Multicore fiber

Abstract

To provide a high-performance or multi-functional multicore fiber.SOLUTION: A multicore fiber provided herein comprises multiple cores including at least one solid core and at least one hollow core. The solid core may be made of quartz glass. Light may be trapped in the hollow core by the anti-resonant light confinement effect. Light may be trapped in the hollow core by the photonic bandgap light confinement effect.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multicore fiber. [Background technology]

[0002] As a multi-core fiber having multiple cores, techniques for improving the characteristics by providing holes between the cores have been studied (Non-Patent Documents 1 to 3). These cores are also called solid cores because they are made of a solid medium such as glass.

[0003] On the other hand, air-hole-core fibers are also being actively studied. Air-hole-core fibers are optical fibers that have an air-hole-shaped core (air-hole core) that is not filled with a solid medium. Air-hole-core fibers include anti-resonant and photonic band-gap types (Patent Documents 1 and 2, Non-Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2017-520804 [Patent Document 2] International Publication No. 2009 / 040902 [Non-patent literature]

[0005] [Non-Patent Document 1] K. Saitoh et al, “Multi-core hole-assisted fibers for high core density space division multiplexing”, OECC 2010, 7C2-1 (2010). [Non-Patent Document 2] B. Yao et al., “Reduction of Crosstalk by Hole-Walled Multi-Core Fiber”, OFC 2012, paper OM2D.5. (2012). [Non-Patent Document 3] K. Mukasa et al, “Uncoupled 6-core Fibers with a Standard 125mm Cladding, ITU-T G.652 Optical Properties, and Low XT”, OFC 2023, paper M3B.2 (2023). [Non-Patent Document 4] Gregory T. Jasion et al., “0.174 dB / km Hollow Core Double Nested Antiresonant Nodeless Fiber (DNANF)”, OFC 2022, paper Th4C.7 (2022). Summary of the Invention [Problem to be solved by the invention]

[0006] As optical transmission technology becomes more sophisticated, unprecedented high functionality or multiple functions are required of multicore fibers. However, known multicore fibers cannot fully satisfy these requirements.

[0007] The present invention has been made in view of the above, and an object of the present invention is to provide a high-performance or multi-function multi-core fiber. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention is a multi-core fiber having a plurality of core portions, the plurality of core portions including at least one solid core portion and at least one hole core portion.

[0009] The solid core portion may be made of silica glass.

[0010] The air hole core may confine light by an antiresonant type light confinement effect.

[0011] The air hole core may confine light by a photonic band gap type light confinement effect.

[0012] The solid core portion may confine light by a total reflection type light confinement effect.

[0013] The instrument may further include an outer tubular body surrounding the plurality of core portions.

[0014] The solid core may have a refractive index lower than the maximum refractive index of the solid core, and may be in contact with the solid core and surround the solid core, and the solid core and the solid clad may form a core structure.

[0015] The core structure may have any one of a step-type, W-type, staircase-type, and trench-type refractive index profile.

[0016] The solid core portion may be made of silica-based glass containing germanium, and the solid clad portion may be made of silica-based glass containing no dopants other than chlorine.

[0017] The solid core portion may be made of silica-based glass that does not contain germanium, and the solid clad portion may be made of silica-based glass that contains fluorine.

[0018] The device may further include an outer tubular body that surrounds the plurality of core portions, the outer tubular body supporting the core structure.

[0019] A plurality of the core structures may be provided, with gaps being present between the plurality of core structures.

[0020] The optical fiber may further include a plurality of tubular bodies surrounding the air hole core portion and having the effect of confining light in the air hole core portion by an antiresonant phenomenon, the plurality of tubular bodies including a first tubular body, and the first tubular body may house the solid core portion.

[0021] The optical fiber may include a plurality of tubular bodies surrounding the air hole core portion and having the effect of confining light in the air hole core portion by an antiresonant phenomenon, the plurality of tubular bodies including a second tubular body and a third tubular body, and the second tubular body may house the third tubular body. Effect of the Invention

