JP2001247330A - Method for producing optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber perform, capable of simplifying its production process, and obtaining a sufficient uniformity regarding its outer diameter in its longitudinal direction. SOLUTION: This method for producing an optical fiber preform is provided by poling up a porous glass-based layer 11 on core rod 10 by traversing a glass synthesizing burner 25 in longitudinal direction of the core rod 10 (a porous glass mother material 1), measuring the surface-heating temperature at the heated part A of the poled up surface of the porous glass-based layer 11 heated by a flame from the synthesizing burner 25, also controlling the synthesizing burner 25 so as to make the fluctuation range of the surface-heating temperature within ±50 deg.C against a standard temperature, thereby uniformizing the synthesizing condition of the porous glass-based layer 11 in longitudinal direction of the porous glass mother material 1 and improving the uniformity of the outer diameter, etc., of the obtained porous glass-based layer 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber preform for synthesizing a porous glass layer by moving a burner for glass synthesis with respect to a starting rod.

[0002]

2. Description of the Related Art When a porous glass preform to be used as an optical fiber preform is produced by an external method such as an OVD method, the outside of a glass porous layer deposited as glass fine particles (soot) on a starting rod. It is necessary to make the diameter and thickness sufficiently uniform in the longitudinal direction. By making the outer diameter and the like of the glass porous layer uniform, the drawing process of the optical fiber preform can be performed under favorable conditions, and the characteristics of the drawn optical fiber can be stabilized. .

A conventional manufacturing method for making the outer diameter uniform in the longitudinal direction is disclosed, for example, in Japanese Patent Laid-Open No. 6-92667. In this manufacturing method, after depositing soot, a correction for making the outer diameter uniform is performed. That is, the deviation of the outer diameter and the thickness of the soot body at each position is obtained by a method such as measuring the weight change during the synthesis of the soot body. Then, using an auxiliary burner provided separately from the synthesis burner, an auxiliary soot is provided so that the obtained deviation is corrected and a porous glass base material having a uniform outer diameter in the longitudinal direction is obtained. Is going.

[0004]

In the above-described manufacturing method in which the correction is performed using the auxiliary burner, a sooting step for correction is added to the manufacturing process of the porous glass base material. However, there arises a problem that the manufacturing cost increases and the manufacturing cost increases. In addition, by performing this correction process, a new unique problem occurs in the obtained optical fiber preform.

For example, when a flame is again blown by a burner to the porous glass base material cooled to around room temperature after the first synthesis, the base material undergoes rapid thermal expansion due to the temperature change. In some cases, cracks may occur in the base material. In addition, dust easily adheres to the surface of the cooled base material, and if soot is further applied thereon, the dust is taken into the base material, causing disconnection and fiber diameter variation during drawing. .

[0006] Furthermore, the effect of correcting the outer diameter itself is not the same in the correction method using the auxiliary burner for correction, because the flame of the auxiliary burner has a certain degree of positional spread. It is not possible to correct the deviation with sufficient accuracy.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an optical fiber preform capable of simplifying a manufacturing process and obtaining sufficient uniformity in an outer diameter and the like in a longitudinal direction. It is an object of the present invention to provide a method for producing the same.

[0008]

In order to achieve the above object, a method for manufacturing an optical fiber preform according to the present invention comprises:
A method for producing an optical fiber preform for synthesizing a glass porous layer on an outer periphery of a starting rod by moving a burner for glass synthesis within a predetermined range in a longitudinal direction with respect to a starting rod, comprising: During the movement within the predetermined range, while measuring the surface heating temperature of the glass porous layer at the heating site being heated by the flame from the glass synthesis burner, the surface temperature with respect to a preset reference temperature The heating condition of the porous glass layer is controlled such that the fluctuation range of the heating temperature is equal to or less than a predetermined temperature range.

