Optical cable and method for manufacturing the same

Abstract

[Solution] An optical cable according to the present disclosure comprises a plurality of optical fiber units each having a fiber bundle formed from a plurality of optical fibers. The plurality of optical fiber units are twisted together in an SZ shape by inverting a twisting direction of the optical fiber units. The present invention is characterized in that the twisted angle at which the optical fiber units are twisted in a circumferential direction at a section between an inversion part and the next inversion part of the twisting direction is not less than 540 degrees.

Description

[Technical field]

[0001] The present invention relates to an optical cable and a method for manufacturing an optical cable. This application claims priority based on Japanese Patent Application No. 2021-124564, filed in Japan on July 29, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] In order to suppress the difference in optical fiber length when the optical cable is bent, it is known to construct an optical cable by twisting together a plurality of optical fiber units each of which is a bundle of optical fibers. Patent Document 1 describes twisting together a plurality of optical fiber units in an SZ shape (or in one direction). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-159078 A Summary of the Invention [Problem to be solved by the invention]

[0004] To reduce the allowable bending radius of an optical cable, it is desirable to twist the optical fiber units at a short pitch. However, if the optical fiber units are twisted in an SZ shape at a short pitch, the twist is likely to be untwisted (the twist is likely to return) at the part where the twisting direction is reversed, and as a result, the optical fiber may become aligned along the longitudinal direction of the optical cable near the reversed part. If the proportion of the optical fiber parts aligned along the longitudinal direction (straight parts) increases, the transmission loss may increase when the optical cable is bent.

[0005] An object of the present invention is to reduce transmission loss in an optical cable. [Means for solving the problem]

[0006] The main invention for achieving the above-mentioned object is an optical cable comprising a plurality of optical fiber units each having a fiber bundle composed of a plurality of optical fibers, the optical fiber units being twisted together in an SZ shape by reversing the twisting direction, and the twisting angle at which the optical fiber units are twisted circumferentially from one reversal point of the twisting direction to the next reversal point is 540 degrees or more.

[0007] Other features of the present invention will become apparent from the following specification and drawings. Effect of the Invention

[0008] According to the present invention, the transmission loss in an optical cable can be suppressed. [Brief description of the drawings]

[0009] [Figure 1] Fig. 1A is an explanatory diagram of an optical cable 1. Fig. 1B is an explanatory diagram of an optical fiber unit 10. [Diagram 2] FIG. 13 is an explanatory diagram of another optical cable. [Diagram 3] FIG. 3 is an explanatory diagram of a manufacturing system 40 for the optical cable 1. As shown in FIG. [Figure 4] 4A to 4C are explanatory diagrams of how to twist a plurality of optical fiber units 10. FIG. [Diagram 5] FIG. 5 is a comparison table of the first embodiment. [Figure 6] FIG. 6 is a comparison table of the second embodiment. [Figure 7] FIG. 7 is a comparison table of the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] At least the following aspects will become apparent from the following description and drawings.

[0011] A first aspect is an optical cable including a plurality of optical fiber units each having a fiber bundle composed of a plurality of optical fibers, the optical fiber units being twisted together in an SZ shape by reversing the twisting direction, and the twisting angle at which the optical fiber units are twisted in the circumferential direction from one reversal part of the twisting direction to the next reversal part is 540 degrees or more. With such an optical cable, transmission loss can be suppressed.

[0012] A second aspect of the present invention is the optical cable of the first aspect, characterized in that the twist angle is 1800 degrees or less. A third aspect is the optical cable of the second aspect, characterized in that the twist angle is 1440 degrees or less, thereby making it possible to suppress transmission loss.

[0013] A fourth aspect is the optical cable according to any one of the first to third aspects, characterized in that the optical fiber unit includes a bundling material that bundles the optical fibers. This makes it possible to bundle the optical fibers with the bundling material.

[0014] A fifth aspect is the optical cable of the fourth aspect, characterized in that the optical fiber unit is composed of an intermittently connected optical fiber ribbon, which makes it easier to bundle a plurality of optical fibers that constitute the optical fiber unit.

[0015] A sixth aspect is the optical cable according to any one of the first to fifth aspects, characterized in that the twist angle in the S direction and the twist angle in the Z direction are substantially equal.

