Abstract:
A subassembly for use in fiber optic communications systems where multiple optical fibers are used in either transmitting or receiving optical signals. The subassembly is adapted for being mechanically and optically connected with a ferrule supporting a set of optical communications fibers. The subassembly uses a carrier assembly to support an optoelectronic device having a corresponding set of photoactive components which are operative for either converting photonic signals to electrical signals (in a receiver) or converting electrical signals to photonic signals (in a transmitter). The subassembly includes a lens and alignment frame having a set of guide pins and an array of lenses for interfacing the fibers of the ferrule with the photoactive components of the optoelectronic device on the carrier assembly. The carrier assembly may also include signal processing devices and a circuit board having an edge connector for removably connecting the subassembly with a computer or communications system.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to optoelectronic devices, and more specifically to parallel optics assemblies for use in fiber optic communications.  
         BACKGROUND OF THE INVENTION  
         [0002]    The majority of computer and communication networks today rely on copper wiring to transmit data between nodes in the network. However, copper wiring has relatively limited bandwidth for carrying electrical signals which greatly constrains the amounts of data that it can be used to transmit.  
           [0003]    Many computer and communication networks, including large parts of the Internet, are now being built using fiber optic cabling which has superior bandwidth capabilities and can be used to transmit much greater amounts of data. With fiber optic cabling, data is transmitted using optical or light signals (also called photonic signals), rather than with electrical signals. However, since computers use electrical signals as opposed to optical signals the light signals used to transmit data over fiber optic links must be translated to electrical signals and vice-versa during the optical communication process. Building such fiber optic networks therefore requires optoelectronic modules which mechanically and optically interface optical transmission mediums such as fiber optic cables to electronic computing and communications devices and transform optical signals to electronic signals and electronic signals to photonic signals. Further, in order to provide the required bandwidth for high-speed communications multiple fiber optic elements must be used in systems often referred to as “parallel optics” systems for concurrently transmitting multiple signals over a single cable. The optoelectronic modules must therefore also be adapted for accommodating cables having multiple fibers which are presented for connection purposes in closely spaced arrays of fiber optic elements supported in special ferrules attached to the ends of the cables.  
           [0004]    Signal conversion from electrical to optical and optical to electrical may be provided for through the use of arrays of semiconductor elements (photoactive components) which are deployed on semiconductor or integrated circuit chips (optoelectronic devices). These photoactive components may be devices such as photodiodes which act as photo-receivers or laser diodes which act as photo-transmitters. While modules using such devices can provide satisfactory signal conversion performance, the building of effective parallel optics subassemblies is a challenge. The optical alignment of the photoactive devices with the ends of the thread-like fiber optic elements must be precise for an effective transfer of optical power. Since the fiber optic ends in parallel optics modules are closely spaced the complexity of this alignment task is further increased. Further, the module must be designed to efficiently handle the processing of the electrical signals and to efficiently interface with outside computer and communication systems.  
           [0005]    One past alignment technique for use in constructing parallel optics modules was to etch alignment grooves along the surface of a silicon substrate using photolithography techniques. These grooves were then used in precisely positioning the fibers and fiber optic ends in aligned relationships to edge-emitting laser diodes. Although this technique can accurately align the optical components, the arrays must be manually assembled. Consequently, the process is labor intensive and results in low yields due to assembly errors and quality assurance problems.  
           [0006]    More recently some parallel optics modules have come to use metal lead frames for mounting the photoactive devices. The lead frames then have alignment holes that cooperate with guide pins for alignment purposes. The guide pins extend from the holes in the lead frame to corresponding holes in a ferrule supporting the optic fibers in order to provide for the alignment of the ferrule with the lead frame and the fibers with the photoactive devices. However, for this design to be effective the optoelectronic device must be very accurately mounted onto the metal lead frame at the same time the alignment holes extending through the lead frame must be very accurately positioned. This alignment is hard to achieve and should the optoelectronic device or alignment holes be inaccurately positioned serious optical misalignment may occur even though the optical fibers may seem to be correctly aligned.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention relates to parallel optics modules for use in fiber optic communications and more particularly to subassemblies for use in transmitting and receiving photonic (light) signals. Parallel optics modules provide for communications between computer and communication systems over fiber optic cables containing multiple fibers for carrying multiple concurrent signals. The subassembly of the present invention is adapted for interfacing between computer or communication systems and the ferrules on the ends of the fiber optic cables which are used to support and present the ends of the fiber optic elements.  
           [0008]    The subassembly includes a receptacle, a lens and alignment frame, a carrier assembly and a casing structure for mounting and supporting these components. The carrier assembly includes a carrier frame section which is attached to the lens and alignment frame. An optoelectronic device comprising either an array of photoactive components such as either VCSELS for converting electrical signals to optical signals or PIN diodes for converting optical signals to electrical signals is mounted on the frame section. The lens and alignment frame includes a tower structure having a set of guide pins and an array of lenses precisely positioned with respect to the guide pins. The tower and guide pins are operative for providing accurate mechanical alignment between the lens and alignment frame and the ferrule as the guide pins mate with alignment holes in the ferrules and as the tower is fixed into a window in the inner end of the receptacle which helps position receptacle holding the ferrule with respect to the lens and alignment frame. The lenses are operative for accurately directing photonic signals through the lens and alignment frame between the fiber ends presented by the ferrule and the photoactive components of the optoelectronic device mounted on the carrier frame section. The lens and alignment frame functions to interface the fibers of the ferrule with the photoactive components of the optoelectronic device. The carrier assembly also includes one or more semiconductor chips for use in signal processing, a flex circuit section for a facilitating communications among its components and a small circuit board with an edge connector formed on one of its ends. The edge connecter is used to removably connect the subassembly to a jack which may be mounted on a circuit board in a computer or communications system. The carrier assembly also provides for the processing of the electrical signals and for the connection of the subassembly to a computer or communications system.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The invention and its advantages may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:  
         [0010]    [0010]FIG. 1 is an overhead, perspective view of a fiber optic communications module constructed in accordance with the principles of the present invention showing a ferrule supporting optical communications fibers interconnected with an optoelectronic subassembly for use in converting optical signals to electrical signals or vice-versa.  
         [0011]    [0011]FIG. 2 is an overhead, perspective view of the fiber optics communications assembly shown in FIG. 1 with the ferrule disconnected from the subassembly and the subassembly unplugged from the jack to or from which it transfers electrical signals.  
         [0012]    [0012]FIG. 3 is a front view of the ferrule shown in FIGS.  1 - 2 , showing, among other things, the optical fiber ends and alignment holes.  
         [0013]    [0013]FIG. 4 is a front view of the optoelectronic subassembly shown in FIGS.  1 - 2  showing, among other things, the lens and alignment frame including the lens array and the guide pins.  
         [0014]    [0014]FIG. 5 is a side view of the fiber optic communications module shown in FIG. 1 illustrating, among other things, the position of the carrier assembly within the subassembly and how the optoelectronic subassembly may be pluggably connected to a jack mounted on printed circuit board of a communications system or the like.  
         [0015]    [0015]FIG. 6 is an exploded, overhead perspective view of the subassembly of the present invention showing, among other things, how the casing structure, receptacle, lens and interface frame, carrier frame section, circuit board, edge connector and the other components of the optoelectronic subassembly relate to one another.  
         [0016]    [0016]FIG. 7 is an enlarged exploded, overhead perspective view of the front portion of the subassembly of the present invention showing, among other things, how the casing structure, receptacle, lens and interface frame, and carrier frame section relate to one another.  
         [0017]    [0017]FIG. 8 is a perspective view of the lens and alignment frame component of the present invention showing, among other things, the tower structure and the lens array and guide pins which are built into the tower structure.  
         [0018]    [0018]FIG. 9 is a vertical cross sectional view of the lens and alignment frame of the present invention taken along lines  9 - 9  of FIG. 8 showing again, among other things, the arrangement of the tower structure, lens array and guide pins.  
