Abstract:
A small form factor pluggable optoelectronic transceiver module comprises top and bottom housings ( 1, 2 ), a chassis ( 3 ), a receptacle ( 4 ), a PCB ( 5 ), an optoelectronic subassembly ( 6 ), and a shielding shell ( 9 ). The optoelectronic subassembly is received in the receptacle. The shielding shell is fixed on the PCB, and encases a transmitting circuit on the PCB. The chassis is attached to the PCB with screws, and accommodates and protects the PCB. The top housing is attached to the chassis and the receptacle. The top and bottom housings are attached together, encapsulating therein the receptacle, the chassis, the PCB and the shielding shell. The shielding shell provides EMI protection and ESD shielding, and reduces electrical crosstalk. The module also forms multiple grounding paths between a grounding circuit of the PCB and the top and bottom housings.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to small form factor pluggable optical transceiver modules, and particularly to such modules which provide protection from electromagnetic interference (EMI) and electrostatic discharge (ESD), and which reduce electrical crosstalk between transmitting circuits and receiving circuits thereof.  
           [0003]    2. Description of the Related Art  
           [0004]    Optoelectronic transceiver modules are widely used for bi-directional transmission of data between an electrical interface and an optical data link. The module receives electrically encoded data signals which are converted into optical signals and transmitted over the optical data link. The module also receives optically encoded data signals which are converted into electrical signals and transmitted onto the electrical interface.  
           [0005]    High transmission frequencies utilized in fiber optic communications generate significant electrical crosstalk between received and transmitted signals. Additionally, high frequency operation of fiber optic modules generates proportionately high electromagnetic interference (EMI). Shielding of electrical components of a module is required to reduce EMI. A metal shield is commonly attached to a substrate of the module and connected to a ground source.  
           [0006]    U.S. Pat. No. 6,213,651 B1 discloses a small form factor optoelectronic transceiver module for reducing EMI and electrical crosstalk between printed circuit boards (PCBs). The transmitting and receiving circuits are implemented on two separate and substantially parallel PCBs. The transmitter PCB and the receiver PCB are also offset from each other and separated by a ground plane to minimize electrical crosstalk. Using separate PCBs reduces the size of the module, and allows the light transmitting diode and the light receiving diode to be mounted substantially face to face. However, the ground plane does not effectively isolate the transmitting circuit from the receiving circuit. The level of electrical crosstalk is still unduly high.  
           [0007]    U.S. Pat. No. 5,047,835 discloses another conventional optoelectronic transceiver module. A pair of molded plastic frame housings encases the PCB. A metallic heat sink on the underside of a lid of the package provides heat removal, EMI protection and ESD shielding for the electronic components. The heat sink further includes a central metallic partition, which divides the package into separate regions and separates the circuitry associated with the optical subassembly. This isolation reduces electrical crosstalk between components. However, the module still does not have effective shielding.  
           [0008]    In view of the above, there is a need for an optoelectronic transceiver module which not only has effective isolation between transmitting circuits and receiving circuits but also effective ESD shielding.  
         SUMMARY OF THE INVENTION  
         [0009]    A primary object of the present invention is to provide a small form factor pluggable optoelectronic transceiver module having a metallic element for EMI protection and ESD shielding, and for reducing electrical crosstalk.  
           [0010]    Another object of the present invention is to provide a small form factor pluggable optoelectronic transceiver module having components which are fixed together easily, quickly and reliably.  
           [0011]    To achieve the above objects, a small form factor pluggable optoelectronic transceiver module of the present invention comprises top and bottom housings, a chassis, a receptacle, a PCB, an optoelectronic subassembly and a shielding shell. The optoelectronic subassembly is received in the receptacle. Conductive leads of the optoelectronic subassembly are soldered to the PCB. The shielding shell is fixed on the PCB, and encases a transmitting circuit on the PCB. The chassis is attached to the PCB with screws, and accommodates and protects the PCB. The top housing is attached to the chassis and the receptacle. The top and bottom housings are attached together, encapsulating therein the receptacle, the chassis, the PCB and the shielding shell. The shielding shell provides EMI protection and ESD shielding, and reduces electrical crosstalk. The module also forms multiple grounding paths between a grounding circuit of the PCB and the top and bottom housings.  
           [0012]    Other objects, advantages and novel features of the present invention will be drawn from the following detailed description of preferred embodiments of the present invention with the attached drawings, in which: 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is an exploded perspective view of an optoelectronic transceiver module in accordance with a preferred embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is similar to FIG. 1, but viewed from another aspect;  
         [0015]    [0015]FIG. 3 is similar to FIG. 1, but viewed from still another aspect;  
         [0016]    [0016]FIG. 4 is a perspective view of a shielding shell of the optoelectronic transceiver module of FIG. 1; and  
         [0017]    [0017]FIG. 5 is an assembled view of FIG. 1, together with a labeling tape attached on the optoelectronic transceiver module. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    Referring to FIG. 1, an optoelectronic transceiver module  99  in accordance with a preferred embodiment of the present invention has a top housing  1 , a bottom housing  2 , a chassis  3 , a receptacle  4 , a printed circuit board (PCB)  5 , an optoelectronic subassembly  6  (see FIG. 3), and a shielding shell  9 .  
