Patent Description:
Construction of an optical network is in progress to cope with bidirectional communication and large capacity communication in addition to the speeding up of communication and the increase of an information amount caused by the spread of information communication such as the Internet. In the optical network, FTTH (Fiber To The Home) that provides a high-speed communication service by directly connecting a telecommunications carrier and each home by an optical fiber is started. As the optical fiber is drawn to such a subscriber's home and campus network is expanded, there is an increasing demand for wiring work in which the optical fiber is split from a middle portion of an optical fiber cable storing the plurality of optical fibers (referred to as intermediate splitting of the optical fiber) and is distributed to a plurality of homes and terminals.

In order to make it easy to take out the optical fiber at the time of performing the intermediate splitting of the optical fiber, the optical fiber may be stored in a loose tube divided into colors. For example, a structure of a loose tube type optical fiber cable is disclosed in Patent Literature <NUM>. Further, a structure of a slotless type optical fiber cable is disclosed in Patent Literature <NUM>.

Further related prior art may be found in <CIT>, which describes an optical fiber ribbon and optical fiber cable, in <CIT>, which describes a utility optical fiber cable and in <CIT> which describes a manufacturing method and a manufacturing device of an optical fiber cable. The latter discloses an optical fiber cable, capable of sufficiently suppressing the degradation of transmission characteristics due to distortion of optical fibers in an optical fiber cable having an aggregate core of intermittently fixed optical fiber ribbons housed in a sheath, even when the optical fiber cable is laid at a smaller bend angle. Each of intermittently fixed optical fiber ribbons is subjected to unidirectional twisting or SZ twisting, and then the respective intermittently fixed optical fiber ribbons are collected to constitute an aggregate core, enclosed in a sheath.

<CIT> discloses an optical communication cable comprising a core of light-transmitting optical fibers surrounded by a inner jacket. The core fibers are buckled into a slackened state under noload conditions to allow for stress-free elongation of the core fibers during tensile pulling of the cable. The core comprises linear arrays of optical fibers packaged in a plurality of ribbon structures which are stacked and helically stranded for further strain-relief around a compliant center member. The arrays are specifically configured to permit mass cable splicing.

The present invention is defined by the appended independent claim. The dependent claims describe optional features and distinct embodiments.

However, in the case of the loose tube type as described in Patent Document <NUM>, since a space for a loose tube itself is required in the optical fiber cable and a space between the loose tubes becomes a dead space, high density mounting becomes difficult.

On the other hand, in the case of the slotless type as described in Patent Document <NUM>, even though the high density mounting is possible, a tension member is not disposed at a central position but is disposed at two positions within a cable jacket, bending directionality occurs in the optical fiber cable, thereby making it difficult to lay the cable.

The present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide an optical fiber cable which can be easily laid and can achieve high density mounting in comparison with a cable of a related art.

A slotless type optical fiber cable according to the appended claims.

According to the above description, the present invention can be easily laid, and can achieve high density mounting in comparison with a cable of a related art.

First, contents of examples of the present disclosure will be listed and described.

Hereinafter, desirable embodiments of an optical fiber cable according to the present invention will be described with reference to the accompanying drawings.

<FIG> is a diagram illustrating an example of an optical fiber cable according to a first embodiment of the present invention, and <FIG> are diagrams illustrating an example of a structure of an intermittent ribbon.

An optical fiber cable <NUM> illustrated in <FIG> is a slotless type, and includes, for example, a round cable core <NUM> and a cable jacket <NUM> formed around the cable core <NUM>.

The cable core <NUM> accommodates, for example, <NUM> cores using <NUM> pieces of the intermittent ribbons <NUM> of <NUM> cores.

In the intermittent ribbon, a plurality of optical fibers are arranged in a parallel line, and the optical fibers adjacent to each other are intermittently connected by a connection part and a non-connection part. <FIG> illustrates a state in which the intermittent ribbon is opened in the arrangement direction; and <FIG> respectively illustrates a cross sectional view taken along the line B-B of <FIG>. The illustrated intermittent ribbon <NUM> is formed in such a manner that the ribbons of <NUM> cores are intermittently connected to each other every two cores.

As illustrated in <FIG>, a ribbon coating <NUM> made of an ultraviolet curing resin is provided around each optical fiber <NUM>, and for example, core wires integrated with two cores are intermittently connected by a connection part <NUM> and a non-connection part <NUM>. In the connection part <NUM>, the ribbon coatings <NUM> are connected to each other, and in the non-connection part <NUM>, the ribbon coatings <NUM> adjacent to each other are separated without being connected to each other. Further, the intermittent ribbon may not be provided with the connection part and the non-connection part every two cores, and for example, may be intermittently connected with the connection part and the non-connection part every one core.

For example, the optical fiber <NUM> accommodated in the intermittent ribbon is further coated with coloring on the outside of what is referred to as an optical fiber which is coated with a coating outer diameter of about <NUM> on a glass fiber with a standard outer diameter of <NUM>, but is not limited thereto, and may be a small diameter fiber having a coating outer diameter in the range of <NUM> to <NUM>, for example, about <NUM> or <NUM>. The use of a small diameter fiber makes high density mounting easier.

