may be configured as a polarization conversion element or a polarization separation element provided with the above-described intensity adjustment unit, or may be configured as a method for manufacturing such a polarization conversion element.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
A. overall structure:
FIG. 1 is an explanatory diagram showing a schematic configuration of a projector as an embodiment. The projector 1000 includes an illumination optical system 100, a color light separation optical system 200, a relay optical system 220, three liquid crystal panels 300R, 300G, 300B, a cross dichroic prism 520, and a projection lens 540.
[0020]
The illumination optical system 100 emits light from the light source device 120. The color light separation optical system 200 separates this light into three colors of red (R), green (G), and blue (B) by dichroic mirrors 202 and 204. The dichroic mirror 202 separates the red light R by transmitting the red light R and reflecting the blue light B and the green light G. The dichroic mirror 204 separates the blue light B and the green light G by transmitting the blue light B and reflecting the green light G.
[0021]
The red light R is reflected by the reflection mirror 208, passes through the field lens 232, and enters the liquid crystal panel 300R. The field lens 232 converts the incident light into a light flux substantially parallel to the central axis. The green light G is reflected by the dichroic mirror 204, passes through the field lens 234, and enters the liquid crystal panel 300G. The blue light is incident on the liquid crystal panel 300B by the relay optical system 220. The relay optical system 220 includes three lenses, namely, an entrance lens 222, a relay lens 226, and a field lens 230, and two reflection mirrors 224 and 228.
[0022]
Each color light is modulated by the liquid crystal panels 300R, 300G, and 300B according to image information. The modulated color lights are combined by the cross dichroic prism 520 and projected onto the screen SC via the projection lens 540.
[0023]
In this embodiment, a high-pressure mercury lamp is used as the light source device 120. The high-pressure mercury lamp has a characteristic that the intensity of R is relatively weaker than the intensity of G and B.
[0024]
B. Illumination optics:
FIG. 2 is an enlarged view of the illumination optical system 100. In this embodiment, an integrator optical system, that is, an optical system that splits a light beam from a light source into a plurality of partial light beams and superimposes the light beam on a liquid crystal panel is used.
[0025]
In the illumination optical system 100, the light source device 120 emits a substantially parallel light beam. Light emitted from the light source lamp 122 is reflected by the reflector 124. In this embodiment, the reflector 124 has a spheroidal concave surface, but may have a paraboloidal concave surface. The reflected light is converted by the collimating lens 126 into light substantially parallel to the light source optical axis 120ax.
[0026]
The first lens array 140 has a plurality of plano-convex lenses 142 arranged in a matrix. The outer shape of each plano-convex lens 142 when viewed from the z direction is similar to the liquid crystal panel LA. The first lens array 140 divides the light beam emitted from the light source device 120 into a plurality of partial light beams.
[0027]
Like the first lens array 140, the second lens array 150 has a plurality of plano-convex lenses 152 arranged in a matrix. The second lens array 150 has a function of aligning the respective central axes of the partial light beams so as to be substantially parallel to the system optical axis 100ax.
[0028]
The polarization conversion element 160 includes a light shielding plate 62, a polarization beam splitter array 64, and a selective phase difference plate 66.
[0029]
In the polarization beam splitter array 64, a plurality of columnar translucent plate members having a substantially parallelogram cross section are bonded. Polarized light separating films 64a and reflecting films 64b are alternately formed on the interface between the light transmitting plate members. The polarization splitting film 64a separates the incident partial light beam into s-polarized light and p-polarized light by transmitting p-polarized light and reflecting s-polarized light. The polarization separation film 64a can be formed of, for example, a dielectric multilayer film. The reflection film 64b is a film that reflects the entire light flux, and can be formed of a dielectric multilayer film or a metal film.
[0030]
The light shielding plate 62 has a light shielding surface 62b and an opening surface 62a arranged in a stripe pattern. The light-shielding surface 62b is arranged to block light from entering the reflection film 64b, and the aperture surface 62a is arranged to allow light to enter the polarization separation film 64a. As the light-shielding plate 62, a light-shielding film (for example, a chromium film, an aluminum film, a dielectric multilayer film, or the like) partially formed on a flat transparent body (for example, a glass plate) can be used. A light-shielding flat plate such as an aluminum plate provided with an opening may be used.
