Patent Publication Number: US-2022236631-A1

Title: Light source apparatus and projector

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-008994, filed Jan. 22, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a light source apparatus and a projector. 
     2. Related Art 
     There has been a proposed light source apparatus using fluorescence emitted from a phosphor when the phosphor is irradiated with excitation light outputted from a light source. JP-A-2012-3923 discloses a transmissive phosphor unit that emits fluorescence via the surface opposite from the surface on which excitation light is incident. In the phosphor unit, the phosphor is provided on a transparent substrate. 
     In the phosphor unit disclosed in JP-A-2012-3923, in which the excitation light passes through the transparent substrate and enters the phosphor, part of the excitation light is reflected off the interface between the phosphor and the transparent substrate to form stray light in the transparent substrate, resulting in a decrease in the excitation light utilization efficiency. 
     SUMMARY 
     To solve the problem described above, according to an aspect of the present disclosure, there is provided a light source apparatus including a substrate, a transmissive ceramic phosphor supported by one surface of the substrate and having an exposed surface that is part of a first surface exposed via the substrate, and an excitation light source that radiates excitation light to the exposed surface of the ceramic phosphor, and the distance from an irradiated region of the exposed surface that is the region irradiated with the excitation light to the substrate is 0.34 mm or greater. 
     According to another aspect of the present disclosure, there is provided a projector including the light source apparatus according to the aspect described above, a light modulator that modulates light outputted from the light source apparatus in accordance with image information to form image light, and a projection optical apparatus that projects the image light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic configuration of a projector according to a first embodiment. 
         FIG. 2  shows a schematic configuration of a light source apparatus. 
         FIG. 3  is a cross-sectional view showing the configurations of key parts of a wavelength converter. 
         FIG. 4  shows the state in which a ceramic phosphor emits fluorescence. 
         FIG. 5  shows the relationship between a spread width over which the fluorescence spreads due to bleeding and a BY ratio. 
         FIG. 6  is a cross-sectional view showing the configurations of key parts of the wavelength converter in a second embodiment. 
         FIG. 7  is a cross-sectional view showing the configurations of key parts of the wavelength converter in a third embodiment. 
         FIG. 8  is a cross-sectional view showing the configurations of key parts of the wavelength converter in a fourth embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Embodiments of the present disclosure will be described below in detail with reference to the drawings. 
     In the drawings used in the description below, a characteristic portion is enlarged for convenience in some cases for clarity of the characteristic thereof, and the dimension ratio and other factors of each component are therefore not always equal to actual values. 
     First Embodiment 
       FIG. 1  shows a schematic configuration of a projector according to a first embodiment.  FIG. 2  shows a schematic configuration of a light source apparatus. 
     A projector  1  according to the present embodiment is a projection-type image display apparatus that displays video images on a screen SCR, as shown in  FIG. 1 . The projector  1  includes a light source apparatus  2 , a color separation system  3 , light modulators  4 R,  4 G, and  4 B, a light combining system  5 , and a projection optical apparatus  6 . 
     The light source apparatus  2  outputs white illumination light WL toward the color separation system  3 . 
     The color separation system  3  separates the illumination light WL outputted from the light source apparatus  2  into red light LR, green light LG, and blue light LB. The color separation system  3  includes a first dichroic mirror  7   a , a second dichroic mirror  7   b , a first total reflection mirror  8   a , a second total reflection mirror  8   b , a third total reflection mirror  8   c , a first relay lens  9   a , and a second relay lens  9   b.    
     The first dichroic mirror  7   a  separates the illumination light WL from the light source apparatus  2  into the red light LR and the other light (green light LG and blue light LB). The first dichroic mirror  7   a  transmits the red light LR and reflects the other light (green light LG and blue light LB). On the other hand, the second dichroic mirror  7   b  reflects the green light LG and transmits the blue light LB to separate the other light (green light LG and blue light LB) into the green light LG and the blue light LB. 
     The first total reflection mirror  8   a  is disposed in the optical path of the red light LR and reflects the red light LR having passed through the first dichroic mirror  7   a  toward the light modulator  4 R. On the other hand, the second total reflection mirror  8   b  and the third total reflection mirror  8   c  are disposed in the optical path of the blue light LB and guide the blue light LB having passed through the second dichroic mirror  7   b  toward the light modulator  4 B. The green light LG is reflected off the second dichroic mirror  7   b  toward the light modulator  4 G. 
     The first relay lens  9   a  and the second relay lens  9   b  are disposed in the optical path of the blue light LB on the light exiting side of the second total reflection mirror  8   b . The first relay lens  9   a  and the second relay lens  9   b  have the function of compensating optical loss of the blue light LB resulting from the fact that the optical path length of the blue light LB is longer than the optical path lengths of the red light LR and the green light LG. 
     The light modulator  4 R modulates the red light LR in accordance with image information to form image light corresponding to the red light LR. The light modulator  4 G modulates the green light LG in accordance with image information to form image light corresponding to the green light LG. The light modulator  4 B modulates the blue light LB in accordance with image information to form image light corresponding to the blue light LB. 
     The light modulators  4 R,  4 G, and  4 B are each, for example, a transmissive liquid crystal panel. Polarizers (not shown) are disposed on the light incident and exiting sides of each of the liquid crystal panels. 
     Field lens  10 R,  10 G, and  10 B are disposed on the light incident side of the light modulators  4 R,  4 G, and  4 B, respectively. The field lens  10 R,  10 G, and  10 B parallelize the red light LR, the green light LG, and the blue light LB to be incident on the respective light modulators  4 R,  4 G, and  4 B. 
