Patent Publication Number: US-2023147353-A1

Title: Photoconversion device and illumination system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a National Phase entry based on PCT Application No. PCT/JP2021/013905 filed on Mar. 31, 2021, entitled “LIGHT CONVERSION DEVICE AND LIGHTING SYSTEM”, which claims the benefit of Japanese Patent Application Nos. 2020-063652, 2020-063678, and 2020-064387, filed on Mar. 31, 2020, entitled “PHOTOCONVERSION DEVICE AND ILLUMINATION SYSTEM”. The contents of which are incorporated by reference herein in their entirety. 
    
    
     FIELD 
     The present disclosure relates to a photoconversion device and an illumination system. 
     BACKGROUND 
     Known light source devices convert laser light to fluorescence having a different wavelength using a phosphor and emit the fluorescence in a predetermined direction (e.g., Japanese Unexamined Patent Application Publication Nos. 2012-243617, 2013-12358, and 2011-221502). 
     SUMMARY 
     One or more aspects of the present disclosure are directed to a photoconversion device and an illumination system. 
     In one aspect, a photoconversion device includes a holder, a wavelength converter, and an optical element. The holder holds an output portion that outputs excitation light. The wavelength converter includes an incident surface section including a protruding surface to receive the excitation light from the output portion and emits fluorescence in response to the excitation light incident on the incident surface section. The optical element includes a focal point surrounded by the incident surface section to direct the fluorescence emitted by the wavelength converter in a predetermined direction. 
     In one aspect, a photoconversion device includes a holder, a wavelength converter, and an optical element. The holder holds an output portion that outputs excitation light. The wavelength converter includes an incident surface section including a protruding surface to receive the excitation light from the output portion and emits fluorescence in response to the excitation light incident on the incident surface section. The optical element includes a focusing element that focuses the fluorescence emitted by the wavelength converter onto a focusing plane. The optical element includes a conjugate point having a conjugate relation with a point on the focusing plane. The conjugate point is surrounded by the incident surface section. 
     In one aspect, an illumination system includes a light-emitting module, a first optical transmitter, a relay, a second optical transmitter, and an optical radiation module. The light-emitting module emits excitation light. The first optical transmitter transmits the excitation light from the light-emitting module. The relay includes the photoconversion device according to any one the above aspects. The second optical transmitter transmits the fluorescence from the relay. The optical radiation module radiates the fluorescence transmitted by the second optical transmitter into an external space. The output portion includes an output end of the first optical transmitter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of an example illumination system according to a first embodiment. 
         FIG.  2    is a schematic cross-sectional view of a photoconversion device with a first structure according to the first embodiment. 
         FIG.  3    is a schematic perspective view of a wavelength converter with an example structure. 
         FIG.  4    is a schematic perspective view of a wavelength converter with another example structure. 
         FIG.  5    is a schematic perspective view of a wavelength converter with another example structure. 
         FIG.  6    is a schematic perspective view of a wavelength converter with another example structure. 
         FIG.  7    is a schematic cross-sectional view of a photoconversion device with a second structure according to the first embodiment. 
         FIG.  8    is a schematic cross-sectional view of a photoconversion device with a third structure according to the first embodiment. 
         FIG.  9    is a schematic cross-sectional view of a photoconversion device with a first structure according to a second embodiment. 
         FIG.  10    is a schematic cross-sectional view of a photoconversion device with a second structure according to the second embodiment. 
         FIG.  11    is a schematic diagram of an example illumination system according to a third embodiment. 
         FIG.  12    is a schematic cross-sectional view of a photoconversion device with a first structure according to the third embodiment. 
         FIG.  13    is a schematic cross-sectional view of a photoconversion device with a second structure according to the third embodiment. 
         FIG.  14    is a schematic diagram of an example illumination system according to a fourth embodiment. 
         FIG.  15    is a schematic cross-sectional view of an example photoconversion device according to the fourth embodiment. 
         FIG.  16    is a schematic perspective view of a wavelength converter with an example structure according to a fifth embodiment. 
         FIG.  17    is a schematic cross-sectional view of an example photoconversion device according to the fifth embodiment. 
         FIG.  18    is a schematic cross-sectional view of the photoconversion device according to the fifth embodiment. 
         FIG.  19    is a schematic cross-sectional view of a photoconversion device with a first structure according to a sixth embodiment. 
         FIGS.  20 A and  20 B  are diagrams of example multiple phosphor areas describing example movement of an illuminating area in a wavelength converter. 
         FIG.  21    is a schematic cross-sectional view of a photoconversion device with a second structure according to the sixth embodiment. 
         FIGS.  22 A and  22 B  are diagrams of example multiple phosphor areas describing example movement of an illuminating area in a wavelength converter. 
         FIG.  23    is a schematic cross-sectional view of a photoconversion device with a third structure according to the sixth embodiment. 
         FIGS.  24 A to  24 C  are diagrams of example multiple phosphor areas describing example movement of an illuminating area in a wavelength converter. 
         FIG.  25    is a schematic cross-sectional view of a photoconversion device with a fourth structure according to the sixth embodiment. 
         FIGS.  26 A to  26 C  are diagrams of example multiple phosphor areas describing example movement of an illuminating area in a wavelength converter. 
         FIG.  27    is a schematic cross-sectional view of an example photoconversion device according to a variation. 
         FIG.  28    is a schematic cross-sectional view of a photoconversion device with an example structure according to a seventh embodiment. 
         FIG.  29    is a schematic perspective view of a wavelength converter with an example structure. 
         FIG.  30    is a schematic perspective view of a splitter with an example structure. 
         FIG.  31    is a schematic cross-sectional view of a photoconversion device with an example structure according to an eighth embodiment. 
         FIG.  32    is a schematic cross-sectional view of a photoconversion device with an example structure according to a tenth embodiment. 
         FIG.  33    is a schematic cross-sectional view of a photoconversion device with an example structure including a splitter moved in the positive Z-direction. 
         FIG.  34    is a schematic perspective view of a splitter and a color adjuster drive in an example structure. 
         FIG.  35    is a schematic cross-sectional view of a photoconversion device with an example structure according to an eleventh embodiment. 
         FIG.  36    is a schematic cross-sectional view of a photoconversion device with an example structure including an output portion moved in the negative Z-direction. 
         FIG.  37    is a schematic cross-sectional view of a photoconversion device with an example structure according to a twelfth embodiment. 
         FIG.  38    is a schematic cross-sectional view of a photoconversion device with an example structure according to a thirteenth embodiment. 
         FIG.  39    is a schematic cross-sectional view of an optical radiation module with an example structure according to a fourteenth embodiment. 
         FIG.  40    is a schematic cross-sectional view of a light-emitting module with an example structure according to a fifteenth embodiment. 
         FIG.  41 A  is a schematic cross-sectional view of a photoconversion device with an example structure according to a sixteenth embodiment, and  FIG.  41 B  is a schematic cross-sectional view of the photoconversion device with the example structure according to the sixteenth embodiment describing conversion of excitation light to fluorescence. 
         FIG.  42 A  is a schematic cross-sectional view of a photoconversion device with an example structure according to a seventeenth embodiment, and  FIG.  42 B  is a schematic cross-sectional view of the photoconversion device with the example structure according to the seventeenth embodiment describing conversion of excitation light to fluorescence. 
         FIG.  43 A  is a schematic cross-sectional view of a photoconversion device with an example structure according to an eighteenth embodiment, and  FIG.  43 B  is a schematic cross-sectional view of the photoconversion device with the example structure according to the eighteenth embodiment describing conversion of excitation light to fluorescence. 
         FIG.  44 A  is a schematic cross-sectional view of a heat sink and a wavelength converter in an example structure according to the eighteenth embodiment, and  FIG.  44 B  is a schematic perspective view of the heat sink and the wavelength converter in the example structure according to the eighteenth embodiment. 
         FIG.  45 A  is a schematic cross-sectional view of a photoconversion device with an example structure according to a nineteenth embodiment, and  FIG.  45 B  is a schematic cross-sectional view of the photoconversion device with the example structure according to the nineteenth embodiment describing conversion of excitation light to fluorescence. 
         FIG.  46 A  is a schematic cross-sectional view of a heat sink and a wavelength converter in a first structure according to the nineteenth embodiment, and  FIG.  46 B  is a schematic perspective view of the heat sink and the wavelength converter each in the first structure according to the nineteenth embodiment. 
         FIG.  47 A  is a schematic cross-sectional view of a heat sink and a wavelength converter in a second structure according to the nineteenth embodiment, and  FIG.  47 B  is a schematic perspective view of the heat sink and the wavelength converter in the second structure according to the nineteenth embodiment. 
         FIG.  48    is a schematic cross-sectional view of a heat sink and a wavelength converter in a third structure according to the nineteenth embodiment. 
         FIG.  49 A  is a schematic cross-sectional view of a photoconversion device with an example structure according to a twentieth embodiment, and  FIG.  49 B  is a schematic cross-sectional view of the photoconversion device with the example structure according to the twentieth embodiment describing conversion of excitation light to fluorescence. 
         FIG.  50 A  is a schematic cross-sectional view of a heat sink, a wavelength converter, and a transparent member in a first structure according to the twentieth embodiment, and  FIG.  50 B  is a schematic cross-sectional view of a heat sink, a wavelength converter, and a transparent member in a second structure according to the twentieth embodiment. 
         FIG.  51 A  is a schematic cross-sectional view of a heat sink, a wavelength converter, and a transparent member in a first variation of the twentieth embodiment, and  FIG.  51 B  is a schematic cross-sectional view of a heat sink, a wavelength converter, and a transparent member in a second variation of the twentieth embodiment. 
         FIG.  52 A  is a schematic cross-sectional view of a photoconversion device with an example structure according to a twenty-first embodiment, and  FIG.  52 B  is a schematic cross-sectional view of the photoconversion device with the example structure according to the twenty-first embodiment describing conversion of excitation light to fluorescence. 
         FIG.  53 A  is a schematic cross-sectional view of an optical radiation module with an example structure according to a twenty-second embodiment, and  FIG.  53 B  is a schematic cross-sectional view of the optical radiation module with the example structure according to the twenty-second embodiment describing conversion of excitation light to fluorescence. 
         FIG.  54 A  is a schematic cross-sectional view of a light-emitting module with an example structure according to a twenty-third embodiment, and FIG, and  54 B is a schematic cross-sectional view of the light-emitting module with the example structure according to the twenty-third embodiment describing conversion of excitation light to fluorescence. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A known illumination device converts monochromatic excitation light emitted by a light-emitting element to light with a different wavelength using a phosphor and emits pseudo white light. Such an illumination device includes a phosphor portion containing a phosphor. The phosphor portion includes a flat surface. The phosphor portion has this surface perpendicular to the optical axis. The surface of the phosphor portion receives, for example, excitation light incident along the optical axis. The phosphor portion is excited by the excitation light to emit fluorescence. The fluorescence emitted from the phosphor portion is reflected from a reflector to travel in a predetermined direction. The reflector may include, for example, a reflective surface along an imaginary ellipsoid. The phosphor portion is located at a first focal point of the reflector. This causes the excitation light to enter the phosphor portion near the first focal point. The phosphor portion thus emits fluorescence near the first focal point. The reflector can direct the fluorescence emitted near the first focal point to be focused near a second focal point with high directivity. 
     However, with the excitation light entering the phosphor portion near the first focal point alone, an illuminating area to receive the excitation light on the surface of the phosphor portion can have a smaller area size. As the area size of the illuminating area is smaller, the phosphor portion emits fluorescence with lower intensity. The light intensity of fluorescence is thus compromised by increased directivity. 
     The inventors of the present disclosure thus have developed a technique for allowing emission of fluorescence with high directivity and with high light intensity from a photoconversion device and an illumination system including the photoconversion device. 
     Embodiments of the present disclosure will now be described with reference to the drawings. Throughout the drawings, the same reference numerals denote the same or similar components and functions, and such components and the functions will not be described repeatedly. The drawings are schematic. 
     1-1 First Embodiment 
     1-1-1 Illumination System 
     As illustrated in  FIG.  1   , an illumination system  100  according to a first embodiment includes, for example, a light-emitting module  1 , a first optical transmission fiber  2  as a first optical transmitter, a relay  3 , a second optical transmission fiber  4  as a second optical transmitter, and an optical radiation module  5 . 
     The light-emitting module  1  can emit, for example, excitation light P 0 . The light-emitting module  1  includes a light-emitting element  10 . The light-emitting element  10  includes, for example, a laser element such as a laser diode (LD), or an element such as a light-emitting diode (LED), a vertical-cavity surface-emitting laser (VCSEL), or a superluminescent diode (SLD). The excitation light P 0  emitted by the light-emitting element  10  is monochromatic light, such as violet, blue-violet, or blue light. The light-emitting element  10  may be, for example, a gallium nitride (GaN) semiconductor laser that emits violet laser light with 405 nanometers (nm). In the light-emitting module  1 , for example, the excitation light P 0  emitted by the light-emitting element  10  is directed to be focused at one end  2   e   1  (also referred to as a first input end) of the first optical transmission fiber  2  by an optical system for focusing light. The light-emitting module  1  includes, for example, the housing  1   b  accommodating various components. 
     The first optical transmission fiber  2  can transmit, for example, the excitation light P 0  from the light-emitting module  1 . The first optical transmission fiber  2  extends, for example, from the light-emitting module  1  to the relay  3 . More specifically, the first optical transmission fiber  2  includes the first input end  2   e   1  in the longitudinal direction located inside the light-emitting module  1  and another end  2   e   2  (also referred to as a first output end) opposite to the first input end  2   e   1  in the longitudinal direction located inside the relay  3 . Thus, the first optical transmission fiber  2  provides, for example, an optical transmission path for transmitting the excitation light P 0  from the light-emitting module  1  to the relay  3 . The first optical transmission fiber  2  may be, for example, an optical fiber. The optical fiber includes, for example, a core and a cladding. The cladding surrounds the core and has a lower refractive index of light than the core. In this case, for example, the first optical transmission fiber  2  can transmit the excitation light P 0  in the longitudinal direction in the core. The first optical transmission fiber  2  has, in the longitudinal direction, a length of, for example, several tens of centimeters (cm) to several tens of meters (m). 
     The relay  3  includes, for example, a photoconversion device  30 . The photoconversion device  30  can, for example, receive the excitation light P 0  transmitted by the first optical transmission fiber  2  and emit fluorescence W 0 . In this example, the photoconversion device  30  receives the excitation light P 0  output through the first output end  2   e   2  of the first optical transmission fiber  2 . The first output end  2   e   2  serves as an output portion. The fluorescence W 0  emitted from the photoconversion device  30  in response to the excitation light P 0  includes, for example, light with a wavelength different from the excitation light P 0 , and more specifically, light with a wavelength longer than the excitation light P 0 . More specifically, the fluorescence W 0  includes, for example, red (R) fluorescence, green (G) fluorescence, and blue (B) fluorescence. The photoconversion device  30  can thus emit, for example, the fluorescence W 0  as pseudo white light in response to the monochromatic excitation light P 0 . The relay  3  includes, for example, a housing  3   b  accommodating various components. The housing  3   b  may include, for example, fins for dissipating, to the outside, heat generated by the photoconversion device  30  in response to received excitation light P 0 . 
     The second optical transmission fiber  4  can transmit, for example, the fluorescence W 0  from the relay  3 . The second optical transmission fiber  4  extends, for example, from the relay  3  to the optical radiation module  5 . More specifically, the second optical transmission fiber  4  includes one end  4   e   1  in the longitudinal direction (also referred to as a second input end) located inside the relay  3 . The second optical transmission fiber  4  includes an end  4   e   2  opposite to the second input end  4   e   1  in the longitudinal direction (also referred to as a second output end) located inside the optical radiation module  5 . Thus, the second optical transmission fiber  4  provides, for example, an optical transmission path for transmitting the fluorescence W 0  from the relay  3  to the optical radiation module  5 . The photoconversion device  30  included in the relay  3  has, for example, the surface onto which the fluorescence W 0  is focused (also referred to as a focusing plane) at the second input end  4   e   1  of the second optical transmission fiber  4 . The second optical transmission fiber  4  may be, for example, an optical fiber. The same or similar optical fiber as for the first optical transmission fiber  2  may be used. 
     The optical radiation module  5  can radiate, for example, the fluorescence W 0  transmitted by the second optical transmission fiber  4  into a space  200  outside the illumination system  100  (also referred to as an external space). The optical radiation module  5  illuminates an intended area in the external space  200  with the fluorescence W 0  as illumination light I 0  through, for example, a lens or a diffuser. The optical radiation module  5  includes, for example, a housing  5   b  accommodating various components. 
     In the illumination system  100  with the above structure, for example, the photoconversion device  30  emits fluorescence W 0  in response to the excitation light P 0  transmitted by the first optical transmission fiber  2  from the light-emitting module  1 . This structure can, for example, shorten the distance over which the fluorescence W 0  is transmitted by the optical transmission fiber. The structure thus reduces light loss (also referred to as optical transmission loss) that may occur when, for example, the fluorescence W 0  travels through the optical transmission fiber in a direction inclined at various angles to the longitudinal direction of the optical transmission fiber and is partly scattered during transmission. Thus, the illumination system  100  can radiate, for example, fluorescence W 0  with higher light intensity in response to the excitation light P 0 . In this example, the optical radiation module  5  does not include the photoconversion device  30 . The optical radiation module  5  is, for example, less likely to undergo temperature increase and is easily miniaturized. The structure thus allows, for example, miniaturization of the optical radiation module  5  that radiates the illumination light I 0  into the external space  200  of the illumination system  100  while increasing the light intensity of the fluorescence W 0  emitted from the illumination system  100  in response to the excitation light P 0 . 
     1-1-2. Photoconversion Device 
       FIG.  2    is a schematic diagram of the photoconversion device  30  with an example structure. In  FIG.  2   , the housing  3   b  is not illustrated. The housing may not be illustrated in other drawings referred to below. In the drawings referred to below, the XYZ coordinate system is illustrated as appropriate. One direction along the X-axis may also referred to as the positive X-direction, and the opposite direction may be referred to as the negative X-direction. The same applies to the directions along the Y-axis and the Z-axis. In the XYZ coordinate system, the direction from the first output end  2   e   2  of the first optical transmission fiber  2  as an output portion or from an output portion  10   f  of the light-emitting element  10  toward a wavelength converter  132  is the negative X-direction. A direction perpendicular to the positive X-direction is referred to as the positive Y-direction. Also, the direction perpendicular to both the positive X-direction and the positive Y-direction is referred to as the positive Z-direction. 
     As illustrated in  FIG.  2   , the photoconversion device  30  includes, for example, a holder  131 , the wavelength converter  132 , and an optical element  133 . These components of the photoconversion device  30  are fixed to the housing  3   b  of the relay  3  either directly or indirectly with, for example, another member. An optical axis AX 1  is used to describe the positional relationship between the components. The optical axis AX 1  is, for example, an optical axis of the optical element  133 . In the example of  FIG.  2   , the optical axis AX 1  extends in the X-direction. 
     The holder  131  holds the first output end  2   e   2  that serves as an output portion. In the example of  FIG.  2   , the holder  131  holds the first output end  2   e   2  to cause the first output end  2   e   2  to be located on the optical axis AX 1  and cause excitation light P 0  to be emitted in the negative X-direction through the first output end  2   e   2 . The holder  131  includes, for example, a cylindrical portion through which the first output end  2   e   2  of the first optical transmission fiber  2  is placed. The holder  131  may, for example, hold or be bonded to the outer periphery of the cylindrical portion. 
     The wavelength converter  132  can emit, for example, fluorescence W 0  in response to the excitation light P 0  output through the first output end  2   e   2  as an output portion. The wavelength converter  132  includes a phosphor portion  1321 . The phosphor portion  1321  includes a phosphor. The phosphor can emit fluorescence W 0  in response to the excitation light P 0 . The fluorescence W 0  has, for example, a longer wavelength than the excitation light P 0 . The phosphor portion  1321  may be, for example, a pellet-like phosphor portion (also referred to as a phosphor pellet) including a transparent sealant such as resin or glass containing numerous particles of phosphors that each emit fluorescence in response to the excitation light P 0 . numerous particles of phosphors may be, for example, particles of multiple types of phosphors that each emit fluorescence in response to the excitation light P 0 . The multiple types of phosphors may include, for example, a phosphor that emits fluorescence of a first color in response to the excitation light P 0  and a phosphor that emits fluorescence of a second color different from the first color in response to the excitation light P 0 . More specifically, the multiple types of phosphors include, for example, a phosphor that emits red (R) fluorescence in response to the excitation light P 0  (also referred to as a red phosphor), a phosphor that emits green (G) fluorescence in response to the excitation light P 0  (also referred to as a green phosphor), a phosphor that emits blue (B) fluorescence in response to the excitation light P 0  (also referred to as a blue phosphor). In another example, the multiple types of phosphors include, for example, a phosphor that emits blue-green fluorescence in response to the excitation light P 0  (also referred to as a blue-green phosphor), a phosphor that emits yellow fluorescence in response to the excitation light P 0  (also referred to as a yellow phosphor), and other various phosphors that each emit fluorescence with a different wavelength in response to the excitation light P 0 . 
     The red phosphor is, for example, a phosphor with a peak wavelength of fluorescence in a range of about 620 to 750 nm emitted in response to the excitation light P 0 . The red phosphor material is, for example, CaAlSiN 3 :Eu, Y 3 O 3 S:Eu, Y 3 O 3 :Eu, SrCaClAlSiN 3 :Eu 2+ , CaAlSiN 3 :Eu, or CaAlSi(ON) 3 :Eu. The green phosphor is, for example, a phosphor with a peak wavelength of fluorescence in a range of about 495 to 570 nm emitted in response to the excitation light P 0 . The green phosphor material is, for example, β-SiAlON:Eu, SrSi 3 (O, Cl) 3 N 3 :Eu, (Sr, Ba, Mg) 2 SiO 4 :Eu 2+ , ZnS:Cu, Al, or Zn 3 SiO 4 :Mn. The blue phosphor is, for example, a phosphor with a peak wavelength of fluorescence in a range of about 450 to 495 nm emitted in response to the excitation light P 0 . The blue phosphor material is, for example, (BaSr)MgAl 10 O 17 :Eu, BaMgAl 10 O 17 :Eu, (Sr, Ca, Ba) 10 (PO 4 ) 6 Cl 2 :Eu, or (Sr, Ba) 10 (PO 4 ) 6 Cl 3 :Eu. The blue-green phosphor is, for example, a phosphor with a peak wavelength of fluorescence at about 495 nm emitted in response to the excitation light P 0 . The blue-green phosphor material is, for example, Sr 4 Al 14 O 35 :Eu. The yellow phosphor is, for example, a phosphor with a peak wavelength of fluorescence in a range of about 570 to 590 nm emitted in response to the excitation light P 0 . The yellow phosphor material is, for example, SrSi 3 (O, Cl) 3 N 3 :Eu. The ratio of the elements in the parentheses herein may be changed as appropriate without deviating from the molecular formulas. 
     The phosphor portion  1321  in the wavelength converter  132  is, for example, on the optical axis AX 1  in the negative X-direction from the first output end  2   e   2 . The phosphor portion  1321  includes an incident surface section  132   a  protruding (protruding surface) to receive incident excitation light P 0 . The incident surface section  132   a  includes, for example, a protruding surface with its middle portion being in the positive X-direction from its peripheral portion. In other words, the incident surface section  132   a  includes a protruding surface protruding in the positive X-direction. The incident surface section  132   a  may be a single curved surface, may include multiple flat or curved surfaces connected together, or may include flat and curved surfaces connected together. 
       FIG.  3    is a schematic diagram of the phosphor portion  1321  with an example structure. As illustrated in  FIG.  3   , the phosphor portion  1321  may be in the shape of a triangular prism. The phosphor portion  1321  is installed to have one rectangular side surface of the triangular prism (referred to as a surface  132   d ) perpendicular to the optical axis AX 1  and one side of the triangular prism facing the first output end  2   e   2  (specifically, in the positive X-direction). The phosphor portion  1321  has the other two rectangular side surfaces corresponding to the incident surface section  132   a . This incident surface section  132   a  is V-shaped in a ZX cross section including the optical axis AX 1  that is incident on the incident surface section  132   a . The phosphor portion  1321  includes a triangular side surface in the shape of, for example, an isosceles triangle. The triangular prism has each side with a length of, for example, 1 mm or more. 
     The incident surface section  132   a  may include two sides surfaces that are hereafter referred to as an incident surface  132   b  and an incident surface  132   c . The incident surface  132   b  and the incident surface  132   c  are inclined in different directions. For example, the incident surface  132   b  is located in the positive Z-direction from the incident surface  132   c . In the positive X-direction, the incident surface  132   b  is inclined in the negative Z-direction. In the positive X-direction, the incident surface  132   c  is inclined in the positive Z-direction. The incident surface  132   b  has its side edge in the positive X-direction joined to the side edge of the incident surface  132   c  in the positive X-direction. 
     The incident surface section  132   a  includes the protruding surface protruding toward the first output end  2   e   2 . Thus, the phosphor portion  1321  has, for example, the width in the direction perpendicular to the optical axis AX 1  (e.g., in the Z-direction) decreasing monotonically toward the first output end  2   e   2  (specifically, in the positive X-direction). 
     The excitation light P 0  output through the first output end  2   e   2  is incident on the incident surface section  132   a  of the phosphor portion  1321 . More specifically, the excitation light P 0  is incident across both the incident surface  132   b  and the incident surface  132   c . The phosphor portion  1321  receives the excitation light P 0  and emits fluorescence W 0 .  FIG.  2    illustrates beams representing the fluorescence W 0  radiated from a single point on the incident surface  132   b  and beams representing the fluorescence W 0  radiated from a single point on the incident surface  132   c . In an actual operation, phosphors at multiple points in the phosphor portion  1321  receiving the excitation light P 0  each emit fluorescence W 0 . 
     As illustrated in  FIG.  2   , the wavelength converter  132  may further include a substrate  1322 . As illustrated in  FIG.  2   , the substrate  1322  may be, for example, a plate. The substrate  1322  is located to have, for example, a thickness along the optical axis AX 1 . The substrate  1322  is located, for example, opposite to the first output end  2   e   2  from the phosphor portion  1321  (specifically, in the negative X-direction). The substrate  1322  includes a surface  1322   a  in the positive X-direction on which, for example, the phosphor portion  1321  is located. More specifically, the surface  1322   a  of the substrate  1322  is, for example, joined to the surface  132   d  of the phosphor portion  1321 . 
     The substrate  1322  may be transparent or reflective. In the example described below, the substrate  1322  includes a reflective surface as the surface  1322   a . For the reflective substrate  1322 , for example, the excitation light P 0  passing through the phosphor portion  1321  is reflected from the surface  1322   a  of the substrate  1322  and enters the phosphor portion  1321  again. This can increase, for example, the light intensity of the fluorescence W 0  emitted from the phosphor portion  1321  and increase, for example, the light intensity of the fluorescence W 0  emitted in response to the excitation light P 0 . 
     The substrate  1322  may be made of, for example, a metal material. The metal material may be, for example, copper (Cu), aluminum (Al), magnesium (Mg), gold (Au), silver (Ag), iron (Fe), chromium (Cr), cobalt (Co), beryllium (Be), molybdenum (Mo), tungsten (W), or an alloy of any of these metals. The substrate  1322  made of, for example, Cu, Al, Mg, Fe, Cr, Co, or Be as the metal material may be fabricated easily by molding, such as die casting. The substrate  1322  made of, for example, Al, Mg, Ag, Fe, Cr, or Co as the metal material may include the surface  1322   a  with a higher reflectance against visible light. This can increase, for example, the light intensity of the fluorescence W 0  emitted in response to the excitation light P 0 . The substrate  1322  may be made of, for example, a nonmetallic material. The nonmetallic material may be, for example, aluminum nitride (AlN), silicon nitride (Si 3 N 4 ), carbon (C), or aluminum oxide (Al 2 O 3 ). The nonmetallic material may be, for example, crystalline or non-crystalline. The crystalline nonmetallic material may be, for example, silicon carbide (SiC) or Si 3 N 4 . 
