Optical Fiber

Abstract

In order to provide an optical fiber that is highly compatible with the G.652 standard and that has a smaller diameter, this optical fiber comprises: a core part made of quartz glass; a clad part that covers the outer periphery of the core part and that is made of quartz glass having a refractive index which is smaller than the greatest refractive index of the core part; and a coating part including a primary coating layer that covers the outer periphery of the clad part and that is located on the clad part side, and a secondary coating layer located on the outer periphery side of the primary coating layer. The outer diameter of the clad part is less than 100 µm, the thickness of the primary coating layer is 15 µm or more. The mode field diameter at a wavelength of 1,310 nm is 8.6-9.2 µm. The effective cutoff wavelength is 1,260 µm or less. If the optical fiber has a diameter of 60 mm and is bent, the bending loss at a wavelength of 1,550 nm is 0.1 dB / 100 turns or less.

Description

[Technical field]

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

[0002] In the fields of datacom and telecom, small-diameter optical fibers have been attracting attention as optical fibers that can realize high-density optical fiber cables. Here, a small-diameter optical fiber is an optical fiber in which the glass portion of the optical fiber is thinned, and the cladding diameter is thin. However, small-diameter optical fibers also include those in which the outer diameter, including the coating portion formed to cover the outer periphery of the cladding portion, is thinned as a result of the thinning of the cladding diameter.

[0003] Conventionally, a configuration in which the relative refractive index difference of the core portion with respect to the cladding portion is high has been disclosed as a small-diameter optical fiber (Non-Patent Document 1). Since the optical fiber of Non-Patent Document 1 has a high relative refractive index difference, its characteristics do not comply with the standard of a standard single-mode optical fiber defined by ITU-T (International Telecommunication Union) G.652 (hereinafter, G.652 standard). Also, a configuration in which a trench layer with a relative refractive index difference of -0.08% or more is provided has been disclosed as a small-diameter optical fiber (Patent Document 1). The optical fiber of Patent Document 1 complies with the G.652 standard, and its cladding diameter is about 100 μm to 125 μm. Also, a configuration in which a primary coating layer and a secondary coating layer are provided as coating portions, and the secondary coating layer is set to 25 μm or less has been disclosed as a small-diameter optical fiber (Patent Document 2). The optical fiber of Patent Document 2 has a cladding diameter of 125 μm, but the diameter is reduced by reducing the coating thickness.

[0004] In addition, Patent Document 3 describes a 130 μm 2A configuration for suppressing microbending loss in a relatively large optical fiber is disclosed. The optical fiber in Patent Document 3 has an outer diameter of a primary coating layer of 185 μm or more and 220 μm or less, and an outer diameter of a secondary coating layer of 225 μm or more and 260 μm or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2016 / 190297 [Patent Document 2] Japanese Patent Application Publication No. 5-19144 [Patent Document 3] JP 2015-219271 A [Non-patent literature]

[0006] [Non-Patent Document 1] Murase et al., "Development of Thin-Clad Fibers," Showa Electric Wire Review, vol. 53, No. 1 (2003), pp. 32-36 Summary of the Invention [Problem to be solved by the invention]

[0007] Optical fibers conforming to the G.652 standard are widely used, for example, in applications where they are laid on land, etc. Therefore, there is a demand for optical fibers that are highly compatible with the G.652 standard and have a smaller diameter.

[0008] The present invention has been made in view of the above, and an object of the present invention is to provide an optical fiber that is highly compatible with the G.652 standard and has a smaller diameter. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, an optical fiber according to one embodiment of the present invention comprises a core portion made of silica-based glass, a cladding portion covering the outer periphery of the core portion and made of silica-based glass having a refractive index lower than the maximum refractive index of the core portion, and a coating portion covering the outer periphery of the cladding portion and having a primary coating layer located on the cladding portion side and a secondary coating layer located on the outer periphery side of the primary coating layer, wherein the outer diameter of the cladding portion is less than 100 μm, the thickness of the primary coating layer is 15 μm or more, the mode field diameter at a wavelength of 1310 nm is 8.6 μm or more and 9.2 μm or less, the effective cutoff wavelength is 1260 μm or less, and the bending loss at a wavelength of 1550 nm when bent at a diameter of 60 mm is 0.1 dB / 100 turns or less.

