Abstract:
A simply constructed and economical optical connector, wherein a fiber ribbon or waveguide ribbon cable incorporates a plurality of projecting fiber or waveguide ends adapted to engage into a guiding feature in a structure that incorporates an array of microlenses, upon said structure being aligned with and attached to a ferrule housing the ribbon cable. The guiding feature enables apertures in the ferrule within which the projecting fiber or waveguide ends are guides towards engagement with guiding feature in the microlens containing structure, to be formed or dimensioned with relaxed tolerances relative to the fiber or waveguide ends, thereby considerable reducing manufacturing costs for the ferrule.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a lens optical connector possessing passive alignment features, and more particularly pertains to a self-aligning optical interconnect structure for the connection of the fiber ends or optical wave guides to arrays of microlenses. 
         [0002]    In the technological field of data processing and architecturally larger multi-core processing system arrangements there is an ever-increasing need for high speed optical interconnects with the utilization of optical fiber arrays. 
         [0003]    With respect to the foregoing, it has become readily evident in the technology that the employment of optical waveguides will provide an efficient and economical method of managing the employment of large numbers of optical channels, wherein in particular, there is a present need for the provision of structurally simple, low cost waveguide connectorizations which are not bound to precise waveguide thickness controls. In that connection, the use of novel optical connectors employing optical flex sheets, i.e., comprising optical fiber ribbon cables or waveguide ribbon cables, which are interconnected in a simple and low cost manner, satisfies the need of future high performance computers which may contain literally thousands of optical channels. Such a multitude of optical channels may be employed with waveguide optical flex sheets consisting of polymer, which by way of example, may be either connected to the top or upper surface of a printed circuit board (PCB), embedded in the board, or installed as interconnect cables between such boards. 
       The PRIOR ART 
       [0004]    Kang, et al., U.S. Pat. No. 6,629,780 B2 discloses a high precision format multi-fiber connector which is adapted to provide for and maintain a higher degree of accuracy and low-precision loss over repeated connectorizations of the connector components. Although the connected structure discloses a solution to various problems that are encountered by fiber connectors, such as loss of accuracy, it does not incorporate any optical microlenses which are intended to be mated in a precise manner with an array of the optical fibers, and also fails to disclose the manner in which a stack of waveguides is aligned to another component in a precise mode. 
         [0005]    Concerning Dautartas, et al., U.S. Pat. No. 6,442,306 B1 this publication discloses a self aligned fiber optic connector for N×M arrays of optical fibers, wherein the optical fibers of the array incorporate aligning structures such as ball lenses, which provide for a desired coupling or connectorization efficiency. However, in that instance, the disclosed connector structure is extremely complex in nature, and is not adapted to provide for the simple and economically inexpensive connection of an array of multiple microlenses with the ends of fiber optic strands extending from an optical flex or waveguide ribbon cable housed in a suitable ferrule. 
       SUMMARY OF THE INVENTION 
       [0006]    Pursuant to the present invention, there is accordingly provided a simply constructed and economical optical connector, wherein a fiber ribbon or waveguide ribbon cable incorporates a plurality of projecting fiber or waveguide ends adapted to engage into a guiding feature in a structure that incorporates an array of microlenses, upon said structure being aligned with and attached to a ferrule housing the ribbon cable. The guiding feature enables apertures in the ferrule within which the projecting fiber or waveguide ends are guided towards engagement with guiding feature in the microlens containing structure, to be formed or dimensioned with relaxed tolerances relative to the fiber or waveguide ends, thereby considerable reducing manufacturing costs for the ferrule. 
         [0007]    Moreover, the waveguide ribbon cables, which may be essentially each flat in shape, may be stacked within the ferrule without the necessity for providing a precise thickness control, inasmuch as the desired alignment with the array of microlenses will be ensured by the provision of the guiding feature in the microlens-containing structure, into which the projecting contiguous ends of the stacked waveguides are inserted, and which optically communicate with respective therewith associated microlenses. 
         [0008]    Accordingly, it is an object of the present invention to provide a novel and advantageous connector for fiber or waveguide cables with arrays of microlenses in a structure which incorporate passive guiding features ensuring an accurate optically aligned communication between these components. 
