The present application claims priority to U.S. provisional patent application 60/317,836 filed Sep. 6, 2001, which is hereby incorporated by reference. 
   RELATED APPLICATIONS 
   The present application is related to co-pending U.S. non-provisional application Ser. No. 10/101,260 entitled Compact Laser Package With Integrated Temperature Control, filed herewith and, co-pending U.S. non-provisional application Ser. No. 10/101,248 entitled Control Circuit for Optoelectronic Module with Integrated Temperature Control, filed herewith. These related applications are hereby incorporated by reference. 


   BRIEF DESCRIPTION OF THE INVENTION 
   The present invention is generally related to optoelectronic devices. More specifically, the present invention pertains to an optoelectronic module having thermally isolated components. 
   BACKGROUND OF THE INVENTION 
   It is known that varying the temperature of a laser emitter may affect the wavelength (λ) of the emitted light. In applications where the wavelength of the laser is not critical, it is not important to precisely control the temperature of the laser emitter, and a heat sink is usually sufficient for cooling the laser emitter. However, in some applications such as Dense Wavelength Division Multiplexing (DWDM), it is important to produce light at precise wavelengths and to maintain the laser emitter at precise temperatures. For those applications, a heat sink alone is not sufficient. 
   Some conventional laser packages contain a large built-in temperature controller to control the temperature of the laser emitter. Some laser packages even contain an elaborate built-in coolant-circulation system for cooling the laser emitter (e.g., a laser diode). Such conventional laser emitter packages, due to their large size, cannot be easily incorporated within pluggable fiber optic transceiver modules, which typically have strict form factor requirements. Miniaturizing the built-in temperature controller, unfortunately, is not an ideal solution because small temperature controllers may not have the necessary heat transfer capability. 
   Accordingly, there exists a need for an apparatus for precisely controlling the temperature of a laser emitter without using a laser package that contains a large built-in temperature controller such that temperature control functionality can be implemented in an optoelectronic transceiver or transmitter module. 
   SUMMARY OF THE INVENTION 
   An embodiment of the present invention is a thermally-regulated optoelectronic transceiver module that conforms with industry standard form factors. The optoelectronic transceiver module in this embodiment utilizes a conventional transistor outline (“TO”) laser package, sometimes called a “TO can.” The TO laser package is disposed in a module housing that conforms to a predetermined form factor (e.g., the GBIC transceiver form factor). Within the module housing, the optoelectronic transceiver module includes a temperature controller operable to regulate the temperature of the laser package. The optoelectronic transceiver module further includes a thermal isolator that thermally isolates the TO laser package from some of the optically passive and temperature insensitive components. 
   In the absence of the thermal isolator, the temperature controller regulates the temperature of the entire optoelectronic transceiver module including the temperature insensitive components. The presence of the thermal isolator eliminates the need for heating or cooling temperature insensitive components and thereby substantially increases the effectiveness of the temperature controller. The increased effectiveness allows the use of temperature controllers that use less power and that are compact enough to fit into pluggable transceiver or transmitter modules. 
   In one embodiment of the present invention, the thermal isolator is a piece of ceramic with low thermal conductivity disposed between a laser mount structure and an optical fiber receptacle structure. In other embodiments, the thermal isolator may include a plurality of round elements that are made of a ceramic material with low thermal conductivity. Additional thermal isolation may be achieved by using spacing elements to reduce the contact area between the optical fiber receptacle structure and the module housing and by using spacing elements to eliminate direct contact between a set of screws and the laser mount structure. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  depicts a perspective view of a Transmitter Optical SubAssembly (TOSA) in accordance with an embodiment of the present invention; 
       FIG. 2  depicts an exploded view of the TOSA of  FIG. 1 ; 
       FIG. 3  depicts a top view of the TOSA of  FIG. 1 ; 
       FIG. 4  depicts a side cross-sectional view of the TOSA of  FIG. 1 ; 
       FIG. 5  depicts the TOSA of  FIG. 1  disposed on a portion of a transceiver module housing in furtherance with an embodiment of the present invention; and 
       FIG. 6  is a block diagram depicting circuitry that may be used in accordance with an embodiment of the invention. 
