Multicore fiber and method for manufacturing multicore fiber

Abstract

To provide a multicore fiber in which deformation of the cross-sectional shape from a circular shape is suppressed.SOLUTION: The multicore fiber includes: a plurality of core parts; a cladding part that surrounds outer peripheries of the plurality of core parts and has a lower refractive index than the plurality of core parts; and a plurality of deformation correction parts disposed inside the cladding part. The plurality of core parts are arranged along a first radial direction in a cross section perpendicular to the longitudinal direction of the multicore fiber, and the plurality of deformation correction parts are arranged along a second radial direction substantially orthogonal to the first radial direction in the cross section.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multicore fiber and a method for manufacturing a multicore fiber. [Background technology]

[0002] A known multicore fiber is one that has two core portions (Patent Document 1). The two core portions are arranged along a predetermined radial direction in a cross section perpendicular to the longitudinal direction of the multicore fiber. Such a multicore fiber is also called a two-core multicore fiber. [Prior art documents] [Non-patent literature]

[0003] [Patent Document 1] Special Publication No. 2023-518466 Summary of the Invention [Problem to be solved by the invention]

[0004] This type of multicore fiber has a problem in that the cross-sectional shape is easily non-circular due to low rotational symmetry in the cross section, which may cause problems such as a decrease in the precision of the cladding diameter or a non-circular core, which may result in a deterioration in PMD (Polarization Mode Dispersion) characteristics.

[0005] The present invention has been made in view of the above, and an object of the present invention is to provide a multicore fiber in which the cross-sectional shape is prevented from becoming non-circular, and a method for manufacturing a multicore fiber. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention is a multi-core fiber comprising: a plurality of core portions; a cladding portion surrounding the outer peripheries of the plurality of core portions and having a refractive index lower than that of the plurality of core portions; and a plurality of deformation correction portions arranged inside the cladding portion, wherein the plurality of core portions are arranged along a first radial direction in a cross section perpendicular to a longitudinal direction of the multi-core fiber, and the plurality of deformation correction portions are arranged along a second radial direction substantially perpendicular to the first radial direction in the cross section.

[0007] The plurality of deformation correction portions may have a stress profile or a refractive index different from that of the cladding portion.

[0008] The number of the plurality of core portions and the plurality of deformation correction portions may be two.

[0009] The multi-core fiber may include a low refractive index portion disposed between the two core portions and having a refractive index lower than that of the cladding portion.

[0010] One aspect of the present invention is a method for manufacturing a multicore fiber, the method comprising: inserting a core rod including a portion that will become the core portion into each of the first holes of a glass rod having a plurality of first holes arranged along the first radial direction and a plurality of second holes arranged along the second radial direction; inserting a rod including a portion that will become the deformation correction portion into each of the second holes of the glass rod; heating and integrating the glass rod, the core rod, and the rod; and drawing the integrated glass rod, the core rod, and the rod to form the multicore fiber. [Effects of the Invention]

[0011] According to the present invention, it is possible to realize a multi-core fiber in which the cross-sectional shape is prevented from becoming non-circular. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of a multi-core fiber according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram of a method for manufacturing a multi-core fiber according to a comparative embodiment. [Figure 3] FIG. 3 is an explanatory diagram of a method for manufacturing a multi-core fiber according to the first embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view of a multi-core fiber according to the second embodiment. [Figure 5] FIG. 5 is an explanatory diagram of a method for manufacturing a multi-core fiber according to the second embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view of a multi-core fiber according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below. Furthermore, in each drawing, the same or corresponding components are appropriately designated by the same reference numerals, and duplicate explanations are appropriately omitted. Furthermore, terms not specifically defined in this specification shall follow the definitions and measurement methods in G.650.1 and G.650.2.

[0014] (Embodiment 1) 1 is a schematic cross-sectional view of a multi-core fiber according to embodiment 1, which is a cross-sectional view of a cross section perpendicular to the longitudinal direction of the multi-core fiber. The multi-core fiber 10 includes two core portions 11 and 12, a cladding portion 13, and two deformation correction portions 14 and 15. Here, the two core portions 11 and 12 are an example of a plurality of core portions, and the two deformation correction portions 14 and 15 are an example of a plurality of deformation correction portions.

