Abstract:
An illumination device includes a light source including plural light emitting devices arranged in a pattern and that generate and guide light, the light emitting devices having tilted gain regions wherein guiding directions of the light are tilted with respect to a perpendicular of output surfaces of the light source, an optical axis conversion device that bends optical axes of the light output from the light source, and a light distribution control device that controls a light distribution angle of the light output from the optical axis conversion device, wherein the light emitting devices are super luminescent diodes, and the light output from the light distribution control device diverge.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to an illumination device and a projector. 
         [0003]    2. Related Art 
         [0004]    The development of projectors using an array of light sources with plural semiconductor light emitting devices is being advanced. Known semiconductor light emitting devices include, for example, a semiconductor laser (laser diode), a super luminescent diode (hereinafter, may be referred to as “SLD”), an LED (light emitting diode), and an OLED (organic light emitting diode). 
         [0005]    Among these devices, the SLD has a slight disadvantage with respect to light output, but has the advantage of an inherently smaller speckle noise due to the presence of a different gain region structure as compared to a semiconductor laser. However, due to a nonresonant structure in which the gain region is provided at a tilt with respect to an end surface (output surface) of a substrate with the semiconductor light emitting device formed thereon, the output light has an angular distribution with low symmetry similar to a crescent shape. 
         [0006]    Generally, many light modulation devices used for projectors have display properties dependent on the incident angles of incident illumination light. Accordingly, to realize a projection image with high image quality, it is desirable to use illumination light having high angular distribution symmetry (which may be referred to as “symmetry of sectional shape of light”) and a uniform intensity distribution. This is because angular distribution asymmetry and intensity distribution nonuniformity cause brightness irregularities and contrast irregularities. 
         [0007]    For example, International Publication WO 99/49358 discloses an optical configuration that illuminates an image display device by using a light emitter in which plural semiconductor lasers are arranged in a two-dimensional array and parallelizing a beam output from the light emitter. In a typical edge-emitting semiconductor laser, the gain region is formed perpendicularly to the substrate end surface, the output light has an oval sectional shape, and the angular distribution has high symmetry. Accordingly, the output light from the light emitter may be converted into parallel light relatively easily and an optical switch (light modulation device) may be illuminated with light having a nearly uniform intensity distribution. 
         [0008]    However, in the configuration of International Publication WO 99/49358, if the semiconductor lasers are simply replaced with SLDs, the angular distributions of the output light are very different due to the difference in the gain region structure between the semiconductor lasers and the SLDs as described above, and thus, it is difficult to obtain a desired illumination condition. 
       SUMMARY 
       [0009]    An advantage of some aspects of the invention is to provide an illumination device that may improve the symmetry of illumination light in a light source using SLDs. Another advantage of some aspects of the invention is to provide a projector having the illumination device. 
         [0010]    An illumination device according to an aspect of the invention includes a light source including plural light emitting devices arranged in a pattern and that generate and guide light, the light emitting devices have tilted gain regions in which guiding directions of the light are tilted with respect to a perpendicular of output surfaces of the light source, an optical axis conversion device that bends optical axes of the light output from the light source, and a light distribution control device that controls a light distribution angle of the light output from the optical axis conversion device, wherein the light emitting devices are super luminescent diodes, and the light output from the light distribution control device diverge. 
         [0011]    According to the illumination device, the light distribution angle of the light output from the optical axis conversion device may be controlled by the light distribution control device. Thereby, the light having an arched sectional shape like a crescent and an angular distribution with low symmetry generated by the tilted gain region may be converted into light having a nearly oval sectional shape and an angular distribution with high symmetry. Therefore, the symmetry of the illumination light that illuminates an illumination target may be improved. 
         [0012]    Further, the light output from the light distribution control device may diverge. Accordingly, the light output from the respective plural output surfaces may partially overlap at least with the light output from the adjacent output surfaces on the illumination target. Thereby, for example, as compared to the case where the illumination target is illuminated by light output from the adjacent output surfaces that does not even partially overlap with each other, the illumination target may be illuminated with uniform intensity (illuminance distribution). 
         [0013]    The illumination device according to the aspect of the invention may further include a diffusion device that diffuses the light output from the light distribution control device. 
         [0014]    According to such an illumination device, intensity distributions of the light output from the respective output surfaces may be made (nearly) uniform, and illumination light with less illuminance irregularities may be obtained. 
         [0015]    The illumination device according to the aspect of the invention may further include a light guide that guides the light output from the diffusion device to the illumination target. 
         [0016]    According to such an illumination device, more light may illuminate the illumination target. Accordingly, the illumination efficiency may be improved without significant reduction of illumination uniformity. 
         [0017]    In the illumination device according to the aspect of the invention, the optical axis conversion device and the light distribution control device may be integrally formed. 
         [0018]    According to such an illumination device, light loss at the interface between the optical axis conversion device and the light distribution control device may be reduced. Further, the cost may be reduced. 
         [0019]    In the illumination device according to the aspect of the invention, the light emitting device may have a plurality of the tilted gain regions, the guiding direction of the light of a first tilted gain region of the plurality of the tilted gain regions may be tilted to one side (e.g., in a first direction) with respect to the perpendicular of the output surfaces, and the guiding direction of the light of a second tilted gain region of the plurality of the tilted gain regions may be tilted to the other side (e.g., in a second (different) direction) with respect to the perpendicular of the output surface. 
         [0020]    According to such an illumination device, the symmetry seen as the entire illumination light may be further improved. 
         [0021]    In the illumination device according to the aspect of the invention, the light source may include a first light emitting device having a first tilted gain region in which the guiding direction of the light is tilted to one side (e.g., in a first direction) with respect to the perpendicular of the output surface, and a second light emitting device having a second tilted gain region in which the guiding direction of the light is tilted to the other side (e.g., in a second (different) direction) with respect to the perpendicular of the output surface. 
         [0022]    According to such an illumination device, the symmetry seen as the entire illumination light may be further improved. 
