Patent Publication Number: US-2010127034-A1

Title: Optical Fiber Cleave Tool

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of provisional application Ser. No. 60/914,416 filed Apr. 27, 2007, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to cleaving optical fibers, and more specifically to a method and apparatus for cleaving an optical fiber with a cutting motion. 
     2. Discussion of the Background 
     For efficient light transmission from a terminal end surface (end face) of an optical fiber, the end face should be flat, perpendicular to the axis of the fiber, and provided with a smooth finish to provide the maximum optical transmission area on the fiber end face and to minimize light losses resulting from reflection and refraction of the light. 
     Most commercially available cleave tools for optical fibers perform well only if the glass optical fiber has had it&#39;s polymer coating (also known as “buffer” in some cases) removed. Most commercially available cleave tools for optical fiber utilize a method of initiating a cleave propagation point by means of a scribing motion or a direct force normal to the longitudinal axis of the optical fiber. For example,  FIG. 7  shows a conventional cleaving method using a scribing motion. As seen in this figure, a glass optical fiber  810  (having its coating removed) is held, and a blade  820  is moved in the direction of the arrow in  FIG. 7  such that the blade cutting, surface  822  is made to contact the fiber  810  at a scribe point  812 .  FIG. 8  shows a conventional cleaving method using a direct force normal to a longitudinal axis of the optical fiber. As seen in  FIG. 8 , the glass optical fiber  910  having its coating removed is held and a cleaving blade  930  is moved in a linear direction of the arrow in  FIG. 8  to provide a direct force normal to the fiber  910 . The cleaving blade comes in contact with the fiber  910 , and the cutting surface  932  of the cleaving blade  930  initiates a crack that propagates through the optical fiber  910 . 
       FIG. 9  shows a conventional method for cleaving a coated optical fiber without the need to remove the coating. As seen in this figure, the optical fiber  1010  includes a glass optical core  1012  and a coating  1014  such as a polymer coating. The optical fiber  1010  is held while a cleaving tool  1020  is moved in a direction of the arrow in  FIG. 9  to provide a direct force normal to a longitudinal axis of the fiber  1010 . This force causes the cleaving blade  1022  to penetrate the coating and reach the glass surface to initiate cleaving of the glass. For example, U.S. Pat. No. 5,108,021 shows a method for cleaving an optical fiber wherein the cleaving blade penetrates the coating until it reaches the glass surface so that it can initiate the cleave in the glass. The entire content of U.S. Pat. No. 5,108,021 is incorporated herein by reference. A cleave tool of this type (for example DT03130-03 provided by OFS Fitel, LLC, “OFS”, which is a wholly owned subsidiary of Furukawa Electric North America) has been used for cleaving optical fibers such as the CF01493-10 fiber (also provided by OFS). The CF01493-10 fiber includes a medium NA HCS® polymer coated silica optical fiber having mechanical properties, such as a relatively hard polymer coating, which allow the cleave tool such as that shown in  FIG. 9  to provide a direct force sufficient to penetrate the HCS® coating and reach the glass optical fiber surface to successfully initiate the cleave in the glass. 
     The present inventors have recognized, however, that there are occasions when the glass optical fiber has a polymer coating which obstructs the cleave blade from reaching the glass surface in a timely manner; if at all. Such polymer coatings may, for example, have characteristics (i.e. harder, softer, thicker wall, etc.) which cause the direct force normal to longitudinal blade motion to not perform well. For example, new high bandwidth optical fibers such as the F14404 fiber manufactured by OFS include a non-optical polymer coating that behaves differently than the medium NA HCS® optical fiber when a force is applied normal to the fiber axis as shown in  FIG. 9 . 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to address the above and/or other issues relating to cleaving optical fibers. 
     One embodiment of the invention includes a method for cleaving an optical fiber, the method including supporting a connector in a fixed axial position along an axis of an optical fiber extending from an end of the connector, and placing an axial tension along the axis of the optical fiber. A fiber engaging member is moved along an arcuate path such that a sharpened blade tip of the fiber engaging member cuts across a cut location of the optical fiber, whereby the axial tension induces crack propagation through the thickness of the optical fiber at the cut location. 
