Abstract:
An image display device includes: at least one illumination system adapted to emit a light beam; at least one light modulation element adapted to modulate the light beam emitted from the illumination system; and a projection optical system adapted to project the light beam modulated by the light modulation element, wherein a proceeding direction of a principal ray of the light beam modulated by the light modulation element is nonparallel to an optical axis of the projection optical system when the light beam modulated by the light modulation element enters the projection optical system.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to an image display device. 
     2. Related Art 
     In the past, projectors have been known as image display devices capable of displaying large-screen images. As light sources for the projectors, laser sources are thought to be hopeful from the viewpoint that high contrast ratio, excellent color reproducibility, quick lighting, downsizing, longer life, and so on become achievable. Use of the laser source makes it possible to obtain a number of advantages described above on the one hand, but it also makes it easy for the speckle noise due to the coherent property of laser beams to occur on the other hand. If the speckle noise is viewed, the sensation of glare might be provided to the observer of the displayed image to thereby degrade the image quality in some cases. 
     As one of the methods capable of reducing the speckle noise, there can be cited a method of superimposing high-frequency noise on the speckle noise, for example, a method of widening the diffusion angle of the image light (reduction in F-number). In particular, it is preferable to widen the diffusion angle of the image light so that the light intensity in the Fourier transform plane of the projection optical system has a ring-like distribution having a peak around the light axis. By making the light intensity have the ring-like distribution, it becomes possible to increase the light contributing to the reduction of the speckle noise, and at the same time, to reduce the light covered by the projection optical system compared to the case of forming a broad distribution around the light axis. Thus, it becomes possible to effectively reduce the speckle noise, and at the same time, degradation of the light efficiency can also be prevented. 
     In order for widening the diffusion angle of the image light, it is sufficient to dispose the diffusion section at the position where the image light is focused into an image (see, e.g., JP-A-2009-42372 (Document 1)). In Document 1, a diffusion plate formed of a diffraction optical element such as a computer generated hologram (CGH) is disposed at the position where an intermediate image is formed in the projection optical system, and thus, the diffusion angle of the image light is widened by the diffusion plate. 
     According to the technology of Document 1, the speckle noise can effectively be reduced, but there arises a problem of growing in size of the projection optical system. As a method of widening the diffusion angle of the image light at a position other than the position where the intermediate image is formed, there can be cited a method of disposing the diffusion section in the vicinity of the image formation surface (e.g., a liquid crystal layer) in a light modulation element (e.g., a liquid crystal light valve). 
     According to this method, although the growing in size of the device can be avoided, the following problems might be caused. In order for assuring the good light efficiency in this method, it is required to incorporate the diffusion section capable of controlling the light intensity to have a desired distribution such as a CGH into the light modulation element. In order for making the pattern of the CGH correspond to the pixels, microfabrication becomes necessary, and therefore, the device cost of the light modulation element might rise, or the device configuration might be complicated. Further, if microlenses are disposed on the light entrance side of the light modulation element for the purpose of guiding the source light to the pixels, the diffusion section might fail to function accurately due to the disturbance of the wavefront caused by the microlenses. If the diffusion section becomes to fail to function accurately, it becomes unachievable to make the light intensity distribution of the image light have a desired pattern, and therefore, the light efficiency is degraded. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a projector capable of reducing the speckle noise with a simple configuration, and moreover, of preventing the degradation of the light efficiency. 
     In order for obtaining the advantage described above, the following configurations are adopted as some aspects of the invention. 
     An image display device according to an aspect of the invention includes at least one illumination system adapted to emit a light beam, at least one light modulation element adapted to modulate the light beam emitted from the illumination system, and a projection optical system adapted to project the light beam modulated by the light modulation element, wherein a proceeding direction of a principal ray of the light beam modulated by the light modulation element is nonparallel to an optical axis of the projection optical system when the light beam modulated by the light modulation element enters the projection optical system. 
     According to the configuration described above, since the proceeding direction of the principal ray of the light beam (hereinafter referred to as an image light beam) modulated by the light modulation element is set to be nonparallel to the optical axis of the projection optical system, the barycentric position of the light intensity is located distant from the optical axis of the projection optical system in the Fourier transform plane of the projection optical system. Therefore, since the high-frequency noise on the imaging surface increases, and the high-frequency noise is superimposed on the speckle noise on the imaging surface, the speckle noise can effectively be reduced. Therefore, the necessity of widening the diffusion angle of the image light beam in the projection optical system is reduced, and it becomes possible to simplify the configuration of the projection optical system. Further, since the necessity of widening the width of the diffusion angle of the image light in terms of reducing the speckle noise is reduced, the light beam the projection optical system fails to cover can be reduced, and therefore, the degradation of the light efficiency can be prevented. 
     The image display device according to the aspect of the invention can take the following aspects as representative aspects of the invention. 
     It is preferable that the proceeding direction of the light beam emitted from the illumination system is nonorthogonal to an arranging direction of a plurality of pixels of the light modulation element when the light beam emitted from the illumination system enters the light modulation element as an incident light beam. 
     According to the configuration described above, since the proceeding direction of the light beam emitted from the illumination system is set to be nonparallel to the arranging direction of the plurality of pixels of the light modulating element, the proceeding direction of the principal ray of the image light becomes nonorthogonal to the arranging direction of the plurality of pixels, and it becomes easy to make the proceeding direction of the principal ray of the image light beam nonparallel to the optical axis of the projection optical system. Further, since the necessity of controlling the diffusion angle of the image light beam by the light modulation element is reduced, it becomes possible to simplify the configuration of the light modulation element. 
     It is preferable to provide a lens array adapted to converge the light beam emitted from the illumination system to the plurality of pixels of the light modulation element. 
     According to this configuration, since the lens array converges the incident light beam to the plurality of pixels, the light beam entering outside the pixels can be reduced irrespective of the light beam entering in a direction nonorthogonal to the arranging direction of the pixels, the degradation of the light efficiency can be prevented. 
     It is preferable that one of the plurality of pixels of the light modulation element includes a plurality of modulation elements adapted to modulate the incident light beam independently of each other, and the illumination system includes a first light source and a second light source adapted to emit laser beams with wavelengths different from each other, and is arranged so that a light beam emitted from the first light source enters a first modulation element of the plurality of modulation elements of the pixel as the incident light beam, and a light beam emitted from the second light source enters a second modulation element of the plurality of modulation elements of the pixel as the incident light beam. 
