Abstract:
A ferrule connectable to a fiber optic cable having an exposed portion of a length of optical fiber extending from a protective buffer. The ferrule includes a cylindrical body including an optical fiber bore coaxial with the body which extends longitudinally from a proximal end of the body through a distal end portion thereof sized to slidably receive the optical fiber therethrough. The distal end portion is mechanically deformable to frictionally engage the optical fiber within the bore, the distal end being either conically shaped or including an outwardly extending ring resulting in the distal end being a substantially planar surface, whereby a projecting length of the optical fiber extending beyond the distal end may be cleaved in very close proximity to the distal end.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of application Ser. No. 11/593,828 filed Nov. 7, 2006. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to fiber optic connectors and ferrules therefor and more particularly to an improved ferrule which minimizes subsequent end polishing required after the optical fiber has been mechanically secured within the ferrule. 
   2. Description of Related Art 
   Fiber optic cables are utilized for carrying various forms of signals in countless industrial installations, in equipment and in apparatus, and in consumer and commercial products of all types. Typically, each end of the optical fiber held within a deformable ferrule which is secured within a connector must be polished in a plane generally orthogonal to the length of the fiber optic cable for proper signal transmission to occur with a mating optical fiber element. 
   To accomplish the polishing of the end of the optical fiber, as well as to provide support structure to effect the mechanical engagement between fiber optic cable ends, the fiber optic connector such as that shown in FIGS. 7 and 8 of U.S. Pat. No. 5,305,406 invented by Rondeau and incorporated by reference includes a metallic or deformable ferrule or core 166 mechanically attached around the optical fiber 168 extending from the buffer 232. The ferrule 168 is secured within the surrounding connector 162 for additional stabilizing support of the ferrule 168. An additional metallic sleeve 230 is also provided to interconnect the distal portion of the buffer 232 and the proximal end of the ferrule 168 as best seen in FIG. 8 of the &#39;406 patent. 
   Both the &#39;406 patent and U.S. Pat. No. 6,510,271 invented by applicant herein, disclose apparatus and methodology to reduce the amount of projecting optical fiber which extends beyond the distal tip of the ferrule 168 and to minimize the amount of looseness or side clearance between the optical fiber and the distal end portion of the ferrule 168 after it has been mechanically crimped or swaged around the optical fiber to mechanically secure this relationship. Thereafter, a small amount of the projecting optical fiber and the distal end surface of the ferrule is typically polished substantially flat and orthogonal to the longitudinal axis of the ferrule so as to maximize the signal transmission between polished end surfaces of adjoining optical fiber connections. However, alternate polished distal tip ends such as radiused or tapered for specialized situations, are also used. 
   The current prior art is shown in  FIGS. 1 to 11 . Referring first to  FIGS. 1 to 4 , a number of metallic deformable ferrules which are used in conjunction with the method disclosed in the &#39;406 patent are there shown generally at numerals  1 ,  1   a ,  1   b  and  1   c . This type of ferrule has been utilized for a number of years in standard SMA, ST, SC, and FC connectors as well as in custom fiber optic connectors. These metallic ferrules are normally held at the rear or proximal end portion  9  and  9   c  to the body of a connector previously described in FIGS. 7 and 8 of the &#39;406 patent. The connector itself forms no portion of the present invention and is being described for reference only. 
   Each of these ferrules  1 ,  1   a  and  1   b  include an elongated cylindrical body  3 ,  3   a  and  3   b , respectively, each having a hollow cylindrical interior  10  open at a proximal end thereof to receive an end portion of the buffer or protective sheath around the optical fiber or optical fiber bundle. The exposed optical fiber is inserted through the proximal end  7  of the ferrule body and, with respect to the prior art ferrule embodiment of  FIGS. 1 to 3 , is passed through the cylindrical cavity  10  and is guided by tapered transitional region  11  into and through a longitudinal optical fiber bore  6  to extend longitudinally beyond the distal end  2 . 
