JPS5899132A - Production of base material for optical fiber - Google Patents

Abstract

PURPOSE:To obtain a base material for homogeneous optical fibers, having good dimensional accuracy and improved reproducibility of refractive index distributions by gelling colloidal silica to make a porous base material and doping metallic ions therein then drying and sintering the base material. CONSTITUTION:Colloidal silica 1 is poured into a glass vessel 2 or the like and the vessel is sealed with a cover 3. The temp. in the vessel is held to allow the silica to gel. The liquid phase content of the gel-like silica is decreased to <=5wt% by providing a fine hole to the cover 3 or the like whereby a porous base material 4 is obtained. The material 4 is immersed in a dopant soln. 6 which is an aq. phosphoric acid soln. or the like in a diffusing tank 5 and is heated to dope metallic ions therein. The base material is taken in an silica tube etc. and heated, dried while gaseous oxygen, etc. is flowed. Then gaseous chlorine is flowed to cause dehydroxylating reaction and further gaseous He or the like is fed to sinter the base material by heating, whereby the optical fiber base material is obtained as a transparent glass body.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a preform for optical fibers, and particularly to a method of manufacturing a preform using a wet method.

The base material for optical fibers is made using highly purified silica by refining raw materials, and various methods are known for producing it. However, it has the disadvantage that it takes time to manufacture and is not suitable for mass production, and it is difficult to make the length of the base material uniform.

It is an object of the present invention to provide a method for manufacturing an optical fiber base material that is homogeneous, has good dimensional accuracy, and can improve the reproducibility of the refractive index distribution, eliminating the drawbacks of the above-mentioned prior art. , its features are a process of gelling colloidal silica in a container, a process of reducing the liquid phase content of gelled silica in the container to 5% or less to obtain a porous matrix, and a porous matrix. The method uses a step of immersing the material in a liquid phase containing metal ions for controlling the refractive index, and a step of drying and then sintering the porous base material to which the metal ions have been added.

1 to 4 are diagrams showing the steps of a method for manufacturing an optical fiber base material according to an embodiment of the present invention, which will be explained below in the order of figure numbers.

Figure 1 shows the gelation of colloidal silica in a prismatic glass container 2, in which colloidal silica with a silica content of 40% by weight (particle size of 300 A' or less) is adjusted to a pH value to control the gelation rate. is adjusted to 4 to 6 and poured into glass container 2.

This glass container 2 is sealed with a lid 3 made of a thin aluminum plate to prevent the intrusion of dust and gas, and is kept warm at 50° C. for gelation. After that, several 1m+9 pores were made in the lid, and 6
The glass container is kept warm at 0° C. to dehydrate it, and the container is removed from the glass container 2 when the weight is measured and about 5% by weight has been dehydrated.

The reason why the amount of water removed was limited to 5% by weight was to prevent the dopant solution from rapidly seeping through and causing cracks when immersed in the dopant solution.

FIG. 2 shows the porous base material formed in the glass container 2 taken out, which is immersed in the dopant solution 6 in the diffusion tank 5 shown in FIG. This dopant solution 6 is heated to 25° C. with a 50-thiphosphoric acid aqueous solution, and the porous base material 4 is immersed in it for several hours. As the dopant solution 6, phosphoric acid,
Boric acid, NaOH.

Aqueous solutions such as K OH, Li OH, Ba (OH) 2 etc. are used, but nitrates such as Pb, C1%Ba1At; chlorides such as Ba, Ca, K, Na, etc.
, , (so 4) B or the like, or a solution of a polar solvent can be used. Furthermore, mixtures thereof, such as an aqueous solution of NaOH-1-KOH, may also be used. The steps up to this point are carried out at a temperature close to room temperature, but if the porous base material 4 is thick, the temperature is gradually raised to increase the diffusion rate.

FIG. 4 is an explanatory diagram of the drying and sintering process of the porous base material 4, in which the porous base material 4 doped with metal ions is a quartz boat 7.
and housed in the quartz tube 8. This quartz tube 8 is surrounded by an electric furnace, and gas can be introduced and circulated through an inlet at the left end. When drying the porous base material 4, in order to avoid rapid dehydration, the porous base material 4 is gradually heated at a temperature of 80° C. or lower while flowing oxygen. The temperature increase rate is 0.
Raise the temperature to 100°C in 5'C/step order.

Next, from the gas inlet of the quartz tube 8 to 800°d, chlorine gas Ot2 is flowed at a rate of 200 ca/= to perform a deOH reaction, and then switched to helium gas at a rate of 50 cc/=.
A transparent glass body was obtained by keeping it warm at 1200° C. for 2 hours while transporting it using #III+. In addition, in the above oxygen gas substitute 9, Ar
A gas such as pN2 can be used, but when a polar solvent such as methanol is used as the dopant solution, it is necessary to flow oxygen gas to oxidize the methyl group and remove it before sintering. .

The method for manufacturing the optical fiber base material of this embodiment provides the following effects.

(1) Glass container 2 containing colloidal silica 1
The dimensions of the optical fiber base material can be arbitrarily determined depending on the dimensions and the amount of colloidal silica 1. Further, the refractive index can be arbitrarily adjusted by adjusting the concentration of the dopant solution 6, etc.

(2) Since the water-containing porous base material 4 is immersed in the dopant solution 6 and the temperature is raised, diffusion is rapid and a large diameter base material can be obtained.

(6) Since there is almost no loss of raw materials and a large number of optical fiber base materials can be manufactured, it is suitable for mass production.

The following is also possible as an application example of the above embodiment. In FIG. 3, the porous base material 4 is immersed in a dopant solution 6 for a long time to uniformly impregnate the center with the dopant metal, and then immersed in pure water to diffuse the dopant metal into the pure water. As a result, a concentration distribution of the dopant metal can be obtained in the porous base material 4. By drying and sintering this porous preform 4 in the same manner as in the above embodiment, a graded optical fiber preform can be obtained.

The method for manufacturing an optical fiber preform of the present invention can produce an optical fiber preform exhibiting a uniform refractive index distribution or a gradient refractive index distribution with good dimensional accuracy and reproducibility of the refractive index distribution by the sol-gel method. , the effect of being suitable for mass production can be obtained.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a glass container in which colloidal silica is gelled, Figure 2 is a front view of the porous base material taken out from the glass container in Figure 1, and Figure 3 is a porous base material 4 with metal. A cross-sectional view of the diffusion tank for doping, Figure 4 shows the drying of the porous base material.
FIG. 2 is a cross-sectional view of an electric furnace using a sintered quartz tube. 1: colloidal silica, 2 glass container, 6: lid, 4:
Porous base material, 5: 2 diffusion tanks, 6: dopant solution, 7: 2 quartz boats, 8: quartz tube, 9: electric furnace.

Claims (1)

[Claims] 1. A step of gelling colloidal silica in a container,
A step of obtaining a porous base material by reducing the liquid phase content of the gelled silica in the container to 5% by weight or less, and immersing the porous base material in a liquid phase containing metal ions for controlling the refractive index. 1. A method for producing an optical fiber preform, comprising: drying the porous preform to which the metal ions have been added, and then sintering the porous preform.