Abstract:
A heat dissipating mechanism from an optical assembly to housing without stressing the assembly against the housing is disclosed. The optical assembly has a box-shaped portion to install the optical device and the heat generating device. Among six walls of the box-shaped portion, rear and one side wall are provided for the signal transmission, and two side walls continuous to each other are provided for the heat conduction. The housing forms a hollow within which the optical assembly is set such that the two side walls of the optical assembly come in thermally contact with the bottom and one side wall of the hollow.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an optical transceiver, in particular, the invention relates to a pluggable optical transceiver with a function of the optical transmission and the optical reception. 
         [0003]    2. Related Prior Art 
         [0004]    The pluggable transceiver has a function to be set within the host system, such as a computer and a network router, without turning off the electrical power of the host system. When the transmission speed enters a giga-hertz band (GHz), it becomes inevitable to apply a semiconductor laser diode (LD) as an optical signal source, in particular, when the transmission speed exceeds 10 GHz, the LD with a temperature controlling device is installed within a package whose shape is, what is called, the butterfly package with a box-shaped body portion and a cylindrical portion extending from one side wall of the box portion, because the performance of the LD strongly depends on the temperature thereof and it is inevitable to lower the operation temperature of the LD and to make it constant. 
         [0005]    Typical temperature control device is the Peltier device with two plates and Peltier elements put between plates. When one of plates mounts the LD and cools down the temperature thereof, the other plate is necessary to be heated up to balance the thermal condition of the Peltier device. When the heat dissipating mechanism for the other plate is ineffective, the LD is unable to be cooled down enough to cause the failure of the optical transceiver. Various mechanisms and techniques have been proposed in the field. 
         [0006]    For instance, the U.S. patent, the U.S. Pat. No. 6,522,486, has disclosed an semiconductor laser module with a box-shaped package installing the LD and the Peltier device. An auxiliary member caps this module and mechanically fixes the module to the board. The optical assembly applied in the pluggable transceiver further provides a sleeve that constitutes an optical receptacle and optically couples with the optical connected inserted in this optical receptacle. This sleeve is necessary to be physically aligned with the receptacle because the sleeve must mate with a ferrule in the optical connector. Therefore, when the module is pressed against the board to conduct heat effectively to the board, as disclosed in the prior art mentioned above, the physical relationship between the sleeve and the optical receptacle is occasionally violated. 
         [0007]    Moreover, when the transceiver follows the standard of the XENPAK or the X2, which is ruled by the IEEE 802.3ae in the package thereof, the transceiver is necessary to form the mechanism, such as latch bar or hook, in the side of the transceiver to fix it with the host system, which restricts the place where the heat-dissipating mechanism to be built. Only the top or the bottom of the transceiver package may be left for the heat dissipation. Accordingly, the present invention is to provide an optical transceiver with a new arrangement to conduct heat of an optical module effectively without pressing the module against the housing of the transceiver. 
       SUMMARY OF THE INVENTION 
       [0008]    A feature of an optical transceiver according to the present invention is that, the optical transceiver includes a semiconductor optical device, an optical assembly with a body portion and a cylindrical portion and a frame. The body portion has a box-shape with six walls of front, rear, top, bottom and a pair of side walls. The cylindrical portion extends from the front wall. The top wall mounts the semiconductor optical device thereon within the box portion. The frame, which installs the optical assembly therein, provides a hollow in an inner surface thereof This hollow has a bottom and at least an inner wall formed in a center side of the frame. The hollow receives the box portion of the optical assembly as leaving a gap therebetween such that the top wall of said box portion faces the bottom of the hollow and one of the side walls faces the inner wall of the hollow. Moreover, in the optical transceiver of the invention, the gap between the box portion and the frame is filled with a gelled thermal compound. 
         [0009]    According to the arrangement of the optical assembly of the present invention, even the optical assembly is rigidly fixed to the frame to realize the optical coupling function between the semiconductor optical device and the optical receptacle, the body portion of the optical assembly is mechanically released from the frame with a gap, but is thermally in contact with the frame by interposing a gelled thermal compound within the gap. Accordingly, the mechanical conditions and the thermal relations between the optical assembly and the frame may be consistent. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1A  is a perspective view and the  FIG. 1B  is a top plan view of the optical transceiver according to the present invention; 
           [0011]      FIG. 2  is an exploded view of the optical transceiver according to the present invention; 
           [0012]      FIG. 3  illustrates an inside of the optical transceiver, where the TOSA and the ROSA are assembled with the optical receptacle and the circuit board; 
           [0013]      FIG. 4A  is a top plan view,  FIG. 4B  is a side view and  FIG. 4C  is a perspective view of the TOSA according to the embodiment of the present invention, where the TOSA is assembled with two types of FPC boards in  FIG. 4C ; 
           [0014]      FIG. 5  illustrates an inner structure of the upper frame; 
           [0015]      FIG. 6  shows the TOSA set within the hollow of the upper frame with the thermal compound filled within the gap between the TOSA and the frame; and 
           [0016]      FIG. 7  is a cross section taken along the ling A-A shown in  FIG. 1 , which shows the thermal compound filled within the gap between the TOSA and the frame. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0017]      FIGS. from 1A to 3  explain the optical transceiver according to the present invention, where  FIG. 1A  is a perspective view,  FIG. 1B  is a top plan view,  FIG. 2  is an exploded view, and  FIG. 3  shows an inside of the transceiver that removes an upper frame from the primary assembly. 
