Patent Document

TECHNICAL FIELD 
       [0001]    The present invention relates to a light emitting element that emits light in a uniform polarization state, and an image display apparatus using the light emitting element. 
       BACKGROUND ART 
       [0002]    There is proposed an image display apparatus in which a light emitting diode (LED) is used as the light emitting element. Such a type of image display apparatus is configured to include: a plurality of LEDs that emit each color of red (R), green (G), and blue (B); an illumination optical system into which lights from the plurality of LEDs are made to enter; a light valve having a liquid crystal display board into which the light from the illumination optical system enters; a color synthesis prism that synthesizes the light from the light valve; and a projection optical system for projecting the light from the color synthesis prism to a projection plane. 
         [0003]    In an image display apparatus having the above-described configuration, it is desired that optical loss in the optical path from the light emitting element to the light valve is reduced as much as possible to increase the luminance of a projected picture. 
         [0004]    Among the above-described components, the liquid crystal display board and the color synthesis prism have a polarization dependence, and to increase the efficiency of the optical system, it is desired that the light emitting element emit light in a uniform polarization state. 
         [0005]    Moreover, as described in Non Patent Literature  1 , there is restriction by etendue which is determined by the product of the area and the radiation angle of the light emitting element. That is, unless the value of the product of the light emission area and radiation angle of the light emitting element is made equal to or less than the value of the product of the area of incident surface of the light valve and an acceptance angle (solid angle) determined by the F number of the illumination optical system, the light from the light emitting element will not be utilized as the projection light. 
         [0006]    For that reason, in an image display apparatus using LEDs, the issue is to reduce the optical loss described above without increasing the emission surface of the light emitting element in order to reduce the etendue of the emitted light of the light emitting element. 
         [0007]    Patent Literature 1 (JP2009-111012A) discloses a semiconductor light emitting apparatus in which the surface orientation of the growth principal surface is prescribed for the purpose of achieving light emission having a large polarization ratio. 
         [0008]    Patent Literature 2 (JP2007-109689A) discloses a light emitting element, which has as its object providing a light emitting element or the like capable of reducing etendue and supplying light with a high polarization conversion efficiency, and includes a light emitting section that is provided on a reference surface and supplies light, and a structure provided at the emission side of the light emitting section, wherein the structure includes a reflective polarizing plate that transmits polarized light in a first vibration direction, and reflects polarized light in a second vibration direction nearly orthogonal to the first vibration direction, and an optical section that transmits light from the reflective polarizing plate and is formed such that a refractive index changes periodically with respect to a two-dimensional direction substantially parallel with the reference surface. 
       Citation List 
     Patent Literature 
     [Patent Literature 1] JP2009-111012A 
     [Patent Literature 2] JP2007-109689A 
     [Patent Literature 3] JP2001-51122A 
     Non Patent Literature 
     [Non Patent Literature 1] SID 06 DIGEST, 2006, pp. 1808-1811, 61.1, Photonic Lattice LEDs for RPTV Light Engines, Christian Hoepiher 
     SUMMARY OF INVENTION 
     Technical Problem 
       [0009]    Since the semiconductor light emitting apparatus described in Patent Literature 1 uses the surface orientation of a growth principal surface, its growth condition is limited and this will lead to productivity issues. This will cause a problem especially when a substrate having a large area is used. 
         [0010]    While the light emitting element described in Patent Literature 2 uses a reflective polarization plate to align the polarization orientation of the light to be emitted therefrom, since the light reflected by the reflective polarizing plate is configured to change its vibration direction at a reflection section and since a phase plate is provided closer to the light emitting section than the reflective polarizing plate and since light reenter the reflective polarizing plate, there is a problem in that the efficiency of polarization conversion is poor when considering the attenuation in the reflection, and achieving a high luminance is difficult. 
         [0011]    The present invention has been made in view of the above-described problems of related art, and has as its object realizing a light emitting element for emitting light in a uniform polarization state, the light emitting element being easy to fabricate, having good efficiency, and being able to achieve a high luminance. 
         [0012]    Solution to Problem 
         [0013]    The light emitting element of the present invention is a light emitting element including an active layer for generating light, the light emitting element including: 
         [0014]    a polarizer layer including a first region that transmits polarized light in a first direction and reflects other light from among the light generated at the active layer, and a second region that transmits polarized light in a second direction orthogonal to the first direction and reflects other light; 
         [0015]    a wave plate layer including a third region and a fourth region that allow the lights exited from the first region and the second region to enter, and to exit as light in the same polarization state; and 
         [0016]    a reflection layer that reflects the lights reflected at the first region and the second region. 
