Abstract:
Provided is a mounting member having a light receiving element, capable of constraining increase in size and of arranging a plurality of laser element portions closer to each other. The mounting member includes three or more electrodes, which respectively include element mounting portions arranged in a first direction, and a light receiving element disposed in a second direction intersecting with the first direction relative to the element mounting portions. The length in the second direction of at least one of the element mounting portions disposed at both ends in the first direction among the three or more element mounting portions is smaller than the length in the second direction of an element mounting portion disposed at an inner position in the first direction among the three or more element mounting portions.

Description:
This application is based on Japanese Patent Application No. 2009-213322 filed on Sep. 15, 2009, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a mounting member and a semiconductor laser apparatus having the same, and, more particularly, to a mounting member provided with a plurality of electrodes and a semiconductor laser apparatus having the same. 
     2. Description of Related Art 
     A mounting member provided with a plurality of electrodes has hitherto been known (see, e.g., Japanese Laid-Open Patent Publication No. 2004-55744). 
     Japanese Laid-Open Patent Publication No. 2004-55744 discloses a semiconductor laser apparatus having three semiconductor laser elements arranged in a predetermined direction and a block (mounting member) provided with three electrodes respectively mounted with the three semiconductor laser elements. 
     The block is provided with a photodiode (light receiving element) for monitoring an optical output of the semiconductor laser element at a position confronting a rear emission surface (back end surface) of the semiconductor laser element. Therefore, as compared to the case of separately providing a photodiode for monitoring the optical output of the semiconductor laser element, this semiconductor laser apparatus enables a simplified structure and constraint of increase in size. 
     Each of the electrodes of the block includes an element mounting portion mounted with the semiconductor laser element and a portion (wiring portion) connected to the element mounting portion and bonded with a conductive wire. 
     The portion bonded with the conductive wire of the center electrode of the three electrodes is formed between the element mounting portion of the center electrode and the element mounting portion of the adjacent electrode on one side. This makes it difficult to arrange the element mounting portion of the center electrode closer to the element mounting portion of the adjacent electrode on one side and hence to arrange the center semiconductor laser element of the three semiconductor laser elements closer to the semiconductor laser element on one side. As a result, it becomes inconveniently difficult to share among the three semiconductor laser elements an optical member such as a lens for receiving light emitted from them. 
     To improve this inconvenience, a semiconductor laser apparatus has been proposed that includes a portion bonded with a conductive wire of the center electrode projecting in a direction orthogonal to the direction in which the semiconductor laser elements are arranged (see, e.g., Japanese Laid-Open Patent Publication No. 2009-27149). 
     Japanese Laid-Open Patent Publication No. 2009-27149 discloses a semiconductor laser apparatus having three semiconductor laser elements (laser element portions) arranged in a predetermined direction and a base mounted with the three semiconductor laser elements. 
     The base is provided with three electrode layers respectively mounted with the three semiconductor laser elements. Each of the electrode layers includes an element mounting portion mounted with the semiconductor laser element and an area (wiring portion) connected to the element mounting portion and bonded with an Au wire. The area bonded with the Au wire of the center electrode layer of the three electrode layers is formed to project from the element mounting portion in the direction opposite to the light emitting surface of the semiconductor laser element. 
     This semiconductor laser apparatus therefore enables the element mounting portion of the center electrode layer and the element mounting portions of the adjacent electrode layers to be arranged closer and hence enables the three semiconductor laser elements to be arranged closer. This makes it possible to share among the three semiconductor laser elements an optical member such as a lens for receiving light emitted from them. 
     Japanese Laid-Open Patent Publication No. 2009-27149 is however different from Japanese Laid-Open Patent Publication No. 2004-55744 in that the base is not provided with a light receiving element for monitoring an optical output from the semiconductor laser element (laser element portion). Thus, since Japanese Laid-Open Patent Publication No. 2009-27149 necessitates separately providing the light receiving element to monitor the optical output from the semiconductor laser element, problematically, it is difficult to simplify the structure and the apparatus tends to be large. 
     It may be conceivable that the photodiode (light receiving element) of Japanese Laid-Open Patent Publication No. 2004-55744 is formed on the base (mounting member) of Japanese Laid-Open Patent Publication No. 2009-27149. Since, however, the area bonded with the Au wire of the center electrode layer must be formed to project from the element mounting portion in the direction opposite to the light emitting surface of the semiconductor laser element (toward the photodiode), the area bonded with the Au wire of the center electrode layer is disposed between the element mounting portion and the photodiode. This results in an increased distance between the element mounting portion and the photodiode, problematically making it difficult to constrain the base from increasing in size. 
     SUMMARY OF THE INVENTION 
     The present invention was conceived to address problems and inconveniences as discussed above and it is therefore the object of the present invention to provide a mounting member provided with a light receiving element and a semiconductor laser apparatus having the same, capable of constraining the increase in size and arranging a plurality of laser element portions closer to each other. 
