Abstract:
An optical fiber link module adapted to receive a fiber optic cable. The optical fiber link module comprises a multiple array lens and a female connector. The female connector is disposed around the multiple array lens, and has an internal cavity. An electromagnetic shield is disposed in the internal cavity, and has a single central aperture sized to permit communication by the multiple array lens through the central aperture.

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]    “External EMI Shield For Multiple Array Optoelectronic Devices”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010690US1);  
           [0005]    “Packaging Architecture For A Multiple Array Transceiver Using A Continuous Flexible Circuit”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010591 US1);  
           [0006]    “Flexible Cable Stiffener for An Optical Transceiver”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010729US1);  
           [0007]    “Enhanced Folded Flexible Cable Packaging for Use in Optical Transceivers, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010727US1);  
           [0008]    “Apparatus and Method for Controlling an Optical Transceiver”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010728US1);  
           [0009]    “Multiple Array Optoelectronic Connector with Integrated Latch”, by Johnny R. Brezina, et al. (IBM Docket No. AUS920010731 US1);  
           [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 internal 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 energy to escape.  
         SUMMARY OF THE INVENTION  
         [0018]    The present invention is an optical fiber link module adapted to receive a fiber optic cable. The optical fiber link module comprises a multiple array lens and a female connector. The female connector is disposed around the multiple array lens, and has an internal cavity. An electromagnetic shield is disposed in the internal cavity, and has a single central aperture sized to permit communication by the multiple array lens through the central aperture.  
           [0019]    It is an object of the present invention to provide an optical fiber link module of the type described above having an internal shield that inhibits EMI.  
           [0020]    Another object of the present invention is to provide an optical fiber 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 fiber 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; and  
         [0024]    [0024]FIG. 2 is a perspective view of the underside of the optical link module with a cover, stiffener, and flexible circuit removed to shown an internal shield. 
     
    
     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, and may be joined to the upper portion  12  in any known fashion. 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  20  situated on the distal end of a fiber optic cable  22 . In a preferred embodiment, the male end  20  of the fiber  22  includes a multiple array  24  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  22  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  22 . 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  22 . 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]    Unit  10  also retains an internal EMI shield  30  within an internal cavity formed by the upper connector  16  and the lower housing portion  14 . The EMI shield  30  is located between the optical lens assembly  32  and the end of the removable connector housing  20 . The major, planar section of the EMI shield  30  abuts a corresponding vertical surface of the upper connector  16 , and may be secured thereto with an adhesive such as a silver epoxy. A series of vertically-and horizontally-disposed spring arms  33  are situated around the major planar surface of the EMI shield  30 . When the EMI shield  30  is in place within the internal cavity formed by the upper connector  16  and the lower housing portion  14 , the spring arms  33  hold the EMI shield in place by engaging the inner surfaces of the upper connector and of the lower housing portion.  
         [0029]    The EMI shield  30  has an aperture  34  that aligns with the lens housing  32  to allow the light energy to pass through the EMI shield. The spring arms  33  are situated at a distance from the aperture  34  sufficient to avoid interfering with the mating of the male connector  20  and the lens housing  32 . The internal shield  30  is preferably fabricated from a thin sheet of a metal possessing good EMI characteristics. Suitable materials for the shield  30  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 0.2 mm in thickness provide suitable EMI characteristics.  
         [0030]    The EMI shield  30  provides a barrier to any EMI radiation escaping from the interface of the array  24 . To facilitate this end, the shield  30  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. At the same time, the aperture  34  in the shield allows the light energy to pass between the fiber optic components. The location of the shield  30  allows the removal of the male connector  20  without moving the shield out of position, and provides EMI shielding even while the male connector and cable  22  are removed. 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.  
         [0031]    It should be appreciated that the internal EMI shield of the present invention can be implemented in a number of ways. Furthermore, the optical link module is also suitable for use in other communications systems or optical transmission networks, such as those used in telephone service. Various 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.