Abstract:
An optical transceiver with an enhanced EMI shielding is disclosed. The optical transceiver of the invention provides an optical receptacle made of metal and an optical subassembly with a metal cover assembled with the optical receptacle. The metal cover electro-magnetically divides the inside from the outside of the transceiver. The metal cover provides a plate portion and an edge portion, where the former portion forms an opening through which the sleeve passes without coming in contact with the metal cover, while, the latter of which comes in contact with the receptacle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention related to an optical transceiver with enhance electro-magnetic interference (EMI) tolerance. 
     2. Related Prior Art 
     The U.S. Pat. No. 6,817,782, has disclosed an optical transceiver with a metal shell and two optical ports each exposing a sleeve of the OSA outward. The optical port receives the external optical connector to perform the optical communication. In such an optical transceiver, the EMI shielding is necessary to prevent the radiation from leaking out from the optical transceiver, in particular, the operating speed of the optical transceiver exceeds 10 Gb/s or greater. The optical transceiver disclosed in the patent mentioned above provides, in addition to the metal shell, a disk shaped cap for the exposed sleeve to prevent the EMI radiation leaking from the vicinity around the sleeve. 
     The present invention is to provide a means to prevent the EMI radiation from leaking without affecting mechanical stress inducing the misalignment between the optical receptacle and the optical subassembly. 
     SUMMARY OF THE INVENTION 
     An optical transceiver of the present invention comprises a metal frame, a receptacle, and an optical subassembly. The optical subassembly includes a sleeve and a body, wherein the latter of which is enclosed in a space formed by the frame and the receptacle. The space may be electrically shielded to enhance the EMI tolerance of the optical transceiver, except for a portion where the sleeve exposes to receive an optical connector. A feature of the preset invention is that the optical transceiver may further comprise a metal cover that is fixed to the receptacle and has an opening through which the sleeve of the optical subassembly passes but the metal cover is physically apart from the sleeve. Because the metal cover of the present invention is thus configured, the sleeve becomes free from the mechanical stress influenced by the metal cover by fixing to the receptacle, and the optically misalignment may be prevented even the optical subassembly with the metal cover is aligned and fixed to the receptacle. 
     Because the metal cover may shield a portion close to an outer periphery of the sleeve, the EMI radiation leaking from the optical transceiver, in particular, the radiation propagating along the longitudinal direction from the front side of the optical transceiver, may be effectively and reduced. 
     The optical transceiver of the present invention may further provide a side cover made of metal that covers whole sides of the body of the optical subassembly. The side cover may have a cross section of an Ω-shape with a pair of legs folded outward and a flat top. The leg may come in contact with the metal frame of the optical transceiver, while, the flat top may come in contact with a rear portion of the receptacle. 
     The optical transceiver may still further provide a ground finger. The receptacle in the rear portion thereof may have an overhung portion, and the ground finger in the cross section thereof may provide a shape tracing the overhung portion of the receptacle. The flat top of the side cover may come in contact with the overhung portion through the ground finger. 
