JP6875227B2 - Manufacturing method of multi-core optical fiber base material and manufacturing method of multi-core optical fiber - Google Patents

Description

The present invention relates to a method for manufacturing a multi-core optical fiber base material and a method for manufacturing a multi-core optical fiber.

In recent years, with the spread of optical fiber communication systems, the amount of information transmitted by optical fibers has dramatically increased. Against this background, a multi-core optical fiber in which the outer circumferences of a plurality of cores are surrounded by one clad is used. Since a multi-core optical fiber can transmit a plurality of signals by light propagating in each of the plurality of cores, the transmission capacity per optical fiber is increased.

From the viewpoint of reducing light loss at the connection portion between the multi-core optical fibers or between the multi-core optical fiber and another optical element, it is desired to improve the arrangement accuracy of each core of the multi-core optical fiber. As a method for manufacturing a multi-core optical fiber, for example, there is a perforation method for manufacturing a multi-core optical fiber base material by making a through hole in a clad base material to be a clad, inserting a core rod to be a core, and integrating these. .. When a multi-core optical fiber is manufactured by the perforation method, the accuracy of the position of the hole for inserting the core rod formed in the clad base material, and the inner peripheral surface of the hole for inserting the core rod and the outer peripheral surface of the core rod. The size of the gap between the cores affects the placement accuracy of each core.

The smaller the gap between the inner peripheral surface of the hole for inserting the core rod and the outer peripheral surface of the core rod, the more difficult it is for the core rod to move when integrating the clad base material and the core rod. Therefore, when a multi-core optical fiber is manufactured using the multi-core optical fiber base material thus manufactured, the core arrangement accuracy is improved. However, if the gap between the inner peripheral surface of the hole for inserting the core rod and the outer peripheral surface of the core rod is too small, it becomes difficult to insert the core rod into the hole. Therefore, in Patent Document 1 below, multi-core optical fiber that can improve the core placement accuracy while ensuring a gap between the inner peripheral surface of the hole for inserting the core rod and the outer peripheral surface of the core rod by satisfying a predetermined condition. A method for producing a fiber base material is disclosed. Specifically, in the method for manufacturing a multi-core optical fiber base material described in Patent Document 1 below, the distance between the center position of the core portion not located on the central axis of the multi-core optical fiber base material and the central axis of the multi-core optical fiber base material. Is d, the radius of the core rod serving as the core portion is r, the radius of the hole into which the core rod is inserted is R, the distance between the center of the hole and the central axis of the multi-core optical fiber base material is D, and d <D ≦ The condition is that d + R−r is satisfied.

By the way, when connecting multi-core optical fibers to each other or between a multi-core optical fiber and another optical element, a marker may be arranged on a cladding to identify each core of the multi-core optical fiber. For example, the multi-core optical fiber described in Patent Document 2 below includes a plurality of cores arranged so as to have symmetry, a marker, and a clad surrounding the core and the marker. Each core of the multi-core optical fiber can be identified by the relative position with respect to the marker.

Japanese Patent No. 6036386 Japanese Unexamined Patent Publication No. 2014-97094

According to the method disclosed in Patent Document 1, deterioration of the placement accuracy of each core due to the size of the gap between the inner peripheral surface of the hole for inserting the core rod and the outer peripheral surface of the core rod is suppressed. .. Further, the deterioration of the placement accuracy of each core due to the accuracy of the position where the hole for inserting the core rod is formed is that the position of the hole is measured after the hole is opened and the accuracy of the hole formation position is high. It can be suppressed by selecting the material.

However, when a marker as disclosed in Patent Document 2 is arranged, the position of the core rod may shift when the clad base material, the core rod, and the marker rod serving as the marker are integrated. When the position of the core rod is deviated in this way, the position of the core portion made of the core rod tends to deviate from the desired position in the multi-core optical fiber base material. As a result, when a multi-core optical fiber is manufactured using this multi-core optical fiber base material, the position of the core of the multi-core optical fiber tends to deviate from a desired position.

Therefore, an object of the present invention is to provide a method for manufacturing a multi-core optical fiber base material and a method for manufacturing a multi-core optical fiber, which can improve the arrangement accuracy of each core of the multi-core optical fiber.

In the method for producing a multi-core optical fiber base material of the present invention for solving the above problems, a plurality of core rod insertion holes for inserting core core rods are formed around the central axis of the clad base material to be clad. When drawing a half straight line extending from the center of the clad base material and passing through the center of each core rod insertion hole in one drilling step and a cross section perpendicular to the longitudinal direction of the clad base material, the half straight lines adjacent to each other are drawn. A second drilling step of forming a marker rod insertion hole for inserting a marker rod to be a marker in a region sandwiched by the two half straight lines forming the maximum angle among the angles formed by the above, and the core rod insertion hole. It is characterized by including a rod insertion step of inserting the core rod into the marker rod and inserting the marker rod into the marker rod insertion hole, and an integration step of integrating the clad base material, the core rod, and the marker rod. And.

In a multi-core optical fiber, from the viewpoint of suppressing crosstalk between the cores, the cores arranged around the central axis of the multi-core optical fiber are preferably arranged at positions that are rotationally symmetric n times. Note that n is the number of cores arranged around the central axis of the multi-core optical fiber. Therefore, it is preferable that the core rod insertion hole formed in the clad base material is formed at a position that is rotationally symmetric n times. When the core rod is inserted into the core rod insertion hole formed in this way to integrate the clad base material and the core rod, the clad base material fills the gap between the inner peripheral surface of the core rod insertion hole and the outer peripheral surface of the core rod. Shrinks. The core rod moves as the clad base material shrinks. When a plurality of core rod insertion holes are formed at positions that are rotationally symmetric exactly n times and the size of the gap between the inner peripheral surface of each core rod insertion hole and the outer peripheral surface of the core rod is constant, the above The core rods can be evenly spaced even after the core rods have moved. However, when the marker is arranged in the clad as described below, the position of the core rod tends to shift easily. When a marker rod insertion hole is formed in the clad base material and the marker rod is inserted into the marker rod insertion hole, the gap between the inner peripheral surface of the marker rod insertion hole and the outer peripheral surface of the marker rod is filled in the integration step. The clad base material shrinks so that it can be used. At this time, the core rods arranged so as to sandwich the marker rod insertion hole can easily move to the marker rod insertion hole side. Therefore, the distance between the core rods arranged so as to sandwich the marker rod insertion hole becomes narrow. In the method for manufacturing a multi-core optical fiber base material of the present invention, the marker rod insertion hole is formed in a region sandwiched by the two half straight lines forming the maximum angle. That is, the marker rod insertion holes are formed between the core rod insertion holes that are farthest from each other among the core rod insertion holes that are adjacent to each other and are formed around the central axis of the clad base material. Therefore, in the integration step, the distance between the core rods arranged at the farthest positions from the adjacent core rods arranged around the central axis of the clad base material is narrowed. Therefore, the distance between the plurality of core rods arranged around the central axis of the clad base material can approach equal intervals. Since the position of the core rod can be corrected when the multi-core optical fiber base material is obtained in this way, the placement accuracy of each core of the multi-core optical fiber obtained from the multi-core optical fiber base material can be improved.

Further, it is preferable to include a measurement step for measuring the position of each core rod insertion hole before the second drilling step.

By measuring the position of the core rod insertion hole before the second drilling step, the position where the marker rod insertion hole should be formed in the second drilling step can be grasped more accurately.

Further, at least three core rod insertion holes are formed around the central axis of the clad base material, and one of the two half lines forming the maximum angle is the first half line and the other is the second half. The first angle is a straight line, and the angle formed by the first half line and the other half line adjacent to the first half line on the side opposite to the second half line side of the first half line is the first angle. The angle formed by the second half line and the other half line adjacent to the second half line on the side opposite to the first half line side of the second half line is defined as the second angle. When doing so, it is preferable that the marker rod insertion hole is formed so that the central axis is closer to the smaller of the first angle and the second angle than the bisector of the maximum angle.

When the marker rod insertion hole is formed closer to one of the first angle and the second angle than the bisector of the maximum angle, the marker rod is inserted among the core rods arranged at the positions sandwiching the marker rod insertion hole. The core rod closer to the hole is easier to move to the marker rod insertion hole side in the integration process. Therefore, the marker rod insertion hole is formed closer to the smaller of the first and second corners, so that the smaller of the first and second corners becomes relatively large in the integration process. obtain. Therefore, the distance between the plurality of core rods arranged around the central axis of the clad base material can be closer to equal distance. Therefore, when the multi-core optical fiber base material is obtained in this way, the position of the core rod can be more appropriately corrected, and the arrangement accuracy of each core of the multi-core optical fiber obtained from the multi-core optical fiber base material is further improved. obtain.

Further, the inner peripheral surface of the marker rod insertion hole is based on the difference between the size obtained by dividing 360 degrees by the number of the core rod insertion holes formed around the central axis of the clad base material and the size of the maximum angle. It is preferable to determine the size of the gap between the marker rod and the outer peripheral surface of the marker rod.

The greater the difference between the size obtained by dividing 360 degrees by the number of core rod insertion holes formed around the central axis of the clad base material and the size of the maximum angle, the more core rod insertion holes formed across the marker rod insertion holes. Means that they are separated. By the way, the larger the gap between the inner peripheral surface of the marker rod insertion hole and the outer peripheral surface of the marker rod, the larger the clad base material shrinks in order to fill the gap in the integration process. The core rods to be formed tend to come close to each other in the integration process. Therefore, the larger the above difference, the larger the gap between the inner peripheral surface of the marker rod insertion hole and the outer peripheral surface of the marker rod, so that the distance between the plurality of core rods arranged around the central axis of the clad base material becomes larger. It can be closer to equal intervals. Therefore, when the multi-core optical fiber base material is obtained in this way, the position of the core rod can be more appropriately corrected, and the arrangement accuracy of each core of the multi-core optical fiber obtained from the multi-core optical fiber base material is further improved. obtain.

Further, it is preferable to adjust the size of the gap between the inner peripheral surface of the marker rod insertion hole and the outer peripheral surface of the marker rod by adjusting the size of the outer diameter of the marker rod.

By adjusting the size of the outer diameter of the marker rod, the size of the gap between the inner peripheral surface of the marker rod insertion hole and the outer peripheral surface of the marker rod can be adjusted.

It is also preferable to adjust the size of the gap between the inner peripheral surface of the marker rod insertion hole and the outer peripheral surface of the marker rod by adjusting the size of the inner diameter of the marker rod insertion hole.

By adjusting the size of the inner diameter of the marker rod insertion hole, the size of the gap between the inner peripheral surface of the marker rod insertion hole and the outer peripheral surface of the marker rod can also be adjusted.

Further, the method for manufacturing a multi-core optical fiber of the present invention for solving the above-mentioned problems includes a drawing step for drawing a multi-core optical fiber base material manufactured by the above-mentioned method for manufacturing a multi-core optical fiber base material of the present invention. It is characterized by.

As described above, according to the method for manufacturing a multi-core optical fiber base material of the present invention, the arrangement of core rods can be modified in the integration step. Therefore, by drawing the multi-core optical fiber base material, the placement accuracy of each core of the multi-core optical fiber can be improved.

Further, in the method for manufacturing a multi-core optical fiber of the present invention for solving the above problems, a plurality of core rod insertion holes for inserting core rods to be inserted are formed around the central axis of the clad base material to be clad. When drawing a half line extending from the center of the clad base material and passing through the center of each core rod insertion hole in one drilling step and a cross section perpendicular to the longitudinal direction of the clad base material, the half lines adjacent to each other are drawn. A second drilling step of forming a marker rod insertion hole for inserting a marker rod to be a marker in a region sandwiched by the two half straight lines forming the maximum angle among the angles formed by the above, and the core rod insertion hole. A rod insertion step of inserting the core rod into the marker rod and inserting the marker rod into the marker rod insertion hole, and a drawing step of drawing a line while integrating the clad base material, the core rod, and the marker rod are provided. It is characterized by that.

When the markers are arranged in the clad, the distance between the core rods arranged so as to sandwich the marker rod insertion holes as described above becomes narrow, and the positions of the core rods tend to shift easily. In the method for manufacturing a multi-core optical fiber of the present invention, the marker rod insertion holes are formed between the core rod insertion holes farthest from each other among the adjacent core rod insertion holes formed around the central axis of the clad base material. Will be done. Therefore, in the drawing process of drawing the clad base material, the core rod, and the marker rod while integrating them, they are arranged at the positions farthest from each other among the core rods adjacent to each other arranged around the central axis of the clad base material. The distance between the core rods becomes narrower. Therefore, the distance between the plurality of core rods arranged around the central axis of the clad base material can approach equal intervals. Since the position of the core rod can be corrected when the multi-core optical fiber is obtained in this way, the placement accuracy of each core can be improved.

As described above, according to the present invention, there are provided a method for manufacturing a multi-core optical fiber base material and a method for manufacturing a multi-core optical fiber, which can improve the arrangement accuracy of each core of the multi-core optical fiber.

It is a figure which shows the cross section perpendicular to the longitudinal direction of the multi-core optical fiber which concerns on embodiment of this invention. It is a figure which shows the cross section perpendicular to the longitudinal direction of the multi-core optical fiber base material used for manufacturing the multi-core optical fiber of FIG. It is a flowchart which shows the process of the manufacturing method of the multi-core optical fiber of FIG. It is a figure which shows the cross section perpendicular to the longitudinal direction of the clad base material after the 1st drilling process. It is a figure which shows the cross section perpendicular to the longitudinal direction of the clad base material after the 2nd drilling process. It is a figure which shows the cross section perpendicular to the longitudinal direction of a clad base material after a rod insertion process. It is a figure which shows the state of a part of the integration process. It is a figure which shows the state of the drawing process. It is a figure which shows the cross section perpendicular to the longitudinal direction of the multi-core optical fiber which concerns on the modification of this invention. It is a figure which shows the cross section perpendicular to the longitudinal direction of the clad base material after the 2nd drilling process in the manufacturing method of the multi-core optical fiber which concerns on the modification of this invention. It is sectional drawing which shows the state of a part of the integration process which concerns on other modification of this invention. It is a figure which shows the state of the drawing process which concerns on the further modification of this invention.

Hereinafter, a method for producing a multi-core optical fiber base material and a preferred embodiment of a method for producing a multi-core optical fiber according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a cross section perpendicular to the longitudinal direction of the multi-core optical fiber according to the embodiment of the present invention. The multi-core optical fiber 1 of the present embodiment includes four cores 10, a marker 15, a clad 20 that surrounds the outer peripheral surfaces of the four cores 10 and the marker 15 without gaps, an inner coating layer 31 that covers the outer peripheral surface of the clad 20, and an inner coating. An outer coating layer 32 that covers the outer peripheral surface of the layer 31 is provided.

In the multi-core optical fiber 1 of the present embodiment, one core 10 is arranged along the central axis of the multi-core optical fiber 1, and the remaining three cores 10 are arranged around the central axis of the multi-core optical fiber 1. Each core 10 is arranged at a predetermined interval. In the multi-core optical fiber 1 of the present embodiment, the three cores 10 arranged around the central axis of the multi-core optical fiber 1 are centered on the center of the multi-core optical fiber 1 in a cross section perpendicular to the longitudinal direction of the multi-core optical fiber 1. It is arranged so as to be rotationally symmetric about three times. That is, in the cross section perpendicular to the longitudinal direction of the multi-core optical fiber 1, the three cores 10 arranged around the center of the multi-core optical fiber 1 are arranged substantially equidistant from the center. In other words, in the cross section perpendicular to the longitudinal direction of the multi-core optical fiber 1, the three cores 10 arranged around the center of the multi-core optical fiber 1 substantially overlap each apex of an equilateral triangle having the center as the center of gravity. Is placed in. Further, in a cross section perpendicular to the longitudinal direction of the multi-core optical fiber 1, three half straight lines passing through the centers of the three cores 10 arranged around the center of the multi-core optical fiber 1 are drawn. The angle formed by the half straight lines adjacent to each other is approximately 120 degrees. The diameter of such a core 10 is, for example, 4 μm or more and 10 μm or less.

The marker 15 is arranged between two predetermined cores 10 as described later. Further, the clad 20 surrounds all the cores 10 and the outer peripheral surfaces of the markers 15 provided in the multi-core optical fiber 1 without gaps. The diameter of the clad 20 is, for example, 125 μm or more and 230 μm or less.

The refractive index of each core 10 is higher than the refractive index of the clad 20, and the difference in the specific refractive index of each core 10 with respect to the clad 20 is, for example, 0.2% or more and 2.0% or less. Such a core 10 is made of silica glass to which a dopant having a high refractive index such as germanium is added, and the clad 20 is made of silica glass to which a dopant is not added, for example. Further, the core 10 may be made of silica glass to which no dopant is added, and the clad 20 may be made of silica glass to which a dopant having a low refractive index such as fluorine is added. The marker 15 is made of silica glass having a refractive index different from that of the clad 20. The refractive index of the marker 15 may be higher or lower than that of the clad 20.

The inner coating layer 31 and the outer coating layer 32 are each made of a resin such as an ultraviolet curable resin, and the inner coating layer 31 and the outer coating layer 32 are made of different resins.

FIG. 2 is a diagram showing a cross section perpendicular to the longitudinal direction of the multi-core optical fiber base material used for manufacturing the multi-core optical fiber 1 shown in FIG. The multi-core optical fiber base material 1P shown in FIG. 2 has a substantially columnar shape. Further, the multi-core optical fiber base material 1P includes a core portion 10P serving as each core 10, a marker portion 15P serving as a marker 15, and a clad portion 20P serving as a clad 20. The core portion 10P is made of the same material as the core 10, the marker portion 15P is made of the same material as the marker 15, and the clad portion 20P is made of the same material as the clad 20. Further, the shape of the cross section perpendicular to the longitudinal direction of the multi-core optical fiber base material 1P is substantially similar to the shape of the cross section perpendicular to the longitudinal direction of the multi-core optical fiber 1 excluding the inner coating layer 31 and the outer coating layer 32. Will be done. Such a multi-core optical fiber base material 1P is drawn as described later, and the outer peripheral surface of the drawn optical fiber strand is coated with the inner coating layer 31 and the outer coating layer 32, so that the multi-core optical fiber 1 shown in FIG. 1 is formed. can get.

Next, a method for manufacturing the multi-core optical fiber base material 1P shown in FIG. 2 and a method for manufacturing the multi-core optical fiber 1 shown in FIG. 1 using the multi-core optical fiber base material 1P will be described.

FIG. 3 is a flowchart showing the steps of the manufacturing method of the multi-core optical fiber base material 1P and the manufacturing method of the multi-core optical fiber 1. As shown in FIG. 3, the method for manufacturing the multi-core optical fiber base material 1P includes a first drilling step P1, a measuring step P2, a second drilling step P3, a rod insertion step P4, and an integration step P5. The method for manufacturing the multi-core optical fiber 1 further includes a drawing step P6 for drawing the multi-core optical fiber base material 1P manufactured through each of the above steps. Hereinafter, each of these steps will be described in detail.

<First drilling step P1>
FIG. 4 is a view showing a cross section perpendicular to the longitudinal direction of the clad base material after this step. This step is a step of preparing a clad base material 20R to be the clad 20 and forming a plurality of core rod insertion holes 10H for inserting the core rod to be the core 10 in the rod insertion step P4 described later. The clad base material 20R is a columnar glass rod. In the present embodiment, one core rod insertion hole 10H is formed along the central axis of the clad base material 20R, and three core rod insertion holes 10H are formed around the central axis of the clad base material 20R. Each core rod insertion hole 10H is a through hole that penetrates the clad base material 20R in the longitudinal direction, and the diameter of each core rod insertion hole 10H is made larger than the outer diameter of the core rod inserted therein.

The method for forming each core rod insertion hole 10H is not particularly limited, and examples thereof include machining using a drill. The inner peripheral surface of the core rod insertion hole 10H is a portion in contact with the outer peripheral surface of the core rod, and is preferably smoothed. By smoothing the inner peripheral surface of the core rod insertion hole 10H, the outer peripheral surface of the core rod is damaged in the rod insertion step P4 described later, and the outer peripheral surface of the core rod and the core rod insertion hole in the integration step P5 described later. It is possible to suppress the formation of an unnecessary space between the inner peripheral surface of 10H and the like. From the viewpoint of smoothing the inner peripheral surface of the core rod insertion hole 10H as described above, for example, the inner peripheral surface of the core rod insertion hole 10H may be smoothed by etching after the core rod insertion hole 10H is drilled by machining. ..

Examples of the etching process include a vapor phase method. In the case of etching in the gas phase, for example, SF ₆ can be used. _{SF 6} known as an etching gas does not show an etching action by itself, but is used for etching by being an active gas species having an etching action by thermal decomposition, plasma, or the like. Nachi Suwa, by activating the SF ₆ and the like for heating by circulating SF ₆ to the core rod insertion hole 10H, etching is performed. By such an etching process, small irregularities on the inner peripheral surface of the core rod insertion hole 10H can be removed, and impurities such as hydroxyl groups can be removed from the inner peripheral surface of the core rod insertion hole 10H. As an etching gas used for the etching process, for example, in addition to _{CF 4,} C ₂ F 6, etc. fluoride gas such as SiF ₄ and the like of SF _6.

<Measurement process P2>
This step is a step of measuring the position of each core rod insertion hole 10H after the first drilling step P1 and before the second drilling step P3 described later. The position of the core rod insertion hole 10H can be measured by, for example, a three-dimensional measuring device or the like. Even when the core rod insertion hole 10H is not formed as designed in the first drilling step P1, the formation position of the core rod insertion hole 10H can be grasped by the measurement step P2.

<Second drilling process P3>
This step is a step of forming a marker rod insertion hole for inserting the marker rod to be the marker 15 in the rod insertion step P4 described later. FIG. 5 is a view showing a cross section perpendicular to the longitudinal direction of the clad base material 20R after the second drilling step P3. The formation position of the marker rod insertion hole 15H is determined as follows. First, in a cross section perpendicular to the longitudinal direction of the clad base material 20R, half straight lines L1, L2, and L3 extending from the center of the clad base material 20R and passing through the centers of the respective core rod insertion holes 10H are drawn. Then, two half straight lines L1 and L2 forming the _{maximum angle θ max} among the angles formed by the half straight lines L1, L2 and L3 adjacent to each other are determined. Then, the marker rod insertion hole 15H is formed in the region sandwiched by these two half straight lines L1 and L2. In the present embodiment, since the position of the core rod insertion hole 10H is measured in the measurement step P2 as described above, the maximum angle θ _max can be easily obtained. The half straight lines L1, L2, and L3 may be virtual lines.

Further, when at least three core rod insertion holes 10H are formed around the central axis of the clad base material 20R as in the present embodiment, one half of the two half straight lines L1 and L2 forming the _{maximum angle θ max.} Let the straight line L1 be the first half straight line and the other half straight line L2 be the second half straight line. Further, the angle formed by the half straight line L1 which is the first half straight line and the half straight line L1 which is opposite to the half straight line L2 side which is the second half straight line of the half straight line L1 and another half straight line L3 which is adjacent to each other is formed. Let the first angle θ be ₁ . Further, the angle formed by the half straight line L2 which is the second half straight line and the half straight line L2 which is opposite to the half straight line L1 side which is the first half straight line of the half straight line L2 and another half straight line L3 which is adjacent to each other is formed. Let the second angle θ ₂ be. At this time, the marker rod insertion hole 15H is formed so that the central axis is closer to the smaller of the first angle θ ₁ and the second angle θ _{2 than the bisector LB having the maximum angle θ max.} In the second drilling step P3 of the present embodiment, since the first angle θ ₁ is smaller than the second angle θ ₂ , the marker rod insertion hole 15H is formed on _{the first angle θ 1 side of the bisector LB.}

<Rod insertion process P4>
FIG. 6 is a view showing a cross section perpendicular to the longitudinal direction of the clad base material 20R after the rod insertion step P4. This step is a step of inserting the core rod 10R into the core rod insertion hole 10H and inserting the marker rod 15R into the marker rod insertion hole 15H. In this step, first, the core rod 10R and the marker rod 15R are prepared. The core rod 10R is a cylindrical glass body, and is made of a material constituting the core 10. However, a coating layer (not shown) made of the same material as the clad 20 may be formed on the outer peripheral surface of the core rod 10R. Further, the marker rod 15R is a cylindrical glass body, and is made of a material constituting the marker 15. However, a coating layer (not shown) made of the same material as the clad 20 may be formed on the outer peripheral surface of the marker rod 15R. The core rod 10R and the marker rod 15R may be prepared by this step, and may be prepared before, for example, the first drilling step P1 and the second drilling step P3.

The size of the gap between the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R is 360 degrees divided by the number of core rod insertion holes 10H formed around the central axis of the clad base material 20R. It is determined based on the difference between the size of the _{rod and} the size of the maximum angle θ max. That is, in the present embodiment, the size of the gap between the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R is determined based on the difference between the size of _{120 degrees and the size of the maximum angle θ max.} The larger the difference, the larger the gap between the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R, and the smaller the difference, the larger the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R. The gap with the surface is reduced.

The size of the gap between the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R may be adjusted by adjusting the size of the outer diameter of the marker rod 15R. It may be adjusted by adjusting the size of the inner diameter. However, in general, it is easier to adjust the size of the outer diameter of the marker rod 15R than to adjust the size of the inner diameter of the marker rod insertion hole 15H. The size of the outer diameter of the marker rod 15R and the size of the inner diameter of the marker rod insertion hole 15H can be adjusted by, for example, machining or etching.

<Integration process P5>
This step is a step of integrating the clad base material 20R, the core rod 10R, and the marker rod 15R.

In this step, first, one opening of the core rod insertion hole 10H and the marker rod insertion hole 15H is sealed. As a method of sealing, for example, a plate-shaped sealing material is welded to the bottom surface of one of the clad base materials 20R, and one opening of all the core rod insertion holes 10H and the marker rod insertion hole 15H is provided by the sealing material. A method of covering the part can be mentioned. For this sealing material, for example, a glass plate can be used.

Next, the inner peripheral surface of each core rod insertion hole 10H and the outer peripheral surface of the core rod 10R inserted into each core rod insertion hole 10H are integrated, and the inner peripheral surface of the marker rod insertion hole 15H and the marker rod insertion hole are integrated. The outer peripheral surface of the marker rod 15R inserted into the 15H is integrated. For example, the clad base material 20R into which the core rod 10R and the marker rod 15R are inserted is installed on a horizontal lathe, and the clad base material 20R, the core rod 10R, and the marker rod 15R are integrated by heating while rotating the clad base material 20R. To make it. FIG. 7 is a diagram showing a part of the integration step P5, and is a diagram showing a horizontal lathe in a state in which a clad base material 20R into which a core rod 10R and a marker rod 15R are inserted is set. As shown in FIG. 7, the horizontal lathe 50 can evacuate the inside of a pair of chucking portions 55a and 55b capable of chucking both ends of the clad base material 20R, the core rod insertion hole 10H, and the marker rod insertion hole 15H. The main configuration includes a vacuum pump 51 and a burner 58 that is movable in the longitudinal direction of the clad base material 20R and can heat the outer peripheral surface of the clad base material 20R.

In the present embodiment, the chucking portion 55a chucks one end of the clad base material 20R, and the chucking portion 55b chucks the other end of the clad base material 20R. The clad base material 20R is supported by 55b. The burner 58 is, for example, an oxyhydrogen burner, and is configured to be movable along the longitudinal direction of the clad base material 20R as described above.

In this step, the clad base material 20R is heated by reciprocating the burner 58 or the clad base material 20R along the longitudinal direction of the clad base material 20R. By this heating, the core rod insertion hole 10H and the marker rod insertion hole 15H formed in the clad base material 20R are reduced in diameter, and the inner peripheral surface of each core rod insertion hole 10H and the outer peripheral surface of each core rod 10R are integrated. At the same time, the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R are integrated. By integrating each of the core rods 10R and the marker rod 15R with the clad base material 20R in this way, the outer peripheral surface of each core rod 10R and the inner peripheral surface of the core rod insertion hole 10H, and the marker rod 15R It is possible to suppress the formation of an unnecessary space between the outer peripheral surface and the inner peripheral surface of the marker rod insertion hole 15H. At this time, when the core rod 10R and the marker rod 15R have the coating layer, these coating layers are a part of the clad portion 20P. In this way, the multi-core optical fiber base material 1P shown in FIG. 2 is obtained.

Further, in this step, it is preferable to evacuate the inside of the core rod insertion hole 10H and the marker rod insertion hole 15H by the vacuum pump 51 at the same time as the above heating. The vacuum pump 51 is not particularly limited as long as it is a pump capable of evacuating the inside of the core rod insertion hole 10H and the marker rod insertion hole 15H. Prior to evacuation by the vacuum pump 51, a glass tube was opened in the core rod insertion hole 10H and the marker rod insertion hole 15H at the end of the clad base material 20R on the side opposite to the side where the sealing material was welded. 54 is attached. Through the glass tube 54, the vacuum pump 51 allows the outer peripheral surface of each core rod 10R and the inner peripheral surface of the core rod insertion hole 10H, and the outer peripheral surface of the marker rod 15R and the inner peripheral surface of the marker rod insertion hole 15H. Vacuum the space between and. By evacuating in this way, between the outer peripheral surface of each core rod 10R and the inner peripheral surface of the core rod insertion hole 10H, and between the outer peripheral surface of the marker rod 15R and the inner peripheral surface of the marker rod insertion hole 15H. It can be suppressed that air remains in the air. Although shown in a simplified manner in FIG. 7, the glass tube 54 is attached to the openings of all the core rod insertion holes 10H and the marker rod insertion holes 15H, and all the core rod insertion holes 10H and the marker rod insertion holes 15H are made of glass. It is evacuated by the vacuum pump 51 via the tube 54.

<Drawing process P6>
FIG. 8 is a diagram showing a state of the drawing step P6. In this step, first, the multi-core optical fiber base material 1P is installed in the spinning furnace 110. Then, the heating unit 111 of the spinning furnace 110 is heated to heat the multi-core optical fiber base material 1P. At this time, the lower end of the multi-core optical fiber base material 1P is heated to, for example, 2000 ° C. and becomes a molten state. Then, the glass is melted from the multi-core optical fiber base material 1P, and the glass is drawn. Then, the drawn molten glass immediately solidifies when it comes out of the spinning furnace 110, each core portion 10P becomes each core 10, the marker portion 15P becomes the marker 15, and the clad portion 20P becomes the clad 20. It becomes. In this way, a wire of a multi-core optical fiber composed of a plurality of cores 10, a marker 15, and a clad 20 is obtained. After that, the wire of this multi-core optical fiber passes through the cooling device 120 and is cooled to an appropriate temperature. When entering the cooling device 120, the temperature of the wire of the multi-core optical fiber is, for example, about 1300 ° C., but when leaving the cooling device 120, it is, for example, 40 ° C. to 50 ° C.

Next, the wire of the multi-core optical fiber passes through the coating device 131 containing the ultraviolet curable resin serving as the inner coating layer 31, and the outer peripheral surface of the wire of the multi-core optical fiber is coated with the UV curable resin. To. Further, when the ultraviolet curable resin is irradiated with ultraviolet rays in the ultraviolet irradiation device 132, the ultraviolet curable resin is cured and the inner coating layer 31 is formed. Next, the wire of the multi-core optical fiber coated with the inner coating layer 31 passes through the coating device 133 containing the ultraviolet curable resin serving as the outer coating layer 32, and the outer peripheral surface of the inner coating layer 31 is the ultraviolet curable resin. Covered with. Further, when the ultraviolet curable resin is irradiated with ultraviolet rays in the ultraviolet irradiation device 134, the ultraviolet curable resin is cured and the outer coating layer 32 is formed. In this way, the multi-core optical fiber 1 shown in FIG. 1 is manufactured.

Then, the direction of the multi-core optical fiber 1 is changed by the turn pulley 141, and the multi-core optical fiber 1 is wound by the reel 142.

In the multi-core optical fiber 1 manufactured in this way, the cores 10 arranged around the central axis of the multi-core optical fiber 1 are positioned so as to be rotationally symmetric three times from the viewpoint of suppressing crosstalk between the respective cores 10. It is preferable to be arranged. Therefore, it is preferable that the core rod insertion hole 10H formed in the clad base material 20R in the first drilling step P1 is formed at a position that is rotationally symmetric three times. When the core rod 10R is inserted into each of the plurality of core rod insertion holes 10H formed in the clad base material 20R and the integration step P5 is performed, the inner peripheral surface of the core rod insertion hole 10H and the outer peripheral surface of the core rod 10R become The clad base material 20R shrinks so as to fill the gap. The core rod 10R moves to the clad base material 20R as it shrinks. The three core rod insertion holes 10H formed around the central axis of the clad base material 20R are formed at positions that are rotationally symmetric exactly three times, and the inner peripheral surface of each core rod insertion hole 10H and the outer peripheral surface of the core rod 10R are formed. When the size of the gap between the two is constant, the core rods 10R can be arranged at equal intervals even after the core rods 10R have moved as described above.

However, even if the plurality of core rod insertion holes 10H are formed at positions that are rotationally symmetric exactly three times in the first drilling step P1, the positions of the core rod insertion holes 10H may be slightly displaced. Further, as described below, when the marker 15 is arranged in the clad 20, the position of the core rod 10R tends to shift easily. When the marker rod insertion hole 15H is formed in the clad base material 20R and the marker rod 15R is inserted into the marker rod insertion hole 15H, in the integration step P5, the inner peripheral surface of the marker rod insertion hole 15H and the outer circumference of the marker rod 15R The clad base material 20R shrinks so as to fill the gap with the surface. At this time, the core rods 10R arranged so as to sandwich the marker rod insertion hole 15H can easily move to the marker rod insertion hole 15H side. Therefore, the distance between the core rods 10R arranged so as to sandwich the marker rod insertion hole 15H is narrowed.

In the method for manufacturing the multi-core optical fiber base material 1P of the present embodiment, the marker rod insertion hole 15H is formed by a half straight line L1 which is a first half line and a half line L2 which is a second half line forming a _{maximum angle θ max.} It is formed in the sandwiched area. That is, the marker rod insertion holes 15H are formed between the core rod insertion holes 10H that are farthest from each other among the core rod insertion holes 10H that are adjacent to each other and are formed around the central axis of the clad base material 20R. Therefore, in the integration step P5, the distance between the core rods 10R arranged at the farthest positions from the adjacent core rods 10R arranged around the central axis of the clad base material 20R is narrowed. Therefore, the intervals of the plurality of core rods 10R arranged around the central axis of the clad base material 20R can approach equal intervals. Since the position of the core rod 10R can be corrected when the multi-core optical fiber base material 1P is obtained in this way, the placement accuracy of each core 10 of the multi-core optical fiber 1 obtained from the multi-core optical fiber base material 1P can be improved.

Further, in the method for manufacturing the multi-core optical fiber base material 1P of the present embodiment, the marker rod insertion hole 15H is smaller than the bisector LB _{having the maximum angle θ max} among _{the first angle θ 1} and the second angle θ _2. It is formed with the central axis closer to the direction. When the marker rod insertion hole 15H is formed closer to one of the first angle θ ₁ and the second angle θ ₂ than the bisector LB having the maximum angle θ _max , it is arranged at a position sandwiching the marker rod insertion hole 15H. Of the core rods 10R to be formed, the core rod 10R closer to the marker rod insertion hole 15H is more likely to move to the marker rod insertion hole 15H side in the integration step P5. Therefore, by the marker rod insertion hole 15H is formed closer to the smaller of the first angle theta ₁ and the second angle theta _2, the smaller of the first angle theta ₁ and the second angle theta _2, It can be relatively large in the integration step P5. Therefore, the intervals of the plurality of core rods 10R arranged around the central axis of the clad base material 20R can be closer to equal intervals. Therefore, when the multi-core optical fiber base material 1P is obtained in this way, the position of the core rod 10R can be more appropriately corrected, and the placement accuracy of each core of the multi-core optical fiber 1 obtained from the multi-core optical fiber base material 1P can be improved. Can be improved.

Further, in the method for manufacturing the multi-core optical fiber base material 1P of the present embodiment, the size obtained by dividing 360 degrees by the number of core rod insertion holes 10H formed around the central axis of the clad base material 20R and the size of the maximum angle θ _max . The size of the gap between the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R is determined based on the difference from the above. The larger the difference between the size obtained by dividing 360 degrees by the number of core rod insertion holes 10H formed around the central axis of the clad base material 20R and the size of the maximum angle θ _max , the more the marker rod insertion holes 15H are sandwiched between the core rod insertion holes 15H. It means that the core rod insertion holes 10H are separated from each other. By the way, the larger the gap between the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R, the larger the clad base material 20R shrinks in order to fill the gap in the integration step P5. The core rods 10R arranged with the 15H in between are easily brought close to each other in the integration step P5. Therefore, the larger the above difference, the larger the gap between the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R, so that a plurality of core rods arranged around the central axis of the clad base material 20R The intervals of 10R can be closer to equal intervals. Therefore, when the multi-core optical fiber base material 1P is obtained in this way, the position of the core rod 10R can be more appropriately corrected, and the placement accuracy of each core 10 of the multi-core optical fiber 1 obtained from the multi-core optical fiber base material 1P becomes easier. Can be improved.

As described above, according to the method for manufacturing the multi-core optical fiber base material 1P of the present embodiment, the arrangement of the core rod 10R can be modified in the integration step P5. Therefore, according to the method for manufacturing the multi-core optical fiber 1 of the present embodiment using the multi-core optical fiber base material 1P, the placement accuracy of each core 10 of the multi-core optical fiber 1 can be improved.

Although the present invention has been described above by taking the above-described embodiment as an example, the present invention is not limited thereto. For example, the core 10 arranged along the central axis of the clad 20 is not essential. Further, in the above embodiment, the embodiment in which the three cores 10 are arranged around the central axis of the clad 20 has been described as an example, but the number of cores 10 arranged around the central axis of the clad 20 is plural. If there is, there is no particular limitation. For example, the number of cores 10 arranged around the central axis of the clad 20 may be two or four or more.

FIG. 9 is a view showing a cross section perpendicular to the longitudinal direction of the multi-core optical fiber according to the modified example of the present invention, and FIG. 10 is a diagram after the second drilling step P3 in the method for manufacturing the multi-core optical fiber according to the modified example of the present invention. It is a figure which shows the cross section perpendicular to the longitudinal direction of a clad base material. In FIGS. 9 and 10, the same components as those in the above embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in FIG. 9, in the multi-core optical fiber 2 according to this modification, six cores 10 are arranged around the central axis of the clad 20. When the number of cores 10 arranged around the central axis of the clad 20 is six in this way, six core rod insertion holes 10H are formed in the clad base material 20R as shown in FIG. Further, the marker rod insertion hole 15H is formed between the half straight line L1 which is the first half straight line and the half straight line L2 which is the second half straight line forming the _{maximum angle θ max. Further, in this modification, the first angle θ 1} formed by the half straight line L1 and the other half straight line L3 formed by the half straight line L1 and the other half straight line L3 adjacent to each other on the side opposite to the half straight line L2 side of the half straight line L1 and the half. _{Of the second angle θ 2} formed by the straight line L2 and the other half line L4 adjacent to the half line L2 on the side opposite to the half line L1 side of the half line L2, the first angle θ ₁ is smaller. .. The marker rod insertion hole 15H is formed with the central axis aligned with the first angle θ ₁ which is smaller than the first angle θ ₁ and the second angle θ _{2 of the bisector LB having the maximum angle θ max.} When at least three core rod insertion holes 10H are formed around the central axis of the clad base material 20R in this way, _{the first angle θ 1} and the second angle θ ₂ are larger than the bisector LB _{having the maximum angle θ max.} It is preferable that the central axis is closer to the smaller of the two.

Further, in the above embodiment, an example in which the integration step P5 is performed using a horizontal lathe has been described, but the present invention is not limited thereto. FIG. 11 is a cross-sectional view showing a part of the integration step P5 according to another modification of the present invention. In FIG. 11, the same components as those in the above embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

In the integration step P5 according to this modification, first, the plate-shaped sealing material 60 is welded to the bottom surface of one of the clad base materials 20R. The sealing material 60 is welded to the clad base material 20R so as to cover one opening of all the core rod insertion holes 10H and the marker rod insertion hole 15H, and the sealing material 60 is welded to one opening of the core rod insertion hole 10H and the marker rod insertion hole 15H. Is sealed in the sealing material 60. For this sealing material 60, for example, a glass plate can be used. Next, the lower dummy rod 61 made of rod-shaped glass is welded to the surface of the sealing material 60 opposite to the clad base material 20R side.

Further, the upper dummy tube 62 is welded to the bottom surface of the clad base material 20R on the side opposite to the side to which the sealing material 60 is welded. In the upper dummy pipe 62, the inner peripheral surface of the upper dummy pipe 62 surrounds all the core rod insertion holes 10H and the marker rod insertion holes 15H, and the through holes of the upper dummy pipe 62 and the core rod insertion holes 10H and the marker rod of the clad base material 20R are enclosed. It is welded so as to communicate with the insertion hole 15H. Further, the lid 66 is welded to the upper part of the upper dummy tube 62. A hole is formed in the lid 66.

Next, the lower dummy rod 61 is chucked by one chucking portion 63, and the upper dummy pipe 62 is chucked by the other chucking portion 64 to support the clad base material 20R. At this time, the pipe 67 is connected to the hole formed in the lid 66, and air is evacuated from the pipe 67 by the vacuum pump 51.

The clad base material 20R supported in this way is passed through the heating furnace 65 so that the longitudinal direction is the vertical direction. In this step, the clad base material 20R is passed through the heating furnace 65 from the lower end side to move the clad base material 20R downward, so that the entire clad base material 20R is heated by the heating furnace 65. At this time, the inside of the core rod insertion hole 10H and the marker rod insertion hole 15H is evacuated by the vacuum pump 51. By this heating and evacuation, the core rod insertion hole 10H and the marker rod insertion hole 15H formed in the clad base material 20R are reduced in diameter, and the inner peripheral surface of each core rod insertion hole 10H and the outer peripheral surface of each core rod 10R are brought into contact with each other. At the same time, the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R are integrated. Further, at this time, by increasing the relative distance between the chucking portions 63 and 64, the clad base material 20R, the respective core rods 10R, and the marker rods 15R are integrated while being stretched in the longitudinal direction. .. By integrating each of the core rods 10R and the marker rod 15R with the clad base material 20R in this way, the outer peripheral surface of each core rod 10R and the inner peripheral surface of the core rod insertion hole 10H, and the marker rod 15R It is possible to suppress the formation of an unnecessary space between the outer peripheral surface and the inner peripheral surface of the marker rod insertion hole 15H.

Further, in the above embodiment, the drawing step P6 is performed after the multi-core optical fiber base material 1P is produced through the integration step P5, but the present invention is not limited to this. FIG. 12 is a diagram showing a state of a drawing process according to a further modification of the present invention. In FIG. 12, for ease of understanding, the core rod 10R, the marker rod 15R, and the clad base material 20R are shown in a cross section parallel to the longitudinal direction, as in FIG. In the description of this modification, components equivalent to those of the above-described embodiment and modification are designated by the same reference numerals and duplicated description will be omitted unless otherwise specified. In this modification, after performing the first drilling step P1, the measuring step P2, the second drilling step P3, and the rod insertion step P4 in the same manner as in the above embodiment, the clad base material 20R and the core rod 10R are performed in the drawing step P6. , And the marker rod 15R are integrated and drawn. That is, the drawing step P6 of this modification also serves as the integration step P5 of the above embodiment. In this modification, prior to the drawing step P6, the upper dummy tube 62 is welded to the upper part of the clad base material 20R, and a hole is formed in the end of the upper dummy tube 62 on the opposite side of the clad base material 20R. The lid 66 formed by the above is welded. In the drawing step P6 of this modification, the drawing step P6 is performed as follows while removing air by the vacuum pump 51 through the pipe 67 connected to the hole of the lid 66. In the drawing step P6 of this modification, as shown in FIG. 12, the clad base material 20R and the core rods 10R and the marker rods 15R inserted into the clad base material 20R are erected so as to be vertical in the longitudinal direction. It is installed in the spinning furnace 110. Next, the clad base material 20R, the respective core rods 10R, and the lower end portions of the marker rods 15R are heated by the heating unit 111 and drawn while being integrated. When this integration is performed, between the outer peripheral surface of each core rod 10R and the inner peripheral surface of the core rod insertion hole 10H, and between the outer peripheral surface of the marker rod 15R and the inner peripheral surface of the marker rod insertion hole 15H. Space is crushed.

Further, in the description so far, an example including the measurement step P2 has been described, but the measurement step P2 is not an indispensable step. For example, in the first drilling step P1, the measurement step P2 is indispensable when the plurality of core rod insertion holes 10H are intentionally formed so as to be non-uniform and the _{place where the maximum angle θ max is formed can be grasped.} is not it.

Further, in the above embodiment, the marker rod insertion hole 15H is formed with the central axis closer to the smaller of the first angle θ ₁ and the second angle θ _{2 than the bisector LB having the maximum angle θ max.} However, the present invention is not limited to such a form. The marker rod insertion hole 15H may be formed in a region sandwiched by two half lines forming _{at least a maximum angle θ max.}

Further, in the above embodiment, the marker rod is inserted based on the difference between the size obtained by dividing 360 degrees by the number of core rod insertion holes 10H formed around the central axis of the clad base material 20R and the size of the maximum angle θ _max. An example of determining the size of the distance between the inner peripheral surface of the hole 15H and the outer peripheral surface of the marker rod 15R has been described. However, the size of the distance between the inner peripheral surface of the marker rod insertion hole 15H and the outer peripheral surface of the marker rod 15R is not limited to this.

Hereinafter, the contents of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Example 1)
Four core rods 10R having an eccentricity of 10 μm or less were prepared. After that, four core rod insertion holes 10H were formed in the clad base material 20R using a hole opening machine. One core rod insertion hole 10H is formed along the central axis of the clad base material 20R, and the other three core rod insertion holes 10H are rotationally symmetric three times at a position separated from the central axis of the clad base material 20R by a certain distance. It was formed with the aim of being formed at a certain position. Then, the position of each core rod insertion hole 10H was measured by a three-dimensional measuring device. The measurement results are shown in Table 1 below as "measurement results with the base material". The three core rod insertion holes 10H formed around the central axis of the clad base material 20R were formed with the aim of being formed at positions that are rotationally symmetric three times as described above. As shown in Table 1. It was formed at a slightly offset position. Next, the marker rod insertion hole 15H was formed in the region between the half straight lines L1 and L2 forming the _{maximum angle θ max.}

Next, the core rod 10R is inserted into the core rod insertion hole 10H formed as described above, the marker rod 15R is inserted into the marker rod insertion hole 15H, and the clad base material 20R, the core rod 10R, and the marker rod 15R are integrated. A multi-core optical fiber base material 1P was obtained. Further, the multi-core optical fiber base material 1P was drawn to obtain a multi-core optical fiber 1. After that, the positions of the respective cores 10 are measured by a three-dimensional measuring device, and the measurement results are shown in Table 1 below as "measurement results on fiber". _{Θ max} , θ ₁ , and θ ₂ in the “measurement result on fiber” are the angles of the positions corresponding to _{θ max} , θ ₁ , and θ ₂ in the “measurement result on the base material”, respectively. Since the position of each core rod 10R moves in the integration step P5, θ _max is not the maximum angle among _{θ max} , θ ₁ , and θ _{2 in the “measurement result with the base material”. Further, for Δθ max} , Δθ ₁ , and Δθ ₂ in the “difference in measurement results” shown in Table 1, the values of the measurement results of the base material are subtracted from the values of the measurement results of the fiber for θ _max , θ ₁ , and θ _2. Value.

(Examples 2 to 8)
Table 1 shows the results of manufacturing seven multi-core optical fibers according to Examples 2 to 8 in the same manner as in Example 1 and evaluating them in the same manner as in Example 1.

(Comparative Example 1)
In the measurement result of the base material, the same as in Example 1 except that the marker rod insertion hole 15H is formed in the region sandwiched by the two half lines forming the smallest angle θ _{1 among θ max} , θ ₁ , and θ _2. A multi-core optical fiber according to Comparative Example 1 was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

As shown in Table 1, in the multi-core optical fibers according to Examples 1 to 8, θ _max in the measurement result of the base material became smaller in the measurement result of the fiber, and the arrangement intervals of the respective cores became close to equal intervals. You can see that. On the other hand, in the multi-core optical fiber according to Comparative Example 1, theta _max in the measurement result of the base _material, theta _1, most small was theta ₁ of theta ₂ is further reduced in the measurement results of fiber, of each core It can be seen that the arrangement intervals are not uniform.

(Examples 9 to 13)
The multi-core optical fibers according to Examples 9 to 13 were manufactured in the same manner as in Example 1 except that the size of the outer diameter of the marker rod 15R was changed according to the size _{of θ max} in the measurement result of the base material. .. More specifically, the multi-core optical fiber base materials according to Examples 9 to 13 were used in order from the one having the smallest _{θ max} in the measurement results of the base material. _{Further, the larger the value obtained by subtracting 120 degrees from θ max} in the measurement result of the base material, the smaller the outer diameter of the marker rod 15R. _{That is, the larger the θ max} in the measurement result of the base material, the larger the gap between the inner diameter of the marker rod insertion hole 15H and the outer diameter of the marker rod 15R. Note that "120 degrees" is a value obtained by dividing 360 degrees by 3, which is the number of cores arranged around the central axis of the clad base material.

Table 2 shows the results of evaluating the multi-core optical fibers according to Examples 9 to 13 produced in this manner in the same manner as in Example 1. In Table 2, "clearance" is a value obtained by subtracting the diameter of the marker rod 15R from the diameter of the marker rod insertion hole 15H.

As shown in Table 2, the inner circumference of the marker rod insertion hole is based on the difference between the size obtained by dividing 360 degrees by the number of core rod insertion holes formed around the central axis of the clad base material and the size of the maximum angle. By determining the size of the gap between the surface and the outer peripheral surface of the marker rod, it can be seen that the arrangement intervals of the cores are close to equal intervals.

As described above, according to the present invention, a method for manufacturing a multi-core optical fiber base material and a method for manufacturing a multi-core optical fiber, which can improve the arrangement accuracy of each core of the multi-core optical fiber, are provided, and optical fiber communication is provided. It can be used in the field of the above and other devices using optical fibers.

1, 2, ... Multi-core optical fiber 1P ... Multi-core optical fiber base material 10 ... Core 10P ... Core part 10R ... Core rod 10H ... Core rod insertion hole 15 ... Marker 15P ... Marker portion 15R ... Marker rod 15H ... Marker rod insertion hole 20 ... Clad 20P ... Clad portion 20R ... Clad base material 31 ... Inner coating layer 32 ... Outer coating layer P1 ...・ ・ First drilling process P2 ・ ・ ・ Measurement step P3 ・ ・ ・ Second drilling process P4 ・ ・ ・ Rod insertion process P5 ・ ・ ・ Integration process P6 ・ ・ ・ Drawing process

Claims (8)

The first drilling step of forming a plurality of core rod insertion holes for inserting the core rod to be the core around the central axis of the clad base material to be the clad, and
In a cross section perpendicular to the longitudinal direction of the clad base material, when a half line extending from the center of the clad base material and passing through the center of each core rod insertion hole is drawn, the angle formed by the half lines adjacent to each other. A second drilling step of forming a marker rod insertion hole for inserting a marker rod to be a marker in a region sandwiched by the two half straight lines forming the maximum angle among the two.
A rod insertion step of inserting the core rod into the core rod insertion hole and inserting the marker rod into the marker rod insertion hole.
An integration step of integrating the clad base material, the core rod, and the marker rod,
A method for manufacturing a multi-core optical fiber base material. The method for manufacturing a multi-core optical fiber base material according to claim 1, further comprising a measuring step of measuring the position of each of the core rod insertion holes prior to the second drilling step. At least three core rod insertion holes are formed around the central axis of the clad base material.
One of the two half lines forming the maximum angle is the first half line and the other is the second half line.
The angle formed by the first half line and the other half line adjacent to the first half line on the side opposite to the second half line side of the first half line is defined as the first angle.
When the angle formed by the second half line and the other half line adjacent to the second half line on the side opposite to the first half line side of the second half line is defined as the second angle. ,
According to claim 1 or 2, the marker rod insertion hole is formed so that the central axis is closer to the smaller of the first angle and the second angle than the bisector of the maximum angle. The method for manufacturing a multi-core optical fiber base material according to the description. The inner peripheral surface of the marker rod insertion hole and the size based on the difference between the size obtained by dividing 360 degrees by the number of the core rod insertion holes formed around the central axis of the clad base material and the size of the maximum angle. The method for manufacturing a multi-core optical fiber base material according to any one of claims 1 to 3, wherein the size of the gap between the marker rod and the outer peripheral surface is determined. The fourth aspect of claim 4, wherein the size of the gap between the inner peripheral surface of the marker rod insertion hole and the outer peripheral surface of the marker rod is adjusted by adjusting the size of the outer diameter of the marker rod. A method for manufacturing a multi-core optical fiber base material. The fourth aspect of claim 4, wherein the size of the gap between the inner peripheral surface of the marker rod insertion hole and the outer peripheral surface of the marker rod is adjusted by adjusting the size of the inner diameter of the marker rod insertion hole. How to manufacture a multi-core optical fiber base material. A method for producing a multi-core optical fiber, which comprises a drawing step for drawing a multi-core optical fiber base material produced by the method for producing a multi-core optical fiber base material according to any one of claims 1 to 6. The first drilling step of forming a plurality of core rod insertion holes for inserting the core rod to be the core around the central axis of the clad base material to be the clad, and
In a cross section perpendicular to the longitudinal direction of the clad base material, when a half line extending from the center of the clad base material and passing through the center of each core rod insertion hole is drawn, the angle formed by the half lines adjacent to each other. A second drilling step of forming a marker rod insertion hole for inserting a marker rod to be a marker in a region sandwiched by the two half straight lines forming the maximum angle among the two.
A rod insertion step of inserting the core rod into the core rod insertion hole and inserting the marker rod into the marker rod insertion hole.
A drawing step of drawing a line while integrating the clad base material, the core rod, and the marker rod.
A method for manufacturing a multi-core optical fiber.

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