JPH06144862A - Production of perform for optical fiber - Google Patents

Abstract

PURPOSE:To produce a preform for optical fiber, capable of providing a preform for optical fiber having no separation of core material from a molded article formed on the outside of the core material, no cracking, no fragment, no crack, etc., and low content of impurities. CONSTITUTION:A production of a preform for optical fiber comprises a process for fitting a core material composed of a quartz-based material to a mold and packing quartz-based powder to the mold, a process for molding the quartz- based powder under pressure to give a porous preform and a process for purifying and transparently vitrifying the porous preform to give a preform for optical fiber. In the operation, quartz-based powder having an average particle diameter smaller than that of quartz-based powder used in the region except the region including both the ends of the porous preform is used as the quartz-based powder used in a region including both the ends of the porous preform.

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 an optical fiber preform.

[0002]

2. Description of the Related Art As a conventional method for producing a base material for optical fibers, a core material made of a silica-based material is placed in a mold having elasticity, and the mold is filled with silica-based powder. A method is used in which a molded body is formed on the outside of a core material by pressurizing a mold to produce a porous base material, and the porous base material is purified and vitrified to obtain an optical fiber base material. . As such a pressure molding method, an isotropic hydrostatic pressure method (CIP method: Cold Isostatic Pressing) is mainly used.

Generally, the silica-based powder used in the method involving pressure molding as described above, especially the silica-based powder used in the CIP method, is a granulated powder for facilitating filling into a molding die. Often used. When molding using a silica-based powder, if the average particle size of the primary particles is large, the strength of the resulting porous base material decreases, so depending on the average particle size of the silica-based powder to be used, it may occur during granulation. A molding aid is added.

Usually, in order to obtain a porous base material having sufficient strength without adding a molding aid to silica powder, especially silica powder, the average particle size of silica powder before granulation is particularly 1 μm or less. preferable. However, since the porous base material obtained by using the powder having the average particle diameter of 1 μm or less has a small average pore diameter, it is very difficult to remove impurities contained in the porous base material. . This tendency is particularly noticeable when a large-sized optical fiber preform is obtained. The impurities that have not been removed cause a transmission loss increase in an optical fiber obtained by drawing the optical fiber preform by refining the porous preform and making it into a transparent glass.

On the other hand, in order to facilitate the removal of impurities, the average particle size of the silica powder before granulation is at least 5 μm.
The above is desirable. However, in order to granulate a powder having an average particle size of 5 μm or more, a molding aid must be used to improve the strength of the porous base material. When the molding aid is added, the obtained porous base material must be subjected to heat treatment to remove the molding aid (degreasing treatment). Also, since the average particle size of the powder used is large, the adhesion between the molded body and the core material is poor, and since the strength of the molded body itself is low, cracks, chips, cracks, etc. may occur when external force is applied. It is easy to occur. Therefore, there is a problem that the yield in obtaining an optical fiber preform by converting the porous preform into transparent glass is very poor.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above points, and there is no peeling between the core material and the molded body formed on the outside thereof, and there is no crack, chip, crack or the like. It is an object of the present invention to provide a method for manufacturing an optical fiber preform that can efficiently obtain an optical fiber preform with few impurities.

[0007]

According to the present invention, there is provided a step of mounting a core material made of a quartz material on a molding die and filling the molding die with the silica powder, and press-molding the quartz powder. In a method for manufacturing an optical fiber preform, which comprises a step of obtaining a porous preform and a step of purifying and vitrifying the porous preform to obtain an optical fiber preform, both ends of the porous preform are provided. As the silica-based powder used in the region containing the powder, one having an average particle size smaller than the average particle size of the silica-based powder used in the region other than the region including both ends of the porous base material is used. A method for manufacturing a base material for an optical fiber is provided.

In this case, it is preferable to use, as the silica-based powder used in the region including both ends of the porous matrix, one having an average particle diameter of 1 μm or less.

Here, the core material made of a quartz material is
The core rod is used alone, or the support rod is attached to at least one end of the core rod, and the core rod also includes a part of the clad material outside the core material. In addition to the transparent glass material, the core rod includes a porous body.

As the silica powder, silica powder, doped silica powder containing a refractive index adjusting dopant, and the like can be used.

For the purification and vitrification of the porous molded body, the conditions generally used are adopted.

In the present invention, the region including both ends of the porous base material means, for example, the tapered portion 11 in the porous base material 10 shown in FIG. Further, the region other than the region including both ends of the porous base material refers to, for example, the cylindrical portion 12 in the porous base material 10 shown in FIG.

The average particle diameter of the primary particles of the silica-based powder used in the area including both ends of the porous base material is the primary particle of the silica-based powder used in areas other than the area including both ends of the porous base material. The average particle size is smaller than the average particle size. In this case, the average particle diameter of the primary particles of the silica-based powder used in the area including both ends of the porous base material is 1 μm or less, and the average particle diameter of the silica-based powder used in the areas other than the area including both ends of the porous base material is The average particle diameter of the primary particles is preferably 5 μm or more.

In the present invention, the silica-based powder used for the taper portion can sufficiently exert its effect even if a molding aid is not added during granulation.

[0015]

In the method for producing an optical fiber preform according to the present invention, the primary particles of the silica-based powder used in the region including both ends of the porous preform are used in the region other than the region including both ends of the porous preform. The silica-based powder used is characterized by having an average particle size smaller than the average particle size of the primary particles.

The primary particles of the silica-based powder having a relatively small average particle diameter used in the region including both ends of the porous base material are firmly adhered to the core material by pressure molding. Therefore, even if the molded body formed in a region other than the region including both ends of the porous base material has poor adhesion to the core material, the molded body in the region including both ends of the porous base material firmly adheres to the core material. Since they are in close contact, this part plays a role of non-slip, and prevents the molded body from peeling off from the core material and falling off. In addition, since the strength of the region including both ends of the porous base material is increased, the occurrence of cracks, chips, cracks, etc. during handling is prevented.

On the other hand, since the primary particles of the silica-based powder having a relatively large average particle diameter are used in the area other than the area including both ends of the porous base material, the average pore diameter becomes large and the impurities can be removed by the heat treatment. It will be easy.

[0018]

EXAMPLES Examples of the present invention will be specifically described below.

Embodiment An embodiment of the present invention will be described with reference to FIG.

First, pure water was added to a commercially available quartz glass powder having an average particle size of 0.4 μm to prepare a slurry having a concentration of 60%. NH ₃ was added to this slurry to adjust the pH to 8.4, and this slurry was mixed at 45 ° C. for 12 hours. The obtained slurry was spray-dried at 110 ° C. to obtain solid first granulated particles 20 having an average particle size of 92 μm.

Then, pure water and 3% by weight of polyvinyl alcohol relative to the quartz glass powder as a molding aid were added to a commercially available quartz glass powder having an average particle size of 15 μm to prepare a slurry having a concentration of 60%. Add this slurry to 14
By spray drying at 0 ° C., second granulated particles 21 having an average particle size of 150 μm were obtained.

On the other hand, it is made of urethane and has an inner diameter of 70 mm,
Lower lid 2 of molded rubber mold 22 having a cylindrical portion with a length of 300 mm
The quartz glass rod 24 was inserted into the rod insertion hole of No. 3.
The quartz glass rod 24 is made by manufacturing a glass rod by the VAD method and connecting supporting rods to both ends thereof. The quartz glass rod 24 has an outer diameter of 7.
The length was about 5 mm, the length was about 300 mm, the relative refractive index difference was about 0.35%, and the clad / core ratio was 3.0.