     While, the ground finger may come in contact with the metal cage provided in the host system, into which the optical transceiver is inserted; in order to stabilize the ground potential of the optical transceiver. Thus, the side cover of the invention may come in contact with the ground, exactly, the frame ground of the host system, not only to stabilize the ground potential thereof but the effectively shield the optical subassembly by the frame ground. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is an external appearance of an optical transceiver that installs optical subassemblies according to the present invention; 
         FIG. 2  shows a front portion of the optical transceiver, wherein the receptacle receives one of optical connectors for the optical reception; 
         FIG. 3  is a plan view showing a positional relation between two optical subassemblies, the ROSA and the TOSA, and the metal cover in the optical transceiver shown in  FIG. 1 ; 
         FIG. 4  shows two optical subassemblies and the metal cover installed in the optical transceiver, wherein  FIG. 4  is viewed from the front of the optical transceiver; 
         FIG. 5  is a partial cross section of the front portion of the optical transceiver, wherein the receptacle and the sleeve are broken to show the cross section thereof; 
         FIGS. 6A and 6B  show the metal cover, wherein  FIG. 6A  is viewed from the rear; while,  FIG. 6B  is viewed from the front; 
         FIG. 7  schematically shows a process to set the metal cover and the flange of the optical subassembly in the groove of the receptacle; 
         FIG. 8  is a cross section taken along the line VIII-VIII, marked in  FIG. 3 ; 
         FIG. 9  shows a process to set the metal cover in the sleeve of the optical subassembly; 
         FIG. 10  shows a process subsequent to the process shown in  FIG. 9 ; 
         FIG. 11  shows an optical subassembly assembled with a side cover according to the second embodiment of the invention; 
         FIG. 12  is a perspective view of the side cover shown in  FIG. 11 ; 
         FIG. 13  shows the optical transceiver installing the optical subassembly attached with the side cover and assembled in the receptacle, wherein the receptacle and the frame are shown in the cross section thereof; and 
         FIG. 14  is a side view of the optical subassembly attached with the side cover. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Next, preferred embodiments according to the present invention will be described as referring to accompanying drawings. In the description of the drawings, the same numerals or the same symbols will refer to the same elements without overlapping explanations thereof. 
     (First Embodiment) 
     An optical transceiver  1  shown in  FIG. 1  is an apparatus that couples with and optical connector C 1  for the optical reception and that C 3  for the optical transmission, each of which is inserted from the forward of the optical transceiver  1  to communicate optically with an external apparatus. The description presented herein below assumes that the front corresponds to a side where the optical connectors, C 1  and C 3 , are inserted therein, while the rear is opposite thereto. 
     The optical transceiver  1  has a metal housing  3  which includes a frame  3   a  and a receptacle  3   b  assembled with the frame  3   a  and extended forwardly therefrom. The receptacle  3   b  provides two openings,  5   a  and  5   b , in the front end thereof, into which the optical connectors, C 1  and C 3 , are inserted. In the deep end of the openings,  5   a  and  5   b , is provided with a mechanism to prevent the optical connector from slipping out from the opening unintentionally. 
     Referring to  FIGS. 2 and 3 , the openings,  5   a  and  5   b , each provides in the deep end thereof with an optical subassembly, specifically, a receiver optical subassembly (ROSA)  11  for the receiver connector C 1  and a transmitter optical subassembly (TOSA)  13  for the transmitter connector C 3 , respectively. The ROSA  11  includes a semiconductor device, typically a semiconductor photodiode (PD), to convert an optical signal into a corresponding electrical signal and an optical coupling mechanism to couple the optical fiber in the connector C 1  with the PD. While, the TOSA  13  includes another semiconductor device to convert an electrical signal into an optical signal, typically a semiconductor laser diode (LD), and an optical coupling mechanism to couple the LD optically with the optical fiber secured in the connector C 3 . The ROSA  11  and the TOSA  13  are secured and fixed to the receptacle  3   b.    
     In the rear side of the ROSA  11  and the TOSA  13  is provided with a circuit board  17 . The circuit board  17 , which is fixed to the frame  3   a , mounts various electrical components constituting circuits to control the ROSA  11  and the TOSA  13 . The ROSA  11  is electrically connected with the circuit board with a flexible printed circuit (FPC) board  21 , while, the other FPC board  23  connects the TOSA  13  electrically with the other circuit on the circuit board  17 . 
     In a front end of the ROSA  11  is provided with a sleeve  11   a  made of resin, which optically couples the ROSA  11 , in particular, the PD in the ROSA  11 , with the optical connector C 1  by receiving a ferrule secured in the connector C 1 . The sleeve  11   a  has a bore  11   b  into which the ferrule of the connector C 1  is inserted, as illustrated in  FIG. 4 . The bore  11   b  is arranged behind the opening  5   a  of the receptacle  3   b . Thus, the ROSA  11  may receive light emitted rearward from the optical fiber secured in the ferrule of the connector C 1  and transmit an electrical signal converted from the light to the circuit on the circuit board  17  through the FPC board  21 . 
