Abstract:
Provided is an optical module which can be efficiently manufactured. The optical module of the present invention comprises a housing having a lower casing, an upper casing, and a cover; an optical sub-assembly; a circuit board; and a block. The lower casing includes a receptacle mating with an optical connector, and a mount. The upper casing engages with the lower casing. The cover covers the upper casing. The optical sub-assembly optically couples with the optical connector in the receptacle. The circuit board is electrically connected to the optical sub-assembly and mounted to the mount of the lower casing. The block is mounted to the lower casing, and defines relative positions of the lower casing, upper casing, optical sub-assembly, and circuit board.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an optical module including a positioning member for positioning an optical device and a circuit board formed with a circuit for driving the optical device.  
           [0003]    2. Related Background Art  
           [0004]    Known is an optical module constituted by a circuit board implemented with an optical sub-assembly and its driving circuit, a signal amplifying circuit, and the like, and a housing enclosing them. This optical module comprises a receptacle for receiving an optical connector provide data leading end of an optical fiber, whereby optical coupling is achieved between the optical sub-assembly and the optical connector within the receptacle. For optical coupling, the position of the optical sub-assembly must be determined with respect to the optical connector. For positioning the optical sub-assembly with respect to the receptacle, conventional optical modules form the receptacle with an opening for inserting the optical sub-assembly and insert the optical device into the opening, while defining the shape of the receptacle such that the relative position of the optical connector is determined with respect to the opening, whereby optical coupling is achieved between them (see, for example, U.S. Pat. No. 6,335,869).  
           [0005]    [0005]FIG. 10 is an exploded perspective view showing an example of a conventional optical module  60 . Conventionally, optical sub-assemblies  62  are inserted into openings  64  of a housing  61 , a circuit board  63  is enclosed in the housing  61 , and then lead pins of the optical sub-assemblies  62  and the circuit board  63  are fixed to each other.  
         SUMMARY OF THE INVENTION  
         [0006]    However, assembly efficiency is inferior in the method comprising the steps of separately setting the optical sub-assemblies  62  and the circuit board  63  into the housing  61  and then bonding them to each other.  
           [0007]    Therefore, it is an object of the present invention to provide an optical module having an efficient assembling procedure.  
           [0008]    The optical module in accordance with one aspect of the present invention comprises a housing having a lower casing including a receptacle to mate with an optical connector, and a mount, an upper casing to engage the lower casing, and a cover for covering the upper casing; an optical sub-assembly optically coupling with the optical connector in the receptacle; a circuit board electrically connected to the optical sub-assembly and mounted on the mount of the lower casing; and a block, mounted on the lower casing, for defining relative positions of the lower casing, upper casing, optical sub-assembly, and circuit board.  
           [0009]    According to the present invention, the block can position the circuit board and optical sub-assembly, whereby the circuit board and the optical sub-assembly can be positioned with respect to the upper and lower casings together with the block. Hence, prior to the completion of assembling, the circuit board and the optical sub-assembly can be fixed to each other in the final positional relationship, thus providing an optical module with efficient assembling.  
           [0010]    The optical module in accordance with another aspect comprises an optical sub-assembly mounted with an optical device; a circuit board electrically connected to the optical sub-assembly; a lower casing having a receptacle for receiving an optical connector holding an optical fiber, and a mount for mounting the circuit board; an upper casing to engage the lower casing; and a resin block for defining positions of the optical sub-assembly, circuit board, lower casing, and upper casing. The receptacle includes an abutting surface having an opening for receiving one end of the optical sub-assembly. The block comprises a front wall including one surface, in contact with the abutting surface, having an opening corresponding to the opening of the receptacle and receiving one end of the optical sub-assembly; a center wall; and a pair of side walls disposing the center wall therebetween. The center wall has a holding portion for holding the circuit board. Each of the pair of side walls has a pressing portion for pressing the circuit board. Holding the circuit board between the holding portion and pressing portions defines relative positions of the block and circuit board. The mount in the lower casing provides a projection. The block is held between one side face of the projection and the abutting surface. A side wall of the block provides a first cutout. A side wall of the lower casing provides a second cutout. The upper casing is formed with first and second protrusions. The first and second cutouts engage with the first and second protrusions, respectively, thereby defining relative positions of the lower casing, upper casing, and block.  
