JP2001075174A - Picture display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a compact, lightweight and bright picture display device. SOLUTION: After rotating the polarization direction of only the light beam of a blue component out of the light beams of three primary colors, red, green and blue, from a light source 101 by a polarized light control element 104, the light beams are made incident on a light separation element. The red and green light beams made incident on the light separation element are reflected and the blue light beam is transmitted. The red and green light beams are made incident on a color separation element 106, and the red light beam is reflected and the green light beam is transmitted. The light beams separated to red, green and blue are made incident on picture display elements 107 corresponding to the respective light beams, and modulated in accordance with a picture signal. Thereafter, the red, green and blue light beams are made incident on the light separation element again, and only the light beam whose polarization direction is modulated is selectively made incident on the screen so as to project the picture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device, such as a liquid crystal projector, for enlarging and projecting light from a light source through an image display device onto a screen.

[0002]

2. Description of the Related Art A liquid crystal display element displays images and characters by changing the optical characteristics of a liquid crystal by applying a driving voltage corresponding to an image signal to pixel electrodes arranged regularly in a matrix. It is configured as follows.
As a method for applying an independent drive voltage to the pixel electrodes described above, a simple matrix method, a non-linear two-terminal element,
There is an active matrix type in which a terminal element is provided in a liquid crystal display element.

In the latter case, 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 a pixel electrode are provided. There is a need.

When strong light is incident on the switching element, the element resistance in the OFF state is reduced, and not only the charge charged when a voltage is applied is discharged, but also the liquid crystal present in the region where the switching element and the wiring electrode are formed. Since a normal drive voltage is not applied to the portion and the original display operation is not performed, there is a problem that light leaks even in a black state and the contrast ratio is reduced.

Accordingly, when the liquid crystal display element is of a transmission type, as shown in FIG. 15, a switching element such as a TFT 601 and a TF provided with a pixel electrode 605 are provided.
It is necessary to provide light blocking means called a black matrix 602 on a counter substrate facing the T substrate with a liquid crystal layer interposed therebetween to block light incident on the above-mentioned light incident region. Therefore, in the case of a transmissive liquid crystal display element, in addition to the TFT 601, the gate bus line 603, and the source bus line 604 each having a light shielding property, a black matrix 602 is provided.
Therefore, the effective pixel opening area occupying the pixel section, that is, the aperture ratio is reduced.

Furthermore, it is difficult to form these switching elements and wiring electrodes in a size smaller than a certain size due to restrictions on their electrical performance and manufacturing technology. Therefore,
As the definition and the size of the liquid crystal display element increase, the aperture ratio further decreases as the pitch of the pixel electrodes decreases.

In order to solve this problem, a reflection type liquid crystal display device has been developed.

In the reflection type liquid crystal display element, as shown in FIG. 16, a reflection type pixel electrode 655 can be formed on a TFT 651 as a switching element. The aperture ratio can be made larger than that, which is very effective for improving the brightness of the projection type liquid crystal display device.

A system in which such a reflection type liquid crystal display element is applied to a projection type image display device is disclosed in Electronic Display Forum 97 (P.3-27 to 3-32) and JP-A-4-338.
No. 721 proposes this.

At the electronic display forum 97, as shown in FIG. 17, the light emitted from the light source 701 is converted into light of three primary colors of red, green, and blue (hereinafter, referred to as R, G, and B) by a dichroic mirror. The light is separated, and each light is made incident on a corresponding polarizing beam splitter (PBS) 702. The polarization beam splitter 702 separates incident light into linearly polarized light components in two directions orthogonal to each other, and one of the light is incident on a corresponding reflection type 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. .

In Japanese Patent Application Laid-Open No. 4-338721, FIG.
As shown in FIGS. 8A and 8B, 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. 18A) or Philips type prism (FIG. 18). The light is separated into R, G, and B light by the color separation / combination element (b), and the light reflected by the reflective liquid crystal display elements 107-R, 107-G, and 107-B is color-combined by the same element. Thereafter, 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.

This method is called a three-panel type liquid crystal projection, and since R, G and B light from a light source can be used efficiently, a very bright image can be realized.

[0013]

However, the above-mentioned projection type image display device using the reflection type liquid crystal display device has the following problems.

In the method proposed in the electronic display forum 97, the P, R, G and B colors
Since three BSs are required and an optical system for color separation and a cross dichroic prism for color synthesis are required, not only the cost of the system becomes extremely high, but also the system size becomes extremely large. Has disadvantages.

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, the cross dichroic prism is used. In the method using, the light is normally incident at an angle of 45 degrees with respect to the film surface on which the color separation is performed, so that the polarization dependence of the spectral characteristic on the color separation surface is large as shown in FIG. , B, the spectral characteristics of the color separation surface are displayed). When color separation and color synthesis are performed by the same element, the bandwidth in which light can be used is greatly limited, light use efficiency is deteriorated, and color purity is reduced. I will.

When the 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 above-described influence of the polarization dependence is reduced. The optical path of the light passing through 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.

SUMMARY OF THE INVENTION 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, light, and bright reflective liquid crystal display element. is there.

[0018]

An image display apparatus according to the present invention is capable of converting light of three primary colors, red, green and blue, into two different colors if the polarization directions of the two colors are different from the polarization direction of the other one color light. An illumination optical system (illuminating means) for emitting the light, a light separating element (light separating means) for separating the light emitted from the illumination optical system according to a polarization direction, and modulating the light separated by the light separating element. A plurality of reflective image display elements, a color separating element (color separating means) for separating the two colors of light having the same polarization direction, and a projection optical system for projecting light modulated by the plurality of reflective image display elements (Projecting means), whereby the object is achieved.

