Patent Description:
In an area where optical fibers may be damaged because of the batting by birds such as woodpeckers or the biting by animals such as squirrels, optical fiber cables each incorporating a metal sheath are used as a countermeasure against bird, insect, and animal damages (see, for example, Patent Literature <NUM>). A cross-sectional structure of a related optical fiber cable will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, a metal sheath <NUM>, and a polyethylene jacket <NUM>. The optical fiber cable provided with the bird-insect-animal damage countermeasure is formed from the cable core <NUM>, the metal sheath <NUM> coated so as to cover the cable core <NUM>, and the polyethylene jacket <NUM>. The optical fiber cable has the metal sheath <NUM>, and thus when accessing the cable core <NUM> from the optical fiber cable, a high-strength cable jacket cutter is used as a dedicated tool to tear the metal sheath <NUM>.

However, when tearing the metal sheath using the high-strength cable jacket cutter, which is the dedicated tool, an event in which an optical fiber accommodated in the cable core <NUM> is cut unintentionally because of excessive entering of a blade of the tool occurs occasionally. In addition, the work for tearing the metal sheath while making fine adjustment to avoid excessive entering of the blade is highly skillful, and accordingly the work is time consuming. Publication <CIT> discloses examples of optical fiber cables.

An object of the present disclosure is to facilitate tearing a metal sheath even in a case where the metal sheath is incorporated in an optical fiber cable.

To achieve the above object, the present invention provides an optical fiber cable according to independent claim <NUM>. A further embodiment is provided in the dependent claim. The optical fiber cable of the present disclosure includes an outer sheath tearing string extending in a longitudinal direction inside the metal sheath.

Including the outer sheath tearing string can facilitate tearing the metal sheath.

Specifically, the optical fiber cable of the present disclosure includes a cable core arranged at a central portion and accommodating a plurality of optical fibers gathered together, an inner layer sheath arranged on an outer circumference of the cable core and sheathing the cable core, a metal sheath arranged on an outer circumference of the inner layer sheath and wound around the inner layer sheath, an outer layer sheath arranged on an outer circumference of the metal sheath and sheathing the metal sheath, and at least one outer sheath tearing string arranged in a longitudinal direction inside the metal sheath.

In the optical fiber cable of the present disclosure, the outer sheath tearing string is arranged between the metal sheath and the inner layer sheath. Including the outer sheath tearing string can facilitate tearing the metal sheath.

In the optical fiber cable of the present disclosure, the outer sheath tearing string is arranged in such a manner that at least a part thereof is embedded in an outer peripheral surface of the inner layer sheath.

This arrangement can prevent the outer sheath tearing string from moving in the longitudinal direction inside the metal sheath.

The optical fiber cable of the present disclosure may further include at least one inner sheath tearing string arranged in a longitudinal direction inside a layer of the inner layer sheath.

Including the inner sheath tearing string can facilitate tearing the inner layer sheath.

The optical fiber cable of the present disclosure further includes a continuous protrusion arranged on the outer peripheral surface of the inner layer sheath and extending along the outer sheath tearing string.

Identifying a position of the outer sheath tearing string becomes easy.

The optical fiber cable of the present disclosure may further include the continuous protrusion arranged on the outer peripheral surface of the inner layer sheath and extending along the outer sheath tearing string, and the inner sheath tearing string and the outer sheath tearing string may be arranged on the same radial axis of the optical fiber cable.

Identifying the positions of the inner sheath tearing string and the outer sheath tearing string becomes easy.

In the optical fiber cable of the present disclosure, it is desirable that the metal sheath has a part single-wounded and the rest double-wounded around the outer circumference of the cable core, and the at least one outer sheath tearing string is arranged inside the single-wounded part.

The outer sheath tearing string facilitates tearing the metal sheath.

According to the present disclosure, it is possible to facilitate tearing a metal sheath even when the metal sheath is incorporated in an optical fiber cable.

