fiber optic cable

Abstract

To provide an optical fiber cable capable of suppressing an increase in polarization mode dispersion.SOLUTION: A twisted direction of a plurality of optical fiber ribbons 3 and that of a plurality of optical fiber units 5 are set reverse to each other. Moreover, when a twist pitch of the optical fiber ribbons 3 is defined as P1 and that of the optical fiber units 5 is defined as P2, a twist pitch P of the optical fiber ribbons 3 inside the optical fiber units 5, in an axial direction of a cable in a state of being processed into a cable is represented by P=1 / (|(1 / P1-1 / P2)|), and the pitch P is preferably 833 mm to 1600 mm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical fiber cable in which a plurality of optical fiber ribbons are assembled. [Background technology]

[0002] To increase the amount of information transmitted through a single optical fiber cable, the number of optical fibers stored in the optical fiber cable is increased, for example, by storing a large number of optical fiber ribbons at high density. As the number of fibers stored in an optical fiber cable increases, it becomes difficult to identify the optical fiber core wires, so a method of bundling multiple optical fiber ribbons to make identification easier is used. Such a bundle of multiple optical fiber ribbons is called an optical fiber unit. When in use, the required optical fiber ribbons are extracted from this optical fiber unit and branched.

[0003] In such optical fiber cables, a plurality of optical fiber cores are usually twisted together to form an optical fiber unit, and the optical fiber units are then twisted together to form an optical fiber cable. By twisting the optical fiber cores in this way, it is possible to suppress variations in the position of the optical fiber cores.

[0004] In this case, there is an optical fiber cable in which the twisting direction of the plurality of optical fibers and the twisting direction of the plurality of optical fiber units are different (Patent Document 1).

[0005] There is also an optical fiber cable in which the twisting direction of a plurality of optical fibers and the twisting direction of a plurality of optical fiber units are the same (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-109400 A [Patent Document 2] Japanese Patent Publication No. 2021-157062 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Document 1 aims to cancel out the force that tends to untwist the optical fiber unit and the force that tends to untwist the optical fiber core when tension is applied by making the twisting direction of the optical fiber unit different from the twisting direction of the optical fibers that make up the optical fiber unit.

[0008] FIG. 6 is a conceptual diagram showing the twisting of optical fiber cores 103 in an optical fiber unit 101 (left diagram) and the twisting of optical fiber units 101 in an optical fiber cable 100 (right diagram).

[0009] As shown in the left diagram of FIG. 6, the optical fiber unit 101 is formed by twisting together a plurality of optical fiber cores 103. In the illustrated example, the optical fiber cores 103 are twisted clockwise. On the other hand, as shown in the right diagram of FIG. 6, the core of the optical fiber cable 100 is formed by twisting together a plurality of optical fiber units 101. In the illustrated example, the optical fiber units 101 are twisted counterclockwise. That is, the twisting direction of the optical fiber cores 103 and the twisting direction of the optical fiber unit 101 are opposite. In this case, according to Patent Document 1, by making the twist pitch of the optical fiber cores 103 and the twist pitch of the optical fiber unit 101 approximately the same but in opposite directions, it is possible to cancel out the untwisting forces that occur when tension is applied. Although both the optical fiber cores 103 and the optical fiber units 101 are twisted together "without twisting," according to the above-mentioned conditions, the resulting configuration is substantially the same as when only the optical fiber units 101 are twisted together "with twisting" without twisting the optical fiber cores 103. The twisting will be described later.

[0010] However, because the twisting direction of the optical fiber unit and the twisting direction of the optical fibers constituting the optical fiber unit are opposite, the twisting of the optical fiber core wires inside the optical fiber unit is canceled, and the optical fiber core wires 103 inside the optical fiber unit 101 are always located at a fixed position (upper in the figure) in the state where the optical fiber cable 100 is formed. That is, either the optical fiber core wires 103 inside the optical fiber unit 101 in the cabled state are not twisted in the axial direction of the cable (twist pitch = infinity), or even if there is a slight deviation between the twist pitch of the optical fiber core wires 103 and the twist pitch of the optical fiber unit 101, the twist pitch of the optical fiber core wires 103 inside the optical fiber unit 101 becomes an extremely long period.

