Method for measuring eccentricity quantity of optical fiber and method for manufacturing optical fiber

Abstract

To provide an optical fiber capable of being reduced in diameter while suppressing degradation of low-temperature characteristics and side pressure-resistant characteristics.SOLUTION: An optical fiber comprises a glass fiber including a core and a cladding, and a coated resin layer covering an outer circumference of the glass fiber. The coated resin layer has a primary resin layer covering the glass fiber in contact with the glass fiber and a secondary resin layer covering an outer circumference of the primary resin layer. An outer diameter of the glass fiber is 124.5 μm or more and 125.5 μm or less. A thickness of the primary resin layer is 7.5 μm or more and 17.5 μm or less. A Young's modulus of the primary resin layer at 23°C is 0.10 MPa or more and 0.50 MPa or less. A thickness of the secondary resin layer is 5.0 μm or more and 17.5 μm or less. An outer diameter of the secondary resin layer is 165 μm or more and 175 μm or less. A Young's modulus of the secondary resin layer at 23°C is 1200 MPa or more and 2800 MPa or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for measuring the eccentricity of an optical fiber and a method for manufacturing an optical fiber. [Background technology]

[0002] Patent Document 1 describes an optical fiber. The optical fiber includes a glass fiber, a primary coating surrounding the glass fiber, and a secondary coating surrounding the primary coating. The glass fiber has a diameter of 125 μm and a structure that satisfies the ITU-T G.657.A standard and / or the ITU-T G.657.B standard. The primary coating has an in situ elastic modulus greater than 0.2 MPa and less than 0.65 MPa, a glass transition temperature of -50°C or lower, and an outer diameter of 135 μm to 175 μm. When an ink layer is included, the outer diameter of the optical fiber is 210 μm or less.

[0003] Patent Document 2 describes an optical fiber. A non-glass protective coating having an outer diameter of 210 μm or less is provided on the outer surface of the cladding. The non-glass protective coating includes a primary coating directly adjacent to the outer surface of the cladding and a secondary coating directly adjacent to the primary coating. The primary coating has an in situ elastic modulus of less than 1 MPa. The secondary coating has an elastic modulus of greater than 1200 MPa. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2010 / 053356 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0041623 [Patent Document 3] International Publication No. 2017 / 172714 [Patent Document 4] Japanese Patent Publication No. 2020-129037 Summary of the Invention [Problem to be solved by the invention]

[0005] With the recent increase in optical communication capacity, there is a demand for more optical fibers to be installed in optical cables. To achieve this, it is important to reduce the diameter of the optical fiber core, which generally has an outer diameter of 250 μm. In this case, it is preferable to maintain the outer diameter of a typical glass fiber (125 μm ± 0.5 μm) without reducing the diameter.

[0006] However, reducing the diameter of the optical fiber core while maintaining the outer diameter of the glass fiber results in a thinner coating resin layer. A thinner coating resin layer is likely to increase transmission loss (microbend loss) induced by minute bends that occur when lateral pressure is applied to the optical fiber. This results in a deterioration of the optical fiber's lateral pressure resistance. While this deterioration in lateral pressure resistance can be suppressed to some extent by reducing the Young's modulus of the primary resin layer, reducing the Young's modulus of the primary resin layer too much can cause a problem of deterioration in low-temperature characteristics (when the optical fiber is placed at a low temperature of -60°C, the increase in transmission loss of light with a wavelength of 1550 nm compared to room temperature is +0.1 dB / km or more).

[0007] An object of the present disclosure is to provide a method for measuring the eccentricity of an optical fiber and a method for manufacturing an optical fiber that can reduce the diameter while suppressing deterioration of low-temperature characteristics and lateral pressure resistance characteristics. [Means for solving the problem]

[0008] An optical fiber eccentricity measuring method according to one aspect of the present disclosure is a method for measuring the eccentricity of an optical fiber using an eccentricity fluctuation observation device. The eccentricity fluctuation observation device includes a first light source, a first imaging unit, a second light source, and a second imaging unit. The first light source and the second light source are arranged to irradiate first light and second light, respectively, in the short direction of the optical fiber. The first light and the second light include wavelengths that transmit through the coating resin layer of the optical fiber. The first imaging unit is arranged to face the first light source across the optical fiber. The second imaging unit is arranged to face the second light source across the optical fiber. The opposing direction of the second light source and the second imaging unit is perpendicular to the opposing direction of the first light source and the first imaging unit. In this eccentricity measurement method, the outer and inner peripheral positions of the coating resin layer are determined based on a first image obtained by capturing, with a first imaging unit, a first light beam transmitted through the optical fiber at a plurality of measurement points set at predetermined intervals in the axial direction of the optical fiber, and a second image obtained by capturing, with a second imaging unit, a second light beam transmitted through the optical fiber at the plurality of measurement points, thereby calculating the eccentricity as the distance between the centers of the outer and inner peripheral positions. Then, in a spectrum obtained by Fourier transforming a waveform indicating the eccentricity for each of the plurality of measurement points, it is confirmed that the maximum value of the amplitude of the eccentricity is greater than 0 μm and less than or equal to 3.6 μm, and that the wavelength at which the amplitude of the eccentricity is maximum is greater than or equal to 0.1 m and less than or equal to 1 m. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a method for measuring the eccentricity of an optical fiber and a method for manufacturing an optical fiber that can reduce the diameter while suppressing deterioration of low-temperature characteristics and lateral pressure resistance characteristics. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a cross section perpendicular to the axial direction of an optical fiber according to the first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view for explaining the definition of the eccentricity of a glass fiber. [Figure 3]FIG. 3 is a diagram of an eccentricity waveform showing the eccentricity of the glass fiber relative to the axial position of the glass fiber. [Figure 4] FIG. 4 is a diagram showing an example of a spectrum obtained by Fourier transforming the eccentricity waveform. [Figure 5] FIG. 5 is a schematic diagram showing the configuration of an optical fiber manufacturing apparatus according to this embodiment. [Figure 6] FIG. 6 is a diagram showing a cross section perpendicular to the axial direction of the optical fiber according to the third embodiment. [Figure 7] FIG. 7 is a diagram showing a cross section perpendicular to the axial direction of an optical fiber as a modification of the third embodiment. [Figure 8] FIG. 8 is a diagram showing a cross section perpendicular to the axial direction of the optical fiber of the fourth embodiment. [Figure 9] FIG. 9 is a diagram showing the refractive index distribution in the radial direction of a glass fiber. [Figure 10] FIG. 10 is a graph showing the relationship between the variation (3σ) in the outer diameter fluctuation of glass fibers and the percentage of optical fibers with a transmission loss of 0.32 dB / km or less at a wavelength of 1.31 μm. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. [1] An eccentricity measurement method for an optical fiber according to one aspect of the present disclosure is a method for measuring the eccentricity of an optical fiber using an eccentricity fluctuation observation device. The eccentricity fluctuation observation device includes a first light source, a first imaging unit, a second light source, and the second imaging unit. The first light source and the second light source are arranged to irradiate first light and second light, respectively, in the short direction of the optical fiber. The first light and the second light include wavelengths that transmit through the coating resin layer of the optical fiber. The first imaging unit is arranged to face the first light source across the optical fiber. The second imaging unit is arranged to face the second light source across the optical fiber. The opposing direction of the second light source and the second imaging unit is perpendicular to the opposing direction of the first light source and the first imaging unit. In this eccentricity measurement method, the outer and inner peripheral positions of the coating resin layer are determined based on a first image obtained by capturing, with a first imaging unit, a first light beam transmitted through the optical fiber at a plurality of measurement points set at predetermined intervals in the axial direction of the optical fiber, and a second image obtained by capturing, with a second imaging unit, a second light beam transmitted through the optical fiber at the plurality of measurement points, thereby calculating the eccentricity as the distance between the centers of the outer and inner peripheral positions. Then, in a spectrum obtained by Fourier transforming a waveform indicating the eccentricity for each of the plurality of measurement points, it is confirmed that the maximum value of the amplitude of the eccentricity is greater than 0 μm and less than or equal to 3.6 μm, and that the wavelength at which the amplitude of the eccentricity is maximum is greater than or equal to 0.1 m and less than or equal to 1 m.

[0012] [2] A method for manufacturing an optical fiber according to one embodiment of the present disclosure includes the steps of forming a glass fiber, forming a coating resin layer so as to cover the outer periphery of the glass fiber, irradiating the coating resin layer with ultraviolet light to harden the coating resin layer, and calculating the eccentricity of the optical fiber by the method for measuring eccentricity of an optical fiber described in claim 1, and confirming that the maximum value of the amplitude of the eccentricity is greater than 0 μm and less than or equal to 3.6 μm, and that the wavelength at which the amplitude of the eccentricity is maximum is greater than or equal to 0.1 m and less than or equal to 1 m.

[0013] [3] In the manufacturing method of [2] above, a direct-below roller may be disposed directly below the curing device that performs the curing step, and multiple guide rollers may be disposed downstream of the direct-below roller, and the circumference of the largest roller among all rollers including the direct-below roller and the multiple guide rollers may be set to 0.2 m or more.

[0014] [4] In the manufacturing method of [2] above, a direct-below roller may be disposed directly below a curing device that performs the curing step, and a vibration suppression unit may be disposed downstream of the curing device and upstream of the direct-below roller, and the vibration suppression unit may include two rollers that contact the optical fiber from different directions to suppress vibration of the optical fiber.

