JPS62167238A - Production of base material for optical fiber - Google Patents

Abstract

PURPOSE:To precisely regulate the refractive index distribution with an inexpensive device by controlling the rotational frequency of a starting material to regulate the refractive index distribution when an optical fiber base material is produced by the VAD method. CONSTITUTION:A gaseous glass material, a combustion gas, a combustion improving gas, a carrier gas, etc., are sent from a burner 2, the glass material is flame-hydrolyzed in an oxyhydrogen flame 3, the formed fine glass particles are deposited on the rotating starting material 6, and a porous glass body 1 is produced. In this case, the distribution of the surface temps. of the porous base material 1 and the gas passage are controlled by changing the rotational speed of the starting material 6, the concn. of an additive for regulating the refractive index such as P, F, and Ge to be added to the porous base material 1 is controlled, and hence the shape of the refractive index distribution in the optical fiber core is controlled. When the rotational speed of the starting material 6 is increased, the distribution index of the refractive indexes of the base material 1 is proportionally increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling refractive index distribution when manufacturing an optical fiber base material by the MAD method.

[Conventional technology]

One of the manufacturing methods for glass base materials for optical fibers is the vapor phase axial method (VAD method).
There is a deposition method (deposition method), which is an excellent method for efficiently producing a high-quality glass base material.

In this method, as shown in FIG. 1, frit gas, combustion gas, auxiliary combustion gas, carrier gas, etc. are flowed from a burner 2, and frit 4 is flame-hydrolyzed in an oxyhydrogen flame 5 to produce glass. In this method, a glass fine particle deposit (porous base material) 1 is obtained by depositing fine particles on a support whose central axis is a rotating shaft 6.

When manufacturing a base material for optical fiber, especially when manufacturing a base material for 1 grade index fiber (Gl fiber), it is possible to arbitrarily control the refractive index distribution.
This is an essential technology. Regarding the refractive index distribution of a GI type fiber, for example, the following equation (1) holds true, where the index i: the refractive index difference at ri; the maximum refractive index difference a: the core radius α is called the refractive index distribution index.

This occurs as shown in Figure 2. In Figure 2, when α on the solid line A gets smaller, it becomes like the dashed line, and α
When becomes larger, it becomes a chain line.

C) For type I fibers, there is an optimal α value depending on the wavelength of the light used, and the closer the α value of the actual fiber is to the optimal value, the wider the band of the fiber will be.
Controlling the α value is a critical issue.

Conventionally, in the VAD method, as a method for controlling this refractive index distribution, (1) the flow rate of raw material such as 5ick blown out from a burner is controlled.

■ Control the amount of O, H, blown out from the burner.

■ Control the burner position.

Such methods are known.

[Problem that the invention seeks to solve]

However, in order to minutely adjust the refractive index distribution using the methods described in (1) to (3) above, a high-precision flow rate control device or a high-precision fine adjustment table is required, which inevitably leads to expensive manufacturing equipment and, of course, manufacturing costs. The drawback was that it was expensive.

The present invention provides an inexpensive and effective method for controlling refractive index distribution in the production of optical fiber preforms using the VAD method.

[Means for solving problems]

The present invention provides a method for producing an optical fiber base material in which a porous glass body is obtained by introducing glass raw material gas into a flame and depositing glass particles generated by flame hydrolysis on a rotating starting material. A method for manufacturing an optical fiber base material, characterized in that the refractive index distribution is adjusted by controlling the rotation speed of the starting material.

Ge is used in the production of optical fiber base materials in the VAD method.
, P, F and other refractive index adjusting additives in S10! Although the mechanism of addition to the porous base material consisting of
It is thought that the surface temperature distribution of the surface has a major influence.

The present invention controls the surface temperature distribution and gas flow path of the porous base material by changing the rotation speed of the porous base material that continues to rotate.
It controls the concentration of P, F, etc., and in turn controls the refractive index distribution shape within the optical fiber core.

〔Example〕

Example 1 Raw material gas: 5iC24240 medium, GeC4150
(Xy”h.

pocts 2 Other gases: H, t8t/min, O, &Ot/min, Ar
Refractive index distribution of transparent base material obtained by producing a porous base material with a length of 301 by VAD method under the conditions of 1.4 t/min He470 CC/min rotation speed: 30 rpm, dehydrating and sintering was measured. As a result, the refractive index index of this base material was 1.
It was 95.

Example 2 The refractive index distribution was measured under the same conditions as in Example 1, with the rotational speed changed to 50 rpm, and the same method as in Example 1, and the refractive index distribution index α was 2-02. Ta.

Example 3 Similar to Example 2, the rotation speed was changed to 70 rpm, and the refractive index distribution index α was 2.10.

The results of Examples 1 to 3 are summarized in FIG. 3, in which the horizontal axis represents the rotational speed of the porous base material and the vertical axis represents the refractive index distribution index α. As is clear from Figure 3, by controlling the rotation speed of the porous base material, it is possible to control the refractive index distribution of the porous base material, or in other words, the concentration distribution of Ge I P gF, etc. be.

Furthermore, it goes without saying that the present invention allows feedback control from the porous base material shape, temperature, etc., which are substitute characteristics representing the refractive index distribution.

〔Effect of the invention〕

Since the refractive index distribution of the present invention can be precisely controlled using the VAD method, it is possible to manufacture an optical fiber with an optimal α value, that is, a wide band.As a specific means, the rotation speed is controlled, which reduces equipment costs. First, it is an advantageous method that is superior in terms of quality and economy, as it can reduce fiber manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of manufacturing a porous base material by the VAD method. FIG. 2 is an explanatory diagram of the refractive index distribution index α. FIG. 3 is an explanatory diagram of the relationship between the rotation speed of the porous base material and the refractive index distribution index α.

Claims (1)

[Claims] In a method for producing an optical fiber base material in which a porous glass body is obtained by depositing glass fine particles generated by introducing frit gas into a flame and flame hydrolyzing it on a rotating starting material, the starting material is rotated. 1. A method for producing a base material for optical fiber, characterized by adjusting the refractive index distribution by controlling the number of fibers.