JP2020125227A - Method for manufacturing rod assembly for forming multi-core optical fiber, method for manufacturing multi-core optical fiber preform using the same and method for manufacturing multi-core optical fiber - Google Patents

Abstract

To provide a method, etc., for manufacturing a rod assembly for forming a multi-core optical fiber, capable of manufacturing the multi-core optical fiber suppressed in the formation of air bubbles.SOLUTION: The method for manufacturing a rod assembly for forming a multi-core optical fiber comprises: the main rod preparation step of processing a rod to be processed to prepare a main rod; and the rod assembly formation step of bundling a plurality of rods including a plurality of main rods to form the rod assembly for forming a multi-core optical fiber. In the main rod preparation step: the main rod includes a plurality of contact surfaces contacting the other main rods and at least one integral formation part integrally forming two contact surfaces adjacent to each other in the plurality of contact surfaces; the rod to be processed has a corner portion formed in the longitudinal direction; at least two main rods in the plurality of main rods includes a cladding formation material for forming the cladding of the multi-core optical fiber around a core part used as the core of the multi-core optical fiber; and the integral formation part in the main rod is formed by rounding the corner portion of the rod to be processed.SELECTED DRAWING: None

Description

The present invention relates to a method for manufacturing a rod assembly for forming a multicore optical fiber, a method for manufacturing a multicore optical fiber preform using the same, and a method for manufacturing a multicore optical fiber.

In recent years, the communication volume of networks has increased rapidly, and as an optical fiber capable of greatly expanding the transmission capacity, a multi-core optical fiber (MCF) having a plurality of cores in one optical fiber has attracted attention.

A so-called OBR (Over-cladding Bundled Rods) method is known as a method for manufacturing such a multi-core optical fiber. In the OBR method, first, a plurality of glass rods having a core portion that becomes a core of a multi-core optical fiber are bundled, and glass fine particles (soot) are deposited on the outer peripheral surface of the obtained rod assembly by the OVD (Outside Vaper Deposition) method. .. After that, the rod assembly on which the soot is deposited is heated in an electric furnace to sinter the soot into transparent glass and obtain a multicore optical fiber preform. Then, a multi-core optical fiber can be obtained by drawing this optical fiber preform.

As the rod assembly as described above, for example, Patent Document 1 below discloses a rod assembly in which a plurality of glass rods each having a regular polygonal cross section are bundled to eliminate a gap between the plurality of glass rods. This rod assembly is manufactured by bundling a plurality of glass rods.

JP, 9-5541, A

However, the method for manufacturing the rod assembly described in Patent Document 1 has the following problems.

That is, in the method for manufacturing a rod assembly described in Patent Document 1, when glass rods are bundled to form a rod assembly, a soot is formed outside the rod assembly to manufacture a multi-core optical fiber preform. After that, when the multicore optical fiber preform is drawn to manufacture the multicore optical fiber, bubbles may be formed in the obtained multicore optical fiber. This bubble can affect the strength and transmission characteristics of the multicore optical fiber. Therefore, it is desirable to suppress the formation of such bubbles as much as possible.

The present invention has been made in view of the above circumstances, and a method for manufacturing a multicore optical fiber forming rod assembly capable of manufacturing a multicore optical fiber in which formation of bubbles is suppressed, and a multicore optical fiber using the same. An object of the present invention is to provide a method for manufacturing a base material and a method for manufacturing a multicore optical fiber.

The present inventors examined the cause of formation of bubbles in the multicore optical fiber when manufacturing the multicore optical fiber using the rod assembly described in Patent Document 1. As a result, the present inventors considered that the reason is that the glass rod has corners along the longitudinal direction for the following reason. That is, since the glass rod has corners along its longitudinal direction, if the glass rods collide with each other when bundling a plurality of glass rods, stress is likely to be concentrated on the corners and the corners of the glass rod are chipped. It is easy to occur. Further, since the corners of the glass rod are sharp, when the corners collide with the surface of another glass rod, excessive stress is easily applied to the surface, and the surface is scratched and a recess is formed on the surface. Is likely to occur. In particular, when the glass rod has a large cross-sectional area and becomes long, it becomes difficult to handle the glass rod, and a chip or a recess is likely to be formed. As a result, when forming a rod aggregate by bundling a plurality of glass rods, there are no chipped corners or recesses on the surface of the glass rod, and no chipped corners or recesses on the glass rod surface in the longitudinal direction of the glass rod. A larger space is formed between the glass rod and another glass rod as compared with the point. Then, this larger space is obtained when the multi-core optical fiber preform is manufactured by forming the soot on the outside of the rod assembly and then the multicore optical fiber preform is drawn to manufacture the multicore optical fiber. The present inventors considered that bubbles might be formed in the multi-core optical fiber. Then, as a result of intensive studies, the present inventors have found that the above invention can solve the above problems.

That is, the present invention provides a main rod preparing step of treating a rod to be processed to prepare a main rod, and a rod for forming a multi-core optical fiber forming rod assembly by bundling a plurality of rods including a plurality of the main rods. In the main rod preparation step, the main rod includes a plurality of contact surfaces that come into contact with other main rods, and two adjacent contact surfaces of the plurality of contact surfaces that are adjacent to each other. Forming at least one integrally formed portion, the rod to be processed has a corner formed along the longitudinal direction thereof, and at least two main rods of the plurality of main rods are A clad forming material for forming a clad of the multi-core optical fiber is provided around a core part which is a core of the multi-core optical fiber, and the main part is processed by rounding the corner part of the rod to be processed. It is a method of manufacturing a rod assembly for forming a multi-core optical fiber, in which the integrally formed portion of the rod is formed.

According to the method for manufacturing a multicore optical fiber forming rod assembly of the present invention, since the corners formed along the longitudinal direction of the rod to be processed are processed to be rounded, the integrally formed part of the main rod is It is formed into a round shape. Therefore, when bundling a plurality of rods including a plurality of main rods in a state where the contact surface of the main rod is in contact with another main rod, even if the other rod collides with the integrally formed portion of the main rod. As compared with the case where the integrally formed portion of the main rod is not formed to have a round shape and has a corner, the stress acting on the integrally formed portion is more easily dispersed, so that the integrally formed portion of the main rod is less likely to be chipped. Further, since the integrally formed portion of the main rod is not sharp, even if the integrally formed portion collides with the contact surface of another main rod, it is difficult to apply excessive stress to the contact surface and the contact surface is damaged. It becomes difficult for a concave portion to be formed on the contact surface. Therefore, when a plurality of rods including a plurality of main rods are bundled to form a rod assembly, an integrally formed portion between another main rod and an integrally formed portion in the longitudinal direction of the main rod. It is possible to suppress the formation of a larger space due to the lack of a groove or the concave portion of the contact surface of the main rod. Therefore, according to the method for manufacturing a rod assembly of the present invention, the multi-core optical fiber is drawn by drawing the multi-core optical fiber preform manufactured by drawing the rod assembly or forming the soot on the outside of the rod assembly. A rod assembly capable of manufacturing a multi-core optical fiber in which formation of bubbles is suppressed can be manufactured.

In the method for manufacturing a multi-core optical fiber forming rod assembly, the rod to be treated is formed by grinding or cutting an original rod, and the rod to be treated is treated by the main rod preparing step. When the main rod has a plurality of processed surfaces to be the contact surface, it is preferable that the rod to be processed is heat-treated in the main rod preparing step.

In this case, the rod to be processed is formed by grinding or cutting the original rod, and the rod to be processed has a plurality of processed surfaces to be contact surfaces of the main rod due to the processing in the main rod preparing step. In particular, the machined surface is rougher than the surface that has not been ground or cut. On the other hand, when the rod to be treated is heat-treated, not only the corners of the rod to be treated are rounded, but also the contact surface of the main rod becomes smoother than the processed surface. Therefore, when the rod aggregate is formed by bundling the rods in a state where the contact surfaces of the main rod, which are smoother than the machined surface, are in contact with each other, the contact surface of the main rod and other main rods are elongated in the longitudinal direction of the main rod. It is further suppressed that a larger space is formed between the contact surface and the contact surface due to the unevenness formed on the contact surface. Therefore, according to the method for manufacturing a rod assembly of the present invention, the multi-core optical fiber is drawn by drawing the multi-core optical fiber preform manufactured by drawing the rod assembly or forming the soot on the outside of the rod assembly. It is possible to manufacture a rod assembly capable of manufacturing a multi-core optical fiber in which formation of bubbles is further suppressed during manufacturing.

In the method for manufacturing a multi-core optical fiber forming rod assembly, the rod to be treated may be treated by non-heat treatment in the main rod preparing step.

In the method for manufacturing a multicore optical fiber forming rod assembly, in the main rod preparing step, A represented by the following formula (1) is 0.20 to 0.24 in the integrally forming portion of the main rod. It is preferable to treat the rod to be treated so that
A=R/Rmax (1)
(In the above formula (1), R represents a radius of curvature of the integrally formed portion, and Rmax represents a diameter of a circumscribed circle with respect to a cross section orthogonal to the longitudinal direction of the main rod.)

Here, the "radius of curvature of the integrally formed portion" refers to the radius of curvature obtained by the following procedure.
(1) On the end face of the main rod, two intersections between the two straight lines drawn along each of the two contact surfaces adjacent to each other through the integrally formed portion and the integrally formed portion, and a straight line connecting the two intersections The maximum height point at which the height of the integrally formed part is maximum is obtained.
(2) Determine an arc passing through the three points of the above two intersections and the maximum height point.
(3) From the arc determined in (2), the radius corresponding to the arc is calculated as the radius of curvature. Specifically, when the maximum height of the integrally formed portion from the straight line passing through the two intersections is a and the length between the two intersections is b, the radius of curvature r is calculated by the following formula.
r=a/2+b ² /8a

In this case, as compared with the case where the value of A is less than 0.20, when the rod aggregate is formed by bundling the rods in a state where the contact surfaces of the main rods are in contact with each other, in the longitudinal direction of the main rods, It is further suppressed that a larger space is formed between the contact surface of the main rod and the contact surface of the other main rod due to the lack of the integrally formed portion or the recess or the unevenness of the contact surface of the main rod. Further, compared with the case where the value of A exceeds 0.24, in the rod assembly, the deformation of the core portion of the main rod during drawing is suppressed, and the multicore optical fiber in which the deformation of the core is suppressed can be manufactured.

Further, the present invention is a soot forming step of forming a soot on the outside of the multi-core optical fiber forming rod assembly obtained by the method for manufacturing a multi-core optical fiber forming rod assembly described above, and vitrifying the soot to form a multi-core. A soot vitrification step of obtaining an optical fiber preform, and a method for producing a multicore optical fiber preform.

According to this method of manufacturing a multi-core optical fiber preform, when the rod assembly is formed, the processed rod is processed so that the corners formed along the longitudinal direction thereof are rounded. The forming part is formed in a round shape. Therefore, when bundling a plurality of rods including a plurality of main rods in a state where the contact surface of the main rod is in contact with another main rod, even if the other rod collides with the integrally formed portion of the main rod. Since the integrally formed portion of the main rod is not sharp, the stress acting on the integrally formed portion is easily dispersed as compared with the case where the integrally formed portion of the main rod is not rounded and has a corner. Therefore, chipping is less likely to occur in the integrally formed portion of the main rod. Further, since the integrally formed portion of the main rod is not sharp, even if the integrally formed portion collides with the contact surface of another main rod, it is difficult to apply excessive stress to the contact surface and the contact surface is damaged. It becomes difficult for a concave portion to be formed on the contact surface. For this reason, when a plurality of rods including a plurality of main rods are bundled to form a rod assembly, in the longitudinal direction of the main rods, a chip of the integrally formed portion or contact of the main rods with other main rods occurs. The formation of a larger space due to the concave portion of the surface is suppressed. Therefore, according to the method for producing a multicore optical fiber preform of the present invention, when producing a multicore optical fiber by drawing, a multicore optical fiber preform capable of producing a multicore optical fiber in which formation of bubbles is suppressed is produced. can do.

Further, the present invention is a rod assembly forming step of forming a multi-core optical fiber forming rod assembly by the method for manufacturing a multi-core optical fiber forming rod assembly described above, and drawing the multi-core optical fiber forming rod assembly. And a drawing step of manufacturing the multi-core optical fiber.

According to this method for producing a multi-core optical fiber, when forming the rod assembly, the processed rod is processed so that the corners formed in the longitudinal direction thereof are rounded, so that the integrally formed portion of the main rod is rounded. It is formed. Therefore, when bundling a plurality of rods including a plurality of main rods in a state where the contact surface of the main rod is in contact with another main rod, even if the other rod collides with the integrally formed portion of the main rod. Since the integrally formed portion of the main rod is not sharp, the stress acting on the integrally formed portion is easily dispersed as compared with the case where the integrally formed portion of the main rod is not rounded and has a corner. Therefore, chipping is less likely to occur in the integrally formed portion of the main rod. Further, since the integrally formed portion of the main rod is not sharp, even if the integrally formed portion collides with the contact surface of another main rod, it is difficult to apply excessive stress to the contact surface and the contact surface is damaged. It becomes difficult for a concave portion to be formed on the contact surface. Therefore, when a plurality of rods including a plurality of main rods are bundled together to form a rod assembly, in the longitudinal direction of the main rod, due to a chip or a recess of the integrally formed portion with another main rod. The formation of a larger space is suppressed. Therefore, according to the method for producing a multicore optical fiber of the present invention, it is possible to produce a multicore optical fiber in which the formation of bubbles is further suppressed when a rod assembly is drawn to produce a multicore optical fiber.

Furthermore, the present invention is a preform forming step of forming a multicore optical fiber preform by the method for producing a multicore optical fiber preform described above, and a drawing step of producing a multicore optical fiber by drawing the multicore optical fiber preform. Is a method of manufacturing a multi-core optical fiber including.

According to this method for producing a multi-core optical fiber, when forming the rod assembly, the processed rod is processed so that the corners formed in the longitudinal direction thereof are rounded, so that the integrally formed portion of the main rod is rounded. It is formed. Therefore, when bundling a plurality of rods including a plurality of main rods in a state where the contact surface of the main rod is in contact with another main rod, even if the other rod collides with the integrally formed portion of the main rod. Since the integrally formed portion of the main rod is not sharp, the stress acting on the integrally formed portion is easily dispersed as compared with the case where the integrally formed portion of the main rod is not rounded and has a corner. Therefore, chipping is less likely to occur in the integrally formed portion of the main rod. Further, since the integrally formed portion of the main rod is not sharp, even if the integrally formed portion collides with the contact surface of another main rod, it is difficult to apply excessive stress to the contact surface and the contact surface is damaged. It becomes difficult for a concave portion to be formed on the contact surface. Therefore, when a plurality of rods including a plurality of main rods are bundled together to form a rod assembly, in the longitudinal direction of the main rod, due to a chip or a recess of the integrally formed portion with another main rod. The formation of a larger space is suppressed. Therefore, according to the method for producing a multi-core optical fiber of the present invention, when a multi-core optical fiber base material produced by forming a soot on the outside of the rod assembly is drawn to produce a multi-core optical fiber, formation of bubbles It is possible to manufacture a multi-core optical fiber in which is suppressed.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the rod assembly for multicore optical fiber formation which can manufacture the multicore optical fiber in which bubble formation was suppressed, the manufacturing method of a multicore optical fiber preform using this, and a multicore optical fiber. A method of manufacturing the same is provided.

It is a cross-sectional view showing an example of a multi-core optical fiber manufactured by the method for manufacturing a multi-core optical fiber of the present invention. It is a side view which shows the multi-core optical fiber preform for manufacturing the optical fiber of FIG. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. FIG. 3 is a cross-sectional view showing an embodiment of a multicore optical fiber forming rod assembly for producing the multicore optical fiber preform of FIG. 2. FIG. 3 is a vertical cross-sectional view showing an embodiment of a multi-core optical fiber forming rod assembly for manufacturing the multi-core optical fiber preform of FIG. 2. FIG. 5 is a cross-sectional view showing a cylindrical core rod for manufacturing the core rod of FIG. 4. It is a cross-sectional view which shows the to-be-processed core rod obtained by processing the cylindrical core rod of FIG. FIG. 5 is a cross-sectional view showing a precursor of a multicore optical fiber preform in which soot is formed outside the multicore optical fiber forming rod assembly of FIG. 4. FIG. 6 is a cross-sectional view showing another embodiment of a multicore optical fiber forming rod assembly for manufacturing the multicore optical fiber preform of FIG. 2. FIG. 8 is a cross-sectional view showing still another embodiment of a multicore optical fiber forming rod assembly for manufacturing the multicore optical fiber preform of FIG. 2.

Hereinafter, embodiments of the method for producing a multi-core optical fiber of the present invention will be described in detail.

《Multi-core optical fiber》
First, a multicore optical fiber obtained by the method for producing a multicore optical fiber of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing an example of a multicore optical fiber manufactured by the method for manufacturing a multicore optical fiber of the present invention.

As shown in FIG. 1, a multi-core optical fiber (hereinafter, simply referred to as “optical fiber”) 10 includes a plurality of cores 1 and a clad 2 provided around the cores 1. The refractive index of the core 1 is larger than that of the cladding 2. In this embodiment, the core 1 is formed by adding germanium to silica glass, and the clad 2 is formed by adding fluorine to silica glass.

