Patent Publication Number: US-2006018351-A1

Title: Semiconductor laser device

Description:
This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2004-214266 filed in Japan on 22 Jul. 2004, the entire contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      The present invention relates to a semiconductor laser device and an optical pickup device having the semiconductor laser device.  
     BACKGROUND ART  
      Among optical pickup devices used for optical recording mediums such as CD-ROMs (Compact Disc Read Only Memories) and MDs (Mini Discs) to read signals therefrom, there is known an optical pickup device employing a semiconductor laser device according to a “hologram laser system”. The hologram laser system is a system that, with a semiconductor laser element, a holographic element, and a signal light receiving element incorporated in one package, a light beam is emitted from the semiconductor laser element and the light beam reflected and returned from the optical disc, which is an optical recording medium, is diffracted by the holographic element so as to be led to the light receiving element set at a place away from the optical axis.  
      An example of conventional semiconductor laser devices employing the hologram laser system is disclosed in JP 06-5990 A. This semiconductor laser device, as shown in  FIG. 9A , includes a stem  1 , a cap  5  placed on the stem  1 , and a holographic element  6  placed on the cap  5 . The stem  1  is provided with a plurality of leads  7 . The stem  1  and the cap  5  are generally elliptical in their top shape for smaller thickness.  
       FIG. 9B  shows a schematic perspective view of the semiconductor laser device from which the cap  5  and the holographic element  6  have been removed.  
      A block  2  integrally molded with the stem  1  has a semiconductor laser element  3  and a light receiving element  4  mounted thereon. That is, as shown in  FIG. 9C , the semiconductor laser element  3  is fixed to a side face  13  of the block  2 , and the light receiving element  4  is fixed to a top face  14  of the block  2 .  
      Further, the semiconductor laser element  3  and the light receiving element  4  are connected to end faces of the leads  7  exposed from the top face of the stem  1  via wires  9 . Thus, electric currents can be fed to the semiconductor laser element  3  by using the leads  7 , and a detection signal of the light receiving element  4  can be extracted outside.  
      However, in this semiconductor laser device, since the semiconductor laser element  3  is fixed to the side face  13  of the block  2  and the light receiving element  4  is fixed to the top face  14  of the block  2 , there arises a need for mounting operations from two directions to the block  2 . Accordingly, manufacturing processes related to the mounting of the semiconductor laser element  3  and the light receiving element  4  become more complex, which eventually causes a drawback of increased manufacturing costs related to their mounting.  
      In the above semiconductor laser device, with a plurality of through-holes provided in the stem  1 , after insertion of the leads  7  into the through-holes one by one, clearances between the through-holes and the leads  7  are filled with an insulator. Because of this, a manufacturing process related to the packaging is complex, which also disadvantageously increases the manufacturing cost.  
     SUMMARY OF THE INVENTION  
      Accordingly, an object of the present invention is to provide a semiconductor laser device which allows a semiconductor laser element and a light receiving element to be surface mounted on a block from one direction and which can also eliminate the use of a stem-and-lead structure to thereby reduce the manufacturing cost, and also to provide an optical pickup device having such a semiconductor laser device.  
      In order to accomplish the above object, a semiconductor laser device according to the present invention comprises: 
          a wiring board having wiring patterns on at least one surface thereof;     a block mounted on the one surface of the wiring board, the block having first and second mounting surfaces both facing in an identical direction, and including a mirror part for changing an optical axis of light;     a semiconductor laser element mounted on the first mounting surface and emitting laser light; and     a first light receiving element mounted on the second mounting surface and receiving reflected light of the laser light.        

      In this semiconductor laser device, since the first mounting surface to carry the semiconductor laser element and the second mounting surface to carry the light receiving element face in the same direction, the semiconductor laser element and the light receiving element can be surface mounted on the block from one direction. Accordingly, a manufacturing process related to the mounting of the semiconductor laser element and the light receiving element is simplified. This allows a reduction in manufacturing cost of the semiconductor laser device to be achieved.  
