JP2001221988A - Optical parts and liquid crystal projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the effect of shielding unnecessary light produced inside prisms from color light of all three colors and to prevent occurrence of color irregularity due to lowering of ambient illuminace of effective light, with respect to the liquid crystal projector using prisms for a color synthesizing optical system. SOLUTION: The first, the second and the third prisms are arranged in the color synthesizing optical system. The first shading frame is arranged between the first and the second prisms and the second shading frame is arranged between the third and the second prisms. Besides the first and the second shading frames have the same opening widths and are arranged symmetrically with the center line corresponding to the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical component using three liquid crystal display elements and a liquid crystal projector.
The present invention relates to a light shielding technique for an optical component including at least one prism in a color combining optical system that combines image light of primary colors.

[0002]

2. Description of the Related Art In an apparatus using a prism, not only a liquid crystal projector but also a prism used in a three-panel video camera, etc., unnecessary light in the prism is removed to eliminate ghosts and flares, thereby achieving good contrast. Various light-shielding techniques have been proposed for the purpose of obtaining images. As a technique for blocking unnecessary light in a prism of this type, there is, for example, a color separation prism device described in Japanese Patent Application Laid-Open No. 5-346501.

According to this known technique, in the color separation prism, a part of the incident light flux which does not contribute to image formation is reflected in the prism and enters the imaging surface,
There is a statement that causing flare was a problem. Hereinafter, light that does not contribute to imaging such as flare will be referred to as unnecessary light. Conventionally, in order to eliminate the unnecessary light, a cut has been made in a part of the prism to prevent the unnecessary light from being incident on the imaging surface. With the conventional cut-off light shielding technology, the problem that the light blocking effect of unnecessary light varies due to the processing accuracy of the cut and the assembly accuracy of the prism, and the occurrence of new unnecessary reflected light at the tip of the cut as a side effect of the cut There was a problem to say.

Therefore, in the prior art described in the above publication, a prism for guiding the divided color light flux to the CCD is provided with two prisms.
There has been proposed a configuration in which a light-shielding frame made of an organic film is provided on a divided surface and joined to each other as a divided structure. According to this configuration, the position where the light flux is regulated can be adjusted at the time of assembling the prism, the variation in the light blocking effect can be suppressed, the range of the organic film can be set arbitrarily, and the organic film absorbs light. There is a description that it will not cause unnecessary light.

[0005]

However, according to the technique described in the above publication, the divided color luminous flux is converted into CC light.
The prism leading to D is divided into two parts, and only two of the three colors can form a light-shielding frame on the divided surface. One color cannot be divided into prisms, so that a light-shielding frame cannot be formed. In fact, in FIG. 1 of the above publication, a light-shielding frame 4a is formed between the prism 1a and the prism 3a for guiding the color light corresponding to the CCD 2a, and a light-shielding film is formed between the prism 1c and the prism 3c for guiding the color light corresponding to the CCD 2c. 4c is formed, but since the prism 1b for guiding the color light corresponding to the CCD 2b cannot be divided for securing a necessary optical path, no light shielding frame is formed. For this reason, in the light-shielding technology described in the above-mentioned publication, there is no light-shielding effect of unnecessary light for the color light corresponding to the CCD 2b.

That is, it is desirable to provide a light-shielding means for obtaining the same light-shielding effect for all of R, G, and B, but this is not the case. There is the same problem that the same light-shielding effect cannot be obtained for R, G, and B even if the light-shielding means is a cutout or a light-shielding frame. Also, as a side effect of the light blocking effect of unnecessary light due to the light blocking frame, if the size of the light blocking frame is not appropriate, a part of the effective light may be blurred by the light blocking frame, and the peripheral illuminance may decrease. Of the three colors, two with a light-blocking frame
The peripheral illuminance of the color is reduced and the peripheral illuminance of one color that does not form a light-shielding frame is not reduced. Therefore, when three colors are combined, color unevenness may occur at the peripheral portion of the screen. That is, if the light-shielding means is provided only for a part of the color light, color unevenness occurs particularly in the peripheral portion of the screen.

As described above, in the conventional technique, there is a problem that the light blocking effect for removing unnecessary light generated in the prism is only specific color light among the three colors, and there is no light blocking effect for all three color lights. In addition, the light-shielding means has a side effect of reducing the peripheral illuminance of the effective light, and the peripheral illuminance of only a specific color light among the three colors is reduced. Therefore, when the three colors are combined, color unevenness occurs in the periphery. There's a problem.

Although the above publication discloses a technique for blocking unnecessary light in a color separation prism device used in a three-panel video camera or the like, it is generated in a prism of a color combining optical system used in a liquid crystal projector. No technique is described for blocking unnecessary light. Further, the above publication aims at eliminating unnecessary light in a combination of three prisms having a special shape called a so-called Philips type prism. On the other hand, a liquid crystal projector aims at removing unnecessary light in a combination of a generally rectangular prism formed by joining two generally used triangular prisms. If the type of the prism is different, the position where the unnecessary light which causes a problem is generated in the prism is different, but this point is not considered. In addition,
In the above description, it is assumed that light shielding means is provided around the liquid crystal display element itself around the screen of the liquid crystal display element, and that there is no problem with unnecessary light around the screen of the liquid crystal display element. ing.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical technique using a prism in a color synthesizing optical system, which has an effect of blocking unnecessary light generated in the prism from all three color lights. Another object of the present invention is to provide an optical technique using a prism for a color combining optical system, which has an effect of blocking unnecessary light generated in the prism from all three colors of color light, and has a peripheral illuminance of effective light. An object of the present invention is to provide an optical technique that does not cause color unevenness due to a decrease.

[0010]

In order to achieve the above object, in the first invention, the optical component comprises a first light from the first liquid crystal display element and a second light from the second liquid crystal display element. A first prism that combines the first light, a second prism that transmits the third light from the third liquid crystal display element, and a third prism that combines the first, second, and third lights. Prism and
A first light-shielding frame provided between the first prism and the third prism; and a second light-shielding frame provided between the second prism and the third prism. Making the opening widths of the first light shielding frame and the second light shielding frame substantially equal;
The first light-shielding frame and the second light-shielding frame are arranged substantially symmetrically with respect to the optical axis.

In the second aspect, the optical component transmits the first light from the first liquid crystal display element and reflects the second light from the second liquid crystal display element, thereby providing the first component. A first prism that combines the light and the second light, a second prism that transmits the third light from the third liquid crystal display element,
The first light and the second light are transmitted by transmitting the first and second lights emitted from the first prism and reflecting the third light emitted from the second prism.
A third prism that combines and emits the third light and the third light, a first light-blocking frame provided between the first prism and the third prism, and a second prism. A second light-shielding frame provided between the third prisms,
The opening widths of the first light-shielding frame and the second light-shielding frame are made substantially equal, and the first light-shielding frame and the second light-shielding frame are arranged substantially symmetrically with respect to the optical axis.

In the first or second claws, the first light-shielding frame and the second light-shielding frame are respectively connected to the first and second light-shielding frames.
And the directions of the absorption axes of the first and second polarizers are the same as the polarization direction of unnecessary light incident on the first and second polarizers. To place.

According to a third aspect of the invention, there is provided a liquid crystal projector for separating light from a light source and irradiating the light to first to third liquid crystal display elements, respectively.
Light and the second light from the second liquid crystal display element enter the second prism through the first prism and the first light-shielding frame, and the third light from the third liquid crystal display element. Is input to the second prism through a third prism and the second light-shielding frame, and the first to third lights are emitted through the second prism. The opening widths of the first light-shielding frame and the second light-shielding frame are the same, and the first light-shielding frame and the second light-shielding frame are arranged substantially symmetrically with respect to the optical axis.

In a fourth aspect, a light source, a color separation optical system,
A liquid crystal display element, a color synthesizing optical system including at least one prism, and a projection lens, wherein the illumination light from the light source is separated into three primary colors of RGB by the color separation optical system, and each of the three liquid crystals is separated. In the liquid crystal projector, the image light of the three primary colors emitted by the liquid crystal display element is synthesized into color image light by the color synthesizing optical system, and the color image light is enlarged and projected by the projection lens. A first prism and a second prism in the color combining optical system;
And a third prism, and a first light shielding frame is provided between the first prism and the second prism, and a first light-shielding frame is provided between the third prism and the second prism. 2 light-shielding frames, and the opening widths of the first light-shielding frame and the second light-shielding frame are the same, and the first light-shielding frame and the second light-shielding frame are moved right and left with respect to the optical axis. They are arranged almost symmetrically.

In the third or fourth invention, the screen width of the liquid crystal display element is a, and the width of the prism of the first prism, the width of the prism of the second prism, and the width of the prism of the third prism are included. When the maximum prism width is b, and the opening width of the first light shielding frame and the opening width of the second light shielding frame are c, the opening width c of the second light shielding frame is c> (a + b).
/ 2. In the third or fourth invention, the first light-shielding frame and the second light-shielding frame are formed on first and second polarizing plates, respectively, and an absorption axis of the first and second polarizing plates is formed. The direction is set to be the same as the direction of polarization of unnecessary light incident on the first polarizing plate and the second polarizing plate.