     The image light from the light modulator  4 R, the image light from the light modulator  4 G, and the image light from the light modulator  4 B enter the light combing system  5 . The light combining system  5  combines the image light corresponding to the red light LR, the image light corresponding to the green light LG, and the image light corresponding to the blue light LB with one another and outputs the combined image light toward the projection optical apparatus  6 . The light combining system  5  is formed, for example, of a cross dichroic prism. 
     The projection optical apparatus  6  is formed of a projection lens group, enlarges the combined image light from the light combining system  5 , and projects the enlarged image light toward the screen SCR. Enlarged video images are thus displayed on the screen SCR. 
     Light Source Apparatus 
     The configuration of the light source apparatus  2  will be subsequently described. 
     The light source apparatus  2  includes an excitation light source  10 , an afocal optical system  11 , a homogenizer optical system  12 , a condenser optical system  13 , a wavelength converter  20 , a pickup optical system  30 , and a uniform illumination optical system  80 , as shown in  FIG. 2 . 
     The excitation light source  10  is formed of a plurality of semiconductor lasers  10   a , which each output blue excitation light E formed of laser light, and a plurality of collimator lenses  10   b . The plurality of semiconductor lasers  10   a  are arranged in an array in a plane perpendicular to an illumination optical axis  100   ax . The collimator lenses  10   b  are arranged in an array in a plane perpendicular to the illumination optical axis  100   ax  in correspondence with the semiconductor lasers  10   a . The collimator lenses  10   b  each convert the excitation light E outputted from the corresponding semiconductor laser  10   a  into parallelized light. 
     The afocal optical system  11  includes, for example, a convex lens  11   a  and a concave lens  11   b . The afocal optical system  11  reduces the luminous flux diameter of the excitation light E, which is formed of a parallelized luminous flux outputted from the excitation light source  10 . 
     The homogenizer optical system  12  includes, for example, a first multi-lens array  12   a  and a second multi-lens array  12   b . The homogenizer optical system  12  achieves a uniform optical intensity distribution of the excitation light on the wavelength converter  20 , which will be described later, or what is called a top-hat distribution. The homogenizer optical system  12  superimposes, along with the condenser optical system  13 , a plurality of thin luminous fluxes having exited out of a plurality of lenses of the first multi-lens array  12   a  and the second multi-lens array  12   b  on one another on the wavelength converter  20 . The light intensity distribution of the excitation light E radiated on the wavelength converter  20  is thus made uniform. 
     The condenser optical system  13  includes, for example, a first lens  13   a  and a second lens  13   b . In the present embodiment, the first lens  13   a  and the second lens  13   b  are each formed of a convex lens. The condenser optical system  13  is disposed in the optical path from the homogenizer optical system  12  to the wavelength converter  20 , collects the excitation light E, and causes the collected excitation light E to enter the wavelength converter  20 . The configuration of the wavelength converter  20  will be described later. 
     The pickup optical system  30  includes, for example, a first collimation lens  31  and a second collimation lens  32 . The pickup optical system  30  is a parallelizing optical system that substantially parallelizes the light having exited out of the wavelength converter  20 . The first collimation lens  31  and the second collimation lens  32  are each formed of a convex lens. The light parallelized by the pickup optical system  30  enters the uniform illumination optical system  80 . 
     The uniform illumination system  80  includes a first lens array  81 , a second lens array  82 , a polarization converter  83 , and a superimposing lens  84 . 
     The first lens array  81  includes a plurality of first lenses  81   a  for dividing the illumination light WL from the light source apparatus  2  into a plurality of sub-luminous fluxes. The plurality of first lenses  81   a  are arranged in a matrix in a plane perpendicular to the illumination optical axis  100   ax.    
     The second lens array  82  includes a plurality of second lenses  82   a  corresponding to the plurality of first lenses  81   a  in the first lens array  81 . The plurality of second lenses  82   a  are arranged in a matrix in a plane perpendicular to the illumination optical axis  100   ax.    
     The second lens array  82  along with the superimposing lens  84  brings images of the first lenses  81   a  in the first lens array  81  into focus in the vicinity of an image formation region of each of the light modulators  4 R,  4 G, and  4 B. 
     The polarization converter  83  converts the light having exited out of the second lens array  82  into linearly polarized light. The polarization converter  83  includes, for example, polarization separation films and retardation films (not shown). 
     The superimposing lens  84  collects the sub-luminous fluxes having exited out of the polarization converter  83  and superimposes the collected sub-luminous fluxes on one another in the vicinity of the image formation region of each of the light modulators  4 R,  4 G, and  4 B. 
     Wavelength Converter 
     The configuration of the wavelength converter will next be described. 
       FIG. 3  is a cross-sectional view showing the configurations of key parts of the wavelength converter  20 .  FIG. 3  corresponds to the cross section of the wavelength converter  20  taken along a plane containing the illumination optical axis  100   ax  in  FIG. 2 . 
     The wavelength converter  20  in the present embodiment includes a substrate  21 , a ceramic phosphor  22 , a dichroic layer (optical layer)  23 , and a bonding member  24 , as shown in  FIG. 3 . The wavelength converter  20  in the present embodiment is an immobile phosphor so configured that the position where the excitation light E enters the ceramic phosphor  22  does not change over time. 