     The substrate  1322  may include, as the surface  1322   a , a layer of a metal material with, for example, a higher light reflectance than its main part (also referred to as a high light reflectance layer). For example, the substrate  1322  may use Cu as the material for the main part, and may use Ag or Cr, which has a high reflectance against visible light, as the metal material with a high light reflectance. In this case, for example, the main part of the substrate  1322  is fabricated by molding, or for example, by die casting. The surface of the main part then undergoes vapor deposition or plating to form a high light reflectance layer of, for example, Ag or Cr. For example, a dielectric multilayer film may further be formed on the high light reflectance layer on the surface  1322   a  of the substrate  1322 . The dielectric multilayer film may include, for example, dielectric thin films repeatedly stacked on one another. The dielectric may be at least one material selected from the group consisting of titanium dioxide (TiO 3 ), silicon dioxide (SiO 2 ), niobium pentoxide (Nb 2 O 5 ), tantalum pentoxide (Ta 2 O 5 ), and magnesium fluoride (MgF 2 ). 
     The optical element  133  directs fluorescence W 0  emitted by the wavelength converter  132  in a predetermined direction. More specifically, for example, the optical element  133  focuses the fluorescence W 0  onto a focusing plane  33   f  The optical element  133  includes, for example, a reflector  1331 . The reflector  1331  includes a concave reflective surface  133   r . The reflective surface  133   r  is, for example, an ellipsoidal mirror that is shaped along an imaginary ellipsoid  33   e . The reflector  1331  includes, for example, the reflective surface  133   r  with the axis of symmetry aligned with the optical axis AX 1 . The reflective surface  133   r  directs the fluorescence W 0  emitted by the wavelength converter  132  to be focused onto the focusing plane  33   f  The reflector  1331  may be, for example, a parabolic reflector. 
     In the example of  FIG.  2   , the reflective surface  133   r  is concave in the direction from the wavelength converter  132  toward the first output end  2   e   2  and surrounds the wavelength converter  132 . In other words, the wavelength converter  132  is located inside the reflective surface  133   r . The imaginary YZ cross section of the reflective surface  133   r  is, for example, circular. More specifically, for example, the imaginary YZ cross section of the reflective surface  133   r  may be circular and centered at a point on the optical axis AX 1 . The imaginary circular cross section of the reflective surface  133   r  along a YZ plane has a maximum diameter of, for example, about 1 to 10 cm. The reflector  1331  includes, for example, a through-hole  133   h  extending along the optical axis AX 1 . This structure allows, for example, excitation light P 0  to be emitted through the first output end  2   e   2  toward the wavelength converter  132 . The first optical transmission fiber  2  may have, for example, its portion including the first output end  2   e   2  placed through the through-hole  133   h.    
     The ellipsoid  33   e  along which the reflective surface  133   r  extends includes a focal point F 1  (also referred to as a first focal point) located, for example, inside the wavelength converter  132  (more specifically, for example, the phosphor portion  1321 ). In other words, the wavelength converter  132  is located, for example, on the first focal point F 1  of the reflective surface  133   r . More specifically, for example, the wavelength converter  132  may include the incident surface section  132   a  surrounding the first focal point F 1 . In other words, the wavelength converter  132  may be located to have, for example, the first focal point F 1  inside the incident surface section  132   a . More specifically, the wavelength converter  132  includes the incident surface  132   b  and the incident surface  132   c  sandwiching the first focal point F 1  on the optical axis AX 1  in the cross section illustrated in  FIG.  2   . The first focal point F 1  is adjacent to the side edge at which the incident surface  132   b  and the incident surface  132   c  are joined together. In this structure, excitation light P 0  enters the wavelength converter  132  at a position near the first focal point F 1 . The wavelength converter  132  thus emits fluorescence W 0  near the first focal point F 1 . The reflector  1331  can receive the fluorescence W 0  emitted near the first focal point F 1  and focus the fluorescence W 0  near a second focal point F 2 . The second focal point F 2  is another focal point of the ellipsoid  33   e . The second focal point F 2  is different from the first focal point F 1 . Being near the first focal point F 1  may be, for example, being at a distance of 1/10 or less of the inter-focal distance (distance between the first focal point and the second focal point). 
     The focusing plane  33   f  is aligned with the second focal point F 2 . The focusing plane  33   f  may be either an imaginary plane or an actual surface. In the first embodiment, for example, the focusing plane  33   f  is aligned with the second input end  4   e   1  of the second optical transmission fiber  4 . 
     In this structure, the fluorescence W 0  emitted by the wavelength converter  132  near the first focal point F 1  is reflected from the reflective surface  133   r  and is focused at the second input end  4   e   1  of the second optical transmission fiber  4  located at the second focal point F 2 . This can increase, for example, the light intensity of the fluorescence W 0  transmitted by the second optical transmission fiber  4 . 
     The photoconversion device  30  may further include an optical system (not illustrated), such as a lens, that focuses the excitation light P 0  output through the first output end  2   e   2  of the first optical transmission fiber  2  toward the wavelength converter  132 . 
     1-1-3. Overview of First Embodiment 
     The photoconversion device  30  includes, for example, the holder  131 , the wavelength converter  132 , and the optical element  133 . The holder  131  holds the first output end  2   e   2  that serves as an output portion. The wavelength converter  132  includes the incident surface section  132   a  including a protruding surface to receive excitation light P 0  and emits fluorescence W 0  in response to the excitation light P 0 . The optical element  133  has the first focal point F 1  surrounded by the incident surface section  132   a  and directs the fluorescence W 0  in a predetermined direction. The optical element  133  includes, for example, the reflector  1331  that reflects the fluorescence W 0  on its reflective surface  133   r  and focuses the fluorescence W 0  onto the focusing plane  33   f . This structure allows, for example, the fluorescence W 0  to enter the second optical transmission fiber  4 . The optical radiation module  5  can then radiate the fluorescence W 0  as illumination light TO. 
     The photoconversion device  30  uses the reflector  1331  to focus the fluorescence W 0  onto the focusing plane  33   f , and thus optically converts a first image formed using the fluorescence W 0  in the wavelength converter  132  to a second image formed with a magnification on the focusing plane  33   f  The wavelength converter  132  may be regarded as a light source of the fluorescence W 0 . In this case, the first image formed using the fluorescence W 0  in the wavelength converter  132  can have the size corresponding to the size of the area of the phosphor portion  1321  receiving the excitation light P 0 , whereas the second image formed on the focusing plane  33   f  has the size corresponding to the size of the area of the focusing plane  33   f  receiving the excitation light P 0 . 
     In the Z-direction, for ease of explanation, the first image formed using the fluorescence W 0  has the size corresponding to a width H 1  of an illuminating area I 1  on the incident surface section  132   a  that receives the excitation light P 0 . The width H 1  is the dimension of the illuminating area I 1  in the Z-direction perpendicular to the optical axis AX 1  in a plan view of the incident surface section  132   a  along the optical axis AX 1 . The second image formed using the fluorescence W 0  has the size corresponding to a width H 2  of an illuminating area of the focusing plane  33   f  The width H 2  is the width of the illuminating area in the Z-direction in the focusing plane  33   f  The width H 1  may be, for example, about 1 mm or more. The width H 2  may be less than the width H 1 , and may be, for example, several hundred micrometers to several millimeters. More specifically, the reflector  1331  reduces the image formed using the fluorescence W 0  by a magnification of H 2 /H 1  in the Z-direction. As the magnification (=H 2 /H 1 ) of the reflector  1331  is smaller, the aberration of the reflector  1331  tends to increase. In other words, as the magnification is larger, the aberration of the reflector  1331  tends to decrease. When the aberration is large, light on the focusing plane deviates more from an ideal imaging point due to the aberration of the fluorescence W 0  reflected from the reflector  1331 , thus lowering the efficiency of focusing light onto the focusing plane  33   f . The width H 1  is reduced to enhance the degree of focusing. 
     When the illuminating area I 1  on the incident surface section  132   a  is larger, the phosphor portion  1321  receives excitation light P 0  in a wider area and thus can emit fluorescence W 0  with higher light intensity. In the present embodiment, the incident surface section  132   a  includes the protruding surface to cause the illuminating area I 1  to have a larger area size without increasing the width H 1 . In a comparative example, an incident surface section  132   a  is a flat surface parallel to a YZ plane. An illuminating area I 1  in this example (hereafter referred to as an illuminating area I 10 ) has the area size corresponding to the area size of a portion through which excitation light P 0  travels on a YZ plane (refer to  FIG.  3   ). With the incident surface section  132   a  including a protruding surface in the present embodiment, the illuminating area I 1  has a larger area size than the illuminating area I 10 . 
     The difference in the area size between the illuminating area I 1  and the illuminating area I 10  may be quantitatively represented using, for example, an angle θ. The angle θ is half the angle of the tip of the incident surface section  132   a , or specifically, half the angle between the incident surface  132   b  and the incident surface  132   c . The area size of the illuminating area I 1  is 1/sin θ times the area size of the illuminating area I 10 . More specifically, the illuminating area can have a larger area size by a factor of 1/sin θ than the structure with the incident surface section  132   a  parallel to a YZ plane. When, for example, the angle θ is 45 degrees, the illuminating area can have a larger area size by a factor of V 2 . Thus, the fluorescence W 0  can have higher light intensity with the reflector  1331  having a smaller aberration. 
     This will be described with reference to the first focal point F 1  as well. In a comparative example, an incident surface section  132   a  is a flat surface parallel to a YZ plane. When, for example, the first focal point F 1  is at the center of the illuminating area I 10  in  FIG.  3   , the illuminating area I 10  may be extended by increasing the diameter of the excitation light P 0  to cause the edge of the illuminating area I 10  to be apart from the first focal point F 1 . In the comparison example, the maximum value of a distance D 1  between each point in the illuminating area I 10  and the first focal point F 1  increases as the area size of the illuminating area I 10  increases. Although being reflected from the reflector  1331 , the fluorescence W 0  generated at a position largely apart from the first focal point F 1  travels toward a position deviating from the second focal point F 2  and does not reach the focusing plane  33   f . This lowers the directivity of the fluorescence W 0  toward the focusing plane  33   f.    
     In contrast, the incident surface section  132   a  includes the protruding surface in the present embodiment. Thus, the illuminating area I 1  can have a large area size, without increasing the diameter of the excitation light P 0 . In other words, the illuminating area I 1  can have a larger area size, without increasing the maximum value of the distance D 1  between each point in the illuminating area I 1  and the first focal point F 1 . Thus, the photoconversion device  30  can focus the fluorescence W 0  onto the focusing plane  33   f  with high directivity and with high light intensity. 
     In the present embodiment, the incident surface section  132   a  including the protruding surface as described above allows the illuminating area I 1  to have a larger area size without increasing the width H 1  or the distance D 1  from the first focal point F 1 . In other words, the photoconversion device  30  including the reflector  1331  with a small aberration can emit fluorescence W 0  with high directivity and with high light intensity. 
     To increase the intensity of the fluorescence W 0 , the intensity of the excitation light P 0  (light intensity per unit area size) may be increased. However, when the intensity of the excitation light P 0  increases, the wavelength converter  132  can have more local heat. A phosphor or a sealant (also referred to as a binder) included in the wavelength converter  132  can be degraded or altered under heat, possibly causing temperature quenching. 
     In contrast, the structure in the present embodiment includes the incident surface section  132   a  including the protruding surface to extend the illuminating area I 1  and thus to increase the light intensity of the fluorescence W 0 , without increasing the intensity of the excitation light P 0 . The temperature increase in the wavelength converter  132  is reduced to reduce heat that can possibly cause the issues described above. 
     For another comparison, an incident surface section  132   a  may be concave in the negative X-direction. In the example described below, the incident surface section  132   a  is concave and is V-shaped. The incident surface section  132   a  includes a first surface and a second surface. In this case, a portion of the fluorescence W 0  from the first surface is incident on the second surface, and a portion of the fluorescence W 0  from the second surface is incident on the first surface. In this manner, such portions of the fluorescence W 0  are incident on the phosphor portion in an overlapping manner. Such incidence of fluorescence in an overlapping manner can lower the light intensity of the fluorescence W 0 . 
     In contrast, the incident surface section  132   a  includes the protruding surface in the present embodiment. This structure reduces such incidence of the fluorescence W 0  in an overlapping manner on the phosphor portion  1321 . This structure is less likely to lower the light intensity of the fluorescence W 0 . 
     1-1-4. Substrate 
     1-1-4-1. Shape 
     As illustrated in  FIG.  2   , the surface  1322   a  of the substrate  1322  may be flat and parallel to a YZ plane. In some embodiments, as illustrated in  FIG.  4   , the surface  1322   a  of the substrate  1322  may also include a protruding surface. In the example of  FIG.  4   , the surface  1322   a  of the substrate  1322  includes a protruding surface, similarly to the incident surface section  132   a  of the phosphor portion  1321 . For example, the surface  1322   a  of the substrate  1322  protrudes toward the first output end  2   e   2  (specifically, in the positive X-direction). The substrate  1322  in a specific example may be in the shape of a triangular prism. The substrate  1322  may be located to have one rectangular side surface of the triangular prism perpendicular to the optical axis AX 1  and one side of the triangular prism facing the first output end  2   e   2 . The other two side surfaces of the triangular prism correspond to the surface  1322   a  of the substrate  1322 . The phosphor portion  1321  is located on the surface  1322   a  of the substrate  1322 . The incident surface section  132   a  of the phosphor portion  1321  has a protruding surface similar to the surface  1322   a  of the substrate  1322 . The phosphor portion  1321  may have a substantially constant thickness. 
     The wavelength converter  132  also includes the incident surface section  132   a  including a protruding surface. Thus, the illuminating area I 1  can have a larger area size without increasing its width H 1  or the distance D 1  from the first focal point F 1 . Thus, the photoconversion device  30  can emit fluorescence W 0  with high directivity and with high light intensity. 
     1-1-5. Phosphor Portion 
     1-1-5-1. Shape 
     Although the phosphor portion  1321  in the above example is in the shape of a triangular prism, the structure is not limited to this example. As illustrated in  FIG.  5   , the phosphor portion  1321  may be in the shape of a cone. More specifically, the phosphor portion  1321  may be in the shape of, for example, a circular cone. The phosphor portion  1321  has, for example, its bottom surface perpendicular to the optical axis AX 1  and its tip facing the first output end  2   e   2 . The side surface of the circular cone corresponds to the incident surface section  132   a  of the phosphor portion  1321 . In other words, the incident surface section  132   a  extends along the side surface of the cone. The bottom surface of the circular cone corresponds to the surface  132   d  of the phosphor portion  1321 . The diameter of the surface  132   d  and the height of the cone may be, for example, 1 mm or more. The shape of the phosphor portion  1321  may not be a circular cone but may be a pyramid. 
     In this case as well, the first focal point F 1  of the reflector  1331  may be, for example, inside the wavelength converter  132 . More specifically, the phosphor portion  1321  may have, for example, the incident surface section  132   a  surrounding the first focal point F 1 . In other words, the phosphor portion  1321  may be located to have, for example, the first focal point F 1  inside the incident surface section  132   a.    
     The phosphor portion  1321  also includes the incident surface section  132   a  including a protruding surface, thus allowing the illuminating area I 1  to have a larger area size without increasing the width H 1  or the maximum value of the distance D 1  from the first focal point F 1 . More specifically, the illuminating area can have a larger area size by a factor of 1/sin θ than when the incident surface section  132   a  is parallel to a YZ plane. The angle θ is formed between the center line of the circular cone and the side surface of the circular cone in the cross section including the center line of the circular cone. 
     The incident surface section  132   a  is circular in any YZ cross section. In this structure, the phosphor portion  1321  can emit the fluorescence W 0  more isotropically in a plan view of the phosphor portion  1321  along the optical axis AX 1 . 
     As illustrated in  FIG.  6   , the incident surface section  132   a  of the phosphor portion  1321  may include, for example, a protruding surface and may curve smoothly without being angled. More specifically, the phosphor portion  1321  may be, for example, hemispherical. The phosphor portion  1321  is installed to have, for example, its bottom surface perpendicular to the optical axis AX 1  and its spherical surface facing the first output end  2   e   2 . The hemispherical surface of the phosphor portion  1321  corresponds to the incident surface section  132   a . In other words, the incident surface section  132   a  extends along a spherical surface. The bottom surface of the hemisphere corresponds to the surface  132   d  of the phosphor portion  1321 . The diameter of the surface  132   d  may be, for example, 1 mm or more. 
     In this case as well, the first focal point F 1  of the reflector  1331  may be, for example, inside the wavelength converter  132 . More specifically, the phosphor portion  1321  may have, for example, the incident surface section  132   a  surrounding the first focal point F 1 . In other words, the phosphor portion  1321  may be located to have, for example, the first focal point F 1  inside the incident surface section  132   a.    
     The phosphor portion  1321  also includes the incident surface section  132   a  including a protruding surface, thus allowing the illuminating area I 1  to have a larger area size without increasing the width H 1  or the maximum value of the distance D 1  from the first focal point F 1 . 
     The area size of the illuminating area I 1  in each of  FIGS.  5  and  6    will be described. In the examples described below, the excitation light P 0  is incident substantially across the entire incident surface section  132   a . The illuminating area I 1  in  FIG.  5    corresponds to the side surface of the circular cone. The illuminating area I 1  in  FIG.  6    corresponds to the hemispherical surface. For the phosphor portions  1321  illustrated in  FIGS.  5  and  6    to have the same size, the height of the circular cone in  FIG.  5    may be equal to the radius of the bottom surface (specifically, the surface  132   d ). The angle θ of the circular cone is 45 degrees in this example. The surfaces  132   d  in  FIGS.  5  and  6    have the same radius. The area size of the surface  132   d  may be the area size of the illuminating area I 10  when the incident surface section  132   a  is a flat surface. In the example of  FIG.  5   , the area size of the illuminating area I 1  is √2 times the area size of the illuminating area I 10 . In the example of  FIG.  6   , the area size of the illuminating area I 1  is 2 times the area size of the illuminating area I 10 . When the angle θ is 45 degrees in the example of  FIG.  3   , the area size of the illuminating area I 1  is √2 times the area size of the illuminating area I 10 . For the incident surface section  132   a  being a hemispherical surface, the area size of the illuminating area I 1  can be the greatest of all the area sizes in  FIGS.  3 ,  5 , and  6    when the excitation light P 0  is incident substantially across the entire incident surface section  132   a.    
     The incident surface section  132   a  along the hemispherical surface is circular in any YZ cross section. In this structure, the phosphor portion  1321  can emit the fluorescence W 0  more isotropically in a plan view along the optical axis AX 1 . The incident surface section  132   a  along the hemispherical surface has no large corners, thus facilitating entry of the excitation light P 0  into the phosphor portion  1321 . The photoconversion device  30  including the phosphor portion  1321  illustrated in  FIG.  6    can emit fluorescence W 0  with still higher directivity and with still higher light intensity. 
     1-1-6. Output Portion 
     1-1-6-1. Multiple Output Portions 
     As illustrated in  FIG.  7   , the photoconversion device  30  may include multiple holders  131 . In the example of  FIG.  7   , the photoconversion device  30  includes two holders  131  each holding a first output end  2   e   2  of a first optical transmission fiber  2 . The two first optical transmission fibers  2  are hereafter referred to as a first optical transmission fiber  2   a  and a first optical transmission fiber  2   b.    
     The reflector  1331  includes a through-hole  133   ha  through which excitation light P 0  from the first optical transmission fiber  2   a  passes and a through-hole  133   hb  through which excitation light P 0  from the first optical transmission fiber  2   b  passes. The through-hole  133   ha  receives, for example, the reflector  1331  being placed in the thickness direction at a position in the positive Z-direction from the optical axis AX 1 . The excitation light P 0  from the first optical transmission fiber  2   a  passes through the through-hole  133   ha , travels from outside the reflector  1331  inward, and is incident on the incident surface  132   b  of the wavelength converter  132 . The through-hole  133   hb  receives, for example, the reflector  1331  being placed in the thickness direction at a position in the negative Z-direction from the optical axis AX 1 . The excitation light P 0  from the first optical transmission fiber  2   b  passes through the through-hole  133   hb , travels from outside the reflector  1331  inward, and is incident on the incident surface  132   c  of the wavelength converter  132 . This structure causes an illuminating area I 1  on the incident surface  132   b  and an illuminating area I 1  on the incident surface  132   c  to be apart from each other. 
     The wavelength converter  132  emits fluorescence W 0  in response to the excitation light P 0  from the first optical transmission fiber  2   a  and from the first optical transmission fiber  2   b . The reflector  1331  reflects the fluorescence W 0  emitted by the wavelength converter  132  and focuses the fluorescence W 0  onto the focusing plane  33   f . The reflector  1331  thus reduces a first image formed using the fluorescence W 0  in the wavelength converter  132  to a second image formed using the fluorescence W 0  on the focusing plane  33   f . In the Z-direction, the size of the first image formed using the fluorescence W 0  corresponds to the width H 1  between the first end and the second end furthest in the positive Z-direction and furthest in the negative Z-direction in the two illuminating areas I 1  on the incident surface section  132   a  when the incident surface section  132   a  is viewed in plan along the optical axis AX 1 . More specifically, the width H 1  is the dimension between the first end and the second end in the Z-direction perpendicular to the optical axis AX 1 . As the width H 1  of the reflector  1331  increases, the magnification (=H 2 /H 1 ) of the reflector  1331  decreases, and thus the aberration of the reflector  1331  tends to increase. 
     The photoconversion device  30  also includes the incident surface section  132   a  including a protruding surface. At the same width H 1 , the total area of the illuminating area I 1  is larger than when the incident surface section  132   a  is a flat surface parallel to a YZ plane. This structure increases the light intensity of the fluorescence W 0  with the reflector  1331  having a small aberration. The incident surface section  132   a  including a protruding surface also allows the illuminating area I 1  to have a larger area size without increasing the maximum value of the distance D 1  from the first focal point F 1 . This allows the fluorescence W 0  to be focused onto the focusing plane  33   f  with high directivity while increasing the light intensity of the fluorescence W 0 . In other words, the photoconversion device  30  including the reflector  1331  with a small aberration can emit fluorescence W 0  with high directivity and with high light intensity. 
     1-1-6-2. Splitting Excitation Light 
     As illustrated in  FIG.  8   , a single beam of excitation light P 0  may be split into multiple beams of excitation light P 0 . In the example of  FIG.  8   , the photoconversion device  30  has the same or similar structure as the photoconversion device  30  illustrated in  FIG.  2   , except that it includes an optical system  134 . 
     The optical system  134  splits a single beam of excitation light P 0  output through the first output end  2   e   2  into first excitation light P 1  and second excitation light P 2 , and causes the first excitation light P 1  to be incident on the incident surface  132   b  of the wavelength converter  132  and the second excitation light P 2  to be incident on the incident surface  132   c  of the wavelength converter  132 . The optical system  134  includes, for example, a semitransparent mirror  1341  and an optical path changer  1342 . The semitransparent mirror  1341  is located between the wavelength converter  132  and the first output end  2   e   2 . The semitransparent mirror  1341  transmits, for example, a portion of the excitation light P 0  output through the first output end  2   e   2  to the wavelength converter  132  as the first excitation light P 1 . The first excitation light P 1  passes, for example, through the through-hole  133   h  in the reflector  1331  and is incident on the incident surface  132   b  of the wavelength converter  132 . The semitransparent mirror  1341  reflects the remaining portion of the excitation light P 0  as the second excitation light P 2  toward the optical path changer  1342 . The optical path changer  1342  is, for example, a mirror that reflects the second excitation light P 2  to be incident on the incident surface  132   c  of the wavelength converter  132 . The second excitation light P 2  passes, for example, through the through-hole  133   h  in the reflector  1331  and is incident on the incident surface  132   c  of the wavelength converter  132 . This structure also causes the illuminating area I 1  on the incident surface  132   b  and the illuminating area I 1  on the incident surface  132   b  to be apart from each other. 
     This photoconversion device  30  also includes the incident surface section  132   a  including a protruding surface, and thus can emit, using the reflector  1331  with a small aberration, fluorescence W 0  with high directivity and with high light intensity, similarly to the photoconversion device  30  illustrated in  FIG.  7   . 
     Although the optical system  134  is located outside the reflector  1331  in the example of  FIG.  8   , the optical system  134  may be located inside the reflector  1331 . More specifically, the optical system  134  may be located between the wavelength converter  132  and the through-hole  133   h.    
     1-2. Other Embodiments 
     The present disclosure is not limited to the above first embodiment and may be changed or varied without departing from the spirit and scope of the present disclosure. 
     1-2-1. Second Embodiment 
     A photoconversion device  30  with a first structure according to a second embodiment differs from the photoconversion device  30  according to the first embodiment in the structure of the optical element  133 . As illustrated in  FIG.  9   , the optical element  133  includes a lens  1332  as a focusing element. The lens  1332  focuses fluorescence W 0  emitted by the wavelength converter  132  onto the focusing plane  33   f . In the example of  FIG.  9   , the first optical transmission fiber  2  is indicated schematically with a square block. The holder  131  is not illustrated. The lens  1332  is located between the first output end  2   e   2  and the wavelength converter  132 . As illustrated in  FIG.  9   , the first output end  2   e   2  and the wavelength converter  132  may be, for example, on the optical axis AX 1  of the lens  1332 . The lens  1332  includes, for example, a convex lens. The wavelength converter  132  is installed to have the incident surface section  132   a  protruding toward the lens  1332 . 
     The first output end  2   e   2  outputs excitation light P 0  in the positive X-direction. The excitation light P 0  passes through the lens  1332  and is incident on the protruding surface of the incident surface section  132   a  of the wavelength converter  132 . The wavelength converter  132  can emit fluorescence W 0  in response to the excitation light P 0 . 
     The fluorescence W 0  emitted by the wavelength converter  132  passes through the lens  1332  and is focused onto the focusing plane  33   f . The substrate  1322  being reflective can reflect the fluorescence W 0  toward the lens  1332 , and can increase the light intensity of the fluorescence W 0  entering the lens  1332 . This increases the light intensity of the fluorescence W 0  focused on the focusing plane  33   f  In the example of  FIG.  9   , the second optical transmission fiber  4  is also indicated schematically with a square block. The second input end  4   e   1  of the second optical transmission fiber  4  is aligned with the focusing plane  33   f  The focusing plane  33   f  is, for example, located opposite to the lens  1332  from the first output end  2   e   2  on the optical axis AX 1 . 
     A conjugate point C 1 , which has a conjugate relation with a point C 2  on the focusing plane  33   f  with respect to the lens  1332 , is located inside the wavelength converter  132 . The point C 2  is, for example, a point of intersection between the focusing plane  33   f  and the optical axis AX 1 . The wavelength converter  132  is installed to have the conjugate point C 1  surrounded by the incident surface section  132   a . The excitation light P 0  output through the first output end  2   e   2  thus enters the wavelength converter  132  near the conjugate point C 1 . Thus, the wavelength converter  132  emits the fluorescence W 0  near the conjugate point C 1 . The fluorescence W 0  generated near the conjugate point C 1  is easily focused through the lens  1332  onto the focusing plane  33   f  This structure increases the light intensity of the fluorescence W 0  focused on the focusing plane  33   f.    