[0015] [5] In the manufacturing method of [2] above, a roller directly below the curing device that performs the curing step may be disposed, and the roller directly below may be fixed independently from other equipment components involved in the manufacturing of optical fiber. [Details of the embodiments of the present disclosure]

[0016] Specific examples of the method for measuring the eccentricity of an optical fiber and the method for manufacturing an optical fiber according to the present embodiment will be described with reference to the drawings as necessary. The present invention 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. In the following description, identical elements in the description of the drawings will be given the same reference numerals, and redundant explanations will be omitted. In the following description, the "outer diameter" of a certain element refers to the outer diameter of the element in a direction perpendicular to the axis of the optical fiber. The "thickness" of a certain element refers to the thickness of the element in the radial direction of the optical fiber (direction perpendicular to the axis). (First embodiment)

[0017] 1 is a diagram showing a cross section perpendicular to the axial direction of an optical fiber 10A according to a first embodiment. The optical fiber 10A is a so-called optical fiber strand and complies with at least one of the ITU-T G.652 standard and the ITU-T G.657 standard. Compliant with the ITU-T G.652 standard means compliance with at least one of G.652.A, G.652.B, G.652.C, and G.652.D. Compliant with the ITU-T G.657 standard means compliance with at least one of G.657.A and G.657.B. The optical fiber 10A includes a glass fiber 13A including a core 11 and a cladding 12, and a coating resin layer 16A including a primary resin layer 14 and a secondary resin layer 15 provided on the outer periphery of the glass fiber 13A.

[0018] The cladding 12 surrounds the core 11. The core 11 and the cladding 12 mainly contain glass such as silica glass, and for example, germanium-doped silica glass or pure silica glass can be used for the core 11, and pure silica glass or fluorine-doped silica glass can be used for the cladding 12. Here, pure silica glass means that it does not substantially contain impurities.

[0019] The outer diameter D2 of the glass fiber 13A, i.e., the outer diameter of the cladding 12, is 125 μm±0.5 μm, i.e., 124.5 μm or more and 125.5 μm or less, and the diameter D1 of the core 11 is 6.0 μm or more and 12.0 μm or less. Since the outer diameter D2 of the glass fiber 13A is the same as the outer diameter of a typical glass fiber, typical peripheral devices such as connectors and fusion splicers can be used, facilitating the replacement of existing optical fibers. For example, the optical fiber 10A can be easily applied to microduct cables, ultra-multicore cables for data centers, and various other cables.

[0020] The thickness t2 of the secondary resin layer 15 is 5.0 μm or more and 17.5 μm or less. When forming the coating resin layer 16A, vibration of the glass fiber 13A causes coating eccentricity (the distance between the center of the glass fiber 13A and the center of the outer periphery of the coating resin layer 16A) of several μm, which can locally thin the secondary resin layer 15. If foreign matter adhering to the roller during the drawing process overlaps with such locally thinned areas, it can cause breakage of the optical fiber 10A and reduce the yield of the optical fiber 10A. By ensuring that the average thickness of the secondary resin layer 15 is 5.0 μm or more, extreme thinning of the secondary resin layer 15 due to coating eccentricity can be prevented, reducing breakage of the optical fiber 10A. The outer diameter D4 of the secondary resin layer 15 is 170 μm ± 5 μm, i.e., 165 μm or more and 175 μm or less. By setting the outer diameter D4 of the secondary resin layer 15 to this value, an optical fiber wire having a smaller outer diameter than the outer diameter of a conventional optical fiber wire can be realized, allowing more optical fibers to be implemented within the optical cable.

[0021] The Young's modulus of the secondary resin layer 15 at 23°C is preferably 1200 MPa or more and 2800 MPa or less, more preferably 1500 MPa or more and 2800 MPa or less, and even more preferably 2000 MPa or more and 2700 MPa or less. When the Young's modulus of the secondary resin layer 15 is 1200 MPa or more, the lateral pressure resistance is easily improved, and when it is 2800 MPa or less, appropriate toughness is imparted to the secondary resin layer 15, which makes it easy to improve the tensile strength resistance and low-temperature characteristics. Furthermore, when the Young's modulus of the secondary resin layer 15 is 2800 MPa or less, the secondary resin layer 15 is less likely to suffer from deterioration in appearance due to external damage and is less likely to crack.

[0022] The secondary resin layer 15 having the above-described properties can be formed by curing a base resin containing an oligomer, a monomer, and a photopolymerization initiator containing urethane (meth)acrylate, or a resin composition containing the base resin and hydrophobic inorganic oxide particles. (Meth)acrylate refers to acrylate or its corresponding methacrylate. The same applies to (meth)acrylic acid, etc. The inorganic oxide particles are spherical particles. The inorganic oxide particles are at least one selected from the group consisting of silicon dioxide (silica), zirconium dioxide (zirconia), aluminum oxide (alumina), magnesium oxide (magnesia), titanium oxide (titania), tin oxide, and zinc oxide. To impart appropriate toughness to the secondary resin layer 15, the average primary particle size of the inorganic oxide particles may be 500 nm or less. To increase the Young's modulus of the secondary resin layer 15, the average primary particle size of the inorganic oxide particles is preferably 5 nm or more, more preferably 10 nm or more.

[0023] The surfaces of the inorganic oxide particles are hydrophobically treated. Hydrophobically treated refers to the introduction of hydrophobic groups onto the surfaces of the inorganic oxide particles. The hydrophobic groups may be reactive groups (ultraviolet-curable functional groups) such as (meth)acryloyl groups, or non-reactive groups such as aliphatic hydrocarbon groups (e.g., alkyl groups) or aromatic hydrocarbon groups (e.g., phenyl groups). When the inorganic oxide particles have reactive groups, it becomes easier to form a resin layer with a high Young's modulus. Furthermore, ultraviolet-curable functional groups may be introduced onto the surfaces of the inorganic oxide particles. By treating the inorganic oxide particles with a silane compound having ultraviolet-curable functional groups, ultraviolet-curable functional groups can be introduced onto the surfaces of the inorganic oxide particles. Examples of silane compounds having ultraviolet-curable functional groups include 3-methacryloxypropyltrimethoxysilane.

[0024] As the urethane (meth)acrylate, an oligomer obtained by reacting a polyol compound, a polyisocyanate compound, and a hydroxyl group-containing (meth)acrylate compound can be used. Examples of the polyol compound include polytetramethylene glycol. Examples of the polyisocyanate compound include 2,4-tolylene diisocyanate. Examples of the hydroxyl group-containing (meth)acrylate compound include 2-hydroxyethyl (meth)acrylate.

[0025] The base resin may further contain an epoxy (meth)acrylate as an oligomer, which may be an oligomer obtained by reacting an epoxy resin having two or more glycidyl groups with a compound having a (meth)acryloyl group.

[0026] The monomer may be at least one selected from the group consisting of a monofunctional monomer having one polymerizable group and a polyfunctional monomer having two or more polymerizable groups. Two or more types of monomers may be mixed and used. Examples of the monofunctional monomer include methyl (meth)acrylate. Examples of the polyfunctional monomer include ethylene glycol di(meth)acrylate. From the viewpoint of increasing the Young's modulus of the resin layer, the monomer preferably includes a polyfunctional monomer, and more preferably includes a monomer having two polymerizable groups.

[0027] The photopolymerization initiator can be appropriately selected from radical photopolymerization initiators.

[0028] The thickness t1 of the primary resin layer 14 is 7.5 μm or more and 17.5 μm or less. In other words, the outer diameter D3 of the primary resin layer 14 is 140 μm or more and 160 μm or less. In addition to satisfying the Young's modulus range of the primary resin layer 14 described below, by having the primary diameter be 140 μm or more (i.e., the thickness t1 of the primary resin layer 14 be 7.5 μm or more), sufficient lateral pressure resistance characteristics are ensured and an increase in loss due to lateral pressure can be suppressed. Furthermore, by having the outer diameter D3 of the primary resin layer 14 be 160 μm or less (i.e., the thickness t1 of the primary resin layer 14 be 17.5 μm or less), the thickness t2 (5.0 μm or more) of the secondary resin layer 15 can be sufficiently ensured within a predetermined range of the outer diameter of the optical fiber 10A (165 μm or more and 175 μm or less).

[0029] In one aspect of this embodiment, the Young's modulus of the primary resin layer 14 may be 0.10 MPa or more and 0.30 MPa or less at 23°C. If the Young's modulus of the primary resin layer 14 is 0.10 MPa or more, coating cracks called voids and coating delamination are unlikely to occur in the primary resin layer 14 at a screening tension of 1.5 kg or more. This optical fiber 10A does not have problems with low-temperature characteristics. If the Young's modulus of the primary resin layer 14 is 0.30 MPa or less, particularly excellent lateral pressure resistance characteristics can be obtained within the above-mentioned range of thickness t1 of the primary resin layer 14. In the following description, the optical fiber 10A including the primary resin layer 14 having a Young's modulus of 0.10 MPa or more and 0.30 MPa or less may be referred to as an optical fiber specialized for lateral pressure resistance.

[0030] In another aspect of this embodiment, the Young's modulus of the primary resin layer 14 may be 0.30 MPa or more and 0.50 MPa or less at 23°C. When the Young's modulus of the primary resin layer 14 is 0.30 MPa or more, coating cracks called voids and coating delamination are less likely to occur in the primary resin layer 14 at a screening tension of 2.0 kg or more, making breaks less likely to occur when the primary resin layer 14 is made into a tape or cable, and improving productivity. When the Young's modulus of the primary resin layer 14 is 0.50 MPa or less, the lateral pressure resistance characteristics can be obtained within the thickness t1 of the primary resin layer 14 described above. In the following description, an optical fiber 10A including a primary resin layer 14 having a Young's modulus of 0.30 MPa or more and 0.50 MPa or less may be referred to as a high screening tension optical fiber.

[0031] The primary resin layer 14 having the above-described properties can be formed, for example, by curing a resin composition containing an oligomer containing urethane (meth)acrylate, a monomer, a photopolymerization initiator, and a silane coupling agent. The urethane (meth)acrylate, the monomer, and the photopolymerization initiator may be appropriately selected from the compounds exemplified for the base resin above. However, the resin composition forming the primary resin layer 14 has a different composition from the base resin forming the secondary resin layer 15. (First Example)

[0032] The results of evaluation tests using examples and comparative examples according to the first embodiment are shown below, but the present invention is not limited to these examples.

