optical fiber

Abstract

An optical fiber comprises: a core having a central portion (a portion having a diameter of 0.5 μm or more and 4 μm or less) including a central axis and made of silica glass, and a cladding covering the core and made of silica glass. The core contains chlorine. The average chlorine concentration of the core is 10,000 ppm or more and 50,000 ppm or less. The difference between the average chlorine concentration of the core and the average chlorine concentration of the central portion is 4,500 ppm or more and 13,500 ppm or less.

Description

[0001] This patent application claims the priority based on Japanese Patent Application No. 2019-239383 filed on December 27, 2019, and cites all the contents described in the Japanese Patent Application. Technical Field

[0002] The present invention relates to optical fibers. Background Art

[0003] In an optical fiber whose core contains chlorine at a mass fraction of 1.0% or more, it is easy to obtain low transmission loss even at a high drawing speed compared to an optical fiber whose core is composed of quartz glass without additives and to which fluorine is added to the cladding. In an optical fiber whose core is composed of quartz glass without additives and to which fluorine is added to the cladding, the stress applied to the core region during drawing becomes a tensile stress. Therefore, it is difficult to achieve structural buffering of the glass. Therefore, in order to reduce the transmission loss, the drawing speed has to be reduced to reduce the drawing tension. In contrast, in an optical fiber whose core is added with chlorine at a mass fraction of 1.0% or more, the stress applied to the core region during drawing becomes a compressive stress. Therefore, sufficient room for increasing the drawing tension to increase the drawing speed can be ensured.

[0004] Japanese Patent Application Publication No. 2017-526601 discloses a single-mode optical fiber whose core contains chlorine at a mass fraction of 1.5% or more. Summary of the invention

[0005] An optical fiber according to one embodiment of the present invention comprises: a core having a central portion (a portion having a diameter of 0.5 μm or more and 4 μm or less) including a central axis and made of silica glass, and a cladding covering the core and made of silica glass. The core contains chlorine. The average chlorine concentration of the core is 10,000 ppm or more and 50,000 ppm or less. The difference between the average chlorine concentration of the core and the average chlorine concentration of the central portion is 4,500 ppm or more and 13,500 ppm or less.

[0006] The optical fiber according to other embodiments of the present invention comprises: a core having a central portion (a portion having a diameter of 0.5 μm to 4 μm) including a central axis, and a cladding covering the core. The core contains chlorine. The average chlorine concentration of the core is 10,000 ppm to 50,000 ppm. The relative refractive index difference of the average refractive index of the core at a wavelength of 1550 nm with respect to the average refractive index of the cladding is 0.25% to 0.40%. The diameter of the core is 8.5 μm to 13.5 μm. The relative refractive index difference of the average refractive index of the core at a wavelength of 1550 nm with respect to the refractive index of pure quartz is set to Δn plus, when the relative refractive index difference of the minimum refractive index at the center portion at a wavelength of 1550nm with respect to the refractive index of pure quartz is defined as Δdip, Δn plus -Δdip is 0.05% to 0.15%. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] [ Figure 1 ] is a cross-sectional view of the optical fiber involved in the implementation method.

[0008] [ Figure 2 ] is a schematic representation Figure 1 Diagram of the refractive index distribution of optical fiber.

[0009] [ Figure 3 ] is a graph showing the relationship between the ratio of the effective cross-sectional area to the cable cut-off wavelength and the bending loss. DETAILED DESCRIPTION

[0010] [Problems to be Solved by the Invention]

[0011] As a method for forming a core glass rod containing chlorine at a mass fraction of 1.0% or more, there is a method in which a glass tube containing chlorine at a mass fraction of 1.0% or more is formed by an OVD (Outside Vapor Deposition) method, an MCVD (Modified Chemical Vapor Deposition) method, or a PCVD (Plasma Chemical Vapor Deposition) method, and then the opening of the glass tube is closed by a collapse method to form a core glass rod. However, bubbles are likely to remain in the center of the core glass rod formed by this method.