     According to this configuration, since one of the plurality of pixels of the image is composed of the light beam (hereinafter referred to as a first colored light beam) emitted from the first light source and the light beam (hereinafter referred to as a second colored light beam) emitted from the second light source, and the wavelengths of the first and second colored light beams are different from each other, it becomes possible to display an image with a plurality of colors. Since the light modulation element modulates both of the first and second colored light beams, the number of light modulation elements for displaying the image with a plurality of colors can be reduced, and the configuration of the image display device can be simplified. 
     It is preferable that the lens array has a plurality of lens elements, one of the plurality of lens elements is disposed corresponding one-to-one to one of the plurality of pixels of the light modulation element, and a central position of one of the plurality of lens elements corresponding to one of the plurality of pixels is shifted toward an opposite direction to the proceeding direction of the light beam entering the one of the plurality of lens elements, in a condition of viewing the plurality of pixels in a planar manner, from a central positions of one of the plurality of modulation elements constituting the one of the plurality of pixels. 
     According to this configuration, since one of the plurality of lens elements is disposed so as to correspond one-to-one to one of the plurality of pixels, and the lens element is used commonly to the plurality of modulation elements constituting the pixel, the cost of the lens array can be reduced. Since the incident light beam is converged by the lens element so as to be fitted into the respective modulation elements constituting the pixel, the intensity of the light entering outside the modulation elements can be reduced, and thus the degradation of the light efficiency can be prevented. 
     It is preferable that the illumination system includes a first diffusion section adapted to diffuse the light beam emitted from the first light source, a second diffusion section adapted to diffuse the light beam emitted from the second light source, and a collimating lens adapted to collimate a light beam diffused by the first diffusion section and to collimate a light beam diffused by the second diffusion section, and the light beam diffused by the first diffusion section and the light beam diffused by the second diffusion section enter the light modulation element at incident angles different from each other as the incident light beam via the collimating lens. 
     According to this configuration, since the first and second colored light beams are diffused by the first and second diffusion sections, it becomes easy to make the spot sizes of the first and second colored light beams match the area where the plurality of pixels are arranged in the light modulation element. Since the first and second diffusion sections can be designed independently in accordance with the wavelengths of the first and second colored light beams, it becomes easy to provide desired characteristics to the first and second diffusion sections. Since the light beams diffused by the first and second diffusion sections are collimated by the collimating lens, the incident angle to the light modulation element can be aligned among the first colored light beams and can be aligned among the second colored light beams. Since the incident angle to the light modulation element is different between the first and second colored light beams, it becomes easy to make the first and second colored light beams separately enter the first and second modulation elements. 
     It is preferable that the light modulation element has a plurality of modulation elements adapted to modulate the incident light beam independently of each other, and one of the plurality of pixels of the light modulation element is composed of one of the plurality of modulation elements, the lens array has a plurality of lens elements, one the plurality of lens elements is disposed corresponding one-to-one to the one of the plurality of pixels of the light modulation element, and a central position of the one of the plurality of lens element corresponding to the one of the plurality of pixels is shifted toward an opposite direction to the proceeding direction of the light beam entering the one of the plurality of lens elements, in a condition of viewing the plurality of pixels in a planar manner, from a central position of one of the plurality of modulation elements constituting the one of the plurality of pixels. 
     According to this configuration, since the incident light beam is converged by the lens element so as to be fitted into the modulation elements constituting the pixel, the intensity of the light entering outside the modulation elements can be reduced, and thus the degradation of the light efficiency can be prevented. 
     It is preferable to provide a plurality of the illumination systems adapted to emit laser beams with wavelengths different from each other, a plurality of the light modulation elements composed of the light modulation elements provided so as to correspond one-to-one to the illumination systems, and a color combination element disposed on a light path between the plurality of the light modulation elements and the projection optical element, and adapted to combine light beams emitted from the plurality of light modulation elements. 
     According to this configuration, the image light beams having the wavelengths different from each other are combined by the color combination element, and then projected by the projection optical system, and thus the image with a plurality of colors can be displayed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a diagram showing a projector according to a first embodiment of the invention. 
         FIG. 2A  is a plan view showing a lens array and a light modulation element, and  FIG. 2B  is a cross-sectional view of the lens array and the light modulation element shown in  FIG. 2A  along the line indicated by the arrows B 1 , B 2 . 
         FIG. 3A  is a diagram showing a light beam passing through the lens array and the light modulation element, and  FIG. 3B  is a graph showing the light intensity with respect to the diffusion angle of the light beam emitted from the light modulation element. 
         FIG. 4  is an explanatory diagram showing the mechanism of reducing the speckle noise. 
         FIG. 5  is a diagram showing a projector according to a first modified example. 
         FIG. 6  is a configuration diagram showing a projector according to a second embodiment of the invention. 
         FIG. 7A  is a plan view of a lens array and a light modulation element, and  FIG. 7B  is an explanatory diagram showing a light beam passing through the lens array and the light modulation element. 
         FIGS. 8A and 8B  are diagrams showing a projector according to a second modified example, wherein  FIG. 8A  is a perspective view, and  FIG. 8B  is a configuration diagram. 
         FIG. 9A  is a diagram showing an incident light beam to the light modulation element, and  FIG. 9B  is a diagram showing light distributions in a Fourier transform plane of a projection optical system. 
         FIG. 10  is a schematic configuration diagram showing a projector according to a third modified example. 
         FIG. 11  is a configuration diagram showing a projector according to a third embodiment of the invention. 
         FIG. 12A  is an arrangement diagram of a color combination element and an illumination system,  FIG. 12B  is a plan view of a light beam entering the color combination element, and  FIG. 12C  is a diagram showing a light distribution in the Fourier transform plane of a projection optical system. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, some embodiments of the invention will be explained with reference to the accompanying drawings. In the drawings used in the explanation, the sizes and the scales of the structures in the drawings might be made different from the actual structures in some cases in order for showing characteristic portions in an easy-to-understand manner. Further, the constituents substantially identical to each other in the embodiments are shown with the same reference numerals in the drawings, and the detailed explanation therefor might be omitted in some cases. 