[0033] A plurality of samples of optical fiber 10A were fabricated by forming a primary resin layer 14 on the outer periphery of a glass fiber 13A having a diameter of 125 μm and composed of a core 11 and a cladding 12, and further forming a secondary resin layer 15 on the outer periphery of the primary resin layer 14. Tables 1 and 2 below show the outer diameter, thickness, and Young's modulus at 23° C. of the primary resin layer 14, the outer diameter, thickness, and Young's modulus at 23° C. of the secondary resin layer 15, lateral pressure resistance characteristics, screening tension, and other characteristics of each of the fabricated samples. [Table 1] [Table 2]

[0034] In this example, a primary resin layer 14 having a Young's modulus of 0.10 MPa and a primary resin layer 14 having a Young's modulus of 0.20 MPa were obtained using resin composition 1 shown in Table 3 (hereinafter referred to as resin P1). A primary resin layer 14 having a Young's modulus of 0.30 MPa and a primary resin layer 14 having a Young's modulus of 0.40 MPa were obtained using resin composition 2 shown in Table 3 (hereinafter referred to as resin P2). A primary resin layer 14 having a Young's modulus of 0.50 MPa was obtained using resin composition 3 shown in Table 3 (hereinafter referred to as resin P3). A primary resin layer 14 having a Young's modulus of 0.07 MPa was obtained using resin composition 4 shown in Table 3. A primary resin layer 14 having a Young's modulus of 0.65 MPa was obtained using resin composition 5 shown in Table 3. Specifically, the urethane oligomer (I) was HEA-TDI-(PPG3000-TDI). 2,1 -HEA, and the urethane oligomer (II) is specifically HEA-TDI-(PPG3000-TDI) 2,1 -EH, and the urethane oligomer (III) is specifically HEA-TDI-(PPG3000-TDI) 2,1 -SiI. [Table 3]

[0035] In this example, for the secondary resin layers 15 of each sample with Young's moduli of 1100 MPa and 1200 MPa (hereinafter referred to as resin S1), differences in Young's moduli were obtained by adjusting the UV power or by sorting based on variations in each sample, based on Table 4 below. UA1 was prepared by reacting 2,4-tolylene diisocyanate with polypropylene glycol (number average molecular weight 2000) at a weight ratio of 1:5.7. UA2 was prepared by reacting 2,4-tolylene diisocyanate with polypropylene glycol (number average molecular weight 10000) at a weight ratio of 1:28. [Table 4]

[0036] In this example, the secondary resin layers 15 of each sample with Young's moduli of 2800 MPa and 2900 MPa (hereinafter referred to as resin S2) had the compositions shown in Table 5 below, and differences in Young's moduli were obtained by adjusting the UV power or by selecting samples based on variations in each sample. UA is a urethane acrylate obtained by reacting polypropylene glycol with a molecular weight of 600, 2,4-tolylene diisocyanate, and hydroxyethyl acrylate. EA is epoxy diacrylate. [Table 5]

[0037] In this example, the Young's modulus of the primary resin layer 14 was measured at 23°C using the pullout modulus (POM) method. Metal cylinders were bonded to two locations (separated by a predetermined distance) on the optical fiber 10A. The coating resin layer (primary resin layer 14 and secondary resin layer 15) between the cylinders was removed to expose the glass. The optical fiber was cut on the outer side of the metal cylinder (the side away from the other metal cylinder). (The length of the optical fiber was the sum of the length of the portion bonded to both metal cylinders and the length of the portion between the metal cylinders.) Next, one metal cylinder was fixed, and the other metal cylinder was gently moved slightly in the opposite direction from the fixed metal cylinder. The Young's modulus of the primary resin layer 14 was calculated using the following formula, where L is the length of the metal cylinder (the length to which the optical fiber 10A is bonded), Z is the amount of movement of the chuck, Dp is the outer diameter of the primary resin layer 14, Df is the outer diameter of the glass fiber 13A, n is the Poisson's ratio of the primary resin layer 14, and W is the load applied when the chuck device is moved. Young's modulus (MPa) = ((1 + n)W / πLZ) × ln(Dp / Df) At this time, it is assumed that the glass fiber 13A, the secondary resin layer 15, and the adhesive portion are not deformed (do not stretch), and the primary resin layer 14 is deformed, causing the metal cylinder to move.

[0038] In addition, the Young's modulus of the secondary resin layer 15 was determined by performing a tensile test (gauge length: 25 mm) under an environment of 23±2°C and 50±10% RH using a pipe-shaped coating resin layer (length: 50 mm or more) obtained by removing the glass fiber 13A from the optical fiber 10A, and obtaining the Young's modulus from the 2.5% secant value.

[0039] The lateral pressure resistance characteristics were evaluated using the following method. 500 m of optical fiber 10A was wound in a single layer at a tension of 80 g around a bobbin with a body diameter of 405 mm, which was wrapped with a flat-wound plain-woven metal mesh with a wire outer diameter of 50 μm and a pitch of 150 μm. The transmission loss of the optical fiber was measured in this state. The optical fiber 10A was then wound around a bobbin with a body diameter of 280 mm, and then removed from the bobbin, leaving it wound in a circular shape with a diameter of approximately 280 mm. The transmission loss of the optical fiber was measured in this state (each measurement was made three times and the average value was calculated). The difference between the two average values ​​was taken as the transmission loss difference. Here, the transmission loss was the transmission loss of light with a wavelength of 1550 nm, and was calculated from the loss spectrum measured using the cutback method. When the difference in transmission loss is 1.0 dB / km or less, the lateral pressure resistance characteristic is evaluated as "A." When the difference in transmission loss is more than 1.0 dB / km but less than 1.5 dB / km, the lateral pressure resistance characteristic is evaluated as "B." When the difference in transmission loss is more than 1.5 dB / km, the lateral pressure resistance characteristic is evaluated as "C."

[0040] The screening tension was evaluated using the following method. 1000 km of optical fiber was rewound under tension. When the number of breaks was five or less when rewounding 1000 km of optical fiber at a tension of 2.0 kg (more specifically, between 1.9 kg and 2.3 kg), the screening tension was evaluated as "A." In tension tests using a tension of 2.0 kg, more than five breaks occurred when rewounding 1000 km of optical fiber. However, when the tension was 1.5 kg (more specifically, between 1.4 kg and 1.6 kg), the screening tension was evaluated as "B." When the number of breaks was more than five when rewounding 1000 km of optical fiber at a tension of 1.5 kg, the screening tension was evaluated as "C." Note that there is a correlation between the tension resistance and low-temperature characteristics of optical fiber. That is, for an optical fiber that can withstand a screening tension of 2.0 kg, the difference in transmission loss between 23°C and -60°C is 0.1 dB / km or less, and for an optical fiber that can withstand a screening tension of 1.5 kg, the difference in transmission loss between 23°C and -60°C is 1.2 dB / km or less. The difference in transmission loss between 23°C and -60°C can be found by loosely winding a 1 km long optical fiber into a ring with a diameter of 280 mm, measuring the transmission loss of signal light with a wavelength of 1550 nm under each temperature condition using the OTDR method, and subtracting the transmission loss at 23°C from the transmission loss at -60°C.

[0041] According to this embodiment, when the thickness of the primary resin layer 14 is 7.5 μm or more and 17.5 μm or less, the thickness of the secondary resin layer 15 is 5.0 μm or more and 17.5 μm or less, the Young's modulus of the primary resin layer is 0.10 MPa or more and 0.50 MPa or less, and the Young's modulus of the secondary resin layer at 23° C. is 1200 MPa or more and 2800 MPa or less, the lateral pressure resistance characteristic is evaluated as A or B, and the screening tension is evaluated as A or B, and an optical fiber 10A having a thinned diameter while suppressing deterioration of the lateral pressure resistance characteristic and tension resistance (low-temperature characteristics) can be provided. In particular, when the Young's modulus of the primary resin layer is 0.10 MPa or more and 0.30 MPa or less, an optical fiber 10A specialized for lateral pressure resistance can be provided, in which the lateral pressure resistance characteristic is evaluated as A. Furthermore, in particular, when the Young's modulus of the primary resin layer is 0.30 MPa or more and 0.50 MPa or less, an optical fiber 10A having a high screening tension type (specialized for low-temperature characteristics) can be provided, in which the screening tension is evaluated as A. The higher the screening tension, the less likely the optical fiber 10A will break in the tape-making process that follows, and the higher the yield of the multi-core cable will be.

[0042] As shown in Table 2, when the thickness of the secondary resin layer 15 was less than 5.0 μm, breakage of the optical fiber 10A occurred frequently, making it unsuitable for manufacturing products. Also, when the Young's modulus of the secondary resin layer 15 exceeded 2800 MPa, the coating became brittle, cracks occurred in the secondary resin layer 15, and the appearance was poor. (Second embodiment)

[0043] In the manufacturing process of an optical fiber 10A having a small outer diameter D4, the optical fiber tends to break more frequently than an optical fiber having a conventional outer diameter (e.g., 250 μm). If the optical fiber 10A breaks during the manufacturing process, there is a risk that the manufacturing efficiency of the optical fiber 10A will decrease. In response to this problem, the inventors have found that the frequency of breakage of the optical fiber 10A during the manufacturing process depends on the eccentricity of the glass fiber 13A in the optical fiber 10A.

[0044] When passing through the die in the resin coating device, the glass fiber 13A vibrates in the radial direction of the glass fiber 13A, causing the glass fiber 13A to become eccentric with respect to the die opening, resulting in the formation of the coating resin layer 16A in this state. As a result, the coating resin layer 16A becomes thinner in the direction in which the central axis of the glass fiber 13A is offset from the central axis of the optical fiber 10A. In this case, when the optical fiber 10A comes into contact with burrs on the guide roller or foreign matter on the guide roller, large stress may be locally applied to the glass fiber 13A through the thin portion of the coating resin layer 16A. This may cause damage such as cracks in the glass fiber 13A. As a result, the damage to the glass fiber 13A may cause the optical fiber 10A to break. Optical fibers with small outer diameters may break even when eccentricity is small enough to cause breakage in conventional optical fibers.

