Abstract:
An optoelectronic transceiver module that is simple and inexpensive to manufacture and assemble and that provides easy access to the optical and electronic components therein during and after manufacture. The module also provides for movement of the optical subassemblies allowing adjustability in alignment with an optical fiber.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention pertains to optoelectronic transmitter, receiver and transceiver modules. More particularly, the invention relates to optoelectronic modules that are inexpensive to manufacture, and easy to assemble and disassemble.  
         BACKGROUND OF THE INVENTION  
         [0002]    Optoelectronic transmitter, receiver and transceiver modules (herienafter modules) provide for the conversion of data between electrical signals and optical signals and the transfer of that data between an optical fiber and electronic circuitry. The term receiver is applied to a device that receives optical data and converts it to electrical data for transmission to further electronic circuitry. The term transmitter refers to a device that receives electrical data and converts it to optical data for transmission over an optical fiber. A transceiver generally refers to a device that contains both a receiver and a transmitter within a single housing and thus provides bidirectional communication. An optoelectronic module typically will be mounted onto a host circuit card that forms part of a host computer, input/output system, peripheral device or switch and also will be coupled, at the opposite end of the communication path through the module, to an optical fiber. Electrical signals are transferred between the host circuit card and the module. Optical signals are transferred between the optical fiber and the module.  
           [0003]    An optoelectronic module typically comprises at least an optical subassembly (OSA), including an optical connector to couple the optical signals to and/or from an optical fiber electronic circuitry, electronic circuitry, including electrical connectors to couple the electrical signals to and/or from external electrical circuitry, such as a host circuit card, and a housing to enclose and protect the aforementioned optical and electronic components. Commonly, the electronic circuitry takes the form of a printed circuit board (PCB) containing various circuit components. The electrical connectors may comprise pins that protrude from the bottom of the PCB through the bottom of the housing for solder connection to the circuit card. Flexible ribbon cable and other connectors are also known. Each OSA includes a ferrule receiving bore for accepting the ferrule of the plug on the end of an optical fiber and precisely aligning the optical fiber contained in the ferrule with the optical axis of the OSA. The OSA further typically includes a lens system and an LED (in the case of a transmit OSA) or a photodiode (in the case of a receive OSA).  
           [0004]    The module also includes a front end or nose designed to physically mate to a plug on the end of an optical fiber in accordance with one of the many well defined International standards. Some of the more common standards are SC, FC, and ST. These standards specify physical form factors and tolerances for the plugs and connectors that are to be matable in accordance with the standard. The nose is designed in accordance with the applicable form factor so that the plug body can be inserted into the nose and allow the ferrule of the plug to fit within the ferrule receiving bore of the OSA so that the optical fiber aligns properly with the optical path in the OSA.  
           [0005]    In one common scheme, the housing for an optoelectronic module is comprised of an encapsulant that is injection molded around the optoelectronic components and cured. The optical connector or nose is a separate piece that mounts onto the front of the housing. In many prior art designs, the bottom of the PCB forms the bottom of the housing. In others, the PCB is set into a tray and then the assembly is encapsulated.  
           [0006]    This encapsulation method has several draw backs. For instance, once the module is encapsulated, if any component of the device fails, either during testing during subsequent manufacturing stages or in the field, the module must be discarded since the individual components are inaccessible without destroying the module.  
           [0007]    Further, as previously noted, when the optical subassembly is coupled to a mating plug on the end of an optical fiber, the optical path of the OSA and the fiber must align extremely precisely in order to minimize signal power loss. However, since the OSA is immovable within the encapsulant, there is no ability for the OSA to move relative to the nose. This could be a problem in terms of insertion of the ferrule into the ferrule receiving bore of the OSA and the alignment of the optical axis of the OSA with the optical fiber. Particularly, the coupling of the plug of the optical fiber to the module involves mating components of the nose of the module with the plug body as well as mating the ferrule of the plug with the ferrule receiving bore of the OSA. Any misalignment between the OSA within the module and the module nose could adversely affect alignment of the optical fiber to the optical axis of the OSA.  
