Abstract:
This specification discloses a polarizing. element for dividing light into first and second polarized lights differing in polarized state from each other by a polarizing dividing surface, directing the first polarized light in a first direction, reflecting the second polarized light by a reflecting surface and directing it in the first direction, and varying the polarized state of at least one of the first and second polarized lights to thereby make the polarized states of the first and second polarized lights coincident with each other, characterized in that the polarizing dividing surface is disposed on one surface of a plane parallel plate and the reflecting surface is disposed on the other surface of the plane parallel plate, and the light enters obliquely from the one surface or the other surface. The specification also discloses a polarizing conversion unit provided with such polarizing element, and a projector provided with such polarizing conversion unit.

Description:
This is a divisional of application Ser. No. 07/865.076 filed Apr. 8, 1992, now U.S. Pat. No. 5,751,480. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a polarizing element from which incident light having random polarization direction components emerges with the polarization direction uniformized, and a projector using such polarizing element. 
     2. Related Background Art 
     There is known a projector of the construction as shown in  FIG. 1  of the accompanying drawings. 
     A light beam emitted from a light source  1550  is separated into red, green and blue lights by dichroic mirrors  1551  and  1552 , and the red, green and blue lights are directed to liquid crystal light bulbs  1554 ,  1555  and  1556 , respectively, by the use of a total reflection mirror  1553  and further, the optical paths of these lights are bent by a total reflection mirror  1557 , and the three red, green and blue images are combined by dichroic mirrors  1558  and  1559  and the combined image is projected onto a screen, not shown, by a projection lens  1560 . 
     Such a projector adopts a construction in which the liquid crystal light bulbs  1554 ,  1555  and  1556  assume a form in which a liquid crystal plate is interposed between two polarizing plates which are polarizing elements and when natural light having random polarization directions enters the incidence side polarizing plate, polarized lights in the other polarization directions than one polarization direction are absorbed by said incidence side polarizing plate and only the light in one polarization direction enters the liquid crystal plate. 
     On the other hand, the projector described in Japanese Patent Laid-Open Application No. 61-90584 adopts a construction in which the incidence side polarizing plate is eliminated and instead, by the use of a prism and a beam splitter which is a polarizing element, light is caused to enter a liquid crystal plate with the polarization directions thereof uniformized in one direction. 
     However, the projector shown in  FIG. 1  suffers from the problem that lights in the other polarization directions than the polarization direction of the polarized light transmitted through the incidence side polarizing plate are absorbed by the incidence side polarizing plate and therefore the projection image field becomes dark, and further suffers from the problem that the temperature of the liquid crystal plate is increased by the absorbed lights, thus resulting in the deterioration of the liquid crystal plate. 
     On the other hand, in the projector described in Japanese Patent Laid-Open Application No. 61-90584, the use of the polarizing beam splitter and the prism leads to the bulkiness of the apparatus and moreover, there is the problem that labor and cost are required for the polarizing of the prism. Also, the use of a glass block such as a prism leads to too great a weight, which in turn leads to bad portability as a projector. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to realize a polarizing element which can efficiently use incident light and can realize a low-cost and compact projector. 
     The polarizing element of the present invention is provided on one surface of a transparent plane parallel plate with polarizing separating film for dividing incident light entering the plane parallel plate from said one surface or the other surface side into reflected light and transmitted light, and reflects one of said reflected light and said transmitted light by a reflecting surface provided on said other surface of said transparent plane parallel light and directs it to an optical path substantially parallel to the optical path of the other light, and varies the polarized state of at least one of said reflected light and said transmitted light to thereby make the polarized states of the two lights coincident with each other. 
     Also, the polarizing conversion unit of the present invention is provided with an illuminating system for supplying non-polarized light having polarized components in lattice-like random directions, and a polarizing element provided obliquely with respect to the optical axis of said illuminating system to convert said non-polarized light into substantially dense polarized light, said polarizing element having a transparent plane parallel plate provided with polarizing separating film on one surface thereof, one of lattice-like reflected light and lattice-like transmitted light created by said polarizing separating film being reflected by a reflecting surface provided on the other surface of the transparent plane parallel plate and being directed to an optical path substantially parallel to the optical path of the other light, the polarized state of at least one of said lattice-like reflected light and said lattice-like transmitted light being varied to thereby make the polarized states of the two lights coincident with each other. 
