Image display apparatus

The present invention relates to an image display apparatus including a plurality of spatial light modulation elements corresponding to respective colors and an illumination optical system illuminating the plural spatial light modulation elements. The image display apparatus includes a dichroic prism (5) which color-separates illumination light from an illumination optical system (2) to direct thus separated lights to respective spatial light elements (3R), (3G), (3B) as well as composites reflection lights from those spatial light elements (3R), (3G), (3B), and a projection lens (6) which projects the light outgoing from the dichroic prism (5) to display an image. A retarder stack (7), which is disposed on an optical path between the illumination optical system (2) and the dichroic prism (5), causes light of wavelength band which is supposed to pass through reflection planes of the dichroic prism (5) to be of P-polarized light, and causes light of wavelength band which is supposed to be reflected by the reflection planes to be of S-polarized light.

TECHNICAL FIELD

The present invention relates to an image display apparatus which modulates illumination light according to a predetermined image using spatial light modulation elements and projects thus modulated light to display the image.

This application claims priority to Japanese Patent Application Number JP2002-098042, filed Mar. 29, 2002 which is incorporated herein by reference.

BACKGROUND ART

Up to now, there has been proposed an image display apparatus which illuminates spatial light modulation elements utilizing polarization made of such as liquid crystal using an illuminator having a light source e.g. a discharge lamp, and projects an image of the spatial light modulation elements using a projection lens.

Such a projection-type image display apparatus has come into practical use, particularly as a large-sized image display apparatus. For example, in an image display apparatus which employs reflection-type liquid crystal elements having reflecting electrodes as spatial light modulation elements, the numerical aperture of the spatial light modulation elements can be enlarged to realize miniaturization of the configuration of the apparatus and high-definition image displaying.

The reflection-type spatial light modulation elements modulate polarization direction of incoming illumination light and reflect thus modulated light, according to an image to be displayed at respective pixels. Thus, when using reflection-type spatial light modulation elements, a polarizer which polarizes incoming light into the spatial light modulation elements and an analyzer which analyzes polarized components of predetermined direction alone from the light reflected by the spatial light modulation elements are necessary to be provided.

As the polarizer and analyzer, a polarization beam splitter (PBS)101can be used, as shown inFIG. 1. In the image display apparatus, illumination light emitted from a discharge lamp102outgoes from an illumination optical system103consisting of a parabolic mirror and a fly-eye lens, and comes into the polarization beam splitter101via a first condenser lens104, a mirror105and a second condenser lens106. The reflection plane of the polarization beam splitter101, which is laid obliquely against the incoming illumination light, reflects S-polarized component alone of the incoming illumination light, and causes the S-polarized component to outgo to a dichroic prism107working as a color separation/composition element. Here, the polarization beam splitter101works as a polarizer.

The dichroic prism107separates the illumination light into R (red) light, G (green) light and B (blue) light, each of which comes into spatial light modulation elements108,109and110corresponding to each color, respectively. The spatial light modulation elements108,109and110modulate polarization directions of the separated color lights according to an image to be displayed. Then, thus modulated color lights are composited at the dichroic prism107, and thus composited light returns to the polarization beam splitter101. At this time, the polarization beam splitter101allows P-polarized component alone, toward the reflection plane, of the illumination light returned from the dichroic prism107to pass through the reflection plane, and causes the P-polarized component to outgo to a projection lens111. Here, the polarization beam splitter101works as an analyzer for converting polarization modulation to intensity modulation.

The projection lens111projects the light of an image from the spatial light modulation elements108,109and110onto a screen, not shown, to display an image.

In the image display apparatus described above, the reflection plane of the polarization beam splitter is made of dielectric multilayer films, which select polarized light in accordance with the difference of reflectance between P-polarized light and S-polarized light at respective interfaces of the dielectric multilayer films. Therefore, the reflection plane of the polarization beam splitter selects polarized light depending highly on wavelength and angle.

In the image display apparatus, when using bright illumination light of small F-number, the range of incident angle of illumination light toward the reflection plane of the polarization beam splitter becomes wide, which undesirably deteriorates the function of the polarization beam splitter as a polarizer. Namely, the image display apparatus employing the polarization beam splitter working as a polarizer as well as an analyzer cannot use bright illumination light, thus efficiency of light utilization in an illumination optical system can not be improved.

