Abstract:
A fiber cable distortion detection system includes a broadband source, an optical source fiber disposed in optical communication with the broadband source, an optical fiber under test (FUT) disposed in optical communication with the optical source fiber and an optical spectrum analyzer disposed in optical communication with the optical source fiber. The system combines the refection of the distortion with the reflection from the source/FUT interface using a 1×2 fiber coupler, the location of the distortion is precisely determined with high resolution by the spectrum of the combined signal. The system is miniaturized to the size of a hand-held device suitable for use in airplane cable plant installation or in an environment where space is limited.

Description:
TECHNICAL FIELD 
     The present disclosure relates to fiber optic cables. More particularly, the present disclosure relates to a fiber cable distortion locator system and method for locating a distortion in a fiber optic cable at a short distance from an end face of the cable. Distortion in the cable may cause optical signal discontinuity. 
     BACKGROUND 
     Current and future generations of composite airplanes may extensively use fiber optic cables for size, weight, cost and EMI reduction. The number of fiber optic cables in a composite airplane may be many times that which is used in a conventional metal frame airplane. As the number of fiber optic cables increases, the potential for distortions which may arise in the optical fiber cable during installation may need to be addressed. Distortions in the fiber optic cables are rare and in some applications it may be desirable to verify their absence from the cables. 
     Due to the high density of fiber optic cable in the cable bundle, optical fibers may be bundled in tight spaces near the connector panel. Most distortions in the cable may occur at locations near the cable&#39;s end face which is coupled to the LRU (line replaceable unit) connectors&#39; termini or inside its own termini. Conventional equipment (such as photon-counting, Michelson Interferometer, Optical Backscatter Reflectometer) for cable distortion detection may detect distortions in fiber optic cable with highest resolution of 5 cm. But these cable distortion detecting equipments that can detect cable distortions at a distance of less than 5 cm from the end face of the cable may be expensive, bulky, heavy and have limitations for testing multi-mode (MM) glass fiber and large core plastic optical fiber (POF). They are not suitable for field use onboard airplanes during the cable installation process. 
     Therefore, a low-cost, compact and easy-to-use fiber optic cable distortion detection system is needed for fiber optic cable installation. 
     SUMMARY 
     The present disclosure is generally directed to a fiber cable distortion detection system. An illustrative embodiment of the system includes a broadband source, an optical source fiber disposed in optical communication with the broadband source, an optical fiber under test disposed in optical communication with the optical source fiber and an optical spectrum analyzer disposed in optical communication with the optical source fiber. 
     In some embodiments, the fiber cable distortion detection system may include an LED driver circuit; a broadband LED disposed in electrical communication with the LED driver circuit; an optical source fiber disposed in optical communication with the broadband LED; and an optical spectrometer disposed in optical communication with the optical source fiber. 
     The present disclosure is further generally directed to a fiber cable distortion detection method. An illustrative embodiment of the method includes providing an optical source fiber; providing an optical fiber under test in optical communication with the optical source fiber; reflecting a fiber interface reflection signal from an interface between the optical fiber under test and the optical source fiber; transmitting a second signal into said optical fiber under test; forming a combined output signal; and forming a combined optical spectrum based on the combined output signal 
     In some embodiments, the fiber cable distortion detection system may include a housing; an LED driver circuit provided in the housing; a broadband LED disposed in electrical communication with the LED driver circuit; an input fiber disposed in optical communication with the broadband LED; a fiber optic coupler disposed in optical communication with the input fiber; an optical source fiber disposed in optical communication with the fiber optic coupler; a fiber optic connector provided on the housing and disposed in optical communication with the optic source fiber; an output fiber disposed in optical communication with the fiber optic coupler; an optical spectrometer disposed in optical communication with the output fiber; a USB port provided on the housing and connected to the optical spectrometer; an alarm circuit connected to the optical spectrometer; and an alarm provided on the housing and connected to the alarm circuit. 
     In some embodiments, the fiber cable distortion detection method may include providing an optical source fiber; providing an optical fiber under test having a fiber distortion in optical communication with the optical source fiber; transmitting a broadband input optical signal through the optical source fiber; reflecting a fiber interface reflection signal from an interface between the optical fiber under test and the optical source fiber; transmitting a remaining portion of the input optical signal through the optical fiber under test; reflecting a fiber distortion reflection signal from the fiber distortion in the optical fiber under test; forming a combined output signal by combining the fiber distortion reflection signal with the fiber interface reflection signal; displaying a spectrum of the combined output signal; and calculating a location of the fiber distortion in the optical fiber under test using the spectrum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram which illustrates a distortion detection principle utilized by an illustrative embodiment of the fiber cable distortion detection system. 