      Further, by the block being mounted on one surface of the wiring board, the wiring patterns of the wiring board are electrically connected to the semiconductor laser element and the light receiving element, so that an electric current can be fed to the semiconductor laser element via a wiring pattern while a signal detected by the light receiving element can be extracted outside via a wiring pattern. Accordingly, it is no longer necessary to use, for example, a stem-and-lead structure in the semiconductor laser device, so that a manufacturing process related to the packaging of the semiconductor laser device is simplified. This enables a further reduction in cost for manufacturing the semiconductor laser device.  
      In one embodiment, the mirror part changes the optical axis of light by about 90°.  
      In one embodiment, the wiring board includes a heat sink having through-holes, a first printed board placed on the heat sink, and a second printed board placed under the heat sink and connecting to the first printed board via the through-holes.  
      In one embodiment, the wiring board has a main body made of ceramics.  
      In one embodiment, the semiconductor laser device further includes a cap which covers the block, the semiconductor laser element and the light receiving element.  
      In one embodiment, the semiconductor laser device further includes a holographic element placed on the cap for leading the reflected light to the light receiving element.  
      In one embodiment, a far-field pattern of the semiconductor laser element is an ellipse whose major axis is inclined at an angle of about 45° with respect to the second mounting surface.  
      In one embodiment, the semiconductor laser device further includes a second light receiving element which the laser light partially enters.  
      In one embodiment, the mirror part is a half mirror part, and part of the laser light that has passed through the half mirror part enters the second light receiving element.  
      In one embodiment, the half mirror part has a polarization property.  
      In one embodiment, electrode portions of the semiconductor laser element and the light receiving element are connected to the wiring patterns via wires.  
      In one embodiment, the block is formed of an insulator.  
      An optical pickup device for performing reproduction, erasing, and/or recording of information on an optical disc, according to the present invention, includes: 
          the semiconductor laser device as described above;     a collimator lens placed in an optical path between the semiconductor laser device and the optical disc; and     an objective lens placed in an optical path between the collimator lens and the optical disc.        

      Because the optical pickup device includes the semiconductor laser device, it can be fabricated at a reduced cost.  
      In one embodiment, the first and second mounting surfaces are roughly parallel to a recording surface of the optical disc.  
      In one embodiment, the objective lens has a numerical aperture larger than a numerical aperture of the collimator lens.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not intended to limit the present invention, and wherein:  
       FIG. 1  is a schematic perspective view of a semiconductor laser device according to en embodiment of the present invention;  
       FIG. 2  is a schematic top view of the semiconductor laser device of  FIG. 1 ;  
       FIG. 3A  is a schematic side view of a wiring board of the semiconductor laser device of  FIG. 1 ;  
       FIG. 3B  is a schematic bottom view of the wiring board;  
       FIGS. 4A  to  4 F are manufacturing process diagrams of the semiconductor laser device of  FIG. 1 ;  
       FIG. 5A  is a schematic side view of an optical pickup device according to en embodiment of the invention;  
       FIG. 5B  is a schematic bottom view of the optical pickup device;  
       FIGS. 6A  to  6 D are manufacturing process diagrams of a semiconductor laser device according to another embodiment of the invention;  
       FIG. 7A  is a schematic perspective view of a block of the semiconductor laser device of  FIG. 1 ;  
       FIG. 7B  is a view showing a general shape of a beam spot formed by a semiconductor laser element on the block of  FIG. 7A ;  
       FIG. 7C  is a schematic perspective view of a block of a semiconductor laser device according to another embodiment of the present invention;  
       FIG. 7D  is a view showing a general shape of a beam spot formed by a semiconductor laser element on the block of  FIG. 7C ;  
       FIG. 7E  is a schematic perspective view of a block of a semiconductor laser device according to another embodiment of the present invention;  
       FIG. 7F  is a view showing a general shape of a beam spot formed by a semiconductor laser element on the block of  FIG. 7E ;  
       FIG. 7G  is a schematic perspective view of a block of a semiconductor laser device according to another embodiment of the present invention;  
       FIG. 7H  is a view showing a general shape of a beam spot formed by a semiconductor laser element on the block of  FIG. 7G ;  
       FIG. 8  is a schematic sectional view of a semiconductor laser device according to still another embodiment of the invention;  
       FIG. 9A  is a schematic perspective view of a prior art semiconductor laser device;  
       FIG. 9B  is a schematic perspective view of the prior art semiconductor laser device from which the cap and the holographic element have been removed; and  
       FIG. 9C  is a schematic perspective view of the prior art semiconductor laser device before a laser element and a light receiving element are mounted. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinbelow, the semiconductor laser device and the optical pickup device having it according to the present invention will be described in detail by embodiments thereof illustrated in the accompanying drawings.  
