JPS61291432A - Production of base material for optical fiber - Google Patents

Abstract

PURPOSE:To obtain a base material for optical fibers having high purity, quality, characteristics and dimensional accuracy, by inserting a transparentized and vitrified glass rod into a semisintered glass pipe and transparentizing and vitrifying the pipe in an atmosphere containing fluorine. CONSTITUTION:For example, a porous glass rod for a core is prepared by the vapor-phase axial deposition (VAD) method, and a porous glass rod and porous glass pipe are semisintered. In the process, the semisintering treatment is carried out to give a hardness such that the rod and pipe may not be broken in the subsequent grind working. The outer and inner peripheral surfaces of the resultant semisintered glass rod and pipe are ground by a mechanical grind ing means to finish the rod and pipe to desired dimensions. The semisintered glass rod is then completely sintered, transparentized and vitrified. The resultant transparent glass rod is inserted into the semisintered glass pipe and the rod-in- pipe is heat-treated in an atmosphere containing fluorine to sinter completely, transparentized and vitrify the semisintered glass pipe.

Description

[Detailed description of the invention] r Industrial application field 1 The present invention relates to a method for manufacturing an optical fiber preform.

rPrior art 1 One of the means for manufacturing optical fiber preforms is to put glass powder raw materials into predetermined molds and press mold them, thereby forming a porous glass rod for the core and a porous glass pipe for the cladding. After manufacturing, there is a method of inserting the porous glass rod into a porous glass pipe and sintering them.

``Problem to be solved by the invention j When press-molding powdered raw materials in the above method, the peripheral area is easy to compress during molding, but the central area is difficult to compress, so each part is not compressed uniformly. In some cases, it becomes difficult to obtain a porous molded product, and the porous molded product is then sintered.

Sintering begins in advance from the periphery of the molded product, and the sintered peripheral portion loses its air permeability, so air bubbles remain inside the molded product, making it impossible to achieve complete transparency.

In addition, during the process of handling the raw material powder, there is a risk that surrounding impurities may be mixed into the raw material powder, making it difficult to obtain a high-purity, high-quality optical fiber preform.

In view of the above-mentioned problems, the present invention aims to provide a method for obtaining an optical fiber preform with high purity, high quality, high characteristics, and high dimensional accuracy.

The present invention provides a method for manufacturing an optical fiber preform by integrating a glass rod for a core and a glass pipe for a cladding, in which fine glass particles are deposited in a predetermined shape. After making a porous glass rod for the core and a porous glass pipe for the cladding, and semi-sintering these porous glass rods and porous glass pipes respectively, the outer peripheral surface and inner surface of the semi-sintered glass rod and semi-sintered glass pipe are The peripheral surface is ground to the desired dimensions, the semi-sintered glass rod after grinding is completely sintered to become transparent glass, and the transparent glass rod is inserted into a semi-sintered glass pipe to contain fluorine. It is characterized by converting semi-sintered glass pipes into transparent glass in an atmosphere.

V Effect 1 In the case of the method of the present invention, a porous glass rod for the core is produced by, for example, the VAD method, and a porous glass pipe for the cladding is produced by, for example, the OVD method.

Porous glass rods made via these methods,
Porous glass pipes are made by homogeneously depositing soot-like glass particles produced by flame hydrolysis, etc., so they have high purity and do not have the non-uniformity of the conventional method (press forming method). .

Next, the porous glass rod and porous glass pipe are semi-sintered, but in this semi-sintering process, these rods and pipes are finished to a hardness that will not be damaged during the subsequent grinding process.

Thereafter, the outer and inner peripheral surfaces of the semi-sintered glass rod and semi-sintered glass pipe obtained above are ground by mechanical grinding means.

In this grinding process, the semi-sintered glass rod and semi-sintered glass pipe can be finished to the desired dimensions without being damaged, and therefore the semi-sintered glass rod and semi-sintered glass pipe can be obtained with high dimensional accuracy in terms of inner and outer diameters. Even if impurities are attached to the surface of these glass pipes, the impurities are removed by the grinding.

After the above grinding, the semi-sintered glass rod is completely sintered to become transparent glass, and the resulting transparent glass rod is inserted into a semi-sintered glass pipe, and the rod-in-pipe is heat-treated in a fluorine-containing atmosphere. By doing this, the semi-sintered glass pipe is completely sintered and turned into transparent glass.

In this way, an optical fiber preform with high purity, high quality, high dimensional accuracy, and high characteristics can be obtained.

rExample 1 Examples of the method of the present invention will be described below with reference to the drawings.

First, a porous glass rod 1a and a porous glass pipe 2a for cladding are manufactured by the vAD method and the OVD method shown in FIGS. 1(a) and 1(b), respectively.

When carrying out the WAD method shown in FIG. 1(A), as is known, a burner U with a multi-tube structure is used to store glass raw materials in a gas phase (sometimes containing dope raw materials in a gas phase), combustion gas, auxiliary combustion gas, and a seal. The soot-like glass particles generated by supplying gas (inert gas) or the like and keeping the burner 11 in a combustion state are injected and deposited on the lower end of the target 12 that rises in a rotating state to form a porous glass rod. 1a is prepared.

When carrying out the OVD method shown in FIG. 1(b), as is known, a burner 13 with a multi-tube structure is filled with a vapor phase glass raw material (sometimes containing a vapor phase dope material), a combustion gas, an auxiliary combustion gas, and a seal. Soot-like glass particles are generated by supplying gas (inert gas) or the like and maintaining the burner 13 in a combustion state. In this case, the burner 1a and the mandrel 14 are aligned in the axial direction of the mandrel 14. The soot-like glass particles are injected and deposited on the outer periphery of the rotating mandrel by relative movement, thereby producing the porous glass pipe 2a.

The thus obtained porous glass loft 1a and porous glass pipe 2a are semi-sintered by heat treatment in a heating furnace (electric furnace) 15 as shown in FIGS. 2(a) and 2(b), and each has a predetermined hardness. This results in a semi-sintered glass rod 1b and a semi-sintered glass pipe 2b.

Note that these semi-sintered glass rod tb and semi-sintered glass pipe 2b have a hardness that can be machined.

Next, as shown in FIGS. 3(a) and 3(b), the outer circumferential surface of the semi-sintered glass rod lb and the inner and outer circumferential surfaces of the semi-sintered glass pipe 2b are ground with the rotary grindstone 1B to obtain the desired outer diameter, inner diameter, etc. Finish to the dimensions.

In addition, when grinding the inner circumferential surface of the semi-sintered glass pipe 2b, the mandrel 14 is pulled out from the axis of the semi-sintered glass pipe 2b, and the inner circumferential surface of the pipe is ground with, for example, a rod-shaped rotating grindstone.

Thereafter, as shown in FIG. 4, the semi-sintered glass rod 1b is inserted into the heating furnace 15 and completely sintered, thereby making the semi-sintered glass rod 1b into a transparent glass rod lc.

Below is a transparent glass rod 1c and a semi-sintered glass pipe 2b.
The semi-sintered glass pipe 2b is made into transparent glass by inserting the rod-in pipe into the heating furnace 15 shown in FIG. The atmosphere in the furnace is made into a fluorine-containing atmosphere, and the glass pipe at the time of transparent vitrification is doped with fluorine.

In this way, the semi-sintered glass pipe 2b also becomes the transparent glass pipe 2c.
Thus, the optical fiber preform 3 shown in FIG. 6 in which the transparent glass rod and the transparent glass pipe are integrated is obtained.

Note that when the semi-sintered glass pipe 2b is made into transparent glass in the rod-in state as described above, deformation of the pipe can be prevented by the rod inside the pipe.

The optical fiber preform 3 is turned into a depressed clad type optical fiber by spinning it using a heated drawing means.

rEffects of the Invention As explained above, when using the method of the present invention, a highly pure and uniform porous glass rod is produced by depositing glass fine particles.
After making a porous glass pipe and semi-sintering these porous glass rods and porous glass pipes to give them a predetermined mechanical strength, the outer peripheral surface and inner peripheral surface of the semi-sintered glass rod and semi-sintered glass pipe are Semi-sintered glass with high dimensional accuracy and no impurities is used for grinding, etc.
A semi-sintered glass pipe is obtained, and since the glass rod after transparent glass is placed inside the semi-sintered glass pipe and the pipe is made into transparent glass, the glass is unlikely to be deformed at this time, and therefore has a purity of 1 quality. An optical fiber preform that can satisfy dimensional accuracy, characteristics, etc. can be obtained, and is especially convenient for manufacturing depressed clad type single mode optical fiber preforms that require a high degree of dimensional accuracy.

[Brief explanation of drawings]

1 to 5 are schematic explanatory diagrams showing the main steps in an embodiment of the method of the present invention, and FIG. 6 is a sectional view of an optical fiber preform manufactured by the method of the present invention. 1a...Porous glass rod tb@-・Fist semi-sintered glass rod 1cφ11・Transparent glass rod 2a...Porous glass pipe 2b...Semi-sintered glass pipe 2c...Transparent glass pipe 3... Optical fiber base material 1111 - Burner 12@... Target 1311... Burner 14 fist... Mandrel 15 - Heating furnace 16 Φ... Rotary grindstone agent Patent attorney Sai Yoshio Fuji No. 1m (A) Figure 2 No. 3WJ (A〉(0) C No. by0 r

Claims (1)

[Claims] In a method of manufacturing an optical fiber base material by integrating a glass rod for the core and a glass pipe for the cladding, glass fine particles are deposited in a predetermined shape to form a porous glass rod for the core and a porous glass for the cladding. After making a pipe and semi-sintering these porous glass rods and porous glass pipes, the outer and inner peripheral surfaces of the semi-sintered glass rods and semi-sintered glass pipes are ground to the desired dimensions, and then After completely sintering the semi-sintered glass rod after grinding and turning it into transparent glass, the transparent glass rod is inserted into a semi-sintered glass pipe, and the semi-sintered glass pipe is turned into transparent glass in an atmosphere containing fluorine. Characteristic method for manufacturing optical fiber preform.