JP7184526B2 - fiber optic cable - Google Patents

Description

The present invention relates to slotless optical fiber cables.

As a slotless type optical fiber cable that suppresses the movement of the optical fiber core wire (so-called "core wire movement"), it is a string-shaped cable coated with an ultraviolet curable resin between a plurality of optical fiber core wires and a pressure winding tape. There is known one in which the body is interposed (see Patent Document 1, for example).

JP 2014-139609 A

In the optical fiber cable described above, the string-like body is provided to suppress the movement of the core wire, and there is a problem that the number of parts constituting the optical fiber cable increases.

The problem to be solved by the present invention is to provide an optical fiber cable capable of suppressing movement of core wires without increasing the number of parts.

[1] An optical fiber cable according to the present invention comprises an optical fiber assembly including a plurality of mutually bundled optical fibers, a pressure winding tape covering the optical fiber assembly, a sheath covering the pressure winding tape, wherein the pressure winding tape is an optical fiber cable including a body portion that wraps the outer periphery of the optical fiber assembly and at least one folded portion that is folded back at an end or intermediate portion of the body portion be.

[2] In the above invention, the folded portion may be positioned outside the body portion, inside the body portion, or between ends of the body portion in the radial direction of the optical fiber cable. good.

[3] In the above invention, the following formula (1) may be satisfied.
0.05≦Lb/La≦0.50 (1)
However, in the above equation (1), La is the inner circumference of the sheath, and Lb is the length of the folded portion.

[4] In the above invention, the pressure winding tape may be longitudinally wound around the outer periphery of the optical fiber assembly.

[5] In the above invention, the length of the folded back portion of the pressure winding tape may be 20% or more of the total length of the pressure winding tape.

[6] In the above invention, the folding point of the folding portion may be bent in an angular shape or an arc shape.

According to the present invention, the folded portion of the pressing tape can increase the frictional force between the pressing tape and the optical fiber assembly, so that the movement of the optical fiber assembly can be suppressed. Moreover, since the folded part is formed of a part of the pressing tape, the number of parts of the optical fiber cable does not increase. Therefore, it is possible to suppress the movement of the core wire without increasing the number of parts of the optical fiber cable.

1 is an exploded perspective view of an optical fiber cable according to a first embodiment of the present invention; FIG. FIG. 2 is a cross-sectional view taken along line II-II of FIG. FIG. 3 is a perspective view showing an intermittently fixed optical fiber ribbon according to the first embodiment of the present invention. FIG. 4 is a perspective view showing an optical fiber unit according to the first embodiment of the invention. FIG. 5 is a cross-sectional view for explaining the configuration of the pressure winding tape according to the first embodiment of the present invention. 6(a) to 6(c) are cross-sectional views showing first to third modified examples of the pressure winding tape according to the first embodiment of the present invention. 7(a) and 7(b) are cross-sectional views showing fourth and fifth modifications of the pressure winding tape in the first embodiment of the present invention. 8(a) and 8(b) are cross-sectional views showing sixth and seventh modifications of the pressure winding tape in the first embodiment of the present invention. 9(a) and 9(b) are cross-sectional views showing eighth and ninth modifications of the pressure winding tape according to the first embodiment of the present invention. FIG. 10 is a cross-sectional view showing an optical fiber cable according to a second embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

1 and 2 are an exploded perspective view and a cross-sectional view showing an optical fiber cable according to this embodiment, FIG. 3 is a perspective view showing an intermittently fixed optical fiber ribbon according to this embodiment, and FIG. FIG. 5 is a perspective view showing an optical fiber unit, and FIG. 5 is a cross-sectional view for explaining the structure of the pressing tape in this embodiment. 5, the illustration of the optical fiber assembly 10 is omitted for the sake of convenience, and the same applies to FIGS. 6(a) to 9(b) described later.

The optical fiber cable 1 in this embodiment is a so-called slotless type optical fiber cable that does not use a slot rod. As shown in FIGS. , a sheath 30 , a strength member 40 and a tear string 50 .

The optical fiber assembly 10 is an assembly in which a plurality of optical fibers 13 are assembled. Specifically, in this embodiment, the optical fiber aggregate 10 is formed by bundling a plurality of optical fiber units 11, and each optical fiber unit 11 includes a plurality of optical fiber tape core wires 12, A bundle material 15 is provided.

