JP4429993B2 - Optical fiber preform manufacturing method - Google Patents

Description

  The present invention relates to an optical fiber mother made of quartz glass used for manufacturing an optical fiber by the VAD method (Vapor-phase axial deposition method) or the OVD method (Outside vapor deposition method). In particular, a light that enables the production of large base materials by making it possible to produce porous glass bodies with an increased bulk density while preventing soot cracking and air bubble generation. The present invention relates to a method for manufacturing a fiber preform.

To manufacture the optical fiber preform by VAD method or OVD method, as shown in FIG. 3, by supplying glass raw material gas such as SiCl ₄ or SiCl ₄ and GeCl _4,, oxygen gas and hydrogen gas to the burner 12, An oxyhydrogen flame 13 containing glass fine particles is applied to the starting rod 11 to deposit glass fine particles to produce a glass fine particle porous body 10, which is made transparent to produce an optical fiber preform for optical fiber production. . FIG. 4 illustrates the case where the glass particulate porous body 10 is manufactured while the surface temperature of the glass particulate porous body 10 is measured by the radiation thermometer 14 and the surface temperature is monitored.

  Conventionally, in the manufacture of optical fiber preforms by the VAD method or the OVD method, there is a demand for reducing the size of the dehydration / sintering apparatus while increasing the size of the optical fiber preform to be manufactured. As a method for satisfying this demand, adjusting the bulk density of the glass fine particle porous body can be mentioned. When the bulk density of the glass fine particle porous body is increased, the size of the glass fine particle porous body is reduced, and the size of the dehydration / sintering apparatus can be reduced. In addition, a higher bulk density is also easier to handle because it prevents cracks during transport and prevents cracks.

However, in order to increase the bulk density of the glass fine particle porous body, it is necessary to adjust the temperature during the deposition and the bulk density. If the temperature and bulk density during deposition are not appropriate, the following problems (A) and (B) will occur.
(A) Cracks during deposition of glass particles (decrease in yield)
In regions where the temperature and bulk density are high, soot cracks occur due to large shrinkage.
(B) Residual air bubbles in the base material after sintering (yield, quality degradation)
In the region where the temperature and bulk density are high, the welding of the fine particles proceeds too much during the deposition, so that the atmospheric gas is trapped and bubbles are formed. This is a cause of disconnection during spinning, a decrease in strength of the optical fiber, an increase in optical fiber loss, an increase in polarization dispersion of the optical fiber, a fluctuation in the outer diameter of the optical fiber, and the like.

Conventionally, for example, techniques disclosed in Patent Documents 1 to 3 have been proposed as methods for adjusting the temperature and bulk density during the deposition of glass particles.
Patent Document 1 discloses a method for reducing the deposition thickness and keeping the temperature of the deposition surface within a predetermined range as a method for producing a large base material without soot cracking or bubble generation.
Patent Document 2 discloses an optical fiber preform that adjusts the temperature of the outer diameter steady portion and the outer diameter unsteady portion to a predetermined range and controls to suppress a local increase in the temperature of the outer diameter unsteady portion at the end. A manufacturing method is disclosed.
Patent Document 3 discloses a method of measuring a temperature and controlling a heating condition so that the temperature is within a predetermined range with respect to a reference temperature.

In addition, as a method for preventing soot cracks and bubbles in the porous glass fine particle, conventionally, for example, techniques disclosed in Patent Documents 4 to 6 have been proposed.
Patent Document 4 discloses an ineffective portion formed at both ends of a glass particulate deposit by maintaining the temperature at a position of 50 mm or more from the deposition surface of the oxyhydrogen flame coming out of the glass particulate synthesis burner at 1500 ° C. or higher. A method for producing a glass fine particle deposited body in which the bulk density in the vicinity of the most advanced portion is 0.6 to 1.5 g / cm ³ is disclosed.
In Patent Document 5, the volume density of the glass fine particle deposit that first adheres to the starting material is adjusted to 0.2 to 0.6 g / cm ^3, and the thickness is 50% or less of the outer diameter of the starting material. Disclosed is a method for producing a glass particulate deposit, which comprises depositing a glass particulate deposition layer and then forming a glass particulate deposition layer of a desired thickness thereon.
Patent Document 6 discloses a method of manufacturing an optical fiber preform in which the bulk density from the starting material surface of the glass fine particle deposition layer to a predetermined layer is controlled to 0.5 g / cm ³ or more.
JP 2000-272930 A Japanese Patent No. 3521681 JP 2001-247330 A JP 2003-40625 A Japanese Patent Publication No. 7-17390 JP-A-215727

  As described above, in the prior art, the formation state of the glass fine particle porous body is managed using the temperature and bulk density as parameters. However, with the above-described conventional technology, reproducibility may not be obtained for the suppression effect of soot cracking and bubble generation of the glass particulate porous body, increasing the bulk density to the limit and reducing the deposition of the glass particulate porous body. As a result, there is a limit to downsizing the apparatus, and a margin for manufacturing conditions has to be increased.

That is, if the formation state of the glass fine particle porous body is performed only by temperature control, the bulk density cannot be determined. This is because the progress of necking (melting and sintering of glass fine particles constituting the porous base material) is greatly related to a thermal history that is a composite of temperature and time.
Further, even when the formation state of the glass fine particle porous body is performed only by the bulk density, the information that can be known is information on the average density, and it cannot be confirmed until the progress of excessive necking locally.
Furthermore, even if the relationship between temperature and bulk density measurement values and soot cracks and bubbles are empirically grasped, there are aspects that are influenced by variations in individual burners and deterioration, etc. I must.
Furthermore, when a dopant is used, even if it sets the same temperature, a bulk density differs and the said problem is produced. Temperature cannot be an indicator.

  The present invention has been made in view of the above circumstances, and at the time of manufacturing a glass fine particle porous body, the bulk density is increased to the limit, the volume of the glass fine particle porous body is reduced, a large base material can be manufactured, and the device is made compact. An object of the present invention is to provide a method for manufacturing an optical fiber preform that can be used.

In order to achieve the above-mentioned object, the present invention supplies a glass raw material gas, oxygen gas and hydrogen gas to a burner, applies an oxyhydrogen flame containing glass fine particles to a starting rod, and deposits the glass fine particles to form a porous glass fine particle. In the method for producing an optical fiber preform by making this transparent, the effective portion deposition surface of the glass fine particle porous body is examined, and the number of spotted convex portions having a diameter of 3 mm or more is 100/10 cm ² or less. There is provided a method for producing an optical fiber preform characterized by producing a porous glass fine particle while controlling deposition conditions.

In the method for producing an optical fiber preform of the present invention, the surface temperature (B) ° C. of the effective portion deposition surface is 0.5-10 spots / 10 cm ² of spotted convex portions having a diameter of 3 mm or more on the effective portion deposition surface. It is preferable to manufacture the glass fine particle porous body while controlling the deposition conditions so that the temperature (A) ° C. is in the range of A ≦ B <(A + 50).

  In the method for manufacturing an optical fiber preform of the present invention, it is preferable that the spot-like convex portion has a simple raised structure with one step.

  In the method for producing an optical fiber preform of the present invention, the effective portion deposition surface of the glass fine particle porous body is examined by an image processing apparatus, and the number of spotted convex portions is measured per unit area so that it is within an appropriate range. It is preferable to produce a glass fine particle porous body while controlling the deposition conditions.

  In the optical fiber preform manufacturing method of the present invention, the gas flow rate, the distance between the burner and the effective portion deposition surface, the rotation speed of the effective portion deposition surface, and the relative movement speed between the effective portion deposition surface and the burner are selected. Preferably, one or more deposition conditions are controlled.

In the manufacturing method of the optical fiber preform of the present invention, it is preferable to manufacture the glass fine particle porous body so that the average bulk density is in the range of 0.6 to 0.8 g / cm ³ .

  According to the present invention, in a manufacturing process of an optical fiber preform, it becomes possible to manufacture a porous glass fine particle having a bulk density increased to the limit while preventing soot cracking and air bubble generation, thereby easily making a large preform. Can be manufactured.

  The inventors of the present invention have intensively studied a method for obtaining a glass fine particle porous body having an increased bulk density in the production of a glass fine particle porous body. As a result, the essence is that a portion where the bulk density is too high locally. It was found that it should not occur, and that the optimum index is a spot-like convex portion generated on the effective portion deposition surface of the porous glass fine particle. In the present invention, the “effective portion deposition surface” refers to the outer diameter of the central portion excluding the outer diameter fluctuation portions (ineffective portions) at both ends of the porous glass particulate material deposited on the starting rod. An almost constant area.

The cause of the occurrence of the spot-like convex part is (1) the change in the surface shape caused by excessively grown SiO ₂ fine particles adhering to the deposition surface, and then continuing the deposition of soot, or (2) the heat Due to soot contraction. Here, when (1) occurs, (2) tends to be promoted.
In the case of higher temperatures, surface bulges due to gas expansion in the closed glass also occur in parallel.