     In this photoconversion device  30  as well, the lens  1332  reduces the first image formed using the fluorescence W 0  in the wavelength converter  132  to the second image formed using the fluorescence W 0  on the focusing plane  33   f , similarly to the reflector  1331 . In the Z-direction, the lens  1332  reduces the image formed using the fluorescence W 0  by a magnification of H 2 /H 1 . The aberration of the lens  1332  tends to be smaller as the magnification increases. The width H 1  is thus reduced to enhance the degree of focusing. 
     In the second embodiment as well, the incident surface section  132   a  of the wavelength converter  132  includes a protruding surface to have the illuminating area I 1  with a larger area size without increasing the width H 1 . Thus, the fluorescence W 0  can have higher light intensity with the lens  1332  having a small aberration. The incident surface section  132   a  including a protruding surface also allows the illuminating area I 1  to have a larger area size without increasing the maximum value of a distance D 2  from the conjugate point C 1 . Thus, the photoconversion device  30  can emit fluorescence W 0  with high directivity and with high light intensity. 
     As illustrated in  FIG.  10   , a photoconversion device  30  with a second structure according to the second embodiment includes a holder  131 , a wavelength converter  132 , an optical element  133 , and an optical system  134 . The holder  131  holds the first output end  2   e   2  of the first optical transmission fiber  2 . The first output end  2   e   2  outputs excitation light P 0  in the negative X-direction. The optical system  134  splits the excitation light P 0  output through the first output end  2   e   2  into third excitation light P 3  and fourth excitation light P 4 , and causes the third excitation light P 3  and the fourth excitation light P 4  to be incident on the incident surface section  132   a  of the wavelength converter  132 . The optical system  134  includes, for example, a splitter  1343 , an optical path changer  1344 , and an optical path changer  1345 . 
     The splitter  1343  is located, for example, between the wavelength converter  132  and the first output end  2   e   2  on the optical axis AX 1 . The splitter  1343  splits the excitation light P 0  output through the first output end  2   e   2  into the third excitation light P 3  and the fourth excitation light P 4 . 
     The splitter  1343  includes, for example, an incident surface  1343   a  and an incident surface  1343   b . The incident surface  1343   a  and the incident surface  1343   b  are continuous with each other. The excitation light P 0  is incident across the boundary between the incident surface  1343   a  and the incident surface  1343   b . More specifically, a portion of the excitation light P 0  is incident on the incident surface  1343   a , and the remaining portion of the excitation light P 0  is incident on the incident surface  1343   b.    
     The incident surface  1343   a  and the incident surface  1343   b  are inclined in different directions. The incident surface  1343   a  and the incident surface  1343   b  are, for example, flat surfaces and together define a V shape. More specifically, the incident surface  1343   a  and the incident surface  1343   b  are joined to each other at an acute angle. The incident surface  1343   a  and the incident surface  1343   b  are inclined toward each other in the Z-direction toward the first output end  2   e   2  in the X-direction. In the example of  FIG.  10   , the boundary between the incident surface  1343   a  and the incident surface  1343   b  is aligned with the optical axis AX 1 . 
     The splitter  1343  splits the excitation light P 0  into a first portion of the excitation light P 0  that is incident on the incident surface  1343   a  and a second portion of the excitation light P 0  that is incident on the incident surface  1343   b  to allow these light portions to travel in different directions. The first portion corresponds to the third excitation light P 3 . The second portion corresponds to the fourth excitation light P 4 . The incident surface  1343   a  and the incident surface  1343   b  are, for example, reflective surfaces. With the incident surface  1343   a  and the incident surface  1343   b  inclined in different directions, the third excitation light P 3  reflected from the incident surface  1343   a  and the fourth excitation light P 4  reflected from the incident surface  1343   b  travel in different directions. This allows spatial splitting of the excitation light P 0  into the third excitation light P 3  and the fourth excitation light P 4 . 
     The splitter  1343  may be in the shape of a triangular prism similar to, for example, the wavelength converter  132  illustrated in  FIG.  3   . The splitter  1343  is installed to have one rectangular side surface of the triangular prism (referred to as a surface  1343   c ) perpendicular to the optical axis AX 1  and one side of the triangular prism facing the first output end  2   e   2 . The remaining two rectangular side surfaces of the splitter  1343  correspond to the incident surface  1343   a  and the incident surface  1343   b . A material for the splitter  1343  may be, for example, the same as or similar to the material for the substrate  1322  described above. 
     In the example of  FIG.  10   , the incident surface  1343   a  is located in the positive Z-direction from the incident surface  1343   b . Thus, the first portion of the excitation light P 0  reflected from the incident surface  1343   a  travels in the positive Z-direction as the third excitation light P 3 . The second portion of the excitation light P 0  reflected from the incident surface  1343   b  travels in the negative Z-direction as the fourth excitation light P 4 . 
     The optical path changer  1344  is an optical element that directs the third excitation light P 3  from the splitter  1343  to the incident surface section  132   a  of the wavelength converter  132 . In the example of  FIG.  10   , the third excitation light P 3  travels in the positive Z-direction from the splitter  1343 . The optical path changer  1344  is thus located in the positive Z-direction from the splitter  1343 . The optical path changer  1344  includes, for example, a mirror that reflects the third excitation light P 3  to be incident on the incident surface section  132   a  of the wavelength converter  132  (more specifically, the incident surface  132   b ). In the example of  FIG.  10   , the third excitation light P 3  is obliquely incident on the incident surface  132   b.    
     The optical path changer  1345  is an optical element that directs the fourth excitation light P 4  from the splitter  1343  to the incident surface section  132   a  of the wavelength converter  132 . In the example of  FIG.  10   , the fourth excitation light P 4  travels in the negative Z-direction from the splitter  1343 . The optical path changer  1345  is thus located in the negative Z-direction from the splitter  1343 . The optical path changer  1345  includes, for example, a mirror that reflects the fourth excitation light P 4  to be incident on the incident surface section  132   a  of the wavelength converter  132  (more specifically, the incident surface  132   c ). In the example of  FIG.  10   , the fourth excitation light P 4  is obliquely incident on the incident surface  132   c . The illuminating area I 1  on the incident surface  132   b  and the illuminating area I 1  on the incident surface  132   c  can thus be apart from each other. 
     As illustrated in  FIG.  10   , the incident surface section  132   a  of the wavelength converter  132  includes a protruding surface protruding in the direction opposite to (specifically, in the negative X-direction from) the first output end  2   e   2 . As illustrated in  FIG.  10   , the wavelength converter  132  may be connected to the splitter  1343 . More specifically, the surface  1343   c  of the splitter  1343  may be joined to the surface  132   d  of the wavelength converter  132  in the positive X-direction. In this case, the splitter  1343  may function as the substrate for the phosphor portion  1321  of the wavelength converter  132 . The wavelength converter  132  may not include the substrate  1322 . 
     The wavelength converter  132  can emit fluorescence W 0  in response to the third excitation light P 3  and the fourth excitation light P 4 . The incident surface section  132   a  of the wavelength converter  132  includes a protruding surface protruding in the negative X-direction. The wavelength converter  132  can thus emit more fluorescence W 0  in the negative X-direction. 
     The optical element  133  includes the lens  1332  located opposite to (specifically, in the negative X-direction from) the first output end  2   e   2  from the wavelength converter  132 . The lens  1332  includes, for example, a convex lens that focuses the fluorescence W 0  from the wavelength converter  132  onto the focusing plane  33   f  The focusing plane  33   f  is, for example, at a position opposite to the wavelength converter  132  from the lens  1332  on the optical axis AX 1 . 
     The substrate  1322  being reflective reflects the fluorescence W 0  toward the lens  1332 , thus increasing the light intensity of the fluorescence W 0  entering the lens  1332 . This increases the light intensity of the fluorescence W 0  focused on the focusing plane  33   f.    
     A conjugate point C 1 , which has a conjugate relation with a point C 2  on the focusing plane  33   f  with respect to the lens  1332 , is located, for example, inside the wavelength converter  132 . More specifically, the conjugate point C 1  is surrounded by, for example, the incident surface section  132   a.    
     In this photoconversion device  30  as well, the lens  1332  reduces the first image formed using the fluorescence W 0  in the wavelength converter  132  to the second image formed using the fluorescence W 0  on the focusing plane  33   f . In the Z-direction, the lens  1332  reduces the image formed using the fluorescence W 0  by a magnification of H 2 /H 1 . The aberration of the lens  1332  tends to be smaller as the magnification increases. The width H 1  is thus reduced to enhance the degree of focusing. 
     The wavelength converter  132  also includes the incident surface section  132   a  including a protruding surface, thus allowing the illuminating area I 1  to have a larger area size without increasing the width H 1  of the illuminating area I 1  and the maximum value of the distance D 2  from the conjugate point C 1 . Thus, the photoconversion device  30  including the lens  1332  with a small aberration can emit fluorescence W 0  with high directivity and with high light intensity. 
     1-2-2. Third Embodiment 
     In the above embodiments, as illustrated in, for example,  FIG.  11   , the first optical transmission fiber  2  extends from the light-emitting module  1  to the optical radiation module  5 , without the relay  3  or the second optical transmission fiber  4 . The optical radiation module  5  may include a photoconversion device  30 F with the same or similar structure as the photoconversion device  30  according to the first embodiment or the second embodiment described above. 
     As illustrated in  FIG.  11   , an illumination system  100 F according to a third embodiment includes, for example, a light-emitting module  1 , a first optical transmission fiber  2 , and an optical radiation module  5 . In this example, the first optical transmission fiber  2  includes a first input end  2   e   1  located inside the light-emitting module  1  and a first output end  2   e   2  located inside the optical radiation module  5 . The first optical transmission fiber  2  can thus transmit, for example, excitation light P 0  from the light-emitting module  1  to the optical radiation module  5 . In the optical radiation module  5 , for example, the photoconversion device  30 F can receive excitation light P 0  output through the first output end  2   e   2  of the first optical transmission fiber  2  as an output portion to emit fluorescence W 0 . The optical radiation module  5  can then radiate, for example, fluorescence W 0  emitted from the photoconversion device  30 F into an external space  200  of the illumination system  100 F as illumination light I 0 . 
     An optical radiation module  5  with a first structure according to the third embodiment illustrated in  FIG.  12    includes a photoconversion device  30 F and an optical radiator  50 . In this example, the photoconversion device  30 F has the same or similar structure as the photoconversion device  30  with the structure according to the first embodiment illustrated in  FIG.  2   . The optical radiator  50  includes, for example, a lightguide  51  and an optical system L 53 . The lightguide  51  can transmit, for example, fluorescence W 0  from the second focal point F 2  toward the optical system L 53 . The lightguide  51  includes, for example, an optical fiber or a cylindrical member with a mirror-like inner surface. The lightguide  51  includes, for example, one end  5   e   1  (also referred to as a third input end) for receiving fluorescence W 0  and another end  5   e   2  (also referred to as a third output end) for outputting the fluorescence W 0 . The third output end  5   e   2  is located opposite to the third input end  5   e   1 . In the example of  FIG.  12   , the optical system L 53  is aligned with, for example, the third output end  5   e   2  of the lightguide  51 . The optical system L 53  can radiate, for example, the fluorescence W 0  transmitted by the lightguide  51  into the external space  200  at an intended angle of light distribution. The optical system L 53  may include, for example, a lens or a diffuser. In this structure, for example, the optical radiation module  5  can include a smaller portion to radiate the fluorescence W 0  into the external space  200  as illumination light I 0 . 
     Although the optical element  133  is the reflector  1331  in the example of  FIG.  12   , the optical element  133  may be a lens  1332  as illustrated in  FIGS.  9  and  10   . 
     The photoconversion device  30 F with the first structure also includes a holder  131 , a wavelength converter  132 , and an optical element  133 . The holder  131  holds the first output end  2   e   2  that serves as an output portion. The wavelength converter  132  includes the incident surface section  132   a  including a protruding surface to receive excitation light P 0  and emits fluorescence W 0  in response to the excitation light P 0 . The optical element  133  has a first focal point F 1  or a conjugate point C 1  surrounded by the incident surface section  132   a  to focus the fluorescence W 0  onto the focusing plane  33   f  Thus, the photoconversion device  30 F including the optical element  133  with a small aberration can focus the fluorescence W 0  onto the focusing plane  33   f  with high directivity and with high light intensity. This allows the fluorescence W 0  with higher light intensity to enter the optical radiator  50 , thus allowing the optical radiation module  5  to emit the fluorescence W 0  with higher light intensity. 
     An optical radiation module  5  with a second structure according to the third embodiment may not include the optical radiator  50 , as illustrated in, for example,  FIG.  13   . In the example of  FIG.  13   , the reflective surface  133   r  extends along an imaginary paraboloid. A focal point F 0  of the paraboloid is located, for example, inside the wavelength converter  132 . More specifically, the focal point F 0  of the paraboloid is surrounded by, for example, the incident surface section  132   a  of the wavelength converter  132 . Thus, the wavelength converter  132  can emit fluorescence W 0  near the focal point F 0 . The reflector  1331  can convert the fluorescence W 0  emitted near the focal point F 0  to collimated light with higher directivity. The collimated light may be, for example, radiated into the external space  200  as illumination light I 0  directly or through various optical systems such as a lens or a diffuser. 
     Although the optical element  133  is the reflector  1331  in the example of  FIG.  13   , the optical element  133  may be the lens  1332  as illustrated in  FIGS.  9  and  10   . In this case, the lens  1332  may be a collimating lens. More specifically, the focal point of the lens  1332  may be located inside the wavelength converter  132 . In other words, the phosphor portion  1321  may be located to have the incident surface section  132   a  surrounding the focal point of the lens  1332 . In this structure, the lens  1332  can convert the fluorescence W 0  emitted by the wavelength converter  132  near the focal point to collimated light with high directivity. 
     The photoconversion device  30 F with the second structure also includes a holder  131 , a wavelength converter  132 , and an optical element  133 . The holder  131  holds the first output end  2   e   2  that serves as an output portion. The wavelength converter  132  includes the incident surface section  132   a  including a protruding surface to receive excitation light P 0  and emits fluorescence W 0  in response to the excitation light P 0 . The optical element  133  has the focal point surrounded by the incident surface section  132   a  and converts the fluorescence W 0  to collimated light. Thus, the photoconversion device  30 F (and thus the optical radiation module  5 ) including the optical element  133  with a small aberration can emit the fluorescence W 0  with high directivity and with high light intensity. 
     In the illumination system  100 F, the wavelength converter  132  in the optical radiation module  5  emits fluorescence W 0  in response to the excitation light P 0  transmitted by the first optical transmission fiber  2  from the light-emitting module  1 . This structure reduces optical transmission loss that may occur when, for example, the fluorescence W 0  travels through the optical transmission fiber in a direction inclined at various angles to the longitudinal direction of the optical transmission fiber and is partly scattered during transmission. Thus, the illumination system  100 F can radiate, for example, fluorescence W 0  with higher light intensity in response to the excitation light P 0 . 
     Although the optical element  133  converts the fluorescence W 0  to collimated light, a focusing optical system including a lens (not illustrated) between the optical element  133  and the focusing plane  33   f  may be used to focus the fluorescence W 0  onto the focusing plane  33   f.    
     1-2-3. Fourth Embodiment 
     The structure according to each of the above first and second embodiments may not include the relay  3  or the first optical transmission fiber  2 , and may include a second optical transmission fiber  4  extending from a light-emitting module  1  to an optical radiation module  5 , and the light-emitting module  1  may include a photoconversion device  30 G with the same or similar structure as the photoconversion device  30  according to either of the first or second embodiment, as illustrated in, for example,  FIG.  14   . 
     As illustrated in  FIG.  14   , an illumination system  100 G according to a fourth embodiment includes, for example, a light-emitting module  1 , a second optical transmission fiber  4 , and an optical radiation module  5 . In this example, the second optical transmission fiber  4  includes a second input end  4   e   1  located inside the light-emitting module  1  and a second output end  4   e   2  located inside the optical radiation module  5 . The second optical transmission fiber  4  can thus, for example, transmit fluorescence W 0  from the light-emitting module  1  to the optical radiation module  5 . In the light-emitting module  1 , for example, the photoconversion device  30 G can receive excitation light P 0  emitted by the light-emitting element  10  as an output portion to emit fluorescence W 0 . The fluorescence W 0  emitted from the photoconversion device  30 G in the light-emitting module  1  is, for example, transmitted to the optical radiation module  5  through the second optical transmission fiber  4 . The optical radiation module  5  can then radiate, for example, the fluorescence W 0  transmitted by the second optical transmission fiber  4  into an external space  200  of the illumination system  100 G as illumination light I 0 . 
     A light-emitting module  1  with an example structure according to the fourth embodiment illustrated in  FIG.  15    includes a light-emitting element  10  and a photoconversion device  30 G. In this example, the photoconversion device  30 G has the same or similar structure as the photoconversion device  30  according to the first embodiment illustrated in  FIG.  2   . In the example of  FIG.  15   , excitation light P 0  is emitted from an output portion  10   f  of the light-emitting element  10  toward the wavelength converter  132 , instead of being through the first output end  2   e   2  of the first optical transmission fiber  2 . The holder  131  holds the light-emitting element  10 . The holder  131  may have, for example, a shape selected from various shapes and may hold the light-emitting element  10  in a manner selected from various manners. The photoconversion device  30 G may be the photoconversion device  30  described in either of the first or second embodiment. 
     In this structure as well, the photoconversion device  30 G includes, for example, the holder  131 , the wavelength converter  132 , and the optical element  133 . The holder  131  holds the output portion  10   f  that serves as an output portion. The wavelength converter  132  includes the incident surface section  132   a  including a protruding surface to receive excitation light P 0  and emits fluorescence W 0  in response to the excitation light P 0 . The optical element  133  has a first focal point F 1  or a conjugate point C 1  surrounded by the incident surface section  132   a  to focus the fluorescence W 0  onto the focusing plane  33   f  Thus, the photoconversion device  30 G including the optical element  133  with a small aberration can input the fluorescence W 0  into the second optical transmission fiber  4  with high directivity and with high light intensity. The optical radiation module  5  can radiate the fluorescence W 0  with high light intensity as illumination light I 0 . 
     In the illumination system  100 G, for example, the optical radiation module  5  may not include the wavelength converter  132 . The optical radiation module  5  is, for example, less likely to undergo temperature increase and can be miniaturized. 
     The optical element  133  included in the photoconversion device  30 G may convert the fluorescence W 0  to collimated light, similarly to the photoconversion device  30 F. This structure may include a focusing optical system including a lens (not illustrated) between the optical element  133  and the focusing plane  33   f  to input the fluorescence W 0  into the second input end  4   e   1  of the second optical transmission fiber  4 . 
     1-2-4. Fifth Embodiment 
     In the first to fourth embodiments described above, the wavelength converter  132  may include, for example, multiple phosphor areas  1320 , as illustrated in  FIGS.  16  and  17   . In other words, the wavelength converter  132  (more specifically, the phosphor portion  1321 ) may include multiple phosphor areas  1320 . The multiple phosphor areas  1320  include, for example, a first phosphor area  1320   a  and a second phosphor area  1320   b . In the example of  FIG.  16   , the phosphor portion  1321  is in the shape of a triangular prism, and may have two portions into which the phosphor portion  1321  is equally divided with an XY plane. The two portions correspond to the first phosphor area  1320   a  and the second phosphor area  1320   b . For example, the first phosphor area  1320   a  corresponds to the incident surface  132   b , and the second phosphor area  1320   b  corresponds to the incident surface  132   c . In other words, the surface of the first phosphor area  1320   a  in the positive X-direction is the incident surface  132   b , and the surface of the second phosphor area  1320   b  in the positive X-direction is the incident surface  132   c.    
     The first phosphor area  1320   a  emits, for example, fluorescence with a first wavelength spectrum in response to the excitation light P 0 . The second phosphor area  1320   b  emits, for example, fluorescence with a second wavelength spectrum different from the first wavelength spectrum in response to the excitation light P 0 . The fluorescence with the first wavelength spectrum and the fluorescence with the second wavelength spectrum may have, for example, different color temperatures. More specifically, the fluorescence with the first wavelength spectrum may be, for example, light with a first color temperature. The fluorescence with the second wavelength spectrum may be, for example, light with a second color temperature. The first color temperature may be, for example, 2650 Kelvin (K). The second color temperature may be, for example, 6500 K. The color temperature herein refers to, for example, the color temperature or the correlated color temperature specified in JIS Z 8725:2015. 
     Each phosphor area  1320  contains, for example, numerous phosphor particles of multiple types that each emit light with a different color. The ratio of the phosphor particles is different for each phosphor area  1320 . For example, when each phosphor area  1320  contains red, green, and blue phosphors, the ratio of the red, green, and blue phosphors contained in the first phosphor area  1320   a  is different from the ratio of the red, green and blue phosphors contained in the second phosphor area  1320   b . Each phosphor area  1320  can thus emit fluorescence W 0  with a different wavelength spectrum. The fluorescence W 0  emitted from the first phosphor area  1320   a  is also referred to as fluorescence W 1 , and the fluorescence W 0  emitted from the second phosphor area  1320   b  is also referred to as fluorescence W 2 . 
     In the example of  FIGS.  16  and  17   , the excitation light P 0  is incident across both the first phosphor area  1320   a  and the second phosphor area  1320   b . More specifically, the illuminating area I 1  is located across both the first phosphor area  1320   a  and the second phosphor area  1320   b . In the example of  FIGS.  16  and  17   , the proportion of the first phosphor area  1320   a  and the proportion of the second phosphor area  1320   b  in the illuminating area I 1  are similar to each other. The first phosphor area  1320   a  receives excitation light P 0  and emits fluorescence W 1 . The second phosphor area  1320   b  receives excitation light P 0  and emits fluorescence W 2 . 
     The photoconversion device  30  including the wavelength converter  132  can emit the fluorescence W 1  and the fluorescence W 2  that have wavelength spectra different from each other. 
     As in the first embodiment, the optical element  133  may focus, for example, the fluorescence W 1  and the fluorescence W 2  at the second input end  4   e   1  of the second optical transmission fiber  4  (refer also to  FIG.  2   ). The fluorescence W 1  and the fluorescence W 2  mix spatially when being transmitted by the second optical transmission fiber  4 . The illumination light  10  radiated from the optical radiation module  5  is thus less likely to have a color distribution. In this case, the optical radiation module  5  can radiate the illumination light  10  as a mixture of the colors of the fluorescence W 1  and the fluorescence W 2 . 
     As illustrated in, for example,  FIG.  18   , the photoconversion device  30  may also emit the fluorescence W 1  and the fluorescence W 2  into the external space  200  as illumination light  10  without being through the second optical transmission fiber  4 . The photoconversion device  30  illustrated in  FIG.  18    corresponds to the photoconversion device  30 F in  FIG.  13    with its wavelength converter  132  replaced by the wavelength converter  132  illustrated in  FIGS.  16  and  17   . The reflector  1331  reflects the fluorescence W 1  and the fluorescence W 2  emitted by the wavelength converter  132  and converts the fluorescence W 1  and the fluorescence W 2  to collimated light. 
     In the example of  FIGS.  16  and  17   , the incident surface  132   b  of the first phosphor area  1320   a  and the incident surface  132   c  of the second phosphor area  1320   b  are inclined in different directions. The fluorescence W 1  emitted from the first phosphor area  1320   a  and the fluorescence W 2  emitted from the second phosphor area  1320   b  can travel mainly in different directions. In the example of  FIG.  18   , the first phosphor area  1320   a  is located in the positive Z-direction from the second phosphor area  1320   b , and the incident surface  132   b  of the first phosphor area  1320   a  faces in the positive Z-direction. In this structure, the first phosphor area  1320   a  can emit more fluorescence W 1  mainly in the positive Z-direction. In contrast, the second phosphor area  1320   b  is located in the negative Z-direction from the first phosphor area  1320   a , and the incident surface  132   c  of the second phosphor area  1320   b  faces in the negative Z-direction. In this structure, the second phosphor area  1320   b  can emit more fluorescence W 2  mainly in the negative Z-direction. 
     Thus, the illumination light  10  emitted from the photoconversion device  30  in  FIG.  18    can have a spatial color distribution in the Z-direction. The color distribution of the illumination light  10  is reflected in the color tones of an illumination object. The color tones of the illumination object can thus be changed partially. More specifically, the color tones can be varied between a part of the illumination object receiving more fluorescence W 1  and a part of the illumination object receiving more fluorescence W 2 . 
     The photoconversion device  30  may be used for, for example, illumination in a stage performance to change the distribution of the color tones of an illumination object. The photoconversion device  30  may also be used as illumination for inspection equipment for inspecting an inspection object. For example, detecting defects in an inspection object including a substrate such as a semiconductor substrate may use illumination light with a different color depending on the type of defects to be detected. The first phosphor area  1320   a  is thus designed to emit fluorescence W 1  for detecting a defect of a first type, and the second phosphor area  1320   b  is designed to emit fluorescence W 2  for detecting a defect of a second type. This facilitates detection of defects of a first type in a portion receiving the fluorescence W 1 , and detection of defects of a second type in a portion receiving the fluorescence W 2 . The inspection object can be, for example, scanned using this illumination light to allow inspection entirely across the inspection object. 
     For the surface  1322   a  of the substrate  1322  being a reflective surface having the same or similar shape as the incident surface section  132   a  of the phosphor portion  1321  (refer also to  FIG.  4   ) as well, the illumination light can have a notable spatial color distribution. This results from the fluorescence W 1  from the first phosphor area  1320   a  traveling in the negative Z-direction and reflected from the surface  1322   a  of the substrate  1322  to travel in the positive Z-direction, and also from the fluorescence W 2  traveling in the negative Z-direction likewise. An illumination object can thus have a more notable distribution of color tones. 
     When the optical element  133  focuses the fluorescence W 1  and the fluorescence W 2  onto the focusing plane  33   f , the photoconversion device  30  may emit the fluorescence W 1  and the fluorescence W 2  as illumination light without being through the second optical transmission fiber  4 . This can change the distribution of the color tones of the illumination object. 
     As described above, the color distribution of the illumination light I 0  can be reduced by causing the light to travel through the second optical transmission fiber  4 . However, when, for example, the second optical transmission fiber  4  is short, the illumination light I 0  after traveling through the second optical transmission fiber  4  may possibly have a viewable color distribution. In this case, the illumination light I 0  after traveling through the second optical transmission fiber  4  can also change the distribution of the color tones of the illumination object. 
     In the example of  FIG.  17   , the multiple phosphor areas  1320  in the wavelength converter  132  may have substantially the same size or may have different sizes. Although the two phosphor areas  1320  are illustrated in the example of  FIG.  17   , three or more phosphor areas  1320  may be provided. In this case, the excitation light P 0  may be applied across three or more phosphor areas  1320 . 
     1-2-5. Sixth Embodiment 
     A photoconversion device  30  with a first structure according to a sixth embodiment illustrated in  FIG.  19    has the same or similar structure as in the fifth embodiment, except that it includes a drive  135  and a controller  36 . The drive  135  changes an illuminating area I 1  that receives excitation light P 0  in the multiple phosphor areas  1320 . The drive  135  moves, for example, a part of at least one of the holder  131  or the wavelength converter  132  to change the relative positional relationship between the first output end  2   e   2  and the multiple phosphor areas  1320 . 
     1-2-5-1. Linear Driving 
     The first structure according to the sixth embodiment includes the drive  135  including a first linear mover  1353  as an example first mover for moving the wavelength converter  132  in the Z-direction intersecting with the optical axis AX 1  as a first intersecting direction. The first linear mover  1353  includes, for example, a rod  1353   r  and a driver  1353   m . The rod  1353   r  is, for example, an L-shaped rod having one end connected to the wavelength converter  132 . The rod  1353   r  has its other opposite end connected to the driver  1353   m . The driver  1353   m  moves, for example, the rod  1353   r  in the Z-direction. The driver  1353   m  includes, for example, a motor and a ball screw. In this example, the driver  1353   m  moves the rod  1353   r  in the Z-direction to move the wavelength converter  132  in the Z-direction. As illustrated in  FIGS.  20 A and  20 B , for example, the multiple phosphor areas  1320  may move integrally in the Z-direction. The driver  1353   m  may be, for example, an actuator selected from various actuators. 