Hereinafter, embodiments of the present disclosure will be described in detail below with reference to attached drawings. The present disclosure is not limited to the following embodiments. These embodiments are merely examples, and the present disclosure can be carried out in the form of various modifications and improvements, based on the knowledge of those skilled in the art, being made. In the present specification and the drawings, constituent components suffixed by the same reference numerals shall indicate the same components.

An exemplary cross-sectional structure of an optical fiber cable, not forming part of the claimed invention, will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, an inner layer sheath <NUM>, a metal sheath <NUM>, an outer layer sheath <NUM>, and an outer sheath tearing string <NUM>. The cable core <NUM> is arranged at a central portion of the optical fiber cable, and includes a plurality of optical fibers gathered together. The inner layer sheath <NUM> is arranged on an outer circumference of the cable core <NUM> to sheath the cable core <NUM>. The inner layer sheath <NUM> may include a tension member that protects the optical fibers against a tensile force acting on the optical fiber cable. The material of the inner layer sheath <NUM> is, for example, polyethylene, frame-retardant polyethylene, polyvinyl chloride, or the like. The cable core <NUM> and the inner layer sheath <NUM> are collectively referred to as a cable body. The metal sheath <NUM> is arranged on an outer circumference of the inner layer sheath <NUM>, and is wound around the inner layer sheath <NUM>. The material of the metal sheath <NUM> is, for example, stainless steel, steel, iron or the like. The outer layer sheath <NUM> is arranged on an outer circumference of the metal sheath <NUM> to sheath the metal sheath <NUM>. The material of the outer layer sheath <NUM> is, for example, polyethylene, frame-retardant polyethylene, polyvinyl chloride, or the like. The metal sheath <NUM> and the outer layer sheath <NUM> are collectively referred to as an external sheath. The optical fiber cable according to the present disclosure includes at least one outer sheath tearing string <NUM> arranged in the longitudinal direction inside the metal sheath <NUM> to tear the metal sheath <NUM> and the outer layer sheath <NUM>. The outer sheath tearing string <NUM> is required to be arranged inside the metal sheath <NUM>. The at least one outer sheath tearing string <NUM> needs to be provided, or two or more outer sheath tearing strings may be provided. The material of the outer sheath tearing string <NUM> is, for example, Tetron fiber, Kevlar fiber, aramid fiber, polyester fiber, or the like, which are excellent in tensile strength and can be used as they are or twisted together. These structures are the same in the following embodiments.

In the optical fiber cable according to the present embodiment, the outer sheath tearing string <NUM> may be arranged between the metal sheath <NUM> and the inner layer sheath <NUM>, as illustrated in <FIG>. Arranging the outer sheath tearing string <NUM> between the metal sheath <NUM> and the inner layer sheath <NUM> facilitates taking out the outer sheath tearing string <NUM>.

Even if there is the metal sheath <NUM> introduced as the countermeasure against bird, insect, and animal damages, providing the outer sheath tearing string <NUM> can facilitate tearing the metal sheath <NUM> and the outer layer sheath <NUM>. That is, the optical fiber cable can be disassembled using the outer sheath tearing string <NUM>, without using a dedicated tool, and without damaging the optical fiber. The disassembling method using the outer sheath tearing string <NUM> requires no high-degree skill and can shorten the required time.

An exemplary cross-sectional structure of an optical fiber cable, not forming part of the claimed invention, but useful to understand the claimed invention, will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, an inner layer sheath <NUM>, a metal sheath <NUM>, an outer layer sheath <NUM>, and an outer sheath tearing string <NUM>. At least a part of the outer sheath tearing string <NUM> may be embedded in an outer peripheral surface of the inner layer sheath <NUM>. That is, the outer sheath tearing string <NUM> may have a part embedded in the inner layer sheath <NUM> and another part exposed from the inner layer sheath <NUM>. The outer sheath tearing string <NUM> may be entirely embedded in the inner layer sheath <NUM>. Being partly embedded in this case indicates a state where a part of the outer sheath tearing string <NUM> is embedded in the inner layer sheath <NUM> in a cross section perpendicular to a longitudinal direction of the optical fiber cable, as illustrated in <FIG>.