As a method for making the outer diameter of the glass porous layer formed on the outer periphery of a starting rod such as a core rod uniform in the longitudinal direction, in addition to the above-mentioned method after soot deposition, soot is used. A method of synthesizing a soot body such that the deposition conditions of the soot are uniform in the longitudinal direction is possible. In the above-described method for manufacturing an optical fiber preform, attention is paid to the effect of the heating temperature of each part of the preform in the longitudinal direction on the outer diameter and the like of the synthesized glass porous layer, and control using this heating temperature is performed. Is performed, soot deposition conditions are made uniform during synthesis of the soot body.

That is, the synthesis burner for sooting is traversed (moved) in the longitudinal direction with respect to the starting rod.
At this time, the surface heating temperature of the heating portion (moving in the longitudinal direction together with the synthesis burner) heated by the flame of the synthesis burner at each time point is measured, and the fluctuation range of the surface heating temperature is determined to be a predetermined temperature range. The heating conditions of the synthesis burner are controlled so as to be within the range. Here, the degree of shrinkage of the porous glass body varies depending on the heating temperature. Therefore, if the heating temperature of each portion is different, the outer diameter of the porous body may be undulated in the longitudinal direction.

On the other hand, by controlling the surface heating temperature at each part to fall within a predetermined fluctuation range as described above, it is possible to obtain sufficient uniformity in the longitudinal direction of the outer diameter and the like. Becomes Further, at this time, since it is not necessary to add a step of performing correction after the synthesis of the porous glass layer to the manufacturing process, the manufacturing process can be simplified and the manufacturing cost can be reduced. Further, problems such as generation of cracks in the base material by performing soot for correction separately from the synthesis step are solved.

The predetermined temperature range with respect to the above-mentioned surface heating temperature is set to ± 5 as a temperature condition under which sufficient uniformity can be realized.
The temperature is preferably set to 0 ° C. However, different temperature ranges may be set for the fluctuation range depending on the conditions for synthesizing the porous glass layer and the required accuracy of uniformity.

In addition, the surface heating temperature is measured at predetermined measurement time intervals, and the heating condition of the glass porous layer is controlled based on the difference between the surface heating temperature measured at each measurement time point and the reference temperature. Is performed.

As described above, by measuring the surface heating temperature and controlling the heating conditions by the synthesis burner, the effect of sufficiently uniformizing the soot at each time when the soot is deposited by the flame from the synthesis burner can be obtained. Can be realized. The measurement time interval is set based on a time scale of fluctuation of the surface heating temperature or the like (for example, ± 50 degrees).
It is preferable to set appropriately so as to obtain a fluctuation range within (° C).

A specific method of controlling the heating conditions is characterized in that the heating conditions of the glass porous layer are controlled by changing the flow rate of the fuel gas supplied to the burner for glass synthesis. preferable. In addition, a method of changing the distance of the synthesis burner from the glass porous layer can be used.

Further, a plurality of temperature measurement points respectively arranged at predetermined positions with respect to the heating portion are set on the glass porous layer, and the surface heating temperature is determined from the surface temperature measured at each temperature measurement point. It is characterized by seeking.

As a result, the accuracy of measuring the surface heating temperature can be improved. In addition, even when the distribution of the surface temperature is asymmetric with respect to the center point of the heating portion, it is possible to evaluate the surface heating temperature taking in the effect of the distribution. As a specific setting of the temperature measurement points, for example, there is a method of arranging the measurement points at equal intervals in the longitudinal direction with respect to the center point of the heated portion, a method of arranging the measurement points in a two-dimensional matrix, and the like.

As a method of obtaining the surface heating temperature from the surface temperatures at a plurality of temperature measurement points, it is preferable to obtain the surface heating temperature from the highest surface temperature measured at each of the plurality of temperature measurement points. Alternatively, the surface heating temperature is preferably determined from the average of the surface temperatures measured at each of the plurality of temperature measurement points. It is also possible to use methods other than these. A single temperature measurement point may be used depending on the traversing speed of the synthesis burner, the required accuracy of the outer diameter uniformity, and the like.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method for manufacturing an optical fiber preform according to the present invention will be described below in detail with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.

