JP2007140014A - Optical low-pass filter, image display device, and projector - Google Patents

Abstract

An optical low-pass filter, an image display device, and a projector capable of ensuring sufficient brightness of a display image without a moiré of a display image are provided.
A light refracting surface provided on a low-pass filter has a predetermined angle α with respect to a substrate surface, and the density of the light refracting surface is measured from a reference point on a substrate. Since the light refracting surface 28f is arranged so as to form a distribution over the outer periphery 28y, a light refracting region that refracts light and a non-refractive region that transmits light without being refracted are formed on the substrate 28a. It becomes possible.
[Selection] Figure 4

Description

  The present invention relates to an optical low-pass filter, an image display device, and a projector.

  In recent years, the development of display devices has been remarkable. In particular, a projection display device (projector) such as a liquid crystal projector or a DLP (Digital Light Processing (trademark)) projector is capable of displaying on a large screen and is an effective display device for reproducing the reality and power of a display image. . In this field, the following proposals have been made to expand the luminance dynamic range.

  A basic configuration for expanding the luminance dynamic range in a projector is, for example, as disclosed in Patent Document 1, by modulating a light beam emitted from a light source with a first light modulation element to form a desired illumination light amount distribution, and The light with the distribution formed is imaged on the second light modulation element by an image forming unit such as a relay lens, and second light modulation is performed by the second light modulation element. In many cases, the first light modulation element and the second light modulation element have the same size and pixel arrangement, and in this case, the magnification of the relay lens is designed to be one.

  As the light modulation element, a transmission type modulation element having a pixel structure or a segment structure whose transmittance can be controlled independently and capable of controlling a two-dimensional transmittance distribution is used. A typical example is a liquid crystal light valve. A reflective modulation element may be used instead of the transmission modulation element, and a typical example thereof is a DMD (Digital Micromirror Device) element.

Consider a case where a light modulation element having a dark display transmittance of 0.2% and a bright display transmittance of 60% is used. With a single light modulation element, the luminance dynamic range is 60 / 0.2 = 300. Since the display device corresponds to optically arranging light modulation elements having a luminance dynamic range of 300 in series, theoretically, a luminance dynamic range of 300 × 300 = 90000 can be realized. The same idea holds for the number of gradations, and an 8-bit gradation light modulation element is optically arranged in series, whereby a gradation number exceeding 8 bits can be obtained.
The first light modulation element and the second light modulation element are separately driven by a modulation signal generated from the video signal.

  Incidentally, for example, as shown in FIG. 14, the transmissive liquid crystal light valve used as the first light modulation element 122 and the second light modulation element 125 is configured by wiring, black stripes, and the like around the pixel opening 123. It has a grid-shaped light shielding portion 124 that is regularly arranged. Therefore, the optical image of the light transmitted through the first light modulation element 122 has an image (bright part) of each pixel opening and an image (dark part) of the light shielding part.

  On the other hand, when the first light modulation element, the second light modulation element, and the relay lens are mechanically displaced, or when the relay lens that forms the imaging unit has an imaging error, There may be a design error. For this reason, when the light having the optical image as described above is imaged by the imaging unit and applied to the second light modulation element, the bright part image modulated by the first light modulation element is the second light. An image may be formed at a position shifted from the pixel opening of the modulation element.

  For example, FIG. 15 shows a state of the second light modulation element 125 when the magnification of the relay lens is smaller than 1 due to an imaging error. The optical image 126 by the light from the first light modulation element 122 is reduced toward the center of the second light modulation element 125 by the relay lens. At this time, the deviation from the pixel opening 123 is larger on the outer peripheral side than on the central side of the optical image 126.

  FIG. 16 shows the state of the second light modulation element 125 when the magnification of the relay lens is larger than 1 due to an imaging error. The optical image by the light from the first light modulation element 122 spreads toward the outer periphery of the second light modulation element 125 by the relay lens. Also in this case, the deviation from the pixel opening 123 is larger on the outer peripheral side than on the central side of the optical image 126.

  In both cases of FIGS. 15 and 16, the optical image 126 is displaced and protrudes from the light-shielding portion 124, so that it does not contribute to the display image. For this reason, bright and dark moiré occurs, and there is a problem that image quality deteriorates.