       FIG. 1  is a schematic perspective view of a semiconductor laser device  100  according to an embodiment of the invention.  
      The semiconductor laser device  100  includes a wiring board  101 , a block  102  mounted on a top face of the wiring board  101  as an example of the claimed one surface, a semiconductor laser element  103  which emits laser light L, a light receiving element  104  which receives reflected light of the laser light, a rectangular-parallelopiped cap  105  which covers the block  102 , the semiconductor laser element  103  and the light receiving element  104 , and a holographic element  106  which is placed on the cap  105 . The block  102  is an example of the claimed block, and the light receiving element  104  is an example of the claimed first light receiving element.  
      The block  102 , which is formed of an insulator, has a first mounting surface  113  on which the semiconductor laser element  103  is mounted, a second mounting surface  114  on which the light receiving element  104  is mounted, and a raising mirror  111  for reflecting the laser light L emitted by the semiconductor laser element  103 . The raising mirror  111  is an example of the mirror part.  
      The first mounting surface  113  is generally parallel to the second mounting surface  114 . That is, the first mounting surface  113  and the second mounting surface  114  are oriented in the same direction. Then, the first, second mounting surfaces  113 ,  114  are generally parallel to the top face of the wiring board  101 .  
      The raising mirror  111  connects the first mounting surface  113  and the second mounting surface  114  to each other. Also, the raising mirror  111  is inclined at an angle of 45° with respect to an optical axis of the laser light L. As a result of this, the raising mirror  111  changes the direction of the optical axis of the laser light L by about 90°.  
      The holographic element  106  leads reflected light of the laser light to the light receiving element  104 .  
       FIG. 2  is a schematic top view of the semiconductor laser device  100  in which the cap  105  and the holographic element  106  have been removed.  
      On the top of the wiring board  101  are provided pad patterns  120  as an example of the wiring patterns. The pad patterns  120  are electrically connected to input/output terminals (electrode portions) of the semiconductor laser element  103  and the light receiving element  104  via wires  140 .  
       FIG. 3A  is a schematic side view of the wiring board  101 .  FIG. 3B  is a schematic bottom view of the wiring board  101 .  
      The wiring board  101 , as shown in  FIG. 3A , has a three-layer structure consisting of a top-face printed board  121  as an example of a first printed board, a Cu (copper) plate  122 , and a bottom-face printed board  123  as an example of the second printed board. The Cu plate  122  has through-holes  124  bored through the thickness of the Cu plate  122 . These through-holes  124  are covered at their inner walls with an insulator, and filled with an electrical conductor placed inside of the insulator. The top-face printed board  121  is placed on the Cu plate  122 , and the bottom-face printed board  123  is placed under the Cu plate  122 . Then, as shown in  FIG. 3B , the wiring board  101  is provided with a plurality of electrode portions  130  at specified intervals on its bottom face, i.e. on a bottom face of the bottom-face printed board  123 . These electrode portions  130  and the pad patterns  120  are placed in a conducting state via the conductor within the through-holes  124 . The Cu plate  122  is an example of the heat sink, and the electrode portions  130  are an example of the wiring patterns.  
      Now, the manufacturing process of the semiconductor laser device  100  will be described with reference to  FIGS. 4A  to  4 F.  
      First, as shown in  FIG. 4A , the semiconductor laser element  103  is mounted on the first mounting surface  113  of the block  102 . The semiconductor laser element  103  is fixed to the first mounting surface  113  with a bond or a brazing material.  
      Next, the light receiving element  104  is mounted on the second mounting surface  114  of the block  102 . The light receiving element  104  is fixed to the second mounting surface  114  also with a bond or a brazing material.  
