Patent Publication Number: US-2018045969-A1

Title: Light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application filed under 35 U.S.C. 111(a) claiming the benefit under 35 U.S.C. 120 and 365(c) of PCT International Application No. PCT/JP2016/068148 filed on Jun. 17, 2016, which is based upon and claims priority to Japanese Priority Application No. 2015-161163 filed on Aug. 18, 2015, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light-emitting device including a plurality of laser light sources. 
     2. Description of the Related Art 
     Patent Document 1 discloses a laser module in which diverging light rays output from a plurality of semiconductor laser elements are made to be parallel light rays by a collimator lens, and the parallel light rays are condensed by a condenser lens. Patent Document 2 discloses a semiconductor laser device in which light rays output from a plurality of laser diodes are made to be parallel light rays by a collimator lens, and the parallel light rays are condensed by a condenser lens into an optical fiber.
     Patent Document 1: Japanese Laid-open Patent Publication No. 2006-66875   Patent Document 2: Japanese Laid-open Patent Publication No. 2013-251394   

     For a so-called CAN laser which is packaged by inserting a laser diode in a metal can, embodiments in which a plurality of laser diodes are inserted are becoming to be used for actualizing high-power. However, according to the conventional CAN laser, optical axes of a plurality of semiconductor laser elements or a plurality of laser diodes are provided to be in parallel to an optical axis of a condenser lens, as described as the laser module of Patent Document 1 or the semiconductor laser device of Patent Document 2. Thus, even when the laser light rays output from these light sources are condensed by the condenser lens, because a plurality of spots may exist, or even if a single spot is formed, the diameter of which may be large and may not be sufficiently converged, it was difficult to provide light of a desired high intensity on a small irradiation target. 
     SUMMARY OF THE INVENTION 
     The present invention is made in light of the above problems, and provides a light-emitting device capable of condensing laser light rays output from a plurality of light sources to be a spot whose diameter is less than or equal to a predetermined size to increase a light intensity per unit area. 
     According to the invention, there is provided a light-emitting device including a light source unit including a plurality of laser light sources; a dioptric system that refracts each light ray input from each of the plurality of laser light sources; a condensing optical system that condenses a plurality of refracted light rays input from the dioptric system, respectively, wherein the dioptric system is configured to refract a plurality of center light beams that are output along optical axes of the plurality of laser light sources, respectively, to proceed in directions each departing from an optical axis of the condensing optical system as proceeding toward the condensing optical system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating a structure of a light-emitting device of a first embodiment of the invention; 
         FIG. 2  is an elevation view illustrating a structure of a light source unit of the light-emitting device illustrated in  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating a structure of a prism of the light-emitting device illustrated in  FIG. 1 ; 
         FIG. 4  is a view illustrating a simulation model of a light-emitting device of example 1 of the first embodiment; 
         FIG. 5  is a view illustrating a simulation model of a light-emitting device of a comparative example; 
         FIG. 6  is a view in which (A) indicates a simulation result of the model illustrated in  FIG. 4  at a position P 11 , (B) indicates a simulation result of the model illustrated in  FIG. 4  at a position P 12 , and (C) indicates a simulation result of the model illustrated in  FIG. 4  at a position P 13 ; 
         FIG. 7  is a view in which (A) indicates a simulation result of the model illustrated in  FIG. 5  at a position P 21 , (B) indicates a simulation result of the model illustrated in  FIG. 5  at a position P 22 , and (C) indicates a simulation result of the model illustrated in  FIG. 5  at a position P 23 ; 
         FIG. 8  is an elevation view illustrating a structure of a light source unit of a light-emitting device of a second embodiment of the invention; 
         FIG. 9A  is a perspective view illustrating a structure of a prism of the light-emitting device of the second embodiment; and 
         FIG. 9B  is a plan view of the prism illustrated in  FIG. 9A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a light-emitting device of embodiments of the invention is described in detail with reference to drawings. 
     First Embodiment 
       FIG. 1  is a plan view illustrating a structure of a light-emitting device  10  of a first embodiment.  FIG. 2  is an elevation view illustrating a structure of a light source unit  20  of the light-emitting device  10 .  FIG. 3  is a perspective view illustrating a structure of a prism  40  of the light-emitting device  10 . In each of the drawings, an X-Y-Z coordinate is illustrated as a standard coordinate. An X 1 -X 2  direction is a direction that extends along an optical axis  30   c  of a condenser lens  30 , and a Y-Z plane is a plane that is perpendicular to the X 1 -X 2  direction. 
