JPS5918327B2 - Manufacturing method of optical transmission line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for manufacturing an optical transmission line using a gas phase chemical reaction.

As a method suitable for manufacturing high-quality optical transmission lines, quartz (SiO
Step 2) Precipitating and depositing a core glass layer containing 2) as the main component, then further heating to obtain a rod-shaped solid base material with no center void, and stretching this base material to form an optical fiber. is well known, for example, from Japanese Patent Laid-Open No. 120352/1983.

In this method, in order to control the refractive index of the core glass, an additive that increases the refractive index of quartz glass, such as germanium dioxide (GeO2), is added to silicon nitride (such as silicon tetrachloride), which is the raw material for quartz. It is also mixed in the form of a halide and reacted at the same time, causing it to precipitate on the inner wall of the glass tube along with SiO2. In this way, the shape of the refractive index profile of the core can be easily made into a desired shape. Therefore, it is possible to easily produce a focusing optical fiber having a refractive index profile that gradually decreases from the center in the radial direction by this method.
I can do 5. However, optical fibers manufactured by the above method are often prone to abnormal changes in the refractive index at the center.

FIG. 1 shows an example of a refractive index profile in which the above-mentioned abnormal change occurred, and a sharp spike-shaped depression a is observed in the center. Naturally, when such an abnormality occurs, the optical transmission performance of the optical fiber is significantly degraded. The example shown in the figure is Ge0 as an additive to the core glass.
2, and the cause of the above-mentioned abnormality is thought to be as follows. 25 The solidification process (called the collapse process) that eliminates the empty spaces in the glass tube described earlier is 20
It is carried out at a high temperature of about 00°C.

Therefore, Si is removed from the glass layer once deposited in the coplus process.
Evaporation of both O2 and GeO2 occurs, but since GeO2 is inherently more easily evaporated than 305102, the GeO2 concentration in the evaporated gas phase is considered to be higher than the concentration in the solid phase, and as a result, GeO2 is in a free state at the surface layer of the glass layer. Furthermore, once evaporated SiO2 and Ge02,
GeO2 is redeposited again as a solid phase in the low temperature region, but the GeO2 concentration in this redeposited layer is estimated to be quite low, and as a result, through this evaporation-solidification redeposition process, it becomes a solid phase and is redeposited during the process. The contact area, that is, the surface of the glass layer deposited from the gas phase,
It is believed that in very thin layers the concentration of the refractive index enhancing additive (GeO2 in this case) is reduced, resulting in the defective refractive index profile shown in FIG.

The present invention has been made in view of the above-mentioned points, and is a novel method for obtaining a desired refractive index profile by bringing additive vapor into contact with a glass layer precipitated by a gas phase chemical reaction and carrying out a solidification process. The present invention aims to provide a method for manufacturing an optical transmission line. An embodiment of the present invention will be described in detail below. FIG. 2 shows an example of the manufacturing process of a focusing optical fiber according to the method of the present invention, in which 1 is a tube made of pure SiO2, and the inner diameter is about 10 or so. 2 is SiO2 and GeO2 formed by vitrifying a mixed oxide layer deposited in the form of fine powder on the inner wall of tube 1 through a gas phase chemical reaction, for example, an oxidation reaction of SiCl4 and GeCl4.
It is a glass layer with.

It is well known that this glass layer 2 becomes core glass when completed. 3 is an oxyhydrogen burner that moves along the tube 1, and by the movement of this burner 3, the aforementioned mixed oxide layer is sequentially vitrified to form the required amount of glass layer 2, and then
If the heating temperature is further increased to soften the SlO2 tube 1,
The diameter becomes smaller as shown in 1a.

In the conventional collapse process, collapse is performed until the internal pores disappear and the glass rod becomes a solid glass rod.
In the present invention, it is stopped when the inner diameter reaches about 1 Um. This is to pass the vapor of the GeO2 raw material as an additive into the tube during the collapse. That is, once the required glass layer 2 is deposited, S! The introduction of Cl4 vapor is stopped, and collapse is performed while passing only a mixed gas of GeCl4 vapor and oxygen gas (02) for oxidizing GeCl4 into the SiO2 tube 1. As shown in the figure, the gas flow path is to flow in the opposite direction to the flow path in a general nozzle, etc., as shown by arrow 4, from the heated part, that is, the small diameter part, to the unheated part. Good. The reason for this is that GeO is added before the redeposited layer of mixed oxide evaporated by heating during collapse becomes vitrified. That is, if you do as shown in Figure 2, the above The mixed gas of the additive and the oxidizer causes a gas phase chemical reaction near the burner 3 to generate GeO2, and this GeO2 is evaporated by the heating of the burner 3 during the collapse, together with the mixed oxide of SlO and GeO2. It is redeposited in the form 2a on the glass layer 2 in the downstream low-temperature part of the burner.Therefore, when this redeposited layer 2a is vitrified again by the movement of the burner 3, the surface layer (the inner surface of the hole) ) in the redeposited layer 2 after vitrification.
The GeO2 concentration at the surface of a depends on the degree of GeO2 addition in the collapse process shown in Fig. 2, and depending on the conditions, it may not be sufficiently compensated, or the GeO2 concentration at the center may be overcompensated. may increase unreasonably. However, according to the experimental results of the present inventors, it is possible to greatly adjust the degree of compensation by changing the flow rate of the mixed gas flowing into the tube, and therefore, by adjusting the degree of compensation, it is possible to create an optical fiber with an almost ideal refractive index profile. It became clear that it was possible to obtain In addition, the quartz tube with the inner diameter of the hole made small as described above,
Further, it is formed into a solid glass rod through a process similar to the conventional collapse process, and then stretched to form a fibrous optical transmission line. Figures 3A and 3B compare the refractive index profile of an optical fiber manufactured by a conventional manufacturing method and that of an optical fiber manufactured by the manufacturing method of the present invention, and the materials are the same in both. be.

In other words, the conventional manufacturing method shown in Figure 3A is
This is a reprint of the figure, and specifically, the flow rate of SiCl4 is 4.5
m01/Min,. O2 flow rate 1000CC/Min
and fixed the GeCl4 flow rate to 0.68×10
-4m01/Min to 3.4X10-3m01/Mi
Inner diameter 127 while increasing the amount divided into 50 equal parts up to n
The refractive index profile is shown when 50 glass layers are deposited in a nanometer SiO2 tube and collapsed into a fiber using conventional methods. On the other hand, after depositing 50 glass layers under the same conditions as the conventional example, according to the present invention, the flow rate of oxygen (1000 CC/M
in) without changing GeC! 4 to 4.0X10″5m0
When flowing at a flow rate of 1/Min, the defect a at the center of the refractive index profile seen in the conventional example is almost safely compensated for, and it is possible to obtain a nearly ideal foil as shown in Figure 3B. Ta. If the flow rate of GeCl4 is higher than this, overcompensation will occur and the refractive index at the center will become too high, and if the flow rate is lower than this, the compensation will be insufficient. Incidentally, it is well known that reactive raw material gases are flowed during collapse in the previously referenced Japanese Patent Application Laid-open No. 50-120352, etc., but it seems that both SiCl4 and GeCl4 gases were flowed in the same way as during glass deposition. However, no matter how rich GeCl4 is kept, it is difficult to obtain the effect of the present invention.

Figure 4 shows that after forming 50 glass deposited layers using the conventional method described above, the SiCl4 gas flow rate was kept at 4.5 x 10-3 m01/Min, the same as when forming the final layer, and the GeCl4
The figure shows a refractive index profile obtained by increasing the flow rate to 1.3 x 10-2 m01/Min and collapsing it. As is clear from FIG. 4, no matter how rich GeCl4 is, as long as a gas containing SiCl4 is used, the refractive index will increase due to the redeposited layer in part b around the center.
When the redeposited layer is vitrified, a large amount of GeO2 evaporates from the surface layer, and SlO2 preferentially remains, and as a result, it is not possible to compensate for the depressed portion a of the refractive index. The embodiments described above are cases where the manufacturing method of the present invention is applied to an optical fiber whose core has a gentle refractive index profile, but it can also be applied to the case where the manufacturing method of the present invention is applied to an optical fiber whose core has a uniform refractive index throughout. As long as an easily evaporable substance is used as an additive in the core material, it is natural that the concentration of the additive in the center will decrease, and therefore the refractive index profile will drop.If the method of the present invention is used in this case as well, Good results can be obtained.

According to the manufacturing method of the present invention, SlO2 or the like containing an easily evaporable additive is used as the core glass of the optical transmission line, and the change in the additive concentration occurs when the core glass is formed by a vapor phase chemical reaction method. There is an excellent advantage that abnormalities in the refractive index profile can be prevented and that an optical transmission line having an ideal refractive index profile and therefore ideal optical transmission characteristics can be manufactured. It is therefore particularly advantageous to apply it to the production of convergent optical transmission lines.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the refractive index profile of a convergent optical transmission line manufactured by a conventional manufacturing method, FIG. 2 is a cross-sectional view for explaining one embodiment of the manufacturing method according to the present invention, 3
Figure A is a diagram showing the refractive index profile of an optical transmission line manufactured by the conventional manufacturing method, and Figure B is a diagram showing the refractive index profile of the optical transmission line manufactured by the manufacturing method of the present invention.
The figure is a diagram showing the refractive index profile when a mixed gas of SiCl4 and GeCl4 is flowed during collapse. a: drop in refractive index, 1: quartz tube, 2: glass layer, 2
a: redeposition layer, 3: burner, 4: flow direction of additive vapor.

Claims (1)

[Claims] 1. A gas containing a raw material for quartz and a raw material for an additive for controlling the refractive index for quartz is introduced into a glass tube, and a required amount of glass layer is deposited on the inner wall of the glass tube by a vapor phase chemical reaction. The introduction of the raw material is stopped, and the glass tube is heated while the raw material for the additive and the reactant for converting the raw material into the required additive are flowed in a gaseous state to sufficiently reduce the diameter of the cavity inside the tube. , and then solidifying it into a linear glass body.