Optical fiber core wire

Abstract

An optical fiber core is provided with a glass fiber and a coating resin layer covering the glass fiber, and the number of extreme values satisfying both conditions (A) and (B) in a differential molecular weight distribution curve obtained by gel permeation chromatography in an extract obtained by extracting the optical fiber core with tetrahydrofuran is 4 or less, and the number of extreme values satisfying both conditions (A) and (B) in a differential molecular weight distribution curve obtained by gel permeation chromatography is 4 or less. The horizontal axis of the differential molecular weight distribution curve is the logarithm value logM of the molecular weight M, and the longitudinal axis is dw / dlogM obtained by differentiating the concentration fraction w with the logarithm value logM of the molecular weight: (A) the extreme value is in the molecular weight range of 3.5 < = logM < = 5.5; (B) When the maximum value of dw / dlogM in the molecular weight range is 1, the difference between the extreme value and the dw / dlogM of an extreme value adjacent thereto is 0.15 or more.

Description

Technical Field

[0001] The present disclosure relates to an optical fiber core wire. This application claims priority based on Japanese Patent Application No. 2022-194069 filed on December 5, 2022, and incorporates by reference the entire content described in the Japanese patent application. Background Art

[0002] Generally, an optical fiber core wire has a glass fiber and a protective coating layer for protecting the glass fiber. Patent Document 1 discloses that in a glass fiber having a plurality of protective coating layers, if the Young's modulus of the protective coating layer in contact with the glass fiber is small, the side pressure characteristics are likely to be improved.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: International Publication No. 2016 / 088801 Summary of the Invention

[0006] The optical fiber core wire according to an embodiment of the present disclosure is an optical fiber core wire including a glass fiber and a coating resin layer covering the glass fiber. For the extraction liquid obtained by extracting the optical fiber core wire with tetrahydrofuran, in the differential molecular weight distribution curve obtained by gel permeation chromatography, the number of extrema satisfying both conditions (A) and (B) is 4 or less. The horizontal axis of the differential molecular weight distribution curve is the logarithm of the molecular weight M, logM, and the vertical axis is dw / dlogM obtained by differentiating the concentration fraction w with respect to the logarithm of the molecular weight logM:

[0007] (A) The extremum is in the molecular weight range of 3.5 ≤ logM ≤ 5.5;

[0008] (B) When the maximum value of dw / dlogM in the molecular weight range is set to 1, the difference in dw / dlogM between the extremum and the adjacent extremum is 0.15 or more. Brief Description of the Drawings

[0009] Figure 1 It is a cross-sectional view showing an example of the optical fiber core wire according to the present embodiment.

[0010] Figure 2 It is a differential molecular weight distribution curve obtained by gel permeation chromatography of the optical fiber core wire according to the example.

[0011] Figure 3 It is a differential molecular weight distribution curve obtained by gel permeation chromatography of the optical fiber core wire according to the comparative example. Detailed Description of the Embodiments

[0012] [Technical problems to be solved by the present disclosure]

[0013] If the Young's modulus of the protective coating layer in contact with the glass fiber is small, voids and cracks are likely to occur in the protective coating layer in a low-temperature environment where the protective coating layer is prone to shrinkage, and there is a tendency for an increase in transmission loss. Therefore, an optical fiber core wire with a reduced increase in transmission loss in a low-temperature environment is required.

[0014] An object of the present disclosure is to provide an optical fiber core wire with a reduced increase in transmission loss in a low-temperature environment.

[0015] [Effects of the present disclosure]

[0016] According to the present disclosure, an optical fiber core wire with a reduced increase in transmission loss in a low-temperature environment can be provided.