     As illustrated in  FIG. 1 , the light-emitting device  10  includes the light source unit  20 , the condenser lens  30  as a condensing optical system, and a prism  40  as a dioptric system. 
     In the light source unit  20 , two laser diodes  22  and  23  as laser light sources are bonded to a stem  21 . Further, a semiconductor chip (not illustrated in the drawings) for driving the laser diodes  22  and  23  and a lead frame (not illustrated in the drawings) for supporting the semiconductor chip are provided at the stem  21 . A plurality of terminals  24  connected to the lead frame are extending outside by penetrating the stem  21  in the X 2  direction. A hollow metal cap  25  is fixed to the stem  21  so as to cover the lead frame, the semiconductor chip and the laser diodes  22  and  23 . Resin is filled in the cap  25 , and with this, positions of the laser diodes  22  and  23  are fixed. 
     As illustrated in  FIG. 1  and  FIG. 2 , for the laser diodes  22  and  23 , light exiting surfaces  22   e  and  23   e  are provided at a surface (a front end surface in the X 1  direction) of the cap  25 , respectively. The laser diodes  22  and  23  are provided such that their optical axes  22   c  and  23   c , respectively, are in parallel to the optical axis  30   c  of the condenser lens  30 . 
     As illustrated in  FIG. 1 , the condenser lens  30  as the condensing optical system is a double-convex plus lens. Here, as the condensing optical system, it is not limited to the double-convex plus lens as illustrated in  FIG. 1 , and as long as having a positive refractive power, a lens having another shape may be used. Further, not limited to a single lens, and an optical system in which a plurality of lenses are combined to have a condensing property may be used. 
     As illustrated in  FIG. 1  and  FIG. 3 , the prism  40  includes two refraction parts  44  and  45  provided at an upper side and a lower side, respectively, in a Y 1 -Y 2  direction. These refraction parts  44  and  45  have shapes that are symmetrical with respect to an XZ-plane. In the prism  40 , the two refraction parts  44  and  45  are integrally formed using a glass or a plastic, for example. 
     The first refraction part  44  of the prism  40  at a Y 1  direction side has a bilateral symmetrical trapezoidal shape when seen in a Z 1 -Z 2  direction. Two side surfaces  44   c  and  44   d , corresponding to an upper base and a lower base of the trapezoidal shape, are planes parallel to each other, and extending in the XZ-plane, respectively. An incident surface  44   a  and a light exiting surface  44   b , corresponding to remaining two sides of the trapezoidal shape, are planes each having an inclined angle such that a distance therebetween becomes larger as departing from the optical axis  30   c  of the condenser lens  30 , and provided in this order from a light source unit  20  side in the X 1 -X 2  direction. When the incident surface  44   a  and the light exiting surface  44   b  are virtually extended in the Y 2  direction, a vertex angle “θ” is formed at a crossing position when seen in the Z 1 -Z 2  direction ( FIG. 1 ). As illustrated in  FIG. 3 , the incident surface  44   a  is inclined with respect to a plane S 1  that is in parallel to the YZ-plane in an X 2  direction side, and the light exiting surface  44   b  is inclined with respect to a plane S 2  that is in parallel to the YZ-plane in an X 1  direction side, wherein an inclined angle is “α”, respectively. The inclined angle “α” is set in accordance with an arrangement of the laser diode  22  with respect to the optical axis  30   c  of the condenser lens  30 , a refractive index of the first refraction part  44 , a refractive power of the condenser lens  30  or the like. In this embodiment, the inclined angle “α” is set to be ½ of the vertex angle “θ”. 