According to the claimed invention, a subunit <NUM> illustrated in <FIG> is a <NUM>-core unit formed by, for example, collecting <NUM> pieces of the intermittent ribbons <NUM> of <NUM> cores and twisting the collected intermittent ribbons <NUM> in a spiral shape, and an optical unit <NUM> formed by, for example, collecting <NUM> pieces of the subunits <NUM> and twisting the collected subunits <NUM> in a spiral shape is accommodated in the cable core <NUM>. The intermittent ribbon <NUM> is more flexible than a general ribbon, and when the optical unit <NUM> is formed of the intermittent ribbon, an occupancy ratio of the optical fiber <NUM> can be increased. As an example not forming part of the claimed invention, such an intermittent ribbon may not be used as the ribbon which forms the optical unit <NUM>, and a connected type ribbon may be used, or one in which a plurality of single core optical fibers are arranged may be used.

The occupancy ratio of the optical unit <NUM> is calculated from a total cross-sectional area of the optical unit <NUM> with respect to a cross-sectional area of the cable core <NUM>. Further, the total cross-sectional area of the optical unit <NUM> also includes a cross-sectional area of the ribbon coating <NUM> described in <FIG>.

Further, the intermittent ribbon <NUM> and the subunit <NUM> may be twisted in an SZ shape, which is periodically reversed, in addition to the spiral shape in one direction.

Further, a tension member <NUM> made of a fiber body is also accommodated in the cable core <NUM>. One tension member <NUM> illustrated in <FIG> is disposed at a central position of the optical unit <NUM> along the longitudinal direction of the optical unit <NUM>. Further, the optical unit <NUM> of the embodiment is formed by twisting and collecting the subunits <NUM> around the tension member <NUM>.

The tension member <NUM> is formed of a nonmetallic material such as, for example, a glass fiber reinforced plastic (GFRP) formed of a glass fiber and an aramid fiber reinforced plastic (AFRP, KFRP) formed of an aramid-based fiber as a wire having resistance against tension and compression. Thus, the weight reduction of the cable can be achieved in comparison with a case where a metal tension member is provided. Further, since the cable is light in weight, it is difficult to apply side pressure to the optical fiber in the cable core <NUM>. Further, water absorbing powder may be applied to the tension member <NUM> in order to stop water from flowing into the cable core <NUM>.

On the other hand, the cable core <NUM> is formed as a round shape by vertically placing or horizontally winding the optical unit <NUM> with a press-winding tape <NUM>. A non-woven fabric including, for example, polyethylene terephthalate (PET) is used for the press-winding tape <NUM> and is wound around from the outside of the optical unit <NUM>.

The outer side of the press-winding tape <NUM> is covered with the cable jacket <NUM> formed of, for example, PE (polyethylene) and PVC (polyvinyl chloride).

A tear string <NUM> for tearing the cable jacket <NUM> in the longitudinal direction of the cable is embedded in the cable jacket <NUM> when the cable jacket <NUM> is extruded. The tear strings <NUM> are provided one by one on opposite sides of the cable core <NUM>, for example, with the cable core <NUM> interposed therebetween. The tear string <NUM> is, for example, a string-like member such as nylon and polyester. Further, a projection part <NUM> may be formed on the cable jacket <NUM> at the time of extrusion molding so that the embedded position of the tear string <NUM> can be visually recognized from the outside.

According to the optical fiber cable according to the first embodiment, since the optical fiber cable has the slotless type structure, the high density mounting can be achieved.

Further, since the tension member <NUM> made of the fiber body is disposed at the central position of the cable core <NUM>, it is possible to provide an optical fiber cable which has no bending directionality and can be easily laid in a pipeline. Further, since the plurality of subunits <NUM> are twisted and collected around the tension member <NUM>, even though the cable is bent, it is difficult for the tension member <NUM> to move toward the bending center of the cable, and it is difficult to apply the side pressure to the optical fiber.

<FIG> is a table for describing an evaluation result of a transmission characteristic of an optical fiber.

In the evaluation of the transmission characteristic, the influence of side pressure applied to the optical fiber (hereinafter referred to as "cable transmission loss") and the influence of compression strain applied to the optical fiber (hereinafter referred to as "cable bending loss") are evaluated.

In the former evaluation of the cable transmission loss, the transmission loss (measurement wavelength <NUM> (nm)) is measured by changing the occupancy ratio of the optical unit <NUM> with respect to several samples of the cable <NUM> in a straight line state. Then, among the measured several samples, a case where the maximum value of the transmission loss is less than <NUM> (dB/km) is determined to be good (O) and a case where the maximum value thereof is not less than <NUM> (dB/km) is determined to be defective (×).

When the occupancy ratio of the optical unit <NUM> is <NUM>% (referred to as a "sample <NUM>"), the maximum value of the transmission loss becomes <NUM> dB/km, which is determined to be good.