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.

The illumination optical system includes a light source that emits light of three primary colors, and a first polarization control element (polarization control device) that changes the polarization direction of at least one of the light of the three primary colors from the light source. Means).

A configuration may be adopted in which a polarization selection element that transmits or reflects only one polarization direction is disposed on the light path on the light incident side of the first polarization control element.

It is preferable that the color separation surface of the color separation element is 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 an optical path of light incident on one of the plurality of reflective image display elements without passing through the color separation element. It is preferable to dispose a substrate having a thickness corresponding to 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.

The color separation element may be a quadrangular prism formed by bonding two triangular prisms.

The principal rays of the incident light and the outgoing light to and from the quadrangular prism enter and exit substantially parallel to the surface normal of the light incident surface and the exit surface of the quadrangular prism. It is preferable that the light is incident at an angle smaller than 45 ° with respect to the surface normal of the light separating surface.

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 a polarization direction. The same two colors of light may be configured to include blue light.

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 is disposed on the projection optical system side of the light separation element. It may be.

[0027] A configuration may be adopted in which a polarization selection element that transmits or reflects only one polarization direction is disposed on the optical path on the light emission side of the second polarization control element.

It is preferable that at least one wavelength regulating element (wavelength regulating means) is inserted in an optical path between the light source and the projection optical system.

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.

The wavelength regulating element is disposed on at least one of the optical paths of the light separated by the light separating element, and the light corresponding to the reflection type image display element disposed on the optical path into which the wavelength regulating element is inserted. It is preferable to cut out light other than the above.

Preferably, the wavelength regulating element cuts off at least one of a boundary wavelength range between red and green and a boundary wavelength range between green and blue. When the polarization directions of green and blue light are aligned, it is preferable to cut light in the boundary wavelength region between red and green, and when the polarization directions of red and green are aligned, green and blue It is preferable to cut off light in the boundary wavelength range.

The wavelength regulating element is disposed between the light separating element and the reflection type image display element, and the light regulating surface of the wavelength regulating element has an angle with the image display surface of the reflection type image display element. Preferably, that is, they are arranged non-parallel. The angle between the light regulating surface of the wavelength regulating element and the image display surface of the reflective image display element is 1.5
It is preferable that the angle be in the range of ° to 13.5 °.

It is preferable that, of the three primary colors of red, green and blue, light of two colors having the same polarization direction includes green light.

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 It is preferable that the light is incident on two or more of the plurality of reflective image display elements.

Either the transmittance for the P-polarized light or the reflectance for the 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. It is preferable to adopt a configuration in which

The operation of the present invention will be described below.

The illumination optical system of the image display device according to the present invention
Light of three primary colors is emitted such that the polarization direction of one of the primary colors of light 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. Accordingly, light of two colors having the same polarization direction and light of another one color are separated. The color separation element included in the image display device of the present invention,
Light of two colors having the same polarization direction is separated.

Therefore, the image display device of the present invention does not require the use of a cross dichroic prism or a Philips type prism for color separation (and color synthesis) as in the prior art, and the polarization dependence of the dichroic prism or the Philips type prism is not required. It is possible to improve the reduction in brightness, color purity, and contrast ratio, and reduce the size of the image display device, as well as to significantly reduce the cost.

A light separating surface of a light separating element (for example, PBS) and a color separating element (for example, a dichroic mirror)
By adopting a configuration in which the color separation surface forms an angle of 20 ° (absolute value) or less, the contrast ratio can be further improved. The angle formed between the light separating surface and the color separating surface is preferably 10 ° or less, and is substantially parallel (about 0 °).
Is more preferred. Hereinafter, the reason will be described with reference to FIG.

The light separating element usually converts incident light into P-polarized light and S-polarized light.
Separate into polarized light. P-polarized light and S-polarized light respectively
It is defined by the direction of polarization with respect to a plane that includes the incident optical path of light to the light separation plane and the plane normal. Light incident on the light separating element generally has a certain spread angle θ instead of perfectly parallel light. Therefore, the polarization direction (vibration direction) of the light separated as reflected light or transmitted light by the light separating element. )
Is the P-polarized light and S
The polarization direction is different from the polarization direction.

The light having the spread angle is transmitted to the light separating element 105.
After passing through, the light is incident on the color separation surface of the color separation element 106 ′ arranged (substantially perpendicular to the light separation surface) as shown in FIG. , P
It has a polarization direction deviated from polarized light or S-polarized light. 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, light having a divergence angle is affected by this and is emitted from the color separation element 106 'as elliptically polarized light, which causes a decrease in contrast ratio.

On the other hand, as shown in FIG. 20B, 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 are changed. Each of them coincides 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.

FIG. 20 (b) 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, and the angle of the color separating surface is shown in FIG. The indicated angle (0
°), the effect is reduced, for example, by about ± 20 degrees, but a higher contrast ratio than the arrangement of FIG. 20A can be obtained.

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. It is constituted by and. By adopting this configuration, light of a predetermined polarization direction can be efficiently made incident on the corresponding reflective image display element, 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.

