JP3554520B2 - Image display device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image display device, such as a liquid crystal projector, for enlarging and projecting light transmitted from a light source through an image display element onto a screen.
[0002]
[Prior art]
The liquid crystal display device is configured to change the optical characteristics of the liquid crystal by applying a driving voltage corresponding to an image signal to pixel electrodes arranged regularly in a matrix to display images, characters, and the like. I have. As a method of applying an independent drive voltage to the pixel electrodes described above, there are a simple matrix method and an active matrix method in which a non-linear two-terminal element or a three-terminal element is provided in a liquid crystal display element.
[0003]
In the case of the latter active matrix method, it is necessary to provide a switching element such as an MIM (metal-insulator-metal) element or a TFT (thin film transistor) element and a wiring electrode for supplying a driving voltage to the pixel electrode. .
[0004]
When strong light is incident on this switching element, the element resistance in the OFF state decreases, and not only the charge charged when a voltage is applied is discharged, but also the liquid crystal portion existing in the area where the switching element and the wiring electrode are formed. In addition, since a proper driving voltage is not applied and the original display operation is not performed, there is a problem that light leaks even in a black state and a contrast ratio is reduced.
[0005]
Therefore, when the liquid crystal display element is a transmissive type, as shown in FIG. 15, a black matrix is provided on a counter substrate facing a TFT substrate provided with a switching element such as a TFT 601 and a pixel electrode 605 with a liquid crystal layer therebetween. It is necessary to provide a light-blocking means called 602 to block light incident on the above-mentioned light incident area. Therefore, in the case of a transmissive liquid crystal display element, since the light is shielded by the black matrix 602 in addition to the TFT 601, the gate bus line 603, and the source bus line 604 each having a light shielding property, the effective pixel area is occupied in the pixel section. The area of the pixel opening, that is, the aperture ratio, is reduced.
[0006]
Further, it is difficult to form these switching elements and wiring electrodes in a size smaller than a certain size due to restrictions on electrical performance and manufacturing technology. Therefore, as the resolution of the liquid crystal display element becomes higher and smaller, the aperture ratio further decreases as the pitch of the pixel electrodes becomes smaller.
[0007]
In order to solve this problem, a reflection type liquid crystal display device has been developed.
[0008]
In the reflective liquid crystal display element, as shown in FIG. 16, a reflective pixel electrode 655 can be formed on a TFT 651 as a switching element. The ratio can be increased, which is very effective in improving the brightness of the projection type liquid crystal display device.
[0009]
A system in which such a reflection type liquid crystal display element is applied to a projection type image display device is proposed in Electronic Display Forum 97 (P.3-27 to 3-32) and JP-A-4-338721.
[0010]
In the electronic display forum 97, as shown in FIG. 17, light emitted from the light source 701 is separated by a dichroic mirror into light of three primary colors of red, green, and blue (hereinafter, referred to as R, G, and B in order). Each light is made incident on a corresponding polarizing beam splitter (PBS) 702. In the polarization beam splitter 702, the incident light is split into linearly polarized light components in two directions orthogonal to each other, and one of the light is incident on the corresponding reflective liquid crystal display element 704. The R, G, and B lights reflected by the reflective liquid crystal display element 704 and having their polarization directions modulated enter the PBS 702 again, are combined by the cross dichroic mirror 703, and then projected on the screen by the projection lens 705. .
[0011]
In Japanese Patent Application Laid-Open No. 4-338721, as shown in FIGS. 18A and 18B, after the light from the light source 101 is separated into two linearly polarized lights by the PBS 105, one of the lights is cross-dichroic prism (FIG. a)) or a Philips type prism (FIG. 18 (b)) to separate R, G, and B light by a color separation / combination element, and reflected by reflective liquid crystal display elements 107-R, 107-G, 107-B. After the combined light is subjected to color synthesis by the same element, the light is again incident on the PBS 105, and only the light whose polarization direction is modulated is incident on the projection lens 108 and projected on the screen.
[0012]
This method is called a three-panel type liquid crystal projection, and since R, G, and B light from a light source can be efficiently used, a very bright image can be realized.
[0013]
[Problems to be solved by the invention]
However, the above-described projection type image display device using the reflection type liquid crystal display device has the following problems.
[0014]
The method proposed in the Electronic Display Forum 97 requires three PBSs corresponding to each of R, G, and B colors, and also requires an optical system for color separation and a cross dichroic prism for color synthesis. Therefore, not only is the cost of the system very high, but also the system size is very large.
[0015]
In Japanese Patent Application Laid-Open No. 4-338721, the color separation and the color synthesis are performed by one element, and only one PBS is required, so that the system size can be reduced. However, a method using a cross dichroic prism is used. In FIG. 19, light is normally incident at an angle of 45 degrees with respect to the film surface on which color separation is performed, so that the polarization dependence of the spectral characteristics on the color separation surface is large as shown in FIG. If the same element performs color separation and color synthesis, the bandwidth in which light can be used is greatly limited, the light use efficiency is reduced, and the color purity is reduced.
[0016]
When a Philips type prism is used, the angle of incidence of light on the color separation surface is smaller than that of the cross dichroic prism, so that the influence of the polarization dependence as described above is reduced, but the light passes through the Philips type prism. The optical path of the light is long, and in order to allow the incident light to pass through without being kicked by the side surface of the Philips type prism, the prism and the projection lens must be increased in size, which increases the cost.
[0017]
The present invention has been made to solve the above problems, and an object of the present invention is to realize a projection type image display device using a small, lightweight, and bright reflective liquid crystal display element.
[0018]
[Means for Solving the Problems]
The image display device of the present invention provides an illumination optical system (illumination) that emits light of three primary colors, red, green, and blue, with the polarization directions of the two colors being different from the polarization directions of the other one color. Means), a light separating element (light separating means) for separating light emitted from the illumination optical system according to a polarization direction, and a plurality of reflective image display elements for modulating the light separated by the light separating element. A color separation element (color separation means) for separating the two colors of light having the same polarization direction, and a projection optical system (projection means) for projecting light modulated by the plurality of reflective image display elements; Thereby, the above object is achieved.
[0019]
It is preferable that the angle formed between the light separating surface of the light separating element and the color separating surface of the color separating element is 20 ° or less.
[0020]
The illumination optical system includes: a light source that emits light of three primary colors; a first polarization control element (polarization control unit) that converts a polarization direction of light of at least one of the three primary colors from the light source. May be provided.
[0021]
A configuration may be adopted in which a polarization selection element that transmits or reflects only one polarization direction is disposed on an optical path on the light incident side of the first polarization control element.
[0022]
It is preferable that the color separation surface of the color separation element be sandwiched between two substrates. At this time, it is preferable that a transparent substrate is disposed on at least one of the optical paths of the light separated by the light separating element. In particular, among the lights separated by the light separation element, the color separation element has on the optical path of light that enters one of the plurality of reflective image display elements without passing through the color separation element. It is preferable to dispose a substrate having the thickness of the two substrates. In addition, this transparent substrate may be used for a configuration other than the light separation element in which the color separation surface is provided between the two substrates, if necessary.
[0023]
The color separating element may be a quadrangular prism formed by bonding two triangular prisms together.
[0024]
Principal rays of the incident light and the outgoing light to and from the quadrangular prism enter and exit substantially parallel to a surface normal of a light incident surface and an exit surface of the quadrangular prism, and a light separating surface of the quadrangular prism. It is preferable that the light is incident at an angle smaller than 45 ° with respect to the normal to the surface.
[0025]
The color separation surface of the color separation element is formed on one surface of the substrate, is arranged so as to face the light separation element side, transmits blue light, and has the same polarization direction. The color light may include blue light.
[0026]
A second polarization control element (polarization control means) for aligning the polarization directions of the three primary colors of red, green, and blue lights in the same direction may be arranged on the projection optical system side of the light separation element. .
[0027]
A configuration may be adopted in which a polarization selection element that transmits or reflects only one polarization direction is disposed on an optical path on the light emission side of the second polarization control element.
