Optical fiber assembly for optical cable and optical cable

Abstract

In this optical fiber unit constituting an optical fiber assembly and being obtained by layering a plurality of optical fiber ribbons, a plurality of inner-layer fiber units positioned on the radial inside of the optical fiber assembly, and a plurality of outer-layer fiber units positioned on the radial outside of the optical fiber assembly relative to the inner-layer fiber units are present in a certain cross section of the optical fiber assembly. Regarding the sine value of the angle formed by a straight line in the radial direction connecting the center of the optical fiber assembly and the center of gravity of the optical fiber ribbons, and a straight line in the width direction of the ribbons and connecting both ends of the optical fiber ribbons, the average sine value in the outer-layer fiber units is 0.366 or greater in the certain cross section, where the average sine value is the average of the sine values of the plurality of optical fiber ribbons of the same optical fiber unit.

Description

Technical Field

[0001] The present invention relates to an optical fiber assembly and an optical cable. This application claims priority based on Japanese Patent Application No. 2021-212141 filed in Japan on December 27, 2021, the content of which is incorporated herein by reference.

Background Art

[0002] Patent Document 1 discloses an optical fiber cable (optical cable) having a cable core (optical fiber assembly) formed by stacking and bundling a plurality of optical fiber tapes to form an optical fiber unit (tape core unit) and aggregating a plurality of the optical fiber units.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When an optical cable having the above-described optical fiber assembly is manufactured without a plan, if bending occurs in the optical cable or shrinkage occurs in the outer sheath of the optical cable in a low-temperature environment, stress (mainly bending stress) often concentrates on the optical fibers of a specific optical fiber unit. When stress concentrates on a specific optical fiber, there is a problem that the transmission loss of the optical fiber increases.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical fiber assembly capable of suppressing an increase in the transmission loss of an optical fiber and an optical cable including the same.

Means for Solving the Problems

[0006] The optical fiber assembly according to the first aspect of the present invention is an optical fiber assembly formed by bundling a plurality of optical fiber units each formed by laminating a plurality of optical fiber tapes. In a cross-section of the optical fiber assembly perpendicular to the longitudinal direction at at least one position in the longitudinal direction of the optical fiber assembly, the laminated state of at least one of the optical fiber tapes constituting the optical fiber unit is disrupted so that the tape surface of the optical fiber tape is curved. In the plurality of optical fiber units, in a cross-section of the optical fiber assembly perpendicular to the longitudinal direction, there are a plurality of inner layer fiber units located on the inner side in the radial direction of the optical fiber assembly and a plurality of outer layer fiber units located on the outer side in the radial direction of the optical fiber assembly than the inner layer fiber units. Regarding the sine value sinα of the angle α formed by a radial straight line connecting the center of the optical fiber assembly and the center of gravity of the optical fiber tape and a straight line in the tape width direction connecting both ends of the optical fiber tape, the average value of the sine values sinα of the plurality of optical fiber tapes in the same optical fiber unit is defined as the average sine value sinα ave and at least at one position in the longitudinal direction of the optical fiber assembly, in a cross-section of the optical fiber assembly perpendicular to the longitudinal direction, the average sine value sinα ave in the outer layer fiber unit is 0.366 or more.

[0007] The optical cable according to the second aspect of the present invention includes the optical fiber assembly of the first aspect and an outer jacket that houses the optical fiber assembly inside.

Advantages of the Invention

[0008] According to the present invention, an increase in the transmission loss of the optical fiber can be suppressed.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0010] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 9. As shown in FIG. 1, the optical fiber assembly 2 of the present embodiment constitutes a part of the optical cable 1. The optical cable 1 of the present embodiment is a so-called slotless type optical cable that does not have a slot rod in which a groove (slot) for accommodating an optical fiber is formed. The optical cable 1 has an optical fiber assembly 2 and an outer sheath 3.

[0011] The optical fiber assembly 2 is configured by bundling a plurality of optical fiber units 11. The optical fiber unit 11 is a structure in which a plurality of optical fibers 13 are bundled. The specific structure of the optical fiber unit 11 will be described later. The optical fiber assembly 2 of the present embodiment constitutes the core of the optical cable 1. The core of the optical cable 1 of the present embodiment further has a holding tape 5 that covers a plurality of optical fiber units 11. The holding tape 5 may be composed of, for example, a water-absorbing tape. In the present embodiment, the holding tape 5 constitutes the internal space of the optical fiber assembly 2 in which the plurality of optical fiber units 11 are arranged. The above-described holding tape 5 may not be provided, for example. In that case, the inner surface of the outer sheath 3 described later forms the internal space of the optical fiber assembly 2.

[0012] The outer sheath 3 is formed in a cylindrical shape. The optical fiber assembly 2 is housed inside the outer sheath 3. The plurality of optical fiber units 11 may be housed inside the outer sheath 3, for example, in a state of being twisted in one direction or in an SZ shape. Inside the outer sheath 3, inclusions (not shown) may be housed in addition to the plurality of optical fiber units 11. The inclusions may be, for example, water-absorbing materials. The inclusions may be arranged inside, outside, or both inside and outside the holding tape 5. The above-described inclusions may not be provided, for example.

