JPS59232932A - Production of preform for optical fiber - Google Patents

Abstract

PURPOSE:To produce a titled preform having a step type refractive index distribution of an approximately accurate shape by ejecting only the dopant contg. no SiCl4 from the second nozzle from the center in a multiple-pipe burner. CONSTITUTION:SiCl4 added with H2 is ejected from a central nozzle 1 and GeCl4 added with H2 from the 2nd nozzle 3; further gaseous Ar and O2 are ejected from nozzles 5, 7 on he outside thereof and are brought into combustion and reaction. Then the concn. of GeO2 in the flame is higher the further from the center toward the radial direction at the outlet of the burner; on the contrary, the temp. is higher the nearer the center on the flame surface and therefore the ratio at which GeO2 is formed a solid solution to SiO2 is relatively high and the concn. of GeO2 approximately uniform in the radial direction of the base material of soot is provided, by which a preform having a refractive index distribution of a step type is produced. The effect by which an optical fiber having less light loss is produced is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical fiber, particularly a preform for an optical fiber having a step-type refractive index distribution.

Conventionally, in general, a multi-tube burner was used to prepare the starting material in the axial direction 1 (in the case of manufacturing a soot base material by laminating glass particles, as shown in FIG. 5i in which C4/GeCA!+ was ejected and H2 gas was added from the second nozzle 3 just outside the center hole.
The soot base material was manufactured by ejecting C4 and growing the soot base material in the axial direction of the starting material through the following reaction.

5iC4+2H20-+SiO,+4HCIGeC4+
2H2Q-+GeO2+4HCA! In addition, Ar is ejected from the third nozzle 5 shown in FIG. 1, and 02 is ejected from the fourth nozzle 7.

In such a case, since GeC4 is ejected from the center, the distribution of Gem2 decreases as it moves away from the center of the flame. In addition, the temperature distribution on the flame surface is high at the center (low at the periphery), so the solid solution yield (dopant yield) of G e Ot into 5in2 particles is high at the center and low at the periphery. The concentration of CeO2 on the radial line of the obtained preform is high in the center and low in the periphery, generally resulting in a graded type 9 distribution as shown in Figure 2. Therefore, in the manufacturing method of the prior art, step It was extremely difficult to obtain a μ refractive index distribution of the type. ゛ Fig. 2 11 shows the refractive index distribution of the step type. In addition, n is the refractive index and r is the distance from the center of the fiber. .

However, optical fibers with a step-type refractive index distribution have a narrower range of frequencies that can be transmitted compared to graded-type fibers, and although they have a so-called band limit, the numerical aperture <Nf A
, ), it has good coupling efficiency with the light source and the light receiver, and is particularly suitable for short-distance optical transmission (for example, for medical equipment), and demand is increasing. Therefore, there is a growing need to develop a method for manufacturing an optical fiber having a substantially accurate step-type refractive index distribution.

The present invention has been made to meet these needs and to eliminate the shortcomings of the prior art described above, and which provides a method for manufacturing optical fibers that provides a more precisely shaped stepped index profile. The method is disclosed below.

That is, the manufacturing method of the present invention is a method of forming a preform in the axial direction of a pile material using a so-called multi-tube burner, in which 5tcA4. Orha 5
iC4ic refractive index control raw material')j GeC4, PO
Cls +T i CIJ4. AlC4, GaCl3
One or more selected from the above are mixed and ejected, and one or more selected from the refractive index control material gases not containing SiO4 is ejected from the second nozzle from the center. For example, SiO4 is ejected from the center nozzle and the second
From the second nozzle, eject one or more dopants that do not contain 5ick4, that is, one or more selected from GeC4, POC&, TiO4, AAC&, or eject a mixture of 5iClt and the same dopant as described above from the center nozzle, A dopant similar to the above but not containing 5iC7+ is ejected from the second nozzle from the center.

Hereinafter, the contents of the present invention and its effects will be specifically explained with reference to the accompanying drawings.

As shown in FIG. 6, in the method of the present invention, the H2
5iCJ% added with G e C& added with the second nozzle filter is ejected, and further outside nozzle 5,
Ar and 02 gases are ejected from 7 to cause a combustion reaction. In this way, the concentration of GeO2 in the flame increases as it moves radially away from the center at the exit of the burner;
On the other hand, on the surface of the flame, the temperature is higher near the center, so S i O
The solid solution ratio of Gem 2 to 2 becomes relatively high. In other words, according to this method, the doping amount of Gem into SiO2 and the temperature dependence are compensated by the Gem2 concentration distribution in the flame, and the soot base material has a substantially uniform GeO2 concentration in the radial direction. As described above, according to the method of the present invention, it is possible to manufacture an optical fiber preform having a step-type refractive index distribution.

Moreover, as shown in FIG. 5, the center nozzle 1. Second nozzle 6
Instead of H2 in the above case, 02 was added as an additive to SiO4 and G e C& ejected from the above, and Ar was sequentially added from the outer nozzles 5, 7, 13, and 15.

It has been found that substantially the same effect can be achieved even when H21Ar+02 is injected. That is, an optical fiber preform having a step-type refractive index distribution can be manufactured.

As explained above, and as will be described in detail in the examples below, in the preform manufacturing method using a multi-tube burner, the conventional technology has adopted a method in which only SiO4 is ejected from the second nozzle from the center. However, in the present invention, in particular, by using a method characterized by ejecting only the dopant agent that does not contain 5iC4 from the second nozzle, a substantially accurate step-type refractive index distribution that could not be obtained with the conventional method is obtained. A preform was obtained, which produced the effect that an optical fiber with a large numerical aperture and low optical loss could be manufactured.

Example 1 Raw material gas arrangement using multiple burners as shown in FIG.
e Cllt and quick, Ar+ 4th from 6th nozzle 5
02 was ejected from the nozzle 7, and glass fine particles were successively deposited on the starting material placed above the burner to produce a soot base material. The amount of each raw material gas used per unit time was as shown in Table 1 below. In addition, the glass raw material was carried by He.

A soot base material is prepared by using the raw material gases listed in Table 1 above,
After sintering in a He atmosphere to obtain a transparent glass base material, it was stretched to a diameter of 10+n+aO and placed in a commercially available quartz tube to produce a preform base material for optical fiber.

This base material was heated to approximately 2,000°C with a graphite heating element and drawn to an outer diameter of 140/'yx, and the refractive index distribution of the fiber cross section was measured, as shown in Figure 4-11. A fiber close to a precise step type was obtained.

Embodiment 2 The raw material gas arrangement used in the multiple burner shown in FIG. G e CIl + and 0□ from the second nozzle 6, Ar + 4th from the third nozzle 5
H from the nozzle 7, A r + 6th from the fifth nozzle 16
A preform was manufactured by blowing out O from the nostle 15 and depositing fine particles on the starting material placed above the burner. The amount of each raw material gas used per unit time was as shown in Table 2 below.

Table 2 Example 1: Soot base material prepared using the above raw material gas
An optical fiber with an outer diameter of 140 μm was manufactured using the same procedure as above. When the refractive index distribution of the obtained fiber was measured using the same measuring means as in Example 1, a similar step-type refractive index distribution was obtained. The peak value of the refractive index was △n=1.9% (△n-Nikoko, n,
, core refractive index.

2 n2: cladding refractive index).

[Brief explanation of drawings]

Figure 1 shows the usage of a multi-tube burner using the vertical method.
FIG. 2 is an explanatory diagram of the refractive index distribution. FIG. 6 shows the usage of a multi-tube burner according to the present invention, and FIG. 4 shows a refractive index distribution diagram obtained thereby. FIG. The usage status of the tube burner is shown. 1... Center nozzle, 3... Second nozzle. 5... Sixth nozzle, 7... Fourth nozzle. 16... Fifth nozzle, 15...・6th nozzle sleeve/diagram
Figure 2, Hata 3, Continuation of Figure 1, page 1, author: Bunmei Hanawa, 162 Shirakata, Shirane, Tokai-mura, Naka-gun, Ibaraki Prefecture, Nippon Telegraph and Telephone Public Corporation, Ibaraki Denkan Communication Research Institute (for company use, applicant: Nippon Telegraph and Telephone Public Corporation)

Claims (1)

[Claims] An optical fiber preform is produced by mixing and burning raw material gas and fuel gas using a multi-tube burner having a plurality of nozzles, stacking glass particles in the axial direction of the starting material, and sintering the mixture. In the method, a raw material gas GeC4 for controlling the refractive index is added to 5iC14* or SiC14 from the center nozzle of the multi-tube burner. PQC4t T I CA! 4 * All C4+
One or more selected from GcLClls are mixed and ejected, and 5iC1 is ejected from the second nozzle from the center.
A method for producing an optical fiber preform, comprising ejecting one or more selected from the refractive index control material gases that do not contain .