         [0017]    The image display apparatus of the present invention uses a light emitting element of the above-described configuration. 
       Advantageous Effects of Invention 
       [0018]    In the present invention, a polarized light in a first direction and a polarized light in a second direction orthogonal to the first direction are made to exit from the polarizer layer. Since these polarized lights are thereafter made to exit, without being reflected, at the wave plate layer as a light having the same polarization state, they are efficient and can achieve a high luminance. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  is a cross-sectional view showing the configuration of an exemplary embodiment of a light emitting element. 
           [0020]      FIG. 2  is a perspective view showing one configuration example of polarizer layer  108  in  FIG. 1 . 
           [0021]      FIG. 3  is a perspective view showing another configuration example of polarizer layer  108  in  FIG. 1 . 
           [0022]      FIG. 4  is a perspective view showing one configuration example of half-wave plate layer  109  in  FIG. 1 . 
           [0023]      FIG. 5  is a perspective view showing another configuration example of half-wave plate layer  109  in  FIG. 1 . 
           [0024]      FIG. 6  is a perspective view showing another configuration example of polarizer layer  108  in  FIG. 1 . 
           [0025]      FIG. 7  is a perspective view showing another configuration example of polarizer layer  108  in  FIG. 1 . 
           [0026]      FIG. 8  is a perspective view showing another configuration example of half-wave plate layer  109  in  FIG. 1 . 
           [0027]      FIG. 9  is a perspective view showing another configuration example of half-wave plate layer  109  in  FIG. 1 . 
           [0028]      FIG. 10  is diagram to illustrate the period of a first region and a second region which are formed in polarizer layer  108  and half-wave plate layer  109 . 
           [0029]      FIG. 11  is a diagram showing the relationship between a relative period and an angular width. 
           [0030]      FIG. 12  is a block diagram showing the configuration of one exemplary embodiment of an image display apparatus using a light emitting element. 
           [0031]      FIG. 13  is a block diagram showing the configuration of another exemplary embodiment of the image display apparatus using the light emitting element. 
           [0032]      FIG. 14  is a block diagram showing the configuration of another exemplary embodiment of the image display apparatus using the light emitting element. 
           [0033]      FIG. 15  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 12 . 
           [0034]      FIG. 16  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 13 . 
           [0035]      FIG. 17  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 14 . 
           [0036]      FIG. 18   a  is a cross-sectional view showing the configuration of another exemplary embodiment of a light emitting element. 
           [0037]      FIG. 18   b  is a diagram showing the configuration of another exemplary embodiment of the light emitting element, which is a cross-sectional view showing the configuration of polarizer layer  1808  in  FIG. 18   a  in more detail. 
           [0038]      FIG. 18   c  is a diagram showing the configuration of another exemplary embodiment of the light emitting element, which is a cross-sectional view showing the configuration of quarter-wave plate layer  1809  in  FIG. 18   a  in more detail. 
           [0039]      FIG. 18   d  is a diagram showing the configuration of another exemplary embodiment of the light emitting element, which is a perspective view showing a configuration example of quarter-wave plate layer  1809  in  FIG. 18   a.    
           [0040]      FIG. 18   e  is a diagram showing the configuration of another exemplary embodiment of the light emitting element, which is a perspective view showing a configuration example of quarter-wave plate layer  1809  in  FIG. 18   a.    
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0041]    Hereafter, specific exemplary embodiments will be described with reference to the drawings. 
         [0042]      FIG. 1  is a cross-sectional view showing the configuration of an exemplary embodiment of light emitting element  100 . It is noted that in light emitting element  100 , since the actual thicknesses of individual layers are very thin and the differences in the thickness between respective layers are very large, it is difficult to draw a picture of each layer at an accurate scale and proportion. Accordingly, each layer is not drawn to an actual scale in the drawings, and instead, each layer is schematically shown. 
         [0043]    P-type electrode  102  made up of Ni/Au/Ti/Au and reflection layer  103  made up of Ag are formed on submount  101  which is made of Si. 
         [0044]    P-type semiconductor layer  104  which is made of GaN doped with Mg, active layer  105  in which GaN and InGaN are alternately stacked to constitute a multiple quantum well (MQW), and N-type semiconductor layer  106  which is made of GaN doped with Si are stacked in order on reflection layer  103 . N-type electrode  107  made up of Ti/Al/Ti/Au, and polarizer layer  108  are formed on N-type semiconductor layer  106 , and further half-wave plate layer  109  is provided on polarizer layer  108 . 
