Abstract:
The present invention provides a configuration to improve a heat-radiating effect of an optical subassembly having a co-axial package and a pluralilty of lead pins arranged in an arrayed shape. The heat generated inside the subaasembly may be dissipated through the heat-radiating fin attached to a flat surfce, not a curved side surface of the subassembly such that the lead pins provided in the subassembly pass through the slot provided in the heat-radiating fin. The heat-radiating fin has a slab portion attached to the cover of the transciver, when the subassembly is installed witbin the t transciver. Thus, the hea gneratied in the subassembly can be easily and effectively diipated to the cover.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of prior filed U.S. Provisional Application 60/579,969 filed on Jun. 16, 2004 entitled “An optical sub-assembly with a radiating fin and an optical transciver installing the same” by inventors Yoshikawa; S., and Mizue; T., which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an optical assembly (hereinafter denoted as OSA), in particular, to configuration for heat dissipation thereof that installs a device generating a large heat.  
         [0004]     2. Related Prior Art  
         [0005]     The OSA installs an optical semiconductor device therein. A semiconductor laser diode and a semiconductor photodiode are well known as the optical semiconductor device. The OSA installing the laser diode is called as a transmitting optical sub-assembly (TOSA), while the OSA installing the photodiode is called as a receiving optical sub-assembly (ROSA). Recently, as the tramsmission speed of the optical communication increases, the optical semiconductor device must be operated in high speed, which inevitably enhances the heat dissipation of the semiconductor device. Therefore, the TOSA or the ROSA should require the configuration by which the heat generated thereof effectively dissipates to the outside of the TOSA or the ROSA.  
         [0006]     United States patent application published as US 20030021310A1 has disclosed various configurations for the heat dissipation of the OSA with a co-axial shape.  FIG. 1  of this application has illustrated a radiating fin  140  having an opening mating with the stem of the OSA. The radiating fin  140  is extended from the header  104  and attached to the heat sink  146 .  FIG. 3  of this application has illustrated another arrangement in which a member  306 , fitting to the outer shape of the stem  312 , touches thereto in one end thereof, and the other end is extended from the stem  312  and attached to the heat sink  304 . Further, a metal member  404  surrounding the stem  410  directly touches the heat sink  406  in  FIG. 4  of this application.  
         [0007]     Generally, the OSA is used as one of components for an optical data link or an optical transceiver. The arrangement of the heat dissipation of the OSA should take the structure. of the data link or the optical transceiver into account. Moreover, from the material point of view, a cost saving material such as alloy of copper and tungsten (CuW) should be avoided even if such material has good thermal conductivity.  
         [0008]     Based on the background described above, one object of the present invention is to provide an OSA and an optical transceiver using the OSA with an effective heat dissipating arrangement and without using a cost ineffective material.  
       SUMMARY OF THE INVENTION  
       [0009]     One aspect of the present invention relates to an optical subassmbly that is coupled with an optical fiber. The optical sub assembly comprises a semiconductor optical device, a co-axial packagem a plurality of cylindrical members, and a heat-radiating fin. The semiconductor optical device may be a semiconductor light-transmitting device such as laser diode, or a semiconductor light-receiving device such as photodiode. The co-axial package comprises a disk-shaped stem, a plurality of lead pins, and a cap. The stem and the cap, combined with each other, form a cavity to install the semiconductor optical device therein. The stem has first and second flat surfaces and a curved side surface connecting these first and second surface. The cylindrical member, attached to the co-axial package, optically couples the semiconductor optical device with the optical fiber to be received by the cylindrical members. The heat-radiating fin is attached to the second surface of the stem such that the lead pins pass through the heat-radiating fin.  
         [0010]     In the present invention, since the heart-radiating fin is attached to the one of the flat surface of the stem and the other flat surfacce mounts the semiconductor optical device that generates heat, the heat can be effectively dissipated through the stem and the heat-radiating fin to the outside of the subassembly.  
         [0011]     The lead pins provided in the stem of the optical subassembly may be grouped in two groups. Each group forms an array of lead pins, and the array extends in parallel to each other. The heat-radiating fin attached to the stem may provide slots to pass these arrayed-lead pins. Therefore, the positioning between the subassembly and the heat-radiating fin may be facilitated.  