[0012] Even after the core glass rod is formed into a matrix, the bubbles still remain in the center of the core of the matrix. In addition, even after the preform (matrix) is formed into an optical fiber through a drawing process, the bubbles still remain in the center of the core of the optical fiber, resulting in deterioration of transmission loss or reduction of mechanical reliability. Therefore, the portion where the bubbles remain is removed as a defective portion. In other words, there is the following problem: even if chlorine is added to the core to increase the productivity of the drawing process by increasing the drawing speed, the defective portion of the optical fiber increases, the yield rate deteriorates, and thus the productivity cannot be improved comprehensively.

[0013] Therefore, an object of the present invention is to provide an optical fiber capable of suppressing reduction in yield and productivity.

[0014] [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an optical fiber capable of suppressing reduction in yield and productivity.

[0016] [Description of Embodiments of the Invention]

[0017] First, the embodiments of the present invention are listed and described. An optical fiber involved in one embodiment comprises: a core having a central portion (a portion with a diameter of 0.5 μm or more and 4 μm or less) including a central axis and made of quartz glass, and a cladding covering the core and made of quartz glass. The core contains chlorine. The average chlorine concentration of the core is 10,000 ppm or more and 50,000 ppm or less. The difference between the average chlorine concentration of the core and the average chlorine concentration of the center is 4,500 ppm or more and 13,500 ppm or less. Here, the concentration of chlorine is expressed as a mass fraction (the ratio of the mass of chlorine contained in the object to the total mass of the object).

[0018] In the optical fiber according to the above embodiment, in the process of solidifying the core glass tube to form the core glass rod, the chlorine concentration on the inner surface of the glass tube can be suppressed to be low, so that the generation of bubbles on the inner surface due to chlorine can be suppressed. Therefore, bubbles in the central part of the core of the optical fiber can be suppressed. As a result, the reduction in the yield and productivity of the optical fiber can be suppressed.

[0019] The relative refractive index difference of the average refractive index of the core can be 0.25% to 0.40% at a wavelength of 1550nm, with the average refractive index of the cladding as a reference, and the diameter of the core can be 8.5μm to 13.5μm. Thus, microbending and the increase of excessive loss and connection loss caused by microbending can be suppressed. In order to achieve the above-mentioned relative refractive index difference, it is desirable that the core does not contain germanium, does not contain fluorine, or suppresses fluorine to a concentration lower than that of chlorine. In addition, it is preferred to use pure quartz glass or quartz glass with fluorine added to form the cladding.

[0020] The relative refractive index difference of the average refractive index of the core at a wavelength of 1550 nm with respect to the refractive index of pure quartz is denoted as Δn plus , when the relative refractive index difference of the minimum refractive index at the center portion at a wavelength of 1550nm with respect to the refractive index of pure quartz is defined as Δdip, Δn plus -Δdip may be 0.05% or more and 0.15% or less. In this case, the difference between the average chlorine concentration in the core portion and the average chlorine concentration in the center portion can be easily set to 4500 ppm or more and 13500 ppm or less.

[0021] The optical fiber involved in other embodiments comprises: a core having a central portion (a portion with a diameter of 0.5 μm to 4 μm) including a central axis, and a cladding covering the core. The core contains chlorine. The average chlorine concentration of the core is 10,000 ppm to 50,000 ppm. The relative refractive index difference of the average refractive index of the core at a wavelength of 1550 nm with respect to the average refractive index of the cladding is 0.25% to 0.40%. The core diameter is 8.5 μm to 13.5 μm. The relative refractive index difference of the average refractive index of the core at a wavelength of 1550 nm with respect to the refractive index of pure quartz is set to Δn plus , when the relative refractive index difference of the minimum refractive index at the center of the crystal at a wavelength of 1550nm is set to Δdip, Δn plus -Δdip is 0.05% to 0.15%.

[0022] In the optical fiber involved in the above-mentioned embodiment, it is easy to make the difference between the average chlorine concentration of the core and the average chlorine concentration of the center be 4500 ppm or more and 13500 ppm or less. Therefore, in the process of forming the core glass rod, it is easy to suppress the generation of chlorine bubbles on the inner surface of the glass tube. Therefore, it is possible to suppress bubbles in the center of the core of the optical fiber. As a result, it is easy to suppress the reduction of the yield and productivity of the optical fiber.

[0023] The cladding may also contain fluorine. In this case, even if the chlorine concentration in the core is low, the relative refractive index difference of the average refractive index of the core at a wavelength of 1550nm can be made to be 0.25% or more when the average refractive index of the cladding is used as a reference. Therefore, the fundamental mode light can be captured.