As shown in FIG. 3, each optical fiber ribbon 12 is an intermittently fixed optical fiber in which a plurality of (four in this example) optical fibers (optical fiber strands) 13 are arranged in parallel and intermittently connected. It's tape. Specifically, the optical fibers 13 adjacent to each other are intermittently bonded by the bonding portion 14 at predetermined intervals. The adhesive portion 14 is made of, for example, an ultraviolet curable resin or a thermoplastic resin. The bonded portions 14 are arranged to be offset from each other in the longitudinal direction of the optical fiber ribbon 12, and the optical fibers 13 are restrained in the region other than the bonded portions 14 in the optical fiber ribbon 12. There are no non-adhesive areas. Therefore, the optical fiber ribbon 12 can be rolled into a tubular shape (bundle shape) or folded, and a large number of optical fibers 13 can be bundled at a high density.

A plurality of optical fiber tape core wires 12 are bundled with each other, and as shown in FIG. formed. The bundle material 15 is a member wrapped around the outer circumference of the bundle of the optical fiber tape core wires 12 in a net shape. Although not shown, the bundle material 15 may be a string-like member spirally wound around the bundle of the optical fiber ribbons 12 .

Then, as shown in FIGS. 1 and 2, the optical fiber assembly 10 is formed by twisting the plurality of optical fiber units 11 together. Specific examples of the method of twisting the optical fiber units include SZ twist and unidirectional twist. SZ twisting is a method of twisting a plurality of linear bodies while reversing the twisting direction at predetermined intervals. On the other hand, unidirectional twisting is a method of twisting a plurality of filaments in only one direction, that is, a method of twisting a plurality of filaments in a spiral.

The configuration of the optical fiber unit 11 is not particularly limited to the configuration described above. For example, the optical fiber unit 11 can be configured by simply bundling a plurality of optical fiber strands 13 without using the optical fiber ribbon 12. may Also, the configuration of the optical fiber assembly 10 is not particularly limited to the configuration described above. For example, the optical fiber assembly 10 may be configured by simply twisting a plurality of optical fiber strands 13 without using the optical fiber unit 11 .

As shown in FIGS. 1 and 2, this optical fiber assembly 10 is covered with a pressing tape 20. As shown in FIG. In this embodiment, the longitudinal direction of the pressure winding tape 20 substantially coincides with the axial direction of the optical fiber cable 1, and the width direction of the pressure winding tape 20 substantially coincides with the circumferential direction of the optical fiber cable 1. A pressure winding tape 20 is longitudinally wound around the outer periphery of the optical fiber assembly 10 so as to do so. By winding the pressing tape 20 vertically, the workability of removing the optical fiber 13 from the optical fiber cable 1 is improved. It should be noted that the winding method of the pressure winding tape 20 is not limited to vertical winding, and may be, for example, horizontal winding (spiral winding).

This pressing tape 20 is composed of a non-woven fabric or a film. A specific example of the nonwoven fabric forming the pressing tape 20 is not particularly limited, but nonwoven fabrics made of fibers such as polyester, polyethylene, and polypropylene can be mentioned. The thickness of this nonwoven fabric is not particularly limited, but it is preferably about 50 μm to 500 μm.

On the other hand, specific examples of the film constituting the pressure winding tape 20 are not particularly limited. can be mentioned. The thickness of this film is not particularly limited, but the thickness is preferably about 25 μm to 100 μm.

When the pressing tape 20 is made of non-woven fabric, water-absorbing powder may be added to the non-woven fabric to function as a water-absorbing layer for stopping water in the optical fiber cable 1 . When the optical fiber cable 1 is flooded with water, the water-absorbing powder swells and closes the gap in the optical fiber cable 1, thereby stopping the water inside the optical fiber cable 1. - 特許庁

Specific examples of such water-absorbing powders are not particularly limited. can be mentioned. Moreover, as a method of applying the water-absorbing powder to the nonwoven fabric, it may be attached (applied) to the surface of the nonwoven fabric, or may be interposed between two nonwoven fabrics.

The sheath (outer covering) 30 is a cylindrical member whose outer circumference is covered with the pressing tape 20 , and the optical fiber assembly 10 wrapped in the pressing tape 20 is accommodated in the inner hole 31 of the sheath 30 . there is This sheath 30 is made of a resin material such as polyvinyl chloride (PVC), polyethylene (PE), nylon, fluoroethylene, or polypropylene (PP). A pair of tension members 40 and a pair of tear cords 50 are embedded in the sheath 30 .

