JPS593032A - Manufacture of base material for optical fiber - Google Patents

Abstract

PURPOSE:To economically manufacture a base material for an optical fiber having a low concn. of OH groups and causing little transmission loss with superior productivity when a base material for an optical fiber is manufactured by hydrolyzing gaseous starting materials, by removing OH groups from a base material by means of only halogen contained in the material. CONSTITUTION:Gaseous SiCl4, GeCl4 and POCl3 as starting materials, together with Ar as a carrier gas, are fed to the central part of a burner 1 having a quadruple structure in a gas chamber 6, Ar, H2 and O2 are successively fed to the outer parts of the burner 1, and a porous base material 7 is deposited by a hydrolysis reaction. Gaseous N2 is then fed to the outside of the carbon core tube 22 of a furnace, gaseous He is fed to the inside to make the internal pressure of the tube 22 higher than the external pressure, and the base material 7 is slowly pulled up in the He atmosphere while being rotated. The residual OH groups in the material 7 are removed by means of only Cl2 contained in the material 7, and a base material for an optical fiber causing little optical transmission loss is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a method of manufacturing an optical fiber preform by a vapor phase axial method.

The porous base material used in the vapor phase deposition method is deposited using a hydrolysis reaction of raw materials, so it contains several tens of ppm of OH groups. This will increase transmission loss.

Therefore, the OH group is generally removed by halogenation in an atmosphere of a halogen agent such as at 2J3oct . However, in this method, it is necessary to perform the above-mentioned treatment before sintering and vitrification. Furthermore, the effectiveness of removing OH groups depends on the bulk density, processing temperature, flow rate of the rogens agent, purity of the rogens agent, etc., and the optimum range is narrow. We often see cases where losses become large.

The present invention was made in view of the above-mentioned situation, and eliminates the need to perform OH group removal treatment in a halogen agent atmosphere (OH
The object of the present invention is to provide a method for producing an optical fiber preform with a reduced group concentration.

In the method for producing an optical fiber base material of the present invention, a raw material is fed into a burner flame and is blown onto the tip of a quartz target of a rod-like body above the burner to grow a porous base material made of fine oxide powder, and then an inert gas When producing an optical fiber base material by sintering and vitrifying in an atmosphere, the bulk density of the porous base material is set to 0.03 to 0.159/crl and OH
This is a method in which the group concentration is lowered and the inert gas atmosphere pressure during the sintering and vitrification is made higher than the ambient pressure.

An embodiment of the method for manufacturing an optical fiber base material according to the present invention will be described below with reference to FIG. FIG. 1 is a longitudinal cross-sectional view of an apparatus for carrying out the method of the present invention, in which 1 is a quadruple tube burner, 2 is a gas introduction glass tube, 6 is one chamber, 4 is a differential pressure gauge, 5 is a glass tube, 6 1 is a glass chamber with an exhaust hole, 7 is a porous base material, 8 is a partition glass plate, 9 is a flange, and 1o is a differential pressure gauge.

t, Il is the flange, 12 is the carbore heater, 1
6 is a furnace body cover, 14 is a glass curtain, 15 is a differential pressure gauge, 16 is a glass chamber, 17 is a carbon sheet sealing plate, 18 is a sintered glass base material, 19 is a quartz target, 20
2 is a burner support stand, 21 is a flame, and 22 is a carbon furnace tube.

In the case of manufacturing optical fiber base material, 5iCt4 at 1200mf/min, Ge0t4 at 150mt/min, POO73 at 26t/min, Ar
Carrier gas was flowed at 800 cc/min, and on the outside, Ar was supplied at o, 59 z/min, N2 was supplied at 3 t/min, and O2 was supplied at 6 t.
/It is deposited on the tip of the quartz rod above the quadruple tube burner 1 by a diversion hydrolysis reaction. The bulk density of the porous base material 7 at this time was 0.59/ca, the outer diameter was 60 mm, and the length was 60 mm.

Next, N2 gas was flowed for 717 minutes outside the carbon furnace core tube 22, and the differential pressure with respect to the atmospheric pressure at that time was set to 10.0 water column.
Inside the carbon furnace core tube 22, 20 t/minute of He gas is flowed downward from the top of the furnace to make the differential pressure with respect to atmospheric pressure +2.0 columns of water.At this time, the pressure inside and outside the carbon furnace core tube 22 is higher on the inside. The differential pressure is 1. ONn water column. In this atmosphere, the porous base material 7 is rotated from below at 2 rpm and pulled up for 21 minutes, and the inner wall temperature of the carbon furnace core tube 22 is 1.
Vitrify at 45° to 1500°C.

The absorption loss due to OH at this time has a spectral characteristic as shown in curve A in Figure 2, where the horizontal axis is the wavelength and the vertical axis is the transmission loss, and the transmission loss is 0.43 dB at 1.6 μm.
, the OH group concentration was 11 ppb.

Even if the result of manufacturing 10 pieces of sintered glass base material under the same conditions is 1
．． The transmission loss at 6 μm was 1 dB/Km or less, and the OH group concentration was in the range of 2 to 25 ppb.

In addition, the bulk density of the porous base material 7 is o, 11 y /c
In case a, the same result is obtained even if the moving direction of the porous base material 7 during vitrification is changed from top to bottom.

The bulk density of the porous base material 7 is 0.06 to 0.1
5y/crA is preferable; below o, o3f/crl, the porous base material 7 will fall during deposition, and above 0.15 f/cd, the OH group removal effect of the halogen agent in the porous base material will be significantly reduced. Further, the pressure of the inert gas atmosphere is made higher than the surrounding atmosphere by 0.5+ran water column or more. and o, 5
If it is less than 1 Mn water column, impurities may enter from the surrounding atmosphere due to pressure fluctuations, etc., causing an increase in transmission loss, so it is preferable that it is 0.5 Mn water column or more.

In this way, in the method for manufacturing the optical fiber base material of this example,
The OH baseline is removed only using the halogen agent C4,2 contained in the porous base material with a predetermined bulk density without entering the halogen agent atmosphere, and at the same time, the inert gas atmosphere during sintering and gasification is removed from the outside. This is a method in which the pressure in the atmosphere is made higher than the surrounding pressure in order to prevent contamination by impurities, and it is possible to wave an optical fiber base material with a low OH group concentration while improving productivity and economic efficiency.

In addition, the porous base material can be immediately vitrified while being deposited, improving productivity and economic efficiency.

As described above, according to the method for manufacturing an optical fiber base material of the present invention, an optical fiber can be produced that can reduce the OH group concentration and improve productivity and economic efficiency without performing OH baseline removal treatment in a logogen atmosphere. This has the effect of making it possible to manufacture the base material.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an apparatus for carrying out the method of manufacturing an optical fiber preform of the present invention, and FIG. 2 is a transmission loss characteristic curve diagram of the optical fiber preform manufactured by the apparatus of FIG. 1: Quadruple tube burner 7: Porous base material 19: Quartz target.

Claims (1)

[Claims] 1. Raw materials are fed into the burner flame and blown onto the tip of the rod-shaped quartz target above the burner to grow a porous base material extending from the oxide fine powder, and then sintered and vitrified in an inert gas atmosphere to form an optical fiber base material. In the method for manufacturing, the bulk density of the porous base material during growth is 0.06 to 0.06.
A method for producing an optical fiber base material, characterized in that the OH group concentration is lowered to 0.15 f/c4, and the inert gas atmosphere pressure during the sintering and vitrification is made higher than the ambient pressure.