         [0009]    A more specific object of the present invention resides in the provision of a ferrule housing the fiber or waveguide cables whereby the ends of the fibers or waveguides projecting towards the structure containing the microlenses are conveyed through apertures possessing relaxed tolerances relative to the cables so as to facilitate appreciable reductions in the manufacturing costs of the ferrule. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Reference may now be made to the following detailed description of preferred embodiments of the invention, taken in conjunction with the accompanying drawings, in which: 
           [0011]      FIGS. 1A-1C  illustrates, respectively, top sectional, side and front views of a ferrule housing a fiber ribbon cable with polished leading fiber ends pursuant to the prior art; 
           [0012]      FIGS. 2A-2D  illustrate, respectively, front, side, cross-sectional and enlarged fragmentary views of a microlens containing structure pursuant to the prior art; 
           [0013]      FIGS. 3A-3D  illustrate the ferrule with the prior art microlens containing structures of  FIGS. 2A-2D  aligned therewith in, respectively, front, side, cross-sectional and enlarged fragmentary views; 
           [0014]      FIGS. 4A-4G  illustrates, respectively, front, side, back, cross-sectional and enlarged fragmentary views of a first embodiment of a microlens containing structure with guide features pursuant to the invention; 
           [0015]      FIGS. 5A-5D  illustrate respectively front, side, cross-sectional and enlarged fragmentary views of a embodiment of a ferrule aligned with the structure shown in  FIGS. 4A-4E  pursuant to the invention; 
           [0016]      FIGS. 6A-6E  illustrate respectively front, side, back, cross-sectional and enlarged fragmentary views of a modified embodiment of a microlens containing structure pursuant to the invention; and 
           [0017]      FIGS. 7A-7D  illustrate, respectively, front, side, cross-sectional and enlarged fragmentary views of a ferrule aligned with the structure shown in  FIGS. 6A-6E  pursuant to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring now in detail to the drawings, in particular the prior art embodiment representation of  FIGS. 1A-1C , there is disclosed a simple ferrule  10  having an aperture  12  for the receipt of a fiber ribbon cable  14 . The cable  14  includes a 3-dimensional array of optical fibers  16  extending forwardly from the cable  14  through small holes  18  in the ferrule communicating with aperture  12 , so as to terminate in polished fiber ends  20  coextensive with the front surface  22  of the ferrule. The ferrule holes  18  form close-fitting guide holes for the respective optical fibers  16  and whereby the polished front ends of the fibers are intended to be aligned with optical lenses as detailed hereinbelow. The ferrule also contains at least two guide holes  24  adapted to be aligned with similar guide holes in a microlens-containing member, and for receiving suitable connectors (not shown.). 
         [0019]    Concerning the foregoing, the holes  18  which guide the respective optical fibers  16  towards the leading end of the ferrule, are manufactured so as to provide a highly-accurate guidance for the leading or polished front ends  20  of the optical fibers  16  which are coplanar with the surface  22  on the ferrule adapted to contact the housing  26  for an arrays of microlenses  28 . This entails a relatively expensive procedure in the manufacture of the accurately sized and spaced array of holes  18  for receiving and guiding the leading ends of the optical fibers emanating from the fiber ribbon cable which extends into the ferrule. As a result, the manufacture of the ferrule  10  is relatively expensive in nature inasmuch as it necessitates the use of sophisticated tooling and manufacturing techniques which will ensure the proper alignment of the holes  18  through which the optical fibers  16  are guided into optical alignment with the array of microlenses  28  with which they are to be communicating. 
         [0020]    In particular, as illustrated in  FIGS. 2A-2D  of the drawings, there is illustrated the prior art housing structure  26  of essentially a configuration, the surface towards the ferrule of which conforms to the front end surface  22  of the ferrule. Within the housing structure there is incorporated an array of the microlenses  28  as described hereinbelow there are also provided alignment holes  30  which are in conformance with the alignment holes  24  of the ferrule  10  so as to enable the housing structure to be accurately attached thereto by means of suitable fasteners (not shown). 
         [0021]    In this instance, the prior art housing  26  incorporating the microlens array  28  includes a polished surface  32  which is in accurate contact with the end surface  22  of the ferrule, and whereby the distal or opposite surface  34  of the housing  26  includes a recessed surface portion  36  which is configured to provide for the microlens array  28  which are in optical alignment with the respective leading or front ends  20  of the optical fibers  16 . The material of the housing  26  which contains the array of microlenses is optically transmissive and is preferably constituted of a transparent plastic or a glass material, as is well known in the art. 
         [0022]    As shown in  FIGS. 3A-3D , which represents essentially different views of the assembly of the ferrule  10  and of the housing  26  for the microlens array  28 , this illustrates the front optical fiber ends  20  in alignment with an optical transmissive path leading to each respective microlens of the array of microlenses  28  formed in the opposite recessed surface  34  in the microlens-containing housing. The leading optical fiber ends  20  are cleaved and may be manufactured by means of laser processing so as to be in accurate alignment with the microlenses  28  in the opposite end of the surface  34  in the housing  26 . 
