Patent Publication Number: US-2019196119-A1

Title: Fiber optic connector ferrule with improved alignment mechanism

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/737,619, filed on Dec. 18, 2017, which is a National Stage Application of PCT/US2016/037382, filed on Jun. 14, 2016, which claims the benefit of U.S. Patent Application Ser. No. 62/182,195, filed on Jun. 19, 2015, the disclosures of which are incorporated herein by reference in their entireties. To the extent appropriate, a claim of priority is made to each of the above disclosed applications. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to optical fiber communication systems. More particularly, the present disclosure relates to fiber optic connector ferrules used in optical fiber communication systems. 
     BACKGROUND 
     Fiber optic communication systems are becoming prevalent in part because service providers want to deliver high bandwidth communication capabilities (e.g., data and voice) to customers. Fiber optic communication systems employ a network of fiber optic cables to transmit large volumes of data and voice signals over relatively long distances. Optical fiber connectors are an important part of most fiber optic communication systems. Fiber optic connectors allow two optical fibers to be quickly optically connected without requiring a splice. Fiber optic connectors can be used to optically interconnect two lengths of optical fiber. Fiber optic connectors can also be used to interconnect lengths of optical fiber to passive and active equipment. 
     A typical fiber optic connector includes a ferrule assembly supported at a distal end of a connector housing. A spring is used to bias the ferrule assembly in a distal direction relative to the connector housing. The ferrule functions to support an end portion of at least one optical fiber (in the case of a multi-fiber ferrule, the ends of multiple fibers are supported). The ferrule has a distal end face at which a polished end of the optical fiber is located. When two fiber optic connectors are interconnected, the distal end faces of the ferrules abut one another and the ferrules are forced proximally relative to their respective connector housings against the bias of their respective springs. With the fiber optic connectors connected, their respective optical fibers are coaxially aligned such that the end faces of the optical fibers directly oppose one another. In this way, an optical signal can be transmitted from optical fiber to optical fiber through the aligned end faces of the optical fibers. The fibers in a multi-fiber ferrule must all be brought into contact. Preferably, the tips of the fibers should all lie in a line (for a single row of fibers) or plane (multiple rows of fibers). Polishing results in a nearly planar surface; however this surface is not consistently oriented with respect to the axis defined by the guide pins. For example, the fiber slope angle, which is nominally zero, is not well controlled. It is difficult to measure this angle accurately, since it involves features that extend in three dimensions: the axes of the alignment pin passageways extend along a longitudinal axis, and the contact face of the ferrule extends along major (or lateral) and minor (or vertical) axes. The pins are held very rigidly by the ferrules, such that the ferrules cannot rotate about the minor axis to allow the ends of the fibers to come into contact when the ferrules are urged forward by a spring force. 
     Alignment connection systems have been developed to improve the loss of physical contact between fiber-optic connectors. However, there is a need to reduce the rotational stiffness of the ferrule and guide pin mechanical system such that physical contact can be made between all fibers in a multi-fiber connector. 
     SUMMARY 
     One aspect of the present disclosure relates to rotational interplay between an alignment pin and different sections of an alignment pin passageway extending through a multi-fiber ferrule body. The alignment pin can have a transverse cross-sectional profile that engages a tight-fit section of the alignment pin passageway, thus limiting rotational movement of the ferrule body about a major axis and a minor axis. The ferrule body also has a loose-fit flex section that engages the alignment pin along the minor axis to limit rotational movement about the major axis. Along the major axis, the flex section has a width that provides a clearance from the alignment pin to allow for rotational movement about the minor axis. This freedom for rotational movement about the minor axis aids in maintaining optical contact between the multi-fiber ferrule body and a corresponding similar multi-fiber ferrule body. 
