Optical fiber

Abstract

The average refractive index of a core of this optical fiber is higher than the average refractive index of an inner cladding and the minimum refractive index of an outer cladding; and the average refractive index of a trench is lower than the average refractive index of the inner cladding and the minimum refractive index of the outer cladding. The core contains germanium dioxide; the relative refractive index difference of the core with respect to the refractive index of pure silica glass is 0.12% to 0.30%; the value obtained by subtracting the relative refractive index difference of the outer cladding with respect to the refractive index of pure silica glass from the relative refractive index difference of the core is 0.25% or more; and the diameter of the core is 4.0 µm to 9.2 µm. The mode field diameter with respect to light having a wavelength of 1,310 nm is 8.2 µm to 9.6 µm; the zero dispersion wavelength is 1,300 nm to 1,324 nm; the zero dispersion slope is 0.073 ps / (nm2∙km) to 0.92 ps / (nm2∙km); the cable cutoff wavelength is 1,260 nm or less; and the bending loss with respect to light having a wavelength of 1,625 nm when wound around a mandrel that has a diameter of 60 mm is 0.1 dB or less per 100 turns.

Description

optical fiber

[0001] This application claims priority to Japanese Patent Application No. 2022-140078, filed on September 2, 2022, and incorporates by reference the entire contents of said Japanese application.

[0002] Patent Document 1 discloses the structure of a single-mode optical fiber. This optical fiber includes a core layer and a cladding layer. The core layer is a silica glass layer co-doped with germanium and fluorine. The core layer has a radius of 3.0 μm to 3.9 μm. The relative refractive index difference of the core layer is -0.04% to 0.12%. The doping contribution of germanium to the relative refractive index difference of the core layer is 0.02% to 0.10%. The cladding layer includes an inner cladding layer, a depressed inner cladding layer, an auxiliary outer cladding layer, and an outer cladding layer. The radius of the inner cladding layer is 8 μm to 14 μm. The relative refractive index difference of the inner cladding layer is -0.35% to -0.10%. The radius of the depressed inner cladding layer is 14 μm to 20 μm. The relative refractive index difference of the depressed inner cladding layer is -0.6% to -0.2%. The radius of the auxiliary outer cladding layer is 35 μm to 50 μm, and the relative refractive index difference of the auxiliary outer cladding layer is −0.4% to −0.15%.

[0003] Patent Document 2 discloses an optical fiber structure. This optical fiber includes a core and a cladding having a refractive index lower than that of the core. The cladding contains fluorine (F). The fluorine concentration in the cladding is adjusted to be minimum at the outermost part of the cladding.

[0004] JP 2018-511077 A International Publication No. 2020-013297 A

[0005] In order to increase the transmission distance and transmission capacity in optical fiber transmission systems, it is desirable for the optical fiber to have low transmission loss. Optical fibers that achieve low transmission loss include optical fibers using pure silica glass for the core and optical fibers doped with alkali elements. From the viewpoint of keeping the manufacturing cost lower than these optical fibers, optical fibers using germanium dioxide (GeO ２ ) doped optical fibers exist.

[0006] Optical fibers for communication are required to reduce transmission loss and bending loss in order to transmit optical signals over long distances, that is, to satisfy standards regarding transmission loss and bending loss (for example, ITU-T G.652.B or G.652.D).

[0007] The core is made of germanium dioxide (GeO ２ ) doped optical fiber, the smaller the relative refractive index difference of the core with respect to the refractive index of pure silica glass (in other words, GeO ２ The lower the concentration of , the higher the viscosity of the core. When manufacturing optical fiber, an optical fiber preform is drawn while tension is applied. Internal stress remains in the optical fiber extracted by drawing. If the viscosity of the core is greater than that of the cladding, tensile stress remains in the core. If excessive tensile stress remains in the core, through which most of the signal light is guided, the core is pulled, increasing glass structural defects and increasing transmission loss. The smaller the relative refractive index difference of the core, the smaller the refractive index difference between the core and the cladding. As a result, the effect of confining light propagating through the core in the core becomes weaker, increasing bending loss. Furthermore, the fundamental mode becomes less likely to be confined in the core, which may result in blocking of the fundamental mode. For example, in the configuration described in Patent Document 2, the relative refractive index difference of the core layer is -0.04% to 0.12%. In such a configuration, the relative refractive index difference of the core layer is considered to be too small, raising concerns about increased transmission loss and bending loss. When germanium dioxide (GeO ２ ) doped optical fiber, the larger the relative refractive index difference of the core (in other words, the ２ The higher the concentration of GeO ２ This increases Rayleigh scattering due to concentration fluctuations, resulting in increased transmission loss.

[0008] The present disclosure provides a method for manufacturing a semiconductor device using GeO ２ The present invention aims to reduce bending loss and transmission loss in an optical fiber doped with .

[0009] An optical fiber according to one aspect of the present disclosure comprises a glass fiber including a core and a cladding. The cladding includes an inner cladding surrounding the core, a trench surrounding the inner cladding, and an outer cladding surrounding the trench. The average refractive index of the inner cladding and the minimum refractive index of the outer cladding are lower than the average refractive index of the core. The average refractive index of the trench is lower than the average refractive index of the inner cladding and the minimum refractive index of the outer cladding. The core contains germanium dioxide. The relative refractive index difference of the core with respect to the refractive index of pure silica glass is 0.12% or more and 0.30% or less. The core diameter is 4.0 μm or more and 9.2 μm or less. The mode field diameter for light with a wavelength of 1310 nm is 8.2 μm or more and 9.6 μm or less. The zero-dispersion wavelength is 1300 nm or more and 1324 nm or less. The zero-dispersion slope is 0.073 ps / (nm ２ ・km) or more 0.092 ps / (nm ２ The cable cutoff wavelength is 1260 nm or less. When wound around a 60 mm diameter mandrel, the bending loss for light with a wavelength of 1625 nm is 0.1 dB or less per 100 turns.