On the other hand, an optical low-pass filter in which a light refracting surface that refracts a part of light from the first light modulation element is provided on the entire surface of the low-pass filter is considered. The optical low-pass filter is used to disperse and equalize the light for each pixel, and the moire can be eliminated by reducing the light / dark distribution due to the deviation between the optical image of the light and the pixel in the second light modulation element. Is.
Japanese Patent Laid-Open No. 2001-1000068

However, when the above-described optical low-pass filter is used, the light from the first light modulation element is dispersed for all the pixels, so that the deviation of the imaging position, for example, near the optical axis, is relatively small and inherently disperses the light. Light will be dispersed even in parts where necessity is low. For this reason, although there is no moire, there is a problem that sufficient brightness cannot be secured at the center of the display image 207.
In view of the circumstances as described above, an object of the present invention is to provide an optical low-pass filter, an image display device, and a projector that are free from moiré of a display image and can sufficiently secure the brightness of the display image. is there.

  In order to achieve the above object, an optical low-pass filter according to the present invention is provided on a substrate capable of transmitting light, and has a predetermined angle with respect to the substrate surface on the substrate, and transmits the substrate. A plurality of light refracting surfaces that refract part of the light, and at least one of the density of the light refracting surfaces and the predetermined angle extends from a reference point on the center side on the substrate to the outer periphery of the substrate. The plurality of light refracting surfaces are arranged so as to have a predetermined distribution.

  In the present invention, the light refracting surface is provided on the substrate so as to have a predetermined angle with respect to the substrate surface, and at least one of the density and the predetermined angle of the light refracting surface is the substrate. Since it is arranged so as to have a predetermined distribution from the upper reference point to the outer periphery of the substrate, a region where light is refracted and separated and uniformed and a region where light is transmitted without being refracted are formed on the substrate. It becomes possible to do.

  Here, the “density of light refracting surfaces” means the number of light refracting surfaces per unit area on the substrate surface or the number of light refracting surfaces per unit length in the radial direction around the reference point. is there. Therefore, for example, by reducing the density of the light refracting surface near the reference point of the substrate and increasing the density of the light refracting surface near the outer periphery of the substrate, the light incident on the outer peripheral side of the substrate is refracted and uniformed. It is also possible to transmit the light incident on the central portion of the light as it is without being refracted.

Further, it is preferable that the predetermined angle gradually increases from the reference point to the outer periphery.
According to the present invention, since the predetermined angle gradually increases from the reference point on the substrate to the outer periphery of the substrate, the angle of light refraction by the photorefractive surface increases as it approaches the outer periphery of the substrate.
Here, for example, in an image display device having a first light modulation element and a second light modulation element having the same dimensions and a relay lens provided between them, the error is included in the magnification of the relay lens. The optical image irradiated to the two light modulation elements is enlarged / reduced, and a deviation occurs between the optical image and the second light modulation element. The effect of deviation due to the enlargement / reduction of the optical image is greater toward the outside of the second light modulation element. Therefore, when the optical low-pass filter according to the present invention is used in the image display apparatus, the deviation can be accurately suppressed by refracting the outside light having a large influence of the deviation more greatly.

The plurality of light refracting surfaces preferably refract light transmitted through the substrate in a direction from the reference point toward the outer periphery.
According to the present invention, since the light refracting surface refracts the light transmitted through the substrate in the direction from the reference point toward the outer periphery, for example, in the above image display device, the magnification is less than 1 due to the error of the relay lens. In such a case, it is effective to use the optical low-pass filter according to the present invention. That is, light incident on a position close to the outer periphery of the optical low-pass filter is refracted outward, so that the optical image can be prevented from being reduced toward the center of the second light modulation element.

The plurality of light refracting surfaces preferably refract light transmitted through the substrate in a direction from the outer periphery toward the reference point.
According to the present invention, since the light refracting surface refracts the light transmitted through the substrate in the direction from the outer periphery toward the reference point, for example, in the above image display device, the magnification exceeds 1 × due to the error of the relay lens. In such a case, it is effective to use the optical low-pass filter according to the present invention. That is, since the light incident on the position near the outer periphery of the optical low-pass filter is refracted inward, it is possible to suppress the optical image from being expanded to the outer periphery side of the second light modulation element.