     To achieve the object, according to a first aspect of the present invention, a mounting member mounted with a first semiconductor laser element and a second semiconductor laser element, the second semiconductor laser element being a monolithic multi-wavelength semiconductor laser element, includes: three or more electrodes respectively having element mounting portions arranged in a first direction; and a light receiving element disposed in a second direction, which intersects with the first direction, with respect to the element mounting portions. Here, the length in the second direction of at least one of the element mounting portions disposed at both ends in the first direction among the three or more element mounting portions is smaller than the length in the second direction of an element mounting portion disposed at an inner position in the first direction among the three or more element mounting portions. Moreover, the electrode having the element mounting portion disposed at the inner position includes a wiring portion which is connected to the element mounting portion disposed at the inner position and which extends outward in the first direction further than the at least one of the element mounting portions disposed at both ends. 
     As described above, the mounting member of the first aspect is provided with the light receiving element on a portion in the second direction from the element mounting portions. This simplifies the structure of the semiconductor laser apparatus and constrains the apparatus from increasing in size as compared to the case of providing the light receiving element separately from the mounting member. 
     In the mounting member of the first aspect, as described above, the length in the second direction of at least one of the element mounting portions disposed at both ends in the first direction among the three or more element mounting portions is made less than the length in the second direction of the element mounting portion disposed on the inside in the first direction among the three or more element mounting portions, and the electrode having the element mounting portion disposed on the inside is provided with the wiring portion extending outward in the first direction further than the at least one of the element mounting portions disposed at both ends. This eliminates the need for disposing the wiring portion between the element mounting portions, and enables the three or more element mounting portions to be arranged closer to each other. Therefore, the laser element portion of the first semiconductor laser element and the laser element portion of the second semiconductor laser element are arranged closer to each other. This enables an optical member such as a lens receiving light emitted from the first semiconductor laser element and the second semiconductor laser element to be shared by the first semiconductor laser element and the second semiconductor laser element. As a result, the number of parts such as optical members can be constrained from increasing and the apparatus can be constrained from increasing in size. 
     In the mounting member of the first aspect, as described above, the length in the second direction of at least one of the element mounting portions disposed at both ends is made less than the length in the second direction of the element mounting portion disposed on the inside. This ensures that the wiring portion is formed outward in the first direction further than the at least one of the element mounting portions disposed at both ends without projecting from the element mounting portion disposed on the inside in the second direction and without contacting with the element mounting portions disposed at both ends. Since the wiring portion is not required to project from the element mounting portion in the second direction in this manner, the distance can be constrained from increasing between the element mounting portions and the light receiving element. This constrains the mounting member from increasing in size. 
     In the mounting member of the first aspect, preferably, the wiring portion has an element mounting area on a portion thereof in the second direction with respect to the at least one of the element mounting portions disposed at both ends, and an insulating layer is disposed on the element mounting area. Since such an arrangement constrains the wiring portion from electrically connecting with a portion disposed on the element mounting area of the first semiconductor laser element or the second semiconductor laser element, the wiring portion can be disposed to pass under at least one of the laser element portions of the first semiconductor laser element and the second semiconductor laser element. 
     In the mounting member with the element mounting area disposed on the wiring portion, preferably, a first adhesive layer is disposed between the element mounting area and the insulating layer. Such an arrangement enables adhesive strength to be easily enhanced between the element mounting area of the wiring portion and the insulating layer. 
     In the mounting member of the first aspect, preferably, a conductive adhesive layer is disposed on the element mounting portion. By disposing the conductive adhesive layer on the element mounting portion of the mounting member in advance, the manufacturing process can be simplified when the first semiconductor laser element and the second semiconductor laser element are mounted on the mounting member. 
     In the mounting member with the conductive adhesive layer disposed on the element mounting portion, preferably, the wiring portion has an element mounting area on a portion thereof in the second direction with respect to the at least one of the element mounting portions disposed at both ends; an insulating layer is disposed on the element mounting area; a portion of the conductive adhesive layer is disposed on the insulating layer; and a second adhesive layer is disposed between the insulating layer and the conductive adhesive layer. Since the insulating layer is disposed on the element mounting area of the wiring portion to thereby constrain the wiring portion from electrically connecting with a portion disposed on the element mounting area of the first semiconductor laser element or the second semiconductor laser element, the wiring portion can be disposed to pass under at least one of the laser element portions of the first semiconductor laser element and the second semiconductor laser element. 
     By disposing the second adhesive layer between the insulating layer and the conductive adhesive layer, adhesive strength can easily be enhanced between the insulating layer and the conductive adhesive layer. 
