Optical fiber

Abstract

This optical fiber comprises: a glass fiber having a core, an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding; and a covering resin layer covering the outer periphery of the glass fiber. The core contains germanium. When the diameter of the core is 2r1 and the diameter of the inner cladding is 2r2, 3 ≤ r2 / r1 ≤ 6 holds. The diameter of the core is 4.6-8.9 μm inclusive. When the relative refractive index difference of the core is ∆1, the relative refractive index difference of the inner cladding is ∆2, and the relative refractive index difference of the outer cladding is ∆3, 0.40% ≤ ∆1−∆2 ≤ 0.80% and −0.10% ≤ ∆2−∆3 ≤ 0.10% hold. Residual stress in the core is compressive stress. The mode field diameter at a wavelength of 1310 nm is 8.4 μm or less. The cable cutoff wavelength is less than 1530 nm. The diameter of the covering resin layer is 180 μm or less.

Description

fiber optic

[0001] This disclosure relates to optical fibers. This application claims priority under Japanese application No. 2024-232792, filed on 27 December 2024, and incorporates all the provisions contained herein.

[0002] Macrobend loss is considered a factor that causes increased transmission loss in optical cables. Macrobend loss is known to correlate with the MAC value, which is the value obtained by dividing the mode field diameter at a wavelength of 1310 nm (hereinafter also called MFD1.31) by the cable cutoff wavelength (hereinafter also called λcc). The smaller the MAC value, the smaller the macrobend loss.

[0003] Patent Document 1 describes an optical fiber having a cutoff wavelength of 1260 nm or less and a mode field diameter of 8.0 μm or less at a wavelength of 1550 nm.

[0004] Japanese Patent Publication No. 2003-279780

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

[0006] An optical fiber according to one aspect of this disclosure comprises a glass fiber having a core, an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding, and a coating resin layer covering the outer periphery of the glass fiber, wherein the core contains germanium, the diameter of the glass fiber is 124 μm or more and 126 μm or less, and if the diameter of the core is 2r1 and the diameter of the inner cladding is 2r2, then 3 ≤ r2 / r1 ≤ 6, and the diameter of the core is 4.6 μm or more and 8.9 μm. The following conditions apply: if the relative refractive index difference of the core is Δ1, the relative refractive index difference of the inner cladding is Δ2, and the relative refractive index difference of the outer cladding is Δ3, then 0.40% ≤ Δ1 - Δ2 ≤ 0.80% and -0.10% ≤ Δ2 - Δ3 ≤ 0.10%. The residual stress in the core is compressive stress. The mode field diameter at a wavelength of 1310 nm is 8.4 μm or less. The cable cutoff wavelength is less than 1530 nm. The diameter of the coating resin layer is 180 μm or less.

[0007] Figure 1 is a cross-sectional view of an optical fiber according to an embodiment. Figure 2 is a diagram showing the refractive index distribution in the radial direction of a glass fiber. Figure 3 is a schematic cross-sectional view illustrating the definition of coating eccentricity. Figure 4 is a graph showing the relationship between MFD 1.31 and the relative value of microbend loss. Figure 5 is a graph showing the relationship between MFD 1.31 and the relative value of microbend loss.

[0008] Increasing the fiber packing density to over 60% to enable the reduction of optical cable diameter increases macrobend loss, leading to increased transmission loss in the optical cable. The MFD 1.31 of general-purpose optical fibers is around 9.2 μm. Reducing the MFD 1.31 to around 6 μm reduces the MAC value and improves macrobend loss. However, this increases the difference in MFD 1.31 compared to general-purpose optical fibers, resulting in increased connection loss. There is a need for optical fibers that can reduce macrobend loss and connection loss, which are effective in reducing the diameter of optical cables, assuming use in the C-band (wavelengths from 1530 nm to 1565 nm) and L-band (wavelengths from 1565 nm to 1625 nm).

[0009] This disclosure aims to provide an optical fiber capable of reducing macrobend loss and connection loss.

[0010] This disclosure provides an optical fiber capable of reducing macrobend loss and connection loss.

