JPH0526733B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the dimensions of an optical fiber preform, and a manufacturing apparatus that enables dimension control.

[Conventional technology]

FIG. 1 is a cross-sectional view of the porous base material, in which 1 is a porous glass body for the core, and 2 is a porous glass layer for the cladding.

Conventionally, as a method for adjusting the core/cladding ratio (D ₁ /D ₂ ) in the base material manufactured by the VAD method, a porous glass layer for the cladding is formed on the side surface of a porous base material for the core having predetermined dimensions. The method used was to adjust the thickness of the core to achieve the desired core/cladding ratio. However, this conventional method has several problems as shown below.

First, when manufacturing a base material with a desired core/cladding ratio using conventional methods, it is difficult to achieve the desired core/cladding ratio with high precision, especially for single mode fibers that require a thick cladding. It was extremely difficult to make the material.

In addition, in the conventional method, it is difficult to reduce the size of the porous base material for the core.
It is difficult to achieve a cladding diameter (D ₂ ≧ 10 × D ₁ ) that is 10 times or more than the core diameter, and even if a cladding diameter that is 10 times or more the core diameter is achieved, the dimensions of the porous base material The problem was that it became extremely large, making it difficult to sinter and make it transparent.

[Problem that the invention seeks to solve]

As explained above, conventional methods have problems in that it is difficult to achieve a desired core/cladding ratio with high precision, and it is also difficult to obtain a cladding thickness that is 10 times or more larger than the core diameter. .

The purpose of the present invention is to solve the above-mentioned problems and provide a method and apparatus for manufacturing an optical fiber base material that achieves a desired core/cladding ratio with high precision and a cladding diameter that is 10 times or more the core diameter. It is about providing.

[Means for solving problems]

To summarize the present invention, the first invention of the present invention relates to a method for manufacturing an optical fiber base material, which includes:
Fine glass particles synthesized in a flame are deposited in the axial direction of the starting material to form a porous glass body for the core,
Next, glass fine particles are deposited on the side surface of the porous glass body for the core to form a porous glass layer for the cladding, and then heated and sintered at a high temperature to form a transparent glass body.A method for manufacturing an optical fiber base material. In this step, prior to forming the porous glass layer for the cladding, the porous glass body for the core is exposed to a flame or a reactive atmosphere containing a fluorine compound at a temperature of 100°C or higher to be etched to the desired dimensions. After that, a porous glass layer for the cladding is formed on the side surface of the porous glass body for the core.

A second invention of the present invention relates to an apparatus for manufacturing an optical fiber base material, and the second invention relates to an apparatus for manufacturing an optical fiber base material, and includes means for depositing glass particles in the axial direction of a rotating starting material to form a porous glass body for a core, and a means for forming a porous glass body for a core. A means for etching a porous glass body for use by exposing it to a flame or a reactive atmosphere containing a fluorine compound, a means for measuring the dimensions of the etched porous glass body for a core and adjusting the amount of etching, and a means for etching the core after etching. The present invention is characterized by having means for forming a porous glass layer for cladding on the side surface of the porous glass body for use as a cladding, and means for heating and sintering the porous glass body within the same process or in a separate process.

In the present invention, prior to forming the porous glass layer for the cladding, the porous glass body for the core is etched by exposing it to a flame or a reactive atmosphere containing a fluorine compound to obtain a desired size, and then the porous glass body for the cladding is formed. The most important feature is the formation of a high-quality glass layer, and as a result, a desired core/clad ratio (D ₁ /D ₂ ) can be achieved with high precision. The present invention also provides a method for manufacturing an optical fiber base material having such functions. Therefore, the conventional method adopts a method in which the thickness of the porous glass layer for the cladding formed on the side surface of the porous glass body for the core having predetermined dimensions is adjusted to achieve a desired core/cladding ratio. The technical contents are essentially different.

The basic principle of the method of the present invention will now be explained as follows. That is, in the base material structure shown in Fig. 1, the desired core/clad ratio (D ₁ /D ₂ )
Methods to achieve this include (1) adjusting the thickness of the cladding layer deposited on the side surface of a given core porous body, and (2) changing the dimensions of the core porous body while keeping the thickness of the cladding layer constant. ,You could think so. While the conventional method belongs to method (1), the present invention
This method belongs to method (2).

Therefore, in the present invention, first, the core porous base material is etched to adjust the dimensions using the reaction of formula (1): SiO ₂ +4F→SiF ₄ ↑+O ₂ ↑ ...(1) .

Generally, as shown in Fig. 1, the diameter of the core porous matrix is _D1 , the diameter of the clad porous layer is _D2 ,
When the core/clad ratio R is R=D ₁ /D ₂ , D ₁ ,
Considering the rate of change in R when D ₂ is changed, it is as follows. That is, the change in R with respect to D ₁ is R
When differentiated by D ₁ , dR/dD ₁ =1/D ₂ ...(2) Moreover, the rate of change of R with respect to D ₂ is dR/dD ₂ =-D ₁ /D ₂ ² ...(3). Therefore, comparing the magnitude of the rate of change in equations (2) and (3), |dR/dD ₁ |-|dR/dD ₂ |=1/D ₂ (1-D ₁ /D ₂ )...
...(4), and since D ₁ <D ₂ as shown in Fig. 1, from equation (4), |dR/dD ₁ |>|dR/dD ₂ | ...(5). Therefore, it can be seen that R can be changed significantly by changing _D1 , and the core/clad ratio can be easily adjusted. Therefore, in the present invention,
R is controlled by keeping D ₂ constant and varying D ₁ .

As a method for changing D ₁ , etching with a fluorine compound shown in formula (1) is effective, and this can be achieved by introducing CF ₄ or the like into the flame. FIG. 2 shows the etching rate when a porous glass body is etched by introducing CF ₄ into a flame.

That is, FIG. 2 is a graph showing the relationship between the CF ₄ gas concentration in the flame (mol %, horizontal axis) and the etching rate (mm/min, vertical axis).

When the CF ₄ concentration in the flame is changed between 0 and 0.1 mol%, the etching rate changes as shown in Figure 2.
The dimensions of the porous glass body can be easily changed.

The reaction rate of SiO ₂ and fluorine increases with temperature, and it is preferable to carry out the reaction at a temperature of 100° C. or higher. When CF ₄ is flowed into the flame formed by oxyhydrogen, a reaction temperature of about 600°C can be obtained.
However, if the reaction rate is significantly increased,
The etched surface of the base material becomes rough and causes problems such as foaming when turning into transparent glass. This problem also occurs when the amount of etching is significantly increased. A part of the fluorine used in etching is incorporated into the base material. Fluorine is known as an element that lowers the refractive index of SiO ₂ , but the fluorine incorporated into the base material during etching is completely removed during the process of making the base material transparent, and the refractive index of the transparent glass is reduced. There is no effect on the rate.

The fluorine compound for etching of the present invention includes:
In addition to CF ₄ , fluorine compounds such as SF ₆ , C ₂ F ₆ and C ₃ F ₈ can be used. Further, when a high temperature gas of 100° C. or higher is flowed out together with the fluorine compound instead of a flame, the same etching operation as in the example described later can be easily performed.

Further, in the present invention, since the core/cladding ratio can be realized with high accuracy, when the optical fiber base material obtained according to the present invention was drawn, an optical fiber with extremely high dimensional accuracy was obtained.

Furthermore, the method of etching a porous glass body using a flame or reactive atmospheric gas containing a fluorine compound disclosed in the present invention can be used not only for a core porous glass body but also for a clad porous glass layer. be.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

3 and 5 are configuration diagrams of an example of the apparatus of the present invention, FIG. 4 is an enlarged sectional view of the core porous glass body forming part in FIG. 3, and FIG.
7 and 7 are configuration diagrams of a core forming section in another example of the device of the present invention.

Example 1 FIG. 3 shows Example 1 of the present invention. In FIG. 3, 21 is a rotating and pulling part, 22 is a starting material,
23 is a porous glass layer for the cladding, 24 is a porous glass body for the core, 25 is a porous glass body for the core with a reduced diameter, 26 is a torch for the core, 27 is a torch for etching, 28 is a torch for the cladding, 29 210 is an exhaust port, 210 is a protective container, and 211 is an exhaust regulator.

In Figure 3, first, SiCl ₄ was applied to the 26 core torches,
A frit gas such as GeCl ₄ and flame gas such as H ₂ and O ₂ are introduced to form a core porous glass body 24 at the tip of the starting material 22 which is pulled up while rotating. Next, the core porous glass body 24 is exposed to a flame containing CF ₄ ejected from an etching torch 27 to form a small-diameter core porous glass body 25 having the desired dimensions. A porous glass layer 23 for the cladding is formed on the side surface of the porous glass body for the small diameter core.
Thereafter, the porous glass body is heated to a high temperature and sintered to form a transparent optical fiber base material.

In addition, the exhaust gas and excess glass particles from the reaction are exhausted from 29 exhaust ports, and the amount of emissions is 21.
Adjusted by 1. The protective container 210 has the role of insulating the reaction section from the outside air and keeping it clean. Further, D ₁ and D ₁ ' in FIG. 4 represent the diameter of the core porous glass body 24 and the diameter of the small-diameter core porous glass body 25, respectively.

For example, apply _O2 to the core torch 26 at 10 per minute.
After forming a porous glass body for the core with an outer diameter D ₁ = 15 mmφ by supplying H ₂ at 5 c.c./min, SiCl ₄ at 50 c.c./min, and GeCl ₄ at 5 c.c./min, O ₂ per minute 5
, the porous glass body for core 25 is etched to a diameter of 10 mmφ using an etching torch that supplies H ₂ at 5 per minute and CF ₄ at 0.5 per minute. After that,
A 150 mmφ cladding layer was formed using a torch 28. At this time, the cladding torch 28 is filled with O ₂
50, H ₂ and SiCl ₄ at 50 and 2 per minute, respectively. As a result, the core/clad ratio is D ₁ /D ₂
A porous base material with a ratio of D 1 /D 2 = 1/15 was obtained, and was further made into transparent glass to obtain an optical fiber base material with a ratio of D ₁ /D ₂ = 1/15.
Also, the relative refractive index difference between the core and cladding of this base material △
n is 0.3%, and the optical loss of the single mode optical fiber obtained by drawing from this base material is at a wavelength of 1.3 μm,
0.3dB/1cm and 0.2dB/1cm at 1.55μm, respectively
It was hot.

Example 2 FIG. 5 shows Example 2 of the present invention. In FIG. 5, 31 is a rotating and pulling part, 32 is a starting material, and 3
3 is a porous glass layer for the cladding, 34 is a porous glass body for the core, 35 is a porous glass body for the core with a reduced diameter, 36 is a torch for the core, 37 is an etching torch, 38 is a torch for the cladding, 39 is an exhaust port, 310 is a protective container, 311 is a dimension measuring device, 3
12 is a comparator, and 313 is a flow rate regulator.

In the embodiment shown in FIG. 5, first, the outer diameter of the porous glass body 35 for the core, which is obtained by reducing the diameter of the porous glass body 34 for the core, is measured using a dimension measuring device 311. Next, after this result is compared with a set value by a comparator 312, the flow rate regulator 313 is controlled depending on the magnitude thereof, thereby realizing a desired outer diameter dimension.

For example, in the second embodiment, first, the torch 3
6 to form a porous glass body for the core with an outer diameter of 15 mmφ, and the set value is 10 mmφ, the value measured by the dimension measuring device 311 (15 mmφ) and the set value 10
mmφ is compared in the comparator 312, and this difference (5 mm
The output corresponding to φ) is sent to the flow rate regulator 313 as a signal.
is input. As a result, the flow rate regulator 313 adjusts H ₂ :5, O ₂ :5, and CF ₄ :0.5, respectively, and supplies them to the torch 37.
Porous glass body 35 for core with 10mmφ same as setting value
will be formed. Also, change the setting value to 13mmφ
In this case, the output corresponding to the difference from the measured value is input from the comparator 312 to the flow rate regulator 313, and H ₂ ,
The flow rate of gases such as O ₂ and CF ₄ is adjusted and controlled.

By this method, it was easy to keep the difference from the set value to 0.01 mm or less, and as a result, the core/clad ratio matched the set value with high precision.

Furthermore, in the present invention, by changing the amount of etching, a porous glass body for the core with a reduced diameter can be easily obtained, so the core/cladding ratio can be adjusted to 1/10 to 20.
This makes it easy to achieve a cladding diameter that is 10 times or more the core diameter.

Example 3 In Examples 1 and 2 above, the etching operation was performed separately from the formation of the porous glass body for the core.
The etching operation can be performed simultaneously with the formation of the porous glass body for the core. That is, a fluorine compound is introduced into a core-forming torch, and the dimensions are adjusted during the formation of the core porous glass body. FIG. 6 shows a third embodiment of the present invention.

In FIG. 6, 41 is a core torch, 42 is a raw material nozzle, 43 is an etching nozzle, 44 is a flame flow, 45 is a particulate flow, 46 is an etching gas flow,
47 is a porous glass body for the core with a reduced diameter; 48
is the porous glass body for the core before diameter reduction. 6th
The figure is a diagrammatic representation of the situation during diameter reduction. In FIG. 6, a core porous glass body is formed by a flame stream 44 and a particulate stream 45 blown out from a core torch 41, but the etching nozzle 4
3, when no etching gas is introduced, 48 porous glass bodies (diameter D ₁ ) are obtained, and when etching gas is introduced, 47 porous glass bodies (diameter D ₁ ') are obtained. . At this time, when CF ₄ was introduced as etching gas, 0.1/min ~
At a flow rate of 1/min, D ₁ '/D ₁ can be changed by about 0.95 to 0.5.

In addition, the dimension measuring device and comparator shown in Example 2,
By adjusting the inflow amount of etching gas (CF ₄ ) using a flow rate regulator, a core porous glass body of desired dimensions can be formed. Further, by forming a thick cladding layer on the side surface of the porous glass body for the core formed in this manner, an optical fiber base material in which the core/cladding ratio is precisely adjusted can be manufactured.

Example 4 The change in thickness of the cladding porous glass layer caused by the diameter reduction of the core porous glass body shown in Examples 1 to 3 above was solved according to Example 4 shown in FIG. This is to compensate for the damage. In Figure 7, 5
1 is a core porous glass body, 52 is a core porous glass body with a reduced diameter, 53 is a clad porous glass layer, 54 is a dimension measuring device, 55 is a core torch, 5
6 is a torch for the cladding, 57 is a comparator, 58 is a flow rate regulator, and Dc is the diameter of the cladding porous glass layer. In FIG. 7, the core torch 5
When a fluorine compound such as CF ₄ is introduced into the core 5, a core porous glass body 52 with a reduced diameter is formed as shown in Example 3. Along with this, the thickness of the cladding porous glass layer 53 formed by the cladding torch 56 changes, and the diameter Dc changes. The flow rate regulator 58 is controlled through a comparator 57 so that Dc is a constant value. As a result, even if the core diameter changes when the core porous glass body is made smaller in diameter, the diameter of the cladding layer does not change and can be kept at a constant value. Therefore, a desired core/cladding ratio can be achieved with high precision.

As shown in FIG. 7, the core porous glass body 5
A long base material can be obtained by setting the diameter of 1 to a desired value while adjusting the amount of CF ₄ flowing into the core torch 55 and continuing synthesis with Dc constant.

Further, the thickness control of the clad porous glass layer can be carried out using the cladding torch shown in FIGS. 3 and 5.
28, 38, as well as 2
It is also possible to provide a cladding torch separate from the cladding torches 8 and 38.

