Abstract:
A new fiber optic cable splice for splicing optical fiber cables together and reconstructing fiber-optic cable that provide substantially enhanced reliability and broadened operating temperature range is disclosed. The disclosed cable splice offer reliable and user friendly solutions to applications in many harsh environments such as avionics, field vehicles, and defense related instrumentation. The cable splice consists of a preassembled one piece splice core and outer mechanical and thermal shielding layers. A simple splicing procedure and key fixtures are also disclosed.

Description:
RELATED CASES/PRIORITY CLAIM 
       [0001]    This application is a continuation-in-part and claims priority under 35 USC 120 to pending application Ser. No. 11/805,742 filed on My 24, 2007 and entitled “Fiber optic cable splice”, which is a continuation-in-part to an utility patent application Ser. No. 11/329,413 filed on Jan. 9, 2006 and entitled “Apparatus and Method for Splicing Optical Fibers and Reconstructing Fiber-optic Cables” that was later issued with U.S. Pat. No. 7,306,382 on Dec. 11, 2007 and entitled “Mechanical splice optical fiber connector.” The Prior applications are incorporated herein by way of reference. 
     
    
     GOVERNMENT SUPPORT 
       [0002]    This invention was made with Government support under contract No. N68335-05-C-0140 awarded by the Department of Defense. The Government may have certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates generally to the field of optical fiber communication and more particularly to the reconstruction of an optical fiber cable. 
         [0005]    2. Background Art 
         [0006]    In the past decade, applications involving optical fiber based communication systems are becoming more practical and are gradually replacing copper based systems. A common task required by these applications is to repair damaged fiber optic cables. There are three prior art technologies that are used to repair fiber-optic cables and the most relevant patents to this invention appear to be the one by Thomas Scanzillo, Aug. 10, 2004, U.S. Pat. No. 6,773,167; by Toshiyuki Tanaka, Oct. 5, 1999, U.S. Pat. No. 5,963,699 and by Bruno Daguet, and by Gery Marlier, May 24, 1994, U.S. Pat. No. 5,315,682. These patents are thereby included herein by way of reference. 
         [0007]    A typical prior art fusion spliced optical fiber is illustrated in  FIG. 1 . The splice consists of an input optical fiber  110  with a protective coating  120 , and an output optical fiber  115  with a protective coating  125 . The optical fibers are joined at the interface  130  using an automated apparatus following precision alignment and discharge induced fusion splicing process. In order to protect the splicing region, a rigid rod  150  is used and typically the splice and the rigid rod are both enclosed in a heat shrinking enclosure  140 . 
         [0008]    An alternative prior art mechanical fiber-optic splice is illustrated in  FIG. 2 . The splice consists of an input optical fiber  210  with a protective coating  220 , and an output optical fiber  215  with a protective coating  225 , a capillary glass tube  250  containing a precision through channel, placed inside of a protective outer tube  240  and with protective end caps  260  and  265 . Typically, the input and output fibers are placed inside of the glass capillary, an index matching fluid  230  is used to form an air free contact. For certain splices, there is an added small perpendicular channel in the capillary tube  255 . To aid the fiber insertion into the glass capillary tube, two ends of the capillary tube are normally tapered to form interfacing cones. The inner diameter of the capillary tube is made substantially close to the outer diameter of the optical fiber with typical tolerances within one micrometer for a single-mode fiber splice, and a few micrometers for a multimode fiber splice. The index matching fluid is transparent and has a refractive index very close to that of the core of the optical fiber. Frequently, the optical fiber and splice interfaces are further protected by flexible boots  270  and  275 . The prior art fiber splice is often protected with a plastic outer package (not shown) for mechanical stability. 
         [0009]    A related prior art fiber optic cable is illustrated in  FIG. 3 . The cable consists of a coating protected optical fiber  310 , a buffer tube  320 , a layer of cable strengthening fibers  380  and an outer jacket  390 . These cables are designed for reliable operation in challenging environments. 
         [0010]    Although most of the commercially available fiber optic splices do not reconstruct the broken fiber optic cable, prior arts do exist for undersea cable reconstruction. In such a case, reconstruction is typically welded, very bulky and extensive to protect splice from extreme undersea water pressure. Due to the small temperature fluctuations in the undersea environment, materials with substantially different coefficient of thermal expansion (e.g., copper and stainless steel) can be employed without compromising device reliability. 