   


   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described. It will be appreciated that in the development of any such implementation, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints and compliance with the constraints of various existing and yet to be determined form factors. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     FIGS. 1 ,  2  and  3  depict, respectively, a perspective view, an exploded view, and a top view of a Transmitter Optical SubAssembly (TOSA)  100  according to an embodiment of the present invention.  FIG. 4  depicts a cross-sectional view of the TOSA  100 . The plane upon which the cross-sectional view is taken is indicated on  FIG. 3  by broken line A—A. As shown in these figures, the TOSA  100  includes a laser mount structure  110  and an optical fiber receptacle structure  120 . Mounted on the laser mount structure  110  is a transistor outline (TO) laser package  115 , which contains a laser emitter  116  (FIG.  6 ). The optical fiber receptacle structure  120  includes a fiber aligning sleeve  196  and a fiber stop  192  for receiving and aligning an optical fiber with the laser package  115 . In this embodiment, the optical fiber receptacle structure  120  further includes an optical isolator  194  for preventing light from reflecting back into the laser package  115 . In some embodiments, the optical fiber receptacle structure  120  may include a lens that focuses light emitted from the laser package  115 . For mechanical stability, both the laser mount structure  110  and the optical fiber receptacle structure  120  are preferably made of stainless steel. 
   In the present discussion, a laser emitter is a temperature sensitive and optically active component. Furthermore, in the present discussion, optically passive components include optical fibers, optical fiber receptacle structures, and laser mount structures. 
   With reference still to  FIGS. 1-4 , at least one portion of the laser mount structure  110  is separated from the optical fiber receptacle structure  120  by a thermal break  150 , also herein called a thermal isolator. In the illustrated embodiment, the thermal break  150  is formed from a piece of ceramic with low thermal conductivity. In other implementations, the thermal break  150  includes a piece of ceramic with low thermal conductivity, as well as other materials. In some embodiments, the thermal break  150  may include a plurality of spacing elements that are made of poor thermal conductors, such as ceramic balls. The presence of the thermal break  150  substantially reduces heat flow between the laser mount structure  110  and the optical fiber receptacle structure  120 . 
   Also illustrated in  FIGS. 1-3  are screws  170  for securing the laser mount structure  110 , the optical fiber receptacle structure  120  and the thermal break  150  together. In some embodiments, other securing means, such as epoxy, may be used to secure these components together. In order to reduce heat flow between the laser mount structure  110  and the optical fiber receptacle structure  120  via the screws  170 , ceramic washers  172  are used in the present embodiment to reduce or eliminate direct contact between the screws  170  and the laser mount structure  110 .  FIGS. 1-3  also illustrate a thermistor  160  disposed adjacent to the laser package  115  for detecting the laser package&#39;s temperature. For most applications, the laser package&#39;s temperature is a sufficiently close approximation of that of the laser emitter contained therein to allow the use of a thermistor outside the laser package for accurate temperature control of the laser. 
     FIG. 5  depicts the TOSA  100  disposed on a bottom portion of an optoelectronic transceiver module housing  200  in furtherance of an embodiment of the present invention. The module housing  200  is preferably made of metal for heat dissipation. A top portion of the module housing  200 , the Receiver Optical Sub-assembly (ROSA), and printed circuit board(s) containing electronic circuitry are not illustrated in FIG.  5 . In the present embodiment, the physical dimensions of the module housing  200  are as follows: width, 3 cm or less; length, 6.5 cm or less, and height, 1.2 cm or less. A GBIC standard (SFF-8053 GBIC standard version 5.5) requires the dimensions of a module housing to be approximately 3 cm×6.5 cm×1.2 cm. Thus, the module housing  200  of this embodiment meets the form factor requirements of the GBIC standard. 
   In another embodiment, the physical dimensions of the module housing are: width, 0.54 inches or less; length, 2.24 inches or less; and height, 0.34 inches or less. The SFP MSA (Small Form Factor Pluggable Multisource Agreement) requires the dimensions of a compliant module housing to be approximately 0.54″×2.24″×0.34″. Thus, the module housing in that embodiment meets the form factor requirements of the SFP standard. Note that the present invention is not limited to the form factor requirements described above. A person of ordinary skill in the art having the benefit of this disclosure will appreciate that the present invention is adaptable to various existing or yet to be determined form factors, some of which can be smaller. 
   The laser mount structure  110  is not in direct contact with the module housing  200 . Specifically, the laser mount structure  110  is separated from the top portion of the module housing  200  by a gap when the module housing  200  is assembled. Further, the laser mount structure  110  is separated from the bottom portion of the module housing  200  by a temperature controller  300 . Although the optical fiber receptacle structure  120  is in direct contact with the module housing  200 , protrusions  128  of the optical fiber receptacle structure  120  act as spacing elements and reduce the contact area between the structure  120  and the module housing  200 . 
