Optical fiber colored core wire, optical fiber ribbon, aggregate cable of single core fibers, ribbon cable, and manufacturing method thereof

Abstract

The present invention provides a colored optical fiber core wire wherein a primary layer is easy to form. This colored optical fiber core wire (1) is provided with: a bare optical fiber (2); a primary layer (3) which is formed of an ultraviolet curable resin so as to cover the bare optical fiber (2); and a secondary layer (4) which is formed of an ultraviolet curable resin so as to cover the primary layer (3). The Young's modulus of the primary layer (3) is less than 70% with respect to the saturated Young's modulus of the primary layer (3); and the saturated Young's modulus of the primary layer (3) is 0.84 MPa or more.

Description

Technical Field

[0001] The present invention relates to an optical fiber colored core wire, an optical fiber ribbon, an aggregate cable of single-core fibers, a ribbon cable, and a manufacturing method thereof.

Background Art

[0002] In an optical fiber colored core wire, a technique is known in which each of a primary layer covering an optical fiber bare wire, a secondary layer covering the primary layer, and a colored layer covering the secondary layer is set to a desired Young's modulus by an ultraviolet-curable resin (Patent Documents 1 and 2). For example, the Young's modulus of the primary layer is set low, and the primary layer buffers the external force applied to the optical fiber bare wire, suppressing the optical transmission loss (microbend loss) due to minute deformation of the optical fiber bare wire. Further, the Young's modulus of the secondary layer is set higher than that of the primary layer, and the secondary layer protects the optical fiber bare wire and the primary layer from external forces.

[0003] Since it is desirable that the Young's modulus of the primary layer is low, the techniques described in Patent Documents 3 and 4 use an ultraviolet-curable resin having a low saturated Young's modulus for the primary layer and cure the primary layer with ultraviolet rays until the Young's modulus approaches the saturated Young's modulus.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, since an ultraviolet curable resin having a low saturated Young's modulus has a high viscosity, it is difficult to handle. Further, in the wire drawing process, when the ultraviolet curable resin is exposed to a high temperature, problems such as the curing reaction being suppressed and the Young's modulus becoming too low may occur.

[0006] The present invention has been made in view of the above-described problems, and an object thereof is to effectively suppress microbend loss while avoiding the problems associated with an ultraviolet curable resin having a low saturated Young's modulus.

Means for Solving the Problems

[0007] According to one aspect of the present invention, there is provided an optical fiber colored core wire including an optical fiber bare wire, a primary layer formed of an ultraviolet curable resin covering the optical fiber bare wire, and a secondary layer formed of an ultraviolet curable resin covering the primary layer, wherein a Young's modulus of the primary layer is less than 70% of a saturated Young's modulus of the primary layer, and the saturated Young's modulus of the primary layer is 0.84 MPa or more.

[0008] Further, according to another aspect of the present invention, there is provided a method for manufacturing an optical fiber colored core wire including a step of wire drawing an optical fiber bare wire from an optical fiber base material, a step of applying an ultraviolet curable resin around the optical fiber bare wire to form a primary layer, and a step of applying an ultraviolet curable resin around the primary layer and irradiating the ultraviolet curable resin with ultraviolet light to form a secondary layer, wherein after manufacturing the optical fiber colored core wire, a Young's modulus of the primary layer is less than 70% of a saturated Young's modulus of the primary layer, and the saturated Young's modulus of the primary layer is 0.84 MPa or more.

Effects of the Invention

[0009] According to the present invention, it is possible to effectively suppress microbend loss while avoiding problems associated with an ultraviolet curable resin having a low saturation Young's modulus.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. Elements having common functions throughout the drawings are denoted by the same reference numerals, and redundant descriptions may be omitted or simplified.

[0012] [First Embodiment] FIG. 1 is a cross-sectional view of an optical fiber colored core wire 1 according to the first embodiment. The optical fiber colored core wire 1 includes an optical fiber bare wire 2, a primary layer 3 coated on the outer periphery of the optical fiber bare wire 2, a secondary layer 4 coated on the outer periphery of the primary layer 3, and a colored layer 5 coated on the outer periphery of the secondary layer 4. The optical fiber bare wire 2 is coated with three coating layers of the primary layer 3, the secondary layer 4, and the colored layer 5.