Moreover, it is preferable that the plurality of light refracting surfaces are arranged on the substrate at arbitrary intervals.
When a plurality of light refracting surfaces are arranged at a constant interval, interference may occur when light is refracted. When interference occurs, interference fringes are formed in the light emitted from the substrate, and the optical image is disturbed. According to the present invention, since the plurality of light refracting surfaces are arranged on the substrate at an arbitrary interval, it is possible to avoid interference with light emitted from the substrate.

The plurality of light refracting surfaces are preferably provided on a plurality of concentric circles centered on the reference point.
When the light incident on the optical low-pass filter according to the present invention has an optical shift via an optical member such as a relay lens, the shift is influenced by the shape of the relay lens and is generated concentrically. There is a high possibility. In the present invention, since the photorefractive surface is provided on a plurality of concentric circles centered on the reference point, the deviation generated in the concentric circles can be accurately suppressed.

  An image display device according to the present invention includes a light source, a first light modulation element that modulates light from the light source, a second light modulation element that modulates light from the first light modulation element, and the first light. An imaging unit that is provided between the modulation element and the second light modulation element and forms an image of light from the first light modulation element on the second light modulation element; the first light modulation element; And the optical low-pass filter provided between the two light modulation elements, the optical low-pass filter being arranged so that the reference point is located on the optical axis of the light from the light source It is characterized by being.

  In the present invention, since the optical low-pass filter is provided between the first light modulation element and the second light modulation element, even if there is an error in the imaging magnification of the imaging unit, For example, light can be transmitted without being refracted at a site where the shift of the imaging position by the imaging unit is relatively small, such as near the optical axis. Further, for example, in a portion where the displacement of the coupling position is large, such as light at a position away from the optical axis, the light can be refracted and made uniform. As a result, an image display device can be obtained in which there is no moiré of the display image and the brightness of the display image can be sufficiently secured.

A projector according to the present invention includes the above-described image display device.
In the present invention, since the image display device that does not have moiré of the display image and can sufficiently ensure the brightness of the display image is provided, a projector with a high display characteristic and a bright display can be obtained.

[First Embodiment]
A first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing an internal configuration of a projector 1 as a projector.
The projector 1 is mainly composed of an image display device 2 and a projection lens 3.
The image display device 2 roughly includes a light source unit 4, a uniform illumination unit 5, a color modulation unit 6, a relay lens 27, a liquid crystal light valve 25, and a projection lens 3.
The light source unit 4 is mainly composed of a lamp 11 and a reflector 12. The lamp 11 is a light source of the image display device 2 and eventually the projector 1, and for example, a high-pressure mercury lamp that emits white light is used. The reflector 12 is a reflecting member that reflects the white light, and is arranged so that, for example, the white light from the lamp 11 travels in a direction in which it enters the uniform illumination unit 5.

  The uniform illumination unit 5 is mainly composed of fly-eye lenses 13 and 14, a polarization conversion element 15, and a condenser lens 16. The fly eye lens 13 on the lamp 11 side forms a plurality of secondary light source images. The fly-eye lens 14 and the condenser lens 16 on the color modulation unit 6 side superimpose the secondary light source image formed by the fly-eye lens 13 on the liquid crystal light valves 22, 23 and 24.

The color modulation unit 6 (please set the range of the color modulation unit 6 in FIG. 1 to the dichroic prism 26), dichroic mirrors 17, 18, reflection mirrors 19, 20, 21, liquid crystal light valves 22, 23, 24, The dichroic prism 26 is mainly used. The dichroic mirrors 17 and 18 are color separation means for separating light from the light source into a plurality of color lights. The dichroic mirror 17, out of the white light emitted from the lamp 11 transmits a red light L _R, and reflects the blue light L _B and the green light L _G. The dichroic mirror 18 reflects the green light _{L G,} which transmits the blue light _{L B.}
Reflecting mirror 19 reflects the red light L _R the dichroic prism 26 side. Reflecting mirrors 20 and 21, the blue light _{L B} is reflected at a right angle, respectively, for guiding the dichroic prism 26.

Liquid crystal light valve 22 is a color modulation light valves for modulating the blue light L _B to the image light based on the color signal. Liquid crystal light valve 23 is a color modulation light valves for modulating the green light L _G to the image light based on the color signal. The liquid crystal light valve 24 is a color modulation light valve that modulates red light _LR into image light based on a color signal. In the following description, the liquid crystal light valves 22 to 24 (first light modulation elements) are referred to as color modulation light valves 22 to 24, and the liquid crystal light valve 25 (second light modulation element) is referred to as a luminance modulation light valve 25. There are things to do.

