JP4329777B2 - Light selection prism and projection display device using the same - Google Patents

Description

  The present invention relates to a light selection prism and a projection display device using the same.

  In a projection display device that projects a color image, a cross dichroic prism is often used as a light selection prism. The cross dichroic prism has two types of dichroic films intersecting in a substantially X shape, and functions as a color light combining optical system that combines three colors of red, green, and blue light and emits them in the same direction. Have

  FIG. 12 is a conceptual diagram showing a main part of the projection display device. The projection display device includes three liquid crystal light valves 42, 44, 46, a cross dichroic prism 48, and a projection lens 50. At the center of the cross dichroic prism 48, a red reflecting film 48R and a blue reflecting film 48B are formed in a substantially X shape. The cross dichroic prism 48 synthesizes light of the three colors red, green, and blue modulated by the three liquid crystal light valves 42, 44, and 46 and emits the light in the direction of the projection lens 50. The projection lens 50 forms an image of the combined light on the projection screen 52.

  A normal cross dichroic prism is created by bonding the side surfaces of four columnar prisms of the same size. The red reflecting film 48R is formed in advance on predetermined side surfaces of the two columnar prisms so as to form the same plane when the four columnar prisms are bonded together. Similarly, the blue reflecting film 48B is also formed in advance on predetermined side surfaces of the two columnar prisms.

  The red reflection film 48R separates and reflects only red light and transmits other color light. The blue reflective film 48B separates and reflects only blue light and transmits other color light. A dielectric multilayer film called a dichroic film is usually used for the reflective film having such characteristics. These reflecting films function to bend the light from the liquid crystal light valves 42 and 46 by 90 ° and direct the light to the projection lens 50 evenly. Therefore, it is preferable that the reflection film formed in a substantially X shape on the cross dichroic prism is formed on a plane.

  However, in the case of creating a cross dichroic prism by bonding four columnar prisms of the same size, the bonding is performed accurately so that the surfaces of the red reflecting film 48R and the blue reflecting film 48B are flat surfaces. It is quite difficult to do. Therefore, a gap or a step is generated in each of the red reflecting film 48R and the blue reflecting film 48B in the vicinity of the intersection at the center of the cross dichroic prism. For this reason, with respect to the light passing near the intersection, the reflection characteristics and transmission characteristics of the red reflection film 48R and the blue reflection film 48B change, and as a result, the characteristics of the cross dichroic prism 48 deteriorate, and the light at the intersection There was a problem of scattering. When such a cross dichroic prism is applied to a projection display device, there is a problem that a streak caused by light scattering in the cross dichroic prism can be seen in the approximate center of the projected image. In addition, there is a problem that the image at the center of the projection screen partially overlaps and the screen size is different for each color.

  Note that the cross dichroic prism can also be used to separate light, and the above-described problem of characteristic deterioration of the cross dichroic prism is also common in such a case. In addition to the cross dichroic prism, another type of light selection prism in which a light selection film for selectively transmitting or reflecting light is formed in an approximately X shape may be used as the optical element. . The above-described problem of characteristic deterioration is a problem common to such various light selection prisms.

  The present invention has been made in order to solve the above-described problems in the prior art, and an object thereof is to provide a technique for improving the characteristics of the light selection prism.

At least some of the above problems can be solved by the light selection prism of the present invention. This light selection prism is a light selection prism having two types of light selection films intersecting in a substantially X shape,
Four columnar prisms joined on the sides of each other;
Two light selective films formed so as to intersect in a substantially X shape along the side surfaces of the four columnar prisms,
One of the two photoselective films is continuously formed without being divided at an intersection position of the two photoselective films,
The surface on which the light selective film is continuously formed is a curved surface.

  According to the light selection prism having the above-described configuration, one of the two light selection films is continuously formed without being divided at the intersection position, so that the light selection film near the substantially X-shaped intersection is formed. Characteristics can be improved. In addition, the size of the image formed by the light reflected from the light selection film formed on the curved surface can be adjusted. Thereby, the characteristics of the light selection prism can be improved.

The cross dichroic prism as the light selection prism according to the present invention can also be applied to a projection display device. The projection display device is a projection display device that projects and displays an image.
An illumination optical system that emits illumination light;
A color light separation optical system for separating the illumination light into three colors of light;
Three sets of light modulation means for modulating the light of the three colors based on a given image signal;
A cross dichroic prism for combining three colors of light modulated by the three sets of light modulation means;
A projection optical system for projecting light synthesized by the cross dichroic prism,
The cross dichroic prism is
Four columnar prisms joined on the sides of each other;
Two dichroic films formed so as to intersect in a substantially X shape along the side surfaces of the four columnar prisms,
One of the two dichroic films is formed continuously without being divided at the intersection position of the two dichroic films,
The surface on which the dichroic film is continuously formed is a curved surface.