         [0012]     Moreover, the heat-radiating fin may provide a finger and the stem may provide a groove in the side surface thereof. Since these finger and the groove may mate with each other. This arrangement may be further facilitated in the positioning between the stem and the heat-radiating fin.  
         [0013]     The heat-radiating fin of the present invention may provide a body portion and a slab portion extending and bending from the body portion. The slab portion has a relatively wide area, and the body portion is attached to the stem. Therefore, the heat generated in the subassembly and transmitted to the heat-radiating fin through the stem can be effectively dissipated to the outside of the subassembly through the slab portion. When the slab portion is attached to a medium or a heat sink, the heat dissipating effect can be further enhganced.  
         [0014]     Another aspect of the invention relates to an optical transceiver that includes at last an optical subassembly with an enhanced heat-radiating mechanism mentioned above. The optical transceiver comprises, lower and upper covers, a frame sandwiched by the lower and upper covers, the optical subassembly, and a substrate. The optical subassembly provides a heat-radiating fin and two arrayed-lead pins. The arrayed-lead pins are connected to the substrate by sandwiching the substrate therebetween. Further, the heat-radiating fin may provide legs extending from the body portion. These legs, with a gap therebetween coincident with a gap between two arrayed-lead pins, also sandwich the substrate. Thus, the arrayed-lead pin and the leg of the heat-radiating fin may be sooldered with surface mounting. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]      FIG. 1A  is a perspective view illustrating an optical subassembly with a heat-radiating fin according to the present invention; and  
         [0016]      FIG. 1B  is an exploded view of the optical subassembly and the heat-radiating fin;  
         [0017]      FIG. 2A  illustrates the optical subassembly; while  
         [0018]      FIG. 2B  shows a cross section of the optical subassembly along the optical axis;  
         [0019]      FIG. 3A  is a perspective view from the top direction of the heat-radiating fin of the present invention; and  
         [0020]      FIG. 3B  illustrates the heat-radiating fin viewing from the different direction to that of  FIG. 3B ;  
         [0021]      FIG. 4A  is a cross section of the subassembly with the heat-radiating fin;  
         [0022]      FIG. 4B  is a cross section of the subassembly rotated by a right angle to that of  FIG. 4A ; and  
         [0023]      FIG. 4C  is a bottom view of the subassembly with a heat-radiating fin; and  
         [0024]      FIG. 5A  is an exploded view of the optical transceiver installing the optical subassembly with the heat-radiating fin according to the present invention; and  
         [0025]      FIG. 5B  is an exploded drawing of the optical transceiver viewed from the bottom side. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
     First Embodiment  
       [0026]     Next, preferred embodiments of the present invention will be described as referring to accompanying drawings.  FIG. 1A  is a perspective view of an OSA with a heat-radiating fin, and  FIG. 1B  is an exploded view of the OSA according to the present invention. Next, the OSA, and the radiating fin will be described in detail.  
         [0027]      FIG. 2A  is a perspective view of the OSA, and  FIG. 2B  is a cross sectional view of the OSA. The OSA assembles several tubular members, namely, the OSA having a co-axial package, includes a stem  11  with a disk shape, a cap  12 , an alignment member  21 , a bush  22 , a stub  23 , a sleeve  24 , and asleeve cover  25 .  
         [0028]     The stem  11  is made of, for example iron coated with nickel or coated with nickel and gold. A plurality of grooves,  11   b  and  11   c , extending along the center axis of the cylindrical members is provided in a side of the stem  11 . The groove  11   c , as described later, is provided for positioning the heat-radiating fin  50 , while the other groove  11   b , which is wider and shallower than the former groove  11   b , is for the identification of the lead pin  16 . On the stem  11  is arranged with a light-transmitting device  10 , such as semiconductor laser diode, via a sub-mount  11   a . The sub-mount  11   a , protrudes from the primary surface of the stem  11 , and includes the mounting surface  11   b  where the heat sink  13  is disposed thereon. The light-transmitting device  10  is mounte on the heat sink  13  to alighn the optical axis thereof coinciding with the center axis of cylindrical members  21  to  24 .  
         [0029]     The cap  12  is also a cylindrical member that includes a first bore  12   a , a second bore  12   b , and a wall  12   c  partitioning the first and second bores,  12   a  and  12   b . The cap  12  is placed on the stem  11  with a flange  12   d  provided in an end portion thereof facing the stem  11 . That is, the end surface of the flange  12   d  is resistance welded to the primary surface of the stem  11  under inert atmosphere such as dry nitrogen. Accordingly, the semiconductor light-transmitting device  10  is airtightly sealed within the first bore  12   a , which forms a cavity. An outer diameter of the cap  12  is slightly smaller than that of the stem  11 .  
         [0030]     An aperture is provided on the center of the partition  12   c , and a lens  14  is secured to the cap  12  to seal the aperture  12   c . Generally, the optical axis of the lens  14  coincides with that of the light transmitting device  10 . However, in order to prevent light reflected from the surface of the lens  14  from returning the light transmitting device  10 , the optical axis of the lens  14  and that of the light transmitting device  10  may be intentionally inclined with respect to each other.  
         [0031]     The alignment member  21  includes side portion  21   a  and a bottom portion  21   b . The side portion  21   a  forms a bore  21   c , the inner diameter of which is slightly larger than the outer diameter of the cap  12 . Accordingly, by sliding the inner surface  21   e  of the alignment member  21  on the outer surface  21   e  of the cap  12 , an optical alignment along the optical axis, which along the center axis of cylindrical members, can be performed. Thickness of the side portion  21   a  is thin to enable the YAG-laser welding between the side portion  21   a  and the outer surfacce  12   e  of the cap  12  from the outside of the side potion  21   a . After optical alignment, the alignment member  21  and the cap are YAG-laser welded.  
         [0032]     On the center of the bottom portion  21   b  is provided with an aperture  21   f  for passing light emitted from the light transmitting device  10  and concentrated by the lens  14 . A portion of the aperture  21   f  may expand its diameter into which an optical isolator  15  may be arranged to enable the alignment member  21 , the bottom portion  21   b  thereof, close tothe cap  12 . Therefore, even the lens  14  with a shorter focal length may be applicable in the present arrangement. The outer surface  21   d , the top surface thereof, is processed in flat to enable the optical alignment of the bush  22 , the stub  23 , and the sleeve  24  with the light transmitting device  10  by adding these members on the top surface  21   d.    
         [0033]     The bush  22  secures the sleeve  24  therein. The sleeve  24  is press fitted by the bush  22 . In another word, the bush  22  is press-fitter between the sleeve  24  and sleeve cover  25 . An end of the bush  22 , integrally with the sleeve  24  and the stub  23 , may slide on the flat surface  21   d  of the alignment member  21 . Thus, the optical alignment in directions perpendicular to the center axis of cylindrical members can be carried out. One end  22   a  of the bush  22  provides a flange, and the YAG-laser welding between the bush  22  and the flat surface  21   d  of the alinment member  21  is performed at this flange after the optical alignment therebetween is completed.  
         [0034]     Onthe outer surface of the bush  22 is provided with a flange  22   a  to receive, as explained later, the root portion  25   c  of sleeve cover  25 . Although the sleeve cover  25  is a member independent of the optical alignment, when the subassembly  2  is installed in, for example, the optical transceiver, the position of the subassembly must be defined within the transceiver. The flange  22   a  cooperated with another flange  25   c ,which will be explained later, may decide the position of the subassembly  2  within the transceiver.  
         [0035]     Generally, the split sleeve is used for the sleeve  24 . The split sleeve has a slit along the axis thereof, and may expand to directions perpendicular to the optical axis when a ferrule with a diameter slightly larger than that of the ferrule. However, a rigid sleeve may be used as the sleeve  24  in the present invention. The rigid sleeve includes no slit and has a diameter slightly larger than that of the ferrule. The sleeve  24 , independent of the split sleeve, may be made of ceramic such as zarconia, metal such as stainless steel, or new material such as amorphous metal. The outer diameter of the sleeve  24  is slightly larger than the diameter of the inner surface  22   b  of the bush  22 , accordingly, the bush  22  is press-fitted between the sleeve  22  and the sleeve cover  25 , whic mechanically secures the stub  23  with the end portion of the sleeve  24 . The end of the sleeve  24  and that of the bush  22  coincide to each other.  
