JPH02304B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in a method for manufacturing an optical fiber preform by an internal chemical vapor deposition method.

The internal chemical vapor deposition method, which is one of the manufacturing methods for the quartz-based optical fiber base material, is a raw material for glass.
Raw material gases such as SiCl ₄ , GeCl ₄ , POCl ₃ , and BBr ₃ are sent together with oxygen into a heated quartz tube, forming a cladding layer on the inner wall of the quartz tube and a core layer having a higher refractive index than the cladding layer. This is a method of depositing and synthesizing.

At this time, there is a strong demand that the optical fiber obtained by spinning the optical fiber base material not only has a low transmission loss, but also that the formation time of the deposited layer is quick.

FIG. 3 is a cross-sectional view showing a method of manufacturing an optical fiber base material by internal chemical vapor deposition method, in which 1 is a material forming the cladding of the optical fiber, for example, an outer diameter of 25 mm;
It is a quartz tube with an inner diameter of 22 mm and a length of 800 mm.

Support tubes for mounting and rotating the quartz tube 1 on a glass lathe 7 are fused to both ends of the quartz tube 1, and one of these two support tubes is attached to a driving chuck 5 mounted on the bed of the glass lathe 7. The exhaust side support pipe 3 is supported, and the driven side chuck 6
The input side support pipe 2 is supported by the input side support pipe 2.

The end of the input side support pipe 2 is constricted and connected to a raw material gas supply device 10 via a rotation joint 9.

The raw material gas supply device 10 is a raw material for glass.
Raw material gases such as SiCl ₄ , GeCl ₄ , POCl ₃ , BBr ₃ and
This is a device that stores O ₂ and supplies it to the quartz tube 1 at a desired temperature (for example, 40° C.), adjusting the supply amount to a predetermined amount for each raw material gas.

The oxyhydrogen burner 8, which reciprocates on the bed of the glass lathe 7 parallel to the axis of the quartz tube 1, heats the outer peripheral surface of the quartz tube 1 to 1300°C to 1600°C, and injects the raw material gas into the quartz tube 1. This causes a thermal oxidation reaction.

The forward movement of this oxyhydrogen burner 8 (movement from the input side support pipe 2 side to the exhaust side support pipe 3 side, indicated by the symbol X ₁ ) is normally 20 cm/min, and the backward speed (indicated by the symbol X ₂ ) is 20 cm/min. is a fast speed of 500 cm/min, for example.

Therefore, it took more than 4 minutes to deposit one glass layer on the 80 cm long quartz tube 1.
Further, since 50 core deposited layers are normally required in order to smooth the refractive index distribution shape, it takes a long time of 200 minutes or more to form the core deposited layer.

[Conventional technology]

By increasing the moving speed of this oxyhydrogen burner 8,
In order to shorten the manufacturing time of the optical fiber base material, the following measures have been conventionally taken.

The oxyhydrogen burner 8 was moved repeatedly at a forward speed of 25 cm/min, and SiCl ₄ gas was poured into the quartz tube 1 at a rate of 1000 cm/min.
cc/min, POCl ₃ gas was supplied at a supply rate of 100 c.c./min, and five layers of SiO ₂ -P ₂ O ₅ cladding deposited layer 21 were formed.
It is formed on the inner wall surface of the quartz tube 1.

Thereafter, 50 core deposit layers 22 having a composition of SiO ₂ --GeO ₂ --P ₂ O ₅ are formed on the inner surface of the clad deposit layer 21.

In Figure 2, the vertical axis shows the supply flow rate (cc/min) of raw material gas.
, the horizontal axis shows the number of core deposited layers, and the curve M ₁ is
It is the supply flow rate of _GeCl4 , and the straight line _N1 is the supply flow rate of _SiCl4 .

SiCl ₄ gas and O ₂ are constant throughout the formation process of the core deposit layer 22, and the supply flow rate is 1000 c.c./min, and the POCl ₃ gas is constant at 350 c.c./min.

The amount of GeCl ₄ is determined at the initial stage of the number of core deposited layers in order to make the refractive index distribution curve of the optical fiber almost trapezoidal and the refractive index distribution index to be 4.
It is low at approximately 150 c.c./min, and gradually increases as the number of core deposited layers 22 increases, as shown by curve _M1 . This is the innermost layer of the core deposit layer 22.
In the 50th layer, it is 1800c.c./min.

Conventionally, to adjust and form the refractive index distribution index as described above, the SiCl ₄ gas was kept constant and the GeCl ₄ gas supply amount was adjusted and supplied, and the moving speed of the oxyhydrogen burner 8 was increased to form the optical fiber matrix. It shortens the manufacturing time of materials.

[Problems to be solved by the invention] However, the optical fiber obtained by spinning the optical fiber base material by the above conventional manufacturing method has a low transmission loss of 0.68 dB/Km for light waves with a wavelength of 1.3 μm. However, the transmission loss of light waves with a wavelength of 0.85 μm is
There is a problem that it is high at 2.85dB/Km.

[Means for solving problems]

In order to solve the above conventional problems, in the present invention, the amount of GeCl ₄ gas supplied is made larger when forming the intermediate deposited layer of the core deposited layer than when forming the initial deposited layer and the later deposited _layer , and The amount of gas supplied is decreased as the number of layers increases from when the core deposited layer is initially formed, so that the refractive index distribution curve of the core of the optical fiber is adjusted to a desired value. .