[0011] First, embodiments of the present disclosure will be listed and described. (1) An optical fiber according to a first aspect of the present disclosure comprises a glass fiber having a core, an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding, and a coating resin layer covering the outer circumference of the glass fiber, wherein the core contains germanium, the diameter of the glass fiber is 124 μm or more and 126 μm or less, and if the diameter of the core is 2r1 and the diameter of the inner cladding is 2r2, then 3 ≤ r2 / r1 ≤ 6, and the diameter of the core is 4.6 μm or more and 8.9 μm or less. The coefficient of refractive index is less than or equal to μm, and if the specific refractive index difference of the core is Δ1, the specific refractive index difference of the inner cladding is Δ2, and the specific refractive index difference of the outer cladding is Δ3, then 0.40% ≤ Δ1 - Δ2 ≤ 0.80% and -0.10% ≤ Δ2 - Δ3 ≤ 0.10%. The residual stress in the core is compressive stress, the mode field diameter at a wavelength of 1310 nm is 8.4 μm or less, the cable cutoff wavelength is less than 1530 nm, and the diameter of the coating resin layer is 180 μm or less.

[0012] In the optical fiber described above, the wavelength of λcc is increased, allowing for a larger MFD 1.31 while maintaining the MAC value, thus reducing macrobend loss while expanding the MFD 1.31. Furthermore, because the MFD 1.31 can be increased, connection loss can be reduced.

[0013] (2) In (1) above, the microbend loss in the optical fiber is expressed as a relative value with respect to the microbend loss of a reference optical fiber conforming to ITU-T G.657.A2, which has a mode field diameter of 8.4 μm and a coating resin layer diameter of 180 μm. The relative microbend loss value may be 1 or less. In this case, even if the diameter of the optical fiber is reduced, the microbend loss can be reduced. Since microbend loss is also a factor that causes an increase in the transmission loss of the optical fiber, the transmission loss can be reduced by reducing the microbend loss. The microbend loss in this specification is measured according to IEC-TR62221 Method-B. First, sandpaper with a surface roughness of #240 is attached to a bobbin with a body diameter of 280 mm, and the optical fiber sample is wound onto the sandpaper to a length of 600 m with a tension of 80 g. Next, the transmission loss of the optical fiber sample at a wavelength of 1550 nm is measured. The difference in transmission loss of the optical fiber sample before and after winding is the microbend loss.

[0014] (3) An optical fiber according to a second aspect of the present disclosure comprises a glass fiber having a core, an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding, and a coating resin layer covering the outer circumference of the glass fiber, wherein the core contains germanium, the diameter of the glass fiber is 124 μm or more and 126 μm or less, and if the diameter of the core is 2r1 and the diameter of the inner cladding is 2r2, then 4.0 ≤ r2 / r1 ≤ 5.5, and the diameter of the core is 5.0 μm or more and 6 The diameter is 4 μm or less, and assuming the relative refractive index difference of the core is Δ1, the relative refractive index difference of the inner cladding is Δ2, and the relative refractive index difference of the outer cladding is Δ3, then 0.45% ≤ Δ1 - Δ2 ≤ 0.75% and -0.10% ≤ Δ2 - Δ3 ≤ 0.10%. The residual stress in the core is compressive stress, the mode field diameter at a wavelength of 1310 nm is 7.4 μm or less, the cable cutoff wavelength is less than 1530 nm, and the diameter of the coating resin layer is 165 μm or less.

[0015] In the optical fiber described above, the wavelength of λcc is increased, allowing for a larger MFD 1.31 while maintaining the MAC value, thus reducing macrobend loss while expanding the MFD 1.31. Furthermore, because the MFD 1.31 can be increased, connection loss can be reduced.

[0016] (4) In (3) above, the microbend loss in the optical fiber is expressed as a relative value with respect to the microbend loss of a reference optical fiber having a mode field diameter of 8.4 μm and a coating resin layer diameter of 200 μm, in accordance with ITU-T G.657.A2. The relative microbend loss value may be 1 or less. In this case, even if the diameter of the optical fiber is reduced, the microbend loss can be reduced. Since microbend loss is a factor that causes an increase in the transmission loss of the optical fiber, the transmission loss can be reduced by reducing the microbend loss.