      Next, as shown in  FIG. 4B , the block  102  mounted with the semiconductor laser element  103  and the light receiving element  104  is mounted on top of the wiring board  101  with a bond or the like. Then, as shown in  FIG. 4C , the pad patterns  120  are located on both sides of the block  102 .  
      Next, a wire bonding process is performed, so that input/output terminals of the semiconductor laser element  103  and the light receiving element  104  are electrically connected to the pad patterns  120  via the wires  140  as shown in  FIG. 4D .  
      Next, as shown in  FIG. 4E , the generally rectangular-parallelopiped cap  105  is fitted to the wiring board  101  with a bond. As a result of this, the block  102 , the semiconductor laser element  103 , the light receiving element  104 , the pad patterns  120  and the wires  140  are covered with the cap  105  (see  FIG. 1 ). The cap  105  has, on its top, an opening  112  through which the laser light L passes.  
      Finally, as shown in  FIG. 4F , the holographic element  106  is placed on the cap  103  so that the opening  112  of the cap  103  is closed by the holographic element  106 . Thereafter, the holographic element  106  is fixed to the cap  105  with a bond.  
      As described above, the first mounting surface  113  to carry the semiconductor laser element  103  and the second mounting surface  114  to carry the light receiving element  104  are set to face in the same direction, so that the semiconductor laser element  103  and the light receiving element  104  are able to be surface mounted on the block  102  from one direction. Accordingly, the manufacturing process related to the mounting of the semiconductor laser element  103  and the light receiving element  104  is simplified, so that the manufacturing cost reduction is achievable.  
      Also, since the manufacturing process related to the mounting of the semiconductor laser element  103  and the light receiving element  104  is simplified, it is possible to improve the yield of the semiconductor laser devices  100 .  
      Further, by virtue of the mounting of the block  102  on the top face of the wiring board  101 , electrically connecting the pad patterns  120  on the top face of the wiring board  101  to the semiconductor laser element  103  and the light receiving element  104  makes it possible to feed electric currents to the semiconductor laser element  103  via the pad patterns  120  and also to extract signals, which have been detected by the light receiving element  104 , outside via the pad patterns  120 . Accordingly, it is no longer necessary to use a structure having a stem and leads as shown in  FIGS. 9A  to  9 C in the semiconductor laser device  100 , so that manufacturing process steps related to the packaging are simplified. This also contributes to the manufacturing cost reduction.  
      Furthermore, because the wiring board  101  is structured such that the Cu plate  122  is sandwiched between the top-face printed board  121  and the bottom-face printed board  123 , heat in the cap  105  is efficiently radiated outside via the Cu plate  122 , so that the reliability of the semiconductor laser device  100  is assured. That is, by virtue of the Cu plate  122  of the wiring board  101 , a good heat dissipation property and reliability of the semiconductor laser device  100  are obtainable.  
      A flexible board or the like may be joined to the bottom face of the wiring board  101  with a view to extracting signals detected by the light receiving element  104  to the outside via the pad patterns  120 .  
       FIG. 5A  schematically shows main parts of an optical pickup device  200  incorporating the semiconductor laser device  100 , as viewed sideways.  FIG. 5B  is a schematic view of the optical pickup device  200  as viewed from below. It is noted that the cap  5  is partly removed in  FIGS. 5A and 5B .  
      The optical pickup device  200  includes a semiconductor laser device  100 , a collimator lens  151  placed in an optical path between the semiconductor laser device  100  and an optical disc  153 , an objective lens  152  placed in an optical path between the collimator lens  151  and the optical disc  153 , and a raising mirror  150  placed in an optical path between the collimator lens  151  and the semiconductor laser device  100 .  
      The raising mirror  150  is inclined at an angle of 45° with respect to an optical axis of laser light L emitted from the semiconductor laser device  100 . As a result of this, the raising mirror  150  changes the direction of the optical axis of the laser light L emitted from the semiconductor laser device  100  by 90°.  
      According to the optical pickup device  200  of this construction, the laser light L emitted from the semiconductor laser element  103  is changed in its optical axis direction by 90° by the raising mirror  111 , then passes through the holographic element  106 , and is further changed in its optical axis direction by 90° by the raising mirror  150 , collimated by the collimator lens  151 , and condensed onto a recording surface of the optical disc  153  by the objective lens  152 . The light reflected by the recording surface of the optical disc  153  passes through the objective lens  152 , the collimator lens  151  and the raising mirror  150  successively, and then is diffracted by the holographic element  106  so as to be led to the light receiving element  104 . Thus, the light receiving element  104  outputs an electric signal corresponding to the reflected light. Information of the recording surface of the optical disc  153  is obtained based on the electric signal.  
      In this embodiment, the semiconductor laser device  100  is positioned such that the first and second mounting surfaces  113 ,  114  are generally vertical to the recording surface of the optical disc  153 . However, the semiconductor laser device  100  may also be positioned such that the first and second mounting surfaces  113 ,  114  are generally parallel to the recording surface of the optical disc  153 . With the semiconductor laser device  100  positioned in this way, the mirror  150  may be eliminated, which allows the parts count to be reduced.  
      Although the wiring board  101  formed of the top-face printed board  121 , the Cu plate  122  and the bottom-face printed board  123  is used in the above embodiment, it is also possible to use a wiring board whose body is formed of ceramics.  
      Also, as an example of the claimed block, the block  102  is mounted on the top face of the wiring board  101  in the above embodiment. Alternatively, as shown in  FIGS. 6A  to  6 D, a block  202  may be mounted on a top face of a wiring board  201 .  
      The way of mounting of the block  202  onto the top face of the wiring board  201  will be described below.  
      First, as shown in  FIG. 6A , the semiconductor laser element  103  is mounted on a first mounting surface  213  of the block  202 . The semiconductor laser element  103  is fixed to the first mounting surface  213  with a bond or a brazing material.  
      The block  202 , which is formed of an insulator, has the first mounting surface  213 , a second mounting surface  214 , and a raising mirror  211  as an example of the mirror part. The first and second mounting surfaces  213 ,  214  have electrode portions  232 , respectively. Although not shown, electrode portions are provided also on the bottom face of the block  202 . The electrode portions of the bottom face of the block  202  are electrically connected to the electrode portions  232  of the top face of the block  202  via wiring patterns within the block  202 . The first mounting surface  213  is generally parallel to the second mounting surface  214 . The raising mirror  211  is inclined at an angle of about 45° with respect to the first mounting surface  213  and the second mounting surface  214 . As a result of this, the raising mirror  211  is enabled to change the direction of the optical axis of the laser light L by about 90°.  
      Next, the light receiving element  104  is mounted on the second mounting surface  214  of the block  202 . The light receiving element  104  is fixed to the second mounting surface  214  also with a bond or a brazing material.  
      Next, as shown in  FIG. 6B , the input/output terminals of the semiconductor laser element  103  and the light receiving element  104  are connected to the electrode portions  232  at the top face of the block  202  via wires  240 .  
      Next, as shown in  FIG. 6C , the block  102  mounted with the semiconductor laser element  103  and the light receiving element  104  is mounted on top of the wiring board  201  with a bond or the like.  
      Electrode portions  231  as an example of the wiring patterns are placed on the top face of the wiring board  201  in positions in correspondence with the electrode portions at the bottom face of the block  202 . As a result of this, when the block  202  is mounted on the top face of the wiring board  201 , the electrode portions at the bottom face of the block  202  are electrically connected to the electrode portions  231  at the top face of the wiring board  201 . Therefore, electric currents can be fed to the semiconductor laser element  103  via the pad-pattern electrode portions  231 , and moreover signals detected by the light receiving element  104  can be extracted outside via the electrode portions  231 .  
      After that, performing processes similar to those of  FIGS. 4E and 4F  leads to completion of a semiconductor laser device of another embodiment of the invention.  
      It is noted that the structure of the wiring board  201  is similar to that of the wiring board  101 , except for the electrode portions  231 . That is, the wiring board  201  is composed of a Cu plate, a top-face printed board placed on the Cu plate, and a bottom-face printed board placed under the Cu plate. The Cu plate has through-holes, and electrode portions are provided at the bottom face of the wiring board  101  (bottom face of the bottom-face printed board) at the specified intervals. These electrode portions are connected to the electrode portions  231  via the through-holes of the Cu plate.  