     The substrate  21  is made of a metal material that excels in heat dissipation, for example, aluminum or copper. The substrate  21  is a support member that supports the ceramic phosphor  22 . The substrate  21  in the present embodiment is formed of a non-light-transmissive member. The thermal conductivity of the substrate  21  in the present embodiment is higher than that of the that of the ceramic phosphor  22 . The substrate  21  has a support surface  21   a , which supports the ceramic phosphor  22 . 
     The ceramic phosphor  22  has a first surface  22   a  and a second surface  22   b  different from the first surface  22   a . The first surface  22   a  is the surface on which the excitation light E outputted from the excitation light source  10  is incident. The second surface  22   b  is the surface via which fluorescence Y exits. The ceramic phosphor  22  in the present embodiment is a transmissive wavelength converter that causes the fluorescence Y generated by the excitation light E incident via the first surface  22   a  to exit via the second surface  22   b , which is opposite from the first surface  22   a.    
     The ceramic phosphor  22  has a phosphor phase  25  and a matrix phase  26 . The phosphor phase  25  contains an oxide phosphor to which an activator has been added. The phosphor phase  25  contains, for example, yttrium aluminum garnet (YAG(Y 3 Al 5 O 12 ):Ce) to which cerium (Ce) has been added as the activator. 
     Consider YAG:Ce by way of example, and phosphor particles can be made, for example, of a material produced by mixing raw powder materials containing Y 2 O 3 , Al 2 O 3 , CeO 3 , and other constituent elements with one another and causes the mixture to undergo a solid-phase reaction, Y—Al—O amorphous particles produced by using a coprecipitation method, a sol-gel method, or any other wet method, or YAG particles produced by using a spray-drying method, a flame-based thermal decomposition method, a thermal plasma method, or any other gas-phase method. 
     The oxide phosphor that forms the phosphor phase  25  may include at least one of Y 3  (Al, Ga) 5 O 12 , Lu 3 Al 5 O 12 , and TbAl 5 O 12  in addition to Y 3 Al 5 O 12 . The phosphor phase  25  may contain europium (Eu) in place of cerium (Ce) as the activator. 
     The matrix phase  26  functions as a binder that binds a plurality of phosphor particles that form the phosphor phase  25  together. The matrix phase  26  is made of a material containing MgO (magnesium oxide) as a light transmissive ceramic material. The thermal conductivity of the magnesium oxide, which forms the matrix phase  26 , is about 50 W/m·K, and the thermal conductivity of YAG, which forms the phosphor phase  25 , is about 12 W/m·K. In the present embodiment, the light transmissive ceramic material contained in the matrix phase  26  has thermal conductivity higher than that of the phosphor phase  25 . 
     The metal oxide that forms the matrix phase  26  may contain at least one of Al 2 O 3 , ZnO, TiO 2 , Y 2 O 3 , YAlO 3 , BeO, and MgAl 2 O 4  in addition to MgO described above. 
     The thermal conductivity of Al 2 O 3  is about 30 W/m·K, the thermal conductivity of ZnO is about 25 W/m·K, the thermal conductivity of TiO 2  is about 43 W/m·K, the thermal conductivity of Y 2 O 3  is about 27 W/m·K, the thermal conductivity of YAlO 3  is about 12 W/m·K, the thermal conductivity of BeO is about 250 W/m·K, and the thermal conductivity of MgAl 2 O 4  is about 14 W/m·K. 
     The thus configured ceramic phosphor  22  can be manufactured, for example, by the following steps. 
     Predetermined amounts of Al 2 O 3  powder, Y 2 O 3  powder, and CeO 2  powder, which are raw material powder of YAG:Ce, are mixed with a predetermined amount of ethanol, and ball milling is performed on the mixture in a pot to produce slurry. The slurry is dried, granulated, then degreased, and sintered to produce YAG:Ce powder. 
     A predetermined amount of YAG:Ce powder produced by carrying out the steps described above is mixed with a predetermined amount of MgO powder and a predetermined amount of ethanol, and ball milling is performed on the mixture in a pot to produce slurry. The slurry is then dried, granulated, molded, degreased, and sintered in the presented order to produce the ceramic phosphor  22  in the present embodiment, which is made of a composite sintered compact of YAG:Ce, YAG, and MgO (magnesium oxide). To increase the density of the sintered compact, a hot isotropic pressing process of sintering the compact under pressure may be additionally performed. 
     The dichroic layer  23  is provided at the first surface  22   a  of the ceramic phosphor  22  and serves as a reflective layer that reflects light having a specific wavelength. The dichroic layer  23  is characterized in that it transmits the excitation light E and reflects the fluorescence Y emitted from the ceramic phosphor  22 . Providing the dichroic layer  23  prevents the fluorescence Y generated in the ceramic phosphor  22  from exiting out thereof via the first surface  22   a . The fluorescence Y generated in the ceramic phosphor  22  can thus be efficiently extracted from the ceramic phosphor  22 . 
     A through hole (opening)  210  is formed in the substrate  21  in the present embodiment. Part of the first surface  22   a  of the ceramic phosphor  22  is exposed via the through hole  210 . In the ceramic phosphor  22 , a portion of the first surface  22   a  that is the portion exposed via the through hole  210  is hereinafter referred to as an exposed portion  211 . In the ceramic phosphor  22  in the present embodiment, the excitation light E is incident on the exposed portion  211 . 
