Patent Publication Number: US-6669797-B2

Title: Manufacturing method for polarizing conversion elements

Description:
This is a Continuation of Application Ser. No 09/609,069 filed Jun. 30, 2000, now U.S. Pat. No. 6,436,214. The entire disclosure of the prior application(s) is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a manufacturing method for a polarizing conversion element for converting incident non-polarized light into specified polarized light. 
     2. Description of Related Art 
     In a projector, a light-modulating device for modulating light corresponding to image signals is used. As the light-modulating device, the type of using only one type of linear polarized light, such as a transmissive liquid crystal panel and a reflective liquid crystal panel, is usually used. In the projector which only uses such one type of linear polarized light, a polarizing conversion element for converting emitted non-polarized light from a light source into one type of a linear polarized light component (S-polarized light component or P-polarized light component, for example) is provided. 
     FIGS.  8 (A)-(B) are schematic representations showing a polarizing conversion element  320 . FIG.  8 (A) shows the polarizing conversion element  320  in the x-z plane, while FIG.  8 (A) shows the polarizing conversion element  320  in the x-y plane. 
     The polarizing conversion element  320  may consist of a polarizing beam splitter array (polarized light separating element)  340  and a plurality of λ/2 phase films  381  selectively arranged on portions of emitting surface of the polarizing beam splitter array  340 . The polarizing beam splitter array  340  has a height of h and a shape in which a plurality of column-shaped light transmissive members  324 , each having a parallelogram cross-section, are sequentially bonded to each other, and column-shaped light transmissive members  325  and  326 , each having a trapezoidal cross-section, are respectively bonded to the two ends of the bonded members  324 . Polarization separating films  331  and reflecting films  332  are alternately formed on each of boundary surfaces between light transmissive members  324 ,  325 , and  326 . The λ/2 phase films  381  are selectively arranged at mapping portions in the x-direction of emitting light from the polarization separating film  331  or the reflecting film  332 . In this example, the λ/2 phase films  381  are selectively arranged at mapping portions in the x-direction of emitting light from the polarization separating film  331 . 
     The polarizing conversion element  320  separates incident light on the polarization separating film  331  into an S-polarized light component and a P-polarized light component. The S-polarized light is reflected by the polarization separating film  331  and is further reflected by the reflecting film  332  to be emitted therefrom. On the other hand, the P-polarized light component is allowed to pass through the polarization separating film  331  just as it is. On the emitting surface of the transmitted light from the polarization separating film  331 , the λ/2 phase film  381  is arranged, whereby the P-polarized light component is transformed to the S-polarized light component to be emitted therefrom. Therefore, a set of the polarization separating film  331 , the reflecting film  332 , and the λ/2 phase film  381 , which adjoin each other, corresponds to one polarizing conversion unit. In addition, the polarizing conversion element  320  in this example has three lines of polarizing conversion unit  350  and one line of dummy unit  350   d.  In such a manner, the polarizing conversion element  320  is an optical element for converting incident light on the polarization separating film  331  into substantially one kind of a linearly polarized light component. 
     SUMMARY OF THE INVENTION 
     FIG. 9 is a schematic representation showing a manufacturing example for the polarizing beam splitter array  340 . In the polarizing beam splitter array  340 , for example, a first glass plate  321  having the polarization separating film  331  and the reflecting film  332  formed thereon and a second glass plate  322  having no film formed thereon are alternately bonded to each other by an optical adhesive  327 , so that the polarization separating film  331  and the reflecting film  332  are alternately arranged. Then, an ultra violet ray (UV ray) is irradiated thereon to cure the optical adhesive  327 . At this time, third glass plates  323  having a different thickness from that of the first and the second glass plates  321  and  322  are used as first and the last plates of the bonded plates, to form a composite plate member  400 . Light transmissive blocks are cut substantially in parallel with each other off the composite plate member  400  formed as above along sections (shown by broken lines in the drawing) inclining at the predetermined angle “θ” with the surface of the composite plate member  400 , using a multi-wire saw or a multi-blade saw. The value “θ” is preferably about 45°. Here, “the surface of the composite plate member  400 ” indicates the surface of the third plates  323  bonded at the both ends. Protruding portions of both ends of the block are cut off by a dicing saw or a laser cutting apparatus so that the block has a substantially rectangular shape. Surfaces (cutting sections) of the light transmissive block cut in such a manner are polished to obtain the polarizing beam splitter array  340  (FIGS.  8 (A)-(B)). In addition, portions formed by the first and the second glass plates  321  and  322  correspond to the light transmissive members  324 , while one of the portions formed by the third glass plates  323  at one of the two ends corresponds to the light transmissive member  325 , and the other thereof at the other end corresponds to the light transmissive member  326 . The thickness of the third glass plate  323  corresponding to the light transmissive members  325  may be different from that of the third glass plate  323  corresponding to the light transmissive members  326 . 