  In any state, defects such as bubbles are likely to remain after transparent vitrification. Conventionally, proposals have been made to adjust the temperature so that soot is deposited without unevenness. For example, even in Patent Document 4, the ineffective portion is in a high temperature state where unevenness is generated and the soot crack is prevented by increasing the bulk density, but the effective portion has a condition that unevenness at a lower temperature is not generated.

However, as a result of investigations by the present inventors, it was found that even if irregularities occur in the glass fine particle porous body, there is a spot-like region where defects such as bubbles do not occur after transparent vitrification, and this region is utilized. As a result, it was confirmed that a glass fine particle porous body having a higher bulk density than that of the prior art and free from defects after being made transparent can be produced.
This region is a limited range of about 50 ° C. as a temperature range.
・ Because it can be a pinpoint index, controllability can be greatly improved.
・ Also, it can provide an absolute indicator that does not depend on the presence or absence of the dopant, the flame temperature, the structure of the burner that forms it, the gas conditions, etc.
It has effects such as.

  In the present invention, the spot-like convex portions to be detected are intended for hemispherical ridges having a height of 0.3 mm or more and a diameter of 3 mm or more. However, in the range in which the inventors have conducted experiments, the diameter is 15 mm or more. In many cases, when the ridge is raised, it becomes a multi-stage ridge, and defects are likely to occur in the glass after transparent vitrification. Is preferable.

  The spotted convex portions are easy to handle because visual observation and image processing are possible. In addition, the parameters correspond well to essential causes such as soot cracking and bubble generation. It is a parameter that can be confirmed online.

  Further, in addition to the fact that the spot-like convex portions may be used as an index of bulk density, it has been confirmed that there is no problem in characteristics within a certain range even when the temperature at which the spot-like convex portions are generated is exceeded. The limit was confirmed by detailed examination. That is, the present invention is characterized in that, in the production of a glass fine particle porous body, a visually easy-to-understand index called a spot-like convex portion generated on the effective portion deposition surface is used. On the other hand, management by temperature requires calibration of a thermometer, and if it is shifted, a defect occurs.

  In the present invention, in the production of the glass fine particle porous body, the gas flow rate, the burner and the effective portion deposition can be confirmed when spotted convex portions appear on the effective portion deposition surface and the defect does not appear. By controlling one or more deposition conditions selected from the group consisting of the distance between the surfaces, the rotation speed of the effective portion deposition surface, and the relative movement speed of the effective portion deposition surface and the burner, Occurrence can be suppressed.

  Furthermore, when the state of occurrence of the spotted protrusions on the surface of the glass fine particle porous body was closely observed, there was no problem in characteristics when the spotted protrusions were one step, and even smaller undulations were formed on the spotted protrusions. It was found that quality could be affected in the finished state. For example, the manufacturing may be performed in a state where the first-stage spotted convex portion is generated, and the adjustment may be performed when the second-stage undulation disappears or the undulations are multistaged. Adjustment can be easily performed by previously obtaining correlation data with temperature, fuel flow rate, and the like.

FIG. 1 is a configuration diagram showing an example of a manufacturing process of a glass fine particle porous body to which the manufacturing method of the present invention is applied. In the manufacturing process of the glass fine particle porous body according to the present example, the glass raw material gas such as SiCl ₄ , oxygen gas and hydrogen gas are supplied to the burner 12, and the oxyhydrogen flame 13 containing the glass fine particles is applied to the starting rod 11 to form the glass fine particles. When the glass particulate porous body 10 is manufactured by depositing the glass, the effective portion deposition surface of the glass particulate porous body 10 is imaged by the camera 15, and the image data is sent to the image processing device 16, and the spot-like convex portions are formed. It can be detected.

  Moreover, FIG. 2 is a block diagram which shows another example of the manufacturing process of the glass fine particle porous body to which the manufacturing method of this invention is applied. The manufacturing process of the glass fine particle porous body according to the present example includes the same components as those in FIG. 1, and the surface temperature of the effective portion deposition surface of the glass fine particle porous body 10 is measured by the radiation thermometer 14. The case where the glass fine particle porous body 10 is manufactured while monitoring the above is illustrated.

As shown in FIG. 1 and FIG. 2, the effective portion deposition surface of the glass fine particle porous body 10 is imaged with a camera 15, and the data is sent to the image processing device 16, and per unit area of spotted convex portions having a diameter of 3 mm or more. The number of particles is measured, and a glass fine particle porous body is manufactured while controlling the deposition conditions so that the number of the spot-like convex portions is 100/10 cm ² or less. If the number of the spot-like convex portions exceeds 100/10 cm ² , the bulk density becomes too high locally, and defects such as bubbles are likely to remain after transparent vitrification, which is not preferable.

  Here, the deposition conditions to be controlled are selected from the group consisting of the gas flow rate, the distance between the burner and the effective portion deposition surface, the rotation speed of the effective portion deposition surface, and the relative movement speed of the effective portion deposition surface and the burner. There can be one or more conditions.

In the method for producing an optical fiber preform of the present invention, the surface temperature (B) ° C. of the effective portion deposition surface is 0.5-10 spots / 10 cm ² of spotted convex portions having a diameter of 3 mm or more on the effective portion deposition surface. It is preferable to manufacture the glass fine particle porous body while controlling the deposition conditions so that the temperature (A) ° C. is in the range of A ≦ B <(A + 50). If the temperature (B) ° C. is lower than the temperature (A) ° C., the bulk density is too low, the size of the porous body becomes too large, and compactness cannot be achieved. In addition, when the temperature (B) ° C. is higher than A + 50 ° C., the bulk density becomes too high locally or as a whole, so that defects such as bubbles are easily left after vitrification.

In the manufacturing method of the optical fiber preform of the present invention, it is preferable to manufacture the glass fine particle porous body so that the average bulk density is in the range of 0.6 to 0.8 g / cm ³ . When the bulk density is within the above range, soot size can be made compact, and a high-density glass fine particle porous body that does not easily cause soot cracking can be obtained. If the average bulk density is smaller than the above range, the size of the porous body becomes too large, and compactness cannot be achieved. On the other hand, if the average bulk density exceeds the above range, it is not preferable because defoaming cannot be sufficiently performed at the time of sintering, and bubbles remain or dehydration cannot be sufficiently performed when there is a dehydration process.

  The range of the number of the spot-like protrusions is determined by changing the surface temperature within a predetermined range when determining the manufacturing conditions of the glass fine particle porous body 10, and confirming the occurrence of the spot-like protrusions under each temperature condition. By confirming the manufacturing conditions so that And in manufacture of the glass fine particle porous body 10, it is desirable to manufacture, adjusting temperature from the correlation of the temperature at that time, and a spot-like convex part. Moreover, you may confirm whether adjustment was implemented as intended by the surface state of the porous body after deposition. Further, the deposited surface may be image-processed to monitor the appearance of the spot-like convex portion online.

In addition, instead of measuring the number of the spot-like convex portions, the change in the number of the spot-like convex portions can be regarded as a luminance change on the surface of the glass fine particle porous body 10 and image processing can be performed. Then, feedback for adjusting the temperature is applied based on the image processing result. In this case, it is desirable to make it easy to capture the luminance change due to the spot-like convex portions by applying illumination light so that image processing is easy.
In addition, when manufacturing is performed in a temperature region lower than the temperature at which the spot-like convex portions are generated and the spot-like convex portions are generated, feedback for adjusting the temperature according to the generation state may be applied.

(Examples 1-3)
Glass fine particles were externally attached to a core material having a diameter of 30 mm and a length of 1000 mm so that the glass diameter after sintering was 110 mm, thereby producing a porous glass fine particle. When the glass fine particle porous body is manufactured by the external method, the surface of the glass fine particle porous body is examined by an image processing apparatus (manufactured by Hitachi Engineering Co., Ltd., image processing apparatus MIP-77). The glass fine particle porous body was manufactured while feeding back to hydrogen and oxygen gas so that the number was in an appropriate range, and controlling the flame temperature and the surface temperature of the deposition surface. The surface temperature of the glass fine particle porous body was measured using a thermotracer manufactured by NEC Sanei Co., Ltd.
Table 1 shows the results when the burner A, which is a multi-tube burner, is used by supplying SiCl ₄ gas, oxygen gas and hydrogen gas as raw materials to the burner A. The burner A nozzle used was SiCl ₄ gas from the innermost tube at the center, inert gas (Ar gas) from the second tube, hydrogen gas from the third tube, and oxygen gas from the outer tube. It has become a structure.
Table 2 shows the results when the burner B, which is a multi-nozzle burner, is used by supplying SiCl ₄ gas, oxygen gas and hydrogen gas as raw materials to the burner A. The nozzle of the burner B used is SiCl ₄ gas from the innermost tube at the center, inert gas (Ar gas) from the second tube, hydrogen gas from the outside, and oxygen gas from a plurality of ports arranged separately from it. Each has a structure that is ejected.
Table 3 shows the results when the burner A is doped with 0.5% by mass of GeO ₂ .
The surface temperature was described as A-10 ° C. when the temperature was 10 ° C. higher than A + 10 ° C. by 10 ° C., based on the temperature A at which the spot-like convex portions became 0.5-10 pieces / 10 cm ² .
Further, the number of the spot-like convex portions is the number per unit area 10 cm ² .
Bubbles are represented by the number of bubbles having a diameter of 0.3 mm or more observed per base material in a base material that can be transparently vitrified without soot cracking.
Soot cracking is expressed as the number of times when the soot cracks during the production of the porous body and the formation of the porous body is not completed once.
The bulk density was calculated by measuring the mass of a soot sample with a constant deposition and bulk density = sample mass / sample volume.