     The ceramic phosphor  22  is bonded to the substrate  21  via the bonding member  24 . The bonding material  24  in the present embodiment contains electrically conductive fillers having high thermal conductivity. For example, at least one of metal, Al 2 O 3 , ZrO 2 , MgO, and AlN is used as the material of the electrically conductive fillers contained in the bonding member  24 . Using the bonding member  24  containing the electrically conductive fillers allows heat of the ceramic phosphor  22  to be efficiently transferred toward the substrate  21 . 
     The substrate  21  is in contact with a region of the ceramic phosphor  22  that is the region different from the excitation light incident region. The substrate  21  therefore also functions as a member that dissipates the heat generated in the ceramic phosphor  22 . The substrate  21  except for the through hole  210  is in contact with the ceramic phosphor  22 . 
     The ceramic phosphor  22  in the present embodiment outputs the white illumination light WL, which is the combination of blue light (transmitted light) E 1 , which is a portion of the blue excitation light E outputted from the excitation light source  10  that is the portion  22   b  that has not been converted in terms of wavelength but directly exits via the second surface, and the yellow fluorescence Y generated by the ceramic phosphor  22  through the wavelength conversion of the excitation light E. 
     The white balance of the illumination light WL emitted from the ceramic phosphor  22  is determined by the ratio between the amount of the blue light E 1  and the amount of the fluorescence Y. In the present specification, the ratio between the two types of light is hereinafter referred to as a BY ratio. The condition under which a practical white balance of the illumination light WL used in the projector is that the BY ratio ranges from 30% to 50%. 
     It has been ascertained that the BY ratio is affected by the thickness of the ceramic phosphor  22 . For example, relatively reducing the thickness of the ceramic phosphor  22  allows an increase in the amount of the blue light E 1  passing through the ceramic phosphor  22 . The thickness of the ceramic phosphor  22  smaller than 40 μm, however, makes it difficult to manufacture the ceramic phosphor  22 . It is therefore desirable to set the lower limit of the thickness of the ceramic phosphor  22  at 40 μm from a manufacturing viewpoint. 
     On the other hand, relatively increasing the thickness of the ceramic phosphor  22  causes a decrease in the amount of the blue light E 1  passing through the ceramic phosphor  22 . Furthermore, the thickness of the ceramic phosphor  22  greater than 150 μm tends to increase the amount of the fluorescence Y reabsorbed by the ceramic phosphor  22 , undesirably resulting in a decrease in the amount of the fluorescence Y extractable via the second surface  22   b . It is therefore desirable to set the upper limit of the thickness of the ceramic phosphor  22  at 150 μm from a viewpoint of efficiency of utilization of the fluorescence Y. 
     Based on the viewpoints described above, in the light source apparatus  2  according to the present embodiment, the thickness of the ceramic phosphor  22  is set at a value greater than or equal to 40 μm but smaller than or equal to 150 μm. 
     In general, the width of the fluorescence emission region of a phosphor is wider than the width of the excitation light incident region of the phosphor. This is because the excitation light having entered the phosphor is diffused and propagates beyond the excitation light incident region, resulting in an increase in the width of the fluorescence emission region or what is called fluorescence bleeding. 
       FIG. 4  shows the state in which the ceramic phosphor  22  emits the fluorescence. 
     In the light source apparatus  2  according to the present embodiment, an irradiated region SP, which is irradiated with the excitation light E, is formed on the exposed portion  211  of the ceramic phosphor  22 . In the ceramic phosphor  22  in the present embodiment, a width W 2  of the light emission region of the exposed portion  211  that is the region from which the fluorescence Y is emitted is greater than a width W 1  of the irradiated region SP due to the fluorescence bleeding, as shown in  FIG. 4 . The difference between the width W 2  of the light emission region, from which the fluorescence Y is emitted, and the width W 1  of the irradiated region SP corresponds to a spread width W 3  over which the fluorescence Y spreads due to the bleeding, as shown in  FIG. 4 . 
     Consider now a case where the light emission region of the exposed portion  211 , which is the region from which the fluorescence Y is emitted, reaches the substrate  21  due to the bleeding. The state in which the light emission region, from which the fluorescence Y is emitted, reaches the substrate  21  is the same as the state in which the excitation light E reaches the substrate  21 . Therefore, when the light emission region, from which the fluorescence Y is emitted, reaches the substrate  21 , part of the excitation light E is directly incident on and absorbed by the substrate  21 , resulting in loss of the excitation light E. 
     In contrast, in the light source apparatus  2  according to the present embodiment, the distance in the exposed portion  211  from the irradiated region SP, which is irradiated with the excitation light E, to the substrate  21  is greater than a predetermined value, so that the excitation light E having entered the ceramic phosphor  22  is not directly incident on the substrate  21 . 
       FIG. 5  shows the relationship between the spread width, over which fluorescence spreads due to the bleeding, and the BY ratio. The horizontal axis of  FIG. 5  represents the spread width W 3  (in mm), over which the fluorescence spreads due to the bleeding, shown in  FIG. 4 . The vertical axis of  FIG. 5  corresponds to the BY ratio (in %). The graphs in  FIG. 5  show the relationship between the fluorescence spread width and the BY ratio in ceramic phosphors  22  having different thicknesses. 
       FIG. 5  shows that the bleeding width, over which the fluorescence Y bleeds, increases as the thickness of the ceramic phosphor  22  increases from 40 to 150 μm. 
     For example, using the ceramic phosphor  22  having the lower limit thickness (40 μm) demonstrates that the spread width, over which the fluorescence Y spreads due to the bleeding, is about 0.15 mm to achieve a desired white balance (BY ratio from 30% to 50%) of the illumination light WL emitted from the ceramic phosphor  22 . 
     On the other hand, using the ceramic phosphor  22  having the upper limit thickness (150 μm) demonstrates that the spread width, over which the fluorescence Y spreads due to the bleeding, is about 0.31 mm to achieve a desired white balance (BY ratio of 30%) of the illumination light WL emitted from the ceramic phosphor  22 . Using the ceramic phosphor  22  having the upper limit thickness demonstrates that the spread width, over which the fluorescence Y spreads, is about 0.34 mm to achieve a desired white balance (BY ratio of 50%) of the illumination light WL. 
     In the light source apparatus  2  according to the present embodiment, to achieve the desired white balance (BY ratio from 30% to 50%) by using any of the ceramic phosphors  22  having thicknesses ranging from 40 to 150 μm, the substrate  21  is separated by a value greater than the maximum of the spread width (0.34 mm), over which the fluorescence Y spreads. 
     In the light source apparatus  2  according to the present embodiment, the distance D in the exposed portion  211  from the irradiated region SP, which is irradiated with the excitation light E, to the through hole  210  in the substrate  21  is set at 0.34 mm or greater. The configuration described above prevents the excitation light E from reaching the substrate  21  even when the ceramic phosphor  22  having the thickness of 150 μm, which maximizes the spread width, over which the fluorescence Y spreads due to the bleeding, to achieve the white balance corresponding to the BY ratio of 50%. The distance D is defined as the distance between the irradiated region SP and the inner surface of the through hole  210  in the direction along the support surface  21   a  of the substrate  21 . 
     Effects of First Embodiment 
     The light source apparatus  2  according to the present embodiment includes the excitation light source  10 , which outputs the excitation light E, the ceramic phosphor  22  having the first surface  22   a , and the substrate  21 , which supports the first surface  22   a  of the ceramic phosphor  22 . The excitation light E outputted from the excitation light source  10  is incident on the exposed portion  211  of the first surface  22   a , which is the portion exposed via the substrate  21 , and the distance D in the exposed portion  211  from the irradiated region SP, which is irradiated with the excitation light E, to the substrate  21  is 0.34 mm or greater. 
     In the light source apparatus  2  according to the present embodiment, since the excitation light E is directly incident on the ceramic phosphor  22  via the exposed portion  211 , the excitation light E can be used more efficiently than in a configuration in which the excitation light is incident on the phosphor via a light transmissive substrate. 
     The light source apparatus  2  according to the present embodiment, in which the distance D from the irradiated region SP, which is irradiated with the excitation light E, to the substrate  21  is 0.34 mm or greater in the exposed portion  211 , suppresses a situation in which the excitation light E, which may be irregularly reflected in the ceramic phosphor  22  and may cause the bleeding of the fluorescence Y, is directly incident on the substrate  21 . The amount of the excitation light E absorbed by the substrate  21  is thus suppressed, whereby the efficiency of the conversion into the fluorescence Y can be improved by improvement in the efficiency of the utilization of the excitation light E. 
     In the light source apparatus  2  according to the present embodiment, it is desirable that the thickness of the ceramic phosphor  22  is greater than or equal to 40 μm but smaller than or equal to 150 μm, that the ceramic phosphor  22  has the second surface  22   b  different from the first surface  22   a , that part of the excitation light E with which the exposed portion  211  of the first surface  22   a  is irradiated is converted in terms of wavelength to generate the fluorescence Y and the fluorescence Y exits via the second surface  22   b , that the blue light E 1 , which is the other part of the excitation light E, exits via the second surface  22   b , and that the BY ratio between blue light E 1  and fluorescence Y ranges from 30% to 50%. 
     The illumination light WL having a proper white balance can thus be generated by setting the BY ratio at a value ranging from 30% to 50%. Furthermore, the ceramic phosphor  22  can be readily manufactured by setting the thickness of the ceramic phosphor  22  at a value greater than or equal to 40 μm but smaller than or equal to 150 μm. 
     In the light source apparatus  2  according to the present embodiment, the substrate  21  is formed of a non-light-transmissive member having thermal conductivity higher than that of the ceramic phosphor  22 . 
     According to the configuration described above, since the substrate  21  is formed of a non-light-transmissive member, loss of the excitation light E due to leakage thereof into the substrate  21  can be suppressed. Furthermore, the heat of the ceramic phosphor  22  can be dissipated via the substrate  21 . 
     In the light source apparatus  2  according to the present embodiment, the exposed portion  211  of the ceramic phosphor  22  is exposed via the through hole  210  formed in the substrate  21 . 
     According to the configuration described above, the exposed portion  211  can be readily configured, whereby the configuration of the light source apparatus itself can be downsized. 
     The light source apparatus  2  according to the present embodiment further includes the dichroic layer  23 , which is provided at the first surface  22   a  of the ceramic phosphor  22 , transmits the excitation light E, and reflects the fluorescence Y. 
     According to the configuration described above, the dichroic layer  23  provided at the first surface  22   a  prevents the fluorescence Y generated in the ceramic phosphor  22  from exiting out thereof via the first surface  22   a . The fluorescence Y generated in the ceramic phosphor  22  can thus be efficiently extracted from the ceramic phosphor  22 . 
     The projector  1  according to the present embodiment includes the light source apparatus  2 , the light modulators  4 R,  4 G, and  4 B, which modulate the light outputted from the light source apparatus  2  in accordance with image information to form image light, and the projection optical apparatus  6 , which projects the image light. 
