Slotless optical cable

Abstract

Optical fiber units constituting an optical fiber assembly and each formed by stacking a plurality of optical fiber ribbons include, in some cross section of the optical fiber assembly, a first fiber unit located on a neutral line and a second fiber unit located farthest from the neutral line. Regarding the sine value of an angle formed by a straight line in a radial direction connecting the center of the optical fiber assembly and the center of gravity of the optical fiber ribbon and a straight line in a ribbon width direction connecting both ends of the optical fiber ribbon, the average value of the sine values of the plurality of optical fiber ribbons of the same optical fiber unit is defined as an average sine value, and in the some cross section, the average sine value in the second fiber unit is larger than the average sine value in at least one first fiber unit.

Description

[Technical Field]

[0001] The present invention relates to an optical fiber assemblage and an optical cable. This application claims priority based on Japanese Patent Application No. 2021-212173, filed on December 27, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Patent document 1 discloses an optical fiber cable (optical cable) that has an optical fiber unit (tape core unit) made by stacking and bundling multiple optical fiber ribbons, and a cable core (optical fiber assembly) that aggregates multiple such optical fiber units. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2007-233252 Summary of the Invention [Problem to be solved by the invention]

[0004] If an optical cable having the above-described optical fiber assembly is manufactured carelessly, stress (mainly bending stress) will often be concentrated on the optical fibers of a specific optical fiber unit if the optical cable is bent or if the jacket of the optical cable shrinks in a low-temperature environment. When stress is concentrated on a specific optical fiber, there is a problem that the transmission loss of the optical fiber increases. In recent years, there has been a demand for optical fiber cables with a larger number of optical fibers. This has led to a demand for more optical fiber units to be placed in the limited internal space of the optical fiber assemblage. In other words, there is a demand for improving the utilization efficiency of the internal space of the optical fiber assemblage by the optical fiber units.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide an optical fiber assembly and an optical cable including the same that can suppress an increase in transmission loss of optical fibers and improve the utilization efficiency of the internal space in which multiple optical fiber units are arranged. [Means for solving the problem]

[0006] An optical fiber assemblage according to a first aspect of the present invention is an optical fiber assemblage configured by bundling a plurality of optical fiber units, each of which is formed by stacking a plurality of optical fiber ribbons, and the stacking state of the plurality of optical fiber ribbons in the optical fiber unit is disrupted so that a tape surface of at least one of the optical fiber ribbons constituting the optical fiber unit is curved at least at a certain position in the longitudinal direction of the optical fiber assemblage in a cross section of the optical fiber assemblage perpendicular to the longitudinal direction, and the plurality of optical fiber units include a first fiber unit located on a neutral line of bending of the optical fiber assemblage in a cross section of the optical fiber assemblage perpendicular to the longitudinal direction, and a second fiber unit located farthest from the neutral line, and with respect to a sine value sin α of an angle α formed by a radial line connecting the center of the optical fiber assemblage and the center of gravity of the optical fiber ribbon and a tape width direction line connecting both ends of the optical fiber ribbon, an average value of the sine values ​​sin α of the plurality of optical fiber ribbons in the same optical fiber unit is defined as an average sine value sin α ave and the average sine value sin α of the second fiber unit is ave is the average sine value sin α in at least one of the first fiber units. ave is greater than.

[0007] An optical cable according to a second aspect of the present invention comprises the optical fiber assemblage of the first aspect and an imparting member that imparts bending anisotropy to the optical cable, making it easier to bend in a direction centered on the neutral line. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress an increase in transmission loss of an optical fiber, and to improve the utilization efficiency of the internal space in which a plurality of optical fiber units are arranged. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional schematic diagram of an optical cable including an optical fiber assemblage according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view schematically showing an optical fiber unit included in the optical fiber assemblage of FIG. [Figure 3] FIG. 3 is a perspective view schematically showing an optical fiber ribbon included in the optical fiber unit of FIG. 2. [Figure 4] 3 is a diagram showing an example of a cross-sectional shape of the optical fiber unit of FIG. 2. FIG. [Figure 5] 1 is a cross-sectional view schematically showing an example of the arrangement of a plurality of optical fiber units in an optical fiber assemblage according to the present embodiment. [Figure 6] 10 is a cross-sectional view schematically showing a comparative example of the arrangement of a plurality of optical fiber units in an optical fiber assemblage. FIG. [Figure 7] 1 is a diagram showing the angle α formed by a radial line R1 connecting the center C of the optical fiber assemblage and the center of gravity G of the optical fiber ribbon, and a tape width direction line W1 connecting both ends of the optical fiber ribbon. [Figure 8] 6 is a table showing the relationship between the average sine value sinαave of a plurality of optical fiber units and the increase in transmission loss of the optical fiber in the embodiment of FIG. 5. [Figure 9] 7 is a table showing the relationship between the average sine value sinαave of a plurality of optical fiber units and the increase in transmission loss of the optical fiber in the comparative example of FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, one embodiment of the present invention will be described with reference to FIGS. As shown in Fig. 1, the optical fiber assemblage 2 of this embodiment constitutes a part of an optical cable 1. The optical cable 1 of this embodiment is a so-called slotless optical cable that does not have a slot rod formed with grooves (slots) for accommodating optical fibers. The optical cable 1 has the optical fiber assemblage 2 and an outer jacket 3.

[0011] The optical fiber assemblage 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 assemblage 2 of this embodiment constitutes the core of the optical cable 1. The core of the optical cable 1 of this embodiment further includes a holding and winding tape 5 that covers the multiple optical fiber units 11. The holding and winding tape 5 may be made of, for example, a water-absorbing tape. In this embodiment, the holding and winding tape 5 forms the internal space of the optical fiber assembly 2 in which the multiple optical fiber units 11 are arranged. For example, the above-mentioned holding and winding tape 5 may be omitted. In that case, the inner surface of the jacket 3 (described later) forms the internal space of the optical fiber assemblage 2.

