Patent Publication Number: US-2012033696-A1

Title: Semiconductor laser apparatus and optical apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The priority application numbers JP2010-175698, Semiconductor Laser Apparatus and Optical Apparatus, Aug. 4, 2010, Nobuhiko Hayashi et al., and JP2010-203861, Semiconductor Laser Apparatus and Optical Apparatus, Sep. 13, 2010, Nobuhiko Hayashi et al., upon which this patent application is based are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor laser apparatus and an optical apparatus, and more particularly, it relates to a semiconductor laser apparatus comprising a package sealing a semiconductor laser chip and an optical apparatus employing the same. 
     2. Description of the Background Art 
     A blue-violet semiconductor laser apparatus emitting a laser beam having a wavelength of about 405 nm has been put into practice as a light source for a Blu-ray disc. This blue-violet semiconductor laser apparatus includes a package sealing a semiconductor laser chip. Such a semiconductor laser apparatus is disclosed in Japanese Patent Laying-Open No. 2004-22918, for example. 
     In a semiconductor laser apparatus disclosed in Japanese Patent Laying-Open No. 2004-22918, a semiconductor laser chip is hermetically sealed with a package constituted by a metal stem and a container (cap). A glass window through which a laser beam is emitted is mounted on this cap. This glass window is mounted through low-melting-point glass having a thermal expansion coefficient close to a thermal expansion coefficient of metal in order to hermetically seal the package. A lead wire is mounted to the stem so as to pass through the package, and the stem and the lead wire are electrically insulated from each other. In order to hermetically seal a portion where this lead wire passes through the stem, the lead wire is fusion bonded (sealed) with the aforementioned similar low-melting-point glass. The stem and the cap are mounted by resistance welding to be hermetically sealed. 
     In the semiconductor laser apparatus disclosed in Japanese Patent Laying-Open No. 2004-22918, however, the package is hermetically sealed with the low-melting-point glass or by resistance welding as described above, and hence a manufacturing process is complicated and the manufacturing cost is disadvantageously increased. Further, a portion hermetically sealed with the low-melting-point glass is not resistant to external shock or the like, and hence the reliability is disadvantageously low. 
     SUMMARY OF THE INVENTION 
     A semiconductor laser apparatus according to a first aspect of the present invention includes a package having sealed space inside, and a semiconductor laser chip arranged in the sealed space, wherein the package has a first member and a second member bonded to each other with an adhesive, a covering agent made of an ethylene-vinyl alcohol copolymer is formed on a bonded region of the first member and the second member in the sealed space, and the adhesive is covered with the covering agent. 
     In the semiconductor laser apparatus according to the first aspect of the present invention, the first member and the second member constituting the package are bonded to each other with the adhesive, and hence a manufacturing process can be simplified, and the semiconductor laser apparatus can be manufactured at a lower cost. Further, as compared with a case where the first member and the second member are bonded to each other with low-melting-point glass or the like, the adhesive has high flexibility, and hence the adhesive is rarely influenced by external force. 
     Further, the adhesive is covered with the covering agent in the sealed space, and hence even if the adhesive contains low molecular siloxane or a volatile resin component, the low molecular siloxane or the volatile resin component can be inhibited from entering the sealed space. Further, an ethylene-vinyl alcohol copolymer (EVOH) having excellent gas barrier properties and hardly generating volatile gas is employed as the covering agent, and hence the aforementioned gas can be inhibited from entering the sealed space. Consequently, an adherent substance can be inhibited from being formed on a laser emitting facet, and hence the semiconductor laser chip can be easily inhibited from degradation. 
     In the aforementioned semiconductor laser apparatus according to the first aspect, the covering agent is preferably arranged to be closer to the sealed space than the adhesive in the bonded region. According to this structure, the adhesive is not exposed in the sealed space, and hence even if the adhesive contains low molecular siloxane or a volatile resin component, the covering agent arranged to be closer to the sealed space than the adhesive can inhibit the component contained in the adhesive from directly entering the sealed space. 
     In the aforementioned semiconductor laser apparatus according to the first aspect, the covering agent preferably has a surface coming into contact with the sealed space, and the adhesive preferably has a surface exposed to an outside of the package. According to this structure, the covering agent covering the adhesive can partially form an inner surface of the sealed space. Further, the first member and the second member can be reliably bonded with the adhesive in not only the bonded region of the first member and the second member but also an outer surface of the package. 
     In the aforementioned semiconductor laser apparatus according to the first aspect, the covering agent is preferably arranged to come into contact with the adhesive and cover the adhesive. According to this structure, the covering agent can directly inhibit the component contained in the adhesive from entering the sealed space. 
     In this case, a contact interface between the covering agent and the adhesive is preferably located on substantially the same plane as an outer surface of the package or located to be closer to the sealed space than the outer surface of the package. According to this structure, the covering agent formed on the bonded region of the first member and the second member does not protrude to the outside of the package, and hence the first member and the second member can be more reliably bonded to each other with the adhesive. 
     In the aforementioned semiconductor laser apparatus according to the first aspect, the covering agent preferably continuously covers the adhesive along the bonded region of the first member and the second member not to expose the adhesive in the sealed space. According to this structure, the covering agent can reliably prevent the adhesive provided along the bonded region from being exposed in the sealed space, and hence the component contained in the adhesive can be reliably prevented from entering the sealed space. 
     In the aforementioned semiconductor laser apparatus according to the first aspect, resin having larger elasticity than the adhesive is preferably arranged between the adhesive and the covering agent, and the resin is preferably covered with the covering agent. According to this structure, even if cracks or separation is generated in the adhesive due to a difference in thermal expansion coefficient between the first member and the second member or external impact, the resin can enter clearances generated due to the cracks or the separation. Thus, airtightness and reliability are further improved. 
     In the aforementioned structure having the resin arranged between the adhesive and the covering agent, the resin having larger elasticity than the adhesive is preferably sealed with the adhesive and the covering agent not to be exposed to an inside and an outside of the sealed space in the bonded region. According to this structure, the airtightness of the package can be reliably inhibited from decrease due to resin exposed to the inside and the outside of the sealed space. 