  Since this projection type display device uses the cross dichroic prism according to the present invention to synthesize light, there is a problem that a streak caused by light scattering in the cross dichroic prism can be seen at the approximate center of the projected image. Can be relaxed. In addition, the size of the image formed by the light reflected from the dichroic film formed on the curved surface can be adjusted. Thereby, the characteristics of the cross dichroic prism as the light selection prism can be improved, and chromatic aberration generated in the optical system of the projection display device can be corrected.

A. First light selection prism:
Next, embodiments of the present invention will be described based on examples. FIG. 1 is an explanatory view showing a cross dichroic prism which is a first embodiment of a light selection prism according to the present invention. The cross dichroic prism 260 includes four right-angle prisms (columnar prisms) 261, 262, 263, and 264. The four right-angle prisms 261 to 264 have a right-angled isosceles triangular prism shape having the same height. The cross dichroic prism 260 is a quadrangular prism (a rectangular parallelepiped or a cube) formed by joining right-angled prism side surfaces (hereinafter referred to as “right-angle surfaces” or “joint surfaces”) to each other with an adhesive 267.

  As shown in FIG. 1B, a red reflecting film 266R and a blue reflecting film 266B are formed in a substantially X shape on the joint surface formed by the right-angle surfaces of the four right-angle prisms 261 to 264. Further, the red reflecting film 266R is continuous over the entire red reflecting film forming surface formed by the bonding surface between the two right-angle prisms 261 and 263 and the bonding surface between the other two right-angle prisms 262 and 264. It is a dichroic film (photoselective film) formed as described above. On the other hand, the blue reflecting film 266B is a dichroic film formed on each of the bonding surface between the two right-angle prisms 261 and 262 and the bonding surface between the other two right-angle prisms 263 and 264. The blue reflective film 266B formed on the two bonding surfaces is isolated by the red reflective film 266R and the adhesive 267.

  As described above, the cross dichroic prism 260 is continuously formed over one whole (entire surface) of two film formation surfaces where the red reflection film 266R intersects in a substantially X shape. Thereby, the characteristic (reflection / transmission characteristic) of the red reflecting film 266R does not deteriorate even at the center of the cross dichroic prism 260. The blue reflective film 266B is separated by the red reflective film 266R and the adhesive 267, but is disposed with high accuracy so as to exist on the same plane. A blue reflective surface with good transmission characteristics can be obtained. Thereby, the characteristic of the cross dichroic prism 260 can be improved. The reason why the blue reflective film 266B side is separated is that blue light has lower relative visibility than red light, and the resolution of the human eye is lower.

  Note that the four columnar prisms 261, 262, 263, and 264 may have a triangular shape having substantially right angles instead of a right-angled isosceles triangle.

B. First manufacturing method:
Next, a first manufacturing method of the cross dichroic prism shown in FIG. 1 will be described with reference to FIGS. FIG. 2 is an explanatory diagram showing a process of cutting out the cross dichroic prism from the prism column. In the manufacturing process of the cross dichroic prism 260, first, a prism column 320 that is long in the longitudinal direction as shown in FIG. 2 is formed, and a prism having a desired length is cut out from the prism column 320.

  The prism column 320 is configured by bonding a first prism pair 321 and a second prism pair 322. The first prism pair 321 is configured by bonding a relatively long rectangular prism 325 (hereinafter simply referred to as “long rectangular prism”) and a relatively short rectangular prism 326 (hereinafter simply referred to as “short rectangular prism”). ing. Similarly, the second prism pair 322 includes a long rectangular prism 327 and a short rectangular prism 328 that are bonded together. The lengths of the right-angle prisms 325 to 328 may be set so that the short-angle prisms 326 and 328 are shorter than the long-angle right-angle prisms 325 and 327. Need not be equal. In addition, when the lengths of the long right-angle prisms and the short right-angle prisms are equal, the types of the right-angle prisms to be prepared can be minimized, and the manufacture is easy. In each drawing of the present embodiment, long right-angle prisms and short right-angle prisms are shown with the same size.

  FIG. 3 is an explanatory view showing a manufacturing process of the prism pair 321 and 322. The first prism pair 321 is manufactured as follows. First, a long right-angle prism 325 shown in FIG. 3A and a short right-angle prism 326 shown in FIG. 3B are prepared. Each of the three side surfaces of the long right-angle prism 325 and the short right-angle prism 326 is a light passing surface, and thus is a polished surface that is polished flat. A blue reflecting film 266B (shown by an oblique broken line in FIG. 3B) is formed on the right-angle plane 326a of the short right-angle prism 326. This blue reflective film 266B is a dielectric multilayer film in which inorganic thin films are formed in multiple layers, and is formed by vacuum deposition or sputtering. Then, the right-angle surface 325a of the long right-angle prism 325 and the right-angle surface 326a of the short right-angle prism 326 are bonded together to produce the first prism pair 321 shown in FIG. At this time, the long rectangular prism 325 is bonded so that the exposed portions 321d and 321e are formed above and below the right angle surface 325a. For the bonding, a first assembly jig 500 shown in FIG. 4 is used. The first assembly jig 500 includes a base 502 including reference surface portions 502a and 502b provided at both left and right ends and a substantially rectangular groove portion 502c. The upper surfaces of the reference surface portions 502a and 502b are processed so as to be substantially the same plane. The groove 502c is an escape portion when the adhesive applied to the joint surface overflows.