[0022] According to the present invention, an effect is achieved in that a high-function or multi-function multi-core fiber can be realized. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic cross-sectional view of a multi-core fiber according to a first embodiment, taken along a plane perpendicular to the longitudinal direction thereof. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a multi-core fiber according to a second embodiment, taken along a plane perpendicular to the longitudinal direction thereof. [Diagram 3] FIG. 3 is a schematic cross-sectional view of a multi-core fiber according to a third embodiment in a plane perpendicular to the longitudinal direction. [Figure 4] FIG. 4 is a schematic cross-sectional view of a multi-core fiber according to a fourth embodiment, taken along a plane perpendicular to the longitudinal direction thereof. [Diagram 5] FIG. 5 is a schematic cross-sectional view of a multi-core fiber according to a fifth embodiment, taken along a plane perpendicular to the longitudinal direction thereof. [Figure 6] FIG. 6 is a schematic cross-sectional view of a multi-core fiber according to a sixth embodiment in a plane perpendicular to the longitudinal direction. [Figure 7] FIG. 7 is a schematic cross-sectional view of a multi-core fiber according to a seventh embodiment in a plane perpendicular to the longitudinal direction. [Figure 8]FIG. 8 is a schematic cross-sectional view of a multi-core fiber according to an eighth embodiment in a plane perpendicular to the longitudinal direction. [Figure 9] FIG. 9 is a schematic cross-sectional view of a multi-core fiber according to a ninth embodiment in a plane perpendicular to the longitudinal direction. [Figure 10] FIG. 10 is a schematic cross-sectional view of a multi-core fiber according to a tenth embodiment in a plane perpendicular to the longitudinal direction. [Figure 11] FIG. 11 is a schematic cross-sectional view of a multi-core fiber according to an eleventh embodiment in a plane perpendicular to the longitudinal direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present inventors have conceived of the possibility of realizing a highly functional or multifunctional multi-core fiber by using a novel configuration including both solid core portions and hole core portions, and have completed the present invention.

[0025] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below. In addition, in each drawing, the same or corresponding components are appropriately assigned the same reference numerals. In addition, in this specification, the cutoff wavelength or effective cutoff wavelength refers to the cable cutoff wavelength (λcc) defined in ITU-T G.650.1 of the International Telecommunications Union (ITU). In addition, other terms not specifically defined in this specification shall follow the definitions and measurement methods in G.650.1 and G.650.2.

[0026] (Embodiment 1) 1 is a schematic cross-sectional view in a plane perpendicular to the longitudinal direction of a multi-core fiber according to embodiment 1. The multi-core fiber 100 includes four core structures 10, four tubular bodies 20, a hollow core portion 21, and an outer tubular body 30. The four core structures 10 are an example of a plurality of core structures.

[0027] In the following, first the core structure 10 will be described, then the tubular body 20 and the hollow core portion 21 will be described, and finally the outer tubular body 30 will be described.

[0028] [Core Structure] The core structure 10 includes a solid core portion 11 having a circular cross section, and a solid clad portion 12 having a circular cross section. That is, the solid core portion 11 and the solid clad portion 12 constitute the core structure 10. The solid clad portion 12 has a refractive index lower than the maximum refractive index of the solid core portion 11, and is in contact with and surrounds the solid core portion 11. The four solid core portions 11 are an example of at least one solid core portion.

[0029] The solid core portion 11 and the solid clad portion 12 are made of a solid medium such as silica-based glass. For example, the solid core portion 11 is made of silica-based glass containing germanium, and the solid clad portion 12 is made of silica-based glass containing no dopants other than chlorine. As a result, the solid clad portion 12 has a refractive index lower than the maximum refractive index of the solid core portion 11. In this case, the solid clad portion 12 does not need to be doped with a dopant that reduces the refractive index, such as fluorine, so the multi-core fiber 100 can be made cheaper. Here, chlorine is doped into the silica-based glass in a dehydration process or the like in the manufacturing process of the core structure 10. In addition, the solid core portion 11 may be made of silica-based glass containing no germanium, and the solid clad portion 12 may be made of silica-based glass containing fluorine. As a result, the scattering loss in the solid core portion 11 can be reduced, so that the multi-core fiber 100 can have a lower loss. The silica-based glass containing no germanium is, for example, silica-based glass containing no dopants other than chlorine.

[0030] The refractive index profile of the core structure 10 is not particularly limited, but may be, for example, any one of a step type, a W type, a staircase type, and a trench type. The refractive index profile of the core structure 10 is set, for example, so that the input light propagates in a single mode, but may be set so that the input light propagates in a multimode.

[0031] With the above configuration, light is confined and propagated in the solid core portion 11 by a total reflection type light confinement effect. For example, 80% or more of the field of the propagating light is present in the solid core portion 11, and the remaining 20% ​​or less of the light field is present in the solid clad portion 12. The wavelength of the light propagating through the solid core portion 11 is, for example, a wavelength included in a communication wavelength band such as the 1.55 μm band, but is not particularly limited.

[0032] Furthermore, there are gaps between the core structures 10 .

[0033] [Tubular body and hollow core] The four tubular bodies 20 are circular and arranged to form a quadrangular lattice in cross section. The quadrangular lattice is, for example, a square lattice. The tubular bodies 20 are, for example, silica glass tubes having a predetermined thickness.

[0034] The air hole core portion 21 is a region surrounded by the tubular body 20 and is formed in a region close to the central axis of the multi-core fiber 100. That is, the tubular body 20 surrounds the periphery of the air hole core portion 21. The multiple tubular bodies 20 have the effect of confining light in the air hole core portion 21 by the antiresonant phenomenon. That is, the air hole core portion 21 confines light by the antiresonant type light confinement effect and propagates. For example, 80% or more of the field of propagating light exists in the air hole core portion 21, and the remaining 20% ​​or less of the light field exists in the tubular body 20, etc. In FIG. 1, the field F indicates the field of light propagating through the air hole core portion 21. In the field F, the intensity of the field is indicated by the shading of the dot pattern, and the higher the dot density, the higher the field intensity. The wavelength of the light propagating through the air hole core portion 21 can be changed by adjusting the wall thickness of the tubular body 20. That is, the thickness of the tubular body 20 is set according to the wavelength of the light propagated through the air hole core portion 21. The wavelength of the light propagated through the air hole core portion 21 is, for example, a wavelength included in a communication wavelength band such as the 1.55 μm band, but is not particularly limited. For example, the light propagated through the air hole core portion 21 may be light used for power transmission such as optical power feeding. The air hole core portion 21 is an example of at least one air hole core portion.

[0035] The tubular bodies 20 are arranged with appropriate gaps between them. If there are no gaps and the tubular bodies 20 are in contact with each other, the light propagating through the air hole cores 21 may leak through the contacting parts of the tubular bodies 20. If the gaps are too large, the light leaks excessively from the gaps.

[0036] Moreover, each of the tubular bodies 20 houses a core structure 10 including a solid core portion 11. The core structure 10 is mechanically connected to the tubular body 20 by welding or the like. The tubular body 20 is an example of a first tubular body.

[0037] [Outer tubular body] The outer tubular body 30 is a circular tube. The outer tubular body 30 is, for example, a silica glass tube having a predetermined thickness. The outer tubular body 30 accommodates the core structure 10, the tubular body 20, and the hole core portion 21. That is, the outer tubular body 30 surrounds the solid core portion 11 and the hole core portion 21 as a plurality of core portions. The outer tubular body 30 is mechanically connected to the tubular body 20 by welding or the like. As a result, the tubular body 20 is supported by the outer tubular body 30. The core structure 10 is supported by the outer tubular body 30 with the tubular body 20 interposed therebetween.

[0038] The multi-core fiber 100 configured as above includes, as the multiple core portions, solid core portions 11 and hole core portions 21. This enables the multi-core fiber 100 to achieve high functionality or multiple functions that cannot be achieved by known multi-core fibers.

[0039] For example, the solid core 11 and the optical transmission technology using it are mature technologies that have been put to practical use in various applications and are highly practical. On the other hand, the air hole core 21 and the optical transmission technology using it can realize innovative high performance by eliminating various limitations caused by solid media such as glass. Such limitations include optical delay, power tolerance limits, absorption and scattering losses due to the medium, and resistance to harsh environments. Therefore, the air hole core 21 can be suitably used for optical power supply and ultra-low latency optical transmission, for example.

[0040] According to the multi-core fiber 100, it is possible to enjoy the above-mentioned practicality and high functionality. Moreover, the multi-core fiber 100 can provide a usage in which the solid core portion 11 is used for normal applications and the hole core portion 21 is used for applications with higher added value than the normal applications. Furthermore, when the multi-core fiber 100 is laid in the field, it is possible to provide a usage in which the solid core portion 11, which has high practicality, is used for the time being, and the use of the hole core portion 21 is started when a demand for applications with higher added value arises or when the practicality of the technology using the hole core portion 21 is further improved. In this case, a lower cost is realized than when an optical fiber having a hole core portion is additionally laid later.

[0041] Furthermore, in the multi-core fiber 100, since the tubular body 20 houses the core structure 10 including the solid core portion 11, the cross-sectional area of ​​the multi-core fiber 100 can be reduced compared to a structure in which the tubular body 20 does not house the core structure 10. Also, it is easy to ensure a space for providing the air hole core portion 21 near the central axis of the multi-core fiber 100.

[0042] Furthermore, in the multi-core fiber 100, since the outer tubular body 30 supports the core structure 10 and the tubular body 20, the mechanical strength of the multi-core fiber 100 can be sufficiently ensured.

[0043] Furthermore, in the multi-core fiber 100, since there are gaps between the core structures 10, the inter-core crosstalk value between the solid core portions 11 can be made sufficiently low.