In the fifth invention, the light source, the color separation optical system,
A light-reflecting liquid crystal display element, a polarizing plate, a color combining optical system including at least one prism, a projection lens, and a polarization rotating element for rotating polarized light of a specific wavelength range, and illumination from the light source. The light is separated into the three primary colors of RGB by the color separation optical system, and is incident on the three reflective liquid crystal display elements, respectively, and the image light of the three primary colors reflected by the reflective liquid crystal display elements is reflected by the color combining optical system. A liquid crystal projector that combines the color image light with a color image light by a system and enlarges and projects the color image light by the projection lens. A first polarization beam splitter prism, a first polarization rotation element, a first polarization rotation element, Polarizing plate, second polarizing beam splitter prism, second polarization rotating element, second polarizing plate, third polarizing plate
And a first light-shielding frame is provided between the first polarizing beam splitter prism and the second polarizing beam splitter prism, and the third light-shielding frame is provided between the first polarizing beam splitter prism and the second polarizing beam splitter prism. A second light shielding frame is provided between the polarization beam splitter prism and the second polarization beam splitter prism, and the first light shielding frame and the second light shielding frame have the same opening width; And the second light-shielding frame are disposed substantially symmetrically with respect to the optical axis.

In the fifth invention, the screen width of the reflective liquid crystal display element is a, the prism width of the first polarizing beam splitter prism, the prism width of the second polarizing beam splitter prism, and the third polarization. When the maximum prism width among the prism widths of the beam splitter prism is b, and the opening width of the first light shielding frame and the opening width of the second light shielding frame are c, the width c of the light shielding frame is c> c. (A + b) /
Let it be 2. Further, the first light shielding frame is formed on one of the first polarization rotation element and the first polarizing plate,
The second light shielding frame is formed on one of the second polarization rotation element and the second polarizing plate.

Further, in the fifth invention, the first light-shielding frame is provided with a third polarizing plate in a frame portion of the first polarizing plate, and the direction of the absorption axis of the third polarizing plate is different from that of the third polarizing plate. The first polarizing plate is formed so that the directions of the absorption axes thereof are orthogonal to each other. The second light-shielding frame is provided with a fourth polarizing plate in a frame portion of the second polarizing plate. The polarizing plate of No. 4 and the direction of the absorption axis of the second polarizing plate are arranged so as to be orthogonal to each other.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an optical component and a liquid crystal projector according to the present invention will be described below with reference to the drawings by using embodiments. FIG. 1 is a schematic top view showing one embodiment of a liquid crystal projector according to the present invention. In the figure, white light emitted from a light source 1 is reflected by a reflector 40.
Thus, the light is converted into substantially parallel light 2. The substantially parallel light 2 is R
(Red) light component 2R, G (green) light component 2G, B
(Blue) Light component 2B, which is converted into S-polarized light by the polarization conversion element 3, and is converted into S-polarized light 4R of R and S-polarized light 4 of G.
G and B S-polarized light 4B is obtained. In the drawing, black points indicate S-polarized light which is polarized light perpendicular to the paper surface, and short parallel lines perpendicular to the traveling direction of the light indicate P-polarized light which is polarized light horizontal to the paper surface.

The R-polarized S-polarized light 4R and the B-polarized S-polarized light 4B incident on the G reflection RB transmission dichroic mirror 5 pass through the dichroic surface, then pass through the polarizing plate 7, and the P polarization component is almost completely cut off. S polarized light 8R, B S polarized light 8
B. The reason for disposing the polarizing plate 7 at this position is as follows.
The rectification of the polarized light by the polarization conversion element 3 is not complete, and the incident light 4R, 4G, and 4B at this time partially contain P-polarized light, which deteriorates the image contrast.
The object of the present invention is to obtain a higher image contrast by making the polarization more uniform. The R s-polarized light 8R and the B s-polarized light 8B are polarization rotators 9 for rotating the polarization of only the B light.
Is incident on. Therefore, the S polarization of R does not change,
The polarization becomes 10R, the polarization of the B S-polarized light is rotated,
The polarization becomes 10B. R-polarized S-polarized light 10R incident on the polarization beam splitter prism 11 corresponding to the first prism
Is reflected by the splitter surface 11a,
R, which is incident on the reflective liquid crystal display element 13R. Here, the light to be displayed brightly is reflected as R P-polarized light 14R by the reflective liquid crystal display element 13R, and the light to be displayed darkly is reflected as R S-polarized light. In FIG. 1,
Light for displaying darkly is omitted for both RGB. The light to be displayed brightly, the R P-polarized light 14R, again enters the polarization beam splitter prism 11, and this time, because it is P-polarized light, passes through the splitter surface 11a and becomes the R P-polarized light 15R.

On the other hand, the B P-polarized light 10B transmitted through the polarization rotating element 9 for rotating the B polarized light is incident on the polarization beam splitter prism 11, transmitted through the splitter surface 11a, and transmitted to the B reflection type liquid crystal display element 13B. Incident. Here, the light to be displayed brightly is reflected as the S-polarized light 14B of B by the reflective liquid crystal display element 13B of B, and the light to be displayed darkly is reflected as the P-polarized light of B. The B S-polarized light 14B, which is light to be displayed brightly, re-enters the polarizing beam splitter prism 11 and is reflected by the splitter surface 11a because it is S-polarized light this time.
5B, and is combined with the R polarized light 15R.

