Patent Publication Number: US-2022239061-A1

Title: Semiconductor laser device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/918,321, filed on Jul. 1, 2020, which is a continuation of U.S. patent application Ser. No. 16/665,299, filed on Oct. 28, 2019 (now U.S. Pat. No. 10,734,784), which is a continuation of U.S. patent application Ser. No. 16/218,275, filed on Dec. 12, 2018 (now U.S. Pat. No. 10,490,970), which is a continuation of U.S. patent application Ser. No. 15/433,368, filed on Feb. 15, 2017 (now U.S. Pat. No. 10,199,796), which claims priority to Japanese Patent Application No. 2016-027113, filed on Feb. 16, 2016, the disclosures of which are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates to a semiconductor laser device. 
     A semiconductor laser device includes a semiconductor laser element, a protective element and a submount on which the semiconductor laser element and the protective element are fixed, as described in, for example, Japanese Patent No. 5659876. The submount includes a fixing part on which the semiconductor laser element is fixed, and a fixing part on which the protective element is fixed. The position of each of the fixing parts on the submount is previously determined in accordance with the position where an optical waveguide region of the semiconductor laser element is formed. 
     Normally, semiconductor laser elements of one type are obtained from a single piece of wafer. In some cases, semiconductor laser elements differing from each other in the formation position of the optical waveguide region are obtained from a single piece of wafer, as described in, for example, Japanese Unexamined Patent Publication No. 2009-200341. 
     SUMMARY 
     With a semiconductor laser device in which the semiconductor laser element provided with an optical waveguide region around its center is disposed around the center of the submount, aligning the submount with another member of the semiconductor laser device substantially aligns the light output part of the semiconductor laser element with that other member. 
     However, a change in the position of the optical waveguide region on the semiconductor laser element changes the position on the submount where the semiconductor laser element is fixed, unless any change is made in the disposition position of the submount to which the semiconductor laser element is fixed. In accordance therewith, the position on the submount where the protective element is fixed also changes. The fixing part on the submount to which the semiconductor laser element or the protective element is fixed is a metal layer obtained from patterning or the like. Accordingly, in the case where the position on the submount where the semiconductor laser element or the protective element is fixed is to be changed, a submount of different type, that is, a submount having the fixing part at the position corresponding to the change is used. 
     However, as disclosed in JP 2009-200341 A, for example, in the case in which a plurality of semiconductor laser elements differing from each other in the formation position of the optical waveguide region is obtained from a single piece of wafer, providing a submount corresponding to the difference in the formation position necessitates using a submount of a plurality of types. Such an increase in the number of types of the submount may disadvantageously make inventory control of the submount troublesome. 
     The problem described above may be solved by certain embodiments of the present invention. 
     In one embodiment, a semiconductor laser device includes a base; a heat sink protruding upward from the base and including an upper surface and a lateral surface extending from the base to the upper surface; a plurality of lead electrodes separated from the heat sink; a submount including: a first main surface fixed to the lateral surface of the heat sink, and a second main surface having an upper half region and a lower half region, an upper edge, a lower edge, and a first lateral edge extending from the upper edge to the lower edge, the second main surface including a first fixing part, an upper second fixing part, and a lower second fixing part, wherein the upper second fixing part is disposed between the first fixing part and the first lateral edge in the upper half region, and the lower second fixing part is disposed between the first fixing part and the first lateral edge in the lower half region; a semiconductor laser element including: a light output surface, a light reflecting surface, a first lateral surface, a second lateral surface opposite the first lateral surface, a fixing surface that is fixed to the first fixing part, a wire connecting surface opposite the fixing surface, and an optical waveguide region, wherein the optical waveguide region is disposed closer to the first lateral surface than the second lateral surface, wherein the fixing surface is fixed to the first fixing part such that the light output surface is directed upward and the optical waveguide region is disposed on or around an area between a midpoint of the upper edge and a midpoint of the lower edge of the second main surface as seen in a front view; a protective element fixed to the upper second fixing part; and a wire connecting the protective element and one of the plurality of lead electrodes. 
     In another embodiment, a semiconductor laser device includes a housing including: an insulating part, a plurality of wiring parts, and a recess defined by a bottom surface and inner lateral surfaces surrounding the bottom surface, wherein the wiring parts are partially exposed from the insulating part at the recess; a submount including: a first main surface fixed to the bottom surface of the recess, a second main surface having a front half region and a rear half region, a front edge, a rear edge, and a first lateral edge extending from the front edge to the rear edge, the second main surface including a first fixing part, a front second fixing part, and a rear second fixing part, wherein the front second fixing part is disposed between the first fixing part and the first lateral edge in the front half region, and the rear second fixing part is disposed between the first fixing part and the first lateral edge in the rear half region; a semiconductor laser element including: a light output surface, a light reflecting surface, a first lateral surface, a second lateral surface opposite the first lateral surface, a fixing surface that is fixed to the first fixing part, and a wire connecting surface opposite the fixing surface, and an optical waveguide region, wherein the optical waveguide region is disposed closer to the first lateral surface than the second lateral surface, wherein the fixing surface is fixed to the first fixing part such that the light output surface is directed frontward and the optical waveguide region is disposed on or around an area between a midpoint of the front edge and a midpoint of the rear edge of the second main surface as seen in a top view; a protective element fixed to the front second fixing part; and a wire connecting the protective element and one of the plurality of wiring parts. 