[0011] As a result, when the manufactured optical fiber cable is wound around a drum for transportation or when the optical fiber cable is bent along the installation route, deformation may not be uniform among the optical fiber core wires 103 in the optical fiber unit 101, and some of the optical fiber core wires 103 may be excessively distorted. However, if the twist pitch of the optical fiber core wires 103 and the twist pitch of the optical fiber unit 101 are significantly different, the object of Patent Document 1, which is to cancel out the untwist forces when tension is applied, cannot be achieved.

[0012] In contrast, Patent Document 2 aims to make the twisting direction of the optical fiber unit the same as the twisting direction of the optical fibers that make up the optical fiber unit, thereby relaxing the twist of the optical fiber core wires when twisting the optical fiber unit and preventing the twisting pitch of the optical fiber core wires from becoming long-period.

[0013] According to Patent Document 2, the twisting direction of the optical fiber unit and the twisting direction of the optical fibers that make up the optical fiber unit are the same, so even when the optical fiber unit is cabled, the twisting of the optical fiber core wires inside the optical fiber unit is not canceled out. Furthermore, although the twisting pitch of the optical fiber core wires when finally cabled is even shorter than the twisting pitch of the optical fibers that make up the optical fiber unit, this does not pose a particular problem as long as it does not result in an increase in transmission loss.

[0014] On the other hand, in Patent Document 2, for example, if the twist pitch of the optical fiber units is increased, the twist of the optical fiber units may not be maintained uniformly and may come apart. Therefore, when a winding tape is placed vertically on a core in which optical fiber units are twisted together, the optical fiber units may come loose from the joint. This may be a factor in increasing transmission loss.

[0015] In conventional optical fiber cables, the twisting pitch of optical fiber cores or optical fiber units is set to prevent increases in transmission loss and breakage during winding onto a drum or installation. However, the inventors have noticed that polarization mode dispersion (PMD) can be a major cause of optical signal degradation, especially in optical communication systems exceeding 10 Gbps. PMD is the difference in group delay between two orthogonal polarization modes of light propagating through an optical fiber. For this reason, focusing only on increased loss, as in the past, is not sufficient; it is necessary to suppress the increase in PMD.

[0016] The present invention has been made in view of the above problems, and has an object to provide an optical fiber cable that can suppress an increase in polarization mode dispersion. [Means for solving the problem]

[0017] In order to achieve the above object, the first invention provides a core formed by twisting together a plurality of optical fiber units without twisting them back together, an outer jacket provided on the outer periphery of the core, a tension member disposed on the outer periphery of the core;the optical fiber unit is formed by twisting together a plurality of optical fiber core wires, the twisting direction of the plurality of optical fiber core wires is opposite to the twisting direction of the optical fiber unit, and when the twisting pitch of the optical fiber core wires is P1 and the twisting pitch of the optical fiber unit is P2, the twisting pitch P=1 / (|(1 / P1-1 / P2)|) of the optical fiber core wires in the optical fiber unit relative to the axial direction of the cable in a cabled state is 833 mm to 1600 mm.

[0018] The second invention is a cable comprising a core formed by twisting a plurality of optical fiber units together without twisting, an outer jacket provided on the outer periphery of the core, and a tension member arranged on the outer periphery of the core, wherein the optical fiber unit is formed by gathering a plurality of optical fiber cores together without twisting them, and the twist pitch P of the optical fiber cores in the optical fiber unit with respect to the axial direction of the cable in a cabled state is 8. 50 The optical fiber cable is characterized by a length of 1600 mm to 1600 mm.

[0019] In the first and second aspects of the present invention, it is desirable that the twist pitch P of the optical fibers in the optical fiber unit in the axial direction of the cable in a cabled state is 1000 mm to 1400 mm.

[0020] In the first and second inventions, the optical fiber core is Multiple optical fibers are bonded intermittently in the longitudinal direction. It is an intermittently adhesive optical fiber ribbon. In the optical fiber unit, adjacent optical fibers are bent in a parallel direction at at least a part of the non-bonded portion of the optical fiber core wire. That's fine.

[0021] According to the first and second inventions, by making the twisting direction of the optical fiber core wires and the twisting direction of the optical fiber unit different from each other and by keeping the twisting pitch of the optical fiber core wires in the optical fiber unit relative to the axial direction of the cable in a cabled state within a predetermined range, it is possible to suppress an increase in loss when the optical fiber cable is bent and to suppress an increase in PMD due to an increase in lateral pressure.

