Patent Description:
For general prior art, reference is made to PTL2, PTL3, and PTL4.

PTL2 discloses an optical fiber cable, in which a plurality of optical fibers are placed outside a buffer layer on the outer circumference of a tension member. An interposing cord is placed between the optical fibers. A tape-wrapped layer is formed around the circumference of the interposing cord and the optical fibers, and a sheath is coated on the outside of the interposing cord and the tape-wrapped layer. At least one of the interposing cord and the tape-wrapped layer contains a substance that becomes gelatinous when water is absorbed and exudes from the interposing cord or the tape-wrapped layer, thereby sealing the surrounding voids.

PTL3 discloses an optical cable that includes an optical module which includes a strength member, a plurality of optical fibers arranged about the strength member, the optical fibers being arranged substantially on a circumference concentric with the strength member, and a retaining element arranged about the plurality of optical fibers. PTL4 discloses a cable whose inner opening space has been sealed with a polyurethane resin formed with a polyurethane resin-forming sealing material comprising components (A) and (B). (A): a component comprising a dispersion of a water-insoluble water absorbent resin or its hydrogel in a polyol, wherein said resin is formed by polymerizing in the polyol a water soluble monomer or its precursor and crosslinking agent and/or polysaccharide; and (B): a component comprising an organic polyisocyanate; and sealing process of the same.

At present, optical fibers having low loss and wide band characteristics have been introduced into communication networks in order to provide various and wide-band multimedia services. In usage of optical fibers in a communication network, the optical fibers are bundled and covered to be used as an optical cable. Conventionally, for designing a structure of an optical cable, it is important to (<NUM>) prevent loss in optical fibers from increasing and (<NUM>) secure long-term reliability, with respect to external forces such as tension and bending, acting on the optical fibers during manufacturing, laying and using, in long-term, the optical cable. In other words, it is an important problem to select a structure which prevents, as much as possible, external forces, such as tension and bending, from acting on the optical fibers. In particular, it is important to provide a design free from increase in optical loss due to bending of the optical fibers.

In addition, in constructing a communication network using optical cables, together with increase in demand for optical fibers, underground conduits, ducts in buildings and the like may become insufficient so that a plurality of optical cables have to be laid in one conduit, duct, or the like. In this situation, depending on a diameter of a previously-laid optical cable, the conduit, duct, or the like may have a space that is too small to make a desired optical cable laid therein and then needs another conduit or duct for installation, which results in increasing the cost, so that optical cables having a smaller diameter and a higher density have been proposed (for example, PTL <NUM>). By applying optical fibers that are resistant to bending, long-term reliability of such an optical cable can be secured without increase in loss of the optical fibers.

On the other hand, in recent years, research and development on optical fibers have greatly progressed, and optical fibers suitable for transmitting a large amount of data at a high speed have been proposed. However, due to poor bending strength of such an optical fiber, the optical fiber is made into a cable as shown in <FIG>, where an optical fiber <NUM> is mounted in a groove of a slot rod <NUM> to protect the optical fiber <NUM> from external force and prevent a large force from acting on the optical fiber <NUM> as much as possible. Recently, in order to realize a small-diameter and high-density optical cable using the optical fiber <NUM> with poor bending strength, a technique for reducing mounting density by adjustment to leave a slight gap in the optical cable, so as to prevent the optical fibers <NUM> from coming into strong contact with each other, has been examined (for example, NPL <NUM>).

However, under the condition of decreasing mounting density of the optical fibers <NUM> in the optical cable, while loss of the optical fibers <NUM> can be suppressed, movement of the optical fibers <NUM> in the optical cable causes the optical fibers <NUM> to bend in a housing used at a location where optical cables are connected to each other, making it difficult to secure long-term reliability. Furthermore, although outer peripheries of a plurality of optical fibers <NUM> in the optical cable can be bundled, this brings the optical fibers <NUM> into contact with each other and increases optical loss.

An object of the present disclosure is to prevent optical fibers from moving and from having increased optical loss, by reducing a mounting density of the optical fibers and preventing the optical fibers from coming into contact with each other.

In order to achieve the object described above, an optical cable according to the present disclosure is an optical cable according to claim <NUM>.

According to an optical cable of the present disclosure, a mounting density of optical fibers is reduced by providing the interposition in the bundle tape, and the optical fibers are prevented from moving and from having increased optical loss, increasing by preventing the optical fibers from coming into contact with each other.

