JPH0648762A - Production of preformed material for optical fiber - Google Patents

Abstract

PURPOSE:To provide a production method enabling high-quality and large-sized preformed material for optical fibers to be obtained in high efficiency. CONSTITUTION:A form 12 is made using silica powder on the outer periphery of a glass rod made of silica material to make a porous preformed material, which is then sintered to produce the objective preformed material for optical fibers. In this case, the glass rod has, at least at one end, such portion(s) 11 as to be larger in diameter than the rod, the form 12 being made on the outer peripheral region of the rod 10 including the portion(s) 11.

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 Conventionally, as a method of manufacturing a base material for an optical fiber, a pressure molding method disclosed in Japanese Patent Laid-Open No. 61-256937 and a vacuum proposed in Japanese Patent Application No. 2-244815. Extrusion method, JP-A-64-563
A method is used in which a porous base material is produced by the slurry casting method disclosed in Japanese Patent No. 31 and the porous base material is sintered.

When manufacturing a porous base material, as shown in FIG. 3 (A), the support rods 31 are provided on both ends of the glass rod for core 30.
Attached, and the silica-based powder 3 on the outer circumference of the glass rod 30 for core.
2 is formed, or as shown in FIG. 3 (B), a support rod 33 or a protrusion 34 having a diameter larger than the diameter of the glass rod for core 30 is attached to both ends of the glass rod for core 30 to support it. A silica-based powder 32 is molded on the outer periphery of the glass rod 30 for core excluding the rod 33 and the protrusion 34.

[0004]

However, as shown in FIG.
When the porous base material is manufactured by the method as shown in (A) and (B), the adhesion between the glass rod for core and the molded body formed on the outer periphery of the porous base material is poor. In the refining process, the dehydration process, and the sintering process, the molded body shifts along the glass rod for core. In particular, in the sintering step, before the core glass rod-shaped body and the molded body are completely integrated into glass, the core glass rod-shaped body may elongate and the molded body may fall off. Also, bubbles are generated at the interface between the glass rod-shaped body for core and the molded body,
Inconsistencies may occur.

An optical fiber obtained by drawing such an optical fiber preform has remarkably poor optical characteristics. This tendency is particularly remarkable in a large-sized optical fiber preform having a weight of 5 kg or more and a fiber length of more than 100 km / piece. Such a problem occurs regardless of the molding method such as the pressure molding method, the vacuum extrusion method, and the slurry casting method.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of manufacturing an optical fiber preform capable of efficiently obtaining a large-sized optical fiber preform of high quality. .

[0007]

According to the present invention, a porous base material is produced by forming a molded body using a silica-based powder on the outer periphery of a rod-shaped body made of a silica-based material, and firing the porous base material. In the method of producing a preform for optical fibers by subjecting to a binding treatment, the rod-shaped body has a portion having a diameter larger than the diameter of the rod-shaped body at least at one end thereof, and the molded body has the large-diameter portion. A method for manufacturing an optical fiber preform, characterized in that the optical fiber preform is formed in an outer peripheral region of the rod-shaped body including.

As the rod-shaped body made of a quartz material, a glass rod-shaped body having an arbitrary refractive index conventionally used for manufacturing an optical fiber can be used. This rod is
Although it may be formed only of the core material or may be formed of the core material and a part of the clad material, the rod-shaped body is preferably formed of the core material and a part of the clad material.

There is no particular limitation on the shape of the portion of the rod-shaped body having a diameter larger than the diameter of the rod-shaped body (hereinafter abbreviated as the large diameter portion).

As the silica-based powder, it is possible to use silica powder obtained by hydrolysis of an alkoxy compound or a water glass method, silica powder doped for adjusting the refractive index, and the like. Preferred quartz-based powders are powders of silicon tetrachloride obtained by a flame hydrolysis method, metallic silicon obtained by a dry method such as a direct oxidation method, or particles obtained by granulating this powder.