[0022] Furthermore, if the optical fiber is an intermittently bonded optical fiber ribbon, the increase in loss when the optical fiber cable is bent can be more efficiently suppressed, and the increase in PMD due to an increase in lateral pressure can be suppressed. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide an optical fiber cable capable of suppressing an increase in polarization mode dispersion. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view showing an optical fiber cable 1. FIG. [Figure 2] FIG. 2 is a diagram showing an optical fiber ribbon 3. [Figure 3] 3A to 3C are diagrams showing a process of twisting together the optical fiber ribbon 3. [Figure 4] FIG. 1( a ) is a diagram showing a method of twisting optical fiber units without twisting back, and FIG. 1( b ) is a diagram showing a method of twisting optical fiber units with twisting back. [Figure 5] 4A to 4C are diagrams showing a process of twisting together optical fiber units 5. [Figure 6] 1 is a conceptual diagram showing the state of twisting of conventional optical fiber cores 103 and the state of twisting of an optical fiber unit 101. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view of an optical fiber cable 1. The optical fiber cable 1 is a slotless cable that does not use a slot, and is composed of a core 4, a pressure winding 7, a tension member 9, a tear cord 11, an outer jacket 13, etc.

[0026] The core 4 is formed by twisting together a plurality of optical fiber units 5 without twisting back. Twisting back will be described later. The optical fiber unit 5 is formed by twisting together a plurality of intermittently bonded optical fiber ribbons 3, for example.

[0027] 2 is a perspective view showing an intermittently bonded optical fiber ribbon 3. The optical fiber ribbon 3 is formed by arranging a plurality of optical fibers 2a, 2b, 2c, and 2d in parallel and bonding them together. The number of optical fibers constituting the optical fiber ribbon 3 is not limited to the example shown in the figure. Furthermore, the optical fiber ribbon does not necessarily have to be an intermittently bonded optical fiber ribbon.

[0028] 2, in this embodiment, adjacent optical fibers 2a, 2b, 2c, and 2d are bonded together at adhesive joints 6 at predetermined intervals in the longitudinal direction of the optical fiber ribbon 3. It is desirable that adjacent adhesive joints 6 in the width direction are shifted from each other in the longitudinal direction of the optical fiber ribbon 3. For example, it is desirable that adjacent adhesive joints 6 are formed so as to be shifted by half a pitch in the longitudinal direction of the optical fiber ribbon 3. It is noted that the length and pitch of the adhesive joints 6 are not limited to the example shown in the figure.

[0029] In this way, by arranging the adhesive portions 6 intermittently in the longitudinal direction of the optical fiber ribbon 3, adjacent optical fibers 2a, 2b, 2c, and 2d in the non-adhesive portions can be easily folded (bent) relative to the parallel direction of the optical fibers 2a, 2b, 2c, and 2d.

[0030] As shown in Fig. 1, a pressure wrap 7 is provided on the outer periphery of the plurality of optical fiber units 5. The pressure wrap 7 is a tape-like member, a nonwoven fabric, or the like, and is arranged, for example, by longitudinal splicing to collectively cover the outer periphery of the plurality of optical fiber units 5. That is, the pressure wrap 7 is longitudinally spliced ​​around the outer periphery of the plurality of optical fiber units 5 so that the longitudinal direction of the pressure wrap 7 substantially coincides with the axial direction of the optical fiber cable 1 and the width direction of the pressure wrap 7 coincides with the circumferential direction of the optical fiber cable 1. Note that the pressure wrap 7 is not necessarily required, and the pressure wrap 7 may also be referred to as the core 4.

[0031] An outer jacket 13 is provided on the outer periphery of the core 4. The outer jacket 13 is a layer that covers and protects the optical fiber cable 1. In a cross section perpendicular to the longitudinal direction of the optical fiber cable 1, a pair of tension members 9 are provided inside the outer jacket 13 at positions facing each other with the core 4 in between. In addition, tear cords 11 are provided in a direction approximately perpendicular to the facing direction of the tension members 9, facing each other with the core 4 in between. The tension members 9 and the tear cords 11 are embedded in the outer jacket 13.

