Method for manufacturing optical fiber

Abstract

The invention provides an optical fiber manufacturing method capable of suppressing generation of spikes. The method for manufacturing an optical fiber includes a drawing step in which a glass base material having a core rod and a cladding tube into which the core rod is inserted is drawn while being fed to a heating furnace to manufacture an optical fiber, and a support tube is joined to an upper end of the cladding tube and communicates with a gap between the core rod and the cladding tube. The method is characterized in that the internal space of the gap and the support tube is in a state of lower pressure than atmospheric pressure, and the atmosphere within 1 m around the glass base material is a clean environment in which the number of particles of 0.3 [mu] m or more and less than 0.5 [mu] m is 15000 / CF or less, and the number of particles of 0.5 [mu] m or more and less than 1.0 [mu] m is 3500 / CF or less.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an optical fiber. Background Art

[0002] Patent Document 1 discloses a method for manufacturing an optical fiber in a state where a support tube is joined to a glass base material. The optical fiber is manufactured by melting and thinning the glass base material in a heating furnace.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-173895 Summary of the Invention

[0006] Technical Problem to be Solved by the Invention

[0007] The method for manufacturing an optical fiber disclosed in Patent Document 1 is a method called Rod-In-Tube (RIT).

[0008] However, in RIT drawing, suppressing the generation of spikes becomes a technical problem. It is considered that one of the reasons for the generation of spikes is that foreign matter enters the inside of the glass base material before and during drawing.

[0009] An object of the present disclosure is to provide a method for manufacturing an optical fiber in which the generation of spikes is suppressed.

[0010] Solution to the Technical Problem

[0011] A method for manufacturing an optical fiber according to one aspect of the present disclosure

[0012] includes a drawing step of manufacturing an optical fiber by drawing while feeding a glass base material to a heating furnace,

[0013] the glass base material has a core rod and a cladding tube into which the core rod is inserted,

[0014] a support tube is joined to the upper end of the cladding tube and communicates with the gap between the core rod and the cladding tube,

[0015] in the drawing step, it includes making the gap and the internal space of the support tube in a state where the pressure is lower than the atmospheric pressure,

[0016] 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.

[0017] Advantageous Effects of the Invention

[0018] According to the present disclosure, a method for manufacturing an optical fiber capable of suppressing the generation of spikes can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of a manufacturing apparatus for an optical fiber according to the present embodiment.

[0020] Figure 2 It is a cross-sectional view of the surrounding portion and the glass base material. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] (Description of the Embodiment of the Present Disclosure)

[0022] First, the embodiments of the present disclosure will be listed and described.

[0023] (1) A method for manufacturing an optical fiber according to one aspect of the present disclosure,

[0024] includes a drawing step of manufacturing an optical fiber by drawing while feeding a glass base material to a heating furnace,

[0025] the glass base material has a core rod and a cladding tube into which the core rod is inserted,

[0026] a support tube is joined to the upper end of the cladding tube and communicates with the gap between the core rod and the cladding tube,

[0027] in the drawing step, it includes making the gap and the internal space of the support tube in a state where the pressure is lower than the atmospheric pressure,

[0028] 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.

[0029] According to the above method for manufacturing an optical fiber, in the atmosphere within 1 m around the glass base material, since it is the above clean environment, foreign substances are difficult to enter the periphery of the glass base material. Thus, foreign substances are difficult to adhere to the glass base material, and therefore the generation of spikes in the manufacturing of the optical fiber can be suppressed.

[0030] (2) Optionally, in the method for manufacturing an optical fiber according to (1) above,

[0031] the drawing step includes blowing clean air onto the glass base material.

[0032] In the above method for manufacturing an optical fiber, by blowing clean air onto the glass base material, the clean environment around the glass base material can be maintained. Thus, the adhesion of foreign substances to the glass base material in the drawing step can be suppressed.

[0033] (3) Alternatively, it can also be the manufacturing method of the optical fiber involved in the above (2),

[0034] The drawing process includes blowing the clean air to the glass base material from at least two different directions.

[0035] In the above manufacturing method of the optical fiber, by blowing clean air to the glass base material from two different directions, it is easier to maintain a clean environment around the glass base material. Thus, foreign matter attachment to the glass base material during the drawing process can be suppressed.

[0036] (4) Alternatively, it can also be the manufacturing method of the optical fiber involved in any one of the above (1) to (3),

[0037] The drawing process includes maintaining a positive pressure of 5 Pa or more higher than the atmospheric pressure within 1 m around the glass base material.

[0038] According to the above manufacturing method of the optical fiber, by maintaining a positive pressure within 1 m around the glass base material relative to the space outside 1 m around the glass base material, foreign matter mixing from the space outside 1 m around the glass base material into the vicinity of the glass base material can be particularly suppressed. Thus, foreign matter attachment to the glass base material during the drawing process can be suppressed.

[0039] (5) Alternatively, in the drawing process of the manufacturing method of the optical fiber involved in any one of the above (1) to (4),

[0040] The glass base material is surrounded by a surrounding portion, and the surrounding portion is provided at a position higher than the heating furnace.

[0041] Clean air is blown from the surrounding portion.

[0042] According to the above manufacturing method of the optical fiber, since the glass base material is surrounded by the surrounding portion, foreign matter attachment to the glass base material can be suppressed. Furthermore, since clean air is blown from the surface of the surrounding portion, foreign matter attachment to the glass base material during the drawing process can be suppressed.

[0043] (Details of the embodiments of the present disclosure)

[0044] Hereinafter, a specific example of the manufacturing method of the optical fiber according to the embodiments of the present disclosure will be described with reference to the drawings. It should be noted that the present disclosure is not limited to these examples, but is represented by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0045] In addition, in the description of the present embodiment, the reference numeral U in the drawings indicates the upward direction. The reference numeral D indicates the downward direction. The reference numeral L indicates the left direction. The reference numeral R indicates the right direction.

[0046] (Manufacturing apparatus)

[0047] Figure 1 This is a schematic diagram of the optical fiber manufacturing apparatus 1 according to this embodiment. Figure 1 The illustrated manufacturing apparatus 1 is configured to manufacture an optical fiber through a drawing process in which a glass base material G is fed to a heating furnace H while being drawn. The heating furnace H is configured to melt the glass base material G by a heater or the like.

[0048] The glass base material G includes a core rod G1. The core rod G1 is formed of quartz glass. The core rod G1 forms the core portion in the optical fiber.

[0049] The glass base material G includes a cladding tube G2. The cladding tube G2 is formed 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 a cladding portion provided around the core portion in the optical fiber. The core rod G1 and the cladding tube G2 are configured such that a refractive index adjusting agent is added to at least one of them, and the refractive index of light in the core rod G1 is higher than that of the cladding tube G2.

[0050] 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 formed of quartz glass, for example. The length of the support tube 10 can be, for example, 250 mm or more and 1250 mm or less.

[0051] The optical fiber manufacturing apparatus 1 includes a holding member 20, a feeder having a movable portion 30, and an enclosing portion 40.

[0052] The holding member 20 holds the upper portion of the support tube 10. The holding member 20 is made of metal. An exhaust port 21 and a lid portion 22 are provided on the holding member 20.

[0053] A recess is provided on the side surface of the support tube 10, and the glass base material G and the support tube 10 are suspended by hanging the holding member 20 on the recess. The holding member 20 holds the upper portion of the support tube 10 by sandwiching it together with the lid portion 22 with a fastening member such as a bolt. The lid portion 22 is fixed to the feeder.

[0054] 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 support tube through the exhaust port, and the gap S1 and the internal space S2 become negative pressure.

[0055] The glass base material G, the support tube 10, and the holding member 20 are displaced by the feeder. The feeder is configured to gradually feed the glass base material G, the support tube 10, and the holding member 20 to the heating furnace by gradually lowering them as the optical fiber manufacturing progresses. The feeder includes a movable portion 30 that is displaced together with the glass base material G.

[0056] AsFigure 1 As illustrated, the surrounding portion 40 is provided at a position higher than the heating furnace H. Figure 2 It is a cross-sectional view of the surrounding portion 40 and the glass base material G. Figure 2 Four faces of the surrounding portion 40 facing the surface of the glass base material G are illustrated. It includes a first face 41, a second face 42, a third face 43, and a fourth face 44. The glass base material G is covered by the surrounding portion 40 of at least four faces that are opposite to the glass base material G in the horizontal direction around the glass base material G.

[0057] The surrounding portion 40 is configured to blow clean air in the direction toward the glass base material G from the first face 41, the second face 42, the third face 43, and the fourth face 44 which are each face. The surrounding portion 40 can suck air from the face opposite to the glass base material G and remove dust through an internal filter. The cleanliness of the clean air is, for example, the number of particles of 0.3 μm or more and less than 0.5 μm is 15,000 / CF or less, and the number of particles of 0.5 μm or more and less than 1.0 μm is 3,500 / CF or less.

[0058] 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 process of manufacturing an optical fiber by drawing while feeding the glass base material G to the heating furnace H.

[0059] In the drawing process, the glass base material G is fed to the heating furnace H by a feeder in a state where the support tube 10 is installed and the holding member 20 is installed above the support tube 10. Therefore, the glass base material G, the support tube 10, and the holding member 20 are displaced toward the heating furnace H at the same speed.

[0060] The method for manufacturing an optical fiber of this embodiment includes making the gap S1 and the internal space of the support tube 10 in a vacuum state in the drawing process. The vacuum state refers to a state of a specific section filled with a gas having a pressure lower than the atmospheric pressure. By installing a hose (not shown) on the exhaust port 21 to suck the air in the gap S1 and the internal space of the support tube 10, the gap S1 and the internal space of the support tube 10 are made in a vacuum state. Thereby, bubbles can be suppressed from being mixed into the drawn optical fiber.

[0061] Here, Figure 2 The chain double-dashed line in it represents the boundary of the region A that is within 1 m from the surface of the glass base material G and above the heating furnace H. The method for manufacturing an optical fiber includes making the atmosphere in the region A a clean environment where the number of particles of 0.3 μm or more and less than 0.5 μm is 15,000 / CF or less, and the number of particles of 0.5 μm or more and less than 1.0 μm is 3,500 / CF or less.

[0062] By setting the above-mentioned clean environment, it is difficult for foreign substances to exist around the glass base material G. It should be noted that foreign substances refer to, for example, metal foreign substances such as brass, iron, stainless steel, and cemented carbide, alumina, Ca compounds, Na compounds, and glass powder.

[0063] The drawing process includes blowing clean air to the glass base material G. Alternatively, the drawing process may blow clean air to the glass base material G from at least two different directions. In the present embodiment, as Figure 2 illustrated, 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 surrounding portion 40. Therefore, the surrounding portion 40 blows clean air from four different directions.

[0064] During the drawing process, the blowing of clean air is continuously performed. As a result, the air around the glass base material G flows out above or below the surrounding portion 40, so that the clean environment in the area A can be maintained. In addition, since clean air is blown from at least two different directions, the distance surrounding the glass base material G is shorter than when clean air is blown from one direction, and the clean air is less likely to stagnate around the glass base material G.

[0065] In this way, by blowing clean air from the surrounding portion 40, the inside of the area A can be made to have a positive pressure with respect to the space outside the area A. The space outside the area A refers to the space more than 1 m around the glass base material G.

[0066] The method for manufacturing an optical fiber according to the present embodiment makes the atmosphere within 1 m around the glass base material G have 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 in a state where there are few foreign substances around the glass base material G. As a result, foreign substances are less likely to adhere to the glass base material G, so that the generation of peaks can be suppressed in the method for manufacturing an optical fiber.

[0067] In the method for manufacturing an optical fiber according to the present embodiment, the drawing process is performed while blowing clean air to the glass base material G. Therefore, the clean environment around the glass base material G can be maintained. As a result, the adhesion of foreign substances to the glass base material G during the drawing process can be suppressed.

[0068] In the method for manufacturing an optical fiber according to the present embodiment, by blowing clean air to the glass base material from two different directions, it is easier to maintain the clean environment around the glass base material. As a result, the mixing of foreign substances into the glass base material during the drawing process can be suppressed.

[0069] In the method for manufacturing an optical fiber according to the present embodiment, with respect to the space outside 1 m around the glass mother body G (the space outside region A), by maintaining a positive pressure within 1 m around the glass mother body G, it is possible to particularly suppress foreign matter from mixing into the periphery of the glass mother body G from the space outside region A. Thereby, it is possible to suppress foreign matter from adhering to the glass mother body G in the drawing process. It should be noted that, alternatively, a positive pressure of 5 Pa or more higher than the space outside region A may be maintained within 1 m around the glass mother body G.

[0070] According to the method for manufacturing an optical fiber of the present embodiment, since the periphery of the glass mother body G is covered by the surrounding portion 40, it is possible to suppress foreign matter from adhering to the glass mother body G. Furthermore, since clean air is blown from each surface of the surrounding portion 40, it is possible to suppress foreign matter from adhering to the glass mother body G in the drawing process.

[0071] Next, the verification results of the generation frequency of spikes caused by differences in the clean environment around the glass mother body in the drawing process will be described. Table 1 shows the generation frequency of spikes when manufacturing an optical fiber by changing the clean environment for the atmosphere within 1 m around the glass mother body ( Figure 2 region A therein). Mm in Table 1 represents million meters.

[0072] [Table 1]

[0073]

[0074] As exemplified in Table 1, the fewer the number of particles present in region A, the fewer the generation frequency of spikes. Here, in the manufacturing of an optical fiber, the generation frequency of spikes can be 30 times or less per 1 million meters. Therefore, it was confirmed that the atmosphere within 1 m around the glass mother body can be a clean environment with the number of particles of 0.3 μm or more and less than 0.5 μm being 15,000 particles / CF or less, and the number of particles of 0.5 μm or more and less than 1.0 μm being 3,500 particles / CF or less. It should be noted that the generation frequency of spikes can be 10 times or less per 1 million meters, and furthermore, it can be 5 times or less.

[0075] As described above, the present disclosure has been described in detail with reference to specific embodiments, but various changes or modifications can be made without departing from the spirit and scope of the present disclosure, which will be apparent to those skilled in the art. In addition, the number, position, shape, etc. of the constituent components described above are not limited to the above embodiments, and can be changed to the number, position, shape, etc. that are preferable when implementing the present disclosure.

[0076] In the present embodiment, a method for manufacturing a multi-core optical fiber has been exemplified, but alternatively, it can be a method for manufacturing a single-core optical fiber having one core portion in the optical fiber.

[0077] Description of reference numerals

[0078] 1 manufacturing device; 10 supporting tube; 20 holding member; 21 exhaust port; 22 cover; 30 movable part; 40 surrounding 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. A method for manufacturing an optical fiber, comprising a drawing step of manufacturing an optical fiber by drawing a glass base material while feeding it into a heating furnace, wherein the glass base material has a core rod and a cladding tube into which the core rod is inserted, a support tube is joined to the upper end of the cladding tube and communicates with the gap between the core rod and the cladding tube, in the 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, and 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.

2. The method for manufacturing an optical fiber according to claim 1, wherein, the drawing step includes blowing clean air onto the glass base material.

3. The method for manufacturing an optical fiber according to claim 2, wherein, the drawing step includes blowing the clean air onto the glass base material from at least two different directions.

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

5. The method for manufacturing an optical fiber according to claim 1, wherein, in the drawing step, the glass base material is surrounded by a surrounding portion provided at a position higher than the heating furnace, and clean air is blown from the surrounding portion.

Images