Optical fiber and optical cable

Abstract

In the present invention a primary resin layer has a thickness of 4 µm or more and a Young's modulus of 0.3 MPa or less. A secondary resin layer has a radius of 85 µm or less, a thickness of 7.5 µm or more, and a Young's modulus of 1250 MPa or more. The MFD of the optical fiber at a wavelength of 1310 nm is greater than 8.2 µm, and the MFD at a wavelength of 1550 nm is 9.40-10.5 µm. The bending loss of the optical fiber at a wavelength of 1550 nm when wound with a bending diameter of 10 mm is 1 dB / turn or less. In the ratio D / H2 indicating the relationship between the lateral rigidity D of the optical fiber and the flexural rigidity H thereof, the relative ratio with respect to a 200 µm strand as a reference is 540 or less. The cross-sectional area of a portion of a coating layer excluding the primary resin layer is 4400 µm2 or more and 12,000 µm2 or less. The optical fiber has a zero dispersion slope of 0.092 ps / nm2 / km or less.

Description

Optical Fiber and Cable

[0001] This application claims priority to Japanese Application No. 2024-120905, filed on July 26, 2024, and incorporates by reference the entire contents of said Japanese application.

[0002] With the increase in communication traffic, it is becoming increasingly important to build economical optical networks. In order to achieve this, it is expected that optical cables will become thinner and more densely packed to reduce transportation and installation costs. At the same time, there is also a demand for thinner optical fibers themselves. Patent Documents 1 to 4 disclose examples of thin-diameter optical fibers. However, the reduction in diameter poses a challenge in terms of the increase in microbending loss that occurs during cabling. Therefore, it is necessary to conduct structural studies based on analytical formulas that can systematically estimate the effects of optical fiber structure.

[0003] Non-Patent Document 1 describes that the microbending resistance characteristics of an optical fiber are related to the lateral rigidity D and bending rigidity H of the optical fiber and can be determined by an approximate formula. Patent Document 5 describes that the approximate formula of Non-Patent Document 1 has been expanded to a form closer to reality.

[0004] US Patent No. 11,874,494 US Patent No. 1,118,1687 US Patent No. 1,171,9878 US Patent No. 1,170,9313 International Publication No. 2018 / 025896

[0005] F. Cocchini, “The Lateral Rigidity of Double-Coated Optical Fibers”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 13, NO. 8, AUGUST 1995

[0006] As the diameter of an optical fiber is reduced, microbending loss may increase, so it is desirable to reduce the microbending loss even when the diameter of the optical fiber is reduced.

[0007] An object of the present disclosure is to provide a small-diameter optical fiber and optical cable that can reduce microbending loss.

[0008] According to the present disclosure, it is possible to reduce microbending loss in a small-diameter optical fiber and an optical cable including the small-diameter optical fiber.

[0009] [1] An optical fiber according to one aspect of the present disclosure comprises a glass fiber including a core and a cladding surrounding the core, and a coating layer surrounding the glass fiber. The core is formed from silica glass doped with at least one of germanium, titanium, chlorine, fluorine, and an alkali metal. The cladding includes an inner cladding in contact with and surrounding the core, an outer cladding surrounding the inner cladding, and a trench disposed radially between the inner cladding and the outer cladding. The coating layer includes a primary resin layer surrounding the cladding and a secondary resin layer surrounding the primary resin layer. The core has a radius of 3.6 μm or more and 5.4 μm or less, and the relative refractive index difference of the core to the refractive index of the cladding is greater than the refractive index of the cladding by 0.32% or more and 0.40% or less. The volume of the trench is -30% μm ２ The radius of the cladding is 63 μm or less. The thickness of the primary resin layer is 4 μm or more, and the Young's modulus of the primary resin layer is 0.3 MPa or less. The radius of the secondary resin layer is 85 μm or less, the thickness of the secondary resin layer is 7.5 μm or more, and the Young's modulus of the secondary resin layer is 1250 MPa or more. The effective cross-sectional area of ​​the optical fiber at a wavelength of 1550 nm is 100 μm or less. ２ The mode field diameter of the optical fiber at a wavelength of 1310 nm is greater than 8.2 μm. The mode field diameter of the optical fiber at a wavelength of 1550 nm is 9.40 μm or greater and 10.5 μm or less. The cable cutoff wavelength of the optical fiber is less than 1420 nm. The bending loss of the optical fiber at a wavelength of 1550 nm when wound with a bending diameter of 10 mm is 1 dB / turn or less. D / H, which shows the relationship between the lateral rigidity D and bending rigidity H of the optical fiber, ２ The D / H of the standard 200 μm wire ２ The relative ratio to the cross-sectional area of ​​the coating layer excluding the primary resin layer is 540 or less. ２ 12000 μm or more２ The absolute difference between the refractive index of the cladding and the refractive index of the coating layer is greater than 0.01. The optical fiber has a refractive index of 0.092 ps / nm or less. ２ / km or less.

[0010] In the optical fiber of the above [1], the radius of the cladding is 63 μm or less, and the radius of the secondary resin layer is 85 μm or less, so that a small-diameter optical fiber can be provided. ２ is related to the microbending loss, and the microbending loss Δα ｍｉｃｒｏ = A x D / H ２ A is a constant that depends on the refractive index structure of the optical fiber. Here, the D / H of the 200 μm fiber ２ The relative ratio of D / H to the standard 200 μm strand is set to 540 or less. By using an optical fiber with such a rigidity ratio, it is possible to reduce microbending loss. This also reduces cable loss when each optical fiber is cabled. If the rigidity ratio is greater than 540, transmission loss increases even with slight lateral pressure, making it difficult to improve the fiber density when the optical fiber is cabled or coded. Here, the D / H of the standard 200 μm strand is set to 540 or less. ２ The calculation conditions are, for example, as follows: The radius of the glass fiber is 62.5 μm. The radius of the primary resin layer is 85 μm. The radius of the secondary resin layer is 96.5 μm. The Young's modulus of the glass fiber is 72,500 [MPa]. The Young's modulus of the primary resin layer is 0.4 [MPa]. The Young's modulus of the secondary resin layer is 1,500 [MPa].

[0011] [2] In the optical fiber of [1] above, the volume of the trench is −380% μm ２ Above -126% μm ２ In this case, the mode field diameter at 1310 nm can be expanded to, for example, 8.7 μm or more while maintaining low microbending loss.

[0012] [3] In the optical fiber of the above [1] or [2], the radius of the glass fiber is R0 [m], and the Young's modulus of the glass fiber is E0 [N / m ２ ], the radius of the primary resin layer is R1 [m], and the Young's modulus of the primary resin layer is E1 [N / m ２ ], the radius of the secondary resin layer is R2 [m], and the Young's modulus of the secondary resin layer is E2 [N / m ２ ], the lateral stiffness D [N / m ２ ] and the bending rigidity H [N / m ２ ] satisfies formula (3), and the coating eccentricity may be 8 μm or less. Here, c1 = 0.209367, c2 = 1.206659, c3 = 0.401169, and c ｉｊｋ is as follows: ０００ =-0.611554c １００ =3.615414c ０１０ =0.253128c ００１ =-7.130445c ２００ =0.787599c １１０ =0.329243c １０１ =2.320080c ０２０ =-0.062024c ０１１ =-0.985974c ００２ = -8.696048

[0013] The approximation formula in Patent Document 5 was calculated by numerical analysis with the glass fiber diameter (glass diameter) limited to 125 μm. Therefore, it was found that when applied to optical fibers with different glass diameters, the difference between the calculated and measured microbending loss values ​​may become large. In other words, the optical fiber described in Patent Document 5 may not be able to suppress microbending loss. In contrast, the optical fiber described in [3] above has lateral rigidity D and flexural rigidity H that satisfy equation (3), so it can reliably reduce microbending loss. Furthermore, because the coating eccentricity is low, the difference between the calculated and measured microbending loss values ​​is unlikely to become large. Therefore, it is possible to more reliably reduce microbending loss.

[0014] [4] In the optical fiber according to any one of [1] to [3] above, the coating layer may further include a colored layer surrounding the secondary resin layer. ２ 12000 μm or more ２ The cross-sectional area of ​​the portion of the coating layer may be 4,400 μm or less. ２ By setting the cross-sectional area of ​​the coating layer at 12000 μm or more, the influence of external damage on the optical fiber can be easily reduced. ２ By satisfying the condition below, it is possible to reduce cracks in the coating due to external damage to the optical fiber.

[0015] [5] In the optical fiber of any one of [1] to [4] above, the radius of the secondary resin layer may be 81 μm or less. In this case, the optical fiber can be made thinner and denser.

[0016] [6] In the optical fiber of any one of [1] to [4] above, the radius of the secondary resin layer may be 51 μm or less. In this case, the diameter of the optical fiber is reduced, and further density can be increased.

[0017] [7] In the optical fiber of any one of [1] to [6] above, the median breaking stress of the optical fiber may be 1.5 GPa or more when a tensile test is performed using a tensile tester having a first mandrel and a second mandrel, with sandpaper having an average particle size of 15 μm or more and 25 μm or less wrapped around the first mandrel. In this case, the durability and external damage resistance of the small-diameter optical fiber can be improved.