A pair of tension members (tension members) 40 are linear members that suppress strain and bending applied to the optical fiber 13 due to contraction of the sheath 30 . The tensile member 40 is embedded in the sheath 30 so as to extend substantially parallel across the inner hole 31 . Non-metallic materials and metallic materials can be exemplified as the material forming the tensile strength member 40 . Specific examples of the non-metallic material are not particularly limited, but for example, glass fiber reinforced plastic (GFRP), aramid fiber reinforced plastic (KFRP) reinforced with Kevlar (registered trademark), polyethylene fiber reinforced plastic reinforced with polyethylene fiber, etc. of fiber reinforced plastics (FRP) can be mentioned. Specific examples of the metallic material include, but are not particularly limited to, metal wires such as steel wires.

A pair of tear cords (rip cords) 50 are cord-like members for tearing the sheath 30 at the intermediate portion of the optical fiber cable 1 to take out the optical fiber 13 . The tearing string 50 is embedded in the sheath 30 so as to extend substantially parallel across the inner hole 31, and along a direction substantially perpendicular to the facing direction of the above-described tensile member 40. facing each other. Although not particularly limited, the tearing string 50 is made of, for example, a twisted yarn made of polyester, or a fibrous string-like body such as aramid fiber or glass fiber.

In this embodiment, as shown in FIG. 5, a cross-sectional view of the optical fiber cable 1 (when the optical fiber cable 1 is cut along a direction substantially perpendicular to the longitudinal direction of the optical fiber cable 1) In a cross-sectional view), the pressing tape 20 has a body portion 21 and a folded portion 22 . The body portion 21 is a portion that wraps the outer periphery of the optical fiber assembly 10 . One end portion 211 of the main body portion 21 overlaps the other end portion 212 of the main body portion 21 in the radial direction of the optical fiber cable 1 , forming an overlapping portion of the pressing tape 20 . The length of the winding portion 213 excluding this overlapped portion in the body portion 21 corresponds to the length of one circumference of the outer circumference of the optical fiber assembly 10 , and can be approximated to the inner circumference La of the inner hole 31 of the sheath 30 . length.

The folded portion 22 is a portion folded back from one end 211 of the body portion 21 . In this embodiment, the folded portion 22 is folded outward from the end portion 211 of the main body portion 21, and positioned outside the main body portion 21 in the radial direction of the optical fiber cable 1. overlaps with

By forming such a folded portion 22 on the tape 20, the occupancy rate of the optical fiber assembly 10 in the sheath 30 can be reduced, and the elastic force of the folded portion 22 can be used to make the inside of the sheath 30 flexible. The optical fiber assembly 10 can be pressed with a moderate force. Therefore, the frictional force between the pressing tape 20 and the optical fiber assembly 10 can be strengthened, so that the optical fiber assembly 10 can be prevented from moving within the sheath 30 . Moreover, since the frictional force between the optical fibers 13 can be strengthened, it is possible to suppress the movement of the optical fibers 13 within the optical fiber assembly 10 . By changing the thickness of the pressing tape 20, the frictional force between the pressing tape 20 and the optical fiber assembly 10 can be adjusted, and the frictional force between the optical fibers 13 can also be adjusted. can.

By the way, if the pressure winding tape and the optical fiber assembly are firmly fixed with an adhesive or the like, the optical fibers may be bent excessively, deteriorating the transmission characteristics. Therefore, it is necessary to fix the optical fiber assembly by the frictional force of the pressing tape.

In this embodiment, the folded portion 22 is provided over the entire length of the optical fiber cable 1, as shown in FIG. As a result, the frictional force on the optical fiber assembly 10 can be made uniform throughout the optical fiber cable 1, and the frictional force between the optical fibers 13 can be made uniform. Note that the folded portion 22 does not necessarily have to be provided over the entire length of the optical fiber cable 1 . If the length of the portion of the tape 20 where the folded back portion 22 is provided is 20% or more of the total length of the tape 20, the above-described effect of suppressing movement of the core wire can be obtained. Therefore, for example, the folded portions 22 may be intermittently provided in the longitudinal direction of the optical fiber cable 1 .