[0013] The outer shape of the optical fiber assembly 2 in a cross section orthogonal to the longitudinal direction of the optical cable 1 (a direction orthogonal to both the vertical direction and the horizontal direction in FIG. 1, the direction in which the optical cable 1 extends) may be an arbitrary shape, but in the present embodiment, it is substantially circular. In this specification, the substantially circular shape includes not only a perfect circle but also an ellipse, an oblong, and the like. Note that the outer shape of the optical fiber assembly 2 in the above-described cross section may be, for example, a rectangular shape.

[0014] The outer sheath 3 is a member that covers the optical fiber assembly 2. The inner surface of the outer sheath 3 forms a space for housing the optical fiber assembly 2. In the present embodiment, the inner surface of the outer sheath 3 is substantially circular corresponding to the optical fiber assembly 2 in a cross section orthogonal to the longitudinal direction of the optical cable 1. Note that the cross-sectional shape of the inner surface of the outer sheath 3 may be, for example, a rectangular shape. In the present embodiment, a holding tape 5 that wraps a plurality of optical fiber units 11 is housed inside the outer sheath 3. The tension member 7 is disposed in the jacket 3. All of the tension members 7 may be disposed within the jacket 3, or a part of the tension member 7 may be disposed within the jacket 3 and the other part of the tension member 7 may be exposed from the jacket 3. Other members such as, for example, a lip cord may be disposed in the jacket 3.

[0015] A plurality of tension members 7 are arranged so as to sandwich the optical fiber aggregate 2 in a cross section orthogonal to the longitudinal direction of the optical cable 1. In the cross section, the plurality of tension members 7 are arranged so as to face each other with the optical fiber aggregate 2 therebetween in a first direction orthogonal to the longitudinal direction. In the present embodiment, in the cross section, no other tension members are arranged so as to face each other with the optical fiber aggregate 2 therebetween in a second direction orthogonal to both the longitudinal direction and the first direction, but the present invention is not limited thereto, and other tension members may be arranged so as to face each other with the optical fiber aggregate 2 therebetween in the second direction. Each tension member 7 extends in the longitudinal direction of the optical cable 1. Each tension member 7 may be arranged parallel to the longitudinal direction of the optical fiber aggregate 2, or may be arranged in a spiral shape centered on the optical fiber aggregate 2. Further, each tension member 7 may be included, for example, inside the optical fiber aggregate 2. In FIG. 1, two tension members 7 are taken as a set, and a pair of sets are respectively arranged on both sides of the optical fiber aggregate 2, but the present invention is not limited thereto. For example, three or more tension members 7 may be taken as a set, and a pair of sets may be respectively arranged on both sides of the optical fiber aggregate 2, or the tension members 7 may be arranged one by one on both sides of the optical fiber aggregate 2. Further, in FIG. 1, the plurality of tension members 7 forming a set are separated from each other, but they may be in contact with each other, for example. Further, the plurality of tension members 7 forming a set may be twisted.

[0016] As shown in Fig. 2, the optical fiber unit 11 of the present embodiment has a structure in which a plurality of optical fibers 13 are bundled by a strip body 20 (bundling material). The strip body 20 is wound around the outer peripheries of the plurality of optical fibers 13 so that the plurality of optical fibers 13 do not separate from each other. Note that the optical fiber unit 11 may have a structure in which a plurality of optical fibers 13 are bundled by twisting them together without using the strip body 20, for example. The optical fiber unit 11 of the present embodiment is configured by bundling a plurality of optical fiber tapes 12 each having a plurality of optical fibers 13. Note that the optical fiber unit 11 may contain a mixture of the optical fiber tapes 12 and the non-taped optical fibers 13. The optical fiber 13 has a glass body including a core and a cladding, and a coating layer covering the glass body. The coating layer may include a coloring layer for identifying the optical fiber 13. The diameter of the glass body is, for example, 125 μm, and the diameter of the coating layer (that is, the diameter of the optical fiber 13) is, for example, 200 to 250 μm. However, the diameter of the glass body can be changed and may be less than 125 μm, such as 60 μm, 80 μm, 100 μm, etc. The diameter of the coating layer can also be changed and may be 200 μm or less, such as 160 μm, 180 μm, 200 μm, etc.

[0017] As shown in Fig. 3, the optical fiber tape 12 is configured by arranging a plurality of optical fibers 13 in parallel and connecting adjacent optical fibers 13 to each other. In the following description, in the optical fiber tape 12, the direction in which the optical fiber 13 extends may be referred to as the longitudinal direction of the optical fiber tape 12, and the arrangement direction of the plurality of optical fibers 13 may be referred to as the width direction of the optical fiber tape 12. Also, the direction orthogonal to the longitudinal direction and the width direction of the optical fiber tape 12 is defined as the thickness direction of the optical fiber tape 12, and the surface facing the thickness direction may be referred to as the tape surface.