     In addition, the polarizing beam splitter array may be referred to as “a light transmissive block” below. 
     Conventionally, the polarizing conversion element has been manufactured in the manner described above to improve efficiency. However, a further improvement in manufacturing efficiency is desirable. 
     The present invention is made to at least solve the above-mentioned problems, and it is an object of the present invention to at least provide a technology to manufacture a polarizing conversion element more efficiently. 
     Accordingly, a first method for manufacturing a polarizing conversion element according to the present invention may consist of the steps of: 
     preparing k sets of light transmissive members, k being an integer of 2 or greater, where each of the sets may consist of a plurality of first light transmissive plates and a plurality of second light transmissive plates having substantially a same thickness as that of the first light transmissive plates; 
     preparing (K+1) third light transmissive plates having a greater thickness than those of the first light transmissive plates and the second light transmissive plates; 
     producing a composite plate member by alternately arranging and bonding one set of the plurality of first light transmissive plates and the plurality of second light transmissive plates to each of spaces between the (K+1) third light transmissive plates, and alternately arranging a plurality of polarization separating films and a plurality of reflecting films on each interface between the first light transmissive plates, the second light transmissive plates and third light transmissive plates in the composite plate member; 
     producing a block substrate having a light receiving surface and a light emitting surface by cutting the composite plate member along a first section parallel to a surface inclining at a predetermined angle with a surface of the composite plate member, the light receiving surface and the light emitting surface being in parallel to the first section; 
     polishing the light receiving surface and the light emitting surface of the block substrate; and 
     producing k light transmissive blocks from the one block substrate by dividing the block substrate at positions of the third light transmissive plates disposed inside the block substrate. 
     A second method for manufacturing a polarizing conversion element according to the present invention may consist of the steps of: 
     preparing k sets of light transmissive members, k being an integer of 2 or greater, each of the sets comprising a plurality of first light transmissive plates and a plurality of second light transmissive plates; 
     preparing (K+1) third light transmissive plates having a greater thickness than those of the first light transmissive plates and the second light transmissive plates; 
     producing a composite plate member by alternately arranging and bonding one set of the plurality of first light transmissive plates and the plurality of second light transmissive plates to each of spaces between the (K+1) third light transmissive plates, and alternately arranging a plurality of polarization separating films and a plurality of reflecting films in each interface between the first light transmissive plates, the second light transmissive plates and the third light transmissive plates in the composite plate member; 
     producing a block substrate having a light receiving surface and a light emitting surface by cutting the composite plate member along a first section parallel to a surface inclining at a predetermined angle with a surface of the composite plate member, the light receiving surface and the light emitting surface being in parallel to the first section; and 
     producing k light transmissive blocks from one of the block substrates by dividing the block substrate at positions of the third light transmissive plates that are disposed inside the block substrate. 
     In the conventional manufacturing method, 2·k third light transmissive plates have to be prepared in order to produce k light transmissive blocks. However, in the manufacturing methods according to the present invention, (K+1) third light transmissive plates are enough to be prepared, whereby the number of parts for producing the polarizing conversion element can be reduced, resulting in reduction in the manufacturing cost. 
     In particular, according to the first manufacturing method of the present invention, a block substrate including k light transmissive blocks per one substrate is produced from a composite plate member; after the produced block substrate is polished, k light transmissive blocks per one substrate can be produced. Thereby, the number of steps for cutting the composite plate member and polishing the light receiving and light emitting surfaces can be reduced to be 1/k compared with that in producing k light transmissive blocks by a conventional manufacturing method, so that the polarizing conversion element can be more efficiently manufactured than ever. 
