Abstract:
In accordance with this invention, fiber optic cables are provided whose shape may be formed and retained while maintaining a limited bend radius. These features are produced by incorporating a compact compliant internal cable member into the cable structure. The compliant internal member consists not only of the fiber optic cable, but also of ductile and non-ductile elements. The ductile element is advantageously a tube or a wire which readily deforms to retain a given shape, and may be reshaped if desired. The non-ductile element, which resists sharp bending of the cable during shaping, comprises a substantially non-ductile elongated element disposed within the cable and configured to oppose excessively sharp bending along its length. Proper selection of the cross-sections and materials used in these elongated members produces a proper balance between shape retention and bending radius.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This disclosure claims priority on U.S. Provisional Application No. 60/819,306 entitled “Shape-Retaining Fiber Optic Cables Using a Compliant Insert” by A. Kewitsch and filed on Jul. 6, 2006. 
     
     FIELD OF THE INVENTION 
       [0002]    This invention relates to interconnects using fiber optic cables to transmit illumination and/or signals, and more particularly to shape-retaining and bend radius limited fiber optic patch cords. 
       BACKGROUND OF THE INVENTION 
       [0003]    The development of improved techniques to interconnect and deliver optical power and signals in optical fiber systems is of growing importance as optical fiber technologies spread to various telecommunications, networking, industrial and medical applications. A unique characteristic of fiber-based transmission media is that considerable care must be taken in handling fiber optic cables because of the potential to damage the internal glass optical fiber. Unlike most electrical cables, which can be sharply bent or subjected to significant forces without impacting their performance characteristics, fiber optic cables are readily damaged under small shear forces and must maintain greater than a minimum bend radius. Sharp bends result in increased insertion loss, stress birefringence and ultimately fiber failure. In addition, the interface between the polished fiber optic connector and cable is susceptible to damage arising from the concentration of stress at the point the cable enters the connector body. 
         [0004]    The preparation of fiber optic patchcords requires the use of a polishing process which adds cost relative to electronic cabling. Optical fiber cables can not be readily cut to length in the field, nor can they be folded to take up excess length. Optical connectors are also highly susceptible to contamination or scratching. This damage results in potential data corruption or complete loss of data transmission. Therefore, techniques and cable designs to mitigate damage to fiber optic cables address an important problem. 
         [0005]    Various fiber optic cable designs have been disclosed that armor and isolate the delicate optical fiber from damage. For example, U.S. Pat. No. 6,233,384 by Sowell et al. discloses a crush, kink and torque resistant flexible fiber optic cable having a spiraled, rigid, metal wire layer circumferentially disposed around the cable. The prior art has also disclosed optical fibers with shape memory activated by the application of heat to the cable, for example, as in Japan Patent Application JP2000338373. In this disclosure, a shape memory alloy ribbon is coated on the outside of the optical fiber, which can spring into a predetermined shape by application of heat. In the art of suspended optical fiber cables, it is common practice to spiral optical fiber elements about a metallic “tension member” which supports the cable to prevent the optical fibers from being tensioned excessively. Such tension members are typically braided wire, which do not have appropriate mechanical characteristics to enable the cable to retain a shape. 
         [0006]    Japanese patent JP59187303 describes an optical fiber which is plated or evaporated with a thin metal layer to retain a bend. However, this approach does not provide a means of limiting the bend radius in the bent state. An alternate approach to mechanically support a fiber optic bundle and retain its shape is described in U.S. Pat. No. 5,879,075 by Conner et al. This segmented, metallic gooseneck design is used for large diameter fiber bundles. These factors make such a cable impractical for most applications, which require a solution that satisfies multiple requirements including low cost, light weight and small form factor. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with this invention, fiber optic cables are provided whose shape may be formed and retained while maintaining an acceptable bend radius. These features are produced by incorporating a compact compliant internal cable member into the cable structure. The compliant internal member consists not only of the fiber optic cable, but also ductile and non-ductile elements. The ductile element is advantageously a tube or a wire which readily deforms to retain a given shape and may be reshaped if desired. The non-ductile element, which resists sharp bending of the cable during shaping, comprises a substantially non-ductile elongated element disposed within the cable and configured to oppose excessively sharp bending radius along its length. Proper selection of the cross-sections and materials used in these elongated members produces a proper balance between shape retention and bending radius. 