[0017] (5) In any of (1) to (4) above, the fracture frequency in the screening test with a 1% tensile strain applied may be 10 times / mm or less. In this case, the strength remains high even when the diameter of the optical fiber is reduced.

[0018] (6) In any of (1) to (5) above, the coating eccentricity, which is the distance from the central axis of the coating resin layer to the central axis of the glass fiber in a cross section perpendicular to the axial direction, is measured at a plurality of measurement points set at predetermined intervals in the axial direction, and the maximum amplitude of the coating eccentricity in the spectrum obtained by Fourier transforming the waveforms showing the coating eccentricity for each position of the plurality of measurement points may be 8 μm or less. In this case, the local thinning of the coating resin layer can be reduced. Therefore, the frequency of optical fiber breakage can be reduced.

[0019] (7) In any of (1) to (6) above, the coating resin layer has a primary resin layer and a secondary resin layer, 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 . Then, the transverse rigidity D [N / m ２ shown in Equation (1) of the optical fiber and the bending rigidity H [N / m ２ satisfy Equation (3). In the cross-section orthogonal to the axial direction, the coating eccentricity, which is the distance from the central axis of the glass fiber to the central axis of the coating resin layer based on the outer periphery of the coating resin layer, may be 8 μm or less. Here, 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 In this case, since the transverse rigidity D and the bending rigidity H satisfy Equation (3), microbend loss can be reliably reduced. Moreover, since the coating eccentricity is low, the deviation between the calculated value and the measured value of the microbend loss is unlikely to increase. Therefore, microbend loss can be more reliably reduced.

[0020] [Details of Embodiments of the Present Disclosure] A specific example of the optical fiber of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, and is intended to be represented by the claims and to include all modifications within the meaning and scope equivalent to the claims. In the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted.

[0021] FIG. 1 is a diagram showing a cross section perpendicular to the axial direction of the optical fiber 10 according to an embodiment. As shown in the figure, the optical fiber 10 includes a glass fiber 13 and a coating resin layer 16. The optical fiber 10 is a so-called optical fiber core wire. The diameter of the optical fiber 10 (hereinafter also referred to as the core diameter) is 180 μm or less, or 165 μm or less. The core diameter is also the diameter of the coating resin layer 16 (coating diameter).

[0022] The glass fiber 13 includes a core 11 and a cladding 12. The cladding 12 surrounds the core 11. The cladding 12 includes an inner cladding 121 and an outer cladding 122. The inner cladding 121 surrounds the core 11 and is in contact with the outer periphery of the core 11. The outer cladding 122 surrounds the inner cladding 121 and is in contact with the outer periphery of the inner cladding 121. The glass fiber 13 has a three-layer structure.

[0023] The radius of the core 11 is the distance from the central axis of the optical fiber 10 to the outer periphery of the core 11. The radius of the inner cladding 121 is the distance from the central axis of the optical fiber 10 to the outer periphery of the inner cladding 121. The radius of the outer cladding 122 is the distance from the central axis of the optical fiber 10 to the outer periphery of the outer cladding 122. The radius of the outer cladding 122 is also the radius of the glass fiber 13 and the radius of the cladding 12.

[0024] Let the radii of the core 11, the inner cladding 121, and the outer cladding 122 be r1, r2, and r3, respectively. The diameter of the core 11 (2r1) is, for example, 4.6 μm or more and 8.9 μm or less when the core diameter is 180 μm or less, and 5.0 μm or more and 6.4 μm or less when the core diameter is 165 μm or less. The diameter of the inner cladding 121 (2r2) is, for example, 13.8 μm or more and 53.4 μm or less when the core diameter is 180 μm or less, and 20.0 μm or more and 35.2 μm or less when the core diameter is 165 μm or less. The ratio of the diameter of the inner cladding 121 (2r2) to the diameter of the core 11 (2r1) is, for example, 3.0 or more and 6.0 or less (3.0 ≤ r2 / r1 ≤ 6.0) when the core diameter is 180 μm or less, and 4.0 or more and 5.5 or less (4.0 ≤ r2 / r1 ≤ 5.5) when the core diameter is 165 μm or less.

