Abstract:
The invention provides an internal electromagnetic shield that prevents the radiation of electromagnetic emissions from electro-optical components in high speed data transfer systems. The present invention provides an internal shield with at least one aperture to allow the connector portion of an electro-optic component to pass through for connection to an optical fiber. By providing an internal shield, electromagnetic interference (EMI) is substantially reduced without interfering with the mechanical connection between an electro-optical component and an optical fiber. The internal shield typically is formed of a thin metallic sheet having apertures to receive the connector portion of electro-optical components. In a shield for an input/output device, which includes an optical signal generator and optical signal receiver, the shield may include two bores.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 09/457,285, filed Dec. 18, 1999 now U.S. Pat. No. 6,200,041 by David P. Gaio et al. and entitled “Data Transfer System Incorporating Optical Fiber Link Module With Internal Electromagnetic Shield”, which is a divisional of U.S. Ser. No. 08/928,119, filed on Sep. 12, 1998 by David P. Gaio et al. and entitled “Optical Fiber Link Module With Internal Electromagnetic Shield” (now U.S. Pat. No. 6,085,006), which applications are incorporated by reference herein. 
    
    
     GOVERNMENT RIGHTS 
     This invention was made with U.S. Government support under Cooperative Agreement F33615-94-2-1582 awarded by the U.S. Department of Air Force. The government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The invention is generally related to an internal shield for use in electro-optic ports, and more particularly, to shields that prevent electromagnetic emissions from optical fiber link modules. 
     BACKGROUND OF THE INVENTION 
     In order to transfer data between computer systems rapidly and reliably, electro-optic data transmission is increasingly being used as the method of choice. Optical fibers provide resistance to electro-magnetic interference, increased security, and increased speed due to a wide potential band width. Optical fibers transmit data from an electro-optical transducer, such as a laser or Light Emitting Diode (LED) to an electro-optical receiver that generates electrical information based upon the signal received. 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. The optical fibers are typically either threaded onto the electro-optical components or latched by the use of connectors such “SC” connectors. 
     State of the art optical links operate at over 1000 Mbits/second that generates very high electromagnetic emissions in the range of 100 MHZ-5 GHz. FCC regulations constrain the field strength of radiated emission from certain unintentional radiators such as personal computers, CPU boards, power supplies, and peripherals. FCC regulations provide that the radiated emission from such unintentional radiators at a distance of three meters shall not exceed the following values: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Frequency of emmision 
                 Field Strength 
               
               
                   
                 MHZ 
                 (micro volts/meter) 
               
               
                   
                   
               
             
             
               
                   
                 30-88 
                 100 
               
               
                   
                  88-216 
                 150 
               
               
                   
                 216-960 
                 200 
               
               
                   
                 Above 960 
                 500 
               
               
                   
                   
               
             
          
         
       