      The block  102  and its modification examples will be described below.  
      The block  102  of  FIG. 7A  is the one used in the above embodiment, where the direction of the optical axis of the laser light L emitted from the semiconductor laser element  103  is changed by about 90° by the raising mirror  111 .  
      The laser light L whose optical axis direction has been changed by the raising mirror  111  is applied to the recording surface of an optical disc having pits  160 , as shown in  FIG. 7B . Then, an elliptical beam spot  161  is formed on the recording surface of the optical disc by the laser light L. The major axis of the beam spot  161  is generally parallel to or coincides with the direction in which the pits  160  are arrayed.  
      A block  302  of  FIG. 7C  is to carry the semiconductor laser element  103  on its first mounting surface  313 . The semiconductor laser element  103  is fixed on a side face of a submount  315  which is provided independent of the block  302 . The side face of the submount  315  is generally vertical to the first and second mounting surfaces  313 ,  314 . Further, the first mounting surface  313  is generally parallel to the second mounting surface  314 . That is, the first mounting surface  313  and the second mounting surface  314  are oriented so as to face in the same direction. Besides, a raising mirror  311  for reflecting the laser light L emitted from the semiconductor laser element  103  is provided on the block  302 . The raising mirror  311  is inclined at an angle of about 45° with respect to the optical axis of the laser light L. As a result of this, the raising mirror  311  is enabled to change the direction of the optical axis of the laser light L by about 90°. It is noted that the block  302  is formed of an insulator.  
      The laser light L whose optical axis direction has been changed by the raising mirror  311  is, as shown in  FIG. 7D , applied to the recording surface of the optical disc having pits  160 . Then, an elliptical beam spot  361  is formed on the recording surface of the optical disc. The major axis of the beam spot  361  intersects at an angle of about 90° with the direction in which the pits  160  are arrayed.  
      A block  402  of  FIG. 7E  carries the semiconductor laser element  103  on its first mounting surface  413 . The semiconductor laser element  103  is fixed on a side face of a submount  415  which is provided independent of the block  402 . The side face of the submount  415  is inclined at an angle of about 45° with respect to the first and second mounting surfaces  413 ,  414 . Further, the first mounting surface  413  is generally parallel to the second mounting surface  414 . That is, the first mounting surface  413  and the second mounting surface  414  are oriented in the same direction. Besides, a raising mirror  411  for reflecting the laser light L emitted from the semiconductor laser element  103  is provided on the block  402 . The raising mirror  411  is inclined at an angle of about 45° with respect to the optical axis of the laser light L. As a result of this, the raising mirror  411  is enabled to change the direction of the optical axis of the laser light L by about 90°. The block  402  is formed of an insulator.  
      The laser light L having an optical axis of which the direction has been changed by the raising mirror  411  is, as shown in  FIG. 7F , applied to the recording surface of the optical disc having the pits  160 . Then, an elliptical beam spot  461  is formed on the recording surface of the optical disc. The major axis of the beam spot  461  intersects at an angle of about 45° with the direction in which the pits  160  are arrayed.  
      A block  502  of  FIG. 7G  carries the semiconductor laser element  103  on its first mounting surface  513 . The first mounting surface  513  is a bottom face of a recessed portion  516  provided in the block  502 . Also, the first mounting surface  513  is generally parallel to a second mounting surface  514  on which the light receiving element  104  is mounted. That is, the first mounting surface  513  and the second mounting surface  514  are oriented so as to face in the same direction. Besides, a raising mirror  511  for reflecting the laser light L emitted from the semiconductor laser element  103  is provided on the block  502 . The raising mirror  511  is inclined at an angle of 45° with respect to the optical axis of the laser light L. As a result of this, the raising mirror  511  is enabled to change the direction of the optical axis of the laser light L by about 90°. It is noted that the raising mirror  511  forms part of inner wall surfaces of the recessed portion  516 . The block  502  is formed of an insulator.  
