Patent Publication Number: US-2023152677-A1

Title: Lighting device and projection display apparatus

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a lighting device and a projection display apparatus including the lighting device. 
     2. Description of the Related Art 
     As described in Patent Literature (PTL) 1, a lighting device that is used in a projection display apparatus and illuminates high-luminance illumination light by collecting light emitted from a plurality of light sources such as an LED and a laser element at high density is known. In the case of the lighting device described in PTL 1, light fluxes from a plurality of light source units each including a plurality of light sources are densely gathered via an optical element such as a mirror, thereby realizing irradiation of high-luminance illumination light. 
     PTL 1 is Unexamined Japanese Patent Publication No. 2017-211603. 
     SUMMARY 
     However, in a case where light fluxes of a plurality of light source units each including a plurality of light sources are gathered at a high density to realize irradiation of high-luminance illumination light as in the lighting device described in PTL 1, the close arrangement of the light source units may be limited depending on the size and shape of the light source unit, the optional size and shape of the light source unit such as a cooling device, and the like, thereby limiting the high-density gathering of light fluxes. 
     Therefore, an object of the present disclosure is to provide a lighting device including the plurality of light source units each including the plurality of laser elements, even if the close arrangement of the plurality of light source units is restricted, the light fluxes of the light source units can be gathered at high density, and the high-luminance illumination light can be illuminated. 
     In order to solve the above problem, according to one aspect of the present disclosure, there is provided a lighting device including: 
     a first light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the first light source unit emitting a first light flux in a first direction; 
     a second light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the second light source unit being arranged to emit a second light flux in the first direction and to be spaced apart from the first light source unit by a first distance in a second direction orthogonal to the first direction; and 
     an optical path shift optical system including: a first reflecting surface that reflects the second light flux emitted from the second light source unit toward the first light flux; and a second reflecting surface that is parallel to the first reflecting surface and reflects the second light flux reflected by the first reflecting surface to be parallel to the first light flux at a second distance shorter than the first distance. 
     According to another aspect of the present disclosure, 
     there is provided a projection display apparatus including: 
     a lighting unit including at least one lighting device; 
     an image display unit configured to modulate illumination light from the lighting unit and output the modulated illumination light as image light; and 
     a projection optical system configured to enlarge and project the image light. The at least one lighting device includes: 
     a first light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the first light source unit emitting a first light flux in a first direction; 
     a second light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the second light source unit being arranged to emit a second light flux in the first direction and to be spaced apart from the first light source unit by a first distance in a second direction orthogonal to the first direction; and 
     an optical path shift optical system including: a first reflecting surface that reflects the second light flux emitted from the second light source unit toward the first light flux; 
     and a second reflecting surface that is parallel to the first reflecting surface and reflects the second light flux reflected by the first reflecting surface to be parallel to the first light flux at a second distance shorter than the first distance. 
     According to the present disclosure, in the lighting device including the plurality of light source units each including the plurality of laser elements, even if the approach arrangement of the plurality of light source units is restricted, the light fluxes of the light source units can be gathered at high density, and the illumination light with high luminance can be illuminated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic configuration diagram of a projection display apparatus according to a first exemplary embodiment of the present disclosure. 
         FIG.  2    is a perspective view of a lighting device according to the first exemplary embodiment. 
         FIG.  3    is a front view of the lighting device according to the first exemplary embodiment. 
         FIG.  4    is a side view of the lighting device according to the first exemplary embodiment. 
         FIG.  5    is a top view of the lighting device according to the first exemplary embodiment. 
         FIG.  6    is a diagram illustrating an image of a first light flux and an image of a second light flux. 
         FIG.  7    is a front view of a lighting device in a projection display apparatus according to a second exemplary embodiment of the present disclosure. 
         FIG.  8    is a front view of a lighting device in a projection display apparatus according to a third exemplary embodiment of the present disclosure. 
         FIG.  9    is a front view of a lighting device in a projection display apparatus according to a fourth exemplary embodiment of the present disclosure. 
         FIG.  10    is a top view of the lighting device according to the fourth exemplary embodiment. 
         FIG.  11    is a front view of the lighting device in a projection display apparatus according to a fifth exemplary embodiment of the present disclosure. 
         FIG.  12    is a top view of the lighting device according to the fifth exemplary embodiment. 
         FIG.  13    is a schematic configuration diagram of a projection display apparatus according to another example  1  of the present disclosure. 
         FIG.  14    is a diagram illustrating images of a plurality of light fluxes. 
         FIG.  15    is a top view of a light source unit of another example  2 . 
         FIG.  16    is a front view of a lighting device of another example  3  including three light source units. 
     
    
    
     DETAILED DESCRIPTION 
     A lighting device according to one aspect of the present disclosure includes: a first light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the first light source unit emitting a first light flux in a first direction; a second light source unit including a plurality of laser elements optical axes arranged in parallel and in a matrix, the second light source unit being arranged to emit a second light flux in the first direction and to be spaced apart from the first light source unit by a first distance in a second direction orthogonal to the first direction; and an optical path shift optical system including: a first reflecting surface that reflects the second light flux emitted from the second light source unit toward the first light flux; and a second reflecting surface that is parallel to the first reflecting surface and reflects the second light flux reflected by the first reflecting surface so as to be parallel to the first light flux at a second distance shorter than the first distance. 