[0045] Therefore, in order to study the eccentricity of the glass fiber 13A, the inventors performed a Fourier transform on a waveform indicating the eccentricity of the glass fiber 13A relative to the axial position of the glass fiber 13A, and analyzed the spectrum obtained by the Fourier transform.

[0046] As a result, the inventors have succeeded in suppressing breakage of the optical fiber 10A by adjusting the manufacturing conditions and manufacturing equipment so as to suppress the maximum amplitude to a predetermined value or less in the spectrum obtained by Fourier transforming the eccentricity waveform of the glass fiber 13A. This embodiment is based on the above-mentioned findings discovered by the inventors.

[0047] The eccentricity of the glass fiber 13A in this embodiment will be described with reference to Figures 2, 3, and 4. Figure 2 is a schematic cross-sectional view for explaining the definition of the eccentricity of the glass fiber 13A. Figure 3 is a diagram of an eccentricity waveform showing the eccentricity of the glass fiber 13A relative to the axial position of the glass fiber 13A. Figure 4 is a diagram showing an example of a spectrum obtained by Fourier transforming the eccentricity waveform.

[0048] First, the definition of the eccentricity of the glass fiber 13A will be explained with reference to Fig. 2. Note that Fig. 2 is merely an explanatory diagram and does not show the state of the optical fiber 10A of this embodiment. However, for the sake of simplicity, the same reference numerals as in Fig. 1 are used.

[0049] 2, the eccentricity d of the glass fiber 13A is defined as the distance (radial deviation, radial displacement) from the central axis RC of the coating resin layer 16A relative to the outer periphery of the glass fiber 13A to the central axis GC of the glass fiber 13A. Here, the eccentricity of the glass fiber 13A is measured, for example, by an eccentricity fluctuation observation device.

[0050] The eccentricity amount variation observation device is configured as an eccentricity image recognition device and includes, for example, a first light source, a first imaging unit, a second light source, and a second imaging unit. The first light source is arranged to irradiate light in the short direction of the optical fiber 10A to be measured. The light from the first light source includes a wavelength that is transmitted through the coating resin layer 16A. The first imaging unit is arranged to face the first light source across the optical fiber 10A to be measured, and is configured to acquire an image of the light that has passed through the optical fiber 10A. The second light source and the second imaging unit are configured similarly to the first light source and the first imaging unit, except that they are arranged perpendicular to the opposing direction of the first light source and the first imaging unit.

[0051] With this configuration, the outer circumferential position of the coating resin layer 16A and the inner circumferential position of the coating resin layer 16A (the outer circumferential position of the glass fiber 13A) can be determined based on the light transmitted through the optical fiber 10A in two axial directions that are perpendicular to the central axis of the optical fiber 10A and are orthogonal to each other, and the eccentricity of the glass fiber 13A, which is the distance between their centers, can be measured. In other words, the eccentricity of the glass fiber 13A can be measured without destroying the optical fiber 10A.

[0052] The eccentricity of the glass fiber 13A is measured at a plurality of measurement points set at predetermined intervals in the axial direction of the glass fiber 13A. Then, by plotting the measurement results with the positions of the plurality of measurement points on the horizontal axis and the eccentricity at each position on the vertical axis, a waveform (distribution) of the eccentricity can be obtained. Hereinafter, the waveform of the eccentricity of the glass fiber 13A is also referred to as the "eccentricity waveform."

[0053] By the above-mentioned measurement, for example, the eccentricity waveform shown in Fig. 3 can be obtained. Note that the "eccentricity" on the vertical axis of Fig. 3 is the absolute value of the eccentricity regardless of the direction. As shown in Fig. 3, the eccentricity waveform of the actual optical fiber 10A has a complex shape. Therefore, the inventors performed a Fourier transform on the eccentricity waveform of the optical fiber 10A and analyzed the spectrum obtained by the Fourier transform, as shown in Fig. 4.

[0054] As a result, the inventors succeeded in reducing the frequency of wire breakage by suppressing the "maximum amplitude of eccentricity" in the spectrum obtained by Fourier transforming the eccentricity waveform. The component with the maximum amplitude of eccentricity is also called the "maximum amplitude component."

[0055] Based on the above findings, it is preferable that the optical fiber 10A of this embodiment satisfies at least one of the following requirements regarding the eccentricity of the glass fiber 13A.

[0056] As shown in FIG. 4 , in this embodiment, in the spectrum obtained by Fourier transforming the eccentricity waveform of the glass fiber 13A, the maximum value of the amplitude of the eccentricity (the amplitude value of the maximum amplitude component) is 6 μm or less. If the maximum value of the amplitude of the eccentricity exceeds 6 μm, the glass fiber 13A will be locally eccentric at a position where the peaks of the eccentricity at frequency components of the eccentricity having different periods overlap. This will likely cause the coating resin layer 16A to become locally thin. As a result, there is a risk of an increase in the frequency of breakage of the glass fiber 13A. In contrast, in this embodiment, the maximum value of the amplitude of the eccentricity is set to 6 μm or less. In this case, even if the peaks of the eccentricity at frequency components of the eccentricity having different periods overlap, locally large eccentricity of the glass fiber 13A can be suppressed. This can suppress local thinning of the coating resin layer 16A. As a result, the frequency of breakage of the glass fiber 13A can be reduced. Note that the maximum value of the amplitude of the eccentricity is not particularly limited, and it is preferably as close to 0 μm as possible.

[0057] Furthermore, as shown in FIG. 4 , in this embodiment, in the spectrum obtained by Fourier transforming the eccentricity waveform of the glass fiber 13A, the wavelength at which the amplitude of the eccentricity is maximized (the wavelength of the maximum amplitude component) is 0.1 m or longer. If the wavelength at which the amplitude of the eccentricity is maximized is less than 0.1 m, the component at which the amplitude of the eccentricity is maximized and other components having wavelengths different from each other often overlap. This often results in locally thin coating resin layer 16A. In other words, the number of thin portions of coating resin layer 16A per unit axial length of glass fiber 13A increases. As a result, the frequency of breakage of glass fiber 13A may increase. In contrast, in this embodiment, by setting the wavelength at which the amplitude of the eccentricity is maximized to 0.1 m or longer, it is possible to reduce the number of “other components having different wavelengths” that overlap with the component at which the amplitude of the eccentricity is maximized. This prevents localized thinning of coating resin layer 16A. In other words, it is possible to prevent an increase in the number of thin portions of coating resin layer 16A per unit axial length of glass fiber 13A. As a result, the frequency of breakage of the glass fiber 13A can be reduced.

[0058] The upper limit of the wavelength at which the amplitude of the eccentricity is maximized is not particularly limited, and is preferably as large as possible. However, taking into consideration the drawing speed of the optical fiber manufacturing apparatus 50 described below, the wavelength at which the amplitude of the eccentricity is maximized is, for example, 1 m or less.

[0059] FIG. 5 is a schematic diagram showing the configuration of an optical fiber manufacturing apparatus 50 according to this embodiment. Referring to FIG. 5, the optical fiber manufacturing apparatus 50 according to this embodiment will be described. The optical fiber manufacturing apparatus 50 includes, for example, a drawing furnace 510, a fiber position measurement unit 522, a cooling device 523, an outer diameter measurement unit 524, a resin coating device 530, a curing device 540, a conveying unit 550, a bobbin 560, and a control unit 590. The equipment components other than the control unit 590 are provided in the stated order. The drawing furnace 510 includes a holding mechanism 512, a furnace core tube 514, a heating element 516, and a gas supply unit 518. Hereinafter, of the equipment components of the optical fiber manufacturing apparatus 50, the side closer to the holding mechanism 512 will be referred to as "upstream," and the side closer to the bobbin 560 will be referred to as "downstream."

[0060] The drawing furnace 510 is configured to form the glass fiber 13A. The glass preform G is heated in the drawing furnace 510, and the softened glass is drawn out to form the glass fiber 13A having a small diameter. The fiber position measuring unit 522 is configured to measure the horizontal position of the glass fiber 13A. The cooling device 523 is configured to cool the glass fiber 13A formed in the drawing furnace 510. The outer diameter measuring unit 524 is configured to measure the outer diameter of the glass fiber 13A before it is resin-coated.

[0061] The resin coating device 530 is configured to form a coating resin layer 16A so as to cover the outer periphery of the glass fiber 13A. The coating resin layer 16A has a die that applies an ultraviolet-curable resin composition to the outer periphery of the glass fiber 13A while inserting the glass fiber 13A. In this embodiment, the resin coating device 530 has two dies that form the primary resin layer 14 and the secondary resin layer 15 in this order from the central axis side toward the outer periphery of the glass fiber 13A. The curing device 540 is configured to irradiate the coating resin layer 16A with ultraviolet light to cure the coating resin layer 16A.

[0062] The conveying unit 550 is configured to convey the optical fiber 10A with the cured coating resin layer 16A. Specifically, the conveying unit 550 has, for example, multiple guide rollers 552 and 556 and a capstan 554. A directly below roller 552a, which is one of the multiple guide rollers 552, is located, for example, directly below the curing device 540. The capstan 554 is provided, for example, downstream of the directly below roller 552a and configured to convey (pull) the optical fiber 10A with a predetermined tension while holding the optical fiber 10A between the belt and the roller. The guide roller 552b of the multiple guide rollers 552 is provided between the directly below roller 552a and the capstan 554. Screening rollers 552c, 552d, and 552e of the multiple guide rollers 552 are provided downstream of the capstan 554 and configured to apply a screening tension to the optical fiber 10A together with the capstan 554. The guide roller 556 is provided downstream of the screening roller 552e, and is configured to adjust the tension of the optical fiber 10A by moving up and down in response to fluctuations in the tension of the optical fiber 10A.

[0063] The bobbin 560 is provided, for example, downstream of the guide roller 556 and configured to wind up the optical fiber 10A. The control unit 590 is configured, for example, to be connected to each unit of the optical fiber manufacturing apparatus 50 and to control them. The control unit 590 is configured, for example, as a computer.

[0064] In this embodiment, in order to manufacture the optical fiber 10A that satisfies the requirements for the eccentricity of the glass fiber 13A described above, the optical fiber manufacturing apparatus 50 is configured, for example, as follows.

