PATENT DOCUMENT

Abstract:
A transceiver comprising a plurality of CMOS chips may be operable to communicate an optical source signal from a semiconductor laser into a first CMOS chip via optical couplers. The optical source signal may be used to generate first optical signals that are transmitted from the first CMOS chip to optical fibers coupled to the first CMOS chip via one or more optical couplers. Second optical signals may be received from the optical fibers and converted to electrical signals via photodetectors in the first CMOS chip. The optical source signal may be communicated from the semiconductor laser into the first CMOS chip via optical fibers in to a top surface and the first optical signals may be communicated out of a top surface of the first CMOS chip. The electrical signals may be communicated to at least a second of the plurality of CMOS chips comprising electronic devices.

Full Description:
RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 12/483,699, which is a divisional application of U.S. application Ser. No. 11/611,084 filed Dec. 14, 2006, which in turn makes reference to, claims priority to and claims the benefit of: U.S. Provisional Patent Application No. 60/750,488 filed Dec. 14, 2005. 
     This application relates to U.S. patent application Ser. No. 11/611,042, titled “INTEGRATED TRANSCEIVER USING EDGE DETECTING PHOTODETECTOR,” U.S. patent application Ser. No. 11/611,065, titled “INTEGRATED TRANSCEIVER USING SURFACE DETECTING PHOTODETECTOR,” and U.S. patent application Ser. No. 11/611,093, titled “INTEGRATED TRANSCEIVER USING SUBMOUNT,” each filed on Dec. 14, 2006. 
    
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     [Not Applicable] 
     MICROFICHE/COPYRIGHT REFERENCE 
     [Not Applicable] 
     BACKGROUND OF THE INVENTION 
     1. Field 
     The present disclosure generally relates to optoelectronic devices, and more particularly, to integrated transceivers having emitter and detector incorporated therewith. 
     2. Description of the Related Art 
     A transceiver is a device that has both a transmitter and a receiver. Typically, the transmitter and receiver share at least some common circuitry, and sometimes, the same housing. 
     An optical transceiver is a device that receives and transmits optical signals. The transmitter in the optical transceiver is typically a device such as a laser that modulates light outputs based on electrical input signals. The receiver in the optical transceiver is typically a device such as a photo-detector that converts optical input signals into electrical output signals. 
     Optical transceivers are commonly used in digital data communication applications, such as telecommunication. What is needed are optical transceivers that are fast, provide high bandwidth, and have reduced form factor. 
     BRIEF SUMMARY OF THE INVENTION 
     A wide variety of systems, devices, methods, and processes comprising embodiments of the invention are described herein. Systems and methods for configuring an integrated transceiver can include, in one embodiment among others, a very small form factor transceiver that can be configured to allow 10G optical interconnects over distances up to 2 km. In one embodiment, transceiver circuitry can be integrated on a single die, and be electrically connected to a transmitter such as a laser-diode and a receiver such as a photo-diode. In one embodiment, the laser and photodiodes can be edge-operating, and be mounted on the die. In one embodiment, one or both of the diodes can be surface-operating so as to allow relaxation of alignment requirement. In one embodiment, one or both of the diodes can be mounted on a submount that is separate from the die so as to facilitate separate assembly and testing. In one embodiment, the diodes can be optically coupled to a ferrule via an optical coupling element so as to manage loss in certain situations. 
     For example, one embodiment of the present disclosure relates to an integrated transceiver that includes a die including a plurality of semiconductor electronic devices. The integrated transceiver further includes an edge detecting photodetector and a semiconductor laser such as an edge emitting semiconductor laser. The plurality of semiconductor electronic devices are electrically coupled to the photodetector and the laser to process optical input received by the photodetector and control optical output produced by the laser. The photodetector may be integrated in the die and may be optically coupled to the fiber via a waveguide and a grating coupler. In this manner, light may be coupled vertically into and out of the surface of the die. The die may comprise a complementary metal oxide semiconductor (CMOS) die, for example, which enables the integration of optical, optoelectronic, and electronic devices on the die. 
     Another embodiment of the present disclosure relates to an integrated transceiver that includes a die having semiconductor electronics. The integrated transceiver further includes a photodetector mounted on the die. The integrated transceiver further includes a laser also mounted on the die, with the semiconductor electronics electrically coupled to the photodetector and the laser to process optical input received by the photodetector and control optical output produced by the laser. The electronic die, the photodetector, and the laser form an integral unit having a largest dimension that is less than approximately 10 mm×9 mm×4 mm. 
     Yet another embodiment of the present disclosure relates to an integrated transceiver that includes a die having top and bottom surfaces, with the die including a plurality of semiconductor electronic devices thereon. The integrated transceiver further includes a semiconductor laser mounted to the die, with the laser electrically coupled to at least one of the semiconductor electronic devices on the die to drive the laser. The integrated transceiver further includes a photodetector electrically coupled to at least one of the semiconductor electronic devices on the die to process optical input received by the photodetector. The semiconductor photodetector includes a semiconductor region having an optical input surface for receiving light, with the optical input surface being oriented at an angle with respect to the top surface of the die. 
     Yet another embodiment of the present disclosure relates to an integrated transceiver that includes at least one die including a plurality of semiconductor electronic devices thereon. The integrated transceiver further includes a semiconductor laser having an optical output region configured to output laser light. The integrated transceiver further includes a photodetector having an optical input region including an input surface configured to receive light to be detected. The photodetector and the semiconductor laser are electrically coupled to the semiconductor electronic devices, and the optical input region of the photodetector and the optical output region of the laser are directed in substantially the same direction and separated by a distance of less than about 1000 microns. 
     Yet another embodiment of the present disclosure relates to an integrated transceiver that includes at least one die including electronics thereon. The integrated transceiver further includes a semiconductor laser having an optical output region configured to output laser light, with the laser in electrical communication with the electronics. The integrated transceiver further includes a photodetector having an optical input region configured to receive light to be detected, with the photodetector in electrical communication with the electronics. The integrated transceiver further includes a support assembly on which the semiconductor laser and the photodetector are mounted such that the optical output region of the laser and the optical input region of the photodetector are separated by a distance of less than about 1000 microns. 
