JP2721944B2 - Method for manufacturing optical fiber preform and apparatus for manufacturing optical fiber preform - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber preform in which glass fine particles are produced by a flame hydrolysis reaction and deposited on a starting material to obtain a porous glass body. The present invention relates to an optical fiber preform manufacturing method and an optical fiber preform manufacturing apparatus capable of obtaining an optical fiber preform excellent in transmission loss and transmission band using the same.

[0002]

2. Description of the Related Art Generally, in an optical fiber, light propagates through the core while undergoing total reflection at the interface between the core and the clad of the optical fiber. The manner of propagation varies depending on the refractive index distribution of the core. When the core diameter of the step index type or the graded index type is several tens μm or more, the light path differs depending on the incident angle of light, and a large number of optical paths are generated. When the outer diameter of the core is about 5 to 15 μm, light travels straight through the core without being reflected on the boundary surface between the core and the clad, and the optical path becomes one. Such an optical fiber is a single mode optical fiber.

In such an optical fiber, it is ideal that the intensity of the incident light is emitted without attenuating. However, various kinds of light are propagated while propagating through the core of the optical fiber. This causes transmission loss. The degree to which the light intensity becomes weaker while propagating through the optical fiber is the transmission loss of the optical fiber. The transmission loss of an optical fiber is mainly caused by absorption due to electron transition in the ultraviolet region, absorption due to molecular vibration in the infrared region, Rayleigh scattering inversely proportional to the fourth power of wavelength, and absorption due to impurities, particularly water (hydroxyl ions / OH groups). And has a wavelength dependency as a sum of these.

[0004] In an optical fiber, the larger the transmission band, the larger the information transmission capacity. That is, the wider the transmission band, the more signals can be sent at once. This transmission band is represented by a value where a signal having a constant amplitude having a band from DC to high frequency is input to one end of an optical fiber having a length of 1 km and the amplitude of a received signal at an output end is reduced by 6 dB. is there.

[0005] Since these transmission loss and transmission band affect the performance of the optical fiber, a method for improving the transmission loss and transmission band has been conventionally devised in a method of manufacturing the optical fiber. It is known to add Ge to the core in order to increase the refractive index of the core. However, this Ge
Is an impurity for the core of the optical fiber, which causes Rayleigh scattering of light propagating in the core and causes transmission loss. Therefore, fluorine is added to the cladding layer to reduce scattering and attenuation of light from the core, thereby preventing an increase in transmission loss.

As a method of manufacturing an optical fiber preform by adding fluorine to the cladding layer, conventionally, an external method (O
VD method There is a method as shown in JP-A-1-230445 by Outside Vapor Deposition. In this conventional example, as shown in FIG. 4, a porous base material 120 in which SiO ₂ glass particles are deposited on a pure quartz or Ge-containing quartz rod 100 by a torch 110 is transparently vitrified in an atmosphere containing SF _6. The fluorine is added to the cladding layer.

Similarly, as a method of manufacturing an optical fiber preform by adding fluorine to a cladding layer, a conventional method of attaching an optical fiber (V
AD method (Vapor Phase Axial Deposition) as disclosed in JP-A-1-270533. In this manufacturing method, as shown in FIG. 5, a core torch 200 hydrolyzes SiCl ₄ vapor using flammable gas (H ₂ ) and oxygen, deposits soot of air-rich SiO ₂ in multiple layers, and forms a porous layer. The core part 210 is obtained. The cladding torch 220 places SiCl on the porous core 210.
The steam of No. ₄ is hydrolyzed using combustible gas (H ₂ ) and oxygen to deposit air-rich SiO ₂ to obtain the porous clad portion 230. At this time, by changing the manufacturing conditions at the time of manufacturing the core and the manufacturing conditions at the time of manufacturing the clad, the density distribution of the entire porous preform becomes higher as shown in FIG. In this way, the film is made transparent in the atmosphere of SF ₆ . This prevents SF ₆ in the atmosphere from entering the core.

