Optical fiber

Abstract

An optical fiber (1) is provided with: a core (10) containing at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements; and a cladding layer (20) wrapping the fiber core (10). The optical fiber (1) has a cutoff wavelength of 1260 nm or more and 1460 nm or less. The effective cross-sectional area of the optical fiber at a wavelength of 1450 nm is 75 [mu] m2 or more and 85 [mu] m2 or less. The effective cross-sectional area of the optical fiber at a wavelength of 1550 nm is 83 [mu] m2 or more and 95 [mu] m2 or less. The effective cross-sectional area of the optical fiber at a wavelength of 1625 nm is 100 [mu] m2 or less. The transmission loss of the optical fiber at a wavelength of 1550 nm is 0.160 dB / km or less. The wavelength dispersion of the optical fiber at a wavelength of 1550 nm is 15.0 ps / nm / km or more.

Description

Technical Field

[0001] This application claims the benefit of priority based on Japanese Patent Application No. 2023-002157, filed on January 11, 2023, the entire contents of which are incorporated herein by reference. Background Art

[0002] Optical communication systems using an optical fiber cable having multiple optical fibers as a transmission path are known (eg, Patent Document 1). As the amount of information transmitted in optical communication systems increases, technology for increasing the transmission capacity of optical fiber cables is required.

[0003] As one method of increasing the transmission capacity, increasing the number of optical fibers housed in an optical fiber cable (multi-core transmission) is known. In addition, as another method, widening the wavelength band used for transmission (broadband transmission) is known.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2011-197667 Summary of the Invention

[0007] An optical fiber according to one aspect of the present disclosure comprises: a core comprising at least one element of an alkali element group consisting of an alkali metal element and an alkaline earth metal element; and a cladding surrounding the core, wherein the optical fiber has a cutoff wavelength of 1260 nm to 1460 nm, and an effective cross-sectional area of 75 μm at a wavelength of 1450 nm. 2 Above and 85μm 2 Below, the effective cross-sectional area at a wavelength of 1550nm is 83μm 2 Above and 95μm 2 Below, the effective cross-sectional area at a wavelength of 1625nm is 100μm 2 The transmission loss at a wavelength of 1550 nm is less than 0.160 dB / km, and the chromatic dispersion at a wavelength of 1550 nm is greater than 15.0 ps / nm / km. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 2 is a cross-sectional view showing an optical fiber according to an embodiment.

[0009] Figure 2 It is a diagram showing the appearance of an optical fiber according to an embodiment.

[0010] Figure 3 It is a graph schematically showing the refractive index distribution of the optical fiber according to the embodiment.

[0011] Figure 4 This is a table showing the optical characteristics of optical fibers according to Examples and Comparative Examples.

[0012] Figure 5 Graph schematically showing the refractive index distribution of an optical fiber according to a modified example. DETAILED DESCRIPTION

[0013] [Technical Problems to be Solved by the Present Disclosure]

[0014] When optical fibers are multi-core to increase transmission capacity, the lateral pressure applied to each fiber increases, making it more susceptible to local bending. Such local bending increases the microbend loss (transmission loss) of the fiber. Furthermore, when using shorter wavelength bands for transmission to achieve broadband transmission, it is necessary to shorten the cutoff wavelength of the fiber. Shortening the cutoff wavelength of an optical fiber reduces the confinement strength of light entering the fiber core, increasing transmission loss caused by bending.

[0015] The present disclosure provides an optical fiber that can achieve multi-core and broadband transmission while reducing the increase in transmission loss and increasing the transmission capacity.

[0016] [Effects of the Present Disclosure]

[0017] According to the present disclosure, it is possible to provide an optical fiber that can achieve multi-core and broadband transmission while reducing an increase in transmission loss and increasing transmission capacity.

[0018] [Description of the Implementation Aspects of the Present Disclosure]

[0019] First, implementation aspects of the present disclosure are listed for description.

[0020] (1) An optical fiber according to one aspect of the present disclosure comprises: a core comprising at least one element of an alkali element group consisting of an alkali metal element and an alkaline earth metal element; and a cladding surrounding the core, wherein the optical fiber has a cutoff wavelength of not less than 1260 nm and not more than 1460 nm, and an effective cross-sectional area of 75 μm at a wavelength of 1450 nm. 2 Above and 85μm 2 Below, the effective cross-sectional area at a wavelength of 1550nm is 83μm 2 Above and 95μm 2 Below, the effective cross-sectional area at a wavelength of 1625nm is 100μm 2 The transmission loss at a wavelength of 1550 nm is less than 0.160 dB / km, and the chromatic dispersion at a wavelength of 1550 nm is greater than 15.0 ps / nm / km.

[0021] In this optical fiber, the effective cross-sectional area is of an appropriate size that is neither too large nor too small. For this reason, the bending resistance can be improved while maintaining the transmission capacity of the optical fiber. Therefore, even in the case of multi-core transmission, the occurrence of microbend loss can be reduced. In addition, the above-mentioned optical fiber has a cutoff wavelength of not less than 1260nm and not more than 1460nm. Thus, the S band can be used for transmission, thereby enabling broadband transmission. On the other hand, when the cutoff wavelength is set shorter in order to achieve broadband transmission, the transmission loss caused by bending may increase. As described above, in the above-mentioned optical fiber, the bending resistance can be improved, thereby reducing the increase in transmission loss caused by bending. Therefore, the above-mentioned optical fiber can achieve multi-core transmission and broadband transmission while reducing the increase in transmission loss, and increase the transmission capacity.

[0022] (2) Alternatively, the cladding in (1) may include an inner cladding surrounding the core and an outer cladding surrounding the inner cladding, wherein the relative refractive index difference between the core and the inner cladding is 0.32 or greater. In this case, the large relative refractive index difference between the core and the inner cladding facilitates confinement of light within the core, thereby reducing transmission loss.

[0023] (3) The cladding of (2) above may further include a trench located between the inner cladding and the outer cladding and surrounding the inner cladding, wherein the average refractive index of the trench is smaller than the average refractive index of the inner cladding and the average refractive index of the outer cladding.

[0024] (4) The optical fiber of any one of (1) to (3) above may further include a cladding layer covering the outer periphery of the cladding, the cladding layer including a first layer and a second layer covering the first layer, the Young's modulus of the first layer being 0.15 MPa or more and 0.60 MPa or less. By having the Young's modulus of the first layer being 0.60 MPa or less, the cladding is covered by the relatively soft first layer. For this reason, the lateral pressure characteristics of the optical fiber can be improved, and the occurrence of microbend loss can be reduced. In addition, by having the Young's modulus of the first layer being 0.15 MPa or more, the manufacturing efficiency of the cladding layer can be improved.

[0025] (5) The Young's modulus of the second layer in (4) may be 700 MPa or more and 1600 MPa or less.

[0026] (6) Alternatively, the optical fiber of (4) or (5) may further include a plurality of annular marks formed on the cladding layer, wherein the plurality of annular marks are formed at intervals of 50 mm or more and 1000 mm or less from adjacent annular marks in the axial direction of the optical fiber. In this case, for example, the type of optical fiber can be identified by the annular marks. In addition, by having the annular marks spaced at intervals of 50 mm or more, the increase in lateral pressure on the optical fiber can be reduced, and the occurrence of microbend loss can be reduced. Furthermore, by having the annular marks spaced at intervals of 1000 mm or less, the recognizability of the annular marks can be improved.

[0027] (7) The plurality of annular marks of (6) may be formed continuously in the circumferential direction of the optical fiber.

[0028] (8) In any of the above (4) to (7), the outer diameter of the cladding layer may be 210 μm or less. In this case, it is easy to make the optical fiber multi-core.

[0029] (9) The core of any one of (1) to (8) above may be formed of silica-based glass.

[0030] [Details of the embodiments of the present disclosure]

[0031] Specific examples of the optical fiber disclosed herein are described below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to these examples but is defined by the claims, which are intended to encompass all modifications within the meaning and scope of the claims. In the description of the drawings, identical elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

[0032] Figure 1 2 is a cross-sectional view showing an optical fiber according to an embodiment. Figure 2 This figure shows the appearance of an optical fiber according to an embodiment. An optical fiber 1 according to an embodiment includes a core 10 extending along a central axis 1a, a cladding 20 surrounding the core 10, a coating 30 covering the outer periphery of the cladding 20, and a plurality of annular marks 40 formed on the coating 30. As an example, a plurality of optical fibers 1 are housed in a single optical fiber cable. The optical fibers 1 can be used, for example, for long-distance, high-capacity transmission.

