JPS62187133A - Method and device for producing base material for optical fiber - Google Patents

Abstract

PURPOSE:To precisely produce a base material for optical fiber having a required core cladding ratio by etching a porous glass material for a core which is formed by building-up the fine glass particles and thereafter depositing a glass material for cladding thereon. CONSTITUTION:A porous glass material 24 for a core is formed in a protective vessel 210 provided with an exhaust port 29 by building-up the following fine glass particle in the axial direction of a starting material 22 drawn up while rotating which are synthesized in the flames generating in a torch 26 for the core. Then the above-mentioned porous glass material 24 for the core is etched to the required size by a torch 27 for etching while exposing it to the flames contg. fluorocompd. such as CF4 or to the reactive atmosphere at >=100 deg.C temp. Then a porous glass material 23 for cladding is formed by depositing the following fine glass particles from the side face of the porous glass material 25 for the core that is formed thereby and made to a small diameter which are synthesized in the flames generated in a torch 28 for cladding. Thereafter the obtained porous glass material is heated and sintered to make it transparent and the base material for optical fiber is obtained.

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.

The core/clad ratio (DI
/D2) has conventionally been achieved by adjusting the thickness of a porous glass layer for cladding formed on the side surface of a porous base material for core having predetermined dimensions to achieve a desired core/cladding ratio. method was adopted. however,
This traditional method suffers from several problems, which are listed 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 precision, especially for single mode fibers that require a thick cladding. Preparing the base material is extremely difficult and difficult.

In addition, in the conventional method, it is difficult to reduce the size of the porous base material for the core, and therefore it is difficult to achieve a cladding (D, ≧10XD1) diameter that is 10 times or more that of the core. Furthermore, even if a cladding diameter that is 10 times or more the core diameter was achieved, the size of the porous base material would become extremely large, making it difficult to sinter and make it transparent. Problems to be Solved] As explained above, with the conventional methods, it is difficult to achieve a desired core/cladding ratio with high accuracy, and it is difficult to obtain a cladding thickness with a diameter of 10 times or more than the core diameter. The problem was that it was small.

It is an object of the present invention to solve the above problems and provide a desired core/
It is an object of the present invention to provide a method and apparatus for manufacturing an original fiber base material that not only achieves a cladding ratio with high precision but also achieves a cladding diameter that is 10 times or more the core diameter.

[Means for solving problems]

To summarize the present invention, the first invention of the present invention relates to a method for producing an original fiber base material, in which fine glass particles synthesized in a flame are deposited in the axial direction of the starting material to form porous glass for the core. Next, fine glass 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. In the method for producing an IPA base material, 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 at a temperature of 100°C or higher. After the desired dimensions are obtained, a porous glass layer for cladding is formed on the side surface of the porous glass body for core.

A second invention of the present invention relates to an apparatus for manufacturing a base fiber base material, and includes means for depositing glass fine particles in the axial direction of a rotating starting material to form a porous glass body for a core; A means for etching a porous glass body 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 the core and adjusting the amount of etching, and a means for etching the porous glass body for the core after etching. It is characterized by having means for forming porous glass for cladding *'i on the side surface of the porous glass body, 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. The most important feature is the formation of a glass layer.As a result, a desired core/cladding ratio (Dt/Dx) can be achieved with high accuracy. The present invention provides a method for manufacturing a fiber base material having such functions. Therefore, the conventional method adopts a method of adjusting the thickness f:X of the porous glass layer for cladding formed on the side surface of a porous glass body for core having predetermined dimensions 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, the method of achieving a desired core/cladding ratio (Dx/D2) in the matrix structure shown in FIG. 1 is to: 1) adjust the thickness of the cladding layer deposited on the side surface of a given core porous body; 2) a method in which the thickness of the cladding layer is kept constant and the dimensions of the core porous body are varied. While the conventional method belongs to method 1),
The present invention belongs to method 2).

Therefore, in the present invention, first, the core porous base material is etched to adjust the dimensions by utilizing the reaction of (11 formula: % formula % (1)).

Generally, the diameter of the core porous matrix shown in Figure 1 is D.
! , the diameter of the cladding porous layer t"Dz, and the core/cladding ratio R' (I-R=Di/D, Dl.

Considering the rate of change of R when changing D, we get the following equation. In other words, the change in R with respect to DI is calculated by differentiating R by dR/dDl=1/D-... (2) Also, D
Rf relative to l) The rate of change is (IR/dDl = Dt/D:
...(3). Therefore, comparing the magnitudes of the rates of change in equations (2) and (3), we find that the equation (D) shown in Figure 1 is (D, ), so equation (4) is: Therefore, Dl is It turns out that R can be greatly changed by changing the ratio, making it easier to adjust the core/cladding ratio. Therefore, in the present invention, R is controlled by changing Dl with Dx t" constant. .

As a method of changing Dl, etching with a fluorine compound shown in formula (1) is effective, and CF
It becomes possible by introducing 4th grade. In Figure 2,
The figure shows the etching rate when a porous glass body is etched by introducing CF into a flame.

In other words, Figure 2 shows the concentration of CF and scum in the flame (molti,
2 is a graph showing the relationship between etching speed (I/min, vertical axis) and etching rate (I/min, vertical axis).

When the CF4 concentration in the flame is changed between 0 and α1 molt, the etching rate changes to 15 in FIG. 2, and the dimensions of the porous glass body can be easily changed.

810, and the reaction rate of fluorine decreases with temperature 5.1
It is preferable to carry out the reaction at a temperature of 00°C or higher. In the flame formed by oxyhydrogen, C! When F'4 is flowed, a reaction temperature of about 600°C is obtained. However, if the reaction rate is increased significantly, the etched surface of the base material becomes rough, leading to problems such as foaming during transparent vitrification.

This problem also occurs when the amount of etching is significantly increased. A portion of the fluorine used in etching is incorporated into the base material. Fluorine is 810. Fluorine is known as an element that lowers the refractive index of transparent glass, but the fluorine incorporated into the base material during etching is completely removed during the process of making the base material transparent, which affects the refractive index of transparent glass. There isn't.

In addition to CF4, the fluorine compounds for etching of the present invention include SFg, C! Fluorine compounds such as F@ and O3Fm can be used. Further, when a high-temperature gas of 100° C. or higher is flowed out together with a fluorine compound instead of a flame, the same etching operation as in the example described later can be easily performed.

Furthermore, in the present invention, a core/cladding ratio of 8' can be achieved with a good 8' degree. When the original fiber base material obtained by the present invention was drawn fc, an original 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 the core porous glass body but also for the cladding porous glass layer. .

〔Example〕

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 block diagrams of one example of the apparatus of the present invention, and FIG. 4 is an enlarged sectional view of the core porous glass body forming part in FIG. 3, and FIG. 6 and FIG. FIG. 7 is a configuration diagram 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 Figure 3, 2
1 is a rotating and pulling part, 22 is a starting material, 23 is a porous glass layer for cladding, 24 is a porous glass body for core, 25
26 is a core torch, 27 is an etching torch, 28 is a cladding torch, 29 is an exhaust port, 210 is a protective container, and 211 is an exhaust regulator.

In Figure 3, first, 5ick and Gθ are applied to the 26 core torches.
Frit gas such as ct4 and H,,O! A porous glass body 24 for the core is formed at the tip of the starting material 22 which is pulled up while rotating. Next, the porous glass body 24 for the core is exposed to a flame containing CF4'i ejected from the etching torch 27 to form the porous glass body 25 for the small diameter core having the desired size. A thick porous glass layer 23 for cladding is formed on the side surface of the porous glass body for small diameter core. Thereafter, the porous glass body is heated to a high temperature and sintered to form a transparent original fiber base material.

Second, the exhaust gas from the reaction and the excess glass particles are 2.
It is discharged from the exhaust port 9, and the discharge amount is adjusted by 211. The protective container 210 has the role of insulating the reaction section from the outside air and keeping it clean. Also, the glue in Figure 4,
D' represents the diameter of the core porous glass body 24 and the diameter of the small core porous glass body 25, respectively.

For example, o to the core torch 26, a total of 10t1Hz' per minute.
t'51.5 IC4'@: 50 cc per minute, G4
5 cc per minute is supplied to C41, and the outer diameter D1=
After forming a porous glass body for the core with a diameter of 15 mφ, oa
k5t/min, Ha to SL/min, CF4 to IIL5t/min
After etching the core porous glass body 25 to a diameter of 10 mm using the supplied etching torches,
8 to form a 1501111+1φ clad *1-90 At this time, the cladding torch 28 was heated with 02 at 50 t/min, Hat" 50 t, and 81C'4' at 2
1 was supplied respectively. As a result, the core/clad ratio is D
A porous matrix with I/D2 = 1/15 was obtained, and further,
Transparent vitrification was performed to obtain an optical fiber base material with Di/D snow = 1/15. In addition, the relative refractive index difference Δn between the core and cladding of this base material is 113%, and the optical loss of a single mode fiber obtained by drawing from this base material is at a wavelength of 1.3 μs.
, 15 dB 71 cm at tss μm, respectively.
l 2 aB/1 cm.

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, 33 is a porous glass layer for cladding, 34 is a porous glass body for core, 35 is a porous glass body for core having a reduced diameter, 36 is a core torch, 37 is an etching torch, 58 is a cladding torch, 39 is an exhaust port, 310 is a protective container, 311 is a dimension measuring device, 312 is a comparator, and 313 is a flow rate regulator.
In the embodiment shown in the figure, 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 54 for the core, is set to a size 311.
@Measure with a measuring device.

Next, this result is compared with a set value by a comparator 512, and then, depending on the magnitude, the flow'Ik regulator 313 is controlled to realize the desired outer diameter dimension. In Example 2, first, a porous glass body for a core with an outer diameter of 15- is formed using a torch 56, and if the set value is 10-, the value measured by the dimension measuring device 311 (15-) and the set value 1O- are compared in the comparator 312, and an output corresponding to this difference (5-) is inputted as a signal to the flow regulator 313. As a result, by setting the flow-ILilJ regulator 313, Hl: 5 A, 02: 5 t
, CF4: α5t, and are supplied to the torch 37 to form a core porous glass body S5 of 10 −, which is the same as the set value. In addition, when the set value is 13-9, the output corresponding to the difference from the measured value is inputted to the comparator 512 and the regulator 315, and H,, O,
, CF4, etc., are controlled.

By this method, the difference from the set value can be easily made less than (LOI), and as a result, the core/clad ratio matches the set value with high precision.

In addition, in the present invention, a porous glass body for a core having a smaller diameter can be easily obtained by changing the amount of etching.
It is easy to set the core/cladding ratio Q1/10 to 20, and it is possible to easily realize a cladding diameter that is 10 times or more the core diameter.

Example 3 In Example 1.2 above, the etching operation was performed separately from the formation of the porous glass body for the core, but 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 the core-forming torch to adjust the dimensions 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, and 4
3f'X, etching nozzle, 44 flame flow, 45f
'i fine particle flow, 46 is an etching gas flow, 47 is a porous glass body for a core whose diameter has been reduced, and 48 is a porous glass body for a core before its diameter is reduced.

FIG. 6 is a diagram illustrating the situation during diameter reduction.

In FIG. 6, a porous glass body for the core is formed by the flame flow 44 and the particle flow 45 blown out from the core torch 41, but when no etching gas flows into the etching nozzle 43, a porous glass body 48 is formed. When the etching gas is introduced into the hole (diameter), a porous glass body having a diameter of 47 (diameter) is obtained.

At this time, when CF, 'i flows in as an etching gas, D'l/DI is [[
195-(Can vary by about 15.

Further, by adjusting the inflow rate of the etching gas (CF4) using the dimension measuring device, comparator, and flow rate regulator shown in Example 2, a core porous glass body with desired dimensions can be formed. Furthermore, by forming a thick cladding layer on the side surface of the porous glass body for the core thus formed, a fiber preform with a precisely adjusted core/cladding ratio 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 is compensated for by Example 4 shown in FIG. . In FIG. 7, 51 is a core porous glass body;
2 is a core porous glass body with a reduced diameter, 53 is a cladding porous glass layer, 54 is a dimension measuring device, 55 is a core torch, 56 is a cladding torch, 57 is a comparator, 58 is a flow rate regulator, The dimensional DO is the diameter of the cladding porous glass layer. In FIG. 7, when a fluorine compound such as CF4 is introduced into the core torch 55 for the initially formed core porous glass body 51, the core pores are reduced in diameter as shown in Example 3. A solid glass body 52 is formed. Along with this, the thickness of the cladding porous glass layer 53 formed in the cladding torch 56 changes, and the diameter Dc
However, in this Example 4, the diameter 1) c is measured by a 54 size measuring device, and Da is kept at a constant value.
A flow rate regulator 58 is controlled through the comparator 57. As a result, even if the core diameter changes when reducing the diameter of the core porous glass body, the diameter of the cladding layer does not change and can be kept at a constant value.

Then, the desired core/cladding ratio kA can be achieved with good accuracy.

As shown in FIG. 7, the diameter of the porous glass body 51 for the core is set to a desired value while adjusting the amount of CF4 flowing into the core torch 55, and by continuing the synthesis at a constant Dc, a long length can be obtained. You can get the whole base material.

In addition, the thickness control of the Korikishikyu clad porous glass layer is
The cladding torch 28.38 shown in FIGS.

Example 5 In the process shown in Examples 1 to 3 above, when forming a thick porous glass layer for cladding on the side surface of a porous glass body for a core having a single diameter, the sintering degree of the porous glass body for a core was If the degree of sintering of the porous glass layer for the cladding is high and the degree of sintering of the porous glass layer for the cladding is low to form a porous base material, then the core and The amount of fluorine added to the cladding is different, and a rainbow or core-clad structure can be formed in this. Moreover, in this case, the above Example 1
In steps 3 to 3, the dimensions of the shear porous glass body can be adjusted, a thick cladding layer can be formed, and a high-quality source fiber can be easily obtained.

〔Effect of the invention〕

As explained above, in the present invention, the core porous glass body can be etched in a flame or a reactive atmosphere containing a fluorine compound to obtain the desired dimensions, so that the core/clad ratio is In addition to the advantage of being able to precisely match the set value, it also has the advantage of being able to easily achieve a cladding thickness that is 10 times or more the core diameter, since a core porous glass body with a reduced diameter can be formed. 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 kilometers of high-quality optical fibers, and since drawing and jacketing processes are not necessary, the number of processes can be completely reduced.
There is a 7fu point where the price of the original fiber can be completely reduced.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the porous base material, Fig. 2 is a graph showing the etching rate when a porous glass body is etched by introducing CF4 into a flame, and Figs. FIG. 4 is an enlarged cross-sectional view of the core porous glass body forming part in FIG. 3, and FIGS. 6 and 7 are diagrams showing the core formation in another example of the apparatus of the present invention. FIG. 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 35: Porous glass layer for cladding,
24 and 34: 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: torch for etching, 28 and 38: torch for cladding, 29 and 39: exhaust port, 2
10 and 310: Agricultural preservation container, 211: Exhaust regulator, 5
11: Dimension measuring device, 512: Comparator, 313: Flow tp
m adjustment device, 41: core torch, 42: raw material nozzle, 43
: Etching nozzle, 44: Flame flow, 45: Fine particle flow, 46: Etching gas flow, 47: Porous glass body for core with reduced diameter, 48: Porous glass body for core before diameter reduction 51 : core porous glass body, 52: m-polarized core porous glass body, 53: cladding porous glass layer,
54: Dimension measuring device, 55: Core torch, 56: Cladding torch, 57: Comparator, 58: Flow 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 surface of the porous glass body for the core. In a method for producing an optical fiber preform in which a porous glass layer for cladding is deposited and then heated and sintered at a high temperature to form a transparent glass body, prior to forming the porous glass layer for cladding, 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 a desired dimension, and then the porous glass body for the cladding is formed into the porous glass body for the core. A method for manufacturing an optical fiber preform, 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; 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.