JPS636498B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a gas burner used for laminating fine particle aggregates (soot bodies) by the VAD method in the production of optical fiber preforms.

Figure 1 shows the production of soot by the VAD method.
In Matsufuru 3, raw material gases such as SiCl ₄ , GeCl ₄ , POCl ₃ , BBr ₃ , etc. are passed from gas burner 4 through pipe 5 together with H ₂ , O ₂ , Ar _{2 ,} etc., and oxide fine particles are generated in an oxyhydrogen flame. The fine particles are sprayed onto the tip of a starting member 1, such as a quartz rod, which is being rotated and pulled up, to deposit and grow the porous base material in the length direction. The material is called a particulate aggregate (soot body) 2. This soot body is further heated and melted to become a transparent base material.

As the gas burner 4, multiple burners having a round cross section or a square cross section as shown in FIG. 2 are widely used, and the dopant concentration is changed in each layer of the multiple burner.

When producing an optical fiber porous base material by the VAD method, it is necessary to create a soot GeO ₂ concentration distribution such that the GeO ₂ concentration distribution after fiberization is a square distribution. However, even if manufacturing is performed under manufacturing conditions that provide a square distribution, the distribution will change as manufacturing continues. One of the causes of this is the adhesion of soot to the tip of the burner.

The amount of soot attached to each port that makes up the multiple tubes of the burner depends on the difference in the dopant concentration, etc.
Since each boat is different, the apparent protrusion amount of the burner changes due to soot adhesion, and as shown in Figure 3, each port P of the burner B after use is uneven due to the attached soot S compared to A before use. It is in a state of

The purpose of the present invention is to prevent changes in the mixing state of raw material gas from each port and misalignment of the relative position between the soot body and the burner tip due to such adhesion of soot. Using a burner that can change the amount of protrusion,
This is characterized by preventing the burner from deteriorating over time by lowering each port of the burner by an amount corresponding to the amount of soot attached.

That is, the present invention provides a multi-tube burner used for manufacturing an optical fiber base material by the VAD method, which is provided with a moving means that allows each tube forming the multi-tube to move independently in the direction of the central axis of the burner. Regarding burners.

A particularly preferred embodiment of the present invention is the multi-tube burner described above, in which the moving means has a device for measuring the deviation of the burner tip from a predetermined position during glass particle synthesis. This is shown in Figure 4.
C before control and D after control. At this time, as shown in FIG. 5, by measuring the amount of soot attached using a laser beam R, etc., each port P ₁ , P ₂ ,
It is also possible to automatically drive P ₃ with each port drive motor M ₁ , M ₂ , M ₃ to further improve accuracy. Further, the tips of each port do not necessarily have to be on the same plane; in short, it is sufficient to suppress changes in the tip position of each port over time.

Furthermore, if the amount of soot adhesion is continuously measured during manufacturing using X-ray fluoroscopy, etc., and a feedback circuit is configured by connecting the output signal of the X-ray detector to each port drive device, it is possible to maintain a constant fiber distribution even during manufacturing. is obtained.

Conventional non-adjustable burners have a bandwidth of 1.0G
By using the adjustable burner of the present invention,
A stable glass fiber can always be obtained with a transmission band of 0.8 to 1 GHz/Km.

Example A soot body with a GI-type refractive index distribution was synthesized by the VAD method using a quadruple tube burner in which the tips of each port were on the same plane. When this soot material was dehydrated and made transparent, it was stretched, and an optical fiber base material covered with a quartz tube was drawn, resulting in a broadband fiber with a transmission band of 1 GHz/km.

After continuous production for about 10 days, the bandwidth of the resulting fiber gradually deteriorated to 600MHz/Km. When the quadruple tube burner was observed using a measuring device, it was found that glass was adhered uniformly and firmly to the tip of the second port, and its thickness was 0.3 mm.
Therefore, we installed this second port by 0.3 in the direction of the burner axis.
When the GI type soot body was synthesized again by moving it by mm so that the tip of the second port was on the same plane as the other ports and making it into a fiber, the transmission band of the fiber was restored to 1 GHz·Km.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the outline of soot body production using the VAD method, Figure 2 is a cross-sectional view of an example of a multiple burner, and Figure 3 is a diagram showing each port of the multiple burner before and after use. It is a side sectional view showing the state of
FIG. 4 is a side sectional view showing the state of each port of the multiplex burner used before control and after the control according to the present invention;
The figure shows one embodiment of the method of the present invention.

Claims (1)

[Claims] 1. A multi-tube burner used for manufacturing an optical fiber base material by the VAD method, which is provided with a moving means that allows each tube forming the multi-tube to move independently in the direction of the central axis of the burner. Multi-tube burner. 2. The multi-tube burner according to claim 1, wherein the moving means includes a device for measuring the deviation of the burner tip from a predetermined position during glass particle synthesis.