     Another aspect of the present disclosure relates to a fiber optic connector ferrule that includes a ferrule body with a depth along a longitudinal axis that extends from a front end to a rear end of the ferrule. The ferrule includes a contact face at the front end of the ferrule. The contact face includes a major dimension that extends along a major axis and a minor dimension that extends along a minor axis. The major and minor axes are perpendicular to one another and perpendicular to the longitudinal axis. The ferrule also defines alignment pin receivers that extend rearwardly from the front end of the ferrule. The alignment pin receivers define a tight-fit section that is defined by a first transverse cross-sectional profile extending into the ferrule body from the contact face and a loose-fit flex section defined by a second transverse cross-sectional profile extending from the first transverse cross-sectional profile to the rear end. The second transverse cross-sectional profile comprises a different clearance than the first transverse cross-sectional profile. The fiber optic connector ferrule also has plurality of optical fibers that extend through the ferrule body. The optical fibers have end faces that are accessible at the contact face of the ferrule. The fiber optic ferrule also has a pair of alignment pins with proximal ends positioned within the alignment pin receivers and distal ends protruding outwardly away from the contact face. The proximal end portions have a third transverse cross-sectional profile that is different than the alignment pin opening second transverse cross-sectional profiles. The different third and second transverse cross-sectional profiles are relatively configured to provide rotational flexibility between the alignment pins and the ferrule body. The different dimensions of the first and second transverse cross-sectional profiles define the degree of rotational flexibility between the alignment pins and the ferrule body. 
     A still further aspect of the present disclosure relates to a fiber optic connector ferrule that has a ferrule body with a depth along a longitudinal axis that extends from a front end to a rear end of the ferrule. The ferrule includes a contact face at the front end of the ferrule. The contact face includes a major dimension that extends along a major axis and a minor dimension that extends along a minor axis. The major and minor axes are perpendicular to one another and perpendicular to the longitudinal axis. The ferrule also defines alignment pin receivers that extend along the longitudinal axis rearwardly from the front end of the ferrule body toward the rear end of the ferrule body. The fiber optic connector also includes a plurality of optical fibers that extend along the longitudinal axis through the ferrule body generally from the front end to the rear end of the ferrule body. The optical fibers have end faces that are accessible at the contact face of the ferrule. The fiber optic connector also includes a pair of alignment pins that have proximal ends positioned within the alignment pin receivers and distal ends protruding outwardly away from the contact face. The alignment pin receivers and the alignment pins are configured such that a tight fit region is defined between the proximal ends of the alignment pins and the alignment pin receivers immediately adjacent to the contact face. The alignment pin receivers and the alignment pins also are configured such that a looser fit region is defined between the proximal ends of the alignment pins and the alignment pin receivers immediately rearward of the tight fit region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows example multi-fiber ferrule contact face geometry parameters for physical contact, showing fiber slope (SX), minus coplanarity (CF) and fiber tip radius (RF). 
         FIGS. 2A-2B  show cross-sectional views of interplay between an alignment pin and tight-fit and flex sections of an alignment pin passageway extending through a multi-fiber ferrule body. 
         FIG. 3  shows a contact-face-end perspective view of a multi-fiber ferrule according to an example embodiment of the present disclosure, showing a freedom to slightly rotate about the Y-axis, so that fiber slope angle is compensated. 
         FIG. 4  shows a top perspective see-through view of the multi-fiber ferrule shown in  FIG. 3 , shown with alignment pins to maintain contact-face optical connection with a second multi-fiber ferrule. 
         FIG. 5  shows a top cross-sectional view of the optically-connected multi-fiber ferrules shown in  FIG. 4 . 
         FIG. 6  shows an enlarged cross sectional view of an alignment pin extending across the optically-connected multi-fiber ferrules shown in  FIG. 5 . 
         FIG. 7  shows a top perspective see-through view of the multi-fiber ferrules shown in  FIG. 4 , shown separated from contact face optical connection. 
         FIG. 8  shows a top see-through view of the multi-fiber ferrule shown in  FIG. 4 , shown without alignment pins. 