[0013] The optical fiber bare wire 2 is formed of, for example, silica glass or the like and transmits light. The primary layer 3, the secondary layer 4, and the coloring layer 5 are each formed by curing an ultraviolet curable resin by irradiation with ultraviolet rays. The ultraviolet curable resin is not particularly limited as long as it can be polymerized by irradiation with ultraviolet rays. The ultraviolet curable resin is, for example, a resin that can be polymerized by photoradical polymerization or the like. The ultraviolet curable resin is, for example, a urethane (meth) acrylate such as a polyether-based urethane (meth) acrylate and a polyester-based urethane (meth) acrylate, an epoxy (meth) acrylate, a polyester (meth) acrylate, or the like, and is an ultraviolet curable resin having a polymerizable unsaturated group such as an ethylenically unsaturated group that polymerizes and cures with ultraviolet rays, and preferably has at least two polymerizable unsaturated groups. Examples of the polymerizable unsaturated group in the ultraviolet curable resin include groups having an unsaturated double bond such as a vinyl group, an allyl group, an acryloyl group, and a methacryloyl group, and groups having an unsaturated triple bond such as a propargyl group. Among these, an acryloyl group and a methacryloyl group are preferable in terms of polymerizability. The ultraviolet curable resin can be a monomer, oligomer, or polymer that starts polymerization and cures by irradiation with ultraviolet rays, but is preferably an oligomer. Note that an oligomer is a polymer having a degree of polymerization of 2 to 100. In addition, in the present specification, “(meth) acrylate” means one or both of acrylate and methacrylate.

[0014] The polyether-based urethane (meth) acrylate is a compound having a polyether segment, a (meth) acrylate, and a urethane bond, such as a reaction product of a polyol having a polyether skeleton, an organic polyisocyanate compound, and a hydroxyalkyl (meth) acrylate. The polyester-based urethane (meth) acrylate is a compound having a polyester segment, a (meth) acrylate, and a urethane bond, such as a reaction product of a polyol having a polyester skeleton, an organic polyisocyanate compound, and a hydroxyalkyl (meth) acrylate.

[0015] Furthermore, in addition to the oligomer and the photoinitiator, the ultraviolet curable resin may contain, for example, a diluent monomer, a photosensitizer, a chain transfer agent, and various additives. As the diluent monomer, a monofunctional (meth)acrylate or a polyfunctional (meth)acrylate is used. Here, the diluent monomer means a monomer for diluting the ultraviolet curable resin.

[0016] The primary layer 3 is a soft layer having a Young's modulus of 0.1 MPa or more and 5 MPa or less, and has a function of buffering an external force applied to the bare optical fiber 2. When the maximum Young's modulus that the resin can exhibit is defined as the "saturation Young's modulus", the primary layer 3 preferably has a Young's modulus of less than 70% with respect to the saturation Young's modulus, and the saturation Young's modulus of the primary layer 3 is preferably 0.84 MPa or more. The secondary layer 4 is a hard layer preferably having a Young's modulus of 500 MPa or more, and has a function of protecting the bare optical fiber 2 and the primary layer 3 from an external force. The coloring layer 5 is colored to identify the optical fiber colored core 1.

[0017] The optical fiber colored core 1 is not limited to the configuration shown in FIG. 1. For example, the bare optical fiber 2 may be coated with four or more layers. Further, instead of the optical fiber colored core 1, it may take the form of an optical fiber having no coloring layer 5. Furthermore, instead of coating the secondary layer 4 with the coloring layer 5, the secondary layer 4 may be colored.

[0018] The diameter of the bare optical fiber 2 is 80 μm or more and 150 μm or less, and may preferably be 124 μm or more and 126 μm or less. The thickness of the primary layer 3 can be 5 μm or more and 60 μm or less. The thickness of the secondary layer 4 can be 5 μm or more and 60 μm or less. Also, the thickness of the coloring layer 5 can be about several μm.

[0019] FIG. 2 is a schematic diagram of a manufacturing apparatus 10 used for a method of manufacturing an optical fiber colored core wire 1 according to the first embodiment. The manufacturing apparatus 10 includes a heating device 20, a primary layer coating device 30, a secondary layer coating device 40, a colored layer coating device 50, guide rollers 60, 61, 62, a bobbin 70, and a winding device 71. The manufacturing apparatus 10 is an apparatus for manufacturing the optical fiber colored core wire 1 from an optical fiber preform 6. The optical fiber preform 6 is made of, for example, quartz-based glass and is manufactured by a well-known method such as the VAD method, the OVD method, or the MCVD method. The heating device 20 has a heater 21. The heater 21 can be any heat source such as a tape heater, a ribbon heater, a rubber heater, an oven heater, a ceramic heater, or a halogen heater. The end of the optical fiber preform 6 is heated and melted by the heater 21 disposed around the optical fiber preform 6, and is drawn to pull out an optical fiber bare wire 2.

[0020] Below the heating device 20, a primary layer coating device 30 is provided. The primary layer coating device 30 includes a resin coating device 31 and an ultraviolet irradiation device 32. The resin coating device 31 holds a coating material (also referred to as a primary layer material) for the primary layer 3. The optical fiber bare wire 2 drawn from the optical fiber preform 6 is coated with the primary layer material by the resin coating device 31. Below the resin coating device 31, an ultraviolet irradiation device 32 is provided. The ultraviolet irradiation device 32 includes any ultraviolet light source such as a metal halide lamp, a mercury lamp, or a UV-LED. The optical fiber bare wire 2 is coated with the primary layer material by the resin coating device 31, and the optical fiber bare wire 2 enters the ultraviolet irradiation device 32 and is irradiated with ultraviolet light. As a result, the primary layer material mainly composed of an ultraviolet curable resin is cured, and the primary layer 3 is formed.