[0032] Next, we will explain how to twist the optical fiber ribbons 3. Fig. 3 is a cross-sectional conceptual diagram showing the orientation of each optical fiber ribbon 3 when the optical fiber ribbons 3 constituting the optical fiber unit 5 are twisted together. For simplicity, the following explanation will be given on an example where the optical fiber unit 5 is made up of four optical fiber ribbons 3a, 3b, 3c, and 3d (the optical fiber ribbons 3a, 3b, 3c, and 3d may be collectively referred to as the optical fiber ribbon 3).

[0033] 3 shows a state (hereinafter referred to as state S1) in which optical fiber ribbons 3a, 3b, 3c, and 3d are arranged in a predetermined direction around the twist center Z (black circle) of the optical fiber ribbon 3. In addition, the optical fibers at one end of each of the optical fiber ribbons 3a, 3b, 3c, and 3d are designated A1, B1, C1, and D1, respectively.

[0034] In the illustrated example, in state S1, all of the optical fiber ribbons 3a, 3b, 3c, and 3d are arranged parallel to one another and all point in the same direction, but this arrangement is not necessary. For example, they may all be arranged in different directions.

[0035] Furthermore, although all of the optical fiber ribbons 3a, 3b, 3c, and 3d have their optical fibers arranged in a straight line, this arrangement is not necessary. For example, each of the optical fiber ribbons 3a, 3b, 3c, and 3d may be bent. In this case, as described above, the optical fiber ribbons 3a, 3b, 3c, and 3d can be bent into any shape as long as adjacent optical fibers are intermittently bonded to each other.

[0036] For example, in the state S1 of Fig. 3, in the areas where the overall width is wide, such as the optical fiber ribbons 3a and 3c, the optical fiber ribbons 3a and 3c are bent, which allows each optical fiber to be closer to the twisting center Z and achieve a stable arrangement. For simplicity, the following figures do not take into consideration the bending of the optical fiber ribbon 3, and show it as being arranged in a straight line.

[0037] 3, there are roughly two conceivable methods for twisting the optical fiber ribbon 3 from state S1. One is a method of twisting in the steps of state S2 (arrow E on the left side of the figure) and state S3 (arrow F), and the other is a method of twisting in the steps of state S4 (arrow G on the right side of the figure) and state S5 (arrow H). The former is a so-called "no-twist" twisting, and the latter is a so-called "with-twist" twisting.

[0038] First, a detailed description will be given of the case where the optical fiber ribbon 3 is twisted without twisting back. State S2 (arrow E) shows the state where the optical fiber ribbon 3 is twisted from state S1 by 45° clockwise around the twisting center Z, and state S3 (arrow F) shows the state where the optical fiber ribbon 3 is twisted from state S2 by a further 45° clockwise around the twisting center Z.

[0039] In state S2, the circumferential arrangement of each optical fiber ribbon 3 with respect to the twist center Z moves by 45° (arrow Q in the figure), and at this time, the orientation of each optical fiber ribbon 3 changes. That is, the orientation of the optical fiber ribbon 3 also rotates by 45° as the arrangement moves. For example, the orientations of A1, B1, C1, and D1 of each of the optical fiber ribbons 3a, 3b, 3c, and 3d rotate by 45° from state S1 to state S2.

[0040] Similarly, in state S3, the circumferential arrangement of each optical fiber ribbon 3 with respect to the twist center Z moves another 45° from state S2 (arrow Q in the figure), and the orientation of each optical fiber ribbon 3 also changes. That is, the optical fiber ribbon 3 is twisted at an angle of 90° from state S1 to state S3, but the entire optical fiber ribbon 3 rotates with respect to the twist center Z.

[0041] Next, a detailed description will be given of twisting the optical fiber ribbon 3 with twisting back. State S4 (arrow G) shows the state in which the optical fiber ribbon 3 is twisted from state S1 by 45° clockwise around the twisting center Z, and state S5 (arrow H) shows the state in which the optical fiber ribbon 3 is twisted from state S4 by a further 45° clockwise around the twisting center Z.

[0042] In state S4, the circumferential arrangement of each optical fiber ribbon 3 with respect to the twist center Z moves by 45° (arrow P in the figure), but the orientation of each optical fiber ribbon 3 does not change. That is, the optical fiber ribbon 3 remains oriented in a substantially fixed direction, and only the circumferential arrangement with respect to the twist center Z changes. For example, the orientations A1, B1, C1, and D1 of each of the optical fiber ribbon 3a, 3b, 3c, and 3d do not change from state S1 to S4 (all point to the left in the figure).

[0043] Similarly, in state S5, the circumferential arrangement of each optical fiber ribbon 3 with respect to the twist center Z moves another 45° from state S4 (arrow P in the figure), but the orientation of each optical fiber ribbon 3 does not change. That is, the optical fiber ribbon 3 is twisted at an angle of 90° in the steps of states S1, S4, and S5, but only the circumferential arrangement with respect to the twist center Z changes while each is facing in a substantially fixed direction.

[0044] Next, we will explain the manufacturing methods of the optical fiber units 5 with and without twisting. Figure 4(a) is a diagram showing a method of twisting optical fiber ribbons 3 without twisting. The center of the figure is the twisting center Z, and the twisted optical fiber unit 5 flows perpendicular to the plane of the paper. Note that the illustration of bundle materials and the like is omitted.

[0045] The bobbins 15 around which a plurality of optical fiber ribbons 3 are wound are arranged at predetermined intervals in the circumferential direction with respect to the twisting center Z of the optical fiber ribbon (U1, U2, U3, U4 in the figure). The optical fiber ribbons 3 are supplied from each bobbin 15 to the twisting center Z (Y in the figure), and each bobbin 15 moves around the twisting center Z (X in the figure). For example, the bobbin 15 at the position U1 moves sequentially to the positions U2, U3, and U4. As a result, the optical fiber ribbons 3 supplied from each bobbin 15 are twisted together.

[0046] In this method, the orientation of the bobbins 15 varies depending on their position relative to the twisting center Z. Specifically, the bobbins 15 rotate so as to always face the twisting center Z, while each bobbin 15 moves around the twisting center Z. Conversely, when viewed from the center Z, the bobbins 15 do not rotate at each position, but always rotate around the center Z in a constant direction. This allows the optical fiber ribbons 3 to be twisted together without twisting back.

[0047] On the other hand, FIG. 4(b) is a diagram showing a method of twisting the optical fiber ribbon 3 together with twisting back.

[0048] The bobbins 15 on which a plurality of optical fiber ribbons 3 are wound are arranged at predetermined intervals in the circumferential direction around the twist center Z of the optical fiber ribbon (T1, T2, T3, T4 in the figure), and the optical fiber ribbons 3 are supplied from each bobbin 15 to the twist center Z (W in the figure), and each bobbin 15 moves around the twist center Z (V in the figure), as in Figure 4(a). For example, the bobbin 15 at the position T1 moves sequentially to the positions T2, T3, and T4.

[0049] In this method, each bobbin 15 moves around the twisting center Z while facing in a substantially constant direction at any position relative to the twisting center Z. That is, the bobbins 15 move in the circumferential direction around the outer periphery of the twisting center Z without changing their orientation. Conversely, when viewed from the center Z, the bobbins 15 appear to rotate (revolve) around the center Z while rotating (spinning) in the opposite direction to the direction of this rotation (revolution). In this way, the optical fiber ribbons 3 can be twisted together with twisting back.

[0050] By twisting the optical fiber ribbons 3 together with twisting back, it is possible to suppress untwisting of the optical fiber ribbon 3. In other words, when twisting back is performed, when the optical fiber ribbons 3 are twisted together to form the optical fiber unit 5, the optical fiber ribbon 3 is less likely to untwist, making it easier to handle.

[0051] On the other hand, in order to perform twisting with twisting in this manner, a special device is required because it is necessary to control rotation in addition to revolution in a device for twisting without twisting. Therefore, if the optical fiber ribbon 3 is twisted without twisting in consideration of manufacturability, the special twisting device for providing twisting as described above is not required, and therefore the manufacturing cost can be reduced.

[0052] Next, a method for twisting the optical fiber units 5 manufactured in this manner will be described. In the present invention, the twisting direction of the plurality of optical fiber ribbons 3 is opposite to the twisting direction of the optical fiber unit 5. If the twisting direction of the optical fiber ribbons 3 is the same as the twisting direction of the optical fiber unit 5, the twisting pitch of the optical fiber ribbons 3 inside will be shorter when twisting the optical fiber unit 5.

[0053] 5 is a cross-sectional conceptual diagram showing the orientation of each optical fiber unit 5 when the optical fiber units 5 are twisted together, similar to FIG. 3. For simplicity, the following description will be given of an example in which four sets of optical fiber units 5a, 5b, 5c, and 5d (the optical fiber units 5a, 5b, 5c, and 5d may be collectively referred to as the optical fiber units 5a, 5b, 5c, and 5d) are twisted together. The illustration also shows the optical fiber cores not twisted together.

[0054] 5 shows a state (hereinafter referred to as state S11) in which optical fiber units 5a, 5b, 5c, and 5d are arranged in a predetermined direction around twist center Z of optical fiber unit 5. In addition, in each of optical fiber units 5a, 5b, 5c, and 5d, the optical fiber ribbons at one end are designated as A11, B11, C11, and D11, respectively.

[0055] First, a method of twisting the optical fiber unit 5 without twisting it back will be described. State S22 (arrow I) shows a state in which the optical fiber unit 5 is twisted from state S11 by 45° counterclockwise around the twist center Z, and state S33 (arrow J) shows a state in which the optical fiber unit 5 is twisted from state S22 by a further 45° counterclockwise around the twist center Z.

[0056] In states S22 and S33, the circumferential arrangement of each optical fiber unit 5 with respect to the twist center Z shifts by 45° (arrow N in the figure), and at this time, the orientation of each optical fiber unit 5 changes. That is, the orientation of the optical fiber unit 5 also rotates by 45° as the arrangement shifts. For example, the orientations of A11, B11, C11, and D11 of each of the optical fiber units 5a, 5b, 5c, and 5d rotate by 45° in states S11 to S33. That is, the optical fiber units 5 are twisted at an angle of 90° from state S11 to state S33, but the entire optical fiber unit 5 rotates with respect to the twist center Z.

[0057] Next, a method of twisting the optical fiber unit 5 with twisting back will be described. As described above, state S44 (arrow K) shows a state in which the optical fiber unit 5 is twisted from state S11 by 45° counterclockwise around the twist center Z, and state S55 (arrow L) shows a state in which the optical fiber unit 5 is twisted from state S44 by a further 45° counterclockwise around the twist center Z.

[0058] In states S44 and S55, the circumferential arrangement of each optical fiber unit 5 with respect to the twist center Z moves by 45° (arrow M in the figure), but the orientation of each optical fiber unit 5 does not change. That is, the optical fiber units 5 each face in a substantially fixed direction, and only the circumferential arrangement with respect to the twist center Z changes. For example, the orientations of A11, B11, C11, and D11 of each optical fiber unit 5 do not change in states S11, S44, and S55. That is, the optical fiber units 5 are twisted at an angle of 90° up to states S11, S44, and S55, but each face in a substantially fixed direction, and only the circumferential arrangement with respect to the twist center Z changes.

[0059] As with the optical fiber ribbon 3, twisting the optical fiber unit 5 with twisting back can reduce untwisting after twisting. However, in the present invention, it is desirable to twist the optical fiber unit 5 without twisting back. This is because, as mentioned above, twisting with twisting back requires a special device. Furthermore, since the number of optical fiber units 5 to be twisted is often large, twisting with twisting back may increase the manufacturing cost, for example, by increasing the size of the device.

[0060] Here, when the optical fiber ribbon 3 and the optical fiber unit 5 are twisted together in opposite directions, if the twist pitch of the optical fiber ribbon 3 is P1 and the twist pitch of the optical fiber unit 5 is P2, the twist pitch P of the optical fiber ribbon 3 in the optical fiber unit 5 in the axial direction of the cable in a cabled state is P=1 / (|(1 / P1-1 / P2)|) (Equation 1) In the present invention, the twist pitch P of the optical fiber ribbon 3 in the optical fiber unit 5 in a cabled state is preferably 833 mm to 1600 mm, and more preferably 1000 mm to 1400 mm.

[0061] If the twist pitch P of the optical fiber ribbon 3 in the optical fiber unit 5 in a cabled state is too small, the lateral pressure of the optical fiber ribbon 3 tends to increase. Here, the inventors have found that if the lateral pressure of the optical fiber ribbon 3 increases, it can cause an increase in PMD, even if the effect on an increase in transmission loss is small. In other words, if the twist pitch P of the optical fiber ribbon 3 in the optical fiber unit 5 in a cabled state becomes small, it can cause an increase in PMD. On the other hand, if the twist pitch P of the optical fiber ribbon 3 in the optical fiber unit 5 in a cabled state is too large, loss increases, especially during heat cycles.

