Optical fiber unit, optical fiber cable, and method for manufacturing optical fiber unit

Abstract

This optical fiber unit comprises: a plurality of optical fiber core wires; an inner layer covering the plurality of optical fiber core wires; and an outer layer disposed further to the outside than the inner layer. The plurality of optical fiber core wires are integrated by being covered by the inner layer in a bundled state. The Young's modulus of the inner layer is lower than the Young's modulus of the outer layer, the Young's modulus of the outer layer is 100 MPa-1500 MPa inclusive, and the yield point stress of the outer layer is 10 MPa or more.

Description

Optical fiber unit, optical fiber cable, and method of manufacturing the optical fiber unit

[0001] This disclosure relates to an optical fiber unit, an optical fiber cable, and a method for manufacturing the optical fiber unit. This application claims priority to Japanese Application No. 2023-201235, filed November 29, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Document 1 discloses a single-fiber separate optical fiber unit in which a plurality of ultraviolet-curable resin-coated optical fibers are assembled and collectively coated with two layers of ultraviolet-curable resin. Patent Document 2 discloses an optical fiber unit having an optical fiber ribbon including a plurality of optical fibers and a ribbon resin that integrates the plurality of optical fibers in a parallel state, and a coating resin that covers the optical fiber ribbon in an assembled form.

[0003] Japanese Patent Application Publication No. 05-107432 International Publication No. 2019 / 088256

[0004] An optical fiber unit according to one aspect for achieving the above object is an optical fiber unit comprising a plurality of optical fiber cores, an inner layer covering the plurality of optical fiber cores, and an outer layer arranged outside the inner layer, wherein the plurality of optical fiber cores are integrated by being covered by the inner layer in a bundled state, the Young's modulus of the inner layer is lower than the Young's modulus of the outer layer, the Young's modulus of the outer layer is 100 MPa or more and 1500 MPa or less, and the yield point stress of the outer layer is 10 MPa or more.

[0005] Fig. 1 is a cross-sectional view of an optical fiber unit according to this embodiment. Fig. 2 is a diagram illustrating an SS curve when the yield point is clear and the breaking stress is equal to or less than the yield point. Fig. 3 is a diagram illustrating an SS curve when the yield point is clear and the breaking stress is equal to or greater than the yield point. Fig. 4 is a diagram illustrating an SS curve when there is no clear yield point. Fig. 5 is a schematic diagram of a manufacturing apparatus for an optical fiber unit according to this embodiment. Fig. 6 is a flowchart illustrating a manufacturing method for an optical fiber unit according to this embodiment. Fig. 7 is a cross-sectional view of an optical fiber cable including six optical fiber units. Fig. 8 is a cross-sectional view of an optical fiber cable including 24 optical fiber units.

[0006] [Problem to be Solved by the Present Disclosure] In an optical fiber unit having a two-layer structure including an inner layer and an outer layer disposed outside the inner layer, both fiber extraction capability and lateral pressure resistance can be improved by making the inner layer soft and the outer layer hard. However, if the outer layer is thin, the optical fiber unit may lack rigidity and buckle when bent to a small diameter. To increase the rigidity of the optical fiber unit, for example, increasing the diameter of the outer layer or increasing the rigidity of the outer layer is conceivable. However, increasing the diameter of the outer layer reduces the core density of the optical fiber unit, and increasing the rigidity of the outer layer reduces fiber extraction capability. In other words, there is a trade-off between the diameter of the outer layer and the core density of the optical fiber unit, and there is also a trade-off between the rigidity of the outer layer and fiber extraction capability. For this reason, there is a demand for an optical fiber unit that has high fiber extraction capability and lateral pressure resistance while being less likely to buckle when bent to a small diameter.

[0007] [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide an optical fiber unit, an optical fiber cable, and a method for manufacturing an optical fiber unit that are less likely to buckle when bent to a small diameter while improving fiber extraction ability and lateral pressure resistance.

[0008] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be described. An optical fiber unit according to one aspect of the present disclosure is: (1) an optical fiber unit comprising: a plurality of optical fibers; an inner layer covering the plurality of optical fibers; and an outer layer disposed outside the inner layer; wherein the plurality of optical fibers are integrated by being covered by the inner layer in a bundled state; the Young's modulus of the inner layer is lower than that of the outer layer; the Young's modulus of the outer layer is 100 MPa or more and 1500 MPa or less; and the yield stress of the outer layer is 10 MPa or more. According to this configuration, the Young's modulus of the inner layer is lower than that of the outer layer, so the inner layer is relatively soft. On the other hand, the Young's modulus of the outer layer is 100 MPa or more and 1500 MPa or less, and the yield stress of the outer layer is 10 MPa or more, so the outer layer is relatively hard but is not prone to buckling. Therefore, the optical fiber unit according to the above configuration has high fiber extraction ease and lateral pressure resistance, and is not prone to buckling when bent to a small diameter.

[0009] (2) In the optical fiber unit described in (1) above, the optical fiber unit may have a circular outer shape in a cross-sectional view. This configuration simplifies the structure of the optical fiber unit.