         FIG. 9  shows an enlarged perspective see-through view of multi-fiber ferrules aligned with an alignment pin according to a second example embodiment of the present disclosure. 
         FIG. 10  shows a cross-sectional view of the multi-fiber ferrules shown in  FIG. 9 . 
         FIG. 11  shows a perspective rear-end see-through view of a multi-fiber ferrule according to a third example embodiment of the present disclosure. 
         FIG. 12  shows a perspective rear-end see-through view of a multi-fiber ferrule according to a fourth example embodiment of the present disclosure. 
         FIG. 13  shows a perspective rear-end see-through view of a multi-fiber ferrule according to a fifth example embodiment of the present disclosure. 
         FIG. 14  shows a perspective rear-end see-through view of a multi-fiber ferrule according to a sixth example embodiment of the present disclosure. 
         FIG. 15  shows a perspective rear-end see-through view of a multi-fiber ferrule according to a seventh example embodiment of the present disclosure. 
     
    
    
     DESCRIPTION 
     To ensure a low loss, reliable connection between two multi-fiber ferrules, physical contact of all mating ferrules is critical. As fibers are protruding above the ferrule contact face, the physical contact is achieved under a spring force and is affected by the contact-face geometry. As illustrated in  FIG. 1 , a multi-fiber optical contact interface defines three parameters, fiber slope (SX), minus coplanarity (CF) and fiber tip radius (RF). Fiber radius (RF) is defined by the sharpness (radius/diameter) of the tip end of a fiber, such that a sharper (smaller radius/diameter) tip creates easier deformation. Minus coplanarity (CF) defines how far away the fiber tip is from the contact line. Fiber slope (SX) defines the angle of the fiber tips to a reference plane that is perpendicular to a fiber guide pin hole axis. 
     Fiber slope (SX) has the largest impact on physical contact due to the amount of variation in current manufacturing. To maintain optical contact, the fiber slope (SX) value is preferably less than 0.06°. 
       FIGS. 2A-2B  illustrate cross-sectional views of interplay between an alignment pin  7  within different sections of an alignment pin passageway extending through a multi-fiber ferrule body  3 , according to an example embodiment. As illustrated in  FIG. 2A , the alignment pin  7  has a transverse cross-sectional profile that engages a tight-fit section  5  that has a transverse cross-sectional profile, thus limiting rotational movement of the ferrule body  3  about a major axis X and a minor axis Y. As illustrated in  FIG. 2B , the ferrule body  3  also has a loose-fit flex section  9  with a transverse cross-sectional profile that has a height along the minor axis Y that engages the alignment pin  7  to limit rotational movement about the major axis X. Along the major axis X, the flex section  9  has a width that provides a clearance from the alignment pin  7  to allow for rotational movement about the minor axis Y. 
       FIG. 3  illustrates an example multi-fiber ferrule that includes a body  10  with a front end  12  and a rear end  14 . A contact face  16  is positioned along the front end  12  opposite the rear end  14 . A support face  22  is positioned along the rear end  14  opposite the front end  12 . The ferrule body  10  has a major axis X and a minor axis Y extending perpendicularly with respect to each other relative to the contact face  16 . A longitudinal axis Z extends through the ferrule body  10  from the front end  12  to the rear end  14 . A pair of alignment pin passageways  18  extends, in parallel with the longitudinal axis Z, from the contact face  16 . The alignment pin passageways  18  are positioned along the major axis X on either side of a plurality of optical fibers  20 . The optical fibers  20  protrude outwardly away from the contact face  16  and extend through the ferrule body  10  from the contact face to the rear end  14  parallel to the longitudinal axis Z. 
