optical fiber

Abstract

This optical fiber comprises a core part, a side core layer surrounding the outer periphery of the core part, and a clad part surrounding the outer periphery of the side core layer. When the average maximum relative refractive index difference of the core part and the relative refractive index difference of the average refractive index of the side core layer with respect to the average refractive index of the clad part are denoted by Δ1 and Δ2, respectively, and the relative refractive index difference of the average refractive index of the clad part with respect to pure silica glass is denoted by ΔClad, Δ1>ΔClad>Δ2 and 0>Δ2 hold, Δ1is 0.24-0.30%,Δ2 is -0.27 to -0.08%, (Δ1-Δ2) is 0.36-0.57%, when the core diameter of the core part is denoted by 2a and the outer diameter of the side core layer is denoted by 2b, b / a is 2 or more, and the effective core cross-sectional area at a wavelength of 1550 nm is 107 μm2 to 130 μm2.

Description

[Technical Field]

[0001] The present invention relates to optical fibers. [Background technology]

[0002] Optical fibers employing a W-shaped refractive index profile are being actively studied (Patent Documents 1 to 4). A W-shaped refractive index profile is employed, for example, to increase the effective core area of ​​an optical fiber. Optical fibers with a large effective core area suppress the occurrence of nonlinear optical effects within the optical fiber, making them suitable for use as, for example, long-distance optical transmission lines. The effective core area is sometimes abbreviated as Aeff. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6500451 [Patent Document 2] Patent No. 6527973 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-66259 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-122277 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, there is a trade-off between the effective core area and the cutoff wavelength, and increasing the effective core area tends to increase the cutoff wavelength. However, in order to achieve single-mode transmission in the wavelength band used for optical transmission, it is sometimes necessary to lower the cutoff wavelength of the optical fiber. Therefore, there is room for further study on achieving both an increase in the effective core area and a decrease in the cutoff wavelength. Furthermore, optical fibers are generally installed and used in an optical cable. However, since optical fibers are at least partially bent when housed in an optical cable, it is also necessary to consider the bending loss characteristics of the optical fiber.

[0005] The present invention has been made in view of the above, and an object of the present invention is to provide an optical fiber that has an enlarged effective core area, a low cutoff wavelength, and low bending loss. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention is a fiber optic optical fiber comprising a core portion, a side core layer surrounding the outer periphery of the core portion, and a clad portion surrounding the outer periphery of the side core layer, wherein the average refractive index of the core portion relative to the average refractive index of the clad portion is Ratio of If the refractive index difference is Δ1, the relative refractive index difference of the average refractive index of the side core layer is Δ2, and the relative refractive index difference of the average refractive index of the cladding portion with respect to pure silica glass is ΔClad, then Δ1 +ΔClad >ΔClad>Δ2 +ΔClad and 0>Δ2 holds, Δ1 is 0.24% or more and 0.30% or less, Δ2 is -0.27% or more and -0.08% or less, (Δ1-Δ2) is 0.36% or more and 0.57% or less, and when the core diameter of the core portion is 2a and the outer diameter of the side core layer is 2b, b / a is 2 or more. 4 or less The effective core area at a wavelength of 1550 nm is 107 μm 2 More than 130 μm 2 Below is The cable cutoff wavelength is 1460 nm or less, the bending loss at a wavelength of 1550 nm when bent at a diameter of 30 mm is 1 dB / m or less, and 2a is 12.4 μm or more and 13.8 μm or less. , optical fiber.

[0009] The bending loss may be 0.5 dB / m or less.

[0011] The cable cutoff wavelength may be 1386 nm or more.

[0012] ΔClad may be less than 0%.

[0013] The core may contain a dopant that increases the refractive index of the material that constitutes the core.