         FIG. 2  is a schematic block diagram of an illustrative embodiment of the fiber cable distortion detection system in implementation of the system. 
         FIG. 3  is an optical spectrum analyzer (OSA) spectrum display in implementation of an illustrative embodiment of the fiber cable distortion detection system, more particularly illustrating an OSA spectrum in which a distorted fiber under test is connected to the system. 
         FIG. 4  is an optical spectrum analyzer (OSA) spectrum display in implementation of an illustrative embodiment of the fiber cable distortion detection system, more particularly illustrating an OSA spectrum in which a fiber under test is not connected to the system. 
         FIG. 5  is an optical spectrum analyzer (OSA) spectrum display in implementation of an illustrative embodiment of the fiber cable distortion detection system, more particularly illustrating an OSA spectrum in which an undistorted fiber under test is connected to the system. 
         FIG. 6  is a block diagram which illustrates an illustrative hand-held embodiment of the fiber cable distortion detection system. 
         FIG. 7  is a block diagram which illustrates an engineering design of an illustrative hand-held embodiment of the fiber cable distortion detection system. 
         FIG. 8  is a top view of the fiber cable distortion detection system illustrated in  FIG. 7 . 
         FIG. 9  is a flow diagram of an illustrative embodiment of the fiber cable distortion detection method. 
         FIG. 10  is a flow diagram of an aircraft production and service methodology. 
         FIG. 11  is a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the applications and uses of the described embodiments. As used herein, the word “exemplary” or “illustrative” means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to make or use the invention and are not intended to limit the scope of the invention, which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     The fiber cable distortion detecting system and method of the present disclosure may be based on testing the interference of an input optical signal with an optical signal which is reflected from a distortion in a fiber optic cable using a broadband source which may operate in a continuous wave (CW) condition. The broadband source may be any wavelength range and may be capable of testing all types of fibers including single mode, multimode and large core plastic optical fibers (POF), for example and without limitation. 
     Referring initially to  FIG. 1 , schematic block diagram which illustrates a distortion detection principle utilized by an illustrative embodiment of the fiber cable distortion detection system  1 , hereinafter system, is shown. A broadband source  2  is adapted to emit an input optical signal  3  which may have a large number of wavelength components λ 1 , λ 2 , λ 3  . . . λ n  and may be coupled to an optical source fiber  4 . An optical fiber under test (FUT)  5  may be coupled to the optical source fiber  4 . In some embodiments, the broadband source  2  may be an LED, for example and without limitation. The input optical signal  3  may be emitted from the broadband source  2  and into and through the optical source fiber  4 . At the fiber interface  9  between the optical fiber under test  5  and the optical source fiber  4 , a portion of the input optical signal  3  may be reflected back through the optical source fiber  4  as a fiber interface reflection signal  12 . The remaining portion of the input optical signal  3  may be transmitted beyond the fiber interface  9  through the optical fiber under test  5 . In the event that the optical fiber under test  5  has a fiber distortion  6  at a distance (L) from the optical source fiber  4 , the remaining portion of the input optical signal  3  may be reflected from the fiber distortion  6  and back through the optical fiber under test  5  and the optical source fiber  4  as a fiber distortion reflection signal  14 . The fiber distortion reflection signal  14  may combine either constructively or destructively with the fiber interface reflection signal  12  to form a combined output optical signal  8 . 
     Depending on the distance (L) of the fiber distortion  6  from the optical source fiber  4 , for wavelengths of the fiber distortion reflection signal  14  which form a 2π phase shift relative to the phase of the input optical signal  3  after traveling a distance of 2 L, the constructive interference of the fiber distortion reflection signal  14  and the fiber interface reflection signal  12  may form the “peaks” and “valleys” on the combined output optical signal  8 . For wavelengths of the fiber distortion reflection signal  14  which form a π phase shift relative to the phase of the fiber interface reflection signal  12  after traveling a distance of 2 L, the destructive interference of the fiber distortion reflection signal  14  and the fiber interface reflection signal  12  become zero on the combined output optical signal  8 . By detecting the spacing between the peaks or valleys in the combined output optical signal  8 , the location of the fiber distortion  6  at a short distance from the fiber interface  9  may be determined with a resolution of better than about 0.1 mm. This phenomenon is based on the principle of the Fabry-Perot resonator theory in optics. The spacing of the peaks or valleys in the combined output optical signal  8  is known as the free spectral range (FSR) of the resonator. 
     In the example shown in  FIG. 1 , the relation between FSR (Δλ) and L is described by the equation (I) below:
 