     In the mounting member of the first aspect, preferably, laser element portions of the second semiconductor laser element are respectively mounted on the element mounting portion disposed at the inner position and on one of the element mounting portions disposed at both ends; the length in the second direction of one of the element mounting portions disposed at both ends is smaller than the length in the second direction of the element mounting portion disposed at the inner position; the wiring portion is formed to extend outward in the first direction further than the one of the element mounting portions disposed at both ends. Such an arrangement eliminates the need for reducing the length in the second direction of the element mounting portion mounted with the first semiconductor laser element, thus constraining the adhesive strength from deteriorating between the mounting member and the first semiconductor laser element. Even if the length in the second direction of one of the element mounting portions disposed at both ends is less than the lengths in the second direction of the element mounting portion disposed on the inside and the element mounting portion mounted with the first semiconductor laser element, the second semiconductor laser element adheres not only to one of the element mounting portions disposed on both ends but also to the element mounting portion disposed on the inside, thus ensuring the sufficient adhesive strength between the mounting member and the second semiconductor laser element. 
     In the mounting member of the first aspect, preferably, the length in the second direction of the electrode having the element mounting portion disposed at the inner position is substantially the same as the length in the second direction of the element mounting portion disposed at the inner position. Since the wiring portions does not project in the second direction from the element mounting portion disposed on the inside in such an arrangement, the distance can further be constrained from increasing between the element mounting portion and the light receiving element. 
     In the mounting member of the first aspect, preferably, the mounting member further includes a first conductivity type semiconductor substrate having the three or more electrodes formed on a surface thereof, and here the light receiving element is formed by disposing a second conductivity type area in a portion of the semiconductor substrate in the second direction with respect to the element mounting portion. Such an arrangement facilitates disposing the light receiving element on the mounting member. 
     In the mounting member of the first aspect, preferably, the first semiconductor laser element and the second semiconductor laser element are mounted junction-down. Since such an arrangement enables the laser element portion of the first semiconductor laser element and the laser element portion of the second semiconductor laser element to be arranged closer to the surface of the mounting member, the lights emitted from the first semiconductor laser element and the second semiconductor laser element can easily be made incident on the light receiving element even when the light receiving element is disposed closer to the element mounting portions. 
     According to a second aspect of the present invention, a semiconductor laser apparatus includes: a mounting member, a first semiconductor laser element mounted on the mounting member, and a second semiconductor laser element mounted on the mounting member, the second semiconductor laser element being a monolithic multi-wavelength semiconductor laser element. Here, the mounting member includes three or more electrodes respectively having element mounting portions arranged in a first direction, and a light receiving element disposed in a second direction, which intersects with the first direction, with respect to the element mounting portions. Moreover, the length in the second direction of at least one of the element mounting portions disposed at both ends in the first direction among the three or more element mounting portions is smaller than the length in the second direction of an element mounting portion disposed at an inner position in the first direction among the three or more element mounting portions. Moreover, the electrode having the element mounting portion disposed at the inner position includes a wiring portion which is connected to the element mounting portion disposed at the inner position and which extends outward in the first direction further than the at least one of the element mounting portions disposed at both ends. With such an arrangement, the semiconductor laser apparatus can be acquired that is capable of constraining increase in size and arranging a plurality of laser element portions closer to each other and that is provided with a light receiving element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a structure of a three-wavelength semiconductor laser apparatus including a sub-mount according to one embodiment of the present invention; 
         FIG. 2  is a diagram of a structure of the three-wavelength semiconductor laser apparatus including the sub-mount according to one embodiment of the present invention depicted in  FIG. 1 ; 
         FIG. 3  is a perspective view of a structure of the sub-mount according to one embodiment of the present invention depicted in  FIG. 1 ; 
         FIG. 4  is a perspective view of the structure except a solder layer and an insulating layer of the sub-mount according to one embodiment of the present invention depicted in  FIG. 1 ; 
         FIG. 5  is a perspective view of the structure except the solder layer of the sub-mount according to one embodiment of the present invention depicted in  FIG. 1 ; 
         FIG. 6  is an enlarged cross-section view of the structure around the insulating layer of the sub-mount according to one embodiment of the present invention depicted in  FIG. 1 ; 
         FIG. 7  is a perspective view for explaining a structure of a sub-mount according to a first variation of the present invention; and 
         FIG. 8  is a perspective view for explaining a structure of a sub-mount according to a second variation of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. 
     A structure of a three-wavelength semiconductor laser apparatus  1  including a sub-mount  50  according to one embodiment of the present invention will be described with reference to  FIGS. 1 to 6 . The three-wavelength semiconductor laser apparatus  1  is an example of a “semiconductor laser apparatus” of the present invention. 