[0021] Below the primary layer coating device 30, a secondary layer coating device 40 is provided. The secondary layer coating device 40 includes a resin coating device 41 and an ultraviolet irradiation device 42. The resin coating device 41 holds a coating material for the secondary layer 4 (also referred to as the secondary layer material). The secondary layer material is applied to the primary layer 3 by the resin coating device 41. Below the resin coating device 41, an ultraviolet irradiation device 42 is provided. The ultraviolet irradiation device 42 can have the same configuration as the ultraviolet irradiation device 32. The optical fiber bare wire 2 enters the ultraviolet irradiation device 42, and the secondary layer material is irradiated with ultraviolet light. As a result, the secondary layer material mainly composed of an ultraviolet curable resin is cured, and the secondary layer 4 is formed. After the primary layer 3 and the secondary layer 4 are formed, the optical fiber bare wire 2 is guided to a guide roller 60 provided below the secondary layer coating device 40 and wound around a bobbin 70. Note that after the formation of the primary layer 3 and the secondary layer 4, the optical fiber bare wire 2 coated with the primary layer 3 and the secondary layer 4 is wound around a bobbin once, and then the coloring layer 5 is formed again.

[0022] Note that the resin coating device 31 may be configured to hold the primary layer material and the secondary layer material separately. In this case, the resin coating device 31 applies the primary layer material to the optical fiber bare wire 2, and then applies the secondary layer material on top of the primary layer material. The ultraviolet irradiation device 32 irradiates the primary layer material and the secondary layer material applied to the optical fiber bare wire 2 with ultraviolet light, and the primary layer 3 and the secondary layer 4 are formed. In this case, the manufacturing device 10 does not necessarily need to have the secondary layer coating device 40.

[0023] The optical fiber bare wire 2 wound around the bobbin 70 is guided by the guide roller 61 and enters the coloring layer coating device 50. The coloring layer coating device 50 includes a resin coating device 51 and an ultraviolet irradiation device 52. The resin coating device 51 holds the coating material (also referred to as the coloring layer material) of the coloring layer 5. The optical fiber bare wire 2 coated with the primary layer 3 and the secondary layer 4 has the coloring layer material applied thereto by the resin coating device 51. Below the resin coating device 51, an ultraviolet irradiation device 52 is provided. The ultraviolet irradiation device 52 can be configured in the same manner as the ultraviolet irradiation devices 32 and 42. The optical fiber bare wire 2 with the coloring layer material applied to the outer periphery of the secondary layer 4 enters the ultraviolet irradiation device 52, and the optical fiber bare wire 2 is irradiated with ultraviolet rays. As a result, the coloring layer material mainly composed of an ultraviolet curable resin is cured to form the coloring layer 5. The primary layer 3, the secondary layer 4, and the coloring layer 5 are coated on the optical fiber bare wire 2 to form the optical fiber colored core wire 1. The optical fiber colored core wire 1 is guided by a guide roller 62 provided below the coloring layer coating device 50 and wound around a winding device 71.

[0024] Figure 3 is a flowchart of a method for manufacturing the optical fiber colored core wire 1 according to the first embodiment. First, the user installs the optical fiber base material 6 in the manufacturing apparatus 10 (step S101). Next, the heater 21 provided in the heating device 20 heats the optical fiber base material 6 and starts drawing the optical fiber bare wire 2 (step S102).

[0025] The primary layer coating device 30 applies a primary layer material containing an ultraviolet curable resin around the drawn optical fiber bare wire 2, irradiates the primary layer material with ultraviolet rays, and forms the primary layer 3 (step S103). Next, the secondary layer coating device 40 applies a secondary layer material containing an ultraviolet curable resin around the primary layer 3, irradiates the secondary layer material with ultraviolet rays, and forms the secondary layer 4 (step S104). Subsequently, the colored layer coating device 50 applies a colored layer material containing an ultraviolet curable resin around the secondary layer 4, irradiates the colored layer material with ultraviolet rays, and forms the colored layer 5 (step S105). Thus, the optical fiber colored core wire 1 is obtained. Note that it is not always necessary to irradiate ultraviolet rays in the step of forming the primary layer (step S103). In this case, the primary layer 3 can be cured by the irradiation of ultraviolet rays in the step of forming the secondary layer 4 (step S104).

