Patent Publication Number: US-2010118213-A1

Title: Projection display device

Description:
TECHNICAL FIELD 
     The present invention relates to a projection display device that magnifies and projects an optical image formed on a light valve onto a screen. 
     BACKGROUND ART 
     A projection display device such as a projector is well known, which forms an optical image based on a video signal on a light valve, and illuminates the optical image with light so as to magnify and project the optical image onto a screen with a projection lens, whereby a large screen video image is obtained. 
     In such a projection display device, when a reflection-type light valve is used as a light valve, both a high resolution and a high pixel aperture ratio can be achieved, whereby it becomes possible to display a high-brightness projected image with high light utilization efficiency. 
       FIG. 4  shows a configuration of an optical system in a conventional projection display device using a reflection-type light valve as described above. Such a configuration is disclosed in Patent Document 1, for example. 
     In  FIG. 4 , light emitted from a lamp  1  as a light source is focused on a reflection-type light valve  9  via a total reflection prism  6   a  by an illumination optical system including a concave mirror  2 , a rod prism  3 , and a condenser lens  4 . The rod prism  3  has a quadratic prism shape in cross section, and has substantially the same aspect ratio as that of an effective display area of the reflection-type light valve  9 . A color wheel  5  is provided between the concave mirror  2  and the rod prism  3 . The light reflected from the reflection-type light valve  9  passes through a dichroic prism  6   b  as a color separator and combiner optical system to be projected onto a screen (not shown) by a projection lens  10 . 
     The concave mirror  2 , in which a cross-sectional shape of a reflection surface forms an ellipse, has a first focal point and a second focal point. The concave mirror  2  is arranged so that a center of an illuminant of the lamp  1  is located in the vicinity of the first focal point of the concave mirror  2  and a light incident surface of the rod prism  3  is located in the vicinity of the second focal point. The concave mirror  2  is formed of a member obtained by forming an optical multilayer film that allows infrared light to pass therethrough and reflects visible light on an inner surface of a glass material. 
     The light emitted from the lamp  1  is reflected and condensed by the concave mirror  2 , so that an illuminant image of the lamp  1  is formed at the second focal point of the concave mirror  2 . There is a tendency for the illuminant image of the lamp  1  to be brightest in a central region dose to an optical axis and become dark rapidly toward the circumference, so that the brightness is non-uniform. 
     To avoid this problem, the incident surface of the rod prism  3  is arranged in the vicinity of the second focal point, so that the incident light is subjected to multiple reflection on a side surface of the rod prism  3 , thereby making the brightness uniform. In this manner, by forming a secondary surface light source at an exiting surface of the rod prism  3 , and forming an image on the reflection-type light valve  9  with the downstream condenser lens  4 , uniform illumination light can be secured. 
     The color wheel  5  is composed of a combination of three color filters, each allowing only one of light beams of three primary colors to pass therethrough. By the color wheel  5  arranged in the vicinity of the second focal point of the concave mirror  2 , the white light output from the lamp  1  is time-divided into light beams of three primary colors of red, green, and blue. More specifically, by rotating the color wheel  5 , the light beams of three primary colors of red, green, and blue sequentially illuminate the reflection-type light valve  9  in a time-division manner. Thus, a full-color projected image can be displayed by using the one display element (reflection-type light valve  9 ). 
     A diaphragm  11  is provided at a position of a pupil of the illumination optical system so as to eliminate unnecessary light to be described later. The diaphragm  11  is arranged such that the center of gravity of an aperture is eccentric with respect to the optical axis of the illumination optical system, for the purpose of achieving higher contrast performance while minimizing brightness degradation by suppressing the blocking of necessary light. 
     Next, a configuration and an operation of the reflection-type light valve  9  will be described with reference to  FIGS. 5A to 5C . In general, the reflection-type light valve  9  controls a traveling direction of light based on a video signal so as to form an optical image as a change in reflection angle.  FIGS. 5A to 5C  are cross-sectional views for explaining the configuration and the operation of the reflection-type light valve in the conventional projection display device. 