Also, separating color using a dichroic prism depends highly on polarization state. Namely, in the dichroic prism, the dichroic surface for separating color has different properties between for incoming light being S-polarized light and for outgoing light being P-polarized light. The polarization direction of the modulated light reflected by the spatial light modulation element is perpendicular to that of the incoming light, consequently, the efficiency of light utilization is deteriorated.

Further, in the case the dichroic surface is so constructed as to reflect R (red) light and B (blue) light of incoming S-polarized illumination light, G (green) light needs to pass through the dichroic surface. Generally, the dichotic surface has higher reflectance R (p) for S-polarized light as compared with reflectance R (s) for P-polarized light. Accordingly, actually, G (green) light component is also partially reflected to come into the spatial light modulation elements for R (red) light and B (blue) light, as shown inFIG. 2. The phenomenon described above consequently deteriorates color separation property and color reproduction property of an image to be displayed.

In case of using a light source of irregular emission spectrum distribution, illumination light of regular wavelength distribution may not be obtained. In this case, when the illumination light is separated into R (red) light, G (green) light and B (blue) light to be modulated and thus modulated lights are composited, desirable color reproduction range may not be obtained.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing a new image display apparatus.

Furthermore, the present invention has another object to provide an image display apparatus including a plurality of spatial light modulation elements and an illumination optical system which illuminate those spatial light modulation elements, which can realize desirable color separation property and color reproduction property.

The above object can be attained by provide an image display apparatus including:an illumination optical system having a light source;a plurality of spatial light modulation elements each having reflecting electrodes;polarization elements corresponding to the plural spatial light modulation elements;a color separation/composition element for color-separating illumination light from the illumination optical system into transmission light and reflection light to direct thus generated transmission light and reflection light to the respective spatial light modulation elements via the corresponding polarization elements and for compositing reflection lights from the spatial light modulation elements, the color separation/composition element having reflection planes laid obliquely against the illumination light where the illumination light is color-separated and the reflection lights are composited;a projection optical system for projecting composited light outgoing from the color separation/composition element to display an image of the respective spatial light modulation elements; and

a polarization change means for, of the illumination light, causing light of wavelength band which is supposed to pass through the reflection planes of the color separation/composition element to be of P-polarized light toward the reflection planes and causing light of wavelength band which is supposed to be reflected by the reflection planes of the color separation/composition element to be of S-polarized light toward the reflection planes, the polarization change means being disposed on an optical path between the illumination optical system and the color separation/composition element.

According to the image display apparatus, of illumination light, the polarization change means which is disposed on the optical path between the illumination optical system and the color separation/composition element causes light of wavelength band which is supposed to pass through the reflection planes of the color separation/composition element to be of P-polarized light toward the reflection planes, and causes light of wavelength band which is supposed to be reflected by the reflection planes of the color separation/composition element to be of S-polarized light toward the reflection planes, which can improve color separation property.

Furthermore, according to the image display apparatus, a second polarization change means for, of the illumination light, rotating polarization direction of light of wavelength band which is supposed to be blocked by the polarization element, is disposed on an optical path between the color separation/composition element and the polarization element corresponding to the spatial light modulation element.

According to the image display apparatus, of illumination light, the second polarization change means which is disposed on the optical path between the color separation/composition element and the polarization element corresponding to the spatial light modulation element rotates polarization direction of light of wavelength band which is supposed to be blocked by the polarization element, which can improve color reproduction property.

These objects and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The image display apparatus according to the present invention will be described in detail concerning the best modes for carrying out the present invention with reference to the accompanying drawings.

An image display apparatus according to the present invention includes an illumination optical system2having a light source1, and three spatial light modulation elements3R,3G, and3B which are illuminated by illumination light from the illumination optical system2and modulates the illumination light, as shown inFIG. 3. The light source1is, for example, UHP lamp (ultra-high pressure mercury lamp) etc. The illumination optical system2includes the light source1, a parabolic mirror8which reflects the illumination light emitted from the light source1to make the illumination light approximately parallel light, a fly-eye lens9into which the light reflected by the parabolic mirror8comes, a polarizing plate10, and a first condenser lens11.

Illumination light outgoing from the illumination optical system2passes through the polarizing plate10to be approximately linearly polarized light. The illumination light from the illumination optical system2comes into a second condenser lens12whose optical axis is directed obliquely against the illumination light, and then comes into a dichroic prism5working as a color separation/composition element. The dichroic prism5is configured in the form of a cubic shape, as shown inFIG. 4, and one plane thereof is an incidence plane into which illumination light comes. In the dichroic prism5, three planes or a plane which faces and is parallel with the incidence plane and two planes which face each other and are perpendicular to the incidence plane are exit planes.