[0018] The optical fiber tape 12 of the present embodiment is an intermittently connected type optical fiber tape in which a plurality (12 in FIG. 3) of optical fibers 13 are arranged in parallel and intermittently (partially) connected. Two adjacent optical fibers 13 are connected by a connecting portion 14A. A plurality of connecting portions 14A are arranged at intervals in the longitudinal direction of the optical fiber tape 12 between two adjacent optical fibers 13. Further, a connecting portion 14A that connects a predetermined optical fiber 13 and an optical fiber 13 adjacent to one side of the optical fiber 13, and a connecting portion 14A that connects a predetermined optical fiber 13 and an optical fiber 13 adjacent to the other side of the optical fiber 13 are displaced in the longitudinal direction. That is, the plurality of connecting portions 14A are two-dimensionally and intermittently arranged in the longitudinal direction and the width direction of the optical fiber tape 12. Regions between two adjacent optical fibers 13 that are not connected by the connecting portion 14A are non-connecting portions 14B. In the non-connecting portion 14B, two adjacent optical fibers 13 are not constrained.

[0019] The intermittently connected type optical fiber tape 12 is not limited to that illustrated in FIG. 3. For example, the arrangement pattern of the connecting portions 14A arranged intermittently does not have to be a fixed pattern. Further, in the intermittently connected type optical fiber tape 12, for example, a plurality (for example, two) of optical fibers 13 may be grouped together, a plurality of groups may be arranged in parallel, and the optical fibers 13 of adjacent groups may be intermittently connected by the connecting portions 14A. Further, adjacent optical fibers 13 in the optical fiber tape 12 may be separated or in contact with each other. Further, although the number of optical fibers 13 in the optical fiber tape 12 is generally a multiple of 4 (4-core, 8-core, 12-core, 16-core), it is not limited thereto. The number of optical fibers 13 in the optical fiber tape 12 may be, for example, an odd number.

[0020] The optical fiber tape 12 can be flexibly deformed in its width direction. For example, the optical fiber tape 12 can be deformed to curve such that one of its tape surfaces becomes convex. Also, for example, the optical fiber tape 12 can be deformed such that its tape surface is convex and concave (meanders) in the width direction. In particular, since the intermittently connected optical fiber tape 12 has remarkable flexibility in the width direction, the characteristics of the optical fiber 13 are less likely to deteriorate even when densely mounted.

[0021] As shown in FIG. 2, the strip 20 that bundles a plurality of optical fiber tapes 12 (optical fibers 13) is a flexible filamentous, cord-like, or tape-like member. The strip 20 is wound around the outer periphery of the bundle of the plurality of optical fiber tapes 12. The plurality of optical fiber tapes 12 may be bundled by, for example, one or three or more strips 20. In the optical fiber unit 11 illustrated in FIG. 2, the plurality of optical fiber tapes 12 are bundled by two strips 20. The plurality of optical fiber tapes 12 are not limited to being bundled by winding the strip 20, and may be bundled, for example, by being inserted into a flexible tube or by winding a flexible film.

[0022] The two strips 20 may be wound around the bundle of the optical fiber tapes 12, for example, in a spiral shape. In the present embodiment, the two strips 20 are each wound around the bundle of the optical fiber tapes 12 in an SZ shape. That is, the winding direction of each strip 20 is reversed so as to be wound around half of the outer periphery of the bundle of the optical fiber tapes 12. Then, the two strips 20 are joined to each other at the position where the winding direction is reversed. Reference numeral 21 in FIG. 2 indicates the joining portion of the two strips 20. The joining of the two strips 20 may be performed, for example, by heat welding or adhesion. The strip 20 is attached so as to follow the outer shape of the bundle of the optical fiber tapes 12. Therefore, the outer shape of the bundle of the optical fiber tapes 12 can be maintained. As a result, the plurality of optical fiber tapes 12 can be held even in a state where the laminated state is disrupted (described later).

[0023] As shown in Fig. 4, the optical fiber unit 11 is configured by bundling a plurality of optical fiber tapes 12 with a strip body 20 in a stacked state. In the optical fiber unit 11 of the present embodiment, in a cross section orthogonal to the longitudinal direction of the optical fiber assembly 2, the stacked state of the plurality of bundled optical fiber tapes 12 is collapsed. "The stacked state of the plurality of optical fiber tapes 12 is collapsed" means a state different from a state in which the plurality of optical fiber tapes 12 are stacked with their tape surfaces flat without being bent in their width directions, and means a state in which the tape surface of at least one optical fiber tape 12 constituting the optical fiber unit 11 is curved in the width direction. Further, the state in which the tape surface of the optical fiber tape 12 is curved means that in a cross section orthogonal to the longitudinal direction of the optical fiber tape 12, the midpoints of the optical fibers 13 at both ends in the width direction of the optical fiber tape 12 and the center of gravity (i.e., the geometric center) of the optical fiber tape 12 are displaced. In the optical fiber unit 11 illustrated in Fig. 4, the plurality of optical fiber tapes 12 with the collapsed stacked state are all curved or meandering in the width direction.

[0024] In the present embodiment, the plurality of optical fiber tapes 12 constituting the same optical fiber unit 11 are bundled with the strip body 20, so that the stacked state of these plurality of optical fiber tapes 12 is collapsed. The outer shape of the optical fiber unit 11 shown in Fig. 4 is not neat with the collapse of the stacked state of the plurality of optical fiber tapes 12, different from the outer shape of the optical fiber unit 11 illustrated in Fig. 1. The state in which the stacked state of the plurality of optical fiber tapes 12 is collapsed may be established at an arbitrary position (or all positions) in the longitudinal direction of the optical fiber unit 11 (optical fiber assembly 2), but it is sufficient that it is established at at least a certain position in the longitudinal direction of the optical fiber unit 11 (optical fiber assembly 2).

