Method for drop cable having an oval cavity

Abstract

A method of forming a low-cost drop cable ( 10 ) is disclosed. The method includes providing a protective cover material ( 352 ) having an extrusion temperature of 140° C.≦TE≦160° C. The protective cover material is extruded through a die ( 420 ) having a single aperture ( 424 ) that defines the cable's elongate cross-sectional shape. The extrusion process involves covering first and second strength members ( 30 ) on either side of at least one optical fiber ( 50 ). The combination of the low temperature of the extrudable protective cover material and the elongate shape of the single die aperture cause the formation of an oval cavity ( 20 ) within the extruded protective cover material. The oval cavity has major and central axes (A 1 , A C ) and surrounds the at least one optical fiber. The strength members lie along the cavity major axis. Tensioning the strength members during extrusion and then releasing the tension causes the drop cable length to be reduced. This gives rise to an excess fiber length, which adopts a serpentine configuration substantially in a plane (PF) defined by the major and central axes (A 1 , A 2 ) of the oval cavity.

1 . A method of forming a drop cable having a length L, comprising:
 providing an extruder tip with an end through which at least one optical fiber is fed, and arranging the extruder tip to extend within a die;   flowing a protective cover material:
 i) around the extruder tip and through the die to form a longitudinally extending central oval cavity that contains the at least one optical fiber and that has a major axis and a central axis; and 
 ii) around first and second strength members that reside substantially along the major axis on opposite sides of the oval cavity and that extend substantially parallel thereto; 
   tensioning the first and second strength members during said flowing of the protective cover material; and   releasing the tension in the first and second strength members to shorten their length, to reduce the length of the drop cable, and to cause the at least one optical fiber to adopt a serpentine configuration within the oval cavity substantially in a plane defined by the major and central axes of the oval cavity.   
   
   
       2 . The method of  claim 1 , wherein the protective coating material has an extrusion temperature, TE, of: 140° C.≦TE≦160° C. 
   
   
       3 . The method of  claim 1 , wherein the at least one optical fiber has a strain limit S T , and further including providing the at least one optical fiber with an amount of strain S wherein (0.25)S T ≦S≦S T . 
   
   
       4 . The method of  claim 1 , wherein, compared to the drop cable length, L, the at least one optical fiber has an amount of excess fiber length, EFL, of: (0.001)L≦EFL≦(0.004)L. 
   
   
       5 . The method of  claim 4 , including selecting the amount of excess fiber length that is associated with a low-temperate attenuation limit at a fiber strain limit S T . 
   
   
       6 . The method of  claim 1 , including covering the at least one optical fiber with at least one water-blocking material, and flowing the protective cover material around the at least one optical fiber and the at least one water-blocking material. 
   
   
       7 . The method of  claim 1 , including forming the oval cavity to have a nominal major axis diameter (DO 1 ) of about 0.66 mm and a minor axis diameter (DO 2 ) of about 0.30 mm. 
   
   
       8 . The method of  claim 1 , wherein the at least one optical fiber is a bend-insensitive optical fiber. 
   
   
       9 . The method of  claim 1 , wherein the serpentine configuration is substantially sinusoidal. 
   
   
       10 . A method of forming a drop cable having a length L and an elongate cross-sectional shape, comprising:
 extruding a protective cover material having an extrusion temperature TE defined by 140° C.≦TE≦160° C., through a die with a single aperture that defines the cable's elongate cross-sectional shape to cover first and second strength members on either side of at least one optical fiber and form an oval cavity having major and central axes and that surrounds the at least one optical fiber.   
   
   
       11 . The method of  claim 10 , further comprising:
 tensioning the first and second strength members during said extruding; and   terminating said tensioning after said extruding to reduce the length of the drop cable and cause the at least one fiber to adopt a serpentine configuration substantially in a plane defined by the major and central axes.   
   
   
       12 . The method of  claim 11 , wherein the serpentine configuration is substantially sinusoidal. 
   
   
       13 . The method of  claim 11 , wherein as compared to the drop cable length L, the at least one optical fiber has an amount of excess fiber length (EFL) of: (0.001)L≦EFL≦(0.004)L. 
   
   
       14 . The method of  claim 10 , wherein the at least one optical fiber has a strain limit S T , and an amount of strain S where (0.25)S T ≦S≦S T . 
   
   
       15 . The method of  claim 10 , wherein the at least one optical fiber is bend-insensitive. 
   
   
       16 . The method of  claim 10 , wherein the elongate cross-sectional shape is substantially oval. 
   
   
       17 . A method of forming a drop cable having a length L, a protective cover, and an elongate cross-sectional shape, comprising:
 configuring an extruder with a tip with a fiber exit end that resides within a die having a single elongate aperture that defines the protective cover elongate cross-sectional shape;   extruding a protective cover material having an extrusion temperature (TE) of 140° C.≦TE≦160° C., through a die and around at least one optical fiber to cause the protective cover material to define an oval cavity surrounding the at least one fiber and having major and central axes; and   providing first and second support members on respective sides of the extruder tip so that said extruding of the protective cover extrusion material covers the first and second support members substantially in a plane defined by the major and central axes.   
   
   
       18 . The method of  claim 17 , further comprising:
 tensioning the first and second strength members during said extruding;   terminating said tensioning after said extruding to reduce the length of the drop cable and cause the at least one fiber to adopt a serpentine configuration substantially in a plane defined by the major and central axes.   
   
   
       19 . The method of  claim 18 , wherein the serpentine configuration is substantially sinusoidal. 
   
   
       20 . The method of  claim 18 , wherein, compared to the drop cable length L, the at least one optical fiber has an amount of excess fiber length (EFL) of (0.001)L≦EFL≦(0.004)L.