     In addition, preparing the k sets of light transmissive members may preferably consist of forming the polarization separating film on a first surface of the first light transmissive plate, and forming a reflecting film on a second surface of the first light transmissive plate. Also, preferably, preparing the k sets of light transmissive members may consist of forming a polarization separating film on one surface of the first light transmissive plate, and forming a reflecting film on one surface of the second light transmissive plate. 
     In either way, a plurality of polarization separating films and a plurality of reflecting films can be alternately arranged on each interface between light transmissive plates. 
     The above-mentioned manufacturing methods may further consist of dividing a light transmissive block of the light transmissive blocks produced from the one of the block substrates into a plurality of light transmissive blocks by cutting the light transmissive block along a second section in parallel with a surface substantially perpendicular to a longitudinal direction of the plurality of polarization separating films and the plurality of reflecting films arranged inside the light transmissive block. 
     In this manner, a plurality of light transmissive blocks can be produced from one light transmissive block produced, thereby enabling the polarizing conversion element to be manufactured more efficiently. 
     Further, the polarizing conversion element manufactured by above methods may be employed by a projector. In this manner, resulting in reduction in the manufacturing cost for manufacturing the projector and enabling the projector to be manufactured more efficiently. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS.  1 (A)-(C) include schematic representations showing first to third glass plates  321 ,  322 , and  323  used for manufacturing a polarizing conversion element  320 ; 
     FIGS.  2 (A)-(B) include schematic representations showing a process of producing a first glass plate  321   a  on which a polarization separating film  331  and a reflecting film  332  are formed; 
     FIGS.  3 (A)-(B) include schematic representations showing a process of producing a composite plate member  500  so as to produce a block substrate  520 ; 
     FIGS.  4 (A)-(C) include schematic representations showing a process of producing light transmissive blocks  340  from the block substrate  520 ; 
     FIG. 5 is a schematic representation showing another method for manufacturing the composite plate member  500  shown in FIGS.  3 (A)-(B).; 
     FIG. 6 is a front view of the light transmissive block  340 ; 
     FIG. 7 is a block diagram showing a principal part of a projector which may consist of a polarizing conversion element produced by the manufacturing method according to the present invention; 
     FIGS.  8 (A)-(B) include schematic representations for showing a structure of the polarizing conversion element  320 ; and 
     FIG. 9 is a schematic representation for showing a manufacturing method example of a polarizing beam splitter array  340 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A. A Method for Manufacturing Polarizing Conversion Elements: 
     A method according to the present invention will be described below by way of an example of manufacturing of the polarizing conversion element  320 , shown in FIGS.  8 (A)-(B), which may consist of three lines of polarizing light conversion units  350  and one line of a dummy unit  350   d . FIGS.  1 (A) to  4 (C) are schematic representations showing manufacturing processes of the polarizing conversion element  320 . 
     First, k sets of three first glass plates and two second glass plates, and the (k+1) third glass plates  323  are prepared (where “k” is an integer of 2 or greater). The following example will be described as k=2, that is, three third glass plates  323  are prepared. 
     As shown in FIGS.  1 (A) to (C), the first glass plate  321 , the second glass plate  322 , and the third glass plate  323  are rectangular-shaped glass plates having the longitudinal length “m” and the transverse length “1”. The thickness “d 2 ” of the second glass plate  322  is substantially the same as that “d 1 ” of the first glass plate  321 . The thickness “d 3 ” of the third glass plate  323  is larger than that “d 1 ” of the first glass plate  321 . The meaning of “substantially the same” indicates that differences in the length are not more than several percent. In addition, the thickness “d 1 ” of the first glass plate  321  and that “d 2 ” of the second glass plate  322  are determined by considering the thickness of the optical adhesive  327  so that polarization separating films  331  and reflecting films  332  are arranged at equal intervals when the first glass plate  321  and the second glass plate  322  are alternately bonded to each other, as will be described later. 
     In addition, the first to third glass plates  321 ,  322 , and  323  are equivalent to the first to third light transmissive plates according to the present invention. 
     Next, as shown in FIG.  2 (A), on one surface of the first glass plate  321 , the polarization separating film  331  is formed, while, as shown in FIG.  2 (B), on the opposite surface thereof, the reflecting film  332  is formed to form a first glass plate  321   a  having the polarization separating film  331  and the reflecting film  332  formed thereon. 