     Also, the projector of the present invention is a projector provided with a light source emitting non-polarized lights an illuminating optical system for converting the non-polarized light from said light source into polarized light, an image generator for modulating said polarized light in conformity with a video signal to thereby generate an image, and a projecting optical system for projecting said image, said illuminating optical system having a converting system for converting said non-polarized light into a lattice-like light pattern, and a polarizing element provided obliquely with respect to the optical axis of said converting system to convert said lattice-like light pattern into substantially dense polarized light, said polarizing element having a transparent plane parallel plate provided with polarizing separating film on one surface thereof, one of lattice-like reflected light and lattice-like transmitted light created by said polarizing separating film being reflected by a reflecting surface provided on the other surface of the transparent plane parallel plate and being directed to an optical path substantially parallel to the optical path of the other light, the polarized state of at least one of said lattice-like reflected light and said lattice-like transmitted light being varied to thereby make the polarized states of the two lights coincident with each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the construction of a projector according to the prior art. 
         FIG. 2  shows the construction of a first embodiment of the present invention. 
         FIG. 3  shows the construction of a projector according to the first embodiment of the present invention. 
         FIG. 4  shows the construction of a second embodiment of the present invention. 
         FIG. 5  shows the construction of a third embodiment of the present invention. 
         FIG. 6  shows the construction of a fourth embodiment of the present invention. 
         FIG. 7  shows the construction of a fifth embodiment of the present invention. 
         FIG. 8  shows the construction of a sixth embodiment of the present invention. 
         FIG. 9  shows the construction of a seventh embodiment of the present invention. 
         FIG. 10  shows the construction of an eighth embodiment of the present invention. 
         FIG. 11  shows the construction of a ninth embodiment of the present invention. 
         FIG. 12  shows the construction of a tenth embodiment of the present invention. 
         FIG. 13  shows the construction of an eleventh embodiment of the present invention. 
         FIG. 14  shows the construction of a twelfth embodiment of the present invention. 
         FIG. 15  shows the construction of a thirteenth embodiment of the present invention. 
         FIG. 16  shows the construction of a fourteenth embodiment of the present invention. 
         FIG. 17  shows the construction of a fifteenth embodiment of the present invention. 
         FIG. 18  shows a contruction of a sixteenth embodiment of the present invention. 
         FIG. 19  illustrates a projector system including a polarizing conversion unit according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2  shows the construction of a first embodiment of the present invention. 
     The present embodiment is comprised of a condensing lens  101  which is a resin molded article comprising cylindrical minute lenses  101   1 ,  101   2  and  101   3  and which is an illuminating system emitting incident light as lattice-like non-polarized light, and a plane parallel plate  103  of a transparent optical material provided at an angle of 45° with respect to the optical axis of the condensing lens  101 . The incidence side surface and the emergence side surface of each of the cylindrical minute lenses  101   1 ,  101   2  and  101   3  have positive power and negative power, respectively, and the negative power has magnitude twice as great as the positive power, and each of the cylindrical minute lenses has the function of an afocal converter from which the incident light which is parallel light emerges as parallel light having ½ of the width thereof. 
     On that side of the plane parallel plate  103  which is adjacent to the condensing lens  101 , pairs of polarizing separating film  104  formed of multilayer film of a dielectric material or the like and film-like half wavelength plates (half wavelength film)  106  are provided in a stripe-like pattern at the pitch of the cylindrical minute lenses  101   1 - 101   3  as viewed from the direction of 45° and so that the width of each of them may be substantially equal to the width of the light beam condensed by the cylindrical minute lens  101   1 - 101   3 . On the whole of that surface of the plane parallel plate  103  which is opposite to the condensing lens  101 , there is provided aluminum total reflection film  105  subjected to high reflection treatment. 
     Assuming that the light beam  102  incident on the condensing lens  101  is substantially parallel light, this light beam  102  is compressed into lattice-like substantially parallel light of a half width by the cylindrical minute lenses  101   1 - 101   3  of the condensing lens  101 , and is separated as follows by the polarizing separating film  104  provided on that surface of the plane parallel plate  103  which is adjacent to the condensing lens  101 . 
     S-polarized light  102 S is reflected in a direction orthogonal to the incident light, and P-polarized light  102 P is transmitted. The transmitted P-polarized light  102 P is reflected by the aluminum total reflection film  105  provided on that surface of the plane parallel plate  103  which is opposite to the incidence side, whereafter it passes through the half wavelength plate  106 , whereby the polarization direction thereof is rotated by 90° and this light emerges as S-polarized light. The incident natural light is uniformized into S-polarized lights in this manner. Alternatively, the aluminum total reflection film  105  may not be formed and that surface of the plane parallel plate  103  which is opposite to the incidence side may be set as a total reflection surface, and P-polarized light may be reflected by this surface. 
       FIG. 3  shows the construction of a projector which incorporates therein the polarizing element constructed as described above. 
     A parallel light beam having various polarization directions which is emitted from a light source  250  is converted into only S-polarized light by the polarizing element shown in FIG.  2  and emerges. 