     As depicted in  FIG. 1 , the three-wavelength semiconductor laser apparatus  1  according to one embodiment of the present invention includes a blue-violet semiconductor laser element  10 , a two-wavelength semiconductor laser element  20 , and a sub-mount  50  mounted junction-down with the blue-violet semiconductor laser element  10  and the two-wavelength semiconductor laser element  20 . The blue-violet semiconductor laser element  10  is an example of a “first semiconductor laser element” of the present invention and the two-wavelength semiconductor laser element  20  is an example of a “second semiconductor laser element” of the present invention. The sub-mount  50  is an example of a “mounting member” of the present invention. 
     As depicted in  FIG. 2 , the blue-violet semiconductor laser element  10  and the two-wavelength semiconductor laser element  20  are adjacently arranged in the width direction (X-direction). The blue-violet semiconductor laser element  10  is disposed on one side (X 1 -direction side) in the X-direction of the two-wavelength semiconductor laser element  20 . The X-direction is an example of a “first direction” of the present invention. 
     The blue-violet semiconductor laser element  10  has a function of emitting a laser beam in a wavelength band of about 405-nm (blue-violet laser beam), for example, and is used for recording/reproduction on BD (Blu-ray Disc (registered trademark)). 
     The blue-violet semiconductor laser element  10  includes a semiconductor substrate  11 , a semiconductor layer  12  formed on a principal surface  11   a  of the semiconductor substrate  11 , an electrode layer  13  having a thickness of a few μm formed on the semiconductor layer  12 , and an electrode layer  14  formed on a rear surface of the semiconductor substrate  11 . The semiconductor layer  12  and the electrode layer  13  make up a semiconductor laser element portion  10   a.    
     An optical waveguide (not shown) is formed in the semiconductor layer  12  and extends in a direction (Y-direction (see  FIG. 1 )) orthogonal to the X-direction. A front end portion (an end portion in the Y 1 -direction (see  FIG. 1 )) of the optical waveguide acts as a light emitting portion (not shown) that emits a laser beam. A back end portion (an end portion in the Y 2 -direction (see  FIG. 1 )) of the optical waveguide acts as a light emitting portion  12   a  that emits a portion of the laser beam. The laser beam emitted from the light emitting portion  12   a  has an output power lower than the laser beam emitted from the light emitting portion at the front end (in the Y 1 -direction) and is used for monitoring the optical output of the blue-violet semiconductor laser element  10 . The Y-direction is an example of a “second direction” of the present invention. 
     The electrode layer  13  is disposed on an electrode  52  described later of the sub-mount  50 . 
     The electrode layer  14  is bonded with an Au wire not shown. 
     The two-wavelength semiconductor laser element  20  is a monolithic two-wavelength (multi-wavelength) semiconductor laser element and includes a semiconductor substrate  21 , a red semiconductor laser element portion  30  and an infrared semiconductor laser element portion  40  provided in a predetermined area on a principal surface  21   a  of the semiconductor substrate  21 , and a common electrode layer  22  formed on a rear surface of the semiconductor substrate  21 . The red semiconductor laser element portion  30  and the infrared semiconductor laser element portion  40  are examples of a “laser element portion” of the present invention. 
     The red semiconductor laser element portion  30  has a function of emitting a laser beam in a wavelength band of about 660-nm (red laser beam), for example, and is used for recording/reproduction on DVD (Digital Versatile Disc). The infrared semiconductor laser element portion  40  has a function of emitting a laser beam in a wavelength band of about 785-nm (infrared laser beam), for example, and is used for recording/reproduction on CD (Compact Disc). 
     The red semiconductor laser element portion  30  is formed on a portion on one side (X 1 -direction side) in the X-direction of the principal surface  21   a  of the semiconductor substrate  21  and the infrared semiconductor laser element portion  40  is formed on a portion on the other side (X 2 -direction side) in the X-direction of the principal surface  21   a  of the semiconductor substrate  21 . The red semiconductor laser element portion  30  and the infrared semiconductor laser element portion  40  are arranged with a predetermined space therebetween in the X-direction. 
     The red semiconductor laser element portion  30  includes a semiconductor layer  31  and an electrode layer  32  having a thickness of a few μm formed on the semiconductor layer  31 . 
     An optical waveguide (not shown) is formed in the semiconductor layer  31  and extends in the Y-direction (see  FIG. 1 ). A front end portion (an end portion in the Y 1 -direction (see  FIG. 1 )) of the optical waveguide acts as a light emitting portion (not shown) that emits a laser beam. A back end portion (an end portion in the Y 2 -direction (see  FIG. 1 )) of the optical waveguide acts as a light emitting portion  31   a  that emits a portion of the laser beam. The laser beam emitted from the light emitting portion  31   a  has an output power lower than the laser beam emitted from the light emitting portion at the front end (in the Y 1 -direction) and is used for monitoring the optical output of the red semiconductor laser element portion  30 . 