[0065] In this embodiment, the circumferential length of the largest roller among all rollers including the immediately below roller 552a and the plurality of guide rollers 552 downstream of the immediately below roller 552a is, for example, 0.2 m or more. Note that the circumferential length of the largest guide roller 552 is preferably, for example, 0.9 m or less.

[0066] 5, the conveying unit 550 includes, for example, a vibration suppression unit 555. The vibration suppression unit 555 is installed, for example, downstream of the curing device 540 and upstream of a roller 552a located directly below the curing device 540. The vibration suppression unit 555 is configured, for example, such that two rollers contact the optical fiber 10A from different directions to suppress vibration of the optical fiber 10A. By suppressing vibration of the optical fiber 10A using the vibration suppression unit 555, the position of the central axis of the glass fiber 13A can be stably maintained. In other words, eccentricity of the glass fiber 13A can be suppressed.

[0067] 5, in this embodiment, the immediately below roller 552a located immediately below the curing device 540 is fixed, for example, independently from other equipment components involved in the manufacture of the optical fiber 10A. Specifically, the immediately below roller 552a is fixed, for example, to the floor without being connected to other equipment components. By using the immediately below roller 552a in a fixed state independent from other equipment components involved in the manufacture of the optical fiber 10A, it is possible to suppress the immediately below roller 552a from being subjected to vibrations from other equipment components. As a result, in the spectrum obtained by Fourier transforming the eccentricity waveform of the glass fiber 13A, the maximum value of the amplitude of the eccentricity can be reduced, and the wavelength at which the amplitude of the eccentricity is maximum can be lengthened.

[0068] In the above description, in order to manufacture an optical fiber 10A that satisfies the above requirements for the eccentricity of the glass fiber 13A, all of the following (x), (y), and (z) are implemented, but this is not limited to this case. (x) The circumference of the largest roller among all rollers, including the immediately below roller 552a located immediately below the curing device 540 and the plurality of guide rollers 552 downstream of the immediately below roller 552a, is set to 0.2 m or more. (y) The vibration suppressing unit 555, which is installed downstream of the curing device 540 and upstream of the roller 552a located directly below the curing device 540, suppresses vibration of the optical fiber 10A. (z) The roller 552a located directly below the curing device 540 is used in a fixed state independent of other equipment members involved in the manufacture of the optical fiber 10A. By implementing at least one of (x), (y), and (z), the above-mentioned effects can be obtained to a certain extent. However, by implementing many of (x), (y), and (z), the above-mentioned effects can be obtained more stably.

[0069] In this embodiment, when a first eccentricity of the glass fiber 13A from the central axis, which is based on the outer periphery of the primary resin layer 14, is measured at a plurality of measurement points set at predetermined intervals in the axial direction of the glass fiber 13A, and a second eccentricity of the glass fiber 13A from the central axis, which is based on the outer periphery of the secondary resin layer 15, is measured, the average value of the first eccentricity may be smaller than the average value of the second eccentricity. In this case, the eccentricity of the primary resin layer 14, which has a buffering effect, is reduced, and the lateral pressure resistance characteristics are improved. The plurality of measurement points may be, for example, five or more. (Second Example)

[0070] Next, examples of the second embodiment will be described. These examples are examples of the present disclosure, and the present disclosure is not limited to these examples.

[0071] First, optical fibers of sample numbers 15 to 20 were produced under the conditions shown in Table 6 below. Common conditions not shown in Table 6 are as follows. Glass fiber 13A outer diameter: 125 μm Number of layers of coating resin layer 16A: 2 layers The compositions and thicknesses of the primary resin layer and secondary resin layer of sample numbers 15 to 18 are the same as those of sample number 1 in Table 1.

[0072] [Eccentricity measurement] Using an eccentricity fluctuation observation device, the eccentricity of the glass fiber 13A was measured at multiple measurement points set at predetermined intervals along the axial direction of the glass fiber 13A, thereby obtaining an eccentricity waveform for each of the multiple measurement points. The eccentricity waveform of the optical fiber 10A was then Fourier transformed (FFT: Fast Fourier Transform), and the spectrum obtained by the Fourier transform was analyzed. In this manner, the "maximum amplitude of the eccentricity" and the "wavelength at which the amplitude of the eccentricity is maximum" were determined from the spectrum obtained by the Fourier transform of the eccentricity waveform. Note that the "wavelength at which the amplitude of the eccentricity is maximum" is hereinafter referred to as the "wavelength of the maximum amplitude component."

[0073] [Measurement of frequency of wire breakage] The optical fiber 10A of each sample described above was rewound under a tension of 1.5 kg during the manufacturing process, and the number of breaks in the optical fiber 10A was measured. For each sample, the break frequency was calculated as the number of breaks per 1000 kilometers (mm). As a result, a break frequency of less than 5 times / mm was evaluated as "good," and a break frequency of 5 times / mm or more was evaluated as "poor." The results of the evaluation of each sample are explained with reference to Table 6 below. [Table 6]

[0074] [Sample Nos. 19 and 20] In sample numbers 19 and 20, the maximum amplitude of the eccentricity exceeded 6 μm in the spectrum obtained by Fourier transforming the eccentricity waveform. Furthermore, the wavelength at which the amplitude of the eccentricity reached its maximum in the spectrum obtained by Fourier transforming the eccentricity waveform was less than 0.1 m. As a result, in sample numbers 19 and 20, the optical fiber 10A was prone to breakage, with a breakage frequency of 5 times / mm or more. Furthermore, sample number 19, which had a relatively small diameter, tended to have a higher breakage frequency than sample number 20, which had a conventional outer diameter.

[0075] In sample numbers 19 and 20, the peripheral length of the largest guide roller was less than 0.2 m, so the optical fiber 10A could not be stably transported by the largest guide roller. Furthermore, in sample numbers 19 and 20, the vibration suppression unit 555 was not provided, so the position of the central axis of the glass fiber 13A was shifted significantly or at short intervals when the coating resin layer 16A was coated due to vibrations from the transport unit 550. Furthermore, in sample numbers 19 and 20, the directly below roller 552a was used in a state connected to other device components, so the vibration of the directly below roller 552a was large or at short intervals.

[0076] For these reasons, in the spectrum obtained by Fourier transforming the eccentricity waveform, the maximum amplitude of the eccentricity increased and the wavelength at which the amplitude of the eccentricity reached its maximum decreased in sample numbers 19 and 20. As a result, it is believed that the frequency of breakage increased in sample numbers 19 and 20. It is also believed that the smaller the diameter of the optical fiber 10A, the more likely it was to break.

[0077] [Sample numbers 15-18] In contrast, in the spectrum obtained by Fourier transforming the eccentricity waveform, the maximum amplitude of the eccentricity was 6 μm or less for samples 15 to 18. Also, in the spectrum obtained by Fourier transforming the eccentricity waveform, the wavelength at which the amplitude of the eccentricity was maximum was 0.1 m or more.

[0078] As a result, in sample numbers 15 to 18, the optical fiber 10A was less likely to break, with the breakage frequency being less than 5 times / mm. In sample numbers 15 to 18, the circumferential length of the largest guide roller was set to 0.2 m or more, which enabled the optical fiber 10A to be stably transported by the largest guide roller. In sample numbers 15 and 16, the vibration suppression unit 555 was provided, which enabled the position of the central axis of the glass fiber 13A to be stably maintained when coating the coating resin layer 16A, due to vibration from the transport unit 550. In sample numbers 15 to 17, the directly below roller 552a was used in a fixed state independent of other device components, which enabled the increase in vibration of the directly below roller 552a and the shortening of its period to be suppressed.

[0079] As a result, in sample numbers 15 to 18, it was possible to reduce the maximum amplitude of the eccentricity in the spectrum obtained by Fourier transforming the eccentricity waveform, and to lengthen the wavelength at which the amplitude of the eccentricity is maximum. As a result, it was confirmed that sample numbers 15 to 18 were able to reduce the frequency of wire breakage, even though they had smaller diameters than sample number 19. (Third embodiment)

[0080] 6 is a diagram showing a cross section perpendicular to the axial direction of an optical fiber 10B according to the third embodiment. The optical fiber 10B is a so-called optical fiber core, and includes a glass fiber 13A including a core 11 and a cladding 12, and a coating resin layer 16B including a primary resin layer 14, a secondary resin layer 15, and a colored layer 17 (first colored layer) provided on the outer periphery of the glass fiber 13A. Of these components, the structures and properties of the glass fiber 13A and the secondary resin layer 15 are the same as those of the first embodiment described above.

[0081] The colored layer 17 contacts the outer peripheral surface of the secondary resin layer 15 and coats the entire secondary resin layer 15. The colored layer 17 constitutes the outermost layer of the coating resin layer 16B. The colored layer 17 is made of, for example, a pigment-containing ultraviolet-curable resin. The thickness t3 of the colored layer 17 is 3.0 μm or more and 10.0 μm or less. The outer diameter D5 of the colored layer 17, i.e., the outer diameter of the coating resin layer 16B, is 180 μm ± 5 μm, i.e., 175 μm or more and 185 μm or less. The colored layer 17 is made of a cured product of a resin composition containing a colored ink. When the coating resin layer 16B has the colored layer 17 as in this embodiment, the colored layer 17 makes it easy to identify the optical fiber 10B.

[0082] By setting the thickness t3 of the coloring layer 17 to 3.0 μm or more, the color of the core wire is sufficiently darkened on the outside, improving its distinguishability. Furthermore, color unevenness due to vibration of the optical fiber 10B during the manufacturing process can be suppressed. Furthermore, because the coloring layer 17 contains a pigment, if the coloring layer 17 is excessively thick, the ultraviolet light used to harden the coloring layer 17 may not reach deep enough into the coloring layer 17, resulting in insufficient hardening of the coloring layer 17. If the coloring layer 17 is not hardened enough, the adhesion between the coloring layer 17 and the secondary resin layer 15 decreases, resulting in the coloring layer 17 separating from the secondary resin layer 15 rather than from the tape material when the tape material is peeled off, a phenomenon known as "color peeling." By setting the thickness t3 of the coloring layer 17 to 10.0 μm or less, the ultraviolet light used to harden the coloring layer 17 may reach deep enough into the coloring layer 17, reducing the aforementioned "color peeling."

