Patent Publication Number: US-2021167255-A1

Title: Light-emitting device and connection method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority of Japanese Patent Application Number 2019-214800, filed on Nov. 28, 2019, the entire content of which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a light-emitting device and a connection method. 
     BACKGROUND ART 
     Conventionally, light source devices for illumination each of which use a plastic optical fiber to which a glass rod is connected to an entrance end portion having a connector portion attached have been disclosed (for example, see Japanese Unexamined Patent Application Publication No. 2002-075046). 
     SUMMARY 
     Technical Problem 
     In a conventional light source device for illumination, a glass rod is connected to an entrance end portion of a plastic optical fiber, and an air space is present at an interface between the glass rod and the plastic optical fiber. In this case, luminance and color irregularities occur in light that passes through the glass rod and the plastic fiber. 
     In view of the above, the present disclosure aims to provide a light-emitting device and a connection method which are capable of reducing luminance and color irregularities. 
     Solution to Problem 
     A light-emitting device according to an aspect of the present disclosure includes: a solid-state light-emitting element that radiates blue-based light as primary light; a wavelength converting member that emits secondary light, the secondary light including wavelength-converted light, the wavelength-converted light being the primary light converted into light having more long-wavelength components than the primary light; a first light-guiding member that transmits the secondary light emitted by the wavelength converting member; and a second light-guiding member which includes a resin material, and transmits the secondary light transmitted by the first light-guiding member. In the light emitting device, a first end face of the first light-guiding member and a second end face of the second light-guiding member are in direct contact with each other, and each of a residual stress in the first end face of the first light-guiding member and a residual stress in the second end face of the second light-guiding member decreases with distance from a center of an interface between the first end face of the first light-guiding member and the second end face of the second light-guiding member. 
     In addition, a connection method according to an aspect of the present disclosure is a connection method of connecting the first light-guiding member and the second light-guiding member. The first end face of the first light-guiding member has a flat surface or a concave surface, and the second end face of the second light-guiding member has a flat surface or a concave surface. When the first light-guiding member and the second light-guiding member are optically connected, the second end face of the second light-guiding member deforms by at least one of the first light-guiding member and the second light-guiding member being pressed as the first light-guiding member and the second light-guiding member are brought into contact with each other. 
     It should be noted that this comprehensive or concrete aspect of the present disclosure may be realized by optionally combining a system, a method, or an integrated circuit. 
     Advantageous Effect 
     A light-emitting device and a connection method according to the present disclosure are capable of reducing luminance and color irregularities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures depict one or more implementations in accordance with the present teaching, by way of examples only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements. 
         FIG. 1  is a perspective view illustrating a lighting system for an endoscope which includes a light-emitting device according to an embodiment. 
         FIG. 2  is a block diagram illustrating the light-emitting device according to the embodiment. 
         FIG. 3  is a diagram schematically illustrating the light-emitting device, a first light-guiding member, connectors, and a second light-guiding member according to the embodiment. 
         FIG. 4  is a partially enlarged cross sectional view illustrating the first light-guiding member, the connectors, and the second light-guiding member according to the embodiment. 
         FIG. 5  is a diagram schematically illustrating a state before the second light-guiding member is connected to the first light-guiding member and a state after the second light-guiding member is connected to the first light-guiding member. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. The embodiments described below each show an example of the present disclosure. Therefore, numerical values, shapes, materials, structural elements, the arrangement and connection of the elements, etc. presented in the embodiments below are mere examples and do not limit the present disclosure. Furthermore, among the structural elements in the embodiments below, those not recited in any one of the independent claims will be described as optional structural elements. 
     It should be noted that the drawings are schematic diagrams, and do not necessarily provide strictly accurate illustrations. Throughout the drawings, the same reference numeral is given to the same structural components. 
     Moreover, the embodiments described below use an expression such as substantially plane-shaped. For example, substantially plane-shaped not only means that which is perfectly plane-shaped, but also means that which is practically plane-shaped. In addition, the substantially plane-shaped is considered as plane-shaped within the scope in which an advantageous effect can be produced by the present disclosure. The same applies to other expressions using “substantially”. 
     Hereinafter, a light-emitting device and a connection method according to an embodiment of the present disclosure will be described. 
     Embodiment 
     [Configuration: Light-Emitting Device  1 ] 
       FIG. 1  is a perspective view illustrating lighting system for endoscope  100  which includes light-emitting device  1  according to an embodiment. 
     As illustrated in  FIG. 1 , light-emitting device  1  according to the embodiment is a reflective lighting device that uses laser light, and included in, for example, lighting system for endoscope  100  which is used for an endoscope. It should be noted that light-emitting device  1  may be used for, for example, a downlight, a spotlight, and the like. Lighting system for endoscope  100  includes light-emitting device  1  and camera control unit  110 . 
     Laser light that light-emitting device  1  emits is blue-based light, for example. Light-emitting device  1  emits laser light that is blue-based light and quasi-white secondary light that is produced by combining a portion of the absorbed laser light and green to yellow wavelength-converted light. 