     The controller  36  may drive, for example, the drive  135  to change the illuminating area I 1  receiving the excitation light P 0  in the multiple phosphor areas  1320  and stop driving the drive  135  to define the illuminating area I 1  in the multiple phosphor areas  1320 . In the example of  FIG.  19   , the controller  36  drives the drive  135  to change the relative positional relationship between the first output end  2   e   2  as an output portion and the multiple phosphor areas  1320 . In this example, the controller  36  controls the degree of movement of the wavelength converter  132  with the first linear mover  1353  by, for example, controlling the driver  1353   m  included in the first linear mover  1353 . The controller  36  detects, for example, the rotation angle of the motor included in the driver  1353   m  to control the time to stop the motor. The controller  36  is, for example, a control board or a microcomputer. The microcomputer is a large-scale integration circuit (LSI) in which, for example, a central processing unit (CPU) and a memory are integrated. The controller  36  controls the operation of the drive  135  by, for example, transmitting and receiving a signal to and from the drive  135 . The controller  36  may control, for example, the operation of the drive  135  in response to a signal from a device external to the photoconversion device  30 . 
     The controller  36  may serve as a control circuit. The controller  36  includes at least one processor that performs control and processing for implementing various functions, as described in more detail below. 
     In various embodiments, the at least one processor may be a single integrated circuit (IC), multiple ICs connected to one another for mutual communication, and/or discrete circuits. The at least one processor may be implemented in accordance with various known technologies. 
     In one embodiment, the processor includes one or more circuits or units that perform one or more data computation procedures or processes by, for example, executing instructions stored in an associated memory. In another embodiment, the processor may be a piece of firmware (e.g., a discrete logic component) to perform one or more data computation procedures or processes. 
     In various embodiments, the processor may be one or more processors, controllers, microprocessors, microcontrollers, application-specific integrated circuits (ASICs), digital signal processors, programmable logic devices, field-programmable gate arrays, or may include any combination of these devices or components or any combination of other known devices and components, and may implement the functions described below. 
     The functions of the controller  36  may be implemented entirely or partially using hardware circuits, without using software to implement the functions. 
     In the example illustrated in  FIG.  20   , the wavelength converter  132  includes the multiple phosphor areas  1320  including the first phosphor area  1320   a  and the second phosphor area  1320   b . When, for example, the wavelength converter  132  is viewed in plan in the direction along the optical axis AX 1  of excitation light P 0  as illustrated in  FIG.  20   , the multiple phosphor areas  1320  may be arranged in the Z-direction as the first intersection direction. In the example of  FIG.  20   , the first phosphor area  1320   a  and the second phosphor area  1320   b  are arranged in this order in the negative Z-direction. 
     The drive  135  can move, for example, the wavelength converter  132  in the Z-direction to move the illuminating area I 1  on the multiple phosphor areas  1320 . This movement changes the proportions of the multiple phosphor areas  1320  in the illuminating area I 1 . This thus changes, for example, the wavelength spectrum of the fluorescence W 0  emitted by the wavelength converter  132 . 
     In the example of  FIGS.  20 A and  20 B , the illuminating area I 1  is located across both the first phosphor area  1320   a  and the second phosphor area  1320   b . In this case, for example, the fluorescence W 0  emitted by the wavelength converter  132  is a mixture of the fluorescence with the first color temperature emitted from the first phosphor area  1320   a  and the fluorescence with the second color temperature emitted from the second phosphor area  1320   b . For example, the mixing ratio of the fluorescence W 1  having the first color temperature and the fluorescence W 2  having the second color temperature may be determined in accordance with, for example, the proportions of the first phosphor area  1320   a  and the second phosphor area  1320   b  in the illuminating area I 1 . As illustrated in  FIG.  20 A , the proportion of the first phosphor area  1320   a  in the illuminating area I 1  increases as the wavelength converter  132  moves more in the negative Z-direction. Thus, the proportion of the fluorescence W 1  in the fluorescence W 0  increases as the wavelength converter  132  moves more in the negative Z-direction. As illustrated in  FIG.  20 B , the proportion of the second phosphor area  1320   b  in the illuminating area I 1  increases as the wavelength converter  132  moves more in the positive Z-direction. Thus, the proportion of the fluorescence W 2  in the fluorescence W 0  increases as the wavelength converter  132  moves more in the positive Z-direction. 
     In the example of  FIG.  19   , the optical element  133  focuses, for example, the fluorescence W 1  and the fluorescence W 2  at the second input end  4   e   1  of the second optical transmission fiber  4 . The fluorescence W 1  and the fluorescence W 2  are transmitted by the second optical transmission fiber  4  and emitted from the optical radiation module  5  as illumination light I 0 . The fluorescence W 1  and the fluorescence W 2  mix spatially when being transmitted by the second optical transmission fiber  4 . The illumination light I 0  including the fluorescence W 1  and the fluorescence W 2  is then emitted from the optical radiation module  5 . 
     The drive  135  thus moves the wavelength converter  132  to adjust the light intensity ratio between the fluorescence W 1  and the fluorescence W 2  and thus adjust the color tones of the illumination light I 0 . In other words, the colors of the illumination light I 0  can be adjusted. When, for example, the second optical transmission fiber  4  is short, the illumination light I 0  can have a spatial color distribution. This color distribution can also be adjusted. 
     The photoconversion device  30  may emit the fluorescence W 1  and the fluorescence W 2  into the external space  200  as illumination light I 0  without being through the second optical transmission fiber  4  and the optical radiation module  5 . In this case, the illumination light I 0  can have a more notable color distribution. 
     In the first structure according to the sixth embodiment, the drive  135  moves the wavelength converter  132  to change the position of the first focal point F 1  of the optical element  133  relative to the wavelength converter  132 . The first focal point F 1  may be surrounded by the incident surface section  132   a  of the wavelength converter  132  at least in a part of the range of movement of the wavelength converter  132  by the drive  135 . With the first focal point F 1  being surrounded by the incident surface section  132   a  of the phosphor portion  1321  when the wavelength converter  132  is within the part of its movement range, the photoconversion device  30  can emit fluorescence W 1  and fluorescence W 2  with higher directivity and with higher light intensity. 
     When the directivity and the light intensity are not to be considered, the first focal point F 1  may be constantly outside the movement range of the wavelength converter  132 . In this structure as well, the drive  135  can move the wavelength converter  132  to adjust the colors (or further the color distribution) of the illumination light I 0 . 
     Although the drive  135  moves the wavelength converter  132  in the above example, the drive  135  may move the holder  131  instead. More specifically, the drive  135  may move the holder  131  to change the relative positional relationship between the first output end  2   e   2  as an output portion and the multiple phosphor areas  1320 . In other words, the drive  135  may move, for example, a part of at least one of the holder  131  or the wavelength converter  132  to change the relative positional relationship between the first output end  2   e   2  as an output portion and the multiple phosphor areas  1320 . In this structure as well, the controller  36  may, for example, drive the drive  135  to change the illuminating area I 1  receiving the excitation light P 0  in the multiple phosphor areas  1320  and stop driving the drive  135  to define the illuminating area I 1  in the multiple phosphor areas  1320 . 
     In the photoconversion device  30  with the second structure according to the sixth embodiment illustrated in  FIG.  21   , the drive  135  moves the holder  131 . More specifically, the drive  135  includes a second linear mover  1354  as a first mover for moving the holder  131  in the Z-direction as the first intersecting direction. The second linear mover  1354  includes, for example, a rod  1354   r  and a driver  1354   m . The rod  1354   r  is connected to, for example, the holder  131 . The driver  1354   m  moves, for example, the rod  1354   r  in the Z-direction. The driver  1354   m  includes, for example, a motor and a ball screw. In this example, the driver  1354   m  moves, for example, the rod  1354   r  in the Z-direction to move the holder  131  and the first output end  2   e   2  in the Z-direction. The controller  36  controls, for example, the degree of movement and the position of the holder  131  in the Z-direction by controlling the rotational speed of the motor included in the driver  1354   m . The controller  36  may control the time to stop the motor by, for example, detecting the rotational speed of the motor in the driver  1354   m . The driver  1354   m  may be, for example, an actuator selected from various actuators. 
     The drive  135  moves the holder  131  to cause, for example, the illuminating area I 1  to move in the first intersecting direction (Z-direction) on the multiple phosphor areas  1320 , as illustrated in  FIGS.  22 A and  22 B . For example, the illuminating area I 1  in the multiple phosphor areas  1320  may thus be changed. This structure also facilitates adjustment of the colors (or further the color distribution) of emission light from the photoconversion device  30 , in the same manner as described above. 
     In the above example, the multiple phosphor areas  1320  in the wavelength converter  132  may have substantially the same size or may have different sizes. 
     The boundary between the first phosphor area  1320   a  and the second phosphor area  1320   b  is perpendicular to the first intersecting direction (Z-direction in this example), which is the direction of movement of the drive  135 . However, the boundary between the phosphor areas  1320  may be inclined with respect to the first intersecting direction. 
     Although the two phosphor areas  1320  are illustrated in the above example, three or more phosphor areas  1320  may be provided. The three or more phosphor areas  1320  may not be all arranged in the first intersecting direction. When the wavelength converter  132  is viewed in plan along the optical axis AX 1 , the multiple phosphor areas  1320  may be arranged two-dimensionally and adjacent to each other. For example, the multiple phosphor areas  1320  may be arranged in a matrix. In this case, the drive  135  may move the wavelength converter  132  two-dimensionally. More specifically, the drive  135  may include both the first linear mover  1353  that moves at least one of the holder  131  or the wavelength converter  132  in the first intersecting direction (e.g., in the Z-direction) and another linear mover (not illustrated) that moves at least one of the holder  131  or the wavelength converter  132  along the optical axis AX 1  and in the second intersecting direction (e.g., in the Y-direction) intersecting with the first intersecting direction. The other linear mover has the same or similar structure as the first linear mover  1353  except the direction of its movement. 
     In the example of  FIGS.  20 A,  20 B,  22 A, and  22 B , the illuminating area I 1  is located across both the first phosphor area  1320   a  and the second phosphor area  1320   b . However, the drive  135  may move the illuminating area I 1  in the positive Z-direction from the first phosphor area  1320   a  and the second phosphor area  1320   b  to position the illuminating area I 1  in the first phosphor area  1320   a  alone. Similarly, the drive  135  may position the illuminating area I 1  in the second phosphor area  1320   b  alone. 
     1-2-5-2. Rotational Driving 
     A photoconversion device  30  with a third structure according to the sixth embodiment illustrated in  FIG.  23    includes a drive  135  including, for example, a unit  1351  (also referred to as a first rotator) that rotates the wavelength converter  132  about an imaginary rotation axis R 1  (also referred to as a first rotation axis) different from the optical axis AX 1  of the excitation light P 0  that is applied to the wavelength converter  132 . 
     In the example of  FIG.  23   , the drive  135  moves, for example, the rod  132   r  connected to the wavelength converter  132  to change the illuminating area I 1  in the multiple phosphor areas  1320 . The rod  132   r  protrudes in the negative X-direction from the wavelength converter  132 . The rod  132   r  has its distal end in the negative X-direction to which a bevel gear  132   g  is fixed. The rod  132   r  is, for example, supported by a housing  3   b  directly or indirectly with another member and can rotate about the first rotation axis R 1  extending in the X-direction. The first rotator  1351  includes, for example, a motor  1351   m , a rod  1351   r , and a gear  1351   g . The rod  1351   r  is elongated in the Z-direction. The rod  1351   r  has its distal end in the positive Z-direction to which, for example, a bevel gear  1351   g  is fixed. The gear  1351   g  meshes with the gear  132   g . The motor  1351   m  rotates the rod  1351   r  and the gear  1351   g  about an imaginary rotation axis R 35  extending in the Z-direction. Thus, for example, the torque of the gear  1351   g  is transmitted to the gear  132   g  to rotate the wavelength converter  132  about the first rotation axis R 1 . As illustrated in  FIGS.  24 A to  24 C , for example, the multiple phosphor areas  1320  may thus rotate integrally about the first rotation axis R 1 . 
     The wavelength converter  132  includes multiple phosphor areas  1320  as illustrated in, for example,  FIGS.  24 A to  24 C . In the example of  FIGS.  24 A to  24 C , the multiple phosphor areas  1320  include a first phosphor area  1320   a , a second phosphor area  1320   b , and a third phosphor area  1320   c . The first phosphor area  1320   a  emits, for example, fluorescence with a first wavelength spectrum in response to the excitation light P 0 . The second phosphor area  1320   b  emits, for example, fluorescence with a second wavelength spectrum different from the first wavelength spectrum in response to the excitation light P 0 . The third phosphor area  1320   c  emits, for example, fluorescence with a third wavelength spectrum different from the first wavelength spectrum and the second wavelength spectrum in response to the excitation light P 0 . The fluorescence with the first wavelength spectrum and the fluorescence with the second wavelength spectrum may have, for example, different color temperatures. The fluorescence with the third wavelength spectrum may be, for example, fluorescence with a color temperature different from the color temperature of fluorescence with the first wavelength spectrum and from the color temperature of fluorescence with the second wavelength spectrum. More specifically, the fluorescence with the first wavelength spectrum may be, for example, light with a first color temperature. The fluorescence with the second wavelength spectrum may be, for example, light with a second color temperature. The fluorescence with the third wavelength spectrum may be, for example, light with the third color temperature. The first color temperature may be, for example, 2650 K. The second color temperature may be, for example, 6500 K. The third color temperature may be 4000 K. 
     When, for example, the wavelength converter  132  is viewed in plan in the direction along the first rotation axis R 1  as illustrated in  FIGS.  24 A to  24 C , the multiple phosphor areas  1320  may be arranged circumferentially about the first rotation axis R 1 . For example, the first phosphor area  1320   a , the second phosphor area  1320   b , and the third phosphor area  1320   c  may be arranged in this order circumferentially about the first rotation axis R 1 . 
     In this case, the phosphor portion  1321  in the wavelength converter  132  may be in the shape of, for example, a circular cone or a hemisphere. The phosphor portion  1321  is circular as viewed in plan and may be used for the multiple phosphor areas  1320  arranged in the circumferential direction. The incident surface section  132   a  of the phosphor portion  1321  is defined by the surfaces of the first phosphor area  1320   a , the second phosphor area  1320   b , and the third phosphor area  1320   c  in the positive X-direction. 
     In this case, for example, the drive  135  rotates the wavelength converter  132  about the first rotation axis R 1 . This easily changes the proportions of the multiple phosphor areas  1320  in the illuminating area I 1 . Thus, the color temperature of the fluorescence emitted by the wavelength converter  132  can also be changed based on the proportions of the phosphor areas  1320 . This structure facilitates adjustment of the colors (or further the color distribution) of illumination light I 0  emitted from the photoconversion device  30 . 
     In the above example, the drive  135  includes the first rotator  1351  that rotates the wavelength converter  132 . However, the drive  135  may include a second rotator (not illustrated) that rotates the first output end  2   e   2 , instead of or in addition to the first rotator  1351 . In other words, the drive  135  may rotate at least one of the wavelength converter  132  or the first output end  2   e   2  to move the illuminating area I 1  relative to the phosphor portion  1321 , as illustrated in  FIGS.  24 A to  24 C . 
     In the example of  FIGS.  24 A to  24 C , the illuminating area I 1  includes the first rotation axis R 1 . Thus, the illuminating area I 1  includes the first phosphor area  1320   a , the second phosphor area  1320   b , and the third phosphor area  1320   c . However, the positional relationship between the wavelength converter  132  and the first output end  2   e   2  may be defined to cause the illuminating area I 1  to exclude the first rotation axis R 1 . In this case, the illuminating area I 1  is located in a single phosphor area  1320  or across two adjacent phosphor areas  1320  depending on the position of rotation. 
     The multiple phosphor areas  1320  in the wavelength converter  132  may have substantially the same size or different sizes. 
     The wavelength converter  132  may include two, four, or more phosphor areas  1320 . In other words, the wavelength converter  132  may include, for example, two or more phosphor areas  1320  arranged in the circumferential direction. 
     When the wavelength converter  132  is viewed in plan along the optical axis AX 1 , one of the multiple phosphor areas  1320  may be circular and include the optical axis AX 1 , and the other phosphor areas  1320  may be arranged circumferentially around the circular phosphor area  1320 . With the illuminating area I 1  partly in the circular phosphor area  1320  at any position of rotation, the photoconversion device  30  is used as appropriate for frequent use of fluorescence with the color temperature emitted from the circular phosphor area  1320 . The circular phosphor area  1320  in the center may emit fluorescence with the same wavelength spectrum as fluorescence emitted from at least one phosphor area  1320  located adjacent to the phosphor area  1320  in the center. 
     1-2-5-3. Size of Illuminating Area 
     In a photoconversion device  30  with a fourth structure according to the sixth embodiment, the drive  135  may include, for example, a unit (also referred to as a second mover) that changes the distance between the holder  131  and the wavelength converter  132 . In this case, for example, the drive  135  changes the distance between the first output end  2   e   2  as an output portion and the wavelength converter  132  to change the size of the illuminating area I 1 . The drive  135  thus changes, for example, the illuminating area I 1  receiving the excitation light P 0  in the multiple phosphor areas  1320 . In this case as well, the controller  36  may drive, for example, the drive  135  to change the illuminating area I 1  receiving the excitation light P 0  in the multiple phosphor areas  1320  and stop driving the drive  135  to define the illuminating area I 1  in the multiple phosphor areas  1320 . This changes, for example, the wavelength spectrum of fluorescence W 0  emitted by the wavelength converter  132  to adjust the colors of emission light from the photoconversion device  30 . 
     In a photoconversion device  30  with the fourth structure according to the sixth embodiment illustrated in  FIG.  25   , the drive  135  includes a third linear mover  1355  as an example second mover for moving the holder  131  in the X-direction as the direction along the optical axis AX 1 . The third linear mover  1355  includes, for example, a rod  1355   r  and a driver  1355   m . The rod  1355   r  is connected to, for example, the holder  131 . The driver  1355   m  moves, for example, the rod  1355   r  in the X-direction. The driver  1355   m  includes, for example, a motor and a ball screw. In this example, the driver  1355   m  moves the rod  1355   r  in the X-direction to move the holder  131  in the X-direction. The controller  36  controls, for example, the degree of movement and the position of the holder  131  in the X-direction by controlling the rotational speed of the motor included in the driver  1355   m . The controller  36  may control the time to stop the motor by, for example, detecting the rotational speed of the motor in the driver  1355   m . The driver  1355   m  may be, for example, an actuator selected from various actuators. 
     In the photoconversion device  30  with the fourth structure according to the sixth embodiment illustrated in  FIG.  25   , the drive  135  includes a fourth linear mover  1356  as an example second mover for moving the wavelength converter  132  in the X-direction as the direction along the optical axis AX 1 . The fourth linear mover  1356  includes, for example, a rod  1356   r  and a driver  1356   m . The rod  1356   r  is connected to, for example, the wavelength converter  132 . The driver  1356   m  moves, for example, the rod  1356   r  in the X-direction. The driver  1356   m  includes, for example, a motor and a ball screw. In this example, the driver  1356   m  moves the rod  1356   r  in the X-direction to move the wavelength converter  132  in the X-direction. The controller  36  controls, for example, the degree of movement and the position of the wavelength converter  132  in the X-direction by controlling the rotational speed of the motor included in the driver  1356   m . The controller  36  may control the time to stop the motor by, for example, detecting the rotational speed of the motor in the driver  1356   m . The driver  1356   m  may be, for example, an actuator selected from various actuators. For example, the photoconversion device  30  may include at least one of the third linear mover  1355  or the fourth linear mover  1356 . 
     When, for example, the wavelength converter  132  is viewed in plan in the X-direction (more specifically, in the negative X-direction) as the optical axis direction of the excitation light P 0  as illustrated in  FIGS.  26 A to  26 C , the multiple phosphor areas  1320  may be arranged in a direction apart from the optical axis AX 1 . 
     In the example of  FIGS.  26 A to  26 C , the first to third phosphor areas  1320   a  to  1320   c  are arranged concentrically. In this case, the phosphor portion  1321  in the wavelength converter  132  may be in the shape of, for example, a circular cone or a hemisphere. The phosphor portion  1321  is circular as viewed in plan and may be used for multiple phosphor areas  1320  arranged concentrically. The incident surface section  132   a  of the phosphor portion  1321  is defined by the surfaces of the first phosphor area  1320   a , the second phosphor area  1320   b , and the third phosphor area  1320   c  in the positive X-direction. 
     The driving performed by the drive  135  allows, for example, the distance between the first output end  2   e   2  and the wavelength converter  132  to be changed to change the size of the illuminating area I 1  as illustrated in  FIGS.  26 A to  26 C . This easily changes the proportions of the multiple phosphor areas  1320  in the illuminating area I 1 . This structure thus facilitates, for example, adjustment of the colors of fluorescence in the photoconversion device  30 . In the example of  FIG.  26 A , the illuminating area I 1  includes the first phosphor area  1320   a  alone. Thus, for example, the fluorescence W 0  emitted by the wavelength converter  132  is fluorescence with the first color temperature emitted from the first phosphor area  1320   a . When, for example, the distance between the first output end  2   e   2  and the wavelength converter  132  is longer, the illuminating area I 1  has a greater diameter. In this case, the illuminating area I 1  includes the first phosphor area  1320   a  and the third phosphor area  1320   c  as illustrated in  FIG.  26 B . In this case, for example, the fluorescence W 0  emitted by the wavelength converter  132  is a mixture of fluorescence with the first color temperature emitted from the first phosphor area  1320   a  and fluorescence with the third color temperature emitted from the third phosphor area  1320   c . For example, the mixing ratio of the fluorescence with the first color temperature and the fluorescence with the third color temperature may be determined in accordance with, for example, the proportions of the first phosphor area  1320   a  and the third phosphor area  1320   c  in the illuminating area I 1 . When, for example, the distance between the first output end  2   e   2  and the wavelength converter  132  is still longer, the illuminating area I 1  has a still greater diameter. In this case, the illuminating area I 1  includes the first phosphor area  1320   a , the third phosphor area  1320   c , and the second phosphor area  1320   b  as illustrated in  FIG.  26 C . In this case, for example, the fluorescence W 0  emitted by the wavelength converter  132  is a mixture of fluorescence with the first color temperature emitted from the first phosphor area  1320   a , fluorescence with the third color temperature emitted from the third phosphor area  1320   c , and fluorescence with the second color temperature emitted from the second phosphor area  1320   b . For example, the mixing ratio of the fluorescence with the first color temperature, the fluorescence with the third color temperature, and the fluorescence with the second color temperature may be determined in accordance with, for example, the proportions of the first phosphor area  1320   a , the third phosphor area  1320   c , and the second phosphor area  1320   b  in the illuminating area I 1 . 
     The wavelength converter  132  (specifically, the surface  132   d  of the phosphor portion  1321 ) has a diameter of, for example, about 0.1 to 20 mm. The first phosphor area  1320   a  has a diameter of about 0.1 to 10 mm. The illuminating area I 1  has a diameter of, for example, about 0.1 to 10 mm. When, for example, viewed in plan in the direction along the optical axis AX 1 , the wavelength converter  132  and the multiple phosphor areas  1320  may each have a shape other than a circle, such as a rectangle. 
     1-3. Others 
     In each of the above embodiments, for example, the fluorescence with the first wavelength spectrum, the fluorescence with the second wavelength spectrum, and the fluorescence with the third wavelength spectrum may each be fluorescence with a specific color. For example, the fluorescence with the first wavelength spectrum may be red (R) fluorescence, the fluorescence with the second wavelength spectrum may be green (G) fluorescence, and the fluorescence with the third wavelength spectrum may be blue (B) fluorescence. In this case, for example, the first phosphor area  1320   a  may contain a red phosphor, the second phosphor area  1320   b  may contain a green phosphor, and the third phosphor area  1320   c  may contain a blue phosphor. 
     In each of the above embodiments, for example, the wavelength converter  132  may include multiple phosphor areas  1320  that are integral with one another, or may include two or more portions formed separately and then multiple phosphor areas  1320  are arranged in the multiple portions as appropriate. 
     In each of the above embodiments, for example, the color temperature or the color of the fluorescence W 0  emitted from each of the photoconversion devices  30 ,  30 F, and  30 G may be detected by a sensor, and the controller  36  may control the driving of the drive  135  based on the detection result. 
     In each of the above embodiments, for example, the reflective surface  133   r  may be a concave surface displaced from the imaginary ellipsoid  33   e , and may reflect the fluorescence W 0  focused using an optical system. For example, the reflective surface  133   r  may extend along a paraboloid, and collimated light of the fluorescence W 0  reflected from the reflective surface  133   r  may be focused through a condenser lens. 
     In each of the above embodiments, for example, any of the X-direction, Y-direction, and Z-direction may be the vertical direction, or any other direction may be the vertical direction. 
     In the first structure and the second structure according to the above sixth embodiment, for example, the drive  135  may include rods  1353   r  and  1354   r  both elongated in the Y-direction and to be swung with the drivers  1353   m  and  1354   m . In these structures as well, the drive  135  moves, for example, the wavelength converter  132  and the holder  131  relative to each other in the direction intersecting with the optical axis AX 1 . 
     In each of the above embodiments, for example, the drive  135  may include, between the output portion and the wavelength converter  132 , an optical system that is moved to change the illuminating area I 1  receiving the excitation light P 0  in the multiple phosphor areas  1320 . The optical system may include various components including a lens, a prism, and a reflector. The optical system may be moved by translating, rotating, and swinging various components. The illuminating area I 1  being changed includes, for example, the illuminating area I 1  being moved by redirecting the traveling direction of the excitation light P 0 , or the illuminating area I 1  with the diameter being increased or decreased by increasing or decreasing the beam diameter of the excitation light P 0 . 
     In the above example, the optical element  133  includes the reflector  1331 , and the incident surface section  132   a  of the wavelength converter  132  includes a protruding surface protruding toward the through-hole  133   h  (specifically, in the positive X-direction) of the reflector  1331  (refer to, for example,  FIG.  2   ). The excitation light P 0  is then output through the first output end  2   e   2  from the through-hole  133   h  of the reflector  1331  toward the incident surface section  132   a  of the wavelength converter  132 . As illustrated in  FIG.  27   , the wavelength converter  132  may be installed to have the incident surface section  132   a  protruding in the opposite direction (specifically, in the negative X-direction). In this case, the first output end  2   e   2  may be located in the negative X-direction from the wavelength converter  132 . With the incident surface section  132   a  of the wavelength converter  132  including a protruding surface in this case as well, the photoconversion device  30  can emit fluorescence W 0  with high directivity and with high light intensity as in the first embodiment. 
     For the reflector  1331  focusing the fluorescence W 0  onto the focusing plane  33   f , the first optical transmission fiber  2  may be located to avoid an area in which the fluorescence W 0  travels from each point on the reflective surface  133   r  to the focusing plane  33   f . The first optical transmission fiber  2  can thus avoid blocking the fluorescence W 0 . 
     The through-hole  133   h  may not be formed. With the drive  135  driving the wavelength converter  132  as in, for example, the sixth embodiment, the rod may extend in the negative X-direction from the surface of the wavelength converter  132  in the negative X-direction and may extend through the through-hole  133   h . In this case, the drive  135  may drive the rod. This structure allows the drive  135  to be outside the reflector  1331 . The drive  135  can thus avoid blocking the fluorescence W 0 . 