           [0011]    According to this aspect, inserting the optical sub-assembly into the opening of the front wall and holding the circuit board between the holding portion and pressing portions can position the optical sub-assembly and circuit board with respect to the block. Therefore, before being assembled into the casings, the circuit board and the optical sub-assembly can be fixed to each other in the final positional relationship within the casings. Also, holding the block between the abutting surface of the receptacle and the projection in the lower casing can easily position the block with respect to the lower casing. Further, causing the first and second cutouts to engage with the first and second protrusions, respectively, can easily determine the relative positions of the lower casing, upper casing, and block. Hence, an optical module with easily assembled configuration.  
           [0012]    The optical module in accordance with still another aspect comprises an optical sub-assembly having an optical device; a circuit board electrically connected to the optical sub-assembly; a lower casing having a receptacle for receiving an optical connector holding an optical fiber, and a mount for mounting the circuit board; an upper casing to engage with the lower casing; and a resin block for defining positions of the optical sub-assembly, circuit board, lower casing, and upper casing. The receptacle includes an abutting surface having an opening for receiving one end of the optical sub-assembly. The block comprises a front wall including one surface, in contact with the abutting surface, having an opening corresponding to the opening of the receptacle and receiving one end of the optical sub-assembly; a center wall; and a pair of side walls disposing the center wall therebetween. The center wall has a holding portion for holding the circuit board. Each of the pair of side walls has a pressing portion for pressing the circuit board. Holding the circuit board between the holding portion and pressing portions defines relative positions of the block and circuit board. An inner face of the upper casing provides a projection. The center wall of the block provides a cutout. One surface of the projection and one surface of the cutout of the center wall come into contact with each other, whereby the block is held between the projection and the abutting surface of the receptacle. A side wall of the block provides a first cutout. A side wall of the lower casing provides a second cutout. The upper casing provides first and second protrusions. The first and second cutouts engage with the first and second protrusions, respectively, thereby defining relative positions of the lower casing, upper casing, and block.  
           [0013]    According to this aspect, inserting the optical sub-assembly into the opening of the front wall and holding the circuit board between the holding portion and pressing portions can position the optical sub-assembly and circuit board with respect to the block. Therefore, before being assembled in the casings, the circuit board and the optical sub-assembly can be fixed to each other in the final positional relationship within the casings. Also, holding the block between the abutting surface of the receptacle in the lower casing and the projection in the upper casing can easily position the block with respect to the lower casing. Further, engaging the first and second cutouts with the first and second protrusions, respectively, can easily determine the relative positions of the lower casing, upper casing, and block. Hence, an optical module which can be easily assembled is provided.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is an exploded perspective view showing the optical module in accordance with a first embodiment;  
         [0015]    [0015]FIG. 2 is a perspective view showing the optical module in accordance with the first embodiment;  
         [0016]    [0016]FIGS. 3A and 3B are perspective views showing a block;  
         [0017]    [0017]FIG. 4 is a side view showing a state where an optical sub-assembly is accommodated in a lower casing;  
         [0018]    [0018]FIGS. 5A and 5B are views showing respective steps of making the assembly;  
         [0019]    [0019]FIG. 6 is a perspective view showing the assembly;  
         [0020]    [0020]FIG. 7 is a partial perspective view showing the lower casing in the first embodiment;  
         [0021]    [0021]FIGS. 8A, 8B, and  8 C are views showing a process of inserting the assembly into the lower casing;  
         [0022]    [0022]FIG. 9 is a partial perspective view showing the upper casing in the first embodiment;  
         [0023]    [0023]FIG. 10 is a perspective view showing a conventional optical module; and  
         [0024]    [0024]FIG. 11 is a perspective view showing the upper casing in a second embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    In the following, preferred embodiments of the positioning member and optical module of the present invention will be explained in detail with reference to the drawings. In the explanation, elements identical to each other will be referred to with numerals identical to each other without overlapping descriptions.  
