Abstract:
An optical module to enhance the heat dissipating function is disclosed. The optical module includes an optical assembly, a heat spreader, and a holder. The optical assembly emits light and dissipates heat in directions opposite to each other. The heat spreader is attached to the bottom of the optical assembly to conduct heat from the optical assembly effective to the outside. The holder securely holds the intermediate assembly of the optical assembly and the heat spreader.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an optical module that provides an enhanced heat dissipating function. 
       BACKGROUND ART 
       [0002]    Optical modules with a box shaped package and lead terminals laterally extending from the sides of the box shaped package have been well known as, what is called, the butterfly module. Such butterfly modules emit light in a direction substantially in parallel to the bottom thereof Even when the butterfly module implements a thermo-electric cooler (hereafter denoted as TEC) to control a temperature of a light-emitting device, typically a semiconductor laser diode (hereafter denoted as LD), the TEC may be mounted on the bottom of the module, because the light is extracted from a side of the module. 
         [0003]    The butterfly module, in particular, the box shape package thereof is generally less preferable from viewpoints of cost and size factor thereof As one of substitutions of the butterfly module, a multi-layered ceramic package widely used in electronic devices has been attracted. The ceramic package has not only the superior size factor but an advantage to form interconnections for high frequency signals. However, the, multi-layered ceramic package inherently provides a disadvantage that light is necessary to be extracted from the ceiling thereof and the heat generated therein is necessary to be extracted from the bottom thereof, that is, a direction along which the heat is conducted to the outside of the package is substantially in parallel with the optical axis thereof The present application is to provide one of solutions to dissipate heat from the ceramic package effectively. 
       SUMMARY OF INVENTION 
       [0004]    One aspect of the present application relates to an optical module that comprises an optical assembly, a heat spreader, and a holder. The optical assembly includes a package, a semiconductor light-emitting device, a mirror and a thermo-electric cooler (hereafter denoted as TEC). The package has a frame, a ceiling, and a bottom, where they are forming a cavity into which the light-emitting device, the mirror, and the TEC are installed. The frame is made of multi-layered ceramics. The semiconductor light-emitting device emits signal light in a direction substantially in parallel with the bottom of the package. The mirror reflects the signal light toward a direction substantially perpendicular to the bottom of the package. The TEC mounts the semiconductor light-emitting device and the mirror thereon; while, the TEC is mounted on the bottom of the package. The heat spreader has a front and a bottom making substantially right angle therebetween. The front is attached to the bottom of the optical assembly. The bottom of the heat spreader is attached to a host board to dissipate heat generated in the optical assembly to the host board. The holder securely holds an intermediate assembly of the optical assembly with the heat spreader, and fastens the intermediate assembly to the host board securely. 
         [0005]    In the optical module according to an embodiment, even when the optical assembly has an architecture that the direction along which the heat generated in the optical assembly is dissipated is in parallel to the optical axis but opposite thereto, the heat is effectively conducted to the outside via the heat spreader. Moreover, the intermediate assembly of the optical assembly with the heat spreader is securely held by the holder made of metal sheet. Thus, the present arrangement of the optical module effectively dissipates heat to the outside by a cost-effective arrangement. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0006]      FIG. 1A  is a perspective view of an optical module, while,  FIG. 1B  is an exploded view of the optical module according to an embodiment. 
           [0007]      FIG. 2  is an exploded view of the optical assembly shown in  FIG. 1A . 
           [0008]      FIG. 3  is a cut view of the optical assembly taken along the line III-III appeared in  FIG. 2 . 
           [0009]      FIG. 4  is a perspective view of the optical assembly assembled with the heat spreader  15 . 
           [0010]      FIGS. 5A and 5B  are perspective views of the FPC board, where  FIG. 5A  shows the FPC board before the forming, while,  FIG. 5B  shows the FPC board after the forming. 
           [0011]      FIG. 6A  is a perspective view of the holder, while,  FIG. 6B  is a plan view of the holder before the forming. 
           [0012]      FIGS. 7A to 7C  are the top view, the side view, and the side cross section of the optical module, where  FIG. 7C  is taken along the line VIIC-VIIC appeared in  FIG. 7A . 
           [0013]      FIGS. 8A to 8C  show the outer appearance of the optical module  11  assembled with the heat spreader, the holder, and the FPC board  19 , where  FIG. 8A  is the optical module viewed from the front top,  FIG. 8B  is viewed from the front bottom, and  FIG. 8C  is viewed from the rear top. 
           [0014]      FIG. 9  shows an outer appearance of the optical module when the module is set on the host board. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0015]    Next, some embodiments according to the present invention will be described as referring to drawings. In the description of the drawings, numerals or symbols same or similar to each other will refer to elements same or similar to each other without overlapping explanations. 