     According to such an aspect, in the lighting device including the plurality of light source units each including the plurality of laser elements, even if the approach arrangement of the plurality of light source units is restricted, the light fluxes of the light source units can be gathered at high density, and the illumination light with high luminance can be illuminated. 
     For example, the optical path shift optical system may be a prism having a parallelogram shape. The prism may include the first reflecting surface, the second reflecting surface, a first transmission surface through which the second light flux emitted from the second light source unit passes, and a second transmission surface parallel to the first transmission surface and through which the second light flux reflected by the second reflecting surface passes. 
     For example, the optical path shift optical system may include a first mirror including the first reflecting surface and a second mirror including the second reflecting surface. 
     For example, each of the plurality of laser elements of each of the first and second light source units may be semiconductor laser elements, and each of the first and second light source units may include a collimating lens provided for each of the semiconductor laser elements. 
     For example, each of the first and second light source units may include a collimating lens array in which a plurality of collimating lenses each being the collimating lens are arranged and integrated at a same arrangement pitch as an arrangement pitch of the plurality of semiconductor laser elements. 
     For example, the lighting device may further include: a heat transfer plate including a first heat transfer surface to which the first and second light source units are attached and a second heat transfer surface opposite to the first heat transfer surface; and a cooling device attached to the second heat transfer surface of the heat transfer plate. 
     For example, the cooling device includes a first cooling device arranged to face the first light source unit with the heat transfer plate interposed between the cooling device and the first cooling device, and a second cooling device arranged to face the second light source unit with the heat transfer plate interposed between the cooling device and the second cooling device. 
     For example, the lighting device may further include: a first thermoelectric element including a heat absorption surface in contact with the second heat transfer surface of the heat transfer plate and a heat dissipating surface to which the first cooling device is attached; and a second thermoelectric element including a heat absorption surface in contact with the second heat transfer surface of the heat transfer plate and a heat dissipating surface to which the second cooling device is attached. 
     For example, as viewed in a first direction, the first light source unit may be arranged at a central portion of the heat absorption surface of the first thermoelectric element, and the second light source unit may be arranged at a central portion of the heat absorption surface of the second thermoelectric element. 
     For example, the heat transfer plate may include a first heat transfer plate to which the first light source unit is attached and which abuts on the first thermoelectric element, and a second heat transfer plate to which the second light source unit is attached and which abuts on the second thermoelectric element. 
     For example, the semiconductor laser element may emit red laser light. 
     A projection display apparatus according to another aspect of the present disclosure includes: a lighting unit including at least one lighting device; an image display unit configured to modulate illumination light from the lighting unit and output the modulated illumination light as image light; and a projection optical system configured to enlarge and project the image light. The lighting device includes: a first light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the at least one first light source unit emitting a first light flux in a first direction; a second light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the second light source unit being arranged to emit a second light flux in the first direction and to be spaced apart from the first light source unit by a first distance in a second direction orthogonal to the first direction; and an optical path shift optical system including: a first reflecting surface that reflects the second light flux emitted from the second light source unit toward the first light flux; and a second reflecting surface that is parallel to the first reflecting surface and reflects the second light flux reflected by the first reflecting surface so as to be parallel to the first light flux at a second distance shorter than the first distance. 
     According to such an aspect, in the lighting device of the projection display apparatus which includes the plurality of light source units each including the plurality of laser elements, even if the approach arrangement of the plurality of light source units is restricted, the light fluxes of the light source units can be gathered at high density, and the illumination light with high luminance can be illuminated. 
     An exemplary embodiment of the present disclosure will be described below with reference to the drawings. 
     First Exemplary Embodiment 
       FIG.  1    is a schematic configuration diagram of a projection display apparatus according to an exemplary embodiment of the present disclosure. 
     As illustrated in  FIG.  1   , projection display apparatus  10  according to the first exemplary embodiment is a so-called DLP projector, and includes lighting unit  12 , image display unit  14  that modulates at least part of illumination light from lighting unit  12  and outputs image light, and projection optical system  16  that enlarges and projects the image light output from image display unit  14 . 
     Lighting unit  12  of projection display apparatus  10  includes lighting device  20  that emits red light, lighting device  22  that emits green light, and lighting device  24  that emits blue light. Further, lighting unit  12  includes green selective reflection mirror  26  that emits green light from lighting device  22  and blue light from lighting device  24  in a superimposed manner, red selective reflection mirror  28  that emits light emitted from green selective reflection mirror  26  and red light from lighting device  20  in a superimposed manner, and rod integrator  30  that collects the light emitted from red selective reflection mirror  28 . Lighting unit  12  further includes lens  32 , mirror  34 , and lens  36  arranged between red selective reflection mirror  28  and rod integrator  30 . Lighting devices  20 ,  22 ,  24  have substantially the same configuration except that colors of irradiation light are different, and details thereof will be described later. 
