Optical fibers and optical cables

Abstract

The present invention relates to an optical fiber or the like for an optical transceiver that is applicable to a short wavelength band of 850 nm or more and 1060 nm or less while maintaining compatibility with an existing SMF. An optical fiber according to one embodiment has a core portion (61), a cladding (62), and resin coating layers (63, 64), and has a mode field diameter of 8.2 μm or more and 9.6 μm or less at a wavelength of 1310 nm, an optical cable cut-off wavelength of the LP11 mode of 1060 nm or more and 1260 nm or less, and an optical cable cut-off wavelength of the LP02 mode of 1060 nm or less.

Description

Technical Field

[0001] The present invention relates to optical fibers and optical cables.

[0002] This application claims the priority of Japanese Patent Application No. 2019-193666 filed on October 24, 2019, and the content thereof is incorporated into this specification by reference in its entirety. Background Art

[0003] In an optical communication system composed of a combination of an optical cable and an optical transceiver, there is a problem of maximizing the ratio of the system transmission performance to the cost required to construct the system. Generally, in long-haul transmission over about 100 km or more, an EDFA (Erbium Doped Fiber Amplifier) with excellent cost-effectiveness is adopted due to the necessity of an optical amplifier. As a transmission medium, an optical cable composed of multiple single-mode fibers (Single Mode Fiber, hereinafter referred to as "SMF") for a wavelength band of 1530 nm or more and 1625 nm or less is used. On the other hand, the cost required for manufacturing and laying an optical cable with a long transmission distance is also high. Currently, a high-performance and expensive coherent optical transceiver is usually adopted. In contrast, in short-haul transmission of less than 100 km, especially less than 10 km, a lower-cost optical transceiver is preferably used, and an optical cable suitable for the lower-cost optical transceiver is sometimes used. The most typical example is a combination of an optical transceiver using a multimode VCSEL (Vertical Cavity Surface Emitting Laser) and an optical cable composed of multiple multimode fibers (Multimode Fiber, hereinafter referred to as "MMF"). Such an optical communication system is particularly suitable for extremely short-distance transmission of less than 100 m due to the excellent low cost of the optical transceiver and optical connection.

[0004] In addition, Patent Document 1 discloses an optical fiber that can operate in single mode in short wavelength bands such as 850 nm, 980 nm, and 1060 nm bands, and has a large effective area of 30 μm 2 or more and 110 μm 2 or less in these short wavelength bands. The above optical characteristics (effective cross-sectional area in the short wavelength band) are achieved, for example, by a core having a radius of 3.0 μm or more and 6.0 μm or less and a relative refractive index difference of 0.12% or more and 0.35% or less, and a cladding having a relative refractive index difference of -0.1% or less and 20%·μm 2It is realized by an optical fiber with a depressed cladding having the above-mentioned groove volume. Such an optical fiber is suitable for combination with an optical transceiver using a single-mode VCSEL in a wavelength band of 850 nm or more and 1060 nm or less. Since the optical transceiver using a single-mode VCSEL is inexpensive and capable of high-speed transmission, it is expected to improve the cost-effectiveness related to building a system.

[0005] Prior art documents

[0006] Patent documents

[0007] Patent Document 1: US Patent No. 9,995,873 Specification;

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2018-45028. Summary of the invention

[0009] The optical fiber according to an embodiment of the present invention has a core, a cladding, and a resin coating layer. The core extends along the optical fiber axis (central axis) and is formed of silica glass. The cladding is provided on the outer peripheral surface of the core, is formed of silica glass, and has a maximum refractive index lower than the maximum refractive index of the core. The resin coating layer is provided on the outer peripheral surface of the cladding. The optical fiber having such a structure has a mode field diameter of 8.2 μm or more and 9.6 μm or less at a wavelength of 1310 nm, an optical cable cut-off wavelength of the LP11 mode of 1060 nm or more and 1260 nm or less, and an optical cable cut-off wavelength of the LP02 mode of 1060 nm or less. Brief description of the drawings

[0010] Figure 1 It is a diagram showing an example of the structure of an optical communication system using an optical fiber cable to which an embodiment of the present invention can be applied.

[0011] Figure 2 It is a diagram showing an example of the structure of an optical fiber according to an embodiment of the present invention.

[0012] Figure 3A It is the refractive index distribution of an example of the optical fiber according to an embodiment of the present invention and an optical fiber of a comparative example, respectively.

[0013] Figure 3B It is a graph showing the relationship between the exponent α and the modal dispersion for a plurality of samples of the optical fiber according to an embodiment of the present invention and a plurality of comparative examples, respectively. Detailed description of the invention

[0014] Problems to be solved by the invention

[0015] The present inventors have studied the above-mentioned prior art and found the following problems. That is, when the optical fiber of Patent Document 1 is used in the existing long-distance transmission in the wavelength band above 1310 nm and below 1625 nm, due to high bending loss or high connection loss caused by a small mode field diameter, it is not compatible with the existing single-mode optical fiber. This is because the optical fiber of Patent Document 1 requires single-mode operation in short wavelength bands such as 850 nm band, 980 nm band or 1060 nm band. Technically, by sequentially arranging an inner cladding, a trench layer and an outer cladding outside the core, and reducing the refractive index of the trench layer, the bending loss can be reduced. However, the manufacturing of such a multi-layer cladding structure has the problem of low productivity.