[0016] === Implementation form === <Configuration of Optical Cable 1> Fig. 1A is an explanatory diagram of an optical cable 1. Fig. 1B is an explanatory diagram of an optical fiber unit 10.

[0017] The optical cable 1 is a cable that houses an optical fiber 11. The optical cable 1 of this embodiment is an optical cable that does not have a slot rod in which a slot (a groove that houses the optical fiber 11) is formed, and is a so-called slotless optical cable. The optical cable 1 has a plurality of optical fiber units 10 and an outer jacket 20.

[0018] The optical fiber unit 10 is a structure in which a plurality of optical fibers 11 are bundled together. The optical fiber unit 10 shown in the drawing includes a fiber bundle and a bundle material 12.

[0019] The fiber bundle is a bundle of a plurality of optical fibers 11. In this embodiment, the fiber bundle is configured by bundling a plurality of intermittently connected optical fiber tapes. In the intermittently connected optical fiber tape, a plurality of optical fibers 11 are intermittently connected by a connection portion, and the optical fibers 11 are not constrained to each other at a portion other than the connection portion (separation portion). For this reason, by configuring the optical fiber unit 10 using the intermittently connected optical fiber tape, it becomes easy to bundle a plurality of optical fibers 11. However, the fiber bundle does not have to be configured by a plurality of intermittently connected optical fiber tapes, and may be configured by, for example, one intermittently connected optical fiber tape or may be configured by a plurality of single-core optical fibers. The plurality of optical fibers 11 configuring the optical fiber unit 10 may be twisted or not twisted.

[0020] The bundle material 12 is a member that bundles a plurality of optical fibers 11 that constitute a fiber bundle. The bundle material 12 is, for example, a string-like member. The bundle material 12 is wound around the outer circumference of the fiber bundle. The optical fiber unit 10 in the figure has a pair of bundle materials 12, and each bundle material 12 is wound around the outer circumference of the fiber bundle in an SZ shape so that the winding direction is opposite at the joint point. However, the bundle material 12 is not limited to being wound in an SZ shape, and may be wound in a spiral shape in one direction around the outer circumference of the fiber bundle. In addition, the number of bundle materials 12 is not limited to two. In addition, the optical fiber unit 10 may not include the bundle material 12. For example, when the optical fiber unit 10 is composed of one intermittently connected optical fiber tape, the bundle of optical fibers 11 does not fall apart, so the optical fiber unit 10 may not include the bundle material 12. In addition, the fiber unit 12 may be configured by covering the fiber bundle with a bundle material such as a tube or a film.

[0021] In this embodiment, the optical cable 1 has a plurality of optical fiber units 10. In Fig. 1A and Fig. 1B, the optical fiber units 10 are depicted extending linearly in the longitudinal direction, but in this embodiment, as described later, the plurality of optical fiber units 10 are twisted together in an SZ shape. Therefore, each optical fiber unit 10 is twisted at a predetermined twist angle around an axis along the longitudinal direction of the optical cable 1. The method of twisting the plurality of optical fiber units 10 will be described later.

[0022] 1A, a plurality of optical fiber units 10 are housed in an outer jacket 20 while being wrapped in a pressure winding tape 15. However, the optical cable 1 does not necessarily have to include the pressure winding tape 15.

[0023] The jacket 20 is a member that covers the multiple optical fiber units 10 (and the pressure winding tape 15). Here, the outer shape of the jacket 20 has a cross section that is approximately circular, but the outer shape of the jacket 20 is not limited to a circular shape. A tension member 21 is embedded in the jacket 20. In addition to the tension member 21, other members (e.g., a rip cord 22) may be embedded in the jacket 20. Furthermore, a member other than the multiple optical fiber units 10 and the pressure winding tape 15 may be housed inside the jacket 20.

