Abstract:
The present invention is intended to realize a light emitting element which is easy to fabricate, is efficient, and is able to emit light in a uniform polarization state enabling the achievement of high luminance. A light emitting element of the present invention is a light emitting element including an active layer for generating light, the light emitting element including: a first reflection layer that allows the light generated at the active layer to reflect at a reflection section in which reflection members are periodically provided, and to exit from an exiting section between the reflection members; a polarization beam splitter layer that transmits a polarized light oriented in a first direction and diffracts a polarized light oriented in a second direction orthogonal to the first direction among the light exited from the exiting section; a wave plate layer that allows the light transmitted through the polarization beam splitter layer and the light diffracted at the polarization beam splitter layer to enter, and to exit as a light of a same polarization state; and a second reflection layer that reflects the light reflected at the first reflection light.

Description:
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. 
         [0009]    Patent Literature 3 (JP2006-165423A) discloses, in an embodiment shown in FIG. 21 thereof, an arrangement which allows light, which is generated at a light emitting layer and which is made to exit from between upper side electrode layers, to enter a polarization separation film, which transmits a P-polarized component and reflects an s-polarized component, via a microlens element, and allows the reflected S-polarized component to reflect in the same direction as that of the light of P-polarized component by means of a reflection film, and to enter an a half-wavelength plate, thereby achieving a light with the same polarization orientation as that of the light of the P-polarized component. 
       CITATION LIST 
     Patent Literature 
       [0010]    [Patent Literature 1] JP2009-111012A 
         [0011]    [Patent Literature 2] JP2007-109689A 
         [0012]    [Patent Literature 3] JP2006-162354A 
         [0013]    [Patent Literature 4] JP2001-51122A 
       Non Patent Literature 
       [0014]    [Non Patent Literature 1] SID 06 DIGEST, 2006, pp. 1808-1811, 61.1, Photonic Lattice LEDs for RPTV Light Engines, Christian Hoepfner 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0015]    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. 
         [0016]    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. 
         [0017]    The arrangement disclosed in Patent Literature 3 is provided with a polarization separation film corresponding to the light which is generated at a light emitting layer and which is made to exit from between upper electrode layers. From among the light generated at the light emitting layer, only a small part thereof directly exits from between the upper side electrode layers and a major part thereof exits after being reflected. Since as the number of reflections increases, attenuation occurs according to the number thereof, the installation interval of the upper side electrodes has to be made small. For this reason, the polarization separation film corresponding to the upper side electrode layer has to be made small as well, making the fabrication thereof difficult. 
         [0018]    The present invention has been made in view of the problems of such related arts as described above, and its object is to realize a light emitting element which is easy to fabricate, good in efficiency, and able to emit light in a uniform polarization state, thus enabling the achievement of high luminance. 
       Solution to Problem 
       [0019]    A light emitting element of the present invention is a light emitting element including an active layer for generating light, the light emitting element including: 
         [0020]    a first reflection layer that allows the light generated at the active layer to reflect at a reflection section in which reflection members are periodically provided, and to exit from an exiting section between the reflection members; 
         [0021]    a polarization beam splitter layer that transmits polarized light oriented in a first direction and diffracts polarized light oriented in a second direction orthogonal to the first direction among the light exited from the exiting section; 
         [0022]    a wave plate layer that allows the light transmitted through the polarization beam splitter layer and the light diffracted at the polarization beam splitter layer to enter, and to exit as light of a same polarization state; and 
         [0023]    a second reflection layer that reflects the light reflected at the first reflection light. 
         [0024]    An image display apparatus of the present invention utilizes the light emitting element of the above-described configuration. 
       Advantageous Effects of Invention 
       [0025]    In the present invention, a polarized light oriented in a first direction and a polarized light oriented in a second direction orthogonal to the first direction are made to exit from the polarization beam splitter layer. Since these polarized lights are thereafter made to exit,  3   0  without being reflected, as a light in the same polarization state at the wave plate layer, they are efficient and can achieve a high luminance. Moreover, since the polarization beam splitter layer has a flat plate shape, even if the installation interval of the reflection members is reduced, it can be provided accordingly and therefore is easy to fabricate. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0026]      FIG. 1(   a ) is a cross-sectional view showing the configuration of an exemplary embodiment of light emitting element  100 , and  FIG. 1(   b ) is a cross-sectional view showing the configuration of a principal part thereof. 
           [0027]      FIG. 2  is a perspective view showing one configuration example of reflection layer  108  in  FIG. 1 . 
           [0028]      FIG. 3  is a perspective view showing one configuration example of polarization beam splitter layer  109  in  FIG. 1 . 