   With respect to the prior art embodiment  1   c  of  FIG. 4 , the optical fiber bore  6   c  extends longitudinally through almost the entire ferrule body  3   c  from the tapered transition  11   a  which also defines the proximal opening  7   c  of the proximal end portion  9   c  to the distal end  2   c  of the distal end portion  8   c.    
   After the optical fiber  12  has been inserted through the optical fiber bore  6  as seen in  FIG. 5  with the buffer  12   a  also inserted fully into the cylindrical interior  10 , an impact forming or an impact swaging tool  13  having a truncated conical opening  16  defining a conical or tapered surface  14  and a longitudinal cylindrical bore  15  is brought together against the edge  5  of the distal end portion  8   a ,  8   b  or  8   c  of  FIGS. 1 to 4 , to mechanically deform the reduced diameter distal end portion  4  so as to mechanically crimp and frictionally engage the optical fiber  12  within the deformed bore  6 ′ in  FIG. 6 . Note in  FIG. 5  that the distal end  2  is initially flat and orthogonal with respect to the longitudinal axis and bore  6  of the ferrule  50  itself. 
   In  FIG. 6 , the tool  13  has been forcibly urged against the outer distal corner  5  of the now deformed distal end portion  4 ′ so as to cause inward deformation of this region at  17  of the ferrule in compliance against the tapered surface  14 . Several deformations occur during this impact swaging or impact forming operation, the first of which is that the outer corner  5  are severely deformed inwardly so as to at least partially collapse the bore  6 ′ in the region  18 . The deformable material of the ferrule at deformed surface  17  causes tightening around the optical fiber  12  in the region  18  to reduce and eliminate any clearance which has been pre-established by the sizing between the diameter of the optical fiber  12  and that of the undeformed bore  6 , now  6 ′ when deformed. Additionally, the previously flat distal end  2  has now taken a dish or crater configuration  19  with the distal end portion of the optical fiber  12  extending longitudinally therebeyond. Typically, the length of the optical fiber gripping region  18  is in the range of 0.2 mm, creating a frictional resistance to movement of the optical fiber  12  in the range of approximately 400 gms. 
   The depth of the concaved crater  19  as referenced in  FIG. 7  is in the range of 0.1 mm and obviously will increase in proportion to the amount of force exerted by tool  13 . The excess projection of the optical fiber  12  must be removed before the end polishing operation is commenced. To do this, typically the optical fiber  12  is cleaved at cutting line  20   a  in  FIG. 7 . However, the cleaving operation is typically only able to sever the optical fiber  12  in a range of approximately 0.05 mm at  20   a  from the edges of the crater  19 . Thereafter, an end grinding and polishing operation must reduce the remaining exposed portion of the optical fiber  20   a  in  FIG. 8 . Manual cleaving or the use of a cleaving device such as that shown in the &#39;271 patent may be utilized after the optical fiber  12  has been cleaved to establish distal end  2   d . The projecting small portion of optical fiber  12 , along with the crater  19  must be ground or sanded and polished down to the bottom of the crater at  21  to create preferably a substantially flat orthogonal surface as best seen in  FIG. 11 . During the grinding or sanding and polishing operation, a lateral force in the direction of the array of arrows shown in  FIG. 10  is imposed along the gripping area  18  between the optical fiber  12  and the deformed bore  6 ′. As a result, the gripping force in gripping region  18  may be reduced by as much as 50% or more or even totally lost, rendering the ferrule unusable. Moreover, the overall length of this gripping region  18  may be reduced if excess material from the ferrule as well as the optical fiber  12  is removed inadvertently or carelessly during this polishing operation. The variables which affect the overall quality of this gripping force in this prior art arrangement are controlled by the impact of the swaging die process shown in  FIG. 6 , the reduced diameter of the deformable tip  4 , and the angle of the conical surface  14  of the swaging tool  13 . 
