Abstract:
An optical fiber link module comprises upper and lower portions and a shield. One of the upper portion or lower portion has a groove, and one of the upper portion or lower portion has at least one tab extending therefrom. The shield has a detent and at least one cutout, the detent engaging the groove and the at least one cutout cooperating with the at least one tab.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims priority to U.S. patent application Ser. No. 09/956,771 filed on Sep. 20, 2001 entitled “Fiber Optic Transceiver, Connector, And Method of Dissipating Heat” by Johnny R. Brezina, et al., the entire disclosure of which is incorporated by reference, herein.  
         [0002]    This application also relates to the following applications, filed concurrently herewith:  
         [0003]    “Optical Alignment In A Fiber Optic Transceiver”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010689US1);  
         [0004]    “Packaging Architecture For A Multiple Array Transceiver Using A Continuous Flexible Circuit”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010591US1);  
         [0005]    “Flexible Cable Stiffener for An Optical Transceiver”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010729US1);  
         [0006]    “Enhanced Folded Flexible Cable Packaging for Use in Optical Transceivers, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010727US1);  
         [0007]    “Apparatus and Method for Controlling an Optical Transceiver”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010728US1);  
         [0008]    “Internal EMI Shield for Multiple Array Optoelectronic Devices”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010730US1);  
         [0009]    “Multiple Array Optoelectronic Connector with Integrated Latch”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010731US1);  
         [0010]    “Mounting a Lens Array in a Fiber Optic Transceiver”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010733US1);  
         [0011]    “Packaging Architecture for a Multiple Array Transceiver Using a Flexible Cable”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010734US1);  
         [0012]    “Packaging Architecture for a Multiple Array Transceiver Using a Flexible Cable and Stiffener for Customer Attachment”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010735US1);  
         [0013]    “Packaging Architecture for a Multiple Array Transceiver Using a Winged Flexible Cable for Optimal Wiring”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010736US1); and  
         [0014]    “Horizontal Carrier Assembly for Multiple Array Optoelectronic Devices”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010763US1). 
     
    
     
       TECHNICAL FIELD OF THE INVENTION  
         [0015]    This invention is generally related to an external shield for use in optoelectronic ports, and more particularly related to shields that prevent electromagnetic emissions from optical fiber link modules.  
         BACKGROUND OF THE INVENTION  
         [0016]    Optical fiber is widely used to rapidly and reliably transfer data between computer systems. In general, an optical fiber includes a core region that is coated by an annular clad. The core region has an index of refraction greater than that of the clad, so that light is transmitted through the core by total internal refraction. Optical fibers transmit data from an optoelectronic transducer, such as a laser or Light Emitting Diode (LED), to an optoelectronic receiver that generates electrical information based upon the signal received.  
           [0017]    Optical transceivers tend to generate electromagnetic interference (EMI) in the range of about 100 megahertz to 5 gigahertz, and this radiation is most likely to escape from the point at which the fiber is connected to the optoelectronic component. The fibers are typically either threaded onto the optoelectronic components or latched by the use of connectors such MTP or MTO connectors. Because these connectors are typically plastic, however, they are not effective EMI shields. In order to limit EMI, external shielding has therefore been provided in various forms. These shields have an opening that allows the connector to attach to the optoelectronic component. This opening is in effect an electromagnetic hole in the shield that allows EMI to escape.  
         SUMMARY OF THE INVENTION  
         [0018]    The present invention is an optical fiber link module comprising upper and lower portions and a shield. One of the upper portion or lower portion has a groove, and one of the upper portion or lower portion has at least one tab extending therefrom. The shield has a detent and at least one cutout. The detent engages the groove, and the at least one cutout cooperates with the at least one tab.  
           [0019]    It is an object of the present invention to provide an optical fiber link module of the type described above that inhibits EMI.  
           [0020]    Another object of the present invention is to provide an optical link module of the type described above that permits easy access to the connector and fiber cable by the end user.  
           [0021]    Still another object of the present invention is to provide an optical link module of the type described above that is cost effective.  
           [0022]    These and other advantages and features, which characterize the invention, are set forth in the claims annexed hereto and forming a further part hereof. However, for a better understanding of the invention, and of the advantages and objectives attained through its use, reference should be made to the drawings, and to the accompanying descriptive matter, in which there is described exemplary embodiments of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a perspective view showing an optical link module according to the present invention including an external shield; and  
         [0024]    [0024]FIG. 2 is a perspective view of the underside of the optical link module shown without a stiffener and flexible circuit. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    [0025]FIGS. 1 and 2 show the general configuration of an exemplary optical link module  10 . Optical link module  10  represents a fiber optic communications package which is mounted within a component such as a router that transfers data to and from another component of the router or other computer systems such as network servers, mid-range computers, mainframe computers, work stations, desktop computers, portable computers, and the like.  
