JPS5914410B2 - Manufacturing method of quartz glass tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a quartz glass tube having a pipe-like structure.

5 Optical fiber has a structure in which the core layer is surrounded by a cladding layer with a lower refractive index than the core layer, but the loss has been further reduced and the wavelength band used has shifted to longer wavelength bands of 1.3 μm and 1.5 μm. With this trend, it has become necessary to make the quartz glass layer forming the cladding layer thicker and with a higher purity of 10 (less OH groups, bubbles and other impurities).

By the way, CVD (Chemical VaporDe-
According to the quartz glass tube position method, a core layer is attached to the inner wall of the starting quartz glass tube, and a VAD (Vapor 15P
According to the haseAxialDeposition method, a jacket tube is wrapped around a base material that is to become a solid cylindrical core layer grown in the length direction, thereby producing a single mode optical fiber.

Therefore, the cladding layer is the starting stone 20-English glass tube in the former case, and the jacket tube in the latter case. Therefore, it is necessary to use high-purity and thicker quartz glass tubes. Here, as a high-purity quartz glass tube, the OH group 25 is at least O, OI
PPM or less, it contains only enough bubbles that even a strong light source (such as a laser) will not cause scattering points due to bubbles, and other impurities are O, lppb for most metals.
The following is desirable.

Such high-purity quartz glass tubes can be produced using a method applying the VAD method (Japanese Patent Application No. 54-12), for which 30 applications have already been filed.
No. 4426-Japanese Patent Application Laid-Open No. 56-50139), but this method is not suitable for mass production because it is difficult to make a large base material. 35 Conventionally, anhydrous silica glass tubes have been produced in large quantities by creating glass tubes using anhydrous flame such as plasma flame and drawing the tubes.

However, the anhydrous silica glass tube obtained in this way cannot be expected to be of high purity. In view of the fact that conventional quartz glass tubes that are mass-produced have low purity, and that high-purity quartz glass tubes cannot be mass-produced, the present invention is a compromise between the two, with a high-purity inner layer and a low-purity outer layer. Provides a method for manufacturing a quartz glass tube with a two-layer structure by welding, and facilitates mass production of the quartz glass tube.
As a result, the object is to contribute to the mass production of optical fibers having a thick and highly pure cladding layer.

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

In the figure, a high-purity quartz glass tube base material 1 is placed in a hollow portion of a low-purity quartz glass tube base material 2, and these are placed in a carbon heater 3 housed inside a high-frequency coil 8.
The base material 1 is pressed downward from above by the lowering device 9, and inert gas is fed into the hollow portion of the base material 1 from the gas inlet 5. This high-purity quartz glass tube base material 1 is made by a method of obtaining a pipe-shaped base material by modifying the VAD method (Japanese Patent Application No. 124426/1982), and the low-purity quartz glass tube base material 2 is It is mass-produced using conventional methods. These base materials 1 and 2 are the carbon heater 3
heated by and melted at the carbon die 4,
Weld. Then, by being pulled downward by the pulling machine 7, a two-layered quartz glass tube 6 is produced in which an inner layer of high-purity quartz glass and an outer layer of low-purity quartz glass are welded together. In addition, by feeding an inert gas into the hollow part of the base material 1 as described above, it is possible to prevent impurities from entering the inner surface of the finished quartz glass tube 6, and also to adjust the tube internal pressure and reduce the wall thickness of the tube. can be controlled. The quartz glass tube 6 made in this way has a smooth inner surface because it is once melted, so it has rough edges (Gr!Nding).
), a free surface can be obtained only by polishing (POlish
ing) step is not necessary. Next, two specific examples will be described.

<Example 1> As the base material 1, a high-purity pipe-shaped quartz glass tube obtained by modifying the VAD method, with an inner diameter of 18111, an outer diameter of 441,211, a length of 12511, and a weight of about 3509 was used. After welding an ordinary quartz glass tube as a dummy to the upper end of this base material 1, the lowering device 9 and the gas inlet 5 are connected.

The base material 2 placed on the outside is a low-purity quartz glass tube made into a pipe by crushing ordinary crystal and melting it with an oxyhydrogen flame.
11 Weight 2.85kf! I used the one from Then, dry N2 is fed in from the gas inlet 5 at a rate of 4.5 N/h. Apply electric power to the high frequency coil 8 and turn the carbon heater 3 to 2200
It was heated to .degree. C. and pulled down by a pulling machine 7. In this way, the quartz glass tube 6 has a two-layer structure with an outer diameter of 24111 and an inner diameter of 2011.
However, the thickness of the high purity inner layer portion was 0.511. Using this quartz glass tube 6 as a starting base material tube, CV
When a single-mode optical fiber was manufactured by internally attaching a core layer by method D, the cladding layer was formed as the inner layer of the quartz glass tube 6 used as the starting base material tube, so the cladding layer was Since there is no need to internally attach the parts, the manufacturing time is reduced to about 1/4, and the number of depositions can be reduced, making it possible to obtain a homogeneous optical fiber with little variation in tube diameter and no change in the length direction. was completed.

Example 2> In this example, the same base material 1 as in Example 1,
2 was used to pull out a two-layered quartz glass tube 6 with an outer diameter of 41111 and an inner diameter of 13 mm.

In this quartz glass tube 6, the high purity inner layer had a thickness of 2.711 mm. In the hollow part of this quartz glass tube 6, VA
Core diameter obtained by stretching the base material made by the D method 3.
When a 2111 clad base material with a diameter of 10 mm was inserted and both were welded, a single mode optical fiber base material with an outer diameter of 40 mm and a core diameter of 3.2 mm was obtained.

Here, the two-structure quartz glass tube 6 is used as a jacket tube, and since the inner layer of high-purity quartz glass forms a cladding layer, the base material inserted into the quartz glass tube 6 is Together with the cladding layer that had been formed as the outer layer, a thick cladding layer was formed, and the ratio of the diameters of the cladding layer and the core layer was 1.
:5.1. Therefore, since the cladding layer is made of high-purity and thick silica glass, loss can be sufficiently reduced, and it is not affected by OH groups from the outermost layer of low-purity silica glass. As described above with respect to the embodiments, according to the method for manufacturing a quartz glass tube according to the present invention, it is possible to produce a large amount of quartz glass tubes consisting of a high-purity quartz glass inner layer and a low-purity quartz glass outer layer. This can contribute to the mass production of low-loss optical fibers.

[Brief explanation of the drawing]

The figure is a sectional view showing one embodiment of the present invention. 1... High purity quartz glass tube base material, 2...
・Low-purity quartz glass tube base material, 3... Carbon heater, 4... Carbon die, 5...
Gas inlet, 6...Two-layered quartz glass tube, 7
・・・・・・Collection machine, 8・・・High frequency coil, 9
・・・・・・Descent device.

Claims (1)

[Claims] 1 Place a small-diameter high-purity quartz glass tube base material in the hollow part of a large-diameter low-purity quartz glass tube base material, heat them in a heating furnace to melt and stick them together, and While feeding an inert gas from one end of the unmelted side of the pure quartz glass tube base material, a wire is drawn from the molten side through a die placed on the molten side to form a two-layered quartz glass tube having an inner layer of high purity quartz glass and an outer layer of low purity quartz glass. Method of manufacturing structural quartz glass tubes.