JP2001039727A - Optical fiber preform and method or processing preform for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical fiber preform to which glass particulates do not stick by one piece of burner in flame processing of the optical fiber preform or the preform having the maximum temperature rising as high as >=2000 deg.C or a method for processing the preform. SOLUTION: The flame processing, such as stretching of the optical fiber preform or flame polishing of the preform, is executed by heating with the flame of the burner from one direction while rotating the optical fiber preform or the preform and while relatively moving the flame heating position of the burner. At this time, the temperature fall gradient before the temperature falls down to 1900 to 1500 deg.C in a longitudinal direction from the flame heating position is controlled so as to enter a range of -20.0 to -1.0 deg.C/mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to flame processing such as stretching and flame polishing of an optical fiber preform or an optical fiber preform.

[0002]

2. Description of the Related Art In general, in stretching, an optical fiber preform is held on a glass lathe and 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 one of the rotary chucks to increase the distance between the two rotary chucks, a pulling force is applied to the softened portion to reduce the diameter to a predetermined diameter, and the heating source is sequentially moved to substantially extend the entire length of the optical fiber preform. The preform for optical fiber is obtained by stretching and reducing the diameter of the preform.

[0003] SiO evaporates from the surface of the optical fiber preform heated by the flame of the burner. This SiO combines with moisture in the atmosphere and becomes fine silicon dioxide (SiO ₂ ) particles, that is, fine silica glass particles, and adheres to the surface of the optical fiber preform. For this reason, surface treatment is indispensable in order to remove glass particles attached to the surface and surface scratches generated during handling. As described above, the preform obtained by stretching the optical fiber preform is further subjected to flame polishing in order to remove adhered glass particles and surface scratches and reduce residual stress. The large-diameter preform is further stretched to a predetermined diameter by a glass lathe.

An optical fiber is obtained by welding a dummy glass rod to one or both ends of the preform drawn to a predetermined diameter, mounting the dummy glass rod on a drawing machine, heating and drawing. The temperature at the time of stretching to a predetermined diameter, welding of a dummy glass rod, and the like must be maintained at 1600 ° C. or more at the radial center of the preform. 16 in the center of the preform
In order to increase the temperature to 00 ° C. or higher, the temperature of the preform surface must be 2000 ° C. or higher, and this state must be maintained for more than ten minutes.

When the quartz glass is exposed to such a high-temperature flame atmosphere, a part thereof becomes SiO and evaporates, and then becomes fine glass particles again and adheres around the flame heating position.
This phenomenon is considered that the evaporated quartz glass component reacts with moisture and the like in the air to become fine silicon dioxide (SiO ₂ ) particles, which are condensed by being rapidly cooled and adhere to the surroundings. When a preform with glass particles attached to the surface is drawn, the atmosphere in the electric furnace is contaminated with SiO ₂ particles, and the attached glass particles damage the surface of the optical fiber, and cause mechanical damage. There is a risk of reducing the target strength.

When a preform is drawn with scratches or foreign matter adhered to the surface, the strength of the optical fiber is remarkably reduced, and disconnection often occurs during drawing. If a disconnection occurs during drawing, the time required for restarting and the amount of work performed by the operator will be about two times less than if no disconnection occurred.
Double the time and work volume, and the productivity of the device decreases. Therefore, conventionally, in order to remove foreign matters and scratches attached to the surface, an optical fiber preform is drawn to a predetermined diameter by a glass lathe to form a preform, and then flame polishing is performed.

When the surface temperature of the preform reaches about 2000 ° C. due to the burner flame, a part of the quartz glass becomes SiO and evaporates. Due to the evaporation of the SiO, the diameter of the preform is slightly reduced, and accordingly, surface flaws and attached foreign matter are removed. Further, when the surface temperature of the preform becomes about 2000 ° C. or higher, the viscosity of the quartz glass decreases to about 10 ⁴ to 10 ⁵ poise, and the quartz glass can be easily deformed with a small force. The scratch on the preform surface
When the glass viscosity decreases, the surface tension acts and disappears, and the surface becomes smooth.

