JP3177308B2 - Manufacturing method of optical fiber preform - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 rod for an optical fiber core, a plastic container is filled with a powder of an optical substance, sealed, and then molded under pressure by a liquid pressure to form a molded body. There is known a method of manufacturing a rod for an optical fiber core by vitrifying a molded product taken out of a plus container into a transparent glass (JP-A-59-198991).
issue).

[0003] Further, as a method of manufacturing an optical fiber preform, a quartz glass rod having a predetermined refractive index is arranged in an elastic plastic mold, and a silica fine particle is filled around the quartz glass rod. A method for producing an optical fiber preform from a molded article by forming a molded article by pressurizing the molded article with a liquid pressure is known (Japanese Unexamined Patent Publication No.
1-256937).

[0004]

By the way, a glass rod for the core of an optical fiber is installed at the center of a mold installed inside the hydrostatic pressurizing apparatus, and quartz is placed around the glass rod in this mold. After filling the system glass powder or its granulated powder,
In the method of producing an optical fiber preform by applying pressure to the powder by applying a liquid pressure and further sintering the obtained compact, the glass rod for the core is displaced (eccentric) during the pressure molding.
In many cases, the core glass rod breaks or breaks at the portion located inside or at the boundary surface (surface) of the powder filling portion. This causes a reduction in the yield of optical fiber preform manufacturing.

The present invention has been made in view of the above circumstances, and has as its object to provide a method for manufacturing an optical fiber preform at a high yield.

[0006]

SUMMARY OF THE INVENTION According to the present invention, there is provided a step of installing a rod-shaped body having at least a central portion thereof serving as a core glass of an optical fiber at a center of a mold installed inside a hydrostatic pressurizing apparatus. Filling a quartz glass powder or a granulated powder thereof around the rod-shaped body in the molding die; and applying a liquid pressure to the powder in the molding die inside a hydrostatic pressure pressing device to form the powder. A method for producing an optical fiber preform, comprising: a molding step for forming a body; and a step of sintering the molded body, wherein the rod-shaped body has both ends protruding from a powder filling portion in the molding die. Installed in the mold,
The molding step is performed so that a liquid pressure is applied to the end face and the side face of the rod-shaped body projection.

As the molding die, a molding die set in a cold isostatic pressing device (CIP device) can be suitably used. Specifically, an upper and lower lid (a rod-shaped support member) made of an elastic material can be used. And a wet-type C comprising a combination of a cylindrical molded rubber mold having a metal support tube disposed outside.
An IP molding die or a wet type molding die composed of a combination of an upper and lower lid (including a rod-shaped support member) made of an elastic body and a cylindrical molded rubber die can be used.

As a material for forming the upper and lower lids of the molding die and the cylindrical molded rubber mold, plastics or rubber having a high elastic modulus is desirable.

As the quartz glass powder or its granulated powder, it is desirable to use a powder obtained by a flame hydrolysis method such as silicon tetrachloride or a direct oxidation method of metallic silicon, or a particle obtained by granulating this powder. Alternatively, a powder obtained by a hydrolysis method of an alkoxysilicon compound or a water glass method can be used.

As the quartz glass powder or the granulated powder thereof, pure quartz glass may be used, or quartz glass mixed with a dopant for an optical fiber may be used.

[0011]

According to the production method of the present invention, the rod is placed in the mold so that both ends protrude from the powder filling portion in the mold, and the rod is molded by applying liquid pressure to the powder in the mold. The molding process is performed such that hydraulic pressure is also applied to the end face and side face of the rod-shaped body projection. Thereby, a uniform pressure in the same direction is applied to the pre-positioned rod during the molding process, so that the concentric displacement (eccentricity of the rod) between the rod and the powder filling portion is suppressed. Non-uniform stress on the rod is also suppressed. As a result, the rod-shaped body can be prevented from being eccentric (positionally displaced) or broken, and furthermore, it is possible to prevent the powder portion of the molded body from being damaged due to the positional deviation, breakage or the like of the rod-shaped body. Therefore, an optical fiber preform can be manufactured with a high yield.

[0012]

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

Embodiment 1 First, as shown in FIG. 1A, a diameter of 14 mm and a length of 50 mm were used.
A rod-shaped body 3 in which a supporting glass rod 2 having a diameter larger than that of the glass rod 1 was attached to both ends of a core glass rod 1 of an optical fiber of 0 mm was produced. The core glass rod 1 is manufactured by a VAD method, which is one of the gas phase methods, and has a cross-sectional area ratio of core: clad = 1: 3 and a refractive index difference ((core-clad) / core). ) Is 0.35%.

Next, as shown in FIG.
A lower rubber lid 5a having a hole in the center is fitted into the lower opening end of the cylindrical molded rubber mold 4 of 0 mm, and a lower rubber lid 5b for waterproofing having a hole in the center in the hole of the lower rubber lid 5a. And the supporting glass rod 2 as one end of the rod 3 was inserted into the hole of the lower rubber lid 5b. As a result, the rod 3 was set on the central axis in the molded rubber mold 4.

Next, as shown in FIG. 1C, a silica granulated powder 6 having an average particle size of about 80 μm is charged into the molded rubber mold 4 and filled while applying vibration. An upper rubber lid 7a having a hole at the center at the end is fitted, an upper rubber lid 7b having a hole at the center is fitted into the hole of the upper rubber lid 7a, and the upper rubber lid 7b is The supporting glass rod 2 as the other end of the rod 3 was inserted into the hole. Thereby, the rod-shaped body 3 was set so that both ends thereof protruded from the silica granulated powder 6 filled in the molding die composed of the molded rubber mold 4, the lower rubber lids 5a and 5b, and the upper rubber lids 7a and 7b. . In this case, both end surfaces of the rod-shaped body 3 were aligned with the lower surfaces of the lower rubber covers 5a and 5b and the upper surfaces of the upper rubber covers 7a and 7b, respectively.

Next, as shown in FIG. 1D, the molding dies 4, 5a, 5b, 7a, 7b, the rod 3 and the granulated silica powder 6 are put into a pressure medium 9 in a pressure vessel 8 of a CIP device. I put it. Water was used as the pressure medium 9. As the pressure medium 9, a liquid other than water, for example, oil such as lubricating oil may be used. Subsequently, the pressure in the pressure vessel 8 was increased and maintained at a molding pressure of 1000 kg / cm ² for about 1 minute, and then the pressure was gradually reduced by spending about 3 minutes. The reason why the pressure is reduced in this way is that in the low pressure region of 200 kg / cm ² or less, cracks are generated in the silica granulated powder 6 due to separation of the molding dies 4, 5a, 5b, 7a, 7b and the silica granulated powder 6. This is to prevent this. As a result, a compact having a diameter of about 90 mm was formed in which the silica granulated powder 6 formed under pressure was arranged around the core glass rod 1 of the rod 3.

The molded body obtained in this way can be used to break the core glass rod 1 of the rod-shaped body 3, break the silica granulated powder 6 part,
There were no cracks or the like, and the eccentricity of the core glass rod 1 of the rod 3 was within 0.5%. This is because a uniform pressure in the same direction is applied to the rod-shaped body 3 when the molded body is formed, so that the concentric deviation between the rod-shaped body 1 and the filling portion of the powder 6 is suppressed and the rod-shaped body 3 is formed. This is due to the fact that the non-uniform stress on 1 is also suppressed.

The obtained molded body is degreased at a temperature of 600 ° C. in the atmosphere, purified and dehydrated at a temperature of 1250 ° C. in an atmosphere containing about 10% by volume of chlorine with respect to helium, and further dehydrated in a helium atmosphere. Was sintered at a temperature of 1600 ° C. to make 6 parts of the silica granulated powder into a transparent glass, thereby producing an optical fiber preform. There were no defects such as bubbles near the interface of the core glass rod 1 portion of the optical fiber preform. Thereafter, the optical fiber preform was drawn by a usual method to manufacture an optical fiber. The obtained optical fiber had characteristics equivalent to those of a single mode optical fiber manufactured by a gas phase method.

Embodiment 2 As shown in FIG. 2 (a), a cylindrical molded rubber mold 4 and a supporting glass rod which is fitted to the lower opening end of the molded rubber mold 4 and is one end of the rod 3 A lower rubber cover 11 having a hole for inserting the center 2 in the center, and a hole for inserting the supporting glass rod 2 which is fitted to the upper open end of the molded rubber mold 4 and is the other end of the rod 3. A molding die including the upper rubber lid 12 provided in the portion was used. In this case, both end surfaces of the rod-shaped body 3 are located in the middle of the holes of the lower rubber cover 11 and the upper rubber cover 12, respectively, and the rubber stoppers 13 for filling the holes of the lower rubber cover 11 and the upper rubber cover 12 are used. Was. Except for this point, the same procedure as in Example 1 was performed. In this case as well, a uniform pressure in the same direction was applied to the end face and the side face of the rod 3 via the rubber stopper 13, the lower rubber lid 11, the upper rubber lid 12, and the like. The same result as in Example 1 was obtained.

Embodiment 3 As shown in FIG. 2 (b), a cylindrical molded rubber mold 4 and a supporting glass rod which is fitted to the lower open end of the molded rubber mold 4 and is one end of the rod 3 A lower rubber cover 14 having a hole for inserting the glass rod 2 at the center, and a hole for inserting the supporting glass rod 2 which is fitted to the upper open end of the molded rubber mold 4 and is the other end of the rod 3. A molding die including the upper rubber lid 15 provided in the portion was used. In this case, both end surfaces of the rod 3 are protruded from the lower surface of the lower rubber cover 14 and the upper surface of the upper rubber lid 15, respectively, and a waterproof rubber sheet 16 is used so as to cover both protruding portions of the rod 3 respectively. . Except for this, when the same procedure was performed as in Example 1, a uniform pressure in the same direction was applied to the end face and the side face of the rod-shaped body 3, and the same result as in Example 1 was obtained.

Embodiment 4 As shown in FIG. 2C, a supporting glass rod 17 having the same diameter as that of the glass rod 1 is attached to both ends of a core glass rod 1 similar to that of the first embodiment.
Was used by welding.

As shown in FIG. 2C, a cylindrical molded rubber mold 4 and a supporting glass rod which is fitted to the lower open end of the molded rubber mold 4 and is one end of the rod 18. 17
The lower rubber lid 19 having a hole at the center thereof for inserting a hole, and the hole for inserting the supporting glass rod 17 which is the other end of the rod-shaped body 18 and which is fitted to the upper open end of the molded rubber mold 4 is located at the center. A molding die composed of the upper rubber lid 20 provided in the above was used. In this case, both end surfaces of the rod 18 were made to coincide with the lower surface of the lower rubber cover 19 and the upper surface of the upper rubber cover 20, respectively.

Other than the above, the same procedure as in Example 1 was carried out, and the same result as in Example 1 was obtained.

Comparative Example 1 As shown in FIG. 3, a rod-shaped body 18 was used, in which a supporting glass rod 17 having the same diameter as the glass rod 1 was attached to both ends of the same core glass rod 1 as in Example 1 by welding. .

Further, as shown in FIG. 3, a cylindrical molded rubber mold 4 and an auxiliary cylindrical metal pipe 21 disposed outside the molded rubber mold 4 and having a hole through which a pressure medium passes are provided. ,
The supporting glass rod 17 which is fitted to the lower opening end of the molded rubber mold 4 and the metal tube 21 and is one end of the rod 18
A metal lower lid 22 having a hollow at the center for inserting
The supporting glass rod 17 which is fitted to the upper opening end of the molded rubber mold 4 and the metal tube 21 and is the other end of the rod 18
A metal mold having a metal upper lid 23 having a hollow at the center portion into which the metal is inserted is used.

Except for this, when the formation of a molded body was attempted in the same manner as in Example 1, the core glass rod 1 of the rod 3 was broken, and the resulting silica granulated powder 6 was damaged. The body percentage was as high as over 70%. The reason is presumed to be that the lower lid 22 and the upper lid 23 were made of metal, so that uniform pressure in the same direction was not applied to both end faces of the rod-shaped body 18 and side faces near both end faces. When an optical fiber preform was manufactured in the same manner as in Example 1 by using the obtained molded product, a large number of bubbles were generated at the interface of the core glass rod 1. Further, when this optical fiber preform was drawn by an ordinary method to produce an optical fiber, the obtained optical fiber was inferior in characteristics to a single mode optical fiber produced by a gas phase method.

[0027]

As described in detail above, according to the present invention, there is provided a method capable of producing an optical fiber preform at a high yield. Such a method is particularly effective when producing a high-quality and large-sized optical fiber preform.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a manufacturing process of an optical fiber preform of Example 1.

FIG. 2 is an explanatory view showing a state of a mold and a rod used in Examples 2 to 4.

FIG. 3 is an explanatory diagram showing a state of a mold and a rod used in Comparative Example 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass rod for optical fiber core, 2,17 ... Glass rod for support, 3,18 ... Bar-shaped body, 4 ... Molding mold (cylindrical molded rubber mold), 5a, 5b, 11, 14, 19 ... Molding Mold (lower rubber lid), 6: Granulated powder of silica glass powder (silica granulated powder), 7a, 7b, 12, 15, 20 ... Mold (upper rubber lid), 8: Pressure vessel, 9: Pressure Medium, 13: rubber stopper, 16: rubber sheet.

Continued on the front page (72) Inventor Mitsuo Sato 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. (72) Inventor Kazuaki Yoshida 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric (56) References JP-A-61-256937 (JP, A) JP-A-4-124043 (JP, A) JP-A-5-58656 (JP, A) JP-B-59-19891 (JP, A) B1) European Patent 553 868 (EP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/00 356 C03B 20/00 C03B 37/012

Claims (1)

(57) [Claims] 1. A step of installing a rod-shaped body at least in the center of which is a glass for an optical fiber core at a center of a molding die installed inside a hydrostatic pressurizing device; A step of filling a quartz glass powder or a granulated powder thereof around a rod-shaped body, and a molding step of applying a liquid pressure to the powder in the molding die to form a molded body inside an isostatic pressing device, Sintering a molded body, comprising: a step of sintering the molded body, wherein the rod-shaped body is installed in the mold so that both ends thereof protrude from a powder filling portion in the mold, The molding step is performed such that liquid pressure is applied to the end face and the side face of the rod-shaped projecting portion.