optical fiber

Abstract

The present invention provides an optical fiber having a refractive index distribution shape with less structural imperfection. An optical fiber, which is composed of a core, a first cladding, a second cladding, and a third cladding, the core is located at the center part and has a radius of r1, the first cladding is adjacent to the core at a radius position r1 and covers the outer periphery thereof, and has an outermost periphery radius of r2, the second cladding is adjacent to the first cladding at a radius position r2 and covers the outer periphery thereof, and has an outermost periphery radius of r3, and the third cladding is adjacent to the second cladding at a radius position r3 and covers the outer periphery thereof. The refractive index of the first cladding continuously and smoothly decreases from the inside to the outside, and has a maximum value at the radius position r1 and a minimum value at the radius position r2. The refractive index of the second cladding continuously and smoothly increases from the inside to the outside, and has a minimum value at the radius position r2 and a maximum value at the radius position r3.

Description

Technical Field

[0001] This invention relates to optical fibers for optical communication, and more particularly to optical fibers that have the same transmission characteristics as existing single-mode optical fibers, such as cutoff wavelength, mode field diameter, and zero dispersion wavelength, while having low transmission loss due to bending and reduced transmission loss at all wavelengths. Background Technology

[0002] Existing single-mode optical fibers have the following characteristics: signal light is transmitted in the fiber core, and signals can be transmitted even when the fiber is somewhat bent. Generally, in single-mode optical fibers, as the bending radius decreases, the proportion of light that is not fully transmitted and leaks from the core increases exponentially, resulting in increased transmission loss. This is called bending loss. In recent years, it has become possible to use optical fibers with a bending radius of less than 15 mm to 10 mm, while on the other hand, there is a need for optical fibers with even lower loss.

[0003] To reduce bending loss, increasing the refractive index of the core to concentrate light more effectively is effective. This can be improved by reducing the mode field diameter (MFD). Therefore, existing technologies often use optical fibers with an MFD of approximately 8.2–8.8 μm. This allows for bending losses of, for example, below 0.5 dB / turn at a wavelength of 1550 nm when the fiber is wound around a core rod (cylinder) with a diameter of r10 mm.

[0004] However, the MFD of optical fibers using the ITU-T G.652.D standard, which is generally used in long-distance optical communication, is about 8.8 to 9.6 μm. Therefore, when connecting the aforementioned fiber with reduced bending loss and standard-compliant optical fibers, there will be a problem of increased connection loss due to the difference in MFD.

[0005] To address this issue, Patent Document 1 discloses a method that uses trench-type optical fibers to design a large MFD while reducing bending loss. This is a well-known technique, but its excellent bending loss characteristics have attracted attention in recent years.

[0006] However, in the case of optical fibers with a grooved refractive index distribution, residual stress is generated in regions of significant refractive index variation due to the presence of interfaces where the glass composition changes dramatically, leading to increased transmission loss. This transmission loss, because it has low wavelength dependence and is not absorption loss caused by specific impurities, is generally referred to as structural imperfection loss.

[0007] Patent Document 2 discloses an attempt to reduce structural imperfection losses by limiting the slope of the covered portion of the trench. However, the method described in Patent Document 2 only limits the coverage to a portion, and fails to sufficiently reduce structural imperfection losses.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: US Patent No. 4,852,968

[0011] Patent Document 2: Japanese Patent No. 5799903 Summary of the Invention

[0012] The problem the invention aims to solve

[0013] In view of the above-mentioned prior art, the object of the present invention is to provide an optical fiber with a refractive index distribution shape having fewer structural imperfections.

[0014] Solution for solving the problem

[0015] In the first embodiment of the present invention, the optical fiber comprises a core, a first cladding, a second cladding, and a third cladding. The core is located at the center and has a radius of r1. The first cladding is adjacent to the core at radius r1 and covers its outer perimeter, with an outermost radius of r2. The second cladding is adjacent to the first cladding at radius r2 and covers its outer perimeter, with an outermost radius of r3. The third cladding is adjacent to the second cladding at radius r3 and covers its outer perimeter. The refractive index of the first cladding decreases continuously and smoothly from the inside to the outside, reaching its maximum value at radius r1 and its minimum value at radius r2. The refractive index of the second cladding increases continuously and smoothly from the inside to the outside, reaching its minimum value at radius r2 and its maximum value at radius r3.