   BRIEF SUMMARY OF THE INVENTION 
   This invention is directed to a ferrule connectable to a fiber optic cable having an exposed portion of a length of optical fiber extending from a protective buffer. The ferrule includes an elongated cylindrical body having a substantially hollow longitudinally extending cylindrical interior open at a proximal end thereof adapted in size to receive an end portion of the buffer. An optical fiber bore coaxial with the hollow interior extends longitudinally through a distal end portion of the body sized to snugably slidably receive the optical fiber passing therethrough. The distal end portion is mechanically inwardly deformable to frictionally engage the optical fiber within the bore, the distal end being either conically shaped having a cone angle such that the distal end is also deformed into a substantially planar surface or the end portion including an outwardly extending ring whereby a projecting length of the optical fiber extending beyond the distal end may be cleaved in very close proximity to the distal end. 
   It is therefore an object of this invention to provide a fiber optic ferrule with enhanced optical fiber retention characteristics. 
   Yet another object of this invention to provide a ferrule which substantially reduces the cost of the after-assembly polishing process of the end of the ferrule/optical fiber end configuration. 
   Still another object of this invention is to provide a fiber optic ferrule which, by design choice, facilitates selected location of the mechanical gripping force region for enhanced optical fiber retention within the ferrule. 
   Yet another object of this invention is to provide a fiber optic ferrule which is substantially less impervious to loosening of the optical fiber after mechanical assembly thereof to the ferrule during final end polishing operations. 
   And another object of this invention is to provide a fiber optic ferrule which, when mechanically deformed to establish permanent connection with an optical fiber therewithin, substantially reduces the projected length of the optical fiber remaining for polishing removal after cleaving of the excess optical fiber from the distal end of the assembly. 
   In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
     Prior Art 
       FIGS. 1 to 4  are longitudinal section views of typical metallic deformable prior ferrules for use in conjunction with a fiber optic cable. 
       FIG. 5  is an enlarged exploded view of the distal portion of the prior art ferrule embodiment of  FIG. 1  in relation to an impact deforming or swaging tool. 
       FIG. 6  is a view of  FIG. 5  showing the tool after deforming impact with the distal end of the prior art ferrule. 
       FIG. 7  is a view of  FIG. 6  with the tool removed. 
       FIG. 8  is a view of  FIG. 7  after cleavage of the projected distal portion of the optical fiber. 
       FIG. 9  is an enlarged view of the distal end portion of  FIG. 8 . 
       FIG. 10  is a further enlarged view of  FIG. 9  showing the ferrule material required to be removed as shaded. 
       FIG. 11  is a view of  FIG. 9  after polishing of the distal end thereof has been accomplished. 
     The Instant Invention 
       FIG. 12  is an enlarged section view of a distal end portion of one embodiment of the ferrule of the present invention with the fiber optic cable in place ready for assembly. 
       FIG. 13  is a view of  FIG. 12  after mechanical deformation of the distal tip portion around the optical fiber. 
       FIG. 14  is a view of  FIG. 13  after cleavage of the projecting portion of the optical fiber beyond the distal end of the ferrule. 
       FIG. 15  is an enlarged partial section view of the distal tip portion of another embodiment of the invention with the optical fiber cable in position prior to assembly. 
       FIG. 16  is a view of  FIG. 15  showing the deforming tool at the point of impact with an outwardly laterally projecting ring or bead formed as a part of the distal tip portion. 
       FIG. 17  is a view of  FIG. 16  at the maximum impact of the deforming tool against the distal end portion of the ferrule. 
       FIG. 18  is an enlarged view of the deformed ferrule and optical fiber of  FIG. 17 . 
       FIG. 19  is a view similar to  FIG. 15  of still another embodiment of the invention. 
       FIG. 12A  is an alternate embodiment of  FIG. 12   
       FIG. 19A  is an alternate embodiment of  FIG. 19 . 
       FIG. 20  is a section view similar to  FIG. 19  showing the deforming tool at the point of impact with an outwardly laterally projecting annular ring or bead formed as a part of the distal tip portion. 
       FIG. 21  is a section view of  FIG. 20  at the maximum impact of the deforming tool against the distal end portion of the ferrule. 
       FIG. 22  is a view similar to  FIG. 15  of still another embodiment of the invention. 
       FIG. 23  is a view similar to  FIG. 15  showing yet another embodiment of the invention. 