         [0023]    A projector according to another aspect of the invention includes an illumination device, a light modulation device that modulates light output from the illumination device in response to image information, and a projection device that projects an image formed by the light modulation device, and the illumination device includes a light source including plural light emitting devices arranged in a predetermined pattern and that generate and guide light, the light emitting devices having tilted gain regions in which guiding directions of the light are tilted with respect to a perpendicular of output surfaces of the light source, an optical axis conversion device that bends optical axes of the light output from the light source, and a light distribution control device that controls a light distribution angle of the light output from the optical axis conversion device, wherein the light emitting devices are super luminescent diodes, and the light output from the light distribution control device diverge. 
         [0024]    According to the projector, since the illumination device having high symmetry of illumination light is provided, higher image quality of a projection image may be realized. 
         [0025]    In the projector according to the aspect of the invention, a light distribution angle of the light controlled by the light distribution control device may be an angle projectable by the projection device. 
         [0026]    According to such a projector, since the illumination device according to the aspect of the invention is provided, higher image quality of a projection image may be realized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
           [0028]      FIG. 1  schematically shows an illumination device according to an embodiment. 
           [0029]      FIG. 2  schematically shows a light source of the illumination device according to the embodiment. 
           [0030]      FIG. 3  schematically shows an angular distribution of light output from the light source of the illumination device according to the embodiment. 
           [0031]      FIG. 4  schematically shows an angular distribution of light output from a light distribution control device of the illumination device according to the embodiment. 
           [0032]      FIG. 5  schematically shows a sectional shape of light output from a diffusion device of the illumination device according to the embodiment. 
           [0033]      FIG. 6  schematically shows an angular distribution of the light output from the diffusion device of the illumination device according to the embodiment. 
           [0034]      FIG. 7  is a perspective view schematically showing a light emitting device of the illumination device according to the embodiment. 
           [0035]      FIG. 8  is a plan view schematically showing the light emitting device of the illumination device according to the embodiment. 
           [0036]      FIG. 9  is a sectional view schematically showing the light emitting device of the illumination device according to the embodiment. 
           [0037]      FIG. 10  schematically shows an illumination device according to a first modified example of the embodiment. 
           [0038]      FIG. 11  is a plan view schematically showing a light emitting device of an illumination device according to a second modified example of the embodiment. 
           [0039]      FIG. 12  schematically shows a light source of an illumination device according to a third modified example of the embodiment. 
           [0040]      FIG. 13  is a plan view schematically showing a light emitting device of the illumination device according to the third modified example of the embodiment. 
           [0041]      FIG. 14  is a plan view schematically showing the light emitting device of the illumination device according to the third modified example of the embodiment. 
           [0042]      FIG. 15  schematically shows a light source of an illumination device according to a fourth modified example of the embodiment. 
           [0043]      FIG. 16  schematically shows sectional shapes of light output from light distribution control devices of the illumination device according to the fourth modified example of the embodiment. 
           [0044]      FIG. 17  is a plan view schematically showing a light emitting device of an illumination device according to a fifth modified example of the embodiment. 
           [0045]      FIG. 18  is a plan view schematically showing a light emitting device of an illumination device according to a sixth modified example of the embodiment. 
           [0046]      FIG. 19  is a plan view schematically showing a light emitting device of an illumination device according to a seventh modified example of the embodiment. 
           [0047]      FIG. 20  schematically shows a projector according to an embodiment. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0048]    A preferred embodiment of the invention will be explained below with reference to the drawings. 
       1. ILLUMINATION DEVICE 
       [0049]    First, a light emitting device according to an embodiment will be explained with reference to the drawings.  FIG. 1  schematically shows an illumination device  100  according to the embodiment.  FIG. 2  schematically shows a light source  10  of the illumination device  100  according to the embodiment as seen from an output surface  180  side, which will be described later. Note that, in  FIG. 1 , for convenience, a light emitting device  110  forming the light source  10  will be simplified for ease of illustration. 
         [0050]    As shown in  FIG. 1 , the illumination device  100  includes the light source  10 , an optical axis conversion device  20 , and a light distribution control device  30 . Further, the illumination device  100  may include a diffusion device  40 . 
         [0051]    The light source  10  may output light. The light source  10  may include the light emitting device  110  and a support substrate  12  as shown in  FIG. 2 . 
         [0052]    As shown in  FIG. 2 , a plurality of the light emitting devices  110  are provided, and they are arranged at equal intervals along the Y-axis direction. In the illustrated embodiment, six of the light emitting devices  110  are provided, however, the number is not particularly limited. 
         [0053]    Each light emitting device  110  has plural tilted gain regions  160  as shown in  FIG. 1 . That is, the plural tilted gain regions  160  are formed on the same substrate. Thereby, the alignment of the light source  10  with the optical axis conversion device  20 , the light distribution control device  30 , and other elements becomes easier and control of the light distribution properties of the illumination light illuminating an illumination target  50  becomes easier. The plural tilted gain regions  160  are provided in parallel to one another, for example. In the example shown in  FIG. 1 , six of the tilted gain regions  160  are provided, however, the number is not particularly limited. The tilted gain regions  160  are arranged at equal intervals along the X-axis direction, for example, in one light emitting device  110 . Each tilted gain region  160  has an output surface  180  that outputs light. The output surfaces  180  are arranged at equal intervals Dx along the X-axis direction as shown in  FIG. 2 . 
         [0054]    As stated above, the light source  10  includes plural light emitting devices  110  arranged in the Y-axis direction as shown in  FIG. 2 . The output surfaces  180  are arranged at equal intervals Dy along the Y-axis direction. For example, in the example shown in  FIG. 2 , the output surfaces  180  are arranged at equal intervals (Dx=Dy) in a matrix (in a two-dimensional array) in the XY plane. 