  Each of the liquid crystal light valves 22, 23, 24, and 25 has the same dimensions, for example, about 4.6 square centimeters (about 0.7 square inches). It is configured. Further, the number of pixels formed in the liquid crystal light valves 22, 23, 24, and 25 is the same, and the arrangement and pitch of the pixels are also the same.

The dichroic prism (color combining member) 26 is formed by bonding four right-angle prisms made of a transparent material such as glass or resin. On the inner surface, and a dielectric multilayer film 26b which reflects the dielectric multilayer film 26a and the red light L _R reflected blue light L _B is formed in a cross shape. Further, the dielectric multilayer film 26a, 26b are both designed to transmit the green light _{L G.} Three color lights are synthesized by the dielectric multilayer films 26a and 26b, and light (image light) representing a color image is formed.

  The relay lens (imaging unit) 27 is an optical system that forms an image of the color modulation liquid crystal light valves 22, 23, 24 combined by the dichroic prism 26 on the luminance modulation light valve 25. , 23, 24 and the luminance modulation light valve 25, here, between the dichroic prism 26 and the liquid crystal light valve 25.

Liquid crystal light valve 25, based on the luminance signal, modulates the red light L _R, the luminance of the synthesized light of the green light L _G and the blue light L _B.

  In the present embodiment, since the color modulation light valves 22, 23, 24 and the luminance modulation light valve 25 have the same dimensions, the ideal magnification of the relay lens 27 is 1. In practice, errors often occur due to the magnification of each lens in the relay lens 27. In the present embodiment, a case where the magnification is less than 1 due to an error of the relay lens 27 will be described.

  Next, in order to make the effect of the optical low-pass filter (hereinafter simply referred to as “low-pass filter”) 28 in the present embodiment easy to understand, a problem when it is not provided will be described with reference to FIG. When the magnification of the relay lens 27 is less than 1, as shown in FIG. 2A, the image of the pixel opening 123 of the color modulation light valve is shifted from the pixel opening of the corresponding pixel of the luminance modulation light valve. It will form an image. Specifically, along the radial direction of the relay lens, the image is formed at a position shifted from the optical axis from the position where the image is originally formed (the position where the image is formed when the magnification of the relay lens 27 is 1). . Then, a part of the opening image is blocked by the light blocking portion 124 of the luminance modulation light valve, so that the amount of transmitted light is reduced. By the way, the amount of deviation of the aperture image is not uniform over the luminance modulation light valve surface, but increases as the distance from the optical axis increases. As a result, moire fringes having a regular transmitted light amount distribution = brightness / darkness distribution as shown in FIG. 2B are generated in the luminance modulation light valve surface, and the image quality of the display image is significantly lowered.

  An optical low-pass filter (hereinafter simply referred to as “low-pass filter”) 28 is provided between the color modulation light valves 22, 23, and 24 and the luminance modulation light valve 25, here, between the dichroic prism 26 and the relay lens 27. Is provided. The low-pass filter 28 is a filter that transmits the combined light emitted from the dichroic prism 26.

FIG. 3 is a view of the low-pass filter 28 when viewed from the dichroic prism 26 side. FIG. 4 is a diagram showing a configuration along the section AA in FIG.
As shown in FIG. 3, the low-pass filter 28 is mainly composed of a substrate 28a formed of a material that can transmit light, such as glass, quartz, or plastic. The low-pass filter 28 is arranged so that a reference point O provided at the center of the substrate 28a (for example, the intersection of diagonal lines) coincides with the optical axis of the combined light emitted from the dichroic prism 26.

  The size of the substrate 28a is larger than that of the liquid crystal light valve, for example, in order to prevent the luminous flux emitted from the liquid crystal light valve from being scattered, that is, to ensure a dimension that causes no light loss. A light refracting region 28b that refracts and transmits a part of the combined light emitted from the dichroic prism 26 (a region outside the broken line portion in FIG. 2) and a non-refractive region 28c that transmits the combined light without refracting it ( In FIG. 2, it is partitioned into a region inside the broken line portion. The photorefractive region 28b is provided in a region having a predetermined length or more in the radial direction with the reference point O as the center.