[0033] The core 10 is formed, for example, of silica-based glass having silica glass as its main component. The silica-based glass contains 60% or more silicon dioxide. The core 10 contains at least one element from the alkali element group consisting of alkali metal elements and alkaline earth metal elements. Examples of alkali metal elements include lithium (Li), sodium (Na), potassium (K), and rubidium (Rb). Examples of alkaline earth metal elements include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). The core 10 does not contain germanium (Ge). The core 10 does not contain germanium, meaning that the core 10 does not substantially contain germanium. Specifically, the mass fraction of germanium in the core 10 is 500 ppm or less.

[0034] The cladding 20 includes an inner cladding 21 surrounding the core 10 and an outer cladding 22 surrounding the inner cladding 21. The inner cladding 21 and the outer cladding 22 are formed of silica-based glass primarily composed of silica glass. The silica-based glass contains at least 60% silicon dioxide. Fluorine (F) may be added to the inner cladding 21 and the outer cladding 22.

[0035] The covering layer 30 includes a primary resin layer 31 (first layer), a secondary resin layer 32 (second layer), and a colored layer 33. The primary resin layer 31 is in close contact with the outer peripheral surface of the outer covering layer 22 and surrounds the outer covering layer 22. The secondary resin layer 32 is in close contact with the outer peripheral surface of the primary resin layer 31 and surrounds the primary resin layer 31. The primary resin layer 31 and the secondary resin layer 32 can be formed of, for example, a resin that cures by ultraviolet irradiation (ultraviolet curing resin).

[0036] The Young's modulus of the primary resin layer 31 is smaller than that of the secondary resin layer 32. The Young's modulus of the primary resin layer 31 is, for example, 0.15 MPa to 0.60 MPa, while the Young's modulus of the secondary resin layer 32 is, for example, 700 MPa to 1600 MPa.

[0037] The Young's modulus of the primary resin layer 31 is measured, for example, by the pullout modulus (POM) method at 23°C. Specifically, first, a first metal cylinder and a second metal cylinder are bonded one by one at two locations separated by a predetermined interval in the optical fiber 1. The coating 30 between the first metal cylinder and the second metal cylinder is removed to expose the coating 20. The optical fiber 1 is cut on the outside of the first metal cylinder, that is, on the side where the second metal cylinder is not attached. Next, the first metal cylinder is fixed, and the second metal cylinder is slowly moved away from the fixed first metal cylinder. The length of the second metal cylinder is set to Lc [mm], the movement amount of the chuck is set to Z [mm], the outer diameter of the primary resin layer 31 is set to Dp [μm], the outer diameter of the cladding 20 is set to Df [μm], the Poisson's ratio of the primary resin layer 31 is set to ν, and the load when the chuck device moves is set to W [N]. The Young's modulus [MPa] of the primary resin layer 31 is measured according to the following formula.

[0038] Young's modulus [MPa] = ((1 + ν)W / πLcZ) × ln(Dp / Df)

[0039] At this time, it is considered that the cladding layer 20 , the secondary resin layer 32 , and the adhesive portion do not deform, and the primary resin layer 31 deforms to move the second metal cylinder.

[0040] For example, a tubular cladding layer 30 (length: 50 mm or more) obtained by extracting the core 10 and the cladding 20 from the optical fiber 1 is subjected to a tensile test (distance between marking lines: 25 mm) in an environment of 23±2°C and 50±10% RH, and the Young's modulus of the secondary resin layer 32 is calculated based on the 2.5% secant value.

[0041] The colored layer 33 adheres closely to the outer circumference of the secondary resin layer 32 and encapsulates the secondary resin layer 32. The colored layer 33 can be formed, for example, from a UV-curable resin containing a pigment. In this embodiment, the outer diameter of the colored layer 33 is 210 μm or less. In this embodiment, the outer diameter of the colored layer 33 is equal to the outer diameter of the covering layer 30. That is, the outer diameter of the covering layer 30 is 210 μm or less.

[0042] A plurality of ring marks 40 are formed on the outer peripheral surface of the colored layer 33. The ring marks 40 function as identification marks indicating the type of the optical fiber 1. The ring marks 40 can be formed, for example, by using an inkjet method for ejecting ink. Figure 2As shown, a plurality of annular marks 40 are formed in the axial direction of the optical fiber, with intervals L between adjacent annular marks. In this embodiment, the intervals L are greater than 50 mm and less than 1000 mm. Each annular mark 40 is formed continuously in the circumferential direction of the optical fiber 1. In other words, when the optical fiber 1 is viewed in a cross-section perpendicular to the central axis 1a, each annular mark 40 is formed in a ring shape.

[0043] Optical fiber 1 has a cutoff wavelength of 1260 nm to 1460 nm. In this case, single-mode optical communication is possible in the S-band (1460 nm to 1530 nm), C-band (1530 nm to 1565 nm), and L-band (1565 nm to 1625 nm). Common general-purpose optical fibers have a cutoff wavelength shorter than 1260 nm. Therefore, optical fiber 1 has a larger cutoff wavelength than common optical fibers.

[0044] The effective cross-sectional area of optical fiber 1 at a wavelength of 1450 nm is 75 μm 2 Above and 85μm 2 The effective cross-sectional area of the optical fiber 1 at a wavelength of 1550 nm is 83 μm 2 Above and 95μm 2 The effective cross-sectional area of the optical fiber 1 at a wavelength of 1625 nm is 100 μm 2 the following.

[0045] The mode field diameter (MFD) of the optical fiber 1 at a wavelength of 1450 nm is 9.9 μm to 10.0 μm. The MFD of the optical fiber 1 at a wavelength of 1550 nm is 10.3 μm to 10.6 μm. The MFD of the optical fiber 1 at a wavelength of 1625 nm is 10.6 μm to 11.1 μm.

[0046] The transmission loss of optical fiber 1 at a wavelength of 1450 nm is greater than or equal to 0.195 dB / km and less than or equal to 0.202 dB / km. The transmission loss of optical fiber 1 at a wavelength of 1550 nm is greater than or equal to 0.154 dB / km and less than or equal to 0.160 dB / km. The transmission loss of optical fiber 1 at a wavelength of 1625 nm is greater than or equal to 0.175 dB / km and less than or equal to 0.180 dB / km. The chromatic dispersion of optical fiber 1 at a wavelength of 1550 nm is greater than or equal to 15.0 ps / nm / km and less than or equal to 19.8 ps / nm / km. By setting the chromatic dispersion of optical fiber 1 at a wavelength of 1550 nm to greater than or equal to 15.0 ps / nm / km, the effective cross-sectional area of optical fiber 1 can be increased, and low nonlinearity can be achieved.

[0047] Figure 3 : is a graph schematically showing the refractive index distribution of the optical fiber involved in the embodiment. The horizontal axis represents the radial position of the optical fiber 1, and the vertical axis represents the refractive index of the optical fiber 1. Figure 3 , the refractive indices of the core 10 and cladding 20 (inner cladding 21 and outer cladding 22) are shown. The radial position r of the central axis 1a of the optical fiber 1 is 0. If the radius of the core 10 is ra (diameter 2ra) and the radius of the inner cladding 21 is rb (diameter 2rb), the ratio rb / ra of the radius rb of the inner cladding to the radius ra of the core 10 is 3.5 or more and 5 or less.

[0048] The core 10 has an average refractive index n1, the inner cladding 21 has an average refractive index n2, and the outer cladding 22 has an average refractive index n3. The average refractive index n1 of the core 10 is greater than the average refractive index n2 of the inner cladding 21 and the average refractive index n3 of the outer cladding 22. The average refractive index n3 of the outer cladding 22 is greater than the average refractive index n2 of the inner cladding 21. That is, in this example, the relationship of average refractive index n1 > average refractive index n3 > average refractive index n2 holds.