[0012] The jacket 3 is formed in a cylindrical shape. The optical fiber assembly 2 is housed inside the jacket 3. The plurality of optical fiber units 11 may be housed inside the jacket 3, for example, in a state where they are twisted in one direction or in an SZ shape. In addition to the plurality of optical fiber units 11, an inclusion (not shown) may also be housed inside the jacket 3. The inclusion may be, for example, a water-absorbing material. The inclusion may be placed inside or outside the holding winding tape 5, or both. The above-mentioned inclusions may be omitted, for example.

[0013] The outer shape of the optical fiber assemblage 2 in a cross section perpendicular to the longitudinal direction of the optical cable 1 (a direction perpendicular to both the up-down direction and the left-right direction in FIG. 1, the extending direction of the optical cable 1) may be any shape, but in this embodiment it is approximately circular. In this specification, approximately circular includes not only a perfect circle but also an ellipse or an oval. Note that the outer shape of the optical fiber assemblage 2 in the above cross section may be, for example, rectangular.

[0014] The jacket 3 is a member that covers the optical fiber assemblage 2. The inner surface of the jacket 3 forms a space that houses the optical fiber assemblage 2. In this embodiment, the inner surface of the jacket 3 has a substantially circular shape corresponding to the optical fiber assemblage 2 in a cross section perpendicular to the longitudinal direction of the optical cable 1. The cross-sectional shape of the inner surface of the jacket 3 may be, for example, rectangular. In this embodiment, a holding winding tape 5 that wraps a plurality of optical fiber units 11 is housed inside the jacket 3. A tension member 7 is disposed in the outer sheath 3. The entire tension member 7 may be disposed within the outer sheath 3, or a portion of the tension member 7 may be disposed within the outer sheath 3, with the other portion of the tension member 7 exposed from the outer sheath 3. Other members, such as a rip cord, may also be disposed in the outer sheath 3.

[0015] A plurality of tension members 7 are arranged to sandwich the optical fiber assemblage 2 in a cross section perpendicular to the longitudinal direction of the optical cable 1. In the cross section, the plurality of tension members 7 are arranged to face each other across the optical fiber assemblage 2 in a first direction perpendicular to the longitudinal direction. In this embodiment, in the cross section, other tension members are not arranged to face each other across the optical fiber assemblage 2 in a second direction perpendicular to both the longitudinal direction and the first direction. However, this is not limited thereto, and other tension members may be arranged to face each other across the optical fiber assemblage 2 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 assemblage 2, or may be arranged spirally around the optical fiber assemblage 2. Furthermore, each tension member 7 may be included inside the optical fiber assemblage 2, for example. In FIG. 1, two tension members 7 are arranged as a set, and the pair is arranged on each side of the optical fiber assemblage 2, but this is not limited to this. For example, three or more tension members 7 may be arranged as a set, and the pair may be arranged on each side of the optical fiber assemblage 2. Also, one tension member 7 may be arranged on each side of the optical fiber assemblage 2. Also, in FIG. 1, the multiple tension members 7 that make up a set are spaced apart, but they may be in contact, for example. Also, the multiple tension members 7 that make up a set may be twisted. Note that the area where one tension member 7 or a set of multiple tension members 7 is arranged may be referred to as a tension member arrangement area.

[0016] In Figure 1, the line indicated by the symbol NL indicates the neutral line NL of bending of the optical cable 1 (optical fiber assembly 2) that connects the centers of a pair of tension members 7 (or tension member placement areas). The neutral line NL indicates the position of the optical cable 1 where the expansion and contraction of the optical cable 1 in the longitudinal direction is small when the optical cable 1 is bent. For example, in Figure 1, when the optical cable 1 is bent so that the optical cable 1 is convex above the neutral line NL, the portion of the optical cable 1 located above the neutral line NL extends in the longitudinal direction of the optical cable 1, and the portion of the optical cable 1 located below the neutral line NL contracts in the longitudinal direction of the optical cable 1. By positioning the tension member 7 (or tension member placement area) on the neutral line NL, the optical cable 1 is easily bent in a direction centered on the neutral line NL and is difficult to bend in other directions. In other words, the tension member 7 functions as a member that imparts bending anisotropy to the optical cable, making it easier to bend in a direction centered on the neutral line NL.

[0017] In the present embodiment, bending anisotropy is imparted to the optical cable 1 by the arrangement of the tension members 7, but this is not limited thereto. For example, when the cross-sectional shape of the optical cable 1 (e.g., the cross-sectional shape of the outer shape of the jacket 3) is elliptical or rectangular, the neutral line NL of bending in the cross section of the optical cable 1 passes through the center of the minor axis of the ellipse or rectangle and is parallel to the major axis of the ellipse or rectangle. Even if the cross-sectional shape of the optical cable 1 is circular, bending anisotropy will occur in the optical cable 1 if the space (accommodation space) in the jacket 3 that accommodates the optical fiber assembly 2 is offset from the center of the optical cable 1 or if the accommodation space has anisotropy. The neutral line NL of bending can be estimated by calculation from the spatial arrangement and elastic modulus (Young's modulus) of each component in the cross section of the optical cable 1. When the cross-sectional shape of the optical cable 1 that imparts bending anisotropy to the optical cable 1 is determined by the jacket 3, the jacket 3 functions as an imparting component that imparts bending anisotropy to the optical cable, making it easier to bend in a direction centered on the neutral line NL.

[0018] 2, the optical fiber unit 11 of this embodiment has a structure in which a plurality of optical fibers 13 are bundled by a filament 20 (bundle material). The filament 20 is wound around the outer periphery of the plurality of optical fibers 13 to prevent the plurality of optical fibers 13 from separating from one another. Note that the optical fiber unit 11 may have a structure in which the plurality of optical fibers 13 are bundled by twisting them together, without using the filament 20, for example. The optical fiber unit 11 of this embodiment is configured by bundling a plurality of optical fiber ribbons 12, each having a plurality of optical fibers 13. Note that the optical fiber unit 11 may contain a mixture of optical fiber ribbons 12 and optical fibers 13 that are not tapered. 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 colored 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 (i.e., 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, for example, 60 μm, 80 μm, 100 μm, etc. The diameter of the coating layer can also be changed and may be 200 μm or less, for example, 160 μm, 180 μm, 200 μm, etc.