[0024] The mode field diameter of the optical fiber at a wavelength of 1310 nm can be between 8.6 μm and 13.0 μm. The effective cross-sectional area of ​​the optical fiber at a wavelength of 1550 nm can be 70 μm. 2 Above 130μm 2 The cable cutoff wavelength of the optical fiber can be 1530 nm or less. In this case, the optical signal-to-noise ratio of the optical communication system can be improved. In addition, it can be connected to the optical fiber recommended by the widely used ITU-TG.654.

[0025] The mode field diameter of the optical fiber at a wavelength of 1310 nm can be 8.6 μm or more and 11.0 μm or less. The effective cross-sectional area of ​​the optical fiber at a wavelength of 1550 nm can be 70 μm 2 Above 115μm 2 The cable cutoff wavelength of the optical fiber can be 1260nm or less. In this case, the optical signal-to-noise ratio of the optical communication system can also be improved. In addition, it can be connected to the optical fiber recommended by the widely used ITU-TG.652.

[0026] The transmission loss of the optical fiber at a wavelength of 1550 nm may be greater than 0.15 dB / km and less than 0.18 dB / km. The transmission loss of the optical fiber at a wavelength of 1310 nm may be greater than 0.24 dB / km and less than 0.40 dB / km.

[0027] The cladding layer may be further provided with a coating resin layer made of an acrylic resin, and the diameter of the coating resin layer may be 190 μm or more and less than 255 μm. In this case, microbending loss can be suppressed.

[0028] The cladding layer may be further provided with a coating resin layer made of an acrylic resin, and the diameter of the coating resin layer may be 190 μm or more and less than 210 μm. In this case, microbending loss can also be suppressed.

[0029] [Detailed description of embodiments of the present invention]

[0030] Specific examples of the optical fiber of the present invention will be described below with reference to the accompanying drawings. It should be noted that the present invention is not limited to these examples, but is represented by the scope of the claims, and is intended to include all changes within the meaning and scope equivalent to the scope of the claims. In the description of the drawings, the same elements are marked with the same symbols, and repeated descriptions are omitted.

[0031] According to the findings of the present inventors, in the process of collapsing a glass tube body to which chlorine of a mass fraction of 1.0% (10000 ppm) or more is added to solidify, chlorine bubbles (referring to bubbles containing chlorine and its compounds) are generated on the inner surface of the glass tube body. This phenomenon occurs when the chlorine concentration on the inner surface of the glass tube body is high. That is, when a glass tube body to which chlorine is added at a high concentration until the inner surface is heated, chlorine bubbles are generated on the inner surface, and the generated chlorine bubbles remain in the center of the core glass rod after collapse. Therefore, chlorine bubbles are suppressed by reducing the chlorine concentration on the inner surface of the glass tube body.

[0032] A method for reducing the chlorine concentration on the inner surface of a glass tube body is described. In the MCVD method and the PCVD method, the concentration of the chlorine raw material gas flowing when depositing glass is adjusted. By reducing the concentration of chlorine gas in the area that will become the center after the deposition collapses, the chlorine concentration on the inner surface of the glass tube body can be reduced.

[0033] In the OVD method, after chlorine is added to the soot tube, the chlorine concentration on the inner surface of the glass tube body can be reduced by fully burning it and then collapsing it. In addition, in the process of depositing soot on the starting rod of the OVD method, the soot is deposited in a manner that increases the volume density of the portion near the inner surface of the tube.

[0034] Figure 1is a cross-sectional view of an optical fiber according to an embodiment of the present invention. Figure 1 As shown, the optical fiber 1 of the present embodiment includes a glass fiber 2 and a coating resin layer 3 that covers the glass fiber 2. The glass fiber 2 includes a core 10 and a cladding 20 that covers the core 10. Figure 1 The cross-sectional view shows a cross section perpendicular to the central axis C of the optical fiber 1 .

[0035] The core 10 has a central portion 11 including a central axis C, and an outer core 12 covering the central portion 11. The diameter (outer diameter) 2a of the core 10 is, for example, 8.5 μm to 13.5 μm. The diameter 2a can be, for example, 8.5 μm to 12.5 μm, or 8.5 μm to 11.5 μm. The definition of the central portion 11 will be described later. The diameter (outer diameter) of the outer core 12 is, for example, equal to the diameter 2a.

