Method for manufacturing optical fiber

Abstract

To provide a method for manufacturing an optical fiber, in which generation of spikes is prevented.SOLUTION: A method includes a drawing step to manufacture an optical fiber by drawing while feeding a glass preform into a heating furnace. The glass preform has a core rod and a clad tube into which the core rod is inserted, a support tube is joined to an upper end of the clad tube so as to communicate with a gap between the core rod and the clad tube. During the drawing step, the gap and an internal space of the support tube are brought into a state where pressure is lower than atmospheric pressure. An atmosphere within 1 m around the glass preform is set to a clean environment in which the number of particles having a size of 0.3 μm or more and less than 0.5 μm is 15000 per CF or less, and the number of particles having a size of 0.5 μm or more but less than 1.0 μm is 3500 per CF or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to methods for manufacturing optical fibers. [Background technology]

[0002] Patent Document 1 discloses a method for manufacturing an optical fiber in a state where a support tube is joined to a glass preform. The glass preform is melted in a heating furnace and thinned to produce an optical fiber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-173895 Summary of the Invention [Problem to be solved by the invention]

[0004] The method for manufacturing an optical fiber disclosed in Patent Document 1 is a method called Rod-In-Tube (RIT).

[0005] However, in RIT drawing, suppressing the occurrence of spikes is a challenge. One of the causes of spikes is thought to be the intrusion of foreign matter into the glass base material before and during drawing.

[0006] An object of the present disclosure is to provide a method for manufacturing an optical fiber in which spike generation is suppressed. [Means for solving the problem]

[0007] A method for manufacturing an optical fiber according to one aspect of the present disclosure includes: a drawing process in which a glass preform is drawn while being fed into a heating furnace to manufacture an optical fiber; the glass preform has a core rod and a cladding tube into which the core rod is inserted; Join a support tube to the upper end of the clad tube to communicate with the gap between the core rod and the clad tube. In the wire drawing step, the gap and the internal space of the support tube are in a state where the pressure is lower than the atmospheric pressure. The atmosphere within 1 m around the glass base material is a clean environment where the number of particles of 0.3 μm or more and less than 0.5 μm is 15,000 particles / CF or less, and the number of particles of 0.5 μm or more and less than 1.0 μm is 3,500 particles / CF or less.

Advantages of the Invention

[0008] According to the present disclosure, a method for manufacturing an optical fiber in which the generation of spikes is suppressed can be provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0010] (Description of Embodiments of the Present Disclosure) First, embodiments of the present disclosure will be listed and described. A method for manufacturing an optical fiber according to one aspect of the present disclosure includes (1) a wire drawing step of manufacturing an optical fiber by wire drawing while feeding a glass base material into a heating furnace, The glass base material has a core rod and a clad tube into which the core rod is inserted. Join a support tube to the upper end of the clad tube to communicate with the gap between the core rod and the clad tube. In the wire drawing step, the gap and the internal space of the support tube are in a state where the pressure is lower than the atmospheric pressure. The atmosphere within 1 m around the glass base material shall be a clean environment where the number of particles of 0.3 μm or more and less than 0.5 μm is 15,000 particles / CF or less, and the number of particles of 0.5 μm or more and less than 1.0 μm is 3,500 particles / CF or less. According to the above method for manufacturing an optical fiber, since the atmosphere within 1 m around the glass base material is the above clean environment, foreign matter is less likely to enter the periphery of the glass base material. As a result, foreign matter is less likely to adhere to the glass base material, and thus the occurrence of spikes in the manufacture of the optical fiber is suppressed.

[0011] (2) The method for manufacturing an optical fiber according to (1) above The wire drawing step may include blowing clean air against the glass base material. In the above method for manufacturing an optical fiber, by blowing clean air against the glass base material, the clean environment around the glass base material is maintained. Thereby, the adhesion of foreign matter to the glass base material in the wire drawing step is suppressed.

[0012] (3) The method for manufacturing an optical fiber according to (2) above The wire drawing step may include blowing the clean air against the glass base material from at least two different directions. In the above method for manufacturing an optical fiber, by blowing clean air against the glass base material from two different directions, the clean environment around the glass base material is more easily maintained. Thereby, the adhesion of foreign matter to the glass base material in the wire drawing step is suppressed.