     With the above-described semiconductor laser device, the submount of a single type in which the fixing part is formed at a unique position can be used for both the semiconductor laser elements differing from each other in the position of the optical waveguide region. This prevents an increase in the number of types of the submount, making the inventory control less troublesome. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic front view of a semiconductor laser device according to a first embodiment. 
         FIG. 1B  is a schematic front view of the semiconductor laser device according to the first embodiment (in which a cap is not shown). 
         FIG. 1C  is an enlarged view of a portion surrounded by a broken line in  FIG. 1B . 
         FIG. 1D  is a schematic rear view of the semiconductor laser device according to the first embodiment. 
         FIG. 1E  is a schematic plan view of the semiconductor laser device according to the first embodiment. 
         FIG. 1F  is a schematic plan view of the semiconductor laser device according to the first embodiment (in which the cap is not shown). 
         FIG. 1G  is an enlarged view of a portion surrounded by a broken line in  FIG. 1F . 
         FIG. 1H  is a schematic front view of a submount according to the first embodiment. 
         FIG. 2A  is a schematic front view of a semiconductor laser device according to a second embodiment (in which a cap is not shown). 
         FIG. 2B  is an enlarged view of a portion surrounded by a broken line in  FIG. 2A . 
         FIG. 2C  is a schematic front view of a submount according to the second embodiment. 
         FIG. 3A  is a schematic side view showing the positional relationship between the semiconductor laser element and a collet. 
         FIG. 3B  is an enlarged view of a portion surrounded by a broken line in  FIG. 3A . 
         FIG. 4A  is a schematic side view showing the positional relationship between a protective element and the collet. 
         FIG. 4B  is an enlarged view of a portion surrounded by a broken line in  FIG. 4A . 
         FIG. 5A  is a schematic top view of a semiconductor laser device according to a third embodiment (in which a cap is not shown). 
         FIG. 5B  is a schematic cross-sectional view taken along line  5 B- 5 B in  FIG. 5A . 
         FIG. 5C  is a schematic cross-sectional view taken along line  5 C- 5 C in  FIG. 5A . 
         FIG. 5D  is an enlarged view of a portion surrounded by a broken line in  FIG. 5A . 
     
    
    
     DETAILED DESCRIPTION 
     [Semiconductor Laser Device  1  According to First Embodiment] 
       FIGS. 1A, 1B, and 1C  are a schematic front view of a semiconductor laser device  1  according to the first embodiment, a schematic front view (in which a cap is not shown) thereof, and an enlarged view of a portion surrounded by a broken line in  FIG. 1B , respectively.  FIGS. 1D, 1E, 1F, and 1G  are a schematic rear view of the semiconductor laser device  1 , a schematic plan view thereof, a schematic plan view (in which the cap is not shown) thereof, and an enlarged view of a portion surrounded by a broken line in  FIG. 1F , respectively.  FIG. 1H  is a schematic front view of a submount  40  according to the first embodiment. For ease of understanding,  FIG. 1A  illustrates each member covered with a cap  80  with a broken line, showing each member through the cap  80 . 
     As shown in  FIGS. 1A to 1H , the semiconductor laser device  1  includes: a base  10 ; a heat sink  20  disposed above the base  10 ; a plurality of lead electrodes  31 ,  32  disposed laterally relative to the heat sink  20 ; a submount  40  including a first main surface  41  and a second main surface  42 , the first main surface  41  being fixed to a lateral surface of the heat sink  20 , the second main surface  42  including a first fixing part  43  and two second fixing parts  44   a ,  44   b  disposed laterally relative to the first fixing part  43  and respectively in an upper half region and a lower half region of the second main surface  42 ; a semiconductor laser element  50  including a light output surface  51 , a light reflecting surface  52 , two lateral surfaces  53 ,  54  intersecting the light output surface  51 , and an optical waveguide region  55  formed to be offset toward one of the two lateral surfaces  53 ,  54 , the semiconductor laser element  50  being fixed to the first fixing part  43  so that the light output surface  51  is directed upward and the optical waveguide region  55  is disposed on or around a line A that passes through the midpoint of the upper edge and the midpoint of the lower edge of the second main surface  42  as seen in a front view; a protective element  60  fixed to upper one of the two second fixing parts  44   a ,  44   b ; and a wire  70  connecting between the protective element  60  and one of the plurality of lead electrodes  31 ,  32 . In the following, a detailed description is given. 
     (Base  10 ) 
     Preferably, the base  10  is made of a material exhibiting relatively high thermal conductivity, e.g., about 20 W/mK or greater, so that heat generated at the semiconductor laser element  50  is efficiently released to the outside. Specifically, use of metal such as Cu, Al, Fe, Ni, Mo, CuW, CuMo or the like is preferable. 
     Exemplary shapes of the base  10  as seen in a plan view include a circle, an ellipse, a polygon such as a quadrangle, and any shape similar to the foregoing. More specifically, for example a circular and flat member having a diameter of about 3 mm to 10 mm may be employed as the base  10 . Preferably, the thickness of the base  10  is, for example, about 0.5 mm to 5 mm. 