[0049] The relative refractive index difference Δ1 of the core 10 with respect to the inner cladding 21 is given by (n1 2 -n2 2 ) / 2n1 2 The relative refractive index difference Δ1 of the core 10 with respect to the inner cladding 21 is 0.32% or more and 0.4% or less. The relative refractive index difference Δ2 of the outer cladding 22 with respect to the inner cladding 21 is given by (n3 2 -n2 2 ) / 2n3 2 ×100[%] Definition: The relative refractive index difference Δ2 of the outer cladding 22 with respect to the inner cladding 21 is 0.01% or more and 0.1% or less.

[0050] As described above, in the optical fiber 1, the effective cross-sectional area at a wavelength of 1450 nm is 75 μm 2 Above and 85μm 2 Below, the effective cross-sectional area at a wavelength of 1550nm is 83μm 2 Above and 95μm 2 Below, the effective cross-sectional area at a wavelength of 1625nm is 100μm 2Below. In this way, the effective cross-sectional area of the optical fiber 1 is of an appropriate size that is neither too large nor too small. For this reason, it is possible to improve the bending resistance while maintaining the transmission capacity of the optical fiber 1. Therefore, even in the case of multi-core, the occurrence of microbending loss can be reduced. In addition, the optical fiber 1 has a cutoff wavelength of not less than 1260nm and not more than 1460nm. Thus, the S band can be used for transmission, thereby enabling broadband transmission. On the other hand, when the cutoff wavelength is set shorter in order to achieve broadband transmission, the transmission loss caused by bending may increase, but as described above, in the optical fiber 1, the bending resistance can be improved, thereby reducing the increase in transmission loss caused by bending. Therefore, the optical fiber 1 can achieve multi-core and broadband transmission while reducing the increase in transmission loss, and increase the transmission capacity.

[0051] Generally speaking, in order to improve the signal-to-noise ratio (SN ratio), optical fibers used for long-distance transmission are required to have low loss and low nonlinearity. In order to reduce the nonlinearity of the optical fiber, it is effective to increase the effective cross-sectional area of the optical fiber. On the other hand, it is known that the microbend characteristics of optical fibers with large effective cross-sectional areas deteriorate. In addition, in long-distance transmission, Raman amplification is sometimes applied in combination with amplification by an erbium-doped fiber amplifier (EDFA). It is also known that if the effective cross-sectional area becomes larger, the Raman amplification efficiency decreases. In contrast, as described above, the effective cross-sectional area of the optical fiber 1 is of an appropriate size that is not too large, so it is possible to reduce the reduction in Raman amplification efficiency while maintaining the transmission characteristics of the optical fiber 1.

[0052] Furthermore, while using a cladding with improved microbend loss characteristics is effective in reducing increases in transmission loss, such claddings are generally expensive, leading to increased production costs for the optical fiber. In contrast, the optical fiber 1 can reduce the occurrence of microbend loss without increasing production costs for the optical fiber.

[0053] The above-mentioned broadband transmission will be described in more detail. As an example, when the C-band is used for transmission, in order to ensure single-mode operation, the cutoff wavelength must be set to be less than the cutoff wavelength of 1530nm (the shortest wavelength of the C-band) specified in the ITU-T G.650.1 standard. Furthermore, when the S-band and L-band are used in addition to the C-band to expand transmission capacity, the cutoff wavelength must be set to be less than 1460nm, the shortest wavelength of the S-band. In other words, the cutoff wavelength must be set shorter. However, when the cutoff wavelength is set shorter, the transmission loss caused by bending in the L-band may increase. In contrast, in the optical fiber 1, as described above, such an increase in transmission loss caused by bending can be reduced.

[0054] The cladding 20 includes an inner cladding 21 surrounding the core 10 and an outer cladding 22 surrounding the inner cladding 21. The relative refractive index difference between the core 10 and the inner cladding 21 is 0.32% or greater. This large relative refractive index difference between the core 10 and the inner cladding 21 facilitates confinement of light within the core 10, thereby reducing transmission loss.