[0014] (Δ1+ΔClad) may be 0.03% or more and 0.18% or less. [Effects of the Invention]

[0015] The present invention has the effect of realizing an optical fiber having a low cutoff wavelength and low bending loss while having an enlarged effective core area. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic cross-sectional view of an optical fiber according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of a refractive index profile of the optical fiber according to the embodiment. [Figure 3] FIG. 3 is a diagram showing an example of the relationship between Δ1, the cutoff wavelength, and the effective core. [Figure 4] FIG. 4 is a diagram showing an example of the relationship between Δ1 and bending loss. [Figure 5] FIG. 5 is a diagram showing an example of the relationship between (Δ1−Δ2) and the bending loss and the effective core area. [Figure 6] FIG. 6 is a diagram showing an example of a fitting function for the bending loss data points of FIG. [Figure 7] FIG. 7 is a diagram showing an example of the relationship between Δ2 and the cutoff wavelength and the effective core area. [Figure 8] FIG. 8 is a diagram showing an example of the relationship between the effective core area and the cutoff wavelength. [Figure 9] FIG. 9 is a diagram showing an example of the relationship between the effective core area and the bending loss in several cases of b / a. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the embodiments described below. Furthermore, in each drawing, the same or corresponding components are appropriately designated by the same reference numerals. Furthermore, in this specification, cutoff wavelength or effective cutoff wavelength refers to the cable cutoff wavelength defined in ITU-T G.650.1 of the International Telecommunications Union (ITU). Furthermore, other terms not specifically defined in this specification shall follow the definitions and measurement methods in G.650.1 and G.650.2.

[0018] (Embodiment) 1 is a schematic cross-sectional view of an optical fiber according to an embodiment. The optical fiber 10 is made of silica-based glass and includes a core 11, a side core layer 12 surrounding the outer periphery of the core 11, and a cladding 13 surrounding the outer periphery of the side core layer 12. The optical fiber 10 may also include a coating layer surrounding the outer periphery of the cladding 13.

[0019] 2 is a diagram showing the refractive index profile of the optical fiber 10. Profile P1 is the refractive index profile of the core region 11, and has a so-called step type. Profile P2 is the refractive index profile of the side core layer 12. Profile P3 is the refractive index profile of the cladding region 13.

[0020] Here, the refractive index profile of the core region 11 may not only be a geometrically ideal stepped shape, but also may have an uneven top shape due to manufacturing characteristics, or may have a shape that trails from the top. In this case, the refractive index of a region that is approximately flat at the top of the refractive index profile within the range of the core diameter 2a of the core region 11 in the manufacturing design becomes an index for determining Δ1.

[0021] The following describes the structural parameters of the optical fiber 10. As described above, the core diameter of the core region 11 is 2a. The outer diameter of the side core layer 12 is 2b.

[0022] Furthermore, the relative refractive index difference (maximum relative refractive index difference) of the average maximum refractive index of the core portion 11 with respect to the average refractive index of the cladding portion 13 is Δ1. The relative refractive index difference of the average refractive index of the side core layer 12 with respect to the average refractive index of the cladding portion 13 is Δ2. The average maximum refractive index of the core portion 11 is the average value in the radial direction of the refractive index of the region that is approximately flat at the top of the refractive index profile. The average refractive index of the side core layer 12 or the cladding portion 13 is the average value of the refractive index in the radial direction of the refractive index profile.

[0023] The relative refractive index difference of the average refractive index of the cladding portion 13 with respect to the refractive index of pure silica glass is ΔClad. Here, pure silica glass refers to extremely high-purity silica glass that contains substantially no dopants that change the refractive index and has a refractive index of approximately 1.444 at a wavelength of 1550 nm. In Figure 2, the dashed line indicates the relative refractive index difference of pure silica glass with respect to the average refractive index of the cladding portion 13.

[0024] For Δ1, Δ2, and ΔClad, Δ1 +ΔClad >ΔClad>Δ2 +ΔClad Furthermore, 0>Δ2 holds. That is, the optical fiber 10 has a W-shaped refractive index profile. Although part of FIG. 2 and Table 1 shows a case where ΔClad is less than 0%, ΔClad may be 0% or more.