[0024] The shape of the optical cable is not limited to that shown in Fig. 1. Fig. 2 is an explanatory diagram of another optical cable 1. The optical cable 1 shown in FIG. 2 is a flat optical cable (square optical cable) with a substantially rectangular cross section. This optical cable 1 also has a plurality of optical fiber units 10 and an outer jacket 20. Each optical fiber unit 10 is composed of, for example, one intermittently connected optical fiber tape. Since the optical fiber unit 10 is composed of one optical fiber tape, the optical fiber unit 10 of the optical cable 1 shown in FIG. 2 does not include a bundle material 12. A plurality of (for example, six) optical fiber units 10 are twisted together in an SZ shape and are housed in the outer jacket 20 in a state wrapped with a pressure winding tape 15. In addition, an inclusion 17 for filling the space is housed inside the pressure winding tape 15. However, the optical cable 1 does not need to include the pressure winding tape 15 or the inclusion 17. A method of twisting a plurality of optical fiber units 10 will be described later. 2, a notch 20A is provided in the jacket 20. The notch 20A is a groove along the longitudinal direction. By making an incision in the notch 20A of the jacket 20 with a splitting tool, the jacket 20 can be split and the optical fiber unit 10 can be taken out. However, the optical cable 1 does not necessarily have to have the notch 20A. 2, a pair of tension members are embedded in the jacket 20, and a separator 23 is also embedded therein. The separator 23 is a sheet-like member, and is disposed directly below the notch 20A. The optical fiber units 10 are housed in the jacket 20 while being sandwiched between the pair of separators 23. The separator 23 has a function of protecting the optical fiber 11 from the blade of a splitting tool, and a function of facilitating the operation of removing the optical fiber 11 from inside the jacket 20. However, the optical cable 1 does not necessarily have to have the separator 23. The shape and configuration of the optical cable are not limited to those shown in Figure 1 and Figure 2. The optical cable of this embodiment may include a plurality of optical fiber units 10 twisted together in an SZ shape.

[0025] <Method of manufacturing optical cable 1> Fig. 3 is an explanatory diagram of a manufacturing system 40 for the optical cable 1. The manufacturing system 40 in the figure is a system that manufactures the optical cable 1 shown in Fig. 1. However, the manufacturing system may manufacture the optical cable 1 shown in Fig. 2, or may manufacture optical cables of other shapes and configurations. The manufacturing system 40 has a supply unit 42, a twisting unit (not shown) having a batten 44, an extrusion molding unit 46, and a control unit 48.

[0026] The supply unit 42 is a device (supply source) that supplies the optical fiber units 10. The supply unit 42 is configured, for example, with a bobbin that supplies a plurality of optical fiber tapes, and a bundling device that winds the bundle material 12 around the outer circumference of a fiber bundle composed of a plurality of optical fiber tapes. However, the supply unit 42 may be equipped with a tape manufacturing device that manufactures optical fiber tapes, or a fiber manufacturing device that manufactures the optical fibers 11, instead of a bobbin that supplies the optical fiber tape. Furthermore, the supply unit 42 does not have to be equipped with a bundling device that winds the bundle material 12 around the fiber bundle. The supply unit 42 supplies the optical fiber units 10 to the mesh plate 44. The speed at which the supply unit 42 supplies the optical fiber units 10 can be adjusted by the control unit 48.

[0027] The twisting section is a device for twisting together a plurality of optical fiber units 10, and includes a mesh plate 44 and a drive section for rotating (swinging) the mesh plate 44. The mesh plate 44 is a member for twisting together a plurality of optical fiber units 10, and is a plate-like member having a plurality of insertion holes. An optical fiber unit 10 is inserted into each of the insertion holes of the mesh plate 44. The mesh plate 44 swings about a central rotation axis, so that the plurality of optical fiber units 10 are twisted together in an SZ shape. The plurality of optical fiber units 10 that have passed through the mesh plate 44 are supplied to the extrusion molding section 46 in an SZ-twisted state. The rotation speed of the mesh plate 44 and the timing of reversing the swing can be adjusted by a control section 48. In addition, since the rotation angle of the mesh plate 44 and the twist angle of the optical fiber unit 10 (the angle at which the optical fiber unit is twisted in the circumferential direction; described later) do not match (because the twist of the optical fiber unit 10 loosens), the rotation angle of the mesh plate 44 is set to be larger than the twist angle of the optical fiber unit 10. For example, to set the twist angle of the optical fiber unit 10 to 540 degrees, the mesh plate 44 is swung at a rotation angle larger than 540 degrees. The rotation angle (swing angle) of the mesh plate 44 corresponding to the twist angle of the optical fiber unit 10 is appropriately determined in consideration of other manufacturing conditions such as the time and distance until a member (loosening prevention member) for preventing loosening of the twist of the multiple optical fiber units 10 is applied. In this embodiment, the loosening prevention member is the outer jacket 20. However, the loosening prevention member is not limited to the outer jacket 20. For example, before the jacket 20 is extrusion-molded, a string- or tape-shaped anti-slack member may be wound around the optical fiber units 10 to prevent the twisting of the optical fiber units 10 from becoming loose.