In this embodiment, it is preferable that the pressing tape 20 is wound around the outer periphery of the optical fiber assembly 10 so that the following formula (2) is satisfied. However, in the following equation (2), La is the inner circumference of the inner hole 31 of the sheath 30 (the length of one round of the inner hole 31 of the sheath 30), and Lb is the length of the folded portion 22. More specifically, Lb is the length from the folding point 221 (one end of the folded portion 22 ) of the end portion 211 of the body portion 21 to the other end of the folded portion 22 .

0.05≦Lb/La≦0.50 (2)

Note that La may be calculated according to the following equation (3). In this equation (3), S is the cross-sectional area of the inner hole 31 of the sheath 30. For example, the cross-sectional area S can be derived from an image of the cross section of the optical fiber cable.

La=2×(S/π) ^1/2 ×π (3)

When the ratio of the length Lb of the folded portion 22 to the inner circumference La of the sheath 30 is 0.05 or more (Lb/La≧0.05), the folded portion 22 becomes excessively small with respect to the winding portion 213. There is no Therefore, the frictional force between the pressing tape 20 and the optical fiber assembly 10 can be moderately increased, and the movement of the optical fiber assembly 10 within the sheath 30 can be reliably suppressed.

On the other hand, since the ratio of the length Lb of the folded portion 22 to the inner circumference La of the sheath 30 is 0.50 or less (Lb/La≤0.50), the folded portion 22 is excessively large relative to the winding portion 213. never become. Therefore, it is possible to prevent the folded portion 22 from pressing the optical fiber assembly 10 and affecting the transmission characteristics of the optical fiber 13 .

Note that the position of the folded back portion of the pressure winding tape is not particularly limited to the example shown in FIG. 6(a) to 7(b) are cross-sectional views showing first to fifth modifications of the pressing tape according to the present embodiment.

For example, as shown in FIG. 6( a ), the folded portion 22 may be positioned inside the body portion 21 by folding the end portion of the pressing tape 20 inward. Alternatively, as shown in FIGS. 6(b) and 6(c), the folded portion 22 may be interposed between the ends 211, 212 of the body portion 21. FIG. 6(a) to 6(c), it is preferable that the optical fiber 13 is not interposed between the main body portion 21 and the folded portion 22. FIG.

Alternatively, the folded portion 22 may be provided in the intermediate portion of the pressing tape 20 . Specifically, in the modification shown in FIGS. 7(a) and 7(b), in the cross-sectional view of the optical fiber cable 1, the body portion of the pressure winding tape 20 includes two body portions 21A and 21B. The folded portion 22 is provided between the first body portion 21A and the second body portion 21B.

In the modification shown in FIG. 7A, the folded portion 22 is folded back from the end of the first body portion 21A and positioned inside the first body portion 21A. In addition, in the modification shown in FIG. 7B, the folded portion 22 is folded back from the end of the first main body portion 21A and positioned outside the first main body portion 21A. The length Lb of the folded portion 22 in the modified example shown in FIGS. 7A and 7B is from the first folded point 221 at the end of the first body portion 21A to the second folded portion. It is the length from point 222 to the end of second body portion 21B.

In addition, in the modification shown in FIG. 7A, it is preferable that the optical fiber 13 is not interposed between the first main body portion 21A and the folded portion 22. As shown in FIG. In addition, in the modification shown in FIG. 7B, it is preferable that the optical fiber 13 is not interposed in the folded portion 22.

Although not shown, the folded portion 22 may be folded back from the end of the second main body portion 21B and positioned inside the second main body portion 21B. Alternatively, the folded portion 22 may be folded back from the end of the second body portion 21B and positioned outside the second body portion 21B.

Also, the number of folded portions 22 in the pressing tape 20 is not particularly limited to the example shown in FIG. 8(a) and 8(b) are cross-sectional views showing sixth and seventh modifications of the pressing tape according to the present embodiment.

For example, as shown in FIG. 8( a ), a plurality of folded portions 22 may be formed at the end portion 212 of the body portion 21 by folding the pressing tape 20 a plurality of times (twice in this example). Alternatively, as shown in FIG. 8(b), by folding back both ends of the pressing tape 20, the folded portion 22 is formed at one end 211 of the body portion 21 and the other end 212 of the body portion 21 is formed. A folded portion 22 may also be formed on the .

