JP4543680B2 - Illumination optics - Google Patents

Description

  The present invention relates to illumination optics for illuminating a spatial light modulation element by guiding a light beam emitted from a light source in an image display for forming an image by imaging a light beam modulated by a spatial light modulation element such as a liquid crystal light valve. Regarding the system.

  Conventionally, an image display apparatus using a spatial light modulation element such as a liquid crystal display element (LCD) has been proposed. Since this image display device can obtain a display image with a high resolution and a high contrast ratio, devices having various configurations have been developed and commercialized.

  Many of such image display apparatuses are configured to include three spatial light modulation elements, and are configured as so-called “three-plate color projectors”. This "three-plate color projector" separates white light obtained from a powerful light source such as a metal halide lamp into three primary colors, and spatial light modulation such as a liquid crystal display element corresponding to each color for each color light thus separated. It is configured to perform image display by guiding each spatial light modulator to drive the element and driving it with an image signal corresponding to each color, and further combining and projecting the modulated light of each color to form an image. ing.

  In such image display devices, along with recent advances in LSI technology, spatial light modulation elements have become increasingly fine and miniaturized, and in addition to conventional demands for large screen images, high resolution of display images has been achieved. There is an increasing demand for higher quality such as higher brightness, higher brightness, higher contrast, and good color reproducibility.

  A liquid crystal display element known as a spatial light modulation element modulates the polarization state of the illumination light beam according to the display image by controlling the applied voltage for each pixel according to the input image signal, and transmits or reflects it. Let The image display light can be read by passing the light beam (modulated light) that has passed through the liquid crystal display element through a polarizing plate or a polarizing beam splitter (PBS).

  By using one (three in total) liquid crystal display elements corresponding to each color of R (red), G (green), and B (blue), a high-definition color image can be reproduced and projected. By enlarging and projecting using a lens, a high-definition large-screen display image can be obtained.

  Such an image display apparatus is provided with an illumination optical system for guiding a light beam emitted from a light source to a spatial light modulation element and illuminating the spatial light modulation element. This illumination optical system needs to be able to illuminate the spatial light modulation element with high efficiency and uniformity by a light beam emitted from a light source having a finite size.

  An integrator optical system is known as such an illumination optical system. As this integrator optical system, a so-called “fly eye lens array type” illumination optical system and a so-called “rod integrator type” illumination optical system are known.

  The fly-eye lens array type illumination optical system is configured such that an illumination light beam is incident on a fly-eye lens array in which a plurality of small-diameter lenses similar in shape to the illumination region are arranged in a fly-eye shape (two-dimensionally). Is divided for each cell having a shape similar to that of the illumination area, and these light beams are overlapped to obtain high-efficiency and uniform illumination light.

  The rod integrator type illumination optical system efficiently collects the illumination light beam from the incident end surface and makes it incident on the rod-shaped rod integrator whose both end surfaces, which are the incident end surface and the output end surface, are similar to the illumination area. In this rod integrator, the light beam is subjected to multiple reflection, and the illumination end face is configured to obtain uniform illumination light with high efficiency. Then, a high-efficiency uniform illumination can be obtained by forming an image of the light flux distribution on the exit end face on the illumination area (on the spatial light modulation element) at a desired magnification.

  By the way, the contrast of the display image in such an image display device is represented by a ratio between the brightest white level (bright illuminance) of the image display light and the darkest black level (dark illuminance). Or “several 1000: 1”. Such a contrast is determined by the overall performance of the contrast as the illumination optical system and the contrast by driving the liquid crystal display element in the projection type image display apparatus.

  What determines the contrast as the illumination optical system is the polarization separation performance of the polarizing plate or the polarizing beam splitter. The polarization separation performance of the polarizing plate and the polarizing beam splitter is degraded as the incident angle of the incident light beam is increased, that is, as the F number of the illumination optical system is decreased. Therefore, when the F number of the illumination optical system is reduced, the illumination optical system becomes brighter, but the contrast of the display image is deteriorated.