[0018] [8] In the optical fiber according to any one of [1] to [7] above, the bending loss of the optical fiber at a wavelength of 1625 nm when wound with a bending diameter of 10 mm may be 3 dB / turn or less. In this case, the transmission loss in the small-diameter optical fiber can be reduced.

[0019] [9] An optical cable according to an embodiment of the present disclosure includes a plurality of optical fibers according to any one of [1] to [8] above. In this case, the optical cable can have reduced microbending loss. Furthermore, since a small-diameter optical fiber is used, the cable can be made denser.

[0020] Fig. 1 is a cross-sectional view perpendicular to the fiber axis of an optical fiber according to an embodiment. Fig. 2 is a cross-sectional view showing a modified example of the optical fiber shown in Fig. 1. Fig. 3 is a cross-sectional view perpendicular to the central axis of an optical cable according to an embodiment.

[0021] First, the details of the embodiments of the present disclosure will be listed and explained. [1] An optical fiber according to one aspect of the present disclosure comprises a glass fiber including a core and a cladding surrounding the core, and a coating layer surrounding the glass fiber. The core is formed from silica glass doped with at least one of germanium, titanium, chlorine, fluorine, and an alkali metal. The cladding includes an inner cladding in contact with and surrounding the core, an outer cladding surrounding the inner cladding, and a trench disposed radially between the inner cladding and the outer cladding. The coating layer includes a primary resin layer surrounding the cladding and a secondary resin layer surrounding the primary resin layer. The core has a radius of 3.6 μm or more and 5.4 μm or less, and the relative refractive index difference of the core with respect to the refractive index of the cladding is 0.32% or more and 0.40% or less compared to the refractive index of the cladding. The volume of the trench is -30% μm ２ The radius of the cladding is 63 μm or less. The thickness of the primary resin layer is 4 μm or more, and the Young's modulus of the primary resin layer is 0.3 MPa or less. The radius of the secondary resin layer is 85 μm or less, the thickness of the secondary resin layer is 7.5 μm or more, and the Young's modulus of the secondary resin layer is 1250 MPa or more. The effective cross-sectional area of ​​the optical fiber at a wavelength of 1550 nm is 100 μm or less. ２The mode field diameter of the optical fiber at a wavelength of 1310 nm is greater than 8.2 μm. The mode field diameter of the optical fiber at a wavelength of 1550 nm is 9.40 μm or greater and 10.5 μm or less. The cable cutoff wavelength of the optical fiber is less than 1420 nm. The bending loss of the optical fiber at a wavelength of 1550 nm when wound with a bending diameter of 10 mm is 1 dB / turn or less. D / H, which shows the relationship between the lateral rigidity D and bending rigidity H of the optical fiber, ２ The D / H of the standard 200 μm wire ２ The relative ratio to the cross-sectional area of ​​the coating layer excluding the primary resin layer is 540 or less. ２ 12000 μm or more ２ The absolute difference between the refractive index of the cladding and the refractive index of the coating layer is greater than 0.01. The optical fiber has a refractive index of 0.092 ps / nm or less. ２ / km or less.

[0022] Specific examples of optical fibers and optical cables 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 of the claims. In the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted.

[0023] 1 is a cross-sectional view of an optical fiber according to an embodiment, taken along a line perpendicular to the fiber axis, in which the optical fiber 1 includes a glass fiber 10 and a coating resin 20 (coating layer).

[0024] The glass fiber 10 is made of silica glass (SiO ２). The glass fiber 10 includes a core 11 and a clad 12. The core 11 extends along the fiber axis of the optical fiber 1. The radius of the core 11 is 3.6 μm or more and 5.6 μm or less. The refractive index of the core 11 is higher than the refractive index of the clad 12. The relative refractive index difference of the core 11 with respect to the clad 12 is, for example, 0.32% or more and 0.40% or less. In this embodiment, microbending loss is reduced, so the relative refractive index difference of the core 11 can be reduced. The core 11 is formed from silica glass doped with at least one of germanium, titanium, chlorine, fluorine, and an alkali metal element. The alkali metal element doped to the core 11 is, for example, sodium (Na), potassium (K), lithium (Li), rubidium (Rb), or cesium (Cs).

