WO2006075460A1

WO2006075460A1 - Process for producing optical fiber preform and optical fiber preform

Info

Publication number: WO2006075460A1
Application number: PCT/JP2005/022486
Authority: WO
Inventors: Jun Abe; Nobuyasu Mantoku
Original assignee: Shin-Etsu Chemical Co., Ltd.
Priority date: 2005-01-13
Filing date: 2005-12-07
Publication date: 2006-07-20
Also published as: JP4704760B2; JP2006193371A; TW200628422A; TWI399349B

Abstract

A process for producing an optical fiber preform having a core portion and, surrounding the core portion, a clad portion, comprising the steps of connecting dummy tubes (300) for gas supply and discharge to both ends of clad tube (100) consisting of a clad portion constituting material, the dummy tube (300) having an inner diameter greater than that of the clad tube (100); providing core rod portion (200) consisting of a core portion constituting material which has head portion (220) with an outer diameter greater than the inner diameter of the clad tube (100) but smaller than the inner diameter of the dummy tube (300) and has straight trunk portion (210) with an outer diameter smaller than the inner diameter of the clad tube (100), inserting the straight trunk portion (210) in the clad tube (100), and passing a treating gas through the dummy tube (300) and clad tube (100) to thereby clean the internal surface of the clad tube (100) and the surface of the core rod portion (200); and heating the core rod portion (200) and clad tube (100) to thereby effect fusion integration.

Description

Specification

Optical fiber preform manufacturing method and optical fiber preform

Technical field

The present invention relates to an optical fiber preform manufacturing method and an optical fiber preform. More specifically

Unlike optical fiber preforms used in the manufacture of general-purpose optical fibers called single-mode fibers, the present invention relates to optical fiber preform manufacturing methods and optical fiber preforms used in the manufacture of relatively special optical fibers. Relates to a jacketing method in which a core rod and a tube are melted together.

[0002] For designated countries where incorporation by reference of documents is permitted, the contents described in the specification of the following patent application are incorporated into the present application by reference and made a part of the description of the present specification.

Japanese Patent Application No. 2005-006435 Application No.

Background art

[0003] An optical fiber preform used for manufacturing a single mode fiber can be manufactured by, for example, the VAD method. In the VAD method, the content of GeCl in the raw material gas supplied to the core burner

4 is changed to adjust the refractive index profile of the core part, and then the core part is formed, and glass clad containing SiO is deposited thereon with a cladding burner to form the cladding part. Furthermore, it is deposited

2

It is manufactured by dehydrating and forming transparent glass particles.

[0004] Another manufacturing method is a jacketing method. In the jacketing method, a core rod prepared by adjusting the refractive index distribution in advance is set in a clad tube and melted together. The optical fiber preform manufactured by the jacketing method may be left with defects such as bubbles and impurities at the interface between the core rod and the cladding tube in the process of melting and integrating. Therefore, it is known that the optical fiber produced by this method has a large optical transmission loss.

[0005] Patent Documents 1 and 2 describe measures against the above defects. According to these documents, the gap between the core rod and the clad tube is filled with a halogen gas and melted together to remove the dirt and adsorbed moisture on the glass surface to obtain an optical fiber preform. Are listed. It is also described that such a method reduces the optical transmission loss of the optical fiber manufactured by the optical fiber preform.

[0006] In carrying out the above method, it is important that the clad tube and the core rod are not brought into contact with each other. Patent Documents 3 to 5 describe such a core rod setting method.

[0007] Patent Documents 3 and 4 describe a two-point support method for both ends of the core rod, a support method for the lower end portion, a support member, and the like when the jacketing method is performed in a vertical furnace. Patent Document 5 discloses a method of setting a core rod in a cladding tube by providing notches in the core rod for vapor phase etching and decompression, reducing the diameter of dummy tubes connected to both ends of the cladding tube. Are listed.