[0025] In FIGS. 5 and 6, the region where the optical fiber unit 11 in a stacked state has collapsed is schematically shown in an elliptical shape. The direction of the major axis of each ellipse generally corresponds to the width direction of the optical fiber tape 12. The direction of the minor axis of each ellipse generally corresponds to the stacking direction of the plurality of optical fiber tapes 12.

[0026] As shown in FIGS. 5 and 6, in the optical fiber assembly 2, the plurality of optical fiber units 11 are stacked in layers in the radial direction of the optical fiber assembly 2 (in FIGS. 5 and 6, the direction orthogonal to the center line passing through the center (geometric center) of the optical fiber assembly 2), thereby constituting a plurality of fiber unit layers 10 arranged in the radial direction of the optical fiber assembly 2. The number of fiber unit layers 10 in FIGS. 5 and 6 is, for example, three. Among the three fiber unit layers 10, the two fiber unit layers 10 located on the inner side in the radial direction of the optical fiber assembly 2 are the inner layers 10A (10A-1, 10A-2), and the one fiber unit layer 10 located on the outer side in the radial direction is the outer layer 10B (or the outermost peripheral layer 10B). The two inner layers 10A include the first inner layer 10A-1 and the second inner layer 10A-2 located on the outer side in the radial direction with respect to the first inner layer 10A-1.

[0027] The plurality of optical fiber units 11 included in the inner layer 10A are a plurality of inner layer fiber units 11A located on the inner side in the radial direction of the optical fiber assembly 2. The plurality of inner layer fiber units 11A are located, for example, including the center of the optical fiber assembly 2 or near the center. Also, the plurality of optical fiber units 11 included in the outer layer 10B are outer layer fiber units 11B located on the outer side in the radial direction of the optical fiber assembly 2 than the inner layer fiber units 11A. In the present embodiment, the outer layer fiber units 11B are included in the fiber unit layer 10 (outer layer 10B) located on the outermost periphery.

[0028] Next, the arrangement (orientation) of the inner layer fiber units 11A and the outer layer fiber units 11B in the cross section of the optical fiber assembly 2 orthogonal to the longitudinal direction will be described. First, with reference to FIG. 7, an index indicating the orientation of each optical fiber unit 11 will be described in the cross section of the optical fiber assembly 2. As shown in FIG. 7, in the cross section of the optical fiber assembly 2 orthogonal to the longitudinal direction, a straight line connecting the center C of the optical fiber assembly 2 and the center of gravity G of a predetermined optical fiber tape 12 among the predetermined optical fiber units 11 is defined as the radial straight line R1. Also, a straight line connecting both ends of the predetermined optical fiber tape 12 of the predetermined optical fiber unit 11 (optical fibers 13 located at both ends in the width direction of the optical fiber tape 12) is defined as the tape width direction straight line W1.

[0029] Then, in the cross section orthogonal to the longitudinal direction, the orientation of the predetermined optical fiber tape 12 included in the predetermined optical fiber unit 11 is indicated by the sine value sinα (0° ≦ α ≦ 180°) of the angle α formed by these radial straight line R1 and tape width direction straight line W1. When the sine value sinα indicating the orientation of the optical fiber tape 12 is large (close to 1), the optical fiber tape 12 is arranged such that its width direction (or tape surface) is along the circumferential direction of the optical fiber assembly 2 (the direction around the center of the optical fiber assembly 2 in FIGS. 5 and 6). On the other hand, when the sine value sinα indicating the orientation of the optical fiber tape 12 is small (close to 0), the optical fiber tape 12 is arranged such that its width direction (or tape surface) is along the radial direction of the optical fiber assembly 2.

[0030] In the cross section orthogonal to the longitudinal direction, the orientation of the optical fiber unit 11 is represented by the average value of the sine values sinα of the plurality of optical fiber tapes 12 in the same optical fiber unit 11 (average sine value sinα ave ). That is, the average sine value sinα ave represents the average of the directions in which the plurality of optical fiber tapes 12 constituting the same optical fiber unit 11 are oriented. A large average sine value sinα ave (close to 1) indicating the orientation of the optical fiber unit 11 means that the stacking direction of the plurality of optical fiber tapes 12 in the optical fiber unit 11 faces the radial direction of the optical fiber assembly 2 (or is close to the radial direction). On the other hand, the average sine value sinα aveThe fact that it is small (close to 0) means that the stacking direction of the plurality of optical fiber tapes 12 in the optical fiber unit 11 faces (or is close to) the circumferential direction of the optical fiber assembly 2.

[0031] In the optical fiber assembly 2 of the present embodiment, in a cross section orthogonal to the longitudinal direction thereof, the average sine value sinα in the outer layer fiber unit 11B shown in FIGS. 5 and 6 ave is 0.366 or more. The reason for this will be described later.

[0032] Also, in this specification, the average of the average sine values sinα in all the inner layer fiber units 11A ave is called the "inner index", and the average of the average sine values sinα in all the outer layer fiber units 11B ave is called the "outer index". The inner index is preferably smaller than the outer index.