         [0055]      FIG. 3  schematically shows an angular distribution of light L 1  output from the light emitting device  110  (from the tilted gain region  160 ). The tilted gain region  160  is tilted with respect to the perpendicular of the output surface  180  as shown in  FIG. 1 . Accordingly, the light L 1  output from the tilted gain region  160  has an arched angular distribution similar to a crescent shape as shown in  FIG. 3 . In the illustrated example, the light distribution angle in the X-axis direction is about ±10° and the light distribution angle in the Y-axis direction is about ±35°, and the angular distribution spreads greatly in the Y-axis direction as compared to that in the X-axis direction. As described above, since the angular distribution of the light L 1  output from the light emitting device  110  has an arched shape like a crescent, the sectional shape of the luminous flux is also arched like a crescent (in the downstream position slightly spaced apart from the light emitting device  110 ). The detailed configuration of the light emitting device  110  will be described later. 
         [0056]    Each support substrate  12  supports a light emitting device  110  as shown in  FIG. 2 . A plurality of the support substrates  12  are provided for the light emitting devices  110 . The material of the support substrate  12  is not particularly limited, and copper or aluminum may be used, for example. 
         [0057]    As shown in  FIG. 1 , the light output from the light source  10  enters the optical axis conversion device  20 . The optical axis of the light output from the light emitting device  110  is tilted to a greater extent than the tilt angle of the tilted gain region  160  (with respect to the perpendicular of the output surface  180 ) due to a difference in refractive index between the light emitting device  110  and the air. That is, the optical axis of the light output from the light emitting device  110  is tilted with respect to an illumination optical axis P (also referred to as “the perpendicular of the illuminated surface of the illumination target  50 ”). The optical axis conversion device  20  may bring the optical axis of the light tilted with respect to the illumination optical axis P (nearly) in parallel to the illumination optical axis P. That is, the light output from the optical axis conversion device  20  may have an optical axis (nearly) in parallel to the illumination optical axis P. 
         [0058]    As the optical axis conversion device  20 , a prism having slopes  22  forming predetermined angles with respect to the illumination optical axis P arranged to correspond to the output surfaces  180  in an array may be used. In the illustrated example, the optical axis conversion device  20  has six slopes  22  corresponding to the six output surfaces  180 . The slope  22  may be a flat surface. The tilt angle of the slope  22  with respect to the illumination optical axis P is determined by a refractive index of a material forming the prism and the tilt angle of the optical axis (with respect to the illumination optical axis P) of the light entering the optical axis conversion device  20 . 
         [0059]    Note that, as the optical axis conversion device  20 , a holographic optical device may be used, or a combination of a prism and a holographic optical device may be used, for example. 
         [0060]    The light output from the optical axis conversion device  20  enters the light distribution control device  30 . The light distribution control device  30  converts the angular distribution of the output light into predetermined values and the asymmetry in the angular distribution may be improved and brought closer to a symmetric angular distribution.  FIG. 4  schematically shows an angular distribution of light L 2  output from the light distribution control device  30  (showing output light from one light emitting device  110 ). As can be seen in  FIGS. 3 and 4 , for example, the light distribution angle in the X-axis direction becomes narrower from about ±10° before incidence to the light distribution control device  30  to about ±2° after incidence and the light distribution angle in the Y-axis direction becomes narrower from about ±35° before incidence to the light distribution control device  30  to about ±4° after incidence, and the asymmetry in the angular distribution is improved at the same time. As a result of the improvement of the asymmetry in the angular distribution, the sectional shape of the light L 2  output from the light distribution control device  30  becomes an oval shape with high symmetry from the arched shape similar to a crescent. 
         [0061]    The light output from the light distribution control device  30  enters the diffusion device  40 . The diffusion device  40  diffuses the light output from the respective plural output surfaces  180 , and thereby, may further improve the symmetry of the sectional shape of each light and make the light intensity distribution (illuminance distribution) of the entire illumination light on the illumination target  50  (nearly) uniform. As the diffusion device  40 , for example, a diffusion plate, a holographic optical device, a lens array, or a combination of these may be used. In the illustrated example, a diffusion plate is used as the diffusion device  40 .  FIG. 5  schematically shows a sectional shape of light L 3  output from the diffusion device  40  (showing output light from one light emitting device  110 ), and  FIG. 6  schematically shows an angular distribution of the light L 3  output from the diffusion device  40 . As can be seen in  FIGS. 5 and 6 , the sectional shape is an oval shape close to a circular shape, and the angular distribution has high symmetry close to a circular shape. 
         [0062]    As the light distribution control device  30 , a lens array including lenses  32  having collecting action in an array may be used as shown in  FIG. 1 . In the illustrated example, the plural lenses  32  are provided to correspond to the output surfaces  180  of the light source  10 . As the lens  32 , a spherical lens, an aspherical lens having an axis of symmetry, a toric lens having different radii of curvature in the X-axis direction and the Y-axis direction, a free-form surface lens having no axis of symmetry, a Fresnel lens having a discontinuous curved surface, or the like may be used. In the case of the SLD, the radiation angles of light output from the light emitting device are often different in the X-axis direction and the Y-axis direction in  FIG. 1 . Therefore, in the case where the aspherical lens, the toric lens, the free-form surface lens, or the like is used as the lens  32 , the direction of the light output from the light distribution control device  30  may be independently controlled with respect to the X-axis direction and the Y-axis direction and the light distribution of the light L 2  output from the light distribution control device  30  may be finely controlled, and thus, the sectional shape may be brought close to a circular shape having high symmetry. However, the spherical lens is easily employed in respect of costs. 
         [0063]    Note that, as the light distribution control device  30 , a holographic optical device may be used, or a combination of a prism and a holographic optical device may be used, for example. 
         [0064]    As shown in  FIG. 1 , with the light distribution control device  30  and the diffusion device  40 , the light output from the respective plural output surfaces  180  may diverge to partially overlap at least with the light output from the adjacent output surfaces  180  on the illumination target  50 . Therefore, for example, as compared to the case where the illumination target is illuminated by the light output from the adjacent plural output surfaces  180  but not partially overlapping with each other, the illumination target may be illuminated with uniform intensity (illuminance distribution). In the case of illumination using light not partially overlapping on the illumination target, the illumination intensity is significantly lower at the boundaries between adjacent light, and a non-uniform illuminance distribution is often formed. 
