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

Abstract

A multi-core plastic optical fiber comprising: a plurality of core parts; and a cladding part that covers the periphery of the core parts, wherein a core part group having 300 or more core parts each having a core part outer diameter of 25 μm or more and 60 μm or less is formed, in the core part group (hereinafter referred to as an inner core part group) except the core parts disposed on the outermost periphery of the core part group, the CV value of the thickness of the cladding part along a line connecting each of the centers of gravity of the core parts forming the inner core part group and being adjacent to each other is 20% or less.　The present invention provides a multi-core plastic optical fiber in which variation in transmission light amount is small among cores and a transmission band is wide, an optical communication cable, and an optical communication system.

Description

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

[0001] The present invention relates to a multi-core plastic optical fiber, an optical communication cable, and an optical communication system.

[0002] Taking advantage of their light weight and flexible properties, plastic optical fibers are used in a wide range of fields, including decorative lighting, medical care, in-vehicle lighting, various sensors, and communications. For communications applications, spatial division multiplexing (SDMA), which transmits multiple signals using a single multi-core plastic optical fiber, is being considered. In particular, the amount of communication data has increased dramatically in recent years, creating a demand for higher communication capacity per unit width of transceivers that connect optical fibers. Various development efforts have been underway.

[0003] For example, Patent Document 1 discloses a method of arranging a colored sea around a transparent core and a cladding in order to suppress crosstalk between cores in spatial multiplexing communications.

[0004] Furthermore, Patent Document 2 discloses a multi-core plastic optical fiber (hereinafter referred to as a two-component optical fiber) having three or more cores, in which the average core diameter 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 is 20% or less for cores other than the core located at the outermost periphery. It also discloses a multi-core plastic optical fiber (hereinafter referred to as a three-component optical fiber) in which the core portion has a sheath-core structure, the coating layer thickness of the sheath portion is 1 μm or more, and the CV value of the difference in layer thickness between the thinnest and thickest portions of the coating layer is 20% or less. And, as a method for producing a multi-core plastic optical fiber, a spinning method is disclosed in which a cladding component surrounds the outer periphery of a core, a two-layer composite flow is formed, and then multiple two-layer composite flow streams are merged. In addition, a spinning method has been disclosed in which, for a three-component optical fiber, the cladding component surrounds the outer periphery of the core to form a two-layer composite flow, and the sea component further surrounds the outer periphery of the two-layer composite flow to form a three-layer composite flow, and then multiple three-layer composite flows are merged. In this case, it has been disclosed that by reducing the melt viscosity of the polymer arranged on the periphery, a stable composite flow can be formed and thickness variations of the cladding layer and coating layer can be reduced.

[0005] Furthermore, Patent Document 3 discloses a method for obtaining a light transmission amount equivalent to that of a single-core optical fiber from a two-component optical fiber or a three-component optical fiber, in which the cores are made hexagonal and arranged in a close-packed manner, thereby increasing the total cross-sectional area of ​​the core portion.

[0006] Furthermore, Patent Document 4 discloses an image fiber for image transmission, not for communication purposes. A fiber with a large number of cores is desired for clear image display, and an optimal fiber structure is proposed.

[0007] Furthermore, Patent Document 6 discloses another method for manufacturing a multi-core plastic optical fiber. Patent Document 5 describes a method for manufacturing an optical fiber using a composite spinneret, generally called a pipe-type spinneret. This composite spinneret has pipes arranged in the same number as the number of cores, and molten polymer that will become the core component is discharged from each pipe, and molten polymer that will become the cladding component is supplied from the outer periphery of the pipe. In this way, the cladding component is coated on the outer periphery of the core component, forming a composite polymer that forms multiple cores / claddings, and the composite polymer is finally discharged from the nozzle of the spinneret, thereby manufacturing a multi-core plastic optical fiber.

[0008] JP 11-258432, JP 2001-174661, JP 11-160553, JP 6-18725, JP 2013-231817

[0009] However, the conventional multi-core plastic optical fiber and its manufacturing method have the following problems.

[0010] The technology disclosed in Patent Document 1 is an optical fiber with a small number of cores and a large core diameter (in the example, the number of cores is 37 and the core diameter is 100 μm), and according to the findings of the present inventors, if the core diameter is too large, the transmission bandwidth in multiplex communication may deteriorate. Furthermore, if the number of cores in a single optical fiber is as high as 300 or more, the diameter of the optical fiber increases, and the bending characteristics may be significantly reduced.

[0011] Furthermore, Patent Document 2 discloses a method for manufacturing an optical fiber having a small number of cores and a large core diameter, specifically, in the examples, an optical fiber having 37 cores (core outer diameter 150 μm) and 151 cores (core outer diameter 75 μm). However, according to the findings of the present inventors, when an optical fiber has a large number of cores (300 or more) and a small core diameter (60 μm or less), it becomes very difficult to control the cross section of the polymer in the composite spinneret, which can cause adjacent cores to merge or a core shape defect, making it impossible to obtain the desired optical fiber cross section. This is because, as the number of cores increases, the size of the composite spinneret increases, and it is necessary to supply the cladding component polymer and the sea component polymer from the outer periphery of the composite spinneret toward the center. However, because there are many polymer composite flow paths for forming the core / cladding layer, it is not possible to supply the polymer sufficiently to the center of the composite spinneret. As a result, adjacent cores can merge or a core shape defect can occur. If the density of the polymer composite flow passages were increased in order to reduce the size of the composite spinneret, the flow passages themselves would become very narrow, making the above problem more pronounced. Furthermore, as a method for equalizing the thickness variations of the cladding layer of a two-component optical fiber or the coating layer of a three-component optical fiber, it has been disclosed that the polymer viscosity on the outer periphery of the polymer composite flow passage is reduced, but no other solutions have been described.

[0012] Furthermore, Patent Document 3 discloses an optical fiber with a small number of cores (151 cores in the example), but according to the knowledge of the present inventors, this may not be feasible when the number of cores in one optical fiber is as large as 300 or more and the core diameter is small (60 μm or less). Furthermore, although it is possible to obtain a certain amount of transmitted light with one multi-core plastic optical fiber, it does not disclose any technology related to suppressing the variation in the amount of transmitted light per core, which is an important indicator.

[0013] Furthermore, the technology disclosed in Patent Document 4 is limited to optical fibers for image transmission, and the characteristics required for optical fibers for spatial multiplexing communications are different, so the optimal fiber structure is not the same. Furthermore, according to the findings of the present inventors, since the fiber length for image transmission applications is several meters, it is desirable to increase resolution by arranging multiple cores and reducing the core diameter, even at the expense of transmission loss. On the other hand, for multiplexing communications applications, a larger core diameter is preferable from the perspective of transmission loss, while a smaller core diameter is preferable from the perspective of transmission bandwidth. Achieving both is a technical key, but Patent Document 4 does not disclose any description of this. An example of Patent Document 4 discloses an optical fiber with 3,247 cores and a core diameter of 10 μm. However, due to its extremely high transmission loss of 1,200 dB / km, it may not be usable for multiplexing communications applications.

[0014] A major problem with the pipe-type base disclosed in Patent Document 5 is that the area per pipe increases because the pipe thickness is added to produce one island. Furthermore, since the pipes are press-fitted into the base and welded to secure them, a welding allowance is required. Furthermore, since holes for inserting the pipes are required, the gap between the pipes cannot be narrowed due to strength issues. Therefore, the pipes cannot be densely arranged per unit area, and it may be difficult to manufacture a multi-core plastic optical fiber with a large number of cores and a small core outer diameter. Furthermore, since a cylindrical pipe is used, the island shape obtained is limited to a circle or a similar elliptical shape. Therefore, it may be impossible to obtain a multi-core plastic optical fiber having a polygonal core shape, for example. Furthermore, since a cladding component polymer introduction channel is arranged around the periphery of a pipe group in which pipes are densely arranged, it is difficult to sufficiently supply the cladding component polymer to the center of the pipe group. In particular, the core component polymers discharged from the pipe at the center of the pipe group may merge. According to the findings of the present inventors, it may be structurally difficult to freely arrange the introduction flow paths for the clad component polymer within the group of pipes.

[0015] Therefore, an object of the present invention is to provide a multi-core plastic optical fiber, an optical communication cable, and an optical communication system that have little variation in the transmission amount per core and a wide transmission band.

