JP2020125226A - 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 rod assembly, etc., for forming a multi-core optical fiber, capable of manufacturing the multi-core optical fiber sufficiently suppressed in the deformation of a core and the formation of air bubbles.SOLUTION: The rod assembly for forming a multi-core optical fiber includes a plurality of main rods. The main rod includes a plurality of contact surfaces contacting the other main rods and at least one of integral formation parts integrally forming two contact surfaces adjacent to each other in the plurality of contact surfaces. A continuous hole continuously extended in the longitudinal direction of the main rod from one end surface side of the main rod is formed so as to be surrounded by the integral formation parts of the plurality of main rods in the state of contacting the other main rods to the plurality of contact surfaces of the main rod, and 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.SELECTED DRAWING: None

Description

The present invention relates to a multi-core optical fiber forming rod assembly, a method for manufacturing a multi-core optical fiber preform using the same, and a method for manufacturing a multi-core 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, in Patent Document 1 below, a plurality of columnar glass rods having a clad forming material around a core portion are bundled, and a clad forming material is provided in a gap between the glass rods. Also disclosed is a rod assembly in which glass rods for filling having a low softening point are arranged.

Further, Patent Document 2 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.

JP, 2005-178444, A JP, 9-5541, A

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

That is, in the rod assembly described in Patent Document 1, since the filling glass rods are arranged in the gaps between the plurality of glass rods, compared to the case where there is no filling glass rod, the rod assembly. The deformation of the glass rod is suppressed when the optical fiber preform formed by using is drawn. However, when the softening point of the filling glass rod is lower than the softening point of the cladding forming material of the glass rod, the rod assembly described in Patent Document 1 is still improved in terms of suppressing deformation of the glass rod. There was room.

On the other hand, although the rod assembly described in Patent Document 2 eliminates the gap between the plurality of glass rods, there is a limit to the processing accuracy of the glass rod, and the gap can be completely eliminated. I can't say. For example, gaps may be formed discontinuously along the longitudinal direction of the glass rod. In that case, even when the multi-core optical fiber preform is placed in a depressurized environment when drawing the optical fiber preform formed using the rod assembly, the air in the gap cannot be sufficiently removed, In the finally obtained multi-core optical fiber, bubbles may be formed discontinuously along the longitudinal direction.

The present invention has been made in view of the above circumstances, and uses a multi-core optical fiber forming rod assembly capable of manufacturing a multi-core optical fiber in which deformation of a core and formation of bubbles are sufficiently suppressed. An object of the present invention is to provide a method for manufacturing a multicore optical fiber preform and a method for manufacturing a multicore optical fiber.

As a result of intensive studies to solve the above problems, the present inventors have found that intentionally providing small continuous holes between glass rods in the rod assembly is effective in solving the above problems. The present invention has been completed and the present invention has been completed.

That is, the present invention is a multi-core optical fiber forming rod assembly comprising a plurality of main rods, wherein the main rods are in contact with other main rods, and among the plurality of contact faces. At least one integrally forming part that integrally forms two contact surfaces that meet each other, and in a state where the other main rod is in contact with the plurality of contact surfaces of the main rod, one of the main rods A continuous hole extending continuously from the end face side along the longitudinal direction of the main rod is formed so as to be surrounded by the integrally formed portion of the plurality of main rods, and at least two of the plurality of main rods are formed. The main rod of the book is a rod assembly for forming a multi-core optical fiber, in which a clad forming material for forming a clad of the multi-core optical fiber is provided around a core portion which is a core of the multi-core optical fiber.

According to the multi-core optical fiber forming rod assembly of the present invention, in the rod assembly, the other main rod is in contact with the plurality of contact surfaces of the main rod, and the main rod from one end surface side of the main rod Since the continuous hole extending continuously along the longitudinal direction is formed so as to be surrounded by the integrally formed portion of the plurality of main rods, the continuous hole is sufficiently formed as compared with the case where the main rod has no contact surface. Can be made smaller. Therefore, according to the rod assembly, when performing a soot forming step of forming a soot on the outer side thereof, or a soot vitrification step of vitrifying the soot thereafter, the clad forming material of the core rod should fill the continuous hole. It is possible to obtain a multi-core optical fiber preform in which large deformation is sufficiently suppressed and deformation of the core portion is sufficiently suppressed. Therefore, when the multicore optical fiber preform is drawn, a multicore optical fiber in which the deformation of the core is sufficiently suppressed can be obtained.