         [0065]    In the case where the illumination device  100  is used for a projector, the light distribution angle of the light output from the diffusion device  40  (may be referred to as “tilt angle”, or “diverging angle” with respect to the illumination optical axis P) is set to an angle at which the illumination target (the light modulation device for the projector) can receive light or an angle at which projection can be performed in the projection system (projection device). In the case of a typical projector, given that the maximum reception angle of the light modulation device and the maximum projectable angle are about 20°, it is desirable that the light distribution angle (angular distribution range) of the light output from the diffusion device  40  is set in a range from more than 0° to equal to or less than 20°. 
         [0066]    In the illustrated example, the light output from the respective plural output surfaces  180  overlap with the light output from the next output surfaces  180  on the illumination target  50 , however, the light may overlap with the light output from other output surfaces  180 . For example, from the output surfaces  180  next to the next. Note that the light output from the respective plural output surfaces  180  do not completely overlap. Therefore, by controlling light intensity of output light with respect to each tilted gain region  160 , local regions on the illumination target  50  may be independently illuminated with arbitrary light intensity. Especially, in the case where a light modulation device such as a liquid crystal light valve is illuminated, light intensity modulation by the illumination device and light intensity modulation by the light modulation device are simultaneously performed, and thereby, both high brightness and high contrast may be realized and higher image quality of displayed images may be realized. 
         [0067]    Note that, in the description of the embodiment of the invention, for example, overlapping of light A and light B on the illumination target means overlapping of illumination region of the light A and the illumination region of the light B on the illumination target, and the illumination regions of the light A and the light B mean regions having an intensity equal to or more than 10% relative to the intensity at the center of the light. 
         [0068]    In the example shown in  FIG. 1 , the optical axis conversion device  20  and the light distribution control device  30  are formed in contact with each other, however, they may be formed apart. Alternatively, the optical axis conversion device  20  and the light distribution control device  30  may be integrally formed. For example, the optical axis conversion device  20  may be obtained by forming plural slopes  22  on one surface of one glass substrate and the light distribution control device  30  may be obtained by forming plural lenses  32  on the other surface (the opposite surface to the one surface). Thereby, light loss at the interface between the optical axis conversion device  20  and the light distribution control device  30  may be reduced. Further, the cost may be reduced. 
         [0069]    The diffusion device  40  is provided in a position apart from the light distribution control device  30 , however, the device  40  may be integrated with the light distribution control device  30  for reduction of light loss at the interface. For example, in the case where the light distribution control device  30  includes a lens array, the diffusion device  40  may be formed on the surface of the lens array for integrated configuration. 
         [0070]    The light output from the diffusion device  40  illuminates the illumination target  50 . As the illumination target  50 , although not particularly limited, a liquid crystal light valve (light modulation device) may be cited in the case where the illumination device  100  is used for a projector. 
         [0071]    Next, the detailed configuration of the light emitting device  110  will be explained.  FIG. 7  is a perspective view schematically showing the light emitting device  110  according to the embodiment.  FIG. 8  is a plan view schematically showing the light emitting device  110  according to the embodiment.  FIG. 9  is a sectional view schematically showing the light emitting device  110  according to the embodiment along IX-IX line in  FIG. 8 . Note that, in  FIGS. 7 to 9 , for convenience, two tilted gain regions  160  are shown. 
         [0072]    Below, a case where the light emitting device  110  is an SLD that emits red light of an InGaAlP system will be explained. Unlike a semiconductor laser, the SLD can prevent laser oscillation by suppressing the formation of a resonator due to edge reflection. Accordingly, speckle noise may be reduced. 
         [0073]    As shown in  FIGS. 7 to 9 , the light emitting device  110  includes a substrate  102 , a first cladding layer  104 , an active layer  106 , a second cladding layer  108 , a contact layer  109 , a first electrode  112 , a second electrode  114 , and a reflection film  130 . 
         [0074]    As the substrate  102 , for example, a first conductivity-type (for example, n-type) GaAs substrate or the like may be used. 
         [0075]    The first cladding layer  104  is formed on the substrate  102 . As the first cladding layer  104 , for example, an n-type InGaAlp layer or the like may be used. 
         [0076]    The active layer  106  is formed on the first cladding layer  104 . The active layer  106  has a multiple quantum well (MQW) structure in which three quantum well structures each including an InGaP well layer and an InGaAlP barrier layer, for example, are stacked. 
         [0077]    The shape of the active layer  106  is a rectangular parallelepiped (including the case of a cube), for example. The active layer  106  may have a first side surface  105  and a second side surface  107  as shown in  FIGS. 7 and 8 . The first side surface  105  and the second side surface  107  are opposed to each other, and in parallel in the illustrated example. 
         [0078]    Parts of the active layer  106  form the tilted gain regions  160  that may serve as current channels. In the tilted gain region  160 , light may be generated and the light may be amplified within the tilted gain regions  160 . The tilted gain region  160  may be referred to as “light propagation region (waveguide region)”. The planar shape of the tilted gain region  160  seen from the stacking direction of the light emitting device  110  is a parallelogram, for example. 
         [0079]    In a wavelength band of light generated in the tilted gain region  160 , for example, reflectance of the second side surface  107  is higher than reflectance of the first side surface  105 . For example, by covering the second side surface  107  with the reflection film  130 , higher reflectance may be obtained. The reflection film  130  is a dielectric multilayer mirror, for example. Specifically, as the reflection film  130 , a mirror in which four pairs of an Al 2 O 3  layer and a TiO 2  layer are stacked from the second side surface  107  side in this order may be used. It is desirable that the reflectance of the second side surface  107  is just or nearly 100%. On the other hand, it is desirable that the reflectance of the first side surface  105  is just or nearly 0%. For example, by covering the first side surface  105  with an antireflection film (not shown), lower reflectance may be obtained. As the antireflection film, an Al 2 O 3  single layer may be used, for example. 
         [0080]    The tilted gain regions  160  are provided so that the extension direction from the first side surface  105  to the second side surface  107  (guiding direction of light) may be tilted with respect to a perpendicular line Q of the first side surface  105  in the plan view (seen from the Y-axis direction) as shown in  FIG. 8 . Thereby, laser oscillation of the light generated in the tilted gain regions  160  may be suppressed or prevented. As shown in  FIGS. 1 and 8 , the plural tilted gain regions  160  are provided at tilts in the same direction with respect to the perpendicular line Q. 
