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. 11/329,413 filed on Jan. 9, 2006 and entitled “Apparatus and Method for Splicing Optical Fibers and Reconstructing Fiber-optic Cables”. The pending application is incorporated herein by way of reference. 
     
    
     GOVERNMENT SUPPORT  
       [0002]     This invention was made with Government support under SBIR 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 in side 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 cable-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 extreme undersea water pressure. Due to the small temperature fluctuations in the undersea environment, materials with substantially different coefficient of thermal expansion (i.e., stainless steel and copper) can be employed without compromising splice 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 cables such as the one illustrated in  FIG. 3 , one must have structure improvements such that the mechanical and chemical resistance properties of the cable restored. Such a restoration needs to provide a compact packaging, mechanical and chemical integrity, as well as a thermal protection of fast changing environmental temperature. There is a need, therefore, to make improvements to these prior arts, 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 will enable fiber-optic cable reconstruction and restore 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, and 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 reconstructed cable;  
         [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 splice incorporating a structure for reconstructed cable and further incorporating thermal, mechanical and environmental stress reduction elements;  
         [0020]      FIG. 7  illustrates an improved 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 source 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 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 . 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 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 outer tube  460 . Similarly the output fiber-optic cable strengthening fibers  485  are crimped in between a bridging flange  468  and its outer tube  465 . For enhanced mechanical properties of the splice, it is preferable to have one end of the bridging flanges  463  and  468  inserted inside of the layer of the strengthening fibers. Both the input and output bridging flanges  463  and  468 , are crimped with their corresponding input and output tubes  460 , and  465 , respectively. The mechanical property of the fiber optic cable is restored by crimping an outer tube  445  with both input tube  460  and output tube  465 , 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 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 . 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 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 outer tube  560 . Similarly the output fiber-optic cable strengthening fibers  585  are crimped in between a bridging flange  568  and its outer tube  565 . For enhanced mechanical properties of the splice, it is preferable to have one end of the bridging flanges  563  and  568  inserted inside of the layer of the strengthening fibers. Both the input and output bridging flanges  563  and  568 , are crimped with their corresponding input and output tubes  560 , and  565 , respectively. The mechanical property of the fiber optic cable is restored by crimping an outer tube  545  with both input tube  560  and output tube  565 , 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 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 . 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 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 outer tube  660 . Similarly the output fiber-optic cable strengthening fibers  685  are crimped in between a bridging flange  668  and its outer tube  665 . For enhanced mechanical properties of the splice, it is preferable to have one end of the bridging flanges  663  and  668  inserted inside of the layer of the strengthening fibers. Both the input and output bridging flanges  663  and  668 , are crimped with their corresponding input and output tubes  660 , and  665 , respectively. The mechanical property of the fiber optic cable is restored by crimping an outer tube  645  with both input tube  660  and output tube  665 , 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 outer package tubes related to crimping ( 445 ,  460 ,  463 ,  465 ,  468 ,  545 ,  560 ,  563 ,  565 ,  568 ,  645 ,  660 ,  663 ,  665 , and  668 ) are metallic and can preferably be 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 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 enclosed the cable splice core and fiber cable, also enabling 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 where 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 cure, the index matching liquid is converted to an index matching solid which also bond 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) prepare optical fiber cables for the splicing (stripping outer cable jacket, stripping fiber protection tube, and cleaving optical fiber, all to specified lengths); (c) insertion of one of the optical fiber cable into the splice core with the aid of a fixture; (d) remove the partially inserted cable and splice core from the fixture; (e) complete the insertion of the cable and crimp the cable with respect to the splice core; (f) repeating steps (c), (d), and (e) for the second optical fiber cable; (g) UV cure the partially made splice in a UV curing fixture; (h) assemble and crimp the outer crimp tube to enclose the splice core; (i) assemble thermal insulation, rubber boots; and finally (j) 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: