JPS58125623A - Production of parent material for optical fiber - Google Patents

Abstract

PURPOSE:In the production of parent material for optical fiber through the VAD process, a part of glass starting materials is blown out of the sub-burner which is set on the side of the parent material to control its outer diameter and refractive index distribution. CONSTITUTION:Glass starting materials and refractive index-controlling materials such as SiCl4, O2, H2, GeCl4, BBr3, POCl3 and other compounds are jetted from the oxyhydrogen flame burner to effect flame hydrolysis and the resultant glass particles are deposited on the support rod 2 to give the parent material rod for optical fiber. In this process, a burner for adjustment 5 is set on the side of the parent material 3 to blow a prescribed amount of glass forming and refractive index controlling materials (preferably the amount is about less than 1/10 at the oxyhydrogen flame burner).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a porous optical fiber base material by a vapor phase attachment method that suppresses outer diameter fluctuations and refractive index distribution fluctuations.

One of the manufacturing methods for silica-based fiber, which is expected to have a promising future as an optical fiber for communications, is the vapor deposition method (VAD method), which can extremely reduce loss.

This is done by ejecting a glass raw material and a refractive index control material (dopant raw material) that changes its refractive index from an oxyhydrogen flame burner in a predetermined spatial distribution, flame hydrolyzing them, and then using the oxyhydrogen flame burner. After depositing granular glass (soot) on the lower end of the support rod facing the support rod to obtain a porous base material for Hikari 7 Eyeper, this was heated and melted to be treated with Sycoraps to make it transparent vitrified and further to form a predetermined shape. The fiber is spun to a diameter K to form a Hikari 7 Aipa wire.

By the way, in the gas-phase shafting method, the spatial temperature distribution of the flame from the oxyhydrogen flame burner is not exactly uniform, so the bulk density (in unit volume) of the center of the rod-shaped porous optical fiber base material is It is difficult to make the bulk density at the periphery (the percentage of glass particles occupied) uniform, and the bulk density tends to be higher at the high temperature center than at the periphery. For this reason, when collapsing a porous optical fiber base material, internal stress is generated due to distortion, and cracks often occur in the transparent glass optical fiber base material.

Therefore, in order to prevent the occurrence of cracks in the transparent vitrified optical fiber base material by making the bulk density of the porous optical fiber base material uniform, recently, in addition to the oxyhydrogen flame burner, porous optical fiber base material A bulk density adjusting burner is now provided on the side of the base material to heat the circumferential pressure of the rod-shaped optical fiber base material to uniformly adjust its bulk density.

However, when using such a bulk density adjusting burner, heating efficiency must be improved because the optical fiber base material has a high melting point. It is necessary to spray the base material for optical fiber. Therefore, the flow of combustion gas exerts a form I# on the gas flow of the glass raw material and the raw material for refractive index control, and the outer diameter variation and the refractive index distribution of the optical fiber strand are changed by collapsing and drawing. This may cause fluctuations, etc.1
It turned out that.

The present invention solves various problems when using the conventional bulk adjustment burner described above, suppresses changes in outer diameter and refractive index distribution, etc., and replaces the porous optical fiber base material with transparent glass. An object of the present invention is to provide a method for manufacturing an optical fiber base material that is designed to prevent cracks from occurring when the base material is cracked.

The structure of the method for manufacturing an optical fiber base material of the present invention that achieves this object is as follows: gaseous glass raw material f is ejected from an acid water cumulative flame burner and then hydrolyzed, and the resulting granular glass is shaped into rods. When producing a porous optical fiber preform by depositing the optical fiber on the optical fiber, a burner is installed on the side of the optical fiber preform and heats the optical fiber preform to adjust its bulk density t-pI. It is characterized in that at least a part of the raw material for glass as a gas is ejected from the glass.

As shown in the drawings illustrating the principle of the present invention, glass raw materials and refractive index control raw materials such as silicon tetrachloride, oxygen, water, germanium tetrachloride, boron tribromide, and sodium oxychloride are used. The granular glass is ejected from the oxyhydrogen flame burner 1 and flame-hydrolyzed, and the resulting granular glass is deposited on the lower end of the support #2 facing the oxyhydrogen flame burner 1 to form a rod-shaped porous optical fiber. A base material 3 is formed. In this case, as the work progresses, the distance between the growth part of the optical fiber base material 3 and the oxyhydrogen flame burner 1 gradually narrows, and the spatial distribution of the glass raw material and the refractive index control raw material changes.
In order to keep these intervals constant, the support rod 2 is raised while rotating at a constant speed as the optical fiber base material 3 grows. On the other hand, on the side of the optical fiber base material 3, silicon tetrachloride, phosphorus oxychloride, etc.
Glass raw materials such as tribromide compounds and raw materials for refractive index control'fr
A blowout bulk density adjustment burner 5 is provided, but it is sufficient to blow out only the gas that is desired to be regulated.
When formed of granular glass, there is no need to blow out the refractive index controlling raw material from the bulk density NN burner 5. The granular glass produced by the bulk density adjusting burner 5 adheres to the outer periphery of the optical fiber base material 3 and efficiently transmits the thermal energy of the combustion gas to the surface of the optical fiber base material 3. The bulk density at the periphery of the material 3 increases, making it possible to maintain Kt to the same extent as the bulk density at the center. Therefore, the bulk density of the entire optical fiber preform 3 can be made uniform, and the rate at which cracks occur when the preform 3 is heated and melted to form transparent glass can be significantly reduced compared to the conventional method.

In addition, as a result of the granular glass efficiently transmitting the thermal energy generated by the bulk density adjusting burner 5 to the surface of the optical fiber base material 3, the same effect as the conventional one can be obtained even if the combustion gas flow is reduced to 1 tt - approximately equal to the conventional one. It turns out that it can be obtained. In this case, the amount of the glass raw material and the refractive index control raw material spouted from the bulk density adjustment burner 5 is kept to about one-tenth of the glass raw material and the refractive index control raw material spouted from the oxyhydrogen flame burner 1. Jin is desirable. Is this a raw material for glass? - If too much of the raw material for controlling the refractive index is used, a new layer of granular glass will be deposited on the surface of the optical fiber base material 3, and cracks may occur at the boundary between them when the material is made into transparent glass. This is because the quality of the product increases.

Apply 1 liter of hydrogen and 14 liters of acid from a bulk density adjustment burner to the outer peripheral surface of a porous graded optical fiber base material with an outer diameter of 100 < IJ meters.

Mixed gas of phosphorus oxychloride and argon 10mm IJ I
When J-Tol was flowed, a graded optical fiber base material with less disturbance in the refractive index distribution and a cracking rate of less than 5% was obtained, and a graded optical fiber with a transmission band of 700 MHz-km or more was obtained. . Also, the outer diameter is 120 mm! 1.5 liters of hydrogen is applied to the outer circumferential surface of the base material for a step-type optical fiber of J meter quality from a bulk density adjustment burner.

5 liters of hydrogen, 2 mixed gases of silicon tetrahydride and argon
It has been confirmed through experiments that a preform 7 for a stepped optical fiber having an outer diameter variation of 2% or less and a cracking rate of 6% or less can be obtained when 0 ml't is poured.

As described above, according to the method for manufacturing an optical fiber base material of the present invention, a glass raw material is blown out from a bulk density adjusting burner,
The thermal energy of the combustion gas is transferred to the surface of the optical fiber matrix through the granular glass produced by this, changing the form of heat transfer from a conventional gas to a solid, significantly increasing efficiency. It became possible. As a result, the flow fJ- of the combustion gas can be halved, so there is no possibility that the flow of the glass material or the refractive index control material gas blown out from the acid water flame burner will be affected by the form w. At least as much as possible, it is possible to suppress the outer diameter variation and the refractive index distribution variation @, in addition to suppressing the occurrence of cracks.

[Brief explanation of drawings]

The drawing is a principle diagram showing the working conditions of the present invention. In the drawing, 1 is an oxyhydrogen flame burner, ail is a base material for optical fiber, and 5 is a bulk density adjusting burner. Representative Patent Attorney: Shibu Mitsuishi (1 other person)

Claims (1)

[Claims] When manufacturing a porous optical fiber base material by ejecting a gaseous glass raw material from an oxyhydrogen flame burner and flame hydrolyzing it, and depositing the resulting granular glass in the shape of a rod, the optical fiber base material is An optical fiber base material, characterized in that at least a part of the gaseous glass raw material is ejected from a burner installed on the side and which heats the optical fiber base material and adjusts its bulk density t. manufacturing method.