  When the two right-angle prisms 325 and 326 are bonded together, first, an adhesive is applied to at least one of the bonding surfaces of the two right-angle prisms and bonded. After that, as shown in FIG. 4, the two prisms 325 and 326 are placed on the base 502, that is, on the reference surface portions 502a and 502b. Then, the two prisms are pressed against the reference surface portions 502a and 502b. By doing so, the prisms can be set parallel to the longitudinal direction.

  Thus, after setting the relative positional relationship between the two right-angle prisms 325 and 326, the adhesive applied to the bonding surface is solidified. As a result, the first prism pair 321 can be obtained.

  Further, in the same manner, the right-angle prism 327 and the right-angle prism 328 on which the blue reflecting film 266B is formed are bonded together to produce the second right-angle prism pair 322.

  FIG. 5 is an explanatory diagram showing, in an enlarged manner, the joint surface 321c of the first prism pair 321 out of the two prism pairs manufactured as described above. As shown in FIG. 3C, the joint surface 321c is a surface sandwiched between two right-angle surfaces 321a and 321b of the first prism pair 321. The second prism pair 322 is formed on the joint surface 321c. Be joined.

  The joint surface 321c includes the right-angle surfaces 325b and 326b of the two right-angle prisms 325 and 326, and is a surface pressed against the reference surface portions 502a and 502b of the first assembly jig 500. As shown in FIG. 5A, the right-angle surface 326b may have a protrusion in which the blue reflecting film 266B formed on the right-angle surface 326a wraps around a right-angle corner. Further, depending on the pressing force of the right-angle prisms 325 and 326 against the first assembly jig 500, there may be a slight level difference between the right-angle surface 325b and the right-angle surface 326b. As a result, the joining surface 321c of the first right-angle prism pair 321 is often not flat. Therefore, as shown in FIG. 5B, the bonding surface 321c is polished so as to be flat. Then, as shown in FIG. 5C, a red reflective film 266R is formed on the flat bonding surface 321c. The red reflective film 266R is also formed by vapor deposition or sputtering, like the blue reflective film 266B. As described above, if the red reflecting film 266R is formed on a flat surface, the red reflecting film 266R is constituted by one continuous film, and therefore, light scattering particularly in the vicinity of the joint portion between the two right-angle prisms 325 and 326. As a result, streaks due to the scattering of light do not occur on the screen. In addition, when the bonding surface 321c is a flat surface, the reflective film is formed on the same plane with high accuracy. Therefore, there is an advantage that the size of the image on the screen does not change from side to side even if light is reflected by 90 °. is there. The “flat surface” in the present invention means a continuous surface without a step, and is not necessarily a geometrically strict plane.

  Also for the second prism pair 322, the joint surface 322 c is polished in the same manner as the first prism pair 321. As described above, when the red reflecting film 266R is formed on the bonding surface 321c of the first prism pair 321, it is necessary to form the red reflecting film 266R on the bonding surface 322c of the second prism pair 322. Absent. Further, the red reflecting film 266R may be formed on the joint surface 322c of the second prism pair 322 instead of being formed on the joint surface 321c of the first prism pair 321.

  By the way, when comparing two colors of red and blue light reflected on the reflecting surface, the red light has higher specific sensitivity (that is, it is more conspicuous with the naked eye). Therefore, it is preferable that the red reflecting film constitutes a flat surface with as few steps as possible. In the manufacturing method of this embodiment, since the red reflecting film 266R shown in FIG. 5C is formed continuously over the entire bonding surface 321c, a cross dichroic prism excellent also in this respect is manufactured. be able to. Since the relative luminous sensitivity is in the order of green> red> blue, when the green reflective film is used instead of the red reflective film or the blue reflective film, the green reflective film is formed according to the method shown in FIG. It is preferable to produce it on the bonding surface 321c.