     Yet another embodiment of the present disclosure relates to an integrated transceiver that includes at least one die including electronics thereon. The integrated transceiver further includes a semiconductor laser disposed on the at least one die and in electrical communication with the electronics. The integrated transceiver further includes a photodetector disposed on the at least one die and in electrical communication with the electronics. The integrated transceiver further includes a light pipe having a length of substantially optically transmissive material having a first end and a second end, with the second end disposed proximal to the photodetector, the second end having a sloping reflective surface angled such that light propagating along the length from the first end to the second end is redirected to the photodetector. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows a block diagram of one embodiment of an integrated transceiver that includes a die, a photo-detector such as a photo-diode, and an emitter such as a laser-diode; 
         FIG. 2  shows that in one embodiment, the integrated transceiver of  FIG. 1  can have a very small form factor (VSSF); 
         FIG. 3  shows a perspective view of one embodiment of the integrated transceiver of  FIG. 1 ; 
         FIGS. 4A-4C  show different views of one embodiment of the integrated transceiver, where the photo-diode and the laser-diode can be configured for edge-detecting and edge-emitting of signals, respectively; 
         FIGS. 5A and 5B  show different views of one embodiment of a packaged assembly having the die-mounted edge-detecting/emitting diodes so as to facilitate optical coupling with a coupler such as a multi-fiber assembly; 
         FIGS. 6A-6D  show different views of one embodiment of the integrated transceiver, where the photo-diode can be configured for surface-detection of signals; 
         FIG. 7A  shows one embodiment of a package configured to allow mounting of a die and a surface-detecting photo-diode; 
         FIGS. 7B and 7C  show different views of the package of  FIG. 7A  with the die and the surface-detecting photo-diode mounted so as to facilitate optical coupling with the multi-fiber assembly; 
         FIGS. 8A and 8B  show example geometric design considerations for placement of various components of the integrated transceiver; 
         FIGS. 9A-9D  shows different views of one embodiment of the integrated transceiver, where the photo-diode and the laser-diode can be mounted on a submount and electrically coupled to the die; 
         FIG. 10  shows a more detailed view of one embodiment of the submount; 
         FIGS. 11A-11C  show different views of one embodiment of the integrated transceiver, where the surface-detecting photo-diode can be optically coupled with the multi-fiber assembly via an optical coupling element; 
         FIGS. 12A-12C  show different views of one embodiment of the integrated transceiver, where the surface-detecting photo-diode and the surface-emitting laser-diode can be coupled with the multi-fiber assembly via the optical coupling element; 
         FIGS. 13A-13C  show different views of one embodiment of the integrated transceiver, where the emitter and the detector can be integrated into a single chip and be coupled with the multi-fiber assembly via the optical coupling element; and 
         FIGS. 14A and 14B  show examples of some design considerations for the example edge-detecting photo-diode. 
     
    
    
     These and other aspects, advantages, and novel features of the present teachings will become apparent upon reading the following detailed description and upon reference to the accompanying drawings. In the drawings, similar elements have similar reference numerals. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain embodiments of the present disclosure relates to integrated transceivers. In some embodiments, such transceivers can have small form factors (SFF) or very small form factors (VSFF). 
     In some embodiments, the SFF or VSFF integrated transceivers can be packaged in a relatively low cost manner and enable 10G optical interconnects over distances up to 2 km. Such economical packaging can lead to proliferation of 10G interconnects, and can lead to faster optical interconnects with data rates of 100 G (Gb/s) and higher. 
     In designing such integrated transceivers, cost can be an important factor. Cost associated with the integrated transceivers can include, for example, component costs, cable and connectorization costs, footprint, and cooling cost. In some embodiments, such design costs can be addressed by packaging the integrated transceiver in a VSFF configuration. 
     For example, the transceiver&#39;s size can be reduced (thus reducing the footprint) significantly by integrating various functionalities of the transceiver on one or more dies. In a typical transceiver, a PCB (printed circuit board) is usually the largest part; thus in one embodiment, the electronic components associated with the PCB can be integrated on a single die. In some embodiments, such integration of electrical components on a die can reduce electrical parasitics associated with various connections in the PCB, and thereby improve high speed performance of the transceiver. 
     Typically, the second largest parts in a transceiver are transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA). Thus in one embodiment, various functionalities of TOSA and ROSA can be consolidated so as to reduce the size of the transmitter. 
     In one embodiment, the transceiver can also be made to be less expensive by consolidating all or substantially all of the electronic components on a single die. Such integration can reduce the number of optical alignments. Moreover, integration of the various components can provide features such as elimination of at least two laser welding steps (one for ROSA and one for TOSA), elimination of a need for pigtailed devices, and/or improved heat sinking of laser and die. 
       FIG. 1  shows a block diagram of one embodiment of an integrated transceiver  100  that includes a die  102 , an emitter  104  such as a laser-diode, and a photodetector  106  such as a photo-diode. In one embodiment, the integrated transceiver  100  can have a single die. In one embodiment, the integrated transceiver  100  can have two dies. In one embodiment, the integrated transceiver  100  can have more than two dies. 
     As further shown in  FIG. 1 , the integrated transceiver  100  can be configured to facilitate optical coupling with a coupler  108 . In one embodiment, the coupler  108  can be a multi-fiber assembly. In one embodiment, the multi-fiber assembly can include an assembly that holds two or more fibers. In one embodiment, the multi-fiber assembly can include injection molded plastic with holes dimensioned to hold fiber ends or stubs. In one embodiment, the multi-fiber assembly can be a device that conforms to an industry standard. For example, the multi-fiber assembly can be any one of mini-MT or MT type connectors. 
       FIG. 2  shows that in one embodiment, the integrated transceiver  100  of  FIG. 1  can be a configured to be a VSFF transceiver  110 . Accordingly, a die  112 , a laser-diode  114 , and a photo-diode  116  can be configured to conform to the VSFF configuration, and to allow optical coupling with a ferrule  118 . 
       FIG. 3  shows a perspective view of one embodiment of an integrated transceiver assembly  120  having a die  122  mounted to a packaging substrate  130 . In one embodiment, the substrate  130  can be formed from ceramic. In one embodiment, the substrate  130  can be dimensioned to facilitate positioning of a ferrule  140 . The ferrule  140  can include input and output optical fibers  144  that terminate at a housing so as to allow optical coupling with transmitter and/or receiver components. 
     As further shown in  FIG. 3 , the integrated transceiver assembly  120  also includes transmitter and receiver components ( 124  and  126 ) that can be mounted to or about the die  122 . Various transceiver and receiver placement configurations are described below in greater detail. 