       FIGS. 4-7  illustrate a pair of the example ferrule bodies  10  ( FIG. 2 ) in physical contact with each other. Each ferrule body  10  optically contacts the other with their respective contact faces  16 . The optical fibers  20  of each ferrule body  10  contact the other. Each depicted alignment pin passageway  18  provides a continuous passageway with a tight-fit section  26  defined by a first transverse cross-sectional profile extending into the ferrule body  10  from the contact face  16  and a flex section  28  defined by a second transverse cross-sectional profile extending from the first transverse cross-sectional shape to the support face  22  along the rear end  14 . As illustrated, the flex section  28  second transverse cross-sectional profiles can provide a clearance, for example a greater width along the major axis X, and/or a greater height along the minor axis Y, from the tight-fit section  26  first transverse cross-sectional profiles. 
     As illustrated particularly in  FIGS. 4-7 , in operation the ferrule  10  can receive a pair of alignment pins  24  within the alignment pin passageways  18 . The illustrated alignment pins  24  can have proximal base end portions that are received in the alignment pin receivers  18  and distal tips that protrude outwardly away from the contact face  16 . The proximal base end portions of the alignment pins  24  have a third transverse cross-sectional profile that is nearly identical to the first transverse cross-sectional profile of the tight-fit section  26 . Preferably, the first transverse cross-sectional profile of the tight-fit section  26  is defined by the third transverse cross-sectional profile of the alignment pins  24  in order to maintain a tight fit between the alignment pins within the tight-fit sections. For example, the first transverse cross-sectional profile and the third transverse cross-sectional profile can both be oval, rectangular, octagonal, rectangular, or any predetermined shape that matches and maintains a tight fit. 
     By contrast, the third transverse cross-sectional profile of the alignment pins  24  is different than the second transverse cross-sectional profile of the flex section  28  of the alignment pin receivers  18 . Preferably the difference between the second and third transverse cross-sectional profiles is defined by a degree of rotational freedom about the minor axis Y of the ferrule body  10  with respect to the alignment pin  18 , illustrated by the curved arrow in  FIG. 3 . The degree of rotational freedom increases with an increased dimensional difference between the second and third transverse cross-sectional profiles, and vice versa. During such rotation, one alignment pin  24  inserts into a corresponding alignment pin receiver  18  of an opposing ferrule body  10  a deeper distance than the other. For example, the second transverse cross-sectional profile can have a greater dimension along the major axis X than the third transverse cross-sectional profile to provide flexibility along the major axis. Alternatively, the second transverse cross-sectional profile can have a greater dimension along the minor axis Y than the third transverse cross-sectional profile to provide flexibility along the minor axis. Alternatively still, the second transverse cross-sectional profile can have greater dimensions along the major axis X and the minor axis Y than the third transverse cross-sectional profile to provide flexibility along both axes. The tight-fit section  26  can maintain its transverse cross-sectional profile throughout its entire length. The flex section  28  can maintain its transverse cross-sectional profile throughout its entire length, or it can taper. 
     As illustrated in  FIGS. 4-8 , the tight-fit section  26  first transverse cross-sectional profiles can be circular with a first diameter. As illustrated particularly in  FIGS. 4 and 7 , the second transverse cross-sectional profiles can be circular with a second diameter that is greater than the first diameter. The third transverse cross-sectional profiles can have a third diameter that allows for a tight engaging fit within the first diameter of the tight-fit section  26 . This allows the outwardly extending distal tips of the alignment pins  24  to tightly fit within the tight-fit section  26  of an optically connecting ferrule  10 , as depicted. The different third and second transverse cross-sectional profiles are relatively configured so that the ferrule body  10  provides less resistance to the alignment pins  24  when they pivot or flex along the major axis X. For example, a gap can exist between the third diameter of the alignment pins  24  and the the second diameter of the flex section  28  to allow the proximal base end of the alignment pins to pivot within the flex section. As particularly shown in  FIGS. 1 and 3 , the extent to which the contact faces  16  can pivot with respect to each other and still maintain an optical connection is defined by a plane that extends across the plurality of optical fibers  20 . 