     This reflection-type light valve  9 , which is called a DMD (Digital Micro-mirror Device), has mirror elements  12  formed in a matrix on a pixel basis. An inclination angle of each of the mirror elements  12  with respect to a reference plane  13  perpendicular to an optical axis of the projection lens  10  (see  FIG. 4 ) is controlled based on an ON signal for a white image and an OFF signal for a black image. An illumination principal ray  15  passes through a cover glass  14 , is incident on and reflected from the mirror elements  12 , and passes through the cover glass  14  again to exit. 
     At the time of the ON signal, as shown in  FIG. 5A , the mirror elements  12  are controlled so as to form an angle of +θ° with respect to the reference plane  13 . At this time, an incident angle of the illumination principal ray  15  is set so that an ON-light principal ray  16  is reflected in a direction perpendicular to the reference plane  13 , i.e., a direction along the optical axis of the projection lens  10 . Accordingly, an angle formed between the illumination principal ray  15  and the ON-light principal ray  16  is 2θ. 
     At the time of the OFF signal, as shown in  FIG. 5B , the mirror elements  12  are controlled so as to form an angle of −θ° with respect to the reference plane  13 . At this time, an angle formed between the illumination principal ray  15  and an OFF-light principal ray  17  is 6θ. As a result, the OFF-light principal ray  17  is reflected and travels in a direction in which it is not incident on the projection lens  10 . 
     Further, as shown in  FIG. 5C , the illumination light is reflected from a surface of the cover glass  14  as flat light  18 . Regardless of whether it is the time of the ON signal or the OFF signal, an angle formed between the illumination principal ray  15  and a principal ray of the flat light  18  is 4θ. At either of the times of the ON signal and the OFF signal, the flat light  18  is partially incident on the projection lens  10 , which results in a problem that the flat light  18  causes significant contrast performance degradation, particularly at the time of the OFF signal for a black image. 
     Next, a description will be given of the reason why the flat light  18  causes contrast degradation, with reference to  FIG. 6  for explaining the incidence and reflection in the illumination optical system. In  FIG. 6 , among the light beams incident on the reflection-type light valve  9 , a light beam that is inclined most with respect to the optical axis of the illumination light forms an illuminating angle θa. In other words, the illumination light is incident on the reflection-type light valve  9  within a range of the illuminating angle θa with the illumination principal ray  15  as a center. Reference numeral  19  denotes the pupil of the illumination optical system, and reference numeral  20  denotes a pupil of the projection lens  10 . Reference numeral  21  denotes a spot of the flat light  18  at a position corresponding to the pupil  20  of the projection lens  10 . 
     The ON-light principal ray  16  reflected from the reflection-type light valve  9  in a direction forming an angle of 2θ with respect to the illumination principal ray  15  is incident on the projection lens  10  through the pupil  20  to be projected onto a screen. On the other hand, the flat light  18  is reflected from the reflection-type light valve  9  in a direction forming an angle of 4θ with respect to the illumination principal ray  15 . 
     Here, when the illuminating angle θa is not less than θ, the flat light  18  is partially incident on the projection lens  10  as unnecessary light  22 . An overlapping range between the pupil  20  of the projection lens  10  and the spot  21  of the flat light  18  corresponds to the unnecessary light  22 . The unnecessary light  22  causes significant contrast performance degradation, particularly at the time of the OFF signal. 
     In general, in the projection video device with the reflection-type light valve, the illuminating angle θa is larger than θ since an illumination F value of the illumination optical system is set to be small so as to achieve high light utilization efficiency. 
     In order to eliminate the unnecessary light  22 , the diaphragm  11  is provided at the position of the pupil of the illumination optical system as shown in  FIG. 4 . As shown in  FIG. 6 , a light shielding region  23  of the diaphragm  11  in the pupil  19  of the illumination optical system is set so as to correspond to the region of the unnecessary light  22  in the spot  21  of the flat light  18  reflected from the reflection-type light valve  9 . 
     The light shielding region  23  of the diaphragm  11  has a shape corresponding to that of the region of the unnecessary light  22 . The region of the unnecessary light  22  is a range in which the spot  21  of the flat light  18  overlaps the pupil  20  of the projection lens  10 , i.e., an overlapping region between the two circles. Thus, as shown in  FIG. 7 , the light shielding region  23  has a biconvex lens shape surrounded by two arcs having the same curvature as that of a periphery of the pupil  19  of the illumination optical system. In the following description, this shape will be merely referred to as a “lens shape”. 
     The light shielding region  23  in the pupil  19  is arranged structurally as follows. That is, the light shielding region  23  is arranged such that one of the arcs of the lens shape follows the periphery of the region of the pupil  19 . The symmetry axis of the lens shape is directed toward a direction of an intersection line of a plane including the illumination principal ray  15  and the ON-light principal ray  16  with a plane of the pupil  19 . And, the light shielding region  23  is arranged on one end side of the diameter of the pupil  19  closer to the ON-light principal ray  16  at a position where the light is just before being incident on the reflection-type light valve  9 . 
     The light shielding region  23  can prevent the unnecessary light  22  from being incident on the pupil  20  of the projection lens  10 . More specifically, among the illumination light having the illuminating angle θa with the illumination principal ray  15  as a center, light that will become the unnecessary light  22  is prevented from being incident on the reflection-type light valve  9  by the light shielding region  23  of the diaphragm  11 . 
     Patent Document 1: JP 2004-94262 A 
     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     The brightness distribution in a pupil is such that it is brightest in a central region close to the optical axis and becomes dark rapidly toward the circumference. Thus, as shown in  FIG. 7  for explaining a light shielding state, the light shielding region  23  of the diaphragm  11  having the above-described lens shape blocks a luminous flux in the vicinity of the optical axis having high brightness, which thus results in a large brightness loss. 
     In order to solve the above-described problem, it is an object of the present invention to provide a projection display device that efficiently eliminates unnecessary light of flat light incident on a projection lens by optimizing the shape of a diaphragm, thereby achieving high brightness performance. 
     Means for Solving Problem 
     A projection display device according to the present invention includes: a light source; a reflection-type light valve that controls a relationship of a traveling direction of exiting light with respect to incident light based on an input signal; an illumination optical system that focuses light from the light source on the reflection-type light valve as illumination light; a projection lens that projects exiting light from the reflection-type light valve; and a first diaphragm provided at a position of a pupil of the illumination optical system so as to block a part of the light from the light source. The first diaphragm forms a light shielding region for a part of a region of the pupil of the illumination optical system that corresponds to a range in which light, among the illumination light, reflected from a surface of the reflection-type light valve is incident on a pupil of the projection lens as unnecessary light. 
     In order to solve the above-described problem, the projection display device according to the present invention further includes a second diaphragm provided at a position of the pupil of the projection lens so as to block a part of the exiting light from the reflection-type light valve. The light shielding region of the first diaphragm corresponds to a divided region on an outer peripheral side between two divided regions obtained by dividing the region of the pupil of the illumination optical system corresponding to the range of the unnecessary light by a line in a chord direction. The second diaphragm forms a light shielding region that has a shape corresponding to the divided region on a center side and is arranged at a position corresponding to the divided region on the center side. 
     EFFECTS OF THE INVENTION 
     With this configuration, it is possible to reduce a loss of the illumination light caused by the first diaphragm, while securing the light shielding property for the unnecessary light, thereby suppressing a decrease in contrast. Thus, it is possible to achieve higher brightness in a projection display device such as a projector. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view showing a configuration of an optical system of a projection display device according to an embodiment of the present invention. 
         FIG. 2  is a view showing a state of light incidence and reflection in an illumination optical system of the same projection display device. 
         FIG. 3A  is a view showing light shielding states in pupils of an illumination optical system and a projection lens due to a diaphragm of a conventional projection display device. 
         FIG. 3B  is a view showing an example of light shielding states in pupils of the illumination optical system and a projection lens due to diaphragms of the projection display device according to the embodiment of the present invention. 
         FIG. 3C  is a view showing another example of light shielding states in the pupils of the illumination optical system and the projection lens due to the diaphragms of the same projection display device. 
         FIG. 4  is a view showing a configuration of an optical system of a conventional projection display device. 
         FIG. 5A  is a view showing a configuration and an operation of a reflection-type light valve in the same projection display device. 
         FIG. 5B  is a view showing another operation of the reflection-type light valve in the same projection display device. 
         FIG. 5C  is a view showing still another operation of the reflection-type light valve in the same projection display device. 
         FIG. 6  is a view showing a state of light incidence and reflection in the illumination optical system of the same projection display device. 
         FIG. 7  is a view showing a light shielding state due to the diaphragm of the same projection display device. 