Embedding at least a part of the outer sheath tearing string <NUM> in the inner layer sheath <NUM> can prevent the outer sheath tearing string <NUM> from moving in the circumferential direction or coming off in the longitudinal direction between the inner layer sheath <NUM> and the metal sheath <NUM>. Increasing an embedment rate of the outer sheath tearing string <NUM> in the inner layer sheath <NUM> enhances the above effect. This results in facilitating tearing the metal sheath <NUM> and the outer layer sheath <NUM>.

An exemplary cross-sectional structure of an optical fiber cable, not forming part of the claimed invention, will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, an inner layer sheath <NUM>, a metal sheath <NUM>, an outer layer sheath <NUM>, an outer sheath tearing string <NUM>, and an inner sheath tearing string <NUM>. The optical fiber cable according to the present disclosure includes at least one inner sheath tearing string <NUM> that is arranged in a longitudinal direction inside a layer of the inner layer sheath <NUM> to tear the inner layer sheath <NUM>.

The optical fiber cable illustrated in <FIG> has an exemplary structure including the inner sheath tearing string <NUM> in addition to the optical fiber cable described in the embodiment <NUM>. The at least one inner sheath tearing string <NUM> needs to be provided, or two or more inner sheath tearing strings may be provided. Including the inner sheath tearing string <NUM> can facilitate tearing the inner layer sheath <NUM>.

An exemplary cross-sectional structure of an optical fiber cable, not forming part of the claimed invention, but useful to understand the claimed invention. will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, an inner layer sheath <NUM>, a metal sheath <NUM>, an outer layer sheath <NUM>, an outer sheath tearing string <NUM>, and an inner sheath tearing string <NUM>. The optical fiber cable according to the present disclosure includes at least one inner sheath tearing string <NUM> arranged in a longitudinal direction inside a layer of the inner layer sheath <NUM> to tear the inner layer sheath <NUM>.

The cross-sectional structure of an optical fiber cable according to the claimed invention will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, an inner layer sheath <NUM>, a metal sheath <NUM>, an outer layer sheath <NUM>, an outer sheath tearing string <NUM>, and a continuous protrusion <NUM>. The optical fiber cable according to the present disclosure includes the continuous protrusion <NUM> arranged on an outer peripheral surface of the inner layer sheath <NUM> and extending along the outer sheath tearing string <NUM>.

The optical fiber cable illustrated in <FIG> has an exemplary structure including the continuous protrusion <NUM> in addition to the optical fiber cable described in the embodiment <NUM>. When there are multiple outer sheath tearing strings <NUM>, the continuous protrusion <NUM> may be provided along one outer sheath tearing string <NUM>, or the continuous protrusion <NUM> may be provided along any one of the multiple outer sheath tearing strings <NUM>. Including the continuous protrusion <NUM> additionally can easily identify a position of the outer sheath tearing string <NUM>, and the work for taking out the outer sheath tearing string <NUM> becomes easy. This results in facilitating tearing the metal sheath <NUM> and the outer layer sheath <NUM>.

The cross-sectional structure of an optical fiber cable according to the claimed invention will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, an inner layer sheath <NUM>, a metal sheath <NUM>, an outer layer sheath <NUM>, an outer sheath tearing string <NUM>, an inner sheath tearing string <NUM>, and a continuous protrusion <NUM>. The optical fiber cable according to the present disclosure includes the continuous protrusion <NUM> arranged on the outer peripheral surface of the inner layer sheath <NUM> and extending along the outer sheath tearing string <NUM>, and the inner sheath tearing string <NUM> and the outer sheath tearing string <NUM> are arranged on the same radial axis of the optical fiber cable. The radial axis is an axis extending radially in an outer circumference direction from a center point of the optical fiber cable.