     The first optical transmission fiber  2  as a first transmitter and the second optical transmission fiber  4  as a second transmitter may each include multiple dads. In some embodiments, the first optical transmitter and the second optical transmitter may be, for example, light guides. Each light guide may be, for example, a bundle of multiple optical fibers, or a flexible tube (made of, for example, acrylic resin) that allows excitation light P 0  to be reflected from its inner circumferential surface, or a flexible linear light-transmissive member without dads or coating that allows excitation light P 0  to be transmitted inside the light-transmissive member. 
     2-1. Seventh Embodiment 
     A known light source directs excitation light toward a first phosphor and a second phosphor arranged adjacent to each other in a predetermined direction and allows the light to be incident on the first phosphor and the second phosphor from the opposite sides. This light source directs first excitation light emitted from a first light source to be incident on the first phosphor from the side opposite to the second phosphor, and directs second excitation light emitted from a second light source to be incident on the second phosphor from the side opposite to the first phosphor. The first phosphor receives the first excitation light and emits fluorescence. The second phosphor receives the second excitation light and emits fluorescence. The first phosphor and the second phosphor each emit fluorescence with the same color. The light source reflects the fluorescence with a reflector and emits the fluorescence in a predetermined direction. When the first phosphor and the second phosphor each contain phosphor substances that emit red (R) fluorescence, green (G) fluorescence, and blue (B) fluorescence, for example, the light source emits pseudo white light. 
     However, this light source includes multiple light sources, thus complicating the structure of the light source system and increasing the manufacturing cost. 
     The inventors of the present disclosure thus have developed a technique for simplifying the structures of a photoconversion device and an illumination system including the photoconversion device. 
     2-1-1. Illumination System 
     An example illuminating system according to a seventh embodiment is the same as or similar to the system in  FIG.  1   . 
     2-1-2. Photoconversion Device 
       FIG.  28    is a schematic diagram of a photoconversion device  30  with an example structure according to the seventh embodiment. As illustrated in  FIG.  28   , the photoconversion device  30  includes, for example, a first wavelength converter  231  and a splitter optical system  232 . These components of the photoconversion device  30  are fixed to a housing  3   b  of a relay  3  either directly or indirectly with, for example, another member. An optical axis AX 1  is hereafter, for example, an optical axis of the first output end  2   e   2 . In the example of  FIG.  28   , the optical axis AX 1  extends in the X-direction. 
     The first wavelength converter  231  can emit fluorescence W 0  in response to the excitation light P 0 . The first wavelength converter  231  is, for example, on the optical axis AX 1 . The first wavelength converter  231  includes a surface  231   a  (hereafter referred to as a first incident surface) and another surface opposite to the first incident surface  231   a  (hereafter referred to as a second incident surface  231   b ). The first incident surface  231   a  and the second incident surface  231   b  face each other in the direction intersecting with the optical axis AX 1  (e.g., in the Z-direction). The first incident surface  231   a  and the second incident surface  231   b  are, for example, flat surfaces parallel to each other. The first wavelength converter  231  may be, for example, rectangular. The first incident surface  231   a  receives first excitation light P 1 . The second incident surface  231   b  receives second excitation light P 2 . The first excitation light P 1  and the second excitation light P 2  are split from the excitation light P 0  as described below. The first wavelength converter  231  including the first incident surface  231   a  and the second incident surface  231   b  protrudes in the positive X-direction. In other words, the protruding surface of the incident surface section of the first wavelength converter  231  includes the first incident surface  231   a  and the second incident surface  231   b.    
     The first wavelength converter  231  contains a phosphor. The first wavelength converter  231  contains the same or similar phosphor as the phosphor portion  1321 . The phosphor portion may be, for example, located on a predetermined substrate.  FIG.  29    is a schematic perspective view of a first wavelength converter  231  with an example structure. As illustrated in  FIG.  29   , the first wavelength converter  231  may include a first phosphor portion  2311 , a second phosphor portion  2312 , and a substrate  2313 . 
     The substrate  2313  is a plate with a thickness in the Z-direction. The substrate  2313  includes a main surface  2313   a  in the positive Z-direction on which the first phosphor portion  2311  is located, and a main surface  2313   b  in the negative Z-direction on which the second phosphor portion  2312  is located. 
     The first phosphor portion  2311  includes a first incident surface  231   a . More specifically, the surface of the first phosphor portion  2311  opposite to the substrate  2313  is the first incident surface  231   a . The first phosphor portion  2311  emits fluorescence W 0  based on first excitation light P 1  incident on the first incident surface  231   a . The first phosphor portion  2311  has an example structure described above. 
     The second phosphor portion  2312  includes a second incident surface  231   b . More specifically, the surface of the second phosphor portion  2312  opposite to the substrate  2313  is the second incident surface  231   b . The second phosphor portion  2312  emits fluorescence W 0  based on second excitation light P 2  incident on the second incident surface  231   b . The second phosphor portion  2312  has an example structure described above. 
     The first phosphor portion  2311  and the second phosphor portion  2312  may each have, for example, the same structure. The first phosphor portion  2311  and the second phosphor portion  2312  having the same structure refer to, for example, these phosphor portions manufactured under the same specifications. Thus, the first phosphor portion  2311  and the second phosphor portion  2312  each emit fluorescence W 0  with substantially the same wavelength spectrum. The first phosphor portion  2311  and the second phosphor portion  2312  each emit fluorescence W 0  with substantially the same color. 
     The substrate  2313  may be transparent or reflective. In the example described below, the substrate  2313  has reflective surfaces as the main surface  2313   a  and the main surface  2313   b . A material for the substrate  2313  may be, for example, the same as or similar to the material for the substrate  1322  described above. 
     Similarly to the substrate  1322 , the substrate  2313  may include the main surface  2313   a  and the main surface  2313   b  being layers of a metal material with a higher light reflectance than its main part (also referred to as high light reflection layers). 
     Although the substrate  2313  is between the first phosphor portion  2311  and the second phosphor portion  2312  in the example of  FIG.  29   , the structure is not limited to this example. For the substrate  2313  being transparent, for example, a structure including the first phosphor portion  2311  and the second phosphor portion  2312  may be located on the main surface  2313   a  of the substrate  2313 . In this case, the first phosphor portion  2311  and the second phosphor portion  2312  may be integral with each other. The substrate  2313  may be located to have a thickness in the X-direction or the Y-direction. In this case, the substrate  2313  may be located on a side surface of the structure including the first phosphor portion  2311  and the second phosphor portion  2312  that are integral with each other. 
     Referring now to  FIG.  28   , the splitter optical system  232  includes, for example, a splitter  2321 , a first optical path changer  2322 , and a second optical path changer  2323 . The splitter optical system  232  splits excitation light P 0  output through the first output end  2   e   2  of the first optical transmission fiber  2  into first excitation light P 1  and second excitation light P 2 . The splitter optical system  223  directs the first excitation light P 1  to the first incident surface  231   a  of the first wavelength converter  231  and the second excitation light P 2  to the second incident surface  231   b  of the first wavelength converter  231 . 
     The splitter  2321  is located, for example, between the first wavelength converter  231  and the first output end  2   e   2  on the optical axis AX 1 . The splitter  2321  splits the excitation light P 0  output through the first output end  2   e   2  into the first excitation light P 1  and the second excitation light P 2 . 
       FIG.  30    is a schematic perspective view of an example splitter  2321 . The splitter  2321  includes, for example, a third incident surface  2321   a  and a fourth incident surface  2321   b . The third incident surface  2321   a  and the fourth incident surface  2321   b  are continuous with each other. The excitation light P 0  is incident across the boundary between the third incident surface  2321   a  and the fourth incident surface  2321   b  (refer also to  FIG.  28   ). More specifically, a portion of the excitation light P 0  is incident on the third incident surface  2321   a , and the remaining portion of the excitation light P 0  is incident on the fourth incident surface  2321   b.    
     The fourth incident surface  2321   b  is inclined with respect to the third incident surface  2321   a . In the example of  FIGS.  28  and  30   , the third incident surface  2321   a  and the fourth incident surface  2321   b  are, for example, flat surfaces and together define a V shape. More specifically, the third incident surface  2321   a  and the fourth incident surface  2321   b  are joined to each other at an acute angle. The third incident surface  2321   a  and the fourth incident surface  2321   b  are inclined toward each other in the Z-direction toward the first output end  2   e   2  in the X-direction. In the example of  FIG.  28   , the boundary between the third incident surface  2321   a  and the fourth incident surface  2321   b  is aligned with the optical axis AX 1 . 
     The splitter  2321  causes the excitation light P 0  to be incident on the third incident surface  2321   a  and the fourth incident surface  2321   b  to split the excitation light P 0  into a first portion and a second portion. More specifically, the splitter  2321  causes the first portion of the excitation light P 0  that is incident on the third incident surface  2321   a  and the second portion of the excitation light P 0  that is incident on the fourth incident surface  2321   b  to travel in different directions to split the excitation light P 0  into the first portion and the second portion. The first portion corresponds to the first excitation light P 1 . The second portion corresponds to the second excitation light P 2 . In other words, the first portion is the first excitation light P 1  before being split, whereas the second portion is the second excitation light P 2  before being split. The third incident surface  2321   a  and the fourth incident surface  2321   b  are, for example, reflective surfaces. With the third incident surface  2321   a  and the fourth incident surface  2321   b  inclined in different directions, the first excitation light P 1  reflected from the third incident surface  2321   a  and the second excitation light P 2  reflected from the fourth incident surface  2321   b  travel in different directions. This allows spatial splitting of the excitation light P 0  into the first excitation light P 1  and the second excitation light P 2 . 
     As illustrated in  FIG.  30   , the splitter  2321  may be in the shape of a triangular prism. The splitter  2321  is installed to have one rectangular side surface of the triangular prism (referred to as a surface  2321   c ) perpendicular to the optical axis AX 1  and one side of the triangular prism facing the first output end  2   e   2 . The remaining two rectangular side surfaces of the splitter  2321  correspond to the third incident surface  2321   a  and the fourth incident surface  2321   b . A material for the splitter  2321  may be, for example, the same as or similar to the material for the substrate  2313  described above. 
     In the example of  FIG.  28   , the third incident surface  2321   a  is located in the positive Z-direction from the fourth incident surface  2321   b . Thus, the first portion of the excitation light P 0  reflected from the third incident surface  2321   a  travels in the positive Z-direction as the first excitation light P 1 . The second portion of the excitation light P 0  reflected from the fourth incident surface  2321   b  travels in the negative Z-direction as the second excitation light P 2 . 
     As illustrated in  FIG.  28   , the splitter  2321  may be connected to the first wavelength converter  231 . More specifically, the surface  2321   c  of the splitter  2321  may be joined to the surface of the first wavelength converter  231  in the positive X-direction. In this case, the splitter  2321  may serve as a substrate for the first wavelength converter  231 . In this case, the first wavelength converter  231  may not include the substrate  2313 . The first phosphor portion  2311  and the second phosphor portion  2312  may be integral with each other. 
     The first optical path changer  2322  is an optical element that directs the first excitation light P 1  from the splitter  2321  to the first incident surface  231   a  of the first wavelength converter  231 . In the example of  FIG.  28   , the first excitation light P 1  travels from the splitter  2321  in the positive Z-direction. The first optical path changer  2322  is thus located in the positive Z-direction from the splitter  2321 . The first optical path changer  2322  includes, for example, a mirror that reflects the first excitation light P 1  to be incident on the first incident surface  231   a  of the first wavelength converter  231 . In the example of  FIG.  28   , the first excitation light P 1  is obliquely incident on the first incident surface  231   a.    
     The second optical path changer  2323  is an optical element that directs the second excitation light P 2  from the splitter  2321  to the second incident surface  231   b  of the first wavelength converter  231 . In the example of  FIG.  28   , the second excitation light P 2  travels from the splitter  2321  in the negative Z-direction. The second optical path changer  2323  is thus located in the negative Z-direction from the splitter  2321 . The second optical path changer  2323  includes, for example, a mirror that reflects the second excitation light P 2  to be incident on the second incident surface  231   b  of the first wavelength converter  231 . In the example of  FIG.  28   , the second excitation light P 2  is obliquely incident on the second incident surface  231   b.    
     The first wavelength converter  231  emits fluorescence W 0  based on the first excitation light P 1  and the second excitation light P 2 .  FIG.  28    illustrates beams representing the fluorescence W 0  radiated from a single point on the first incident surface  231   a  and beams representing the fluorescence W 0  radiated from a single point on the second incident surface  231   b . In an actual operation, the phosphors at multiple positions in the first wavelength converter  231  each emit the fluorescence W 0 . The same applies to any other wavelength converter described below. 
     In the example of  FIG.  28   , the photoconversion device  30  also includes a reflector  233 . The reflector  233  is also accommodated in, for example, the housing  3   b  for the relay  3  (not illustrated in  FIG.  2   ) and is fixed directly or indirectly to the housing  3   b . In the example of  FIG.  28   , the reflector  233  includes a reflective surface  233   r  that is the same as or similar to the reflective surface  133   r  of the reflector  1331 . 
     In the example of  FIG.  28   , the reflective surface  233   r  is concave in the direction from the first wavelength converter  231  toward the splitter  2321  and surrounds the first wavelength converter  231  and the splitter optical system  232 . In other words, the first wavelength converter  231  and the splitter optical system  232  are located inside the reflective surface  233   r . An imaginary YZ cross section of the reflective surface  233   r  is, for example, circular. More specifically, for example, the imaginary YZ cross section of the reflective surface  233   r  may be circular and centered at a point on the optical axis AX 1 . The imaginary circular cross section of the reflective surface  233   r  along a YZ plane has a maximum diameter of, for example, about 1 to 10 cm. 
     The reflector  233  includes, for example, a through-hole  233   h  through which the excitation light P 0  passes. The first optical transmission fiber  2  may have, for example, its part including the first output end  2   e   2  being received in the through-hole  233   h . In this case, the excitation light P 0  is transmitted through this part of the first optical transmission fiber  2  to pass through the through-hole  233   h.    
     The ellipsoid  33   e  along which the reflective surface  233   r  extends has a focal point F 1  (also referred to as a first focal point) located, for example, inside the first wavelength converter  231 . In other words, the first wavelength converter  231  is aligned with the first focal point F 1  on the reflective surface  233   r . This structure allows the fluorescence W 0  emitted by the first wavelength converter  231  to be focused near a second focal point F 2  with the reflector  233 . The second focal point F 2  is another focal point of the ellipsoid  33   e . The second focal point F 2  is different from the first focal point F 1 . 
     The focusing plane  33   f  is aligned with the second focal point F 2 . In other words, the focusing plane  33   f  is aligned with the second focal point F 2 . The focusing plane  33   f  may be either an imaginary plane or an actual surface. In the seventh embodiment, for example, the focusing plane  33   f  is aligned with the second input end  4   e   1  of the second optical transmission fiber  4 . 
     In this structure, the fluorescence W 0  emitted by the first wavelength converter  231  near the first focal point F 1  is reflected from the reflective surface  233   r  and is focused onto the focusing plane  33   f  aligned with the second focal point F 2 . This can increase, for example, the light intensity of the fluorescence W 0  transmitted by the second optical transmission fiber  4 . 
     The first optical path changer  2322  and the second optical path changer  2323  included in the splitter optical system  232  may be attached to the reflector  233  as illustrated in  FIG.  28   . 
     As illustrated in, for example,  FIG.  28   , the photoconversion device  30  may also include an optical system L 31  including, for example, a lens that directs the excitation light P 0  output through the first output end  2   e   2  of the first optical transmission fiber  2  to be focused on the splitter  2321 . 
     The photoconversion device  30  may further include, for example, an optical system (not illustrated), such as a lens, that focuses the fluorescence W 0  emitted by the first wavelength converter  231  and reflected from the reflective surface  233   r  toward the second input end  4   e   1  of the second optical transmission fiber  4 . 
     2-1-3. Overview of Seventh Embodiment 
     The photoconversion device  30  includes, for example, the first wavelength converter  231  and the splitter optical system  232 . The first wavelength converter  231  includes the first incident surface  231   a  on its first end (e.g., in the positive Z-direction) and the second incident surface  231   b  on its second end (e.g., in the negative Z-direction) opposite to the first end, and emits fluorescence W 0  in response to the excitation light P 0 . In the example of  FIG.  28   , the first end and the second end are opposite to each other in the direction intersecting with the optical axis AX 1 . The splitter optical system  232  splits, for example, the excitation light P 0  output through the first output end  2   e   2  into first excitation light P 1  and second excitation light P 2 , and directs the first excitation light P 1  to the first incident surface  231   a  of the first wavelength converter  231  and the second excitation light P 2  to the second incident surface  231   b  of the first wavelength converter  231 . This structure allows the first excitation light P 1  to be incident on the first incident surface  231   a  of the first wavelength converter  231  and the second excitation light P 2  to be incident on the second incident surface  231   b  of the first wavelength converter  231  using the single output portion (in other words, the single first output end  2   e   2 ) for outputting the excitation light P 0 . This simplifies the structure of the light source system and reduces the manufacturing cost. 
     The first excitation light P 1  is incident on the first incident surface  231   a , and the second excitation light P 2  is incident on the second incident surface  231   b . As compared with when the excitation light is incident on either of the two surfaces alone, the excitation light P 0  is incident on a larger area of the first wavelength converter  231 . This increases, for example, the light intensity of the fluorescence W 0 . The first incident surface  231   a  and the second incident surface  231   b  are located opposite to each other with respect to the first focal point F 1 . More specifically, the first focal point F 1  is located inside the first wavelength converter  231 . Thus, the first wavelength converter  231  can emit fluorescence W 0  near the first focal point F 1 . The reflector  233  can focus the fluorescence W 0  onto the focusing plane  33   f  with high directivity. This improves the coupling efficiency of the second optical transmission fiber  4 . 
     In the above example, the splitter optical system  232  is surrounded by the reflector  233 . The splitter optical system  232  splits a single beam of excitation light P 0  passing through the through-hole  233   h  of the reflector  233  into first excitation light P 1  and second excitation light P 2  inside the reflector  233 . The splitter optical system  232  may then direct the first excitation light P 1  onto the first incident surface  231   a  and the second excitation light P 2  onto the second incident surface  231   b.    
     A comparative structure including a splitter optical system  232  and a first output end  2   e   2  located outside a reflector  233  will now be described. In this comparative example, the splitter optical system  232  and the first output end  2   e   2  are located in the positive X-direction from the reflector  233 . In this structure as well, the splitter optical system  232  can split the excitation light P 0  into first excitation light P 1  and second excitation light P 2 . To allow the first excitation light P 1  and the second excitation light P 2  outside the reflector  233  to enter the internal space, the reflector  233  includes one through-hole for the first excitation light P 1  and another through-hole for the second excitation light P 2 . In other words, the reflector  233  includes the two through-holes to allow the excitation light to pass through. 
     In contrast, the splitter optical system  232  in the above example splits the excitation light P 0  into the first excitation light P 1  and the second excitation light P 2  inside the reflector  233 . The reflector  233  thus includes the single through-hole  233   h  to allow the excitation light P 0  to enter the internal space of the reflector  233  and can have a simplified structure. This reduces the manufacturing cost of the reflector  233 . 
     As illustrated in  FIG.  28   , the splitter optical system  232  may allow the first excitation light P 1  to be obliquely incident on the first incident surface  231   a . This allows the first excitation light P 1  to be incident on a larger area of the first incident surface  231   a . This reduces the light intensity of the first excitation light P 1  per unit area. The same applies to the second excitation light P 2 . This thus reduces the amount of heat per unit area generated in the first wavelength converter  231  and reduces the temperature increase in the first wavelength converter  231 . 
     A phosphor or a sealant (also referred to as a binder) included in the first wavelength converter  231  can be degraded or altered under heat, possibly causing temperature quenching. The temperature increase in the first wavelength converter  231  is reduced to reduce heat that may cause issues described above. 
     Although the splitter  2321  is a mirror with the third incident surface  2321   a  and the fourth incident surface  2321   b  being reflective surfaces in the above example, the structure is not limited to this example. For example, the splitter  2321  may include a prism or a semitransparent mirror. The splitter  2321  may be any optical element that can spatially split the excitation light P 0 . 
     2-2. Other Embodiments 
     The present disclosure is not limited to the seventh embodiment described above and may be changed or varied without departing from the spirit and scope of the present disclosure. 
     2-2-1. Eighth Embodiment 
     A reflector  233  included in a photoconversion device  30  according to an eighth embodiment differs from the reflector in the seventh embodiment.  FIG.  31    is a block diagram of the photoconversion device  30  with an example structure according to the eighth embodiment. The reflector  233  may be, for example, a parabolic mirror with a reflective surface  233   r  shaped along a parabolic plane as illustrated in, for example,  FIG.  31   . The parabolic plane along which the reflective surface  233   r  extends has a focal point F 3  located, for example, inside the first wavelength converter  231 . In other words, the first wavelength converter  231  is located on the focal point F 3 . This structure allows, for example, conversion of fluorescence W 0  emitted by the first wavelength converter  231  to collimated light with the reflector  233 . 
     In this case, the second optical transmission fiber  4  and the optical radiation module  5  may be eliminated. The photoconversion device  30  may emit the fluorescence W 0  from the reflector  233  into an external space as illumination light I 0  without being through the second optical transmission fiber  4  and the optical radiation module  5 . 
     As in the seventh embodiment, the second optical transmission fiber  4  and the optical radiation module  5  may be provided. This structure may include a lens to focus the collimated fluorescence W 0  onto the focusing plane  33   f.    
     In the eighth embodiment as well, the first excitation light P 1  is incident on the first incident surface  231   a , and the second excitation light P 2  is incident on the second incident surface  231   b . As compared with when the excitation light is incident on either of the two surfaces alone, the light intensity of the fluorescence W 0  can be increased. 
     The first incident surface  231   a  and the second incident surface  231   b  are located opposite to each other with respect to the focal point F 3 . More specifically, the focal point F 3  is located inside the first wavelength converter  231 . Thus, the first wavelength converter  231  can emit fluorescence W 0  near the focal point F 3 . The reflector  233  can convert the fluorescence W 0  to collimated light with high directivity. 
     2-2-2. Ninth Embodiment 
     A photoconversion device  30  according to a ninth embodiment has the same or similar structure as the structure according to the seventh embodiment or the eighth embodiment. In the ninth embodiment, the structure of the first wavelength converter  231  differs from the corresponding structure in the seventh embodiment and the eighth embodiment. In the ninth embodiment, the first wavelength converter  231  includes a first phosphor portion  2311  and a second phosphor portion  2312  with different compositions. Thus, the wavelength spectrum of fluorescence W 0  emitted from the first phosphor portion  2311  is different from the wavelength spectrum of fluorescence W 0  emitted from the second phosphor portion  2312 . The fluorescence W 0  emitted from the first phosphor portion  2311  is also referred to as fluorescence W 1 , and the fluorescence W 0  emitted from the second phosphor portion  2312  is also referred to as fluorescence W 2 . The wavelength spectra being different from each other include, for example, at least one peak wavelength in the wavelength spectrum of the fluorescence W 1  being different from at least one peak wavelength in the wavelength spectrum of the fluorescence W 2 . This may also include the compositions of the first phosphor portion  2311  and the second phosphor portion  2312  being different from each other to provide a color difference of, for example, 0.6 or greater between the fluorescence W 1  and the fluorescence W 2 . 
     For example, the first phosphor portion  2311  and the second phosphor portion  2312  may contain different types of phosphors. For example, the first phosphor portion  2311  may contain a red phosphor, and the second phosphor portion  2312  may contain a green phosphor and a blue phosphor. The first phosphor portion  2311  and the second phosphor portion  2312  may each contain a common phosphor, in addition to such different phosphors. For example, the first phosphor portion  2311  may contain a red phosphor and a green phosphor, and the second phosphor portion  2312  may contain a green phosphor and a blue phosphor. When the first phosphor portion  2311  and the second phosphor portion  2312  contain different types of phosphors, the fluorescence W 1  and the fluorescence W 2  have wavelength spectra different from each other. 
     For example, the first phosphor portion  2311  and the second phosphor portion  2312  may contain phosphors of the same types but with different compositions. For example, the first phosphor portion  2311  and the second phosphor portion  2312  may both contain a red phosphor, a green phosphor, and a blue phosphor. In this case, the proportions of these phosphors in the first phosphor portion  2311  are different from the proportions of the phosphors in the second phosphor portion  2312 . This also causes the fluorescence W 1  and the fluorescence W 2  to have wavelength spectra different from each other. 
     When the fluorescence W 1  and the fluorescence W 2  are pseudo white light, the fluorescence W 1  and the fluorescence W 2  can express a difference between them with a color temperature. For example, the first phosphor portion  2311  and the second phosphor portion  2312  may be designed to have a color temperature difference of 100 K or more between the first phosphor portion  2311  and the second phosphor portion  2312 . In a specific example, the compositions of the first phosphor portion  2311  and the second phosphor portion  2312  may be any two selected from multiple compositions that achieve the color temperatures of 2650 K, 3000 K, 4000 K, 5000 K, and 6500 K. 
     As described above, the photoconversion device  30  according to the ninth embodiment can emit the fluorescence W 1  and the fluorescence W 2  that have wavelength spectra different from each other. 
     As in the seventh embodiment, the photoconversion device  30  may focus, for example, the fluorescence W 1  and the fluorescence W 2  at the second input end  4   e   1  of the second optical transmission fiber  4  (refer to  FIG.  28   ). The fluorescence W 1  and the fluorescence W 2  mix spatially when being transmitted by the second optical transmission fiber  4 . The illumination light  10  radiated from the optical radiation module  5  is thus less likely to have a color distribution. In this case, the optical radiation module  5  can radiate the illumination light  10  as a mixture of the colors of the fluorescence W 1  and the fluorescence W 2 . 
     As in the eighth embodiment, the photoconversion device  30  may also emit, for example, the fluorescence W 1  and the fluorescence W 2  as illumination light into the external space without being through the second optical transmission fiber  4  (refer to  FIG.  31   ). The first phosphor portion  2311  is located in the positive Z-direction from the second phosphor portion  2312  and receives the first excitation light P 1  in the positive Z-direction. In this structure, the first phosphor portion  2311  can emit more fluorescence W 1  mainly in the positive Z-direction. The second phosphor portion  2312  is located in the negative Z-direction from the first phosphor portion  2311  and receives the second excitation light P 2  in the negative Z-direction. In this structure, the second phosphor portion  2312  can emit more fluorescence W 2  mainly in the negative Z-direction. Thus, the illumination light emitted from the photoconversion device  30  can have a spatial color distribution in the Z-direction. The color distribution of the illumination light is reflected in the color tones of an illumination object. The color tones of the illumination object can thus be changed partially. More specifically, the color tones can be changed between a part of the illumination object receiving more fluorescence W 1  and a part of the illumination object receiving more fluorescence W 2 . 
     The photoconversion device  30  may be used for, for example, illumination in a stage performance to change the distribution of the color tones of an illumination object. The photoconversion device  30  may also be used as illumination for inspection equipment for inspecting an inspection object. For example, detecting defects in an inspection object including a substrate such as a semiconductor substrate may use illumination light with a different color depending on the types of defects to be detected. The first phosphor portion  2311  is thus designed to emit fluorescence W 1  for detecting a defect of a first type, and the second phosphor portion  2312  is designed to emit fluorescence W 2  for detecting a defect of a second type. This facilitates detection of defects of a first type in a portion receiving the fluorescence W 1  and detection of defects of a second type in a portion receiving the fluorescence W 2 . The inspection object can be, for example, scanned using this illumination light to allow inspection entirely across the inspection object. 