      The laser light L having an optical axis of which the direction has been changed by the raising mirror  511  is, as shown in  FIG. 7H , applied to the recording surface of the optical disc having the pits  160 . Then, an elliptical beam spot  561  is formed on the recording surface of the optical disc. The major axis of the beam spot  561  intersects at an angle of about 90° with the direction in which the pits  160  are arrayed.  
      The reason why the beam spots  161 ,  361 ,  461 ,  561  have an elliptical shape is that a far-field pattern of the semiconductor laser element  103  is elliptical.  
      As compared to the case where the block  102  is used in the optical pickup device, attenuation and variations in light intensity of reflected light due to birefringence on the recording surface of the optical disc are lessened when the block  302  or  502  is used in the optical pickup device, so that the quantity of received light of the light receiving element  104  is stabilized. Thus, the S/N (Signal-to-Noise) ratio can be improved.  
      As compared with the cases where the block  302  or  502  is used in the optical pickup device, attenuation and variations in light intensity of reflected light due to birefringence on the recording surface of the optical disc are lessened when the block  402  is used in the optical pickup device, so that the quantity of received light of the light receiving element  104  is stabilized. Thus, the S/N (Signal-to-Noise) ratio can be improved.  
      That is, the blocks  302 ,  502  are higher in S/N ratio improving effect than the block  102 , and the block  402  is higher in S/N ratio improving effect than the blocks  302 ,  502 .  
      Further, when the semiconductor laser device having the block  402  is used in the optical pickup device  200 , the numerical aperture of the objective lens  152  is set larger than that of the collimator lens  151 .  
      In the above described embodiment, the semiconductor laser device  100  is incorporated in the optical pickup device  200 . Alternatively, a semiconductor laser device  600  shown in  FIG. 8  may be incorporated in the optical pickup device  200 .  
      The semiconductor laser device  600  includes a block  602  which internally contains a light receiving element  617  as an example of the second light receiving element.  
      The block  602 , which is formed of an insulator, has a first mounting surface  613 , a second mounting surface  614  and a raising half mirror  611 . The raising half mirror  611  is inclined at an angle of 45° with respect to the optical axis of laser light L emitted from the semiconductor laser element  103 . The raising half mirror  611  is an example of the claimed half mirror part.  
      The first mounting surface  613  carries the semiconductor laser element  103 , and the second mounting surface  614  carries the light receiving element  104 . Also, the first mounting surface  613  is generally parallel to the second mounting surface  614 . That is, the first mounting surface  613  and the second mounting surface  614  face in the same direction. The first and second mounting surfaces  613 ,  614  are generally parallel to the top face of the wiring board  101 .  
      According to the semiconductor laser device  600  of this construction, part of the laser light L emitted from the semiconductor laser element  103  is transmitted by the raising half mirror  611  to be incident on the light receiving element  617 , while the rest of the laser light L is reflected by the raising half mirror  611 . Since part of the laser light L is received by the light receiving element  617 , the quantity of light to be outputted by the semiconductor laser element  103  can be controlled and maintained constant on the basis of an electric signal outputted by the light receiving element  617 . Consequently, optical output control over the semiconductor laser element  103  can be implemented.  
      Instead of the raising half mirror  611 , a raising half mirror having a membrane having a polarization property may also be used. That is, a raising half mirror for reflecting only one of p wave or s wave of the laser light L may be used instead of the raising half mirror  611 .  
      The constitution of the semiconductor laser device of the present invention can be applied to dual-wavelength semiconductor laser devices. When the constitution of the semiconductor laser device of the present invention is applied to a dual-wavelength semiconductor laser device, a first semiconductor laser element for emitting laser light of a first wavelength and a second semiconductor laser element for emitting laser light of a second wavelength different from the first wavelength are mounted on the first mounting surface of the block.  
      Although in the above embodiments, the submounts  315 ,  415  are provided independently of the blocks  302 ,  402 , namely, as different pieces from the blocks, yet the submounts  315 ,  415  may also be formed by integral molding with the blocks  302 ,  402 .  
      The Cu plate  122  is used in the above embodiment. However, it is also possible to use ceramic plates or other metallic plates of good heat dissipation property instead of the Cu plate  122 . That is, the heat sink of the present invention may be a ceramic plate or any other metallic plate which has a good heat dissipation property.  
      Embodiments of the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.