JPH03232732A - Production of glass preform for hydrogen-resistant optical fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (A field of application) The present invention relates to a method for manufacturing a glass base material for hydrogen-resistant optical fibers;
In particular, the present invention relates to a method for manufacturing a hydrogen-resistant glass preform for an optical fiber, which provides an optical fiber that is hydrogen-resistant and has no absorption at a wavelength of 1,520 nm, and therefore has low transmission loss at this wavelength.

(Prior art) Optical fibers are made by subjecting gaseous glass raw materials such as silicon tetrachloride to flame hydrolysis in an oxyhydrogen flame and depositing the glass particles generated thereon on a carrier to create a porous glass base material. This is then heated and made into transparent glass to form a glass base material for optical fibers, which is then drawn.

The optical fiber obtained in this way has 700
Very low transmission loss is required over the entire wavelength of ~1,700 mm, but this is because the glass contains a large amount of residual moisture in the form of There is a problem that transmission loss increases.

Therefore, in the production of this glass base material for optical fibers, when the porous glass base material is sintered to become transparent glass, the atmosphere is made to contain helium and chlorine. ) A method of manufacturing a water-free glass base material for optical fibers by replacing one ion with chlorine ion has been proposed (see Japanese Patent Laid-Open No. 149356/1983).

(Problem to be solved by the invention) However, the optical fiber made from the glass base material for optical fiber obtained by such a method has poor hydrogen resistance, and when examining hydrogen resistance in an atmosphere of 100% hydrogen gas, the wavelength 1
, 520 nm.

(Means for Solving the Problems) The present invention relates to a method for manufacturing a hydrogen-resistant glass base material for optical fibers that solves the above-mentioned disadvantages. The glass particles generated by this flame hydrolysis are deposited on a carrier to create a porous glass matrix, which is then heated to a temperature of 1.200°C or less in an atmosphere containing helium, chlorine, and oxygen. 1,2 in the atmosphere
It is characterized in that it is heated to a temperature of 00°C or higher and becomes transparent vitrified.

That is, the inventors have determined that the wavelength of the optical fiber is 1,520n.
As a result of considering a method to solve the absorption of hydrogen gas in m, it was found that this is due to structural defects in the glass base material for optical fibers that are based on the temperature and oxygen content during the reaction when converting the porous glass base material into transparent glass. Considering that the dehydration reaction using chlorine is carried out at low temperature and changing the amount of oxygen, the porous glass base material is dehydrated in an atmosphere containing helium, chlorine, and oxygen. After carrying out the dehydration reaction under mild dehydration reaction conditions of 200°C or lower, the material is then sintered at a temperature of 1,200°C or higher in an oxygen-free helium atmosphere to prevent excessive oxygen reaction, resulting in transparent glass. Having discovered this, they conducted research on the amount of oxygen to be used, etc., and completed the present invention.

This will be explained in further detail below.

(Function) The present invention involves heating transparent vitrification of a porous glass base material made by a known method at 1,200°C or less in an atmosphere containing helium, chlorine, and oxygen, and then heating it at 1,200°C or less in a helium atmosphere. It is heated to a temperature above ℃ and becomes transparent vitrified.

The production of the porous glass base material in the present invention is carried out using the known VAD method.
This may be carried out by a method such as a method or an OVD method. For example, a gaseous glass raw material such as silicon tetrachloride is introduced into an oxyhydrogen flame burner using oxygen gas as a carrier gas, and the glass fine particles generated by flame hydrolysis are transferred to the end surface of a heat-resistant carrier such as a quartz glass rod. It can be manufactured by depositing it on the shaft.

The porous glass base material thus obtained is heated and made into a transparent glass base material to be used as a glass base material for optical fibers. Since it contains water, it is necessary to remove it. Therefore, it is necessary to heat this porous glass base material in a well-known atmosphere containing helium and chlorine gas to replace this moisture with chlorine ions, but in the present invention, this atmosphere is replaced with oxygen gas to control this reaction. It is said to consist of helium and chlorine. In addition, heating in this atmosphere at high temperatures such as 1,200°C or higher tends to cause defects, so dehydration is performed by heating under gentle conditions of 1,200°C or lower, preferably 900 to 1,100°C. Although necessary, the amount of chlorine at this time is preferably 0.1 to 15% by volume, preferably 3 to 10% by volume for dehydration by chlorine ions, and the amount of oxygen is 0.1 to 15% by volume, preferably 3 to 10%.
If it is less than 0.02% by volume, the wavelength in the hydrogen gas test will be 1.52.
Absorption of light with a wavelength of 0 nm occurs, and even if the amount exceeds 5.0% by volume, the absorption increases, so the range is preferably from 0.02 to 5.0% by volume.

In addition, the porous glass base material heat-treated under these conditions is then heated to a high temperature of 1,200°C or higher to become transparent vitrification and used as a glass base material for optical fibers, but the atmosphere at this time is must be carried out in an oxygen-free helium atmosphere in order to prevent excessive reaction in the presence of oxygen, and the heating temperature is preferably 1.200°C or higher, since transparent vitrification of the porous glass base material cannot be achieved at a heating temperature of 1.200°C or lower. It is necessary to carry out the process at 1,300 to 1,700°C.

Optical fibers using the glass base material for optical fibers obtained through heat treatment and transparent vitrification are heat treated in a chlorine gas atmosphere, so they do not contain moisture, and they do not contain moisture in an atmosphere containing oxygen gas. Since it is heated gently inside, it has excellent hydrogen resistance, and hydrogen gas 1
Even when examining hydrogen resistance in an atmosphere of 0.00%, the wavelength is 1.52.
The advantage is that no absorption of 0 nm light occurs.

(Example) Examples of the present invention will be given below.

Example 1.2J27 minutes of hydrogen gas and 3.2J27 minutes of oxygen gas were supplied to a quartz concentric multi-tube oxyhydrogen flame burner for the core to generate an oxyhydrogen flame, and 5 oxygen scum was placed in the center of the burner.
Silicon tetrachloride 31cc/min and germanium tetrachloride 3.5cc with 0cc/min and 20cc/min as carrier gas.
/min, and 8J of hydrogen gas is supplied to a similar cladding burner.
2/min, oxygen gas is supplied at 12°C/min to generate an oxyhydrogen flame, and 380 cc/min of silicon tetrachloride is supplied to the center of the burner using 300 cc/min of oxygen gas as a carrier gas, and this flame is used as a carrier gas. 30rp with a diameter of 20mm as
The glass particles generated by flame hydrolysis are deposited and grown in the axial direction of the carrier by applying it to a quartz glass rod rotating at m.
After operating for 16 hours, eight porous glass preforms with a diameter of 80 mm, a length of 800 mm, and a clad/core ratio of 0.2 were produced.

Next, this porous glass base material was heat-treated in a synthetic quartz heating furnace, and the atmosphere inside the furnace was changed to 55% chlorine gas.
Volume %, oxygen gas 0.01.0.02.0.1.0.
2.1.0.2.0.5.0.10.0% by volume and the rest is helium gas,
After heating at 1,000°C for 1 hour, this was heated and sintered at 1,700°C in a synthetic quartz heating furnace with a helium gas atmosphere, and was made into transparent glass with a diameter of 35 mm and a length of 40 mm.
Eight pieces of glass base material for the core with a diameter of 0 mm were made, and then eight optical fiber preforms were made using the lot-in-tube method.

Finally, after drawing these eight preforms to make optical fibers with a diameter of 125 μm, they were placed in a container containing 100% hydrogen gas and left for 24 hours, and the transmission loss at a wavelength of 1,520 nm was measured. When the correlation with the oxygen gas concentration in the above heat treatment step was investigated, the results shown in FIG. 1 were obtained.

(Effects of the Invention) The present invention relates to a method for manufacturing a hydrogen-resistant glass base material for optical fibers, and this involves using a porous glass base material made by a known method as described above, containing helium, chlorine, and oxygen. This method involves heating the porous glass base material to a temperature of 1.200°C or lower in an atmosphere, and then heating it to a temperature of 1.200°C or higher in a helium atmosphere to make it transparent. 1,200°C in an atmosphere containing helium, chlorine and oxygen prior to vitrification.
Optical fibers made using this method have good hydrogen resistance and have excellent hydrogen resistance as well as dehydration since they are heated under the following gentle conditions.
The advantage is that there is no absorption of light at 20 nm, and the transmission loss at this wavelength is less than 0.3 dB/km.

[Brief explanation of drawings]

Figure 1 shows a correlation graph between oxygen gas concentration and transmission loss at a wavelength of 1,520 nm during the heat treatment process of optical fibers made from the eight optical fiber preforms obtained in the example. .

Claims (1)

[Claims] 1. A gaseous glass raw material is introduced into an oxyhydrogen flame burner, and glass fine particles generated by this flame hydrolysis are deposited on a carrier to create a porous glass base material, which is then heated with helium,
After heating to a temperature of 1,200℃ or less in an atmosphere containing chlorine and oxygen,
, a method for producing a hydrogen-resistant glass preform for optical fiber, which comprises heating it to a temperature of 200° C. or higher to make it transparent vitrified. 2. The method for producing a hydrogen-resistant glass preform for optical fiber according to claim 1, wherein the content of oxygen in the atmosphere is 0.02 to 5.0%.