     The illumination light from lighting unit  12  reaches image display unit  14  via relay lenses  38 ,  40 , mirror  42 , and field lens  44 . 
     Image display unit  14  includes total reflection prism  46  that totally reflects the illumination light from lighting unit  12 . Total reflection prism  46  includes triangular prism  48  and triangular prism  50  that forms an air gap with triangular prism  48 . The illumination light is totally reflected by surface  48   a  of triangular prism  48  in contact with the air gap, passes through surface  48   b,  and enters color prism unit  52 . 
     Color prism unit  52  of image display unit  14  is configured to disperse the illumination light reflected by total reflection prism  46  into three light beams, respectively emit the dispersed light beams to the corresponding digital mirror devices (DMDs)  54 R,  54 G,  54 B, combine the reflected light beams from DMDs  54 R,  54 G,  54 B, and emit the combined light beams toward total reflection prism  46 . 
     Specifically, color prism unit  52  includes first prism  56  having dichroic mirror surface  56   a  that reflects blue light, second prism  58  having dichroic mirror surface  58   a  that reflects red light and blue light, and third prism  60 . An air gap for total reflection is provided between first prism  56  and second prism  58 . Color prism unit  52  emits red light to DMD  54 R, green light to DMD  54 G, and blue light to DMD  54 B. 
     DMDs  54 R,  54 G,  54 B are devices having substantially the same configuration, and each of the devices schematically includes a base portion and a plurality of micromirrors provided on the base portion in a matrix form such that a slope angle can be changed in a two-alternative manner. The slope angle of the micromirror is changed on the basis of an image signal from the outside, for example, the micromirror is selectively inclined at a first slope angle at which the reflected light is incident on color prism unit  52  at an incident angle of 0 degrees and a second slope angle at which the reflected light is incident on color prism unit  52  at an angle larger than 0 degrees. With such a configuration, DMD  54 R outputs at least partially modulated red light (red image light), and DMDs  54 G,  54 B similarly output green image light and blue image light. 
     The red image light, the green image light, and the blue image light from DMDs  54 R,  54 G,  54 B are synthesized by color prism unit  52 , and the synthesized image light (color image light) is emitted toward total reflection prism  46 . The color image light is transmitted through total reflection prism  46 , and is enlarged and projected on a screen or the like through projection optical system  16  including a projection lens or the like. 
     Hereinafter, lighting devices  20 ,  22 ,  24  of lighting unit  12  of projection display apparatus  10  will be described in detail. lighting devices  20 ,  22 ,  24  have substantially the same configuration except that colors of illumination light are different. Therefore, lighting device  20  will be described, and description of remaining lighting devices  22 ,  24  will be omitted. 
       FIG.  2    is a perspective view of a lighting device according to the first exemplary embodiment.  FIG.  3    is a front view of the lighting device according to the first exemplary embodiment. Further,  FIG.  4    is a side view of the lighting device according to the first exemplary embodiment.  FIG.  5    is a top view of the lighting device according to the first exemplary embodiment. An XYZ Cartesian coordinate system illustrated in the drawings is for facilitating understanding of the present disclosure and does not limit the exemplary embodiment. The Z-axis direction indicates the irradiation direction of the irradiation light of the lighting device. 
     As illustrated in  FIGS.  2  and  3   , lighting device  20  according to the first exemplary embodiment includes first and second light source units  70 ,  72 . In the first exemplary embodiment, first and second light source units  70 ,  72  have the same configuration. 
     As illustrated in  FIG.  5   , first and second light source units  70 ,  72  include a plurality of laser elements  74  whose optical axes are arranged in parallel (extending in the Z-axis direction) and in a matrix (on the X-Y plane). Laser element  74  is, for example, a semiconductor laser element. In the case of the first exemplary embodiment,  20  laser elements  74  are arranged in a 5×4 matrix in each of first and second light source units  70 ,  72 . 
     In the case of the first exemplary embodiment, each of first and second light source units  70 ,  72  is provided with laser element  74 , and includes collimating lens  76  that substantially collimates the laser light from laser element  74 . In the case of the first exemplary embodiment, the plurality of collimating lenses  76  are integrated to constitute collimating lens array  78 . In collimating lens array  78 , the plurality of collimating lenses  76  are arranged at the same arrangement pitch as the arrangement pitch of the laser elements  74 . 
     As illustrated in  FIG.  3   , first and second light source units  70 ,  72  including the plurality of laser elements  74  emit first and second light fluxes LF 1 , LF 2  including a plurality of parallel light beams. First and second light source units  70 ,  72  are arranged to emit first and second light fluxes LF 1 , LF 2  in the same direction (Z-axis direction). In the case of the first exemplary embodiment, lighting device  20  includes heat transfer plate  80  made of a material having high thermal conductivity such as copper, and first and second light source units  70 ,  72  are attached to planar first heat transfer surface  80   a  of heat transfer plate  80  with screws. 