[0062] The twisting pitch of the optical fiber ribbon 3 is preferably 500 mm or more. There is no particular upper limit to the twisting pitch of the optical fiber ribbon 3, and the optical fiber ribbon 3 may not be twisted at all (i.e., the twisting pitch P1 of the optical fiber ribbon 3 = infinity). Even when the optical fiber unit 5 is formed by assembling a plurality of optical fiber ribbons 3 without twisting them together, the twisting pitch P of the optical fiber ribbon 3 in the optical fiber unit 5 in the axial direction of the cable in a cabled state is preferably 833 mm to 1600 mm. That is, in this case, P = P2, and the twisting pitch P2 of the optical fiber unit 5 may be set to 833 mm to 1600 mm.

[0063] When a plurality of optical fiber ribbons 3 are twisted together, it is desirable that the twisting pitch P1 be shorter than the twisting pitch P2 of the plurality of optical fiber units 5.

[0064] As described above, according to this embodiment, by twisting the optical fiber ribbon 3 and the optical fiber unit 5 in opposite directions, it is possible to appropriately set the twist pitch P of the optical fiber ribbon 3 in the optical fiber unit 5 with respect to the axial direction of the cable in a cabled state without excessively shortening the twist pitch of the optical fiber ribbon 3. Furthermore, since the optical fiber units 5 can be twisted without twisting back, no device for twisting back is required when twisting the optical fiber units 5, and loosening of the twist of the optical fiber ribbon 3 when twisting the optical fiber units 5 can be more reliably suppressed.

[0065] In this case, by setting the twist pitch P of the optical fiber ribbon 3 within the optical fiber unit 5 in the axial direction of the cable in a cabled state within a predetermined range, it is possible to suppress an increase in PMD while also suppressing an increase in transmission loss. [Example]

[0066] Several optical fiber cables were created and evaluated for loss increase, etc. The optical fiber cables had a structure roughly as shown in Figure 1. First, eight 250um diameter ITU-T G.657.A1 compliant optical fibers were intermittently bonded to create an intermittently bonded eight-fiber optical fiber ribbon. Ten of these optical fiber ribbons were assembled to form an 80-fiber optical fiber unit wrapped with a 2mm wide plastic ribbon, and five optical fiber ribbons were assembled to form a 40-fiber optical fiber unit wrapped with a 2mm wide plastic ribbon.

[0067] Twelve 80-core optical fiber units and one 40-core optical fiber unit were supplied, twisted together without twisting, and then absorbent nonwoven fabric was attached vertically. The pieces were rolled up in a forming jig and then wrapped with nylon holding thread to create a 1,000-core core.

[0068] The optical fiber cable was created by sheathing the core thus created, a tension member using a 1.6 mm diameter steel wire, and a rip cord for ripping the jacket into a cylindrical shape with jacket material. The jacket material was LLDPE.

[0069] Various prototypes were created by varying the twisting and twisting pitch of the optical fiber ribbon, and the twisting direction and twisting pitch of the optical fiber unit, and various properties were confirmed. The results are shown in Tables 1 and 2.

[0070] [Table 1]

[0071] [Table 2]

[0072] In the table, "Tape fiber twist direction" and "Tape fiber twist pitch" refer to the twist direction and twist pitch of the optical fiber ribbon, while "Unit twist direction" and "Unit twist pitch" refer to the twist direction and twist pitch of the optical fiber unit. Note that the right and left twist directions indicate relative orientations, and when the "Tape fiber twist direction" is "right" and the "Unit twist direction" is "left," the fibers are twisted in opposite directions. Note that both the optical fiber ribbon and the optical fiber unit were twisted without twisting. When the "Tape fiber twist direction" is "none," the fibers are assembled without being twisted.

[0073] The "twisting direction of the ribbon fiber in the cable state" and "twisting pitch of the ribbon fiber in the cable state" in the table represent the direction and pitch of the change in the circumferential position of the optical fiber fiber within the optical fiber unit in the cable state, and the twisting pitch P of the ribbon fiber in the cable state is calculated using Equation 1 (however, if the ribbon fiber is not twisted, P1 = infinity).

