Abstract:
An opto-electric module adapted to be coupled with an optical fiber on a first side and a plurality of electrical conductors on a second side. The opto-electric module includes a header with a plurality of pins extending through the header a thermo-electric cooler with a hot plate of the thermo-electric cooler disposed against a second, opposing side of the header and a plurality of active and passive optical components adapted to convert between an optical signal format within the optical fiber and an electrical signal format within at least one conductor of the plurality of conductors, said plurality of active and passive optical components all being in thermal contact with a cold plate of the thermo-electric cooler.

Description:
FIELD OF THE INVENTION 
     The invention relates to electro-optical converters, and more particularly to integrated laser assemblies or modules that provide a communications interface between a computer or communications unit having an electrical connector or interface and an optical fiber, such as used in fiber optic communications links. 
     BACKGROUND OF THE INVENTION 
     This application is related to copending U.S. patent application Ser. No. 11/059,790 filed on Feb. 16, 2005 (pending), assigned to the common assignee. 
     A variety of electro-optic transceivers are known in the art. Such devices typically include an optical laser module that converts an electrical signal into a modulated light beam that is coupled to an optical fiber, and a receiver that receives an optical signal from an optical fiber and converts it into an electrical signal. Traditionally, the optical laser module includes a laser diode (LD) and other optic components and it focus or directs the light from the laser diode onto the optic fiber, which in turn, is connected to network transmission line. The laser module is typically packaged in a hermetically sealed package in order to protect the laser diode from harsh environmental conditions. 
     The laser diode is provided as semiconductor chip that is typically a few hundred microns wide and 100–500 microns thick. The package in which they are sealed is typically in the butterfly or coaxial form factors with several electrical leads coming out of the package. These electrical leads are typically soldered to the circuit board containing the amplifier/limiter. 
     The coaxial laser modules have seen some use in fiber optic telecommunication and CATV applications. Such modules typically use transistor outline (TO) packages and provide a relatively low cost solution in some markets. However, for applications where the laser consumes a relatively large amount of power or the laser is operated over a wide range of ambient temperatures, the laser diode and other optical components must be cooled in order to meet the requirements of an extremely narrow frequency spectrum and stable LD performance. External, forced air cooling has been the method of choice. 
     The use of internal cooling with TO packages has proven difficult due to the limited space within the TO header and the size of the active and passive components found therein. One previous effort in this regard involved the cooling of a converter module using very small custom thermo-electric coolers (TECs) and was limited to the cooling of only the active components (i.e., the LD) and not the passive components (i.e., lens and isolator). The cooling of only the active components has been found to result in unstable optical performance where a wide range of operating temperatures are involved. 
     In order to address these deficiencies in prior designs, a new style of coaxial cooled laser module based on an optimized thermal and mechanical design is described below under illustrated embodiments of the invention. This proposed cooled laser module uses a commercially available miniaturized TEC and integrates both the active and the passive optical components on a temperature controllable platform to provide a stable laser and optical performance. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved optical laser module using an integrated thermal electric cooler and other optical subassemblies. 
     It is another object of the present invention to provide an optical laser module subassembly for use with different optical transmission systems. 
     It is also another object of the present invention to provide a cooled optical laser module for use in an optical transmission system with a housing that meets industry standards. 
     It is also another object of the present invention to provide a cooled optical transceiver for use in an optical wavelength division multiplexed (WDM) transmission system. 
     It is still another object of the present invention to provide improved heat dissipation in an optical transceiver by using a TEC subassembly inside the housing. 
     It is another object of the present invention to provide a cooled optical transceiver for use in an optical transmission system with key optical components packaged in a hermetically sealed enclosure to protect them from exposure to environmental conditions. 
     It is another object of the present invention to provide a cooled optical laser module that is easily manufactured by using simplified optical component mounting and alignment techniques. 
     These and other objects are provided by an opto-electric module adapted to be coupled with an optical fiber on a first side and a plurality of electrical conductors on a second side. The opto-electric module includes a header with a plurality of pins extending through the header, each pin of the plurality of pins extending through the header and each pin of the plurality of pins being adapted to engage a respective conductor of the plurality of conductors on a first side of the header, a thermo-electric cooler with a hot plate of the thermo-electric cooler disposed against a second, opposing side of the header and a plurality of active and passive optical components adapted to convert between an optical signal format within the optical fiber and an electrical signal format within at least one conductor of the plurality of conductors, said plurality of active and passive optical components all being in thermal contact with a cold plate of the thermo-electric cooler. 