[0033] The fact that the inner index is smaller than the outer index means that, as in the first arrangement example shown in FIG. 5, the width direction of the optical fiber tape 12 in the inner layer fiber unit 11A has a tendency to be at a larger angle with respect to the circumferential direction of the optical fiber assembly 2 compared to the width direction of the optical fiber tape 12 in the outer layer fiber unit 11B. In other words, at least some of the plurality of inner layer fiber units 11A are arranged such that the width direction of the optical fiber tape 12 faces the radial direction of the optical fiber assembly 2 compared to the outer layer fiber unit 11B. Also, it can be said that the plurality of inner layer fiber units 11A are arranged such that the width direction of the optical fiber tape 12 faces various directions when viewed from the center of the optical fiber assembly 2 compared to the outer layer fiber unit 11B. Also, in the first arrangement example shown in FIG. 5, regarding the thickness of the fiber unit 11 in the radial direction of the fiber assembly 2, the thickness of the outer layer fiber unit 11B located at the outermost periphery is the thinnest among all the fiber units 11 constituting the fiber assembly 2.

[0034] In the second arrangement example shown in Fig. 6, with respect to the circumferential direction of the optical fiber assembly 2, the angle in the width direction of the optical fiber tape 12 that constitutes the inner layer fiber unit 11A is approximately the same as the angle in the width direction of the optical fiber tape 12 that constitutes the outer layer fiber unit 11B. That is, in the second arrangement example shown in Fig. 6, the average sine value sinα ave in the inner layer fiber unit 11A ave is approximately the same as the average sine value sinα

[0035] in the outer layer fiber unit 11B. In other words, there is no difference between the inner index and the outer index. ave Note that the above two conditions (the average sine value sinα in the outer layer fiber unit 11B is 0.366 or more, and the inner index is smaller than the outer index) do not necessarily have to hold at all positions in the longitudinal direction of the optical fiber assembly 2, and it is sufficient if they hold at at least some position in the longitudinal direction. The above two conditions may hold, for example, in a certain cross-section (a certain cross-section) of the optical fiber assembly 2 perpendicular to the longitudinal direction at a certain position within the range of each twist pitch (one pitch) in the longitudinal direction. That is, in a cross-section different from the above-mentioned certain cross-section within the range of the twist pitch, the above two conditions do not necessarily have to hold. Note that the above two conditions may hold, for example, throughout the entire longitudinal direction of the optical fiber assembly 2.

[0036] The above-mentioned twist pitch (one pitch) is the longitudinal length for one turn in the circumferential direction of the helically arranged optical fiber units 11 when a plurality of optical fiber units 11 are twisted in one direction. Also, when a plurality of optical fiber units 11 are twisted in an SZ shape, the twist pitch (one pitch) is the longitudinal length (interval) from the position where the twist direction reverses to the position where it reverses in the same direction next. That is, the twist pitch (one pitch) is the length obtained by adding one section in the S direction and one section in the Z direction.

[0037] Next, an example of the manufacturing method of the optical cable 1 of the present embodiment will be described. When manufacturing the optical cable 1 of the present embodiment, first, as illustrated in FIG. 4, a plurality of optical fiber units 11 are prepared by bundling a plurality of optical fiber tapes 12 so that the stacked state of the plurality of optical fiber tapes 12 collapses. When preparing the optical fiber unit 11, in order to collapse the stacked state of the plurality of optical fiber tapes 12, for example, the stacked plurality of optical fiber tapes 12 may be deformed in the width direction by narrowing them in the width direction. Next, these plurality of optical fiber units 11 are bundled to perform an aggregate forming step of forming the optical fiber aggregate 2.

[0038] In the aggregate forming step, at least at a certain position in the longitudinal direction of the optical fiber aggregate 2, in a cross section (a certain cross section) orthogonal to the longitudinal direction, the average sine value sinα in the outer layer fiber unit 11B ave should be arranged so that it is 0.366 or more. In order to arrange the outer layer fiber unit 11B in this way, for example, the direction of the outer layer fiber unit 11B may be adjusted until the plurality of optical fiber units 11 reach the convergence point (the position of the optical fiber unit 11 when the formation of the optical fiber aggregate 2 is completed). Further, in the aggregate forming step, in at least a certain cross section of the optical fiber aggregate 2, for example, the inner layer fiber unit 11A and the outer layer fiber unit 11B may be arranged so that the inner index is smaller than the outer index.

[0039] Also, when the plurality of optical fiber units 11 are twisted in one direction or in an SZ shape in the aggregate forming step, in this step, in a certain cross section within the range of the twist pitch (one pitch), the average sine value sinα in the outer layer fiber unit 11B ave should be arranged so that it is 0.366 or more, and the inner layer fiber unit 11A and the outer layer fiber unit 11B may be arranged so that the inner index is smaller than the outer index.

[0040] The above-described aggregate forming process may be performed, for example, when accommodating a plurality of optical fiber units 11 inside the jacket 3 (see FIG. 1), or may be performed, for example, before accommodating the optical fiber aggregate 2 inside the jacket 3. By accommodating the optical fiber aggregate 2 (a plurality of bundled optical fiber units 11) inside the jacket 3, the production of the optical cable 1 is completed.

[0041] As described above, in the optical fiber aggregate 2 of the present embodiment and the optical cable 1 including the same, the average sine value sinα in the outer layer fiber unit 11B ave is 0.366 or more. Thereby, an increase in the transmission loss of the optical fiber 13 in the outer layer fiber unit 11B can be suppressed. Hereinafter, this point will be described with reference to the experimental examples shown in FIGS. 8 and 9.