         [0081]    The tilted gain region  160  may have a first end surface  180  provided on the first side surface  105  and a second end surface  182  provided on the second side surface  107  as shown in  FIG. 8 . Accordingly, in the wavelength band of light generated in the tilted gain region  160 , reflectance of the first end surface  180  is just or nearly 0%, for example, and reflectance of the second end surface  182  is just or nearly 100%, for example. Therefore, the first end surface  180  is an output surface that outputs light generated in the tilted gain region  160  (corresponding to the output surface  180  in  FIG. 1 ), and the second end surface  182  is a reflection surface that reflects the light generated in the tilted gain region  160 . That is, the first side surface  105  may have plural output surfaces  180  (first end surfaces  180 ) and the perpendicular line Q of the first side surface  105  is also the perpendicular line Q of the output surfaces  180 . 
         [0082]    The second cladding layer  108  is formed on the active layer  106  as shown in  FIGS. 7 and 9 . As the second cladding layer  108 , a second conductivity-type (for example, p-type) AlGaInP layer or the like may be used. 
         [0083]    For example, the p-type second cladding layer  108 , the active layer  106  not doped with impurity, and the n-type first cladding layer  104  form a pin diode. Each of the first cladding layer  104  and the second cladding layer  108  is a layer having a larger forbidden band width and a lower refractive index than those of the active layer  106 . The active layer  106  has a function of generating and guiding light and amplifying the light by injecting carriers (electrons and holes). The first cladding layer  104  and the second cladding layer  108  sandwich the active layer  106  and have a function of confining injected carriers (electrons and holes) and light. 
         [0084]    In the light emitting device  110 , when a forward bias voltage of the pin diode is applied between the first electrode  112  and the second electrode  114 , recombination of electrons and holes occurs in the tilted gain region  160  of the active layer  106 . Light is emitted by the recombination. Starting from the generated light, chained stimulated emission occurs and the intensity of the light is amplified within the tilted gain region  160 . Then, the light with amplified intensity is output from the output surface  180  of the tilted gain region  160  as light L 1  as shown in  FIG. 7 . 
         [0085]    The contact layer  109  is formed on the second cladding layer  108  as shown in  FIGS. 7 and 9 . As the contact layer  109 , a layer in ohmic contact with the second electrode  114  may be used. As the contact layer  109 , for example, a p-type GaAs layer may be used. 
         [0086]    The first electrode  112  is formed on the entire surface under the substrate  102 . The first electrode  112  may be in contact with a layer (the substrate  102  in the illustrated example) in ohmic contact with the first electrode  112 . The first electrode  112  is electrically connected to the first cladding layer  104  via the substrate  102 . The first electrode  112  is one electrode for driving the light emitting device  110 . As the first electrode  112 , for example, an electrode formed by stacking a Cr layer, an AuGe layer, an Ni layer, and an Au layer in this order from the substrate  102  side may be used. 
         [0087]    The second electrode  114  is formed on the contact layer  109 . The second electrode  114  is electrically connected to the second cladding layer  108  via the contact layer  109 . The second electrode  114  is the other electrode for driving the light emitting device  110 . As the second electrode  114 , for example, an electrode formed by stacking a Cr layer, an AuZn layer, and an Au layer in this order from the contact layer  109  side may be used. The lower surface of the second electrode  114  (the contact surface between the second electrode  114  and the contact layer  109 ) may have the same planar shape as that of the tilted gain region  160 . By the planar shape of the contact surface between the second electrode  114  and the contact layer  109 , current channels between the electrodes  112 ,  114  are determined and, as a result, the planar shape of the tilted gain region  160  may be determined. 
         [0088]    In the above described example, a so-called gain-guiding type light emitting device  110  has been explained, however, for example, the light emitting device  110  may be of a refractive index-guiding type that confines light by patterning the contact layer  109  and the second cladding layer  108  to form columnar parts and providing refractive index differences between regions where the columnar parts are formed and regions the columnar parts are not formed may be used. 
         [0089]    So far, the case of the InGaAlP system has been explained as an example of the light emitting device  110  according to the embodiment, and any material system that can form an emission gain region may be used in the light emitting device  110 . As a semiconductor material, for example, a semiconductor material of an AlGaN system, an InGaN system, a GaAs system, an AlGaAs system, an InGaAs system, an InGaAsP system, a ZnCdSe system, or the like may be used. 
         [0090]    According to the illumination device  100  of the embodiment, for example, the following characteristics are provided. 
         [0091]    According to the illumination device  100 , the optical axis of the output light from the light emitting device  110  and the illumination optical axis P may be nearly aligned by the optical axis conversion device  20 , and the light distribution angle (anglular distribution) of the illumination light may be controlled to a desired value by the light distribution control device  30  and the diffusion device  40 . Thereby, the light having the arched sectional shape like a crescent and the angular distribution with low symmetry generated by the tilted gain region  160  may be converted into light having a nearly circular sectional shape and an angular distribution with high symmetry. Therefore, the illumination device  100  may improve the symmetry of the illumination light that illuminates the illumination target  50 . 
         [0092]    Further, the light output from the light distribution control device  30  and the diffusion device  40  may diverge. Accordingly, the light output from the respective plural output surfaces  180  may partially overlap at least with the light output from the adjacent output surfaces  180  on the illumination target  50 . Thereby, in the illumination device  100 , for example, as compared to the case where the illumination target is illuminated by light that does not even partially overlap, the illumination target may be illuminated with uniform intensity (illuminance distribution). 
         [0093]    Note that, in the embodiment, the diffusion device  40  has been provided, however, depending on the properties (the sectional shape and the angular distribution) of the output light from the light emitting device  110 , illumination light having desired properties may be obtained without using the diffusion device  40 , and instead only using the light distribution control device  30 . 
