Method for producing optical fiber and method for producing optical cable

Abstract

This method for producing an optical fiber, which has a glass fiber having a diameter of 125 µm or less, a primary resin layer, and a secondary resin layer having a diameter of 150 µm to 210 µm, comprises: a step in which the lateral stiffness D0, the bending stiffness H0, the transmission loss α1 at the wavelength of 1.55 µm before being mounted in an optical cable, and the transmission loss α2 at the wavelength of 1.55 µm when mounted in the optical cable are determined with respect to a reference optical fiber; and a step in which the range of Dg that satisfies formula (3) at 125 µm or less is set with respect to the optical fiber, if D (N / m2) is the lateral stiffness of the optical fiber represented by formula (1) and H (N∙m2) is the bending stiffness of the optical fiber represented by formula (2).

Description

Optical fiber manufacturing method and optical cable manufacturing method

[0001] The present disclosure relates to a method for manufacturing an optical fiber and a method for manufacturing an optical cable. This application claims priority to Japanese Patent Application No. 2023-022232 filed on February 16, 2023, and Japanese Patent Application No. 2023-141381 filed on August 31, 2023, and incorporates the entire contents of said Japanese applications by reference.

[0002] Due to the increase in communication traffic, it is important to increase the density of optical fibers per unit cross-sectional area in optical cables. To increase the density of optical cables, it is necessary to reduce the diameter of the optical fibers.

[0003] Patent Document 1 describes an optical fiber in which the outer diameter of the cladding portion is 70 μm or more and 120 μm or less.

[0004] JP 2022-153101 A International Publication No. 2018 / 025896 A

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

[0006] The method for manufacturing an optical fiber according to the present disclosure is a method for manufacturing an optical fiber for use in an optical cable, the optical fiber having a glass fiber with a diameter of 125 μm or less, a primary resin layer surrounding the glass fiber, and a secondary resin layer surrounding the primary resin layer and having a diameter of 150 μm or more and 210 μm or less, the method comprising the steps of: determining, for a reference optical fiber, a lateral rigidity D0, a bending rigidity H0, a transmission loss α1 at a wavelength of 1.55 μm before being mounted in an optical cable, and a transmission loss α2 at a wavelength of 1.55 μm when mounted in an optical cable; and determining, for the optical fiber, a diameter Dg [μm], a radius R0 [m], and a Young's modulus 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 ], and the lateral stiffness of the optical fiber shown in equation (1) is D [N / m ２ ] and the bending rigidity of the optical fiber shown in formula (2) is H [N m ２ and setting a range of Dg that satisfies formula (3) to 125 μm or less when the thickness of the film is 125 μm or less. In formula (1), 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

[0007] 1 is a cross-sectional view of an optical fiber manufactured by a method for manufacturing an optical fiber according to an embodiment, taken perpendicular to the fiber axis, and FIG. 2 is a graph showing the relationship between cladding diameter and transmission loss.

[0008] [Problem to be Solved by the Present Disclosure] However, when the diameter of an optical fiber is reduced, the microbending loss that occurs when the optical fiber is cabled increases.

[0009] An object of the present disclosure is to provide a method for manufacturing an optical fiber and a method for manufacturing an optical cable that can suppress an increase in microbending loss even when the density is increased.

[0010] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a method for manufacturing an optical fiber and a method for manufacturing an optical cable that can suppress an increase in microbending loss even when the density is increased.

[0011] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be described below. (1) A method for manufacturing an optical fiber according to one aspect of the present disclosure is a method for manufacturing an optical fiber for use in an optical cable, the optical fiber having a glass fiber with a diameter of 125 μm or less, a primary resin layer surrounding the glass fiber, and a secondary resin layer surrounding the primary resin layer and having a diameter of 150 μm or more and 210 μm or less, the method comprising the steps of: determining, for a reference optical fiber, a lateral rigidity D0, a bending rigidity H0, a transmission loss α1 at a wavelength of 1.55 μm before being mounted in an optical cable, and a transmission loss α2 at a wavelength of 1.55 μm after being mounted in the optical cable; and determining, for the optical fiber, a diameter Dg [μm], a radius R0 [m], and a Young's modulus 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 ], and the lateral stiffness of the optical fiber shown in equation (1) is D [N / m ２ ] and the bending rigidity of the optical fiber shown in formula (2) is H [N m ２ and setting a range of Dg that satisfies formula (3) to 125 μm or less when the thickness of the film is 125 μm or less. In formula (1), 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 In this optical fiber, a range of Dg is set in which the lateral rigidity D and bending rigidity H of the optical fiber satisfy formula (3). Therefore, by setting the diameter of the glass fiber within the Dg range, it is possible to manufacture an optical fiber that can suppress an increase in microbending loss even when high density is achieved. By reducing the diameter of the optical fiber, it is possible to increase the number of optical fibers mounted in an optical cable. Even an optical cable with the same diameter as a conventional optical cable can contain more optical fibers and transmit a greater amount of information. Furthermore, compared to conventional optical cables with the same number of cores, it uses less material and is more economical.