Example 5 As shown in Examples 1 to 3 above, when forming a thick porous glass layer for a cladding on the side surface of a porous glass body for a core having a reduced diameter, the degree of sintering of the porous glass body for a core was adjusted. After forming a porous base material by increasing the sintering degree of the porous glass layer for the cladding and lowering the degree of sintering of the porous glass layer for the cladding, if fluorine is added by exposing it to an atmospheric gas containing fluorine during sintering, the core and The amount of fluorine added varies depending on the cladding, and this allows the formation of a core-clad structure. Furthermore, in this case, the dimensions of the core porous glass body can be adjusted as in Examples 1 to 3, and a thick cladding layer can be formed, so that a high-quality optical fiber can be easily obtained.

〔Effect of the invention〕

As explained above, according to the present invention, the core porous glass body can be etched with a flame or a reactive atmosphere containing a fluorine compound to obtain desired dimensions, so that the core/cladding ratio can be adjusted with high accuracy. In addition to being able to adjust to the set value, it also has the advantage of being able to form a core porous glass body with a smaller diameter, making it easier to achieve a cladding thickness that is 10 times or more the core diameter. Furthermore, as a result, there is an advantage that a fully synthetic single mode base material with good dimensional accuracy can be easily obtained.
Therefore, it is easy to manufacture high-quality optical fibers, and since drawing and jacketing processes are not necessary, the number of processes can be reduced, which has the advantage of lowering the price of optical fibers.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the porous base material, Figure 2 is a graph showing the etching rate when a porous glass body is etched by introducing CF ₄ into a flame, and Figures 3 and 5 are the apparatus of the present invention. This is a configuration diagram of an example of the fourth
This figure is an enlarged sectional view of the core porous glass body forming section in FIG. 3, and FIGS. 6 and 7 are configuration diagrams of the core forming section in another example of the apparatus of the present invention. 1: Porous glass body for core, 2: Porous glass layer for cladding, 21 and 31: Rotating and pulling part, 22 and 32: Starting material, 23 and 33: Porous glass layer for cladding, 24 and 34: Core Porous glass body for core, 25 and 35: Porous glass body for core with reduced diameter, 26 and 36: Torch for core,
27 and 37: Etching torch, 28 and 3
8: Cladding torch, 29 and 39: Exhaust port,
210 and 310: Protective container, 211: Exhaust regulator, 311: Dimension measuring device, 312: Comparator, 31
3: Flow rate regulator, 41: Core torch, 42: Raw material nozzle, 43: Etching nozzle, 44: Flame flow, 45: Particulate flow, 46: Etching gas flow, 47: Fine-diameter core pore quality glass body,
48: Porous glass body for core before diameter reduction, 51:
Core porous glass body, 52: Fine-diameter core porous glass body, 53: Clad porous glass layer,
54: Dimension measuring instrument, 55: Core torch, 56:
Cladding torch, 57: Comparator, 58: Flow rate regulator.

Claims (1)

[Claims] 1. Glass particles synthesized in a flame are deposited in the axial direction of the starting material to form a porous glass body for the core, and then glass particles are deposited on the side surfaces of the porous glass body for the core. In a method for manufacturing an optical fiber base material, in which a porous glass layer for a cladding is formed and then heated and sintered at a high temperature to form a transparent glass body, the porous glass layer for a cladding is formed. The porous glass body for the core is etched by exposing it to a flame or a reactive atmosphere containing a fluorine compound at a temperature of 100°C or higher to obtain the desired size, and then the porous glass layer for the cladding is formed into the porous glass body for the core. A method for producing an optical fiber base material, characterized in that it is formed on the side of a body. 2. Means for depositing glass particles in the axial direction of a rotating starting material to form a porous glass body for the core, and means for etching the porous glass body for the core by exposing it to a flame or a reactive atmosphere containing a fluorine compound. , means for measuring the dimensions of the etched porous glass body for the core and adjusting the amount of etching, means for forming a porous glass layer for the cladding on the side surface of the porous glass body for the core after etching;
and a means for heating and sintering the porous glass body within the same process or in a separate process.