         [0019]    The receptacle  4  is generally shaped like an oblong box. The receptacle  4  comprises a front portion  43  and a rear portion  44 . A profile of the front portion  43  is larger than a corresponding profile of the rear portion  44 . Thus a rear step (not labeled) is defined on the front portion  43  around a periphery of a junction of the front and rear portions  43 ,  44 , for abutting the top housing  1 . Referring also to FIG. 3, two openings  41 ,  42  are respectively defined though both the front portion  43  and rear portion  44 . Rear portions of the openings  41 ,  42  are for receiving the optoelectronic subassembly  6 , and front portions of the openings  41 ,  42  are for connecting with an optical connector (not shown) to output optical signals. The optoelectronic subassembly  6  comprises a transceiver. The transceiver comprises a transmitter  61  and a receiver  62 . The transmitter  61  may typically be a laser diode (LD) or light emitting diode (LED), and the receiver  62  may typically be a photo diode. A plurality of conductive leads  605  extends from a rear of the transceiver, for soldering to the PCB  5 . Two T-shaped grooves  441  are defined in a bottom surface of the rear portion  44  of the receptacle  4 , for engagement of the receptacle  4  with the bottom housing  2 . A pair of protuberances  442  is formed on a top surface of the receptacle  4 .  
         [0020]    Referring also to FIG. 2, the PCB  5  has a wide front section  51  and a narrow rear section  52 . Three positioning holes  511  are defined in the PCB  5 , in the vicinity of three edges thereof respectively. The PCB  5  at the positioning holes  511  is coated with conductive material, and the conductive material is connected with a grounding circuit (not labeled) of the PCB  5 . A transmitting circuit (not labeled) and a receiving circuit (not labeled) are disposed on the front section  51  of the PCB  5 , for respective electrical connection with the transmitter  61  and receiver  62  of the optoelectronic subassembly  6 . The rear section  52  of the PCB  5  has a row of electrical contacts  520  at a rear end thereof, for electrical connection of the PCB  5  with an electrical connector (not shown).  
         [0021]    Referring particularly to FIG. 4, the shielding shell  9  comprises two side walls  91 ,  92 , a top cover  94  and a rear wall  93 . A plurality of ventilating holes  941  is defined in the top cover  94  and side walls  91 ,  92 . A plurality of engaging tabs  931  depends from the side walls  91 ,  92  and rear wall  93 , for mechanically and electrically engaging with the grounding circuit (not labeled) of the PCB  5 .  
         [0022]    Referring particularly to FIG. 1, the chassis  3  is preferably made of metal but may be made of plastic or other suitable material. The chassis  3  is generally shaped like an oblong box, for accommodating and protecting the PCB  5 . Three poles  313  depend from a bottom face of the chassis  3 . Three screw holes  312  are defined through both a top face of the chassis  3  and the three poles  313  respectively. The screw holes  312  correspond to the positioning holes  511  of the PCB  5 . A rear of the chassis  3  forms a seat  33 . A support plate  330  extends forwardly from a bottom of the seat  33 . Two spaced screw holes  311  are defined in the chassis  3 . The chassis  3  has a pair of opposite side walls  32 . Two spaced recesses  320  are defined in a top of each side wall  32 , for engagement of the chassis  3  with the bottom housing  2 . A pair of depressions  321  (see FIG. 3) is respectively defined in opposite sides of a top portion of a rear end of the chassis  3 . Three fastening components, such as screws  8  (only one shown), are for fixing the PCB  5  on the chassis  3 .  
         [0023]    The bottom housing  2  is made of metal, and has a generally U-shaped configuration. The bottom housing  2  has a rectangular bottom wall  20 , and two side walls  21  extending perpendicularly upwardly from the bottom wall  20 . Two protrusions  212  are inwardly formed at front and rear ends respectively of a top of each side wall  21 , for engaging in the recesses  320  of the chassis  3 . A slot  213  is defined below each protrusion  212  of each side wall  32 . A rectangular opening  211  is defined in each side wall  21  below each slot  213 . The slots  213  and the rectangular openings  211  are for mating with the top housing  1 .  