         [0016]      FIG. 1A  is a perspective view of an optical module  11 , while,  FIG. 1B  is an exploded view of the optical module  11  according to an embodiment of the invention. As shown in  FIGS. 1A and 1B , the optical module  11  includes an optical assembly  13  with a coupling unit  47 , a heat spreader  15 , a holder  17 , and a flexible printed circuit (hereafter denoted as FPC) board  19 . The optical assembly  13  is set in a pocket  15   m  of the heat spreader  15  via a thermal sheet  45 . The FPC board  19  is electrically coupled with the optical assembly  13  so as to escape the heat spreader  15 . The holder  17  holds and supports an intermediate assembly of the optical assembly  13 , the heat spreader  15  and the FPC board  19 . 
         [0017]      FIG. 2  is an exploded view of the optical assembly  13  shown in  FIG. 1A . The optical assembly  13  includes a package  21  comprised of a housing  23  and a ceiling  25 , where the housing  23  and the ceiling  25  forms a cavity into which optical components and electrical components are air-tightly enclosed. The housing  23 , which has a box shape in the present embodiment, includes a frame  29  made of multi-layered ceramics, a metal seal ring  31  on the top of the frame  29 , and a bottom plate  27 . The metal seal ring  31  is put between the frame  29  and the ceiling  25 , which is melted after the installation of components within the cavity to seal the cavity air-tightly. The ceiling  25  provides an aperture  25   a  covered with a window  25   b  in a center portion thereof, through which light generated in the cavity is extracted. 
         [0018]    The optical assembly  13  has a plurality of electrodes in two sides adjacent to each other, with which pads provided in the FPC board  19  come in electrically contact. 
         [0019]      FIG. 3  is a cut view of the optical assembly  13  taken along the line III-III appeared in  FIG. 2 . The embodiment shown in the figures is a type of an optical transmitter assembly implementing a semiconductor laser diode (hereafter denoted as LD) as an optical signal source. The cavity installs a primary assembly  33  including the LD  35  therein. That is, the primary assembly  33  includes the LD  35 , a lens  39  to collimate light emitted from the LD  35 , a mirror  37  to reflect the light emitted from the LD  35  and collimated with lens  43  toward an upward direction, that is, the mirror  37  bends the optical axis of the LD  35  by substantially 90°. The light emitted from the LD  35  advances substantially in parallel to the bottom  23   b  of the housing  23 , and is bent by the mirror  37  toward a direction perpendicular to the bottom  23   b.  The light is extracted through the window  25   b  covering the aperture  25   a  of the ceiling  25 . 
         [0020]    These components of the LD  35 , the lens  39 , and the mirror  37  are mounted on a thermo-electric controller (hereafter denoted as TEC)  41  to control a temperature of the LD  3 , and the TEC  41  is mounted on the top  23   b  of the bottom plate  27 . Thus, the LD  35 , the lens  39 , the mirror  37 , and the TEC  41  constitute the primary portion of the optical assembly  13 . 
         [0021]    The frame  29  provides a plurality of electrodes  38  in two sides adjacent to each other. The embodiment shown in  FIG. 2  provides the electrodes  38  on the top of the frame  29 . However, the electrodes  29   c  may be formed within the multi-layer, namely, between the layers. These electrodes  38  are coupled with the FPC board  19 . 
         [0022]      FIG. 4  is a perspective view of the optical assembly  13  assembled with the heat spreader  15 . The heat spreader  15 , which may be made of metal block, made of material with good thermal conductivity, provides a front  15   a,  a rear  15   b,  two sides  15   c,  and a bottom  15   e.  The front  15   a  provides a pocket  15   m  at which the housing  23  of the optical assembly  13  is set as putting a thermal sheet  45  therebetween. The thermal sheet  45  is an elastic material with good thermal conductivity. The sides  15   c  provide a grove  15   j  extending in substantially parallel to the bottom  15   e  thereof from the front  15   a  to the rear  15   b.  The grooves  15   j  have a function to guide the holder  17 , which will be described later in this specification. 