[0010] According to the present disclosure, the core is GeO ２ In an optical fiber doped with , bending loss and transmission loss can be reduced.

[0011] FIG. 1 is a diagram showing a cross section perpendicular to the axial direction of an optical fiber according to one embodiment. FIG. 2 is a diagram showing the refractive index distribution in the radial direction of the glass fiber. FIG. 3 is a graph showing the relationship between the relative refractive index difference of the core and the predicted transmission loss (dB / km) for light with a wavelength of 1550 nm. FIG. 4 is a table showing six examples of optical fiber and one comparative example. FIG. 5 is a table showing six examples of optical fiber and one comparative example. FIG. 6 is a table showing the relationship between the relative refractive index difference and the average residual stress in the core for five samples of optical fiber. FIG. 7 is a graph showing the distribution of the relative refractive index difference in the radial direction for the five samples of FIG. 6.

[0012] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0013] [1] An optical fiber according to one aspect of the present disclosure comprises a glass fiber including a core and a cladding. The cladding includes an inner cladding surrounding the core, a trench surrounding the inner cladding, and an outer cladding surrounding the trench. The average refractive index of the core is greater than the average refractive index of the inner cladding and the minimum refractive index of the outer cladding. The average refractive index of the trench is less than the average refractive index of the inner cladding and the minimum refractive index of the outer cladding. The core contains germanium dioxide. The relative refractive index difference of the core with respect to the refractive index of pure silica glass is 0.12% or more and 0.30% or less. The value obtained by subtracting the relative refractive index difference of the outer cladding with respect to the refractive index of pure silica glass from the relative refractive index difference of the core is 0.25% or more. The radius of the core is 4.0 μm or more and 9.2 μm or less. The mode field diameter for light with a wavelength of 1310 nm is 8.2 μm or more and 9.6 μm or less. The zero-dispersion wavelength is 1300 nm or more and 1324 nm or less. The zero dispersion slope is 0.073 ps / (nm ２ ・km) or more 0.092 ps / (nm ２ The cable cutoff wavelength is 1260 nm or less. When wound around a 60 mm diameter mandrel, the bending loss for light with a wavelength of 1625 nm is 0.1 dB or less per 100 turns.

[0014] An optical fiber with these parameters would produce a GeO ２ The relative refractive index difference of the doped core can be kept within an appropriate range, and bending loss and transmission loss can be reduced to a level that complies with G.652.D.

[0015] [2] In the optical fiber of [1] above, the relative refractive index difference of the inner cladding with respect to the refractive index of pure silica glass may be -0.12% or more and 0.10% or less. Furthermore, the relative refractive index difference of the trench with respect to the refractive index of pure silica glass may be -0.70% or more and -0.20% or less. Furthermore, when the radius of the outer circumferential circle of the core is r1, the radius of the outer circumferential circle of the inner cladding is r2, and the radius of the outer circumferential circle of the trench is r3, r2 / r1 may be 2.2 or more and 3.8 or less, and r3 - r2 may be 4 μm or more and 15 μm or less. In this case, the optical fiber can have a refractive index profile structure that complies with G.652.D.

[0016] [3] In the optical fiber according to [1] or [2] above, when wound around a mandrel having a diameter of 20 mm, the bending loss for light having a wavelength of 1550 nm may be 0.75 dB or less per turn. Furthermore, when wound around a mandrel having a diameter of 20 mm, the bending loss for light having a wavelength of 1625 nm may be 1.5 dB or less per turn. Furthermore, when wound around a mandrel having a diameter of 30 mm, the bending loss for light having a wavelength of 1550 nm may be 0.25 dB or less per 10 turns. Furthermore, when wound around a mandrel having a diameter of 30 mm, the bending loss for light having a wavelength of 1625 nm may be 1.0 dB or less per 10 turns. In this case, the optical fiber can comply with G.652.D and G.657.A1, a standard relating to bending loss.

[0017] [4] In the optical fiber of any one of [1] to [3] above, the outer cladding may be made of pure silica glass. In this case, tensile stress is concentrated in the outer cladding, which prevents tensile stress from remaining in the core, thereby reducing transmission loss.

[0018] [5] In the optical fiber of any one of [1] to [3] above, the outer cladding may contain fluorine. In this case, the refractive index difference between the core and the outer cladding is increased, so that even if the relative refractive index difference of the core is reduced, the fundamental mode is less likely to be cut off.

[0019] [6] In the fluorine concentration distribution in the outer cladding of the optical fiber according to [5] above, when the outer cladding is divided into a first region including the outer peripheral surface of the outer cladding and a second region located inside the first region, the average fluorine concentration in the first region may be smaller than the average fluorine concentration in the second region. In this case, tensile stress is concentrated near the outer peripheral surface of the outer cladding, so that compressive stress can be left in the core, or even if tensile stress remains in the core, the tensile stress can be reduced. Therefore, transmission loss can be reduced.

[0020] [7] In the optical fiber according to any one of [1] to [6] above, the average residual stress in the core may be a compressive stress or a tensile stress of 30 MPa or less. In this case, glass structural defects caused in the core by excessive tensile stress can be reduced, thereby reducing an increase in transmission loss due to glass structural defects.

[0021] [8] In the optical fiber of any one of [1] to [7] above, the core may be substantially free of alkali elements, which can reduce the manufacturing cost of the optical fiber.

[0022] [9] In any one of the optical fibers [1] to [8] above, the bending loss for light with a wavelength of 1625 nm when wound around a mandrel with a diameter of 100 mm is 1.0 × 10 per turn. －５ dB or less. In this case, leakage loss due to blocking of the fundamental mode can be reduced. If it is difficult to actually measure this bending loss, this bending loss may be obtained by extrapolation based on the dependency of the bending loss on the bending radius.

[0023]

[10] In the optical fiber of any one of [1] to [9] above, the core may contain fluorine, and the relative refractive index difference of the core due to the fluorine with respect to the refractive index of pure silica glass may be -0.12% or more and less than 0%. In this case, the core may contain GeO ２ and F are co-doped. This allows the viscosity of the core to be reduced even if the relative refractive index difference of the core is the same compared to when no fluorine is included. This makes it easy to make the residual stress in the core a compressive stress. In addition, since the fluorine concentration in the core is not too high, it is possible to suppress an increase in transmission loss due to fluorine. [Details of the embodiment of the present disclosure]

[0024] Specific examples of optical fibers according to the present embodiment will be described with reference to the drawings as necessary. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims. In the following description, identical elements in the drawings will be denoted by the same reference numerals, and redundant explanations will be omitted. In the following description, the "outer diameter" of a certain element refers to the average value of the outer diameter of the element at each position in the axial direction of the optical fiber. The "thickness" of a certain element refers to the average value of the thickness of the element at each position in the axial direction of the optical fiber.

[0025] 1 is a diagram showing a cross section perpendicular to the axial direction of an optical fiber 10 according to one embodiment. The optical fiber 10 is a so-called optical fiber strand and conforms to both the ITU-T G.652.D standard and the ITU-T G.657.A standard. The optical fiber 10 includes a glass fiber 13 including a core 11 and a cladding 12, and a resin layer 16 provided on the outer periphery of the glass fiber 13. The resin layer 16 includes a primary resin layer 14 surrounding the glass fiber 13 and a secondary resin layer 15 surrounding the primary resin layer 14.

[0026] The cladding 12 surrounds the core 11. The cladding 12 includes an inner cladding 121, a trench 122, and an outer cladding 123. The inner cladding 121 surrounds the core 11 and is in contact with the outer peripheral surface of the core 11. The trench 122 surrounds the inner cladding 121 and is in contact with the outer peripheral surface of the inner cladding 121. The outer cladding 123 surrounds the trench 122 and is in contact with the outer peripheral surface of the trench 122.

[0027] 2 is a diagram showing the refractive index distribution in the radial direction of the glass fiber 13. In FIG. 2, the range E1 corresponds to the core 11, the range E2 corresponds to the inner cladding 121, the range E3 corresponds to the trench 122, and the range E4 corresponds to the outer cladding 123. The vertical axis indicates the relative refractive index difference, and the horizontal axis indicates the radial position. As shown in FIG. 2, in the glass fiber 13, pure silica glass (SiO ２The relative refractive index differences of the core 11, the inner cladding 121, the trench 122, and the outer cladding 123 with respect to the refractive index of the core 11, the inner cladding 121, the trench 122, and the outer cladding 123 are respectively Δ1, Δ2, Δ3, and Δ4. Δ1, Δ2, Δ3, and Δ4 are numerical values ​​(unit: %) expressed by the following formula: Δ1=100·(n １ａｖｅ -n ０ ) / n １ａｖｅ Δ2 = 100 · (n ２ａｖｅ -n ０ ) / n ２ａｖｅ Δ3 = 100 · (n ３ａｖｅ -n ０ ) / n ３ａｖｅ Δ4 = 100 · (n ４ｍｉｎ -n ０ ) / n ４ｍｉｎ However, n ０ is the refractive index of pure silica glass, n １ａｖｅ is the average refractive index of the core 11, n ２ａｖｅ is the average refractive index of the inner cladding 121, n ３ａｖｅ is the average value of the refractive index of the trench 122, n ４ｍｉｎ is the minimum value of the refractive index of the outer cladding 123.

[0028] The relative refractive index difference Δ1 of the core 11 is larger than the relative refractive index difference Δ2 of the inner cladding 121, the relative refractive index difference Δ3 of the trench 122, and the relative refractive index difference Δ4 of the outer cladding 123. In other words, the average refractive index n １ａｖｅ is the average refractive index n of the inner cladding 121 ２ａｖｅ , the average refractive index n of the trench 122 ３ａｖｅ , and the minimum refractive index n of the outer cladding 123 ４ｍｉｎ The relative refractive index difference Δ3 of the trench 122 is smaller than the relative refractive index difference Δ1 of the core 11, the relative refractive index difference Δ2 of the inner cladding 121, and the relative refractive index difference Δ4 of the outer cladding 123. In other words, the average refractive index n ３ａｖｅ is the average refractive index n of the core 11 １ａｖｅ , the average refractive index n of the inner cladding 121 ２ａｖｅ , and the minimum refractive index n of the outer cladding 123 ４ｍｉｎThe relative refractive index difference Δ2 of the inner cladding 121 may be the same as the relative refractive index difference Δ4 of the outer cladding 123, or may be larger than the relative refractive index difference Δ4, or may be smaller than the relative refractive index difference Δ4. In other words, the average refractive index n ２ａｖｅ is the minimum refractive index n of the outer cladding 123 ４ｍｉｎ and the minimum refractive index n ４ｍｉｎ or the minimum refractive index n ４ｍｉｎ The sign of the relative refractive index difference Δ3 of the trench 122 is negative, and the sign of the relative refractive index difference Δ1 of the core 11 is positive. A negative sign of the relative refractive index difference means that the average refractive index is smaller than the refractive index of pure silica glass. A positive sign of the relative refractive index difference means that the average refractive index is larger than the refractive index of pure silica glass.

[0029] The relative refractive index difference Δ1 of the core 11 is 0.12% or more and 0.30% or less. The relative refractive index difference Δ2 of the inner cladding 121 is, for example, -0.12% or more and 0.10% or less. The value (Δ1 - Δ2) obtained by subtracting the relative refractive index difference Δ2 of the inner cladding 121 from the relative refractive index difference Δ1 of the core 11 is, for example, 0.15% or more and 0.40% or less. In one embodiment, the value (Δ1 - Δ2) is 0.34%. Such a relatively small value (Δ1 - Δ2) allows for an expansion of the mode field diameter of the optical fiber 10. The relative refractive index difference Δ3 of the trench 122 is, for example, -0.70% or more and -0.20% or less. When the relative refractive index difference Δ3 of the trench 122 is within this range, it is not necessary to add an extremely large amount of fluorine in the glass sintering process. The relative refractive index difference Δ3 of the trench 122 may be smaller than -0.25%. The value (Δ1−Δ4) obtained by subtracting the relative refractive index difference Δ4 of the outer cladding 123 from the relative refractive index difference Δ1 of the core 11 is 0.25% or more and 0.70% or less. If the relative refractive index difference Δ1 of the core 11 is smaller than 0.25%, the relative refractive index difference Δ4 may be made a negative value by adding fluorine (F) to the outer cladding 123. The higher the concentration of fluorine (F), the more the relative refractive index difference Δ4 of the outer cladding 123 can be reduced (the absolute value can be increased).

[0030] As shown in FIGS. 1 and 2 , the radius of the outer circumferential circle of the core 11 is r1, the radius of the outer circumferential circle of the inner cladding 121 is r2, the radius of the outer circumferential circle of the trench 122 is r3, and the radius of the outer circumferential circle of the outer cladding 123 is r4. The radius r1 of the core 11 is, for example, 2.0 μm or more and 4.6 μm or less. The value (r2 / r1) obtained by dividing the radius r2 of the inner cladding 121 by the radius r1 of the core 11 is, for example, 2.2 or more and 3.8 or less. The value (r3−r2) obtained by subtracting the radius r2 of the inner cladding 121 from the radius r3 of the trench 122 is, for example, 4 μm or more and 15 μm or less. In one embodiment, the value (r3−r2) is 6.0 μm. In one embodiment, the radius r1 of the core 11 is 3.8 μm, the radius r2 of the inner cladding 121 is 10.65 μm, and the radius r3 of the trench 122 is 16.65 μm.

[0031] The diameter D1 of the core 11 is, for example, 4.0 μm or more and 9.2 μm or less. The outer diameter D2 of the glass fiber 13, i.e., the outer diameter of the cladding 12, is, for example, 125 μm±0.7 μm, i.e., 124.3 μm or more and 125.7 μm or less. Since the outer diameter D2 of the glass fiber 13 is the same as the outer diameter of a typical glass fiber, typical peripheral devices such as connectors and fusion splicers can be used, facilitating the replacement of existing optical fibers. For example, the optical fiber 10 can be easily applied to microduct cables, ultra-multicore cables for data centers, and various other cables.

[0032] The core 11 and the clad 12 mainly contain silica glass (quartz glass). The core 11 contains, for example, germanium dioxide (GeO ２The core 11 is made of silica glass containing germanium dioxide. Adding germanium dioxide to the material constituting the core 11 reduces the optical transmission loss of the optical fiber 10. The silica glass of the core 11 may further contain fluorine (F) as an additive material. The relative refractive index difference Δ1 of the core 11, which is attributable to fluorine, is, for example, −0.12% or more and less than 0%. When the material constituting the core 11 is co-doped with germanium dioxide and fluorine, the residual stress in the core 11 tends to become compressive stress. The fluorine concentration in the core 11 is, for example, 200 ppm or more. This makes it easier for the residual stress in the core 11 to become compressive stress. A fluorine concentration of 200 ppm corresponds to a relative refractive index difference of −0.007%. The average residual stress in the core 11 is compressive stress or a tensile stress of 30 MPa or less. The residual stress in the core 11 is measured, for example, using an IFA-100 (manufactured by Interfiber Analysis, Inc., USA).

[0033] The core 11 does not substantially contain alkali elements such as lithium (Li), sodium (Na), or potassium (K). In other words, the average alkali element mass concentration of the core 11 is substantially zero. In this specification, "substantially zero" specifically means 50 ppm or less.

[0034] The inner cladding 121 primarily contains silica glass and contains, for example, chlorine (Cl) as an additive material. The average chlorine mass concentration of the inner cladding 121 is, for example, 500 ppm to 5000 ppm, or, for example, 500 ppm to 3000 ppm. The trench 122 primarily contains silica glass and contains, for example, fluorine (F) as an additive material. The outer cladding 123 is made of pure silica glass. Pure silica glass refers to silica glass that contains substantially no impurities (made of pure silica). Alternatively, the outer cladding 123 may primarily contain silica glass and contain, for example, fluorine (F) as an additive material. The relative refractive index difference Δ4 of the outer cladding 123, attributable to fluorine, is, for example, -0.40% to less than 0%.

[0035] In the optical fiber 10, the mode field diameter for light with a wavelength of 1310 nm is centered between 8.6 μm and 9.2 μm, with an error of ±0.4 μm. That is, the mode field diameter is 8.2 μm or more and 9.6 μm or less. The mode field diameter is defined by Petermann-II. When the optical fiber 10 is wound around a mandrel with a diameter of 20 mm, the bending loss for light with a wavelength of 1550 nm is 0.75 dB or less per turn. When the optical fiber 10 is wound around a mandrel with a diameter of 20 mm, the bending loss for light with a wavelength of 1625 nm is 1.5 dB or less per turn. When the optical fiber 10 is wound around a mandrel with a diameter of 30 mm, the bending loss for light with a wavelength of 1550 nm is 0.25 dB or less per 10 turns. When the optical fiber 10 is wound around a mandrel with a diameter of 30 mm, the bending loss for light with a wavelength of 1625 nm is 1.0 dB or less per 10 turns. When the optical fiber 10 is wound around a mandrel having a diameter of 60 mm, the bending loss of the optical fiber 10 for light having a wavelength of 1625 nm is 0.1 dB or less per 100 turns. When the optical fiber 10 is wound around a mandrel having a diameter of 100 mm, the bending loss for light having a wavelength of 1625 nm is 1.0×10 per turn. －５ dB or less.

[0036] The bending loss characteristics described above can be achieved by setting the value (r2 / r1) obtained by dividing the radius r2 of the inner cladding 121 by the radius r1 of the core 11 to a small value, such as 3.8 or less. Thus, the optical fiber 10 satisfies the bending loss level specified in G.657.A1 while having a larger mode field diameter than a typical optical fiber (an optical fiber in which the core and cladding each have only one refractive index profile step), with the mode field diameter centered at 8.9 μm. Therefore, the optical fiber 10 functions satisfactorily as a single-mode fiber. The bending loss when wound around a diameter of 100 mm is so small that it is immeasurable. Therefore, the bending loss at several bending diameters within the range of 20 mm to 60 mm is measured, and the bending loss when wound around a diameter of 100 mm is calculated by extrapolation based on the bending diameter dependency of the bending loss.

[0037] The zero-dispersion wavelength of the optical fiber 10 is 1300 nm or more and 1324 nm or less. That is, the zero-dispersion wavelength of the optical fiber 10 complies with the provisions of G.652.D and G.657.A1. Such a zero-dispersion wavelength can be achieved by setting the value (r2 / r1) obtained by dividing the radius r2 of the inner cladding 121 by the radius r1 of the core 11 to 2.2 or more. The chromatic dispersion of the optical fiber 10 for light with a wavelength of 1550 nm is 13.3 ps / (nm km) or more and 18.6 ps / (nm km) or less. The zero-dispersion slope of the optical fiber 10 is 0.073 ps / (nm km). ２ ・km) or more 0.092 ps / (nm ２ When the chromatic dispersion and the zero-dispersion slope are within these ranges, a bend-resistant optical fiber conforming to the G.652.D and G.657.A1 standards can be obtained.

[0038] The cable cutoff wavelength of the optical fiber 10 is 1260 nm or less. That is, the cable cutoff wavelength of the optical fiber 10 complies with the specifications of G.652.D and G.657.A1.

[0039] To enable longer transmission distances and increased transmission capacity, the optical fiber 10 has a transmission loss of 0.180 dB / km or less for light with a wavelength of 1550 nm, or 0.174 dB / km or less. In other words, the average OH mass concentration of the core 11 and the cladding 12 is small enough to result in a transmission loss of 0.180 dB / km or less for light with a wavelength of 1550 nm, or 0.174 dB / km or less. By keeping the transmission loss within this range, an optical fiber 10 that meets the low-loss grade can be provided.

[0040] Fig. 3 is a graph showing the relationship between the relative refractive index difference Δ1 of the core 11 and the predicted transmission loss (dB / km) for light with a wavelength of 1550 nm. In Fig. 3, the horizontal axis represents the relative refractive index difference Δ1 (%) of the core 11, and the vertical axis represents the predicted loss (dB / km) at a wavelength of 1550 nm. The transmission loss shown in Fig. 3 is the sum of the loss due to Rayleigh scattering, the loss due to structural imperfections, and the loss due to infrared and ultraviolet absorption of the glass. The transmission loss shown in Fig. 3 does not include the absorption loss due to OH groups and the loss due to structural defects in the glass. As shown in Fig. 3, the transmission loss at a wavelength of 1550 nm has an approximately linear relationship with the relative refractive index difference Δ1 of the core 11. Lowering the relative refractive index difference Δ1 of the core 11 reduces the amount of GeO ２ This means lowering the concentration of GeO ２ By reducing the concentration of GeO ２ This reduces Rayleigh scattering caused by concentration fluctuations in the core 11, resulting in a reduction in transmission loss. To reduce the transmission loss to 0.180 dB / km or less, the relative refractive index difference Δ1 of the core 11 should be 0.30% or less. To reduce the transmission loss to 0.174 dB / km or less, the relative refractive index difference Δ1 of the core 11 should be 0.20% or less.

[0041] Core 11 GeO ２ If the concentration is too low, the viscosity of the core 11 increases, and the core 11 bears the majority of the tension during drawing. As a result, tensile stress is likely to remain in the core 11. If a large tensile stress remains in the core 11, through which most of the signal light is guided, the core 11 is pulled, increasing glass structural defects and resulting in increased transmission loss. Therefore, in this embodiment, the relative refractive index difference Δ1 of the core 11 is set to 0.12% or more. Fluorine (F) as an additive material acts to lower the refractive index of the core 11, so GeO ２ In addition, by doping the core 11 with fluorine, the relative refractive index difference Δ1 of the core 11 is kept small while GeO ２ By increasing the concentration, the viscosity of the core 11 can be reduced. Therefore, by adding fluorine (F) to the core 11, the tensile stress of the core 11 can be reduced or made compressive. However, if too much fluorine is added, the relative refractive index difference Δ1 is maintained. ２As the doping amount increases, the transmission loss caused by Ge increases. For this reason, in this embodiment, the relative refractive index difference caused by fluorine in the core 11 is set to be equal to or greater than −0.12% and less than 0%.

[0042] 4 and 5 are diagrams showing six Examples 1 to 6 and one Comparative Example 1 of the optical fiber 10. These diagrams show the structural parameters and optical characteristics of the optical fiber 10. In Examples 1 to 6 and Comparative Example 1, the relative refractive index difference Δ1 due to fluorine in the core 11 is −0.02%.