The combined R P-polarized light 15R and B S-polarized light 15B are incident on a polarization rotation element 16 for rotating the polarization of the B light. The R P-polarized light 15R is emitted without being changed and remains as the R P-polarized light 17R, but the B S-polarized light 15B is rotated to become the B P-polarized light 17B. The light that has become P-polarized light for both R and B is then incident on a polarizing plate 18 arranged so as to pass only P-polarized light, unnecessary stray light of S-polarized light is cut, and R-polarized light 19R of R having high contrast is obtained. And B P-polarized light 19B. The R P-polarized light 19R and the B P-polarized light 19B enter the polarization beam splitter prism 20 corresponding to the second prism, pass through the splitter surface 20a, and emerge as R P-polarized light 21R and B P-polarized light 21B. Is done.

As for the G light, the G light 2G emitted from the light source 1 is converted by the polarization conversion element 3 into the G S-polarized light 4G.
After being converted to G, the light is reflected by the G reflection RB transmission dichroic mirror 5 to become G S-polarized light 6G.
5 is incident. The P-polarized light component is almost completely cut by the polarizing plate 25, and becomes G-polarized light 26G, which is incident on a polarizing beam splitter prism 27 corresponding to a third prism. The G S-polarized light 26G incident on the polarization beam splitter prism 27 is reflected by the splitter surface 27a and is incident on the G reflective liquid crystal display element 29G as G S-polarized light 28G. Here, the light to be displayed brightly is G
Is reflected as the P-polarized light 30G, and is again incident on the polarization beam splitter prism 27. Since the light is the P-polarized light this time, it is transmitted through the splitter surface 27a to become the G P-polarized light 31G. The G P-polarized light 31G here passes through the polarizing plate 32 arranged so as to transmit only the P-polarized light, and becomes a polarized light 33G. Then, the polarized light is incident on the polarization rotation element 34, and the polarization is rotated, thereby the G S-polarized light 35G. Becomes

The G S-polarized light 35G is incident on the polarization beam splitter prism 20 and is split by the splitter surface 20a.
Is reflected by the light, and becomes G s-polarized light 36G, and R p-polarized light 2
It is mixed with 1R, B P-polarized light 21B.

Here, R P polarized light 21R, G S polarized light 3
The 6G and B P-polarized light 21B is incident on the polarization rotation element 22 for rotating the polarization of only the R light and the B light,
G remains unchanged and becomes G S-polarized light 37G, R-polarized light 21R rotates in polarization, R becomes S-polarized light 23R, B P-polarized light 21B rotates in polarization, and B S-polarized light 23R.
B, the combined image light has R, G, and B components of S polarization, and becomes projection light 38 by the projection lens 24,
The image is enlarged and projected on a screen or the like. By making the polarization planes emitted from the projection lens 24 all the same S-polarized light,
It is possible to cope with a polarizing screen and a rear-projection screen in which the incidence of light in a predetermined polarization direction is specified.

According to this embodiment, the G image light 31G reflected by the G reflection type liquid crystal display element 29G is incident on the polarizing plate 32 before passing through the polarization rotation element 34, so that the polarization disturbance is small. High contrast. Therefore, a particularly high image contrast can be obtained for the G light having a large influence on the image contrast.

According to this embodiment, the polarization rotator 1
The R light 15R and the B light 15B passing through No. 6 do not include the G light and do not include the light having the wavelength in the transition region of the wavelength rotation angle (the wavelength of the G light is between the R light and the B light). Although it has a wavelength, if G light is not included, the band between the wavelengths of R light and B light is widened, and the R light and B light are separated between them. There is little elliptically polarized light afterward, and a high image contrast can be obtained after passing through the polarizing plate 18. Further, in the present embodiment, it is not necessary to cut the light between the R light and the G light and between the G light and the B light in order to improve the contrast of the image, and a high light utilization factor can be obtained.

Further, according to this embodiment, the distances from the polarization conversion element 3 to the reflection type liquid crystal display elements 13R, 13G and 13B can all be made equal, and the illuminance distributions of the R light, G light and B light are the same. Therefore, an image with less color unevenness can be obtained. Further, in the present embodiment, since a prism having a substantially rectangular parallelepiped shape or a quadrangular prism shape is used, the distance from the polarization conversion element 3 to the reflection type liquid crystal display element and the distance from the reflection type liquid crystal display element to the projection lens 24 are: In both cases, the length of the lateral side of the reflection type liquid crystal display element can be set to about 2.5 times, and the back focus of the projection lens (each liquid crystal display) can be compared with the case of using a prism used in the prior art. The distances between the elements 13R, 13B, and 29G and the polarization rotation element 22) can be reduced, the size and weight of the entire optical system can be reduced, and the light use efficiency can be improved at the same time.