     First Embodiment 
       FIG. 1  is a schematic diagram showing a schematic configuration of the projector  1  in the first embodiment. As shown in  FIG. 1 , the projector (an image display device)  1  is provided with an illumination system  11 , a light modulation element  12 , a projection optical system  13 , and a lens array  14 . The illumination system  11  has a light source  15 , a diffusion section  16 , and a collimating lens  17 . The lens array  14  has a plurality of lens elements  141 . 
     A general operation of the projector  1  is as follows. The light beam L emitted from the light source  15  is diffused by the diffusion section  16 , and is then collimated by the collimating lens  17 . The light beam L collimated by the collimating lens  17  is collected by each of the lens elements  141  of the lens array  14 , and enters the light modulating element  12  while being separated so as to correspond to the respective pixels. The light beam L having entered the light modulation element  12  is modulated and controlled in each of the pixels to thereby form the light with grayscales corresponding to the pixels of the display image. The light beam L emitted from the light modulation element  12  enters the projection optical system  13 , and is projected on the imaging surface S such as a screen in an enlarged manner, and thus the image is displayed by the light beam L imaged on the imaging surface S. 
     Then, the constituents of the projector  1  will be explained in detail. 
     The illumination system  11  is for illuminating the light modulation element  12  so that the proceeding direction of the principal ray becomes nonparallel to the optical axis  130  of the projection optical system  13  when the light beam L modulated by the light modulation element  12  enters the projection optical system  13 . In the present embodiment, the optical axis  170  of the collimating lens  17  roughly coincides with the optical axis  130  of the projection optical system  13 , and is roughly perpendicular to a light entrance area  120  of the light modulation element  12 . The optical axis  150  of the light source  15  is arranged to be roughly parallel to the optical axis  170  of the collimating lens  17 , but located differently therefrom. 
     The light source  15  is for emitting a coherent light beam such as a laser beam, and is composed of, for example, a laser diode. An external resonator or a wavelength conversion element is provided together with the laser diode of the light source  15  if necessary. For example, in the case of constituting the light source for emitting a green laser beam, a light source having a laser diode for emitting a red laser beam combined with the wavelength conversion element or the like is used. 
     The diffusion section  16  is for diffusing the light beam. The diffusion section  16  is composed of, for example, a diffusion plate formed of a light transmissive substrate having diffusing particles dispersed, a diffusion plate obtained by forming random irregularity on the surface of a light transmissive substrate, or a diffraction optical element such as a CGH. The diffusion section  16  of the present embodiment is composed of a diffraction optical element. The diffusion section  16  diffuses the light beam L so that the central axis of the light beam L becomes nonparallel to the optical axis  170  of the collimating lens  17 . Further, the diffusion section  16  modulates the spot shape of the light beam L to have a similar shape (e.g., a roughly rectangular shape) to the light entrance area  120  of the light modulation element  12 . 
     The collimating lens  17  is, for example, a field lens. Since the central axis of the light beam L entering the collimating lens  17  is arranged to be nonparallel to the optical axis  170 , the light beam L having passed through the collimating lens  17  proceeds in a direction nonparallel to the optical axis  170 . The light beam L emitted from the collimating lens  17  enters the lens array  14  from a direction nonparallel to the normal direction of the light entrance area  120  of the light modulation element  12 . It should be noted that the collimating lens  17  can be disposed independently from the light modulation element  12 , or can be disposed substantially integrally with the light modulation element  12  together with the lens array  14 . 
       FIG. 2A  is a plan view of the lens array  14  and the light modulation element  12  when viewing the light entrance area  120  of the light modulation element  12  in a planar manner, and  FIG. 2B  is a cross-sectional diagram of the lens array  14  and the light modulation element  12  viewed along the line indicated by the arrows B 1 , B 2  shown in  FIG. 2A . The light modulation element  12  of the present embodiment is composed of a transmissive liquid crystal light valve. As shown in FIG.  2 A, the light modulation element  12  has a plurality of pixels P arranged two-dimensionally. The light entrance area  120  is formed as an area including roughly all of the arranged pixels P out of the planar area along the two arranging directions of the plurality of pixels P. In the present embodiment, the pixel P is composed of a single modulation element  121 . The modulation element  121  has a pixel opening A 1  and a light blocking area A 2  surrounding the pixel opening A 1 . 
     The lens array  14  has a plurality of lens elements  141 . The lens element  141  has, for example, a rectangular planar shape, and is disposed so as to correspond one-to-one to the modulation element  121 . The optical axis  140  of the lens element  141  is set to be located at the center of the lens element  141 . In the condition of viewing the light entrance area  120  in a planar manner, the position of the optical axis  140  is shifted from the central position C 1  of the pixel opening A 1  in the opposite direction to the proceeding direction of the light beam entering the lens element  141 . The amount of shift between the position of the optical axis  140  and the central position C 1  of the pixel opening A 1  is set in accordance with, for example, the incident angle of the light beam entering the lens element  141 . The lens array  14  of the present embodiment is substantially integrated with the light modulation element  12 . The lens array  14  can be disposed as a part of the illumination system  11 , or can be disposed as a part of the light modulation element  12 . 
     As shown in  FIG. 2B , the light modulation element  12  has light transmissive substrates  122   a ,  122   b , a liquid crystal layer  123 , switching elements  124 , light transmissive electrodes  125   a ,  125   b , a planarizing layer  126 , insulating sections  127 , and oriented films  128   a ,  128   b . The light transmissive substrates  122   a ,  122   b  are disposed so as to be opposed to each other, and the liquid crystal layer  123  is disposed in a space sandwiched between the light transmissive substrates  122   a ,  122   b . The thickness direction of the liquid crystal layer  123  is set to a direction roughly parallel to the optical axis  140  of the lens element  141 . The light entrance area  120  is set to be roughly parallel to the central plane in the thickness direction of the liquid crystal layer  123 . 
     The switching element  124  is provided to every modulation element  121 , and is disposed on the liquid crystal layer  123  side of the light transmissive substrate  122   a . The switching element  124  switches the electrical signal supplied to the light transmissive electrode  125   a . The light blocking section not shown is provided to the switching element  124  so as to cover the light entrance side thereof. The light blocking section is disposed on the periphery of the modulation element  121 , and the area overlapping the light blocking section in the condition of viewing the light entrance area  120  in a planar manner corresponds to the light blocking area A 2 . 