[0026] In the manufacturing process of the optical fiber colored core wire 1, the irradiation of ultraviolet rays is performed in the step of forming the primary layer 3 (step S103), the step of forming the secondary layer 4 (step S104), and the step of forming the colored layer 5 (step S105). Therefore, after the primary layer 3 is formed, ultraviolet rays are also irradiated onto the primary layer 3 during the formation of the secondary layer 4 and the colored layer 5, and the primary layer 3 can be cured. More specifically, the ultraviolet rays transmitted through the secondary layer 4 and the colored layer 5 can be absorbed by the primary layer 3, and the curing of the primary layer 3 can further proceed. If the ultraviolet curable resin is cured too much, the Young's modulus of the primary layer 3 increases, and it may become difficult for the primary layer 3 to sufficiently buffer the external force applied to the optical fiber bare wire 2. As a result, microbend loss may occur.

[0027] In this embodiment, while reducing the Young's modulus of the primary layer 3 with respect to the saturated Young's modulus, the curing of the primary layer 3 is suppressed, and microbend loss is effectively avoided. Hereinafter, a method for suppressing the curing of the primary layer 3 will be described. The primary layer 3 is cured by the polymerization of the ultraviolet-curable resin contained in the primary layer material. In addition, a part of the low-molecular-weight components contained in the primary layer material volatilizes under high-temperature conditions, for example, after the wire drawing step (step S102). By irradiating the primary layer material with ultraviolet rays while the primary layer material is at a high temperature, the polymerization and volatilization of the primary layer material proceed simultaneously. When the polymerization and volatilization of the primary layer material proceed simultaneously, the polymerization of the primary layer material is suppressed. That is, by irradiating the primary layer material with ultraviolet rays under the condition that the primary layer material is at a high temperature, the progress of the curing of the primary layer 3 can be suppressed, and the Young's modulus of the primary layer 3 can be kept low. At this time, due to the volatilization of the primary layer material, the composition of the primary layer material changes, and the curing of the primary layer 3 is suppressed. In other words, the composition of the primary layer 3 has changed so that the progress of curing is suppressed. That is, even when additional ultraviolet rays are irradiated on the optical fiber colored core 1, the curing of the primary layer 3 can be suppressed. Note that methods for raising the temperature of the primary layer material include, for example, shortening the period from the end of the wire drawing step (step S102) to the start of the step of coating the primary layer 3 (step S103). In this case, since the primary layer material is applied around the relatively high-temperature optical fiber bare wire 2, the primary layer material can be irradiated with ultraviolet rays while the primary layer material is at a high temperature.

[0028] The method for suppressing the progress of the curing of the primary layer 3 is not limited to the method of raising the temperature of the primary layer material. Other methods include, for example, a method of adjusting the amount of additives contained in the primary layer material, a method of adjusting the amount of light of the irradiated ultraviolet rays, and the like. By arbitrarily selecting or combining these methods, appropriate settings can be made so that the primary layer 3 having the required Young's modulus can be obtained.

[0029] In this embodiment, the UV-curable resin used for the primary layer material preferably has a saturated Young's modulus of 0.84 MPa or more. The viscosity of a UV-curable resin having a high saturated Young's modulus is lower than that of a UV-curable resin having a low saturated Young's modulus. This makes it easier to apply the primary layer material uniformly, for example, to the outer periphery of the bare optical fiber 2, facilitating the formation of the primary layer.

[0030] [Second embodiment] The optical fiber ribbon, the manufacturing apparatus and the manufacturing method of the optical fiber ribbon according to the second embodiment of the present invention will be described. The same components as those of the colored optical fiber 1, the manufacturing apparatus 10 and the manufacturing method of the colored optical fiber 1 according to the first embodiment are given the same reference numerals, and the description will be omitted or simplified.

[0031] In this embodiment, an optical fiber ribbon constituted by the colored optical fiber 1 according to the first embodiment will be described as an example of a cable to which the colored optical fiber 1 according to the first embodiment is applied. Note that the application example of the colored optical fiber according to the first embodiment is not limited to the form of an optical fiber ribbon, and may be, for example, a form of a single-fiber aggregate cable in which the colored optical fiber is housed in a sheath.

[0032] FIG. 4 is a cross-sectional view of an optical fiber ribbon 100 according to the second embodiment. The optical fiber ribbon 100 is configured by bundling a plurality of colored optical fiber core wires 1 in a band shape via an adhesive layer 101. The adhesive layer 101 is formed by irradiating a coating material containing an ultraviolet-curable resin with ultraviolet light to cure it. The ultraviolet-curable resin forming the adhesive layer 101 is configured of the same resin as the ultraviolet-curable resin forming the primary layer 3, the secondary layer 4, and the colored layer 5. The colored optical fiber core wires 1 can be bundled at a high density by taking the form of the optical fiber ribbon 100. Note that the optical fiber ribbon 100 is not limited to the configuration shown in FIG. 4. In addition, the optical fiber ribbon 100 may take the form of a ribbon cable in which the optical fiber ribbon 100 is housed in a sheath, or may take an intermittent adhesion structure in which the colored optical fiber core wires 1 are intermittently adhered in the longitudinal direction.

