Abstract:
An optical transceiver that copes with both the enhanced heat dissipation from heat generating components and the electrical isolation of components processing faint signals from other components generating EMI noises is disclosed. The optical transceiver provides, in addition to a bottom of a frame, a bottom cover made by material with higher thermal conductivity. The former components are directly mounted on the bottom cover through openings in the frame, while, other component to be electrically isolated from the chassis are mounted by putting an insulating support between them and the bottom cover.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    Embodiments of the present application relate to an optical transceiver, in particular, the application relates to a physical arrangement of a housing of the optical transceiver. 
         [0003]    2. Description of Related Art 
         [0004]    An optical transceiver generally includes an optical transmitter to transmit an optical signal, an optical receiver to receive another optical signal, a circuit to communicate with the optical transmitter, the optical receiver and the host system, and a housing, typically made of metal, to install the optical transmitter, the optical receiver, and the circuit therein. Thus, an optical transceiver realizes the full-duplex optical communication. As the transmission speed of an optical transceiver continuously increases, components installed within an optical transceiver have generated more heat, which leads to needs for a mechanism for the optical transceiver to dissipate heat further efficiently. 
         [0005]    On the other hand, both of the optical transmitter and the optical receiver process electrical signals but signal levels are far different. That is, the optical transmitter switches a large current to drive a light-emitting device, while, the optical receiver receives a faint signal converted from the received optical signal. Accordingly, the optical receiver is necessary to be isolated from EMI noises caused by the optical transmitter. Generally, this isolation is carried out by distinguishing the receiver ground from the transmitter ground. However, when all the housing of the optical receiver, that of the optical transmitter and the transceiver housing are made of metal, the electrical isolation of the optical receiver from the optical transmitter has been left to be a subject to be solved. 
       SUMMARY 
       [0006]    An aspect according to an example of the present application relates to an optical transceiver. The optical transceiver of the example comprises an optical transmitter, an optical receiver, a metal frame, and a bottom cover. The metal frame mounts the optical transmitter and the optical receiver thereof; and openings corresponding to the optical transmitter and the optical receiver. The bottom cover is made of metal and has thermal conductivity greater than that of the metal frame. A feature of the optical transceiver of the example, the optical transmitter is directly in contact with the bottom cover through the opening for the optical transmitter; while, the optical receiver is set in another opening for the optical receiver but electrically isolated from the bottom cover and the metal frame. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The foregoing and other purposes, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which: 
           [0008]      FIGS. 1A and 1B  show an outer appearance of an optical transceiver according to an example of the present application; 
           [0009]      FIGS. 2A and 2B  show an inside of the optical transceiver  1 ; 
           [0010]      FIG. 3  is an outer appearance of a frame; 
           [0011]      FIG. 4A  is a perspective view of an assembled support  31 ; while,  FIG. 4B  is an exploded view of the support; 
           [0012]      FIG. 5  is a plan view of the support; 
           [0013]      FIG. 6  shows a process to assemble the support with the frame; 
           [0014]      FIGS. 7A and 7B  show processes to assemble the support with the frame subsequent to the process shown in  FIG. 6 ; 
           [0015]      FIG. 8  magnifies a process to assemble the support with the frame subsequent to the process shown in  FIG. 7B ; 
           [0016]      FIGS. 9A and 9B  show a process to set an optical receiver on the support; 
           [0017]      FIG. 10A  is a perspective view of a metal cover, and  FIG. 10B  is a cross section of the metal cover; 
           [0018]      FIGS. 11A and 11B  show a process to assemble the metal cover with the support as putting the optical receiver between them; 
           [0019]      FIG. 12  is a cross section showing the assembly of the metal cover with the support; 
           [0020]      FIG. 13A  is a perspective view of another support, and  FIG. 13B  is a side view of the another support; 
           [0021]      FIG. 14  is a cross section shown an assembly of the metal cover with the another support shown in  FIG. 13A ; 