Alternatively, although not particularly shown, the folded back portions 22 may be provided at both the end portion and the intermediate portion of the pressing tape 20 . Specifically, a folded portion 22 is provided at the end of the pressing tape 20 (see, for example, FIGS. 5 and 6(a) to 6(c)), and the other folded portion 22 is attached to the pressing tape 20. (See, for example, FIGS. 7(a) and 7(b)). In addition, when the press winding tape 20 is provided with a plurality of folded portions 22, the value of Lb in the above equation (2) is the total value of the lengths of the plurality of folded portions 22. FIG. By increasing the number of folded portions 22, the frictional force between the pressing tape 20 and the optical fiber assembly 10 can be strengthened, and the frictional force between the optical fibers 13 can be strengthened.

In addition, in the example shown in FIGS. 5 and 7(a), the folding point 221 between the main body portion and the folding portion is angularly bent, but as shown in FIGS. 9(a) and 9(b), Moreover, the turning point 221 may be bent in an arc shape. Similarly, in the example shown in FIG. 7A, the second folding point 222 of the folding portion is bent into an angular shape, but as shown in FIG. 9B, the folding point 222 is arc-shaped. It may be bent. Although not shown, the same applies to FIGS. 6 and 7(b) to 8(b). FIG. 9A is a cross-sectional view showing an eighth modification in which the folding point 221 is bent in an arc shape, and corresponds to FIG. On the other hand, FIG. 9(b) is a cross-sectional view showing a ninth modification in which folding points 221 and 222 are bent in an arc shape, and corresponds to FIG. 7(a).

Since the film is harder than the nonwoven fabric, as shown in FIGS. 9(a) and 9(b), the presser winding tape 20 made of the film tends to bend in an arc shape at the folding points 221 and 222. . Therefore, even if the pressure winding tape 20 is made of a thin film, the occupancy rate of the optical fiber assembly 10 in the sheath 30 can be reduced. On the other hand, since the presser tape 20 made of nonwoven fabric is relatively soft, the folding points 221 and 222 tend to be angularly bent (see FIGS. 5 to 8B), but the nonwoven fabric is relatively thick. , the occupation rate of the optical fiber assembly 10 in the sheath 30 can be reduced even if the folding points 221 and 222 are not arc-shaped.

As described above, in the present embodiment, the folded portion 22 is formed at the end portion or intermediate portion of the body portion 21 of the pressing tape 20 . The folded portion 22 can increase the frictional force between the pressing tape 20 and the optical fiber assembly 10, so that movement of the optical fiber assembly 10 within the sheath 30 can be suppressed. Moreover, since the frictional force between the optical fibers 13 can be strengthened by the folded portion 22, movement of the optical fibers 13 within the optical fiber assembly 10 can be suppressed. Moreover, since the folded portion 22 is formed of a portion of the pressing tape 20, the number of parts of the optical fiber cable 1 does not increase.

It should be noted that the embodiments described above are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is meant to include all design changes and equivalents that fall within the technical scope of the present invention.

For example, the cross-sectional shape of the optical fiber cable is not particularly limited to circular. FIG. 10 is a cross-sectional view showing an optical fiber cable according to the second embodiment of the invention. As shown in FIG. 10, the shape of the sheath 30B of the optical fiber cable 1B may be substantially rectangular. In this case, the inner hole 31 of the sheath 30B also has a substantially rectangular shape, and the shapes of the optical fiber assembly 10 and the pressure winding tape 20 also follow the shape of the inner hole 31 of the sheath 30B.

Incidentally, in the example shown in FIG. 10, instead of the tear string 50, a notch 32 is formed on the outer peripheral surface of the sheath 30B. This notch 32 is formed so that the sheath 30B can be easily split. By cutting the notch 32 with a tool, the optical fiber cable 1 can be easily cut and the work of taking out the optical fiber 13 is facilitated.

By the way, in the optical fiber cable having the configuration as described above, the optical fiber assembly is difficult to move within the sheath even when, for example, wind vibrates or the temperature changes. It is required that the transmission loss of the fiber 13 hardly increases. Therefore, an optical fiber cable was actually fabricated, and the core wire movement under vibration and the transmission loss under temperature change were evaluated. However, the present invention is not limited to these examples.