[0033] FIG. 5 is a schematic diagram of a ribbonizing apparatus 80 used in a method for manufacturing an optical fiber ribbon 100 according to the second embodiment. The ribbonizing apparatus 80 holds a coating material (also referred to as an adhesive layer material) for the adhesive layer 101. The ribbonizing apparatus 80 is also provided with an ultraviolet light source similar to the ultraviolet light sources provided in the ultraviolet irradiation devices 32, 42, and 52. A plurality of prepared optical fiber colored cores 1 enter the ribbonizing apparatus 80 and are coated with the adhesive layer material. The optical fiber colored cores 1 coated with the adhesive layer material are bundled together with a plurality of other optical fiber colored cores 1 coated with the adhesive layer material. The bundled plurality of optical fiber colored cores 1 are irradiated with ultraviolet light by the ultraviolet light source provided in the ribbonizing apparatus 80. As a result, the adhesive layer material mainly composed of an ultraviolet curable resin is cured to form the adhesive layer 101. A plurality of optical fiber colored cores 1 arranged in parallel are connected via the adhesive layer 101. In this way, the optical fiber ribbon 100 is formed from the optical fiber colored cores 1.

[0034] FIG. 6 is a flowchart of a method for manufacturing an optical fiber ribbon 100 according to the second embodiment. Steps S101 to S105 are the same as those in the first embodiment. In the flowchart of FIG. 6, in addition to the flowchart of the first embodiment, a ribbonizing process of the optical fiber colored cores 1 is performed. That is, after the coloring layer 5 is formed in step S105, the ribbonizing apparatus 80 applies an ultraviolet curable resin to a plurality of prepared optical fiber colored cores 1 and irradiates the ultraviolet curable resin with ultraviolet light to connect the plurality of optical fiber colored cores 1 (step S106). Thereby, the optical fiber ribbon 100 is manufactured.

[0035] In the process of manufacturing the optical fiber ribbon 100 from the optical fiber colored core wire 1, the optical fiber colored core wire 1 is irradiated with ultraviolet rays. Further, even when the optical fiber colored core wire 1 is irradiated with additional ultraviolet rays after production, the curing of the primary layer 3 can be suppressed. Therefore, even in the ribbonizing process of the optical fiber colored core wire, the curing of the primary layer 3 due to ultraviolet irradiation can be suppressed. Accordingly, an optical fiber ribbon 100 can be obtained in which an increase in microbend loss in the ribbonizing process is suppressed.

Example

[0036] Hereinafter, the results of experiments on the optical fiber colored core wire and the optical fiber ribbon according to the embodiments of the present invention will be described.

[0037]

Table 1

[0038] Table 1 shows the evaluation of the Young's modulus of the primary layer and the microbend loss in the examples and comparative examples of the optical fiber colored core wire or the optical fiber ribbon. That is, Table 1 shows the saturated Young's modulus (MPa), Young's modulus (MPa), Young's modulus / saturated Young's modulus (%), Young's modulus after additional UV irradiation (MPa), Young's modulus / saturated Young's modulus after additional UV irradiation (%), change in Young's modulus / saturated Young's modulus (%), and evaluation of microbend loss in Examples 1 to 9 and Comparative Examples 1 and 2.

[0039] The "saturated Young's modulus" in Table 1 is the Young's modulus when a UV-curable resin forming the primary layer 3 is formed into a film and irradiated with ultraviolet rays using a mercury lamp, UV-LED, etc. at room temperature to be completely cured. The "Young's modulus" in Table 1 is the ISM (In Situ Modulus) of the primary layer 3 of the optical fiber colored core wire 1. In this specification, ISM is defined as measured by the following method.

[0040] First, using a commercially available stripper, after stripping the primary layer 3 and the secondary layer 4 in the middle part of the optical fiber serving as a sample for a length of several millimeters, a load F is applied to the other end of the optical fiber on which the coating layer is formed. In this state, the displacement δ of the primary layer 3 at the boundary between the part where the coating layer has been stripped and the part where the coating layer is formed is read with a microscope. Then, by setting the load F to 10, 20, 30, 50, and 70 gf (i.e., 98, 196, 294, 490, and 686 mN in sequence), a graph of the displacement δ with respect to the load F is created. Then, the primary elastic modulus is calculated using the slope obtained from the graph and the following formula (1). Since the calculated primary elastic modulus corresponds to the so-called ISM, it will be hereinafter referred to as P-ISM as appropriate. P-ISM = (3F / δ) * (1 / 2πl) * ln(DP / DG) ···(Formula 1)

[0041] Here, the unit of P-ISM is [MPa]. Also, F / δ is the slope shown by the graph of the displacement (δ) [μm] with respect to the load (F) [gf], l is the sample length (for example, 10 mm), and DP / DG is the ratio of the outer diameter (DP) [μm] of the primary layer 3 to the outer diameter (DG) [μm] of the cladding part of the optical fiber. Therefore, when calculating P-ISM using the above formula from the used F, δ, and l, it is necessary to perform a predetermined unit conversion. Note that the outer diameter of the primary layer 3 and the outer diameter of the cladding part can be measured by observing the cross-section of the optical fiber cut by a fiber cutter with a microscope.