     In the aforementioned structure having the resin arranged between the adhesive and the covering agent, the resin having larger elasticity than the adhesive is preferably silicon resin. Thus, the aforementioned function of the “resin having larger elasticity than the adhesive” in the present invention can be effectively utilized by employing the silicon resin. 
     In the aforementioned semiconductor laser apparatus according to the first aspect, the first member and the second member may be made of different materials. In this case, materials can be easily selected on the basis of shapes and functions of these members. 
     In this case, either the first member or the second member is preferably made of metal while either the second member or the first member is preferably made of glass, and the first member and the second member are preferably bonded to each other with the adhesive and the covering agent in the bonded region. According to this structure, the package can be constituted by strongly bonding the first member and the second member made of the different materials to each other with the adhesive and the covering agent. 
     In the aforementioned semiconductor laser apparatus according to the first aspect, the first member is preferably transparent and bonded onto an opening of the second member, a laser beam emitted from the semiconductor laser chip is preferably transmitted through the first member and emitted to an outside of the package, and the covering agent is preferably formed on a bonded region of the second member and the first member other than the opening. According to this structure, the package can be easily sealed also in a window portion (bonded region) for emitting a laser beam such that the component contained in the adhesive is inhibited from entering the sealed space. 
     In this case, the first member is preferably bonded onto a surface of the second member in the sealed space of the package or a surface of the second member on the outside of the package opposite to the sealed space, and the first member and the second member are preferably bonded to each other with the adhesive and the covering agent arranged on a surface of the second member other than the opening. According to this structure, the package can be easily sealed with the first member (window portion) for emitting a laser beam without harmful effects such as contact of the laser beam with the covering agent. 
     In the aforementioned semiconductor laser apparatus according to the first aspect, the first member preferably has conductivity and is preferably bonded onto an opening of the second member, the first member is preferably arranged to extend from an outside of the package to an inside of the sealed space in a state electrically isolated from the second member, and the covering agent is preferably formed in the opening of the second member. According to this structure, the package can be easily sealed also in a wiring portion for power supply to the semiconductor laser chip arranged in the sealed space and a wiring portion for a monitor signal from a photodiode (photodetector) such that the component contained in the adhesive is inhibited from entering the sealed space. 
     In this case, the first member is preferably a lead frame, the second member is preferably a base for fixing the semiconductor laser chip in the sealed space, the lead frame preferably extends from the outside of the package to the inside of the sealed space in a state held in an opening of the base by the adhesive sealing the opening of the base, and a surface of the adhesive in a portion on which the lead frame is mounted is preferably covered with the covering agent in the sealed space. According to this structure, the package can be easily sealed in the wiring portion for power supply to the semiconductor laser chip arranged in the sealed space and the wiring portion for a monitor signal from the photodiode (photodetector). 
     In the aforementioned semiconductor laser apparatus according to the first aspect, the first member is preferably a sealing member sealing the package, the second member is preferably a base for fixing the semiconductor laser chip in the sealed space, the sealing member and the base are preferably bonded to each other with the adhesive, and the covering agent covering the adhesive preferably extends onto a surface of the sealing member other than the bonded region on a side bonded to the base. According to this structure, the covering agent can be easily formed on one surface (inner surface) of the sealing member in the manufacturing process. Further, the surface of the sealing member located in the sealed space can be reliably covered with the covering agent regardless of a bonding position (mounting method) of the sealing member to the base. 
     The aforementioned semiconductor laser apparatus according to the first aspect preferably further includes a photodetector arranged in the sealed space, monitoring intensity of a laser beam from the semiconductor laser chip, wherein the photodetector is fixed in the sealed space through a conductive adhesive containing a volatile component, and a surface of the conductive adhesive fixing the photodetector exposed in the sealed space is covered with the covering agent. According to this structure, the covering agent can block volatile organic gas from penetrating into the sealed space of the package even if the volatile organic gas is generated from the conductive adhesive. Consequently, formation of an adherent substance on a photodetecting surface of the photodetector in addition to the laser emitting facet can be inhibited, and hence output of a laser beam from the semiconductor laser chip can be accurately controlled with this photodetector 
     In the aforementioned semiconductor laser apparatus according to the first aspect, the adhesive is preferably made of a resin material containing a volatile component. Thus, even if the resin material containing the volatile component is employed as the adhesive, the “covering agent” in the present invention covers the adhesive, and hence the effects of the present invention can be effectively achieved. 
     In the aforementioned semiconductor laser apparatus according to the first aspect, the semiconductor laser chip preferably includes a nitride-based semiconductor laser chip. Thus, in the nitride-based semiconductor laser chip having a short lasing wavelength and requiring a higher output power, an adherent substance is easily formed on a laser emitting facet thereof, and hence the use of the aforementioned “covering agent” in the present invention is highly effective in inhibiting degradation of the nitride-based semiconductor laser chip. 
     An optical apparatus according to a second aspect of the present invention includes a semiconductor laser apparatus including a package having sealed space inside and a semiconductor laser chip arranged in the sealed space, and an optical system controlling a beam emitted from the semiconductor laser chip, wherein the package has a first member and a second member bonded to each other with an adhesive, a covering agent made of an ethylene-vinyl alcohol copolymer is formed on a bonded region of the first member and the second member in the sealed space, and the adhesive is covered with the covering agent. 
     In the optical apparatus according to the second aspect of the present invention, the first member and the second member in the sealed space are bonded to each other with the adhesive, and hence a manufacturing process can be simplified, and the semiconductor laser apparatus can be manufactured at a lower cost. Further, as compared with a case where the first member and the second member are bonded to each other with low-melting-point glass or the like, the adhesive has high flexibility, and hence the adhesive is rarely influenced by external force. 
     Further, the adhesive is covered with the covering agent, and hence even if the adhesive contains low molecular siloxane or a volatile resin component, the low molecular siloxane or the volatile resin component can be inhibited from entering the sealed space. Further, an ethylene-vinyl alcohol copolymer (EVOH) having excellent gas barrier properties and hardly generating volatile gas is employed as the covering agent, and hence the aforementioned gas can be inhibited from entering the sealed space. Consequently, an adherent substance can be inhibited from being formed on a laser emitting facet, and hence the semiconductor laser chip can be easily inhibited from degradation. Thus, the reliable optical apparatus can be easily attained at a lower cost. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a semiconductor laser apparatus  100  in which a base  10  and a sealing member  20  are separated from each other; 
         FIG. 2  is a longitudinal sectional view taken along the center line of the semiconductor laser apparatus  100  in the width direction; 
         FIG. 3  is a longitudinal sectional view of the vicinity of a through hole  11   c  ( 11   d ) in the semiconductor laser apparatus  100 ; 
         FIG. 4  is a longitudinal sectional view taken along the center line of a semiconductor laser apparatus  110  in the width direction; 
         FIG. 5  is an exploded perspective view of a semiconductor laser apparatus  200  in which a base  10  and a sealing member  20  are separated from each other; 
         FIG. 6  is a longitudinal sectional view taken along the center line of the semiconductor laser apparatus  200  in the width direction; 
         FIG. 7  is a partial sectional view of a terminal holding portion  55  through which a lead frame  14  ( 15 ) of the semiconductor laser apparatus  200  passes; 
         FIG. 8  is an exploded perspective view of a semiconductor laser apparatus  210  in which a base  10  and a sealing member  20  are separated from each other; 
         FIG. 9  is an exploded perspective view of a semiconductor laser apparatus  220  in which a base  10  and a sealing member  20  are separated from each other; 
         FIG. 10  is a longitudinal sectional view taken along the center line of the semiconductor laser apparatus  220  in the width direction; 
         FIG. 11  is a longitudinal sectional view of the vicinity of a through hole  11   c  ( 11   d ) in the semiconductor laser apparatus  220 ; and 
         FIG. 12  is a schematic diagram showing the structure of an optical pickup  300  including the semiconductor laser apparatus  210 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention are hereinafter described with reference to the drawings. 
     First Embodiment 
     A semiconductor laser apparatus  100  according to a first embodiment of the present invention is now described. As shown in  FIGS. 1 to 3 , this semiconductor laser apparatus  100  includes a package  30  having a base  10  and a sealing member  20 , and a blue-violet semiconductor laser chip  40  having a lasing wavelength of about 405 nm is sealed in the package. The blue-violet semiconductor laser chip  40  is an example of the “semiconductor laser chip” in the present invention. 
     The base  10  is made of kovar, which is a Fe—Ni—Co alloy with a Ni—Au plated surface, and has a disc-shaped stem  11  and a protruding block  12  protruding forward from a front surface  11   a  of the stem  11 . 
     Lead frames  13 ,  14  and  15  extending backward (in a direction A 2 ) are provided on a rear surface  11   b  of the stem  11 . The lead frame  13  is formed integrally with the base  10  and electrically connected with the base  10 . Through holes  11   c  and  11   d  are formed on the same plane parallel to an upper surface (surface on a C 2  side) of the protruding block  12  in the stem  11 . The lead frames  14  and  15  pass through the through holes  11   c  and  11   d  and extend to the front (on an A 1  side) of the stem  11 . The lead frames  14  and  15  are bonded with adhesives  50  and  51  made of epoxy resin filled into the through holes  11   c  and  11   d  in a state electrically insulated from the base  10 . The through holes  11   c  and  11   d  are examples of the “opening” in the present invention. 
     Silicon resins  60  and  61  are filled into front portions of the through holes  11   c  and  11   d  not to expose the adhesives  50  and  51  on the front side. The silicon resins  60  and  61  are examples of the “resin having larger elasticity than the adhesive” in the present invention. Covering agents  70  and  71  each made of an ethylene-polyvinyl alcohol copolymer (EVOH resin) are formed on openings of the through holes  11   c  and  11   d  in the front surface  11   a  not to expose the silicon resins  60  and  61 . In other words, contact interfaces between the silicon resins  60  and  61  and the adhesives  50  and  51  are not exposed to the outside of the package  30 . Contact interfaces between the silicon resins  60  and  61  and the covering agents  70  and  71  are also not exposed to sealed space  31 . In this case, the covering agents  70  and  71  have surfaces coming into contact with the sealed space  31 . The adhesives  50  and  51  are exposed to the outside of the package  30 . A film of EVOH resin is arranged to cover the silicon resins  60  and  61 , and thereafter melted by heat of about 200° C., whereby the covering agents  70  and  71  are formed. 
     The blue-violet semiconductor laser chip  40  is bonded onto the upper surface of the protruding block  12  through a submount  45 . The blue-violet semiconductor laser chip  40  is arranged such that in a pair of cavity facets of the blue-violet semiconductor laser chip  40 , that (light-emitting surface) emitting a laser beam having relatively large light intensity faces frontward (in a direction A 1 ) and that (light-reflecting surface) emitting a laser beam having relatively small light intensity faces backward (in the direction A 2 ). 
     An n-side electrode (not shown) formed on a lower surface (surface on a C 1  side) of the blue-violet semiconductor laser chip  40  is electrically connected with the protruding block  12  and the lead frame  13  through the submount  45 . A p-side electrode (not shown) formed on an upper surface (surface on the C 2  side) of the blue-violet semiconductor laser chip  40  is electrically connected with a front end of the lead frame  14  through a metal wire  80  made of Au or the like. 
     A photodiode (PD)  90  is mounted on the front surface  11   a  of the stem  11 . The photodiode (PD)  90  is an example of the “photodetector” in the present invention. The PD  90  is arranged such that a front surface (photodetecting surface) thereof is opposed to the light-reflecting surface of the blue-violet semiconductor laser chip  40 . An n-side electrode (not shown) formed on a rear surface of the PD  90  is electrically connected with the stem  11  and the lead frame  13  through a conductive adhesive  52  containing a volatile component or the like. A p-side electrode (not shown) formed on the front surface of the PD  90  is electrically connected with a front end of the lead frame  15  through a metal wire  81  made of Au or the like. A covering agent  72  made of EVOH resin is formed between a side surface of the PD  90  and the front surface  11   a  of the stem  11  to cover the conductive adhesive  52 . Similarly to the covering agent  71 , a film of EVOH resin is arranged around the PD  90 , and thereafter melted by heat of about 200° C., whereby the covering agent  72  is formed. 
     The sealing member  20  is made of kovar with a Ni-plated surface and formed in the form of a cap, which opens on the rear side. The sealing member  20  has a side wall portion  20   a  cylindrically formed, a bottom portion  20   b  closing the front side of the side wall portion  20   a , and a mounting portion  20   c  formed on the rear side of the side wall portion  20  and jutting out toward the outer periphery similarly to the outer shape of the stem  11 . 