[0042] The table of the experimental example shown in FIG. 8 shows the relationship between the average sine value sinα ave of 12 optical fiber units 11 and the increase amount of the transmission loss of the optical fiber 13. The "unit number" in FIG. 8 corresponds to each of the 12 optical fiber units 11. In the experimental example shown in FIG. 8, the 1st to 3rd optical fiber units 11 are inner layer fiber units 11A, and the 4th to 12th optical fiber units 11 are outer layer fiber units 11B. Also, the "tape number" in FIG. 8 corresponds to each of the 6 optical fiber tapes 12 included in each optical fiber unit 11.

[0043] Further, in the table shown in FIG. 8, the sine values sinα of all (72) optical fiber tapes 12 constituting the optical fiber aggregate 2 are shown in association with the optical fiber units 11. For example, in the table of FIG. 8, the sine value sinα of the 1st optical fiber tape 12 among the 1st optical fiber unit 11 is 0.80. The sine value sinα of each optical fiber tape 12 is based on the angle α (see FIG. 7) of each optical fiber tape 12 measured at any 5 cross-sections within the twist pitch in the longitudinal direction of the optical fiber aggregate 2.

[0044] "Average sinα" in Fig. 8 is the average value of the sine values sinα of the six optical fiber tapes 12 that make up the same optical fiber unit 11 (i.e., the average sine value sinα ave ). "Increase in loss" in Fig. 8 indicates the maximum transmission loss increase of the optical fiber 13 measured by the following measurement method (hereinafter simply referred to as the "increase in loss"). In the measurement method for measuring the loss increase of the transmission of the optical fiber 13, first, a mandrel with a diameter 20 times that of the optical cable 1 is prepared. Next, with the state where the optical cable 1 is placed linearly as the reference bending angle (0°), the optical cable 1 is pressed against the outer circumference of the mandrel and bent by 90° (+90°), and then the optical cable 1 is pressed against the outer circumference of the mandrel in the direction opposite to the bent direction and bent by 90° (-90°) in a bending process. The transmission loss increase of the optical fiber 13 of the optical cable 1 at the three bending angles 0°, +90°, and -90° when the bending process is repeated 25 times was measured with light of a wavelength of 1.55 μm (in accordance with GR-20-CORE Issue4, 6.5.8).

[0045] The graph shown in Fig. 9 is a graph showing the relationship between the average sine value sinα of the optical fiber unit 11 and the increase in the transmission loss of the optical fiber 13 in the experimental example shown in Fig. 8. ave In the graph of Fig. 9, plot points of three inner layer fiber units 11A (the first to third optical fiber units 11 in the table of Fig. 8) and an approximate straight line based on these three plot points are described. Also, plot points of nine outer layer fiber units 11B (the fourth to twelfth optical fiber units 11 in the table of Fig. 8) and an approximate straight line based on these nine plot points are described.

[0046] In the graph of Fig. 9, focusing on the approximate straight lines of the inner layer fiber unit 11A and the outer layer fiber unit 11B, both the inner layer fiber unit 11A and the outer layer fiber unit 11B have an average sine value sinα aveAs it becomes smaller (that is, as the angle in the width direction of the optical fiber tape 12 with respect to the radial direction of the optical fiber assembly 2 becomes smaller), it can be seen that the amount of increase in transmission loss tends to increase. Hereinafter, this tendency will be described.

[0047] For example, when the width direction of the optical fiber tape 12 constituting the optical fiber unit 11 is arranged along the radial direction of the optical cable 1 (that is, when the average sine value sinα ave is small). In such a configuration, for example, when the optical cable 1 (optical fiber assembly 2) is bent, a large stress (bending stress) associated with a large stretching and shrinking strain acts on the optical fiber 13 that is located farthest from the neutral line of the bending of the optical cable 1 (the axis where no compression or elongation occurs when the optical cable 1 is bent) among the above-mentioned optical fiber tapes 12, compared with the other optical fibers 13 of the optical fiber tape 12. Therefore, in the optical fiber unit 11 where the average sine value sinα ave is small, the amount of increase in the transmission loss of the optical fiber 13 becomes large.

[0048] On the other hand, consider the case where the width direction of the optical fiber tape 12 constituting the optical fiber unit 11 is arranged along the circumferential direction of the optical fiber assembly 2 (that is, when the average sine value sinα ave is large). When the optical cable 1 is bent in such a configuration, the difference in the stretching and shrinking strain generated in the plurality of optical fibers 13 of the same optical fiber tape 12 is small. Therefore, the bending stress acting on these optical fibers 13 also becomes small. As a result, in the optical fiber unit 11 where the average sine value sinα ave is large, the amount of increase in the transmission loss of the optical fiber 13 becomes small.

[0049] Also, in the graph of FIG. 9, when comparing the approximate straight lines of the inner layer fiber unit 11A and the outer layer fiber unit 11B, the average sine value sinα aveAs the [[ID=]], the increasing amount of transmission loss tends to be larger for the outer fiber unit 11B than for the inner fiber unit 11A. This indicates that the bending stress acting on the optical fiber 13 when the optical cable 1 is bent becomes larger as the optical fiber unit 11 is located farther from the neutral line of the bending of the optical cable 1. From the graph of Fig. 9, in the outer fiber unit 11B, by increasing the average sine value sinα ave it can be seen that an increase in the transmission loss of the optical fiber 13 in the outer fiber unit 11B can be suppressed.

