Abstract:
A structure and method for detecting a broken optical fiber includes providing a fiber optic cable holding a first optical fiber and a jacket, and breaking the first optical fiber to trigger an alarm. In preferred embodiments, an outer conduit is provided around the fiber optic cable, and the conduit carries a second optical fiber. The second optical fiber creates a circuit path with a control device, and upon breakage of the first optical fiber, the second optical fiber is burnt through to break the circuit path. This break in the circuit path is detected by the control device, which stops the transmission of signals across the optical fiber cable and/or triggers an alarm.

Description:
TECHNICAL FIELD  
         [0001]    This disclosure relates to fiber optic cables and methods. In particular, this disclosure relates to structure and methods for detecting a broken optical fiber.  
         BACKGROUND  
         [0002]    Fiber optic cables are utilized to communicate by sending light waves over the fiber optics. A signal is sent in, circuitry converts the signal to voltage/current to drive a light source (LED or laser), and then the light is delivered to the fiber. The signal travels down the fiber to a receiver where it is converted back from an optical signal to an electrical signal. In some uses, the fiber can be carrying high powers, on the order of 1-2 watts of energy or more. Periodically, these fibers may break. Upon breakage, the energy escapes and can lead to a fire or other damage, and/or bodily injury to personnel. Improvements in fiber optic cables are desirable.  
         SUMMARY  
         [0003]    In one aspect, the disclosure is directed to a fiber optic cable including a protective, outer covering that is constructed and arranged to provide an alarm if an optical fiber breaks.  
           [0004]    In particular, in one embodiment, a fiber optic cable includes a first extension of optical fiber core and cladding; a buffer covering the fiber core and cladding; a strength member covering the buffer; a jacket covering the strength member; a conduit covering the jacket; and a second extension of low temperature optical fiber along the conduit exterior surface.  
           [0005]    In one embodiment, an optical fiber system includes an optical fiber cable, as described herein, and a control device. The control device is in optical contact with opposite ends of the second optical fiber to form a circuit path. The control device includes an alarm that is triggered in response to a break in the circuit path.  
           [0006]    In another aspect, a method for protecting conventional optical fiber is provided. The method includes a step of inserting the conventional optical cable assembly into a protective conduit. The conduit has a second optical fiber, wherein the second optical fiber has opposite ends. A circuit path is formed with each end of the second optical fiber, and an alarm is provided that is triggered upon breakage of the circuit path.  
           [0007]    In another aspect, a method for detecting a broken optical fiber is provided. When the primary optical fiber breaks, the outer optical fiber melts and triggers an alarm. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a schematic, perspective view of one embodiment of an optical fiber system, constructed according to principles of this disclosure;  
         [0009]    [0009]FIG. 2 is a schematic, top plan view of one embodiment of a fiber optic cable and detection device, constructed according to principles of this disclosure;  
         [0010]    [0010]FIG. 3 is a schematic, fragmented, perspective view of the fiber optic cable depicted in FIG. 2, constructed according to principles of this disclosure;  
         [0011]    [0011]FIG. 4 is a schematic, cross-sectional view of another embodiment of a fiber optic cable and detection device, constructed according to principles of this disclosure; and  
         [0012]    [0012]FIG. 5 is a schematic, fragmented, perspective view of another embodiment of a fiber optic cable, analogous to the view shown in FIG. 3, constructed according to principles of this disclosure. 
     
    
     DETAILED DESCRIPTION  
       [0013]    [0013]FIG. 1 depicts, schematically, one example embodiment of a system  10  constructed according to principles of this disclosure. In FIG. 1, the system  10  includes equipment  12 , such as a distributing frame  13 , outside plant (OSP) fiber optic cables  14 , equipment patch cords  16 , and cross-connect patch cords  18 . Also shown schematically in FIG. 1 is a control device  20  and an optical fiber  22  in optical contact with the control device  20 . If the patch cord  18  were to break, the control device  20  will detect this breakage, and shut down the system  10 , and preferably, provide an alarm. This is described further below.  
         [0014]    It should be understood that the system  10  illustrated in FIG. 1 is merely one example embodiment of a myriad of contemplated embodiments.  
         [0015]    Attention is now directed to FIG. 2. In FIG. 2, a system  21  is shown including the control device  20  optically connected to a fiber optic cable assembly  24 . The fiber optic cable assembly  24  may be the OSP cables  14 , equipment patch cord  16 , cross-connect patch cords  18 , or many other types of uses for fiber optic cables. The particular fiber optic cable assembly  24  illustrated is a patch cord  26 . The patch cord  26  has first and second opposite ends  28 ,  29 , each having a connector  30 ,  31  terminating each end. The connector  30  may be one of many types of connectors, including, for example, the connector described in U.S. Pat. No. 5,883,995, assigned to ADC Telecommunications, Inc., Minnetonka, Minn., the assignee of this patent application. U.S. Pat. No. 5,883,995 is incorporated herein by reference.  