[0010] (3) In the optical fiber unit according to (1) or (2), the optical fiber included in the coated optical fiber may be a multi-core fiber. With this configuration, the core density of the optical fiber unit can be increased.

[0011] (4) In the optical fiber unit according to any one of (1) to (3), the Young's modulus of the inner layer may be 10 MPa or more. With this configuration, since the Young's modulus of the inner layer is 10 MPa or more, it is possible to impart resistance to buckling to the optical fiber unit.

[0012] (5) In the optical fiber unit according to any one of (1) to (4), the outer layer may be a colored layer to which a pigment is added. This configuration can improve the distinguishability of the optical fiber unit.

[0013] An optical fiber cable according to one aspect of the present disclosure includes: (6) a plurality of the optical fiber units according to any one of (1) to (5) above; and a cable jacket covering the plurality of the optical fiber units. This configuration can achieve a structure that is less likely to buckle when bent to a small diameter while improving fiber extraction ease and lateral pressure resistance. Furthermore, this configuration can also prevent breakage of the optical fiber core when the plurality of cable units are covered with the cable jacket to form a cable.

[0014] (7) The optical fiber cable described in (6) above may further include a strength member disposed at the center of the optical fiber cable, and the plurality of optical fiber units may be disposed in an area formed between the strength member and the cable jacket. According to this configuration, the plurality of optical fiber units are disposed in an area formed between the strength member and the cable jacket. Therefore, such an optical fiber cable can be configured to include a relatively large number of optical fiber units while having a small outer diameter. In other words, the optical fiber cable according to the above configuration can increase the core density of the optical fiber cable while having a small outer diameter.

[0015] (8) The optical fiber cable described in (6) above may further include a strength member disposed at the center of the optical fiber cable, and a water-absorbing tape disposed between the strength member and the cable jacket, wherein the optical fiber units are disposed in each of a first region formed between the strength member and the water-absorbing tape and a second region formed between the cable jacket and the water-absorbing tape. With this configuration, since the optical fiber units are disposed in each of the first region and the second region, the core density of the optical fiber cable can be increased while maintaining a relatively small outer diameter.

[0016] (9) In the optical fiber cable according to any one of (6) to (8), the core density obtained by dividing the number of cores included in the coated optical fiber by the cross-sectional area of ​​the optical fiber cable is 10 cores / mm ２ According to this configuration, by using the optical fiber unit, it is possible to increase the core density of the optical fiber cable.

[0017] A method for manufacturing an optical fiber unit according to one aspect of the present disclosure includes: (10) a step of concentrating a plurality of optical fiber core wires; a step of passing the plurality of optical fiber core wires through a die; a step of covering the plurality of optical fiber core wires with a first resin composition and covering the first resin composition with a second resin composition while the plurality of optical fiber core wires are bundled in the die; and a step of forming an inner layer covering the plurality of optical fiber core wires by irradiating the first resin composition with ultraviolet light to harden the first resin composition, and forming an outer layer covering the inner layer by irradiating the second resin composition with ultraviolet light to harden the second resin composition, wherein the optical fiber unit comprises a plurality of the optical fiber core wires, the inner layer, and the outer layer, wherein the Young's modulus of the inner layer is lower than the Young's modulus of the outer layer, the Young's modulus of the outer layer is 100 MPa or more and 1500 MPa or less, and the yield point stress of the outer layer is 10 MPa or more. According to this configuration, the Young's modulus of the inner layer of the optical fiber unit manufactured by this optical fiber unit manufacturing method is lower than that of the outer layer, so the inner layer is relatively soft. On the other hand, the Young's modulus of the outer layer of the optical fiber unit is 100 MPa or more and 1500 MPa or less, and the yield point stress of the outer layer is 10 MPa or more, so the outer layer is relatively hard but is not prone to buckling. Therefore, the optical fiber unit manufactured by the optical fiber unit manufacturing method according to the above configuration has high fiber extraction ease and lateral pressure resistance, and is not prone to buckling when bent to a small diameter.

[0018] [Details of the embodiments of the present disclosure] Specific examples of an optical fiber unit, an optical fiber cable, and a method for manufacturing an optical fiber unit according to embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0019] (Optical fiber unit 10) The optical fiber unit 10 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view of the optical fiber unit 10 according to this embodiment. As illustrated in Fig. 1, the optical fiber unit 10 includes a plurality of optical fiber cores 11, an inner layer 12 that covers the plurality of optical fiber cores 11, and an outer layer 13 that is disposed outside the inner layer 12.

[0020] The outer diameter of the optical fiber 11 is 200 μm or less, and preferably less than 180 μm. The outer diameter of the optical fiber 11 is, for example, 160 μm. The optical fiber 11 includes an optical fiber 110 including four cores 111 and a cladding 112, and a protective coating 113 that covers the optical fiber 110. Therefore, the optical fiber 110 included in the optical fiber 11 is a multi-core fiber (MCF). The optical fiber 110 is, for example, a glass fiber in which the cores 111 and the cladding 112 are made of silica glass.