[0025] The diameter (2r3) of the outer cladding 122 is, for example, 124 μm or more and 126 μm or less. The diameter (2r3) of the outer cladding 122 is also the diameter of the glass fiber 13 and the diameter of the cladding 12. In this specification, the “diameter” of an element is, for example, the average value of the diameter of that element at multiple positions in the axial direction of the optical fiber.

[0026] The glass fiber 13 is made of quartz glass. The core 11 is made of quartz glass with added germanium (Ge). In other words, the core 11 contains germanium. The addition of germanium increases the refractive index of the core 11, so the refractive index difference between the core 11 and the cladding 12 becomes large. In addition, the residual stress in the core 11 is compressive stress. As a result, transmission loss can be reduced.

[0027] The inner cladding 121 may be made of pure quartz glass substantially free of additives, or of quartz glass to which additives have been added. The outer cladding 122 may be made of pure quartz glass substantially free of additives, or of quartz glass to which additives have been added. Examples of additives to be added to the inner cladding 121 and the outer cladding 122 include chlorine.

[0028] The coating resin layer 16 surrounds the glass fiber 13. The coating resin layer 16 includes a primary resin layer 14 and a secondary resin layer 15. The primary resin layer 14 covers the outer periphery of the outer cladding 122 and is in contact with the outer periphery of the outer cladding 122. The secondary resin layer 15 covers the outer periphery of the primary resin layer 14 and is in contact with the outer periphery of the primary resin layer 14. The diameter of the primary resin layer 14 is, for example, 135 μm to 170 μm when the core wire diameter is 180 μm or less, and 130 μm to 160 μm when the core wire diameter is 165 μm or less. The diameter of the secondary resin layer 15 is the diameter of the coating resin layer 16 and the core wire diameter.

[0029] Figure 2 shows the refractive index distribution in the radial direction of the glass fiber 13. In this figure, range A1 corresponds to the core 11, range A2 to the inner cladding 121, and range A3 to the outer cladding 122. The vertical axis shows the relative refractive index difference, and the horizontal axis shows the radial position. As shown in this figure, in the glass fiber 13, the relative refractive index differences of the core 11, inner cladding 121, and outer cladding 122 with respect to the refractive index of pure quartz glass are Δ1, Δ2, and Δ3, respectively. Specifically, the relative refractive index differences Δ1, Δ2, and Δ3 are defined by the following formulas: Δ1 (%) = ((n1 ２ -n0 ２ ) / (2×n1 ２ ))×100 Δ2(%)=((n2 ２ -n0 ２ ) / (2 × n² ２ ))×100 Δ3(%)=((n3 ２ -n0 ２ ) / (2 × n³ ２ )) × 100

[0030] However, n0 is the refractive index of the pure quartz glass. n1 is the refractive index of the core 11. n1 is, for example, the maximum refractive index of the core 11. n2 is the refractive index of the inner cladding 121. The refractive index of the inner cladding 121 may be constant regardless of the radial position, or it may change continuously as it moves away from the core 11 and approaches the outer cladding 122. If the refractive index changes, n2 is, for example, the average refractive index in the range from 0.6 to 0.8 times the thickness of the inner cladding 121, i.e., the range of radii from r1 + 0.6 × (r2 - r1) to r1 + 0.8 × (r2 - r1). n3 is the refractive index of the outer cladding 122. n3 is, for example, the average refractive index of the outer cladding 122. The relative refractive index difference is evaluated, for example, using a refractive index distribution measuring device (IFA-100 manufactured by Interfiber Analysis Co., Ltd.) with a measurement interval of 0.2 μm or less.

[0031] The specific refractive index difference of core 11 is higher than the specific refractive index difference of inner cladding 121 and outer cladding 122 (Δ1 > Δ2 and Δ1 > Δ3). The specific refractive index difference of inner cladding 121 may be lower than the specific refractive index difference of outer cladding 122 (Δ2 < Δ3), or it may be higher than the specific refractive index difference of outer cladding 122 (Δ2 > Δ3).