         [0023]    Although the foregoing structure and assembly of the ferrule containing the optical fibers in alignment with the array of microlenses is essentially satisfactory, this necessitates a highly accurate machining or manufacturing process for forming the array of holes  18  interiorly of the ferrule  10  so as to afford a precise alignment with the respective array of microlenses. Accordingly, any encountered minor offset of the alignment holes in, respectively, the ferrule  10  and the housing  26  containing the microlenses, and any slight misalignment of the holes  18  containing the leading ends of the optical fibers  16  will adversely affect the effectiveness of the microlenses in their respective housing, and provide for either distorted or non-existent optical projections or paths. 
         [0024]    Accordingly, in order to obviate the foregoing disadvantages, pursuant to the invention as illustrated particularly in  FIGS. 4A-4E  of the drawings, wherein similar or identical components are identified by the same reference numerals, a housing  40  containing an array of microlenses  28 , similar to the structure shown in  3 A through  3 D of the drawings, incorporates in the surface  32  facing towards a ferrule  10  with which it is to be mated, incorporates an array of recessed blind apertures  42  essentially tapering down in size towards the bottom  44 , or towards the top  44 , thereof, essentially providing the guiding features as recesses spaced in conformance with the microlens arrays. Each of the openings forming the blind holes  42  is optically aligned with a respective one of the microlenses  28  while also essentially in number correlating with the optical fibers  16  which extend from the leading or front end surface of the ferrule  10 . For the remainder, the housing structure which contains the array of microlenses, is analogous to that shown in  FIGS. 3A-3D  of the drawings, the parts of which are identical or similar thereto are being identified by the same reference numerals. It is understood that the guide holes  42  can take on several different shapes. For example the bottom of the guide hole may be concave or convex. The guide holes could be triangular, square, pentagonal, or beyond. As shown in  FIGS. 4F-4G , venting slots  45  could intersect the guide holes in order to provide a channel for adhesive to escape when the fibers are inserted. 
         [0025]    Similarly, as illustrated in  FIGS. 5A-5D  of the drawings, wherein the ferrule  10  of the invention is essentially analogous to the ferrule shown in  FIGS. 1A-1C , however in this instance, the openings or holes  18  which contain and guide each respective one of the leading end portions  48  of the optical fibers  16  extending forwardly from the fiber ribbon cable  19 , may be somewhat larger in size than the outside diameters of each respective optical fiber; in effect, providing for a looser tolerance therewith. 
         [0026]    In connection with the foregoing, in this instance, the forward or front ends  48  of each of the optical fibers  16  extend forwardly so as to project from the front plane or surface  22  of the ferrule  10  so as to be each in general alignment with a respective, associated one of a recesses or blind holes  42  in the housing  26  containing the microlens array  28 , and as illustrated in  FIG. 5D  of the drawings on a larger scale, each of the projecting front ends  48  of the optical fibers  16 , whereby the fiber ends may be cleaved through laser trimming, has the leading end  50  received within a guiding feature, i.e., blind hole  42  formed in the surface  32  of the housing for the microlens array. The fibers may be held in place using an optically transparent adhesive. Consequently, any slight offset of the leading ends  50  of the respective optical fibers  16  which may be caused by the slightly larger dimensioned holes  18  in which they are guided in the ferrule  10  and which afford looser manufacturing tolerances will be compensated for in that the leading end  50  of each respective optical fiber  16  is guided into the respective therewith associated guiding feature or blind hole  42  to contact the bottom  44  formed in the housing for the microlens array, thereby ensuring a correct alignment and resulting optical communication between the optical fibers  16  and therewith associated microlenses  28 . This facilitated relaxing in the tolerances in forming the guide holes  18  within the front portion of the ferrule  10  receiving the optical fibers  16 , will enable the manufacturing costs of the ferrule to be considerably reduced, rendering the structure highly economical, particularly in the contemplated large scale usage thereof. 
         [0027]    Although the lens housing  40  and ferrule  10  in  FIGS. 5A-5D  are shown as separate pieces it is understood that these may be molded as a single piece, thereby further reducing costs. 
         [0028]    As shown in  FIGS. 6A-6E , there is illustrated a modification of the housing  60  containing an array of microlenses  28 , as shown in  FIGS. 4A-4G  of the drawings, whereby in this instance, the guiding feature  62  formed in the surface  32  of the housing  60  which is adapted to mate with the front end surface of a ferrule rather than containing individual blind holes  42  into which the leading ends of the respective optical fibers are to be introduced, guiding features comprise at least a pair or plurality of superimposed elongated slots  66  in close parallel spacing, which extend recessed into the surface  32  of the microlens array-containing housing  60  in optical alignment with the array of microlenses. 