[0044] The multi-core fiber 100 can be manufactured, for example, as follows. First, a core preform to become the core structure 10 is prepared. The core preform can be formed, for example, by using a known method such as a Vapor Axial Deposition (VAD) method, a Modified Chemical Vapor Deposition (MCVD) method, or an Outside Vapor Deposition (OVD) method. At this time, the core diameter / cladding diameter ratio in the core preform may be set to the core diameter / cladding diameter ratio to be realized in the core structure 10. Next, a first glass tube to become the tubular body 20 and a second glass tube to become the outer tubular body 30 are prepared. As the first glass tube and the second glass tube, a commercially available glass tube may be used, or a glass tube manufactured by drilling a hole in a glass rod manufactured by the VAD method may be used. Next, a structure as shown in FIG. 1, that is, a structure in which the core preform is accommodated in the first glass tube and the first glass tube is accommodated in the second glass tube, is formed to form an optical fiber preform. Next, this optical fiber preform is drawn in the same manner as known multicore fibers to manufacture the multicore fiber 100. Since the tubular body 20 is required to have a relatively thin wall thickness, a first glass tube having a relatively thick wall thickness may be prepared, and the desired wall thickness of the tubular body 20 may be achieved by adjusting the drawing conditions during drawing.

[0045] (Embodiment 2) 2 is a schematic cross-sectional view in a plane perpendicular to the longitudinal direction of a multi-core fiber according to embodiment 2. The multi-core fiber 100A differs from the multi-core fiber 100 according to embodiment 1 in that the multi-core fiber 100A has five core structures 10 and five tubular bodies 20.

[0046] The five tubular bodies 20 are arranged to form a pentagonal lattice in cross section. The pentagonal lattice is, for example, a regular pentagonal lattice. As a result, air hole core portions 21A are formed in areas surrounded by the tubular bodies 20. A field FA indicates a field of light propagating through the air hole core portions 21A.

[0047] According to the multi-core fiber 100A configured as above, it is possible to achieve high performance or multiple functions similar to those of the multi-core fiber 100 according to the first embodiment as described above.

[0048] As can be seen from the multi-core fibers 100 and 100A, the number of core structures 10 and tubular bodies 20 is not particularly limited, but the number of tubular bodies 20 is preferably three or more.

[0049] Here, specific examples of numerical values ​​of the structural parameters of the multi-core fiber according to the embodiment will be described, taking the multi-core fiber 100A as an example.

[0050] First, the outer diameter of the outer tubular body 30, i.e., the fiber diameter of the multi-core fiber 100A, is preferably 125 μm from the viewpoint of compatibility with many known optical fibers. The inner diameter of the outer tubular body 30 is, for example, 100 μm. The wall thickness of the tubular body 20 is, for example, 0.65 μm from the viewpoint of confining light in the 1.55 μm wavelength band. The outer diameter of the tubular body 20 is, for example, 35 μm. The outer diameter of the core structure 10 is, for example, 30 μm. Moreover, the solid core portion 11 is made of, for example, germanium-doped silica glass. Moreover, the core structure 10 has a step-type refractive index profile, the core diameter of the solid core portion 11 is, for example, 9 μm, and the relative refractive index difference of the maximum refractive index of the solid core portion 11 with respect to the refractive index of the solid clad portion 12 is, for example, 0.37%.

[0051] For the multi-core fiber 100A having the above-described structure, the confinement loss of the solid core portion 11 at a wavelength of 1550 nm was calculated to be 0.001 dB / km, which is sufficiently small. Also, the confinement loss of the air-hole core portion 21 at a wavelength of 1550 nm was calculated to be 0.3 dB / km, which is sufficiently small.

[0052] (Embodiment 3) FIG. 3 is a schematic cross-sectional view of a multi-core fiber according to the third embodiment in a plane perpendicular to the longitudinal direction. The multi-core fiber 100B has a configuration in which four tubular bodies 20B are added to the multi-core fiber 100 according to the first embodiment. Each of the four tubular bodies 20B is housed in the tubular body 20 and houses a core structure 10. The wall thickness of the tubular body 20B is also set so as to realize anti-resonant type light confinement according to the wavelength of light propagated in the air hole core portion 21B. The tubular body 20B is an example of a first tubular body that houses a core structure, and is also an example of a third tubular body. The tubular body 20 is an example of a second tubular body that houses the tubular body 20B.

[0053] In the multi-core fiber 100B, the tubular bodies 20, 20B form an anti-resonant double light confinement structure for the air hole core portion 21B, and a field such as the field FB is formed in the air hole core portion 21B.

[0054] The multi-core fiber 100B configured as above can achieve high performance or multiple functions similar to those of the multi-core fiber 100 according to the first embodiment as described above. Furthermore, since the tubular bodies 20, 20B configure a double light confinement structure for the air hole core portion 21B, for example, the light field leaking from the tubular body 20 is also confined by the tubular body 20B. As a result, the multi-core fiber 100B can reduce the confinement loss in the air hole core portion 21B more than the multi-core fiber 100.

[0055] (Embodiment 4) 4 is a schematic cross-sectional view in a plane perpendicular to the longitudinal direction of a multi-core fiber according to embodiment 4. The multi-core fiber 100C differs from the multi-core fiber 100B according to embodiment 3 in that the multi-core fiber 100C has five core structures 10 and five tubular bodies 20, 20B.