[0016] In order to solve the above problems, the present invention employs any of the following configurations. (1) A multi-core plastic optical fiber having a plurality of cores, a plurality of sheath-core portions in which cladding portions are formed around the plurality of cores, and a sea portion covering the plurality of sheath-core portions, wherein the number of the plurality of sheath-core portions is 300 or more, the plurality of sheath-core portions form a sheath-core portion group with outer diameters of 25 μm to 60 μm, and for the sheath-core portion group excluding the portion arranged at the outermost periphery of the sheath-core portion group (hereinafter referred to as an internal sheath-core portion group), the CV value of the cladding thickness defined by the gap between adjacent sheath-core portions constituting the internal sheath-core portion group along a line connecting the centers of gravity of the adjacent sheath-core portions is 15% or less. (2) The multi-core plastic optical fiber of (1), in which the sheath-core portions are arranged in a close-packed structure that is either a hexagonal lattice, a square lattice, or a trigonal lattice. (3) The multi-core plastic optical fiber of (2), in which the sheath-core portions constituting one of the internal sheath-core portion groups have parallel sides between adjacent sheath-core portions. (4) The multi-core plastic optical fiber according to (1), wherein, when the outer diameter of the sheath-core portions forming the internal sheath-core portion group is D, the CV value of the cladding thickness is 20% or less in an area sandwiched between two lines spaced D / 6 from the line connecting the centers of gravity of adjacent sheath-core portions. (5) A plastic optical fiber having a plurality of core portions and a plurality of cladding portions surrounding the plurality of core portions, wherein the number of the plurality of core portions is 300 or more, forming a core portion group with outer diameters of the plurality of core portions ranging from 25 μm to 60 μm, and in a core portion group excluding core portions arranged at the outermost periphery of the core portion group (hereinafter referred to as an internal core portion group), the CV value of the cladding thickness defined by the gap between adjacent core portions forming the internal core portion group along a line connecting the centers of gravity of the adjacent core portions is 20% or less. (6) The multi-core plastic optical fiber according to (5), wherein the cores forming the internal core portion group are arranged in a close-packed structure of either a hexagonal lattice, a square lattice, or a trigonal lattice. (7) The multi-core plastic optical fiber according to (6), wherein the core portions forming one of the internal core portion groups have parallel sides between adjacent core portions.(8) The multi-core plastic optical fiber according to (5), wherein the CV value of the cladding thickness is 30% or less in an area sandwiched between two lines spaced apart by C / 6 from the line connecting the centers of gravity of adjacent cores, where C is the outer diameter of the cores forming the internal core group. (9) The multi-core optical fiber according to (1), wherein at least some of the sheath-core portions forming the internal core group form a hexagonal lattice, and in a triangle connecting the centers of gravity of any three adjacent sheath-core portions excluding the outermost sheath-core portion of the plurality of core-sheath portions, the ratio of the area occupied by the sheath-core portions is 50% or more and 75% or less, and the outer diameters of the plurality of core-sheath portions are 30 μm or more and 60 μm or less. (10) The multi-core plastic optical fiber according to (1), wherein, on a line connecting the center of gravity of any one of the sheath-core portions constituting the internal sheath-core portion group and the center of gravity of a portion adjacent to the any one of the sheath-core portions, a cladding thickness obtained as a gap between the adjacent sheath-core portions is 1 μm or more, and a sea thickness obtained as a gap between the adjacent sheath-core portions is 2 μm or more. (11) The multi-core plastic optical fiber according to claim 1, wherein, in a cross section of the multi-core plastic optical fiber, a minimum distance from a sheath outline of a core-sheath portion closest to the outline of the multi-core plastic optical fiber to the outline of the multi-core plastic optical fiber (hereinafter sometimes referred to as "outer circumferential sea thickness") is 5 μm or more. (12) The multi-core plastic optical fiber according to (5), wherein at least some of the core portions forming the internal core portion group form a hexagonal lattice, and in a triangle connecting the centers of gravity of any three adjacent core portions excluding a core portion arranged on the outermost periphery of the plurality of core portions, the ratio of the area occupied by the core portions is 50% or more and 75% or less, and the outer diameters of the plurality of core portions are 30 μm or more and 60 μm or less. (13) The multi-core plastic optical fiber according to (5), wherein a cladding thickness calculated as a gap between the adjacent core portions on a line connecting the center of gravity of any core portion among the core portions forming the internal core portion group and the center of gravity of a core portion adjacent to the any core portion is 1 μm or more.(14) The multi-core plastic optical fiber according to claim 5, wherein in a cross section of the multi-core plastic optical fiber, a minimum distance from a contour line of a core portion closest to the contour line of the multi-core plastic optical fiber to the contour line of the multi-core plastic optical fiber (hereinafter sometimes referred to as "outer circumferential sea portion thickness") is 5 μm or more. (15) The multi-core plastic optical fiber according to (1) or (5), wherein a transmission loss is 250 dB / km or less when measured by irradiating one of the core portions in the internal core-sheath portion group or one of the core portions in the internal core portion group with a 650 nm laser light. (16) The multi-core plastic optical fiber according to (1) or (5), wherein a bandwidth of 400 MHz or more at a fiber length of 25 m is measured by irradiating multimode VCSEL light of a wavelength of 670 nm with an incident NA of 0.2 so that the light enters the multiple cores. (17) An optical communication cable comprising the multi-core plastic optical fiber according to (1) or (5). (18) An optical communication system that performs spatial multiplexing communication using a plurality of signal light beams by using the multi-core plastic optical fiber according to (1) or (5). (19) An optical communication system that performs multiplexing spatial communication by using the optical communication cable according to (17), in which the light source wavelength is 400 nm or more and 700 nm or less. (20) The optical communication system according to (19), in which the number of multiple light sources used for optical communication is 50% or more of the number of the multiple core portions or the multiple core-sheath portions, and the multiple light sources correspond one-to-one to the multiple core portions or the multiple core-sheath portions.

[0017] According to the present invention, it is possible to provide a multi-core plastic optical fiber, an optical communication cable, and an optical communication system that have little variation in the amount of light transmitted from each core and a wide transmission band.

[0018] 1 is a partially enlarged cross-sectional view of a multi-core plastic optical fiber according to a typical embodiment of the present invention; FIG. 2 is a schematic cross-sectional view of a composite spinneret used in an embodiment of the present invention, and peripheral equipment such as a spin pack and a cooling device; FIG. 3 is a schematic cross-sectional view of a composite spinneret showing an embodiment of the present invention; FIG. 4 is a view taken along the arrows X-X in FIG. 2, showing an overall view of the discharge surface of a discharge plate; FIG. 5 is a partially enlarged cross-sectional view of the discharge surface of a discharge plate used in a typical embodiment of the present invention; FIG. 6 is a partially enlarged cross-sectional view of a multi-core plastic optical fiber according to another embodiment of the present invention; FIG. 7 is a partially enlarged cross-sectional view of a multi-core plastic optical fiber, where (a) is a diagram explaining the measurement points of the cladding thickness according to claim 5, and (b) is a diagram explaining the measurement points of the cladding thickness according to claim 1; FIG. 8 is a partially enlarged cross-sectional view of a multi-core plastic optical fiber, where (a) is a diagram explaining the measurement points of the cladding thickness according to claims 8 and 13, and (b) is a diagram explaining the measurement points of the cladding thickness and the sea portion thickness according to claims 4 and 10. 9(a) and 9(b) are cross-sectional views of a multi-core plastic optical fiber, where (a) is a diagram explaining the thickness of the outer sea portion (cladding portion) according to claim 5, and (b) is a diagram explaining the thickness of the outer sea portion according to claim 1. (a) is a partially enlarged view of Fig. 9(a), and (b) is a partially enlarged view of Fig. 9(b). (b) are partially enlarged cross-sectional views of a multi-core plastic optical fiber, where (a) is a diagram explaining a method for calculating the ratio of the area occupied by the core according to claim 12, and (b) is a diagram explaining a method for calculating the ratio of the area occupied by the core-sheath portion according to claim 9.

[0019]

[0023] Hereinafter, embodiments of the multi-core plastic optical fiber, the optical communication cable, and the optical communication system of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments, and can be modified in various ways depending on the purpose and application. [Configuration of Optical Fiber] A second aspect 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 that covers the core component resins 18, as shown in Figure 1, and has the following configuration.