[0016] Furthermore, when laying an optical cable containing the optical fiber of Patent Document 1, the cost benefit brought by a high-performance optical transceiver for the wavelength band above 850 nm and below 1060 nm can be enjoyed just after laying. However, the technological development of optical transceivers for the wavelength band above 1310 nm and below 1625 nm in the future also needs to be considered. That is, it can be seen that when there is a need to combine the optical fiber of Patent Document 1 with the optical transceiver for the wavelength band above 1310 nm and below 1625 nm, the transmission performance of such a combination is significantly worse than the combination of the optical transceiver for the wavelength band above 1310 nm and below 1625 nm and the optical cable containing the existing SMF. Re-laying the optical cable is a solution, but in this case, there are problems such as an increase in the number of cores (the number of optical fibers accommodated in the optical cable) and an increase in the transmission distance, and the cost of re-laying the optical cable also increases.

[0017] The present invention has been completed to solve the above problems, and an object thereof is to provide an optical fiber and an optical cable that can be applied to an optical transceiver for short wavelength bands above 850 nm and below 1060 nm while maintaining compatibility with the existing SMF.

[0018] Advantages of the Invention

[0019] The optical fiber and the optical cable according to the present invention can construct an optical transmission line that can be applied to an inexpensive optical transceiver for the wavelength band above 850 nm and below 1060 nm while maintaining compatibility with the existing SMF (the existing long-distance transmission medium in the wavelength band above 1310 nm and below 1625 nm).

[0020] [Description of Embodiments of the Present Invention]

[0021] First, the contents of the embodiments of the present invention will be separately listed and described.

[0022] (1) As an aspect of the optical fiber according to an embodiment of the present invention, it has a core, a cladding, and a resin coating layer. The core extends along the optical fiber axis (central axis) and is formed of silica glass. The cladding is provided on the outer peripheral surface of the core, is formed of silica glass, and has a maximum refractive index lower than the maximum refractive index of the core. The resin coating layer is provided on the outer peripheral surface of the cladding. The optical fiber having such a structure has a mode field diameter of 8.2 μm or more and 9.6 μm or less at a wavelength of 1310 nm, a cable cut-off wavelength of the LP11 mode of 1060 nm or more and 1260 nm or less, and a cable cut-off wavelength of the LP02 mode of 1060 nm or less. In addition, in this specification, the relative refractive index difference Δ of a certain medium (refractive index n) based on pure silica glass (refractive index n0) is given by the following formula:

[0023] Δ=(n / n0)-1.

[0024] In addition, the cut-off wavelength of a specified mode is defined as the minimum value of the wavelength at which the transmission loss of the mode is 19.3 dB or more in an optical fiber of a specified length having a specified bending state. In the case of the cable cut-off wavelength, it is measured in a state where one turn of a bend with a diameter of 80 mm is given to each of the two end portions of 1 m in length in a 22 m optical fiber and the middle portion of 20 m in length is wound into a diameter of 280 mm.

[0025] This optical fiber operates in single mode at a wavelength of 1260 nm or more, operates in two LP modes of LP01 and LP11 at a wavelength of 1060 nm or more and 1260 nm or less, and operates in three or more LP modes including LP01, LP02, and LP11 at a wavelength of 1060 nm or less. The LP11 mode is an odd mode, and the LP01 mode is an even mode. Therefore, by suppressing the axial offset and angular offset at the connection point, the mode coupling between the LP01 mode and the LP11 mode can be suppressed. In contrast, the LP02 mode and the LP11 mode are both even modes. Therefore, even if the axial offset and angular offset are suppressed, mode coupling between the LP01 mode and the LP02 mode will occur due to deviations in the core diameter and NA. Therefore, by suppressing the axial offset and angular offset at the connection point, the lower limit wavelength of operating in single mode can be effectively extended from 1260 nm to 1060 nm.

[0026] In this optical fiber, the eccentricity of the center of the core from the center of the cladding is preferably 0..5 μm or less, more preferably 0.3 μm or less. In addition, the non-circularity of the cladding is preferably 1.0% or less, more preferably 0.7% or less. Thus, by suppressing the axial offset and angular offset at the connection point, the lower limit wavelength of operating in single mode can be effectively extended from 1260 nm to 1060 nm.

[0027] With this structure, the optical fiber can be used as a transmission medium that maintains compatibility with existing single-mode fibers (SMFs) for long-distance transmission in the wavelength band above 1310 nm and below 1625 nm while also being applicable to high-speed transmission in the short wavelength band around 1060 nm, enabling signal transmission over a wider wavelength band.

[0028] (2) As an aspect of the optical fiber according to an embodiment of the present invention, the cut-off wavelength of the LP02 mode of the optical cable can be 980 nm or less. In this case, as a transmission medium that maintains the above-mentioned compatibility with existing SMFs while also being applicable to high-speed transmission in the short wavelength band around 980 nm, signal transmission over a wider wavelength band can also be achieved.

[0029] In this optical fiber, the eccentricity of the core center from the cladding center is preferably 0.5 μm or less, more preferably 0.3 μm or less. In addition, the non-circularity of the cladding is preferably 1.0% or less, more preferably 0.7% or less. Thus, by suppressing the axial offset and angular offset at the connection point, the lower limit wavelength for operating in single mode can be effectively extended from 1260 nm to 980 nm.

[0030] (3) As an aspect of the optical fiber according to an embodiment of the present invention, the cut-off wavelength of the LP02 mode of the optical cable can be 850 nm or less. In this case, as a transmission medium that maintains the above-mentioned compatibility with existing SMFs while also being applicable to high-speed transmission in the short wavelength band around 850 nm, signal transmission over a wider wavelength band can also be achieved.

[0031] In this optical fiber, the eccentricity of the core center from the cladding center is preferably 0.5 μm or less, more preferably 0.3 μm or less. In addition, the non-circularity of the cladding is preferably 1.0% or less, more preferably 0.7% or less. Thus, by suppressing the axial offset and angular offset at the connection point, the lower limit wavelength for operating in single mode can be effectively extended from 1260 nm to 850 nm.