 L=λ   2   i /2× n   eff ×Δλ
 
Where n eff  is the index refraction (or group index) of the optical fiber and λ i  is the operating wavelength of the broadband source.
 
     Under circumstances in which a fiber distortion  6  is not present in the optical fiber under test  5 , the input optical signal  3  may be transmitted beyond the fiber interface  9  and through the optical fiber under test  5  without a fiber distortion reflection signal  14  forming and combining with the fiber interface reflection signal  12  to form the combined output optical signal  8 . In that case, no interference to the fiber interface reflection signal  12  may occur. Therefore, the combined optical spectrum which is displayed on the OSA spectrum display  32  may correspond to the OSA spectrum of the fiber interface reflection signal  12 , indicating that no fiber distortion  6  is present in the optical fiber under test  5 . 
     Referring next to  FIG. 2 , a schematic block diagram of an illustrative embodiment of the fiber cable distortion detection system  21  is shown. The system  21  may include a broadband source  22  which may be adapted to emit an input optical signal  3  having a large number of wavelength components λ 1 , λ 2 , λ 3  . . . λ n . A 1×2 fiber optic coupler  28  may be provided in optical communication with the broadband source  22  through an input fiber  23 . An optical spectrum analyzer (OSA)  31  may be provided in optical communication with the fiber optic coupler  28  through an output fiber  30 . An OSA spectrum display  32  may interface with the optical spectrum analyzer  31 . An optical source fiber  25  may be provided in optical communication with the fiber optic coupler  28 . An optical fiber under test (FUT)  26  may be coupled to the optical source fiber  25  through an optical fiber connector  24  and may have a fiber distortion  27  at a known distance from the optical source fiber  25 . 
     In operation of the system  21 , an optical fiber under test  26  having a fiber distortion  27  is connected to the optical source fiber  25  at the optical fiber connector  24 . In an exemplary application, the fiber distortion  27  may be located 3.6 cm (by physical measurement) from the optical source fiber  25 . A broadband input optical signal  3  is emitted from the broadband source  22  and through the input fiber  23 , the fiber optic coupler  28  and the optic source fiber  25 . At the fiber interface  29  between the optical fiber under test  26  and the optical source fiber  25 , a portion of the input optical signal  3  may be reflected back through the optical source fiber  25  and the fiber optic coupler  28  as a fiber interface reflection signal  12 . The remaining portion of the input optical signal  3  may be transmitted beyond the fiber interface  29  through the optical fiber connector  24  and optical fiber under test  26  as a remaining broadband optical signal  16 . The remaining broadband optical signal  16  of the input optical signal  3  may be reflected from the fiber distortion  27  and back through the optical fiber under test  26  and the optical source fiber  25  as a fiber distortion reflection signal  14 . In the fiber optic coupler  28 , the fiber interface reflection signal  12  and the fiber distortion reflection signal  14  may combine to form the output optical signal  8 . The output optical signal  8  may be transmitted from the fiber optic coupler  28  to the optical spectrum analyzer  31  through the output fiber  30 . 
     An exemplary spectrum of the combined output optical signal  8  as measured and analyzed by the optical spectrum analyzer  31  and displayed on the OSA spectrum display  32  is shown in  FIG. 3 . The measured FSR (Free Spectral Range) from the spectrum in  FIG. 3  is 0.022 nm. The parameters for calculation of the location of the fiber distortion  27  using equation (I) above are presented in Table (I) below. The value for L calculated using equation (I) is 3.64 cm, which is in good agreement with the measured results of L using a physical measurement technique mentioned above. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Fiber distortion distance calculations 
               
