Abstract:
An optical transceiver for converting and coupling an infornation-containing electrical signal with an optical fiber including a housing, an electro-optical subassembly in the housing for converting between an information-containing electrical signal and a modulated optical signal corresponding to the electrical signal from which at least two optical fibers extends; and a flexible substrate for securing each of the optical fibers to prevent tangling in the housing interior and to enable said fibers to bend from a first orientation to a second orientation. An optical fiber receptacle or connector is provided on the housing to couple to an external optical fiber.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is related to copending U.S. patent application Ser. No. 10/879,775 filed Jun. 28, 2004, assigned to the common assignee. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to optical transceivers, and in particular to coupling assemblies or modules that provide a communications interface between a computer or communications unit having an electrical input/output connector or interface and an optical fiber, such as used in fiber optic communications links.  
         [0004]     2. Description of the Related Art  
         [0005]     A variety of optical transceivers are known in the art which include an optical transmit portion that converts an electrical signal into a modulated light beam that is coupled to an optical fiber, and a receive portion that receives an optical signal from an optical fiber and converts it into an electrical signal. In a high-speed unit, optical transmitter subassemblies include several lasers operating at different wavelengths and modulated with respective electrical signals for emitting a plurality of laser light beams. There beams are coupled into a plurality of optical fibers, which converge in an optical multiplexer for receiving the beams and multiplexing the respective optical signals into a single multi-wavelength beam that is coupled to a fiber optic connector for transmitting the optical signal to an external optical fiber.  
       SUMMARY OF THE INVENTION  
       [0006]     1. Objects of the Invention  
         [0007]     It is an object of the present to provide an improved optical transceiver using a flexible substrate to route and secure optical fibers from a transmitter subassembly.  
         [0008]     It is also an object of the present to provide an improved optical transceiver using a flexible substrate to route and secure optical fibers from a subassembly.  
         [0009]     It is another object of the present invention to provide a fused biconic tapered (FBT) coupler or similar multiplexing device mounted on a flexible substrate for use in a multi-laser optical transmission subassembly.  
         [0010]     It is still another object of the present invention to provide an optical transceiver for use in an optical transmission system with an industry standard XENPAK housing and including a flexible substrate therein for routing optical fibers.  
         [0011]     2. Features of the Invention  
         [0012]     Briefly, and in general terms, the invention provides an optical transceiver for converting and coupling an information-containing electrical signal with an optical fiber, including a housing and electro-optical subassembly in the housing for converting between an information-containing electrical signal and a modulated optical signal corresponding to the electrical signal from which at least two optical fibers extend; and a flexible substrate for securing each of said optical fibers to prevent tangling or breakage during manufacturing and assembly and to enable said fibers to bend from a first orientation to a second orientation.  
         [0013]     In another aspect of the invention, there is provided an optical transceiver including an optical multiplexer mounted on a flexible substrate for receiving at least first and second optical fibers and multiplexing the respective optical signals on the optical fibers into a single multi-wavelength beam in a single third optical fiber.  
         [0014]     Additional objects, advantages, and novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description as well as by practice of the invention. While the invention is described below with reference to preferred embodiments, it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional applications, modifications and embodiments in other fields, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of utility.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     These and other features and advantages of this invention will be better understood and more fully appreciated by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein:  
         [0016]      FIG. 1  is an exploded perspective view of an optical transceiver in an exemplary embodiment in accordance with aspects of the present invention;  
         [0017]      FIG. 2  is a top view of the flexible substrate for securing the optical fibers; and  
         [0018]      FIG. 3  is a rear view of the flexible substrate of  FIG. 2 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     Details of the present invention will now be described, including exemplary aspects and embodiments thereof. Referring to the drawings and the following description, like reference numbers are used to identify like or functionally similar elements, and are intended to illustrate major features of exemplary embodiments in a highly simplified diagrammatic manner. Moreover, the drawings are not intended to depict every feature of actual embodiments or the relative dimensions of the depicted elements, and are not drawn to scale.  