[0008]

However [0007], than previous accounting former method, SiO ₂ constituting the core portion
In order to deposit glass particles, pure quartz or Ge
It is necessary to prepare the containing quartz rod, and there is a problem that the manufacturing process of the optical fiber preform becomes complicated. Pure quartz or G, which is a starting material for depositing the core portion,
When depositing SiO ₂ glass fine particles, the surface of the e-containing quartz rod is exposed to the flame 130, and OH groups are mixed in the core portion, resulting in an increase in transmission loss of the optical fiber. have.

According to the conventional latter method, it is possible to prevent SF ₆ in the atmosphere from entering the core by forming a step in the density distribution of the entire porous base material. Gas such as Cl ₂ for the purpose of dehydration to remove the OH group contained in
The H group cannot be removed. That is, the vapor of SiCl ₄ is converted to combustible gas (H ₂ ) by the core torch 200.
When it is hydrolyzed and deposited using oxygen, impurities such as OH groups contained in the soot of SiO ₂ remain in the porous core portion 210 itself, thereby increasing transmission loss. ing.

It is an object of the present invention to provide a method for manufacturing an optical fiber preform and an apparatus for manufacturing an optical fiber preform with a small transmission loss even when fluorine is added to the cladding layer and fluorine does not enter the core. The purpose is.

[0011]

To achieve the above object, according to the solution to ## in the method for manufacturing an optical fiber preform, pure SiO ₂
Is uniformly deposited SiO ₂ -GeO ₂ skin layer on the core soot, the predetermined clad amount porous preform created by depositing a flame hydrolysis and then dehydrated by Cl _2, thereafter SiO ₂ baked Heat treatment at a temperature lower than the sintering temperature to sinter only the skin layer, and then heat treatment at a clearing temperature of SiO ₂ while introducing an atmosphere gas containing SF ₆ to sinter the clad layer. It is like that.

[0012] To achieve the above object, the apparatus for manufacturing an optical fiber preform includes a core torch to deposit a pure SiO ₂ core soot, SiO on pure SiO ₂ core soot formed by the core torch _2- Ge
A porous preform manufacturing apparatus provided with a cladding layer torch for depositing an O ₂ cladding layer, and a dehydration / clearing treatment apparatus for dehydrating / clearing a porous preform manufactured by the porous preform manufacturing apparatus In the apparatus for manufacturing an optical fiber preform constituted by the above, the porous preform manufacturing apparatus is provided with S on a pure SiO ₂ core soot formed by the core torch.
A skin layer torch for depositing an iO ₂ -GeO ₂ skin layer is provided.

[0013]

[Function] 3% as a mole fraction on pure SiO ₂ core soot
The following SiO ₂ -GeO ₂ skin layer is uniformly deposited,
Further, a clad is deposited on the skin layer. The porous base material thus prepared, including the skin layer and the core, is subjected to dehydration treatment with Cl ₂ . Then, below the sintering temperature of the SiO ₂ SiO ₂ -GeO ₂ sintering temperature (1
(About 400 ° C.) to sinter only the skin layer. Further, while introducing an atmosphere gas containing SF ₆ ,
The core and the clad layer are sintered by performing a heat treatment at a clearing temperature of iO ₂ (about 1450 ° C.).

[0014]

Embodiments of the present invention will be described below. FIG. 1 is a process flowchart showing an embodiment of a method for manufacturing an optical fiber preform according to the present invention. A method for manufacturing an optical fiber preform will be described according to the processing procedure shown in the figure.

First, in step 1, the vapor of SiCl ₄ is hydrolyzed using combustible gas (H ₂ ) and oxygen to deposit pure SiO ₂ core soot. The pure SiO ₂ core obtained at this time is a porous core containing much air. When the porous core is formed in step 1, in step 2, SiCl ₄ and GeCl _{4 are formed.}
Is vaporized using combustible gas (H ₂ ) and oxygen to uniformly deposit a SiO ₂ —GeO ₂ skin layer having a mole fraction of 3% or less on the porous core. This skin layer does not need to be formed thick. And in step 3,
Hydrolyzing the vapor of SiCl ₄ with combustible gas (H ₂ ) and oxygen to deposit SiO ₂ to form a cladding layer,
A porous matrix is formed. This cladding layer is a porous cladding containing much air.