[0015] The two cores 11 and 12 are arranged along the x direction in a cross section perpendicular to the longitudinal direction of the multicore fiber 10. Here, the x direction is an example of a first radial direction. The cores 11 and 12 have a substantially circular shape in cross section. The cores 11 and 12 are made of, for example, silica-based glass and may contain at least one of germanium, fluorine, chlorine, potassium, and sodium. The refractive index profile of the cores 11 and 12 may be a step type, W type, trench type, or the like, but is not particularly limited. Furthermore, the cores 11 and 12 are arranged, for example, equidistant from the central axis of the cladding 13.

[0016] The cladding portion 13 surrounds the outer periphery of the core portions 11 and 12 and has a lower refractive index than the core portions 11 and 12. The cladding portion 13 is made of, for example, silica-based glass or pure silica glass containing at least a portion of fluorine. The cladding portion 13 has a substantially circular cross section.

[0017] The two deformation correction units 14, 15 are disposed inside the cladding portion 13. The deformation correction units 14, 15 are arranged along the y direction, which is orthogonal to the x direction, in a cross section perpendicular to the longitudinal direction of the multicore fiber 10. Here, the y direction is an example of a second radial direction, which is approximately orthogonal to the first radial direction. The deformation correction units 14, 15 have an approximately circular shape in cross section. The deformation correction units 14, 15 have a refractive index that is approximately the same as or lower than that of the cladding portion 13. The deformation correction units 14, 15 are made of, for example, silica-based glass or pure silica glass, at least a portion of which contains fluorine. The outer diameters of the deformation correction units 14, 15 are approximately the same as those of the cores 11, 12, for example. Furthermore, the deformation correction units 14, 15 are disposed, for example, equidistant from the central axis of the cladding portion 13. The distance of the deformation correction units 14 and 15 from the central axis is, for example, equal to the distance of the core units 11 and 12 from the central axis, but does not have to be equal.

[0018] Here, the deformation correction units 14, 15 may have a different stress profile or refractive index from the cladding unit 13. The stress profile is a profile showing the distribution of residual stress, and is expressed by a graph showing the amount of residual stress at each position in a cross section. Such differences in stress profiles can be distinguished by cutting the multicore fiber 10 to form a mirror-like end face, and observing the end face with an optical microscope while irradiating transmitted light into the multicore fiber 10 and incident light onto the end face. Specifically, when the stress profiles are different, the shading of the image observed with the optical microscope appears different. Note that differences in refractive index can also be distinguished by similar observation.

[0019] The multi-core fiber 10 configured as above is prevented from having a non-circular cross-sectional shape, for the following reasons.

[0020] FIG. 2 is an explanatory diagram of a manufacturing method of a multi-core fiber according to a comparative embodiment. The multi-core fiber according to the comparative embodiment is a multi-core fiber that has two core portions like the multi-core fiber 10 according to the first embodiment, but does not have a deformation correction portion. Such a multi-core fiber according to the comparative embodiment is manufactured as follows. First, a glass rod 100A that will become the cladding portion of the multi-core fiber is prepared. Air holes 101A and 102A are formed in the glass rod 100A at positions along the x direction that correspond to the core portions. Next, core rods 201A and 202A that include portions that will become the core portions of the multi-core fiber are inserted into the air holes 101A and 102A, respectively. Note that the core rods 201A and 202A may include portions that will become the cladding portion of the multi-core fiber. In this case, a gap G is always present between the inner walls of the air holes 101A and 102A and the outer walls of the core rods 201A and 202A. This is because the core rods 201A and 202A cannot be inserted into the holes 101A and 102A without the existence of such gap G. The width of such gap G is, for example, 0.2 mm to 1.0 mm.

[0021] Next, when the glass rod 100A and the core rods 201A and 202A are heated and integrated while being drawn, the gap G collapses, and a multi-core fiber 10A according to a comparative example is formed, which includes cores 11A and 12A and a cladding 13A. The integration and drawing may be performed in a single process or separately. As can be seen from FIG. 2 , there are four gaps G in the x direction and two gaps in the y direction, which is perpendicular to the x direction. As a result, when the gap G collapses, the glass rod 100A is deformed more in the x direction than in the y direction. Specifically, the glass rod 100A is deformed so as to become smaller in the directions indicated by arrows Ar1 and Ar2. As a result, the multi-core fiber 10A has an elliptical cross section with a minor axis in the x direction and a major axis in the y direction, resulting in a non-circular cross section.