   The temperature controller  300 , preferably a thermal-electric cooler (TEC), is disposed between the laser mount structure  110  and the bottom portion of the module housing  200 . In one embodiment, a layer of thermal grease forms a compliant, thermally-conductive interface between the temperature controller  300  and the laser mount structure  110 . The temperature controller  300  is configured to indirectly regulate the temperature of the laser emitter within the laser package  115  by transferring heat between the laser mount structure  110  and the module housing  200 . Operation of the temperature controller  300  does not directly regulate the temperature of the optical fiber receptacle structure  120 , due to the thermal break  150  between the laser mount structure  110  and the optical fiber receptacle structure  120 . In addition, due to the thermal isolation provided by the small amount of contact area between the optical fiber receptacle  120  and the module housing  200 , heat is transferred very slowly from the module housing  200  to the optical fiber receptacle structure  120 . The combined effect of the thermal break  150  and the small contact area between the optical fiber receptacle structure  120  and the module housing  200  is that the temperature controller  300  does not substantially affect the temperature of the optical fiber receptacle structure  120 . 
   The thermal break  150 , the ceramic washers  172 , the gap between the top portion of the module housing  200  and the laser mount structure  110 , and the protrusions  128  together provide thermal isolation for the laser mount structure  110 . In most transceivers, such a thermal break would be undesirable because a significant amount of heat generated by the laser would build up in and around the laser mount structure. But in the absence of the thermal break  150 , a “thermal short” (e.g., a path of high thermal conductivity) among the laser mount structure  110 , the temperature controller  300 , the module housing  200 , and the optical fiber receptacle structure  120  will be formed. That is, heat drawn from the laser mount structure  110  would flow through the module housing  200  and the optical fiber receptacle structure  120 , and the heat would be recycled back into the laser mount structure  110 . In that case, the effectiveness and efficiency of the temperature controller  300  would be very low and might not be able to adequately regulate the temperature of the laser package  115 . 
   According to the present embodiment, the thermal isolation breaks up the “thermal short” between the laser mount structure  110  and other components of the optoelectronic transceiver module, and relieves the temperature controller  300  of the responsibility of heating or cooling non-temperature critical portions of the optoelectronic transceiver module. Consequently, a temperature controller that is sufficiently compact to fit inside the housing  200  may be used. In addition, because the temperature-critical portions of the optoelectronic transceiver module make up a very small portion of the transceiver module (e.g., less than 5% of the mass of the transceiver  100  is contained within the laser mount structure  110  and laser package  115  in the preferred embodiments), the amount of power required by the temperature controller  300  will be limited. Thus, the temperature-controlled transceiver module according to the present invention meets the power consumption restrictions of certain transceiver module standards. 
     FIG. 6  is a block diagram illustrating circuitry that may be used in conjunction with embodiments of the present invention. As shown in  FIG. 6 , the temperature controller  300  and the thermistor  160  are coupled to a control circuit  310 , which compares the measured temperature against a reference temperature and generates control signals based on the temperature difference. The control signals are then provided to a drive circuit  320 , which generates a drive current for the temperature controller  300  according to the control signals. A control circuit that may be used is described in greater detail in the above-mentioned co-pending patent application(s). 
   The present invention, an optoelectronic module with thermally isolated components, has thus been disclosed. The foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations suitable to the particular use contemplated are possible in view of the above teachings. For instance, although an embodiment configured for a TO laser package is described, in other embodiments the present invention is used in combination with laser packages described in the above mentioned patent application(s). Further, although an optoelectronic transceiver embodiment is described, it should be apparent to those of ordinary skill in the art having the benefit of this disclosure that embodiments of the present invention include optoelectronic transmitter modules and other apparatuses.
A temperature-controlled optoelectronic module that includes a module housing, a laser mount structure for affixing a laser package in the module housing, an optical fiber receptacle structure disposed adjacent to the laser mount structure, a thermal isolator affixed between the laser mount structure and the optical fiber receptacle structure, and a temperature controller coupled to the laser mount structure and operable to regulate temperature of the laser package is disclosed. In the absence of the thermal isolator, a "thermal short" may be created between the module housing and the laser package, substantially reducing the efficiency of the temperature controller. The presence of the thermal isolator eliminates the "thermal short," substantially increases the effectiveness of the temperature controller and enables the miniaturization of temperature-controlled optoelectronic transceiver modules.