JPH0239458B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a base material for an optical fiber designed to prevent the refractive index distribution at the boundary between a core portion and a cladding portion from sagging, and particularly for a single mode transmission optical fiber. It is suitable for use.

Optical fibers for single-mode transmission have extremely wide transmission bands, so they are expected to be used as large-capacity, long-distance communication transmission lines. Manufactured in

The internal attachment method involves forming a cladding part on the inner peripheral surface of a quartz glass tube that will serve as a jacket, then forming a core part, and then collapsing it to obtain the base material for the optical fiber, resulting in less transmission loss. It is possible to use high quality optical fiber. However, with this internal attachment method, it is difficult to manufacture long optical fibers, and it is not suitable for mass production.In addition, since the quartz glass tube is heated with an oxyhydrogen flame, moisture essentially diffuses internally. There was a drawback that it was not possible to avoid the adverse effects on durability, etc.

In addition, in the rod incubation method, a glass rod that serves as a core synthesized by a vapor phase axis method or a plasma method is inserted into a quartz glass tube of an appropriate diameter, and a base material for optical fiber is obtained by a collapse process. This makes it possible to manufacture longer optical fibers than with the internal attachment method. However, in this rod inch tube method, the quartz glass tube becomes the cladding part directly, so an anhydrous tube with a very low residual moisture content must be used, making it extremely expensive and causing transmission loss. However, there is a relatively large drawback. This is due to the waveguide characteristics of the optical fiber for single-mode transmission, and in a single-mode optical fiber, a considerable amount of the light beam propagates not only in the core but also in the cladding. This is because it is affected by irregularities in the interface between the cladding part and the cladding part and by impurities.

Therefore, it is believed that the vapor phase axial method, in which the core and cladding parts are synthesized almost simultaneously, is the most suitable for producing optical fibers for single mode transmission in terms of quality and industry. As shown in Fig. 1, which shows the principle of this vapor phase axising method, a core burner 1 is used to flame-hydrolyze the glass raw material that will become the core.
A crud burner 2 for flame hydrolyzing the glass raw material that will become the crud is positioned at the lower end of the matsuful 3, and the core soot 5 is deposited in a rod shape on the mead rod 4 which is being pulled up while rotating. , and then the cladding section stow 6 is placed around it.
After depositing the gas, the sintering furnace 9 inside the Matsufuru 3 has a carrier gas inlet 7 and an exhaust port 8 formed therein.
Optical fiber base material 10 made into transparent glass by
We are trying to manufacture. In this way, in the conventional vapor phase axial mounting method, the core burner 1 and the cladding burner 2 are positioned adjacently in the muffle 3, so that the dopant for controlling the refractive index of the core part is not mixed into the cladding part. It has been found that, as a result, these boundaries do not form a clear step shape, but instead become sagging. If the boundary between the core and the cladding becomes sagging, it will inevitably cause a large loss, especially in single-mode transmission optical fibers with small core diameters, and this is one of the points that should be improved in the future. There is.

Based on this knowledge, it is an object of the present invention to provide a method for manufacturing a smooth optical fiber in which the boundary between the core portion and the cladding portion is formed into a clear step shape without impairing the advantages of the vapor phase axial mounting method. It is something.

The structure of the method for manufacturing an optical fiber base material of the present invention that achieves this objective is to flame-hydrolyze the glass raw material that will become the core in the core sintering chamber in the lower part of Matsufuru, which is divided into upper and lower parts by a partition plate. The soot thus obtained is grown into a rod shape and transformed into transparent glass at the same time as dehydration.The glass raw material that will become the cladding is grown in the cladding sintering chamber at the top of the matsufuru, which is divided into upper and lower halves by a partition plate. Flame hydrolysis is carried out, and the soot obtained thereby is continuously deposited around the rod-shaped core part which has been made into transparent vitrification in the core part pulling process, and this soot is dehydrated and made into transparent vitrification at the same time. It is characterized by the following.

Hereinafter, an embodiment of the method for manufacturing an optical fiber base material according to the present invention will be described in detail with reference to FIG. 2 showing the principle thereof. The pine full 11 is divided into upper and lower halves by a partition plate 12, forming a clad sintering chamber 13 and a core sintering chamber 14. Inside the core sintering chamber 14, there are installed a core burner 15 for flame hydrolyzing the glass raw material that will become the core, and a core sintering furnace 17 for converting the soot 16 of the core that has grown into a rod shape into transparent vitrification. Further, a balancing air supply pipe 18 and an exhaust pipe 19 are connected to the core sintering chamber 14. On the other hand, in the cladding part sintering chamber 13, there is a cladding burner 20 for flame hydrolyzing the glass raw material that will become the cladding part, and a cladding burner 20 for flame-hydrolyzing the glass raw material that will become the cladding part, and a soot 22 of the cladding part deposited around the transparent vitrified core part 21 to be made into transparent vitrification. A sintering furnace 23 for the cladding is installed, and an air supply pipe 24 for balancing and an exhaust pipe 25 are connected to the sintering chamber 1 for the cladding.
Connected to 3. A through hole 27 is provided in the center of the partition plate 12 to allow a mead rod 26, which rotates and rises as the soot 16 of the core portion 21 and the soot 22 of the cladding portion grow, to pass through. The rising speed of the mead rod 26 is determined by the lower end of the core soot 16 growing into a rod shape and the core burner 15.
and the soot 2 of the cladding part adhering to the cladding burner 20 and the core part 21 facing it.
The speed must be set so that the distance between the two is always constant. Therefore, it is necessary to control the amount of glass raw material ejected from the core burner 15 and the cladding burner 20 in relation to each other.

Silicon tetrachloride, germanium tetrachloride, oxygen, hydrogen, etc. are ejected from the core burner 15 at a predetermined ratio so that silicon dioxide and germanium dioxide as a dopant that increases its refractive index are generated by a flame hydrolysis reaction. On the other hand, through hole 27
In order to prevent dopants and the like from flowing into the cladding sintering chamber 13, it is preferable to blow oxygen in addition to nitrogen as a carrier gas into the core sintering chamber 14 from the equilibrium air supply pipe 18. From this point of view, the open end of the balancing air supply pipe 18 is connected to the core sintering furnace 1.
The core burner 15 There is almost no possibility that the generated reactants will flow into the cladding sintering chamber 13 from the through hole 27, and therefore the dopant will not mix into the soot 22 in the cladding portion. In this case, the partition plate 12 may not be provided.

Silicon tetrachloride, oxygen, hydrogen, etc. are ejected from the cladding burner 20 at a predetermined ratio so that silicon dioxide is produced by a flame hydrolysis reaction,
A normal carrier gas is fed into the cladding sintering chamber 13 from the balancing air supply pipe 24. By this,
Core part 2 made into transparent glass in core sintering chamber 14
A soot 22, which will become a cladding part, is deposited around the cladding chamber 1 with a predetermined thickness.
Since there is no dopant that changes the refractive index in 3, the pure frame silicon dioxide becomes the clad part, and the optical fiber base material 28 is obtained by converting the soot 22 into transparent glass in the cladding sintering furnace 23. The refractive index distribution near the boundary between the core portion 21 and the cladding portion 29 has a distinct step shape.

In this example, a method for manufacturing a base material for a step-type optical fiber has been described, but the present invention can also be applied to cases where, for example, a jacket tube is fitted and integrated into a base material for a graded-type optical fiber. can produce higher quality products.

As described above, according to the method for manufacturing an optical fiber base material of the present invention, the soot in the cladding part is made into transparent glass in order to prevent the dopant from entering the cladding part when growing the soot in the core part. Since the base material for the optical fiber is manufactured by depositing it on the glass and turning it into transparent glass, there is no drop in the refractive index at the boundary between the core part and the cladding part, and a clear step shape can be obtained. For this reason,
It has become possible to produce long single-mode transmission optical fibers with extremely low transmission loss.

[Brief explanation of drawings]

Fig. 1 is a working principle diagram showing the concept of the conventional vapor phase shafting method, and Fig. 2 is a working principle diagram showing the manufacturing concept of the step type optical fiber base material according to the present invention. 12 is a partition plate, 13 is a sintering chamber for the cladding, 14 is a sintering chamber for the core, 15 is a burner for the core, 16 is a soot that becomes the core part, 17 is a burner for the core, and 18 is an air supply pipe for balance. , 20 is a burner for the cladding, 21 is a transparent vitrified core part, 22
23 is a sintering furnace for the cladding, 26 is a mead rod, 28 is a base material for an optical fiber, and 29 is a transparent vitrified cladding portion.

Claims (1)

[Claims] 1 In the core sintering chamber at the bottom of Matsufuru, which is divided into upper and lower parts by a partition plate, the glass raw material that will become the core is flame-hydrolyzed, and the resulting soot is grown into a rod shape and dehydrated and made into transparent glass at the same time. In the cladding section sintering chamber at the upper part of the matsuful, which is divided into upper and lower parts by a partition plate, the glass raw material that will become the cladding section is flame-hydrolyzed, and the soot obtained thereby is used in the core section pulling process. A method for manufacturing an optical fiber base material, characterized in that the soot is continuously deposited around the rod-shaped core part which has been transparently vitrified in the middle, and the soot is dehydrated and transparently vitrified at the same time.