[0056] The five tubular bodies 20, 20B are arranged to form a pentagonal lattice in cross section. The pentagonal lattice is, for example, a regular pentagonal lattice. As a result, a hole core portion 21C is formed in a region surrounded by the tubular bodies 20. A field FC indicates a field of light propagating through the hole core portion 21C.

[0057] The multi-core fiber 100C configured as above can achieve the same high performance or multi-function effect as the multi-core fiber 100B according to embodiment 3 as described above. For example, the multi-core fiber 100C can reduce the confinement loss in the air-hole core portions 21C more than the multi-core fiber 100A.

[0058] (Embodiment 5) 5 is a schematic cross-sectional view in a plane perpendicular to the longitudinal direction of a multi-core fiber according to embodiment 5. The multi-core fiber 100D includes four core structures 10, eight tubular bodies 20D, air-hole core portions 21D, and an outer tubular body 30. The outer tubular body 30 accommodates the core structures 10, the tubular bodies 20D, and the air-hole core portions 21D.

[0059] The four core structures 10 are arranged so as to form a square lattice in cross section, and are mechanically connected to the inner wall of the outer tubular body 30 by welding or the like. As a result, the core structure 10 is directly supported by the outer tubular body 30. Furthermore, there are gaps between the core structures 10.

[0060] The eight tubular bodies 20D are arranged to form an octagonal lattice in cross section. The octagonal lattice is, for example, a regular octagonal lattice. As a result, the air hole core portion 21D is formed in an area surrounded by the tubular bodies 20D. The field FD indicates the field of light propagating through the air hole core portion 21D. The thickness of the tubular body 20D is set according to the wavelength of the light propagating through the air hole core portion 21D.

[0061] Moreover, each of the tubular bodies 20D is mechanically connected by welding or the like to any of the four core structures 10. In this way, the tubular body 20D is supported by the core structure 10. The tubular body 20D is an example of a fourth tubular body supported by a core structure.

[0062] According to the multi-core fiber 100D configured as above, it is possible to achieve high performance or multiple functions similar to those of the multi-core fiber 100 according to the first embodiment as described above.

[0063] Furthermore, in the multi-core fiber 100D, since the tubular body 20D is supported by the core structure 10, the arrangement and shape of the air-hole core portions 21D can be set differently from those in the multi-core fiber 100.

[0064] (Embodiment 6) 6 is a schematic cross-sectional view of a multi-core fiber according to the sixth embodiment in a plane perpendicular to the longitudinal direction. The multi-core fiber 100E has a configuration in which eight tubular bodies 20E1 and eight tubular bodies 20E2 are added to the multi-core fiber 100D according to the fifth embodiment. The eight tubular bodies 20E1 are each housed in the tubular body 20D. Moreover, the eight tubular bodies 20E2 are each disposed on the outer tubular body 30 side with respect to the tubular body 20D. The wall thicknesses of the tubular bodies 20E1 and E2 are also set so as to realize anti-resonant type light confinement according to the wavelength of light propagated in the air-hole core portion 21E.

[0065] As a result, the air hole core portion 21E is formed in a region surrounded by the tubular bodies 20D, 20E1, and 20E2. A field FE indicates a field of light propagating through the air hole core portion 21E.

[0066] Furthermore, each of the tubular bodies 20E1 is mechanically connected to one of the four core structures 10 by welding or the like with the eight tubular bodies 20D interposed therebetween. Each of the tubular bodies 20E2 is mechanically connected to one of the four core structures 10 by welding or the like. In this way, the tubular bodies 20E1 and 20E2 are supported by the core structure 10.

[0067] The tubular body 20D is an example of the second tubular body and an example of the fourth tubular body. The tubular body 20E1 is an example of the third tubular body and an example of the fourth tubular body. The tubular body 20E2 is an example of the fourth tubular body.

[0068] The multi-core fiber 100E configured as above can achieve high performance or multiple functions similar to those of the multi-core fiber 100 according to embodiment 1. Furthermore, since the tubular bodies 20D, 20E1, and 20E2 configure a triple light confinement structure for the air hole core portion 21E, the confinement loss in the air hole core portion 21E can be reduced more than in the multi-core fiber 100D.

[0069] (Embodiment 7) 7 is a schematic cross-sectional view in a plane perpendicular to the longitudinal direction of a multi-core fiber according to embodiment 7. The multi-core fiber 100F includes three core structures 10, five tubular bodies 20F, a hole core portion 21F, and an outer tubular body 30. The outer tubular body 30 accommodates the core structure 10, the tubular bodies 20F, and the hole core portion 21F.

[0070] The three core structures 10 are mechanically connected by welding or the like to the inner wall of the outer tubular body 30. Furthermore, there are gaps between the core structures 10.