         [0045]    The method of fabricating light emitting element  100  will be described. First, N-type semiconductor layer  106 , active layer  105 , P-type semiconductor layer  104 , and reflection layer  103  are formed on a substrate. Next, reflection layer  103  is bonded to submount  101  to remove the substrate. Next, polarizer layer  108  is formed on N-type semiconductor layer  106 . Half-wave plate layer  109  is formed by a separate process, and bonded onto polarizer layer  108 . Lastly, P-type electrode  102  and N-type electrode  107  are formed. 
         [0046]    The outline operation of the present exemplary embodiment will be described. Applying a voltage between P-type electrode  102  and N-type electrode  107  to pass an electric current between them will result in the generation of light at active layer  105 . The light generated at active layer  105  contains components which are oriented toward various directions. 
         [0047]    Both polarizer layer  108  and half-wave plate layer  109  each includes a first region and a second region, and the first region and the second region of polarizer layer  108  are provided so as to correspond to the first region and the second region of half-wave plate layer  109  with respect to the emitted light from light emitting element  100 . 
         [0048]    The first region of polarizer layer  108  transmits polarized light in the first direction and reflects other light from among light generated at the active layer. The second region of polarizer layer  108  transmits polarized light in a second direction, which is orthogonal to the polarized light in the first direction, and reflects other light. While the light reflected at polarizer layer  108  is reflected at reflection layer  103  toward polarizer layer  108 , at this moment, the light is reflected with a certain angle, and therefore it reenters polarizer layer  108  at a position different from the reflection position. For this reason, the light that has reentered polarizer layer  108  includes light that passes through polarizer layer  108 . 
         [0049]    The first region and the second region of half-wave plate layer  109  are configured to allow an incident light to exit after giving a predetermined polarization rotation angle thereto, and the second region allows the incident light to exit after adding a polarization rotation angle of 90 degrees to the polarization rotation angle of the incident light which is given thereto at the first region. For this reason, the light exited from half-wave plate layer  109  is made to have a uniform polarization orientation. 
         [0050]    Hereafter, specific configurations of polarizer layer  108  and half-wave plate layer  109  will be described. 
         [0051]      FIG. 2  is a perspective view showing one configuration example of polarizer layer  108  in  FIG. 1 . 
         [0052]    In the example shown in  FIG. 2 , a polarizer, in which a plurality of metal nanowires  202  made of Al are formed in parallel, is formed on N-type semiconductor layer  201  which is made of GaN doped with Si. Metal nanowire  202  is provided alternately with first region  203  and second region  204 , in which longitudinal directions are orthogonal to each other. 
         [0053]    First region  203  transmits polarized light in a first direction (X direction), and reflects polarized light in a second direction (Y direction), which is orthogonal to the polarized light in the first direction. 
         [0054]    Second region  204  transmits polarized light in the second direction and reflects polarized light in the first direction. 
         [0055]      FIG. 3  is a perspective view showing another configuration example of polarizer layer  108  in  FIG. 1 . 
         [0056]    In the example shown in  FIG. 3 , a polarizer in which a plurality of semiconductors  302 , in which GaN and AN are alternately stacked, are placed in parallel is formed on N-type semiconductor layer  301  which is made of GaN doped with Si. Semiconductor  302  is provided alternately with first region  303  and second region  304 , in which longitudinal directions are orthogonal to each other. 
         [0057]    First region  303  transmits polarized light in a first direction, and reflects polarized light in a second direction, which is orthogonal to the polarized light in the first direction. 
         [0058]    Second region  304  transmits polarized light in the second direction and reflects polarized light in the first direction. 
         [0059]      FIG. 4  is a perspective view showing one configuration example of half-wave plate layer  109  in  FIG. 1 . 
         [0060]    In the example shown in  FIG. 4 , dielectric  402  in which SiO 2  and TiO 2  are alternately stacked is formed on substrate  401  which is made of quartz. Dielectric  402  is provided with first region  403  and second region  404 , which respectively correspond to first regions  203  and  303 , and second regions  204  and  304  shown in  FIGS. 2 and 3 , respectively. 
         [0061]    Since first region  403  is formed into a flat shape, it allows the polarized light in the first direction, which has passed through first regions  203  and  303 , to pass through as is. 
         [0062]    Since second region  404  has a periodic structure, which has a periodic concavo-convex shape in one direction, and a uniform shape in the direction orthogonal thereto, in the XY plane as disclosed in Patent Literature 3 (JP2001-51122A), it acts as a half-wave plate so that the polarized light in the second direction, which has passed through second regions  204  and  304 , is converted into a polarized light in the first direction and is made to exit. 