The optical fiber cable illustrated in <FIG> has an exemplary structure including the continuous protrusion <NUM> in addition to the optical fiber cable described in the embodiment <NUM>. When there are multiple outer sheath tearing strings <NUM>, the continuous protrusion <NUM> may be provided along one outer sheath tearing string <NUM>, or the continuous protrusion <NUM> may be provided along any one of the multiple outer sheath tearing strings <NUM>. Including the continuous protrusion <NUM> additionally can easily identify positions of the outer sheath tearing string <NUM> and the inner sheath tearing string <NUM>, and the work for taking out the outer sheath tearing string <NUM> becomes easy. This results in facilitating tearing the metal sheath <NUM> and the outer layer sheath <NUM>.

An exemplary cross-sectional structure of an optical fiber cable, not forming part of the claimed invention, will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, an inner layer sheath <NUM>, a metal sheath <NUM>, an outer layer sheath <NUM>, and an outer sheath tearing string <NUM>. In the optical fiber cable according to the present disclosure, the metal sheath <NUM> has a part single-wounded and the rest double-wounded around an outer circumference of the cable core <NUM>, and at least one outer sheath tearing string <NUM> is arranged inside the single-wounded part of the metal sheath <NUM>.

When there is only one outer sheath tearing string <NUM>, it is desirable that the one outer sheath tearing string <NUM> is arranged inside the single-wounded part of the metal sheath <NUM>. When there are multiple outer sheath tearing strings <NUM>, it is desirable that at least one of these outer sheath tearing strings <NUM> is arranged inside the single-wounded part of the metal sheath <NUM>, and it is further desirable that two or more outer sheath tearing strings <NUM> are arranged inside the single-wounded part of the metal sheath <NUM>. Arranging at least one outer sheath tearing string <NUM> inside the single-wounded part of the metal sheath <NUM> facilitates the work for taking out the outer sheath tearing string <NUM>. Further, the metal sheath <NUM> and the outer layer sheath <NUM> can be easily torn. The same applies even when the continuous protrusion <NUM> is arranged as in the embodiment <NUM> or <NUM>.

An exemplary design in which there are two outer sheath tearing strings <NUM> will be described with reference to <FIG>. In <FIG>, when θ1 (degree) and θ2 (degree) represent angles formed by two lines connecting two outer sheath tearing strings <NUM> and the center point of the optical fiber cable respectively with respect to a line perpendicular to a line connecting a center of the double-wounded part of the metal sheath <NUM> and the center point of the optical fiber cable, d represents a diameter of a cable body, and L represents a width of the metal sheath <NUM> in a circumferential direction, it is configured to satisfy the following relationships. <MAT> and <MAT>.

The validity of Expression (<NUM>) was verified using a <NUM> cores optical fiber cable and a <NUM> cores optical fiber cable. <FIG> illustrates verification results. In <FIG>, with the cable body diameter d, angle θ1+θ2, and the width L of the metal sheath <NUM> in the circumferential direction as parameters, the quality of workability was qualitatively determined when Expression (<NUM>) is satisfied ("round mark" in "Expression" column of <FIG>) and when Expression (<NUM>) is not satisfied ("X mark" in "Expression" column of <FIG>). It was verified that the workability was good ("round mark" in "workability" column of <FIG>) when Expression (<NUM>) was satisfied, and the workability was bad ("X mark") in "workability" column of <FIG>) when Expression (<NUM>) was not satisfied.

Adopting such a design can prevent the outer sheath tearing string <NUM> from being arranged inside the double-wounded part of the metal sheath <NUM>, and therefore the work for taking out the outer sheath tearing string <NUM> becomes easy. In addition, the metal sheath <NUM> and the outer layer sheath <NUM> can be easily torn. Although <FIG> illustrates the exemplary structure including two outer sheath tearing strings <NUM>, even when there are three or more outer sheath tearing strings <NUM>, it is desirable to select arbitrary two of them and determine the design so as to satisfy Expression (<NUM>).