[0016] In this invention, it is preferable that |dΔ(r) / dr|≤0.3% / μm is satisfied in the range of r from 0 to r1, and that |dΔ(r) / dr|≤0.05% / μm is satisfied in the range of r from r1 to r2, and that |dΔ(r) / dr|≤0.1% / μm is satisfied in the range of r2 to r3.

[0017] In this invention, the aforementioned core preferably has a maximum relative refractive index difference Δ1max, the aforementioned first cladding has a relative refractive index difference Δ2 at a radius position r1 and a minimum relative refractive index difference Δ3min at a radius position r2, and the aforementioned second cladding has a relative refractive index difference Δ4 at a radius position r3, wherein Δ1max > Δ2, Δ2 > Δ3min, Δ4 > Δ3min, and Δ2 = Δ4.

[0018] In this invention, preferably near the radius position r2 where the first cladding layer and the second cladding layer meet, the slope of the refractive index distribution shape curve changes from negative to positive.

[0019] In this invention, it is preferable that the positive dopant added to the aforementioned core has a concentration distribution in the radial direction, and the positive dopant is added in such a way that the maximum value of the relative refractive index difference of the aforementioned core based on the average refractive index of the third cladding is 0.30 to 0.50%.

[0020] In this invention, the negative dopants added to the aforementioned first and second cladding layers are preferably added in such a manner that the relative refractive index difference between the aforementioned first and second cladding layers, based on the average refractive index of the third cladding layer, is -0.20 to -0.03%.

[0021] In this invention, the aforementioned positive dopant is preferably germanium and / or chlorine, and the negative dopant is fluorine.

[0022] In this invention, it is preferred that the optical fiber has an attenuation of approximately less than 0.1845 dB / km at a wavelength of 1550 nm. Furthermore, it is preferred that the optical fiber has a bending loss of less than 0.5 dB / turn at a wavelength of 1550 nm when subjected to a bend with a radius of 10 mm. Additionally, it is preferred that the zero-dispersion wavelength of the optical fiber is 1300–1324 nm. Furthermore, it is preferred that the mode field diameter of the optical fiber at 1310 nm is 8.8–9.6 μm. Furthermore, it is preferred that the cutoff wavelength of the optical fiber, measured at a length of 22 m, is less than 1260 nm.

[0023] It should be noted that the above description of the invention is not an exhaustive list of features. Furthermore, further combinations of these feature groups can also constitute other inventions.

[0024] The effects of the invention

[0025] According to the present invention, it is possible to obtain optical fibers with low transmission loss, maintaining an MFD of 8.8–9.6 μm and low bending loss. Attached Figure Description

[0026] Figure 1 The cross-sectional structure of the optical fiber 1 in this embodiment is shown.

[0027] Figure 2 An example of the refractive index distribution structure of the optical fiber 1 in this embodiment is shown.

[0028] Figure 3 Shown by Figure 2 The refractive index distribution structure is used to calculate |dΔ(r) / dr|.

[0029] Explanation of reference numerals in the attached figures

[0030] 1. Optical fiber

[0031] 2 cores

[0032] 3 First cladding layer

[0033] 4 Second cladding

[0034] 5 Third Packaging Detailed Implementation

[0035] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0036] Figure 1 The cross-sectional structure of the optical fiber 1 in this embodiment is shown. Additionally, Figure 2 An example of the refractive index distribution structure of the optical fiber 1 according to this embodiment is shown. The optical fiber of this embodiment has transmission characteristics and bending loss that are equal to or higher than those of conventional single-mode optical fibers.

[0037] like Figure 1 As shown, optical fiber 1 has a trench-type refractive index distribution structure comprising a three-layer cladding structure. Specifically, optical fiber 1 consists of a core 2, a first cladding 3, a second cladding 4, and a third cladding 5. The core 2 is located at the center and has a radius r1. The first cladding 3 is adjacent to the core 2 at radius r1 and covers its outer periphery, having an outermost radius r2. The second cladding 4 is adjacent to the first cladding 3 at radius r2 and covers its outer periphery, having an outermost radius r3. The third cladding 5 is adjacent to the second cladding 4 at radius r3 and covers its outer periphery. The radius rf of the third cladding 5 is its outer periphery. The outer periphery of the third cladding 5 forms the outermost surface of optical fiber 1. Figure 2 As shown, the refractive index distribution of optical fiber 1 in the core 2, the first cladding 3, and the second cladding 4 does not exhibit any regions of abrupt refractive index changes. That is, there are no regions of abrupt compositional changes.

[0038] In this specification, the radii of each layer are defined as follows. The refractive index at any location (distance from the center) *r* in the fiber material is defined as *n(r)*. *r2* is the location of the lowest refractive index in the refractive index distribution. When the outer diameter of the fiber material is *rf*, the average refractive index from 1 / 2 *rf* to *rf* is defined as *n0*. *r3* is the point in the refractive index distribution where *n(r)* = *n0* is reached first from *r2* outwards. *r1* is the point in the refractive index distribution where *n(r)* = *n0* is reached first from the center outwards.

[0039] like Figure 2 As shown, the refractive index of the first cladding layer decreases continuously and smoothly from the inside to the outside, reaching its maximum value at radius r1 and its minimum value at radius r2. The refractive index of the second cladding layer increases continuously and smoothly from the inside to the outside, reaching its minimum value at radius r2 and its maximum value at radius r3. That is, near the radius r2 where the first and second cladding layers meet, the slope of the refractive index distribution curve changes from negative to positive.

[0040] Furthermore, the relative refractive index difference between each layer is defined as follows: the relative refractive index difference of r is Δ(r) = 100 × (n(r) - n0) / n(r). Δ1max is the maximum relative refractive index difference within the profile. In addition, Δ2 = Δ(r1), Δ3min = Δ(r2), and Δ0 is the average relative refractive index difference from Δ(1 / 2rf) to Δ(rf).

[0041] To adjust the relative refractive index difference of the core to within the MFD specified in ITU-T G.652.D, a relative refractive index difference of 0.30–0.50% is ideal. When the relative refractive index difference is less than 0.3%, the refractive index difference with the cladding becomes small, making it impossible to achieve the specified bending loss (e.g., bending loss below 0.5 dB / turn at a wavelength of 1550 nm when a bend with a radius of 10 mm is applied). Furthermore, when it exceeds 0.5%, the dopant concentration in the core increases, raising concerns about deterioration in transmission loss due to increased Rayleigh scattering.

[0042] Ideally, the relative refractive index difference between the first and second cladding layers should be between -0.20% and -0.03%. When the relative refractive index difference is greater than -0.03%, the refractive index difference with the core becomes smaller, making it impossible to achieve the specified bending loss (e.g., bending loss below 0.5 dB / turn at a wavelength of 1550 nm when a bend with a radius of 10 mm is applied). Furthermore, when the relative refractive index difference is less than -0.20%, the concentration of negative dopants in the cladding increases, raising concerns about deterioration in transmission loss due to increased Rayleigh scattering.

[0043] The manufacturing method of the single-mode optical fiber of the present invention will be described next. First, a porous glass matrix consisting of a core and an intermediate layer is integrally synthesized using the VAD method. At this time, germanium is doped into the core to increase the refractive index.

[0044] At this point, by controlling the soot deposition temperature, the bulk density of the glass particles (soot) can be adjusted. The higher the bulk density, the better the fluorine doping can be suppressed in the subsequent sintering process under a fluorine atmosphere.

[0045] Next, the flue dust parent material was sintered according to the following steps. First, as a process for removing OH and doping fluorine from the flue dust parent material, the entire length of the parent material was heated at a sintering temperature of 1200℃ and a feed rate of 10mm / min under a mixed gas atmosphere of Ar = 20L / min, Cl2 = 0.5L / min, and SiF4 = 0.1L / min. Next, as a process for achieving transparent vitrification, the entire length of the parent material was heated at a sintering temperature of 1500℃ and a feed rate of 5mm / min under a gas atmosphere of He = 20L / min.

[0046] The resulting transparent glass core is stretched to a specified diameter using a glass turntable, ensuring a uniform outer diameter along its length. During this process, under the influence of the oxy-hydrogen flame on the glass turntable, OH radicals may enter the surface of the core. These radicals are removed by immersing the transparent glass core in an aqueous hydrofluoric acid solution to dissolve the surface. It should be noted that a plasma flame can also be used as the heating source for stretching using the glass turntable. In this case, OH radicals will not be incorporated into the surface of the core, thus eliminating the need for hydrofluoric acid-based treatment.

[0047] Using the transparent core material thus prepared, OVD (Optical Vapor Deposition) was performed to obtain a porous core material. Next, the porous core material was sintered to vitrify it, thus producing an optical fiber core material. By heating the obtained optical fiber core material to approximately 2100°C and drawing it into fibers, an optical fiber with a diameter of 125 μm could be obtained.

[0048] In this optical fiber, a large amount of light passes through the central position, and the amount of light passing through decreases as the distance from the center decreases. However, some transmitted light also leaks into the cladding region. By reducing the refractive index change in the core and cladding regions, structural imperfection losses can be reduced. In this application, the refractive index change is standardized by defining it using the magnitude of |dΔ(r) / dr|, that is, the radial derivative of the relative refractive index difference Δ(r), and the appropriate range of values ​​for |dΔ(r) / dr| at each location is clearly defined.

[0049] Figure 3 Shown by Figure 2 The refractive index distribution structure is used to calculate |dΔ(r) / dr|. The refractive index distribution structure can be obtained as follows: Prepare an optical fiber with a diameter of 125 μm, calculate the relative refractive index difference Δ(r) at 0.15 μm intervals, and plot it. Then, dΔ(r) / dr can be obtained by differentiating the radial distribution of the relative refractive index difference Δ(r). Furthermore, to focus only on the degree of refractive index change without considering the direction of change (increase or decrease), the absolute value of dΔ(r) / dr, |dΔ(r) / dr|, is taken.

[0050] The following explains the appropriate range of values ​​for |dΔ(r) / dr| for each part and the precautions for manufacturing methods to achieve the aforementioned range.

[0051] First, |dΔ(r) / dr| (0~r1) is preferably below 0.3% / μm. By preventing drastic changes in the refractive index, i.e., by suppressing large changes in the glass composition, structural imperfections can be reduced.

[0052] To reduce |dΔ(r) / dr|(0~r1), it is preferable to adjust the feed rate during sintering. Specifically, reducing the descent rate can promote the diffusion of Ge from the center into the cladding, thereby reducing |dΔ(r) / dr|(0~r1). Alternatively, increasing the chlorine concentration during dehydration can also reduce |dΔ(r) / dr|(0~r1).

[0053] The value of |dΔ(r) / dr|(r1~r2) is preferably below 0.05% / μm. When |dΔ(r) / dr|(r1~r2) is greater than 0.05, the loss due to structural imperfections will increase due to the rapid change in refractive index.

[0054] To reduce |dΔ(r) / dr|(r1~r2), it is preferable to adjust the feed rate during sintering. Specifically, |dΔ(r) / dr|(r1~r2) can be reduced by slowing down the feed rate to promote the diffusion of Ge from the center to the cladding. Alternatively, |dΔ(r) / dr|(r1~r2) can also be reduced by increasing the chlorine concentration during dehydration. Furthermore, |dΔ(r) / dr|(r1~r2) can also be reduced by adjusting the concentration of silicon tetrafluoride during dehydration. Additionally, |dΔ(r) / dr|(r1~r2) can be reduced by separating the dehydration process from the fluorine doping process.

[0055] The value of |dΔ(r) / dr| (r2~r3) is preferably below 0.1% / μm. When |dΔ(r) / dr| (r2~r3) is greater than 0.1, the loss due to structural imperfections will increase due to the rapid change in refractive index.

[0056] To reduce |dΔ(r) / dr|(r2~r3), it is preferable to insert a process to remove fluorine from the surface of the porous glass substrate between the dehydration process and the vitrification process.

[0057] Example

[0058] [Example 1-1]

[0059] First, a porous glass matrix consisting of a core and an intermediate layer is integrally synthesized using the VAD method. Germanium is doped into the core to increase its refractive index. The porous glass matrix is ​​heated to approximately 1200°C in a mixed gas atmosphere of 1 liter of chlorine per minute, 0.1 liters of tetrafluorosilane per minute, and 20 liters of Ar per minute, and then fed at a rate of 10 mm / min for dehydration and fluorine doping. Next, it is heated to approximately 1500°C to produce a solid, transparent glass core matrix. It should be noted that tetrafluoromethane, hexafluoroethane, or other alternatives to tetrafluorosilane gas can also be used.

[0060] The transparent glass core is stretched to a specified diameter using a glass turntable, ensuring a uniform outer diameter along its length. During this process, under the influence of the oxy-hydrogen flame on the turntable, OH radicals may penetrate the surface. These radicals are removed by immersing the transparent glass core in an aqueous hydrofluoric acid solution to dissolve the surface. It should be noted that an argon plasma flame can also be used as the heating source for the glass turntable stretching. In this case, OH radicals will not be incorporated into the surface of the core, thus eliminating the need for hydrofluoric acid-based treatment.

[0061] Using the transparent core material thus prepared, consisting of a core, a first cladding, and a second cladding, as the object, OVD (Optical Vapor Deposition) was performed. The resulting porous core material was sintered, and optical fiber material was fabricated by vitrification to make it transparent. The resulting core material was heated to approximately 2100°C and drawn into fibers to obtain optical fibers with a diameter of 125 μm.

[0062] [Examples 1-2]

[0063] First, a porous glass matrix consisting of a core and an intermediate layer was integrally synthesized using the VAD method. Germanium was doped into the core to increase its refractive index. The porous glass matrix was heated to approximately 1200°C in a mixed gas atmosphere of 1.5 liters / min of chlorine, 0.12 liters / min of tetrafluorosilane, and 20 liters / min of Ar, and then fed at a rate of 10 mm / min for dehydration and fluorine doping. Subsequently, as a step to remove surface fluorine, a heating process was added, in which the porous glass matrix was heated to 1300°C for 1 hour. During this time, He was introduced at a rate of 20 liters / min. Then, it was heated to approximately 1500°C to form a solid, transparent glass core matrix. An optical fiber was then obtained using the same method as in Example 1-1.

[0064] [Examples 1-3]

[0065] First, a porous glass matrix consisting of a core and an intermediate layer was integrally synthesized using the VAD method. Germanium was doped into the core to increase its refractive index. The porous glass matrix was heated to approximately 1200°C in a mixed gas atmosphere of 2.0 L / min chlorine, 0.14 L / min tetrafluorosilane, and 20 L / min Ar, and then fed at a rate of 10 mm / min for dehydration and fluorine doping. Subsequently, as a step to remove surface fluorine, a heating process was added, in which the porous glass matrix was heated to 1300°C for 4 hours. During this time, He was introduced at a rate of 20 L / min. Then, it was heated to approximately 1500°C to form a solid, transparent glass core matrix. An optical fiber was then obtained using the same method as in Example 1-1.

[0066] [Comparative Example 1-1]

[0067] First, a porous glass matrix consisting of a core and an intermediate layer was integrally synthesized using the VAD method. Germanium was doped into the core to increase its refractive index. The porous glass matrix was heated to approximately 1200°C in a mixed gas atmosphere of 0.5 L / min chlorine, 0.1 L / min tetrafluorosilane, and 20 L / min Ar, and then fed at a rate of 10 mm / min for dehydration and fluorine doping. Next, it was heated to approximately 1500°C to form a solid, transparent glass core matrix. An optical fiber was then obtained using the same method as in Example 1-1.

[0068] Table 1 shows various parameters of optical fiber 1 obtained from the embodiments and comparative examples.

[0069] [Table 1]

[0070]

[0071] In Example 1-1, the transmission loss at a wavelength of 1550 nm is 0.1842 dB / km, and the bending loss of R10×1 turn (bending radius 10 mm, 1 winding) is 0.27 dB, which are sufficiently low values. Ge diffuses into the first cladding, and dΔ(r) / dr decreases by removing fluorine from the surface during glass transition.

[0072] In Examples 1-2, the transmission loss at 1550 nm was 0.1832 dB / km, and the bending loss of R10×1 turn was 0.31 dB, which are lower than those in Example 1-1. By increasing the chlorine concentration during dehydration, the diffusion of Ge into the first cladding layer was promoted, thus reducing |dΔ(r) / dr|(0~r1) and |dΔ(r) / dr|(r1~r2). Furthermore, by incorporating a fluorine diffusion process, |dΔ(r) / dr|(r2~r3) was reduced. Based on these factors, the structural imperfection loss decreased, and the transmission loss at 1550 nm was lowered.

[0073] In Examples 1-3, the transmission loss at 1550 nm was 0.1820 dB / km, and the bending loss of R10×1 turn was 0.22 dB, which are lower than those in Examples 1-2. By increasing the chlorine concentration during dehydration, the diffusion of Ge into the first cladding layer was promoted, thus reducing |dΔ(r) / dr|(0~r1) and |dΔ(r) / dr|(r1~r2). Furthermore, due to the extended fluorine diffusion process time, |dΔ(r) / dr|(r2~r3) decreased. Based on these factors, the structural imperfection loss decreased, and the transmission loss at 1550 nm was reduced.