     In another embodiment, a cleaving tool for cleaving an optical fiber includes a cleaving assembly configured to support a connector in a fixed axial position along an axis of an optical fiber extending from an end of the connector, the cleaving assembly including a fiber engaging member having a sharpened blade tip. A fiber tensioning assembly is configured to place an axial tension along the axis of the optical fiber. The fiber tensioning assembly including an actuator member configured to actuate the cleaving assembly and the fiber tensioning assembly such that the fiber engaging member is moved along an arcuate path and the sharpened blade tip cuts across a cut location of the optical fiber, whereby the axial tension induces crack propagation through the thickness of the fiber at the cut location. 
     In still another embodiment, a cleaving tool for cleaving an optical fiber includes a cleaving assembly configured to support a connector in a fixed axial position along an axis of an optical fiber extending from an end of the connector, the cleaving assembly including a fiber engaging member having a sharpened blade tip. Also included is a fiber tensioning assembly configured to place an axial tension along the axis of the optical fiber, the fiber tensioning assembly including an actuator member configured to actuate the cleaving assembly and the fiber tensioning assembly. Means are provided for moving the fiber engaging member along an arcuate path such that the sharpened blade tip cuts across a cut location of the optical fiber, whereby the axial tension induces crack propagation through the thickness of the fiber at the cut location. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  shows a perspective view of a cleaving tool in accordance with an embodiment of the present invention; 
         FIG. 2  shows details of the cleaving assembly  200  in accordance with the embodiment of the invention; 
         FIGS. 3A and 3B  show movement of a fiber engaging member relative to an optical fiber in accordance with an embodiment of the invention; 
         FIGS. 4A ,  4 B and  4 C show progressive stages along the radial movement of a blade tip in accordance with an embodiment of the invention; 
         FIG. 5  shows a cleaving assembly having an adjustable fiber engaging member in accordance with one embodiment of the invention; 
         FIG. 6  shows a fiber engaging member according to another embodiment of the invention; 
         FIG. 7  shows a conventional cleaving method using a scribing motion to scribe an optical fiber having a coating removed therefrom; 
         FIG. 8  shows a conventional cleaving method using a direct force normal to a longitudinal axis of the optical fiber having a coating removed therefrom; and 
         FIG. 9  shows a conventional method and device for cleaving a polymer coated optical fiber without the need to remove the coating. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As discussed above, conventional methods of cleaving an optical fiber either require removal of a polymer coating from the optical fiber before cleaving the optical fiber, or are unsuitable for some polymer coated optical fibers. Embodiments of the present invention provide different blade motions compared to the direct three normal to the longitudinal axis motion, which essentially pushes the blade through the polymer coating until the sharp edge of the blade reaches the glass and initiates a cleave in the glass. Specifically, embodiments of the invention provide a cut action through the polymer coating to allow the blade to reach the glass surface more quickly and more effectively. As used herein, the term “cut” refers to providing relative movement of an optical fiber substantially along a surface of the blade. The relative movement may be provided by moving the blade, or the fiber, or both the blade and the fiber. 
       FIG. 1  shows a perspective view of a cleaving tool in accordance with an embodiment of the present invention. As seen in this figure, the cleaving tool  10  includes a fiber tensioning assembly  100  and a cleaving assembly  200 . The fiber tensioning assembly  100  includes an actuator mechanism  150  for activating the fiber tensioning assembly, and for activating the cleaving assembly  200  to cleave an optical fiber, as will be further discussed below. The fiber tensioning assembly  100  includes a tensioning mechanism (not shown) for tensioning an optical fiber to be cleaved. The tensioning mechanism places a fiber under an axial tension to the fiber prior to cleaving. The amount of tension placed on the fiber is preferably adjustable. For small fibers, a small amount of tension is provided to prevent severing of the fiber in an undesirable location due to high tensile stress. For larger fibers, a larger tension is provided to the fiber prior to cleaving. The amount of tension provided on the fiber can depend on a variety of factors, including size of the optical fiber. For example, with a fiber having a glass diameter of 200 μm such as the F14404 OFS fiber noted above, the tension is preferably in the range of 0.6-0.8 lbf. (pound-force). However, other tension ranges may be used based on characteristics and application of the fiber. Tensioning mechanisms are known in the art and shown, for example, in U.S. Pat. No. 5,108,021, which is incorporated herein by reference. 
       FIG. 2  shows details of the cleaving assembly  200  in accordance with an embodiment of the invention. In  FIG. 2 , the fiber tensioning assembly  100  is removed to reveal portions of the cleaving assembly  200 . As seen in  FIG. 2 , a connector  300  is installed on an optical fiber  400  and is held against length wise movement by an interchangeable connector positioning plate  210  of the cleaving assembly  200 . As used herein, the term “optical fiber” refers to any known type of optical fiber having a light guiding core of glass, fused silica or other material capable of transmitting a light signal. The core typically has a cladding with a material having a lower index of refraction than the light-guiding core, thereby enabling non-parallel light rays to be reflected at the core/cladding interface and propagate through the length of the core. One example optical fiber that may be cleaved in accordance with embodiments of the present invention is the F14404 fiber, manufactured by OFS and having a 62.5 μm glass core, a 200 μm glass clad and a 230 μm non-optical HCS® coating. 
     An aperture is formed in the plate  210  to receive the body of the connector  300 , e.g., the ferrule  350 , and the connector positioning plate  210  and aperture cooperate to hold the connector  300  and fiber  400  in a fixed axial extending position. Precision optical fiber connectors are used to effect alignment and abutting engagement of an optical fiber end face with a subsequent optical fiber or fiber optic device. As used herein, the term “optical fiber connector” is intended to refer to a terminal end connection for installation on the end of an optical fiber, typically comprising a ferrule mounted on the fiber against length wise movement and a fastening member to effect aligned connection of the ferrule and included fiber to an optical component or subsequent connector. Connectors are available having ferrules and fastening members of various sizes and shapes depending on the intended use of the connector. The terminal end of the ferrule aligned with the fiber end face is considered to be the “connector end.” Example connector components that may be used in accordance with embodiments of the present invention are the Straight Tip (ST) BP05062-10 sub-assy and BP00147-01 crimp ring, and the Sub-Miniature A (SMA) BP05059-10 sub-assy and BP00147-01 crimp ring, both known to those skilled in the art of optical connectors. 
     In accordance with embodiments of the invention, the connector is held and a fiber extending therefrom is tensioned adjacent to a fiber engaging member which scribes the fiber to initiate cleaving of the optical fiber substantially flush with the connector end. The resultant fiber end face is substantially perpendicular to the axis of the fiber, and preferably has a finish that does not require subsequent treatment to provide the desired smooth end face. In the embodiment of  FIG. 2 , the cleaving assembly includes a pair of levers  220 ,  230  supported for pivotal movement on a pair of pivot points shown by pivot holes  222 ,  232 . The pivot holes  222  and  232  are configured to receive pivot pins (not shown), about which the levers  220  and  230  can pivot respectively. The lever  230  is suitably configured to support a fiber engaging member  234  for engagement with the fiber  400  adjacent to the end of the connector  300 . In one embodiment, each lever  220 ,  230  may slightly move in an axial direction on pivot pins provided within the pivot holes  222 ,  232  to adjust in response to variations in the length of the ferrule  350 . Further, while  FIG. 2  shows both levers provided with pivot holes it is not necessary for both levers to pivot. For example, in one embodiment, the lever  220  airy be held in a fixed position while the lever  230  pivots to move relative to the lever  220 . 
     The fiber engaging member  234  includes a sharpened blade tip  236 , which is sufficiently ship to scribe an optical fiber. As used herein, the term “scribe” refers to a score or scratch in the surface of a glass clad optical fiber, or a cut through a polymer cladding mid score or scratch in the fiber core surface, wherein crack propagation is induced at the scratch or score location through the thickness of a fiber under axial tension. 
     In the embodiment of  FIG. 2 , the levers  220 ,  230  are engaged by lifting tabs  242 ,  244  formed on a floating swivel plate  240 . The swivel plate  240  is also mounted for pivotal movement to a plunger  250  by a dowel (not shown), for example, that can be received in hole  252 . The cleaving assembly  200  is activated by applying a force to the bottom surface  254  of the plunger  250 , which force is transferred by the swivel plate tabs  242 ,  244  to the levers  220 ,  230  for pivoting the levers about the pivot holes  222 ,  232 . The unique floating arrangement of the swivel plate  240  on the plunger  250  in  FIG. 2  forms a compensating linkage which ensures that the force exerted on the plunger bottom surface  254  is equally divided between the levers  220 ,  230 . Therefore, during activation of the cleaving mechanism  200 , the levers  220 ,  230  move in substantially equal and opposite directions toward the fiber. This floating arrangement allows the cleaving mechanism to work, equally as well over a wide range of fiber diameters. In one embodiment, fibers having a diameter in the range of 200 μm to 600 μm cleaved successfully. However, the cleaving method and apparatus of the present invention may be used for fibers smaller than 200 μm and larger than 600 μm in diameter. For example, fibers having a diameter in the range of 100 μm to 1050 μm may be cleaved according to the cleaving method and apparatus of the present invention. Further, as noted above, movement of both levers is not necessary for embodiments of the invention. 