     Heat transfer plate  80  is a member for drawing heat from first and second light source units  70 ,  72  generated by the outputs of first and second light fluxes LF 1 , LF 2 . In order to improve heat transfer efficiency from first and second light source units  70 ,  72  to heat transfer plate  80 , a heat transfer promotion member such as heat conductive grease may be arranged between the first and second light source units. 
     In the case of the first exemplary embodiment, as illustrated in  FIGS.  2  to  4   , lighting device  20  further includes cooling device  82  that cools heat transfer plate  80 . Cooling device  82  is attached to second heat transfer surface  80   b  opposite to first heat transfer surface  80   a  to which first and second light source units  70 ,  72  are attached via screws or the like. In the case of the first exemplary embodiment, cooling device  82  is, for example, a device that cools a member (heat transfer plate  80  in the case of the first Exemplary Embodiment in contact with cooling surface  82   a  with liquid (refrigerant), and includes inlet pipe  82   b  into which the refrigerant flows, outlet pipe  82   c  from which the refrigerant flows out, and a pump (not illustrated) that generates a flow of the refrigerant. By being cooled by cooling device  82  via heat transfer plate  80 , first and second light source units  70 ,  72  can be increased in power and life. As illustrated in  FIG.  5   , first and second light source units  70 ,  72  are preferably located within the contour of cooling surface  82   a  in a top view (viewed in the Z-axis direction) of lighting device  20  in consideration of cooling performance. 
     As illustrated in  FIGS.  3  and  5   , first and second light source units  70 ,  72  are arranged at first distance D 1 . Specifically, first and second light source units  70 ,  72  are arranged in parallel with first distance D 1  in a direction (Y-axis direction) orthogonal to the emission direction (Z-axis direction) of first and second light fluxes LF 1 , LF 2 , under the restriction of the size, shape, and the like, although the first and second light source units are arranged as close as possible. 
     As illustrated in  FIG.  3   , when first and second light source units  70 ,  72  are arranged at first distance D 1 , naturally, first and second light fluxes LF 1 , LF 2  are also emitted at first distance D 1 . As a result, in the image of the illumination light emitted from lighting device  20 , luminance unevenness occurs in which the central portion is dark and the outer portion is bright, and the image quality is impaired. Therefore, in order to increase the density of the illumination light irradiated from lighting device  20  while suppressing the occurrence of luminance unevenness, lighting device  20  includes optical path shift optical system  84 . 
     In the first exemplary embodiment, optical path shift optical system  84  is a parallelogram-shaped prism as illustrated in  FIGS.  2  and  3   . Specifically, optical path shift optical system  84  has a parallelogram shape as viewed in a direction (X-axis direction) orthogonal to the emission direction (Z-axis direction) of first and second light fluxes LF 1 , LF 2  and the parallel direction (Y-axis direction) of first and second light source units  70 ,  72 . 
     As illustrated in  FIG.  3   , optical path shift optical system  84  (parallelogram-shaped prism) is made of a material that can transmit light and is hardly deformed even at a high temperature, for example, glass. Optical path shift optical system  84  (prism) includes first reflecting surface  84   a  that reflects all of second light flux LF 2  emitted from second light source unit  72  in the parallel direction (Y-axis direction) of first and second light source units  70 ,  72  toward first light flux LF 1 . Optical path shift optical system  84  (prism) includes second reflecting surface  84   b  that is parallel to first reflecting surface  84   a  and reflects second light flux LF 2  reflected by first reflecting surface  84   a  so as to be parallel to first light flux LF 1  at second distance D 2  shorter than the first distance. Further, optical path shift optical system  84  (prism) includes first transmission surface  84   c  through which all of second light flux LF 2  before being reflected by first reflecting surface  84   a  is transmitted, and second transmission surface  84   d  that is parallel to first transmission surface  84   c  and through which second light flux LF 2  reflected by second reflecting surface  84   b  is transmitted. Optical path shift optical system  84  (prism) is retained by, for example, a housing (not illustrated) of lighting device  20  that holds heat transfer plate  80 . 
     According to optical path shift optical system  84  (prism), second light flux LF 2  can approach first light flux LF 1  up to second distance D 2  shorter than first distance D 1  between first and second light source units  70 ,  72 . As a result, first and second light fluxes LF 1 , LF 2  gather at a high density. 
     First light flux LF 1  is not related to optical path shift optical system  84  (prism). That is, first light flux LF 1  propagates from first light source unit  70  without being reflected by optical path shift optical system  84  or passing through optical path shift optical system  84 . 
       FIG.  6    is a diagram illustrating an image of a first light flux and an image of a second light flux. 