         [0026]    First Embodiment  
         [0027]    The optical module  1  of a first embodiment of the present invention will be explained. FIG. 1 is an exploded perspective view of the optical module  1 , whereas FIG. 2 is a perspective view of the optical module  1 . The optical module  1  comprises a transmitting optical sub-assembly  21   a  and a receiving optical sub-assembly  21   b  (collectively referred to as “optical sub-assembly  21 ”), a circuit board  20  on which is formed a circuit for driving the optical sub-assembly  21 , and a housing  30  for encasing the optical sub-assembly  21  and circuit board  20 . The optical sub-assembly  21  and the circuit board  20  are electrically connected to each other by leads extending from the optical sub-assembly  21 .  
         [0028]    The housing  30  comprises a lower casing  31  for receiving the optical sub-assembly  21  and circuit board  20 , an upper casing  37 , and a cover  32  for covering the lower casing  31  and upper casing  37 .  
         [0029]    The lower casing  31  has a mount  31   h  for mounting the block  10 , including a mounting surface  31   i  for mounting the circuit board  20 , and a receptacle  31   j  disposed at one end of the mount  31   h.    
         [0030]    The receptacle  31   j  has openings  31   m . Each opening  31   m  receives a leading end of the optical sub-assembly  21 . An optical fiber held by an optical connector inserted into the receptacle  31   j  from the other end is optically coupled to the optical sub-assembly  21  within the opening  31   m . In this embodiment, the receptacle  31   j  is formed with two openings  31   m  for receiving the transmitting optical sub-assembly  21   a  and receiving optical sub-assembly  21   b , respectively.  
         [0031]    The transmitting optical sub-assembly  21   a  and the receiving optical sub-assembly  21   b  are inserted into the openings  31   m  formed in the lower casing  31 , whereas the circuit board  20  mounted on the mount  31   h  of the lower casing  31  is stopped by a substrate stopper  36 , whereby the optical sub-assembly  21  and circuit board  20  are secured to the lower casing  31 .  
         [0032]    The circuit board  20  comprises a first substrate  20   a  and a second substrate  20   b . The first substrate  20   a  and second substrate  20   b  are connected to each other by a flexible substrate  20   c . When the circuit board  20  is assembled in the housing  30 , the flexible substrate  20   c  is bent such that the first substrate  20   a  and second substrate  20   b  faces each other. This can realize a two-story structure as shown in FIG. 2.  
         [0033]    The optical module  1  includes a block  10  for positioning the optical sub-assembly  21  and circuit board  20 , and holders  19  for securing the optical sub-assembly  21  with respect to the block  10 . The optical module  1  also includes brackets  33  and a shield  34  which are used for reducing noise affecting the optical sub-assembly  21 . The optical module  1  further includes a cap  35  attached to an end portion opposite from the receptacle  31   j  of the lower casing  31 , a fin  38 , and an actuator  39  for releasing the engagement with a host board to which the optical module  1  is mounted.  
         [0034]    Specifically, the brackets  33  are attached to the outer surface of the optical sub-assembly  21 . The shield  34  has a substantially planar shape and has holes through which end portions of the optical sub-assembly  21  can pass. The shield  34  is attached to one surface of the block  10  which will be explained later.  