[0043] 4 and 5, in Examples 1 to 6, the mode field diameter (MFD) for light with a wavelength of 1310 nm is 8.2 μm or more and 9.6 μm or less, the zero dispersion wavelength is 1300 nm or more and 1324 nm or less, and the zero dispersion slope is 0.073 ps / (nm ２ ・km) or more 0.092 ps / (nm ２ .km) or less, and the cable cutoff wavelength is 1260 nm or less. In Examples 1 to 6, when the optical fiber 10 is wound around a diameter of 60 mm, the bending loss of the optical fiber 10 for light with a wavelength of 1625 nm is 0.1 dB or less per 100 turns. When the optical fiber 10 is wound around a diameter of 20 mm, the bending loss of the optical fiber 10 for light with a wavelength of 1550 nm is 0.75 dB or less per turn. When the optical fiber 10 is wound around a diameter of 30 mm, the bending loss of the optical fiber 10 for light with a wavelength of 1550 nm is 0.25 dB or less per 10 turns. When the optical fiber 10 is wound around a diameter of 20 mm, the bending loss of the optical fiber 10 for light with a wavelength of 1625 nm is 1.5 dB or less per turn. When the optical fiber 10 is wound around a diameter of 30 mm, the bending loss of the optical fiber 10 for light with a wavelength of 1625 nm is 1.0 dB or less per 10 turns. When the optical fiber 10 is wound to a diameter of 100 mm, the bending loss of the optical fiber 10 for light with a wavelength of 1625 nm is 1.0×10 per turn. －５ The transmission loss of the optical fiber 10 for light with a wavelength of 1550 nm is 0.180 dB / km or less.

[0044] In Comparative Example 1, the mode field diameter, zero-dispersion wavelength, zero-dispersion slope, cable cutoff wavelength, and bending loss for light with a wavelength of 1550 nm and light with a wavelength of 1625 nm when wound around a diameter of 20 mm are all within the above ranges. However, when wound around a diameter of 60 mm, the bending loss for light with a wavelength of 1625 nm exceeds 0.1 dB per 100 turns. When wound around a diameter of 30 mm, the bending loss for light with a wavelength of 1550 nm exceeds 0.25 dB per 10 turns. When wound around a diameter of 30 mm, the bending loss for light with a wavelength of 1625 nm exceeds 1.0 dB per 10 turns. Furthermore, when wound around a diameter of 100 mm, the bending loss for light with a wavelength of 1625 nm is 1.0 × 10 per turn. －５ dB, and the transmission loss for light with a wavelength of 1550 nm exceeds 0.180 dB / km. This result is thought to be due to the following. That is, in Comparative Example 1, the difference (Δ1 - Δ4) between the relative refractive index difference Δ1 of the core 11 and the relative refractive index difference Δ4 of the outer cladding 123 is too small (it is less than 0.25%, unlike Examples 1 to 6). As a result, the bending loss increases when wound around a diameter of 100 mm, and the confinement of light in the fundamental mode (LP01 mode) propagating through the core 11 becomes weaker. As a result, the leakage loss due to fundamental mode cutoff increases at relatively long wavelengths. In Examples 1 to 6, the bending loss when wound around a diameter of 100 mm is 1.0 × 10 －５ The leakage loss due to fundamental mode cutoff is considered to be extremely small.

[0045] In the optical fiber 10 of Example 6, the tensile stress in the core 11 was 30 MPa on average, and the transmission loss at a wavelength of 1550 nm was 0.175 dB / km. In contrast, in another comparative example, the tensile stress in the core 11 was 50 MPa on average, and the transmission loss at a wavelength of 1550 nm was 0.194 dB / km. Thus, when the average residual stress in the core 11 is tensile stress, its magnitude may be 30 MPa or less.

[0046] FIG. 6 is a graph showing the relationship between the relative refractive index differences Δ1 to Δ4 and the average residual stress of the core 11 for five samples 1 to 5 of the optical fiber 10. In addition to the relative refractive index differences Δ1 to Δ4, FIG. 6 also shows the value of the relative refractive index difference Δ1 due to fluorine. Tensile stress is shown as a positive value, and compressive stress is shown as a negative value. The radius r1 of the core 11, the radius r2 of the inner cladding 121, the radius r3 of the trench 122, and the thickness of the trench 122 are all equal among samples 1 to 5. FIG. 7 is a graph showing the radial distribution of the relative refractive index difference for samples 1 to 5. In FIG. 7, the horizontal axis represents the radial position (μm), and the vertical axis represents the relative refractive index difference (%). Line G1 corresponds to sample 1, line G2 corresponds to sample 2, line G3 corresponds to samples 3 and 4, and line G4 corresponds to sample 5. The area E1 corresponds to the core 11, the area E2 corresponds to the inner cladding 121, the area E3 corresponds to the trench 122, and the area E4 corresponds to the outer cladding 123, respectively.

[0047] As is clear from FIG. 6 , to prevent an average tensile stress of +30 MPa or more from remaining in the core 11, the relative refractive index difference Δ1 of the core 11 should be 0.12% or more. In addition, the higher the fluorine concentration of the outer cladding 123, the lower the viscosity of the outer cladding 123. This increases the stress applied to the core 11 during drawing, resulting in a large residual tensile stress in the core 11. Therefore, as shown in FIG. 7 , the outer cladding 123 may be divided into a first region C1 including the outer peripheral surface and a second region C2 located inside the first region C1, and the average fluorine concentration in the first region C1 may be smaller than the average fluorine concentration in the second region C2. In this case, the relative refractive index difference Δ4 of the first region C1 is larger than the relative refractive index difference Δ4 of the second region C2. In the example shown in FIG. 7 , the fluorine concentration of the first region C1 decreases toward the outer peripheral surface of the outer cladding 123. As a result, the relative refractive index difference Δ4 increases toward the outer peripheral surface of the outer cladding 123. In this way, by reducing the fluorine concentration in the first region C1 near the outer peripheral surface of the outer cladding 123, the viscosity near the outer peripheral surface of the outer cladding 123 increases, and tensile stress concentrates near the outer peripheral surface of the outer cladding 123. This allows the drawing tension to be borne near the outer peripheral surface of the outer cladding 123, and either compressive stress remains in the core 11 or, even if tensile stress remains in the core 11, the tensile stress can be reduced. This reduces transmission loss.