         [0008]    In a specific example of a bendable fiber optic structure in accordance with the invention, the ductile element comprises a soft annealed copper or other soft metal tube and the non-ductile element is, for example, spring tempered steel. In one example, elements have outer diameters of 2 mm or less and are disposed, together with the optical fiber within a longitudinally yieldable jacket that assures longitudinal interaction between the elements. 
         [0009]    It is shown that selection of appropriate cross-sections, dimensions, and materials can be used to define a shape-retaining structure with a defined minimum bend radius. Through an analytical or iterative process, the dimensions of the ductile material and the non-ductile element, and their elasticity properties, can be adjusted to limit the minimum bending radius while permitting arbitrary shaping within predetermined limits. 
         [0010]    A number of variations of cables using this approach are shown, including duplex and simplex cables, with the optical fibers, ductile elements and non-ductile elements being arranged in different configurations. In one example the shape of the non-ductile element is configured to limit the bending radius. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  illustrates a partial cutaway, perspective view of a duplex fiber optic patchcord; 
           [0012]      FIG. 2  illustrates cross sectional views of the shape-retaining duplex fiber optic patchcords comprised of opposed ductile and non-ductile elements; 
           [0013]      FIG. 3  illustrates the use of a shape-retaining fiber optic patchcord to interconnect a fiber optic transceiver unit to a network; 
           [0014]      FIG. 4  illustrates the connectorized end of a shape-retaining, bend limited optical cable; 
           [0015]      FIG. 5  schematically illustrates formed shape-retaining fiber optic patchcords, (A) without non-ductile bend limiting element(s) and (B) with non-ductile bend limiting element(s); 
           [0016]      FIG. 6  is a flow chart illustrating the cable design methodology in accordance with this invention; 
           [0017]      FIG. 7  presents calculations and stress relationships of an example shape-retaining member; 
           [0018]      FIG. 8  illustrates additional cross sectional views of shape-retaining cables including ductile and non-ductile elements, and 
           [0019]      FIG. 9  shows a cutaway view of a shape-retaining fiber optic cable implementation in which a non-ductile bend-limiting tube serves as the cable jacket. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    In this invention, we disclose shape-retaining and kink-resistant optical fiber cables incorporating one or more internal compliant members. The compliant member is comprised of a deformable element which can be shaped and holds a desired longitudinal cable configuration, and a non-ductile element which prevents excessively sharp bends of the resulting shaped cable. 
         [0021]    In a first example ( FIG. 1 ), the compliant members are internal to a duplex, fiber optic patch cord for Gigabit Ethernet systems with 3 mm by 6 mm zipcord jacket dimensions. “Zipcord” refers to the style of cable wherein the twin cable elements of the duplex cable can be readily separated into individual cables by separating at an end and pulling apart. Such a cable is illustrated in a partial cutway, prespective view in  FIG. 1 . The duplex cable  10 ″ is comprised of optical fibers  11 , ductile elements  14 - 1  in the form of tubes surrounding the optical fibers  11 , and non-ductile elements  14 - 2  in the form of solid wires. These elements are contained within the twin cavities of the cable jacket  12 . 
         [0022]    In this example, the non-ductile elements  14 - 2  are internal to the cylindrical ductile elements  14 - 1  and longitudinally adjacent. The ductile element  14 - 1  is a soft annealed copper tube with outer diameter of 2 mm and inner diameter of 1.25 mm. The non-ductile element  14 - 2  is spring tempered high carbon steel of 0.787 mm diameter. The outer diameter of jacket  12  is 3.0 mm and its inner diameter is 2.5 mm. The jacket is typically fabricated of flexible polyvinyl chloride (PVC) with 3 mm outer diameter. The optical fibers  11  are 0.125 mm diameter glass fibers with core diameters in the range of 5 to 100 microns and protected with a 0.250 mm diameter acrylate coating. 