[0017] [Description of embodiments of the present disclosure]

[0018] First, embodiments of the present disclosure will be listed and described. The optical fiber core wire according to one embodiment of the present disclosure is

[0019] (1) An optical fiber core wire including a glass fiber and a coating resin layer covering the glass fiber,

[0020] For the extraction liquid obtained by extracting the optical fiber core wire with tetrahydrofuran, in the differential molecular weight distribution curve obtained by gel permeation chromatography, the number of extrema satisfying both conditions (A) and (B) is 4 or less. The horizontal axis of the differential molecular weight distribution curve is the logarithm of the molecular weight M, logM, and the vertical axis is dw / dlogM obtained by differentiating the concentration fraction w with respect to the logarithm of the molecular weight logM:

[0021] (A) The extremum is in the molecular weight range of 3.5 ≤ logM ≤ 5.5;

[0022] (B) When the maximum value of dw / dlogM in the molecular weight range is set to 1, the difference in dw / dlogM between the extremum and the adjacent extremum is 0.15 or more.

[0023] The crosslinking equilibrium of the coating resin layer of the optical fiber core wire according to this embodiment proceeds well, and voids and cracks are not likely to occur even in a low-temperature environment. Thus, an optical fiber core wire with a reduced increase in transmission loss in a low-temperature environment can be obtained.

[0024] (2) Alternatively, in the above (1), the coating resin layer has a primary layer in contact with the glass fiber, and the Young's modulus of the primary layer is 0.6 MPa or less.

[0025] Since the Young's modulus of the primary layer of the optical fiber core wire according to this embodiment is small, the lateral pressure resistance characteristics are improved, and an increase in transmission loss in a low-temperature environment can be reduced.

[0026] (3) Alternatively, in the above (2), the thickness of the primary layer may be 17.5 μm or more and 50 μm or less.

[0027] Since the primary layer of the optical fiber core wire according to this embodiment is thin, it can be suitably applied to a thin-diameter optical fiber core wire.

[0028] (4) Alternatively, in any one of the above (1) to (3), the increase in transmission loss at -60°C relative to the transmission loss at 23°C is less than 0.010 dB / km.

[0029] The optical fiber core wire according to this embodiment significantly reduces the increase in transmission loss in a low-temperature environment.

[0030] [Details of Embodiments of the Present Disclosure]

[0031] Hereinafter, specific examples of the optical fiber core wire according to the embodiments of the present disclosure will be described with reference to the drawings. It should be noted that the present invention is not limited to these examples, but is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0032] Figure 1 is a cross-sectional view showing an example of the optical fiber core wire 1 according to this embodiment. As Figure 1 shown, the optical fiber core wire 1 of this embodiment includes a glass fiber 10 as an optical transmission body and a coating resin layer 20.

[0033] The glass fiber 10 has a core 12 and a cladding 14, and is made of a glass component, such as SiO2 glass. The glass fiber 10 transmits the light introduced into the optical fiber core wire 1. The core 12 is provided, for example, in a region including the central axis of the glass fiber 10. The core 12 may include pure SiO2 glass, or may include GeO2, fluorine element, etc. in pure SiO2 glass. The cladding 14 is provided in a region surrounding the core 12. The cladding 14 has a refractive index lower than that of the core 12. The cladding 14 may be made of pure SiO2 glass, or may be made of SiO2 glass added with fluorine element.

[0034] The diameter of the glass fiber 10 is generally about 125 μm. The total thickness of the coating resin layer 20 is preferably 70 μm or less, more preferably 60 μm or less, and further preferably 42.5 μm or less. The outer diameter of the optical fiber core wire 1 is, for example, 245 μm or more and 265 μm or less, 180 μm or more and 220 μm or less, etc.

[0035] The coating resin layer 20 is a resin layer that covers the glass fiber 10. The coating resin layer 20 may also be composed of multiple layers. For example, when the coating resin layer 20 is composed of two layers, as Figure 1 shown, the coating resin layer 20 is composed of a primary layer 22 in contact with the glass fiber 10 and a secondary layer 24 in contact with the primary layer 22. It should be noted that the number of layers of the coating resin layer 20 is not limited to two layers, and a third layer that becomes an ink layer may be further formed on the outer peripheral surface of the secondary layer 24.

[0036] The coating resin layer 20 can be formed, for example, by curing an ultraviolet curable resin composition containing an oligomer, a monomer, and a photoinitiator.

[0037] As the oligomer, for example, polyurethane (meth)acrylate and epoxy (meth)acrylate can be cited. Two or more kinds of oligomers can also be used in combination.

[0038] As the polyurethane (meth)acrylate, a substance obtained by reacting a polyol compound, a polyisocyanate compound, and a hydroxy group-containing acrylate compound can be cited. As the polyol compound, for example, polytetramethylene glycol, polypropylene glycol, bisphenol A-ethylene oxide adduct diol, etc. can be cited. As the polyisocyanate compound, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, isophorone diisocyanate, etc. can be cited. As the hydroxy group-containing acrylate compound, for example, 2-hydroxy (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 1,6-hexanediol mono (meth)acrylate, pentaerythritol tri (meth)acrylate, 2-hydroxypropyl (meth)acrylate, tripropylene glycol di (meth)acrylate, etc. can be cited. As the epoxy (meth)acrylate, for example, a substance obtained by reacting an epoxy compound with (meth)acrylic acid can be used.

[0039] Here, (meth)acrylate means acrylate or its corresponding methacrylate. The same applies to (meth)acrylic acid.

[0040] Based on the total amount of the ultraviolet curable resin composition, the content of the oligomer is preferably 50% by mass or more and 90% by mass or less, more preferably 35% by mass or more and 85% by mass or less.

[0041] As the monomer, a monofunctional monomer having one polymerizable group and a polyfunctional monomer having two or more polymerizable groups can be used.

[0042] As monofunctional monomers, N-vinyl monomers having a cyclic structure such as N-vinylpyrrolidone, N-vinylcaprolactam, (meth)acryloylmorpholine, etc. can be cited; (meth)acrylate compounds such as isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, benzyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, nonylphenyl (meth)acrylate, phenoxyethyl (meth)acrylate, polypropylene glycol mono(meth)acrylate, etc. Among them, from the aspect of improving the curing speed, N-vinyl monomers having a cyclic structure are preferred.

[0043] As polyfunctional monomers, polyethylene glycol di(meth)acrylate, tricyclodecane dimethylene di(meth)acrylate, bisphenol A-ethylene oxide adduct diol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, etc. can be cited.

[0044] Two or more monomers can be used in combination. Based on the total amount of the ultraviolet curable resin composition, the content of the monomer is preferably 5% by mass or more and 45% by mass or less, more preferably 10% by mass or more and 30% by mass or less.

[0045] As a photopolymerization initiator, it can be appropriately selected and used from known radical photopolymerization initiators. For example, acylphosphine oxide-based initiators and acetophenone-based initiators can be cited.

[0046] As acylphosphine oxide-based initiators, 2,4,6-trimethylbenzoyl diphenylphosphine oxide (manufactured by IGM Resins B.V., trade name: Omnirad TPO H), 2,4,4-trimethylpentylphosphine oxide, 2,4,4-trimethylbenzoyl diphenylphosphine oxide, etc. can be cited.

[0047] As acetophenone-based initiators, 1-hydroxycyclohexyl phenyl ketone (manufactured by BASF, trade name "Irgacure 184"), 2-hydroxy-2-methyl-1-phenyl-propan-1-one (manufactured by BASF, trade name "Dalocure 1173"), 2,2-dimethoxy-1,2-diphenylethane-1-one (manufactured by BASF, trade name "Irgacure 651"), 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one (manufactured by BASF, trade name "Irgacure 907"), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one (manufactured by BASF, trade name "Irgacure 369"), 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, etc. can be cited.