     Aligned recesses  224  may be formed in the levers  220 ,  230  (shown only in the lever  220 ) for receiving a return spring (not shown), which opposes the force of the plunger  250 , thereby separating the levers  220 ,  230  when no force is exerted on the plunger  250 . Additionally, an aperture  226  is formed in lever  220  for receiving a set screw (not shown), which is positioned between the levers to contact the other lever  230  during activation of the cleaving assembly to limit the travel range of the blade tip  236 , as will be further described below. Blade adjustment screw  570  provides for adjusting the position of the fiber engaging member  234  and blade tip  236 , as will also be described below. 
     Operation of the cleaving tool  10  is described with respect to  FIGS. 1-2  and  3 A- 3 B. The cleaving tool  10  is gripped by a user preferably on a handle (not shown) with the operator&#39;s thumb free. Connector  300  is carefully inserted into the plate positioning connector  210  of the cleaving assembly  100  until it bottoms out, and the length of fiber  400  extending from the end of the connector  300  is positioned within the fiber tensioning assembly  100 . The operator then presses on the actuator mechanism  150  with his/her thumb, activating the tensioning assembly  200 . Continued movement of the actuator mechanism  150  will cause a force on the bottom surface  254  of the plunger  250  of the cleaving assembly  200 . The force is substantially equally divided between the levers  220 ,  230  by the pivot plate  240 , and the levers  220 ,  230  pivot about the pivot holes  222 ,  232 . This causes the fiber engaging  234  and the blade tip  236  to move along a substantially arcuate path represented by the arrow in  FIG. 3A , and in contact with the fiber  400  approximately flush with the end of the connector  300 . Such arcuate path may also be provided by pivoting only the lever  220 , for example. 
       FIG. 38  shows details of the fiber  400  in relation to the blade tip  236 . As seen in this figure, the fiber  400  includes an optical glass core  410  and a glass cladding  420  surrounding the core  410 . A polymer coating  430  further surrounds the glass cladding  420 . An example optical fiber having a structure as shown in  FIG. 3B  is the F14404 fiber manufactured by OFS. When the blade tip  236  moves along the substantially arcuate path as represented by the arrow in  FIG. 3B , the blade tip  236  penetrates the polymer coating  430  and scribes the cladding  420  of the optical fiber  400  at a scribe location. This action induces crack propagation through the cladding  420  and core  410  of the optical fiber  400  at the scribe location due to the axial tension on the fiber  400 . As noted above, a set screw (not shown) limits the arcuate travel range of the blade tip  236 , which is selected to ensure effective crack propagation without damaging the fiber or unnecessarily wearing the blade tip  236 . Upon release of the activation mechanism  150 , a spring (not shown) forces the actuator mechanism  150  back into its original position shown in  FIG. 2 , and a return spring forces the levers  220 ,  230  (or only  220 , for example) to pivotally return to their original separation position shown in  FIG. 2 . 
       FIGS. 4A ,  48  and  4 C show progressive stages along the arcuate movement of a blade tip in accordance with an embodiment of the invention. As seen in  FIG. 4A , the blade tip  236  approaches the fiber  400  in a direction shown by the arrow in this figure. As seen in  FIG. 4B , the position of the blade tip  236  is set such that a leading edge of the blade tip  236  (the corner of the fiber engaging member  234  that first approaches the fiber) does not contact the fiber  400 . Specifically, the movement path of the fiber engaging member  234  is set, for example by position of the pivot hole  232  in the lever  230  and the blade adjustment screw  570  such that only the blade tip  236  contacts the fiber  400 . Further movement of the blade tip along its arc brings the blade tip  236  in contact with the fiber  400  as shown in  FIG. 4C  to cut a polymer coating and initiate cleaving of the optical fiber  400 . A set screw, as noted above, can be used to limit the travel range of the fiber engaging member  234  and blade tip  236 . In a preferred embodiment the set screw will prevent the trailing edge of the fiber engaging member  234  (the corner of the fiber engaging member  234  that first approaches the fiber last) will not pass the optical fiber. 