[0031]
In the selective retardation plate 66, an opening layer 66a and a λ / 2 retardation layer 66b are arranged in a stripe shape. The aperture layer 66a transmits polarized light as it is. The λ / 2 retardation layer 66b is a polarization conversion element made of an organic material, and converts the polarization direction of incident light into a direction orthogonal to the light and emits the light. By this function, for example, p-polarized light is converted to s-polarized light. The λ / 2 retardation layer 66b is arranged so that light transmitted through the polarization separation film 64a enters.
[0032]
The partial light beams emitted from the lens arrays 140 and 150 pass through the opening 62a of the light shielding plate 62 and enter the polarization splitting film 64a. Of the incident light, p-polarized light passes through the polarization splitting film 64a, enters the λ / 2 retardation layer 66b, and is converted into s-polarized light. Of the incident light, the s-polarized light is reflected by the polarization separation film 64a, further reflected by the reflection film 64b, and emitted from the aperture layer 66a as it is. As a result, the light emitted from the polarization conversion element 160 is almost unified to s-polarized light. The polarization conversion element 160 may be configured as a mechanism for unifying p-polarized light by exchanging the arrangement of the λ / 2 retardation layer 66b and the aperture layer 66a.
[0033]
The partial light beams emitted from the polarization conversion element 160 are superimposed on the illumination area LA by the superimposing lens 170. At this time, the intensity distribution of the light illuminating the illumination area LA is substantially uniform.
[0034]
C. Polarization conversion element:
FIG. 3 is an enlarged sectional view of the polarization conversion element 160. As described with reference to FIG. 2, at the interface between the light-transmitting plate members constituting the polarization beam splitter array 64, the polarization separation films 64a and the reflection films 64b are alternately formed.
[0035]
In this embodiment, the outermost reflective film 64c is a dichroic mirror that selectively reflects only R. Therefore, as for the light incident from the outermost opening, only the R component of the s-polarized light reflected by the polarization splitting film 64a is emitted, and the G and B components are radiated out of the polarization conversion element 160. . As a result, the light emitted from the polarization conversion element 160 becomes light in which the intensity of the G and B components is reduced as compared with the incident light. Further, the intensity of the G and B components is reduced in the peripheral portion of the light beam emitted from the polarization conversion element 160.
[0036]
The polarization beam splitter array 64 has a symmetric structure. Although the upper half is shown in FIG. 3, the outermost reflective film is also a dichroic mirror that selectively reflects only R in the lower half.
[0037]
The reduction amounts of the G and B components can be adjusted by the opening width D. The aperture width D may be set so as to compensate for the difference in the intensity of each color component in the light emitted from the light source device 120.
[0038]
According to the projector of the present embodiment described above, the intensity difference between the G and B components can be reduced by the dichroic mirror, so that the intensity difference between the color lights included in the light source can be compensated, and the color balance of the projected image can be compensated. Can be improved. In addition, since the intensity adjustment is performed on the peripheral portion of the light beam, high-quality light near the center of the light beam can be directly used for projection for G and B lights.
[0039]
Further, according to the present embodiment, by adjusting the intensity at the peripheral portion of the light beam, it is possible to suppress the light G and B that are incident on the liquid crystal panel while being shifted from the normal direction. In general, a liquid crystal panel has a characteristic that contrast characteristics are low with respect to light incident in a direction shifted from the normal direction. Therefore, in this embodiment, it is possible to improve contrast characteristics by suppressing such components. .
[0040]
D. First modification:
FIG. 4 is an enlarged sectional view of a polarization conversion element 160A as a first modification. In the embodiment, a dichroic mirror that selectively reflects only R in the entire outermost region is used. On the other hand, in the modification, a part of the outermost region 64d2 is a dichroic mirror, and the other region 64d1 is a reflective film that reflects all the color light components.
[0041]
By doing so, as shown by the broken line, all the components of R, G, and B are emitted from the region 64d1 and only the R component is emitted from the region 64d2. Therefore, by adjusting the area of the region 64d2, the intensity compensation amounts of the G and B components can be adjusted.
[0042]
Although FIG. 4 illustrates a case where the dichroic mirror region 64d2 is provided at the outermost ends, the dichroic mirror region 64d2 may be provided at one end. From the viewpoint of reducing the components of the peripheral portion of the light beam, it is preferable to provide the region 64d2 deviated rightward in FIG.