The dichroic prism5has a pair of reflection planes5a,5bwhich are perpendicular to each other and are laid obliquely against the incidence plane, into which the illumination light comes, by 45°. The reflection planes5a,5bare also laid obliquely against the three exit planes by 45°. The dichroic prism5is disposed such that the illumination light coming into the dichroic prism5is S-polarized light toward the reflection planes5a,5b. The reflection planes5a,5bare dielectric films, each of which reflects light of predetermined wavelength band and transmits light of other wavelength band. For example, one reflection plane5areflects light of wavelength band corresponding to R (red) light, and the other reflection plane5breflects light of wavelength band corresponding to B (blue) light. Light of wavelength band corresponding to R (red) light outgoes from a first exit plane which is perpendicular to the incident plane. Light of wavelength band corresponding to B (blue) light outgoes from a second exit plane which faces and is parallel with the first exit plane. Light of wavelength band corresponding to G (green) light passes through both reflection planes5a,5band outgoes from a third exit plane which faces and is parallel with the incidence plane.

Thus, the dichroic prism5color-separates the illumination light into R (red) light, B (blue) light and G (green) light and causes thus separated lights to outgo into three directions respectively.

The three spatial light modulation elements3R,3G and3B are reflection-type light valves each using a liquid crystal element having a reflecting electrode, and are so disposed as to face the respective three exit planes of the dichroic prism5correspondingly, as shown inFIG. 3. The spatial light modulation elements3R,3G and3B has formed thereon polarization elements4R,4G and4B which are so disposed as to be sandwiched between the exit planes of the dichroic prism5and the spatial light modulation elements3R,3G and3B corresponding to the respective exit planes, as shown inFIG. 4. The polarization elements4R,4G and4B are circular polarizing plates each of which consists of a linear polarizing plate facing the dichroic prism5and a quarter-wave plate layered on the linear polarizing plate. Note that, inFIG. 3, the polarization element4R is disposed between the dichroic prism5and the spatial light modulation element3R.

The R (red) light outgoing from the first exit plane of the dichroic prism5passes through the polarization element4R to be circularly polarized light, and thus generated circularly polarized light comes into the spatial light modulation element3R for R (red) light. The B (blue) light outgoing from the second exit plane of the dichroic prism passes through the polarization element4B to be circularly polarized light, and thus generated circularly polarized light comes into the spatial light modulation element3B for B (blue) light. The G (green) light outgoing from the third exit plane of the dichroic prism5passes through the polarization element4G to be circularly polarized light, and thus generated circularly polarized light comes into the spatial light modulation element3G for G (green) light.

The polarization elements4R,4B, into which R (red) light and B (blue) light come, transmit S-polarized light toward respective reflection planes5a,5b. Thus, ideally, the whole R (red) light and B (blue) light outgoing from the dichroic prism5pass through the polarization elements4R,4B and come into the spatial modulators3R,3B, respectively. Since the polarization direction of the G (green) light outgoing from the third exit plane of the dichroic prism5is changed by a retarder stack7, which will be described later, the polarization direction of the G (green) light passing through the polarization element4G is determined according to the property of changing polarization direction of the retarder stack7.

The spatial light modulation elements3R,3G and3B modulate polarization directions of the respective color lights coming thereinto, according to an image to be displayed at respective pixels, and reflects thus modulated lights.

Of components of the reflected lights from the spatial light modulation elements3R,3G and3B, the polarization elements4R,4G and4B block components which are modulated and whose polarization directions are changed, and transmit components which are not modulated to return them to the dichroic prism5. The reflection planes5a,5bof the dichroic prism5composite the reflected lights returned from the spatial light modulation elements3R,3G and3B, and cause thus composited light to outgo from the incidence plane of the dichroic prism5. At this time, as shown inFIG. 3, since the illumination light from the illumination optical system2comes into the second condenser lens12whose optical axis is directed obliquely against the illumination light, the composited light outgoes along a direction opposite to that of the incoming light when viewed from the optical axis of the second condenser lens12. Thus, the outgoing light does not return to the illumination optical system2but comes into a projection light6being a projection optical system.