         [0063]    To align the polarization orientations of the exiting lights of first region  403  and second region  404 , into which lights having orthogonal polarization orientations enter, it becomes necessary for second region  404  to allow the incident light to exit after adding a polarization rotation angle of 90 degrees to the polarization rotation angle of the incident light which is given thereto at first region  403 . 
         [0064]    In the example shown in  FIG. 4 , since first region  403  is formed into a flat shape, the polarization rotation angle to be given to incident light becomes 0 degree. The polarization rotation angle to be added by second region  404  is arranged to be 90 degrees such that the angular difference between these orientations is 90 degrees. 
         [0065]    As a result, the polarized light that has passed through second regions  204  and  304  is converted into polarized light in the first direction and is made to exit. 
         [0066]      FIG. 5  is a perspective view showing another configuration example of half-wave plate layer  109  in  FIG. 1 . 
         [0067]    In the example shown in  FIG. 5 , dielectric  502  in which SiO 2  and TiO 2  are alternately stacked is formed on substrate  501  which is made of quartz. Dielectric  502  is provided with first region  503  and second region  504 , which respectively correspond to first regions  203  and  303 , and second regions  204  and  304  shown in  FIGS. 2 and 3 , respectively. 
         [0068]    Since first region  503  and second region  504  have a periodic structure, which has a periodic concavo-convex shape in one direction, and a uniform shape in the direction orthogonal thereto, in the XY plane as disclosed in JP2001-51122A, they act as a half-wave plate. 
         [0069]    To align the polarization orientations of the exiting lights of first region  503  and second region  504 , into which lights having orthogonal polarization orientations enter, it becomes necessary for second region  504  to allow the incident light to exit after adding a polarization rotation angle of 90 degrees to the polarization rotation angle of the incident light which is given thereto at first region  503 . 
         [0070]    In the example shown in  FIG. 5 , the polarization rotation angle to be given to incident light by first region  503  is arranged to be 45 degrees, and the polarization rotation angle to be added by second region  504  is arranged to be 135 degrees so that the angular difference between these directions is 90 degrees. 
         [0071]    As a result, the polarized light in the second direction, which has passed through second regions  204  and  304 , is converted into polarized light in the first direction and is made to exit. 
         [0072]      FIG. 6  is a perspective view showing another configuration example of polarizer layer  108  in  FIG. 1 . 
         [0073]    In the example shown in  FIG. 6 , a polarizer, in which a plurality of metal nanowires  602  made of Al are formed in parallel, is formed on N-type semiconductor layer  601  which is made of GaN doped with Si. Metal nanowire  602  is adjacently provided with first region  603  and second region  604 , in which longitudinal directions are orthogonal to each other, in a staggered pattern. 
         [0074]    The optical properties of first region  603  and second region  604  are the same as those of first region  203  and second region  204  shown in  FIG. 2 . 
         [0075]      FIG. 7  is a perspective view showing another configuration example of polarizer layer  108  in  FIG. 1 . 
         [0076]    In the example shown in  FIG. 7 , a polarizer, in which a plurality of semiconductors  702  in which GaN and AN are alternately stacked are placed in parallel, is formed on N-type semiconductor layer  701  which is made of GaN doped with Si. Semiconductor  702  is adjacently provided with first region  703  and second region  704 , in which longitudinal directions are orthogonal to each other, in a staggered pattern. 
         [0077]    The optical properties of first region  703  and second region  704  are the same as those of first region  303  and second region  304  shown in  FIG. 3 . 
         [0078]      FIG. 8  is a perspective view showing another configuration example of half-wave plate layer  109  in  FIG. 1 . 
         [0079]    In the example shown in  FIG. 8 , dielectric  802  in which SiO 2  and TiO 2  are alternately stacked is formed on substrate  801  which is made of quartz. Dielectric  802  is provided with first region  803  and second region  804 , which respectively correspond to first regions  603  and  703 , and second regions  604  and  704  shown in  FIGS. 6 and 7 , respectively. 
         [0080]    Since first region  803  is formed into a flat shape, it allows the polarized light in the first direction, which has passed through first regions  603  and  703 , to pass through as is. 
         [0081]    Since second region  804  has a periodic structure, which has a periodic concavo-convex shape in one direction, and a uniform shape in the direction orthogonal thereto, in the XY plane as disclosed in JP2001-51122A, it acts as a half-wave plate so that the polarized light in the second direction, which has passed through second regions  604  and  704 , is converted into polarized light in the first direction and is made to exit. 
