JPS6137212B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a quartz tube for a quartz fiber for optical transmission.

How to make quartz fiber for optical transmission is M.
-CVD method (inner dimension) O-CVD method (outer dimension method),
There is the VAD method (shaft method). In the O-CVD method,
A tube or rod (preform) consisting of a core and a cladding with a predetermined refractive index distribution in the radial direction is first made and then melt spun to make a fiber. The required optical transmission area may be small (for example, 75 μmφ), but
It is common to provide a jacket layer on the outside to improve handling and strength. Furthermore, by making the refractive index and optical transmission loss of this jacket layer larger than those of the cladding, functions such as band improvement and cross talk prevention may be provided.

Conventionally, this purpose has been achieved as follows.

The inner and outer surfaces of a tube made by the O-CVD method are cleaned and smoothed, or the tube is collapsed into a rod at high temperature, or a rod-shaped tube made by the VAD method is made into a quartz glass tube ( A quartz glass block is created by carefully selecting quartz such as crystal from Brazil, heating and melting it with an oxyhydrogen flame, etc., and stacking them to create a quartz glass block, which is then melted and processed into a tubular shape. Then, it is melt-spun into a fiber directly or in a separate process.

When making fibers using such conventional methods, there were the following drawbacks.

It is not possible to make a jacket glass with a predetermined refractive index difference and absorption loss value with respect to the clad glass.

Since the melting temperature of the quartz glass tube is high, the preform inserted into the tube is heated to a high temperature during spinning, and an air current that does not occur at a relatively low temperature may be generated.

Since quartz glass tubes are made through the process of crystal → glass block → tube processing, they are expensive, and because they must be heated to high temperatures to form fibers, they are not economical due to their high fuel consumption.

The present invention provides a method that improves the conventional method having such drawbacks.

One known method for manufacturing quartz glass fiber is to place a high-purity quartz rod into a high silicate glass tube (trade name: Vycor) and use the rod-in-tube method to make the fiber. This fiber has a small refractive index difference (high-purity quartz as the core and Vycor as the cladding) and requires a great deal of effort in practical handling. Also, since it contains B ₂ O ₃ , it has poor fire resistance and short fiber life.

The purpose of the present invention is different from such a method,
In order to perform the function of structural support and transmission characteristic improvement on the preform which already has a predetermined refractive index distribution in the radial direction, which is made up of a core and a cladding, B ₂ O ₃ is added.
The present invention is to provide a jacket layer of high silicate glass substantially free of carbon dioxide by a rod-in-tube method.

Hereinafter, the present invention will be explained based on the drawings. Figure 1 a and b are preforms 11a and 11b.
are placed in high silicate glass tubes 12a and 12b (details of the manufacturing method will be explained later) between gaps 13a and 12b.
While reducing the pressure of the air between the gaps 13b using a vacuum pump, an appropriate temperature distribution is maintained using heaters 14a, 14a', 14b, and 14b'. 14a', 14
b′ may be omitted if the heating effect is due to the rising air current.

Furthermore, if it is desired to perform high-temperature collapse and melt spinning separately, the heater may be separated and a separate furnace may be used.

FIG. 1a shows that the high silicate glass tube 12a as a jacket is lower than the softening temperature of the preform 11a.
This shows the situation when the softening temperature of is low. At this time, 12a is collapsed along 11a. FIG. 2b shows a situation where the softening temperature of the high silicate glass tube 12b as a jacket is higher than the softening temperature of the preform 11b. At this time 11
It collapses while deforming along the inside of a' and 12b.

When the softening temperatures, etc. of the preform and the jacket tube are significantly different, the conditions a and b in FIG. 1 become extreme, and airflow entrainment and deformation become severe. For this reason, it is better that the difference in softening temperature between the preform and the jacket tube is small, and furthermore, if this gap is made small, the above-mentioned drawbacks will not occur. In order to reduce the gap between the preform diameter and the jacket tube, it is necessary to prepare a jacket tube having an inner diameter close to the preform diameter.

In Figure 2a, the jacket tube 21a is placed on a glass lathe, rotated, and the inside of the hole is depressurized by adjusting the pressure with a vacuum pump while the outside is heated with a flame 2 such as an oxyhydrogen flame.
2a to heat and transform. The burner is then moved longitudinally relative to the tube. As the tube collapses, the wall thickness becomes thicker, but the inner diameter becomes smaller.
You can make 3a. On the other hand, in Fig. 2b, the jacket tube 21b is placed on a glass lathe, rotated, and the inside of the hole is dried by applying a small appropriate pressure with _N2 gas, etc., and the outside is heated and deformed with a flame 22b such as an oxyhydrogen flame. . At this time, when the burner is moved in the longitudinal direction relative to the tube, the tube swells and the wall thickness becomes thinner, but a tube 23b with a larger inner diameter can be produced.

Next, a method for manufacturing a high silicic acid glass tube used in the present invention will be explained.

Na ₂ O―B ₂ O ₃ ―SiO ₂ , K ₂ O―B ₂ O ₃ ―SiO ₂ ,
A tube of Na ₂ O―K ₂ O―B ₂ O ₃ -SiO ₂ type split phase glass is made using conventional pulling and pulling methods. This is subjected to phase separation heat treatment, eluted, and then crushed to form fine particles, washed, dried, and then thermally solidified to form glass particles. After this cleaning step, in order to achieve the desired refractive index and transmission loss, it is necessary to immerse the material in an aqueous solution of a compound that can be converted into a dopant compound, then precipitate it and dry it, or The dried porous glass was placed in a gaseous compound that could be converted into a dopant compound, and the pores were filled, and then a reaction was caused to precipitate the dopant compound on the surface of the micropores. After that, it is heat-hardened and made into transparent glass. An example of this is described below.

After immersing the cleaned porous glass in an aqueous FeCl ₃ solution, if NH ₄ OH water is added to make it alkaline, brown Fe(OH) ₃ will precipitate on the inner surface of the pores. When this is dried and thermally solidified, it becomes SiO ₂ doped with Fe ₂ O ₃ and containing some B ₂ O ₃ , which has a refractive index close to that of Vycol, but becomes a glass with a brownish color and a large absorption loss.

To make glass with a higher refractive index, for example, a porous glass tube after cleaning is immersed in a high-temperature Bi(NO ₃ ) ₃ aqueous solution, then cooled to room temperature (at this time, the difference in solubility between high temperature and room temperature is (Bi(NO ₃ ) ₃ precipitates).

Next, when replacing with propanol (here, Bi(NO ₃ ) is precipitated by the difference in solubility between water and propanol), Bi(NO ₃ ) ₃ is precipitated on the inner surface of the micropores. This was gradually dried in a vacuum to drive off the solvent, and then heated to decompose Bi(NO ₃ ) ₃ .
It becomes Bi ₂ O ₃ and is heated to a higher temperature,
When it is thermally solidified, it is possible to create glass with a higher refractive index. If you use a method that combines these two methods,
It is possible to create glass with adjusted refractive index and transmission loss.

These are the dopants that increase transmission loss.
In general, oxides of transition metals can be used, not limited to Fe ₂ O ₃ . As a dopant that increases the refractive index, not only Bi ₂ O ₃ but also oxides of metal elements lower in the periodic table can be used. It is necessary to select a starting compound corresponding to these dopants, a solvent and temperature for dissolving it, and a means of lowering the solubility in order to precipitate the compound.

An example of another method can be shown as follows. The temperature of the dry porous glass is raised and exposed to the high temperature gas of AlBr ₃ to penetrate into the pores.
After filling with AlBr ₃ , when O ₂ gas is introduced, a reaction occurs within the micropores to form Al ₂ O ₃ , which is deposited on the inner surface of the micropores. If this is thermally solidified, a transparent glass tube doped with Al ₂ O ₃ can be made. Here again, it is necessary to select a gas compound compatible with the aforementioned dopant.

The glass particles thus produced are sent into a flame such as an oxyhydrogen flame or a plasma flame, and are laminated on a rotating mandrel while melting.
If the mandrel is removed later, it becomes a high silicate glass tube.

When glass particles are made transparent using flame or plasma flame, extremely high temperatures (~2000℃) are required, but the B ₂ O ₃ remaining in the glass at this time has a low vapor pressure, so it can be easily Almost no B ₂ O ₃ remains in the high silicate glass that evaporates. B ₂ O ₃
Since B 2 O 3 degrades the water resistance of optical fibers and shortens the fiber life, it has not been practical to use high silicate glass as the outermost layer. However, with the present invention, almost all B ₂ O ₃ can be It has become possible to create a device using high-silicate glass that does not contain carbonate, and the fiber lifespan has been improved to a level that can be used for practical purposes at over 25 years. The invention will be explained with reference to FIG.

The mandrel 31 is rotated and reciprocated in the axial direction relative to the burner. On top of this, glass particles are fed through a nozzle 33 into a plasma flame 34 generated by, for example, a high-frequency plasma 32, and molten glass particles 35 are sprayed onto the mandrel. 36 indicates laminated glass. The mandrel must be made of a material with a larger expansion coefficient than the laminated glass 36, such as carbon, so that it can be pulled out by utilizing the difference in thermal expansion caused by the temperature difference between the temperature during lamination and the room temperature after cooling.

For example, the carbon pipe 31B is connected to the heater 31
It is necessary to heat the glass at A, layer the glass on top of it, lower the liquid nitrogen temperature to room temperature or lower, increase the difference in thermal expansion, and then pull it out.

Next, one embodiment of the present invention will be described.

(1) A phase-splitting glass of Na ₂ O―K ₂ O―B ₂ O ₃ ―SiO ₂ was melted in a platinum crucible, and then the pipe was pulled up. This pipe was heat treated at 550℃ x 24 hours and then heated to 95℃.
After eluting with 3NHCl, the porous glass was crushed, washed with pure water, dried in vacuum, and heated until thermal solidification to create glass particles. The glass particles are sent into an oxyhydrogen flame through the center hole of a quartz burner, and the glass particles are melted and layered on a 10mmφ carbon rod to have an outer diameter of 15mmφ, and then slowly cooled to -70℃. After cooling and pulling out the carbon rod, I was able to make a 10mmφ x 15mmφ pipe. This tube was treated in the same manner as in (1) to make the inner and outer surfaces clean and smooth.

After this, a core of 10 mmφ is placed in this tube as P ₂ O ₅ -
A preform consisting of GeO ₂ --SiO ₂ and B ₂ O ₃ --SiO ₂ cladding was inserted and melt-spun to a thickness of 150 μm and a brimary coat was applied to produce an optical fiber. There were some troubles during spinning when a 10φ x 15φ quartz tube was used, but there were no problems with this method.

According to the present invention, it is possible to produce a jacket glass tube having a predetermined refractive index difference and absorption loss value with respect to the clad glass, so that the transmission characteristics of a fiber using this can be greatly improved.

This jacket/glass tube uses cheap raw materials and the manufacturing process is suitable for mass production and is inexpensive, so the cost of the optical fiber is low.

If the fiber is made using a jacket tube that matches the softening temperature of the preform, the problem of air bubbles occurring during melt spinning will not occur.

Since a quartz tube is produced that is substantially free of B ₂ O ₃ , the life of the fiber is significantly improved.

[Brief explanation of the drawing]

Figures 1a and b are diagrams showing a rod-in tube, Figures 2a and b are diagrams showing that the inner diameter of the tube is adjusted while reducing pressure and pressurization, and Figure 3 is a diagram showing a high-capacity tube. It is a diagram for explaining one method of making an acid glass tube. In the figure, 11a and 11b are preform rods,
12a, 12b are high silicate glass tubes, 13a, 1
3b is a void, 14a, 14a', 14b, 14b' are heaters, 21a is a jacket pipe, 22a, 22b
is a burner, 23 is a glass tube, 31 is a mandrel, 32 is a high-frequency plasma, 33 is a nozzle, 34
35 indicates a plasma flame, 35 indicates glass particles, and 36 indicates laminated glass.

Claims (1)

[Claims] 1 Melt phase splitting glass, make a thin rod by pulling up or down, phase splitting heat treatment, elution, crushing, washing,
Create glass particles by drying and heat solidifying,
A method for producing a quartz tube for optical fiber, which comprises laminating layers on a mandrel and then pulling out the mandrel to produce a tube.