[0028]
It is preferable that at least one wavelength regulating element (wavelength regulating means) is inserted on an optical path between the light source and the projection optical system.
[0029]
It is preferable that the wavelength regulating element cuts light in a wavelength region at a boundary between the light whose polarization direction is converted by the first polarization control element and the wavelength of the other light.
[0030]
The wavelength regulating element is disposed on at least one of the optical paths of the light separated by the light separating element, and light other than the light corresponding to the reflection type image display element disposed on the optical path into which the wavelength regulating element is inserted. Is preferably cut.
[0031]
It is preferable that the wavelength regulating element cuts light of at least one of a boundary wavelength region between red and green and a boundary wavelength region between green and blue. When the polarization directions of green and blue light are aligned, it is preferable to cut the light in the boundary wavelength region between red and green, and when the polarization directions of red and green are aligned, the green and blue light It is preferable to cut off light in the boundary wavelength region.
[0032]
The wavelength regulating element is disposed between the light separating element and the reflective image display element, and the light regulating surface of the wavelength regulating element forms an angle with the image display surface of the reflective image display element. That is, they are preferably arranged non-parallel. It is preferable that the angle between the light-regulating surface of the wavelength-limiting element and the image display surface of the reflection-type image display element is in the range of 1.5 ° to 13.5 °.
[0033]
It is preferable that, of the three primary colors of red, green, and blue, two colors having the same polarization direction include green light.
[0034]
One of the transmittance for the P-polarized light and the reflectance for the S-polarized light of the light separating surface of the light separating element is higher than the other, and the light separated by the light separating element as the polarized light having the one is the plurality of reflections. It is preferable that the light is incident on two or more of the image display elements.
[0035]
One of the transmittance for P-polarized light and the reflectance for S-polarized light of the light separating surface of the light separating element is higher than the other, and green light is separated by the light separating element as polarized light having the one. Is preferred.
[0036]
Hereinafter, the operation of the present invention will be described.
[0037]
The illumination optical system of the image display device of the present invention emits light of three primary colors so that the polarization direction of one color light of the three primary colors is different from the polarization direction of the other two colors of light. That is, two of the three primary colors are polarized light having the same polarization direction, and the polarization direction is different from the polarization direction of the other one color light. The light separating element (also referred to as a “polarization separating element”) separates light emitted from the illumination optical system into lights having different polarization directions based on the polarization direction. Therefore, light of two colors having the same polarization direction is separated from light of another color. The color separation element included in the image display device of the present invention separates two colors of light having the same polarization direction.
[0038]
Therefore, the image display device of the present invention does not need to use a cross dichroic prism or a Philips type prism for color separation (and color synthesis) as in the related art, and is caused by the polarization dependence of the dichroic prism or the Philips type prism. It is possible to improve the brightness, the color purity, and the contrast ratio, to reduce the size of the image display device, and to significantly reduce the cost.
[0039]
Further, by adopting a configuration in which the light separating surface of the light separating element (for example, PBS) and the color separating surface of the color separating element (for example, dichroic mirror) form an angle of 20 ° (absolute value) or less. , The contrast ratio can be further improved. The angle formed by the light separating surface and the color separating surface is preferably 10 ° or less, and more preferably substantially parallel (about 0 °). The reason will be described below with reference to FIG.
[0040]
The light separating element usually separates incident light into P-polarized light and S-polarized light. Each of the P-polarized light and the S-polarized light is defined by a polarization direction with respect to a plane including an incident optical path of light to the light separation surface and a surface normal. The light incident on the light separating element generally has not a perfect parallel light but a certain spread angle θ, and therefore, the polarization direction (the vibration direction) of the light separated as reflected light or transmitted light by the light separating element. ) Is different from the polarization direction of P-polarized light or S-polarized light obtained as a result of separation of perfect parallel light.
[0041]
After the light having the divergence angle has passed through the light separation element 105, the light having a divergence angle is applied to the color separation surface of the color separation element 106 'arranged as shown in FIG. When incident, this light will have a polarization direction that is deviated from P-polarized light or S-polarized light with respect to the color separation plane. In the color separation plane, a phase shift that depends on the polarization direction of linearly polarized light (P-polarized light and S-polarized light with respect to the light incident surface) usually occurs. Therefore, the light having the divergence angle is affected by this and is emitted as elliptically polarized light from the color separation element 106 ', which causes a decrease in the contrast ratio.
[0042]
On the other hand, as shown in FIG. 20 (b), when the color separation surface is arranged substantially parallel to the light separation surface, the polarization directions of the S-polarized light and the P-polarized light with respect to the two surfaces coincide with each other. (For example, S-polarized light on the color separation surface is also S-polarized light on the light separation surface). Therefore, even if a phase shift occurs on the color separation surface, since only one of the P-polarized light and the S-polarized light exists, the polarization state does not change, and the contrast ratio can be improved.
[0043]
FIG. 20B shows an example in which the light separating surface of the light separating element and the color separating surface of the color separating element are arranged in parallel, but the angle of the color separating surface is the angle shown in FIG. Even if the angle deviates from (0 °) by, for example, about ± 20 degrees, the effect is reduced, but a higher contrast ratio than the arrangement of FIG. 20A can be obtained.
[0044]
The illumination optical system used in the image display device of the present invention includes, for example, a light source that emits white light, and a first polarization control element that rotates at least one polarization direction of R, G, and B light. Is done. By employing this configuration, light of a predetermined polarization direction can be efficiently made incident on the corresponding reflection-type image display device, and the brightness can be increased. The R, G, and B light emitted from the light source can be converted into linearly polarized light using, for example, a polarizing plate.
[0045]
As the first polarization control element, for example, an element as disclosed in US Pat. No. 5,751,384 can be used. In this element, a plurality of wavelength plates (also referred to as “retardation plates”) are stacked on each other while changing the angle of the axis (optical axis, for example, slow axis), and the polarization direction of only light in a specific wavelength range is obtained. Has the function of rotating. For example, as shown in FIG. 4, when a polarization control element 104 for rotating the polarization direction of the B light is used, when white linearly polarized light enters the polarization control element 104, the R and G lights of the outgoing light are emitted. The polarization direction is maintained, and only the polarization direction of the B light can be rotated.
[0046]
A color separation element having a structure in which a color separation surface is sandwiched between two substrates (parallel flat plates) generates astigmatism of the same degree for the separated two colors of light. The optical system makes it possible to compensate for this astigmatism. In order to make the amounts of astigmatism generated for the separated two colors of light coincide with each other, it is preferable that the two substrates sandwiching the color separation surface have the same refractive index and the same thickness. This will be described below with reference to FIGS. 5 and 21.
[0047]
When projecting an image formed by light modulated by an image display element onto a screen, if a parallel flat plate such as a color separation element enters between the projection lens and the image display element, astigmatism occurs, and the image is displayed on the screen. Is distorted due to astigmatism.
[0048]
A configuration using a color separation element in which a color separation surface (typically, a dielectric multilayer film) CP is formed on one surface of a parallel plate like a conventional color separation element 106 ′ shown in FIG. For example, light reflected on the reflective image display element 107-R and incident on the color separation element 106 'is reflected on the surface (color separation plane CP) of the color separation element 106'. Although no aberration occurs, the light reflected by the reflective image display element 107-G passes through the color separation element 106 '(including a parallel flat plate), so that astigmatism is generated with respect to this light. As described above, since astigmatism occurs only in one of the lights from the reflective image display elements 107-R and 107-G, it is difficult to compensate for astigmatism by the projection optical system. is there.
[0049]
Therefore, as shown in FIG. 5, when the color separation element 106 whose color separation surface is sandwiched between two glass substrates (transparent parallel flat plates) 106a and 106b is used, the reflection type image display elements 107-R and 107 are used. Since the light reflected by -G has the same distance through the glass of the color separation element 106, the astigmatism can be compensated by the projection optical system, and there is no distortion due to astigmatism. Images can be displayed.