         [0035]    The fin  38  transmits the heat generated by the transmitting optical sub-assembly  21   a  itself to the outside of the optical module  1 . One end  38   a  of the fin  38  is disposed at the outer surface of the transmitting optical sub-assembly  21   a , whereas the other end  38   b  is in contact with the upper face of the receptacle  31   j . For enhancing adhesion to the transmitting optical sub-assembly  21   a , a silicone sheet  40  is attached to one end  38   a . For enhancing thermal conductivity, the silicone sheet  40  may contain metal fillers.  
         [0036]    [0036]FIGS. 3A and 3B are perspective views showing the block  10  as seen from respective directions different from each other. As shown in FIG. 3A, the block  10  comprises a mount  11  for mounting the optical sub-assembly  21 , a front wall  12  disposed at one end of the mount  11 , a substrate supporting portion  14  disposed at the other end of the mount  11 , and a substrate pressing portion  15 . The block  10  is molded from a resin.  
         [0037]    The mount  11  is divided into a first region  11   a  for mounting the transmitting optical sub-assembly  21   a , and a second region  11   b  for mounting the receiving optical sub-assembly  21   b.    
         [0038]    The front wall  12  is formed with openings  12   a ,  12   b  into which respective head portions of the transmitting optical sub-assembly  21   a  and receiving optical sub-assembly  21   b  placed on the mount  11  can be inserted. Each of the transmitting optical sub-assembly  21   a  and receiving optical sub-assembly  21   b  has a substantially cylindrical form. The transmitting optical sub-assembly  21   a  and receiving optical sub-assembly  21   b  have respective flanges  21   d ,  21   e , which come into contact with the front wall  12 .  
         [0039]    The first region  11   a  and second region  11   b  of the mount  11  have respective cutouts  11   c ,  11   d . Since the mount  11  has cutouts  11   c ,  11   d , the optical sub-assembly  21  is stably placed on the mount  11 . The mount  11  has a semicircular cross section so as to conform to the outer shape of the optical sub-assembly  21 .  
         [0040]    The side wall  13  is constituted by a pair of outer walls  13   a  and  13   c , and a center wall  13   b  formed therebetween for partitioning the first region  11   a  and second region  11   b.    
         [0041]    A portion of an end face of the center wall  13   b  projects, so as to form the substrate supporting portion  14 . The circuit board  20  is to be positioned on the substrate supporting portion  14 . End faces of the outer walls  13   a  and  13   c  partly project, thereby forming substrate pressing portions  15   a  and  15   b . The rear face of the circuit board  20  is supported by the substrate supporting portion  14 , whereas its front face is pressed by the substrate pressing portions  15   a ,  15   b , whereby the circuit board  20  is positioned.  
         [0042]    [0042]FIGS. 3A and 3B show a configuration in which the substrate supporting portion  14  is formed in the center wall  13   b , whereas the substrate pressing portions  15   a ,  15   b  are formed in the outer walls  13   a ,  13   c , respectively. However, the substrate supporting portion  14  may be formed in both of the outer walls  13   a ,  13   c , whereas the center wall  13   b  may have a substrate pressing portion. The substrate pressing portions  15   a ,  15   b , and the substrate supporting portion  14  may be provided in the same wall as well.  
         [0043]    [0043]FIG. 4 is a side view showing an arrangement where the optical sub-assembly  21  and circuit board  20  positioned by the block  10  are assembled in the lower casing  31 . This drawing does not depict the second substrate  20   b  and flexible substrate  20   c . Referring to FIG. 4, the first substrate  20   a  is positioned by the substrate supporting portion  14  at the rear face and by the substrate pressing portions  15   a ,  15   b  at the front face.  
         [0044]    A method of assembling the optical module  1  will be now explained. First, the transmitting optical sub-assembly  21   a  and receiving optical sub-assembly  21   b  are inserted into the openings  12   a ,  12   b  formed in the front wall  12  of the block  10 , and are pressed against and secured to the front wall  12  by the holders  19 . Subsequently, the circuit board  20  is inserted between the substrate supporting portion  14  and substrate pressing portions  15   a ,  15   b  of the block  10 .  