         [0020]     Referring more particularly to  FIG. 1 , there is provided an optical transceiver  100  for operating over both multimode (MM) and single mode (SM) fiber using multiple laser light sources, multiple photodetectors, and an optical multiplexing and demultiplexing system. This enables a single transceiver module to communicate over multiple protocols and at maximum distance goals. The transceiver  100  and its housing  102  are designed such that maximum operating efficiency is achieved cost effectively and at reduced electromagnetic interference (EMI) and thermal levels in an industry standard form factor or package design.  
         [0021]     Advantageously, the transceiver  100  is manufactured in a modular manner preferably using three separately mounted circuit boards mounted in the housing—a transmitter subassembly, a receiver subassembly, and a protocol processing board, with each board having dedicated functions and electrically connected to each other using either flex circuitry, mating multipin connectors, land grid arrays, or other electrical interconnect devices. This enables the basic transceiver module to be configured to different protocols and to support different optoelectronic devices using a simple subassembly configuration change, thus minimizing manufacturing costs and eliminating the need for manufacturing different transceivers for each different application. In addition, the use of flex circuitry or detachable connectors to interconnect the boards allows for a modular interchangeable board design (e.g., receiver, transmitter and PCS functionality each on separate boards). Although the preferred design uses three boards, any two of the functions may be combined on a single board for an even more compact design.  
         [0022]     The modularity of the board design also enables the placement of heat-sensitive components in the optimal location with respect to the heat-generating components (lasers and ICs) within the module housing  102 . It also makes it convenient and realistic to test and troubleshoot separate modular subassemblies independently before final assembly. In addition, the flex or other interconnects allow for manufacturing of the various boards (RX, TIX, PCS) to proceed in parallel instead of in serial, hence reducing the manufacturing time for the entire unit.  
         [0023]     Referring now to  FIGS. 1, 2 , and  3 , an exemplary optical transceiver module  100  is shown according to a preferred embodiment of the present invention. In this particular embodiment, the module  100  is compliant with the IEEE 802.3ae 10GBASE-LX4 Physical Media Dependent sub-layer (PMD) standard and the XENPAK™ form factor. It is to be noted, however, that the transceiver module  100  may be configured to operate under various other compliant protocols (such a Fibre Channel or SONET) and be manufactured in various alternate form factors such as X2. The module  100  is preferably a 10 Gigabit Coarse Wavelength Division Multiplexed (CWDM) transceiver having four 3.125 Gbps distributed feedback lasers and provides 300 meter transmission over legacy installed multimode fiber and from 10 to 40 km over standard single mode fiber.  
         [0024]     The transceiver module  100  includes a two-piece housing  102  with a base  104  and a cover  106 . In addition, contact strips  152  are provided to ground the module to chassis ground as well. The housing  102  is constructed of die-cast or milled metal, preferably die-cast zinc, although other materials also may be used, such as specialty plastics and the like. Preferably, the particular material used in the housing construction assists in reducing EMI. Further EMI reduction may be achieved by using castellations (not shown) formed along the edges of the housing  102 .  
         [0025]     The front end of the housing  102  includes a faceplate  152  for securing a pair of receptacles  124 ,  126 . The receptacles  124 ,  126  are configured to receive fiber optic connector plugs  128 ,  130 . In the preferred embodiment, the connector receptacles  128 ,  130  are configured to receive industry standard SC duplex connectors (not shown). As such, keying channels  132  and  134  are provided to ensure that the SC connectors are inserted in their correct orientation. Further, as shown in the exemplary embodiment and discussed further herein, the connector receptacle  130  receives an SC transmitting connector and the connector plug  128  receives an SC receiver connector.  