       FIG. 24  is a view similar to  FIG. 15  showing yet another embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIGS. 12 to 14 , the preferred embodiment of the invention is there shown generally at numeral  110 . This ferrule  110  includes the elongated cylindrical body having the hollow cylindrical interior  10  similar to the previously described conventional deformable ferrules. This embodiment  110  includes the reduced-in-diameter distal end portion  4  having a longitudinally extending optical fiber bore  6   b  adapted in size to slidably receive the optical fiber  12  which extends beyond the buffer  12   a  or the protective sheath of the fiber optic cable. This embodiment  110  also includes a tapered transition zone  11  which greatly enhances guiding of the distal tip of the optical fiber  12  into and through the optical fiber bore  6   b.    
   The distal end  22  of the ferrule  110  is uniquely configured initially as will be described with respect to  FIGS. 13 and 14  having a very broad non-flat conical configuration with a cone angle C generally equal to in the range of 170°-179°, preferably 174°. As seen in  FIG. 13 , after the mechanical deformation of the distal corners  23  by the utilization of the deforming tool (not shown as repetitive) against the undeformed distal end portion  4 , the distal corners  23  thus inwardly deform into a tapered truncated cone matching the deforming conical surface of the deforming tool so that the deformable bore tightly binds against the optical fiber  12  and in a manner which leaves the distal end  22 ′ as nearly a flat surface. Then, as seen in  FIG. 14 , the cleaving of the protruding portion of the optical fiber  12  is easily accomplished in very close proximity to the distal end  22 ′, leaving only a very small exposed optical fiber segment D in the range of just a few micrometers from the substantially flat distal end  22 ′. Thereafter, polishing for maximum signal transmission from cable to cable is easily and quickly accomplished. 
   Referring now to  FIG. 12A , an alternate embodiment of that shown in  FIG. 12  is there shown generally at numeral  115 . In this embodiment  115 , the first variation of shoulders of the reduced diameter distal end portion  102  are similar to that described in  FIG. 3  at  3   b . Further, this embodiment which also includes longitudinal bore  6  as previously described for receiving the optical fiber  12 , continues concentrically through the entire cylindrical body  104  absent the transition  11  and hollow cylindrical interior  10 . By this structure, only the optical fiber  12  extends through the entire cylindrical body  104 . 
   This embodiment  115  again includes the reduced in diameter distal end portion  102  and the very broad non-flat conical configuration of the distal end  108  as previously described with respect to  FIG. 12 . 
   Referring now to  FIGS. 15 to 17 , another embodiment of the invention is there shown generally at numeral  120  and, again, this improved ferrule  120  includes the elongated body (not shown) which defines the hollow cylindrical interior  32  for receiving the buffer  12   a , the protruding length of optical fiber  12  inserted through the longitudinally extending optical fiber bore  38  in a fashion as previously described. 
   To accomplish the two-fold objectives of the present invention, i.e., (a) end up with a substantially flat distal end surface  30  after the deformation of the reduced-in-size distal end portion  24  which (b) tightly secures the optical fiber  12  within the bore  38 , a triangular in section outwardly extending preferably annular ring or band  26  is provided formed preferably as an integral part of the reduced-in-size distal end portion  28  of the ferrule  120 . Once the buffer  12   a  and the optical fiber  12  are inserted into the ferrule  120  as shown in  FIG. 16 , the deforming tool  34  with its conically tapered surface  36  is impacted against these triangular rings  26  which radially inwardly deform as shown in  FIG. 17 . 
   As better seen in  FIG. 15 , the undeformed triangular band  26  have an outwardly extending dimension H and an offset from the distal end  30  of G. By this arrangement as seen in  FIG. 18 , an inwardly exerted force distribution E in the direction of arrows  42  clampingly engage around the cylindrical optical fiber  12  at a spacing from the distal end  30  selected by dimension G. Likewise, the degree of compression or retention force  42  exerted to securely retain the optical fiber  12  in the deformed bore  38 ′ as determined by the outward protrusion H of the triangular ring  26  may easily be varied to accomplish a desired level of optical fiber retention. 
