JP2001039726A - Method for processing optical fiber preform and processing device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for processing an optical fiber preform which enables the simultaneous execution of a surface treatment and reduction of residual stress simultaneously with stretching of the large-diameter optical fiber preform and a processing device therefor. SOLUTION: The optical fiber preform 1 is stretched by respectively holding both ends of the optical fiber preform 1 with rotary chucks, rotating the optical fiber preform and widening a spacing between both rotary chucks 2a and 2b while subjecting the optical fiber preform to flame heating with a burner. At this time, at least three movable burners are arranged along the longitudinal direction of the optical fiber preform 1. The optical fiber preform is preheated, successively from a moving direction, by the first burner 3a, is heated and stretched to a softening temperature by the second burner 3b and the surface treatment and the reduction of the residual stress of the optical fiber preform 1 are executed by the third burner 3c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a processing method for drawing and reducing the diameter of an optical fiber preform, and more particularly to the processing of an optical fiber preform for drawing and reducing a large diameter optical fiber preform at low cost. The present invention relates to a method and a processing apparatus.

[0002]

2. Description of the Related Art In recent years, in order to produce optical fibers at lower cost, the diameter of an optical fiber preform has been increased, and accordingly, a large-diameter optical fiber preform is processed at low cost. Technology is being established. If only stretching for the purpose of adjusting the diameter of the optical fiber preform, an electric resistance furnace, a high-frequency electric furnace or the like can be used as a heating source, but the diameter fluctuation of the optical fiber preform along the longitudinal direction is reduced. to do so,
It is advantageous to use a flame burner for the heating source. Silicon monoxide volatilizes from the surface of the optical fiber preform heated by the flame burner, and this silicon monoxide combines with moisture in the atmosphere to become silica glass again and adheres to the surface of the optical fiber preform. For this reason, a surface treatment for removing silica and surface flaws attached to the surface is required, and a treatment with a flame burner is essential. For this reason, flame burners are usually used for processing large-diameter optical fiber preforms.However, flame burners have a narrow heating area and naturally have a limit in the burner diameter. The limit is about 100 mm in diameter. Further, many strains remain inside the optical fiber preform treated at such a high temperature.

[0003] Generally, in drawing, an optical fiber preform is held on a glass lathe, and is heated and softened by a flame of a burner using a chain hydrocarbon or hydrogen as a combustion gas as a heating source to hold the optical fiber preform. By moving the rotary chuck to increase the distance between the two rotary chucks, a tensile force is applied to the softened portion to reduce the diameter to a predetermined diameter, and by sequentially moving the heating source, the optical fiber preform is stretched over substantially the entire length, The diameter is reduced. The drawn optical fiber preform is further subjected to flame polishing in order to remove silica adhering to the surface and reduce residual stress as described above. As described above, the finishing process of the optical fiber preform is roughly divided into a stretching process and a process of removing silica adhering to the surface and reducing a residual stress.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a method and a method for processing an optical fiber preform which enables a large-diameter optical fiber preform to be simultaneously stretched and subjected to surface treatment and reduction of residual stress. It is intended to provide equipment.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and as a result, it has been necessary to stretch the optical fiber preform at 2000 ° C. or higher. Naturally, there is a limit to the caliber of the burner, the heating area in the longitudinal direction of the optical fiber preform is narrow, and
Large-diameter optical fiber preforms cannot be processed with a single flame burner. For this reason, in addition to the heating burner for stretching the optical fiber preform, an auxiliary burner for preheating is arranged, so that the large-diameter optical fiber preform can be stretched by flame heating and further surface treatment and residual treatment. The present inventors have found that by providing an auxiliary burner for reducing stress (reducing strain), it is possible to perform surface treatment and strain removal simultaneously with stretching, and have accomplished the present invention.

That is, in the method of processing an optical fiber preform according to the present invention, the both ends of the optical fiber preform are each held by a rotary chuck and rotated, and the space between the rotary chucks is increased while flame heating is performed by a burner. When stretching the optical fiber preform by, at least three movable burners are arranged along the longitudinal direction of the optical fiber preform,
The optical fiber preform is preheated by the first burner in order from the moving direction, heated to the softening temperature by the second burner and stretched,
An object of the present invention is to perform surface treatment of an optical fiber preform and reduction of residual stress by a third burner.