     As illustrated in  FIG.  29   , when the first phosphor portion  2311  is located on the main surface  2313   a  of the substrate  2313  and the second phosphor portion  2312  is located on the main surface  2313   b  of the substrate  2313 , at least one of the main surface  2313   a  or the main surface  2313   b  may be a reflective surface. In this case, the spatial color distribution can be notable. This results from the fluorescence W 1  from the first phosphor portion  2311  traveling in the negative Z-direction and reflected from the substrate  2313  to travel in the positive Z-direction, and the fluorescence W 2  traveling in the negative Z-direction likewise. The illumination object can thus have a more notable distribution of color tones. 
     In the example of  FIG.  28    as well, the photoconversion device  30  may emit the fluorescence W 1  and the fluorescence W 2  as illumination light without being through the second optical transmission fiber  4 . This can change the distribution of the color tones of the illumination object. 
     As described above, the color distribution of the illumination light can be reduced by causing the light to travel through the second optical transmission fiber  4 . However, when, for example, the second optical transmission fiber  4  is short, the illumination light I 0  after traveling through the second optical transmission fiber  4  may possibly have a viewable color distribution. In this case, the illumination light I 0  after traveling through the second optical transmission fiber  4  can also change the distribution of the color tones of the illumination object. 
     In the ninth embodiment as well, the single output portion is used to simplify the light source system as in the seventh and eighth embodiments. However, multiple output portions may be used when simplifying the light source system is not to be considered. In the ninth embodiment, excitation light may simply be applied to the first incident surface  231   a  of the first phosphor portion  2311  and the second incident surface  231   b  of the second phosphor portion  2312  having the composition different from the first phosphor portion  2311 . This can adjust the colors or the color distribution of the illumination light. 
     The structures according to other embodiments described below may also include multiple output portions when simplifying the light source system is not to be considered. 
     2-2-3. Tenth Embodiment 
     A splitter optical system  232  in a tenth embodiment splits excitation light P 0  output through the first output end  2   e   2  into first excitation light P 1  and second excitation light P 2  at a variable ratio. In other words, the splitter optical system  232  changes the light intensity ratio of the second excitation light P 2  to the first excitation light P 1 .  FIG.  32    is a schematic view of a photoconversion device  30  with an example structure according to the tenth embodiment. This photoconversion device  30  has the same or similar structure as the photoconversion device  30  according to the ninth embodiment except the structure of the splitter optical system  232 .  FIG.  33    is a schematic diagram of the photoconversion device  30  with an example structure having the light intensity ratio of the second excitation light P 2  to the first excitation light P 1  deviating from  1 . In the example of  FIG.  33   , the light intensity ratio of the second excitation light P 2  to the first excitation light P 1  is greater than 1. The light intensity is, for example, the total integral of luminance in a cross section perpendicular to the traveling direction of light. 
     Referring to  FIG.  32   , the splitter optical system  232  further includes a color adjuster drive  234  that moves the splitter  2321  relative to the first output end  2   e   2 . The color adjuster drive  234  moves, for example, the splitter  2321  relative to the first output end  2   e   2  to change the light intensity ratio of the second excitation light P 2  to the first excitation light P 1 . In the example of  FIG.  32   , the splitter  2321  is moved in the positive Z-direction from the first output end  2   e   2  to increase the cross-sectional area of the second excitation light P 2  and thus to increase the light intensity of the second excitation light P 2 . To simplify the drawing, the color adjuster drive  234  is not illustrated in  FIG.  32   . 
     As illustrated in  FIG.  31   , the color adjuster drive  234  includes, for example, a holder  2341  and a displacer  2344 . The holder  2341  is a component for attaching the splitter  2321  to the housing  3   b . The holder  2341  includes, for example, a rod  2342  and an arm  2343 . The rod  2342  is between the reflector  233  and the focusing plane  33   f  in the x-direction. The rod  2342  is, for example, elongated in the Z-direction, and has one end attached to the housing  3   b  with the displacer  2344 . The arm  2343  is, for example, elongated in the X-direction, and has an end in the positive X-direction joined to the splitter  2321  and an end in the negative X-direction joined to the rod  2342 . 
     The displacer  2344  can move the holder  2341  forward and rearward in the Z-direction. Thus, the holder  2341  and the splitter  2321  move forward and rearward integrally in the Z-direction. The displacer  2344  may include, for example, a ball screw. The ball screw includes a screw shaft extending in the Z-direction, a motor that rotates the screw shaft, and a nut that is screwed with the screw shaft and moves in the Z-direction as the screw shaft rotates. The nut is connected to the rod  2342 . In some embodiments, the displacer  2344  may include, for example, a linear motor. The linear motor includes, for example, a stator and a rotor that moves in the Z-direction under a magnetic force between the rotor and the stator. The rotor is connected to the rod  2342 . 
     The color adjuster drive  234  (more specifically, the displacer  2344 ) is controlled by the controller  26 . The controller  26  receives an external instruction and controls the displacer  2344  based on the instruction to adjust the relative positions of the splitter  2321  and the first output end  2   e   2 . The controller  26  thus adjusts the light intensity ratio of the second excitation light P 2  relative to the first excitation light P 1 . 
     The controller  26  may serve as a control circuit. The controller  26  may have the same or similar hardware configuration as the controller  36 . 
     The relative positions of the splitter  2321  and the first output end  2   e   2  will be described based on a reference position. The reference position is the relative position of either the splitter  2321  or the first output end  2   e   2  relative to the other when the light intensity ratio of the second excitation light P 2  to the first excitation light P 1  is 1. In the example of  FIG.  31   , the reference position is the position of the splitter  2321  when the boundary between the third incident surface  2321   a  and the fourth incident surface  2321   b  is aligned with the optical axis AX 1 . 
     As illustrated in  FIG.  32   , when the splitter  2321  moves from the reference position in the positive Z-direction, the third incident surface  2321   a  of the splitter  2321  moves away from the optical axis AX 1  of the first output end  2   e   2  in the positive Z-direction. In this case, a smaller first portion of the excitation light P 0  output through the first output end  2   e   2  is incident on the third incident surface  2321   a . The first portion is smaller as the splitter  2321  is moved more in the positive Z-direction. The first portion of the excitation light P 0  reflected from the third incident surface  2321   a  travels in the positive Z-direction as the first excitation light P 1 . Thus, the first excitation light P 1  has a smaller cross-sectional area as the splitter  2321  is moved more in the positive Z-direction. The light intensity of the first excitation light P 1  is lower as the splitter  2321  is moved more in the positive Z-direction. 
     The center of the fourth incident surface  2321   b  of the splitter  2321  moves toward the optical axis AX 1  of the first output end  2   e   2 . Thus, a larger second portion of the excitation light P 0  is incident on the fourth incident surface  2321   b . The second portion of the excitation light P 0  reflected from the fourth incident surface  2321   b  travels in the positive Z-direction as the second excitation light P 2 . Thus, the second excitation light P 2  has a larger cross-sectional area as the splitter  2321  is moved more in the positive Z-direction. The light intensity of the second excitation light P 2  is higher as the splitter  2321  is moved more in the positive Z-direction. 
     As described above, the light intensity ratio of the second excitation light P 2  to the first excitation light P 1  increases as the splitter  2321  is moved more in the positive Z-direction from the first output end  2   e   2 . As illustrated in  FIG.  32   , the first excitation light P 1  is incident on a smaller area of the first incident surface  231   a  of the first phosphor portion  2311 , and the second excitation light P 2  is incident on a larger area of the second incident surface  231   b  of the second phosphor portion  2312 . Thus, the first phosphor portion  2311  emits fluorescence W 1  with lower light intensity, whereas the second phosphor portion  2312  emits fluorescence W 2  with higher light intensity. The light intensity ratio of the fluorescence W 2  to the fluorescence W 1  thus also increases as the splitter  2321  moves more in the positive Z-direction.  FIG.  32    schematically illustrates the relationship between the light intensity of the fluorescence W 1  and the light intensity of the fluorescence W 2  with lines having the corresponding thicknesses. 
     As illustrated in  FIG.  32   , the first wavelength converter  231  may be installed stationary independently of the position of the splitter  2321 . In other words, the splitter  2321  may be separate from the first wavelength converter  231 . This allows the first wavelength converter  231  that emits the fluorescence W 1  and the fluorescence W 2  to remain at the position of the first focal point F 1  independently of the movement of the splitter  2321 . 
     The light intensity ratio of the second excitation light P 2  to the first excitation light P 1  decreases as the splitter  2321  is moved more in the negative Z-direction from the first output end  2   e   2 . The first excitation light P 1  is incident on a larger area of the first phosphor portion  2311 . The second excitation light P 2  is incident on a smaller area of the second phosphor portion  2312 . The light intensity ratio of the fluorescence W 2  to the fluorescence W 1  thus also decreases as the splitter  2321  moves more in the negative Z-direction. 
     As described above, the light intensity ratio of the fluorescence W 2  to the fluorescence W 1  is adjustable by the color adjuster drive  234  moving the splitter  2321  relative to the first output end  2   e   2 . 
     In the example of  FIGS.  31  and  32   , the reflective surface  233   r  of the reflector  233  is aligned with the ellipsoid  33   e . The photoconversion device  30  focuses, for example, the fluorescence W 1  and the fluorescence W 2  at the second input end  4   e   1  of the second optical transmission fiber  4 . The fluorescence W 1  and the fluorescence W 2  are transmitted by the second optical transmission fiber  4  and emitted from the optical radiation module  5  as illumination light I 0 . The fluorescence W 1  and the fluorescence W 2  mix spatially when being transmitted by the second optical transmission fiber  4 . The illumination light I 0  including the fluorescence W 1  and the fluorescence W 2  is then emitted from the optical radiation module  5 . The color adjuster drive  234  thus adjusts the light intensity ratio between the fluorescence W 1  and the fluorescence W 2  to adjust the color tones of the illumination light I 0 . When, for example, the second optical transmission fiber  4  is short, the illumination light I 0  can have a spatial color distribution. In this case, the color distribution can be adjusted. 
     The controller  26  controls the color adjustment drive  234  (more specifically, the displacer  2344 ) based on an external instruction. For example, the user may input an instruction about the color tones of the illumination light I 0  by operating an input device such as a switch. The input device then outputs the instruction to the controller  26 . The controller  26  controls the color adjuster drive  234  to cause the illumination light I 0  to have the color tones responding to the instruction. The correspondence between each instruction and an operation of the splitter  2321  may be predefined. The controller  26  may determine the position of the splitter  2321  based on an instruction from the input device and the predefined correspondence. As described above, the user can adjust the color tones of the illumination light I 0  by operating the input device. 
     In the above example, the color adjuster drive  234  adjusts the color tones of the illumination light I 0  by moving the splitter  2321  and the first output end  2   e   2  relative to each other. In this manner, the simple structure allows the color adjustment. 
     The photoconversion device  30  may emit the fluorescence W 1  and the fluorescence W 2  into the external space as illumination light without being through the second optical transmission fiber  4  and the optical radiation module  5 . In this case, the color adjuster drive  234  adjusts the light intensity ratio between the fluorescence W 1  and the fluorescence W 2  to adjust the color distribution of the illumination light. 
     The reflective surface  233   r  of the reflector  233  may be along a parabolic plane as in, for example, the second embodiment. In this case, the fluorescence W 1  and the fluorescence W 2  reflected from the reflective surface  233   r  each are output as collimated light. 
     2-2-3-1. Position of Wavelength Converter 
     As described above, the first wavelength converter  231  may be installed substantially stationary independently of the position of the splitter  2321 . This allows the first incident surface  231   a  and the second incident surface  231   b  of the first wavelength converter  231  to remain at substantially equal distances from the first focal point F 1 . Thus, the reflector  233  can focus the fluorescence W 1  and the fluorescence W 2  onto the focusing plane  33   f  with equal directivity, or convert the fluorescence W 1  and the fluorescence W 2  to collimated light with equal directivity. 
     2-2-3-2. Holder 
     The holder  2341  holding the splitter  2321  may be made of a rigid material with high rigidity, such as glass and metal (e.g., stainless steel). The splitter  2321  can be installed with less positional fluctuation. 
     The holder  2341  may be made of a transparent material such as transparent glass. In this case, a portion of the fluorescence W 1  or a portion of the fluorescence W 2  reflected from the reflector  233  is transmitted through the holder  2341 . The holder  2341  is less likely to block the optical paths of the fluorescence W 1  and the fluorescence W 2 . This structure can thus increase the light intensity of the illumination light  10 . 
     The holder  2341  may not be entirely transparent, but may simply include a transparent portion that receives the fluorescence W 1  and the fluorescence W 2  from the reflector  233 . 
     2-2-3-3. Color Adjuster Drive 
     In the above example, the color adjuster drive  234  moves the splitter  2321  parallel to the Z-direction. However, the structure is not limited to this example.  FIG.  34    is a schematic perspective view of the splitter  2321  and the color adjuster drive  234  in an example structure. In the example of  FIG.  34   , the rod  2342  extends in the Y-direction, and has an end opposite to the arm  2343  connected to the displacer  2344 . The displacer  2344  includes, for example, a motor. The rod  2342  is attached to the housing  3   b  in a turnable manner. The displacer  2344  causes, for example, the rod  2342  to turn about the rotation axis Q 1  in the X-direction within a predetermined angular range. Thus, the rod  2342 , the arm  2343 , and the splitter  2321  turn integrally within the predetermined angular range. This turning causes the splitter  2321  to move forward and rearward in the circumferential direction about the rotation axis Q 1  on a YZ cross section. The circumferential direction substantially matches the Z-direction. The displacer  2344  can thus move the splitter  2321  forward and rearward in the Z-direction. For the rod  2342  that is longer, the splitter  2321  is likely to move more parallel to the Z-direction. This movement of the splitter  2321  can also change the proportions of the portions of the excitation light P 0  output through the first output end  2   e   2  and incident on the third incident surface  2321   a  and the fourth incident surface  2321   b  of the splitter  2321 . 
     2-2-4. Eleventh Embodiment 
       FIG.  35    is a block diagram of a photoconversion device  30  with an example structure according to an eleventh embodiment. This photoconversion device  30  has the same or similar structure as the photoconversion device  30  according to the tenth embodiment except the structure of the color adjuster drive  234 . This color adjuster drive  234  moves the first output end  2   e   2 , instead of the splitter  2321 , in the Z-direction to change the light intensity ratio of the second excitation light P 2  to the first excitation light P 1 .  FIG.  36    is a schematic diagram of the photoconversion device  30  with the light intensity ratio of the second excitation light P 2  to the first excitation light P 1  deviating from  1 . In the example of  FIG.  36   , the light intensity ratio of the second excitation light P 2  to the first excitation light P 1  is greater than 1. 
     The color adjuster drive  234  includes a holder  2345  and a displacer  2348  instead of the holder  2341  and the displacer  2344 . The holder  2345  is a component for attaching the first output end  2   e   2  as an output portion to the housing  3   b . The holder  2345  is attached to, for example, the housing  3   b  through the displacer  2348 . The holder  2345  comes in contact with, for example, a side peripheral surface of a portion including the first output end  2   e   2  of the first optical transmission fiber  2  to hold the first optical transmission fiber  2 . In the photoconversion device  30  including the optical system L 31  as illustrated in  FIG.  35   , the holder  2345  may also come in contact with the optical system L 31  and hold both the optical system L 31  and the first optical transmission fiber  2 . In the example of  FIG.  35   , the holder  2345  includes a rod  2346  and a contact member  2347 . The rod  2346  is, for example, elongated in the Z-direction, and has one end attached to the displacer  2348 . The rod  2346  has the opposite end connected to the contact member  2347 . The contact member  2347  may extend, for example, in the X-direction, and includes a surface in the positive Z-direction in contact with and connected to the optical system L 31  and the first optical transmission fiber  2 . 
     The displacer  2348  can move the holder  2345  forward and rearward in the Z-direction. Thus, the holder  2345 , the first optical transmission fiber  2 , and the optical system L 31  move forward and rearward integrally in the Z-direction. A specific example of the displacer  2348  is the same as or similar to the displacer  2344 . 
     The through-hole  233   h  of the reflector  233  has a cross-sectional area large enough to allow the first optical transmission fiber  2  to be movable in the Z-direction. In other words, the first optical transmission fiber  2  can be loosely fitted in the through-hole  233   h  of the reflector  233  and can be movable in the Z-direction from the reflector  233 . 
     As illustrated in  FIG.  36   , when the first output end  2   e   2  and the optical system L 31  move in the negative Z-direction, the excitation light P 0  translates in the negative Z-direction. Thus, a smaller first portion of the excitation light P 0  is incident on the first incident surface  231   a , and a larger second portion of the excitation light P 0  is incident on the second incident surface  231   b . Thus, the light intensity ratio of the second excitation light P 2  to the first excitation light P 1  increases as the first output end  2   e   2  and the optical system L 31  are moved more in the negative Z-direction. 
     As illustrated in  FIG.  36   , the first excitation light P 1  is incident on a smaller area of the first incident surface  231   a  of the first phosphor portion  2311 , and the second excitation light P 2  is incident on a larger area of the second incident surface  231   b  of the second phosphor portion  2312 . Thus, the first phosphor portion  2311  emits fluorescence W 1  with lower light intensity, whereas the second phosphor portion  2312  emits fluorescence W 2  with higher light intensity. More specifically, the light intensity ratio of the fluorescence W 2  to the fluorescence W 1  increases as the first output end  2   e   2  and the optical system L 31  move more in the negative Z-direction. 
     In contrast, the light intensity ratio of the second excitation light P 2  to the first excitation light P 1  decreases as the first output end  2   e   2  and the optical system L 31  are moved more in the positive Z-direction. The first excitation light P 1  is incident on a larger area of the first phosphor portion  2311 . The second excitation light P 2  is incident on a smaller area of the second phosphor portion  2312 . Thus, the first phosphor portion  2311  emits fluorescence W 1  with higher light intensity, whereas the second phosphor portion  2312  emits fluorescence W 2  with lower light intensity. More specifically, the light intensity ratio of the fluorescence W 2  to the fluorescence W 1  decreases as the first output end  2   e   2  and the optical system L 31  move more in the positive Z-direction. 
     As described above, the light intensity ratio of the fluorescence W 2  to the fluorescence W 1  is adjustable by the color adjuster drive  234  moving the first output end  2   e   2  and the optical system L 31  in the Z-direction. This can adjust the color tones or the color distribution of the illumination light I 0 . 
     In the eleventh embodiment, the color adjuster drive  234  that moves the first output end  2   e   2  is located outside the reflector  233  as illustrated in  FIG.  35   . The color adjuster drive  234  can avoid being located on the optical paths of the fluorescence W 1  and the fluorescence W 2  emitted by the first wavelength converter  231 . Thus, the fluorescence W 1  and the fluorescence W 2  avoid entering the color adjuster drive  234  and being blocked by the color adjuster drive  234 . This structure can increase the light intensity of the illumination light  10 . 
     2-2-5. Twelfth Embodiment 
       FIG.  37    is a block diagram of a photoconversion device  30  with an example structure according to a twelfth embodiment. This photoconversion device  30  has the same or similar structure as the photoconversion device  30  according to the ninth embodiment, except that it includes a second wavelength converter  235 . The second wavelength converter  235  is located across the third incident surface  2321   a  and the fourth incident surface  2321   b  of the splitter  2321 . More specifically, a part of the second wavelength converter  235  is located on the third incident surface  2321   a , and the remaining part of the second wavelength converter  235  is located on the fourth incident surface  2321   b.    
     The second wavelength converter  235  can emit, for example, fluorescence W 0  in response to the excitation light P 0  output through the first output end  2   e   2  of the first optical transmission fiber  2 . The second wavelength converter  235  includes a phosphor portion similarly to the first wavelength converter  231 . The second wavelength converter  235  has a different structure from the first wavelength converter  231 . For example, the wavelength spectrum of the fluorescence W 0  emitted by the second wavelength converter  235  differs from the wavelength spectrum of each of the fluorescence W 1  and the fluorescence W 2  emitted by the first wavelength converter  231 . 
     As illustrated in  FIG.  37   , the second wavelength converter  235  may include a third phosphor portion  2351  and a fourth phosphor portion  2352 . The third phosphor portion  2351  and the fourth phosphor portion  2352  also include phosphor pellets containing, for example, a phosphor and a sealant, similarly to the first phosphor portion  2311  and the second phosphor portion  2312 . The first phosphor portion  2311 , the second phosphor portion  2312 , the third phosphor portion  2351 , and the fourth phosphor portion  2352  may have different compositions and may each emit fluorescence W 0  with a different wavelength spectrum. The fluorescence W 0  emitted by the third phosphor portion  2351  is referred to as fluorescence W 3 . The fluorescence W 0  emitted by the fourth phosphor portion  2352  is referred to as fluorescence W 4 . In the example of  FIG.  37   , the third phosphor portion  2351  is located on the third incident surface  2321   a  of the splitter  2321 , and the fourth phosphor portion  2352  is located on the fourth incident surface  2321   b  of the splitter  2321 . 
     The third phosphor portion  2351  receives the first portion of the excitation light P 0  traveling toward the third incident surface  2321   a . The third phosphor portion  2351  emits the fluorescence W 3  in response to the first portion of the excitation light P 0 . In  FIG.  37   , example optical paths of the fluorescence W 3  and the fluorescence W 4  are indicated with thick dashed lines. The thick lines are simply for visibility in the drawing. The thickness of each line does not indicate the light intensity of the fluorescence W 3  or the light intensity of the fluorescence W 4 . 
     A portion of the fluorescence W 3  emitted by the third phosphor portion  2351  travels toward the first focal point through the first optical path changer  2322 . More specifically, the portion of the fluorescence W 3  travels toward the first wavelength converter  231 . The portion of the fluorescence W 3  is reflected from the reflective surface  233   r  of the reflector  233  after passing through the first wavelength converter  231  at the first focal point F 1  and is then focused onto the focusing plane  33   f  aligned with the second focal point F 2 . The remaining portion of the fluorescence W 3  emitted by the third phosphor portion  2351  is mainly reflected from the reflective surface  233   r  of the reflector  233  without passing through the first optical path changer  2322 . The fluorescence W 3  that does not pass through the first optical path changer  2322  does not travel near the first focal point F 1  and is thus less likely to be focused onto the focusing plane  33   f.    
     The fourth phosphor portion  2352  receives the second portion of the excitation light P 0  traveling toward the fourth incident surface  2321   b . The fourth phosphor portion  2352  emits the fluorescence W 4  in response to the second portion of the excitation light P 0 . A portion of the fluorescence W 4  emitted by the fourth phosphor portion  2352  travels toward a position near the first focal point F 1  through the second optical path changer  2323 . In other words, the portion of the fluorescence W 4  travels toward the first wavelength converter  231 . The portion of the fluorescence W 4  is reflected from the reflective surface  233   r  of the reflector  233  after passing through the first wavelength converter  231  at the first focal point F 1  and is then focused onto the focusing plane  33   f  aligned with the second focal point F 2 . The remaining portion of the fluorescence W 4  emitted by the fourth phosphor portion  2352  is mainly reflected from the reflective surface  233   r  of the reflector  233  without passing through the second optical path changer  2323 . The fluorescence W 4  that does not pass through the second optical path changer  2323  does not travel near the first focal point F 1  and is thus less likely to be focused onto the focusing plane  33   f.    
     A portion of the excitation light P 0  not absorbed by the third phosphor portion  2351  and the fourth phosphor portion  2352  is split into the first excitation light P 1  and the second excitation light P 2  by the splitter  2321 . The first excitation light P 1  is directed to the first incident surface  231   a  of the first wavelength converter  231  by the first optical path changer  2322 . The second excitation light P 2  is directed to the second incident surface  231   b  of the first wavelength converter  231  by the second optical path changer  2323 . The first wavelength converter  231  can emit the fluorescence W 1  and the fluorescence W 2  in response to the first excitation light P 1  and the second excitation light P 2 . With the first wavelength converter  231  located at the first focal point F 1 , the fluorescence W 1  and the fluorescence W 2  emitted by the first wavelength converter  231  are focused onto the focusing plane  33   f.    
     In the example of  FIG.  37   , the second input end  4   e   1  of the second optical transmission fiber  4  is aligned with the focusing plane  33   f  Thus, the fluorescence W 1 , the fluorescence W 2 , the fluorescence W 3 , and the fluorescence W 4  enter the second input end  4   e   1  of the second optical transmission fiber  4 . The fluorescence W 1 , the fluorescence W 2 , the fluorescence W 3 , and the fluorescence W 4  are radiated into the external space  200  as illumination light I 0  after passing through the second optical transmission fiber  4  and the optical radiation module  5 . The illumination light I 0  includes the fluorescence W 1 , the fluorescence W 2 , the fluorescence W 3 , and the fluorescence W 4 . The optical radiation module  5  can thus emit the illumination light I 0  having the mixture of multiple colors. 
     When, for example, the second optical transmission fiber  4  is short, the illumination light I 0  can have a color distribution. In this case, the color distribution can include more different colors. When the photoconversion device  30  emits the fluorescence W 1 , the fluorescence W 2 , the fluorescence W 3 , and the fluorescence W 4  reflected from the reflective surface  233   r  of the reflector  233  as illumination light into the external space without being through the second optical transmission fiber  4  and the optical radiation module  5 , the illumination light can have a more notable color distribution. 
     The reflective surface  233   r  of the reflector  233  may be along a parabolic plane, similarly to the reflective surface in the eighth embodiment. 
     As in the ninth and tenth embodiments, the photoconversion device  30  may further include a color adjuster drive  234 . The color adjuster drive  234  can adjust the light intensity ratio of the first excitation light P 1  incident on the first phosphor portion  2311  and the second excitation light P 2  incident on the second phosphor portion  2312 , as in the ninth and tenth embodiments. In the twelfth embodiment, the light intensity ratio of the excitation light P 0  incident on each of the third phosphor portion  2351  and the fourth phosphor portion  2352  can also be adjusted by driving the color adjuster drive  234 . Thus, the color adjuster drive unit  234  can adjust the light intensity ratio of the fluorescence W 1 , the fluorescence W 2 , the fluorescence W 3 , and the fluorescence W 4 . 
     At least one of the first phosphor portion  2311 , the second phosphor portion  2312 , the third phosphor portion  2351 , or the fourth phosphor portion  2352  may have the composition identical to the composition of at least any other phosphor portion. More specifically, at least one of the fluorescence W 1 , fluorescence W 2 , the fluorescence W 3 , or the fluorescence W 4  may have substantially the same color as at least any other fluorescence. At least one of the first phosphor portion  2311 , the second phosphor portion  2312 , the third phosphor portion  2351 , or the fourth phosphor portion  2352  may have the composition different from the composition of any other phosphor portion. This allows the color adjuster drive  234  to adjust the colors or the color distribution of the illumination light. 
     2-2-6. Thirteenth Embodiment 
       FIG.  38    is a block diagram of a photoconversion device  30  with an example structure according to a thirteenth embodiment. This photoconversion device  30  has the same or similar structure as the photoconversion device  30  according to the ninth embodiment, except that it includes a third wavelength converter  236 . As illustrated in  FIG.  38   , the photoconversion device  30  may include two third wavelength converters  236 . The third wavelength converter  236  is located, for example, on the surface of the first optical path changer  2322  in the negative Z-direction and the surface of the second optical path changer  2323  in the positive Z-direction. 
     The third wavelength converter  236  can emit, for example, fluorescence W 0  in response to the excitation light P 0  output through the first output end  2   e   2  of the first optical transmission fiber  2 . The third wavelength converter  236  includes a phosphor portion similarly to the first wavelength converter  231 . The third wavelength converter  236  has a different structure from the first wavelength converter  231 . For example, the wavelength spectrum of the fluorescence W 0  emitted by the third wavelength converter  236  differs from the wavelength spectrum of each of the fluorescence W 1  and the fluorescence W 2  emitted by the first wavelength converter  231 . 