The optical fiber cable illustrated in <FIG> shows the arrangement of the outer sheath tearing string <NUM> by taking the optical fiber cable described in the embodiment <NUM> as an example. The structure of the optical fiber cable of the present embodiment is not limited to the embodiment <NUM> and can be also applied to the optical fiber cable of any one of the embodiments <NUM> to <NUM>.

An exemplary cross-sectional structure of an optical fiber cable, not forming part of the claimed invention, will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, an inner layer sheath <NUM>, a metal sheath <NUM>, an outer layer sheath <NUM>, and a protective sheath tearing string <NUM>. The cable core <NUM> is arranged at a central portion of the optical fiber cable, and includes a plurality of optical fibers gathered together. The inner layer sheath <NUM> is arranged on an outer circumference of the cable core <NUM> to sheath the cable core <NUM>. The inner layer sheath <NUM> may include a tension member that protects the optical fibers against a tensile force acting on the optical fiber cable. The material of the inner layer sheath <NUM> is, for example, polyethylene, frame-retardant polyethylene, polyvinyl chloride, or the like. The cable core <NUM> and the inner layer sheath <NUM> are collectively referred to as a cable body. The metal sheath <NUM> is arranged on an outer circumference of the inner layer sheath <NUM>, and is wound around the inner layer sheath <NUM>. The material of the metal sheath <NUM> is, for example, stainless steel, steel, iron, or the like. The outer layer sheath <NUM> is arranged on an outer circumference of the metal sheath <NUM> to sheath the metal sheath <NUM>. The material of the outer layer sheath <NUM> is, for example, polyethylene, frame-retardant polyethylene, polyvinyl chloride, or the like. The metal sheath <NUM> and the outer layer sheath <NUM> are collectively referred to as an external sheath. The optical fiber cable according to the present disclosure includes at least one protective sheath tearing string <NUM> arranged in the longitudinal direction inside a layer of the inner layer sheath <NUM> to tear the inner layer sheath <NUM>, the metal sheath <NUM>, and the outer layer sheath <NUM>. The at least one protective sheath tearing string <NUM> needs to be provided, or two or more protective sheath tearing strings may be provided. The material of the protective sheath tearing string <NUM> is, for example, Tetron fiber, Kevlar fiber, aramid fiber, polyester fiber, or the like, which are excellent in tensile strength and can be used as they are or twisted together. These structures are the same in the following embodiments.

Even if there is the metal sheath <NUM> introduced as the countermeasure against bird, insect, and animal damages, providing the protective sheath tearing string <NUM> can facilitate tearing the inner layer sheath <NUM>, the metal sheath <NUM>, and the outer layer sheath <NUM>. That is, the optical fiber cable can be disassembled using the protective sheath tearing string <NUM>, without using a dedicated tool, or without damaging the optical fiber. The disassembling method using the protective sheath tearing string <NUM> requires no high-degree skill and can shorten the required time.

An exemplary cross-sectional structure of an optical fiber cable, not forming part of the claimed invention, will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, an inner layer sheath <NUM>, a metal sheath <NUM>, an outer layer sheath <NUM>, a protective sheath tearing string <NUM>, and a continuous protrusion <NUM>. The optical fiber cable according to the present disclosure includes the continuous protrusion <NUM> arranged on an outer peripheral surface of the inner layer sheath <NUM> and extending along the protective sheath tearing string <NUM>.