[0013] (4) The method for manufacturing an optical fiber according to any one of (1) to (3) above The wire drawing step may include a positive pressure of 5 Pa or more higher than the atmospheric pressure within 1 m around the glass base material. According to the above method for manufacturing an optical fiber, within 1 m around the glass preform, by having a positive pressure with respect to the space more than 1 m around the glass preform, it is possible to particularly suppress foreign matter from entering the area around the glass preform from the space more than 1 m around the glass preform. Thereby, adhesion of foreign matter to the glass preform in the fiber drawing process is suppressed.

[0014] (5) In the fiber drawing process of the method for manufacturing an optical fiber according to any one of (1) to (4) above, the glass preform is covered around by an enclosure provided above the heating furnace, clean air may be blown from the enclosure. According to the above method for manufacturing an optical fiber, since the glass preform is covered around by an enclosure, adhesion of foreign matter to the glass preform is suppressed. Further, since clean air is blown from the surface of the enclosure, adhesion of foreign matter to the glass preform in the fiber drawing process is suppressed.

[0015] (Details of Embodiments of the Present Disclosure) A specific example of the method for manufacturing an optical fiber according to an embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, and is intended to be indicated by the claims and to include all modifications within the meaning and scope equivalent to the claims.

[0016] Also, in the description of this embodiment, the symbol U in the figure indicates the upward direction. The symbol D indicates the downward direction. The symbol L indicates the left direction. The symbol R indicates the right direction.

[0017] (Manufacturing Apparatus) FIG. 1 is a schematic diagram of a manufacturing apparatus 1 for an optical fiber according to this embodiment. The manufacturing apparatus 1 illustrated in FIG. 1 is configured to manufacture an optical fiber by a fiber drawing process in which a glass preform G is fed into a heating furnace H while being fiber drawn. The heating furnace H is configured to melt the glass preform G by a heater or the like.

[0018] The glass base material G includes a core rod G1. The core rod G1 is made of quartz glass. The core rod G1 forms the core part in the optical fiber.

[0019] The glass base material G includes a cladding tube G2. The cladding tube G2 is made of quartz glass. The core rod G1 is inserted into the cladding tube G2. A gap S1 is formed between the cladding tube G2 and the core rod G1. The cladding tube G2 forms the cladding part provided around the core part in the optical fiber. At least one of the core rod G1 and the cladding tube G2 is added with a refractive index adjusting agent, and the core rod G1 is configured to have a higher refractive index of light than the cladding tube G2.

[0020] A support tube 10 is joined to the upper end of the cladding tube G2. The internal space S2 of the support tube 10 communicates with the gap S1 between the cladding tube G2 and the core rod G1. The support tube 10 is made of, for example, quartz glass. The length of the support tube 10 may be, for example, 250 mm or more and 1250 mm or less.

[0021] The manufacturing apparatus 1 of the optical fiber includes a gripping part 20, a feeder having a movable part 30, and an enclosing part 40.

[0022] The gripping part 20 grips the upper part of the support tube 10. The gripping part 20 is made of metal. The gripping part 20 is provided with an exhaust port 21 and a lid part 22.

[0023] A recess is provided on the side surface of the support tube 10, and by placing the gripping part 20 in the recess, the glass base material G and the support tube 10 are suspended. The gripping part 20 grips the upper part of the support tube 10 together with the lid part 22 by fastening parts such as bolts. The lid part 22 is fixed to the feeder.

[0024] The exhaust port 21 communicates with the gap S1 between the core rod G1 and the cladding tube G2 and the support tube 10. The gas in the gap S1 and the internal space S2 is discharged from the exhaust port through the support tube, and the gap S1 and the internal space S2 are under negative pressure.

[0025] The glass base material G, the support tube 10, and the gripping component 20 are displaced by a feeder. The feeder is configured to gradually lower the glass base material G, the support tube 10, and the gripping component 20 into the heating furnace by gradually lowering them as the production of the optical fiber progresses. The feeder includes a movable part 30 that displaces together with the glass base material G.

[0026] As illustrated in FIG. 1, the enclosure part 40 is provided above the heating furnace H. FIG. 2 is a cross-sectional view of the enclosure part 40 and the glass base material G. FIG. 2 illustrates four surfaces of the enclosure part 40 facing the surface of the glass base material G. It includes a first surface 41, a second surface 42, a third surface 43, and a fourth surface 44. The glass base material G is covered around by at least four surfaces of the enclosure part 40 facing horizontally with respect to the glass base material G.

[0027] The enclosure part 40 is configured to blow clean air in the direction from each of the first surface 41, the second surface 42, the third surface 43, and the fourth surface 44, which are its respective surfaces, toward the glass base material G. The enclosure part 40 can take in air from the surface opposite to the glass base material G and remove dust by an internal filter. The cleanliness of the clean air is, for example, such that the number of particles of 0.3 μm or more and less than 0.5 μm is 15000 pieces / CF or less, and the number of particles of 0.5 μm or more and less than 1.0 μm is 3500 pieces / CF or less.

[0028] Next, a method for manufacturing an optical fiber using the manufacturing apparatus 1 will be described. The method for manufacturing an optical fiber includes a drawing step of manufacturing an optical fiber by drawing while feeding the glass base material G into the heating furnace H.

[0029] In the drawing process, the glass base material G is sent to the heating furnace H by a feeder in a state where the support pipe 10 is attached and the gripping part 20 is attached to the upper part of the support pipe 10. For this reason, the glass base material G, the support pipe 10, and the gripping part 20 are displaced toward the heating furnace H at the same speed.

[0030] The method for manufacturing an optical fiber according to this embodiment includes making the gap S1 and the internal space of the support pipe 10 in a vacuum state in the drawing process. The vacuum state is a state of a specific section filled with a gas having a pressure lower than the atmospheric pressure. By attaching a hose (not shown) to the exhaust port 21 and sucking the air in the gap S1 and the internal space of the support pipe 10, the gap S1 and the internal space of the support pipe 10 become a vacuum state. Thereby, the inclusion of air bubbles in the drawn optical fiber is suppressed.

[0031] Here, the two-dot chain line in FIG. 2 indicates the boundary of the region A above the heating furnace H where the distance from the surface of the glass base material G is within 1 m. The method for manufacturing an optical fiber includes making the atmosphere in the region A a clean environment in which the number of particles of 0.3 μm or more and less than 0.5 μm is 15,000 particles / CF or less, and the number of particles of 0.5 μm or more and less than 1.0 μm is 3,500 particles / CF or less.

[0032] By making the above clean environment, it becomes difficult for foreign matters to exist around the glass base material G. Note that the foreign matters may include, for example, metal foreign matters such as brass, iron, stainless steel, and cemented carbide, alumina, Ca compounds, Na compounds, and glass powder.

[0033] The drawing process includes blowing clean air against the glass base material G. The drawing process may blow clean air against the glass base material G from at least two different directions. In the present embodiment, as illustrated in FIG. 2, clean air is blown from the first surface 41, the second surface 42, the third surface 43, and the fourth surface 44, which are the respective surfaces of the enclosure part 40. For this reason, the enclosure part 40 blows clean air from four different directions.

[0034] During the fiber drawing process, the supply of clean air continues. As a result, the air around the glass base material G flows out above or below the enclosure 40, so the clean environment in region A is maintained. Also, since the clean air is supplied from at least two different directions, the distance that the clean air wraps around the glass base material G is shorter than when the clean air is supplied from one direction, and it becomes difficult for the clean air to stagnate around the glass base material G.

[0035] By blowing clean air from the enclosure 40 in this way, the inside of region A can be made into a positive pressure with respect to the space outside region A. The space outside region A is a space more than 1 m away from the periphery of the glass base material G.

[0036] The method for manufacturing an optical fiber according to this embodiment sets the atmosphere within 1 m around the glass base material G to a clean environment in which the number of particles of 0.3 μm or more and less than 0.5 μm is 15,000 particles / CF or less, and the number of particles of 0.5 μm or more and less than 1.0 μm is 3,500 particles / CF or less. Therefore, an optical fiber can be manufactured with few foreign substances around the glass base material G. As a result, it becomes difficult for foreign substances to adhere to the glass base material G, so the occurrence of spikes in the method for manufacturing an optical fiber is suppressed.

[0037] In the method for manufacturing an optical fiber according to this embodiment, the fiber drawing process is performed while blowing clean air against the glass base material G. Therefore, the clean environment around the glass base material G is maintained. As a result, the adhesion of foreign substances to the glass base material G in the fiber drawing process is suppressed.

[0038] In the method for manufacturing an optical fiber according to this embodiment, by blowing clean air against the glass base material from two different directions, the clean environment around the glass base material is more easily maintained. As a result, the mixing of foreign substances into the glass base material in the fiber drawing process is suppressed.

[0039] In the method for manufacturing an optical fiber according to the present embodiment, within 1 m around the glass preform G, by having a positive pressure with respect to the space outside 1 m around the glass preform G (the space outside region A), it is possible to particularly suppress foreign matter from entering the periphery of the glass preform G from the space outside region A. Thereby, adhesion of foreign matter to the glass preform G in the drawing process is suppressed. Note that within 1 m around the glass preform G, the positive pressure may be 5 Pa or more with respect to the space outside region A.

[0040] According to the method for manufacturing an optical fiber of the present embodiment, since the glass preform G is covered by the surrounding portion 40 around it, adhesion of foreign matter to the glass preform G is suppressed. Further, since clean air is blown from each surface of the surrounding portion 40, adhesion of foreign matter to the glass preform G in the drawing process is suppressed.

[0041] Next, the verification results regarding the occurrence frequency of spikes due to the difference in the clean environment around the glass preform in the drawing process will be described. Table 1 shows the occurrence frequency of spikes when manufacturing an optical fiber by changing the clean environment for the atmosphere within 1 m around the glass preform (region A in FIG. 2). Mm in Table 1 means million meters.

[0042]

Table 1

[0043] As exemplified in Table 1, the fewer the number of particles present in region A, the lower the occurrence frequency of spikes. Here, in the manufacture of an optical fiber, it is preferable that the occurrence frequency of spikes is 30 or less per 1 million m. For this reason, it was confirmed that it is preferable to set the atmosphere within 1 m around the glass preform to a clean environment in which the number of particles of 0.3 μm or more and less than 0.5 μm is 15,000 particles / CF or less, and the number of particles of 0.5 μm or more and less than 1.0 μm is 3,500 particles / CF or less. Note that the occurrence frequency of spikes may be 10 or less per 1 million m, and further may be 5 or less.

[0044] Although the present disclosure has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure. In addition, the number, position, shape, etc. of the components described above are not limited to the above embodiments, and can be changed to appropriate numbers, positions, shapes, etc. in implementing the present disclosure.

[0045] In the present embodiment, a method for manufacturing a multi-core optical fiber is exemplified, but a method for manufacturing a single-core optical fiber having one core portion in the optical fiber may also be used.

Explanation of Signs

[0046] 1 Manufacturing apparatus 10 Support tube 20 Gripping part 21 Exhaust port 22 Lid part 30 Movable part 40 Enclosing part 41 First surface 42 Second surface 43 Third surface 44 Fourth surface A Region G Glass base material G1 Core rod G2 Cladding tube H Heating furnace S1 Gap S2 Internal space

Claims

1. including a drawing process of manufacturing an optical fiber by drawing while feeding a glass base material into a heating furnace, wherein the glass base material has a core rod and a clad tube into which the core rod is inserted, joining a support tube to the upper end of the clad tube to communicate with the gap between the core rod and the clad tube, including, in the drawing process, making the pressure in the gap and the internal space of the support tube lower than atmospheric pressure, making the atmosphere within 1 m around the glass base material a clean environment where the number of particles of 0.3 μm or more and less than 0.5 μm is 15,000 particles / CF or less, and the number of particles of 0.5 μm or more and less than 1.0 μm is 3,500 particles / CF or less, A method for manufacturing an optical fiber.

2. The drawing process includes blowing clean air against the glass base material. The method for manufacturing an optical fiber according to Claim 1.

3. The drawing process includes blowing the clean air against the glass base material from at least two different directions. The method for manufacturing an optical fiber according to Claim 2.

4. The drawing process is a positive pressure of 5 Pa or more higher than atmospheric pressure within 1 m around the glass base material. The method for manufacturing an optical fiber according to any one of Claims 1 to 3.

5. In the drawing process, the glass base material is covered around by an enclosure provided above the heating furnace, and clean air is blown from the enclosure. The method for manufacturing an optical fiber according to Claim 1.

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