[0021] The core 111 has a circular cross section in the radial direction. The refractive index of the core 111 is higher than the refractive index of the cladding 112. The outer diameter of the core 111 is, for example, not less than 5 μm and not more than 10 μm.

[0022] The clad 112 is provided so as to integrally surround the four cores 111. The outer diameter of the clad 112 is larger than the outer diameter of the cores 111. The outer diameter of the clad 112 is, for example, not less than 80 μm and not more than 125 μm.

[0023] The protective coating 113 is formed from, for example, an acrylate resin, etc. The protective coating 113 is provided so as to cover the periphery of the clad 112 .

[0024] In this embodiment, the optical fiber unit 10 includes, for example, 12 optical fiber cores 11. The 12 optical fiber cores 11 are bundled together and integrated by being covered with an inner layer 12 having a circular outer shape in a cross-sectional view. Therefore, the outer shape of the optical fiber unit 10 in a cross-sectional view is circular. In this specification, "circular" includes not only a perfect circle but also an approximate circle. An approximate circle is, for example, an ellipse that is visually recognized as close to a perfect circle. The outer diameter of the optical fiber unit 10 is, for example, 0.8 mm. The coating structure of the optical fiber unit 10 is a two-layer structure consisting of an inner layer 12 and an outer layer 13.

[0025] The inner layer 12 covers the 12 optical fiber cores 11. The inner layer 12 is in contact with the 12 optical fiber cores 11. The inner layer 12 is, for example, a resin obtained by curing an ultraviolet-curable resin composition such as a urethane acrylate resin. A lubricant is added to the inner layer 12. The lubricant is made of, for example, silicone. The Young's modulus of the inner layer 12 is, for example, 10 MPa or more and 300 MPa or less. However, the upper limit of the Young's modulus of the inner layer 12 is not limited to this.

[0026] The outer layer 13 is disposed outside the inner layer 12. The outer layer 13 is, for example, a resin obtained by curing a UV-curable resin composition containing a monofunctional monomer, a polyfunctional monomer, a photopolymerization initiator, and an oligomer. However, the resin composition does not necessarily contain an oligomer. Examples of the monofunctional monomer include a monofunctional acrylate such as stearyl acrylate, and a monofunctional methacrylate such as tetrahydrofurfuryl methacrylate. Examples of the polyfunctional monomer include a bifunctional acrylate such as diethylene glycol diacrylate, a bifunctional methacrylate such as triethylene glycol dimethacrylate, a trifunctional acrylate such as trimethylolpropane triacrylate, a trifunctional methacrylate such as trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, ethoxylated (4) pentaerythritol tetraacrylate, and pentaacrylate esters. The resin composition forming the outer layer 13 contains a pigment of any color, so that the outer layer 13 is a colored layer to which a pigment is added.

[0027] The Young's modulus of the outer layer 13 is, for example, 100 MPa or more and 1500 MPa or less, preferably 100 MPa or more and 800 MPa or less. In this embodiment, the Young's modulus of the inner layer 12 is lower than that of the outer layer 13. The yield stress of the outer layer 13 is, for example, 10 MPa or more. The yield stress of the outer layer 13 is the magnitude of stress at which, when a load is applied to the outer layer 13, the elastic limit is exceeded and the amount of deformation of the outer layer 13 increases rapidly and no longer returns to its original state.

[0028] The yield stress of the outer layer 13 can be increased by increasing the proportion of polyfunctional monomers in the resin composition forming the outer layer 13. This is because increasing the proportion of polyfunctional monomers in the resin composition increases the Young's modulus, which in turn increases the yield stress. Specifically, for example, the yield stress can be increased by replacing a portion of the monofunctional monomers contained in the resin composition with bifunctional monomers. However, since the yield stress and the elongation at break are inversely proportional to each other, in this embodiment, the resin composition forming the outer layer 13 contains 20% by weight to 50% by weight of monofunctional monomers, 10% by weight to 40% by weight of polyfunctional monomers, approximately 3% by weight of photopolymerization initiator, and 7% by weight to 67% by weight of oligomer, assuming the entire resin composition as 100. This allows the yield stress of the outer layer 13 to be 10 MPa or more. Note that the above proportions are merely examples.

[0029] Here, a method for calculating the yield point in this embodiment will be described with reference to Figures 2 to 4. Figure 2 is a diagram illustrating an SS curve when the yield point is clear and the breaking stress is equal to or less than the yield point (pattern 1). The SS curve is a graph showing the relationship between stress and strain. Figure 3 is a diagram illustrating an SS curve when the yield point is clear and the breaking stress is equal to or greater than the yield point (pattern 2). Figure 4 is a diagram illustrating an SS curve when there is no clear yield point (pattern 3). SS curves related to the outer layer 13 can generally be classified into these three patterns, and therefore, in this specification, a method for calculating the yield point in the three patterns illustrated in Figures 2 to 4 will be described.