     As illustrated in  FIG.  6   , when optical path shift optical system  84  is present, image Im 2  (solid line) of second light flux LF 2  is closer to image Im 1  of first light flux LF 1  than when optical path shift optical system  84  is not present (dotted line). As a result, optical path region Pa (solid line) in lighting device  20  can be made smaller than that in the case where optical path shift optical system  84  is not present (dotted line). As a result, the illumination light of lighting device  20  is reduced in luminance unevenness and increased in density. It is also possible to downsize an optical element such as a lens in projection display apparatus  10 , and as a result, it is possible to downsize projection display apparatus  10 . 
     According to the first exemplary embodiment as described above, in the lighting device including the plurality of light source units each including the plurality of laser elements, even if the close arrangement of the plurality of light source units is restricted, the light fluxes of the light source units can be gathered at high density, and the high-luminance illumination light can be illuminated. 
     Second Exemplary Embodiment 
     A projection display apparatus according to a second exemplary embodiment is different from the first exemplary embodiment in an optical path shift optical system in a lighting device. Therefore, the present second exemplary embodiment will be described while focusing on differences. Components in the second exemplary embodiment that are substantially identical to those in the first exemplary embodiment described above are denoted by the same reference signs. 
       FIG.  7    is a front view of a lighting device in a projection display apparatus according to the second exemplary embodiment of the present disclosure. 
     As illustrated in  FIG.  7   , lighting device  120  according to the second exemplary embodiment includes first and second light source units  70 ,  72  arranged at first distance D 1  as in the first exemplary embodiment. In order to bring second light flux LF 2  of second light source unit  72  close to first light flux LF 1  of first light source unit  70 , lighting device  120  has optical path shift optical system  184 . 
     In the second exemplary embodiment, optical path shift optical system  184  includes first and second mirrors  184 A,  184 B. First mirror  184 A includes first reflecting surface  184 Aa that reflects all of second light flux LF 2  emitted from second light source unit  72  toward first light flux LF 1  in the parallel direction (Y-axis direction) of first and second light source units  70 ,  72 . Second mirror  184 B includes second reflecting surface  184 Ba that is parallel to first reflecting surface  184 Aa of first mirror  184 A and reflects second light flux LF 2  reflected by first reflecting surface  184 Aa to be parallel to first light flux LF 1  at second distance D 2  shorter than first distance D 1 . 
     According to the second exemplary embodiment as described above, similarly to the first exemplary embodiment, in the lighting device including the plurality of light source units each including the plurality of laser elements, even if the close arrangement of the plurality of light source units is restricted, the light fluxes of the light source units can be gathered at high density, and the high-luminance illumination light can be illuminated. 
     Third Exemplary Embodiment 
     A projection display apparatus according to a third exemplary embodiment is different from that of the first exemplary embodiment in that a distance between first and second light source units in a lighting device is different, and thus a cooling device is different. Therefore, the present third exemplary embodiment will be described while focusing on differences. Components in the third exemplary embodiment that are substantially identical to those in the first exemplary embodiment described above are denoted by the same reference signs. 
       FIG.  8    is a front view of a lighting device in a projection display apparatus according to the third exemplary embodiment of the present disclosure. 
     As illustrated in  FIG.  8   , in lighting device  220  according to the third exemplary embodiment, first and second light source units  70 ,  72  are arranged at first distance D 3  (D 3 &gt;D 1 ) larger than first distance D 1  in the first exemplary embodiment. This is because the cooling device in lighting device  220  is different from the cooling device of the first exemplary embodiment. 
     Specifically, in the case of the above-described first exemplary embodiment, as illustrated in  FIG.  3   , one cooling device  82  is commonly used for first and second light source units  70 ,  72 . On the other hand, in the case of the third exemplary embodiment, as illustrated in  FIG.  8   , first and second cooling devices  282 A,  282 B are provided in a state of being maximally close to each other with respect to first and second light source units  70 ,  72 , respectively. First and second light source units  70 ,  72  are arranged on first heat transfer plate  280   a  of heat transfer plate  280 , and first and second cooling devices  282 A,  282 B are arranged on second heat transfer surface  280   b  of heat transfer plate  280 . First cooling device  282 A is arranged to face first light source unit  70  with heat transfer plate  280  interposed therebetween. Second cooling device  282 B is arranged to face second light source unit  72  with heat transfer plate  280  interposed therebetween. 
     First and second light source units  70 ,  72  are arranged at central portions of cooling surfaces  282 Aa,  282 Ba of first and second cooling devices  282 A,  282 B in a top view (as viewed in the Z-axis direction) of lighting device  220 . As a result, first and second light source units  70 ,  72  are separated by first distance D 3 . That is, the close arrangement of first and second light source units  70 ,  72  is limited due to the size constraints of first and second cooling devices  282 A,  282 B. 
     Since first and second light source units  70 ,  72  have first distance D 3  larger than first distance D 1  in the first exemplary embodiment, heat transfer plate  280  and optical path shift optical system  284  (prism) are larger than heat transfer plate  80  and optical path shift optical system  84  in the first exemplary embodiment described above. 