[0048] Two or more photoinitiators can also be used in combination. Based on the total amount of the ultraviolet curable resin composition, the content of the photoinitiator is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more and 7% by mass or less.

[0049] In the case where the coating resin layer 20 has the primary layer 22 in contact with the glass fiber 10, the Young's modulus of the primary layer 22 can be 0.6 MPa or less. If the Young's modulus of the primary layer 22 is 0.6 MPa or less, the side pressure resistance characteristics of the optical fiber core wire 1 are improved. The Young's modulus of the primary layer 22 can be 0.5 MPa or less, or can be 0.4 MPa or less. The lower limit of the Young's modulus of the primary layer 22 is not particularly limited, and for example, it can also be 0.05 MPa or more. The Young's modulus in the present disclosure is measured by the Pullout Modulus (POM) method at room temperature (23°C), and specifically, it is obtained by the method described in the examples below.

[0050] The thickness of the primary layer 22 can be 17.5 μm or more and 50 μm or less. If the thickness of the primary layer 22 is within the above range, it can be appropriately applied to a thin-diameter optical fiber core wire.

[0051] In the case where the coating resin layer 20 has the secondary layer 24 in contact with the outer surface of the primary layer 22, from the viewpoint of protecting the mechanical strength of the glass fiber 10, the Young's modulus of the secondary layer 24 is preferably 600 MPa or more at 23°C. The Young's modulus of the secondary layer 24 is more preferably 800 MPa or more, and further preferably 1000 MPa or more. The upper limit of the Young's modulus of the secondary layer 24 is not particularly limited, and for example, it can be 1600 MPa or less.

[0052] For the extraction liquid obtained by extracting the optical fiber core wire 1 with tetrahydrofuran, in the differential molecular weight distribution curve obtained by gel permeation chromatography, the number of extrema satisfying both conditions (A) and (B) is 4 or less, where the horizontal axis of the differential molecular weight distribution curve is the logarithm of the molecular weight M, logM, and the vertical axis is dw / dlogM obtained by differentiating the concentration fraction w with respect to the logarithm of the molecular weight logM:

[0053] (A) The extremum is in the molecular weight range of 3.5 ≤ logM ≤ 5.5;

[0054] (B) When the maximum value of dw / dlogM in the molecular weight range is set to 1, the difference in dw / dlogM between the extremum and the adjacent extremum is 0.15 or more.

[0055] Here, the extreme values include both the maximum value and the minimum value. Additionally, in a case where there is only one maximum value as in a normal distribution and there is no "extreme value adjacent to the extreme value" defined by condition (B), the number of extreme values satisfying both condition (A) and (B) is 1.

[0056] If the number of extreme values satisfying both condition (A) and (B) is 4 or less, the crosslinking equilibrium of the coating resin layer 20 proceeds well, and even in a low-temperature environment, voids and cracks are less likely to occur in the coating resin layer 20. Thus, an optical fiber core wire 1 with an increased transmission loss reduced in a low-temperature environment can be obtained.

[0057] As defined by condition (A), count the number of extreme values in the molecular weight range of 3.5 ≤ logM ≤ 5.5. The reason for this definition is that it can be considered that the molecular weight distribution in this molecular weight range is derived from the molecular weight distribution of the oligomer that is the raw material of the coating resin layer 20. As will be described later, it can be considered that the molecular weight distribution of the oligomer is related to the crosslinked structure of the coating resin layer 20. It should be noted that unless otherwise specified, the "logarithmic value" and "log" in the present disclosure refer to the common logarithm.

[0058] As defined by condition (B), count the number of extreme values when the maximum value of dw / dlogM in the above molecular weight range is 1 and the difference in dw / dlogM between this extreme value and the extreme value adjacent to this extreme value is 0.15 or more. The "extreme value adjacent to this extreme value" here refers to an extreme value in the molecular weight range of 3.5 ≤ logM ≤ 5.5. That is, "adjacent extreme values" outside the above molecular weight range are not considered. In a case where there are 2 extreme values adjacent to this extreme value within the above molecular weight range, the "difference in dw / dlogM from the extreme value adjacent to this extreme value is 0.15 or more" means that the difference in dw / dlogM from any one of the 2 adjacent extreme values is 0.15 or more.