     As illustrated in  FIG.  38   , the third wavelength converter  236  on the first optical path changer  2322  may include a fifth phosphor portion  2361 , and the third wavelength converter  236  on the second optical path changer  2323  may include a sixth phosphor portion  2362 . The fifth phosphor portion  2361  and the sixth phosphor portion  2362  also each include phosphor pellets containing, for example, a phosphor and a sealant. The first phosphor portion  2311 , the second phosphor portion  2312 , the fifth phosphor portion  2361 , and the sixth phosphor portion  2362  may have different compositions and may each emit fluorescence W 0  with a different wavelength spectrum. The fluorescence W 0  emitted by the fifth phosphor portion  2361  is referred to as fluorescence W 5 . The fluorescence W 0  emitted by the sixth phosphor portion  2362  is referred to as fluorescence W 6 . In  FIG.  38   , example optical paths of the fluorescence W 5  and the fluorescence W 6  are indicated with thick dashed lines. The thick lines are simply for visibility in the drawing. The thickness of each line does not indicate the light intensity of the fluorescence W 5  or the light intensity of the fluorescence W 6 . 
     The excitation light P 0  output through the first output end  2   e   2  is split into the first excitation light P 1  and the second excitation light P 2  by the splitter  2321 . The first excitation light P 1  enters the fifth phosphor portion  2361 . The second excitation light P 2  enters the sixth phosphor portion  2362 . The fifth phosphor portion  2361  receiving the first excitation light P 1  emits fluorescence W 5 . The sixth phosphor portion  2362  receiving second excitation light P 2  emits fluorescence W 6 . 
     A portion of the fluorescence W 5  emitted by the fifth phosphor portion  2361  travels toward a position near the first focal point F 1 . In other words, the portion of the fluorescence W 5  travels toward the first wavelength converter  231 . The portion of the fluorescence W 5  is reflected from the reflective surface  233   r  of the reflector  233  after passing through the first wavelength converter  231  located at the first focal point F 1  and is then focused onto the focusing plane  33   f  aligned with the second focal point F 2 . The remaining portion of the fluorescence W 5  does not travel near the first focal point F 1  (e.g., the first wavelength converter  231 ). The fluorescence W 5  that does not travel near the first focal point F 1  and is thus less likely to be focused onto the focusing plane  33   f.    
     A portion of the fluorescence W 6  emitted by the sixth phosphor portion  2362  travels toward a position near the first focal point F 1 . In other words, the portion of the fluorescence W 6  travels toward the first wavelength converter  231 . The portion of the fluorescence W 6  is reflected from the reflective surface  233   r  of the reflector  233  after passing through the first wavelength converter  231  at the first focal point F 1  and is then focused onto the focusing plane  33   f  aligned with the second focal point F 2 . The remaining portion of the fluorescence W 6  does not travel near the first focal point F 1  (e.g., the first wavelength converter  231 ). The fluorescence W 6  that does not travel near the first focal point F 1  and is thus less likely to be focused onto the focusing plane  33   f.    
     The first excitation light P 1  not absorbed by the fifth phosphor portion  2361  is directed to the first incident surface  231   a  of the first phosphor portion  2311  by the first optical path changer  2322 . The first phosphor portion  2311  receiving the first excitation light P 1  emits fluorescence W 1 . The second excitation light P 2  not absorbed by the sixth phosphor portion  2362  is directed to the second incident surface  231   b  of the second phosphor portion  2312  by the second optical path changer  2323 . The second phosphor portion  2312  receiving the second excitation light P 2  emits fluorescence W 2 . With the first wavelength converter  231  located at the first focal point F 1 , the fluorescence W 1  and the fluorescence W 2  emitted by the first wavelength converter  231  are focused onto the focusing plane  33   f.    
     In the example of  FIG.  38   , the second input end  4   e   1  of the second optical transmission fiber  4  is aligned with the focusing plane  33   f  Thus, the fluorescence W 1 , the fluorescence W 2 , the fluorescence W 5 , and the fluorescence W 6  enter the second input end  4   e   1  of the second optical transmission fiber  4 . The fluorescence W 1 , the fluorescence W 2 , the fluorescence W 5 , and the fluorescence W 6  are radiated into the external space  200  as illumination light I 0  after passing through the second optical transmission fiber  4  and the optical radiation module  5 . The illumination light I 0  includes the fluorescence W 1 , the fluorescence W 2 , the fluorescence W 5 , and the fluorescence W 6 . The optical radiation module  5  can thus emit the illumination light I 0  with the mixture of multiple colors. 
     When, for example, the second optical transmission fiber  4  is short, the illumination light I 0  can have a color distribution. In this case, the color distribution can include more different colors. When the photoconversion device  30  emits the fluorescence W 1 , the fluorescence W 2 , the fluorescence W 5 , and the fluorescence W 6  reflected from the reflective surface  233   r  of the reflector  233  as illumination light into the external space without being through the second optical transmission fiber  4  and the optical radiation module  5 , the illumination light can have a more notable color distribution. 
     The reflective surface  233   r  of the reflector  233  may be along a parabolic plane, similarly to the eighth embodiment. 
     As in the ninth and tenth embodiments, the photoconversion device  30  may further include a color adjuster drive  234 . The color adjuster drive  234  can adjust the light intensity ratio of the first excitation light P 1  and the second excitation light P 2 , as in the ninth and tenth embodiments. In the thirteenth embodiment, the first excitation light P 1  enters the fifth phosphor portion  2361  and the first phosphor portion  2311 , and the second excitation light P 2  enters the sixth phosphor portion  2362  and the second phosphor portion  2312 . Thus, the color adjuster drive unit  234  can adjust the light intensity ratio of the fluorescence W 1 , the fluorescence W 2 , the fluorescence W 5 , and the fluorescence W 6 . 
     At least one of the first phosphor portion  2311 , the second phosphor portion  2312 , the fifth phosphor portion  2361 , or the sixth phosphor portion  2362  may have the composition identical to the composition of any other one of the phosphor portions. More specifically, at least one of the fluorescence W 1 , the fluorescence W 2 , the fluorescence W 5 , or the fluorescence W 6  may substantially have the same color as at least any other fluorescence. At least one of the first phosphor portion  2311 , the second phosphor portion  2312 , the fifth phosphor portion  2361 , or the sixth phosphor portion  2362  may have the composition different from the composition of any other phosphor portion to allow the color adjuster drive  234  to adjust the colors or the color distribution of the illumination light. 
     2-2-7. Fourteenth Embodiment 
     The photoconversion device  30 F in the illumination system  100 F illustrated in  FIG.  11    has the same or similar structure as the photoconversion device  30  according to any of the seventh to thirteenth embodiments described above. 
     In this structure as well, the photoconversion device  30 F includes, for example, a first wavelength converter  231  and a splitter optical system  232 . The first wavelength converter  231  includes a first incident surface  231   a  on its first end (e.g., in the positive Z-direction) intersecting with the optical axis AX 1  and a second incident surface  231   b  on its second end (e.g., in the negative Z-direction) opposite to the first end, and emits fluorescence W 0  in response to the excitation light P 0 . The splitter optical system  232  splits, for example, the excitation light P 0  output through the first output end  2   e   2  into first excitation light P 1  and second excitation light P 2 , and directs the first excitation light P 1  to the first incident surface  231   a  of the first wavelength converter  231  and the second excitation light P 2  to the second incident surface  231   b  of the first wavelength converter  231 . This structure allows the first excitation light P 1  to be incident on the first incident surface  231   a  of the first wavelength converter  231  and the second excitation light P 2  to be incident on the second incident surface  231   b  of the first wavelength converter  231  using the single output portion (in other words, the single first output end  2   e   2 ) for outputting the excitation light P 0 . This eliminates the arrangement of multiple output portions corresponding to the first incident surface  231   a  and the second incident surfaces  231   b  of the first wavelength converter  231 , thus simplifying the structure of the light source system and reducing the manufacturing cost. The photoconversion device  30 F can also produce the above other effects as appropriate. 
     An optical radiation module  5  with an example structure according to the fourteenth embodiment illustrated in  FIG.  39    includes a photoconversion device  30 F and an optical radiator  50 . In this example, the photoconversion device  30 F has the same or similar structure as the photoconversion device  30  according to the seventh embodiment illustrated in  FIG.  28   . The optical radiator  50  is the same as or similar to the optical radiator  50  in  FIG.  12   . 
     2-2-8. Fifteenth Embodiment 
     A photoconversion device  30 G in a light-emitting module  1  illustrated in  FIG.  14    has the same or similar structure as the photoconversion device  30  according to any of the seventh to thirteenth embodiments described above. 
     In this structure as well, the photoconversion device  30 G includes, for example, a first wavelength converter  231  and a splitter optical system  232 . The first wavelength converter  231  includes a first incident surface  231   a  on its first end (e.g., in the positive Z-direction) intersecting with the optical axis AX 1  and a second incident surface  231   b  on its second end (e.g., in the negative Z-direction) opposite to the first end, and emits fluorescence W 0  in response to the excitation light P 0 . The splitter optical system  232  splits, for example, the excitation light P 0  from the light-emitting element  10  into first excitation light P 1  and second excitation light P 2 , and directs the first excitation light P 1  to the first incident surface  231   a  of the first wavelength converter  231  and the second excitation light P 2  to the second incident surface  231   b  of the first wavelength converter  231 . This structure allows the first excitation light P 1  to be incident on the first incident surface  231   a  of the first wavelength converter  231  and the second excitation light P 2  to be incident on the second incident surface  231   b  of the first wavelength converter  231  using the single output portion (in other words, the single first output end  2   e   2 ) for outputting the excitation light P 0 . This eliminates the arrangement of multiple output portions corresponding to the first incident surface  231   a  and the second incident surfaces  231   b  of the first wavelength converter  231 , thus simplifying the structure of the light source system and reducing the manufacturing cost. The photoconversion device  30 G can also produce the above other effects as appropriate. 
       FIG.  40    is a schematic diagram of a light-emitting module  1  with an example structure according to a fifteenth embodiment. The light-emitting module  1  with the example structure includes a light-emitting element  10  and a photoconversion device  30 G. In this example, the photoconversion device  30 G has, for example, the same or similar structure as the photoconversion device  30  according to the seventh embodiment illustrated in  FIG.  28   . In the example of  FIG.  40   , excitation light P 0  is emitted from an output portion  10   f  of the light-emitting element  10  toward the splitter  2321 , instead of being through the first output end  2   e   2  of the first optical transmission fiber  2 . 
     2-3. Others 
     Although the first incident surface  231   a  and the second incident surface  231   b  are, for example, flat surfaces in each of the above embodiments, the structure is not limited to this example. The first incident surface  231   a  and the second incident surface  231   b  may have, for example, multiple uneven portions, or may protrude in the direction to receive incident light, or more specifically, may be curved in an arc or may be in another shape. 
     3-1. Sixteenth Embodiment 
     A known light source device converts excitation light such as laser light emitted by a light source to fluorescence with a different wavelength with a phosphor, reflects the fluorescence with a reflector, and emits the fluorescence in a predetermined direction. With the phosphor containing phosphor substances that emit red (R) fluorescence, green (G) fluorescence, and blue (B) fluorescence, for example, the excitation light is converted to pseudo white light. 
     The light intensity of the fluorescence emitted from the phosphor may be increased by, for example, increasing the energy of the excitation light. 
     However, when the energy of the excitation light is increased, for example, a phosphor substance in the phosphor may deteriorate due to the resultant temperature increase. This may cause emission of fluorescence with lower light intensity in response to the excitation light. 
     The inventors of the present disclosure thus have developed a technique for increasing the light intensity of fluorescence emitted from a photoconversion device and an illumination system including the photoconversion device in response to excitation light. 
     3-1-1. Illumination System 
     An example illuminating system according to a sixteenth embodiment is the same as or similar to the system in  FIG.  1   . 
     3-1-2. Photoconversion Device 
     As illustrated in  FIG.  41 A , the photoconversion device  30  includes, for example, a wavelength converter  331 , a heat sink  332 , and a reflector  333 . These components of the photoconversion device  30  are fixed to a housing  3   b  of a relay  3  either directly or indirectly with, for example, another member. 
     For example, the wavelength converter  331  can receive the excitation light P 0  output through the first output end  2   e   2  as an output portion and emit fluorescence W 0 , as illustrated in  FIG.  41 B . The wavelength converter  331  includes, for example, a first surface (also referred to as a front surface)  331   a  to receive excitation light P 0  output through the first output end  2   e   2  as an output portion, and a second surface (also referred to as a back surface)  331   b  different from the first surface  331   a . The wavelength converter  331  in the sixteenth embodiment includes the second surface  331   b  located opposite to the first surface  331   a . For example, the first surface  331   a  may face in the positive X-direction, and the second surface  331   b  may face in the negative X-direction. The wavelength converter  331  is, for example, a flat plate or a film. In other words, for example, the first surface  331   a  and the second surface  331   b  each are along a YZ plane. In this case, for example, the first output end  2   e   2  is, for example, on an imaginary line A 3  extending along the normal to the first surface  331   a . For example, the excitation light P 0  output through the first output end  2   e   2  along the imaginary line A 3  in the negative X-direction is incident on the first surface  331   a  of the wavelength converter  331 . In this example, the first surface  331   a  and the second surface  331   b  may each be a flat surface, such as a circular surface or a polygonal surface, or a non-flat surface, such as a curved surface or an uneven surface. Thus, for example, the imaginary line A 3  may be aligned with an optical path of the excitation light P 0  output through the first output end  2   e   2  as an output portion toward the first surface  331   a.    
     The wavelength converter  331  includes, for example, a solid member including phosphors (also referred to as a phosphor member), similarly to the wavelength converter  132 . 
     The heat sink  332  includes, for example, a third surface (also referred to as a joining surface)  332   r  to be joined to the second surface  331   b  of the wavelength converter  331 . The heat sink  332  can thus cool, for example, the wavelength converter  331  through the second surface  331   b . The wavelength converter  331  is less likely to undergo temperature increase and resultant deterioration. When, for example, the wavelength converter  331  and the third surface  332   r  of the heat sink  332  are in direct contact with each other, heat generated in the wavelength converter  331  upon receiving the excitation light P 0  is easily transferred from the wavelength converter  331  to the heat sink  332 . For example, phosphor pellets may be formed on the third surface  332   r  of the heat sink  332  using, for example, molding with heat, to directly join the wavelength converter  331  to the third surface  332   r  of the heat sink  332 . For the phosphor pellets containing numerous phosphor particles in glass with a low melting point, for example, the phosphor pellets may be joined to the third surface  332   r  of the heat sink  332  by sharing oxygen between the phosphor particles and the material for the heat sink  332 . The glass with a low melting point may be, for example, a transparent metal oxide with a melting point of about 400 to 500 degrees Celsius (° C.). 
     When, for example, the surface area of the heat sink  332  is larger than the surface area of the wavelength converter  331 , the heat sink  332  has a larger area exposed to outside air than the wavelength converter  331 . This allows, for example, heat transferred from the wavelength converter  331  to the heat sink  332  to be easily dissipated into an atmosphere surrounding the heat sink  332 . This facilitates, for example, cooling of the wavelength converter  331  with the heat sink  332 . The heat sink  332  may have, for example, a larger volume than the wavelength converter  331  to facilitate heat transfer from the wavelength converter  331  to the heat sink  332 . The heat sink  332  may include, for example, heat-dissipating fins  332   f  to facilitate heat transfer between the heat sink  332  and the atmosphere surrounding the heat sink  332 . This allows, for example, heat transferred from the wavelength converter  331  to the heat sink  332  to be easily dissipated into the atmosphere surrounding the heat sink  332 . This facilitates, for example, cooling of the wavelength converter  331  with the heat sink  332 . The heat-dissipating fins  332   f  are projections on a surface of the heat sink  332  different from the third surface  332   r . The surface area of the wavelength converter  331  and the surface area of the heat sink  332  herein each refer to the surface area of the component surface exposed to outside air. The heat-dissipating fins  332   f  may be in any shape that increases the surface area of the heat sink  332  to facilitate cooling of the wavelength converter  331  with the heat sink  332 . 
     In the sixteenth embodiment, for example, the third surface  332   r  of the heat sink  332  can reflect light. This allows, for example, the excitation light P 0  passing through the wavelength converter  331  to be reflected from the third surface  332   r  and enter the wavelength converter  331  again. This may increase, for example, the fluorescence W 0  emitted by the wavelength converter  331 . This may thus increase, for example, the light intensity of the fluorescence W 0  emitted in response to the excitation light P 0 . 
     The heat sink  332  may be made of, for example, a metal material. The metal material may be, for example, copper (Cu), aluminum (Al), magnesium (Mg), gold (Au), silver (Ag), iron (Fe), chromium (Cr), cobalt (Co), beryllium (Be), molybdenum (Mo), tungsten (W), or an alloy of any of these metals. The heat sink  332  made of, for example, Cu, Al, Mg, Fe, Cr, Co, or Be as the metal material may be fabricated easily by molding, such as die casting. The heat sink  332  made of, for example, Al, Mg, Ag, Fe, Cr, or Co as the metal material may have the third surface  332   r  with a higher reflectance against visible light. This can increase, for example, the light intensity of the fluorescence W 0  emitted in response to the excitation light P 0 . The heat sink  332  may be made of, for example, a nonmetallic material. The nonmetallic material may be, for example, aluminum nitride (AlN), silicon nitride (Si 3 N 4 ), carbon (C), or aluminum oxide (Al 2 O 3 ). The nonmetallic material may be, for example, crystalline or non-crystalline. The crystalline nonmetallic material may be, for example, silicon carbide (SiC) or Si 3 N 4 . 
     The heat sink  332  may have, as the third surface  332   r , a layer of a metal material with a higher light reflectance than its main part (also referred to as a high light reflectance layer). For example, the heat sink  332  may use Cu as the material for the main part, and may use Ag or Cr, which has a high reflectance against visible light, as the metal material with a high light reflectance. In this case, for example, the main part of the heat sink  332  is fabricated by molding, or for example, by die casting. The surface of the main part then undergoes vapor deposition or plating to form a high light reflectance layer of, for example, Ag or Cr. A dielectric multilayer film may further be formed on, for example, the high light reflectance layer on the third surface  332   r  of the heat sink  332 . The dielectric multilayer film may include, for example, dielectric thin films repeatedly stacked on one another. The dielectric may be at least one material selected from the group consisting of titanium dioxide (TiO 3 ), silicon dioxide (SiO 2 ), niobium pentoxide (Nb 2 O 5 ), tantalum pentoxide (Ta 2 O 5 ), and magnesium fluoride (MgF 2 ). 
     When, for example, the heat sink  332  has a higher thermal conductivity than the wavelength converter  331 , heat generated in the wavelength converter  331  in response to the excitation light P 0  is easily dissipated by the heat sink  332 . The thermal conductivity of the material for the heat sink  332  may be higher than the thermal conductivity of the material for the wavelength converter  331 . More specifically, for example, the material for the heat sink  332  may have a higher thermal conductivity than the transparent material contained in the wavelength converter  331  or than the phosphor (also referred to as a phosphor substance) contained in the wavelength converter  331 . 
     The reflector  333  has, for example, a reflective surface  333   r  facing the first surface  331   a  of the wavelength converter  331 . As illustrated in  FIG.  41 B , the reflective surface  333   r  directs, for example, the fluorescence W 0  emitted by the wavelength converter  331  to be focused onto the focusing plane  33   f  (corresponding to a focusing portion). In the sixteenth embodiment, the wavelength converter  331  is between the reflective surface  333   r  and the focusing plane  33   f  The reflector  333  herein may be, for example, a parabolic reflector. The reflective surface  333   r  is located, for example, to surround the wavelength converter  331  facing the first surface  331   a , similarly to the reflective surface  133   r  of the reflector  1331 . The reflective surface  333   r  may have, for example, a shape along an imaginary parabolic plane. 
     In the sixteenth embodiment, the heat sink  332  has, for example, a width in a direction (second direction) perpendicular to a direction (first direction) from the wavelength converter  331  toward the focusing plane  33   f . The width of the heat sink  332  decreases in the first direction. In the example of  FIGS.  41 A and  41 B , the first direction is the negative X-direction, and the second direction is the Z-direction. The Z-direction includes the positive Z-direction and the negative Z-direction. For example, the second direction may be the Y-direction. The Y-direction includes the positive Y-direction and the negative Y-direction. The heat sink  332  with this shape is less likely to, for example, block an optical path of the fluorescence W 0  from the reflective surface  333   r  toward the focusing plane  33   f . The wavelength converter  331  is thus less likely to undergo temperature increase and resultant deterioration in the photoconversion device  30  and the illumination system  100 . The photoconversion device  30  and the illumination system  100  can thus emit fluorescence W 0  with higher light intensity in response to the excitation light P 0 . 
     The heat sink  332  with the width in the second direction decreasing in the first direction (negative X-direction) may be, for example, the heat sink  332  with the width in the second direction decreasing in the first direction, or the heat sink  332  with the maximum width in the second direction increasing or decreasing in the first direction while the maximum size of the width decreases in the first direction. For example, the size of the cross section (YZ cross section) of the heat sink  332  perpendicular to the first direction (negative X-direction) may decrease in the first direction, or the size of the cross-section may increase or decrease in the first direction while the maximum size of the cross-section decreases in the first direction. For example, the diameter of the cross section (YZ cross section) of the heat sink  332  perpendicular to the first direction (negative X-direction) may decrease in the first direction, or the diameter may increase or decrease in the first direction while the maximum value of the diameter decreases in the first direction. In other words, the heat sink  332  may have, for example, the width in the second direction decreasing in the first direction (negative X-direction). 
     As illustrated in, for example,  FIGS.  41 A and  41 B , the heat sink  332  includes multiple heat-dissipating fins  332   f  arranged in the first direction (negative X-direction). In this case, for example, each heat-dissipating fin  332   f  protrudes in the second direction (e.g., in the Z-direction) perpendicular to the first direction (negative X-direction), and the height of each heat-dissipating fin  332   f  in the second direction (e.g., in the Z-direction) may decrease in the first direction (negative X-direction). 
     As illustrated in, for example,  FIGS.  41 A and  41 B , the heat sink  332  includes a portion  3321  including a third surface  332   r  to which the wavelength converter  331  is joined (also referred to as a first portion), a portion  3322  (also referred to as the second portion) protruding in the first direction (negative X-direction) from the first portion  3321 . In other words, the first portion  3321  is a part of the heat sink  332  joined to the wavelength converter  331 . The boundary between the first portion  3321  and the second portion  3322  in the heat sink  332  is, for example, aligned with an imaginary plane perpendicular to the first direction (YZ plane in this example) at a position at which the width of the heat sink  332  in the second direction starts decreasing in the first direction (negative X-direction) from the third surface  332   r . In the example of  FIGS.  41 A and  41 B , the second portion  3322  includes two heat-dissipating fins  332   f  The two heat-dissipating fins  332   f  include a first heat-dissipating fin  332   f   1  and a second heat-dissipating fin  332   f   2 . The first heat-dissipating fin  332   f   1  and the second heat-dissipating fin  332   f   2  are arranged in this order in the first direction (negative X-direction). A width Wf 1  of the first portion  3321  is the width in the second direction (e.g., in the Z-direction). A width Wf 2  of the first heat-dissipating fin  332   f   1  is the width in the second direction (e.g., in the Z-direction). A width Wf 3  of the second heat-dissipating fin  332   f   2  is the width in the second direction (e.g., in the Z-direction). In this case, the width Wf 2  is less than the width Wf 1 , and the width Wf 3  is less than the width Wf 2 . In other words, the relationship is Wf 1 &gt;Wf 2 &gt;Wf 3 . The widths Wf 1 , Wf 2 , and Wf 3  each are set to, for example, not more than 1 cm. The width Wf 1  may be the same as the width in the second direction (e.g., in the Z-direction) of the wavelength converter  331 , or may be greater than the width in the second direction (e.g., in the Z-direction) of the wavelength converter  331 . 
     For the heat sink  332  including multiple heat-dissipating fins  332   f  arranged in the first direction, the heat sink  332  having the width in the second direction perpendicular to the first direction decreasing in the first direction refers to the width of each of the multiple heat-dissipating fins  332   f  satisfying the above relationship. More specifically, the performance of the heat sink  332  is affected by the multiple heat-dissipating fins  332   f  as the main part of the heat sink  332 . The heat sink  332  may thus be designed without considering a part of the heat sink  332  between the adjacent heat-dissipating fins  332   f.    
     For example, the third surface  332   r  of the heat sink  332  joined to the wavelength converter  331  may include an uneven surface. This structure has, for example, the anchor effect to increase the strength of the joint between the wavelength converter  331  and the heat sink  332 . In this case, for example, the wavelength converter  331  and the heat sink  332  are less likely to separate from each other. The transfer of heat from the wavelength converter  331  to the heat sink  332  is thus less likely to deteriorate. 
     As illustrated in  FIGS.  41 A and  41 B , the photoconversion device  30  may also include an optical system L 31  including, for example, a lens that directs the excitation light P 0  output through the first output end  2   e   2  of the first optical transmission fiber  2  to be focused toward the wavelength converter  331 . The optical system L 31  may include, for example, a reflective mirror that reflects or focuses the excitation light P 0 , or may be eliminated. 
     As illustrated in  FIGS.  41 A and  41 B , the photoconversion device  30  may also include an optical system L 32  including, for example, a lens that directs the fluorescence W 0  emitted by the wavelength converter  331  and reflected from the reflective surface  333   r  to be focused at the input end (second input end)  4   e   1  of the second optical transmission fiber  4 . The optical system L 32  may include, for example, a reflective mirror that reflects or focuses the fluorescence W 0 , or may be eliminated. 
     3-1-3. Overview of Sixteenth Embodiment 
     The photoconversion device  30  according to the sixteenth embodiment includes, for example, the wavelength converter  331 , the heat sink  332 , and the reflector  333 . The wavelength converter  331  includes the first surface  331   a  to receive the excitation light P 0  output through the first output end  2   e   2 , and the second surface  331   b  different from the first surface  331   a  to emit fluorescence W 0  in response to the excitation light P 0 . The heat sink  332  includes the third surface  332   r  joined to the second surface  331   b . The reflector  333  includes the reflective surface  333   r  facing the first surface  331   a  to focus the fluorescence W 0  emitted by the wavelength converter  331  toward the focusing portion (focusing plane  33   f ). The wavelength converter  331  is between the reflective surface  333   r  and the focusing plane  33   f . The heat sink  332  has, for example, the width in the second direction perpendicular to the negative X-direction as the first direction from the wavelength converter  331  toward the focusing plane  33   f . The heat sink  332  with this structure can thus cool, for example, the wavelength converter  331  through the second surface  331   b . The wavelength converter  331  is thus less likely to undergo temperature increase and resultant deterioration. The heat sink  332  with the width in the second direction decreasing in the first direction from the reflective surface  333   r  toward the focusing plane  33   f  is, for example, less likely to block an optical path of the fluorescence W 0  from the reflective surface  333   r  toward the focusing plane  33   f  The wavelength converter  331  is, for example, less likely to undergo temperature increase and resultant deterioration in the photoconversion device  30  and the illumination system  100 . The photoconversion device  30  and the illumination system  100  can thus emit fluorescence W 0  with higher light intensity in response to the excitation light P 0 . 
     3-2. Other Embodiments 
     The present disclosure is not limited to the sixteenth embodiment and may be changed or varied without departing from the spirit and scope of the present disclosure. 
     3-2-1. Seventeenth Embodiment 
     In the above sixteenth embodiment, as illustrated in, for example,  FIGS.  42 A and  42 B , the reflector  333  may be an ellipsoidal mirror with the reflective surface  333   r  along the ellipsoid  33   e . The ellipsoid  33   e  may include, for example, a focal point F 1  (also referred to as a first focal point) aligned with the area to receive the excitation light P 0  output through the first output end  2   e   2  as an output portion on the first surface  331   a . This structure facilitates, for example, focusing of the fluorescence W 0  emitted by the wavelength converter  331  with the reflector  333 . This, for example, increases the light intensity of the fluorescence W 0  emitted from the photoconversion device  30  and the illumination system  100  in response to the excitation light P 0 . 