[0025] The constituent materials of the optical fiber 10 will now be described. The core 11 is made of silica-based glass containing a dopant for adjusting the refractive index, which increases the refractive index. For example, the core 11 contains at least one, for example, two or more of germanium (Ge), chlorine (Cl), fluorine (F), potassium (K), and sodium (Na) as a dopant. F decreases the refractive index of silica glass, while (Ge), Cl, K, and Na are dopants that increase the refractive index of silica glass.

[0026] On the other hand, the side core layer 12 and the clad portion 13 are made of silica glass doped with only F and Cl. By adjusting the refractive index with these dopants, Δ1>ΔClad +ΔClad >Δ2 +ΔClad Furthermore, 0>Δ2 is established, and further, the preferable ranges of Δ1, Δ2, and ΔClad, which will be described later, are realized.

[0027] Regarding the structural parameters of the optical fiber 10 according to this embodiment, Δ1 is 0.24% or more and 0.30% or less, Δ2 is −0.27% or more and −0.08% or less, (Δ1−Δ2) is 0.36% or more and 0.57% or less, and b / a is 2 or more. In addition, in the optical fiber 10, the structural parameters are as follows: the effective core area at a wavelength of 1550 nm is 107 μm 2 More than 130 μm 2 It is set so as to realize the following characteristic.

[0028] As a result, the optical fiber 10 has an effective core area of ​​107 μm 2 More than 130 μm 2 The optical fiber 10 achieves the characteristics of a low cutoff wavelength and low bending loss while being expanded to the following extent. For example, the optical fiber 10 has a cable cutoff wavelength of 1530 nm or less, and a bending loss of 1 dB / m or less at a wavelength of 1550 nm when bent with a diameter of 30 mm.

[0029] In the following, the bending loss at a wavelength of 1550 nm when bent at a diameter of 30 mm may be referred to simply as bending loss. This type of bending loss may also be referred to as macrobending loss, and the condition of bending at a diameter of 30 mm may also be referred to as "30 mmφ."

[0030] The optical fiber 10 can also achieve an even lower cutoff wavelength characteristic, with a cabled cutoff wavelength of 1460 nm or less. For example, if the cabled cutoff wavelength of the optical fiber 10 is 1530 nm or less, single-mode transmission can be achieved in the optical transmission wavelength bands of the C-band (e.g., 1530 nm to 1565 nm) and the L-band (e.g., 1565 nm to 1625 nm). If the cabled cutoff wavelength is 1460 nm or less, single-mode transmission can be achieved not only in the C-band and L-band but also in the S-band (e.g., 1460 nm to 1530 nm), making it possible to achieve single-mode transmission over an extremely wide bandwidth.

[0031] The optical fiber 10 can also achieve even lower bending loss characteristics, with a bending loss of 0.5 dB / m. According to the inventor's extensive research, if the bending loss is 1 dB / m or less, even when the optical fiber 10 is housed in an optical cable for practical use, an increase in transmission loss due to bending associated with housing in an optical cable is suppressed. Furthermore, if the bending loss is 0.5 dB / m or less, an increase in transmission loss when housed in an optical cable is further suppressed.

[0032] (Favorable combination of structural parameters and characteristics) The following describes the inventor's extensive research into finding the above-mentioned suitable combinations of structural parameters for the optical fiber 10 and the resulting suitable characteristics.

[0033] First, we performed simulation calculations for the effective core area and cable cutoff wavelength for various values ​​of Δ1. The other structural parameters, Δ2, 2a, and b / a, were set to cover a wide range of combinations.

