Patent Publication Number: US-2023147914-A1

Title: Ferrule with molded internal tilted refractive surfaces

Description:
REFERENCE TO RELATED CASE 
     This application claims priority under 35 U.S.C. § 119 (e) to U.S. provisional application No. 62/965,280 filed on Jan. 24, 2020, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Lensed ferrules are used in a variety of mid-board and edges of circuit boards with optoelectronic conversion features, as well as in different optical fiber cabling connection applications. As optical communication moves towards single mode fiber applications, as wells as the introduction of smaller diameter fibers, tighter tolerances are needed for lensed ferrules, including single mode fiber applications. 
     Certain ferrules under development have tilted external lenses, i.e., lenses exposed to the environment on an end face of the fiber optic ferrule that are tilted with respect to the longitudinal axis of the optical fiber. One such external tilted lens is discussed in co-pending application PCT/US20/58794 filed by the Applicant, the contents of which are hereby incorporated by reference in their entirety. Certain other lensed ferrule solutions include total internal reflection (TIR) lenses, typically for mid-board applications, but maybe applicable to fiber-to-fiber connections. 
     External lenses are generally prone to issues resulting from condensation, dust, debris, and/or scratching. Further, the presence of lenses on the end face of the ferrule makes it harder to clean the end face. Ferrules utilizing TIR lenses are bulkier, and mating two TIR lensed ferrules requires more space than other lensed ferrules. TIR fiber optic ferrules are typically single row, and are difficult to migrate to multi-row applications. Further, conventional tilted lens ferrules can be mated only in a particular orientation—key-up to key-down. 
     Thus, there is a need for a fiber optic ferrule with molded internal refractive surfaces at an angle to the longitudinal axis (e.g., tilted lenses). The optical beams pass through a window having a planar surface that is tilted to the end-face at an angle. The tilted arrangement of the internal lenses and the exit window causes the beam of the lensed ferrule to be parallel to the longitudinal axes of the optical fibers. This arrangement makes the fiber optic ferrules polarity immune or self-checking with respect to the orientation during mating with another mating ferrule, and thus can be mated key-up to key-up or key-up to key-down. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a fiber optic ferrule that includes a main body having a front end, a rear end, and a top surface and a bottom surface joined together by opposing side surfaces, the main body having a longitudinal axis extending between the front end and the rear end, plurality of optical fiber support structures disposed between the front end and rear end and configured to receive a plurality of optical fibers, an end face at the front end of the fiber optic ferrule through which an optical beam passes, and a front facing refractive surface and a rear facing refractive surface, the front facing refractive surface and the rear facing refractive surface located between the end face and the plurality of optical fiber support structures, the rear facing refractive surface being closer to the end face than the front facing refractive surface, and being at an angle to the front facing refractive surface. 
     In some embodiments, the front facing refractive surface and the rear facing refractive surface are separated from each other by a lens gap. 
     In some embodiments, the end face has an exit window through which the optical beam passes and the exit window is not orthogonal to the longitudinal axis. 
     In some embodiments, the fiber optic ferrule further includes two guide pins and two guide pin holes extending from the front end toward the rear end, the guide pins being diagonally spaced across the end face. 
     In some embodiments, the convex lenses are integrally molded with the main body. 
     In some embodiments, the main body has a first portion and a second portion, the second portion comprising a portion of the top surface. 
     In yet another aspect, the fiber optic ferrule has a housing in which the fiber optic ferrule is received and securely held. 
     It is to be understood that both the foregoing general description and the following detailed description of the present embodiments of the invention are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention and, together with the description, serve to explain the principles and operations of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of one embodiment of a fiber optic ferrule according to the present invention; 
         FIG.  2    is a top plan view of one portion of the fiber optic ferrule in  FIG.  1    with a second portion removed; 
         FIG.  3    is a perspective view of the fiber optic ferrule in  FIG.  1    from above and behind the fiber optic ferrule; 
         FIG.  4    is a cross sectional view of the fiber optic ferrule in  FIG.  1    along a longitudinal axis; 
         FIG.  5    is a partial cross sectional view of the front of the fiber optic ferrule in  FIG.  1   ; 
         FIG.  6    is a partial cross sectional view of the front end of the fiber optic ferrule in  FIG.  1   ; 
         FIG.  7    illustrates two of the fiber optic ferrules in  FIG.  1    in a mated relationship in a key-up to key-up orientation; 
         FIG.  8    illustrates two of the fiber optic ferrules in  FIG.  1    in a mated relationship in a key-up to key-down orientation; 
         FIG.  9    is side elevation view of the two fiber optic ferrules in  FIG.  8    in a premating configuration; and 
         FIG.  10    is a perspective view of the fiber optic ferrule in  FIG.  1    being inserted into a connector housing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the present preferred embodiment(s) of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. 