         [0045]    Then, the optical sub-assembly  21  and circuit board  20  positioned by the block  10  are set to a jig  50  as shown in FIG. 5A. Thereafter, the jig  50  is covered with a cover  52  as shown in FIG. 5B, and leads of the optical sub-assembly  21  and the circuit board  20  are connected to each other with solder. Here, the brackets  33  are also attached to the optical sub-assembly  21 . FIG. 6 shows an assembly  44  manufactured by the foregoing process. This drawing does not depict the second substrate  20   b  and the flexible substrate  20   c.    
         [0046]    Subsequently, the assembly  44  is set in the lower casing  31 . FIG. 7 is a partial perspective view showing the lower casing  31 . The mounting surface  31   i  of the lower casing  31  has a projection  31   e  matching the substrate supporting portion  14  of the block  10 .  
         [0047]    The projection  31   e  comes into contact with a lower portion of the substrate supporting portion  14 , i.e., a surface  13   e  positioned under the substrate supporting portion  14  pf the center wall  13   b  in FIG. 3B.  
         [0048]    The projection  31   e  and the surface  13   e  of the block  10  come into contact with each other, thereby positioning the block  10  with respect to the lower casing  31 . Namely, the block  10  is secured between one end part  31   k  of the receptacle  31   j  and the projection  31   e.    
         [0049]    Since the block  10  is thus positioned with respect to the lower casing  31 , the optical sub-assembly  21  and circuit board  20  secured to the block  10  are also positioned with respect to the lower casing  31 .  
         [0050]    [0050]FIGS. 8A, 8B, and  8 C are views showing a process of inserting the assembly  44  into the lower casing  31 . These drawings do not depict the second substrate  20   b  and the flexible substrate  20   c . First, as shown in FIG. 8A, the assembly  44  is obliquely inserted into the lower casing  31  such that the optical sub-assembly  21  is inserted into the openings  31   m  of the receptacle  31   j  from the inside.  
         [0051]    After the optical sub-assembly  21  is inserted into the openings  31   m , the circuit board  20  is moved toward the mounting surface  30   i  such that the circuit board  20  becomes parallel to the lower face of the lower casing  31  as shown in FIG. 8B.  
         [0052]    Thereafter, the projection  31   e  of the lower casing  31  and the surface  13   e  of the center wall  13   b  of the block  10  are brought into contact with each other, so as to position and secure the optical sub-assembly  21  (see FIG. 8C).  
         [0053]    Here, as shown in FIG. 3B, the block  10  is formed with abutting surfaces  16   a  to  16   d  for bringing the block  10  into contact with the lower casing  31  without any gap.  
         [0054]    The first abutting surface  16   a  is formed between the two openings  12   a ,  12   b  of the front wall  12 . The first abutting surface  16   a  is disposed so as to come into contact with the rear end part  31   k  of the receptacle  31   j.    
         [0055]    The second abutting surfaces  16   b  are formed at the front wall  12  so as to project sideways therefrom.  
         [0056]    The third abutting surfaces  16   c  are formed at the front wall  12  so as to project downward therefrom. The fourth abutting surfaces  16   d  are formed at the respective bottom faces of the outer walls  13   a  and  13   c  so as to project downward therefrom.  
         [0057]    When the assembly  44  is set in the lower casing  31 , the first abutting surface  16   a  comes into contact with the partition  31   a  between the two openings (see FIG. 7).  
         [0058]    The second abutting surfaces  16   b  come into contact with the side walls  31   b  of the lower casing  31 . As a consequence, the block  10  is held between a pair of side walls  31   b.    
         [0059]    The third abutting surfaces  16   c  come into contact with the bottom face  31   c  of the lower casing  31 , whereas the fourth abutting surfaces  16   d  come into contact with edge portions  31   d  of the lower casing  31 , whereby the block  10  is stably held by the lower casing  31 .  