[0048] The optical fiber 10 of this embodiment is manufactured, for example, as follows. First, to prepare an optical fiber preform, a glass rod is prepared having three layers corresponding to the core 11, the inner cladding 121, and the trench 122. Then, glass particles are deposited on the outer periphery of the glass rod while adding fluorine, to form a glass particle layer covering the outer periphery of the glass rod. This glass particle layer is the base of the outer cladding 123. When preparing samples 2 to 4 shown in FIG. 7, a process is further performed to remove part of the fluorine near the outer periphery of the glass particle layer (first region C1). Next, a gas with a dehydrating effect (for example, chlorine gas (Cl)) is introduced into the glass rod. ２The glass soot layer is heated (baked) while flowing the gas containing air. This dehydrates the glass soot layer. Then, the glass rod and the glass soot layer are heated simultaneously to sinter the glass soot layer. The glass rod and the glass soot layer are simultaneously placed in a heating furnace, whereby the glass rod and the glass soot layer are heated simultaneously. This heating is performed, for example, in a reduced pressure atmosphere. A reduced pressure atmosphere means an atmosphere under a pressure lower than 1 atmosphere. The glass rod and the glass soot layer are heated, for example, at a temperature of 1300°C or higher and 1600°C or lower. In one embodiment, the glass rod and the glass soot layer are heated at a temperature of 1400°C. The outer cladding 123 is formed by sintering the glass soot layer.

[0049] The effects obtained by the optical fiber 10 of this embodiment described above will be described. As described above, the optical fiber 10 of this embodiment comprises a glass fiber 13 including a core 11 and a clad 12. The clad 12 includes an inner clad 121 surrounding the core 11, a trench 122 surrounding the inner clad 121, and an outer clad 123 surrounding the trench 122. The average refractive index n of the core 11 is １ａｖｅ is the average refractive index n of the inner cladding 121 ２ａｖｅ , and the minimum value n of the refractive index of the outer cladding 123 ４ｍｉｎ The average refractive index n of the trench 122 is larger than ３ａｖｅ is the average refractive index n of the inner cladding 121 ２ａｖｅ , and the minimum value n of the refractive index of the outer cladding 123 ４ｍｉｎ The core 11 is GeO ２ The relative refractive index difference Δ1 of the core 11 is 0.12% or more and 0.30% or less. The value obtained by subtracting the relative refractive index difference Δ4 of the outer cladding 123 from the relative refractive index difference Δ1 of the core 11 is 0.25% or more. The radius r1 of the core 11 is 4.0 μm or more and 9.2 μm or less. The mode field diameter of the optical fiber 10 for light with a wavelength of 1310 nm is 8.2 μm or more and 9.6 μm or less. The zero-dispersion wavelength of the optical fiber 10 is 1300 nm or more and 1324 nm or less. The zero-dispersion slope of the optical fiber 10 is 0.073 ps / (nm ２ ・km) or more 0.092 ps / (nm ２The cable cutoff wavelength of the optical fiber 10 is 1260 nm or less. The bending loss of the optical fiber 10 for light with a wavelength of 1625 nm when wound around a mandrel with a diameter of 60 mm is 0.1 dB or less per 100 turns. The optical fiber 10 having these parameters can be used to fabricate a GeO ２ The relative refractive index difference Δ1 of the doped core 11 can be kept within an appropriate range, and bending loss and transmission loss can be reduced to a level that complies with G.652.D.

[0050] As in this embodiment, the relative refractive index difference Δ2 of the inner cladding 121 may be -0.12% or more and 0.10% or less. Furthermore, the relative refractive index difference Δ3 of the trench 122 may be -0.70% or more and -0.20% or less. Furthermore, the ratio (r2 / r1) of the radius r1 of the core 11 to the radius r2 of the inner cladding 121 may be 2.2 or more and 3.8 or less, and the difference (r3-r2) between the radius r3 of the trench 122 and the radius r2 of the inner cladding 121 may be 4 μm or more and 15 μm or less. In this case, the optical fiber can have a refractive index profile structure that complies with G.652.D.

[0051] As in this embodiment, the bending loss of the optical fiber 10 for light with a wavelength of 1550 nm when wound around a mandrel with a diameter of 20 mm may be 0.75 dB or less per turn. Furthermore, the bending loss of the optical fiber 10 for light with a wavelength of 1625 nm when wound around a mandrel with a diameter of 20 mm may be 1.5 dB or less per turn. Furthermore, the bending loss of the optical fiber 10 for light with a wavelength of 1550 nm when wound around a mandrel with a diameter of 30 mm may be 0.25 dB or less per 10 turns. Furthermore, the bending loss of the optical fiber 10 for light with a wavelength of 1625 nm when wound around a mandrel with a diameter of 30 mm may be 1.0 dB or less per 10 turns. In this case, the optical fiber 10 can comply with G.652.D and G.657.A1, a standard related to bending loss.

[0052] As described above, the outer cladding 123 may be made of pure silica glass only. In this case, tensile stress is concentrated in the outer cladding 123, which can prevent tensile stress from remaining in the core 11 and reduce transmission loss. Alternatively, the outer cladding 123 may contain fluorine. In this case, the refractive index difference between the core 11 and the outer cladding 123 increases, making it difficult for the fundamental mode to be blocked even if the relative refractive index difference Δ1 of the core 11 is small. Note that pure silica glass in the present disclosure refers to silica glass to which no dopant is intentionally added, and also includes silica glass containing trace amounts of impurities.