As the first polarization control element, for example, U
Devices such as those disclosed in SP5, 751, 384 can be used. This element consists of a plurality of wave plates ("phase plates").
Also say. ) Are stacked on each other while changing the angle of the axis (optical axis, for example, slow axis), and has a function of rotating the polarization direction of only light in a specific wavelength range. For example, as shown in FIG. 4, a polarization control element 1 for rotating the polarization direction of B light.
04, white linearly polarized light is
4, the polarization directions of the R and G lights of the emitted light are maintained, and only the polarization direction of the B light can be rotated.

A substrate having two color separation surfaces (parallel plate)
Since the color separation element having the structure sandwiched between the two generates the same degree of astigmatism for the separated two colors of light, it is possible to compensate for this astigmatism by the projection optical system. Become. 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 thickness. This will be described below with reference to FIGS.

When an image formed by the light modulated by the image display device is projected on a screen, astigmatism occurs when a parallel flat plate such as a color separation device enters between the projection lens and the image display device. Then, the image on the screen is distorted due to astigmatism.

The conventional color separation element 106 'shown in FIG.
In 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 as described above, for example, the reflection type image display element 107-R
The light reflected by the color separation element 106 ′ is reflected by the surface (color separation plane CP) of the color separation element 106 ′, so that astigmatism does not occur for this light. The light reflected by 107-G is the color separation element 1
06 '(including a parallel flat plate), astigmatism is generated for this light. As described above, astigmatism occurs only in one of the lights from the reflective image display elements 107-R and 107-G, and it is difficult to compensate for astigmatism by the projection optical system. is there.

Therefore, as shown in FIG. 5, two glass substrates (transparent parallel flat plates) 106a and 1
When the color separation element 106 sandwiched between the reflection type image display elements 107-R and 107-G is used.
Since the light reflected by the light separating element 106 has the same distance through the glass of the color separation element 106, astigmatism can be compensated by the projection optical system, and a good image free from distortion due to astigmatism can be obtained. Can be displayed.

The glass substrate 10 of the color separation element 106
The angle of incidence of light on the color separation surface sandwiched between 6a and 106b is smaller than the angle of incidence on the color separation surface of the cross dichroic prism (typically 45 °) because light is refracted on the glass surface. And the problem due to the polarization dependence of the color separation surface described above is greatly reduced.

For example, when three reflective image display elements corresponding to R, G, and B light are arranged as shown in FIG. 1, on the optical path leading to the reflective image display element 107-B. Does not require a color separation element, so that astigmatism does not occur. On the other hand, as described above, the reflective image display element 10
In the optical path reaching 7-R and 107-G, astigmatism is generated by the color separation element 106. Therefore, among the R, G, and B lights projected by the projection optical system (projection lens) 108, astigmatism occurs only for the R and G lights. It is difficult to compensate.

On the other hand, the reflection type image display element 107-
By inserting the transparent substrate 109 on the optical path of the light reflected by B, the amount of astigmatism generated for the R, G, and B light can be made the same, so that the projection optical system (projection lens) 108, and a good image can be obtained. As is apparent from FIG. 1, in order to make the astigmatisms for the three colors of light the same, the transparent substrate 109 is required.
Is the same substrate (thickness is two) as the two substrates of the color separation element 106. The color separation element 106 (light separation surface) for the light path of B light and the light path of R and G light. Is preferably arranged at the same angle as the arrangement angle.

The R, G, and B lights whose polarization directions are modulated by the reflection type image display device have one color (the B light in the example of FIG. 1) of the other two colors. (In the example of FIG. 1, light of R and G), 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 R, G, and The polarization direction of the B light can be made uniform. 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 the polarizing plate and the polarization direction of the light emitted from the projector (projection 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 controlling element (on the side of the projection optical system), it is possible to further improve the contrast ratio.

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 make linearly polarized light incident on the first polarization control element. Color separation / polarization separation (and color synthesis / polarization synthesis) can be efficiently performed by the polarization control element and the light separation element, and a bright image having a high contrast ratio can be displayed.

Further, by providing the polarization selection element on the optical path on the light emission side of the second polarization control element, even if the light originally returned to the light source by the light separation element passes through the light separation element, Since the light is cut by the polarization selection element, an image having a high contrast ratio can be displayed.

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 irradiated to the respective reflection type image display elements. It is possible to improve the contrast ratio and prevent a decrease in the contrast ratio.

Further, since the two colors of light are irradiated with the polarization direction different from that of the other one color light, the P light is emitted in the boundary wavelength region between the two colors of light having the same polarization direction and the other color light. There is a wavelength range in which polarized light and S-polarized light are mixed. By cutting the light in the wavelength region where the polarized light is mixed by the wavelength regulating element, the contrast ratio and the color purity are improved.

In the polarization control element, due to its characteristics, a part of polarization of light whose polarization cannot be completely rotated or light whose polarization should not be rotated is generated. Also,
Since the light separating element cannot completely separate the light according to the polarization direction, color mixing and a decrease in the contrast ratio occur.

Therefore, by inserting a wavelength regulating element for cutting light other than light of a color corresponding to each reflection type image display element 107 between the light separation element and the reflection type image display element 107, color purity is improved. In addition, the contrast ratio can be improved.

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 off 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.

As described above, there is a wavelength range in which P-polarized light and S-polarized light are mixed at the boundary between the wavelengths of two colors of light having the same polarization and light of another color. Since the wavelength region where the polarized light is mixed affects the contrast ratio, it is preferable to cut the wavelength region.