[0020] A multi-core plastic optical fiber having a plurality of core portions and a cladding portion surrounding the core portions, the multi-core plastic optical fiber forming a core portion group including 300 or more core portions and having a core portion outer diameter of 25 μm to 60 μm, wherein, for a core portion group (hereinafter referred to as an inner core portion group) excluding the core portions arranged at the outermost periphery of the core portion group, the CV value of the cladding thickness defined by the gap between adjacent core portions on a line connecting the centers of gravity of the adjacent core portions forming the inner core portion group is 20% or less. With this configuration, the area ratio of the core portions can be increased compared to the second aspect described below, and therefore the number of core portions that can be arranged can be increased. This allows for an increase in the number of channels for spatial multiplexing communication.

[0021] As shown in FIG. 7, the first embodiment of the multi-core plastic optical fiber of the present invention is a three-component optical fiber in which a core component resin 18 and a cladding component resin 19 surrounding the core component resin 18 form a core-sheath portion, and multiple core-sheath portions are disposed in a sea component resin 20, and has the following configuration.

[0022] A multi-core plastic optical fiber having a plurality of cores, a sheath-core portion in which a cladding portion is formed around the cores, and a sea portion that covers the periphery of the sheath-core portion, wherein a sheath-core portion group is formed with 300 or more cores, each having an outer diameter of 25 μm to 60 μm, and wherein for the sheath-core portion group (hereinafter referred to as the internal sheath-core portion group) excluding the cores-in-the-core portion arranged at the outermost periphery of the sheath-core portion group, the CV value of the cladding thickness, which is defined by the gap between adjacent sheath-core portions along a line connecting the centers of gravity of the adjacent sheath-core portions that form the internal sheath-core portion group, is 15% or less.

[0023] By using a three-component optical fiber, the sea component resin 20 is present in the outermost layer, so that optical signals leaking into the sea component are attenuated and lost on the fiber surface, preventing the leaked optical signals from reaching adjacent cores. [Uniform Cladding Thickness] The multi-core plastic optical fiber of the present invention is intended for use in so-called parallel communication, in which multiple data are simultaneously transmitted and received in parallel for each core. Therefore, when a receiver installed at the end of the optical fiber receives data from multiple cores, data synchronization is extremely important. If this synchronization deteriorates, control on the receiver side becomes difficult. In particular, to achieve high-capacity data communication with a single optical fiber, a large number of cores (300 or more) must be densely arranged. In this case, to satisfy data synchronization in all cores, it is extremely important to suppress variations in the input / output characteristics and transmission characteristics of all cores and to uniform them to the utmost.

[0024] In the three-component optical fiber according to the first aspect of the present invention, the sheath-core portions are preferably arranged in a close-packed manner using either a hexagonal lattice, a square lattice, or a trigonal lattice, similar to the core portions forming the internal core group described later in the two-component optical fiber according to the second aspect of the present invention. Furthermore, it is preferable that each sheath-core portion forming the internal core group has parallel sides between adjacent sheath-core portions. This makes it possible to uniformize the cladding thickness over the entire circumference of the core. As a result, it is possible to easily achieve a reduction in the CV value of the cladding thickness on the line connecting the center of gravity of the sheath-core portion and the center of gravity of the adjacent sheath-core portion. When the sheath-core portions have parallel sides, in the case of a hexagonal lattice, the vertices of the hexagonal sheath-core portion have smoothly curved shapes. Furthermore, in the case of a square lattice or a trigonal lattice, the vertices have smoothly curved shapes.

[0025] Furthermore, when the outer diameter of the sheath-core portions forming the internal sheath-core portion group is D, it is preferable that the CV value of the cladding thickness be 20% or less in a range sandwiched between two lines spaced D / 6 away from a line connecting the centers of gravity of adjacent sheath-core portions (hereinafter, this range may be referred to as a "side region"). By doing so, a uniform cladding region can be formed; in other words, the variation in cladding thickness is reduced, scattering at the interface between the core and cladding is reduced, the variation in transmission loss is reduced, and the transmission bandwidth is improved.

[0026] In addition, in the two-component optical fiber according to the second aspect of the present invention, while it is generally important to uniform the circularity of the core shape in order to suppress variations in transmission characteristics, it is also effective to uniform the thickness variations of the claddings (in the case of the three-component optical fiber according to the first aspect of the present invention, the claddings of the core-sheath portions) that form the outer peripheries of each core. It is known that the majority of the signal light propagating through the core is reflected at the interface between the core and the cladding, but a portion of this light is transmitted to or scattered by the cladding components. One of the causes of this is thought to be diffuse reflection due to minute irregularities at this interface. To uniformize the minute irregularities at this interface, the shape of the interface can be stabilized by making the cladding thicker than a certain thickness. Additionally, although the principle is not fully understood, a similar effect can also be achieved by uniforming the thickness of the cladding.

[0027] For this reason, in the two-component optical fiber according to the second aspect of the present invention, it is preferable that the cores forming the internal core group are arranged in a close-packed structure of either a hexagonal lattice, a square lattice, or a trigonal lattice. Furthermore, it is preferable that each core forming the internal core group has parallel sides between adjacent cores. This makes it possible to make the cladding thickness more uniform over the entire circumference of the core. As a result, it is possible to easily achieve a reduction in the CV value of the cladding thickness on the line connecting the center of gravity of the core and the center of gravity of the adjacent core. Here, when the cores have parallel sides, in the case of a hexagonal lattice, the vertices of the hexagonal core have a smoothly curved shape. Furthermore, in the case of a square lattice or a trigonal lattice, the vertices have a smoothly curved shape.

[0028] Furthermore, when the outer diameter of the cores forming the internal core group is C, it is preferable that the CV value of the cladding thickness be 30% or less in a range sandwiched between two lines spaced C / 6 from a line connecting the centers of gravity of adjacent cores (hereinafter, this range may be referred to as a "side region"). By doing so, a uniform cladding region can be formed, in other words, variation in the cladding thickness is reduced, scattering at the interface between the cores and the cladding is reduced, variation in transmission characteristics is reduced, and the transmission band is improved.

[0029] Furthermore, compared to two-component optical fibers, three-component optical fibers tend to have smaller cladding thickness variations because the sea component polymer flows before the cladding component polymer when forming a composite polymer flow in the composite spinneret, which is advantageous. [Core Component Resin] The core is a transmission portion that directly propagates signal light and plays a role in efficiently transmitting the signal light. The resin in the resin composition forming the core is preferably a light-transmitting material with low transmission loss, such as acrylic resin, modified polycarbonate resin, cycloolefin resin, styrene resin, and olefin resin such as polymethylpentene. Among these resins, acrylic resin, which has low transmission loss, is preferred. Examples of the acrylic resin include polymers of methacrylic acid esters and acrylic acid esters. Examples of methacrylic acid esters include alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate; aryl methacrylates such as phenyl methacrylate; and cycloalkyl methacrylates such as cyclohexyl methacrylate and norbornenyl methacrylate. Examples of acrylic acid esters include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, aryl acrylates such as phenyl acrylate, and cycloalkyl acrylates such as cyclohexyl acrylate and norbornenyl acrylate. Other acrylic resins include sodium polyacrylate resins, polyacrylonitrile resins, and polyacrylamide resins. Among these, polymethyl methacrylate resins containing methyl methacrylate as a main component are particularly preferred from the viewpoints of transparency and processability.

[0030] The modified polycarbonate resin may be, for example, a polycarbonate resin substituted with a lower alkyl group or a trifluoromethyl group and having an average molecular weight of 10,000 to 200,000.

[0031] Examples of cycloolefin resins include cycloolefin polymers such as addition copolymers of ring-opening metathesis polymerization polymers and ethylene, and hydrogenated ring-opening metathesis polymerization polymers, as well as cycloolefin copolymers such as ethylene-2-norbornene.

[0032] In order to adjust the refractive index, the resin composition constituting the core portion may be appropriately added with a dopant that increases the refractive index, such as germanium, phosphorus, tin, boron, or the like, or a dopant fluorine-based material that decreases the refractive index, such as a fluorine-based material such as magnesium fluoride.