     
    
    
     EXPLANATION OF LETTERS OR NUMERALS 
     
         
         
           
               1  Lamp 
               2  Concave mirror 
               3  Rod prism 
               4  Condenser lens 
               5  Color wheel 
               6   a  Total reflection prism 
               6   b  Dichroic prism 
               7  First diaphragm 
               8  Second diaphragm 
               9  Reflection-type light valve 
               10  Projection lens 
               11  Diaphragm 
               12  Mirror element 
               13  Reference plane 
               14  Cover glass 
               15  Illumination principal ray 
               16  ON-light principal ray 
               17  OFF-light principal ray 
               18  Flat light 
               19  Pupil of illumination optical system 
               20  Pupil of projection lens 
               21  Spot of flat light 
               22  Unnecessary light 
               23  Light shielding region 
               24 ,  24   a ,  24   b  Light shielding region 
               25 ,  25   a ,  25   b  Light shielding region 
           
         
       
    
     DESCRIPTION OF THE INVENTION 
     Based on the above-described configuration, the projection display device of the present invention may have the following aspects. 
     More specifically, preferably, the reflection-type-light valve is formed of a plurality of mirror elements arranged in a matrix, each controlling a reflection direction of light based on a video signal. 
     Further, preferably, the light shielding region of the first diaphragm has a shape equivalent to that of one of the divided regions obtained by dividing a convex lens shape surrounded by two arcs by a straight line parallel to a line connecting both apexes of the lens shape, and the light shielding region of the second diaphragm has a shape equivalent to that of the other divided region. 
     Further, preferably, on an incident side surface of each of the first diaphragm and the second diaphragm, a reflection mirror formed of a metal or a dielectric multiplayer film is formed so as to reflect at least 80% or more of incident light. 
     Further, preferably, the illumination optical system has a rod prism whose length is set so that circumferential illumination is 90% or more with respect to central illumination. 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 
     Embodiment 
       FIG. 1  is a view showing a configuration of an optical system of a projection display device according to an embodiment of the present invention. In  FIG. 1 , a lamp  1  as a light source, a concave mirror  2 , a rod prism  3 , a condenser lens  4 , a color wheel  5 , a dichroic prism  6 , a reflection-type light valve  9 , and a projection lens  10  have the same configurations as those in the conventional example shown in  FIG. 4 . 
     In the present embodiment, instead of the diaphragm  11  in the conventional example shown in  FIG. 4 , a first diaphragm  7  provided at a position of a pupil of an illumination optical system and a second diaphragm  8  provided at a position of a pupil of the projection lens  10  are used in combination so as to function to block flat light. The configurations of the first diaphragm  7  and the second diaphragm  8  will be described later. 
     As in the conventional example shown in  FIG. 5 , the reflection-type light valve  9  has mirror elements  12  formed in a matrix on a pixel basis, and controls a traveling direction of light based on a video signal so as to form an optical image in accordance with a change in reflection angle. 
     Further, the concave mirror  2  is formed of an ellipsoidal mirror in which a cross-sectional shape of a reflection surface forms an ellipse, and has a first focal point and a second focal point. The lamp  1  may be a high-pressure mercury lamp, and is arranged so that a center of an illuminant is located in the vicinity of the first focal point of the concave mirror  2 . The rod prism  3  is arranged so that its light incident surface is located in the vicinity of the second focal point of the concave mirror  2 . 
     The rod prism  3  has a quadratic prism shape in which a light incident surface and a light exiting surface have the same aspect ratio as that of an effective display area of the reflection-type light valve  9 . The rod prism  3  is provided at a place where light emitted from the lamp  1  is condensed, so that it preferably is made of quartz glass having excellent heat resistance. 
     An illuminant image of the lamp  1  condensed by the concave mirror  2  is formed in the vicinity of the incident surface of the rod prism  3 . There is a tendency for the illuminant image of the lamp  1  condensed by the concave mirror  2  to be brightest in a central region close to the optical axis and become dark rapidly toward the circumference, so that the brightness is non-uniform on the surface. In contrast, a luminous flux incident on the rod prism  3  is subjected to multiple reflection on a side surface of the rod prism  3 , and the illuminant image is divided minutely and overlapped by the number of reflections to be illuminated, so that the brightness is made uniform on the exiting surface of the rod prism  3 . 
     Thus, due to the effect of minute division and overlapping of the illuminant image of the lamp, as the number of reflections in the rod prism  3  is larger, uniformity is enhanced. Therefore, the degree of uniformity depends on the length of the rod prism  3 . In the present embodiment, the length of the rod prism  3  is set so that the circumferential illumination on a screen is 90% or more with respect to the central illumination. 
     As described above, the exiting surface of the rod prism  3 , in which brightness is made uniform, is set as a secondary surface light source, and an image is formed with the condenser lens  4  provided downstream at a magnification that is matched with an effective display area of the reflection-type light valve  9 . Consequently, both the securing of a condensing efficiency and the enhancement of uniformity can be satisfied. 
     Further, by rotating the color wheel  5  arranged in the vicinity of the second focal point of the concave mirror  2 , the white light output from the lamp  1  is divided into light beams of three primary colors of red, green, and blue, which pass sequentially so as to illuminate the reflection-type light valve  9  in a time-division manner. Thus, a full-color projected image can be displayed by using the one reflection-type light valve  9 . 
     Further, as in the conventional example shown in  FIGS. 5A to 5C , the light emitted from the lamp  1  and condensed by the illumination optical system is incident on the reflection-type light valve  9 . As shown in  FIG. 5A , among the illumination principal rays  15  incident on the reflection-type light valve  9 , the ON-light principal ray  16  reflected for a white image is incident on the projection lens  10  to be magnified and projected onto a screen (not shown). On the other hand, as shown in  FIG. 5B , the OFF-light principal ray  17  for a black image travels outside of an effective diameter of the projection lens  10 , and does not reach the screen. 
     Next, with reference to  FIG. 2  for explaining the incidence and reflection in the illumination optical system, a description will be given of the relationship between the shapes of the first diaphragm  7  provided at the position of the pupil  19  of the illumination optical system as well as the second diaphragm  8  provided at the position of the pupil  20  of the projection lens  10  and the blocking of the unnecessary light  22 . In  FIG. 2 , the relationship between the incidence and reflection of the illumination principal ray  15  on/from the reflection-type light valve  9  is the same as that in the conventional example shown in  FIG. 6 , and thus the same components are denoted with the same reference numerals and descriptions thereof will not be repeated. 
     Alight shielding region  24  of the first diaphragm  7  is positioned similarly but shaped differently to/from that of the diaphragm  11  in the conventional example shown in  FIG. 6 . More specifically, the shape of the light shielding region  24  is equivalent to that of a region on an outer peripheral side obtained when the lens shape of the conventional light shielding region is divided by a line in a direction along a chord of an outer shape of the pupil  19 , i.e., a line parallel to a line connecting both apexes of the lens shape. In other words, the shape of the light shielding region  24  is equivalent to that obtained when a region on a center side is deleted from the lens shape of the diaphragm  11  in the conventional example. 
     On the other hand, a light shielding region  25  of the second diaphragm  8  has a shape corresponding to a remaining portion obtained when the light shielding region  24  of the first diaphragm  7  is cut from the conventional light shielding region with the lens shape. The light shielding region  25  is arranged on an outer peripheral side of a region corresponding to the unnecessary light  22  in the pupil  20  of the projection lens  10 . The light shielding region  24  of the first diaphragm  7  corresponds to a region on an outer peripheral side of the region of the unnecessary light  22  in the flat light  18 , and accordingly is located on a center side in the pupil  20 . Thus, similarly to the conventional diaphragm  11 , a combined light shielding region of the light shielding region  24  of the first diaphragm  7  and the light shielding region  25  of the second diaphragm  8  corresponds to the entire region of the unnecessary light  22 . 
     However, the light shielding region  24  of the first diaphragm  7  and the light shielding region  25  of the second diaphragm  8  do not necessarily need to cover the region of the unnecessary light  22  completely. Even if the light shielding region is somewhat inadequate for the region of the unnecessary light  22 , a practically sufficient effect can be achieved. 