     Dichroic mirrors  251 ,  252 ,  258 ,  259 , total reflection mirrors  253 ,  257 , liquid crystal light bulbs  254 ,  255 ,  256  and a projection lens  260  in the present embodiment are similar in construction to the dichroic mirrors  1551 ,  1552 ,  1558 ,  1559 , the total reflection mirrors  1553 ,  1557 , the liquid crystal light bulbs  1554 ,  1555 ,  1556  and the projection lens  1560 , respectively, shown in FIG.  1 . 
     The liquid crystal light bulbs  254 ,  255  and  256  each modulate the orientation of a plurality of liquid crystal elements contained therein inconformity with a video signal input thereto from an image generator (not shown) comprised of three generators for generating red, green and blue images, respectively, whereby images are generated. The dichroic mirrors  251 ,  252 ,  258  and  259  together constitute a color resolving system for resolving the illuminating light converted into only S-polarized light by the polarizing element shown in  FIG. 2  into red, green and blue lights. 
     By the above-described construction, the loss of light in each of the liquid crystal light bulbs  254 ,  255  and  256  is eliminated and therefore, the projected image can be made bright and the generation of heat by the absorption of light does not occur. In this case, polarizing plates need not be provided on the incidence side of the liquid crystal light bulbs, but they may be provided to increase the purity of polarized light. 
     If design is made such that the incidence surface of the polarizing element is perpendicular to the plane of the drawing sheet and the light source  250  is disposed in a direction perpendicular to the plane of the drawing sheet, P-polarized light can be caused to be incident on each dichroic mirror and therefore, color resolution-combination can be accomplished efficiently. 
       FIG. 4  shows the construction of a second embodiment of the present invention. 
     In the present embodiment, polarizing separating film  304  formed of multilayer film is provided on the whole of that surface of a plane parallel plate  103  provided at an angle of 45° with respect to the optical axis of a condensing lens  101  which is adjacent to the condensing lens, and film-like half wavelength plates  306  are provided on the polarizing separating film at the pitch of cylindrical minute lenses  101   1 - 101   3  as viewed from the direction of 45° and so that the width each of them may be substantially equal to the width of the light beam condensed by each cylindrical minute lens. In the other points, the construction of the present embodiment is similar to that of the first embodiment shown in FIG.  2  and therefore, similar elements are given similar reference numerals and need not be described. 
     With the construction as described above, it is not necessary to effect masking when the polarizing separating film is deposited by evaporation and thus, the manufacturing process can be further simplified. 
       FIG. 5  shows the construction of a third embodiment of the present invention. 
     The present embodiment is such that in the second embodiment, film-like half wavelength plate  406  directly formed on the polarizing separating film  304  is formed on a holding plane parallel plate  409  and this holding plane parallel plate  409  is joined to the plane parallel plate  103  through the polarizing separating film  304 . Also, the aluminum total reflection films  305  provided on the whole of that surface which is opposite to the condensing lens  101  are provided as aluminum total reflection films  405  provided at substantially the pitch of the cylindrical minute lenses  101   1 - 101   3  as viewed from the direction of 45° and with the width of each of them substantially equal to the width of the light beam condensed by each cylindrical minute lens so that stray light may not be reflected in the direction of emergence of regular light, and further, absorbent paint  411  covering the whole of that surface of the plane parallel plate  103  which is opposite to the condensing lens  101  is provided to thereby achieve the effect of cutting stray light. Also, a half wavelength plate  406  may be formed in a lattice-like pattern on the plane parallel plate  103  and polarizing separating film  304  may be formed in a lattice-like pattern on the holding plane parallel plate  409  so that their phases may be inverted with respect to each other, and they may be joined together. Also, both of the half wavelength plate  406  and the polarizing separating film  304  may be formed on the holding plane parallel plate  409 . and the plane parallel plate  103  and the holding plane parallel plate  409  may be cemented together. 
       FIG. 6  shows the construction of a fourth embodiment of the present invention. 
     The present embodiment is one in which polarizing rotational means is provided on the whole surface of the plane parallel plate  103 . In the present embodiment, on that surface of the plane parallel plate  103  provided at an angle of 45° with respect to the optical axis of the condensing lens  101  which is adjacent to the condensing lens  101 , polarizing separating films  504  formed of multilayer films are provided at the pitch of the cylindrical minute lenses  101   1 - 101   3  as viewed from the direction of 45° and with substantially the same width as the width of the light beam condensed by each cylindrical minute lens. On the other hand, on the whole of that surface of the plane parallel plate  103  which is opposite to the condensing lens  101 , a film-like quarter wavelength plate  506  is provided and further, a holding plane parallel plate  510  having aluminum total reflection film  505  deposited by evaporation on the whole surface thereof is provided so that the aluminum total reflection film  505  and the quarter wavelength plate  506  may be opposed to each other. 