           [0022]      FIG. 15  is a perspective view showing a bottom cover of another example of the present application; 
           [0023]      FIG. 16  magnifies a front portion of the another bottom cover and the frame; 
           [0024]      FIG. 17  magnifies a front portion of the frame to be engaged with the bottom cover; 
           [0025]      FIG. 18A  magnifies a side portion of the frame providing a groove, and  FIG. 18B  is a cross section of the groove; 
           [0026]      FIG. 19A  is a perspective view of the bottom cover with a snapping mechanism and  FIG. 19B  magnifies an edge of the bottom cover providing a hook to be slid within the groove of the frame; and 
           [0027]      FIG. 20  shows a repulsive mechanism provided in one of the bottom cover and the frame. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIGS. 1A and 1B  show an outer appearance of an optical transceiver according to an example of the present application, where  FIG. 1A  views the optical transceiver  1  from a rear top; while,  FIG. 1B  views it from a front bottom. The optical transceiver  1  provides a frame  2 , a bottom cover  3 , and a lid  4  as a housing. One end of the frame  2  is provided with an optical receptacle  12  to receive an external optical connector, which is not shown in figures. We call that a side where the optical receptacle  12  is provided is the front, the other side, where an electrical plug  13  is provided, is the rear, the side where the lid  4  is assembled is the top, and the side where the bottom cover  3  is provided is the bottom. Moreover, the longitudinal direction extends from the front to the rear, while, the lateral direction crosses the longitudinal direction. However, these directions of the front, rear, top and bottom are defined only for the explanation sake, and do not restrict the scope of the invention. The frame  2  is preferably made of aluminum alloy, zinc alloy, and so on from viewpoints of the productivity and the cost thereof. The bottom cover  3 , which is assembled to a bottom of the frame  2  as shown in  FIG. 1B , is preferably made of copper alloy from a viewpoint of the heat dissipating function. The lid  4  is assembled with the frame  2  as exposing the electrical plug  13 . 
         [0029]      FIGS. 2A and 2B  show an inside of the optical transceiver  1 , where  FIG. 2A  views the optical transceiver  1  from the rear bottom; while,  FIG. 2B  views it from the front top. The frame  2  provides two sides  5  extending longitudinally from the rear end of the optical receptacle  12 . A center portion of respective sides  5  is removed to form a cut  7  for receiving sides of the lid  4 . The bottom  6  of the frame  2  provides a plurality of openings  9 , where the number of the openings  9  in the present example corresponds to a number of optical components installed within the optical transceiver  1 . An example of the optical transceiver shown in the figures has three openings  9 , one is for an optical transmitter  17 , one is for an optical receiver  24 , and one is for an optical source  14 . The bottom  6  further provides a center beam  8  extending in a longitudinal direction between the openings  9 . 
         [0030]    The optical transmitter  17  has a housing larger than that of the optical receiver  24 . That is, the housing  18  of the optical transmitter  17  is made of metal and has a rectangular shape to enclose semiconductor optical devices as optically active devices and some optical components such as a lens and so on as optically passive devices.  FIG. 2B  shows a top  19  of the metal housing  18  of the optical transmitter  17 , and two optical ports,  22   a  and  22   b,  to output modulated optical signal to the optical receptacle  12  and to enter local light coming from the optical source  14 . 
         [0031]    For the optical receiver  24 , it also provides a metal housing  25  with a rectangular shape, namely, the housing  25  provides a top  26 , a bottom  27 , and four sides,  28   a  to  28   d.  The housing  25  installs a photodiode (hereafter denoted as PD) as an optically active device and some optically passive devices, typically lenses. Three sides,  28   a  to  28   c,  of the housing  25  provides lead pins,  30   a  to  30   c,  while, the last side  28   d  provides an input port  29   a  for a received optical signal and another port  29   b  for a local optical signal. 
         [0032]    The optical receptacle  12  provides two optical ports,  12   a  and  12   b,  where the former  12   a  couples with the optical port  22   a  of the optical transmitter  17 , while, the latter  12   b  couples with the optical port  29   a  of the optical receiver  24 . The optical source  14  provides two ports,  14   a  and  14   b,  the former  14   a  couples with the port  22   b  of the optical transmitter  17 , while the latter  14   b  couples with the port  29   b  of the optical receiver  24 . 
         [0033]    Thus, the optical transmitter  17  receives the local light in the port  22   b  from the port  14   a  of the optical source  14 , modulates thus received light, and outputs thus modulated optical signal to the port  12   a  of the optical receptacle  12  from the port  22   a.  While, the optical receiver  24  receives the local light in the port  29   b  from the port  14   b  of the optical source  14  and the signal light in the other port  29   a  from the port  12   b  of the optical receptacle  12 , multiplexes these two light and detects the phase and the amplitude of the optical signal coming from the optical receptacle  12 . 
         [0034]    The sides of the bottom  6 , or the bottom of two sides  5 , provide grooves  11  extending longitudinally. Setting the bottom cover  3  from the rear of the optical transceiver  1  as sliding the edges thereof within the grooves  11 , the bottom cover  3  is assembled with the frame  2 . The bottom  20  of the housing  18  for the optical transmitter  17  is in physical contact with the bottom cover  3  to enhance the heat dissipating function of the optical transmitter  17 . The assembly of the bottom cover  3  with the frame  2 , in particular, a mechanism to fit the bottom cover  3  with the frame  2  will be described later. 
         [0035]      FIG. 3  is an outer appearance of the frame  2  without installing any assemblies,  14 ,  17 , and  24 . The opening  9  for the optical receiver  24  provides a step  10  in the center beam  8  and the inside of the side  5  (not shown in  FIG. 3 ). As described later, the step  10  receives a flange,  39  and  53 , of the support  31  to assemble the optical receiver  24  with the frame  2 . The support  31  is made of electrically insulating material, typically an insulating resin, to isolate the metal housing  25  of the optical receiver  24  from the metal frame  2 . 
         [0036]      FIG. 4A  is a perspective view of the assembled support  31 ,  FIG. 4B  is an exploded view of the support  31 , and  FIG. 5  is a plan view of the support  31 . The support  31  includes a female part  32  and a male part  33 . The female part  32  includes front and rear arms,  35  and  36 , and a longitudinal bar  34  connecting the front and rear arms,  35  and  36 , where they form a “C” like plane shape. The front and rear arms,  35  and  36 , extend from respective end of the longitudinal bar by substantially a right angle. The longitudinal bar  34  provides a cut  37  in a center thereof to expose read pins  30   c  of the optical receiver  24 . The longitudinal bar  34  also provides projections  38 , which is shown in  FIG. 5  but hidden in  FIGS. 4A and 4B , in the outer side of the front and the rear of the longitudinal bar  34 . The outer side of the longitudinal bar  34  also provides in the bottom thereof the flange  39  extending outwardly to be received in the step  10  of the opening  9 . 
         [0037]    The rear arm  35  has a flat surface  42  to support the bottom  27  of the housing  25 . That is, the rear arm  32  has a height substantially equal to a height of the portion of the longitudinal bar  34  left by the cut  37 . The rear arm  35  further provides a projection  43  and a hole  44  in this order from the tip thereof. The projection  43  protrudes inwardly, while, the hole  44  passes through the whole rear arm  35 . The front arm  36  provides a saddle  45  to support the port  29   a  of the optical receiver  24  and a groove  46  in the tip thereof. The groove  46  has a hollow in the bottom thereof. 
         [0038]    The male part  33  also provides a front arm  49 , a rear arm  48 , and a longitudinal bar  47  connecting two arms,  48  and  49 . Two arms,  48  and  49 , extend substantially perpendicular to the longitudinal bar  47  towards the female part  32 . The longitudinal bar  47  provides a cut  51  in a center thereof through which the lead pins  30   a  are exposed. The top of the longitudinal bar  47  is chamfered in the outer corner thereof. The longitudinal bar  47 , instead of the chamfered corner, may have a rounded top. 
         [0039]    Similar to the projections in the longitudinal bar  34  of the female part  32 , the longitudinal bar  47  of the male part  33  also provides circular projections  52  in front and rear of the outer surface, whose top corner is also chamfered. Moreover, the longitudinal bar  47  also provides in a bottom thereof a flange  53  similar to the flange  39  in the female part  32  extending outwardly. 