[0019] 3, the optical fiber ribbon 12 is configured by arranging a plurality of optical fibers 13 in parallel and connecting adjacent optical fibers 13. In the following description, in the optical fiber ribbon 12, the direction in which the optical fibers 13 extend is sometimes referred to as the longitudinal direction of the optical fiber ribbon 12, and the arrangement direction of the plurality of optical fibers 13 is sometimes referred to as the width direction of the optical fiber ribbon 12. Furthermore, the direction perpendicular to the longitudinal and width directions of the optical fiber ribbon 12 is sometimes referred to as the thickness direction of the optical fiber ribbon 12, and the surface facing the thickness direction is sometimes referred to as the tape surface.

[0020] The optical fiber ribbon 12 of this embodiment is an intermittently connected optical fiber ribbon in which a plurality of (12 in FIG. 3 ) 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 ribbon 12 between the two adjacent optical fibers 13. The connecting portion 14A connecting a predetermined optical fiber 13 to the optical fiber 13 adjacent to that optical fiber 13 on one side thereof and the connecting portion 14A connecting the predetermined optical fiber 13 to the optical fiber 13 adjacent to that optical fiber 13 on the other side thereof are positioned with a shift in the longitudinal direction. That is, the plurality of connecting portions 14A are two-dimensionally arranged intermittently in the longitudinal and width directions of the optical fiber ribbon 12. The region of the two adjacent optical fibers 13 that is not connected by the connecting portion 14A is a non-connecting portion 14B. In the non-connecting portion 14B, the two adjacent optical fibers 13 are not constrained from each other.

[0021] The intermittently connected optical fiber ribbon 12 is not limited to the example shown in FIG. 3. For example, the arrangement pattern of the intermittently arranged connecting portions 14A does not have to be a fixed pattern. Furthermore, the intermittently connected optical fiber ribbon 12 may, for example, have a plurality of (e.g., two) optical fibers 13 as a group, the plurality of groups are arranged in parallel, and the optical fibers 13 of adjacent groups are intermittently connected by the connecting portions 14A. Furthermore, adjacent optical fibers 13 in the optical fiber ribbon 12 may be spaced apart or may be in contact with each other. Furthermore, the number of optical fibers 13 in the optical fiber ribbon 12 is generally a multiple of four (4 cores, 8 cores, 12 cores, or 16 cores), but is not limited to this. The number of optical fibers 13 in the optical fiber ribbon 12 may be, for example, an odd number.

[0022] The optical fiber ribbon 12 is flexibly deformable in its width direction. For example, the optical fiber ribbon 12 is deformable so that one of its tape surfaces is curved to be convex. Also, for example, the optical fiber ribbon 12 is deformable so that its tape surface becomes uneven in the width direction (so that it meanders in the width direction). In particular, the intermittently connected optical fiber ribbon 12 has remarkable flexibility in the width direction, so that the characteristics of the optical fibers 13 are unlikely to deteriorate even when they are packaged at high density.

[0023] As shown in FIG. 2, the filament 20 bundling the plurality of optical fiber ribbons 12 (optical fibers 13) is a flexible thread-, string-, or tape-like member. The filament 20 is wound around the outer periphery of the bundle of the plurality of optical fiber ribbons 12. The plurality of optical fiber ribbons 12 may be bundled by, for example, one filament 20 or three or more filaments 20. In the optical fiber unit 11 illustrated in FIG. 2, the plurality of optical fiber ribbons 12 are bundled by two filaments 20. The plurality of optical fiber ribbons 12 may not be bundled by wrapping the filaments 20 around them, but may also be bundled by, for example, inserting them into a flexible tube or wrapping a flexible film around them.

[0024] The two filaments 20 may be wound around the bundle of optical fiber ribbons 12 in, for example, a spiral shape. In this embodiment, the two filaments 20 are wound around the bundle of optical fiber ribbons 12 in an SZ shape. That is, the winding direction of each filament 20 is reversed so that each filament 20 is wound around half of the outer circumference of the bundle of optical fiber ribbons 12. The two filaments 20 are joined to each other at the position where the winding directions are reversed. Reference numeral 21 in FIG. 2 indicates the joint portion of the two filaments 20. The two filaments 20 may be joined by, for example, heat welding or adhesive bonding. The filament 20 is attached so as to follow the outer shape of the bundle of optical fiber ribbons 12. This makes it possible to maintain the outer shape of the bundle of optical fiber ribbons 12. As a result, it is possible to hold a plurality of optical fiber ribbons 12 even when the stacked state is broken (described later).

[0025] As shown in Fig. 4, the optical fiber unit 11 is configured by bundling a plurality of optical fiber tapes 12 in a stacked state using a filament 20. In the optical fiber unit 11 of this embodiment, the stacked state of the bundled plurality of optical fiber tapes 12 is disrupted in a cross section perpendicular to the longitudinal direction of the optical fiber assemblage 2. "The stacked state of the plurality of optical fiber tapes 12 is disrupted" means a state different from a state in which the plurality of optical fiber tapes 12 are stacked without being bent in the width direction and with their tape surfaces flat, and refers to a state in which the tape surface of at least one of the optical fiber tapes 12 constituting the optical fiber unit 11 is curved in the width direction. Furthermore, the state in which the tape surface of the optical fiber tape 12 is curved means that, in a cross section perpendicular 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 are misaligned from the center of gravity (i.e., geometric center) of the optical fiber tape 12. In the optical fiber unit 11 illustrated in FIG. 4, the plurality of optical fiber ribbons 12, whose stacking state has been disrupted, are all curved or meandering in the width direction.

[0026] In this embodiment, the plurality of optical fiber ribbons 12 constituting the same optical fiber unit 11 are bundled by the filament 20, causing the stacked state of the plurality of optical fiber ribbons 12 to become disorganized. The external shape of the optical fiber unit 11 shown in Fig. 4 is different from the external shape of the optical fiber unit 11 exemplified in Fig. 1, and is not regular due to the disorganization of the stacked state of the plurality of optical fiber ribbons 12. The collapsed stacked state of multiple optical fiber tapes 12 may occur, for example, at any position (or all positions) in the longitudinal direction of the optical fiber unit 11 (optical fiber assembly 2), but it is sufficient that this state occurs at at least a certain position in the longitudinal direction of the optical fiber unit 11 (optical fiber assembly 2).

