JP4860307B2 - Image display device - Google Patents

Description

  The present invention relates to an image display device, and in particular, for observing an image by enlarging a modulation element having a plurality of pixels capable of controlling light according to image information with a lens or the like, which can be applied to an electronic display device such as a projection display. The present invention relates to an image display apparatus.

Conventionally, as a liquid crystal projector device that projects an image modulated using a modulation element on a screen, three single-color lights such as red (R) light, green (G) light, and blue (B) light are respectively modulated. There is known an apparatus configured to perform modulation with the above. In a liquid crystal projector device, it is necessary to increase the definition in order to increase the resolution of an image projected on a screen. For this purpose, an increase in the number of pixels of the modulation element, a multi-screen configuration with a plurality of projector devices, and a double arrangement in which the pixels for green light are shifted by a half-pixel pitch are considered. However, when the number of pixels of the modulation element is increased, in the transmissive liquid crystal element, the aperture ratio of the pixel is lowered and a problem such as insufficient projection luminance occurs. Also, in the multi-screen configuration, it is difficult to connect each screen smoothly. Furthermore, the arrangement of double the number of pixels at a half pixel pitch of the green light pixels forms an image of light in all the RGB bands on the screen with one projection lens, so the chromatic aberration of magnification of the projection lens Therefore, the images for each color are not exactly the same size, and a high-resolution image cannot be obtained. In view of this, Japanese Patent Application Laid-Open No. H10-228561 proposes that image shift is performed by a reflective optical path polarizing element such as a mirror disposed in the projection optical path.
Japanese Patent Laid-Open No. 2004-070365

  However, because of the arrangement of the reflective optical path deflecting element, it is necessary to increase the distance between the projection lens and the panel (lens back), and the degree of layout freedom is limited. Furthermore, a space for the parallel plate element is required separately, and it is necessary to lengthen the back focus of the projection lens. In addition, since the reflecting mirror is formed inside the lens system, it becomes a special projection lens, and a general-purpose projection lens cannot be used. It is also necessary to review the layout of the conventional engine optical system.

  The present invention is intended to solve these problems, and an image display apparatus that can increase the pixel density and increase the resolution of a display image with a simple configuration and without changing the optical system layout. The purpose is to provide.

  In order to solve the above problems, an image display device according to the present invention is directed to an illumination light source, a modulation element that displays an image, a projection optical system, illumination light from the illumination light source to the modulation element, and the projection optical system. And an optical path separation element for separating the imaging light. The image forming apparatus of the present invention is characterized in that it has a displacement means for displacing the optical path separation element. Therefore, an optical path shift function can be added without changing the optical path length of the projection system, and the number of pixels can be increased without impairing the layout of the optical system.

Further , since the optical path separation element is constituted by a polarization separation splitter, it can be applied as it is to an optical system using a polarization beam splitter, and high definition can be achieved.

  Furthermore, since the optical path separation element is a flat type polarization separation splitter, it can be displaced at high speed, and a high quality image can be obtained.

  In addition, the flat plate type polarization separation splitter allows the optical path to be shifted even with a slight displacement by reflecting the imaged light on the polarization separation function surface without passing it through the substrate. An optical path shift can be caused without degrading the function.

  The image forming apparatus of the present invention has a displacement means for displacing the optical path separation element. Therefore, an optical path shift function can be added without changing the optical path length of the projection system, and the number of pixels can be increased without impairing the layout of the optical system.

  FIG. 1 is a schematic view showing the principle of the image display apparatus of the present invention. The operation of the optical path shift will be described with reference to FIG. A specific rotation angle of the polarization beam splitter 11 is estimated. In the case where the incident light is transmitted light, the shift amount d is determined as θ within the medium having the refractive index n ′ when the distance t of the medium having the refractive index n ′ is incident at an incident angle θ from the medium having the refractive index n. If it proceeds at an angle of ', it is given by the following equation from Snell's law n · sin θ = n' · sin θ '.

Shift amount d = t × tan θ ′
= T × tan (asin (1 / n ′ × sin θ)) (1)
However, the distance traveled by the medium having n = 1 and the refractive index n ′ is substantially equal to the prism thickness.