         [0040]    The rear arm  48  provides a top flat surface  56  also to support the bottom  27  of the housing  25 , and a combination of a projection  57  and an opening  58 . The projection  57  protrudes outwardly, while, the opening passes through the whole rear arm  48 . On the other hand, the front arm  49  provides a saddle  59  to support the port  29   b  and a projection  60  in a tip thereof. The projection  60  mates with the groove  46  formed in the front arm  36  of the male part  32 . 
         [0041]    Referring to  FIG. 5 , assuming a length L from the front arm to the rear arm, a distance from the rear arm  48  to the front arm  49  of the male part  33  is longer than a distance from the rear arm  35  to the front arm  36  of the female part  32 . Accordingly, assembling the male part  33  with the female part  32 , the rear and front arms,  48  and  49 , of the male part  33  push the rear and front arms,  35  and  36 , of the female part  32  outwardly; concurrently, the rear and front arms,  35  and  36 , of the female part  32  push the rear and front arms,  48  and  49 , of the male part  33  inwardly, which rigidly assembles the male part  32  with the female part  33 . 
         [0042]    Referring to  FIGS. 6 to 8 , a process to assemble the support  31  with the frame  2  is shown. First, the female part  32  in the longitudinal bar  34  is arranged along the longitudinal direction of the opening  9 , and the flange  39  in the bottom of the longitudinal bar  34  is inserted into a gap formed between the bottom cover  3  and the step  10  of the bottom  6  of the frame  2 , which is formed along an edge of the opening  9 . Second, as shown in  FIG. 7A , the male part  33  in the longitudinal part  47  thereof is arranged also along the longitudinal direction of the opening  9 , the flange  53  is inserted into the gap formed between the bottom cover  3  and the step  10  of the frame  2  so as to contact the upper surface of the flange  53  with edge of the step  10  defining the gap. 
         [0043]    Then, the male part  33  is inclined so as to direct the rear and front arms,  48  and  49 , upwardly. Pushing the rear and front arms,  48  and  49 , downwardly, the opening  58  of the male part  33  receives the projection  43  of the rear arm  35  of the female part  32 , then, the projection  57  of the male part  33  is inserted into the opening  44  of the female part  32 . Moreover, the projection  60  of the male part  33  is set within the groove  46  in the female part  32 . Thus, rear arms,  48  and  35 , and the front arms,  49  and  36 , are rigidly assembled to each other. 
         [0044]    Next, as shown in  FIGS. 9A and 9B , the optical receiver  24  is set on the support  31  as facing the ports,  29   a  and  29   b,  to the optical receptacle  12 . Finally, a metal cover  61  fixes the housing  25  in a preset position on the support  31 . The metal cover  61 , as shown in  FIG. 10 , is formed by a metal plate only by cutting and bending. The metal cover  61 , which has a reversed U-shaped cross section to open downwardly, includes a top  62  and two sides  63  bent downwardly at the side of the top  62 . The top  62  provides tabs  64  in the front and rear thereof. The tabs  64  is formed by two longitudinal slits and slightly bent downwardly. The tabs  64  push the top  26  of the housing  25  downwardly against the support  31 . 
         [0045]    The two sides  63 , which are bent downwardly at respective sides of the top  62 , provide a cut  65  through which the lead pins,  30   a  and  30   c,  of the optical receiver  24  are exposed. The sides  63  also provide, in the rear and the front thereof, skirts,  66  and  67 , with circular openings,  68  and  69 , in a center thereof. The circular openings,  68  and  69 , mate with the projections,  38  and  52 , of the support  31  shown in  FIG. 4B  and  FIG. 5 . That is, the projections,  38  and  52 , are hooked with the circular openings,  68  and  69 , of the cover  61 . Moreover, the rear skirt  66  provides a hook  70  hooked with the rear end of the longitudinal bars,  34  and  54 , of the female and male parts,  31  and  32 . Hooking the hook  70  with the rear end of the longitudinal bars,  34  and  54 , the metal cover  61  refines the shape thereof. The rear and the front skirts,  66  and  67 , as described above, are bent downwardly at the sides of the top  62 , but an angle of the rear and the front skirts,  66  and  67 , with respect to the top  62  is slightly smaller than a right angle, which further refines the shape of the cover  61 . 
