Abstract:
An image display apparatus discloed includes a condensing optical system changing illumination light from a light source converging light; separation optical system having separation optical member reflecting color light component in specific wavelength range of the converging light and transmitting color light components the other wavelength ranges; a plurality of image display devices illuminated by a plurality of color flight components separated by the color separation optical system, respectively, color combination optical system image light components from the plurality of image plurality combining colors emanating and display devices; projection optical system for projecting image light components combined by the color combination optical system on surface on which projection is performed, light incident color separation optical member forms an angle smaller than 45 degrees with a normal to light incident surface of the color separation optical member.

Description:
This application is a continuation of 10/126,270, filed Apr. 18, 2002 and now U.S. Pat. No. 6,637,889. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to projection type image display apparatus for color separating illumination light to illuminate a plurality of image display devices with the separated light components and combining image light components emanating from these image display devices for projective display. 
   2. Description of the Related Art 
   In recent years, a projection type image display apparatus with an improved brightness and a compact size is needed. 
     FIG. 4  shows the configuration of a conventional projection type image display apparatus. In  FIG. 4 , white illumination light emitted from an illumination light source  101  is reflected by a reflector  102 , passes through a fly eye lens  103 , further reflected by a mirror M 101 , passes through a fly eye lens  104 , a light polarization converting device  105  and a condenser lens  106 , and then incident on a dichroic mirror DM 101 . 
   In general, as the illumination light source, a halogen lamp, a metal halide lamp, an ultra-high pressure mercury lamp or the like is used. 
   The dichroic mirror DM 101  has a spectral transmittance shown in FIG.  5 ( a ), in which a light component in a wavelength range for blue is reflected and a light component in a wavelength range for green to red is transmitted. The light component in the wavelength range for green to red passing through the dichroic mirror DM 101  is incident on a dichroic mirror DM 102 . The dichroic mirror DM 102  has a spectral transmittance shown in FIG.  5 ( b ), in which a light component in a wavelength range for green is reflected and a light component in a wavelength range for red is transmitted. 
   The light component in the wavelength range for blue reflected by the dichroic mirror DM 101  is turned 90 degrees by a reflecting mirror M 102 , passes through a field lens  107 B, and incident on an image display device  108 B, where the light is modulated in accordance with a signal input to the image display device  108 B. 
   The light component in the wavelength range for green reflected by the dichroic mirror DM 102  passes through a field lens  107 G and is incident on an image display device  108 G, where the light is modulated in accordance with a signal input to the image display device  108 G. 
   The light component in the wavelength range for red transmitted through the dichroic mirror DM 102  passes through a trimming filter TRO having a spectral transmittance shown in FIG.  5 ( c ), a condenser lens  111 , a relay lens  112 , reflecting mirrors M 103 , M 104  and a field lens  107 R, and then is incident on an image display device  108 R, where the light is modulated. 
   The image light component for each color, modulated by the respective image display device  108 R,  108 B and  108 G as described above, is incident on a cross dichroic prism  109 . The light components in the wavelength ranges for blue and red are turned 90 degrees within the cross dichroic prism  109 , while the light component in the wavelength range for green is transmitted as it is through the cross dichroic prism  109 . Then, the light components of all the wavelength ranges emanate in combination. 
   The image light resulting from the color combination in the cross dichroic prism  109  is projected and displayed on a screen, not shown, by a projection lens  110 . 
   In the conventional projection type image display apparatus configured in this manner, the dichroic mirror DM 102  is disposed immediately before the image display device  108 G and is responsible for separating the optical path of the light component in the wavelength range for green from the optical path of the light component in the wavelength range for red and for bending the optical path of the light component in the wavelength range for green. The dichroic mirror DM 102  is arranged such that the optical axis of the light incident on the dichroic mirror DM 102  forms an angle of 45 degrees with the normal to the incident surface of the dichroic mirror DM 102 . 
   In the aforementioned configuration of the apparatus, however, the optical axis of the illumination light from the illumination light source  101  to the reflecting mirror M 101  is arranged in parallel with the optical axis of the projection lens  110 , and the condensing effect of the condenser lens  106  converges the luminous flux toward the image display device  108 R,  108 G and  108 B. Thus, when the apparatus is housed in an outer box  120 , the probability is that spaces S 1 , S 2  with little usefulness are created as shown by hatched portions in  FIG. 6  to increase the apparatus in size. 