         [0036]     The sleeve cover  25  positions in forward of the bush  22  that covers the bush  22  by a portion  25   c  thereof and portions of the sleeve  24  not covered by the bush  22  by a portion  25   b  of the sleeve cover  25 . The inner diameter of the sleeve cover  25  is larger than the outer diameter of the sleeve  24 . Accordingly, a gap is formed therebetween. The opening  25   a , formed at the end portion of the sleeve cover  25 , has a chamfer that facilitates the insertion of the extraction of the ferrule that is not illustrated in  FIG. 2B  and is to be mated with the sleeve  24 .  
         [0037]     The root  25   c  of the sleeve cover  25  has a greater diameter than that of the tip portion  25   b  to form a flange. To insert this flange into the holder, which is illustrated in  FIG. 5 , and to fix the holder to the transceiver body defines the position of the subassembly within the transceiver. The position of the subassembly must conform to the standard of the optical connector mated to the optical receptacle formed by the transceiver&#39;s body. By providing the flange  25   c  in the sleeve cover  25 , the standard can be fulfilled.  
         [0038]     The end of the sleeve  24 , i.e. the end close to the alignment member  21 , inserts the stub  23 , configuration of which is similar to the ferrule. That is, a coupling fiber  23   a  is secured in the center thereof, and an end surface  23   b  thereof is processed with the coupling fiber  23   a  to incline to the optical axis. the light emitted from the light-transmitting device  10 , passing the lens  14  and the optical isolator  15 , enters the tip of the coupling fiber  23   a . Portion of the incident light is reflected by the tip of the coupling fiber  23   a . Because of the inclined surface of the tip of the coupling fiber  23   a , the reflected light does not return the light-transmitting device  10 , which does not make an optical noise source in the light-transmitting device  10 .  
         [0039]     The other end surfacce  23   c  of the stub  23 , the side apart from the light-transmitting device  10  is also processed in spherical with the coupling fiber  23   a . Both end surfaces of the stub  23  and the coupling fiber  23   a  coincidies with each other. The end surface of the ferrule to be mated with the sleeve  24  has the same structure as the stub  23  with the cupling fiber  23   a . That is, the ferrule has an optical fiber in the center thereof, and the end surfacce of the ferrule and that of the fiber not only coincides with each other but also forms in spherical. Therefore, the coupling fiber  23   a  and the optical fiber in the ferrule can be physically in contact to each other, which reduces the optical reflection at the interface therebetween.  
         [0040]     As illustrated in  FIG. 2A  and  FIG. 2B , a plurality of the lead pins  16  protrudes from the outer surface of the stem  11 . In the present embodiment, two groups  16   a  and  16   b  of the lead pin, both groups including four lead pins, are arranged in parallel to each other. Electrical isolation between the lead pins  16  and the stem  11  is performed such that four lead pins in each groups,  16   a    16   b , are collectively glass-sealed. The gap to the nearest pins is about 100 mil (about 2.0 mm). These types of lead pins,  16   a  and  16   b , are called as an arrayed-lead pin, and has an advantage to increase the number of lead pins without enlarging the diameter of the stem  11 .  
         [0041]     Next, the arrangement of fin  50  will be described.  FIG. 3A  and  FIG. 3B  are perspective view showing the radiating fin  50 .  FIG. 3A  is a view from the front side, while  FIG. 3B  is a view from the rear side. The radiating fin  50  includes a base portion  50   a , two slab platforms  50   b  and  50   c , a set of latch  50   d , and four legs  50   e.    
         [0042]     The base portion  50   a  is a rectangular plate with a pair of slots  50   g  in the center thereof, through which the arrayed-lead pins,  16   a  and  16   b , pass.  