     The planarizing layer  126  is disposed so as to cover the switching elements  124 . The light transmissive electrodes  125   a  are, for example, pixel electrodes, and disposed on the liquid crystal layer  123  side of the planarizing layer  126 . The light transmissive electrodes  125   a  are disposed independently to the respective modulation elements  121  like, for example, islands. The insulating sections  127  are each disposed so as to separate the light transmissive electrodes  125   a  adjacent to each other, and are disposed on the liquid crystal layer  123  side of the planarizing layer  126 . A part of each of the light transmissive electrodes  125   a  penetrates the planarizing layer  126 , and is electrically connected to the switching element  124 . The oriented film  128   a  is disposed on the liquid crystal layer  123  side of the light transmissive electrodes  125   a  and the insulating sections  127 . 
     The light transmissive electrode  125   b  is provided in common to the plurality of modulation elements  121 , and is disposed on the liquid crystal layer  123  side of the light transmissive substrate  122   b . The oriented film  128   b  is disposed on the liquid crystal layer  123  side of the light transmissive electrode  125   b . The light transmissive substrates  122   a ,  122   b  are each provided with a polarization plate not shown on the opposite side to the liquid crystal layer  123 . 
       FIG. 3A  is an explanatory diagram showing the light beam passing through the lens array  14  and the light modulation element  12 . As shown in  FIG. 3A , the proceeding direction of the light beam entering the lens array  14  is set to be nonparallel to the optical axis  140  of the lens element  141 . The light beam L having entered the lens array  14  is collected by each of the lens elements  141 . The lens elements  141  of the present embodiment each deflect the light beam L so that the approximately entire light beam L entering each of the lens elements  141  fits into the pixel opening A 1  in the liquid crystal layer  123 . Here, it is arranged that the light beam L passing through each of the lens elements  141  makes the focus in the vicinity of the light exit end of the liquid crystal layer  123  at the central position C 1  of the pixel opening A 1 . The incident angle of the light beam L with respect to the lens element  141 , and the curvature factor and the refractive index of the lens element  141  are set so that the light beam L passing through the liquid crystal layer  123  can be switched taking the variation in the amount of modulation due to the difference in optical path length inside the modulation element  121  and so on into consideration. The proceeding direction of the principal ray L 0  having passed through the center of the lens element  141  forms an angle α° with the thickness direction of the liquid crystal layer  123 . The angle α° is in a range of about 3° through 7°, for example. 
       FIG. 3B  is a graph showing a distribution D 1  of the light intensity with respect to the diffusion angle of the light beam L emitted from the light modulation element  12 . In the graph shown in  FIG. 3B , the lateral axis represents the diffusion angle assuming that the normal direction of the center plane in the thickness direction of the liquid crystal layer  123  is 0°, and the vertical axis represents the light intensity normalized by the maximum value of the light intensity. The graph of  FIG. 3B  also shows an example of the distribution D 2  of the light beam emitted from the light modulation element in a conventional projector for comparison. The distribution D 2  corresponds to the distribution of the light intensity with respect to the diffusion angle of the light beam emitted from the light modulation element when inputting the light beam from the normal direction of the light entrance area of the light modulation element. The distribution D 2  is typically a Gaussian distribution. 
     As shown in  FIG. 3B , the light intensity in the distribution D 1  has a peak at the diffusion angle (the angle α) corresponding to the proceeding direction of the principal ray L 0 . In comparison between the distributions D 1 , D 2 , the distribution range of the light intensity, namely the width of the diffusion angle is in the same level between the distribution D 1  and the distribution D 2 . In the area of the diffusion angle having an absolute value a certain amount distant from the angle 0°, the light intensity in the distribution D 1  is higher than that in the distribution D 2 . 
       FIG. 4  is an explanatory diagram showing the mechanism of reducing the speckle noise. Since the light beam L enters the light modulation element  12  from a direction nonparallel to the normal direction of the light entrance area  120 , the light beam L emitted from the light modulation element  12  proceeds in a direction nonparallel to the optical axis  130  of the projection optical system  13 . Thus, the spot  133  of the light beam L on the Fourier transform plane  131  of the projection optical system  13  is formed in an area shifted from the position  132  where the Fourier transform plane  131  and the optical axis  130  intersect with each other. The distance between the barycentric position  134  of the light intensity of the spot  133  and the position  132  corresponds to the angle α. 
     In contrast thereto, the light beam having the distribution D 2  described above forms a spot having the barycenter of the light intensity at the position overlapping the optical axis on the Fourier transform plane. In other words, compared to the case in which the principal ray of the light beam emitted from the light modulation element roughly coincides with the optical axis of the projection optical system, in the present embodiment the intensity of the light beam passing through a position distant from the optical axis  130  of the projection optical system  13  in the Fourier transform plane  131  increases. In other words, a high frequency component in the Fourier transform plane  131  increases. 
     The light beam L emitted from one of the modulation element  121  of the light modulation element  12  is imaged on the imaging surface S through the spot  133 , and forms a light beam representing one pixel of the image. The light beams emitted from the respective modulation elements  121  are respectively imaged on the imaging surface S, and thus the entire image is displayed. In the case of displaying the image with the light beam having a coherent property such as a laser beam, the speckle noise is normally apt to occur in the displayed image. 
     According to the projector  1  of the present embodiment, since the speckle noise is superimposed on the high-frequency noise due to the high-frequency component in the Fourier transform plane  131 , the speckle noise can be reduced. In particular, since the high-frequency component is increased as described above, the speckle noise can dramatically be reduced. Therefore, the chance of providing the observer of the image with the sensation of glare due to the speckle noise is reduced, and therefore, the projector  1  capable of displaying a high-quality image is obtained. 
     Incidentally, as a method of reducing the speckle noise, there is known a method of disposing a diffusion member at the intermediate image formation position in the projection optical system. This is because, since the information of the diffusion angle of the light beam of each of the pixels is approximately concentrated at the intermediate image formation position, it is easy to control the diffusion angle of each of the pixels. In terms of widening the diffusion angle at the position where the image light beam is imaged, it is also possible to adopt the method of disposing a diffusion member in the vicinity of the part where the image is formed in the light modulation element. 
     In the present embodiment, the speckle noise is reduced by making the proceeding direction of the light beam L emitted from the light modulation element  12  nonparallel to the optical axis  130  of the projection optical system  13 . Therefore, the necessity of widening the diffusion angle in the projection optical system  13  in terms of reducing the speckle noise is reduced, and thus, the configuration of the projection optical system  13  can be simplified. 
     Further, in the present embodiment, the incident angle of the light beam L emitted from the illumination system  11  to the light modulation element  12  is controlled to thereby control the proceeding direction of the light beam L emitted from the light modulation element  12 . Therefore, the necessity of widening the diffusion angle in the vicinity of the part where the image is formed in the light modulation element  12  in terms of reducing the speckle noise is reduced, and thus, the configuration of the light modulation element  12  can be simplified. 
     Further, the barycentric position  134  of the spot  133  in the Fourier transform plane  131  is shifted from the optical axis  130  of the projection optical system  13 , thereby increasing the high-frequency noise. Therefore, the high-frequency noise can be increased while hardly increasing the light beam, which the projection optical system fails to cover, compared to the method of widening the diffusion angle around the optical axis of the projection optical system, and thus it becomes possible to reduce the speckle noise while preventing the degradation of the light efficiency. 
     It should be noted that although in the first embodiment it is arranged that the optical axis  170  of the collimating lens  17  is roughly parallel to the normal direction of the light entrance area  120  of the light modulation element  12 , the configuration of a first modified example shown in  FIG. 5 , for example, is also possible. The projector  1 B of the first modified example is different from that of the first embodiment in the positional relationship between the constituents of the illumination system  11 B, and the characteristics of the diffusion section  16 B. 
     In the illumination system  11 B, it is arranged that the optical axis  170  of the collimating lens  17  is nonparallel to the normal direction of the light entrance area  120  of the light modulation element  12 . The optical axis  150  of the light source  15  is arranged to roughly coincide with the optical axis  170  of the collimating lens  17 . The diffusion section  16 B is arranged to widen the diffusion angle of the light beam L emitted from the light source  15  in an axisymmetrical manner with respect to the optical axis  150  of the light source  15 . 
     Here, the constituents of the illumination system  11 B are attached to the position fixing member or the like to thereby be substantially integrated with each other, and it is arranged that the posture of the illumination system  11 B with respect to the light modulation element  12  can variably be controlled. Thus, the incident angle of the light beam L entering the light modulation element  12  can variably be controlled, and the extent to which the speckle noise is reduced can variably be controlled. 
     Second Embodiment 
     Then, a projector according to a second embodiment will be explained. The projector of the second embodiment is different from the projector of the first embodiment in that the illumination system is configured including a plurality of light sources for emitting respective colored light beams having wavelengths different from each other, and that a single plate projector for modulating the plurality of colored light beams emitted from the illumination system with a single light modulation element to thereby display an image is provided. 
       FIG. 6  is a schematic diagram showing the projector  2  according to the second embodiment,  FIG. 7A  is a plan view of a lens array  24  and a light modulation section  22  when viewing a light entrance area  220  in a planar manner, and  FIG. 7B  is an explanatory diagram showing a light beam passing through the lens array  24  and the light modulation element  22 . 
     As shown in  FIG. 6 , the projector  2  is provided with an illumination system  21 , the light modulation element  22 , the projection optical system  13 , and the lens array  24 . The illumination system  21  has first through third light sources  25   r ,  25   g , and  25   b  (hereinafter collectively referred to as a plurality of light sources  25 ), first through third diffusion sections  26   r ,  26   g , and  26   b  (hereinafter collectively referred to as a plurality of diffusion sections  26 ), and the collimating lens  17 . 
     A general operation of the projector  2  is as follows. The light beams emitted from the plurality of light sources  25  are diffused by the plurality of diffusion sections  26 , and are then collimated by the collimating lens  17 . The light beams collimated by the collimating lens  17  are input to and then collected by the lens array  24 , and then enter the respective modulation elements of the light modulation element  22  separately. The light beams modulated by the light modulation element  22  are projected to the imaging surface S by the projection optical system  13 , and then the image is displayed by the light beams thus imaged on the imaging surface S. 
     The plurality of light sources  25  each emits the light beam having a coherent property such as a laser beam, and the wavelengths of the light beams emitted are different from each other. In the present embodiment, it is arranged that the first light source  25   r  emits a red light beam. Lr, the second light source  25   g  emits a green light beam Lg, and the third light source  25   b  emits a blue light beam Lb. The first light source  25   r  and the second light source  25   g  are disposed in one of the areas located on both sides of the optical axis  170  of the collimating lens  17 , and the third light source  25   b  is disposed in the other of the areas. 
     The light beam Lr emitted from the first light source  25   r  is input to and diffused by the first diffusion section  26   r . Similarly, the light beam Lg emitted from the second light source  25   g  is input to and diffused by the second diffusion section  26   g , and the light beam Lb emitted from the third light source  25   b  is input to and diffused by the third diffusion section  26   b . The plurality of diffusion sections  26  is each composed of a diffraction optical element such as a CGH, but is designed to have characteristics different from each other so as to correspond to the wavelengths of the respective light beams input thereto. 
     In other words, the extent of the diffusion and the orientation of the central axis of the diffused beam by the plurality of diffusion sections  26  are adjusted so that the proceeding directions of the light beams Lr, Lg, and Lb having been diffused and then passed through the collimating lens  17  form angles different from each other with the light entrance area  220  of the light modulation element  22 . Here, the characteristics of the plurality of diffusion sections are adjusted so that the light beams Lr, Lg, and Lb having passed through the collimating lens  17  enter substantially the same area in the light modulation element  12 . 
     As shown in  FIGS. 7A and 7B , the light modulation element  22  has a plurality of pixels P 2  arranged two-dimensionally. Each of the pixels P 2  is composed of three subpixels Pr, Pb, and Pg. Each of the subpixels Pr, Pg, and Pb is composed of one modulation element  221 . In other words, each of the pixels P 2  is composed of the three modulation elements  221 . The configuration of the modulation element  221  is substantially the same as that of the first embodiment. The subpixel Pr has a pixel opening A 3 , the subpixel Pg has a pixel opening A 4 , and the subpixel Pb has a pixel opening A 5 . A light blocking area A 6  is formed so as to surround the pixel openings A 3  through A 5 . 