[0055] To reduce transmission loss, a silica core structure that does not contain germanium can also be used. In such a structure, fluorine (F) is sometimes added to the cladding to create a refractive index difference between the core and the cladding. Rayleigh scattering loss increases in the area where fluorine is added. Therefore, if the confinement of light entering the core becomes weaker, the influence of the cladding becomes stronger, and scattering loss increases. In contrast, in optical fiber 1, as described above, light is easily confined to the core 10, thereby reducing such increases in Rayleigh scattering loss.

[0056] The optical fiber 1 includes a cladding layer 30 that covers the outer periphery of the cladding 20. The cladding 30 includes a primary resin layer 31 and a secondary resin layer 32 that surrounds the primary resin layer 31. The Young's modulus of the primary resin layer 31 is 0.15 MPa or greater and 0.60 MPa or less. The Young's modulus of the primary resin layer 31 is 0.60 MPa or less, allowing the cladding 20 to be covered by the relatively soft primary resin layer 31. This improves the lateral pressure characteristics of the optical fiber 1 and reduces the occurrence of microbend losses. Furthermore, the Young's modulus of the primary resin layer 31 is 0.15 MPa or greater, which improves the manufacturing efficiency of the cladding 30.

[0057] The optical fiber 1 includes multiple annular marks 40 formed on the cladding 30. Each of the multiple annular marks 40 is spaced apart from adjacent ones in the axial direction of the optical fiber 1 by intervals of at least 50 mm and no more than 1000 mm. Therefore, for example, the type of optical fiber 1 can be identified by the annular marks 40. Furthermore, in the optical fiber 1, the spacing of the multiple annular marks 40 by at least 50 mm can reduce the increase in lateral pressure loss generated in the optical fiber 1, thereby reducing the occurrence of microbend losses. Specifically, the outer diameter of the optical fiber 1 increases in the portion where the annular marks 40 are formed. Therefore, when the optical fiber 1 is housed in an optical fiber cable, the portion where the annular marks 40 are formed may experience greater lateral pressure than other portions. In the optical fiber 1, the multiple annular marks 40 are formed with appropriate spacing, so that no more annular marks 40 are formed than necessary. Therefore, the increase in lateral pressure loss generated in the optical fiber 1 can be reduced. Furthermore, the spacing of the multiple annular marks 40 in the optical fiber 1 is no more than 1000 mm. Therefore, the identification of the annular marks 40 can be improved.

[0058] The outer diameter of the cladding layer 30 is 210 μm or less, thereby facilitating the multi-core formation of the optical fiber 1 .

[0059] Example

[0060] Hereinafter, the results of evaluation tests using the examples and comparative examples according to the present disclosure will be shown to further explain the present disclosure in detail. However, the present disclosure is not limited to these examples.

[0061] Figure 4 This is a table showing the optical characteristics of optical fibers according to Examples and Comparative Examples. Figure 4 Experimental Examples 1 to 9 shown in the table are examples, and Experimental Examples 10 and 11 are comparative examples. Figure 4 The table shows the relative refractive index difference Δ1 of the core with respect to the inner cladding, the ratio rb / ra of the radius rb of the inner cladding with respect to the radius ra of the core, the relative refractive index difference Δ2 of the outer cladding with respect to the inner cladding, the MFD of the optical fiber, the effective cross-sectional area Aeff, the wavelength dispersion Disp, the cut-off wavelength λcc and the transmission loss Loss.

[0062] The optical fibers of Experimental Examples 1 to 9 correspond to the optical fiber 1 involved in the embodiment. Figure 4 As shown, in the optical fibers involved in Experimental Examples 1 to 9, the effective cross-sectional area Aeff at a wavelength of 1450 nm is 75 μm 2 Above and 85μm 2 Below, the effective cross-sectional area Aeff at a wavelength of 1550nm is 83μm 2 Above and 95μm 2 Below, the effective cross-sectional area Aeff at a wavelength of 1625nm is 100μm 2 As described above, the effective cross-sectional area of the optical fibers of Experimental Examples 1 to 9 is appropriately sized, thereby improving the bending resistance while maintaining the transmission capacity of the optical fibers. Furthermore, the transmission loss of the optical fibers of Experimental Examples 1 to 9 at a wavelength of 1550 nm is reduced to less than 0.160 dB / km. Therefore, the optical fibers of Experimental Examples 1 to 9 can achieve multi-core and broadband transmission while reducing the increase in transmission loss, thereby increasing the transmission capacity.