[0027] 5 and 6, the area where the optical fiber units 11 with a collapsed stacking state exist is schematically shown by an oval. The direction of the long axis of each oval roughly corresponds to the width direction of the optical fiber ribbon 12. The direction of the short axis of each oval roughly corresponds to the stacking direction of the multiple optical fiber ribbons 12.

[0028] As shown in Figures 5 and 6, in the optical fiber assemblage 2, a plurality of optical fiber units 11 (11-1 to 11-12) are layered in the radial direction of the optical fiber assemblage 2 (in Figures 5 and 6, a direction perpendicular to the center line passing through the center (geometric center) of the optical fiber assemblage 2), thereby constituting a plurality of fiber unit layers 10 arranged in the radial direction of the optical fiber assemblage 2. The number of fiber unit layers 10 in Figures 5 and 6 is, for example, two. In the following description, of the two fiber unit layers 10, the fiber unit layer 10 located radially inside the optical fiber assemblage 2 is the inner layer 10A, and the fiber unit layer 10 located radially outside is the outer layer 10B (or the outermost layer 10B). 5 and 6, the number of optical fiber units 11 (inner layer fiber units) located in the inner layer 10A is three, and the number of optical fiber units 11 (outer layer fiber units) located in the outer layer 10B is nine.

[0029] The plurality of optical fiber units 11 include a first fiber unit 11A and a second fiber unit 11B. The first fiber unit 11A is an optical fiber unit 11 located on the neutral line NL of bending of the optical fiber assemblage 2 (optical cable 1) in a cross section perpendicular to the longitudinal direction. The first fiber unit 11A being located on the neutral line NL means that at least one optical fiber ribbon 12 of the first fiber unit 11A is located on the neutral line NL of bending of the optical fiber assemblage 2.

[0030] The second fiber unit 11B is the optical fiber unit 11 located farthest from the neutral line NL in a cross section perpendicular to the longitudinal direction. The second fiber unit 11B has the optical fiber ribbon 12 located farthest from the neutral line NL among the multiple optical fiber units 11. At least one second fiber unit 11B exists on each side of the neutral line NL in a cross section perpendicular to the longitudinal direction. That is, the second fiber unit 11B is the optical fiber unit 11 located farthest from the neutral line NL in each of two regions obtained by dividing the cross section perpendicular to the longitudinal direction by the neutral line NL. The number of second fiber units 11B is not limited to two and may be, for example, three or more. In this embodiment, the second fiber unit 11B is located on or near the orthogonal line OL that passes through the center of the optical fiber assemblage 2 and is perpendicular to the neutral line NL in a circular cross section of the optical fiber assemblage 2 perpendicular to the longitudinal direction, and is included in the outer layer 10B described above.

[0031] Next, the arrangement (orientation) of the first fiber unit 11A and the second fiber unit 11B in the cross section of the optical fiber assemblage 2 perpendicular to the longitudinal direction will be described. First, the indicators indicating the orientation of each optical fiber unit 11 in the cross section of the optical fiber assemblage 2 will be described with reference to Fig. 7. As shown in Fig. 7, in the cross section of the optical fiber assemblage 2 perpendicular to the longitudinal direction, a radial line R1 is defined as a line connecting the center C of the optical fiber assemblage 2 and the center of gravity G of a predetermined optical fiber tape 12 in a predetermined optical fiber unit 11. Furthermore, a tape width line W1 is defined as a line connecting both ends of a predetermined optical fiber tape 12 in a predetermined optical fiber unit 11 (opticals 13 located at both ends in the width direction of the optical fiber tape 12).

[0032] In a cross section perpendicular to the longitudinal direction, the orientation of a predetermined optical fiber ribbon 12 included in a predetermined optical fiber unit 11 is represented by the sine value sin α of the angle α formed by the radial line R1 and the ribbon width direction line W1. When the sine value sin α indicating the orientation of the optical fiber ribbon 12 is large (close to 1), the optical fiber ribbon 12 is arranged so that its width direction (or ribbon surface) is along the circumferential direction of the optical fiber assemblage 2 (coat 3) (the direction around the center of the optical fiber assemblage 2 in FIGS. 5 and 6). On the other hand, when the sine value sin α indicating the orientation of the optical fiber ribbon 12 is small (close to 0), the optical fiber ribbon 12 is arranged so that its width direction (or ribbon surface) is along the radial direction of the optical fiber assemblage 2.

[0033] The orientation of the optical fiber unit 11 in a cross section perpendicular to the longitudinal direction is determined by the average value of the sine values ​​sin α of the multiple optical fiber tapes 12 in the same optical fiber unit 11 (average sine value sin α ave ) That is, the average sine value sinα ave represents the average of the directions of the optical fiber tapes 12 that make up the same optical fiber unit 11. The average sine value sin α ave is large (close to 1), it means that the stacking direction of the optical fiber ribbons 12 in the optical fiber unit 11 is oriented in the radial direction of the optical fiber assemblage 2 (or close to the radial direction). On the other hand, the average sine value sinα ave A small value (close to 0) means that the stacking direction of the optical fiber ribbons 12 in the optical fiber unit 11 is oriented in the circumferential direction of the optical fiber assemblage 2 (or close to the circumferential direction).

[0034] In the optical fiber assemblage 2 of this embodiment, in a cross section perpendicular to the longitudinal direction thereof, the average sine value sinα ave is the average sine value sinα in at least one first fiber unit 11A. ave is greater than.