     The lens array  24  has a plurality of lens elements  241 . The lens element  241  is disposed so as to correspond one-to-one to the pixel P 2 . The optical axis  240  of the lens element  241  is set to be located at the center of the lens element  241 . The position of the optical axis  240  is shifted toward the opposite direction to the proceeding direction of the light beam entering the lens element  241  with respect to either of the central position C 3  of the pixel opening A 3 , the central position C 4  of the pixel opening A 4 , and the central position C 5  of the pixel opening A 5  in the condition of viewing the light entrance area  220  in a planar manner. 
     The light modulation element  22  has a first substrate  222 , a second substrate  223 , and a liquid crystal layer  224 . Although the detailed configuration of the first and second substrates  222 ,  223  is not shown in the drawings, the first substrate  222  is composed of the light transmissive substrate  122   a , the switching elements  124 , the light transmissive electrodes  125   a , the planarizing layer  126 , the insulating sections  127 , the oriented film  128   a , and so on explained in the first embodiment. The second substrate  223  is composed of the light transmissive substrate  122   b , the light transmissive electrode  125   b , the oriented film  128   b , and so on. The liquid crystal layer  224  is disposed in a space sandwiched between the first and second substrates  222 ,  223 . The thickness direction of the liquid crystal layer  224  is set to a direction roughly parallel to the optical axis  240  of the lens element  241 . The light entrance area  220  is set to be roughly parallel to the central plane in the thickness direction of the liquid crystal layer  224 . 
     The proceeding directions of the light beams Lr, Lg, and Lb entering the lens array  24  are different from each other, and are all set to be nonparallel to the optical axis  240  of the lens element  241 . The light beams Lr, Lg, and Lb having entered the lens array  24  are collected by each of the lens elements  241 . The lens element  241  refracts the light beam Lr so that the light beam Lr fits into the pixel opening A 3  of the subpixel Pr in the liquid crystal layer  224 . Similarly, the lens element  241  refracts the light beams Lg, Lb so that the light beams Lg, Lb fit into the pixel openings A 4 , A 5  of the subpixels Pg, Pb in the liquid crystal layer  224 , respectively. As described above, it is arranged that among the light beams Lr, Lg, and Lb, only the light beam Lr enters the subpixel Pr, only the light beam Lg enters the subpixel Pg, and only the light beam Lb enters the subpixel Pb. 
     The light beams Lr, Lg, and Lb are modulated and controlled in the respective subpixels Pr, Pg, and Pb independently of each other in the liquid crystal layer  224 , and then emitted from the light modulation element  22 . The proceeding direction of the principal ray of each of the light beams Lr, Lg, and Lb emitted from the light modulation element  22  is arranged to be nonparallel to the incident light axis out of the optical axes  130  of the projection optical system  13 . The light beams Lr, Lg, and Lb emitted from the light modulation element  22  are imaged on the imaging surface via the projection optical system  13 . The light beams Lr, Lg, and Lb emitted from the subpixels Pr, Pg, and Pb included in one pixel P 2  are imaged on the imaging surface to form a light beam representing one pixel of a full-color image. 
     In the projector  1  according to the second embodiment, the proceeding directions of the light beams Lr, Lg, and Lb emitted from the light modulation element  22  are all arranged to be nonparallel to the optical axis  130  of the projection optical system  13 . Therefore, on the same ground as explained in the first embodiment, the high-frequency noise is superimposed on the speckle noise in each of the light beams Lr, Lg, and Lb, and thus the speckle noise can be reduced. Further, the light beam the projection optical system  13  fails to cover can be reduced, and thus the degradation of the light efficiency can be prevented. 
     Further, since the image is displayed using the light beams Lr, Lg, and Lb having the wavelengths different from each other, a full-color image can be displayed. Since the light beams Lr, Lg, and Lb with a plurality of wavelengths are modulated by a single light modulation element  22 , the number of light modulation elements can be reduced, and the device configuration of the projector  2  can be simplified. 
     It should be noted that although the three light sources emitting the light beams with the wavelengths different from each other are used in the second embodiment, the number of light sources can be two or more than three, and in the case of using three or more light sources, light sources emitting the light beams with substantially the same wavelengths can be included. Hereinafter, the configuration having four light sources will be explained. 
       FIG. 8A  is a schematic perspective view showing a projector  2 B according to a second modified example, and  FIG. 8B  is a plan view of the projector  2 B when viewing a plane including the optical axis  130  from one of the arranging directions of the light sources in a planar manner. 
     As shown in  FIG. 8A , the projector  2 B is provided with an illumination system  21 B, a light modulation element  22 B, the projection optical system  13 , and a lens array  24 B. The illumination system  21 B has a plurality of light sources  25   r ,  25   g ,  25   b , and  25   x  (hereinafter collectively referred to as a plurality of light sources  25 B), first through fourth diffusion sections  26   r ,  26   g ,  26   b , and  26   x  (hereinafter collectively referred to as a plurality of diffusion sections  26 B), and the collimating lens  17 . 
     The optical axis  170  of the collimating lens  17  roughly coincides with the normal direction of the light entrance area  220 B and the optical axis  130  of the projection optical system  13 . The plurality of light sources  25 B is arranged two-dimensionally in two directions along the light entrance area  220 B of the light modulation element  22 B. Here, the plurality of light sources  25 B is disposed symmetrically around the optical axis  170  of the collimating lens  17 . The optical axes of the plurality of light sources  25 B are all arranged to be parallel to the optical axis  170  of the collimating lens  17 , but located differently therefrom. 
     The first through third light sources  25   r ,  25   g , and  25   b , and the first through third diffusion sections  26   r ,  26   g , and  26   b  are substantially the same as those of the second embodiment. The fourth light source  25   x  can be one emitting a light beam with a wavelength the same as that of either one of the first through third light sources, or can be one emitting a light beam with a wavelength different from that of any of the light beams. The fourth diffusion section  26   x  is for diffusing the light beam emitted from the fourth light source  25   x . Similarly to one explained in the second embodiment, the fourth diffusion section  26   x  has a characteristic adjusted in accordance with the wavelength of the light beam emitted from the fourth light source  25   x.    
