JP2003002678A - Method for stretching glass rod for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stretching a glass rod for optical fibers capable of stretching a silica glass rod for optical fibers in which as silica glass rod for take-off is not separated from the end of the glass rod for optical fibers. SOLUTION: This method for stretching the glass rod for optical fibers 1 comprising heating and softening to stretch the glass rod for optical fibers 1 having a core 2 containing a dopant in the center comprises forming a silica glass part containing substantially none of the dopant at the end 1a of the glass rod for optical fibers 1, welding the silica glass rod for take-off 12 to the silica glass part, heating and softening the glass rod for optical fibers 1, and pulling the silica glass rod for take-off 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of drawing a glass rod for an optical fiber including a core.

[0002]

2. Description of the Related Art In a single mode optical fiber, in order to improve wavelength dispersion characteristics, two layers of clads around a core containing a dopant such as Ge which enhances the refractive index are provided, and the outer second clad has a refractive index. A clad structure having a larger refractive index than the inner first clad is used. The optical fiber preform used for manufacturing the above-mentioned single mode optical fiber is manufactured by the following method, for example. That is, first, a rod-shaped porous glass intermediate having the composition of the core and the first cladding surrounding the core is synthesized by the VAD method. Then, the porous glass intermediate is dehydrated and sintered to produce a transparent glass intermediate including a core and a first cladding surrounding the core. Then, an external porous glass body is synthesized on the outside of the transparent glass intermediate body, and this is dehydrated and sintered to form a second clad,
The optical fiber base material.

In the above-mentioned method for producing an optical fiber preform, a transparent glass intermediate is stretched to reduce its outer diameter, and then an external porous glass body is synthesized on the outside of the transparent glass intermediate and dehydrated. , And forms a second clad. By stretching in this manner, the thickness of the externally attached porous glass body that can be dehydrated and sintered in a dehydration / sintering furnace having a constant inner diameter is increased, and a predetermined core, first clad and second An optical fiber preform having a clad thickness ratio can be produced.

Conventionally, the transparent glass intermediate has been stretched by the following method. That is, as shown in FIG. 4, a transparent glass intermediate body 1 is set vertically in a heater 11 of an electric furnace, and a quartz glass rod 12 for take-up made of quartz glass is fused to the lower end of the transparent glass intermediate body 1. And then
The transparent quartz glass intermediate body 1 is stretched by lowering the quartz glass rod 12 for taking-up while being heated in an inert atmosphere.

[0005]

However, when the transparent quartz glass rod 12 is lowered while the transparent glass intermediate body 1 is heated to stretch the transparent glass intermediate body 1 as described above, the transparent glass intermediate body 1 is pulled out. There is a problem that the quartz glass rod 12 separates from the transparent glass intermediate body 1 and it becomes difficult to stretch the transparent glass intermediate body 1.

When this phenomenon was examined, it was found that it was based on the following causes. That is, the transparent glass intermediate body 1 produced by the VAD method has a shape in which the core 2 at the center is projected at the end 1a, and the silica glass rod 12 for take-up is mainly the core 2 at the center of the transparent glass intermediate body 1. Connected with. By the way, the core 2 contains a dopant such as Ge and has a lower melting point than the first cladding 3. Therefore, when the transparent glass intermediate body 1 is heated and the quartz glass rod 12 for taking down is lowered, the core 2 of the end portion 1a becomes the first.
Before the first clad 3 is softened before the clad 3, the silica glass rod 12 for take-up fused to the core 2 is detached from the end 1a before the first clad 3 is stretched.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an optical fiber glass rod having a core containing a dopant in the center is softened by heating and stretched. In the stretching method, a quartz glass portion that does not substantially contain the dopant is formed at the end of the glass rod for optical fiber, and a quartz glass rod for take-up is fused to the quartz glass portion to form the glass for optical fiber. A method for stretching a glass rod for an optical fiber, characterized in that the rod is heated and softened and the quartz glass rod for pulling is pulled. Here, the "quartz glass portion substantially not containing the dopant" has a portion having a melting point substantially equal to that of pure quartz, and when the pulling fused silica glass rod is pulled, the pulling quartz glass It means the quartz glass part where the rod does not come off.

The present invention was obtained as a result of earnest experiments. That is, as described above, a quartz glass portion containing substantially no dopant is formed at the end of the optical fiber glass rod, the take-up quartz glass rod is fused thereto, and the optical fiber glass rod is heated and softened. When the pulling quartz glass rod for taking off, only the end of the glass rod for optical fiber does not soften first, so the taking quartz glass rod does not separate from the end of the glass rod for optical fiber, The silica glass rod for optical fiber can be drawn.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory diagram of one embodiment of a method for stretching an optical fiber glass rod according to the present invention. In FIG. 1, a glass rod 1 for an optical fiber
Has an outer diameter of 70 mm, and the central core 2 containing a Ge dopant has a diameter of 17 mm. Further, the glass rod 1 for an optical fiber has a shape in which the end portion 1a is projected with a length of 30 mm. The feature of this embodiment is that the glass rod 1 for an optical fiber is manufactured by the VAD method, the supply of GeCl ₄ gas containing Ge which becomes the dopant of the core 2 is stopped during the synthesis of the end 1a, and the end 1a is a Ge dopant. It is that it is a quartz glass that does not contain.

The optical fiber glass rod 1 was drawn as follows. That is, the optical fiber glass rod 1 is vertically inserted into a tubular electric furnace having an inner diameter of 90 mm,
While heating to 0 ° C. to soften the end portion 1a, the end portion 12a of the silica glass rod 12 for taking-in having an outer diameter of 35 mm inserted from the bottom into the electric furnace is also softened in the same manner, and the end portion 1a is joined to the end portion 1a. 12a is fused. Thereafter, while lowering the optical fiber glass rod 1 in the electric furnace, the highest temperature point is moved upward from the lower side of the optical fiber glass rod 1 to soften it, and the take-up quartz glass rod 12 is lowered,
The glass rod 1 for optical fiber was vertically stretched.