     A photoconversion device  30  with an example structure according to a seventeenth embodiment illustrated in  FIGS.  42 A and  42 B  is based on the structure of the photoconversion device  30  according to the above sixteenth embodiment illustrated in  FIGS.  41 A and  41 B . More specifically, the photoconversion device  30  with the example structure according to the seventeenth embodiment includes a reflector  333  being an ellipsoidal mirror, and other components with shapes and arrangement changed as appropriate to cause the first focal point F 1  to be on the first surface  331   a  of the wavelength converter  331 . In this example, the optical systems L 31  and L 32  may be eliminated. 
     3-2-2. Eighteenth Embodiment 
     In the seventeenth embodiment, as illustrated in, for example,  FIGS.  43 A and  43 B , the ellipsoid  33   e  may include a focal point F 2  (also referred to as a second focal point) different from the first focal point F 1 . The second focal point F 2  may be aligned with the focusing plane  33   f . In other words, for example, the second focal point F 2  on the ellipsoid  33   e  may be aligned with the focusing plane  33   f . This structure facilitates, for example, focusing of the fluorescence W 0  emitted by the wavelength converter  331  onto the focusing plane  33   f  with the reflector  333 . This, for example, increases the light intensity of the fluorescence W 0  emitted from the photoconversion device  30  and the illumination system  100  in response to the excitation light P 0 . 
     A photoconversion device  30  with an example structure according to an eighteenth embodiment illustrated in  FIGS.  43 A and  43 B  is based on the structure of the photoconversion device  30  according to the above seventeenth embodiment illustrated in  FIGS.  42 A and  42 B . More specifically, the photoconversion device  30  with the example structure according to the seventeenth embodiment eliminates the optical system L 32  and includes other components with shapes and arrangement changed as appropriate to cause the second focal point F 2  to be on the focusing plane  33   f  In the example of  FIGS.  43 A and  43 B , the second focal point F 2  is aligned with the second input end  4   e   1  of the second optical transmission fiber  4 . 
     As illustrated in, for example,  FIGS.  44 A and  44 B , the first portion  3321  of the heat sink  332  joined to the wavelength converter  331  has an outer edge  3321   e  surrounding a straight imaginary line passing through the first focal point F 1  and the second focal point F 2  (e.g., an imaginary line A 3 ). The outer edge  3321   e  is, for example, an outer circumferential portion of the first portion  3321  centered on the imaginary line A 3 . In the example of  FIGS.  44 A and  44 B , the outer edge  3321   e  is a cylindrical outer portion of the first portion  3321  centered on the imaginary line A 3 . When, for example, an imaginary surface surrounded by the outer edge  3321   e  is a bottom surface B 1  and an imaginary area in the shape of a cone having the second focal point F 2  as a vertex Pf 1  is a first area Cf 1  (also referred to as a first conical area), the second portion  3322  of the heat sink  332  may be located inside the first area Cf 1 . The bottom surface B 1  is, for example, the surface of a closed area defined by cutting the outer edge  3321   e  along an imaginary plane intersecting with the imaginary line A 3 . The imaginary plane may be, for example, perpendicular to or inclined with the imaginary line A 3 . The bottom surface B 1  including an outer peripheral portion located on the outer edge  3321   e  may be, for example, a flat surface or a non-flat surface, such as a curved surface or an uneven surface. In the example below, all the heat-dissipating fins  332   f  included in the second portion  3322  may be inside the first area Cf 1 . In  FIGS.  44 A and  44 B , two-dot-dash lines indicate the outer edges of the bottom surface B 1  and an inclined surface Si of the first area Cf 1 . In the example in  FIGS.  44 A and  44 B , the bottom surface B 1  is circular, and the first area Cf 1  is in the shape of a circular cone. The heat sink  332  with this structure is, for example, less likely to block an optical path of the fluorescence W 0  from the reflective surface  333   r  toward the focusing plane  33   f . This, for example, increases the light intensity of the fluorescence W 0  emitted from the photoconversion device  30  and the illumination system  100  in response to the excitation light P 0 . 
     3-2-3. Nineteenth Embodiment 
     In each of the above sixteenth to eighteenth embodiments, for example, the heat sink  332  may not include the heat-dissipating fins  332   f  as illustrated in  FIGS.  45 A and  45 B . 
     A photoconversion device  30  with an example structure according to a nineteenth embodiment illustrated in  FIGS.  45 A and  45 B  is based on the structure of the photoconversion device  30  according to the above eighteenth embodiment illustrated in  FIGS.  43 A and  43 B . More specifically, the photoconversion device  30  with the example structure according to the nineteenth embodiment may include the second portion  3322  with no heat-dissipating fins  332   f , and may have the shape changed to have the width in the second direction (e.g., in the Z-direction) decreasing in the first direction (negative X-direction). As illustrated in  FIGS.  45 A , the width of the second portion  3322  in the second direction (e.g., in the Z-direction) decreases in the first direction (negative X-direction) at a constant rate from the maximum width Wf 1  to the minimum width Wf 4 . 
     The second portion  3322  may be, for example, in a tapered shape or in the shape of a frustum with its cross section perpendicular to the first direction (YZ cross section in this example) decreasing in the first direction (negative X-direction). As illustrated in, for example,  FIGS.  46 A and  46 B , the second portion  3322  may be in the shape of a circular frustum with its cross section perpendicular to the first direction (YZ cross-section in this example) decreasing in the first direction (negative X-direction). A heat sink  332  with a first structure according to a nineteenth embodiment illustrated in  FIGS.  46 A and  46 B  is based on the example structure of the heat sink  332  according to the above eighteenth embodiment illustrated in  FIGS.  44 A and  44 B . More specifically, the heat sink  332  with the first structure according to the nineteenth embodiment illustrated in  FIGS.  46 A and  46 B  may include the second portion  3322  with no heat-dissipating fins  332   f , and may have the width in the second direction (e.g., in the Z-direction) decreasing in the first direction (negative X-direction). When, for example, an imaginary surface surrounded by the outer edge  3321   e  of the first portion  3321  is the bottom surface B 1  and an imaginary area in the shape of a cone having the second focal point F 2  as a vertex Pf 1  is a first area Cf 1 , the second portion  3322  of the heat sink  332  may also be located inside the first area Cf 1 . In  FIGS.  46 A and  46 B , two-dot-dash lines indicate the outer edges of the bottom surface B 1  and the inclined surface S 1  of the first area Cf 1  as in  FIGS.  44 A and  44 B . The heat sink  332  with this structure is, for example, less likely to block an optical path of the fluorescence W 0  from the reflective surface  333   r  toward the focusing plane  33   f  This, for example, increases the light intensity of the fluorescence W 0  emitted from the photoconversion device  30  and the illumination system  100  in response to the excitation light P 0 . 
     For example, the second portion  3322  may be in the shape of a circular cone with its upper bottom having the diameter Wf 4  smaller than the diameter Wf 1  of its lower bottom. In this example, the minimum width Wf 4  may be zero. The second portion  3322  may be, for example, in the shape of a cone or the shape of a circular cone with its cross section perpendicular to the first direction (YZ cross section in this example) decreasing in the first direction (negative X-direction). 
     The length of the first portion  3321  in the first direction (negative X-direction) may be, for example, short or substantially zero. The heat sink  332  may have, for example, the width in the second direction (e.g., in the Z-direction) decreasing in the first direction (negative X-direction) from the third surface  332   r . For the first portion  3321  with the length of substantially zero in the first direction (negative X-direction), an optical path of the fluorescence W 0  is more difficult to be blocked by the heat sink  332 . 
     The heat sink  332  may be, for example, in a tapered shape or in the shape of a frustum with its cross section perpendicular to the first direction (YZ cross section in this example) decreasing in the first direction (negative X-direction). As illustrated in, for example,  FIGS.  47 A and  47 B , the heat sink  332  may be in the shape of a circular frustum with its cross section perpendicular to the first direction (YZ cross-section in this example) decreasing in the first direction (negative X-direction). A heat sink  332  with a second structure according to the nineteenth embodiment illustrated in  FIGS.  47 A and  47 B  is based on the first structure of the heat sink  332  according to the above nineteenth embodiment illustrated in  FIGS.  46 A and  46 B . More specifically, the heat sink  332  with the second structure according to the nineteenth embodiment illustrated in  FIGS.  47 A and  47 B  may have the width in the second direction (e.g., in the Z-direction) decreasing in the first direction (negative X-direction) from the third surface  332   r . When, for example, an imaginary surface surrounded by the outer edge  3321   e  of the first portion  3321  is the bottom surface B 1  and an imaginary area in the shape of a cone having the second focal point F 2  as a vertex Pf 1  is a first area Cf 1 , the second portion  3322  of the heat sink  332  may also be located inside the first area Cf 1 . In  FIGS.  47 A and  47 B , two-dot-dash lines indicate the outer edges of the bottom surface B 1  and the inclined surface S 1  of the first area Cf 1  as in  FIGS.  46 A and  46 B . The heat sink  332  with this structure is, for example, less likely to block an optical path of the fluorescence W 0  from the reflective surface  333   r  toward the focusing plane  33   f  This, for example, increases the light intensity of the fluorescence W 0  emitted from the photoconversion device  30  and the illumination system  100  in response to the excitation light P 0 . 
     For example, the size of the third surface  332   r  of the heat sink  332  may be substantially smaller than or equal to the size of the second surface  331   b  of the wavelength converter  331 . When, for example, the second surface  331   b  is the bottom surface B 1  and an imaginary area in the shape of a cone (also referred to as a second conical area) having the second focal point F 2  as a vertex Pf 1  is a second area Cf 2 , the heat sink  332  may be located inside the first area Cf 1 . In this example, the second surface  331   b  and the bottom surface B 1  may each be a flat surface, such as a circular surface or a polygonal surface, or a non-flat surface, such as a curved surface or an uneven surface. The heat sink  332  with this structure is, for example, less likely to block an optical path of the fluorescence W 0  from the reflective surface  333   r  toward the focusing plane  33   f . When, for example, the second surface  331   b  is the bottom surface B 1  and an imaginary area in the shape of a cone having the second focal point F 2  as a vertex Pf 1  is a second area Cf 2 , the heat sink  332  located inside the second area Cf 2  may or may not include the heat-dissipating fins  332   f.    
     As illustrated in  FIG.  48   , for example, the size of the third surface  332   r  of the heat sink  332  may be larger than the size of the second surface  331   b  of the wavelength converter  331 . The heat sink  332  with the width in the second direction decreasing in the first direction, depending on the shape of the ellipsoid  33   e  of the reflector  333 , is less likely to block an optical path of the fluorescence W 0  from the reflective surface  333   r  toward the focusing plane  33   f  The heat sink  332  with a larger third surface  332   r  allows more cooling. 
     3-2-4. Twentieth Embodiment 
     In each of the above sixteenth to nineteenth embodiments, for example, the photoconversion device  30  may include a transparent member  334  with high thermal conductivity in contact with the first surface  331   a  of the wavelength converter  331  as illustrated in  FIGS.  49 A and  49 B . The transparent member  334  may be transmissive to, for example, excitation light P 0 . The heat sink  332  with this structure can thus cool, for example, the wavelength converter  331  through the second surface  331   b  and cool the wavelength converter  331  through the first surface  331   a  with the transparent member  334 . The wavelength converter  331  is thus less likely to undergo temperature increase and resultant deterioration. This, for example, increases the light intensity of the fluorescence W 0  emitted from the photoconversion device  30  and the illumination system  100  in response to the excitation light P 0 . The transparent member  334  may be, for example, a plate along the first surface  331   a.    
     When, for example, the transparent member  334  has a higher thermal conductivity than the wavelength converter  331 , heat generated in the wavelength converter  331  in response to the excitation light P 0  is easily dissipated by the transparent member  334 . The thermal conductivity of the material for the transparent member  334  may be, for example, higher than the thermal conductivity of the material for the wavelength converter  331 . More specifically, the transparent member  334  may be referred to as a highly thermally conductive transparent member. More specifically, for example, the material for the transparent member  334  may have a higher thermal conductivity than the phosphor (phosphor substance) contained in the wavelength converter  331  or than the transparent material contained in the wavelength converter  331 . For example, the transparent member  334  may have a higher thermal conductivity than the wavelength converter  331  and a lower thermal conductivity than the heat sink  332 . 
     The transparent member  334  may be made of, for example, a single-crystal inorganic oxide. Examples of the single-crystal inorganic oxide include sapphire and magnesia. For example, phosphor pellets can be formed between the heat sink  332  and the substrate of the transparent member  334  by molding with heat to cause the first surface  331   a  of the wavelength converter  331  and the transparent member  334  to be in contact with each other. For the phosphor pellets containing numerous particles of multiple types of phosphors in glass with a low melting point, for example, the phosphor pellets may be joined to the transparent member  334  by sharing oxygen between the phosphor particles and the material for the transparent member  334 . 
     As illustrated in, for example,  FIG.  50 A , a thickness Df 2  of the transparent member  334  is less than a thickness Df 1  of the wavelength converter  331  in the first direction (negative X-direction) to allow excitation light P 0  output through the first output end  2   e   2  as an output portion to easily pass through the transparent member  334  and reach the wavelength converter  331 . This may increase, for example, the light intensity of the fluorescence W 0  emitted from the photoconversion device  30  and the illumination system  100  in response to the excitation light P 0 . 
     When, for example, the thickness Df 2  of the transparent member  334  is greater than the thickness Df 1  of the wavelength converter  331  in the first direction (negative X-direction), the wavelength converter  331  is easily cooled by the transparent member  334  through the first surface  331   a . The wavelength converter  331  is, for example, thus less likely to undergo temperature increase and resultant deterioration. 
     As illustrated in, for example,  FIG.  50 A , the transparent member  334  may be in an area along the first surface  331   a  of the wavelength converter  331 . As illustrated in, for example,  FIG.  50 B , the transparent member  334  may be in an area along the fourth surface (also referred to as a side surface)  331   s  connecting the first surface  331   a  and the second surface  331   b  of the wavelength converter  331 . In other words, the transparent member  334  may be, for example, in contact with the first surface  331   a  and the fourth surface  331   s  of the wavelength converter  331 . In this case, the transparent member  334  may be a plate along the first surface  331   a  and the fourth surface  331   s . This structure includes, for example, the substrate of the transparent member  334  having a recess filled with phosphor pellets that are formed by molding with heat. The transparent member  334  with this structure can thus cool, for example, the wavelength converter  331  through the first surface  331   a  and the fourth surface  331   s . The wavelength converter  331  is thus less likely to undergo temperature increase and resultant deterioration. With the transparent member  334  connected to the heat sink  332  as illustrated in, for example,  FIG.  50 B , the wavelength converter  331  is easily cooled through the first surface  331   a  by heat transfer from the transparent member  334  to the heat sink  332 . The transparent member  334  may be, for example, indirectly connected to the heat sink  332  with a material having a high thermal conductivity. 
     A heat sink  332 , a wavelength converter  331 , and a transparent member  334  in a first structure according to a twentieth embodiment illustrated in  FIG.  50 A  are based on the example structures of the heat sink  332  and the wavelength converter  331  according to the above eighteenth embodiment illustrated in  FIG.  44 A . More specifically, the first structure including the heat sink  332 , the wavelength converter  331 , and the transparent member  334  according to the twentieth embodiment illustrated in  FIG.  50 A  additionally includes a transparent member  334  extending along and in contact with the first surface  331   a  of the wavelength converter  331 . A heat sink  332 , a wavelength converter  331 , and a transparent member  334  in a second structure according to the twentieth embodiment illustrated in  FIG.  50 B  are based on the heat sink  332 , the wavelength converter  331 , and the transparent member  334  in the first structure according to the above twentieth embodiment illustrated in  FIG.  50 A . More specifically, the second structure including the heat sink  332 , the wavelength converter  331 , and the transparent member  334  according to the twentieth embodiment illustrated in  FIG.  50 B  includes the transparent member  334  with the structure changed to cause the transparent member  334  to be in contact with the first surface  331   a  and the fourth surface  331   s . In the example in  FIG.  50 B , the transparent member  334  is connected to the outer periphery of the first portion  3321  in the heat sink  332 . 
     As illustrated in, for example,  FIGS.  51 A and  51 B , the heat sink  332  may not have the width in the second direction (e.g., in the Z-direction) perpendicular to the first direction (e.g., the negative X-direction) decreasing in the first direction from the wavelength converter  331  to the focusing plane  33   f . When, for example, the photoconversion device  30  includes the wavelength converter  331 , the heat sink  332  including the third surface  332   r  joined to the second surface  331   b  of the wavelength converter  331 , and the transparent member  334  in contact with the first surface  331   a  of the wavelength converter  331 , the heat sink  332  can cool the wavelength converter  331  through the second surface  331   b , and the transparent member  334  can cool the wavelength converter  331  through the first surface  331   a . The wavelength converter  331  is, for example, less likely to undergo temperature increase and resultant deterioration. This, for example, increases the light intensity of the fluorescence W 0  emitted from the photoconversion device  30  and the illumination system  100  in response to the excitation light P 0 . 
     A heat sink  332 , a wavelength converter  331 , and a transparent member  334  according to a first variation of the twentieth embodiment illustrated in  FIG.  51 A  are based on the heat sink  332 , the wavelength converter  331 , and the transparent member  334  in the first structure according to the above twentieth embodiment illustrated in  FIG.  50 A . More specifically, the structure including the heat sink  332 , the wavelength converter  331 , and the transparent member  334  according to the first variation of the twentieth embodiment includes the heat sink  332  with the shape changed to have the first portion  3321  and the two heat-dissipating fins  332   f  of the second portion  3322  each having the same width Wf 1  in the second direction (Z-direction). A heat sink  332 , a wavelength converter  331 , and a transparent member  334  in a second structure according to a second variation of the twentieth embodiment illustrated in  FIG.  51 B  are based on the heat sink  332 , the wavelength converter  331 , and the transparent member  334  in the second structure according to the above twentieth embodiment illustrated in  FIG.  50 B . More specifically, the structure including the heat sink  332 , the wavelength converter  331 , and the transparent member  334  according to the second variation of the twentieth embodiment illustrated in  FIG.  51 B  includes the heat sink  332  with the shape changed to have the first portion  3321  and the two heat-dissipating fins  332   f  of the second portion  3322  each having the same width Wf 1  in the second direction (Z-direction). 
     The heat sink  332  may not include, for example, the heat-dissipating fins  332   f  and may be a plate. 
     3-2-5. Twenty-first Embodiment 
     In each of the above sixteenth to twentieth embodiments, the heat sink  332  may be made of a material transmissive to light as illustrated in  FIGS.  52 A and  52 B . Examples of the material transmissive to light may include gallium nitride (GaN), magnesium oxide (MgO), aluminum nitride (AlN), aluminum oxide (Al 2 O 3 ), yttrium aluminum garnet (YAG), and carbon (C). In this case, the third surface  332   r  of the heat sink  332  is, for example, less likely to reflect light and allows light to pass through the heat sink  332 . This structure may allow, for example, the wavelength converter  331  to emit fluorescence W 0  from both the first surface  331   a  and the second surface  331   b  in response to the excitation light P 0 . As illustrated in, for example,  FIG.  52 B , the fluorescence W 0  emitted from the second surface  331   b  of the wavelength converter  331  can pass through the transparent heat sink  332  toward the second input end  4   e   1  of the second optical transmission fiber  4  along the focusing plane  33   f.    
     The heat sink  332  that is transparent may have the width in the second direction (e.g., in the Z-direction) perpendicular to the negative X-direction as the first direction decreasing in the first direction from the wavelength converter  331  to the focusing plane  33   f . In this case, the fluorescence W 0  from the reflective surface  333   r  to the focusing plane  33   f  is less likely to be reflected and refracted at the heat sink  332 . The heat sink  332  with this structure is, for example, less likely to block an optical path of the fluorescence W 0  from the reflective surface  333   r  toward the focusing plane  33   f . This, for example, increases the light intensity of the fluorescence W 0  emitted from the photoconversion device  30  and the illumination system  100  in response to the excitation light P 0 . 
     3-2-6. Twenty-second Embodiment 
     The photoconversion device  30 F in the illumination system  100 F illustrated in  FIG.  11    has the same or similar structure as the photoconversion device  30  according to any of the sixteenth to twenty-first embodiments described above. 
     The photoconversion device  30 F with this structure also includes, for example, a wavelength converter  331  that receives excitation light P 0  on the first surface  331   a  and emits fluorescence W 0 , a heat sink  332  with a third surface  332   r  joined to the second surface  331   b  of the wavelength converter  331 , and a reflector  333  located opposite to the first surface  331   a  and including a reflective surface  333   r  that focuses the fluorescence W 0  emitted by the wavelength converter  331  toward the focusing plane  33   f  This photoconversion device  30 F includes, for example, the wavelength converter  331  located between the reflective surface  333   r  and the focusing plane  33   f , and the heat sink  332  having the width in the second direction perpendicular to the first direction decreasing in the first direction from the wavelength converter  331  to the focusing plane  33   f  The heat sink  332  can thus cool, for example, the wavelength converter  331  through the second surface  331   b . The wavelength converter  331  is thus less likely to undergo temperature increase and resultant deterioration. The heat sink  332  with the width in the second direction decreasing in the first direction from the reflective surface  333   r  toward the focusing plane  33   f  is, for example, less likely to block an optical path of the fluorescence W 0  from the reflective surface  333   r  toward the focusing plane  33   f  This increases the light intensity of the fluorescence W 0  emitted from the photoconversion device  30 F and the illumination system  100 F in response to the excitation light P 0 . 
     An optical radiation module  5  with an example structure according to a twenty-second embodiment illustrated in  FIGS.  53 A and  53 B  includes a photoconversion device  30 F and an optical radiator  50 . In this example, the photoconversion device  30 F has the same or similar structure as the photoconversion device  30  according to the twentieth embodiment illustrated in  FIGS.  49 A and  49 B . The optical radiator  50  is the same as or similar to the optical radiator  50  in  FIG.  12   . 
     3-2-7. Twenty-third Embodiment 
     A photoconversion device  30 G in the light-emitting module  1  illustrated in  FIG.  14    has the same or similar structure as the photoconversion device  30  according to any of the sixteenth to twenty-first embodiments described above. 
     The photoconversion device  30 G with this structure also includes, for example, a wavelength converter  331  that receives excitation light P 0  on the first surface  331   a  and emits fluorescence W 0 , a heat sink  332  with a third surface  332   r  joined to the second surface  331   b  of the wavelength converter  331 , and a reflector  333  located opposite to the first surface  331   a  and including a reflective surface  333   r  that focuses the fluorescence W 0  emitted by the wavelength converter  331  toward the focusing plane  33   f  This photoconversion device  30 G includes, for example, the wavelength converter  331  located between the reflective surface  333   r  and the focusing plane  33   f , and the heat sink  332  having the width in the second direction perpendicular to the first direction decreasing in the first direction from the wavelength converter  331  to the focusing plane  33   f  The heat sink  332  can thus cool, for example, the wavelength converter  331  through the second surface  331   b . The wavelength converter  331  is thus less likely to undergo temperature increase and resultant deterioration. The heat sink  332  with the width in the second direction decreasing in the first direction from the reflective surface  333   r  toward the focusing plane  33   f  is, for example, less likely to block an optical path of the fluorescence W 0  from the reflective surface  333   r  toward the focusing plane  33   f  This increases the light intensity of the fluorescence W 0  emitted from the photoconversion device  30 G and the illumination system  100 G in response to the excitation light P 0 . 
     A light-emitting module  1  with an example structure according to a twenty-third embodiment illustrated in  FIGS.  54 A and  54 B  includes a light-emitting element  10  and a photoconversion device  30 G. In this example, the photoconversion device  30 G has the same or similar structure as the photoconversion device  30  according to the twentieth embodiment illustrated in  FIGS.  49 A and  49 B . In the example of  FIGS.  54 A and  54 B , excitation light P 0  is emitted from an output portion  10   f  of the light-emitting element  10  toward the first surface  331   a  of the wavelength converter  331 , instead of being through the first output end  2   e   2  of the first optical transmission fiber  2 . 
     3-3. Others 
     In each of the above sixteenth to twenty-third embodiments, for example, the second surface  331   b  of the wavelength converter  331  and the third surface  332   r  of the heat sink  332  may be joined with another layer with a higher thermal conductivity than the wavelength converter  331 . 
     In each of the above fifteenth to twenty-second embodiments, the heat sink  332  having the width in the second direction decreasing in the first direction may be, for example, the heat sink  332  having a part of the second portion  3322  in the first direction with a constant width in the second direction. 
     In each of the above fifteenth to twenty-second embodiments, the second surface  331   b  of the wavelength converter  331  to which the heat sink  332  is joined can be any surface of the wavelength converter  331  with the capability described above. In other words, the heat sink  332  can be joined to any surface of the wavelength converter  331  with the capability described above. For the heat sink  332  with a through-hole, for example, the wavelength converter  331  may be located in the through-hole. 
     In each of the above fifteenth to twenty-second embodiments, the second surface  331   b  of the wavelength converter  331  and the third surface  332   r  of the heat sink  332  are to be simply joined substantially with one of various joining methods. As described above, for example, the second surface  331   b  and the third surface  332   r  may be joined with an adhesive, or the second surface  331   b  and the third surface  332   r  may be joined to each other with a screw or a spring, or by swaging. 
     The first surface  331   a  of the wavelength converter  331  (specifically, the incident surface section) to receive the excitation light P 0  may protrude toward the first output end  2   e   2 . For example, the wavelength converter  331  may have the shape that is the same as or similar to the shape of the wavelength converter  132  in  FIGS.  3  to  6   . 
     In the photoconversion devices  30 ,  30 F, and  30 G according to the above embodiments, for example, a portion of the excitation light P 0  may not be converted to fluorescence W 0  by the wavelength converters  132 ,  231 ,  235 ,  236 , and  331 , and that portion of the excitation light P 0  may form pseudo white light together with the fluorescence W 0 . In this case, the illumination light I 0  radiated from the optical radiation module  5  into the external space  200  of the illumination system  100  may be pseudo white light including for example, the portion of the excitation light P 0  and the fluorescence W 0 . When, for example, the excitation light P 0  is blue light and the fluorescence W 0  is yellow fluorescence, the blue light and the yellow fluorescence can be mixed into pseudo white light. 
     In each of the above embodiments, the illumination light I 0  radiated from the optical radiation module  5  into the external space  200  of the illumination system  100  may not be, for example, pseudo white light. For example, the types, the number of types, and the ratio of phosphors included in each of the wavelength converters  132 ,  231 ,  235 ,  236 , and  331  may be changed as appropriate to cause the illumination light I 0  to exclude light in a specific wavelength range (e.g., blue light) to include more light in a specific wavelength range (e.g., red light). The illumination light I 0  is, for example, controlled in this manner. 
     In the above embodiments, the phosphor portion may include a transparent substrate, such as a resin or glass substrate, and phosphor pellets on the substrate. 
     When the reflectors  1331 ,  233 ,  333  are ellipsoidal mirrors in the above embodiments, the first focal point F 1  of the ellipsoid  33   e  of the ellipsoidal mirror may not be aligned with the illuminating area of the wavelength converters  132 ,  231 ,  235 ,  236 , and  331  to receive the excitation light P 0 , and the second focal point F 2  may not be aligned with the focusing plane  33   f  as the focusing portion. 
     The components described in the above embodiments and variations may be entirely or partially combined as appropriate unless any contradiction arises.