[0042] The "Young's modulus after additional UV irradiation" in Table 1 is the ISM of the primary layer 3 when the optical fiber colored core wire 1 after production is additionally irradiated with ultraviolet rays at 1000 mW / cm2 and 500 mJ / cm2 using a D bulb. Also, the "change amount of Young's modulus / saturated Young's modulus" represents the ratio of the change amount of the Young's modulus before and after additional ultraviolet irradiation to the saturated Young's modulus. The "change amount of Young's modulus" is the value of the change amount from the "Young's modulus" to the "Young's modulus after additional UV irradiation".

[0043] "Evaluation 1" in Table 1 indicates whether the microbend loss in the optical fiber colored core wire 1 before additional ultraviolet irradiation meets the standard (0.15 dB / km or less). "Evaluation 2" indicates whether the microbend loss in the optical fiber colored core wire 1 after additional ultraviolet irradiation meets the standard (0.15 dB / km or less). When the microbend loss meets the standard, Evaluations 1 and 2 are judged to be good (OK), and when the microbend loss does not meet the standard, Evaluations 1 and 2 are judged to be bad (NG).

[0044] Various methods for measuring microbend loss can be considered. In this specification, the transmission loss of the optical fiber to be measured in state A, where an optical fiber with a length of 400 m or more is wound around a relatively large bobbin wrapped with #1000 sandpaper with a tension of 100 gf so that the optical fibers do not overlap each other in a single layer, and the transmission loss of the optical fiber in state B, where the same bobbin as in state A is wound with the same tension and the same length without the sandpaper, are defined as the value of the microbend loss. Here, the transmission loss of the optical fiber in state B does not include the microbend loss and is considered to be the transmission loss inherent to the optical fiber itself.

[0045] This measurement method is similar to the fixed-diameter drum method specified in JIS C6823:2010. Also, this measurement method is also called the sandpaper method. Also, in this measurement method, since the transmission loss is measured at a wavelength of 1550 nm, the following microbend loss is also the value at a wavelength of 1550 nm.

[0046] Note that the effective core area (effective core area) can be cited as an index indicating the susceptibility of the optical fiber to microbend loss. The effective core area is shown by the following formula (2). (Effective core area) = (πk / 4) * (MFD) 2 ···(Formula 2) Here, the effective core cross-sectional area is the value at a wavelength of 1550 nm, the MFD is the mode field diameter (μm), and k is a constant. The effective core cross-sectional area represents the area of the cross-section orthogonal to the axis of the optical fiber bare wire 2 through which light having a predetermined intensity passes. Generally, the larger the effective core cross-sectional area of the optical fiber bare wire 2, the weaker the optical confinement in the cross-section of the optical fiber bare wire 2. That is, when the effective core cross-sectional area of the optical fiber bare wire 2 is large, the light in the optical fiber bare wire 2 is likely to leak due to an external force applied to the optical fiber bare wire 2. For this reason, when the effective core cross-sectional area of the optical fiber bare wire 2 increases, microbend loss of the optical fiber colored core wire 1 is likely to occur.

[0047] Here, the optical fiber colored core wire 1 according to the embodiment of the present invention has a primary layer 3 that can effectively buffer an external force applied to the optical fiber colored core wire 1. Therefore, by sufficiently buffering the external force applied to the optical fiber colored core wire 1 by the primary layer 3, the external force applied to the optical fiber bare wire 2 can be sufficiently reduced. Thereby, even when the effective core cross-sectional area of the optical fiber bare wire 2 is large, the microbend loss of the optical fiber can be effectively suppressed.

[0048] In addition, by increasing the effective core cross-sectional area of the optical fiber bare wire 2, the light intensity per unit area in the cross-section of the optical fiber bare wire 2 can be reduced. Thereby, the nonlinear optical effect caused by the light in the optical fiber bare wire 2 can be suppressed. Therefore, the optical fiber colored core wires 1 of Examples 1 to 9 and Comparative Examples 1 and 2 preferably have an effective core cross-sectional area of 2 100 μm or more and 2 160 μm or less, for example, 2 120 μm or more and 2 160 μm or less. Thereby, an optical fiber colored core wire 1 capable of suppressing the nonlinear optical effect caused by the light in the optical fiber bare wire 2 can be obtained.