The light refraction region 28b is provided with a prism portion 28d and a flat portion 28e sandwiched between the prism portions 28d.
For example, a plurality of prism portions 28d are formed of a light transmissive material similar to the material constituting the substrate 28a, and a plurality of prism portions 28d are provided on concentric circles centered on the reference point O as shown in FIG. They are arranged at predetermined intervals in the radial direction of the concentric circles. Note that FIG. 2 shows a state in which the prism portion 28d is provided on five concentric circles for the sake of simplicity, but actually, the prism portion is within the cross section of the light beam emitted from one point of the liquid crystal light valve. 28d is provided so as to have a density of about 8.

  The cross-sectional shape of the prism portion 28d is a shape protruding in a sawtooth shape on the substrate 28a as shown in FIG. Specifically, it has a light refracting surface 28f provided at a predetermined angle α with respect to the substrate surface 28z, and a side surface 28g provided perpendicular to the substrate surface 28z. The light refracting surface 28f is inclined such that the height from the substrate surface 28z gradually increases from the reference point O (see FIG. 3) to the outer periphery 28y of the substrate 28a.

Returning to FIG. 3, the non-refractive region 28c is not provided with the optical prism portion 28d, and is a flat region like the flat surface 28e of the light refracting region 28b. Therefore, in the non-refractive region 28c, the density of the optical prism portion 28d, that is, the density of the light refracting surface 28f is zero.
Thus, the density distribution of the light refracting surface 28f is formed between the light refracting region 28b and the non-refracting region 28c.

Next, the optical path of light that passes through the low-pass filter 28 will be described.
As shown in FIG. 4, the dichroic prism 26 combined light _{L 1} emitted from enters the substrate 28a, transmitted through the substrate 28a, the outer peripheral 28y side in the light refracting surface 28f of the prism portion 28d (the right side in the drawing) It is refracted and ejected. In this way, the light traveling toward the outer periphery 28y side of the substrate 28a is refracted further toward the outer periphery 28y side.
Dichroic combined light L ₂ emitted from the prism 26 is incident on the substrate 28a, and transmitted through the substrate 28a, is directly emitted without being refracted at the flat portion 28e.

The dichroic prism 26 combined light L ₃ emitted from enters the substrate 28a, transmitted through the substrate 28a, and is emitted is refracted on the outer circumferential 28y side (right side in the drawing) in the light refracting surface 28f of the prism portion 28d . As described above, the light traveling toward the reference point O side of the substrate 28a is also refracted toward the outer periphery 28y.

In addition, what is shown with a broken line in FIG. 4 is an optical path of the synthetic lights L _{1 to} L ₃ when the light refracting surface 28 f is not provided.
The non-refractive region 28c is not provided with the prism portion 28d, and the combined light incident on the non-refractive region 28c is emitted without being refracted (not shown).

Next, an optical image of the combined light that has passed through the low-pass filter 28 will be described.
Of the combined light emitted from one point of the color modulation light valve, the combined light transmitted through the non-refracting region 28c that transmits the combined light without being refracted is shown in FIG. 5A as a relay lens (in FIG. 5). (Shown as a single lens) to form an image on the luminance modulation light valve at one point, but the combined light transmitted through the light refraction region 28b forms an image at a plurality of points at different positions as shown in FIG. Become. That is, the pixel openings of the color modulation light valve are shifted in position and imaged at a plurality of locations.
As a result, as shown in FIG. 6 (a), the secondary aperture image in which the image size spreads outward in the radial direction (28y side in FIG. 4) compared to the original (color modulation light valve) pixel aperture image. Can be imaged on a brightness modulated liquid crystal light valve. As a result, as shown in FIG. 6B, the amount of light blocked by the light shielding portion (of the luminance modulation light valve) is reduced as compared with the case where there is no low-pass filter.
Further, since the height of the light refracting surface 28f from the substrate surface 28z is inclined so as to gradually increase from the reference point O (see FIG. 3) to the outer periphery 28y of the substrate 28a, the light refracting surface. The area ratio of 28f increases. As a result, the light intensity of the aperture image spread by the low-pass filter in FIG. 6A at the outer peripheral portion where the displacement between the pixel aperture portion of the color modulation light valve and the pixel aperture position of the luminance modulation light valve becomes larger. Becomes stronger toward the outer periphery, and a large light loss is reduced when there is no low-pass filter. As a result, the transmitted light amount distribution in the luminance modulation light valve surface is leveled, and moire fringes are not noticeable.