[0050] The approximate straight line of the outer fiber unit 11B in the graph of Fig. 9 is expressed by the following formula with the average sine value sinα ave as X and the loss increase amount as Y. Y = -0.228X + 0.233 In the optical cable 1, it is desirable to suppress the loss increase amount of the optical fiber 13 to 0.15 dB / km or less. Therefore, in the outer fiber unit 11B, based on the above formula, by setting the average sine value sinα ave to 0.366 or less, the loss increase amount of the optical fiber 13 can be suppressed to 0.15 dB / km or less. That is, an increase in the transmission loss of the optical fiber 13 in the outer fiber unit 11B can be suppressed.

[0051] In the optical fiber assembly 2 and the optical cable 1 of the present embodiment, the inner index is smaller than the outer index. Specifically, in the experimental examples shown in Figs. 8 and 9, the average of the average sine value sinα ave in the three inner fiber units 11A (the 1st to 3rd optical fiber units 11) is 0.66, and the average of the average sine value sinα ave in the nine outer fiber units 11B (the 4th to 12th optical fiber units 11) is 0.79.

[0052] As a result, the inner fiber unit 11A can be arranged in a direction different from that of the outer fiber unit 11B. Specifically, as in the first arrangement example shown in FIG. 5, the inner fiber unit 11A can be arranged such that the width direction of the optical fiber tape 12 constituting the inner fiber unit 11A approaches the radial direction of the optical fiber assembly 2 more than the width direction of the optical fiber tape 12 constituting the outer fiber unit 11B. Thereby, as in the second arrangement example shown in FIG. 6, compared with the case where the inner fiber unit 11A is arranged such that the width direction of the optical fiber tape 12 constituting the inner fiber unit 11A faces the circumferential direction in the same manner as the outer fiber unit 11B, it becomes easier to arrange the plurality of optical fiber units 11 without gaps in the internal space of the optical fiber assembly 2. Therefore, it is possible to improve the utilization efficiency of the internal space of the optical fiber assembly 2 in which the plurality of optical fiber units 11 are arranged.

[0053] In the graph of FIG. 9, referring to the approximate straight line of the inner fiber unit 11A, in the inner fiber unit 11A, even when the average sine value sinα ave becomes small, the increase in the transmission loss increase amount is suppressed to a small extent. This is because the inner fiber unit 11A is located at or near the center of the optical fiber assembly 2, resulting in the stretching and shrinking distortion generated in the optical fiber 13 of the inner fiber unit 11A being suppressed to a small extent in response to the bending of the optical cable 1. Therefore, by arranging the inner fiber unit 11A such that the average sine value sinα ave of the inner fiber unit 11A becomes small, while suppressing the increase in the transmission loss of the optical fiber 13 in the inner fiber unit 11A, it is possible to improve the utilization efficiency of the internal space of the optical fiber assembly in which the plurality of optical fiber units are arranged.

[0054] In the optical fiber assembly 2 and the optical cable 1 of the present embodiment, since the stacked state of the plurality of optical fiber tapes 12 in the optical fiber unit 11 is disrupted, the cross-sectional shape of the optical fiber unit 11 can be made different among the plurality of optical fiber units 11. As a result, it becomes easier to arrange the plurality of optical fiber units 11 without gaps in the internal space of the optical fiber assembly 2. Therefore, it is possible to improve the utilization efficiency of the internal space of the optical fiber assembly 2 in which the plurality of optical fiber units 11 are arranged.

[0055] In the optical fiber assembly 2 and the optical cable 1 of the present embodiment, the optical fiber tape 12 constituting the optical fiber unit 11 meanders in its width direction. In this case, the degree of freedom of relative movement of the plurality of optical fibers 13 constituting the same optical fiber tape 12 is greater than when the optical fiber tape 12 does not meander in the width direction. For this reason, when the optical fiber assembly 2 is bent or the like, the adjacent optical fibers 13 in the same optical fiber tape 12 can move so as to relieve the bending stress acting on the optical fiber unit 11. Therefore, an increase in the transmission loss of the optical fiber 13 can be suppressed.

[0056] In the optical fiber assembly 2 and the optical cable 1 of the present embodiment, the optical fiber unit 11 is configured by bundling a plurality of optical fiber tapes 12 in a stacked state with a strip body 20. For this reason, compared with the case where the plurality of optical fiber tapes 12 are bundled with a tube, it is possible to suppress or prevent the entire circumference of the optical fiber unit 11 (the plurality of optical fiber tapes 12) from being covered. For this reason, compared with the case where the optical fiber tape 12 is bundled with a tube, when the optical fiber assembly 2 is bent or the like, the plurality of bundled optical fiber tapes 12 and the optical fibers 13 constituting the same can move freely. As a result, when the optical fiber assembly 2 is bent or the like, the optical fiber tapes 12 and the optical fibers 13 constituting the same optical fiber unit 11 can move relative to each other so as to relieve the bending stress acting on the optical fiber unit 11. Therefore, an increase in the transmission loss of the optical fiber 13 can be suppressed.

