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

Abstract

The purpose of the present invention is to provide a multicore plastic optical fiber, an optical communication cable, and an optical communication system using them that are capable of using multiple cores for communication, excellent in fiber handleability, low in transmission loss, and wide in transmission band.　The present invention provides a multicore plastic optical fiber having a plurality of cores, wherein the number of the plurality of cores is 300 or more, at least a part of the arrangement of the plurality of cores in a cross section perpendicular to the fiber axis direction of the multi-core plastic optical fiber is a hexagonal lattice, the ratio of the area occupied by the cores is 50% to 75% in a triangle connecting the centers of freely selected adjacent three cores excluding the outermost periphery in the arrangement of the plurality of cores, and the average value of the diameters of the plurality of cores is 30 μm to 60 μm.

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 flexibility, plastic optical fibers are used in a wide range of fields, including decorative lighting, medical care, in-vehicle lighting, image fibers, various sensors, and communications.

[0003] For communication applications, spatial division multiplexing communication, which transmits multiple signals using a single multi-core plastic optical fiber, is being considered. For example, in Patent Document 1, crosstalk is suppressed by using a light-blocking resin as a sea component, and in Patent Document 2, crosstalk is suppressed by arranging a colored core around a transparent core.

[0004] Furthermore, with the amount of communication data increasing rapidly in recent years, there is a demand to increase the communication capacity per fiber.

[0005] On the other hand, multi-core plastic optical fibers are widely used as image fibers for image transmission. A fiber with a large number of cores is desired for clearer image display, and an optimal fiber structure has been proposed (Patent Document 3). However, the characteristics required of multi-core plastic optical fibers for image transmission and spatial division multiplexing communication are different, so the optimal fiber structure is not the same.

[0006] Japanese Patent Application Publication No. 11-258432 Japanese Patent Application Publication No. 2009-217172 Japanese Patent Application Publication No. 2013-231817

[0007] To increase the communication volume per fiber, a multicore fiber needs to have a large number of cores. The larger the core diameter, the lower the transmission loss. However, if the number of cores is increased while the core diameter remains large to make the fiber thicker, the fiber becomes physically difficult to bend and becomes less manageable. Furthermore, the larger the core diameter, the smaller the transmission bandwidth, which is an indicator of the maximum communication capacity per core. Patent Document 1 presents an example in which the number of cores is 37 and the core diameter is 70 to 100 μm, but this number of cores is insufficient to increase the communication volume per fiber. Using colored cores, as in Patent Document 2, reduces the number of cores available for communication and is therefore undesirable for increasing the communication capacity per fiber.

[0008] Therefore, the present invention aims to overcome the problems of the conventional technology and to provide a multi-core plastic optical fiber, an optical communication cable, and an optical communication system using the same, which can use a large number of cores for communication, have excellent fiber handling properties, low transmission loss, and a wide transmission bandwidth.

[0009] The present inventors have come up with the idea of ​​the present invention by noticing that in a multi-core optical fiber that performs communication using a large number of cores, the core density becomes high and therefore optimization of the fiber diameter, core diameter, etc. is essential.

[0010] The present invention and its preferred aspects for solving the above problems have the following configurations: (1) A multi-core plastic optical fiber having a plurality of cores, wherein the number of the plurality of cores is 300 or more, at least a part of the arrangement of the plurality of cores in a cross section perpendicular to the fiber axis direction of the multi-core plastic optical fiber forms a hexagonal lattice, the ratio of the area occupied by the cores in a triangle connecting the centers of any three adjacent cores excluding the outermost core in the arrangement of the plurality of cores is 50% to 75%, and the average diameter of the plurality of cores is 30 μm to 60 μm. (2) The multi-core plastic optical fiber according to (1), wherein, in the cross section, a plurality of claddings surround each of the plurality of cores to form a plurality of independent island structures, and a component different from the component forming the plurality of claddings is disposed between the plurality of island structures to form a sea structure. (3) The multi-core plastic optical fiber according to (2), wherein the refractive index of the component forming the sea structure is higher than the refractive index of the plurality of claddings. (4) The multi-core plastic optical fiber according to (2) or (3), wherein the cladding thickness on a line connecting the center of any core excluding the outermost core in the arrangement of the multiple cores in the cross section to the center of an adjacent core is 1 μm or more, and the sea structure thickness is 2 μm or more. (5) The multi-core plastic optical fiber according to any one of (1) to (4), wherein the transmission loss measured by irradiating one of any cores excluding the outermost core in the arrangement of the multiple cores in the cross section with a 650 nm laser beam is 250 dB / km or less. (6) The multi-core plastic optical fiber according to any one of (1) to (5), wherein the maximum value of the circularity (core major axis / core minor axis) of the multiple cores arranged in the outermost periphery is 1.50 or less, and the maximum value of the circularity (core major axis / core minor axis) of the multiple cores excluding the multiple cores arranged in the outermost periphery is 1.30 or less. (7) The multi-core plastic optical fiber according to any one of (1) to (6), wherein, among the plurality of cores arranged on the outermost periphery, a core arranged closest to a surface of the multi-core plastic optical fiber has a minimum distance from an outer edge of the multi-core plastic optical fiber to an outer edge of the core that is closest to the surface of the multi-core plastic optical fiber of 5 μm or more.(8) The multi-core plastic optical fiber according to any one of (1) to (7), wherein a transmission bandwidth measured by incidenting multi-mode VCSEL light having a wavelength of 670 nm onto any one core excluding the outermost core in the arrangement of the multiple cores in the cross section with an incident NA of 0.2 is 400 MHz or more over a fiber length of 25 m. (9) An optical communication cable comprising the multi-core plastic optical fiber according to any one of (1) to (8). (10) An optical communication system performing spatial multiplexing communication using multiple signal light beams with the multi-core plastic optical fiber according to any one of (1) to (8) or the optical communication cable according to (9). (11) The optical communication system according to (10), wherein a light source wavelength is 400 nm or more and 700 nm or less. (12) The optical communication system according to (10) or (11), wherein the number of multiple light sources used for optical communication is 50% or more of the number of cores, and the multiple light sources and the multiple cores are in one-to-one correspondence.

[0011] According to the present invention, it is possible to provide a multi-core plastic optical fiber in which the number of cores used for communication per fiber is large and transmission loss is low.

[0012] Fig. 1 is a partially enlarged cross-sectional view of a typical multi-core plastic optical fiber of the present invention, where (a) shows the [core / clad] structure and (b) shows the [core / clad / sea] structure. Fig. 2 is an explanatory diagram of a method for calculating the core area ratio, where (a) shows the [core / clad] structure and (b) shows the [core / clad / sea] structure. Fig. 3 is an explanatory diagram of measurement points for the clad thickness and the sea structure thickness in the [core / clad / sea] structure of a multi-core plastic optical fiber.

[0013] Hereinafter, embodiments of the multi-core plastic optical fiber, the optical communication cable, and the optical communication system according to the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be modified in various ways depending on the purpose and application.

[0014] The multi-core plastic optical fiber of the present invention has a cross-sectional shape represented by any one of the following:

[0015] <Core / Cladding> This cross-sectional configuration has an islands-in-a-sea structure consisting of multiple cores and claddings.

[0016] <Core / Cladding / Sea> This cross-sectional configuration has a plurality of islands structure in which a plurality of claddings are arranged around a plurality of cores, and a sea structure made of a component different from the component that forms the plurality of claddings.

[0017] [Core] The plurality of cores are transmission portions that directly propagate the signal light, and play a role in efficiently transmitting the signal light.

[0018] The resin in the resin composition forming the multiple cores is preferably a material that is light-transmitting and has low transmission loss, and examples thereof include acrylic resin, modified polycarbonate resin, cycloolefin resin, styrene resin, olefin resin such as polymethylpentene, etc. Among these resins, acrylic resin is preferred because of its low transmission loss.

[0019] Examples of the acrylic resin include polymers of methacrylic acid esters and acrylic acid esters. Examples of the methacrylic acid ester 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 the acrylic acid ester 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 examples of the acrylic resin 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.

[0020] The refractive index of the plurality of cores is preferably 1.45 or more and 1.60 or less. By making the refractive index of the cores 1.45 or more, more preferably 1.48 or more, it is possible to suppress the crystallinity of the resin and reduce transmission loss due to light scattering. Furthermore, by making the refractive index of the plurality of cores 1.60 or less, more preferably 1.55 or less, it is possible to reduce absorption of the resin in the visible light region and reduce transmission loss in the visible light region.

[0021] The refractive index can be measured in accordance with JIS K 7142:2014 using an Abbe refractometer on a 20 mm x 8 mm x 1.4 mm test piece at room temperature (25°C). If it is difficult to directly measure the refractive index of a core, the core can be heated at 210°C for 5 minutes using a press molding machine, then cooled to room temperature to produce a 20 mm x 8 mm x 1.4 mm test piece, and the refractive index can be measured. If the core composition is known, a test piece can be similarly prepared from the known composition, and the refractive index can be measured.

[0022] The cross-sectional shape of the plurality of cores is preferably substantially circular or substantially hexagonal.

[0023] In a cross section perpendicular to the fiber axis direction of the multi-core plastic optical fiber, at least a part of the cores are arranged in a hexagonal lattice pattern. By arranging the cores in a hexagonal lattice pattern, it is easy to increase the core area ratio and keep the transmission loss low even when the number of cores is large.

[0024] In a cross section perpendicular to the fiber axis direction of the multi-core plastic optical fiber, the maximum value of the circularity (core major axis / core minor axis) of the multiple cores arranged at the outermost periphery of the multiple core arrangement is preferably 1.50 or less. By making the circularity 1.50 or less, more preferably 1.40 or less, even more preferably 1.30 or less, and even more preferably 1.20 or less, deterioration of the transmission bandwidth of the core can be more effectively suppressed, and the circularity of the core adjacent to the outermost core can be suppressed to 1.30 or less. Hereinafter, the multiple cores arranged at the outermost periphery refer to a group of cores in a hexagonal lattice arrangement in which there are no six cores adjacent to any one of them. Hereinafter, the multiple cores arranged at the outermost periphery will also be simply referred to as the "outermost core group."

[0025] Furthermore, the maximum circularity of the cores excluding the cores arranged on the outermost periphery is preferably 1.30 or less. By setting the circularity to 1.30 or less, more preferably 1.20 or less, and even more preferably 1.15 or less, deterioration of the transmission bandwidth of the cores can be more effectively suppressed.

[0026] The circularity is calculated by acquiring an image of the core, fitting the core to an ellipse, outputting the major axis and minor axis of the obtained ellipse, and dividing the major axis of the core by the minor axis of the core.

[0027] The average diameter of the multiple cores is 30 μm or more and 60 μm or less. Here, core diameter refers to the diameter of the inscribed circle. When the average diameter is 30 μm or more, preferably 35 μm or more, more preferably 40 μm or more, transmission loss can be reduced. Furthermore, when light from a light source is introduced into one core, simultaneous alignment with multiple light sources becomes easier. Furthermore, when the average diameter is 60 μm or less, preferably 55 μm or less, deterioration of the transmission bandwidth can be suppressed. Furthermore, the fiber diameter of a multi-core optical fiber having many cores is prevented from becoming too thick, resulting in excellent handleability.

[0028] The number of the plurality of cores per multi-core plastic optical fiber is 300 or more. By setting the number of the plurality of cores to 300 or more, preferably 400 or more, and more preferably 500 or more, each core can propagate a different light, thereby realizing a large communication capacity per multi-core plastic optical fiber. On the other hand, by setting the number of the plurality of cores to preferably 1100 or less, more preferably 1000 or less, and even more preferably 900 or less, the fiber diameter does not become too large even when a sufficient core-to-core pitch is ensured, and the flexibility required for a communication fiber can be ensured.

[0029] The distance between the outermost core group and the outer edge of the multi-core plastic optical fiber is preferably 5 μm or more. By making the distance 5 μm or more, more preferably 15 μm or more, and even more preferably 30 μm or more, it is possible to suppress a decrease in the circularity of not only the outermost core but also the cores adjacent to it. Here, the core adjacent to the outermost core refers to a core adjacent to the outermost core that is not the outermost core.

[0030] In the triangle connecting the centers of any three adjacent cores excluding the outermost core in the arrangement of the multiple cores, the ratio of the area occupied by the cores (hereinafter also referred to as the "core area ratio") is 50% or more and 75% or less. Here, the outermost core refers to a core that has no six adjacent cores in a hexagonal lattice arrangement. Here, if the cross-sectional shape of this core is not a perfect circle, the center of gravity of the cross-section of the core is regarded as the center. When the core area ratio is 50% or more, more preferably 60% or more, a multicore fiber having many cores is prevented from becoming too thick, resulting in excellent fiber handleability. Furthermore, when the core area ratio is 75% or less, more preferably 70% or less, light leakage to adjacent cores can be prevented when the distance between adjacent cores becomes too close and light is injected into one core.

[0031] [Cladding] The cladding protects the cores from external environmental factors and, when the multi-core plastic optical fiber of the present invention has a core / cladding / sea structure, reduces the rate at which signal light propagating through the cores is reflected at the cladding interface and leaks into the sea region.

[0032] Examples of the resin constituting the clad include those common to the resin constituting the core, 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.

[0033] The refractive index of the cladding component is lower than that of the core component used. When the refractive index of the cladding component is lower than that of the core component, light is reflected at the interface between the core and the cladding, allowing the light to propagate within the core. The difference in refractive index between the cladding and the core is preferably 0.01 or more and 0.10 or less. When the refractive index difference is 0.01 or more, light is reflected at the interface between the core and the cladding even when the fiber is bent, thereby suppressing light leakage. Furthermore, when the refractive index difference is 0.10 or less, it is possible to prevent the transmission bandwidth from becoming narrower.

[0034] The refractive index of the cladding is preferably 1.35 or more and 1.59 or less, 1.50 or less, or 1.45 or less. When the refractive index of the cladding is 1.35 or more, more preferably 1.36 or more, and even more preferably 1.38 or more, the difference in refractive index between the cladding and the core becomes small, and the number of modes of propagating light decreases, thereby expanding the transmission bandwidth.

[0035] The refractive index of the cladding can be measured in the same manner as the refractive index of the core. If it is difficult to sample the cladding and directly measure its refractive index, the sampled cladding 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. If the composition of the cladding is known, a test piece can be similarly prepared from the known composition, and the refractive index can be measured.

[0036] The cladding thickness is preferably 1 μm or more. When the cladding thickness is 1 μm or more, more preferably 2 μm or more, light leakage to adjacent cores can be more effectively suppressed.

[0037] [Sea Component] In the plastic multi-core optical fiber of the present invention, in a cross section perpendicular to the fiber axis direction, it is also preferable that a plurality of claddings surround each of the plurality of cores to form a plurality of independent island structures, and a component different from the component forming the plurality of claddings is disposed between the plurality of island structures to form a sea structure. By forming the sea structure with a component different from the component forming the cladding, the fiber has advantages such as circularity and flexibility as a whole, and prevention of crosstalk by confining light using the refractive index difference with the cladding. Hereinafter, the component that forms the sea structure and is different from the component forming the cladding will be referred to as the "sea component."

[0038] On the line connecting the centers of gravity of adjacent cores, the thickness of the sea structure sandwiched between adjacent island structures is preferably 2 μm or more, which can more effectively prevent light leakage to adjacent cores.

[0039] The materials proposed for the core and cladding can be used as the material for the sea component. The refractive index of the sea component is preferably higher than that of the cladding component. The refractive index of the sea component is preferably higher than that of the cladding, and the difference in refractive index between the sea component and the cladding is more preferably 0.02 or more, even more preferably 0.04 or more, and still more preferably 0.07 or more. This makes it possible to prevent a decrease in the transmission bandwidth due to interference of reflected light at the interface between the cladding and the sea structure and crosstalk due to light entering an adjacent core when light incident on the core passes through the cladding and reaches the sea structure.

[0040] The sea component preferably contains a coloring substance, which can further enhance the effect of suppressing crosstalk.

[0041] When using the plastic multi-core optical fiber, it is preferable to use a visible light wavelength of 400 to 700 nm as a light source, which has low transmission loss of the core component, and therefore it is preferable that the coloring material also has absorption in visible light, such as carbon black, lead oxide, titanium oxide, and organic pigments.

[0042] The average primary particle size of the carbon black is preferably 0.1 μm or more and 2 μm or less. When the average primary particle size is 0.1 μm or more, it is possible to prevent the carbon black from agglomerating during a long spinning process, thereby preventing the melt viscosity of the sea component from increasing over time. Furthermore, when the average primary particle size is 2 μm or less, it is possible to prevent clogging at the narrowest part of the sea structure.

[0043] The content of the coloring substance in the sea component cannot be generalized because it varies depending on the properties of the coloring substance, but when the coloring substance is carbon black with an average primary particle size of 0.1 to 2 μm, the content is preferably 0.3% by mass or more and 5% by mass or less. A content of 5% by mass or less can prevent a sudden increase in the melt viscosity of the sea component. Furthermore, a content of 0.3% by mass or more can more effectively prevent crosstalk.

[0044] [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 by making the diameter 0.5 mm or more, preferably 0.8 mm or more, more preferably 1.0 mm or more, the number of cores can be increased, thereby increasing the communication capacity. On the other hand, by making the diameter 3.0 mm or less, preferably 2.5 mm or less, more preferably 2.0 mm or less, the fiber can be given appropriate flexibility and the handleability can be improved.

[0045] [Manufacturing Method] As a method for manufacturing the multi-core plastic optical fiber of the present invention, for example, a method for continuously molding each resin composition constituting each part of the multi-core plastic optical fiber into a predetermined shape can be mentioned. Each resin composition constituting each part is a two-component core / clad or a three-component core / clad / sea. As a continuous molding method, it is preferable to form it by a composite spinning method using an extrusion die. Unlike other resin molding dies, this extrusion die does not cool or solidify any resin composition inside the extrusion die, and the resin composition constituting the core and the resin composition constituting the clad are extruded from the core discharge part and the clad discharge part, respectively, and then cooled and solidified, and can be molded into a predetermined shape.

[0046] The timing of discharging the resin compositions constituting each part is preferably as simultaneous as possible, and even if there is a difference, it is preferably less than one second, which is substantially the same as when they are discharged simultaneously.The amount of each resin composition discharged is preferably such that the extrusion stress caused by the resin composition constituting the cladding discharged from the sea discharge portion surrounded by each core, which is applied to the resin composition constituting each core, and conversely, the extrusion stress caused by the resin composition constituting each core discharged from each core discharge portion, which is applied to the resin composition constituting each cladding, is the same at every point, and these stresses continue to cancel each other out, so that the cross-sectional shape of the core can be maintained as a perfect circle.

[0047] [Optical communication cable] The multi-core plastic optical fiber of the present invention can be suitably used for an optical communication cable, that is, the optical communication cable of the present invention includes the multi-core plastic optical fiber of the present invention.

[0048] [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. That is, the optical communication system of the present invention performs spatial multiplexing communication using the multi-core plastic optical fiber or the optical communication cable of the present invention and multiple signal lights. The optical communication system of the present invention enables large-capacity communication.

[0049] Here, spatial multiplexing communication is a communication method that enables large-volume data transfer by using a light-emitting device that can transmit multiple signals, an optical fiber that can transmit multiple light beams, and a light-receiving device that can receive multiple signals.

[0050] The light source of the light emitting device is not particularly limited, but it is preferable to use a light source that can be mounted at high density, such as a surface emitting laser or μLED.

[0051] It is preferable that the plurality of cores correspond one-to-one to the plurality of cores. If the correspondence between the light sources and the plurality of cores is not one-to-one, the number of cores must be at least twice the number of light sources, and if the light sources are densely packed, the core diameter will be small, resulting in high fiber transmission loss. It is also preferable that the number of cores that do not correspond to light sources be as small as possible. Therefore, the number of the plurality of light sources is preferably 50% or more of the number of cores, more preferably 60% or more, and even more preferably 70% or more. Furthermore, if the number of light sources and the number of cores are the same, all of the outermost cores, which have relatively low circularity, will be used, so the number of light sources is preferably 90% or less of the number of cores, and more preferably 85% or less.

[0052] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0053] [Measurement method] (1) Fiber cross-sectional image A randomly selected portion of the multi-core plastic optical fiber in each example and comparative example was cut perpendicular to the fiber axis direction, and a cross-sectional image was obtained using a digital microscope (Keyence VHX-7000).

[0054] (2) Fiber Diameter (μm) The fiber diameter was measured from the cross-sectional image.

[0055] (3) Average Core Diameter (μm) The diameter of the inscribed circle of the core was calculated from the cross-sectional image, and the arithmetic mean value of all the cores was taken as the average core diameter.

[0056] (4) Core Pitch (μm) From the cross-sectional image, the distances between the centers of gravity of all cores other than the cores arranged at the outermost periphery and the adjacent cores were calculated, and the arithmetic mean value was defined as the core pitch.

[0057] (5) Clad Thickness (μm) From the cross-sectional image, cores other than the core located at the outermost periphery were extracted, and the thickness of the clad sandwiched between adjacent cores was measured on the line connecting the center of gravity of the extracted core and the center of gravity of the core adjacent to the extracted core. If a component different from the component forming the clad formed a sea structure, the thickness of one clad between the core and the sea structure (T1 in Figure 3) was also measured, and the average of the measured thicknesses was taken as the clad thickness. The gap between the extracted core and the adjacent core was calculated, and the average value was taken as the clad thickness.

[0058] (6) Thickness of Sea Structure (μm) From the above cross-sectional image, cores excluding those located at the outermost periphery were extracted, and the thickness of the sea structure sandwiched between adjacent island structures (T2 in Figure 3) was measured on the line connecting the center of gravity of the extracted core and the center of gravity of the core adjacent to the extracted core, and the average value of the measured thicknesses was defined as the thickness of the sea structure.

[0059] (7) Core Area Ratio (%) The above cross-sectional image was binarized into core and cladding using image analysis software (winROOF), and then the core area ratio in the triangle connecting the centers of three adjacent cores near the center of the fiber was calculated.

[0060] (8) Transmission loss (dB / km) A laser beam (wavelength 650 nm, incident numerical aperture 0.25) was incident on one core located at the center of a 30 m long sample of the multi-core plastic optical fiber in each example and comparative example from one end, and the amount of light A (dBm) emitted from the other end was measured. Here, dBm (decibel milliwatt) is a unit of logarithmic representation of power, and P [mW] is 10 log １０ This can be converted into P [dBm]. Next, this sample was cut to a length of 2 m, and the same parallel light as in the measurement using the 30 m sample was incident on one end, and the amount of light B (dBm) emitted from the other end was measured. The transmission loss (dB / km) was then calculated using the following formula: Transmission loss (dB / km) = (B - A) / (30 - 2) x 1000.

[0061] (9) Transmission Bandwidth (MHz) The transmission bandwidth was evaluated using a network analyzer (MS46122B manufactured by Anritsu), an E / O converter (VL-670 manufactured by Graviton, VCSEL laser with a wavelength of 670 nm), and an O / E converter (SPA-2 manufactured by Graviton).

[0062] On the light source side, modulated light from the E / O converter was converted into incident light with an effective numerical aperture of 0.2 using a step-index fiber and an objective lens, and the incident light was connected to one core located near the center of the multi-core plastic optical fiber in each example and comparative example. On the light receiving side, the multi-core plastic optical fiber in each example and comparative example was directly connected to the O / E converter.

[0063] In each example and comparative example, two multi-core plastic optical fibers, one 26 m long and one 1 m long, were prepared, and the frequency was swept from 10 MHz to 2 GHz, and the transmission characteristics (S21) were measured at 10 MHz intervals. The measurement value at 1 m was subtracted from the measurement value at 26 m to create a differential profile. In this profile, the frequency at which the transmission characteristics at 10 MHz were reduced by 3 dB was measured as the 25 m transmission band. The transmission band is preferably 400 MHz, more preferably 500 MHz or more, and even more preferably 600 MHz or more.

[0064] In Examples 2 and 11 to 13, the transmission band was also evaluated in the same manner when the outermost core was connected so that the light was incident on the core adjacent to it.

[0065] (10) Light Leakage from Adjacent Cores (Visual Observation) A 5 m sample of a multi-core plastic optical fiber in each example and comparative example was prepared, and light was incident on one core located near the center of the fiber using the same incident method as in the measurement of the transmission bandwidth. The end face on the opposite side was checked with a micrometer to confirm light leakage by checking whether the adjacent core emitted a reddish color. If the core turned even slightly reddish, it was determined that there was light leakage.

[0066] (11) Adjacent Core Light Leakage (Measurement) A 5m sample of a multi-core plastic optical fiber in each example and comparative example was prepared, and modulated light from an E / O converter was incident on one core located near the center of the fiber using the same incident method as in the measurement of the transmission bandwidth. An objective lens with an NA of 0.4 was installed on the opposite side of the output light so that its focus was the output end face of the fiber. The collimated light was observed with a CMOS camera (CS2000-B manufactured by Shodensha), and the difference between the amount of light emitted from the input core and the amount of light emitted from the adjacent core was relatively evaluated using beam analysis software (LaseView manufactured by Kokyo). The smaller the amount of light leakage to the adjacent core, the better, and the difference is preferably 25dB or more, more preferably 35dB or more, and even more preferably 45dB or more.

[0067] (12) Distance from the outer edge of the outermost core to the outer edge of the fiber In the cross-sectional image of the fiber obtained in (1), the distance from the outer edge of the fiber to the outer edge of the core with the shortest distance was measured. Even in a three-component structure consisting of a core, cladding, and sea, the distance to the outer edge of the core was measured, not to the cladding that forms the outer periphery of the island structure.

[0068] (13) Measurement of Circularity In the cross-sectional image of the fiber obtained in (1), the circularity of the outermost core and the core adjacent to the outermost core was measured. The circularity was measured by fitting the core to an ellipse, outputting the major axis and minor axis of the obtained ellipse, and calculating the maximum value of each by dividing the major axis of the core by the minor axis of the core. In the fiber of the example of the present invention, the circularity of the core adjacent to the outermost core was clearly lower than that of the core closer to the center, so the maximum value of the core adjacent to the outermost core was the maximum value of the cores other than the outermost core.

[0069] [Example 1] Polymethyl methacrylate (refractive index 1.49) was prepared as the resin composition constituting the core, 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. They were poured into a spinning pack incorporating an extrusion die with 510 cores in a hexagonal lattice arrangement so that the volume ratio of cores to cladding was 52:48. The resin composition in the spinning pack was melted at 240°C, and then polymer flows were discharged from each discharge port to obtain a multi-core plastic optical fiber. The obtained multi-core plastic optical fiber was evaluated by the above-mentioned methods (1) to (11), and the results are shown in Table 1.

[0070] [Example 2] Polymethyl methacrylate (refractive index 1.49) was prepared as the resin composition constituting the core, 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, and polymethyl methacrylate (refractive index 1.49) was prepared as the resin composition constituting the sea structure. These were then poured into a spinning pack incorporating an extrusion die with 510 cores in a hexagonal lattice arrangement so that the volume ratio of the resin composition constituting the core, the resin composition constituting the cladding, and the resin composition of the sea part was 51:12:37. The resin composition in the spinning pack was melted at 240°C, and polymer flows were discharged from each discharge port to obtain a multi-core plastic optical fiber. The obtained multi-core plastic optical fiber was evaluated by the above-mentioned methods (1) to (11), and the results are shown in Table 1.

[0071] [Examples 3 to 7, 9, and 10] Multi-core plastic optical fibers were fabricated in the same manner as in Example 2, except for adjusting the polymer supply amount, spinning speed, and volume ratio of the resin composition constituting the core to the resin composition constituting the cladding. The obtained multi-core plastic optical fibers were evaluated by the above-mentioned methods (1) to (11), and the results are shown in Table 1.

[0072] [Example 8] A multi-core plastic optical fiber was fabricated in the same manner as in Example 2, except that the resin composition constituting the sea structure was changed to a copolymer of 55 mass % tetrafluoroethylene / 20 mass % hexafluoropropylene / 25 mass % ethylene (refractive index 1.38). The obtained multi-core plastic optical fiber was evaluated by the above-mentioned methods (1) to (11), and the results are shown in Table 1.

[0073] Comparative Example 1 A multi-core plastic optical fiber was fabricated in the same manner as in Example 1, except that the polymer supply amount, spinning speed, and core / cladding volume ratio were adjusted. The obtained multi-core plastic optical fiber was evaluated by the above-mentioned methods (1) to (11), and the results are shown in Table 1.

[0074] [Comparative Examples 2 to 5] Except for adjusting the polymer supply amount, the spinning speed, and the core / cladding volume ratio, multi-core plastic optical fibers were fabricated in the same manner as in Example 2. The obtained multi-core plastic optical fibers were evaluated by the above-mentioned methods (1) to (11), and the results are shown in Table 1.

[0075]

[0076] [Examples 11 to 13] The extrusion die and the amount of resin composition constituting the sea structure flowing into the spin pack were changed, and the number, diameter, and arrangement of cores (including core pitch) and cladding thickness were maintained, while the distance from the outer edge of the outermost core to the outer edge of the fiber was changed as shown in Table 2. Except for these, multi-core plastic optical fibers were fabricated in the same manner as in Example 2. The obtained multi-core plastic optical fibers were evaluated by the above-mentioned methods (1) to (7), (12), and (13), and the results are shown in Table 2.

[0077]

[0078] 1 Core 2 Cladding 3 Sea 4 Center of core (center of gravity) 5 Triangle connecting the centers (centers of gravity) of three adjacent cores 6 Straight line connecting the centers (centers of gravity) of two adjacent cores T1 Thickness of cladding T2 Thickness of sea structure

Claims

1. A multi-core plastic optical fiber having a plurality of cores, the number of the plurality of cores being 300 or more, at least a part of the arrangement of the plurality of cores in a cross section perpendicular to the fiber axis direction of the multi-core plastic optical fiber forming a hexagonal lattice, the ratio of the area occupied by the cores in a triangle connecting the centers of any three adjacent cores excluding the outermost core in the arrangement of the plurality of cores being 50% or more and 75% or less, and the average diameter of the plurality of cores being 30 μm or more and 60 μm or less.

2. A multi-core plastic optical fiber according to claim 1, wherein in the cross section, a plurality of claddings surround each of the plurality of cores to form a plurality of island structures that are independent of each other, and a component different from the component that forms the plurality of claddings is disposed between the plurality of island structures to form a sea structure.

3. The multi-core plastic optical fiber according to claim 2, wherein the refractive index of the component forming the sea structure is higher than the refractive index of the component forming the plurality of claddings.

4. A multi-core plastic optical fiber according to claim 2, wherein the cladding thickness on a line connecting the center of any core excluding the outermost core in the arrangement of the multiple cores in the cross section to the center of an adjacent core is 1 μm or more, and the sea structure thickness is 2 μm or more.

5. A multi-core plastic optical fiber according to claim 1 or 2, wherein the transmission loss measured by irradiating a 650 nm laser beam onto any one of the cores excluding the outermost core in the arrangement of the plurality of cores in the cross section is 250 dB / km or less.

6. A multi-core plastic optical fiber according to claim 1 or 2, wherein the maximum value of the circularity (core major axis / core minor axis) of the cores arranged at the outermost periphery is 1.50 or less, and the maximum value of the circularity (core major axis / core minor axis) of the cores other than the cores arranged at the outermost periphery is 1.30 or less.

7. The multi-core plastic optical fiber according to claim 1 or 2, wherein the minimum distance from the outer edge of the multi-core plastic optical fiber to the outer edge of the core that is located closest to the surface of the multi-core plastic optical fiber among the plurality of cores arranged on the outermost periphery is 5 μm or more.

8. The multi-core plastic optical fiber according to claim 1 or 2, wherein the transmission bandwidth measured by injecting multi-mode VCSEL light having a wavelength of 670 nm into any one core excluding the outermost core in the arrangement of the multiple cores in the cross section with an incident NA of 0.2 is 400 MHz or more at a fiber length of 25 m.

9. An optical communication cable comprising the multi-core plastic optical fiber according to claim 1 or 2.

10. An optical communication system that performs spatial multiplexing communication using the optical communication cable according to claim 9 and a plurality of signal lights.

11. The optical communication system according to claim 10, wherein the light source wavelength is 400 nm or more and 700 nm or less.

12. An optical communication system according to claim 10, wherein the number of multiple light sources used for optical communication is 50% or more of the number of cores, and said multiple light sources correspond one-to-one to said multiple cores.

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