[0059] The reason for defining condition (B) is as follows. In a molecular weight distribution curve, small peaks sometimes occur due to trace components contained in the measurement object. If an extreme value with a small difference in dw / dlogM from an adjacent extreme value is used as the object to be counted, the small peak generated by the trace component is also counted as one extreme value. As a result, even for substantially the same molecular weight distribution curve, the number of extreme values will be different depending on the presence or absence of trace components. To eliminate the influence of such trace components, only extreme values with a difference in dw / dlogM from adjacent extreme values of a certain value or more are counted.

[0060] As a specific reason for reducing the increase in transmission loss in a low-temperature environment when the number of extreme values satisfying both conditions (A) and (B) is four or less, the following reasons are assumed. In the optical fiber core 1 of the present embodiment, it is considered that the number of extreme values in the molecular weight range of 3.5 ≤ logM ≤ 5.5 derived from oligomers in the molecular weight distribution curve is small, and they are uniformly distributed from oligomers with a large number of repetitions (large molecular weight) to oligomers with a small number of repetitions (small molecular weight). As a result, when the coating resin layer 20 is formed, the crosslinking equilibrium proceeds well, and a dense crosslinked structure is formed. As a result, it is considered that even in a low-temperature environment, voids and cracks are less likely to occur in the coating resin layer 20. On the contrary, when the number of extreme values in the molecular weight range of 3.5 ≤ logM ≤ 5.5 is large, there are a large number of oligomers with a specific molecular weight, and only a small amount of oligomers with a specific molecular weight, etc., and the molecular weight distribution is uneven. If the molecular weight distribution of the oligomers is uneven, a dense crosslinked structure cannot be formed when the coating resin layer 20 is formed, and a portion with sparse crosslinking is likely to occur. As a result, it is considered that voids and cracks are likely to occur in the coating resin layer 20 in a low-temperature environment, and the increase in transmission loss becomes large.

[0061] From the viewpoint of reducing the increase in transmission loss in a low-temperature environment, the number of extreme values satisfying both conditions (A) and (B) can be three or less, or one or less.

[0062] In order to make the number of extreme values satisfying both conditions (A) and (B) four or less, it is preferable to use a raw material with a wide molecular weight distribution as the raw material of the oligomer. For example, when using polyurethane (meth) acrylate as the oligomer, a polyol compound with a wide molecular weight distribution can be used as the raw material of the polyurethane (meth) acrylate. Here, "wide molecular weight distribution" means that the ratio of the weight average molecular weight Mw to the number average molecular weight Mn, that is, the polydispersity (Mw / Mn), is large.

[0063] In addition, in order to make the number of extreme values satisfying both conditions (A) and (B) four or less, it is necessary to sufficiently cure the coating resin layer 20. If the curing is not sufficiently performed, the number of extreme values satisfying both conditions (A) and (B) may increase.

[0064] It is also possible that the increase in the transmission loss of the optical fiber core 1 at -60 °C relative to the transmission loss at 23 °C is less than 0.010 dB / km. If the increase in the transmission loss at -60 °C is within this range, the increase in the transmission loss in a low-temperature environment is significantly reduced. The increase in the transmission loss at -60 °C is, for example, a value measured by the method described in the examples.

[0065] Examples

[0066] Next, examples are given to explain the present disclosure in detail, but the present invention is not limited to these examples.

