Multi-core plastic optical fiber, optical communication cable, and optical communication system

Abstract

A multi-core plastic optical fiber is a plastic optical fiber having multiple cores and a cladding covering the cores. It comprises a core group having 300 or more cores with an outer diameter of 25 μm or more and 60 μm or less. In the inner core group (excluding the outermost cores of the core group), the CV value of the cladding thickness on the line connecting the centroids of adjacent cores forming the inner core group is 20% or less. This provides multi-core plastic optical fibers with low optical density deviation per core and wide transmission bandwidth, optical communication cables, and optical communication systems.

Description

Technical Field

[0001] This invention relates to multi-core plastic optical fibers, optical communication cables, and optical communication systems. Background Technology

[0002] Plastic optical fibers, taking advantage of their lightweight and flexible properties, are used in a wide range of fields, including decorative lighting, medical applications, automotive interior lighting, various sensors, and communications. In communications, research is underway into spatial multiplexing communications that utilize a single multi-core plastic optical fiber for transmitting multiple signals. In particular, the dramatic increase in communication data volume in recent years has spurred efforts to improve the communication capacity per unit width of transceivers connected to optical fibers, leading to various development efforts to date.

[0003] For example, Patent Document 1 discloses a method in which colored seams are arranged around a transparent core and a cladding for the purpose of suppressing crosstalk between cores in spatial multiplexing communication.

[0004] Furthermore, Patent Document 2 discloses a multi-core plastic optical fiber (hereinafter referred to as a two-component optical fiber) with three or more cores, wherein the average diameter of the cores is 40 to 300 μm, the average spacing between adjacent cores is 2 μm or more, and the CV value of the gap between the closest portions of adjacent cores, excluding the outermost core, is 20% or less. Additionally, a multi-core plastic optical fiber (hereinafter referred to as a three-component optical fiber) is disclosed, wherein the core forms a core-sheath structure, the cladding layer thickness of the sheath is 1 μm or more, and the CV value of the difference in thickness between the thinnest and thickest portions of the cladding layer is 20% or less. Furthermore, as a method for manufacturing multi-core plastic optical fibers, a spinning method is disclosed for two-component optical fibers where the cladding component surrounds the outer periphery of the core, forming a two-layer composite flow, and then multiple two-layer composite flows are merged. Additionally, a spinning method is disclosed for three-component optical fibers where the cladding component surrounds the outer periphery of the core, forming a two-layer composite flow, and the cladding component further surrounds the outer periphery of the two-layer composite flow, forming a three-layer composite flow, and then multiple three-layer composite flows are merged. It was disclosed that, in this case, by reducing the melt viscosity of the polymer disposed on the periphery, a composite flow can be stably formed, thereby reducing the thickness deviation of the cladding and coating layers.

[0005] In addition, Patent Document 3 discloses a method for obtaining the same amount of transmitted light as a single-core fiber by making the core hexagonal and arranging it in the densest possible filling to increase the total cross-sectional area of ​​the core.

[0006] In addition, patent document 4 discloses image optical fibers used for image transmission that are not intended for communication. For clear image display, a higher core count is desired, and an optimal optical fiber structure has been proposed.

[0007] In addition, as another method for manufacturing multi-core plastic optical fibers, Patent Document 6 is disclosed. Patent Document 5 describes a method for manufacturing optical fibers using a composite spinneret, commonly referred to as a tube-type spinneret. This composite spinneret has tubes arranged according to the number of cores; molten polymer that becomes the core component is ejected from each tube, and molten polymer that becomes the cladding component is supplied from the outer periphery of the tubes. It is described that: thereby, the cladding component coats the outer periphery of the core component, forming a composite polymer with multiple cores / claddings, which is finally ejected from the spinneret's ejection orifice, thereby enabling the manufacture of multi-core plastic optical fibers.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 11-258432

[0011] Patent Document 2: Japanese Patent Application Publication No. 2001-174661

[0012] Patent Document 3: Japanese Patent Application Publication No. 11-160553

[0013] Patent Document 4: Japanese Patent Application Publication No. 6-18725

[0014] Patent Document 5: Japanese Patent Application Publication No. 2013-231817 Summary of the Invention

[0015] The problem that the invention aims to solve

[0016] However, conventional multi-core plastic optical fibers and their manufacturing methods have the following problems.

[0017] The technology disclosed in Patent Document 1 is an optical fiber with a small number of cores and a large core diameter (the embodiment has 37 cores and a core diameter of 100 μm). According to the inventors, when the core diameter is too large, the transmission bandwidth in multiplexed communication sometimes deteriorates. In addition, when an optical fiber is configured with more than 300 cores, the fiber diameter becomes thicker, and sometimes the bending characteristics are significantly reduced.

[0018] Furthermore, Patent Document 2 discloses methods for manufacturing optical fibers with fewer cores and larger core diameters, specifically methods for manufacturing optical fibers with 37 cores (150 μm outer diameter) and 151 cores (75 μm outer diameter) as described in the embodiments. However, according to the inventors, when the number of cores in an optical fiber is as high as 300 or more and the core diameter becomes smaller (less than 60 μm), controlling the cross-section of the polymer at the composite spinneret becomes very difficult. This results in the merging of adjacent cores, poor core shape, and sometimes the undesirable optical fiber cross-section. This is because, as the number of cores increases, the size of the composite spinneret becomes larger, requiring the cladding polymer and the seam polymer to be supplied from the outer periphery of the composite spinneret towards the center. However, due to the arrangement of many polymer composite flow paths for forming the core / cladding, it is impossible to supply the polymer sufficiently to the center of the composite spinneret. As a result, the merging of adjacent cores and poor core shape sometimes occur. When the configuration density of the aforementioned polymer composite flow path is continuously increased in order to reduce the size of the composite spinneret, the flow path itself becomes very narrow, thus making the above-mentioned problems more significant. In addition, as a method to uniformize the thickness deviation of the cladding of two-component optical fibers and the cladding of three-component optical fibers, reducing the polymer viscosity on the outer periphery in the polymer composite flow path is disclosed, but no other solutions are described.

[0019] Furthermore, while Patent Document 3 discloses an optical fiber with a relatively small number of cores (151 cores in the embodiment), according to the inventors, it is sometimes impossible to achieve this when the number of cores in an optical fiber is as high as 300 or more and the core diameter is small (less than 60 μm). Additionally, although it is possible to obtain the transmitted light quantity of a multi-core plastic optical fiber, techniques related to suppressing deviations in the transmitted light quantity of each core, which is an important indicator, are not disclosed.

[0020] Furthermore, the technology disclosed in Patent Document 4 is limited to optical fibers used for image transmission, which have different characteristics than those required for optical fibers used in space multiplexing communication. Therefore, the optimal optical fiber structure is not the same. Additionally, according to the inventors, in image transmission applications, the optical fiber length is several meters, so it is desirable to sacrifice transmission loss by configuring many cores to make the core diameter smaller, thereby improving resolution. On the other hand, in multiplexing communication applications, from the viewpoint of transmission loss, a larger core diameter is better, while from the viewpoint of transmission bandwidth, a smaller core diameter is preferable. Balancing both aspects is a key technical point, but Patent Document 4 does not describe anything related to this. In the embodiments of Patent Document 4, an optical fiber with 3247 cores and a core diameter of 10 μm is disclosed, but the transmission loss is 1200 dB / km, which is very high, and therefore sometimes unsuitable for multiplexing communication applications.

[0021] Furthermore, a major problem with the tube-type spinneret disclosed in Patent Document 5 is that to create an island, the tube thickness is increased, thus increasing the average area of ​​each tube. Additionally, in the spinneret fabrication process, the tube is pressed into the spinneret and welded in place, requiring welding allowance. Moreover, due to the presence of insertion holes for the tubes, the gaps between the tubes cannot be narrowed due to strength issues. Consequently, it is impossible to densely arrange the tubes per unit area, making it difficult to manufacture multi-core plastic optical fibers with a very high core count and small core outer diameter. Furthermore, because a cylindrical tube is used, the resulting island shape is limited to a circle or a similar elliptical shape, making it sometimes impossible to obtain multi-core plastic optical fibers with, for example, polygonal core shapes. Additionally, because a polymer inlet path for the cladding component is arranged around the outer periphery of the densely arranged tube assembly, it is difficult to adequately supply the cladding component polymer to the center of the tube assembly; in particular, sometimes the core component polymer ejected from the tubes at the center of the tube assembly merges with each other. According to the inventors' understanding, it is sometimes structurally difficult to freely arrange the inlet flow path of the cladding component polymer within the tube assembly.

[0022] Therefore, the object of the present invention is to provide multi-core plastic optical fibers, optical communication cables and optical communication systems with less deviation in the transmission volume of each core and a wider transmission bandwidth.