         [0082]    To align the polarization orientations of the exiting lights of first region  803  and second region  804 , into which light having orthogonal polarization orientations enter, it becomes necessary for second region  804  to allow the incident light to exit after adding a polarization rotation angle of 90 degrees to the polarization rotation angle of the incident light which is given thereto at first region  803 . 
         [0083]    In the example shown in  FIG. 8 , since first region  803  is formed into a flat shape, the polarization rotation angle to be given to incident light becomes 0 degree. The polarization rotation angle to be added by second region  804  is arranged to be 90 degrees such that the angular difference between these directions is 90 degrees. 
         [0084]    As a result, the polarized light that has passed through second regions  604  and  704  is converted into polarized light in the first direction and is made to exit. 
         [0085]      FIG. 9  is a perspective view showing another configuration example of half-wave plate layer  109  in  FIG. 1 . 
         [0086]    In the example shown in  FIG. 9 , dielectric  902  in which SiO 2  and TiO 2  are alternately stacked is formed on substrate  901  which is made of quartz. Dielectric  902  is provided with first region  903  and second region  904 , which respectively correspond to first regions  603  and  703 , and second regions  604  and  704  shown in  FIGS. 6 and 7 , respectively. 
         [0087]    Since first region  903  and second region  904  have a periodic structure, which has a periodic concavo-convex shape in one direction, and a uniform shape in the direction orthogonal thereto, in the XY plane as disclosed in JP2001-51122A, they act as a half-wave plate. 
         [0088]    To align the polarization orientations of first region  903  and second region  904 , into which light having orthogonal polarization orientations enters, it becomes necessary for second region  904  to allow the incident light to exit after adding a polarization rotation angle of 90 degrees to the polarization rotation angle of the incident light which is given thereto at first region  903 . 
         [0089]    In the example shown in  FIG. 9 , the polarization rotation angle to be given to incident light by first region  903  is arranged to be 45 degrees, and the polarization rotation angle to be added by second region  904  is arranged to be 135 degrees so that the angular difference between these directions is 90 degrees. 
         [0090]    As a result of this, the polarized light in the second direction, which has passed through second regions  604  and  704 , is converted into a polarized light in the first direction and is made to exit. 
         [0091]    As shown in  FIGS. 2 to 5 , when the first region and the second region are arranged in a striped pattern, it is possible to facilitate fabrication of the element. 
         [0092]    As shown in  FIGS. 6 to 9 , when the first region and the second region are arranged in a staggered pattern, the way light spreads in X direction becomes similar to the way light spreads in Y direction so that it is possible to achieve an illumination light which has a high uniformity and which is easier to manipulate. 
         [0093]      FIG. 10  is diagram to illustrate the period of a first region and a second region which are formed in a polarizer layer and a half-wave plate layer. 
         [0094]    Although it is desired that the light generated at active layer  105  directly exit from polarizer layer  108  without being reflected, one half of the light is reflected. When the light is reflected multiple times, since it is greatly attenuated and is difficult to be used as illumination light, herein, a periodical structure will be studied, which is suitable for causing the light to be reflected once at reflection layer  103  and exit from polarizer layer  108 . 
         [0095]    In  FIG. 10 , the center of polarizer layer  108  in its thickness direction is denoted by A, the center of reflection layer  103  in its thickness direction is denoted by B, and assuming that the widths of the first region and the second region are the same, the sum of the widths of each region is denoted by P. Further, it is assumed that points at which reflection occurs are centers of polarizer layer  108  and reflection layer  103  in respective thickness directions, and the distance between the points is denoted by L 1 , and the distance from the center (light emission point) of active layer  105  to the center of polarizer layer  108  is denoted by L 2 . Furthermore, it is assumed that the position of the light emission point in the XY plane is the center of either the first region or the second region where it is most difficult for light to exit after being reflected once. 
         [0096]    As shown in  FIG. 10 , from among the lights that are generated at the light emission point and that exit after being reflected once, the amount of the light that exits after being reflected once increases as angular width Δθ, which is the angle formed between the light that exits at the shortest distance and the light that exits at a longest distance, becomes larger. The intersection of each of the exiting lights is at a distance of  2 L 1 +L 2  from center A of polarizer layer  108 . 
         [0097]      FIG. 11  is a diagram showing the relationship between a relative period, which is shown by P/( 2 L 1 +L 2 ), and an angular width, in which it is shown that when the relative period is 2.3, the angular width becomes a maximum of 30°. Further, it is seen that the angular width may be not less than 20° if the relative period is in a range from 0.9 to 6.5, and the angular width may be not less than 25° if the relative period is in a range from 1.2 to 4.5. 