[0025] The cladding 12 surrounds the core 11 and covers the outer peripheral surface of the core 11. The cladding 12 is formed of, for example, pure silica glass. The cladding 12 has an inner cladding 13, a trench 14, and an outer cladding 15. The inner cladding 13 contacts and surrounds the core 11. The outer cladding 15 surrounds the inner cladding 13. The trench 14 is disposed between the inner cladding 13 and the outer cladding 15 in the radial direction. The radius of the inner cladding 13 is, for example, 7 μm or more and 20 μm or less. The radius of the trench 14 is, for example, 11 μm or more and 34 μm or less. The radius of the outer cladding 15 is, for example, 20 μm or more and 63 μm or less.

[0026] The Young's modulus of the glass fiber 10 including the core 11 and the cladding 12 is, for example, 70 GPa or more and 80 GPa or less. The volume of the trench 14 is, for example, −380%·μm ２ Above -126% μm ２ Since the trench 14 is provided in the cladding 12 in this manner, the microbending loss in the optical fiber 1 can be reduced.

[0027] The coating resin 20 is made of an ultraviolet curable resin. The coating resin 20 includes a primary resin layer 21 surrounding the clad 12 (outer clad 15) and a secondary resin layer 22 surrounding the primary resin layer 21. The primary resin layer 21 surrounds the glass fiber 10 and covers the outer peripheral surface of the glass fiber 10 (outer clad 15 of the clad 12). The primary resin layer 21 is provided in contact with the clad 12. The radius of the primary resin layer 21 is, for example, 40 μm or more and 70 μm or less. The thickness of the primary resin layer 21 is, for example, 4 μm or more and 30 μm or less, and may be 25 μm or less.

[0028] The Young's modulus of the primary resin layer 21 is, for example, 0.05 MPa or more and 0.3 MPa or less. In order to reduce microbending loss, the lower the Young's modulus of the primary resin layer 21, the better. If the Young's modulus of the primary resin layer 21 exceeds 0.3 MPa, the microbending loss cannot be sufficiently reduced. On the other hand, if the Young's modulus of the primary resin layer 21 is too low, the coating resin 20 including the primary resin layer 21 and the secondary resin layer 22 may be damaged. If the Young's modulus of the primary resin layer 21 is 0.05 MPa or more, damage to the coating resin 20 is prevented.

[0029] The primary resin layer 21 may be made of, for example, a polyether-based or polyester-based urethane acrylate. The primary resin layer 21 may contain a reactive diluent monomer and a photoinitiator as needed. The Young's modulus of the primary resin layer 21 can be adjusted, for example, by the molecular weight of the polyether portion of the ultraviolet-curable resin and the type of diluent monomer.

[0030] The primary resin layer 21 contains, for example, 0.3 mass % to 2.0 mass % of a phosphorus-containing photoinitiator. The primary resin layer 21 contains, for example, polypropylene glycol having a mass average molecular weight of 1,000 to 5,000. This makes it difficult for peeling to occur at the interface between the glass fiber 10 and the primary resin layer 21 or for the resin coating to be broken, even if the optical fiber 1 is subjected to an external force during rewinding, unitization, or the like, in the optical fiber 1 having the primary resin layer 21 with a relatively low Young's modulus.

[0031] The secondary resin layer 22 surrounds the primary resin layer 21 and covers the outer peripheral surface of the primary resin layer 21. The radius of the secondary resin layer 22 is, for example, 50 μm or more and 85 μm or less. The radius of the secondary resin layer 22 may be 81 μm or less, or may be 51 μm or less. The diameter of the secondary resin layer 22 is the diameter (coating diameter) of the coating resin 20 when no additional colored layer (ink layer) is provided on the outer periphery of the secondary resin layer 22. The thickness of the secondary resin layer 22 is, for example, 7.5 μm or more and 25 μm or less, and may be 10 μm or more. The Young's modulus of the secondary resin layer 22 is, for example, 1250 MPa or more and 3000 MPa or less.

[0032] The secondary resin layer 22 may be made of, for example, a polyether-based or polyester-based urethane acrylate. The secondary resin layer 22 may contain a reactive diluent monomer and a photoinitiator as needed. The Young's modulus of the secondary resin layer 22 can be adjusted, for example, by the molecular weight of the polyether portion of the ultraviolet-curable resin and the type of diluent monomer.

[0033] As shown in FIG. 2 , the coating resin 20 may further include a colored layer 23 surrounding the secondary resin layer 22 on the outer periphery of the secondary resin layer 22. The colored layer 23 is a layer formed from colored ink for identification. By applying various colors to each optical fiber 1, it is possible to identify the optical fiber 1. The thickness of the colored layer 23 is, for example, 2 μm or more and 5 μm or less. Furthermore, one or more marks may be provided as a set between the colored layer 23 and the secondary resin layer 22, and these may be provided periodically along the longitudinal axis.

[0034] In the optical fiber 1, the total cross-sectional area of ​​the secondary resin layer 22 and the colored layer 23 (if formed) of the coating resin 20 is, for example, 4400 μm ２ 12000 μm or more ２The "total cross-sectional area of ​​the secondary resin layer 22 and the colored layer 23 (if formed)" here corresponds to the cross-sectional area of ​​the coating resin 20 excluding the primary resin layer 21. In addition, if the colored layer 23 is not formed, the total cross-sectional area of ​​the secondary resin layer 22 of the coating resin 20 is, for example, 4400 μm ２ 12000 μm or more ２ The ratio of the thickness of the primary resin layer 21 to the total thickness of the secondary resin layer 22 and the colored layer 23 (if formed) is, for example, 0.25 or more and 1.50 or less.

[0035] The effective area of ​​the optical fiber 1 at a wavelength of 1550 nm is, for example, 100 μm ２ The mode field diameter (MFD) of the optical fiber 1 at a wavelength of 1310 nm is, for example, greater than 8.2 μm and not greater than 9.50 μm. The mode field diameter (MFD) of the optical fiber 1 at a wavelength of 1550 nm is, for example, not less than 9.40 μm and not greater than 10.5 μm, and may be 10 μm or greater. The mode field diameter (MFD) of the optical fiber 1 at a wavelength of 1625 nm is, for example, not less than 9.70 μm and not greater than 10.90 μm. The cable cutoff wavelength of the optical fiber 1 is, for example, less than 1420 nm, and may be less than 1310 nm.

[0036] The bending loss of the optical fiber 1 at a wavelength of 1550 nm when wound with a bending diameter of 10 mm is, for example, 1 dB / turn or less. The bending loss of the optical fiber 1 at a wavelength of 1550 nm when wound with a bending diameter of 15 mm is, for example, 0.3 dB / turn or less. The bending loss of the optical fiber 1 at a wavelength of 1550 nm when wound with a bending diameter of 20 mm is, for example, 0.05 dB / turn or less. The bending loss of the optical fiber 1 at a wavelength of 1550 nm when wound with a bending diameter of 30 mm is, for example, 0.01 dB / turn or less. The bending loss of the optical fiber 1 at a wavelength of 1625 nm when wound with a bending diameter of 10 mm is, for example, 5.0 dB / turn or less, and may be 3 dB / turn or less.

[0037] In the optical fiber 1, the absolute difference between the refractive index of the cladding 12 and the refractive index of the coating resin 20 including the primary resin layer 21 and the secondary resin layer 22 is greater than 0.01. ２ / km or less.

[0038] The coating eccentricity of the optical fiber 1 is, for example, 8 μm or less. Here, the coating eccentricity is defined as the distance from the central axis of the glass fiber 10, based on the outer periphery of the coating resin 20 (secondary resin layer 22). In a cross section perpendicular to the fiber axis, the coating eccentricity is the deviation between the center of the glass fiber 10, based on the outer periphery of the coating resin 20. The coating eccentricity may be 6 μm or less. Since the coating eccentricity is likely to change with the longitudinal axis of the optical fiber 1, it is desirable to measure it at multiple points on the longitudinal axis of the optical fiber 1. Preferably, the average value of values ​​measured at 500 or more points every 1 mm to 100 mm may be used as the coating eccentricity.

[0039] As described above, when the approximate formula in Patent Document 5 is applied to optical fibers having a glass diameter other than 125 μm, the discrepancy between the calculated value of microbending loss and the actually measured value may become large. It has been found that, particularly for small-diameter optical fibers, the microbending loss calculated by the approximate formula in Patent Document 5 is lower than the actual value. Therefore, the inventors have derived an approximate formula that is expanded to cover a range of glass diameters smaller than 125 μm or a range of coating diameters smaller than 160 μm, and have specified the following optical fiber 1 that can reliably reduce microbending loss even in the case of small diameters.

[0040] That is, the radius of the glass fiber 10 is R0 [m], the Young's modulus of the glass fiber 10 is E0 [N / m ２ ], the radius of the primary resin layer 21 is R1 [m], and the Young's modulus of the primary resin layer 21 is E1 [N / m ２ ], the radius of the secondary resin layer 22 is R2 [m], and the Young's modulus of the secondary resin layer 22 is E2 [N / m ２ ], the lateral stiffness (lateral elastic modulus) D [N / m ２ ] and the bending rigidity (bending elastic modulus) H [N m２ ] satisfies the formula (3). Here, c1 = 0.209367, c2 = 1.206659, c3 = 0.401169, and c ｉｊｋ is as follows: ０００ =-0.611554c １００ =3.615414c ０１０ =0.253128c ００１ =-7.130445c ２００ =0.787599c １１０ =0.329243c １０１ =2.320080c ０２０ =-0.062024c ０１１ =-0.985974c ００２ = -8.696048

[0041] Equation (2) is the equation for the bending rigidity H shown in Non-Patent Document 1. The methods for deriving equations (1) and (3) will be described below.