[0036] The core 10 is made of quartz glass. The core 10 contains chlorine, and the average chlorine concentration of the core 10 is greater than 10000 ppm and less than 50000 ppm. Here, the average chlorine concentration of the core 10 refers to the average chlorine concentration of the core 10 as a whole including the central part 11 and the outer core part 12. The average chlorine concentration of the central part 11 is lower than the average chlorine concentration of the core 10. The difference between the average chlorine concentration of the core 10 and the average chlorine concentration of the central part 11 is greater than 4500 ppm and less than 13500 ppm. The difference may be, for example, greater than 7200 ppm and less than 13500 ppm.

[0037] The diameter (outer diameter) of the cladding 20 is, for example, 124 μm or more and 126 μm or less. The diameter of the cladding 20 is, for example, 125 μm. The diameter of the cladding 20 is, for example, equal to the diameter (outer diameter) of the glass fiber 2. The cladding 20 is made of quartz glass. The cladding 20 may contain fluorine, and the average concentration of fluorine in the cladding 20 is, for example, 0 ppm or more and 8000 ppm or less.

[0038] In particular, the concentration of halogens including chlorine and fluorine in the region outside the radius of 30 μm can be less than 1000 ppm. Therefore, the viscosity of the inner region including the core can be relatively reduced, thereby preventing an increase in transmission loss and a decrease in light confinement intensity caused by the drawing tension remaining in the core.

[0039] The coating resin layer 3 includes a primary resin layer 31 covering the cladding layer 20, and a secondary resin layer 32 covering the primary resin layer 31. The diameter (outer diameter) of the coating resin layer 3 may be greater than or equal to 190 μm and less than or equal to 255 μm, or may be greater than or equal to 190 μm and less than or equal to 210 μm. The thickness of the coating resin layer 3 is, for example, greater than or equal to 30 μm and less than or equal to 68 μm. The diameter (outer diameter) of the primary resin layer 31 is, for example, greater than or equal to 150 μm and less than or equal to 210 μm. The thickness of the primary resin layer 31 is, for example, greater than or equal to 10 μm and less than or equal to 45 μm. The diameter (outer diameter) of the secondary resin layer 32 is, for example, equal to the diameter of the coating resin layer 3. The thickness of the secondary resin layer 32 is, for example, greater than or equal to 20 μm and less than or equal to 35 μm.

[0040] The primary resin layer 31 and the secondary resin layer 32 are both composed of a cured product of an ultraviolet curable resin composition. That is, the coating resin layer 3 contains a cured product of an ultraviolet curable resin composition. The ultraviolet curable resin composition used for the primary resin layer 31 and the secondary resin layer 32 is, for example, urethane acrylate. These resin compositions are coated on the glass fiber 2, and then the resin compositions are cured by irradiating ultraviolet rays, thereby forming the primary resin layer 31 and the secondary resin layer 32.

[0041] The mode field diameter (hereinafter referred to as "MFD") of the optical fiber 1 at a wavelength of 1310 nm is 8.6 μm to 13.0 μm. The MFD may be, for example, 8.6 μm to 12.5 μm, 8.6 μm to 11.0 μm, or 8.6 μm to 9.5 μm.

[0042] The effective cross-sectional area (hereinafter referred to as "Aeff") of the optical fiber 1 at a wavelength of 1550 nm is 70 μm 2 Above 130μm 2 Below. Aeff can be, for example, 70 μm 2 Above 120μm 2 Below, 70μm is also possible 2 Above 115μm 2 Below, 70μm is also possible 2 Above 110μm 2 Below, 70μm is also possible 2 Above 100μm 2 Below. Aeff can also be 75μm 2 Above 105μm 2 the following.

[0043] The cable cutoff wavelength (hereinafter referred to as "λcc") of the optical fiber 1 is 1530 nm or less. In this case, optical communication can be performed in a single-mode form in the C band (1530 nm or more and 1565 nm or less). The λcc of the optical fiber 1 can be, for example, 1260 nm or less. In this case, optical communication can be performed in a single-mode form even in the 1.3 μm band.