[0032] (4) As an aspect of the optical fiber according to an embodiment of the present invention, the bending loss at a diameter of 15 mm is preferably 1 dB / turn or less at a wavelength of 1625 nm. In addition, the cladding may include an inner cladding provided on the outer peripheral surface of the core and an outer cladding provided on the outer peripheral surface of the inner cladding, and the outer cladding has a relative refractive index difference higher than that of the inner cladding. In this case, the optical fiber can be applicable to high-speed transmission in the short wavelength band above 850 nm and below 1060 nm while also being applicable to high spatial density and high-speed transmission at a wavelength of 1625 nm.

[0033] (5) As an aspect of the optical fiber according to an embodiment of the present invention, preferably, the mode dispersion between the LP01 mode and the LP11 mode is 1000 ps / km or less in the wavelength range of 850 nm or more and 1060 nm or less. In this case, even when the LP11 mode is excited due to a low-quality connection or the like in the wide wavelength range of 850 nm or more and 1060 nm or less, it is possible to effectively suppress the generation of noise (noise with respect to the LP01 mode) caused by the LP11 mode, and stable high-speed transmission can be achieved.

[0034] (6) As an aspect of the optical fiber according to an embodiment of the present invention, preferably, the mode dispersion between the LP01 mode and the LP11 mode is 300 ps / km or less at at least one wavelength in the wavelength range of 850 nm or more and 1060 nm or less. Similarly in this case, even when the LP11 mode is excited due to a low-quality connection or the like, it is possible to effectively suppress the generation of noise caused by the LP11 mode, and as a result, stable high-speed transmission can be achieved.

[0035] (7) As an aspect of the optical fiber according to an embodiment of the present invention, preferably, the value 3σ defined by the standard deviation σ of the outer diameter of the cladding that varies along the optical fiber axis (outer diameter variation) is in the range of 0.1 μm or more and 0.5 μm or less. Here, the standard deviation σ is represented by the cladding outer diameter d(z) at the position z in the optical fiber axis direction. When the average values of d(z) and d2(z) in the range of a length L of 100 km or more are represented by <d> and <d2>, respectively, the standard deviation σ is defined by σ = {<d2> - <d>2}. Further preferably, the value 3σ is in the range of 0.2 μm or more and 0.5 μm or less. By setting the upper limit of 3σ of the outer diameter variation to 0.5 μm or less, it is possible to suppress mode coupling caused by structural variations of the optical fiber to a low level. On the other hand, when the lower limit of 3σ is 0.1 μm or more, a long cooling time can be ensured, and when the lower limit of 3σ is 0.2 μm or more, an even longer cooling time can be ensured, so that the transmission loss can be suppressed to a low level. Therefore, by setting 3σ within the above range, long-distance and high-speed transmission can be achieved.

[0036] Furthermore, preferably, the outer diameter variation of the optical fiber caused by the frequency component with a period of 0.1 mm or more and 100 mm or less is in the range of 0.1 μm or more and 0.5 μm or less. In most high-order modes, the reciprocal of the propagation constant difference from the LP01 mode is 0.1 mm or more and 100 mm or less. Therefore, by making the outer diameter variation caused by the specific frequency component as described above within the above range, mode coupling and transmission loss can be suppressed to a low level, enabling long-distance and high-speed transmission. In addition, in order to suppress polarization mode dispersion, the optical fiber is usually given a twist in the longitudinal direction by applying torque during drawing, and preferably the rotational speed of the twist is 0 times / m or more and 10 times / m or less. Since outer diameter variation is likely to occur synchronously with the rotation, by making the rotational speed within the above range, mode coupling and transmission loss can be suppressed to a low level.

[0037] (8) As an aspect of the optical fiber according to an embodiment of the present invention, in order to achieve a mode field diameter of 8.2 μm or more and 9.6 μm or less at a wavelength of 1310 nm, an optical cable cut-off wavelength of the LP11 mode of 1060 nm or more and 1260 nm or less, and an optical cable cut-off wavelength of the LP02 mode of 1060 nm or less, the core radius (or outer diameter) and the refractive index distribution shape of the optical fiber are adjusted. Specifically, preferably, the radius of the core defined in the radial direction orthogonal to the optical fiber axis is 3 μm or more and 10 μm or less (the outer diameter of the core defined in the diameter direction orthogonal to the optical fiber axis is 6 μm or more and 20 μm or less). In addition, in the inner region of the core (the region surrounded by the outer peripheral surface centered on the optical fiber axis and at a distance of 0.2 times the radius of the core from the optical fiber axis), preferably, the refractive index distribution of the core has a shape in which the relative refractive index difference at the core center adjusted to be consistent with the optical fiber axis is 0.8 times or more of the maximum relative refractive index difference of the core (a shape in which the depression of the refractive index distribution is improved). Furthermore, in the outer region of the core surrounding the inner region, the refractive index distribution of the core has the following shape, which satisfies the relative refractive index difference Δ0 at the position at a distance r0 from the optical fiber axis in the radial direction within the inner region where the distance r0 in the radial direction is 0.2 times or less of the distance r1 corresponding to the core radius, the relative refractive index difference Δ1 at the position at a distance r1 from the optical fiber axis, and the relative refractive index difference Δ at the position at a distance r from the optical fiber axis where r is more than r0 and less than r1, as defined by the following formula (1): r Using the following formula (1):

[0038] Δ r = Δ0 + (Δ1 - Δ0) × ((r - r0) / (r1 - r0)) α …(1)

[0039] An approximate relationship. Herein, the "approximate relationship" is defined such that the value on the left side of the above formula (1) is within the range of ±5% as a relative value centered on the value on the right side. When the radius r ≤ r0, Δ r is approximately equal to Δ0. In particular, by adjusting the exponent α in the above formula (1) to be 2.0 or more and 20 or less, as described above, the mode field diameter at a wavelength of 1310 nm is 8.2 μm or more and 9.6 μm or less, the cut-off wavelength of the LP11 mode of the optical fiber cable is 1060 nm or more and 1260 nm or less, and the cut-off wavelength of the LP02 mode of the optical fiber cable is 1060 nm or less.