         [0019]    [0019]FIG. 10 is a vertical sectional view of the carrier frame section, lens and alignment frame, receptacle (inner end) and ferrule (proximal end) in assembled form showing, among other things, the vertical alignment of the ferrule with the lens and alignment frame and the carrier frame section and the alignment of the lens array with the optoelectronic device.  
         [0020]    [0020]FIG. 11 is a lateral sectional view of the carrier frame section, lens and alignment frame, receptacle (inner end) and ferrule (proximal end) in assembled form showing, among other things, the lateral alignment of the ferrule with the lens and alignment frame and the carrier frame section and the alignment of the optical fibers with the lens array and the optoelectronic device.  
         [0021]    [0021]FIG. 12 is an enlarged vertical sectional view around lines  12 - 12  of FIG. 10 illustrating the upper portions of the carrier frame section and lens and alignment frame in assembled form showing, among other things, the lens elements making up the lenses in the lens array and the alignment of the tower of the lens and alignment frame with the window in the back wall of the receptacle and the alignment of the lens elements with the optoelectronic device.  
         [0022]    [0022]FIG. 13 is a plan view of the lens array and lens elements comprising the lenses of the lens array which is part of the lens and alignment frame showing the vertically elongated shaping of these lens elements and their deployment with respect to each other.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    The present invention will now be described in detail with reference to preferred embodiments as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it should be apparent to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances it should be appreciated that well-known process steps have not been described in detail in order to not obscure the present invention.  
         [0024]    Referring now to FIGS. 1 and 2, a fiber optic connector assembly  10  is shown as comprising an optical ferrule  12  of the type sometimes referred to in the industry as an MT ferrule installed on the end of a cable  14  carrying multiple fiber optic communication elements  17  (not shown in FIGS.  1 - 2 ) and an optoelectronic subassembly  16  which operates as a transceiver module for either transmitting light (photonic) signals or receiving light signals and converting these signals to or from electrical signals. The subassembly  16  includes a small printed circuit board (PCB)  18  having an edge connector  20  with connection pads  25  on both sides which can be readily plugged into and out of an electrical connection jack  22  (in phantom) mounted on a circuit board  24  (in phantom) of a computer or communications system to or from which data can then be relayed over the cable  14  through the subassembly  16 . The ferrule  12  and subassembly  16  are adapted for interconnection when the proximal end  26  of the ferrule  12  is inserted and latched within a cavity  28  in the subassembly  16 . The ferrule  12  and subassembly  16  are then positioned and aligned so that optical signals can be transmitted either to or from the ferrule  12  and from or to the subassembly  16  for enabling data flow between the cable  16  and printed circuit board  24  (in phantom).  
         [0025]    Referring now to FIG. 3, the proximal end  26  of the ferrule  12  is shown which includes a pair of alignment holes  30  and a set of twelve optical communications fibers  17  having polished fiber ends  32 . The fibers  17  and their polished ends  32  are rigidly supported within the ferrule  12 . The fiber ends  32  are disposed in a linear array  33  at regular 250 micron intervals along a line extending between the alignment holes  30 . The fiber ends  32  are precisely aligned with the holes  30 .  
         [0026]    Referring now to FIG. 4, the cavity  28  is defined by a receptacle  35  having jaws  42  for latching onto the ferrule  12 . A pair of alignment or guide pins  34  and a set of twelve lenses  46  are disposed in a linear array  48  at regular 250 micron intervals along a line extending between the guide pins  34 . The lenses  46  and guide pins  34  are part of a lens and alignment frame  44  which is deployed at the inner end of the cavity  28 . As will be later described a set of twelve photoactive components  36  (not shown) are disposed behind the lenses  46  as part of an integrated circuit (IC) chip that comprises an optoelectronic is device  40  (not shown in FIG. 4). When the proximal end  26  of the ferrule  12  is latched into the cavity  28  by the jaws  42  the guide pins  34  in the subassembly  16  are engaged with the alignment holes  30  in the ferrule  12  which in turn precisely aligns the lenses  46  in the array  48  (and photoactive components  36  behind the lenses) with the fiber ends  32  in the array  33  so that photonic signals can pass between them.  