[0008] SiO evaporated by stretching or flame polishing is
The place where it becomes glass fine particles of SiO ₂ and adheres to the surface of the preform is immediately outside the portion which is strongly heated by the flame, and a band-like fogging is generated. The glass particles forming the cloud are scattered in the furnace during drawing, contaminate the furnace atmosphere like foreign matters, and may damage the surface of the fiber, so they are removed before drawing. There is a need. This fogging can be removed by heating the surface temperature to about 1900 ° C. with a relatively weak flame.

In this case, depending on the amount of gas and the moving speed of the burner, the center of the preform is not sufficiently heated and strong distortion remains, and cracks may be generated by a slight impact. Conversely, if the heating is carried out more than necessary, the residual strain is reduced, but the quartz glass evaporates again and fogging occurs. For this reason, in the conventional fire polishing (flame polishing) conditions, the remaining strain is measured with a strain gauge or the like, and the gas condition, the burner moving speed condition, and the appearance inspection are performed so that the remaining strain does not cause a problem. Gas conditions that do not cause fogging, burner moving speed conditions, and the like have been found through trial and error. These conditions vary depending on the diameter of the preform and individual burners.

For example, the first flame processing is carried out under the condition that the surface temperature becomes about 2000 ° C. or more in order to remove stretching, surface scratches and attached glass fine particles. The second flame processing is performed under the condition that the surface temperature becomes about 1900 ° C. The method of cleaning the surface of the preform by such two times of flame processing requires an extremely long processing time, and further, after heating and cooling once,
Since heating was performed again, there was much waste in terms of thermal efficiency.

[0011]

In order to solve such a problem, there has been proposed a method in which a plurality of burners are installed and processed by a single flame processing. For example, when an optical fiber preform is drawn, a flame burner is provided by installing a heating burner for drawing and a sub-burner for removing glass fine particles generated by the heating burner. According to this method, the stretching of the optical fiber preform is performed by the conventional method.
For flame polishing performed for the purpose of removing surface flaws and foreign matter by a factor of two or less, it is possible to perform the processing in a time of one half or less. In addition, since the glass fine particles are removed at the same time, the thermal efficiency is improved. However, the method of performing the flame processing by installing a plurality of burners requires a large equipment cost such as an additional burner, a gas control system accompanying the burner, and a change in equipment related thereto.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in the flame processing of an optical fiber preform or a preform (hereinafter, these are collectively referred to as a rod) whose maximum temperature is 2000 ° C. or more. An object of the present invention is to provide a method for processing a rod to which glass fine particles do not adhere using a book burner.

[0013]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted intensive studies in order to obtain flame processing conditions in which glass particles do not adhere with a single burner flame. Rod surface temperature distribution is about 150
It has been found that the adhesion of the glass fine particles is remarkable in the region where the temperature falls to 0 ° C. or lower, and the temperature drop gradient in the surface temperature distribution region where the temperature decreases from about 1900 ° C. to about 1500 ° C.
When it was in the range of 0 ° C./mm to −1.0 ° C./mm, it was found that the adhesion of glass particles could be suppressed,
The present invention has been completed.

That is, the method for processing a rod according to the present invention comprises:
The rod is rotated and heated by a burner flame from one direction.When performing flame processing such as stretching or flame polishing of the optical fiber preform while relatively moving the flame heating position of the burner, from the flame heating position. It is to control the temperature falling gradient during the temperature drop from 1900 ° C. to 1500 ° C. in the longitudinal direction so as to fall within a range of −20.0 to −1.0 ° C./mm. The temperature drop gradient in the longitudinal direction from the flame heating position causes the burner to move 6 degrees with respect to the rod axis.
It can be obtained at an angle of 0 ° to less than 90 °, more preferably 60 ° to 80 °. In addition, when the rod is heated by the burner flame from one direction while rotating the rod, and when the flame heating process of the burner is relatively moved while performing the flame processing such as the extension of the rod or the flame polishing, the flow rate of the gas ejected from the burner is increased. Is performed by providing a distribution in the relative movement direction of the burner.