   In addition, while the aforementioned image display apparatus employs the relay lens  112 , the reflecting mirrors M 103 , M 104  and the like to form the relay system for red light, it is contemplated that a relay system formed of combined concave mirrors is used instead of the above relay system. The concave mirrors, however, are likely to suffer from aberration if light is incident thereon at a large angle, thereby possibly causing loss of light quantity or failing to achieve favorable display images. 
   SUMMARY OF THE INVETION 
   It is an object of the present invention to propose a projection type image display apparatus which has a higher degree of freedom in arranging a color separation optical system with respect to an image light combination/projection optical system to allow the whole apparatus to be compact in size. 
   To achieve the aforementioned object, the present invention provides an image display apparatus comprising:
         a condensing optical system for changing illumination light from a light source to converging light;   a color separation optical system having a color separation optical member for reflecting a color light component in a specific wavelength range of the converging light and transmitting color light components in the other wavelength ranges;   a plurality of image display device illuminated by a plurality of color light components separated by the color separation optical system, respectively,   a color combination optical system for combining image light components of a plurality of colors emanating from the plurality of image display devices; and   a projection optical system for projecting image light components combined by said color combination optical system on a surface on which projection is performed,   wherein the optical axis of light incident on the color separation optical member forms an angle smaller than 45 degrees with the normal to a light incident surface of the color separation optical member.       

   The aforementioned invention further has a relay optical system disposed in an optical path with a length larger than the lengths of the other optical paths of a plurality of optical paths of color light components from the light source to the plurality of image display device, wherein the relay optical system includes a reflecting member having a concave-shaped reflecting surface. An angle which an optical axis of light incident on the reflecting member forms with the normal to the reflecting surface passing through the intersection of the optical axis and the reflecting surface of the reflecting member is smaller than 45 degrees. 
   In addition, in the present invention, an angle which an optical axis of light incident on the reflecting member forms with the normal to the reflecting surface passing through the intersection of the optical axis and the reflecting surface of the reflecting member is smaller than an angle which an optical axis of light incident on the color separation optical member forms with the normal to the light incident surface of the color separation optical member. 
   To achieve the aforementioned object, the present invention provides an image display apparatus comprising:
         a condensing optical system for changing illumination light from a light source to converging light;   a color separation optical system having a color separation optical member for reflecting a color light component in a specific wavelength range of the converging light and transmitting color light components in the other wavelength ranges;   a plurality of image display device illuminated by a plurality of color light components separated by the color separation optical system, respectively;   a color combination optical system for combining image light components of a plurality of colors emanating from the plurality of image display devices;   a projection optical system for projecting image light components combined by the color combination optical system on a surface on which projection is performed; and   an outer box for housing the condensing optical system, the color separation optical system, the plurality of image display device, the color combination optical system and the projection optical system,   wherein a wall surface closest to the condensing optical system and the color separation optical member of wall surfaces substantially perpendicular to the optical axis direction of the projection optical system in the outer box extends along a portion, which is farthest from the projection optical system, of the outer periphery of converging light incident on the color separation optical member from the condensing optical system.       

   The phrase “extends along” means that the wall surface is substantially in parallel with and close tothe portion. 
   Furthermore, to achieve the aforementioned object, the present invention provides an image display apparatus comprising:
         a condensing optical system for changing illumination light from a light source to converging light;   a color separation optical system having a color separation optical member for reflecting a color light component in a specific wavelength range of the converging light and transmitting color light components in the other wavelength ranges;   a plurality of image display device illuminated by a plurality of color light components separated by the color separation optical system, respectively;   a color combination optical system for combining image light components of a plurality of colors emanating from the plurality of image display devices; and   a projection optical system for projecting image light components combined by the color combination optical system on a surface on which projection is performed,   wherein a direction of a portion, which is farthest from the projection optical system, of the outer periphery of converging light incident on the color separation optical member from the condensing optical system is substantially perpendicular to the optical axis direction of the projection optical system.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view showing the configuration of a projection type image display apparatus which is an embodiment of the present invention; 
     FIGS.  2 ( a ) to  2 ( c ) are schematic graphs illustrating the spectral characteristics of dichroic mirrors and a trimming filter used in the aforementioned image display apparatus; 
       FIG. 3  is a sectional view showing the configuration of a projection type image display apparatus which is another embodiment of the present invention; 
       FIG. 4  is a sectional view showing the configuration of a conventional projection type image display apparatus; 
     FIGS.  5 ( a ) to  5 ( c ) are schematic graphs illustrating the spectral characteristics of dichroic mirrors and a trimming filter used in the conventional image display apparatus; and 
       FIG. 6  shows unused spaces in the conventional image display apparatus. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows the configuration of a projection type image display apparatus which is an embodiment of the present invention.  FIG. 2  illustrates spectral transmittances of dichroic mirrors DM 1 , DM 2  and a trimming filter TR. These spectral transmittances are exemplary values in design when an ultra-high pressure mercury lamp is used as an illumination light source. However, the numerical values are only illustrative, and the spectral transmittances are not limited to those values. In other words, various values can be set in accordance with the type of the illumination light source. 
   In  FIG. 1 , part of white light emitted from an illumination light source  1  is incident on a fly eye lens  3  as it is, while the remainder of the light is reflected by a reflector  2  and then incident on the fly eye lens  3 . 
   The illumination light passing through the fly eye lens  3  is turned approximately 90 degrees by a mirror M 1  serving as an illumination reflecting member, passes through a fly eye lens  4 , a light polarization converting device  5  and a condenser lens  6  serving as a condensing optical device, and then incident on a dichroic mirror DM 1 . 
   The illumination light is subjected to a converging (condensing) effect as it passes through the condenser lens  6 , and thus converging in the direction in which the illumination light travels. 
   The dichroic mirror DM 1  has a spectral transmittance shown in FIG.  2 ( a ), in which a light component in a wavelength range for blue is reflected and a light component in a wavelength range for green to red is transmitted. 
   The light component in the wavelength range for green to red transmitted through the dichroic mirror DM 1  is incident on a dichroic mirror DM 2 . The dichroic mirror DM 2  has a spectral transmittance shown in FIG.  2 ( b ), in which a light component in a wavelength range for green is reflected and a light component in a wavelength range for red is transmitted. 
   The light component in the wavelength range for blue reflected by the dichroic mirror DM 1  is turned by a reflecting mirror M 2  serving as a light guide reflecting member, passes through a field lens  7 B, and then is incident on an image display device  8 B, where the light is modulated in accordance with a signal input to the image display device  8 B. 
   The light component in the wavelength range for green reflected by the dichroic mirror DM 2  passes through a field lens  7 G and is incident on an image display device  8 G, where the light is modulated in accordance with a signal input to the image display device  8 G. 
   The light component in the wavelength range for red transmitted through the dichroic mirror DM 2  passes through a relay system composed of a trimming filter TR having a spectral transmittance shown in FIG.  2 ( c ), a concave mirror M 3 , a reflecting mirror M 4  and a concave mirror M 5 , and is incident on an image display device  8 R, where the light is modulated in accordance with an input signal. The reflecting mirror M 4  may be any of a concave mirror, a convex mirror and a plane mirror. 
   Each of the image display devices  8 R,  8 G and  8 B is formed of a liquid crystal display panel or the like. A driving circuit, not shown, inputs driving signals to the image display devices  8 R,  8 G, and  8 B in accordance with image information input from an image information supply apparatus IS such as a personal computer, a DVD player, a television and a VTR. This is the same or the following embodiment. The input driving signal drives each of the image display devices  8 R,  8 G and  8 B to form an image for each color in accordance with the image information. 
   The image light component for each color, modulated by the respective image display devices  8 R,  8 B and  8 G, is incident on a color combination prism  9 . The color combination prism  9  is formed of integrally combined four prisms such as dichroic films DM 3 , DM 4  are formed between respective two paired prisms. 
   The image light component in the blue wavelength range incident on the color combination prism  9  is reflected by the dichroic film DM 3  within the color combination prism  9  and thus turned 90 degrees, and then emanates toward a projection lens  10 . 
   The image light component in the green wavelength range incident on the color combination prism  9  is transmitted through the color combination prism  9  as it is and emanates toward the projection lens  10 . 
   The image light component in the red wavelength range incident on the color combination prism  9  is totally reflected by one surface of the color combination prism  9 , further reflected by the dichroic film DM 4 , and emanates toward the projection lens  10 . 
   The optical axis of the emanating image light component for each color is substantially consistent with each other. In this manner, the image light components for red, green and blue are combined and the combined light is projected and displayed by the projection lens  10  on a screen, not shown. 
   In the present embodiment, the dichroic mirror DM 1  is responsible for separating the optical path of the light component of the wavelength for blue from the optical paths of the light components of the wavelength for the other colors. And the dichroic mirror DM 2  is disposed immediately before the image display device  8 G and is responsible for separating the optical path of the light component of the wavelength for green from the optical path of the light component of the wavelength for red and for bending the optical path of the light component of the wavelength for green. The embodiment is configured such that the optical axis of the light incident on the dichroic mirrors DM 1 , DM 2  forms an angles θ 1 , θ 2  with the normals to the incident surfaces of the dichroic mirrors DM 1 , DM 2 , respectively. In the embodiment, the angle θ 2  is 42.5 degrees (&lt;45 degrees) and the angle θ 1  is smaller than the angle θ 2 . 