[0022] 3 is an explanatory diagram of a manufacturing method of a multicore fiber according to the first embodiment. The multicore fiber 10 is manufactured as follows. First, a glass rod 100 that will become the cladding portion of the multicore fiber is prepared. Air holes 101 and 102 are formed in the glass rod 100 at positions along the x direction that correspond to the core portions. Furthermore, air holes 103 and 104 are formed in the glass rod 100 at positions along the y direction that correspond to the deformation correction portions. Here, the air holes 101 and 102 are an example of a plurality of first air holes, and the air holes 103 and 104 are an example of a plurality of second air holes. Next, core rods 201 and 202 that include portions that will become the core portions of the multicore fiber are inserted into the air holes 101 and 102, respectively. Furthermore, rods 301 and 302 that include portions that will become the deformation correction portions of the multicore fiber are inserted into the air holes 103 and 104, respectively. In this case, too, gaps G always exist between the inner walls of the holes 101 to 104 and the outer walls of the core rods 201 and 202 and the rods 301 and 302 .

[0023] Next, when the glass rod 100, the core rods 201, 202, and the rods 301, 302 are heated and integrated while being drawn, the gaps G are collapsed, and the multi-core fiber 10 is formed. At this time, as can be seen from FIG. 3 , there are four gaps G in the x direction and four gaps in the y direction orthogonal to the x direction. As a result, when the gaps G are collapsed, the glass rod 100 is deformed approximately equally in both the x direction and the y direction. As a result, the cross-sectional shape of the multi-core fiber 10 is prevented from becoming non-circular. Note that, since the stress applied to the rods 301, 302 when the gaps G are collapsed is different from the stress applied to the glass rod 100, the stress profile of the deformation correction units 14, 15 may differ from that of the cladding unit 13.

[0024] (Embodiment 2) 4 is a schematic cross-sectional view of a multi-core fiber according to embodiment 2, which is a cross-sectional view of a cross section perpendicular to the longitudinal direction of the multi-core fiber. The multi-core fiber 20 has a configuration in which a low-refractive-index portion 16 is added to the multi-core fiber 10 shown in FIG.

[0025] The low refractive index portion 16 is disposed between the two core portions 11 and 12. The low refractive index portion 16 has a lower refractive index than the cladding portion 13. The low refractive index portion 16 is made of, for example, silica-based glass containing at least a portion of fluorine. The low refractive index portion 16 has a substantially circular shape in cross section.

[0026] The multi-core fiber 20 configured as above is prevented from having a non-circular cross-sectional shape, and the presence of the low refractive index portion 16 also makes it possible to reduce inter-core crosstalk between the two core portions 11 and 12.

[0027] 5 is an explanatory diagram of a manufacturing method of a multicore fiber according to the second embodiment. The multicore fiber 10 is manufactured as follows. First, a glass rod 200 that will become the cladding portion of the multicore fiber is prepared. Air holes 101, 102, and 105 are formed in the glass rod 200 at positions along the x direction that correspond to the core portions and the low refractive index portion. Furthermore, air holes 103 and 104 are formed in the glass rod 200 at positions along the y direction that correspond to the deformation correction portions. Next, core rods 201 and 202 that include portions that will become the core portions of the multicore fiber are inserted into the air holes 101 and 102, respectively. Furthermore, a rod 401 that includes a portion that will become the low refractive index portion of the multicore fiber is inserted into the air hole 105. Furthermore, rods 301 and 302 that include portions that will become the deformation correction portions of the multicore fiber are inserted into the air holes 103 and 104, respectively.

[0028] Next, when the glass rod 100, the core rods 201, 202, and the rods 301, 302, and 401 are heated and integrated while being drawn, the gaps collapse, and the multi-core fiber 20 is formed. At this time, as can be seen from FIG. 5 , there are six gaps in the x direction and six gaps in the y direction orthogonal to the x direction. As a result, when the gaps collapse, the glass rod 200 is deformed approximately equally in both the x direction and the y direction. As a result, the cross-sectional shape of the multi-core fiber 20 is prevented from becoming non-circular.

[0029] (Embodiment 3) 6 is a schematic cross-sectional view of a multi-core fiber according to embodiment 3, which is a cross-sectional view perpendicular to the longitudinal direction of the multi-core fiber. The multi-core fiber 30 has a configuration in which the deformation correction units 14 and 15 of the multi-core fiber 10 shown in FIG. 1 are replaced with deformation correction units 34 and 35.