     In some embodiments, the die can include a plurality of semiconductor electronic devices. In one embodiment, such semiconductor electronic devices can include a laser driver and a transimpedance amplifier to facilitate operation of laser and photodiode. In one embodiment, the die includes a semiconductor (for example, silicon) substrate or a substrate having semiconductor disposed thereon. 
     In one embodiment, the die can have top and bottom surfaces, and a plurality of sides thereabout. The die can be mounted on a packaging substrate (such as the substrate  130  in  FIG. 3 ) so that the bottom surface of the die is mounted to the packaging substrate, either directly or via one or more intervening layers. The top surface of the die can be configured to allow mounting of the laser and/or photodiode, and/or connections for such diode. 
     In one embodiment, each of the plurality of sides can define an edge. In one embodiment, such an edge can facilitate mounting and operation of edge-emitter and/or edge-detector. 
     An edge detecting photodetector may for example comprise a multilayer structure having a top and a bottom and side surfaces. The bottom of the multilayer structure may be disposed on the top surface of the die. The multilayer structure may comprise a plurality of layers stacked on top of each other. In some embodiments, the layers form a planar waveguide. Light may be coupled into the side of the edge detecting photodiode. In particular, the waveguide has an input and is optically coupled to a photosensitive region of the detector. Light is introduced into the optical input of the optical waveguide and is guided to the photosensitive region that converts the optical signal into an electrical signal. One example of such a device is a commercially available 40G edge detection photo-diode available from Archcom Technology, Inc., of Azusa, Calif. Other configurations are also possible. For example, light may be coupled into the top surface of the die via a grating coupler. 
       FIGS. 4A-4C  show different views (top, side, and front views, respectively) of one embodiment of an integrated transceiver assembly  150 , where a laser-diode  154  and a photo-diode  156  can be configured to provide at least one of edge-emitting and edge-detecting functionalities. Accordingly, at least one of the laser and photodiode  154  and  156  can be mounted on the die  152  at or near one of the edges. 
     In one embodiment, the photo-diode  156  can be an edge-detecting type, and be mounted at or proximal to the edge of the die  152 . In one embodiment, both of the photo and laser diodes can be edge-operating type, and be mounted at or proximal to the edge of the die  152 . In one embodiment, each of the photo and laser diodes  154  and  156  are positioned on the die  152  so that their active edges are within at least about 10 μm from the edge of the die  152 . Other edge-positioning configurations are possible. 
     In one embodiment, the laser and photodiode  154  and  156  can be spaced at a selected distance so as to allow optical coupling with selected fiber ends  176  of a ferrule assembly  170 . Mini-MT multi-fiber assembly is an example of such a ferrule assembly  170 . In one embodiment, the ferrule assembly  170  can include a plurality of fiber ends that are optically coupled to input and output optical paths  174 . In one such ferrule assembly, the fiber ends are spaced at approximately 250 μm. Thus, in the example shown in  FIG. 4A-4C , the laser and photo diode  154  and  156  are spaced apart at about 750 μm. Other spacing configurations are possible. For example, multiple laser diodes  154  and/or multiple photodiodes may be included on the die as discussed below. Such laser diodes  154  and/or photodiodes may be positioned to optically couple to different fibers in the ferrule. 
     In one embodiment, the edge-detecting photo-diode  156  includes a multi-layer structure having top, bottom, and side surfaces. The bottom surface can be disposed on the top surface of the die  152 , either directly or via one or more intervening layers. In one embodiment, a metal layer is disposed between the multi-layer structure of the photo-diode  156  and the top surface of the die  152 . In one embodiment, the multi-layer structure includes a waveguide that receives an optical input. The multi-layer also includes a photosensitive region that converts the optical input into an electrical signal. In certain embodiments the photosensitive region forms part of the waveguide. 
     In one embodiment, the edge-detecting photo-diode  156  can be device comprising a 111-V semiconductor material. As a non-limiting example, the edge-detecting photo-diode  156  may comprise an InGaAs type device. Such a device can be appropriate for use with, for example 1550 nm light. One example of such a device is a commercially available 40G edge detection photo-diode available from Archcom Technology, Inc., of Azusa, Calif. In one embodiment, the edge-detecting photo-diode  156  can be a germanium device. In one embodiment, AlGaAs or Si based photo-diodes can also be used. 
     In one embodiment, the laser diode  154  can be an edge-emitting semiconductor laser. An example of such semiconductor laser can include devices having III-V semiconductor material. In one embodiment, the semiconductor laser can be flip-chip bonded to the die. 
     In one embodiment, the foregoing example semiconductor laser  154  can have an optical output region configured to output laser light. In one embodiment, the above-described edge-detecting photo-diode  156  can include an optical input region configured to receive light to be detected. In one embodiment, the optical output region of the laser-diode  154  and the optical input region of the photo-diode  156  are separated by a distance that is less than about 1,000 μm. Other separation configurations are possible. 
     In one embodiment, the optical output region of the laser-diode  154  and the optical input region of the photo-diode  156  are within about 10 μm of being on the same plane above and parallel the upper surface of the die  152 . In one embodiment, the optical output region of the laser-diode  154  and the optical input region of the photo-diode  156  are substantially coplanar. Other elevation configurations are possible. 
     In one embodiment, the separation and elevation configurations can be in terms of distances with respect to geometric centers of the laser and photo diodes. In one embodiment, such distances can be with respect to an intensity centroids associated with the diodes. Combinations of the above two example conventions, as well as other conventions, are possible. 
     In some embodiments, the optical axes of the fiber ends  176  can be positioned so as to be substantially aligned with optical axes of the laser-diode  154  and photo-diode  156 . In the example configuration shown in  FIG. 4B , the fiber ends  176  are depicted as being substantially aligned with the lower active surface of the laser-diode  154 . If the active surface was on the upper side of the diodes, or anywhere else on the diodes, the fiber ends  176  can be positioned accordingly. 
     In one embodiment, at least some of the plurality of semiconductor electronic devices of the die  152  can be electrically coupled to the laser-diode  154  and the photo-diode  156 , and be configured to control optical output produced by the laser-diode  154  and process optical input received by the photo-diode  156 . In one embodiment, an assembly of such a die  152 , laser-diode  154 , and photo-diode  156  has a dimension that is less than approximately 10 mm (length)×9 mm (width)×4 mm (thickness). In one embodiment, the assembly of the die  152 , laser-diode  154 , and photo-diode  156  form an integral unit having a largest dimension that is less than approximately 10 mm. Other dimensions are possible. 