FIG. 1 is a schematic diagram showing an apparatus for manufacturing an optical fiber preform used in an embodiment of the method for manufacturing an optical fiber preform according to the present invention. This manufacturing apparatus uses a multi-layer OVD method to form a porous glass preform 1
A base material support device 20 for supporting and rotating the porous glass base material 1, and a glass synthesis burner 2
5 and a traverse device 26 for traversing the burner 25 for synthesis. Here, illustration of a reaction furnace in which the porous glass base material 1 and the like are stored, and an exhaust pipe for exhausting gas and undeposited soot from the reaction furnace are omitted.

In the method of manufacturing an optical fiber preform using the manufacturing apparatus shown in FIG. 1, first, a core rod 10 serving as a starting rod for depositing a porous glass layer is formed by a supporting mechanism 21 of a preform supporting device 20. Let them support you. Support mechanism 2
Reference numeral 1 denotes a support shaft having a predetermined length in the longitudinal direction of the core rod 10;
In the above, the core rod 10 is supported along a horizontal axis, and the core rod 10 is rotated about the support axis by a driving device such as a motor.

The composite burner 25 is traversed (moved) in the longitudinal direction (support axis direction) with respect to the core rod 10 supported and rotated by the base material supporting device 20, and is fired by the flame from the composite burner 25. Then, a glass porous layer 11 which is a soot body is synthesized on the outer periphery of the core rod 10.
The synthesis burner 25 is supported by the traverse device 26 at a predetermined position with respect to the porous glass base material 1 and is attached to the core rod 10 (or a starting rod having dummy rods connected to both ends of the core rod 10). On the other hand, the soot is traversed a plurality of times in a predetermined range in the longitudinal direction, and soot of the glass porous layer 11 is deposited for each traverse.

In this embodiment, the burner 25 for synthesis is used.
During the synthesis of the glass porous layer 11 by the traverse, the heating portion A (see FIG. 1) on the glass porous layer 11 which is heated by the flame from the synthesis burner 25 facing the synthesis burner 25, A heated surface temperature (hereinafter, referred to as a surface heating temperature) is measured. The heating portion A is moved along with the traverse of the synthesis burner 25 and the glass porous layer 1.
1 on the deposition surface. Then, the fluctuation range of the surface heating temperature is ± 5 with respect to a preset reference temperature.
By controlling the heating condition of the synthesis burner 25 so as to be 0 ° C. or less, the uniformity of the outer diameter of the porous glass layer 11 in the longitudinal direction of the porous glass preform 1 is improved. I have.

That is, the glass porous body contracts when heated to a high temperature, but if the surface heating temperature at the time of heating is different in each part of the glass porous layer 11, the glass porous body in those parts is reduced. A difference occurs in the degree of shrinkage.
At this time, due to the difference in the degree of shrinkage at each part, a undulation (irregular shape) in the longitudinal direction is generated on the deposition surface of the deposited glass porous layer 11, and the uniformity of the outer diameter and the like is reduced. Becomes

On the other hand, in the manufacturing method described above, the glass porous layer 1 is moved with the movement of the burner 25 for synthesis.
In addition to measuring the surface heating temperature of the heating part A moving on the deposition surface of No. 1 and, based on the measurement result, the synthesis burner is set so that the surface heating temperature at each part is within the range of the reference temperature ± 50 ° C. 25 is controlled. As a result, the heating conditions for each part of the glass porous layer 11 fall within a certain range. Generation is suppressed.

At this time, after synthesizing the glass porous layer 11, it is necessary to further use an auxiliary burner provided separately from the synthesizing burner 25 to make a soot for correcting unevenness of the outer diameter. Therefore, the manufacturing process can be simplified and the manufacturing cost can be reduced. Further, the configuration of the manufacturing apparatus is similarly simplified. Also, if soot for correction is performed separately from the synthesis process, inherent problems such as cracks occurring in the base material and dust being taken into the base material will occur. It is eliminated at the same time.