Incidentally, in order to improve the focus performance of the projection lens 24, each of the reflection type liquid crystal display elements 13R, 13B, 29G
A condenser lens may be arranged between the and the polarizing beam splitter prism, but is omitted in the figure because it is not related to the gist of the present patent.

Here, in the embodiment of the present invention, a polarization beam splitter prism 11, which is a first prism, a polarization beam splitter prism 20, which is a second prism, and a polarization beam, which is a third prism, are provided in a color combining optical system. A beam splitter prism 27 is disposed, and a light-shielding frame 16a is provided around the polarization rotator 16 and a light-shielding frame 18a is provided around the polarizing plate 18 as a first light-shielding frame between the first prism and the second prism. A first light shielding frame 32a around the polarizing plate 32, a light shielding frame 34a around the polarization rotation element 34, and a first light shielding frame 34a as a second light shielding frame between the third prism and the second prism. The light-shielding frame and the second light-shielding frame have the same opening width, and the first light-shielding frame and the second light-shielding frame are arranged symmetrically with respect to the optical axis. Note that, in the present embodiment,
A third prism and polarizers 7, 18, 32, and rotating polarizers 9, 16, 2,
The optical system constituted by 2 and 34 is called an optical component.

FIG. 2 is a schematic top view for explaining the light blocking effect in one embodiment of the liquid crystal projector according to the present invention, and shows how unnecessary light is blocked by the light blocking frame of the present invention. FIG. 3 is a schematic top view of the liquid crystal projector without the light-shielding frame of the present invention, and shows how unnecessary light enters the projection lens 24 without being blocked. FIG.
In 3, the dotted line represents effective light, and the solid line represents unnecessary light.

First, in FIG. 3, when the emission angle θ of reflected light from the range of the screen width a of the reflection type liquid crystal display elements 13R, 29G, and 13B is large, the unnecessary light that poses a problem is the polarization beam splitter prism 11 , 20, and 27, unnecessary light is generated by reflection on the inner surface of the prism having the prism width b. As is clear from FIG. 3, it can be seen that a large amount of unnecessary reflected light is generated on the inner surface of the polarizing beam splitter prism 20 arranged at the position closest to the projection lens 24. These unnecessary reflected lights enter the projection lens 24,
It causes flare and ghost, and significantly lowers the contrast of the image projected on the screen surface. On the other hand, in FIG. 2, the light shielding frames 16a, 18a, 32a, 34a
By this, unnecessary light of all color lights of R, G, B is blocked,
It can be seen that the light does not enter the projection lens 24.

The light shielding frames 16a, 18a, 32a, 3
The smaller the opening width c of 4a, the greater the light blocking effect of unnecessary light. However, if the opening width c is too narrow, the peripheral illuminance decreases due to the effective light being blocked as a side effect. In FIG.
The midpoint of the width of the liquid crystal display element 13R and the polarization rotation element 16
The distance between the polarization rotator 16 and the polarization plate 18 is x1.
Assuming that the distance between the polarizer and the polarizing plate 18 and the distance between the outer surfaces of the polarization rotator 22 are x2 and x1 = x2, c = (a
+ B) / 2 holds. The effective light incident on the projection lens 24 is limited to the range shown by the dotted line due to the prism width b. Therefore, by setting the aperture width c to be c> (a + b) / 2, the effect of the effective light is newly removed. Without causing
A light-shielding effect can be obtained. Strictly speaking, the distance between the liquid crystal display elements 13R, 13B, 29G and the prisms 11, 27 has an effect on the aperture width c, but since this distance is negligibly small with respect to the width b of the prism, a general relational expression is given. Applies the above setting formula.

If the opening width c is set smaller than the above condition, naturally, unnecessary light can be more effectively shielded. In this case, an effective light beam is newly generated. However, since the R, G, and B color light beams are equally generated, the peripheral illuminance is also changed to the R, G, and B color light beams. , The color unevenness does not occur at the periphery of the screen when the colors are combined. This is because the first light-shielding frame and the second light-shielding frame have the same opening width, and the first light-shielding frame and the second light-shielding frame are arranged symmetrically with respect to the optical axis.

By setting each of the prisms 11, 20, and 27 to be a rectangular parallelepiped formed by joining two triangular prisms having the same shape, the light-shielding frame can be accurately positioned with respect to the prisms. In the above-mentioned Philips type prism, the shape of each prism constituting the prism is special, so that the light-shielding frame has to be adjusted at the time of assembling. However, a prism having a rectangular parallelepiped shape as in the present invention does not need to be adjusted.

In this embodiment, the light shielding frames are formed on both the polarization rotator 16 and the polarization plate 18 and on both the polarization plate 32 and the polarization rotator 34. However, the first prism 11 and the second prism 20 are formed. May be formed anywhere between the third prism 27 and the second prism 20. For example, it may be formed only on the polarization rotation element 16 and the polarization rotation element 34, or may be formed directly on the prism surface. Here, the light-shielding frame may be any light-shielding means, and a black paint, chrome, an organic film, or the like can be used as the light-shielding means.