  FIG. 6 is an explanatory diagram showing a process of bonding two pairs of prisms 321 and 322 created according to the method of FIGS. First, the second prism pair 322 shown in FIG. 6A and the first prism pair 321 shown in FIG. 6B are bonded together so that the short prisms and the long prisms are adjacent to each other. A prism column 320 shown in FIG. In this bonding, a second assembly jig 520 shown in FIG. 7 is used. The second assembly jig 520 includes a base 522 including a reference surface portion 522a provided in a frame shape and a groove portion 522c formed in the center of the reference surface portion 522a. The upper surface of the reference surface portion 522a is processed with high accuracy. The width W3 of the groove 522c is set slightly larger than the length L1 in the longitudinal direction of the short right-angle prism 326, and the depth H1 is set larger than the width L3 of the right-angle surfaces of the short right-angle prisms 326 and 328. The width W4 of the base 522 is set larger than the length L2 in the longitudinal direction of the long right-angle prisms 325 and 327.

  When the two pairs of prisms 321 and 322 are bonded to each other, an adhesive is applied to the joint surface, and the short right-angle prisms 326 and 328 are accommodated in the groove 522c as shown in FIG. As described above, the two prism pairs 321 and 322 are placed on the second assembly jig 520. At this time, the long right-angle prisms 325 and 327 are pressed against the upper surfaces of the reference surface portions 522a and 522b. Thus, the mutual positional relationship is set so that the blue reflecting film 266B formed inside the first prism pair 321 and the blue reflecting film 266B formed inside the second prism pair 322 constitute the same surface. can do.

  FIG. 8 is an enlarged side view showing a state where two pairs of prisms 321 and 322 are placed on the second assembly jig 520. In FIG. 8, for ease of explanation, the reference surface portion 522a is shown through. The upper surface 522a (U) of the reference surface portion 522a is in contact with the right-angle surfaces 325a and 327a of the two long right-angle prisms 325 and 327 (bonded surfaces (bonded surfaces) bonded to the short right-angle prisms 326 and 328). Among these, only the exposed portions (321d, 321e, 322d, and 322e in FIG. 6) where no reflective film is formed. Since these exposed portions 321d, 321e, 322d, and 322e are polished surfaces, by placing these exposed portions on the upper surface 522a (U) of the reference surface portion 522a of the base 522, high flatness with respect to these polished surfaces. Can be obtained. Here, “flatness” indicates high continuity of the surface (no step). At this time, as shown in FIGS. 6A and 6B, the blue reflecting film 266B is formed on the polished surface (bonding surface) flush with the exposed portions 321d and 321e, and the exposed portion 322d. , 322e, a blue reflective film 266B is also formed on the polished surface (bonding surface). Therefore, by attaching the prism pairs as shown in FIG. 7, high flatness can be obtained also for the blue reflecting surfaces formed by the respective blue reflecting films 266B.

  Thus, after setting the relative positional relationship between the two pairs of prisms with high accuracy, the adhesive applied to the bonding surface is solidified. As a result, the prism column 320 (FIG. 6C) combined with high accuracy can be obtained. If an adhesive that bonds four right-angle prisms is an ultraviolet curable adhesive having a low viscosity, the curing time can be shortened and the generation of heat during curing can be reduced.

  As shown in FIG. 2, the prism column 320 thus manufactured is cut out of a prism having a desired length by two cut surfaces that are substantially perpendicular to the longitudinal direction and substantially parallel to each other, whereby a cross dichroic prism 260 is obtained. Can be manufactured. In this way, a relatively small cross dichroic prism can be easily manufactured by cutting out a prism having a desired length from the relatively large prism column 320. Thus, the projection display device can be downsized by applying the cross dichroic prism manufactured in this way to the projection display device. The prism column 320 can also be used as a cross dichroic prism.

  In the cross dichroic prism 260 manufactured as described above, the red reflective film 266R is continuously formed over the entire joint surface of the two pairs of prisms, so that the reflection characteristics and transmission characteristics of the red reflective film 266R are improved. Can be made. Thereby, the characteristic of the cross dichroic prism 260 can be improved. The blue reflective film 266B is separated by the red reflective film 266R, but can be arranged with high precision so that it exists on the same surface. A good blue separation reflecting surface can be obtained. This also improves the characteristics of the cross dichroic prism 260.

  In the above manufacturing method, an example is described in which a right-angle prism in which three side surfaces of each of the four right-angle prisms 325, 326, 327, and 328 are polished flatly is used. However, the present invention is not limited thereto. is not. You may make it use the right angle prism by which the side surface mutually joined of two right angle prisms which comprise a prism pair is grind | polished at least. In this case, of the other unpolished side surfaces, the side surfaces corresponding to the joint surfaces 321c and 322c where the two prism pairs 321 and 322 are joined together are polished in the process shown in FIG. Further, the side surface corresponding to the outer surface of the prism 260 may be polished after the prism column 320 is manufactured or after the cross dichroic prism 260 is cut out from the prism column 320. If it does in this way, the damage | wound of the glass surface which is easy to generate | occur | produce in each manufacturing process can be removed at any time.