[0035] The above means that the width direction of the optical fiber tape 12 constituting the second fiber unit 11B forms a smaller angle with respect to the circumferential direction of the optical fiber assemblage 2 than the width direction of the optical fiber tape 12 constituting the first fiber unit 11A. In other words, the width direction of the optical fiber tape 12 constituting the second fiber unit 11B is aligned more in line with the circumferential direction of the optical fiber assemblage 2 than the width direction of the optical fiber tape 12 constituting the first fiber unit 11A. In other words, the above means that the width direction of the optical fiber tapes 12 constituting the second fiber unit 11B forms a smaller angle with respect to the neutral line NL than the width direction of the optical fiber tapes 12 constituting the first fiber unit 11A. That is, the width direction of the optical fiber tapes 12 constituting the second fiber unit 11B is closer to the neutral line NL than the width direction of the optical fiber tapes 12 constituting the first fiber unit 11A.

[0036] Furthermore, the above means that the width direction of the optical fiber tape 12 constituting at least one first fiber unit 11A forms a larger angle with respect to the circumferential direction of the optical fiber assemblage 2 than the width direction of the optical fiber tape 12 constituting the second fiber unit 11B. In other words, the width direction of the optical fiber tape 12 constituting at least one first fiber unit 11A is aligned more radially with respect to the optical fiber assemblage 2 than the width direction of the optical fiber tape 12 constituting the second fiber unit 11B.

[0037] The average sine value sinα in the second fiber unit 11B ave is the average sine value sinα in at least one first fiber unit 11A. ave The fact that the average sine value sin α in the second fiber unit 11B is larger than 1 does not have to be true at all positions in the longitudinal direction of the optical fiber assemblage 2, but only needs to be true at least at a certain position in the longitudinal direction. ave is the average sine value sinα in at least one first fiber unit 11A. aveThe fact that the value is larger than the above may be true, for example, in a cross section (a certain cross section) of the optical fiber assemblage 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, the above may not be true in a cross section other than the above-mentioned certain cross section within the range of the twist pitch. Note that the above two contents may be true, for example, over the entire longitudinal direction of the optical fiber assemblage 2.

[0038] The twist pitch (one pitch) described above is the longitudinal length required for the helically arranged optical fiber units 11 to make one turn in the circumferential direction when multiple optical fiber units 11 are twisted in one direction. Furthermore, when multiple optical fiber units 11 are twisted in an SZ configuration, the twist pitch (one pitch) is the longitudinal length (interval) from the position where the twist direction reverses to the next position where it reverses in the same direction. In other words, the twist pitch (one pitch) is the combined length of one section in the S direction and one section in the Z direction.

[0039] Although not shown, in a cross section perpendicular to the longitudinal direction, the average sine value sinα ave At least one first fiber unit 11A having a diameter smaller than that of the second fiber unit 11B may be located in the inner layer 10A radially inside the optical fiber assemblage 2.

[0040] Next, an example of a method for manufacturing the optical cable 1 of this embodiment will be described. When manufacturing the optical cable 1 of this embodiment, first, a plurality of optical fiber units 11 are prepared by bundling a plurality of optical fiber ribbons 12 so that the stacked state of the plurality of optical fiber ribbons 12 is broken, as illustrated in Fig. 4. In order to break the stacked state of the plurality of optical fiber ribbons 12 when preparing the optical fiber units 11, for example, the stacked plurality of optical fiber ribbons 12 may be narrowed in the width direction, thereby deforming the optical fiber ribbons 12 in the width direction. Next, an assembly forming step is performed in which a plurality of these optical fiber units 11 are bundled together to form an optical fiber assembly 2.

[0041] In the assembly forming step, at least in a cross section (a cross section) perpendicular to the longitudinal direction at a certain position in the longitudinal direction of the optical fiber assemblage 2, the average sine value sin α ave is the average sine value sinα in at least one first fiber unit 11A (see FIG. 5). ave The first fiber unit 11A and the second fiber unit 11B may be arranged so that the distance between the first fiber unit 11A and the second fiber unit 11B is greater than the distance between the first fiber unit 11A and the second fiber unit 11B. In order to arrange the first fiber unit 11A and the second fiber unit 11B in this manner, for example, the orientations of the first fiber unit 11A and the second fiber unit 11B may be adjusted before the multiple optical fiber units 11 reach the assembly point (the position of the optical fiber units 11 when the construction of the optical fiber assemblage 2 is completed). The first fiber unit 11A is the optical fiber unit 11 located on the neutral line NL of bending of the optical fiber assemblage 2 in a cross section perpendicular to the longitudinal direction. The second fiber unit 11B is the optical fiber unit 11 located farthest from the neutral line NL in a cross section perpendicular to the longitudinal direction.

[0042] In addition, when a plurality of optical fiber units 11 are twisted in one direction or in an SZ shape in the assembly forming process, in this process, the average sine value sin α ave is the average sine value sinα in at least one first fiber unit 11A. ave The first fiber unit 11A and the second fiber unit 11B may be arranged so that the distance between the first fiber unit 11A and the second fiber unit 11B is larger than the distance between the first fiber unit 11A and the second fiber unit 11B.

[0043] In the assembly forming step, the average sine value sin α ave The first fiber unit 11A and the second fiber unit 11B may be arranged so that at least one first fiber unit 11A having a diameter smaller than that of the second fiber unit 11B is located in the inner layer 10A of the optical fiber assemblage 2.

[0044] The above-mentioned assembly construction process may be performed, for example, when accommodating multiple optical fiber units 11 inside the jacket 3 (see Figure 1), or may be performed, for example, before accommodating the optical fiber assembly 2 inside the jacket 3. The manufacture of the optical cable 1 is completed by accommodating the optical fiber assemblage 2 (plurality of bundled optical fiber units 11) inside the jacket 3. When accommodating the optical fiber assemblage 2 inside the jacket 3, the circumferential angle of the optical fiber assemblage 2 can be adjusted to match the neutral line NL of bending based on, for example, the arrangement of the tension members 7 and the shape of the jacket 3, thereby manufacturing the optical cable 1 configured as described above.