[0034] Figure 3 shows an example of the relationship between Δ1 and the cutoff wavelength and effective core area. The horizontal axis represents Δ1, and the vertical axis represents the cutoff wavelength (λcc) and the effective core area (Aeff) at a wavelength of 1550 nm. As shown in Figure 3, even for the same value of Δ1, the combinations of structural parameters are different at each data point, so λcc and Aeff take on various values. In particular, in Figure 3, the combination of structural parameters with Δ1 set to 0.27% has the most calculations, so it takes on a correspondingly wide range of values. However, it can be seen that as the value of Δ1 increases, λcc increases and Aeff decreases.

[0035] The inventors have found from FIG. 3 that λcc of 1530 nm or less and λcc of 107 μm 2 To satisfy the above Aeff with some margin, or λcc of 1530 nm or less and 107 μm 2 It was confirmed that in order to ensure a certain number and proportion of data points that satisfy the above Aeff, it is desirable that Δ1 be 0.3% or less.

[0036] Figure 4 shows an example of the relationship between Δ1 and bending loss. As in Figure 3, even for a certain value of Δ1, the data points have different combinations of structural parameters, so bending loss takes on a variety of values. However, it can be seen that bending loss tends to decrease as the value of Δ1 increases.

[0037] The inventors have confirmed from Fig. 4 that in order to achieve a bending loss of 1 dB / m or less with a certain degree of leeway, or to ensure a certain number or percentage of data points that achieve a bending loss of 1 dB / m or less, Δ1 is preferably 0.24% or more. Therefore, from Figs. 3 and 4, it is desirable that Δ1 be 0.24% or more and 0.3% or less.

[0038] Next, the inventors focused on (Δ1-Δ2) as a structural parameter that influences Aeff and bending loss in addition to Δ1 as a result of simulation calculations. Therefore, simulation calculations were performed on the values ​​of Aeff and bending loss for various values ​​of (Δ1-Δ2). Note that Δ1 was set to various values ​​in the range of 0.24% to 0.3%. In addition, the other structural parameters, 2a and b / a, were set to cover various combinations.

[0039] Figure 5 shows an example of the relationship between (Δ1-Δ2) and the bending loss and effective core area. The area A enclosed by the dashed lines L1 and L2 indicates a certain trend of the data points. Figure 5 confirms that (Δ1-Δ2) correlates with the bending loss and Aeff, and that the bending loss and Aeff tend to decrease as the value of (Δ1-Δ2) increases.

[0040] Specifically, the bending loss increased sharply as (Δ1-Δ2) became smaller than 0.36%. Fig. 6 shows an example of a fitting function calculated by the least squares method for the data points of small bending loss along the dashed line L1 among the bending loss data points in Fig. 5. The fitting function is a quartic function of (Δ1-Δ2), specifically, y=2126.5x 4 -3638.2x 3 +2328.4x 2 The bending loss was -660.83x+70.245, but it can be seen that the bending loss increases sharply as (Δ1-Δ2) becomes smaller than 0.36%. From this result, and taking stable manufacturability into consideration, it is desirable that (Δ1-Δ2) is 0.36% or more.

[0041] In addition, when Aeff exceeds 0.57%, it is 107 μm 2 Therefore, it is preferable that (Δ1-Δ2) is 0.36% or more and 0.57% or less.

[0042] Next, the inventors performed simulation calculations for the values ​​of Aeff and λcc for various values ​​of Δ2. Δ1 was set to various values ​​in the range of 0.24% to 0.3%, and (Δ1-Δ2) was set to various values ​​in the range of 0.32% to 0.57%. Furthermore, the other structural parameters, 2a and b / a, were set to cover a wide range of combinations.

[0043] Fig. 7 is a diagram showing an example of the relationship between Δ2 and the cutoff wavelength and effective core area, which shows that λcc and Aeff tend to decrease as the value of Δ2 increases.

[0044] The inventors have found from FIG. 3 that λcc of 1530 nm or less and λcc of 107 μm 2 To satisfy the above Aeff with some margin, or λcc of 1530 nm or less and 107 μm 2 It was confirmed that in order to ensure a certain number and proportion of data points that satisfy the above Aeff, it is desirable that Δ2 be between −0.27% and −0.08%.