As a result, the optical fiber glass rod 1 can be stretched from a length of 1.0 m to a length of 2.5 m without being separated from the end portion 1a of the optical fiber glass rod 1 by the take-up quartz glass rod 12. did it.

FIG. 2 is an explanatory view of another embodiment. The present embodiment is an optical fiber glass rod 1 similar to that used in the above embodiment, and the core 2 uses a normal optical fiber glass rod 1 containing a Ge dopant up to the end 1a. The feature of this embodiment is that the glass rod 1 for optical fiber is used.
Of the core 2 and the cladding 3 (quartz glass containing no Ge dopant) formed around the core 2 are formed on the end face by removing the protruding end 1a of the That is, the quartz glass rod 12 was fused.

As described above, when the pull-out quartz glass rod 12 is fused to the end portion 1b of the optical fiber glass rod 1, the end portion 12a of the pull-out quartz glass rod 12 becomes the core 3 of the end portion 1b and the core. Fused to both. In this state, while lowering the optical fiber glass rod 1 in the electric furnace, the highest temperature point is moved upward from the lower side of the optical fiber glass rod 1 to soften it, and the take-up quartz glass rod 12 is lowered. When the optical fiber glass rod 1 was stretched, the glass fiber rod for optical fiber 12 could be stretched without the silica glass rod for taking-up 12 separating from the end portion 1b of the glass rod for optical fiber 1.

In this embodiment, the removal of the end portion 1a of the optical fiber glass rod 1 from which the core 2 protrudes is carried out by rotating the rotary blade of diamond. At this time, it is desirable that the core 2 is not cracked, but a slight crack can be removed by surface cleaning by flame polishing after stretching.

FIG. 3 is an explanatory view of still another embodiment. The present embodiment is an optical fiber glass rod 1 similar to that used in the above embodiment, and the core 2 uses a normal optical fiber glass rod 1 containing a Ge dopant up to the end 1a. In this embodiment, the silica glass rod 12 for take-up is fused to the glass rod 1 for optical fiber by the following procedure. That is, 1) The optical fiber glass rod 1 is supported horizontally, the end portion 1a containing Ge from which the core 2 projects is heated by a burner, the softened end portion 1a is removed, and the cladding 3 is exposed on the end surface. After that, the end portion 1b where the clad 3 is exposed is heated and softened, and the quartz glass member 13 (external diameter 35 mm, length 30 mm) containing no disk-shaped Ge therein.
Fuse together. In this state, the quartz glass member 13 is connected to the core 2 and the clad 3 of the optical fiber glass rod 1. 2) Next, the optical fiber glass rod 1 is vertically inserted into the electric furnace so that the quartz glass member 13 is on the lower side.
After that, the silica glass rod 12 for take-up is fused to the silica glass member 13. 3) After that, while lowering the glass rod 1 for optical fiber in the electric furnace, the highest temperature point is set to the glass rod 1 for optical fiber.
When the glass fiber rod for optical fiber 1 is stretched by lowering the quartz glass rod for pulling 12 and moving it upward from the lower side to soften it, the quartz glass rod for pulling 12 and the quartz glass member 13 are glass for optical fiber. The glass rod 1 for an optical fiber could be stretched without separating from the end 1b of the rod 1.

In the present embodiment, the fusion of the quartz glass member 13 to the optical fiber glass rod 1 is performed outside the electric furnace, so this fusion operation can be easily performed. Also,
The quartz glass member 13 and the collecting quartz glass rod 12 are
Since it does not contain Ge and is made of the same material, it can be easily fused in an electric furnace. Alternatively, the take-out quartz glass rod 12 may be directly fused to the optical fiber glass rod 1 outside the electric furnace. However, in this case, since the silica glass rod 12 for taking up has a certain length,
The fusion work is not easy, and the work of inserting it into the electric furnace thereafter is difficult.

[0017]

As described above, according to the present invention, it is possible to extend the silica glass rod for optical fiber without separating the silica glass rod for taking-out from the end portion of the glass rod for optical fiber. There is an effect.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of a method for stretching a glass rod for an optical fiber according to the present invention.

FIG. 2 is an explanatory diagram of another embodiment.

FIG. 3 is an explanatory diagram of still another embodiment.

FIG. 4 is an explanatory view of a conventional method for stretching a glass rod for an optical fiber.

[Explanation of symbols] 1 Glass rod for optical fiber 1a, 1b, 12a Ends 2 cores 3 clad 12 Quartz glass rod for collection 13 Quartz glass member

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yukio Kamura             2-6-1, Marunouchi, Chiyoda-ku, Tokyo             Kawa Electric Industry Co., Ltd. F-term (reference) 4G021 BA00

Claims (3)

[Claims] 1. A method of stretching an optical fiber glass rod having a core containing a dopant in the center thereof, wherein the glass rod for an optical fiber is heated and softened to be stretched and stretched. It is characterized in that a quartz glass portion containing no dopant is formed, a quartz glass rod for taking-up is fused to the quartz glass portion, and the glass rod for optical fiber is heated and softened to pull the taking quartz glass rod. A method for stretching a glass rod for an optical fiber. 2. The silica glass portion containing substantially no dopant is formed by synthesizing the end portion of the glass rod for an optical fiber without supplying the dopant. Method for drawing glass rod for optical fiber. 3. The glass for optical fiber according to claim 1, wherein the quartz glass portion containing substantially no dopant is formed by removing the end portion of the glass rod for optical fiber after synthesis. Method of stretching rod.