     In the projector  1  according to the present embodiment, the image light is generated by using bright illumination light WL generated by the light source apparatus  2  described above, whereby the projector  1  can display high-quality images. 
     Second Embodiment 
     A second embodiment of the present disclosure will be described below with reference to  FIG. 6 . 
     The schematic configuration of the projector according to the second embodiment is the same as that in the first embodiment, but the configuration of the wavelength converter in the light source apparatus differs from that in the first embodiment. The configuration of the wavelength converter will therefore be described below, and the other configurations will not be described. 
       FIG. 6  is a cross-sectional view showing the configurations of key parts of the wavelength converter in the present embodiment. A wavelength converter  120  in the present embodiment includes the substrate  21 , a ceramic phosphor  122 , the dichroic layer  23 , and the bonding member  24 , as shown in  FIG. 6 . 
     The ceramic phosphor  122  has a first surface  122   a  and a second surface  122   b . The first surface  122   a  is the surface on which the excitation light E outputted from the excitation light source  10  is incident. The second surface  122   b  is the surface via which the fluorescence Y exits. The ceramic phosphor  122  has a recess  123  formed at the second surface  122   b.    
     In the present embodiment, the ceramic phosphor  122  has a first region A 1  and a second region A 2 . The first region A 1  is a region which contains the irradiated region SP, which is irradiated with the excitation light E, and where the recess  123  described above is provided. The second region A 2  is a region that differs from the first region A 1  and surrounds the first region A 1 . The second region A 2  is a region shifted toward the substrate  21  (outward) from a fluorescence exiting region A 3 , from which the fluorescence Y exits, in a plan view viewed from the side facing the second surface  122   b . That is, the fluorescence Y does not exit from the second region A 2 . 
     In the present embodiment, the first region A 1 , which is provided with the recess  123  as described above, is thinner than the second region A 2 . The thicknesses of the first region A 1  and the second region A 2  are each greater than or equal to 40 μm but smaller than or equal to 150 μm. 
     In the ceramic phosphor  122 , a boundary BL between the first region A 1  and the second region A 2  is located between the irradiated region SP, which is irradiated with the excitation light E, and the substrate  21 , so the first region A 1 , which is relatively thin, is not disposed on the substrate  21 . In the thickness direction of the substrate  21  (vertical direction in  FIG. 6 ), part of the second region A 2  overlaps with the substrate  21 . That is, the second region A 2  is bonded to the substrate  21  via the bonding member  24 . 
     Also in the wavelength converter  120  in the present embodiment, the distance D, in the exposed portion  211  from the irradiated region SP, which is irradiated with the excitation light E, to the substrate  21  is set at 0.34 mm or greater. 
     Effects of Second Embodiment 
     In the wavelength converter  120  in the present embodiment, the thickness of the first region A 1 , on which the excitation light E is incident, is relatively thin, whereby the situation in which the fluorescence Y is guided in the ceramic phosphor  122  can be suppressed, so that an increase in the area of the fluorescence exiting region A 3  can be suppressed. An increase in the etendue of the fluorescence Y can therefore be suppressed. Furthermore, since the second region A 2 , which is located outside the fluorescence exiting region A 3  and bonded to the substrate  21 , is relatively thicker, the thermal resistance of the path along which the heat generated in the first region A 1  is dissipated to the substrate  21  can be reduced. The heat dissipation capability of the ceramic phosphor  122  can thus be improved, whereby the efficiency of the conversion into the fluorescence Y can be improved and bright fluorescence Y can be generated. 
     Furthermore, in the wavelength converter  120  in the present embodiment, the second region A 2 , which is relatively thick, is bonded to the substrate  21 , so that the shear strength of the ceramic phosphor  122  can be improved, whereby damage to the ceramic phosphor  122  can be suppressed. 
     Therefore, in the light source apparatus including the wavelength converter  120  according to the present embodiment, the amount of excitation light E absorbed by the substrate  21  is suppressed so that the excitation light E is efficiently utilized, whereby the efficiency of the conversion into the fluorescence Y is improved, and bright illumination light WL can therefore be generated. 
     Third Embodiment 
     A third embodiment of the present disclosure will be described below with reference to  FIG. 7 . 
     The schematic configuration of the projector according to the third embodiment is the same as that in the first embodiment, but the configuration of the wavelength converter in the light source apparatus differs from that in the first embodiment. The configuration of the wavelength converter will therefore be described below, and the other configurations will not be described. 
       FIG. 7  is a cross-sectional view showing the configurations of key parts of the wavelength converter in the present embodiment. A wavelength converter  220  in the present embodiment includes a substrate  121 , a ceramic phosphor  222 , the dichroic layer  23 , and a motor  125 , as shown in  FIG. 7 . The wavelength converter  220  in the present embodiment is a rotary-wheel-type wavelength converter so configured that the position where the excitation light E enters the ceramic phosphor  222  changes over time. 
     The substrate  121  is made of a metal material that excels in heat dissipation, such as aluminum or copper. The substrate  121  is a rotating substrate rotatable around a predetermined axis of rotation O. The axis of rotation O passes through the center of the substrate  121 . The motor  125  rotates the disc-shaped substrate  121  around the axis of rotation O. 
     The ceramic phosphor  222  in the present embodiment is formed in an annular shape around the axis of rotation O. The ceramic phosphor  222  is formed by shaping the ceramic phosphor  22  in the first embodiment into a ring. The dichroic layer  23  is provided between the substrate  121  and the ceramic phosphor  222 . The substrate  121  dissipates the heat generated by the ceramic phosphor  222 . 