         [0098]    When distance L 1  between polarizer layer  108  and reflection layer  103  is 3 μm and distance L 2  from the center of active layer  105  to the center of polarizer layer  108  is 1.5 μm, in order to get the maximum angular width of 30°, width P which is the sum of the widths of the first region and the second region, may be set to be 17 μm. 
         [0099]      FIG. 12  is a block diagram showing the configuration of one exemplary embodiment of an image display apparatus using a light emitting element. 
         [0100]    An image display apparatus shown in  FIG. 12  includes light source unit  1201 R that generates a red light, light source unit  1201 G that generates a green light, and light source unit  1201 B that generates a blue light. Each of these light source units is constructed by using at least one or more of the light emitting elements according to the present invention, which have been described by using  FIGS. 1 to 11 . 
         [0101]    The red light generated at light source unit  1201 R irradiates liquid crystal display element  1203 R that displays an image for red light, via condenser lens  1202 R so that a red image light generated at liquid crystal display element  1203 R enters into color synthesis prism  1204 . 
         [0102]    The green light generated at light source unit  1201 G irradiates liquid crystal display element  1203 G that displays an image for green light, via condenser lens  1202 G so that a green image light generated at liquid crystal display element  1203 G enters into color synthesis prism  1204 . 
         [0103]    The blue light generated at light source unit  1201 B irradiates liquid crystal display element  1203 B that displays an image for blue light, via condenser lens  1202 B so that a blue image light generated at liquid crystal display element  1203 B enters into color synthesis prism  1204 . 
         [0104]    An image light which is synthesized from the entered red image light, green image light, and blue image light at color synthesis prism  1204  is projected via projection lens  1205 . 
         [0105]      FIG. 13  is a block diagram showing the configuration of another exemplary embodiment of an image display apparatus using a light emitting element. The image display apparatus of the present exemplary embodiment forms an image by using micromirror  1304  that separately controls the angles of multiple micromirrors. 
         [0106]    The image display apparatus of the present exemplary embodiment includes light source unit  1301 R that generates a red light, light source unit  1301 G that generates a green light, and light source unit  1301 B that generates a blue light. Each of these light source units is constructed by using at least one or more of the light emitting elements according to the present invention, which have been described by using  FIGS. 1 to 11 . 
         [0107]    The red light generated at light source unit  1301 R enters into color synthesis prism  1303  via condenser lens  1302 R. The green light generated at light source unit  1301 G enters into color synthesis prism  1303  via condenser lens  1302 G. The blue light generated at light source unit  1301 B enters into color synthesis prism  1303  via condenser lens  1302 B. 
         [0108]    Light source unit  1301 R, light source unit  1301 G, and light source unit  1301 B are controlled such that the lit-up state thereof is successively changed over so that a red light, a green light, and a blue light are projected in sequence toward micromirror  1304  from color synthesis prism  1303 . 
         [0109]    Micromirror  1304  forms an image light according to the colored light with which it is irradiated so that a red image light, a green image light, and a blue image light are projected in sequence via projection lens  1305 . 
         [0110]      FIG. 14  is a block diagram showing the configuration of another exemplary embodiment of an image display apparatus using a light emitting element. The image display apparatus of the present exemplary embodiment forms an image by using micromirror  1405  that separately controls the angles of multiple micromirrors. 
         [0111]    The image display apparatus of the present exemplary embodiment includes light source units  1401 RP and  1401 RS that generate P-polarized light and S-polarized light of red color, light source units  1401 GP and  1401 GS that generate P-polarized light and S-polarized light of green color, and light source units  1401 BP and  1401 BS that generate P-polarized light and S-polarized light of blue color. Each of these light source units is constructed by using at least one or more of the light emitting elements according to the present invention, which have been described by using  FIGS. 1 to 11 . 
         [0112]    The P-polarized light and S-polarized light of red color which are generated at light source units  1401 RP and  1401 RS enter into polarization beam splitter  1402 R. Polarization beam splitter  1402 R transmits the P-polarized light as is, and reflects the S-polarized light. As a result, the P-polarized light and S-polarized light of the red color which are generated at light source units  1401 RP and  1401 RS are made to exit from polarization beam splitter  1402 R. 
         [0113]    Similarly, the P-polarized light and S-polarized light of green color which are generated at light source units  1401 GP and  1401 GS are caused to exit by polarization beam splitter  1402 G, and the P-polarized light and S-polarized light of blue color which are generated at light source units  1401 BP and  1401 BS are caused to exit by polarization beam splitter  1402 B. 