The optical fiber cable illustrated in <FIG> has an exemplary structure including the continuous protrusion <NUM> in addition to the optical fiber cable described in the embodiment <NUM>. When there are multiple protective sheath tearing strings <NUM>, the continuous protrusion <NUM> may be provided along one protective sheath tearing string <NUM>, or the continuous protrusion <NUM> may be provided along any one of the multiple protective sheath tearing strings <NUM>. Including the continuous protrusion <NUM> additionally can easily identify the position of the protective sheath tearing string <NUM>, and the work for taking out the protective sheath tearing string <NUM> becomes easy. This results in facilitating tearing the inner layer sheath <NUM>, the metal sheath <NUM>, and the outer layer sheath <NUM>.

An exemplary cross-sectional structure of an optical fiber cable, not forming part of the claimed invention, will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes a cable core <NUM>, an inner layer sheath <NUM>, a metal sheath <NUM>, an outer layer sheath <NUM>, and a protective sheath tearing string <NUM>. In the optical fiber cable according to the present disclosure, the metal sheath <NUM> has a part single-wounded and the rest double-wounded around the outer circumference of the cable core <NUM>, and at least one protective sheath tearing string <NUM> is arranged inside the single-wounded part of the metal sheath <NUM>.

When there is only one protective sheath tearing string <NUM>, it is desirable that the one protective sheath tearing string <NUM> is arranged inside the single-wounded part of the metal sheath <NUM>. When there are multiple protective sheath tearing strings <NUM>, it is desirable that at least one of these protective sheath tearing strings <NUM> is arranged inside the single-wounded part of the metal sheath <NUM>, and it is further desirable that two or more protective sheath tearing strings <NUM> are arranged inside the single-wounded part of the metal sheath <NUM>. Arranging at least one protective sheath tearing string <NUM> inside the single-wounded part of the metal sheath <NUM> facilitates the work for taking out the protective sheath tearing string <NUM>. Further, the inner layer sheath <NUM>, the metal sheath <NUM>, and the outer layer sheath <NUM> can be easily torn. The same applies even when the continuous protrusion <NUM> is arranged as in the embodiment <NUM>.

An exemplary design in which there are two protective sheath tearing strings <NUM> will be described with reference to <FIG>. In <FIG>, when θ1 (degree) and θ2 (degree) represent angles formed by two lines connecting two protective sheath tearing strings <NUM> and the center point of the optical fiber cable respectively with respect to a line perpendicular to a line connecting a center of the double-wounded part of the metal sheath <NUM> and the center point of the optical fiber cable, d represents a diameter of a cable body, and L represents a width of the metal sheath <NUM> in a circumferential direction, it is configured to satisfy the following relationships. <MAT> and <MAT>.

The validity of Expression (<NUM>) was verified using a <NUM> cores optical fiber cable and a <NUM> cores optical fiber cable. Verification results are similar to those of the embodiment <NUM>, and it was verified that the workability was good when Expression (<NUM>) was satisfied, and the workability was bad when Expression (<NUM>) was not satisfied.

Adopting such a design can prevent the protective sheath tearing string <NUM> from being arranged inside the double-wounded part of the metal sheath <NUM>, and therefore the work for taking out the protective sheath tearing string <NUM> becomes easy. In addition, the inner layer sheath <NUM>, the metal sheath <NUM>, and the outer layer sheath <NUM> can be easily torn. Although <FIG> illustrates the exemplary structure including two protective sheath tearing strings <NUM>, even when there are three or more protective sheath tearing strings <NUM>, it is desirable to select arbitrary two of them and determine the design so as to satisfy Expression (<NUM>).

The optical fiber cable illustrated in <FIG> shows the arrangement of the protective sheath tearing string <NUM> by taking the optical fiber cable described in the embodiment <NUM> as an example. The structure of the optical fiber cable of the present embodiment is not limited to the embodiment <NUM> and can be also applied to the optical fiber cable of the embodiment <NUM>.

An exemplary workflow, not forming part of the claimed invention, for removing a metal sheath of the optical fiber cable according to the present disclosure will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes an inner layer sheath <NUM>, a metal sheath <NUM>, a metal sheath nick <NUM>-<NUM>, an outer layer sheath <NUM>, an outer sheath tearing string <NUM>, an inner sheath tearing string <NUM>, and a fishing line <NUM>. The fishing line <NUM> is an exemplary string for peeling off the outer layer sheath <NUM>.