[0007] A chain hydrocarbon or hydrogen is supplied to each of the first, second and third burners as a combustion gas.
Alternatively, a chain hydrocarbon or hydrogen is supplied to the first and second burners as a combustion gas, and a non-flammable gas, specifically, oxygen, air, nitrogen, argon, and helium is appropriately supplied to the third burner. The selected gas can be supplied to stretch the optical fiber preform.

According to the optical fiber preform processing apparatus of the present invention, both ends of the optical fiber preform are held by rotary chucks, and the optical fiber preform is rotated by flame heating. An apparatus for stretching a material, which is movable along the longitudinal direction of the optical fiber preform,
A first preheating auxiliary burner, a second stretching heating burner, and a third surface treatment / distortion burner are provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The present invention, along the longitudinal direction of the optical fiber preform,
By arranging three movable burners having different purposes, namely, a first preheating auxiliary burner, a second stretching heating burner, and a third surface treatment / distortion burner, the optical fiber motherboard is provided. Elongation of material, removal of adhered silica,
It is possible to reduce the residual stress by a single-step process.

FIG. 1 is a schematic side view showing an example of a processing apparatus according to the present invention. An optical fiber preform 1 is mounted on rotating chucks 2a and 2b of a glass lathe.
The three burners 3a, 3b, 3c are installed along the longitudinal direction of. These burners are, in order from the moving direction, the first burner 3a is a preheater, the second burner 3b is elongated, and the third burner 3c is a heating burner for surface treatment and reduction of residual stress (distortion removal). is there. In order to heat and stretch a large-diameter optical fiber preform with one burner, there is a limit to the heating area of the burner in the longitudinal direction of the optical fiber preform. Therefore, by preheating the first burner 3a immediately before the second burner 3b for stretching, it is possible to expand the heating region of the optical fiber preform 1 in the longitudinal direction.

Although the softening temperature at which stretching can be performed is required to be 2000 ° C. or more, the temperature of the preheating region by the first burner 3a exceeds 2000 ° C. On the contrary, the heating region becomes too wide, and the stretching diameter is controlled. 1500 ~
The temperature may be controlled in a temperature range of 2000 ° C, preferably 1800 to 2000 ° C. The second burner 3b is used to heat the surface of the optical fiber preform to 2000 ° C. or more, which is a softening temperature at which the optical fiber preform can be stretched. It is stretched to the diameter of.

Silicon monoxide is volatilized from the surface of the optical fiber preform heated at such a high temperature by the flame burner, and this silicon monoxide combines with moisture in the atmosphere to form silica glass again to form the optical fiber preform. Attaches to material surface. Therefore, surface treatment with a flame burner is required to remove silica and surface flaws attached to the surface. In addition, many strains remain inside the optical fiber preform treated at such a high temperature. Therefore, after the stretching process is completed,
Further, heat treatment is required.

Further, the third burner 3c reduces the distortion remaining in the optical fiber preform by heating at a temperature of about 1500 to 2000 ° C., which is lower than the drawing temperature, and the silica glass adhered to the surface. Fine particles are removed. When the amount of strain remaining inside the optical fiber preform is large, chain hydrocarbon or hydrogen is supplied to the third burner 3c as a combustion gas, and the third burner 3c is treated by the flame. On the other hand, when the amount of strain remaining inside the optical fiber preform is sufficiently small, the burner 3c adheres to the surface only by flowing a gas such as oxygen, nitrogen, air, or argon which does not adversely affect the optical fiber preform. Silica glass can also be removed.

Further, as described above, if the softening temperature range in which stretching is possible is too wide, the controllability of the diameter is adversely affected. The heating area of the optical fiber preform is about 0.5 to 1.5 times, more preferably 0.8 to 1.2 times, the outer diameter of the optical fiber preform along the longitudinal direction. The interval between the three burners is appropriately set so as to obtain such a temperature distribution. Under the above conditions, preheating by the first burner, main heating by the second burner, heating for surface treatment and strain removal by the third burner, and three burners by the longitudinal length of the optical fiber preform. By installing the optical fiber preform along the direction, the stretching of the large-diameter optical fiber preform by flame heating is completed in one step.