     A circular hole  20   e  is provided in a center of the bottom portion  20   b  of the sealing member  20 , and a rectangular light transmission portion  21  made of borosilicate glass is bonded to cover the hole  20   e  from the front side. The hole  20   e  is an example of the “opening” in the present invention. A covering agent  73  made of EVOH resin is formed between a rear surface of the light transmission portion  21  and a front surface of the bottom portion  20   b  excluding the hole  20   e.  A clearance between the light transmission portion  21  and the bottom portion  20   b  is filled up with the covering agent  73  to be sealed, and the covering agent  73  has a surface (annular inner surface) coming into contact with the sealed space  31 . A film of EVOH resin having an opening with a shape substantially identical to that of the hole  20   e  is held between the light transmission portion  21  and the bottom portion  20   e,  and thereafter melted by heat of about 200° C., whereby the covering agent  73  can be formed. An adhesive  53  made of epoxy resin is formed between a side surface of the light transmission portion  21  and the bottom portion  20   b  of the sealing member  20 , and the light transmission portion  21  and the bottom portion  20   b  are fixed with this adhesive  53 . Thus, a surface of the adhesive  53  partially forms an outer surface of the package  30 . The adhesive  53  can be formed by being applied onto the periphery of the light transmission portion  21  after the covering agent  73  is formed. The covering agent  73  comes into contact with the adhesive  53  and covers the adhesive  53 . A contact interface between the covering agent  73  and the adhesive  53  is located in the vicinity of a boundary between a bonded region of the sealing member  20  and the light transmission portion  21  and the outer surface of the package. 
     The base  10  and the sealing member  20  are sealed with a covering agent  74  made of EVOH resin formed between the front surface  11   a  of the stem  11  and the mounting portion  20   c  of the sealing member  20 , and the covering agent  74  has a surface (annular inner surface) coming into contact with the sealed space  31 . A film of EVOH resin having a substantially identical shape to the mounting portion  20   c  is held between the front surface  11   a  and the mounting portion  20   c,  and thereafter melted by heat of about 200° C., whereby the covering agent  74  can be formed. An adhesive  54  made of epoxy resin is formed between a side surface of the mounting portion  20   c  and a side surface of the stem  11 , and the mounting portion  20   c  and the stem  11  are fixed with this adhesive  54 . Thus, a surface of the adhesive  54  partially forms the outer surface of the package  30 . The adhesive  54  can be formed by being applied onto a region between the side surface of the mounting portion  20   c  and the side surface of the stem  11  after the covering agent  74  is formed. The covering agent  74  comes into contact with the adhesive  54  and covers the adhesive  54 . A contact interface between the covering agent  74  and the adhesive  54  is located in the vicinity of a boundary between a bonded region of the base  10  and the sealing member  20  and the outer surface of the package. Thus, the semiconductor laser apparatus  100  having the blue-violet semiconductor laser chip  40  sealed in the sealed space  31  of the package  30  surrounded by the base  10  and the sealing member  20  is formed. 
     In the relation between the base  10  and the sealing member  20  of the semiconductor laser apparatus  100 , either the base  10  or the sealing member  20  is an example of the “first member” in the present invention, and either the sealing member  20  or the base  10  is an example of the “second member” in the present invention. In the relation between the base  10  and the lead frames  14  and  15 , the lead frames  14  and  15  are examples of the “first member” in the present invention, and the base  10  is an example of the “second member” in the present invention. In the relation between the sealing member  20  and the light transmission portion  21 , the light transmission portion  21  is an example of the “first member” in the present invention, and the sealing member  20  is an example of the “second member” in the present invention. 
     In the semiconductor laser apparatus  100 , the base  10 , the sealing member  20 , the light transmission portion  21  and the lead frames  14  and  15  constituting the package are bonded with the adhesives  50 ,  51 ,  53  and  54 , and hence a manufacturing process for the semiconductor laser apparatus  100  can be simplified, and the semiconductor laser apparatus  100  can be manufactured at a lower cost. Further, the members can be strongly bonded to each other. As compared with a case where the members are bonded to each other with low-melting-point glass or the like, the adhesives have high flexibility, and hence the adhesives are rarely influenced by external force. Further, the adhesives  50 ,  51 ,  53  and  54  are covered with the covering agent  70 ,  71 ,  73  and  74  in the sealed space  31 , and hence even if the adhesives  50 ,  51 ,  53  and  54  contain low molecular siloxane or volatile resin components, the low molecular siloxane or the volatile resin components can be inhibited from entering the sealed space  31 . Further, EVOH having excellent gas barrier properties and hardly generating volatile gas is employed as the covering agents  70 ,  71 ,  73  and  74 , and hence the aforementioned gas can be inhibited from entering the sealed space  31 . Consequently, an adherent substance can be inhibited from being formed on a light-emitting surface of the blue-violet semiconductor laser chip  40 , and hence the blue-violet semiconductor laser chip  40  can be easily inhibited from degradation. Especially in the blue-violet semiconductor laser chip  40  having a short lasing wavelength and requiring a higher output power, an adherent substance is easily formed on a laser emitting facet thereof, and hence it is highly effective to cover the adhesives  50 ,  51 ,  53  and  54  with the covering agents  70 ,  71 ,  73  and  74 . 
     In the semiconductor laser apparatus  100 , the covering agents  70 ,  71 ,  73  and  74  are arranged to be closer to the sealed space  31  than the adhesives  50 ,  51 ,  53  and  54  in bonded regions between the members, and hence the adhesives  50 ,  51 ,  53  and  54  are not exposed in the sealed space  31 . Therefore, even if the adhesives  50 ,  51 ,  53  and  54  contain low molecular siloxane or volatile resin components, the covering agents  70 ,  71 ,  73  and  74  arranged to be closer to the sealed space  31  than the aforementioned adhesives can inhibit the components contained in the adhesives  50 ,  51 ,  53  and  54  from directly entering the sealed space  31 . 