     The second refraction part  45  of the prism  40  at a Y 2  direction side has a bilateral symmetrical trapezoidal shape when seen in the Z 1 -Z 2  direction. Two side surfaces  45   c  and  45   d  corresponding to an upper base and a lower base of the trapezoidal shape, are planes parallel to each other, and extending in the XZ-plane, respectively. An incident surface  45   a  and a light exiting surface  45   b , corresponding to remaining two sides of the trapezoidal shape, are planes each having an inclined angle such that a distance therebetween becomes larger as departing from the optical axis  30   c  of the condenser lens  30 , and provided in this order from the light source unit  20  side in the X 1 -X 2  direction. When the incident surface  45   a  and the light exiting surface  45   b  are virtually extended in the Y 1  direction, a vertex angle “θ” is formed at a crossing position when seen from the Z 1 -Z 2  direction ( FIG. 1 ). This means that the vertex angle formed by the incident surface  45   a  and the light exiting surface  45   b  is the same as the vertex angle formed by the incident surface  44   a  and the light exiting surface  44   b . Further, as illustrated in  FIG. 3 , the incident surface  45   a  is inclined with respect to the plane S 1  in the X 2  direction side, and the light exiting surface  45   b  is inclined with respect to the plane S 2  in the X 1  direction, wherein an inclined angle is “α”, respectively. These inclined angles are set in accordance with an arrangement of the laser diode  23  with respect to the optical axis  30   c  of the condenser lens  30 , a refractive index of the second refraction part  45 , the refractive power of the condenser lens  30  or the like. In this embodiment, this angle is the same as the inclined angle of the incident surface  44   a  and the light exiting surface  44   b  of the first refraction part  44 . 
     In the prism  40 , the side surface  44   d  of the first refraction part  44  and the side surface  45   c  of the second refraction part  45  are formed to be a common surface (shared surface), and as illustrated in  FIG. 3 , the common surface is provided at the XZ-plane including the optical axis  30   c  of the condenser lens  30 . With this, the first refraction part  44  and the second refraction part  45  are provided to be symmetrical with respect to the XZ-plane. 
     In the light-emitting device  10  having the above described structure, a center light beam  22   a  of an outgoing light ray from the laser diode  22  is input in the incident surface  44   a  in parallel to the optical axis  30   c , and a center light beam  23   a  of an outgoing light ray from the laser diode  23  is input in the incident surface  45   a  in parallel to the optical axis  30   c  as well. 
     The center light beam  22   a  is refracted in the first refraction part  44  in accordance with the refractive index of the first refraction part  44  and the setting of the inclined angle “α” of the incident surface  44   a  and the light exiting surface  44   b  to be output from the light exiting surface  44   b . As such, the refracted light ray  42   a  output from the light exiting surface  44   b  proceeds such that to depart from the optical axis  30   c  of the condenser lens  30  as proceeding toward a condenser lens  30  side. 
     Further, the center light beam  23   a  is refracted in the second refraction part  45  in accordance with the refractive index of the second refraction part  45 , and the setting of the inclined angle “α” of the incident surface  45   a  and the light exiting surface  45   b  to be output from the light exiting surface  45   b . The refracted light ray  43   a  output from the light exiting surface  45   b  proceeds such that to depart from the optical axis  30   c  of the condenser lens  30  as proceeding toward the condenser lens  30  side. 
     Thus, the refracted light ray  42   a  and the refracted light ray  43   a  proceed to depart from each other as proceeding toward the condenser lens  30  side. 
     As illustrated in  FIG. 1 , the refracted light rays  42   a  and  43   a  output from the prism  40  are output from the condenser lens  30  as converging light rays  32   a  and  33   a , respectively. Light fluxes of these converging light rays  32   a  and  33   a  overlap and become a pinpoint spot at a condensing position PC, and thereafter, images are formed at an image formation position PI, respectively. Thus, as the two light fluxes are overlapped to form the spot having a pinpoint diameter with a high light intensity at the condensing position PC, a light intensity per unit area can be increased at this position, and high-power can be obtained. Here, the light intensity of the spot formed at the condensing position PC is approximately two times of each of the laser light rays output from the laser diodes  22  and  23 , respectively. Further, the condensing position PC is positioned at a back side of a back focal position PF of the condenser lens  30 , in other words at a proceeded position of an image-side focal point in the X 1  direction. 