The projection lens6projects the light outgoing from the dichroic prism5onto a screen, not shown, to display an image of the spatial light modulation elements3R,3G and3B. Thus, a full color image is displayed on the screen.

The image display apparatus is provided with a retarder stack7working as a polarization change element on the optical path from the illumination optical system2to the dichroic prism5. Of the illumination light from the illumination optical system2, the retarder stack7causes light of wavelength band which is supposed to pass through the reflection planes5a,5bof the dichroic prism5to be of P-polarized light toward the reflection planes5a,5b, and causes light of wavelength band which is supposed to be reflected by the reflection planes5a,5bof the dichroic prism5to be of S-polarized light toward the reflection planes5a,5b.

Namely, the retarder stack7is so configured as to rotate polarization direction of λ light wavelength band corresponding to G (green) light alone by 90°. The reflection wavelength band of the reflection planes5a,5bof the dichroic prism5is set corresponding to the property of the retarder stack7. That is, wavelength band of light passing through the reflection planes5a,5bcorresponds to λ wavelength band which is caused to be of P-polarized light by the retarder stack7.

A retarder stack is composed of plural retardation films, and rotates the polarization direction of light of target wavelength band alone by 90° or by arbitrary angle. As a retarder stack, there is “ColorSelect” (trademark) produced by ColorLink, Inc. for example.

In the image display apparatus, the retarder stack7causes G (green) light to be of P-polarized light toward the respective reflection planes5a,5b. The polarization element4G, which transmits the G (green) light, consists of a linear polarizing plate, which transmits P-polarized light toward the reflection planes5a,5b, and a quarter-wave plate.

In the image display apparatus according to the present invention, since the retarder stack7is provided, in the dichroic prism5, only G (green) light component is of P-polarized light toward the reflection planes5a,5b, and B (blue) light and R (red) light remain of S-polarized light toward the reflection planes5a,5b. Therefore, in the dichroic prism5, the reflection planes5a,5befficiently reflect B (blue) light and R (red) light, and efficiently transmit G (green) light, thus the color separation property is improved.

The modulated lights, which are reflected by the spatial light modulation elements3R,3G and3B and pass through the polarization elements4R,4G and4B, come into the reflection planes5a,5bwith the G (green) light being of P-polarized light toward the reflection planes5a,5b, and B (blue) light and R (red) light being of S-polarized lights toward the reflection planes5a,5b. Thus, in the dichroic prism5, the reflection planes5a,5befficiently reflect B (blue) light and R (red) light, and efficiently transmit G (green) light, thus the color composition property is improved.

The image display apparatus according to the present invention may use a UHP lamp (ultra-high pressure mercury lamp) as a light source1. The UHP lamp has a problem to be solved about color reproduction property of G (green) light and R (red) light after color separation. Namely, since the emission spectrum of the UHP lamp has large emission line at around 580 nm, as shown inFIG. 6, desirable color reproduction property can not be realized without cutting off light of wavelength band around 580 nm, as shown inFIG. 7. Conventional color reproduction property shown by a chain line and a dashed line inFIG. 7indicates undesirable color separation property of G (green) light and R (red) light, respectively. By improving the color separation property of G (green) light and R (red) light, desirable color reproduction property shown by full lines inFIG. 7can be obtained.

An image display apparatus employing a UHP lamp as the light source1uses two sets of retarder stacks7,13, as shown inFIGS. 8 and 9. That is, the retarder stack7included in the foregoing image display apparatus shown inFIG. 3is set to be as a first retarder stack7which works as a first polarization change element, and a second retarder stack13is provided as a second polarization change element. The second retarder stack13is disposed on the optical path from the dichroic prism5to the polarization element4G, as shown inFIG. 9.

Of the illumination light, the second retarder stack13rotates polarization direction of light of wavelength band which is supposed to be blocked by the polarization elements4R,4G and4B alone. In the image display apparatus shown inFIG. 8, parts or components similar to those of the image display apparatus shown inFIG. 3are indicated with the same reference numerals except the second retarder stack13, and detailed explanation of which will be omitted.

Wavelength band of light whose polarization direction is rotated by the first retarder stack7, shown inFIG. 10A, is wide as compared with the wavelength band of light whose polarization direction is rotated by the second reatrder stack13, shown inFIG. 10B. For example, the first retarder stack7is so configured as to cause light of wavelength between 485 nm and 595 nm to be of P-polarized light toward the reflection planes5a,5b, and the second retarder stack13is so configured as to cause light of wavelength between 505 nm and 575 nm to be of S-polarized light toward the reflection planes5a,5b. The wavelength λ indicates an intermediate value of wavelength band at which polarization direction of light changes.