     In the semiconductor laser apparatus  100 , the covering agents  70 ,  71 ,  73  and  74  have the surfaces coming into contact with the sealed space  31 , and the adhesives  50 ,  51 ,  53  and  54  have surfaces exposed to the outside of the package  30 . Thus, the covering agents  70 ,  71 ,  73  and  74  covering the adhesives  50 ,  51 ,  53  and  54 , respectively, can partially form an inner surface of the sealed space  31 . Further, the base  10 , the sealing member  20  and the light transmission portion  21  can be reliably bonded with the adhesives  50 ,  51 ,  53  and  54  in not only the bonded regions between the base  10 , the sealing member  20  and the light transmission portion  21  but also the outer surface of the package  30 . 
     In the semiconductor laser apparatus  100 , the covering agents  73  and  74  are arranged to come into contact with the adhesives  53  and  54  and cover the adhesives  53  and  54 , respectively. Thus, the covering agents  73  and  74  can directly inhibit the components contained in the adhesives  53  and  54  from entering the sealed space  31 . 
     In the semiconductor laser apparatus  100 , the contact interfaces between the covering agents  73  and  74  and the adhesives  53  and  54 , respectively, are located in the vicinity of the outer surface of the package  30  or on substantially the same plane, and hence the covering agents  73  and  74  formed on the bonded regions between the base  10 , the sealing member  20  and the light transmission portion  21  do not protrude to the outside of the package  30 . Therefore, the base  10 , the sealing member  20  and the light transmission portion  21  can be more reliably bonded with the adhesives  53  and  54  in the substantially flat outer surface of the package  30 . 
     In the semiconductor laser apparatus  100 , the covering agents  70 ,  71 ,  73  and  74  continuously cover the adhesives  50 ,  51 ,  53  and  54  along the bonded regions between the base  10 , the lead frames  14  and  15 , the sealing member  20  and the light transmission portion  21  not to expose the adhesives  50 ,  51 ,  53  and  54  in the sealed space  31 . Thus, the aforementioned covering agents can reliably prevent the adhesives provided along the bonded regions from being exposed in the sealed space  31 , and hence the components contained in the adhesives  50 ,  51 ,  53  and  54  can be reliably prevented from entering the sealed space  31 . 
     The semiconductor laser apparatus  100  is formed as described above, and hence materials for the base  10 , the lead frames  14  and  15 , the sealing member  20  and the light transmission portion  21  can be easily selected on the basis of shapes and functions of these members. 
     The semiconductor laser apparatus  100  is formed as described above, and hence the package can be easily sealed also in the light transmission portion  21  (window portion) for emitting a laser beam such that the component contained in the adhesive  53  is inhibited from entering the sealed space  31 . 
     In the semiconductor laser apparatus  100 , the light transmission portion  21  is bonded onto an outer surface of the bottom portion  20   b  of the sealing member  20  constituting the package, and the light transmission portion  21  and the sealing member  20  are bonded to each other with the adhesive  53  and the covering agent  73  arranged on a surface of the sealing member  20  other than the hole  20   e.  Thus, the package can be easily sealed with the light transmission portion  21  (window portion) for emitting a laser beam without harmful effects such as contact of the laser beam with the covering agent  73 . 
     The semiconductor laser apparatus  100  is formed as described above, and hence the package can be easily sealed also in a wiring portion (through hole  11   c ) for power supply to the semiconductor laser chip  40  and a wiring portion (through hole  11   d ) for a monitor signal from the PD  90  such that the components contained in the adhesives  50  and  51  are inhibited from entering the sealed space  31 . 
     In the bonded regions of the lead frames  14  and  15  and the stem  11 , the silicon resins  60  and  61  are arranged between the adhesives  50  and  51  and the covering agents  70  and  71 , respectively. Thus, even if cracks or separation is generated in the adhesives  50  and  51  due to external impact or a difference in thermal expansion coefficient between the lead frames  14  and  15  and the stem  11 , the silicon resins  60  and  61  can enter clearances generated due to the cracks or the separation, and hence airtightness and reliability are further improved. 
     In the semiconductor laser apparatus  100 , the covering agent  72  made of EVOH is formed in the periphery of the PD  90  to cover the conductive adhesive  52  fixing the PD  90 . Thus, even if the conductive adhesive  52  contains low molecular siloxane or a volatile resin component, the low molecular siloxane or the volatile resin component can be inhibited from entering the sealed space  31 . Consequently, an adherent substance can be inhibited from being formed on the photodetecting surface of the photodetector in addition to the laser emitting facet, and hence output of a laser beam from the semiconductor laser chip can be accurately controlled with this photodetector. 
     In the semiconductor laser apparatus  100 , the covering agents  70 ,  71 ,  73  and  74  cover the adhesives  50 ,  51 ,  53  and  54  made of epoxy resin containing a volatile component, respectively, and hence the effects of the present invention can be effectively achieved. 
     Modification of First Embodiment 
     A semiconductor laser apparatus  110  according to a modification of the first embodiment is now described. In this semiconductor laser apparatus  110 , a light transmission portion  21  is mounted on the inside of a bottom portion  20   b  of a sealing member  20 , as shown in  FIG. 4 . In this case, an adhesive  53  fixing the light transmission portion  21  and the bottom portion  20   b  to each other is formed between a front surface of the light transmission portion  21  and an inner surface of the bottom portion  20   b  excluding a hole  20   e.  A covering agent  73  covering the adhesive  53  is formed between a side surface of the light transmission portion  21  and the inner surface of the bottom portion  20   b  on the inside of the sealing member  20  and arranged not to expose the adhesive  53  to the inside of the sealing member  20 . The remaining structure is similar to that of the semiconductor laser apparatus  100 . 
     The semiconductor laser apparatus  110  also achieves effects similar to those of the semiconductor laser apparatus  100 . 
     Second Embodiment 
     A semiconductor laser apparatus  200  according to a second embodiment of the present invention is now described. 
     As shown in  FIGS. 5 to 7 , a base  10  of this semiconductor laser apparatus  200  is made of a frame-shaped metal plate of phosphor bronze having a thickness of about 0.4 mm with a Ni-plated surface. A groove-shaped recess portion  10   a,  which opens on the front side (in a direction A 1 ), the rear side (in a direction A 2 ) and the upper side (in a direction C 2 ), is formed by bending in the base  10 . Regions, which open on the front side and the rear side of the recess portion  10   a,  are examples of the “opening” in the present invention. A lead frame  13  extending backward is integrally formed on a bottom surface  10   b  of the base  10 . Side surfaces  10   c  and  10   d  of the recess portion  10   a  have the same height, and mounting portions  10   e  and  10   f  extending parallel to the bottom surface  10   b  are formed above the side surfaces  10   c  and  10   d.    