         [0011]    These prior art approaches have several areas for improvements. For example, the plastic protective outer package of an optical fiber splice has a very limited range of operating temperature. Furthermore, in avionics applications, a fast temperature-cycled environment requires additional packaging considerations to ensure stable and reliable operations. Additionally, in order to splice fiber optic cable such as the one illustrated in  FIG. 3 , one must have structure improvements such that the mechanical and chemical resistance properties of the cable be restored. Such a restoration needs to have a compact packaging, mechanical and chemical integrity, as well as a thermal protection from a fast changing environmental temperature. There is a need, therefore, to make improvements to these prior art approaches, so that highly reliable fiber-optic cable splices and reconstructed fiber-optic cables can be realized. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention discloses a design of a fiber-optic cable splice that enables fiber-optic cable reconstruction and restores optical signal connection. The new fiber-optic cable splice provides substantially enhanced mechanical and chemical reliability in a temperature cycled environment. The new splice can be employed in applications in many areas such as avionics, automobile and defense related instrumentation. Key fixtures and procedure associated with splice installation are also disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]    The aforementioned objects and advantages of the present invention, as well as additional objects and advantages thereof, will be more fully understood hereinafter as a result of a detailed description of a preferred embodiment when taken in conjunction with the following drawings in which: 
           [0014]      FIG. 1  shows the structure of a prior art fusion spliced optical fiber; 
           [0015]      FIG. 2  displays the structure of a prior art mechanical fiber-optic splice; 
           [0016]      FIG. 3  illustrates the cross sectional view of a high quality prior art fiber-optic cable; 
           [0017]      FIG. 4  depicts the cross sectional view of an improved fiber-optic cable splice incorporating a structure for cable reconstruction; 
           [0018]      FIG. 5  shows the cross sectional view of an improved fiber-optic cable splice incorporating a structure for reconstructed cable and further incorporating thermal and mechanical stress reduction elements; 
           [0019]      FIG. 6  displays the cross sectional view of an improved fiber-optic cable splice incorporating a structure for reconstructed cable and further incorporating thermal, mechanical and environmental stress reduction elements; 
           [0020]      FIG. 7  illustrates an improved cable splice fixture consisting of base plate, Funnel like opening to aid the insertion of an optic fiber cable. 
           [0021]      FIG. 8  shows an improved cable splice fixture consisting of an enclosure, and UV LED light sources for curing the index-matching fluid. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    The present invention discloses the design of a new fiber optic cable splice to obtain a highly reliable mechanically reconstructed fiber-optic cable. The new approach departs from the prior art practice of directly splicing fiber-optic cables. The basic concept is to introduce a compact, leak-tight, thermally shielded, and mechanically robust outer package. In addition, light-cured index matching fluid may be used to permanently fix the optical fibers to the glass capillary. The new approach provides a highly reliable reconstructed fiber-optic cable for hash environment and rough handling. 
         [0023]    The first preferred embodiment of the present invention  400  is illustrated in  FIG. 4 . The core of a reconstructed fiber-optic cable splice consists of an input optical fiber  410  with an outer protective tube  420 , an output optical fiber  415  with an outer protective tube  425 , and a glass capillary tube  450  with a precision capillary channel, and two cable-splice bridging flanges  463  and  468 . The glass capillary tube  450  is preferably enclosed by a protective tube  440 . To enhance the stability of the splice and reduce fiber breakage during assembly, a metallic enclosure with a threaded end  445  is preferred. Correspondingly, one of the cable-splice bridging flanges ( 468  as in  FIG. 4 ) is assembled from two sections; the front section has a threaded tube which interfaces with the metallic enclosure  445  whereas the tail section accommodates the fiber optic cable. The two sections of  468  are coupled in such a way that rotating the front section will only translate the fiber optic cable without substantially rotating it. Typically, the ends of the optical fibers are stripped and cleaved according to splicing specifications. The ends are then inserted into the capillary tube. To aid the splicing process, the ends of the capillary tube are tapered to allow for the ease of the insertion of the optical fibers and to accommodate the protective tubes outside of the optical fiber. Light-cured index matching fluid can preferably be introduced inside of the capillary tube between the optical fiber ends  430  to be spliced, and be cured once a desired insertion loss target is achieved. Typically the inner diameter of the capillary tube is very close to the outer diameter of the optical fiber. For single mode optical fibers, the capillary inner diameter is within one micrometer of the fiber diameter, whereas for multimode fibers it is within a few micrometers. In order to restore mechanical strength of the fiber-optic cable, the input cable strengthening fibers  480  are crimped between the cable-splice bridging flange  463  and an inner tube  460 . Similarly the output fiber-optic cable strengthening fibers  485  are crimped in between the bridging flange  468  and its inner tube  465 . For enhanced mechanical properties of the splice, it is preferable to have these inner tubes crimped to the jacket of the fiber optic cable prior to cable insertions into the splice core. The mechanical property of the fiber optic cable is restored by crimping an outer tube  448  with both input bridging flange  463  and output bridging flange  468 , at respective locations. 
         [0024]    The second preferred embodiment of the present invention  500  is illustrated in  FIG. 5 . The core of a reconstructed fiber-optic cable splice consists of an input optical fiber  510  with an outer protective tube  520 , an output optical fiber  515  with an outer protective tube  525 , and a glass capillary tube  550  with a precision capillary channel, and two cable-splice bridging flanges  563  and  568 . The glass capillary tube  550  is preferably enclosed by a protective tube  540 . To enhance the stability of the splice and reduce fiber breakage during assembly, a metallic enclosure  545  with a threaded end is preferred. Correspondingly, one of the cable-splice bridging flanges ( 568  as in  FIG. 5 ) is assembled from two sections; the front section has a threaded tube which interfaces with the metallic enclosure  545  whereas the tail section accommodates the fiber optic cable. The two sections of  568  are coupled in such a way that rotating the front section will only translate the fiber optic cable without substantially rotating it. Typically, the ends of the optical fibers are stripped and cleaved according to splicing specifications. The ends are then inserted into the capillary tube. To aid the splicing process, the ends of the capillary tube are tapered to allow for the ease of the insertion of the optical fibers and to accommodate the loose tubes outside of the optical fiber. Light-cured index matching fluid can preferably be introduced inside of the capillary tube between the optical fiber ends  530  to be spliced, and be cured once a desired insertion loss target is achieved. Typically the inner diameter of the capillary tube is very close to the outer diameter of the optical fiber. For single mode optical fibers, the capillary inner diameter is within one micrometer of the fiber diameter, whereas for multimode fibers it is within a few micrometers. In order to restore mechanical strength of the fiber-optic cable, the input cable strengthening fibers  580  are crimped between the cable-splice bridging flange  563  and an inner tube  560 . Similarly the output fiber-optic cable strengthening fibers  585  are crimped in between a bridging flange  568  and corresponding inner tube  565 . For enhanced mechanical properties of the splice, it is preferable to have these inner tubes crimped to the jacket of the fiber optic cable prior to cable insertions into the splice core. The mechanical property of the fiber optic cable is restored by crimping an outer tube  545  with both input bridging flange  563  and output bridging flange  568 , at respective locations. In order to improve thermal and mechanical properties of the splice, a thermal insulating tube  555  is placed outside of the splice core whereas two flexible boots  570  and  575  are used to protect the cable-splice interface regions. 
         [0025]    The third preferred embodiment of the present invention  600  is illustrated in  FIG. 6 . The core of a reconstructed fiber-optic cable splice consists of an input optical fiber  610  with an outer protective tube  620 , an output optical fiber  615  with an outer protective tube  625 , and a glass capillary tube  650  with a precision capillary channel, and two cable-splice bridging flanges  663  and  668 . The glass capillary tube  650  is preferably enclosed by a protective tube  640 . To enhance the stability of the splice and reduce fiber breakage during assembly, a metallic enclosure with a threaded end  645  is preferred. Correspondingly, one of the cable-splice bridging flanges ( 668  as in  FIG. 6 ) is assembled from two sections; the front section has a threaded tube which interfaces with the metallic enclosure  645  whereas the tail section accommodates the fiber optic cable. The two sections of  668  are coupled in such a way that rotating the front section will only translate the fiber optic cable without substantially rotating it. Typically, the ends of the optical fibers are stripped and cleaved according to splicing specifications. The ends are then inserted into the capillary tube. To aid the splicing process, the ends of the capillary tube are tapered to allow for the ease of the insertion of the optical fibers and to accommodate the protection tubes outside of the optical fiber. Light-cured index matching fluid can preferably be introduced inside of the capillary tube between the optical fiber ends to be spliced, and be cured once a desired insertion loss target is achieved. Typically the inner diameter of the capillary tube is very close to the outer diameter of the optical fiber. For single mode optical fibers, the capillary inner diameter is within one micrometer of the fiber diameter, whereas for multimode fibers it is within a few micrometers. In order to restore mechanical strength of the fiber-optic cable, the input cable strengthening fibers  680  are crimped between the cable-splice bridging flange  663  and an inner tube  660 . Similarly the output fiber-optic cable strengthening fibers  685  are crimped in between a bridging flange  668  and corresponding inner tube  665 . For enhanced mechanical properties of the splice, it is preferable to have these inner tubes crimped to the jacket of the fiber optic cable prior to cable insertions into the splice core. The mechanical property of the fiber optic cable is restored by crimping an outer tube  645  with both input bridging flange  663  and output bridging flange  668 , at respective locations. In order to improve thermal and mechanical properties of the splice, a thermal insulating tube  655  is placed outside of the splice core whereas two flexible boots  670  and  675  are used to protect the cable-splice interface regions. The splice is further protected by a heat shrinking outer tube  678 . 