   Once the deformation of these triangular ring  26  into the configuration  26 ′ shown in  FIGS. 17 and 18  is accomplished, cleavage of the protruding portion of the optical fiber  12  is accomplished at  40  in very close proximity to the flat distal end  30 , leaving only a minimal amount of polishing of the end surface  40 , the distal end  30  remaining substantially flat and orthogonally oriented to the longitudinal axis of the ferrule itself. 
   It is here noted that the diameter of the bore  38  is generally selected to be slightly larger than the outside diameter of the optical fiber  12  to allow sliding translation installation therebetween and to allow for the bore deformation to occur into the configuration shown in  FIG. 18 . 
   Another embodiment of the invention is shown at numeral  130  in  FIGS. 19 to 21 . In this ferrule embodiment  130 , the distal end portion  50  includes a tapered portion  52  and a triangular laterally or radially outwardly extending annular ring  54  positioned on the tapered portion  52  which is established at a conical angle F of preferably less than 30° or more preferably in the range of about 20°. 
   This conical angle F generally is equal to the taper  60  of the deforming tool  58  so as to provide an even more uniform inward deformation of the ring  54  as seen in  FIG. 21 . The deformed triangular ring  54 ′ and the slightly compressed tapered portion  52 ′ greatly enhance the strength of retention of the optical fiber  12  within the compressed and deformed bore  64 ′ around the optical fiber  12 . As in previous embodiment  120 , this embodiment  130  also leaves the distal end  56  in a substantially flattened configuration and orthogonally oriented to the longitudinal axis of the ferrule  120  thus facilitating close cleavage of the protruding portion of the optical fiber  12  and requiring minimal polishing thereafter for maximum signal transmission. 
   Referring now to  FIG. 19A , an alternate embodiment of  130  is there shown generally at  135 . In this embodiment  135 , substantially all of the structure and description with respect to  FIG. 19  is reiterated except that the main cylindrical body  132  is of a diameter substantially equal to that of the beginning diameter of taper  135 . A cylindrical bore  142  designed and configured to slidably receive the optical fiber  12  entirely therethrough is provided in this embodiment  135  and, as with respect to embodiment  130  in  FIG. 19 , the distal end  136  is in a substantially flattened configuration and orthogonally oriented with respect to the longitudinal axis of the main body  132  thus facilitating close cleavage of the protruding portion of the optical fiber  12 . 
   Three additional embodiments of the radially outwardly extending annular ring concept of the invention are shown in  FIGS. 22 ,  23  and  24 . In  FIG. 22 , this embodiment  140  includes trapezoidally configured radially outwardly extending ring  68  integrally formed with the cylindrical reduced-in-diameter distal portion  66 . The smaller length  70  of the distal portion  66  positioned between the ring  68  and the distal end  72  of the ferrule  140  is preselected in longitudinal position so that a desired distribution and location of clamping forces of bore  76  as described in  FIG. 18  against the optical fiber  12  is accomplished. As in previous embodiments, the buffer  12   a  is provided for within the hollow cylindrical interior  74 . 
   In  FIG. 23 , this embodiment  150  includes an orthogonally configured radially outwardly extending ring  82  formed as a part of the reduced-in-diameter distal portion  80 , a small amount of which at  84  is provided to achieve a particularly desired clamping location and distribution against the optical fiber  12  when inward deformation of the bore  88  distal end portion and the ring  82  is accomplished. The cylindrical hollow interior  90 , again, accommodates the buffer  12   a.    
   Lastly, in  FIG. 24 , a semi-circular in cross section annular ring  94  is provided which outwardly extends from the distal portion  92  leaving a small distal portion  96  spaced from the distal end  98 . The optical fiber  12  extends through the longitudinal bore  100  as previously described in sliding fashion so that the deformation of the ring  94  will collapse the bore  100  slightly, resulting in the desired degree and tightness distribution of the clamping forces for optical fiber retention. 
   While the instant invention has been shown and described herein in what are conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein, but is to be afforded the full scope of the claims so as to embrace any and all equivalent apparatus and articles.