         [0060]    Subsequently, the upper casing  37  is put on the lower casing  31  mounted with the assembly  44 . FIG. 9 is a partial perspective view showing the upper casing  37 .  
         [0061]    The upper casing  37  constitutes an outer case of the optical module  1 . The first substrate  20   a  is held between the upper casing  37  and lower casing  31 , whereas the second substrate  20   b  is mounted thereon.  
         [0062]    As shown in FIG. 9, engagement structures  37   a  to  37   d  are formed on each side of the upper casing  37 . As shown in FIGS. 3A and 3B, both side walls  13   a ,  13   c  of the block  10  have respective cutouts. The protrusions  37   a  are inserted into these cutouts, and press the block  10 . The surfaces  37   b ,  37   c  of the protrusions  37   a  come into contact with the surfaces  12   d ,  12   e  of the block  10  exposed at the cutouts, thereby determining the positions of the block  10  and upper casing  37  with respect to each other in one direction.  
         [0063]    As shown in FIG. 7, on the other hand, both side walls of the lower casing  31  have respective engagement structures  31   n  as cutting out these side walls. The engagement structures  37   d  of the upper casing  37  engage their corresponding engagement structures  31   n  of the lower casing  31 , thereby positioning the upper casing  37  and the lower casing  31  with respect to each other.  
         [0064]    After the upper casing  37  is thus put on, the lower casing  31  is covered with the cover  32 , whereby the optical module  1  is completed.  
         [0065]    Second Embodiment  
         [0066]    The optical module  1   a  in accordance with a second embodiment will now be explained. FIG. 11 is an exploded perspective view of the optical module  1   a  of the second embodiment. As shown in FIG. 11, the optical module la comprises a block  10 , a transmitting optical sub-assembly  21   a  and a receiving optical sub-assembly  21   b  (collectively referred to as “optical sub-assembly  21 ”), a first substrate  20   a  and a second substrate  20   b  (collectively referred to as “circuit board  20 ”) which are used for driving the optical sub-assembly  21 , a housing  30  for enclosing the optical sub-assembly  21  and circuit board  20 , holders  19 , brackets  33 , a shield  34 , an actuator  39 , a fin  38 , and heat transfer sheets  40 ,  42 . The optical module  1   a  differs from that of the structure embodiment in the form of the upper casing.  
         [0067]    [0067]FIG. 11 is a perspective view of the uppercasing  54  of the second embodiment. The upper casing  54  has a positioning part  54   e  in addition to the structures of the upper casing  37  in the first embodiment.  
         [0068]    The positioning portion  54   e  comes into contact with the surface  12   g  of the front wall  12  exposed at the cutout formed in the center wall  13   b  of the block  10 . This can define mutual positional relationships between the block  10 , upper casing  54 , and lower casing  31  together with engagement structures  54   a  to  54   d  provided at both side walls of the upper casing  54 , cutout structures formed in both side walls  13   a ,  13   c  of the block  10 , and cutout structures  31   n  formed in both side walls of the lower casing  31 .  
         [0069]    By using the block  10 , the optical modules  1 ,  1   a  in accordance with the foregoing embodiments can position the optical sub-assembly  21  and circuit board  20  before mounting them to the lower casing  31 . Therefore, the optical sub-assembly  21  and the circuit board  20  can efficiently be fixed to each other on the outside of the housing  30 .  
         [0070]    Since the block  10  itself can be assembled in the lower casing  31  with the optical sub-assembly  21  and circuit board  20  in the state where the optical sub-assembly  21  and circuit board  20  are positioned with respect to each other, each of the optical modules  1  and  1   a  can be assembled easily.  
         [0071]    In the foregoing embodiments, the holders  19  are provided as a positioning member, so that the optical sub-assembly  21  can be secured after being inserted into the openings  12   a ,  12   b  of the block  10 , whereby the optical sub-assembly  21  can be reliably positioned and fixed to the circuit board  20 .