[0074] All of the above embodiments 1-1 to 1-3 fall within the range of 1300–1324 nm for the zero-dispersion wavelength λ0. Furthermore, the mode field diameter at 1310 nm falls within the range of 8.8–9.6 μm. Additionally, the cutoff wavelength λcc, measured with a fiber length of 22 m, is below 1260 nm. All characteristics of these embodiments conform to the recommendations of ITU-T G.652.D.

[0075] In Comparative Example 1, the transmission loss at a wavelength of 1550 nm is 0.1868 dB / km, and the bending loss at R10×1 turn is 0.25 dB, which are higher than those of the other examples.

Claims

1. An optical fiber comprising a core, a first cladding, a second cladding, and a third cladding, wherein the core is located at a center and has a radius of r1, the first cladding is adjacent to the core at radius r1 and covers its outer perimeter, and has an outermost radius of r2, the second cladding is adjacent to the first cladding at radius r2 and covers its outer perimeter, and has an outermost radius of r3, and the third cladding is adjacent to the second cladding at radius r3 and covers its outer perimeter, characterized in that... The refractive index of the first cladding layer decreases continuously and smoothly from the inside to the outside, reaching its maximum value at radius r1 and its minimum value at radius r2; and... The refractive index of the second cladding increases continuously and smoothly from the inside to the outside, reaching a minimum at radius r2 and a maximum at radius r3. The radii of each layer are defined as follows: the refractive index at any position in the fiber material, i.e., at a distance r from the center, is set as n(r), the outer diameter of the fiber material is set as rf, and the average refractive index from 1 / 2rf to rf is set as n0. The relative refractive index difference between each layer is defined as follows: the relative refractive index difference Δ(r) of r is 100×(n(r)-n0) / n(r); where, in the range of r from 0 to r1, |dΔ(r) / dr| ≤ 0.3% / μm, and in the range of r from r1 to r2, |dΔ(r) / dr| ≤ 0.05% / μm, and in the range of r2 to r3, |dΔ(r) / dr| ≤ 0.1% / μm.

2. The optical fiber of claim 1, wherein, The core has a maximum relative refractive index difference Δ1max, the first cladding has a relative refractive index difference Δ2 at radius r1 and a minimum relative refractive index difference Δ3min at radius r2, and the second cladding has a relative refractive index difference Δ4 at radius r3. Δ1max>Δ2, Δ2>Δ3min, Δ4>Δ3min, Δ2=Δ4.

3. The optical fiber according to claim 1 or 2, characterized in that, Near the radius r2 where the first cladding layer and the second cladding layer meet, the slope of the refractive index distribution shape curve changes from negative to positive.

4. The optical fiber according to claim 1 or 2, characterized in that, The positive dopant added to the core has a concentration distribution in the radial direction, and the positive dopant is added in such a way that the maximum value of the relative refractive index difference of the core based on the average refractive index of the third cladding is 0.30% to 0.50%.

5. The optical fiber according to claim 1 or 2, characterized in that, The negative dopants added to the first and second cladding layers are added in such a way that the relative refractive index difference between the first and second cladding layers, based on the average refractive index of the third cladding layer, is -0.20% to -0.03%.

6. The optical fiber of claim 4, wherein, The positive dopant is germanium and / or chlorine.

7. The optical fiber according to claim 5, characterized in that, The negative dopant is fluorine.

8. The optical fiber according to claim 1 or 2, characterized by It exhibits an attenuation of less than 0.1845 dB / km at a wavelength of 1550 nm.

9. The optical fiber according to claim 1 or 2, characterized by When a bend with a radius of 10 mm is applied, the bending loss at a wavelength of 1550 nm is less than 0.5 dB / turn.

10. The optical fiber according to claim 1 or 2, characterized by The zero-dispersion wavelength is 1300nm~1324nm.

11. The optical fiber according to claim 1 or 2, characterized by The mode field diameter at 1310 nm is 8.8 μm to 9.6 μm.

12. The optical fiber according to claim 1 or 2, characterized in that, The cutoff wavelength, measured with a fiber length of 22m, is below 1260nm.

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