         [0018]    The optical transceiver  1 , which is inserted into an opening formed in the face panel of the host system, comprises the upper frame  11 , the lower frame  13  and the cover  13 . These components form a package with the type of, what is called as, the XENPAK and the X2. The upper and lower frames,  11  and  12 , form an optical receptacle  21  into which an optical connected is inserted. The description below assumes a side where this optical receptacle is formed to be the front side, while the other side to be the rear. 
         [0019]    A side of the frames, as shown in  FIG. 1B , forms a latch tab  20   a.  When the optical transceiver  1  is set within the rail system provided on the host substrate, this latch tab  20   a  mates with an aperture provided in the side of the rail system to secure the transceiver  1  within and on the host system. On the front of the frame is provided with a grip  14  that may manipulate the latch tab  20   a , by sliding front and rear around the optical receptacle  21 , to release the transceiver  1  from the rail system on the host board. The upper frame  11  provides, in the outer surface thereof, a plurality of thermal fins  11   a  to radiate heat generated by, for instance, a semiconductor optical device within the transceiver  1 . 
         [0020]    The transceiver  1  encloses a transmitter optical sub-assembly (TOSA)  15 , a receiver optical sub-assembly (ROSA)  16 , a holder  17 , a cover  18 , a substrate  19  and a latch member  20  within the frame. The TOSA  15  has a body  15   a  with a rectangular shape that installs a semiconductor optical device such as a laser diode (LD) and a Peltier device therein. The top wall  15   b  and one of sides  15   c  facing inside of the transceiver  1  come in thermally contact with the hollow formed inside of the upper frame  11  via a gelled thermal compound to conduct heat generated within the body portion  15   a  efficiently to the upper frame  11  through the top wall  15   b  and the side wall  15   c  of the body portion  15   a  interposing the thermal compound, and to radiate heat from the fins  11   a  of the upper frame  11 . The ROSA  16 , on the other hand, installs a photodiode as a semiconductor optical device which is insensitive to a temperature compared to the LD, accordingly, the ROSA  16  is unnecessary to provide a specific mechanism to dissipate heat in the present embodiment. 
         [0021]    The holder  17  secures the TOSA  15  and the ROSA  16  against the lower frame  12 . The holder  17  also provides two pairs of latch tabs whose shapes and functions follow the standard of the SC type connector. The bracket  18  fixes the TOSA  15  in a center portion thereof to the holder  17 , in which the TOSA  15  is put between the holder  17  and the bracket  18  in a center portion to align the position along a direction perpendicular to the optical axis of the TOSA  18 . That is, the arrangement shown determines the up-and-down direction of the TOSA  18  with respect to the optical axis. The circuit board  19  mounts an electronic circuit including a plurality of ICs. Flexible printed circuit (FPC) boards,  19   a  and  19   b , electrically connect the TOSA  15  and ROSA  16  with the circuit board, respectively. The latch member includes the latch tab  20   a , which extrudes from the side of the frame to mate with the rail on the host board, and a leaf spring  20   b  to elastically push out the latch tab  15 , which enables the latch tab  15   a  to mate with the rail. 
         [0022]    Next, the upper frame of the optical transceiver  1  and the TOSA  18  will be described in detail.  FIGS. 4A to 4C  illustrates the appearance of the TOSA  15 , where  FIG. 4A  is a plan view,  FIG. 4B  is a side view and  FIG. 4C  is a perspective view of the TOSA  15  assembled with the FPC board  19   a.    
         [0023]    The TOSA  15  comprises the body portion  15   a  with the box shape and a cylindrical portion  15 i extending from one side wall of the body portion  15   a . The optical axis of the TOSA  15  is identical with a center of the cylindrical portion  15   i,  which is also identical with the optical axis of the receptacle. The body portion  15   a  encloses the LD and the Peltier device with lower and upper plates, which are shown by dotted lines in the figure. The upper plates of the Peltier device mounts the LD thereof, while, the lower plate thereof comes in directly contact with the inner surface of the top  15   b  of the body portion  15   a . That is, the Peltier device is installed within the body portion  15   a  in upside-down. When the upper plate of the Peltier device is cooled down to set the temperature of the LD to be a preset condition, the lower plate in contact with the top wall  15   b  is heated up. The TOSA  15  is necessary to dissipate this heat of the Peltier device through the top  15   b.    