When the polarization directions of R and B are aligned, FIG.
The short wavelength side (B side) and the long wavelength side (R
Side), it is necessary to cut off the light. Therefore, when the wavelength band of G is secured, the wavelength bands of R and B are narrowed. Conversely, when the wavelength bands of R and B are secured, the wavelength band of G is narrowed. Become. Therefore, brightness and color purity are reduced.

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 shows a case where the polarization directions of R and G are the same). Example), since it is only necessary to cut off the light in the wavelength band indicated by the hatched portion in the figure, the color purity can be greatly improved while suppressing the decrease in brightness.

In a configuration in which the wavelength regulating element is disposed between the light separating element and the reflective image display element, the wavelength regulating surface of the wavelength regulating element is formed at an angle with the image display surface of the reflective image display element. By arranging, the contrast ratio can be improved (see FIG. 7B). The reason will be described below.

If the extinction ratio (polarization selectivity) of the light separation element is not sufficient, unnecessary polarized light that should be removed (to be emitted toward another reflective image display element) is mixed with the original polarized light. The light is emitted toward the reflective image display device. 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 reflective image display device, 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.

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 a special design for compensating astigmatism in the projection optical system. When a plate-like 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. 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 quadratic prism formed by bonding two triangular prisms, 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.

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 in which a right-angled triangular prism is bonded is 45 °, the polarization dependence is large, and the efficiency of color separation is low. Therefore, for example, when a parallelogram prism having an obtuse obtuse angle attached to an isosceles triangular prism is used, the angle of incidence on the color separation surface is 45 °.
And the polarization dependence of the color separation characteristics can be suppressed. As a result, the efficiency of color separation by the color separation element can be improved.

It is preferable to use a dichroic mirror or a dichroic prism having a sandwich structure as the color separation element, but a dichroic mirror having a color separation plane CP on one surface of a transparent substrate (see FIG. 21).
May be used. At this time, by disposing the color separation surface CP so as to face the direction of the light separation element (PBS),
The occurrence 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 with the lowest luminous efficiency, it is possible to further suppress the occurrence of ghost and to suppress the reduction in resolution due to astigmatism.

Further, in the polarization control element manufactured by superposing the plurality of wavelength plates on each other, the light of R and B or the light of R
Rotating the polarization direction of the light of G and G is expensive because the number of layers is increased. On the other hand, if the polarization control element is configured to rotate the polarization direction of the R or B light, the number of layers may be smaller than that of rotating the polarization direction of the R and B light or the R and G light. Cost can be reduced.

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. Further, 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 (reflection for S-polarized light) will be difficult. Rate) decreases.

Accordingly, 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. The display quality can be improved by arranging the light so as to be incident on the element. Alternatively, the display quality can be improved by separating the G light having the highest visibility among the three primary colors as polarized light having optimized characteristics by the light separating element.

[0072]

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a schematic view 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.

The image display apparatus 100 emits light of three primary colors, 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 PBS 105 as a light separating element for separating the light emitted from the illumination optical system 100a according to the polarization direction, a dichroic mirror 106 as a color separating element for separating the two colors of light having the same polarization direction, a PBS 105 and a dichroic Reflection type image display elements 107-R, 107-G and 107-B for modulating light (R, G and B) separated by the mirror 106, respectively, and modulation with the reflection type image display elements 107-R, G and B And a projection optical system (projection lens) 108 for projecting the obtained light.

The illumination optical system 100a includes a white light source 101
And a trimming filter 102 as a wavelength regulating element
And a polarization plate 103 as a polarization selection element and a polarization control element 104.

In the present embodiment, 120 is used as the light source 101.
W, Philips UHP with 1.4 mm arc length
A lamp was used. As the light source 101, a halogen lamp, a xenon lamp, or a metal halide lamp can be used.

The light from the light source 101 is applied to a parabolic mirror 101a.
Then, the light is converted into substantially parallel light, and then enters the trimming filter 102 and the polarizing plate 103.

The polarizing plate 103 transmits only light in the direction perpendicular to the plane of the paper, and the obtained linearly polarized light is
4 is incident.

The polarization control element 104 has a characteristic 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.

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.

In this embodiment, as the polarization control element 104, an element as 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. As in the present embodiment, B
When an element for rotating the polarization direction of the polarized light is used, FIG.
As shown in the figure, when white linearly polarized light enters this device,
The polarization directions of the R and G lights of the emitted light are maintained, and only the polarization direction of the B light can be rotated.

In this embodiment, the above-described element is used as the polarization control element 104. However, any element having the same function can be used. For example, a cholesteric liquid crystal may be used.

The trimming filter 102 rotates the polarization direction by the polarization control element 104 indicated by the hatched portion in FIG.
The function of cutting the wavelength range at the boundary between G light and the light whose polarization does not rotate, and the boundary wavelength range between R and G (570 nm to 590 nm).
nm).

The light emitted from the polarization control element 104 is PBS
When the light is incident on the PBS 105, the R and G light
Is reflected by the light separating surface PP,
Is transmitted through the light separation plane PP because it becomes P-polarized light.

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 disposed substantially parallel to the light separation plane PP of the PBS 105, as described above, the color separation plane CP
The disturbance of the polarization state due to is suppressed, and the contrast ratio is improved.

The light transmitted and reflected by the PBS 105 and the dichroic mirror 106 are incident on the corresponding reflection type image display elements 107-R, 107-G and 107-B, and are modulated according to the image signals. Then, R
And G light 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 the 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.