<Examples 1 to 5>
In Examples 1 to 5, the outer circumference of the 200-core optical fiber assembly using four intermittently fixed optical fiber tape core wires is longitudinally wound with a pressure winding tape, and this pressure winding tape is placed in the sheath. By housing, an optical fiber cable as shown in FIG. 2 was produced (hereinafter also simply referred to as "structure 1"). A polyester non-woven fabric having a thickness of 100 μm was used as the pressing tape. At this time, in Examples 1 to 5, the values of Lb/La were set to 0.03, 0.05, 0.10, 0.50 and 0.80, respectively.

<Examples 6 to 10>
In Examples 6 to 10, optical fiber cables having the same configuration as in Examples 1 to 5 were produced except that the position of the folded portion of the pressure winding tape was changed as shown in FIG. Also simply referred to as "structure 2"). At this time, in Examples 6 to 10, the values of Lb/La were set to 0.03, 0.05, 0.10, 0.50 and 0.80, respectively.

<Examples 11 to 15>
In Examples 11 to 15, optical fiber cables having the same configuration as in Examples 1 to 5 were produced, except that the position of the folded portion of the pressure winding tape was changed as shown in FIG. Also simply referred to as "structure 3"). At this time, in Examples 11 to 15, the values of Lb/La were set to 0.03, 0.05, 0.10, 0.50 and 0.80, respectively.

<Examples 16 to 20>
In Examples 16 to 20, optical fiber cables having the same configuration as in Examples 1 to 5 were produced, except that the position of the folded portion of the pressure winding tape was changed as shown in FIG. Also simply referred to as "structure 4"). At this time, in Examples 16 to 20, the values of Lb/La were set to 0.03, 0.05, 0.10, 0.50 and 0.80, respectively.

<Examples 21 to 25>
In Examples 21 to 25, a PET film having a thickness of 25 μm was used as the pressure winding tape, and the position of the folded portion of the pressure winding tape was set as shown in FIG. 7(a). An optical fiber cable having a similar configuration was produced (hereinafter also simply referred to as "structure 5"). At this time, in Examples 21 to 25, the values of Lb/La were set to 0.03, 0.05, 0.10, 0.50 and 0.80, respectively.

<Examples 26 to 30>
Examples 26 to 30 were the same as Examples 1 to 5 above, except that a 25 μm PET film was used as the pressure winding tape, and the position of the folded portion of the pressure winding tape was set as shown in FIG. 7(b). An optical fiber cable having the configuration of (hereinafter also simply referred to as "structure 6") was produced. At this time, in Examples 26 to 30, the values of Lb/La were set to 0.03, 0.05, 0.10, 0.50 and 0.80, respectively.

<Comparative example>
In a comparative example, an optical fiber cable having the same structure as that of the above-described Example 1 except that the pressure winding tape was not provided with a folded portion was produced (hereinafter also simply referred to as "structure 7"). In this comparative example, the value of Lb/La is 0, since the pressure winding tape is not provided with a folded portion.

<Wire migration test>
A wire migration test was performed on Examples 1 to 30 and Comparative Example manufactured under the above conditions. In this fiber migration test, the optical fiber cables of Examples 1 to 30 and the comparative example were laid for 30 m, and after applying vibration with a frequency of 1.3 Hz and an amplitude of 430 mm 10,000 times, the optical fiber assembly in the sheath was measured. The displacement along the longitudinal direction was measured. At this time, when the amount of movement of the optical fiber assembly was 20 mm or less, the result was evaluated as "A" as being extremely good, and when the amount of movement was 30 mm or less, the result was good. When the movement amount exceeds 30 mm, it was evaluated as "C" because the result was insufficient. The results are shown in Table 1 below.

As shown in the column of "wire shift" in Table 1 above, the result of the wire shift test was "C" in the comparative example of structure 7 in which the pressure winding tape was not provided with the folded portion. This is probably because the pressure winding tape does not have a folded portion, so that sufficient frictional force does not act between the pressure winding tape and the optical fiber assembly.

On the other hand, Examples 1 to 30 of Structures 1 to 6, in which the pressure winding tape was provided with a folded portion, gave "A" or "B" in the cardiac migration test. It is considered that this is because the folded portion can strengthen the frictional force between the pressure winding tape and the optical fiber assembly. Therefore, it was confirmed that the movement of the optical fiber aggregate can be suppressed by providing the folded portion on the pressure winding tape regardless of the direction of folding and the position of the folded portion.