           [0029]      FIG. 4  is a perspective view showing one configuration example of polarization beam splitter layer  109  in  FIG. 1 . 
           [0030]      FIG. 5  is a perspective view showing one configuration example of half-wave plate layer  110  in  FIG. 1 . 
           [0031]      FIG. 6  is a perspective view showing one configuration example of half-wave plate layer  110  in  FIG. 1 . 
           [0032]      FIG. 7  is a perspective view showing another configuration example of reflection layer  108  in  FIG. 1 . 
           [0033]      FIG. 8  is a perspective view showing another configuration example of polarization beam splitter layer  109  in  FIG. 1 . 
           [0034]      FIG. 9  is a perspective view showing another configuration example of polarization beam splitter layer  109  in  FIG. 1 . 
           [0035]      FIG. 10  is a perspective view showing another configuration example of half-wave plate layer  110  in  FIG. 1 . 
           [0036]      FIG. 11  is a perspective view showing another configuration example of half-wave plate layer  110  in  FIG. 1 . 
           [0037]      FIG. 12  is a diagram to illustrate the periods of reflection members formed in reflection layer  108 , a polarizing diffraction grating formed in polarization beam splitter layer  109 , and a half-wave plate formed in half-wave plate layer  110 . 
           [0038]      FIG. 13  is a diagram showing the relationship between a relative period and an angular width. 
           [0039]      FIG. 14  is a block diagram showing the configuration of one exemplary embodiment of an image display apparatus using a light emitting element according to the present invention. 
           [0040]      FIG. 15  is a block diagram showing the configuration of another exemplary embodiment of the image display apparatus using the light emitting element according to the present invention. 
           [0041]      FIG. 16  is a block diagram showing the configuration of another exemplary embodiment of the image display apparatus using the light emitting element according to the present invention. 
           [0042]      FIG. 17  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 14 . 
           [0043]      FIG. 18  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 15 . 
           [0044]      FIG. 19  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 16 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0045]    Hereafter, specific exemplary embodiments will be described with reference to the drawings. 
         [0046]      FIG. 1(   a ) is a cross-sectional view showing the configuration of an exemplary embodiment of light emitting element  100 , and  FIG. 1(   b ) is a cross-sectional view showing the configuration of a principal part thereof. 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 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. 
         [0047]    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. 
         [0048]    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 reflection layer  108  which is made of Ag are formed on N-type semiconductor layer  106 , and further polarization beam splitter layer  109  and half-wave plate layer  110  are provided on reflection layer  108 . 
         [0049]    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, reflection layer  108  is formed on N-type semiconductor layer  106 . Polarization beam splitter layer  109  and half-wave plate layer  110  are formed by a separate process, and bonded onto reflection layer  108 . Lastly, P-type electrode  102  and N-type electrode  107  are formed. 
         [0050]    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. 
         [0051]    Reflection layer  108  is made up of a portion that reflects the light generated at active layer  105  and a portion that allows the light generated at active layer  105  to exit. Both polarization beam splitter layer  109  and half-wave plate layer  110  respectively include a first region and a second region, and each of these regions is provided so as to correspond to a reflection section and an exiting section in reflection layer  108 . 
         [0052]    As shown in  FIG. 1(   b ), polarization beam splitter layer  109  is provided with polarizing diffraction grating  111  in a region corresponding to the exiting section of reflection layer  108 . Moreover, half-wave plate layer  110  is provided with half-wave plate  112  in a region corresponding to the reflection section of reflection layer  108 . 
         [0053]    Polarizing diffraction grating  111  is configured to transmit a polarized wave oriented in a first direction (for example, TM wave), and diffracts a polarized wave oriented in a second direction (for example, TE wave), which is orthogonal to the first direction, to a predetermined direction, and in the case of the present exemplary embodiment, it diffracts the polarized wave oriented in the second direction toward half-wave plate  112 . 
         [0054]    Half-wave plate  112  allows the incident polarized wave oriented in the second direction to exit as a polarized wave oriented in the first direction. As a result of this, light of a polarized wave oriented in the first direction will be made to exit from both of the portions, where half-wave plate  112  is provided and where half-wave plate  112  is not provided, of half-wave plate layer  110 . 
         [0055]    Hereafter, specific configurations of reflection layer  108 , polarization beam splitter layer  109 , and half-wave plate layer  110  will be described. 
         [0056]      FIG. 2  is a perspective view showing one configuration example of reflection layer  108  in  FIG. 1 . 