         [0027]    Referring now to FIG. 5, the parallel optics assembly  10  is shown with the ferrule  12  latched into the subassembly  16  and with the edge connector  20  (in phantom) plugged into the jack  22  so that the pads  25  are in electrical contact with the elements of a connector lead frame (not shown) within the jack  22 . The jack  22  is surface mounted on the circuit board  24  and thereby electrically interconnected with the circuitry on the board  24  and the computer or communication system of which the board is a part. The edge connector  20  and jack  22  enable the subassembly  16  to be removably connected to the board  24 . The subassembly  16  includes a carrier assembly  50  (mostly in phantom) which has a planar carrier frame section  52  at one end which is sandwiched in between the ferrule  12  and a heat sink  54  along with the lens and alignment frame  44 . The lens and alignment frame  44  is positioned between the carrier frame section  52  and the ferrule  12  and acts as an interface between them and the components supported in or mounted on them. The carrier assembly  50  also includes a flex circuit  60  (in phantom) which is bendable and which also serves as an integral part of both the frame section  52  and the circuit board  18 . The flex circuit  60  extends under the heat sink  54  from the carrier frame section  52  at its one end to the circuit board  18  at its opposite end.  
         [0028]    Referring now to FIGS. 6 and 7, the subassembly  10  includes the receptacle  35 , metal casing structure  45 , lens and alignment frame  44 , carrier assembly  50 , heat sink  54  and casing structure  47 . As previously explained the receptacle  35  is adapted for receiving the ferrule  12  in the cavity  28 . The receptacle is mounted in the recess  29  in the casing structure  45  so that it abuts the back wall  51  of the recess  29 . The carrier assembly  50  includes the printed circuit board  18 , the flex circuit  60  and the carrier frame section  52 . The lens and alignment frame  44  is mounted in between the frame section  52  of the carrier assembly  50  and the back wall  51  of the casing structure  45  so that it is immediately adjacent to the fiber ends  32  on the proximal end  26  of the ferrule  12  when the ferrule is latched into the subassembly  16 . The flex circuit  60  connects the frame section  52  to the circuit board  18  serving as a medium for providing a large number of connection lines between components on the carrier frame section  52  and the circuit board  18  including the microcontroller chip  23  and the edge connecter  20 . The circuit board  18  fits along the back shelf  53  of the casing structure  45  underneath the heat sink  54 . The front end  59  of the heat sink  54  abuts the backside of the carrier frame section  52  for dissipating heat generated during operation by the electrical components mounted onto the frame section  52 . Except for the heat sink the metal cover  47  fits around the subassembly  16  providing a covering and protection for the receptacle  35 , casing structure  45  and the components of the carrier assembly  50  including the circuit board  18  extending along the back shelf  53  of the casing structure  45 . The bolts  58  help retain the heat sink  54  and circuit board  18  in position. As shown more clearly in FIG. 7, the casing structure  45  includes a window  37  in its back wall  51 . The lens and alignment frame  44  includes a mostly planar base  56  and a rectangular tower structure  43  projecting forward of the base  56  on which the guide pins  34  and lens array  48  are mounted. The tower  43  of the lens and alignment frame  44  fits through the window  37  of the casing structure  45  in the assembled device. The lens and alignment frame  44  is one-piece precision plastic injection-molded part including the tower  53 , guide pins  34  and lens array  48 . The frame section  52  of the carrier assembly  50  preferably includes one or more layers of printed circuit board material including a layer of flex circuit material  61  which is an extended part of the flex circuit  60 . The optoelectronic device  40  is precisely mounted on the frame section  52  and includes the photoactive semiconductor components  36  which are deployed on and as part of an integrated circuit (IC) chip that comprises an optoelectronic device  40 . The photoactive components  36  may be either semiconductor transmitter elements or semiconductor receiver elements and are disposed in a linear array  38  at regular 250 micron intervals corresponding to the linear array  48  of lenses and the linear array  33  of fibers. When the lens and alignment frame  44  is mounted on the frame section  52  the optoelectronic device  40  and photoactive components  36  are precisely aligned with the lens array  48  and the guide pins  34 . If the photoactive elements  36  are intended to be transmitter elements (a transmitter subassembly) they may, for example, be light emitting diodes (LEDs) or laser diodes. They are preferably vertical cavity surface-emitting lasers (VCSELs). If the photoactive elements  36  are intended to be receivers elements (a receiver subassembly) they may, for example, be PIN photodiodes or avalanche photodiodes (APDs) although they are preferably PIN photodiodes. One or more signal processing chips  41  may be mounted on the frame section  52  for communicating with the optoelectronic device  40  and more particularly providing drive signals to transmitter elements or providing signal amplification and conditioning in the case of receiver elements.  