         [0026]    The optical link module  10  generally includes an upper portion  12  and a lower portion  14 . The upper portion  12  is preferably die cast as a single piece, and includes an upper connector  16  and a heat sink  18 . The lower portion  14  of the module  10  is also preferably die cast from a relatively high thermal conductivity material such as aluminum. Together, the upper connector  16  and the lower portion  14  form a female part of a standard MTP or MTO connector adapted to receive a male part situated on the distal end of a fiber optic cable. In a preferred embodiment, the male end of the fiber includes a multiple array similar to that shown in U.S. Pat. No. 5,499,311, the disclosure of which is hereby incorporated by reference.  
         [0027]    An aluminum stiffener  26  is provided on the underside of the heat sink  18 , with a flexible circuit  28  attached thereto. The flexible circuit may carry integrated circuit chips, resistors and other structure which operate to convert and route the fiber optic light signals from the fiber to and from other areas of the router of which the module  10  is a part. Although the details of such conversion and routing are considered to be well within the level of ordinary skill in the art, further information is available in U.S. Pat. No. 6,085,006, the disclosure of which is hereby incorporated by reference. Normally, the module  10  receives serial electrical signals from a CPU, and an emitter (which may be an LED or laser) converts the serial electrical signal to a serial optical signal for transmission through the optical fiber. The module may also receive parallel electrical signals from the CPU, and convert the parallel electrical signal to a serial electrical signal that is provided to the emitter. The emitter in turn converts the serial electrical signal to a serial optical signal for transmission through the fiber. Similarly, incoming serial optical signals are converted by a receiver (which may be a photodiode) to a serial electrical signal. The serial electrical signal may be output to the CPU as a serial signal or converted to a parallel electrical signal and transmitted to the CPU. The emitter and the receiver may also transmit a parallel signal, in which case it is possible to omit the parallel to serial conversion or it may be possible to convert a serial electrical signal to a parallel signal for parallel optical transmission. In a preferred embodiment, signals are transmitted over the optical fibers at a frequency of about 2.5 gigahertz.  
         [0028]    The upper connector  16  and the lower portion  14  are provided with backwardly projecting tabs  30 . An external EMI shield  32  is also provided having a front lip  34  and a series of cutouts  36 . The external shield  32  is slidably received over the unit  10  until detent features  38  on each side of the shield snap into grooves  40  in the sides of the connector housing and lock the EMI shield in position. The front lip  34  prevents any significant travel of the EMI shield  32  further on to the unit  10 , while cooperation of the tabs  30  extending into the corresponding cutouts  36  prevents the shield from coming off of the unit.  
         [0029]    The EMI shield  32  holds together the two halves  14  and  16  of the connector housing without the use of any additional fasteners, adhesives, or other normal fastening devices. After the external shield  32  is applied, the male end of the connector may be inserted. If any problem with the module  10  is noted during manufacturing, the EMI shield  32  can be removed and the module can be easily disassembled for rework of the parts.  
         [0030]    The shield  32  is preferably fabricated from a thin sheet of a metal possessing good EMI characteristics. Suitable materials for the shield  32  include gold, silver, and what is known in the art as nickel silver which is 59 percent by weight copper, 12 percent by weight nickel, and 29 percent by weight zinc. Sheets on the order of about 0.2 mm in thickness provide suitable EMI characteristics. The EMI shield  32  provides a barrier to any escaping EMI radiation. To facilitate this end, the shield  32  is grounded to the upper connector  16 , and thus to the heat sink  18 . Because the heat sink  18  is in turn electrically grounded, either logically or to a chassis, the EMI energy is dissipated.  
         [0031]    The present invention thus provides a relatively simple, low cost method of achieving EMI suppression for the optical device, while at the same time allowing accessibility and removability of the fiber optic connector and cable. It should be appreciated that the optical link module is suitable for use in other communications systems or optical transmission networks, such as those used in telephone service. Various other modifications may be made to the illustrated embodiments without departing from the spirit and scope of the invention. Therefore, the invention lies solely in the claims hereinafter appended.