     In one embodiment, as shown in  FIGS. 4B and 4C , the die  152  can be mounted to the packaging substrate (for example,  130  in  FIG. 3 ) via an adhesive layer  160 . In one embodiment, the adhesive can be selected based on its thermal conductivity property. For example, an adhesive that has a relatively good thermal conducting property can be selected to reduce thermal resistance between the die  152  and the packaging substrate. Other attachment configurations are possible. 
     In one embodiment, various functionalities described in  FIGS. 4A-4C  can be implemented in more than one die. In such a configuration, the plurality of dies can be packaged on a multi-chip module (MCM) to provide substantially similar functionalities. 
     In one embodiment, the integrated transceiver can be configured to have more than one transmitter, and correspondingly more than one receiver. As shown in  FIG. 4A , the ferrule assembly  170  can house more than two fiber ends  176 . The example ferrule  170  is depicted as having four fiber ends. Thus, the integrated transceiver  150  can have a second laser-diode (not shown) mounted on the die  152 , and a second photo-diode (not shown) mounted on the die  152  so as to provide two-channel functionality. 
     In one embodiment, as described above, spacing between the fiber ends can be approximately 250 μm. Thus, the example four components (two lasers and two photo-diodes) can be arranged with approximately 250 μm spacing intervals, such that the two outer-most components are separated by approximately 750 μm. 
       FIG. 5A  shows a front sectional view of one embodiment of a packaged edge-operating integrated transceiver  180 .  FIG. 5B  shows a top view of the packaged transceiver  180 . As shown, the packaged transceiver  180  can includes a packaging substrate  190  that defines a first recess  194  dimensioned to allow mounting of a die  182 . The example die  182  is shown to have mounted on it an edge-emitting laser-diode  184  and an edge-detecting photo-diode  186 . In one embodiment, the die  182 , laser-diode  184 , and photo-diode  186  assembly can be similar to that described above in reference to  FIGS. 4A-4C . 
     In one embodiment, as shown in  FIG. 5A , the packaging substrate  190  can also define a second recess  192  that allows access to the mounted die  182  (or access to the first recess for mounting the die  182 ), and/or to provide protection of the die/laser/photo-diode assembly. As described above in reference to  FIG. 3 , the packaging substrate ( 130  in  FIG. 3 ) does not necessarily need to have a recess for mounting of the die ( 122 ). Thus, it will be understood that any number of die/substrate mounting configurations are possible. 
     In one embodiment, as shown in  FIG. 5B , the packaging substrate  190  can also be configured to allow mounting of a monitor photo-detector (MPD)  188 . The MPD  188  can be configured to monitor the output of the laser  184 . 
     In one embodiment, as shown in  FIG. 5B , the packaging substrate  190  can be dimensioned to allow positioning of a ferrule assembly  200 . Such dimensioning can include one or more recesses or features that allow positioning of the fiber ends (not shown) at desired locations relative to the optical output and input regions of the laser-diode  184  and photo-diode  186 . 
       FIGS. 6A-6D  show various views (top, first side, second side, and front views, respectively) of one embodiment of a transceiver assembly  210 , where at least one of the transmitter and receiver is a surface-operating device. For the purpose of description, a photo-diode  216  is depicted as being a surface-detecting device and a laser-diode  214  is depicted as an edge-emitting device. However, it will be understood that in one embodiment, the photo-diode can be edge-detecting, and the laser-diode can be surface-emitting. 
     In one embodiment, the edge-emitting laser-diode  214  can be mounted to a die  212 , and the surface-detecting photo-diode  216  can be mounted to a mounting sub-assembly  218 . In one embodiment, the die  212  can include a plurality of semiconductor electronic devices. At least some of those devices can be electrically coupled to the laser-diode  214  mounted on the die  212 , and to the photo-diode  216  (wire lead coupling depicted as  222 ); and be configured to control optical output produced by the laser-diode  214  and process optical input received by the photo-diode  216 . 
     In one embodiment, the structure and configuration of the die  212  can be similar to that described above in reference to  FIGS. 4A-4C . 
     In one embodiment, the example laser-diode  214  can be configured and mounted to the die  212  in a manner similar to the laser-diode  154  described above in reference to  FIGS. 4A-4C . 
     In one embodiment, a photo-diode  216  that is mountable on the mounting sub-assembly  218  can be a standardized component. For example, photo-diode products from companies such as Kyocera can be mounted to the sub-assembly  218 . Similarly, laser-diode products from companies such as Kyocera can also be mounted to a sub-assembly. 
     In one embodiment, the some or all of the mounting sub-assembly  218  can be formed from ceramic. The ceramic support structure can include one or more pathways for facilitating electrical connections between the photo-diode  216  and the die. 
     In one embodiment, a support structure (such as ceramic structure) that supports the die  212  can be the part of the same structure that supports the photo-detector  216 . In another embodiment, the support structure for the die  212  is not part of the structure that supports the photo-detector  216 . These two separate structures may or may not be coupled mechanically. 
     In one embodiment, the photo-detector  216  can be a semiconductor photo-detector that includes a semiconductor region having an optical input surface  224  for receiving light. The optical input surface can be oriented at an angle with respect to the top surface of the die  212 . 
     In one embodiment, the photo-detector  216  can include a plurality of electrical leads that extend away from the detecting surface (rearward if the detecting surface faces front). The plurality of electrical leads contact the semiconductor region through bonds on a rearward side of the semiconductor region (on the side opposite to the fiber). The bonds and leads extending from the photo-detector may in some embodiments have a thickness that would otherwise prevent the fiber from being brought sufficiently close to the detecting surface of the photo-detector if the lead were on the front side of photodetector. Accordingly, the bonds may be on the rear side of the photo-detector with the fiber on the front side of the detector. In one embodiment, a packaging of the photo-detector  216  can include an optically transmissive panel forward of the semiconductor region that transmits light to the semiconductor region. For example, the photodiode may comprise semiconductor having a photosensitive detecting surface mounted downward onto a package with an optically transmissive aperture that permits light to pass through the package to the photosensitive detector surface of the semiconductor. The opposite side of the semiconductor may include the electrical leads to provide access for the fiber. 