     When first and second cooling devices  282 A,  282 B are provided for first and second light source units  70 ,  72 , respectively, the close arrangement of first and second light source units  70 ,  72  is restricted. However, second light flux LF 2  of second light source unit  72  can be brought close to first light flux LF 1  of first light source unit  70  by optical path shift optical system  284  (prism) similarly to the first exemplary embodiment. 
     Since first and second cooling devices  282 A,  282 B are provided for first and second light source units  70 ,  72 , respectively, cooling control of first and second light source units  70 ,  72  can be performed independently. 
     According to the third exemplary embodiment as described above, similarly to the first exemplary embodiment, in the lighting device including the plurality of light source units each including the plurality of laser elements, even if the close arrangement of the plurality of light source units is restricted, the light fluxes of the light source units can be gathered at high density, and the high-luminance illumination light can be illuminated. 
     Fourth Exemplary Embodiment 
     The present fourth exemplary embodiment is an improvement of the third exemplary embodiment described above. The fourth exemplary embodiment will now be described while focusing on the third exemplary embodiments. Components in the fourth exemplary embodiment that are substantially identical to those in the third exemplary embodiment described above are denoted by the same reference signs. 
       FIG.  9    is a front view of a lighting device in a projection display apparatus according to the fourth exemplary embodiment of the present disclosure.  FIG.  10    is a top view of the lighting device according to the fourth exemplary embodiment. 
     As illustrated in  FIGS.  9  and  10   , lighting device  320  according to the fourth exemplary embodiment includes first thermoelectric element  386 A and second thermoelectric element  386 B. 
     First and second thermoelectric elements  386 A,  386 B are, for example, Peltier elements, and include heat absorption surfaces  386 Aa,  386 Ba that absorb heat of a cooling target (first and second light source units  70 ,  72  in the case of the present fourth exemplary embodiment) and heat dissipating surfaces  386 Ab,  386 Bb that release the absorbed heat. 
     Specifically, first thermoelectric element  386 A is arranged between heat transfer plate  280  and first cooling device  282 A. Heat absorption surface  386 Aa of first thermoelectric element  386 A abuts on second heat transfer surface  280   b  of heat transfer plate  280 , and heat dissipating surface  386 Ab abuts on cooling surface  282 Aa of first cooling device  282 A. Specifically, as illustrated in  FIG.  10   , heat absorption surface  386 Aa overlaps first light source unit  70  in a top view (viewed in the Z-axis direction) of lighting device  320 . 
     Second thermoelectric element  386 B is arranged between heat transfer plate  280  and second cooling device  282 B. Heat absorption surface  386 Ba of second thermoelectric element  386 B abuts on second heat transfer surface  280   b  of heat transfer plate  280 , and heat dissipating surface  386 Bb abuts on cooling surface  282 Ba of second cooling device  282 B. Specifically, as illustrated in  FIG.  10   , heat absorption surface  386 Ba overlaps second light source unit  72  in a top view (viewed in the Z-axis direction) of lighting device  320 . 
     Such first and second thermoelectric elements  386 A,  386 B cool (absorb heat) first and second light source units  70 ,  72  via heat transfer plate  280 . Through cooling, heat dissipating surfaces  386 Ab,  386 Bb of first and second thermoelectric elements  386 A,  386 B heated to high temperatures are cooled by first and second cooling devices  282 A,  282 B. 
     Thus, the temperatures of first and second light source units  70 ,  72  can be finely controlled by controlling the drive currents supplied to first and second thermoelectric elements  386 A,  386 B. For example, in a case where a red semiconductor laser element is used as a laser element of each of first and second light source units  70 ,  72 , the output, wavelength, and lifetime of the red semiconductor laser element change depending on the temperature. Therefore, temperature control is performed by first and second thermoelectric elements  386 A,  386 B in order to maintain the temperature constant. 
     As illustrated in  FIG.  10   , in the case of the fourth exemplary embodiment, heat absorption surfaces  386 Aa,  386 Ba of first and second thermoelectric elements  386 A,  386 B are sufficiently larger than those of first and second light source units  70 ,  72  in a top view (viewed in the Z-axis direction) of lighting device  320 . In this case, in a top view, first and second light source units  70 ,  72  are preferably arranged at the central portions of the heat absorption surfaces  386 Aa,  386 Ba. 
     In contrast, when first and second light source units  70 ,  72  are arranged in the vicinity of the outer peripheries of heat absorption surfaces  386 Aa,  386 Ba in a top view (viewed in the Z-axis direction) of lighting device  320 , there is a possibility that dew condensation occurs in a portion of heat transfer plate  280  facing the portion of the heat absorption surfaces  386 Aa,  386 Ba away from first and second light source units  70 ,  72 . That is, in heat transfer plate  280  cooled by first and second thermoelectric elements  386 A,  386 B, there is a possibility that dew condensation occurs at a portion away from first and second light source units  70 ,  72  as a heat source. In order to suppress the generation of such dew condensation, it is preferable that first and second light source units  70 ,  72  are arranged at the central portions of the heat absorption surfaces  386 Aa,  386 Ba of the first and second thermoelectric elements  386 A,  386 B in a top view of lighting device  320 . 