     
     In order to limit such emissions, external shielding has been used around the electro-optical component of such optical links. These shields provide an opening that allows threaded or “SC” type connectors to attach to the electro-optical components. Since these connectors are typically plastic they do not serve as a shield to emissions. This electromagnetic “hole” in the shield allows electromagnetic inference to escape the shielded area and may cause the equipment to exceed the maximum values provided for radiated emissions as specified by the FCC. 
     Consequently, a significant need continues to exist in the art for a shield that will block electromagnetic interference from escaping from the shielded area. Specifically, a significant need continues to exist for a cost effective shield that blocks significant amounts of the emissions yet allows quick, easy and reliable connection to the electro-optic component. 
     SUMMARY OF THE INVENTION 
     The invention addresses these and others problems associated in the art with radiated electromagnetic emissions from electro-optical components in a high speed data transfer system. The present invention provides an internal shield with at least one aperture to allow the connector portion of an electro-optic component to pass through for connection to an optical fiber. By providing an internal shield, electromagnetic interference (EMI) is substantially reduced without interfering with the mechanical connection. 
     In certain embodiments of the invention, the internal shield includes a thin metallic sheet having an aperture to receive the connector portion of an electro-optical component. In a shield for an input/output device, that includes an optical signal generator and optical signal receiver, the shield may include two bores. The first bore receives the connector portion of the generator and the second aperture receives the connector portion of the receiver. 
     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 
     FIG. 1 is a partially exploded perspective view showing an optical link module incorporating an internal shield consistent with the present invention. 
     FIG. 2 is a perspective view of the male end of a duplex “SC” optical connector. 
     FIG. 3 is a plan view of the female end of a duplex “SC” connector. 
     FIG. 4 is a plan view of an internal electromagnetic interference shield consistent with the present invention. 
     FIG. 5 is a perspective view of an optical component suitable for mounting in the optical link module of FIG.  1 . 
     FIG. 6 is a perspective view showing the underside of the optical link module of FIG.  1 . 
     FIGS. 7A-7C illustrate a typical computer system using the module of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning to the Drawings wherein like numbers denote like parts throughout the several views, FIG. 1 illustrates the general configuration of an exemplary optical link module  2  and shows the basic operation of the various embodiments of the present invention. Optical link module  2  represents a fiber optic communications package which is mounted within a component of a data transfer system such as a computer system that transfers data to and from another component of the computer system or other computer systems such as network servers, mid-range computers, mainframe computers, work stations, desktop computers, portable computers, and the like. One such suitable computer system in which the optical link module  2  may be suitably used is a mid-range computer such as the AS/400 computer available from International Business Machines Corporation. The optical link module is also suitable for use in other communications systems or optical transmission networks, such as those used in telephone service. 
     The optical link module  2  generally includes a frame  4  that is integrally connected to a latching mechanism  6  and an optical fiber connection unit  10 . Frame  4 , latches  6  and optical fiber connecting unit  10  generally surround a printed circuit board  8 . The frame includes a release lever  7 , which when raised separates pin connection  5  and latches  6  from the host system. The printed circuit board  8  typically carries integrated circuit chips  46 ,  48 , as well as other electronic components such as resistors  50  and potentiometers  52 . Typically, the circuit board  8  includes a module that performs parallel electrical signal to serial optical conversion at rates of approximately 1000 Mbits/sec. The module also performs serial optical to parallel electrical conversion at a similar rate. 
     Transmitter and receiver integrated circuits are typically located on one side of the circuit board to provide duplex operation. A pair of electro-optical components, namely an emitter  14  and a receiver  16 , perform the conversion between electrical and optical signals. Typically the module receives serial electrical signals from the CPU and emitter  14 , such as an LED or laser, converts the serial electrical signal to a serial optical signal for transmission through an optical fiber. The module may also receive parallel electrical signals from a CPU and convert the parallel electrical signal to a serial electrical signal that is provided to the emitter  14 . Emitter  14  in turn converts the serial electrical signal to a serial optical signal for transmission through an optical fiber. Similarly, incoming serial optical signals are converted by a receiver  16 , such as a PIN photodiode, from the optical signal 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 signals and transmitted to the CPU. Similarly, emitter  14  and receiver  16  may 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. 
     The circuit board  8  is wired to emitter  14  or laser and optical receiver  16  by leads  127 . The emitter  14  and receiver  16  are each held within optical fiber connection unit  10  by pairs of cantilevered opposed latching arms  40 ,  42 . Emitter  14  and receiver  16  each include an optical fiber receiving mechanism  120 , as shown in FIG.  5 . The optical fiber receiving mechanism  120  includes a cylindrical portion  122  in which the emitter or receiver is embedded. A hollow cylindrical projection  124  extends from the larger section  122 . The diameter of the hollow cylindrical section  124  is typically on the order of 4.6 mm with an internal bore  126  with a diameter on the order of 2.5 mm. It should be understood that both the emitter  14  and the receiver  16  have such an optical fiber receiving mechanism  120 . For clarity, the distal end of the emitter that receives a ferrule is labeled  20  in FIG. 1, and the distal end of the receiver is labeled  22  in FIG.  1 . The large cylindrical portions of the optical fiber receiving mechanisms of the emitter  14  and receiver  16  are held within cantilevered latching arms  40 ,  42 . 
