Optical fiber

Abstract

To provide an optical fiber capable of stably forming a core and a sea area to the desired dimensions even when a significant amount of coloring material is included in the sea area.SOLUTION: The optical fiber has multiple cores and a sea area surrounding the core. In the optical fiber, the sea area contains a coloring material and satisfies the conditions of formula (1)-(3); (1) 1.0<L2 / L1≤3.8; (2) 0.002≤C3×(W / 10)3≤3.000; (3) 0.17≤(W / 10)3 / C3≤300.00. (L1: The minimum distance from the sea area periphery to the core at the closest core position to the sea area periphery (μm), L2: for the core located in the second closest position from the sea area periphery, the minimum distance from the sea area periphery to the core (μm), W: the narrowest distance in the sea area (μm), C: optical density per 100 μm of the resin composition constituting the sea area)SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an optical fiber having a sea portion containing a coloring material, and particularly to a multi-core optical fiber applicable to large-capacity communications. [Background technology]

[0002] Previously, there was an invention for an optical fiber sensor characterized by comprising one or more multi-core plastic optical fibers each having a length of 50 cm to 5 m, which are manufactured by a composite spinning method so that 7 to 10,000 core fibers made of a transparent core resin with a high refractive index, a first sheath layer surrounding each of the core fibers and made of a transparent first sheath resin having a refractive index lower than that of the core resin, and a second sheath layer surrounding the outside of each of the first sheath layers and made of a second sheath resin composition in which a coloring substance is dispersed in a second sheath resin having a refractive index lower than that of the first sheath resin, are bundled together into a fiber-like form, a light-emitting element, and a light-receiving element (Patent Document 1).

[0003] In the invention of Patent Document 1, the coloring substance of the second sheath resin composition is carbon black, and the content of carbon black in the second sheath resin composition is 0.1% by weight to 2.0% by weight. The thickness of the first sheath layer is 0.8 to 3.0 μm. Also, looking at Figure 1 of Patent Document 1 (Figure 6 of the present application), it can be seen that the narrowest point of the second sheath layer is between the core fiber at the 7 o'clock position and the core fiber at the 9 o'clock position on a clock, and the distance W is about 1 / 2 to 2 / 3 of the first sheath layer, that is, 0.4 to 2.0 μm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-109300 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when manufacturing optical fiber by a composite spinning method, if a coloring substance is added to the second sheath resin composition, the melt viscosity of the second sheath resin composition increases in accordance with the content thereof, and therefore, unless the extrusion stress during spinning is increased, it becomes difficult to form the second sheath layer (hereinafter referred to as the sea portion) to the desired dimensions, which is a problem.

[0006] The extrusion stress needs to be applied locally to the narrowest part of the sea part, but such fine manipulation is difficult in the conjugate spinning method, and there was a problem that the shorter the interval W of the narrowest part of the sea part, the higher the overall extrusion stress must be. As a result, in the wide region 6 opposite the narrowest part of the sea part, a problem occurred in which the core fiber (hereinafter referred to as the core) 1 and the first sheath layer (hereinafter referred to as the clad) 3 were deformed due to the effect of the high extrusion stress of the resin composition constituting the sea part.

[0007] In particular, in an invention such as that of Patent Document 1, in which the narrowest point W of the sea portion 3 is less than 2 μm, even if the carbon black content of the sea portion 3 is set to be low, there is a problem that, when attempting to form the sea portion 3 to a desired dimension, the cores 1 and clads 2 of all six outer periphery cores 1 and 2 except for the central ones are easily deformed due to the high extrusion stress in the wide region 6 of the sea portion 3 (see FIG. 6 ).

[0008] Therefore, an object of the present invention is to provide an optical fiber in which the difference between the narrowest point and the widest area of ​​the sea portion is as small as possible, and the spacing between each core is efficiently arranged just enough according to the content of coloring material in the sea portion, so that cores and sea portions can be stably formed according to the desired dimensions, even if a considerable amount of coloring material is contained in the sea portion. [Means for solving the problem]

[0009] That is, the present invention is as follows. 1) An optical fiber having a plurality of cores and a sea portion surrounding the cores, The sea portion contains a coloring substance, An optical fiber that satisfies the conditions of formulas (1) to (3). 1.0 <L2 / L1≦3.8 ···(1) 0.002≦C 3 ×(W / 10) 3 ≦3.000 (2) 0.17≦(W / 10) 3 / C 3 ≦300.00 (3) (L1: the minimum distance (μm) from the outer periphery of the sea portion to the core located closest to the outer periphery of the sea portion, L2: the minimum distance (μm) from the outer periphery of the sea portion to the core located second closest to the outer periphery of the sea portion, W: the narrowest distance (μm) of the sea portion, C: the optical density per 100 μm of the resin composition constituting the sea portion) 2) 2. The optical fiber according to claim 1, wherein the core does not contain a coloring substance or the content of the coloring substance is 0.01% by weight or less. 3) The optical fiber according to 1) or 2), further satisfying formula (4): 1≦L1 / W≦25 (4) 4) The optical fiber according to any one of 1) to 3), further comprising a cladding between the core and the sea portion so as to surround the core. 5) The cladding contains a coloring material; The optical fiber according to any one of 1) to 4), wherein the content (wt %) of the coloring substance in the clad is smaller than the content (wt %) of the coloring substance in the sea portion. 6) the coloring substance in the sea portion is carbon black having an average primary particle diameter of 0.1 to 10 μm, The optical fiber according to any one of 1) to 5), wherein the content of the carbon black in the sea portion is 0.3 to 5% by weight. 7) The optical fiber according to any one of 1) to 6), wherein the relationship between the average value D of the inner diameter of the core and the standard deviation value σ satisfies σ / D≦4.0. Effect of the Invention

[0010] In the optical fiber of the present invention, the core and sea portion are arranged so that the difference between the narrowest point of the sea portion and the wide area is minimized as described above, so that the core and sea portion can be stably formed according to the desired dimensions even if a considerable amount of coloring material is contained in the sea portion. As a result, even if the signal light propagating through the core leaks into the sea portion, the coloring material contained in the sea portion prevents the leaked signal light from reaching other adjacent cores. Therefore, there is an effect that the optical fiber is hardly affected by the adverse effects of noise, etc. of the signal light propagating through the adjacent cores.

[0011] Furthermore, as described above, the intervals between the cores are efficiently arranged according to the content of the coloring material in the sea portion, so that the occupancy rate of the cross-sectional area of ​​the entire multi-core area relative to the cross-sectional area of ​​the optical fiber is high. As a result, there is an effect of improving the transmission efficiency compared to conventional multi-core fibers containing a coloring material. Therefore, the optical fiber of the present invention may be applicable to optical fibers for large-capacity communication, even though it has a multi-core structure having many cores. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of one embodiment of the optical fiber of the present invention, showing an optical fiber consisting of a core and a sea portion, the outer circumferential shape of the sea portion being circular, and the cores being arranged in a close-packed structure with equal distances between each other. [Diagram 2] FIG. 1 is a schematic cross-sectional view of one embodiment of the optical fiber of the present invention, which is composed of a core and a sea portion, the outer circumferential shape of the sea portion is circular, and the core closest to the outer circumferential shape of the sea portion is arranged in a structure in which the minimum distance from the outer circumferential shape of the sea portion to the core is equal, and the difference in spacing between each core is arranged as small as possible. [Diagram 3] FIG. 1 is a schematic cross-sectional view of one embodiment of the optical fiber of the present invention, which shows an optical fiber consisting of a core and a sea portion, the outer peripheral shape of the sea portion being hexagonal, and the cores being arranged in a close-packed structure with equal distances between each other. [Figure 4]FIG. 1 is a schematic cross-sectional view of one embodiment of the optical fiber of the present invention, showing an optical fiber consisting of a core and a sea portion, the outer circumferential shape of the sea portion being circular, and the cores being arranged in a matrix-like structure spaced equidistant from each other. [Diagram 5] FIG. 1 is a schematic cross-sectional view of one embodiment of the optical fiber of the present invention, which shows an optical fiber consisting of a core, a cladding, and a sea portion, in which the outer circumferential shape of the sea portion is circular and each core is arranged in a close-packed structure spaced equidistant from each other. [Figure 6] FIG. 2 is a schematic cross-sectional view showing the optical fiber sensor of FIG. 1 of Patent Document 1, illustrating that the narrowest point of the sea portion is very narrow and the difference with the wide area is very large. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention is an optical fiber having a plurality of cores and a sea portion surrounding the cores, the sea portion containing a coloring substance and satisfying the conditions of formulas (1) to (3). 1.0 <L2 / L1≦3.8 ···(1) 0.002≦C 3 ×(W / 10) 3 ≦3.000 (2) 0.17≦(W / 10) 3 / C 3 ≦300.00 (3) (L1: the minimum distance (μm) from the outer periphery of the sea portion to the core located closest to the outer periphery of the sea portion, L2: the minimum distance (μm) from the outer periphery of the sea portion to the core located second closest to the outer periphery of the sea portion, W: the narrowest distance (μm) of the sea portion, C: the optical density per 100 μm of the resin composition constituting the sea portion) The optical fiber of the present invention has a plurality of cores and a sea portion surrounding the cores. In other words, the optical fiber of the present invention has a multi-core structure. Due to the multi-core structure, the optical fiber of the present invention can transmit separate light to each core, thereby realizing high-capacity communication. The number of cores is not particularly limited as long as it is more than one, and a suitable number will be described later. The arrangement of the multiple cores is not particularly limited as long as it satisfies formulas (1) to (3).

[0014] In addition, in the optical fiber of the present invention, the sea portion contains a coloring material. That is, in the optical fiber of the present invention, the resin composition constituting the sea portion contains a coloring material. By containing a coloring material in the sea portion, in the optical fiber of the present invention, when separate light is propagated to each core, the light leaking from each core is less likely to reach an adjacent core, so that noise such as crosstalk can be reduced.

[0015] Moreover, the optical fiber of the present invention satisfies the conditions of the formulas (1) to (3). 1.0 <L2 / L1≦3.8 ···(1) 0.002≦C 3 ×(W / 10) 3 ≦3.000 (2) 0.17≦(W / 10) 3 / C 3 ≦300.00 (3) Here, L1 means the minimum distance (μm) from the outer periphery of the sea part to the core located closest to the outer periphery of the sea part, L2 means the minimum distance (μm) from the outer periphery of the sea part to the core located second closest to the outer periphery of the sea part, W means the narrowest distance (μm) of the sea part, and C means the optical density per 100 μm of the resin composition constituting the sea part. The specific distances represented by L1, L2, and W are as shown in the drawings described later.

[0016] The optical fiber of the present invention will now be described with reference to the drawings.