First, the outer layer sheath <NUM> is peeled off partly by the fishing line <NUM> (see <FIG>), and the metal sheath nick <NUM>-<NUM> is exposed (see <FIG>). The metal sheath nick <NUM>-<NUM> is an outer edge of a part where the metal sheath <NUM> is double-wounded. Next, using a tool such as a nipper, the outer layer sheath <NUM> and the metal sheath <NUM> are peeled off from the exposed metal sheath nick <NUM>-<NUM> in a circumferential direction to expose the outer sheath tearing string <NUM> (see <FIG>). Then, using the exposed outer sheath tearing string <NUM>, the metal sheath <NUM> and the outer layer sheath <NUM> are torn to expose the inner layer sheath <NUM> (see <FIG>). In the case of taking out the cable core (not illustrated) when the inner sheath tearing string <NUM> is arranged, the inner layer sheath <NUM> is further torn using the inner sheath tearing string <NUM> (see <FIG>). After tearing the inner layer sheath <NUM>, the optical fibers of the cable core can be taken out.

An exemplary workflow , not forming part of the claimed invention, for removing a metal sheath of the optical fiber cable according to the present disclosure will be described with reference to <FIG>. The optical fiber cable illustrated in <FIG> includes an inner layer sheath <NUM>, a metal sheath <NUM>, a metal sheath nick <NUM>-<NUM>, an outer layer sheath <NUM>, a protective sheath tearing string <NUM>, and a fishing line <NUM>. The fishing line <NUM> is an exemplary string for peeling off the outer layer sheath <NUM>.

First, the outer layer sheath <NUM> is peeled off partly by the fishing line <NUM> (see <FIG>), and the metal sheath nick <NUM>-<NUM> is exposed (see <FIG>). The metal sheath nick <NUM>-<NUM> is an outer edge of a part where the metal sheath <NUM> is double-wounded. Next, using a tool such as a nipper, the outer layer sheath <NUM> and the metal sheath <NUM> are peeled off from the exposed metal sheath nick <NUM>-<NUM> in a circumferential direction to expose the inner layer sheath <NUM> (see <FIG>). In the case of taking out the cable core (not illustrated), the inner layer sheath <NUM>, the metal sheath <NUM>, and the outer layer sheath <NUM> are torn using the protective sheath tearing string <NUM> (see <FIG>). After tearing the inner layer sheath <NUM>, optical fibers of the cable core can be taken out.

Claim 1:
An optical fiber cable comprising:
a cable core (<NUM>) arranged at a central portion and
accommodating a plurality of optical fibers gathered together; an inner layer sheath (<NUM>) arranged on an outer circumference of the cable core (<NUM>) and sheathing the cable core (<NUM>);
a metal sheath (<NUM>) arranged on an outer circumference of the inner layer sheath (<NUM>) and wound around the inner layer sheath (<NUM>);
an outer layer sheath (<NUM>) arranged on an outer circumference of the metal sheath (<NUM>) and sheathing the metal sheath (<NUM>); and
at least one outer sheath tearing string (<NUM>) arranged in a longitudinal direction inside the metal sheath (<NUM>),
wherein the outer sheath tearing string (<NUM>) has a part embedded in the inner layer sheath (<NUM>) and another part exposed from the inner layer sheath (<NUM>), characterized in that the metal sheath (<NUM>) has a part single-wound and the rest double-wound around the outer circumference of the cable core (<NUM>), and
the at least one outer sheath tearing string (<NUM>) is arranged inside the single-wound part,
the optical fiber cable further comprising a continuous protrusion (<NUM>) arranged on the outer peripheral surface of the inner layer sheath (<NUM>) and extending along the outer sheath tearing string (<NUM>).