Stranded optical fiber cable
An optical fiber cable comprises a plurality of buffer tubes, a hollow-core optical fiber disposed within one of the plurality of buffer tubes, and a central strength member. The plurality of buffer tubes are helically stranded about the central strength member, where a diameter d of the central strength member and a lay length l of the plurality of buffer tubes around the central strength member satisfy the following inequality: d≤0.075l−6.875. A cable jacket surrounds the plurality of buffer tubes, where a radius of curvature of the hollow-core optical fiber, when the optical fiber cable is kept straight at a temperature of 20° C., is 200 mm or greater.
1 . An optical fiber cable, comprising:
a first primary-capillary comprising glass and surrounding an interior passage thereof;
a first nested-capillary positioned within the interior passage of the first primary-capillary,
wherein the first nested-capillary only fills a portion of the interior passage of the first primary-capillary, and wherein the first nested-capillary also comprises an open space extending lengthwise therein;
a cladding having a round cross-section and surrounding the first primary-capillary and in turn the first nested-capillary,
wherein the first primary-capillary is fixed to an interior surface of the cladding;
two other primary-capillaries in addition to the first primary-capillary, the two other primary-capillaries also fixed to the interior surface of the cladding;
wherein portions of exteriors of each of the first primary-capillary and the two other primary-capillaries line a hollow core therebetween, the hollow core configured to convey an optical signal communicated lengthwise therealong, whereby the cladding, the first primary-capillary, the first nested-capillary, and the two other primary-capillaries each form part of a first optical fiber;
a coating layer surrounding the first cladding of the first optical fiber, wherein the coating layer comprises an ultra-violet-light curable and/or thermoset polymer;
a first buffer tube comprising thermoplastic and having a cross-sectional dimension orthogonal to a length thereof, measured from an exterior thereof through a geometric center thereof and to an opposing exterior thereof, that is at least twice that of the coating layer of the first optical fiber;
wherein the first buffer tube surrounds the first optical fiber;
two other buffer tubes in addition to the first buffer tube, wherein the two other buffer tubes each surround at least one other optical fiber;
a strength member comprising fiber-reinforced plastic;
a cable jacket surrounding the strength member, the first buffer tube, and the two other buffer tubes;
wherein each of the first buffer tube and the two other buffer tubes are stranded around the strength member within the cable jacket such that the first optical fiber has a longer length than the optical fiber cable, and
wherein the first optical fiber is loosely positioned in the first buffer tube and/or the first buffer tube is loosely positioned within the cable jacket such that the first optical fiber is at least partially free to move relative to the first buffer tube and/or relative to the strength member, to a lower stress position, as the cable bends in an arc of 500 mm, twists 3° per 2 m length, and/or stretches by 0.3% strain.
2 . The optical fiber cable of claim 1 , wherein the stranding is such that the first buffer tube bends no tighter than an arc of 200 mm radius within the cable jacket.
3 . The optical fiber cable of claim 1 , wherein the first optical fiber has a length greater than or equal to that of the first buffer tube, and less than 3% longer than the first buffer tube.
4 . The optical fiber cable of claim 1 , wherein the coating layer of the first optical fiber comprises both a primary coating and a secondary coating, the primary coating softer than the secondary coating, and the secondary coating exterior to the primary coating.
5 . The optical fiber cable of claim 1 , wherein the first buffer tube is a tight buffer overlaying the coating layer having an outside diameter of at least 500 km.
6 . The optical fiber cable of claim 1 , wherein the cladding comprises glass, wherein the glass of the cladding comprises, in terms of mole percent on a representative oxide basis, at least 60 mol % silica, wherein the glass of the cladding has a coefficient of thermal expansion and a modulus of elasticity, wherein the cable jacket comprises a thermoplastic polymer, wherein the thermoplastic polymer has a coefficient of thermal expansion greater than that of the glass of the cladding and a modulus of elasticity less than that of the glass of the cladding.
7 . The optical fiber cable of claim 1 , wherein when the optical fiber cable is at 50° C., tension in the strength member opposes compression in the cable jacket, while the optical fibers experience stress less than 5 MPa.
8 . The optical fiber cable of claim 1 , wherein when the optical fiber cable is at 50° C., hollow cores of the optical fibers move closer to the strength member on average than when the optical fiber cable is at 20° C.
9 . The optical fiber cable of claim 1 , wherein each of the primary-capillaries are spaced apart from one another around the interior surface of the cladding.
10 . The optical fiber cable of claim 1 , wherein the buffer tubes are a first group, wherein the optical fiber cable further comprises a second group of buffer tubes overlaying the first group, wherein the first and second groups are helically stranded in opposite directions from one another around the strength member, wherein the second group has a lay length that is greater than that of the first group.