     As shown in  FIG. 8B , the light beam Lr emitted from the first light source  25   r  is input to and diffused by the first diffusion section  26   r , and is then collimated by the collimating lens  17 . The light beam Lr having passed through the collimating lens  17  is input to and then collected by the lens array  24 B, and then enters the light modulation element  22 B. Similarly, the light beam Lg emitted from the second light source  25   g  is diffused by the second diffusion section  26   g , then collimated by the collimating lens  17 , then collected by the lens array  24 B, and then enters the light modulation element  22 B. The proceeding directions of the light beams Lr, Lg having passed through the collimating lens  17  are different from each other, and are all set to be nonparallel to the normal direction of the light entrance area  220 B of the light modulation element  22 B. 
     It should be noted that although  FIG. 8B  shows the light beams Lr, Lg emitted from the first light sources  25   r  and the second light source  25   g , the light beams Lr, Lg are disposed on both sides opposite to each other of the optical axis  170  of the collimating lens  17  with respect to the first light source  25   r  and the second light source  25   g . The same is applied to the light beams emitted from the third light source  25   b  and the fourth light source  25   x . In other words, the proceeding directions of the light beams having been emitted from the plurality of light sources  25 B and passed through the collimating lens  17  are different from each other, and are set to be nonparallel to the normal direction of the light entrance area  220 B of the light modulation element  22 B. 
       FIG. 9A  is a plan view showing an incident light beam to the lens array  24 B and the light modulation element  22 B when viewing the light entrance area  220 B of the light modulation element  22 B in a planar manner, and  FIG. 9B  is a conceptual diagram showing the distributions of the light beams in the Fourier transform plane of the projection optical system  13 . 
     The light modulation element  22 B has a plurality of pixels arranged two-dimensionally. As shown in  FIG. 9B , one pixel P 3  is composed of the four subpixels Pr, Pb, Pg, and Px arranged in a 2×2 matrix. Each of the subpixels Pr, Pb, Pg, and Px is composed of one modulation element  221 . In other words, each of the pixels P 3  is composed of the four modulation elements  221 . The configuration of the modulation element  221  is substantially the same as that of the first embodiment. 
     When focusing attention to the light beams Lr, Lx from the first and fourth light sources  25   r ,  25   x  disposed at opposing corners in the matrix of the light sources, the light beam Lr proceeds in one diagonal direction of the pixels P 3  and enters the subpixel Pr, and the light beam Lx proceeds in the reverse direction from that of the light beam. Lr along the one diagonal direction and enters the subpixel Px. When focusing attention to the light beams Lg, Lb from the second and third light sources  25   g ,  25   b  disposed at opposing corners different from those of the first and fourth light sources  25   r ,  25   x , the light beam Lg proceeds in the other diagonal direction of the pixels P 3  and enters the subpixel Pg, and the light beam Lb proceeds in the reverse direction from that of the light beam Lg along the other diagonal direction and enters the subpixel Pb. 
     The light beams Lr, Lg, Lb, and Lx are modulated and controlled in the respective subpixels Pr, Pg, Pb, and Px independently of each other in the liquid crystal layer, and then emitted from the light modulation element  22 B. The proceeding direction of the principal ray of each of the light beams Lr, Lg, Lb, and Lx emitted from the light modulation element  22 B is arranged to be nonparallel to the incident light axis out of the optical axes  130  of the projection optical system  13 . As shown in  FIG. 9B , in the Fourier transform plane  131  of the projection optical system  13 , the spot  133   r  by the light beam Lr is distant from the position  132  of the optical axis  130  in the Fourier transform plane  131 . Similarly, the spots  133   g ,  133   b , and  133   x  by the light beams Lg, Lb, and Lx are also distant from the position  132 . 
     In the projector  2 B according to the second modified example, the proceeding directions of the light beams Lr, Lg, Lb, and Lx emitted from the light modulation element  22 B are all arranged to be nonparallel to the optical axis  130  of the projection optical system  13 . Therefore, since the spots  133   r ,  133   g ,  133   b , and  133   x  are formed in the areas shifted from the position  132  of the optical axis  130  in the Fourier transform plane  131  of the projection optical system  13 , and thus the high-frequency noise can effectively generated, the speckle noise can effectively be reduced. Further, the light beam the projection optical system  13  fails to cover can be reduced, and thus the degradation of the light efficiency can be prevented. 
     Further, since the plurality of light sources  25 B is arranged two-dimensionally, the proceeding directions of the light beams Lr, Lg, Lb, and Lx can be adjusted in the two directions corresponding to the arranging directions of the light sources. Thus, it becomes easy to make the proceeding directions of the light beams Lr, Lg, Lb, and Lx when entering the light modulation element  22 B different from each other. 
     It should be noted that although the transmissive light modulation element is adopted in the first and second embodiments and first and second modified examples, it is also possible to adopt a reflective light modulation element as the case of a third modified example shown in  FIG. 10 .  FIG. 10  is a diagram showing a schematic configuration of a projector  2 C in the third modified example. 
     As shown in  FIG. 10 , the projector  2 C is provided with an illumination system  21 C, a light modulation element  22 C, the projection optical system  13 , a lens array  24 C, and a polarization beam splitter prism (hereinafter referred to as a PBS prism)  27 C. The illumination system  21 C is substantially the same as that of the second modified example, and is provided with the first and second light sources  25   r ,  25   g , the first and second diffusion sections  26   r ,  26   g , and the collimating lens  17 . The first and second light sources  25   r ,  25   g  are arranged to emit an S-polarized light beam with respect to a PBS film  28 C described later. 
     The lens array  24 C of the third modified example is independent of the light modulation element  22 C, and is disposed at the position where the light beams Lr, Lg emitted from the illumination system  21 C enter. The light beams Lr, Lg having passed through the lens array  24 C enter the PBS prism  27 C while converging. The PBS prism  27 C contains a polarization beam splitter film (hereinafter referred to as a PBS film)  28 C. Here, the PBS film  28 C is disposed at an angle of about 45° with the optical axis of the collimating lens  17 . In the light beams Lr, Lg having entered the PBS prism  27 C, the S-polarized light beams with respect to the PBS film  28 C are reflected by the PBS film  28 C, and the proceeding directions are folded, and are emitted from the PBS prism  27 C. 