     (Heat Sink  20 ) 
     The heat sink  20  may be made of the material identical to that of the base  10 , or may be made of a different material. For example, as the material of the base  10 , iron alloy may be employed for welding the cap  80 , and copper or copper alloy being excellent in heat releasing property may be employed as the material of the heat sink  20 . Thus, the heat sink  20  can efficiently release heat from the semiconductor laser element  50 . The heat sink  20  is at least partially disposed above the base  10 . The base  10  and the heat sink  20  may be made of separate members, or they may be parts of a single member. In the present embodiment, a member structured by the base  10  and the heat sink  20  serves as the stem. 
     (Plurality of Lead Electrodes  31 ,  32 ) 
     The lead electrodes  31 ,  32  are members for connecting the semiconductor laser element  50  to the external power supply. An electrically conductive material is employed for the lead electrodes  31 ,  32 . The lead electrodes  31 ,  32  are, for example, rod-like members made of metal. The lead electrodes  31 ,  32  are, for example, disposed so as to penetrate through holes provided at the base  10 , and bonded to the base  10  with low melting point glass or the like. The lead electrodes  31 ,  32  are disposed laterally relative to the heat sink  20 . In the present embodiment, as shown in  FIG. 1F , the lead electrodes  31 ,  32  are disposed at positions on the front side of the heat sink  20  and being spaced apart from the heat sink  20 . Such a disposition is also referred to as “disposed laterally relative to the heat sink  20 ”. 
     (Submount  40 ) 
     The submount  40  is preferably made of a material that shows a smaller difference in thermal expansion coefficient from the semiconductor laser element  50  than the base  10  and the heat sink  20  do, so as to prevent the semiconductor laser element  50  from coming off. Further, the submount  40  is preferably made of a material that exhibits high thermal conductivity so as to be capable of efficiently releasing heat generated at the semiconductor laser element  50 . Specifically, AlN, CuW, diamond, SiC, ceramic or the like may be preferably employed as the submount  40 . 
     The submount  40  includes the first main surface  41  and the second main surface  42 . The first main surface  41  can be fixed to the lateral surface of the heat sink  20  with Au bumps, Au nanoparticles, Ag nanoparticles, AuSn solder, a solder paste member and the like. While the submount  40  and the heat sink  20  may be in direct contact with each other, other member may be interposed between the submount  40  and the heat sink  20 . 
     The second main surface  42  includes the first fixing part  43  and the second fixing parts  44   a ,  44   b . The semiconductor laser element  50  is fixed to the first fixing part  43 , and the protective element  60  is fixed to one of the two second fixing parts  44   a ,  44   b.    
     The first fixing part  43  and the second fixing parts  44   a ,  44   b  are preferably made of a metal material, for example, and particularly preferably have an adhesive layer which is molten by being heated and with which the semiconductor laser element  50  and the like are bonded. Thus, the semiconductor laser element  50  and the like can be surely fixed to the first fixing part  43  and the second fixing parts  44   a ,  44   b . For example, when the first fixing part  43  and the second fixing parts  44   a ,  44   b  are Pt/AuSn/Au, AuSn serves as the adhesive layer, and Pt and Au serve as cover layers that cover the adhesive layer. Note that, in the present embodiment, the first fixing part  43  and the second fixing parts  44   a ,  44   b  are entirely structured by the adhesive layer (e.g., AuSn). 
     The first fixing part  43  is disposed to be positioned on the line A that passes through the midpoint of the upper edge and the midpoint of the lower edge of the second main surface  42  as seen in a front view. Further, the first fixing part  43  is disposed such that the optical waveguide region  55  of the semiconductor laser element  50  is positioned on or around the line A. Thus, aligning the submount  40  with the heat sink  20  such that the line A of the submount  40  matches with the line that passes through the midpoint of the upper edge and the midpoint of the lower edge of the heat sink  20  aligns the light output part of the semiconductor laser element  50  (the end of the optical waveguide region  55  on the light output surface  51  side) with the heat sink  20 . This facilitates alignment of the semiconductor laser element  50  with the heat sink  20 . 
     With such a disposition, turning the submount  40  upside down (that is, fixing the semiconductor laser element  50  to the submount  40  that is rotated by 180 degrees about the center of the second main surface  42 ) depending on whether the semiconductor laser element  50  has its optical waveguide region  55  positioned offset toward the lateral surface  53  (the right lateral surface when the light output surface  51  is the upper surface, and hereinafter referred to as “the first lateral surface  53 ”) or toward the other lateral surface  54  (the left lateral surface when the light output surface  51  is the upper surface, and hereinafter referred to as “the second lateral surface  54 ”) allows the optical waveguide region  55  to be disposed on or around the line A connecting between the midpoint of the upper edge and the midpoint of the lower edge of the second main surface  42 . Accordingly, the submount  40  can be used for both the semiconductor laser elements  50  of two types differing from each other in the position of the optical waveguide region  55 . 
     As used herein, the semiconductor laser elements of two types can be defined as follows. For example, when the semiconductor laser elements of two types are placed adjacent to each other on the right and left sides having their respective light output surfaces directed upward, while they are different in whether the position of the optical waveguide region is offset toward the right side or toward the left side, rotating one of the semiconductor laser element about its center by 180 degrees sets the position of the optical waveguide region in the whole semiconductor laser element identical to that in the other semiconductor laser element. In other words, the semiconductor laser elements of two types are line symmetric to each other. Thus, in the case where the submount  40  is turned upside down also, the position of the optical waveguide region of the semiconductor laser element is substantially the same. 
     The distance between the light output part of the semiconductor laser element  50  and the line A as seen in a front view is preferably 50 μm or smaller, and the angle formed between the optical waveguide region  55  and the line A is preferably 2° or smaller. Thus, the light output part of the semiconductor laser element  50  can be precisely aligned with the heat sink  20 . Note that, the light output part of the semiconductor laser element  50  is representatively disposed so as to be positioned at the center of the semiconductor laser device  1  as seen in a plan view. Accordingly, preferably the heat sink  20  is disposed to achieve the following: disposing the light output part of the semiconductor laser element  50  so as to substantially match with the line that passes through the midpoint of the upper edge and the midpoint of the lower edge of the heat sink  20  as seen in a front view automatically positions the light output part of the semiconductor laser element  50  at the center of the semiconductor laser device  1  as seen in a plan view. 
     The first fixing part  43  is preferably elongated in one direction (the top-bottom direction) for fixing the semiconductor laser element  50 . This is because the optical waveguide region  55  has the shape elongated in one direction, that is, the semiconductor laser element  50  including the optical waveguide region  55  has the shape elongated in one direction. 
     The two second fixing parts  44   a ,  44   b  are disposed laterally relative to the first fixing part  43  and respectively in the upper half region and the lower half region of the second main surface  42 . The side from which the semiconductor laser element  50  emits laser light (the light output surface  51  side) is the upper side, and the side opposite thereto (the light reflecting surface  52  side) is the lower side. The region occupying the upper half of the second main surface  42  is the upper half region, and the region occupying the lower half thereof is the lower half region. The center of the second main surface  42  is a point of intersection of the line A that passes through the midpoint of the upper edge and the midpoint of the lower edge of the second main surface  42  and a line B that passes through the midpoint of the right edge and the midpoint of the left edge of the second main surface  42 . Here, the region being higher than the line B is the upper half region, and the region being lower than the line B is the lower half region. Here, the term “as seen in a front view” refers to viewing the second main surface  42  of the submount  40  in the direction substantially perpendicular to the second main surface  42 . 
     In such a disposition, irrespective of whether the submount  40  is normally oriented or turned upside down, the protective element  60  can be fixed to upper one of the two second fixing parts  44   a ,  44   b . Accordingly, the present embodiment can provide the semiconductor laser device  1  being reduced in size (reduced in length in the top-bottom direction of the semiconductor laser device  1 ), and the semiconductor laser device suitable for mounting the high-power semiconductor laser element  50  with a greater cavity length (the length in the extending direction of the optical waveguide region  55 ). The reason thereof is explained in the following. 
     As shown in  FIGS. 3A to 4B , a collet  100  is used in performing die bonding or wire bonding of the semiconductor laser element  50  and the protective element  60 . The die bonding refers to disposing and fixing the semiconductor laser element  50  and the protective element  60  to respective fixing parts, and the wire bonding refers to connecting the wires  70  to the semiconductor laser element  50  and the protective element  60 . In the die bonding, the semiconductor laser element  50  or the protective element  60  is attached to the tip of the collet  100  under suction, and carried to the bonding position. Further, in the wire bonding, the tip of the wire-bonding collet  100  that discharges the wire is pressed against the semiconductor laser element  50  or the protective element  60 . Therefore, the position of the semiconductor laser element  50  and the protective element  60  must be in the range where contact between the collet  100  and the base  10  during such die bonding or wire bonding is prevented. In  FIGS. 3A and 4A , the collet  100  contacts with the base  10 , so the collet  100  is allowed to move upward from a position shown in  FIGS. 3A and 4A . 
     Meanwhile, assuming that the second fixing part is provided just one in number, when the submount  40  is turned upside down to be used for both the semiconductor laser elements  50  differing from each other in the position of the optical waveguide region  55 , the distance between the second fixing part and the base  10  changes greatly. In this case, the second fixing part must be spaced apart from the base  10  so as to avoid contact between the collet  100  and the base  10  irrespective of whether the submount  40  is normally oriented or turned upside down. When the second fixing part is disposed at the center of the submount  40 , the distance from the base  10  little changes by the submount  40  being turned upside down. However, in this case also, the second fixing part must be fully distanced from the base  10 . In any of the cases, the second fixing part being provided just one in number requires space above and below the second fixing part substantially equally, increasing the length of the submount  40  in the top-bottom direction. 
     In contrast thereto, in the disposition of the present embodiment, the protective element  60  is fixed to upper one of the second fixing parts  44   a ,  44   b . Thus, irrespective of whether the submount  40  is normally oriented or turned upside down, a great distance is reliably obtained from the protective element  60  to the base  10 , whereby contact between the base  10  and the collet  100  is avoided. This eliminates the necessity of providing excessive space between the upper one of the second fixing parts  44   a ,  44   b  and the upper edge of the submount  40 , and thus prevents an increase in length in the top-bottom direction of the submount  40 . Accordingly, a reduction in size of the semiconductor laser device  1  (a reduction in length in the top-bottom direction of the semiconductor laser device  1 ) is achieved. 