     As described above, when first and second light source units  70 ,  72  are arranged at the central portions of heat absorption surfaces  386 Aa,  386 Ba of first and second thermoelectric elements  386 A,  386 B in a top view (viewed in the Z-axis direction) of lighting device  320 , the close arrangement of first and second light source units  70 ,  72  is restricted. However, second light flux LF 2  of second light source unit  72  can be brought close to first light flux LF 1  of first light source unit  70  by optical path shift optical system  284  (prism) similarly to the first exemplary embodiment. 
     According to the fourth exemplary embodiment as described above, similarly to the first exemplary embodiment, in the lighting device including the plurality of light source units each including the plurality of laser elements, even if the close arrangement of the plurality of light source units is restricted, the light fluxes of the light source units can be gathered at high density, and the high-luminance illumination light can be illuminated. 
     Fifth Exemplary Embodiment 
     The present fifth exemplary embodiment is an improvement of the fourth exemplary embodiment described above. The fifth exemplary embodiment will now be described while focusing on the differences from the third exemplary embodiments. Components in the fifth exemplary embodiment that are substantially identical to those in the fourth exemplary embodiment described above are denoted by the same reference signs. 
       FIG.  11    is a front view of a lighting device in a projection display apparatus according to the fifth exemplary embodiment of the present disclosure.  FIG.  12    is a top view of the lighting device according to the present fifth exemplary embodiment. 
     As illustrated in  FIGS.  11  and  12   , lighting device  420  according to the fifth exemplary embodiment is different from lighting device  320  according to the above-described fourth exemplary embodiment illustrated in  FIGS.  9  and  10    in that first and second heat transfer plates  480 A,  480 B are provided for first and second light source units  70 ,  72 , respectively. 
     Specifically, lighting device  420  according to the fifth exemplary embodiment includes first heat transfer plate  480 A to which first light source unit  70  is attached and which is in contact with first thermoelectric element  386 A, and second heat transfer plate  480 B to which second light source unit  72  is attached and which is in contact with second thermoelectric element  386 B. 
     First and second heat transfer plates  480 A,  480 B are separately provided for first and second light source units  70 ,  72 , respectively, so that two thermally separated units are configured. One of the units includes first light source unit  70 , first heat transfer plate  480 A, first thermoelectric element  386 A, and first cooling device  282 A. The other unit includes second light source unit  72 , second heat transfer plate  480 B, second thermoelectric element  386 B, and second cooling device  282 B. As described above, by unitizing one light source unit, one heat transfer plate, one thermoelectric element, and one cooling device, the lighting device can be easily manufactured, and the lighting devices having different numbers of light source units can be easily constructed. Since the light source units are thermally separated, the temperature of each of the plurality of light source units can be easily controlled with high accuracy. 
     According to the fifth exemplary embodiment as described above, similarly to the first exemplary embodiment, in the lighting device including the plurality of light source units each including the plurality of laser elements, even if the close arrangement of the plurality of light source units is restricted, the light fluxes of the light source units can be gathered at high density, and the high-luminance illumination light can be illuminated. 
     Although the present disclosure has been described above by taking the above first to fifth exemplary embodiments as an example, the present disclosure is not limited to the above exemplary embodiments. 
     For example, as illustrated in  FIG.  1   , in the case of the above-described first exemplary embodiment, projection display apparatus  10  is a DLP projector, but is not limited thereto. The projection display apparatus according to the exemplary embodiment of the present disclosure is not a DLP projector but a  3 LCD (liquid crystal display) projector. 
     In the case of the above-described first exemplary embodiment, lighting unit  12  of projection display apparatus  10  includes three lighting devices  20 ,  22 ,  24 . However, the exemplary embodiment of the present disclosure is not limited thereto. 
       FIG.  13    is a schematic configuration diagram of a projection display apparatus according to another example  1  of the present disclosure. 
     In projection display apparatus  510  illustrated in  FIG.  13   , lighting unit  512  includes two lighting devices  520 A,  520 B that emit red light, two lighting devices  522 A,  522 B that emit green light, and two lighting devices  524 A,  524 B that emit blue light. 
     The blue light from two lighting devices  524 A,  524 B is reflected by mirrors  525 A,  525 B, transmitted through green selective reflection mirrors  526 A,  526 B and red selective reflection mirrors  527 A,  527 B, transmitted through lens  528 , mirror  529 , and lens  530 , and incident on rod integrator  532 . 
     The green light from the two lighting devices  522 A,  522 B is reflected by green selective reflection mirrors  526 A,  526 B, transmitted through red selective reflection mirrors  527 A,  527 B, transmitted through lens  528 , mirror  529 , and lens  530 , and incident on rod integrator  532 . 
     Then, the red light from the two lighting devices  520 A,  520 B is reflected by red selective reflection mirrors  527 A,  527 B, transmitted through lens  528 , mirror  529 , and lens  530 , and incident on rod integrator  532 . 