             
          
           
               
                 Parameters 
                 Symbols 
                 Measured data 
                 Units 
               
               
                   
               
             
          
           
               
                 Input wavelength 
                 Λ i   
                 1550 
                 nm 
               
               
                 Free Spectral Range 
                 Δλ 
                 0.022 
                 nm 
               
               
                 (FSR) 
               
               
                 Fiber effective 
                 n eff   
                 1.5 
               
               
                 index of refraction 
               
               
                 index of refraction 
               
               
                 Defect spacing 
                 L = λ 2   i /2 × n eff  × Δλ 
                 3.64 
                 cm 
               
               
                   
               
             
          
         
       
     
     An optical spectrum analyzer (OSA) spectrum display in which the optical fiber under test  26  ( FIG. 2 ) is not connected to the optical source fiber  25  is shown in  FIG. 4 . An OSA spectrum display in which an optical fiber under test  26  without a fiber distortion  27  ( FIG. 2 ) is connected to the optical source fiber  25  is shown in  FIG. 5 . The OSA spectra shown in  FIGS. 4 and 5  have no peaks and valleys due to the absence of a fiber distortion reflection signal  14  ( FIG. 2 ) which would otherwise interfere with the fiber interference reflection signal  12  in the output optical signal  8 . 
     Referring next to  FIGS. 6-8 , a block diagram which illustrates an illustrative hand-held embodiment of the fiber cable distortion detection system  36  is shown in  FIG. 6  and an engineering design of an illustrative hand-held embodiment of the system  36  is shown in  FIGS. 7 and 8 . The system  36  may include a housing  37 . An LED driver circuit with automatic power control (APC)  38  (hereinafter LED driver circuit  38 ) may be provided in the housing  37 . A broadband LED  39  may be electrically connected to the LED driver circuit  38 . A fiber optic coupler  40  may be connected to the broadband LED  39  through an input fiber  45 . A fiber optic connector  44  provided on the outside of the housing  37  may be connected to the fiber optic coupler  40  through an optical source fiber  41 . 
     An optical spectrometer  48 , which may be a miniature Ocean Optics spectrometer (or other high resolution miniature spectrometer), may be connected to the fiber optic coupler  40  through an output fiber  46 . A power supply  42  may be connected to the optic spectrometer  48 . In some embodiments, a peak detector and alarm circuit  43  may be provided in the housing  37  and connected to the optical spectrometer  48 . An alarm  47 , which may be an audio alarm, a visual alarm or both, may be provided on the exterior of the housing  37  and connected to the peak detector and alarm circuit  43 . A laptop connector  50 , which may be a USB port, for example and without limitation, may be provided on the housing  37  and connected to the optical spectrometer  48 . A laptop computer  51  may be connected to the laptop connector  50 . As shown in  FIGS. 7 and 8 , in some embodiments an on/off switch  54  may be provided on the housing  37  and connected between the power supply  42  and the optic spectrometer  48  to facilitate turning the system  36  on and off. 
     In typical operation of the system  36 , an optical fiber under test  49  having a fiber distortion  49   a  is connected to the optical source fiber  41  at the fiber optic connector  44 . The LED driver circuit  38  causes the broadband LED  39  to generate a broadband input optical signal  45   a  through the input fiber  45 , the fiber optic coupler  40  and the optical source fiber  41 . At the fiber interface between the optical source fiber  41  and the optical fiber under test  49 , a portion of the input optical signal  45   a  may be reflected back through the optical source fiber  41  and the fiber optic coupler  40  as a fiber interface reflection signal (not illustrated). The remaining portion of the input optical signal  45   a  may be transmitted beyond the fiber interface (not illustrated) through the optical fiber under test  49  as a remaining broadband optical signal (not illustrated). The remaining broadband optical signal of the input optical signal  45   a  may be reflected from the fiber distortion  49   a  and back through the optical fiber under test  49 , the optical source fiber  41  and the fiber optic coupler  40  as a fiber distortion reflection signal (not illustrated). In the fiber optic coupler  40 , the fiber distortion reflection signal may combine with the interface reflection signal (not illustrated) to form a combined output optical signal  46   a.    