     As described above, the combined light shielding region of the first diaphragm  7  and the second diaphragm  8  blocks the same amount of unnecessary light  22  as that blocked by the light shielding region of the diaphragm  11  provided in the conventional illumination optical system. However, in each of the pupil  19  of the illumination optical system and the pupil  20  of the projection lens  10 , a luminous flux is stopped in the area divided from the periphery. Thus, light in the central region of the luminous flux having high brightness can be included in the ON light without being blocked, and further the unnecessary light  22  of the flat light  18  can be blocked. Consequently, a brightness loss is reduced with equal contrast performance, resulting in higher brightness than that in the conventional example. 
     As described above, the light shielding region  24  of the first diaphragm  7  and the light shielding region  25  of the second diaphragm  8  are arranged so that their respective symmetry axes coincide with planes including the illumination principal ray  15  and the ON-light principal ray  16 . The light shielding region  25  of the second diaphragm  8  is arranged on one end side of the diameter of the pupil  20  closer to the flat light  18 . 
     Next, configurations of the first diaphragm  7  and the second diaphragm  8  will be described with reference to  FIGS. 3A to 3C  for explaining light shielding states.  FIG. 3A  shows a light shielding state when the diaphragm is provided only at the position of the pupil of the illumination optical system, which is the same as that in the conventional example shown in  FIG. 7 . It is understood that no diaphragm is provided at the position of the pupil of the projection lens.  FIGS. 3B and 3C  show light shielding states of the present embodiment. 
     In  FIG. 3A , (a) shows the light shielding region  23  of the diaphragm  11  in the pupil  19  of the illumination optical system in the conventional example. In  FIGS. 3B and 3C , (a) shows light shielding regions  24   a  and  24   b  of the first diaphragm  7  in the pupil  19  of the illumination optical system in the present embodiment. In  FIG. 3A , (b) shows the pupil  20  of the projection lens  10 , in which no light shielding region is provided in this case. In  FIGS. 3B and 3C , (b) shows light shielding regions  25   a  and  25   b  of the second diaphragm  8  in the pupil  20  of the projection lens  10 . 
     The light shielding region of the first diaphragm  7  has a shape equivalent to that of one region obtained when the lens shape is divided by a straight line parallel to a line connecting both apexes of the lens shape. More specifically, the arcuate light shielding region  24   a  surrounded by a chord and an arc of the circle as shown in (a) in  FIG. 3B , or the light shielding region  24   b  having a shape obtained when an actuate portion is cut from the lens shape as shown in (a) in  FIG. 3C  is used. A region on a center side of the pupil  19  is deleted, and a divided region on an outer peripheral side is used. 
     The second diaphragm  8  forms the light shielding region  25   a  or  25   b  having a shape corresponding to a remaining portion obtained when the light shielding region of the first diaphragm  7  is cut from the lens shape. Namely, the conventional light shielding region  23  shown in  FIG. 3A  is divided by the first diaphragm  7  and the second diaphragm  8 , so that the light shielding regions  24   a  and  25   a  or the light shielding regions  24   b  and  25   b  are used in combination as shown in  FIG. 3B  or  3 C. 
     The light shielding regions  24   b  and  25   b  in  FIG. 3C  are different from the light shielding regions  24   a  and  25   a  in  FIG. 3B  in that a smaller weight is assigned to the second diaphragm  8  with respect to the light shielding ratio of a luminous flux. In either case, the sum of a light shielding area of the first diaphragm  7  and a light shielding area of the second diaphragm  8  desirably is the same as a light shielding area of the diaphragm  11  provided in the conventional illumination optical system. 
     By dividing the light shielding region in this manner, light in the central region of the luminous flux having high brightness is not blocked, while peripheral light is blocked, resulting in a smaller brightness loss and higher brightness than in the conventional example. 
     In general, when a diaphragm is provided for a projection lens, the diaphragm absorbs light to cause thermal expansion and contraction of a lens mirror and the like, which may result in deterioration of focusing performance. In such a case, a diaphragm amount of the projection lens may be determined so as not to cause a problem in projection lens performance. 
     Further, it is desirable that a reflective film made of a metal or a dielectric multilayer film is formed on surfaces of the diaphragm of the illumination optical system and the diaphragm of the projection lens so as to reflect 80% or more of incident light. 
     INDUSTRIAL APPLICABILITY 
     The projection display device of the present invention can reduce a light loss caused by the diaphragm for blocking unnecessary light, thereby suppressing a decrease in contrast. Therefore, the present invention is useful as a projection display device such as a projector.