         [0046]      FIGS. 11A and 11B  show a process to assemble the cover  61  with the support  31  as putting the optical receiver  24  between them. First, hooking the projections,  38  and  52 , in both sides of one of the front and rear of the longitudinal bar,  34  and  54 , with the corresponding openings,  68  or  69 , among the openings,  69  and  68 , of the front skirt  67  and the rear skirt  58  of the cover  61 , respectively, as expanding a span between the corresponding skirts  67  or  68  in the two front or two rear skirts,  67  and  68 ; the cover  61  is able to pivot by the hooked projections  38  and  52  as the axis of the rotation. Then, pivoting the cover  61  to hook the rest projections  38  and  52  in the front or rear of the longitudinal bars,  34  and  54 , of the support  31 , the cover  61  is assembled with the support  31  as aligning the optical receiver  24  in the preset position on the support  31 . Because the rear and front tabs  64  of the top  62  of the cover  61  press the top  26  of the optical receiver  24  downwardly, which inversely lifts the cover  61  upwardly, the hooking of the projections  38  and  52  with the openings,  68  and  69 , is secured. Moreover, the rear and front skirts,  66  and  67 , of the cover  61  press the support  31  inwardly to enhance the support of the housing  25  of the optical receiver  24 . Thus, the optical receiver  24  is securely set on the support  31 . Moreover, the support  31  in respective flanges,  39  and  53 , is reliably inserted within the gap formed between the step  10  of the frame  2  and the bottom cover  3 ; accordingly, the optical receiver  24  is securely set within the optical transceiver  1  through the support  31  and the cover  61 . 
         [0047]      FIG. 12  is a cross section of the optical transceiver  1  taken along a line intersecting the front skirts  67 , in which  FIG. 12  omits the optical receiver  24  set on the support  31 . As shown in  FIG. 12 , the front skirts  67 , where the openings  69  are provided in the center thereof, hook the projections  38  and  52  of the support  31 , and put the front portion of respective longitudinal bars,  34  and  47 , therebetween. 
         [0048]    Accordingly, the support  31  is securely held by the cover  61 . Moreover, because the tabs  64  of the cover  61  push the top  26  of the housing  25  downwardly, which also pushes the support  31  downwardly because the optical receiver  24  is set on the support  31 , and the projections,  38  and  52 , are further tightly fastened with the openings  68  and  69 . 
         [0049]      FIG. 13A  is a perspective view showing a modified support  31 A and  FIG. 13B  is a side view of a support  31 A. The modified support  31 A provides, in addition to arrangements shown in  FIG. 5 , ribs  54  beneath the projections  38  and  52  in outer surface of respective longitudinal bars,  34  and  47 . The ribs  54 , which may have a triangular cross section, are crushable when the modified support  31 A is set within the frame  2 . 
         [0050]      FIG. 14  is a cross section taken along the lateral direction at a portion where the front skirt  67  of the cover  61  is engaged with the projections  38  and  52  of the modified support  31 A. An assembly of the modified support  31 A with the frame  2  is carried out by procedures substantially same with the process already described. That is, the female part  32  in the flange  39  thereof is first set within the gap formed between the bottom  6  of the frame  2  and the step  10  of the bottom cover  3 ; then, the male part  33  in the flange  53  thereof is also set within the gap formed between the step  10  of the bottom  6  of the frame  2  and the bottom cover  3  as fitting the projections,  43  and  57 , with the corresponding openings,  58  and  44 , in respective arms,  35  and  48 , and the projection  60  with the groove  46 . Synchronizing with the fitting between the female part  32  and the male part  33 , the ribs  54  in the outer surface thereof are crushed by the bottom  6  of the frame  2 . Thus, the support  31 A may be further tightly set within the opening  9  of the frame  2 . 
         [0051]    Although the modified support  31 A provides ribs  54  in the outer surfaces of respective longitudinal bars,  34  and  57 , the modified support  31 A may further provide other crushable ribs in the top surface of the flanges,  39  and  53 , or the top surfaces,  42  and  56 . These ribs on the flanges,  39  and  53 , may be crushed when the flanges,  39  and  53 , are set within the gap formed between the step  10  of the bottom  6  of the frame  2  and the bottom cover  3  by abutting against the step  10 . 