   More specifically, a condensing optical system of the present embodiment has the reflecting mirror M 1  for turning the optical axis of the illumination light from the illumination light source  1  approximately 90 degrees, and the condenser lens  6  for exerting the converging effect on the light reflected by this reflecting mirror M 1  to cause the converging light to be incident on the dichroic mirrors DM 1 , DM 2 . The condensing optical system is arranged such that the optical axis of the illumination light from the illumination light source  1  to the reflecting mirror M 1  is inclined toward the optical axis Lp (optical axis of the projection lens  10 ) for projection of the image light with respect to the optical axis Lp for projection. 
   With this arrangement, the illumination light source  1  and the reflector  2  are disposed closer to the reflecting mirror M 2  to reduce the hatched space S 1  shown in FIG.  6 . 
   In addition, a portion L, which is farthest from the projection lens  10 , of the outer periphery of the illumination light (converging light) emanating from the condenser lens  6  extends substantially horizontally in  FIG. 1  from near the outer periphery of the condenser lens  6  (in a direction substantially perpendicular to the optical axis for projection). 
   In other words, according to the present embodiment, a wall surface (a lower wall surface in  FIG. 1 )  20   a  closest to the condenser lens  6  and the dichroic mirrors DM 1 , DM 2  of upper and lower wall surfaces in  FIG. 1  substantially perpendicular to the optical axis direction of the projection lens  10  in an outer box  20  can extend along the portion L, which is farthest from the projection lens  10 , of the outer periphery of the converging light incident on the dichroic mirrors DM 1 , DM 2  from the condenser lens  6  such that the wall surface  20   a  is arranged near and substantially in parallel with the portion L. In brief, the wall surface  20   a  is substantially in parallel with and close to the aforementioned portion L of the outer periphery of the converge light. 
   With the configuration as described above, it is possible to substantially eliminate the hatched space S 2  shown in  FIG. 6  formed between the outer box  20  and the outer portion L of the illumination light when the display apparatus is housed in the outer box  20  which is typically formed in a generally rectangular parallelepiped. 
   Therefore, according to the present embodiment, the conventionally wasted spaces S 1 , S 2  can be reduced or eliminated to allow the outer box  20  and the whole apparatus to be compact in size. 
   It should be noted that, with the setting of the 42.5-degree angle which the optical axis of the light incident on the dichroic mirror DM 2  forms with the normal to the incident surface of the dichroic mirror DM 2 , a 42.5-degree angle is also set for the angle which the optical axis of the light incident on the reflecting mirror M 2  arranged symmetrically to the dichroic mirror DM 2  forms with the normal to the reflecting surface of the reflecting mirror M 2 . 
   In the present embodiment, the optical path length of the illumination light component in red wavelength range is larger than the other optical path lengths, and the relay system including at least two concave mirrors M 3 , M 5  is disposed in the optical path for red. The setting of the angle between the optical axis of the incident light on the dichroic mirror DM 2  and the normal to the dichroic mirror DM 2  to be lower than 45 degrees as described above reduces the angle of incidence (the angle which the optical axis of the light incident on the concave mirror M 3  forms with the normal to the reflecting surface of the concave mirror M 3  passing through the intersection of the optical axis and the reflecting surface) θ of the illumination light component in the red wavelength range on the concave mirror M 3 . Thus, aberration is unlikely to occur on the concave mirror M 3  to achieve a reduction in loss of light quantity or a display image of high quality. 
   If the angle between the optical axis of the light incident on the dichroic mirror DM 2  and the normal to the dichroic mirror DM 2  is 45 degrees or more, the large spaces S 1 , S 2  with little usefulness are created as shown in  FIG. 6 , and the angle of the light incident on the concave mirror M 3  is increased to cause aberration on the concave mirror M 3 , resulting in an increase in loss of light quantity. 
   In the present embodiment, the angle of incidence θ on the concave mirror M 3  may be smaller than the angle which the optical axis of the light incident on the dichroic mirror DM 2  forms with the normal to the dichroic mirror DM 2 . 
   While the present embodiment has been described for the setting of the 42.5 degrees as the angle which the optical axis of the light incident on the dichroic mirror DM 2  forms with the normal to the incident surface of the dichroic mirror DM 2 , the present invention is not limited to this angle as long as it is smaller than 45 degrees. 