       FIG. 2  is a block diagram illustrating light-emitting device  1  according to the embodiment.  FIG. 3  is a diagram schematically illustrating light-emitting device  1 , first light-guiding member  50 , connectors  70  (connectors  70   a  and  70   b ), and second light-guiding member  60  according to the embodiment. 
     As illustrated in  FIG. 2  and  FIG. 3 , light-emitting device  1  includes excitation light source  3 , first light-guiding member  50 , second light-guiding member  60 , and connectors  70   a  and  70   b.    
     [Excitation Light Source  3 ] 
     Excitation light source  3  is a device that emits laser light. Excitation light source  3  includes housing body  31 , one or more laser light sources  32 , prism  33 , condenser lens  34 , first glass rod  35 , wavelength converting member  36 , second glass rod  37 , heat sink  38 , and drive circuit  39 . 
     Housing body  31  is a case for excitation light source  3 . Housing body  31  houses laser light sources  32 , prism  33 , condenser lens  34 , first glass rod  35 , heat sink  38 , and drive circuit  39 . In addition, housing body  31  holds wavelength converting member  36  such that wavelength converting member  36  is optically connectable with each of first glass rod  35  and second glass rod  37 . 
     Laser light source  32  is a solid-state light-emitting element that radiates laser light as primary light, and emits substantially collimated laser light. Laser light source  32  is attached to a substrate, and is thermally connected to heat sink  38  via the substrate. In this embodiment, excitation light source  3  uses a plurality of laser light sources  32 , and the plurality of laser light sources  32  are considered as one set. Each of the plurality of laser light sources  32  in the one set of the plurality of laser light sources  32  emits laser light, and the laser light is caused to enter wavelength converting member  36  via prism  33  and first glass rod  35 . 
     It should be noted that although a plurality of laser light sources  32  (e.g. four or eight laser light sources  32 ) are used in this embodiment, only one laser light source  32  may be used. Laser light that laser light source  32  emits in this embodiment is light having a predetermined wavelength within a wavelength band of blue-based light that includes purple to blue. 
     Laser light that laser light source  32  emits in this embodiment has a cross-sectional shape that is oval and 1 m×4 mm in size. In addition, energy distribution of the laser light is in accordance with the Gaussian distribution. 
     In addition, although the one set of laser light sources  32  is used in this embodiment, a plurality of sets of laser light sources  32  may be used. In this case, prism  33  and condenser lens  34  may be provided as a pair corresponding to each set of laser light sources  32 . 
     Although laser light source  32  is a semiconductor laser which is, for example, an InGaN-based laser diode, laser light source  32  may be a semiconductor laser that emits light in a different wavelength (other than the wavelength band of blue-based light) or a light emitting diode (LED), so long as light emitted can excite wavelength converting member  36 . 
     In addition, laser light source  32  outputs laser light under the control of drive circuit  39 . That is, laser light source  32  emits a desired laser light under the control of drive circuit  39 . 
     Prism  33  is disposed in housing body  31  such that laser light emitted by the one set of laser light sources  32  is guided to condenser lens  34  to be condensed onto condenser lens  34 . That is, prism  33  condenses the laser light emitted from laser light sources  32  such that the condensed laser light enters condenser lens  34 . Prism  33  is, for example, a rhomboid prism, a polarizing mirror, etc. 
     Condenser lens  34  is disposed in housing body  31  so as to be located opposite prism  33 . Condenser lens  34  further condenses the laser light exited from prism  33 , and causes the laser light to enter first glass rod  35 . It should be noted that condenser lens  34  is a spherical lens or an aspheric lens, but condenser lens  34  need not be the lenses indicated above so long as condenser lens  34  is an optical device that can condense laser light and can cause the laser light to enter first glass rod  35 . 
     First glass rod  35  is disposed in housing body  31  so as to be located opposite condenser lens  34 . First glass rod  35  is a light pipe that includes glass as a base material and has the inner surface that is coated with a dielectric multilayer so as to highly efficiently reflect laser light that is condensed by and exited from condenser lens  34 . It should be noted that first glass rod  35  may be a light pipe having a metallically-coated surface inside so as to highly efficiently reflect the laser light. 
     First glass rod  35  constitutes a transmission path that transmits the laser light condensed by and exited from condenser lens  34 . First glass rod  35  mixes the laser light by causing the laser light to repeatedly reflect inside while the laser light is guided through first glass rod  35  to even out the Gaussian distribution. That is, tophat laser light whose peak portion is smoothed (substantially evened out) is caused to exit from first glass rod  35 . First glass rod  35  emits laser light that is mixed, and causes the mixed laser light to enter wavelength converting member  36 . 
     When the transmission path in first glass rod  35  is cut on a plane that is perpendicular to a direction in which the laser light transmits, a cross section of the transmission path is polygonally shaped. In this embodiment, a cross section of the transmission path is quadrilaterally shaped. 