Next, in step 4, the formed porous base material is mixed with He gas and oxygen and dehydrated with heated Cl ₂ gas. At this time, dehydration treatment is performed on the clad layer, the skin layer, and the core. When the dehydration process is performed in step 4, in step 5, below the sintering temperature of the SiO _2, sintering only the skin layer is heat treated at a sintering temperature of SiO ₂ -GeO _2. This is SiO
_This utilizes the property that the sintering temperature of _2- GeO ₂ is lower than the sintering temperature of SiO ₂ . The temperature of this heat treatment is about 1400 ° C. This SiO ₂ -GeO ₂
By the heat treatment at the sintering temperature, the core and the clad layer remain in a porous state, and the OH groups have already been removed from the core and the clad layer because the dehydration has already been performed in step 4. It is in the state that it is.

In step 5, when only the skin layer is sintered, in step 6, the sintered porous base material of the skin layer is continuously supplied with He, Cl ₂ and SF ₆ gases. The core and the clad layers are sintered in a gas atmosphere and heated at a temperature for making SiO ₂ transparent for a predetermined time. The clearing temperature of this SiO ₂ is about 1450 ° C. At the time of the transparency heat treatment in step 6, fluorine is added to the cladding layer, and at the same time, fluorine diffuses into the skin layer. However, since the skin layer is already semi-sintered in step 5, the fluorine added to the cladding layer is guarded by the skin layer to prevent the fluorine from entering the core. In addition, since the skin layer itself is mixed with GeO ₂ remaining in the skin layer, fluorine is mixed therein, so that the refractive index is offset by the two components of Ge and fluorine, and the optical fiber base having a good RI distribution as a whole is obtained. Get the material. In this step 6, the transparent heat treatment is not performed.
Is, core, skin layers, the clad layer has finished the production of optical fiber preform having a good RI distribution when transparent.

FIGS. 2 and 3 show an embodiment of an apparatus for manufacturing an optical fiber preform according to the present invention.

In the figure, reference numeral 10 denotes a porous base material manufacturing apparatus, in which an SiO ₂ -GeO ₂ skin layer is deposited on a pure SiO ₂ core soot, and a SiO ₂ cladding layer is deposited on the skin layer. It is used to produce quality base materials.
11 is a core torch, which is pure Si
It supplies O ₂ core soot. That is, the core torch 11 converts the vapor of SiCl ₄ to a combustible gas (H ₂ ).
This is for generating pure SiO ₂ core soot by hydrolysis using oxygen and oxygen to deposit pure SiO ₂ core soot on the tip of a quartz rod serving as a seed. When this quartz rod is pulled up while rotating, a pure SiO ₂ core soot containing a large amount of air supplied from the core torch 11 is continuously deposited and grown. The pure SiO ₂ core obtained at this time is
The porous core 14 contains a lot of air.

Reference numeral 12 denotes a torch for the skin layer, which is provided above the torch for the core 11 and is made of SiO ₂ --GeO _2.
Is supplied continuously. In other words, the skin layer torch 12 hydrolyzes the vapors of SiCl ₄ and GeCl ₄ using combustible gas (H ₂ ) and oxygen to form a SiO ₂ -GeO ₂ skin layer 15 having a mole fraction of 3% or less. This is for uniformly depositing on the porous core 14.
SiO ₂ -G supplied from the skin layer torch 12
The eO ₂ becomes a thin film by rotating and pulling up the quartz rod, and is uniformly and continuously deposited on the porous core 14 to grow. The skin layer 15 does not need to be formed thick.

Reference numeral 13 denotes a clad layer torch, which is provided above the skin layer torch 12 and continuously supplies SiO ₂ . That is, the torch 13 for the cladding layer converts the vapor of SiCl ₄ into a combustible gas (H ₂ ).
This is for depositing SiO ₂ on the skin layer 15 by hydrolysis using oxygen and oxygen. S obtained at this time
The iO ₂ cladding is a porous cladding layer 16 containing a large amount of air.

