JPH0791079B2 - Method for manufacturing glass base material for optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention is attributed to the non-uniform density distribution of glass microparticles in the production of glass preforms for optical fibers by the vapor phase axial attachment method (VAD method). The present invention proposes a method for manufacturing a glass preform for optical fibers, which effectively reduces the disorder of the refractive index distribution.

[Conventional technology]

In the manufacture of optical fiber glass preform by VAD method,
A method of using a plurality of burners for synthesizing glass fine particles to obtain glass fine particles is generally known. Specifically, it is applied as a method for simultaneously synthesizing a core part and a jacket part in a glass fine particle body for a single mode optical fiber or a glass fine particle body for a multimode optical fiber.

FIG. 1 schematically shows an example of a method for producing glass fine particles for a single mode optical fiber by the VAD method. SiCl ₄ than the core burner 1, GeCl _4, H _2, flowing Ar and O ₂ or the like, and from the class each time the burner 2 and 3 flowed SiCl _4, H _2, Ar, and O _2, etc., producing the glass particles member 4 To do. After that, addition treatment (for example, heat treatment in a fluorine compound atmosphere) or dehydration treatment (for example, heat treatment in a chlorine compound atmosphere) is performed on the obtained glass fine particles 4 for the purpose of changing the refractive index. ) Is performed and further heated to a high temperature to sinter and become transparent vitreous to obtain a glass preform for optical fibers.

[Problems to be solved by the invention]

However, the above method has the following problems. In the VAD method, since glass fine particles are obtained using a plurality of burners, the density of the glass fine particles shows a non-uniform distribution in the radial direction. For example, the density distribution in the radial direction of the glass fine particles obtained by the constitution of FIG. 1 in Examples and Comparative Examples described later is as shown in FIG. 2, and corresponds to the temperature distribution formed by each burner, It has a non-uniform distribution in the radial direction.

If the glass microparticles having such a non-uniform density distribution are subjected to the addition treatment as they are, non-uniform addition corresponding to the density distribution is performed. Further, even in the dehydration treatment, a small amount of chlorine compound is added to the glass fine particles, but in this case as well, it is added unevenly corresponding to the density distribution.

Due to these non-uniform additions or dehydration treatments, the refractive index distribution of the glass base material for optical fibers is undulated and disturbed, and finally the transmission characteristics of the optical fiber, such as dispersion and fracturing frequency, are adversely affected. Become.

The present invention proposes a method for solving the above-mentioned problems all at once.

[Means for solving problems]

The present inventors have considered to improve the above-mentioned non-uniform density distribution of the glass fine particles in order to minimize the disorder of the refractive index distribution in the radial direction of the optical fiber glass preform, and therefore It was found that it is effective to carry out a heat treatment (hereinafter referred to as a preliminary heat treatment) in a non-reactive gas atmosphere before the dehydration treatment of the glass fine particles, and arrived at the present invention.

That is, the present invention, the glass fine particles obtained by the VAD method, after heat treatment in a non-reactive gas atmosphere below the sintering temperature of the glass fine particles to adjust the density, in an atmosphere containing Cl ₂ or a chlorine compound It is a method for producing a glass preform for optical fibers, which is characterized in that it is heat-treated at 1, and further heated to a high temperature to make it transparent.

A particularly preferred embodiment of the present invention is the above method in which the non-reactive gas is any one of N ₂ , O ₂ , He and Ar or a mixed gas of two or more thereof.

Furnace preheating treatment in the present invention, for example, N ₂ or less sintering temperature of the glass, O _2, the He, is carried out in a non-reactive gas atmosphere in alone or in combination of Ar, which is where such a condition Hold it inside or let it pass. This pre-heating treatment is carried out in order to make the density distribution of the glass fine particles uniform, so long as it is a temperature range where this purpose is met and sintering is not performed. One example is 1250 ° C or higher and 1500 ° C or lower. Is. The lower limit of the sintering temperature of the glass fine particles is about 1500 ° C.
Is.

Then performing dehydration treatment, but can not be unconditionally limited because the temperature and other conditions differ significantly by other about dehydration in this case, for example, dehydration by a gas atmosphere containing Cl ₂ at, 800 ° C. or higher Conditions such as holding or passing through a furnace kept at.

After the above-mentioned treatments, the sintered transparent vitrification treatment is performed at a higher temperature to obtain a preform for optical fibers having a uniform refractive index distribution.

〔Example〕

Reference Example With the configuration shown in FIG. 1, SiCl ₄ , H ₂ , Ar, and O ₂ are made to flow from the core burner 1, and SiCl ₄ ,
By flowing H _2, Ar and O _2, soot glass body core portion GeO ₂ 5 wt% -SiO ₂ 95 wt% of the glass, is Kuratsudo portion made of glass of SiO ₂ 100 wt% (diameter 130 mm, length 650mm ) Was manufactured. The density distribution of the glass fine particles was as shown in FIG. The obtained glass fine particles were put into He (flow rate 5
10mm / m in a furnace kept at 1450 ℃ in an atmosphere of
After passing through at a speed of in and pre-heat treatment, the glass fine particles were subjected to SF ₆ (flow rate 100 ml / min), He (flow rate 5 / min)
In a furnace kept at 1000 ° C at a speed of 10 mm / min, and then in a furnace kept at 1650 ° C in an atmosphere of He (flow rate 10 / min). Was passed at a speed of 10 mm / min to obtain a glass preform for optical fibers.

The refractive index distribution of the glass preform for optical fibers is as shown by the curve a (solid line) in FIG. 3, and the preheating treatment before the addition treatment is more effective than the case where the preheating treatment described below is not performed. The amount of change in the density distribution of the glass particles is reduced,
A uniform addition was achieved.

Reference Comparative Example The glass microparticles having the density distribution shown in FIG. 2 produced under the same conditions as in the comparative example were treated in the same manner as in the comparative example except that the preheating treatment was not performed, and the glass preform for optical fiber was prepared. Obtained.

The refractive index distribution of the glass base material for optical fibers is as shown by the curve b (dotted line) in FIG. 3, and it was disturbed with undulations almost corresponding to the density distribution of the glass particles in the cladding.

Example 1 About the glass fine particles having the density distribution shown in FIG. 2 manufactured under the same conditions as in the reference example, 10 mm / g in a furnace kept at 1450 ° C. in an atmosphere of He (flow rate 5 / min). After passing through at a speed of min for preheat treatment, Cl ₂ (flow rate 200 ml / mi
n), He (flow rate 5 / min), at a speed of 10 mm / min through a furnace maintained at 1070 ° C, and then He
A glass base material for optical fibers was obtained by passing the material through a furnace maintained at 1650 ° C in a (flow rate of 10 / min) atmosphere at a speed of 10 mm / min.

The refractive index distribution of the glass base material for optical fibers is shown by a curve c (solid line) in FIG. 4, in which the amount of change in the density distribution of the glass fine particles is reduced by the preheating treatment before the dehydration treatment.
The fluctuation of the refractive index could be reduced by adding ₂ .

Comparative Example 1 A glass preform for optical fibers was prepared by the same process as in Example 1 except that the glass fine particles having the density distribution shown in FIG. 2 manufactured under the same conditions as in the reference example were not preheated. Obtained.

The refractive index distribution of the glass base material for optical fibers shows fluctuations due to the addition of Cl ₂ corresponding to the density distribution of the glass particles in the cladding, as shown by the curve d (broken line) in FIG. Has occurred.

As is clear from the above examples and comparative examples, in the glass fine particles obtained by using a plurality of burners by the VAD method, of the refractive index distribution in the glass preform after transparency derived from the non-uniform density distribution The turbulence can be significantly reduced by the preheating treatment of the present invention.

[Effect of the invention] The present invention is a glass fine particle obtained by the VAD method,
In a non-reactive gas atmosphere, hold or let it pass through a furnace kept at a high temperature to perform a pre-heating treatment to make the density distribution uniform, and then dehydration treatment, then sintering / transparency This is a simple and excellent method for obtaining a glass preform for optical fibers having a uniform refractive index distribution by performing vitrification treatment.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a method for obtaining glass microparticles by the VAD method in Examples and Comparative Examples of the present invention, and FIG. 2 is a graph of glass microparticles used in Examples and Comparative columns of the present invention. 3 is a graph showing a density distribution in the radial direction, and FIGS. 3 and 4 are graphs showing a refractive index distribution at a normalized radius (r / ro) of a glass preform for optical fibers. FIG. 3; Reference example (curve a) and reference comparative example (curve b)
The case of the optical fiber base material obtained in 1. is shown. FIG. 4; Example 1 (curve c) and Comparative Example 1 (curve d)
The case of the optical fiber base material obtained in 1. is shown.

Claims (2)

[Claims] 1. A glass fine particle obtained by the VAD method,
After heat treatment at a temperature not higher than the sintering temperature of the glass fine particles in a non-reactive gas atmosphere to adjust the density, heat treatment is performed in an atmosphere containing Cl ₂ or a chlorine compound, and further heating to a high temperature to make it transparent. A method for producing a glass base material for an optical fiber, which is characterized. 2. The glass preform for optical fibers according to claim 1, wherein the non-reactive gas is any one of N ₂ , O ₂ , He and Ar, or a mixed gas thereof. Manufacturing method.