Of illumination light which passed through the first retarder stack7, light of wavelength between 485 nm and 595 nm is caused to be of P-polarized light to pass through the reflection planes5a,5bof the dichroic prism5. Light of other wavelength remains of S-polarized light to come into the reflection planes5a,5b, and is reflected by the reflection planes5a,5bof the dichroic prism5as R (red) light and B (blue) light respectively. Of the light of wavelength between 485 nm and 595 nm, which passed through the reflection planes5a,5bof the dichroic prism5, the second retarder stack13rotates polarization direction of light of wavelength between 505 nm and 575 nm by 90° as shown inFIG. 10Bto cause the light pass through the linear polarizing plate of the polarization element4G. The linear polarizing plate of the polarization element4G in this case is so configured as to transmit S-polarized light toward the reflection planes5a,5bof the dichroic prism5. On the other hand, the linear polarizing plate of the polarization element4G blocks light of wavelength between 485 nm and 505 nm as well as between 575 nm and 595 nm. Consequently, the aforementioned emission line at around 580 nm is cut off.

It is noted that the first retarder stack7may be disposed on anywhere on the optical path of the illumination light from the illumination optical system2to the dichroic prism5. In the image display apparatus shown inFIG. 8, the first retarder stack7is disposed between the fly-eye lens9and the first condenser lens11. The reflection-type polarizing plate10is disposed between the fly-eye lens9and the first retarder stack7. The second retarder stack13is disposed between the dichroic prism5and the linear polarizing plate of the polarization element4G.

Note that a circular polarizing plate15is provided between the second retarder stack13and the polarization element4G.

The second retarder stack13can be so configured as to cut off only light of wavelength at around 580 nm, as shown inFIG. 11B. That is, the second retarder stack13is so configured as to rotate the polarization direction of light of the wavelength equal to or shorter than 575 nm by 90°. Also in this case, the linear polarizing plate of the polarization element4G is so configured as to transmit S-polarized light toward the reflection planes5a,5bof the dichroic prism5.

It should be noted that, as shown inFIG. 11A, the first retarder stack7causes light of wavelength between 485 nm and 595 nm to be of P-polarized light toward the reflection planes5a,5b, as is similar to the case shown inFIG. 10A.

This configuration can also cut off the aforementioned emission line at around 580 nm.

In the image display apparatus inFIG. 8, when transmission axes of the polarization elements4R,4G and4B are rotated against polarization directions of the illumination lights, which outgo from the dichroic prism5to the polarization elements4R,4G and4B, white balance of a display image can be adjusted.

That is, in many cases, it is necessary to reduce optical power of G (green) light to perform white balance of R (red) light, G (green) light and B (blue) light. In the case, the optical power of the G (green) light can be reduced by adjusting rotation angle of polarization direction by the second retarder stack13or by adjusting rotation angle of the polarization element4G transmitting the G (green) light. For example, in the case of reducing the optical power of the G (green) light by 10%, the rotation angle of the polarization direction of the G (green) light by the second retarder stack13is set to be approximately 72°, or the polarization element4G transmitting the G (green) light is rotated by approximately 18° around the optical axis. In the case of reducing the optical power of the B (blue) light by 10%, the polarization element4B transmitting the B (light) is rotated by approximately 18° around the optical axis. Consequently, when a UHP lamp is used as the light source1, desirable color reproduction property can be realized, as shown inFIG. 7.

It is noted that in the image display apparatus according to the present invention, as shown inFIG. 12, a glass material14may be disposed between the illumination optical system2and the dichroic prism5, as well as between the dichroic prism5and the projection lens6.

While the invention has been described in accordance with certain preferred embodiments thereof illustrated in the accompanying drawings and described in the above description in detail, it should be understood by those ordinarily skilled in the art that the invention is not limited to the embodiments, but various modifications, alternative configurations or equivalents can be implemented without departing from the scope and spirit of the present invention as set forth and defined by the appended claims.

INDUSTRIAL APPLICABILITY

The present invention provides an image display apparatus including plural spatial light modulation elements and an illumination optical system illuminating the plural spatial light modulation elements, by which desirable color separation property and color reproduction property can be realized.