[0042] In general, the microbending loss α of an optical fiber is expressed by the approximate formula (4) using lateral rigidity D, bending rigidity H, and a constant A resulting from the optical characteristics of the optical fiber.

[0043] The microbending loss α of a small-diameter optical fiber is desirably 5.0 dB / km or less, preferably 3.0 dB / km or less, and more preferably 1.0 dB / km or less. Therefore, the constant A in equation (4) is calculated from the measured value of the microbending loss α, and the D / H ratio that satisfies the above value is determined. ２ The results are shown in Table 1. From the results shown in Table 1, the D / H ratio that suppresses the microbending loss α to 5.0 dB / km or less is ２ As a conditional expression, the following expression (3) is obtained.

[0044]

[0045] Based on the method of Non-Patent Document 1, the cladding diameter (2R0) is 75 μm or more and 130 μm or less, the primary diameter (2R1) is 0 μm or more and 210 μm or less, the secondary diameter (2R2) is 110 μm or more and 210 μm or less, the Young's modulus E1 of the primary resin layer is 0.05 MPa or more and 0.7 MPa or less, and the Young's modulus E2 of the secondary resin layer is 1000 MPa or more and 3000 MPa or less. For 378 types of combinations, a two-dimensional FEM (finite element method) calculation was performed using the analysis software MSC.Nastran 2020sp1.

[0046] Next, the lateral stiffness D of each component was calculated from the analysis results using the following formula: D = 2FθR2 / uy ＊ where F is the lateral pressure (1 MPa), θ is the stress application angle (0 to 9 degrees), and uy ＊ is the displacement of the pressure part in each structure.

[0047] Furthermore, from the results of the lateral stiffness D obtained for each structure, the following analytical formula was obtained with R0, R1, R2, E0, E1, and E2 as explanatory variables: c1, c2, c3, and c ｉｊｋ is as described above. however,

[0048] By rearranging these equations (5) and (6), equation (1) was obtained. By using equation (1), the lateral stiffness D can be calculated, and D / H in equation (3) can be calculated. ２ is required.

[0049] In addition, in the optical fiber 1 according to this embodiment, D / H, which indicates the relationship between the lateral rigidity D and the bending rigidity H of the optical fiber 1, ２ D / H of 200 μm wire ２ The relative ratio of D / H to the 200 μm wire is adjusted to be 540 or less. The lateral rigidity D and bending rigidity H can be calculated from the above-mentioned formulas (1) and (2). ２The calculation conditions are as follows: The radius of the glass fiber is 62.5 μm. The radius of the primary resin layer is 85 μm. The radius of the secondary resin layer is 96.5 μm. The Young's modulus of the glass fiber is 72,500 [MPa]. The Young's modulus of the primary resin layer is 0.4 [MPa]. The Young's modulus of the secondary resin layer is 1,500 [MPa]. In this case, the bending rigidity H of the 200 μm strand is 3.63808×10 －１２ The lateral rigidity D [MPa] of the 200 μm wire was calculated to be 3.821657426, and D / H ２ is 2.88739 x 10 ２３ It is calculated as follows.

[0050] Alternatively, a plurality of optical fibers 1 having such a structure may be prepared to form an optical cable 30 as shown in Fig. 3. In the optical cable 30, a plurality of optical fibers 1 are housed in a cable jacket 31. As described above, although each optical fiber 1 is a small-diameter fiber, microbending loss is reduced, and therefore cable loss is also reduced. In the optical cable 30, since the housed fibers are small-diameter, more optical fibers 1 can be housed in the cable jacket 31 than in the past, or the outer diameter of the cable jacket 31 can be reduced.

[0051] Here, experimental examples of the optical fiber according to this embodiment will be described. In the following experimental examples, optical fibers 1 having the structures shown in Tables 2 to 6 were fabricated, and various indices were determined from each of the optical fibers that were actually fabricated. These indices are shown in Tables 7 to 11.

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062] The relative values ​​of the lateral pressure sensitivity coefficient (D / H ２ The relative lateral pressure susceptibility coefficient (ratio of 200 μm strand to 100 μm strand) was as shown in Table 12 below. That is, in Experimental Examples 1 to 25, the relative lateral pressure susceptibility coefficient was 540 or less. On the other hand, in Experimental Example 24, the relative lateral pressure susceptibility coefficient exceeded 3000, a fairly large value. This means that the microbending loss and cable loss increased, making it difficult to meet the standard cable loss (less than 0.3 dB / km), for example. In Table 12, a rating of A for cable loss indicates that the standard cable loss (less than 0.3 dB / km) was met, and a rating of B indicates that the standard cable loss (less than 0.3 dB / km) was not met.