[0050]
The angle of incidence of light on the color separation surface sandwiched between the glass substrates 106a and 106b of the color separation element 106 is the angle of incidence on the color separation surface of the cross dichroic prism because the light is refracted on the glass surface. (Typically 45 °), and the above-described problem due to the polarization dependence of the color separation surface is greatly reduced.
[0051]
Further, for example, when three reflective image display elements corresponding to R, G, and B light are arranged as shown in FIG. 1, color separation on the optical path leading to the reflective image display element 107-B is performed. Since no element is needed, no astigmatism occurs. On the other hand, as described above, in the optical path leading to the reflective image display elements 107-R and 107-G, astigmatism occurs due to the color separation element 106. Therefore, among the R, G, and B lights projected by the projection optical system (projection lens) 108, only the R and G lights have astigmatism. It is difficult to compensate.
[0052]
On the other hand, by inserting the transparent substrate 109 on the optical path of the light reflected by the reflective image display element 107-B, the amount of astigmatism generated for the R, G, and B light is the same. Therefore, compensation by the projection optical system (projection lens) 108 becomes possible, and a good image can be obtained. As is clear from FIG. 1, in order to make the astigmatisms for the three colors of light the same, the transparent substrate 109 is the same as the two substrates of the color separation element 106 (the thickness is two). It is preferable that the color separation element 106 (light separation surface) is disposed at the same angle with respect to the light path of R light and the light path of R light as to the light path of B light.
[0053]
The R, G, and B lights whose polarization directions are modulated by the reflection type image display element have one color (the B light in the example of FIG. 1) of the other two colors (FIG. 1). In the example of R, G and R), the second polarization control element is arranged on the projection optical system side of the light separating element (which also functions as a light combining element), so that the R, G and B light Can have the same polarization direction. As a result, a polarizing screen that can maintain a high contrast ratio even under bright illumination can be used as the screen. The polarizing screen has a polarizing plate attached to the screen surface, and cuts half of incident light with random polarization (non-polarization). If the transmission axis of this polarizing plate and the polarization direction of the light emitted from the projector (projection type image display device) are matched, the projection light from the projector is hardly cut and the influence of external light is reduced by half. As a result, a display with a high contrast ratio can be performed. Further, by disposing a polarization selecting element (typically a polarizing plate) described later behind the second polarization control element (on the side of the projection optical system), it is possible to further improve the contrast ratio.
[0054]
Further, by arranging the polarization selection element on the optical path on the light incident side of the first polarization control element, it becomes possible to cause linearly polarized light to enter the first polarization control element. The element and the light separation element can efficiently perform color separation / polarization separation (and color synthesis / polarization synthesis), and can display a bright image having a high contrast ratio.
[0055]
Further, by providing the polarization selection element on the light path on the light emission side of the second polarization control element, even if light originally returned to the light source by the light separation element passes through the light separation element, the polarization selection element , An image with a high contrast ratio can be displayed.
[0056]
Further, since the wavelength regulating element is inserted, it is possible to regulate the light in the wavelength range and the light in the polarization direction which should not be radiated to each reflective image display element, thereby improving the color purity. And a decrease in the contrast ratio can be prevented.
[0057]
In addition, since the two-color light is irradiated with the polarization direction different from that of the other one light, the P-polarized light and the S-polarized light in the boundary wavelength region between the two-color light having the same polarization direction and the other one color light. There is a wavelength range in which polarized light is mixed. The contrast ratio and the color purity are improved by cutting the light in the wavelength region where the polarized light is mixed by the wavelength regulating element.
[0058]
Also, due to the characteristics of the polarization control element, partial polarization disorder of light whose polarization cannot be completely rotated or light whose polarization should not be rotated originally occurs. Further, since the light separating element cannot completely separate light according to the polarization direction, color mixing and a decrease in contrast ratio occur.
[0059]
Therefore, by inserting a wavelength regulating element that cuts light other than the light of the color corresponding to each reflection type image display element 107 between the light separation element and the reflection type image display element 107, the color purity and the contrast ratio are improved. Can be improved.
[0060]
Further, the color purity can be improved by cutting at least one of the boundary wavelength region between red and green and the boundary wavelength region between green and blue with the wavelength regulating element. This wavelength regulating element may be used simultaneously with the wavelength regulating element that cuts light other than the light of the color corresponding to each of the above-mentioned reflective image display elements. In this case, it is preferable to use one having both the spectral characteristics of both wavelength regulating elements.
[0061]
Further, as described above, there is a wavelength region where P-polarized light and S-polarized light are mixed in the boundary region of the wavelength between two colors of light having the same polarization and light of another one color. Since the wavelength range in which the polarized light is mixed affects the contrast ratio, it is preferable to cut the wavelength range.
[0062]
When the polarization directions of R and B are aligned, it is necessary to cut the light on the short wavelength side (B side) and the long wavelength side (R side) of G shown by the hatched portion in FIG. Is secured, the R and B wavelength bands are narrowed, and conversely, if the R and B wavelength bands are secured, the G wavelength band is narrowed. Therefore, brightness and color purity are reduced.
[0063]
On the other hand, when the polarization directions of R and G are aligned or the polarization directions of B and G are aligned, for example, as shown in FIG. 2 (FIG. 2 is an example where the polarization directions of R and G are the same). In addition, since it is only necessary to cut off the light in the wavelength band indicated by the hatched portion in the drawing, the color purity can be significantly improved while suppressing the decrease in brightness.
[0064]
In the configuration in which the wavelength regulating element is arranged between the light separating element and the reflection type image display element, the wavelength regulating surface of the wavelength regulating element is arranged so as to form an angle with the image display surface of the reflection type image display element. Thus, the contrast ratio can be improved (see FIG. 7B). The reason will be described below.
[0065]
If the extinction ratio (polarization selectivity) of the light separating element is not sufficient, unnecessary polarized light that should be removed (should be emitted toward another reflective image display element) is mixed with the original polarized light, resulting in a reflection type image. The light is emitted toward the display element. The unnecessary polarized light is incident on a wavelength regulating element disposed between the light separating element and the reflection type image display element, and is reflected on the wavelength regulating surface. Therefore, if the wavelength regulating surface is arranged in parallel with the surface of the reflection type image display element, unnecessary polarized light reflected by the wavelength regulating surface will be reflected toward the projection optical system, and the display contrast will be reduced. Decrease the ratio. However, if the wavelength regulating surface is arranged so as to form an angle (more than 0 ° and less than 90 °) with the image display surface of the reflection type image display device, unnecessary polarized light is different from the original polarized light used for display. Since the light is reflected toward the projection optical system at different angles, it can be easily removed by the projection optical system. In particular, if the wavelength regulating surface of the wavelength regulating element is set at an angle of about 1.5 ° to 13.5 ° with respect to the image display surface of the reflective image display element, the normally used F number is 1 to 8. Unnecessary polarized light can be easily removed by the projection lens.
[0066]
When a prism-shaped color separation element is used, astigmatism does not occur, so that display quality can be improved. Alternatively, there is no need to provide the projection optical system with a special design for compensating for astigmatism. When a plate-shaped color separation element is used, as shown in FIG. 12, a ghost (a phenomenon in which an image is reflected twice) occurs on a screen due to surface reflection on a surface facing the color separation surface CP. When a prism-shaped color separation element is used, the light reflected by the reflection type image display element returns to the direction of the reflection type image display element even if it is reflected on the surface when entering the prism, so that it is incident on the screen. do not do. Therefore, the display quality does not deteriorate due to the light reflected on the prism surface. The color separation prism is typically a quadrangular prism in which two triangular prisms are bonded together, and a dielectric multilayer film is formed on a bonding surface. The bonding surface (dielectric multilayer film) of the triangular prism functions as a color separation surface.
[0067]
When the angle of incidence of light on the color separation surface of the color separation prism is large, the polarization dependence of the color separation characteristics (wavelength selectivity) of the color separation surface is large, and the efficiency of color separation is low. For example, the incident angle with respect to the separation surface of a typical square prism with a right-angled triangular prism bonded to the separation surface is 45 °, the polarization dependence is large, and the efficiency of color separation is low. Therefore, for example, when a parallelogram prism having an isosceles triangular prism with an obtuse angle bonded thereto is used, the angle of incidence on the color separation surface can be made smaller than 45 °, and the polarization of the color separation characteristics can be reduced. Dependency can be suppressed. As a result, the efficiency of color separation by the color separation element can be improved.
[0068]
As the color separation element, a dichroic mirror or a dichroic prism having a sandwich structure is preferably used, but a dichroic mirror having a color separation surface CP on one surface of a transparent substrate (see FIG. 21) may be used. At this time, by arranging the color separation surface CP so as to face the direction of the light separation element (PBS), generation of ghost can be suppressed more than the arrangement shown in FIG. Further, astigmatism does not occur in the R and G color lights reflected by the (exposed) color separation surface CP formed on the surface of the transparent substrate, and the B light transmitted through the color separation surface CP Only astigmatism occurs, but since the visibility of the B light is the lowest, it does not affect the resolution of the displayed image. Therefore, by using a dichroic mirror that transmits the B color light having the lowest luminous efficiency, it is possible to further suppress the occurrence of ghost and to suppress the reduction in resolution due to astigmatism.
[0069]
Further, in a polarization control element manufactured by laminating a plurality of wavelength plates on top of each other, those that rotate the polarization directions of R and B light or R and G light increase the number of layers and are therefore expensive. On the other hand, if the polarization control element rotates the polarization direction of the R or B light, the number of layers can be reduced as compared with the case where the polarization direction of the R and B light or the R and G light is rotated. Cost can be reduced.
[0070]
Further, the polarization separation characteristics (selectively transmitting P-polarized light and selectively reflecting S-polarized light) of the light separating surface of the light separating element generally depend on the wavelength range of light. In addition, it is difficult to optimize both the transmittance for P-polarized light and the reflectance for S-polarized light. If one characteristic (for example, the transmittance for P-polarized light) is optimized, the other characteristic (for example, the reflectance for S-polarized light) may be reduced. Rate) decreases.
[0071]
Therefore, one of the transmittance for the P-polarized light and the reflectance for the S-polarized light of the light separating surface of the light separating element is optimized, and the polarized light having the optimized characteristics is incident on two or more reflective image display elements. The display quality can be improved by arranging them in such a manner as to be performed. Alternatively, the display quality can be improved by separating the G light having the highest luminosity out of the three primary colors as polarized light having optimized characteristics by the light separating element.
[0072]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
[0073]
FIG. 1 is a schematic diagram of a projection type color image display device 100 according to an embodiment of the present invention. In the following drawings, components having substantially the same function are denoted by common reference numerals.
[0074]
The image display device 100 includes an illumination optical system 100a that emits light of three primary colors, red, green, and blue, with the polarization directions of the two colors being different from the polarization directions of the other color light, and an illumination system 100a. A PBS 105 as a light separating element for separating light emitted from the optical system 100a according to a polarization direction, a dichroic mirror 106 as a color separating element for separating the two colors of light having the same polarization direction, and a PBS 105 and a dichroic mirror 106 Reflective image display elements 107-R, 107-G, and 107-B that modulate the separated lights (R, G, and B), respectively, and light that is modulated by the reflective image display elements 107-R, G, and B. And a projection optical system (projection lens) 108 for projecting
[0075]
The illumination optical system 100a has a white light source 101, a trimming filter 102 as a wavelength regulating element, a polarizing plate 103 as a polarization selection element, and a polarization control element 104.
[0076]
In the present embodiment, a Philips UHP lamp having a power of 120 W and an arc length of 1.4 mm is used as the light source 101. As the light source 101, a halogen lamp, a xenon lamp, or a metal halide lamp can be used.
[0077]
The light from the light source 101 is converted into substantially parallel light by the parabolic mirror 101a, and then enters the trimming filter 102 and the polarizing plate 103.
[0078]
The polarizing plate 103 transmits only light in a direction perpendicular to the paper surface, and the obtained linearly polarized light enters the polarization control element 104.
[0079]
The polarization control element 104 has characteristics as shown in FIG. 2, and rotates only the polarization direction of the B light out of the incident light in a direction parallel to the plane of the paper and makes it incident on the PBS 105.
[0080]
The solid line in FIG. 2 shows the characteristics of the light reflected on the light separation surface PP of the PBS 105 in the optical system shown in FIG. 3, and the broken line shows the characteristics of the light transmitted through the light separation surface PP of the PBS 105.
[0081]
In this embodiment, as the polarization control element 104, an element disclosed in US Pat. No. 5,751,384 is used. This element has a function of laminating a plurality of wavelength plates while changing the angle of their axes, and rotating the polarization direction of only light in a specific wavelength range. When an element for rotating the polarization direction of B polarized light is used as in the present embodiment, as shown in FIG. 4, when white linearly polarized light enters this element, R and G light out of the emitted light Is maintained, and only the polarization direction of the B light can be rotated.
[0082]
In the present embodiment, the above-described element is used as the polarization control element 104, but any element having the same function can be used. For example, a cholesteric liquid crystal may be used.
[0083]
The trimming filter 102 functions to cut the wavelength range at the boundary between the B light whose polarization direction is rotated by the polarization control element 104 indicated by the hatched portion in FIG. 2 and the G light whose polarization is not rotated, and the boundary wavelength between R and G. It also has the function of cutting the region (570 nm to 590 nm).
[0084]
When the light emitted from the polarization control element 104 enters the PBS 105, the R and G lights become S-polarized with respect to the PBS 105 and are reflected on the light separation plane PP, and the B light becomes P-polarized with respect to the PBS 105. Transmit through the plane PP.
[0085]
The R and G lights reflected by the PBS 105 are incident on a dichroic mirror 106 arranged substantially parallel to the light separation surface PP of the PBS 105, where the R light is reflected and the G light is transmitted. Since the color separation plane CP of the dichroic mirror 106 is arranged substantially parallel to the light separation plane PP of the PBS 105, as described above, disturbance of the polarization state due to the color separation plane CP is suppressed, and the contrast ratio is improved.
[0086]
The light transmitted and reflected by the PBS 105 and the dichroic mirror 106 are incident on the corresponding reflective image display elements 107-R, 107-G, and 107-B, and are modulated according to the image signals. Thereafter, the R and G lights again enter the dichroic mirror 106, are combined, and are reflected again toward the PBS 105. The B light is similarly modulated and reflected toward the PBS 105. Only light whose polarization direction is modulated by the PBS 105 is selectively emitted toward the projection lens 108. At this time, the PBS 105 functions as a polarization combining element or a color combining element.
[0087]
As the reflective image display element 107, a 0.9-type XGA panel having a vertically aligned liquid crystal mode was used. As a liquid crystal mode, any reflection type liquid crystal display device such as a TN mode can be used.
[0088]
The dichroic mirror 106 has a structure as shown in FIG. 5, in which a dielectric surface (color separation surface) CP is sandwiched between glass substrates 106a and 106b and optically bonded. Therefore, when the lights separated by the dichroic mirror 106 and reflected by the reflective image display elements 107-R and 107-G are color-combined by the dichroic mirror 106, the respective lights (R and G lights) are The optical path length in the passing glass becomes the same, and the amount of astigmatism generated thereby becomes the same. Of course, it is preferable to use the same glass substrate (parallel plate) as the glass substrates 106a and 106b. Note that, as described above, the color separation plane CP of the dichroic mirror 106 also functions as a color synthesis plane.
[0089]
With this structure, the dichroic mirror 106 changes the incident angle of light on the color separation plane CP due to refraction of light on the glass substrates 106a and 106b, and is in a state similar to the case where the arrangement angle of the dichroic mirror 106 changes. However, since the amount of change is not more than 20 °, there is no effect that significantly lowers the contrast ratio. Of course, the angle of incidence on the color separation plane CP is preferably set to 20 ° or less in consideration of refraction of light on the glass substrates 106a and 106b.