     Alternatively, the tight-fit section  26  first cross-sectional profiles and the flex section  28  second cross-sectional profiles can define shapes other than circles, for example ovals, rectangles, squares, octagons, or any alternative shape that allows for a tight fit of the alignment pins  24  in the tight-fit section and a pivot or flex along the major axis X of the flex section. 
     The length of the tight-fit sections  26  of the alignment pin passageways  18  along the longitudinal axis Z can also define the rotational flexibility of the alignment pins  24  with respect to the ferrule body  10 . The degree of rotational freedom decreases with an increase in the length of the tight-fit sections  26 , and vice versa. For example, a longer tight-fit section  26  reduces the rotational flexibility of the alignment pins  24  with respect to the ferrule body  10 , whereas a shorter tight-fit section increases the rotational flexibility. Preferably, the tight-fit sections  26  of the alignment pin passageways  18  can have a length along the longitudinal axis Z equivalent to a maximum of twice the diameter of the alignment pins  24 . The alignment pins  24  can have a diameter of about 0.7 mm. Alternatively, the tight-fit sections  26  of the alignment pin passageways  18  can extend a length along the longitudinal axis Z a maximum of 1.95 mm from the contact face  16 , and preferably less than 1.95 mm from the contact face, and most preferably about 1.4 mm. The distance between the contact face  16  and the transition location  25  of the proximal base end third transverse cross-sectional profile to the distal tip section can be between about 0.2 mm and about 3.1 mm, more preferably between about 0.2 mm and about 1.6 mm. 
     The ferrule body  10  can be composed of material that provides a defined degree of elasticity and compression, for example PPS glass-filed material. The elasticity preferably has a Young&#39;s modulus of between about 14,000 MPa and 25,000 MPa, more preferably between 14,300 MPa and 20,000 MPa, and most preferably about 15,000 MPa. The material preferably has a Poisson&#39;s ratio of 0.35. 
     The alignment pins  24  can have a stiffness that allows for bending during misalignment of the pins and the alignment pin passageways  18 . For example, the alignment pins  24  can have an elasticity with a Young&#39;s modulus of about 207,000 MPa and a Poisson&#39;s ratio of about 0.25. The coefficient of friction between the alignment pins  24  and the alignment pin passageways  18  can be 0.2, defined by the alignment pin/alignment pin passageway. 
     As illustrated particularly in  FIGS. 9-10 , an alternative ferrule body  30  can include tight-fit sections  34  and flex sections  32  similar to the ferrule described above. The alternative ferrule body  30  can also include a pair of notches  36  cut-out and recessed around each alignment pin passageway, and be defined by the major X and minor Y axes. These recessed notches  36  can provide even greater lateral freedom of the alignment pins  24  with respect to the ferrule body  30 . 
     As illustrated particularly in  FIG. 11 , an alternative ferrule body can include a front end  40 , rear end  42 , contact face  44  and alignment pin passageways  47  with tight-fit sections  46  similarly to the ferrules described above. The alternative ferrule body can also have a flex section  48  defined by oval second transverse cross-sectional shapes that provide a height along the minor axis Y common with the tight-fit sections  46  and a greater width along the major axis X than the tight-fit sections. The flex sections  48  can maintain the oval shape throughout their length. 
     As illustrated particularly in  FIG. 12 , an alternative ferrule body can include a front end  50 , rear end  52 , contact face  54  and alignment pin passageways  57  with tight-fit sections  56  similarly to the ferrules described above. The alternative ferrule body can also have a flex section  58  defined by rectangular second transverse cross-sectional profiles that provide a height along the minor axis Y common with the tight-fit sections  56  and a clearance defined by a greater width along the major axis X than the tight-fit sections. The flex sections  58  can maintain the rectangular shape throughout their length. 