     Similarly, the front end of the TOSA/3 provides a sleeve  13   a  made of resin which receives the ferrule secured in the connector C 3  to couple the LD in the TOSA  13  optically with the fiber in the connector C 3 . The front end of the sleeve  13   a  also has a bore  13   b  into which the ferrule is inserted. This bore  13   b  is arranged behind the opening  5   b  of the receptacle  3   b . The TOSA  13  may electrically couple with the circuit on the circuit board  17  through the FPC board  23 . Thus, by receiving an electrical signal from the circuit on the circuit board  17  through the FPC board  23 , the TOSA  13  may emit signal light toward the optical fiber secured in the optical connector C 3 . The optical transceiver  1  thus described may optically communicate with the optical fibers in the full duplex mode through the connection between the connector C 1  and the ROSA  11  and between the connector C 3  and the TOSA  13 . 
     When the optical transceiver  1  operates in high speeds, for instance, a speed over 10 Gbps, the electro-magnetic interference (EMI) radiation should be reduced as possible because the EMI radiation easily becomes a noise source for peripheral equipments. The optical transceiver  1  according to the present embodiment assembles the receptacle  3   b  made of metal continuously with the metal frame  3   a  without any gaps therebetween, which may electrically isolate an inner space of the housing  3  that installs the ROSA  11 , the TOSA  13  and the circuit board  17  from the periphery of the transceiver  1 ; thus, the inner space may be effectively shielded. 
     However, the sleeve  11   a  of the ROSA  11  and that  13   a  of the TOSA  13  are inevitably exposed to the outer space because those sleeves,  11   a  and  13   a , are necessary to receive the external optical connector. The outer space means an area not shielded by the metal housing  3 , while, the inner space means an area surrounded by the metal housing  3 . Therefore, the area from the openings,  5   a  and  5   b , of the receptacle  3   b  to the sleeves,  11   a  and  13   a , corresponds to the outer space of the housing  3 . The arrangement where the sleeves,  11   a  and  13   a , are exposed in the outer space brings a defective portion for the EMI radiation. Moreover, the resin made sleeves,  11   a  and  13   a , inherently show less EMI tolerance. 
     Accordingly, as illustrated in  FIGS. 4 to 6 , the optical transceiver  1  according to the present embodiment provides a metal cover  30  that receives the sleeve,  11   a  and  13   a , in the center opening  31   a  thereof. The metal cover  30  may be made of metal, preferably aluminum. As shown in  FIGS. 6A and 6B , the metal cover  30  provides a plate portion  31  with the center opening  31   a  whose dimension is slightly greater than the outer diameter of the sleeve,  11   a  and  13   a , which causes a slight gap between the outer surface of the sleeve,  11   a  and  13   a , and the inner edge of the opening  31   a . The metal cover  30  is assembled with the receptacle  3   b  as being apart from the sleeve,  11   a  and  13   a.    
     The metal cover  30  further provides an edge portion  33  extending rearward from the edge of the plate portion  31 . The edge portion  33  includes parallel portions  33   a  putting the opening  31   a  therebetween and an arched portion  33   c  connecting the parallel portions  33   a . The edge portion  33  expands along the longitudinal direction of the optical transceiver  1 , that is, as being apart from the plate portion  31 , before it is assembled with the receptacle  3   b . The metal cover  30  may be formed by spinning of a metal sheet. 
     The metal cover  30  is assembled with the receptacle  3   b . Specifically, as illustrated in  FIGS. 7 and 8 , the receptacle  3   b  provides a pair of grooves  3   c  each facing the other to receive the metal cover  30 . Setting the metal cover  30  into the groove  3   c , the edge portion  33  expanding along the longitudinal direction of the transceiver  1  is deformed so as to shrink the end thereof. The parallel portions  33   a  of the metal cover  30  are pressed to respective bottom of the grooves  3   c  to set the metal cover  30  in the receptacle  3   b , while, the plate portion  31  in the periphery thereof is pressed to the side  3   e  of the groove  3   c  and to set the position of the metal cover  30  along the longitudinal direction. As illustrated in  FIG. 7 , the grooves  3   c  also receive the flange,  11   e  or  13   e , of the ROSA  11  or the TOSA  13 . However, the distance between the parallel portion  33   a  of the metal cover  30  is set to be slightly wider than the diameter of the ROSA  11  and the of the TOSA  13 ; accordingly, the metal cover  30  is set so as to be apart from the flange,  11   e  and  13   e , of the ROSA  11  and that of the TOSA  11 . 
     In the assembly of the optical transceiver  1 , the metal cover  30  is first attached with the sleeve  11   a  of the ROSA  11  such that the edge portion  33  faces rearward so as for the flange  11   e  to be overlaid by the cover  30 , as shown in  FIG. 9 . Next, the ROSA  11  and the metal cover  30  are set in the grooves  3   c  as the arched portion  33   c  of the cover  30  is first inserted therein, which is shown in  FIG. 10 . The parallel portion  33   a  of the cover  30  comes in contact with the bottom  3   d  of the groove  3   c  as being deformed. Thus, the metal cover  30  is securely set within the groove  3   c  and the electrical conduction between the metal cover  30  and the receptacle  3   b  may be performed. A portion of the edge portion  33  opposite to the arched portion  33   c  is formed so as to trace the outer shape of the flange,  11   e  and  13   e , and this portion substantially makes a right angle to the plate portion  31 ; accordingly, the metal cover  30  may be manually set within the groove  3   c  by pushing this portion  33   e . The other metal cover  30  for the TOSA  13  may be assembled with the receptacle  3   b  by a process similar to those described above. 
     The receptacle  3   b  may have a hollow, which comes in contact with the arched portion  33   c  of the cover  30 , whose shape traces the arched shape of the cover  30 . In this arrangement, a gap between the metal cover  30  and the receptacle  3   b  may be further narrowed to enhance the EMI tolerance. 
     Thus, the metal cover  30  may show a function to partition the housing  3  as passing the sleeves,  11   a  and  13   a . Because the metal cover  30  comes in electrically contact with the receptacle  3   b , the metal cover  30  may electrically shield the inner space of the housing  3 . Thus, the optical transceiver  1  according to the present embodiment, viewed from the front, may shield the inner space of the housing  3  except for the opening  31   a  of the metal cover  30  through which the sleeve,  11   a  and  13   a , pass. The optical transceiver  1  may also suppress the opening of the housing  3  to expose the sleeve,  11   a  and  13   a , in minimum, which may effectively enhance the EMI tolerance of the transceiver  1 . 
     Moreover, the ROSA  11  and the TOSA  13  are set on and fixed to the receptacle  3   b . Specifically, as illustrated in  FIG. 7 , the projection  3   h  of the receptacle  3   b  is put between the flange,  11   e  and  13   e , and the front surface, lid and  13   d , of the body of the ROSA  11  and that of the TOSA  13 ; specifically, the projection  3   h  may be a saddle to mount a portion between the flanges of the ROSA  11  or the TOSA  13 . While; the metal cover  30  is also set on and fixed to the receptacle  3   b . Thus, the metal cover  30  and two optical subassemblies,  11  and  13 , are independently set on and fixed to the receptacle  3   b . The metal cover  30  is apart from the flange,  11   e  and  13   e . Therefore, the metal cover  30  does not mechanically operate on the subassemblies,  11  and  13 , which means that the optical coupling between two subassemblies,  11  and  13 , and respective optical connectors, C 1  and C 3 , is not influenced by the metal cover. 
     In the embodiment thus described, the metal cover  30  forms a slight gap to the sleeve,  11   a  and  13   a ; but the metal cover  30  may be in contact with the outer surface of the sleeve,  11   a  and  13   a . Even in this arrangement, it is important that the metal cover  30  does not influence mechanically to the sleeve,  11   a  and  13   a . A metal cover made of relatively soft metal such as aluminum is preferable to absorb the mechanical stress affected to the sleeve,  11   a  and  13   a , even the metal cover  30  comes in contact to the sleeve. 