     Wavelength converting member  36  includes phosphor (wavelength converting element) that converts the laser light that is mixed by first glass rod  35  into wavelength-converted light (fluorescence). That is, wavelength converting member  36  performs wavelength conversion on laser light entered from a first glass rod  35 -side surface, and emits secondary light that includes wavelength-converted light on which the wavelength conversion is performed from the opposite surface (second glass rod  37 -side surface). Specifically, wavelength converting member  36  emits secondary light that includes laser light as primary light and wavelength-converted light that is the laser light as primary light converted into light having more long-wavelength components than the primary light, and causes the secondary light to enter second glass rod  37 . 
     In addition, tophat laser light enters wavelength converting member  36 . Accordingly, wavelength converting member  36  emits secondary light having reduced luminance irregularity in which only a portion of wavelength converting member  36  is brightly illuminated. 
     In wavelength converting member  36 , the phosphor is dispersed in a binder that is a transparent material including ceramic such as glass, silicone resin, or the like. The phosphor is, for example, multicolor phosphor, such as ZnO, an yttrium aluminum garnet (YAG)-based phosphor, a CASN-based phosphor, a SCASN-based phosphor, or a barium, magnesium, aluminum (BAM)-based phosphor, and is selected as appropriate according to a type of laser light. It should be noted that the binder is not limited to include ceramic, silicone resin, or the like, and other transparent materials such as transparent glass, or the like, may be used. 
     In addition, the phosphor may be a red phosphor, a green phosphor, a blue phosphor, etc., and wavelength-converted light, such as red light, green light, and blue light, may be emitted according to the laser light. In this case, these red, green, and blue wavelength-converted lights may be combined to produce white light. In this embodiment, the phosphor emits quasi-white secondary light. 
     In addition, wavelength converting member  36  is a flat plate-shaped structure in which a phosphor layer etc. are disposed on a sapphire substrate, for example. Wavelength converting member  36  is fixed to housing body  31  in a state in which wavelength converting member  36  is in contact with housing body  31 . That is, wavelength converting member  36  dissipates heat produced in the phosphor by causing housing body  31  to function as heat sink  38 . 
     Second glass rod  37  is fixed to housing body  31 , and optically connects wavelength converting member  36  and first light-guiding member  50 . Second glass rod  37  is disposed so as to be located opposite wavelength converting member  36 . Second glass rod  37  is a light pipe that includes glass as a base material, and has the inner surface that is coated with a dielectric multilayer so as to highly efficiently reflect secondary light that is exited from wavelength converting member  36 . It should be noted that second glass rod  37  may be a light pipe having a metallically-coated surface inside so as to highly efficiently reflect the secondary light. 
     It should be noted that second glass rod  37  may have the same configuration as first glass rod  35 , but second glass rod  37  may be provided with a reflective film inside which enhances transmission efficiency of white light. 
     Second glass rod  37  constitutes a transmission path that transmits secondary light including wavelength-converted light whose wavelength is converted and which is emitted by wavelength converting member  36 . Second glass rod  37  causes the secondary light to repeatedly reflect inside while the secondary light is guided through second glass rod  37 . Second glass rod  37  mixes the secondary light while the secondary light is guided through second glass rod  37  to emit secondary light whose Gaussian distribution is evened out. That is, second glass rod  37  emits tophat secondary light whose peak portion is smoothed. Second glass rod  37  emits the mixed secondary light, and causes the mixed secondary light to enter first light-guiding member  50 . 
     When the transmission path in second glass rod  37  is cut on a plane that is perpendicular to a direction in which the secondary light transmits, a cross section of the transmission path is polygonally shaped. In this embodiment, second glass rod  37  has the transmission path whose cross section is quadrilaterally shaped. 
     Heat sink  38  is a heat dissipation member for dissipating heat produced in laser light sources  32 , and includes a plurality of fins. In addition, the substrate to which laser light sources  32  are attached is fixed by heat sink  38 . 
     Drive circuit  39  is electrically connected with an electric power system via an electric power line etc., and supplies electric power to each laser light source  32 . In addition, laser light sources  32  output laser light under the control of drive circuit  39  such that laser light sources  32  emit predetermined laser light. 
     Drive circuit  39  may have a function of modulating laser light that laser light sources  32  emit. In addition, drive circuit  39  may include, for example, an oscillator that drives laser light sources  32  based on a pulse signal. 
     [First Light-Guiding Member  50 ] 
     First light-guiding member  50  is an optical fiber cable that transmits secondary light exited from wavelength converting member  36 . First light-guiding member  50  has a dual structure in which a core having a high refractive index is surrounded with a clad layer having a refractive index lower than the refractive index of the core, and includes a cladding that covers the clad layer, for example. It should be noted that when light-emitting device  1  includes a plurality of sets of laser light sources  32 , a plurality of first light-guiding members  50  may also be provided. 
     First light-guiding member  50  is made of a material, such as glass having high heat resistance or resin having excellent heat resistance. This enables laser light exited from second glass rod  37  to enter first light-guiding member  50 . 
     In the embodiment, first light-guiding member  50  is a bundle fiber consisting of multi-component glass fibers each of which is approximately 25 μm to 50 μm in diameter and which are bundled together and bonded with adhesive. In addition, in this embodiment, the diameter of first light-guiding member  50  is approximately 0.1 mm to 0.4 mm, and the numerical aperture of first light-guiding member  50  is 0.8 to 0.9. 
     First light-guiding member  50  has one end on a side opposite a second glass rod  37  side which is removably fixed to connector  70   a.  In addition, first light-guiding member  50  has the other end on the second glass rod  37  side which is optically connected with and fixed to second glass rod  37  and from which secondary light exited from wavelength converting member  36  enters. 
     It should be noted that first light-guiding member  50  may be directly connected to second light-guiding member  60  not via connectors  70   a  and  70   b . In this case, first light-guiding member  50  may be removably fixed to second light-guiding member  60 . 
     Specifically, first light-guiding member  50  has entrance face  51  from which secondary light enters, and exit face  52  from which the secondary light entered from entrance face  51  and guided through first light-guiding member  50  exits. 
     Exit face  52  is substantially plane-shaped and is one end face of first light-guiding member  50 . Exit face  52  is disposed so as to be located opposite second light-guiding member  60  via connectors  70   a  and  70   b . In addition, entrance face  51  is substantially plane-shaped and is the other end face of first light-guiding member  50 . Entrance face  51  is disposed so as to be located opposite second glass rod  37 . First light-guiding member  50  is disposed such that the central axis of entrance face  51  substantially aligns with the central axis of the transmission path in second glass rod  37 . 
     Specifically, exit face  52  of first light-guiding member  50  is directly connected with and adhered to entrance face  61  of second light-guiding member  60 . Each of a residual stress present in exit face  52  of first light-guiding member  50  and a residual stress present in entrance face  61  of second light-guiding member  60  decreases with distance from the center of an interface between exit face  52  of first light-guiding member  50  and entrance face  61  of second light-guiding member  60 . In addition, exit face  52  of first light-guiding member  50  is optically connected with entrance face  61  of second light-guiding member  60  by being coupled with entrance face  61  of second light-guiding member  60 . Exit face  52  of first light-guiding member  50  is an example of one end face of first light-guiding member  50 . In addition, entrance face  61  of second light-guiding member  60  is an example of the other end face of second light-guiding member  60 . 
     Here, the interface is a face to which exit face  52  and entrance face  61  adhere and at which exit face  52  and entrance face  61  optically connect with each other. Since the area of entrance face  61  is greater than that of exit face  52  in this embodiment, the interface to which entrance face  61  adheres means a portion in which entrance face  61  and exit face  52  overlap with each other. 
       FIG. 4  is a partially enlarged cross sectional view illustrating first light-guiding member  50 , connectors  70   a  and  70   b , and second light-guiding member  60  according to the embodiment. 
     As illustrated in  FIG. 4 , first light-guiding member  50  includes, on a one end side, connecting terminal  150  that is mechanically connected with connector  70   a . Connecting terminal  150  is connected with connecting terminal  160  of second light-guiding member  60  via connectors  70   a  and  70   b . Connecting terminal  150  includes ferrule  151 , housing  154 , flange  152 , and spring  153 . 
     Ferrule  151  includes zirconia, nickel, etc., and is an aligning component that holds first light-guiding member  50  in a predetermined orientation, for example. Ferrule  151  includes an insertion hole in which an end portion of first light-guiding member  50  is inserted. The end portion is on a side opposite a second glass rod  37  (excitation light source  3 ) side. The end portion of first light-guiding member  50  which is inserted in the insertion hole is an end portion on a connector  70   a  side. In addition, when connecting terminal  150  is connected to connector  70   a , ferrule  151  is inserted in connector  70   a , and is held so as to be located opposite second light-guiding member  60  and adhered to ferrule  161  of second light-guiding member  60 . Ferrule  151  holds the end portion of first light-guiding member  50  such that exit face  52  of first light-guiding member  50  and entrance face  61  of second light-guiding member  60  face and adhere to each other. 
     Housing  154  holds ferrule  151 , and has a tubular shape that forms the outline of connecting terminal  150 . Housing  154  houses flange  152 , spring  153 , etc. Housing  154  is engaged with and fixed to connector  70   a . In this embodiment, a female screw portion is formed in housing  154 , and a male screw portion is formed in connection portion to be connected  71   a  in connector  70   a , and thus housing  154  is being screwed and coupled to connection portion to be connected  71   a  in connector  70   a.    
     Flange  152  is held by housing  154  in a state in which flange  152  is connected to one end portion of ferrule  151 . In addition, flange  152  receives stress from spring  153  by being connected to spring  153 , and this energizes ferrule  151  to a direction to which the stress is applied. 