     With the construction as described above, the film-like quarter wavelength plate  506  can be attached to the whole of that surface of the plane parallel plate  103  which is opposite to the condensing lens  101  and therefore, the manufacturing process can be simplified. 
     Assuming that the light beam  102  entering the polarizing conversion element is a substantially parallel light beam, the width of the light beam is compressed by the cylindrical minute lenses  101   1 - 101   3  constituting the condensing lens  101 , and S-polarized light  102 S is reflected by the polarizing separating film  504  provided on that surface of the plane parallel plate  103  which is adjacent to the condensing lens  101  and P-polarized light  102 P is transmitted through the polarizing separating film  504 . The transmitted P-polarized light  102 P passes through the quarter wavelength plate  506  provided on that surface of the plane parallel plate  103  which is opposite to the condensing lens  101 , whereby it becomes circularly polarized light and is reflected by the aluminum total reflection film  505 , whereafter it passes through the quarter wavelength plate  506  again, whereby it becomes S-polarized light whose polarizing direction has been rotated by 90° and emerges from among the polarizing separating films  504 . 
     The incident natural light can be uniformized into S-polarized light in the manner described above. 
       FIG. 7  shows a fifth embodiment of the present invention. 
     The present embodiment, like the fourth embodiment shown in  FIG. 6 , is one in which polarizing rotational means is provided on the whole surface of the plane parallel plate  103 . 
     In the present embodiment, a film-like quarter wavelength plate  606  is provided on the whole of that surface of the plane parallel plate  103  provided at an angle of 45° with respect to the optical axis of the condensing lens  101  which is adjacent to the condensing lens  101 . On the quarter wavelength plate  606 , polarizing separating films  604  are provided at the pitch of the cylindrical minute lenses  101   1 - 101   3  as viewed from the direction of 45° and with substantially the same width as the width of the light beam condensed by each cylindrical minute lens, and on the other hand, aluminum total reflection film  605  is deposited by evaporation on that surface of the plane parallel plate  103  which is opposite to the condensing lens  101 . 
     As described above, the film-like quarter wavelength plate  606  is attached to the whole of that surface of the plane parallel plate  103  which is adjacent to the condensing lens  101 , whereby the manufacturing process can be simplified. 
     The light beam  102  entering the polarizing element has its beam width compressed by the cylindrical minute lenses  101   1 - 101   3  constituting the condensing lens  101 , and S-polarized light  102 S is reflected in a direction orthogonal to the incident light by the polarizing separating films  604  provided on that surface of the plane parallel plate  103  which is adjacent to the condensing lens  101 , and P-polarized light  102 P is transmitted through the polarizing separating films  604 . The transmitted P-polarized light  102 P passes through the quarter wavelength plate  606 , whereby it becomes circularly polarized light and is reflected by the aluminum total reflection film  605  provided on that surface of the plane parallel plate  103  which is opposite to the condensing lens  101 , whereafter it passes through the quarter wavelength plate  606  again, whereby it becomes S-polarized light whose polarization direction has been rotated by 90° and emerges from among the polarizing separating films  604 . 
     The incident natural light can be uniformized into S-polarized light in the manner described above. 
     In the present embodiment, in order that the illuminating light which has deviated from the parallel light may not become stray light, a light intercepting plate  612  which intercepts the illuminating light which has deviated from the parallel light and passes the emergent light therethrough is provided on that portion of the plane parallel plate  103  which is adjacent to the condensing lens  101  substantially in parallelism to the emergent light to thereby improve the purity of the polarization of the emergent light. 
       FIG. 8  shows the construction of a sixth embodiment of the present invention. 
     The present embodiment is one in which minute prisms are combined with a plane parallel plate. 
     On that surface of the plane parallel plate  103  provided at an angle of 45° with respect to the optical axis of the condensing lens  101  which is adjacent to the condensing lens  101 , pairs of polarizing separating films  704  formed by multilayer film and half wavelength plates  706  are provided at the pitch of the cylindrical minute lenses  101   1 - 101   3  as viewed from the direction of 45° and with substantially the same width as the width of the light beam condensed by each cylindrical minute lens, and aluminum total reflection film  705  is provided on the whole of that surface of the plane parallel plate  103  which is opposite to the condensing lens  101 . Further, on that surface of the plane parallel plate  103  which is adjacent to the condensing lens  101 , a prism plate  708  comprising minute prisms  708   1 - 708   5  each having a flat surface substantially perpendicular to the optical axis of the condensing lens  101  and a flat surface substantially perpendicular to the emergent light is provided in contact with the plane parallel plate  103 . 