[0023] Methods for solving problems

[0024] To address the aforementioned issues, the present invention employs any of the following configurations.

[0025] (1) A multi-core plastic optical fiber having a plurality of cores, a plurality of core sheaths having a cladding portion formed around the plurality of cores, and a portion covering the periphery of the plurality of core sheaths, wherein a core sheath group is formed, wherein the number of the plurality of core sheaths in the core sheath group is 300 or more and the outer diameter of the plurality of core sheaths is 25 μm or more and 60 μm or less, and regarding the core sheath group other than the core sheaths disposed on the outermost periphery of the core sheath group, i.e. the inner core sheath group, the CV value of the cladding portion thickness defined by the gap between the adjacent core sheaths is 15% or less on the line connecting the centroids of the adjacent core sheaths forming the inner core sheath group.

[0026] (2) The multi-core plastic optical fiber according to (1), wherein the core sheath is configured with the densest filling structure of any one of hexagonal lattice, square lattice, and triangular lattice.

[0027] (3) The multi-core plastic optical fiber according to (2), wherein one core sheath portion forming the inner core sheath portion group has parallel edges with the adjacent core sheath portion.

[0028] (4) According to the multi-core plastic optical fiber of (1), wherein when the outer diameter of the core sheath forming the inner core sheath assembly is set to D, the CV value of the cladding thickness is 20% or less within the range between two lines that are D / 6 apart from the line connecting the centroids of adjacent core sheaths.

[0029] (5) A multi-core plastic optical fiber having a plurality of cores and a plurality of cladding portions covering the periphery of the plurality of cores, wherein a core group is formed, wherein the number of the plurality of cores in the core group is 300 or more and the outer diameter of the plurality of cores is 25 μm or more and 60 μm or less, and regarding the core group other than the cores disposed on the outermost periphery of the core group, i.e. the inner core group, the CV value of the cladding portion thickness defined by the gap between the adjacent cores is 20% or less on the line connecting the centroids of the inner core group and adjacent cores to each other.

[0030] (6) The multi-core plastic optical fiber according to (5), wherein the cores forming the inner core group are configured with the densest filling structure of any one of hexagonal lattice, square lattice, and triangular lattice.

[0031] (7) The multi-core plastic optical fiber according to (6), wherein one core forming the inner core group has parallel edges with the adjacent core.

[0032] (8) The multi-core plastic optical fiber according to (5), wherein when the outer diameter of the core forming the inner core group is set to C, the CV value of the cladding thickness is 30% or less within the range sandwiched by two lines that are C / 6 apart from the line connecting the centroids of adjacent cores.

[0033] (9) The multi-core optical fiber according to (1), wherein at least a portion of the core sheath portion forming the inner core sheath portion group forms a hexagonal lattice, and in a triangle connecting the centroids of any three adjacent core sheath portions other than the core sheath portion disposed at the outermost periphery of the plurality of core sheath portions, the ratio of the area occupied by the core sheath portion is more than 50% and less than 75%, and the outer diameter of the plurality of core sheath portions is more than 30 μm and less than 60 μm.

[0034] (10) According to the multi-core plastic optical fiber of (1), wherein, on the line connecting the centroid of any core sheath in the core sheath group forming the inner core sheath group and the centroid of the core sheath adjacent to the arbitrary core sheath, the cladding thickness, calculated as the gap between the adjacent core sheaths, is 1 μm or more, and the seam thickness, calculated as the gap between the adjacent core sheaths, is 2 μm or more.

[0035] (11) The multi-core plastic optical fiber according to claim 1, wherein, in the cross section of the multi-core plastic optical fiber, the minimum distance (hereinafter, sometimes referred to as "the outer perimeter thickness") from the sheath profile of the core sheath located at the position closest to the profile of the multi-core plastic optical fiber to the profile of the multi-core plastic optical fiber is 5 μm or more.

[0036] (12) The multi-core plastic optical fiber according to (5), wherein at least a portion of the cores forming the inner core group forms a hexagonal lattice, and in a triangle connecting the centroids of any three adjacent cores other than the cores disposed on the outermost periphery of the plurality of cores, the ratio of the area occupied by the cores is more than 50% and less than 75%, and the outer diameter of the plurality of cores is more than 30 μm and less than 60 μm.

[0037] (13) According to the multi-core plastic optical fiber of (5), wherein the cladding thickness, which is determined as the gap between the adjacent cores, is 1 μm or more on the line connecting the centroid of any core in the cores forming the inner core group and the centroid of the core adjacent to the arbitrary core.

[0038] (14) The multi-core plastic optical fiber according to claim 5, wherein, in the cross section of the multi-core plastic optical fiber, the minimum distance (hereinafter sometimes referred to as "the outer periphery thickness") from the outline of the core located at the position closest to the outline of the multi-core plastic optical fiber to the outline of the multi-core plastic optical fiber is 5 μm or more.

[0039] (15) The multi-core plastic optical fiber according to (1) or (5), wherein the transmission loss is less than 250 dB / km when measured by irradiating one of the core sheaths in the inner core sheath group or one of the cores in the inner core group with a 650 nm laser.

[0040] (16) The multi-core plastic optical fiber according to (1) or (5), wherein when the multimode VCSEL light of wavelength 670 nm is incident on the multiple cores at an incident NA0.2, it has a frequency band of more than 400 MHz at a fiber length of 25 m.

[0041] (17) An optical communication cable, wherein the cable includes the multi-core plastic optical fiber described in (1) or (5).

[0042] (18) An optical communication system wherein a multi-core plastic optical fiber as described in (1) or (5) is used to perform spatial multiplexing communication using multiple signal lights.

[0043] (19) An optical communication system wherein the wavelength of the light source is above 400nm and below 700nm, and spatial multiplexing communication is performed using the optical communication cable described in (17).

[0044] (20) The optical communication system according to (19) wherein the number of multiple light sources for optical communication is more than 50% of the number of multiple cores or more than 50% of the number of multiple core sheaths, such that the multiple light sources correspond one-to-one with the multiple cores or the multiple core sheaths.

[0045] Invention Effects

[0046] According to the present invention, multi-core plastic optical fibers, optical communication cables, and optical communication systems can be provided with less deviation in the amount of transmitted light per core and a wider transmission bandwidth. Attached Figure Description

[0047] Figure 1 This is a partially enlarged cross-sectional view of a multi-core plastic optical fiber, which is a representative embodiment of the present invention.

[0048] Figure 2 This is a schematic cross-sectional view of the peripheral equipment such as the composite spinneret, spinning assembly, and cooling device used in the embodiments of the present invention.

[0049] Figure 3 This is a schematic cross-sectional view showing a composite spinneret according to an embodiment of the present invention.

[0050] Figure 4 yes Figure 2 The XX-direction view is an overall view of the ejection surface of the ejection plate.

[0051] Figure 5 This is a partially enlarged cross-sectional view of the ejection surface of the ejection plate used in a representative embodiment of the present invention.

[0052] Figure 6 This is a partially enlarged cross-sectional view of the ejection surface of the ejection plate used in another embodiment of the present invention.

[0053] Figure 7 This is a partially enlarged cross-sectional view of a multi-core plastic optical fiber according to another embodiment of the present invention.

[0054] Figure 8 These are partial enlarged cross-sectional views of a multi-core plastic optical fiber. (a) is a diagram illustrating the measurement location of the cladding thickness as described in claim 5, and (b) is a diagram illustrating the measurement location of the cladding thickness as described in claim 1.

[0055] Figure 9 The diagram shows a partially enlarged cross-sectional view of a multi-core plastic optical fiber. (a) is a diagram illustrating the measurement location of the cladding thickness as described in claims 8 and 13, and (b) is a diagram illustrating the measurement location of the cladding thickness as described in claims 4 and 10, and the seam thickness as described in claim 10.

[0056] Figure 10 These are cross-sectional views of a multi-core plastic optical fiber, (a) is a diagram illustrating the thickness of the outer periphery (cladding portion) as described in claim 5, and (b) is a diagram illustrating the thickness of the outer periphery as described in claim 1.

[0057] Figure 11 (a) is Figure 9 A magnified view of part (a). Figure 11 (b) is Figure 9 A magnified view of (b).

[0058] Figure 12 (a) is a partial enlarged cross-sectional view of a multi-core plastic optical fiber, and (b) is an explanatory diagram of the method for calculating the ratio of the area occupied by the core as described in claim 12. Detailed Implementation

[0059] Hereinafter, embodiments of the multi-core plastic optical fiber, optical communication cable, and optical communication system of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments and can be implemented with various modifications depending on the purpose and application.