Further, the polarization rotator 16, the polarization plate 18, the polarization plate 32, and the polarization rotator 34 disposed between the prisms are set to have the same size as the effective light passing range, that is, the same width as the opening width b of the light shielding frame. Alternatively, a light-shielding frame may be provided outside the opening width b. In this case, the means for forming the light-shielding frame is most easily and inexpensively black-painted. Of course, the means for forming the light-blocking frame is not limited to black coating, and any member may be used as long as it can effectively block light.

In particular, in the reflection type liquid crystal projector shown in FIG.
32, the first light shielding frame 16a is formed of a polarizing plate, and the direction of the absorption axis of the polarizing plate light shielding frame 16a and the polarizing plate 1
8 are arranged so that the directions of the absorption axes are orthogonal to each other.
The light shielding frame 34a is formed of a polarizing plate, and the polarizing plate light shielding frame 3
The direction of the absorption axis of 4a and the direction of the absorption axis of the polarizing plate 32 may be arranged so as to be orthogonal to each other.

The light shielding means using a polarizing plate can be generally expressed as follows. That is, the first light-shielding frame and the second light-shielding frame are formed of a polarizing plate, and the direction of the absorption axis of the polarizing plate is set in the same direction as the polarization direction of unnecessary light incident on the first light-shielding frame and the second light-shielding frame. It is arranged so that it becomes. Since the polarizing plate is in the form of a film and has an adhesive, a light-shielding frame can be easily formed by using the polarizing plate. Further, in the case of black coating, the black paint may protrude and adhere to undesired portions, but in the case of a polarizing plate, the light shielding range can be set accurately.

It is generally preferable to form the light-shielding frame on the left, right, up, and down, but it is not limited to this. The left and right light shielding frames are essential, but the upper and lower light shielding frames are not essential and can be omitted. This is limited because the width b of the prism affects the size of the entire optical system, but the height of the prism is not limited because it does not significantly affect the size of the entire optical system. Therefore, by setting the height of the prism to a sufficient height so that the reflected light at the angle θ is not reflected by the inner surface of the prism, the width of the light-shielding frame may be increased for the upper and lower light-shielding frames, or the upper and lower light-shielding frames may be enlarged. May be omitted.

In this embodiment, only the light-shielding frame arranged between the prisms is described as a means for shielding unnecessary light. However, the prism surface is painted black to reduce the reflectance on the prism surface where unnecessary light is generated. In addition, a more effective light-shielding effect can be obtained by using the conventional light-shielding technique such as a notch of a prism. In particular, it is easier to design the prism upper and lower surfaces to have a sufficient prism height as described above and to blacken the upper and lower surfaces of the prism that are not used for entering and exiting light, rather than providing upper and lower light shielding frames. It is cheap.

In this embodiment, the widths of the prisms are all described as the same prism width b. However, the present invention is not limited to this, and the widths of the constituent prisms may be different.
For example, only the polarization beam splitter prism 20 has a larger prism width b than the other polarization beam splitter prisms 11 and 27. Prism width b in this case
In this case, the maximum value of each prism width, that is, the polarization beam splitter prism 20 may be adopted as the prism width b, and the opening width c of the light shielding frame may be set.

In this embodiment, a technique for blocking unnecessary light generated by a prism used in a color combining optical system of a reflection type liquid crystal projector has been proposed. Since the color synthesizing optical system of the reflection type liquid crystal projector of this embodiment is constituted by three prisms, there is no need to newly divide the prism of each color light into two in order to provide a light-shielding frame unlike the related art. There is also.

The technique for shielding unnecessary light generated on the inner surface of the prism according to the present invention is not limited to the above-mentioned reflection type liquid crystal projector, and even in a transmission type liquid crystal projector, at least one prism is provided in the color combining optical system. It is applicable as long as the configuration includes. In other words, any configuration may be used as long as the configuration includes two prisms between the liquid crystal display element and the projection lens, and a light-shielding frame is provided between each prism.

The polarization beam splitter prism 1
1. Bonding the polarization rotator 16, the polarization plate 18, the polarization beam splitter prism 20, the polarization rotator 34, the polarization plate 32, and the polarization beam splitter prism 27 to each other minimizes interfacial reflection between optical components. be able to. Further, by bonding, the positional shift due to the temporal change of each optical component can be suppressed, and the convergence accuracy of the image of each color light of R, G, B can be maintained.

[0046]

As described above, according to the present invention,
In a liquid crystal projector or an optical component using a prism for a color combining optical system, unnecessary light generated in the prism
A light-shielding effect can be obtained for all color light. Further, according to the present invention, in a liquid crystal projector or an optical component using a prism for a color synthesizing optical system, an unnecessary light generated in the prism has a light shielding effect on all three color lights, and a peripheral light of the effective light. It is possible to prevent the occurrence of color unevenness due to a decrease in illuminance.