       FIG.  14    illustrates images of light fluxes from two lighting devices. 
     As illustrated in  FIG.  14   , for example, image Im 1 -A of the first light flux of the first light source unit in lighting device  520 A, image Im 2 -A of the second light flux of the second light source unit in lighting device  520 A, image Im 1 -B of the first light flux of the first light source unit in lighting device  520 B, and image Im 2 -B of the second light flux of the second light source unit in lighting device  520 B constitute a red light image. 
     In this case, as compared with projection display apparatus  10  illustrated in  FIG.  1   , since the number of light source units used for irradiation with the illumination light of each color is doubled, the luminance is improved. 
     Further, in the exemplary embodiment of the present disclosure, the light source unit is not limited to first and second light source units  70 ,  72  in the above-described first to fifth exemplary embodiments. 
       FIG.  15    is a top view of a light source unit of another example  2 . 
     Light source unit  670  of another example  2  illustrated in  FIG.  15    includes eight laser elements  674  arranged in a matrix. Collimating lens  676  is provided in each of laser elements  674 . In light source unit  670 , the plurality of collimating lenses  676  are not integrated. It is needless to say that in the laser element  674 , similarly to laser element  74 , when a plurality of laser elements are arranged, the emitted light can be arranged at high density using the present disclosure. 
     Further, in the case of the above-described first exemplary embodiment, the number of light source units included in lighting device  20  is two, but the embodiment of the present disclosure is not limited thereto. 
       FIG.  16    is a front view of a lighting device including three light source units according to another example  3 . In  FIG.  16   , a cooling device and a thermoelectric element are omitted. 
     As illustrated in  FIG.  16   , lighting device  720  includes first to third light source units  770 ,  772 ,  774 . Lighting device  720  includes first optical path shift optical system  776  for causing second light flux LF 2  of second light source unit  772  to approach first light flux LF 1  of first light source unit  770 . Further, lighting device  720  includes second optical path shift optical system  778  for causing third light flux LF 3  of third light source unit  774  to approach first light flux LF 1 . As illustrated in  FIG.  16   , each of the plurality of light source units included in the lighting device may have a different configuration, for example, a different number of laser elements. 
     In the above-described exemplary embodiment, an example has been described in which the second light flux reflected by the first reflecting surface of the optical path shift optical system travels in the Y-axis direction (second direction) toward the first light flux, but the second light flux may not be strictly reflected in the Y-axis direction as long as the second light flux is reflected toward the first light flux, that is, in a direction approaching the first light flux. The second light flux reflected by the first reflecting surface may advance toward the first light flux such that a distance (second distance) between the first light flux and the second light flux is shorter than a distance (first distance) between the first light source unit and the second light source unit. 
     That is, in a broad sense, the lighting device according to the exemplary embodiment of the present disclosure includes: a first light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the first light source unit emitting a first light flux in a first direction (Z-axis direction); a second light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the second light source unit being arranged to emit a second light flux in the first direction and to be spaced apart from the first light source unit by a first distance in a second direction (Y-axis direction) orthogonal to the first direction; and an optical path shift optical system including: a first reflecting surface that reflects all the second light flux emitted from the second light source unit toward the first light flux; and a second reflecting surface that is parallel to the first reflecting surface and reflects the second light flux reflected by the first reflecting surface to be parallel to the first light flux at a second distance shorter than the first distance. 
     Further, in a broad sense, the projection display apparatus according to the exemplary embodiment of the present disclosure includes: a lighting unit including at least one lighting device; an image display unit configured to modulate illumination light from the lighting unit and output the modulated illumination light as image light; and a projection optical system configured to enlarge and project the image light. The at least one lighting device includes: a first light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the first light source unit emitting a first light flux in a first direction (Z-axis direction); a second light source unit including a plurality of laser elements having optical axes arranged in parallel and in a matrix, the second light source unit being arranged to emit a second light flux in the first direction and to be spaced apart from the first light source unit by a first distance in a second direction (Y-axis direction) orthogonal to the first direction; and an optical path shift optical system including: a first reflecting surface that reflects all the second light flux emitted from the second light source unit toward the first light flux; and a second reflecting surface that is parallel to the first reflecting surface and reflects the second light flux reflected by the first reflecting surface to be parallel to the first light flux at a second distance shorter than the first distance. 
     As described above, the above exemplary embodiment has been described as examples of the techniques in the present disclosure. To this end, the drawings and detailed description are provided. Thus, in order to exemplify the above-described techniques, the components illustrated in the drawings and described in the detailed description include not only components essential for solving the problem but also components not essential for solving the problem. Therefore, the fact that such non-essential components are illustrated in the drawings or described in the detailed description should not immediately determine that these non-essential components are essential. 
     Since the above-described exemplary embodiment is intended to exemplify the technique according to the present disclosure, various modifications, replacements, additions, and omissions can be made within the scope of the appended claims or of their equivalents. 
     The present disclosure is applicable to a lighting device used in a projection display apparatus.