     The polarization separating film  331  may be formed by depositing a dielectric multi-layer film, and the reflecting film  332  may be formed by depositing a dielectric multi-layer film which may be the same as or different from the dielectric multi-layer film for the polarization separating film  331 . In addition, the reflecting film  332  may also be formed by an evaporating process of a metallic reflecting film such as aluminum. 
     Then, as shown in FIG.  3 (A), in each of spaces between three third glass plates  323 , three first glass plates  321   a  and two second glass plates  322  are alternately arranged so as to be bonded together by the optical adhesive  327  so that the polarization separating films  331  and the reflecting films  332  are alternately arranged on each of interfaces between glass plates  321 ,  322 , and  323  to form a composite plate member  500 . The optical adhesive  327  is cured by irradiation of an ultra violet ray. 
     By cutting the composite plate member  500  thus produced along first sections c 1  (shown by broken lines in the drawing) inclining at a predetermined angle “θ” with the surface of the composite plate member  500  substantially parallel with each other by using a multi-wire saw or a multi-blade saw, for example, a block substrate  520  shown in FIG.  3 (B) is cut. Here “the surface of the composite plate member” indicates the surface of the third plates  323  bonded at the both ends. The value “θ” is preferably about 45°, In addition, surfaces parallel with the first sections of the block substrate  520  cut in such a manner are equivalent to a light receiving surface  522  and a light emitting surface  524 . 
     Then as shown in FIG.  4 (A), protruding portions (portions of equivalents to the third glass plates  323 ) on both ends of the block substrate  520  are cut off by a dicing saw or a laser cutting apparatus so that the block substrate  520  has a substantially rectangular shape, to form a substantially rectangular block substrate  520   a  as shown in FIG.  4 (B). After grinding and polishing surfaces of the block substrate  520   a,  the block substrate  520   a  is divided at the positions within the portion formed by the third glass plate  323  disposed inside the block substrate  520   a  by a dicing saw or a laser cutting apparatus to thereby produce two light transmissive blocks  340  (polarizing beam splitter arrays) from the one block substrate  520   a , as shown in FIG.  4 (C). At this time, although the effectiveness of the economizing steps will be reduced, the surface grinding and polishing may be performed after the division of the substantially rectangular block substrate  520   a  shown in FIG.  4 (B). 
     On the light emitting surface of the light transmissive block  340  (polarizing beam splitter array) formed as above, the λ/2 phase films  381  are selectively bonded thereon, as shown in FIG.  8 (A), thereby enabling the polarizing conversion element  320  to be formed. 
     In the above-mentioned manufacturing method, the block substrate  520   a  including two light transmissive blocks  340  is produced from the composite plate member  500 . After grinding and polishing the produced block substrate  520   a , two light transmissive blocks  340  from one block substrate  520   a  can be produced. Therefore, one step of cutting the composite plate member  500  and one step of grinding and polishing the light receiving surface  522  and the light emitting surface  524  of the block substrate  520   a  can be eliminated in comparison with the steps for manufacturing two light transmissive blocks  340  by the conventional manufacturing method (FIG.  9 ). Accordingly, the light transmissive blocks  340  can be more efficiently manufactured than previously possible. Also, in order to produce the two light transmissive blocks  340  by the conventional manufacturing method, four of the third glass plates  323  (FIG. 9) have to be prepared. However, in the above-mentioned manufacturing method, the number of the required third glass plates  323  can be reduced to be three thereby enabling the number of parts for manufacturing the polarizing conversion element  320  to be reduced, resulting in reduction in the manufacturing cost. 
     In addition, the manufacturing method has been described in an example in which two light transmissive blocks  340  are produced from one block substrate  520   a.  However, it is not limited thereto. By preparing three sets of three first glass plates  321  and two second glass plates  322 , and four third glass plates  323  to produce a composite plate member, a block substrate including the three light transmissive blocks  340  may be produced from the produced composite plate member. Also, after grinding and polishing the produced composite plate member, the three light transmissive blocks  340  may be produced from one composite plate member. That is, in the above-mentioned manufacturing method, by preparing k sets (herein “k” is referred to an integer of 2 or more) of the three first glass plates  321  and the two second glass plates  322 , and the (K+1) third glass plates  323  to produce a composite plate member, a block substrate including the k light transmissive blocks  340  may be produced from the produced composite plate member. After grinding and polishing the produced composite plate member, the k light transmissive blocks  340  may be produced from one composite plate member. In such a manner, the polarizing conversion element  320  can be more efficiently manufactured than being previously possible. Also, the number of the required third glass plates  323  can be reduced to be (K+1) from 2k plates in the conventional manufacturing method, thereby enabling the number of parts for manufacturing the polarizing conversion element to be reduced, resulting in reduction in the manufacturing cost. 