[0040] (9) As an aspect of the optical fiber according to an embodiment of the present invention, it is preferable that the exponent α in the above formula is 2.5 or more and 5.0 or less. In this case, even when the LP11 mode is excited due to a low-quality connection or the like, the generation of noise caused by the LP11 mode can be effectively suppressed, and as a result, stable high-speed transmission can be achieved.

[0041] (10) As an aspect of the optical fiber cable according to an embodiment of the present invention, it has a plurality of optical fibers and a sheath surrounding the plurality of optical fibers. In particular, at least two of the plurality of optical fibers each have a core, a cladding, and a resin coating layer. The core extends along the optical fiber axis and is formed of silica glass. The cladding is provided on the outer peripheral surface of the core, is formed of silica glass, and has a maximum refractive index lower than the maximum refractive index of the core. The resin coating layer is provided on the outer peripheral surface of the cladding. In particular, at least two optical fibers having such a structure have a mode field diameter of 8.2 μm or more and 9.6 μm or less at a wavelength of 1310 nm, a cut-off wavelength of the LP11 mode of the optical fiber cable of 1060 nm or more and 1260 nm or less, and a cut-off wavelength of the LP02 mode of the optical fiber cable of 1060 nm or less. In this case, in addition to being applicable to existing optical transceivers used in optical communication in the wavelength band of 1310 nm or more and 1625 nm or less, it is also applicable to optical transceivers used in optical communication at a wavelength of 1060 nm (optical communication at a wavelength of 1060 nm can be achieved).

[0042] (11) As an aspect of the optical fiber cable according to an embodiment of the present invention, it is preferable that in each of at least two optical fibers, the cut-off wavelength of the LP02 mode of the optical fiber cable is 980 nm or less. In this case, in addition to being applicable to existing optical transceivers used in optical communication in the wavelength band of 1310 nm or more and 1625 nm or less, it is also applicable to optical transceivers used in optical communication at a wavelength of 980 nm.

[0043] (12) As an aspect of the optical fiber cable according to an embodiment of the present invention, in each of at least two optical fibers, the cut-off wavelength of the LP02 mode of the optical fiber cable can be 850 nm or less. In this case, in addition to being applicable to optical transceivers used in optical communications in a wavelength band of 1310 nm or more and 1625 nm or less, it can also be applicable to optical transceivers with a wavelength of 850 nm.

[0044] (13) As an aspect of the optical fiber cable according to an embodiment of the present invention, preferably in each of at least two optical fibers, the bending loss at a diameter of 15 mm is 1 dB / turn or less at a wavelength of 1625 nm. In this case, in addition to being applicable to optical transceivers used in optical communications in a wavelength band of 850 nm or more and 1060 nm or less, it can also be applicable to high spatial density high-speed transmission in a wavelength band of 1310 nm or more and 1625 nm or less.

[0045] (14) As an aspect of the optical fiber cable according to an embodiment of the present invention, in each of at least two optical fibers, in order to achieve a mode field diameter of 8.2 μm or more and 9.6 μm or less at a wavelength of 1310 nm, a cut-off wavelength of the LP11 mode of the optical fiber cable of 1060 nm or more and 1260 nm or less, and a cut-off wavelength of the LP02 mode of the optical fiber cable of 1060 nm or less, the core radius (or outer diameter) and the refractive index distribution shape are adjusted. Specifically, preferably, the radius of the core defined in the radial direction orthogonal to the optical fiber axis is 3 μm or more and 10 μm or less (the core outer diameter is 6 μm or more and 20 μm or less). In addition, in the inner region of the core (the region surrounded by the outer peripheral surface centered on the optical fiber axis and at a distance of 0.2 times the radius of the core from the optical fiber axis), preferably, the refractive index distribution of the core has a shape in which the relative refractive index difference of the core center adjusted to be consistent with the optical fiber axis is 0.8 times or more of the maximum relative refractive index difference of the core (a shape in which the depression of the refractive index distribution is improved). Further, in the outer region of the core surrounding the inner region, the refractive index distribution of the core has the following shape, which satisfies the relative refractive index difference Δ0 at a position at a distance r0 in the radial direction equivalent to 0.2 times the core radius, the relative refractive index difference Δ1 at a position at a distance r1 from the optical fiber axis, and the relative refractive index difference Δ at a position at a distance r of r0 or more and r1 or less from the optical fiber axis defined in the inner region. r The relationship approximated by the above formula (1). In particular, by adjusting the exponent α in the above formula to 2.0 or more and 20 or less, as described above, the mode field diameter at a wavelength of 1310 nm is 8.2 μm or more and 9.6 μm or less, the cut-off wavelength of the LP11 mode of the optical fiber cable is 1060 nm or more and 1260 nm or less, and the cut-off wavelength of the LP02 mode of the optical fiber cable is 1060 nm or less.

[0046] (15) As an aspect of the optical cable according to an embodiment of the present invention, it is preferable that the exponent α in the above formula is 2.5 or more and 5.0 or less. In this case, even when the LP11 mode is excited due to a low-quality connection or the like, the generation of noise caused by the LP11 mode can be effectively suppressed, and as a result, stable high-speed transmission can be achieved.

[0047] As described above, each aspect listed in the [Description of the Embodiment of the Present Invention] column can be applied to each of all the remaining aspects, or can be applied to all combinations of these remaining aspects.