     With reference to FIG. 1, the optical fiber connection unit  10  is typically an injection molded unit that is attached to the optical link module frame  4 . The optical fiber connection unit  10  includes a lower platform  28  that supports emitter  14 , receiver  16 , and the female end of a duplex “SC” connector. A suitable connection unit is disclosed in U.S. Pat. No. 5,901,263 entitled “Hot Pluggable Module Integrated Lock/Extraction Tool” to Gaio et al., which is incorporated in its entirety by reference herein. The lower surface  28  supports left and right side walls  30 ,  32 , respectively as viewed in FIG.  3 . Lower surface  28  also supports a medial T-shaped bar  24  that separates the send and receive fiber connectors of the duplex “SC” connectors  60 , as shown in FIG.  2 . Grooves  29  are located on the lower surface  28  to receive ridges  70 ,  82  (shown in FIG. 2) of the male duplex “SC” connector. 
     Unit  10  of FIGS. 1 and 6 also retains an internal shield  12  within an internal cavity therein supported by lower platform  28 . Internal shield  12  is fabricated from a thin sheet of a metal possessing good electromagnetic interference (EMI) characteristics, such as 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 3 mm in thickness provide suitable EMI characteristics. Side walls  30 ,  32  of unit  10  include shield retainers  36 ,  38  extending transverse thereto. In addition, a central shield retainer  34  is defined by the top section of the medial T-shaped bar  24  that is the same plain as retainers  36 ,  38 . 
     An external shield  18  is fabricated from a thin sheet of an EMI shielding material such as gold, silver, or nickel silver. Shield  18  is slidably received over unit  10  to cooperatively shield the same with internal shield  12 . 
     In assembling the optical link module  10 , the apertures  114 ,  116  shown in FIG. 4 of shield  12  are slipped over the distal ferrule receiving ends of the emitter and receiver  20 ,  22 , respectively. The emitter  14  and receiver  16  are then snapped in place between cantilevered arms  40 ,  42 . Shield  12  is maintained on the emitter and receiver between the large cylindrical portion  122  of the optical fiber receiving mechanisms  120  therefor and the shield retainers  34 ,  36 ,  38 . As shown in FIG. 6, tabs  118  extend from the lower platform  28  of the optical fiber connection unit  10 . 
     Once the receiver  14 , emitter  16  and shield  12  are in place, external shield  18  is slid over the optical fiber connection unit  10  to fold ears  118 , and snapped into place with detent of cantilevered arms  19 . The contact between the internal and external shield provides a path to ground any errant electrical charge. The internal shield  12  may include one or more tabs  118  on the upper and/or lower surfaces thereof to minimize gaps that could allows the escape of EMI. Shield  12  is vertically dimensioned so that tabs  118  are folded over by the sliding of external shield  18 . 
     After the external shield is applied, the male end of the duplex “SC” connector, show in FIG. 2,  60  is inserted. Optical fibers  62 ,  64  pass through the back plate  66  of the male end of the duplex “SC” connector  60 . Connector  60  includes a fiber connector  68  that is generally in the form of a right rectangular parallelepiped having a medial ridge  70  to ensure proper alignment. The medial ridge  70  mates with grove  29  that is included in the lower surface  28  of the optical fiber connection unit  10 . The connector portion  68  includes a cylindrical bore  74  at the center of which a ferrule  76  is located. The optical fiber  64  is threaded through the back plate  66  and through ferrule  76 . The connection unit  68  is inserted into optical fiber connection unit  10  so that ferrule  76  is received within bore  126  of the distal ferrule receiving end  20  of emitter  14 . The optical fiber receiving unit  68  includes depressed regions  78  on opposite sides to receive the detents of cantilevered arms  19 . 
     Similarly, connector  60  includes another fiber connector  80 , which is of the same structure as fiber connector  68 . The medial ridge  82  mates with grove  29  included in the lower surface  28  of the optical fiber connection unit  10 . The cylindrical bore  84  includes a ferrule  86  having optical fiber  62  threaded therethrough. The connection unit  80  is inserted into optical fiber connection unit  10  so that ferrule  86  is received within bore  126  of the distal ferrule receiving end  22  of receiver  16 . The optical fiber receiving unit  80  includes depressed regions  88  on opposite sides to receive the detents of cantilevered arms  19 . 
     As seen in FIGS. 7A-7C, a typical computer system using module  2  may include a system processing unit  200  including a system processor  202 , a main storage unit  204 , a local bus attachment card  206  including modules  2 , a storage controller  208 , with storage device  208 ′, and work station controller  210 , with work station  210 ′. The local bus attachment card  206  connects system processing unit  200  to input/output expansion units  220 ,  240  and  250  by dual fiber cables  63 . Input/output expansion unit  220 , includes remote bus attachment card  222 , linked via I/O buses to storage controller  224 , with storage device  224 ′, work station controller  226 , with work station  226 ′, tape controller  228 , with tape drive  228 ′, and a comm or LAN controller  230 , with comm or LAN  230 ′. Input/output expansion unit  240 , includes remote bus attachment card  242 , linked via I/O buses to various components (not shown). Input/output expansion unit  250 , includes remote bus attachment card  252 , linked via I/O buses to various components (not shown). 
     It should be appreciated that the above-described internal EMI shield may be implemented in any number of manners known in the art. In particular, the above-described shielded duplexed “SC” connector could be configured as a single “SC” connector or the connect could be any other known type of connector. Other configurations of optical links may also be used with the internal shield of the present invention. It should be appreciated that implementation of the internal shield with other optical links is well within the capabilities of one of ordinary skill in the art. 
     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.