     A light transmission portion  21  made of borosilicate glass with a shape identical to that of the cross section of the recess portion  10   a  is fitted into a front portion of the recess portion  10   a.  A covering agent  73  made of EVOH resin with a thickness of about 0.5 mm is formed between the light transmission portion  21  and the bottom surface  10   b  and the side surfaces  10   c  and  10   d  of the recess portion  10   a.  A clearance between the light transmission portion  21  and the recess portion  10   a  is filled up with the covering agent  73  to seal a package, and the light transmission portion  21  is bonded with the covering agent  73  in the recess portion  21 . 
     A terminal holding portion  55  made of epoxy resin with a shape identical to that of the cross section of the recess portion  10   a  is formed on a rear portion of the base  10 . The terminal holding portion  55  is an example of the “adhesive” in the present invention. A covering agent  71  made of EVOH resin is formed on a front surface  55   a  (surface inside the recess portion  10   a ) of the terminal holding portion  55 . The covering agent  71  covers the front surface  55   a  not to expose the terminal holding portion  55  as viewed from the inside of the recess portion  10   a.  Lead frames  14  and  15  pass through the terminal holding portion  55  and the covering agent  71  on the same plane parallel to the bottom surface  10   b  of the recess portion  10   a  and extend to the inside of the recess portion  10   a.  The lead frames  14  and  15  are held in a state electrically insulated from each other by the terminal holding portion  55 . The terminal holding portion  55  is formed by pouring epoxy resin into the rear portion of the recess portion  10   a  while holding the lead frames  14  and  15  at prescribed positions. The covering agent  71  is formed by applying EVOH resin onto the front surface  55   a  of the terminal holding portion  55  in a state where the base  10  is heated to about 220° C. after the terminal holding portion  55  is formed. 
     A blue-violet semiconductor laser chip  40  is bonded onto the bottom surface  10   b  of the recess portion  10   a  through a submount  45 . The blue-violet semiconductor laser chip  40  is arranged on a front portion of an upper surface of the submount  45 , and a PD  90  is bonded onto a rear portion of the upper surface of the submount  45  such that a photodetecting surface (not shown) faces upward. 
     A sealing member  20  is made of a metal plate  20   a  of nickel silver with a thickness of about 15 μm and has a shape similar to the planar shape of the base  10 . A covering agent  74  made of EVOH resin with a thickness of about 0.5 mm is formed on a lower surface of the sealing member  20 , and the sealing member  20  is bonded onto upper surfaces of the mounting portions  10   e  and  10   f  of the base  10 , the terminal holding portion  55  and the light transmission portion  21  through the covering agent  74 . 
     Thus, the semiconductor laser apparatus  200  having the blue-violet semiconductor laser chip  40  sealed in sealed space  31  of the package  30  surrounded by the base  10 , the terminal holding portion  55 , the light transmission portion  21  and the sealing member  20  is formed. The remaining structure of the semiconductor laser apparatus  200  is similar to that of the semiconductor laser apparatus  100 . 
     In the relation between the sealing member  20  and the base  10 , the lead frames  14  and  15  and the light transmission portion  21  of the semiconductor laser apparatus  200 , either the sealing member  20  or the base  10 , the lead frames  14  and  15  and the light transmission portion  21  are examples of the “first member” in the present invention, and either the base  10 , the lead frames  14  and  15  and the light transmission portion  21  or the sealing member  20  is an example of the “second member” in the present invention. In the relation between the base  10  and the lead frames  14  and  15 , the lead frames  14  and  15  are examples of the “first member” in the present invention, and the base  10  is an example of the “second member” in the present invention. In the relation between the base  10  and the light transmission portion  21 , the light transmission portion  21  is an example of the “first member” in the present invention, and the base  10  is an example of the “second member” in the present invention. 
     In the semiconductor laser apparatus  200 , the base  10  and the sealing member  20  each are made of a metal plate, and hence the semiconductor laser apparatus  200  can be manufactured at a lower cost. Further, the light transmission portion  21  and the sealing member  20  are bonded with the covering agents  73  and  74 , respectively. In other words, no adhesive is employed in those bonded regions, and hence a volatile resin component contained in an adhesive hardly enters the sealed space  31 . Further, the semiconductor laser apparatus  200  can be manufactured at a lower cost. 
     The remaining effects of the semiconductor laser apparatus  200  are similar to those of the semiconductor laser apparatus  100 . 
     First Modification of Second Embodiment 
     A semiconductor laser apparatus  210  according to a first modification of a second embodiment is now described. In this semiconductor laser apparatus  210 , a blue-violet semiconductor laser chip  40  having a lasing wavelength of about 405 nm, a red semiconductor laser chip  41  having a lasing wavelength of about 650 nm and an infrared semiconductor laser chip  42  having a lasing wavelength of about 780 nm are aligned on a submount  45  and bonded thereto, as shown in  FIG. 8 . Laser beams are emitted parallel to an anterior direction (direction A 1 ) from these semiconductor laser chips. The blue-violet semiconductor laser chip  40 , the red semiconductor laser chip  41  and the infrared semiconductor laser chip  42  are examples of the “semiconductor laser chip” in the present invention. 
     In the semiconductor laser apparatus  210 , four lead frames  14 ,  15 ,  16  and  17  pass through a terminal holding portion  55  and a covering agent  71  on the same plane parallel to a bottom surface  10   b  of a recess portion  10   a  are arranged in this order in the width direction (direction B 1 ). The lead frame  14  is connected with the blue-violet semiconductor laser chip  40  through a metal wire  80 , the lead frame  15  is connected with a PD  90  through a metal wire  81 , the lead frame  16  is connected with the red semiconductor laser chip  41  through a metal wire  82  and the lead frame  17  is connected with the infrared semiconductor laser chip  42  through a metal wire  83 . The remaining structure is similar to that of the semiconductor laser apparatus  200 . 