[0045] From the results of the above comprehensive simulation calculations, it was confirmed that, with regard to the structural parameters of the optical fiber 10 according to this embodiment, it is desirable that Δ1 is 0.24% or more and 0.30% or less, Δ2 is −0.27% or more and −0.08% or less, and (Δ1−Δ2) is 0.36% or more and 0.57% or less.

[0046] 8 is a diagram showing an example of the relationship between the effective core area and the cutoff wavelength obtained as a result of the above-mentioned desirable combinations of Δ1, Δ2, and (Δ1-Δ2). 2 In order to further satisfy the condition that λcc is 1530 nm or less, Aeff must be 130 μm 2 Furthermore, in order to satisfy the condition that λcc is 1460 nm or less, Aeff should be 125 μm 2 It is desirable to do the following:

[0047] Furthermore, the inventors investigated the optimization of the structural parameter b / a. First, various values ​​of b / a were set, and then other structural parameters were set so that the relationship between Aeff and λcc was constant for each b / a, and the relationship between Aeff and bending loss was investigated.

[0048] Fig. 9 shows an example of the relationship between the effective core area and bending loss for several b / a ratios. In Fig. 9, b / a is set to 2, 2.5, 3, and 4. Fig. 9 shows that when b / a is less than 3, bending loss increases, and when b / a is less than 2, bending loss may exceed 1 dB / m. Therefore, b / a of 2 or more is desirable. Furthermore, even if b / a is increased above 3, for example to 4, bending loss does not decrease significantly. Therefore, from the perspective of bending loss, a b / a of about 3 is sufficient. As a result of the above considerations, b / a is, for example, between 2 and 6, and further preferably between 2.5 and 4.

[0049] Finally, for the core diameter 2a, the values ​​of Δ1, Δ2, (Δ1-Δ2), and b / a are selected from the desired ranges described above, and then the values ​​are appropriately set so that the desired characteristics of Aeff, λcc, and bending loss are obtained.

[0050] As described above, the optical fiber 10 according to this embodiment has an enlarged effective core area, a low cutoff wavelength, and low bending loss.

[0051] The optical fiber 10 according to this embodiment can be easily manufactured by producing an optical fiber preform using a known method such as a VAD (Vapor Axial Deposition) method, an OVD (Outside Vapor Deposition) method, an MCVD (Modified Chemical Vapor Deposition) method, or a plasma CVD method, and then drawing the optical fiber 10 from this optical fiber preform.

[0052] For example, dopants such as Ge, F, K, and Na can be added to the optical fiber preform by using a gas containing the dopant during soot synthesis. Cl can be added to the optical fiber preform by leaving chlorine gas used in the dehydration process. F can be added to the optical fiber preform by flowing fluorine gas during vitrification and sintering.

[0053] Here, the average maximum relative refractive index difference of the core region 11 with respect to the refractive index of pure silica glass is expressed as (Δ1+ΔClad), but (Δ1+ΔClad) does not necessarily have to be a positive value. For example, the core region 11 may be made of pure silica glass so that (Δ1+ΔClad)=0 holds, or a dopant that reduces the refractive index may be added to the core region 11 so that (Δ1+ΔClad)<0 holds.

[0054] Furthermore, when the refractive index of the side core layer 12 is achieved by doping F, making Δ2 too small increases the difficulty of manufacturing and may increase the transmission loss of the optical fiber 10. Therefore, a dopant that increases the refractive index may be added to the core region 11 to achieve the desired (Δ1 - Δ2) while preventing Δ2 from becoming too small. In this case, it is preferable to dope the core region 11 with a dopant so that (Δ1 + ΔClad) is, for example, 0.03% or more and 0.18% or less.