[0033] The refractive index of the core portion is preferably 1.45 or more and 1.60 or less. By having the refractive index of the core portion be 1.45 or more, more preferably 1.48 or more, the refractive index difference with the cladding portion can be increased, thereby reducing the rate at which signal light leaks into the sea portion. Furthermore, by having the refractive index of the core portion be 1.60 or less, more preferably 1.52 or less, the refractive index difference with the cladding portion can be suppressed, thereby reducing the number of modes of propagating light, thereby expanding the transmission bandwidth. The refractive index can be measured using an Abbe refractometer on a 20 mm x 8 mm x 1.4 mm test piece in accordance with JIS K 7142:2014 at room temperature (25°C). If it is difficult to directly measure the refractive index of a core portion, the core portion can be heated at 210°C for 5 minutes in a press molding machine, then cooled to room temperature to prepare a test piece molded to a size of 20 mm x 8 mm x 1.4 mm, and the refractive index can be measured. Furthermore, if the composition of the core portion is known, a test piece can be similarly prepared from the known composition, and the refractive index can be measured. [Resin Component of Cladding Portion] The cladding portion serves to protect the core portion from external environmental factors and also to reduce the rate at which signal light propagating through the core portion is reflected at the cladding portion interface and leaks into the sea portion. Examples of resins that can be used to form the cladding portion include those that are the same as those used to form the core portion, such as acrylic resin, as well as fluororesins such as vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer, vinylidene fluoride / trifluoroethylene copolymer, acrylic acid fluorinated ester polymer, polyperfluorobutyl methacrylate, polyperfluoroisopropyl methacrylate, and polyhexafluoro2-propyl methacrylate.

[0034] The cladding resin may also contain a dopant, such as a fluorine-based material such as magnesium fluoride, to adjust the refractive index. The cladding resin may also contain a coloring material. Incorporating a coloring material into the cladding can reduce signal light leakage into the sea. However, since the cladding is relatively thin, if the cladding contains a coloring material, the content (mass %) of the coloring material in the cladding is preferably smaller than the content (mass %) of the coloring material in the sea. If the content (mass %) of the coloring material in the cladding is greater than the content (mass %) of the coloring material in the sea, the melt viscosity of the resin composition during cladding formation may increase, making it difficult to form the cladding to the desired dimensions without increasing the extrusion stress, or the extrusion stress may deform the core or sea. In other words, if the optical fiber of the present invention contains a coloring material in the cladding, the content (mass %) of the coloring material in the cladding is preferably smaller than the content (mass %) of the coloring material in the sea. Specifically, the content is preferably less than 3 mass %.

[0035] The refractive index of the cladding is preferably 1.35 or more, more preferably 1.38 or more, so that the difference in refractive index between the cladding and the core is small, and the number of modes of propagating light is reduced, thereby expanding the transmission bandwidth. Furthermore, the refractive index of the cladding is preferably 1.50 or less, more preferably 1.42 or less, so that the rate at which signal light propagating through the core is reflected at the cladding interface and leaks into the sea can be reduced.

[0036] Here, the refractive index of the cladding portion can be measured in the same manner as the refractive index of the core portion. If it is difficult to sample the cladding portion and directly measure its refractive index, the sampled cladding portion can be heated at 210°C for 5 minutes using a press molding machine, then cooled to room temperature to prepare a test piece measuring 20 mm x 8 mm x 1.4 mm, and the refractive index can be measured. Furthermore, if the composition of the cladding portion is known, a test piece can be similarly prepared from the known composition, and the refractive index can be measured.

[0037] In order to reflect light at the interface between the core and cladding, the refractive index of the cladding must be lower than that of the core. By making the refractive index of the cladding lower than that of the core, preferably by making the difference between the refractive index of the core and the refractive index of the cladding 0.02 or more, more preferably 0.05 or more, the rate at which signal light propagating through the core is reflected at the cladding interface and leaks into the sea can be reduced. On the other hand, by making the difference between the refractive index of the core and the refractive index of the cladding preferably 0.20 or less, more preferably 0.09 or less, the number of modes of propagating light can be reduced, thereby expanding the transmission bandwidth. [Sea Component Resin] The three-component optical fiber according to the first aspect of the present invention has a sea portion outside the cladding. The sea portion plays a role in determining the outer diameter and flexibility of the optical fiber, confining and radiating light by utilizing the refractive index difference with the cladding, and preventing crosstalk by adding a light-blocking agent.

[0038] The material used for the sea portion is selected in combination with the previously selected core and cladding materials, taking into consideration the above-mentioned functions, such as flexibility, light confinement and radiation utilizing the refractive index difference with the cladding portion, and the role of preventing crosstalk by adding a light-blocking agent. [Circularity of Core Portion and Circularity of Core-Sheath Portion] In the two-component optical fiber according to the second aspect of the present invention, it is preferable that the circularity of the core portion arranged at the outermost periphery of the core portion group is 1.5 or less, and that the circularity of the core portions forming the inner core portion group, excluding the core portion arranged at the outermost periphery of the core portion group, is 1.3 or less. Here, the core portion arranged at the outermost periphery of the core portion group refers, in the case of a hexagonal lattice structure, to a core portion having six core portions adjacent to it in the hexagonal lattice structure. In the case of a square lattice structure, it refers to a core portion having four core portions adjacent to it in the square lattice structure, and in the case of a trigonal lattice structure, it refers to a core portion having three core portions adjacent to it in the trigonal lattice structure. When the circularity of the core parts arranged at the outermost periphery of the core part group is 1.5 or less, it becomes easy to set the circularity of the core parts forming the internal core part group to 1.3 or less. When the circularity of the core parts forming the internal core part group is 1.3 or less, the transmission band of the core parts becomes good.

[0039] Here, the circularity of the core portion is the value obtained by acquiring an image of the core portion of a multi-core plastic optical fiber in the internal core portion group, calculating the long core diameter and short core diameter, and dividing the long core diameter by the short core diameter (long core diameter ÷ short core diameter).

[0040] In the three-component optical fiber according to the first aspect of the present invention, it is preferable that the circularity of the core of the sheath-core portion arranged at the outermost periphery of the sheath-core portion group is 1.3 or less, and that the circularity of the core of the sheath-core portion forming the inner sheath-core portion group, excluding the sheath-core portion arranged at the outermost periphery of the sheath-core portion group, is 1.2 or less. By using a three-layer structure of a core portion, a cladding portion, and a sea portion, the core portion is less susceptible to flow changes in the sea portion, so the circularity of the core of the sheath-core portion can be reduced. As with two-component optical fibers, in three-component optical fibers, if the circularity of the core of the sheath-core portion arranged at the outermost periphery of the sheath-core portion group is 1.3 or less, the transmission bandwidth is improved.

[0041] Here, the circularity of the core-sheath portion is a value obtained by acquiring a core-sheath portion image of a multi-core plastic optical fiber in the inner core-sheath portion group, calculating the major diameter and minor diameter, and dividing the major diameter by the minor diameter of the core-sheath portion (core-sheath portion diameter ÷ core-sheath portion minor diameter). [Core portion outer diameter and core-sheath portion outer diameter] In the three-component optical fiber of the first aspect of the present invention, the core-sheath portion outer diameter is 25 μm or more and 60 μm or less. Here, the core-sheath portion outer diameter refers to the average value of the major diameter of the core-sheath portion and the minor diameter of the core-sheath portion obtained when calculating the circularity of the core-sheath portion, as described above.

[0042] In the two-component optical fiber according to the second aspect of the present invention, the core outer diameter is 25 μm or more and 65 μm or less. Here, the core outer diameter refers to the average value of the major core diameter and the minor core diameter obtained when calculating the core circularity, as described above. If the core outer diameter is less than 25 μm, the transmission loss significantly deteriorates, and if the core diameter exceeds 65 μm, the transmission bandwidth deteriorates. [Number of Cores and Number of Core-Sheath Portions] In the two-component optical fiber according to the second aspect of the present invention, the number of cores arranged in one optical fiber is 300 or more. By having 300 or more cores, each core can transmit a different light, thereby enabling high-capacity spatial multiplexing communications. Here, if the number of cores is less than 300, sufficient capacity cannot be obtained in spatial multiplexing communications. Furthermore, if the number of cores is 5,200 or less, a fiber outer diameter that allows stable spinning can be obtained. In this case, the core diameter can be made larger than 25 μm, resulting in good transmission loss. [Manufacturing Method] Fig. 3 is a schematic cross-sectional view of a composite spinneret used in an embodiment of the present invention, and Fig. 4 is a view taken along the arrows X-X in Fig. 3, showing the overall view of the nozzle surface of the nozzle plate. Fig. 5 is a partially enlarged cross-sectional view of the nozzle surface of the nozzle plate used in a second embodiment of the present invention, and Fig. 6 is a partially enlarged cross-sectional view of the nozzle surface of the nozzle plate used in the first embodiment of the present invention. Fig. 2 is a schematic cross-sectional view of the composite spinneret, spin pack, and cooling device periphery used in an embodiment of the present invention. Note that these are conceptual diagrams that accurately convey the gist of the present invention and are simplified, and the composite spinneret of the present invention is not particularly limited, and the number of holes and grooves, their dimensional ratios, etc. can be changed according to the embodiment.

[0043] 3, the composite spinneret 13 used in the embodiment of the present invention is mounted on a spin pack 14 and fixed in a spin block 12, and a cooling device 17 is provided directly below the composite spinneret 13. The core component polymer 9, cladding component polymer 10, and sea component polymer 11 introduced into the composite spinneret 13 pass through the distribution plate 6 and the discharge plate 4, and are discharged from the spinneret discharge holes 16 of the discharge plate 5, and then cooled by airflow blown out by a cooling device 25 and taken up as a multi-core plastic optical fiber 21. Furthermore, the components mounted upstream of the distribution plate 6 may use the flow paths and the like used in the existing spin pack 14, and there is no need to specially dedicate them.

[0044] 2, the composite spinneret 13 used in the embodiment of the invention is constructed by stacking at least one or more distributor plates 6, discharge plates 4, and spinneret discharge plates 5 in this order, and it is particularly preferable that the discharge plate 4 be constructed of a thin plate. In this case, the distributor plates 6, discharge plates 4, and spinneret discharge plates 5 are positioned with positioning pins so that the centers (cores) of the spin packs 14 are aligned, and after stacking, they may be fixed with screws, bolts, etc., or may be metal-bonded by thermocompression.

[0045] The polymers of each component supplied to the distribution plate 6 pass through the distribution grooves and distribution holes of at least one or more stacked distribution plates 6, and are then discharged from the core component discharge hole 1 for discharging the core component polymer 9, the cladding component discharge hole 2 for discharging the cladding component polymer 10, and the sea component discharge hole 3 for discharging the sea component polymer of the discharge plate 4. The polymers discharged from the respective discharge holes merge at the merge hole 22 to form a composite polymer 8. The composite polymer 8 is then discharged from the die discharge hole 16 of the die discharge plate 5. As shown in FIG. 4 , one multi-core plastic optical fiber is formed by discharging from the discharge hole 7 (a combination of the core component discharge hole 1, the cladding component discharge hole 2, and the sea component discharge hole 3) and discharging the merged composite polymer 8 from the die discharge hole 16. FIG. 4 shows a schematic diagram of how four multi-core plastic optical fibers can be formed.

[0046] To manufacture the two-component optical fiber according to the second embodiment of the present invention, as shown in FIG. 5 , cladding component discharge holes 2 are arranged around the core component discharge hole 1 on the discharge surface 15 of the discharge plate 4. While FIG. 5 shows three cladding component discharge holes 2 arranged around the core component discharge hole 1, this arrangement is not limited thereto, and the number and arrangement of the discharge holes may be changed depending on the cross section of the optical fiber. Thus, the cladding component polymer 10 surrounds the outer periphery of the core component polymer 9 discharged from the core component discharge hole 1, thereby forming a composite polymer flow 8 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 the multiple stacked distribution plates 6, and each polymer can be uniformly discharged from each discharge hole. This not only makes the core shape uniform, but also makes it possible to form a uniform cladding around the core. In particular, as the number of cores in the optical fiber increases (as the number of core component polymers 9 in the composite polymer flow 8 increases), the composite spinneret 13 becomes larger, and therefore, in a conventional pipe-type spinneret, the cladding component polymer 10 is supplied from the outer periphery of the pipe group, making it difficult to supply the polymer uniformly to the pipes arranged in the center. On the other hand, in the distribution-type composite spinneret 13 used in the present invention, even if the spinneret size becomes large, each polymer supplied from the upstream side of the composite spinneret 13 can be received by the entire surface of the distribution plate 6, making it possible to distribute it uniformly.

[0047] To manufacture the three-component optical fiber according to the first embodiment of the present invention, as shown in Fig. 6, cladding component discharge holes 2 are arranged around the core component discharge hole 1 on the discharge surface 15 of the discharge plate 4, and sea component discharge holes 3 are arranged around the core component discharge holes 2. While Fig. 6 shows three cladding component discharge holes 2 arranged around the core component discharge hole 1 and three sea component discharge holes 3 arranged around the cladding component discharge holes 2, this arrangement and the number of discharge holes can be changed depending on the cross section of the optical fiber. Thus, the core component polymer 9 discharged from the core component discharge hole 1 is surrounded by the cladding component polymer 10 to form a sheath-core polymer. Furthermore, sea component polymer 11 is supplied from the outer periphery of the core component polymer 9, forming a composite polymer flow 8 in which multiple sheath-core polymers are arranged within the sea component polymer 11. In this case, the effects of the composite spinneret 13 of the present invention are realized, just as in the case of the two-component optical fiber described above. [Optical fiber] The cross section of the multi-core plastic optical fiber of the present invention is preferably circular from the viewpoint of handling, 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, 300 or more cores can be arranged in the optical fiber, and if it is 3 mm or less, it has appropriate flexibility and is easy to handle.

[0048] In the three-component system of the first aspect, it is preferable that at least some of the sheath-core portions constituting the internal sheath-core portion group form a hexagonal lattice, and that, when the area of ​​a triangle connecting the centers of gravity of any three adjacent sheath-core portions excluding the sheath-core portion arranged at the outermost periphery of the plurality of sheath-core portions is taken as 100%, the ratio of the area occupied by the sheath-core portions is 50% to 75%, and that the outer diameters of the plurality of sheath-core portions are 30 μm to 60 μm. This allows the sheath-core portion area to be maintained at a certain ratio or more while ensuring a sufficient distance between adjacent sheath-core portions, thereby keeping transmission loss low and preventing light that has entered one sheath-core portion from leaking to an adjacent sheath-core portion.

[0049] Furthermore, on a line connecting the center of gravity of any one of the sheath-core portions constituting the internal sheath-core portion group to the center of gravity of a portion adjacent to that portion, it is preferable that the cladding thickness required as the gap between the adjacent sheath-core portions is 1 μm or more, and the sea thickness required as the gap between the adjacent sheath-core portions is 2 μm or more. This improves the circularity of the cross-sectional shape of the core, reduces transmission loss, and prevents light that has entered one sheath-core portion from leaking to an adjacent sheath-core portion.

[0050] In the two-component system of the second aspect, it is preferable that at least some of the core parts constituting the internal core part group form a hexagonal lattice, and that, when the area of ​​a triangle connecting the centers of gravity of any three adjacent core parts excluding the core parts arranged at the outermost periphery of the plurality of core parts is taken as 100%, the ratio of the area occupied by the core parts is 50% to 75%, and that the outer diameters of the plurality of core parts are 30 μm to 60 μm. This makes it possible to increase the core part area, ensure a distance between adjacent core parts, and keep transmission loss low.

[0051] Furthermore, it is preferable that the cladding thickness required as the gap between the adjacent core portions on a line connecting the center of gravity of any one of the core portions forming the internal core portion group to the center of gravity of a core portion adjacent to the any one of the core portions is 1 μm or more, thereby improving the circularity of the cross-sectional shape of the core, suppressing transmission loss, and preventing light entering one core portion from leaking to an adjacent core portion.

[0052] In the optical fiber of the second aspect, the two-component system preferably has a cross section in which the minimum distance (outer sea thickness) from the contour line of the core closest to the contour line of the optical fiber to the contour line of the optical fiber is 5 μm or more. This makes it possible to uniformize the circularity of the cores arranged at the outermost periphery of the core group and the variation in cladding thickness. In the three-component system of the first aspect, the minimum distance (outer sea thickness) from the contour line of the core closest to the contour line of the optical fiber to the contour line of the optical fiber is preferably 5 μm or more. This makes it possible to uniformize the circularity of the sheath-core parts arranged at the outermost periphery of the sheath-core part group and the variation in cladding thickness.

[0053] The multi-core plastic optical fiber of the present invention preferably has a bandwidth of 400 MHz or more at a fiber length of 25 m when measured with multimode VCSEL light of 670 nm wavelength entering one core or the core-sheath portion at an incident NA of 0.2. Here, VCSEL stands for Vertical Cavity Surface Emitting Laser, a type of semiconductor laser that emits a laser beam vertically from the top surface. A single light source emits laser light with a diameter of several tens of micrometers, but one feature is that multiple light sources can be arranged in a two-dimensional array. Coupling each of these light sources to each of the multi-core cores enables high-capacity communication. NA stands for Numerical Aperture, and an incident NA of 0.2 means that the light is incident at an angle of sinθ = 0.2. The transmission bandwidth is a value that indicates the range of frequencies used to transmit data, and is measured in units of Hz (Hertz). The wider the transmission bandwidth, the better. Generally, as the core diameter decreases, light with a large propagation angle is radiated out of the fiber, and only light with a shallow propagation angle is propagated. Therefore, a smaller core diameter results in a wider transmission bandwidth, but on the other hand, a trade-off occurs in that a smaller core diameter results in increased transmission loss. Transmission loss refers to the attenuation per unit length of an optical signal, and is measured in dB / km. In the optical fiber of the present invention, the transmission loss measured by irradiating one of the cores forming the internal core group or one of the core-sheath portions forming the internal core group with a 650 nm laser beam is preferably 250 dB / km or less, and more preferably 200 dB / km or less. Achieving both a low transmission bandwidth and a low transmission loss is important. [Optical Communication Cable] The multi-core plastic optical fiber of the present invention can be suitably used in optical communication cables. In other words, the optical communication cable of the present invention is an optical communication cable in which a coating of polyethylene or the like is applied to the outer periphery of the optical fiber of the present invention. [Optical Communication System] The multi-core plastic optical fiber or optical communication cable of the present invention can be suitably used in an optical communication system.The optical communication system of the present invention uses the multi-core plastic optical fiber or optical communication cable of the present invention and performs spatial multiplexing communication using a plurality of signal lights, thereby enabling large-capacity communication.

[0054] Here, it is preferable that the light source wavelength is a visible light wavelength of 400 to 700 nm or less, as this is highly safe for the human body and is unlikely to cause radio wave interference with existing devices that use radio waves.

[0055] Furthermore, it is preferable that the number of multiple light sources used for optical communications is 50% or more of the number of multiple cores or multiple sheath-core portions, and that the multiple light sources correspond one-to-one to the multiple cores or multiple sheath-core portions. By making the number of multiple light sources used for optical communications 50% or more of the number of multiple cores or multiple sheath-core portions, one light source can be associated with two or more cores or two or more sheath-core portions, making high-capacity communication possible even with low alignment accuracy. By corresponding the multiple light sources one-to-one to the multiple cores or multiple sheath-core portions, light leakage from the cores to the cladding portion or light leakage from the sheath-core portions to the sea portion is reduced, making high-capacity communication possible.

[0056] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. [Measurement Method] (1) Refractive Index (-) of Core, Cladding, and Sea Regions Test pieces measuring 20 mm x 8 mm x 1.4 mm were prepared from the core, cladding, and sea regions used in each example and comparative example, and the refractive indexes were measured using an Abbe refractometer in an atmosphere at room temperature of 25°C. (2) Measurement of Core Outer Diameter, Measurement of Core-Sheath Outer Diameter, and Core Circularity Randomly selected portions of the optical fiber were cut perpendicular to the drawing direction, and the cross section was polished so that the core / cladding / sea region interface could be observed. The cross section was then observed using a VHX-7000 digital microscope (manufactured by Keyence Corporation). The magnification for observation was between 10 and 200 times, and an appropriate range was selected so that the entire cross section was within the field of view and the interface could be observed. Then, for the two-component optical fiber consisting of the core component resin and the cladding component resin, the major axis and minor axis were calculated for each core in the obtained image using image analysis software (WinROOF, Mitani Corporation). The average of the major axis and minor axis of all cores was taken as the core outer diameter. At this time, the average value of the major core diameter of all cores divided by the minor core diameter was calculated, and this was taken as the core circularity.

[0057] In addition, for three-component optical fibers consisting of a core component resin, a cladding component resin, and a sea component resin, the average of the major and minor axes of the entire sheath-core portion was used as the sheath-core outer diameter, using the same method as for measuring the core outer diameter described above. (3) Cladding Thickness Measurement and CV Value of Cladding Thickness: Randomly selected locations from a multi-core plastic optical fiber were cut perpendicular to the drawing direction, and the cross section was polished so that the core / cladding / sea interface could be observed. The cross section was then observed using a VHX-7000 digital microscope (manufactured by Keyence Corporation). The magnification for observation was between 10 and 200 times, and an appropriate range was selected so that the entire cross section was within the field of view and the interface could be observed. The thickness of each core and each sheath-core cladding portion in the obtained image was measured as follows.

[0058] In a two-component optical fiber consisting of a core component resin and a cladding component resin, as shown in Fig. 8(a), in the internal core group excluding the cores arranged at the outermost periphery of the core group, the cladding thickness is the average value of the values ​​found as the gap between adjacent cores on a line connecting the center of gravity of any core among the cores forming the internal core group and the center of gravity of a core adjacent to the any core. When arranged in a hexagonal lattice, the cladding thickness is the average value of the values ​​found as the gap between adjacent cores on a line connecting the center of gravity of any core among the cores forming the internal core group and the center of gravity of a core adjacent to the any core. １ , i ２ , i ３ , i ４ , i ５ , i ６ ), and the cladding thicknesses of all cores in the internal core group were calculated, and the average value of the cladding thicknesses and the standard deviation of the cladding thicknesses were calculated. Here, when the cores are arranged in a tetragonal lattice, the number of adjacent cores is four (i １ , i ２ , i ３ , i ４ ), when the core parts are arranged in a trigonal lattice, there are three adjacent core parts (i １ , i ２ , i ３ ) Then, the CV value of the cladding thickness was calculated using the following formula:

[0059] CV value of cladding thickness = (standard deviation of cladding thickness / average cladding thickness) × 100. Furthermore, as a detailed method of measuring the cladding thickness specified in claim 8, as shown in FIG. 9(a), the core outer diameter calculated by the method described in (2) above is taken as outer diameter C, and in the range (side region) sandwiched between two lines spaced C / 6 from the line connecting the centers of gravity of adjacent cores, the cladding thickness (k) at positions dividing this range into four equal parts is measured. １ , k ２ , k ３ , k ４ , k ５ ) was calculated. １ ~k ５ The cladding thickness is shown as k １ ~k ５ The cladding thickness of each sample was calculated, and the average value of the cladding thickness and the standard deviation of the cladding thickness were calculated.

[0060] In addition, in a three-component optical fiber consisting of a core component resin, a cladding component resin, and a sea component resin, as shown in Fig. 8(b), the cladding thickness is the average value of the gaps between adjacent core-sheath portions on a line connecting the center of gravity of any one of the core-sheath portions forming the inner core-sheath portion group excluding the core-sheath portion arranged at the outermost periphery and the center of gravity of a core-sheath portion adjacent to the any one of the core-sheath portions. When the adjacent core-sheath portions are arranged in a hexagonal lattice, the cladding thickness is the average value of the gaps between adjacent core-sheath portions on a line connecting the center of gravity of the adjacent core-sheath portion. １ ~i ６ The cladding thicknesses of all sheath-core portions except for the outermost sheath-core portion were calculated, and the average value and standard deviation of the cladding thicknesses were calculated. The CV value of the cladding thickness was then calculated using the following formula:

[0061] CV value of cladding thickness = (standard deviation of cladding thickness / average cladding thickness) x 100. Furthermore, as a detailed method of measuring the cladding thickness specified in claim 4, as shown in Figure 9(b), the outer diameter of the core-sheath portion calculated by the method described in (2) above is D, and the cladding thickness (k) at positions that divide this range into four equal parts in the range (side region) sandwiched between two lines that are D / 6 away from the line connecting the centers of gravity of adjacent core portions is measured. １ , k ２ , k ３ , k ４ , k ５ ) was calculated. １ ~k ５ The cladding thickness is shown as k １ ~k ５The cladding thickness of each of the above was calculated, and the average value and standard deviation of the cladding thickness were calculated. (4) Transmission Loss (dB / km) The transmission loss was measured by using an optical fiber cut to a length of 30 m, illuminating one core with laser light (wavelength 650 nm, incident NA = 0.25) from one end of the optical fiber, and measuring the amount of light A (dBm) emitted from the other end. Next, this 30 m sample was cut to a length of 2 m, illuminating the same parallel light from one end, and measuring the amount of light B (dBm) emitted from the other end. The transmission loss C (dB / km) was calculated from (B - A) / (30 - 2). The average value of the data for 25 islands was calculated, and a value of 500 dB / km or less was deemed acceptable. (5) Transmission Bandwidth (GHz) A network analyzer (MS46122B manufactured by Anritsu Corporation) was connected to a VCSEL laser with a wavelength of 670 nm and an O / E converter (SPA-2_650 nm manufactured by Graviton Corporation). Subsequently, two multi-core plastic optical fibers, one 30 m long and one 1 m long, were cut from each of the examples and comparative examples, and both end faces were mirror-polished using a polishing sheet. The light emitted from the VCSEL laser was focused onto one core of the multi-core plastic optical fiber using an objective lens with a numerical aperture (NA) of 0.2, and the other end of the optical fiber was connected to an O / E converter. The frequency was swept from 0 GHz to 2 GHz, and the transmission characteristics (S21) were measured at 0.1 GHz intervals. A differential profile was created by subtracting the measurement value at 1 m from the measurement value at 30 m. In this profile, the frequency at which the transmission characteristics at 0 GHz were reduced by 3 dB was measured as the transmission band. (6) Outer sea thickness (μm) A randomly selected portion of a multi-core plastic optical fiber was cut perpendicular to the drawing direction, and the cross section was polished so that the core / cladding / sea interface could be observed. Then, as shown in Fig. 10(b), for a three-component optical fiber, a circumscribing circle of the sheath-core portion located at the outermost periphery of the sheath-core portion group was drawn, and the average value of the distance between the circumscribing circle and the fiber diameter was taken as the outer sea thickness. Similarly, for a two-component optical fiber, a circumscribing circle of the core portion located at the outermost periphery of the core portion group was drawn, and the average value of the distance between the circumscribing circle and the fiber diameter was taken as the outer sea thickness.The outer sea thickness in the two-component optical fiber shown in Figure 10(a) is synonymous with the outer cladding thickness. (7) Sea Thickness (μm) A randomly selected portion of a multi-core plastic optical fiber was cut perpendicular to the drawing direction, and the cross section was polished so that the core / cladding / sea interface could be observed. The cross section was then observed using a digital microscope VHX-7000 (manufactured by Keyence Corporation). The magnification for observation was between 10 and 200 times, and an appropriate range was selected so that the entire cross section was within the field of view and the interface could be observed. The sea thickness of the obtained image was then measured as follows.

[0062] In a three-component optical fiber consisting of a core component resin, a cladding component resin, and a sea component resin, the sea thickness is the average value of the values ​​found as the gap between adjacent core-sheath portions on a line connecting the center of gravity of any of the core-sheath portions forming the internal core-sheath portion group, excluding the core-sheath portion located at the outermost periphery as shown in Figure 8(b), and the center of gravity of the core-sheath portion adjacent to the any of the core-sheath portions.

[0063] When arranged in a hexagonal lattice, there are six adjacent core-sheath portions (i １ ~i ６ ) and the thicknesses of the sea parts of all the sheath-core parts other than the sheath-core part arranged at the outermost periphery were calculated, and the average value of the sea part thicknesses was taken as the sea part thickness.

[0064] As a detailed method for measuring the sea portion thickness defined in claim 4, as shown in FIG. 9(b), when the outer diameter of the core-sheath portion calculated by the method described in (2) above is D, the sea portion thickness (h) at positions dividing this range into four equal parts in a range (side region) sandwiched between two lines spaced apart by D / 6 from a line connecting the centers of gravity of adjacent core-sheath portions is measured. １ , h ２ , h ３ , h ４ , h ５ ) was calculated. １ ~h ５ This shows the thickness of the sea area. １ ~h ５The thickness of each sea portion was calculated, and the average value of the sea portion thicknesses was calculated. (8) The ratio of the area occupied by the core-sheath portion as defined in claim 9, and the ratio of the area occupied by the core portion as defined in claim 12 Randomly selected portions of the multi-core plastic optical fiber were cut perpendicular to the drawing direction, and the cross section was polished so that the core / clad / sea interface could be observed, and then observed using a digital microscope VHX-7000 (manufactured by Keyence Corporation). The magnification for observation was between 10 and 200 times, and an appropriate range was selected so that the entire cross section was within the field of view and the interface could be observed.

[0065] The detailed method for measuring the ratio of the area occupied by the sheath-core portion as defined in claim 9 is as follows: for a triangle connecting the centers of gravity of any three adjacent sheath-core portions excluding the outermost one in the obtained image, as shown in Figure 12(b), the area of ​​each triangle and the area of ​​the sheath-core portion within each triangle are measured, and the average values ​​of the calculated areas of each triangle and the sheath-core portion within each triangle are defined as the area of ​​the triangle and the area of ​​the sheath-core portion within the triangle, respectively. The ratio (%) of the area of ​​the sheath-core portion within the triangle to the area of ​​the triangle is defined as the ratio of the area occupied by the sheath-core portion as defined in claim 9.

[0066] Similarly, as a detailed method for measuring the ratio of the area occupied by the core portion defined in claim 12, as shown in Figure 12(a), for a triangle connecting the centers of gravity of any three adjacent core portions excluding the core portion located at the outermost periphery of the obtained image, the area of ​​each triangle and the area of ​​each core portion within each triangle were measured, and the average values ​​of the calculated areas of each triangle and the core portions within each triangle were defined as the area of ​​the triangle and the area of ​​the core portion within the triangle, respectively. The ratio (%) of the area of ​​the core portion within the triangle to the area of ​​the triangle was defined as the ratio of the area occupied by the core portion defined in claim 12. [Example 1] Polymethyl methacrylate (refractive index 1.49) was prepared as the resin composition constituting the core portion component 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 clad portion component polymer, and each polymer was supplied to a composite spinneret so that the volume ratio of the core portion component polymer to the clad portion component polymer was 70:30. After melting at 240°C, the composite polymer was distributed in a composite spinneret so that the number of cores was 510 in a hexagonal lattice arrangement, and the composite polymer was discharged from the spinneret's discharge holes to obtain a multi-core plastic optical fiber. Here, core component discharge holes and cladding component discharge holes were arranged on the discharge surface of the composite spinneret's discharge plate as shown in Figure 5. The results of evaluating the obtained multi-core plastic optical fiber using the above-mentioned method are shown in Table 1-1. [Example 2] Polymethyl methacrylate (refractive index 1.49) was prepared as the resin composition constituting the core component polymer and the sea component polymer, and a copolymer of 75% by mass of vinylidene fluoride and 25% by mass of tetrafluoroethylene (refractive index 1.41) was prepared as the resin composition constituting the cladding component polymer. Each polymer was supplied to the composite spinneret of the present invention so that the volume ratio of the core component polymer, cladding component polymer, and sea component polymer was 51:12:37. After melting at 240°C, the cores were distributed in a composite spinneret so that the number of cores consisting of the core-sheath parts was 510 in a hexagonal lattice arrangement, and the composite polymer was discharged from the nozzle of the spinneret to obtain a multi-core plastic optical fiber. Here, the nozzle surface of the nozzle plate of the composite spinneret was provided with the core component nozzle, the cladding component nozzle, and the sea component nozzle, as shown in Figure 6.The obtained multi-core plastic optical fiber was evaluated by the above-mentioned method, and the results are shown in Table 1-1. [Example 3] A multi-core plastic optical fiber was fabricated in the same manner as in Example 1, except that the arrangement of the cladding component discharge holes on the composite spinneret was changed to confirm the influence of the cladding thickness variation. As shown in Table 1-1, compared to Example 1, the transmission loss increased and the transmission bandwidth decreased as the cladding thickness variation worsened. [Example 4] A multi-core plastic optical fiber was fabricated in the same manner as in Example 2, except that the arrangement of the cladding component discharge holes on the composite spinneret was changed to make the outer sea portion thickness thinner to confirm the influence of the cladding thickness variation. As shown in Table 1-1, compared to Example 2, the transmission loss increased and the transmission bandwidth decreased as the cladding thickness variation worsened. [Example 5] Example 5 was carried out as an example in which the number of cores was increased. A multi-core plastic optical fiber was fabricated in the same manner as in Example 1, except that the hole diameters of the core component discharge holes and cladding component discharge holes arranged on the discharge plate of the composite spinneret were adjusted to be smaller as the number of cores increased. As shown in Table 1-1, compared to Example 1, the transmission loss increased, but the transmission bandwidth increased. [Example 6] In order to confirm the influence of the cladding thickness variation, the arrangement of the cladding component discharge from the composite spinneret was changed and the outer sea region thickness was increased, except that a multi-core plastic optical fiber was fabricated in the same manner as Example 2. As shown in Table 1-1, compared to Examples 2 and 4, the transmission loss decreased and the transmission bandwidth increased due to the improvement in the cladding thickness variation. [Example 7] In order to confirm the influence of the cladding thickness variation, the arrangement of the cladding component discharge from the composite spinneret was changed and the outer sea region thickness was decreased, except that a multi-core plastic optical fiber was fabricated in the same manner as Example 3. As shown in Table 1-2, compared to Example 3, the transmission loss increased and the transmission bandwidth decreased due to the deterioration in the cladding thickness variation. [Example 8] In order to confirm the influence of the cladding thickness variation, the arrangement of the cladding component discharge from the composite spinneret was changed and the outer sea region thickness was increased.As shown in Table 1-2, compared to Examples 2, 4, and 6, the transmission loss was reduced and the transmission bandwidth was increased due to the improvement in the cladding thickness variation. [Example 9] In order to confirm the influence of the cladding thickness variation, a multi-core plastic optical fiber was fabricated in the same manner as in Example 3, except that the arrangement of the cladding component ejection from the composite spinneret was changed, the core diameter was reduced, the cladding thickness was increased, and the outer sea region thickness was increased. As shown in Table 1-2, the cladding thickness variation was improved compared to Example 3, but the smaller core diameter increased the transmission loss and the transmission bandwidth. [Example 10] In order to confirm the influence of the cladding thickness variation, a multi-core plastic optical fiber was fabricated in the same manner as in Example 9, except that the arrangement of the cladding component ejection from the composite spinneret was changed, and the outer sea region thickness was increased. As shown in Table 1-2, compared to Example 9, the cladding thickness variation was improved, the transmission loss was reduced, and the transmission bandwidth was increased. [Comparative Example 1] A multi-core plastic optical fiber was produced under the same spinning conditions as in Example 1, except that a pipe-type spinneret, which is a conventional technology, was used. As shown in Table 1-2, as the cladding thickness variation worsened, the transmission loss increased and the transmission bandwidth decreased, making it unsuitable for large-capacity communication. [Comparative Example 2] A multi-core plastic optical fiber was produced under the same spinning conditions as in Example 2, except that a pipe-type spinneret, which is a conventional technology, was used. As shown in Table 1-2, as the cladding thickness variation worsened, the transmission loss increased and the transmission bandwidth decreased, making it unsuitable for large-capacity communication.