     The light beams Lr, Lg emitted from the PBS prism  27 C enter the light modulation element  22 C. The light modulation element  22 C is composed of a reflective liquid crystal light valve, a digital mirror device (DMD), or the like. The light modulation element  22 C has a plurality of subpixels Pr, Pg arranged two-dimensionally. The light beams Lr, Lg enter the light modulation element  22 C from a direction nonorthogonal to the plane along the two arranging directions of the subpixels Pr, Pg. The proceeding directions of the light beams Lr, Lg when entering the light modulation element  22 C are different from each other. The light beams Lr, Lg are reflected by the light modulation element  22 C while being modulated by the light modulation element  22 C. 
     The light beams Lr, Lg are emitted from the light modulation element  22 C, and are then input again to the PBS film  28 C. In the light beams Lr, Lg, the P-polarized light beams with respect to the PBS film  28 C are transmitted through the PBS film  28 C, and proceed toward the projection optical system  13 . When entering the projection optical system  13 , the proceeding directions of the light beams Lr, Lg are nonparallel to the optical axis of the projection optical system  13 . The light beams Lr, Lg are projected to the imaging surface by the projection optical system  13 , and the image is displayed by the light beams Lr, Lg thus imaged. Also in the projector  2 C according to the third modified example having the configuration described above, for the reason described above, the speckle noise can be reduced while preventing the degradation of the light efficiency even with a simplified configuration. 
     Third Embodiment 
     Then, a projector according to a third embodiment will be explained. The third embodiment is different from the second embodiment in that a plurality of illumination systems is provided, and the light modulation element is provided to each of the illumination systems, and thus a three-panel projector is provided. 
       FIG. 11  is a schematic diagram showing a general configuration of the projector  3  according to the third embodiment,  FIG. 12A  is an arrangement diagram of a color combination element and an illumination system,  FIG. 12B  is a plan view of a light beam entering the color combination element viewed from the optical axis of the projection optical system  13 , and  FIG. 12C  is a diagram showing a light distribution in the Fourier transform plane of the projection optical system. In  FIG. 12B , the first through third collimating lenses  33   r ,  33   g , and  33   b  are omitted from the illustration. 
     As shown in  FIG. 11 , the projector  3  is provided with first through third illumination systems  31   r ,  31   g , and  31   b , first through third light modulation elements  32   r ,  32   g , and  32   b , the color combination element  34 , and the projection optical system  13 . The first through third illumination systems  31   r ,  31   g , and  31   b  each have the configuration substantially the same as the illumination system of the first embodiment, but the wavelengths of the light beams emitted by the first through third illumination systems are different from each other. 
     The first illumination system  31   r  has the first light source  25   r , the first diffusion section  26   r , and the first collimating lens  33   r . The second illumination system  31   g  has the second light source  25   g , the second diffusion section  26   g , and the second collimating lens  33   g . The third illumination system  31   b  has the third light source  25   b , the third diffusion section  26   b , and the third collimating lens  33   b.    
     The color combination element  34  is composed of a dichroic prism or the like. The color combination element  34  of the present embodiment has a roughly rectangular solid shape, and contains two types of wavelength selection films for selectively reflecting or transmitting the input light beam in accordance with the difference in wavelength. The two types of the wavelength selection films are disposed in a diagonal direction of the color combination element  34  viewed from one direction (a Z direction) and intersect with each other. The first illumination system  31   r  and the first light modulation element  32   r  are disposed on a first side of the color combination element  34  viewed from the Z direction in a planar manner. The second illumination system  31   g  and the second light modulation element  32   g  are disposed on the second side of the color combination element  34  adjacent to the first side thereof. The third illumination system  31   b  and the third light modulation element  32   b  are disposed on the opposite side of the color combination element  34  to the first side thereof. 
     As shown in  FIGS. 12A and 12B , the first and third illumination systems  31   r ,  31   b  are disposed at positions shifted in the positive Z direction from the respective positions of the normal line of the light entrance areas in the first and third light modulation elements  32   r ,  32   b  passing through the central positions of the light entrance areas. The second illumination system  31   g  is disposed at the position shifted in the negative Z direction from the position on the normal line of the light entrance area in the second light modulation element  32   g  passing through the central position of the light entrance area. 
     The light beam Lr emitted from the first illumination system  31   r  is reflected by the wavelength selection film of the color combination element  34 , and thus the proceeding direction thereof is folded. Then, the light beam Lr is emitted from the opposite side (in an X direction) of the color combination element  34  to the side of the second illumination system  31   g . The light beam Lg emitted from the second illumination system  31   g  is transmitted through the wavelength selection film of the color combination element  34 , and is then emitted from the color combination element  34 . The light beam Lb emitted from the third illumination system  31   b  is reflected by the wavelength selection film of the color combination element  34 , and thus the proceeding direction thereof is folded. Then, the light beam Lb is emitted from the opposite side of the color combination element  34  to the side of the second illumination system  31   g.    
     In other words, the light beams Lr, Lg, and Lb respectively modulated by the first through third light modulation elements are emitted from one side of the color combination element  34  viewed from the Z direction in a planar manner via the color combination element  34 . As described above, since the first through third illumination systems  31   r ,  31   g , and  31   b  are disposed at the positions shifted in the positive or negative Z direction from the central positions of the light entrance areas of the first through third light modulation elements  32   r ,  32   g , and  32   b , the proceeding directions of the light beams Lr, Lg, and Lb emitted from the color combination element  34  are different from each other, and are nonparallel to the optical axis  130  of the projection optical system  13 . 
     As shown in  FIG. 12C , in the Fourier transform plane  131  of the projection optical system  13 , the spot  133   r  by the light beam Lr is distant from the position  132  of the optical axis  130  in the Fourier transform plane  131 . Similarly, the spots  133   g  and  133   b  by the light beams Lg, Lb are also distant from the position  132 . 
     In the projector  3  according to the third embodiment, the proceeding directions of the light beams Lr, Lg, and Lb emitted from the color combination element  34  are all arranged to be nonparallel to the optical axis  130  of the projection optical system  13 . Therefore, the high-frequency noise can effectively be generated, and thus the speckle noise can effectively be reduced. Further, the light beam the projection optical system  13  fails to cover can be reduced, and thus the degradation of the light efficiency can be prevented. 
     It should be noted that the scope of the invention is not limited to the embodiments described above. Various modifications are possible within the scope or the spirit of the invention. 
     The entire disclosure of Japanese Patent Application No. 2009-283963, filed Dec. 15, 2009 is expressly incorporated by reference herein.