In addition, after forming a soot on the outside of the rod assembly, the soot is vitrified to produce a multi-core optical fiber preform, and this multi-core optical fiber preform has continuous holes in the rod aggregate and a multi-core optical fiber preform. It is left as a continuous hole extending continuously from one end face side of the material along the longitudinal direction of the multi-core optical fiber preform. For this reason, when drawing the multi-core optical fiber preform, if the continuous hole is placed in a negative pressure state, the part of the inner wall surface forming the continuous hole that originates from each integrally formed part of the main rod of the multi-core optical fiber preform It moves so as to contact each other at all points along the longitudinal direction to close the continuous hole. Thereby, the formation of bubbles can be sufficiently suppressed in the obtained multi-core optical fiber.

From the above, according to the multi-core optical fiber forming rod assembly of the present invention, it is possible to manufacture a multi-core optical fiber in which the deformation of the core and the formation of bubbles are sufficiently suppressed.

In the above-mentioned multi-core optical fiber forming rod assembly, it is preferable that the integrally formed portion of the main rod is projected to the continuous hole side with respect to a flat surface connecting the two adjacent contact surfaces.

In this case, the continuous hole becomes smaller with the other main rods in contact with the plurality of contact surfaces of the main rod. Moreover, since the integrally formed portion of the main rod has already protruded toward the continuous hole side from the flat surface connecting the two adjacent contact surfaces, even if the main rod is heated, the integrally formed portion is expanded from the flat surface due to thermal expansion. It is even more difficult to project to the continuous hole side. Therefore, when performing a soot forming step of forming a soot on the outer side of the rod assembly, or after that, when performing a soot vitrification step of vitrifying the soot, the clad forming material of the core rod may be largely deformed to fill the continuous hole. It is possible to obtain a multi-core optical fiber preform in which the deformation of the core portion is more sufficiently suppressed and the deformation of the core portion is more sufficiently suppressed. For this reason, when the multi-core optical fiber preform is drawn, a multi-core optical fiber in which the deformation of the core is sufficiently suppressed can be obtained.

Further, the present invention, a preparatory step of preparing the above-mentioned multi-core optical fiber forming rod aggregate, a soot forming step of forming a soot on the outer side of the multi-core optical fiber forming rod aggregate, and vitrifying the soot. A soot vitrification step of obtaining a multi-core optical fiber preform, in the soot vitrification step, the multicore optical fiber preform, the continuous hole, from one end face side of the multicore optical fiber preform A method for producing a multi-core optical fiber preform in which the soot is vitrified so that it is left as a continuous hole extending continuously along the longitudinal direction of the multicore optical fiber preform.

According to this method for producing a multi-core optical fiber preform, in the rod assembly, in the state where other main rods are in contact with the plurality of contact surfaces of the main rod, the longitudinal direction of the main rod from one end surface side of the main rod. Since the continuous hole that continuously extends along the main rod is formed so as to be surrounded by the integrally formed portion of the plurality of main rods, the continuous hole is sufficiently small as compared with the case where the main rod does not have a contact surface. can do. Therefore, according to the rod assembly, the clad forming material of the main rod should fill the continuous hole when performing the soot forming step of forming the soot on the outer side thereof, or the soot vitrifying step of vitrifying the soot thereafter. It is possible to obtain a multi-core optical fiber preform in which large deformation is sufficiently suppressed and deformation of the core portion is sufficiently suppressed. Therefore, when the multicore optical fiber preform is drawn, a multicore optical fiber in which the deformation of the core is sufficiently suppressed can be obtained.

In addition, after forming a soot on the outside of the rod assembly, the soot is vitrified to produce a multi-core optical fiber preform, and this multi-core optical fiber preform has continuous holes in the rod assembly and a multi-core optical fiber preform. It is left as a continuous hole extending continuously from one end face side of the material along the longitudinal direction of the multi-core optical fiber preform. For this reason, when drawing the multi-core optical fiber preform, if the continuous hole is placed in a negative pressure state, the part of the inner wall surface forming the continuous hole that originates from each integrally formed part of the main rod of the multi-core optical fiber preform It moves so as to contact each other at all points along the longitudinal direction to close the continuous hole. Thereby, the formation of bubbles can be sufficiently suppressed in the obtained multi-core optical fiber.

From the above, according to the method for producing a multicore optical fiber preform of the present invention, a multicore optical fiber preform capable of producing a multicore optical fiber in which deformation of the core and formation of bubbles are sufficiently suppressed is obtained. To be

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 the multicore optical fiber preform is drawn while the continuous hole is in a negative pressure state. And a drawing step for producing a multi-core optical fiber.

According to this method for producing a multi-core optical fiber, in the base material forming step, in the rod assembly, in the state where the other main rods are in contact with the plurality of contact surfaces of the main rod, from one end surface side of the main rod. Since the continuous hole that continuously extends along the longitudinal direction of the main rod is formed so as to be surrounded by the integrally formed portion of the plurality of main rods, it is more continuous than when the main rod does not have a contact surface. The holes can be made sufficiently small. Therefore, according to the rod assembly, when performing a soot forming step of forming a soot on the outer side thereof, or a soot vitrification step of vitrifying the soot thereafter, the clad forming material of the core rod is large so as to fill the continuous hole. It is possible to obtain a multi-core optical fiber preform in which deformation is sufficiently suppressed and deformation of the core portion is sufficiently suppressed. Therefore, it is possible to obtain a multicore optical fiber in which the deformation of the core is sufficiently suppressed in the drawing step of drawing the multicore optical fiber preform.

Further, in the base material forming step, after forming the soot on the outside of the rod assembly, when the soot is vitrified to produce a multi-core optical fiber base material, the multi-core optical fiber base material is continuous in the rod assembly. The holes are left as continuous holes that extend continuously from one end surface side of the multicore optical fiber preform along the longitudinal direction of the multicore optical fiber preform. Therefore, in the drawing step, when drawing the multicore optical fiber preform, if the continuous hole is placed in a negative pressure state, the portion of the inner wall surface forming the continuous hole that originates from each integrally formed part of the main rod The fibers move in contact with each other at all points along the longitudinal direction of the fiber preform so as to close the continuous hole. Thereby, the formation of bubbles can be sufficiently suppressed in the obtained multi-core optical fiber.

From the above, according to the method for producing a multi-core optical fiber of the present invention, it is possible to produce a multi-core optical fiber in which the deformation of the core and the formation of bubbles are sufficiently suppressed.

According to the present invention, a multicore optical fiber forming rod assembly capable of manufacturing a multicore optical fiber in which deformation of a core and formation of bubbles are sufficiently suppressed, a method of manufacturing a multicore optical fiber preform using the same, and A method of manufacturing a multi-core optical fiber 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 the core rod of FIG. 4. FIG. 5 is a cross-sectional view showing a cylindrical core rod for manufacturing the core rod of FIG. 4. FIG. 8 is a cross-sectional view showing a processed core rod obtained by processing the cylindrical core rod of FIG. 7. 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.

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 higher 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.

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 9. 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. 8 is a longitudinal sectional view showing an embodiment of the assembly, FIG. 6 is a transverse sectional view showing the core rod of FIG. 4, FIG. 7 is a transverse sectional view showing a cylindrical core rod for manufacturing the core rod of FIG. 4, and FIG. 9 is a cross-sectional view showing a processed core rod obtained by processing the cylindrical core rod of FIG. 7, and FIG. 9 is a multicore optical fiber preform on which a soot is formed outside the multicore optical fiber forming rod assembly of FIG. 3 is a cross-sectional view showing the precursor of FIG.

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.

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 (preparing step). ..

The rod assembly 201 has four core rods 202 as main rods and four columnar filling rods 102B as sub-rods provided outside the four core rods 202.

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 contact surface S is a flat surface. Further, the integrally formed portion X continuously extends from one end surface 202a side of the core rod 202A along the longitudinal direction L of the core rod 202A to the other end surface 202b side of the core rod 202A (see FIG. 5). Then, the integrally formed portion X is a surface that projects outside the flat surface connecting the two adjacent contact surfaces S (on the side opposite to the core portion 101 with respect to the flat surface). In other words, the integrally formed portion X is a surface projecting toward the continuous hole G side with respect to the flat surface connecting the two adjacent contact surfaces S in FIG.

Further, in the cross section of the core rod 202A orthogonal to the longitudinal direction L of the core rod 202A, the length of the perpendicular line from the center of the core portion 101 to the contact surface S is R1, and the distance from the center of the core portion 101 to the integrally formed portion X Is R2, R2 is larger than R1. Here, the ratio r of R2 with respect to R1 is particularly limited as long as it is greater than 1 and smaller than the ratio of R2 with respect to R1 with respect to the integrally formed portion X (hereinafter referred to as “maximum ratio”). However, the ratio r is preferably not less than the maximum ratio of 85 cos θ/100. In this case, when performing a soot forming step of forming a soot on the outside of the rod assembly 201 or a soot vitrifying step of vitrifying the soot, as compared with the case where the ratio r is less than the maximum ratio of 85 cos θ/100. In addition, it is possible to obtain the optical fiber preform 110 in which the cladding forming material 102A of the core rod 202 is sufficiently suppressed from being greatly deformed to fill the continuous hole, and the deformation of the core portion 101 is sufficiently suppressed. However, the ratio r is preferably 99 cos θ/100 or less, which is the maximum ratio. In this case, the continuous hole G can be formed larger than when the ratio r exceeds the maximum ratio of 99 cos θ/100, and the continuous hole G is formed discontinuously when the optical fiber preform 110 is drawn. Can be suppressed more sufficiently. Therefore, it is possible to obtain the optical fiber 10 in which the formation of bubbles is sufficiently suppressed. In addition, when the integrally formed portion X is a point, if an angle formed by a perpendicular line from the center of the core portion 101 to the contact surface S and a straight line from the center of the core portion 101 to the integrally formed portion X is θ, The maximum ratio is represented by sec θ (=1/cos θ). For example, when θ is 45°, the maximum ratio is 2 ^1/2 .

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.

The core rod 202 can be prepared as follows, for example. That is, first, the cylindrical core rod 202A2 shown in FIG. 7 is prepared. At this time, as the cylindrical core rod 202A2, a cylindrical rod whose radius is the distance from the center of the core portion 101 of the core rod 202 to the non-contact surface N of the clad 102 is prepared. The cylindrical 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.

Next, two machined surfaces S1 are formed on the cylindrical core rod 202A2 by, for example, grinding to form the machined core rod 202A1 shown in FIG. The 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 machined core rod 202A1 has two machined surfaces S1 and a non-machined surface N1, and is formed so that the integrally formed portion X1 integrally forming the two machined surfaces S1 in FIG. 8 becomes a point. ..

Then, the integrally formed portion X1 of the processed core rod 202A1 is continuously processed along the longitudinal direction L of the processed core rod 202A1. At this time, the integrally formed portion X1 is processed so as to project outside the case where the integrally formed portion X1 has a flat surface, that is, to the side opposite to the core portion 101 as compared with the case where the integrally formed portion X1 has a flat surface. To do. The processing of the processed core rod 202A1 can be performed by, for example, flame polishing with a flame burner or grinding. In this way, the core rod 202 is obtained. At this time, the contact surface S1 of the processed core rod 202A1 becomes the contact surface S, and the integrally formed portion X1 becomes the integrally formed portion X.

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 102 is prepared, and the cylindrical rod is processed to form two processed surfaces. It can also be obtained by forming a processed core rod by using the above method and then stretching the processed core rod.

In order to maintain the state, the rod assembly 201 is in a state of being bundled with a binding band, and after the glass rods serving as the dummy are melt-bonded to both end faces, the binding band is removed. At this time, in a state where the rod assembly 201 is in a depressurized environment, a dummy glass rod is melt-bonded so as to block the openings of the continuous holes G in the one end surface 202a and the other end surface 202b of the core rod 202. When the rod assembly 201 is placed under the atmospheric pressure environment, the continuous hole G of the rod assembly 201 is in a negative pressure state.

Next, glass particles are deposited on the outer side of the rod assembly 201 to form the soot 102C, and the precursor 200 of the optical fiber preform 110 is formed as shown in FIG. 9 (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 above-described optical fiber manufacturing method, in the base material forming step, one end surface of the core rod 202 in the rod assembly 201 is in a state where the other core rods 202 are in contact with the plurality of contact surfaces S of the core rod 202. Since the continuous hole G continuously extending from the 202a side to the other end surface 202b side of the core rod 202 along the longitudinal direction L 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. As compared with the case where the core rod 202 does not have the contact surface S, the continuous hole G can be made sufficiently small. 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 thereafter, the clad forming material 102A of the core rod 202 is continuously formed. It is possible to obtain the optical fiber preform 110 in which the large deformation to sufficiently fill the hole G is sufficiently suppressed and the deformation of the core portion 101 is sufficiently suppressed. Therefore, in the drawing step of drawing the optical fiber preform 110, the optical fiber 10 in which the deformation of the core 1 is sufficiently suppressed can be obtained.

In the base material 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 base material 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, formation of bubbles in the obtained optical fiber 10 can be sufficiently suppressed.

From the above, according to the optical fiber manufacturing method, it is possible to manufacture the optical fiber 10 in which the deformation of the core 1 and the formation of bubbles are sufficiently suppressed.

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 large deformation is more sufficiently suppressed and the deformation of the core portion 101 is more sufficiently suppressed. Therefore, when the optical fiber preform 110 is drawn, the optical fiber 10 in which the deformation of the core 1 is sufficiently 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 sufficiently 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, formation of unnecessary voids in the obtained optical fiber preform 110 is sufficiently suppressed.

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 more sufficiently suppressed.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, in the core rod 202, the integrally formed portion X of the two contact surfaces S is a surface protruding outward from the flat surface connecting the two contact surfaces S, but the integrally formed portion X is not necessarily flat. The surface does not have to project outward from the surface. For example, the integrally formed portion X may be a flat surface. In this case, the integrally formed portion X can be obtained by processing the integrally formed portion X1 of the processed core rod 202A1 by grinding so as to have a flat surface.

Further, in the above-described embodiment, in the cross section of the rod assembly 201, all the integrally formed portions X of the four core rods 202 that form the continuous hole G are configured by one line, but the four core rods 202 of the four core rods 202 are formed. In at least one of the core rods 202, the integrally formed portion X may be formed by one line. For example, in some of the four core rods 202, the integrally formed portion X may be formed by one line, and in the remaining core rods 202, the integrally formed portion X may be formed by dots. Further, the integrally formed portion X may be configured by two or more continuous lines that project toward the core portion 101 side or the side opposite to the core portion 101 instead of one line.

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.

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.

Furthermore, the cross-sectional shape of the 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. 10, the core rod 302 may have a quadrangular cross-sectional shape. Further, like the core rod 402 of the rod assembly 401 shown in FIG. 11, the core rod 402 may have a hexagonal cross-sectional shape.

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 serving as a main rod, and at least one contact surface. Since there is one integral forming portion, and the integral forming portion of the filling rod 102B and the core rod 202 form a continuous hole, the filling rod 102B constitutes a main rod.

Further, in the above embodiment, the continuous hole G1 in the optical fiber preform 110 is closed by the glass rod serving as a dummy to be in a negative pressure state, but the continuous hole G1 in the optical fiber preform 110 is formed by the glass rod. When the continuous hole G1 is not blocked, it is possible to bring the continuous hole G1 into a negative pressure state by evacuating the continuous hole G1. In this case, when the continuous hole G does not extend to the other end surface 202b side of the core rod 202, the drawing of the optical fiber preform 110 is performed from the other end surface 201b side 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)
G, G1... Continuous hole L... Longitudinal direction of core rod L1... Longitudinal direction of multi-core optical fiber preform S... Contact surface X... Integral forming part

Claims (4)

A multicore optical fiber forming rod assembly comprising a plurality of main rods,
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 plurality of continuous holes continuously extending along the longitudinal direction of the main rod from one end surface side of the main rod in a state where the other main rod is in contact with the plurality of contact surfaces of the main rod. Is formed to be surrounded by the integrally formed portion of the main rod of
A multi-core optical fiber in which 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 that is a core of the multi-core optical fiber. Forming rod assembly. The rod assembly for forming a multi-core optical fiber according to claim 1, wherein the integrally formed portion of the main rod extends beyond the flat surface connecting the two adjacent contact surfaces to the continuous hole side. A preparatory step of preparing the multicore optical fiber forming rod assembly according to claim 1 or 2;
A soot forming step of forming a soot on the outside of the multi-core optical fiber forming rod assembly;
Vitrifying the soot, soot vitrification step of obtaining a multi-core optical fiber preform,
In the soot vitrification step, the multi-core optical fiber preform, the continuous hole, continuously extending along the longitudinal direction of the multicore optical fiber preform from one end face side of the multicore optical fiber preform. A method for producing a multi-core optical fiber preform, wherein the soot is vitrified so as to be left as holes. A preform forming step of forming a multicore optical fiber preform by the method for producing a multicore optical fiber preform according to claim 3;
A method of manufacturing a multi-core optical fiber, comprising a step of drawing the multi-core optical fiber base material while manufacturing the multi-core optical fiber while drawing a negative pressure in the continuous hole.

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