[0071] The five tubular bodies 20F are arranged to form a pentagonal lattice in cross section. The pentagonal lattice is, for example, a regular pentagonal lattice. As a result, the air hole core portion 21F is formed in a region surrounded by the tubular bodies 20F. The field FF indicates the field of light propagating through the air hole core portion 21F. The thickness of the tubular body 20F is set according to the wavelength of the light propagating through the air hole core portion 21F.

[0072] The five tubular bodies 20F include two tubular bodies 20F1 and three tubular bodies 20F2. The two tubular bodies 20F1 are mechanically connected to the inner wall of the outer tubular body 30 by welding or the like. As a result, the tubular body 20F1 is directly supported by the outer tubular body 30. The three tubular bodies 20F2 are mechanically connected to the core structure 10 by welding or the like. As a result, the tubular body 20F2 is supported by the core structure 10. The tubular body 20F2 is an example of a fourth tubular body supported by the core structure.

[0073] According to the multi-core fiber 100F configured as above, it is possible to achieve high performance or multiple functions similar to those of the multi-core fiber 100 according to the first embodiment as described above.

[0074] Furthermore, in the multi-core fiber 100F, the tubular body 20F forming the hole core portion 21F includes the tubular body 20F1 and the tubular body 20F2, so that the arrangement and shape of the hole core portion 21F can be set with a higher degree of freedom. For example, in the multi-core fiber 100F, the hole core portion 21F can be formed at a position shifted from the central axis of the multi-core fiber 100F. This allows the existence region of the solid core portion 11 and the existence region of the hole core portion 21F to be separated in the left-right direction of the drawing.

[0075] (Embodiment 8) 8 is a schematic cross-sectional view in a plane perpendicular to the longitudinal direction of a multi-core fiber according to embodiment 8. The multi-core fiber 100G includes two core structures 10, ten tubular bodies 20G, two air-hole core portions 21G, and an outer tubular body 30. The outer tubular body 30 accommodates the core structure 10, the tubular bodies 20G, and the air-hole core portions 21G.

[0076] The two core structures 10 are mechanically connected by welding or the like to the inner wall of the outer tubular body 30. As a result, the core structure 10 is directly supported by the outer tubular body 30. In addition, a gap exists between the core structures 10.

[0077] The ten tubular bodies 20F are arranged to form two hexagonal lattices in the cross section. The hexagonal lattices are, for example, regular hexagonal lattices. As a result, air hole core portions 21G are formed in each of the two regions surrounded by the tubular bodies 20G. A field FG indicates a field of light propagating through the air hole core portions 21G. The thickness of the tubular body 20G is set according to the wavelength of the light propagating through the air hole core portions 21G.

[0078] The ten tubular bodies 20G include four tubular bodies 20G1, four tubular bodies 20G2, and two tubular bodies 20G3. The four tubular bodies 20G1 are mechanically connected to the inner wall of the outer tubular body 30 by welding or the like. As a result, the core structure 10 is directly supported by the outer tubular body 30. The four tubular bodies 20G2 are mechanically connected to the core structure 10 by welding or the like. As a result, the tubular bodies 20G2 are supported by the core structure 10. The two tubular bodies 20G3 are mechanically connected to the core structure 10 by welding or the like, and are shared between the two air hole core portions 21G. That is, each of the two tubular bodies 20G3 contributes to the light confinement of each of the two air hole core portions 21G. The tubular body 20G3 is an example of a fifth tubular body shared between a plurality of air hole core portions.

[0079] According to the multi-core fiber 100G configured as above, it is possible to achieve high performance or multiple functions similar to those of the multi-core fiber 100 according to the first embodiment as described above.

[0080] Furthermore, the multi-core fiber 100G has two air-hole core portions 21G, and the air-hole core portions also have a multi-core structure, so that it can be applied to a wider variety of applications. Also, in the multi-core fiber 100G, the tubular body 20F is shared between a plurality of air-hole core portions, so that the number of tubular bodies used and the cross-sectional area of ​​the multi-core fiber 100G can be reduced.

[0081] (Embodiment 9) 9 is a schematic cross-sectional view in a plane perpendicular to the longitudinal direction of a multi-core fiber according to embodiment 9. The multi-core fiber 100H includes 27 core structures 10H, 24 tubular bodies 20H, four air-hole core portions 21H, and an outer tubular body 30. The outer tubular body 30 accommodates the core structure 10H, the tubular bodies 20H, and the air-hole core portions 21H.