[0045] As described above, in the optical fiber assemblage 2 of this embodiment and the optical cable 1 including the same, the average sine value sinα of the second fiber unit 11B located away from the neutral line NL ave is the average sine value sinα of at least one first fiber unit 11A located on the neutral line NL. ave is larger than that. Therefore, the angle of the width direction of the optical fiber tapes 12 constituting the second fiber unit 11B relative to the circumferential direction (or neutral line NL) of the optical fiber assemblage 2 is smaller than that of the width direction of the optical fiber tapes 12 constituting one first fiber unit 11A. In other words, the second fiber unit 11B is arranged so that the width direction of the optical fiber tapes 12 constituting it is closer to the circumferential direction (neutral line NL) of the optical fiber assemblage 2 than the width direction of the optical fiber tapes 12 constituting the first fiber unit 11A. Therefore, even if bending stress occurs in the optical fiber unit 11 due to bending of the optical cable 1 (optical fiber assembly 2) around the neutral line NL or shrinkage of the jacket 3 of the optical cable 1 in a low-temperature environment, stress concentration on the optical fibers 13 of the optical fiber ribbon 12 constituting the second fiber unit 11B located away from the neutral line NL can be suppressed. Therefore, an increase in transmission loss of the optical fibers 13 in the second fiber unit 11B can be suppressed. This point will be explained below.

[0046] For example, when the width direction of the optical fiber ribbons 12 constituting the optical fiber unit 11 is arranged along the radial direction of the optical cable 1 (approximately perpendicular to the neutral line NL), the average sine value sinα ave In this configuration, the multiple optical fibers 13 constituting the same optical fiber unit 11 are aligned in a direction substantially perpendicular to the neutral line NL. When the optical cable 1 is bent around the neutral line NL in this configuration, the optical fiber 13 of the optical fiber ribbon 12 that is located farthest from the neutral line NL is subjected to a large stress (bending stress) due to a large expansion and contraction strain compared to the other optical fibers 13 of the optical fiber ribbon 12.

[0047] The bending stress described above increases as the optical fiber unit 11 is positioned farther from the neutral line NL. Therefore, when the second fiber unit 11B, which is positioned farthest from the neutral line NL, is positioned as described above, the difference in expansion and contraction strain between the optical fibers 13 at both ends in the width direction of the optical fiber ribbon 12 increases, and the bending stress acting on the second fiber unit 11B also increases. Therefore, the transmission loss of the optical fibers 13 in the second fiber unit 11B increases.

[0048] Next, when the width direction of the optical fiber ribbons 12 constituting the optical fiber unit 11 is arranged along the circumferential direction of the optical fiber assemblage 2 (approximately along the neutral line NL), (i.e., the mean sine value sinα ave Consider the case where the neutral line NL is large. In this configuration, the multiple optical fibers 13 constituting the same optical fiber unit 11 are aligned substantially along the neutral line NL. In this configuration, when the optical cable 1 is bent around the neutral line NL, the difference in expansion and contraction strain occurring among the multiple optical fibers 13 of the same optical fiber ribbon 12 is small. Therefore, even if the second fiber unit 11B located away from the neutral line NL is arranged as described above, the bending stress acting on the second fiber unit 11B is small. Therefore, an increase in the transmission loss of the optical fibers 13 in the second fiber unit 11B can be suppressed.

[0049] In addition, even if the first fiber unit 11A located near or on the neutral line NL is arranged so that the width direction of the optical fiber ribbon 12 is approximately perpendicular to the neutral line NL (i.e., the average sine value sinα ave Even if the bending stress acting on the first fiber unit 11A is small, the expansion and contraction strain occurring in the optical fiber 13 of the first fiber unit 11A is kept small. Therefore, the bending stress acting on the first fiber unit 11A is kept small, and as a result, an increase in the transmission loss of the optical fiber 13 in the first fiber unit 11A can also be suppressed.

[0050] In addition, the average sine value sinα in a predetermined first fiber unit 11A ave is the average sine value sinα in the second fiber unit 11B ave Since the distance between the first and second fiber units 11A and 11B is smaller than the distance between the first and second fiber units 11A and 11B, a predetermined first fiber unit 11A can be arranged in a different direction from the second fiber unit 11B. This makes it easier to arrange a plurality of optical fiber units 11 without gaps in the internal space of the optical fiber assemblage 2. Therefore, it is possible to improve the utilization efficiency of the internal space of the optical fiber assemblage 2 in which the plurality of optical fiber units 11 are arranged.

[0051] Furthermore, since the stacking state of the multiple optical fiber ribbons 12 in the optical fiber unit 11 is disrupted, the cross-sectional shapes of the multiple optical fiber units 11 can be made different among the multiple optical fiber units 11. This makes it easier to arrange the multiple optical fiber units 11 without gaps in the internal space of the optical fiber assemblage 2. Therefore, it is possible to improve the utilization efficiency of the internal space of the optical fiber assemblage 2 in which the multiple optical fiber units 11 are arranged.

[0052] Next, the effects of the present embodiment will be described using an example shown in FIGS. 5 and 8 and a comparative example shown in FIGS. The optical fiber assemblage 2 of the embodiment shown in Fig. 5 has 12 optical fiber units 11 (11-1 to 11-12). The 12 optical fiber units 11 constitute two fiber unit layers 10 arranged in the radial direction of the optical fiber assemblage 2. Three optical fiber units 11 (optical fiber units 11-1 to 11-3, numbered 1 to 3) constitute an inner layer 10A of the two fiber unit layers 10. The remaining nine optical fiber units 11 (optical fiber units 11-4 to 11-12, numbered 4 to 12) constitute an outer layer 10B (outermost layer 10B) of the two fiber unit layers 10, and are arranged in order in the circumferential direction of the optical fiber assemblage 2. Also, in the embodiment of Figure 5, optical fiber units 11-1, 11-7, and 11-12, numbered 1, 7, and 12, are three first fiber units 11A located on the neutral line NL, and optical fiber units 11-4, 11-5, 11-9, and 11-10, numbered 4, 5, 9, and 10, are four second fiber units 11B located furthest from the neutral line NL.