When forming a molded body in the outer peripheral region of a rod-shaped body including a large diameter portion, a molded body 12 is formed in a region including both large diameter portions 11 of the rod-shaped body 10 as shown in FIG. 1 (A). Alternatively, as shown in FIGS. 1B and 1C, the molded body 12 may be formed in a region including one large diameter portion 11. In this case, the other large-diameter portion that does not form the molded body 12 is
It may be a protrusion 13 as shown in FIG. Also,
As shown in FIG. 1C, the molded body 12 may be formed up to the stepped portion 14 constituted by the rod-shaped body 10 and the large diameter portion 11. Further, as shown in FIG. 1 (D), the molded body 12 may be formed by embedding the entire one large diameter portion. The large diameter portion may be formed directly on the rod-shaped body, or may be formed by attaching a support rod having a large diameter portion to one end or both ends of the rod-shaped body.

As a method for forming a molded body on the outer periphery of a rod-shaped body, a pressure molding method disclosed in Japanese Patent Application Laid-Open No. 61-256937 and an extrusion method proposed in Japanese Patent Application No. 2-244815. Molding method, JP-A-64-56
Examples thereof include a slurry casting method disclosed in Japanese Patent No. 331.

As a molding die used for forming a molded body, a CIP such as a wet type CIP molding die including an upper and lower lids having a rod-shaped support, a molded rubber die, and a metal outer tube. It is possible to use a molding die installed in a molding apparatus, or a dry type molding die composed of an upper and lower lids having a rod-shaped support and a molding rubber die.

[0014]

According to the method for producing a base material for an optical fiber of the present invention, a rod-shaped body made of a quartz material having a large diameter portion at least at one end is used, and a molded body is formed in the outer peripheral region of the rod-shaped body including the large diameter portion. Since this is formed, the binding force between the rod-shaped body and the molded body is further improved. As a result, in the degreasing process for removing the molding aid from the molded product, the purification / dehydration process for removing impurities from the molded product, and the subsequent sintering process, the molded product shifts along the glass rod for the optical fiber core. Can be prevented.

Further, since the elongation of the rod-shaped body at the time of sintering is suppressed, generation of bubbles and inconsistency in the vicinity of the interface between the rod-shaped body and the molded body are eliminated. Therefore, the optical fiber drawn from the obtained optical fiber preform exhibits excellent transmission characteristics.

[0016]

【Example】

Example 1 As shown in FIG. 2, a core-clad ratio of 1: 3 produced by the VAD method, a refractive index difference of 0.35%, an outer diameter of 14 mm, and a diameter of 500 mm at both ends of a core glass rod 20. A glass rod 21 having a length of 800 mm was prepared by attaching a supporting glass rod 21 of 25 mm.

This glass rod was placed in the center of the lower rubber lid 22, and a cylindrical rubber mold 23 having an inner diameter of 110 mm and a length of 800 mm (however, the filling portion had a length of 580 mm) was attached.
A silica granulated powder 24 having an average particle diameter of 80 μm was put into a filling portion constituted by the lower rubber lid 22 and the rubber mold 23, and was filled while vibrating. Next, after attaching the upper rubber lid 25, waterproofing is performed, and this is subjected to a hydrostatic pressure device (CI).
(P apparatus) 26, and pressure molding was performed to form a molded body on the outer periphery of the glass rod for core 20 to manufacture a porous base material. At this time, the molding conditions are a pressure of 1.0 (t / cm ² ),
The molding time was about 1 minute. When decompressing, 200kg /
Since a low-pressure part of cm ² or less often cracks when the molded body and the rubber mold are separated from each other, the pressure was gradually reduced by spending about 3 minutes. The obtained porous base material has an outer diameter of about 90 mm,
The weight was about 5 kg.

After degreasing this porous base material at 600 ° C. in the atmosphere, it is purified (including dehydration) at 1250 ° C. in a helium gas atmosphere containing about 10% chlorine, and further in a helium atmosphere at 1600 ° C. Was sintered to prepare an optical fiber preform. At this time, in the degreasing, dehydration and sintering steps, no dropout of the molded body was confirmed.

The obtained optical fiber preform has an outer diameter of about 7
It was 0 mm, and there were no bubbles or the like near the interface between the core glass rod and the clad material. When this was drawn by a usual method to manufacture an optical fiber and its transmission characteristics were examined, it was equivalent to a single mode fiber prepared by a vapor phase method.

Example 2 A glass rod for support having a diameter of 35 mm was attached to both ends of a glass rod for core having the same optical conditions as in Example 1, and a total length of 145.
A 0 mm glass rod was made. Using this glass rod, a large-sized porous base material having a length of 1200 mm was produced in the same manner as in Example 1. At this time, the molding conditions are pressure 1.5 (t / cm
² ) The molding time was 1 minute. The obtained porous matrix is
The weight was about 11 kg.

This porous preform was degreased, dehydrated and sintered in the same manner as in Example 1 to prepare an optical fiber preform.
Also in this case, no dropout of the molded body was confirmed in the degreasing, refining (including dehydration) and sintering steps.

The obtained optical fiber preform has an outer diameter of 70.
mm, and there were no bubbles or the like near the interface between the glass rod for core and the clad material. When this was drawn by a usual method to manufacture an optical fiber and its transmission characteristics were examined, it was equivalent to a single mode fiber prepared by a vapor phase method.

Comparative Example A glass rod having a constant diameter was used in place of the glass rod for core used in Examples 1 and 2, and a porous base material (outer diameter of about 70 mm, length) was used in the same manner as in Example 1. 580 mm, an outer diameter of about 70 mm, and a length of 1000 mm) were prepared, and degreasing, refining (including dehydration), and sintering were performed under the same conditions as in Example 1 to prepare an optical fiber preform.

However, in this case, since the adhesion at the interface between the glass rod for core and the molded body made of silica powder formed on the outer periphery thereof is insufficient, a degreasing step for removing the molding aid from the molded body, In the refining / dehydration step of removing impurities from the molded body and the subsequent sintering step, the molded body was displaced along the glass rod for core. The ratio was about 60% or more.

Further, during sintering, the glass rod serving as the core was elongated, and as a result, bubbles and inconsistency (a portion with insufficient adhesion) were generated near the interface between the glass rod and the molded body.
In addition, this optical fiber preform is drawn in the usual way,
The transmission characteristics were investigated, but it was inferior to the single mode fiber prepared by the vapor phase method.

[0026]

As described above, according to the method for producing a base material for an optical fiber of the present invention, the adhesion between the rod-shaped body for core and the molded body formed on the outer periphery thereof, that is, the bonding force is improved. A high-quality, large-sized optical fiber preform can be efficiently obtained.

[Brief description of drawings]

1 (A) to 1 (D) are explanatory views showing a porous base material in the method of the present invention.

FIG. 2 is a schematic diagram showing an apparatus used in the method of the present invention.

3A and 3B are explanatory views showing a porous base material in a conventional method.

[Explanation of Codes] 10 ... Rod-shaped body, 11 ... Large diameter portion, 12 ... Molded body, 13 ... Projection body, 14 ... Step portion, 20 ... Core glass rod, 21 ... Support glass rod, 22 ... Lower rubber lid , 23 ... rubber mold, 24 ...
Silica granulated powder, 25 ... Upper rubber lid, 26 ... Hydrostatic pressure device (CIP device).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Sato 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Kazuaki Yoshida 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (1)

[Claims] 1. A porous base material is produced by forming a molded body using a silica-based powder on the outer periphery of a rod-shaped body made of a silica-based material,
In the method for producing an optical fiber preform by subjecting the porous preform to a sintering treatment, the rod-shaped body has a portion having a diameter larger than the diameter of the rod-shaped body at least at one end thereof, and A method for manufacturing an optical fiber preform, wherein a molded body is formed in an outer peripheral region of the rod-shaped body including the large-diameter portion.