[0060] [Structure of optical fiber]

[0061] like Figure 1 As shown, the second embodiment of the multi-core plastic optical fiber of the present invention is a two-component optical fiber composed of a plurality of core component resins 18 and a cladding component resin 19 covering the core component resins 18, having the following structure.

[0062] A multi-core plastic optical fiber is a plastic optical fiber having multiple cores and a cladding covering the cores. A core group is formed, wherein the core group has 300 or more cores with an outer diameter of 25 μm or more and 60 μm or less. Regarding the core group excluding the cores arranged at the outermost periphery of the core group, i.e., the inner core group, the CV value of the cladding thickness, defined by the gap between the adjacent cores, on the line connecting the centroids of the inner core group and adjacent cores, is 20% or less. By adopting this structure, compared to the second embodiment described below, the core area ratio can be increased, thus increasing the number of configurable cores. This, in turn, increases the number of channels for spatial multiplexing communication.

[0063] like Figure 7 As shown, the first embodiment of the multi-core plastic optical fiber of the present invention is a three-component optical fiber in which the core component resin 18 and the cladding component resin 19 covering the core component resin 18 form a core sheath portion and a plurality of core sheath portions are disposed in the core component resin 20, having the following structure.

[0064] A multi-core plastic optical fiber is a plastic optical fiber having multiple cores, core sheaths with cladding portions formed around the cores, and a sheath covering the periphery of the core sheaths. A core sheath group is formed, wherein the core sheath group has 300 or more core sheaths and the outer diameter of the core sheaths is 25 μm or more and 60 μm or less. Regarding the core sheath group excluding the outermost core sheaths arranged in the core sheath group, i.e., the inner core sheath group, the CV value of the cladding thickness, defined by the gap between the adjacent core sheaths, on the line connecting the centroids of adjacent core sheaths forming the inner core sheath group is 15% or less.

[0065] By configuring the fiber as a three-component fiber, the marine component resin 20 exists in the outermost layer. As a result, the light signal leaking into the marine component is attenuated and disappears on the surface of the fiber, which can prevent the leaked light signal from reaching other adjacent cores.

[0066] [Uniformity of cladding thickness]

[0067] The multi-core plastic optical fiber of the present invention is based on so-called parallel communication, which involves simultaneously transmitting and receiving multiple data points in parallel with each core. Therefore, when receiving data from multiple cores at the receiver side located at the end of the optical fiber, data synchronization is crucial; when this synchronization deteriorates, control at the receiver side becomes difficult. In particular, to achieve high-capacity data communication using a single optical fiber, a very large number of cores (more than 300) need to be densely arranged. In this case, it becomes extremely important to suppress deviations in the input-output and transmission characteristics of all cores and homogenize them to the limit in order to ensure data synchronization across all cores.

[0068] In the three-component fiber, which is the first aspect of the present invention, it is preferable that, similar to the core forming the inner core group in the two-component fiber, which is the second aspect of the present invention, the core sheath is configured with the densest filling of any one of hexagonal lattice, square lattice, or triangular lattice. Furthermore, it is preferable that one core sheath forming the inner core sheath group has parallel edges with adjacent core sheaths. This allows for uniform cladding thickness throughout the circumference of the core. As a result, it is easy to obtain a reduction in the CV value of the cladding thickness on the line connecting the centroid of the core sheath to the centroid of the adjacent core sheath. Here, when the core sheath has parallel edges, in the case of a hexagonal lattice, the core sheath becomes a hexagon with a smooth curved shape at the vertices. Similarly, in the cases of square lattices and triangular lattices, the vertices also become smooth curved shapes.

[0069] Furthermore, it is preferable that, when the outer diameter of the core sheath forming the inner core sheath assembly is set to D, the CV value of the cladding thickness is 20% or less within the range (hereinafter sometimes referred to as the "edge region") enclosed by two lines spaced D / 6 apart from the line connecting the centroids of adjacent core sheaths. By doing so, a region with a uniform cladding thickness can be formed; in other words, the deviation in cladding thickness is reduced, scattering at the interface between the core and the cladding is reduced, the deviation in transmission loss is reduced, and the transmission bandwidth becomes better.

[0070] Furthermore, in the two-component fiber, which is the second aspect of the present invention, it is generally important to homogenize the sphericity of the core shape in order to suppress deviations in transmission characteristics. In addition, it is also effective to homogenize the thickness deviation of the cladding portion (or the core-sheath cladding portion in the case of the three-component fiber, which is the first aspect of the present invention) forming the outer periphery of each core. It is known that at the interface between the core and the cladding portion, most of the signal light propagating in the core is reflected, and a portion of it is transmitted or scattered to the cladding component; diffuse reflection caused by minute irregularities at this interface is considered to be one of the causes. To homogenize the minute irregularities at this interface, by setting the cladding portion to a thickness of a certain amount or more, the morphology of the interface can be stabilized. Furthermore, although the principle has not been fully elucidated, homogenizing the thickness of the cladding portion will also exhibit the same effect.

[0071] Therefore, in the two-component fiber, which is the second aspect of the present invention, it is preferable that the cores forming the inner core group are configured with the densest filling structure of any one of hexagonal lattice, square lattice, or triangular lattice. Furthermore, it is preferable that one core forming the inner core group has parallel edges with its adjacent cores. This allows for more uniform cladding thickness throughout the circumference of the core. As a result, it is easy to obtain a reduction in the CV value of the cladding thickness on the line connecting the centroid of the core to the centroid of the adjacent core. Here, when the cores have parallel edges, in the case of a hexagonal lattice, the cores become hexagonal with smooth curved vertices. Similarly, in the cases of square lattices and triangular lattices, the vertices also become smooth curved.

[0072] Furthermore, preferably, when the outer diameter of the core forming the inner core group is set to C, the CV value of the cladding thickness is 30% or less within the range (hereinafter sometimes referred to as the "edge region") enclosed by two lines spaced C / 6 apart from the line connecting the centroids of adjacent cores. By doing so, a region with a uniform cladding can be formed; in other words, the deviation in cladding thickness is reduced, scattering at the interface between the core and the cladding is reduced, the deviation in transmission characteristics is reduced, and the transmission bandwidth becomes better.

[0073] Furthermore, compared to two-component optical fibers, three-component optical fibers have an advantage in that when a composite polymer flow is formed in the composite spinneret, the polymer in the outer layer flows and forms before the polymer in the cladding layer. Therefore, the thickness deviation of the cladding layer tends to be smaller.

[0074] [Core component resin]

[0075] The core is the transmission part that directly transmits signal light, playing a role in efficiently transmitting signal light. The resin in the resin composition forming the core is preferably a material with high light transmittance and low transmission loss; examples include acrylic resins, modified polycarbonate resins, cycloolefin resins, styrene resins, and olefin resins such as polymethylpentene. Among such resins, acrylic resins, which have the characteristic of low transmission loss, are preferred. Examples of acrylic resins include polymers of methacrylates and acrylates. Examples of methacrylates include alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate, aryl methacrylates such as phenyl methacrylate, cyclohexyl methacrylate, and cycloalkyl methacrylates such as norbornene methacrylate. Examples of acrylates include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and alkyl acrylates such as 2-ethylhexyl acrylate, aryl acrylates such as phenyl acrylate, cyclohexyl acrylate, and cycloalkyl acrylates such as norbornene acrylate. Other acrylic resins include sodium polyacrylate resins, polyacrylonitrile resins, and polyacrylamide resins. Among these, polymethyl methacrylate resins, which are mainly composed of methyl methacrylate, are particularly preferred from the viewpoints of transparency and processability.

[0076] Examples of modified polycarbonate resins include polycarbonate resins substituted with lower alkyl or trifluoromethyl groups and having an average molecular weight of 10,000 to 200,000.

[0077] As cyclic olefin resins, for example, in addition to cyclic olefin polymers such as ring-opening metathesis polymers and ethylene addition copolymers, hydrogenated ring-opening metathesis polymers, cyclic olefin copolymers such as ethylene / 2-norbornene can also be cited.

[0078] In the resin composition constituting the core, dopants such as germanium, phosphorus, tin, and boron that increase the refractive index can be appropriately added to adjust the refractive index, while dopants such as magnesium fluoride and other fluorine-based materials that decrease the refractive index can be added.

[0079] The refractive index of the core is preferably 1.45 or higher and 1.60 or lower. A refractive index of 1.45 or higher, more preferably 1.48 or higher, increases the refractive index difference with the cladding, reducing the proportion of signal light leaking out towards the sea. Conversely, a refractive index of 1.60 or lower, more preferably 1.52 or lower, suppresses the refractive index difference with the cladding, reducing the number of modes of the propagated light and thus expanding the transmission bandwidth. The refractive index can be measured using an Abbe refractometer on a 20mm × 8mm × 1.4mm test piece at room temperature (25°C) according to JIS K7142:2014. Furthermore, in cases where it is difficult to directly measure the refractive index by collecting the core sample, a 20mm × 8mm × 1.4mm test piece can be formed by heating the collected core sample at 210°C for 5 minutes using a stamping machine, followed by cooling to room temperature, and then measuring the refractive index. Additionally, if the composition of the core is known, a test piece can be similarly formed based on the known composition, and the refractive index can be measured.

[0080] [Clad layer resin composition]

[0081] The cladding layer protects the core from external environmental factors and reduces the proportion of signal light propagating in the core that leaks out at the interface of the cladding layer. As the resin constituting the cladding layer, in addition to resins common to those constituting the core, such as acrylic resins, fluoropolymers such as vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer, vinylidene fluoride / trifluoroethylene copolymer, fluorinated acrylate polymers, perfluorobutyl polymethacrylate, perfluoroisopropyl polymethacrylate, and hexafluoro-2-propyl polymethacrylate can also be used.

[0082] Furthermore, dopants such as magnesium fluoride or other fluorine-based materials can be added to the cladding resin to adjust the refractive index. Coloring substances can also be included in the cladding. By including coloring substances in the cladding, signal light leakage into the sea can be reduced. However, since the cladding is relatively thin, when coloring substances are included in the cladding, the content (mass%) of the coloring substances in the cladding is preferably lower than the content (mass%) of the coloring substances in the sea. If the content (mass%) of the coloring substances in the cladding is higher than the content (mass%) of the coloring substances in the sea, there are several issues: the melt viscosity of the resin composition during cladding formation increases, making it difficult to form the cladding to the desired size without increasing the extrusion stress; and / or, the core and sea surface may deform under this extrusion stress. In other words, in the optical fiber of the present invention, when coloring substances are included in the cladding, the content (mass%) of the coloring substances in the cladding is preferably lower than the content (mass%) of the coloring substances in the sea. Specifically, the content is preferably less than 3% by mass.

[0083] When the refractive index of the cladding portion is preferably 1.35 or higher, more preferably 1.38 or higher, the refractive index difference with the core portion decreases, the number of modes of the propagated light decreases, and thus the transmission bandwidth can be expanded. In addition, when the refractive index of the cladding portion is preferably 1.50 or lower, more preferably 1.42 or lower, the proportion of signal light propagating in the core that is reflected at the interface of the cladding portion and leaks out into the sea can be reduced.

[0084] Here, the refractive index of the cladding portion can be measured in the same way as that of the core. Furthermore, in cases where it is difficult to directly measure the refractive index of the cladding portion by collecting it, a test piece measuring 20 mm × 8 mm × 1.4 mm can be prepared by heating the collected cladding portion at 210°C for 5 minutes using a stamping machine, followed by cooling to room temperature, and then measuring the refractive index. Alternatively, if the composition of the cladding portion is known, a test piece can be prepared based on the known composition, and the refractive index can be measured.

[0085] In order for light to be reflected at the interface between the core and the cladding, the refractive index of the cladding needs to be lower than that of the core. By making the refractive index of the cladding lower than that of the core, preferably making the difference between the refractive indices of the core and the cladding 0.02 or more, more preferably 0.05 or more, the proportion of signal light propagating in the core that is reflected at the interface of the cladding and leaks out can be reduced. On the other hand, by making the difference between the refractive indices of the core and the cladding preferably 0.20 or less, more preferably 0.09 or less, the number of modes of the propagated light can be reduced, and the transmission bandwidth can be expanded.

[0086] [Sea component resin]

[0087] The first embodiment of the present invention is a three-component optical fiber with a seam on the outside of the cladding. The seam serves the following functions: providing the outer diameter of the optical fiber, flexibility, light blocking and emission via the refractive index difference between the fiber and the cladding, and preventing crosstalk by adding a light-shielding agent.

[0088] The material used for the seabed was selected from a combination of the previously chosen core and cladding materials, taking into account the aforementioned functions such as softness, light containment and emission achieved by utilizing the refractive index difference with the cladding, and prevention of crosstalk by adding a light-blocking agent.

[0089] [The roundness of the core and the roundness of the core sheath]

[0090] In the two-component optical fiber, which is the second aspect of the present invention, it is preferable that the roundness of the cores disposed on the outermost periphery of the core group is 1.5 or less, and the roundness of the cores forming the inner core group (excluding the cores disposed on the outermost periphery of the core group) is 1.3 or less. Here, taking a hexagonal lattice structure as an example, the cores disposed on the outermost periphery of the core group indicate that there are no six cores adjacent to the core in the hexagonal lattice structure. Similarly, in the case of a square lattice structure, it indicates that there are no four cores adjacent to the core in the square lattice structure, and in the case of a triangular lattice structure, it indicates that there are no three cores adjacent to the core in the triangular lattice structure. When the roundness of the cores disposed on the outermost periphery of the core group is 1.5 or less, it is easier to make the roundness of the cores forming the inner core group 1.3 or less. When the roundness of the cores forming the inner core group is 1.3 or less, the transmission bandwidth of the cores becomes good.

[0091] Here, the roundness of the core refers to the value obtained by taking a core image of a multi-core plastic optical fiber in the inner core group, calculating the core length and short diameter, and dividing the core length by the core short diameter (core length ÷ core short diameter).

[0092] Furthermore, in the three-component optical fiber, which is the first aspect of the present invention, it is preferable that the roundness of the core portion of the outermost core sheath portion disposed in the core sheath assembly is 1.3 or less, and the roundness of the core portion of the core sheath portion forming the inner core sheath assembly (excluding the outermost core sheath portion of the core sheath assembly) is 1.2 or less. By providing a three-layer structure of core, cladding, and sheath, the core is less susceptible to flow variations in the sheath, thus reducing the roundness of the core portion of the core sheath. Similar to the two-component optical fiber, in the three-component optical fiber, when the roundness of the core portion of the outermost core sheath portion disposed in the core sheath assembly is 1.3 or less, the transmission bandwidth becomes better.

[0093] Here, the roundness of the core sheath refers to the value obtained by taking an image of the core sheath of a multi-core plastic optical fiber in the inner core sheath assembly, calculating the long and short diameters of the core sheath, and dividing the long diameter of the core sheath by the short diameter of the core sheath (core sheath diameter ÷ core sheath short diameter).

[0094] [Outer diameter of core and outer diameter of core sheath]

[0095] In the three-component optical fiber, which is the first aspect of the present invention, the outer diameter of the core sheath is 25 μm or more and 60 μm or less. Here, as described above, the outer diameter of the core sheath represents the average value of the long diameter and the short diameter of the core sheath obtained when calculating the roundness of the core sheath.

[0096] In the two-component optical fiber, which is the second aspect of the present invention, the core outer diameter is 25 μm or more and 65 μm or less. Here, as described above, the core outer diameter represents the average of the core's long diameter and short diameter, calculated when determining the roundness of the core. When the core outer diameter is less than 25 μm, the transmission loss deteriorates significantly, and when the core diameter exceeds 65 μm, the transmission bandwidth deteriorates.

[0097] [Number of cores and number of core sheaths]

[0098] In the two-component optical fiber, which is the second aspect of the present invention, the number of cores arranged in a single optical fiber is 300 or more. By having 300 or more cores, each core can transmit independent light, thus enabling high-capacity spatial multiplexing communication. Here, when the number of cores is less than 300, sufficient capacity cannot be obtained in spatial multiplexing communication. Furthermore, when the number of cores is 5200 or less, the outer diameter of the optical fiber can be set to allow for stable spinning. In this case, the core diameter can be greater than 25 μm, thus resulting in good transmission loss.

[0099] [Manufacturing Method]

[0100] Figure 3 This is a schematic cross-sectional view of the composite spinneret used in an embodiment of the present invention. Figure 4 yes Figure 3 The XX-direction view is an overall view of the ejection surface of the ejection plate. Figure 5 This is a partially enlarged cross-sectional view of the ejection surface of the ejection plate used in the second embodiment of the present invention. Figure 6 This is a partially enlarged cross-sectional view of the ejection surface of the ejection plate used in the first embodiment of the present invention. Additionally, Figure 2 These are schematic cross-sectional views of the composite spinneret, spinning assembly, and cooling device used in embodiments of the present invention. Furthermore, these figures are conceptual diagrams intended to accurately convey the key points of the present invention; the figures have been simplified. The composite spinneret of the present invention is not particularly limited; the number of holes and slots, as well as their dimensional ratios, can be varied depending on the embodiment.