[0028] The extrusion molding unit 46 is a device that forms the jacket 20. The extrusion molding unit 46 manufactures the optical cable 1 by extruding a resin that will become the jacket 20 around the outer periphery of the multiple optical fiber units 10. Not only the multiple optical fiber units 10 twisted together in an SZ shape, but also the pressure winding tape 15 and tension member 21 are supplied to the extrusion molding unit 46. The optical cable 1 manufactured by the extrusion molding unit 46 is cooled by a cooling device and then wound up on a winding unit (e.g., a drum).

[0029] The control unit 48 is a device that controls the manufacturing system 40. The control unit 48 is configured, for example, by a computer, and controls the operations of the supply unit 42, the mesh plate 44, and the extrusion molding unit 46. Here, the control unit 48 controls the supply unit 42 to control the supply speed of the optical fiber units 10, and controls a drive unit (not shown) of the mesh plate 44 to control the rotation operation of the mesh plate 44 (such as the rotation speed and the timing of reversing the oscillation).

[0030] <About twisting of the optical fiber unit 10> 4A to 4C are explanatory diagrams of how to twist a plurality of optical fiber units 10. In the drawings, an assembly (core) in which a plurality of optical fiber units 10 are twisted together is depicted. The core in which a plurality of optical fiber units 10 are twisted together is housed inside the jacket 20 of the optical cable 1. Note that in these drawings, the optical fibers 11 constituting the optical fiber unit 10 are not individually depicted, and only the outer shape of the optical fiber unit 10 is conceptually depicted.

[0031] In the figure, a plurality of optical fiber units 10 twisted together in an SZ shape are shown. The reversal portion in the figure indicates a position where the twisting direction (twisting direction) of the plurality of optical fiber units 10 is reversed. At the reversal portion, the twisting direction is reversed so that the plurality of optical fiber units 10 twisted in the S direction (or Z direction) are twisted in the Z direction (or S direction). Also, the pitch P in the figure indicates the interval between the reversal portions. The pitch P is the interval between a certain reversal portion and its adjacent reversal portion. In detail, the pitch P is the interval between the reversal portion where the plurality of optical fiber units 10 twisted in the S direction (or Z direction) are reversed in the Z direction (or S direction) and the reversal portion where the plurality of optical fiber units 10 twisted in the Z direction (or S direction) are reversed in the S direction (or Z direction). Here, the plurality of optical fiber units 10 are twisted together in an SZ shape so that the twisting angle in the S direction and the twisting angle in the Z direction are approximately equal. The twist angle is the angle at which the optical fiber unit 10 is twisted in the circumferential direction (the direction around the axis of the optical cable 1; S direction or Z direction) between one inverted portion and the next inverted portion inside the optical cable 1. The twist angle in the S direction and the twist angle in the Z direction of the optical fiber unit 10 may be different, but by making the twist angle in the S direction and the twist angle in the Z direction approximately equal, twisting of the optical cable 1 can be suppressed.

[0032] When the optical fiber unit 10 is twisted in an SZ shape, there is a risk that the optical fibers 11 near the inverted portion will become aligned along the longitudinal direction of the optical cable 1 due to untwisting at the inverted portion. In the figure, the portion (area) where the optical fibers 11 can become aligned along the longitudinal direction due to untwisting at the inverted portion is shown as a "straight portion."

[0033] As shown in Fig. 4A, by twisting a plurality of optical fiber units 10 in a spiral shape, it is possible to suppress the difference in line length of the optical fibers 11 when the optical cable 1 is bent. If the plurality of optical fiber units 10 are twisted in a spiral shape in one direction, the manufacturing system 40 may have a complex configuration, and the task of removing the optical fiber units 10 may become difficult when branching the optical cable 1 at its midpoint. For this reason, as shown in Fig. 4A, the twisting direction is reversed midway to twist a plurality of optical fiber units 10 in an SZ shape.

[0034] Fig. 4B is an explanatory diagram of the case where the optical fiber units 10 are twisted at a shorter pitch than that in Fig. 4A. To reduce the allowable bending radius of the optical cable 1, it is desirable to shorten the pitch P. In other words, to reduce the allowable bending radius of the optical cable 1, it is desirable to increase the twist angle per unit length of the optical fiber unit 10 (=N / P). In other words, to reduce the allowable bending radius of the optical cable 1, the twisting method shown in Fig. 4B is more desirable than the twisting method shown in Fig. 4A.

[0035] On the other hand, when the pitch P is shortened without changing the twist angle N, the twist angle (=N / P) per unit length of the optical fiber unit 10 becomes large. Therefore, when the optical fiber unit 10 is twisted in an SZ shape with a short pitch, the twist is easily unwound at the twist direction reversal part (the twist is easily returned). As a result, the optical fiber 11 is more likely to be in a state along the longitudinal direction of the optical cable 1 near the reversal part, and a straight part is more likely to be formed near the reversal part. If the proportion of the optical fiber part along the longitudinal direction (straight part) increases, the transmission loss may increase when the optical cable 1 is bent. Note that, as shown in the embodiment described later, when the optical fiber unit 10 is twisted in an SZ shape with a short pitch, the twist is easily unwound at the twist direction reversal part (the twist is easily returned), and as a result, the optical fiber unit 10 may not be able to maintain the SZ twisted state.

[0036] Fig. 4C is an explanatory diagram of a case where the twist angle is set larger than that of Fig. 4B. For the sake of explanation, the twist angle (=N / P) per unit length of the optical fiber unit 10 shown in Fig. 4C is set to be the same as the twist angle per unit length of the optical fiber unit 10 shown in Fig. 4B.

[0037] In the twisting method shown in FIG. 4C, the twisting angle (=N / P) per unit length of the optical fiber unit 10 is the same as that shown in FIG. 4B, so that the twisting is easily unwound at the inverted portion in the twisting direction (the twisting is easily restored), and as a result, the possibility of a straight portion being formed near the inverted portion increases. However, in the twisting method shown in FIG. 4C, the twisting angle is set larger than that in FIG. 4B, and as a result, the inversion pitch P shown in FIG. 4C is longer than the inversion pitch shown in FIG. 4B. As a result, in the twisting method shown in FIG. 4C, the number of inverted portions relative to the entire length of the optical cable 1 in the longitudinal direction can be reduced compared to the twisting method shown in FIG. 4B, and the ratio of the portion that can become a straight portion can be reduced. Therefore, in the twisting method shown in FIG. 4C, the transmission loss when the optical cable 1 is bent can be reduced compared to the twisting method shown in FIG. 4B (the bending characteristics described later can be improved).

[0038] Therefore, while the twist angle of the optical fiber unit 10 is usually about 270 degrees (N=270), in this embodiment, the twist angle of the optical fiber unit 10 is set to 540 degrees or more.

[0039] First Example Fig. 5 is a comparison table of Example 1. The twisting methods shown in Fig. 4A, Fig. 4B, and Fig. 4C correspond to the twisting methods of Comparative Example 1A, Comparative Example 1B, and Example 1A in the table, respectively.

[0040] As a first embodiment, an optical cable 1 having the structure shown in Fig. 1A was created. Here, one optical fiber unit 10 was composed of six intermittently connected 12-core optical fiber ribbons, and the six optical fiber units 10 were twisted in an SZ shape to create a 432-core optical cable having 36 intermittently connected optical fiber ribbons. The outer diameter of the optical cable 1 was about 11 mm, and the storage area inside the jacket 20 was about 60 mm 2 Thus, multiple types of optical cables 1 were produced with different twist angles N and pitches P. Note that the twist angle N in the table indicates the angle at which the optical fiber units 10 are twisted in the circumferential direction (the direction around the axis of the optical cable 1) from one inverted portion to the next inverted portion inside the optical cable 1 (the twist angle N in the table is not the rotation angle of the mesh plate 44 when manufacturing the optical cable 1).