     In one embodiment, the semiconductor region of the photo-detector  216  can be a semiconductor diode. In one embodiment, the optical input surface of the semiconductor region can be substantially planar. In one embodiment, the optical input surface can be oriented substantially orthogonal to the top surface of the die. 
     In one embodiment, the laser  214  has an output face. The optical input surface of the photo-detector  216  and the output face of the laser  214  are directed substantially in the same direction. In one embodiment, the optical input surface of the semiconductor region of the photo-detector  216  and the output face of the laser  214  are coplanar. 
     In one embodiment, the output face of the laser  214  and the optical input surface of the photo-detector  216  can be within about 1 to 6 degrees, and within about 60 microns (μm) of being coplanar. In one embodiment, the output face of the laser  214  and the optical input surface of the photo-detector  216  are tilted with respect to each other by about 4 to 0 degrees. The photo-detector may be tilted, for example, to reduce light reflected back into the fiber. 
     In one embodiment, the laser and photo diodes  214  and  216  can be spaced at a selected distance so as to allow optical coupling with selected fiber ends of a ferrule assembly  230 . In one embodiment, the ferrule assembly  230 , and the selected spacing between the diodes, can be similar to the ferrule  170  described above in reference to  FIGS. 4A-4C . For example, the output face of the laser  214  and the optical input surface of the photo-detector  216  can be laterally separated from each other, as measured center-to-center, by about 750 microns for optical interconnection with the selected fibers in the ferrule  230 . In different embodiments, the center-to-center distance may be larger or smaller than 750 microns. In certain embodiments, however, the center-to-center distance is less than 1000 microns. In one embodiment, the center-to-center distance may be less than 750 microns (for example, about 250 microns). 
     In one embodiment, an assembly of such a die  212 , laser-diode  214 , and photo-diode  216  can have dimensions that are similar to the assembly described above in reference to  FIGS. 4A-4C . In one embodiment, the assembly of the die  212 , laser-diode  214 , and photo-diode  216  form an integral unit having a largest dimension that is less than approximately 15 mm. Other dimensions are possible. 
     In one embodiment, as shown in  FIGS. 6B-6D , the die  212  can be mounted to the packaging substrate (for example,  130  in  FIG. 3 ) via an adhesive layer  220 . Other attachment configurations are possible. 
     In one embodiment, various functionalities described in  FIGS. 6A-6D  can be implemented in more than one die. In such a configuration, the plurality of dies can be packaged on a multi-chip module (MCM) to provide substantially similar functionalities. 
     In one embodiment, use of the surface-operating component (such as the surface-detecting photo-detector  216 ) can allow use of standard parts, as well as providing a more relaxed alignment requirement for the surface-operating component. In one embodiment, however, such features can be offset by size limitations that can be imposed by the surface-operating component. For example, use of certain standard surface-detecting photo-detectors may limit the integrated transceiver to a single channel device if coupled to certain type of Mini-MT multi-fiber assembly. 
       FIG. 7A  shows a front sectional view of one embodiment of a packaging assembly  240  that can be dimensioned to receive an integrated transceiver similar to that described above in reference to  FIGS. 4A-4D . In one embodiment, a packaging substrate  242  can define a first recess  244  dimensioned to receive a die (for example, the die  212  of  FIGS. 6A-6D ). In one embodiment, the first recess  244  can be formed within a second larger recess  250  that allows access to the first recess  244  for mounting of the die, or for accessing the mounted die, and/or to provide protection of the die. As described above in reference to  FIG. 3 , the packaging substrate ( 130  in  FIG. 3 ) does not necessarily need to have a recess for mounting of the die. Thus, it will be understood that any number of die/substrate mounting configurations are possible. 
     In one embodiment, as shown in  FIG. 7A , the packaging substrate  242  can define a receptacle opening  246  dimensioned to receive a surface-operating component (for example, the surface-detecting photo-detector  216  of  FIGS. 6A-6D ). The packaging substrate  242  can further define one or more pathways  247  dimensioned to facilitate routing of wires that electrically couple the die with the photo-detector  216 . 
       FIG. 7B  shows a similar view as  FIG. 7A , but with a die  252  and a surface-detecting photo-detector  256  mounted in their respective openings ( 244  and  246 ). An edge-emitting laser  254  can be mounted on the die  252  in a manner described above in reference to  FIGS. 6A-6D . Moreover, the first recess  244  and the receptacle opening  246  can be positioned relative to each other such that the laser  254  and the detecting surface  258  of the photo-detector  256  can be positioned at a desired orientation (desired center-to-center spacing, for example). 
     In some embodiments, the packaging substrate  242  is a monolithic structure to which the photo-detector  216  as well as the die  252  are mounted, with the laser  254  being mounted to the die  252 . Other configurations, however, are possible. 
       FIG. 7C  shows a top view of the packaged assembly of  FIG. 7B . In one embodiment, the packaging substrate  242  can be dimensioned to allow positioning of a ferrule assembly  260 . Such dimensioning can include one or more recesses or features that allow positioning of the fiber ends (not shown) at desired locations relative to the optical output and input regions of the laser  254  and photo-detector  256 . 
     In one embodiment, as shown in  FIG. 7C , the packaging substrate  242  can also be configured to allow mounting of a monitor photo-detector (MPD)  248 . The MPD  248  can be configured to monitor the output of the laser  254 . 
       FIGS. 8A and 8B  show one embodiment of an integrated transceiver  270  having a surface-detecting photo-detector, where certain geometric parameters can be considered.  FIG. 8A  shows a front view of the transceiver  270 , and  FIG. 8B  shows a top view. 
     In  FIG. 8A , a die  272  is shown to be mounted on a packaging substrate  280 . In one embodiment, the substrate  280  can be formed from ceramic material. In one embodiment, the die  272  can be mounted on the substrate  280  via a die attach layer  286  such as an adhesive layer. An edge-emitting laser  274  is shown to be mounted on the die  272 . A surface-detecting photo-detector  276  (having a detecting surface  278 ) is shown to be mounted to the packaging substrate  280  via a mounting sub-assembly  282 . In one embodiment, the die  272 , laser  274 , and photo-detector  276  can be similar to those described above in reference to  FIGS. 6 and 7 . 