[0010] The relative refractive index difference Δ1 of the core portion may be 0.33% or more and 0.40% or less.

[0011] The zero dispersion wavelength is between 1300nm and 1324nm, and the dispersion slope at the zero dispersion wavelength is 0.092ps / nm 2 / km or less.

[0012] The microbending loss at a wavelength of 1550 nm may be 20 times or less than the microbending loss at a wavelength of 1550 nm of a standard optical fiber having characteristics conforming to the standard defined by ITU-T G.652 and having a resin coating portion with a thickness of 62.5 μm on the outer periphery of the cladding portion.

[0013] The microbending loss may be a value measured by an abrasive paper method or a wire mesh method.

[0014] The core portion may be set so that an effective cutoff wavelength is not less than 1000 nm and not more than 1260 nm.

[0015] The core portion may have a central core portion and a depressed layer formed on an outer periphery of the central core portion, and may have a W-shaped refractive index profile.

[0016] When the relative refractive index difference of the depressed layer with respect to the cladding portion is Δ2, Δ2 may be -0.20% or more and less than 0%, and when the core diameter of the central core portion is 2a and the outer diameter of the depressed layer is 2b, b / a may be 5 or less.

[0017] It may have a step-type refractive index profile.

[0018] The outer diameter of the cladding portion may be 75 μm or less, and the thickness of the primary coating layer may be 30 μm or less.

[0019] The optical fiber including the coating may have an outer diameter of 210 μm or less. Effect of the Invention

[0020] The present invention has the effect of realizing an optical fiber that is highly compatible with the G.652 standard and has a smaller diameter. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic cross-sectional view of an optical fiber according to an embodiment. [Figure 2A] FIG. 2A is a schematic diagram of a step-type refractive index profile that can be used in an optical fiber according to an embodiment. [Figure 2B] FIG. 2B is a schematic diagram of a W-shaped refractive index profile that can be used in an optical fiber according to an embodiment. [Diagram 3] FIG. 3 is a diagram showing an example of the relationship between the glass diameter and the normalized microbending loss. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below. In addition, in each drawing, the same or corresponding components are appropriately assigned the same reference numerals. In addition, in this specification, the cutoff wavelength or effective cutoff wavelength refers to the cable cutoff wavelength defined in ITU-T G.650.1. In addition, other terms not specifically defined in this specification shall follow the definitions and measurement methods in G.650.1 and G.650.2.

[0023] (Embodiment) 1 is a schematic cross-sectional view of an optical fiber according to an embodiment. The optical fiber 1 includes a core 1a located approximately at the center, a cladding 1b that covers the outer periphery of the core 1a, and a coating 1c that covers the outer periphery of the cladding 1b.

[0024] Both the core 1a and the cladding 1b are made of silica-based glass. For example, the core 1a is made of silica-based glass doped with a dopant for adjusting the refractive index, such as germanium (Ge) or fluorine (F). The cladding 1b has a refractive index lower than the maximum refractive index of the core 1a. The cladding 1b is made of, for example, pure silica glass that does not contain a dopant for adjusting the refractive index. The portion consisting of the core 1a and the cladding 1b may be referred to as a glass optical fiber.

[0025] The outer diameter of the cladding portion 1b (hereinafter, sometimes referred to as cladding diameter or glass diameter) is less than 100 μm, which is smaller than the cladding diameter of about 125 μm of a single-mode optical fiber conforming to the G.652 standard. From the viewpoint of making the diameter thinner, it is more preferable that the cladding diameter is 85 μm or less, and more preferably 82 μm or less. Hereinafter, the single-mode optical fiber conforming to the G.652 standard may be referred to as a standard optical fiber and referred to as a standard SMF. Such a standard SMF usually has a resin coating portion with a thickness of about 62.5 μm on the outer periphery of the cladding portion. For example, in the case of a two-layer structure, the resin coating portion is composed of a primary coating layer with a thickness of about 37.5 μm and a secondary coating layer with a thickness of about 25 μm located on the outer periphery of the primary coating layer. Therefore, the outer diameter of the resin coating portion is about 250 μm.

[0026] The optical fiber 1 has a refractive index profile as shown in, for example, Figures 2A and 2B. Figures 2A and 2B both show the refractive index profile in the radial direction from the central axis of the core 1a of the optical fiber 1.

[0027] Fig. 2A shows a step-type refractive index profile. In Fig. 2A, profile P11 shows the refractive index profile of the core portion 1a, and profile P12 shows the refractive index profile of the cladding portion 1b. The refractive index profile is shown by the relative refractive index difference with respect to the cladding portion 1b. In the step-type refractive index profile, the diameter (core diameter) of the core portion 1a is 2a, and the relative refractive index difference of the core portion 1a with respect to the cladding portion 1b is Δ1. Δ1 is preferably, for example, 0.33% or more and 0.40% or less.

[0028] FIG. 2B shows a so-called W-shaped refractive index profile. In FIG. 2B, profile P21 shows the refractive index profile of the core portion 1a, and profile P22 shows the refractive index profile of the cladding portion 1b. In the W-shaped refractive index profile, the core portion 1a is composed of a central core portion having a diameter of 2a and a depressed layer formed to surround the outer periphery of the central core portion, with a refractive index smaller than that of the cladding portion, an inner diameter of 2a, and an outer diameter of 2b. The relative refractive index difference of the central core portion with respect to the cladding portion 1b is Δ1. The relative refractive index difference of the depressed layer with respect to the cladding portion 1b is Δ2. Δ1 is preferably, for example, 0.33% or more and 0.40% or less. Δ2 is preferably, for example, -0.20% or more and less than 0%. b / a is preferably, for example, 5 or less.

[0029] Returning to Fig. 1, the coating portion 1c is made of, for example, a resin, and has the function of protecting the glass portion of the optical fiber 1. The coating portion 1c is made of, for example, a UV-curable resin. Examples of UV-curable resins used for the coating portion 1c include urethane acrylate-based, polybutadiene acrylate-based, epoxy acrylate-based, silicone acrylate-based, and polyester acrylate-based resins, but there is no particular limitation as long as they are used for coating optical fibers.

[0030] The coating portion 1c has a primary coating layer 1ca located on the cladding portion 1b side and a secondary coating layer 1cb located on the outer peripheral side of the primary coating layer 1ca. The Young's modulus of the primary coating layer 1ca is about 0.2 to 1.5 MPa, and is 0.5 MPa in this embodiment. The Young's modulus of the secondary coating layer 1cb is about 500 to 2000 MPa, and is 1000 MPa in this embodiment.

[0031] The outer diameter of the optical fiber 1 including the coating portion 1c is, for example, 210 μm or less. The thickness of the primary coating layer 1ca is, for example, 15 μm or more.

[0032] The optical fiber 1 according to this embodiment has the following characteristics: a core diameter is 7 μm to 10 μm (core radius a is 3.5 μm to 5.0 μm), a mode field diameter (MFD) at a wavelength of 1310 nm is 8.6 μm to 9.2 μm, an effective cutoff wavelength (λcc) is 1260 nm or less, and a bending loss at a wavelength of 1550 nm when bent at a diameter of 60 mm (hereinafter referred to as macrobending loss) is 0.1 dB / 100 turns or less, preferably a macrobending loss at a wavelength of 1625 nm when bent at a diameter of 60 mm is 0.1 dB / 100 turns or less. As a result, the optical fiber 1 is an optical fiber that complies with the G.652 standard in terms of MFD, λcc, and macrobending loss, and is highly compatible with the G.652 standard.

[0033] In addition, the optical fiber 1 has a zero dispersion wavelength of 1300 nm or more and 1324 nm or less, and a dispersion slope at the zero dispersion wavelength of 0.092 ps / nm 2 / km or less, and the dispersion slope is preferably 0.073ps / nm 2 It is more preferable that the characteristic be satisfied of 100% by weight per km or more.

[0034] Furthermore, the cladding diameter of the optical fiber 1 is less than 100 μm, which is an order of magnitude smaller than the cladding diameter of standard SMF, which is about 125 μm. As a result, the glass diameter of the optical fiber 1 is significantly smaller, and the cross-sectional area of ​​the optical fiber 1 is significantly reduced, making it suitable for realizing a high-density optical fiber cable.

[0035] In order to realize the above-mentioned effective cutoff, it is preferable that the core 1a is set so that the effective cutoff wavelength is 1260 nm or less, and it is particularly preferable that the diameter 2a is set so that the effective cutoff wavelength is 1260 nm or less. It is also preferable that the core 1a, and particularly the diameter 2a, is set so that the effective cutoff wavelength is 1000 nm or more, since this can reduce macrobending loss.

[0036] Furthermore, if the outer diameter of the optical fiber 1 including the coating portion 1c is 210 μm or less, it can be made smaller than the outer diameter of a standard SMF including the resin coating portion, which is about 250 μm, and the cross-sectional area of ​​the optical fiber 1 is significantly reduced.

[0037] In optical fibers, when the glass diameter, i.e., the cladding diameter, is reduced, the microbending loss (also called lateral pressure loss) increases. Normally, the transmission loss of optical fibers increases when they are assembled into an optical fiber cable. The increase in transmission loss at this time is closely related to the microbending loss, and the greater the microbending loss, the greater the increase.

[0038] In the optical fiber 1 according to the present embodiment, if the microbending loss is 20 times or less than the microbending loss at a wavelength of 1550 nm of a standard SMF, the microbending loss can be made practical. If the value obtained by normalizing the microbending loss with the microbending loss in the standard SMF is defined as the normalized microbending loss, the normalized microbending loss of the optical fiber 1 according to the present embodiment is preferably 20 or less, more preferably 10 or less. In order to suppress the microbending loss, it is preferable that the thickness of the primary coating layer 1ca in the two-layer coating portion 1c is 15 μm or more. Here, when the normalized microbending loss is 20 or less, the value of 20 is a value that can suppress the microbending loss to a practical level even after cable formation.

[0039] The microbending loss may be measured by a fixed diameter drum method (a type of abrasive paper method) specified in JIS C6823:2010_10 or by an extension drum method, which is a type of abrasive paper method. The microbending loss may also be measured by a wire mesh method or other measurement methods (for example, an oblique winding method).

[0040] Hereinafter, the optical fiber according to the embodiment will be described with reference to the results of simulation calculations.

[0041] First, for optical fibers with step-type and W-type refractive index profiles shown in Figure 2, structural parameters such as Δ1, Δ2, 2a, and 2b were comprehensively changed to various values ​​and combined to calculate the optical characteristics. At this time, the combinations were optimized so that the optical characteristics MFD, λcc, and macrobending loss satisfied the G.652 standard. Hereinafter, MFD, λcc, and macrobending loss may be referred to as the main characteristics.

[0042] As a result of the calculation, it was confirmed that for both step-type and W-type, when the relative refractive index difference Δ1 is between 0.33% and 0.40%, there exists a combination of structural parameters whose main characteristics satisfy the G.652 standard. Furthermore, in the case of W-type, when Δ2 is between -0.20% and 0% and b / a is 5 or less, there exists a combination of structural parameters whose main characteristics better satisfy the G.652 standard.

[0043] Next, a systematic study was conducted by varying the glass diameter, the outer diameter of the primary coating layer (primary diameter), and the outer diameter of the secondary coating layer (secondary diameter) for combinations of structural parameters that satisfy the G.652 standard for key characteristics. As a result of the study, it was confirmed that the glass diameter and primary diameter (or primary thickness, which is the thickness of the primary coating layer) are the dominant factors in the microbending loss characteristics of optical fibers in both step-type and W-type configurations.

[0044] Figure 3 shows an example of the relationship between glass diameter and normalized microbending loss when the primary thickness is 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm. The glass diameter was changed around 80 μm, 90 μm, 100 μm, 110 μm, and 120 μm, and the range of the value change is shown by a bar extending along the horizontal axis. The normalized microbending loss has a range of values ​​depending on the combination of structural parameters used in the calculation whose main characteristics satisfy the G.652 standard and the secondary diameter, so the range of the range is shown by a bar extending along the vertical axis.

[0045] It should be noted that in FIG. 3, the lower limit of the error bar in the vertical direction for a glass diameter of 100 μm and a primary thickness of 15 μm extends to 20 or less.

[0046] As a result of a systematic study as shown in Fig. 3, it was confirmed that when the glass diameter is less than 100 μm, by making the primary thickness 15 μm or more, it may be possible to make the normalized microbending loss 20 or less. It was also confirmed that by making the primary thickness 20 μm or more, the normalized microbending loss can be made smaller and the range in which the normalized microbending loss can be made 20 or less can be expanded.

[0047] The optical fiber according to the present embodiment can be manufactured by drawing a glass optical fiber from an optical fiber preform using a known drawing device and forming a coating on the glass optical fiber. Considering the operability of the process of forming the secondary coating layer, it is desirable for the secondary thickness to be 10 μm or more.

[0048] From the above study results, the optical fiber 1 according to the present embodiment can satisfy the G.652 standard in terms of main characteristics, have a glass diameter of less than 100μ, a primary thickness of 15μm or more, preferably 20μm or more, a secondary thickness of 10μm or more, and a normalized microbending loss of 20 or less. In this case, the outer diameter (fiber diameter) of the optical fiber 1 including the coating portion 1c is increased by 50μm or more, or preferably by 60μm or more, relative to the glass diameter. Therefore, the minimum fiber diameter and the preferred fiber diameter at glass diameters of 75μm, 80μm, 85μm, 90μm, and 95μm are as shown in Table 1. As shown in Table 1, the optical fiber 1 according to the present embodiment can have a fiber diameter in the range of 125μm to 155μm. It is preferable to set the glass diameter to 75μm or more, since the glass diameter is easy to handle and the microbending loss is relatively small.

[0049] [Table 1]

[0050] (Example) As an example of the present invention, an optical fiber having a W-shaped refractive index profile was fabricated by a known method. The structural parameters were set to Δ1 of 0.37%, Δ2 of -0.03%, b / a of 2, and 2a of 8 μm. The glass diameter was 90 μm, the primary diameter was 135 μm, and the secondary diameter was 170 μm. The material and Young's modulus of the coating portion were the same as those of the embodiment.

[0051] The optical properties of the optical fiber of the example are shown in Table 2. The normalized microbending loss was measured by the abrasive paper method. As shown in Table 2, the optical fiber of the example has a low transmission loss of 0.19 dB / km at a wavelength of 1550 nm, and the λcc, macrobending loss, MFD, and zero dispersion wavelength (λ 0 ) and dispersion slope satisfied the G.652 standard, showing high compatibility with the G.652 standard. In addition, the bending loss at a wavelength of 1625 nm when bent at a diameter of 60 mm for the optical fiber of the example also fully satisfied the G.652 standard. In addition, the optical fiber of the example had a small normalized microbending loss of 11.9, a glass diameter of 90 μm, and a small fiber diameter of 170 μm.