<<Manufacturing method of multi-core optical fiber>>
Next, a method for manufacturing the optical fiber 10 will be described.

First, a manufacturing method (base material forming step) of an optical fiber base material for manufacturing the optical fiber 10 will be described with reference to FIGS. 2 to 8. 2 is a side view showing a multicore optical fiber preform for manufacturing the optical fiber of FIG. 1, FIG. 3 is a cross-sectional view taken along line III-III of FIG. 2, and FIG. 4 is a multicore of FIG. FIG. 5 is a cross-sectional view showing an embodiment of a multicore optical fiber forming rod assembly for producing an optical fiber preform, and FIG. 5 is a multicore optical fiber forming rod for producing the multicore optical fiber preform of FIG. FIG. 6 is a longitudinal sectional view showing an embodiment of the aggregate, FIG. 6 is a transverse sectional view showing a cylindrical core rod for manufacturing the core rod of FIG. 4, and FIG. 7 is obtained by processing the cylindrical core rod of FIG. FIG. 8 is a cross-sectional view showing a core rod to be processed, and FIG. 8 is a cross-sectional view showing a precursor of a multicore optical fiber preform having soot formed on the outer side of the multicore optical fiber forming rod assembly of FIG.

<Multi-core optical fiber base material>
First, the optical fiber preform 110 manufactured by the method for manufacturing a multicore optical fiber preform (hereinafter referred to as “optical fiber preform”) will be described.

As shown in FIGS. 2 and 3, the optical fiber preform 110 includes a core portion 101 that serves as the core 1 of the optical fiber 10 and a cladding portion 102 that serves as the cladding 2. The optical fiber preform 110 has a continuous hole G1 at a position surrounded by the core portion 101. The continuous hole G1 penetrates the optical fiber preform 110 along the longitudinal direction L1 of the optical fiber preform 110. That is, the continuous hole G1 continuously extends from one end face 110a side of the optical fiber preform 110 along the longitudinal direction L1 of the optical fiber preform 110 to the other end face 110b side of the optical fiber preform 110. Further, in the present embodiment, the softening point of the clad portion 102 is lower than the softening point of the core portion 101.

<Manufacturing method of multi-core optical fiber preform>
Next, a method of manufacturing the optical fiber preform 110 will be described.

In order to form the optical fiber preform 110, first, the optical fiber preform forming rod aggregate (hereinafter, simply referred to as “rod aggregate”) 201 shown in FIGS. 4 and 5 is formed (rod aggregate). Forming process).

(Rod assembly)
The rod assembly 201 is an assembly of rods, and the rods include four core rods 202 as main rods and four columnar filling rods as slave rods provided outside the four core rods 202. 102B and.

The core rod 202 includes a core portion 101 which is the core 1 of the optical fiber 10 and a clad forming material 102A which is provided around the core portion 102 and forms the clad 2 of the optical fiber 10 and the clad portion 102 of the optical fiber preform 110. Have. In the present embodiment, the softening point of the clad forming material 102A is lower than the softening point of the core portion 101.

The filling rod 102B is for forming the clad 2 of the optical fiber 10 and the clad portion 102 of the optical fiber preform 110, and is arranged so as to contact the outer peripheral surfaces of two adjacent core rods 202. In the present embodiment, the filling rod 102B does not form a main rod because it does not have a contact surface that comes into contact with the outer peripheral surface of the core rod 202. Further, the filling rod 102B has a softening point lower than that of the clad forming material 102A. In order for the filling rod 102B to have a softening point lower than that of the cladding forming material 102A, an additive such as fluorine may be contained.

Further, the rod assembly 201 has one continuous hole G formed so as to be surrounded by the four core rods 202, and a gap surrounded by the core rod 202 and the filling rod 102B. The continuous hole G continuously extends from one end surface 202a side of the core rod 202 along the longitudinal direction L of the core rod 202 to the other end surface 202b side of the core rod 202. The four core rods 202 will be referred to as core rods 202A to 202D as necessary.

Here, the core rod 202 will be described. Since the core rods 202A to 202D have the same configuration, the core rod 202A will be described.

The core rod 202A has two contact surfaces S that contact the other core rods 202B and 202C, a non-contact surface N that does not contact the other core rods 202B to 202D, and two adjacent contact surfaces S of the two contact surfaces S. It has the integral formation part X which integrally forms each other. Here, the integrally formed portion X continuously extends from one end surface 202a side of the core rod 202A to the other end surface 202b side of the core rod 202A along the longitudinal direction L of the core rod 202A (see FIG. 5). The integrally formed portion X is formed in a round shape. Specifically, the integrally formed portion X is a curved surface that projects outward from a flat surface that connects two adjacent contact surfaces S (opposite the flat surface to the core portion 101). In other words, the integrally formed portion X is a curved surface projecting to the continuous hole G side with respect to the flat surface connecting the two adjacent contact surfaces S in FIG. 4.

Then, in the rod assembly 201, with the other core rods 202 in contact with the two contact surfaces S of the core rods 202, the core rods 202 from the one end surface 202a side of the core rods 202 along the longitudinal direction L of the core rods 202. A continuous hole G that continuously extends to the other end surface 202b side is formed so as to be surrounded by the integrally formed portion X of the plurality of core rods 202.

(Method of manufacturing rod assembly)
Next, a method of manufacturing the rod assembly 201 will be described.

First, for example, a columnar original core rod 202A2 as an original rod shown in FIG. 6 is prepared as follows. At this time, as the columnar original core rod 202A2, a columnar rod whose radius is a distance from the center of the core portion 101 of the core rod 202 to the non-contact surface N of the clad portion 102 or a length longer than that is prepared. The columnar original core rod 202A2 includes a core portion 101 and a clad forming material 102B2 surrounding the core portion 101. The clad forming material 102B2 is made of the same material as the clad portion 102 of the optical fiber preform 110. The columnar original core rod 202A2 can be manufactured by, for example, a VAD (Vaper-phase Axial Deposition) method. At this time, when adjusting the ratio of the diameter of the core portion 101 in the original core rod 202A2/the outer diameter of the cladding forming material 102B2, an OVD (Outside Vapor Deposition) method can be used as necessary.

Next, two processing surfaces S1 are formed on the columnar original core rod 202A2 by, for example, grinding or cutting to form the core rod 202A1 to be processed shown in FIG. The to-be-processed core rod 202A1 includes a core portion 101 and a clad forming material 102B1 surrounding the core portion 101. The clad forming material 102B1 is made of the same material as the clad portion 102 of the optical fiber preform 110. Further, the core rod 202A1 to be processed has two machined surfaces S1 and a non-machined surface N1, and as a connecting portion between two machined surfaces S1 adjacent to each other in FIG. 7, along the longitudinal direction L2 of the core rod 202A1 to be processed. The corner portion X1 is formed so as to become a point. The machined surface S1 preferably has a small arithmetic average roughness, but is preferably 0.8 μm or less. The arithmetic average roughness of the processed surface S1 is more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less.

The core rod 202A1 to be processed may be washed as necessary in order to remove foreign matter such as a grinding liquid and a grindstone adhered to the surface of the cylindrical original core rod 202A2 during grinding. The washing can be performed using, for example, a washing liquid. Ethanol is usually used as the cleaning liquid, but buffered hydrofluoric acid (BHF) can also be used when the surface of the core rod 202A1 to be processed is shaved. The washing may be performed with ethanol and then with BHF.

Then, the corner portion X1 of the core rod 202A1 to be processed is processed so as to be continuously rounded along the longitudinal direction L2 of the core rod 202A1 to be processed, and the core rod 202 as the main rod is prepared (main rod preparation step). In this way, the processed surface S1 of the core rod 202A1 to be processed becomes the contact surface S, and the corner portion X1 becomes the integrally formed portion X formed in a round shape. Specifically, the corner portion X1 is processed so as to have a curved surface that projects toward the side opposite to the core portion 101 as compared with the case where the corner portion X1 is not rounded.

To round the corner X1 of the core rod 202A1 to be processed, in the present embodiment, the core rod 202A1 to be processed is processed by heat treatment. The heat treatment can be performed by flame polishing with a flame burner or heating in an electric furnace, for example.

The temperature of the heat treatment is not particularly limited as long as the corner X1 can be rounded, but is usually 1000 to 2200°C, preferably 1500 to 1800°C.

Further, since the processed surface S1 is heat-treated by the heat treatment of the core rod 202A1 to be processed, the arithmetic average roughness of the contact surface S becomes smaller than the arithmetic average roughness of the processed surface S1. At this time, the arithmetic mean roughness of the contact surface S is preferably 0.2 μm or less.

Further, it is preferable that the core rod 202A1 to be processed is processed so that the integrally formed portion X of the core rod 202 has a value of A represented by the following formula (1) of 0.20 to 0.24.
A=R/Rmax (1)
(In the above formula (1), R represents the radius of curvature (mm) of the integrally formed portion X, and Rmax represents the diameter (mm) of the circumscribed circle with respect to the cross section orthogonal to the longitudinal direction L of the core rod 202.)

In this case, when the rod aggregate 201 is formed by bundling the rods in a state where the contact surfaces S of the core rods 202 are in contact with each other as compared with the case where the value of A is less than 0.20, in the longitudinal direction L of the core rods 202. It is further suppressed that a larger space is formed between the contact surface S of the core rod 202 and the contact surface S of another core rod 202 due to the lack of the integrally formed portion X or the unevenness of the contact surface S of the core rod 202. To be done. Further, as compared with the case where the value of A exceeds 0.24, in the rod assembly 201, the deformation of the core portion 101 of the core rod 202 during drawing is suppressed, and the deformation of the core 1 is suppressed. Can be manufactured.

It is more preferable that the core rod 202A1 to be processed is processed so that the value of A is 0.204 to 0.237 in the integrally formed portion X of the core rod 202.

As the core rod 202, first, a cylindrical rod having a radius larger than the distance from the center of the core portion 101 to the non-contact surface N of the clad portion 102 is prepared, and the cylindrical rod is ground or cut into two pieces. It can also be obtained by forming a processed surface to form a core rod to be processed, washing the core rod to be processed as needed, and stretching the core rod to be processed. The stretching process can be performed by stretching the core rod to be processed at a predetermined stretching speed in an electric furnace. At this time, the temperature in the electric furnace and the drawing speed are appropriately determined according to the target maximum diameter of the core rod 202 (diameter of the circumscribing circle). The temperature in the electric furnace is usually 1800 to 2200°C. For example, when the diameter of the cylindrical rod is 20 mm and the maximum diameter of the rod to be processed is 9.2 mm, the temperature of the electric furnace is set to 1900° C., for example.

In order to maintain the state, the rod assembly 201 is usually bundled with a binding band, and glass rods (hereinafter referred to as “dummy rods”) that are dummy are melt-bonded to both end faces thereof, and then the binding band. Is taken off. At this time, in a state where the rod assembly 201 is under a reduced pressure environment, the dummy rods are melt-bonded so as to close the openings of the continuous holes G in the one end surface 202a and the other end surface 202b of the core rod 202, and then the rod assembly is assembled. When the body 201 is placed under the atmospheric pressure environment, the continuous hole G of the rod assembly 201 is in a negative pressure state.

Thus, the rod assembly 201 is formed (rod assembly forming step).

Next, glass particles are deposited on the outside of the rod assembly 201 thus obtained to form the soot 102C, and as shown in FIG. 8, the precursor 200 of the optical fiber preform 110 is formed (soot forming step). .. At this time, the soot 102C is formed to have a softening point lower than the softening point of the core portion 101 and higher than the softening point of the filling rod 102B after vitrification. For that purpose, for example, an additive such as fluorine may be added to the soot 102C.

Next, the precursor 200 of the optical fiber preform 110 is dehydrated if necessary, and then the soot 102C is sintered and vitrified (soot vitrification step). At this time, the clad forming material 102A of the core rod 202, the filling rod 102B, and the soot 102C are softened and integrated faster than the core portion 101. At this time, the optical fiber preform 110 continuously connects the continuous hole G from one end face 110a side of the optical fiber preform 110 to the other end face 110b side along the longitudinal direction L1 of the optical fiber preform 110. The soot 102C is vitrified so as to be left as the continuous hole G1 extending.

In this way, the optical fiber preform 110 is obtained.

Next, the optical fiber preform 110 is drawn to obtain the optical fiber 10 (drawing step). At this time, since the continuous hole G1 is in a negative pressure state, the drawing step is performed with the continuous hole G1 in a negative pressure state. Thus, the manufacturing of the optical fiber 10 is completed.

According to the manufacturing method of the optical fiber 10 described above, since the corner portion X1 formed along the longitudinal direction L2 of the core rod 202A1 to be processed is processed to be rounded, the integrally formed portion X of the core rod 202 is formed to be rounded. To be done. Therefore, when a plurality of rods including a plurality of core rods 202 are bundled with the contact surface S of the core rod 202 being in contact with the other core rod 202, the other core rod 202 collides with the integrally formed portion X of the core rod 202. Even if the integrally formed portion X of the core rod 202 is not rounded and has corners, the stress acting on the integrally formed portion X is more likely to be dispersed, so that the integrally formed portion X of the core rod 202 is chipped. It gets harder. Further, since the integrally formed portion X of the core rod 202 is not sharp, even if the integrally formed portion X collides with the contact surface S of another core rod 202, it is difficult to apply excessive stress to the contact surface S, and the contact surface S It is less likely that S will be damaged and a recess will be formed on the contact surface S. Therefore, when a plurality of rods including a plurality of core rods 202 are bundled to form the rod assembly 201, in the longitudinal direction L of the core rod 202, the gap between the core rod 202 and the integrally formed portion X or the contact surface S of another core rod 202 is formed. In addition, it is possible to suppress the formation of a larger space due to the lack of the integrally formed portion X and the concave portion or the concave portion of the contact surface S of the core rod 202. Therefore, according to the method for manufacturing the optical fiber 10, when the optical fiber 10 is manufactured by drawing the multi-core optical fiber preform 110 manufactured by forming the soot 102C on the outer side of the rod assembly 201, formation of bubbles is formed. It is possible to manufacture the optical fiber 10 in which the above is suppressed.

Moreover, in the above-described method for manufacturing the optical fiber 10, the core rod 202A1 to be processed is formed by grinding or cutting the cylindrical core rod 202A2. For this reason, the processed surface S1 of the core rod 202A1 to be processed is in a rougher state than the surface that has not been ground or cut. On the other hand, the core rod 202A1 to be processed is processed by heat treatment. Therefore, not only the corner portion X1 of the core rod 202A1 to be processed is rounded, but also the contact surface S of the core rod 202 is smoother than the processed surface S1. Therefore, when the rod assembly 201 is formed in a state where the contact surfaces S of the core rod 202, which are smoother than the processed surface S1, are in contact with each other, the contact surface S of the core rod 202 and other core rods 202 in the longitudinal direction L of the core rod 202. It is further suppressed that a larger space is formed between the contact surface S of 202 and the contact surface S due to the unevenness formed on the contact surface S. Therefore, according to the method of manufacturing the optical fiber 10, when the optical fiber preform 110 manufactured by forming the soot 102C on the outer side of the rod assembly 201 is drawn to manufacture the optical fiber 10, bubbles are not formed. The more suppressed optical fiber 10 can be manufactured.

Further, in the base material forming step, in the rod assembly 201, with the other core rods 202 being in contact with the plurality of contact surfaces S of the core rod 202, the longitudinal direction L of the core rod 202 from the one end surface 202a side of the core rod 202. A continuous hole G that extends continuously to the other end surface 202b side of the core rod 202 is formed so as to be surrounded by the integrally formed portion X of the plurality of core rods 202. Therefore, the continuous hole G can be made smaller than in the case where the core rod 202 does not have the contact surface S. Therefore, according to the rod assembly 201, when the soot forming step of forming the soot 102C on the outer side thereof or the soot vitrifying step of vitrifying the soot 102C is performed thereafter, the clad forming material 102A of the core rod 202 has continuous holes. It is possible to obtain the optical fiber preform 110 in which the large deformation to suppress G is suppressed and the deformation of the core portion 101 is suppressed. Therefore, in the drawing step of drawing the optical fiber base material 110, the optical fiber 10 in which the deformation of the core 1 is suppressed can be obtained.

Further, in the preform forming step, after the soot 102C is formed on the outer side of the rod assembly 201, the soot 102C is vitrified to manufacture the optical fiber preform 110. The continuous hole G in the body 201 is left as a continuous hole G1 that extends continuously from one end surface 110a side of the optical fiber preform 110 along the longitudinal direction L1 of the optical fiber preform 110. Therefore, in the drawing step, if the continuous hole G1 is placed in a negative pressure state when the optical fiber preform 110 is drawn, a portion of the inner wall surface forming the continuous hole G1 that originates from each integrally formed portion X of the core rod 202. Move in contact with each other at all points along the longitudinal direction L1 of the optical fiber preform 110 to close the continuous hole G1. Thereby, it is possible to suppress the formation of bubbles in the obtained optical fiber 10.

Further, in the rod assembly 201, the integrally formed portion X of the core rod 202 projects to the continuous hole G side from the flat surface connecting the two adjacent contact surfaces S. Therefore, the continuous hole G becomes smaller when the other core rods 202 are in contact with the plurality of contact surfaces S of the core rod 202. Further, since the integrally formed portion X of the core rod 202 has already bulged to the outside of the flat surface connecting the two adjacent contact surfaces S, even if the core rod 202 is heated, the integrally formed portion X is flattened by thermal expansion. More difficult to project outside than Therefore, when the soot forming step of forming the soot 102C on the outer side of the rod assembly 201 or the soot vitrifying step of vitrifying the soot 102C is performed thereafter, the cladding forming material 102A of the core rod 202 fills the continuous hole G. It is possible to obtain the optical fiber preform 110 in which the deformation of the core portion 101 is further suppressed as much as possible. Therefore, when the optical fiber preform 110 is drawn, the optical fiber 10 in which the deformation of the core is further suppressed can be obtained.

Further, the rod assembly 201 has the filling rod 102B, and it is not necessary to deposit glass particles by the amount of the filling rod 102B, so that the soot 102C can be easily formed. Furthermore, since the filling rod 102B has a lower softening point than the clad forming material 102A and the soot 102C, the filling rod 102B deforms earlier than the clad forming material 102A and the soot 102C in the soot vitrification step. The deformation of the core portion 101 is suppressed. Further, the gap between the filling rod 102B before softening and the core rod 202 is easily eliminated by the softening filling rod 102B. As a result, it is possible to suppress the formation of unnecessary voids in the obtained optical fiber preform 110.

The soot 102C is formed to have a softening point lower than that of the core portion 101 after vitrification. Therefore, the deformation of the clad forming material 102A due to surface tension or the like is promoted, and the deformation of the core portion 101 can be further suppressed.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the core rod 202A1 to be processed is treated by heat treatment, but it may be performed by non-heat treatment instead of heat treatment. In this case, at least the corner X1 may be processed. Therefore, the processing may be performed only on the corner portion X1, or the processing may be performed on both the corner portion X1 and the processed surface S1. Examples of non-heat treatment include grinding and polishing using a grindstone.

Further, in the above-described embodiment, in the rod assembly 201, the continuous hole G extends from one end surface 202a side of the core rod 202 to the other end surface 202b side of the core rod 202 along the longitudinal direction L of the core rod 202. The hole G does not have to extend to the other end surface 202b side of the core rod 202. Further, in the optical fiber preform 110, the continuous hole G1 extends from the one end face 110a side of the optical fiber preform 110 along the longitudinal direction L1 of the optical fiber preform 110 to the other end face 110b side of the optical fiber preform 110. The continuous hole G1 extends from one end face 110a side of the optical fiber preform 110 to the other end face 110b side of the optical fiber preform 110 along the longitudinal direction L1 of the optical fiber preform 110. You don't have to. In this case, the drawing of the optical fiber preform 110 is performed from the one end face 110a side of the rod assembly 201.

Further, in the above embodiment, the number of contact surfaces S on the core rod 202 is two, but the number of contact surfaces S may be changed as appropriate according to the number of other core rods 202 contacting the core rod 202. For example, if the number of core rods 202 contacting the core rod 202 is three, the number of contact surfaces S may be three.

Further, in the above embodiment, the number of core rods 202 as main rods is four in the rod assembly 201, but the number of core rods 202 may be at least two, and for example, the number of core rods 202 is two. In the case of a book, the remaining two rods may be filling rods having a softening point equal to or lower than the softening point of the clad forming material 102A of the core rod 202.

Further, in the above-described embodiment, the number of core rods 202 as main rods is four, but the number of main rods may be plural, so the number of core rods 202 may be two to three, or five. It may be more. However, at least two of the plurality of core rods 202 need to be core rods.

Further, in the above embodiment, the softening point of the clad forming material 102A is lower than the softening point of the core portion 101, the filling rod 102B has a lower softening point than the clad forming material 102A, and the soot 102C. Is formed to have a softening point lower than the softening point of the core portion 101 and higher than the softening point of the filling rod 102B after vitrification. For example, the core portion 101 is formed by adding germanium to silica glass. The softening point of the clad forming material 102A may be equal to or higher than the softening point of the core portion 101 as in the case where the clad forming material 102A is made of a material and is made of silica glass. In the above embodiment, the filling rod 102B has a softening point equal to or higher than that of the cladding forming material 102A, as in the case where the cladding forming material 102A and the filling rod 102B are made of silica glass. Good. Further, in the above embodiment, the soot 102C may not be formed to have a softening point lower than the softening point of the core portion 101 and higher than the softening point of the filling rod 102B after vitrification. For example, the softening point of the soot 102C may be higher than the softening point of the core portion 101, or may be equal to or lower than the softening point of the filling rod 102B.

Further, in the above-described embodiment, the optical fiber 10 has a configuration in which the core 1 is formed by adding germanium to silica glass, and the clad 2 is formed by adding fluorine to silica glass. The structure is not limited to such a structure as long as it has a higher refractive index. For example, the optical fiber 10 may have a configuration in which the core 1 is formed by adding germanium to silica glass, and the clad 2 is formed by silica glass. Further, in the above embodiment, in the optical fiber 10, the cladding 2 may have a trench portion having a lower refractive index. Specifically, the optical fiber has a core 1 formed by adding germanium to silica glass, and a clad surrounding the core 1. The clad is concentric with the core 1 in order from the core 1 side. , A first cladding layer, a trench portion and a second cladding layer. Here, the refractive index of the first cladding layer and the second cladding layer is lower than the refractive index of the core 1, and the refractive index of the trench portion is the refractive index of the layer of the first cladding layer and the second cladding layer having the lower refractive index. Lower than the rate. The trench portion is formed by adding fluorine to silica glass, for example.

Furthermore, the cross-sectional shape of the core rod 202 is not limited to the shape shown in the above embodiment, and may be, for example, a polygon. For example, like the core rod 302 of the rod assembly 301 shown in FIG. 9, the core rod 302 may have a quadrangular cross-sectional shape. Furthermore, like the core rod 402 of the rod assembly 401 shown in FIG. 10, the cross-sectional shape of the core rod 402 may be a hexagon.

Furthermore, in the above embodiment, in the rod assembly 201, one core rod 202 is in contact with each of the plurality of contact surfaces S, but only one core rod may be in contact with the plurality of contact surfaces S. ..

Further, in the above embodiment, the rod assembly 201 has the cylindrical filling rod 102B, but the filling rod 102B may have various shapes such as a polygonal column such as a triangular column. Furthermore, the rod assembly 201 does not necessarily have to have the filling rod 102B. Further, in the above embodiment, the filling rod 102B does not constitute a main rod, but the filling rod 102B has a plurality of contact surfaces with the core rod 202 and an integrally formed portion that integrally forms the contact surfaces. If the continuous hole is formed so as to be surrounded by the integrally formed portion, the filling rod 102B can form the main rod. For example, when the filling rod 102B has a polygonal columnar shape and has a shape complementary to the outer shape of the core rod 202, the filling rod 102B has a plurality of contact surfaces that come into contact with the core rod 202 as the main rod, and at least one contact surface. Since it has two integrally formed portions, the filling rod 102B constitutes a main rod.

Furthermore, in the above-described embodiment, the continuous hole G1 in the optical fiber preform 110 is closed by the dummy rod to be in a negative pressure state, but the continuous hole G1 in the optical fiber preform 110 is not closed by the glass rod. In addition, it is also possible to bring the continuous hole G1 into a negative pressure state by evacuating the continuous hole G1. At this time, if the continuous hole G1 in the optical fiber preform 110 is not closed by the glass rod, one end or both ends of each rod may be processed into a tapered shape when the rod assembly 201 is prepared. In this case, when the dummy rod is welded and connected to the end surface of the tapered end portion of the rod of the rod assembly 201, the diameter of the glass rod to be welded becomes small, so that the dummy rod is connected to the tapered end of the rod of the rod assembly 201. There is also an advantage that the heat can be applied to the end faces of the parts with a smaller heating power. Also, the diameter of the dummy rod can be reduced. Furthermore, in the rod assembly 201, since the tapered ends of the rods welded to the dummy rods are separated from each other, the gas in the continuous hole G1 in the optical fiber preform 110 is likely to escape to the outside. For this reason, when the optical fiber preform 110 is drawn while being vacuumed, gas is not accumulated inside, and bubbles are less likely to remain in the obtained optical fiber 10.

Further, in the above-described embodiment, after the soot 102C is formed on the outer circumference of the rod assembly 201 to manufacture the multi-core optical fiber preform 110, the optical fiber 10 is manufactured by drawing the multi-core optical fiber preform 110. However, the optical fiber 10 may be manufactured by directly drawing the rod assembly 201 without forming the soot 102C on the outer periphery of the rod assembly 201.

DESCRIPTION OF SYMBOLS 1... Core 2... Clad 10... Multi-core optical fiber 101... Core part 102A... Clad forming material 102C... Soot 110... Multi-core optical fiber base material 201, 301, 401... Multi-core optical fiber forming rod aggregate 202, 202A, 202B, 202C, 202D, 302, 402... Core rod (main rod)
202A1...Processed core rod (processed rod)
202A2... Original core rod (original rod)
L...longitudinal direction of core rod L1...longitudinal direction of multi-core optical fiber preform S...contact surface S1...machined surface X...integrally formed portion X1...corner

Claims (7)

A main rod preparation step of processing the processed rod to prepare the main rod;
A rod aggregate forming step of forming a multicore optical fiber forming rod aggregate by bundling a plurality of rods including a plurality of the main rods,
In the main rod preparation step,
The main rod has a plurality of contact surfaces that come into contact with other main rods, and at least one integrally formed portion that integrally forms two adjacent contact surfaces of the plurality of contact surfaces,
The rod to be processed has a corner formed in the longitudinal direction thereof,
At least two main rods of the plurality of main rods have a clad forming material for forming a clad of the multi-core optical fiber, around a core portion to be a core of the multi-core optical fiber,
A method for manufacturing a rod assembly for forming a multi-core optical fiber, wherein the corner portion of the rod to be processed is processed to be rounded to form the integrally formed portion of the main rod. The rod to be processed is formed by grinding or cutting an original rod, and the rod to be processed has a plurality of processed surfaces to be the contact surface of the main rod by the processing in the main rod preparing step. In this case, in the main rod preparation step, the rod assembly for forming a multicore optical fiber according to claim 1, wherein the rod to be processed is treated by heat treatment. The method for manufacturing a rod assembly for forming a multi-core optical fiber according to claim 1, wherein in the main rod preparing step, the rod to be processed is treated by non-heat treatment. In the main rod preparing step, in the integrally formed portion of the main rod, the rod to be processed is treated so that A represented by the following formula (1) is 0.20 to 0.24. 4. A method for manufacturing a rod assembly for forming a multi-core optical fiber according to any one of 3 to 3.
A=R/Rmax (1)
(In the above formula (1), R represents a radius of curvature of the integrally formed portion, and Rmax represents a diameter of a circumscribed circle with respect to a cross section orthogonal to the longitudinal direction of the main rod.) A soot forming step of forming a soot on the outer side of the multi-core optical fiber forming rod assembly obtained by the method for manufacturing a multi-core optical fiber forming rod assembly according to any one of claims 1 to 4;
And a soot vitrification step of vitrifying the soot to obtain a multicore optical fiber preform. A rod assembly forming step of forming a multicore optical fiber forming rod assembly by the method for manufacturing a multicore optical fiber forming rod assembly according to claim 1.
And a drawing step of drawing the multi-core optical fiber forming rod assembly to manufacture a multi-core optical fiber. A preform forming step of forming a multicore optical fiber preform by the method for producing a multicore optical fiber preform according to claim 5;
And a drawing step of drawing the multi-core optical fiber preform to manufacture a multi-core optical fiber.

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