[0049] In Examples 1 and 2, a primary layer material with a saturated Young's modulus of 0.84 MPa was used. The primary layer material was UV-cured until the Young's moduli of Examples 1 and 2 reached 0.58 MPa and 0.54 MPa, respectively, and the ratios of the Young's modulus to the saturated Young's modulus were 68.7% and 63.9%. The Young's moduli after additional UV irradiation were 0.59 MPa and 0.54 MPa, and the ratios of the Young's modulus after additional UV irradiation to the saturated Young's modulus were 69.9% and 64.0%. The ratios of the change amount of the Young's modulus to the saturated Young's modulus were 1.2% and 0.0%, and in both cases, the ratios were 16% or less. The microbend loss before and after additional UV irradiation was 0.15 dB / km or less, and both Evaluations 1 and 2 were good (OK).

[0050] In Examples 3, 4, and 5, a primary layer material with a saturated Young's modulus of 1.30 MPa was used. The primary layer material was UV-cured until the Young's moduli of Examples 3, 4, and 5 reached 0.39 MPa, 0.30 MPa, and 0.70 MPa, respectively, and the ratios of the Young's modulus to the saturated Young's modulus were 30.3%, 23.1%, and 53.8%. The Young's moduli after additional UV irradiation were 0.43 MPa, 0.33 MPa, and 0.90 MPa, and the ratios of the Young's modulus after additional UV irradiation to the saturated Young's modulus were 32.7%, 25.4%, and 69.2%. The ratios of the change amount of the Young's modulus to the saturated Young's modulus were 3.1%, 2.3%, and 15.4%, and in both cases, the ratios were 16% or less. The microbend loss before and after additional UV irradiation was 0.15 dB / km or less, and both Evaluations 1 and 2 were good (OK).

[0051] In Examples 6 and 7, a primary layer material with a saturated Young's modulus of 1.74 MPa was used. The primary layer material was UV-cured until the Young's moduli of Examples 6 and 7 reached 1.11 MPa and 0.82 MPa, respectively. The ratios of the Young's modulus to the saturated Young's modulus were 63.6% and 47.0%. The Young's moduli after additional UV irradiation were 1.12 MPa and 0.89 MPa, and the ratios of the Young's moduli after additional UV irradiation to the saturated Young's modulus were 64.1% and 50.9%. The ratios of the change in Young's modulus to the saturated Young's modulus were 0.6% and 4.0%. The microbend loss before and after additional UV irradiation was 0.15 dB / km or less, and both Evaluations 1 and 2 were good (OK).

[0052] In Examples 8 and 9, a primary layer material with a saturated Young's modulus of 2.60 MPa was used. The primary layer material was UV-cured until the Young's moduli of Examples 8 and 9 reached 0.90 MPa and 0.71 MPa, respectively. The ratios of the Young's modulus to the saturated Young's modulus were 34.5% and 27.4%. The Young's moduli after additional UV irradiation were 1.04 MPa and 1.00 MPa, and the ratios of the Young's moduli after additional UV irradiation to the saturated Young's modulus were 40.0% and 38.3%. The ratios of the change in Young's modulus to the saturated Young's modulus were 5.4% and 11.2%. The microbend loss before and after additional UV irradiation was 0.15 dB / km or less, and both Evaluations 1 and 2 were good (OK).

[0053] In Comparative Example 1, a primary layer material with a saturated Young's modulus of 1.30 MPa was used, and the primary layer material was cured until the Young's modulus reached 0.19 MPa. The ratio of the change in Young's modulus to the saturated Young's modulus was 14.4% which was less than 70%, but the ratio of the Young's modulus after additional UV irradiation to the saturated Young's modulus was 97.7% which exceeded 70%. The ratio of the change in Young's modulus before and after additional UV irradiation to the saturated Young's modulus was 83.1%. The microbend loss was 0.15 dB / km, and Evaluation 1 was good (OK), but the microbend loss after additional UV irradiation exceeded 0.15 dB / km, and Evaluation 2 was bad (NG).

[0054] In Comparative Example 2, a primary layer material with a saturation Young's modulus of 1.30 MPa was used, and the primary layer material was cured until the Young's modulus reached 0.95 MPa. The ratio of the change in Young's modulus to the saturation Young's modulus exceeded 70% and was 73.3%. Also, the ratio of the Young's modulus after additional UV irradiation to the saturation Young's modulus exceeded 70% and was 99.1%. The ratio of the change in Young's modulus before and after additional UV irradiation to the saturation Young's modulus was 26.2%. The microbend loss before and after additional UV irradiation exceeded 0.15 dB / km, and both Evaluations 1 and 2 were unacceptable (NG).

[0055] Figure 7 is a diagram showing the relationship between the ratio (%) of Young's modulus to the saturation Young's modulus and the ratio (%) of Young's modulus after additional UV irradiation to the saturation Young's modulus and the microbend loss (dB / km) in Examples 1 to 9 and Comparative Examples 1 and 2 in Table 1. As shown in Figure 7, when the ratio of Young's modulus to the saturation Young's modulus is less than 70%, it was confirmed that the microbend loss of the optical fiber colored core 1 is 0.15 dB / km or less. Therefore, it is preferable that the ratio of Young's modulus to the saturation Young's modulus is less than 70%.