     In one embodiment, as shown in  FIG. 8B , the photo-detector  276  can be electrically interconnected with the die  272  via connection lines  284   b  and  284   c . These connection lines  284   b  and  284   c  extend through the sub-assembly  282  to which the photo-detector  282  is mounted as well as through the portion of the package substrate  280  to which the sub-assembly  282  is mounted. In this embodiment the package substrate  280  is shaped to accommodate mounting of both the die  272  and the sub-assembly  282 . In one embodiment, the laser  274  can be electrically interconnected with the die  272  via one or more connection lines  284   a . Other configuration, however, are possible. 
     In one embodiment, the center of the laser  274  can be positioned at a selected distance from the lateral edge of the die  272  (arrow  290   b ). In one embodiment, the selected distance  290   b  can be approximately 250 μm. The edge of the die  272  can be positioned at a selected distance from the edge of the mounting sub-assembly  282  (arrow  290   c ). In one embodiment, the selected distance  290   c  can be approximately 150 μm. The center of the detecting surface  278  of the photo-detector  276  can be positioned at a selected distance from the lateral edge of the mounting sub-assembly  282  (arrow  290   d ). In one embodiment, the selected distance  290   d  can be approximately 350 μm. Based on the foregoing example configuration, the distance from the center of the laser  274  and the center of the photo-detector  276  (arrow  290   e ) can be approximately 750 μm. 
     In one embodiment, the lateral width of the laser  274  (arrow  290   a ) can be approximately 250 μm, and the length (arrow  290   f ) can be approximately 750 μm. 
     As previously described, the example 750 spacing between the laser and the photo-detector can facilitate optical coupling with certain ferrules, such as the Mini-MT multi-fiber assembly. It will be understood that other spacing configurations are also possible. Accordingly, the center-to-center distance may be larger or smaller than 750 microns. In certain embodiments, however, the center-to-center distance is less than 1000 microns. 
       FIGS. 9A-9D  show various views (top, first side, second side, and front views, respectively) of one embodiment  300 , where both transmitter  304  and receiver  306  are mounted on a submount  310 . In one embodiment, the submount  310  can be a single structure dimensioned to allow mounting of the transmitter  304  and receiver  306 . In one embodiment, the submount  310  can be formed by first and second structures  314  and  316  that are joined together. The first structure  314  can be dimensioned to allow mounting of the transmitter  304 , and the second structure  316  can be dimensioned to allow mounting of the receiver  306 . 
     In one embodiment, the laser  304  and the photo-detector  306  can be electrically coupled to a die via a plurality of electrical interconnects  312 . The electrical interconnects can include, for examples, pins, sockets, wires, traces, conductive pathways imbedded in ridged insulating material, or any combination thereof. Such interconnects can be used to provide electrical connection in other embodiments describe herein as well. 
     The submount assembly  310  can thus be populated with one or more lasers and one or more photo-detectors separate from die-mounting operations. For example, such populating of the submount assembly  310  can be performed without being impacted by die attaching adhesive thickness variations. Because both the laser and the photo-diode are mounted on the same assembly substantially free from such variations, the laser and photo-diode can be more accurately placed relative to each other. 
     Moreover, the use of submount for both transmitter and receiver can allow for separate assembly and testing of the optical subassembly prior to connecting it to the die  302 . 
     In one embodiment, such as the example shown in  FIGS. 9A-9D , the laser  304  can be an edge-emitting type, and the photo-detector  306  can be a surface-detecting type (with a detecting surface  308 ). The example laser  304  and the photo-detector  306  can be similar in configuration and relative orientation to those described above in reference to  FIGS. 6 and 8 . For example, the surface detecting photo-detector  344  may comprise a planar photosensitive surface shown in  FIG. 9D  that receives the light. In the embodiment shown, this planar photosensitive surface is orthogonal to the top surface of the die  302 . Other combinations of laser and photo-detector types mounted on the subassembly  310  are possible. Moreover, the die  302  can be configured in a manner similar to those described above. 
     In one embodiment, as shown in  FIGS. 9B-9D , the die  302  can be mounted to a packaging substrate (not shown) via an attachment layer  330  such as an adhesive layer. Similarly, the subassembly  310  can be mounted to a packaging substrate (not shown) via an attachment layer  332  such as an adhesive layer. The packaging substrate for the die  302  may or may not be part of the same structure as that for the subassembly  310 . The packaging substrate may comprise ceramic in certain embodiments. Ceramic is a material that can provide desired thermal, electrical, and mechanical properties as a packaging substrate. In one embodiment, other materials having such properties can also be used as a packaging substrate. 
     The subassembly  310  is configured couple with ferrule assembly  320 . In particular, optical fiber ends in the ferrule may be aligned with the transmitter  304  and receiver  306  to provided optical coupling between the fiber ends and the transmitter and receiver. 
       FIG. 10  shows a perspective view of one embodiment of a support assembly  340  that can be the subassembly  310  described above in reference to  FIGS. 9A-9D . As previously described, such implementation of a submount can provide various flexibility in manufacturing and/or testing processes. 
     In one embodiment, the support assembly  340  can include mounting substrate  342  having surfaces for mounting of a laser  344  and a photo-detector  346 . The laser  344  is depicted as being an edge-emitting type, and the photo-detector  344  a surface-detecting type (with a detecting surface  348 ). It will be understood, however, that other combinations of laser and photo-detector are possible. In one embodiment, the support assembly  340  can also be dimensioned to facilitate mounting of a monitor photo-detector (not shown). 
     The support assembly  340  is also shown to have a plurality of contacts  352  that facilitate electrical connection of the laser  344  and the photo-detector  346  with the die (not shown). 
     In one embodiment, the laser  344  and the photo-detector  346  can be positioned and oriented relative to each other in a manner similar to those described above in reference to  FIGS. 6-9 . For example, the distance between the centers of the laser  344  and the photo-diode  346  (arrow  350   a ) can be approximately 750 μm. In another example, the length of the laser  344  (arrow  350   b ) can be approximately 250 μm, similar to the example laser described above in reference to  FIG. 8B . Other dimensions, however, are possible. For example, in different embodiments, the center-to-center distance may be larger or smaller than 750 microns. In certain embodiments, however, the center-to-center distance is less than 1000 microns. 
     In one embodiment, the support assembly  340  can be formed from ceramic. In one embodiment, the support assembly  340  can be a monolithic structure that supports both of the laser and photodetector. In one embodiment, the support assembly  340  can include separate first and second subassemblies, with the laser mounted to the first subassembly and the photo-detector mounted to the second subassembly. In one embodiment, the support assembly  340  can comprise insulating material and include conductive pathways therethrough or thereon that provide electrical connections from the laser and the photo-detector to the electronics on the die (not shown). The conductive pathways can lead to the electrical contact  352  to provide electrical connections with the electronics on the die (not shown). In one embodiment, the support assembly  340  is positioned relative to the die so as to butt up against the die. In some embodiments, the electrical contacts  352  mate with other contacts mounted on the die. 
       FIGS. 11-13  show various embodiments of optical coupling configurations between an integrated transceiver and a ferrule. In one embodiment  360  shown in  FIGS. 11A-11C , an optical coupling element  370  is shown to couple light between an integrated transceiver and a ferrule  380 . In one embodiment  390  shown in  FIGS. 12A-12C , an optical coupling element  400  is shown to couple light between another integrated transceiver and a ferrule  410 . In one embodiment  420  shown in  FIGS. 13A-13C , an optical coupling element  430  is shown to couple light between another integrated transceiver and a ferrule  440 . For the purpose of description, it will be assumed that the optical coupling elements  370 ,  400 , and  430  are similar; and ferrules  380 ,  410 , and  440  are similar. Moreover, the dies  362 ,  392 , and  422  can be configured similarly in manners described above (including mounting via their respective mounting layers  374 ,  404 , and  434 ). However, it will be understood that such similarities are not requirements, and that they may be different. 
     In one embodiment, the optical coupling element can include a light pipe or conduit having a length  371 ,  401 ,  431  of substantially optically transmissive material (for example, glass or plastic). The light pipe or light guide can have a first end and a second end, with the second end being disposed proximal to a photo-detector ( 366 ,  396 , and  425 ). In some embodiments, this light pipe may guide light from the first end to the second end in part via total internal reflection at the sidewalls. Much of the light may however propagate forward from the first end to the second end without reflecting from the sidewalls. The second end can include a sloping reflective surface  373 ,  403 ,  433  angled such that light propagating along the length from the first end to the second end is redirected to the photo-detector. In one embodiment, the sloping reflective surface  373 ,  403 ,  433  can be angled such that a difference, between the angle of the sloping reflective surface ( 373 ,  403 ,  433 ) relative to the length of the light pipe and the incident angle of light with respect to a normal to the sloping reflective surface, is between about 4° and 12°. If the length of the light pipe is horizontal and the detector faces upwards, such an angle (e.g., between about 4° and 12°) represents the incident angle on the detector. In one embodiment, the sloping reflective surface  373 ,  403 ,  433  can include a total internal reflection surface. The sidewalls, including the sloping sidewalls can be planar in some embodiments, although the shape should not be so restricted. The sidewalls and in particular the sloping reflective sidewall can be polished in some embodiments to reduce scattering of light undergoing total internal reflection. A reflective coating (e.g., an interference coating or metallization) can be used in some embodiments. Examples of embodiments of optical coupling elements are disclosed in U.S. application Ser. No. 11/109,210 titled “PLC For Connecting Optical Fibers to Optical or Optoelectronic Devices” which is incorporated herein by reference in its entirety. 
     In one embodiment, the first end of the light pipe can be disposed with respect to a multi-fiber ferrule (such as Mini-MT multi-fiber assembly) to permit light coupling into the light pipe. In one embodiment, the multi-fiber assembly can be positioned so that the optical axes of the fibers therein can be substantially aligned with the optical axis of the light pipe or light guide. In particular, the fibers may be positioned, e.g., centered with respect to the length of transmissive material such that light from the fiber can be coupled into the light pipe and propagate directly to the sloping reflective surface. In some embodiments, an anti-reflection coating or index matching can be provided at the first end to increase coupling efficiency. 
     In the example embodiments shown in  FIGS. 11-13 , the photo-detectors  366  (with a detecting surface  368 ),  396  (with a detecting surface  398 ), and  425  can be surface-detecting types. The photo-detectors may include planar photo-sensitive surfaces oriented parallel to the surface of the dies  362 ,  392 ,  422  on which the photodetectors  366 ,  396 ,  425  are mounted. Direct coupling with such surface-detecting photo-detectors with the second end of the light pipe can reduce signal loss. In some embodiments, the bottom surface of the coupler can be disposed with respect to the photo-detector to couple light thereto. In certain embodiments, the bottom surface of the coupler can contact the detector, or be positioned so as to provide a gap between the bottom surface of the coupler and the detector. In certain embodiments, an optically transmissive adhesive, which in some cases may provide index matching, may exist between the bottom surface of the coupler and the detector. The detector may or may not have a glass faceplate in front of the photosensitive surface. In some embodiments, as described below, an intermediate optical component, for example, a spacer, is disposed between the coupler and the photo-detector. 
     In one embodiment, as shown in  FIGS. 11A-11C , a laser  364  can couple light into a waveguide structure  372  having an output disposed with respect to the second end of the light pipe, to thereby couple light into the second end of the light pipe. In one embodiment, the waveguide structure  372  can be a planar waveguide formed on the planar surface of the die  362 . In one embodiment, the planar waveguide can comprise an optical modulator. This modulator may comprise a ring resonator or other type of waveguide resonator or modulator such as a Mach-Zehnder modulator. Examples of different embodiments of ring resonators can be found in U.S. Pat. No. 6,895,148 titled “MODULATOR BASED ON TUNABLE RESONANT CAVITY” which is incorporated herein by reference in its entirety. Examples of different embodiments of Mach-Zehnder modulators can be found in U.S. Pat. No. 7,039,258 titled “DISTRIBUTED AMPLIFIER OPTICAL MODULATORS” and U.S. application Ser. No. 11/540,172 titled “DISTRIBUTED AMPLIFIER OPTICAL MODULATORS”, which are each incorporated herein by reference in their entirety. Modulation of the light from the laser using a modulator may be more advantageous than modulating the laser. In one embodiment, the waveguide structure can further include an optical waveguide grating coupler to couple light from the planar waveguide to the second end of the light pipe. Examples of embodiments of waveguide grating couplers are disclosed in U.S. application Ser. No. 10/776,475 titled “OPTICAL WAVEGUIDE GRATING COUPLER” which is incorporated herein by reference in its entirety. 