[0048] [Details of the Embodiment of the Present Invention]

[0049] Hereinafter, specific examples of the optical fiber and the optical cable of the present invention will be described in detail with reference to the following attached Figure 1 It should be noted that the present invention is not limited to these examples, but is represented by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In addition, in the description of the drawings, the same reference numerals are used for the same elements, and repeated descriptions are omitted.

[0050] Figure 1 FIG. is an example showing the structure of an optical communication system using an optical cable to which an embodiment of the present invention can be applied. Figure 1 The optical communication system 1 shown has: an optical cable 2 as a transmission medium, n optical transceivers 31, 32, 33,..., 3 n configured on one end side of the optical cable 2, and n optical transceivers 41, 42, 43,..., 4 n configured on the other end side of the optical cable 2. Here, "n" is an integer of 2 or more and 100000 or less, and the lower limit condition of the integer "n" is preferably 10 or more, 100 or more, or may be 1000 or more. In addition, n connection optical wirings (optical fibers) 51, 52, 53,..., 5 n extend from the n optical transceivers 31, 32, 33,..., 3 n respectively, and n connection optical wirings (optical fibers) 61, 62, 63,..., 6 n extend from the n optical transceivers 41, 42, 43,..., 4 n respectively.

[0051] The optical cable 2 has: n optical fibers 221, 222, 223,..., 22 n , and a sheath 21 that houses the n optical fibers. In addition, for easy operation, the n optical fibers 221, 222, 223,..., 22 nDivided into multiple groups, after striping each optical fiber group respectively, the obtained multiple strips are then unitized.

[0052] n optical fibers 221, 222, 223, …, 22 n One end of which is respectively connected to n connection optical wirings 51, 52, 53, …, 5 n extending from n optical transceivers 31, 32, 33, …, 3 n through n optical connectors 231, 232, 233, …, 23 n In addition, the other end of n optical fibers 221, 222, 223, …, 22 n is respectively connected to n connection optical wirings 61, 62, 63, …, 6 n extending from n optical transceivers 41, 42, 43, …, 4 n through n optical connectors 241, 242, 243, …, 24 n Here, the optical connector 23 k (k = 1, 2, 3, …, n) includes a structure body with a positioning mechanism for fixing one end of the optical fiber 22 k (k = 1, 2, 3, …, n) and the end of the connection optical wiring 5 k (k = 1, 2, 3, …, n) in an optically connected state (this structure body itself functions as an optical connector). Similarly, the optical connector 24 k (k = 1, 2, 3, …, n) includes a structure body with a positioning mechanism for fixing the other end of the optical fiber 22 k and the end of the connection optical wiring 6 k (k = 1, 2, 3, …, n) in an optically connected state. In Figure 1 the example, a single-core connector structure for optically connecting one optical fiber with one optical connector is shown, but a multi-core connector structure for optically connecting multiple optical fibers with one optical connector can also be adopted.

[0053] In Figure 1 the n optical fibers 221, 222, 223, …, 22 shown nIn each of every one or at least two of these optical fibers, the cut-off wavelength of the LP02 mode in the optical cable is below 1060 nm, preferably below 980 nm, and more preferably below 850 nm. In addition, the cut-off wavelength of the LP11 mode in the optical cable is below 1260 nm. The bending loss at a diameter of 15 mm is below 1 dB / turn at a wavelength of 1625 nm. The mode field diameter at a wavelength of 1310 nm is above 8.2 μm and below 9.6 μm. By using an optical fiber having the above optical characteristics as a transmission medium, not only can optical transmission of an optical transceiver in a wavelength band above 1260 nm and below 1625 nm be performed, but also, by controlling mode coupling caused by axial offset and angular offset of a connection portion (optical connector) to be low, optical transmission of an optical transceiver for a short wavelength band (wavelength range above 850 nm and below 1060 nm) such as the 850 nm band, 980 nm band, 1060 nm band, etc. can be performed. As a result, without having to re-lay the optical cable, the cost performance of the optical communication system can be optimized by using an optical transceiver in the most appropriate wavelength band at that time.

[0054] Furthermore, in each of every one or at least two of the n optical fibers 221, 222, 223, …, 22 n the mode dispersion is preferably also optimized. Specifically, at a wavelength of 1060 nm, 980 nm, or 850 nm, the mode dispersion between the LP01 mode and the LP11 mode is below 1000 ps / km, preferably below 300 ps / km. In this case, even if the LP11 mode is excited due to axial offset and angular offset during connection, generation of noise (noise with respect to the LP01 mode) caused by the LP11 mode can be effectively suppressed, and thus the transmission performance of the optical communication system 1 can be improved or the connection cost can be reduced.

[0055] In addition, most preferably, all of the n optical fibers 221, 222, 223, …, 22 n included in the optical cable 2 satisfy the above optical characteristics of the optical fiber. However, it may also be configured such that, according to requirements for the transmission performance and manufacturing cost of the optical communication system 1, each unit constituting the optical cable 2, or each ribbon constituting each unit (a unit used as a fiber group), has all of the optical fibers included in the target unit or target ribbon satisfy the above optical characteristics, whereby optimization of cost performance can be achieved.

[0056] Figure 2 is a diagram showing Figure 1 an example of the structure of the k-th optical fiber 22 n among the n optical fibers 221, 222, 223, …, 22 k (k = 1, 2, 3, …, n) shown. In addition, Figure 2The structure shown does not need to be applied to all n optical fibers 221, 222, 223, …, 22 housed in the sheath 21 of the optical cable 2 n , and it is sufficient to apply it to at least two optical fibers.

[0057] The optical fiber 22 k has a core 61 extending along the optical fiber axis (central axis) AX, a cladding 62 provided on the outer peripheral surface of the core 61, a first coating layer 63 provided on the outer peripheral surface of the cladding 62, and a second coating layer 64. In addition, the first coating layer 63 and the second coating layer 64 constitute a resin coating layer provided on the outer peripheral surface of the cladding 62.

[0058] In Figure 2 the example, the cladding 62 has an inner cladding 62a provided on the outer peripheral surface of the core and an outer cladding 62b provided on the outer peripheral surface of the inner cladding 62a. Here, the core 61 and the cladding 62 (inner cladding 62a and outer cladding 62b) are formed of silica glass and may contain additives such as Ge, F, Cl, Br, P for adjusting the refractive index. The inner cladding 62a has a refractive index lower than that of the core 61. The outer cladding 62b has a refractive index lower than that of the core 61 and higher than that of the inner cladding. Therefore, the core 61 has a maximum refractive index higher than the maximum refractive index of the cladding 62. The maximum relative refractive index difference of the core 61 (value based on pure silica glass) is 0.2% or more and 0.6% or less. The outer diameter of the core 61 is 6 μm or more and 20 μm or less. That is, the radius of the core 61 (distance from the optical fiber axis AX to the outer periphery of the core) is 3 μm or more and 10 μm or less. With such a core structure, it has a single waveguide mode (can operate in single mode) at a wavelength of 1260 nm. Preferably, the outer diameter of the cladding 62 (outer diameter of the outer cladding 62b) is a standard outer diameter (glass outer diameter) of 124 μm or more and 126 μm or less. In addition, with such a core structure, the optical fiber 22 k can be applicable to high-speed transmission in the short wavelength band of 850 nm or more and 1060 nm or less and can also be applicable to high spatial density and high-speed transmission at a wavelength of 1625 nm.

[0059] The first coating layer 63 and the second coating layer 64 are formed of a urethane acrylate-based ultraviolet curable resin. Preferably, the first coating layer has a thickness (difference between the inner diameter and the outer diameter defined in the radial direction orthogonal to the optical fiber axis AX) of 15 μm or more and 40 μm or less and an elastic modulus of 0.05 MPa or more and 0.5 MPa or less. The second coating layer 64 has a thickness of 15 μm or more and 40 μm or less and an elastic modulus of 500 MPa or more and 2000 MPa or less. Thus, it can effectively shield from the optical fiber 22 kAn external force applied laterally to a glass portion (a portion composed of a core 61 and a cladding 62).

[0060] Next, Figure 3A FIG. 5 shows the refractive index distributions of an example of an optical fiber according to an embodiment of the present invention and an optical fiber of a comparative example. In Figure 3A FIG. 5, 310 is the refractive index distribution of the optical fiber 22 according to the embodiment of the present invention k and 320 is the refractive index distribution of the optical fiber of the comparative example.

[0061] In the inner region of the core 61 (a region surrounded by an outer peripheral surface centered on the optical fiber axis AX and at a distance of 0.2 times the radius of the core 61 from the optical fiber axis AX), the refractive index distribution 310 of the core 61 has a structure in which the depression of the refractive index distribution 310 is reduced or removed such that the relative refractive index difference at the center of the core coinciding with the optical fiber axis AX is 0.8 times or more of the maximum relative refractive index difference of the core 61. Further, in the outer region of the core 61 surrounding the inner region, the refractive index distribution 310 of the core 61 has a shape that satisfies the relative refractive index difference Δ0 at a position at a distance r0 from the optical fiber axis AX in the radial direction, the relative refractive index difference Δ1 at a position at a distance r1 from the optical fiber axis AX, and the relative refractive index difference Δ at a position at a distance r greater than r0 and less than r1 from the optical fiber axis AX, which are defined in the inner region where the radial distance r0 is 0.2 times or less of the distance r1 corresponding to the core radius r using the following formula (2):

[0062] Δ r = Δ0+(Δ1 - Δ0)×((r - r0) / (r1 - r0)) α …(2)

[0063] for an approximate relationship. When the radius r ≤ r0, Δ r is approximately equal to Δ0. In particular, by adjusting the exponent α in the above formula (2), as described above, the mode field diameter at a wavelength of 1310 nm is 8.2 μm or more and 9.6 μm or less, the cable cut-off wavelength of the LP11 mode is 1060 nm or more and 1260 nm or less, and the cable cut-off wavelength of the LP02 mode is 1060 nm or less.

[0064] Specifically, in the optical fiber 22 according to the embodiment of the present invention kIn this case, the core 61 is formed of quartz glass containing Ge, and has a radius of 4.65 μm or more and 5.0 μm or less and a maximum relative refractive index difference of 0.42% ± 0.01%. The value of the exponent α in the above formula (2) that determines the distribution shape of the outer region is 3.4 ± 0.1. The cladding 62 has a double cladding structure composed of an inner cladding 62a and an outer cladding 62b. The inner cladding 62a is formed of quartz glass containing F and has a relative refractive index difference of -0.07% ± 0.01%. The ratio of (radius of the core 61) / (outer radius of the inner cladding 62a) is 0.25 ± 0.02. The outer cladding 62b is formed of pure quartz glass and has an outer radius (cladding outer diameter) of 62.5 μm ± 0.5 μm.

