JPS5858299B2 - Dehydration and sintering method for porous base material for low-loss optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention can be obtained by reacting a frit gas for forming an optical fiber in an oxyhydrogen flame to form a fine glass powder, and depositing this on the tip or outer periphery of a rod-shaped base material. The present invention relates to a method for dehydrating and sintering a porous base material.

Generally, a carbon furnace is used to dehydrate and sinter this type of porous base material to make it transparent vitrified.

Since carbon is a heating element in this carbon furnace, it is necessary to keep the atmosphere inside the furnace inert during sintering.

On the other hand, optical fibers for long wavelength bands are subjected to dehydration treatment because it is necessary to reduce the amount of OH groups mixed in as much as possible.

When using 5OC12, CCl4, etc. as a dehydrating agent,
If the atmosphere is oxygen, the effect is on dogs.

Therefore, in order to make it possible to use a carbon furnace in an oxygen atmosphere, an alumina pine full tube is used to isolate the sintering atmosphere from the carbon heating element.

However, it is difficult to make alumina highly pure, and it contains water due to its hygroscopic property, so impurities and water enter the optical fiber base material during sintering, adversely affecting the transmission loss of the optical fiber and causing heat shock. There is also a problem in its use that it is vulnerable to

From the above points of view, this invention can replace the alumina pine full tube with high purity and low OH content, and
It uses a quartz Matsufuru tube that can withstand sintering temperatures, and its unique feature is that the porous base material for optical fiber is introduced into a heating furnace containing a quartz Matsufuru tube. The purpose is to perform dehydration and sintering in a state where impurities from the heating furnace are blocked.

The method of this invention will be explained below based on the drawings.

FIG. 1 shows an example of a dehydration sintering furnace used to carry out the method of the present invention. First, its configuration will be explained. 1 is a VAD (VapourPhase A
It is a porous optical fiber base material obtained by a xial deposition method, and is deposited on the tip of a rod-shaped base material 2, and is made rotatable and movable up and down.

3 is an electric furnace equipped with a carbon heater 4.

5 is a quartz pine full tube installed inside the furnace 3, 6
, 7 quartz tube furnaces connected by flanges to the upper and lower ends of the quartz pine full tube 5 may be integrated.

8 is a dehydration gas (He,
5OC4, C12, etc.) lower quartz tube 7
A dehydration gas supply port 9 provided at the lower end is an Ar gas inlet for maintaining the inside of the carbon furnace 5 in an inert atmosphere.

In the dehydration sintering furnace configured as above under the conditions shown in Table 1 *V
The porous base material obtained by the AD method was guided, dehydrated and sintered, and then made into a fiber.

For comparison, a conventional carbon furnace equipped with an alumina pine full tube was used to dehydrate and sinter the porous base material under the same conditions as shown in Table 1, and then it was made into a fiber.

FIG. 2 shows an investigation of the influence of impurities on the fiber (I) obtained by the method of the present invention and the fiber (I) obtained by the conventional method.

As is clear from the figure, the fiber (I
) has almost no increase in loss due to absorption of impurities, but
It can be seen that the fiber (II) produced by the conventional method has an increased loss due to the absorption of impurities from the alumina pulp and the atmosphere in the furnace.

Further, FIG. 3 compares the dehydration treatment effects of the fiber (I) according to the method of the present invention and the fiber (II) according to the conventional method.

As is clear from the figure, the fiber (I
), no OH absorption peak appears and the OH content is 1.
It is estimated that the loss is less than ppb, but the conventional fiber (II) shows a loss due to OH absorption near a wavelength of 1.38μ.

In the method of this invention, a porous glass fiber base material obtained by the VAD method or the external method is introduced into a furnace equipped with a high-purity quartz pine full tube with a low OH content. Since dehydration and sintering is carried out in the process, there is no contamination of impurities from the heating element or contamination of impurities and OH from the quartz pine tube, thereby making it possible to obtain an optical fiber with low loss.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a dehydration sintering furnace used to carry out the method of the present invention, and FIG. 2 is an explanatory diagram showing impurity wavelength characteristics of optical fibers obtained by the method of the present invention and the conventional method. Fig. 3 is an explanatory diagram showing the OH wavelength characteristics of optical fibers obtained by the method of this invention and the conventional method.

Claims (1)

[Claims] 1. A low-loss optical fiber characterized in that a porous base material for optical fiber is introduced into a heating furnace equipped with a quartz pine full tube, and dehydrated and sintered in a state where impurities from the heating furnace are blocked. Dehydration and sintering method for porous base materials.