Optical fiber cord

The present invention relates to an optical fiber cord in which tensile strength fibers are vertically attached to a plurality of optical fiber core wires and covered with a jacket.

With the increase in the amount of optical information, an optical fiber cord in which a plurality of optical fiber core wires and the like are assembled to be multi-core is used for wiring in or between optical devices. As the optical fiber core wire for the optical fiber cord, a normal optical fiber having an outer diameter of 0.25 mm coated with nylon and having an outer diameter of 0.9 mm is used (see, for example, Patent Document 1). Further, the optical fiber cord is terminated by accommodating a plurality of optical fibers in a loose state inside the outer cover and attaching multi-core optical connectors to both ends of the cord (see, for example, Patent Document 2).

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2001-221935</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 2003-202473</text></patcit></p>

<p> FIG. 2 is a diagram schematically showing a conventional multi-core optical fiber cord. The optical fiber cord 1 is stored in a loose state without binding a plurality of optical fiber core wires 2 in the jacket 3. It is composed of. In this configuration, the optical fiber core wire 2 has a smaller coefficient of linear expansion than the outer cover 3, so that when the outer cover 3 contracts at a low temperature, the optical fiber core wire 2 becomes longer than the outer cover 3, resulting in extra length and cord length. Meander in the direction. The meandering of the plurality of optical fiber core wires 2 is irregular, and the optical fiber core wires cross each other, and transmission loss due to microbend is likely to occur. Conventionally, in order to reduce the transmission loss due to this microbend, a nylon-coated optical fiber core wire having an outer diameter of 0.9 mm has been used.</p><p> If a multi-core optical fiber cord is made using an optical fiber core wire with an outer diameter of 0.9 mm, the outer diameter of the cord will be about 5.5 mm in the case of 8 cores, and the diameter will become even larger as the number of cores is increased. There is a demand for higher densities and smaller diameters of optical fibers, and there is a need for a structure in which meandering does not occur in the outer cover of a thin-diameter optical fiber core wire. The present invention has been made in view of the above-mentioned actual conditions, and is capable of suppressing meandering in the outer cover of the optical fiber core wire, and uses an optical fiber core wire having a coating outer diameter of 0.25 mm, and has a high density and fineness. An object of the present invention is to provide an optical fiber cord having a reduced diameter.</p>

<p> The optical fiber cord according to the present invention is an optical fiber cord in which a plurality of optical fiber core wires are bundled and covered with a jacket together with tensile strength fibers, and the plurality of optical fiber core wires are divided into two bundles. It is characterized in that it is twisted in opposite directions and arranged in parallel with tensile strength fibers vertically attached. The twist pitch of the bundle of the optical fiber core wires is 200 mm to 400 mm, and the tensile strength fiber is filled with 14200 denier or more.</p>

<p> According to the present invention, a bundle of a plurality of optical fiber core wires is twisted at the same pitch, and the twisting directions of the bundles of the plurality of optical fiber core wires are opposite to each other. The length and area of the portion where the optical fiber core wires intersect with each other at the contact portion between the wire bundles increases, the occurrence of microbend is small, and the increase in transmission loss can be suppressed. Further, since a plurality of optical fiber core wires are twisted, each optical fiber core wire does not meander individually, and the occurrence of microbend can be suppressed from this point as well. As a result, it is possible to realize a high-density and small-diameter optical fiber cord using an optical fiber core wire having a small diameter of 0.25 mm.</p>

<figref num="1">It is a figure explaining the outline of the optical fiber cord of this invention.</figref><figref num="2">It is a schematic diagram explaining the problem of the prior art.</figref>

The outline of the present invention will be described with reference to the drawings. Figure 1 (A) shows a bundle of multiple optical fiber core wires. It shows the state of being housed in the cable, and FIG. 1 (B) is a figure which shows the cross section of the multi-core optical fiber cord. In the figure, 10 is an optical fiber cord, 11 is an optical fiber core wire, 12a and 12b are optical fiber core wire bundles, 13 is a jacket, and 14 is a tensile strength fiber.