         [0029]    As illustrated in  FIGS. 7A-7D  of the drawings, in lieu of a optical fiber ribbon cable  14  as heretofore, in this instance, there are present superimposed special optical waveguide ends  70 , generally a flat surface nature extending from a waveguide ribbon cable  72 , and wherein the ferrule  68  rather than possessing plurality of guiding holes  18  for optical fibers  16 , provides for a single large slot or multiple smaller slots  74  formed therein, through which the outwardly projecting leading end  70  of each of the waveguides is guided within loose tolerances and is insertable into a therewith associated slot  66  formed in the mating surface  32  of the housing containing the microlens array  28 . Consequently, this will also enable leading openings to be formed in the ferrule at looser tolerances. Each of the projecting leading waveguide ends  70  may be laser trimmed in a simple and inexpensive manner, so as to be guidingly and accurately insertable into the correspondingly configured slots formed  66  in the mating surface of the housing containing the array of microlenses, in optical alignment with the latter. This laser trimming is performed accurately with respect the waveguide cores within each waveguide ribbon cable  70 . Conversely there may also be other techniques than laser trimming for accurately sectioning the waveguide ribbon cable with respect to the waveguide cores such as mechanical stamping or chemical etching. For example, a waveguide ribbon cable  70  with an overall thickness of 200 microns may contain 12 or more individual cores (through which light travels, similar to optical fiber cores) that may be 5 to 50+ microns in size. These cores may be positioned on a 250 micron pitch. In this example the outer most cores would be spaced apart by 2,750 microns. The waveguide ribbon cable  70  could be accurately trimmed to a width of 3,000+ microns with care taken to ensure the waveguide cores are precisely centered (side to side) within the waveguide ribbon cable  70 . 
         [0030]    It is noted that guiding features  22  in housing  60  are used to accurately position (side to side) the waveguide ribbon cable  70  with respect to the lens array  28 . Other means may be used to accurately position the waveguide side to side. For example, it is possible to use laser, mechanical stamping, chemical etching or other means to drill holes or notches in the waveguide ribbon cable thereby providing features that are accurately positioned horizontally with respect to the waveguide cores. These horizontal alignment features would then reference and engage corresponding features in the housing  60  or ferrule  68  in order to accurately position the waveguide ribbon cable  70  horizontally with respect the tens array  28 . 
         [0031]    It is noted that guiding features  66  and  62  in housing  60  are used to accurately position (vertically: up/down) the waveguide ribbon cable  70  with respect the lens array  28 . It is noted that within the waveguide ribbon cable the optical cores are accurately positioned vertically to at least one of the outer surfaces of the waveguide film stack. This surface serves as a primary vertical alignment feature when the waveguide ribbon cable engages the vertical guiding features  66  and  62  in housing  60 . 
         [0032]    Conversely, if the optical cores are not accurately positioned vertically to at least one of the outer surfaces of the waveguide film stack, then a waveguide trimming operation may be performed by using a laser, mechanical cutter, chemical etch or other means to trim the top or the bottom of the waveguide film stack in order to accurately reference the optical cores to the top or bottom surface of the waveguide film stack. 
         [0033]    It is understood that the slot may take on many shapes. For example the slot may be nearly horizontal on the side facing the waveguide reference surface, while the other side of the slot may contain a larger taper, thereby pushing the waveguide ribbon towards the reference surface. The slot may contain side vents to allow the optical adhesive to escape from the slot during assembly. 
         [0034]    Although the lens housing  60  and ferrule  68  as shown in  FIGS. 7A-7D  are shown as separate pieces it is understood that these may be molded as a single piece, thereby further reducing costs. 
         [0035]    From the foregoing, it becomes readily apparent that the inventive structures are adapted to reduce manufacturing costs for the ferrules  10 ,  68  containing either the optical fibers or waveguides by considerable amount through incorporating the inventive guiding features, such as therewith aligned holes  42  or slots  66  for receiving, respectively, the leading or projecting ends of the optical fibers or waveguides emanating from the ferrule. 
         [0036]    Moreover, although the foregoing ferrule and housing structure has each been illustrated as being respectively rectangular in nature, showing two rows of microlenses in an array, which will provide for three-dimensional optical fiber or waveguide connections, it is also possible that the ferrule and respectively, the therewith associated housing containing the microlenses, can in cross-section be either square, oval or circular or otherwise configured in nature so as to allow for different configurations in the arrays of optical fibers or waveguides, and in effect, not limited to the configuration disclosed herein. 
         [0037]    While the present invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present invention. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated, but to fall within the spirit and scope of the appended claims.