[0083] In the optical fiber 10B of this embodiment, the Young's modulus of the primary resin layer 14 becomes slightly larger than that of the first embodiment due to the irradiation of ultraviolet light for curing the colored layer 17. This is thought to be because the primary resin layer 14 is further cured by the irradiation of ultraviolet light for curing the colored layer 17.

[0084] That is, in the optical fiber 10B of this embodiment, the Young's modulus of the primary resin layer 14 may be 0.10 MPa or more and 0.40 MPa or less at 23°C. If the Young's modulus of the primary resin layer 14 is 0.10 MPa or more, coating cracks called voids and coating delamination are unlikely to occur in the primary resin layer 14 at a screening tension of 1.5 kg or more. This optical fiber 10B does not have problems with low-temperature characteristics. If the Young's modulus of the primary resin layer 14 is 0.40 MPa or less, particularly excellent lateral pressure resistance characteristics can be obtained within the thickness t1 range of the primary resin layer 14 described in the first embodiment. In the following description, the optical fiber 10B including the primary resin layer 14 having a Young's modulus of 0.10 MPa or more and 0.40 MPa or less may be referred to as a lateral pressure resistance specialized optical fiber (this optical fiber has a colored layer on two coating layers).

[0085] In another aspect of this embodiment, the Young's modulus of the primary resin layer 14 may be 0.40 MPa or more and 0.60 MPa or less at 23°C. When the Young's modulus of the primary resin layer 14 is 0.40 MPa or more, coating cracks called voids and coating delamination are less likely to occur in the primary resin layer 14 at a screening tension of 2.0 kg or more, making breaks less likely to occur when the primary resin layer 14 is made into a tape or cable, thereby improving productivity. When the Young's modulus of the primary resin layer 14 is 0.60 MPa or less, sufficient lateral pressure resistance characteristics can be obtained within the thickness t1 range of the primary resin layer 14 described in the first embodiment. In the following description, the optical fiber 10B including the primary resin layer 14 having a Young's modulus of 0.40 MPa or more and 0.60 MPa or less may be referred to as a high screening tension optical fiber (this optical fiber has a colored layer on two coating layers).

[0086] In this embodiment, the structure and properties of the primary resin layer 14, except for the Young's modulus, are the same as those of the first embodiment described above. (Third Example)

[0087] The results of evaluation tests using examples and comparative examples according to the third embodiment are shown below, but the present invention is not limited to these examples.

[0088] A primary resin layer 14 was formed on the outer periphery of a glass fiber 13A having a diameter of 125 μm and consisting of a core 11 and a cladding 12, a secondary resin layer 15 was further formed on the outer periphery of that, and a colored layer 17 was further formed on the outer periphery of that to produce multiple samples of optical fiber 10B. Tables 7 and 8 below show the outer diameter, thickness, and Young's modulus at 23° C. of the primary resin layer 14, the outer diameter, thickness, and Young's modulus at 23° C. of the secondary resin layer 15, lateral pressure resistance characteristics, screening tension, and other characteristics of each of the produced samples. [Table 7] [Table 8]

[0089] In this example, the specific compositions of the primary resin layer 14 and the secondary resin layer 15 are the same as those in the first example. However, the Young's modulus of the primary resin layer 14 is slightly higher (to about 0 MPa to 0.1 MPa) than in the first example due to the irradiation of ultraviolet light when curing the colored layer 17. The methods for measuring the Young's modulus of the primary resin layer 14 and the secondary resin layer 15, the methods and evaluation criteria for measuring the lateral pressure resistance, and the methods and evaluation criteria for measuring the screening tension are also the same as those in the first example.

[0090] According to this embodiment, when the thickness of the primary resin layer 14 is 7.5 μm or more and 17.5 μm or less, the thickness of the secondary resin layer 15 is 5.0 μm or more and 17.5 μm or less, the Young's modulus of the primary resin layer is 0.10 MPa or more and 0.60 MPa or less, and the Young's modulus of the secondary resin layer at 23° C. is 1200 MPa or more and 2800 MPa or less, the lateral pressure resistance characteristic is evaluated as A or B, and the screening tension is evaluated as A or B, and an optical fiber 10B having a thinned diameter while suppressing deterioration of the lateral pressure resistance characteristic and tension resistance (low-temperature characteristics) can be provided. In particular, when the Young's modulus of the primary resin layer is 0.10 MPa or more and 0.40 MPa or less, an optical fiber 10B specialized for lateral pressure resistance can be provided, in which the lateral pressure resistance characteristic is evaluated as A. Furthermore, in particular, when the Young's modulus of the primary resin layer is 0.40 MPa or more and 0.60 MPa or less, an optical fiber 10B having a high screening tension type (specialized for low-temperature characteristics) in which the screening tension is evaluated as A can be provided. The higher the screening tension, the less likely the optical fiber 10B will break in the tape-making process that follows, and the higher the yield of the multi-core cable.

[0091] As shown in Table 8, when the thickness of the secondary resin layer 15 was less than 5.0 μm, breakage of the optical fiber 10B occurred frequently. When the Young's modulus of the secondary resin layer 15 exceeded 2800 MPa, the coating became brittle, cracks occurred in the secondary resin layer 15, and the appearance was poor. (Variation)

[0092] FIG. 7 is a diagram showing a cross section perpendicular to the axial direction of an optical fiber 10C as a modification of the third embodiment. The optical fiber 10C includes a coating resin layer 16C instead of the coating resin layer 16B of the third embodiment. In addition to the configuration of the coating resin layer 16B of the third embodiment, the coating resin layer 16C further includes a colored layer 18 (second colored layer). The colored layer 18 is formed between the secondary resin layer 15 and the colored layer 17 and is a resin layer with a different color from the colored layer 17. The colored layer 18 includes a plurality of ring patterns formed at intervals in the axial direction of the glass fiber 13A. The colored layer 18 is formed, for example, by an inkjet method that ejects a solvent-diluted ink. Since solvent-diluted ink has the property of being removed by wiping with alcohol or the like, the colored layer 18 is formed on the outer surface of the secondary resin layer 15, and then the colored layer 17 is formed thereon to cover the colored layer 18. The colored layer 18 is a layer whose thickness is discontinuous in the longitudinal direction of the optical fiber. When the optical fiber 10C is viewed along its length, there are also portions where the colored layer 18 is absent.

[0093] According to this modification, the number of distinguishable colors of the optical fiber can be increased by the number of combinations of the number of colors of the colored layer 17 and the number of colors of the colored layer 18. Therefore, the number of distinguishable colors of the optical fiber can be significantly increased. (Fourth embodiment)

[0094] Next, a description will be given of the structure of a glass fiber for further reducing microbending loss while achieving a thinner diameter. Fig. 8 is a diagram showing a cross section perpendicular to the axial direction of an optical fiber 10D of this embodiment. The optical fiber 10D is a so-called optical fiber wire, and includes a glass fiber 13B including a core 11 and a cladding 120, and a coating resin layer 16A including a primary resin layer 14 and a secondary resin layer 15 provided on the outer periphery of the glass fiber 13B. The configuration of the coating resin layer 16A is the same as that of the first embodiment described above. Furthermore, the coating resin layer 16B of the third embodiment may be adopted instead of the coating resin layer 16A, and the optical fiber 10D may be an optical fiber core.

[0095] The cladding 120 surrounds the core 11. The core 11 and the cladding 120 are primarily made of glass, such as silica glass. The core 11 is made of, for example, pure silica glass doped with germanium (Ge). Here, pure silica glass means that it contains substantially no impurities. The cladding 120 includes an inner cladding 121 that surrounds the outer periphery of the core 11 and is in contact with the outer periphery of the core 11, a trench 122 that surrounds the outer periphery of the inner cladding 121 and is in contact with the outer periphery of the inner cladding 121, and an outer cladding 123 that surrounds the outer periphery of the trench 122 and is in contact with the outer periphery of the trench 122. The inner cladding 121 can be made of silica glass doped with chlorine (Cl). The average chlorine mass concentration of the inner cladding 121 is, for example, 500 ppm to 5000 ppm, more preferably, 500 ppm to 3000 ppm. The trench 122 can be made of silica glass doped with fluorine. The outer cladding 123 can be made of pure silica glass. Alternatively, the outer cladding 123 may be doped with chlorine, similar to the inner cladding 121. The average OH mass concentration of the outer cladding 123 is 500 ppm or less, and more preferably, for example, 200 ppm or less. Most preferably, the OH mass concentration is zero. By sintering the outer cladding 123 in a vacuum atmosphere, an optical fiber is realized in which the outer cladding 123 does not contain chlorine and has an OH mass concentration of 5 ppm to 500 ppm.

[0096] FIG. 9 is a diagram showing the refractive index profile in the radial direction of the glass fiber 13B (the portion extending from the center of the glass fiber to the outside). In FIG. 9, range E1 corresponds to the core 11, range E2 corresponds to the inner cladding 121, range E3 corresponds to the trench 122, and range E4 corresponds to the outer cladding 123. The vertical axis represents the relative refractive index difference, and the horizontal axis represents the radial position. As shown in FIG. 9, in the glass fiber 13B, the relative refractive index differences of the core 11, the inner cladding 121, and the trench 122 with respect to the refractive index of the outer cladding 123 are Δ1, Δ2, and Δ3, respectively. In this case, the relative refractive index difference Δ2 of the inner cladding 121 is smaller than the relative refractive index difference Δ1 of the core 11. In other words, the refractive index of the inner cladding 121 is smaller than the refractive index of the core 11. Furthermore, the relative refractive index difference Δ3 of the trench 122 is smaller than the relative refractive index difference Δ2 of the inner cladding 121. In other words, the refractive index of trench 122 is smaller than the refractive index of inner cladding 121. The relative refractive index difference Δ3 of trench 122 has a negative sign, while the relative refractive index difference Δ1 of core 11 has a positive sign. The negative sign of the relative refractive index difference means that the refractive index is smaller than that of outer cladding 123.