[0055] (Example) As examples, optical fiber preforms manufactured using the VAD method were drawn to produce optical fibers having a W-shaped refractive index profile, samples No. 1 to No. 17, and their optical characteristics were measured. The structural parameters of each sample are shown in Table 1, and the optical characteristics are shown in Table 2. Note that "MFD" means mode field diameter, and "Slope" means dispersion slope.

[0056] The W-shaped refractive index profile was achieved using either method (1) or (2) below. Specifically, (1) the core was doped with Ge to increase its refractive index above that of pure silica glass, and the cladding was made of pure silica glass or a silica-based glass with a refractive index close to that of pure silica glass. (2) The core was doped with Cl or K to increase its refractive index above that of pure silica glass, but only to the extent that the refractive index and Rayleigh scattering loss did not increase too much, and the cladding was doped with F to decrease its refractive index below that of pure silica glass. In Tables 1 and 2, samples fabricated using method (1) are indicated with (Ge) along with the sample number, and samples fabricated using method (2) are indicated with (Si) along with the sample number.

[0057] In Table 1, "Δ1 + ΔClad" refers to the maximum average relative refractive index difference of the core portion relative to pure silica glass. "Δ2 + ΔClad" refers to the relative refractive index difference of the average refractive index of the side core layer relative to pure silica glass. Meanwhile, "Δ1" refers to the maximum average relative refractive index difference of the core portion relative to the average refractive index of the cladding portion. "Δ2" refers to the relative refractive index difference of the average refractive index of the side core layer relative to the average refractive index of the cladding portion. Of the optical properties shown in Table 2, "Δ1 + ΔClad" and "Δ2 + ΔClad" mainly affect transmission loss, while "Δ1" and "Δ2" mainly affect other optical properties.

[0058] The cladding diameter of each of the optical fibers of Samples No. 1 to 17 was 125 μm. As shown in Table 1, the Δ1 of each of the optical fibers of Samples No. 1 to 17 was 0.24% or more and 0.30% or less, the Δ2 of each of the optical fibers of Samples No. 1 to 17 was -0.27% or more and -0.08% or less, the (Δ1-Δ2) of each of the optical fibers of Samples No. 1 to 17 was 0.36% or more and 0.57% or less, the ΔClad of each of the optical fibers of Samples No. 1 to 17 was -0.22% or more and 0.03% or less, and the b / a of each of the optical fibers of Samples No. 1 to 17 was 2 or more and 4 or less. The core diameter 2a of each of the optical fibers of Samples No. 1 to 17 was 12.4 μm or more and 13.8 μm or less. As a result, as shown in Table 2, the Aeff of each of the optical fibers of Samples No. 1 to 17 was 107 μm or more. 2 More than 130 μm 2λcc is 1386 nm or more and 1530 nm or less, or even 1460 nm or less, the MFD at a wavelength of 1550 nm is 11.2 μm or more and 12.1 μm or less, the chromatic dispersion at a wavelength of 1550 nm is 20.8 ps / nm / km or more and 21.9 ps / nm / km or less, and the dispersion slope at a wavelength of 1550 nm is 0.062 ps / nm 2 / km or more 0.063ps / nm 2 It was confirmed that good characteristics could be achieved, with a bending loss of 1 dB / m or less, or even 0.5 dB / m or less. Furthermore, for samples manufactured by method (2), such as optical fibers Nos. 1 to 3, 7 to 11, and 15 to 17, where (Δ1 + ΔClad) was set to 0.03% or more, it was confirmed that a low transmission loss of 0.153 dB / km or more and 0.188 dB / km or less, for example, 0.17 dB / km, could be achieved. It was also confirmed that the MFD, chromatic dispersion, and dispersion slope met the standards of, for example, ITU-T G.654.