       2. MODIFIED EXAMPLES OF ILLUMINATION DEVICE 
     2.1. First Modified Example 
       [0094]    Next, an illumination device according to a first modified example of the embodiment will be explained with reference to the drawings.  FIG. 10  schematically shows an illumination device  200  according to the first modified example of the embodiment. 
         [0095]    In the illumination device  200  according to the first modified example of the embodiment, the same reference signs are assigned to members having the same functions as those of the component members of the illumination device  100  according to the embodiment, and a detailed explanation will be omitted. This applies to illumination devices  300 ,  400 ,  500 ,  600  according to second to fifth modified examples of the embodiment, which will be described later. 
         [0096]    As shown in  FIG. 10 , the illumination device  200  includes a light guide  60 . The light guide  60  may guide light output from the diffusion device  40  to the illumination target  50 . The light guide  60  is provided between the diffusion device  40  and the illumination target  50 . As the light guide  60 , for example, one having a mirror body formed on the inner surface of a tubular member, a rod-shaped light transmissive medium, or the like may be used. In the light guide  60 , reflection surfaces  61  are provided except in apart that the light output from the diffusion device  40  enters and a part that outputs the light from the light guide  60  to the illumination target  50 . The reflection surface  61  may include a mirror body or may be formed by a total reflection surface. 
         [0097]    As explained in the example of the illumination device  100 , since the light to illuminate the illumination target  50  diverges as shown in  FIG. 1 , light that does not illuminate the illumination target  50  may be generated and the illumination efficiency may be lower. However, in the illumination device  200 , as shown in  FIG. 10 , the light that would not illuminate the illumination target  50  without the light guide  60  may be reflected by the reflection surfaces  61  of the light guide  60  and thereafter illuminate the illumination target  50 , and thus, more light may illuminate the illumination target  50 . Accordingly, in the illumination device  200 , the illumination efficiency may be improved without significant reduction of illumination uniformity. 
         [0098]    Note that it is desirable that the sectional shape and the size (the shape and the size in the XY plane) of the light output edge of the light guide  60  are made nearly equal to the sectional shape and the size of the illumination target  50 , however, the shape is not limited to these. For example, dimensions and shapes in which the sectional shape of the light output part of the light guide  60  is a similar shape with respect to the sectional shape of the illumination target  50  and the size of the light output part of the light guide  60  is slightly larger than the size of the illumination target  50  or slightly smaller or the like may be employed. That is, it is desirable that the sectional shape and the size of the light output edge of the light guide  60  are set in consideration of the light distribution angle (diverging angle) of the illumination light so that the illumination target  50  may be illuminated (nearly) uniformly. 
       2.2 Second Modified Example 
       [0099]    Next, an illumination device according to a second modified example of the embodiment will be explained with reference to the drawings.  FIG. 11  is a plan view schematically showing a light emitting device  110  of an illumination device  300  according to the second modified example of the embodiment. In  FIG. 11 , for convenience, the light emitting device  110  is simplified for illustration. 
         [0100]    In the example of the illumination device  100 , as shown in  FIGS. 1 and 8 , the plural tilted gain regions  160  of the light emitting device  110  have been tilted toward the same side with respect to the perpendicular Q of the first side surface  105 . 
         [0101]    On the other hand, in the light emitting device  110  of the illumination device  300 , as shown in  FIG. 11 , first tilted gain regions  160   a  of the plural tilted gain regions  160  are tilted toward one side with respect to the perpendicular Q and second tilted gain regions  160   b  of the plural tilted gain regions  160  are tilted toward the other side (different from the one side) with respect to the perpendicular Q. The first tilted gain regions  160   a  and the second tilted gain regions  160   b  may have shapes symmetric with respect to the perpendicular Q. In the illustrated example, the first tilted gain regions  160   a  and the second tilted gain regions  160   b  are provided in the same number and alternately arranged along the X-axis direction. 
         [0102]    As has been explained in the example of the illumination device  100 , the light L 2  output from the light distribution control device  30  has improved symmetry in the angular distribution (symmetry of the sectional shape of light) as shown in  FIG. 4 , however, the sectional shape of the light L 2  may not be completely formed in an oval shape. Accordingly, in the illumination device  300 , as shown in  FIG. 11 , by changing the tilt directions of the plural tilted gain regions  160  and providing them as the first tilted gain regions  160   a  and the second tilted gain regions  160   b , the symmetry in the angular distribution seen as the entire illumination light may be further improved. 
       2.3. Third Modified Example 
       [0103]    Next, an illumination device according to a third modified example of the embodiment will be explained with reference to the drawings.  FIG. 12  schematically shows the light source  10  of an illumination device  400  according to the third modified example of the embodiment corresponding to  FIG. 2 .  FIGS. 13 and 14  are plan views schematically showing the light emitting device  110  of the illumination device  400  according to the third modified example of the embodiment. Note that, in  FIGS. 13 and 14 , for convenience, the light emitting device  110  is simplified for illustration. 
         [0104]    In the light source  10  of the illumination device  400 , as shown in  FIG. 12 , first light emitting devices  110   a  and second light emitting devices  110   b  of the plural light emitting devices  110  are alternately arranged along the Y-axis direction. In the illustrated example, the first light emitting devices  110   a  and the second light emitting devices  110   b  are provided in the same number. 
         [0105]    In the first light emitting device  110   a , as shown in  FIG. 13 , the plural tilted gain regions  160  are the first tilted gain regions  160   a  tilted toward one side with respect to the perpendicular Q of the first side surface  105 . On the other hand, in the second light emitting device  110   b , as shown in  FIG. 14 , the plural tilted gain regions  160  are the second tilted gain regions  160   b  tilted toward the other side (different from the one side) with respect to the perpendicular Q. In the illustrated example, the number of first tilted gain regions  160   a  provided in the first light emitting device  110   a  and the number of second tilted gain regions  160   b  provided in the second light emitting device  110   b  are the same. 
         [0106]    In the illumination device  400 , like the illumination device  300 , the symmetry in the angular distribution seen as the entire illumination light may be further improved as compared to the example of the illumination device  100 . 