   Similar effects to those in the present embodiment can be achieved by setting the angles θ 1 , θ 2  which the optical axis of the light incident on dichroic mirrors DM 1 , DM 2  forms with the normals to the incident surfaces of the dichroic mirrors DM 1 , DM 2  to be 30 degrees or larger and smaller than 45 degrees, more preferably 35 degrees or larger and 44 degrees or smaller. 
   In addition, while the present embodiment has been described for the provision of the relay system in the optical path of the light component in the wavelength range for red, the relay system may be provided in the optical path of a light component in one of the other wavelength ranges. 
   The present embodiment has been described for the relay system including at least two concave mirrors M 3 , M 5  disposed in the optical path with a length larger than the other optical path lengths. The relay system, however, may be composed of a lens  11 ,  12 ,  7 R and mirrors M 6 , M 7  as shown in another embodiment in FIG.  3 . In this case, wasted space can be reduced to achieve a compact apparatus by setting the angles smaller than 45 degrees as the angles which the optical axis of the light incident on the dichroic mirrors DM 1 , DM 2  forms with the normals to the incident surfaces of the dichroic mirrors DM 1 , DM 2 , respectively, similarly to the aforementioned embodiment. 
   In the embodiment shown in  FIG. 3 , components common to the present and aforementioned embodiments are designated with the same reference numerals as the aforementioned embodiment. 
   In the present embodiment, similarly to the aforementioned one, a wall surface (a lower wall surface in  FIG. 3 )  20   a  closest to a condenser lens  6  and dichroic mirrors DM 1 , DM 2  of upper and lower wall surfaces in  FIG. 3  substantially perpendicular to the optical axis direction of a projection lens  10  in an outer box  20  can extend along a portion L, which is farthest from the projection lens  10 , of the outer periphery of the converging light incident on the dichroic mirrors DM 1 , DM 2  from the condenser lens  6  such that the wall surface  20   a  is arranged near and substantially in parallel with the portion L. 
   It is thus possible to substantially eliminate the hatched space S 2  shown in  FIG. 6  formed between the outer box  20  and the outer portion L of the illumination light and allow the outer box  20  and the whole apparatus to be compact in size. 
   As described above, according to the aforementioned respective embodiments, since the angle which the optical axis of the light incident on the color separation optical member forms with the normal to the light incident surface of the color separation optical member is set to be smaller than 45 degrees, the color separation optical system can be arranged with a higher degree of freedom with respect to the image light combination/projection optical system, as compared with the conventional projection type image display apparatus in which the angle between the optical axis of light incident on the color separation optical member and the normal to the light incident surface of the color separation optical member is set to be 45 degrees. 
   Thus, for example, when the condensing optical system is configured to have an illumination reflecting member for turning the optical axis of illumination light from a illumination light source 90 degrees and a condensing optical element for exerting a converging effect on the light reflected by the illumination reflecting member and causing the converging light to be incident on the color separation optical member, the condensing optical system can be arranged such that the optical axis of the illumination light from the illumination light source to the illumination reflecting member is inclined toward the optical axis of the projection optical system with respect to the optical axis of the projection optical system. 
   In addition, according to the present embodiment, the wall surface closest to the condensing optical system and the color separation optical members of the wall surfaces substantially perpendicular to the optical axis direction of the projection optical system in the outer box can extend along the portion, which is farthest from the projection optical system, of the outer periphery of the converging light incident on the color separation optical members from the condensing optical system, and furthermore, the direction of the portion, which is farthest from the projection optical system, of the outer periphery of the converging light incident on the color separation optical members from the condensing optical system can be substantially perpendicular to the optical axis direction of the projection optical system. 
   Therefore, for example, it is possible to substantially eliminate the conventionally wasted spaces shown as the hatched portions in  FIG. 6  to allow the whole apparatus to be compact in size. 
   In addition, when the relay system including the concave surface reflecting members is disposed in the optical path of the color light component with a length larger than the other optical path lengths of the color light components, the angle between the optical axis of the light incident on the concave surface reflecting member and the normal to the reflecting surface of the concave surface reflecting member passing through the intersection of the optical axis and the reflecting surface is set to be smaller than 45 degrees (and smaller than the angle between the optical axis of the light incident on the color separation optical member and the normal to the light incident surface of the color separation optical member), thereby making it possible to suppress the occurrence of aberration in the relay system, and consequently, loss of light quantity is reduced and good-quality display images can be obtained.