         [0024]    The top housing  1  is made of metal, and has a top wall  11 . A shallow trough  110  is formed at a middle portion of the top wall  11 . Two recessed positioning holes  111  are defined in the trough  110 , corresponding to the screw holes  311  of the chassis  3 . A pair of parallel grounding tabs  113  is formed near a front end of the top wall  11 . A pair of parallel rectangular openings  112  is defined in the top wall  11  between the grounding tabs  113  and the trough  110 , corresponding to the protuberances  442  of the receptacle  4 . A pair of forward side walls  14  respectively depends from opposite sides of a front portion of the top wall  11 . A pair of rearward side walls  12  respectively depends from opposite sides of a rear portion of the top wall  11 . Two pairs of locking tabs  13  respectively depend from opposite sides of the top wall  11 , between the forward and rearward side walls  14 ,  12 . A T-shaped flap  142  is inwardly formed at a bottom of each forward side wall  14 , for engaging in the corresponding T-shape groove  441  of the receptacle  4 . Each forward side wall  14  has a grounding tab  113  formed therein. A tab  121  (best seen in FIG. 3) extends inwardly from a rear end of each rearward side wall  12 , for engaging in the corresponding depression  321  of the chassis  3 . Each locking tab  13  is a rectangular plate, and is sized to correspond to each slot  213  of the bottom housing  2 . A spring tongue  131  is outwardly formed at a center of each locking tab  13 . A lower end of each spring tongue  131  is integrally joined with the locking tab  13 , and an upper end of each spring tongue  131  protrudes outwardly from the locking tab  13 . Two fastening components, such as screws  7 , are for attaching the top housing  1  to the chassis  3 .  
         [0025]    Referring to FIG. 5, a labeling tape  991  is for attachment to the optoelectronic transceiver module  99  after assembly thereof.  
         [0026]    In assembly of the optoelectronic transceiver module  99 , the transmitter  61  and receiver  62  are firstly inserted into the openings  41 ,  42  of the receptacle  4 . The conductive leads  605  of the transmitter  61  and receiver  62  are respectively soldered to the transmitting and receiving circuits (not labeled) on the front section  51  of the PCB  5 , to establish electrical contact between the optoelectronic subassembly  6  and the PCB  5 . The shielding shell  9  is then fixed to the PCB  5  to encase the transmitting circuit (not labeled) thereon. The engaging tabs  931  of the shielding shell  9  are engaged with the PCB  5  using solder or conductive fiber. The shielding shell  9  is thereby electrically connected with the grounding circuit (not labeled) of the PCB  5 . The PCB  5  and chassis  3  are then attached together. The rear section  52  of the PCB  5  is inserted into the seat  33  of the chassis  3 . The poles  313  of the chassis  3  press down on the PCB  5 , and the support plate  330  of the chassis  3  supports the PCB  5  by abutting against a bottom face thereof. The screws  8  are extended through the positioning holes  511  of the PCB  5  to threadedly engage in the screw holes  312  of the poles  313 .  
         [0027]    The top housing  1  is then attached to the combined receptacle  4 , PCB  5  and chassis  3 . A front edge of the top housing  1  abuts the step (not labeled) of the front portion  43  of the receptacle  4 . The screws  7  are extended through the positioning holes  111  of the top housing  1  to threadedly engage in the screw holes  311  of the chassis  3 . The protuberances  442  of the receptacle  4  are received in the rectangular openings  112  of the top housing  1 . The T-shaped flaps  142  of the top housing  1  are engaged in the T-shaped grooves  441  of the receptacle  4 . Finally, the bottom housing  2  is attached to the combined receptacle  4 , PCB  5 , chassis  3  and top housing  1 . The locking tabs  13  of the top housing  1  are extended through the slots  213  of the bottom housing  2  until the spring tongues  131  of the locking tabs  13  engage in the openings  211  of the bottom housing  2 . The protrusions  212  of the bottom housing  2  are engaged in the recesses  320  of the chassis  3 . FIG. 5 shows the finally assembled optoelectronic transceiver module  99 . The top and bottom housings  1 ,  2  encapsulate the receptacle  4 , the chassis  3 , the PCB  5  and the shielding shell  9 . The labeling tape  991  is glued to the trough  110  of the top housing  1 , to show information about the optoelectronic transceiver module  99  and to cover the screws  7 .  
         [0028]    In the preferred embodiment of the present invention, the transmitting and receiving circuits on the PCB  5  are shieldingly separated from each other by the shielding shell  9 . The shielding shell  9  accordingly minimizes electrical crosstalk.  
         [0029]    Furthermore, the chassis  3  of the optoelectronic transceiver module  99  is electrically connected with the grounding circuit (not labeled) of the PCB  5  via the screws  8  which engage with the conductive material coated on the PCB  5  at the positioning holes  511 . The top and bottom housings  1 ,  2  electrically contact with the chassis  3 . The optoelectronic transceiver module  99  thus forms a grounding path between the grounding circuit (not labeled) of the PCB  5  and the top and bottom housings  1 ,  2 . Therefore any static charge which develops on the top or bottom housings  1 ,  2  is effectively dissipated.  
         [0030]    In an alternative embodiment of the present invention, a pair of shielding shells is fixed to the PCB  5  to encase the transmitting circuit (not labeled) on the PCB  5 .  
         [0031]    In a further alternative embodiment of the present invention, a pair of shielding shells  9  is fixed to the PCB  5  to respectively encase the transmitting circuit (not labeled) and receiving circuit (not labeled) on the PCB  5 .  
         [0032]    It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present invention and without diminishing the present invention&#39;s advantages. Thus, it is intended that such changes and modifications be covered by the appended claims.