[0067] [Preparation of Resin Composition for Primary Layer]

[0068] (Preparation Example A1)

[0069] Using polypropylene glycol with a number average molecular weight of 2000 as the polyol compound, 2,4-toluene diisocyanate as the polyisocyanate compound, and 2-hydroxyethyl acrylate as the hydroxy-containing (meth)acrylate compound, a polyurethane (meth)acrylate oligomer was synthesized. The obtained polyurethane (meth)acrylate oligomer, nonylphenyl acrylate as the monomer, and TPO (trade name: Omnirad TPO H, manufactured by IGM Resins B.V.) as the photoinitiator were mixed to prepare a resin composition A1 for the primary layer.

[0070] (Preparation Examples A2 - A6)

[0071] Except for using polypropylene glycol with a molecular weight distribution different from that used in Preparation Example A1 as the polyol compound, resin compositions A2 - A6 for the primary layer were prepared in the same manner as Preparation Example A1.

[0072] [Preparation of Resin Composition for Secondary Layer]

[0073] (Preparation Example B1)

[0074] Using polypropylene glycol with a number average molecular weight of 2000 as the polyol compound, 2,4-toluene diisocyanate as the polyisocyanate compound, and 2-hydroxyethyl acrylate as the hydroxy-containing (meth)acrylate compound, a polyurethane (meth)acrylate oligomer was synthesized. The obtained polyurethane (meth)acrylate oligomer, tripropylene glycol diacrylate as the monomer, and TPO (manufactured by IGM Resins B.V., trade name: Omnirad TPO H) as the photoinitiator were mixed to prepare a resin composition B1 for the secondary layer.

[0075] [Fabrication of Optical Fiber Core]

[0076] (Example 1)

[0077] On the outer periphery of a 125 - μm - diameter glass fiber composed of a core and a cladding, a primary layer with a thickness of 35 μm was formed using the resin composition A1 for the primary layer. In addition, a secondary layer with a thickness of 30 μm was formed using the resin composition B1 for the secondary layer on the outer periphery of the primary layer to fabricate an optical fiber core with a diameter of 245 μm.

[0078] (Examples 2 - 6)

[0079] An optical fiber core wire was produced in the same manner as in Example 1, except that A2 to A6 were used instead of A1 for the resin composition of the primary layer, respectively.

[0080] [Evaluation of optical fiber core wire]

[0081] Regarding each of the optical fiber core wires produced in Examples 1 to 6, the molecular weight distribution, Young's modulus of the primary layer and the secondary layer, and the increase in low-temperature transmission loss were measured by the following methods.

[0082] (Molecular weight distribution)

[0083] Regarding each optical fiber core wire, the organic layer was extracted with a tetrahydrofuran (THF) solution, and the molecular weight distribution was measured by gas permeation chromatography of the extract. The specific analysis conditions are as follows.

[0084] Analysis device: AC QUITY APC RI system manufactured by Waters

[0085] Sample concentration: 0.2 mass%

[0086] THF solution injection volume: 20 μL

[0087] Sample temperature: 15 °C

[0088] Mobile phase: THF

[0089] XT column for organic solvents: particle size 2.5 μm, pore size 45 nm, column inner diameter 4.6 × column length 150 mm + particle size 2.5 μm, pore size 12.5 nm, column inner diameter 4.6 × column length 150 mm + particle size 1.7 μm, pore size 4.5 nm, column inner diameter 4.6 × column length 150 mm

[0090] Column temperature: 40 °C

[0091] Flow rate: 0.8 mL / minute

[0092] Standard sample: polystyrene

[0093] Regarding each optical fiber core wire, the number of extreme values satisfying both conditions (A) and (B), the number-average molecular weight Mn, the weight-average molecular weight Mw, and the polydispersity Mw / Mn are shown in Table 1. Examples 1 to 4 are examples, and Examples 5 and 6 are comparative examples. In addition, Figure 2 and Figure 3 The differential molecular weight distribution curves obtained by measuring the molecular weight distribution of each optical fiber core wire are shown. Figure 2 The differential molecular weight distribution curves of Examples 1 to 4 as examples are shown, Figure 3 The differential molecular weight distribution curves of Examples 5 and 6 as comparative examples are shown. Figure 2 andFigure 3 The vertical axis shows the value when the maximum value of dw / dlogM of each curve in the molecular weight range of 3.5 ≤ logM ≤ 5.5 is set to 1.