     On the other hand, if the laser light rays output from the laser diodes  22  and  23  are directly input in the condenser lens  30  without using the prism  40 , light fluxes are not overlapped at the back side of the back focal position PF to form a spot. Further, in such a case, portions of the two light fluxes may be overlapped at a front side of the back focal position PF, but the light fluxes do not form a spot at the position, and there exist portions where the light fluxes are overlapped and portions where the light fluxes are not overlapped. Thus, a light intensity per unit area is uneven, and the maximum value of the light intensity per unit area is approximately 1 to 1.5 times of a case when a single laser light is used. 
     Next, an example of the first embodiment is described. 
       FIG. 4  is a view illustrating a simulation model of a light-emitting device of example 1 of the first embodiment.  FIG. 5  is a view illustrating a simulation model of a light-emitting device of a comparative example. Each of  FIG. 4  and  FIG. 5  illustrates a lens L corresponding to the condenser lens  30  of  FIG. 1 , and an optical path in which light rays output from two laser diodes proceed from a left-side to a right-side. In  FIG. 4 , a prism D corresponding to the prism  40  of  FIG. 1  is illustrated. (A), (B) and (C) of  FIG. 6  illustrate simulation results at positions P 11 , P 12  and P 13 , respectively, in the model of example 1 illustrated in  FIG. 4 . (A), (B) and (C) of  FIG. 7  illustrate simulation results at positions P 21 , P 22  and P 23 , respectively, in the model of the comparative example illustrated in  FIG. 5 . Here, the position P 11  of  FIG. 4  and the position P 21  of  FIG. 5  correspond to the back focal position PF in  FIG. 1 , the position P 12  of  FIG. 4  and the position P 22  of  FIG. 5  correspond to the condensing position PC in  FIG. 1 , and the position P 13  of  FIG. 4  and the position P 23  of  FIG. 5  correspond to the image formation position PI in  FIG. 1 . 
     In example 1 illustrated in  FIG. 4 , light rays B 11  and B 12  are output from two laser diodes under the following conditions. In the comparative example illustrated in  FIG. 5 , light rays B 21  and B 22  are output from two laser diodes, and a simulation was conducted under the same conditions as example 1 except that the prism D is not provided. Here, an output of the laser diode was 1 W (watt) for both example 1 and the comparative example. 
     Example 1 
     Each of the following distances is a distance in a direction along an axis Lc of the lens L, and an axial distance means a distance on the optical axis Lc. 
     (Characteristics of Laser Diode) 
     Light emitting positions: 0.2 mm from the optical axis Lc of the lens L in the Y 1  direction, and 0.2 mm from the optical axis Lc of the lens L in the Y 2  direction 
     Light emitting angle: 0 degree with respect to the optical axis Lc of the lens L 
     Angle of divergence: ±10 degrees with having an optical axis of a laser diode as a center 
     (Characteristics of Prism D) 
     Material: BK7 (product name, borosilicate crown glass, refractive index 1.517, Abbe number 64.2) 
     Inclined angle “α” of the incident surface and the light exiting surface: 10 degrees 
     Thickness in the Z 1 -Z 2  direction (a center portion of the XY-plane): 0.9 mm 
     Distance from a light exiting surface of the laser diode to an incident surface r 21  of the prism D: 0.5 mm 
     (Characteristics of Lens L) 
     Focal length: 1.65 mm 
     Radius of curvature R at a front surface r 1  (light source side surface): 2.1 
     Radius of curvature R at a back surface r 2  (image-side surface): 1.8 
     Lens thickness: 2.5 mm 
     Aperture diameter: diameter 3.6 mm 
     Axial distance from the light exiting surface r 22  of the prism D to the front surface r 1  of the lens L: 1.4 mm 
     Axial distance from the back surface r 2  of the lens L to the image formation position P 13 : 5.0 mm 
     The following results were obtained by the simulations. 
     In example 1, as illustrated in (B) of  FIG. 6 , a single spot was formed at the condensing position P 12 , the spot diameter was 0.15 mm, and the maximum value of the light intensity per unit area (hereinafter, referred to as “Emax”) was 40000 W/cm 2 . Meanwhile, Emax of the two light fluxes at the back focal position P 11  in (A) of  FIG. 6  was 1700 W/cm 2 . 
     On the other hand, as illustrated in (B) of  FIG. 7 , in the comparative example, a single spot was formed at the condensing position P 22 , and Emax of the two light fluxes at the condensing position P 22  was 8000 W/cm 2 . Further, Emax of the two light fluxes at the back focal position P 21  in (A) of  FIG. 7  was 1800 W/cm 2 . 