[0012] (2) In the above (1), in the setting step, a range of Dg that satisfies the formulas (3) and (4) may be set. In this case, an optical fiber having a microbending loss small enough for practical use can be obtained.

[0013] (3) In the above (1) or (2), the diameter of the glass fiber may be less than 125 μm, and in the setting step, a range of Dg less than 125 μm that satisfies formula (3) may be set.

[0014] (4) In the above (1) or (2), the diameter of the glass fiber may be 120 μm or less, and in the setting step, a range of Dg may be set that is 120 μm or less and satisfies formula (3).

[0015] (5) In any one of (1) to (4) above, the Young's modulus of the glass fiber may be 70 GPa or more and 80 GPa or less.

[0016] (6) A method for manufacturing an optical cable according to an aspect of the present disclosure manufactures an optical cable including a plurality of optical fibers according to any one of (1) to (5) above. In this case, since the optical cable includes the optical fiber, it is possible to manufacture an optical cable that can suppress an increase in microbending loss even when the optical cable is highly dense.

[0017] (7) In the above (6), the optical cable may further include an outer jacket, the diameter of which is 3.8 mm or less, and the outer jacket may surround all of the optical fibers. In this case, a small-diameter optical cable can be manufactured.

[0018] (8) In the above (7), the fiber density calculated by dividing the number of optical fibers contained in the optical cable by the cross-sectional area calculated from the diameter of the jacket is 4.4 fibers / mm ２ In this case, a high-density optical cable can be manufactured, and a cable that can transmit an optical signal with a sufficient amount of information even with a small diameter can be manufactured.

[0019] (9) In any of (6) to (8) above, the number of optical fibers included in the optical cable may be 50 or more. In this case, a high-density optical cable can be manufactured.

[0020] [Details of the embodiments of the present disclosure] Specific examples of the optical fiber manufacturing method and the optical cable manufacturing method according to the present embodiments will be described with reference to the drawings as necessary. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted.

[0021] 1 is a cross-sectional view perpendicular to the fiber axis of an optical fiber manufactured by a manufacturing method for an optical fiber according to an embodiment. As shown in FIG. 1, the optical fiber 1 includes a glass fiber 10 and a coating resin 20. The optical fiber 1 is used in an optical cable.

[0022] The glass fiber 10 is made of silica glass. 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 diameter (core diameter) of the core 11 is, for example, 9 μm or more and 14 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, 0.3% or more and 0.5% or less. In this embodiment, microbending loss is suppressed, so the relative refractive index difference of the core 11 can be reduced. The core 11 is made of, for example, germanium-doped silica glass or pure silica glass. Here, pure silica glass refers to silica glass that is substantially free of impurities.

[0023] The cladding 12 surrounds the core 11 and covers the outer peripheral surface of the core 11. The cladding 12 is made of pure silica glass or fluorine-doped silica glass. The diameter of the cladding 12 (cladding diameter) is the diameter of the glass fiber 10 (glass diameter). The glass diameter is, for example, 75 μm or more and 125 μm or less. The glass diameter may be, for example, 75 μm or more and less than 125 μm. The glass diameter may be 75 μm or more and 120 μm or less. The Young's modulus of the glass fiber 10 is, for example, 70 GPa or more and 80 GPa or less. A trench may be provided in the cladding 12. The trench can further suppress microbending loss.

[0024] The coating resin 20 is made of an ultraviolet curable resin. The coating resin 20 includes a primary resin layer 21 and a secondary resin layer 22. The primary resin layer 21 surrounds the glass fiber 10 (clad 12) and covers the outer peripheral surface of the glass fiber 10. The primary resin layer 21 is provided in contact with the glass fiber 10. The thickness of the primary resin layer 21 is, for example, not less than 2 μm and not more than 20 μm.

[0025] The Young's modulus of the primary resin layer 21 is, for example, 0.05 MPa or more and 0.7 MPa or less. In order to suppress 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 0.8 MPa, microbending loss cannot be sufficiently suppressed. If the Young's modulus of the primary resin layer 21 is too low, the coating resin 20 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 suppressed.

[0026] 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 is adjusted by, for example, the molecular weight of the polyether portion of the ultraviolet-curable resin and the type of diluent monomer.

[0027] 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.

[0028] The secondary resin layer 22 surrounds the primary resin layer 21 and covers the outer peripheral surface of the primary resin layer 21. The diameter of the secondary resin layer 22 is, for example, 150 μm or more and 210 μm or less, or may be 150 μm or more and less than 180 μm, or may be 150 μm or more and 165 μm or less. The diameter of the secondary resin layer 22 is the diameter (coating diameter) of the coating resin 20. The thickness of the secondary resin layer 22 is, for example, 5 μm or more. The Young's modulus of the secondary resin layer 22 is, for example, 1000 MPa or more and 3000 MPa or less.

[0029] 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 necessary. The Young's modulus of the secondary resin layer 22 is adjusted, for example, by adjusting the molecular weight of the polyether portion of the ultraviolet-curable resin and the type of diluent monomer. The optical fiber 1 is preferably colored for identification purposes. The secondary resin layer 22 may be colored by including a pigment or dye, or a colored layer several μm thick may be provided on the secondary resin layer 22.

[0030] The optical cable manufactured by the optical cable manufacturing method according to this embodiment is manufactured using optical fibers 1. The optical cable includes a plurality of optical fibers 1 and an outer jacket surrounding the plurality of optical fibers 1. The diameter of the outer jacket is, for example, 3.8 mm or less. The core density calculated by dividing the number of optical fibers 1 mounted in the optical cable by the cross-sectional area calculated from the diameter of the outer jacket is, for example, 4.4 fibers / mm ２ That's all. The number of optical fibers 1 mounted in the optical cable is, for example, 50 or more, and may be 96 or more. Table 1 shows examples of optical cables according to this embodiment. The transmission loss at a wavelength of 1.55 μm of the optical fibers included in each cable was 0.23 dB / km to 0.25 dB / km. An optical cable may simply contain multiple optical fibers 1 housed within a jacket, and is sometimes called an optical cord.

[0031] Non-Patent Document 1 describes that the microbending resistance of an optical fiber is related to the lateral rigidity D and bending rigidity H of the optical fiber and can be determined by an approximate formula. Patent Document 2 describes that the approximate formula of Non-Patent Document 1 has been expanded to a form closer to reality. The approximate formula of Patent Document 2 was calculated by numerical analysis with a glass diameter limited to 125 μm. Therefore, when applied to optical fibers with different glass diameters, the calculated microbending loss value may differ greatly from the actually measured value. In particular, for small-diameter optical fibers, the microbending loss calculated by the approximate formula of Patent Document 2 will be lower than the actual value.

[0032] An approximation that is expanded to the range of glass diameters smaller than 125 μm or coating diameters smaller than 160 μm will be explained below.

[0033] 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 of the optical fiber is expressed by formula (1), and the bending rigidity H is expressed by formula (2). In formula (1), 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

[0034] The method for deriving equation (1) will be explained below.

[0035] In general, the microbending loss β of an optical fiber is expressed by the approximate formula (5) using lateral rigidity D, bending rigidity H, and a constant A resulting from the optical characteristics of the optical fiber. As can be seen from equation (5), the microbending loss β is approximately equal to D / H ２ In other words, D / H ２ is the sensitivity that indicates how much the transmission loss increases due to a force applied from the side.

[0036] 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 analysis software MSC.Nastran 2020sp1.

[0037] 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.

[0038] 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,

[0039] Equation (1) was obtained by rearranging equations (6) and (7).

[0040] The present inventors have derived an analytical formula for predicting the transmission loss α, including the microbending loss β, that occurs when an optical fiber having a glass diameter of 125 μm or less is cabled, using equations (1) and (2). This analytical formula estimates the transmission loss α at a wavelength of 1.55 μm of the optical fiber to be predicted from a comparison with a reference optical fiber whose lateral rigidity, bending rigidity, transmission loss at a wavelength of 1.55 μm before being installed in an optical cable, and transmission loss at a wavelength of 1.55 μm when installed in an optical cable are known. "Known lateral rigidity and bending rigidity" includes cases where the radius (or diameter) and Young's modulus of the glass fiber, primary resin layer, and secondary resin layer are known, and the lateral rigidity and bending rigidity can be calculated from equations (1) and (2).