[0053] The optical fiber assemblage 2 of the comparative example shown in Fig. 6 has 12 optical fiber units 11 (11-1 to 11-12), similar to the embodiment of Fig. 5. The 12 optical fiber units 11 constitute two fiber unit layers 10 arranged in the radial direction of the optical fiber assemblage 2. Three optical fiber units 11 (optical fiber units 11-5, 11-8, and 11-9, numbered 5, 8, and 9) constitute an inner layer 10A of the two fiber unit layers 10. The remaining nine optical fiber units 11 (optical fiber units 11-1 to 11-4, 11-6, 11-7, and 11-10 to 11-12, numbered 1 to 4, 6, 7, and 10 to 12) constitute an outer layer 10B (outermost layer 10B) of the two fiber unit layers 10, and are arranged in the circumferential direction of the optical fiber assemblage 2. In addition, in the comparative example of Figure 6, optical fiber units 11-5, 11-8, 11-10, and 11-12, numbered 5, 8, 10, and 12, are three first fiber units 11A located on the neutral line NL, and optical fiber units 11-2 to 11-4, 11-6, and 11-7, numbered 2 to 4, 6, and 7, are four second fiber units 11B located furthest from the neutral line NL.

[0054] The table shown in FIG. 8 shows the average sine value sinα of the plurality of optical fiber units 11 in the embodiment of FIG. ave and the increase in transmission loss of the optical fiber 13. The "unit numbers" in Fig. 8 correspond to the optical fiber units 11-1 to 11-12, numbered 1 to 12, respectively, in Fig. 5. Also, the "tape numbers" in Fig. 8 correspond to the six optical fiber tapes 12 that each optical fiber unit 11 has.

[0055] The table shown in FIG. 9 shows the average sine value sinα of the plurality of optical fiber units 11 in the comparative example of FIG. ave and the increase in transmission loss of the optical fiber 13. The "unit numbers" in Fig. 9 correspond to the optical fiber units 11-1 to 11-12, numbered 1 to 12, respectively, in Fig. 6. Also, the "tape numbers" in Fig. 9 correspond to the six optical fiber tapes 12 that each optical fiber unit 11 has.

[0056] 8 and 9, the sine values ​​sin α of all (72) optical fiber ribbons 12 constituting the optical fiber assemblage 2 are shown in correspondence with the optical fiber units 11. For example, in the embodiment shown in Fig. 8, the sine value sin α of the first optical fiber ribbon 12 in the first optical fiber unit 11-1 is 0.93. The sine value sin α of each optical fiber ribbon 12 is based on the angle α (see Fig. 7) of each optical fiber ribbon 12 measured at any five cross sections within the twist pitch in the longitudinal direction of the optical fiber assemblage 2.

[0057] 8 and 9, the "average sin α" is the average value of the sine values ​​sin α of the six optical fiber tapes 12 that constitute the same optical fiber unit 11 (i.e., the average sine value sin α ave ) 8 and 9 indicates the maximum transmission loss increase (hereinafter simply referred to as loss increase) of the optical fiber 13 measured by the following measurement method. In the measurement method for measuring the transmission loss increase of the optical fiber 13, first, a mandrel with a diameter 20 times the diameter of the optical cable 1 is prepared. Next, a bending process is performed in which the optical cable 1 is pressed against the outer periphery of the mandrel and bent by 90° (+90°) in the direction opposite to the bending direction, with the optical cable 1 then pressed against the outer periphery of the mandrel and bent by 90° (-90°). This bending process was repeated 25 times, and the transmission loss increase of the optical fiber 13 of the optical cable 1 at three bending angles of 0°, +90°, and -90° was measured using light with a wavelength of 1.55 μm (compliant with GR-20-CORE Issue 4, 6.5.8).

[0058] 8 and 9, the optical fiber ribbon 12 with a loss increase of 0.15 dB / km or less is rated as passing (◯ or ⊚), and the optical fiber ribbon 12 with a loss increase of 0.15 dB / km or more is rated as failing (×). Also, the optical fiber ribbon 12 with a loss increase of 0.05 dB / km or less is rated as excellent (◎) (based on GR-20-CORE Issue 4, 6.5.2 Optical Acceptance Criteria).

[0059] As shown in FIG. 9, in the comparative example of FIG. 6, the average sine value sinα of the optical fiber units 11-2, 11-3, 11-6, and 11-7, which are the second fiber unit 11B, is ave However, the average sine value sinα of the fifth optical fiber unit 11-5, which is one of the first fiber units 11A, ave(=0.52). That is, the optical fiber units 11-2, 11-3, 11-6, and 11-7, numbered 2, 3, 6, and 7, which are the second fiber unit 11B, are arranged so that the width direction of their optical fiber ribbons 12 is roughly along the circumferential direction of the optical fiber assemblage 2. The loss increase amounts in the optical fiber units 11-2, 11-3, 11-6, and 11-7, numbered 2, 3, 6, and 7, are all kept to 0.15 dB / km or less. That is, it can be seen that the increase in transmission loss of the optical fibers 13 in the optical fiber units 11-2, 11-3, 11-6, and 11-7, numbered 2, 3, 6, and 7, can be suppressed.

[0060] However, the average sine value sinα of the fourth optical fiber unit 11-4, which is another one of the second fiber units 11B, ave is the average sine value sinα of any of the optical fiber units 11-5, 11-8, 11-10, and 11-12, which are the first fiber unit 11A, i.e., the fifth, eighth, tenth, and twelfth optical fiber units 11-5, 11-8, 11-10, and 11-12. ave is smaller than 0. That is, the fourth optical fiber unit 11-4 is arranged so that the width direction of its optical fiber ribbon 12 is roughly along the radial direction of the optical fiber assemblage 2. The increase in transmission loss in the fourth optical fiber unit 11-4 exceeds 0.15 dB / km in all cases. That is, it can be seen that the increase in transmission loss of the optical fibers 13 in the fourth optical fiber unit 11-4 is not suppressed.