[Brief description of the drawings]

FIG. 1 is a schematic top view showing one embodiment of a liquid crystal projector according to the present invention.

FIG. 2 is a schematic top view for explaining a light blocking effect in one embodiment of the liquid crystal projector according to the present invention.

FIG. 3 is a schematic top view of a liquid crystal projector without a light shielding frame according to the present invention.

[Explanation of symbols]

1 ... light source, 2 ... substantially parallel light, 2R ... R light, 2G ... G light, 2
B ... B light, 3 ... Polarization conversion element, 4R ... S polarized light of R, 4G
.. G S-polarized light, 4B ... B S-polarized light, 5 ... G reflection RB transmission dichroic mirror, 6R ... R S-polarized light, 6G ... G S-polarized light, 6B ... B S-polarized light, 7 ... Polarizer, 8R ... R for S
Polarized light, 8B ... B S-polarized light, 9 ... Polarization rotation element for rotating B light, 10R ... R S-polarized light, 10B ... B P-polarized light, 11 ... Polarized beam splitter prism, 11a ... Splitter surface, 12R ... R-polarized light, 12B ... B P-polarized light, 13R ... R reflective liquid crystal display element, 13B ... B reflective liquid crystal display element, 14R ... R P-polarized light, 14B ... B S-polarized light, 15R ... R P polarized light, 15B ... B S polarized light, 1
6 ... a polarization rotating element for rotating the polarization of B light, 16a ... a light shielding frame, 17R ... R P-polarization, 17B ... B P-polarization, 18
... Polarizing plate, 18a ... Shading frame, 19R ... P-polarized light of R, 19
B: S polarized light of B, 20: polarized beam splitter prism, 20a: splitter surface, 21R: P polarized light of R, 21
B ... B P-polarized light; 22 ... Polarization rotation element for rotating only R light and B light; 23R ... R S-polarized light; 23B ... B
S-polarized light, 24 ... Projection lens, 25 ... Polarizing plate, 26G ...
G S-polarized light, 27 ... polarizing beam splitter prism, 2
7a: Splitter surface, 28G: S-polarized light of G, 29G: G
, 30G ... G P-polarized light, 31G ...
P polarized light of G, 32: polarizing plate, 32a: light shielding frame, 33G ...
G P-polarized light, 34: polarization rotating element, 34a: light-shielding frame, 3
5G: S-polarized light of G, 36G: S-polarized light of G, a: screen width of the liquid crystal display element, b: prism width, c: opening width of the light shielding frame.

Continued on the front page (72) Inventor Tsutomu Nakajima 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Digital Media System Division of Hitachi, Ltd. (72) Eiji Yamaguchi 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Japan Stock Hitachi, Ltd. Digital Media System Division (72) Inventor Futoshi Yamazaki 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture, Ltd. Digital Media System Division, Hitachi, Ltd. 292, Yoshida-cho, Ward Digital Media System Division, Hitachi, Ltd. (72) Inventor Takashi Kakuda 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term in Digital Media System Division, Hitachi, Ltd. 2H088 EA14 EA15 EA16 HA13 HA14 HA18 HA20 HA23 HA24 HA28 KA30 MA02 MA04

Claims (11)