         [0026]     In particular, the housing  102  holds three circuit boards, including a transmit board  108 , a receive board  110  and a physical coding sublayer (PCS)/physical medium attachment (PMA) board  112 , which is used to provide an electrical interface to external electrical systems (not shown). An optical multiplexer (MUX)  114  interfaces to the transmit board  108  via an assembly of four distributed feedback (DFB) lasers  116  in TO-cans. The lasers  116  are secured in place at the bottom of the housing  104  using a laser brace  118 . The laser brace  118  also functions as a heat sink for cooling the lasers  116 . In addition, the transmit board  108  and receive board  110  are connected to the PCS/PMA board  112  by respective flex interconnect  120 , or other board-to-board connectors. Thermally conductive gap pads  160  and  161  are provided to transmit the heat generated by the lasers or other components to the base  104  or cover  106  of the housing, which acts as a heat sink. The receiver subassembly  110  is directly mounted on the housing base  104  using a thermally conductive adhesive to achieve heat dissipation. Different subassemblies therefore dissipate heat to different portions of the housing for more uniform heat dissipation. As illustrated in  FIGS. 1 and 2 , the output of the four lasers  116  is then input into the optical MUX  114 . The MUX  114  is mounted on a flexible substrate  140 . The substrate  140  may be an optical flexible planar material, such as FlexPlane™ available from Molex, Inc. of Lisle, Ill., although other flexible substrate may be used as well. As shown, the optical fibers  117   a,    117   b,    117   c,    117   d  originating from the laser assembly  116  and being input into the MUX  114  are mounted to the substrate  140 . The output of the MUX  114 , which is routed to the transmit connector plug  130 , is also attached to the substrate  140 . The fibers  117   a,    117   b,    117   c,    117   d  are routed and attached in such a manner as to minimize sharp bends in the optical fibers to avoid optical loss and mechanical failure.  
         [0027]     The substrate  140  includes an opening  142  or hole in a portion of the material that is located directly above the retimer IC or other heat generating components mounted on the PCS/PMA board  112 . The opening  142 , which is substantially an area the size of the unused portion of the substrate  140 , enables the heat sink on the cover to contact a heat transmission gap pad  160 , so as to provide access to the mounted components on the board. This area normally would be inaccessible if not for the opening  142 . For example, a heat sink may be installed in the Clock and Data Recovery components (not shown) without interfering with the routing of the optical fibers on the substrate  140  and without removing the mounted substrate  140  to allow access to the PCS/PMA board  112 .  
         [0028]     Several additional advantages are realized in using the flexible substrate  140 . In particular, attaching the fibers to the substrate  140 , rather than allowing the fibers to move about freely within the transceiver module housing  102 , neatly maintains the routing of the optical fibers to prevent unwanted tangling and breakage during assembly of the transceiver. Furthermore, attaching the optical fibers to the substrate  140  greatly reduces the stress on the fibers, thereby reducing the incidence of microcracks forming in the fiber coatings.  
         [0029]     The present invention implements the transceiver  100  utilizing the four standard, commercially available fiber pigtailed lasers  116  which interface to a Fused Biconic Tapered (FBT) coupler  114  to collect and multiplex laser radiation into a single fiber. Although a FBT is preferred, an arrayed waveguide grating, multimode interference coupler, or combination of spatially fixed optical elements such a lens, optical interference filters, diffractive optical elements, dielectric or metallic mirrors, or other optical components, may be used as well. The fiber that is used in the fiber pigtailed lasers  116  and the FBT  114  is affixed to the flexible substrate material  140 . This prevents fiber tangling and breakage while remaining flexible and therefore easy to work with. The flexible substrate material  140  may be an optical flexible planar material, such as FlexPlane™ available from Molex, Inc, of Lisle, Ill., or Kapton™ available from E. I. Dupont de Nemours and Company of Wilmington Del. Other flexible substrates may be used as well. A conforming coating is used over the entire flex  140  is used to secure the fibers to the flex  140 .  
         [0030]     As previously noted above, several additional advantages are realized when using the flexible substrates  140  rather than allowing the fibers to move about freely within the transceiver module housing  102 . Furthermore, attaching the optical fibers to the substrate  140  greatly reduces the stress on the fibers, thereby reducing the incidence of microcracks forming in the fibers. The fibers are routed and attached in such a manner as to minimize sharp bends.  
         [0031]     It will be understood that each of the elements described above, or two or more together, also may find a useful application in other types of constructions differing from the types described above.  
         [0032]     While the invention has been illustrated and described as embodied in a transceiver for an optical communications network, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
         [0033]     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.