[0097] The value (Δ1-Δ2) obtained by subtracting the relative refractive index difference Δ2 of the inner cladding 121 from the relative refractive index difference Δ1 of the core 11 is 0.15% or more and 0.40% or less. In one embodiment, the value (Δ1-Δ2) is 0.34%. Such a relatively small value (Δ1-Δ2) allows for an increase in the mode field diameter of the optical fiber 10D. The absolute value |Δ2| of the relative refractive index difference Δ2 of the inner cladding 121 is 0.10% or less. The relative refractive index difference Δ3 of the trench 122 is -0.70% or more and -0.20% or less. Since the relative refractive index difference Δ3 of the trench 122 is within this range, it is not necessary to add an extremely large amount of fluorine in the glass sintering process. The relative refractive index difference Δ3 of the trench 122 may be less than -0.25%.

[0098] 8 and 9, the radius of the outer periphery of the core 11 is r1, the radius of the inner cladding 121 is r2, and the radius of the outer periphery of the trench 122 is r3. In this case, the value (r2 / r1) obtained by dividing the radius r2 of the inner cladding 121 by the radius r1 of the core 11 is 2.2 or more and 3.6 or less. Furthermore, the value (r3-r2) obtained by subtracting the radius r2 of the inner cladding 121 from the radius r3 of the trench 122 is 3 μm or more and 10 μm or less. The value (r3-r2) may be greater than 4.5 μm. The outer diameter of the outer cladding 123, i.e., the outer diameter of the glass fiber 13B, is within the range of 125 μm±0.5 μm, as in the above embodiments.

[0099] The mode field diameter of the optical fiber 10D for light with a wavelength of 1310 nm is 9.2 μm±0.4 μm, i.e., 8.8 μm or more and 9.6 μm or less. The mode field diameter is defined by Petermann-I. When the optical fiber 10D is wound around a mandrel with a diameter of 15 mm, the bending loss for light with a wavelength of 1625 nm is 1.0 dB or less per turn. When the optical fiber 10D is wound around a mandrel with a diameter of 30 mm, the bending loss for light with a wavelength of 1625 nm is 0.1 dB or less per 10 turns. When the optical fiber 10D is wound around a mandrel with a diameter of 100 mm, the bending loss for light with a wavelength of 1625 nm is 1.0 × 10 -5 dB or less. Such bending loss characteristics can be achieved by setting the value (r2 / r1) obtained by dividing the radius r2 of the inner cladding 121 by the radius r1 of the core 11 to be 3.6 or less. Thus, the optical fiber 10D satisfies the bending loss level specified in G.657.A2 while having a mode field diameter centered at 9.2 μm that is larger than that of a normal optical fiber (an optical fiber in which the refractive index profiles of the core and cladding each have only one step). Note that the bending loss when wound around a diameter of 100 mm is so small that it cannot be measured, so the bending loss was measured at several bending diameters in the range of 20 mm to 60 mm and calculated by extrapolation based on the bending diameter dependency of the bending loss.

[0100] The zero-dispersion wavelength of the optical fiber 10D is 1300 nm or more and 1324 nm or less. In other words, the zero-dispersion wavelength of the optical fiber 10D complies with the provisions of G.657.A2. Such a zero-dispersion wavelength can be achieved by setting the value (r2 / r1) obtained by dividing the radius r2 of the inner cladding 121 by the radius r1 of the core 11 to 2.2 or more. In addition, the chromatic dispersion of the optical fiber 10D for light with a wavelength of 1550 nm is 18.6 ps / (nm km) or less. The zero-dispersion slope of the optical fiber 10D is 0.092 ps / (nm km). 2 ·km) or less.

[0101] The cable cutoff wavelength of the optical fiber 10D is 1260 nm or less, which is to say, the cable cutoff wavelength of the optical fiber 10D complies with the provisions of G.657.A2.

[0102] The optical fiber 10D has a transmission loss of 0.35 dB / km or less for light with a wavelength of 1383 nm. In other words, the average OH mass concentration in the core 11 and cladding 120 is small enough that the transmission loss for light with a wavelength of 1383 nm is 0.35 dB / km or less. By keeping the transmission loss within this range, it is possible to expand the wavelength range that can be used for information transmission in optical communication systems.

[0103] When the standard deviation of the fluctuation in the outer diameter of the glass fiber 13B in the axial direction is σ, 3σ is, for example, 0.1 μm or more and 0.5 μm or less. Here, the standard deviation σ indicates the variation in the longitudinal fluctuation (i.e., outer diameter fluctuation) of the measured values ​​when measured at regular intervals in the longitudinal direction (e.g., 1 m intervals). Furthermore, the value 3σ is more preferably in the range of 0.2 μm or more and 0.5 μm or less. The outer diameter fluctuation must be less than a specified value to satisfy the international standard for glass diameter.

[0104] Figure 10 is a graph showing the relationship between the variation (3σ) in the outer diameter of the glass fiber 13B and the percentage of optical fibers with a transmission loss of 0.32 dB / km or less at a wavelength of 1.31 μm. As is clear from Figure 10, if the variation (3σ) in the outer diameter is 0.1 μm or more, the percentage of optical fibers with a transmission loss of 0.32 dB / km or less exceeds 90%, indicating that transmission loss can be kept sufficiently low. There is a correlation between the variation in the outer diameter and the transmission loss at a wavelength of 1.31 μm; the smaller the variation in the outer diameter, the greater the transmission loss at the wavelength of 1.31 μm. By slightly varying the outer diameter variation (setting 3σ between 0.1 μm and 0.5 μm), transmission loss at a wavelength of 1.31 μm can be reduced within a range where outer diameter variation is not a problem.

[0105] Here, the specifications and characteristics of the optical fibers according to sample numbers 35 and 36 as examples are shown in Table 9. The radius of the outer cladding 123 is 62.5 μm in all cases. [Table 9] (Fourth Example)

[0106] The results of evaluation tests using examples and comparative examples according to the fourth embodiment are shown below, but the present invention is not limited to these examples.

[0107] A primary resin layer 14 was formed on the outer periphery of a glass fiber 13B having a diameter of 125 μm and composed of a core 11 and a cladding 120, and a secondary resin layer 15 was further formed on the outer periphery of the primary resin layer 14 to produce multiple samples of optical fiber 10D. Table 10 below shows the outer diameter, thickness, and Young's modulus at 23° C. of the primary resin layer 14, the outer diameter, thickness, and Young's modulus at 23° C. of the secondary resin layer 15, lateral pressure resistance characteristics, and screening tension for each of the produced samples. The structure of glass fiber 13B of sample numbers 37 and 38 was the same as that of sample number 35 in Table 9, and the structure of glass fiber 13B of sample number 39 was the same as that of sample number 36 in Table 9. [Table 10] The compositions of the primary resin layer 14 and secondary resin layer 15 of sample number 37 are the same as those of resin P3 and resin S2 of Example 1, respectively. The compositions of the primary resin layer 14 and secondary resin layer 15 of sample number 38 are the same as those of resin P2 and resin S2 of Example 1, respectively. The compositions of the primary resin layer 14 and secondary resin layer 15 of sample number 39 are the same as those of resin P2 and resin S1 of Example 1, respectively.

[0108] In this example, the Young's modulus, lateral pressure resistance, and screening tension of each of the primary resin layer 14 and the secondary resin layer 15 were determined by the same methods as in Example 1. In this example, as in Example 1, the thickness of the primary resin layer 14 is 7.5 μm or more and 17.5 μm or less, the thickness of the secondary resin layer 15 is 5.0 μm or more and 17.5 μm or less, the Young's modulus of the primary resin layer is 0.10 MPa or more and 0.50 MPa or less, and the Young's modulus at 23° C. of the secondary resin layer is 1200 MPa or more and 2800 MPa or less, but both the lateral pressure resistance and the screening tension were evaluated as A, and it is possible to provide a thinned optical fiber 10D that has excellent tension resistance (low-temperature characteristics) while further suppressing deterioration of the lateral pressure resistance characteristics.

[0109] Furthermore, a primary resin layer 14 was formed on the outer periphery of a glass fiber 13B having a diameter of 125 μm and composed of a core 11 and a cladding 120, a secondary resin layer 15 was further formed on the outer periphery of that, and a colored layer 17 was further formed on the outer periphery of that to produce multiple samples of optical fiber cores each having the colored layer 17 added to the optical fiber 10D. Table 11 below shows the outer diameter, thickness, and Young's modulus at 23° C. of the primary resin layer 14, the outer diameter, thickness, and Young's modulus at 23° C. of the secondary resin layer 15, lateral pressure resistance characteristics, and screening tension for each of the produced samples. The structure of the glass fiber 13B of sample numbers 40 and 41 was the same as that of sample number 35 in Table 9, and the structure of the glass fiber 13B of sample number 42 was the same as that of sample number 36 in Table 9. [Table 11] The compositions of the primary resin layer 14 and secondary resin layer 15 of sample number 40 are the same as those of resin P3 and resin S2 of Example 1, respectively. The compositions of the primary resin layer 14 and secondary resin layer 15 of sample number 41 are the same as those of resin P2 and resin S2 of Example 1, respectively. The compositions of the primary resin layer 14 and secondary resin layer 15 of sample number 42 are the same as those of resin P2 and resin S1 of Example 1, respectively.