[0043]
FIG. 4 illustrates a case in which a dichroic mirror that selectively reflects only R is provided, but the outermost portion is divided into three regions, and three types of dichroic mirrors that selectively reflect each of R, G, and B are provided. It may be provided. In this case, by adjusting the areas of the three regions, the intensity compensation between the colors, including the intensity compensation between G and B, can be performed with higher accuracy.
[0044]
The three types of dichroic mirrors that selectively reflect each of R, G, and B are not limited to the configuration of the modified example (FIG. 4), and may be applied to the embodiment (FIG. 3). For example, a layer that selectively reflects R alone may be provided in the uppermost outermost layer, and a layer that selectively reflects G and B may be provided in the lowermost outermost layer.
[0045]
E. FIG. Second modification:
FIG. 5 is an enlarged sectional view of a polarization conversion element as a second modification. In the embodiment, the case where the polarization conversion element is provided on the emission side of the two lens arrays is illustrated. However, in the second modification, the configuration provided between the two lens arrays 240 and 250 is the same. For example. The configuration of the lens arrays 240 and 250 is the same as that of the embodiment in that the plano-convex lenses are arranged in a matrix, but the size of the plano-convex lenses forming the lens array 250 is smaller than the lens array 240. Is different from the embodiment.
[0046]
In the polarization conversion element of the second modification, a prism 260 is disposed between the lens arrays 240 and 250. A polarization separation film 264 and a reflection film 265 are provided on the oblique side of the prism 260. Both ends of the reflection film 265 are dichroic mirrors 266 that selectively reflect only the R component.
[0047]
The light that has passed through the lens array 240 is incident on the prism 260 as shown by the arrow in the figure. Of the incident light, the s-polarized light is reflected by the polarization separation film 264. The p-polarized light is reflected by the reflection film 265 after passing through the polarization separation film 264. The thickness of the polarization separation film 264 and the size and arrangement of the lens array 250 are set so that s-polarized light and p-polarized light are incident on individual plano-convex lenses constituting the lens array 250. Although not shown, by providing the λ / 2 retardation layer only in one of the optical paths of the s-polarized light and the p-polarized light, it is possible to obtain polarized light that is unified into either one. A λ / 4 retardation plate may be provided between the polarization separation film 264 and the reflection film 265.
[0048]
As for the light incident on the dichroic mirrors 266 at both ends, only the R component of the p-polarized light is reflected as shown by the broken line in the figure. Therefore, the intensity of the B and G components can be reduced. The strength reduction amount can be adjusted by the area of the dichroic mirror 266.
[0049]
Also in the second modified example, similarly to the first modified example, a dichroic mirror may be provided so as to be biased to any one end of the reflection film 265. Further, a dichroic mirror that selectively reflects R, G, and B may be provided.
[0050]
F. Third modification:
FIG. 6 is an enlarged sectional view of a polarization conversion element as a third modification. The configuration is similar to that of the second modified example, except that it is divided into two prisms 360a and 360b. A polarization separation film 364 and a reflection film 365 are provided on the oblique sides of the prisms 360a and 360b. Both ends of the reflection film 365 are dichroic mirrors 366 that selectively reflect only the R component.
[0051]
With such a configuration, similarly to the second modification, the strengths of G and B can be reduced. The same is true even if the prism is further divided into multiple stages. Also in the third modified example, similarly to the first modified example, a dichroic mirror may be provided so as to be biased to any one end of the reflection film 265. Further, a dichroic mirror that selectively reflects R, G, and B may be provided. In the above embodiment, the high-pressure mercury lamp having a relatively weak R component has been described. However, when another light source (lamp) having relatively weak two-color light is used, the two-color light is selected. It is also possible to adopt a configuration of transmitting or reflecting light.
[0052]
Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it goes without saying that various configurations can be adopted without departing from the spirit of the present invention.
[0053]
(1) The present invention is applicable not only to a high-pressure mercury lamp but also to a projector using various light sources having an intensity difference between color lights.
[0054]
(2) The present invention is not limited to a liquid crystal projector, and may be applied to a projector using a DMD.
[0055]
(3) The configuration for compensating the intensity between the color lights is not limited to the polarization conversion element, and can be provided at an arbitrary position on the optical path through which the light beam passes. Further, it is only necessary to perform the correction in a partial area of the light beam, and it is not always necessary to perform the intensity compensation in the peripheral portion of the light beam.