         [0023]      FIG. 2  illustrates cross sectional views of typical duplex shape retaining cables. In the example of  FIG. 2A , the non-ductile element  14 - 2  is surrounded by the ductile element  14 - 1 . Alternately, as shown in  FIG. 2B , the non-ductile elements  14 - 2  are located outside of and longitudinally adjacent to ductile tube  14 - 1  with little or no impact on the performance of the compliant member. In this latter configuration, the jacket  12  serves to retain the adjacent, opposing ductile and non-ductile elements along the longitudinal extent of the cable, whereby the jacket wall thickness and strength are adequate to maintain the longitudinal alignment and transfer of forces between these elements upon bending. 
         [0024]    In a particular application, shape-retaining patchcords are provided in coiled form with a typical coil diameter of 100 to 150 mm and length of 1 to 5 meters. During use, one or both ends of the cable are uncoiled and straightened in a simple fashion by hand, without requiring tools. In this manner, a cable with the required length is provided, while excess lengths are retained in a confined loop for convenience and protection of the fiber. Such a patchcord may connect a fiber optic transceiver unit in a workstation  42  to the optical network drop cable terminated in wall interface plate  40 , for example ( FIG. 3 ). The shape-retaining optical patchcord provides a self-supporting and semi-rigid fiber loop that offers strain relief should the workstation  42  be moved. The ability to shape the cable and keep it elevated above the floor of an office, home or industrial facility is an advantage in providing optical cable connectivity to various communications equipment. The compliant element has sufficient strength-to-weight characteristics to enable the cable to be substantially self-supported under gravity when connector body  22  is secured to another mounted connector, such as that of the wallplate  40 . Furthermore, by design the optical fiber  11  is substantially coaxial with the ductile cylinder  14 - 1 , which helps to isolate the internal fiber  11  from damage due to crushing. The optical fiber  11  may in addition be surrounded by aramid fiber, such as Kevlar yard, to provide stress isolation. 
         [0025]    Shape-retaining patchcords require unique connectorization approaches to terminate the compliant member  14  in the fiber optic connector body  22 . As illustrated in  FIG. 4 , where the strain relief boots  20  have been shifted for clarity as shown by the arrow from connector body  22 , the fiber optic cables with compliant members  14  are inserted into crimp sleeves  21  which extend longitudinally from the rear of connector body  22 . By compressing metallic sleeve  21  around the jacketed cable using a suitable plier-like crimp tool, the compliant member is permanently and rigidly affixed to connector body  22 . The optical fibers are located and pass through the central bore of the compliant member  14  into the internal cavity of the connector body  22 . The optical fibers at the connector are then terminated in polished connector ferrules  23  using an industry standard connectorization and polishing process. 
         [0026]      FIG. 5  contrasts two alternate designs of shape-retaining cables, both of which contain a ductile element  14 - 1 , when manually bent to an arbitrary loop form. As illustrated in  FIG. 5A , in the absence of the opposing and stiffness enhancing, non-ductile element  14 - 2 , the cable tends to kink when manipulated by hand and when formed by the user into a desired shape. The highly ductile nature of the insert does not resist sharp bends. As a result, the cable kinks at multiple locations  17  as it is bent, the kinks corresponding to those points along the longitudinal extent of the cable in which the local radius of curvature is less than the minimum acceptable bend radius. 
         [0027]    In accordance with the invention, the addition of a non-ductile element  14 - 2  of suitable stiffness to the cable structure ( FIG. 5B ) opposes the sharp bends and ensures consistent and kink-free loops  18  with acceptable bend radius. The cable still retains the impressed shape, with the exception that those bends which are excessively sharp are automatically and intrinsically rounded out to a radius dictated by the particular cable design. 
       Design Methodology 
       [0028]    In accordance with the invention, the design of shape-retaining cables with defined minimum bend radius requires a selection of appropriate cross sections, dimensions and materials of elements. As is known in the art, the bending characteristics of the ductile and non-ductile elements may be estimated from the calculated moment of inertia of the particular element cross section to determine its mechanical stiffness. For a beam with cylindrical cross section of outer radius R and inner radius r, the elastic stiffness may be calculated by determining the moment of inertia I of this particular cross section: 
         [0000]    
       
         
           
             
               
                 
                   I 
                   = 
                   
                     
                       π 
                       4 
                     
                      
                     
                       
                         ( 
                         
                           
                             R 
                             4 
                           
                           - 
                           
                             r 
                             4 
                           
                         
                         ) 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0029]    The stiffness of a cylindrical beam is proportional to I E s , where E s  is Young&#39;s modulus of elasticity. In addition, from beam theory, the maximum bending stress of a rod or cylinder of maximum radius  r  is: 
         [0000]    
       
         
           
             
               
                 
                   σ 
                   = 
                   
                     
                       E 
                       s 
                     
                      
                     
                       
                         r 
                         _ 
                       
                       
                         r 
                         c 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where r c  is the local radius of curvature. The calculation of an average bending stress and its comparision to the material yield stress for the beam will dictate whether the bending lies in the elastic or inelastic deformation regime. 
         [0030]    The moment required to bend a straight, longitudinally extended cylindrical beam supported at one end and thereby producing a local radius of curvature r c  is: 
         [0000]    
       
         
           
             
               
                 
                   
                     M 
                     = 
                     
                       
                         π 
                         4 
                       
                        
                       
                         
                           E 
                           s 
                         
                         
                           r 
                           c 
                         
                       
                        
                       
                         ( 
                         
                           
                             R 
                             4 
                           
                           - 
                           
                             r 
                             4 
                           
                         
                         ) 
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where the moment M is equal to the product of an applied bending force and the distance from the support point of the beam to the point on the beam at which the force is applied. The moment required to bend a non-ductile element to a minimum specified bend radius is calculated from Equation (3). The non-ductile element has sufficient rigidity (e.g., metal elements are typically spring tempered or full-hard annealed) so it will spring-back to its original form, either straight or weakly coiled, in the absence of an applied moment. This assumes the stress on the non-ductile element is less than its yield strength, a requirement met by use of spring-tempered or hardened metals or rigid composites based on carbon fiber or polymers, for example. The tendency of the non-ductile element to resist sharp bends limits the minimum bend radius of the cable. 
         [0031]    The ductile element is designed to produce a bending moment or local force along the longitudinal extent of the cable which is adequate to ensure that the non-ductile element retains its radiused form. For the ductile element to retain a static shape, it must produce a local force distribution equal and opposite to the local force distribution of the non-ductile element. The induced bend radius of the ductile element resulting from this force is calculated from Equation (3). To hold this radius, it is further required that the average bending stress on the ductile element, estimated from the bend radius using Equation (2), be less than the yield stress of the ductile element. 
         [0032]    The design process for the compliant member  14  follows a methodology which produces the desired cable bending characteristics by iteratively adjusting characteristics of the ductile and non-ductile elements until a self-consistent solution with desired properties is obtained.  FIG. 6  diagrammatically illustrates the design steps for a compliant member comprised of complementary ductile and non-ductile elements. In step  1 , a minimum acceptable bend radius is provided as an input parameter. This minimum bend radius is dictated by the particular requirements of the optical fiber type, as well as its jacket or buffer diameters. The stresses on optical fiber under bending must be limited to prevent crack formation of the glass element. For example, typical unjacketed optical fiber has a minimum bend radius of 2.5 cm, while typical jacketed optical fiber has a minimum bend radius of 3.7 cm. Alternately, specialty bend insensitive fiber and reduced diameter cladding fiber can accommodate a bend radius as small as 5 mm without exhibiting long term, stress induced crack formation. 
         [0033]    In step  2 , preliminary values for the cross sectional dimensions and materials are estimated and Young&#39;s modulus of elasticity of the non-ductile material is provided. These may be initial targets based on the desired diameter of the finished cable, which can be refined later by use of an iterative approach, as described in subsequent step  9 . Using the target values, the moment of inertia for the non-ductile element is calculated in step  3  using Equation (1), from which the bending characteristics of this particular cross section are estimated. In step  4 , the value of the bending moment corresponding to the minimum bend radius is calculated for the non-ductile element using Equation (3), for the cross section selected in step  3 . 
         [0034]    In step  5 , initial values for the cross sectional dimensions and materials, including Young&#39;s modulus of the ductile material, are selected. These initial values may require updating through an iterative approach, as outlined in step  9 . In step  6 , the moment of inertia for the ductile element is calculated using these initial values. In step  7 , the bend radius of the ductile element produced by the bending moment of the non-ductile element is estimated using Equation (3) and the value of moment of inertia calculated in step  6 . In step  8 , the maximum stress of the ductile element at the calculated bend radius of the ductile element is calculated. 
         [0035]    In step  9 , the stress on the ductile element is compared to the ductile material&#39;s inherent yield stress. The value will fall within one of three ranges: First, if the stresses are nominally equal, the design of the ductile and non-ductile elements are satisfactory because the retained cable shape can not maintain a radius of curvature less than the predefined value. Note that the yielding of the ductile element may be best represented by an average stress rather than the maximum stress, so it may be acceptable for the maximum stress to be slightly larger than the inherent material yield stress. 
         [0036]    Second, if the calculated stress is less than the yield stress (step  10 ), it is possible to form the cable with a radius of curvature tighter than the minimum bend radius, which contradicts the original design requirement. This therefore requires that the moment/modulus of the ductile element be decreased, and/or the moment/modulus of the non-ductile element be increased. Some design parameters may be changed based on this result in steps  2  and  5 , and thereafter the iterative process is repeated. 
         [0037]    Third, if the calculated stress is more than the yield stress (step  11 ), the cable is unable to retain a bend with radius of curvature as small as the target minimum bend radius. Therefore, the cable can not be coiled with sufficiently small coil diameter. To correct this situation, the moment/modulus of the ductile element may be increased, and/or the moment/modulus of the non-ductile element may be decreased. Design parameters may be changed in steps  2  and  5 , and thereafter the iterative process is repeated. The bending stress is again compared to the yield stress of the ductile element. Once the selected parameters lead to a self-consistent solution for the bending stress, the design process is complete. 
         [0038]    Note that the cross sectional dimensions of the non-ductile element can not be made arbitrarily small, because this will reduce its stiffness and make it possible to excessively bend the element and exceed its yield stress while shaping the cable. The cable should be able to withstand applied torques of up to about 0.5 kg-cm without bending excessively. For this reason, it is preferred to utilize spring-tempered material which exhibits relatively high yield strength and resists over bending under typical applied forces. The dimensions of the non-ductile element are typically greater than 0.5 mm in diameter, preferentially in the vicinity of 0.75 mm diameter, for a non-ductile element of circular cross section. This provides a restoring force that effectively compensates the bending force applied by a typical user under typical use conditions. 
         [0039]      FIGS. 7A-7C  are a series of calculation results for a particular cable design example in accordance with the methodology outlined in  FIG. 6 . The ductile element  14 - 1  is a soft annealed copper tube with outer diameter of 2 mm and inner diameter of 1.25 mm, and the non-ductile element  14 - 2  is spring tempered 1075, 1085, or 1095 carbon steel of 0.787 mm diameter.  FIG. 7A  plots the calculation results of bending moment for the non-ductile element as a function of bend radius. These results are utilized in step  3 , wherein the maximum bending moment  51  corresponding to desired minimum bend radius  50  is calculated.  FIG. 7B  plots the calculation results of bending moment for the non-ductile element as a function of bend radius. These results are utilized in step  7 , wherein the bend radius  53  of the ductile element induced by the moment  51  of the non-ductile element is determined. To determine whether this cable shape is substantially retained, as in step  10 , the maximum stress  52  of ductile element having this induced bend radius  53  is calculated.  FIG. 7C  plots the maximum stress  52  of the ductile element as a function of bend radius. In this calculation, since the local stress  52  corresponds to that stress produced by a local radius of curvature equal to the bending radius threshold  54  of 52.5 inches, the shape of the bend is retained and the minimum bend radius of 2 inches is achieved. The relationships illustrated graphically in  FIG. 7A-7C  present the interrelations and dependencies of the minimum bend radius on various force and stress considerations 
         [0040]    To summarize the design methodology, the minimum bend radius  50  is first defined, whereby the corresponding bending moment  51  required to produce this radius in the non-ductile member is determined ( FIG. 7A ). The effect of this maximum bending moment  51  on the ductile member is plotted in  FIG. 7B , wherein the bend radius induced on the ductile member is then estimated. Thereafter, in  FIG. 7C  the stress level  52  produced by this degree of bending is compared to the yield point of the ductile member. For bend radii less than the minimum bending radius threshold  54 , the ductile member deforms inelastically and takes a new shape which reduces the radius of curvature. For radii greater than the minimum bend radius threshold  54 , the ductile element substantially retains the bent form. 
       EXAMPLE 
     Simplex Fiber Optic Cables 
       [0041]    Shape retaining fiber optic cables can be provided with a variety of fiber optic cable types, such as simplex, duplex, multi-fiber or ribbon cable. Cross sectional views of various simplex-type shape-retaining patchcords are shown in  FIG. 8 . In the example of  FIG. 8A , the optical fiber  11  and non-ductile element  14 - 2  are surrounded by and substantially coaxial with a cylindrical ductile element  14 - 1 . This ductile element  14 - 1  is jacketed along its longitudinal extent within a flexible plastic  12  sheath. This sheath  12  may be provided in the form of a tube, or may be extruded or coated directly onto ductile element  14 - 1 . In an alternate example, the non-ductile wire  14 - 2  may be placed within plastic jacket  12  but outside of ductile cylinder  14 - 1  ( FIG. 8B ). Alternately, as illustrated in  FIG. 8C , the non-ductile element  14 - 2  may be in the form of an outer bend limiting tube  16  that surrounds both the ductile element  14 - 1  and optical fiber  11 . 
         [0042]    An example of a bend limiting tube  16  serving as an outer fiber optic cable jacket has been disclosed in PCT Publication No. WO 2006/035206A1 by Jenkins et al. This plastic jacket is in the form of a tube  16  with circumferential grooves that limit the bend radius of the cable to a pre-specified value. In this structure, the restriction on bending is a result of the physical geometry of the grooved tube, and is not dependent on stress build-up within the non-ductile element. Typically, the bend limiting tube is fabricated of plastic with outer diameter of 2 mm to 10 mm. A typical minimum bend radius for jacketed fiber optic cable is 32 mm. Such a cable, shown in cross section in  FIG. 8C , is illustrated in partial cutaway view in  FIG. 9 . This or related implementations of a bend limited tube are alternate approaches which equivalently function as the non-ductile element  14 - 2 . 
         [0043]    The minimum fiber bend radius is 25 mm for unjacketed cables consisting of Corning SMF-28 fiber or its equivalents. In implementations with Corning Flex 1060 single mode bend insensitive fiber, the radius can be reduced to 10 mm. Cable manufacturers specify the minimum bend radius for cables under tension and long-term installation. The ANSI TIA/EIA-568B.3 standard specifies a bend radius of 25 mm under no pull load and 50 mm when subject to tensile loading up to the rated limit. Cables comprised of special bend insensitive fiber such as Corning Flex 1060, Lucent D5, Nufern 1550B-HP, or Sumitomo Pure Access or Pure Access-Ultra can withstand a bend radius of 7.5 to 10 mm without exhibiting increased insertion loss or mechanical failure. This is achieved by increasing the numerical aperture of the fiber to increase the guiding characteristics, and in some cases, by reducing the outer diameter of the cladding from 125 μm to 80 μm. Alternately, the constituent fibers making up the cable may include one or more strands of single mode (SM), multimode (MM), dispersion shifted (DS), non-zero dispersion shifted (NZDS), polarization maintaining (PM), photonic crystal (PC) or plastic optical fiber (POF). The typical wavelengths of operation for telecommunications applications include 850 nm, 1310 nm and 1550 nm (S, C, and L bands). The outer diameter of the bare fiber may be 80, 125, or 200 μm with an acrylate coating of 250 μm diameter, for example. The shape-retaining cable may further include a variety of different fiber types fusion spliced together to form a continuous length of fiber. 
         [0044]    Various types of protective jacketing can be incorporated into the shape-retaining, bend-limited cable disclosed herein, such as jacketed optical fiber with 3, 2.9, 2, 1.8 or 1.6 mm outer diameters, containing coated optical fiber of 0.25 to 0.5 mm diameter or tight buffered fiber of 0.5 to 0.9 mm outer diameter. In addition, shape-retaining bend limited cable may incorporate fiber optic ribbon cables comprised of four or more individual fibers, for example. 
         [0045]    The termination of shape-retaining, bend-limited fiber optic cables requires that the compliant member be attached in a semi-rigid fashion to the connector body(s) at the end(s) of the cable. Any of the numerous fiberoptic connector styles can be utilized, including industry standard FC, SC, ST, LC or MTRJ connectors. 
       EXAMPLE 
     Materials 
       [0046]    Suitable materials for use as the ductile element include, but are not limited to, the class of malleable metals which are highly ductile and relatively immune to work-hardening. Excessive work-hardening would potentially cause brittleness of the compliant material and lead to cracking and embrittlement over many cycles of cable shaping and reshaping. Optimal materials include soft annealed copper, brass, tin, aluminum or related alloys. In a particular example, the ductile element is comprised of soft annealed copper with 35,000 psi ultimate strength and 10,000 psi yield strength. In alternate examples, C260 (cartridge) brass with 47,900 psi ultimate strength and 16,000 psi yield strength or 1006-1008 series soft annealed steel may be utilized. 
         [0047]    Materials suitable for the non-ductile element include, but are not limited to, the class of high strength, high carbon steel alloys. In a particular example, the non-compliant element is comprised of 1075-1095 series carbon steel spring tempered wire (piano or music wire) with up to 399,000 psi ultimate strength and 75,000 psi yield strength. Such metallic elements may be additionally treated with a phosphorus coating or galvanized to resist corrosion. Alternately, the non-ductile element is comprised of polymer materials such as composites with fiber reinforcement. The reinforcement materials include fiberglass with high strength (625-665 Kpsi) and high modulus of elasticity (12.6 Kpsi), or aramid fiber with higher modulus of elasticity (11.5-27.0 Mpsi). Carbon or graphite fiber offers the highest strength (1050 Kpsi) and the highest modulus (33-120 Mpsi) reinforcement. Alternately, PEEK plastic or equivalents also provide sufficient rigidity while having the advantage of reduced weight. 
         [0048]    Those skilled in the art will readily observe that numerous modifications and alterations of the cable structure may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.