As the reflection type image display element 107, a 0.1 mm.
A 9-inch XGA panel having a vertically aligned liquid crystal mode was used. As a liquid crystal mode, any reflective liquid crystal display device such as a TN mode can be used.

The dichroic mirror 106 has a structure as shown in FIG. 5, and has a dielectric surface (color separation surface) CP
Are sandwiched between glass substrates 106a and 106b and optically bonded. Therefore, the color is separated by the dichroic mirror 106 and the reflection type image display device 1
When the lights reflected by the 07-R and 107-G are color-combined by the dichroic mirror 106, the respective lights (R
And the light of G) pass through the glass in the same optical path length,
The amount of astigmatism generated thereby is also the same. Of course,
It is preferable to use the same glass substrate (parallel plate) as the glass substrates 106a and 106b. As described above, the color separation surface C of the dichroic mirror 106
P also functions as a color synthesis surface.

With this structure, in the dichroic mirror 106, the refraction of light on the glass substrates 106 a and 106 b changes the incident angle of light on the color separation plane CP, which is the same as when the arrangement angle of the dichroic mirror 106 changes. However, since the amount of change is not more than 20 °, there is no influence that significantly reduces the contrast ratio. Of course, the glass substrates 106a and 106a
In consideration of the refraction of light at 6b, it is preferable that the angle of incidence on the color separation surface CP be 20 ° or less.

On the other hand, the light reflected by the reflective image display element 107-B passes through the transparent glass substrate 109,
The light will enter the PBS 105. Therefore, the thickness of the transparent glass substrate 109 is adjusted by the dichroic mirror 106.
(The sum of the thicknesses of the glass substrates 106a and 106b), the astigmatism amounts for the R, G, and B lights are the same. The glass substrate 10
9 with respect to the optical path, the dichroic mirror 10
Needless to say, it is preferable that the angle is equal to the arrangement angle with respect to the optical path of No. 6. However, another configuration may be used as long as the amount of astigmatism can be matched.

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.

In this embodiment, the dichroic mirror 106 having a sandwich structure is used. However, depending on the required resolution, the dichroic mirror 106 is not necessarily required to have the sandwich structure.
A conventional type in which a color separation surface is formed on the surface of glass may be used. In this case, G, which most affects the resolution,
Either dispose the reflective image display element 107-G corresponding to the above-mentioned light in the optical path where astigmatism does not occur, or design the projection lens so as to take the astigmatism of the reflective image display element 107-G. Is preferred. Similarly, the transparent glass substrate 109 need not necessarily be provided depending on the required resolution.

A polarization control element 110 having the same characteristics as the polarization control element 104 is provided between the PBS 105 and the projection lens 108.
And a polarizing plate 11 for transmitting polarized light perpendicular to the paper surface
1 is arranged.

The polarization control element 110 provided on the projection lens 108 side of the PBS 105 has the function of rotating the polarization direction of only the B light and aligning the polarization directions of R, G and B. As the polarization control element 110, an element similar to the polarization control element 104 can be used. The polarizing plate 1 provided between the polarization control element 110 and the projection lens 108
11 is a PBS 10 out of the light from the polarization control element 110.
In step 5, leakage light of light originally cut is cut to improve 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. .

The PBS 105 and the reflective image display device 107
6A, between FIG. 6A and FIG. 6A, between the PBS 105 and the reflective image display element 107-B.
Dichroic mirror 11 having characteristics as shown in FIG.
2 and 113 are inserted, and each reflective image display element 1
07-R, 107-G, and 107-B have a function of cutting light other than the corresponding light. Dichroic mirror 11
The unnecessary light reflected by 2, 113 returns to the light source 101 via the PBS 105. FIG. 6A shows the spectral characteristics (selective transmission of R and G) of the dichroic mirror 112, and FIG. 6B shows the dichroic mirror 113.
(Selective transmission of B).

In this embodiment, the dichroic mirror 1
Although 12 is disposed immediately after the PBS 105, R and G lights may be disposed 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, they may be arranged on either one of them.

In this embodiment, the dichroic mirrors 1 are provided on both optical paths separated by the PBS 105.
12 and 113 are arranged, but depending on the characteristics of the PBS 105 and the polarization control element 104, the dichroic mirror 11
It is not necessary to dispose 2, 113, and it is also possible to insert only one.

Further, in the present embodiment, the trimming filter 10 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.
In this filter, depending on the characteristics of the PBS 105 and the polarization control element 104 and the wavelength range used,
It is not always necessary to cut light in both boundary wavelength ranges, and it is not always necessary to dispose them depending on required display performance. The position of the trimming filter 102 may be any position on the optical path from the light source to the screen.

The projector 100 having the above configuration is
Although it is very bright and has a high contrast ratio, a compact and low-cost liquid crystal projection was realized.

In this 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, and the color is incident on the PBS 105. The P and S polarizations of each color may be switched.

In the present embodiment, the white light is converted into R light by the PBS 105.
Although the light is separated into light of G and B, the combination of G, B and R can be changed. In this case, it is only necessary to change the color of the light rotated by the polarization control elements 104 and 110.

In this embodiment, the polarizing plate and the polarization control element are arranged on both the light incident side and the light exit side of the PBS 105. However, the polarization control element 110 and the polarization plate 111 on the light emission side are arranged.
Is not necessary.

Next, a structure for further improving the display quality of the image display device 100 shown in FIG. 1 will be described. FIG. 7A shows the PBS in the image display device 100.
FIG. 7B is a diagram schematically showing an arrangement relationship of optical elements around 105, and FIG. 7B schematically shows an arrangement obtained by modifying the arrangement. 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 used for any reflective image display device.

As in the image display device 100, dichroic mirrors 112 and 113 for regulating wavelengths are connected to the corresponding reflection type image display device 107 and PBS 10 respectively.
7, for example, as shown in FIG. 7A, a part of the light B (p) (P polarization of B) that should originally pass through the light separation surface PP of the PBS 105 Since the extinction ratio is not perfect, the light is reflected by the light separating surface PP of the PBS 105 and becomes the light B (p) 'as the dichroic mirror 1
It is incident on 12. Unnecessary P-polarized light of B light is represented as light B (p) ′.

The light B (p) ′ originally passes through the light separation surface PP of the PBS 105 and is reflected by the corresponding reflection type image display element 107.
−B, so that the dichroic mirror 1
The light is reflected at 12 and reenters the PBS 105. PBS
Most of the light B (p) 'incident on 105
Since the light passes through the light separation surface PP of No. 05 and enters a projection lens (not shown), the contrast ratio of display is reduced.

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 mirror 112 And 11
The light B (p) ′ reflected at 3 is reflected by the reflection type image display device 1.
The light enters the PBS 105 at an angle different from the light reflected at 07 (light used for display). Therefore, as schematically shown in FIG. 8, in the projection lens 108, only the light B (p) ′ which causes a decrease in the contrast ratio is cut off 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.

Normally, 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). is there. Accordingly, as shown by the broken line in FIG. 8, 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. 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,
The contrast ratio can be effectively improved. When the wavelength regulating surface of the dichroic mirror 112 is inclined by θ,
Since the reflected light forms an angle of 2θ with the incident light, 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 device 107 is adjusted according to the light receiving angle of the projection lens.

The display quality may be degraded due to the imperfect light separation characteristics of the PBS 105. This phenomenon will be described with reference to FIG. FIG. 9 shows the image display device 10.
FIG. 4 is a diagram schematically illustrating an arrangement relationship of optical elements around a PBS 105 at 0. Note that, for simplicity, optical elements unnecessary for description are omitted.

As shown in FIG. 9, light G (S) (S-polarized light of G) incident on the corresponding reflective image display element 107-G is not modulated by the reflective image display element 107-G. When reflected (typically, the reflective image display element 10
When 7-G is in a 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 returns to the direction of the light source (not shown).
Since the extinction ratio in S105 is not perfect, a part thereof (“G
(S) ′ ”. ) Transmits 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 light separation plane PP of the PBS 105
The polarization direction of a part of G (s) ′ that has passed through is disturbed by the polarization control element 110 and passes through the polarizing plate 111, and as a result, the contrast ratio of display decreases.

In the optical system shown in FIG. 17, the illumination light is separated into R, G, and B lights, and then is incident on the PBS 702 for each color light. In the device 100, all the color lights are PBS
Since the light is incident on the light 105, the PBS 105 is required to have a high extinction ratio for all the wavelength ranges of the R, G, and B lights. However, the PBS 105 has a high extinction ratio for both P-polarized light and S-polarized light over a wide wavelength range.
It is difficult to get. 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.

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. .

In general, the polarization separation characteristic of the PBS 105 is P
Although it may be optimized for either polarized light or s-polarized light, since the polarization separation characteristic for the other polarized light is reduced,
More reflective image display elements (usually R, G and B
Since three panels are used, the polarization direction on the side where two or more sheets are disposed is optimized, or a reflective image display element corresponding to G light having higher visibility is disposed. It is more effective to optimize the polarization separation characteristics of the PBS 105 for polarized light.

FIGS. 11A and 11B schematically show projection type color image display devices 200 and 300 in which the above-described structure is applied to the image display device 100. FIG.

In the image display device 200 shown in FIG.
The dichroic mirrors 112 and 113 respectively move the display surface of the corresponding reflective image display element 107
They are arranged at an angle of about 5 ° (θ in FIG. 8 is about 5 °).
In FIG. 11B, the dichroic mirror 11
The dichroic mirrors 211, 212, and 213 having the same functions as the dichroic mirrors 2 and 113 are arranged at an angle of about 5 ° with respect to the display surface of the corresponding reflective image display element 107.

The image display devices 200 and 300 are both Fno. Is 3.0 (receiving angle ± 9.5 °), and the reflective image display element 10
Illumination light having a degree of parallelism of ± 10 ° was incident on 7.

By employing the above structure, unnecessary light reflected by the dichroic mirrors 112 and 113 or the dichroic mirrors 211, 212 and 213 is directed toward the projection lens 108 by the imperfect polarization separation characteristic of the PBS 105. Even if emitted, this unnecessary light cannot pass through the pupil of the projection lens 108 as shown by the broken line in FIG. 8, so that 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.

In the image display apparatuses 200 and 300, the dichroic mirrors 112 and 113 or the dichroic mirrors 112 and 113 or Although the dichroic mirrors 211, 212 and 213 are tilted, even if the tilt angles of these dichroic mirrors are reduced and a part of unnecessary light is transmitted through the projection lens 108, the contrast is higher than that of the image display device 100. The ratio can be improved.