Next, while the lower lid 23 is vibrated by the vibrator (not shown) of the first granulated particles 20 obtained as described above in the molding rubber die 22, the taper region of the lower lid 23 is formed. Filled. Then, the second granulated particles 21 obtained as described above are placed on the first granulated particles 20 with the lower lid 23.
While being oscillated by a vibrating machine, the cylindrical area of the mold was filled. Further, the first granulated particles 20 were filled in the same manner as above on the portion corresponding to the tapered region of the upper lid 25 described later, that is, on the second granulated particles 21.

After that, the upper lid 25 was attached to the mold 22. This whole is installed in the pressurizing device 26, and the pressurizing device 26
Water 27 was charged therein as a pressure medium, the pressure was increased to 1.0 ton / cm ² for 1 minute, and then the pressure was gradually reduced in 20 minutes. After the pressure reduction was completed, the molded rubber mold including the upper and lower lids was taken out from the pressure device 26, the upper lid 25 was removed, and the porous base material was taken out. No cracks or splits have occurred in this porous base material,
It was also confirmed that the quartz glass rod 24 did not crack. The outer diameter of this porous matrix was about 55 mm.

Next, in order to remove the molding aid contained in the porous base material, N ₂ / O ₂ = 8/2 was added to the porous base material.
(L / min), heating rate 5 ° C / min, degreasing temperature 500
Degreasing treatment was performed at 5 ° C. for 5 hours. In the degreased porous base material, the first granulated particles used for the upper and lower taper portions fixed the upper and lower ends of the porous base material, so that the molded body of the cylindrical portion did not fall off.

Finally, the degreased porous base material is heated to a temperature of 125.
Subjected to purification treatment at 0 ° C. under He and Cl ₂ atmosphere,
Subsequently, a transparent vitrification treatment was performed at a temperature of 1580 ° C. in a He atmosphere. The obtained optical fiber preform had no cracks or bubbles at the interface between the tapered portion and the cylindrical portion.

Comparative Example Second granulated particles 21 as granulated particles to be filled in the molding die.
A porous base material was produced in the same manner as in the example except that only the base material was used. In order to remove the molding aid from this porous base material, the porous base material was subjected to a degreasing treatment in the same manner as in the example. After that, when the porous base material after degreasing was subjected to a refining treatment and a transparent vitrification treatment, it was tried to put this porous base material into a treatment furnace, and the adhesion between the quartz glass rod and the molded body was poor. Since the molded body fell off from the quartz glass rod, the optical fiber preform could not be obtained.

[0028]

As described above, 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 used as primary particles of silica-based powder used in a region including both ends of the porous base material. Since the one having an average particle size smaller than the average particle size of the primary particles of the silica-based powder used in the region other than the containing region is used, there is no separation between the core material and the molded body formed on the outside thereof, and It is possible to efficiently obtain a preform for optical fibers, which is free from cracks, chips, cracks and the like and has few impurities.

[Brief description of drawings]

FIG. 1 is a front view showing a porous base material used in the method of the present invention.

FIG. 2 is a schematic view showing a part of a pressure device used in the method of the present invention.

[Explanation of symbols]

10 ... Porous base material, 11 ... Tapered portion, 12 ... Cylindrical portion, 2
0 ... 1st granulated particle, 21 ... 2nd granulated particle, 22 ... Molding rubber mold, 23 ... Lower lid, 24 ... Quartz glass rod, 25
... Top cover, 26 ... Pressurizing device, 27 ... Water.

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

Claims (2)

[Claims] 1. A step of mounting a core material made of a silica-based material in a molding die and filling the molding die with silica-based powder, and a step of press-molding the silica-based powder to obtain a porous base material. In the method for producing an optical fiber preform, the step of purifying the transparent preform to obtain a transparent vitrification to obtain an optical fiber preform, quartz used in a region including both ends of the porous preform. As the base powder, an optical fiber base material characterized by using an average particle diameter smaller than the average particle diameter of the silica-based powder used in a region other than a region including both ends of the porous base material Production method. 2. The method for producing an optical fiber preform according to claim 1, wherein the silica-based powder used in a region including both ends of the porous preform has an average particle diameter of 1 μm or less.