Embodiments of the present disclosure will be described in detail below with reference to the drawings. It is to be understood that the present disclosure is not limited to the embodiments described below. The embodiments are merely exemplary and the present disclosure can be implemented in various modified and improved modes based on knowledge of those skilled in the art. Constituent elements with the same reference signs in the present specification and in the drawings represent the same constituent elements.

An example of a structure of an optical cable according to the present disclosure will be described with reference to <FIG>. <FIG> shows an example of a structure of an optical cable. In the optical cable according to the present embodiment, one or more units <NUM> are covered by a jacket <NUM>. <FIG> shows an example of a unit that gathers optical fibers. The present optical cable is structured so as to have one or more units <NUM> in which at least one or more optical fibers <NUM> and a first interposition <NUM> that prevents the optical fibers <NUM> from coming into contact with each other are bundled with a bundle tape <NUM>.

The unit <NUM> is an optical fiber bundle in which the optical fibers <NUM> and the first interposition <NUM> are densely gathered in a state of being brought into contact with each other and a bundle tape <NUM> is wound around an outer periphery thereof. The optical fibers <NUM> are single-core coated optical fibers in which a periphery of a bare fiber is covered with a coating or compose a fiber optic tape in which a plurality of single-core coated optical fibers are integrated. The first interposition <NUM> is a freely selected elastic body that is arranged between adjacent optical fibers <NUM> and is arranged in an entire longitudinal direction of the optical fibers <NUM>.

In the optical cable according to the present embodiment, by bundling the optical fibers <NUM> and the first interposition <NUM> together, a mounting density of the optical fibers <NUM> can be reduced and the movement of the optical fibers <NUM> can be prevented. Further, the optical fibers <NUM> can be prevented from coming into contact with each other with the mounting density of the optical fibers <NUM> lowered, and an increase in optical loss can be suppressed.

The first interposition <NUM> is formed of a material softer than that of the coating of the optical fibers <NUM> so as to deform along the outer periphery of the optical fibers <NUM> with the optical fibers <NUM> being in contact therewith. Examples of the material of the first interposition <NUM> include a linear material obtained by bundling fibers of a polymer material such as polypropylene and a thin tape-like material such as a nonwoven fabric or a sponge.

As a material of the jacket <NUM>, polyethylene, flame-retardant polyethylene, polyvinyl chloride or the like can be exemplified. The winding structure can include single winding with one bundle tape <NUM>, cross winding, SZ twisting with two bundle tapes <NUM>, and the like. These structures are similarly adopted in embodiments to be described later.

A structure of the optical cable according to the present disclosure will be described with reference to <FIG> and <FIG>. <FIG> shows an example of a structure of an optical cable. <FIG> shows an example of a unit that gathers optical fibers. The present optical cable has a structure having: a plurality of units <NUM> in which at least one or more optical fibers <NUM> and a first interposition <NUM> that prevents the optical fibers <NUM> from coming into contact with each other are bundled with a bundle tape <NUM>; and a second interposition <NUM> that prevents optical fibers <NUM> each included in different units <NUM> from coming into contact with each other.

The optical cable according to the present embodiment is an optical fiber bundle in which a plurality of units <NUM> and the second interposition <NUM> are densely gathered to be in contact with each other, and a jacket <NUM> is wound around an outer periphery thereof. The second interposition <NUM> may be, for example, a linear interposition or a tape-like interposition spirally wound around the outer periphery of the units <NUM> as shown in <FIG>. While the second interposition <NUM> covers a part of the units <NUM> in <FIG>, the second interposition <NUM> may cover the entire outer periphery of the units <NUM>.

A material of the second interposition <NUM> is preferably a material which deforms along the outer periphery of the optical fibers <NUM> with the plurality of units <NUM> and the second interposition <NUM> densely gathered to be in contact with each other, and a similar material to the material of the first interposition <NUM> can be used. Accordingly, optical fibers <NUM> each included in different units <NUM> can be densely gathered while being prevented from coming into contact with each other.

In the present embodiment, by providing the second interposition <NUM> between the units <NUM>, a plurality of the units <NUM> can be densely gathered. Therefore, the optical cable according to the present embodiment can reduce the mounting density of the optical fibers <NUM> and prevent the movement of the units <NUM> in which the optical fibers <NUM> are bundled. Furthermore, the units <NUM> can be prevented from coming into contact with each other with the mounting density of the optical fibers <NUM> lowered, and an increase in optical loss can be suppressed.

