Multicore plastic optical fiber, optical communication cable, and optical communication system

Abstract

The present invention addresses the problem of providing a multicore plastic optical fiber for high-accuracy optical communication that enables a one-to-one correspondence between a light source and a core.　The present invention relates to a multicore plastic optical fiber having a cross-sectional form comprising two or more island portions and a sea portion surrounding the island portions. The island portion comprises one core and a cladding surrounding the core, and a melt flow index R1 (g / 10 min) measured under the conditions of 230°C and a load of 3.8 kgf of a cladding component forming the cladding and a melt flow index R2 (g / 10 min) measured under the conditions of 230°C and a load of 3.8 kgf of a sea component forming the sea portion satisfy the following relation. R2−R1 ≥ 3

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】 A multi-core plastic optical fiber having a plurality of cores has attracted attention in recent years for communication applications because it can transmit a large amount of information at once. 【0003】 For example, Patent Document 1 discloses a multi-core plastic optical fiber element wire including a plurality of cores made of resin, a first sheath layer made of a first sheath resin surrounding the cores, and a second sheath layer made of a second sheath resin contacting the outer periphery of the first sheath layer, wherein the first sheath resin is fluoroalkyl methacrylate and the second sheath resin is an ethylene unit, a tetrafluoroethylene unit, and a hexafluoropropylene unit. 【0004】 Further, Patent Document 2 discloses a plastic optical fiber element wire having a core and a sheath layer composed of two or more layers formed on the outer periphery of the core, wherein the innermost layer of the sheath layer contains a fluorinated methacrylate resin and the outermost layer of the sheath layer is a copolymer composed of a tetrafluoroethylene monomer, a hexafluoropropene monomer, and a vinylidene fluoride monomer. 【0005】 Japanese Patent No. 5755916 Japanese Patent No. 6210716 【0006】 However, when performing optical data communication using a multi-core optical fiber, the optical fibers according to Patent Document 1 and Patent Document 2 have problems with the reproducibility of the input signal. 【0007】 Therefore, the present invention has been made for the purpose of overcoming the problems of such prior art and providing a multi-core plastic optical fiber excellent in the reproducibility of an input signal. 【0008】 The inventors of the present invention conceived that in order for a multi-core plastic optical fiber to be excellent in the reproducibility of an input signal, it is important to accurately input the light from a light source into the cores of the multi-core optical fiber one-to-one, and thus arrived at the present invention. 【0009】 The present invention and its preferred embodiments for solving the above problems have the following configuration: [1] A plastic optical fiber having a cross-sectional shape consisting of two or more island portions and a sea portion surrounding the island portions, wherein the island portions consist of one core and a cladding surrounding it, and the melt flow index R1 (g / 10 min) of the cladding component forming the cladding, measured at 230°C and a load of 3.8 kgf, and the melt flow index R2 (g / 10 min) of the sea portion forming the sea portion, measured at 230°C and a load of 3.8 kgf, satisfy the following relationship: R2 - R1 ≥ 3. 【0010】 [2] The multicore plastic optical fiber according to [1], wherein the cladding component is a copolymer containing perfluoroalkyl methacrylate and / or perfluoroalkyl acrylate as a copolymer component. 【0011】 [3] The multicore plastic optical fiber according to [1] or [2], wherein the cladding component is a copolymer containing a perfluoroalkyl methacrylate represented by formula (1). ２ = C(CH ３ )-COO(CH ２ )m(CF ２ )nR Equation (1) In Equation (1), R represents a fluorine atom or a hydrogen atom, m is 1 or 2, and n is an integer from 1 to 11. 【0012】 [4] The multicore plastic optical fiber according to any one of [1] to [3], wherein the cladding component is a copolymer containing 60 to 95% by mass of perfluoroalkyl methacrylate and 5 to 40% by mass of methyl methacrylate as copolymer components. 【0013】 [5] The multicore plastic optical fiber according to any one of [1] to [4], wherein the marine component is a copolymer containing vinylidene fluoride units and tetrafluoroethylene units. 【0014】[6] The multicore plastic optical fiber according to any one of [1] to [5], wherein the marine component is a copolymer containing 65 to 85% by mass of vinylidene fluoride and 15 to 35% by mass of tetrafluoroethylene as copolymer components. 【0015】 [7] A multicore plastic optical fiber according to any one of [1] to [6], wherein the difference between the refractive index n1 of the cladding component and the refractive index n2 of the core component satisfies the following relationship: n1 - n2 ≥ 0.000. 【0016】 [8] A multicore plastic optical fiber according to any one of [1] to [7], wherein the melt viscosity W1 (Pa·s) of the cladding component at a shear rate of 100 (1 / sec) and 220°C and the melt viscosity W2 (Pa·s) of the sea portion at a shear rate of 100 (1 / sec) and 220°C satisfy the following relationship: W1 / W2 ≥ 1.00 [9] A multicore plastic optical fiber according to any one of [1] to [8], wherein the core component forming the core is a polymethyl methacrylate resin. 【0017】