  Thus, according to the present embodiment, the light refracting surface 28f provided in the low-pass filter 28 is provided so as to have a predetermined angle α with respect to the substrate surface 28z, and the density of the light refracting surface 28f is Since the light refracting surface 28f is arranged so as to form a distribution from the reference point O on the substrate 28a to the outer periphery 28y, the light refracting region 28b that refracts light and a non-refracting light that is transmitted without being refracted. The refractive region 28c can be formed on the substrate 28a.

  The low-pass filter 28 is provided between the color modulation light valves 22, 23, 24 and the luminance modulation light valve 25, and is arranged so that the reference point O is located on the optical axis of the combined light. Therefore, even if there is an error in the imaging magnification of the relay lens 27, light is transmitted without being refracted at a portion where the displacement of the imaging position by the relay lens 27 is relatively small, for example, near the optical axis. be able to. In addition, at a portion where the displacement of the coupling position is large, such as a position away from the optical axis, light loss can be reduced by refracting light. Thereby, there is no moire of the display image projected on the projection surface of the screen, and the brightness of the display image can be sufficiently secured.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. Similar to the first embodiment, in the following drawings, the scale is appropriately changed to make each member a recognizable size. In the present embodiment, since the configuration of the low-pass filter is different from that of the first embodiment, this point will be mainly described. In the present embodiment, unlike the first embodiment, a case where the magnification exceeds 1 due to an error of the relay lens will be described.

FIG. 7 is a diagram schematically showing the configuration of the low-pass filter 128.
As in the first embodiment, the low-pass filter 128 is mainly configured by a substrate 128a formed of a material that can transmit light, such as glass, quartz, or plastic. Since the configuration of the low-pass filter 128 in plan view is the same as that of the first embodiment, illustration and description thereof are omitted.

In the light refraction region of the low-pass filter 128, a prism portion 28d and a flat portion 28e sandwiched between the prism portions 28d are provided.
The cross-sectional shape of the prism portion 128d is a shape that protrudes in a sawtooth shape on the substrate 128a, as shown in FIG. Specifically, it has a light refracting surface 128f provided at a predetermined angle β with respect to the substrate surface 128z, and a side surface 128g provided perpendicular to the substrate surface 128z. In the present embodiment, the light refracting surface 128f is inclined so that the height from the substrate surface 128z gradually increases from the reference point side to the outer periphery 128y side. In this respect, the direction is opposite to that of the first embodiment.

Next, the optical path of light that passes through the low-pass filter 128 will be described.
As shown in FIG. 6, the dichroic combined light _{L 4} emitted from the prism 26 is incident on the substrate 128a, it passes through the substrate 128a, a reference point side in the optical refracting surfaces 128f of the prism portion 128d (the left side in the drawing) It is refracted and ejected. In this way, the light traveling toward the reference point side of the substrate 128a is refracted further toward the reference point side.
Dichroic emitted from click prism 26 combined light _{L 5} represents incident on the substrate 128a, passes through the substrate 128a, is directly emitted without being refracted at the flat portion 128e.

The dichroic prism 26 combined light _{L 6} emitted from enters the substrate 128a, it passes through the substrate 128a, and is emitted is refracted to the reference point side in the optical refracting surfaces 128f of the prism portion 128d. In this way, the light traveling toward the outer periphery 128y of the substrate 128a is also refracted toward the reference point.
In addition, what is shown with a broken line in FIG. 6 is an optical path of the synthetic lights L _{4 to} L ₆ when the light refracting surface 128 f is not provided.