         [0052]    Next, a mechanism to fit the bottom cover  3  with the frame  2  will be described in detail.  FIG. 15  is a perspective view of the optical transceiver  1  viewed from the bottom thereof. Although the bottom cover  3  shown in  FIG. 2B  covers a front end of the frame  2 , namely, a portion neighbor to the optical receptacle  12 , the bottom cover  3 A of the present example ends just front of the optical receptacle  12 . As already described, the bottom cover  3 A covers the whole bottom of the frame  2  to hide the openings  9  and may be made of, for instance, copper (Cu) or copper alloy; while, the frame  2  may be made of, for instance, aluminum (Al), aluminum alloy, zinc (Zn), zinc alloy, and so on. Generally, the bottom cover  3 A may be made of material having thermal conductivity higher than that of material for the frame  2 . The example shown in  FIG. 15 , the frame  2  is formed by die-casting of aluminum or zinc, while, the bottom cover  3 A is formed by a copper plate whose thermal conductivity is preferably higher than 280 W/m/K. 
         [0053]    When the frame  2  is made of zinc alloy and formed by die-casting and is to be plated with nickel (Ni), the bottom cover  3 A, which is made of copper alloy, may be also plated with nickel after the bottom cover  3 A is assembled with the frame  2  by the combined process of the strike or flash plating, the electro-plating and nickel plating. In an alternative, the frame  2  and the bottom cover  3 A may be individually plated and assembled together after the plating. 
         [0054]    The frame  2 , as already described in  FIGS. 1A to 2B , provides two sides  5  extending longitudinally in both sides of the bottom  6 . Moreover, each of the sides  5  provides the groove  11 . The bottom cover  3 A is slid from the rear of the frame  2  as respective cuffs in respective side edges are guided within the groove  11 . Sliding the bottom cover  3 A to cover the bottom  6  of the frame  2 , the optical transmitter  17  and the local optical source  14  are in contact with the bottom cover  3 A through respective openings  9 . However, the optical receiver  24  mounted on the support  31  is still electrically isolated from the bottom cover  3 A. 
         [0055]    The center beam  8  between the openings  9  is formed thicker to secure the stiffness of the frame  2 . The sides  5  of the example shown in  FIG. 2B  provide large cuts  7  removing the whole sides  5  to expose the bottom  6  in the center portion thereof. That is, each of the sides  5  is divided into a front portion and a rear portion. The bottom  6  is exposed between these two portions of each of the sides  5 . Accordingly, when no center beam  8  is formed in thicker, the stiffness of the frame  2  along the longitudinal direction becomes insufficient. 
         [0056]    Moreover, the optical transmitter  17  and the local optical source  14  are directly in contact with the bottom cover  3  made of copper alloy through the openings  9 , and these modules,  14  and  17 , therefore enhance the heat dissipating efficiency. 
         [0057]      FIG. 16  magnifies a front portion of the bottom cover  3 A; while,  FIG. 17  also magnifies a front portion of the center beam  8  as removing the bottom cover  3 A. The bottom cover  3 A provides an opening  3   a  in a front center thereof, while, the center beam  8  of the frame  2  provides a projection  8   a.  Sliding the bottom cover  3 A on the bottom  6  of the frame  2 , the projection  8   a  engages with the opening  3   a  to prevent the bottom cover  3 A from slipping off from the frame  2 . Although the example provides the opening  3   a  in the bottom cover  3 A and the projection  8   a  in the center beam  8 , a snapping mechanism opposite to the example, that is, the projection in the bottom cover  3  and a hollow receiving the projection in the center beam  8  may be practical. Also, the example of the snapping mechanism shown in figures provides an opening to be latched with the projection; but the snapping mechanism may provide, as an alternative, a hollow to receive the projection. Moreover, the example shown in the figures provides the optical receptacle  12  in a position offset from the center of the frame  2 , the position of the optical receptacle  2  is not restricted to this position. An arrangement of a center receptacle may be applicable to the optical transceiver  1 . 