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 superior to a characteristic (transmittance) for P-polarized light, as shown in FIG. I have. Therefore, PB
S-polarized light separated better than P-polarized light at the light separation plane PP in S105 is incident on the reflective image display elements 107G and 107R of the three reflective image display elements, and P-polarized light having poor polarization separation characteristics. Enters only the reflection type image display element 107B. As described above, by maximizing the polarization splitting characteristics of the PBS 105, light that lowers the contrast ratio can be further reduced.

In image display devices 200 and 300, S
Two reflective image display elements 107G and 107 using PBS 105 with optimized polarization separation characteristics for polarized light
R is arranged on the S-polarized side, but G with high visibility is placed on the S-polarized side.
The same effect can be obtained by arranging one reflective image display element 107G corresponding to the above. In addition, when the PBS 105 that optimizes the polarization separation characteristic with respect to 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.

In the image display devices 200 and 300, the polarization direction of B is rotated by the polarization control element 104. However, the polarization directions of R and G light may be rotated. The S-polarized light may be reversed. Also, PB
The dichroic mirrors 112 and 113 and the dichroic mirror 2 are provided on both of the optical paths separated in S105.
11, 212 and 213 were placed, but PBS 105
Depending on the characteristics of the polarization control element 104, the number of the dichroic mirrors may be reduced. further,
The polarizing plate and the polarization control element are arranged on both the light incident side and the output side of the PBS 105.
0 and the polarizing plate 111 are not always necessary.

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 required.
It is not necessary to use a conventional color separation element 106 ′ in which a color separation surface is formed on one surface of a glass substrate (for example, FIG.
1) may be used.

Next, a configuration using a dichroic prism as a color separation element and its operation will be described.

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 is generated. Special measures (use of the color separation element 106 and the glass substrate 109) for compensating the astigmatism are required.

Further, the conventional dichroic mirror 10
When a parallel-plate color separation element such as 6 ′ is used, FIG.
As shown in FIG. 2, the color separation plane CP of the glass substrate 106a '
Due to the light reflected on the surface facing the surface (referred to as “ghost light”), a phenomenon in which an image is double reflected on a screen, a so-called ghost phenomenon, occurs.

On the other hand, when a prism-shaped color separation element (dichroic prism) 206 is used as in the projection type color image display devices 400 and 500 shown in FIGS. 13A and 13B, astigmatism is reduced. Since this 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. .

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 on the surface when entering the dichroic prism 206. Does not enter the screen. Therefore, the light reflected on the surface of the dichroic prism 206 does not cause a ghost phenomenon.

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 plane CP is relatively large at 45 °, so that the polarization dependence is low. Large, low color separation efficiency. 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, the light incident angle is 40
° using the dichroic prism 206,
The efficiency of color separation was improved, and the brightness and color purity were improved.

When a prism element is used as the color separation element, the dichroic prism 206 is used as shown in FIGS. 13A and 13B in order to make the optical path lengths of the respective colors equal to each other. It is preferable to arrange the glass block 209 in an optical path that does not pass through.

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 described above, and can be appropriately combined with the above-described configuration. The dichroic prism can be replaced with a dichroic mirror. By using this, the above effects can be additionally obtained.

As described above, it is preferable to use the dichroic mirror 106 or the dichroic prism 206 having a sandwich structure 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.

The image display device 100 'shown in FIG.
In this embodiment, the sandwich type dichroic mirror 106 in the image display device 100 shown in FIG. 1 is replaced with a conventional dichroic mirror 106 'having a color separation plane CP on one surface of a glass substrate. The dichroic mirror 106 'is arranged so that the color separation plane CP faces the direction of 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.

In the image display device 100 ′, astigmatism is generated with respect to the B light, but it is combined with the R and G lights, and has little effect on 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.

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 ghost image on the screen is obtained. Can be suppressed to such an extent that it is hardly visible.

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 has reached the color separation plane CP is transmitted through the color separation plane CP. A part of the light of B is reflected by the characteristics of the color separation surface CP, and a part of the reflected light is
The light is reflected again on the surface of the transparent substrate on which the color separation surface CP is not formed, and becomes a ghost. 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 surface CP transmits the light of B having the lowest luminosity in order to suppress the occurrence of ghost,
Even if a configuration that transmits other color light is adopted, the occurrence of ghost is suppressed as compared with the configuration shown in FIG.

The light of B is emitted from the dichroic mirror 10.
Although the effect is lower than that of the configuration transmitting 6 ′, depending on the required image quality, a configuration may be adopted in which the visibility is lower than the B light and the R light transmits through the dichroic mirror 106 ′. .

In the image display device 100 ', the configuration is adopted in which the B and G lights are reflected by the PBS 105, 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.

As described above, 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, the occurrence of ghost can be suppressed. it can.
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]

As described above, according to the present invention, the color separation between the PBS and the dichroic mirror is achieved by making one of R, G and B incident on the PBS different in polarization direction from the other colors. Therefore, a compact and low-cost image display device (for example, a liquid crystal projector) can be realized.

Further, by setting one of the two colors of light of the same polarization direction of R, G and B to be G, the band of usable light can be widened and the brightness and color purity can be increased. .

Further, by adopting a structure in which a color separation surface of a dichroic mirror for color separation is sandwiched between glass substrates and a transparent substrate is inserted on an optical path on which color separation is not performed, each reflection type image display element is formed. Since the amount of astigmatism generated in the image becomes the same and the aberration can be corrected by the projection lens, an image with high resolution can be realized.