     Applicant notes that the term “front” or “forward” means that direction where the fiber optic connector and/or the ferrule would meet with another fiber optic connector or device, while the term “rear” or “rearward” is used to mean the direction from which the optical fibers enter into the fiber-optic ferrule, the fiber optic connector, or the ferrule push. Each of the components will therefore have a front and rear, and the two fronts or forward portions of the fiber optic ferrules would engage one another. Thus, in  FIG.  1   , the “front” of the fiber optic ferrule is on the left side of  FIG.  1    and “forward” is to the left and out of the page. “Rearward” or “rear” is that part of the fiber optic ferrule or cover that is on the right side of the page and “rearward” and “backward” is toward the right and into the page. 
     One embodiment of a fiber optic ferrule  100  according to the present invention is illustrated in  FIGS.  1 - 10   . The fiber optic ferrule  100  has a main body  102 , the main body  102  may have a first portion  104  and a second portion  106 . The main body  102  has a front end  108 , a rear end  110 , and a top surface  112  and a bottom surface  114 , the top surface  112  and the bottom surface  114  being joined by opposing side surfaces  116  and  118  (see  FIG.  2   ). The fiber optic ferrule may also include a larger rear end with a shoulder  120 , but the shoulder  120  could be eliminated and still fall within the scope of the present invention. The second portion  106  may include some of the top surface  112 , the larger rear end  110 , and the shoulder  120 , if present. The main body  102  has a longitudinal axis A extending between the front end  108  and the rear end  110 . In a central opening  122  within the main body  102  (and partially formed by the first portion  104  and a second portion  106  if there are two portions rather than a single element) are a plurality of optical fiber support structures  124 . The optical fiber support structures  124  are positioned between the front end  108  and rear end  110  and configured to receive a plurality of optical fibers (not shown). The optical fiber support structures  124  may be v-grooves, u-grooves, fiber holes, or any other appropriate structures to hold and guide a plurality of optical fibers within the fiber optic ferrule  100 . While there are  12  spaces provided for in a single row in this fiber optic ferrule  100 , there could be a row of two, four, eight, twelve or sixteen fibers. Additionally, there could also be more than one row of optical fibers. When there are more than one row of optical fibers, the optical fiber support structures  124  are arranged in a stepped format, with one set of structures for one row above/below the other. For example, two rows of the optical fiber support structures  124  would require that an optical axis of the optical beam  132  in the optical fiber support structures  124 , as shown in  FIG.  5    would need to be moved up on the first portion  104  (to the right in the  FIG.  5   ), and then all the features making up that optical axis would be accordingly positioned in  FIG.  5   . For example, either additional front facing refractive surfaces and rear facing refractive surfaces may be provided to correspond to and align with the additional rows of optical fibers. Alternatively, the same front facing refractive surface  140  and the rear facing refractive surface  142  may be utilized with appropriate correction for the variation in the optical path of the optical beams from those additional rows prior to interaction with the front facing refractive surface  140  and the rear facing refractive surface  142 . 
     Since at least the first portion  104  is made of an optically clear material, the optical beams transported by the optical fibers of each of these rows can travel in the manner similar to the optical beam in the optical fibers supported by the optical fiber support structures  124 . 
     The optical fiber support structures  124  preferably extend between at least a portion of the distance between the front end  108  and the rear end  110 . However, as illustrated, the optical fiber support structures  124  extend from the rear end  110  towards the front end  108 , but stop short of the front end  108 . Similarly, the optical fiber support structures  124  may start inward (i.e., more toward the front end  108 ) of the rear end  110 , in which case there is a downward ramp (not shown) immediately behind the optical fiber support structures  124  and all the way to the rear end  110  to aid in placing the optical fibers securely without bending or any obstruction. 
     The fiber optic ferrule  100  also has an end face  130  at the front end  108  through which an optical beam  132  passes. As illustrated in  FIG.  5   , the optical beam  132  is illustrated as entering from the rear end  110  and exiting the front end  108 . However, the optical beam  132  can pass in either direction through the fiber optic ferrule  100 —in a front to rear manner or a rear to front manner and still be within the scope of the present invention. 
     The fiber optic ferrule  100  also has a front facing refractive surface  140  and a rear facing refractive surface  142 . See  FIGS.  4 - 6   . The front facing refractive surface  140  and the rear facing refractive surface  142  are disposed in the optical path  132  of the fiber optic ferrule  100  (and determine the path of the optical beams  132 ), and between the optical fiber support structures  124  and the end face  108 . See  FIGS.  5  &amp;  6   . The rear facing refractive surface  142  is closer to the end face  108  than the front facing refractive surface  140 . The refraction provided by these surfaces  140 , 142  may be in the form of curved surfaces, such as convex lenses, or flat surfaces with refraction being controlled by the angle of the surface. However, such refractive surfaces or lens surfaces in the fiber optic ferrule  100  do not cause total-internal reflection, and have very low back reflection into the optical fibers (i.e., low return loss). The rear facing refractive surface  142  is tilted at an angle to the front facing refractive surface  140 . For example, the rear facing refractive surface  142  may be inclined at an angle of 6.4° to a plane perpendicular to the longitudinal axis A and the front facing refractive surface  140  may be inclined at an angle of 9.5°, also to a plane perpendicular to the longitudinal axis A, but in an opposite direction to the 6.4° angle. This results in the angle α=6.4°+9.5°=15.9°, although there may be a variation in the angle α by ±0.05°. Thus, the front facing refractive surface  140  and the rear facing refractive surface  142  are not orthogonal to the longitudinal axis A and the optical beam  132 . It will be appreciated by one of ordinary skill in the art in view of this patent application that the angle above can be varied to accommodate various optical parameter variations (e.g., change is a material of the first portion  104 , optical path traversed by the optical beams, return loss requirements for the fiber optic ferrule  102 , and the like). 
     The front facing refractive surface  140  and the rear facing refractive surface  142  are disposed on opposite sides of a lens gap  144 . The lens gap  144  may be filled with an index matching material (epoxy) having refractive index similar to that of the core of the optical fibers. Alternatively, the lens gap  144  may simply be empty or have air. If the lens gap has air, there may be an anti-reflective coating on the refractive lens surfaces to reduce the back reflections and insertion loss. Generally, the lens gap  144  forms an optical gap between the front facing refractive surface  140  and the rear facing refractive surface  142 . 
     The front facing refractive surface  140  and the rear facing refractive surface  142  are molded with the remainder of the fiber optic ferrule  100 —meaning that the lenses/reflective surfaces are integral with and formed at the same time as the fiber optic ferrule  100 . As best seen in  FIG.  5   , the front facing refractive surface  140  and the rear facing refractive surface  142  are vertically offset from one another, although in alternative aspects of this disclosure, the front facing refractive surface  140  and the rear facing refractive surface  142  may not be vertically offset. The front facing refractive surface  140  is closer to the bottom surface  114  than the rear facing refractive surface  142 . With the appropriate surfaces and angles, it may be possible that the surface are vertically the same or inverted, with the rear facing refractive surface  142  being closer to the bottom surface  114  than the front facing refractive surface  140 . The rear facing refractive surface  142  and the front facing refractive surface  140  are irregular, and only a portion of the lenses are used to control the direction of the optical beam  132  relative to the longitudinal axis A. Further, the rear facing refractive surface  142  and the front facing refractive surface  140  may be parts of two mathematically different lens surfaces or lenses. The lens gap  144  is preferably filled with an index matching epoxy that matches the optical fiber cores, but it may also remain empty (air-filled). 
     The fiber optic ferrule  100  also has an optical fiber facing surface  150 , the optical fiber facing surface  150  is disposed between the front end of the plurality of optical fiber support structures  124  and the front facing refractive surface  140  and can be used as an optical fiber stop surface. When, as discussed in more detail below, the optical fibers are inserted into the fiber optic ferrule  100 , the optical fiber facing surface  150  can be used as a reference and/or stop surface. To reduce the back reflection the fiber facing surface may be designed to not be orthogonal to the fiber support structures. Between the optical fiber facing surface  150  and the plurality of optical fiber support structures  124  is an optical fiber end face receptacle  152 . The optical fiber end face receptacle  152  is configured to receive the ends of the optical fibers when they are laser cleaved. The ends of the laser-cleaved optical fibers tend have a “mushroom effect” caused by an expansion or swelling of the end of the optical fibers from the heat imparted during laser cleaving. This effect is not present in mechanically-cleaved optical fibers. The optical fiber end face receptacle  152  provides a space for the larger ends of the optical fibers and eliminates any potential for mis-alignment of the optical fibers due to the enlarged ends. In an alternative embodiment, the optical fiber end face receptacle  152  may be optional or absent. The fibers may be cleaved with an intentional angle to reduce the back reflection. 