         [0057]    In the example shown in  FIG. 2 , a plurality of reflection members  202  having a longitudinal shape and made of Ag are formed in parallel on N-type semiconductor layer  201  which is made of GaN doped with Si. The portion provided with reflection member  202  serves as a reflection section, and the portion not provided with reflection member  202  serves as an exiting section. 
         [0058]      FIG. 3  is a perspective view showing one configuration example of polarization beam splitter layer  109  in  FIG. 1 , and  FIG. 4  is a perspective view showing the configuration more specifically. 
         [0059]    In the example shown in  FIGS. 3 and 4 , dielectric  302  in which SiO 2  and TiO 2  are alternately stacked is formed on substrate  301  which is made of quartz. The flat portion where polarizing diffraction grating  303  is not provided as shown in  FIG. 3  corresponds to the reflection section of reflection layer  108 , and the portion where polarizing diffraction grating  303  is provided corresponds to the exiting section of reflection layer  108 . 
         [0060]      FIG. 4  is an enlarged view of the portion where polarizing diffraction grating  303  is provided. Polarizing diffraction grating  303  is alternately provided with first region  401  which is formed into a flat shape, and second region  402  which has a periodic structure having a periodic concavo-convex shape in one direction and a uniform shape in the direction orthogonal to the above-described one direction with respect to the XY plane as disclosed in Patent Literature 4 (JP2001-51122A), and works as a polarization-dependent phase diffraction grating. 
         [0061]      FIG. 5  is a perspective view showing one configuration example of half-wave plate layer  110  in  FIG. 1 , and  FIG. 6  is a perspective view showing the configuration more specifically. 
         [0062]    In the example shown in  FIGS. 5 and 6 , dielectric  502  in which SiO 2  and TiO 2  are alternately stacked is formed on substrate  501  which is made of quartz. The portion where half-wave plate  503  is provided as shown in  FIG. 5  corresponds to a reflecting section of reflection layer  108 , and the flat portion where half-wave plate  503  is not provided corresponds to an exiting section of reflection layer  108 . 
         [0063]      FIG. 6  is an enlarged view of a portion where half-wave plate  503  is provided. Half-wave plate  503  has a periodic structure which has a periodic concavo-convex shape in one direction and a uniform shape in the direction orthogonal to the one direction with respect to XY plane as disclosed in jP2001-51122A. 
         [0064]      FIG. 7  is a perspective view showing another configuration example of reflection layer  108  in  FIG. 1 . 
         [0065]    In the example shown in  FIG. 7 , rectangular reflection member  702  which is made of Ag is formed in a staggered pattern on N-type semiconductor layer  701  which is made of GaN doped with Si. A portion where reflection member  707  is provided constitutes a reflection section, and a portion where reflection member  702  is not provided constitutes an exiting section. 
         [0066]      FIG. 8  is a perspective view showing another configuration example of polarization beam splitter layer  109  in  FIG. 1 , and  FIG. 9  is a perspective view showing the configuration more specifically. 
         [0067]    In the example shown in  FIGS. 8 and 9 , dielectric  802  in which SiO 2  and TiO 2  are alternately stacked is formed on substrate  801  which is made of quartz. A flat portion where polarizing diffraction grating  803  is not provided as shown in  FIG. 8  corresponds to the reflection section of reflection layer  108 , and the portion where polarizing diffraction grating  803  is provided corresponds to the exiting section of reflection layer  108 . Polarizing diffraction grating  803  includes gratings whose orientation is Y direction and X direction. 
         [0068]      FIG. 9  is an enlarged view of a portion where polarizing diffraction grating  803  is provided. Among polarizing diffraction gratings  803 , those whose orientation is Y direction are configured such that dielectric  902  in which SiO 2  and TiO 2  are alternately stacked is formed on substrate  901  which is made of quartz. Polarizing diffraction grating  803  is alternately provided with an A region which is formed into a flat shape, and a B region which has a periodic concavo-convex shape in one direction and a uniform shape in the direction orthogonal to the one direction with respect to the XY plane as disclosed in JP2001-51122A, and works as a polarization-dependent phase diffraction grating. Further, among polarizing diffraction grating  803 , those whose orientation is X direction are configured such that dielectric  904  in which SiO 2  and TiO 2  are alternately stacked is formed on substrate  903  which is made of quartz. Polarizing diffraction grating  803  is alternately provided with a D region which is formed into a flat shape, and a C region which has a periodic structure having a periodic concavo-convex shape in one direction and a uniform shape in the direction orthogonal to the one direction with respect XY plane as disclosed in JP2001-51122A, and works as a polarization-dependent phase diffraction grating. 