     Spring  153  is disposed between flange  152  and housing  154 . When connecting terminal  150  is connected to connection portion to be connected  71   a  in connector  70   a , spring  153  energizes ferrule  151  toward a connecting terminal  160  side via flange  152 . When housing  154  is coupled to connection portion to be connected  71   a , spring  153  applies stress to flange  152  by being pushed by housing  154 , and presses ferrule  151  to a ferrule  161  side. 
     It should be noted that the coupling of first light-guiding member  50  and connector  70   a  is not limited to the above-described details. The one end of first light-guiding member  50  may simply be fixed with a fixing member such as a screw. 
     [Second Light-Guiding Member  60 ] 
     Second light-guiding member  60  is an optical fiber cable that transmits secondary light exited from wavelength converting member  36 . Second light-guiding member  60  has a dual structure in which a core having a high refractive index is surrounded with a clad layer having a refractive index lower than the refractive index of the core, and includes a cladding that covers the clad layer, for example. It should be noted that when light-emitting device  1  includes a plurality of sets of laser light sources  32 , a plurality of second light-guiding members  60  may also be provided. 
     Second light-guiding member  60  includes a material different from a material which first light-guiding member  50  includes. Second light-guiding member  60  in this embodiment includes a material that is softer than the material that first light-guiding member  50  includes. Second light-guiding member  60  includes, for example, a light-transmissive resin material. In this embodiment, the diameter of second light-guiding member  60  is 0.4 mm to 3 mm, and the numerical aperture of second light-guiding member  60  is 0.5 to 0.7. 
       FIG. 5  is a diagram schematically illustrating a relationship between first light-guiding member  50  and second light-guiding member  60  according to the embodiment. 
     As illustrated in  FIG. 5 , the transmission path of secondary light in second light-guiding member  60  has diameter A 2  that is greater than diameter A 1  of the transmission path of the secondary light in first light-guiding member  50 . That is, the average diameter of second light-guiding member  60  is greater than the average diameter of first light-guiding member  50 . Accordingly, entrance face  61  of second light-guiding member  60  is larger than exit face  52  of first light-guiding member  50 . Entrance face  61  of second light-guiding member  60  will be described later. 
     Although the area of exit face  52  of first light-guiding member  50  is smaller than that of entrance face  61  of second light-guiding member  60 , first light-guiding member  50  has the numerical aperture greater than the numerical aperture of second light-guiding member  60 . Accordingly, by making diameter A 2  of entrance face  61  of second light-guiding member  60  greater than diameter A 1  of exit face  52  of first light-guiding member  50 , the decrease in light transmission efficiency at the time of optically connecting first light-guiding member  50  and second light-guiding member  60  is reduced, when first light-guiding member  50  and second light-guiding member  60  are optically connected with each other. Although not illustrated, it should be noted that the diameter of first light-guiding member  50  and the diameter of second light-guiding member  60  may be substantially the same. That is, the area of exit face  52  of first light-guiding member  50  and the area of entrance face  61  of second light-guiding member  60  may be substantially the same. 
     As illustrated in  FIG. 4 , second light-guiding member  60  has the other end that is on a first light-guiding member  50  side, and is removably fixed to connector  70   b . Second light-guiding member  60  is optically connected with first light-guiding member  50  via connectors  70   a  and  70   b . Secondary light that is exited from wavelength converting member  36  and guided through first light-guiding member  50  enters second light-guiding member  60 . 
     Specifically, second light-guiding member  60  has entrance face  61  from which the secondary light enters, and exit face  62  from which the secondary light that is entered from entrance face  61  and guided through second light-guiding member  60  exits. 
     Exit face  62  is substantially plane-shaped, and is one end face of second light-guiding member  60 . Exit face  62  is disposed so as to be located opposite first light-guiding member  50  via connectors  70   a  and  70   b . In addition, entrance face  61  is substantially plane-shaped, and is the other end face of second light-guiding member  60 . Entrance face  61  is disposed so as to be located opposite second glass rod  37 . Second light-guiding member  60  may be disposed such that the center of entrance face  61  is within the central axis of the transmission path in second glass rod  37 , for example. 
     In addition, as illustrated in  FIG. 5 , second light-guiding member  60  includes light distribution control structure  60   a  that performs light distribution control on secondary light transmitted by first light-guiding member  50  before emitting the secondary light. 
     Light distribution control structure  60   a  is disposed on the one end face of second light-guiding member  60 . In this embodiment, light distribution control structure  60   a  is integrally formed on the one end face of second light-guiding member  60 , and includes exit face  62  of second light-guiding member  60 . Light distribution control structure  60   a  in this embodiment is in a shape of a convex portion of a hemispherical shape. 
     An angle of radiation of secondary light that is exited from light distribution control structure  60   a  is specified according to an angle of view of camera  116 . That is, the numerical aperture of light distribution control structure  60   a  is specified according to an angle of view of camera  116 . An angle of radiation of the secondary light that is exited from light distribution control structure  60   a  may be equivalent to an angle of view of camera  116 . 