     In different embodiments, the lateral spacing between the photodetector  366  and the waveguide  372  is about 750 microns. In other embodiments, however, the spacing may be larger or smaller than 750 microns. In certain embodiments, for example, the center-to-center distance is less than 1000 microns. In one embodiment, the center-to-center distance may be less than 750 microns (for example, about 250 microns). 
     In one embodiment, a substantially optically transmissive spacer can be disposed between the second end of the light pipe and the die so as to couple light output from the waveguide structure into the second end of the light pipe. In one embodiment, the substantially optically transmissive spacer can include silicon having at least one anti-reflection coating thereon. In one embodiment, the spacer can be held in place by an optically transmissive adhesive. 
     In one embodiment, as shown in  FIGS. 12A-12C , a laser  394  can be a surface-emitting laser. The emitting surface of the laser  394  can have an output that faces upwards, e.g., normal to the top surface of the die  392 , similar to the upward-facing detecting surface  398  of the photo-detector  396 , so as to couple with the second end of the light pipe  400 . Accordingly, the output surface of the laser  394  may be parallel to the top surface of the die  392  on which the laser is mounted. In one embodiment, such surface-emitting laser  394  can be a VCSEL (vertical cavity surface emitting laser). In some embodiments, the surface emitting laser comprises a HCSEL (horizontal cavity surface emitting laser). Example lasers  394  comprising a stack of layers of material with an output face on the top of the stack. 
     In some embodiments the laser  394  and the photo-detector  396  can be separated by 750 microns. In different embodiments, the center-to-center distance may be larger or smaller than 750 microns. In certain embodiments, however, the center-to-center distance is less than 1000 microns. In one embodiment, the center-to-center distance may be less than 750 microns (for example, about 250 microns). 
     In one embodiment, as shown in  FIGS. 13A-13C , a surface-emitting laser and a surface-detecting photo-detector can be monolithically integrated into a single chip unit  425 . As with the example configuration of  FIGS. 12A-12C , the emitting surface of the laser and the detecting surface of the photo-detector can face upward so as to couple with the second end of the light pipe  430 . In one embodiment, the surface-emitting laser can be a VCSEL or a HCSEL. 
     In one embodiment, the laser can be configured to emit light at approximately 1310 nm, and the photo-detector can be configured to detect light at approximately 1490 nm. In one embodiment, the laser can be modulated at a rate of approximately 2.5 Gbps, and the photo-detector can support data rate at approximately 2.5 Gbps. In one embodiment, such monolithically integrated chip can operate uncooled. 
     Based on the foregoing, one can see that there can be many possible variations in selection of lasers and photo-detectors, as well as how they are positioned, oriented, integrated, and mounted. For example, as described above with reference to  FIGS. 3 ,  4 A- 4 C, and  5 A- 5 B, use of edge emitting lasers and edge detectors can provide smaller footprints (for example, an edge-emitting laser can be approximately 250 μm×250 μm) to allow implementation of more than one channel for the integrated transceiver. In another example, described above with reference to  FIGS. 6A-6D ,  7 A- 7 C, and  8 A- 8 B, use of surface-detectors can allow for more relaxed alignment. Surface photodetectors that are commercially available can also be used. Integrating the photodetectors in the die can further reduce package dimensions and cost while improving performance by eliminating external electrical connections. 
     Aside from size and alignment considerations, optical coupling efficiency can also be considered when selecting a configuration for the integrated transceiver. In general, when being optically coupled with a circular-cross-section waveguide (such as an optical fiber), an optical fiber couples with a lesser efficiency to an edge detector than to a surface-photo-detector which has a larger area for receiving the light from the fiber. 
       FIG. 15A  shows an example optical coupling configuration  460  between an edge-detecting photo-diode (depicted as “PD mode”) and a circular fiber (depicted as “Fiber mode”). As shown, portions of the circle above and below the elliptical distribution of the PD mode do not overlap with the detecting region of the PD, thereby reducing the optical coupling efficiency.  FIG. 15B  shows an exemplary relationship between such coupling loss between an example 5 μm single-mode fiber (SMF) separated from the detecting edge of the PD by about 10 μm. The horizontal mode size of the detecting edge is held at a constant value, and the vertical mode size is varied (X-axis). As shown by line  470 , the relationship between coupling loss (Y-axis) and the vertical mode size (X-axis) is generally an inverse relationship. Based on such characterization, one can select a desired operating configuration of an edge-detecting (or edge-emitting) component when being coupled to a fiber. 
     In some situations, coupling loss associated with edge-emitting lasers and edge detectors may be acceptable. In some situations, such coupling loss with for example an edge detector may not be desirable—in which case, surface photo-detector may be used. In some embodiments, loss and power budget considerations may be used to select a desired configuration of the integrated transceiver. 
     Many variations in the selections and/or orientations of lasers and/or detectors are possible. For example, a surface emitting laser can be oriented and mounted such that the output surface faces outward (generally orthogonal to the top surface of the die) instead of the example edge-emitting lasers (for example, in  FIG. 3 ). 
     Various embodiments described herein can provide an integrated transceiver that has a reduced form factor but that provides for high data rates. Various features of the physical, optical, and electrical design may provide these and other advantages. For example, the selection, positioning, orientation, and arrangement of components as described herein may result compactness, ruggedness, efficient optical coupling, high data rates, and ease of manufacture and repair. In some embodiments, the shape of the packaging may be useful in providing a compact and robust platform. Also, various types of electrical connections, which may include for example pins, sockets, wires, traces, conductive pathways imbedded in ridged insulating material, or any combination thereof, may additionally provide for a robust design that is easy to manufacture and that uses largely existing optical and electrical components. Other design features may contribute to the performance and advantages provided by the designs described herein. 
     A wide variety of variations, however, are possible. For example, additional structural elements may be added, elements may be removed or elements may be arranged or configured differently. Similarly, processing steps may be added, removed, or ordered differently. Accordingly, although the above-disclosed embodiments have shown, described, and pointed out the novel features of the invention as applied to the above-disclosed embodiments, it should be understood that various omissions, substitutions, and changes in the form of the detail of the devices, systems, and/or methods shown may be made by those skilled in the art without departing from the scope of the invention. Consequently, the scope of the invention should not be limited to the foregoing description, but should be defined by the appended claims.