  As a result, a secondary aperture image in which the image size spreads inward in the radial direction (reference point side) compared to the original (color modulation light valve) pixel aperture image is formed on the luminance modulation liquid crystal light valve. be able to. As a result, the amount of light blocked by the light shielding portion (of the luminance modulation light valve) is reduced as compared with the case where there is no low-pass filter. Further, since the light refracting surface 128f is inclined so that the height from the substrate surface 128z gradually increases from the reference point side to the outer periphery 128y side, the area ratio of the light refracting surface 128f increases. . As a result, the light intensity of the opening image spread by the low-pass filter becomes stronger at the outer peripheral portion where the displacement between the pixel opening portion of the color modulation light valve and the pixel opening position of the luminance modulation light valve becomes larger. Thus, a large light loss that occurs when there is no low-pass filter is reduced. As a result, the transmitted light amount distribution in the luminance modulation light valve surface is leveled, and moire fringes are not noticeable.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. Similar to the first embodiment, in the following drawings, the scale is appropriately changed to make each member a recognizable size. In the present embodiment, since the configuration of the low-pass filter is different from that of the first embodiment, this point will be mainly described. In this embodiment, a case where the magnification is less than 1 due to an error of the relay lens (similar to the first embodiment) will be described.

FIG. 8 is a diagram schematically showing the configuration of the low-pass filter 228.
The low-pass filter 228 has a light refracting region and a non-refractive region, and a prism portion 228d and a flat portion 228e sandwiched between the prism portions 228d are provided in the light refracting region.
The cross-sectional shape of the prism portion 228d is a shape protruding in a sawtooth shape on the substrate 228a, as shown in FIG. Specifically, it has a light refracting surface 228f provided to have a predetermined angle α _{1 to} α ₄ with respect to the substrate surface 228z, and a side surface 228g provided perpendicular to the substrate surface 228z. In the present embodiment, the angles α _{1 to} α ₄ of the light refracting surface 228f are gradually increased from the reference point side of the substrate 228a to the outer periphery 228y side. This is different from the first embodiment.

Next, the optical path of light that passes through the low-pass filter 228 will be described.
As shown in FIG. 7, the combined lights L _{11 to} L ₁₄ emitted from the dichroic prism 26 are incident on the substrate 228a, pass through the substrate 228a, and are on the outer periphery 228y side (see FIG. Middle right) is refracted and ejected. The refraction angle at this time corresponds to the angles of the light refracting surfaces α _{1 to} α ₄ . Specifically, the angle of refraction has the smallest of the combined light _{L 11,} then the refraction angle in the order of _{L 12, L 13, L 14} is larger.

  As described above, the influence of the shift due to the enlargement / reduction of the optical image by the relay lens is larger toward the outer peripheral side of the luminance modulation light valve 25. Therefore, when the low-pass filter 228 according to the present embodiment is used in the image display device, the light on the outside of the luminance modulation light valve 25 having a large influence of deviation is refracted more greatly, thereby spreading the secondary aperture image. It is possible to further widen and accurately suppress the transmitted light amount distribution caused by the deviation.

The technical scope of the present invention is not limited to the above-described embodiment, and appropriate modifications can be made without departing from the spirit of the present invention.
For example, as shown in FIG. 8, a plurality of prism portions 28, that is, a plurality of light refracting surfaces 28f may be arranged on the substrate 28a at an arbitrary interval.
When the plurality of light refracting surfaces 28f are arranged at a constant interval, interference may occur when light is refracted. When interference occurs, interference fringes are formed in the light emitted from the low-pass filter 28, and the optical image is disturbed. According to the above configuration, since the light refracting surfaces 28f are arranged on the substrate 28a at an arbitrary interval, it is possible to avoid the occurrence of interference in the light emitted from the substrate 28a.

  Further, as shown in FIG. 9, the photorefractive region 28b provided on the substrate 28a is configured to be provided in a region having a predetermined length range in the radial direction centered on the reference point O, and the first embodiment and Similarly, it is preferable that the light is refracted toward the outer periphery 28y side of the substrate 28a by the light refraction region 28b.

  This configuration is related to the distortion of the relay lens 27. FIG. 10 is a graph showing the strength of distortion of the relay lens 27. The vertical axis indicates the distance from the optical axis of the optical image, and the horizontal axis indicates the strength of distortion. The (+) side of the horizontal axis indicates the strength of distortion of the optical image into a barrel shape (thickening), and the (−) side indicates the strength of distortion of the optical image into a pincushion type (thinning). Show.

  As shown in FIG. 10, the intensity of the pincushion type distortion of the optical image increases as the distance from the optical axis increases, and the pincushion type distortion of the optical image becomes the strongest at a position away from the optical axis by a predetermined distance. . As the distance further increases, the distortion gradually weakens. When the optical image is distorted due to the distortion, a pixel image of the color modulation light valve and a pixel of the luminance modulation light valve are displaced when being formed on the luminance modulation light valve 25.