[0082] The 27 core structures 10H include 18 core structures 10, 4 core structures 10H1, 4 core structures 10H2, and 1 core structure 10H3. The core structure 10H1 includes a solid core portion 11H1 having a circular cross section and a solid clad portion 12H1 having a circular cross section. The solid clad portion 12H1 has a refractive index lower than the maximum refractive index of the solid core portion 11H1, and is in contact with the solid core portion 11H1 to surround the periphery of the solid core portion 11H1. The core structure 10H2 includes a solid core portion 11H2 having a circular cross section and a solid clad portion 12H2 having a circular cross section. The solid clad portion 12H2 has a refractive index lower than the maximum refractive index of the solid core portion 11H2, and is in contact with the solid core portion 11H2 to surround the periphery of the solid core portion 11H2. The core structure 10H3 includes a solid core portion 11H3 having a circular cross section and a solid clad portion 12H3 having a circular cross section. The solid clad portion 12H3 has a refractive index lower than the maximum refractive index of the solid core portion 11H3, and is in contact with and surrounds the solid core portion 11H3.

[0083] The solid core portions 11, 11H1, 11H2, and 11H3 are configured as heterogeneous core portions. The heterogeneous core portions are core portions having mutually different effective refractive indices. The heterogeneous core portions are mutually different in at least one of the core diameter, the refractive index profile, and the relative refractive index difference, for example.

[0084] The core structure 10 is mechanically connected to the inner wall of the outer tubular body 30 by welding or the like. As a result, the core structure 10 is directly supported by the outer tubular body 30. Also, there is a gap between the core structures 10. The core structure 10H1 is mechanically connected to the core structure 10 by welding or the like. The core structure 10H2 is mechanically connected to the core structure 10H1 by welding or the like. The core structure 10H3 is mechanically connected to the tubular body 20H by welding or the like.

[0085] The tubular body 20H is mechanically connected to any of the core structures 10H by welding or the like. The 24 tubular bodies 20H are arranged to form four independent hexagonal lattices in the cross section. The hexagonal lattices are, for example, regular hexagonal lattices. As a result, a hole core portion 21H is formed in each of the four regions surrounded by the tubular body 20H. A field FH indicates a field of light propagating through the hole core portion 21H. The thickness of the tubular body 20H is set according to the wavelength of the light propagating through the hole core portion 21H.

[0086] According to the multi-core fiber 100H configured as above, it is possible to achieve high performance or multiple functions similar to those of the multi-core fiber 100 according to the first embodiment as described above.

[0087] In particular, the multicore fiber 100H includes 27 solid cores and 4 air-hole cores, and can achieve extremely high or multiple functions. Note that the core structures 10H1, 10H2, and 10H3 are mechanically and optically connected, but since they have heterogeneous cores, crosstalk between the cores is suppressed.

[0088] (Embodiment 10) 10 is a schematic cross-sectional view in a plane perpendicular to the longitudinal direction of a multicore fiber according to embodiment 10. The multicore fiber 100I includes six core structures 10, one photonic bandgap structure 40I, and an outer tubular body 30. The outer tubular body 30 houses the core structures 10 and the photonic bandgap structure 40I.

[0089] The core structure 10 is mechanically connected to the inner wall of the outer tubular body 30 by welding or the like. As a result, the core structure 10 is directly supported by the outer tubular body 30.

[0090] The photonic bandgap structure 40I extends in the longitudinal direction of the multicore fiber 100I. The photonic bandgap structure 40I includes an air hole core portion 41I, an inner cladding portion 42I, and an outer cladding portion 43I. The inner cladding portion 42I surrounds the periphery of the air hole core portion 41I and is made of glass having a large number of air holes. The large number of air holes are arranged, for example, in a triangular lattice shape so as to form a photonic crystal with the air hole core portion 41I as a crystal defect. The interval between the air holes is set according to the wavelength of the light propagated in the air hole core portion 41I. The field FI indicates the field of light propagated by the air hole core portion 41I. The outer cladding portion 43I surrounds the periphery of the inner cladding portion 42I and is made of solid glass. The photonic bandgap structure 40I is mechanically connected to the core structure 10 at the outer cladding portion 43I by welding or the like. As a result, the photonic bandgap structure 40I is supported by the core structure 10.

[0091] In the multi-core fiber 100I configured as above, light is confined and propagated in the air-hole core portions 41I due to the photonic bandgap type light confinement effect.

[0092] According to the multi-core fiber 100H, it is possible to achieve high performance or multiple functions similar to those of the multi-core fiber 100 according to the first embodiment as described above.

[0093] (Embodiment 11) 11 is a schematic cross-sectional view of a multi-core fiber according to embodiment 11 in a plane perpendicular to the longitudinal direction. The multi-core fiber 100J includes six core structures 10, air-hole core portions 41J, a photonic bandgap structure portion 42J, and an outer tubular body 30J. The outer tubular body 30J has a cylindrical outer diameter and an inner hole with a hexagonal cross section, and houses the core structures 10, the air-hole core portions 41J, and the photonic bandgap structure portion 42J.