The porous core 20, the skin layer 15, and the porous clad layer 16 constitute a porous preform 20.

Reference numeral 30 denotes a dehydration / clearing treatment device for dehydrating / clearing the porous preform 20 produced by the porous preform production device 10 to produce a preform (optical fiber preform). Reference numeral 31 denotes a quartz tube, which is a container for dehydrating and making the porous base material 20 transparent. Reference numeral 32 denotes a heating element for heating the porous base material 20 inserted into the quartz tube 31 to perform dehydration processing and heat sintering processing of the clad layer 16, the skin layer 15, and the core 14.

Reference numeral 33 denotes an atmosphere gas inlet, and the cladding layer 1
6. Atmosphere gas sent into the quartz tube 31 when the skin layer 15 and the core 14 are dehydrated, and inside the quartz tube 31 when the cladding layer 16, the skin layer 15 and the core 14 are heated and sintered. This is for introducing the atmospheric gas to be sent. Reference numeral 34 denotes an atmosphere gas discharge port for discharging the used atmosphere gas used for the dehydration process and the used atmosphere gas used for the heat sintering process inside the quartz tube 31 to the outside of the quartz tube 31. . Reference numeral 35 denotes a lifting device, which is a porous base material 20.
When the substrate is dehydrated / cleared, the optical fiber preform 40 produced by dehydrating / transparenting the porous preform 20 is pulled upward while rotating and rotating as shown by the arrow A.

Next, the operation of the dehydrating / clearing processing apparatus 30 will be described. First, the porous preform 20 manufactured by the porous preform manufacturing apparatus 10 is housed in a quartz tube 31,
He and Cl ₂ are introduced into the quartz tube 31 through the atmospheric gas inlet 33.
Is continuously fed together with oxygen. The porous body 20 is dehydrated by being heated by the heating element 32 while feeding the gas. By this dehydration treatment, the porous base material 20
Is dehydrated including the cladding layer 16, the skin layer 15, and the core 14. When this dehydration treatment is performed, SiO ₂ −
Utilizing the property that the sintering temperature of GeO ₂ (about 1400 ° C.) is lower than that of SiO ₂ (about 1450 ° C.)
The heating element 32 is operated to heat the inside of the quartz tube 31 at a sintering temperature of SiO ₂ -GeO ₂ (about 1400 ° C.) lower than the sintering temperature of SiO ₂ (about 1450 ° C.), and only the skin layer 15 is baked. Tie. At the stage where only the skin layer 15 is sintered, the core 14 and the cladding layer 16 remain in a porous state.

When only the skin layer is sintered, the quartz tube 31
A mixed gas of He, Cl ₂ , and SF ₆ is continuously supplied from the atmosphere gas inlet 33 into the inside, the heating element 32 is operated, and the inside of the quartz tube 31 is kept at a transparent temperature of SiO ₂ (about 1450 ° C.) for a predetermined time. The core 14 and the clad layer 16 are sintered by heating.
The core 14 and the clad layer 1 when performing this transparent heat treatment
No. 6 is in a state where the OH group has already been removed in the dehydration treatment in the previous step. When this transparent heat treatment is performed, fluorine is added to the cladding layer 16, and at the same time, fluorine diffuses into the skin layer (SiO ₂ —GeO ₂ ) 15, and GeO ₂ volatilizes from the skin layer 15. But,
The fluorine added to the cladding layer 16 is in a state in which the skin layer 15 is already semi-sintered, and is protected by the skin layer 15 and does not enter the core 14. Also, skin layer 1
Since fluorine itself is mixed with GeO ₂ remaining on the skin layer 15, the refractive index is offset by the two components of Ge and fluorine, and a good RI distribution is obtained as a whole. The optical fiber preform 40 is manufactured in this manner, and the optical fiber preform 40 having a continuous rod shape is obtained by being pulled up by the elevating device 35.

[0027]

Since the present invention is configured as described above, it has the following effects.