         [0024]    The side wall  15   c  of the TOSA  15  continuous to the top wall  15   b  may be also formed by a metal with good thermal conductivity, which may conduct heat generated by the Peltier device to the outside of the body portion  15   a . This side wall  15   c  of the body portion  15   a  faces the center wall  11   e  of the upper frame  11 , which will be described later. Thus, the top wall  15   b  and the inner side wall  15   c  of the body portion  15   a  operate as a heat conducting surface for the heat generated by the Peltier device. 
         [0025]    The body portion  15   a  provides a plurality of lead pins,  15   f  and  15   g,  one group of which extends from the outer side wall  15   d  and the other group of which extends from the rear side wall  15   e.  The outer side wall  15   d  means that, when the TOSA  15  is set on the upper frame  11 , the outer side wall  15   d  faces the outside of the transceiver  1 , while the inner side wall  15   c  faces the center wall  11   e  of the upper frame  11 . 
         [0026]    One group of lead pins,  15   g,  extending from the real wall  15   e  connect with the FPC board  19   c,  while the other group of lead pins,  15   f,  extending from the outer wall  15   d  are connected with the other FPC board  19   a . Moreover, the former FPC board  19   c,  which transmits signals with high frequency components to drive the LD, is connected with the circuit board  19  in one surface therefore, while, the latter FPC board  19   a , which conducts signals to control the Peltier device and is configured with relatively lower frequency components, is connected with the circuit board  19  in the other surface. Thus, in the present TOSA  15 , two types of signals are provided with individual FPC boards,  19   a  and  19   c , each extending from different surfaces of the circuit board  15 . The FPC board  19   a  connected with the side lead pins  15  is configured to extend downward from the side  15   d , to be bent inward in the bottom of the body portion, and to extend rearward to connect with the circuit board  15 , as shown in  FIG. 4C . 
         [0027]    According to the arrangement of two FPC boards,  19   a  and  19   c , even if two types of signals, one of which includes relatively higher frequency components while the other of which has lower frequency components or the power supply line, are individually provided to the TOSA  15  from the circuit board  19 , the former signals may be transmitted with the shorter FPC board  19   c  so as not to degrade the signal quality even in high frequency regions, while, the latter signals may be provided without affecting the heat dissipating function of the TOSA  15 . 
         [0028]      FIG. 5  illustrates an inside of the upper frame  11 . The upper frame  11 , which may be made of aluminum with nickel plating, provides the thermal fin  11   a  in the outside thereof, while the frame  11  provides the hollow  11   b  and the saddle  11   c  in the inside thereof. When the TOSA  15  is assembled with the frame  11 , the hollow  11   b  receives the body portion  15   a  of the TOSA  15 , while, the saddle  11   c  supports the cylindrical portion  15   c.    
         [0029]    The hollow  11   b  provides three side walls,  11   f  to  11   g,  and bottom  11   d.  When the TOSA  15  is assembled with the upper frame  11 , the bottom  11   d  comes in contact with the top  15   b  of the body portion  15   a , while the side walls,  11   f  to  11   g,  face to the sides,  15   c  to  15   e , of the body portion  15   a , respectively. Moreover, between the top  15   b  and the bottom  11   d,  and between one of the sides  15   c  and one of the side walls  11   e  are filled with a gelled thermal compound  22 . 
         [0030]      FIG. 6  illustrates the TOSA  15  set within the hollow  11   b  of the upper frame  11  with the gelled compound  22  within the gap between the side wall  11   e  and the side  15   c  of the body portion  15   a , while,  FIG. 7  is a cross section taken along the line A-A shown in  FIG. 1B . 
         [0031]    As shown in  FIG. 6 , the TOSA  15  in the body portion  15   a  thereof is set within the hollow  11   b  and the cylindrical portion  15   i  is secured on the saddle  11   c.  Moreover, between the side wall  15   c  of the body portion  15  and the side wall  11   e  of the hollow  11   b  is filled with the gelled thermal compound  22  to secure the heat conducting path. Between the top  15   b  of the body portion  15   a  and the bottom  11   d  of the hollow  11   b  is similarly filled with the gelled thermal compound. Accordingly, two walls,  15   b  and  15   c , of the body portion  15   a  of the TOSA  15  may face to the upper frame  11  via the thermal compound without forming any air-gap, which effectively dissipates heat generated in the TOSA  15  to upper frame  11  and radiates from the thermal fin  11   a  to the outside of the transceiver  1 . Moreover, the gelled thermal compound  22  is in the hollow  11   b  of the frame  11 , which prevents the compound  22  from oozing out and from extending within the frame  11 . 
         [0032]    The gelled thermal compound  22  of the present invention may be a type of silicon resin, which enables for the TOSA  15  to be in thermally contact with the frame  11  without pressing the TOSA against the frame. Although the embodiment described above concentrates on the TOSA, the arrangement of the body portion of the TOSA, the FPC boards, and the inner structure of the frame may be also applicable to the ROSA when the ROSA installs devices to generate large heat. 
         [0033]    While the preferred embodiments of the present invention have been described in detail above, many changes to these embodiments may be made without departing from the true scope and teachings of the present invention. The present invention, therefore, is limited only as claimed below and the equivalents thereof.