[0101] like Figure 3 As shown, the composite spinneret 13 used in the embodiment of the present invention is equipped in the spinning assembly 14 and fixed in the spinning box 12. A cooling device 17 is formed directly below the composite spinneret 13. Therefore, the core component polymer 9, cladding component polymer 10, and sizing component polymer 11, which are guided to the composite spinneret 13, pass through the distribution plate 6 and the ejection plate 4, respectively, and are ejected from the spinneret ejection hole 16 of the spinneret ejection plate 5. They are then cooled by the airflow blown by the cooling device 25 and wound up as a multi-core plastic optical fiber 21. In addition, regarding the components equipped on the upstream side of the distribution plate 6, the flow path used in the existing spinning assembly 14 can be used, and no special proprietary design is required.

[0102] like Figure 2 As shown, the composite spinneret 13 used in the embodiment of the invention is constructed by sequentially stacking at least one distribution plate 6, an ejector plate 4, and a spinneret ejector plate 5. In particular, the ejector plate 4 is preferably made of a thin plate. In this case, the distribution plate 6, the ejector plate 4, and the spinneret ejector plate 5 are positioned and stacked by using positioning pins to align them with the center position (core) of the spinning assembly 14. They can then be fixed by screws, bolts, etc., or by heat pressing for metal bonding.

[0103] Therefore, the polymers of each component supplied to the distribution plate 6 pass through the distribution grooves and distribution holes of at least one distribution plate 6, and are then ejected from the core component ejection hole 1 for ejecting the core component polymer 9, the cladding component ejection hole 2 for ejecting the cladding component polymer 10, and the sea component ejection hole 3 for ejecting the sea component polymer of the ejection plate 4. Then, in the confluence hole 22, the polymers ejected from each ejection hole merge with each other to form a composite polymer 8. Afterwards, the composite polymer 8 is ejected from the spinneret ejection hole 16 of the spinneret ejection plate 5. Figure 4 As shown, a multi-core plastic optical fiber is formed by extruding a composite polymer 8 from the spinneret nozzle 16 after it is extruded from the nozzle 7 (a hole formed by combining the core component nozzle 1, the cladding component nozzle 2, and the seam component nozzle 3). Figure 4 A schematic diagram showing the formation of four multi-core plastic optical fibers is shown.

[0104] Here, in order to manufacture a two-component optical fiber as the second aspect of the present invention, such as Figure 5 As shown, on the ejection surface 15 of the ejection plate 4, cladding component ejection holes 2 are arranged around the core component ejection holes 1. Furthermore, in Figure 5In this design, three cladding component ejection holes 2 are arranged around the core component ejection hole 1, but the arrangement and number of ejection holes can be varied according to the fiber cross-section. Therefore, by surrounding the outer periphery of the core component polymer 9 ejected from the core component ejection hole 1 with the cladding component polymer 10, a composite polymer stream 8 is formed in which multiple core component polymers are arranged within the cladding component polymer 10. In this case, the polymer supplied from the upstream side is uniformly distributed by multiple stacked distribution plates 6, allowing each polymer to be uniformly ejected from each ejection hole. Therefore, not only can the shape of the core be homogenized, but the cladding around the core can also be uniformly formed. In particular, when the number of fiber cores increases (the number of core component polymers 9 in the composite polymer stream 8 increases), the composite spinneret 13 becomes larger. Therefore, in conventional tube-type spinnerets, since the cladding component polymer 10 is supplied from the outer periphery of the tube assembly, it is difficult to uniformly supply polymer to the tube arranged in the center. On the other hand, in the composite spinneret 13 of the distribution method used in this invention, even when the spinneret size becomes large, the polymers supplied from the upstream side of the composite spinneret 13 can be received by the entire surface of the distribution plate 6, thus enabling uniform distribution.

[0105] Furthermore, in order to manufacture the tri-component optical fiber, which is the first aspect of the present invention, such as Figure 6 As shown, on the ejection surface 15 of the ejection plate 4, cladding component ejection holes 2 are arranged around the core component ejection holes 1, and marine component ejection holes 3 are further arranged on its outer periphery. Furthermore, in Figure 6 In this design, three cladding component ejection holes 2 are arranged around the core component ejection hole 1, and three sea component ejection holes 3 are arranged around its outer periphery. However, this design is not limited to these; the arrangement and number of ejection holes can be varied according to the fiber cross-section. Therefore, by surrounding the core component polymer 9 ejected from the core component ejection hole 1 with the cladding component polymer 10, a core-sheath polymer is formed. Furthermore, by supplying sea component polymer 11 from its outer periphery, a composite polymer flow 8 is formed in which multiple core-sheath polymers are disposed within the sea component polymer 11. In this case, the composite spinneret 13 exhibits the same effect as the two-component fiber described above, similar to the distribution method used in this invention.

[0106] [optical fiber]

[0107] From a processing point of view, the cross-section of the multi-core plastic optical fiber of the present invention is preferably circular, and its diameter (the diameter of the circumscribed circle in the case of a hexagon) is preferably 0.8 mm to 3 mm. If the diameter is 0.8 mm or more, more than 300 cores can be configured in the optical fiber; if the diameter is 3 mm or less, it has moderate flexibility and is easy to process.

[0108] In the three-component system of the first scheme, it is preferable that at least a portion of the core sheaths forming the inner core sheath group is formed into a hexagonal lattice. Regarding the triangle connecting the centroids of any three adjacent core sheaths (excluding those located at the outermost periphery of the plurality of core sheaths), when the area of ​​the triangle is set to 100%, the ratio of the area occupied by the core sheath is 50% or more and 75% or less, and the outer diameter of the plurality of core sheaths is 30 μm or more and 60 μm or less. Thus, by maintaining a certain ratio of core sheath area while ensuring a distance from adjacent core sheaths, transmission loss can be minimized, and light entering one core sheath can be prevented from leaking to adjacent core sheaths.

[0109] Furthermore, preferably, the cladding thickness, calculated as the gap between adjacent core sheaths, is 1 μm or more on the line connecting the centroid of any core sheath in the core sheath group forming the inner core sheath group and the centroid of the adjacent core sheath. The seam thickness, also calculated as the gap between adjacent core sheaths, is 2 μm or more. This improves the sphericity of the core's cross-sectional shape, reduces transmission loss, and prevents light entering one core sheath from leaking into adjacent core sheaths.

[0110] In the second two-component system, preferably, at least a portion of the cores forming the inner core group forms a hexagonal lattice. Regarding the triangle connecting the centroids of any three adjacent cores (excluding the cores located at the outermost periphery of the plurality of cores), when the area of ​​the triangle is set to 100%, the ratio of the area occupied by the cores is 50% to 75%, and the outer diameter of the plurality of cores is 30 μm to 60 μm. This increases the core area, ensures sufficient distance between adjacent cores, and minimizes transmission loss.

[0111] Furthermore, preferably, the cladding thickness, calculated as the gap between adjacent cores, is 1 μm or more, along a line connecting the centroid of any core forming the inner core group and the centroid of the adjacent core. This improves the sphericity of the core's cross-sectional shape, reduces transmission loss, and prevents light entering one core from leaking into adjacent cores.

[0112] Furthermore, regarding the optical fiber of the present invention, in the two-component system of the second embodiment, it is preferable that the minimum distance (outer periphery thickness) from the outline of the core located closest to the outline of the optical fiber to the outline of the optical fiber in the cross-section of the optical fiber is 5 μm or more. This allows for the homogenization of the roundness and cladding thickness deviation of the core portion disposed on the outermost periphery of the core assembly. Furthermore, in the three-component system of the first embodiment of the present invention, it is preferable that the minimum distance (outer periphery thickness) from the outline of the core located closest to the outline of the optical fiber to the outline of the optical fiber is 5 μm or more. This allows for the homogenization of the roundness and cladding thickness deviation of the core sheath portion disposed on the outermost periphery of the core sheath assembly.