(Comparative Examples 1 and 2)
A glass fine particle porous body was produced in the same manner as in Examples 1 to 3, except that the flow rates of hydrogen and oxygen gas were adjusted in order to change the surface temperature of the deposition surface.
Table 1 shows the results when the burner A, which is a multi-tube burner, is used by supplying SiCl ₄ gas, oxygen gas and hydrogen gas as raw materials to the burner A.
Table 2 shows the results when the burner B, which is a multi-nozzle burner, is used by supplying SiCl ₄ gas, oxygen gas and hydrogen gas as raw materials to the burner A.
Table 3 shows the results when the burner A is doped with 0.5% by mass of GeO ₂ .

From the results of Tables 1 to 3, it can be seen that in Examples 1 to 3 according to the present invention, it is possible to produce a glass fine particle porous body with a bulk density increased to the limit while preventing soot cracking and bubble generation. .
On the other hand, in Comparative Examples 1 and 2 in which the number of spotted convex portions is not within the range of the present invention, the generation of bubbles and soot cracks occur, and the glass fine particle porous body having a high bulk density Could not be manufactured.

It is a block diagram which shows an example of the manufacturing process of the glass fine particle porous body to which the manufacturing method of this invention is applied. It is a block diagram which shows another example of the manufacturing process of the glass fine particle porous body to which the manufacturing method of this invention is applied. It is a block diagram which shows an example of the manufacturing process of the conventional glass fine particle porous body. It is a block diagram which shows another example of the manufacturing process of the conventional glass fine particle porous body.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Glass fine particle porous body, 11 ... Starting rod, 12 ... Burner, 13 ... Oxyhydrogen flame, 14 ... Radiation thermometer, 15 ... Camera, 16 ... Image processing apparatus.

Claims (6)

A glass raw material gas, oxygen gas and hydrogen gas are supplied to a burner, and an oxyhydrogen flame containing glass fine particles is applied to a starting rod to deposit glass fine particles to produce a glass fine particle porous body, which is made transparent and optical fiber In a method of manufacturing a base material,
The effective part deposition surface of the glass fine particle porous body is examined, and the glass fine particle porous body is manufactured while controlling the deposition conditions so that the number of spot-like convex parts having a diameter of 3 mm or more is 100/10 cm ² or less. A method for manufacturing an optical fiber preform characterized by the above. The surface temperature (B) ° C. of the effective portion deposition surface is such that A ≦ B <with respect to the temperature (A) ° C. at which spot-like convex portions having a diameter of 3 mm or more are generated on the effective portion deposition surface by 0.5 to 10/10 cm ^2. The method for producing an optical fiber preform according to claim 1, wherein the glass fine particle porous body is produced while controlling the deposition conditions so as to be in the range of (A + 50).   3. The method of manufacturing an optical fiber preform according to claim 1, wherein the spot-like convex portion has a simple raised structure with one step.   The effective surface of the glass particulate porous body is examined by an image processing device, the number of spotted convex portions per unit area is measured, and the deposition conditions are controlled so that it falls within the appropriate range. The method for manufacturing an optical fiber preform according to any one of claims 1 to 3, wherein the optical fiber preform is manufactured.   Controls one or more deposition conditions selected from the group consisting of gas flow rate, distance between burner and effective portion deposition surface, rotation speed of effective portion deposition surface, and relative movement speed of effective portion deposition surface and burner. The method for manufacturing an optical fiber preform according to claim 1, wherein: The optical fiber preform according to any one of claims 1 to 5, wherein the average bulk density of the glass fine particle porous body is in the range of 0.6 to 0.8 g / cm ^3. Method.

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