Abstract:
An easily removable modular optical signal transceiver unit for conversion between modulated light signal transmission and electronic data signals and which conforms to the Small Form Factor standard for transceiver interfaces is disclosed. The structural details of its chassis include aspects which insure the proper positioning of electronic circuit boards of a transmitter optical subassembly and a receiver optical subassembly as well as the positioning of electromagnetic radiation shielding on the chassis. In conjunction with an interface device on an electronic circuit board of a host device, the chassis supports electromagnetic radiation shielding which substantially encloses the sources of electromagnetic radiation within the module and suppresses the escape of electromagnetic radiation, thereby preventing electromagnetic interference with sensitive components and devices in proximity to the module. During assembly, the chassis side walls are deflected, so that electronic or electro-optic components can pass over latching surfaces into contact with positioning surfaces for retaining the components in their assembled positions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to: 
     U.S. Pat. No. 6,074,228 issued Jun. 12, 2000, entitled GUIDE RAIL AND CAM SYSTEM WITH INTEGRATED CONNECTOR FOR REMOVABLE TRANSCEIVER, by Jerry Berg, David P. Gaio and William K. Hogan; 
     U.S. Pat. No. 6,459,517 issued Oct. 1, 2002, entitled ENHANCED ELECTROMAGNETIC INTERFERENCE SHIELD, by Timothy Duncan, John Maas, James L. Peacock and Scott Thorvilson; 
     U.S. Pat. No. 6,407,932 issued Jun. 18, 2002, entitled ELECTROMAGNETIC INTERFERENCE SHIELD AND GROUND CAGE, by David P. Gaio, William K. Hogan and Paul Sendelbach; 
     U.S. patent application Ser. No. 09/391,974, filed Sep. 8, 1999, entitled GUIDE RAIL AND CAM SYSTEM WITH INTEGRATED LOCK-DOWN AND KICK-OUT SPRING FOR SMT CONNECTOR FOR PLUGGABLE MODULES, by David P. Gaio, William K. Hogan, Frank Ovanessians and Scott M. Branch; 
     U.S. Pat. No. 6,302,596 issued Oct. 16, 2001, entitled SMALL FORM FACTOR OPTOELECTRONIC TRANSCEIVERS, by Mitch Cohen, Jean Trewhella, David P. Gaio, William K. Hogan, Miles Swain, Phil Isaacs and Pat McKnite; 
     U.S. Pat. No. 6,485,322 issued Nov. 16, 2002, entitled REMOVABLE LATCH AND BEZEL EMI GROUNDING FEATURE FOR FIBER-OPTIC TRANSCEIVERS, by Scott M. Branch, David P. Gaio, and William K. Hogan; and, 
     U.S. Pat. No. 6,335,869 issued Jan. 1, 2002, entitled, REMOVABLE SMALL FORM FACTOR FIBER OPTIC TRANSCEIVER MODULE AND ELECTROMAGNETIC RADIATION SHIELD, by Scott M. Branch, David P. Gaio and William K. Hogan, all of said applications being commonly assigned herewith and all of which are incorporated by reference herein in their entireties, for purposes of disclosure. 
    
    
     THE FIELD OF THE INVENTION 
     This invention relates to the simple fabrication of removable electronic interface modules for connecting fiber optic communication or signal lines to a computer and, more specifically, to the chassis structure which permits efficient and reliable assembly of both the interfacing module electronic components and the shielding of the module to prevent, to the maximum extent possible, electromagnetic radiation from escaping the module. 
     BACKGROUND OF THE INVENTION 
     Computers increasingly are being connected to communications lines and other devices or networks with the computers performing as servers to the peripherally connected computers or devices. The volume of data sent and received by the computer serving as a server of a network is such that the networks are advantageously constructed using fiber optic lines in order to increase the throughput of data. 
     Fiber optic lines and the associated fiber optic signals require transceivers to convert the optical light pulse signals to electronic signals which are usable by the computer. Such a transceiver includes a transmitter optical subassembly and a receiver optical subassembly to send and receive the optical signals. 
     Industry standards have been established to define the physical parameters of the said devices and, particularly, the overall interface. This permits the interconnection of different devices manufactured by different manufacturers without the use of physical adapters. 
     Since about 1990, the fiber optic industry has been using a so-called “SC duplex fiber optic connector system” as the optical fiber connector interface on the front of fiber optic transceivers. The physical separation between the transmitter optical subassembly and receiver optical subassembly (TOSA and ROSA, respectively) for the SC duplex connector is approximately 12.7 mm. However, the industry is now converting to the so-called “Small Form Factor optical connectors” and associated “Small Form Factor optical transceiver.” In the so-called Small Form Factor optical connectors, the separation between the transmitter optical subassembly and receiver optical subassembly is established at approximately 6.25 mm, less than half the separation of the prior SC duplex connector. The Small Form Factor (SFF) standard establishes a module enclosure, having a 9.8 mm height and a width of 13.5 mm and allows a minimum of 24 transceivers arranged across a standard rack opening. The reduction in size from the former SC duplex connector standard to the Small Form Factor standard requires both substantial redevelopment and redesign. 
     Moreover, the Small Form Factor optical fiber connector interface has been adopted as a standardized removable module. The module may be connected to a module interface on the host circuit board of a computer. The transmitter optical subassembly/receiver optical subassembly in the module of the Small Form Factor optical fiber connector interface, the processor, and all long conductors of the transmitter optical subassembly and receiver optical subassembly, individually and collectively, radiate electromagnetic radiation and create electromagnetic interference for other electronic devices and components which are exposed to the electromagnetic radiation. 
     The use of a separate removable module containing a variety of electronic devices requires that the module be easily and inexpensively assembled and that the module further provide its own electromagnetic radiation shielding. Due to the size constraints placed on the interface modules, the shielding must be small but at the same time efficient in collection and grounding of the collected electromagnetic radiation. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to simplify assembly of a modular interface for receiving and sending optical data signals. 
     It is another object of the invention to provide a chassis for an optical interface for data signals whereby the structural characteristics of the chassis permit assembly at precise locations for the electronic components and the shielding permits both accurate connection to the host circuit board and proper alignment of the interface optical subassemblies with the connected optical fibers. 
     It is a further object of the invention to provide reliable assembly of a plurality of parts and components into a module for translation of the data signals between electrical and optical form. 
     It is still another object of the intention to make the module easily removable from the host device as well as effectively suppress electromagnetic radiation to the greatest extent possible. 
     SUMMARY OF THE INVENTION 
     A module for interfacing communication line or lines to the main system of the computer is designed to be removable. In order to provide the removability factor, the module must contain sufficient electronic circuitry to convert signals between optical fiber conveyed light pulses and electrical digital signals or vice-versa. This conversion requires at least a laser driver, post amplifier, and supporting circuitry as well as transmitter optical subassembly and a receiver optical subassembly which comprise light generating and light sensitive electronic devices, respectively. The operation of the electronics causes radiation of electromagnetic energy which may cause interference, if not suppressed, with nearby electromagnetic radiation sensitive equipment and components. 
     An easily removable module is advantageously assembled on a chassis which is molded plastic, preferably, selected for its durability and insulative characteristics. The chassis has an open channel structure for a portion of its length, and a duplex port receiving end for accepting fiber optic conductor connectors. The chassis is formed to include positioning surfaces against which an electronic circuit board is positioned, and a pair of locating pins or projections define the position of the electronic circuit board relative to the chassis. 
     In areas lacking additional stabilization, the walls of the chassis are formed thinly enough that the walls may be deflected to permit snap-in positioning of the circuit board within the chassis and allow retention latches to be forced out of the path of a circuit board once inserted into the chassis. 
     Once assembled, the chassis then is substantially enclosed with shielding to suppress the escape of electromagnetic radiation. The shield is fabricated of electrically conducting sheet metal, such as thin metal plate stock, and formed into a channel shape. The channel shaped shield is provided with edge tabs. Each edge tab may be bent to form spring contacts which contact and electrically ground to a bracket or frame member; additionally, tabs may be bent over walls of the chassis to retain the shielding in its desired position. A separate shielding member is positionable on the chassis and retainable by bending or crimping of the edge tabs as contact between the separate shield and the edge tabs establishes grounding electrical contact therebetween. The emissions of electromagnetic radiation from the duplex port end of the chassis are reduced and modified by extending a shield member between the transmitter optical subassembly/receiver optical subassembly, bridging the separate shield and the channel shaped shield to reduce the effective opening to attenuate the electromagnetic radiation passing through the duplex port end of the chassis. 