[0113] Regarding the multi-core plastic optical fiber of the present invention, it is preferable that, when measurements were taken with 670nm multimode VCSEL light incident at an angle NA0.2 onto a core or core sheath, a bandwidth of 400MHz or higher was observed at a fiber length of 25m. Here, VCSEL is an abbreviation for Vertical Cavity Surface Emitting Laser, a type of semiconductor laser that emits a laser beam perpendicularly from its upper surface. It emits laser light with a diameter of tens of micrometers from a single source, but has the characteristic of being able to arrange multiple sources in a two-dimensional array. By combining individual light sources with individual cores of a multi-core system, high-capacity communication can be achieved. Furthermore, NA is an abbreviation for Numerical Aperture, and incident NA0.2 refers to light incident at an angle of Sinθ = 0.2. The transmission bandwidth is a value representing the width of the frequency used to transmit data, and is measured in Hz (Hertz). A wider transmission bandwidth is generally better. Generally, when the core diameter decreases, light with a deeper propagation angle is emitted outwards from the fiber, while only light with a shallower propagation angle propagates. This results in a trade-off: a smaller core diameter leads to a wider transmission bandwidth, but conversely, a smaller core diameter results in poorer transmission loss. Transmission loss refers to the attenuation of the optical signal per unit length, measured in dB / km. In the optical fiber of this invention, the transmission loss measured when irradiating one of the cores forming the inner core group or one of the core sheaths forming the inner core sheath group with a 650nm laser is preferably 250dB / km or less, more preferably 200dB / km or less. This balance between transmission bandwidth and transmission loss becomes important.

[0114] [Optical communication cables]

[0115] The multi-core plastic optical fiber of the present invention can be appropriately used in optical communication cables. That is, the optical communication cable of the present invention is an optical communication cable obtained by adding a coating such as polyethylene to the outer periphery of the optical fiber of the present invention.

[0116] Optical communication system

[0117] The multi-core plastic optical fiber or optical communication cable of the present invention can be appropriately used in optical communication systems. The optical communication system of the present invention uses the multi-core plastic optical fiber or optical communication cable of the present invention to achieve spatial multiplexing communication using multiple signal beams, thereby enabling high-capacity communication.

[0118] Here, considering the high safety for the human body and the low likelihood of causing electromagnetic interference to devices that utilize existing electromagnetic waves, the wavelength of the light source is preferably below 400-700nm, which is the wavelength of visible light.

[0119] Furthermore, preferably, the number of multiple light sources used for optical communication is 50% or more of the number of multiple cores or multiple core sheaths, so that the multiple light sources correspond one-to-one with the multiple cores or multiple core sheaths. By using multiple light sources for optical communication that are 50% or more of the number of multiple cores or multiple core sheaths, two or more cores or two or more core sheaths can be matched with one light source, enabling high-capacity communication even with low alignment accuracy. By matching the multiple light sources one-to-one with the multiple cores or multiple core sheaths, light leakage from the core to the cladding or from the core sheath to the cladding is reduced, enabling high-capacity communication.

[0120] Example

[0121] The present invention will now be specifically described using examples. However, the present invention is not limited thereto.

[0122] [Determination Method]

[0123] (1) Refractive index of the core, cladding, and seam (-)

[0124] Test pieces of 20 mm × 8 mm × 1.4 mm were prepared using the core, cladding, and seam portions used in the various embodiments and comparative examples, and the refractive index was measured using an Abbe refractometer at room temperature (25 °C).

[0125] (2) Measurement of the outer diameter of the core, measurement of the outer diameter of the core sheath, and the roundness of the core.

[0126] For randomly selected sections of the optical fiber, the cross-section was cut perpendicular to the extension direction and ground to allow observation of the core / cladding / span interface. The cross-section was then observed using a VHX-7000 digital microscope (manufactured by Keyence Corporation). The magnification ranged from 10 to 200x, ensuring the entire cross-section was within the field of view, and the range suitable for interface observation was appropriately selected. Furthermore, in two-component optical fibers (core and cladding resin components), the major and minor diameters of each core in the obtained images were calculated using image analysis software (WinROOF, Mitani Corporation). The average of the major and minor diameters of all cores was taken as the core outer diameter. Then, the average value obtained by dividing the major diameter of all cores by the minor diameter was calculated and taken as the core roundness.

[0127] In addition, in a three-component optical fiber consisting of core resin, cladding resin, and sheath resin, the average value of the major and minor diameters of all core sheaths is set as the outer diameter of the core sheath using the same method as that used to determine the outer diameter of the core sheath described above.

[0128] (3) Measurement of cladding thickness and CV value of cladding thickness

[0129] A section of a multi-core plastic optical fiber was randomly selected and cut perpendicular to the extension direction. The cross-section was then ground to allow observation of the core / cladding / shell interface, and observed using a VHX-7000 digital microscope (manufactured by Keyence Corporation). The magnification ranged from 10 to 200x, ensuring the entire cross-section was within the field of view, and an appropriate range was selected to observe the interface. Furthermore, the thickness of the cladding in each core and core-sheath portion of the obtained images was measured as follows.

[0130] In two-component optical fibers, such as those with core resin and cladding resin, Figure 8 As shown in (a), in the inner core group excluding the cores located at the outermost periphery of the core group, the average value of the values ​​obtained as the gap between adjacent cores is taken as the cladding thickness on the line connecting the centroid of any core forming the inner core group and the centroid of the adjacent core. In the case of a hexagonal grid, there are six adjacent cores (i1, i2, i3, i4, i5, i6). The cladding thickness of all cores in the inner core group is calculated, and the average value and standard deviation of the cladding thickness are calculated. Here, in the case of a square grid, there are four adjacent cores (i1, i2, i3, i4), and in the case of a triangular grid, there are three adjacent cores (i1, i2, i3). Furthermore, the CV value of the cladding thickness is calculated using the following formula.

[0131] The CV value of the cladding thickness = (standard deviation of cladding thickness / average cladding thickness) × 100

[0132] Furthermore, as a detailed method for measuring the thickness of the cladding portion as specified in claim 8, such as... Figure 9 As shown in (a), the outer diameter of the core calculated using the method described in (2) above is set as the outer diameter C. Within the range (side region) sandwiched by two lines that are C / 6 apart from the line connecting the centroids of adjacent cores, the thickness of the cladding portion (k1, k2, k3, k4, k5) at the positions where the range is divided into four equal parts is calculated. Figure 11 (a) shows the cladding thicknesses of k1 to k5. The thicknesses of each cladding portion of k1 to k5 were calculated in this way, and the average value and standard deviation of the cladding thickness were calculated.

[0133] Furthermore, in three-component optical fibers consisting of core resin, cladding resin, and cladding resin, such as... Figure 8 As shown in (b), the average value obtained as the gap between the adjacent core sheaths is set as the cladding thickness on a line connecting the centroid of any core sheath in the inner core sheath group (excluding the outermost core sheath) and the centroid of the core sheath adjacent to that arbitrary core sheath. In the case of a hexagonal lattice configuration, there are six adjacent core sheaths (i1~i6). The cladding thickness of all core sheaths except the outermost core sheath is calculated, and the average value and standard deviation of the cladding thickness are calculated. Furthermore, the CV value of the cladding thickness is calculated using the following formula.

[0134] The CV value of the cladding thickness = (standard deviation of cladding thickness / average cladding thickness) × 100

[0135] Furthermore, as a detailed method for measuring the thickness of the cladding portion as specified in claim 4, such as... Figure 9 As shown in (b), the outer diameter of the core sheath portion calculated using the method described in (2) above is set as D. Within the range (side region) sandwiched by two lines that are D / 6 apart from the line connecting the centroids of adjacent core portions, the thickness of the cladding portion (k1, k2, k3, k4, k5) at the position where the range is divided into four equal parts is calculated. Figure 11 (b) shows the cladding thicknesses of k1 to k5. The thicknesses of each cladding portion of k1 to k5 were calculated in this way, and the average value and standard deviation of the cladding thickness were calculated.

[0136] (4) Transmission loss (dB / km)

[0137] Regarding transmission loss, a 30m long optical fiber was used. A laser beam (wavelength 650nm, incident NA=0.25) was incident from one end of the fiber onto one core, and the amount of light emitted from the other end, A (dBm), was measured. Next, the 30m sample was cut into 2m lengths, and the same parallel light was incident from one end, and the amount of light emitted from the other end, B (dBm), was measured. The transmission loss C (dB / km) was calculated using (BA) / (30-2). The average value of the data from the 25 islands was calculated; a value below 500dB / km was considered acceptable.

[0138] (5) Transmission band (GHz)

[0139] A network analyzer (Anritsu MS46122B) was connected to a 670nm VCSEL laser and an O / E converter (Graviton SPA-2_650nm). Next, two multi-core plastic optical fibers of 30m and 1m lengths were cut from each of the embodiments and comparative examples, respectively, and their end faces were mirror-polished using a polishing wheel. The light emitted from the VCSEL laser was focused onto one core of the multi-core plastic optical fiber using a 0.2 numerical aperture (NA) objective lens, and the opposite side of the fiber was connected to the O / E converter. Transmission characteristics were measured at 0.1GHz intervals, scanning from 0GHz to 2GHz (S21). A differential curve was plotted by subtracting the 1m measurement from the 30m measurement. The frequency at which the transmission characteristics decreased by 3dB from the 0GHz time point was determined as the transmission band in this curve.

