JPH0624781A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To provide a method for producing optical fiber preform capable of efficiently producing the optical fiber preform free from deformation caused by drawing. CONSTITUTION:The method for producing optical fiber preform by passing a porous matrix comprising the powder of quartz through a sintering furnace to sinter the porous matrix is characterized by holding both the ends of the porous matrix for the fixation of the porous matrix and subsequently sintering the porous matrix, while transferring the sintering furnace.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a large preform for optical fibers.

[0002]

2. Description of the Related Art At present, as a method of manufacturing a base material for an optical fiber, a CVD method, an OVD method, a PCVD method, and a VAD
The method has been put to practical use. Among these, the method of manufacturing the porous base material by depositing silica powder is the OVD method or the VAD method.

Another method for producing the above-mentioned porous base material is MSP in Japanese Patent Application No. 60-210539.
(Mechanical Shaped Preform) method has been proposed.
Further, recently, a method has been proposed in which silica-based powder is molded on the outer periphery of a core or a silica rod for core consisting of a core and a part of clad to produce a porous base material. Specifically, Japanese Patent Application No. 4-55572 discloses a method in which silica powder is used as a main raw material, water and a binder are mixed with the powder to plasticize it, and this material is extrusion-molded by a vacuum extruder. ing. Further, Japanese Patent Application No. 2-224732 discloses a method in which silica-based powder is dispersed in water to form a slurry, and the slurry is injected into a water-absorbing mold so that the mold absorbs the water content of the slurry and is molded. There is. Furthermore, Japanese Patent Application No. 3-126723 discloses a method of filling granulated silica-based powder in a rubber mold and performing isostatic pressing. By the way, although such a method has an advantage that a large-sized porous preform can be manufactured at low cost, it is difficult to sinter this porous preform to obtain a preform for optical fibers. There is a problem.

Conventionally, the sintering of the porous base material is carried out in the apparatus shown in FIG. For example, a porous preform 30 manufactured by the VAD method (a preform for a fiber length of 100 km, which is 2.
7 kg), the end portion of the upper support rod 31 supporting the porous base material 30 is grasped by the chuck 32, and the chuck 3
By rotating the drive shaft 33 by the drive motor 34 screwed with 2, the porous preform 30 is gradually pulled down into the core tube 35. At this time, the porous base material 30 is the core tube 35.
The powder is sintered by passing through a region heated by a heating means 36 arranged outside. In addition, the normal core tube 3
The inside of 5 is adjusted to a predetermined atmosphere, and the heating means 36
Is adjusted so that the sintering temperature is 1400 to 1600 ° C.

[0005]

However, a relatively large porous base material is sintered by a conventional method, that is, the porous base material is held only at one end (upper end in FIG. 3). When sintered, the porous base material is stretched and deformed by its own weight during the sintering. If this deformation becomes significant, the porous base material will melt during sintering. In particular, since the porous base material obtained by the above-mentioned method of performing pressure molding is composed of particles having a relatively large particle diameter, it is necessary to raise the sintering temperature. Therefore, the deformation due to the stretching of the porous base material during sintering is further increased.

When an optical fiber is manufactured by subjecting the thus deformed base material for an optical fiber to a drawing process, an optical fiber having an outer diameter variation is obtained. Such an optical fiber cannot exhibit desired optical characteristics.

The above-mentioned deformation during sintering of the optical fiber preform may not be impossible to correct by further heat processing, but the manufacturing process becomes complicated and the manufacturing cost increases. There's a problem.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing an optical fiber preform that can efficiently obtain an optical fiber preform that is not deformed by stretching. .

[0009]

The present invention provides a method for producing an optical fiber preform by sintering the porous preform by passing it through a sintering furnace. , Holding both ends of the porous preform, fixing the porous preform, and sintering the porous preform while moving the sintering furnace to obtain a preform for optical fibers. Provided is a method for producing a characteristic preform for an optical fiber.

The quartz-based powder has a particle size of 0.
It is preferable to use silica powder or the like having a particle size of about 5 to 20 μm.

As the porous base material, various materials such as a porous base material obtained by depositing a silica powder by the VAD method or the OVD method, a porous base material formed by forming the silica powder by the above-described various forming methods, and the like can be used. A porous matrix can be used. In addition, the porous base material is obtained by forming silica powder for clad on the outer periphery of a rod for core prepared in advance by the above-mentioned various methods, and further, integrally molding a part of the core and the clad in advance. It also includes one formed by forming silica powder for cladding on the outer circumference of the rod.

When both ends of the porous base material are gripped, both ends of the porous base material may be directly gripped, or a support rod may be attached to the core rod in advance and the support rod may be gripped.

As a method of moving the sintering furnace, there can be adopted a method of screwing a supporting portion of the sintering furnace to a threaded driving shaft and rotating the driving shaft to move the sintering furnace.

The sintering is carried out under the conditions usually used for sintering a porous preform into an optical fiber preform, for example, in an inert gas atmosphere. Further, in order to uniformly sinter the porous base material, it is preferable to rotate the porous base material.

[0015]

According to the method for producing a base material for an optical fiber of the present invention, both ends of the porous base material are gripped and fixed, and further, the sintering furnace is moved to perform the sintering. It is possible to reliably prevent stretching and deformation during sintering.

[0016]

Embodiments of the present invention will be specifically described below with reference to the drawings.

Example First, the core rod 1 shown in FIG. 1 having a clad / core ratio of 3 by the VAD method, an outer diameter of 16.8 mm and a length of 1 m.
0 was produced. An upper dummy rod 11 and a lower dummy rod 12, which are made of quartz and have an outer diameter of 25 mm and a length of 300 mm, are fusion-bonded to both ends of the core rod 10. A through hole 11a having a diameter of 8 mm is formed at the tip of the upper dummy rod 11.