[0063]

[0064] Table 12 also shows the results of a tensile test on optical fiber 1. In this test, a tensile tester having a first mandrel and a second mandrel was prepared, and sandpaper with an average particle size of 15 μm or more and 25 μm or less was wrapped around the first mandrel. The first mandrel and the second mandrel were positioned a predetermined distance from each other. Then, both ends of optical fiber 1 were wrapped around the first mandrel and the second mandrel, and a tensile test was performed. One end of optical fiber 1 was wrapped around the first mandrel, with the sandpaper wrapped around it. In this test, the median breaking stresses of the optical fibers in Experimental Examples 1 to 25 were measured. As shown in Table 12, it was confirmed that the median breaking stresses in Experimental Examples 1 to 23 were equal to or greater than the specified value of 1.5 GPa. On the other hand, in Experimental Examples 24 and 25, the median breaking stresses were smaller than the specified value of 1.5 GPa. This is thought to be due to the fact that in Experimental Examples 24 and 25, the fibers were small in diameter, and the thickness of the primary resin layer was 4 μm or less and the thickness of the secondary resin layer was 6 μm or less. As described above, the optical fibers according to Experimental Examples 1 to 23 were capable of reducing the diameter of the optical fiber, reducing microbending loss, and providing a predetermined tensile strength.

[0065] As described above, the optical fiber 1 satisfies at least the following requirements: The core radius is 3.6 μm or more and 5.4 μm or less, and the relative refractive index difference of the core with respect to the refractive index of the cladding is 0.32% or more and 0.40% or less greater than the refractive index of the cladding. The trench volume is -30% μm ２ The radius of the cladding is 63 μm or less. The thickness of the primary resin layer is 4 μm or more, and the Young's modulus of the primary resin layer is 0.3 MPa or less. The radius of the secondary resin layer is 85 μm or less, the thickness of the secondary resin layer is 7.5 μm or more, and the Young's modulus of the secondary resin layer is 1250 MPa or more. The effective cross-sectional area of ​​the optical fiber at a wavelength of 1550 nm is 100 μm or less. ２The mode field diameter of the optical fiber at a wavelength of 1310 nm is greater than 8.2 μm. The mode field diameter of the optical fiber at a wavelength of 1550 nm is 9.40 μm or greater and 10.5 μm or less. The cable cutoff wavelength of the optical fiber is less than 1420 nm. The bending loss of the optical fiber at a wavelength of 1550 nm when wound with a bending diameter of 10 mm is 1 dB / turn or less. D / H, which shows the relationship between the lateral rigidity D and bending rigidity H of the optical fiber, ２ The D / H of the standard 200 μm wire ２ The relative ratio to the cross-sectional area of ​​the coating layer excluding the primary resin layer is 540 or less. ２ 12000 μm or more ２ The absolute difference between the refractive index of the cladding and the refractive index of the coating layer is greater than 0.01. The optical fiber has a refractive index of 0.092 ps / nm or less. ２ / km or less.

[0066] As described above, the optical fiber 1 can reduce microbending loss in a small-diameter optical fiber, thereby reducing cable loss when the optical fiber is cabled.

[0067] Furthermore, in optical fiber 1, the lateral rigidity D and bending rigidity H satisfy equation (3), so microbending loss can be reliably reduced. As the coating eccentricity increases, the deviation between the calculated and measured microbending loss values ​​increases. In optical fiber 1, the coating eccentricity is 8 μm or less, so the deviation between the calculated and measured microbending loss values ​​is reduced. Therefore, microbending loss can be more reliably reduced. When the coating eccentricity was 5 μm, the relative error between the calculated and measured values ​​was 5.3%. When the coating eccentricity was 8 μm, the relative error between the calculated and measured values ​​was 9.8%. When the coating eccentricity was 10 μm, the relative error between the calculated and measured values ​​was 21.8%. Since a relative error of 10% or less is desirable, a coating eccentricity of 8 μm or less is preferable. To further reduce the relative error, the lower the coating eccentricity, the better.

[0068] Although the embodiments of the present disclosure have been described above, the present disclosure is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure. It should also be understood that at least one configuration or feature described in each embodiment or example can be combined with other embodiments or examples, or can be modified in various ways.