[0044] The transmission loss of the optical fiber 1 at a wavelength of 1550 nm is 0.15 dB / km to 0.18 dB / km, and may be 0.15 dB / km to less than 0.18 dB / km. The transmission loss of the optical fiber 1 at a wavelength of 1310 nm is 0.24 dB / km to 0.40 dB / km.

[0045] Figure 2 It is schematically indicated Figure 1 The refractive index distribution of the optical fiber is shown in FIG. The horizontal axis represents the radial position r, and the vertical axis represents the refractive index n at a wavelength of 1550nm. The central axis C (refer to Figure 1 ) is 0 (r=0). Here, the refractive index n is correlated with the chlorine concentration.

[0046] like Figure 2 As shown, the core 10 (refer to Figure 1 ) has a total average refractive index n1 at a wavelength of 1550 nm higher than that of the cladding 20 (refer to Figure 1 ) The total average refractive index n2 at a wavelength of 1550 nm. The relative refractive index difference Δn of the average refractive index n1 of the core 10 when the average refractive index n2 of the cladding 20 is used as a reference at a wavelength of 1550 nm is defined as (n1-n2) / n1. Δn is 0.25% to 0.40%. Δn can be 0.25% to 0.38%, or 0.28% to 0.37%.

[0047] In the center portion 11 (refer to Figure 1 ) corresponding to the part, the refractive index increases as it approaches the central axis C (refer to Figure 1 ) and becomes a concave portion. In the concave portion, the chlorine concentration also decreases as it approaches the central axis C. Figure 1 ) The corresponding part covers the concave part. The minimum refractive index n3 of the central part 11 at a wavelength of 1550nm is higher than the refractive index n0 of pure quartz at a wavelength of 1550nm. The average refractive index n1 is higher than the refractive index n0 and the minimum refractive index n3.

[0048] The relative refractive index difference Δn of the average refractive index n1 of the core 10 at a wavelength of 1550 nm with respect to the refractive index n0 of pure quartz is plusThe relative refractive index difference Δdip of the minimum refractive index n3 of the center portion 11 at a wavelength of 1550nm with respect to the refractive index n0 of pure silica glass is defined as (n3-n0) / n0. The refractive index depth of the concave portion is given by Δn plus -Δdip indicates.

[0049] Δn plus -Δdip is 0.05% to 0.15%. When the difference between the average chlorine concentration of the core 10 and the average chlorine concentration of the center 11 is 4500 ppm to 13500 ppm, Δn plus -Δdip becomes this range. Δn plus -Δdip may be 0.08% or more and 0.15% or less. When the difference between the average chlorine concentration of the core 10 and the average chlorine concentration of the center 11 is 7200 ppm or more and 13500 ppm or less, Δn plus -Δdip becomes the range.

[0050] The diameter of the center portion 11 and the effective diameter (diameter) 2r of the concave portion dip Correspondingly, the effective diameter of the concave portion is 2r dip The relative refractive index difference of the concave portion at a wavelength of 1550nm, when the refractive index n0 of pure quartz is taken as the reference, is (Δdip + Δn plus ) / 2. That is, when the optical fiber 1 is observed in a cross section perpendicular to the central axis C, the central portion 11 is the inner portion of a circle whose chlorine concentration is an intermediate value between the average chlorine concentration of the core 10 and the minimum chlorine concentration of the central portion 11, and the diameter of the circle is the diameter of the central portion 11.

[0051] Effective diameter 2r dip (ie, the diameter of the center portion 11) is 0.5 μm or more and 4 μm or less. dip The diameter may be 0.8 μm or more and 3 μm or more, or 1 μm or more and 2.5 μm or less.

[0052] As described above, in the optical fiber 1, the difference between the average chlorine concentration of the core 10 and the average chlorine concentration of the central portion 11 of the core 10 is greater than 4500 ppm and less than 13500 ppm. Therefore, in the process of forming the core glass rod, the generation of chlorine bubbles on the inner surface of the glass tube can be suppressed. Since the bubbles in the central portion of the glass core rod can be suppressed, the bubbles in the central portion of the core of the mother material can also be suppressed. Therefore, the bubbles in the central portion 11 of the optical fiber 1 obtained by drawing the mother material can be suppressed. As a result, the reduction in the yield and productivity of the optical fiber 1 can be suppressed.