The optical fiber cord is composed of a plurality of optical fiber core wires 11, which are divided into two sets to form optical fiber core wire bundles 12a and 12b, which are twisted together so as not to be separated. Tensile fibers 14 are arranged around the optical fiber core wire bundles 12a and 12b, and the outside thereof is covered with a jacket 13 to form an optical fiber cord 10. In the present invention, as the optical fiber core wire 11 housed in the optical fiber cord 10, for example, an optical fiber core wire in which a glass fiber having an outer diameter of 0.125 mm is protected by a fiber coating having an outer diameter of about 0.25 m is used.

For the optical fiber core wire 11, for example, 24 cores are prepared, and it is preferable to divide the optical fiber core wire 11 into two bundles of 12 cores each. One bundle is stacked in two stages, for example, 3 cores and 9 cores, so that the cross-sectional arrangement is close to a circular shape. It is desirable that the 12-core fiber optic core wire be identified by its fiber coating in different colors. If all 24 cores are separated, the distinctiveness is not good, so it is preferable to bundle 12 cores of different colors. This makes the optical fiber core wire for each bundle (12-core optical fiber core wire). Can be identified one by one.

The core wire bundle 12a and the core wire bundle 12b of the optical fiber core wire divided into 12 cores are twisted in one direction with the same twist pitch. A plurality of optical fiber core wires 11 in the same core wire bundle 12a or core wire bundle 12b are twisted in opposite directions at the same twist pitch and are adjacent to each other in a parallel state, so that they are linear without intersecting each other. Since they come into contact with each other, microbends are unlikely to occur, and an increase in transmission loss can be suppressed.

When one core wire bundle 12a divided into two bundles is twisted to the right, the other core wire bundle 12b is twisted to the opposite left direction and assembled so that the twisting directions are different from each other. The two core wire bundles 12a and the core wire bundle 12b are arranged parallel to each other and housed in the outer cover 13, but if the core wire bundle 12a and the core wire bundle 12b are twisted in opposite directions and have the same twist pitch, they are placed on each other. Even if they come into contact with each other adjacent to each other, the inclination directions of the optical fiber core wires are the same, so that microbend is unlikely to occur, and an increase in transmission loss due to this can be suppressed. If the twisting directions of the core wire bundle 12a and the core wire bundle 12b are the same, the inclination directions of the optical fiber core wires intersect at the portions that are adjacent to each other and come into contact with each other, so that microbend is likely to occur.

Further, the twist pitch of the core wire bundle 12a and the core wire bundle 12b is preferably in the range of 200 mm to 400 mm. Optical connectors (not shown) are attached to both ends of the optical fiber cord 10, but when attaching the optical fiber core wire to the connector, remove the outer cover on both ends to a length of about 200 mm to 300 mm to remove the internal coating. The optical fiber core wire 11 is exposed. Since bundled optical fiber core wires are arranged in a row in a tape shape and attached to the optical connector, if this length is at least half the pitch of the twist, it is easy to arrange in a row and workability is good. However, if it is too long, the optical fiber core wires will be separated and will not easily form a bundle, so the twist pitch is preferably 400 mm or less. On the other hand, even if it is too short, productivity will deteriorate, so it is realistic to set it to 200 mm or more.

One core of the optical fiber cord (12 cores) is twisted to the right with a twist pitch of 400 mm, and the other core bundle (12 cores) is twisted to the left with a twist pitch of 400 mm, and the length is 100 m (30 mm in diameter). When a test product (in a state of being wound so as to be) was prepared and the transmission loss was measured, the increase loss was less than 0.1 dB / km at a wavelength of 1300 nm, which was acceptable. On the other hand, in the test product with the same right-twisted test product with a twist pitch of 400 mm for both core wire bundles, the increased loss exceeded 0.1 dB / km and failed.

