Shape-Retaining Fiber Optic Cables Having Limited Bend Radius

• US 20080008430A1
• Filed: 08/25/2006
• Published: 01/10/2008
• Est. Priority Date: 07/06/2006
• Status: Active Grant

• Current Assignee: Telescent Inc.
• Original Assignee: Anthony Stephen Kewitsch
• Inventors: Kewitsch, Anthony Stephen
• Granted Patent: US 7,460,753 B2
• Time in Patent Office: Days
• US Class Current: 385/113
• CPC Class Codes: G02B 6/4478 Bending relief means

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.

Claims

1. An elongated fiber optic conduit structure which can be multiply shaped to follow a desired path while maintaining a minimum bend radius, comprising:

an elongated jacket for confining at least two extended members, the jacket having a longitudinally pliant body with limited radial expandability;

a fiber optic conduit disposed within and along the jacket, the conduit having a low structural rigidity but required to have more than at least a minimum bending radius;

a first elongated structural member disposed within and extending along the jacket, said member being of ductile material which yields under a predetermined force;

a second elongated structural member disposed within and along the jacket, the second adjacent the first structural member, the second member being non-ductile and producing a force when subjected to the minimum bend radius that is nominally equal to the predetermined force which can be sustained by the first structural member without yielding, and

the first and second structural members being juxtaposed within the jacket to provide a combinatorial response to curvature such that the fiber optic conduit system opposes shaping to less than the minimum bend radius.

2. An elongated fiber optic conduit structure in accordance with claim 1 above, wherein the structure can be subsequently re-shaped to follow and retain an alternate path while maintaining a minimum bend radius.

3. A fiber optic conduit structure as set forth in claim 1 above, wherein the first structural element is hollow and the second structural element and the said conduit are disposed therewithin.

4. A fiber optic conduit structure as set forth in claim 1 above, wherein the first structural element is hollow and within said jacket and the conduit is disposed within the first structural element and the second structural element is within the jacket external to the first structural element.

5. A fiber optic conduit structure as set forth in claim 1 above, wherein the conduit structure comprises paired structures with longitudinally adjoining jackets.

6. A fiber optic conduit structure as set forth in claim 1 above, wherein the first structural element defines the jacket and includes a central bore encompassing the second structural element and the conduit.

7. A fiber optic conduit structure as set forth in claim 1 above, wherein the jacket has bend-limited compliance, and wherein the second structural member and conduit are within the jacket, and is in longitudinal physical engagement with the jacket.

8. A structure in accordance with claim 1, wherein the fiber optic conduit is comprised of one or more optical fibers selected from the class of fibers including single mode, multi-mode, dispersion compensating, bend-insensitive, high numerical aperture, photonic crystal and plastic optical fibers.

9. A structure in accordance with claim 8, wherein the optical fibers are fabricated of fused silica with an outer diameter of 125 to 250 microns with a protective coating of 250 to 900 microns.

10. A structure in accordance with claim 1, wherein the first elongated structural member is soft annealed copper, cylindrical in cross section with an outer diameter of 1.5 to 2.0 mm, an inner diameter of 1 to 1.5 mm, and wherein the second elongated structural member is spring steel, circular in cross section with a diameter of 0.5 to 1 mm.

11. A fiber optic structure shapeable to a selected longitudinal configuration that is limited to a minimum bending radius, comprising, in combination,

first and second elongated members in proximate lengthwise relation, one of the members having an elastic bending response when subjected to a radius of curvature along its longitudinal extent, the second member having an inelastic bending response when subjected to a radius of curvature along its longitudinal extent equal to the minimum bending radius, the second member in interaction with the first member,

a fiber optic conduit transversely adjacent the first and second members, and

an element enclosing the first and second members and the conduit to maintain the physical proximity there between.

12. A fiber optic structure in accordance with claim 11 above, wherein the elastic rigidity of the second member exceeds the elastic rigidity of the first member.

13. A fiber optic structure in accordance with claim 11 above, wherein the first member is substantially comprised of a first material and the second member is substantially comprised of a dissimilar, second material, the first material characterized by a yield strength greater than that of the second material.

14. A structure in accordance with claim 13 above, wherein the first material is high carbon steel or a carbon fiber composite, and the second material is soft annealed copper, tin, brass, aluminum or low carbon steel.

15. A structure in accordance with claim 11, wherein the first member is non-ductile with substantially circular cross sections of 0.5 to 1 mm in diameter, and the second member is ductile with substantially cylindrical cross sections with 1 to 1.5 mm inner diameter and 1.5 to 2.0 mm outer diameter.

16. A cable in accordance with claim 11 wherein the limited bend radius is about 37 mm or more.

17. A flexible, fiber optic interconnection cable including opposing first and second compliant elements and a unifying jacket retaining said elements in transverse proximity, wherein, under an applied bending force, the first compliant element exerts an elastic bending force which partially opposes the applied bending force, the second compliant element physically deforms under applied bending force to a new shape, and the second compliant element, upon removal of applied bending force, producing a holding force opposing the elastic bending force produced by the first compliant element to substantially maintain the new shape.

18. A flexible, fiber optic interconnection cable as set forth in claim 17 above, wherein the stiffness of the first compliant element is selected to maintain a bend radius greater than 37 mm under an applied bending moment of less than 0.5 kg-cm.

19. A flexible, fiber optic interconnection cable as set forth in claim 17 above, wherein the cable includes optical fibers internal to the second compliant element so that the optical fibers are substantially isolated from excessive shear, tensile, and/or compressive forces applied to the interconnection cable.

20. A flexible, fiber optic interconnection cable as set forth in claim 17 above, wherein the interconnection cable further includes ends which are terminated in polished fiber optic connectors including a rigid connector body, having a rigid, longitudinally extended support incorporated therein, the first compliant element being inserted therein to allow optical fibers to pass longitudinally therein, the support preventing excessive bending at the insertion point of the cable into the connector body.