[0030] The deformation correction units 34, 35 are arranged along a D direction that forms an angle θ with respect to the x direction, which is different from 90°, in a cross section perpendicular to the longitudinal direction of the multi-core fiber 10. Here, the D direction is an example of a second radial direction that is substantially perpendicular to the first radial direction. The deformation correction units 34, 35 have a substantially circular shape in cross section. The deformation correction units 34, 35 have a refractive index that is substantially the same as or lower than that of the cladding unit 13. The deformation correction units 34, 35 are made of, for example, silica-based glass or pure silica glass that at least partially contains fluorine. The outer diameters of the deformation correction units 34, 35 are, for example, approximately the same as those of the cores 11, 12. Furthermore, the deformation correction units 34, 35 are arranged, for example, equidistant from the central axis of the cladding unit 13. The distances of the deformation correction units 34, 35 from the central axis are, for example, equal to, but not necessarily equal to, the distances of the cores 11, 12 from the central axis of the cladding unit 13.

[0031] The multicore fiber 30 configured as above can also be manufactured by the manufacturing method shown in Fig. 3, and the cross-sectional shape is prevented from becoming non-circular. The angle between the x direction and the D direction may be between 80° and 100°. That is, in this specification, the second radial direction substantially perpendicular to the first radial direction means that the angle between the first radial direction and the second radial direction is between 80° and 100°.

[0032] In the above embodiment, the number of core portions is two and the number of deformation correction portions is two, but the present invention is not limited to this. For example, by replacing the low-refractive-index portions 16 with core portions in embodiment 2, a three-core multicore fiber can be realized. Furthermore, for example, in an n-core multicore fiber (n is an integer of 2 or more) in which n core portions are arranged along the first radial direction, the number of deformation correction portions is preferably n or n-1. Furthermore, as a further embodiment, an (n×m)-core multicore fiber can be realized in which n core portions aligned in the first radial direction are further arranged in m rows (m is an integer of 2 or more, for example, n>m) in a direction perpendicular to the first radial direction. In this case, the number of deformation correction portions is preferably (nm), for example.

[0033] In the above embodiment, the core units are homogeneous cores with the same structural parameters, but heterogeneous cores with different structural parameters may also be used. It is known that heterogeneous cores can suppress inter-core crosstalk.

[0034] In addition, in the above embodiment, the inner diameters of the holes are all equal, but the inner diameters of the holes may be different as long as the totals of the gaps in each radial direction are approximately equal.

[0035] Furthermore, the present invention is not limited to the above-described embodiments. The present invention also includes configurations in which the above-described components are appropriately combined. Furthermore, 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-described embodiments, and various modifications are possible. [Explanation of symbols]

[0036] 10, 20, 30: Multi-core fiber 11, 12: Core section 13: Cladding part 14, 15, 34, 35: Deformation correction section 16: Low refractive index section 100, 200: Glass rod 101, 102, 103, 104, 105: Vacancies 201, 202: Core rod 301, 302, 401: Rod Ar1, Ar2: arrows G: Gap

Claims

1. A multicore fiber, A plurality of cores; a cladding portion that surrounds the outer peripheries of the plurality of core portions and has a refractive index lower than that of the plurality of core portions; a plurality of deformation correction units disposed inside the cladding unit; Equipped with the plurality of core portions are arranged along a first radial direction in a cross section perpendicular to a longitudinal direction of the multicore fiber, The plurality of deformation correction units are arranged in the cross section along a second radial direction that is substantially perpendicular to the first radial direction. Multicore fiber.

2. The plurality of deformation correction portions have a stress profile or a refractive index different from that of the cladding portion. The multicore fiber according to claim 1 .

3. The number of the plurality of core units and the plurality of deformation correction units is two. The multicore fiber according to claim 1 .

4. a low refractive index portion disposed between the two core portions and having a refractive index lower than that of the cladding portion; The multicore fiber according to claim 3 .

5. A method for manufacturing a multi-core fiber according to any one of claims 1 to 4, a glass rod having a plurality of first holes arranged along the first radial direction and a plurality of second holes arranged along the second radial direction, wherein a core rod including a portion to be the core portion is inserted into each of the plurality of first holes; inserting a rod including a portion that will become the deformation correcting portion into each of the plurality of second holes of the glass rod; heating the glass rod, the core rod, and the rod to integrate them; Drawing the integrated glass rod, the core rod, and the rod to form the multi-core fiber. Method for manufacturing multicore fiber.

Images