         [0114]    The lights exited from polarization beam splitter  1402 R, polarization beam splitter  1402 G, and polarization beam splitter  1402 B enter into color synthesis prism  1404  via condenser lenses  1403 R,  1403 G, and  1403 B, respectively. 
         [0115]    Light source units  1401 RP and  1401 RS, light source units  1401 GP and  1401 GS, and light source units  1401 BP and  1401 BS are controlled such that the lit-up state of each color is successively changed so that a red light, a green light, and a blue light are projected in sequence toward micromirror  1405  from color synthesis prism  1404 . Micromirror  1405  forms an image light according to the colored light with which it is irradiated so that a red image light, a green image light, and a blue image light are projected in sequence via projection lens  1406 . 
         [0116]    In the image display apparatus of the present exemplary embodiment compared with the image display apparatus shown in  FIG. 13 , if the number of light emitting elements that constitute each light source unit is the same, the quantity of light is doubled thus enabling a high luminance. 
         [0117]      FIG. 15  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 12 . 
         [0118]    Light source units  1201 R,  1201 G, and  1201 B are turned on into a lit-up state by being driven by driving circuits  1501 R,  1501 G, and  1501 B. It is noted that since light source units  1201 R,  1201 G, and  1201 B are always kept in a lit-up state during image display operation, they may be driven by a single driving circuit. 
         [0119]    Image signal processing circuit  1501  creates signals indicating an image for red color, image for green color, and image for blue color according to input image signals provided from an external PC (personal computer) and an image reproducing apparatus, etc. to supply them to driving circuits  1502 R,  1502 G, and  1502 B, and liquid crystal display apparatuses  1203 R,  1203 G, and  1203 B forms an image for red color, image for green color, and image for blue color by being driven by driving circuits  1502 R,  1502 G, and  1502 B. 
         [0120]      FIG. 16  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 13 . 
         [0121]    Image signal processing circuit  1601  creates image for red color, image for green color, and image for blue color according to input image signals provided from an external PC and an image reproducing apparatus, etc. to drive micromirror  1304  via driving circuit  1604  such that these images are successively formed. Concurrently with this, driving circuits  1602 R,  1602 G, and  1602 B are controlled such that the light source unit for the image color that has been formed is lit up among light source units  1301 R,  1301 G, and  1301 B. 
         [0122]      FIG. 17  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 14 . 
         [0123]    Image signal processing circuit  1701  creates image for red color, image for green color, and image for blue color according to input image signals provided from an external PC and an image reproducing apparatus, etc. to drive micromirror  1405  via driving circuit  1703  such that these images are successively formed. Concurrently with this, driving circuits  1702 RP,  1702 RS,  1702 GP,  1702 GS,  1702 BP and  1702 BS are controlled such that the light source unit for the image color that has been formed is lit up among light source units  1401 RP,  1401 RS,  1401 GP,  1401 GS,  1401 BP, and  1401 BS. 
         [0124]      FIG. 18   a  is a cross-sectional view showing the configuration of another exemplary embodiment of a light emitting element. 
         [0125]    In light emitting element  1800  of the present exemplary embodiment as well, since the actual thicknesses of individual layers are very thin and the differences in the thickness between respective layers are very large, it is difficult to draw a picture of each layer at an accurate scale and proportion. For this reason, each layer is not drawn to an actual scale in the drawings, and instead, each layer is schematically shown. 
         [0126]    P-type electrode  1802  made up of Ni/Au/Ti/Au and reflection layer  1803  made up of Ag are formed on submount  1801  which is made of Si. 
         [0127]    P-type semiconductor layer  1804  which is made of GaN doped with Mg, active layer  1805  in which GaN and InGaN are alternately stacked to constitute a multiple quantum well, and N-type type semiconductor layer  1806  which is made of GaN doped with Si are stacked in order on reflection layer  1803 . N-type electrode  1807  made up of Ti/Al/Ti/Au, and polarizer layer  1808  are formed on N-type semiconductor layer  1806 , and further quarter-wave plate layer  1809  and quarter-wave plate layer  1810  are provided on polarizer layer  1808 . 
         [0128]    The method of fabricating light emitting element  1800  will be described. First, N-type semiconductor layer  1806 , active layer  1805 , P-type semiconductor layer  1804 , and reflection layer  1803  are formed on a substrate. Next, reflection layer  1803  is bonded to submount  1801  to remove the substrate. Next, polarizer layer  1808  is formed on N-type semiconductor layer  1806 . Quarter-wave plate layer  1809  and quarter-wave plate layer  1810  are formed by a separate process, and bonded onto polarizer layer  1808 . Lastly, P-type electrode  1802  and N-type electrode  1807  are formed. 