[0069] REFERENCE SIGNS LIST 1 optical fiber 10 glass fiber 11 core 12 cladding 13 inner cladding 14 trench 15 outer cladding 20 coating resin (coating layer) 21 primary resin layer 22 secondary resin layer 23 colored layer 30 optical cable 31 cable jacket

Claims

1. An optical fiber comprising: a glass fiber including a core and a clad surrounding the core; and a coating layer surrounding the glass fiber, wherein the core is formed from silica glass doped with at least one of germanium, titanium, chlorine, fluorine, and an alkali metal; the clad includes an inner clad in contact with and surrounding the core, an outer clad surrounding the inner clad, and a trench disposed radially between the inner clad and the outer clad; the coating layer includes a primary resin layer surrounding the clad and a secondary resin layer surrounding the primary resin layer; the radius of the core is 3.6 μm or more and 5.4 μm or less, and the relative refractive index difference of the core with respect to the refractive index of the clad is 0.32% or more and 0.40% or less than the refractive index of the clad; and the volume of the trench is -30% μm. ２ the radius of the cladding is 63 μm or less; the thickness of the primary resin layer is 4 μm or more and the Young's modulus of the primary resin layer is 0.3 MPa or less; the radius of the secondary resin layer is 85 μm or less, the thickness of the secondary resin layer is 7.5 μm or more and the Young's modulus of the secondary resin layer is 1250 MPa or more; and the effective cross-sectional area of ​​the optical fiber at a wavelength of 1550 nm is 100 μm or less. ２ the mode field diameter of the optical fiber at a wavelength of 1310 nm is greater than 8.2 μm, the mode field diameter of the optical fiber at a wavelength of 1550 nm is 9.40 μm or more and 10.5 μm or less, the cable cutoff wavelength of the optical fiber is less than 1420 nm, the bending loss of the optical fiber at a wavelength of 1550 nm when wound with a bending diameter of 10 mm is 1 dB / turn or less, and D / H, which indicates the relationship between the lateral rigidity D and the bending rigidity H of the optical fiber, ２ The D / H of the standard 200 μm wire ２ the relative ratio to the cross-sectional area of ​​the coating layer excluding the primary resin layer is 540 or less, ２ 12000 μm or more ２ the absolute difference between the refractive index of the cladding and the refractive index of the coating layer is greater than 0.01 and is 0.092 ps / nm or less; ２ 1. An optical fiber having a zero dispersion slope of 1 / km or less.

2. The volume of the trench is -380% μm ２ Above -126% μm ２ The optical fiber of claim 1 , wherein:

3. The radius of the glass fiber is R0 [m], and the Young's modulus of the glass fiber is E0 [N / m ２ ], the radius of the primary resin layer is R1 [m], and the Young's modulus of the primary resin layer is E1 [N / m ２ ], the radius of the secondary resin layer is R2 [m], and the Young's modulus of the secondary resin layer is E2 [N / m ２ ], the lateral rigidity D [N / m ２ ] and the bending rigidity H [N / m ２ 3. The optical fiber according to claim 1, wherein the relationship between [lambda] and [lambda] satisfies formula (3), and the coating eccentricity is 8 μm or less. Here, c1 = 0.209367, c2 = 1.206659, c3 = 0.401169, and c ｉｊｋ is as follows: ０００ =-0.611554c １００ =3.615414c ０１０ =0.253128c ００１ =-7.130445c ２００ =0.787599c １１０ =0.329243c １０１ =2.320080c ０２０ =-0.062024c ０１１ =-0.985974c ００２ = -8.696048 4. The coating layer further includes a colored layer surrounding the secondary resin layer, and the cross-sectional area of ​​the portion of the coating layer consisting of the secondary resin layer and the colored layer is 4400 μm ２ 12000 μm or more ２ The optical fiber according to any one of claims 1 to 3, wherein:

5. The optical fiber according to any one of claims 1 to 4, wherein the radius of the secondary resin layer is 81 μm or less.

6. The optical fiber according to any one of claims 1 to 4, wherein the radius of the secondary resin layer is 51 μm or less.

7. The optical fiber according to any one of claims 1 to 6, wherein a median breaking stress of the optical fiber is 1.5 GPa or more when a tensile test is conducted in a tensile testing machine having a first mandrel and a second mandrel, with sandpaper having an average particle size of 15 μm or more and 25 μm or less wrapped around the first mandrel.

8. An optical fiber according to any one of claims 1 to 7, wherein the bending loss of the optical fiber at a wavelength of 1625 nm when wound with a bending diameter of 10 mm is 3 dB / turn or less.

9. An optical cable comprising a plurality of optical fibers according to any one of claims 1 to 8.

Images