[0017] FIG. 1 is a schematic cross-sectional view of one embodiment of an optical fiber 100 of the present invention, which is a schematic cross-sectional view of an optical fiber with a multi-core structure having a core 1 and a sea portion 3, where the core 1 is surrounded by the sea portion 3 and the outer circumferential shape of the sea portion 3 is circular.

[0018] It is preferable that the core in the optical fiber of the present invention does not contain a coloring substance or has a coloring substance content of 0.01% by weight or less. By suppressing the amount of coloring substance in the core, that is, by making the core contain no coloring substance or making the coloring substance content in the core 0.01% by weight or less, the light transmittance is improved, and the light propagating through the optical fiber can reach a longer distance.

[0019] In the example of Fig. 1, none of the numerous cores 1 contain a coloring substance, and the sea portion 3 contains a coloring substance. The number of cores 1 is 19, and the cores 1 are arranged in a close-packed structure with the central core 1 at the center, spaced apart at equal intervals of the narrowest distance (µm) W of the sea portion 3. Here, the narrowest distance W of the sea portion refers to the narrowest distance in the sea portion, which corresponds to the shortest distance between cores.

[0020] Therefore, if the core closest to the outer periphery of the sea portion 3 and the core second closest to the outer periphery of the sea portion are defined as the cores of the outermost layer, the centers of the 12 cores 1 in the outermost layer are connected to form a regular hexagon. Of the 12 cores 1 in the outermost layer, the distance between the sea portion 3 from the outer periphery of the sea portion 3 to the core 1 in the outermost layer for six cores is L1 (μm), and the distance between the sea portion 3 from the outer periphery of the sea portion 3 to the core 1 in the outermost layer for six cores is L2 (μm). Therefore, L1 (μm) corresponds to the minimum distance (μm) from the outer periphery of the sea portion to the core closest to the outer periphery of the sea portion 3, and L2 (μm) corresponds to the minimum distance (μm) from the outer periphery of the sea portion to the core second closest to the outer periphery of the sea portion.

[0021] If core 1 is arranged in a structure in which the ratio L2 / L1 exceeds a certain value (i.e., L2 becomes larger than a certain value relative to L1), the extrusion stress of the resin composition in sea portion 3 during spinning at L1 may be insufficient, resulting in a defect of insufficient filling of sea portion 3, or the extrusion stress of the resin composition in sea portion 3 may be excessively large at L2 (i.e., a wide area of ​​sea portion 3), resulting in a defect of core 1 in the vicinity of L2 being crushed and deformed.

[0022] As a result of repeated verification, the threshold value of L2 / L1 at which such a defect does not occur is 3.8, and since the value of L2 / L1 in the arrangement of Fig. 1 is about 2.0, the above defect does not occur if the narrowest distance W (µm) of the sea portion 3 is sufficiently secured. It is preferable to arrange the sea portion 3 so that all distances from the outer circumference to the outermost core 1 are the same (i.e., L2 / L1 is 1) as shown in Fig. 2. In other words, the optical fiber of the present invention satisfies the above-mentioned formula (1).

[0023] However, in the arrangement of Fig. 2 in which the cores in the outermost layer are arranged at equal distances from the outer periphery of the sea portion and the difference in the intervals between the cores is minimized, the intervals between the cores 1 near the center are not equal as in Fig. 1, so unless the numerical value of the interval itself is at least a certain value and the difference in the intervals is small, the cores 1 near the center may be deformed. Therefore, in addition to the numerical value of L2 / L1, it is preferable to ensure that the narrowest distance W (μm) of the sea portion 3 is sufficiently ensured, and in the arrangement shown in Fig. 2, the difference in the intervals between the cores 1 is also minimized.

[0024] In this respect, an ideal arrangement would be one in which the cores 1 are arranged in a close-packed structure, spaced apart from each other at equal intervals of the narrowest distance (μm) W of the sea portions 3, and the outer periphery of the sea portions 3 is not circular but has a regular hexagonal shape similar to the shape connecting the centers of the outermost cores 1, as shown in Fig. 3, so that the distances from the outer periphery of the sea portions 3 to the outermost cores 1.0 are all the same (i.e., L2 / L1 is 1.0). However, since the outer periphery of the sea portions 3 is not circular, it may be difficult to handle. In such cases, a method of providing a protective layer 4 on the outside of the sea portions 3 is preferable.

[0025] Although not shown in the figures, a protective layer 4 may be provided on the outer periphery of the sea portion 3 even in the cases of Figures 1 and 2. In other words, the optical fiber of the present invention can be provided with a protective layer on the outer periphery of the sea portion as necessary. Also, Figures 1 to 3 show examples in which the cores 1 are arranged in a close-packed structure, but the cores 1 may be arranged in a matrix as shown in Figure 4.

[0026] Next, in order to avoid insufficient filling of the narrowest portion or deformation of the core 1 near the wide region during production by spinning, it is preferable to make the narrowest distance (μm) W of the sea portion 3 wider than a certain value. As described above, the original reason for this is that a coloring substance is contained in the sea portion 3, i.e., in the resin composition constituting the sea portion 3, and the melt viscosity of the resin composition constituting the sea portion 3 during spinning increases in accordance with the content of the coloring substance. There is a proportional relationship between the content of the coloring substance in the resin composition constituting the sea portion 3 and the appropriate narrowest distance (μm) W of the sea portion 3.

[0027] That is, it is preferable to widen the narrowest distance (μm) W of the sea portion 3 according to the content of the coloring substance in the sea portion 3. If the content of the coloring substance in the sea portion 3 is expressed in terms of the optical density C per 100 μm of the resin composition constituting the sea portion 3, the cube of the narrowest distance (μm) W of the sea portion 3 and the cube of the optical density C per 100 μm of the material of the sea portion 3 are in a proportional relationship, which indicates that it is important to keep the ratio of ((W / 10)cubed) / ((C)cubed) within a certain range.

[0028] On the other hand, the coloring substance is contained in the sea region 3 in order to obtain the effect of preventing the signal light leaking into the sea region 3 from reaching other adjacent cores 1, and this effect is proportional to the product of the cube of the narrowest distance (μm) W of the sea region 3 and the cube of the optical density C per 100 μm of the material of the sea region 3. In other words, from this point of view, the cube of the narrowest distance (μm) W of the sea region 3 and the cube of the optical density C per 100 μm of the material of the sea region 3 are inversely proportional to each other, indicating that it is important to keep the product of ((W / 10)cubed) × ((C)cubed) within a certain range or more.

[0029] In the above formulas, the reason why the relationship is directly or inversely proportional to the cube of the narrowest distance W of the sea portion 3 and the optical density C per 100 μm of the resin composition constituting the sea portion 3, rather than to the narrowest distance W of the sea portion 3 and the optical density C per 100 μm of the resin composition constituting the sea portion 3, is that this is due to the volume of the sea portion 3, i.e., the three-dimensional space, and a slight change in the narrowest distance W of the sea portion 3 and the optical density C per 100 μm of the resin composition constituting the sea portion 3 has an extremely accelerated effect on the effects of the present invention.

[0030] As a result of verifying these thresholds, the threshold value for obtaining the effect of the present invention is ((W / 10) 3 / C 3 ) is between 0.17 and 300.00, and (C 3 ×(W / 10) 3 On the other hand, if the narrowest distance (μm) W of the sea portion 3 is excessively widened, the occupancy rate of the cross-sectional area of ​​the entire multiplicity of cores 1 relative to the cross-sectional area of ​​the optical fiber 100 decreases, and the transmission efficiency decreases excessively. 3 ×(W / 10) 3 ) has an upper limit of 3.000. In other words, the optical fiber of the present invention satisfies the formulas (2) and (3). 0.002≦C 3 ×(W / 10) 3 ≦3.000 (2) 0.17≦(W / 10) 3 / C 3 ≦300.00 (3) More preferably, ((W / 10) 3 / C 3) is between 0.27 and 250.00, and (C 3 ×(W / 10) 3 ) is 0.003 or more and 2.000 or less. By setting it in these ranges, deformation of the many cores 1 is small, and the relationship between the average value D of the inner diameters of the cores 1 and the standard deviation value σ is σ / D≦4.0, so that an optical fiber with little variation in inner diameter can be obtained.

[0031] The relationship between the average value D of the inner diameter of the core and the standard deviation value σ is preferably σ / D≦4.0, and more preferably σ / D≦3.0. Since there is no particular problem with the relationship σ / D between the average value D of the inner diameter and the standard deviation value σ being small, there is no particularly suitable lower limit, and 0 is preferable. However, since it is practically difficult to manufacture a core with no variation at all, 0<σ / D≦3.0 is preferable.

[0032] In addition, when the narrowest distance W (μm) of the sea portion 3 is sufficiently ensured, the entire core 1 is gathered near the center, and the minimum distance L1 (μm) from the sea portion outer periphery to the core closest to the outer periphery of the sea portion 3 is increased, the conditions of each of the above formulas may be satisfied. However, when L1 (μm) is excessively large compared with W, a wide region 6 of the sea portion 3 may be formed over the entire outer circumference of the outermost core 1 consisting of the core closest to the outer periphery of the sea portion 3 and the core second closest to the outer periphery of the sea portion. The extrusion stress from the wide region 6 of the sea portion 3 is applied almost uniformly to the entire core 1 of the outermost layer, so that local deformation of the core 1 is small, but the size of each core 1 tends to be smaller than the setting.

[0033] Therefore, it is preferable to set a certain range of conditions for the minimum distance (μm) L1 from the outer periphery of the sea portion 3 to the core located closest to the outer periphery of the sea portion 3 in relation to the narrowest distance W of the sea portion 3. As a result of repeated verification, it is preferable that the optical fiber 100 of the present invention satisfies L1 / W between 1 and 25. In other words, it is preferable that the formula (4) is satisfied.

[0034] 1≦L1 / W≦25 (4) For the optical fiber of the present invention, L1 / W is more preferably equal to or greater than 2 and equal to or less than 10. By making the optical fiber 100 satisfy this condition, it becomes possible to maintain each of the cores 1 at a desired size, and the transmission efficiency can be maintained high.

[0035] The optical density is a value that represents the degree to which the signal light is not transmitted or reflected in logarithm, and a larger value indicates a higher content of the coloring substance in the sea portion 3. The method for measuring the optical density C per 100 μm of the resin composition constituting the sea portion will be described later.

[0036] Furthermore, the optical fiber 100 of the present invention preferably has a cladding 2 surrounding the core 1 between the core 1 and the sea region 3, as shown in Fig. 5. When the optical fiber has the cladding 2, most of the signal light is reflected at the interface between the core 1 and the cladding 2, and the amount of signal light leaking to the sea region 3 is relatively reduced, thereby reducing the adverse effects of noise.

[0037] When the optical fiber has a cladding 2, W, L1, and L2 in formulas (1) to (4) are interpreted as follows. That is, as shown in FIG. 5, the narrowest distance W (μm) of the sea portion 3 is interpreted as the narrowest distance between the outer circumferences of the claddings 2 covering the adjacent cores 1, not the narrowest distance between the outer circumferences of the adjacent cores 1. Similarly, L1 (μm) is interpreted as the smallest distance (μm) from the outer circumference of the sea portion 3 to the outer circumference of the cladding 2 of the core closest to the outer circumference of the sea portion 3, and L2 (μm) is interpreted as the smallest distance (μm) from the outer circumference of the sea portion 3 to the cladding 2 of the core next closest to the outer circumference of the sea portion 3.

[0038] Moreover, the cross section of the optical fiber 100 of the present invention is preferably circular from the viewpoint of handling, and the diameter thereof is preferably 0.2 mm to 10 mm. This is because a diameter of 0.2 mm or more provides appropriate rigidity and ease of handling, while a diameter of 10 mm or less provides appropriate flexibility and ease of handling.

[0039] Next, each part constituting the optical fiber 100 will be described in detail.

[0040] Core 1 is the transmission part that directly propagates the signal light, and plays a role in transmitting the signal light efficiently. The cross-sectional shape of core 1 is preferably a perfect circle rather than a polygon, as it is more uniform and has fewer irregularities. In order to propagate the signal light over a long distance, it is preferable that the cross-sectional shape of said core 1 extends uniformly and straight, with as little cylindricity as possible. Cylindricity is an index that indicates the degree of deviation from a geometrically correct true cylinder in accordance with JIS-B-0621 (established in 1972).

[0041] The number of cores 1 is not particularly limited as long as it is plural, but it is preferable to increase it to 19 or more as shown in Figures 1 and 2. For example, in a configuration in which the number of cores 1 is 7 (one in the center and six in the outermost layer) as shown in Figure 6, the size of the wide region 6 of the sea portion 3 is larger than the narrowest distance W (µm) of the sea portion 3, and in order to form the narrowest distance W (µm) of the sea portion 3 according to the desired dimensions, the extrusion stress during spinning of the sea 3 must be made considerably high, and as a result, excessive pressure is applied to the core 1 of the outermost layer sandwiched between the wide regions 6 of the sea portion 3, making it prone to deformation.

[0042] Therefore, it is preferable to make the inner diameter of the core 1 as small as possible, to increase the number of cores 1 as much as possible, to space the cores 1 equally apart, and to arrange the cores 1 as a whole so as to approximate the outer circumferential shape of the sea portion 3. However, if the number of cores 1 exceeds 10,000, the inner diameter of the core 1 must be made small, making it difficult to perform stable spinning processing and causing the cross-sectional shape of the core 1 to become unstable. Therefore, the number of cores 1 is preferably about 60 to 2,000, and more preferably 100 to 1,000.

[0043] The average inner diameter of the multiple cores 1 is preferably 5 to 60 μm. The smaller the average inner diameter of the cores 1, the more the number of cores 1 can be increased to make the core as a whole closer to the outer peripheral shape of the sea portion 3, and the delay time of the signal light reflected by the side wall of the cores 1 and propagating therethrough is reduced, thereby reducing noise due to delay, which is preferable. However, if the average inner diameter is less than 5 μm, it may be difficult to perform stable spinning processing, and the cross-sectional shape of the cores 1 may become unstable. Therefore, the average inner diameter of the cores 1 is more preferably 5 to 40 μm.

[0044] The resin in the resin composition forming the core 1 is preferably a material that is light-transmitting and has low transmission loss, and examples of such materials include acrylic resin, modified polycarbonate resin, cycloolefin resin, styrene resin, and olefin resin such as polymethylpentene. In particular, acrylic resin with low transmission loss is preferable. Examples of such acrylic resin include polymers of methacrylic acid esters and acrylic acid esters.

[0045] Examples of methacrylic acid esters include alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate; aryl methacrylates such as phenyl methacrylate; and cycloalkyl methacrylates such as cyclohexyl methacrylate and norbornenyl methacrylate.

[0046] Examples of the acrylic acid ester include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, aryl acrylates such as phenyl acrylate, and cycloalkyl acrylates such as cyclohexyl acrylate and norbornenyl acrylate, etc. Examples of other acrylic resins include sodium polyacrylate-based resins, polyacrylonitrile-based resins, and polyacrylamide-based resins, etc.

[0047] The modified polycarbonate resin may be a polycarbonate resin substituted with a lower alkyl group or a trifluoromethyl group and having an average molecular weight of 10,000 to 200,000. The cycloolefin resin may be a cycloolefin polymer such as an addition copolymer of a ring-opening metathesis polymerization polymer and ethylene or a hydrogenated ring-opening metathesis polymerization polymer, as well as a cycloolefin copolymer such as ethylene-2-norbornene.

[0048] In addition, in order to adjust the refractive index, dopants such as germanium, phosphorus, tin, boron, etc. that increase the refractive index, and dopants such as fluorine-based materials such as magnesium fluoride, etc. that decrease the refractive index may be appropriately added to the resin composition constituting the core 1.

[0049] The sea portion 3 protects the multiple cores 1 from external environmental factors, and also prevents signal light propagating through a core 1 from reaching other adjacent cores 1 even if the leaked signal light leaks into the sea portion 3. For this reason, the resin composition constituting the sea portion 3 contains a coloring substance that reflects or absorbs signal light.

[0050] The resin composition constituting the sea portion 3 is not particularly limited, but a fluoropolymer having a low refractive index and also a performance as a protective film is used. For example, a copolymer of vinylidene fluoride units and tetrafluoroethylene units has a low refractive index of 1.39 to 1.41 and is excellent in mechanical strength, flexibility, adhesiveness, etc., and can be used as a resin composition material constituting the sea portion 3. In addition, acrylic resins, modified polycarbonate resins, cycloolefin resins, styrene resins, olefin resins such as polymethylpentene, and other thermoplastic polymers used in the core 1 can also be used as a resin composition constituting the sea portion.

[0051] The coloring material contained in the sea portion 3 has a function of blocking the signal light from reaching other adjacent cores 1 over the entire range of the wavelength of the signal light. Therefore, when the wavelength range of the signal light is outside the range of visible light, it is sufficient that the coloring material has the blocking function only for wavelengths in that range, and does not necessarily mean coloring for visible light. For example, if the signal light is an infrared laser light, the coloring material may be transparent in the visible light range as long as it has the blocking function over the entire range of infrared light, and such an infrared absorbing agent is also included in the coloring material of the present invention.

[0052] However, since the signal light used is generally white visible light, generally, a coloring material of black, white, or gray color that can perform the above-mentioned blocking function in the entire range of visible light is preferable, and specific coloring materials include carbon black, lead oxide, titanium oxide, organic pigments, etc. Organic dyes, etc. can also be mentioned, but if they have migration properties, they will migrate from the sea portion 3 to the core 1 when left for a long time, significantly reducing the transmission efficiency of the core 1, so it is necessary to select a material with low migration properties.

[0053] The content of the coloring material in the sea part varies depending on the properties of the coloring material, so it cannot be generally stated. However, when the coloring material in the sea part is carbon black with an average primary particle size of 0.1 to 10 μm, the content of carbon black in the sea part is preferably 0.3 to 5% by weight. Here, the content of carbon black in the sea part is the content based on weight with respect to the entire resin composition constituting the sea part 3. Carbon black with an average primary particle size of less than 0.1 μm may aggregate during a long spinning process, causing the melt viscosity of the resin composition in the sea part 3 to increase over time, and carbon black with an average primary particle size of more than 10 μm may easily clog the narrowest part of the sea part 3. In addition, if the content of carbon black in the sea part is higher than 5% by weight, the melt viscosity of the resin composition in the sea part 3 may increase sharply, and if it is lower than 0.3% by weight, the effects described in the present invention may decrease.

[0054] The cladding 2 serves to protect the multiple cores 1 from external environmental factors, and also serves to reduce the proportion of signal light propagating through the cores 1 that is reflected at the interface of the cladding 2 and leaks into the sea region 3. To increase the proportion of light reflected at the interface, it is preferable to select a material for the cladding 2 that has a refractive index as low as possible compared to that of the cores 1, to increase the refractive index difference with the multiple cores 1, and to select a material with a higher NA value.

[0055] Examples of resin compositions that can be used to form such cladding include copolymers of vinylidene fluoride units and trifluoroethylene units (refractive index 1.39 to 1.41), fluorinated acrylic ester polymers (refractive index 1.35 to 1.37) which have a lower refractive index, good adhesion to the acrylic resin of the core 1, and excellent processability, polyperfluorobutyl methacrylate (refractive index 1.36), polyperfluoroisopropyl methacrylate (refractive index 1.37), and polyhexafluoro-2-propyl methacrylate (refractive index 1.38).

[0056] The thickness of the cladding 2 is preferably 1 / 20 to 1 / 3 of the inner diameter of the cross section of the core 1. By setting the thickness of the cladding 2 within this range, total reflection of light at the interface between the core 1 and the cladding 2 is ensured, and a decrease in the NA value and a decrease in the transmission efficiency can be suppressed. A dopant such as a fluorine-based material such as magnesium fluoride may be added to the cladding 2 in order to lower the refractive index.

[0057] Moreover, the thickness of the cladding 2 is preferably 1 / 10 to 1 / 3 of the inner diameter of the cross section of the core 1. By setting the thickness of the cladding 2 within this range, total reflection of light at the interface between the core 1 and the cladding 2 is ensured, and a decrease in the NA value and a decrease in the transmission efficiency can be suppressed. Furthermore, the cladding 2 may also contain a coloring substance. By containing a coloring substance in the cladding 2, the amount of signal light leaking into the sea region 3 can be reduced.

[0058] However, since the thickness of the clad 2 is relatively thin, when the clad contains a coloring substance, the content (wt%) of the coloring substance in the clad is preferably smaller than the content (wt%) of the coloring substance in the sea portion 3. When the content (wt%) of the coloring substance in the clad is larger than the content (wt%) of the coloring substance in the sea portion 3, the melt viscosity of the resin composition when forming the clad 2 increases, and it may become difficult to form the clad 2 to a desired dimension unless the extrusion stress is increased, or the extrusion stress may deform the core 1 or the sea portion 3. In other words, when the clad contains a coloring substance, the optical fiber of the present invention preferably has a content (wt%) of the coloring substance in the clad smaller than the content (wt%) of the coloring substance in the sea portion. Specifically, the content is preferably smaller than 3 wt%.

[0059] The resin compositions constituting each of the multiple cores 1, clads 2, and sea portions 3 may be continuously molded into a predetermined shape by a composite spinning method using each of the extrusion dies. Unlike other dies for resin molding, the extrusion die does not cool or solidify any of the resin compositions inside the extrusion die, and the resin composition constituting the core 1, the resin composition constituting the clad 2, and the resin composition constituting the sea portion 3 are extruded from the core discharge portion, the clad discharge portion, and the sea portion discharge portion, respectively, and then cooled and solidified to be molded into a predetermined shape.

[0060] The extrusion die is not particularly limited as long as it can form the optical fiber 100 of the present invention, but it is preferable to arrange a plurality of core discharge parts and sea section discharge parts surrounded by the cores so as to surround the outer periphery of the core discharge part. By arranging them in this manner and performing composite spinning under appropriate conditions, it is possible to apply an extrusion stress caused by the resin composition constituting the sea section 3 discharged from the sea section discharge part surrounded by each core to the resin composition constituting each core 1 discharged from each core discharge part with a substantially uniform strength from any direction, including up, down, left, and right.

[0061] If the balance of the extrusion stresses is always maintained, the cross-sectional shape of each core 1 will continue to be the same as the cross-sectional shape of each core discharge part as it cools and solidifies, and the cross-sectional shape of each core discharge part will continue to be reflected as it is in the cross-sectional shape of core 1. If the cross-sectional shape of each core discharge part is processed into a perfect circle with extremely high precision, it will be possible to form optical fiber 100 into a perfect cylinder with extremely little deformation of core 1.

[0062] The shape of the clad discharge portion may be a ring shape with an inner diameter equal to the inner diameter of the clad 2 and an outer diameter equal to the outer diameter of the clad 2, or an inner diameter slightly larger than the inner diameter of the clad 2 and an outer diameter slightly smaller than the outer diameter of the clad 2. That is, the former may be formed with the same width as the width of the clad 2, or the latter may be formed with a ring shape with a width slightly narrower than the width of the clad 2. Alternatively, the clad discharge portion may be formed as multiple spots at equal intervals on the center circle of the ring-shaped clad 2.

[0063] The timing of discharging the resin compositions constituting each of the core 1, clad 2, and sea portion 3 is preferably as simultaneous as possible, and even if there is a difference, it is preferable that the timing is less than one second, which is substantially the same as when the resin compositions are discharged simultaneously. The amount of each resin composition discharged is preferably such that the extrusion stress caused by the resin composition constituting the sea portion 3 discharged from the sea portion discharge portion surrounded by each core, which is applied to the resin composition constituting each core 1, and the extrusion stress caused by the resin composition constituting each core 1 discharged from each core discharge portion, which is applied to the resin composition constituting each sea portion 3, are the same at every location, and the stresses are continuously cancelled out, so that the cross-sectional shape of the core 1 can be maintained as a perfect circle. EXAMPLES

[0064] Examples of the present invention will be described below in comparison with comparative examples, but the present invention is not limited to these examples. Measurements and evaluations are as follows.

[0065] (1) Measurement of L1 (μm), L2 (μm), W (μm), and the inner diameter of the core Cross-sectional samples of the optical fiber were taken at three locations at 500m intervals, and cross-sectional photographs of each location were taken, enlarged, and the distances were measured using a scale. The average of the values ​​at the three locations was then calculated. The values ​​in the table are the weighted average of the three locations.

[0066] The inner diameter of the core was measured for all the cores in each of the three cross-sectional samples, and the average value D and standard deviation value σ were calculated. If the core was not circular, the major axis and inner diameter were measured, and the average value was taken as the inner diameter.

[0067] (2) Measurement of C The resin composition constituting the sea portion was formed into a film having a thickness of 100 μm, and the optical density was measured using a spectrodensitometer manufactured by X-lite.

[0068] The measurement was carried out five times at points at least 5 cm apart on a straight line of the molded film, and the average value was taken as the optical density. (3) Noise evaluation To measure noise, when laser light was incident on one core of an optical fiber, if light was emitted from one core at the output side of the optical fiber, it was determined that there was no noise, and if light was emitted from multiple cores, it was determined that there was noise.

[0069] Specifically, a 650 nm laser light source was used, and the laser light was focused by a lens and incident on one core from one end of an optical fiber (length: 10 m). At that time, the other end, which was the exit side, was observed with an optical microscope to determine whether one or more cores were emitting light.

[0070] Example 1 Polymethyl methacrylate was prepared as the resin composition constituting the core, and a copolymer of vinylidene fluoride units and tetrafluoroethylene units was prepared as the resin composition constituting the clad. A resin composition was prepared by stirring and dispersing 99.7% by weight of acrylic acid fluorinated ester polymer with 0.3% by weight of carbon black having an average particle size of 1 μm as the resin composition constituting the sea portion. Each of these was poured into a spinning pack incorporating an extrusion die, and after melting at 250°C, 265°C, and 270°C, respectively, polymer flows were discharged from each discharge port.

[0071] The extrusion die used was made by laminating four metering plates with metering holes, and a distribution plate with 168 distribution holes as a core discharge section, and a ring-shaped clad discharge section and a sea discharge section surrounding the core discharge section were provided with distribution holes. The discharge amounts of each material discharged from the core discharge section, clad discharge section, and sea discharge section were adjusted to 20.87 mg / min, 5.54 mg / min, and 18.00 mg / min. The spinning conditions were: discharge linear speed 0.3 m / min, take-up speed 5 m / min, take-up speed 5 m / min, draft ratio (= take-up speed / discharge linear speed) 16.7, and optical fiber outer diameter 495 μm.

[0072] Observation of the cross section of this optical fiber revealed that the minimum distance L1 from the sea outer periphery to the core closest to the sea outer periphery was 31 μm, the minimum distance L2 from the sea outer periphery to the core second closest to the sea outer periphery was 58 μm, and the narrowest distance W of the sea was 9 μm. The optical density C per 100 μm of the sea material was 0.9.

[0073] Therefore, L2 / L1 is 1.9, C 3 ×(W / 10) 3 ≦ value of 0.531, (W / 10) 3 / C 3The value of ≦ was 1.00, satisfying all the conditions of formulas (1) to (3). In addition, L1 / W was 3.44, satisfying the condition of 1 to 25. The average value D of the inner diameters of the multiple cores was 23.8 μm, and the standard deviation σ was 0.49 μm, meaning that σ / D was 2.1%, which means that there was very little variation in the inner diameters of the cores and that an optical fiber was obtained that was not adversely affected by noise.

[0074] (Example 2) to (Example 5) and (Comparative Example 1) and (Comparative Example 2) An optical fiber was formed in the same manner as in Example 1, except that the weight percentage of the copolymer and the weight percentage of the carbon black were appropriately changed in the resin composition constituting the sea portion. The results are shown in Table 1, including those of Example 1. From Table 1, when the optical density C per 100 μm of the resin composition constituting the sea portion was 0.14 or more and 1.61 or less, an optical fiber with no noise and a σ / D of 4.0% or less and very little variation in the inner diameter of the core could be obtained. On the other hand, when the optical density C per 100 μm of the sea portion resin composition was 0.13 or less, noise was generated, and when it was 1.62 or more, a part of the core was deformed and σ / D exceeded 4.0.

[0075] [Table 1]

[0076] Example 6 An optical fiber was formed in the same manner as in Example 1, except that the core discharge parts and clad discharge parts in the outermost layers were arranged in a circular shape so that the distances from the outer periphery of the sea part to each of the outermost clad layers were all the same 23 μm as shown in Figure 2, and the distances between the clad outer peripheries increased by 2 μm each from the center to the outermost layers, to 9, 11, and 13. The results are shown in Table 3. Table 2 shows that an optical fiber was obtained with a σ / D of 4.0 or less, with little variation in the inner diameter of the core, and without the adverse effects of noise.

[0077] Example 7 An optical fiber was formed in the same manner as in Example 6, except that the core discharge portion and the clad discharge portion in the outermost layer were partially sealed so that the distance from the outer periphery of the sea portion to each of the outermost clad layers was a maximum of 50 μm. The results are shown in Table 2. As can be seen from Table 2, an optical fiber was obtained in which σ / D was 4.0 or less, there was little variation in the inner diameter of the core, and there was no adverse effect of noise.

[0078] Example 8 An optical fiber was formed in the same manner as in Example 7, except that a portion of the core discharge portion and the clad discharge portion in the outermost layer were further sealed so that the distance from the outer periphery of the sea portion to each of the outermost clad layers was a maximum of 57 μm. The results are shown in Table 2. As can be seen from Table 2, an optical fiber was obtained in which σ / D was 4.0 or less, there was little variation in the inner diameter of the core, and there was no adverse effect of noise.

[0079] [Table 2] [Explanation of symbols]

[0080] 1. Core 2. Clad 3. Kaifu 4...Protective layer 6. Wide area of ​​the sea 100···Optical fiber L1: The minimum distance from the sea periphery to the core closest to the sea periphery (μm) L2: The minimum distance from the sea periphery to the core located second closest to the sea periphery (μm) W: Narrowest distance of the sea area

Claims

1. An optical fiber having a plurality of cores and a sea portion surrounding the cores, The sea portion contains a coloring substance, An optical fiber that satisfies the conditions of formulas (1) to (3). 1.0<L2 / L1≦3.8...(1) 0.002≦C ３ ×(W / 10) ３ ≦3.000 ・・・(2) 0.17≦(W / 10) ３ / C ３ ≦300.00 ・・・(3) (L1: the minimum distance (μm) from the outer periphery of the sea portion to the core located closest to the outer periphery of the sea portion, L2: the minimum distance (μm) from the outer periphery of the sea portion to the core located second closest to the outer periphery of the sea portion, W: the narrowest distance (μm) of the sea portion, C: the optical density per 100 μm of the resin composition constituting the sea portion)

2. 2. The optical fiber according to claim 1, wherein the core does not contain a coloring material or the content of the coloring material is 0.01% by weight or less.

3. The optical fiber according to claim 1 , further satisfying formula (4): 1≦L1 / W≦25 (4)

4. The optical fiber according to claim 1 , further comprising a cladding between the core and the sea portion that surrounds the core.

5. the cladding contains a coloring material; 2. The optical fiber according to claim 1, wherein a content (wt%) of the coloring material in the clad is smaller than a content (wt%) of the coloring material in the sea portion.

6. the coloring substance in the sea portion is carbon black having an average primary particle diameter of 0.1 to 10 μm, 2. The optical fiber according to claim 1, wherein the content of the carbon black in the sea portion is 0.3 to 5% by weight.

7. 2. The optical fiber according to claim 1, wherein the relationship between the average value D of the inner diameter of the core and the standard deviation σ satisfies σ / D≦4.0%.

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