[0053] The depth Δn of the refractive index of the concave portion plus-Δdip is 0.05% or more and 0.15% or less. Therefore, it is easy to make the difference between the average chlorine concentration of the core portion 10 and the average chlorine concentration of the center portion 11 be 4500 ppm or more and 13500 ppm or less.

[0054] The cladding 20 contains fluorine. In this case, even if the chlorine concentration of the core 10 is reduced, the relative refractive index difference Δn of the average refractive index n1 of the core 10 can be made 0.25% or more when the average refractive index n2 of the cladding 20 is used as a reference at a wavelength of 1550 nm. Therefore, fundamental mode light can be captured.

[0055] The MFD at a wavelength of 1310nm is 8.6μm or more and 13.0μm or less, and the Aeff at a wavelength of 1550nm is 70μm 2 Above 130μm 2 Below, and λcc is below 1530nm. MFD can be between 8.6μm and 11.0μm, and Aeff can be 70μm 2 Above 115μm 2 Hereinafter, λcc may be equal to or less than 1260 nm. In the optical fiber 1, since Aeff can be increased, the optical signal-to-noise ratio of the optical communication system can be improved.

[0056] The transmission loss of the optical fiber 1 at a wavelength of 1550 nm is not less than 0.15 dB / km and not more than 0.18 dB / km, and the transmission loss of the optical fiber 1 at a wavelength of 1310 nm is not less than 0.24 dB / km and not more than 0.40 dB / km.

[0057] The diameter of the coating resin layer 3 is 190 μm or more and less than 255 μm. The diameter of the coating resin layer may be 190 μm or more and less than 210 μm. When the diameter of the coating resin layer 3 becomes smaller (the coating resin layer 3 becomes thinner), the microbending loss increases. In the optical fiber 1, if the diameter of the coating resin layer 3 is within this range, the microbending loss can be suppressed.

[0058] Example

[0059] The results of evaluation tests using the examples and comparative examples of the present invention are shown below to explain the present invention in more detail. It should be noted that the present invention is not limited to these examples.

[0060] Table 1 shows the results of measuring the optical properties of the optical fibers involved in the comparative examples and embodiments. In comparative examples 1 and 2, the chlorine concentration on the inner surface of the glass tube body did not decrease. In embodiments 1 to 5, the chlorine concentration on the inner surface of the glass tube body decreased. The number of base material bubbles in Table 1 represents the number of bubbles generated at the center of the base material (the solidified part of the center of the glass core rod) in the longitudinal region of the base material corresponding to an optical fiber with an outer diameter of 125 μm and a length of 1000 km. In addition, the bending loss represents the loss at a wavelength of 1550 nm when the optical fiber is wound 10 times on a reel with a diameter of 30 mm.

[0061] [Table 1]

[0062]

[0063] As shown in Table 1, in the comparative example, the number of bubbles in the base material is 5 or more, and the transmission loss is 0.18 dB / km. In contrast, in the example, the number of bubbles in the base material is suppressed to less than 1, and the transmission loss is suppressed to less than 0.18 dB / km. It is believed that in the comparative example, many tiny chlorine bubbles that cannot be visually confirmed remain in the center of the base material, and these will become scatterers to deteriorate the transmission loss. On the other hand, it is believed that in the example, by reducing the chlorine concentration on the inner surface of the glass tube body, the generation of tiny chlorine bubbles is suppressed, and as a result, the degradation of the transmission loss is suppressed.

[0064] Figure 3 : is a graph showing the relationship between the ratio of Aeff to λcc Aeff / λcc and the bending loss. Figure 3 As shown in the figure, the relationship between Aeff / λcc and bending loss is different between the embodiment and the comparative example. That is, when the same Aeff / λcc is used for comparison, the bending loss of the embodiment is lower than that of the comparative example. It is believed that this is due to the effect of reducing the chlorine concentration in the center of the glass core rod by reducing the chlorine concentration on the inner surface of the glass tube body, and finally the concave part of the refractive index of the optical fiber obtained by drawing the optical fiber mother material.

[0065] When compared with the same Aeff / λcc, the bending loss of the embodiment is lower than that of the comparative example, which means that for the same bending loss and the same λcc, the Aeff of the embodiment is greater than that of the comparative example. That is, the optical communication system using the optical fiber of the embodiment can improve the optical signal-to-noise ratio compared with the optical communication system using the optical fiber of the comparative example.