     Assuming that the light beam  102  entering the polarizing element is a substantially parallel light beam, the width of the light beam is compressed by the cylindrical minute lenses  101   1 - 101   3  constituting the condensing lens  101 , and the light beam enters the minute prisms  708   1 - 708   5  constituting the prism plate  708  and is separated into S-polarized light  102 S and P-polarized light  102 P by the polarizing separating film  704  provided on that surface of the plane parallel plate  103  which is adjacent to the condensing lens  101 . The S-polarized light  102 S is reflected in a direction orthogonal to the incident light  102  and emerges through the minute prisms  708   1 ,  708   3  and  708   5  constituting the prism plate  708 . The P-polarized light  102 P is transmitted through the polarizing separating films  704 , is reflected by the aluminum total reflection film  705  provided on that surface of the plane parallel plate  103  which is opposite to the condensing lens  101 , and passes through the half wavelength plates  706 , whereby it becomes S-polarized light whose polarization direction has been rotated by 90°, and emerges through the minute prisms  708   2  and  708   4  constituting the prism plate  708 . 
     The incident natural light can be uniformized into S-polarized light in the manner described above. 
     If as in the present embodiment, the polarizing separating films are provided in the optical medium, the extinction ratio can be enhanced over a wide band. 
       FIG. 9  shows the construction of a seventh embodiment of the present invention. 
     The present embodiment, like the sixth embodiment shown in  FIG. 8 , is one in which minute prisms are combined with a plane parallel plate. 
     Polarizing separating film  804  formed of multilayer film is provided on the whole of that surface of the plane parallel plate  103  provided at an angle of 45° with respect to the optical axis of the condensing lens  101  which is adjacent to the condensing lens  101 , and aluminum total reflection film  805  is provided on the whole of that surface of the plane parallel plate  103  which is opposite to the condensing lens  101 . Further, on that surface of the plane parallel plate  103  which is adjacent to the condensing lens  101 , a prism plate  808  comprising minute prisms  808   1 - 808   5  each having a flat surface substantially perpendicular to the optical axis of the condensing lens  101  and a flat surface substantially perpendicular to the emergent light is provided in contact with the plane parallel plate  103 . 
     A film-like half wavelength plate  806  is provided on each of the exit portions of those  808   2  and  808   4  of the minute prisms  808   1 - 808   5  constituting the prism plate  808  which are located among the cylindrical minute lenses, and light intercepting members  812  are provided on the surfaces perpendicular to the exit portions. 
     By the construction as described above, as in the sixth embodiment shown in  FIG. 8 , the incident natural light can be uniformized into S-polarized light and further, by the provision of the light intercepting members  812 , stray light can be eliminated and the extinction ratio can be made high. 
       FIG. 10  shows the construction of an eighth embodiment of the present invention which is applied to a transmission type polarizing element. 
     The polarizing element of the present embodiment is comprised of a condensing lens  901  which is a resin molded article comprised of cylindrical minute lenses  901   1 - 901   3  having the function of an afocal converter, and a plane parallel plate  903  disposed so that the planar portion thereof may have an angle of 45° with respect to the optical axis of the condensing lens  901 . On that surface of the plane parallel plate  903  which is opposite to the condensing lens  901 , pairs of polarizing separating films  904  formed of multiplayer film and film-like half wavelength plates  906  are provided at the pitch of the cylindrical minute lenses  901   1 - 901   3  as viewed from the direction of 45° and with substantially the same width as the width of the light beam condensed by each cylindrical minute lens, and on that surface of the plane parallel plate  903  which is adjacent to the condensing lens  901 , aluminum total reflection films  905  are provided at the pitch of the cylindrical minute lenses  901   1 - 901   3  as viewed from the direction of 45° and so that the width of each of them may be substantially the same as the width of the light beam condensed by each cylindrical minute lens. 
     Assuming that the light beam  902  entering the polarizing element is a substantially parallel light beam; the light beam  902  has its beam width compressed by the cylindrical minute lenses  901   1 - 901   3  constituting the condensing lens  901 , and passes through among the aluminum total reflection films  905  provided on that surface of the plane parallel plate  903  which is adjacent to the condensing lens  901 , and enters the polarizing separating films  904  provided on that surface of the plane parallel plate  903  which is opposite to the condensing lens  901 . The light beam  902  which has entered the polarizing separating films  904  is separated into P-polarized light  902 P and S-polarized light  902 S. The P-polarized light  902 P is transmitted through the polarizing separating films  904  and emerges therefrom. On the other hand, the S-polarized light  902 S is reflected, and is further reflected by the aluminum total reflection films  905  provided on that surface of the plane parallel plate  903  which is adjacent to the condensing lens  901 , and emerges condensing lens  901 , and emerges through the half wavelength plates  906  provided on that surface of the plane parallel plate  903  which is opposite to the condensing lens  901 . By passing through the half wavelength plates  906 , the S-polarized light has its polarization direction rotated by 90° and emerges as P-polarized light. 