C. Second light selection prism:
FIG. 9 is an explanatory view showing a cross dichroic prism which is a second embodiment of the light selection prism. The cross dichroic prism 260A includes four columnar prisms 261A, 262A, 263A, and 264A. The four columnar prisms 261A to 264A have a substantially triangular prism shape having the same height. The cross dichroic prism 260 </ b> A is a quadrangular column that is formed by bonding two adhesive side surfaces to each other at two side surfaces forming one corner of each columnar prism.

  On the side surface (hereinafter referred to as “joint surface”) where the four columnar prisms 261A to 264A are joined together, as shown in FIG. 9B, a red reflective film 266R and a blue reflective film 266B are substantially X-shaped. Is formed. Further, the red reflecting film 266R is continuous over the entire surface of the red reflecting film formed by the joining surface between the two columnar prisms 261A and 263A and the joining surface between the other two columnar prisms 262A and 264A. It is a dichroic film (photoselective film) formed as described above. On the other hand, the blue reflecting film 266B is a dichroic film formed on each of the bonding surface between the two columnar prisms 261A and 262A and the bonding surface between the other two columnar prisms 263A and 264A. The blue reflective film 266B formed on the two bonding surfaces is isolated by the red reflective film 266R and the adhesive 267.

  Similarly to the cross dichroic prism 260 of FIG. 1, the cross dichroic prism 260A is also formed continuously over the entire one (entire surface) of two film formation surfaces where the red reflecting film 266R intersects in a substantially X shape. . As a result, the characteristics (reflection / transmission characteristics) of the red reflective film 266R do not deteriorate even at the center of the cross dichroic prism 260A. Similarly to the cross dichroic prism 260, the blue reflective film 266B is separated by the red reflective film 266R and the adhesive 267. However, except for this separation, the blue reflective film 266B is on the same continuous surface (on the same plane in FIG. 9). It is arranged with high accuracy so as to exist almost. For this reason, although there is a loss due to separation, it is possible to obtain a blue reflecting surface with good reflection characteristics and transmission characteristics. From the above, the characteristics of the cross dichroic prism 260A can be improved in the same manner as the cross dichroic prism 260.

  Here, the film formation surface on which the red reflective film 266R is formed has a curved surface as shown in FIG. The curved surface is not limited to a so-called curved surface such as a spherical surface or an elliptical surface, but may be a shape having a plurality of bent planes. Thus, when the red reflecting film 266R is formed on the curved film forming surface, the reflection direction of the red light in the red light reflecting film 266R can be controlled according to the position of the red reflecting film 266R. Can change the screen size by red light. Therefore, when this cross dichroic prism 260A is applied to a projection display device, it is possible to suppress a decrease in image quality due to chromatic aberration occurring in the projection optical system.

  The cross dichroic prism 260A can also be manufactured according to the first manufacturing method. In this case, when the bonding surface 321c described in FIG. 5B is polished flat, the film formation surface can be curved by polishing the bonding surface 321c into a curved surface.

D. Second manufacturing method:
FIG. 10 is an explanatory diagram showing a step of preparing four columnar prisms in the second manufacturing method of the cross dichroic prism. As shown in FIG. 10A, an optical plate glass 400 such as white plate glass is prepared. As the plate glass 400, one managed so as to have a uniform refractive index within the plate glass is used. The upper and lower surfaces 402 and 404 of the plate glass 400 are polished and flattened, and a blue reflective film 266B (shaded portion) is formed on the upper surface 402 as shown in FIG. Then, the plate glass 400 is divided into four along the one-dot chain line in FIG. 10B to cut out four columnar prisms 425, 426O, 427, and 428O as shown in FIG. 10C. Of these four columnar prisms 425, 426O, 427, and 428O, when the columnar prisms 425 and 427 are right-angle prisms, they correspond to the long right-angle prisms 325 and 327 shown in FIG. By cutting the columnar prisms 426O and 428O along the alternate long and short dash line in FIG. 10C, columnar prisms 426 and 428 are produced as shown in FIG. When these columnar prisms 426 and 428 are right angle prisms, they correspond to the short right angle prisms 326 and 328 shown in FIG. Here, the side surfaces 325 a, 326 a, 327 a, and 328 a that are joined to each other when the two prism pairs are formed by the four columnar prisms 425, 426, 427, and 428 are the polished upper surface 402 or lower surface 404 of the plate glass 400. It is.

  By assembling the four columnar prisms 425, 426, 427, and 428 prepared as described above in the same manner as the manufacturing steps shown in FIGS. 3 to 7, the prisms 320 correspond to the prism column 320 shown in FIG. The prism column 420 can be manufactured. A small prism column is cut out by cutting the manufactured prism column 420 in an appropriate length in the longitudinal direction (height direction). Then, by polishing and flattening the outer surface of the cut out small prism column, the cross dichroic prism 260 in FIG. 1 and the cross dichroic prism 260A in FIG. 9 can be manufactured. The outer surface of the cross dichroic prism 260A may be polished to a curved surface as well as a flat surface.