     In the semiconductor laser apparatus  210 , laser beams of three different wavelengths can be emitted. The remaining effects of the semiconductor laser apparatus  210  are similar to those of the semiconductor laser apparatus  200 . 
     Second Modification of Second Embodiment 
     A semiconductor laser apparatus  220  according to a second modification-of a second embodiment is now described. A base  10  of this semiconductor laser apparatus  220  includes a box-shaped recess portion  10   a  formed with a front surface  10   g  and a rear surface  10   i  on the front side (in a direction A 1 ) and the rear side (in a direction A 2 ), respectively in place of the groove-shaped recess portion  10   a  of the semiconductor laser apparatus  200 , as shown in  FIGS. 9 and 10 . The recess portion  10   a  is formed by pressing a metal plate. 
     A circular hole  10   h  is provided in the center of the front surface  10   g  of the recess portion  10   a,  and a rectangular light transmission portion  21  is provided to cover the hole  10   h  from the front side. Methods of fixing and sealing the light transmission portion  21  are similar to those of the light transmission portion  21  of the semiconductor laser apparatus  100 . 
     As shown in  FIG. 11 , through holes  11   c  and  11   d  are formed on the same plane parallel to a bottom surface  10   b  of the recess portion  10   a  in the rear surface  10   i  of the recess portion  10   a.  Lead frames  14  and  15  pass through the through holes  11   c  and  11   d  and extend to the inside of the recess portion  10   a.  The lead frames  14  and  15  are held in a state electrically insulated from each other by adhesives  50  and  51  made of epoxy resin filled into the through holes  11   c  and  11   d.  Covering agents  70  and  71  made of EVOH resin are formed in openings of the through holes  11   c  and  11   d  inside the recess portion  10   a  to cover the adhesives  50  and  51 . The hole  10   h  and the through holes  11   c  and  11   d  are examples of the “opening” in the present invention. 
     A mounting portion  10   e  of an upper surface of the base  10  is formed in a frame shape surrounding the recess portion  10   a,  and a lead frame  13  is integrally formed on a rear portion of the mounting portion  10   e.  A sealing member  20  is bonded onto an upper surface of the mounting portion  10   e  through a covering agent  74 . An adhesive  54  made of epoxy resin is formed on a side surface of the sealing member  20  and a side surface of the mounting portion  10   e  of the base  10 , whereby the sealing member  20  and the base  10  are bonded to each other. The remaining structure of the semiconductor laser apparatus  220  is similar to that of the semiconductor laser apparatus  200 . 
     In the relation between the base  10  and the sealing member  20  of the semiconductor laser apparatus  220 , either the base  10  or the sealing member  20  is an example of the “first member” in the present invention, and either the sealing member  20  or the base  10  is an example of the “second member” in the present invention. In the relation between the lead frames  14  and  15  and the light transmission portion  21  and the base  10 , the lead frames  14  and  15  and the light transmission portion  21  are examples of the “first member” in the present invention, and the base  10  is an example of the “second member” in the present invention. 
     In the semiconductor laser apparatus  220 , the light transmission portion  21  and the sealing member  20  are bonded to the base  10  with adhesives  53  and  54 , and hence the light transmission portion  21  and the sealing member  20  are more strongly fixed and the reliability is high. Further, the aforementioned adhesives  53  and  54  are covered with covering agents  73  and  74  as viewed from the inside of sealed space  31 , and hence even if the adhesives  53  and  54  contain low molecular siloxane or a volatile resin component, the low molecular siloxane or the volatile resin component can be inhibited from entering the sealed space  31 . 
     In the semiconductor laser apparatus  220 , contact interfaces between the covering agents  70  and  71  and the adhesives  50  and  51 , respectively, extend out from bonded regions of the base  10  and the lead frames  14  and  15  toward the sealed space  31 , and hence the covering agents  70  and  71  do not protrude toward the bonded regions of the base  10  and the lead frames  14  and  15 . Therefore, the base  10  and the lead frames  14  and  15  can be reliably bonded with the adhesives  50  and  51  by sufficiently utilizing the bonded regions of the base  10  and the lead frames  14  and  15 . 
     In the semiconductor laser apparatus  220 , the sealing member  20  and the base  10  are bonded to each other with the adhesive  54 , and the covering agent  74  covering the adhesive  54  extends onto an inner surface (back surface) of the sealing member  20  other than a bonded region bonded to the base  10 . Thus, the covering agent  74  can be easily formed on one surface (inner surface) of the sealing member  20  in a manufacturing process. Further, the inner surface of the sealing member  20  can be reliably covered with the covering agent  74  regardless of a bonding position (mounting method) of the sealing member  20  to the base  10 . 
     The remaining effects of the semiconductor laser apparatus  220  are similar to those of the semiconductor laser apparatus  200 . 
     Third Embodiment 
     An optical pickup  300  according to a third embodiment of the present invention is now described. The optical pickup  300  is an example of the “optical apparatus” in the present invention. 
     The optical pickup  300  includes the semiconductor laser apparatus  210  according to the first modification of the second embodiment, an optical system  320  adjusting laser beams emitted from the semiconductor laser apparatus  210  and a light detection portion  330  receiving the laser beams, as shown in  FIG. 12 . 
     The optical system  320  has a polarizing beam splitter (PBS)  321 , a collimator lens  322 , a beam expander  323 , a λ/4 plate  324 , an objective lens  325 , a cylindrical lens  326  and an optical axis correction device  327 . 
     The PBS  321  totally transmits the laser beams emitted from the semiconductor laser apparatus  210 , and totally reflects the laser beams fed back from an optical disc  340 . The collimator lens  322  converts the laser beams emitted from the semiconductor laser apparatus  210  and transmitted through the PBS  321  to parallel beams. The beam expander  323  is constituted by a concave lens, a convex lens and an actuator (not shown). The actuator has a function of correcting wave surface states of the laser beams emitted from the semiconductor laser apparatus  210  by varying a distance between the concave lens and the convex lens in response to a servo signal from a servo circuit described later. 
