JPS5838367B2 - Method of manufacturing optical transmission fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing optical transmission fiber, which makes it possible to manufacture a fiber base material that is particularly highly pure, has a perfectly circular cross section for both core glass and cladding glass, and is not eccentric. This makes it possible to obtain a low-loss optical transmission fiber.

The manufacturing methods for the base material of optical transmission fibers can be roughly divided into: (1) internal attachment method (CVD method), (2) external attachment method (flame hydrolysis method, high-frequency plasma method,
CO2 laser method, etc.).

(1) Internal CVD method is well known as (
(See FIG. 1), the quartz tube 10 is heated with a heater 12, and 02 and raw material gas are fed into the tube to form glass soot on the inner wall.

Typically, a glass soot for the cladding is first formed, and then a soot for the core glass is formed on the inner surface of the cladding glass soot, which is then sintered and core-wrapped to form a solid internal fiber matrix.

This method has the following advantages: (1) there is little contamination because the reaction is carried out in a closed system; (2) a base material containing no OH groups can be obtained; and (2) a relatively simple production equipment is required.

Conventionally, a transmission loss of about 2.5 dBA has been obtained.

However, on the other hand, since the glass for the core and cladding are made inside a quartz tube, there is a limit to the thickness of the base material that can be obtained.

■In order to prevent eccentricity and ovalization of the core glass and cladding glass, extremely careful attention and skill are required, and these problems are still likely to occur. ■The inner surface is perfectly round, Moreover, in order to use a quartz tube with a constant wall thickness, it is necessary to carefully check the dimensions. There are drawbacks such as.

If the core is eccentric in the base material, the core will also be eccentric in the optical fiber made from it, and conventionally it was thought that eccentricity of about 5% was unavoidable.

Therefore, when connecting optical fibers, even if you use a V-groove or the like to match the outside of the fiber perfectly, the center of the core does not necessarily match, and to make a low-loss connection, it is necessary to Alignment work was required to match the cores.

In addition, in the external method (2) above, taking the flame hydrolysis method as an example, as is also well known (see Figure 2), 02, H2, and raw material gas are fed into the burner 16, and the flame 18 A flow of soot 20 is created by oxidizing the soot inside the starting member 2.
This is a method of piling it up on top of 2.

This method has the following advantages: 1. It is also possible to produce a thick base material; 2. In the case of flame hydrolysis, the production equipment is relatively simple.

However, on the other hand, there are drawbacks such as (1) contamination is unavoidable, and (2) OH groups cannot be eliminated, and special equipment is required to reduce them.

Conventionally, the transmission loss of optical fibers made by this method is about 5% dB/Iar1.

The present invention makes it possible to manufacture high-quality optical transmission fibers by making use of the advantages of the above-mentioned internal attachment method and external attachment method and compensating for the drawbacks.

In this invention, first, only core glass soot is generated in a quartz tube by an internal CVD method, and this is sintered and collapsed to form a core glass with a solid interior.

Thereafter, the quartz tube 24 is removed by suitable means, leaving only the core glass 28 as the rod.

Next, a clad glass is formed on the core glass rod by an external deposition method to serve as a base material for the fiber.

This is then spun into a fiber.

Next, this will be explained in more detail.

(1) A quartz tube 24 is prepared (Fig. 3), and a core glass soot 26 made of quartz containing a dopant (for example, Gem2, P205 x AI203, etc.) that increases the refractive index is coated on its inner surface by an internal CVD method. (Figure 4).

In this case, there is no need to strictly check the dimensions of the quartz tube 24 as in the conventional case.

()Next, it is sintered, vitrified, and collapsed to create a core glass 28 with a solid interior (Fig. 5).
.

Is this core glass 28 made in a closed system? Therefore, it is possible to produce highly pure, OH group-free, and sufficiently thick products.

Also, when collapsing, there is no problem with eccentricity since it is only the core, and even if it is not perfectly round, it can be corrected later, so there is no need to pay as much attention as before.

(3) Next, the quartz tube 24 is removed by polishing with, for example, a stone wheel 30, and the core glass 28 is finished into a perfect circle (FIG. 6).

In this way, a core glass rod is made.

Note that instead of cutting off the quartz tube 24, if you do the following, you can use this process many times.

That is, between the core glass soot 26 and the quartz tube 24,
A thin layer of glass sheet with a higher sintering temperature than the core glass soot 26 is made in advance, and after sintering the core glass soot 26, only this soot layer is melted with a solvent (FH etc.) to form a quartz tube. The method is to remove 24.

(4) On the rod of the core glass 28 made in this way, for example, by a flame hydrolysis method, for example, Sl02 z
A soot of clad glass 32 consisting of B203 is produced and vitrified by sintering (FIG. 7).

Note that it is also possible to generate soot and simultaneously sinter and vitrify it by a CO2 laser method or the like.

Note that unlike the core, the cladding does not need to be very pure, and it is sufficient to have a loss of about 20 to 30 dBAan when made into a fiber, so the flame hydrolysis method is sufficient.

(5) Next, if necessary, the top of the clad glass 32 is polished again to make it perfectly circular and at the same time correct the eccentricity (FIG. 8).

As described above, the roundness and eccentricity are both excellent.
A high-purity fiber base material can be obtained.

(6) This is spun into an optical transmission fiber.

Example 1) Using a quartz tube 24 with an outer diameter of 20vtrn and an inner diameter of 18mm, SiCl4120ec/min%Gec
14 4Qcc/minSPoc131 0ec/m
The core glass soot 26 of 8102 Ge02-P205 was deposited to a thickness of 3 cm.

2) Next, sinter at 1600℃ and vitrify it (2 thick)
At the same time, the inside of the quartz tube was heated to -5 imA. ! By lowering the temperature to 9, it collapses and the internal core glass 2
I made 8.

The inner diameter and outer diameter of the quartz tube 24 at that time are 8 and 2, respectively.
It was between 1 and 2.

3) Next, the quartz tube 24 was removed by polishing, and the core glass 28 was finished into a perfect circle with a diameter (18 mm).

4) On the rod of the core glass 28 made in this way, SiC 14200cc/in was applied by flame hydrolysis method.
in%BBr350ec/min, 02500ee/m
in, H2/200ec/min, Ar800cc/m
Traverse speed 3 on a glass lathe under the conditions of i n
0mm/min, rotation speed 24r. p. m.
A soot preform was made by repeating the process 20 times under the following conditions.

This soot preform was sintered in a sintering furnace at 1400°C to obtain a transparent glass rod.

The dimensions at this time were a core diameter of 8 mm and an outer diameter (cladding diameter) of 20 mm.

5) Next, the top of the clad glass 32 was ground again to obtain a base material with a core diameter of 8 mπ and a clad 181ItrIL.

6) The transmission loss of the optical fiber made by spinning this base material was 2.5 dB/k;m, which was comparable to that made by the conventional internal CVD method.

In addition, the eccentricity of the core was 0.1%, which was much improved compared to the 5% of the core made using the conventional internal CVD method.

Effects of the Invention (1) After the quartz tube 24 is internally attached using the CVD method to create a core glass 28 containing only the solid core glass 28, the quartz tube 24 is removed, resulting in a core with very high roundness. A rod of glass 28 is obtained.

This is because, as mentioned above, the roundness of the core glass rod can be physically increased by polishing.

Since the clad glass 32 is formed on such a highly round core glass rod by an external method, the clad glass can also be made round by polishing, and eccentricity with respect to the core glass can be corrected.

Therefore, a fiber with excellent roundness and eccentricity can be obtained compared to that produced by the conventional internal CVD method.

When connecting optical fibers, it is possible to simply match the outer surfaces and omit the subsequent alignment work for matching the cores.

(2) In terms of transmission loss, it is possible to obtain optical fibers of the same high quality as those made by the conventional internal CVD method.

(3) The advantage of the external attachment method that a thick base material can be manufactured (a long fiber can be manufactured) can be utilized as is.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the internal CVD method, Fig. 2 is an explanatory diagram of the flame hydrolysis method (as an example of the external CVD method), and Figs. 3 to 8 are explanatory diagrams showing the method of this invention in the order of steps. It is. 24...Quartz tube, 26...Core glass soot, 28...Core glass, 32...
- Clad glass.

Claims (1)

[Scope of Claims] 1. Only the core glass soot 26 is grown inside the quartz tube 24 by internal CVD method, and this is sintered and the whole is collapsed to create a solid internal structure inside the quartz tube 24. A rod containing only the core glass 28 is made, and from the quartz tube 24 containing only the core glass 28, the quartz tube 24 is removed to make a core glass rod, and a rod of the core glass 28 is placed on top of the rod. A method for manufacturing an optical transmission fiber, comprising: generating a clad glass 32 by an external attachment method to make a fiber preform; and spinning the fiber preform.