JP6091081B2 - Multi-core optical fiber and manufacturing method thereof - Google Patents

Description

  The present invention relates to a multicore optical fiber and a method for manufacturing the same.

  In recent years, multi-core optical fibers have begun to be used as medical applications, particularly as endoscopes. An endoscope is a medical device for the purpose of observing the inside of a body cavity such as a human body, and is roughly classified into a rigid endoscope, a flexible endoscope, and a capsule endoscope. Among these, multi-core optical fibers are used in flexible endoscopes (such as fiberscopes) incorporating a flexible optical system. In general, a flexible endoscope is composed of a flexible tube and a multi-core optical fiber inserted into the flexible tube, and the observation target is to observe one end face of the multi-core optical fiber. This is done by enlarging the output image output to the other end face with a magnifying glass, a microscope or the like, and directly observing it. An objective lens, an eyepiece lens, or the like is provided at the tip of the multi-core optical fiber as necessary.

  As a multi-core optical fiber used in the above-described flexible endoscope (hereinafter, sometimes simply referred to as “endoscope”), for example, Patent Document 1 discloses a multi-core optical fiber having different core shapes. Is disclosed.

Japanese Patent Laid-Open No. 08-094864

  Incidentally, in recent years, it has been desired that the number of pixels of a multicore optical fiber (that is, the number of cores included in the multicore optical fiber) be as large as possible. This is because the larger the number of pixels, the clearer the obtained image. In particular, a medical device with a large number of pixels is desired.

  However, as the number of pixels increases, the number of pixel defects increases. The defect here refers to a defect that causes so-called transmission loss. For example, the presence of a core through which light does not pass, the presence of a core through which light leaks, or adjacent cores stick together. Etc. If there is such a defect, there is a problem that a clear and accurate image cannot be obtained for that portion.

  As described above, the presence of defects in the multi-core optical fiber is not preferable, but a certain amount of defects may be generated. In such a case, a person who performs production management of the multi-core optical fiber or a user needs to grasp the location where the defect exists.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multicore optical fiber in which a defect location can be easily identified.

  As a result of diligent research, the inventors of the present invention have a multicore optical fiber having a plurality of cores and a sheath formed on the outer periphery of the core, and the multicore optical fiber is in the axial direction. In an end section viewed in a cross-section in a substantially orthogonal direction, 80% or more and less than 100% of the total number of the cores included in the end section are cores having a roundness of 2.0 or less, and the roundness is It has been found that the above-mentioned problems can be solved by using a multicore optical fiber in which a core larger than 2.0 is disposed at a position other than the center of the end section, and the present invention has been completed.

That is, the present invention is as follows.
[1]
A multi-core optical fiber having a plurality of cores and a sheath formed on the outer periphery of the core,
In the multi-core optical fiber, in an end cross section viewed in a direction substantially orthogonal to the axial direction,
80% or more and less than 100% of the total number of the cores included in the end section is a core having a roundness of 2.0 or less,
The core having a roundness greater than 2.0 is disposed at a position other than the center of the end cross section,
Multi-core optical fiber.
[2]
A multi-core optical fiber having a plurality of cores and a sheath formed on the outer periphery of the core,
In the multi-core optical fiber, in an end cross section viewed in a direction substantially orthogonal to the axial direction,
Among the plurality of cores, 80% or more and less than 100% of the total number of cores excluding the core arranged on the outermost periphery is a core having a roundness of 2.0 or less,
In the core excluding the core disposed on the outermost periphery, a core having a roundness greater than 2.0 is disposed other than the center of the end cross section,
Multi-core optical fiber.
[3]
In the case where a plurality of cores having a circularity greater than 2.0 are arranged, the cores having a circularity greater than 2.0 are not in a point-symmetrical positional relationship with the center of the end cross section as a symmetry point. ,
The multicore optical fiber according to [1] or [2].
[4]
The multi-core optical fiber according to any one of [1] to [3], wherein the multi-core optical fiber has 50 cores or more.
[5]
A plurality of cores having a roundness of greater than 2.0, and
Two or more cores having a roundness greater than 2.0 are arranged side by side,
The multi-core optical fiber according to any one of [1] to [4].
[6]
At least three cores having a roundness greater than 2.0 are disposed, and
Three or more cores having a roundness greater than 2.0 are arranged on a substantially straight line from the center of the end cross section toward the outer periphery,
The multicore optical fiber according to any one of [1] to [5].
[7]
A method of manufacturing a multi-core optical fiber having a plurality of cores and a sheath formed on the outer periphery of the core,
(1) A molten core resin that is supplied with a molten core resin that forms the core and is discharged from a number of core resin discharge pipes corresponding to the number of the cores is formed into a molten sheath that forms the sheath. Coating with resin and obtaining a plurality of bare optical fibers in a molten state;
(2) bundling a plurality of molten optical fiber bare wires to obtain a molten multi-core optical fiber bare wire bundle;
(3) a step of gradually reducing the molten multi-core optical fiber bare wire bundle while stretching;
(4) The step of obtaining the multi-core optical fiber by curing the gradually refined molten multi-core optical fiber bare wire bundle;
Have
The cross-sectional shape of the inner diameter of the number of core resin discharge pipes that is greater than 0% and not more than 20% of the total number of core resin discharge pipes excluding the core resin discharge pipe corresponding to the core disposed at the center of the multi-core optical fiber, Greater than roundness 2.0,
A manufacturing method of a multi-core optical fiber.
[8]
A method of manufacturing a multi-core optical fiber having a plurality of cores and a sheath formed on the outer periphery of the core,
(1) A molten core resin that is supplied with a molten core resin that forms the core and is discharged from a number of core resin discharge pipes corresponding to the number of the cores is formed into a molten sheath that forms the sheath. Coating with resin to obtain a plurality of molten optical fiber bare wires;
(2) bundling a plurality of molten optical fiber bare wires to obtain a molten multi-core optical fiber bare wire bundle;
(3) a step of gradually reducing the molten multi-core optical fiber bare wire bundle while stretching;
(4) The step of obtaining the multi-core optical fiber by curing the gradually refined molten multi-core optical fiber bare wire bundle;
Have
In the step (1), the number of core resin discharge pipes is greater than 0% and not more than 20% of the total number of core resin discharge pipes excluding the core resin discharge pipe corresponding to the core disposed at the center of the multi-core optical fiber. At least to disturb the flow of the molten core resin by an obstacle disposed in the flow path of the molten core resin discharged from
A manufacturing method of a multi-core optical fiber.

  ADVANTAGE OF THE INVENTION According to this invention, the multi-core optical fiber with which the location of a defect can be specified easily can be provided.

The end sectional view of an example of the multi-core optical fiber bare wire of this embodiment. The conceptual diagram for demonstrating roundness. End sectional drawing of another example of the multi-core optical fiber bare wire of this embodiment. The end sectional view of still another example of the multi-core optical fiber bare wire of this embodiment. The conceptual diagram of another example of the multi-core optical fiber bare wire of this embodiment. The schematic longitudinal cross-sectional view which shows an example of the composite spinning die used in the manufacturing method of this embodiment. The schematic longitudinal cross-sectional view which shows another example of the composite spinning die used in the manufacturing method of this embodiment.

  Hereinafter, modes for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. And this invention can be deform | transformed suitably and implemented within the range of the summary. In the drawings, positional relationships such as up, down, left and right are based on the positional relationships shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. Furthermore, in the present specification, the term “abbreviated” indicates the meaning of the term excluding the “abbreviation” within the scope of technical common knowledge of those skilled in the art, and the meaning itself excluding “abbreviation” Is also included.

  The multi-core optical fiber of the present embodiment is a multi-core optical fiber having a plurality of cores and a sheath formed on the outer periphery of the plurality of cores, the axial direction of the multi-core optical fiber. In an end section viewed in a cross section in a substantially perpendicular direction, 80% or more and less than 100% of the number of cores included in the end section are cores having a roundness of 2.0 or less, and a roundness of 2 A core larger than 0.0 is a multi-core optical fiber disposed at a position other than the center of the end cross section. In this specification, “multi-core optical fiber” refers to so-called “multi-core optical fiber bare wire” and “multi-core optical fiber cable” in which the multi-core optical fiber bare wire is further coated with a coating layer or the like. Both are collectively referred to. Hereinafter, the case of “bare multi-core optical fiber” will be mainly described as an example.

  FIG. 1 shows an end cross-sectional view of an example of a multi-core optical fiber bare wire of the present embodiment. A multi-core optical fiber bare wire 1 according to the present embodiment has a plurality of cores 2 and 3 and a sheath 4 formed on the outer periphery of the cores 2 and 3 and is substantially orthogonal to the axial direction thereof. 80% or more and less than 100% of the total number of the cores 2 and 3 included in the end cross section is the core 2 having a roundness of 2.0 or less, and the roundness is 2.0. A larger core 3 is arranged other than the center of the end section. The multi-core optical fiber bare wire 1 has a structure in which cores 2 and 3 (island parts) are covered with a sheath 4 (sea part), and an image is transmitted by the cores 2 and 3 corresponding to the island parts. The multi-core optical fiber bare wire 1 has a defect 5. In the multi-core optical fiber bare wire 1, in order to specify and explain the position of the defect 5, the core 3 having a roundness greater than 2.0 is arranged at a place other than the center of the end cross section. By arranging the core 3 having a roundness greater than 2.0 other than the center, it is easy to specify and explain the position of the defect 5 using the core 3 as a reference point. From such a viewpoint, the roundness of the core 3 having a roundness greater than 2.0 is preferably 2.2 or more, more preferably 2.5 or more, and further preferably 3.0 or more. More preferably 3.5 or more.

  Usually, from the viewpoint of reducing transmission loss and the like, it is desired to make the shape and size of the core of the multi-core optical fiber bare wire uniform. Therefore, when a defect occurs in a multicore optical fiber bare wire, there is no portion that can serve as a reference point for describing the position in the end cross section, and therefore it may be difficult to specify and explain the position of the defect. For example, when the defect 5 occurs during the production of the multi-core optical fiber bare wire 1, the core filled in the multi-core optical fiber bare wire 1 is specified as the defect 5, and other workers and use I need to teach them. At this time, if the core 3 having a characteristic shape as described above and having a roundness greater than 2.0 is arranged, the position of the defect 5 can be specified and explained using the core 3 as a reference point. For example, in FIG. 1, it can be said that the defect 5 exists at a position adjacent to the core 3 that is the reference point.

The roundness of the core is a ratio of the minimum circumscribed circle radius r ₂ of the core cross-sectional shape to the maximum inscribed circle radius r ₁ of the core cross-sectional shape. Hereinafter, the case where the roundness of the core 3 having a roundness of 2.0 larger than 2.0 in FIG. 1 is obtained will be described as an example. FIG. 2 is a conceptual diagram for explaining a method of measuring roundness. First, the largest inscribed circle C1 and the smallest circumscribed circle C2 of the core 3 are drawn. Then, a ratio (r ₂ / r ₁ ) of the minimum circumscribed circle radius r _{2 to} the maximum inscribed circle radius r ₁ is obtained, and this is set as the roundness of the core 3. Specifically, it can be determined by the following method. Take 1 meter of multi-core optical fiber bare wire, and attach its end cross section to a lighted LED light panel (Lumi Techno Co., "A4G-L1316-SFR23"), and connect the other end cross section to a digital microscope (Keyence). (VH-5500, manufactured by the company) and magnified 200 times before imaging. As an objective lens of the digital microscope, “VH-Z100” manufactured by Keyence Corporation can be used. Next, the captured image of the end cross section is loaded into a computer and binarized using image analysis software (Adobe's “photoshop”) so that the core portion is a white region and the other portions are black regions. To do. The roundness of the core that is the white region is determined by obtaining the maximum inscribed circle radius r ₁ and the minimum circumscribed circle radius r ₂ of the region, and the minimum circumscribed circle radius with respect to the maximum inscribed circle radius r ₁ . It is obtained by determining the ratio of _{r 2 (r 2 / r 1} ). The average roundness of a plurality of cores refers to the arithmetic average of the roundness of each core that is a measurement target.

  From the viewpoint of further reducing transmission loss, the roundness of a core having a roundness of 2.0 or less may be 2.0 or less, preferably 1.8 or less, more preferably 1. It is 5 or less, More preferably, it is 1.2 or less, More preferably, it is 1.1 or less.

Moreover, in the multi-core optical fiber bare wire 1, it is preferable that each cross-sectional area of the core 2 whose roundness is 2.0 or less is substantially equal in the end cross section. By making the cross-sectional areas of the cores 2 having a roundness of 2.0 or less substantially equal, variations in the resolution of the multi-core optical fiber bare wire 1 can be suppressed. As a result, there is less discomfort when the output image is visually observed, and the image is easier to see. Specifically, the number N of wicks 2 having a roundness of 2.0 or less, the average cross-sectional area Sa of the wicks 2, and the cross-sectional area Sn of each wick 2 more preferably satisfy the relationship of the following formula (1). Preferably, the relationship of the following formula (2) is further satisfied, the relationship of the following formula (3) is more preferably satisfied, and the relationship of the following formula (4) is more preferably satisfied.

  The multi-core optical fiber bare wire 1 that satisfies the above relational expression can further suppress variations in resolution, and has a less uncomfortable feeling when the output image is visually observed.

  The shape of the core 2 having a roundness of 2.0 or less is preferably a substantially circular shape or a substantially regular hexagonal shape, more preferably a substantially circular shape, from the viewpoint of easy manufacture. The cores having a roundness of 2.0 or less preferably have substantially the same shape. When the core shapes are substantially the same, there is little variation in resolution, and there is less discomfort when visually observing the output image, resulting in a more easily viewable image.

  The multi-core optical fiber bare wire 1 is a multi-core optical fiber bare wire composed of the cores 2 and 3 and the sheath 4 covering the core, and is a so-called sea-island multi-core optical fiber bare wire. The form is not necessarily limited to such a structure. For example, a multi-core optical fiber bare wire having a structure in which the outer periphery of the core is covered with a sheath layer and further filled with sea resin may be used. In addition, a multi-core optical fiber bare wire having a bundle structure in which single-core optical fiber bare wires are collected may be used, but a multi-core optical fiber bare wire having a sea-island structure is preferable from the viewpoint of easy manufacture. In the present specification, the “sheath” includes a so-called “sheath layer”. Hereinafter, a specific description will be given with reference to FIG.

  FIG. 3 is an end cross-sectional view of another example of the multi-core optical fiber bare wire of the present embodiment. The multi-core optical fiber 6 includes a core 7 having a roundness of 2.0 or less and cores 8a and 8b having a roundness of greater than 2.0 (hereinafter may be collectively referred to as “core 8”). A sheath layer 9 formed on the outer periphery of the cores 7 and 8, and further filled with a sea resin 10. The multicore optical fiber bare wire 6 has a roundness of 80% or more and less than 100% of the total number of the cores 7 and 8 included in the end cross section in the end cross section viewed in a direction substantially orthogonal to the axial direction. Is a core 7 having a circularity of 2.0 or less, and a core 8 having a roundness greater than 2.0 is disposed at a position other than the center of the end cross section. When the defect 11 exists in the end cross section of the multi-core optical fiber bare wire 6, the position of the defect 11 is specified by using the core 8 as a reference point by arranging the core 8 having a roundness greater than 2.0 other than the center.・ Easy to explain.

  From the viewpoint of facilitating the identification and explanation of the position of the defect 11, it is preferable to arrange a plurality of the cores 8 having a roundness greater than 2.0 used as the reference point. Specifically, the number of cores 8 having a roundness greater than 2.0 is preferably 2 or more, more preferably 3 or more, and still more preferably 4 or more. The upper limit of the number of cores 8 having a roundness greater than 2.0 is not particularly limited, but is preferably 30 or less, more preferably 20 or less, and particularly preferably 10 or less. In addition, when there are a plurality of cores having a roundness greater than 2.0, it is sufficient that at least one of the cores is arranged at a position other than the center of the end cross section. It is preferable to arrange other than the center of the cross section.

  The radius of the multi-core optical fiber bare wire 1 is not particularly limited, but is preferably 100 μm to 1500 μm, more preferably 100 μm to 1000 μm, and more preferably 100 μm to 500 μm from the viewpoint of medical use such as an endoscope. It is still more preferable that it is 100 micrometers-350 micrometers.

  FIG. 4 is an end cross-sectional view of still another example of the multi-core optical fiber bare wire of the present embodiment. FIG. 4 differs from FIG. 3 in the shape, number and arrangement of cores with roundness greater than 2.0. Hereinafter, the description of the configuration similar to the configuration of the multicore optical fiber bare wire in FIG. 3 will be omitted, and different points will be mainly described.

  The multi-core optical fiber bare wire 12 is collectively referred to as a core 13 having a roundness of 2.0 or less and cores 14a, 14b, 14c, and 14d having a roundness of greater than 2.0 (hereinafter referred to as “core 14”). And a sheath layer 15 formed on the outer periphery of the cores 13 and 14 and further filled with a sea resin 16. The multicore optical fiber bare wire 12 has a roundness of 80% or more and less than 100% of the total number of the cores 13 and 14 included in the end cross section in the end cross section viewed in a direction substantially orthogonal to the axial direction. Is the core 13 having 2.0 or less. The cores 14a and 14b having a roundness greater than 2.0 are arranged adjacent to each other, and the cores 14a and 14b having a roundness greater than 2.0 are arranged adjacent to each other. Are arranged at positions other than the center of the end cross section. Although the defect 17 exists in the end cross section of the multi-core optical fiber bare wire 12, since the four cores 14 having a roundness greater than 2.0 are arranged, the location and position of the defect 17 can be specified and explained. Easy.

  By the way, depending on the manufacturing process of the multi-core optical fiber bare wire 12, it is difficult to adjust the pressure applied to the core 14 disposed on the outermost periphery, or the roundness of the core 14 disposed on the outermost periphery is adjusted. Since it may be difficult, it is preferable not to use the core 14 arranged on the outermost periphery as a defect identifying mark. From this point of view, in the multicore optical fiber bare wire 12, the number of cores having a roundness of 2.0 or less is 80% or more and less than 100% of the total number of cores excluding the cores arranged on the outermost periphery. It is preferable.

  When a plurality of cores 14 with roundness greater than 2.0 are arranged, the centers of the end cross-sections are symmetrical points (symmetric centers), and the cores 14 with roundness greater than 2.0 are point-symmetrical positional relationships. Preferably not. Such an arrangement makes it easier to understand as a reference point for specifying the position of the defect. For example, when the defect 17 is specified, all the four cores 14a, 14b, 14c, and 14d can be used as the reference points. For example, in the end section where the cores 14a, 14b are arranged at the same position (the same height) in the vertical direction and the cores 14a, 14c, 14d are arranged at the same position in the horizontal direction, the cores 14b are moved upward from the core 14b. It is possible to specify that the defect 17 exists at the third position and at the first position in the right direction from the core 14d (see FIG. 4).

  From the viewpoint of easily specifying the position of the defect, in the end cross section of the multi-core optical fiber, a plurality of the cores 14 having a roundness greater than 2.0 are arranged and the roundness is greater than 2.0. It is preferable that two or more of the cores 14 are arranged side by side. That is, the cores 14a and 14b having a roundness greater than 2.0 are disposed adjacent to each other, and the cores 14c and 14d having a roundness greater than 2.0 are disposed adjacent to each other. Since there is a region where the cores 14 that can serve as reference points are arranged adjacent to each other (hereinafter sometimes referred to as “reference region”), it is easier to understand as a reference for specifying the position of the defect. In particular, even when the number of cores of the multi-core optical fiber bare wire (the total number of cores 13 and 14) is large and the cores are arranged at high density, the position of the defect 17 can be specified and explained.

  The arrangement of the core 18 in the end cross section of the multi-core optical fiber bare wire 18 of the present embodiment is not particularly limited, and a random arrangement, a radial arrangement, a stacked arrangement, and the like can be adopted. Among these, a stacked arrangement is preferable from the viewpoint that the cores can be arranged at high density. As used herein, “stacking” refers to stacking other cores in a valley formed between adjacent cores. This configuration is preferable because a useless space can be reduced as much as possible in the arrangement of the core 11 and the filling rate of the core can be improved.

  Further, although not shown, a protective layer or a coating layer may be provided on the outer periphery of the multi-core optical fiber bare wire 18. Examples of the protective layer include vinylidene fluoride resins. Examples of the coating layer include polyolefin resins and polyamide resins.

  The total number of the cores 14 of the multi-core optical fiber bare wire 18 of the present embodiment is preferably 50 or more, more preferably 100 or more, still more preferably 200 or more, 1000 cores or more are particularly preferable, and 3000 cores or more are more preferable. In particular, when the number of cores is large (in the case of high density arrangement), it is difficult to specify the position of the defect. For this reason, the use of a core having a core circularity of greater than 2.0 as the reference point / reference region makes it easier to identify and explain the position of the defect. The upper limit is preferably 40000 cores or less, more preferably 30000 cores or less, and particularly preferably 15000 cores or less from the viewpoint of manufacturability.

FIG. 5 is a conceptual diagram of still another example of the multi-core optical fiber bare wire of the present embodiment. In the multi-core optical fiber bare wire 18, cores 19 a, 19 b, 19 c, 19 d, and 19 e (hereinafter, may be collectively referred to as “core 19”) that are reference points and have a roundness greater than 2.0. It is arranged on a substantially straight line l from the center C _{3 of the} end section toward the outer periphery. Thus, the position of the defect is that three or more cores having a roundness greater than 2.0 are arranged on a substantially straight line from the center to the outer periphery in the end cross section of the multi-core optical fiber bare wire. Is preferable from the viewpoint of facilitating identification. In FIG. 5, as an example, a structure having a core and a sheath layer formed on the outer periphery of the core and filled with sea resin is described as an example. It may be composed of a core and a sheath.

  Hereinafter, the material of each member used for the multicore optical fiber bare wire of this embodiment is demonstrated.

The core material of the multi-core optical fiber bare wire of the present embodiment is not particularly limited. Various transparent resins can be used as the core material. The same material can be used for the core having a roundness of 2.0 or less and the core having a roundness of 2.0 or more. The transparent resin constituting the core (hereinafter sometimes referred to as “core resin”) includes methyl methacrylate resin, styrene resin, polycarbonate resin, lactone compound represented by the following formula (a), and amorphous resin It is preferably at least one selected from the group consisting of polyolefin resins, and among these, methyl methacrylate resins are more preferable.
(In the formula, R ₁ represents a methyl group, an ethyl group or a propyl group, and X is represented by the following formula (b) or formula (c)).
(In the formula, R ₂ and R ₃ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a fluorine-containing alkyl group having 1 to 12 carbon atoms, a phenyl group, or a cyclohexyl group.)

  Examples of the methyl methacrylate resin include, for example, methyl methacrylate homopolymer; methyl methacrylate and other components copolymerizable with methyl methacrylate (acrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, Methacrylic acid esters of ethyl methacrylate, propyl methacrylate, cyclohexyl methacrylate, maleimides, acrylic acid, methacrylic acid, maleic anhydride, styrene and the like) and copolymers thereof. In the copolymer of methyl methacrylate and another monomer, the content of methyl methacrylate is preferably 50% by mass or more, and more preferably 70% by mass or more. Since the methyl methacrylate resin has high transparency, it has an advantage that image transmission over a long distance is possible in a multi-core optical fiber bare wire.

  Examples of the styrenic resin include a styrene homopolymer; styrene and other components copolymerizable with styrene (acrylonitrile-styrene copolymer, styrene-methyl methacrylate copolymer, styrene-maleic anhydride copolymer, Styrene-six-membered cyclic acid anhydride copolymer, etc.) and copolymers with one or more types. In the copolymer of styrene and another monomer, the styrene content is preferably 50% by mass or more, and more preferably 70% by mass or more. Since the styrene resin has low hygroscopicity, it has an advantage that it is hardly affected by moisture.

  Examples of the lactone compounds represented by the above formula (a) include α-methylene-β-methyl-γ-butyrolactone (βMMBL), α-methylene-β-ethyl-γ-butyrolactone (βEMBL), α-methylene. -Β-propyl-γ-butyrolactone (βPMBL), α-methylene-β-methyl-γ-methyl-γ-butyrolactone (βMγMMBL), α-methylene-β-methyl-γ-dimethyl-γ-butyrolactone (βMγDMMBL), α-methylene-β-methyl-γ-ethyl-γ-butyrolactone (βMγEMBL), α-methylene-β-methyl-γ-propyl-γ-butyrolactone (βMγPMBL), α-methylene-β-methyl-γ-cyclohexyl- γ-butyrolactone (βMγCHMBL), α-methylene-β-ethyl-γ-methyl-γ-butyrolactone (βEγ) MBL), α-methylene-β-ethyl-γ, γ-dimethyl-γ-butyrolactone (βEγDMMBL), α-methylene-β-ethyl-γ-ethyl-γ-butyrolactone (βEγEMBL), α-methylene-β-ethyl. -Γ-propyl-γ-butyrolactone (βEγPMBL), α-methylene-β-ethyl-γ-cyclohexyl-γ-butyrolactone (βEγCHMBL). When a lactone compound is used as the core resin, only the above lactone compound; a copolymer of the lactone compound and a (meth) acrylic acid ester monomer; or a mixture thereof may be used.

  In the copolymer of the lactone compound and the (meth) acrylic acid ester monomer, the content of the lactone compound depends on the physical properties such as the glass transition temperature (Tg) and mechanical strength of the resin. Although it can be selected if it is appropriately determined so as to be a value suitable for the application and use environment, it is preferably 5 to 50% by mass.

In particular, in the above formula (b), R ₂ and R ₃ are both hydrogen atoms (α-methylene-β-methyl-γ-butyrolactone (βMMBL), α-methylene-β-ethyl-γ-butyrolactone (βEMBL) , Α-methylene-β-propyl-γ-butyrolactone (βPMBL) or the like) is preferably used as the core resin. A multi-core optical fiber bare wire using these as a core resin is preferable because it has very high optical transparency. Among these, βMMBL and βEMBL are more preferable because they can significantly increase the glass transition temperature of the resin even when added in a small amount.

  Examples of the polycarbonate-based resin include aliphatic polycarbonates and aromatic polycarbonates, and these and dioxy compounds such as 4,4-dioxyphenyl ether, ethylene glycol, p-xylene glycol, and 1,6-hexanediol. Examples thereof include a copolymer and a hetero bond copolymer having an ester bond in addition to a carbonate bond. Polycarbonate resins have the advantages of high heat resistance and low hygroscopicity.

  Commercial products can also be used as the amorphous polyolefin resin. For example, commercially available products such as “Arton” manufactured by JSR, “Apel” manufactured by Mitsui Chemicals, and “ZEONEX” manufactured by Nippon Zeon Co., Ltd. can be used. Amorphous polyolefin resin has the advantage of excellent heat resistance.

  It is preferable that the core resins constituting each core of the multicore optical fiber bare wire are of the same type. By configuring the core from the same core resin, variations in transmission loss can be suppressed. As a result, an output image with little difference in brightness for each core can be obtained, and the uncomfortable feeling when observing the output image can be reduced.

  The melt index (MI) of the core resin is preferably 0.5 to 10.0 g / 10 minutes. The melt index here is measured in accordance with ASTM-D1238 under conditions of a test temperature of 230 ° C., a load of 3.8 kg, and a die inner diameter of 2.0955 mm. By setting the melt index of the core resin within the above range, composite spinning with a sheath resin described later becomes easy.

  As a material constituting the sheath and the sheath layer, a resin (hereinafter, also referred to as “sheath resin”) can be used. As the sheath resin, a resin having a refractive index 0.005 to 0.250 lower than the refractive index of the core resin is preferable, and a resin having a refractive index 0.005 to 0.040 lower than the refractive index of the core resin is more preferable. preferable. By controlling the refractive indexes of the core resin and the sheath resin as described above, the numerical aperture of the multi-core optical fiber bare wire can be adjusted. The refractive index referred to here is a value when measured using sodium D-line as a light source in a constant temperature room at 23 ° C. using an Abbe refractometer.

The type of the sheath resin is not particularly limited, but a methacrylate resin, an acrylate resin, a vinylidene fluoride resin, a lactone compound represented by the following formula (d), and the like are preferable.
(In the formula, R ₄ and R ₅ each independently represent a hydrogen atom, a methyl group or an ethyl group, and the total number of carbon atoms of R ₄ and R ₅ is 1 to 3).

  Examples of the methacrylate resin include fluorinated methacrylate (trifluoroethyl methacrylate, tetrafluoropropyl methacrylate, pentafluoropropyl methacrylate, heptadecafluorodecyl methacrylate, octafluoropropentyl methacrylate, etc.), methyl methacrylate, ethyl methacrylate, propyl methacrylate, A homopolymer of a methacrylate monomer such as butyl methacrylate; a copolymer of 50% by mass or more of a methacrylate monomer and one or more other components copolymerizable with methyl methacrylate. Methacrylate resins have the advantages of high transparency and low light transmission loss.

  Examples of the acrylate resin include homopolymers of acrylate monomers such as fluorinated acrylates (trifluoroethyl acrylate, tetrafluoropropyl acrylate, octafluoropentyl acrylate, etc.), methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, etc. And a copolymer of 50% by mass or more of the monomer and one or more other components copolymerizable with the acrylate monomer.

  Further, it may be a copolymer of the above-mentioned methacrylate monomer and the above-mentioned acrylate monomer.

Examples of the lactone compound represented by the formula (d) include α-methylene-β-methyl-γ-butyrolactone, α-methylene-β, β-dimethyl-γ-butyrolactone, α-methylene-β-ethyl-γ-butyrolactone. Etc. Among these, α-methylene-β-methyl-γ-butyrolactone, in which either one of R ₄ and R ₅ represents a hydrogen atom and the other represents a methyl group, is a resin glass even in a small amount. The transition temperature can be significantly increased, the copolymerizability with the fluoroalkyl (meth) acrylate is good, and the transparency of the resulting copolymer is further enhanced, which is preferable.

  Preferred fluoroalkyl (meth) acrylates for copolymerization with the lactone compound include 2- (perfluorooctyl) ethyl methacrylate (17FMA), 2,2,2-trifluoroethyl (3FMA) (meth) acrylate, (Meth) acrylic acid 2,2,3,3,3-pentafluoropropyl (5FMA), 2- (perfluorooctyl) ethyl methacrylate (17FMA), α-fluoroacrylic acid 2,2,2-trifluoroethyl (Α3FA), α-fluoroacrylic acid 2,2,3,3,3-pentafluoropropyl (α5FA), (meth) acrylic acid 2,2,3,3-tetrafluoropropyl (4FMA), (meth) acrylic Acid 2,2,3,3,4,4,5,5-octafluoropentyl (8FMA), methyl α-fluoroacrylate (ΑFMe) and the like. In particular, copolymerization with 2- (perfluorooctyl) ethyl methacrylate (17FMA) is more preferable because it can impart mechanical strength to the sheath material without impairing transparency.

  As vinylidene fluoride resin, one or more types of vinylidene fluoride resin; vinylidene fluoride and other components copolymerizable with vinylidene fluoride (tetrafluoroethylene, trifluoroethylene, hexafluoropropylene, hexafluoroacetone, etc.) And a copolymer. In the copolymer of vinylidene fluoride and another monomer, the content of vinylidene fluoride is preferably 50% by mass or more, and more preferably 70% by mass or more.

  The sheath resin may be a single resin as described above or a blend thereof. Furthermore, if necessary, for example, a modifier such as methacrylic acid, o-methylphenylmaleimide, maleimide, maleic anhydride, styrene, acrylic acid, methacrylic acid six-membered cyclized product, etc. is introduced into the above-mentioned resin for modification. It can also be made. The modifier is preferably 5 parts by mass or less with respect to 100 parts by mass of the resin. Specific examples of such a modified (co) polymer include, for example, a copolymer of heptadecafluorodecyl methacrylate and methyl methacrylate, a copolymer of tetrafluoropropyl methacrylate and methyl methacrylate, trifluoroethyl methacrylate and methyl. Copolymer of methacrylate, copolymer of pentafluoropropyl methacrylate and methyl methacrylate, copolymer of heptadecafluorodecyl methacrylate, tetrafluoropropyl methacrylate and methyl methacrylate, heptadecafluorodecyl methacrylate and trifluoroethyl methacrylate Copolymer with methyl methacrylate, heptadecafluorodecyl methacrylate, trifluoroethyl methacrylate and tetrafluoropropyl methacrylate Copolymers of methyl methacrylate with.

  The sheath resin can be appropriately selected in consideration of the refractive index of the core and the refractive index of the sheath (sheath layer), but from the viewpoint of balance of heat resistance, transparency, mechanical properties, etc. It is preferable to use a vinylidene resin as the sheath resin.

  The melt index (MI) of the sheath resin is preferably 1 to 200 g / 10 minutes. By setting the melt index of the sheath resin within the above range, composite spinning with the sheath resin described later becomes easy.

  In addition, when using sea resin (for example, refer FIG.3 and FIG.4) other than a core and a sheath, as the material of sea resin, the same thing as sheath resin can be used. Examples of the sea resin include vinylidene fluoride resins.

  Moreover, the multi-core optical fiber bare wire according to the present embodiment can be applied to a hollow multi-core optical fiber in which a central portion of the multi-core optical fiber is hollow as described in JP-A-06-186445. .

  Hereinafter, the suitable example of the manufacturing method of the multi-core optical fiber bare wire of this embodiment is demonstrated.

First, as a first manufacturing method, a manufacturing method of a multi-core optical fiber having a plurality of cores and a sheath formed on the outer periphery of the plurality of cores,
(1) A molten core resin that is supplied with a molten core resin that forms the core and is discharged from a number of core resin discharge pipes corresponding to the number of the cores is formed into a molten sheath that forms the sheath. Coating with resin to obtain a plurality of molten optical fiber bare wires;
(2) bundling a plurality of molten optical fiber bare wires to obtain a molten multi-core optical fiber bare wire bundle;
(3) a step of gradually reducing the molten multi-core optical fiber bare wire bundle while stretching;
(4) obtaining the multi-core optical fiber bare wire by curing the gradually refined molten multi-core optical fiber bare wire bundle;
Have
The cross-sectional shape of the inner diameter of the number of core resin discharge pipes that is greater than 0% and 20% or less of the total number of core resin discharge pipes excluding the core resin discharge pipe corresponding to the core disposed at the center of the multi-core optical fiber, And a method for producing a bare multi-core optical fiber having a roundness greater than 2.0.

The second manufacturing method is a method of manufacturing a multi-core optical fiber bare wire having a plurality of cores and a sheath formed on the outer periphery of the core,
(1) A molten core resin that is supplied with a molten core resin that forms the core and is discharged from a number of core resin discharge pipes corresponding to the number of the cores is formed into a molten sheath that forms the sheath. Coating with resin to obtain a plurality of molten optical fiber bare wires;
(2) bundling a plurality of molten optical fiber bare wires to obtain a molten multi-core optical fiber bare wire bundle;
(3) a step of gradually reducing the molten multi-core optical fiber bare wire bundle while stretching;
(4) obtaining the multi-core optical fiber bare wire by curing the gradually refined molten multi-core optical fiber bare wire bundle;
Have
In the step (1), the number of core resins is greater than 0% and not more than 20% of the total number of core resin discharge tubes excluding the core resin discharge tube corresponding to the core disposed at the center of the multi-core optical fiber bare wire. A method for manufacturing a multi-core optical fiber bare wire that at least disturbs the flow path of the molten core resin by an obstacle disposed in the flow path of the molten core resin discharged from the discharge pipe It is done.

  The production method of the present embodiment is only required to satisfy the above conditions, and examples thereof include a spinning method using a composite spinning die (hereinafter sometimes simply referred to as “die”). As a method for manufacturing the multi-core optical fiber bare wire of the present embodiment, for example, a molten core resin and a molten sheath resin are supplied to a die, and the melted core resin is used as a pixel of the multi-core optical fiber bare wire. The molten core resin is extruded from the distribution plate provided with the number of holes corresponding to the number, and a molten core is prepared. Subsequently, the molten core resin is evenly supplied around the molten core, so that the molten core (core resin) serving as the core is directly covered with the molten sheath resin. A plurality of core optical fiber bare wires (the number of holes provided in the distribution plate) are produced. After that, a molten single-core optical fiber bare wire is integrated in the vicinity of the discharge hole of the die to form a molten multi-core optical fiber bare wire bundle, which is then drawn down, drawn into a fiber, and cured. preferable.

  Subsequently, the manufacturing method of the present embodiment will be described more specifically by taking a method using a composite spinning die as an example. In the method shown below, a molten core resin as a core is coated with a molten sheath resin as a sheath to obtain a plurality of molten optical fiber bare wires, and the molten optical fiber bare And bundling a plurality of wires to produce a molten optical fiber bare wire bundle to obtain a molten optical fiber bare wire bundle. Each step can be performed by extruding a molten core resin and sheath resin using a die. Here, a case where a multi-core optical fiber bare wire having a substantially circular cross section is manufactured will be described as an example, and in particular, a die will be described in more detail.

(First manufacturing method)
FIG. 6 is a schematic longitudinal sectional view showing an example of a composite spinning die used in the manufacturing method of the present embodiment. A composite spinning die (die) 20 includes an upper distribution plate 21, a lower distribution plate 22 disposed in a vertical lower portion of the upper distribution plate 21, a collecting base 23 disposed in a vertical lower portion of the lower distribution plate 22, and a core resin. And a discharge pipe 24 (hereinafter, simply referred to as “pipe 24”).

  The upper distribution plate 21 has a core resin distribution chamber 25 for distributing and supplying molten core resin so as to constitute each core. On the bottom surface of the core resin distribution chamber 25, a plurality of first through holes H1 for introducing the tube 24 are provided.

  The lower distribution plate 22 has a sheath resin distribution chamber 26 for distributing and supplying the molten sheath resin so as to cover the melt-extruded core resin (melted core). The bottom surface of the sheath resin distribution chamber 26 is provided with a plurality of substantially circular second through holes H2 serving as a flow path for the melted sheath resin.

  The tube 24 is inserted into both the upper distribution plate 21 and the lower distribution plate 22 by being inserted into both the first through hole H1 of the upper distribution plate 21 and the second through hole H2 of the lower distribution plate 22. Yes.

  The collecting base 23 is provided with an inverted frustoconical gap H3 where the molten core resin pumped from the upper distribution plate 21 and the molten sheath resin pumped from the lower distribution plate 22 merge. A discharge hole H4 for discharging the molten multi-core optical fiber bare wire to the outside is provided on the bottom surface of the collecting base 23.

  The inclination angle α (sometimes referred to as “die angle”) of the discharge hole H4 of the collecting base 23 is preferably 15 to 35 degrees (see FIG. 4). By setting the inclination angle α to 15 to 35 degrees, the core resin (island component resin) discharged from the bottom surface of the lower distribution plate 22 and the sheath resin (sea component resin) covering the periphery thereof are discharged into the discharge holes H4 of the collecting base 23. Can be assembled smoothly.

  The hole diameter (diameter) of the discharge hole H4 is preferably 1.5 to 15.5 times the diameter of the multi-core optical fiber bare wire. By setting the size of the hole diameter of the discharge hole H4 to the above value, sufficient stretching becomes possible, breakage of the bare multi-core optical fiber can be suppressed, and an appropriate drop rate can be obtained. As a result, the resulting multi-core optical fiber bare wire has fewer pixel defects.

  The core resin supplied to the core resin distribution chamber 25 passes through the pipe 24 and is discharged from the bottom surface of the lower distribution plate 22. The sheath resin supplied to the sheath resin distribution chamber 26 is discharged from the bottom surface of the lower distribution plate 22 through the second through hole H2. As a result, a molten single-core optical fiber bare wire in which the periphery of one molten core formed of the molten core resin is coated with the molten sheath resin is discharged. These molten single-core optical fiber bare wires are bundled at the collecting base 23 to form a molten multi-core optical fiber bare wire bundle. In addition, it is preferable to use a gear pump (not shown) for flow control from the viewpoint of accurately controlling the flow rates of the core resin and the sheath resin.

  In the present embodiment, the number of pixels of the multi-core optical fiber corresponds to the number of cores of the multi-core optical fiber bare wire. The number of cores of the multi-core optical fiber corresponds to the number of first through holes H1 and tubes 24 of the die 20. The cross-sectional area and shape of the core correspond to the size and shape of the inner diameter of the corresponding tube 24. The arrangement of the cores in the multi-core optical fiber bare wire corresponds to the arrangement of the first through holes H1 and the tubes 24 in the die 20. For example, in order to obtain a multi-core optical fiber bare wire with a high pixel density, it is preferable to arrange the first through holes H1 and the tubes 24 in a stacked manner, and to close the arrangement interval. The thickness of the sheath corresponds to the flow rate of the molten sheath resin passing through the second through hole H2.

  Therefore, in order to form a core having a roundness of greater than 2.0, the cross-sectional shape of the inner diameter of the tube 24 forming the core may be a shape having a roundness of greater than 2.0. At that time, since the roundness of the inner diameter of the tube 24 only needs to be larger than 2.0, the outer diameter of the tube 24 and the size and shape of the second through hole H2 arranged around the tube 24 are There is no particular limitation. The roundness is preferably 2.2 or more, more preferably 2.5 or more, still more preferably 3.0 or more, and still more preferably 3.5 or more. By setting the roundness within the above range, it is easy to understand as a reference point for specifying and explaining the position of the defect described above.

  In order to configure the above-described core having a roundness of 2.0 or less, the cross-sectional shape of the tube 24 for forming the core may be a shape having a roundness of 2.0 or less. At that time, since the roundness of the inner diameter of the tube 24 may be 2.0 or less, the outer diameter of the tube 24 and the size and shape of the second through hole H2 arranged around the tube 24 are There is no particular limitation. The roundness is preferably 1.8 or less, more preferably 1.5 or less, still more preferably 1.2 or less, and still more preferably 1.1 or less. By setting the roundness to a smaller value, a multi-core optical fiber bare wire with less transmission loss can be obtained.

  The cross-sectional shape of the inner diameter of the tube 24 having a roundness of 2.0 or less is preferably a substantially circular shape or a substantially regular hexagonal shape, more preferably a substantially circular shape, from the viewpoint of easy manufacture.

  The arrangement ratio of the tubes 24 having a roundness of 2.0 or less is preferably 80% or more and less than 100% of the total number of the tubes 24 of the die 2, and more preferably 90% or more and less than 100%. 95% or more and less than 100%, more preferably 99% or more and less than 100%. On the other hand, the cross-sectional shape of the inner diameter of the remaining tube 24 is greater than the roundness 2.0.

As a specific example of the above-described tube 24 for the core having an inner diameter roundness of 2.0 or less, a circular tube 24 having a cross section of 0.20 mm to 2.00 mm in outer diameter is preferable. Moreover, it is preferable that the value of the ratio (E1 / E2) represented using the following E1 and E2 is 0.1-5.0 from a viewpoint which comprises a sheath.
E1: (Cross sectional area of second through hole H2−Cross sectional area of outer diameter of tube 24)
E2: (Cross sectional area of the inner diameter of the tube 24)

  About the die | dye 20, it is preferable that the 2nd through-hole H2 is arrange | positioned at equal intervals and a pile shape.

  When vinylidene fluoride resin is used as the sheath resin, the temperature of the die 20 is preferably 230 ° C. to 250 ° C., the diameter of the distribution plate is 15 cm to 30 cm, and the thickness is 0.3 cm to 4 cm. It is preferable. Moreover, when using fluorinated acrylate-type resin as sheath resin, it is preferable that the temperature of the die | dye 20 is 220 to 250 degreeC. When an ethylene-tetrafluoroethylene resin is used as the sheath resin, the temperature of the die 20 is preferably 220 ° C to 260 ° C.

  As described above, in the multi-core optical fiber bare wire, it is preferable that the shapes of the cores having a roundness of 2.0 or less are substantially the same, so that the cores having a roundness of 2.0 or less are used. It is preferable that the volume of the core resin discharged per unit time from the tube 24 to be formed is substantially the same in each tube.

  Furthermore, from the viewpoint of facilitating control, it is preferable that the positional relationship between the pipe 24 and the second through hole H2 into which the pipe 24 is inserted is arranged substantially concentrically. In order to form a core having a roundness of 2.0 or less, the inner diameter and the outer diameter of each pipe 24 are all substantially the same, or the pipe 24 and the corresponding second through hole H2 are arranged outside. It is preferable that the diameter ratios are substantially the same in each tube 24.

More specifically, the number M of the tubes 24 forming the core having a roundness of 2.0 or less and the pipe 24 forming the core having a roundness of 2.0 or less are discharged per unit time. The volume amount Sm of the core resin (where m is an integer from 1 to M), from the tube 24 forming the core having a roundness of 2.0 or less represented by the following formula (5) per unit time The average volume Sb of the core resin to be discharged preferably satisfies the relationship of the following formula (6), more preferably satisfies the relationship of the following formula (8), and satisfies the relationship of the following formula (9). More preferably, it is still more preferable to satisfy | fill the relationship of following formula (10). By controlling so that the following relational expression is satisfied, it becomes possible to make the size of each core of the multi-core optical fiber bare wire substantially the same, and there is little variation in resolution, and multi-core light suitable for direct visual observation. A bare fiber can be produced.

  Then, a step of gradually thinning the molten multi-core optical fiber bare wire bundle extruded (spun) from the die 2 while being stretched is performed. The draw ratio is not particularly limited, but is preferably 1.1 to 10 times. The stretching process may be performed a plurality of times.

  Then, the process of obtaining a multi-core optical fiber bare wire is performed by hardening the optical fiber bare wire bundle in the molten state gradually refined. The curing method is not particularly limited, but is usually performed by cooling. Moreover, after producing a multi-core optical fiber bare wire by the manufacturing method mentioned above, you may perform the process of providing a protective layer and a coating layer in the outer periphery.

(Second manufacturing method)
FIG. 7 is a schematic longitudinal sectional view showing another example of the composite spinning die used in the manufacturing method of the present embodiment. FIG. 7 differs from FIG. 6 in that an obstacle 27 is formed on the collecting base 23. The die 20 shown in FIG. 7 includes an upper distribution plate 21, a lower distribution plate 22 disposed in a vertical lower portion of the upper distribution plate 21, a collecting base 23 disposed in a vertical lower portion of the lower distribution plate 22, and a tube 24. The obstacle 27 is formed on the wall surface of the collecting base 23 so as to be located on the flow path of the molten core resin.

  The obstacle 27 discharges the core resin with a number that is greater than 0% and not more than 20% of the total number of the core resin discharge pipes 24 excluding the core resin discharge pipe 24 corresponding to the core disposed at the center of the bare core of the multicore optical fiber. It is arranged in the flow path of the molten core resin discharged from the tube 24. As a result, a part of the molten core resin discharged from the core resin discharge pipe 24 comes into contact with the obstacle 27 so that the flow is disturbed and deformed. That is, a part of the molten optical fiber bare wire obtained by the step (1) (the molten core resin is coated with the molten sheath resin) comes into contact with the obstacle 27 at the gap H3. To form a core having a roundness of greater than 2.0.

  As described above, the core having a roundness of greater than 2.0 serves as a reference point (or a reference region) for specifying the position of the defect, and thus it is necessary that the core is not disposed at the center of the end cross section. Therefore, it is necessary not to arrange the obstacle 27 only on the flow path of the tube 24 corresponding to the center core of the end cross section.

  As the obstacle 27, for example, a protrusion protruding into the flow path of the melted core resin (the space of the gap H3 in FIG. 7) can be used. The shape of the obstacle 27 is not particularly limited, and examples thereof include a rod-shaped protrusion. Specifically, a rod-like pipe or the like is preferable. In particular, by providing an obstacle such as a pipe from the center of the lower distribution plate 22 toward the outer periphery, a core having a roundness greater than 2.0 as shown in FIG. A multi-core optical fiber arranged in a plurality of substantially straight lines can be manufactured.

  The ratio of the pipe 24 whose flow of molten resin is disturbed by the obstacle 27 is more than 0% and 20% or less, preferably more than 0% and 10% or less, more preferably more than 0% and 5% or less. More preferably, it is more than 0% and 1% or less.

  The outer diameter and inner diameter of the tube 24 for forming a core having a roundness of 2.0 or less, and the size and shape of the second through hole H2 are not particularly limited, as in the die 20 shown in FIG.

  The multi-core optical fiber according to the present invention can be used in a wide range of fields as a medical optical fiber such as an endoscope.

1, 6, 12, 18 ... multi-core optical fiber bare wire, 2, 7, 13 ... (roundness is 2.0 or less) core, 3, 8, 8a, 8b, 14, 14a, 14b, 14c , 14d, 19, 19a, 19b, 19c, 19d, 19e ... (roundness is greater than 2.0) core, 4 ... sheath, 5, 11, 17 ... defect, 9, 15 ... sheath layer, 10, 16 ... Sea resin, 20 ... Die, 21 ... Upper distribution plate, 22 ... Lower distribution plate, 23 ... Collecting base, 24 ... Core resin discharge pipe, 25 ... Core resin distribution chamber, 26 ... Sheath resin distribution chamber, 27 ... Obstacle , C ₁ ... inscribed circle, C ₂ ... circumscribed circle, C ₃ ... center, r ₁ ... inscribed circle radius, r ₂ ... circumscribed circle radius, H1 ... first through hole, H2 ... second through hole, H3 ... Gap, H4 ... discharge hole

Claims (6)

A multi-core optical fiber having a plurality of cores and a sheath formed on the outer periphery of the core,
In the multi-core optical fiber, in an end cross section viewed in a direction substantially orthogonal to the axial direction,
Among the plurality of cores, 80% or more and less than 100% of the total number of cores excluding the core arranged on the outermost periphery is a core having a roundness of 2.0 or less,
In the core excluding the core disposed on the outermost periphery, at least one of the cores having a roundness greater than 2.0 is disposed at a position other than the center of the end cross section, and the core having a roundness of greater than 2.0. Are arranged in a plurality, and two or more cores having a roundness greater than 2.0 are arranged next to each other.
Multi-core optical fiber. In the case where a plurality of cores having a circularity greater than 2.0 are arranged, the cores having a circularity greater than 2.0 are not in a point-symmetrical positional relationship with the center of the end cross section as a symmetry point. ,
The multi-core optical fiber according to claim 1.   The multi-core optical fiber according to claim 1 or 2, wherein the multi-core optical fiber has 50 cores or more. At least three cores having a roundness greater than 2.0 are disposed, and
Three or more cores having a roundness greater than 2.0 are arranged on a substantially straight line from the center of the end cross section toward the outer periphery,
The multi-core optical fiber according to any one of claims 1 to 3 . A method of manufacturing a multi-core optical fiber having a plurality of cores and a sheath formed on the outer periphery of the core,
(1) A molten core resin that is supplied with a molten core resin that forms the core and is discharged from a number of core resin discharge pipes corresponding to the number of the cores is formed into a molten sheath that forms the sheath. Coating with resin and obtaining a plurality of bare optical fibers in a molten state;
(2) bundling a plurality of molten optical fiber bare wires to obtain a molten multi-core optical fiber bare wire bundle;
(3) a step of gradually reducing the molten multi-core optical fiber bare wire bundle while stretching;
(4) The step of obtaining the multi-core optical fiber by curing the gradually refined molten multi-core optical fiber bare wire bundle;
Have
The cross-sectional shape of the inner diameter of the number of core resin discharge pipes that is greater than 0% and not more than 20% of the total number of core resin discharge pipes excluding the core resin discharge pipe corresponding to the core disposed at the center of the multi-core optical fiber, Greater than roundness 2.0,
A manufacturing method of a multi-core optical fiber. A method of manufacturing a multi-core optical fiber having a plurality of cores and a sheath formed on the outer periphery of the core,
(1) A molten core resin that is supplied with a molten core resin that forms the core and is discharged from a number of core resin discharge pipes corresponding to the number of the cores is formed into a molten sheath that forms the sheath. Coating with resin to obtain a plurality of molten optical fiber bare wires;
(2) bundling a plurality of molten optical fiber bare wires to obtain a molten multi-core optical fiber bare wire bundle;
(3) a step of gradually reducing the molten multi-core optical fiber bare wire bundle while stretching;
(4) The step of obtaining the multi-core optical fiber by curing the gradually refined molten multi-core optical fiber bare wire bundle;
Have
In the step (1), the number of core resin discharge pipes is greater than 0% and not more than 20% of the total number of core resin discharge pipes excluding the core resin discharge pipe corresponding to the core disposed at the center of the multi-core optical fiber. At least forming a core having a roundness greater than 2.0 by disturbing the flow of the molten core resin by an obstacle disposed in the flow path of the molten core resin discharged from
A manufacturing method of a multi-core optical fiber.