         [0026]    In the disclosed preferred embodiments outlined above, typically, the metallic parts ( 445 ,  448 ,  463 ,  468 ,  545 ,  548 ,  563 ,  568 ,  645 ,  648 ,  663 , and  668 ) are preferably made with low thermal expansion alloys such as Invar which is a commercially available alloy formed primarily of iron and nickel, and Kovar which is a commercially available alloy formed primarily of nickel, cobalt and iron. The flexible boots ( 570 ,  575 ,  670 ,  675 ) are made of rubber materials that can withstand extreme temperature conditions (from −60 to 150° C.). The protection tube enclosing the glass capillary ( 440 ,  540 ,  640 ) can be made from Teflon like materials such as PTFE(poly tetra fluoro ethylene), PFA(perfluoro alkoxy), FEP(fluorinated ethylene propylene) and ETFE(ethylene tetra fluoro ethylene). The insulating layer ( 555  and  655 ) can be made with materials such as insulation fiberglass or Teflon fibers. 
         [0027]    The forth preferred embodiment of the present invention is illustrated in  FIG. 7 . The alignment fixture of the fiber optic splice consists of two base plates  725  (only one is shown). The structure of the base plate contains a fennel like opening  727  to aid fiber cable  710  insertion, a narrower channel to allow for the alignment of the fiber cable end with the cable splice core  730 , a larger chamber  750  that fits the splice core with precision, and an exit channel  720  for through optical fiber cable (not shown) in a partially (half) assembled cable splice (i.e., one of the cable already inserted and crimped). In a preferred arrangement, two of the base plates are placed together to form axially symmetric cavities which can enclose the cable splice core and fiber cable, also enable the insertion of an optic fiber cable end to be spliced. The two base plates can be separated which releases the partially made splice and allowing user to crimp the optical fiber cable to the cable splice core. Additionally, the two base plates are preferably attached to a mechanical clip wherein the opening of the clip allows for the loading of the splice core and the release of the partially assembled splice. When the clip is closed, the two base plates are brought together to form an alignment fixture where optic fiber cable ends can be inserted into the splice core as illustrated in  FIG. 7 . 
         [0028]    In an additional preferred embodiment, as shown in  FIG. 8 , a partially assembled cable splice  830  containing an input  810  and an output  820  optical fiber cables is placed in an enclosure  840  where UV-LED are placed closely to the splice core to cure the index matching fluid. Following the curing step, the index matching liquid is converted to an index matching solid which also bonds the two ends of the optical fiber cables together. Typical index matching liquids are optical adhesives such as NOA61 from Norland, OG142-13 from Epotek, and UV15 from Master Bond. 
         [0029]    Although UV-curable index matching fluid is preferred in the disclosed cable splice embodiments described above, other index matching fluids which do not need curing may also be preferred in certain applications. 
         [0030]    A typical preferred optical fiber cable splicing procedure consists of the following steps which can be carried out in certain logical order: (a) placing outer packaging materials through the cable (heat shrink tube, rubber boots, thermal insulation, and outer crimping tube); (b) insertion of the optical fiber cable ends through inner tubes and crimp these tubes at specified locations; (c) preparing optical fiber cables for the splicing (stripping outer cable jacket, stripping fiber protection tube, and cleaving optical fiber, all to specified lengths); (d) insertion of one of the optical fiber cable into the splice core with the aid of a fixture; (e) remove the partially inserted cable and splice core from the fixture; (f) complete the insertion of the cable and crimp the cable with respect to the splice core; (g) repeating steps (d), (e), and (f) for the second optical fiber cable; (h) fine tune the distance between the fiber ends to minimize insertion loss; (i) UV cure the partially made splice in a UV curing fixture; (j) assemble and crimp the outer crimp tube to enclose the splice core; (k) assemble thermal insulation, rubber boots; and finally (l) to assemble and heat shrink the heat shrink tube. 
         [0031]    It will be apparent to those with ordinary skill of the art that many variations and modifications can be made to the fiber-optic cable splice, fixtures and procedure disclosed herein without departing form the spirit and scope of the present invention. It is therefore intended that the present invention cover the modifications and variations of this invention provided that they come within the scope of the appended claims and their equivalents, we claim: