Abstract:
A hermetically sealed optical transmitter module for use in an optical transceiver converting and coupling an information-containing electrical signal with an optical fiber. A plurality of semiconductor lasers are provided on a common support in the housing for converting between an information-containing electrical signal and a modulated optical signal corresponding to the electrical signal according to a standardized optical communications protocol, such as the IEEE 802.3ae 10 Gigabit BASE LX4 physical layer.

Description:
REFERENCE TO RELATED APPLICATIONS 
     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 
     1. Field of the Invention 
     The invention relates to optical transceivers, and in particular to multi-laser transmitter assemblies or modules that provide an communications interface between a computer or communications unit having an electrical output connector or interface and an optical fiber, such as used in high speed fiber optic communications links such as wide wavelength division multiplexed (WWDM) networks. 
     2. Description of the Related Art 
     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. Traditionally, optical transmitter sections include one or more semiconductor lasers and an optical assembly to focus or direct the light from the lasers into an optical fiber, which in turn, is connected to a receptacle or connector on the transceiver to allow an external optical fiber to be connected thereto. The semiconductor lasers are typically packaged in a hermetically sealed can or similar housing in order to protect the laser from humidity and other harsh environmental conditions. The semiconductor laser chip is typically a few hundred microns to a couple of millimeters wide and 100-500 microns thick. The package in which they are mounted typically includes a heat sink or spreader, and has several electrical leads coming out of the package to provide power and signal inputs to the laser chips. These electrical leads are then soldered to the circuit board in the optical transceiver. 
     In high speed systems requiring the use of several lasers, the hermetic packages take considerable space, and it is desirable to provide a more compact arrangement. 
     SUMMARY OF THE INVENTION 
     1. Objects of the Invention 
     It is an object of the present to provide an improved optical transceiver using a modular, interchangeable transmitter subassembly. 
     It is another object of the present invention to provide a hermetically sealed transmitter module for use with different optical data transmission standards and containing a plurality of optoelectronic components. 
     It is also another object of the present invention to provide an optical transmitter for use in an optical fiber transmission system with an industry standard 10GBASE-LX4 physical layer. 
     It is still another object of the present invention to provide an optical transmitter for use in an optical wavelength division multiplexed (WDM) transmission system suitable for short range and long haul applications using multiple semiconductor laser chips mounted in a single hermetically sealed package. 
     It is still another object of the present invention to provide an optical transceiver capable of field upgrade of the optical transmitter module. 
     It is still another object of the present to provide improved heat dissipation in an optical transmitter by using heat conductive pathways from semiconductor lasers to the housing or case. 
     It is still another object of the present invention to provide an optical multiplexer in an assembly that may be quickly and easily aligned with a multiple laser subassembly and permanently affixed thereto by spot laser welding. 
     It is also another object of the present invention to provide an optical transceiver for use in an optical transmission system with key components packaged in hermetically sealed enclosures to protect them from exposure to environmental conditions. 
     It is still another object of the present invention to provide an optical transmitter that is easily manufacturable by using simplified electro-optical component mounting and alignment techniques. 
     2. Features of the Invention 
     Briefly, and in general terms, the present invention provides an optical transceiver for converting and coupling an information-containing electrical signal with an optical fiber including a housing including an electrical connector for coupling with an external electrical cable or information system device and a fiber optic connector adapted for coupling with an external optical fiber, at least one electro-optical subassembly in the housing for converting between an information containing electrical signal and a modulated optical signal corresponding to the electrical including a transmitter subassembly including first and second lasers operating at different wavelengths and modulated with respective first and second electrical signals for emitting first and second laser light beams, and an optical multiplexer for receiving the first and second beams and multiplexing the respective optical signals into a single multi-wavelength beam. 
     In still another aspect of the invention, there is provided a transmitter subassembly including an optical multiplexer coupled to a fiber optic connector for transmitting a multi-wavelength optical signal having a plurality of information-containing signals each with a different predetermined wavelength. The optical multiplexer functions to convert the optical signals into a single optical signal composed of signals on different predetermined wavelengths. The subassembly includes a hermetically sealed housing including an array of plurality of lasers disposed therein for generating a plurality of laser beams at different wavelengths. 
     In another aspect of the invention, the invention provides a modular transmitter subassembly that includes interchangeable or reprogrammable circuit subcomponents, such as lasers, laser drivers, and electrically programmable read only memory. Such subcomponents enable simplified manufacturability and mass customization for a wide variety of different optical band requirements, fiber types, communications protocols, range options, or applications. It also enables the unit to be quickly reconfigured to handle a different optical network or protocol, physical layer, or upper media access control layers, by simply removing one module board and substituting another, or reprogramming an EEPROM on the board. 
     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 DRAWING 
       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: 
         FIG. 1  is an exploded perspective view of an optical transceiver in an exemplary embodiment in accordance with aspects of the present invention; 
         FIG. 2  is a top perspective view of the transmitter subassembly in the transceiver of  FIG. 1 ; 
         FIG. 3  is an exploded view of the transmitter subassembly shown in  FIG. 2 ; and 
         FIGS. 4A and 4B  are cross-sectional views of the transmitter subassembly through the A-A and B-B planes respectively shown in  FIG. 3   
     