     Light distribution control structure  60   a  is obtained by melting the one end face of second light-guiding member  60  to form a curved surface having a desired curvature, or obtained by grinding the one end face of second light-guiding member  60  to form a curved surface having a desired curvature, for example. The curvature according to the embodiment is approximately 20 mm, for example. 
     It should be noted that light distribution control structure  60   a  is integrally formed with second light-guiding member  60 , but light distribution control structure  60   a  may be a member separated from second light-guiding member  60 . That is, light distribution control structure  60   a  may be a convex lens, a concave lens, or the like. In this case, light distribution control structure  60   a  is located opposite the one end face of second light-guiding member  60 , and is held in end portion  115  illustrated in  FIG. 1  in an orientation in which light distribution control is to be performed on secondary light exited from the one end face of second light-guiding member  60 . 
     In addition, second light-guiding member  60  includes, on the other end side, connecting terminal  160  that is mechanically connected with connection portion to be connected  71   b  in connector  70   b . Connecting terminal  160  includes ferrule  161 , housing  164 , flange  162 , and spring  163 . Since connecting terminal  160  included in second light-guiding member  60  has the same configuration as connecting terminal  150  included in first light-guiding member  50  which includes ferrule  151 , housing  154 , flange  152 , and spring  153 , descriptions of ferrule  161 , housing  164 , flange  162 , and spring  163  are omitted. 
     [Connectors  70   a  and  70   b]   
     Connector  70   a  and connector  70   b  are optical connectors that optically connect the transmission path in first light-guiding member  50  and the transmission path in second light-guiding member  60 , respectively, for converting the difference between the numerical aperture of first light-guiding member  50  and the numerical aperture of second light-guiding member  60 . Specifically, connector  70   a  is mechanically connected with connecting terminal  150  of first light-guiding member  50 , and connector  70   b  is mechanically connected with connecting terminal  160  of second light-guiding member  60 . In addition, since connector  70   a  and connector  70   b  are fixed with a screw so as to overlap with each other, connector  70   a  and connector  70   b  optically connect connecting terminal  150  (the one end portion on an exit face  52  side of first light-guiding member  50 ) of first light-guiding member  50  and connecting terminal  160  (the other end portion on an entrance face  61  side of second light-guiding member  60 ) of second light-guiding member  60 . 
     Connector  70   a  and connector  70   b  include connection portion to be connected  71   a  and connection portion to be connected  71   b , respectively. Each of connector  70   a  and connector  70   b  also includes sleeve  73 . Since connector  70   a  and connector  70   b  have the same configuration, duplicate descriptions may be omitted. 
     Connection portion to be connected  71   a  in connector  70   a  is mechanically connected with connecting terminal  150  of first light-guiding member  50 , and connection portion to be connected  71   b  in connector  70   b  is mechanically connected with connecting terminal  160  of second light-guiding member  60 . Connection portion to be connected  71   a  is held in an orientation in which connection portion to be connected  71   a  faces exit face  52  of first light-guiding member  50 . Connection portion to be connected  71   b  is held in an orientation in which connection portion to be connected  71   b  faces entrance face  61  of second light-guiding member  60 . 
     Sleeve  73  has a tubular body shape having unclosed ends. Ferrules  151  and  161  are inserted in respective sleeves  73 . Sleeves  73  are disposed extending from an insertion hole in connector  70   a  in which ferrule  151  is inserted to an insertion hole in connector  70   b  in which ferrule  161  is inserted. Sleeves  73  are disposed around the outer surfaces of respective ferrules  151  and  161 . That is, sleeves  73  guide ferrules  151  and  161 . Specifically, sleeves  73  produce a compressive force toward the central axis direction, and carry out axis alignment of ferrules  151  and  161 . 
     Sleeves  73  in this embodiment are split sleeves, and are cut in a lengthwise direction. Sleeves  73  in this embodiment include phosphor bronze, zirconia, and the like. 
     Since first light-guiding member  50  includes glass and second light-guiding member  60  includes a resin material in this embodiment, the embodiment has a characteristic in which the numerical aperture of first light-guiding member  50  (angle of radiation of light exited from first light-guiding member  50 ) is greater than the numerical aperture of second light-guiding member  60  (angle of radiation of light exited from second light-guiding member  60 ). 
     [Camera Control Unit  110 ] 
     Camera control unit  110  is a unit that processes images imaged by camera  116  provided in end portion  115 . Camera control unit  110  includes, for example, image processor  111 , controller  112 , and storage  113 . 
     Although not illustrated, the one end of second light-guiding member  60  and one end of image transmission cable  117  are connected to end portion  115 . Camera  116  that images a subject is included in end portion  115 . 
     Camera  116  is, for example, a charge-coupled device (CCD) camera. Camera  116  transmits an image signal in which a subject is imaged to image processor  111  included in camera control unit  110  via video transmission cable  117 . In image processor  111 , image processing is performed as appropriate after the inputted image signal is converted into image data, and desired image information for output is generated. Then, the obtained image information is displayed on a display, which is not illustrated, via controller  112 , as an examination image of an endoscope. In addition, controller  112  stores, as necessary, the image information in storage  113  which includes a memory, or the like. 