           [0008]    Accordingly, it is an object of the present invention to provide an improved optoelectronic module.  
         SUMMARY OF THE INVENTION  
         [0009]    The invention is an optoelectronic module, such as a transmitter, receiver or transceiver, comprising electronic circuitry and one or more optical subassemblies enclosed within a two-piece housing that can be opened at any time to expose the internal components for testing or replacement.  
           [0010]    According to one embodiment of the invention, the two parts of the housing attach together by means of one or more latches that engage with mating shoulders on the other half.  
           [0011]    According to another aspect of the invention, the optical subassembly(ies) are coupled to the printed circuit board via flex circuits. This enables the optical subassemblies to move when a plug is connected to them in order to facilitate better alignment of the optical subassembly with the optical fiber and/or nose of the module, if necessary.  
           [0012]    According to another aspect of the invention, a conductive gasket may be provided circumscribing the nose of the module with fingers extending radially therefrom and adapted to contact the face plate of a chassis when the module is mounted to protrude through a face plate. The gasket provides electromagnetic interference shielding.  
           [0013]    In accordance with an even further aspect of the present invention, the housing may be provided with flow-through slots to facilitate bathing of the module in aqueous solution, which is a common fabrication step. The flow-through slots allow the solution superior infiltration within the housing and superior flushing of the optoelectronic components within the housing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a perspective view of a fully assembled optoelectronic transceiver module in accordance with the present invention.  
         [0015]    [0015]FIG. 2 is an exploded view of an optoelectronic transceiver module in accordance with the present invention.  
         [0016]    [0016]FIG. 3 is a perspective view of the top housing portion of an optoelectronic transceiver module in accordance with the present invention.  
         [0017]    [0017]FIG. 4 is a perspective view of the bottom of the bottom housing portion of an optoelectronic transceiver module in accordance with the present invention.  
         [0018]    [0018]FIG. 5 is a perspective view of the inside of the bottom housing portion of an optoelectronic transceiver module in accordance with the present invention.  
         [0019]    [0019]FIG. 6 is a left side view of the printed circuit board and receive optical subassembly of an optoelectronic transceiver module in accordance with the present invention.  
         [0020]    [0020]FIG. 7 is a right side view of the printed circuit board and transmit optical subassembly of an optoelectronic transceiver module in accordance with the present invention.  
         [0021]    [0021]FIG. 8 is a bottom perspective view of an electromagnetic interference gasket that may be mounted on the nose of the optoelectronic transceiver module in accordance with the present invention.  
         [0022]    [0022]FIG. 9 is a front elevation view of a fully assembled optoelectronic transceiver module in accordance with the present invention.  
         [0023]    [0023]FIG. 10 is a plan view of the module with the optional electromagnetic interference gasket mounted on the nose thereof. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    The invention is herein described in connection with an SC, single mode, 9-pin, transceiver module for OC3, OC12 and gigabit applications. SC specifies the connector form factor. Single mode specifies that the fibers carry a single ray or mode of light as a carrier. OC3, OC12 and gigabit specify particular wavelength bands for the carrier channel. Finally, 9-pin specifies a particular electrical signal interface that includes 9 interface signal lines. However, it should be understood that this embodiment is exemplary and that the invention can be applied to receivers and transmitters. Further, the invention is not limited to the particular form factor, wavelength or mode type of the exemplary embodiment.  
         [0025]    Referring now to the drawings and particularly FIG. 1, which is a perspective view of an optoelectronic SC transceiver in accordance with one preferred embodiment of the present invention, the transceiver  10  comprises a housing  100  formed from two mating portions  101  and  103 . The housing portions preferably are non-conductive and may be fabricated from any of the polymers that are commonly used for optoelectronic module housings.  