    
    
     The novel features and characteristics of the invention are set forth in the appended claims. The invention itself, however, as well as other features and advantages thereof, will be best understood by reference to a detailed description of a specific embodiment, when read in conjunction with the accompanying drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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. 
     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 design enables a single transceiver to be adaptable or configurable to communicate over different optical networks using multiple protocols and satisfying maximum range and 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. 
     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 or 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. 
     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, TX, PCS) to proceed in parallel instead of in serial, hence reducing the manufacturing time for the entire unit. 
     Referring now to  FIG. 1  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) and is implemented in the XENPAK™ form factor. It is to be noted, however, that the transceiver module  100  may be configured to operate under various other standard protocols (such a Fibre Channel or SONET) and be manufactured in various alternate form factors such as X2 or XFP. The module  100  is preferably a 10 Gigabit Wide Wavelength Division Multiplexed (WWDM) 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. 
     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 . 
     The front end of the housing  102  includes a faceplate  153  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 plugs or receptacle  128 ,  130  are configured to receive industry standard SC duplex connectors (not shown) which are attached to the end of an optical fiber. 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. 
     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) via connector  113  that is implemented by a sequence of parallel printed contact pads on the upper and lower surface of the board  112 . The transmit board  108  includes a transmitter subassembly  400 , as shown in more detail in  FIG. 2 , which includes four distributed feedback (DFB) semiconductor lasers  403  mounted in a single, hermetically sealed enclosure  402 . The transmit board  108  is secured in place at the bottom of the housing  102  using a brace  418  attached to the coupling subassembly  401 . The brace  418  also functions as a heat sink for dissipating heat from the metallic coupling subassembly  401 . 
     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 in the transmitter subassembly 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 a more uniform heat dissipation. As illustrated more particularly in  FIG. 2 , the transmitter subassembly  400  includes the output of the four lasers  403  is input into a single optical fiber  117  which coils and reverses direction and is attached or 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 fiber  117  originating from the transmitter subassembly  400  mounted to the substrate  140  and routed to the transmit connector plug  130 , which is attached to the housing  102 . The fiber  117  is routed and attached in such a manner as to minimize sharp bends in the optical fiber to avoid optical loss and mechanical failure. 
       FIG. 2  is a top perspective view of the transmitter subassembly  400  depicting the hermetically sealed laser subassembly  402  and the coupling subassembly  401 . The laser subassembly includes four semiconductor lasers  403  in die form which are mounted on an optical bench  416  to achieve alignment with an external optical multiplexer (or MUX). 
     The coupling subassembly  401  includes a cylindrical weld sleeve  404  that is illuminated through the sapphire window  415 , shown in  FIG. 4A . The coupling subassembly  401  further includes an optical multiplexer disposed within a housing  405 , and a concentric cylindrical sleeve  406   b  attached to the housing  405 . The optical fiber  117  is contained within a ferrule assembly  408 , which aligns with an attaches to a ferrule-isolator housing  406   a . The sleeve extending between cylindrical sleeve  406   b  and housing  406   a  allows the ferrule assembly  408  to be aligned to the output port of the multiplexer, and fixed in place using coaxial laser welding, as diagrammatically depicted at  407   a  and  407   b.    
       FIG. 3  is an exploded view of the components within the cylindrical weld sleeve  404 . More particularly, there is shown a laser lens array, a collimator, and the optical multiplexer, and a cylindrical housing  405  which supports the multiplexer  412 . 
       FIG. 4A  depicts a cross-sectional view of the transmitter subassembly through the A-A plane shown in  FIG. 2 . The B-B plane is 90 degrees, or orthogonal, to the A-A plane.  FIG. 4B  is the cross-sectional view of the transmitter subassembly through the B-B plane. 
     The combination of a cylindrical housing  405  the optical multiplexer  412  and the concentric cylindrical sleeve  404  allows the multiplexer  412  to be aligned and fixed in place with high precision housing  405  using environmentally robust adhesive materials. Once micron-scale alignment between the laser sources and the multiplexer channels is established using active alignment, coaxial laser welding can lock the position of the multiplexer housing  405  with respect to the cylindrical weld sleeve  404 . The sleeve  404  is then attached to the front of the hermetic package  402  in a fashion that preserves alignment accuracy. 
     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. 
     While the invention has been illustrated and described as embodied in a hermetically sealed optical transmitter for use in an optical transceiver, 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. 
     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.