         [0016]    In FIG. 2, the exterior of the patch cord  26  is visible. The exterior of the patch cord  26  includes a cover or conduit  32  and an extension of optical fiber  34  along the conduit  32 . In preferred embodiments, the optical fiber  34  is wrapped around the exterior surface of the conduit  32 . Indeed, in preferred embodiments, the optical fiber  34  is spirally wrapped around the exterior surface of the conduit  32 . The reason for this is explained further below.  
         [0017]    With this background in mind, a general overview of operation of the system  21  can be appreciated. The fiber optical cable assembly  24  includes, at its core, an optical fiber, which may be carrying a high amount of power, such as 1-2 watts of energy or more. If this fiber core breaks, the energy will melt the outer conduit  32  and break the optical fiber  34 . A break in the optical fiber  34  will cause an interruption of the circuit path  36  created by opposite ends  39 ,  40  of the optical fiber  34  with the control device  20 . The break in the circuit path  36  will cause a detection system  23  in the control device  20  to detect this break. The control device  20  will preferably provide an alarm, in the form of video, audio, or both. The control device  20  will also shut down the appropriate system that includes the fiber optic cable assembly  24 .  
         [0018]    Attention is now directed to FIG. 3. The fiber optic cable assembly  24  is shown in fragmented, perspective view. As can be seen in FIG. 3, the fiber optic cable assembly  24  includes fiber optic cable  41 . The fiber optic cable  41  preferably includes a central fiber  42  (including a core and a cladding); a buffer  44 ; a strength member  46 ; and a jacket  48 . The fiber  42  is what translates the signals across the cable  24 . The fiber  42  may be covered with a coating. Covering the fiber  42  is buffer  44 . The buffer  44  protects the fiber core and cladding  42 . Covering and surrounding the buffer  44  is strength member  46 . The strength member  46  adds mechanical strength to the cable  24 . In particular, tensile stresses are applied to the cable  24  both during installation and after. The strength member  46  protects the fiber  42  against such stresses. Typical materials utilized for strength member  46  include aramid yam, steel, epoxy, and other suitable materials.  
         [0019]    The fiber optic cable  41  also further include a jacket  48  covering and surrounding the strength member  46 . The jacket  48  provides protection against damage caused by crushing, abrasions, and other physical damage, as well as elements such as ozone, alkali, acids, and other chemical damage. Jacket  48  may be made of a variety of materials, depending upon the resistance required and the cost.  
         [0020]    Covering and surrounding the jacket  48  is the conduit  32 . As can be seen in FIG. 3, the conduit  32  generally is a tubular wall  33  defining a hollow interior  37  and an exterior surface  50 . The fiber optic cable  41  is received by and passes through the interior  37 . Preferably, the conduit  32  comprises a material with a melting point sufficiently low to permit energy from a broken fiber  42  to melt through the conduit  32 . For example, the conduit  32  may be constructed from materials having a melting point no greater than 400° F. Usable materials for the conduit  32  include: PVC or HDPE.  
         [0021]    The conduit  32  may be constructed from a material that is bendable in order to permit flexibility in the cable  24 . By the term “bendable”, it is meant that the material may be altered from a straight line configuration under a force no greater than  2  pounds. In other embodiments, the conduit  34  may be semi-rigid. By “semi-rigid”, it is meant that the material is not easily bent, such that it takes a force of at least 2 pounds to bend the material.  
         [0022]    Extending along the exterior surface  50  of the conduit  32  is the optical fiber  34 . Of course, this optical fiber  34  is separate and independent from the central, signal communicating optical fiber  42 . The optical fiber  34  forms a second extension  35  of optical fiber in the cable  24 . The optical fiber  34  preferably comprises a low temperature, plastic, optical fiber. By “low temperature”, it is meant that it has a melting point no greater than 600° F., preferably no greater than 500° F. With melting points on this order, the signals provided across the fiber  34  will be interrupted in the case of the fiber  42  breaking, releasing energy and melting through fiber  34 . As explained earlier, by breaking the signal in the fiber  34 , the circuit path  36  will be broken and cause an alarm to activate.  
         [0023]    In preferred embodiments, the fiber  34  extends along the exterior surface  50  of the conduit  32  in a manner that offers a large amount of coverage of the surface area of the exterior surface  50 . In this way, it will not matter at what point the breakage in the fiber  42  occurs; there will be a fiber  34  located adjacent to the breakage. In the particular preferred embodiment illustrated, the fiber  34  is wrapped around the exterior surface  50  of the conduit  34 . In alternate embodiments, the fiber  34  may be secured to and extend along the interior surface of the conduit  32 . The fiber  34  may also be oriented axially along the surface  50  of the conduit  34 .  