     However, it is known that an aperture will attenuate electromagnetic radiation waves when the aperture is less than ½ of the wavelength λ to be attenuated (i.e., length of aperture &gt;½λ). Moreover, the smaller the aperture, the greater the attenuation of the electromagnetic radiation waves. The attenuation of electromagnetic radiation waves due to passage through an aperture can be determined using the following formula: 
     
       
           S =20 log(λ/2 L ), where 
       
     
     S=the shielding effectiveness of the aperture (in decibels); 
     λ=the wavelength of the electromagnetic radiation; and 
     L=the maximum linear length of the aperture (in meters). 
     Moreover, the wavelength λ can be determined by dividing the velocity of the electromagnetic radiation wave (i.e., the wave speed, which is approximately 3×10 8  m/sec 2 ) by the frequency of the electromagnetic radiation emissions. 
     Thus as the operational frequency (and hence, speed) of an electrical device increases, the associated wavelengths become smaller, thus requiring smaller apertures. However, the apertures are typically limited in minimum size to allow for the passage of associated cables or connections, for example. If the size of the apertures are reduced too much, then passage of the associated cables or connections therethrough may be prohibited. Therefore, it is clear that the size of the aperture, which typically has a minimum size, may limit the speed (i.e., bandwidth) of the associated electrical device. 
    
    
     A more complete understanding of the invention may be had from the detailed description of the invention that follows and the attached drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevated right perspective view of a host device circuit board, connection interface, and the insertable/removable transceiver module of the invention. 
     FIG. 2 is a depressed perspective view of a portion of the interior of the module chassis of the invention. 
     FIG. 3 is a depressed perspective view of an partially assembled transceiver module without the electromagnetic radiation shield. 
     FIG. 3B is a partially cut away perspective view of the middle section of the module of the present invention. 
     FIG. 4 is a top view of the module without the electromagnetic radiation shield. 
     FIG. 5 is an elevated rear perspective view of the module of the invention with the electromagnetic radiation shield positioned but not completely installed on the chassis. 
     FIG. 6 is an elevated perspective view of the duplex connector of the end of the module partially enclosed by the electromagnetic radiation shield. 
     FIG. 7 is an elevated perspective view of the separate bottom electromagnetic radiation shield and its position relative to the transmitter optical subassembly and receiver optical subassembly of the invention. 
     FIG. 8 is a bottom view of the module with the bottom electromagnetic radiation shield installed, leaving exposed contacts for connection with the interface connection on the host circuit board. 
    
    
     DETAILED DESCRIPTION 
     OF THE PREFERRED EMBODIMENT OF THE BEST MODE OF IMPLEMENTING THE INVENTION AS CONTEMPLATED BY THE INVENTORS 
     An insertable and removable electronic module is illustrated in the various figures of the drawings. The preferred type module is a duplex transceiver module incorporating a transmission optical subassembly and a receiver optical subassembly, also sometimes referred to as TOSA and ROSA, respectively. 
     Computers and particularly those computers which act as and are used as servers and controllers for networks are connected to communication lines which, in turn, are typically connected to other devices such as modems or other computers either directly or through other network connection lines. 
     Many connections between peripheral computers and servers are now being made through the use of fiber optic cable. Fiber optics present completely different requirements for interconnection to the electronic circuits and the previously widely used copper wire cable connections. The optical fiber must connect or interface with a light actuated diode or a light emitting diode which convert some incoming light signals into electrical signals and outgoing electronic signals to modulated light signals. 
     Although this description is made with reference to any or all of the drawing figures, in certain instances, references may be made to specific figures. An element of the disclosed module  10  may be observed in more than one figure. 
     In FIG. 1, a module  10  permitting easy connection of the optical fibers is illustrated mated to a host electronic circuit board  12 . The electronic circuit board  12  is attached to a mounting bracket  14  which serves as a portal for insertion of the module  10 , representing the machine frame or bezel. The mounting bracket  14  typically is connected to an electrical machine ground (not shown). 
     Module  10  supports and encloses transmitter and receiver optical subassemblies  54  and  56 , respectively, with electronic leads  16  electrically connected to a circuit board  18 , as illustrated in FIGS. 3 and 4, by solder (not shown) or other effective and well known means. The receiver optical subassembly  56  functions to convert the incoming optical modulated light signals to electronic signals used by the computer or server (not shown). Similarly, the electronic signals from the host device are converted to modulated light pulses and presented to the end of the outbound optical fiber using the transmitter optical subassembly  54 . 