[10] A multicore plastic optical fiber according to any one of [1] to [9], wherein carbon black is contained in the ocean portion. 【0018】

[11] An optical communication cable containing a multicore plastic optical fiber as described in any of [1] to

[10] . 【0019】

[12] An optical communication system that uses the optical communication cable described in

[11] and performs spatial multiplex communication using multiple light sources. 【0020】 According to the present invention, it is possible to provide a high-precision multi-core plastic optical fiber that has excellent reproducibility of input signals, as it is possible to create a one-to-one correspondence between the light source and the core. 【0021】 The following describes in detail embodiments of the multicore plastic optical fiber according to the present invention. However, the present invention is not limited to the following embodiments and can be implemented with various modifications depending on the purpose and application. 【0022】In this invention, "greater than or equal to" means the same as or greater than the numerical value shown. Similarly, "less than or equal to" means the same as or less than the numerical value shown. 【0023】 The multicore plastic optical fiber of the present invention has a cross-sectional shape consisting of two or more island portions and a sea portion surrounding the island portions. Each of the island portions consists of a core and a cladding surrounding it. 【0024】 [Core] The core is the transmission part that directly propagates the signal light and plays a role in efficiently transmitting the signal light. 【0025】 The core component resin forming the core is preferably a material that is light-transmitting and has low transmission loss. Examples include acrylic resin, modified polycarbonate resin, cycloolefin resin, styrene resin, and olefin resins such as polymethylpentene. Among these resins, acrylic resin, which has low transmission loss characteristics, is preferred. 【0026】 Examples of acrylic resins include polymers such as 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. Examples of other acrylic resins include sodium polyacrylate resins, polyacrylonitrile resins, and polyacrylamide resins. Among these, polymethyl methacrylate resins, mainly composed of methyl methacrylate, are particularly preferred from the viewpoint of transparency and processability. 【0027】Examples of the modified polycarbonate resin include polycarbonate resins with an average molecular weight of 10,000 to 200,000 due to substitution with lower alkyl groups or trifluoromethyl groups. 【0028】 Examples of the cycloolefin resins include cycloolefin polymers such as addition copolymer polymers of ring-opening metathesis polymers and ethylene, and hydrogenation ring-opening metathesis polymers, as well as cycloolefin copolymers such as ethylene-2-norbornene. 【0029】 The core component may be appropriately supplemented with dopants that increase the refractive index, such as germanium, phosphorus, tin, or boron, or with dopant fluorine-based materials that decrease the refractive index, such as magnesium fluoride or other fluorine-based materials, for the purpose of adjusting the refractive index. 【0030】 The refractive index (n0) of the core component is preferably 1.45 or higher and 1.60 or lower. When n0 is 1.45 or higher, more preferably 1.48 or higher, the refractive index difference with the cladding can be widened, reducing the proportion of signal light that leaks into the ocean portion. Furthermore, when n0 is 1.60 or lower, more preferably 1.52 or lower, the refractive index difference with the cladding can be suppressed, reducing the number of higher-order modes that propagate. 【0031】 The refractive index of the core component can be measured using an Abbe refractometer in a room temperature atmosphere of 25°C, in accordance with JIS K 7142:2014, on a test specimen measuring 20 mm × 8 mm × 1.4 mm. If it is difficult to directly measure the refractive index by taking a core sample, the collected core can be heated at 210°C for 5 minutes using a press molding machine, then cooled to room temperature to prepare a test specimen measuring 20 mm × 8 mm × 1.4 mm, and the refractive index can be measured. Furthermore, if the composition of the core component is known, a test specimen can be prepared similarly from the known composition, and the refractive index can be measured. 【0032】The average diameter of the core is preferably 5 to 100 μm. By setting the average diameter to 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more, stable spinning can be performed, the cross-sectional shape of the core is stabilized, and the light transmittance of the core is improved, thereby improving propagation efficiency and enabling more effective transmission over long distances. Furthermore, by setting the average diameter to 100 μm or less, more preferably 80 μm or less, and even more preferably 70 μm or less, the transmission bandwidth can be expanded. 【0033】 [Cladding] The cladding protects the core from external environmental factors and reduces the amount of signal light propagating through the core that is reflected at the cladding interface and leaks out into the ocean. 