         [0129]    The outline operation of the present exemplary embodiment will be described. Applying a voltage between P-type electrode  1802  and N-type electrode  1807  to pass an electric current between them will result in light being generated at active layer  1805 . The light generated at active layer  1805  contains components which are oriented in various directions. 
         [0130]      FIGS. 18   b  and  18   c  are cross-sectional views showing the configurations of polarizer layer  1808  and quarter-wave plate layer  1809  in  FIG. 18   a  in more detail. 
         [0131]    As shown in  FIGS. 18   b  and  18   c , both polarizer layer  1808  and quarter-wave plate layer  1809  respectively include a first region and a second region. 
         [0132]    First region  1808   1  and second region  1808   2  of polarizer layer  1808  are provided so as to correspond to first region  1809   1  and second region  1809   2  of quarter-wave plate layer  1809  with respect to the emitted light of light emitting element  1800 . 
         [0133]    First region  1808   1  of polarizer layer  1808  transmits polarized light in the first direction and reflects other light. Second region  1808   2  of polarizer layer  1808  transmits polarized light in the second direction, which is orthogonal to the polarized light in the first direction, and reflects other light. While the light reflected at polarizer layer  1808  is reflected at reflection layer  1803  toward polarizer layer  1808 , at this moment, the light is reflected at a certain angle, and therefore it reenters polarizer layer  1808  at a position different from the reflection position. For this reason, the light that has reentered polarizer layer  1808  includes light that passes through polarizer layer  1808 . 
         [0134]    First region  1809   1  and second region  1809   2  of quarter-wave plate layer  1809  are configured to allow incident light to exit after giving a phase difference of a quarter wavelength to two orthogonal polarization components of the incident light, and the first region and the second region respectively give a phase difference of an opposite sign to two orthogonal polarization components of incident light. 
         [0135]    As described above, since orthogonal linearly polarized lights enter into first region  1809   1  and second region  1809   2  of quarter-wave plate layer  1809 , the exiting lights thereof are aligned in circularly polarized lights which rotate in the same direction. 
         [0136]    Quarter-wave plate layer  1810  gives a phase difference of a quarter wavelength to two orthogonal polarization components of the circularly polarized light exited by quarter-wave plate layer  1809  and allows the same to exit as a linearly polarized light. 
         [0137]    A specific configuration of polarizer layer  1808  that constitutes light emitting element  1800  may include the configurations shown in  FIGS. 2 ,  3 ,  6 , and  7 . Moreover, a specific configuration of quarter-wave plate layer  1809  may include the configurations shown in  FIGS. 18   d  and  18   e.    
         [0138]    In the examples shown in  FIGS. 18   d  and  18   e , dielectrics  1811 ′ and  1811 ″ in which SiO 2  and TiO 2  are alternately stacked are formed on substrates  1810 ′ and  1810 ″ which are made of quartz. Dielectrics  1811 ′ and  1811 ″ are provided with first regions  1808   1 ′ and  1808   1 ″, and second regions  1808   2 ′ and  1808   2 ″. 
         [0139]    Since first regions  1808   1 ′ and  1808   1 ″ and second regions  1808   2 ′ and  1808   2 ″ have a periodic structure, which has a periodic concavo-convex shape in one direction, and a uniform shape in the direction orthogonal thereto, in the XY plane as disclosed in JP2001-51122A, they act as a quarter-wave plate. 
         [0140]    In the example shown in  FIG. 18   d , the first region and the second region are arranged in a striped pattern, and in the example shown in  FIG. 18   e , the first region and the second region are arranged in a staggered pattern. 
         [0141]    Moreover, the image display apparatus using light emitting element  1800  may include the configurations shown in  FIGS. 12 to 17 . 
         [0142]    Further, the relationship between the relative period and the angular width, which have been described by using  FIGS. 10 and 11 , is maintained in light emitting element  1800  of the present exemplary embodiment as well. 
         [0143]    The present application claims priority of Japanese Patent Application No. 2009-243367 filed on Oct. 22, 2009, which is herein incorporated by reference in its entirety. 
       REFERENCE SIGNS LIST 
       [0144]      100  Light emitting element 
         [0145]      101  Submount 
         [0146]      102  P-type electrode 
         [0147]      103  Reflection layer 
         [0148]      104  P-type semiconductor layer 
         [0149]      105  Active layer 
         [0150]      106  N-type semiconductor layer 
         [0151]      107  N-type electrode 
         [0152]      108  Polarizer layer 
         [0153]      109  half-wave plate layer

Technology Category: h