  According to the second manufacturing method, since the cross dichroic prism can be manufactured from one sheet glass, the refractive index in the cross dichroic prism can be made uniform. As a result, there is no difference in the optical path of light generated by light refraction in the cross dichroic prism. Moreover, since the surface required in each manufacturing process is produced for every process, the damage | wound of the glass surface which generate | occur | produces during a manufacturing process can be reduced, and the flatness of a reflective surface can be improved.

  In the above description of the second manufacturing method, the case where a small prism column is cut out from the prism column 420 and then the outer surface thereof is polished has been described. However, the present invention is not limited to this. The outer surface of the prism column 420 may be polished.

  In the description of the second manufacturing method, the case where the plate glass 400 is divided into four parts after the blue reflective film 266B is formed on the plate glass 400 is explained. A blue reflective film 266B may be formed on the side surfaces of the prisms 426 and 428.

  In the description of the second manufacturing method, the case where two prism pairs are configured by the combination of the columnar prisms 425 and 426 and the combination of the columnar prisms 427 and 428 is described. However, the combination of the columnar prisms 425 and 428 is described. And columnar prisms 426 and 427, or a combination of columnar prisms 425 and 427 and a columnar prism 426 and 428. Preferably, the combination is such that the refractive indexes of adjacent columnar prisms are close to each other. In this way, it is possible to prevent image degradation due to light refraction within the prism.

  Also in the first manufacturing method, if four columnar prisms made from one sheet glass are used, as in the second manufacturing method, image degradation due to light refraction in the prism, etc. Can be prevented.

  Also in the first manufacturing method, the outer surface of the prism column 320 and the outer surface of the small prism column cut out from the prism column 320 can be polished to a curved surface instead of a flat surface. The four prisms constituting the cross dichroic prism manufactured in this case are not prisms but columnar prisms.

E. Configuration of the projection display device:
FIG. 11 is a schematic plan view showing a main part of a projection display apparatus using the cross dichroic prism 260 according to the embodiment of the present invention. The projection display device includes an illumination optical system 100, dichroic mirrors 210 and 212, reflection mirrors 220, 222, and 224, an incident side lens 230, a relay lens 232, and three field lenses 240, 242, and 244. And three liquid crystal light valves (liquid crystal panels) 250, 252 and 254, a cross dichroic prism 260, and a projection lens system 270.

  The illumination optical system 100 includes a light source 110 that emits substantially parallel light bundles, a first lens array 120, a second lens array 130, a polarization conversion element 140, a reflection mirror 150, and a superimposing lens 160. I have. The illumination optical system 100 is an integrator optical system for substantially uniformly illuminating the three liquid crystal light valves 250, 252, and 254 that are illumination areas.

  The light source 110 includes a light source lamp 112 as a radiation light source that emits a radial light beam, and a concave mirror 114 that emits radiation light emitted from the light source lamp 112 as a substantially parallel light beam. As the light source lamp 112, a high pressure discharge lamp such as a metal halide lamp or a high pressure mercury lamp is usually used. As the concave mirror 114, a parabolic mirror is preferably used. In place of the parabolic mirror, an ellipsoidal mirror or a spherical mirror can be used.

  The first lens array 120 includes a plurality of first small lenses 122. The second lens array 130 includes a plurality of second small lenses 132 corresponding to each of the plurality of first small lenses. The substantially parallel light bundle emitted from the light source 110 is divided into a plurality of partial light beams by the first and second lens arrays 120 and 130 and enters the polarization conversion element 140. The polarization conversion element 140 has a function of converting non-polarized light into predetermined linearly polarized light, for example, s-polarized light or p-polarized light and emitting it. Accordingly, the plurality of partial light bundles incident on the polarization conversion element 140 are each converted into predetermined linearly polarized light and emitted. The partial light beam emitted from the polarization conversion element 140 is reflected by the reflection mirror 150 and enters the superimposing lens 160. The plurality of partial beam bundles incident on the superimposing lens 160 are superposed on the liquid crystal light valves 250, 252 and 254, which are illumination areas, by the superimposing action of the superimposing lens 160. As a result, the liquid crystal light valves 250, 252, and 254 are illuminated almost uniformly.

  The two dichroic mirrors 210 and 212 function as a color light separating optical system that separates the light emitted from the illumination optical system 100 into three color lights of red (R), green (G), and blue (B). Have The first dichroic mirror 210 transmits the red light component of the light emitted from the illumination optical system 100 and reflects the blue light component and the green light component.

  The red light transmitted through the first dichroic mirror 210 is reflected by the reflection mirror 220, passes through the field lens 240, and reaches the liquid crystal light valve 250 for red light. The field lens 240 has a function of condensing each of the partial light fluxes that have passed through the field lens 240 so as to become a light bundle parallel to the principal ray (central axis). The same applies to the field lenses 242 and 244 provided in front of other liquid crystal light valves.