     The electrode layer  32  is disposed on an electrode  53  described later of the sub-mount  50 . 
     The infrared semiconductor laser element portion  40  includes a semiconductor layer  41  and an electrode layer  42  having a thickness of a few μm formed on the semiconductor layer  41 . 
     An optical waveguide (not shown) is formed in the semiconductor layer  41  and extends in the Y-direction (see  FIG. 1 ). A front end portion (an end portion in the Y 1 -direction (see  FIG. 1 )) of the optical waveguide acts as a light emitting portion (not shown) that emits a laser beam. A back end portion (an end portion in the Y 2 -direction (see  FIG. 1 )) of the optical waveguide acts as a light emitting portion  41   a  that emits a portion of the laser beam. The laser beam emitted from the light emitting portion  41   a  has an output power lower than the laser beam emitted from the light emitting portion at the front end (in the Y 1 -direction) and is used for monitoring the optical output of the infrared semiconductor laser element portion  40 . 
     A distance between the light emitting portion  31   a  and the light emitting portion  12   a  of the blue-violet semiconductor laser element  10  is about 110 μm and a distance between the light emitting portion  31   a  and the light emitting portion  41   a  is also about 110 μm. 
     As depicted in  FIG. 1 , the electrode layer  42  (see  FIG. 2 ) is disposed on electrodes  53  and  54  described later of the sub-mount  50 . 
     The common electrode layer  22  is bonded with an Au wire not shown. 
     In this embodiment, as depicted in  FIG. 3 , the sub-mount  50  includes a semiconductor substrate  51  made of n-type silicon, electrodes  52 ,  53 , and  54  formed on a top surface  51   a  of the semiconductor substrate  51 . The n-type is an example of a “first conductivity type” of the present invention and the top surface  51   a  is an example of a “surface” of the present invention. 
     A p-type area  51   b  is formed in a predetermined area on the Y 2 -direction side of the top surface  51   a  of the semiconductor substrate  51  by doping with a p-type impurity. This p-type area  51   b  and the n-type area under the p-type area  51   b  of the semiconductor substrate  51  make up a photodiode  55  for monitoring the optical outputs of the blue-violet semiconductor laser element  10  and the two-wavelength semiconductor laser element  20 . As depicted in  FIG. 4 , the p-type area  51   b  (photodiode  55 ) is formed on the Y 2 -direction side of an element mounting portion  52   a  described later of the electrode  52 , an element mounting portion  53   a  described later of the electrode  53 , and an element mounting portion  54   a  described later of the electrode  54 . The p-type is an example of a “second conductivity type” of the present invention and the p-type area  51   b  is an example of a “second conductivity type area” of the present invention. The photodiode  55  is an example of a “light receiving element” of the present invention. 
     An electrode  56  is formed on a predetermined area of the p-type area  51   b  to output a monitor current generated by the photodiode  55  to the outside. This electrode  56  is formed by depositing (vapor-depositing) Al, etc. The electrode  56  is bonded with an Au wire not shown. 
     The electrodes  52 ,  53 , and  54  are formed by depositing Al, etc., and are formed with a thickness of about 1 μm, for example. 
     The element mounting portion  52   a  described later of the electrode  52 , the element mounting portion  53   a  described later of the electrode  53 , and the element mounting portion  54   a  described later of the electrode  54  are arranged in the X-direction in this order. 
     The electrode  52  includes the element mounting portion  52   a  mounted with the semiconductor laser element portion  10   a  (see  FIG. 1 ) of the blue-violet semiconductor laser element  10  and a wiring portion  52   b  connected to the element mounting portion  52   a . The element mounting portion  52   a  is an example of “element mounting portions disposed at both ends” of the present invention. 
     The wiring portion  52   b  projects from the element mounting portion  52   a  only in the X 1 -direction without projecting in the Y-direction. The length of the element mounting portion  52   a  in the Y-direction is the same as the length of the electrode  52  in the Y-direction. The length of the element mounting portion  52   a  in the Y-direction is substantially the same as the length of the semiconductor laser element portion  10   a  (see  FIG. 1 ) of the blue-violet semiconductor laser element  10  in the Y-direction. 
     As depicted in  FIG. 3 , on the element mounting portion  52   a  (see  FIG. 4 ), a solder layer  57  is provided for electrically connecting the semiconductor laser element portion  10   a  (see  FIG. 1 ) of the blue-violet semiconductor laser element  10  to the electrode  52 . The solder layer  57  is formed by depositing AuSn, etc., and is formed with a thickness of about 0.2 μm, for example. The solder layer  57  is an example of a “conductive adhesive layer” of the present invention. 
     The wiring portion  52   b  is bonded with an Au wire not shown. 