     From the above results, compared with the comparative example in which the outgoing light rays from the laser diodes were directly input in the lens L, in example 1 in which the prism D was provided between the laser diodes and the lens L, the light fluxes were overlapped to be a small spot at the condensing position P 12 , and the light intensity was increased. This light intensity was higher than the light intensity at the back focal position P 21  in the comparative example. 
     Alternative examples are described in the following. 
     In the above described embodiment, both of the incident surface and the light exiting surface of each of the first refraction part  44  and the second refraction part  45  of the prism  40  are formed to be the inclined surfaces, respectively. However, as long as the plurality of outgoing light rays from the first refraction part  44  and the second refraction part  45  can proceed such that a distance therebetween becomes larger as proceeding toward the condenser lens  30  side, only one of the incident surface and the light exiting surface may be formed to be the inclined surface. Further, even for a case where both of the incident surface and the light exiting surface are formed to be the inclined surfaces, respectively, as long as the plurality of outgoing light rays from the first refraction part  44  and the second refraction part  45  can proceed such that a distance therebetween becomes larger as proceeding toward the condenser lens  30  side, the inclined angles may be different for the incident surface and the light exiting surface. Further, the inclined surface is not limited to a plane, and may be an aspheric surface or a hemispherical curved surface, or only an input area from each of the laser diodes  22  and  23  and an output area from the prism  40  may be configured by a desired inclined surface or a curved surface. 
     When three or more of the laser diodes are provided in series in the Y 1 -Y 2  direction, inclined angles of the inclined surfaces of areas of the prism  40  at which the outgoing light rays from the laser diodes are varied in accordance with distances from the optical axis  30   c  of the condenser lens  30  in the Y 1 -Y 2  direction, respectively, so that the outgoing light rays from the condenser lens  30  can be condensed as a spot at the condensing position PC. This is the same for a case when laser diodes are aligned in series in a direction other than the Y 1 -Y 2  direction. 
     In the above described embodiment, the single prism  40  is used as the dioptric system. However, as long as refracted light rays can be generated from the outgoing light rays from the laser diodes  22  and  23 , respectively, similarly by the prism  40 , another configuration may be used. For example, an optical member in which the outgoing light ray from the laser diode  22  is input, and an optical member in which the outgoing light ray from the laser diode  23  is input, may be separately provided. 
     In the above described embodiment, the two laser diodes  22  and  23  are provided such that their optical axes are in parallel to each other. However, as long as a desired spot can be formed by converging light rays output from the condenser lens  30 , the optical axes of the laser diodes  22  and  23  may be inclined by a predetermined angle with respect to the optical axis  30   c  of the condenser lens  30 , respectively. 
     According to the light-emitting device of the first embodiment and its alternative examples, as configured as above description, following effects can be obtained. 
     (1) By refracting each of the outgoing light rays from the laser diodes  22  and  23  by using the prism  40 , the plurality of converging light rays output from the condenser lens  30  can be overlapped and condensed to be a small spot. Thus, light whose light intensity per unit area is large can be obtained.
 
(2) As the first refraction part  44  and the second refraction part  45  are formed to have shapes symmetrical with respect to the XZ-plane, the spot formed by overlapping the converging light rays  32   a  and  33   a  output from the condenser lens  30  becomes smaller and nearly a circular shape. Thus, the light intensity can be furthermore increased.
 
(3) In order to input a plurality of light beams that proceed to depart from each other to the condenser lens  30 , the configuration as the light-emitting device of the first embodiment in which the prism  40  as the dioptric system is provided between the laser diodes  22  and  23  and the condenser lens  30  is considered. Aside from this configuration, without using the dioptric system, a configuration in which a direction of an outgoing light ray from each of the plurality of laser diodes is inclined with respect to the optical axis  30   c  of the condenser lens  30  may be considered. However, It is very difficult to accurately set inclined angles of all of the laser diodes to a degree that the plurality of outgoing light rays from the condenser lens  30  can be condensed to be a small spot. On the other hand, according to the light-emitting device of the first embodiment, as the prism  40  is used, it is only necessary to provide the laser diodes  22  and  23  to be in parallel to each other, and a plurality of outgoing light rays from the condenser lens  30  can be accurately condensed at a desired position as a small spot.