  The contrast caused by driving the liquid crystal display element has less influence on the contrast of the display image than the contrast of the illumination optical system. However, in the projection type image display apparatus (projector) using three liquid crystal display elements as described above, white balance is achieved by controlling the modulation state in each liquid crystal display element corresponding to each RGB color. ing. For example, in order to increase the color temperature of the display image, the B (blue) light is set so as to increase. Conversely, in order to decrease the color temperature of the display image, the R (red) light is increased. Set. As described above, when white balance is achieved by signal control on the liquid crystal display element, the maximum level is suppressed for a color having a high light modulation level, and the contrast in the display image is lowered.

  The present inventors have already proposed an image display device in which white balance is optically balanced without lowering the contrast of a display image. In this image display apparatus, a tertiary light source image is formed on the entrance pupil of the illumination optical system, that is, on the second fly-eye lens array in the fly-eye lens array illumination optical system and in the rod integrator system illumination optical system. At the position where the light is formed, the light beam passing outside the entrance pupil is filtered and dimmed to increase the F number of the illumination optical system to achieve white balance.

In this image display device, the white balance can be adjusted well without reducing the contrast of the display image.
JP-A-8-254699

  By the way, as described above, when the means for filtering the light beam passing outside the entrance pupil on the entrance pupil of the illumination optical system is used, the optical path length of the light beam filtered and attenuated is the center of the entrance pupil. It differs with respect to the optical path length of the light beam that passes through the part and is not filtered.

  Therefore, the light flux filtered in this way and the light flux that has passed through the central part of the entrance pupil cause a deviation (longitudinal aberration) in the direction of the optical axis of the condensing position in the illumination area, and the illumination efficiency is improved. There was a problem of deterioration.

  Here, it is conceivable to use as a filtering means a thin glass plate in which the central part is a transmission part having no wavelength selectivity (spectral characteristics) and a film having wavelength selectivity is arranged in the peripheral part. By using such a filtering means, the filtered (dimmed) light beam and the light beam that has passed through the center of the entrance pupil do not cause an optical path difference, and a highly efficient illumination optical system can be configured. It becomes.

  However, such a filtering means must be formed as a filter with a central portion removed, such as a rectangular frame or donut shape. And since it is necessary to form an antireflection film in the central part, it is necessary to change the masking and pass through at least three film forming steps in order to produce such a filtering means. Therefore, such filtering means is complicated and difficult to manufacture, and the productivity is low.

  Moreover, in such a filtering means, since it is a transmissive filter, there are many factors that reduce the utilization efficiency of the illumination light flux, such as the transmittance inside the member and the reflection loss on each surface.

  The present invention has been proposed in view of the above-described circumstances, and is an illumination optical system used in an image display device, which does not reduce the contrast of a display image and improves the use efficiency of an illumination light beam. An object of the present invention is to provide an illumination optical system that can adjust white balance well without deteriorating, is easy to manufacture, and has high productivity.

In order to solve the above-described problems, an illumination optical system according to the present invention emits illumination light including a visible light band from a light source as image light by performing light modulation using a spatial light modulation element, and the spatial light modulation An illumination optical system used in an image display apparatus that projects an enlarged image light emitted from an element, the light collecting means for condensing a light beam of the illumination light emitted from the light source, and the light collecting means When the condensed light beam of the illumination light is incident from the incident end surface, the rod integrator that emits from the output end surface as the light beam of the illumination light in which the incident illumination light is internally reflected and the illuminance is uniformed, and Irradiating means for irradiating a predetermined region of the spatial light modulator with the luminous flux emitted from the rod integrator, and connecting the incident end surface and the emitting end surface of the rod integrator The surface, spectral reflection film having a spectral characteristic for dimming the light in a predetermined wavelength band in the visible light band is formed.
The spectral reflection film is formed on each side over the entering-morphism end face or al a predetermined distance.

  By using this illumination optical system in an image display device, it is possible to display an image with high brightness, high contrast, and good white balance. It can be provided.