         [0058]    The opening  3   a  of the present example may have a diameter larger than an outer diameter of the projection  8   a  by about 0.1 mm to facilitate the engagement between them. The height of the projection  8   a  is optional, but preferably less than a thickness of the bottom cover  3 A. The present example of the frame  2  provides the projection  8   a  with a height of 0.1 to 0.2 mm. Moreover, the projection  8   a  and/or the opening may have chamfered edge. 
         [0059]      FIG. 18A  magnifies a front portion of the frame  2  including the optical receptacle  12 , in particular,  FIG. 18A  shows the groove  11  to set the bottom cover  3 A, while,  FIG. 18B  is a cross section of the groove  11 . The groove  11  is formed by a rib  11   a  and a hollow  11   b  formed between the rib  11   a  and the body of the side  5   a.  The rib  11   a  has a length from the bottom of the hollow  11   b  to the top thereof smaller than the length from the bottom of the hollow  11   b  to a surface of the side  5   a  by an amount corresponding to a thickness of the bottom cover  3 A. 
         [0060]      FIG. 19A  is a perspective view of the bottom cover  3 A of the present example. As shown in  FIG. 19A , the side edges  3   b  of the bottom cover  3 A are bent twice to form the hook  3   b,  with the U-shaped cross section. The tip  3   d  of the hook  3   b  is set within the hollow  11   b  of the groove  11  when the bottom cover  3 A is slid on the bottom  6  of the frame  2  until the projection  8   a  is engaged with the opening  3   a  of the bottom cover  3 A. Because the hook  3   b  is formed in respective sides of the bottom cover  3 A, the stiffness of the bottom cover  3 A is secured along the longitudinal direction. 
         [0061]      FIG. 19B  magnifies the hook  3   b  in the edge of the bottom cover  3 A. As described above, the hook  3   b  is formed by bending the bottom plate  3 A twice but angles by the bending are slightly different. That is, the first bending in the tip side  3   d  of the bottom cover  3 A makes an angle less than a right angle; while, the second bending  3   c  closer to the center of the bottom cover  3 A makes a substantially right angle. Accordingly, when the tip  3   d  of the hook  3   b  is set in the hollow  11   b  of the groove, the U-shaped hook tightly catches the rib  11   a  of the groove  11 . 
         [0062]      FIG. 20  is a perspective view showing another snapping mechanism between a bottom cover  3 B and the frame  2 . The example shown in  FIG. 20  provides in the bottom cover  3 B thereof a repulsive mechanism to give a repulsive force against the bottom cover  3 B in addition to the opening  3   a.  That is, the repulsive mechanism includes a protrusion  3   t  and a lateral slit  3   s  behind the protrusion  3   t.  Sliding the bottom cover  3 B from the rear of the frame  2  to the front end of the groove  11 , the protrusion  3   t  abuts against the rear wall of the front end of the optical transceiver  1 . The lateral slit  3   s  is formed behind the projection  3   t  to provide areas  3   n  with a shortened length between the lateral slit  3   s  and the edge of the bottom cover  3 B. Moreover, the tip of the protrusion  3   t  protrudes from the front edge of the bottom cover  3 B, then, the tip of the protrusion  3   t  first comes in contact with the rear wall  2   a  of the front portion of the frame  2 . Then, the portions  3   n  with the shortened length to the edge in both sides of the protrusion  3   t  elastically push the bottom cover  3 B rearward, but the engagement of the projection  8   a  with the opening  3   a  compensates this rearward motion of the bottom cover  3 B. Thus, the bottom cover  3 B may be further tightly set with the frame  2 . 
         [0063]    Although the example shown in  FIG. 20  provides the mechanism to cause repulsive force in the bottom cover  3 B, this mechanism may be realized in the frame  2  in the front portion thereof. Thus, according to examples described above, the bottom cover,  3 ,  3 A and  3 B, may be securely assembled with the frame  2 . Because the bottom cover  3  is made of copper (Cu) with relatively larger thermal conductivity, the bottom cover  3  securely assembled with the frame  2  enhance the heat dissipating function of the components installed within the optical transceiver  1 , typically, an optical transmitter  17 , and/or a local signal source when the optical transceiver  1  is applied to, what we call, the optically coherent communication system. 
         [0064]    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. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.