[0140] (6) Thickness of the outer perimeter sea surface (μm)

[0141] After randomly selecting a portion of the multi-core plastic optical fiber and cutting it perpendicular to the extension direction, the cross-section is ground in a manner that allows observation of the core / cladding / substructure interface. Figure 10 As shown in (b), in a three-component fiber, the circumcircle of the outermost core sheath portion disposed in the core sheath assembly is depicted, and the average distance between this circumcircle and the fiber diameter is set as the thickness of the outer perimeter. Similarly, in a two-component fiber, as... Figure 10 As shown in (a), the circumcircle of the core portion disposed on the outermost periphery of the core assembly is depicted, and the average distance between this circumcircle and the fiber diameter is set as the outer periphery thickness. Furthermore, Figure 10 In the two-component optical fiber shown in (a), the thickness of the outer periphery of the cladding portion is synonymous with the thickness of the outer periphery.

[0142] (7) Thickness at sea (μm)

[0143] A randomly selected section of a multi-core plastic optical fiber was cut perpendicular to its extension direction. The cross-section was then ground to allow observation of the core / cladding / sub-fiber interface, and observed using a VHX-7000 digital microscope (manufactured by Keyence Corporation). The magnification ranged from 10 to 200x, ensuring the entire cross-section was within the field of view, and an appropriate area was selected to observe the interface. Furthermore, the sub-fiber thickness in the obtained images was measured as follows.

[0144] In a three-component optical fiber consisting of core resin, cladding resin, and cladding resin, such as Figure 8 As shown in (b), the average value of the value obtained as the gap between the adjacent core sheaths is set as the sea thickness on the line connecting the centroid of any core sheath in the inner core sheath group (excluding the core sheath portion arranged on the outermost periphery) and the centroid of the core sheath adjacent to the arbitrary core sheath portion.

[0145] When configured as a hexagonal grid, there are six adjacent core sheaths (i1~i6). Calculate the sea layer thickness of all core sheaths except the outermost core sheath, and set the average value of the sea layer thickness as the sea layer thickness.

[0146] As a detailed method for measuring the seabed thickness as specified in claim 4, such as Figure 9 As shown in (b), when the outer diameter of the core sheath portion calculated using the method described in (2) above is set to D, the thickness of the sea portion (h1, h2, h3, h4, h5) at the positions where the range is divided into four equal parts is calculated within the range (side region) between two lines that are D / 6 apart from the line connecting the centroids of adjacent core sheath portions. Figure 11 (b) shows the sea layer thicknesses from h1 to h5. The thicknesses of each sea layer from h1 to h5 were calculated, and the average value of the sea layer thickness was calculated.

[0147] (8) The ratio of the area occupied by the core sheath as specified in claim 9, and the ratio of the area occupied by the core as specified in claim 12.

[0148] A randomly selected section of a multi-core plastic optical fiber was cut perpendicular to its extension direction. The cross-section was then ground to allow observation of the core / cladding / substructure interface, and observed using a VHX-7000 digital microscope (manufactured by Keyence Corporation). The magnification ranged from 10x to 200x, ensuring the entire cross-section was within the field of view, with an appropriate range selected to allow for interface observation.

[0149] Furthermore, as a detailed method for measuring the ratio of the area occupied by the core sheath portion as specified in claim 9, such as... Figure 12As shown in (b), for any triangle connecting the centroids of three adjacent core sheaths (excluding the core sheaths located at the outermost periphery of the obtained image), the area of ​​each triangle and the area of ​​the core sheaths within each triangle are measured. The average of the calculated areas of each triangle and the areas of the core sheaths within each triangle are respectively set as the area of ​​the triangle and the area of ​​the core sheaths within the triangle. The ratio (%) of the area of ​​the core sheaths within the triangle to the area of ​​the triangle is set as the ratio of the area occupied by the core sheaths as specified in claim 9.

[0150] Similarly, as a detailed method for determining the ratio of the area occupied by the core as specified in claim 12, such as Figure 12 As shown in (a), for a triangle connecting the centroids of any three adjacent cores (excluding the cores located at the outermost periphery of the obtained image), the area of ​​each triangle and the area of ​​each core within each triangle are measured. The average of the calculated areas of each triangle and the areas of the cores within each triangle are respectively set as the area of ​​the triangle and the area of ​​the core within the triangle. The ratio (%) of the area of ​​the core within the triangle to the area of ​​the triangle is set as the ratio of the area occupied by the core as specified in claim 12.

[0151] [Example 1]

[0152] Polymethyl methacrylate (refractive index 1.49) was prepared as the resin composition constituting the core polymer, and a copolymer of 70% by mass of vinylidene fluoride and 30% by mass of tetrafluoroethylene (refractive index 1.41) was prepared as the resin composition constituting the cladding polymer. The polymers were supplied to the composite spinneret in a volume ratio of 70:30 between the core and cladding polymers. After melting at 240°C, the composite polymer was distributed in the composite spinneret with 510 cores arranged in a hexagonal lattice, and extruded from the spinneret orifice to collect a multi-core plastic optical fiber. Here, as... Figure 5 As shown, the ejection surface of the composite spinneret's ejection plate is equipped with core component ejection holes and cladding component ejection holes. The results of evaluating the obtained multi-core plastic optical fiber using the aforementioned method are shown in Table 1-1.

[0153] [Example 2]

[0154] As the resin composition constituting the core polymer and the sheath polymer, polymethyl methacrylate (refractive index 1.49) was prepared, and as the resin composition constituting the cladding polymer, a copolymer of 75% by mass of vinylidene fluoride and 25% by mass of tetrafluoroethylene (refractive index 1.41) was prepared. The polymers were supplied to the composite spinneret of the present invention in a volume ratio of 51:12:37 for the core polymer, cladding polymer, and sheath polymer. After melting at 240°C, the composite polymer was distributed in the composite spinneret with 510 cores (composed of a core sheath) arranged in a hexagonal lattice, and extruded from the spinneret orifice to collect a multi-core plastic optical fiber. Here, as... Figure 6 As shown, the ejection surface of the ejection plate of the composite spinneret is provided with core component ejection holes, cladding component ejection holes, and styrene component ejection holes. The results of evaluating the obtained multi-core plastic optical fiber using the aforementioned method are shown in Table 1-1.

[0155] [Example 3]

[0156] To confirm the impact of cladding thickness deviation, the configuration of the cladding component ejected from the composite spinneret was changed. Otherwise, a multi-core plastic optical fiber was fabricated in the same manner as in Example 1. As shown in Table 1-1, compared to Example 1, as the cladding thickness deviation worsened, the transmission loss increased and the transmission bandwidth decreased.

[0157] [Example 4]

[0158] To confirm the impact of cladding thickness deviation, the configuration of the cladding component ejected from the composite spinneret was changed, and the outer periphery thickness was reduced. Otherwise, a multi-core plastic optical fiber was fabricated in the same manner as in Example 2. As shown in Table 1-1, compared to Example 2, as the cladding thickness deviation worsened, the transmission loss increased and the transmission bandwidth decreased.

[0159] [Example 5]

[0160] Example 5 was implemented as an embodiment with an increased number of cores. With the increased number of cores, the apertures of the core component ejection holes and cladding component ejection holes in the ejection plate of the composite spinneret were adjusted to be smaller. Otherwise, a multi-core plastic optical fiber was fabricated in the same manner as in Example 1. As shown in Table 1-1, compared to Example 1, the transmission loss increased, but the transmission bandwidth increased.

[0161] [Example 6]

[0162] To confirm the impact of cladding thickness deviation, the configuration of the cladding component ejected from the composite spinneret was changed, and the outer periphery thickness was increased. Otherwise, a multi-core plastic optical fiber was fabricated in the same manner as in Example 2. As shown in Table 1-1, compared to Examples 2 and 4, with the improvement of cladding thickness deviation, transmission loss decreased and transmission bandwidth increased.

[0163] [Example 7]

[0164] To confirm the impact of cladding thickness deviation, the configuration of the cladding component ejected from the composite spinneret was changed, and the outer periphery thickness was reduced. Otherwise, a multi-core plastic optical fiber was fabricated in the same manner as in Example 3. As shown in Tables 1-2, compared to Example 3, as the cladding thickness deviation worsened, the transmission loss increased and the transmission bandwidth decreased.

[0165] [Example 8]

[0166] To confirm the impact of cladding thickness deviation, the configuration of the cladding component ejected from the composite spinneret was changed, and the outer periphery thickness was increased. Otherwise, a multi-core plastic optical fiber was fabricated in the same manner as in Example 2. As shown in Tables 1-2, compared to Examples 2, 4, and 6, with the improvement of cladding thickness deviation, transmission loss decreased and transmission bandwidth increased.

[0167] [Example 9]

[0168] To confirm the impact of cladding thickness deviation, the configuration of the cladding components ejected from the composite spinneret was changed, the core diameter was reduced, the cladding thickness was increased, and the outer periphery thickness was thickened. Otherwise, a multi-core plastic optical fiber was fabricated in the same manner as in Example 3. As shown in Tables 1-2, compared to Example 3, the cladding thickness deviation was improved, but due to the reduction in core diameter, transmission loss increased and transmission bandwidth decreased.

[0169] [Example 10]

[0170] To confirm the impact of cladding thickness deviation, the configuration of the cladding component ejected from the composite spinneret was changed, and the outer periphery thickness was increased. Otherwise, a multi-core plastic optical fiber was fabricated in the same manner as in Example 9. As shown in Tables 1-2, compared to Example 9, the cladding thickness deviation was improved, transmission loss was reduced, and transmission bandwidth was increased.

[0171] [Comparative Example 1]

[0172] Except for using a tubular spinneret, which is a conventional technique, multi-core plastic optical fibers were fabricated under the same spinning conditions as in Example 1. As shown in Tables 1-2, as the cladding thickness deviation worsened, the transmission loss increased and the transmission bandwidth decreased, making it unsuitable for high-capacity communication.

[0173] [Comparative Example 2]

[0174] Except for using a tubular spinneret, a conventional technique, multi-core plastic optical fibers were fabricated under the same spinning conditions as in Example 2. As shown in Tables 1-2, as the cladding thickness deviation worsened, transmission loss increased and transmission bandwidth decreased, making it unsuitable for high-capacity communication.

[0175] [Table 1-1]

[0176]

[0177] [Table 1-2]

[0178]

[0179] Explanation of reference numerals in the attached figures

[0180] 1. Core component ejection port

[0181] 2. Component ejection orifice in the cladding section

[0182] 3 Marine component ejection holes

[0183] 4. Spray plate

[0184] 5. Spinneret ejection plate

[0185] 6. Distribution board

[0186] 7. Ejector Holes

[0187] 8 Composite polymers

[0188] 9. Core component polymer

[0189] 10. Polymer components of the cladding layer

[0190] 11 Marine component polymers

[0191] 12 Spinning box

[0192] 13 Composite spinnerets

[0193] 14 Spinning assembly

[0194] 15 Spraying surface

[0195] 16 Spinneret nozzles

[0196] 17 Cooling device

[0197] 18 Core component resin

[0198] 19. Resin composition of the cladding layer

[0199] 20 marine component resin

[0200] 21-core plastic optical fiber

[0201] 22 Confluence Orifices

[0202] 23. Center of gravity of the core (core sheath)

[0203] 24. The line connecting the centers of gravity of the core (core sheath)

[0204] 25. A triangle connecting the centroids of three adjacent cores (core sheaths).

[0205] h1~h5 Sea thickness

[0206] i1~i6 Adjacent core or adjacent core sheath

[0207] thickness of cladding portion (k1~k5)

Claims

1. A multi-core plastic optical fiber, comprising a plurality of cores, a plurality of core sheaths having cladding portions formed around the plurality of cores, and a portion covering the periphery of the plurality of core sheaths, wherein, A core sheath assembly is formed, wherein the number of the plurality of core sheaths in the core sheath assembly is 300 or more and the outer diameter of the plurality of core sheaths is 25 μm or more and 60 μm or less. Regarding the core sheath assembly other than the core sheaths disposed on the outermost periphery of the core sheath assembly, i.e., the inner core sheath assembly, the CV value of the cladding thickness defined by the gap between the adjacent core sheaths is 15% or less on the line connecting the centroids of the adjacent core sheaths that form the inner core sheath assembly.

2. The multi-core plastic optical fiber according to claim 1, wherein, The core sheath is configured with the densest filling structure of any one of hexagonal lattice, square lattice, or triangular lattice.

3. The multi-core plastic optical fiber according to claim 2, wherein, One core sheath portion forming the internal core sheath portion group has parallel edges with the adjacent core sheath portion.

4. The multi-core plastic optical fiber according to claim 1, wherein, When the outer diameter of the core sheath portion forming the inner core sheath portion assembly is set to D, the CV value of the cladding portion thickness is 20% or less within the range between two lines that are D / 6 apart from the line connecting the centroids of adjacent core sheath portions.

5. A multi-core plastic optical fiber, comprising a plurality of cores and a plurality of cladding portions covering the periphery of the plurality of cores, wherein, A core group is formed, wherein the number of the plurality of cores in the core group is 300 or more and the outer diameter of the plurality of cores is 25 μm or more and 60 μm or less. Regarding the core group other than the cores disposed on the outermost periphery of the core group, i.e. the inner core group, the CV value of the cladding thickness defined by the gap between the adjacent cores on the line connecting the centroids of the inner core group and the adjacent cores is 20% or less.

6. The multi-core plastic optical fiber according to claim 5, wherein, The cores forming the internal core group are configured with the densest filling structure of any one of hexagonal lattice, square lattice, or triangular lattice.

7. The multi-core plastic optical fiber according to claim 6, wherein, One core forming the inner core group has parallel edges with the adjacent core.

8. The multi-core plastic optical fiber according to claim 5, wherein, When the outer diameter of the core forming the inner core group is set to C, the CV value of the cladding thickness is 30% or less within the range between two lines that are C / 6 apart from the line connecting the centroids of adjacent cores.

9. The multi-core optical fiber according to claim 1, wherein, At least a portion of the core sheath portion forming the internal core sheath portion group forms a hexagonal lattice, wherein in a triangle connecting the centroids of any three adjacent core sheath portions other than the core sheath portion disposed at the outermost periphery of the plurality of core sheath portions, the ratio of the area occupied by the core sheath portion is more than 50% and less than 75%, and the outer diameter of the plurality of core sheath portions is more than 30 μm and less than 60 μm.

10. The multi-core plastic optical fiber according to claim 1, wherein, On the line connecting the centroid of any core sheath in the core sheath group that forms the inner core sheath group and the centroid of the core sheath adjacent to the arbitrary core sheath, the cladding thickness, calculated as the gap between the adjacent core sheaths, is 1 μm or more, and the seam thickness, calculated as the gap between the adjacent core sheaths, is 2 μm or more.

11. The multi-core plastic optical fiber according to claim 1, wherein, In the cross-section of the multi-core plastic optical fiber, the minimum distance from the sheath profile of the core sheath portion located closest to the profile of the multi-core plastic optical fiber to the profile of the multi-core plastic optical fiber is 5 μm or more.

12. The multi-core plastic optical fiber according to claim 5, wherein, At least a portion of the cores forming the internal core group forms a hexagonal lattice, wherein the area occupied by the cores is 50% or more and 75% or less in a triangle connecting the centroids of any three adjacent cores other than the cores located at the outermost periphery of the plurality of cores, and the outer diameter of the plurality of cores is 30 μm or more and 60 μm or less.

13. The multi-core plastic optical fiber according to claim 5, wherein, The cladding thickness, calculated as the gap between adjacent cores, is 1 μm or more on the line connecting the centroid of any core in the core group that forms the inner core group and the centroid of the core adjacent to that arbitrary core.

14. The multi-core plastic optical fiber according to claim 5, wherein, In the cross-section of the multi-core plastic optical fiber, the minimum distance from the outline of the core located closest to the outline of the multi-core plastic optical fiber to the outline of the multi-core plastic optical fiber is 5 μm or more.

15. The multi-core plastic optical fiber according to claim 1 or 5, wherein, The transmission loss was less than 250 dB / km when a 650 nm laser was irradiated onto one of the core sheaths in the inner core sheath assembly or one of the cores in the inner core assembly.

16. The multi-core plastic optical fiber according to claim 1 or 5, wherein, When multimode VCSEL light with a wavelength of 670 nm was incident on the multiple cores at an incident NA0.2, it had a bandwidth of over 400 MHz at a fiber length of 25 m.

17. An optical communication cable, wherein, Including the multi-core plastic optical fiber as described in claim 1 or 5.

18. An optical communication system, wherein, Using the multi-core plastic optical fiber as described in claim 1 or 5, spatial multiplexing communication is achieved using multiple signal beams.

19. An optical communication system, wherein, The light source wavelength is above 400nm and below 700nm, and spatial multiplexing communication is performed using the optical communication cable described in claim 17.

20. The optical communication system according to claim 19, wherein, The number of multiple light sources used for optical communication is more than 50% of the number of multiple cores or more than 50% of the number of multiple core sheaths, so that the multiple light sources correspond one-to-one with the multiple cores or the multiple core sheaths.

Images