[0065] On the other hand, the optical fiber of the comparative example has the same structure as the above-described optical fiber 22 except for the distribution shape of the inner region of the core 61. k That is, in the inner region of the core, the refractive index distribution 320 has a shape according to the above formula (2) (the relative refractive index difference at the core center is Δ0, the relative refractive index difference at the outer periphery of the inner region is Δ1, and the exponent α is 3.4). The relative refractive index difference Δ0 at the core center is as low as 0.8 ± 0.1 times the maximum relative refractive index difference. Due to the influence of the core manufacturing technology, such a depression in the refractive index at the core center occurs. In contrast, the optical fiber 22 of the embodiment of the present invention k has a refractive index distribution 310 that removes the depression in the refractive index at the core center by adjusting the manufacturing conditions. In particular, it is preferable to manufacture the core by the VAD method because the depression in the refractive index at the core center can be suppressed. In the case of the OVD method and the CVD method, when solidifying the cylindrical vitreous body, a depression in the refractive index at the core center may occur due to the separation of the additive, but it is preferable to add in advance an amount of the additive that will separate.

[0066] Figure 3B is a graph showing the relationship between the exponent α and the modal dispersion for a plurality of samples of the optical fiber 22 k (the optical fiber of the embodiment of the present invention) and a plurality of comparative examples. Specifically, Figure 3B the shown graph shows the change in the modal dispersion of the samples and the comparative examples when the exponent α in the above formula (2) is changed in the range of 2.6 or more and 5.0 or less.

[0067] In addition, in Figure 3B it, the graph 311 shows the measurement results (the relationship between the exponent α and the modal dispersion) of the first sample of the optical fiber 22 k in which the cable cut-off wavelength of the LP02 mode is set to 850 nm, and the graph 312 shows the optical fiber 22 kMeasurement results of the second sample, Figure 313 shows the optical fiber 22 with the cut-off wavelength of the LP02 mode of the optical cable set to 1060 nm k Measurement results of the third sample. On the other hand, point 321 shows the measurement results (relationship between the exponent α and the modal dispersion) of the first comparative example where the cut-off wavelength of the LP02 mode of the optical cable is set to 850 nm, point 322 shows the measurement results of the second comparative example where the cut-off wavelength of the LP02 mode of the optical cable is set to 980 nm, and point 323 shows the measurement results of the third comparative example where the cut-off wavelength of the LP02 mode of the optical cable is set to 1060 nm.

[0068] From Figure 3B it can be seen that the optical fiber 22 k For the first sample, second sample, and third sample, the modal dispersion can be suppressed to 300 ps / km or less at the optimal value of the exponent α, so it is suitable for high-speed transmission. In addition, the optimal value of the exponent α of the first sample is around 2.8 ± 0.1, the optimal value of the exponent α of the second sample is around 3.4 ± 0.1, and the optimal value of the exponent α of the third sample is around 4.6 ± 0.1. Furthermore, by setting the value of the exponent α to 3.4 ± 0.1 (in the range of 3.3 or more and 3.5 or less), the modal dispersion can be suppressed to 1000 ps / km or less in all bands of the 850 nm band, 980 nm band, and 1060 nm band (wavelength range of 850 nm or more and 1060 nm or less). In addition, in this α, Figures 311, 312, and 313 all have lower modal dispersion compared to points 321, 322, and 323. This shows the effect of reducing the depression of the refractive index at the center of the core.

[0069] In addition, the optical fiber 22 of the embodiment of the present invention k Preferably, the value 3σ defined by the standard deviation σ of the deviation of the outer diameter of the cladding 62 (outer diameter of the glass part) (outer diameter deviation in the length direction along the optical fiber axis AX) is 0.1 μm or more and 0.5 μm or less. Furthermore, it is more preferably that the value 3σ is 0.2 μm or more and 0.5 μm or less. By the value 3σ being 0.5 μm or less, the noise caused by modal coupling from the LP01 mode to the LP02 mode can be effectively suppressed, and stable transmission performance can be maintained. In addition, as known from the above Patent Document 2, by drawing the optical fiber under the cooling condition where the value 3σ is 0.1 μm or more, Rayleigh scattering can be suppressed to a low level, and by drawing the optical fiber under the cooling condition where the value 3σ is 0.2 μm or more, Rayleigh scattering can be suppressed even lower.

[0070] Description of reference numerals

[0071] 1... Optical communication system; 2... Optical cable; 31, 32, 33,..., 3 n 3 k(k = 1, 2, 3, …, n), 41, 42, 43, …, 4 n , 4 k (k = 1, 2, 3, …, n) … optical transceiver; 51, 52, 53, …, 5 n , 5 k (k = 1, 2, 3, …, n), 61, 62, 63, …, 6 n , 6 k (k = 1, 2, 3, …, n) … optical wiring (optical fiber); 221, 222, 223, …, 22 n , 22 k (k = 1, 2, 3, …, n) … optical fiber; 231, 232, 233, …, 23 n , 23 k (k = 1, 2, 3, …, n), 241, 242, 243, …, 24 n , 24 k (k = 1, 2, 3, …, n) … optical connector; 61 … core; 62 … cladding; 62a … inner cladding; 62b … outer cladding; 63 … first coating layer; 64 … second coating layer; AX … optical fiber axis (central axis).