[0094] The core structure 10 is mechanically connected to the inner wall of the outer tubular body 30J by welding, etc. In this way, the core structure 10 is directly supported by the outer tubular body 30J.

[0095] The photonic bandgap structure 42J is provided in the hole of the outer tubular body 30J, and surrounds the periphery of the air hole core 41I and extends in the longitudinal direction. The photonic bandgap structure 42J is made of glass having a large number of air holes. The large number of air holes are arranged, for example, in a triangular lattice shape so as to form a photonic crystal with the air hole core 41J as a crystal defect. The spacing between the air holes is set according to the wavelength of the light propagating through the air hole core 41J. A field FJ indicates the field of light propagating through the air hole core 41J.

[0096] In the multi-core fiber 100J configured as above, light is confined and propagated in the air-hole core portions 41J due to the photonic bandgap type light confinement effect.

[0097] According to the multi-core fiber 100J, it is possible to achieve high performance or multiple functions similar to those of the multi-core fiber 100 according to the first embodiment as described above.

[0098] In the multi-core fiber 100J, the holes in the outer tubular body 30J have a hexagonal cross section, but may have a circular or other polygonal shape.

[0099] In the above embodiment, the solid core portion is configured to confine and propagate light by a total reflection type light confinement effect, but may be configured to confine and propagate light by a photonic band gap type light confinement effect. In this case, the solid core portion is surrounded by a cladding portion made of glass having a large number of holes. The large number of holes are arranged, for example, in a triangular lattice shape so as to form a photonic crystal with the solid core portion as a crystal defect. The spacing between the holes is set according to the wavelength of the light propagating in the solid core portion.

[0100] In the above embodiment, the tubular body has a circular cross section, but the tubular body may have a polygonal cross section or the like.

[0101] Furthermore, the present invention is not limited to the above-mentioned embodiment. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-mentioned embodiment, and various modifications are possible. [Explanation of symbols]

[0102] 10, 10H, 10H1, 10H2, 10H3: Core structure 11, 11H1, 11H2, 11H3: Solid core section 12, 12H1, 12H2, 12H3: Solid clad section 20, 20B, 20D, 20E1, 20E2, 20F, 20F1, 20F2, 20G, 20G1, 20G2, 20G3, 20H: Tubular body 21, 21A, 21B, 21C, 21D, 21E, 21F, 21G, 21H, 41I, 41J: Hole core part 30, 30J: Outer tubular body 40I: Photonic band gap structure 42I: Inner cladding 42J: Photonic band gap structure 43I: Outer clad part 100, 100A, 100B, 100C, 100D, 100E, 100F, 100G, 100H, 100I, 100J: Multi-core fiber F, FA, FB, FC, FD, FE, FF, FG, FH, FJ: Field

Claims

1. A plurality of cores are provided. The plurality of core portions include at least one solid core portion and at least one hollow core portion. Multicore fiber.

2. The solid core portion is made of silica glass. The multicore fiber according to claim 1 .

3. The air hole core portion confines light by an antiresonant type light confinement effect. The multicore fiber according to claim 1 .

4. The air hole core portion confines light by a photonic band gap type light confinement effect. The multicore fiber according to claim 1 .

5. The solid core portion confines light by a total reflection type light confinement effect. The multicore fiber according to claim 1 .

6. An outer tubular body surrounding the plurality of core portions The multicore fiber according to claim 1 .

7. The solid core has a refractive index lower than the maximum refractive index of the solid core, and the solid clad is in contact with the solid core and surrounds the solid core, and the solid core and the solid clad constitute a core structure. The multicore fiber according to claim 1 .

8. The core structure has a refractive index profile of any one of a step type, a W type, a staircase type, and a trench type. The multicore fiber according to claim 7.

9. The solid core portion is made of silica-based glass containing germanium, and the solid clad portion is made of silica-based glass containing no dopants other than chlorine. The multicore fiber according to claim 7.

10. The solid core portion is made of silica-based glass that does not contain germanium, and the solid clad portion is made of silica-based glass that contains fluorine. The multicore fiber according to claim 7.

11. An outer tubular body is provided surrounding the plurality of core portions, and the outer tubular body supports the core structure. The multicore fiber according to claim 7.

12. A plurality of the core structures are provided, and gaps are present between the plurality of core structures. The multicore fiber according to claim 7.

13. a plurality of tubular bodies surrounding the periphery of the air hole core portion and having an effect of confining light in the air hole core portion by an antiresonant phenomenon; The plurality of tubular bodies includes a first tubular body, and the first tubular body houses the solid core portion. The multicore fiber according to claim 3 .

14. a plurality of tubular bodies surrounding the periphery of the air hole core portion and having an effect of confining light in the air hole core portion by an antiresonant phenomenon; The plurality of tubular bodies include a second tubular body and a third tubular body, the second tubular body containing the third tubular body. The multicore fiber according to claim 3 .

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