【0034】 The cladding component forming the cladding is preferably a copolymer containing perfluoroalkyl methacrylate and / or perfluoroalkyl acrylate as copolymer components. By using a copolymer containing perfluoroalkyl methacrylate and / or perfluoroalkyl acrylate as copolymer components in the cladding, the positional accuracy of the core as a multicore optical fiber is effectively improved in combination with the ocean component forming the ocean portion described later, and light from the light source can be more effectively and accurately introduced into the core of the multicore optical fiber in a one-to-one ratio. 【0035】 A polymer containing perfluoroalkyl (meth)acrylate as a polymerization component is preferably one represented by formula (1). CH ２ = C(CH ３ )-COO(CH ２ )m(CF ２ )nR (1) In formula (1), R is a fluorine atom or a hydrogen atom, m is 1 or 2, and n is an integer from 1 to 11. By setting n to 11 or less, preferably 7 or less, more preferably 5 or less, and even more preferably 3 or less, the polymer represented by formula (1) can be made to have high viscosity, and consequently the accuracy of core misalignment can be improved more effectively. 【0036】Examples of polymers represented by formula (1) include perfluoroalkyl methacrylates such as trifluoroethyl methacrylate, tetrafluoropropyl methacrylate, pentafluoropropyl methacrylate, heptadecafluorodecyl methacrylate, and octafluoropentyl methacrylate. 【0037】 Examples of perfluoroalkyl acrylates include trifluoroethyl acrylate, tetrafluoropropyl acrylate, and octafluoropentyl acrylate. 【0038】 In addition to these low refractive index components, which are fluorine-based monomers, high refractive index components such as methacrylate monomers like methyl methacrylate and ethyl methacrylate, acrylate monomers like methyl acrylate, ethyl acrylate and butyl acrylate, methacrylic acid and acrylic acid may be copolymerized into copolymers using these as cladding components. 【0039】 The cladding component is preferably a copolymer containing 60 to 95% by mass of perfluoroalkyl methacrylate and 5 to 40% by mass of methyl methacrylate as copolymer components. Having 60% or more by mass of perfluoroalkyl methacrylate, more preferably 70% or more by mass, allows for a lower refractive index of the cladding, making it easier to confine light and increasing light intensity. Furthermore, it lowers the glass transition temperature, making spinning easier. Additionally, having 5% or more by mass of methyl methacrylate, more preferably 10% or more by mass, increases the elastic modulus, improving the ease of handling the fiber. It also stabilizes extrusion, making spinning easier. 【0040】(Melt Flow Index of Cladding Component) The melt flow index R1 (g / 10 min) measured under the conditions of 230°C and a load of 3.8 kgf for the cladding component is preferably 1.0 or more and 20.0 or less. By setting R1 to 1.0 or more, more preferably 2.0 or more, it becomes easier to perform melt spinning. Also, by setting R1 to 20.0 or less, more preferably 15.0 or less, the discharge can be stabilized and spinning becomes easier. When it is difficult to collect the cladding component, if the composition of the polymer constituting the cladding is known, a polymer with a known composition may be prepared and measured. 【0041】 (Refractive Index of Cladding Component) The refractive index (n1) of the cladding component is preferably 1.38 or more and 1.50 or less. When n1 is 1.38 or more, more preferably 1.40 or more, the refractive index difference from the core becomes smaller, the number of higher-order modes of the propagating light can be reduced, and high-speed optical communication can be achieved. Also, when n1 is 1.50 or less, more preferably 1.45 or less, the ratio of the signal light propagating through the core leaking out to the sea part by reflection at the interface of the cladding can be reduced. When it is difficult to collect the cladding component, if the composition of the polymer constituting the cladding is known, a polymer with a known composition may be prepared and measured. 【0042】 In order to reflect light at the interface between the core and the cladding, the refractive index (n1) of the cladding needs to be lower than the refractive index (n0) of the core. By setting n1 lower than n0, preferably the difference between n0 and n1 is 0.02 or more, more preferably 0.05 or more, the ratio of the signal light propagating through the core leaking out to the sea part by reflection at the interface of the cladding can be reduced. On the other hand, by setting the difference between n0 and n1 to preferably 0.20 or less, more preferably 0.09 or less, the number of higher-order modes of the propagating light can be reduced, and high-speed optical communication can be achieved. 【0043】 The cladding corresponds one-to-one with the core and surrounds the core, and each cladding is independent of the other claddings. That is, one core and the cladding surrounding it constitute each of the independent island parts. With such a structure, it is possible to prevent light leaking out from one core from crosstalking to other cores through the cladding. 【0044】 Further, a dopant such as a fluorine-based material such as magnesium fluoride may be added to the clad component for the purpose of adjusting the refractive index. And a coloring substance may be contained in the clad component. By also containing a coloring substance in the clad, the signal light leaking out to the sea portion can be reduced. 【0045】 (Melting Viscosity of Clad Component) The melt viscosity W1 (Pa·s) of the clad component at a shear rate of 100 (1 / sec) and 220°C is preferably 200 Pa·s or more and 5000 Pa·s or less. By setting W1 to 5000 Pa·s or less, more preferably 3000 Pa·s or less, the rotational load of the screw for melt spinning can be reduced. Also, by setting W1 to 200 Pa·s or more, more preferably 1000 Pa·s or more, the discharge can be stabilized. 【0046】 (Glass Transition Temperature of Clad Component) The glass transition temperature Tg1 of the clad component is preferably 40°C or more and 150°C or less. By setting Tg1 to 150°C or less, more preferably 130°C or less, flexibility can be maintained. Also, by setting Tg1 to 40°C or more, more preferably 60°C or more, the elastic force can be increased. 【0047】 (Thickness of Clad) The thickness of the clad is preferably 1 / 50 to 1 / 3 times the diameter of the core, more preferably 1 / 40 to 1 / 5 times. By setting the thickness of the clad within this range, total reflection of light at the interface between the core and the clad can be more reliably performed, and a decrease in transmission efficiency can be suppressed. 【0048】[Island Sections] The multicore plastic optical fiber of the present invention has two or more island sections per fiber. By setting the number of island sections to two or more, preferably 60 or more, and more preferably 100 or more, each island section's core can propagate a different light, thereby enabling high-capacity communication. On the other hand, by setting the number of island sections to preferably 10,000 or less, more preferably 5,000 or less, and even more preferably 3,000 or less, the inner diameter of the core is not made too small, stable spinning can be performed, the cross-sectional shape of the core is stabilized, and long-distance transmission can be more effectively improved. 【0049】 In the multicore plastic optical fiber of the present invention, it is preferable that the cores in the island portions are arranged in a square grid or in a close-packed manner. These arrangement structures are relatively easy to control, and because the cores are arranged as designed, a one-to-one correspondence with the arrangement of the light source can be achieved, thereby improving the light transmittance of the multicore plastic optical fiber. 【0050】 In this invention, "cores arranged in a square grid" means a structure in which cores are regularly arranged at equal intervals in a grid pattern both vertically and horizontally. In other words, it means that there are multiple lines formed by cores arranged vertically and multiple lines formed by cores arranged horizontally, and that the vertical and horizontal lines intersect. Furthermore, in this invention, "cores in a close-packed state" means that six cores are arranged around the outer circumference of one core, and three adjacent cores form a triangle, creating a staggered grid pattern. 【0051】 [Sea portion] The sea portion serves to protect multiple island portions from external environmental factors, and also prevents signal light propagating through the island portions from reaching other adjacent cores even if such signal light leaks into the sea portion. 【0052】The ocean component forming the ocean portion is preferably a copolymer containing vinylidene fluoride units and tetrafluoroethylene units. By using a copolymer containing vinylidene fluoride units and tetrafluoroethylene units in the ocean component, the positional accuracy of the core as a multicore plastic optical fiber is effectively improved in combination with the cladding component, and light from the light source can be more effectively and accurately introduced into the core of the multicore plastic optical fiber in a one-to-one ratio. 【0053】 The copolymer of the marine components is preferably a copolymer containing 65 to 85% by mass of vinylidene fluoride and 15 to 35% by mass of tetrafluoroethylene as copolymer components. By using 65% by mass, more preferably 70% by mass or more of vinylidene fluoride, adhesion with methyl methacrylate can be improved. Furthermore, by using 85% by mass or less, more preferably 80% by mass or less of vinylidene fluoride, transparency can be improved. 【0054】 The aforementioned ocean component preferably contains a coloring substance. By containing a coloring substance, the multicore plastic optical fiber of the present invention can reduce noise such as crosstalk because, when different light is propagated to each core, light leaking from each core is less likely to reach adjacent cores. 【0055】 The coloring substance contained in the aforementioned marine component has the function of preventing the signal light from reaching other adjacent cores across the entire wavelength range of the signal light. Therefore, if the wavelength range of the signal light is outside the visible light range, it is sufficient for the coloring substance to have the aforementioned blocking function only in the wavelength range within that range, and it does not necessarily mean that it is colored in the visible light range. For example, if the signal light is infrared laser light, it is acceptable for the coloring substance to be transparent in the visible light range as long as it has the aforementioned blocking function across the entire infrared range, and such infrared absorbers are also included in the category of coloring substances. 【0056】However, since the signal light used is generally white visible light, a black, white, or gray coloring substance that can perform the blocking function across the entire visible light spectrum is generally preferred. Specific coloring substances include carbon black, lead oxide, titanium oxide, or organic pigments. Organic dyes are also an option, but if they are migratory, they can migrate from the ocean to the core over long periods of time, significantly reducing the transmission efficiency of the core. Therefore, it is necessary to select a material with low migratory properties. Carbon black is preferred from the viewpoint of material cost and processability. 【0057】 (Melt flow index of marine components) The melt flow index (R2) of marine components is preferably 10.0 or more and 50.0 or less. Setting R2 to 10.0 or more, more preferably 20.0 or more, makes melt spinning easier. Setting R2 to 50.0 or less, more preferably 40.0 or less, stabilizes the extrusion. If it is difficult to collect marine components, if the composition of marine components is known, a polymer of the known composition may be prepared and measured. 【0058】 The melt flow index R1 (g / 10 min) measured under the conditions of 230°C and 3.8 kgf load for the cladding component and the melt flow index R2 (g / 10 min) measured under the conditions of 230°C and 3.8 kgf load for the marine component satisfy the following relationship: R2 - R1 ≥ 3. By setting R2 - R1 to 3 g / 10 min or more, preferably 5 g / 10 min or more, more preferably 10 g / 10 min or more, and even more preferably 15 g / 10 min or more, the positional accuracy of the core is further improved. Furthermore, by setting R2 - R1 to preferably 35 g / 10 min or less, more preferably 30 g / 10 min or less, and even more preferably 25 g / 10 min or less, the discharge is stabilized. 【0059】(Refractive index of the ocean component) The refractive index (n2) of the ocean component is preferably 1.36 or more and 1.45 or less. When n2 is 1.36 or more, more preferably 1.38 or more, the refractive index difference with the cladding becomes large, which prevents leaked signal light from reaching other adjacent cores, thereby increasing the speed of the optical signal. When n2 is 1.45 or less, more preferably 1.43 or less, the refractive index difference with the cladding becomes small, which can reduce the number of higher-order modes. If it is difficult to collect the ocean component, if the composition of the ocean component is known, a polymer of the known composition may be prepared and measured. 【0060】 The difference between the refractive index n1 of the cladding component and the refractive index n2 of the sea component preferably satisfies the following relationship: n1 - n2 ≥ 0.000. By setting n1 - n2 to 0.000 or more, more preferably 0.012 or more, light can be confined more effectively. On the other hand, by setting n1 - n2 to preferably 0.025 or less, more preferably 0.020 or less, higher-order modes can be more effectively excluded. 【0061】 (Melting viscosity of marine components) The melting viscosity W2 of the marine components at a shear rate of 100 (1 / sec) and 220°C is preferably 200 Pa·s or more and 3000 Pa·s or less. By setting W2 to 3000 Pa·s or less, more preferably 2000 Pa·s or less, the rotational load on the melt spinning screw can be reduced. Furthermore, by setting W2 to 200 Pa·s or more, more preferably 700 Pa·s or more, the discharge can be stabilized. 【0062】It is preferable that the following relationship is satisfied between the melt viscosity W1 (Pa·s) of the cladding component at a shear rate of 100 (1 / sec) and 220°C and the melt viscosity W2 (Pa·s) of the marine component at a shear rate of 100 (1 / sec) and 220°C: W1 / W2 ≥ 1.00. By setting W1 / W2 to 1.00 or higher, more preferably 1.10 or higher, and even more preferably 1.20 or higher, the positional accuracy of the core can be more effectively improved. Furthermore, by setting W1 / W2 to preferably 4.00 or lower, more preferably 2.50 or lower, and even more preferably 2.00 or lower, the discharge can be stabilized. If it is difficult to collect the marine component, if the composition of the marine component is known, a polymer of the known composition may be prepared and measured. 【0063】 (Glass transition temperature of the sea component) The glass transition temperature Tg2 of the sea component is preferably between -60°C and 30°C. By setting Tg2 to 30°C or lower, more preferably 20°C or lower, flexibility can be maintained. Furthermore, by setting Tg2 to -60°C or higher, more preferably -50°C or higher, elastic force can be maintained even at low temperatures. 【0064】 The glass transition temperature Tg1 of the cladding component and the glass transition temperature Tg2 of the marine component preferably satisfy the following relationship: Tg1 - Tg2 ≥ 100. By setting Tg1 - Tg2 to 100°C or higher, more preferably 120°C or higher, the cladding can maintain a state of high elastic modulus and the marine component can maintain a state of flexibility, thereby more effectively maintaining core position accuracy. Furthermore, by setting Tg1 - Tg2 to 140°C or lower, discharge can be stabilized. 【0065】 In the multicore plastic optical fiber of the present invention, it is preferable that the sea portion is the outermost layer. Having the sea portion as the outermost layer allows signal light leaking into the sea portion to be attenuated and disappear at the fiber surface, preventing the leaked signal light from reaching adjacent cores. 【0066】[Optical Fiber] The cross-section of the multicore plastic optical fiber of the present invention is preferably circular in shape from the viewpoint of handling, and its diameter is preferably 0.2 mm to 10 mm. A diameter of 0.2 mm or more provides appropriate rigidity and is easy to handle, while a diameter of 10 mm or less, 3 mm or less, or 2 mm or less provides appropriate flexibility and is easy to handle. 【0067】 [Manufacturing Method] One example of a method for manufacturing the multicore plastic optical fiber of the present invention is a method of continuously molding the core component, cladding component, and occlusion component into a predetermined shape. The continuous molding method may be formed by a composite spinning method using an extrusion die. Unlike other molds for resin molding, none of the resin compositions cool or solidify inside the extrusion die. The core component is extruded from the core component discharge section, the cladding component from the cladding component discharge section, and the occlusion component from the occlusion component discharge section, and then they are cooled and solidified after being molded into a predetermined shape. 【0068】 The extrusion die is not particularly limited as long as it can form the multicore plastic optical fiber of the present invention, but it is preferable that the marine component discharge section be arranged to surround the outer periphery of the core component discharge section and the cladding component discharge section. By arranging them in this way and performing composite spinning under appropriate conditions, the extrusion stress caused by the marine component discharged from the marine component discharge section can be applied with substantially uniform strength from any direction (up, down, left, or right) to each core component discharged from each core component discharge section and each cladding component discharged from each cladding component discharge section. 【0069】 If the balance of the extrusion stress is constantly maintained, the cross-sectional shape of each core will continue to be maintained as it cools and solidifies, and the cross-sectional shape of each core component extrusion will continue to be reflected in the cross-sectional shape of the core. If the cross-sectional shape of each core component extrusion is processed to be perfectly circular with extremely high precision, it will be possible to form a multi-core plastic optical fiber with a perfectly cylindrical shape that has very little deformation. 【0070】The multicore 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 includes the multicore plastic optical fiber of the present invention. 【0071】 The multicore plastic optical fiber and optical communication cable of the present invention can be suitably used in optical communication systems. In other words, the optical communication system of the present invention can enable high-capacity communication by using the optical communication cable of the present invention and performing spatial multiplexing communication using multiple signal lights. 【0072】 The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples. 【0073】 [Measurement Method] (1) Refractive index of cladding and marine components (-) Test specimens measuring 20 mm × 8 mm × 1.4 mm were prepared from the cladding and marine components used in each example and comparative example, and the refractive index was measured using an Abbe refractometer in an atmosphere at room temperature of 25°C. 【0074】 (2) Melt viscosity (Pa·s) of cladding and marine components The melt viscosity of the cladding and marine components used in each example and comparative example was measured using a capillary rheometer under the conditions of a die diameter of 1.0 mm, a length of 10 mm, a temperature of 200 to 270°C in 10°C increments, and a shear rate of 100 (1 / sec). More specifically, after the sample was introduced, it was left to stand for 5 minutes, and the piston descent speed was set to 8.23 ​​mm / min (shear rate 100 (1 / sec)), and the average value of 8 points sampled every 10 mm of piston descent was calculated. 【0075】 (3) Melt flow index (g / 10 min) of cladding and marine components The melt flow index was measured in accordance with JIS K7210 under conditions of 230°C and a load of 3.8 kgf. 【0076】(4) Core position accuracy A randomly selected location from the multicore plastic optical fiber in each example and comparative example was cut perpendicular to the fiber axis direction, and a cross-sectional image was acquired using a digital microscope (Keyence VHX-7000). From the obtained images, the position of the centroid of all cores constituting one multicore plastic optical fiber was calculated, and the deviation of the core from the theoretical position was measured. Out of 512 cores, the number of cores with a position deviation of 5 μm or less was counted and evaluated according to the following criteria: A: 400 or more B: 350 or more but less than 400 C: 300 or more but less than 350 D: 250 or more but less than 300 E: 200 or more but less than 250 F: Less than 200 A to D were judged to have excellent reproducibility of the input signal. 【0077】 [Materials] PMMA: Polymethyl methacrylate PC: Polycarbonate MMA: Methyl methacrylate 2F: Vinylidene fluoride 4F: Tetrafluoroethylene 6F: Hexafluoroethylene 4FM: Tetrafluoropropyl methacrylate 5FM: Pentafluoropropyl methacrylate 8FM: Octafluoropentyl methacrylate 17FM: Heptadecafluorodecyl methacrylate. 【0078】 [Other abbreviations] MFI: Meltflow Index. 【0079】 [Example 1] A copolymer was prepared containing PMMA as the core component and MMA / 4FM / 5FM as the cladding component in a mass ratio of 20 / 20 / 60, and a copolymer containing 2F / 4F as the cladding component in a mass ratio of 75 / 25. Each copolymer was introduced into a spinning pack incorporating an extrusion die, melted at 245°C, and then polymer streams were extruded from each extrusion section to obtain a multicore plastic optical fiber. The extrusion die used had a core component extrusion section, a cladding component extrusion section surrounding the core component extrusion section, and distribution holes for the cladding component extrusion section surrounding the island sections. In the cross-section of the fiber, the obtained optical fiber had 512 cores, a core diameter of 52 μm, a core center spacing of 60 μm, and a cladding thickness of 3.0 μm. The results of evaluation using the method described above are shown in Table 3. 【0080】 [Examples 2-4] Copolymers of the copolymer components shown in Tables 1 and 2 and their mass ratios were used as cladding components. Optical fibers were prepared in the same manner as in Example 1. The obtained optical fibers had a core diameter of 52 μm, a core center-to-center distance of 60 μm, and a cladding thickness of 3.0 μm. The results of evaluation using the method described above are shown in Table 3. 【0081】 [Example 5] An optical fiber was fabricated in the same manner as in Example 1, except that PC was used as the core component. The obtained optical fiber had a core diameter of 52 μm, a core center spacing of 60 μm, and a cladding thickness of 3.0 μm. The results of evaluation using the method described above are shown in Table 3. 【0082】 [Example 6] Copolymers of the copolymer components shown in Tables 1 and 2 and their mass ratios were used as the marine components. Optical fibers were prepared in the same manner as in Example 1. The obtained optical fibers had a core diameter of 52 μm, a core center-to-center distance of 60 μm, and a cladding thickness of 3.0 μm. The results of evaluation using the method described above are shown in Table 3. 【0083】 [Examples 7 and 8] As the marine components, copolymers with the polymerization components and their mass ratios shown in Tables 1 and 2 were used. Optical fibers were prepared in the same manner as in Example 1. The obtained optical fibers had a core diameter of 52 μm, a core center-to-center distance of 60 μm, and a cladding thickness of 3.0 μm. The results of evaluation using the method described above are shown in Table 3. 【0084】 [Comparative Example 1] As the marine components, polymers with the polymerization components and their mass ratios shown in Tables 1 and 2 were used. Optical fibers were prepared in the same manner as in Example 1. The obtained optical fibers had a core diameter of 52 μm, a core center-to-center distance of 60 μm, and a cladding thickness of 3.0 μm. The results of evaluation using the method described above are shown in Table 3. 【0085】[Comparative Examples 2-5] Polymers with the polymer components and their mass ratios shown in Tables 1 and 2 were used as the cladding and core components. Optical fibers were prepared in the same manner as in Example 1. The obtained optical fibers had a core diameter of 52 μm, a core center-to-center distance of 60 μm, and a cladding thickness of 3.0 μm. The results of evaluation using the method described above are shown in Table 3. 【0086】 【0087】 【0088】

Claims

1. A multicore plastic optical fiber having a cross-sectional shape consisting of two or more island portions and a sea portion surrounding the island portions, wherein each island portion consists of a core and a cladding surrounding it, and the melt flow index R1 (g / 10 min) of the cladding component forming the cladding, measured at 230°C and a load of 3.8 kgf, and the melt flow index R2 (g / 10 min) of the sea portion forming the sea portion, measured at 230°C and a load of 3.8 kgf, satisfy the following relationship: R2 - R1 ≥ 3 2. The multicore plastic optical fiber according to claim 1, wherein the cladding component is a copolymer containing perfluoroalkyl methacrylate and / or perfluoroalkyl acrylate as a copolymer component.

3. The multicore plastic optical fiber according to claim 1 or 2, wherein the cladding component is a copolymer containing a perfluoroalkyl methacrylate represented by formula (1). ２ = C(CH ３ )-COO(CH ２ )m(CF ２ )nR Equation (1) In Equation (1), R represents a fluorine atom or a hydrogen atom, m is 1 or 2, and n is an integer from 1 to 11.

4. The multicore plastic optical fiber according to claim 1 or 2, wherein the cladding component is a copolymer containing 60 to 95% by mass of perfluoroalkyl methacrylate and 5 to 40% by mass of methyl methacrylate as copolymer components.

5. The multicore plastic optical fiber according to claim 1 or 2, wherein the marine component is a copolymer containing vinylidene fluoride units and tetrafluoroethylene units.

6. The multicore plastic optical fiber according to claim 1 or 2, wherein the marine component is a copolymer containing 65 to 85% by mass of vinylidene fluoride and 15 to 35% by mass of tetrafluoroethylene as copolymer components.

7. The multicore plastic optical fiber according to claim 1 or 2, wherein the difference between the refractive index n1 of the cladding component and the refractive index n2 of the core component satisfies the following relationship: n1 - n2 ≥ 0.000 8. The multicore plastic optical fiber according to claim 1 or 2, wherein the melt viscosity W1 (Pa·s) of the cladding component at a shear rate of 100 (1 / sec) and 220°C and the melt viscosity W2 (Pa·s) of the core component at a shear rate of 100 (1 / sec) and 220°C satisfy the following relationship: W1 / W2 ≥ 1.00 9. The multicore plastic optical fiber according to claim 1 or 2, wherein the core component forming the core is a polymethyl methacrylate resin.

10. The multicore plastic optical fiber according to claim 1 or 2, wherein the marine component contains carbon black.

11. An optical communication cable comprising a multicore plastic optical fiber as described in claim 1 or 2.

12. An optical communication system that uses the optical communication cable described in claim 11 and performs spatial multiplex communication using multiple light sources.

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