Here, the results of the fiber migration test of Examples 2 to 5, 7 to 10, 12 to 15, 17 to 20, 22 to 25, and 27 to 30 in which Lb/La is 0.05 or more are "A". In contrast, the results of the fiber migration test of Examples 1, 6, 11, 16, 21 and 26 with Lb/La of 0.03 were "B". This is probably because in Examples 1, 6, 11, 16, 21, and 26, the folded portion of the pressure winding tape was short, and the frictional force between the pressure winding tape and the optical fiber assembly was slightly weak. . From these facts, it was confirmed that Lb/La is preferably 0.05 or more (Lb/La≧0.05).

<Temperature characteristics test>
Further, a temperature characteristic test was conducted for Examples 1 to 30 and Comparative Example. In this temperature characteristic test, the optical fiber cables of Examples 1 to 30 and Comparative Example were subjected to two cycles in the range of -40°C to +70°C in accordance with the provisions of "Temperature cycling" in "Telcordia Technologies Generic Requirements GR-20-CORE". The temperature was changed and the maximum loss variation was measured at a measurement wavelength of 1.55 μm.

In Examples 5, 10, 15, 20, 25, and 30 in which Lb/La was 0.80, the maximum loss variation exceeded 0.15 dB/km in this temperature characteristic test. It is considered that this is because the folded portion of the pressing tape is long, and the folded portion presses the optical fiber assembly. On the other hand, in Examples 1 to 4, 6 to 9, 11 to 14, 16 to 19, 21 to 24, and 26 to 29 in which Lb/La is 0.50 or less, the maximum loss variation in this temperature characteristic test was 0.15 dB/km or less. From these facts, it was confirmed that Lb/La is preferably 0.50 or less (Lb/La≦0.50).

From the above, it is possible to suppress the movement of the optical fiber assembly by providing the folded portion on the pressing tape. Further, since Lb/La is in the range of 0.05 to 0.50 (0.05≦Lb/La≦0.50), movement of the optical fiber assembly can be suppressed more reliably, and the optical fiber deterioration of transmission characteristics can also be suppressed.

DESCRIPTION OF SYMBOLS 1, 1B... Optical fiber cable 10... Optical fiber assembly 11... Optical fiber unit 12... Tape core wire 13... Optical fiber 14... Adhesion part 15... Bundle material 20... Press winding tape 21, 21A, 21B... Main body part 211, 212... End 213... Wrapping part 22... Folding part 221, 222... Folding point 30, 30B... Sheath 31... Inner hole 32... Notch 40... Tensile member 50... Tear string

Claims (5)

A slotless optical fiber cable,
an optical fiber assembly including a plurality of optical fibers bundled together;
a pressure winding tape that covers the entire outer periphery of the optical fiber assembly;
a sheath that covers the pressure winding tape,
The pressure winding tape is
a body portion that surrounds the outer periphery of the optical fiber assembly;
at least one folded portion folded at an end or intermediate portion of said body portion and directly facing said body portion ;
The pressure winding tape is longitudinally wound around the outer periphery of the optical fiber assembly,
The length of the portion of the pressure winding tape provided with the folded portion is 20% or more of the total length of the pressure winding tape,
The folded portion is interposed between an accommodating portion that accommodates the optical fiber assembly in the sheath and an inner peripheral surface of the sheath ,
The body portion has an overlapping portion where one end and the other end of the body portion overlap,
An optical fiber cable that satisfies the following formula (1) .
0.05≦Lb/La≦0.50 (1)
However, in the above equation (1), La is the inner circumference of the sheath, and Lb is the length of the folded portion. The optical fiber cable according to claim 1,
The folded portion is positioned outside the body portion, inside the body portion, or between ends of the body portion in a radial direction of the fiber optic cable. The optical fiber cable according to claim 1 or 2,
The optical fiber cable , wherein the pressure winding tape includes a plurality of folded portions formed by folding multiple times . The optical fiber cable according to any one of claims 1 to 3,
The optical fiber cable, wherein the pressure winding tape includes a plurality of the folded portions arranged at both ends of the main body portion, or at the ends of the main body portion and the intermediate portion.
The optical fiber cable according to any one of claims 1 to 4 ,
The optical fiber cable in which the folding point of the folding portion is bent in an angular shape or an arc shape.

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