[0063] In contrast, the transmission loss at a wavelength of 1550 nm in the optical fiber of Experimental Example 10 was 0.162 dB / km, exceeding 0.160 dB / km. Therefore, the optical fiber of Experimental Example 10 could not achieve multi-core and broadband transmission while reducing the increase in transmission loss.

[0064] In addition, in the optical fiber involved in Experimental Example 11, the effective cross-sectional area Aeff at a wavelength of 1450 nm is 87 μm 2 , than 85μm 2The optical fiber of Experimental Example 11 exhibits a transmission loss of 0.164 dB / km at a wavelength of 1550 nm, exceeding 0.160 dB / km. Therefore, the optical fiber of Experimental Example 11 cannot achieve multi-core fiberization and broadband transmission while minimizing the increase in transmission loss.

[0065] (Variation)

[0066] Reference Figure 5 Modifications of the optical fiber 1 will be described. Figure 5 This graph schematically illustrates the refractive index profile of an optical fiber according to a modified example. In this modified example, a refractive index dip (Dip) is generated at the center of core 10. The average refractive index n1 of core 10 in this modified example is the average refractive index along the radial direction of optical fiber 1, including the Dip portion.

[0067] According to the optical fiber 1 of this modification, the MFD can be reduced while maintaining the effective cross-sectional area of the optical fiber 1 by generating a dip in the refractive index at the center of the core 10. This can reduce connection loss compared to conventional optical fibers with relatively small MFD.

[0068] Although the embodiments have been described above, the present disclosure is not necessarily limited to the above embodiments and modifications, and various modifications can be made without departing from the spirit and scope of the present disclosure. The above embodiments and modifications can also be appropriately combined.

[0069] For example, the Young's modulus of the primary resin layer 31 may be greater than or equal to the Young's modulus of the secondary resin layer 32. The Young's modulus of the primary resin layer 31 may be, for example, less than 0.15 MPa or greater than 0.60 MPa. The Young's modulus of the secondary resin layer 32 may be, for example, less than 700 MPa or greater than 1600 MPa.

[0070] The number of layers of the coating layer 30 is not limited. For example, the coating layer 30 may have only one or two layers, or may have four or more layers. The coating layer 30 may not have the colored layer 33. The outer diameter of the coating layer 30 may be larger than 210 μm.

[0071] The interval L between the plurality of ring marks 40 may be smaller than 50 mm or larger than 1000 mm. Each ring mark 40 may be formed discontinuously in the circumferential direction of the optical fiber 1. The plurality of ring marks 40 may be formed inside the cladding layer 30 (for example, inside the colored layer 33). As an example, the ring mark 40 may be formed between the secondary resin layer 32 and the colored layer 33, or between the primary resin layer 31 and the secondary resin layer 32. In this case, the layer located further outside than the ring mark 40 may be formed of a material (a material that is transmissive to visible light) that allows the ring mark 40 to be visually confirmed from the outside. Transmissive to visible light means that the transmittance of light with a wavelength of greater than 400 nm and less than 750 nm is greater than 20%.

[0072] The MFD of optical fiber 1 at a wavelength of 1450 nm can be smaller than 9.9 μm or larger than 10.0 μm. The MFD of optical fiber 1 at a wavelength of 1550 nm can be smaller than 10.3 μm or larger than 10.6 μm. The MFD of optical fiber 1 at a wavelength of 1625 nm can be smaller than 10.6 μm or larger than 11.1 μm.

[0073] The transmission loss of optical fiber 1 at a wavelength of 1450 nm can be less than 0.195 dB / km or greater than 0.202 dB / km. The transmission loss of optical fiber 1 at a wavelength of 1550 nm can be less than 0.154 dB / km. The transmission loss of optical fiber 1 at a wavelength of 1625 nm can be less than 0.175 dB / km or greater than 0.180 dB / km. The chromatic dispersion of optical fiber 1 at a wavelength of 1550 nm can be greater than 19.8 ps / nm / km.