     (Second Embodiment) 
       FIG. 11  is a perspective view of a ROSA according to the second embodiment of the present invention. The ROSA  11  shown in  FIG. 11  provides a metal cover  30 A with a circular outer shape, while, the metal cover  30  of the first embodiment has the U-shaped appearance. In a center of the plate portion  31  of the metal cover  30 A is formed with the opening  31   a  through which the sleeve  11   a  passes. The bore of the opening  31   a  is slightly greater than the outer diameter of the sleeve  11   a , which is the same with those of the first embodiment. 
     The metal cover  30 A of the present embodiment provides a finger  34  rising from the edge of the opening  31   a ; but the inner surface of the finger  34  positions in the outside of an imaginary circle of the opening  31   a . Accordingly, the inner edge of the finger  34  does not come in contact to the sleeve  11   a  after the ROSA  11  is set within the transceiver. The finger  34  has a length of around 0.3 mm and has a function to prevent the metal cover  30 A from slipping out from the sleeve  11   a  during the assembly of the ROSA  11 . 
     The ROSA  11  further provides a side cover  40  whose shape is shown in  FIG. 12  in detail. The side cover  40 , which is made from a metal sheet, has a cross section of Ω-shape with a flat top  42  and two legs  41  folded outwardly. In a root portion of the legs  41  is formed with a longitudinal opening not only to form the folding back easily but to soften the elasticity of the folded legs. In the front edge of the side cover  40  is provided with a finger  44 , which is not shown in  FIG. 12  but illustrated in  FIG. 11 . The body of the ROSA  11  is inserted into a center opening of the side cover  40 , and the finger  44  may prevent the side cover  40  from slipping out from the body of the ROSA  11  during the assembly. 
       FIG. 13  is a perspective view of the ROSA  11  assembled with the side cover  40 , where the ROSA  11  is installed in the transceiver  1 , and  FIG. 14  is a side cross section of the transceiver  1 . In  FIGS. 13 and 14 , the frame  3   a  and the receptacle  3   b  are partially cut to show the ROSA  11  explicitly. 
     As shown in  FIGS. 13 and 14 , the leg  41  of the side cover  40  comes in contact with the bottom of the frame  3   a , while, the flat top  42  thereof comes in contact with the overhung portion  3   f  of the receptacle  3   b . The rear portion of the receptacle  3   b  provides the ground finger  4  whose shape traces the cross section of the receptacle  3   b . This ground finger  4  has a front portion  4   a  which is bent outwardly to come in securely contact with the inner surface of the cage of the host system, where the transceiver  1  shown in  FIG. 13  is practically used by inserting into the cage. Because the ground finger  4  in the front portion  4   a  thereof comes in contact with the cage, the chassis ground (frame ground) may be stably conducted from the host system to the optical transceiver  1 . The side cover  40 , assembled with the body of the ROSA  11  so as to surround it, comes in contact with the ground finger  4  in the overhung portion  3   f  by the flat top  42  thereof and also comes in contact with the frame  3   a  by the leg  41  thereof. Thus, the arrangement of the side cover  40  may not only stabilize the frame ground but securely prevent the EMI radiation from leaking out from the optical transceiver  1 . The height of the metal cover  40 , from the bottom of the leg  41  to the flat top  42 , is set to be slightly greater by around 1 mm than a space from the bottom of the frame  3   a  to the underside of the overhung portion  3   f . Accordingly, assembling the optical transceiver  1 , the metal cover  40  is hard to be disassembled. Moreover, the softened leg  41  of the metal cover  40  may cause a lesser mechanical influence to the frame  3   a  and the receptacle  3   b.    
     Moreover, the finger  44  of the side cover  40  shows a repulsive force against the front surface of the body of the ROSA  11  because the finger  44  is folded inwardly. This repulsive force pushes the side cover  40  forward, which makes the front edge of the side cover  40  in securely contact with the rear surface of the ground finger  4 , which further stabilize the frame ground. 
     Although the present invention has been fully described in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, it is to be understood that various changes and modifications may be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.