     The incident natural light can be uniformized into P-polarized in the manner described above. 
       FIG. 11  shows the construction of a ninth embodiment of the present invention which, like the eighth embodiment shown in  FIG. 10 , is applied to a transmission type polarizing element. 
     In the present embodiment, on that surface of the plane parallel plate  903  which is opposite to the condensing lens  901 , film-like half wavelength plates  1006  are provided at the pitch of the cylindrical minute lenses  901   1 - 901   3  as viewed from the direction of 45° and so that the width of each of them may be substantially the same as the width of the light beam condensed by each cylindrical minute lens, and polarizing separating film  1004  formed of multilayer film is provided fully thereon. On the other hand, on that surface of the plane parallel plate  903  which is adjacent to the condensing lens  901 , aluminum (or silver) total reflection films  1005  are provided at the pitch of the cylindrical minute lenses  901   1 - 901   3  as viewed from the direction of 45° and so that the width of each of them may be substantially the same as the width of the light beam condensed by each cylindrical lens. In the other points, the construction of the present embodiment is similar to that of the eighth embodiment shown in FIG.  10  and therefore, similar elements are given similar reference numerals and need not be described. 
     By the construction as described above, the incident natural light can be uniformized into P-polarized light as in the eighth embodiment shown in FIG.  10 . Also, in the present embodiment, the polarizing separating film is provided on the whole surface and therefore, it is not necessary to effect masking when it is formed and thus, the manufacturing process can be simplified. 
       FIG. 12  shows the construction of a tenth embodiment of the present invention which, like the eighth and ninth embodiments shown in  FIGS. 10 and 11  is applied to a transmission type polarizing element. 
     In the present embodiment, on that surface of the plane parallel plate  903  which is opposite to the condensing lens  901 , polarizing separating films  1104  are provided at the pitch of the cylindrical minute lenses  901   1 - 901   3  as viewed from the direction of 45° and so that the width of each of them may be substantially the same as the width of the light beam condensed by each cylindrical minute lens, and on the other hand, on that surface of the plane parallel plate  903  which is adjacent to the condensing lens  901 , a film-like quarter wavelength plate  1106  is provided, and further on the quarter wavelength plate  1106 , aluminum (or silver) total reflection films  1105  are provided at the pitch of the cylindrical minute lenses  901   1 - 901   3  as viewed from the direction of 45° and so that the width of each of them may be substantially the same as the width of the light beam condensed by each cylindrical minute lens. Also, absorbing members  1116  for absorbing and eliminating any unnecessary light are provided on both sides of each polarizing separating film  1104  on that surface of the plane parallel plate which is opposite to the condensing lens  901 . In the other points, the construction of the present embodiment is similar to the construction of the eighth and ninth embodiments shown in  FIGS. 10 and 11  and therefore, similar elements are given similar reference numerals and need not be described. 
       FIG. 13  shows the construction of an eleventh embodiment of the present invention. 
     In the present embodiment, a condensing lens  1301  is comprised of cylindrical minute lenses  1301   1 - 1301   3  and the plane parallel plate  903  is provided at an angle of 45° with respect to the optical axis of the condensing lens  1301 . Half wavelength plates  1306  are provided at predetermined locations on that surface of the plane parallel plate  903  which is opposite to the condensing lens  1301 , and polarizing separating film  1304  formed of multilayer film is further provided on the whole of said surface. Aluminum total reflection films  1305  subjected to high reflection treatment are provided on that surface of the plane parallel plate  903  which is adjacent to the condensing lens  1301 . The half wavelength plates  1306  and the aluminum total reflection films  1305  are provided at the pitch of the cylindrical minute lenses  1301   1 - 1301   3  as viewed from the direction of 45° and so that the width of each of them may be substantially the same as the width of the light beam condensed by each cylindrical minute lens. An emergence side prism plate  1307  and an incidence side prism plate  1308  covering the whole surface of the plane parallel plate  903  are provided on top of the polarizing separating film  1304  and aluminum total reflection films  1305 , respectively. The emergence side prism plate  1307  is comprised of minute prisms  1307   1 - 1307   5  and the incidence side prism plate  1308  is comprised of minute prisms  1308   1 - 1308   3  Each of these minute prisms  1307   1 - 1307   5  and  1308   1 - 1308   3  has a flat surface parallel to a flat surface (exit portion) perpendicular to the optical axis of the condensing lens  1301 , and two of the minute prisms constituting the emergence side prism plate  1307  are provided for each cylindrical minute lens, and one of the minute prisms constituting the incidence side prism plate  1308  is provided for each cylindrical minute lens. The cylindrical minute lenses  130   1 - 1301   3  constituting the condensing lens  1301  are disposed with level differences to prevent any light deviating from the parallel light beam from becoming lost light, and are constructed so as to be proximate to the corresponding minute prisms  1308   1 - 1308   3 . 