[0030] 2, the yield point is at point P1 and the breaking point is at point P2 in pattern 1. Therefore, the yield stress in pattern 1 is the stress at point P1, and the breaking stress is equal to or less than the yield point.

[0031] 3, the yield point is at point P3 and the breaking point is at point P4 in pattern 2. Therefore, the yield point stress in pattern 2 is the stress at point P3, and the breaking stress is equal to or greater than the yield point.

[0032] As illustrated in Figure 4, unlike patterns 1 and 2, pattern 3 does not have a clear yield point. Therefore, in this embodiment, the stress point for elongation at point P5, which is the intersection of line L1 obtained by linearly approximating the slope at the rising point and line L2 obtained by linearly approximating the slope near the breaking point, is set as a provisional yield point (provisional yield point) in this case. That is, in this embodiment, point P5 is the yield point in pattern 3. Therefore, the yield point stress in pattern 3 is the stress at point P5.

[0033] (Apparatus 1 for manufacturing optical fiber unit 10) Next, the apparatus 1 for manufacturing the optical fiber unit 10 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a schematic diagram of the apparatus 1 for manufacturing the optical fiber unit 10 according to this embodiment.

[0034] As illustrated in Fig. 5, the manufacturing apparatus 1 for the optical fiber unit 10 includes a supply device 100. The supply device 100 includes 12 bobbins 101 corresponding to the number of fibers in the optical fiber unit 10, 12 dancer rollers 102, and a first guide roller 103. An optical fiber 11 is wound around each of the bobbins 101. The optical fiber 11 is unwound from each of the bobbins 101, the tension of each optical fiber 11 is adjusted by the dancer rollers 102, and the optical fiber 11 is arranged on a single arrangement surface when passing through the first guide roller 103. The optical fiber 11 is further collected by an immediately above guide roller 104 and sent to the resin application device 200.

[0035] The resin application device 200 includes a point 210 and a die 220. The optical fiber 11 is inserted into the resin application device 200 and pulled with a predetermined tension. As a result, the inserted optical fiber 11 is guided by the point 210 into a desired arrangement and sent to the die 220. Note that in this embodiment, when the 12 optical fibers 11 are guided by the point 210, they are bundled so that the cross-sectional outer shape is nearly circular, unlike a commonly used tape-shaped optical fiber ribbon.

[0036] The die 220 includes a first portion 220A and a second portion 220B. The first portion 220A is positioned closer to the point 210 than the second portion 220B. Therefore, the 12 optical fibers 11 are first fed to the first portion 220A and then fed to the second portion 220B. The first portion 220A applies a first resin composition (a resin composition forming the inner layer 12) to the 12 optical fibers 11. The second portion 220B applies a second resin composition (a resin composition forming the outer layer 13) to the 12 optical fibers 11 so as to cover the first resin composition applied to the 12 optical fibers 11. The outlet holes of the first portion 220A and the second portion 220B are circular, and the resin composition is applied around the 12 optical fibers 11 so as to form a circular cross-sectional outline. The first resin composition is supplied from a first resin tank 230A. The second resin composition is supplied from a second resin tank 230B. The first resin tank 230A and the second resin tank 230B are, for example, pressurized resin tanks. The twelve optical fibers 11 covered with the first resin composition and the second resin composition are sent to an ultraviolet irradiation device 240.

[0037] In the ultraviolet irradiation device 240, ultraviolet rays are irradiated onto the first resin composition and the second resin composition. As a result, an inner layer 12 (see FIG. 1) covering the 12 optical fibers 11 is formed, and an outer layer 13 (see FIG. 1) covering the inner layer 12 is formed. The 12 optical fibers 11 are integrated by being covered by the inner layer 12 in a bundled state. In this way, an optical fiber unit 10 is formed, which includes the 12 optical fibers 11, the inner layer 12 covering the 48 optical fibers 11, and the outer layer 13 arranged outside the inner layer 12. The formed optical fiber unit 10 is sent to the marking device 250.

[0038] The marking device 250 is, for example, a dispenser, an inkjet printer, etc. A dispenser is a device that ejects liquid such as ink onto an object. The marking device 250 applies, for example, a band-shaped marking to the optical fiber unit 10.

[0039] The marked optical fiber unit 10 is sent to a winding device 310 having a second guide roller 260 and a bobbin. In the winding device 310, the optical fiber unit 10 is wound onto the bobbin after passing through a guide. In this manner, the optical fiber unit 10 is manufactured.

[0040] (Method for Manufacturing Optical Fiber Unit 10) Next, a method for manufacturing the optical fiber unit 10 will be described with reference to Fig. 5 and Fig. 6. As illustrated in Fig. 6, for example, 12 optical fibers 11 unwound from each bobbin 101 are collected by an upper guide roller 104 (STEP 01). The collected 12 optical fibers 11 are sent to a resin coating device 200.

[0041] The 12 optical fiber cores 11 sent to the resin applying device 200 are arranged in a desired arrangement at a point 210 and then passed through a die 220 (STEP 02).