     As depicted in  FIG. 4 , the electrode  53  includes the element mounting portion  53   a  mounted with the red semiconductor laser element portion  30  (see  FIG. 1 ) of the two-wavelength semiconductor laser element  20  and a wiring portion  53   b  connected to the element mounting portion  53   a . The element mounting portion  53   a  is an example of an “element mounting portions disposed at an inner position” of the present invention. 
     The wiring portion  53   b  projects from the element mounting portion  53   a  only in the X 2 -direction without projecting in the Y-direction. The length of the element mounting portion  53   a  in the Y-direction is the same as the length of the electrode  53  in the Y-direction. The length of the element mounting portion  53   a  in the Y-direction is substantially the same as the length of the red semiconductor laser element portion  30  (see  FIG. 1 ) in the Y-direction. 
     As depicted in  FIG. 3 , on the element mounting portion  53   a  (see  FIG. 4 ), a solder layer  58  is provided for electrically connecting the red semiconductor laser element portion  30  (see  FIG. 1 ) to the electrode  53 . The solder layer  58  is formed by depositing AuSn, etc., and is formed with a thickness of about 0.2 μm, for example. The solder layer  58  is an example of the “conductive adhesive layer” of the present invention. 
     In this embodiment, as depicted in  FIG. 4 , the wiring portion  53   b  is formed to extend outward further than the element mounting portion  54   a  described later of the electrode  54  in the X 2 -direction. 
     The wiring portion  53   b  is formed to pass between the element mounting portion  54   a  described later of the electrode  54  and the photodiode  55 . As depicted in  FIG. 1 , the wiring portion  53   b  is formed to pass under the infrared semiconductor laser element portion  40  of the two-wavelength semiconductor laser element  20 . 
     In this embodiment, as depicted in  FIG. 5 , the wiring portion  53   b  includes an element mounting area  53   c  mounted with a portion of the infrared semiconductor laser element portion  40  (see  FIG. 1 ) and an insulating layer  60  is disposed on the element mounting area  53   c . The insulating layer  60  is formed by depositing SiO 2 , etc., and is formed with a thickness of about 0.1 μm to about 0.2 μm, for example. The element mounting area  53   c  is formed on a portion of the wiring portion  53   b  in the Y 2  direction from the element mounting portion  54   a  described later of the electrode  54 . 
     As depicted in  FIG. 3 , a portion of a solder layer  59  described later is disposed on the insulating layer  60 . As depicted in  FIG. 5 , the insulating layer  60  has an area greater than the element mounting area  53   c  of the wiring portion  53   b . This facilitates preventing the electrode  53  and the solder layer  59  (see  FIG. 3 ) from being electrically connected. 
     Although a portion of the insulating layer  60  is disposed on the Y 2 -direction side end of the element mounting portion Ma described later in this embodiment, the insulating layer  60  does not have to be disposed on the Y 2 -direction side end of the element mounting portion  54   a.    
     As depicted in  FIG. 6 , an adhesive layer  61  is formed on the top surface of the insulating layer  60  (between the insulating layer  60  and the solder layer  59  described later). An adhesive layer  62  is formed on the under surface of the insulating layer  60  (between the insulating layer  60  and the element mounting area  53   c  (the electrode  53 )). Each of the adhesive layers  61  and  62  is made up of a chrome layer having a thickness of about 0.01 μm or less. The adhesive layer  61  is an example of a “second adhesive layer” of the present invention. The adhesive layer  62  is an example of a “first adhesive layer” of the present invention. 
     The adhesive layer  61  is provided to enhance adhesive strength between the insulating layer  60  and the solder layer  59  described later and the adhesive layer  62  is provided to enhance adhesive strength between electrode  53  and the insulating layer  60 . 
     An Au wire not shown is bonded to a portion of the wiring portion  53   b  (see  FIG. 5 ) on the X 2 -direction side of the insulating layer  60 . 
     As depicted in  FIG. 4 , the electrode  54  includes the element mounting portion  54   a  mounted with a portion of the infrared semiconductor laser element portion  40  (see  FIG. 1 ) of the two-wavelength semiconductor laser element  20  and a wiring portion  54   b  connected to the element mounting portion  54   a . The element mounting portion  54   a  is an example of the “element mounting portions disposed at both ends” of the present invention. 
     The wiring portion  54   b  projects from the element mounting portion  54   a  only in the X 2 -direction without projecting in the Y-direction. The length of the element mounting portion  54   a  in the Y-direction is the same as the length of the electrode  54  in the Y-direction. 
     The length of the element mounting portion  54   a  in the Y-direction is less than the length of the infrared semiconductor laser element portion  40  (see  FIG. 1 ) in the Y-direction. The length of the element mounting portion  54   a  in the Y-direction is less than the lengths of the element mounting portions  52   a  and  53   a  in the Y-direction. 
     As depicted in  FIG. 3 , on the element mounting portion  54   a  (see  FIG. 4 ), the solder layer  59  is provided for electrically connecting the infrared semiconductor laser element portion  40  (see  FIG. 1 ) to the electrode  54 . The solder layer  59  is formed by depositing AuSn, etc., and is formed with a thickness of about 0.2 μm, for example. The solder layer  59  is an example of the “conductive adhesive layer” of the present invention. 
     As depicted in  FIGS. 1 and 2 , when the infrared semiconductor laser element portion  40  is mounted on the solder layer  59 , the solder layer  59  and the electrode layer  42  of the infrared semiconductor laser element portion  40  can absorb the step (thickness) of the insulating layer  60  and the infrared semiconductor laser element portion  40  (two-wavelength semiconductor laser element  20 ) is disposed parallel to the top surface  51   a  of the semiconductor substrate  51  of the sub-mount  50 . 
     The wiring portion  54   b  (see  FIG. 1 ) is bonded with an Au wire not shown. 
     In this embodiment, the photodiode  55  is disposed on the sub-mount  50  as described above to thereby simplify the structure of the three-wavelength semiconductor laser apparatus  1  and constrain the apparatus from increasing in size as compared to the case of providing a photodiode (light receiving element) separately from the sub-mount  50 . 
     In this embodiment, as described above, the length of the element mounting portion  54   a  in the Y-direction is made less than the length of the element mounting portion  53   a  in the Y-direction and the electrode  53  is provided with the wiring portion  53   b  extending outward further in the X 2 -direction than the element mounting portion  54   a . Since this eliminates the need for disposing the wiring portion  53   b  between the element mounting portion  53   a  and the element mounting portion  52   a  or between the element mounting portion  53   a  and the element mounting portion  54   a , this enables the element mounting portion  52   a , the element mounting portion  53   a , and the element mounting portion  54   a  to be arranged closer to each other. Therefore, the semiconductor laser element portion  10   a  of the blue-violet semiconductor laser element  10  and the red semiconductor laser element portion  30  and the infrared semiconductor laser element portion  40  of the two-wavelength semiconductor laser element  20  are arranged closer to each other. This enables an optical member such as a lens receiving light emitted from the blue-violet semiconductor laser element  10  and the two-wavelength semiconductor laser element  20  to be shared by the blue-violet semiconductor laser element  10  and the two-wavelength semiconductor laser element  20 . As a result, the number of parts such as optical members can be constrained from increasing and the apparatus can be constrained from increasing in size. 
     In this embodiment, the length of the element mounting portion  54   a  in the Y-direction is made less than the length of the element mounting portion  53   a  in the Y-direction as described above, to thereby ensure that the wiring portion  53   b  of the electrode  53  is formed outward in the X 2 -direction further than the element mounting portion  54   a  without projecting from the element mounting portion  53   a  in the Y-direction and without contacting with the electrode  54 . Since the wiring portion  53   b  is formed without projecting from the element mounting portion  53   a  in the Y-direction as described above, the distance can be constrained from increasing between the blue-violet semiconductor laser element  10  and the photodiode  55 , and between the two-wavelength semiconductor laser element  20  and the photodiode  55 . 
     In this embodiment, the insulating layer  60  is disposed on the element mounting area  53   c  as described above to thereby constrain the electrode  53  from electrically connecting with the infrared semiconductor laser element portion  40  and to dispose the wiring portion  53   b  passing under the infrared semiconductor laser element portion  40 . 
     In this embodiment, since the solder layers  57 ,  58 , and  59  are disposed in advance on the element mounting portions  52   a ,  53   a , and  54   a  of the sub-mount  50  as described above to eliminate the need for disposing the solder layers  57 ,  58 , and  59  on the element mounting portions  52   a ,  53   a , and  54   a  when the blue-violet semiconductor laser element  10  and the two-wavelength semiconductor laser element  20  are mounted on the sub-mount  50 , the manufacturing process can be simplified when the blue-violet semiconductor laser element  10  and the two-wavelength semiconductor laser element  20  are mounted on the sub-mount  50 . 
     In this embodiment, the length of the element mounting portion  54   a  in the Y-direction is made less than the length of the element mounting portion  53   a  in the Y-direction and the wiring portion  53   b  is formed to extend in the X 2 -direction as described above to eliminate the need for reducing the length of the element mounting portion  52   a  in the Y-direction, thus constraining the adhesive strength from deteriorating between the sub-mount  50  (element mounting portion  52   a ) and the blue-violet semiconductor laser element  10 . Although the length of the element mounting portion  54   a  in the Y-direction is less than the lengths of the element mounting portion  52   a  and the element mounting portion  53   a  in the Y-direction, the two-wavelength semiconductor laser element  20  adheres not only to the element mounting portion  54   a  but also to the element mounting portion  53   a , thus ensuring the sufficient adhesive strength between the sub-mount  50  and the two-wavelength semiconductor laser element  20 . 