     [Connection Method] 
     Hereinafter, a connection method of connecting first light-guiding member  50  and second light-guiding member  60  will be described with reference to  FIG. 5 .  FIG. 5  is a diagram which also schematically illustrates a state in which second light-guiding member  60  is connected to first light-guiding member  50 . 
     First, as a state before connection which is illustrated in  FIG. 5 , first light-guiding member  50  whose exit face  52  has a flat surface or a convex surface, and second light-guiding member  60  whose entrance face  61  has a flat surface or a convex surface are prepared. The embodiment describes a case in which exit face  52  has a flat surface and entrance face  61  has a convex surface. The convex surface in this embodiment is a hemispherical face having a predetermined curvature. The predetermined curvature in this embodiment is, for example, approximately 20 mm. 
     In addition, the surface of exit face  52  and the surface of entrance face  61  are to be grinded. That is, plane surface grinding is performed on exit face  52  and curved surface grinding is performed on entrance face  61 . This reduces the generation of an air interface between exit face  52  and entrance face  61 . 
     Connecting terminal  150  of first light-guiding member  50  is connected to connection portion to be connected  71   a  in connector  70   a . Then, connecting terminal  160  of second light-guiding member  60  is inserted in connection portion to be connected  71   b  in connector  70   b  in a connecting direction indicated by the solid arrow. At this time, by a female screw portion in housing  164  being screwed to a male screw portion in connection portion to be connected  71   b , housing  164  presses spring  163  in an insertion direction. Spring  163  presses ferrule  161  against ferrule  151  of connecting terminal  150  via flange  152 . 
     Specifically, entrance face  61  of second light-guiding member  60  is pressed to exit face  52  of first light-guiding member  50  after entrance face  61  of second light-guiding member  60  comes in contact with exit face  52  of first light-guiding member  50 . Since second light-guiding member  60  includes a resin material and first light-guiding member  50  includes glass, second light-guiding member  60  is softer than first light-guiding member  50 . Accordingly, concave-shaped entrance face  61  of second light-guiding member  60  is pressed by exit face  52  of first light-guiding member  50 , and entrance face  61  of second light-guiding member  60  is shaped according to exit face  52  of first light-guiding member  50 . That is, entrance face  61  of second light-guiding member  60  deforms according to the shape of exit face  52  of first light-guiding member  50 . Entrance face  61  of second light-guiding member  60  is adhered to exit face  52  of first light-guiding member  50  such that an air interface between entrance face  61  of second light-guiding member  60  and exit face  52  of first light-guiding member  50  vanishes. In other words, there is no member present between exit face  52  and entrance face  61 . 
     Specifically, since air is squeezed from the center of entrance face  61  and pushed out in a radial direction of second light-guiding member  60 , it is very unlikely that an air interface is present between entrance face  61  and exit face  52 . 
     At this time, exit face  52  and entrance face  61  are adhered to each other such that the central axis of exit face  52  and the central axis of entrance face  61  align with each other. In addition, since part of entrance face  61  of second light-guiding member  60  is pressed, a residual stress exerted at the center of exit face  52  of first light-guiding member  50  is the highest. Furthermore, since a pressed amount of entrance face  61  decreases with distance from the central axis of entrance face  61  of second light-guiding member  60 , the residual stress at the center of exit face  52  gradually decreases. 
     It should be noted that when exit face  52  has a flat surface or a convex surface and entrance face  61  has a flat surface or a convex surface, an air interface between entrance face  61  and exit face  52  vanishes in the same manner as has been described above. 
     [Operation] 
     In such light-emitting device  1 , secondary light emitted from excitation light source  3  enters first light-guiding member  50 , is guided through the inside of first light-guiding member  50 , exits from exit face  52  of first light-guiding member  50 , and enters entrance face  61  of second light-guiding member  60 . Then, the secondary light enters second light-guiding member  60 , is guided through the inside of second light-guiding member  60 , is guided to exit face  62  of second light-guiding member  60  which is disposed in end portion  115 , and exits from exit face  62  of second light-guiding member  60 . In this way, a subject can be illuminated by the secondary light that is emitted on the subject. Accordingly, it is possible to understand a state of the subject by camera  116  imaging the subject on which the secondary light is emitted. 
     [Advantageous Effect] 
     Next, advantageous effects that light-emitting device  1  and the connection method according to the embodiment demonstrate will be described. 