[0094] (Young's modulus)

[0095] The Young's modulus of each coating resin layer (primary layer and secondary layer) of the optical fiber core was measured at room temperature (23 °C) by the Pullout Modulus (POM) method. Two parts of the optical fiber core were fixed with two chuck devices, and the coating resin layer part between the two chuck devices was removed. Then, one chuck device was fixed, and the other chuck device was slowly moved in the opposite direction to the fixed chuck device. When the length of the part of the optical fiber core clamped by the moving chuck device is set to L, the movement amount of the chuck is set to Z, the outer diameter of the coating resin layer (primary layer or secondary layer) to be measured is set to Dp, the outer diameter of the glass fiber is set to Df, the Poisson's ratio of the coating resin layer to be measured is set to n, and the load during the movement of the chuck device is set to W, the Young's modulus (POM value) of the coating resin layer to be measured is calculated according to the following formula.

[0096] Young's modulus (MPa) = ((1 + n)W / πLZ) × ln(Dp / Df)

[0097] The measurement results of the Young's modulus of the primary layer and secondary layer of each optical fiber core are shown in Table 1.

[0098] (Increase in low-temperature transmission loss)

[0099] The transmission loss of light with a wavelength of 1550 nm of the optical fiber core applied with a screening tension of 2 kg was measured at 23 °C, and then the optical fiber core was placed in an environment of -40 °C or -60 °C for 2 hours, and the transmission loss of light with a wavelength of 1550 nm was measured. The increase in the transmission loss of the optical fiber core placed at -40 °C (or -60 °C) relative to the optical fiber core before being placed at -40 °C (or -60 °C) was taken as the increase in low-temperature transmission loss. The measurement results of the increase in low-temperature transmission loss of each optical fiber core are shown in Table 1.

[0100]

[0101] As can be seen from Table 1, the increase in low-temperature transmission loss of the optical fiber core with the number of extrema satisfying conditions (A) and (B) less than 4 is less than 0.010 dB / km before and after being placed at -60 °C, reducing the increase in transmission loss in a low-temperature environment.

[0102] Description of reference numerals

[0103] 1: Optical fiber core wire; 10: Glass fiber; 12: Core; 14: Cladding; 20: Coating resin layer; 22: Primary layer; 24: Secondary layer.

Claims

1. An optical fiber core wire includes a glass fiber and a coating resin layer covering the glass fiber. For the extraction liquid obtained by extracting the optical fiber core wire with tetrahydrofuran, in the differential molecular weight distribution curve obtained by gel permeation chromatography, the number of extrema that satisfy both condition (A) and condition (B) is 4 or less. The horizontal axis of the differential molecular weight distribution curve is the logarithm of the molecular weight M, logM, and the vertical axis is dw / dlogM obtained by differentiating the concentration fraction w with respect to the logarithm of the molecular weight logM. (A) The extremum is in the molecular weight range of 3.5 ≤ logM ≤ 5.

5. (B) When the maximum value of dw / dlogM in the molecular weight range is set to 1, the difference in dw / dlogM between the extremum and the adjacent extremum is 0.15 or more.

2. The optical fiber core wire according to claim 1, wherein the coating resin layer has a primary layer in contact with the glass fiber, and the Young's modulus of the primary layer is 0.6 MPa or less.

3. The optical fiber core wire according to claim 2, wherein the thickness of the primary layer is 17.5 μm or more and 50 μm or less.

4. The optical fiber core wire according to any one of claims 1 to 3, wherein the increase in transmission loss at -60°C relative to the transmission loss at 23°C is less than 0.010 dB / km.

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