     Briefly, and in alternate and general terms, the present invention provides an optical laser module for converting an information-containing electrical signal into an optical signal and coupling the converted optical signal into an optical fiber. The optical laser module includes a housing including an electrical connector for coupling with an external mount, such as a receptacle on a printed circuit board and also a transparent window adapted for coupling an optical signal with an external optical fiber subassembly in the housing. 
     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 
       These and other features 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 a perspective view of the proposed coaxial cooled laser module. 
         FIG. 2  ( a ) and ( b ) are typical views of the TO-can package and the cap of  FIG. 1  with a flat window; 
         FIG. 3  shows the TO header of  FIG. 1  and its pin orientation; 
         FIG. 4  shows an alternative TO header that may be used with the module of  FIG. 1 ; 
         FIG. 5  shows an example of miniature TEC that may be used with the module of  FIG. 1 ; 
         FIG. 6  shows the compact LD-MPD placement within the module of  FIG. 1 ; 
         FIG. 7  ( a ) and ( b ) show the optical lens and isolator combo of  FIG. 1 ; and 
         FIG. 8  ( a ) and ( b ) show an alternative carrier module with lens and isolator combo that may be used with the module of  FIG. 1 . 
     
    
    
     It should be noted that the dimensions and scales shown in above figures are not accurate and are for illustration and explanation only. Similarly, the components shown in the figures also are for illustration and explanation purpose. Actual components may vary. For simplicity, the wirebonds between the components are omitted herein. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Details of 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. 
     With this in mind,  FIG. 1  shows a coaxially cooled laser module  10  under illustrated embodiments of the invention. The coaxial cooled laser module  10  shown in  FIG. 1  consists of a TO-can and a fiber pigtail module  12  which functions to align an axis of light transmission between the TO-can and the optical fiber. 
     The embodiments described herein are associated with the TO-can design. Therefore, the discussion provided herein is focused primarily on the TO-can and similar packaging. The TO-can package shown in  FIG. 2  typically consists of a TO header subassembly  14  shown in  FIG. 2(   a ) and a sealing cap  16  with a flat window  18  shown in  FIG. 2  ( b ). 
     The TO header subassembly  14  may include a TO header  20  with a number of electrical conductor pins  22  extending through the TO header  20 . The TO header subassembly  14  may also include a thermo-electric cooler (TEC)  24  and a carrier module  26  that supports active and passive optical components, i.e., LD, MPD, optical lens and isolator (the lens and isolator combo). The TO header  20  may be made of a number of different materials, like cold roll steel, Kovar or other alloys. The diameter of the header should be large enough to accommodate a selected TEC  24 . One example may be a TO header  24  that is 9 mm in diameter. 
     The header pins  20  may be of an inline layout or alternatively of a circular layout as shown in  FIGS. 3 and 4 . In order to get better RF performance at high frequency ranges, the RF pin  300  may be designed to have good impedance match. Under illustrated embodiments, a coaxial pin configuration is used as shown in  FIGS. 3 and 4 . The coaxial pin consists of metal tubing and a glass filler. The diameters of the tubing and pin are determined by the matching impedance and dielectric constant of the glass filler. The metal tubing is brazed on the header. 
     The TEC  24  may be any commercial available miniature cooler that consists of a hot, a cold plate and thermal electric semiconductor elements as shown in  FIG. 5 . The thermal electric semiconductor elements are placed in couples. The thermal capacity of the TEC should be chosen so that it has a sufficient number of thermal couples that are able to keep the cost low and yet are still adequate to dissipate both the active heat load generated by LD and the passive heat load leaked into the package from the surrounding environment. One example is the TEC with footprint of approx. 5×4 mm. 
     There may be two wirebond pads  500 ,  502  located in opposite ends of the TEC  24 . Other configurations of the wirebond pads are possible. The TEC may be soldered to the center of the TO header. The wirebond pads  500 ,  502  may be connected to pins  22  via a pair of wirebonds  32 . 