         [0023]      FIGS. 5A and 5B  are perspective views of the FPC board  19 , where  FIG. 5A  shows the FPC board  19  before the forming, while,  FIG. 5B  shows the FPC board  19  after the forming. The FPC board  19  has a plane shape of E-character with outer legs,  19   e  and  19   f,  connected by the vertical leg  19   c.  A center leg  19   b,  which corresponds to the center bar of E-character, extends from the vertical leg  19   c.  The outer legs,  19   e  and  19   f , provide a plurality of pads  19   a  arranged along the outer edge thereof. The center leg  19   b  provides two arms,  19   m  and  19   n,  forming a right corner. Each of two arms,  19   m  and  19   n,  provides a plurality of pads  19   g  corresponding to and connected to the electrodes  38  of the frame  29  of the optical assembly  13 . The pads  19   g  in two arms,  19   m  and  19   n,  are connected to the pads  19   a  on the outer legs,  19   e  and  19   f,  by interconnections  19   j  formed on the vertical  19   c  and the outer legs,  19   e  and  19   f.  The vertical leg  19   c  is supported by a rigid substrate  19   h  in the back surface thereof, which is not explicitly in the figures, while, the center leg  19   b  is not supported by any rigid substrate; accordingly, the center leg  19   b  may be flexibly bent as shown in  FIGS. 5A and 5B . Specifically, the center leg  19   b  in two arms,  19   m  and  19   n,  thereof is extended downward to make the electrical connection between the pads  19   g  and the electrodes  38  in the optical assembly  13 . 
         [0024]      FIG. 6A  is a perspective view of the holder  17 , while,  FIG. 6B  is a plan view of the holder  17  before the forming. The holder  17  is formed only by cutting and bending a metal sheet without any welding and so on. The holder  17  according to the present embodiment is made of stainless steel with a thickness of 0.3 mm only by cutting and bending. The holder  17  includes a top  17   c  and a plurality of legs bent from the top  17   c  so as to leave the top  17   c  with a rectangular plane shape. Specifically, in the front portion, the front edge of the top  17   c  is first bent downward to form the front wall  17   a  and further bent forward to form two legs  17   d.  The front  17   a  provides a U-shaped cut  17   x  through which the coupling portion  47  accompanied with the optical assembly  13  extends frontward. Further, another cut  17   t  is formed along the line by which the second bent of the legs  17   d  is done. The legs  17   d  provides screw cuts  17   e  to fasten the holder  17  to the host board  51 . 
         [0025]    The holder  17  further provides front skirts  17   h  and rear skirts  17   i  each bent downward from the front side and the rear side of the top  17   c  by a right angle, respectively. The front and rear skirts provide U-shaped cuts,  17   g  and  17   i,  each having an inner tab slightly bent outwardly. The tabs,  17   g  and  17   i,  are set in the groove  15   j  of the heat spreader  15 . Thus, the holder  17  may fit with the heat spreader  15 . 
         [0026]    The holder  17  in the rear portion thereof also provides two legs  17   b  bent downwardly from the top  17   c.  The legs  17   b  are further bent rearward to form flanges  17   k  each providing an opening  17   m  to fix the assembly of the holder  17 , the heat spreader  15 , and the optical assembly  13  to the host board  61 . The rear legs  17   b  provide cuts  17   u  to facilitate the bending. Moreover, a center of the rear portion provides a tab  17   y  bent downward from the top  17   c,  but the length of the tab  17   y  is shorter than the length H1 of the rear legs  17   b.  The tab  17   y  is bent deeper than the bend of the rear legs  17   b.  That is, the rear legs  17   b  is bent downward by substantially right angle, while, the tab  17   y  is bent more than right angle. Thus, a tip of the tab  17   y  pushes the rear  15   b  of the heat spreader  15  frontward. 
         [0027]      FIGS. 7A to 7C  are the top view, the side view, and the side cross section of the optical module  11 , where  FIG. 7C  is taken along the line VIIC-VIIC appeared in  FIG. 7A . The optical module  11 , as previously described, includes the optical assembly  13 , the heat spreader  15 , the holder  17  and the FPC board  19 . The heat spreader  15  is arranged in the rear of the optical assembly  13 , where the directions of the front and the rear are temporarily defined in one side on which the coupling unit  47  is provided and another side opposite to the coupling unit  47  for the explanation sake; and does not restrict the scope of the invention. 
         [0028]    The optical assembly  13  in the housing  23  thereof is set within a pocket  15   m  of the holder  15  as putting the elastic thermal sheet  45  therebetween. The optical assembly  13  of the embodiment, as shown in  FIGS. 2 and 3 , mounts the primary portion  33  thereof on the top  23   b  of the bottom plate  27  thereof. Accordingly; the heat generated within the package  21 , in particular, by the TEC  41  is dissipated via the bottom plate  27 . Also, the optical assembly  13  of the embodiment emits signal light toward a direction perpendicular to the ceiling  25  thereof, namely, perpendicular to the bottom plate  27 , which is the direction opposite to a direction along which the external fiber  49  is extracted from the optical assembly  13 . This arrangement makes it hard to dissipate heat conducted to the bottom plate  27  to the outside of the package  21 . The embodiment shown in figures provides the heat spreader  15  that receives the optical assembly  13  in the pocket  15   m  thereof and dissipates heat conducted thereat to the external via the bottom  15   e  thereof. 
