JPS5917054B2 - Manufacturing method of optical fiber base material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the method of manufacturing an optical fiber preform.

Silicon tetrachloride (S1Cl4) mixed with germanium tetrachloride (GeCl4) as a dopant for controlling the refractive index and oxygen (O2) gas are introduced into a reaction tube made of quartz, and the outer wall of the reaction tube is moved in the tube axis direction. Heat it with a heating burner,
A method for producing an optical fiber preform is well known, in which the glass-forming raw material gas, such as SlCl4, is oxidized and then deposited as a zero glass layer in a reaction tube. Conventionally, this type of internal C
When manufacturing an optical fiber base material by the VD method, as shown in FIG. Then, the heating burner 3 is reciprocated in the tube axis direction to heat the outer wall of the reaction tube and deposit the glass layer 4 inside the reaction tube.

Here, 5 is an exhaust pipe connected to the gas exhaust end 6 of the reaction tube and having an inner diameter j0 larger than that of the reaction tube to deposit unnecessary glass-forming oxides. However, when optical fiber base materials are manufactured using this method, the oxides of the raw material gas that are formed are deposited with a trail in the direction of movement of the heating burner, and the oxides are deposited in the direction of movement of the heating burner. Therefore, since the glass layer 4 is successively vitrified, it becomes inconvenient that the formed glass layer 4 becomes thick enough to reach the gas discharge end 5 of the reaction tube.

When 30 optical fiber preforms are formed using the glass layer thus formed as a core glass layer and optical fibers are manufactured from the preforms, the core diameter of the optical fibers is not uniform in the longitudinal direction of the optical fibers. This causes the following drawbacks. The present invention eliminates the above-mentioned drawbacks, introduces a raw material gas for glass formation into a reaction tube, heats the outer wall of the reaction tube with a heating burner that moves in the tube axis direction, and deposits a glass layer inside the reaction tube. An object of the present invention is to provide a method for manufacturing an optical fiber preform in which the thickness of the deposited glass layer is uniform from the gas introduction end to the discharge end of the reaction tube. That is.

A method for producing an optical fiber base material to achieve such an objective is to provide an auxiliary heating burner at the gas introduction end of the reaction tube, separate from the moving main heating burner, to control the raw material gas introduced into the reaction tube. The vitrification is performed using the moving main heating burner and the auxiliary heating burner, and the vitrification is deposited in the reaction tube.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a schematic diagram for explaining the method for manufacturing the optical fiber base material of the present invention.

As shown in the figure, in the method for manufacturing the optical fiber base material of the present invention, in addition to the main heating burner 11 that moves from the gas introduction end 2 of the reaction tube 1 to the gas discharge end 6 of the reaction tube, a separate auxiliary heating burner 11 is used. A heating burner 12 is provided and fixed at the gas introduction end 2 of the reaction tube. Ar gas and O2 gas carrying SlCl4 and GeCl4 are introduced into the reaction tube from the gas introduction end 2 into the reaction tube, the auxiliary heating burner 12 is fixed, and only the main heating burner 11 is connected to the gas introduction end 2.
After being moved to the gas discharge end 6, it is returned to the gas introduction end 2 again. In this case, the moving speed of the main heating burner is 60f.
The material gas is moved from the gas inlet end to the gas outlet end at a slow speed of about n/min to sufficiently oxidize the raw material gas, the product is vitrified, and then quickly moved from the gas outlet end to the gas inlet end. When the main heating burner is moved from the gas introduction end to the gas discharge end, the heating power of the auxiliary heating burner is kept low to prevent too much glass-forming oxide from being generated at the gas introduction end. Thereafter, when the main heating burner is quickly returned from the gas discharge end to the gas introduction end, the heating power of the auxiliary heating burner is increased to deposit a thick glass-forming oxide at the gas introduction end. Next, when the main heating burner starts to move from the gas inlet end to the gas discharge end again, the heating power of the auxiliary heating burner is weakened to remove the glass that has already been thickly deposited on the gas inlet end by the main heating burner. The glass-forming oxides, including the formed oxides, are vitrified and deposited in the reaction tube. In this way, the disadvantage that the glass layer becomes thicker as it approaches the gas discharge end of the reaction tube due to the increased amount of glass deposited on the gas introduction end side is eliminated, and a glass layer of almost uniform thickness can be achieved. is formed within the reaction tube over the entire length of the tube. In addition, by using the auxiliary heating burner, the raw material gas introduced into the reaction tube is sufficiently vitrified, so that unnecessary glass-forming oxides are not flown in the direction of the discharge pipe connected to the reaction tube. There is also the added advantage that there is far less adhesion, and therefore it is easier to remove unwanted glass-forming oxides deposited on the discharge pipe. Of course, the same procedure may be used when the cladding glass is first deposited and then the core glass is deposited. As described above, if an optical fiber base material is formed by the method of the present invention, a core glass layer will be deposited uniformly in the reaction tube, and if an optical fiber is formed using such an optical fiber base material, the core glass layer will be deposited uniformly in the reaction tube. An advantage is that it is possible to obtain a long optical fiber with a uniform diameter to cladding layer diameter ratio.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of manufacturing an optical fiber base material by the conventional method, and FIG. 2 is an explanatory diagram showing an example of manufacturing an optical fiber base material by the method of the present invention. 1...Reaction tube, 2...Gas introduction end, 3
... Heating burner, 4 ... Glass layer, 5
...Exhaust pipe, 6...Gas discharge end, 11
...Main heating burner, 12...Auxiliary heating burner.

Claims (1)

[Claims] 1. A method for producing an optical fiber preform in which a glass-forming raw material gas is introduced into a reaction tube, and a heating burner that moves back and forth in the longitudinal direction of the reaction tube heats the outer wall of the reaction tube to deposit a glass layer inside the reaction tube. , an auxiliary heating burner is provided at the gas introduction end of the reaction tube separately from the moving main heating burner, and the gas near the gas introduction end is heated by the auxiliary heating burner, so that the gas introduction end is heated. A glass layer is deposited near the reaction tube, and the glass layer deposited at the gas introduction end is heated by the auxiliary heating burner, and the glass layer deposited inside the reaction tube is heated by the main heating burner. 1. A method for manufacturing an optical fiber preform, characterized in that the preform is made into a preform.