Patent Document 1: JP-A-6-117126

Patent Document 2: Japanese Patent Laid-Open No. 2003-48737

Patent Document 3: Japanese Patent Laid-Open No. U-139841

Patent Document 4: Japanese Patent Laid-Open No. 2001-247326

Patent Document 5: Japanese Patent Laid-Open No. 2003-160351

Disclosure of the invention

Problems to be solved by the invention

[0008] However, in the methods described in Patent Documents 3 to 5 described above, if the weight of the core rod is light, the core rod may move due to the momentum of the gas flow introduced into the cladding tube. In such a case, (a) the inner surface of the tube and the outer surface of the core rod are damaged (b)

,, (C) The core rod that has moved has a problem that it is difficult to return it to its original position. These problems also affect the properties of the final optical fiber obtained from the manufactured optical fiber preform. Therefore, there is a need for a technique for treating the inside of the core rod and the tube with a sufficient amount of halogen gas without damaging the core rod.

[0009] Therefore, according to the present invention, even if a sufficient amount of processing gas is allowed to flow between the cladding tube and the core rod, the core rod set therein is moved by the gas flow, and the cladding is not damaged. The purpose is to provide a manufacturing method of the material. Another object of the present invention is to provide a high-performance and high-quality optical fiber manufactured by the jacketing method. One.

Means for solving the problem

[0010] As a first aspect of the present invention, there is provided a method of manufacturing an optical fiber preform having a core portion and a clad portion surrounding the core portion, the constant being formed by a material that becomes the clad portion. Connecting a dummy tube for air supply / exhaust having an inner diameter larger than the inner diameter of the cladding tube to the gas at both ends, and an inner diameter of the dummy tube larger than the inner diameter of the cladding tube A core rod having a head having a smaller outer diameter and a straight body having an outer diameter smaller than the inner diameter of the clad tube, and formed of a material that becomes a core, the head and the dummy tube In addition, after forming the gas flow path through which the gas flows between the clad tube and the straight body portion into the clad tube, the dummy tube and the clad tube are inserted. A method of manufacturing an optical fiber preform including a step of flowing a processing gas into the inner tube to clean the inner surface of the cladding tube and the surface of the core rod, and a step of heating and melting and integrating the core rod and the cladding tube. Provided. As a result, it is possible to manufacture a high-quality recorded fiber base material having no defects, in which the core rod is prevented from shifting in the longitudinal direction in the step of melting and integrating.

[0011] Further, according to one embodiment, in the process of melting and integrating in the optical fiber manufacturing method, the core tube and the clad tube may be melted and integrated together. As a result, the core rod in the clad tube can be stabilized and a high-quality optical fiber preform can be manufactured.

[0012] In the method for manufacturing an optical fiber, the length of the head portion of the core rod is preferably 30 mm or more. As a result, in the melt-integrating process, a part of the head of the core rod does not soften and contributes to the positioning of the core rod, so that the positioning of the core rod is stabilized.

[0013] According to another embodiment, in the step of fusing and integrating the above-described optical fiber manufacturing method, only the same part of the core rod of the straight moon may be fused and integrated with the clad tube. As a result, an optical fiber preform that does not contribute to the formation of the core portion that will ultimately become the core of the optical fiber is produced, so that an optical fiber preform that can efficiently produce an optical fiber is provided. The [0014] In the method for manufacturing an optical fiber, the length of the head portion of the core rod is preferably 30 mm or less. As a result, the core rod material can be saved and the optical fiber material cost can be reduced.

[0015] Furthermore, as a second embodiment of the present invention, there is provided an optical fiber preform manufactured by the method for manufacturing an optical fiber preform. This provides an optical fiber in which each of the core and the cladding has desired optical characteristics.

[0016] However, the above summary of the invention does not enumerate all the necessary features of the present invention. Sub-combinations of these feature groups can also be an invention.

The invention's effect

[0017] According to the optical fiber preform manufacturing method described above, a sufficient amount of processing gas is supplied because the core rod is not moved by the processing gas supplied between the cladding tube and the core rod during jacketing. be able to. Therefore, an optical fiber preform with no defects at the interface between the core rod and the clad tube, which has good workability, can be obtained, which contributes to improving quality and reducing production costs. The optical fiber preform manufactured by the above method is a high-quality optical fiber preform with no defects at the interface between the core rod and the clad tube, and is a preform that can produce an optical fiber with little transmission loss.

Brief Description of Drawings

FIG. 1 is a schematic explanatory view for explaining a method of manufacturing an optical fiber preform according to Example 1.

FIG. 2 is a schematic explanatory view for explaining a method of manufacturing an optical fiber preform according to Example 2.

FIG. 3 is a schematic explanatory view illustrating a method for manufacturing an optical fiber preform according to Comparative Example 1.

Hereinafter, the present invention will be described through embodiments of the present invention. However, the following embodiments do not limit the claimed invention. In addition, all the combinations of features described in the embodiments are not necessarily essential for the solution of the invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0020] (Example 1)

FIG. 1 is a schematic diagram illustrating a method for manufacturing the optical fiber preform 10 according to the first embodiment. As shown in the figure, a dummy tube 300 having an inner diameter larger than that of the cladding tube 100 is coupled to both ends of the cladding tube 100 having a constant inner diameter. Cladch Since the tube 100 and the dummy tube 300 are in communication with each other, the gas can be circulated from one end to the other end. In Example 1, the left force in the figure is also directed to the right for dehydration treatment. Of gas.

In addition, a straight body portion 210 of the core rod 200 is passed through the clad tube 100. The corrod 200 has a straight part 210 that is thinner than the inner diameter of the clad tube 100 and a head 220 that is larger in diameter than the inner diameter of the clad tube 100 and smaller in diameter than the dummy tube 300. It is inserted through the dummy tube 300 from the upstream side of the flow. Accordingly, when the head 220 comes into contact with the end face of the clad tube 100, the core rod 200 does not move rightward any further.

First, a quartz tube having an inner diameter of 10 mmφ and a length of 300 mm was prepared as the cladding tube 100. Next, a dummy tube 300 having an inner diameter of 19 mm was welded to the clad tube 100. Furthermore, as the core rod 200, a core rod having an outer diameter 8πιπι φ, a straight part 210 with a length of 320 mm, and a head 220 with an outer diameter 15 πιπι φ, a length of 50 mm, is prepared. As shown in FIG. Set within 100.

[0023] From the left side of the dummy tube 300 in the figure, the inner surface of the cladding tube 100 and the surface of the core rod 200 are sufficiently dehydrated by flowing chlorine gas of 500 ml / min and helium of 2000 ml / min as dehydration gas. Thereafter, the entire core rod 200 including the head 220 was melted and integrated. Thus, an optical fiber preform including the clad part and the core part was obtained.

[0024] In the above operation, a force that allows a sufficient amount of processing gas to flow into the tube. Since the head of the core rod is processed to be thicker than the inner diameter of the cladding tube, the core rod is pushed and moved downstream by the processing gas. The workability was also good.

[Example 2]

FIG. 2 is a schematic diagram illustrating a method for manufacturing the optical fiber preform 11 according to the second embodiment. In the figure, the same members as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

[0026] As shown in the figure, the clad tube 100 and the dummy tube 300 used in the second embodiment are the same as those used in the first embodiment including specifications such as dimensions. On the other hand, for the core rod 200, the length force of its head 222 is compared with that used in Example 1. It is getting shorter.

That is, in the core rod 200 used in the second embodiment, a head 222 having an outer diameter of 15 mm and a length of 10 mm is formed at one end of the straight part 210 having an outer diameter of 8 mm and a length of 320 mm. . Such a core rod 200 was set in the clad tube 100 as shown in FIG. In the figure, 500 ml / min of chlorine gas and 2000 ml / min of helium gas were allowed to flow from the dummy tube 300 on the left as dehydration gas, and the inner surface of the cladding tube 100 and the surface of the core rod 200 were sufficiently dehydrated.

[0028] Next, fusion integration of the clad tube 100 and the core rod 200 was started from one end of the clad tube 100 and integrated to the other end. Therefore, the head 222 located outside the clad tube 100 is not united.

In Example 2 as described above, since the length of the head 222 of the core rod 200 is short, the change in the position of the core rod 200 is greater than that in Example 1. For this reason, a slightly defective part was formed. However, the core rod was also excellent in workability without being pushed and moved downstream by the processing gas.

[0030] (Comparative Example 1)

FIG. 3 is a schematic diagram for explaining a method of manufacturing the optical fiber preform 20 according to the comparative example. In the figure, the same members as those in the first embodiment and the second embodiment are denoted by the same reference numerals, and redundant description is omitted.

[0031] As shown in the figure, the clad tube 100 and the dummy tube 300 used in Comparative Example 1 are the same as those used in Example 1 and Example 2, including specifications such as dimensions. On the other hand, the core rod 200 has an outer diameter smaller than the inner diameter of the clad tube 100 as a whole, and a head having a different outer diameter is not formed. Specifically, the core rod 200 used in Comparative Example 1 is a glass rod with an outer diameter of 8 mm over the entire length of 320 mm.

[0032] The core rod 200 as described above was set in the quad tube 100 to which the dummy tube 300 was attached as shown in FIG. From the left side of the dummy tube 300 in the figure, 500 mlZ of chlorine gas and 2000 mlZ of helium are allowed to flow as dehydration gas to sufficiently dehydrate the inner surface of the cladding tube 100 and the surface of the core rod 200, and then Melting Integrated. Thus, an optical fiber preform including the clad part and the core part was obtained.

[0033] However, in the manufacturing process of the optical fiber preform 20 according to Comparative Example 1, if a dehydration gas having a flow rate as described above that is sufficient for the effect of the dehydration is flowed, the gas flow As a result, the core rod 200 was pushed downstream and moved. For this reason, before melting and integrating, the core rod 200, which also moved the downstream resultant force of the clad tube 100, was pushed with a clean glass rod, and it was necessary to work to return to the original set position. Further, during this operation, the core rod 200 and the clad tube 100 were rubbed against each other and damaged, which eventually caused bubbles in the integrated optical fiber preform 20.

[0034] Further, since the processing chamber was opened when the core rod was pushed back, the clad tube 100 and the core rod 200 were exposed to the atmosphere. For this reason, water vapor, dust, etc. in the atmosphere adhere to the clad tube 100 and the core rod 200 that have been dehydrated once, and in the optical fiber preform 20 that has been fused and integrated, defects that occur between the core and the clad are eliminated. Increased. Therefore, the optical transmission loss of the optical fiber manufactured using the optical fiber preform 20 as a raw material is also clearly compared with those using the optical fiber preforms 10 and 11 according to Examples 1 and 2. It was increasing.

[0035] Table 1 shows the specifications of the clad tube 100 and the core rod 200 used in Examples 1 and 2 and Comparative Example 1 and the evaluation of the work for manufacturing the optical fiber preforms 10, 11, and 20 together.

[table 1]

Industrial applicability

According to the above optical fiber manufacturing method, an optical fiber preform having no defect on the interface between the core rod 200 and the cladding tube 100 can be obtained. Further, by using the optical fiber preform manufactured in this way, an optical fiber with a small transmission loss can be obtained.

Claims

The scope of the claims

[1] A method for manufacturing an optical fiber preform having a core portion and a cladding portion surrounding the core portion,

Connecting a supply / exhaust dummy tube having an inner diameter larger than the inner diameter of the cladding tube to both ends of a cladding tube having a certain inner diameter formed of the material to be the cladding portion; ,

The core portion has a head portion having an outer diameter larger than the inner diameter of the cladding tube and smaller than the inner diameter of the dummy tube, and a straight part having an outer diameter smaller than the inner diameter of the cladding tube. After inserting the straight body part into the clad tube while forming a gas flow path for allowing the gas to flow between the head and the dummy tube and the clad tube, the core rod formed of a material is formed. Flowing a processing gas into the dummy tube and the clad tube to clean the inner surface of the clad tube and the surface of the core rod;

Heating the core rod and the clad tube and fusing them together to produce an optical fiber preform.

[2] The method for producing an optical fiber preform according to [1], wherein in the step of melting and integrating, the core tube is melted and integrated including the head portion of the core rod.

[3] The method of manufacturing an optical fiber preform according to [2], wherein the length of the head of the core rod is 30 mm or more.

4. The method of manufacturing an optical fiber preform according to claim 1, wherein, in the step of melting and integrating, only the straight body portion of the core rod is melted and integrated with the clad tube.

5. The method for manufacturing an optical fiber preform according to claim 4, wherein the length of the head of the core rod is 30 mm or less.

[6] An optical fiber preform manufactured by the optical fiber preform manufacturing method according to any one of claims 1 to 5.