     Also, the method has been described in the context in which k sets of the three first glass plates  321  and the two second glass plates  322  are prepared. However, it is not limited thereto. K sets of a plurality of first glass plates  321  and a plurality of second glass plates  322  may be prepared. Thereby, the polarizing conversion element having multiple lines of polarizing conversion units can be efficiently manufactured. 
     In addition, the manufacturing method has been described in the context in which the third glass plates  323  have the same thickness; however, it is not limited thereto. For example, the thickness of the third glass plates  323  disposed at the two ends may be different from that of the third glass plates  323  disposed inside. Also, plates having a different thickness may be used depending on which ends they are disposed on. That is, a third glass plate  323  having different thicknesses may be used depending on the position it is placed in. 
     Further, the manufacturing method has been described in the context in which the thickness d 1  of the first glass plates  321  and the thickness d 2  of the second glass plates  322  are substantially the same; however, d 1  and/or d 2  may be the same with regard to the thickness of the optical adhesive  327 . Moreover, the manufacturing method has been described in the context in which the light transmissive block  340  is produced after grinding and polishing the surface of the block substrate  520   a ; however, the light transmissive block  340  may be produced without grinding and polishing the surface of the block substrate  520   a . In the latter case, the surface of the light transmissive block  340  is grinded and polished. 
     FIG. 5 is a schematic representation showing a different manufacturing method for the composite plate member  500  shown in FIG.  3 . This is a method for forming and bonding the reflecting film  332  to the surface of the second glass plate  322  and the third glass plate  323  in FIGS.  3 (A)-(B) that is attached via optical adhesive  327  to the side of the first glass plate  321   a  where reflecting film  332  is. 
     By this method, substantially the same composite plate member  500 ′ as the composite plate member  500  shown in FIG. 3 can also be manufactured. In addition, the composite plate member  500 ′ has the same functions except for having the different positional relationship between the reflecting film  332  and the optical adhesive  327 . 
     FIG. 6 is a front view of the light transmissive block  340  manufactured by the above-mentioned manufacturing method. When the light transmissive block  340  manufactured by the manufacturing method is cut, by a dicing saw or a laser cutting apparatus, parallel to a second section substantially parallel to the direction in which the polarization separating films  331  and the reflecting films  332  are arranged, a plurality of light transmissive blocks  340  can be further manufactured. For example, when the height “h” of the polarizing conversion element  320  is ½ of the height “1” of the light transmissive block  340 , two light transmissive blocks can be manufactured by dividing the light transmissive block  340  into two. 
     In this method, as well as the foregoing method, k sets of the three first glass plates  321  and the two second glass plates  322  are prepared; however, the method is not limited thereto. K sets of a plurality of first glass plates  321  and a plurality of second glass plates  322  may be prepared. Thereby, the polarizing conversion element having multiple lines of polarizing conversion units can be efficiently manufactured. In addition, in this method, the third glass plates  323  have the same thickness; however, the method is not limited thereto. For example, the thickness of the third glass plates  323  disposed at the two ends may be different from that of the third glass plates  323  disposed inside. Also, plates having different thicknesses may be used depending on which ends they are disposed on. That is, third glass plates  323  having different thicknesses may be used depending on the position they are placed in. 
     Further, in this method, the thickness d 1  of the first glass plates  321  and the thickness d 2  of the second glass plates  322  are substantially the same; however, d 1  and/or d 2  may be the same with regard to the thickness of the optical adhesive  327 . Moreover, in this method, the light transmissive block  340  is produced after grinding and polishing the surface of the block substrate  520   a ; however, the light transmissive block  340  may be produced without grinding and polishing the surface of the block substrate  520   a . In the latter case, the surface of the light transmissive block  340  is grinded and polished. 