[0059] For sample No. 8, Δ1 is 0.27%, Δ2 is -0.11%, (Δ1-Δ2) is 0.38%, ΔClad is -0.2%, and b / a is 3. The core diameter 2a is 13.3 μm. As a result, Aeff is 121 μm. 2 , λcc is 1492 nm, MFD is 12 μm, chromatic dispersion is 21.1 ps / nm / km, and dispersion slope is 0.063 ps / nm 2 It was confirmed that excellent characteristics could be achieved, with a bending loss of 0.09 dB / m and a transmission loss of 0.167 dB / km.

[0060] For sample No. 11, Δ1 is 0.25%, Δ2 is -0.11%, (Δ1-Δ2) is 0.36%, ΔClad is -0.1%, and b / a is 3. The core diameter 2a is 13.3 μm. As a result, Aeff is 123 μm. 2, λcc is 1430 nm, MFD is 12.1 μm, chromatic dispersion is 21.1 ps / nm / km, and dispersion slope is 0.062 ps / nm 2 It was confirmed that good characteristics could be achieved, with a bending loss of 0.36 dB / km and a transmission loss of 0.157 dB / km.

[0061] For sample No. 17, Δ1 is 0.27%, Δ2 is -0.1%, (Δ1-Δ2) is 0.37%, ΔClad is -0.24%, and b / a is 4. The core diameter 2a is 12.5 μm. As a result, Aeff is 114 μm. 2 , λcc is 1488 nm, MFD is 11.7 μm, chromatic dispersion is 20.9 ps / nm / km, and dispersion slope is 0.062 ps / nm 2 It was confirmed that excellent characteristics could be achieved, with a bending loss of 0.04 dB / m and a transmission loss of 0.169 dB / km.

[0062] Furthermore, the optical fibers of Samples No. 1 to 17 were checked for their connection characteristics with other optical fibers and cable characteristics (such as loss after cable construction), and no particular problems were found in the characteristics. [Table 1]

[0063] [Table 2]

[0064] It should be noted that the present invention is not limited to the above-described embodiments. The present invention also includes configurations in which the above-described components are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible. [Industrial Applicability]

[0065] As described above, the present invention is suitable for use in optical fibers as long-distance transmission lines, for example. [Explanation of symbols]

[0066] 10: Optical fiber 11: Core part 12: Side core layer 13: Cladding part A :Area L1, L2: dashed lines P1, P2, P3: Profiles

Claims

1. A core portion, a side core layer surrounding the outer periphery of the core portion; a clad portion surrounding the outer periphery of the side core layer; Equipped with When the average relative refractive index difference of the core portion with respect to the average refractive index of the cladding portion is Δ1, the relative refractive index difference of the average refractive index of the side core layer is Δ2, and the relative refractive index difference of the average refractive index of the cladding portion with respect to pure silica glass is ΔClad, then Δ1+ΔClad>ΔClad>Δ2+ΔClad and 0>Δ2 hold true, Δ1 is 0.24% or more and 0.30% or less, Δ2 is −0.27% or more and −0.08% or less, (Δ1−Δ2) is 0.36% or more and 0.57% or less, (Δ1 + ΔClad) is 0.03% or more and 0.18% or less, The cable cutoff wavelength is 1460 nm or less, When the core diameter of the core portion is 2a and the outer diameter of the side core layer is 2b, b / a is 2 or more and 4 or less, The effective core area at a wavelength of 1550 nm is 107 μm ２ More than 130 μm ２ is as follows: The cable cutoff wavelength is 1460 nm or less, When bent at a diameter of 30 mm, the bending loss at a wavelength of 1550 nm is 1 dB / m or less, 2a is 12.4 μm or more and 13.8 μm or less Optical fiber.

2. The bending loss is 0.5 dB / m or less. The optical fiber of claim 1 .

3. The cable cutoff wavelength is 1386 nm or more.

3. The optical fiber according to claim 1 or 2.

4. ΔClad is less than 0% The optical fiber according to any one of claims 1 to 3.

5. The core portion contains a dopant that increases the refractive index of the material that constitutes the core portion. The optical fiber according to any one of claims 1 to 4.

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