A structure of the optical cable according to the present disclosure will be described with reference to <FIG> and <FIG>. <FIG> shows an example of a structure of an optical cable. <FIG> shows an example of a state in which a jacket has been removed. The optical cable according to the present embodiment has a structure including a plurality of units <NUM> and a second interposition <NUM> between the units <NUM> which prevents optical fibers <NUM> from coming into contact with each other and including a third interposition <NUM> in an outer periphery of the plurality of units <NUM> that prevents a jacket <NUM> and the optical fibers <NUM> from coming into contact with each other. The units <NUM> may have any of the structures shown in <FIG> and <FIG>.

The optical cable according to the present embodiment is an optical fiber bundle in which a plurality of units <NUM> and second interposition <NUM> are densely gathered in contact with each other, the third interposition <NUM> is wound around an outer periphery thereof, and the jacket <NUM> is further wound around an outer periphery thereof. As the third interposition <NUM>, for example, a linear interposition or a tape-like interposition spirally wound around the outer periphery of the plurality of units <NUM> as shown in <FIG> can be exemplified. While the third interposition <NUM> covers a part of the plurality of units <NUM> in <FIG>, the third interposition <NUM> may cover the whole outer periphery of the plurality of units <NUM>.

A material of the third interposition <NUM> is preferably a material which deforms along the outer periphery of each optical fiber <NUM> included in the plurality of units <NUM> with the plurality of units <NUM> and the second interposition <NUM> densely gathered to be in contact with each other. As the material of the third interposition <NUM>, a similar material to the material of the first interposition <NUM> may be used and, for example, a linear material obtained by bundling fibers of a polymer material such as polypropylene or a thin tape-like material such as a nonwoven fabric or sponge can be exemplified.

In the optical cable according to the present embodiment, by providing the third interposition <NUM> on the outer periphery of the plurality of units <NUM>, it is possible to prevent the jacket <NUM> and an optical fiber <NUM> from coming into contact with each other. Therefore, the optical cable according to the present embodiment can absorb a force from the jacket <NUM> due to curving or bending of the optical cable, using the third interposition <NUM>, and can suppress an increase in optical loss.

A structure of the optical cable according to the present disclosure will be described with reference to <FIG> and <FIG>. <FIG> shows an example of a structure of an optical cable. <FIG> shows an example of a unit that gathers optical fibers. An optical cable according to the present embodiment has a structure having a plurality of units <NUM> in which at least one or more optical fibers <NUM> and a first interposition <NUM> for preventing the optical fibers <NUM> from coming into contact with each other are bundled by a bundle tape <NUM>, and a part or all of the first interposition <NUM> and a second interposition <NUM> are water-absorbent.

The same applies to an optical cable having a structure in which a third interposition <NUM> is provided between the jacket <NUM> and the units <NUM>. By providing the water-absorbent interposition, water penetration into the optical cable can be prevented when a housing installed at a connection point of the optical cable is immersed in water. Therefore, the present embodiment is effective for an optical cable laid in an underground section.

Further, in each of the embodiments described above, by making a color of the first interposition <NUM>, for preventing the optical fibers <NUM> from coming into contact with each other, different from colors of the bundle tape <NUM> and the optical fibers <NUM>, distinguishability of the first interposition <NUM> can be improved. Therefore, in an operation of removing the first interposition <NUM> to disassemble the optical cable, the bundle tape <NUM> and the optical fibers <NUM> can be prevented from being cut by mistake.

The present disclosure is applicable to any optical fiber capable of propagating light including a single-mode fiber, a multi-mode fiber, a multi-core optical fiber having a plurality of cores, and a photonic crystal fiber having a plurality of holes in a cross section of the optical fiber. Further, optical fibers, which are included in each unit, and units, which are provided in an optical cable, are not limited to being bundled in a straight shape and may be twisted together.

Claim 1:
An optical cable comprising one or more units (<NUM>) each including only a plurality of optical fibers (<NUM>), a first interposition (<NUM>), and a bundle tape (<NUM>); wherein:
the plurality of optical fibers (<NUM>)is bundled by the bundle tape (<NUM>)
the first interposition (<NUM>)is provided between the optical fibers (<NUM>) for preventing the optical fibers (<NUM>) from coming into contact with each other, and
the optical fibers (<NUM>) and the first interposition (<NUM>) are bundled by the bundle tape (<NUM>) in a state where the optical fibers (<NUM>) and the first interposition (<NUM>) are in contact with each other.