According to the present embodiment, the optical refraction region 28b is provided at a position where the distortion is particularly strong in the optical image, and the light incident on the light refraction region 28b is refracted toward the outer periphery 28y. Therefore, such pin cushion type distortion of the relay lens 27 can be corrected.
In this case, the range of the photorefractive region 28b on the substrate 28a is preferably changed as appropriate depending on the strength and type of distortion of the relay lens 27.

Further, the prism portion 28d is not formed concentrically, but may be formed in a rectangular shape according to the shape of the outer periphery 28y of the substrate 28a, for example, as shown in FIG.
Further, as shown in FIG. 12, the prism portion 28d may be formed in the light refraction region 28b without any gap, and the flat portion 28e may not be formed. In this case, as shown in the figure, it is preferable that the angles α _{11 to} α ₁₅ of the light refracting surface 28f are formed so as to gradually increase from the reference point side to the outer periphery 28y side of the substrate 28a.

  In each of the above embodiments, an example of a front projector that projects on a separately provided screen 7 is shown as a projector. However, the projector can also be used for a rear projector that includes a screen and a housing.

1 is a diagram showing a configuration of a projector according to a first embodiment of the invention. The figure which shows a mode when not using a low-pass filter. The figure which shows the planar structure of the low-pass filter of the projector which concerns on this embodiment. FIG. 3 is a diagram illustrating a cross-sectional configuration of a low-pass filter of the projector according to the present embodiment. The figure which shows the optical image of the light which permeate | transmitted the low-pass filter. The figure which shows the optical image of the light which permeate | transmitted the relay lens. The figure which shows the cross-sectional structure of the low-pass filter which concerns on 2nd Embodiment of this invention. The figure which shows the cross-sectional structure of the low-pass filter which concerns on 3rd Embodiment of this invention. The figure which shows the other cross-sectional structure of the low-pass filter which concerns on this invention. The figure which shows the other plane structure of the low-pass filter which concerns on this invention. The graph which showed the distortion characteristic of the relay lens. The figure which shows the other plane structure of the low-pass filter which concerns on this invention. The figure which shows the other cross-sectional structure of the low-pass filter which concerns on this invention. The figure which shows the planar structure of a liquid crystal light valve. The figure which shows a mode that an optical image is irradiated to a luminance modulation light valve. The figure which shows a mode that an optical image is irradiated to a luminance modulation light valve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Projector 2 ... Image display apparatus 4 ... Light source part 6 ... Color modulation part 22-25 ... Liquid crystal light valve 27 ... Relay lens 28 ... Optical low-pass filter

Claims (8)

A substrate capable of transmitting light;
A plurality of light refracting surfaces provided on the substrate so as to have a predetermined angle with respect to the substrate surface and refracting a part of the light transmitted through the substrate;
The plurality of light refracting surfaces are arranged such that at least one of the density of the light refracting surfaces and the predetermined angle has a predetermined distribution from a reference point on the center side on the substrate to the outer periphery of the substrate. An optical low-pass filter characterized by that. The optical low-pass filter according to claim 1, wherein the predetermined angle gradually increases from the reference point to the outer periphery.   3. The optical low-pass filter according to claim 1, wherein the plurality of light refracting surfaces refract light transmitted through the substrate in a direction from the reference point toward the outer periphery. 4.   3. The optical low-pass filter according to claim 1, wherein the plurality of light refracting surfaces refract light transmitted through the substrate in a direction from the outer periphery toward the reference point. 4. The optical low-pass filter according to any one of claims 1 to 4, wherein the plurality of light refracting surfaces are arranged on the substrate at arbitrary intervals. The optical low-pass filter according to any one of claims 1 to 5, wherein the plurality of light refracting surfaces are provided on a plurality of concentric circles centered on the reference point. A light source;
A first light modulation element for modulating light from the light source;
A second light modulation element that modulates light from the first light modulation element;
An imaging unit that is provided between the first light modulation element and the second light modulation element and forms an image of the light from the first light modulation element on the second light modulation element;
The optical low-pass filter according to any one of claims 1 to 6, provided between the first light modulation element and the second light modulation element,
The image display device, wherein the optical low-pass filter is arranged such that the reference point is located on an optical axis of light from the light source. A projector comprising the image display device according to claim 7.

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