       2.4. Fourth Modified Example 
       [0107]    Next, an illumination device according to a fourth modified example of the embodiment will be explained with reference to the drawings.  FIG. 15  schematically shows the light source  10  of an illumination device  500  according to the fourth modified example of the embodiment corresponding to  FIG. 2 . 
         [0108]    In the example of the illumination device  100 , as shown in  FIG. 2 , the output surfaces  180  of the light source  10  are arranged in a matrix at equal intervals in the XY plane. 
         [0109]    On the other hand, in the light source  10  of the illumination device  500 , as shown in  FIG. 15 , the plural output surfaces  180  are arranged so that the distance Dy between the adjacent output surfaces  180  in the Y-axis direction is larger than the distance Dx between the adjacent output surfaces  180  in the X-axis direction. 
         [0110]    As has been explained in the example of the illumination device  100 , the light L 2  output from the light distribution control device  30  has improved symmetry in the angular distribution as shown in  FIG. 4 , however, the angular distribution is often different between the X-axis direction and the Y-axis direction. Accordingly, if the output surfaces  180  are arranged in the XY plane at equal intervals, the illuminance distribution of illumination light may not be uniform in the X-axis direction and the Y-axis direction. For example, in the example shown in  FIG. 2 , since the Y-axis direction is the stacking direction of the light emitting device  110 , the confinement width of light within the light emitting device  110  in the Y-axis direction is smaller than the confinement width of light in the X-axis direction. Therefore, regarding the light L 2 , the light distribution angle in the Y-axis direction is larger than the light distribution angle in the X-axis direction. In the illumination device  500 , by making the arrangement of the output surfaces  180  denser in the X-axis direction than that in the Y-axis direction, as shown in  FIG. 16 , the plural lights L 2  may be made closer in the X-axis direction and the Y-axis direction. Alternatively, in the case where the adjacent lights L 2  partially overlap, the degree of overlapping may be made closer in the X-axis direction and the Y-axis direction. Thereby, in the illumination device  500 , the uniformity of the illuminance distribution of illumination light on the illumination target may be improved. 
         [0111]    Note that, in  FIG. 16 , the sectional shapes of the light L 2  output from the plural light distribution control devices  30  are schematically shown and the sectional shapes of the light L 2  are illustrated as oval shapes for convenience. 
       2.5. Fifth Modified Example 
       [0112]    Next, an illumination device according to a fifth modified example of the embodiment will be explained with reference to the drawings.  FIG. 17  is a plan view schematically showing the light emitting device  110  of an illumination device  600  according to the fifth modified example of the embodiment corresponding to  FIG. 8 . 
         [0113]    As the light emitting device  110  of the illumination device  600 , as shown in  FIG. 17 , a pair of gain regions  163  including a first gain region  161  and a second gain region  162  is used as the tilted gain region  160 . Although not illustrated, for example, plural pairs of gain regions  163  are provided and arranged along the X-axis direction. 
         [0114]    The first gain region  161  is tilted toward one side with respect to the perpendicular Q of the first side surface  105  and provided from the first side surface  105  to the second side surface  107 . The second gain region  162  is tilted toward the other side (different from the one side) with respect to the perpendicular Q and provided from the first side surface  105  to the second side surface  107 . In the illustrated example, the first gain region  161  and the second gain region  162  are provided symmetrically with respect to the perpendicular Q. 
         [0115]    A first end surface  180  (output surface  180 ) of the first gain region  161  and a first end surface  180  of the second gain region  162  are separated from each other. On the other hand, a second end surface  182  (reflection surface  182 ) of the first gain region  161  and a second end surface  182  of the second gain region  162  overlap at least partially on the second side surface  107 , and completely overlap in the illustrated example. That is, the pair of gain regions  163  may have a planar shape of a V shape seen from the stacking direction of the light emitting device  110 . 
         [0116]    For example, part of the light generated in the first gain region  161  is reflected on the second side surface  107  (second end surface  182 ) and output from the first end surface  180  of the second gain region  162 , and its light intensity is amplified in the meantime. Similarly, part of the light generated in the second gain region  162  is reflected on the second side surface  107  and output from the first end surface  180  of the first gain region  161 , and its light intensity is amplified in the meantime. Note that, the light generated in the first gain region  161  may include light directly output from the first end surface  180  of the first gain region  161 . Similarly, the light generated in the second gain region  162  may include light directly output from the first end surface  180  of the second gain region  162 . 
         [0117]    According to the illumination device  600 , like the illumination device  300 , the symmetry in the angular distribution seen as the entire illumination light may be further improved as compared to the example of the illumination device  100 . 
       2.6. Sixth Modified Example 
       [0118]    Next, an illumination device according to a sixth modified example of the embodiment will be explained with reference to the drawings.  FIG. 18  is a plan view schematically showing the light emitting device  110  of an illumination device  700  according to the sixth modified example of the embodiment corresponding to  FIG. 17 . In the illumination device  700  according to the sixth modified example of the embodiment, the same reference signs are assigned to members having the same functions as the component members of the illumination device  600  according to the fifth modified example of the embodiment, and their detailed explanation will be omitted. 
         [0119]    The light emitting device  110  of the illumination device  700  has a reflection part  140  as shown in  FIG. 18 . The reflection part  140  is provided inside of an outer periphery of the active layer  106  in a plan view (seen from the Y-axis direction). As the reflection part  140 , for example, a DBR (Distributed Bragg Reflector) mirror including plural grooves  142  arranged at predetermined intervals may be used. Although not illustrated, it is desirable that the bottom surfaces of the grooves  142  are located lower than the lower surface of the active layer  106 . The interior of the groove  142  may be hollow (air) or filled with an insulating member. In the illustrated example, four of the grooves  142  are provided, however, the number of grooves is not limited thereto. The reflection part  140  may reflect the light generated in the first gain region  161  and the second gain region  162 . 