[0074] PMD was measured using the Jones matrix method with a 1km cable wound on a drum with a body diameter of 1400mm. A maximum measured value of 0.15 (ps / √km) or more was marked "×", a value of 0.10 (ps / √km) or more but less than 0.15 ps / √km was marked "○", and a value less than 0.10 (ps / √km) was marked "◎".

[0075] The increase in loss during heat cycles was measured by placing a 1 km cable wound on a drum with a diameter of 1400 mm in a thermostatic chamber, varying the temperature of the chamber between -30°C and 70°C, and measuring the difference at a wavelength of 1550 nm with an OTDR. A maximum measured value of 0.15 dB / km or greater was marked "x", a value between 0.10 dB / km and less than 0.15 dB / km was marked "o", and a value less than 0.10 dB / km was marked "◎".

[0076] The results showed that by setting the twist pitch of the ribbon fiber within the optical fiber unit to 833mm to 1600mm, it was possible to suppress loss fluctuations during heat cycles while also reducing PMD. In particular, this effect was further enhanced by setting the twist pitch of the ribbon fiber within the optical fiber unit to 1000mm to 1400mm. In this case, by reversing the twist direction of the ribbon fiber within the unit and the twist direction between the units, it was possible to appropriately set the twist pitch of each individual fiber and also adjust the twist pitch of the ribbon fiber within the unit to the desired value. This made it easier to maintain a uniform twist when twisting the units together and also increased the design freedom of the twist pitch.

[0077] On the other hand, in Comparative Examples 1 and 3, the twist pitch of the ribbon fiber in the optical fiber unit was small, so the PMD was "×". In addition, in Comparative Examples 2 and 4, the twist pitch of the ribbon fiber in the optical fiber unit was large, so the increase in loss due to heat cycles was "×".

[0078] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical scope of the present invention is not limited to the above-described embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the technical ideas described in the claims, and it is understood that these modifications and alterations also fall within the technical scope of the present invention.

[0079] For example, if the optical fiber cable is on the slotless side, it does not have to have the cross-sectional shape shown in FIG. [Explanation of symbols]

[0080] 1....Optical fiber cable 2a, 2b, 2c, 2d....Optical fiber 3, 3a, 3b, 3c, 3d....Optical fiber ribbon 4... Core 5, 5a, 5b, 5c, 5d....Optical fiber unit 6……Adhesive part 7. Press down 9...Tension member 11...Tear cord 13……Outer cover 15...Bobbin 100....Optical fiber cable 101: Optical fiber unit 103: Optical fiber ribbon

Claims

1. a core formed by twisting together a plurality of optical fiber units without twisting back; an outer covering provided on the outer periphery of the core; a tension member disposed on the outer periphery of the core; Equipped with The optical fiber unit is formed by twisting together a plurality of optical fiber cores, the twisting direction of the plurality of optical fiber cores is opposite to the twisting direction of the optical fiber unit; The twist pitch of the optical fiber core is P １ and the twist pitch of the optical fiber unit is P ２ When I said, The twist pitch P of the optical fiber core wires in the optical fiber unit in the axial direction of the cable in a cabled state is P=1 / (|(1 / P １ -1 / P ２ )|) is 833 mm to 1600 mm.

2. a core formed by twisting together a plurality of optical fiber units without twisting back; an outer covering provided on the outer periphery of the core; a tension member disposed on the outer periphery of the core; Equipped with The optical fiber unit is formed by assembling a plurality of optical fiber cores without twisting them together, An optical fiber cable characterized in that the twist pitch P of the optical fiber core wires in the optical fiber unit in the axial direction of the cable in a cabled state is 850 mm to 1600 mm.

3. 3. The optical fiber cable according to claim 1, wherein the twist pitch P of the optical fiber core wires within the optical fiber unit in the axial direction of the cable in a cabled state is 1000 mm to 1400 mm.

4. An optical fiber cable as described in any one of claims 1 to 3, characterized in that the optical fiber core is an intermittently bonded optical fiber ribbon core in which multiple optical fibers are intermittently bonded in the longitudinal direction, and in the optical fiber unit, adjacent optical fibers are bent in the parallel direction in at least some of the non-bonded portions of the optical fiber core.

Images