  Of the blue light and green light reflected by the first dichroic mirror 210, the green light is reflected by the second dichroic mirror 212, passes through the field lens 242 and reaches the liquid crystal light valve 252 for green light. On the other hand, the blue light passes through the second dichroic mirror 212 and passes through the incident side lens 230, the relay lens system including the relay lens 232 and the reflection mirrors 222 and 224. The blue light that has passed through the relay lens system further passes through the field lens 244 and reaches the liquid crystal light valve 254 for blue light.

  The reason why the relay lens system is used for the blue light is to prevent a decrease in the efficiency of use of light generated because the optical path length of the blue light is longer than the optical path lengths of the other color lights. . That is, the blue light incident on the incident side lens 230 is transmitted to the exit side lens (field lens) 244 as it is.

  The three liquid crystal light valves 250, 252, and 254 are used as light modulation means for modulating the light of each color incident on the liquid crystal light valves 250, 252, and 254 according to given image information (image signal) and emitting light representing the image. It has a function. Since the light incident surfaces of the liquid crystal light valves 250, 252, and 254 are usually provided with polarizing plates, the polarization direction of the linearly polarized light emitted from the illumination optical system 100 is the transmission axis of these polarizing plates. Is set to a polarization direction substantially equal to. In this way, the illumination light emitted from the illumination optical system 100 can be used efficiently. The cross dichroic prism 260 has a function as a color light combining optical system (light selection prism) that combines the three color lights emitted from the three liquid crystal light valves 250, 252, and 254. In the cross dichroic prism 260, a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are formed in an approximately X shape at the interface of four columnar prisms. The three color lights are synthesized by these dielectric multilayer films to form synthesized light for projecting a color image. The combined light generated by the cross dichroic prism 260 is emitted in the direction of the projection lens system 270. The projection lens system 270 functions as a projection optical system that projects the combined light on the projection screen 300 and displays a color image.

  This projection display apparatus uses the cross dichroic prism 260 of the above-described embodiment. Therefore, it is possible to alleviate the problem of streaking at the center of the projected image, and to alleviate the problem that the image size changes on the left and right of the screen. Further, since the cross dichroic prism 260 is a small prism cut out from the prism column 320 or the prism column 420, the projection display device can be downsized.

  In place of the cross dichroic prism 260, the cross dichroic prism 260A shown in FIG. 9 may be used. In this case, it is possible to further suppress deterioration in image quality due to chromatic aberration generated in the projection lens system 270.

  The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

(1) Various arrangements and configurations of the dichroic film in the cross dichroic prism can be considered other than the above embodiments. For example, the formation positions of the red reflection film and the blue reflection film may be switched. Further, instead of the blue reflective film, a green reflective film may be provided. Further, the color light to be reflected is not limited to red, green, and blue, and it is possible to use a combination of films that reflect various color lights in consideration of the characteristics of the film.

(2) In the above embodiment, the dichroic film (blue reflection film in the above embodiment) formed on the surface where two right angle prisms constituting one prism pair are joined is formed on the right angle surface of the short right angle prism. In this example, it may be formed on a right-angle plane of a long right-angle prism. Also, as the prism, a columnar prism other than the right-angle prism can be used. However, in the case of forming a light selection prism by bonding four columnar prisms, the cross section of each columnar prism generally has a triangular shape that can be bonded together with the side surfaces in close contact with each other. It is preferable to have.

(3) In the above-described embodiment, the four right-angle prisms constituting the prism column use right-angle prisms having the same length in the longitudinal direction of the long right-angle prisms and the short right-angle prisms. Is shorter than a long right-angle prism. That is, when the two short right-angle prisms are bonded together and stored in the groove 522c of the second assembly jig 520 (FIG. 7), the length in the longitudinal direction of the two short right-angle prisms bonded is the first. As long as it is smaller than the width W3 of the groove portion 522c of the second assembly jig 520, it is sufficient that the two long right-angle prisms are pressed against the upper surfaces of the reference surface portions 522a and 522b. In this way, the first dichroic film (blue reflective film in the embodiment) formed on each of the two pairs of prisms can be accurately arranged on the same plane.

(4) In the above-described embodiment, an example in which the present invention is applied to a transmissive projection display device has been described. However, the present invention can also be applied to a reflective projection display device. Here, “transmission type” means that the light modulation means such as a liquid crystal light valve transmits light, and “reflection type” means that the light modulation means reflects light. It means that there is. In a reflective projection display device, the cross dichroic prism is used as a color light separating means for separating light into three colors of red, green, and blue, and again combines the modulated three colors of light. It is also used as color light combining means for emitting in the same direction. Even when the present invention is applied to a reflective projection display device, substantially the same effect as that of a transmissive projection display device can be obtained.