     As has been described above, light-emitting device  1  according to the embodiment includes: laser light source  32  (solid-state light-emitting element) that radiates blue-based light as primary light; wavelength converting member  36  that emits secondary light, the secondary light including wavelength-converted light, the wavelength-converted light being the primary light converted into light having more long-wavelength components than the primary light; first light-guiding member  50  that transmits the secondary light emitted by wavelength converting member  36 ; and second light-guiding member  60  which includes a resin material, and transmits the secondary light transmitted by first light-guiding member  50 . Exit face  52  of first light-guiding member  50  and entrance face  61  of second light-guiding member  60  are in direct contact with each other. Each of a residual stress in exit face  52  of first light-guiding member  50  and a residual stress in entrance face  61  of second light-guiding member  60  decreases with distance from a center of an interface between exit face  52  of first light-guiding member  50  and entrance face  61  of second light-guiding member  60 . 
     Accordingly, a residual stress present between exit face  52  of first light-light guiding member  50  and entrance face  61  of second light-guiding member  60  is highest at the center of the interface. That is, when exit face  52  and entrance face  61  are connected, air is pushed out in a radial direction from the center of the interface between exit face  52  and entrance face  61 , and thus it is very unlikely that an air interface is present between entrance face  61  and exit face  52 . For this reason, secondary light guided through first light-guiding member  50  and exited from exit face  52  can enter entrance face  61  of second light-guiding member  60  as is. 
     Therefore, light-emitting device  1  can reduce luminance and color irregularities. 
     Particularly, when light-emitting device  1  is used for an endoscope, second light-guiding member  60  is desired to be disposable for preventing infectious diseases since second light-guiding member  60  is inserted in, for example, a human body. For this reason, only second light-guiding member  60  which is a portion inserted in a human body etc. can be removed from first light-guiding member  50  and discarded. Accordingly, a rise in the entire cost of manufacturing the light-guiding members can be reduced. 
     In addition, a connection method according to the embodiment is a connection method of connecting first light-guiding member  50  and second light-guiding member  60 . Exit face  52  of first light-guiding member  50  has a flat surface or a concave surface, and entrance face  61  of second light-guiding member  60  has a flat surface or a concave surface. When first light-guiding member  50  and second light-guiding member  60  are optically connected, entrance face  61  of second light-guiding member  60  deforms by at least one of first light-guiding member  50  and second light-guiding member  60  being pressed as first light-guiding member  50  and second light-guiding member  60  are brought into contact with each other. 
     This connection method produces the same advantageous effects as the advantageous effects described above. 
     In addition, in light-emitting device  1  according to the embodiment, first light-guiding member  50  includes connecting terminal  150  on an exit face  52  side, second light-guiding member  60  includes connecting terminal  160  that is optically connected with first light-guiding member  50  by being removably coupled with connecting terminal  150  of first light-guiding member  50 , and connecting terminal  160  of second light-guiding member  60  is disposed on an entrance face  61  side. 
     With this, first light-guiding member  50  and second light-guiding member  60  can be readily connected with each other, and the used second light-guiding member  60  can also be removed from first light-guiding member  50 . For this reason, light-emitting device  1  provides excellent usability. 
     In addition, in light-emitting device  1  according to the embodiment, the transmission path of the secondary light in second light-guiding member  60  has a diameter greater than a diameter of the transmission path of the secondary light in first light-guiding member  50 . 
     With this, it is possible to cause the secondary light that is guided through first light-guiding member  50  to efficiently enter second light-guiding member  60 . For this reason, it is possible to reduce a decrease in the light transmission efficiency in connectors  70   a  and  70   b , which are components optically connecting first light-guiding member  50  and second light-guiding member  60 . 
     In addition, in light-emitting device  1  according to the embodiment, second light-guiding member  60  includes light distribution control structure  60   a  for performing light distribution control on the secondary light transmitted by first light-guiding member  50  before emitting the secondary light. 
     With this, when camera  116  is disposed in the vicinity of light distribution control structure  60   a , the secondary light exited from second light-guiding member  60  can be adjusted to an angle of view of camera  116 , by preparing light distribution control structure  60   a  to be adjusted to the angle of view of camera  116 . For this reason, it is possible to reduce narrowing of the field of view of camera  116 . 
     In addition, in light-emitting device  1  according to the embodiment, light distribution control structure  60   a  has a hemispherical shape. 
     With this, second light-guiding member  60  can emit, by only changing curvature of light distribution control structure  60   a , light on which light distribution control is performed according to an angle of view of camera  116 . 
     Variation 
     The present disclosure has been described according to the embodiments, yet the present disclosure is not limited to such embodiments. 
     For example, in the light-emitting device according to the embodiments, the excitation light source need not include the prism, the condenser lens, the first glass rod, the wavelength converting member, and the second glass rod. Furthermore, the excitation light source need not house, in the case, the prism, the condenser lens, the first glass rod, the wavelength converting member, and the second glass rod. The prism, the condenser lens, the first glass rod, the wavelength converting member, and the second glass rod are not essential structural elements of the excitation light source. 
     The present disclosure also encompasses: embodiments achieved by applying various modifications conceivable to those skilled in the art to each embodiment; and embodiments achieved by optionally combining the structural elements and the functions of each embodiment without departing from the essence of the present disclosure. 
     While the foregoing has described one or more embodiments and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present teachings.