     The combined output optical signal  46   a  may be transmitted through the output fiber  46  to the optical spectrometer  48 . The optical spectrometer  48  may analyze the combined output optical signal  46   a , generate a spectrum and transmit the spectrum of the combined output optical signal  46   a  to the laptop computer  51 , which may display the spectrum. The laptop computer  51  may also calculate and display the location of the fiber distortion  49   a  from the end of the optical fiber under test  49  using equation (I) above. Under some circumstances, the optic spectrometer  48  may activate the peak detector and alarm circuit  43  to turn on the alarm  47 . With the alarm and alarm circuit built in, system  36  may be designed to be operable without the laptop computer  51 , further facilitating its use in an environment with very limited space. 
     Referring next to  FIG. 9 , a flow diagram  900  which illustrates an illustrative embodiment of the fiber cable distortion detection method is shown. In block  902 , an optical source fiber is provided. In block  904 , an optical fiber under test having a fiber distortion an unknown distance from the end of the optical fiber under test is coupled to the optical source fiber. In block  906 , an input optical signal which may be a broadband input optical signal is transmitted through the optical source fiber. In some embodiments, the broadband input optical signal may be emitted from a broadband LED. In block  908 , a fiber interface reflection signal is reflected from the interface between the optical fiber under test and the optical source fiber. In block  910 , the remaining portion of the broadband input optical signal is transmitted through the optical fiber under test. In block  912 , a fiber distortion reflection signal is reflected from the fiber distortion in the optical fiber under test. In block  914 , a combined output optical signal is formed by combining the optical fiber distortion reflection signal with the fiber interface reflection signal. In block  916 , a combined optical spectrum based on the combined output optical signal is formed and displayed. In block  918 , the location of the fiber distortion in the optical fiber under test (distance of the fiber distortion from the end of the fiber coupled to the optical source fiber) is calculated using the parameters of the spectrum. This may be performed using equation (I) as was described herein above. 
     Referring next to  FIGS. 10 and 11 , embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method  78  as shown in  FIG. 10  and an aircraft  94  as shown in  FIG. 11 . During pre-production, exemplary method  78  may include specification and design  80  of the aircraft  94  and material procurement  82 . During production, component and subassembly manufacturing  84  and system integration  86  of the aircraft  94  takes place. Thereafter, the aircraft  94  may go through certification and delivery  88  in order to be placed in service  90 . While in service by a customer, the aircraft  94  may be scheduled for routine maintenance and service  92  (which may also include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of method  78  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 11 , the aircraft  94  produced by exemplary method  78  may include an airframe  98  with a plurality of systems  96  and an interior  100 . Examples of high-level systems  96  include one or more of a propulsion system  102 , an electrical system  104 , a hydraulic system  106 , and an environmental system  108 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry. 
     The apparatus embodied herein may be employed during any one or more of the stages of the production and service method  78 . For example, components or subassemblies corresponding to production process  84  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  94  is in service. Also one or more apparatus embodiments may be utilized during the production stages  84  and  86 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  94 . Similarly, one or more apparatus embodiments may be utilized while the aircraft  94  is in service, for example and without limitation, to maintenance and service  92 . 
     Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.