[0042] The twelve optical fibers 11 passed through the die 220 are bundled in the die 220 so that the cross-sectional shape is nearly circular, and are then covered with the first resin composition, which is then covered with the second resin composition (STEP 03). The twelve optical fibers 11 covered with the first resin composition and the second resin composition are sent to the ultraviolet irradiation device 240.

[0043] The ultraviolet irradiation device 240 irradiates the first resin composition and the second resin composition with ultraviolet light, thereby forming an inner layer 12 that covers the twelve optical fibers 11, and forming an outer layer 13 that covers the inner layer 12 (STEP 04). As a result, the optical fiber unit 10 is formed.

[0044] According to the optical fiber unit 10 and the method for manufacturing the optical fiber unit 10 described above, the Young's modulus of the inner layer 12 is lower than that of the outer layer 13, and therefore the inner layer 12 is relatively soft. On the other hand, the Young's modulus of the outer layer 13 is 100 MPa or more and 1500 MPa or less, and the yield stress of the outer layer 13 is 10 MPa or more, and therefore the outer layer 13 is relatively hard but is not prone to buckling. Therefore, the optical fiber unit 10 has high fiber extraction properties and lateral pressure resistance, and is not prone to buckling when bent to a small diameter.

[0045] Furthermore, according to the optical fiber unit 10 as described above, the outer shape of the optical fiber unit 10 is circular in a cross-sectional view of the optical fiber unit 10. In this way, the structure of the optical fiber unit 10 can be simplified.

[0046] Furthermore, according to the optical fiber unit 10 described above, since the optical fiber 110 included in the optical fiber core 11 is a multi-core fiber, it is possible to increase the core density of the optical fiber unit 10. The core density of the optical fiber unit 10 refers to the number of cores per unit area of ​​the optical fiber unit 10.

[0047] Furthermore, in the optical fiber unit 10 as described above, the Young's modulus of the inner layer 12 is 10 MPa or more, so that the optical fiber unit 10 can be made less susceptible to buckling.

[0048] Furthermore, according to the optical fiber unit 10 as described above, since the outer layer 13 is a colored layer to which a pigment is added, the optical fiber unit 10 can be more easily distinguished.

[0049] (Experiments on Transmission Characteristics, Fiber Accessibility, and Small Radius Bending) The inventors conducted experiments on transmission characteristics, fiber accessibility, and small radius bending for the optical fiber units according to Experimental Examples 1 to 8 in Table 1. The evaluation index in the experiments on transmission characteristics was the average transmission loss of the optical fiber unit at a wavelength of 1.55 μm (the average value of the transmission losses of the multiple optical fibers included in the optical fiber unit) measured using an optical time domain reflectometer (OTDR) after winding 1000 m of the optical fiber unit around a bobbin. When the average transmission loss was 0.19 dB / km or less, the transmission characteristics were rated as good (rating A). When the average transmission loss was greater than 0.19 dB / km and less than 0.25 dB / km, the transmission characteristics were rated as fair (rating B). When the average transmission loss was 0.25 dB / km or more, the transmission characteristics were rated as poor (rating C). The evaluation index for the experiment on fiber take-out performance was the number of times a commercially available fiber separation tool (a simple tool with protrusions) was reciprocated through each optical fiber unit shown in Table 1 until the optical fiber inside the optical fiber unit could be manually removed. When the number of reciprocation was three or fewer, fiber take-out performance was rated good (rating A). When the number of reciprocation was four to six, fiber take-out performance was rated fair (rating B). When the number of reciprocation was seven or more, fiber take-out performance was rated poor (rating C). The evaluation index for the experiment on small-diameter bending was the minimum bending diameter at which kinking or buckling did not occur, as determined by observing whether kinking or buckling occurred in the outer layer when the optical fiber unit was wound around multiple mandrels of different diameters. When the minimum bending diameter was less than 40 mmφ, the evaluation on small-diameter bending was rated very good (rating S). When the minimum bending diameter was 40 mmφ or more but less than 60 mmφ, the evaluation on small-diameter bending was rated good (rating A). When the minimum bending diameter was 60 mm or more and less than 90 mm, the evaluation of small diameter bending was rated as somewhat good (rating B). When the minimum bending diameter was 90 mm or more, the evaluation of small diameter bending was rated as poor (rating C).

[0050] A comparison of Experimental Example 1 and Experimental Example 3 revealed that when the yield point stress of the outer layer 13 is 10 MPa, coating buckling is less likely to occur during small-diameter bending than when the yield point stress of the outer layer 13 is 7 MPa (i.e., less than 10 MPa). Furthermore, a comparison of Experimental Example 1 and Experimental Example 6 revealed that when the yield point stress of the outer layer 13 is a value exceeding 10 MPa (e.g., 20 MPa), coating buckling is less likely to occur during small-diameter bending than when the yield point stress of the outer layer 13 is 10 MPa. Therefore, it was found that the yield point stress of the outer layer 13 should be 10 MPa or more.