On the other hand, silica powder 10 having an average particle size of 8 μm
3 parts by weight of polyvinyl alcohol (PA-05 manufactured by Shin-Etsu Chemical Co., Ltd.) as a binder and 67 parts by weight of pure water as a solvent were mixed with 0 part by weight to prepare a slurry, and the slurry was granulated by a spray drying method. Thus, a granulated powder having an average particle size of 100 μm was obtained.

Using this granulated powder in a hydrostatic pressure device,
A porous base material 1 having an outer diameter of 82 mm and a length of 1 m was produced. Then, after drying the porous base material at 110 ° C. for 12 hours,
Degreasing treatment was performed by heating in air at 500 ° C. for 5 hours. Then, a lower support rod 13 made of quartz and having an outer diameter of 25 mm and a length of 1 m was attached to the end of the lower dummy rod 12.

FIG. 2A shows a porous base material 1 having a lower support rod 13 at one end and an upper dummy rod 11 at the other end.
It was attached to the sintering apparatus shown in. Reference numeral 15 in FIG. 2 (A) indicates a base. A support 16 and a lower chuck 17 are placed on the base 15. A base material moving shaft 18 is attached to the upper surface of the support 16, and a sintering furnace moving shaft 19 is attached to the center of the support 16. A base material moving motor 20 is connected to the base material moving shaft 18, and a sintering furnace moving motor 21 is connected to the sintering furnace moving shaft 19. A male screw is threaded on the base material moving shaft 18, and this male screw is screwed with a female screw threaded on the upper chuck arm 22. Further, the shaft 19 for moving the sintering furnace is also externally threaded, and this external screw is used for the sintering furnace arm 2.
It is screwed with the female screw cut in 3.

An upper chuck 24 is connected to the upper chuck arm 22, and the upper chuck 24 is installed right above the lower chuck 17. The porous base material 1 is fixed by the upper chuck 24 and the lower chuck 17. Further, the core tube 25 is aligned and installed so that the porous base material 1 is inserted. Further, a sintering furnace 26 having a through hole in the center is connected to the sintering furnace arm 23, and the furnace core tube 25 is positioned so as to be inserted into the through hole.

First, as shown in FIG. 2 (B), the upper chuck 24 is held by the upper support rod 14 made of quartz, which is fitted with the upper dummy rod 11 of the porous base material 1 and has a common through hole. did. The upper dummy rod 11 of the porous base material 1 is fitted to the upper support rod 14, and the pin 30 made of quartz is inserted into the through hole 11a.
It was inserted and fixed. The base material moving shaft 20 was rotated by the base material moving motor 20, the porous base material 1 was lowered, and the lower support rod 12 was gripped by the lower chuck 17. At this time, the porous base material 1 was held in the core tube 25 for dust prevention. Then, He gas is passed through the furnace core tube 25 to rotate the porous base material 1, and further, the sintering furnace moving shaft 19 is rotated by the sintering furnace moving motor 21 to move the sintering furnace 26 every minute. Raised at 3mm. In this way, the porous base material 1
A base material for an optical fiber was produced by sintering from below at 600 ° C. The obtained optical fiber preform had a weight of 8.5 kg and was not deformed by stretching at all.

Comparative Example A porous base material was prepared in the same manner as in the example. The lower support rod was not attached to this porous base material after the degreasing treatment.

The porous base material is held by the chuck 32 of the apparatus shown in FIG. 3, He gas is passed through the core tube 35 to rotate the porous base material, and the drive motor 34 drives the drive shaft 33. The porous base material was rotated and lowered at 4 mm / min. In this manner, the porous preform was sintered at 1600 ° C. from below to produce a preform for optical fibers. The obtained base material for optical fiber was deformed by stretching due to its own weight and had a substantially gourd shape, which was not suitable for practical use.

In the present embodiment, the case where the porous preform obtained by isostatic pressing is sintered into the preform for optical fiber has been described, but the present invention is not limited to the porous preform obtained by other methods. It can also be applied to the case of sintering a base material into an optical fiber base material.

[0026]

As described above, the method for manufacturing an optical fiber preform according to the present invention can efficiently obtain an optical fiber preform that is not deformed in the longitudinal direction.

[Brief description of drawings]

FIG. 1 is a schematic view showing a porous base material.

FIG. 2A is a schematic view showing an apparatus used in the method for producing a preform for optical fibers of the present invention. (B) is (A)
Partial detail view.

FIG. 3 is a schematic view showing an apparatus used in a conventional method for manufacturing a base material for an optical fiber.

[Explanation of symbols]

10 ... Core rod, 11 ... Upper dummy rod, 11a ... Through hole, 12 ... Lower dummy rod, 13 ... Lower support rod, 14 ... Upper support rod, 15 ... Base, 16 ... Support base, 17 ... Lower chuck, 18 ... Base material moving shaft, 19 ... Sintering furnace moving shaft, 2
0 ... Motor for moving base material, 21 ... Motor for moving sintering furnace, 2
2 ... Upper chuck arm, 23 ... Sintering furnace arm, 24
... upper chuck, 25 ... core tube, 26 ... sintering furnace, 30 ...
pin.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kazuaki Yoshida 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (1)

[Claims] 1. A method for producing an optical fiber preform by passing a porous preform made of quartz-based powder through a sintering furnace to produce an optical fiber preform, wherein both ends of the porous preform are provided. Holding part, fixing the porous preform, and sintering the porous preform while moving the sintering furnace to obtain the preform for optical fiber. Manufacturing method.