(5) In the above embodiment, an example of a cross dichroic prism has been described as the light selection prism. However, the present invention can also be applied to a light selection prism other than the cross dichroic prism. For example, the present invention can also be applied to a light selection prism that uses a film having polarization selectivity (polarization separation film) as two light selection films. Further, the present invention can also be applied to a light selection prism using two types of light selection films having different light selectivity with respect to colored light and polarized light.

(6) In the above embodiment, the liquid crystal light valve (liquid crystal panel) is used as the light modulation means of the projection display device, but the present invention is not limited to this. For example, it is possible to use a digital micromirror device (trademark of TI). That is, as the light modulation means, various devices that modulate incident light into light representing an image according to an image signal can be used.

It is explanatory drawing which shows the cross dichroic prism which is 1st Example of a light selection prism. It is explanatory drawing which shows the process of cutting out a cross dichroic prism from a prism column. It is explanatory drawing which shows the manufacturing process of a prism pair. It is a perspective view which shows the 1st assembly jig 500. FIG. It is explanatory drawing which expands and shows the joint surface 321c of the 1st prism pair. It is explanatory drawing which shows the process of bonding 2 pairs of prism pairs 321,322. It is a perspective view of the 2nd assembly jig 520. FIG. FIG. 6 is an enlarged side view showing a state where two pairs of prisms 321 and 322 are placed on a second assembly jig 520. It is explanatory drawing which shows the cross dichroic prism which is the 2nd Example of a light selection prism. It is explanatory drawing which shows the process of preparing four columnar prisms among the 2nd manufacturing methods of a cross dichroic prism. It is a schematic plan view which shows the principal part of the projection type display apparatus using the cross dichroic prism 260 of the Example of this invention. It is a conceptual diagram which shows the principal part of a projection type display apparatus.

Explanation of symbols

42, 44, 46 ... Liquid crystal light valve 48 ... Cross dichroic prism 48B ... Blue reflective film 48R ... Red reflective film 50 ... Projection lens 52 ... Projection screen 100 ... Illumination optics System 110 ... light source 112 ... light source lamp 114 ... concave mirror 120 ... first lens array 122 ... small lens 130 ... second lens array 132 ... small lens 140 .. .Polarization conversion element 150 ... reflection mirror 160 ... superimposing lens 210 ... first dichroic mirror 212 ... second dichroic mirror 220, 222, 224 ... reflection mirror 230 ... incident side Lens 232 ... Relay lens 240, 242, 244 ... Field lens 250, 252, 254 ... Liquid crystal light valve 260 ... Cross dichroic prism 261, 262, 263, 264 ... Right angle prism (columnar) prism)
266B ... Blue reflective film 266R ... Red reflective film 260A ... Cross dichroic prism 261A, 262A, 263A, 264A ... Columnar prism 270 ... Projection lens 300 ... Projection screen 320 ... Prism Column 321 ... First prism pair 321a, 321b ... Right-angled surface 321c ... Joint surface 321d, 321e ... Exposed portion 322 ... Second prism pair 322d, 322e ... Exposed portion 325 , 327 ... long right-angle prism 326,328 ... short right-angle prism 325a ... right angle surface 325b ... right angle surface 326a ... right angle surface 326b ... right angle surface 400 ... sheet glass 402 ... Upper surface 404 ... Lower surface 425, 426, 427, 428 ... Columnar prism 426O, 428O ... Columnar prism 500 ... First assembly jig 502 ... Base plate 502a, 502b ... Reference surface portion 502c ...groove 504 ... stepped setting member 520 ... upper surface 522c ... hole of the second assembly jig 522 ... base 522a ... reference surface 522a (U) ... reference surface 522a

Claims (2)

A light selection prism having two types of light selection films intersecting in a substantially X shape,
Four columnar prisms joined on the sides of each other;
Two light selective films formed so as to intersect in a substantially X shape along the side surfaces of the four columnar prisms,
One of the two photoselective films is continuously formed without being divided at an intersection position of the two photoselective films,
Light selection prism, wherein a surface of the light selection film is formed continuously curved surface der is, the surface of the other of the light selective membrane is formed is a flat surface. A projection display device that projects and displays an image,
An illumination optical system that emits illumination light;
A color light separation optical system for separating the illumination light into three colors of light;
Three sets of light modulation means for modulating the light of the three colors based on a given image signal;
A cross dichroic prism for combining three colors of light modulated by the three sets of light modulation means;
A projection optical system for projecting light synthesized by the cross dichroic prism,
The cross dichroic prism is
Four columnar prisms joined on the sides of each other;
Two dichroic films formed so as to intersect in a substantially X shape along the side surfaces of the four columnar prisms,
One of the two dichroic films is formed continuously without being divided at the intersection position of the two dichroic films,
The surface on which the dichroic film is formed in succession Ri curved der and the other surface of the light selection film is formed a projection display device which is a flat surface.

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