     Assuming that the light beam  902  entering the polarizing element constructed as described above is a parallel light beam, the light beam  902  is compressed to a half width by the cylindrical minute lenses  1301   1 - 1301   3  constituting the condensing lens  1301 . enters the minute prisms  1308   1 - 1308   3  constituting the incidence side prism plate  1308 , and passes through the gaps among the aluminum total reflection films  1305  provided on that surface of the plane parallel plate  903  which is adjacent to the condensing lens  1301 , whereafter it is separated into P-polarized light  902 P and S-polarized light  902 S by the polarizing separating film  1304  provided on that surface of the plane parallel plate  903  which is opposite to the condensing lens  1301 . The P-polarized light  902 P is transmitted through the polarizing separating film  1304  and emerges through the minute prisms  1307   1  and  1307   3  constituting the emergence side prism plate  1307 . On the other hand, the S-polarized light  902 S is reflected in a direction orthogonal to the incident light, and is reflected by the aluminum total reflection films  1305  provided on that surface of the plane parallel plate  903  which is adjacent to the condensing lens  1301 , whereafter it emerges through the half wavelength plates  1306 , the polarizing separating film  1304  and the minute prisms  1307   2  and  1307   4  constituting the emergence side prism plate  1307 . The S-polarized light, when it passes through the half wavelength plates  1306 , has its polarization direction rotated by 90° and becomes P-polarized light, and because it further passes through the polarizing separating film  1304 , all the emergent light becomes P-polarized light of high purity. 
     The incident natural light can be uniformized into P-polarized light in the manner described above. 
     By adopting a construction like that of the present embodiment wherein the polarizing separating film in the optical medium, the extinction ratio can be made high over a wide band. 
       FIG. 14  shows the construction of a twelfth embodiment of the present invention. 
     The present embodiment is one in which use is made of conversion units  1401   1 - 1401   3  similar in construction to the embodiment shown in FIG.  13  and the end portions of these units are uniformized and installed parallel to one another to thereby save the space. 
     By adopting such a construction, the volume occupied by the polarizing conversion element, particularly the dimensions of the condensing lens in the direction of the optical axis thereof, can be made small. For example, by the polarizing conversion element being divided into three units as shown, the dimensions of the condensing lens in the direction of the optical axis thereof can be reduced to about ⅓, and this can contribute to the compactness of the projector constructed by the use of it. 
       FIG. 15  shows a thirteenth embodiment of the present invention. 
     The difference of this embodiment from the embodiment of  FIG. 11  is that in the embodiment of  FIG. 11 , the half wavelength plates are intermittently provided, whereas in the present embodiment, a quarter wavelength plate is provided on substantially the whole of that surface of the plane parallel plate  903  which is opposite to the condensing lens  901 . In the other points, the present embodiment is similar to the embodiment of FIG.  1 . 
     Of the light beam  902  having had its beam width compressed by the condensing lens  901 , P-polarized light  902 P is transmitted through polarizing separating film  1004  provided on that surface of the plane parallel plate  903  which is opposite to the condensing lens  901  and S-polarized light is reflected by the polarizing separating film  104 . The S-polarized light passes through a quarter wavelength plate  506  provided on that surface of the plane parallel plate  903  which is opposite to the condensing lens  901 , whereby it becomes circularly polarized light  902 C. The circularly polarized light  902 C is reflected by aluminum total reflection films  1005 , whereafter it passes through the quarter wavelength plate  506  again and thereby becomes P-polarized light whose polarization direction has been rotated by 90°, and passes through polarizing separating film  1004 . 
     The incident natural light can be uniformized into P-polarized light in the manner described above. 
       FIG. 16  shows a fourteenth embodiment of the present invention. 
     The difference of this embodiment from the embodiment of  FIG. 13  is that in the embodiment of  FIG. 13 , the half wavelength plates are intermittently provided, whereas in this embodiment, a quarter wavelength plate is provided on substantially the whole of that surface of the plane parallel plate  903  which is adjacent to the condensing lens  1301 . In the other points, the present embodiment is similar to the embodiment of FIG.  13 . 