[0032] The difference between the relative refractive index difference of the core 11 and the relative refractive index difference of the inner cladding 121 is between 0.40% and 0.80% (0.40% ≤ Δ1 - Δ2 ≤ 0.80%), and may be between 0.45% and 0.75% (0.45% ≤ Δ1 - Δ2 ≤ 0.75%). The difference between the relative refractive index difference of the inner cladding 121 and the relative refractive index difference of the outer cladding 122 is between -0.10% and 0.10% (-0.10% ≤ Δ2 - Δ3 ≤ 0.10%).

[0033] In optical fiber 10, when the core diameter is 180 μm or less, the MFD 1.31 is 8.4 μm or less. This reduces macrobend loss. When the core diameter is 165 μm or less, the MFD 1.31 is 7.4 μm or less. This also reduces macrobend loss. The MFD 1.31 may be 7.2 μm or more. This reduces connection loss with general-purpose optical fibers. The mode field diameter is defined according to the Petermann-II definition.

[0034] The λcc of the optical fiber 10 is longer than 1260 nm and less than or equal to 1530 nm. Since the optical fiber 10 is intended for use in the C-band and L-band, the λcc can be made to a longer wavelength. This makes it possible to reduce the MAC value without reducing the MFD 1.31. Therefore, it is possible to increase the MFD 1.31 while reducing macrobend loss.

[0035] When optical fiber 10 is applied to an optical cable with a packing density of 50%, the transmission loss at a wavelength of 1550 nm and 25°C is 0.300 dB / km or less. When optical fiber 10 is applied to an optical cable with a packing density of 60%, the transmission loss at a wavelength of 1550 nm and 25°C may also be 0.300 dB / km or less.

[0036] When optical fiber 10 is applied to an optical cable with a packing density of 50%, the transmission loss at a wavelength of 1625 nm and 25°C is 0.400 dB / km or less. When optical fiber 10 is applied to an optical cable with a packing density of 60%, the transmission loss at a wavelength of 1625 nm and 25°C may be 0.300 dB / km or less.

[0037] The fracture frequency in a screening test applying a 1% tensile strain to the optical fiber 10 may be 10 times / mm or less. In this screening test, a tension of approximately 1 kg may be applied to the optical fiber 10 as the tension that applies a 1% tensile strain to the optical fiber 10.

[0038] Figure 3 is a schematic cross-sectional view illustrating the definition of coating eccentricity. As shown in Figure 3, coating eccentricity d is defined as the distance (radial deviation, radial displacement) between the central axis RC of the coating resin layer 16 and the central axis GC of the glass fiber 13 in a cross-section perpendicular to the axial direction, with reference to the outer circumference of the coating resin layer 16. The coating eccentricity d is, for example, 8 μm or less, may be 6 μm or less, or may be 4 μm or less.

[0039] The coating eccentricity d is likely to vary along the longitudinal direction of the optical fiber 10. Therefore, the coating eccentricity d is measured at multiple points along the longitudinal direction of the optical fiber 10, for example, using an eccentricity variation observation device. For example, the average value of the values ​​measured at multiple measurement points set at predetermined measurement intervals may be used as the coating eccentricity d. The measurement interval is, for example, 1 mm to 100 mm. The number of measurement points is, for example, 500 or more.

[0040] By plotting the measurement results with the positions of multiple measurement points on the horizontal axis and the coating eccentricity d at each position on the vertical axis, the waveform (distribution) of the coating eccentricity d can be obtained. The waveform of the coating eccentricity d of the optical fiber 10 is also called the "eccentricity waveform". The eccentricity waveform is a waveform that shows the coating eccentricity d for each position of the multiple measurement points. In the spectrum obtained by Fourier transforming the eccentricity waveform, the maximum value of the amplitude of the coating eccentricity (amplitude value of the maximum amplitude component) may be 8 μm or less, 6 μm or less, or 4 μm or less.

[0041] The radius of the glass fiber 13 is R0 [m], and the Young's modulus of the glass fiber 13 is E0 [N / m]. ２ The radius of the primary resin layer 14 is R1 [m], and the Young's modulus of the primary resin layer 14 is E1 [N / m]. ２ The radius of the secondary resin layer 15 is R2 [m], and the Young's modulus of the secondary resin layer 15 is E2 [N / m]. ２ If ] then the transverse stiffness (lateral modulus) D [N / m] of the optical fiber 10 shown in equation (1) is ２ The bending stiffness (flexural modulus) H [N / m] shown in equation (2) is also expressed as ] and equation (2). ２ The relationship between ] may also satisfy equation (3). Here, c1 = 0.209367, c2 = 1.206659, c3 = 0.401169, and c ｉｊｋ The following applies: c 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

[0042] Equation (2) is the equation for bending stiffness H shown in Non-Patent Document 1. The derivation methods for equations (1) and (3) are described below.