         [0043]     Two slab portions,  50   b  and  50   c , are formed to bend from two side opposite to each other of the base portion  50   a . The first slab  50   b  is wider than the second slab  50   c . Both slabs  50   b  and  50   c  include openings,  50   h  and  50   i , in the root thereof, i.e. respective corners to the base portion  50   a . Fingers,  50   j  and  50   k , protrude from theslabs,  50   b  and  50   c , within respective openings,  50   h  and  50   i , and bend to the inward side in the tips of the fingers. These fingers,  50   j  and  50   k , mate with grooves  11   c  provided in the outer side surface of the stem  11 , thus positioning the radiating fin  50  relative to the stem  11 .  
         [0044]     From another pair of sides of the base portion  50   a , a pair of sides not continuing to the slabs  50   b  and  50   c , a pair of latches  50   d  is protruded tp the same direction to which the slabs,  50   b  and  50   c , are extended. The latch  50   d , at the tip thereof, is bent in inward and in arcuate. The latches  50   d  may fit with the flange  12   f  of cap  12 , which is welded to the stem  11 , thereby fixing the radiating fin  50  to the stem  11 . The slabs,  50   b  and  50   c , and the base portion  50   a  form a space into which the stem  11  of the OSA  2  is received. Further, the fingers,  50   j  and  50   k , and the latches  50   d  position and fix the radiating fin  50  to the stem  11 .  
         [0045]     Four legs  50   e  are extended from sides, where the latches  50   d  extend therefrom, to a direction opposite to the direction where the latch  50   d  being projected thereto. These legs  50   e  may mechanically support the OSA  2 , when the OSA  2  is installed within the transceiver and connected their lead pins  16  to the substrate implemented in the transceiver, by connecting the legs  50   e  to the ground on the substrate. This arrangement may stabilize the ground potential in the OSA  2 .  
         [0046]     From  FIG. 4A  to  FIG. 4C  are appearances when the radiating fin  50  is attached to the OSA  2 .  FIG. 4A  is a view shown from one side,  FIG. 4B  is a view shown from another side, and  FIG. 4C  is a plan view of the assembly.  
         [0047]     The base portion  50   a  of the radiating fin  50  is fixed to the stem  11  with solder. Within the space surrounded by slabs,  50   b  and  50   c , and a pair of latches  50   d  is received by the stem  11  such that the latches  50   d  fit the flange  12   f  of the cap  12 . The fingers,  50   j  and  50   k , are mated with the corresponding groove  11   c  provided in the side of the stem  11 , thereby positioning the radiating fin  50  relative to the stem  11 , thus the arrayed-lead pins,  16   b  and  16   c , can exactly pass through the corrsponding slots  50   g  of the radiating fin  50 .  
         [0048]     According to the present invention, the radiating fin  50 , which is made of thermally conductive material such as copper, is fixedin the base portions  50   a  thereof to the surface of the stem  11 , and the slab platforms,  50   b  and  50   c , continued to the base portion  50   a  is opened for the material having a good heat dissipating characteristic. On the other hand, the light-transmitting device  10  that generates large heat is mounted on the stem  11 . Accordingly, the heat generated by the light-transmitting device  10  is effectively dissipated to the outside of the OSA  2 , even when the stem  11  is made of metal having less thermal conductivity such as iron coated with nickel or nickel liminated with gold, or Kovar™, because the radiating fin  50  is in directly contact with or fixed to the stem  11  mounting the light-transmitting device  10  thereon.  
         [0049]     From a viewpoint of the heat dissipation, the slabs  50   b  and the  50   c  preferably has large area. However, the area thereof is restricted to take the inner space of the optical transciver into which the OSA  2  is to be installed. Although the radiating fin  50  is preferably thick for the thermal conductivity, another subject is manufacturing the fin  50  may occur, for example, the thicker the material of the fin  50 , the harder to bend and to cut it. The present embodiment adopts the thickness of 0.5 mm for the radiating fin  50 , which can cope with the heat dissipating function and the manufacturing. the complex structure shown in  FIG. 3A  and  FIG. 3B  can be realized with no problem.  