     B. A Structure of Projector: 
     FIG. 7 is a block diagram showing a principal part of a projector which may consist of a polarizing conversion element produced by the manufacturing method according to the present invention. The projector  800  may consist of a polarization-illuminating device  50 , dichroic mirrors  801  and  804 , a reflecting mirror  802 , a light guide  850  consisting of relay lenses  806 ,  808 , and  810 , and reflecting mirrors  807  and  809 , three light valves  803 ,  805 , and  811 , a cross-dichroic prism  813 , and a projection lens  814 . 
     The polarization-illuminating device  50  may consist of a light-source unit  60  and a polarized-light generating device  70 . The light-source unit  60  emits non-polarized light including an S-polarized light component and a P-polarized light component. The light emitted from the light-source unit  60  is converted by the polarized-light generating device  70  into specific linearly polarized light (S-polarized light in this embodiment) having a substantially aligned polarizing direction, to illuminate an illumination region. The three light valves  803 ,  805 , and  811  are equivalent to the illumination region. 
     The polarized-light generating device  70  may consist of a first optical component  200  and a second optical component  600 . The first optical component  200  is a lens array arranged in a matrix of small lenses having a rectangular profile. The second optical component  600  may consist of an optical element  300  and an emitting-side lens  390 . 
     The optical element  300  may consist of a condensing lens array  310  and two polarizing conversion elements  320   a  and  320   b.  The condensing lens array  310  is of the same structure as that of the first optical component  200 , and is arranged in the direction opposing the first optical component  200 . The condensing lens array  310  has a function, together with the first optical component  200 , for respectively condensing plural partial light beams divided by each small lens  201  of the first optical component  200  to guide them toward incident regions of polarizing conversion elements  320   a  and  320   b.  The polarizing conversion elements  320   a  and  320   b  are formed by arranging the polarizing conversion elements  320  (FIG. 8) produced by the manufacturing method according to the present invention so that respective polarization separating films  331  and respective reflecting films  332  symmetrically oppose each other about the optical axis, by sandwiching it. Therefore, the light beam emitted from the light-source unit  60  is converted into substantially specific linearly polarized light (S-polarized light in this embodiment) by the polarized-light generating device  70 . 
     The emitting-side lens  390  has a function for superimposing each of plural sub light beams emitted from the optical element  300  on respective liquid-crystal light-valves  803 ,  805 , and  811 . 
     The light emitted from the polarization-illuminating device  50  is separated into colored light beams of three colors, red, green, and blue by the dichroic mirrors  801  and  804  as a color separating optical system. Each of separated colored light beams of the three colors is modulated corresponding to given image information (image signals) by respective liquid-crystal light-valves  803 ,  805 , and  811  for each color. These liquid-crystal light-valves  803 ,  805 , and  811  correspond to the light-modulating device according to the present invention. Each of modulated colored light beams by the liquid-crystal light-valves  803 ,  805 , and  811  is combined by the cross-dichroic prism  813  as a color synthesizing optical system to be projected onto a screen  815  by the projection lens  814  as a projection optical system. Thereby, color images are displayed on the screen  815 . In addition, the structure and the function of each unit of the projector shown in FIG. 7 are disclosed in detail by the applicant of this application in Japanese Unexamined Patent Application Publication No. 10-177151, for example, so that the description thereof is not given in this application. 
     Since the polarizing conversion elements  320   a  and  320   b  produced by the manufacturing method according to the present invention are used in the polarization-illuminating device  50  of the projector  800 , the manufacturing cost of the apparatus can be reduced. 
     While the projector  800  shown in FIG. 7 has been described with reference to an example in which the polarizing conversion element produced by the manufacturing method according to the present invention is used in the polarization-illuminating device in a projector for displaying color images, it is apparent that the element is not so limited, but can be applied to various devices. For example, it may be applied to a projector for projecting monochromatic images. In this case, in the apparatus shown in FIG. 7, one liquid-crystal light-valve is only needed, and the color separation optical system for separating the light into colored beams of three colors and the color synthesizing optical system for combining colored beams of three colors can be eliminated. Furthermore, the present invention can be applied to a projector using only one light valve. Also, the present invention can be applied to an image display apparatus using illuminating polarized-light such as a projector using a reflection-type liquid-crystal light-valve and a rear-type display apparatus. 
     In addition, the present invention is not limited to the above-described examples and embodiments, and it is intended to embrace all such variations and modifications that fall within the spirit and scope of the invention.