[0052] [Table 2]

[0053] When the optical fiber of the example was bent at a diameter of 30 mm at a wavelength of 1550 nm, the bending loss was greater than 0.25 dB / 10 turns, which meant that the optical fiber of the example did not satisfy the bending loss requirement of the G.657 standard.

[0054] As a comparative example, an optical fiber was fabricated that had the same W-shaped refractive index profile as the example, but had a glass diameter of 90 μm, a primary diameter of 110 μm, i.e., a primary thickness of 10 μm, and a secondary diameter of 145 μm. The normalized microbending loss was 73.1, which was significantly increased compared to the example. This suggests that setting the primary thickness to an appropriate value of 15 μm or more is effective in suppressing the microbending loss.

[0055] In the above embodiment, the step type and W type are exemplified as the refractive index profile. The step type and W type are preferable because they are simple refractive index profiles and are easy to manufacture. However, the present invention is not limited to this, and can be applied to other refractive index profiles such as a trench type, a segment core type, and a W+side core type.

[0056] Furthermore, the present invention is not limited to the above-mentioned embodiment. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-mentioned embodiment, and various modifications are possible. [Industrial Applicability]

[0057] The optical fiber according to the present invention can be suitably used in the field of optical communications such as datacom and telecom. [Explanation of symbols]

[0058] 1. Optical fiber 1a Core section 1b Clad section 1c Coating section 1ca Primary Coating Layer 1cb secondary coating layer P11, P12, P21, P22 Profiles

Claims

1. A core portion made of silica-based glass; a cladding portion covering the outer periphery of the core portion and made of silica-based glass having a refractive index lower than the maximum refractive index of the core portion; a coating portion covering an outer periphery of the clad portion and including a primary coating layer located on the clad portion side and a secondary coating layer located on the outer periphery side of the primary coating layer; Equipped with The outer diameter of the cladding portion is 75 μm or more and less than 100 μm, The thickness of the primary coating layer is 15 μm or more and 30 μm or less, The mode field diameter at a wavelength of 1310 nm is 8.6 μm or more and 9.2 μm or less, The effective cutoff wavelength is 1260 nm or less; When bent at a diameter of 60 mm, the bending loss at a wavelength of 1550 nm is 0.1 dB / 100 turns or less. A relative refractive index difference Δ1 of the core portion with respect to the cladding portion is 0.33% or more and 0.40% or less, The core portion has a central core portion and a depressed layer formed on an outer periphery of the central core portion, It has a W-shaped refractive index profile, a relative refractive index difference Δ2 of the depressed layer with respect to the cladding portion is −0.20% or more and less than 0%, When the core diameter of the central core portion is 2a and the outer diameter of the depressed layer is 2b, b / a is 5 or less; The outer diameter of the optical fiber including the coating portion is 125 μm or more and 155 μm or less.

1. An optical fiber comprising:

2. The core portion is made of germanium-doped silica glass.

2. The optical fiber according to claim 1 .

3. The zero dispersion wavelength is 1300 nm or more and 1324 nm or less, and the dispersion slope at the zero dispersion wavelength is 0.092 ps / nm ２ / km or less 3. The optical fiber according to claim 1 or 2.

4. The microbending loss at a wavelength of 1550 nm is 20 times or less than the microbending loss at a wavelength of 1550 nm of a standard optical fiber having characteristics conforming to the standard defined in ITU-T G.652 and having a resin coating part with a thickness of 62.5 μm on the outer periphery of the cladding part.

4. The optical fiber according to claim 1, wherein the first and second fibers are arranged in a first direction.

5. The microbend loss is a value measured by the abrasive paper method or the wire mesh method.

5. The optical fiber according to claim 4.

6. The core portion is set so that the effective cutoff wavelength is 1000 nm or more and 1260 nm or less.

6. The optical fiber according to claim 1,

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