[0041] The ribbon state, twisted state, core wire pull-out force, transmission loss, and bending characteristics of each of the multiple types of optical cables 1 thus produced were evaluated. To evaluate the ribbon condition, the presence or absence of damage to the joints of the intermittently connected optical fiber ribbons (the parts that intermittently connect two adjacent optical fibers 11) was confirmed. If the joints were not damaged, they were rated as "Excellent" (◎), and if they were damaged, they were rated as "Failed" (×). To evaluate the twisting state, it was confirmed whether the optical fiber unit 10 was twisted at a specified twist angle. If the optical fiber unit 10 was twisted at the specified twist angle, it was evaluated as "Excellent" (◎), and if the optical fiber unit 10 was not twisted at the specified twist angle, it was evaluated as "Failed" (×). To evaluate the core wire pull-out force, the tension (core wire pull-out force) was measured when the optical fiber 11 (optical fiber core) of the optical fiber cable cut to 10 m was pulled out and the optical fiber 11 started to move on the side opposite the pulling end. If this core wire pull-out force was 25 N / 10 m or more, it was evaluated as "◎ (excellent)", if it was less than 25 N / 10 m and 15 N / 10 m or more, it was evaluated as "○ (good)", and if it was less than 15 N / 10 m or more, it was evaluated as "× (fail)". To evaluate the transmission loss, the transmission loss was measured at a wavelength of 1550 nm by the OTDR method for the drum-wound optical cable 1. If the transmission loss was 0.25 dB / km or less, it was marked as "◎ (excellent)", if the transmission loss was 0.30 dB / km or less (and greater than 0.25 dB / km), it was marked as "○ (good)", and if the transmission loss was greater than 0.30 dB / km, it was marked as "× (fail)". To evaluate the bending properties, a winding test based on IEC60794-1-21E11A / IEC60794-3-10 was performed to measure the transmission loss of optical cable 1. In the winding test, the mandrel diameter was set to 20 times the cable outer diameter, the number of winding turns was set to 4, and the number of cycles (the number of times the same test was repeated) was set to 3. If the increase in transmission loss after the winding test was 0.05 dB or less per optical fiber and the increase in transmission loss during the test was also 0.05 dB or less per optical fiber, it was evaluated as "◎ (excellent)". If the increase in transmission loss after the winding test was 0.05 dB or less per optical fiber, it was evaluated as "○ (good)". If the increase in transmission loss after the winding test was 0.05 dB or less per optical fiber, it was evaluated as "× (fail)". In addition, as an overall judgment, if all evaluation items were rated as "◎ (excellent)", the evaluation was marked as "◎ (excellent)", if none of the evaluation items included an "× (fail)", the evaluation was marked as "○ (good)", and if any of the evaluation items included an "× (fail)", the evaluation was marked as "× (poor)".

[0042] In Comparative Example 1A and Comparative Example 1B, the twist angle N was set to be the same, but in Comparative Example 1B, the pitch P was set to be shortened to half that of Comparative Example 1A. However, in Comparative Example 1B, since the twist angle per unit length (=N / P) was large, the twist came undone at the inverted portion, and as a result, the optical fiber unit 10 could not maintain the SZ twisted state (for this reason, the pull-out force, transmission loss, and bending characteristics could not be evaluated in Comparative Example 1B). On the other hand, in Example 1A, the twist angle (=N / P) per unit length is set to be the same as that of Comparative Example 1B. However, in Example 1A, since the pitch P is set longer than that of Comparative Example 1B, although a straight portion is formed near the inverted portion, it is possible to maintain the optical fiber unit 10 twisted in an SZ shape. In this way, even if the twist angle (=N / P) per unit length is large (even if the value of N / P is so large that the twist state is × (failed) when the twist angle N is 360 degrees), it was confirmed that the twist state is improved by setting the twist angle N large and the pitch P long. Note that, in Example 1B, as in Example 1A, the twist angle N is set larger and the pitch P is set longer than that of Comparative Example 1B, and it was confirmed that the twist state is improved.

[0043] Moreover, in Example 1A, the bending characteristics were improved compared to Comparative Example 1A. This is believed to be because, in Example 1A, the twist angle per unit length (=N / P) of the optical fiber unit 10 was larger compared to Comparative Example 1A, so that the transmission loss when the optical cable 1 was bent could be suppressed. Note that, similarly to Example 1A, in Example 1B, the bending characteristics were also improved compared to Comparative Example 1A. This is believed to be because, in Example 1B, the twist angle per unit length (=N / P) of the optical fiber unit 10 was larger compared to Comparative Example 1A, so that the transmission loss when the optical cable 1 was bent could be suppressed.

[0044] In Example 1C, the twist angle per unit length (=N / P) is set to be the same as that of Comparative Example 1A. On the other hand, in Example 1C, the twist angle is set to be larger and the pitch P is set to be longer than those of Comparative Example 1A. Such a relationship between Comparative Example 1A and Example 1C corresponds to the relationship between the twisting method of FIG. 4B and the twisting method shown in FIG. 4C. Therefore, in Example 1C, the ratio of the straight portion to the entire length of the optical cable 1 in the longitudinal direction can be reduced compared to Comparative Example 1A. Therefore, the reason why Example 1C has slightly improved core wire pull-out force and bending characteristics compared to Comparative Example 1A is considered to be because the ratio of the straight portion to the entire length of the optical cable 1 in the longitudinal direction can be reduced. Thus, it was confirmed that it is effective to set the twist angle N to be larger and the pitch P to be longer not only from the comparison between Comparative Example 1B and Example 1A but also from the comparison between Comparative Example 1A and Example 1C.

[0045] Second Example Fig. 6 is a comparison table of Example 2. Note that Comparative Example 1A, Example 1A, and Example 1B in Fig. 5 correspond to Comparative Example 2, Example 2F, and Example 2G in Fig. 6.

[0046] In the second embodiment, as in the first embodiment, an optical cable 1 having the structure shown in Fig. 1A was also produced. Specifically, one optical fiber unit 10 was composed of six intermittently connected 12-core optical fiber ribbons, and the six optical fiber units 10 were twisted in an SZ shape to produce a 432-core optical cable having 36 intermittently connected optical fiber ribbons. The outer diameter of the optical cable 1 was about 11 mm, and the storage area inside the jacket 20 was about 60 mm 2 A number of types of optical cables 1 were created with a twist angle N of 360 to 720 degrees, a pitch P of 800 mm, and different twist angles N in the range of 360 to 720 degrees. Note that the twist angle N in the table indicates the angle at which the optical fiber units 10 are twisted in the circumferential direction (direction around the axis of the optical cable 1) inside the optical cable 1 from one inverted portion to the next inverted portion.

[0047] As shown in Fig. 6, when the twist angle N was 540 degrees or more, the bending characteristics were improved compared to Comparative Example 2. This is probably because in Examples 2A to 2J, the twist angle per unit length of the optical fiber unit 10 (=N / P) was larger compared to Comparative Example 2, and therefore the transmission loss when the optical cable 1 was bent could be suppressed. For this reason, as shown in Fig. 6, it is desirable that the twist angle N of the optical fiber unit 10 is 540 degrees or more.

[0048] Furthermore, as shown in Fig. 6, when the twist angle N was 2160 degrees, breakage was observed in the connection portion of the intermittently connected optical fiber ribbon. The reason for the breakage in the connection portion is believed to be that the optical fiber ribbon was twisted too strongly. For this reason, it is desirable that the twist angle N of the optical fiber unit 10 is less than 2160 degrees. In other words, it is desirable that the twist angle N of the optical fiber unit 10 is 540 degrees or more and 1800 degrees or less.

[0049] Furthermore, as shown in Fig. 6, when the twist angle N was 1800 degrees or more, the transmission loss worsened. This is thought to be because the optical fiber ribbon was twisted strongly, which locally increased the packaging density of the optical fibers 11 and increased the microbend loss. For this reason, it is more preferable that the twist angle N of the optical fiber unit 10 is less than 1800 degrees. In other words, it is more preferable that the twist angle N of the optical fiber unit 10 is 540 degrees or more and 1440 degrees or less.

[0050] Third Example FIG. 7 is a comparison table of the third embodiment.

[0051] As a third embodiment, the optical cable shown in Fig. 2 was created. Here, one optical fiber unit 10 was composed of one intermittently connected four-core optical fiber ribbon, and six optical fiber units 10 were twisted in an SZ shape to create a 24-core optical cable equipped with six intermittently connected optical fiber ribbons. The flat optical cable had a minor diameter of 3.5 mm and a major diameter of 5.5 mm, and the storage area inside the jacket 20 was 2.5 mm. 2A number of types of optical cables were created with different twist angles N and pitches P. The twist angle N in the table indicates the angle at which the optical fiber units 10 are twisted in the circumferential direction (the direction around the axis of the optical cable) from one inverted portion to the next inverted portion inside the optical cable.