Further, by providing a wavelength regulating element for cutting light other than light corresponding to each reflection type image display element or light in a wavelength region where S-polarized light and P-polarized light are mixed, the R, G and B colors are provided. It is possible to improve the purity and the contrast.

Further, 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 reflection type image display element.

Further, the use of the prism-shaped color separation element can further improve the display quality.

Furthermore, a light separating element whose polarization separation characteristic is optimized for one of P-polarized light and S-polarized light is used, and is arranged so that G light is separated as optimized polarized light. Alternatively, 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 arrangement. 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 caused by a conventional dichroic mirror 106 ′.

FIGS. 13A and 13B are diagrams schematically showing projection type 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 transmission type liquid crystal display element.

FIG. 16 is an explanatory diagram of a reflective liquid crystal display element.

FIG. 17 is an explanatory diagram of a three-panel type 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 reflection type 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 a diagram illustrating 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]

 REFERENCE SIGNS LIST 100 Projection color image display device 100 a Illumination optical system 101 Light source 102 Trimming filter 103 Polarizer 104 Polarization control element 105 PBS 106 Dichroic mirror for color separation 107 Reflection type image display element 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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/00 360 G09F 9/00 360D 5G435 H04N 5/74 H04N 5/74 K 9/31 9/31 C BF term (reference) 2H088 EA14 EA15 EA16 HA03 HA11 HA13 HA24 MA06 MA20 2H091 FA05X FA05Z FA14Y FA14Z FD01 GA06 HA07 LA11 2H099 AA12 BA09 CA00 CA02 CA11 DA05 5C058 AB03 AB05 EA02 EA12 HC05 HC05 HC05 HC05 5G435 AA01 AA02 AA04 AA18 BB12 BB16 DD04 FF05 GG03 GG04 GG11 GG23 KK07

Claims (20)

[Claims] 1. An illumination optical system for emitting light of three primary colors of red, green, and blue with the polarization directions of two of the colors being different from the polarization directions of the other color light, and the illumination optical system. A light separating element for separating the light emitted from the system according to the polarization direction; a color separating element for separating the two colors of light having the same polarization direction; and a light modulator for modulating the light separated by the light separating element and the color separating element. An image display device, comprising: a plurality of reflective image display elements to perform light; and a projection optical system that projects light modulated by the plurality of reflective image display elements. 2. An angle between a light separating surface of the light separating element and a color separating surface of the color separating element is 20 ° or less.
The image display device as described in the above. 3. 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. The image display device according to claim 1, further comprising: 4. The image display device according to claim 3, wherein a polarization selection element that transmits or reflects only polarized light in one polarization direction is disposed on an optical path on the light incident side of the first polarization control element. . 5. The image display device according to claim 1, wherein the color separation surface of the color separation element is sandwiched between two substrates. 6. The image display device according to claim 5, wherein a transparent substrate is disposed on at least one of the optical paths of the light separated by the light separating element. 7. The image display device according to claim 1, wherein the color separation element is a quadrangular prism formed by bonding two triangular prisms. 8. The principal ray of the incident light and the outgoing light to and from the quadrangular prism enters and exits substantially parallel to the surface normal of the light incident surface and the exit surface of the quadrangular prism, and The image display device according to claim 7, wherein the light is incident at an angle smaller than 45 ° with respect to the surface normal of the light separating surface of the prism. 9. A color separation surface of the color separation element is formed on one surface of a substrate, is disposed so as to face the light separation element, transmits blue light, and is polarized. The light of the two colors having the same direction includes blue light.
The image display device according to any one of the above. 10. A second polarization control element for aligning the polarization directions of the red, green, and blue primary colors in the same direction is disposed on the projection optical system side of the light separation element. 9
The image display device according to any one of the above. 11. The image display device according to claim 10, wherein 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. 12. The image display device according to claim 1, wherein at least one wavelength regulating element is inserted in an optical path between the light source and the projection optical system. 13. The image according to claim 12, 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. Display device. 14. The plurality of reflective image display elements, wherein the wavelength regulating element is disposed on at least one of the optical paths of the light separated by the light separating element, and the plurality of reflective image display elements are disposed on an optical path into which the wavelength regulating element is inserted. 13. The image display device according to claim 12, wherein any one of the light sources cuts light other than the corresponding light. 15. The image display device according to claim 12, 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. 16. 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 is in contact with the image display surface of the reflective image display element. 3. The method according to claim 1, wherein the elements are arranged at an angle.
6. The image display device according to any one of 5. 17. An angle between a light regulating surface of the wavelength regulating element and an image display surface of the reflection type image display element is 1.5.
The image display device according to claim 16, wherein the angle is in the range of ° to 13.5 °. 18. The light of three primary colors of red, green and blue,
18. The image display device according to claim 1, wherein the two colors of light having the same polarization direction include green light. 19. Light separated by the light separating element as polarized light having one of a transmittance of P-polarized light and a reflectance of S-polarized light of the light separating surface of the light separating element is higher than the other. The image display device according to any one of claims 1 to 18, wherein light is incident on two or more of the plurality of reflective image display elements. 20. One of a transmittance of P-polarized light and a reflectance of S-polarized light of a light separating surface of the light separating element is higher than the other, and green light is polarized light having the one by the light separating element. 19. The image display device according to claim 1, wherein the image display device is separated.