[0051] A comparison of Experimental Examples 1 and 5 revealed that a low Young's modulus of the outer layer 13 improves fiber extraction. On the other hand, the results of Experimental Example 2 also revealed that when the Young's modulus of the outer layer 13 is significantly low (e.g., less than 100 MPa), lateral pressure is easily transmitted to the optical fiber inside the optical fiber unit, resulting in a deterioration in transmission characteristics (i.e., low lateral pressure resistance). Furthermore, a comparison of Experimental Examples 1 and 8 revealed that when the Young's modulus of the outer layer 13 exceeds 1500 MPa (e.g., 1600 MPa), fiber extraction deteriorates and the fiber tends to buckle during small-diameter bending. Therefore, it was found that the Young's modulus of the outer layer 13 should preferably be in the range of 100 MPa to 1500 MPa.

[0052] Therefore, as in Experimental Examples 1 and 4 to 7, when the Young's modulus of the inner layer is lower than that of the outer layer, the Young's modulus of the outer layer is 100 MPa or more and 1500 MPa or less, and the yield point stress of the outer layer is 10 MPa or more, it was found that the core wire extraction ability and lateral pressure resistance are high, and buckling is less likely to occur when bent to a small diameter.

[0053] Furthermore, a comparison between Experimental Examples 1 and 4 revealed that when the Young's modulus of the inner layer 12 is 10 MPa or more, coating buckling is less likely to occur during small-diameter bending. A comparison between Experimental Examples 1 and 4 also revealed that when the Young's modulus of the inner layer 12 is low, coating buckling is more likely to occur during small-diameter bending, but cord extraction is improved. A comparison between Experimental Examples 1 and 7 also revealed that when the Young's modulus of the inner layer 12 is a value greater than 10 MPa (e.g., 30 MPa), coating buckling is less likely to occur during small-diameter bending than when the Young's modulus of the inner layer 12 is 10 MPa. Therefore, it was found that a Young's modulus of 10 MPa or more is preferable for the inner layer 12.

[0054] (Optical fiber cable 20 manufactured using optical fiber units 10) Next, with reference to Fig. 7, an optical fiber cable 20 manufactured using the optical fiber units 10 will be described. As illustrated in Fig. 7, the optical fiber cable 20 includes six optical fiber units 10, a tensile strength member 21, a water-absorbent fiber 22, a cable jacket 23, and a tear cord 24. Therefore, the optical fiber cable 20 is a 288-fiber optical fiber cable. The outer diameter of the optical fiber cable 20 is, for example, 3.6 mm. The cross-sectional area of ​​the optical fiber cable 20 is, for example, about 10 mm. ２ Therefore, the core density (number of cores per unit area) obtained by dividing the number of cores 111 included in the coated optical fiber 11 by the cross-sectional area of ​​the optical fiber cable 20 is, for example, about 29 cores / mm ２ is.

[0055] The optical fiber cable 20 is produced, for example, by arranging six optical fiber units 10 in a ring shape around the strength member 21, with the strength member 21 at the center, and extrusion coating the cable jacket 23 so as to cover the six optical fiber units 10. Therefore, the six optical fiber units 10 are arranged outside the strength member 21 and are covered by the cable jacket 23. In other words, the six optical fiber units 10 are arranged in a region R1 formed between the strength member 21 and the cable jacket 23.

[0056] The strength member 21 is made of, for example, fiber reinforced plastic (FRP). Examples of fiber reinforced plastic include glass fiber reinforced plastic (GFRP) and aramid fiber reinforced plastic (AFRP). The strength member 21 has a substantially circular shape in a cross-sectional view of the optical fiber cable 20. The outer diameter of the strength member 21 is, for example, 0.7 mm or more and 0.8 mm or less. The strength member 21 is located approximately in the center of the optical fiber cable 20 in a cross-sectional view of the optical fiber cable 20.

[0057] The water-absorbent fibers 22 are, for example, plastic fibers coated with water-absorbent powder, or fibers that have been given water-absorbency themselves. The water-absorbent fibers 22 are, for example, linear members with an outer diameter of about 0.1 mm in a dry state. The water-absorbent fibers 22 are arranged along the longitudinal direction of the optical fiber cable 20. The water-absorbent fibers 22 are arranged between the tensile strength members 21 and the cable jacket 23.

[0058] The cable jacket 23 is formed from, for example, polyethylene resin, flame-retardant polyethylene resin, or the like. The cable jacket 23 has a relatively high Young's modulus of, for example, 1500 MPa or more at 23°C. The cable jacket 23 also preferably has low shrinkage, low friction, and flame retardancy. Identification marks such as numbers and letters may be printed on the cable jacket 23 using a laser printer or the like.

[0059] The tear cord 24 is used to tear the cable jacket 23 and is embedded in the cable jacket 23 along the longitudinal direction of the optical fiber cable 20. In this embodiment, two tear cords 24 are provided. The two tear cords 24 are arranged in opposite positions relative to the tensile strength member 21 in a cross-sectional view of the optical fiber cable 20. By pulling out the tear cord 24, the cable jacket 23 is torn in the longitudinal direction of the optical fiber cable 20, and the optical fiber unit 10 can be removed. The tear cord 24 is made of, for example, a tensile-resistant plastic material (e.g., polyester) or the like.

[0060] The optical fiber cable 20 as described above is manufactured using the optical fiber units 10, and therefore can have a structure that is less likely to buckle when bent to a small diameter while improving the ease of fiber extraction and lateral pressure resistance. Furthermore, the optical fiber cable 20 as described above can also prevent breakage of the optical fiber cores 11 when the six optical fiber units 10 are covered with the cable jacket 23 to form a cable.

[0061] Furthermore, with the optical fiber cable 20 described above, six optical fiber units 10 are arranged in the region R1 formed between the tension members 21 and the cable jacket 23. Therefore, the optical fiber cable 20 can be configured to include a relatively large number of optical fiber units 10 while having a small outer diameter. In other words, with the optical fiber cable 20, the core density of the optical fiber cable 20 can be increased while having a small outer diameter.

[0062] Furthermore, according to the optical fiber cable 20 described above, the core density is 10 cores / mm ２ That is, the optical fiber cable 20 has a high core density.

[0063] (Optical fiber cable 20A manufactured using optical fiber unit 10) Next, with reference to Fig. 8, an optical fiber cable 20A manufactured using the optical fiber unit 10 will be described. However, in the description of the optical fiber cable 20A, the same components as those in the optical fiber cable 20 will be described using the same reference numerals, and descriptions of overlapping parts will be omitted as appropriate. As illustrated in Fig. 8, the optical fiber cable 20A includes 24 optical fiber units 10, a tensile strength member 21A, a cable jacket 23, a tear string 24, and a water-absorbing tape 25. Therefore, the optical fiber cable 20A is an optical fiber cable with 1152 fibers. The outer diameter of the optical fiber cable 20A is, for example, 6.0 mm. The cross-sectional area of ​​the optical fiber cable 20A is, for example, approximately 28 mm ２ Therefore, the core density (number of cores per unit area) obtained by dividing the number of cores 111 included in the coated optical fiber 11 by the cross-sectional area of ​​the optical fiber cable 20A is, for example, about 41 cores / mm ２ is.

[0064] The optical fiber cable 20A has a structure in which the optical fiber units 10 are housed in two layers. For example, the one-layer portion is produced by arranging eight optical fiber units 10 in a ring shape around the strength member 21A at the center and wrapping the water-absorbing tape 25 around the eight optical fiber units 10. The two-layer portion is produced by arranging the remaining 16 optical fiber units 10 in a ring shape to cover the water-absorbing tape 25 and extrusion-coating the cable jacket 23 to cover the 16 optical fiber units 10. Therefore, eight optical fiber units 10 are arranged in the first region R11 formed between the strength member 21A and the water-absorbing tape 25, and 16 optical fiber units 10 are arranged in the second region R12 formed between the cable jacket 23 and the water-absorbing tape 25.

[0065] The tension member 21A may have the same configuration as the tension member 21 of the optical fiber cable 20. However, the outer diameter of the tension member 21A is, for example, 1.2 mm or more and 1.3 mm or less. The tension member 21A is located approximately in the center of the optical fiber cable 20A in a cross-sectional view of the optical fiber cable 20A.

[0066] The water-absorbing tape 25 is disposed between the tension member 21A and the cable jacket 23. The water-absorbing tape 25 is wound, for example, vertically or horizontally, around the eight optical fiber units 10 arranged in the first region R11 formed between the tension member 21A and the water-absorbing tape 25. The water-absorbing tape 25 is formed by applying a water-absorbing powder to a base fabric made of polyester or the like, for example, to absorb water.

[0067] The optical fiber cable 20A as described above also provides the same effects as the optical fiber unit 10 and the optical fiber cable 20.

[0068] Furthermore, according to the optical fiber cable 20A described above, the optical fiber units 10 are arranged in each of the first region R11 and the second region R12, so that the core density of the optical fiber cable 20A can be increased while maintaining a relatively small outer diameter.

[0069] Although the present disclosure has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure. Furthermore, the number, position, shape, etc. of the components described above are not limited to the above embodiments, and can be changed to the number, position, shape, etc. that are suitable for implementing the present disclosure.

[0070] In the above embodiment, the optical fiber unit 10 includes twelve optical fiber cores 11, but the number of optical fiber cores 11 included in the optical fiber unit 10 may be two or more, and is not limited to twelve.

[0071] In the above embodiment, the optical fiber cable 20 includes six optical fiber units 10, and the optical fiber cable 20A includes 24 optical fiber units 10. However, the number of optical fiber units 10 included in the optical fiber cables 20 and 20A may be two or more, and is not limited to these.

[0072] In the above embodiment, the optical fiber cable 20 includes six optical fiber units 10, a strength member 21, a water-absorbent fiber 22, a cable jacket 23, and a tear string 24, but the present disclosure is not limited to this. The optical fiber cable 20 does not have to include, for example, the water-absorbent fiber 22 and the tear string 24. Furthermore, the optical fiber cable 20A includes 24 optical fiber units 10, a strength member 21A, a cable jacket 23, a tear string 24, and a water-absorbent tape 25, but the present disclosure is not limited to this. The optical fiber cable 20A does not have to include, for example, the tear string 24.

[0073] In the above embodiment, the optical fiber 11 has four cores 111, but the number of cores 111 included in the optical fiber 11 is not limited to four. The optical fiber 11 may also have one core 111. In other words, the optical fiber 110 included in the optical fiber 11 may be a single-core fiber.

[0074] In the above embodiment, a band-shaped marking is made on the optical fiber unit 10 by the marking device 250, but other markings may be made on the optical fiber unit 10. Also, no markings may be made on the optical fiber unit 10. Furthermore, the manufacturing apparatus 1 for the optical fiber unit 10 may not be equipped with the marking device 250.

[0075] In the above embodiment, the outer shape of the optical fiber unit 10 in a cross-sectional view is circular, but the outer shape of the optical fiber unit 10 in a cross-sectional view may be other shapes, such as rectangular. Also, the optical fiber unit 10 may be a normal tape-shaped optical fiber ribbon.

[0076] 1: Manufacturing equipment 10: Optical fiber unit 11: Optical fiber core 12: Inner layer 13: Outer layer 20, 20A: Optical fiber cable 21, 21A: Tensile strength member 22: Absorbent fiber 23: Cable jacket 24: Tear string 25: Absorbent tape 100: Supply device 101: Bobbin 102: Dancer roller 103: First guide roller 104: Directly above guide roller 110: Optical fiber 111: Core 112: Cladding 113: Protective coating 200: Resin application device 210: Point 220: Die 220A: First part 220B: Second part 230A: First resin tank 230B: Second resin tank 240: Ultraviolet irradiation device 250: Marking device 260: Second guide roller 310: Winding device L1: A line obtained by linearly approximating the slope at the rising point in pattern 3. L2: A line obtained by linearly approximating the slope near the breaking point in pattern 3. P1: Yield point in pattern 1. P2: Breaking point in pattern 1. P3: Yield point in pattern 2. P4: Breaking point in pattern 2. P5: Intersection of line L1 and line L2. R1: Region formed between the strength member and the cable jacket. R11: First region. R12: Second region.

Claims

1. An optical fiber unit comprising: a plurality of optical fiber cores; an inner layer covering the plurality of optical fiber cores; and an outer layer arranged outside the inner layer, wherein the plurality of optical fiber cores are integrated by being covered by the inner layer in a bundled state, the Young's modulus of the inner layer is lower than the Young's modulus of the outer layer, the Young's modulus of the outer layer is 100 MPa or more and 1500 MPa or less, and the yield point stress of the outer layer is 10 MPa or more.

2. The optical fiber unit according to claim 1, wherein the outer shape of said optical fiber unit is circular in a cross-sectional view.

3. The optical fiber unit according to claim 1 or 2, wherein the optical fiber included in the optical fiber core is a multi-core fiber.

4. An optical fiber unit according to any one of claims 1 to 3, wherein the Young's modulus of the inner layer is 10 MPa or more.

5. An optical fiber unit according to any one of claims 1 to 4, wherein the outer layer is a colored layer to which a pigment is added.

6. An optical fiber cable comprising: a plurality of optical fiber units according to any one of claims 1 to 5; and a cable jacket surrounding the plurality of optical fiber units.

7. The optical fiber cable according to claim 6, further comprising a strength member disposed at the center of said optical fiber cable, and a plurality of said optical fiber units are disposed in an area formed between said strength member and said cable jacket.

8. The optical fiber cable according to claim 6, further comprising a strength member disposed at the center of the optical fiber cable, and a water-absorbing tape disposed between the strength member and the cable jacket, the optical fiber unit being disposed in each of a first region formed between the strength member and the water-absorbing tape and a second region formed between the cable jacket and the water-absorbing tape.

9. The core density, calculated by dividing the number of cores contained in the optical fiber core by the cross-sectional area of ​​the optical fiber cable, is 10 cores / mm ２ The optical fiber cable according to any one of claims 6 to 8.

10. A method for manufacturing an optical fiber unit, comprising the steps of: collecting a plurality of optical fiber core wires; passing the plurality of optical fiber core wires through a die; covering the plurality of optical fiber core wires in a bundled state in the die with a first resin composition and covering the first resin composition with a second resin composition; irradiating the first resin composition with ultraviolet light to harden the first resin composition to form an inner layer covering the plurality of optical fiber core wires, and irradiating the second resin composition with ultraviolet light to harden the second resin composition to form an outer layer covering the inner layer, wherein the optical fiber unit comprises a plurality of the optical fiber core wires, the inner layer, and the outer layer, wherein the Young's modulus of the inner layer is lower than the Young's modulus of the outer layer, the Young's modulus of the outer layer is 100 MPa or more and 1500 MPa or less, and the yield point stress of the outer layer is 10 MPa or more.

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