  Here, in FIG. 2, when the prism thickness of the polarizing beam splitter 11 of FIG. 1 is t = 30 mm, 40 mm, 50 mm, and the refractive index is 1.54, the rotation angle and the optical path shift amount are obtained from Equation (1). The results are shown. FIG. 3 shows the result of obtaining the optical path shift amount when the rotation angle is changed with the prism thickness of the polarizing beam splitter 11 of FIG. 1 fixed at t = 40 mm. As can be seen from FIGS. 2 and 3, the optical path of several μm can be shifted with a prism thickness of about t = 40 mm and an angle of displacement of several tens of seconds. For example, when the pixel pitch is 14 μm, in order to obtain a shift amount of 7 μm of the half pitch, it is understood that t = 40 mm and the rotation angle should be 55.6 seconds. The same relationship is also obtained when the light is reflected inside the prism. If the pixel pitch is about ½, it is sufficient to cause an angular displacement of several tens of seconds to several minutes, so that the optical path is not affected without affecting the original optical path separation function and the polarization characteristics of the polarization beam splitter. Shifting can be performed. Also, with respect to the illumination light, the illumination area on the panel surface is shifted, but since the value is at the pixel level, the illumination uniformity is not impaired. Thus, the optical path can be shifted by the thickness of the polarizing beam splitter and the displacement of the polarizing beam splitter. Furthermore, a desired optical path can be shifted by a minute displacement. In addition, although the example of the prism type beam splitter was given, the same applies to a flat plate.

  Using the principle of such a shift function, the present invention is characterized in that the shift function of the present invention is incorporated in an optical path separation image forming system of an image display device.

  As the illumination light source, a halogen lamp, a xenon lamp, a metal halide lamp, an ultrahigh pressure mercury lamp, or the like is used. In addition, monochromatic light such as an LED lamp or LD is also used. In recent years, white LEDs with high luminance have appeared and may be applied as the illumination light source of the present invention. An illumination optical system may be mounted so that high illumination efficiency can be obtained. Specific examples of the illumination optical system include a reflector (integrated with the light source) arranged near the light source, such as an ultra-high pressure mercury lamp, and an integrator optical system (direct light beam reflected by this reflector). An illumination optical system may be mounted so that an illumination distribution can be obtained uniformly on the panel surface by means of illuminance equalization called a fly-eye lens pair. When the light valve, which is the modulation element, is a reflection type, although not shown, it is preferable to perform efficient illumination using a polarization conversion element or the like.

  As described above, in the optical path shift method and apparatus performed by the conventional mirror, it is necessary to dispose these deflecting elements between the projection lens and the panel, and the space and the like thereof are necessary. However, by adopting the configuration of the present invention, an optical path shift function can be added without changing the optical path length. Further, the layout of the optical system caused by the addition of the optical path shifting function is not impaired.

  FIG. 4 is a schematic diagram showing the configuration of the image display apparatus according to the first embodiment of the present invention. The image display apparatus according to this embodiment shown in the figure includes at least an illumination light source (not shown), a light valve 21 that is a modulation element for displaying an image, a projection optical system (not shown), and an optical path. The separation element 22 is included. The light valve 21 is preferably a reflective liquid crystal panel (Lcos), a micromirror device, or the like. Further, as the optical path separation element 22, total reflection prisms 23 and 24 are used, and the total reflection prism 23 and the total reflection prism 24 have the same refractive index, and an air gap 25 is provided between them facing each other. Examples of the optical path separation element include those made of materials such as glass, ceramic, sapphire, and plastic. As shown in (a) of the figure, the illumination light is reflected by the polarization plane of the total reflection prism 23 and incident on the light valve 21, and is formed by the light valve 21 as shown in the enlarged view of the portion surrounded by the alternate long and short dash line. The modulated image light is refracted by the polarization plane of the total reflection prism 23 and the air gap 25, further refracted and incident on the total reflection prism 24, and emitted from the total reflection prism 24 as imaging light, and a screen (not shown). Is imaged. When the rotation angle of the entire optical path separation element 22 is changed, the illumination light is reflected by the polarization plane of the total reflection prism 23 as shown in FIG. ), And the modulated image light formed by the light valve 21 is refracted by the polarization plane of the total reflection prism 23 and the air gap 25 as shown in the enlarged view of the portion surrounded by the alternate long and short dash line, and further totally reflected. It is emitted from the total reflection prism 24 as image forming light that is refracted and incident on the prism 24 and shifted by a predetermined shift amount, and forms an image on a screen (not shown). Thus, by alternately switching the state shown in FIG. 4A and the state shown in FIG. 4B (solid line), the images are switched at the respective image projection positions at high speed. If the substantial thickness t ′ of the light beam reflected by the total reflection prism is replaced with the prism thickness t described with reference to FIG. 1, the shift amount can be calculated. Even in an optical system having such a configuration that does not handle polarized light, the number of pixels can be increased without impairing the layout of the optical system by using the total reflection prism as an optical path shift function.

  In addition to the embodiment shown in FIG. 4, for example, a polarizing beam splitter, an image forming system using a reflective liquid crystal panel (Lcos) as a light valve, and an embodiment using a polarizing beam splitter (PBS) are conceivable. The reason why the polarization beam splitter as the optical path separating element functions as an optical path separating function is that it can be separated from the illumination light by changing the polarization of the illumination light and the polarization by being modulated by the light valve. For example, it is assumed that the illumination light is P-polarized light and illuminates the light valve through the polarization beam splitter. The modulated image light is reflected as S-polarized light in white display, reflected by the polarization beam splitter, and separated from the illumination light to the projection lens by displacing the optical path separation element by a minute angle so that the projection image The optical path is deflected, pixel shift is performed at a position that does not overlap with adjacent pixels, and the sub-frame image at that position is modulated at high speed by the light valve, so that the number of pixels can be apparently increased and displayed. In FIG. 4, only the light path to the light valve, the polarization beam splitter, and the projection lens are shown for explanation, and the shift amount is exaggerated.

  In addition, drive control means for displaying a modulated image on the light valve and means for controlling the optical path shift function in accordance with subframe image display are not shown, but are necessary for high-definition display. is there.

  Furthermore, the number of subframes and the shift position corresponding to the number of subframes are not necessarily limited to two, and three or four shift positions can be achieved with three or four times higher definition.

  Further, the shift direction may be performed not only in one direction but also in multiple directions. Further, it may be performed in multiple stages. For example, by giving a displacement that results in two shift positions in the vertical direction and the horizontal direction, it is possible to increase the number of pixels by two times in the vertical and horizontal directions, for a total of four times. Of course, the present invention may be applied only in one direction, and the multi-direction may be combined with a conventional pixel shift technique.

  Furthermore, not only the present invention is necessarily used as a means for doubling the pixels, but also by displaying the same frame image as a shift, a smoothing effect works particularly in moving image display, and an image with higher visibility can be obtained. Can also be expected.

  FIG. 5 is a schematic diagram showing the configuration of an image display apparatus according to the second embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 4 denote the same components. A cube-type polarization beam splitter 31 is used as an optical path separation element in the image display apparatus of the present embodiment, and the illumination light is reflected and transmitted through the imaging system. Also in the image display device of the present embodiment, by alternately switching between the state shown in FIG. 5A and the state shown in FIG. 5B (solid line), an image is displayed at each image projection position at high speed. Can be switched. When transmitting through a prism, the rotational angle of the prism and the amount of optical path shift do not change regardless of the position in the optical path. As shown in equation (1), this is a function of the thickness of the prism, and therefore when the positional relationship between the panel and the optical path separation element changes, for example, when focusing is performed on the projection screen, the relative positional relationship between the panel and the prism changes. However, the positioning does not affect the shift amount, and a stable shift amount can be obtained.