[0028] SiO ₂ -Ge on the pure SiO ₂ core soot
A porous base material formed by depositing an O ₂ skin layer uniformly and depositing a predetermined clad amount is subjected to flame hydrolysis and dehydration treatment with Cl ₂ , and then a temperature lower than the sintering temperature of SiO _2. Sintering only the skin layer, and then, while introducing an atmosphere gas containing SF ₆ ,
Since the clad layer is manufactured by heat treatment at the transparentizing temperature of O ₂ to sinter the clad layer, fluorine can be added to the clad layer without fluorine penetrating into the core, and an optical fiber with low transmission loss A base material can be obtained.

A core torch for depositing a pure SiO ₂ core soot and a porous torch having a cladding layer torch for depositing a SiO ₂ -GeO ₂ cladding layer on the pure SiO ₂ core soot formed by the core torch. A porous matrix of an optical fiber preform manufacturing apparatus comprising a porous preform manufacturing apparatus and a dehydration / clearing processing apparatus for dehydrating / clarifying the porous preform manufactured by the porous preform manufacturing apparatus Since the material manufacturing apparatus is provided with the skin layer torch for depositing the SiO ₂ —GeO ₂ skin layer on the pure SiO ₂ core soot formed by the core torch, the skin layer can be formed on the core portion. Since fluorine can be prevented from entering the core when fluorine is added to the cladding layer by this skin layer, fluorine is added only to the cladding layer. Thus, an optical fiber preform having a small transmission loss can be obtained.

[Brief description of the drawings]

FIG. 1 is a process flowchart showing an embodiment of a method for manufacturing an optical fiber preform according to the present invention.

FIG. 2 is a schematic view showing an embodiment of a porous preform manufacturing apparatus of the optical fiber preform manufacturing apparatus according to the present invention.

FIG. 3 is a schematic view showing an embodiment of an apparatus for dehydrating / clearing an optical fiber preform manufacturing apparatus according to the present invention.

FIG. 4 is a view showing a method of manufacturing an optical fiber preform by adding fluorine to a cladding layer by a conventional external method.

FIG. 5 is a view showing a method of manufacturing an optical fiber preform by adding fluorine to a cladding layer by a conventional VAD method.

FIG. 6 is a diagram showing a density distribution of the entire porous preform shown in FIG. 5;

[Explanation of symbols]

10 Porous base material manufacturing device 11 Core torch 12 ………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………………………………………………………………. ……………………… Porous core 15 …………………………………… Skin layer 16 ……………… ... Porous cladding layer 20 Porous cladding layer 30 Porous base material 30 ……………………………………………………………………………………………………………… Quartz tube 32 ………………………… ………………………………………………………………………………… Atmospheric gas introduction 34 …………………………………………………………………………………………………………………………………………………………………………………………… 40 ……………………………… Optical fiber preform

Claims (2)

(57) [Claims] Claims 1. An SiO ₂ -G on a pure SiO ₂ core soot.
An eO ₂ skin layer is uniformly deposited, and a porous base material formed by depositing a predetermined clad amount is subjected to flame hydrolysis and dehydration treatment with Cl ₂ , and then to a temperature lower than the sintering temperature of SiO _2. Sintering only the skin layer by heat treatment,
Then, while introducing an atmosphere gas containing SF ₆ ,
method for manufacturing an optical fiber preform by heating at clearing temperature of iO _2, characterized in that the cladding layer so as to sinter. 2. A core torch for depositing a pure SiO ₂ core soot, and a pure S formed by the core torch.
A porous base material manufacturing apparatus provided with a cladding layer torch for depositing a SiO ₂ -GeO ₂ cladding layer on an iO ₂ core soot, and a porous base material manufactured by the porous base material manufacturing apparatus is dehydrated and transparent. In the manufacturing apparatus of the optical fiber preform constituted by the dehydration and transparency processing apparatus
SiO ₂ in the porous base material manufacturing apparatus on pure SiO ₂ core soot formed by the core torch -GeO ₂
An apparatus for producing an optical fiber preform, comprising a skin layer torch for depositing a skin layer.