[0074] The ratio rb / ra of the radius rb of the inner cladding 21 to the radius ra of the core 10 may be smaller than 3.5 or larger than 5. The relative refractive index difference Δ1 of the core 10 with respect to the inner cladding 21 may be larger than 0.4%. The relative refractive index difference Δ2 of the outer cladding 22 with respect to the inner cladding 21 may be smaller than 0.01% or larger than 0.1%.

[0075] The cladding 20 may further include a trench surrounding the inner cladding 21. The trench may be located between the inner cladding 21 and the outer cladding 22 and contact the outer circumference of the inner cladding 21. The trench may be formed of silica-based glass primarily composed of silica glass. The silica-based glass contains at least 60% silicon dioxide. The average refractive index of the trench is lower than the average refractive index n2 of the inner cladding 21 and the average refractive index n3 of the outer cladding 22.

[0076] The above-mentioned optical fiber characteristics can be measured by the following methods. The elements contained in the core can be detected using EPMA (Electron Probe Micro Analyzer). The cutoff wavelength, effective cross-sectional area, transmission loss and wavelength dispersion can be measured by the method described in ITU-TG650.1. The refractive index can be measured by the method described in AD Yablon, "Multi-Wavelength Optical Fiber Refractive Index Profiling by Spatially Resolved Fourier Transform Spectroscopy", J. Lightwave Technol., vol. 28, pp. 360-364 (2010). The outer diameter of the cladding can be measured by the method described in IEC60793-1-21, for example.

[0077] Description of Reference Numerals

[0078] 1. Fiber Optic

[0079] 1a Central axis

[0080] 10 fiber core

[0081] 20 cladding

[0082] 21 inner cladding

[0083] 22 outer layer

[0084] 30 cladding layer

[0085] 31 primary resin layer (first layer)

[0086] 32 Secondary resin layer (second layer)

[0087] 33 Coloring Layers

[0088] 40 ring marks.

Claims

1. An optical fiber comprising: a core comprising at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements; and a cladding, surrounding the core, The optical fiber has a cutoff wavelength of 1260 nm or more and 1460 nm or less, The effective cross-sectional area at a wavelength of 1450nm is 75μm 2 Above and 85μm 2 the following, The effective cross-sectional area at a wavelength of 1550nm is 83μm 2 Above and 95μm 2 the following, The effective cross-sectional area at a wavelength of 1625 nm is 100 μm 2 the following, The transmission loss at a wavelength of 1550nm is less than 0.160dB / km. The wavelength dispersion at a wavelength of 1550 nm is 15.0 ps / nm / km or more.

2. The optical fiber according to claim 1, wherein The cladding comprises an inner cladding surrounding the core and an outer cladding surrounding the inner cladding, The relative refractive index difference of the core with respect to the inner cladding is 0.32% or more.

3. The optical fiber according to claim 2, wherein The cladding further comprises a groove located between the inner cladding and the outer cladding and wrapping the inner cladding. An average refractive index of the trench is smaller than an average refractive index of the inner cladding and an average refractive index of the outer cladding.

4. The optical fiber according to any one of claims 1 to 3, wherein The optical fiber further comprises a cladding layer covering the outer periphery of the cladding layer. The covering layer comprises a first layer and a second layer wrapping the first layer, The Young's modulus of the first layer is 0.15 MPa or more and 0.60 MPa or less.

5. The optical fiber according to claim 4, wherein The Young's modulus of the second layer is 700 MPa or more and 1600 MPa or less.

6. The optical fiber according to claim 4 or 5, wherein: The optical fiber further comprises a plurality of annular marks formed on the cladding layer. The plurality of ring marks are formed so as to be spaced apart from adjacent ring marks by an interval of 50 mm to 1000 mm in the axial direction of the optical fiber.

7. The optical fiber according to claim 6, wherein The plurality of annular marks are respectively formed continuously in the circumferential direction of the optical fiber.

8. The optical fiber according to any one of claims 4 to 7, wherein The outer diameter of the coating layer is 210 μm or less.

9. The optical fiber according to any one of claims 1 to 8, wherein The core is formed of silica-based glass.

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