Plastic optical fiber, hybrid cable, repeater cable, and active optical cable

Abstract

The plastic optical fiber 10 of the present invention includes a core 11 and a cladding 12 disposed around the core 11. The core 11 contains a first resin, and the cladding 12 contains a second resin. The first glass transition temperature Tg 1 of the first resin is 120°C or higher. The second glass transition temperature Tg 2 of the second resin is 120°C or higher. When the plastic optical fiber 10 is bent once at 25°C to 180 degrees with a radius of curvature R, the minimum value of the radius of curvature R at which the bent portion of the plastic optical fiber 10 will not crack is 5 mm or less.

Description

Technical Field

[0001] This invention relates to a plastic optical fiber, a hybrid cable, a repeater cable, and an active optical cable. Prior Technology

[0002] Plastic optical fiber has a core at its center and a cladding covering the core as the portion for transmitting light. The core is formed of a resin material with a high refractive index. The cladding is formed of a resin material with a lower refractive index than the resin material of the core, so that light is retained within the core.

[0003] In most cases, high heat resistance is required for plastic optical fibers. Previously, various configurations for improving heat resistance have been proposed for plastic optical fibers. For example, as a plastic optical fiber with excellent heat resistance, Patent Document 1 discloses a plastic optical fiber in which the inner layer of the core uses a non-crystalline fluoropolymer (a) that does not substantially have CH bonds, and the outer layer of the cladding uses a fluoropolymer (c) that has a lower refractive index than the fluoropolymer (a) and has an affinity for the fluoropolymer (a). [Previous Technical Documents] [Patent Literature]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2002-71972 Summary of the Invention

[0005] [The problem the invention aims to solve]

[0006] In recent years, there has been a demand for plastic optical fibers to possess both heat resistance and flexibility. However, when only improving heat resistance is considered when selecting core and cladding materials, flexibility may sometimes be reduced.

[0007] Therefore, the object of the present invention is to provide a plastic optical fiber that achieves both good flexibility and improved heat resistance. Furthermore, the object of the present invention is also to provide a hybrid cable, repeater cable, and active optical cable incorporating this plastic optical fiber that possesses both flexibility and heat resistance. [Technical means to solve the problem]

[0008] The first embodiment of this invention provides a plastic optical fiber. It comprises a core and a cladding disposed around the periphery of the aforementioned core. The core described above contains a first resin. The aforementioned coating includes a second resin. The first glass transition temperature Tg 1 of the first resin mentioned above is 120°C or higher. The second glass transition temperature Tg 2 of the aforementioned second resin is 120°C or higher. When the aforementioned plastic optical fiber is bent to 180 degrees with a radius of curvature R once at 25°C, the minimum value of the radius of curvature R at which the bent portion of the aforementioned plastic optical fiber will not crack is 5 mm or less.

[0009] The second embodiment of the present invention provides a plastic optical fiber. It comprises a core and a cladding disposed around the periphery of the aforementioned core. The core described above contains a first resin. The aforementioned coating includes a second resin. The first glass transition temperature Tg 1 of the first resin mentioned above is 120°C or higher. The second glass transition temperature Tg 2 of the aforementioned second resin is 120°C or higher. The birefringence of the fiber structure comprising the aforementioned core and cladding is 2.0 × 10⁻⁴ or higher.

[0010] The third embodiment of the present invention provides a hybrid cable having the plastic optical fiber as described in the first embodiment above.

[0011] A fourth embodiment of the present invention provides a repeater cable comprising: a cable housing a plastic optical fiber as described in the first embodiment; and A connector, which is mounted on at least one end of the aforementioned cable.

[0012] The fifth aspect of the present invention provides an active optical cable comprising: a cable that houses a plastic optical fiber as described in the first aspect above. The first connector, which is mounted at the first end of the aforementioned cable, and has a first conversion unit that converts electrical signals into optical signals; and The second connector is installed at the second end of the aforementioned cable and has a second conversion unit that converts optical signals into electrical signals. [Effects of the Invention]

[0013] According to the present invention, a plastic optical fiber that achieves both good flexibility and improved heat resistance can be provided. Furthermore, according to the present invention, a hybrid cable, a repeater cable, and an active optical cable comprising a plastic optical fiber possessing both flexibility and heat resistance can be provided. Simple Explanation of the Diagram

[0014] Figure 1 is a schematic diagram showing an example of the cross-sectional structure of a plastic optical fiber according to an embodiment of the present invention. Figure 2 is a schematic diagram showing another example of the cross-sectional structure of the plastic optical fiber according to an embodiment of the present invention. Figure 3 is a cross-sectional view showing an example of a hybrid cable according to an embodiment of the present invention. Figure 4 is a schematic diagram illustrating an example of a relay cable in an embodiment of the present invention. Figure 5 is a schematic diagram illustrating an example of an active optical cable according to an embodiment of the present invention. Figure 6 is a schematic cross-sectional view of an example of a manufacturing apparatus for producing plastic optical fibers that can be used to manufacture embodiments of the present invention. Implementation

[0015] An embodiment of the plastic optical fiber (hereinafter referred to as "POF") of the present invention will be described. The POF of this embodiment has a core and a cladding disposed around the outer periphery of the core. The POF of this embodiment is, for example, a refractive index distribution (GI) type POF.

[0016] Figure 1 shows an example of the cross-sectional structure of the POF in this embodiment.

[0017] The POF10 shown in Figure 1 has a core 11 and a cladding 12 disposed around the core 11.

[0018] In the POF10 of this embodiment, the core 11 comprises a first resin. The glass transition temperature (first glass transition temperature Tg 1) of the first resin is 120°C or higher. Furthermore, the cladding 12 comprises a second resin. The glass transition temperature (second glass transition temperature Tg 2) of the second resin is 120°C or higher. When the POF10 of this embodiment is bent once at 25°C to 180 degrees with a radius of curvature R, the minimum value of the radius of curvature R at which the bent portion of the POF10 will not crack is 5 mm or less. Furthermore, the minimum value of the radius of curvature R at which the bent portion will not crack will be referred to as the "minimum radius of curvature". Preferably, the minimum radius of curvature is less than 5 mm.

[0019] In this specification, glass transition temperature refers to the midpoint glass transition temperature (T mg) obtained in accordance with JIS K7121:1987.

[0020] The POF10 of this embodiment, by having the above-described structure, can improve heat resistance while ensuring good flexibility. That is, the POF10 of this embodiment can improve heat resistance while ensuring flexibility within the scope of practical use. Specifically, by making the first glass transition temperature Tg 1 of the first resin contained in the core 11 and the second glass transition temperature Tg 2 of the second resin contained in the cladding 12 both 120°C or higher, the heat resistance of the POF10 of this embodiment can be improved. Even when exposed to high temperatures of, for example, around 105°C, the POF10 of this embodiment can suppress the resulting dimensional changes to a small extent. To further improve heat resistance, the first glass transition temperature Tg 1 and the second glass transition temperature Tg 2 are preferably 125°C or higher, and more preferably 130°C or higher. Furthermore, the POF10 of this embodiment has excellent flexibility, for example, reducing the minimum radius of curvature, i.e., the radius of curvature at which a crack occurs when bent to 180 degrees, to less than 5 mm. Therefore, the POF10 of this embodiment can be used for applications that require heat resistance while ensuring the required softness of POF.

[0021] Here, as a method for determining the minimum radius of curvature of POF10 in this embodiment, for example, a 180-degree bend is applied to POF10 with a target radius of curvature R, bending POF10 once, then the bend is released, restoring it to its original shape. Afterwards, the bent portion of POF10 is observed using a microscope to confirm the presence or absence of cracks. The radius of curvature R is varied, and this 180-degree bend test is performed once for each radius of curvature R. Using the results of 180-degree bend tests performed with multiple radii of curvature R, the minimum radius of curvature that will not produce cracks can be determined. For example, 180-degree bend tests are performed with radii of curvature R = 10 mm, 5 mm, 2.5 mm, 2 mm, and 1 mm. In this case, for example, if no cracks are produced in the 180-degree bending test with curvature radii R = 10 mm, 5 mm, and 2.5 mm, but cracks are produced in the 180-degree bending test with curvature radius R = 2 mm, it can be determined that the minimum curvature radius of the POF is less than 2.5 mm. Furthermore, the 180-degree bending of POF10 can be performed, for example, as follows: prepare a test apparatus with a groove having a target curvature radius R, place the POF10 into the groove, and bend it. Regarding this 180-degree bending test, the minimum curvature radius can be determined by changing the curvature radius R as described above and performing the test multiple times. Alternatively, if it is confirmed that the minimum curvature radius is less than 5 mm, a 180-degree bending test can be performed with a curvature radius R = 5 mm. When it is confirmed that no cracks are produced in the bent portion of the POF10, it is determined that the minimum curvature radius is less than 5 mm.

[0022] The radius of curvature R when bent at 180 degrees is the inner diameter of POF10 (i.e., the radius of curvature measured along the inner surface of POF10).

[0023] Generally, while the presence of resins with high glass transition temperatures can improve heat resistance, it is difficult to simultaneously achieve excellent flexibility. Regarding the POF10 of this embodiment, both the first resin contained in the core 11 and the second resin contained in the cladding 12 have high glass transition temperatures of 120°C or higher, and achieve excellent flexibility with a minimum radius of curvature of 5 mm or less. This excellent flexibility can be achieved, for example, by improving the orientation of the first and second resins in the core 11 and cladding 12. In this embodiment, the orientation of the first resin in the core 11 and the second resin in the cladding 12 can be represented by birefringence. For example, the birefringence of the fiber structure including the core 11 and the cladding 12 is preferably 2.0 × 10⁻⁴ or higher, more preferably 2.5 × 10⁻⁴ or higher, even more preferably 2.7 × 10⁻⁴ or higher, even more preferably 3.0 × 10⁻⁴ or higher, even more preferably 4.0 × 10⁻⁴ or higher, even more preferably 5.0 × 10⁻⁴ or higher, even more preferably 6.0 × 10⁻⁴ or higher. In the case of a POF10 having the configuration shown in FIG. 1, the fiber structure system POF10 includes the core 11 and the cladding 12. Furthermore, when another layer (such as the reinforcing layer 21 described later) is further provided on the periphery of the cladding 12, the portion including the core 11 and the cladding 12, excluding this other layer, becomes the aforementioned fiber structure. By giving the fiber structure a birefringence of 2.0 × 10⁻⁴ or higher, and by aligning the molecular chains of the first and second resins highly along the fiber axis, the flexibility of the fiber structure is improved. Therefore, the POF10 of this embodiment exhibits excellent flexibility.

[0024] As described above, by giving the fiber structure a birefringence of 2.0 × 10⁻⁴ or higher, the molecular chains of the first and second resins are highly aligned along the fiber axis, thereby improving the flexibility of the fiber structure and the flexibility of POF10. Therefore, as another embodiment, the POF10 of this embodiment may also have the following configuration: POF10 has a core 11 and a cladding 12 disposed around the core 11. Core 11 contains the first resin. The cladding layer 12 contains a second resin. The first glass transition temperature (Tg 1) of the first resin is above 120°C. The second glass transition temperature (Tg 2) of the second resin is above 120°C. The birefringence of the fiber structure, including the core 11 and the cladding 12, is greater than 2.0 × 10⁻⁴.

[0025] When POF10 has the above-described structure, the molecular chains of the first and second resins are highly aligned along the fiber axis, thus achieving excellent flexibility. For example, the radius of curvature at which cracks occur when bent to 180 degrees can be reduced to less than 5 mm. That is, POF10 with this structure can also improve heat resistance while ensuring good flexibility. Furthermore, in this case, the birefringence of the fiber structure is preferably 2.5 × 10⁻⁴ or higher, more preferably 2.7 × 10⁻⁴ or higher, even more preferably 3.0 × 10⁻⁴ or higher, even more preferably 4.0 × 10⁻⁴ or higher, even more preferably 5.0 × 10⁻⁴ or higher, even more preferably 6.0 × 10⁻⁴ or higher.

[0026] At least one of the resins selected from the group consisting of the first resin and the second resin may be a fluorinated resin. Preferably, both the first resin and the second resin are fluorinated resins. Fluorinated resins can achieve lower transmission loss over a wide wavelength range. Therefore, fluorinated resins are suitable as resins constituting the core 11 and the cladding 12.

[0027] The components of POF10 in this embodiment will be described in more detail below.

[0028] (Core 11) Core 11 is the region for transmitting light. Core 11 has a higher refractive index than cladding 12. With this configuration, light incident into core 11 is confined inside core 11 by cladding 12, allowing light to be transmitted within POF 10.

[0029] Core 11 may contain a first resin as a main component. Here, "core 11 contains a first resin as a main component" means that the first resin is the component contained in the core 11 by mass percentage. Core 11 may contain more than 80% by mass of the first resin, more than 90% by mass, or more than 95% by mass.

[0030] In addition to the first resin, the core 11 may also contain additives. Additives may include, for example, a refractive index modifier. That is, the core 11 may also be formed from a resin composition containing the first resin and additives such as a refractive index modifier. As a refractive index modifier, for example, a known refractive index modifier used in the material of the POF10 core 11 may be used. The material of the core 11 may also contain other additives besides the refractive index modifier. The glass transition temperature of the material constituting the core 11 is preferably 105°C or higher. Here, when the material of the core 11 includes additives such as a refractive index modifier in addition to the first resin, it refers to a resin composition containing the first resin and such additives. For example, when the core 11 includes the first resin and the refractive index modifier, the glass transition temperature of the mixture of the first resin and the refractive index modifier (resin composition) is preferably 105°C or higher.

[0031] In the case where the POF10 in this embodiment is, for example, of type GI, the core 11 has a refractive index distribution in which the refractive index varies radially. This refractive index distribution can be formed, for example, by adding a refractive index modifier to the first resin, allowing the refractive index modifier to diffuse (e.g., thermally diffuse) within the first resin.

[0032] The first resin included in core 11 is not particularly limited, as long as it is a resin with high transparency. Examples of the first resin include: fluorinated resins, acrylic resins such as methyl methacrylate, styrene resins, and carbonate resins. Among these, fluorinated resins are suitable because they can achieve low transmission loss over a wide wavelength range.

[0033] The first resin of core 11 is preferably a fluorinated resin containing a fluorinated polymer. Hereinafter, the fluorinated resin contained in core 11 will be referred to as the first fluorinated resin, and the fluorinated polymer contained in the first fluorinated resin will be referred to as the first fluorinated polymer.

[0034] From the viewpoint of suppressing light absorption caused by the stretching energy of CH bonds, the first fluorinated polymer contained in the first fluorinated resin is preferably substantially free of hydrogen atoms, and more preferably, all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. That is, the first fluorinated polymer is preferably substantially free of hydrogen atoms and is perfluorinated. In this specification, "substantially free of hydrogen atoms" means that the hydrogen atom content in the fluorinated polymer is less than 1 mol%.

[0035] The first fluoropolymer preferably has a fluorinated aliphatic ring structure. The fluorinated aliphatic ring structure may be contained in the main chain of the fluoropolymer or in the side chain of the first fluoropolymer. The first fluoropolymer, for example, has a constituent unit (A) represented by the following structural formula (1). [Chemistry 1]

[0036] In formula (1), Rff1 to Rff4 each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. Rff1 and Rff2 can also be linked to form a ring. "Perfluoro" means that all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. In formula (1), the perfluoroalkyl group preferably has 1 to 5 carbon atoms, more preferably 1 to 3, and even more preferably 1. The perfluoroalkyl group can be linear or branched. Examples of perfluoroalkyl groups include trifluoromethyl, pentafluoroethyl, and heptafluoropropyl.

[0037] In formula (1), the number of carbon atoms in the perfluoroalkyl ether group is preferably 1 to 5, more preferably 1 to 3. The perfluoroalkyl ether group can be linear or branched. Examples of perfluoroalkyl ether groups include perfluoromethoxymethyl.

[0038] When Rff1 and Rff2 are linked to form a ring, the ring can be a 5-membered ring or a 6-membered ring. Examples of such rings include perfluorotetrahydrofuran rings, perfluorocyclopentane rings, and perfluorocyclohexane rings.

[0039] As a specific example of a constituent unit (A), the constituent units represented by the following formulas (A1) to (A8) can be cited. [Chemistry 5]

[0040] Among the constituent units represented by the above formulas (A1) to (A8), constituent unit (A) is preferably constituent unit (A2), that is, the constituent unit represented by the following formula (5). [Chemistry 6]

[0041] The first fluoropolymer may contain one or more constituent units (A). In the first fluoropolymer, the content of constituent unit (A) relative to the total number of constituent units is preferably 20 mol% or more, more preferably 40 mol% or more. By containing 20 mol% or more of constituent unit (A), the first fluoropolymer tends to have higher heat resistance. When containing 40 mol% or more of constituent unit (A), the first fluoropolymer, in addition to higher heat resistance, also tends to have higher transparency and higher mechanical strength. In the first fluoropolymer, the content of constituent unit (A) relative to the total number of constituent units is preferably 95 mol% or less, more preferably 70 mol% or less.

[0042] The constituent unit (A) is, for example, derived from the compound represented by the following formula (6). In formula (6), Rff1 to Rff4 are the same as in formula (1). Furthermore, the compound represented by formula (6) can be obtained, for example, by a known manufacturing method, represented by the manufacturing method disclosed in Japanese Patent Publication No. 2007-504125. [Chemistry 7]

[0043] As a specific example of the compound represented by the above formula (6), for example, the compounds represented by the following formulas (M1) to (M8) can be cited. [Chemistry 8]

[0044] In addition to unit (A), fluoropolymers may also contain other constituent units. Examples of other constituent units include (B) to (D).

[0045] The constituent unit (B) is represented by the following formula (2). [Chemistry 2]

[0046] In formula (2), R1 to R3 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. R4 represents a perfluoroalkyl group having 1 to 7 carbon atoms. Perfluoroalkyl groups may have a cyclic structure. Part of the fluorine atom may be replaced by a halogen atom other than the fluorine atom. Part of the fluorine atom in a perfluoroalkyl group may also be replaced by a halogen atom other than the fluorine atom.

[0047] Fluoropolymers may contain one or more constituent units (B). In fluoropolymers, the content of constituent unit (B) is preferably 5 to 10 mol% relative to the total number of constituent units. The content of constituent unit (B) may be less than 9 mol% or less than 8 mol%.

[0048] The constituent unit (B) is, for example, derived from a compound represented by the following formula (7). In formula (7), R1 to R4 are the same as in formula (2). The compound represented by formula (7) is a fluorinated vinyl ether such as a perfluoroethylene ether. [Chemistry 9]

[0049] The constituent unit (C) is represented by the following formula (3). [Chemistry 3]

[0050] In formula (3), R5 to R8 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may have a cyclic structure. Part of the fluorine atom may be replaced by a halogen atom other than the fluorine atom. Part of the fluorine atom in the perfluoroalkyl group may also be replaced by a halogen atom other than the fluorine atom.

[0051] Fluoropolymers may contain one or more constituent units (C). In fluoropolymers, the content of constituent unit (C) relative to the total number of constituent units is preferably 5 to 10 mol%. The content of constituent unit (C) may be less than 9 mol or less than 8 mol.

[0052] The constituent unit (C) is, for example, derived from the compound represented by the following formula (8). In formula (8), R5 to R8 are the same as in formula (3). The compound represented by formula (8) is a fluorinated olefin such as tetrafluoroethylene and trifluorochloroethylene. [Chemistry 10]

[0053] The constituent unit (D) is represented by the following equation (4). [Chemistry 4]

[0054] In formula (4), Z represents an oxygen atom, a single bond, or -OC(R 19R 20)O-, and R 9 to R 20 each independently represent a fluorine atom, a perfluoroalkyl group with 1 to 5 carbon atoms, or a perfluoroalkoxy group with 1 to 5 carbon atoms. Part of the fluorine atom can be replaced by a halogen atom other than the fluorine atom. Part of the fluorine atom in the perfluoroalkyl group can be replaced by a halogen atom other than the fluorine atom. Part of the fluorine atom in the perfluoroalkoxy group can also be replaced by a halogen atom other than the fluorine atom. s and t each independently represent 0 to 5 and s+t is an integer from 1 to 6 (wherein, in the case of Z being -OC(R 19R 20)O-, s+t can also be 0).

[0055] The constituent unit (D) is preferably represented by the following equation (9). Furthermore, the constituent unit represented by the following equation (9) is the case where Z is an oxygen atom, s is 0 and t is 2 in the above equation (4). [Chemistry 11]

[0056] In formula (9), R 141, R 142, R 151, and R 152 each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. A portion of the fluorine atom may be substituted with a halogen atom other than the fluorine atom. A portion of the fluorine atom in the perfluoroalkyl group may be substituted with a halogen atom other than the fluorine atom. A portion of the fluorine atom in the perfluoroalkoxy group may also be substituted with a halogen atom other than the fluorine atom.

[0057] Fluoropolymers may contain one or more constituent units (D). In fluoropolymers, the content of constituent units (D) relative to the total number of constituent units is preferably 30 to 67 mol%. The content of constituent units (D) may be, for example, 35 mol% or more, 60 mol% or less, or 55 mol% or less.

[0058] The constituent unit (D) is, for example, derived from a compound represented by the following formula (10). In formula (10), Z, R9~R18, s, and t are the same as in formula (4). The compound represented by formula (10) is a fluorinated compound having two or more polymerizable double bonds and capable of cyclization polymerization. [Chemistry 12]

[0059] The constituent unit (D) is preferably derived from the compound represented by the following formula (11). In formula (11), R 141, R 142, R 151 and R 152 are the same as those in formula (9). [Chemistry 13]

[0060] As specific examples of compounds represented by formula (10) or formula (11), the following compounds can be cited. CF 2 = CFOCF 2CF = CF 2 CF 2 = CFOCF(CF 3) CF = CF 2 CF 2 = CFOCF 2CF 2CF = CF 2 CF 2 = CFOCF 2CF(CF 3)CF = CF 2 CF 2 = CFOCF(CF 3) CF 2CF = CF 2 CF 2=CFOCFClCF 2CF=CF 2 CF 2=CFOCCl 2CF 2CF=CF 2 CF² = CFOCF² + 2OCF = CF² CF² = CFOC(CF³) 2OCF = CF² CF 2 = CFOCF 2CF(OCF 3)CF = CF 2 CF 2=CFCF 2CF=CF 2 CF 2=CFCF 2CF 2CF=CF 2 CF² = CFCF² + 2OCF² + 2CF = CF² CF 2=CFOCF 2CFClCF=CF 2 CF 2 = CFOCF 2CF 2CCl = CF 2 CF 2=CFOCF 2CF 2CF=CFCl CF 2 = CFOCF 2CF(CF 3)CCl = CF 2 CF² = CFOCF² + 2OCF = CF² CF² = CFOCCl 2OCF = CF² CF 2=CClOCF 2OCCl=CF 2

[0061] Although the first fluoropolymer may further include other constituent units besides (A) to (D), it is preferable that it substantially does not contain other constituent units besides (A) to (D). Furthermore, the statement that the fluoropolymer substantially does not contain other constituent units besides (A) to (D) means that, relative to the total number of constituent units in the fluoropolymer, the total of constituent units (A) to (D) is 95 mol% or more, preferably 98 mol% or more.

[0062] The polymerization method for the first fluoropolymer is not particularly limited; for example, general polymerization methods such as free radical polymerization can be used. The polymerization initiator used to polymerize the fluoropolymer can be a perfluorinated compound.

[0063] The first fluoropolymer constitutes the first fluoropolymer used as the first resin. As described above, the first glass transition temperature Tg 1 of the first resin is 120°C or higher. Therefore, the glass transition temperature of the first fluoropolymer is preferably 120°C or higher, more preferably 125°C or higher, and even more preferably 130°C or higher.

[0064] The higher the refractive index of the core 11 compared to the cladding 12, the better; therefore, there is no particular limitation. To achieve a higher aperture number in the POF 10, it is preferable that the difference between the refractive index of the core 11 and the refractive index of the cladding 12 is greater at the wavelength of the light used. For example, at the wavelength of the light used (e.g., 850 nm), the refractive index of the core 11 can be 1.340 or higher, or 1.360 or higher. There is no particular upper limit to the refractive index of the core; for example, it can be below 1.4000.

[0065] (Clad 12) As described above, in the POF10 of this embodiment, the coating 12 includes a second resin. The coating 12 may also include the second resin as a main component. Here, "the coating 12 includes the second resin as a main component" means that the second resin is the component contained in the coating 12 in the largest mass percentage. The coating 12 may contain 80% or more, 90% or more, or 95% or more of the second resin. The coating 12 may be composed solely of the second resin. The coating 12 may also include additives in addition to the second resin.

[0066] The second resin included in the cladding 12 is not particularly limited, as long as it is a resin with high transparency. Examples of the second resin include: fluorinated resins, acrylic resins such as methyl methacrylate, styrene resins, and carbonate resins. Among these, fluorinated resins are suitable because they can achieve low transmission loss over a wide wavelength range.

[0067] The second resin of the coating layer 12 is preferably a fluorinated resin containing a fluorinated polymer. Hereinafter, the fluorinated resin contained in the coating layer 12 will be referred to as the second fluorinated resin, and the fluorinated polymer contained in the second fluorinated resin will be referred to as the second fluorinated polymer.

[0068] Examples of fluorinated resins that can be used as the second fluorinated resin are the same as those exemplified as the first fluorinated resin. That is, examples of fluorinated polymers that can be used as the second fluorinated polymer are the same as those exemplified as the first fluorinated polymer.

[0069] The second fluoropolymer constitutes the second fluoropolymer used as the second resin. As described above, the second glass transition temperature Tg 2 of the second resin is 120°C or higher. Therefore, the glass transition temperature of the second fluoropolymer is preferably 120°C or higher, more preferably 125°C or higher, and even more preferably 130°C or higher.

[0070] The second resin can be a different resin from the first resin, but preferably has an affinity for the first resin. For example, the second resin can contain polymeric units that are the same as those contained in the first resin, or it can be the same as the first resin. In this way, delamination is less likely to occur at the interface between the core 11 and the cladding 12, for example, transmission loss can be suppressed to a lower level.

[0071] The refractive index of the cladding 12 can be designed based on the refractive index of the core 11, and therefore there is no particular limitation. The cladding 12 may have a refractive index of less than 1.310 or less than 1.300 at the wavelength of the light used (e.g., 850 nm).

[0072] Figure 2 shows a variation of the POF of this embodiment. Compared to POF10, the POF20 shown in Figure 2 has a structure in which a reinforcing layer 21 is further provided on the outer periphery of the cladding 12. The reinforcing layer 21 is provided to improve the mechanical strength of POF10. For the reinforcing layer 21, for example, materials and structures known for reinforcing layers in POFs can be used. Examples of materials for the reinforcing layer 21 include various engineering plastics such as polycarbonate, polyesters, cyclic olefin polymers, cyclic olefin copolymers, polytetrafluoroethylene (PTFE), modified PTFE, and tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), or copolymers or mixtures thereof.

[0073] The POF20 of this embodiment, which has a reinforcing layer 21, can achieve a dimensional retention rate of 95% or higher after being held at 105°C for 250 hours. Furthermore, the POF20 of this embodiment can also achieve a dimensional retention rate of 96% or higher, or even 98% or higher, after being held at 105°C for 250 hours. Here, the dimensional retention rate refers to the ratio of the length of the POF20 after being held at 105°C for 250 hours to the length of the POF20 before being held at 105°C for 250 hours.

[0074] Since the POF of this embodiment possesses both heat resistance and flexibility, it can also be applied to applications requiring a high degree of heat resistance and flexibility. The POF of this embodiment is also suitable for, for example, hybrid cables, repeater cables, and active optical cables.

[0075] Figure 3 is a cross-sectional view showing an example of a hybrid cable equipped with the POF20 of this embodiment. The hybrid cable 30 shown in Figure 3 includes: the POF20 of this embodiment, a plurality of conductors 31 disposed around the POF20, and a coating layer 32 covering the POF20 and the conductors 31.

[0076] Figure 4 is a schematic diagram showing an example of a repeater cable equipped with the POF20 of this embodiment. The repeater cable 40 shown in Figure 4 includes: a cable 41 that houses the POF20 of this embodiment; and a connector 42 that is installed at at least one end of the cable 41.

[0077] Figure 5 is a schematic diagram showing an example of an active optical cable equipped with the POF20 of this embodiment. The active optical cable 50 shown in Figure 5 includes: a cable 51 that houses the POF20 of this embodiment; a first connector 52 that is installed at a first end 51a of the cable 51 and has a first conversion section (not shown) for converting electrical signals into optical signals; and a second connector 53 that is installed at a second end 51b of the cable 51 and has a second conversion section (not shown) for converting optical signals into electrical signals.

[0078] (Manufacturing method of POF) The POF in this embodiment is manufactured, for example, using melt spinning. That is, one example of the manufacturing method of the POF in this embodiment includes: The core material is melted and extruded into a fibrous shape to create a fibrous molded body containing the aforementioned core material; The cladding material is melted and extruded to cover the surface of the molded body, thereby creating a laminate in which the core material and the cladding material are stacked in a concentric circle; and The laminated body is heated to a specific temperature and stretched, and then spun. The core material comprises a first resin, and the cladding material comprises a second resin.

[0079] Regarding the POF of this embodiment, both the first resin contained in the core and the second resin contained in the cladding have a high glass transition temperature of 120°C or higher, and also possess excellent flexibility, for example, a minimum radius of curvature of 5 mm or less. To achieve this excellent flexibility using resins with high glass transition temperatures, it is preferable, for example, that the first and second resins in the core and cladding have high alignment. To manufacture a core and cladding in which the molecular chains of the first and second resins are highly aligned along the fiber axis, for example, the stretching temperature of the laminated core and cladding materials in a concentric circle shape is set to a temperature at which the molecular chains of the first and second resins are highly aligned along the fiber axis. The stretching temperature of the laminate is typically determined taking into account the glass transition temperatures of the core and cladding materials. In contrast, in this embodiment, to ensure that the molecular chains of the first and second resins are highly aligned along the fiber axis, it is preferable to set the stretching temperature of the laminate to be lower than the previously common stretching temperature determined based on the glass transition temperatures of the core and cladding materials. The stretching temperature of the laminate can be determined by considering the glass transition temperatures of the first and second resins used, as well as the content ratio of additives such as refractive index modifiers contained in the core material, and is therefore not particularly limited. Ideally, it should be low enough not to cause breakage of the manufactured POF.

[0080] Relative to the first glass transition temperature Tg 1 of the first resin, the stretching temperature of the laminate is preferably in the range of Tg 1+50℃ to Tg 1+150℃, more preferably in the range of Tg 1+70℃ to Tg 1+140℃. Similarly, relative to the second glass transition temperature Tg 2 of the second resin, the stretching temperature of the laminate is preferably in the range of Tg 2+50℃ to Tg 2+150℃, more preferably in the range of Tg 1+70℃ to Tg 1+140℃. When the core material contains a refractive index modifier, and the core material is a resin composition containing the first resin and the refractive index modifier, the stretching temperature relative to the glass transition temperature Tg 1a of the resin composition is preferably in the range of Tg 1a+60℃ to Tg 1a+170℃, more preferably in the range of Tg 1a+80℃ to Tg 1a+160℃. Ideally, a suitable temperature is selected from the preferred temperature range described above, determined by the first glass transition temperature Tg 1 of the first resin used, the glass transition temperature Tg 1a of the resin composition containing the first resin and the refractive index modifier, and the second glass transition temperature Tg 2 of the second resin, and set as the stretching temperature. By setting this stretching temperature, for example, it is possible to manufacture POFs with a birefringence of 2.0 × 10⁻⁴ or higher, i.e., the first resin and the second resin are highly aligned in the fiber axis direction, such as a core and cladding fiber structure.

[0081] Figure 6 is a schematic cross-sectional view of an example of a manufacturing apparatus that can be used to manufacture the POF20 embodiment of the present invention.

[0082] The apparatus 100 shown in Figure 6 includes a first extrusion apparatus 101a for core formation, a second extrusion apparatus 101b for cladding formation, and a third extrusion apparatus 101c for reinforcing layer formation. The apparatus 100 further includes a first chamber 110 and a second chamber 120. The first chamber 110 and the second chamber 120 are arranged sequentially downward in the vertical direction.

[0083] The first extrusion apparatus 101a has a first receiving portion 102a for receiving core material 1a and a first extrusion portion 103a for extruding the core material 1a contained in the first receiving portion 102a from the first receiving portion 102a. The first extrusion apparatus 101a may further be provided with a heating element (not shown) such as a heater, so that the core material 1a can be melted in the first receiving portion 102a, thereby maintaining the molten core material 1a in a molten state before molding. In this case, for example, a rod-shaped core material (preform) 1a is inserted into the first receiving portion 102a through an opening at the top of the first receiving portion 102a, and melted by heating within the first receiving portion 102a.

[0084] In the first extrusion apparatus 101a, core material 1a is extruded outward from the first receiving portion 102a via the first extrusion portion 103a, for example, by gas extrusion, to form core 2. The core material 1a extruded via the first extrusion portion 103a to form core 2 then moves downward in a vertical direction and is sequentially supplied to the first chamber 110 and the second chamber 120.

[0085] The second extrusion apparatus 101b has a second receiving section 102b for receiving cladding material 1b and a second extrusion section 103b for extruding the cladding material 1b received in the second receiving section 102b. The second extrusion apparatus 101b extrudes molten cladding material 1b to cover the outer periphery of a core 2 formed from core material 1a extruded from the first extrusion apparatus 102a. Specifically, the cladding material 1b extruded from the second extrusion apparatus 101b is supplied to the first chamber 110. In the first chamber 110, by covering the core 2 formed from core material 1a with cladding material 1b, a cladding 3 covering the outer periphery of the core 2 can be formed. The laminate formed by the core 2 and the cladding 3 covering the outer periphery of the core 2 moves from the first chamber 110 to the second chamber 120.

[0086] The third extrusion apparatus 101c includes, for example, a third receiving section 102c that receives the reinforcing layer material 1c; a screw 104 disposed within the third receiving section 102c; and a funnel 105 connected to the third receiving section 102c. In the third extrusion apparatus 101c, for example, granular reinforcing layer material 1c is supplied to the third receiving section 102c through the funnel 105. The reinforcing layer material 1c supplied to the third receiving section 102c is, for example, heated while being kneaded using the screw 104, thereby softening it and making it flowable. The softened reinforcing layer material 1c is extruded from the third receiving section 102c using the screw 104.

[0087] The reinforcing layer material 1c extruded from the third extrusion device 101c is supplied to the second chamber 120. In the second chamber 120, a reinforcing layer 4 is formed on the outer periphery of the covered layer 3 by covering the surface of the laminate formed by the core 2 and the cladding 3 with the reinforcing layer material 1c.

[0088] A laminate 5, consisting of a core 2, a cladding layer 3, and a reinforcing layer 4 stacked concentrically, moves from the second chamber 120 toward a diffuser 130 disposed vertically below the second chamber 120. A heater (not shown) for heating the laminate can be disposed in the diffuser 130, for example. The temperature and viscosity of the laminate 5 passing through the diffuser 130 are appropriately adjusted, for example. Ideally, the stretching temperature of the laminate 5 passing through the diffuser 130 is set to the aforementioned temperature range. That is, relative to the first glass transition temperature Tg 1 of the first resin constituting the core material 1a, the stretching temperature of the laminate 5 in the diffuser 130 is preferably in the range of Tg 1+50℃ to Tg 1+150℃, and more preferably in the range of Tg 1+70℃ to Tg 1+140℃. Furthermore, relative to the second glass transition temperature Tg 2 of the second resin constituting the cladding material, the stretching temperature of the laminate 5 is preferably in the range of Tg 2+50℃ to Tg 2+150℃, and more preferably in the range of Tg 1+70℃ to Tg 1+140℃. Also, relative to the glass transition temperature Tg 1a of the resin composition serving as the core material 1a, the stretching temperature of the laminate 5 is preferably in the range of Tg 1a+60℃ to Tg 1a+170℃, and more preferably in the range of Tg 1a+80℃ to Tg 1a+160℃. The diffuser 130 allows dopants such as refractive index modifiers contained in the laminate 5, which pass through the interior of the diffuser 130, to diffuse within the laminate 5.

[0089] The diffuser tube 130 is connected to the internal flow path of the nozzle 140. That is, the lower opening of the diffuser tube 130 is connected to the inlet of the nozzle 140, and the laminated body 5 of the diffuser tube 130 flows into the internal flow path through the inlet of the nozzle 140. After passing through the internal flow path, the diameter of the laminated body 5 decreases, and it is ejected from the outlet of the nozzle 140 in a fibrous form.

[0090] The positions of the second chamber 120 and the diffuser tube 130 can be interchanged. That is, it can be a device in which the diffuser tube 130 is arranged below the first chamber 110, the second chamber 120 is arranged below it, and the nozzle 140 is arranged further below the second chamber.

[0091] The fibrous deposit 5 ejected from the nozzle 140 flows into the internal space 151 of the condenser tube 150, where it is cooled as it passes through the internal space 151, and is then released from the opening to the outside of the condenser tube 150. The fibrous deposit 5 released from the condenser tube 150 passes between the two rollers 161 and 162 of the clamping roller 160, and then passes through the guide rollers 163-165, where it is wound up as POF20 by the take-up roller 166. Near the take-up roller 166, for example between the guide roller 165 and the take-up roller 166, a displacement gauge 170 for measuring the outer diameter of the POF20 may be provided. [Example]

[0092] The present invention will now be described in detail with reference to examples and comparative examples, but the present invention is not limited thereto.

[0093] (Example 1) [Preparation of Fluorine-Containing Resin 1 and Fluorine-Containing Resin 2] As the first and second fluorinated resins, polymers of perfluoro-4-methyl-2-methylene-1,3-dioxolane (the compound of formula (M2) above, "PFMMD") are prepared. Perfluoro-4-methyl-2-methylene-1,3-dioxolane is synthesized by first synthesizing 2-carboxymethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, fluorinating it, and then decarboxylating the resulting carboxylate. Perfluorobenzoyl peroxide is used as a polymerization initiator in the polymerization of perfluoro-4-methyl-2-methylene-1,3-dioxolane.

[0094] The synthesis of 2-carboxymethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, the fluorination of 2-carboxymethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, the synthesis of perfluoro-4-methyl-2-methylene-1,3-dioxolane, and the polymerization of perfluoro-4-methyl-2-methylene-1,3-dioxolane are described in detail below.

[0095] Synthesis of 2-carboxymethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane Prepare a 3 L three-necked flask equipped with a water-cooled condenser, a thermometer, a magnetic stirrer, and an isobaric dropping funnel. Add 139.4 g (1.4 moles) of a mixture of 2-chloro-1-propanol and 1-chloro-2-propanol to the flask. Cool the flask to 0°C, slowly add methyl trifluoropyruvate, and stir for 2 hours. After 1 hour, add 100 mL of dimethyl sulfoxide (DMSO) and 194 g of potassium carbonate, and continue stirring for 8 hours to obtain a reaction mixture. Mix the resulting reaction mixture with 1 L of water, separate the aqueous phase, and extract it with dichloromethane. Mix the dichloromethane solution with the organic reaction mixture phase, and dry the solution with magnesium sulfate. After solvent removal, 245.5 g of crude product is obtained. The crude product was fractionated under reduced pressure (12 Torr) to obtain 230.9 g of purified 2-carboxymethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane. The boiling point of the purified product was 77-78 °C, and the yield was 77%. Furthermore, the purified product was confirmed to be 2-carboxymethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane by ¹H NMR and ¹⁹F NMR.

[0096] HNMR (ppm): 4.2-4.6,3.8-3.6 (CHCH 2, muliplet, 3H), 3.85-3.88 (COOCH 3, multiplet, 3H), 1.36-1.43 (CCH 3, multiplet, 3H) 19FNMR (ppm): -81.3 (CF 3, s, 3F)

[0097] Fluorination of 2-carboxymethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane> 4 L of 1,1,2-trichlorotrifluoroethane was injected into a 10 L stirred reactor. Nitrogen gas was introduced into the reactor at a flow rate of 1340 cc / min, and fluorine gas was introduced at a flow rate of 580 cc / min to create a nitrogen / fluorine atmosphere. After 5 minutes, 290 g of the previously prepared 2-carboxymethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane was dissolved in 750 mL of 1,1,2-trichlorotrifluoroethane solution, and this solution was added to the reactor at a rate of 0.5 mL / min. The reactor was cooled to 0°C. After 24 hours of adding all the dioxolane, the fluorine gas flow was stopped. After purging with nitrogen, potassium hydroxide aqueous solution was added until the solution became weakly alkaline.

[0098] After removing volatile substances under reduced pressure, the reaction vessel was cooled, and then dried at 70°C under reduced pressure for 48 hours to obtain a solid reaction product. The solid reaction product was dissolved in 500 mL of water, and excess hydrochloric acid was added to separate it into an organic phase and an aqueous phase. The organic phase was separated and distilled under reduced pressure to give perfluoro-2,4-dimethyl-1,3-dioxolane-2-carboxylic acid. The boiling point of the main distillate was 103-106°C / 100 mmHg. The fluorination yield was 85%.

[0099] Synthesis of perfluoro-4-methyl-2-methylene-1,3-dioxolane The distillate was neutralized with an aqueous solution of potassium hydroxide to give potassium perfluoro-2,4-dimethyl-2-carboxylate-1,3-dioxolane. The potassium salt was dried under vacuum at 70 °C for one day. The salt was then decomposed at 250–280 °C under a nitrogen or argon atmosphere. Condensation was achieved using a freeze trap cooled to -78 °C, yielding perfluoro-4-methyl-2-methylene-1,3-dioxolane in 82% yield. The product had a boiling point of 45 °C / 760 mmHg. The product was identified using 19F NMR and GC-MS.

[0100] 19FNMR: -84 ppm (3F, CF 3), -129 ppm (2F, =CF 2) GC-MS: m / e 244 (molecular ion) 225, 197, 169, 150, 131, 100, 75, 50.

[0101] Polymerization of perfluoro-4-methyl-2-methylene-1,3-dioxolane 100 g of perfluoro-4-methyl-2-methylene-1,3-dioxolane and 1 g of perfluorobenzoyl peroxide obtained by the above method were sealed in a glass tube. The glass tube was then degassed by cryogenic degassing, and subsequently filled with argon gas and heated at 50°C for several hours. Although the contents were solid, further heating at 70°C overnight yielded 100 g of a transparent rod-shaped object.

[0102] The obtained transparent rod-shaped material was dissolved in Fluorinert FC-75 (manufactured by Sumitomo 3M Corporation), and the resulting solution was poured onto a glass plate to obtain a polymer film. The resulting polymer had a glass transition temperature of 117°C and was completely amorphous. The transparent rod-shaped material was dissolved in hexafluorobenzene, and chloroform was added to precipitate it, thereby purifying the product. The purified polymer had a glass transition temperature of approximately 131°C. This polymer was used as the first and second fluorinated resins.

[0103] [Refractive index adjuster] The refractive index adjuster uses trifluorochloroethylene oligomer (molecular weight 585). Specifically, "DAIFLOIL#10" manufactured by Daikin Industries, Ltd. is distilled, and only the component with a molecular weight of 585 is extracted for use.

[0104] [Core Materials] The first fluorinated resin prepared by the above method and the above refractive index adjuster are melt-mixed at 260°C to prepare a resin composition. The concentration of the refractive index adjuster in the resin composition is 3% by mass. This resin composition is used as a core material.

[0105] Cladding material The second fluorinated resin produced by the above method will be used as the coating material.

[0106] [Reinforcement layer material] Xylex (manufactured by SABIC, glass transition temperature: 113°C) was used as the reinforcing layer material.

[0107] [POF] A POF with the same structure as POF20 shown in Figure 2 was fabricated. Using the core material, cladding material, and reinforcing layer prepared by the above method, a POF with the same structure as POF20 shown in Figure 2 was fabricated by melt spinning. The manufacturing apparatus 100 shown in Figure 6 was used in the fabrication of the POF. The melting temperature of the core material was 250°C, the melting temperature of the cladding material was 255°C, and the melting temperature of the reinforcing layer material was 240°C. Furthermore, the temperature of the diffuser tube was set to 220°C. That is, the stretching temperature of the laminate including the core, cladding, and reinforcing layer was 220°C. In the obtained POF, the outer diameter of the core was 80 μm, the outer diameter of the cladding was 125 μm, and the outer diameter of the reinforcing layer (i.e., the outer diameter of the POF) was 490 μm.

[0108] [Evaluation of the orientation of fiber structures including core and cladding] The alignment was evaluated by measuring birefringence. The reinforcing layer was removed from the fabricated POF, yielding a fiber structure comprising a core and cladding. The reinforcing layer was removed by immersing the POF in dichloromethane, dissolving only the reinforcing layer. The birefringence of the fiber structure was measured from the side of the fiber structure using a "WPA-micro" instrument manufactured by Photonic Lattice. The results of the birefringence measurements are shown in Table 1.

[0109] [Evaluation of flexibility] For the fabricated POF, 180-degree bending tests were conducted at 25°C with curvature radii R = 10 mm, 5 mm, 2.5 mm, 2 mm, and 1 mm. Test apparatus with grooves having curvature radii R = 10 mm, 5 mm, 2.5 mm, 2 mm, or 1 mm was prepared. POF was placed in the grooves and bent to 180 degrees, then returned to its original shape. The bent portion of the POF was then observed using a microscope (200x magnification) to confirm the presence or absence of cracks. The POF was bent once at each curvature radius. The results of the bending tests are shown in Table 1. In Table 1, "○" indicates no cracks were detected, and "×" indicates cracks were detected.

[0110] [Evaluation of heat resistance] The fabricated POF was cut into 1-meter lengths and placed in an oven at 105°C. After 250 hours, the POF was removed and its length was measured. The ratio of the length after 250 hours at 105°C to the length of the POF before 250 hours at 105°C was calculated as the dimensional retention rate. The dimensional retention rates are shown in Table 1.

[0111] (Example 2) In the fabrication of the POF, the temperature of the diffuser tube was set to 230°C. Apart from this, the POF was fabricated using the same method as in Example 1. In the resulting POF, the outer diameter of the core was 80 μm, the outer diameter of the cladding was 125 μm, and the outer diameter of the reinforcing layer (i.e., the outer diameter of the POF) was 490 μm. Furthermore, the characteristics of the resulting POF were evaluated using the same method as in Example 1. The results are shown in Table 1.

[0112] (Example 3) In the fabrication of the POF, the temperature of the diffuser tube was set to 260°C. The concentration of the refractive index modifier in the core material was set to 8% by mass. The POF was fabricated with an outer diameter of 52 μm for the core, 55 μm for the cladding, and 232 μm for the reinforcing layer (i.e., the outer diameter of the POF). Except for these aspects, the POF was fabricated using the same method as in Example 1. Furthermore, the characteristics of the obtained POF were evaluated using the same method as in Example 1. The results are shown in Table 1.

[0113] (Example 4) In the fabrication of the POF, the temperature of the diffuser tube was set to 260°C. The concentration of the refractive index modifier in the core material was set to 12% by mass. The POF was fabricated with an outer diameter of 47 μm for the core, 49 μm for the cladding, and 232 μm for the reinforcing layer (i.e., the outer diameter of the POF). Except for these aspects, the POF was fabricated using the same method as in Example 1. Furthermore, the characteristics of the obtained POF were evaluated using the same method as in Example 1. The results are shown in Table 1.

[0114] (Comparative Example 1) As Comparative Example 1, the POF "Giga-POF62SR" manufactured by Chromis Fiberoptics was used for evaluation of flexibility and heat resistance. In Comparative Example 1, the outer diameter of the core was 62.5 μm, the outer diameter of the cladding was 90 μm, and the outer diameter of the reinforcing layer (i.e., the outer diameter of the POF) was 490 μm. In Comparative Example 1, the resins used as the first and second fluorinated resins were perfluorobutenyl vinyl ether (PBVE) polymers. Furthermore, the refractive index modifier used was perfluoro-1,3,5-triphenylbenzene. The reinforcing layer material was Xylex (manufactured by SABIC Corporation, glass transition temperature: 113°C).

[0115] [Evaluation of each feature] Each characteristic was evaluated using the same method as in Example 1.

[0116] (Comparative Example 2) In the fabrication of the POF, the temperature of the diffuser tube was set to 250°C. Apart from this, the POF was fabricated using the same method as in Example 1. In the resulting POF, the outer diameter of the core was 80 μm, the outer diameter of the cladding was 125 μm, and the outer diameter of the reinforcing layer (i.e., the outer diameter of the POF) was 490 μm. Furthermore, the characteristics of the resulting POF were evaluated using the same method as in Example 1. The results are shown in Table 1.

[0117] (Comparative Example 3) The concentration of the refractive index modifier in the core material was set to 10% by mass, and the temperature of the diffuser tube was set to 230°C during the fabrication of the POF. Except for these aspects, the POF was fabricated using the same method as in Example 1. In the resulting POF, the outer diameter of the core was 80 μm, the outer diameter of the cladding was 125 μm, and the outer diameter of the reinforcing layer (i.e., the outer diameter of the POF) was 490 μm. Furthermore, the characteristics of the resulting POF were evaluated using the same method as in Example 1. The results are shown in Table 1.

[0118] (Comparative Example 4) Except for the following aspects, POF is produced by the same method as in Example 1. • Set the concentration of the refractive index modifier in the core material to 10 by mass. • As a reinforcing layer material, DURABIO T-7450 (manufactured by Mitsubishi Chemical Corporation, glass transition temperature: 129°C) is used. • Set the melting temperature of the reinforcing layer material to 230℃. • In the fabrication of POF, the temperature of the diffuser tube is set to 230℃.

[0119] In the obtained POF, the outer diameter of the core is 80 μm, the outer diameter of the cladding is 125 μm, and the outer diameter of the reinforcing layer (i.e., the outer diameter of the POF) is 490 μm.

[0120] Each characteristic was evaluated using the same method as in Example 1. The results are shown in Table 1.

[0121] (Comparative Example 5) Except for the following aspects, POF was produced by the same method as in Example 1. • Set the concentration of the refractive index modifier in the core material to 10 by mass. • As a reinforcing layer material, DURABIO T-7450 (manufactured by Mitsubishi Chemical Corporation, glass transition temperature: 129°C) is used. • Set the melting temperature of the reinforcing layer material to 230℃ • In the fabrication of POF, the temperature of the diffuser tube is set to 240℃.

[0122] In the obtained POF, the outer diameter of the core is 80 μm, the outer diameter of the cladding is 125 μm, and the outer diameter of the reinforcing layer (i.e., the outer diameter of the POF) is 490 μm.

[0123] Each characteristic was evaluated using the same method as in Example 1. The results are shown in Table 1.

[0124] [Table 1] Core material / cladding material Reinforcement layer Material Orientation evaluation Flexibility evaluation (180-degree bending test) Heat resistance evaluation First Resin Second resin Core materials Tg Core + Cladding Birefringence radius of curvature Minimum radius of curvature size Retention rate (%) 10 mm 5 mm 2.5 mm 2 mm 1 mm Example 1 PFMMD polymer (Tg: 131℃) 125℃ Xylex 6.6×10⁻⁴ ○ ○ ○ ○ × Less than 2 mm 96.6 Example 2 PFMMD polymer (Tg: 131℃) 125℃ Xylex 2.7×10⁻⁴ ○ ○ × × × Less than 5 mm 98.9 Example 3 PFMMD polymer (Tg: 131℃) 116℃ Xylex 3.0×10⁻⁴ ○ ○ ○ ○ ○ Less than 1 mm 96.2 Example 4 PFMMD polymer (Tg: 131℃) 107℃ Xylex 2.2×10⁻⁴ ○ ○ ○ ○ ○ Less than 1 mm 96.8 Comparative Example 1 PBVE polymer (Tg: 108℃) unknown Xylex 2.0×10⁻⁴ ○ ○ ○ ○ × Less than 2 mm 94.4 Comparative Example 2 PFMMD polymer (Tg: 131℃) 125℃ Xylex 0.5×10⁻⁴ ○ × × × × More than 5 mm 99.4 Comparative Example 3 PFMMD polymer (Tg: 131℃) 110℃ Xylex 1.9×10⁻⁴ ○ × × × × More than 5 mm 98.8 Comparative Example 4 PFMMD polymer (Tg: 131℃) 110℃ DURABIO 1.8×10⁻⁴ ○ × × × × More than 5 mm 99.2 Comparative Example 5 PFMMD polymer (Tg: 131℃) 110℃ DURABIO 0.6×10⁻⁴ ○ × × × × More than 5 mm 99.4

[0125] [Table 2] Outer diameter of cladding (diameter) Orientation (Core + Cladding Birefringence) Orientation÷ Outer diameter of the cladding (radius (unit: μm)) Example 1 125 μm 6.6×10⁻⁴ 1.1×10⁻⁵ Example 2 125 μm 2.7×10⁻⁴ 4.4×10⁻⁶ Example 3 55 μm 3.0×10⁻⁴ 1.1×10⁻⁵ Example 4 49 μm 2.2×10⁻⁴ 9.0×10⁻⁶ Comparative Example 1 62.5 μm 2.0×10⁻⁴ 6.2×10⁻⁶ Comparative Example 2 125 μm 0.5×10⁻⁴ 8.0×10⁻⁷ Comparative Example 3 125 μm 1.9×10⁻⁴ 3.0×10⁻⁶ Comparative Example 4 125 μm 1.8×10⁻⁴ 2.9×10⁻⁶ Comparative Example 5 125 μm 0.6×10⁻⁴ 9.9×10⁻⁷

[0126] The POFs of Examples 1-4 achieved dimensional stability of over 95% while ensuring flexibility with a minimum radius of curvature of less than 5 mm, even after prolonged exposure to 105°C. Regarding the POFs of Examples 1 and 2, the fiber structure including the core and cladding has a birefringence of 2.2 × 10⁻⁴ or higher, and the resin is highly oriented along the fiber axis. It is believed that this structure allows the POFs of Examples 1-4 to improve heat resistance while ensuring good flexibility. On the other hand, the POF of Comparative Example 1 has excellent flexibility, but the glass transition temperature of the resin used in the core and cladding does not reach 120°C. Therefore, the dimensional retention rate is less than 95% after prolonged exposure to 105°C, and heat resistance is not improved. Since the POFs of Comparative Examples 2-5 use the same resin in the core and cladding as those of Examples 1 and 2, although excellent heat resistance is achieved, a minimum radius of curvature of less than 5 mm cannot be ensured. [Industrial Applicability]

[0127] The POF of this invention is suitable for applications requiring heat resistance and flexibility.

[0128] 1a: Core material 1b: Cladding material 1c: Reinforcing layer material 2: core 3: Cladding 4: Reinforcement layer 5: Laminated body 10:POF 11:Core 12: Cladding 20:POF 21: Covering layer 30: Hybrid cable 31: Conductor 32: Covering layer 40: Relay cable 41: Cable 42: Connector 50: Active optical cable 51: Cable 51a: First end 5 51b: Second end 52: Connector 1 53: Second Connector 100: Manufacturing equipment 101a: First extrusion unit 101b: Second extrusion unit 101c: Third extrusion unit 102a: First Containment Division 102b: Second Containment Division 102c: Third Containment Division 103a: First extrusion section 103b: Second extrusion section 104: Screw 105: Funnel 110: Room 1 120: Room 2 130: Diffuser tube 140: Nozzle 150: Condenser 151: Interior Space 160: Pinch Roller 161: Roller 162: Roller 163: Guide roller 164: Guide roller 165: Guide roller 166: Take-up roller 170: Displacement gauge

Claims

1. A plastic optical fiber comprising a core and a cladding disposed around the core, wherein the core comprises a first resin, the cladding comprises a second resin, the first resin has a first glass transition temperature Tg1 of 120°C or higher, the second resin has a second glass transition temperature Tg2 of 120°C or higher, and when the plastic optical fiber is bent once at 25°C to 180° with a radius of curvature R, the minimum value of the radius of curvature R at which the bent portion of the plastic optical fiber will not crack is 5 mm or lower, and the birefringence of the fiber structure comprising the core and the cladding is 2.0 × 10⁻⁴ or higher.

2. For the plastic optical fiber of Request 1, wherein the minimum value of the aforementioned radius of curvature R does not reach 5 mm.

3. A plastic optical fiber comprising a core and a cladding disposed around the core, wherein the core comprises a first resin, the cladding comprises a second resin, the first resin has a first glass transition temperature Tg1 of 120°C or higher, the second resin has a second glass transition temperature Tg2 of 120°C or higher, and the fiber structure comprising the core and the cladding has a birefringence of 2.0 × 10⁻⁴ or higher.

4. The plastic optical fiber of claim 1 or 3, wherein at least one of the group consisting of the first resin and the second resin is a fluorinated resin.

5. The plastic optical fiber of claim 4, wherein the fluorinated resin comprises a fluorinated polymer containing a constituent unit (A) represented by the following formula (1), [Chemical 1] (in formula (1), Rff1 to Rff4 each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms; Rff1 and Rff2 may also be linked to form a ring).

6. The plastic optical fiber of claim 5, wherein the fluoropolymer further contains the constituent unit (B) represented by the following formula (2), [Chemical 2] (in formula (2), R1 to R3 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms; R4 represents a perfluoroalkyl group having 1 to 7 carbon atoms; the perfluoroalkyl group may have a ring structure; a portion of the fluorine atom may be replaced by a halogen atom other than the fluorine atom; a portion of the fluorine atom in the perfluoroalkyl group may also be replaced by a halogen atom other than the fluorine atom).

7. The plastic optical fiber of claim 5, wherein the fluoropolymer further contains the constituent unit (C) represented by the following formula (3), [Chemical 3] (in formula (3), R5 to R8 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms; the perfluoroalkyl group may have a ring structure; a portion of the fluorine atom may be replaced by a halogen atom other than the fluorine atom; a portion of the fluorine atom in the perfluoroalkyl group may also be replaced by a halogen atom other than the fluorine atom).

8. The plastic optical fiber of claim 5, wherein the fluoropolymer further contains the constituent unit (D) represented by the following formula (4), [Chemical 4] (in formula (4), Z represents an oxygen atom, a single bond, or -OC(R19R20)O-, R9 to R20 each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms; a portion of the fluorine atom may be replaced by a halogen atom other than a fluorine atom; a portion of the fluorine atom in the perfluoroalkyl group may be replaced by a halogen atom other than a fluorine atom; a portion of the fluorine atom in the perfluoroalkoxy group may also be replaced by a halogen atom other than a fluorine atom; s and t each independently represent 0 to 5 and s+t is an integer from 1 to 6 (wherein, When Z is -OC(R19R20)O-, s+t can also be 0).

9. The plastic optical fiber as claimed in claim 1 or 3 further includes a reinforcing layer disposed on the periphery of the aforementioned cladding.

10. The plastic optical fiber of claim 9, wherein the dimensional retention rate of the plastic optical fiber after being kept at 105°C for 250 hours is 95% or more, wherein the dimensional retention rate is the ratio of the length of the plastic optical fiber after being kept at 105°C for 250 hours to the length of the plastic optical fiber before being kept at 105°C for 250 hours.

11. The plastic optical fiber as requested in item 1 or 3, wherein the glass transition temperature of the core material is 105°C or higher.

12. A hybrid cable having a plastic optical fiber as claimed in any one of claims 1 to 11.

13. A repeater cable comprising: a cable housing a plastic optical fiber as claimed in any one of claims 1 to 11; and a connector mounted at at least one end of the cable.

14. An active optical cable comprising: a cable housing a plastic optical fiber as claimed in any one of claims 1 to 11; a first connector mounted at a first end of the cable and having a first conversion part for converting an electrical signal into an optical signal; and a second connector mounted at a second end of the cable and having a second conversion part for converting an optical signal into an electrical signal.

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