     The carrier module  26  is mounted onto the cold plate  504  of the TEC and is populated with a LD  600 , a MPD  604 , a reflection mirror  602  and the lens and isolator combo ( FIGS. 7 and 8 ). The LD  600  may be mounted on a LD submount  606  that is made of a material with good thermal conductivity. One example is aluminum nitride (AIN). There may be several Au metalized pads on the LD submount (not shown in the figure) to allow soldering of the leads of the LD and other possible components to an intermediate connection point and then on to the leads  22 . The LD  600  may be an edge emitting laser and may be soldered vertically on the submount. 
     Alternatively, a surface emitting laser is also suitable for this application with slight modification of the LD submount  606 . The edge emitting laser emits laser light in two directions, one is in a forward direction from a front facet and the other is backward from a rear facet. 
     In a traditional uncooled TO laser package where the edge-emitting laser is used, the MPD is mounted beneath the LD to catch the laser light from the rear facet of the LD for purposes of monitoring laser performance. This configuration has a drawback, i.e., it raises the profile of the components on the cold plate of the TEC, resulting in poor mechanical and thermal stability. Under illustrated embodiments, a compact LD-MPD configuration is provided as shown in  FIG. 6 . 
     A wedge shaped mirror reflector  602  is used to reflect the laser light and to redirect it to the MPD  604  that is mounted in front of the LD. In this way, the profile of the components is lower significantly. The wedge shaped mirror is made of metal, ceramic or silicon with Au plated on the reflective surface. The surface quality is not critical because it is for monitoring purpose only. The angle of the wedge varies depending on the position and height of the MPD (e.g., 30–60 degrees). The MPD orientation may be slightly adjusted to avoid saturation and back reflection. 
     Referring now to  FIGS. 7 and 8 , a projection and shoulder combination  702  on an upper surface of the optical lens and isolator combo  30  may engage the flat window (aperture)  18  of the sealing cap  16 . Alternatively, the flat window  18  may be comprised of an optically transparent material disposed in the upper surface of the sealing cap  16 . 
     Where the flat window  18  is a transparent material, the optical lens and isolator combo  30  may be separated from the window by a short distance (e.g., less than 1 mm). Separation of the optical lens and isolator combo  30  allows the combo  30  to be thermally isolated from the sealing cap  16 , yet still allows the optical signal to be transmitted by the combo  30  through the window  16  into the optical fiber. 
     The optical lens and isolator combo  30  may be fabricated by integrating an optical lens and an isolator in a housing to form a single compact component as shown in  FIG. 7  ( a ). The optical lens  700  may be a ball lens or aspheric lens depending on optic design and coupling efficiency. The surface of the lens may have an anti-reflective (AR) coating. The optical isolator  703  may be suspended by the lens  700  in free space with the only connection being made to the carrier. 
     Alternatively, a supporting stand  800  can be integrated into the combo component as shown in  FIG. 7  ( b ). The housing is made of Kovar or other appropriate metals. 
     In order to get good optical performance, the lens and isolator combo  30  may be cooled by the cold plate of the TEC. Therefore, it may be mounted on the carrier module  26  along with the LD and MPD. If there is no supporting stand on the combo component, a bonding ring  802  may be needed as shown in  FIG. 8  ( a ). The bonding ring is made of metal, like Kovar or stainless steel. However, if the supporting stand is integrated into the combo component, the combo component can be directly mounted on the carrier as shown in  FIG. 8(   b ). 
     There may be two configurations of the carrier, one is extruded and the other is flat as shown in  FIG. 8  ( a ) and ( b ). The carrier can be made of Kovar or stainless steel. Two methods can be employed to bond the combo component on the carrier, one is laser welding and the other is epoxy bonding. The placement of the lens-isolator component should be done using either active or passive alignment depending on the manufacturing process and requirement of coupling efficiency. 
     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. 
     Compared with the TO package currently reported, this coaxial package provides cooling for both active components and passive components on the cooled platform instead of active components only. The coaxial package ensures stable laser performance over a wide range of operation temperature. 
     The coaxial package may include a commercially available TO header and TEC, so it is more economical and flexible in key components selection. 
     Compared with a traditional butterfly package, the coaxial package described herein consumes much less DC power than the butterfly package, for substantially the same laser output. Typically only ½ of the DC consumed by the butterfly package is needed by the module described above. Therefore, the package reliability is increased and thermal efficiency is also increased. 
     The coaxial package simplifies the manufacturing processes and significantly reduces component and labor cost. Material costs are significantly reduced by ⅓ to ½. 
     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 laser module or 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. 
     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.