By gradually decreasing the temperature gradient from 1900 ° C. to about 1500 ° C. at which the SiO evaporated from the rod surface begins to condense, the temperature is gradually reduced from −20.0 ° C./mm to −1.0 ° C./mm. The vapor generated is diffused to the surroundings before it reaches the point where it is cooled and a certain distance is maintained from the point where evaporation takes place to the point where the glass particles are generated by condensation. The rod is 2000 ℃
Since the rod is gradually cooled from the above high temperature, almost no distortion remains in the rod after processing.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The processing method of the present invention will be described below in more detail with reference to the drawings. FIG. 1 (b)
The single burner is tilted in the direction opposite to the direction of relative movement of the burner flame, so that the single
Temperature drop gradient from 900 ° C to 1500 ° C is -12
The temperature distribution region A from −5 ° C. to −5 ° C./min is expanded. FIG. 1A shows the surface temperature of the rod. The inclination angle of the burner is 60 ° ≦ θ <9 with respect to the axis of the rod.
0 °.

FIG. 2 shows the burner crater having a rectangular crater and varying the flow rate of gas flowing out in the longitudinal direction.
(C) shows the crater, and (d) shows the gas flow rate ratio when the left end is 1 with respect to the longitudinal direction of the burner crater. In addition, the embodiment shown in FIG. 3 is a burner in which the crater of the burner is rectangular, and the flow velocity ratio of the gas with the flow velocity at the longitudinal center of the burner being 1 decreases symmetrically toward both ends of the burner. It is used. In addition, FIG. 4 shows a state in which flame processing such as elongation of a rod and flame polishing is performed using a glass lathe. In the flame processing, one of a rod and a burner is relatively moved while rotating the rod. It is done by doing. In any of the apparatuses of the above-described embodiments 1 to 3, a desired temperature distribution can be obtained on the rod surface.

[0018]

(Embodiment 1) As shown in FIG. 1, the burner is turned by 60 ° in a direction opposite to the relative movement direction of the burner flame.
It is placed at an angle, giving a temperature distribution as shown in FIG. 1 to the flame heating surface of the rod, and is approximately 1000 mm long and 65 mm in diameter.
Was reduced to a diameter of 60 mmφ. At this time, the gas flow rate to the heating burner was H ₂ : 300 l / min,
O ₂ : 130 l / min, the relative movement speed of the burner is 10 mm / min, and the temperature decrease gradient during the fall from 1900 ° C. to 1500 ° C. is from −10 ° C./mm to −5 ° C./min.
mm. The processing time required for stretching was 100 minutes. No adhesion of glass particles was observed on the rod surface after stretching, and the residual strain was small.

Example 2 A burner having a rectangular crater as shown in FIG. 2 was used, and the gas flow distribution flowing out in the longitudinal direction of the crater was changed. Given the temperature distribution, length about 1000m
m, a rod having a diameter of 65 mmφ was reduced to a diameter of 60 mmφ. At this time, the gas flow rate to the heating burner is H ₂ :
300 l / min, O ₂ : 130 l / min, the relative movement speed of the burner was 10 mm / min, and 1900
The temperature gradient during the fall from 1500 ° C to 1500 ° C is -8 ° C /
It was controlled to be between mm and −4 ° C./mm. The processing time required for stretching was 100 minutes. No adhesion of glass particles was observed on the rod surface after stretching, and the residual strain was small.

(Embodiment 3) As shown in FIG. 3, a burner whose burner crater has a rectangular shape is used, and the gas flow distribution is changed symmetrically from the longitudinal center of the crater toward both ends.
By giving a temperature distribution as shown in FIG. 3 to the flame heating surface of the rod, a rod having a length of about 1000 mm and a diameter of 65 mmφ was reduced to a diameter of 60 mmφ. At this time, the gas flow rate to the heating burner was 300 l / min for H _{2 and} 130 l for O ₂ .
/ Min, the relative movement speed of the burner is 10 mm / mi
n, and the temperature was controlled so that the temperature falling gradient during the period from 1900 ° C to 1500 ° C was between -12 ° C / mm and -8 ° C / mm. Processing time required for stretching is 100 min
Met. No adhesion of glass particles was observed on the rod surface after stretching, and the residual strain was small.