     The λ/4 plate  324  converts the linearly polarized laser beams, substantially converted to the parallel beams by the collimator lens  322 , to circularly polarized beams. Further, the λ/4 plate  324  converts the circularly polarized laser beams fed back from the optical disc  340  to linearly polarized beams. A direction of linear polarization in this case is orthogonal to a direction of linear polarization of the laser beams emitted from the semiconductor laser apparatus  210 . Thus, the PBS  321  substantially totally reflects the laser beams fed back from the optical disc  340 . The objective lens  325  converges the laser beams transmitted through the λ/4 plate  324  on a surface (recording layer) of the optical disc  340 . An objective lens actuator (not shown) renders the objective lens  325  movable in a focus direction, a tracking direction and a tilt direction in response to servo signals (a tracking servo signal, a focus servo signal and a tilt servo signal) from the servo circuit described later. 
     The cylindrical lens  326 , the optical axis correction device  327  and the light detection portion  330  are arranged to be along optical axes of the laser beams totally reflected by the PBS  321 . The cylindrical lens  326  provides the incident laser beams with astigmatic action. The optical axis correction device  327  is constituted by a diffraction grating and so arranged that spots of zero-order diffracted beams of blue-violet, red and infrared laser beams transmitted through the cylindrical lens  326  coincide with each other on a detection region of the light detection portion  330  described later. 
     The light detection portion  330  outputs a playback signal on the basis of intensity distribution of the received laser beams. The light detection portion  330  has a detection region of a prescribed pattern, to obtain a focus error signal, a tracking error signal and a tilt error signal along with the playback signal. Thus, the optical pickup  300  including the semiconductor laser apparatus  210  is formed. 
     In this optical pickup  300 , blue-violet, red and infrared laser beams are independently emitted from the blue-violet semiconductor laser chip  40 , the red semiconductor laser chip  41  and the infrared semiconductor laser chip  42  sealed in the semiconductor laser apparatus  210 . The laser beams emitted from the semiconductor laser apparatus  210  are adjusted by the PBS  321 , the collimator lens  322 , the beam expander  323 , the λ/4 plate  324 , the objective lens  325 , the cylindrical lens  326  and the optical axis correction device  327  as described above, and thereafter applied onto the detection region of the light detection portion  330 . 
     When data recorded in the optical disc  340  is play backed, the laser beam emitted from the semiconductor laser chip  40  ( 41 ,  42 ) selected depending on the type of the optical disc  340  is controlled to have constant power and applied to the recording layer of the optical disc  340 , so that the playback signal output from the light detection portion  330  can be obtained. The actuator of the beam expander  323  and the objective lens actuator driving the objective lens  325  can be feedback-controlled by the focus error signal, the tracking error signal and the tilt error signal simultaneously output. 
     When data is recorded in the optical disc  340 , the laser beam emitted from the semiconductor laser chip  40  ( 41 ,  42 ) selected depending on the type of the optical disc  340  is controlled in power on the basis of the data to be recorded and applied to the optical disc  340 . Thus, the data can be recorded in the recording layer of the optical disc  340 . Similarly to the above, the actuator of the beam expander  323  and the objective lens actuator driving the objective lens  325  can be feedback-controlled by the focus error signal, the tracking error signal and the tilt error signal output from the light detection portion  330 . 
     Thus, the data can be recorded in or played back from the optical disc  340  with the optical pickup  300  including the semiconductor laser apparatus  210 . 
     The optical pickup  300  includes the aforementioned semiconductor laser apparatus  210 , and hence the low-cost and reliable optical pickup  300  capable of enduring the use for a long time can be obtained. The remaining effects of the optical pickup  300  are similar to those of the semiconductor laser apparatus  210 . 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. 
     For example, while the silicon resins  60  and  61  are formed between the adhesives  50  and  51  and the covering agents  70  and  71 , respectively, in the semiconductor laser apparatus  100 , the silicon resins  60  and  61  may not be formed therebetween. Alternatively, there may be clearances in regions where the silicon resins  60  and  61  are formed. Alternatively, the silicon resins  60  and  61  may be formed on openings of the through holes  11   c  and  11   d  (outside the package  30 ) in the rear surface  11   b.  The same is true in bonded regions where other members are bonded. Alternatively, resin made of another resin material such as rubber and having larger elasticity than the adhesives  50  and  51 , for example, can be employed in place of silicon resin. 
     Bonded portions of all the members of the semiconductor laser apparatus may not be bonded with the adhesives, but part of the bonded portions may be bonded by conventional resistance welding or with kovar glass to be hermetically sealed. While the light transmission portion  21  and the sealing member  20  are bonded only with the covering agents  73  and  74  in the semiconductor laser apparatuses  200  and  210 , the adhesives  53  and  54  may be employed together with the covering agents  73  and  74 , similarly to the semiconductor laser apparatus  220 . 
     A light curing or thermosetting material other than epoxy resin can be employed as the adhesives. A material with low water vapor permeability is preferably employed as the adhesives or an inorganic binder such as silica particles is preferably mixed in order to prevent entry of moisture into the package. Further, an oxide film of SiO 2 , Al 2 O 3  or the like or a metal film of Au, Ni, Cr or the like is more preferably formed as a gas barrier film on the surfaces of the adhesives. Thus, the EVOH resin can be prevented from absorbing moisture, and hence gas barrier properties can be prevented from decrease. 
     The wavelength of a laser beam emitted from the semiconductor laser chip may not be limited to the aforementioned wavelength, and semiconductor laser chips having another wavelengths may be combined and sealed also in the semiconductor laser apparatus  210  having the sealed different semiconductor laser chips. Three-wavelength laser beams of red (R), green (G) and blue (B), for example, are selected, whereby an RGB three-wavelength laser apparatus can be formed. Further, a projector or a display can be formed as an optical apparatus mounted with this RGB three-wavelength laser apparatus. 
     In addition to the aforementioned materials, an alloy of Al, Cu, Sn, Ni, stainless steel, Mg and the like can be employed as materials for the base, the lead frames and the sealing member. Ni-plated resin (polyphenylene sulfide, polyamide, a liquid crystal polymer or the like, for example) may be employed for the sealing member. Thus, the sealing member can be manufactured at a lower cost. 
     In addition to the aforementioned material, another type of glass or a translucent material can be employed as a material for the light transmission portion. A single layer or multilayer metal oxide film (dielectric film) of Al 2 O 3 , SiO 2 , ZrO 2  or the like may be formed on the surface of the light transmission portion.