The occupancy ratio is changed and when the occupancy ratio is <NUM>% (referred to as a "sample <NUM>"), the maximum value of the transmission loss becomes <NUM> dB/km; when the occupancy ratio is <NUM>% (referred to as a "sample <NUM>"), the maximum value of the transmission loss becomes <NUM> dB/km; when the occupancy ratio is <NUM>% (referred to as a "sample <NUM>"), the maximum value of the transmission loss becomes <NUM> dB/km; when the occupancy ratio is <NUM>% (referred to as a "sample <NUM>"), the maximum value of the transmission loss becomes <NUM> dB/km; and when the occupancy ratio is <NUM>% (referred to as a "sample <NUM>"), the maximum value of the transmission loss becomes <NUM> dB/km, all of which are determined to be good.

On the other hand, when the occupancy ratio of the optical unit <NUM> is <NUM>% (referred to as a "sample <NUM>"), the maximum value of the transmission loss becomes <NUM> dB/km which is greater than <NUM> dB/km, such that this case is determined to be defective.

Thus, it can be seen that when the occupancy ratio is equal to or less than <NUM>% in a state where the optical unit is twisted, it is difficult to apply the side pressure to the optical fiber and thus the cable transmission characteristic can be improved.

In the latter evaluation of the cable bending loss, the samples <NUM> to <NUM> are wound around a rod-like member (a member whose diameter is about <NUM> times the outer diameter of the cable) for one turn, and a case where the increase of the transmission loss (measurement wavelength <NUM> (nm)) after one turn becomes equal to or less than <NUM> (dB) at the maximum with respect to the transmission loss in a straight line state is determined to be good (O), whereas if not, the case is determined to be defective (×).

In the case of the sample <NUM>, the maximum value of the bending loss becomes <NUM> dB, which is determined to be good.

Further, in the case of the sample <NUM>, the maximum value of the bending loss becomes <NUM> dB; in the case of the sample <NUM>, the maximum value of the bending loss becomes <NUM> dB; in the case of the sample <NUM>, the maximum value of the bending loss becomes <NUM> dB; and in the case of the sample <NUM>, the maximum value of the bending loss becomes <NUM> dB, all of which are determined to be good.

On the other hand, in the case of the sample <NUM>, since the maximum value of the bending loss becomes <NUM> dB which becomes greater than <NUM> dB, this case is determined to be defective. Further, in the case of the sample <NUM>, since the maximum value of the bending loss is <NUM> dB/km, this case is determined to be defective.

Accordingly, when the occupancy ratio is equal to or less than <NUM>%, as described above, it is difficult to apply the side pressure to the optical fiber, but since the compression strain is dispersed even though the cable is bent in a circular arc shape, the cable bending characteristic can be also improved. Further, when the occupancy ratio of the twisted optical unit <NUM> is equal to or greater than <NUM>%, even though the cable is bent in a circular arc shape, since it is difficult for the tension member <NUM> to move toward the bending center of the cable and a phenomenon in which a part of the optical fiber is pinched by the tension member <NUM> hardly occurs, it can be seen that the cable bending characteristic can be improved.

<FIG> is a diagram illustrating an example of an optical fiber cable according to a second embodiment which does not form part of the claimed invention.

The optical fiber cable <NUM> illustrated in <FIG> is also a slotless type, and includes, for example, the round cable core <NUM>.

The subunit <NUM> is formed by, for example, twisting and collecting the intermittent ribbon <NUM> in a spiral shape, and is bundled by a bundle material <NUM> for identification. The optical unit <NUM> formed by, for example, collecting the plurality of the subunits <NUM> and twisting the collected subunits <NUM> in a spiral shape is accommodated in the cable core <NUM>.

Further, the tension member <NUM> made of a fiber body is also accommodated in the cable core <NUM>, and the plurality of tension members <NUM> illustrated in <FIG> are vertically disposed along the longitudinal direction of the optical unit <NUM> at the outside position of the optical unit <NUM>. The tension member <NUM> is formed of a glass fiber such as, for example, an optical fiber not contributing to transmission as a wire having resistance against tension and compression. Further, the configuration of the cable jacket <NUM> is the same as that of the first embodiment, and the detailed description thereof will be omitted.

The optical fiber cable according to the second embodiment has the same slotless structure as that of the first embodiment, thereby making it possible to achieve the high density mounting.

Further, since the tension member <NUM> made of a fiber body is disposed approximately uniformly at the outside position of the optical unit <NUM> in the cable core <NUM>, it is possible to provide an optical fiber cable which has no bending directionality and can be easily laid in a pipeline.

Claim 1:
A slotless type optical fiber cable (<NUM>), comprising:
an optical unit (<NUM>) formed by twisting a plurality of subunits (<NUM>) in a spiral shape around a tension member (<NUM>) made of a fiber body, each subunit (<NUM>) being formed by collecting a plurality of ribbons in which a plurality of optical fibers are arranged and by twisting the collected ribbons in a spiral shape;
a cable core (<NUM>) that accommodates the optical unit; and
a cable jacket (<NUM>) provided around the cable core; wherein
the tension member (<NUM>) is disposed at a central position of the optical unit (<NUM>), and
the ribbons are intermittent ribbons in which a connection part (<NUM>) and a non-connection part (<NUM>) are intermittently formed in the longitudinal direction between the optical fibers adjacent to each other.