 
     Second Embodiment 
     Next, a second embodiment of the invention is described. In the second embodiment, the number of laser diodes, as the laser light sources, are four. In the following description, the same components as those described in the first embodiment are given the same reference numerals. 
       FIG. 8  is an elevation view illustrating a structure of a light source unit  120  of a light-emitting device of a second embodiment.  FIG. 9A  is a perspective view illustrating a structure of a prism  140  of the light-emitting device of the second embodiment, and  FIG. 9B  is a plan view of the prism  140  illustrated in  FIG. 9A . In  FIG. 9B , center light beams  123   a  and  125   a , and refracted light rays  143   a  and  145   a  are not illustrated. 
     As illustrated in  FIG. 8 , in the second embodiment, four laser diodes  122 ,  123 ,  124  and  125  are provided as laser light sources such that each optical axis is positioned on a circle  120   c  whose center is the optical axis  30   c  of the condenser lens  30 , and these laser diodes are bonded to the stem  21 . Each optical axis of each of the laser diodes  122 ,  123 ,  124  and  125  is in parallel to the optical axis  30   c  of the condenser lens  30 , similarly as the first embodiment. The laser diode  122  is provided at the Y 1  direction side, the laser diode  123  is provided at the Z 1  direction side, the laser diode  124  is provided at the Y 2  direction side, and the laser diode  125  is provided at the Z 2  side, with respect to the optical axis  30   c.    
     In the second embodiment, instead of the prism  40  of the first embodiment, the prism  140  illustrated in  FIG. 9A  and  FIG. 9B  is used as the dioptric system. As illustrated in  FIG. 9A , the prism  140  has a rectangular outer shape when seen in the X 1 -X 2  direction, and four refraction parts  142 ,  143 ,  144  and  145  are provided to correspond to the four laser diodes  122 ,  123 ,  124  and  125 , respectively. More specifically, the refraction part  142  is provided at the Y 1  direction side, the refraction part  143  is provided at the Z 1  direction side, the refraction part  144  is provided at the Y 2  direction, and the refraction part  145  is provided at the Z 2 , with respect to the optical axis  30   c , with equiangular intervals. The four refraction parts  142 ,  143 ,  144  and  145  are integrally formed by using a glass or a plastic, for example. 
     Each of the refraction parts  142 ,  143 ,  144  and  145  includes an incident surface to which an outgoing light ray from the respective laser diode  122 ,  123 ,  124  or  125  is input, and a light exiting surface from which the input light ray is output after being refracted, from the light source unit  120  side in this order in the X 1 -X 2  direction. The incident surface and the light exiting surface of the same refraction part are planes including inclined angles such that a distance therebetween becomes larger as departing from the optical axis  30   c  of the condenser lens  30 . For example, as illustrated in  FIG. 9B , an incident surface  142   b  and a light exiting surface  142   c  are provided in the refraction part  142 , and an incident surface  144   b  and a light exiting surface  144   c  are provided in the refraction part  144 . In the refraction part  142 , the incident surface  142   b  is inclined toward the X 2  direction side with respect to a plane S 3  that is in parallel to the YZ-plane, the light exiting surface  142   c  is inclined toward the X 1  direction side with respect to a plane S 4  that is in parallel to the YZ-plane, and each inclined angle is “β”. Further, in the refraction part  144 , the incident surface  144   b  is inclined toward the X 2  direction side with respect to the plane S 3 , the light exiting surface  144   c  is inclined toward the X 1  direction side with respect to the plane S 4 , and each inclined angle is “β”. Such a structure is the same for each of the refraction parts  143  and  145 . 
     In the prism  140  having the structure as described above, the outgoing light rays (center light beams  122   a ,  123   a ,  124   a  and  125   a ) from the laser diodes  122 ,  123 ,  124  and  125  are input in the refraction parts  142 ,  143 ,  144  and  145 , and refracted to be output to the condenser lens  30  as refracted light rays  142   a ,  143   a ,  144   a  and  145   a , respectively. These refracted light rays proceed such that to depart from the optical axis  30   c  of the condenser lens  30  as proceeding toward the condenser lens  30  side and are input in the condenser lens  30 , and light fluxes of the converging light rays condensed by the condenser lens  30  overlap at the condensing position PC to become a pinpoint spot. 