[0043] Generally, the microbend loss α of an optical fiber can be expressed by the approximate formula in equation (4), using the lateral stiffness D, the bending stiffness H, and a constant A that is due to the optical properties of the optical fiber.

[0044] The microbend loss α of a small-diameter optical fiber may be 5.0 dB / km or less, 3.0 dB / km or less, or 1.0 dB / km or less. Therefore, the constant A in equation (4) is calculated from the measured value of the microbend loss α, and the D / H that satisfies the above value is calculated. ２The results of this calculation are shown in Table 1. From the results shown in Table 1, the D / H ratio that reduces microbend loss α to 5.0 dB / km or less is shown. ２ Equation (3) was obtained as the conditional expression.

[0045]

[0046] Based on the method described in Non-Patent Document 1, 2D FEM (Finite Element Method) calculations were performed using the analysis software MSC. Nastran 2020sp1 for 378 combinations where 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.

[0047] Next, the lateral stiffness D of each component was calculated from the analysis results based on the following formula: D = 2FθR² / uy ＊ Here, F is the lateral pressure (1 MPa), θ is the stress application angle (0 to 9 degrees), and uy ＊ This represents the displacement of the pressurized part in each structure.

[0048] 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 This is as stated above. however,

[0049] By rearranging equations (5) and (6), equation (1) was obtained. Using equation (1), the lateral stiffness D can be calculated, and D / H in equation (3) ２ This is required.

[0050] Figure 4 is a graph showing the relationship between MFD 1.31 and the relative microbend loss. Here, the relative microbend loss was calculated for an optical fiber with a core diameter of 180 μm, using a reference optical fiber with a core diameter of 180 μm. The horizontal axis represents MFD 1.31, and the vertical axis represents the relative microbend loss. Figure 4 shows the measured value of the relative microbend loss and an approximate curve. The relative microbend loss is a value that expresses the microbend loss as a relative value with the microbend loss of the reference optical fiber as the reference value. In other words, the relative microbend loss of the reference optical fiber is 1. The reference optical fiber has an MFD 1.31 of 8.4 μm and is an optical fiber whose microbend loss conforms to ITU-T G.657.A2. In the region below the reference line shown in Figure 4, that is, the region where the relative microbend loss is 1 or less, it can be said that the microbend loss can be reduced. For a core wire diameter of 180 μm, when the MFD 1.31 is 8.4 μm or less, the relative microbend loss value becomes 1 or less, indicating that microbend loss can be reduced.

[0051] Figure 5 is a graph showing the relationship between MFD 1.31 and the relative microbend loss. Here, the relative microbend loss was calculated for an optical fiber with a core diameter of 165 μm using a reference optical fiber with a core diameter of 200 μm. The horizontal axis represents MFD 1.31, and the vertical axis represents the relative microbend loss. Figure 5 shows the measured value of the relative microbend loss and an approximate curve. In the region below the reference line shown in Figure 5, that is, in the region where the relative microbend loss is 1 or less, it can be said that the microbend loss can be reduced. In the case of a core diameter of 165 μm, when MFD 1.31 is 7.4 μm or less, the relative microbend loss is 1 or less, and it can be said that the microbend loss can be reduced.

[0052] While embodiments and modifications have been described above, this disclosure is not necessarily limited to the embodiments and modifications described herein, and various modifications are possible without departing from its essence. The above embodiments and modifications may be combined as appropriate.