     As illustrated particularly in  FIGS. 13-14 , alternative ferrule bodies can include a front end  60 ,  70 , rear end  62 ,  72 , contact face  64 ,  74  and alignment pin passageways  67 ,  77  with tight-fit sections  66 ,  76  similarly to the ferrules described above. The alignment pin passageways  67 ,  77  can also have flex sections  68 ,  78  that can taper wider along the longitudinal axis Z between the tight-fit sections  66 ,  76  and the rear end  62 ,  72 . In particular,  FIG. 13  illustrates that the flex sections  68  can taper from a circular first diameter of the tight-fit sections  66  to a shape at the rear end  62  that includes a pair of opposing semi-circles separated by a pair of parallel top and bottom surfaces. The pair of opposing semi-circles can have the same diameter as the first diameter of the first transverse cross-sectional shapes in the tight-fit sections  66  and the pair of parallel top and bottom surfaces can be separated by a distance equal to the first diameter. Alternatively,  FIG. 14  illustrates that the flex sections  78  can taper wider from a circular first diameter of the tight-fit sections  76  to a rectangular shape at the rear end  72 . 
     As illustrated particularly in  FIG. 15 , an alternative ferrule body  80  can include a contact face  84  and alignment pin passageways  87  with tight-fit sections  86  similarly to the ferrules described above. The depicted ferrule body  80  can also have flex sections  88  defined by a transverse cross-sectional profile defined by a pair of opposing semi-circles separated by a pair of parallel top and bottom surfaces, similarly to the embodiment in  FIG. 12 . The pair of parallel top and bottom surfaces can be separated along the minor axis Y by a distance equal to the height of the transverse cross-sectional profile of the tight-fit section  80  along the minor axis Y. The transverse cross-sectional profile of the flex sections  88  has a clearance defined by a greater width along the major axis X than the tight-fit sections. The flex sections  88  maintain this transverse cross-sectional profile consistently throughout their length, similarly to the embodiment in  FIG. 11 . 
     PARTS LIST 
     
         
           3 —Multi-fiber ferrule body 
           5 —Tight-fit section of alignment pin passageway 
           7 —Alignment pin 
           9 —Loose-fit flex section of alignment pin passageway 
           10 —Multifiber ferrule body 
           12 —Ferrule body front end 
           14 —Ferrule body rear end 
           16 —Ferrule contact face 
           18 —Alignment pin passageway 
           20 —Optical fibers 
           22 —Ferrule support surface 
           24 —Alignment pin 
           25 —Transition point between proximal end cross-sectional profile and distal tip end 
           26 —Tight-fit section 
           28 —Loose-fit flex section 
           30 —Alternative ferrule body 
           32 —loose-fit flex section 
           34 —tight-fit section 
           36 —recessed notch 
           40 —front end 
           42 —rear end 
           44 —contact face 
           46 —tight-fit section 
           47 —alignment pin passageway 
           48 —loose-fit flex section 
           50 —front end 
           52 —rear end 
           54 —contact face 
           56 —tight-fit section 
           57 —alignment pin passageway 
           58 —loose-fit flex section 
           60 —front end 
           62 —rear end 
           64 —contact face 
           66 —tight-fit section 
           67 —alignment pin passageway 
           68 —loose-fit flex section 
           70 —front end 
           72 —rear end 
           74 —contact face 
           76 —tight-fit section 
           77 —alignment pin passageway 
           78 —loose-fit flex section 
           80 —front end 
           82 —rear end 
           84 —contact face 
           86 —tight-fit section 
           87 —alignment pin passageway 
           88 —loose-fit flex section 
       
    
     Although specific embodiments of the disclosure have been described, numerous other modifications and alternative embodiments are within the scope of the disclosure. For example, any of the functionality described with respect to a particular device or component may be performed by another device or component. Further, while specific device characteristics have been described, embodiments of the disclosure may relate to numerous other device characteristics. Further, although embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the disclosure is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as illustrative forms of implementing the embodiments. Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments could include, while other embodiments may not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements, and/or steps are in any way required for one or more embodiments.