In addition, one core bundle (12 cores) of the optical fiber cord is twisted to the right with a twist pitch of 330 mm (upper limit of twist pitch 300 mm ± 10%), and the other core bundle (12 cores) is left with a twist pitch of 270 mm. Twisted (twisting pitch 300 mm ± 10% lower limit), a test product with a length of 100 m was prepared in the same manner as above, and the transmission loss was measured. there were. On the other hand, in the test product in which one core wire bundle was right-twisted with a twist pitch of 200 mm and the other core wire bundle was left-twisted with a twist pitch of 400 mm, the increase loss exceeded 0.1 dB / km and failed. .. Since the twist pitch is overwhelmingly longer than the diameter of the optical fiber cord, the increase in loss due to the twist pitch was not so large even if there was a difference of about ± 10% with respect to the twist pitch of 300 mm.

The tensile strength fibers 14 are vertically attached between the outer cover 13 and the core wire bundles 12a and 12b of the optical fiber so as not to have a gap. Aramid fiber (for example, registered trademark Kevlar) or the like is used as the tensile strength fiber 14, and it is desirable that the tensile strength fiber 14 has an allowable tension of 1320 N or more with the optical fiber core wire extended by 0.3%. Therefore, it is preferable that 5 bundles (14200 denier in total) or more of 2840 denier fiber bundles are filled.

The jacket 13 is formed by extrusion molding of flame-retardant polyethylene or the like. It is desirable that the outer cover 13 has mechanical strength so that it will not be crushed even if a slight load is applied, and it is desirable that the thickness T of the outer cover 13 is 0.5 mm or more. As for the mechanical strength, the outer cover does not collapse even when a load of 100 kg / 100 mm is applied, and even if a weight with a circular bottom diameter of 20 mm and a weight of 500 g is dropped from a height of 600 mm, it is inside. It is preferable that the optical fiber core wire is configured so as not to be damaged.

As shown in FIG. 1 (B), when an optical fiber core wire 11 having a coating outer diameter (d1) of 0.25 mm is used, the bundle outer diameters (d2) of the 12 core wire bundles 12a and 12b are different. It will be about 1.0 mm, and the total outer diameter of the two bundles will be about 2.0 mm. Considering the space of the tensile strength fiber and the outer diameter of 0.5 mm or more, the inner diameter (D1) of the outer cover 13 is about 2.6 mm, and the outer diameter (D2) is about 3.8 mm.

When the inner diameter (D1) of the outer cover 13 is 2.6 mm, the outer diameter (D2) is 3.8 mm, and the tensile strength fiber bundle is 2840 denier x 2 bundles, the elongation of the optical fiber core wire is required during the laying work. The tension was 1.4% at 660N, which exceeded the 60% value of the screening level of 1.0%, which was 0.6%, and the reliability was a concern in terms of the breaking probability of the optical fiber. In addition, when the inner diameter (D1) of the outer cover 13 is 2.6 mm, the outer diameter (D2) is 3.6 mm, and the tensile strength fiber bundle is 2840 denier x 5 bundles, the elongation of the optical fiber core wire is required during the laying work. At a tension of 660N, it was 0.55%, which was lower than the 60% value of the screening level of 1.0%, which was 0.6%, which was a reliable value in terms of the breaking probability of the optical fiber.

When an optical connector can be attached to the end of the optical fiber cord 10, in the case of this example, it is preferable to use a 12-core × 2-stage optical connector. It is easy to identify by using one bundle of 12 color-coded optical fiber cores as one stage of the optical connector. In addition, since the optical connector is attached to the ferrule in bundle units, work mistakes can be reduced and productivity can be improved. Moreover, although the optical fiber core wire has been described in the example of 24 cores, it may be more or less than this.

10 ... fiber optic cord, 11 ... fiber optic core, 12a, 12b ... fiber optic bundle, 13 ... jacket, 14 ... tensile strength fiber.