     In this embodiment, the blue-violet semiconductor laser element  10  and the two-wavelength semiconductor laser element  20  are mounted junction-down on the sub-mount  50  as described above to arrange the light emitting portion  12   a  (the semiconductor laser element portion  10   a ) of the blue-violet semiconductor laser element  10  and the light emitting portion  31   a  (the red semiconductor laser element portion  30 ) and the light emitting portion  41   a  (the infrared semiconductor laser element portion  40 ) of the two-wavelength semiconductor laser element  20  closer to the top surface  51   a  of the semiconductor substrate  51  of the sub-mount  50 . Therefore, even when the photodiode  55  is disposed closer to the blue-violet semiconductor laser element  10  and the two-wavelength semiconductor laser element  20 , the lights emitted from the light emitting portion  12   a  of the blue-violet semiconductor laser element  10  and the light emitting portions  31   a  and  41   a  of the two-wavelength semiconductor laser element  20  can easily be made incident on the photodiode  55 . 
     The embodiment disclosed herein should be considered to be illustrative in every respect and not limitative. The range of the present invention is indicated by claims rather than the description of the embodiment and includes meaning equivalent to claims and all the modifications within the range. 
     For example, although the first conductivity type and the second conductivity type are n-type and p-type, respectively, in the example described in the embodiment, this is not a limitation to the present invention and the first conductivity type and the second conductivity type may be p-type and n-type, respectively. 
     Although a two-wavelength semiconductor laser element including two semiconductor laser element portions is used for the second semiconductor laser element (multi-wavelength semiconductor laser element) in the example described in the embodiment, this is not a limitation to the present invention and a multi-wavelength semiconductor laser element including three or more semiconductor laser element portions may be used. 
     A multi-wavelength semiconductor laser element may be used for the first semiconductor laser element. 
     Although the sub-mount is provided with three electrodes each including an element mounting portion in the example described in the embodiment, this is not a limitation to the present invention and the sub-mount may be provided with four or more electrodes each including an element mounting portion. For example, if the sub-mount is provided with four electrodes each including an element mounting portion, the wiring portions of the two electrodes at inner positions may be formed to extend outward in X-directions further than the electrodes at both ends. 
     Although the blue-violet semiconductor laser element emitting a blue-violet laser beam is used for the first semiconductor laser element in the example described in the embodiment, this is not a limitation to the present invention and a semiconductor laser element emitting a laser beam other than the blue-violet laser beam may be used. 
     Although the second semiconductor laser element (multi-wavelength laser element) includes the red semiconductor laser element portion that emits a red laser beam and the infrared semiconductor laser element portion that emits an infrared laser beam in the example described in the embodiment, this is not a limitation to the present invention and the second semiconductor laser element may include semiconductor laser element portions emitting laser beams other than red and infrared laser beams. 
     Although the blue-violet semiconductor laser element and the two-wavelength semiconductor laser element are mounted on the sub-mount in the example described in the embodiment, this is not a limitation to the present invention and the blue-violet semiconductor laser element and the two-wavelength semiconductor laser element may be mounted on a mounting member other than the sub-mount. 
     Although the wiring portion  53   b  of the electrode  53  is formed to pass between the element mounting portion  54   a  of the electrode  54  and the photodiode  55  in the example described in the embodiment, this is not a limitation to the present invention and, as in a first variation of the present invention depicted in  FIG. 7 , a wiring portion  153   b  of an electrode  153  may be formed not to pass between an element mounting portion  154   a  of an electrode  154  and the photodiode  55 . 
     Although the wiring portion  53   b  of the electrode  53  is formed to pass under the infrared semiconductor laser element portion in the example described in the embodiment, this is not a limitation to the present invention and, as in a second variation of the present invention depicted in  FIG. 8 , a wiring portion  253   b  of an electrode  253  may be formed to pass under the blue-violet semiconductor laser element. 
     Although the wiring portion  53   b  of the electrode  53  is formed to extend on one side of the X-direction (in the X 2 -direction) in the example described in the embodiment, this is not a limitation to the present invention and the wiring portion  53   b  may be formed to extend on both sides of the X-direction (in the X 1 -direction and the X 2 -direction). 
     Although the sub-mount having the solder layers disposed on the electrodes is used in the example described in the embodiment, this is not a limitation to the present invention and the solder layers may not be disposed on the electrodes of the sub-mount in advance. 
     Although the electrodes and the solder layers of the sub-mount are formed by deposition in the example described in the embodiment, this is not a limitation to the present invention and the electrodes and the solder layers of the sub-mount may be formed by using a plating method, for example.