[0057] As described above in detail, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

[0058] In the present invention, the outer layer fiber unit 11B is not limited to being included only in the outermost fiber unit layer 10 (the outermost layer 10B in FIGS. 5 and 6), and may be included, for example, in the outermost layer and one or more layers adjacent to the inside in the radial direction of the outermost layer. The fiber unit layer 10 including the outer layer fiber unit 11B may include, for example, the second inner layer 10A-2 in addition to the outer layer 10B in FIGS. 5 and 6. Further, although the inner layer 10A is composed of two layers in the above embodiment, it may be, for example, one layer or three or more layers.

[0059] The present invention is not limited to being applied to a slottedless type optical cable, and may be applied to, for example, a slotted type optical cable having a slotted rod. In that case, an optical fiber assembly may be accommodated in each slot. Even when the optical fiber unit is divided into an inner layer and an outer layer in each slot, the same effect can be obtained by applying the relationship between the inner layer fiber unit and the outer layer fiber unit in the above embodiment.

Explanation of Reference Numerals

[0060] 1... optical cable, 2... optical fiber assembly, 3... outer sheath, 10... fiber unit layer, 11... optical fiber unit, 11A... inner layer fiber unit, 11B... outer layer fiber unit, 12... optical fiber tape, C... center of the optical fiber assembly 2, G... center of gravity of the optical fiber tape 12, R1... radial straight line, W1... tape width direction straight line, α... angle

Claims

1. An optical fiber aggregate for an optical cable, which is configured by bundling a plurality of bundles of an optical fiber unit formed by laminating a plurality of optical fiber tapes, In a cross section of the optical fiber aggregate perpendicular to the longitudinal direction at at least one position in the longitudinal direction of the optical fiber aggregate, the laminated state of the plurality of optical fiber tapes constituting the optical fiber unit is collapsed so that the tape surface of at least one of the optical fiber tapes is curved, In the plurality of optical fiber units, in a cross section of the optical cable perpendicular to the longitudinal direction, there are a plurality of inner layer fiber units located on the inner side in the radial direction perpendicular to the center line passing through the center of the optical cable, and a plurality of outer layer fiber units located on the outer side in the radial direction of the optical fiber aggregate with respect to the inner layer fiber units, Regarding the sine value sinα of the angle α formed by the straight line connecting the center of the optical cable and the centroid of the optical fiber tape, and the straight line in the tape width direction connecting both ends of the optical fiber tape, the average value of the sine values sinα of the plurality of optical fiber tapes in the same optical fiber unit is defined as the average sine value sinα ａｖｅ and At least at a certain position in the longitudinal direction of the optical fiber assembly, in the cross-section of the optical fiber assembly orthogonal to the longitudinal direction, the average sine value sinα in the outer layer fiber unit ａｖｅ An optical fiber assembly for an optical cable in which is 0.366 or more.

2. The plurality of optical fiber units are twisted in one direction or in an SZ shape, In any of the cross-sections within the range of each twist pitch, the average sine value sinα in the outer layer fiber unit ａｖｅ The optical fiber assembly for an optical cable according to claim 1, wherein the value is 0.366 or more.

3. Over the entire longitudinal direction of the optical fiber assembly, the average sine value sinα in the outer layer fiber unit ａｖｅ The optical fiber assembly for an optical cable according to claim 1, wherein is 0.366 or more.

4. At least at a certain position in the longitudinal direction of the optical fiber assembly, in the cross-section of the optical fiber assembly orthogonal to the longitudinal direction, the average sine value sinα in all of the inner layer fiber units ａｖｅ has an average that is smaller than the average of the average sine value sinα ａｖｅ in all of the outer layer fiber units. The optical fiber assembly for an optical cable according to claim 1.

5. The plurality of optical fiber units are twisted in one direction or in an SZ shape, In any of the cross-sections within the range of each twist pitch, the average of the average sine values sinα in the plurality of the inner layer fiber units ａｖｅ is smaller than the average of the average sine values sinα ａｖｅ in the plurality of the outer layer fiber units. The optical fiber aggregate for an optical cable according to claim 4

6. Over the entire longitudinal direction of the optical fiber assembly, the average value of the average sine value sinα in the plurality of the inner layer fiber units ａｖｅ is smaller than the average value of the average sine value sinα in the plurality of the outer layer fiber units ａｖｅ The optical fiber assembly for an optical cable according to claim 4, wherein the average is smaller than the average of the average sine value sinα in the plurality of the outer layer fiber units

7. The optical fiber aggregate for an optical cable according to claim 1, wherein the optical fiber unit is bundled by a strip.

8. The optical fiber aggregate for an optical cable according to claim 1, wherein the optical fiber unit having the thinnest thickness in the radial direction among all the optical fiber units is the outer layer fiber unit located on the outermost periphery.

9. The optical fiber aggregate for an optical cable according to claim 1, wherein the outer layer fiber unit is included in at least the layer located on the outermost periphery.

10. The optical fiber aggregate for an optical cable according to claim 1, wherein the optical fiber tape is an intermittently connected optical fiber tape.

11. An optical cable comprising the optical fiber aggregate for an optical cable according to any one of claims 1 to 10, and an outer sheath covering the optical fiber aggregate.

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