       FIG. 5  shows a cleaving assembly having an adjustable fiber engaging member in accordance with one embodiment of the invention. As seen in this figure, the cleaving mechanism  500  includes similar components to those described in  FIG. 2 , the description of which is not repeated. The lever  530  includes a threaded bore  560  for receiving a blade adjusting screw  570  therein, and a pin screw hole  580  for receiving screw that fixes fiber engaging member  534  to the lever  530 . Rotation of the blade adjusting screw  570  moves the blade adjusting screw along the arrow  590 . The fiber engaging member  534  includes a slot  538 , which allows the fiber engaging member and the blade tip  536  to move along arrow  595 . An end of the blade adjusting screw  570  engages an end of the movable fiber engaging member  534  such that rotation of the blade adjusting set screw will move the blade tip  536  in relation to the fiber  400 . Thus, the blade tip  536  can be adjusted to achieve the movement path shown in  FIGS. 4A-4C , for example. 
     According to one method of adjusting the blade tip  536 , a connector is inserted into the cleaver tool such as the cleaver tool of  FIG. 1 , with the fiber protruding from the ferrule. The fiber engaging member  534  is initially set to its farthest position from the fiber, and the operator activates the actuator member and observes motion of the blade tip  236 , which should swing past the fiber without contacting it. The blade adjustment screw  570  is used to push the fiber engaging member  534  and blade tip  236  toward to fiber, and the user repeats activation of the actuator member until the blade tip  236  cleaves the fiber. Preferably, the fiber engaging member  534  is positioned such that blade tip  236  comes in contact with the optical fiber glass core at a center of the blade cutting surface. The screw (provided in hole  580 ) fixing the fiber engaging member  534  to the lever  530  must be loosened prior to adjustment, and must be tightened again to lock the fiber engaging member  534  and blade tip  236 . 
     Thus, according to the embodiments of  FIGS. 1-5  of the present invention, the outer coating of the optical fiber is penetrated and the glass optical fiber is scribed by the blade tip cutting across the optical fiber. The present inventors have recognized that this movement of the blade can provide effective and efficient cleaving of a wide range of optical fiber types without the need to remove a coating of the fiber. For example, this cutting motion is more effective in cleaving the F14404 fiber manufactured by OFS, than conventional cleaving tools that provide a force normal to an axis of the fiber. 
     As will be appreciated by one skilled in the art, in the embodiments described above, as the blade tip cuts across the fiber a greater force is applied by the blade tip to the fiber. The inventors recognized that this may impede the cutting action and/or damage the optical fiber during the cleaving operation. To provide minimum force to keep the coating from pushing the blade around a pivot point, a spring may be utilized.  FIG. 6  shows a fiber engaging member according to another embodiment of the invention. The fiber engaging member  710  includes a first portion  712  coupled to a second portion  714  by a spring  716 . The second portion  714  of the fiber engaging member  710  includes a tapered blade tip  718  and a pivot point  719  such that the blade introduces an arcuate motion when cleaving the fiber. When the blade tip  718  makes contact with the fiber  720 , the blade tip  718  first cuts the polymer coating  722  and then scribes the glass optical core  724  to initiate cleaving of the fiber  720 . The spring  716  biases the second portion  714  of the blade tip  718  to control a contact force with the fiber  720  as the second portion  714  rotates about the pivot point  719  to provide a compound motion of the blade. Controlling the contact force of the blade against the fiber can provide better optical coupling characteristics from the cleaved fiber, and may further minimize the precision necessary from adjusting the blade tip. For example, providing the compound motion of the blade can enhance the cutting action of the blade to facilitate the blade cutting through the coating  722  and reaching the glass core  724 . 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein. For example, the invention is illustrated as being used with a fiber having a connector installed intermediate its length; however, the invention will work equally as well with a fiber not having a connector installed which is directly held against length wise movement by the positioning plate.