     The main body  102  may have a first portion  104  and a second portion  106  which allows for easier molding of the fiber optic ferrule  100 . The first portion  104  and the second portion  106  may be made of the same material or may be made of different materials. The second portion  106  includes a portion of the top surface  112  and the shoulder  120 . The second portion  106  can be attached to the first portion  104  in a number of ways, including a friction-fit, the use of adhesives, welding, etc. Optical fibers can be inserted into the fiber optic ferrule  100  from the top when the second portion  106  is removed by placing the optical fibers into the optical fiber support structures  124 . A user can ensure placement within the optical fiber support structures  124  and that the optical fiber ends engage the optical fiber end face receptacle  152 . The optical fibers can be secured within the plurality of optical fiber support structures  124  using an index matching epoxy that matches the optical fiber cores. If the main body  102  does not have two pieces, then the optical fibers can be guided into the plurality of optical fiber support structures  124  from the rear end  110 . The plurality of optical fiber support structures  124  may also be configured to accept smaller diameter optical fibers. For example, the optical fibers could have a smaller diameter (80 μm) or have a pitch (distance between the optical fibers) of less than the standard 250 μm. After the optical fibers are secured within the first portion  104 , the second portion  106  can be attached thereto. 
     The fiber optic ferrule  100  has an end face  130  at the front end  108 . The end face  130  has two guide pins  156  and two guide pin holes  158 . As seen best in  FIG.  1   , on each side of the fiber optic ferrule  100  are one guide pin  156  and one guide pin hole  158 . The guide pins  156  are disposed diagonally across from one another as too are the guide pin holes  158 . As noted below, this allows for the fiber optic ferrule  100  to be mated with another fiber optic ferrule key-up to key-up, or key-up to key-down. That is, due to this diagonal spatial relationship between the two guide pins  156  (and similarly between the two guide pin holes  158 ), the orientation of two identical mating ferrules  100  about their respective longitudinal axes A is irrelevant, as long as the optical beams passing through the exit window  160  follow the same optical path between the two mating ferrules  100 . 
     The end face  130  also has an exit window  160  through which the optical beam  132  passes. See  FIGS.  1  and  4 - 6   . As best seen in  FIG.  6   , the exit window  160  is not orthogonal to the longitudinal axis A or the rest of the end face  130  and is preferably flat. However, it may also have a curvature to it as well. Yet alternatively, the exit window  160  may be orthogonal to the longitudinal axis A (albeit with some added back reflection). The exit window  160  is tilted at an angle θ—preferably ±2.3°, i.e., the angled exit window may tilt in a direction opposite to that shown. The exit window  160  or the end face  130  in general may be coated with an anti-reflection coating to reduce back reflection. The flatness of the exit window  160  allows for easier cleaning of the fiber optic ferrule  100  and also mitigates the effects of any liquid residue between two mating fiber optic ferrules since the exit window  160  is not a lens surface. It also directs the optical beam  132  to be parallel to the longitudinal axis A. The exit window  160  is also preferably located symmetrically within the front end  108  and covers all of the plurality of optical fibers and refractive surfaces  140 , 142  for all of the optical fibers, when viewed in an elevation view from the front end  108 . However, it may be disposed elsewhere at the front end  108  depending on the placement of the other fiber optic ferrule structures on the optical fibers. 
     The structures of the fiber optic ferrules  100  allows for two of the fiber optic ferrules  100  to be mated in a key-up to key-up configuration as illustrated in  FIG.  7   . As noted above with regard to the guide pins  156  and the guide pin holes  158 , two of the fiber optic ferrules could also be mated in a key-up to key-down configuration as illustrated in  FIGS.  8  and  9   .  FIG.  9    shows that internal structures of the fiber optic ferrules allow for the alignment in the key-up to key-down configuration. It should be noted that the fiber optic ferrules  100  could be mated as illustrated. As can be seen in  FIG.  9   , even if one of the fiber optic ferrules  100  were flipped about the respective longitudinal axis A (i.e., to result in the key-up to key-up configuration of  FIG.  7   ), the optical connection would not be affected since the optical beams between the two fiber optic ferrules  100  would still follow the same path. In this sense, the fiber optic ferrules  100  are polarity immune and are self-checking in terms of connecting to each other. 
     However, if polarity is not a concern, then the fiber optic ferrule  100  may not have the diagonally placed hermaphroditic guide pin arrangement, such as the one shown in  FIGS.  1 - 19   . In that case, a single guide-pin and a single guide hole may be provided on either side of the exit window  160  in a central location relative to a vertical plane of the end face  130  (perpendicular to the longitudinal axis A). Yet alternatively, the guide pins may not be integrally molded and may instead be removable metallic guide pins, used with certain other conventional fiber optic ferrules known to one of ordinary skill in the art. 
     In certain applications, the fiber optic ferrules  100  would be first secured within a housing  200  of a fiber optic connector, the housing  200  is illustrated in  FIG.  10   . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.