[0090]
On the other hand, the light reflected by the reflection type image display element 107-B passes through the transparent glass substrate 109 and then enters the PBS 105. Therefore, if the thickness of the transparent glass substrate 109 is set to be the same as the thickness of the dichroic mirror 106 (the sum of the thicknesses of the glass substrates 106a and 106b), the astigmatism amounts with respect to the R, G, and B lights are mutually different. Will be the same. It is needless to say that the arrangement angle of the glass substrate 109 with respect to the optical path is preferably equal to the arrangement angle of the dichroic mirror 106 with respect to the optical path. However, another configuration may be used as long as the astigmatism amounts can be matched.
[0091]
The projection lens 108 is designed to compensate (correct) these astigmatisms. As described above, a color separation element having a color separation surface sandwiched between substrates is used, and a transparent layer having the same thickness as the color separation element is provided on the optical path to the reflective image display element without passing through the color separation element. By arranging the substrates, astigmatism for all colors of light can be equalized, so that astigmatism can be compensated only by changing the design of the projection lens 108.
[0092]
In the present embodiment, the dichroic mirror 106 having the sandwich structure is used. However, depending on the required resolution, the dichroic mirror 106 is not necessarily required to have the sandwich structure, and a conventional type in which the color separation surface is formed on the surface of glass is used. Is also good. In this case, the reflective image display element 107-G corresponding to the G light that most affects the resolution is disposed on an optical path where astigmatism does not occur, or the astigmatism of the reflective image display element 107-G is reduced. It is preferred to design the projection lens to take. Similarly, the transparent glass substrate 109 need not necessarily be arranged depending on the required resolution.
[0093]
Between the PBS 105 and the projection lens 108, a polarization control element 110 having the same characteristics as the polarization control element 104 and a polarizing plate 111 for passing polarized light in a direction perpendicular to the plane of the drawing are arranged.
[0094]
The polarization control element 110 provided on the projection lens 108 side of the PBS 105 has a function of rotating the polarization direction of only the B light and aligning the R, G, and B polarization directions. As the polarization control element 110, an element similar to the polarization control element 104 can be used. Further, the polarizing plate 111 provided between the polarization control element 110 and the projection lens 108 cuts out leak light of light originally cut by the PBS 105 out of the light from the polarization control element 110 and improves the contrast ratio. . As described above, if all the R, G, and B lights projected by the projection lens 108 and used for display have the same polarization, the contrast ratio of the display can be improved by projecting the light on the polarizing screen. .
[0095]
A dichroic having characteristics as shown in FIGS. 6A and 6B is provided between the PBS 105 and the reflective image display elements 107-R and 107-G and between the PBS 105 and the reflective image display element 107-B, respectively. Mirrors 112 and 113 are inserted, and each of the reflective image display elements 107-R, 107-G and 107-B has a function of cutting light other than the corresponding light. The unnecessary light reflected by the dichroic mirrors 112 and 113 returns to the light source 101 via the PBS 105. 6A shows the spectral characteristics of the dichroic mirror 112 (selectively transmitting R and G), and FIG. 6B shows the spectral characteristics of the dichroic mirror 113 (selectively transmitting B). .
[0096]
In the present embodiment, the dichroic mirror 112 is arranged immediately after the PBS 105. However, the R and G lights may be arranged after the light is separated by the dichroic mirror 106. In this case, the spectral characteristics are such that the dichroic mirror corresponding to the G reflective image display element 107-G transmits only G, and the dichroic mirror corresponding to the R reflective image display element 107-R transmits only R. It may be used, and depending on the characteristics of the PBS 105 and the polarization control element 104, it may be arranged on one of them.
[0097]
Further, in the present embodiment, the dichroic mirrors 112 and 113 are disposed on both of the optical paths separated by the PBS 105, but the dichroic mirrors 112 and 113 may not be disposed depending on the characteristics of the PBS 105 and the polarization control element 104. You may insert in only one side.
[0098]
Further, in the present embodiment, the trimming filter 102 having both the function of cutting the boundary wavelength region of B and G light and the function of cutting the boundary wavelength region of R and G light is used. Depending on the characteristics of the polarization control element 104 and the wavelength region to be used, it is not always necessary to cut off the light in both boundary wavelength regions, and depending on the required display performance, it is not always necessary to dispose the light. . The position of the trimming filter 102 may be any position on the optical path from the light source to the screen.
[0099]
The projector 100 having the above configuration can realize a compact and low-cost liquid crystal projection while being extremely bright and having a high contrast ratio.
[0100]
In the present embodiment, the polarization control elements 104 and 110 for rotating the polarization direction of the B light are used. However, the color for rotating the polarization direction is not limited to this. , S-polarized light may be exchanged.
[0101]
In the present embodiment, the white light is separated into R, G, and B light by the PBS 105, but a combination such as G, B, and R can be changed. In this case, it is only necessary to change the color of the light to be rotated by the polarization control elements 104 and 110.
[0102]
Further, in the present embodiment, the polarizing plate and the polarization control element are arranged on both the light incident side and the emission side of the PBS 105, but the polarization control element 110 and the polarizing plate 111 on the light emission side are not necessarily required.
[0103]
Next, a structure for further improving the display quality of the image display device 100 shown in FIG. 1 will be described. FIG. 7A is a diagram schematically illustrating an arrangement relationship of optical elements around the PBS 105 in the image display device 100, and FIG. 7B is a schematic diagram illustrating an arrangement obtained by modifying the optical element. In FIG. 7, the dichroic mirror 106 for color separation is omitted, and one of the reflective image display elements 107-R and 107-G is shown as the reflective image display element 107. Note that reference numeral 107 is also used for any reflective image display device.
[0104]
As in the image display device 100, when the dichroic mirrors 112 and 113 for regulating the wavelength are arranged between the corresponding reflective image display element 107 and the PBS 105, for example, as shown in FIG. In addition, part of the light B (p) (P-polarized light of B) that should originally pass through the light separation surface PP of the PBS 105 is reflected by the light separation surface PP of the PBS 105 because the extinction ratio of the PBS 105 is not perfect, and the light B The light enters the dichroic mirror 112 as (p) ′. Unnecessary P-polarized light of B light is represented as light B (p) ′.
[0105]
Since the light B (p) ′ is light that originally passes through the light separation surface PP of the PBS 105 and enters the corresponding reflective image display element 107-B, it is reflected by the dichroic mirror 112 and enters the PBS 105 again. Most of the light B (p) ′ incident on the PBS 105 passes through the light separation surface PP of the PBS 105 and is incident on a projection lens (not shown), thereby lowering the display contrast ratio.
[0106]
Here, as shown in FIG. 7B, when the light control surfaces of the dichroic mirrors 112 and 113 and the image display surface of the reflection type image display element 107 are arranged at an angle, the dichroic mirrors 112 and 113 can be used. The reflected light B (p) 'enters the PBS 105 at an angle different from the light reflected by the reflective image display element 107 (light used for display). Therefore, as shown schematically in FIG. 8, in the projection lens 108, only the light B (p) ′ which causes a decrease in the contrast ratio is eclipsed by the pupil. As a result, it is possible to prevent a decrease in the contrast ratio due to the imperfect color separation characteristics of the PBS 105.
[0107]
Usually, the light receiving angle of the projection lens 108 used in the projection type image display device varies depending on the size of the image display element used, but is generally in the range of 3 ° to 27 ° (F number 1 to 8). Therefore, the wavelength control of the dichroic mirror 112 is performed so that the unnecessary light B (p) ′ which causes a decrease in the contrast ratio is incident at an angle larger than the light receiving angle of the projection lens 108 as shown by the broken line in FIG. The angle θ of the surface (typically, a dielectric multilayer film) with respect to the image surface of the reflective image display element 107 is within a range of about 1.5 ° to 13.5 ° according to the light receiving angle of the projection lens. By adjusting, unnecessary light B (p) ′ is cut, and the contrast ratio can be effectively improved. When the wavelength regulating surface of the dichroic mirror 112 is tilted by θ, the reflected light forms an angle of 2θ with respect to the incident light. At this time, the light receiving angle of the projection lens needs to be 2θ or less. Within the range that satisfies this relationship, the angle θ of the wavelength regulating surface of the dichroic mirror 112 with respect to the image surface of the reflective image display element 107 is adjusted according to the light receiving angle of the projection lens.