  FIG. 6 is a schematic diagram showing the configuration of an image display apparatus according to the third embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 4 denote the same components. A plate-type polarization separation splitter 41 is used as the optical path separation element in the image display apparatus of the present embodiment. As shown in FIG. 6, the optical path is shifted when the modulated image light from the light valve 21 passes through the flat plate type polarization separation splitter 41. The flat plate type polarization separation splitter 41 is slightly displaced, That is, by rotating by a small angle, an optical path shift can be caused by the relationship of Expression (1), and the number of pixels can be increased. In such a configuration, since the member to be displaced is a flat plate type, the mass is relatively light, and it is very effective for displacement at high speed. Specific examples of the flat plate type polarization separation splitter include a dielectric multilayer film formed on a glass substrate, a gold wire grating type polarization beam splitter in which a metal pattern is formed on a glass substrate with a nanostructure period, and the like. A wire grid type PBS (polarized beam splitter) or the like is suitable.

  FIG. 7 is a schematic diagram showing the configuration of an image display apparatus according to the fourth embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 4 denote the same components. As the optical path separation element in the image display apparatus according to the present embodiment, a flat plate type polarization separation splitter 41 is used, and the imaging light is reflected by the polarization separation function surface without passing through the polarization separation splitter 41. Yes. With such a configuration, even if the displacement is slight, the optical path can be shifted, and the optical path can be shifted and the number of pixels can be increased without deteriorating the function of the optical path separation element.

  FIG. 8 is a schematic view showing an example of a specific configuration of the image display apparatus of the present invention. In the figure, the same reference numerals as those in FIG. 4 denote the same components. As shown in the figure, a holding member 51 for holding a polarization separation splitter 41 as an optical path separation element is provided, and the polarization separation splitter 41 as an optical path separation element is displaced by a small amount by displacing the holding member 51. Yes. As a means for displacing, an actuator 52 such as a piezoelectric element is attached to one end of the holding member 51, and as a method for causing displacement, a fixing member 53 is attached to the other end of the holding member 51 and the fixing member 53 is used as a fulcrum. By reciprocating 52, the polarization splitting splitter 41 held by the holding member 51 is displaced by a minute angle. Note that not only the angle but also the entire holding member 51 may be shifted as shown in FIG. Note that an electromagnetic coil or the like can be used as the actuator 52 other than the piezoelectric element. In order to prevent the optical component as the optical path separation element from being affected, if the micro path of the optical path separation element such as a polarization beam splitter or the like is generated through the holding member, the displacement means, the shape of the holding member, There is no limitation on the support position or the position at which the displacement means causes displacement.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications and substitutions are possible as long as they are described within the scope of the claims.

It is the schematic which shows the principle of the image display apparatus of this invention. It is a figure which shows the rotation angle and optical path shift amount which were calculated | required from Formula (1) from the prism thickness and refractive index of the polarizing beam splitter. It is a figure which shows the rotation angle and optical path shift amount which were calculated | required from Formula (1) from the prism thickness and refractive index of the polarizing beam splitter. 1 is a schematic diagram illustrating a configuration of an image display device according to a first exemplary embodiment of the present invention. It is the schematic which shows the structure of the image display apparatus which concerns on the 2nd Example of this invention. It is the schematic which shows the structure of the image display apparatus which concerns on the 3rd Example of this invention. It is the schematic which shows the structure of the image display apparatus which concerns on the 4th Example of this invention. It is the schematic which shows an example of the specific structure of the image display apparatus of this invention. It is the schematic which shows another example of the specific structure of the image display apparatus of this invention.

Explanation of symbols

11, 31; polarizing beam splitter, 21; light valve,
22; optical path separation element; 23, 24; total reflection prism;
25; air gap, 41; polarization separation splitter,
51; holding member; 52; actuator; 53; fixing member.

Claims (4)

An illumination light source, a modulation element that displays an image, a projection optical system, and an optical path separation element that separates the illumination light from the illumination light source to the modulation element and the imaging light toward the projection optical system In the image display device to
An image display device comprising a displacement means for displacing the optical path separation element. The image display device according to claim 1 , wherein the optical path separation element is a polarization separation splitter . The image display device according to claim 1 , wherein the optical path separation element is a flat plate type polarization separation splitter . The image display apparatus according to claim 3, wherein the flat-plate-type polarization separation splitter reflects the image- forming light on a polarization separation function surface without passing it through the substrate .

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