[Claims] 1. A method according to claim 1, further comprising the steps of:
A first prism for synthesizing the second light from the liquid crystal display element, a second prism for transmitting the third light from the third liquid crystal display element, and the first, second and third prisms. A third prism that combines the three lights, a first light-blocking frame provided between the first prism and the third prism,
A second light-shielding frame provided between the second prism and the third prism; the first light-shielding frame and the second light-shielding frame;
An optical component wherein the opening widths of the light-shielding frames are substantially equal, and the first light-shielding frame and the second light-shielding frame are disposed substantially symmetrically with respect to an optical axis. 2. The first light and the second light are combined by transmitting the first light from the first liquid crystal display element and reflecting the second light from the second liquid crystal display element. A first prism that transmits light, a second prism that transmits third light from a third liquid crystal display element, and a light that transmits the first and second lights emitted from the first prism, By reflecting the third light emitted from the second prism,
A third prism that combines and emits the first light, the second light, and the third light, and a first light shield provided between the first prism and the third prism. A frame, and a second light-blocking frame provided between the second prism and the third prism, wherein the opening widths of the first light-blocking frame and the second light-blocking frame are substantially equal, and An optical component, wherein the first light-shielding frame and the second light-shielding frame are arranged substantially symmetrically with respect to an optical axis. 3. The optical component according to claim 1, wherein
The first light-shielding frame and the second light-shielding frame are formed on first and second polarizing plates, respectively, and the direction of the absorption axis of the first and second polarizing plates is changed to the first polarizing plate. An optical component, wherein the optical component is disposed so as to be in the same direction as the polarization direction of unnecessary light incident on the second polarizing plate. 4. A liquid crystal projector that separates light from a light source and irradiates the light to first to third liquid crystal display elements, respectively, wherein the first light from the first liquid crystal display element and the second light are
The second light from the liquid crystal display element of the above enters the second prism through the first prism and the first light shielding frame,
Third light from the third liquid crystal display element is incident on the second prism through a third prism and the second light shielding frame, and the first to third lights are transmitted to the second prism. The first light-blocking frame and the second light-blocking frame have the same opening width, and the first light-blocking frame and the second light-blocking frame are connected by an optical axis. A liquid crystal projector characterized by being disposed substantially symmetrically with respect to the right and left. 5. A light source, a color separation optical system, three liquid crystal display elements, a color synthesizing optical system including at least one prism, and a projection lens, and illumination light from the light source is subjected to RGB by the color separation optical system. And the three primary colors are incident on the three liquid crystal display elements, respectively, and the image light of the three primary colors emitted by the liquid crystal display elements is synthesized into color image light by the color synthesizing optical system. In a liquid crystal projector for enlarging and projecting light by the projection lens, a first prism, a second prism, and a third prism are arranged in the color combining optical system, and the first prism and the second prism are arranged. A first light-shielding frame between the third prism and the second prism; a second light-shielding frame between the third prism and the second prism; and an opening between the first light-shielding frame and the second light-shielding frame. The width is the same width, One of the first liquid crystal projector, characterized in that arranged on the left and right substantially symmetrically shielding frame and the second light shielding frame with respect to the optical axis. 6. The liquid crystal projector according to claim 4, wherein a screen width of the liquid crystal display element is a, a prism width of the first prism, a prism width of the second prism, and a width of the third prism. When the maximum prism width among the prism widths is b, and the opening width of the first light shielding frame and the opening width of the second light shielding frame are c, the opening width c of the second light shielding frame is c> A liquid crystal projector characterized by (a + b) / 2. 7. The liquid crystal projector according to claim 4, wherein the first light-shielding frame and the second light-shielding frame are formed on first and second polarizing plates, respectively, and the first and second light-shielding frames are formed. A liquid crystal projector, wherein the direction of the absorption axis of the polarizing plate is arranged in the same direction as the polarizing direction of unnecessary light incident on the first polarizing plate and the second polarizing plate. 8. A light source, a color separation optical system, three reflection type liquid crystal display elements, a polarizing plate, a color combining optical system including at least one prism, a projection lens, and a light source for rotating polarized light of a specific wavelength range. A polarization rotation element for causing the illumination light from the light source to be separated into three primary colors of RGB by the color separation optical system and to be incident on the three reflective liquid crystal display elements, respectively. In a liquid crystal projector for combining reflected three primary colors of image light into color image light by the color combining optical system and enlarging and projecting the color image light by the projection lens, a first polarized beam is provided in the color combining optical system. Splitter prism, first polarization rotator, first
Polarizing plate, second polarizing beam splitter prism, second polarizing beam splitter prism
A polarization rotator, a second polarizing plate, and a third polarizing beam splitter prism are arranged close to or joined to each other,
A first light shielding frame is provided between the first polarizing beam splitter prism and the second polarizing beam splitter prism; and a third light shielding frame is provided between the third polarizing beam splitter prism and the second polarizing beam splitter prism. A second light-shielding frame, the opening width of the first light-shielding frame and the opening width of the second light-shielding frame are the same, and the first light-shielding frame and the second light-shielding frame are positioned with respect to the optical axis. A liquid crystal projector characterized in that the liquid crystal projector is arranged substantially symmetrically. 9. A liquid crystal projector according to claim 8, wherein a screen width of said reflection type liquid crystal display element is a, a prism width of said first polarizing beam splitter prism and said second width.
B, the maximum prism width of the prism width of the polarizing beam splitter prism and the prism width of the third polarizing beam splitter prism, and c the opening width of the first light shielding frame and the opening width of the second light shielding frame. Wherein the width c of the light-shielding frame is c> (a + b) / 2. 10. The liquid crystal projector according to claim 8, wherein said first light shielding frame is formed on one of said first polarization rotating element and said first polarizing plate, and said second light shielding frame is formed on said first polarizing plate. A liquid crystal projector, wherein the liquid crystal projector is formed on one of the second polarization rotating element and the second polarizing plate. 11. A liquid crystal projector according to claim 8, wherein said first light shielding frame is provided with a third polarizing plate in a frame portion of said first polarizing plate, and said third light shielding frame has an absorption axis. Direction and the direction of the absorption axis of the first polarizing plate are arranged so as to be orthogonal to each other, the second light-shielding frame is provided with a fourth polarizing plate in a frame portion of the second polarizing plate, A liquid crystal projector, wherein the direction of the absorption axis of the fourth polarizing plate and the direction of the absorption axis of the second polarizing plate are arranged so as to be orthogonal to each other.