  In the illumination optical system according to the present invention, the rod integrator has wavelength selectivity at least in the vicinity of the incident end surface corresponding to a light beam having an incident angle larger than a predetermined angle on the inner reflection surface excluding the incident end surface and the output end surface. Since the spectral reflection film is formed, the luminous flux having an incident angle larger than the predetermined angle out of the luminous flux incident on the rod integrator is attenuated and reflected by the spectral reflection film in a predetermined wavelength band. . In this illumination optical system, the F-number of the light flux in the wavelength band dimmed by the spectral reflection film in this way is adjusted, and the white balance is adjusted without reducing the contrast of the display image in the image display device. The

  In addition, this illumination optical system is easy to manufacture and reduces the efficiency of use of the illumination light flux, such as the transmittance inside the member and the loss due to reflection on each surface, such as when using a transmissive filter. There is no factor to make it.

  That is, the present invention can satisfactorily adjust the white balance in an illumination optical system used in an image display device without reducing the contrast of the display image and without reducing the efficiency of use of the illumination light beam. It is possible to provide an illumination optical system that can be manufactured easily and has high productivity.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of an illumination optical system according to the present invention will be described in detail with reference to the drawings.

[Embodiment of Image Display Device]
FIG. 1 is a side view showing a configuration of an image display device to which an illumination optical system according to the present invention is applied.

  In this image display device, as shown in FIG. 1, the luminous flux emitted from the light source 1 that emits light including light in the visible light band is made uniform by the illumination optical system 2 according to the present invention, and is polarized. The light enters the first polarizing beam splitter 6 through the conversion element (PCS) 3 and the field lenses 4 and 5, through a wavelength selective wave plate (not shown).

  The polarization conversion element 3 is an element that emits light with the polarization direction aligned in a certain direction by rotating the polarization direction by 90 ° for one polarization direction component of the incident light flux. In the wavelength selective wave plate, B (blue) light is converted to P-polarized light with respect to the polarization reflection surface of the first polarizing beam splitter 6, and R (red) light and G (blue) light are converted to the first polarizing beam splitter 6. S polarized light with respect to the polarized light reflection surface. On the polarization reflection surface of the first polarization beam splitter 6, B light is transmitted and R light and G light are reflected.

  The B light that has passed through the first polarizing beam splitter 6 also passes through the second polarizing beam splitter 7 and enters the B-use reflective spatial light modulator 8. In this embodiment, each spatial light modulation element is a reflective liquid crystal display element.

  On the other hand, the R light and G light reflected by the first polarizing beam splitter 6 are incident on the third polarizing beam splitter 9 through a wavelength selective wave plate (not shown). In the wavelength selective wave plate 9, the R light becomes P-polarized light with respect to the polarization reflection surface of the third polarization beam splitter 9, and the G light becomes S-polarization with respect to the polarization reflection surface of the third polarization beam splitter 9. On the polarization reflection surface of the third polarization beam splitter 9, the R light is transmitted and the G light is reflected.

  The R light transmitted through the third polarizing beam splitter 9 enters the R reflective spatial light modulator 10. Further, the G light reflected by the third polarizing beam splitter 9 enters the G reflective spatial light modulator 11.

  In the B, R, and G reflective spatial light modulators 8, 10, and 11, the incident light beams are images corresponding to the colors supplied to the reflective spatial light modulators 8, 10, and 11. Depending on the signal, it is polarization-modulated and reflected.

  The reflected light that has been polarization-modulated by the reflective spatial light modulator 8 for B is reflected by the polarization reflection surface of the second polarization beam splitter 7 and enters the fourth polarization beam splitter 12.

  The reflected light that has been polarization-modulated by the reflective spatial light modulator 10 for R is reflected by the polarization reflection surface of the third polarization beam splitter 9, passes through a wavelength-selective wavelength plate (not shown), and is converted into a fourth polarization beam. The light enters the splitter 12. In addition, the reflected light that has been polarization-modulated by the reflective spatial light modulator for G 11 passes through the polarization reflection surface of the third polarization beam splitter 9, passes through a wavelength-selective wavelength plate (not shown), The light enters the polarization beam splitter 12. In this wavelength selective wave plate, the polarization direction is rotated by 90 ° for only the R light out of the transmitted R light and G light.

  In the fourth polarization beam splitter 12, the B light is S-polarized light, and the R light and G light are P-polarized light with respect to the polarization reflection surface. Therefore, in the fourth polarization beam splitter 12, the B light is reflected by the polarization reflection surface, and the R light and the G light are transmitted through the polarization reflection surface, whereby the B light, the R light, and the G light are combined. The

  The B light, R light, and G light synthesized in this way are incident on the projection lens 13 through a wavelength selective wave plate (not shown). In this wavelength selective wave plate, the polarization direction is rotated by 90 ° for only the B light out of the transmitted B light, R light and G light. In the light beam transmitted through the wavelength selective wave plate, the polarization directions of the B light, the R light, and the G light are all aligned.

  The projection lens 13 projects incident light on the screen 14 to form an image, and performs image display.

[Embodiment of illumination optical system]
FIG. 2 is a side view showing the configuration of the illumination optical system according to the present invention.

  In the illumination optical system 2 of the image display apparatus, the light beam emitted from the light source 1 is condensed by a concave reflecting mirror 14 serving as a condensing unit and incident on a rod integrator 15 as shown in FIG. The rod integrator 15 is formed of a transparent material such as glass in the shape of a rod whose both end portions are an incident end surface 15a and an output end surface 15b. The entrance end surface 15a and the exit end surface 15b of the rod integrator 15 have a rectangular shape corresponding to the shape of the spatial light modulator. The cross-sectional shape of the rod integrator 15 is the same as that of the incident end face 15a and the outgoing end face 15b.

  The light beam from the light source 1 enters the rod integrator 15 from the incident end face 15a of the rod integrator 15, repeats multiple internal reflections inside the rod integrator 15, and is emitted from the opposite exit end face 15b.

  The light beam emitted from the rod integrator 15 is condensed by the condensing lenses 16 and 17 serving as condensing means. On the condensing surface of the light flux emitted from the rod integrator 15 by the condensing lenses 16 and 17, a light amount distribution is formed according to the incident angle to the rod integrator 15 and the number of internal reflections. The polarization conversion element 3 is installed on a condensing surface by the condensing lenses 16 and 17.

  By installing the polarization conversion element 3 at a position where such a light quantity distribution is formed, it is possible to align the polarization direction in a certain direction (PS synthesis).

  In the rod integrator 15 of this illumination optical system, a spectral reflection film 15c having wavelength selectivity (spectral characteristics) is formed on the inner reflection surface near the incident end face 15a by vapor deposition or the like. Of the incident light to the rod integrator 15, the light beam internally reflected in the region where the spectral reflection film 15c is formed is attenuated for a predetermined wavelength band according to the spectral reflection characteristics of the spectral reflection film 15c. Reflected or blocked.

  In the rod integrator 15, since the spectral reflection film 15c is formed in the vicinity of the incident end face 15a, a light beam having a large incident angle reflects only a wavelength band corresponding to the spectral reflection characteristics of the spectral reflection film 15c. Therefore, the pupil image in this illumination optical system has a shape filtered into a quadrangle. That is, in this illumination optical system, the outer peripheral portion of the pupil, that is, the portion with a small F number is filtered as white balance adjustment, and the light intensity distribution as the illumination optical system is concentrated in a region with a large F number. .

  Therefore, in this illumination optical system, the incident angle (cone angle) to the polarizing beam splitter constituting the image display device can be suppressed to be small, the polarization selection characteristic of the polarizing beam splitter becomes good, and a display image with high contrast can be obtained. Can be obtained.

  In the rod integrator 15 in this illumination optical system, as shown in FIG. 2, it can be seen that incident light having a larger incident angle is totally reflected on the inner reflecting surface near the incident end face 15a.

At this time, the number K of internal reflections varies depending on the incident angle (F #) of the light beam incident on the rod integrator, the length of the rod integrator is L, the refractive index in the rod integrator is n, and the height direction of the rod integrator is If the width is D, there is a relationship as shown in the following formulas (1) and (2). However, Int [•] in the equation (1) is a function that rounds off the decimal part to make it an integer.

NA = (1/2) F # (2)
When the light flux from the exit end face 15 b of the rod integrator 15 is condensed, a light quantity distribution corresponding to the number of internal reflections inside the rod integrator 15 is obtained. This light quantity distribution is conjugate with the incident end face 15a of the rod integrator 15, and the center of the pupil image corresponds to a light beam image that has been transmitted without undergoing internal reflection in the rod integrator 15 once. In an actual light source, the center of the pupil image is behind the electrode or the like, so that the image has almost no luminous flux. The image formed in a matrix form in the vertical and horizontal directions from the center is a light beam focused and formed on the incident end face 15a of the rod integrator 15, and is a light source image reflected once from the center toward the periphery, and reflected twice. Light source image, light source image reflected three times,..., Light source image reflected n times.

  FIG. 3 is a side view showing an optical system from the rod integrator 15 to the spatial light modulator 8.

  Here, the focal length of the condensing lenses 16 and 17 for condensing the light flux emitted from the rod integrator 15 is f1, and the focal length of the field lenses 4 and 5 on which the light flux that has passed through the polarization conversion element 3 is incident is f2. The F number (Fd) as an optical system for illuminating the spatial light modulator 8 is determined by the exit pupil diameter Y of the illumination optical system. There is a relationship of the following formula (3) between them.

Y = f1 / F # = f2 / Fd (3)
At this time, the main light fluxes of the light fluxes transmitted through the polarization conversion element 3 are all parallel to the optical axis.

  FIG. 4 is a side view showing the relationship between the light beam incident angle (F #) and the first internal reflection position L ′ in the rod integrator 15.

  Here, if the F-number for each of the RGB colors in the spatial light modulator is determined by taking the white balance of the display image, the incident angle of the light flux on the rod integrator 15 corresponding to each of the RGB colors depending on the aperture on the pupil. (F # ′) is determined.

From this incident angle F # ′ and the distance L ′ from the incident end surface to the position (K = 1) where the light beam is first reflected in the rod integrator, the following equations (4) and (5) are obtained. In addition, a reflection region L ′ corresponding to each incident F # ′ of the light beam incident on the rod integrator is obtained.

NA ′ = (1/2) F # ′ (5)
Therefore, by forming the spectral reflection film 15c having wavelength selectivity in the reflection region L ′, the pupil image in the illumination optical system can be filtered into a quadrangle.

  In this way, in order to filter the light flux having a desired angular distribution, it can be seen in which reflective region of the rod integrator 15 the spectral reflection film 15c having wavelength selectivity should be formed.

  FIG. 5 is a front view showing a region to be filtered in the pupil image when the spectral reflecting film 15c is formed on the four surfaces in the vicinity of the incident end surface 15a in the rod integrator 15. FIG.

  When the spectral reflection film 15c is formed on the four inner reflection surfaces from the incident end surface 15a to L ′ of the rod integrator 15, as shown in FIG. 5, the pupil image has a predetermined F number or less (a predetermined cone angle or more). ) Are all filtered.

  FIG. 6 is a front view showing a region to be filtered in the pupil image when the spectral reflection film 15c is formed on only one surface in the vicinity of the incident end surface 15a in the rod integrator 15. FIG.

  When the spectral reflection film 15c is formed on only one of the inner reflection surfaces from the incident end face 15a to L ′ of the rod integrator 15, as shown in FIG. 6, the pupil image has a predetermined F number or less (predetermined Only one side portion of the luminous flux (cone angle or greater) is filtered.

  Such filtering is useful when considering the polarization separation characteristics of the polarization beam splitter used in the image display device. That is, the polarization reflection film formed by tilting 45 ° with respect to the optical axis by the dielectric multilayer film usually deteriorates in polarization separation characteristics as the incident angle of the light beam approaches the normal to the polarization reflection film. is there. By filtering a light beam having a small incident angle with respect to the polarizing reflection film (close to the normal line), it is possible to efficiently adjust the white balance and contrast of the display image in the image display device.

  FIG. 7 is a front view showing a region to be filtered in the pupil image when the spectral reflection film 15c is formed on the four surfaces in the region away from the incident end surface 15a in the rod integrator 15. FIG.

  When it is desired to filter only a light beam having a specific incident angle distribution, a spectral reflection film 15c is formed in a region away from the incident end face 15a as shown in FIG. For example, when it is desired to filter a light beam having a light beam incident angle from Fθ to Fθ ′, the region Lθ and the region Lθ ′ in the rod integrator 15 where the light beam within this angular distribution is internally reflected for the first time are obtained, and these regions Lθ The spectral reflection film 15c may be formed in the region Lθ ′.

  By the way, the specific spectral reflection characteristic of the spectral reflection film 15c can be determined in accordance with the spectral emission characteristic of the light source in the image display device.

  FIG. 8 is a graph showing the spectral emission characteristics of a lamp serving as a light source.

  FIG. 9 is a graph showing an example of the spectral reflection characteristics of the spectral reflection film 15c.

  As the light source in the image display device described above, an ultra high pressure (UHP) mercury lamp is generally used. In the spectral emission characteristics of this ultra-high pressure mercury lamp, as shown in FIG. 8, strong emission lines exist in the green band of 550 nm band and the 585 nm band (orange), and in contrast, the red band of 600 nm. The amount of light in the above wavelength band is small.

  Therefore, the white balance adjustment of the display image is generally performed in accordance with the red band having a small amount of light. Therefore, as shown in FIG. 9, the spectral reflection characteristic of the spectral reflection film 15c of the rod integrator 15 may be a characteristic that reflects blue and red well and reduces only green (does not reflect).

  Note that the white balance adjustment varies depending on the usage of the projected image. If the subject is a movie (so-called “cinema mode”), warm reddish white (6500 ° K) with a low color temperature is preferred. On the other hand, for images in television broadcasting, bluish white (9000 ° K or higher) having a high color temperature is preferred. In such a case, optimal white balance adjustment can be performed by setting the spectral reflection characteristic of the spectral reflection film 15c according to each application.

It is a side view which shows the structure of the image display apparatus to which the illumination optical system which concerns on this invention is applied. It is a side view which shows the structure of the illumination optical system which concerns on this invention. FIG. 3 is a side view showing an optical system from a rod integrator to a spatial light modulation element in the illumination optical system. In the illumination optical system, it is a side view showing the relationship between the light beam incident angle and the first internal reflection position in the rod integrator. FIG. 4 is a front view showing a region to be filtered in a pupil image when spectral reflection films are formed on four surfaces in the vicinity of an incident end surface in a rod integrator in the illumination optical system. In the illumination optical system, when the spectral reflection film is formed on only one surface in the vicinity of the incident end surface in the rod integrator, it is a front view showing a region to be filtered in the pupil image. FIG. 4 is a front view showing a region that is filtered in a pupil image when spectral reflection films are formed on four surfaces in a region away from the incident end surface in the rod integrator in the illumination optical system. 4 is a graph illustrating spectral light emission characteristics of a lamp serving as a light source in the image display device. 4 is a graph showing an example of spectral reflection characteristics of a spectral reflection film formed on a rod integrator in the illumination optical system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Illumination optical system 8, 10, 11 Spatial light modulation element 13 Projection lens 14 Concave-surface reflective mirror 15 Rod integrator 16, 17 Condensing lens

Claims (2)

Illumination light including a visible light band from a light source is emitted as image light by light modulation using a spatial light modulation element, and is used for an image display device that projects an enlarged image light emitted from the spatial light modulation element. An illumination optical system,
Condensing means for condensing the luminous flux of the illumination light emitted from the light source;
When the light beam of the illumination light condensed by the light converging unit is incident from the incident end surface, the incident illumination light exits from the output end surface as a light beam of the illumination light that is internally reflected and uniform in illuminance. A rod integrator,
Irradiating means for irradiating a predetermined region of the spatial light modulator with the luminous flux emitted from the rod integrator;
With
Illumination characterized in that a spectral reflection film having spectral characteristics for reducing light in a predetermined wavelength band in the visible light band is formed on a side surface connecting the entrance end face and the exit end face of the rod integrator. Optical system. The spectral reflection film, an illumination optical system according to claim 1, characterized in that it is formed on each side over the entering-morphism end face or al a predetermined distance.

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