         [0026]    Referring now to FIG. 2, which is an exploded perspective view of the transceiver  10 , enclosed within the housing are a printed circuit board  105 , a transmit optical subassembly  107 , and a receive optical subassembly  109 . The printed circuit board  105  is populated with electronic circuitry that conditions the electrical signals as necessary. Such circuitry likely includes at least an amplifier, filters, and a digital potentiometer for adjusting the gain of the amplifier.  
         [0027]    Nine pins  111  protrude from the bottom of the printed circuit board  105  and couple electrical signals between the printed circuit board  105  and external circuitry, such as a host circuit card. Particularly, the printed circuit board  105  is sized and shaped to rest flat in the back portion of the bottom half  103  of the housing with the pins  111  protruding through the holes  113  in the bottom housing half  103 . See also FIG. 4, which is a perspective view of the bottom of bottom housing half  103  better showing holes  113  and FIG. 9, which is a front plan view of the assembled module showing pins  111  protruding from the bottom of the module  10 . As best shown in FIG. 4, the module further includes two mounting pins  115 , which are electrically isolated from the optoelectronic circuitry in the transceiver module  10 . Mounting pins  115  may be formed of stainless steel. The proximal end of pins  115  press fit within holes  119  in the bottom surface of the bottom housing half  103 . The proximal ends of the pins  115  may include downwardly-angled, circumferential ridges  116  that allow the pins to be inserted upwardly into the holes  119  with the circumferential ridges  116  pressing against the walls of the holes  119 ,  121  to form a pressure fit within the holes. However, the pins cannot be easily removed because the downwardly directed circumferential ridges  116  bite into the inner walls of the holes  119  when the pins are forced downwardly and prevent downward motion of the pin relative to the hole. Flanges  123  are integrally formed on the pins  115  near the proximal ends of the pins and have a circumference larger than the circumference of the hole and thus limit the extent to which the pins  115  can be inserted into the holes  119  on the bottom of the housing half  103 .  
         [0028]    The distal ends of the mounting pins  115  will be inserted into mating holes in the host circuit card to physically mount the module on the card. The distal ends of the mounting pins  115  may be soldered or adhered within the holes.  
         [0029]    As is well known in the art, electromagnetic interference (EMI) is a particular problem for optoelectronic modules. Accordingly, referring again to FIG. 2, perforated metal EMI shields  127 ,  129  can be optionally mounted to the top surface of the printed circuit board  105  to cover the electronic circuitry on the printed circuit board and the back ends of the OSAs. Particularly, shields  127  and  129  generally take the form of five sided rectangular boxes with the bottom side open. The side walls include pins  130  that protrude downwardly and engage with mating holes on the printed circuit board  105 . The pins  130  may be soldered or adhered within the holes The top surfaces  127   a  and  129   a  are perforated. In addition, there may be one or more openings  128  in the side walls to accommodate circuitry populating the PCB  105  and/or the rear portions of the optical subassemblies  107 ,  109 .  
         [0030]    With reference to FIGS. 2, 6 and  7 , optical subassemblies  107  and  109  are mounted to the printed circuit board by flex circuits  131 . Particularly, a flex circuit comprises a flexible circuit board  131   a  and flexible wires  131   b  extending therefrom. The flex circuit boards  131   a  are epoxied to the backs of the optical subassemblies  107 ,  109 . The flexible wires  131   b  extend therefrom and curl around the edge of the PCB  105  and are soldered to the bottom side of the PCB  105 .  
         [0031]    Referring now to FIG. 5, which shows the inside of the bottom housing half  103 , the bottom half  103  of the housing preferably, includes formations that engage the optical subassemblies  107 ,  109  when the printed circuit board  105  and optical subassemblies,  107 ,  109  are inserted into the bottom half of the housing. For instance, extending upwardly from the inner bottom surface of bottom half  103  are two semicircular cutouts  132 ,  134  that engage circumferential slots  141 ,  143  in the optical subassemblies  107 ,  109  (see FIGS. 6 and 7) and generally define the position and orientation of the optical subassemblies.  