     Circuit board  18  typically includes electronic elements that inherently propagate and radiate electromagnetic radiation. Electromagnetic radiation becomes electromagnetic interference when received by other electronic elements, components or devices either within the same host device (not shown) or other electronic devices within close proximity. 
     In order to provide electromagnetic radiation suppression to the greatest extent possible, an electrically conductive shield  100  (as shown in FIGS. 1,  5  and  6 ) and separate shield  120  (in FIGS. 7 and 8) are used to absorb the electromagnetic radiation and conduct the resulting electrical current to electrical ground. The more complete the enclosure of the electromagnetic radiation source, the more effective the suppression of the electromagnetic radiation. 
     As illustrated in FIGS. 2,  3  and  4 , the module chassis  20  supports and contains an electronic circuit board  18 . Electronic circuit board  18  is illustrated in only a partially populated state; note, it should be understood that the exact circuits and precise population of circuit board  18  are not part of the invention except for specifically described and illustrated components, and that the circuitry  16  may be any useful circuit elements requiring shielding. 
     The module chassis  20  is generally a parallelepiped shaped structure, although two sides may be sloped toward each other if desired. The module chassis  20  is preferably formed of an insulative material such as a non-conductive molded plastic. The module chassis  20  forms a box-like structure with one substantially open end  30  and an opposing end forming duplex receptacles  32 . Side walls  34  are formed integral with the top wall  36  which may be provided with an opening  38 . While not required, the opening  38  in the top wall  36  facilitates assembly of the circuit board  18  into the chassis  20 . The opening  38  increases the deflectability of the side walls  34  and permits an easier assembly of the module chassis  20  and circuit board  18 , which involves the insertion and positioning of circuit board  18  into chassis  20 . 
     FIG. 2 illustrates side walls  34  of the chassis  20  provided with protrusions  40  on interior surfaces  42  thereof. The protrusions  40  form positioning or stop surfaces  44  which may be engaged by a circuit board  18 . Additionally, supported by the interior surface  46  of top wall  36  and interior surface  42  of the side walls  34  is a further positioning surface  48  or stop surface  48  and a locating pin  50  extending from the stop surface  48 . Locating pin  50  mates with locating hole  52  in circuit board  18 , as best observed in FIG. 3, to precisely define the position of circuit board  18  relative to the long axis of module chassis  20 . 
     As may be best observed in FIG. 3, locating pin  50  insures that circuit board  18  is properly positioned within chassis  20  so that the optical interfaces  128  of the transmitter optical subassembly  54  and receiver optical subassembly  56  are properly disposed to align and be properly spaced relative to connectors terminating optical fibers (not shown) once inserted into duplex ports  32 . 
     As viewed in FIG. 2, chassis side walls  34  and top wall  36  are stabilized relative to each other by a support  58  joining side walls  34  and top wall  36  and forming positioning surface  48 . While the chassis structure  20  is stabilized in the region of supports  58 , the mid-sections  60  of side walls  34  remain unstabilized. 
     FIGS. 2 and 3 illustrate side walls  34  which include additional projections  64 ,  66 . The projections  64  serve as guide lugs  64  engagable with channel  76  of the interface connection device  68  attached to circuit board  12  in FIG.  1 . The guide lugs  64  as seen in FIGS. 2,  3 ,  5  and  8  must be maintained at a controlled spacing from each other to insure that the chassis  20  does not disengage from interface connection device  68  whenever mounted thereon. Additional stability of the side walls  34  at the open end  30  is provided by fillets  74 , preventing further undesirable spreading of guide lugs  64 . Similarly, the attachment of the support  58  to the side walls  34  and the top wall  36  along with the engagement of pins  50  in holes  52  of circuit board  18  further prevents undue spread of guide lugs  64  and latches  66 . 
     Continuing reference to FIGS. 2 and 3, projections  66  form latch members  66  with latch surfaces  70  spaced by the thickness of an electronic circuit board  18  from the plane formed by stop surfaces  44  and  48 . Latches  66  are conveniently provided with a champhered surface  72  to ease the passage of the electronic circuit board  18  past latches  66  upon being inserted into chassis  20 . For assembly purposes, the side walls of  34  are subject to deformation or deflection in the region of the latches  66 . Sidewalls  34  may be spread to remove latches  66  from interference with an electronic circuit board  18 . Similarly, circuit board  18  may be released and removed from chassis  20  by spreading side walls  34  and latches  66 . 
     During assembly, while the side walls  34  are deflected, the transmitter optical subassembly  54  and the receiver optical subassembly  56  are also inserted into the module chassis  20 . Apertures  81  and  83  are provided in the mid-sections  60  of side walls  34  for engaging the transmitter optical subassembly  54  and the receiver optical subassembly  56 , respectively, thereby retaining the optical subassemblies  54  and  56  in an assembled position. Projections  85  (FIG. 2, only one shown) extend from the interior surface  46  of the top wall  36  for engaging slots  87  (see FIG. 7) in the transmitter and receiver optical subassemblies  81  and  83 , respectively, to ensure stability and provide proper alignment thereof in the assembled position. 
     As the fully assembled module  10  is inserted into the host apparatus, as best viewed in FIG. 1, the module  10  is retained in the host device by a retainer  80  which has a latching aperture  82  formed therein. Latching aperture  82  is positionable surrounding retainer lug  84 , best illustrated in FIG. 3, on the bottom wall  86  of chassis  20 . Retaining member  80  is formed with a surface configuration (not shown) on the underside thereof that meets with a complementary, interlocking surface configuration (not shown) on the interface connection device  68 . The retaining member  80  may be depressed to release lug  84  and raised to engage and retain lug  84 . Bottom surface  86  of the chassis  20  engages the inner end  90  of retainer  80  and biases it so that aperture  82  seats around lug  84 . The inward portion  88  of lug  84  is inclined to cam retainer  80  past retainer lug  84 . 
     Refer now to FIGS. 1,  3 ,  5 ,  6 ,  7  and  8 . In order to prevent the leakage or escape of electromagnetic radiation from the electronic elements and, specifically, electronics  92  and well as other circuitry within the module  10  and similar electronic components (not shown), it is necessary to shield the electronics  92  and any similar electronic components (not shown) with an electromagnetic radiation shield  100  and bottom shield  120 . FIG. 1 shows the module  10  with the electromagnetic radiation shield  100  enclosing portions of three sides of module chassis  20 . 
     Electromagnetic radiation shield  100  may be fabricated from any desired sheet metal material but preferably from a thin sheet nickel-silver stock, chosen for its relatively high rigidity and high electrical conductivity. The shield  100  must conduct the electrical current created by the electromagnetic radiation collected within the shield  100  sheet material. 
     The sheet metal material is punched or cut to the desired shape and bent to form a channel as well as form other details and structure of the shield  100 . Along the edges  102  of the shield  100  are formed a plurality of tabs  104  and  106 . Tabs  104  are deformed during assembly to retain shield  100  on chassis  20 . 
     Tabs  106  are formed creating smooth bends resulting in a contact area  108  for progressively engaging a portion of the host device, such as the mounting bracket  14 . Tabs  106  are formed during the stamping process or as supplemental operations and bent to project the contact area  108  away from the chassis  20 . The sloping surface  110  on tabs  106  acts as a cam and first engages mounting bracket  14 , forcing the tabs  106  to flex and thus act as a beam spring. The deflection of tabs  106  flexes the contact surface  108  toward the chassis  20  and creates a restore force which firmly holds contact surface  108  against the inside edge  112  of the opening  114  in mounting bracket  14 , establishing an electrical contact between the shield  100  and the mounting bracket  14 , thus grounding shield  100  through mounting bracket  14 , and into a connection to machine ground (not shown). 
     To at least partially enclose the bottom of chassis  20  with an electromagnetic radiation shield, a generally flat piece  120  of conductive sheet metal is cut to extend across the open side of chassis  20 , and so extending to the extent possible without blocking or interfering with connections between the electronic circuit board  18  and the connection device attached to circuit board  12 . The bottom shield  120  is best illustrated in FIGS. 7 and  8 . 
     Bottom shield  120  is further formed to include tabs  122  which are spaced apart on each side edge  126  by the same distance as two of the tabs  104  are spaced apart on an edge of bottom shield  120 . The tabs  122  are formed or bent to extend away from the electronic circuit board  18  and parallel to the side walls  34  of chassis  20 . Upon assembly, the tabs  122  will ultimately be trapped by and electrically connected with some of tabs  104  on shield  100 . The tabs  104  will overlie tabs  122  and the interlocking will retain shield  120  in place relative to chassis  20 . 
     The end  124  of shield  120 , which is disposable adjacent to transmitter optical subassembly  54  and receiver optical subassembly  56 , is formed with a plurality of tabs  134  and  136 . Tabs  134  cover the transmitter optical subassembly  54  and receiver optical subassembly  56  and, particularly, the opening  138  in chassis  20  in FIG. 2 into which the transmitter optical subassembly  54  and receiver optical subassembly  56  are inserted. This shielding structure provides a barrier to electromagnetic radiation escape in that region of chassis  20 . 
     Referring to FIG. 7, end  124  of the shielding  120  is cut to form an appendage  136  between tabs  134  and is bent or otherwise formed to project generally perpendicularly to the plane of shield  120 . This appendage  136  is interdigitated between the transmitter optical subassembly  54  and receiver optical subassembly  56 . Appendage  136  is long enough to extend completely through an opening  138  in chassis  20  (shown in FIGS. 4 and 8) and engage the interior surface of shield  100 . The engagement of the appendage  136  with the interior surface of shield  100  provides a redundant electrical connection between shield  100  and shield  120 . 
     Of further significance is the positioning of the appendage  136  intermediate the otherwise open duplex ports  32  of chassis  20 , thereby forming two openings through which the electromagnetic radiation may escape. The open duplex ports  32  of chassis  20  cannot be totally sealed to electromagnetic radiation escape due to the need to connect fiber optic strands to the electronic circuit boards  18  and particularly to the circuitry. If an opening is reduced in size, the electromagnetic radiation escaping through the reduced opening is rendered less interfering; passing through the reduced size hole attenuates the electromagnetic radiation passing through the end of the chassis  20 , thereby minimizing the deleterious effects of the escaping radiation. Accordingly, the appendage  136  is made as wide as possible while fitting between the transmitter optical subassembly  54  and receiver optical subassembly  56  connector alignment portions  138 . 
     The appendage  136  may be further provided with a punched and projecting tab  140  which makes contact with the plastic chassis  20  and serves to prevent the shield  120  from deforming when shield  100  deflects and compresses appendage  136 . 
     As viewed in FIG. 7, the end  142  of shield  120 , opposite end  124 , is preferably formed into at least one section deviating from the plane of the shield  120  in a direction toward electronic circuit board  18 . End  142  will engage circuit board  18  and further close escape paths for electromagnetic radiation from electronics  92  or other electronic devices or conductors radiating electromagnetic emissions. Additionally, the bending or forming of shield  120  near its end  142  adds rigidity to the shield  120  and reduces deflection of shield  120  which may otherwise cause contact with electronic components or conductors and a possible short. If desired, the electronic circuit board  18  may be designed with contact pads (not shown) connecting to the ground plane (not shown) of the electronic circuit board  18  and the contact pads disposed to be engaged by edge  142  of shield  120 . This additional ground contact forms further redundancy in grounding shield  120 . 
     As illustrated in FIG. 8, the end  142  of shield  120  may be formed into multiple formed tabs  144  of varying lengths and widths, if desired. 
     As illustrated in FIGS. 1,  6  and  8 , crimping tabs  104  around the edges of side walls  34  of chassis  20  and trapping tabs  122  on shield  120  supplies additional rigidity and stability to side walls  34 , particularly in the region of latch members  66 , thereby preventing inadvertent spreading of latches members  66 . The interlocking nature of the shield  100  and shield  120  renders the module very rigid. 
     Because the transmitter optical subassembly  54 , receiver optical subassembly  56  and the associated electronics  92  are all contained in the removable module  10 , the easy removability of module  10  aids greatly in the event of a component failure and makes replacement quick and simplified and permits a rapid return to service of the host device. Module  10  is hot pluggable and can be inserted and removed without turning off the power supplies within the host machine. Similarly, if the communications lines are copper wire or coaxial cable, the transmitter optical subassembly  54  and receiver optical subassembly  56  would be incompatible, easily replaced with a substitute module and the appropriate interface circuitry inserted. Of necessity, the substitute module still will require a electromagnetic radiation shielding similar to that disclosed herein. 
     Although the dimensional parameters of the module  10  are established by the so-called “Small Form Factor” standard for transceiver modules for optical fiber interfaces, the construction and implementation details of the module  10  are left to designers of the particular system into which the module  10  will be incorporated. Accordingly, one of ordinary skill in the art will understand that minor modifications and changes may be made to the details of chassis  10  and of the electromagnetic radiation shielding  100 ,  120  without removing the module from the scope of protection afforded by the attached claims.