     Further, while the semiconductor laser element  50  of higher power can be obtained by increasing the cavity length (the length in the extending direction of the optical waveguide region  55 ), an increase in the cavity length increases the length in the top-bottom direction of the submount  40 . However, in the disposition of the present embodiment, as has been described above, an increase in length in the top-bottom direction of the submount  40  is prevented as compared to the case where the second fixing part is provided just one in number. Accordingly, also in the case where the semiconductor laser element  50  being greater in the cavity length is mounted, an increase in size of the semiconductor laser device  1  (an increase in length in the top-bottom direction of the semiconductor laser device  1 ) can be prevented. Hence, the present embodiment is suitable for mounting such a semiconductor laser element  50 . 
     In the case where the second main surface  42  is quadrangular being elongated in the top-bottom direction, preferably, the distance d 1  between a first  42   a  of two long edges of the second main surface  42  and the first fixing part  43  is greater than the distance d 2  between a second  42   b  of the two long edges and the first fixing part  43 , and the second fixing parts  44   a ,  44   b  are disposed between the first fixing part  43  and the first long edge  42   a . Thus, the region provided with neither the first fixing part  43  nor the second fixing parts  44   a ,  44   b  can be reduced in size. Therefore, the second main surface  42  can be reduced in area, whereby the submount  40  can be reduced in size. The distance d 2  between the other long edge and the first fixing part  43  is, for example, 10% to 80% as great as the distance d 1  between the first long edge  42   a  and the first fixing part  43 . Further, the distance d 2  is preferably great enough to prevent the first fixing part  43  from erroneously being cut in singulation of the submount  40 , that is, for example, the distance d 2  is preferably 30 μm or greater. 
     The area of the first fixing part  43  is preferably at least as great as the area of the semiconductor laser element  50  as seen in a front view. Similarly, the area of each of the second fixing parts  44   a ,  44   b  is preferably at least as great as the area of the protective element  60  as seen in a front view. Normally, the protective element  60  is smaller in size than the semiconductor laser element  50 , and therefore the area of each of the second fixing parts  44   a ,  44   b  is preferably smaller than the first fixing part  43 . Thus, the second main surface  42  is reduced in area within a range allowing the area of each of the fixing parts to be great enough for the elements to be surely fixed, whereby the submount  40  is reduced in size. Representatively, the total area of the two second fixing parts  44   a ,  44   b  is smaller than the area of the first fixing part  43 . The length of the first fixing part  43  (the length in the top-bottom direction) is specifically greater than the length of the semiconductor laser element  50 . Further, an increase in length of the submount  40  necessitates an increase in length of the heat sink  20 , resulting in an increase in length of the semiconductor laser device  1 . Accordingly, the length of the first fixing part  43  is preferably equal to or smaller than the value obtained by adding about 100 μm to the length of the semiconductor laser element  50 . This suppresses an increase in length of the semiconductor laser device  1 . 
     (Semiconductor Laser Element  50 ) 
     The semiconductor laser element  50  may be a compound semiconductor such as a Group III-V compound semiconductor. For example, the semiconductor laser element  50  includes an active layer being a nitride semiconductor such as InGaN, GaN or the like. The semiconductor laser element  50  includes, for example, on an electrically conductive or insulating substrate, a semiconductor layered body which includes an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, and further includes an n-electrode electrically connected to the n-type semiconductor layer, and a p-electrode electrically connected to the p-type semiconductor layer. As described above, the submount  40  according to the present embodiment is suitable for mounting the semiconductor laser element  50  with a great cavity length. The great cavity length specifically means that the cavity length is at least half as great as the length of the heat sink  20  (the length in the top-bottom direction). Such a semiconductor laser element  50  with a great cavity length is representatively high-power. 
     The semiconductor laser element  50  includes the light output surface  51  and the light reflecting surface  52 , and is fixed to the first fixing part  43  so that the light output surface  51  is directed upward. Specifically, the semiconductor laser element  50  may be fixed with a fixing layer made of Au nanoparticles, Ag nanoparticles, AuSn solder, a solder paste member or the like. The semiconductor laser element  50  may have its semiconductor layer fixed to the first fixing part  43  (junction-down mounting), or may have its substrate fixed to the first fixing part  43  (junction-up mounting). The optical waveguide region  55  is a region elongated in one direction and connects between the light output surface  51  and the light reflecting surface  52 . The semiconductor layered body may be provided with a ridge for current confinement and light confinement. In this case, the portion where the ridge exists as seen in a front view is regarded as the optical waveguide region  55 . 
     The semiconductor laser element  50  includes two lateral surfaces  53 ,  54  that intersect with the light output surface  51 . The lateral surfaces  53 ,  54  are not in parallel to the first main surface  41  and the second main surface  42 , and are representatively substantially perpendicular to the first main surface  41  and the second main surface  42 . The optical waveguide region  55  of the semiconductor laser element  50  is formed to be offset toward one (in the present embodiment, the first lateral surface  53 ) of the two lateral surfaces  53 ,  54 . That is, the optical waveguide region  55  is disposed so as to exclude the line that passes through the midpoint of the upper edge (the edge formed by the light output surface  51 ) and the midpoint of the lower edge (the edge formed by the light reflecting surface  52 ) as seen in a front view. Here, the term “as seen in a front view” refers to viewing in the direction substantially perpendicular to the wire connected surface of the semiconductor laser element  50 . The wire connected surface is the surface opposite to the surface fixed to the first fixing part  43 . 
     The shape of the semiconductor laser element  50  as seen in a front view is substantially quadrangular, for example. 
     As shown in  FIGS. 1B and 1C , in the case where the optical waveguide region  55  of the semiconductor laser element  50  is formed to be offset toward the first lateral surface  53 , the two second fixing parts  44   a ,  44   b  are preferably disposed on the first lateral surface  53  side. This enables a reduction in size of the region provided with neither the first fixing part  43  nor the second fixing parts  44   a ,  44   b  when the first fixing part  43  is disposed such that the optical waveguide region  55  is disposed on or around the line A connecting between the midpoint of the upper edge and the midpoint of the lower edge of the second main surface  42 . Thus, the second main surface  42  can be reduced in area, whereby the submount  40  can be reduced in size. The same holds true for the case where the optical waveguide region  55  of the semiconductor laser element  50  is formed to be offset toward the second lateral surface  54 . That is, in this case, the two second fixing parts  44   a ,  44   b  are preferably formed on the second lateral surface  54  side. 
     The distance between the tip of the collet  100  brought into contact with the semiconductor laser element  50  and the base  10 , in other words, the distance between the region on the semiconductor laser element  50  that is brought into contact with the tip of the collet  100  and the base  10  is the distance that avoids contact between the collet  100  and the base  10 , for example, about 760 μm to 1.0 mm. Accordingly, for example in the case where the tip of the collet  100  is brought into contact with the center of an electrode of the semiconductor laser element  50 , the distance between the center of the electrode and the base  10  falls within such a range. Note that, the collet  100  normally has a tapered shape which becomes smaller toward the tip. Accordingly, the collet  100  being brought into contact with the base  10  refers to a portion of the collet  100 , which portion is distanced from the tip and relatively thick, abutting on the base  10 . Further, normally, the semiconductor laser element  50  is greater in size than the tip of the collet  100 . Therefore, the distance between the semiconductor laser element  50  and the base  10  becomes smaller than the distance between the contact position at the tip of the collet  100  and the base  10 , unless the contact position of the collet  100  is the lower end of the semiconductor laser element  50 . The smallest distance between the semiconductor laser element  50  and the base  10  is, for example, from 100 μm to 300 μm. 
     (Protective Element  60 ) 
     The protective element  60  is a member for protecting the semiconductor laser element  50  from electrical breakdown caused by surge current. The protective element  60  is connected in antiparallel to the semiconductor laser element  50 . In the case where a voltage is applied to the semiconductor laser element  50  in the reverse direction, or an excessive voltage is applied thereto in the forward direction, current is caused to pass through protective element  60  instead of the semiconductor laser element  50 . Thus, the protective element  60  prevents the semiconductor laser device  1  from being damaged. The protective element  60  may be, for example, a Zener diode. The Zener diode may be made of Si, GaAs and the like. 
     The protective element  60  is fixed to the upper one of the two second fixing parts  44   a ,  44   b . Specifically, the protective element  60  may be fixed with a fixing layer made of Au nanoparticles, Ag nanoparticles, AuSn solder, a solder paste member or the like. 
     As shown in  FIGS. 4A and 4B , normally, the protective element  60  is smaller in size than the semiconductor laser element  50 , and for example, substantially as great as the tip of the collet  100 . Accordingly, when the distance between the tip of the collet  100  being brought into contact with the protective element  60  and the base  10  is the distance with which the collet  100  is not brought into contact with the base  10 , for example, about 760 μm or greater, the distance between the protective element  60  and the base  10  also assumes the similar value. Further, in order to set the two second fixing parts  44   a ,  44   b  to be spaced apart, the distance between the protective element  60  and the base  10  may be greater than the foregoing value, and may be, for example, about 1.0 mm to 1.2 mm. As described above, since the protective element  60  is substantially as great as the tip of the collet  100 , the distance between the lower end of the protective element  60  and the base  10  is, for example, about 1.0 mm at a minimum. Accordingly, the protective element  60  is disposed such that its lower end is spaced apart from the base  10  farther than the lower end of the semiconductor laser element  50 . 
     Representatively, as shown in  FIGS. 1B and 1C , the protective element  60  is disposed to be higher than the wires  70  connected to the semiconductor laser element  50 . 
     In one semiconductor laser device  1 , just a single protective element  60  will suffice. That is, the protective element  60  should be fixed to just one of the two second fixing parts  44   a ,  44   b  (to just the upper second fixing part  44   a ), and other one of the second fixing parts  44   a ,  44   b  (the lower second fixing part  44   b ) should be left unused. 