[0052] As shown in Fig. 7, when the twist angle N was 540 degrees or more, the bending characteristics were improved compared to Comparative Example 3. This is probably because, in Examples 3A to 3F, the twist angle per unit length of the optical fiber unit 10 (=N / P) was larger compared to Comparative Example 3, so that the transmission loss when the optical cable was bent could be suppressed. For this reason, as shown in Fig. 7, it is desirable that the twist angle N of the optical fiber unit 10 is 540 degrees or more.

[0053] Furthermore, as shown in Fig. 7, when the twist angle N was 2160 degrees, breakage was observed in the connection portion of the intermittently connected optical fiber ribbon. The reason for the breakage in the connection portion is believed to be that the optical fiber ribbon was twisted too strongly. For this reason, also in the third embodiment, it is desirable that the twist angle N of the optical fiber unit 10 is less than 2160 degrees. In other words, it is desirable that the twist angle N of the optical fiber unit 10 is 540 degrees or more and 1800 degrees or less.

[0054] Furthermore, as shown in Fig. 7, when the twist angle N was 1800 degrees or more, the transmission loss worsened. This is thought to be because the optical fiber ribbon was twisted strongly, which locally increased the packaging density of the optical fibers 11 and increased the microbend loss. For this reason, it is more preferable that the twist angle N of the optical fiber unit 10 is less than 1800 degrees. In other words, it is more preferable that the twist angle N of the optical fiber unit 10 is 540 degrees or more and 1440 degrees or less.

[0055] The housing area inside the outer cover 20 is 1.8 mm 2 , 2.0mm 2 Similarly, several types of flat optical cables were produced with different twist angles N and pitches P. The storage area inside the jacket 20 was set to 1.8 mm 2In the case of a flat optical cable having a diameter of 1.0 mm and a length of 2.0 mm, it was not possible to twist the optical fiber units 10 in an SZ pattern under any of the conditions. 2 For the flat optical cable having the above structure, the same results as those shown in Fig. 7 were obtained. Therefore, it was confirmed that under the conditions where a plurality of optical fiber units 10 can be twisted in an SZ shape, the twist angle N of the optical fiber units 10 is 540 degrees or more.

[0056] ===Other embodiments=== The above-described embodiments are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit of the present invention, and it goes without saying that the present invention includes equivalents thereof. In addition, the above-described embodiments may be appropriately combined. [Explanation of symbols]

[0057] 1 Optical cable, 10 Optical fiber unit, 11 Optical fiber, 12 Bundle material, 15 Presser tape, 17 Inclusions, 20 jacket, 20A notch, 21 tension member, 22 rip cord, 23 Separator, 40 Manufacturing System, 42 Supply Department, 44 batten, 46 extrusion molding section, 48 control section

Claims

1. A plurality of optical fiber units each having a fiber bundle made up of a plurality of optical fibers are provided, The optical fiber units are twisted together in an SZ shape by reversing the twisting direction, The twist angle at which the optical fiber unit is twisted in the circumferential direction between the twist direction reversal portion and the next twist direction reversal portion is 540 degrees or more and 1800 degrees or less. An optical cable characterized by:

2. The optical cable according to claim 1, The optical cable according to the present invention is characterized in that the twist angle is 1440 degrees or less.

3. An optical cable according to claim 1 or 2, The optical fiber unit comprises a bundling material for bundling the optical fibers.

4. An optical cable as claimed in claim 3, The optical cable is characterized in that the optical fiber unit is composed of an intermittently connected optical fiber ribbon.

5. An optical cable according to claim 1 or 2, An optical cable characterized in that the twist angle in the S direction and the twist angle in the Z direction are equal.

6. A method for producing an optical cable according to claim 1 or 2, comprising the steps of: A method for manufacturing an optical cable, characterized in that a member for winding the optical fiber units is not provided, and the optical fiber units are twisted together in an SZ shape by reversing the twisting direction.

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