[0041] For the reference optical fiber, if the lateral rigidity is D0, the bending rigidity is H0, the transmission loss at a wavelength of 1.55 μm before being mounted in an optical cable is α1, and the transmission loss at a wavelength of 1.55 μm after being mounted in an optical cable is α2, the analytical formula can be expressed as follows:

[0042] Fig. 2 is a graph showing the relationship between cladding diameter and transmission loss. The horizontal axis of Fig. 2 represents the cladding diameter Dg of the optical fiber to be predicted, and the vertical axis represents the transmission loss α at a wavelength of 1.55 μm. Fig. 2 is a graph of the analytical formula, using as an example a reference optical fiber an optical fiber having a glass fiber diameter of 125 μm, a primary resin layer diameter of 135 μm, a secondary resin layer diameter of 155 μm, a glass fiber Young's modulus of 72,500 MPa, a primary resin layer Young's modulus of 0.4 MPa, and a secondary resin layer Young's modulus of 1,500 MPa.

[0043] In the optical fiber of the present disclosure, the cladding diameter (2R0) is 75 μm or more and 125 μm or less, the primary diameter (2R1) is 79 μm or more and 164 μm or less, and the secondary diameter (2R2) is 89 μm or more and 210 μm or less.

[0044] 2 shows cases where α2, the transmission loss of the reference optical fiber after cabled, is 0.205 dB / km, 0.21 dB / km, and 0.23 dB / km. As shown in FIG. 2, the larger α2, the larger the transmission loss α of the optical fiber to be predicted. α1, the transmission loss of the reference optical fiber before cabled, is, for example, the average value of the transmission loss of the reference optical fiber wound on a 50 km bobbin. α1 may also be the average value of the transmission losses measured at multiple different points along the longitudinal direction of the reference optical fiber. In this example, α1 was 0.2 dB / km.

[0045] To suppress the increase in microbending loss, the transmission loss α needs to be set to 0.3 dB / km or less, which is equivalent to that of currently mainstream optical cables using optical fibers with an outer diameter of 250 μm. In other words, according to the optical fiber 1 in which Dg is set within a range that satisfies the following formula (3), the increase in microbending loss is suppressed.

[0046] Referring to Figure 2, if α2 = 0.23, the cladding diameter must be 93 μm or greater to achieve a transmission loss α of 0.3 dB / km or less at a wavelength of 1.55 μm. The transmission loss (α2) of the optical fiber can be changed by varying the Young's modulus after curing of the resin used in the coating layers (primary resin layer and secondary resin layer) of the optical fiber and the thickness of each layer. As a result, a specific curve such as that shown in Figure 2 is obtained. From these curves, it is possible to predict how small an optical fiber can be obtained while achieving the desired transmission loss, and then manufacture the optical fiber.

[0047] The lower limit of the transmission loss α is, for example, 0.18 dB / km. That is, Dg is set so as to satisfy the following equation (4) in addition to equation (3).

[0048] A method for manufacturing an optical fiber and an optical cable according to this embodiment will be described. The method for manufacturing an optical fiber is a method for manufacturing an optical fiber 1, and includes steps for determining the lateral rigidity D0, bending rigidity H0, transmission loss α1, and transmission loss α2 for a reference optical fiber. The lateral rigidity D0 can be determined from equation (1). The bending rigidity H0 can be determined from equation (2). The transmission loss α1 and transmission loss α2 can be determined by actual measurement.

[0049] The method for manufacturing an optical fiber further includes a step of setting a range of cladding diameter Dg of glass fiber 10 for optical fiber 1 that is 125 μm or less and satisfies formula (3). In this step, a range of cladding diameter Dg that satisfies formulas (3) and (4) may be set. With optical fiber 1 manufactured with cladding diameter Dg set in such a range, an increase in microbending loss can be suppressed even when optical cable density is increased.

[0050] The method for manufacturing an optical cable includes a step of forming a jacket having a diameter of, for example, 3.8 mm or less on a plurality of optical fibers 1. The method for manufacturing an optical cable includes a step of forming a cable having a core density of, for example, 4.4 fibers / mm, which is calculated by dividing the number of optical fibers included in the optical cable by the cross-sectional area calculated from the diameter of the jacket. ２The optical cable manufacturing method is performed so that the number of optical fibers 1 included in the optical cable is, for example, 50 or more. Since the optical cable includes the optical fibers 1, the optical cable manufacturing method can manufacture an optical cable that can suppress an increase in microbending loss even when the optical cable is highly dense.