     (Wires  70 ) 
     The wire  70  connects between the semiconductor laser element  50  and at least one of a plurality of lead electrodes  31 ,  32 . Further, the wire  70  connects between the protective element  60  and at least one of the plurality of lead electrodes  31 ,  32 . In  FIGS. 1B and 1C , the wire  70  connects between the anode of the semiconductor laser element  50  and the second lead electrode  32 . Further, the wire  70  connects between the cathode of the protective element  60  and the second lead electrode  32 . The cathode of the semiconductor laser element  50  and the anode of the protective element  60  are both electrically connected to an electrically conductive layer  110  provided at the second main surface  42  of the submount  40  with an electrically conductive adhesive agent. The electrically conductive layer  110  is connected to the first lead electrode  31  with the wire  70 . Accordingly, the cathode of the semiconductor laser element  50  and the anode of the protective element  60  are both electrically connected to the first lead electrode  31 . A connecting portion connecting between the electrically conductive layer  110  and the wire  70  is positioned between the first fixing part  43  and the other long edge of the submount  40  (the long edge on the side where the second fixing parts  44   a ,  44   b  are not disposed). Note that, when the protective element  60  and the like have their anode and cathode on the identical surface, the electrodes should be directly connected to the first lead electrode  31  and the second lead electrode  32  with the wires  70 , respectively. 
     The wire  70  is a linear member made of metal such as Au, Ag or the like, and may have a diameter of about 10 μm to 50 μm. 
     The semiconductor laser element  50  and at least one of the plurality of lead electrodes  31 ,  32  may be connected to each other with a single wire  70 , or may be connected to each other with a plurality of wires  70 . Similarly, the protective element  60  and at least one of the plurality of lead electrodes  31 ,  32  may be connected to each other with a single wire  70 , or may be connected to each other with a plurality of wires  70 . 
     (Others) 
     The semiconductor laser device  1  may further include a cap  80  that is disposed to cover the semiconductor laser element  50  and the protective element  60 . The cap  80  may be made of, for example, Ni, Co, Fe, Ni—Fe alloy, Kovar, brass or the like. The cap  80  may be bonded to the base  10  by resistance welding or the like. Preferably, the bonding the cap  80  to the base  10  airtightly seals the semiconductor laser element  50 . Thus, the semiconductor laser element  50  is prevented from attracting dust due to laser oscillation. 
     The cap  80  has an opening X at its upper surface, for allowing laser light to transmit. In the present embodiment, as shown in  FIG. 1E , the opening X is provided at the top of the cap  80  bonded to the base  10 . To the opening X, a light-transmissive member  90  for extracting laser light can be provided. The light-transmissive member  90  may be made of, for example, glass, sapphire, ceramic or the like. A functional membrane that selectively reflects light of a particular wavelength or a particular angle may be provided at the surface of the light-transmissive member  90 . The light-transmissive member  90  may contain a wavelength conversion member, a light diffusing member and the like. 
     (Manufacturing Method) 
     In the following, a description will be given of a method of manufacturing the semiconductor laser device  1 . 
     Firstly, the base  10 , the heat sink  20 , and a plurality of lead electrodes  31 ,  32  are provided. Next, simultaneously with, before, or after disposition of the submount  40  at the heat sink  20 , the semiconductor laser element  50  is disposed at the first fixing part  43 . Simultaneously with, before, or after disposition of the semiconductor laser element  50 , the protective element  60  is disposed at the upper one of the two second fixing parts  44   a ,  44   b . Then, the protective element  60  and one of the plurality of lead electrodes  31 ,  32  are connected to each other with the wire  70 . 
     The semiconductor laser element  50  used herein is selected from a group consisting of a semiconductor laser element in which the optical waveguide region  55  is offset toward one lateral surface (the first lateral surface  53 ), and a semiconductor laser element in which the optical waveguide region  55  is offset toward other lateral surface (the second lateral surface  54 ). The orientation of the submount  40  is determined based on the position of the optical waveguide region  55  of the selected semiconductor laser element  50 . That is, the submount  40  is disposed at the heat sink  20  as being oriented so that the optical waveguide region  55  of the semiconductor laser element  50  is disposed on or around the line A connecting between the midpoint of the upper edge and the midpoint of the lower edge of the second main surface  42 . 
     Note that, the first fixing part  43  is provided at the submount  40  in the shape and position with which, irrespective of whether the optical waveguide region  55  is offset toward one lateral surface (the first lateral surface  53 ) or toward the other lateral surface (the second lateral surface  54 ), properly setting the upper edge and the lower edge of the submount  40  disposes the optical waveguide region  55  on or around the line A. 
     Through the foregoing operations, the semiconductor laser device  1  can be manufactured. 
     As has been described above, according to the present embodiment, turning the submount  40  upside down depending on whether the semiconductor laser element  50  has its optical waveguide region  55  positioned offset toward the first lateral surface  53  or toward the second lateral surface  54  allows the optical waveguide region  55  to be disposed on or around the line A connecting between the midpoint of the upper edge and the midpoint of the lower edge of the second main surface  42 . Accordingly, the submount  40  of a single type in which the fixing part is formed at a unique position can be used for both the semiconductor laser elements  50  differing from each other in the position of the optical waveguide region  55 . This prevents an increase in the number of types of the submount  40 , making the inventory control less troublesome. 