     Of the light beam  902  having had its beam width compressed by the condensing lens  1301 , P-polarized light  902 P is transmitted through polarizing separating film  1304  provided on that surface of the plane parallel plate  903  which is opposite to the condensing lens  1301  and S-polarized light  902 S is reflected by the polarizing separating film  1304 . the S-polarized light  902 S passes through a quarter wavelength plate  606  provided on that surface of the plane parallel plate  903  which is adjacent to the condensing lens  1301 , whereby it becomes circularly polarized light. The circularly polarized light is reflected by aluminum total reflection films  1305 , whereafter it passes through the quarter wavelength plate  606  again, whereby it becomes P-polarized light whose polarization direction has been rotated by 90°, and passes through the polarizing separating film  1304 . 
     The incident natural light can be uniformized into P-polarized light in the manner described above. 
     In the embodiments of the  FIGS. 15 and 16 , the polarizing separating film and the quarter wavelength plate are provided on substantially the whole surface of the plane parallel plate and therefore, masking is not necessary when they are formed and thus, the manufacturing process can be simplified. Also, as compared with the aluminum reflection film, the polarizing separating film and the wavelength plate are great in the deterioration of performance in their end portions and therefore, the construction in which the polarizing separating film and the wavelength plate need not be intermittently provided is more preferable from the viewpoint of maintaining the performance of the polarizing element. 
     In the above-described embodiments, a half wavelength plate or a quarter wavelength plate has been described as being used as polarizing rotational means, but besides these, use may be made of resin film, an optically active substance such as a liquid crystal plate, or a polarization plane rotating device such as a Faraday cell to rotate the polarization direction. For example,  FIG. 17  shows a fifteenth embodiment of the present invention in which plane parallel plate  1503  includes an optically active substance, thereby forming an optically active substrate. The light beam  102  entering the polarizing element has its beam width compressed by the cylindrical minute lenses constituting the condensing lens  101 , and S-polarized light  102 S is reflected in a direction orthogonal to the incident light by the polarizing separating films  604  provided on that surface on the plane parallel plate  1503  which is adjacent to the condensing lens  101 , and P-polarized light  102 P is transmitted through the polarizing separating films  604 . The transmitted P-polarized light  102 P passes through the plane parallel plate  1503  (i.e., optically active substrate) and is reflected by the aluminum total reflection film  605  provided on that surface of the plane parallel plate  1503  which is opposite to the condensing lens  101 , whereafter it passes through the plane parallel plate  1503  again, whereby it becomes S-polarized light whose polarization direction has been rotated by 90 degree. due to traversal of the plane parallel plate  1503  (i.e., optically active substrate), and emerges from the polarizing separating films  604 .
         Also, in the above described embodiments, the illuminating system has been described as a condensing lens comprised of cylindrical minute lenses, but the illuminating system may be one provided with a light source portion comprising a number of light emitting elements arranged side by side, and a fly-eye lens for averaging the light emitted by the light source portion or dividing said light into a plurality of lights. For example,  FIG. 18  shows a sixteenth embodiment of the present invention, in which the illuminating system  1601  includes LED array  1601   1 , and fly-eye lens  1061   2 . The LED array  1601   1 , includes a plurality of LEDs  1601   A ,  1601   B ,  1601   C , spaced in coordination with the geometry of the fly-eye lens  1601   2 .     FIG. 19  illustrates a projector constructed according to a polarizing conversion unit  1904  according to the above embodiments of the present invention, the projector further including light source  1902 , image forming panel  1906 , and projection system  1908 .       

     Although the optical surface of each of the cylindrical minute lenses constituting the condensing lens has not been specifically described, said surface can be made into an aspherical surface to thereby enhance the light condensing performance and greatly decrease the loss of the quantity of light and the occurrence of flare light. 
     As for the light condensing member, it may be comprised of a prism. Also, the light condensing member may be a lens to be rotated and a plurality of such members may be arranged in a checkered pattern. In such case, those of the total reflection mirror, the polarizing separating film and the polarizing rotational means (such as the half wavelength plate) which are discretely arranged can be arranged in conformity with the arrangement of the light condensing members. 
     The projectors using the polarizing units shown in FIGS.  2  and  4 - 16  are endowed with the above-described effects. 
     The present invention is constructed as described above and therefore achieves the following effects:
         1. It has the effect of utilizing the incident light efficiently and brightening the image projected by the projector.   2. The polarized state can be uniformized by a simple construction in which polarizing separating film, total reflection film and an element (film) creating a polarizing rotating action are provided on a plane parallel plate.   3. The polarizing conversion unit can be made compact and light in weight, whereby the projector can be made compact.