[0051] Although the embodiments and modifications have been described above, the present disclosure is not necessarily limited to the above-described embodiments and modifications, and various modifications are possible without departing from the spirit of the present disclosure. The above-described embodiments and modifications may be combined as appropriate.

[0052] REFERENCE SIGNS LIST 1... Optical fiber 10... Glass fiber 11... Core 12... Cladding 20... Coating resin 21... Primary resin layer 22... Secondary resin layer

Claims

1. A method for manufacturing an optical fiber for use in an optical cable, the optical fiber having a diameter of 125 μm or less, a primary resin layer surrounding the glass fiber, and a secondary resin layer surrounding the primary resin layer and having a diameter of 150 μm or more and 210 μm or less, comprising: Regarding the reference optical fiber, the lateral rigidity is D0, the bending rigidity is H0, the transmission loss at a wavelength of 1.55 μm before being mounted in an optical cable is α1, and the transmission loss at a wavelength of 1.55 μm when mounted in an optical cable is α2, Regarding the optical fiber, the diameter of the glass fiber is Dg [μm], 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 ], and the lateral stiffness of the optical fiber represented by formula (1) is D [N / m ２ ] and the bending rigidity of the optical fiber represented by formula (2) is H [N m ２ ], the manufacturing method of the optical fiber satisfies the formula (3). [Equation 1] In formula (1), c1 = 0.209367, c2 = 1.206659, c3 = 0.401169, and c ｉｊｋ is as follows: c ０００ =-0.611554 c １００ =3.615414 c ０１０ =0.253128 c ００１ =-7.130445 c ２００ =0.787599 c １１０ =0.329243 c １０１ =2.320080 c ０２０ =-0.062024 c ０１１ =-0.985974 c ００２ =-8.696048

2. The method for producing an optical fiber according to claim 1 , wherein formulas (3) and (4) are satisfied. [Equation 2]

3. 3. The method of claim 1, wherein the glass fiber has a diameter of less than 125 μm.

4. 3. The method for producing an optical fiber according to claim 1, wherein the diameter of the glass fiber is 120 [mu]m or less.

5. 3. The method for producing an optical fiber according to claim 1, wherein the Young's modulus of the glass fiber is 70 GPa or more and 80 GPa or less.

6. An optical cable manufacturing method comprising manufacturing an optical cable comprising a plurality of optical fibers according to claim 1 or 2.

7. The optical cable further comprises an outer jacket; The diameter of the jacket is 3.8 mm or less, and the jacket surrounds all of the optical fibers. The method for manufacturing an optical cable according to claim 6 .

8. The number of optical fibers included in the optical cable is divided by the cross-sectional area calculated from the diameter of the jacket to obtain a core density of 4.4 fibers / mm ２ That is all. The method for manufacturing an optical cable according to claim 7 .

9. The number of the optical fibers included in the optical cable is 50 or more. The method for manufacturing an optical cable according to claim 6 .

10. An optical fiber for use in an optical cable, comprising: a glass fiber having a diameter of 125 μm or less; a primary resin layer surrounding the glass fiber; and a secondary resin layer surrounding the primary resin layer and having a diameter of 150 μm or more and 210 μm or less, Regarding the reference optical fiber, the lateral rigidity is D0, the bending rigidity is H0, the transmission loss at a wavelength of 1.55 μm before being mounted in an optical cable is α1, and the transmission loss at a wavelength of 1.55 μm when mounted in an optical cable is α2, Regarding the optical fiber, the diameter of the glass fiber is Dg [μm], 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 ], and the lateral stiffness of the optical fiber represented by formula (1) is D [N / m ２ ] and the bending rigidity of the optical fiber represented by formula (2) is H [N m ２ ], an optical fiber that satisfies formula (3). [Equation 3] In formula (1), c1 = 0.209367, c2 = 1.206659, c3 = 0.401169, and c ｉｊｋ is as follows: c ０００ =-0.611554 c １００ =3.615414 c ０１０ =0.253128 c ００１ =-7.130445 c ２００ =0.787599 c １１０ =0.329243 c １０１ =2.320080 c ０２０ =-0.062024 c ０１１ =-0.985974 c ００２ =-8.696048

Images