(Comparative Example 1) As shown in FIG. 5, a flame distribution as shown in FIG. 5 is given to the flame heating surface of the rod by a conventional method in which the outflow direction of the flame from the burner is perpendicular to the rod. A rod having a length of about 1000 mm and a diameter of 65 mm was reduced to a diameter of 60 mm. At this time, the gas flow rate to the heating burner was 300 l / min for H _{2 and} 13 for O _2.
At 0 l / min, the relative movement speed of the burner is 10 mm / min.
min, and the temperature descending gradient during the period from 1900 ° C to 1500 ° C was between -30 ° C / mm and -20 ° C / mm. The processing time required for stretching was 100 minutes. Since the glass fine particles had adhered to the rod surface after the stretching, flame polishing was further performed under the following conditions. The gas flow rate to the heating burner is H ₂ : 250 l / min, O ₂ : 12
At 0 l / min, the relative movement speed of the burner is 20 mm / m
and the temperature drop gradient during the period from 1900 ° C to 1500 ° C was controlled between -10 ° C / mm and -5 ° C / mm. The time required for this flame polishing was 50 minutes. The time required for elongating and reducing the diameter to 60 mmφ and flame polishing for removing glass particles was 150 minutes in total.

[0022]

According to the present invention, the above-mentioned structure is provided.
A rod having no residual particles and no glass particles adhered to the surface can be obtained. In addition, the processing method of the present invention requires only one burner, and can simultaneously perform stretching and removal of glass fine particles by a single flame processing, so that thermal efficiency and productivity are improved and the burner is inclined. Alternatively, it is only necessary to replace the crater of the burner, and it can be easily implemented without requiring large equipment costs such as adding a burner and changing a gas control system associated therewith, and equipment related thereto.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram illustrating an embodiment of the present invention, in which (a) shows a temperature distribution on a rod surface, and (b) shows how a rod surface is heated by a flame.

FIGS. 2A and 2B show aspects of a second embodiment of the present invention, wherein FIG. 2A shows the temperature distribution on the rod surface, FIG. 2B shows the state of flame heating on the rod surface by a burner, FIG.
(D) is explanatory drawing which shows the change of the flow velocity ratio of the gas to the longitudinal direction of a burner crater.

FIG. 3 shows an embodiment of the present invention, in which (a) shows the temperature distribution on the rod surface, (b) shows the state of flame heating of the rod surface by a burner, (c) shows the crater of the burner,
(D) is explanatory drawing which shows the change of the flow velocity ratio of the gas to the longitudinal direction of a burner crater.

FIG. 4 is a diagram illustrating flame processing such as stretching of a rod and flame polishing using a glass lathe.

5A and 5B are diagrams illustrating a conventional method, in which FIG. 5A is a diagram illustrating a temperature distribution on a rod surface, and FIG. 5B is a diagram illustrating a state of flame heating of a rod surface by a burner.

Continued on the front page (72) Inventor Hideo Hirasawa 2-13-1, Isobe, Annaka-shi, Gunma F-term in Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory 4G015 BA01 BB01 4G021 BA00

Claims (3)

[Claims] 1. An optical fiber preform or an optical fiber preform is heated by a burner flame from one direction while rotating, and a flame processing such as stretching or flame polishing is performed while relatively moving the flame heating position of the burner. When doing
Temperature from 1900 ° C to 1 in the longitudinal direction from the flame heating position
The temperature falling gradient during the fall to 500 ° C.
A method for processing an optical fiber preform and an optical fiber preform, wherein the method is controlled to fall within a range of 1.0 ° C./mm. 2. The optical fiber preform according to claim 1, wherein the temperature drop gradient is obtained by inclining the burner by 60 ° to less than 90 ° with respect to the axis of the optical fiber preform or the optical fiber preform. Processing method of preform for optical fiber. 3. An optical fiber preform or an optical fiber preform is heated by a burner flame from one direction while rotating, and a flame processing such as stretching or flame polishing is performed while relatively moving the flame heating position of the burner. When doing
A method for processing an optical fiber preform and an optical fiber preform, characterized in that the flow rate of gas emitted from the burner is distributed in the direction of relative movement of the burner.