[0108]
Due to imperfect light separation characteristics of the PBS 105, display quality may be degraded. This phenomenon will be described with reference to FIG. FIG. 9 is a diagram schematically illustrating an arrangement relationship of optical elements around the PBS 105 in the image display device 100. Note that, for simplicity, optical elements unnecessary for description are omitted.
[0109]
As shown in FIG. 9, light G (S) (S-polarized light of G) incident on the corresponding reflective image display element 107-G is reflected without being modulated by the reflective image display element 107-G. At this time (typically, when the reflective image display element 107-G is in the black display state), most of the light G (S) incident on the PBS 105 again is reflected by the light separating surface PP of the PBS 105, and Returning to the direction shown in the figure, since the extinction ratio of the PBS 105 is not perfect, a part thereof (denoted as “G (s) ′”) passes through the light separation surface PP of the PBS 105. Most of the light G (s) ′ is cut by the polarizing plate 111. However, in particular, when the polarization control element 110 is disposed between the PBS 105 and the polarizing plate 111, the polarization direction of a part of G (s) ′ transmitted through the light separation surface PP of the PBS 105 is changed by the polarization control element 110. The light is disturbed and transmitted through the polarizing plate 111, and as a result, the contrast ratio of the display decreases.
[0110]
In the optical system shown in FIG. 17, the illumination light is separated into R, G, and B light, and then is incident on the PBS 702 for each color light. On the other hand, in the image display device 100 of the present embodiment, , All the color lights are incident on the PBS 105, so that the PBS 105 is required to have a high extinction ratio for all the wavelength ranges of the R, G, and B lights. However, it is difficult to obtain a PBS 105 having a high extinction ratio for both P-polarized light and S-polarized light over a wide wavelength range. For example, when the characteristics (reflectance) for S-polarized light are designed to be good, the characteristics (transmittance) for P-polarized light are reduced. That is, color separation characteristics as shown in FIG. 10 are obtained.
[0111]
As shown in FIG. 10, when a PBS exhibiting high characteristics with respect to S-polarized light is used as the PBS 105 in FIG. 9, the light G (s) ′ can be reduced and the contrast ratio can be improved.
[0112]
In general, the polarization splitting characteristic of the PBS 105 may be optimized for either P-polarized light or S-polarized light. However, since the polarization splitting characteristic for the other polarized light is reduced, more reflective image display elements (usually, R, Since three panels of G and B are used, the polarization direction on the side where two or more panels are disposed is optimized, or a reflective image display element corresponding to G light with higher visibility is disposed. It is more effective to optimize the polarization separation characteristics of the PBS 105 for the polarized light.
[0113]
FIGS. 11A and 11B schematically show projection color image display devices 200 and 300 in which the above-described structure is applied to the image display device 100.
[0114]
In the image display device 200 of FIG. 11A, the dichroic mirrors 112 and 113 are arranged at an angle of about 5 ° with respect to the display surface of the corresponding reflective image display element 107 (see FIG. 8). θ is about 5 °). In FIG. 11B, dichroic mirrors 211, 212, and 213 having the same functions as the dichroic mirrors 112, 113 are arranged at an angle of about 5 ° with respect to the corresponding display surface of the reflective image display element 107. Have been.
[0115]
Image display devices 200 and 300 are both Fno. Was used (light receiving angle ± 9.5 °), and illumination light having a parallelism of ± 10 ° was incident on the reflective image display element 107.
[0116]
By employing the above structure, unnecessary light reflected by the dichroic mirrors 112 and 113 or the dichroic mirrors 211, 212 and 213 is emitted toward the projection lens 108 by the imperfect polarization separation characteristics of the PBS 105. However, since this unnecessary light cannot pass through the pupil of the projection lens 108 as shown by the broken line in FIG. 8, a decrease in the contrast ratio is prevented. The image display devices 200 and 300 were able to realize a display with a higher contrast ratio than the image display device 100 without lowering the brightness.
[0117]
In the image display devices 200 and 300, the dichroic mirrors 112 and 113 or the dichroic mirror 211 are arranged such that all unnecessary light reflected by the dichroic mirrors 112 and 113 or the dichroic mirrors 211, 212 and 213 is cut by the projection lens 108. , 212 and 213 are tilted. However, even if the tilt angle of these dichroic mirrors is reduced and a configuration in which a part of unnecessary light is transmitted through the projection lens 108 is adopted, the contrast ratio is improved as compared with the image display apparatus 100. can do.
[0118]
Further, in the image display devices 200 and 300, as shown in FIG. 10, a PBS 105 having a characteristic (reflectance) for S-polarized light is better than a characteristic (transmittance) for P-polarized light, as shown in FIG. Accordingly, the S-polarized light separated better than the P-polarized light at the light separation surface PP of the PBS 105 enters the reflection image display elements 107G and 107R of the three reflection image display elements, and the polarization separation characteristics are inferior. The P-polarized light enters only the reflection type image display element 107B. As described above, by maximizing the polarization splitting characteristic of the PBS 105, light that lowers the contrast ratio can be further reduced.
[0119]
In the image display devices 200 and 300, the two reflective image display elements 107G and 107R are arranged on the S-polarized side using the PBS 105 in which the polarization separation characteristic for the S-polarized light is optimized. The same effect can be obtained even if one reflective image display element 107G corresponding to G is arranged. In addition, when the PBS 105 in which the polarization separation characteristic is optimized for the P-polarized light is used, a configuration in which two reflective image display elements 107 are arranged on the P-polarized light side may be adopted, The same effect can be obtained by adopting a configuration in which one reflective image display element 107G corresponding to G light with high sensitivity is arranged.
[0120]
In the image display devices 200 and 300, the polarization direction of the B light is rotated by the polarization control element 104. However, the polarization directions of the R light and the G light may be rotated. It may be reversed. In addition, the dichroic mirrors 112 and 113 and the dichroic mirrors 211, 212 and 213 are arranged on both of the optical paths separated by the PBS 105. May be. Furthermore, although the polarizing plate and the polarization control element are arranged on both the light incident side and the light emission side of the PBS 105, the polarization control element 110 and the polarizing plate 111 on the light emission side are not necessarily required.
[0121]
Also, in the image display devices 200 and 300, the color separation element 106 in which the color separation surface is sandwiched between two glass substrates is used. However, depending on the required resolution, the color separation element 106 having a sandwich structure is not necessarily used. Instead, a conventional color separation element 106 '(for example, see FIG. 21) in which a color separation surface is formed on one surface of a glass substrate may be used.
[0122]
Next, a configuration using a dichroic prism as a color separation element and its operation will be described.
[0123]
As described above, when a conventional dichroic mirror 106 ′ having a color separation surface formed on one surface of a parallel plate is used as a color separation element, astigmatism occurs. A special device (use of the color separation element 106 and the glass substrate 109) for compensating aberration is required.
[0124]
Further, when a parallel-plate color separation element such as a conventional dichroic mirror 106 'is used, as shown in FIG. 12, the light reflected on the surface of the glass substrate 106a' facing the color separation plane CP ("ghost"). This causes a phenomenon in which an image is double reflected on the screen, a so-called ghost phenomenon.
[0125]
On the other hand, as in the case of the projection type color image display devices 400 and 500 shown in FIGS. 13A and 13B, when a prism-shaped color separation element (dichroic prism) 206 is used, astigmatism does not occur. The display quality can be improved without special measures such as the image display device 100 shown in FIG. The dichroic prism 206 is typically a quadrangular prism formed by bonding two triangular prisms together, a dielectric multilayer film is formed on a bonding surface, and the bonding surface functions as a color separation surface CP. .
[0126]
Further, when the dichroic prism 206 is used, the light reflected by the reflection type image display element returns to the direction of the reflection type image display element even if it is reflected by the surface when entering the dichroic prism 206. Does not enter. Therefore, the light reflected on the surface of the dichroic prism 206 does not cause a ghost phenomenon.
[0127]
Since the dichroic prism 206 of the image display device 400 is a square prism formed by bonding right-angled triangular prisms, the angle of incidence of light on the color separation surface CP is relatively large at 45 °. Low efficiency of separation. Therefore, as in the image display device 500 of FIG. 13B, for example, if a dichroic prism 206 composed of a parallelogram prism bonded to an isosceles triangular prism having an obtuse angle is used, the color separation plane CP is reduced. Becomes less than 45 °, and the polarization dependence of the color separation characteristics can be suppressed. In this example, as a result of using the dichroic prism 206 having a light incident angle of 40 °, the efficiency of color separation was improved, and the brightness and color purity were able to be improved.
[0128]
When a prism element is used as the color separation element, the light does not pass through the dichroic prism 206 as shown in FIGS. 13A and 13B in order to equalize the optical path lengths of the lights of the respective colors. It is preferable to dispose the glass block 209 in the optical path.
[0129]
The configuration of the image display device using the dichroic prism as the color separation element is not limited to the image display devices 400 and 500 illustrated above, and can be appropriately combined with the above-described configuration, and by using the dichroic prism instead of the dichroic mirror. The above-described effects can be additionally obtained.
[0130]
As described above, the dichroic mirror 106 or the dichroic prism 206 having a sandwich structure is preferably used as the color separation element, but a conventional dichroic mirror 106 'may be used. FIG. 14 schematically shows another projection type color image display device 100 ′ according to the present invention.
[0131]
The image display device 100 'shown in FIG. 14 replaces the sandwich dichroic mirror 106 in the image display device 100 shown in FIG. 1 with a conventional dichroic mirror 106' having a color separation surface CP on one surface of a glass substrate. It is something. The dichroic mirror 106 'is arranged so that the color separation plane CP faces the PBS 105. Further, a dichroic mirror 106 'that transmits B light is used. Further, when the dichroic mirror 106 'is arranged as described above, the G or R color light is reflected by the exposed color separation surface CP, and therefore, no astigmatism occurs in these color lights. Therefore, the transparent substrate 109 in the image display device 100 of FIG. 1 is not provided.
[0132]
In the image display device 100 ′, astigmatism is generated with respect to the B light, but is combined with the R and G lights, and hardly affects the resolution of the image projected on the screen. This is because the visibility of the human eye with respect to the B light is lower than the visibility with respect to the R and G light, so that the resolution of the projected and displayed image is dominated by the resolution of the R and G images. It is.
[0133]
Further, by adopting a configuration in which the color separation surface CP of the dichroic mirror 106 'is directed toward the PBS 105 and the color separation surface CP transmits B light having the lowest visibility, the occurrence of ghost on the screen is reduced. It can be suppressed to a level that can hardly be visually recognized.
[0134]
In the arrangement shown in FIG. 14, the light reflected by the reflective image display elements 107-R and 107-G is directly reflected by the color separation plane CP, so that no ghost occurs. The light reflected by the reflective image display element 107-B is reflected by a surface of the transparent substrate on which the color separation surface CP is not formed, but this reflected light does not enter the projection lens. Most of the B light that reaches the color separation surface CP passes through the color separation surface CP. A part of the B light is reflected by the characteristics of the color separation surface CP, and a part of the reflected light is reflected again on the surface of the transparent substrate on which the color separation surface CP is not formed, and a ghost and Become. However, this ghost is much lighter than a ghost generated in a configuration in which the color separation surface CP is arranged to face the reflective image display element 107 (see FIG. 12). Of course, it is preferable to adopt a configuration in which the color separation plane CP transmits the B light with the lowest luminosity in order to suppress the occurrence of ghost. The occurrence of ghost is suppressed as compared with the configuration shown in FIG.
[0135]
Further, although the effect is lower than the configuration in which the B light is transmitted through the dichroic mirror 106 ', depending on the required image quality, the visibility is the second lowest after the B light, and the R light is transmitted through the dichroic mirror 106'. A configuration may be adopted.
[0136]
In the image display device 100 ′, the configuration in which the B and G lights are reflected by the PBS 105 is adopted, but the B and R lights may be reflected. Further, a configuration that transmits B and G light or B and R light may be adopted.
[0137]
As described above, the ghost can be suppressed by arranging the color separation surface CP formed on one surface of the transparent substrate of the conventional dichroic mirror 106 'so as to face the PBS 105. Furthermore, by using the dichroic mirror 106 'that transmits the B color light having the lowest luminosity, it is possible not only to further suppress the occurrence of ghost, but also to suppress the reduction in resolution due to astigmatism.
[0138]
【The invention's effect】
As described above, according to the present invention, by making one of R, G, and B colors incident on the PBS different in polarization direction from the other colors, color separation can be performed between the PBS and the dichroic mirror. A low-cost image display device (for example, a liquid crystal projector) can be realized.
[0139]
Further, by setting one of the two colors of light of the same polarization direction among the R, G, and B lights to be G, the band of usable light can be widened, and the brightness and color purity can be increased.
[0140]
In addition, a structure in which the color separation surface of the dichroic mirror for color separation is sandwiched between glass substrates, and a transparent substrate is inserted on the optical path on which color separation is not performed, which is generated in each reflective image display element. Since the aberration amount of astigmatism becomes the same and the aberration can be corrected by the projection lens, an image with high resolution can be realized.
[0141]
Furthermore, by providing a wavelength regulating element that cuts light other than light corresponding to each reflective image display element and light in a wavelength range where S-polarized light and P-polarized light are mixed, the color purity of R, G, and B is improved. And the contrast can be improved.
[0142]
Furthermore, the contrast ratio can be further improved by arranging the wavelength regulating surface of the wavelength regulating element at an angle with respect to the image display surface of the reflective image display element.
[0143]
When a prism-shaped color separation element is used, display quality can be further improved.
[0144]
Further, a polarization separation characteristic is optimized using one of the P-polarized light and the S-polarized light using a light separating element, and is arranged so that G light is separated as optimized polarized light, or The display quality can be further improved by arranging two or more reflective image display elements corresponding to the optimum polarization.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a projection type color image display device 100 according to an embodiment of the present invention.
FIG. 2 shows spectral characteristics of a polarization control element used in an embodiment of the present invention.
FIG. 3 is an optical system used for measuring spectral characteristics of a polarization control element.
FIG. 4 is an explanatory diagram of functions of a polarization control element.
FIG. 5 is a structural diagram of a dichroic mirror.
FIG. 6 shows spectral characteristics of a dichroic mirror used in the embodiment of the present invention.
FIG. 7A is a diagram schematically illustrating an arrangement relationship of optical elements around a PBS 105 in the projection type color image display device 100, and FIG. 7B is a diagram schematically illustrating an arrangement obtained by modifying the optical element. It is.
FIG. 8 is a schematic diagram showing that the arrangement of FIG. 7B can prevent a decrease in contrast ratio.
FIG. 9 is a schematic diagram for explaining a mechanism in which a contrast ratio is reduced by incomplete polarization separation characteristics of a PBS.
FIG. 10 is a graph showing polarization separation characteristics of a PBS used in a projection type color image display device according to an embodiment of the present invention.
FIGS. 11A and 11B are diagrams schematically showing projection type color image display devices 200 and 300 according to an embodiment of the present invention, respectively.
FIG. 12 is a schematic diagram for explaining a ghost phenomenon by a conventional dichroic mirror 106 ′.
FIGS. 13A and 13B are diagrams schematically showing projection color image display devices 400 and 500 according to an embodiment of the present invention, respectively.
FIG. 14 is a diagram schematically showing a projection type color image display device 100 ′ according to an embodiment of the present invention.
FIG. 15 is an explanatory diagram of a pixel portion of a transmissive liquid crystal display element.
FIG. 16 is an explanatory diagram of a reflection type liquid crystal display element.
FIG. 17 is an explanatory diagram of a three-panel liquid crystal projection using a reflective liquid crystal display element.
FIG. 18 is an explanatory diagram of another three-panel liquid crystal projection using a reflective liquid crystal display element.
FIG. 19 is an explanatory diagram of polarization dependence of a cross dichroic prism.
FIG. 20 is an explanatory diagram of an arrangement direction of a dichroic mirror for color separation.
FIG. 21 is an explanatory view of a conventional dichroic mirror for color separation.
FIG. 22 shows spectral characteristics of the polarization control element when the polarization directions of red and blue are aligned.
[Explanation of symbols]
100 Projection type color image display device
100a illumination optical system
101 light source
102 Trimming filter
103 Polarizing plate
104 Polarization control element
105 PBS
Dichroic mirror for 106 color separation
107 Reflective image display device
108 Projection lens (projection optical system)
109 Transparent substrate
110 Polarization control element
111 polarizing plate
112 dichroic mirror
113 dichroic mirror
206 dichroic prism for color separation
209 Glass block
211, 212, 213 Dichroic mirror
601 TFT
602 black matrix
603 Gate bus line
604 source bus line
601 Reflective pixel electrode
701 Light source
702 PBS
703 Cross dichroic mirror
704 reflective liquid crystal display device
705 Projection lens

Claims (18)

An illumination optical system that emits light of the three primary colors of red, green, and blue with the polarization directions of the two colors of light being different from the polarization directions of the other one of the colors;
A light separating element that separates light emitted from the illumination optical system according to a polarization direction,
A color separation element that separates the two colors of light having the same polarization direction;
A plurality of reflective image display elements that modulate the light separated by the light separation element and the color separation element,
A projection optical system for projecting light modulated by the plurality of reflective image display elements,
Has,
An image display device wherein a color separation surface of the color separation element is sandwiched between two substrates . The image display apparatus according to claim 1, wherein that have a transparent substrate on at least one is disposed on the optical path of the light separated by the light separating element. An illumination optical system that emits light of the three primary colors of red, green, and blue with the polarization directions of the two colors of light being different from the polarization directions of the other one of the colors;
A light separating element that separates light emitted from the illumination optical system according to a polarization direction,
A color separation element that separates the two colors of light having the same polarization direction;
A plurality of reflective image display elements that modulate the light separated by the light separation element and the color separation element,
A projection optical system for projecting light modulated by the plurality of reflective image display elements,
Has,
The color separation element is a quadrangular prism formed by bonding two triangular prisms,
Principal rays of the incident light and the outgoing light to and from the quadrangular prism enter and exit substantially parallel to a surface normal of a light incident surface and an exit surface of the quadrangular prism, and a light separating surface of the quadrangular prism. Image display device which is incident at an angle smaller than 45 ° with respect to the surface normal of An illumination optical system that emits light of the three primary colors of red, green, and blue with the polarization directions of the two colors of light being different from the polarization directions of the other one of the colors;
A light separating element that separates light emitted from the illumination optical system according to a polarization direction,
A color separation element that separates the two colors of light having the same polarization direction;
A plurality of reflective image display elements that modulate the light separated by the light separation element and the color separation element,
A projection optical system for projecting light modulated by the plurality of reflective image display elements,
Has,
The color separation surface of the color separation element is formed on one surface of the substrate, is arranged so as to face the light separation element side, transmits blue light, and has the same polarization direction. An image display device in which the color light includes blue light . An illumination optical system that emits light of the three primary colors of red, green, and blue with the polarization directions of the two colors of light being different from the polarization directions of the other one of the colors;
A light separating element that separates light emitted from the illumination optical system according to a polarization direction,
A color separation element that separates the two colors of light having the same polarization direction;
A plurality of reflective image display elements that modulate the light separated by the light separation element and the color separation element,
A projection optical system for projecting light modulated by the plurality of reflective image display elements,
Has,
The illumination optical system includes a light source that emits light of three primary colors, and a first polarization control element that changes a polarization direction of at least one of the light of the three primary colors from the light source. ,
An image display device, wherein a second polarization control element for aligning the polarization directions of the three primary colors of red, green, and blue lights in the same direction is disposed on the projection optical system side of the light separation element . The image display apparatus in one direction of the polarization direction only transmission or polarization selective reflecting that have been arranged according to claim 5, wherein the optical path of the light emission side of said second polarization control element. An illumination optical system that emits light of the three primary colors of red, green, and blue with the polarization directions of the two colors of light being different from the polarization directions of the other one of the colors;
A light separating element that separates light emitted from the illumination optical system according to a polarization direction,
A color separation element that separates the two colors of light having the same polarization direction;
A plurality of reflective image display elements that modulate the light separated by the light separation element and the color separation element,
A projection optical system for projecting light modulated by the plurality of reflective image display elements,
Has,
On the optical path between the light source and the projection optical system, at least one wavelength regulating element is inserted,
The wavelength regulating element is disposed between the light separating element and the reflective image display element, and the light regulating surface of the wavelength regulating element forms an angle with the image display surface of the reflective image display element. The image display device that is arranged . The illumination optical system includes a light source that emits light of three primary colors, and a first polarization control element that changes a polarization direction of at least one of the light of the three primary colors from the light source. ,
8. The image display device according to claim 7 , wherein the wavelength regulating element cuts light in a wavelength region at a boundary between the light whose polarization direction is converted by the first polarization control element and the wavelength of the other light . The wavelength regulating element is disposed on at least one of the optical paths of the light separated by the light separating element, and any one of the plurality of reflective image display elements disposed on the optical path into which the wavelength regulating element is inserted corresponds. The image display device according to claim 7, wherein light other than light to be emitted is cut . The image display device according to any one of claims 7 to 9 , wherein the wavelength regulating element cuts off at least one of a boundary wavelength region between red and green and a boundary wavelength region between green and blue . 11. The angle according to claim 7, wherein an angle between the light-regulating surface of the wavelength-limiting element and the image display surface of the reflection-type image display element is in a range of 1.5 ° to 13.5 ° . Image display device. An illumination optical system that emits light of the three primary colors of red, green, and blue with the polarization directions of the two colors of light being different from the polarization directions of the other one of the colors;
A light separating element that separates light emitted from the illumination optical system according to a polarization direction,
A color separation element that separates the two colors of light having the same polarization direction;
A plurality of reflective image display elements that modulate the light separated by the light separation element and the color separation element,
A projection optical system for projecting light modulated by the plurality of reflective image display elements,
Has,
Either the transmittance for P-polarized light or the reflectance for S-polarized light of the light separating surface of the light separating element is higher than the other,
An image display device in which light separated by the light separating element as polarized light having one of the above is incident on two or more of the plurality of reflective image display elements . An illumination optical system that emits light of the three primary colors of red, green, and blue with the polarization directions of the two colors of light being different from the polarization directions of the other one of the colors;
A light separating element that separates light emitted from the illumination optical system according to a polarization direction,
A color separation element that separates the two colors of light having the same polarization direction;
A plurality of reflective image display elements that modulate the light separated by the light separation element and the color separation element,
A projection optical system for projecting light modulated by the plurality of reflective image display elements,
Has,
One of the transmittance for P-polarized light and the reflectance for S-polarized light of the light separating surface of the light separating element is higher than the other, and green light is separated by the light separating element as polarized light having the one. apparatus. 14. The image display device according to claim 1, wherein an angle formed between a light separating surface of the light separating element and a color separating surface of the color separating element is 20 ° or less . 15. The image display device according to claim 1, wherein , among the three primary colors of red, green, and blue, two colors of light having the same polarization direction include green light . 2. The illumination optical system includes a light source that emits light of three primary colors, and a first polarization control element that converts a polarization direction of at least one of the light of the three primary colors from the light source. 14. The image display device according to any one of items 1 to 4, 7, 9 to 13 . 17. The polarization selector according to claim 5, wherein a polarization selector that transmits or reflects only polarized light in one polarization direction is disposed on an optical path on a light incident side of the first polarization control element. Image display device. 18. The image display device according to claim 5, wherein the first polarization control element is formed by laminating a plurality of wavelength plates with different axes at different angles .

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