         [0024]    Preferably, the fiber  34  is spirally wrapped around the conduit  32 . As can be seen in FIG. 2, the fiber  34  includes a lead or free portion  52  extending between the end  39  and the end  54  of the cable assembly  24 . This free portion  52  lacks physical contact with the conduit  32 ; that is, it is the portion that extends between the conduit  32  and the control device  20 . Similarly, the fiber  34  includes a lead or free portion  56  that extends between end  40  and end  58  of the cable assembly  24 . The end  58  is an opposite end of the cable as the end  54 . While the free portions  52 ,  56  are shown in the particular illustrated embodiment as extending from opposite ends  54 ,  58  of the cable assembly  24 , in other embodiments, the fiber  34  can be doubled back against itself such that one or both of the free portions  52 ,  56  extends from any portion of the conduit  32 , including from a common end  54  or  58 .  
         [0025]    In some embodiments, the fiber  34  may be merely spirally wound around the conduit  32  without any other types of security therebetween. In other embodiments, the fiber  34  may be adhered to the conduit  32  with a suitable adhesive. In some embodiments, the fiber  34  may be protected with an outer layer of material.  
         [0026]    Preferably, the control device  20  includes an alarm  60 . The alarm  60  may include a variety of mechanisms to alert those operating the system that there has been a break in the fiber  42 . In the particular embodiment illustrated, the alarm  60  includes a blinking light  62  and an audio siren  64 . Upon breaking of the circuit path  36 , the detection system  23  will preferably cause the alarm  60  to be activated. Preferably, the detection system  23  will also cause the cable  24  to shut down (that is, signals will no longer be sent through the cable  24 ). Other features of the control device  20  include a power switch  66  and appropriate electrical cabling  68 . The electrical cabling  68  can, in some embodiments, lead to a control office that includes a warning system for monitoring.  
         [0027]    The conduit  32  is usable to hold at least one fiber optic cable  41  and may hold a plurality of such cables  41 . Attention is directed to FIG. 4. FIG. 4 illustrates a schematic, cross-sectional view of a fiber optic cable assembly  24 ′ including the conduit  32  with the optical fiber  34  held thereon, and enclosing a plurality of cables  41 . In the embodiment shown in FIG. 4, there are six cables  41  that are held by the conduit  32 . If any one of the cables  41  includes a fiber  22  that is broken, the release of energy will cause the conduit  32  to melt and to break the outer fiber  34 .  
         [0028]    In FIG. 5, an alternative embodiment is illustrated. In the embodiment shown in FIG. 5, the conduit  34  is eliminated all together; instead, a specially adapted jacket-conduit  80  is utilized. The jacket-conduit  80  is analogous to the jacket  48  described above, but in this embodiment, the jacket-conduit  80  includes an optical fiber  82  extending therealong. The jacket-conduit  80 , in this embodiment, is also analogous to the conduit  34  of the previous embodiment. As can be seen in FIG. 5, in particular, the optical fiber  82  is spirally wrapped around the jacket-conduit  80 . The fiber optic cable assembly  24 ″ shown in FIG. 5 otherwise includes all of the parts described above, including fiber core and cladding  84 , buffer  86 , and strength member  88 . If the optical fiber core  84  breaks, the energy will melt the jacket-conduit  80  and cause the fiber  82  to break. The breaking of this fiber  82  will break the circuit path  36  and cause an alarm to be activated.  
         [0029]    Fiber optic cable assembly  24  may be protected utilizing the principles discussed herein as described below. Optical cable  41  including a first optical fiber and a jacket covering the optical fiber is provided. The optical cable may include the fiber core and cladding  42 , buffer  44  and strength member  46 , as described herein. The jacket may include the type of jacket  48  described herein. The jacket  48  is covered with conduit  32 , which includes a second optical fiber, such as optical fiber  34 . The second optical fiber  34  has opposite ends  39 ,  40 . Circuit path  36  is formed with each end  39 ,  40  of the optical fiber  34 . Detection system  23  is provided that is triggered upon breakage of the circuit path  36 .  
         [0030]    A method for detecting a broken optical fiber may be conducted utilizing the structures and principles described herein. In general, the optical fiber  42  with the jacket  48  is provided. The optical fiber  42  is broken to trigger the alarm  60  in the detection system  23 . The alarm  60  may be either blinking light  62 , audio siren  64 , or both. As explained above, the step of breaking the optical fiber  42  includes breaking the fiber  42  to emit energy that burns through the second optical fiber  34 , which breaks the circuit path  36  and triggers alarm  60 . This also preferably includes burning through the outer conduit  32 , in order to burn through the optical fiber  34 .