         [0032]    As best seen in FIGS. 1, 2,  3  and  4 , transverse flow-through slots  177  are formed in the rear portions of both halves  101 ,  103  of the housing  100 . As is well known in the art, it is common to immerse an optoelectronic module in an aqueous liquid bath during or at the end of fabrication in order to clean the module. The flow-through slots  177  allow better infiltration of the aqueous solution into the housing and thus allow better cleansing of the OSAs and PCB.  
         [0033]    With reference to FIGS. 3 and 5, the top and bottom halves  101 ,  103  are shaped to mate with each other and enclose the internal components. They couple to each other via latches  150  on one half and mating shoulders  155  on the other half. Preferably, housing halves  101 ,  103  each include two latches and two shoulders. Each latch  150  comprises a resilient bar  160  that is attached to or integral with the corresponding housing half at its proximal end and includes a dog  162  at its distal end. The dogs  162  comprise an angled outer surface  162   a  and an inner surface  162   b  that is normal to the length of the bar portion  160 . When the two halves  101 ,  103  are pushed together, the angled outer surfaces  162   a  of the dogs  162  engage vertical surfaces  156  adjacent the corresponding shoulders  155  on the other housing half. Because the outer surface  162   a  of dogs  162  are angled as shown, when the outer surface  162   a  of the dog  162  encounters the surface  156  adjacent the corresponding shoulder  155  of the other half, it forces the resilient bar  160  to bend outwardly. When the two halves  101 ,  103  reach the final mating position, the dogs  162  clear the shoulders  155 , thus allowing the resilient bars  160  to snap back to their neutral position, thus engaging the inner surface  162   b  of the dog against the mating shoulder  155  on the other half. The two halves  101 ,  103  are thus locked together by the latches  150  and shoulders  155 .  
         [0034]    Because the inner surface  162   b  of the dogs  162  are parallel to the shoulder, the two halves  101 ,  103  cannot be separated from each other. However, by simultaneously biasing the bars  160  of all four latches  150  outwardly, the dogs  162  can be disengaged from the corresponding shoulders  155  and the two halves separated. Accordingly, the two halves  101 ,  103  provide a secure housing that encloses and protects the electronic and optical components of the module, yet the housing can be opened at any stage during manufacturing or afterwards to allow access to the internal components.  
         [0035]    This is a substantial advantage over prior art housings in which the optical and electronic circuitry were permanently encapsulated such that access could not be obtained to the optical and electronic circuitry without destruction of the module and/or circuitry itself.  
         [0036]    With reference to FIG. 5, in the front end or nose of the bottom half  103  of the housing, four more latches  164  are designed to engage mating shoulders of an SC duplex plug (not shown), as is well known in the art. Integral with the bottom housing half  103  is a wall  163  between the two optical subassemblies  107 ,  109 . Referring to FIG. 3, a mating wall  165  is found in the top housing half  101 . When the two halves  101 ,  103  are brought together, walls  163  and  165  meet and form a full height internal wall that separates the front ends of the optical subassemblies  107  and  109  from each other. The top and bottom housing halves  101 ,  103  meet to form a front opening  167  of the module (see FIG. 1, for instance). The front of the housing has a recessed wall  171  between the two optical subassemblies. Otherwise the front of the module is open. As best shown in FIGS. 1, 2 and  3 , the top half  101  includes two slots  173  and  174  that are open to the front end  167  of the housing. These slots  173  and  174  are generally aligned with the OSAs in the plan views of FIGS. 2 and 3. Slots  173  and  174  accept the key or polarizing member that is found on one side surface of a SC plug. The key on an SC plug and the mating channel or slot on an SC connector is included as part of the SC standard in order to assure that an SC plug can be inserted into an SC connector in only one orientation. The key provides an asymmetric feature in the otherwise symmetric SC form factor.  
         [0037]    An external EMI gasket  180  can be mounted on the front end or nose piece of the housing to provide enhanced EMI shielding. With reference to FIG. 8, the gasket  180  includes a main body portion  182  sized and shaped to circumscribe the front end of the housing. The gasket  180  is conductive and is preferably formed of a thin, flexible sheet metal. The bottom surface of the gasket has its rear corners cut out to accommodate the mounting pins  115  and  117 . The front end of the gasket includes a plurality of flexible fingers  183  extending generally radially outwardly from the gasket. The front end also includes a support member  184  running vertically down the center of the front of the gasket (see FIG. 2), but is otherwise open at the front and back. The gasket  180  slides onto the front end of the housing until support member  184  meets wall  171  of the housing (best shown in FIGS. 3, 4, and  5 ), thus defining the proper position of the gasket. FIG. 10 shows the position of the gasket  180  in outline form when mounted on the front end of the module  100 .  
         [0038]    The gasket further includes two cutout tabs  187  and  188  in the top and bottom sides, respectively. The tabs are resilient and extend from the body of the gasket toward the front opening of the gasket  180  and slightly inwardly. The tabs, preferably, are formed integrally with the gasket by cutting out the surrounding metal. Accordingly, when the gasket is slid onto the nose piece of the module, the tabs  185  and  186  bend outwardly as they contact the top and bottom surfaces of the housing until the gasket is fully inserted, at which point tabs  185  and  186  meet apertures  190 ,  191  on the top and bottom surfaces, respectively, of the housing (see FIGS. 1 and 4). At that point, they resiliently snap into the apertures and thus prevent the gasket from being slid forward off of the housing. However, if necessary, the gasket can be removed, by bending both tabs  185  and  186  outwardly. This may be accomplished by slipping thin sheets between the gasket  180  and the housing from the rear of the housing so as to bend the tabs outwardly and release them from engagement with the edges of the apertures  190 ,  191 .  
         [0039]    In one preferred embodiment of the invention, the gasket is stamped from a single sheet. The sheet is then folded into the shape of the gasket. Plates  189  are then spot welded to the two side surfaces of the gasket. A gap  190  may remain at the sides. Finally, the fingers  183  are bent outwardly.  
         [0040]    The fingers  183  of the gasket, are designed to contact the front surface of the face plate or bulk head when the module  100  is mounted in a host device in which the nose extends through a face plate or bulk head. Accordingly, the conductive gasket surrounding the nose piece makes electrical and physical contact with the face plate of the chassis or host device, which, presumably is electrically coupled to chassis ground and thus helps enhance EMI shielding of the module. Since the fingers are resilient, they provide some leeway in the positioning of the module relative to the face plate in the direction of the optical axis of the module. The fingers can flex to accommodate slightly different depths of the module behind the faceplate with the fingers still contacting the front of the faceplate.  
         [0041]    Referring again to FIG. 1, a rubber boot  201  may be provided with the module. The boot  201  has a handle  207  and is designed to be inserted into the front end  167  of the module so that the two plugs  203 ,  205  surround the optical subassemblies  107 ,  109 , respectively. The plugs  203 ,  205  define cylindrical openings (not seen in the Figures) that slip over and surround the OSAs to protect them prior to deployment of the module. The plugs protect the OSAs in two respects. First, they assist in holding the OSAs steady prior to being coupled to an optical fiber. Recall that the OSAs are coupled to the PCB by flex circuit and thus can move about within the module and possibly damage the wire connectors of the flex circuit. Secondly, the plugs cover the front openings of the OSAs during the aqueous bath stage of fabrication and thus help prevent liquid from entering internally to the OSAs. The boot  201 , of course, is removed prior to deployment of the module so that optical fibers can be coupled to the OSAs.  
         [0042]    Having thus described a few particular embodiments of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications and improvements as are made obvious by this disclosure are intended to be part of this description though not expressly stated herein, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only, and not limiting. The invention is limited only as defined in the following claims and equivalents thereto.