[0066] Furthermore, when compared at the same Aeff / λcc, the bending loss of the example is lower than that of the comparative example, so that the microbending loss which is feared to increase when the diameter of the coating resin layer is reduced (the coating resin layer is thinned) can be suppressed.

Claims

1. An optical fiber having: a core having a central portion including a central axis and made of quartz glass, wherein the diameter of the central portion is 0.5 μm or more and 4 μm or less, and a cladding layer covering the core and consisting of quartz glass, wherein The core contains chlorine, The average chlorine concentration of the core is 10000 ppm or more and 50000 ppm or less, The difference between the average chlorine concentration of the core portion and the average chlorine concentration of the center portion is 4500 ppm or more and 13500 ppm or less, In a portion corresponding to the central portion, the refractive index decreases as it approaches the central axis, forming a concave portion. In the concave portion, the chlorine concentration decreases as it approaches the central axis.

2. The optical fiber according to claim 1, At a wavelength of 1550 nm, the relative refractive index difference of the average refractive index of the core is 0.25% or more and 0.40% or less, based on the average refractive index of the cladding. The core has a diameter of 8.5 μm or more and 13.5 μm or less.

3. The optical fiber according to claim 2, The relative refractive index difference of the average refractive index of the core portion at a wavelength of 1550 nm with respect to the refractive index of pure quartz is denoted as Δn plus , and the relative refractive index difference of the minimum refractive index of the central portion when the refractive index of pure quartz is referenced at a wavelength of 1550nm is set as Δdip, Δn plus -Δdip is 0.05% to 0.15%.

4. An optical fiber having: a core having a central portion including a central axis, wherein a diameter of the central portion is 0.5 μm or more and 4 μm or less, and a cladding covering the core, wherein The core contains chlorine, The average chlorine concentration of the core is 10000 ppm or more and 50000 ppm or less, In a portion corresponding to the central portion, the refractive index decreases as it approaches the central axis, forming a concave portion, and in the concave portion, the chlorine concentration decreases as it approaches the central axis. At a wavelength of 1550 nm, the relative refractive index difference of the average refractive index of the core is 0.25% to 0.40% based on the average refractive index of the cladding, and the diameter of the core is 8.5 μm to 13.5 μm. The relative refractive index difference of the average refractive index of the core portion at a wavelength of 1550 nm with respect to the refractive index of pure quartz is denoted as Δn plus , and the relative refractive index difference of the minimum refractive index of the central portion when the refractive index of pure quartz is referenced at a wavelength of 1550nm is set as Δdip, Δn plus -Δdip is 0.05% to 0.15%.

5. The optical fiber according to any one of claims 1 to 4, The cladding contains fluorine.

6. The optical fiber according to any one of claims 1 to 5, The mode field diameter of the optical fiber at a wavelength of 1310 nm is not less than 8.6 μm and not more than 13.0 μm, The effective cross-sectional area of ​​the optical fiber at a wavelength of 1550 nm is 70 μm 2 Above 130μm 2 the following, The cable cutoff wavelength of the optical fiber is below 1530 nm.

7. The optical fiber according to any one of claims 1 to 5, The mode field diameter of the optical fiber at a wavelength of 1310 nm is not less than 8.6 μm and not more than 11.0 μm, The effective cross-sectional area of ​​the optical fiber at a wavelength of 1550 nm is 70 μm 2 Above 115μm 2 the following, The cable cutoff wavelength of the optical fiber is below 1260 nm.

8. The optical fiber according to any one of claims 1 to 7, The transmission loss of the optical fiber at a wavelength of 1550nm is not less than 0.15dB / km and not more than 0.18dB / km, The transmission loss of the optical fiber at a wavelength of 1310 nm is greater than 0.24 dB / km and less than 0.40 dB / km.

9. The optical fiber according to any one of claims 1 to 8, further comprising a coating resin layer covering the coating layer and consisting of an acrylic resin, The coating resin layer has a diameter of 190 μm or more and less than 255 μm.

10. The optical fiber according to any one of claims 1 to 8, further comprising a coating resin layer covering the coating layer and consisting of an acrylic resin, The coating resin layer has a diameter of 190 μm or more and less than 210 μm.

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