[0056]
(4) Instead of a dichroic mirror that selectively reflects only part of the color light, a transmission film that selectively transmits light may be used. A material that selectively absorbs a color whose intensity is to be reduced may be used.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating a schematic configuration of a projector as an embodiment.
FIG. 2 is an enlarged view of the illumination optical system 100.
FIG. 3 is an enlarged cross-sectional view of a polarization conversion element 160.
FIG. 4 is an enlarged cross-sectional view of a polarization conversion element 160A as a first modification.
FIG. 5 is an enlarged sectional view of a polarization conversion element as a second modification.
FIG. 6 is an enlarged cross-sectional view of a polarization conversion element as a third modification.
[Explanation of symbols]
62 light shielding plate 62b light shielding surface 62a opening surface 64 polarizing beam splitter array 64a polarization separation film 64b reflection film 64c reflection film 66 selective phase plate 66a opening layer 66b λ / 2 phase difference layer 100ax ... System optical axis 100 ... Illumination optical system 120 ... Light source device 120ax ... Light source optical axis 122 ... Light source lamp 124 ... Reflector 126 ... Parallizing lens 140 ... First lens array 142 ... Plano-convex lens 150 ... Second lens array 152 ... Plano-convex lenses 160, 160A polarization conversion element 170 superimposing lens 200 color light separation optical systems 202, 204 dichroic mirror 208 reflection mirror 220 relay optical system 222 incident lens 224 reflection mirror 226 relay lenses 230, 232 234 field lens 240, 250 lens array 2 0 ... Prism 264 ... Polarization separation film 265 ... Reflection film 266 ... Dichroic mirror 300R, 300G, 300B ... Liquid crystal panel 360a, 360b ... Prism 364 ... Polarization separation film 365 ... Reflection film 366 ... Dichroic mirror 520 ... Cross dichroic prism 540 ... Projection Lens 1000: Projector

Claims (9)

A projector for projecting an image,
A light source that emits a light flux having a relative intensity difference between a plurality of color lights;
An optical path through which the light beam passes from the light source to the projection lens;
A projector having an intensity adjusting unit on the optical path, which separates the luminous flux into the color light for a part of the luminous flux and guides the color light having the relatively weak intensity into the optical path. The projector according to claim 1, wherein
A lens array that divides the light beam into a plurality of partial light beams,
The projector, wherein the intensity adjustment unit is provided on any optical path through which the partial light beam passes. The projector according to claim 1 or 2,
The projector further includes a color separation unit that selectively transmits or reflects the color light having the relatively low intensity. The projector according to claim 1,
The projector, wherein the intensity adjustment unit is provided to separate light in a peripheral portion of the light beam. The projector according to claim 1, wherein
On the optical path,
A liquid crystal panel for modulating the color light, and a polarization conversion element for aligning the light beam with a predetermined s-polarized light or p-polarized light;
In the polarization conversion element, a polarization separation film for separating s-polarized light and p-polarized light, and a reflection film for reflecting polarized light separated by the polarization separation film in an emission direction are laminated via a light-transmitting member. Has been
A projector in which at least a part of the reflection film selectively reflects the color light having the relatively low intensity. The projector according to claim 5, wherein
In the polarization conversion element, a plurality of the polarization separation film and the reflection film are alternately laminated via a translucent member,
A projector in which at least a part of the reflection film selectively reflects the color light having the relatively low intensity. The projector according to claim 1,
The light source is a high-pressure mercury lamp,
The color light having a relatively low intensity is a red projector. A polarization conversion element for aligning light beams having relatively different intensities between a plurality of color lights into s-polarized light or p-polarized light,
A polarization separation film for separating the light beam into s-polarized light and p-polarized light;
A reflection film that reflects the polarized light separated by the polarization separation film in the emission direction is laminated via a light-transmitting member,
A polarization conversion element in which at least a part of the reflection film selectively reflects the color light having the relatively low intensity. A polarization separation element for separating a light flux having a relatively different intensity between a plurality of color lights into s-polarized light or p-polarized light,
A polarization separation film for separating the light beam into s-polarized light and p-polarized light;
On the back surface of the polarization separation film, a reflection film that reflects the separated polarized light in the emission direction is provided via a light-transmitting member,
At least a part of the reflection film is a polarization separation element that selectively reflects the color light having the relatively low intensity.

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