         [0029]    Referring now to FIGS. 8 and 9, the lens and alignment frame  44  includes a main body or base  56  and a tower  43 . The base  56  is mostly planar and includes cavities  57  into which adhesive materials can flow during mounting and a large but shallow recess  55  for accommodating components and wiring on the front side of the carrier frame section  52  on which the lens and alignment frame  44  is mounted. The tower  43  resides on the front side of the frame section  52  and projects well forward of the base  56 . The tower  43  includes a pair of turret-like elevated end sections  49  on top of which the guide pins  34  are mounted so as to project outward and forward from the base  56  and lens array  48 . The lenses  46  in the array  48  are deployed at regular 250 micron intervals along a line extending between the elevated end sections  49  and guide pins  34  in a manner corresponding to the arrangement of the photoactive components  36  of the optoelectronic device  40  and fibers  17  of the ferrule  12 . The lenses  36  are precisely aligned with the guide pins  34 . Each lens  46  in the array  48  includes a front lens element  46   a  and a rear lens element  46   b  for directing light to and from the fiber ends  32  and photoactive components  36 , respectively.  
         [0030]    Referring now to FIGS. 10 and 14, the lens and alignment frame  44  is precisely mounted on the carrier frame section  52  and cooperates with the receptacle  35  in achieving alignment with the ferrule  12 . The frame section  44  is mounted flush on the front side of the frame section  52  using epoxy adhesive so as to carefully center the lens array  48  over the optoelectronic device  40  and more particularly the array  38  of photoactive components  36  which comprises the optoelectronic device  40 . The recess  55  in the frame  44  provides space to accommodate the chips  40  and  41  and to accommodate the wire bonds whereby the chips  40  and  41  are interconnected and connected to the signal traces on the flex circuit  60  part of the carrier assembly  50 . The frame section  52  preferably includes a flex circuit layer  61 , a layer of FR-4 printed circuit board material and a thin layer  63  of copper plate. The signal processing chip  41  may then be mounted in a small well  65  in the flex circuit layer  61  and circuit board layer  62  of the frame section  52  so that it is in direct contact with the copper layer  63  to improve heat dissipation in connection with the operation of the heat sink  54  which is attached to the layer  63  on the backside of the frame section  52 . The tower  43  passes through the window  37  in the casing structure  47  and fits into a second window  31  in the back wall at the inner end of the receptacle  35  which assists in making sure that the receptacle is aligned with the frame  44  and the frame section  52  and ferrule  12  are then aligned as the ferrule  12  is latched into the receptacle  35 . The guide pin  34  of the lens and alignment frame  44  fits into the alignment hole  30  in the ferule  12  for precisely aligning the array  33  of optical fibers  17  (not shown in FIG. 10) with the lens array  48 .  
         [0031]    Referring now to FIG. 11, it can seen again that the lens and alignment frame  44  is mounted on carrier frame section  52  so that the array  48  of lenses  46  is aligned with the optoelectronic device  40  and accordingly with the linear array  38  of photoactive components  36  which comprise the optoelectronic device  40 . The ferrule  12  is in turn coupled to the lens and alignment frame  52  by the action of the guide pins  34  which closely fit into the alignment holes  30  when the ferrule is inserted and latched into the receptacle  35  of the subassembly  16 . Since the lens array  48  and fiber array  33  are accurately positioned with respect to the guide pins  34  and alignment holes  30 , the guide pins and alignment holes  30  are operative for aligning the array  33  of optical fibers  17  with the array  48  of lenses  46 . The lens and interface frame  44  thereby provides for the alignment of the array  33  of fibers  17  with the array  48  of lenses  46  and with the optoelectronic device  40  and more particularly with the array  38  (not shown) of photoactive components  36  (not shown) in the optoelectronic device  40 . The alignment of the fibers  17  with the lenses  46  and the photoactive components of the optoelectronic device  40  (semiconductor chip) enables the transmission of photonic (light) signals from the optoelectronic device  40  to the fibers  17  in a transmitter subassembly  16  or from the fibers  17  to the optoelectronic device  40  in a receiver subassembly  16 . The lens and alignment platform  44  also serves to fix the distances over which light is focused by the lenses  46 . These distances are established by the offsets from the lenses  46  in the frame  44  to the frame section  52  and optoelectronic device  40  one side (across the recess  55 ) and to the ferrule  12  and fibers  17  on the other side.  
         [0032]    Referring now to FIG. 12, the lenses  46  are biconvex in shape and are each comprised of two planoconvex lens elements  46   a  and  46   b  on the front and back sides of the central section of the tower  43  of the lens and alignment frame  44  between the elevated end sections. Also referring again to FIG. 11, the individual lenses  46  are operative for directing light to and from the individual is fibers  17 , through the lens and alignment frame  44  and to and from the individual photoactive components in the optoelectronic device  40 . The lens elements  46   a  are adapted for focusing light to and from the fibers  17  while the lenses elements  46   b  are adapted for focusing light to and from the optoelectronic device  40 . In the preferred embodiment the lens elements  46   a  and  46   b  making up the lenses  46  may, by way of example, be characterized by the values shown in TABLE I.  
                                                                             TABLE I                           Lens Element Key Parameter Values                LENS 1 (46b)   LENS 2 (46a)                    N (index) (um)   1.632   1.632       D (focus) (um)   300   450       k   −2.663424   −2.663424       R (radius at apex)   189.6   284.4       half aperture (um)   200   200       z (sag) (um)   78.47245944   59.84856468       LENS 1   element 46b   Device side       LENS 2   element 46a   Fiber side                    Lens Element Sag Values                LENS 1   LENS 2       r (um)   z (um)   z (um)                    50   6.412449   4.340131       100   23.87155   16.75945       150   48.86220   35.80733       200   78.47245   59.84856                  
 
         [0033]    The lens element  46   a  (fiber side) has a focal length D of about 450 microns and the lens  46   b  (device side) has a focal length D of about 300 microns with the fibers  17  and optoelectronic device  40  being positioned at or near the focal points of these lens elements. However, the fibers  17  may be preferably positioned away from the focal points by about 100-200 microns toward the lens element  46   a . This may allow the some of the light emitted in transmitter subassemblies at higher off-axis angles by transnitter components  36  such as VCSELs which is subject to slower modulation patterns to be focused (or rather defocused) away from the fiber ends  32  of the fibers  17 . The optimal amount of defocusing depends on the numerical aperture values of the VCSELs and the fibers.  
         [0034]    Referring now to FIG. 13, the lenses  46  are collinearly and contiguously positioned in the lateral direction from end to end across the array  48 . The lenses  46  are characterized by a vertically elongated shape and have a greater height than width. The lenses  75  on the interior of the array  48  are about 400 microns high in the vertical direction  70  and are about 250 microns wide in the lateral direction  72 . The lenses  46  intersect along extended common boundaries  76  extending out from the centerline of the array  48  by about 156 microns with each boundary measuring about  312  microns in total length. The lenses  46  are in effect truncated in the lateral direction at their boundaries  76 . In effect the lenses  46  are extended vertically and are larger than the natural 250 micron pitch (center-of-lens to center-of-lens distance) of the array  48 . The elongated lenses  46  provide improved light gathering characteristics and improved tolerance to mechanical misaligniments affecting optical coupling efficiency as compared to smaller symmetrically shaped lens designed to intersect at a point along the centerline of the array  48 .  
         [0035]    Although only a few embodiments of the present invention have been described in detail, it should be understood that the invention may be embodied in other forms without departing from its overall spirit or scope.