Patent Application
20240329296
The present invention relates to a plastic optical fiber, an optical cord, and an active optical cable.
An optical fiber includes: a core located in a central portion of the optical fiber and configured to transmit light; and a region called a cladding or a trench, the region being located on an outer circumference of the core and configured to keep light within the core.
Optical fibers are categorized into plastic optical fibers (hereinafter referred to as “POFs”) whose core is made of a resin material and glass optical fibers (hereinafter referred to as “GOFs”) whose core is made of a glass material. POFs are superior to GOFs in pliability and have better bending resistance (i.e., flexibility) and processability than GOFs. Hence, POFs are commonly used for short-distance use in a terminal section (e.g., in-home wiring) of an optical fiber transmission network.
POFs include step-index (SI) POFs and grated-index (GI) POFs. An SI-POF is a POF in which the refractive index of the core is uniform. A GI-POF is a POF having a refractive-index distribution in which the refractive index of the core decreases from the center of the core toward the outer edge of the core. For an SI-POF, the propagation time varies according to the path (mode) of light; therefore, a signal pulse is broadened, and the SI-POF has a degraded band. On the other hand, a GI-POF has an improved band and is capable of high-speed communication because the refractive-index distribution thereof dramatically narrows a propagation time difference.
A GI-POF is provided with a trench on the outer circumference of the core so that a bending loss will be smaller and light from a wider angular range can be received (i.e., the numerical aperture (NA) can be larger), the trench being optically designed to have a refractive index that is lower than the refractive index at the outer edge of the core.
For example, JP 2016-527547 A discloses a multi-mode optical fiber less affected by a leaky mode and highly resistant to bending, the multi-mode optical fiber being achieved through optical design of a trench.
However, a trench provided for the purpose of, for example, making a bending loss smaller degrades the band by reflecting light incident on the trench. Degradation of the band by reflecting light in the trench is more significant in the case of a POF extending over a shorter distance and is less influential in the case of a POF extending over a longer distance. The reason is that while light is guided through a POF, constituents, such as scattered light and light incident on the POF at a greater angle than the numerical aperture (NA) of the POF, of the light are lost, the constituents contributing to degrading the band. In other words, the longer the distance over which a POF extends is, the more such band-degrading constituents of the light decreases.
As described above, POFs are commonly used for a short-distance (e.g., 1 m or longer and 100 m or shorter) use, and are likely to be affected by band-degrading constituents of light in a shorter distance. However, in the field of optical fibers, no techniques focusing on improvement of the band of a POF, particularly a POF provided with a trench for making a bending loss smaller, in a short distance have been proposed.
The present disclosure aims to provide a POF including a trench for decreasing the bending loss, the POF having an improved band in a short distance. The present disclosure also aims to provide an optical cord and an active optical cable each including the POF having an improved band in a short distance.
A POF according to a first aspect of the present disclosure includes:
An optical cord according to a second aspect of the present disclosure includes the POF according to the first aspect of the present disclosure.
An active optical cable according to a third aspect of the present disclosure includes:
The present disclosure can provide a POF having an improved band in a short distance. The present disclosure can also provide an optical cord and an active optical cable each including the POF having an improved band in a short distance.
A refractive index herein means a value measured by a prism coupler method.
An optical loss of a plastic optical fiber (POF) bent into a U-shape at a bending radius of R mm herein means an optical loss determined by the following procedure.
A POF according to an embodiment of the present disclosure will be described.
A POF 10 according to the present embodiment includes: a core 11; and a trench 12 disposed on an outer circumference of the core 11. The core 11 includes a first region 111 and a second region 112. The first region 111 has a refractive index n1 decreasing in a direction from a center 11a of the core 11 toward an outer edge 11b of the core 11. The second region 112 is positioned on an outer circumference of the first region 111, includes the outer edge 11b of the core 11, and has a refractive index n2 being constant. The refractive index n2 of the second region 112 is equal to or lower than the refractive index n1 of the first region 111. A thickness of the second region 112 is 2 μm or more and less than 5 μm. A refractive index n3 of the trench 12 is lower than the refractive index n2 of the second region 112 of the core 11. It should be noted that the refractive indices of the core 11 (the first region 111 and the second region 112) and the trench 12 are refractive indices for light with a wavelength (e.g., 850 nm) equal to that of light propagating within the core 11.
In the POF 10 according to the present embodiment, the refractive index n1 of the first region 111 of the core 11 has a refractive-index distribution. Therefore, the POF 10 according to the present embodiment is a GI-POI. Specifically speaking, as shown in
Additionally, the vertical axis in
The POF 10 according to the present embodiment has a configuration in which the second region 112 having the constant refractive index n2 satisfying a relation n1≥n2>n3 is provided between the first region 111 (having the refractive index n1) of the core 11 having a refractive-index distribution and the trench 12 (having the refractive index n3) provided to keep light within the core 11. Furthermore, the thickness of the second region 112 is 2 μm or more and less than 5 μm. This configuration can prevent light propagating through the core 11 from reaching the trench 12, i.e., from being incident on the trench 12. Hence, the POF 10 according to the present embodiment can reduce degradation of the band due to reflection of light incident on the trench 12. Hence, the POF 10 according to the present embodiment can have a small bending loss and can achieve an improved band in a short distance.
The POF for a short distance use has a length of, for example, 30 m or shorter, desirably 10 m or shorter, and more desirably 5 m or shorter. The POF for a short distance use has a length of, for example, 1 m or longer.
For example, when overfill light is incident on the POF 10 according to the present embodiment having a length of 5 m, a −1.5 dB band value of the POF 10 can be 40 MHz-km or more. As just described, the POF 10 according to the present embodiment can achieve an improved band demonstrated by 40 MHz-km or more even in a short distance, namely, 5 m. It should be noted that the band of the POF 10 according to the present embodiment is a value measured by a pulse method which is one of methods according to IEC 60793-1-41, and the excitation condition under which the measurement is performed is overfilled launch using overfill light. The term “overfill light” refers to incident light whose numerical aperture (NA) is greater than the numerical aperture (NA) of a POF to be measured and whose beam diameter is greater than a core diameter of the POF to be measured.
The term “core diameter” of a POF herein refers to an outer diameter of the core of the POF. The outer diameter of the core refers to a diameter of 5% light intensity, the diameter being measured by a near field pattern method (hereinafter referred to as “NFP method”), which is one of methods according to IEC 60793-1-20 and IEC 60793-2-40 subcategory A4h, using light with a wavelength of 850 nm. The diameter of 5% light intensity refers to a diameter of an approximate circle defined by points where the light intensity is 5% of a peak value of the light intensity. Additionally, a point where the luminance is 100% means a point where the luminance is maximum in the core. Incidentally, the outer edge 11b of the core 11 can be determined by the same method as for the core diameter, namely, by the NFP method.
For the POF 10 according to the present embodiment, the first region 111 and the second region 112 of the core 11 can be determined by the NFP method as for the above measurement of the core diameter of the POF. The refractive index in the core 11 can be determined by a plane distribution of light intensity of output light, the plane distribution being obtained by measurement by the NFP method. Therefore, using the plane distribution of the light intensity of output light, the first region 111 having a refractive-index distribution and the second region 112 having a constant refractive index can be distinguished by finding an inflection point by differentiation of the plane distribution. An outer edge of the second region 112 is the outer edge 11b of the core 11, i.e., the interface (core-trench interface) between the core 11 and the trench 12. Hence, the second region 112 is a region between the above inflection point and the core-trench interface. The outer diameter of the first region 111 can be determined by the above inflection point, and the outer diameter of the second region 112 can be determined by the core-trench interface. The thickness of the second region 112 can be found by determining the outer diameters of the regions.
As well as the core diameter, the outer diameter of the trench 12 can be determined by the NFP method.
The refractive index n1 of the first region 111 of the core 11, the refractive index n2 of the second region 112 of the core 11, and the refractive index n3 of the trench 12 can be determined by the following method. A core material and a trench material are used to produce sheet-shaped test pieces by hot pressing. Using the test pieces, refractive indices of the core material and the trench material are determined by a prism coupler method. Subsequently, an angular aperture was measured by a far field pattern method, and a difference between refractive indices of the core and the trench was determined. Then, the refractive index n1 of the first region 111 of the core 11, the refractive index n2 of the second region 112 of the core 11, and the refractive index n3 of the trench 12 are calculated according to 2.4 of a paper (Mitsuhiro Tachibana, “Method for measuring refractive-index distribution of optical fiber”, OYO BUTURI, vol. 48, no. 8).
A first optical loss of the POF 10 according to the present embodiment bent into a U shape at a bending radius of 1.5 mm is, for example, preferably 3.0 dB or less, and more preferably 1.0 dB or less. Since the POF 10 according to the present embodiment is a POF including the core 11 made of a resin material, the POF 10 according to the present embodiment has a small bending loss compared to GOFs. Since the POF 10 according to the present embodiment further includes the trench 12, the POF 10 according to the present embodiment can reduce the bending loss to the above range. This configuration allows the POF 10 according to the present embodiment to further reduce the bending loss to the above range and achieve an improved band in a short distance. The first optical loss is, for example, 0.5 dB or more, 0.7 dB or more, or 0.75 dB or more. The method for measuring the first optical loss being a bending loss will be described below in EXAMPLES.
Moreover, a second optical loss of the POF 10 according to the present embodiment bent into a U shape at a bending radius of 2.0 mm is, for example, preferably 0.5 dB or less. This configuration allows the POF 10 according to the present embodiment to further reduce the bending loss to the above range and achieve an improved band in a short distance. The second optical loss is, for example, 0.1 dB or more, 0.3 dB or more, or 0.4 dB or more. The method for measuring the second optical loss being a bending loss will be described below in EXAMPLES.
For a better band, the thickness of the second region 112 of the core 11 of the POF 10 according to the present embodiment is, for example, preferably 2.9 μm or more and 4.8 μm or less. For a much better band, the thickness of the second region 112 is more preferably 2.9 μm or more and 4.5 μm or less. For an even better band, the thickness of the second region 112 is more preferably 3.5 μm or more and 4.4 μm or less.
The POF 10 according to the present embodiment can achieve a large numerical aperture (NA) by virtue of the presence of the trench 12. Therefore, the POF 10 according to the present embodiment can receive light from a wider angular range. The POF 10 according to the present embodiment has, for example, a numerical aperture (NA) of 0.190 or more and 0.235 or less.
The constituents of the POF 10 of the present embodiment will be hereinafter described in more details.
The core 11 is a region configured to transmit light. As described above, the core 11 includes the first region 111 having a refractive-index distribution (the refractive index n1) and the second region 112 having the refractive index n2 being constant. The refractive indices (namely, the refractive index n1 and the refractive index n2) of the first region 111 and the second region 112 are higher than the refractive index n3 of the trench 12. Because of this configuration, light incident on the core 11 is kept within the core 11 by the trench 12 and propagates in the POF 10.
The core 11 includes a first resin. The core 11 may include the first resin as its main component. Here, saying that the core 11 includes the first resin as its main component means that the first resin is a component whose content is highest in the core 11 on a mass basis. The first resin content in the core 11 may be 75 mass % or more, 80 mass % or more, or 85 mass % or more.
The core 11 may further include an additive in addition to the first resin. The additive is, for example, a refractive index modifier. That is, the core 11 may be made of a resin composition including the first resin and an additive such as the refractive index modifier. The refractive index modifier can be, for example, a known refractive index modifier included in the material of the core 11 of the POF 10. The material of the core 11 may include an additive other than the refractive index modifier.
The first region 111 of the core 11 has the refractive-index distribution in which the refractive index decreases in the direction from the center 11a of the core 11 toward the outer edge 11b thereof. Such a refractive-index distribution can be formed, for example, by adding a refractive index modifier to the first resin and diffusing the refractive index modifier in the first resin (for example, by thermal diffusion). The second region 112 of the core 11 can be formed by adjusting, for example, conditions (e.g., a diffusion temperature and a diffusion time) for diffusing the refractive index modifier in the first resin (for example, by thermal diffusion) and, in the case of manufacturing the POF 10 according to the present embodiment by melt spinning, an amount of the core material discharged, the second region 112 having the constant refractive index n2.
The first resin included in the core 11 is not limited to a particular one as long as the first resin is a resin having high transparency. Examples of the first resin include fluorine-containing resins, acrylic resins such as methyl methacrylate, styrene resins, and carbonate resins.
The first resin included in the core 11 may be at least one selected from the group consisting of a fully-fluorinated resin, a partially-fluorinated resin, a partially-chlorinated resin, and a partially-deuterated resin. A partially-fluorinated resin, a partially-chlorinated resin, and a partially-deuterated resin herein each refer to a resin which is based on a resin known as a core material of POFs in this technical field and in which one or some of hydrogen atoms in a C—H bond are fluorinated, chlorinated, or deuterated. A fully-fluorinated resin herein refers to a resin which is based on a resin known as a core material of POFs in this technical field and in which every hydrogen atom in a C—H bond is fluorinated. Examples of the resins known as core materials in this technical field include, as described above, acrylic resins such as methyl methacrylate, styrene resins, and carbonate resins. A polymer having an aliphatic ring structure, such as a polymer having a dioxolane structure, may be used.
The first resin is desirably at least one selected from the group consisting of a fully-fluorinated resin and a partially-fluorinated resin. That is, the first resin is desirably a fluorine-containing resin.
The first resin of the core 11 is preferably a fluorine-containing resin including a fluorine-containing polymer. Hereinafter, the fluorine-containing resin included in the core 11 is referred to as a first fluorine-containing resin, and the fluorine-containing polymer included in the first fluorine-containing resin is referred to as a first fluorine-containing polymer.
It is preferred that the first fluorine-containing polymer included in the first fluorine-containing resin be substantially free of a hydrogen atom from the viewpoint of reducing light absorption attributable to stretching energy of a C—H bond. It is particularly preferred that every hydrogen atom bonded to a carbon atom be substituted by a fluorine atom. That is, it is preferred that the first fluorine-containing polymer be substantially free of a hydrogen atom and be fully-fluorinated. Herein, saying that the fluorine-containing polymer is substantially free of a hydrogen atom means that the hydrogen atom content in the fluorine-containing polymer is 1 mol % or less.
The first fluorine-containing polymer preferably has a fluorine-containing aliphatic ring structure. The fluorine-containing aliphatic ring structure may be included in a main chain of the fluorine-containing polymer, or may be included in a side chain of the first fluorine-containing polymer. The first fluorine-containing polymer has, for example, a structural unit (A) represented by the following structural formula (1).
In the 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 are optionally linked to form a ring. “Perfluoro” indicates that every hydrogen atom bonded to a carbon atom is substituted by a fluorine atom. In the formula (1), the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1. The perfluoroalkyl group may be linear or branched. Examples of the perfluoroalkyl group include a trifluoromethyl group, a pentafluoroethyl group, and a heptafluoropropyl group.
In the formula (1), the number of carbon atoms in the perfluoroalkyl ether group is preferably 1 to 5 and more preferably 1 to 3. The perfluoroalkyl ether group may be linear or branched. Examples of the perfluoroalkyl ether group include a perfluoromethoxymethyl group.
In the case where Rff1 and Rff2 are linked to form a ring, the ring may be a five-membered ring or a six-membered ring. Examples of the ring include a perfluorotetrahydrofuran ring, a perfluorocyclopentane ring, and a perfluorocyclohexane ring.
Specific examples of the structural unit (A) include structural units represented by the following formulae (A1) to (A8).
Among the structural units represented by the above formulae (A1) to (A8), the structural unit (A) is preferably the structural unit (A2), i.e., a structural unit represented by the following formula (2).
The first fluorine-containing polymer may include one or more structural units (A). In the first fluorine-containing polymer, the amount of the structural unit (A) is preferably 20 mol % or more and more preferably 40 mol % or more of a total amount of all structural units. When the structural unit (A) accounts for 20 mol % or more of the first fluorine-containing polymer, the first fluorine-containing polymer tends to have much higher thermal resistance. When the structural unit (A) accounts for 40 mol % or more of the first fluorine-containing polymer, the first fluorine-containing polymer tends to have much higher transparency and much higher mechanical strength in addition to high thermal resistance. In the first fluorine-containing polymer, the amount of the structural unit (A) is preferably 95 mol % or less and more preferably 70 mol % or less of the total amount of all structural units.
The structural unit (A) is derived from, for example, a compound represented by the following formula (3). In the formula (3), Rff1 to Rff4 are as described in the formula (1). It should be noted that the compound represented by the formula (3) can be obtained, for example, by an already-known manufacturing method such as a manufacturing method disclosed in JP 2007-504125 A.
Specific examples of the compound represented by the above formula (3) include compounds represented by the following formulae (M1) to (M8).
The fluorine-containing polymer may further include an additional structural unit other than the structural unit (A). Examples of the additional structural unit include the following structural units (B) to (D).
The structural unit (B) is represented by the following formula (4).
In the formula (4), 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. One or some of the fluorine atoms may be substituted by a halogen atom other than a fluorine atom. One or some of fluorine atoms in the perfluoroalkyl group may be substituted by a halogen atom other than a fluorine atom.
The fluorine-containing polymer may include one or more structural units (B). In the fluorine-containing polymer, the amount of the structural unit (B) is preferably 5 to 10 mol % of the total amount of all structural units. The amount of the structural unit (B) may be 9 mol % or less or 8 mol % or less.
The structural unit (B) is derived from, for example, a compound represented by the following formula (5). In the formula (5), R1 to R4 are as described for the formula (4). The compound represented by the formula (5) is a fluorine-containing vinyl ether such as perfluorovinyl ether.
The structural unit (C) is represented by the following formula (6).
In the formula (6), 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. One or some of the fluorine atoms may be substituted by a halogen atom other than a fluorine atom. One or some of fluorine atoms in the perfluoroalkyl group may be substituted by a halogen atom other than a fluorine atom.
The fluorine-containing polymer may include one or more structural units (C). In the fluorine-containing polymer, the amount of the structural unit (C) is preferably 5 to 10 mol % of the total amount of all structural units. The amount of the structural unit (C) may be 9 mol % or less or 8 mol % or less.
The structural unit (C) is derived from, for example, a compound represented by the following formula (7). In the formula (7), R5 to R8 are as described for the formula (6). The compound represented by the formula (7) is a fluorine-containing olefin such as tetrafluoroethylene or chlorotrifluoroethylene.
The structural unit (D) is represented by the following formula (8).
In the formula (8), 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. One or some of the fluorine atoms may be substituted by a halogen atom other than a fluorine atom. One or some of fluorine atoms in the perfluoroalkyl group may be substituted by a halogen atom other than a fluorine atom. One or some of fluorine atoms in the perfluoroalkoxy group may be substituted by a halogen atom other than a fluorine atom. Symbols s and t are each independently 0 to 5, and s+t is an integer of 1 to 6 (when Z is —OC(R19R20)O—, s+t may be 0).
The structural unit (D) is preferably represented by the following formula (9). The structural unit represented by the following formula (9) is a structural unit represented by the above formula (8), where Z is an oxygen atom, s is 0, and t is 2.
In the formula (9), R141, R142, R151, and R152 are each independently a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. One or some of the fluorine atoms may be substituted by a halogen atom other than a fluorine atom. One or some of fluorine atoms in the perfluoroalkyl group may be substituted by a halogen atom other than a fluorine atom. One or some of fluorine atoms in the perfluoroalkoxy group may be substituted by a halogen atom other than a fluorine atom.
The fluorine-containing polymer may include one or more structural units (D). In the fluorine-containing polymer, the amount of the structural unit (D) is preferably 30 to 67 mol % of the total amount of all structural units. The amount of the structural unit (D) is, for example, 35 mol % or more, and may be 60 mol % or less or 55 mol % or less.
The structural unit (D) is, for example, derived from a compound represented by the following formula (10). In the formula (10), Z, R9 to R18, s, and t are as described for the formula (4). The compound represented by the formula (10) is a cyclopolymerizable fluorine-containing compound having two or more polymerizable double bonds.
The structural unit (D) is preferably derived from a compound represented by the following formula (11). In the formula (11), R141, R142, R151, and R152 are as described for the formula (9).
Specific examples of the compound represented by the formula (10) or the formula (11) include the following compounds.
The first fluorine-containing polymer may further include an additional structural unit other than the structural units (A) to (D). However, the fluorine-containing polymer is preferably substantially free of an additional structural unit other than the structural units (A) to (D). Saying that the fluorine-containing polymer is substantially free of an additional structural unit other than the structural units (A) to (D) means that the sum of the amounts of the structural units (A) to (D) is 95 mol % or more and preferably 98 mol % or more of the total amount of all structural units in the fluorine-containing polymer.
The method for polymerizing the first fluorine-containing polymer is not limited to a particular one, and a common polymerization method such as radical polymerization can be used. A polymerization initiator for the polymerization of the fluorine-containing polymer may be a fully-fluorinated compound.
The first fluorine-containing polymer is included in the first fluorine-containing resin used as the first resin. A first glass transition temperature Tg1 of the first resin is, for example, but not particularly limited to, 100° C. to 140° C., and may be 105° C. or higher or 120° C. or higher. Herein, “Tg” refers to a midpoint glass transition temperature (Tmg) determined according to JIS K 7121: 1987.
The refractive index n1 of the first region 111 of the core 11 preferably has a refractive-index distribution where, for example, g in the following mathematical expression (1) satisfies 1.9≤g≤2.1. Incidentally, Δ in the mathematical expression (1) is represented by the following mathematical expression (2).
n1(r)=nA[1-2Δ(r/a)g]1/2 Mathematical expression (1)
Δ=(nA2-nB2)/2nA2 Mathematical expression (2)
In the mathematical expressions (1) and (2), r, a, nA, and nB are as follows.
The refractive index n1 of the first region 111 can be, for example, 1.329 or more and 1.341 or less at a wavelength of 850 nm.
The refractive index n2 of the second region 112 is required to be equal to or lower than the refractive index n1, and can be, for example, 1.327 or more and 1.331 or less at a wavelength of 850 nm.
In the POF 10 according to the present embodiment, the trench 12 includes, for example, a second resin. The trench 12 may include the second resin as its main component. Here, saying that the trench 12 includes the second resin as its main component means that the second resin is a component whose content is highest in the trench 12 on a mass basis. The second resin content in the trench 12 may be 80 mass % or more, 90 mass % or more, or 95 mass % or more. The trench 12 may consist of the second resin. The trench 12 may further include an additive in addition to the second resin.
The second resin included in the trench 12 is not limited to a particular one as long as the second resin is a resin having high transparency. Examples of the second resin are the same as those mentioned as examples of the resin that can be used as the first resin. As in the case of the first resin, a fluorine-containing resin is suitably used as the second resin.
The second resin of the trench 12 is preferably a fluorine-containing resin including a fluorine-containing polymer. Hereinafter, the fluorine-containing resin included in the trench 12 is referred to as a second fluorine-containing resin, and the fluorine-containing polymer included in the second fluorine-containing resin is referred to as a second fluorine-containing polymer.
Those mentioned as examples of the fluorine-containing resin that can be used as the first fluorine-containing resin can be used as the second fluorine-containing resin.
A fluorine-containing resin including a fluorine-containing polymer and a fluorine-containing plasticizer can be used as the second fluorine-containing resin, the fluorine-containing polymer including a structural unit (E) represented by the following formula (12), the fluorine-containing polymer having an amorphous structure.
In the formula (12), Z represents an oxygen atom, a single bond, or —OC(R31R32)O—, R21 to R32 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. “Perfluoro” indicates that every hydrogen atom bonded to a carbon atom is substituted by a fluorine atom. One or some of the fluorine atoms may be substituted by a halogen atom other than a fluorine atom. One or some of fluorine atoms in the perfluoroalkyl group may be substituted by a halogen atom other than a fluorine atom. One or some of fluorine atoms in the perfluoroalkoxy group may be substituted by a halogen atom other than a fluorine atom. Symbols s and t are each independently 0 to 5, and s+t is an integer of 1 to 6 (when Z is —OC(R31R32)O—, s+t may be 0). The symbols u and v are each independently 0 or 1.
The fluorine-containing polymer including the structural unit (E) may further include a structural unit (F) represented by the following formula (13).
In the formula (13), R33 to R36 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may have a ring structure. One or some of the fluorine atoms may be substituted by a halogen atom other than a fluorine atom. One or some of fluorine atoms in the perfluoroalkyl group may be substituted by a halogen atom other than a fluorine atom.
When the second fluorine-containing polymer is the above copolymer, a proportion between the structural unit (E) and the structural unit (F) is any proportion and is not limited to a particular one.
The second fluorine-containing polymer is preferably, for example, at least one selected from the group consisting of a fluorine-containing polymer A and a fluorine-containing polymer B shown below.
The fluorine-containing polymerA includes a structural unit (G) represented by the following formula (14) and a structural unit (H) represented by the following formula (15). In the following formula (14), R23, R24, R31, and R32 are as described in the above formula (12).
In the formula (15), R37 to R40 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may have a ring structure. One or some of the fluorine atoms may be substituted by a halogen atom other than a fluorine atom. One or some of fluorine atoms in the perfluoroalkyl group may be substituted by a halogen atom other than a fluorine atom.
The fluorine-containing polymer B includes a structural unit (I) represented by the following formula (16). In the following formula (16), R21 to R24, R27 to R30, R31, and R32 are as described in the above formula (12).
The fluorine-containing polymerA and the fluorine-containing polymer B have very high transparency, and moreover can have a very low refractive index compared to a common refractive index of the first fluorine-containing resin used as the material of the core 11. Therefore, the second fluorine-containing resin including at least one selected from the group consisting of the fluorine-containing polymerA and the fluorine-containing polymer B as the second fluorine-containing polymer can maintain high transparency of the trench 12 and can decrease the refractive index further. That makes it possible to widen a difference between the refractive index of the core 11 and that of the trench 12 even greater. As a result, the effect of the trench 12's keeping light within the core 11 is further enhanced and it becomes easier for the POF 10 to achieve a low transmission loss.
The second fluorine-containing polymer preferably includes a structural unit (J) represented by the following formula (17).
In the formula (17), m and n are any integer.
The second fluorine-containing polymer is included in the second fluorine-containing resin used as the second resin. A second glass transition temperature Tg2 of the second resin is, for example, but not particularly limited to, 100° C. to 150° C., and may be 105° C. or higher or 125° C. or higher.
The refractive index n3 of the trench 12 is required to be designed with reference to the refractive index n2 of the second region 112 of the core 11 and is not limited to a particular one. The refractive index n3 of the trench 12 may be, for example, 1.34 or less or 1.33 or less at a wavelength of 850 nm. The refractive index n3 of the trench 12 may be, for example, 1.32 or more at a wavelength of 850 nm.
A difference between the refractive index n3 of the trench 12 and the refractive index n2 of the second region 112 of the core 11 is preferably 0.005 or more and 0.010 or less.
The POF of the present embodiment is manufactured, for example, by melt spinning. That is, one example of the method for manufacturing the POF of the present embodiment includes:
When the fiber-shaped molded body made of the core material is produced, a core inner layer portion may be formed first by extrusion-molding a first core material including a refractive index modifier, and extrusion-molding of a second core material may be performed subsequently so as to coat an outer circumference of the core inner layer portion 2 made of the first core material 1a. In this case, the first region 111 and the second region 112 of the core 11 can be formed by diffusing the refractive index modifier included in the first core material toward a core outer circumferential portion made of the second core material. For example, conditions (e.g., a diffusion temperature and a diffusion time) for diffusing the refractive index modifier (for example, by thermal diffusion), amounts of the first core material discharged and the second core material discharged, and the like are adjusted to form the second region 112 of the core 11, the second region 112 having the constant refractive index n2.
An apparatus 1000 shown in
The first extrusion apparatus 101a includes a first holding portion 102a that holds the first core material 1a and a first extrusion portion 103a that extrudes the first core material 1a held in the first holding portion 102a from the first holding portion 102a. The first extrusion apparatus 101a is further provided with a heating unit (not illustrated) so that the first core material 1a can be molten in the first holding portion 102a and that the molten first core material 1a can be kept in a molten state until molded. The first core material (preform) 1a in a rod shape is molten by being put in the first holding portion 102a through an upper opening portion of the first holding portion 102a and then being heated in the first holding portion 102a.
In the first extrusion apparatus 101a, the first core material 1a is extruded outside from the first holding portion 102a through the first extrusion portion 103a by gas to form the core inner layer portion 2. The first core material 1a extruded through the first extrusion portion 103a to form the core inner layer portion 2 then moves vertically downward to be supplied to the first chamber 110.
The second extrusion apparatus 101b includes a second holding portion 102b that holds a second core material 1b and a second extrusion portion 103b that extrudes the second core material 1b held in the second holding portion 102b from the second holding portion 102b. The second extrusion apparatus 101b extrudes the second core material in a molten state to coat an outer circumference of the core inner layer portion 2 made of the first core material 1a extruded from the first extrusion apparatus 101a.
Specifically, the second core material extruded from the second extrusion apparatus 101b is supplied to the first chamber 110. In the first chamber 110, a core outer circumferential portion 3 coating the outer circumference of the core inner layer portion 2 can be formed by coating the core inner layer portion 2 made of the first core material 1a with the second core material. A layered body 4 composed of the core inner layer portion 2 and the core outer circumferential portion 3 coating the outer circumference of the core inner layer portion 2 moves from the first chamber 110 to a diffusion tube 120 disposed vertically under the first chamber 110. A heater (not illustrated) for heating the layered body is disposed in the diffusion tube 120. The diffusion tube 120 diffuses a dopant such as a refractive index modifier toward the core outer circumferential portion 3, the dopant being included in the core inner layer portion 2 of the layered body 4 passing through the diffusion tube 120. That is, the core inner layer portion 2 and the core outer circumferential portion 3 form a core eventually.
The third extrusion apparatus 101c includes a third holding portion 102c that holds a trench material 1c and a third extrusion portion 103c that extrudes the trench material 1c held in the third holding portion 102c from the third holding portion 102c.
The third extrusion apparatus 101c extrudes the trench material 1c in a molten state to coat an outer circumference of the layered body 4 having passed through the diffusion tube 120. Specifically, the trench material 1c extruded from the third extrusion apparatus 101c is supplied to the second chamber 130. In the second chamber 130, a trench 5 coating the outer circumference of the layered body 4 (namely, the core) can be formed by coating the core with the trench material 1c. The layered body 4 is hereinafter referred to as the core 4. The layered body composed of the core 4 and the trench 5 moves from the second chamber 130 to a third chamber 140 disposed vertically under the second chamber 130.
The fourth extrusion apparatus 101d includes a fourth holding portion 102d that holds a coating layer material 1d, a screw 104 disposed in the fourth holding portion 102d, and a hopper 105 connected to the fourth holding portion 102d. In the fourth extrusion apparatus 101d, for example, the coating layer material 1d in a pellet shape is supplied to the fourth holding portion 102d through the hopper 105. The coating layer material 1d supplied to the fourth holding portion 102d becomes soft and flowable by being kneaded by the screw 104 under heating. The softened coating layer material 1d is extruded from the fourth holding portion 102d by the screw 104.
The coating layer material 1d extruded from the fourth extrusion apparatus 101d is supplied to the third chamber 140. In the third chamber 140, a coating layer 6 coating an outer circumference of the trench 5 is formed by coating a surface of the layered body composed of the core 4 and the trench 5 with the coating layer material 1d.
A layered body 7 including the core 4, the trench 5, and the coating layer 6 concentrically layered flows from the third chamber 140 into an internal flow path through an inlet of the nozzle 150. The layered body 7 passes through the internal flow path to be reduced in diameter, and is then discharged into a fiber shape through an outlet of the nozzle 150.
The layered body 7 discharged into a fiber shape through the outlet of the nozzle 150 flows into an internal space 161 of a cooling pipe 160. The layered body 7 is cooled while passing through the internal space 161. The layered body 7 is then discharged from the cooling pipe 160 through an opening portion. The layered body 7 discharged from the cooling pipe 160, for example, passes between two rolls 171 and 172 of a nip roll 170 and then along guide rolls 173 to 175, and is wound as the POF 10 onto a winding roll 176. A displacement meter 180 for measuring the outer diameter of the POF 10 may also be disposed near the winding roll 176, for example, between the guide roll 175 and the winding roll 176.
The POF according to the present embodiment can also be included in optical cords, active optical cables, and the like.
A polymer of perfluoro-4-methyl-2-methylene-1,3-dioxolane (PFMMD) was prepared as the first fluorine-containing resin. The perfluoro-4-methyl-2-methylene-1,3-dioxolane was synthesized by synthesizing 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, fluorinating the 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, and then decarboxylating the resulting carboxylic acid salt. In the polymerization of the perfluoro-4-methyl-2-methylene-1,3-dioxolane, perfluorobenzoyl peroxide was used as a polymerization initiator.
The synthesis of 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, the fluorination of 2-carbomethyl-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 will be described hereinafter in details.
A 3 L three-neck flask equipped with a water-cooled chiller, a thermometer, a magnetic stirrer, and a pressure equalizing dropping funnel were prepared. An amount of 139.4 g (1.4 mols in total) of a mixture of 2-chloro-1-propanol and 1-chloro-2-propanol was put in the flask. The flask was cooled to 0° C., methyl trifluoropyruvate was slowly added thereto, and the contents were stirred for two hours. An amount of 100 mL of dimethyl sulfoxide (DMSO) and 194 g of potassium carbonate were added thereto over one hour followed by eight-hour stirring to obtain a reaction mixture. The reaction mixture generated was mixed with 1 L of water, and an aqueous phase of the resulting mixture was separated out. After extraction was performed with dichloromethylene, the dichloromethylene solution was mixed with an organic reaction mixture phase. The resulting solution was dried with magnesium sulfate. After the removal of the solvent, 245.5 g of an unrefined product was obtained. This unrefined product was fractionated under a reduced pressure (12 Torr) to obtain 230.9 g of a purified product, 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane. The boiling point of the purified product was 77 to 78° C., and the percentage yield was 77%. HNMR and 19F NMR were used to confirm that the obtained purified product was 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane.
HNMR (ppm): 4.2 to 4.6, 3.8 to 3.6 (CHCH2, multiplet, 3H), 3.85 to 3.88 (COOCH3, multiplet, 3H), 1.36 to 1.43 (CCH3, multiplet, 3H)
19F NMR (ppm): −81.3 (CF3, s, 3F)
An amount of 4 L of 1,1,2-trichlorotrifluoroethane was introduced into a 10 L stirred reaction vessel. In the stirred reaction vessel, nitrogen and fluorine were allowed to flow at a flow rate of 1340 cc/min and 580 cc/min, respectively, to create a nitrogen-fluorine atmosphere. Five minutes later, 290 g of the 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane prepared beforehand was dissolved in 750 mL of a 1,1,2-trichlorotrifluoroethane solution, which was then added into the reaction vessel at 0.5 ml/min. The reaction vessel was cooled to 0° C. After the dioxolan was all added over 24 hours, the fluorine gas flow was stopped. The nitrogen gas was purged, and subsequently an aqueous potassium hydroxide solution was added until the mixture became weak alkaline.
After a volatile substance was removed under a reduced pressure, the reaction vessel was cooled. The cooling was followed by a 48-hour drying under a reduced pressure at 70° C. to obtain a solid reaction product. The solid reaction product was dissolved in 500 mL of water, to which an excessive amount of hydrochloric acid was added to separate the mixture into an organic phase and an aqueous phase. The organic phase was separated and distilled under a reduced pressure to obtain perfluoro-2,4-dimethyl-1,3-dioxolane-2-carboxylic acid. The boiling point of the main distillate was 103° C.-106° C./100 mmHg. The percentage yield of the fluorination was 85%.
The above distillate was neutralized with an aqueous potassium hydroxide solution to obtain perfluoro-2,4-dimethyl-2-potassium carboxylate-1,3-dioxolane. This potassium salt was vacuum-dried at 70° C. for one day. The salt was decomposed at 250° C. to 280° C. under a nitrogen or argon atmosphere. Through condensation in a cold trap cooled at −78° C., perfluoro-4-methyl-2-methylene-1,3-dioxolane was obtained at a percentage yield of 82%. The boiling point of the product was 45° C./760 mmHg. The product was identified by 19F NMR and GC-MS.
19F NMR: −84 ppm (3F, CF3), −129 ppm (2F, ═CF2)
GC-MS: m/e244 (Molecular ion) 225, 197, 169, 150, 131, 100, 75, 50.
An amount of 100 g of the perfluoro-4-methyl-2-methylene-1,3-dioxolane obtained in the above manner and 1 g of perfluorobenzoyl peroxide were put in a glass tube, which was then sealed. After oxygen in the system was removed by freeze-pump-thaw cycling, the glass tube was charged with argon and then heated at 50° C. for several hours. The contents thereby turned solids, which were further heated at 70° C. overnight to obtain 100 g of a transparent stick.
The transparent stick obtained was dissolved in Fluorinert FC-75 (manufactured by Sumitomo 3M), and the resulting solution was poured onto a glass sheet to obtain a thin polymer film. The polymer had a glass transition temperature of 117° C., and was completely amorphous. The transparent stick was dissolved in a hexafluorobenzene solution, to which chloroform was added for precipitation. The product was thereby purified. A polymer resulting from the purification had a glass transition temperature of approximately 131° C. This polymer was used as the first fluorine-containing resin.
A chlorotrifluoroethylene oligomer (molecular weight: 585) was used as a refractive index modifier. Specifically, distillation of DAIFLOIL #10 manufactured by DAIKIN INDUSTRIES, LTD. was performed to take out only a component having a molecular weight of 585. The component taken out and having a molecular weight of 585 was filtered through a filter “DFA1ANDESW44” (manufactured by Pall Corporation) having a pore diameter of 40 nm to obtain a refractive index modifier.
The first fluorine-containing resin produced in the above manner was dissolved in Vertrel XF-UP (manufactured by Chemours-Mitsui Fluoroproducts Co., Ltd.) serving as a solvent. The solution was filtered twice by a filter “LPJ-CTA-001-N3” (manufactured by ROKI TECHNO CO., LTD.) having a pore diameter of 100 nm, and the filtrate was dropped on a Hastelloy container heated at 260° C. to evaporate the solvent to dryness. The filtered fluorine-containing resin obtained by the drying and the above refractive index modifier were molten and mixed at 260° C. to produce a resin composition. The refractive index modifier concentration in the resin composition was 12 mass %. This resin composition was used as the first core material.
The first fluorine-containing resin produced in the above manner was filtered in the same manner as for the filtration of the fluorine-containing resin in the production of the first core material, and thus a filtered fluorine-containing resin was obtained. This filtered fluorine-containing resin was used as the second core material.
The second fluorine-containing resin was prepared as a trench material. “Teflon AF1600” (manufactured by Chemours-Mitsui Fluoroproducts Co., Ltd.) serving as the second fluorine-containing resin and “Fomblin YR” (manufactured by Solvay S. A.) serving as a viscosity modifier were dissolved in Vertrel XF-UP (manufactured by Chemours-Mitsui Fluoroproducts Co., Ltd.) serving as a solvent. A mixing ratio between “Teflon AF1600” and “Fomblin YR” was “Teflon AF1600”: “Fomblin YR”=7:3 in mass. The solution obtained was filtered by a filter “LPA-SLF-003-N2” (manufactured by ROKI TECHNO CO., LTD.) having a pore diameter of 300 nm, and the filtrate was dropped on a Hastelloy container heated at 260° C. to evaporate the solvent to dryness. The resin composition obtained by the drying was used as a trench material.
Xylex (manufactured by SABIC Innovative Plastics; glass transition temperature: 113° C.) was used as a coating layer material.
A POF having the same configuration as that of the POF 20 as shown in
In the present example, the diffusion tube 120 had an inner diameter of 6.3 mm. The length of the diffusion tube 120 was set so that the diffusion time would be 120 minutes.
In the present example, the first core material had a melting temperature of 250° C., the second core material had a melting temperature of 255° C., the trench material had a melting temperature of 260° C., and the coating layer material had a melting temperature of 240° C. The temperature of the diffusion tube 120 was set to 275° C. A core was formed using the first core material and the second core material. The temperature at which the layered body 7 composed of the core, the trench, and the coating layer was drawn was 240° C.
Melt extrusion was performed in which volume rates of the materials discharged was the second core material: 1.04; the trench material: 0.705; and the coating layer material: 40.438, with respect to the first core material: 1.
In the first chamber 110 as shown in
The POF produced in Example 1 was measured by the methods described below. The core diameter (the outer diameter of the core) was 50 μm, the thickness of the second region of the core was 2.85 μm, the outer diameter of the trench was 58 μm (that is, the thickness of the trench was 4 μm), and the outer diameter of the coating layer was 230 μm.
A POF of Example 2 was produced in the same manner as in Example 1, except that, in the production of the POF, the volume rates of the materials discharged were changed to the second core material: 1.441; the trench material: 1.559; and the coating layer material: 47.660, with respect to the first core material: 1.
The POF produced in Example 2 was measured by the methods described below. The core diameter (the outer diameter of the core) was 50 μm, the thickness of the second region of the core was 4.01 μm, the outer diameter of the trench was 64 μm (that is, the thickness of the trench was 7 μm), and the outer diameter of the coating layer was 230 μm.
A POF of Example 3 was produced in the same manner as in Example 1, except that, in the production of the POF, the volume rates of the materials discharged were changed to the second core material: 1.602; the trench material: 1.661; and the coating layer material: 50.785, with respect to the first core material: 1.
The POF produced in Example 3 was measured by the methods described below. The core diameter (the outer diameter of the core) was 50 μm, the thickness of the second region of the core was 4.53 μm, the outer diameter of the trench was 64 μm (that is, the thickness of the trench was 7 μm), and the outer diameter of the coating layer was 230 μm.
A POF of Example 4 was produced in the same manner as in Example 1, except that, in the production of the POF, the volume rates of the materials discharged were changed to the second core material: 1.74; the trench material: 1.47; and the coating layer material: 53.787, with respect to the first core material: 1.
The POF produced in Example 4 was measured by the methods described below. The core diameter (the outer diameter of the core) was 50 μm, the thickness of the second region of the core was 4.96 μm, the outer diameter of the trench was 62 μm (that is, the thickness of the trench was 6 μm), and the outer diameter of the coating layer was 230 μm.
A POF of Example 5 was produced in the same manner as in Example 1, except that, in the production of the POF, the volume rates of the materials discharged were changed to the second core material: 1.100; the trench material: 0.726; and the coating layer material: 41.618, with respect to the first core material: 1.
The POF produced in Example 5 was measured by the methods described below. The core diameter (the outer diameter of the core) was 50 μm, the thickness of the second region of the core was 2.89 μm, the outer diameter of the trench was 58 μm (that is, the thickness of the trench was 4 μm), and the outer diameter of the coating layer was 230 μm.
FONTEX (manufactured by AGC Inc.) was prepared as a POF of Comparative Example 1. The POF of Comparative Example 1 was measured by the methods described below. The core diameter (the outer diameter of the core) was 55 μm, the thickness of the second region of the core was 0 μm, the outer diameter of the trench was 65 μm (that is, the thickness of the trench was 5 μm), and the outer diameter of the coating layer was 490 μm.
A POF of Comparative Example 2 was produced in the same manner as in Example 1, except that, in the production of the POF, the volume rates of the materials discharged were changed to the second core material: 1.815; the trench material: 1.513; and the coating layer material: 55.241, with respect to the first core material: 1.
The POF produced in Example 2 was measured by the methods described below. The core diameter (the outer diameter of the core) was 50 μm, the thickness of the second region of the core was 5.00 μm, the outer diameter of the trench was 62 μm (that is, the thickness of the trench was 6 μm), and the outer diameter of the coating layer was 230 μm.
A POF of Comparative Example 3 was produced in the same manner as in Example 1, except that, in the production of the POF, the volume rates of the materials discharged were changed to the second core material: 1.873; the trench material: 1.544; and the coating layer material: 56.370, with respect to the first core material: 1.
The POF produced in Example 3 was measured by the methods described below. The core diameter (the outer diameter of the core) was 50 μm, the thickness of the second region of the core was 5.12 μm, the outer diameter of the trench was 62 μm (that is, the thickness of the trench was 6 μm), and the outer diameter of the coating layer was 230 μm.
A POF of Comparative Example 4 was produced in the same manner as in Example 1, except that, in the production of the POF, the volume rates of the materials discharged were changed to the second core material: 1.973; the trench material: 1.898; and the coating layer material: 58.031, with respect to the first core material: 1.
The POF produced in Example 4 was measured by the methods described below. The core diameter (the outer diameter of the core) was 50 μm, the thickness of the second region of the core was 5.22 μm, the outer diameter of the trench was 64 μm (that is, the thickness of the trench was 7 μm), and the outer diameter of the coating layer was 230 μm.
GigaPOF-50SR (manufactured by Chromis Fiberoptics) was prepared as a POF of Comparative Example 5. The POF of Comparative Example 5 was measured by the methods described below. The core diameter (the outer diameter of the core) was 50 μm, the thickness of the second region of the core was 0 μm, and the outer diameter of the coating layer was 490 μm. It should be noted that the POF of Comparative Example was not provided with a trench.
The core diameter, the thickness of the second region of the core, and the outer diameter of the trench were determined by an NFP method, which is one of the methods according to IEC 60793-1-20 and IEC 60793-2-40 subcategory A4h, using light with a wavelength of 850 nm. Specifically, the outer edge 11b of the core 11 and the outer edge of the trench were determined using a plane distribution of the light intensity of output light from each POF, and then the core diameter and the outer diameter of the trench were determined. Incidentally, the outer edge 11b of the core 11 corresponds to the interface (core-trench interface) between the core 11 and the trench 12. Furthermore, using the plane distribution of the light intensity of output light from the POF, the first region 111 having a refractive-index distribution and the second region 112 having a constant refractive index were distinguished by finding an inflection point by differentiation of the plane distribution. Thereby the outer diameter of the first region 111 was determined. Since the outer edge of the second region 112 is the outer edge 11b (namely, the core-trench interface) of the core 11, the core-trench interface determined by the NFP method was determined as the outer edge of the second region 112. The thickness of the second region 112 was found from the determined outer diameters of the regions.
Each POF was cut to a length of 2 cm, and was set such that the axis of the POF was perpendicular to a specimen stub of a digital microscope VHX-950F manufactured by Keyence Corporation. One end of the POF was irradiated with a light source attached to the microscope, and transmitted light output from the other end was observed to measure the coating layer of the POF.
The refractive index n1 of the first region of the core, the refractive index n2 of the second region of the core, and the refractive index n3 of the trench were measured using a prism coupler (model: 2010/M) manufactured by Metricon Corporation in an environment at room temperature (approximately 23° C.). Specifically, the materials of the core and the trench were each molded by hot pressing at approximately 210° C. to obtain sheets having a thickness of approximately 100 μm. Each sheet was then set in a prism coupler (model: 2010/M) manufactured by Metricon Corporation to determine a refractive index thereof. Furthermore, an angular aperture was measured by a far field pattern method, and a difference between refractive indices of the core and the trench was determined. Finally, the refractive index n1 of the first region of the core, the refractive index n2 of the second region of the core, and the refractive index n3 of the trench 12 were calculated according to 2.4 of a paper (Mitsuhiro Tachibana, “Method for measuring refractive-index distribution of optical fiber”, OYO BUTURI, vol. 48, no. 8). By this method, it was confirmed that the POFs of Examples 1 to 5 satisfied the relation between the refractive indices, n1≥n2 >n3. By the same method, it was confirmed that the POFs of Comparative Examples 2 to 4 also satisfied the relation between the refractive indices, n1≥n2>n3.
Bands of the POFs of Examples 1 to 5 and Comparative Examples 1 to 5 were measured for a distance of 5 m by a pulse method which is one of the methods according to IEC 60793-1-41. To measure the bands of the POFs for such a very short distance as m, an apparatus capable of oscillating ultra-high-speed pulses was used as an optical pulse generator and an apparatus capable of recognizing images in a short time was used as a light receiver. Specifically, the bands were measured by the following method.
InSight X3+ manufactured by Spectra-Physics, Inc. was used as the optical pulse generator. A laser with a wavelength of 850 nm was oscillated with this optical pulse generator. The oscillated laser was coupled to an OM1 fiber (“M31L01-OM1, 0.275 NA, Graded-Index Patch Cable” manufactured by Thorlabs, Inc.) through a lens, and mode scrambling was performed with FM-1 manufactured by Newport Corporation. An output side of the OM1 fiber was connected to a 2 m-long OM1 fiber (test reference cord MRC-625-EFC-SCFC manufactured by Fluke Networks, Inc.) with a mode filter, and each POF to be measured was connected to an output side of the OM1 fiber.
The core diameter and the numerical aperture (NA) of incident light incident on the POF to be measured were respectively 57.3 μm and 0.26, which were confirmed to be greater than the core diameter and the numerical aperture (NA) of the POF to be measured. In other words, overfill light was allowed to be incident on the POF to measure the band of the POF.
A universal streak camera C10910 series manufactured by Hamamatsu Photonics K. K. was used as the light receiver. A pulse waveform was obtained with this light receiver.
Measurement for a distance of 5 m was performed in the following manner. First, a 7 m-long POF was prepared. An optical pulse was allowed to be incident on one end portion of the POF, and an optical pulse of output light was measured at a distance of 7 m. After that, the POF was cut to a length of 2 m. In the same manner, an optical pulse was allowed to be incident thereon and an output pulse was measured. For the two output pulses, a transfer function was determined by Fourier transform specified in IEC 60793-1-41, and a frequency at an optical power of −1.5 dB was determined. Table 1 shows the results. Table 1 shows both the band measurement result (unit: GHz) obtained by the measurement for a distance of 5 m and that converted to the unit “MHz-km”. Additionally, “Band value for 5 m” shown in Table 1 refers to the value of the band determined by the evaluation of the band.
A5 m-long POF was prepared.
The numerical aperture (NA) was measured by a far field pattern (FFP) method, which is one of the methods according to IEC 60793-1-43 and IEC 60793-2-40 subcategory A4h, using light with a wavelength of 850 nm. A 6 m-long POF was prepared, and LED light with a wavelength of 850 nm was allowed to be incident on one end portion of the POF. Measurement for a light intensity distribution at angular positions of output light was performed at a distance of 6 m, and then the numerical aperture (NA) was calculated.
As shown in Table 1, the POFs of Examples 1 to 5 each including a trench and a core including a second region having a thickness of 2 μm or more and less than 5 μm were able to reduce their bending losses] and achieve an improved band demonstrated by 40 MHz-km or more for a short distance, namely, 5 m. On the other hand, the POF of Comparative Example 1 provided with a trench but not with a second region had a low band value because the band was degraded by light reflected by the trench. As for the POFs of Comparative Examples 2 to 4 each provided with a trench but including a second region having a thickness of 5 μm or more, the thick second region caused reflection of light incident on the second region and thereby degraded the band; therefore, the band value was higher than that of Comparative Example 1 but lower than that of Examples. The POF of Comparative Example 5 had a high band value owing to the lack of a trench; however, the bending loss was large and the numerical aperture (NA) was small.
In summary, the invention of the present disclosure has the following aspects.
(1)
A plastic optical fiber including:
The plastic optical fiber according to (1), wherein when overfill light is incident on the plastic optical fiber having a length of 5 m, a −1.5 dB band value is 40 MHz-km or more.
(3)
The plastic optical fiber according to (1) or (2), wherein a first optical loss of the plastic optical fiber bent into a U shape at a bending radius of 1.5 mm is 3.0 dB or less.
(4)
The plastic optical fiber according to (3), wherein the first optical loss is 1.0 dB or less.
(5)
The plastic optical fiber according to any one of (1) to (4), wherein a second optical loss of the plastic optical fiber bent into a U shape at a bending radius of 2.0 mm is 0.5 dB or less.
(6)
The plastic optical fiber according to any one of (1) to (5), wherein the thickness of the second region is 2.9 μm or more and 4.8 μm or less.
(7)
The plastic optical fiber according to (6), wherein the thickness of the second region is 2.9 μm or more and 4.5 μm or less.
(8)
The plastic optical fiber according to (7), wherein the thickness of the second region is 3.5 μm or more and 4.4 μm or less.
(9)
The plastic optical fiber according to any one of (1) to (8), wherein a numerical aperture (NA) of the plastic optical fiber is 0.190 or more and 0.235 or less.
(10)
An optical cord including the plastic optical fiber according to any one of (1) to (9).
(11)
An active optical cable including:
The POF of the present disclosure can reduce a bending loss and achieve an improved band in a short distance. Therefore, the POF of the present disclosure is suitable for applications such as signal transmission in a short distance, for example, in home.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-052389 | Mar 2023 | JP | national |