         [0050]     Moreover, the description aboveis primarily concerning to the transmitting optical assembly (TOSA). However, the arrangement of the OSA mentioned above and the heat-radiating fin may be applied to a receiveing optical subassembly (ROSA) that includes, for example, a photodiode for a semiconductor optical device.  
       Second Embodiment  
       [0051]      FIG. 5A  and  FIG. 5B  are exploded view showing an optical transceiver that installs the OSA  2  according to the present invention.  FIG. 5A  is a view shown from the front-up side, while  FIG. 5B  is a view from a rear-bottom side. This transceiver has a configuration following the so-called GBIC (Giga-Bit Interface Converter) standard.  
         [0052]     The optical transceiver  100  comprises a lower cover  101 , a frame  102 , two OSAs (the TOSA  111  and the ROSA  112 ), an OSA holder  103 , and an upper cover  104 . The frame  102  provides a rceptacle  121  havbing two openings in the front side. The head portion of the TOSA  111  and the ROSA  112  are protruded within the opening of the receptacle  121 , thus, within the receptacle, optically coupling between the ferrule included in the optical connector that is to be mated with the receptacle and the two OSAs are realized. The OSA holder  103  and the frame  102  define the positions of two OSAs,  111  and  112 , in the frame by sandwiching them. The front wall of the OSA holder  103  serves as the partition of the receptacle  121 .  
         [0053]     A substrate  131  is implemented in the rear side of the TOSA  111  and the ROSA  112 , on which an electronic circuit with a plurality of electronic components is mounted. This substrate  131  includes the electrical plug  132  in the rear end thereof. The electrical plug  132  mates with the other electrical connector provided on the motherboard, which is not shown in figures, onto which the transceiver is to be mounted. The electrical plug  132  transfers the signals and the electrical power to/from the circuit provided on the substrate  131 .  
         [0054]     The substrrate  131  is physically and electrically connected with the TOSA  111  and ROSA  112  with lead pins  16   b  and  16   c , and four legs  50   e  provided in the radiating pin  50 . That is, in the present invention, the lead pins  16   b  and  16   c  are put into two groups, each including four lead pins and assembled in parallel to each other. The TOSA  111  and the ROSA  112  are installed such that these two groups sandwich the substrate  131 . Moreover, four legs  50   e  are also put into two groups sandwich the substrate  131 . Moreover, four legs  50   e  are also put into two groups sandwiching the substrate  131  therebetween. To connect the legs  50   e  to the conduction pattern on the substrate  131  not only stabilizes the ground potential of subassemblies, but forms, in addition to the slabs,  50   b  and  50   c , another heat dissipation path from the subassemblies to the conduction pattern on the substrate  131 . This enhances the heat dissipating efficiency from the subassemblies.  
         [0055]     Referring to  FIG. 4B , the gap between two arrayed-lead pins,  16   a  and  16   b , and that between legs  50   e  coincide to each other. Accordingly, the Tosa  111  and the ROSA  112  can be rigidly fixed to the substrate  131  by the surface mounting technique, in which no via holes passing the lead pin therethrough are provided on the substrate  131 .  
         [0056]     The slab  50   b  of the radiating fin  50  is thermally coupled with the upper cover  104  via a thermal sheet such as silicone rubber. Heat generating device within the OSA is the laser diode for the TOSA  111 , while the pre-amplifier for the ROSA  112 . These devices are mounted on the stem  11 , and the radiating fin  50  is directly attached to the stem  11 . Accordingly, heat generated by these devices effectively dissipates to the upper cover  104  via the radiating fin  50 , which enhances the thermal stability of the transceiver.  
         [0057]     Another slab  50   c  of the radiatin g fin  50 , relatively narrower flange than the aforementioned slab  50   b , thermally couples to the lower cover  101 . As shown in  FIG. 5B , a portion of the frame  102  is cut to expose a portion of the stem  11 , so the radiating fin  50 . Accordingly, another slab  50   c  may thermally couple with the lower cover  101  through another thermal sheet.  
         [0058]     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided the come within the scope of the appended claims and their equivalents.