     Here, although a planar shape of the prism  140  seen in the X 1 -X 2  direction is configured to have a rectangular shape, as long as input areas from the laser diodes  122 ,  123 ,  124  and  125  and output areas of the refracted light rays, respectively, can be ensured, a shape other than the rectangular shape, for example, a circular shape may be used. 
     Here, other functions, effects and alternative examples are the same as those of the first embodiment. Although the present invention has been illustrated and described with reference to the embodiments, it is to be understood that modifications may be made therein without departing from the spirit and scope of the invention as defined by the claims. 
     As described above, as it is possible to obtain a spot light flux with a high light intensity at a condensing position according to the light-emitting device of the embodiment, it is usable for light working or illumination. 
     With the above configuration of the embodiment, a plurality of converging light rays output from the condensing optical system can be overlapped and condensed to be a small spot, and light with a high light intensity per unit area can be obtained. 
     In the light-emitting device of the invention, it is preferable that the dioptric system includes a plurality of inclined surfaces each having an inclined angle corresponding to each of the plurality of laser light sources. 
     With this, as reflected light rays can be output from the dioptric system to the condensing optical system with desired angles by inclined surfaces corresponding to an arrangement or the like of the plurality of laser light sources with respect to the optical axis of the condensing optical system, the plurality of converging light rays can be condensed to be a small spot. 
     In the light-emitting device of the invention, it is preferable that the plurality of inclined surfaces are provided at at least one of an incident surface and a light exiting surface of the dioptric system. 
     With this, degree of freedom in design of the dioptric system can be increased, and further, manufacturing cost of the dioptric system can be reduced. 
     In the light-emitting device of the invention, it is preferable that the dioptric system is a single optical component including the plurality of inclined surfaces. 
     With this, an area necessary for the dioptric system can be made small, and the size of the light-emitting device can be made small. 
     In the light-emitting device of the invention, it is preferable that the plurality of inclined surfaces are provided at both of an incident surface and a light exiting surface of the dioptric system, and that the incident surface and the light exiting surface from which a light ray input from the respective incident surface is output are inclined such that a distance therebetween becomes larger as departing from the optical axis of the condensing optical system. By providing the inclined surfaces to both of the incident surface and the light exiting surface of the dioptric system, degree of refraction for each surface can be made small, and the dioptric system can be formed in a shape easy to design and easy to manufacture. In the light-emitting device of the invention, it is preferable that optical axes of the plurality of laser light sources, respectively, are in parallel to the optical axis of the condensing optical system. 
     With this, the plurality of laser light sources can be arranged by a known technique. 
     In the light-emitting device of the invention, it is preferable that the condensing optical system is made of a single condenser lens. 
     With this, an area necessary for the condensing optical system can be made small, and the size of the light-emitting device can be made small. 
     According to the invention, it is possible to condense laser light rays output from a plurality of light sources to be a spot whose diameter is less than or equal to a predetermined size to increase a light intensity per unit area.
       10  light-emitting device     20  light source unit     22   a ,  23   a  center light beam     22   c ,  23   c  optical axis     22   e ,  23   e  light exiting surface     22 ,  23  laser diode     30  condenser lens (condensing optical system)     30   c  optical axis     32   a ,  33   a  converging light ray     40  prism (dioptric system)     42   a ,  43   a  refracted light ray     44  first refraction part     44   a  incident surface     44   b  light exiting surface     45  second refraction part     45   a  incident surface     45   b  light exiting surface     120  light source unit     122 ,  123 ,  124 ,  125  laser diode     122   a ,  123   a ,  124   a ,  125   a  center light beam     140  prism (dioptric system)     142 ,  143 ,  144 ,  145  refraction part     142   a ,  143   a ,  144   a ,  145   a  refracted light ray     142   b ,  144   b  incident surface     142   c ,  144   c  light exiting surface   D prism (dioptric system)   L lens (condensing optical system)   Lc optical axis   PF, P 11 , P 21  back focal position   PC, P 12 , P 22  condensing position   PI, P 13 , P 23  image formation position   r 1  front surface   r 21  incident surface   r 2  back surface   r 22  light exiting surface