[0053] As described above, the average stress remaining in the core 11 may be compressive stress or tensile stress of 30 MPa or less. In this case, glass structural defects caused in the core 11 by excessive tensile stress can be reduced, thereby reducing an increase in transmission loss due to glass structural defects.

[0054] As described above, the core 11 may be substantially free of alkali elements, which can reduce the manufacturing cost of the optical fiber 10.

[0055] As in this embodiment, the bending loss of the optical fiber 10 for light with a wavelength of 1625 nm when wound around a mandrel with a diameter of 100 mm is 1.0×10 per turn. －５ dB or less. In this case, leakage loss due to blocking of the fundamental mode can be reduced. If it is difficult to actually measure this bending loss, this bending loss may be obtained by extrapolation based on the dependency of the bending loss on the bending radius.

[0056] As in this embodiment, the core 11 may further contain fluorine. The relative refractive index difference Δ1 of the core 11 due to fluorine may be −0.12% or more and less than 0%. In this case, the core 11 may contain GeO ２and fluorine are co-doped. This allows the viscosity of the core 11 to be reduced compared to when no fluorine is included, even if the relative refractive index difference Δ1 of the core 11 is the same. This makes it easy to change the residual stress in the core 11 to compressive stress. In addition, since the fluorine concentration in the core 11 is not too high, an increase in transmission loss due to fluorine can be suppressed.

[0057] REFERENCE SIGNS LIST 10... Optical fiber 11... Core 12... Cladding 13... Glass fiber 14... Primary resin layer 15... Secondary resin layer 16... Resin layer 121... Inner cladding 122... Trench 123... Outer cladding C1... First region C2... Second region D1... Diameter D2... Outer diameter E1, E2, E3, E4... Range G1, G2, G3, G4... Line r1, r2, r3, r4... Radius Δ1, Δ2, Δ3, Δ4... Relative refractive index difference

Claims

1. A glass fiber including a core and a cladding, the cladding includes an inner cladding surrounding the core, a trench surrounding the inner cladding, and an outer cladding surrounding the trench; the average value of the refractive index of the core is greater than the average value of the refractive index of the inner cladding and the minimum value of the refractive index of the outer cladding; the average value of the refractive index of the trench is less than the average value of the refractive index of the inner cladding and the minimum value of the refractive index of the outer cladding; the core comprises germanium dioxide; a relative refractive index difference of the core with respect to the refractive index of pure silica glass is 0.12% or more and 0.30% or less; a value obtained by subtracting a relative refractive index difference of the outer cladding with respect to a refractive index of pure silica glass from a relative refractive index difference of the core is 0.25% or more; The diameter of the core is 4.0 μm or more and 9.2 μm or less, The mode field diameter for light having a wavelength of 1310 nm is 8.2 μm or more and 9.6 μm or less, The zero dispersion wavelength is 1300 nm or more and 1324 nm or less, Zero dispersion slope is 0.073 ps / (nm ２ ・km) or more 0.092 ps / (nm ２ ・km) or less, The cable cutoff wavelength is 1260 nm or less; An optical fiber having a bending loss of 0.1 dB or less per 100 turns for light having a wavelength of 1625 nm when wound around a mandrel having a diameter of 60 mm.

2. a relative refractive index difference of the inner cladding with respect to the refractive index of pure silica glass is −0.12% or more and 0.10% or less; The relative refractive index difference of the trench with respect to the refractive index of pure silica glass is −0.70% or more and −0.20% or less; 2. The optical fiber according to claim 1, wherein, when the radius of the outer circumferential circle of the core is r1, the radius of the outer circumferential circle of the inner cladding is r2, and the radius of the outer circumferential circle of the trench is r3, r2 / r1 is 2.2 or more and 3.8 or less, and r3-r2 is 4 μm or more and 15 μm or less.

3. When wound around a mandrel having a diameter of 20 mm, the bending loss for light having a wavelength of 1550 nm is 0.75 dB or less per turn; When wound around a mandrel having a diameter of 20 mm, the bending loss for light having a wavelength of 1625 nm is 1.5 dB or less per turn; When wound around a mandrel having a diameter of 30 mm, the bending loss for light having a wavelength of 1550 nm is 0.25 dB or less per 10 turns; 3. The optical fiber according to claim 1, wherein a bending loss for light having a wavelength of 1625 nm when wound around a mandrel having a diameter of 30 mm is 1.0 dB or less per 10 turns.

4. 3. The optical fiber according to claim 1, wherein said outer cladding consists solely of pure silica glass.

5. The optical fiber of claim 1 or 2, wherein the outer cladding comprises fluorine.

6. 6. The optical fiber according to claim 5, wherein in a fluorine concentration distribution in the outer cladding, when the outer cladding is divided into a first region including an outer peripheral surface of the outer cladding and a second region located inside the first region, an average fluorine concentration in the first region is smaller than an average fluorine concentration in the second region.

7. 3. The optical fiber according to claim 1, wherein an average stress remaining in the core is a compressive stress or a tensile stress of 30 MPa or less.

8. The optical fiber of claim 1 or 2, wherein the core is substantially free of alkali elements.

9. The bending loss for light with a wavelength of 1625 nm when wound around a mandrel with a diameter of 100 mm is 1.0×10 per turn. －５ 3. The optical fiber according to claim 1, wherein the optical fiber has a transmission loss of 0.5 dB or less.

10. the core comprises fluorine; 3. The optical fiber according to claim 1, wherein a relative refractive index difference due to fluorine in the core with respect to a refractive index of pure silica glass is equal to or greater than −0.12% and less than 0%.