[0061] In contrast, as shown in FIG. 8, in the embodiment of FIG. 5, the average sine value sinα of the optical fiber units 11-4, 11-5, 11-9, and 11-10, which are the second fiber unit 11B, is ave However, the average sine value sinα of the optical fiber units 11-7 and 11-12, both of which are the first fiber unit 11A, is aveis greater than 0.15 dB / km. That is, all of the optical fiber units 11-4, 11-5, 11-9, and 11-10 (Nos. 4, 5, 9, and 10) constituting the second fiber unit 11B are arranged so that the width direction of their optical fiber ribbons 12 is approximately along the circumferential direction of the optical fiber assemblage 2. The increase in transmission loss in all of the optical fiber units 11-4, 11-5, 11-9, and 11-10 constituting the second fiber unit 11B is kept to 0.15 dB / km or less. That is, it can be seen that the increase in transmission loss of the optical fibers 13 is suppressed in all of the optical fiber units 11-4, 11-5, 11-9, and 11-10 constituting the second fiber unit 11B.

[0062] In the optical fiber assemblage 2 and the optical cable 1 of this embodiment, the mean sine value sinα ave When at least one first fiber unit 11A having a length smaller than that of the second fiber unit 11B (i.e., the width direction of the optical fiber ribbon 12 is approximately along the neutral line NL) is located in the inner layer 10A of the optical fiber assemblage 2, the expansion and contraction strain generated in the optical fibers 13 of the first fiber unit 11A is kept small compared to when the first fiber unit 11A is located in the outer layer 10B of the optical fiber assemblage 2. Therefore, the bending stress acting on the first fiber unit 11A is kept small, and as a result, an increase in the transmission loss of the optical fibers 13 in the first fiber unit 11A can also be suppressed.

[0063] Furthermore, in the optical fiber assemblage 2 and the optical cable 1 of this embodiment, the optical fiber ribbons 12 constituting the optical fiber unit 11 meander in their width direction. In this case, the degree of freedom of relative movement of the multiple optical fibers 13 constituting the same optical fiber ribbon 12 is greater than when the optical fiber ribbon 12 does not meander in the width direction. Therefore, when the optical fiber assemblage 2 is bent, for example, the adjacent optical fibers 13 in the same optical fiber ribbon 12 can move relative to each other so as to alleviate the bending stress acting on the optical fiber unit 11. Therefore, an increase in the transmission loss of the optical fibers 13 can be suppressed.

[0064] Furthermore, in the optical fiber assemblage 2 and the optical cable 1 of this embodiment, the optical fiber unit 11 is configured by bundling a plurality of optical fiber ribbons 12 in a stacked state with a filament 20. Therefore, compared to when a plurality of optical fiber ribbons 12 are bundled in a tube, it is possible to suppress or prevent the entire circumference of the optical fiber unit 11 (a plurality of optical fiber ribbons 12) from being covered. Therefore, compared to when the optical fiber ribbons 12 are bundled in a tube, when the optical fiber assemblage 2 is bent, the bundled plurality of optical fiber ribbons 12 and the optical fibers 13 constituting the same optical fiber ribbons 12 can move freely. As a result, when the optical fiber assemblage 2 is bent, the optical fiber ribbons 12 and the optical fibers 13 constituting the same optical fiber unit 11 can move relative to each other so as to alleviate the bending stress acting on the optical fiber unit 11. Therefore, it is possible to suppress an increase in the transmission loss of the optical fibers 13.

[0065] Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0066] The present invention is not limited to being applied to slotless optical cables, but may also be applied to, for example, slotted optical cables having slot rods. [Explanation of symbols]

[0067] 2...optical fiber assembly, 7...tension member (applying member), 10A...inner layer, 11...optical fiber unit, 11A...first fiber unit, 11B...second fiber unit, 12...optical fiber tape, 13...optical fiber, C...center of optical fiber assembly 2, G...center of gravity of optical fiber tape 12, NL...neutral line, R1...radial line, W1...tape width line, α...angle

Claims

1. A slotless optical cable including an optical fiber assembly formed by bundling a plurality of optical fiber units each formed by stacking a plurality of optical fiber ribbons, At least at a certain position in the longitudinal direction of the optical fiber assemblage, in a cross section of the optical fiber assemblage perpendicular to the longitudinal direction, the stacking state of the plurality of optical fiber ribbons in the optical fiber unit is disrupted so that the tape surface of at least one of the optical fiber ribbons constituting the optical fiber unit is curved; The plurality of optical fiber units include a first fiber unit located on a neutral line of bending of the optical fiber assemblage in a cross section of the optical fiber assemblage perpendicular to the longitudinal direction, and a second fiber unit located farthest from the neutral line, With respect to the sine value sin α of the angle α formed by the radial line connecting the center of the optical cable and the center of gravity of the optical fiber ribbon and the tape width direction line connecting both ends of the optical fiber ribbon, the average value of the sine values ​​sin α of the plurality of optical fiber ribbons in the same optical fiber unit is defined as the average sine value sin α ａｖｅ year, In a cross section of the optical fiber assemblage perpendicular to the longitudinal direction at least at a certain position in the longitudinal direction, the average sine value sin α of the second fiber unit ａｖｅ is the average sine value sin α in at least one of the first fiber units. ａｖｅ A slotless optical cable that is larger than

2. At least at a certain position in the longitudinal direction, in a cross section of the optical fiber assemblage perpendicular to the longitudinal direction, the average sine value sin α ａｖｅ 2. The slotless optical cable according to claim 1, wherein at least one of the first fiber units having a diameter smaller than that of the second fiber unit is located in an inner layer radially inside the optical fiber assemblage.

3. The plurality of optical fiber units are twisted in one direction or in an SZ configuration, In a cross section of the optical fiber assemblage perpendicular to the longitudinal direction at a certain position within the range of the twist pitch, the average sine value sin α of the second fiber unit ａｖｅ is the average sine value sin α in at least one of the first fiber units. ａｖｅ 2. The slotless optical cable according to claim 1, wherein the slotless optical cable is larger than

4. 2. The slotless optical cable according to claim 1, wherein the optical fiber unit has a structure in which a plurality of the optical fiber ribbons are stacked and bundled by a filament.

5. 5. The slotless optical cable according to claim 1, further comprising an imparting member that imparts bending anisotropy to the optical cable, making it easier to bend the optical cable in a direction centered on the neutral line.

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