         [0029]    Moreover, the intermediate assembly of the heat spreader  15  with the optical assembly  13  is held by the holder  17 . That is, as shown in  FIGS. 7A to 7C , the holder  17  puts the intermediate assembly between the front  17   a  and the rear  17   b,  and the rear tab  17   y  pushes the heat spreader  15  frontward to abut the flange of the coupling unit  47  of the optical assembly  13  against the front  17   a.  In addition, the heat spreader  15  is set between the front and rear skirts,  17   h  and  17   i,  respectively, of the holder  17 . Thus, the heat spreader  15  is securely held by the holder  17 . 
         [0030]    The height of front  17   a  and the rear  17   b,  which is denoted as H1 in  FIG. 6B , is slightly greater than the height H2 of the heat spreader  15 . The cuts,  17   t  and  17   u,  provided in the end of the front  17   a  and the end of the rear  17   b  facilitate the bending of the front legs  17   d  and that of the rear legs  17   k  as keeping the dimensional accuracy against the height H2 of the holder  17  described above. The holder  17  may hook the tabs formed by the U-shaped cuts,  17   g  and  17   i,  and be bent inwardly within the groove  15   j  of the heat spreader  15 , which securely holds the heat spreader  15  by the holder  17 . 
         [0031]    The holder  17  provides the opening  17   s  in the top  17   c  thereof The FPC board  19  in an arched portion of one of the arms  19   m  extrudes from the opening  17   s.  While, the heat spreader  15  in the top  15   d  thereof provides a hummock  15   k  in the rear end thereof to form a depression into which the FPC board  19  in the center leg  19   c  thereof is set therein and extracted between two skirts  17   h  and  17   i.  Thus, even when the holder  17  fully covers the top  15   d  of the heat spreader  15 , the FPC board  19  is set between the holder  17  and the heat spreader  15 , and extracted therefrom between two skirts,  17   h  and  17   i.  Moreover, because the arm  19   m  in the arched portion thereof extrudes from the opening  17   s  in the top  17   c  of the holder  17 , the pads  19   g  formed on the arms,  19   m  and  19   n,  are soldered with the electrodes  38  of the optical assembly  13 . 
         [0032]      FIGS. 8A to 8C  show the outer appearance of the optical module  11  assembled with the heat spreader  15 , the holder  17 , and the FPC board  19 , where  FIG. 8A  is the optical module  11  viewed from the front top,  FIG. 8B  is viewed from the front bottom, and  FIG. 8C  is viewed from the rear top. As described, the intermediate assembly of the optical assembly  13 , the heat spreader  15 , and the FPC board  19  are securely held by the holder  17 . Two legs,  19   e  and  19   f,  of the FPC board  19  are extracted between two skirts,  17   h  and  17   i,  of the holder  17  such that two legs  19   e  and  19   f,  seems to spread the wings laterally. 
         [0033]      FIG. 9  shows an outer appearance of the optical module  11  when the module is set on the host board  51 . The host board  51  provides a groove  51   b  in the top  51   a  thereof The coupling unit  47  is set within the groove  51   b.  The host board  51  further provides a pocket  51   c  into which the primary portion of the optical module  11  is set and fastened by screws  53  passing the holes  17   m  and the screw cuts  17   e.  The pocket  51   c  of the host board  51  has a depth substantially equal to the height of the heat spreader  15 . Because two legs,  19   e  and  19   f,  have the level substantially equal to the top  15   d  of the heat spreader  15 , and the legs,  17   d  and  17   k,  of the holder  17  have the level substantially equal to the bottom  15   e  of the heat spreader  15 , the FPC board  19  may be smoothly connected with the interconnections  51  d provided on the top  51  a of the host board  51  even when the screws  53  tightly fasten the legs,  17   d  and  17   k,  to the host board  51 . 
         [0034]    While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. For instance, the embodiment shown in  FIG. 9  provides the pocket  51   c  into which the optical module  11  is set, and the groove  51   b  in which the coupling unit  47  is set. However, the host board  51  may provide a cut into which only the optical assembly  13  and the heat spreader  15  are set. The edge of the host board  51  is aligned with the edge of the legs,  19   e  and  19   f,  of the FPC board  19 . The legs,  17   d  and  17   k,  are fastened with a bottom of the host system, such as an optical transceiver into which the optical module  11  is set. Even in such an arrangement, the optical assembly  13  effectively dissipates heat to the host system via the heat spreader  15 . Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.