     Further, according to the present embodiment, irrespective of whether the submount  40  is normally oriented or turned upside down, the protective element  60  can be fixed to the upper one of the second fixing parts  44   a ,  44   b . Accordingly, in the case where the submount  40  of a single type is used for both the semiconductor laser elements  50  differing from each other in the position of the optical waveguide region  55 , an increase in length in the top-bottom direction of the submount  40  can be prevented. This achieves a reduction in size of the semiconductor laser device  1  (a reduction in length in the top-bottom direction of the semiconductor laser device  1 ), and it becomes possible to provide the semiconductor laser device  1  reduced in size while being equipped with the high-power semiconductor laser element  50  of a great cavity length (the length in the extending direction of the optical waveguide region  55 ). 
     [Semiconductor Laser Device  2  According to Second Embodiment] 
       FIG. 2A  is a schematic front view of a semiconductor laser device  2  according to a second embodiment (in which the cap is not shown).  FIG. 2B  is an enlarged view of a portion surrounded by a broken line in  FIG. 2A .  FIG. 2C  is a schematic front view of the submount  40  according to the second embodiment. As shown in  FIGS. 2A to 2C , in the second embodiment, the optical waveguide region  55  of the semiconductor laser element  50  is offset toward the opposite side relative to the first embodiment. That is, the optical waveguide region  55  of the semiconductor laser element  50  is offset toward the second lateral surface  54 . Therefore, as has been described above, the submount  40  is turned upside down. In this manner, using the submount  40 , the optical waveguide region  55  can be disposed on or around the line A connecting between the midpoint of the upper edge and the midpoint of the lower edge of the second main surface  42 , irrespective of whether the semiconductor laser element  50  is of the type in which the optical waveguide region  55  is offset toward the first lateral surface  53  or of the type in which the optical waveguide region  55  is offset toward the second lateral surface  54 . 
     [Semiconductor Laser Device  3  According to Third Embodiment] 
       FIG. 5A  is a schematic top view of a semiconductor laser device  3  according to a third embodiment (in which the cap is not shown).  FIG. 5B  is a schematic cross-sectional view taken along line  5 B- 5 B in  FIG. 5A .  FIG. 5C  is a schematic cross-sectional view taken along line  5 C- 5 C in  FIG. 5A .  FIG. 5D  is an enlarged view of a portion surrounded by a broken line in  FIG. 5A . As shown in  FIGS. 5A to 5D , the semiconductor laser device  3  includes a housing  120 , the submount  40 , the semiconductor laser element  50 , the protective element  60 , and the wires  70 . The members denoted by the reference characters identical to those in the first and second embodiments may be similarly structured as in the first and second embodiments. 
     The housing  120  includes an insulating part  122  and a plurality of wiring parts  124 . The housing  120  includes a recess Y. The recess Y is defined by a bottom surface Y 1 , and inner lateral surfaces Y 2  surrounding the bottom surface Y 1 . In the recess Y, part of the wiring parts  124  is exposed outside the insulating part  122 . 
     The submount  40  includes the first main surface  41  and the second main surface  42 . The first main surface  41  is fixed to the bottom surface Y 1 . The second main surface  42  includes the first fixing part  43  and the two second fixing parts  44   a ,  44   b . The two second fixing parts  44   a ,  44   b  are disposed laterally relative to the first fixing part  43  and respectively in the front half region and the rear half region of the second main surface  42 . The side from which the semiconductor laser element  50  emits laser light (the light output surface  51  side) is the front side, and the side opposite thereto (the light reflecting surface  52  side) is the rear side. The region occupying the front half of the second main surface  42  is the front half region, and the region occupying the rear half thereof is the rear half region. 
     The semiconductor laser element  50  includes the light output surface  51 , the light reflecting surface  52 , two lateral surfaces  53 ,  54  intersecting the light output surface  51 , and the optical waveguide region  55 . The optical waveguide region  55  is formed to be offset toward one of the two lateral surfaces  53 ,  54 . The semiconductor laser element  50  is fixed to the first fixing part  43  so that the light output surface  51  is directed frontward and the optical waveguide region  55  is disposed on or around a line that passes through the midpoint of the front edge and the midpoint of the rear edge of the second main surface  42  as seen in a top view. The term “as seen in a top view” refers to viewing the second main surface  42  of the submount  40  in the direction substantially perpendicular to the second main surface  42 . 
     The protective element  60  is fixed to front one of the two second fixing parts  44   a ,  44   b . The wire  70  connects between the protective element  60  and one of a plurality of wiring parts  124 . 
     The semiconductor laser device  3  includes a light reflecting member  130  that is disposed at the bottom surface Y 1 , for example. The laser light output from the semiconductor laser element  50  has its direction changed by the light reflecting member  130 , and extracted from the opening X at the cap  80 . 
     The semiconductor laser device  3  having such a structure can exhibit the effect similar to that exhibited by the semiconductor laser devices  1 ,  2  according to the first and second embodiments. 
     It is to be understood that although the present invention has been described with regard to preferred embodiments thereof, various other embodiments and variants may occur to those skilled in the art, which are within the scope and spirit of the invention, and such other embodiments and variants are intended to be covered by the following claims.