[0056] Also, the saturation Young's modulus of the primary layer 3 preferably has a relatively high saturation Young's modulus of, for example, 0.84 MPa or more. Since an ultraviolet curable resin having a high saturation Young's modulus has a relatively low viscosity, it is easy to handle. For this reason, manufacturing advantages such as being able to easily form a uniform primary layer 3 can be achieved.

[0057] Also, in the wire drawing process, since the primary layer 3 is exposed to high temperatures, the curing reaction by additional UV irradiation can be suppressed. In this embodiment, by using an ultraviolet curable resin having a high saturation Young's modulus, it is possible to avoid the Young's modulus from becoming too low even when the primary layer 3 is exposed to high temperatures in the wire drawing process.

[0058] Furthermore, it is preferable that the ratio of the Young's modulus after additional UV irradiation to the saturated Young's modulus is less than 70%, and the ratio of the change amount of the Young's modulus before and after the additional UV irradiation to the saturated Young's modulus is 16% or less. Thereby, when the manufactured optical fiber colored core wire 1 is irradiated with additional ultraviolet rays, microbend loss due to the curing of the primary layer 3 can be suppressed.

[0059] As described above, according to the present embodiment, it is possible to effectively suppress microbend loss while avoiding problems associated with an ultraviolet curable resin having a low saturated Young's modulus.

[0060] The present invention is not limited to the above embodiment, and various modifications are possible. For example, an example in which a part of the configuration of any one of the embodiments is added to another embodiment, or an example in which a part of the configuration of another embodiment is replaced, is also an embodiment of the present invention. In addition, regarding parts that are not particularly described or illustrated in the embodiments, well-known techniques and publicly known techniques in the relevant technical field can be appropriately applied.

[0061] This application claims priority from Japanese Patent Application No. 2020-181724 filed on October 29, 2020, the content of which is incorporated herein by reference in its entirety.

Explanation of Reference Numerals

[0062] 1 Optical fiber colored core wire 2 Optical fiber bare wire 3 Primary layer 4 Secondary layer 5 Coloring layer

Claims

1. An optical fiber bare wire, A primary layer formed of an ultraviolet curable resin covering the optical fiber bare wire, A secondary layer formed of an ultraviolet curable resin covering the primary layer, Comprising, The Young's modulus of the primary layer is less than 70% of the saturated Young's modulus of the primary layer, The saturated Young's modulus of the primary layer is 0.84 MPa or more, An optical fiber colored core wire characterized in that the Young's modulus of the primary layer is 1.12 MPa or less.

2. A plurality of optical fiber colored core wires according to Claim 1, An optical fiber ribbon characterized by comprising an adhesive layer connecting the plurality of optical fiber colored core wires.

3. An optical fiber colored core wire according to Claim 1, An aggregate cable of single-core fibers characterized by comprising a sheath for accommodating the optical fiber colored core wire therein.

4. An optical fiber ribbon according to Claim 2, A ribbon cable characterized by comprising a sheath for accommodating the optical fiber ribbon.

5. A step of drawing an optical fiber bare wire from an optical fiber base material, A step of applying an ultraviolet curable resin around the optical fiber bare wire to form a primary layer, A method for manufacturing an optical fiber colored core wire comprising a step of applying an ultraviolet curable resin around the primary layer and irradiating the ultraviolet curable resin with ultraviolet rays to form a secondary layer, After manufacturing the optical fiber colored core wire, The Young's modulus of the primary layer is less than 70% of the saturated Young's modulus of the primary layer, The saturated Young's modulus of the primary layer is 0.84 MPa or more, The Young's modulus of the primary layer is 1.12 MPa or less A method for manufacturing an optical fiber colored core wire, characterized in that.

6. The method for manufacturing an optical fiber colored core wire according to Claim 5, characterized in that, in the step of forming the primary layer, the ultraviolet curable resin is irradiated with ultraviolet rays.

7. The method for manufacturing an optical fiber colored core wire according to Claim 5 or 6, further comprising a step of applying an ultraviolet curable resin around the secondary layer and irradiating the ultraviolet curable resin with ultraviolet rays to form a colored layer.

8. The method for manufacturing an optical fiber colored core wire according to Claim 5 or 6, characterized in that the Young's modulus of the primary layer after irradiating the optical fiber colored core wire with ultraviolet rays is less than 70% of the saturated Young's modulus of the primary layer.

9. The method for manufacturing an optical fiber colored core wire according to claim 5 or 6, characterized in that the secondary layer is colored.

10. A step of preparing a plurality of optical fiber colored core wires according to any one of claims 5 to 9, A step of applying an ultraviolet curable resin to the plurality of optical fiber colored core wires and irradiating the ultraviolet curable resin with ultraviolet rays to connect the plurality of optical fiber colored core wires, characterized in that the method for manufacturing an optical fiber ribbon is provided.

Images