[0110] In this example, the Young's modulus, lateral pressure resistance, and screening tension of each of the primary resin layer 14 and the secondary resin layer 15 were determined by the same method as in Example 1. In this example, as in Example 2, the thickness of the primary resin layer 14 is 7.5 μm or more and 17.5 μm or less, the thickness of the secondary resin layer 15 is 5.0 μm or more and 17.5 μm or less, the Young's modulus of the primary resin layer is 0.10 MPa or more and 0.60 MPa or less, and the Young's modulus at 23° C. of the secondary resin layer is 1200 MPa or more and 2800 MPa or less, but the evaluations of the lateral pressure resistance and the screening tension were both A, and it is possible to provide a thinned optical fiber that is excellent in tension resistance (low-temperature characteristics) while further suppressing deterioration of the lateral pressure resistance. [Note]

[0111] A first optical fiber according to one embodiment of the present disclosure includes a glass fiber including a core and a cladding, and a coating resin layer coating the outer periphery of the glass fiber. The coating resin layer includes a primary resin layer and a secondary resin layer. The primary resin layer is in contact with the glass fiber and coats the glass fiber. The secondary resin layer coats the outer periphery of the primary resin layer. The outer diameter of the glass fiber is 124.5 μm or more and 125.5 μm or less. The thickness of the primary resin layer is 7.5 μm or more and 17.5 μm or less. The Young's modulus of the primary resin layer at 23°C is 0.10 MPa or more and 0.50 MPa or less. The thickness of the secondary resin layer is 5.0 μm or more and 17.5 μm or less. The outer diameter of the secondary resin layer is 165 μm or more and 175 μm or less. The Young's modulus of the secondary resin layer at 23°C is 1200 MPa or more and 2800 MPa or less.

[0112] A second optical fiber according to one embodiment of the present disclosure includes a glass fiber including a core and a cladding, and a coating resin layer coating the outer periphery of the glass fiber. The coating resin layer includes a primary resin layer, a secondary resin layer, and a first colored layer. The primary resin layer is in contact with the glass fiber and coats the glass fiber. The secondary resin layer coats the outer periphery of the primary resin layer. The first colored layer coats the outer periphery of the secondary resin layer. The outer diameter of the glass fiber is 124.5 μm or more and 125.5 μm or less. The thickness of the primary resin layer is 7.5 μm or more and 17.5 μm or less. The Young's modulus of the primary resin layer at 23°C is 0.10 MPa or more and 0.60 MPa or less. The thickness of the secondary resin layer is 5.0 μm or more and 17.5 μm or less. The outer diameter of the secondary resin layer is 165 μm or more and 175 μm or less. The Young's modulus of the secondary resin layer at 23°C is 1200 MPa or more and 2800 MPa or less.

[0113] Experiments have shown that an optical fiber having these parameters can be made thinner while suppressing deterioration in low-temperature characteristics and lateral pressure resistance characteristics.

[0114] In the first optical fiber, the Young's modulus of the primary resin layer at 23° C. may be 0.10 MPa or more and 0.30 MPa or less. Alternatively, in the first optical fiber, the Young's modulus of the primary resin layer at 23° C. may be 0.30 MPa or more and 0.50 MPa or less.

[0115] In the second optical fiber, the Young's modulus of the primary resin layer at 23° C. may be 0.10 MPa or more and 0.40 MPa or less. Alternatively, in the second optical fiber, the Young's modulus of the primary resin layer at 23° C. may be 0.40 MPa or more and 0.60 MPa or less.

[0116] The coating resin layer may further include a second colored layer formed between the secondary resin layer and the first colored layer and having a color different from that of the first colored layer. The second colored layer may include a plurality of ring patterns formed at intervals in the axial direction of the glass fiber.

[0117] The eccentricity of the glass fiber from a central axis based on the outer periphery of the secondary resin layer is measured at a plurality of measurement points set at predetermined intervals in the axial direction of the glass fiber, and a spectrum obtained by Fourier transforming a waveform showing the eccentricity for each position of the plurality of measurement points may have a maximum amplitude of 6 μm or less.

[0118] At a plurality of measurement points set at predetermined intervals in the axial direction of the glass fiber, a first eccentricity of the glass fiber from a central axis based on the outer periphery of the primary resin layer is measured, and a second eccentricity of the glass fiber from a central axis based on the outer periphery of the secondary resin layer is measured, and the average value of the first eccentricity is smaller than the average value of the second eccentricity.

[0119] The difference in transmission loss, calculated by subtracting the transmission loss when the optical fiber is not wound around a bobbin but rolled into a ring with a diameter of 280 mm from the transmission loss when the optical fiber is wound in one layer around a bobbin with a diameter of 405 mm and a metal mesh with a pitch of 150 μm, may be 1.5 dB / km or less.

[0120] The cladding may include an inner cladding that covers the outer periphery of the core, a trench that covers the outer periphery of the inner cladding, and an outer cladding that covers the outer periphery of the trench. The refractive index of the inner cladding is lower than that of the core, the refractive index of the trench is lower than that of the inner cladding, and the refractive index of the outer cladding is higher than that of the trench and lower than that of the core, and the core may be doped with germanium. where Δ1 is the relative refractive index difference of the core to the refractive index of the outer cladding, Δ2 is the relative refractive index difference of the inner cladding to the refractive index of the outer cladding, Δ3 is the relative refractive index difference of the trench to the refractive index of the outer cladding, r1 is the radius of the core, r2 is the radius of the inner cladding, and r3 is the radius of the trench, r2 / r1 may be 2.2 to 3.6, r3 - r2 may be 3 μm to 10 μm, Δ1 - Δ2 may be 0.15% to 0.40%, |Δ2| may be 0.10% or less, and Δ3 may be -0.70% to -0.20%. The mode field diameter for light with a wavelength of 1310 nm may be 8.8 μm to 9.6 μm. The bending loss for light with a wavelength of 1625 nm when wound into a circular ring with a diameter of 15 mm may be 1.0 dB or less per turn, and the bending loss for light with a wavelength of 1625 nm when wound into a circular ring with a diameter of 30 mm may be 0.1 dB or less per 10 turns. The zero-dispersion wavelength may be 1300 nm or more and 1324 nm or less, the cable cutoff wavelength may be 1260 nm or less, and the average chlorine mass concentration of the inner cladding may be 500 ppm or more and 5000 ppm or less.

[0121] The average OH mass concentration of the outer cladding may be 500 ppm or less.

[0122] When the standard deviation of the outer diameter fluctuation in the axial (or length) direction of the glass fiber is defined as σ, 3σ may be 0.1 μm or more and 0.5 μm or less. [Explanation of symbols]

[0123] 10A, 10B, 10C, 10D...Optical fiber 11...Core 12...Clad 13A, 13B...Glass fiber 14...Primary resin layer 15...Secondary resin layer 16A, 16B, 16C...coating resin layer 17...Colored layer (first colored layer) 18...Colored layer (second colored layer) 50...Optical fiber manufacturing equipment 120...Clad 121...Inner cladding 122...Trench 123...Outer cladding 510...Wire drawing furnace 512...Gripping mechanism 514...Furnace tube 516...heating element 518...Gas supply section 522...Fiber position measurement unit 523…Cooling device 524...Outer diameter measuring section 530...Resin coating device 540…Curing equipment 550...Transport unit 552...Guide roller 552a...Directly below roller 552b...Guide roller 552c, 552d, 552e...Screening rollers 554...Capstan 555...Vibration suppression part 556...Guide roller 560...Bobbin 590...Control unit G: Glass base material GC,RC…center axis

Claims

1. A method for measuring the eccentricity of an optical fiber using an eccentricity fluctuation observation device, comprising: the eccentricity fluctuation observation device includes a first light source, a first imaging unit, a second light source, and a second imaging unit; the first light source and the second light source are arranged to irradiate the first light and the second light, respectively, in a short direction of the optical fiber; the first light and the second light include wavelengths that are transmitted through a coating resin layer of the optical fiber, the first imaging unit is disposed to face the first light source across the optical fiber, the second imaging unit is disposed to face the second light source across the optical fiber, and a facing direction of the second light source and the second imaging unit is perpendicular to a facing direction of the first light source and the first imaging unit; a first image obtained by capturing, in the first imaging unit, the first light transmitted through the optical fiber at a plurality of measurement points set at predetermined intervals in the axial direction of the optical fiber, and a second image obtained by capturing, in the second imaging unit, the second light transmitted through the optical fiber at the plurality of measurement points, and by determining the outer periphery position and the inner periphery position of the coating resin layer based on the first image and the second image, the second light transmitted through the optical fiber at the plurality of measurement points, and calculating the eccentricity amount as the distance between the centers of the outer periphery position and the inner periphery position; a spectrum obtained by Fourier transforming a waveform indicating the amount of eccentricity for each of the positions of the plurality of measurement points, in which it is confirmed that the maximum value of the amplitude of the amount of eccentricity is greater than 0 μm and not greater than 3.6 μm, and that the wavelength at which the amplitude of the amount of eccentricity is maximum is greater than 0.1 m and not greater than 1 m.

2. 1. A method of manufacturing an optical fiber, comprising: forming a glass fiber; forming the coating resin layer so as to cover the outer periphery of the glass fiber; a step of irradiating the coating resin layer with ultraviolet light to cure the coating resin layer; a step of calculating the eccentricity of the optical fiber by the method for measuring eccentricity of an optical fiber according to claim 1, and confirming that the maximum value of the amplitude of the eccentricity is greater than 0 μm and not greater than 3.6 μm, and that the wavelength at which the amplitude of the eccentricity is maximum is not less than 0.1 m and not greater than 1 m; A method for manufacturing an optical fiber, comprising:

3. a direct-below roller is disposed directly below a curing device that performs the curing step, and a plurality of guide rollers are disposed downstream of the direct-below roller; 3. The method for manufacturing an optical fiber according to claim 2, wherein the largest roller among all the rollers including the immediately below roller and the plurality of guide rollers has a circumferential length of 0.2 m or more.

4. a direct-below roller is disposed directly below a curing device that performs the curing step, and a vibration suppression unit is disposed downstream of the curing device and upstream of the direct-below roller; The method for manufacturing an optical fiber according to claim 2 , wherein the vibration suppressing unit includes two rollers that contact the optical fiber from different directions to suppress vibration of the optical fiber.

5. 3. The method for manufacturing an optical fiber according to claim 2, wherein a roller is disposed directly below a curing device that performs the curing step, and the roller is fixed independently from other equipment components involved in the manufacturing of the optical fiber.

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