     The dichroic layer  23  is provided at a first surface  222   a  of the ceramic phosphor  222 . In the annular ceramic phosphor  222 , the first surface  222   a  has a radially inner end section  222   a   1  fixed to the substrate  21  via the bonding member  24 . That is, in the plan view viewed in the direction along the axis of rotation O, the ceramic phosphor  222  is provided so as to protrude outward beyond the substrate  121  in the radial direction. The excitation light E is incident on an overhanging portion (exposed portion)  1220  of the ceramic phosphor  222 , which is the portion extending outward beyond the substrate  121  in the radial direction. In the present embodiment, the substrate  21  is in contact with a region of the ceramic phosphor  222  that is the region different from the region on which the excitation light E is incident and dissipates the heat generated by the ceramic phosphor  322 . 
     In the wavelength converter  220  in the present embodiment, the excitation light E is incident on the overhanging portion  1220  of the rotating ceramic phosphor  222 . When the excitation light E enters the ceramic phosphor  222 , heat is generated in the overhanging portion  1220  of the ceramic phosphor  222 . In the present embodiment, in which the motor  125  rotates the ceramic phosphor  222 , the position where the excitation light E is incident on the overhanging portion  1220  of the ceramic phosphor  222  is moved over time. The configuration described above prevents degradation of the ceramic phosphor  222  that occurs when only part of the ceramic phosphor  222  is locally heated by constant radiation of the excitation light E to the same position on the overhanging portion  1220  of the ceramic phosphor  222 . 
     In the present embodiment, in which the ceramic phosphor  222  is rotated, the heat dissipation capability of the ceramic phosphor  222  can be further increased. 
     Also in the wavelength converter  220  in the present embodiment, the substrate  121  in contact with the ceramic phosphor  222  is formed of a non-light-transmissive member. Therefore, in the wavelength converter  220 , the fluorescence Y generated by the ceramic phosphor  222  is efficiently extracted out thereof without leaking out into the substrate  121 . 
     Also in the wavelength converter  220  in the present embodiment, the distance D in the overhanging portion  1220  from the irradiated region SP, which is irradiated with the excitation light E, to the substrate  121  is set at 0.34 mm or greater. 
     Effects of Third Embodiment 
     In the light source apparatus including the wavelength converter  220  according to the present embodiment, which uses the rotating wavelength converter, the amount of excitation light E absorbed by the substrate  121  can be suppressed so that the excitation light E can be efficiently utilized, as in the first embodiment. Furthermore, the improvement in the heat dissipation capability of the ceramic phosphor  222  can suppress a decrease in the amount of fluorescence due to a decrease in the wavelength conversion efficiency of the ceramic phosphor  222 . 
     Fourth Embodiment 
     A fourth embodiment of the present disclosure will be described below with reference to  FIG. 8 . 
     The schematic configuration of the projector according to the fourth embodiment is the same as that in the third embodiment, but the configuration of the wavelength converter in the light source apparatus differs from that in the third embodiment. Specifically, the wavelength converter in the present embodiment has a structure that is the combination of the wavelength converter in the third embodiment and the wavelength converter in the second embodiment. The configuration of the wavelength converter will be described below, and the other configurations will not be described. 
       FIG. 8  is a cross-sectional view showing the configurations of key parts of the wavelength converter in the present embodiment. 
     A wavelength converter  320  in the present embodiment includes the substrate  121 , a ceramic phosphor  322 , the dichroic layer  23 , and the motor  125 , as shown in  FIG. 8 . The wavelength converter  320  in the present embodiment is a rotary-wheel-type wavelength converter so configured that the position where the excitation light E enters the ceramic phosphor  322  changes over time. 
     The ceramic phosphor  322  has a first surface  322   a , on which the excitation light E outputted from the excitation light source  10  is incident, and a second surface  322   b , via which the fluorescence Y exits. The ceramic phosphor  322  has a recess  323  formed in a predetermined region of the second surface  322   b.    
     The ceramic phosphor  322  in the present embodiment has a first region A 11  and a second region A 12 . The first region A 11  is a region which contains the irradiated region SP, which is irradiated with the excitation light E, and where the recess  323  described above is provided. The second region A 12  is a region that differs from the first region A 11  and is a ring-shaped region shifted inward from the first region A 11  in the radial direction. The first region A 11  is thinner than the second region A 12 . In the present embodiment, an overhanging portion  1320  of the ceramic phosphor  322  is formed of the first region A 11  and part of the second region A 12 . In the present embodiment, the first region A 11 , which is provided with the recess  323  as described above, is thinner than the second region A 12 . The thicknesses of the first region A 11  and the second region A 12  are each greater than or equal to 40 μm but smaller than or equal to 150 μm. 
     In the thickness direction of the substrate  121  (vertical direction in  FIG. 8 ), part of the second region A 12  overlaps with the substrate  121 . That is, the second region A 12  is bonded to the substrate  121  via the bonding member  24 . In the ceramic phosphor  322 , a boundary BL between the first region A 11  and the second region A 12  is located between the irradiated region SP, which is irradiated with the excitation light E, and the substrate  121 . Also in the wavelength converter  320  in the present embodiment, the distance D in the overhanging portion  1220  from the irradiated region SP, which is irradiated with the excitation light E, to the substrate  121  is set at 0.34 mm or greater. 