[0067]

[0068]

[0069] REFERENCE SIGNS LIST 1 Core component discharge hole 2 Clad component discharge hole 3 Sea component discharge hole 4 Discharge plate 5 Spinneret discharge plate 6 Distribution plate 7 Discharge hole 8 Composite polymer 9 Core component polymer 10 Clad component polymer 11 Sea component polymer 12 Spin block 13 Composite spinneret 14 Spinning pack 15 Discharge surface 16 Spinneret discharge hole 17 Cooling device 18 Core component resin 19 Clad component resin 20 Sea component resin 21 Multi-core plastic optical fiber 22 Merging hole 23 Center of gravity of core (sheath-core portion) 24 Line connecting the centers of gravity of core (sheath-core portion) 25 Triangle connecting the centers of gravity of three adjacent cores (sheath-core portions) h １ ~h ５ Sea thickness i １ ~i ６ Adjacent core portion or adjacent core-sheath portion k １ ~k ５ Cladding thickness

Claims

1. A multi-core plastic optical fiber having a plurality of cores, a plurality of sheath-core sections in which a cladding section is formed around the plurality of cores, and a sea section that covers the periphery of the plurality of sheath-core sections, wherein the number of the plurality of sheath-core sections is 300 or more, the plurality of sheath-core sections form a sheath-core section group with outer diameters of 25 μm to 60 μm, and for the sheath-core section group (hereinafter referred to as the internal sheath-core section group) excluding the core section arranged at the outermost periphery of the sheath-core section group, the CV value of the cladding thickness, which is defined by the gap between adjacent sheath-core sections along a line connecting the centers of gravity of the adjacent sheath-core sections that form the internal sheath-core section group, is 15% or less.

2. The multi-core plastic optical fiber according to claim 1, wherein the core-sheath portions are arranged in a close-packed structure of either a hexagonal lattice, a square lattice, or a trigonal lattice.

3. The multi-core plastic optical fiber according to claim 2, wherein one of the core-sheath portions forming the inner core-sheath portion group has parallel sides between adjacent core-sheath portions.

4. A multi-core plastic optical fiber according to claim 1, wherein, when the outer diameter of the core-sheath portions forming the internal core-sheath portion group is D, the CV value of the cladding thickness is 20% or less within the range sandwiched between two lines that are D / 6 away from a line connecting the centers of gravity of adjacent core-sheath portions.

5. A multi-core plastic optical fiber having a plurality of core portions and a plurality of cladding portions surrounding the plurality of core portions, wherein the number of the plurality of core portions is 300 or more, the plurality of core portions form a core portion group with outer diameters of 25 μm or more and 60 μm or less, and for core portion groups (hereinafter referred to as internal core portion groups) excluding core portions arranged at the outermost periphery of the core portion groups, the CV value of the cladding thickness defined by the gap between adjacent core portions on a line connecting the centers of gravity of the adjacent core portions that form the internal core portion group is 20% or less.

6. The multi-core plastic optical fiber according to claim 5, wherein the cores forming said internal core group are arranged in a closest-packed structure of either a hexagonal lattice, a square lattice, or a trigonal lattice.

7. The multi-core plastic optical fiber according to claim 6, wherein one of the core portions forming the group of internal core portions has parallel sides between adjacent core portions.

8. The multi-core plastic optical fiber according to claim 5, wherein, when the outer diameter of the cores forming the internal core group is C, the CV value of the cladding thickness is 30% or less within a range sandwiched between two lines spaced C / 6 apart from a line connecting the centers of gravity of adjacent cores.

9. The multi-core optical fiber according to claim 1, wherein at least some of the sheath-core portions constituting the internal sheath-core portion group form a hexagonal lattice, and the ratio of the area occupied by the sheath-core portions to a triangle connecting the centers of gravity of any three adjacent sheath-core portions excluding the sheath-core portion arranged at the outermost periphery of the plurality of sheath-core portions is 50% or more and 75% or less, and the outer diameter of the plurality of sheath-core portions is 30 μm or more and 60 μm or less.

10. A multi-core plastic optical fiber according to claim 1, wherein, on a line connecting the center of gravity of any one of the core-sheath portions forming the internal core-sheath portion group and the center of gravity of a core-sheath portion adjacent to said any one of the core-sheath portions, the cladding thickness obtained as the gap between the adjacent core-sheath portions is 1 μm or more, and the sea thickness obtained as the gap between the adjacent core-sheath portions is 2 μm or more.

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

12. A multi-core plastic optical fiber according to claim 5, wherein at least some of the core portions forming the internal core portion group form a hexagonal lattice, the ratio of the area occupied by the core portions to a triangle connecting the centers of gravity of any three adjacent core portions excluding the core portions arranged on the outermost periphery of the plurality of core portions is 50% or more and 75% or less, and the outer diameters of the plurality of core portions are 30 μm or more and 60 μm or less.

13. A multi-core plastic optical fiber according to claim 5, wherein the cladding thickness obtained as the gap between the adjacent core portions on a line connecting the center of gravity of any one of the core portions forming the internal core portion group and the center of gravity of a core portion adjacent to the any one of the core portions is 1 μm or more.

14. The multi-core plastic optical fiber according to claim 5, wherein in a cross section of the multi-core plastic optical fiber, the minimum distance from the contour line of the core portion closest to the contour line of the multi-core plastic optical fiber to the contour line 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 a transmission loss measured by irradiating one of the core-sheath portions in the internal core-sheath portion group or one of the core portions in the internal core portion group with a 650 nm laser beam is 250 dB / km or less.

16. A multi-core plastic optical fiber according to claim 1 or 5, which has a bandwidth of 400 MHz or more at a fiber length of 25 m when measured with multi-mode VCSEL light of 670 nm wavelength entering the multiple cores with an incident NA of 0.

2.

17. An optical communication cable comprising the multi-core plastic optical fiber according to claim 1 or 5.

18. An optical communication system using the multi-core plastic optical fiber according to claim 1 or 5, which performs spatial multiplexing communication using a plurality of signal lights.

19. An optical communication system for carrying out multiplex spatial communication using the optical communication cable according to claim 17, wherein the light source wavelength is 400 nm or more and 700 nm or less.

20. An optical communication system as described in claim 19, wherein the number of multiple light sources used for optical communication is 50% or more of the number of multiple core sections or multiple core-sheath sections, and the multiple light sources and the multiple core sections or multiple core-sheath sections correspond one-to-one.

Images