Claims

1. An optical fiber having: a core extending along the optical fiber axis and formed of silica glass, a cladding provided on the outer peripheral surface of the core, formed of silica glass, and having a maximum refractive index lower than the maximum refractive index of the core, and a resin coating provided on the outer peripheral surface of the cladding; The optical fiber has: a mode field diameter of 8.2 μm or more and 9.6 μm or less at a wavelength of 1310 nm, a cable cut-off wavelength of the LP11 mode of 1060 nm or more and 1260 nm or less, and a cable cut-off wavelength of the LP02 mode of 1060 nm or less, the mode dispersion between the LP01 mode and the LP11 mode is 1000 ps / km or less in a wavelength range of 850 nm or more and 1060 nm or less, the radius of the core defined in the radial direction orthogonal to the optical fiber axis is 3 μm or more and 10 μm or less, in the inner region of the core surrounded by the outer peripheral surface centered on the optical fiber axis at 0.2 times the radius of the core from the optical fiber axis, the refractive index distribution of the core has a shape in which the relative refractive index difference at the core center coinciding with the optical fiber axis is 0.8 times or more of the maximum relative refractive index difference of the core, In the outer region of the core surrounding the inner region, the refractive index distribution of the core has a shape that is defined by the relative refractive index difference Δ0 at a position at a distance r0 from the optical fiber axis in the inner region, the relative refractive index difference Δ1 at a position at a distance r1 from the optical fiber axis, and the relative refractive index difference Δ at a position at a distance r greater than the distance r0 and less than the distance r1 from the optical fiber axis r Satisfy Δ r = Δ0 + (Δ1 - Δ0) × ((r - r0) / (r1 - r0)) α The approximate shape of the mathematical formula of the relationship, the exponent α is 2.0 or more and 20 or less, and the inner region is a region where the distance r0 in the radial direction satisfies the relationship 0 ≤ r0 / r1 ≤ 0.2 with respect to the distance r1 corresponding to the radius of the core portion the optical fiber has a mode field diameter of 8.2 μm or more and 9.6 μm or less at the wavelength of 1310 nm, a cable cut-off wavelength of the LP11 mode of 1060 nm or more and 1260 nm or less, and a cable cut-off wavelength of the LP02 mode of 1060 nm or less.

2. The optical fiber according to claim 1, wherein, The cable cut-off wavelength of the LP02 mode is 980 nm or less.

3. The optical fiber according to claim 2, wherein, The cable cut-off wavelength of the LP02 mode is 850 nm or less.

4. The optical fiber according to any one of claims 1 to 3, wherein, the bending loss at a diameter of 15 mm is 1 dB / turn or less at a wavelength of 1625 nm, the cladding includes an inner cladding and an outer cladding, the inner cladding is provided on the outer peripheral surface of the core, and the outer cladding is provided on the outer peripheral surface of the inner cladding and has a relative refractive index difference higher than that of the inner cladding.

5. The optical fiber according to any one of claims 1 to 3, wherein, The mode dispersion between the LP01 mode and the LP11 mode is 300 ps / km or less at at least one wavelength in a wavelength range of 850 nm or more and 1060 nm or less.

6. The optical fiber according to any one of claims 1 to 3, wherein, The value 3σ defined by the standard deviation σ varying along the optical fiber axis of the outer diameter of the cladding is in the range of 0.1 μm or more and 0.5 μm or less.

7. The optical fiber according to any one of claims 1 to 3, wherein, The exponent α is 2.5 or more and 5.0 or less.

8. An optical cable having a plurality of optical fibers and a sheath surrounding the plurality of optical fibers, at least two of the plurality of optical fibers each have a core, a cladding, and a resin coating, the core extends along the optical fiber axis and is formed of silica glass, the cladding is provided on the outer peripheral surface of the core and is formed of silica glass and has a maximum refractive index lower than the maximum refractive index of the core, and the resin coating is provided on the outer peripheral surface of the cladding, At least two of the multiple optical fibers each have a mode field diameter of 8.2 μm or more and 9.6 μm or less at a wavelength of 1310 nm, an optical cable cut-off wavelength of the LP11 mode of 1060 nm or more and 1260 nm or less, and an optical cable cut-off wavelength of the LP02 mode of 1060 nm or less. The mode dispersion between the LP01 mode and the LP11 mode is 1000 ps / km or less in a wavelength range of 850 nm or more and 1060 nm or less. In each of the at least two optical fibers, the radius of the core defined in the radial direction orthogonal to the optical fiber axis is 3 μm or more and 10 μm or less. In the inner region of the core surrounded by the outer peripheral surface centered on the optical fiber axis at a distance of 0.2 times the radius of the core from the optical fiber axis, the refractive index distribution of the core has a shape in which the relative refractive index difference at the core center coinciding with the optical fiber axis is 0.8 times or more of the maximum relative refractive index difference of the core. In the outer region of the core that surrounds the inner region, the refractive index distribution of the core has a shape that is defined by the relative refractive index difference Δ0 at a position at a distance r0 from the optical fiber axis in the inner region, the relative refractive index difference Δ1 at a position at a distance r1 from the optical fiber axis, and the relative refractive index difference Δ at a position at a distance r greater than the distance r0 and less than the distance r1 from the optical fiber axis r Satisfy Δ r = Δ0 + (Δ1 - Δ0) × ((r - r0) / (r1 - r0)) α The shape approximated by the mathematical formula of the relationship, where the exponent α is 2.0 or more and 20 or less, and the inner region is a region where the distance r0 in the radial direction satisfies the relationship 0 ≤ r0 / r1 ≤ 0.2 with respect to the distance r1 corresponding to the radius of the core portion. The optical fiber has a mode field diameter of 8.2 μm or more and 9.6 μm or less at the wavelength of 1310 nm, an optical cable cut-off wavelength of the LP11 mode of 1060 nm or more and 1260 nm or less, and an optical cable cut-off wavelength of the LP02 mode of 1060 nm or less.

9. The optical cable according to claim 8, wherein, In each of the at least two optical fibers, the optical cable cut-off wavelength of the LP02 mode is 980 nm or less.

10. The optical cable according to claim 9, wherein, In each of the at least two optical fibers, the optical cable cut-off wavelength of the LP02 mode is 850 nm or less.

11. The optical cable according to any one of claims 8 to 10, wherein, In each of the at least two optical fibers, the bending loss at a diameter of 15 mm is 1 dB / turn or less at a wavelength of 1625 nm.

12. The optical cable according to any one of claims 8 to 10, wherein, The exponent α is 2.5 or more and 5.0 or less.

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