     Effects of Fourth Embodiment 
     In the wavelength converter  320  in the present embodiment, which uses the rotating wavelength converter, the improvement in the heat dissipation capability of the ceramic phosphor  322  can improve the fluorescence conversion efficiency to generate bright fluorescence Y, as in the second embodiment. Furthermore, bonding the ceramic phosphor  322  to the substrate  121  in the second region A 12  can suppress damage to the ceramic phosphor  322 . Moreover, the improvement in the heat dissipation capability of the ceramic phosphor  322  improves the efficiency of the conversion into the fluorescence Y, whereby brighter illumination light WL can be generated. 
     The technical scope of the present disclosure is not limited to the embodiments described above, and a variety of changes can be made thereto to the extent that the changes do not depart from the substance of the present disclosure. 
     For example, the aforementioned embodiments have been described with reference to the case where the entire substrates  21  and  121  are each formed of a non-light-transmissive member (made of metal) by way of example. It is, however, noted that light leakage of the fluorescence Y can be avoided as long as at least a portion of each of the substrates  21  and  121  that is the portion in contact with any of the ceramic phosphors  22 ,  122 ,  222 , and  322  is formed of a non-light-transmissive member. The substrates  21  and  121  may therefore be each formed of a light-transmissive member except for the portion in contact with any of the ceramic phosphors  22 ,  122 ,  222 , and  322 . 
     For example, in the ceramic phosphors  22 ,  122 ,  222 , and  322  in the embodiments described above, the phosphor phase  25  contains an oxide phosphor, and the matrix phase  26  contains a metal oxide. In place of the configuration described above, the phosphor phase  25  may contain a nitride phosphor, and the matrix phase  26  may contain a metal nitride. The nitride phosphor can be a sialon phosphor made, for example, of α-SiAlON or β-SiAlON. The metal nitride can, for example, be AlN. The thermal conductivity of AlN is about 255 W/m·K. When the phosphor phase  25  contains a nitride phosphor, and the matrix phase  26  contains a metal oxide, the ceramic phosphor can be stably manufactured, for example, without unnecessary oxidation reactions in each of the phases. 
     In addition to the above, the specific descriptions of the shape, the number, the arrangement, the material, the manufacturing method, and other factors of the components of the light source apparatus and the projector are not limited to those in the embodiments described above and can be changed as appropriate. The above embodiments have been described with reference to the case where the light source apparatus according to the present disclosure is incorporated in a projector using liquid crystal light valves, but not necessarily. The light source apparatus according to the present disclosure may be incorporated in a projector using a digital micromirror device as each of the light modulators. 
     The aforementioned embodiments have been described with reference to the case where the light source apparatus according to the present disclosure is incorporated in a projector, but not necessarily. The light source apparatus according to the present disclosure may be used as a lighting apparatus, a headlight of an automobile, and other components. 
     A light source apparatus according to an aspect of the present disclosure may have the configuration below. 
     A light source apparatus according to an aspect of the present disclosure includes an excitation light source that outputs excitation light, a ceramic phosphor that has a first surface and a second surface, converts in terms of wavelength part of the excitation light outputted from the excitation light source and incident via the first surface to generate fluorescence, and causes the fluorescence to exit via the second surface, and a substrate that supports the first surface of the ceramic phosphor. The excitation light outputted from the excitation light source is incident on an exposed portion of the first surface of the ceramic phosphor that is the portion exposed via the substrate. The distance in the exposed portion from an irradiated region irradiated with the excitation light to the substrate is 0.34 mm or greater. 
     In the light source apparatus according to the aspect of the present disclosure, the thickness of the ceramic phosphor may be greater than or equal to 40 μm but smaller than or equal to 150 μm. The ceramic phosphor may cause the other part of the excitation light to exit as transmitted light along with the fluorescence via the second surface. The ratio between the amount of the transmitted light and the amount of the fluorescence emitted from the ceramic phosphor may range from 30% to 50%. 
     In the light source apparatus according to the aspect of the present disclosure, the ceramic phosphor may have a first region and a second region. The first region may be a region containing the excitation light irradiated region, and the second region may be a region shifted toward the substrate from a fluorescence exiting region from which the fluorescence exits. The first region may be thinner than the second region. The substrate may have thermal conductivity higher than that of the ceramic phosphor. In the thickness direction of the substrate, part of the second region may overlap with the substrate. 
     In the light source apparatus according to the aspect of the present disclosure, the boundary between the first region and the second region of the ceramic phosphor may be located between the excitation light irradiated region and the substrate. 
     In the light source apparatus according to the aspect of the present disclosure, the exposed portion of the ceramic phosphor may be exposed via an opening formed in the substrate. 
     The light source apparatus according to the aspect of the present disclosure may further include an optical layer that is provided at the first surface of the ceramic phosphor, transmits the excitation light, and reflects the fluorescence. 
     In the light source apparatus according to the aspect of the present disclosure, the substrate may be a rotating substrate that rotates around a predetermined axis of rotation. The ceramic phosphor may be provided so as to protrude outward beyond the substrate in the radial direction of the substrate. A portion of the ceramic phosphor that is the portion protruding beyond the substrate may be the exposed portion. 
     A projector according to another aspect of the present disclosure may have the configuration below. 
     The projector according to the other aspect of the present disclosure includes the light source apparatus according to the aspect of the present disclosure, a light modulator that modulates the light outputted from the light source apparatus in accordance with image information to form image light, and a projection optical apparatus that projects the image light.