         [0120]    The second gain region  162  includes a first part  162   a  and a second part  162   b . The first part  162   a  is provided from the first side surface  105  to the reflection part  140 . The first part  162   a  may have a first end surface  180 . The first part  162   a  is parallel to the first gain region  161 , for example. The second part  162   b  is provided from the reflection part  140  to the second side surface  107 . The second part  162   b  may have a second end surface  182 . The first part  162   a  and the second part  162   b  overlap in the reflection part  140 . In the illustrated example, the first part  162   a  and the second part  162   b  are provided symmetrically with respect to an imaginary line R orthogonal to the perpendicular Q of the first side surface  105 . 
         [0121]    For example, part of light generated in the first gain region  161  is reflected on the second side surface  107  and the reflection part  140  and output from the first end surface  180  of the second gain region  162  (first part  162   a ). 
         [0122]    In the illumination device  700 , the optical axis of the light output from the first end surface  180  of the first gain region  161  and the optical axis of the light output from the first end surface  180  of the second gain region  162  may be made (nearly) in parallel. Accordingly, in the illumination device  700 , for example, the design of the optical system including the optical axis conversion device  20  may be simplified as compared to the illumination device  600 . 
       2.7. Seventh Modified Example 
       [0123]    Next, an illumination device according to a seventh modified example of the embodiment will be explained with reference to the drawings.  FIG. 19  is a plan view schematically showing the light emitting device  110  of an illumination device  800  according to the seventh modified example of the embodiment corresponding to  FIG. 18 . In the illumination device  800  according to the seventh modified example of the embodiment, the same reference signs are assigned to members having the same functions as the component members of the illumination device  700  according to the sixth modified example of the embodiment, and their detailed explanation will be omitted. 
         [0124]    The light emitting device  110  of the illumination device  800  does not have the reflection part  140  unlike the light emitting device  110  of the illumination device  700  as shown in  FIG. 19 , however, the optical axis of the light output from the first end surface  180  of the first gain region  161  and the optical axis of the light output from the first end surface  180  of the second gain region  162  may be made (nearly) in parallel. 
         [0125]    In the illumination device  800 , the second gain region  162  has a third part  162   c  having a planar shape of an arc (or an oval arc). The third part  162   c  is provided between the first part  162   a  and the second part  162   b  of the second gain region  162 . More specifically, the first part  162   a  is linearly extended from the first side surface  105  and connected to the third part  162   c . Further, the second part  162   b  is linearly extended from the second side surface  107  and connected to the third part  162   c.    
         [0126]    For example, part of the light generated in the first gain region  161  is reflected on the second side surface  107 , and then, while traveling within the third part  162   c , the traveling direction is bent and output from the first end surface  180  of the first part  162   a . Accordingly, as described above, in the illumination device  800 , the optical axis of the light output from the first end surface  180  of the first gain region  161  and the optical axis of the light output from the first end surface  180  of the second gain region  162  may be made (nearly) in parallel. 
       3. PROJECTOR 
       [0127]    Next, a projector according to the embodiment will be explained with reference to the drawings.  FIG. 20  schematically shows a projector  900  according to the embodiment. Note that, in  FIG. 20 , for convenience, a casing of the projector  900  is omitted for illustration. 
         [0128]    The projector  900  may include a red illumination device that outputs red light, a green illumination device that outputs green light, and a blue illumination device that outputs blue light. As the respective illumination devices of the projector  900 , the illumination devices according to the invention may be used. As shown in  FIG. 20 , an example using the illumination device  100  (the red illumination device  100 R, the green illumination device  100 G, the blue illumination device  100 B) as the illumination device of the projector  900  will be explained. 
         [0129]    The projector  900  further includes transmissive liquid crystal light valves (light modulation devices)  950 R,  950 G,  950 B, a cross dichroic prism (color light combining means)  970 , and a projection lens (projection device)  980 . 
         [0130]    The light output from the respective illumination devices  100 R,  100 G,  100 B enter the respective liquid crystal light valves  950 R,  950 G,  950 B. The respective liquid crystal light valves  950 R,  950 G,  950 B respectively modulate incident light in response to image information. Note that the liquid crystal light valves  950 R,  950 G,  950 B correspond to the illumination target  50  shown in  FIG. 1 . 
         [0131]    The three colors of light modulated by the respective liquid crystal light valves  950 R,  950 G,  950 B enter the cross dichroic prism  970 . The cross dichroic prism  970  is formed by bonding four right angle prisms, for example, and a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are provided crosswise on its inner surface. By the dielectric multilayer films, the three colors of light are combined and light representing a color image is formed. 
         [0132]    The light combined by the cross dichroic prism  970  enters the projection lens  980  as a projection system. The projection lens  980  enlarges the images formed by the liquid crystal light valves  950 R,  950 G,  950 B and projects them on a screen (display surface)  990 . 
         [0133]    Note that, as described above, the light distribution angles (angular distributions) of the light output from the illumination devices  100 R,  100 G,  100 B are set to be projectable angles in the projection lens  980 . More specifically, the light distribution angles of the light output from the illumination devices  100 R,  100 G,  100 B are set to be equal to or less than about 20°. 
         [0134]    Further, in the above described example, the transmissive liquid crystal light valves have been used as light modulation devices, however, other light valves may be used, or reflective light valves may be used. As the light valves, for example, reflective liquid crystal light valves and digital micromirror devices are cited. Further, the configuration of the projection system may be appropriately changed depending on the type of light valves. 
         [0135]    According to the projector  900 , the illumination device according to the invention (for example, the illumination device  100 ) may be included. According to the illumination device  100 , the liquid crystal light valves (light modulation devices) may be uniformly illuminated by illumination light with high symmetry, but without illuminance irregularities. Accordingly, in the projector  900 , higher image quality (higher brightness and higher contrast) of the projection image may be realized. 
         [0136]    The above described embodiments and modified examples are just examples, and the invention is not limited to these. For example, the respective embodiments and the respective modified examples may be appropriately combined. 
         [0137]    The embodiments of the invention have been specifically explained above, and a person skilled in the art could easily understand that many modifications without substantively departing from the spirit and effects of the invention are possible. Therefore, these modified examples are included in the range of the invention. 
         [0138]    The entire disclosure of Japanese Patent Application No. 2011-050397 filed Mar. 8, 2011 is expressly incorporated herein by reference.