[0015]

The present invention will be specifically described below with reference to examples and comparative examples. In addition, this invention is not limited to a following example. (Examples 1 and 2 and Comparative Example 1) An optical fiber preform having an average diameter of φ85 mm is held on a rotary chuck of a glass lathe by three burners arranged along the longitudinal direction of the optical fiber preform. Stretching was performed with a flame. Table 1 shows the diameters before and after stretching, the gas supply conditions for each burner, and the results of the processing. As a comparative example, Table 1 shows the conditions and the results of the processing when stretching was performed using a single conventional burner.

As a result, the total amount of gas used in the stretching process using the three burners of the present invention is smaller than that of the single burner of the comparative example when the original diameter of the optical fiber preform is φ85 mm. Stretching with a smaller amount was possible (see Table 1: Example 1 and Comparative Example 1, Example 2 and Comparative Example 2). Also,
The optical fiber preform according to the embodiment of the present invention has no fogging due to silica glass on the surface and has little distortion inside. On the other hand, in the case of the comparative example, the surface was fogged by silica glass, and surface treatment by flame polishing had to be performed subsequently.

(Examples 3 to 6, Comparative Example 2) A rotating chuck of a glass lathe has an average diameter of φ120 mm and φ150 mm.
The optical fiber preform was held and stretched by flames using three burners arranged along the longitudinal direction of the optical fiber preform. Table 1 shows the diameters before and after stretching, the gas supply conditions for each burner, and the results of the processing. Table 1 also shows, as a comparative example, the conditions and the results of the processing when stretching was performed with a conventional single burner. As a result,
In the case of the examples of the present invention, stretching could be performed with a smaller amount of gas than in the comparative example, and an optical fiber preform having no residual cloud and no residual stress was obtained on the surface. On the other hand, in the case of the single-burner comparative example, even if the gas amount was increased, the temperature was not sufficiently increased, the chucking portion slipped, the optical fiber preform was broken, and the drawing process could not be performed.

[0018]

[Table 1]

[0019]

According to the present invention, the above-mentioned structure is provided.
Surface treatment and strain removal can be performed simultaneously with the stretching process, and an optical fiber preform having no residual stress and having no scratches or fogging on the surface can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing an example of a processing apparatus of the present invention.

[Explanation of symbols]

 1. Optical fiber preforms 2a, 2b Rotary chucks 3a, 3b, 3c Burner

Continuation of the front page (72) Inventor Tadakatsu Shimada 2-3-1-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Industry Co., Ltd. Precision Materials Research Laboratories (72) Inventor Hideo Hirasawa 2--13 Isobe, Annaka-shi, Gunma No. 1 Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory F-term (reference) 4G021 BA00

Claims (5)

[Claims] When the optical fiber preform is stretched by holding the both ends of the optical fiber preform with a rotary chuck and rotating the same, and flame-heating with a burner, and widening the interval between the two rotary chucks, At least three movable burners are arranged along the longitudinal direction of the optical fiber preform, and the optical fiber preform is preheated by the first burner in order from the moving direction, and heated to the softening temperature by the second burner. A surface treatment of the optical fiber preform and reduction of residual stress by a third burner. 2. A chain hydrocarbon or hydrogen is supplied to each of the first, second and third burners as a combustion gas, and the optical fiber preform is drawn by a flame of the combustion gas.
3. The method for processing an optical fiber preform according to item 1. 3. The optical fiber preform is drawn by supplying a chain hydrocarbon or hydrogen as a combustion gas to the first and second burners and supplying a non-combustible gas to the third burner. 3. The method for processing an optical fiber preform according to item 1. 4. The method for processing an optical fiber preform according to claim 3, wherein the nonflammable gas supplied to the third burner is oxygen, air, nitrogen, argon or helium. 5. An apparatus which stretches the optical fiber preform by holding the both ends of the optical fiber preform by rotating chucks, rotating the optical fiber preform while performing flame heating with a burner, and widening the interval between the two rotating chucks. A first preheating auxiliary burner, a second drawing heating burner, and a third surface treatment that are movable along the longitudinal direction of the optical fiber preform.
An optical fiber preform processing apparatus comprising a strain removing burner.