[Effect]

The optical fiber obtained using the conventional method has a wavelength of 1.3 μm.
The reason why the transmission loss is small at the wavelength of 0.85 μm and large at the wavelength of 0.85 μm is due to the ultraviolet absorption of GeO generated in the core deposited layer.

This GeO has a fast moving speed in the oxyhydrogen burner and a large amount of GeCl ₄ to be supplied, so the expected oxidation reaction time of GeCl ₄ +O ₂ →GeO ₂ +2Cl ₂ is insufficient, and 2GeCl ₄ +O ₂ →It is produced by the reaction of GeO + 4Cl ₂ .

According to the means of the present invention, GeCl ₄ gas is adjusted to be supplied in a predetermined small amount even though the oxyhydrogen burner moves quickly, so that GeCl ₄ gas is not oversupplied. Therefore, the generation time for GeO ₂ is secured, and GeO is not generated.

In addition, the amount of SiCl ₄ gas supplied decreases as the number of layers increases from when the initial layer of the core deposited layer is formed, and when the final deposited layer is formed, it is supplied less than the amount of GeCl ₄ gas, so that the desired refraction of the core can be achieved. A rate distribution curve is obtained.

〔Example〕

FIG. 1 is a raw material gas supply composition diagram in one embodiment of the present invention.

The present invention uses the apparatus shown in FIG. 3, moves the oxyhydrogen burner 8 repeatedly at a forward speed of 25 cm/min, and feeds SiCl ₄ gas into the quartz tube 1 at 1000 c.c./min.
A cladding layer 21 of SiO ₂ -P ₂ O ₅ is formed by supplying POCl ₃ gas at a supply rate of 100 c.c./min and O ₂ at a supply rate of 1000 c.c./min.
Five layers are formed on the inner wall surface of the quartz tube 1 in the same manner as before.

Thereafter, 50 core deposit layers 22 having a composition of SiO ₂ --GeO ₂ --P ₂ O ₅ are formed on the inner surface of the clad deposit layer 21.

In this case, the supply amount of each raw material gas is as shown in the raw material gas supply composition diagram of FIG. 3.

Figure 3 shows the raw material gas supply flow rate (cc/min) on the vertical axis.
, the horizontal axis shows the number of core deposited layers, and the curve M ₂ is
It is the supply flow rate of _GeCl4 gas, and the straight line _N2 is the supply flow rate of _SiCl4 .

O ₂ is constant throughout the formation process of the core deposit layer 22 at a rate of 1000 c.c./min, and POCl ₃ gas is supplied at a rate of 1500 c.c./min during the formation of the first layer of the core deposit layer 22. , thereafter, as the number of layers increases, the amount is linearly reduced by a fixed amount until the final deposited layer is formed, at the 50th layer, at 500 c.c./min.

On the other hand, the supply rate of GeCl ₄ is 150 c.c./min for the first layer of the core deposit layer 22, and gradually increases as the number of layers increases, and is approximately 1400 c.c./min for the 25th intermediate layer. reaches its highest value, and then gradually decreases as the number of layers increases, reaching 800 at the 50th layer when the final deposited layer is formed.
cc/min.

In this way, GeCl ₄ gas, which is an additive raw material that increases the refractive index of the optical fiber, is supplied according to the medium-high curve M ₂ , and the refractive index distribution index that the refractive index distribution curve of the optical fiber is almost trapezoidal is obtained. is set to 4.

In the optical fiber base material obtained in this way, the amount of GeCl ₄ gas supplied during the latter stage of core deposition layer formation is significantly lower than in the conventional method, so the amount of GeO produced is extremely small.

Therefore, the optical fiber obtained by spinning such an optical fiber base material not only has a low transmission loss of approximately 0.68 dB/Km for light waves with a wavelength of 1.3 μm, but also has a low transmission loss of approximately 0.68 dB/Km for light waves with a wavelength of 0.85 μm. Transmission loss of light waves
2.30dB/Km, which is 0.5dB/Km lower than the conventional model.

〔Effect of the invention〕

As explained above, the present invention has low transmission loss even in the short wavelength band of 0.85 μm, and
It has excellent practical effects, such as shortening the manufacturing time of the optical fiber base material.

[Brief explanation of drawings]

Fig. 1 shows a raw material gas supply composition diagram of an embodiment of the present invention, Fig. 2 shows a conventional raw material gas supply composition diagram, and Fig. 3 shows a method for manufacturing an optical fiber base material by internal chemical vapor deposition method. FIG. In the figure, 1 is a quartz tube, 2 is an input side support pipe, 3 is an exhaust side support pipe, 5 is a drive side chuck, 6 is a driven side chuck, 7 is a glass lathe, 8 is an oxyhydrogen burner, 9 is a rotating joint, 10 is a raw material gas supply device, 21 is a cladding layer, 22 is a core layer, M ₁ and M ₂ are GeCl ₄ supply curves, N ₁ and N ₂
shows the _SiCl4 supply curve.

Claims (1)

[Claims] 1. In the production of optical fiber base material by internal chemical vapor deposition, the amount of GeCl ₄ gas supplied to the quartz tube is higher when forming the intermediate layer of the core layer than when forming the initial layer and the later layer. increase and
Production of an optical fiber base material characterized in that the supply amount of SiCl ₄ gas is supplied such that it decreases as the number of layers increases from the time of initial layer formation of the core deposited layer to form the core deposited layer. Method.