[0053] 10...Optical fiber 11...Core 12...Cladding 121...Inner cladding 122...Outer cladding 13...Glass fiber 14...Primary resin layer 15...Secondary resin layer 16...Coating resin layer d...Eccentricity GC...Center axis of glass fiber RC...Center axis of coating resin layer A1, A2, A3...Range r1, r2, r3...Radius Δ1, Δ2, Δ3...Difference in specific refractive index R0, R1, R2...Radius

Claims

1. A glass fiber having a core, an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding, and a coating resin layer covering the outer circumference of the glass fiber, wherein the core contains germanium, the diameter of the glass fiber is 124 μm or more and 126 μm or less, if the diameter of the core is 2r1 and the diameter of the inner cladding is 2r2, then 3 ≤ r2 / r1 ≤ 6, the diameter of the core is 4.6 μm or more and 8.9 μm or less, if the relative refractive index difference of the core is Δ1, the relative refractive index difference of the inner cladding is Δ2 and the relative refractive index difference of the outer cladding is Δ3, then 0.40% ≤ Δ1 - Δ2 ≤ 0.80% and -0.10% ≤ Δ2 - Δ3 ≤ 0.10%, the residual stress in the core is compressive stress, and the mode field diameter at a wavelength of 1310 nm is 8.4 μm or less. An optical fiber having a cable cutoff wavelength of less than 1530 nm and a diameter of the coating resin layer of 180 μm or less.

2. The optical fiber according to claim 1, wherein the microbend loss in the optical fiber is expressed as a relative value with respect to the microbend loss of a reference optical fiber having a mode field diameter of 8.4 μm and a coating resin layer diameter of 180 μm, in accordance with ITU-T G.657.A2, and the relative microbend loss value is 1 or less.

3. A glass fiber having a core, an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding, and a coating resin layer covering the outer circumference of the glass fiber, wherein the core contains germanium, the diameter of the glass fiber is 124 μm or more and 126 μm or less, if the diameter of the core is 2r1 and the diameter of the inner cladding is 2r2, then 4.0 ≤ r2 / r1 ≤ 5.5, the diameter of the core is 5.0 μm or more and 6.4 μm or less, if the relative refractive index difference of the core is Δ1, the relative refractive index difference of the inner cladding is Δ2 and the relative refractive index difference of the outer cladding is Δ3, then 0.45% ≤ Δ1 - Δ2 ≤ 0.75% and -0.10% ≤ Δ2 - Δ3 ≤ 0.10%, the residual stress in the core is compressive stress, and the mode field diameter at a wavelength of 1310 nm is 7.4 μm or less. An optical fiber having a cable cutoff wavelength of less than 1530 nm and a diameter of the coating resin layer of 165 μm or less.

4. The optical fiber according to claim 3, wherein the microbend loss in the optical fiber is expressed as a relative value with respect to the microbend loss of a reference optical fiber having a mode field diameter of 8.4 μm and a coating resin layer diameter of 200 μm, in accordance with ITU-T G.657.A2, and the relative microbend loss value is 1 or less.

5. The optical fiber according to claim 1 or claim 3, wherein the fracture frequency in a screening test applying a 1% tensile strain is 10 times / mm or less.

6. In a cross section perpendicular to the axial direction, the coating eccentricity, which is the distance from the central axis of the coating resin layer to the central axis of the glass fiber, is measured at a plurality of measurement points set at predetermined intervals in the axial direction, and in a spectrum obtained by Fourier transforming the waveforms representing the coating eccentricity for each of the plurality of measurement points, the maximum value of the amplitude of the coating eccentricity is 8 μm or less, as described in claim 1 or claim 3.

7. The coating resin layer has a primary resin layer and a secondary resin layer. Let the radius of the glass fiber be R0 [m], the Young's modulus of the glass fiber be E0 [N / m ２ , the radius of the primary resin layer be R1 [m], the Young's modulus of the primary resin layer be E1 [N / m ２ , the radius of the secondary resin layer be R2 [m], and the Young's modulus of the secondary resin layer be E2 [N / m ２ . Then, the relationship between the transverse rigidity D [N / m ２ shown in formula (1) and the bending rigidity H [N / m ２ of the optical fiber satisfies formula (3). In a cross-section orthogonal to the axial direction, the coating eccentricity amount, which is the distance from the central axis of the glass fiber to the central axis of the coating resin layer based on the outer periphery of the coating resin layer, is 8 μm or less. The optical fiber according to claim 1 or claim 3. Here, 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

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