         [0069]      FIG. 10  is a perspective view showing another configuration example of half-wave plate layer  110  in  FIG. 1 , and  FIG. 11  is a perspective view showing the configuration more specifically. 
         [0070]    In the example shown in  FIGS. 10 and 11 , dielectric  1002  in which SiO 2  and TiO 2  are alternately stacked is formed on substrate  1001  which is made of quartz. The portion where half-wave plate  1003  is provided as shown in  FIG. 10  corresponds to the reflection section of reflection layer  108 , and the flat portion where half-wave plate  1003  is not provided corresponds to the exiting section of reflection layer  108 .  FIG. 11  is an enlarged view of a portion where half-wave plate  1003  is provided. Half-wave plate  1003  has a periodic structure having a concavo-convex shape in one direction and a uniform shape in the direction orthogonal to the one direction with respect to XY plane as disclosed in JP2001-51122A. 
         [0071]    As shown in  FIGS. 2 to 6 , when reflection member  202 , polarizing diffraction grating  303 , and half-wave plate  503  are arranged in a striped pattern, it is possible to facilitate the fabrication of the elements. 
         [0072]    As shown in  FIGS. 7 to 11 , when reflection member  702 , polarizing diffraction grating  803 , and half-wave plate  1003  are arranged in a staggered pattern, the way in which light spreads in the X direction becomes similar to the way in which light spreads in Y the direction so that it is possible to achieve a illumination light which has a high uniformity and is easier to handle. 
         [0073]      FIG. 12  is a diagram to illustrate the periods of a reflection member formed in reflection layer  108 , a polarizing diffraction grating formed in polarization beam splitter layer  109 , and a half-wave plate formed on half-wave plate layer  110 . 
         [0074]    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 . 
         [0075]    In  FIG. 12 , 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. 
         [0076]    As shown in  FIG. 12 , 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 2L 1 +L 2  from center A of polarizer layer  108 . 
         [0077]      FIG. 13  is a diagram showing the relationship between a relative period, which is shown by P/(2L 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. 
         [0078]    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. 
         [0079]      FIG. 14  is a block diagram showing the configuration of one exemplary embodiment of an image display apparatus using a light emitting element. 
         [0080]    An image display apparatus shown in  FIG. 14  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 13 . 
         [0081]    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 . 
         [0082]    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 . 
         [0083]    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 . 
         [0084]    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 . 
         [0085]      FIG. 15  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. 
         [0086]    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 13 . 
         [0087]    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. 
         [0088]    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 . 
         [0089]    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 . 
         [0090]      FIG. 16  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. 
         [0091]    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 13 . 
         [0092]    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. 
         [0093]    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. 
         [0094]    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. 
         [0095]    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 . 
         [0096]    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 . 
         [0097]    In the image display apparatus of the present exemplary embodiment compared with the image display apparatus shown in  FIG. 15 , 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. 
         [0098]      FIG. 17  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 14 . 
         [0099]    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. 
         [0100]    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 form 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. 
         [0101]      FIG. 18  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 15 . 
         [0102]    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. 
         [0103]      FIG. 19  is a diagram showing the configuration of a driving system of the image display apparatus shown in  FIG. 16 . 
         [0104]    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. 
         [0105]    It is noted that as the configuration of an exemplary embodiment of a light emitting element, a configuration in which a quarter-wave plate layer is provided in place of half-wave plate layer  110  is also possible. The quarter-wave plate layer is provided with a quarter-wave plate in the region corresponding to the reflection section of reflection layer  108  and the region corresponding to the exiting section. These quarter-wave plates allow two orthogonal polarized components of incident light to exit after giving a quarter-wave phase difference thereto, in which the quarter-wave plate provided in the region corresponding to the reflection section of reflection layer  108  and the quarter-wave plate provided in the region corresponding to the exiting section respectively give a phase difference of opposite sign to the two orthogonal polarized components of incident light. As described above, since orthogonal linearly polarized lights enter the quarter-wave plate provided in the region corresponding to the reflection section of reflection layer  108  and the quarter-wave plate provided in the region corresponding to the exiting section, the exiting lights thereof will be aligned with circularly polarized lights which rotate in the same direction. 
         [0106]    The present application claims priority of Japanese Patent Application No. 2009-243342 filed on Oct. 22, 2009, which is herein incorporated by reference in its entirety. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  Light emitting element 
           101  Submount 
           102  P-type electrode 
           103  Reflection layer 
           104  P-type semiconductor layer 
           105  Active layer 
           106  N-type semiconductor layer 
           107  N-type electrode 
           108  Reflection layer 
           109  Polarization beam splitter layer 
           110  Half-wave plate layer