Regarding the measurement time point at which the measurement of the surface heating temperature is performed, during the traverse of the synthesis burner 25,
The measurement is preferably performed at a predetermined measurement time interval. At this time,
The measurement time interval is determined by taking into account various conditions such as the traverse speed of the synthesis burner 25, the length of the porous glass preform 1 in the longitudinal direction, or the traverse distance of the synthesis burner 25. Must be set to a time interval that can be controlled to ± 50 ° C. or less. Further, it is also possible to continuously measure the temperature during the traverse or to externally instruct the temperature measurement point by an operator or the like. Further, it is preferable to change the heating condition and the synthesis condition by controlling the synthesis burner 25 every time the surface heating temperature is measured.

As for the method of measuring the surface heating temperature of the heating portion A, a method of measuring the surface temperature at the heating center point P ₀ (see FIG. 1) of the heating portion A by using a temperature measuring device such as a radiation thermometer. There is. Alternatively, the heating center point P ₀
Instead of measuring only the surface temperature, a plurality of temperature measurement points are respectively set at predetermined positions in or near the heating portion A, and heating is performed from the surface temperature measured at each temperature measurement point. The surface heating temperature at the portion A may be obtained.

FIG. 2 is a schematic diagram showing one embodiment of the measurement of the surface heating temperature using a plurality of temperature measurement points. In the example shown in FIG. 2, the porous glass preform 1
Longitudinally along (traverse direction of the synthesis burner 25), five temperature measurement point P ₀ as the center of the heating center point P ₀ of the
~P ₄ has been set. These temperature measuring point, temperature measuring points in the drawing temperature measurement points P ₁ and P ₂ on the right side of (heating central point) P _0, also arranged at equal intervals temperature measuring points P ₃ and P ₄ on the left Have been.

The surface temperatures at the respective temperature measuring points P _{0 to} P ₄ are measured by radiation thermometers 27 _{0 to} 27 ₄ , respectively. The radiation thermometer 27 _{0-27 4} are both synthetic burner 2
The traverse device 26 or a moving device associated therewith is movably installed so as to be moved with the movement of the heating portion A by the traverse 5.

The measurement results of the surface temperatures at the respective temperature measurement points P _{0 to} P ₄ by the radiation thermometers 27 _{0 to} 27 _{4 are obtained} by the burner controller 28.
Is input to The burner control unit 28 determines the heating area A based on the input measurement result of the surface temperature at each measurement point.
To determine the surface heating temperature. Then, based on the determined surface heating temperature at each measurement point, the synthesis burner 2
5 is controlled as needed.

As described above, the accuracy of the required surface heating temperature can be improved by setting a plurality of temperature measurement points for determining the surface heating temperature and determining the surface heating temperature at the heating portion A from the surface temperatures. It is possible to improve the uniformity of the obtained porous glass base material 1 in the longitudinal direction. It is preferable to set the number of temperature measurement points and the arrangement intervals appropriately according to various conditions such as the required degree of uniformity and the traverse speed of the burner 25 for synthesis.

When a plurality of temperature measurement points are set as shown in FIG. 2, the maximum temperature of each surface temperature obtained at those temperature measurement points is set as the surface heating temperature at the heating portion A. Is preferred. For example, in the case of traversing to the right synthesis burner 25 from the left in the figure 2, the heating center point P ₀ is heated state for site right and left different. Therefore, portions having a surface temperature of the highest temperature is located on the left side of the heating center point P _0. If you want to traverse from right to left,
The highest temperature on the right side than the heating central point P _0.

On the other hand, as shown in FIG. 2, by arranging a plurality of temperature measurement points P _{0 to} P ₄ at predetermined intervals in the traverse direction around the heating center point P ₀ , the surface temperature can be reduced. Even when the distribution is asymmetric with respect to the center of the heating portion A, it is possible to evaluate the surface heating temperature by taking in the effect of the distribution. Specifically, the maximum temperature of the surface temperature measured for each temperature measurement point is
By setting the surface heating temperature as described above, the heating temperature can be controlled based on the surface temperature of the most heated portion at each measurement time.

Further, regarding the control of the synthesizing burner 25 performed based on the measurement result of the surface heating temperature at each time point, the difference between the surface heating temperature and the reference temperature at each measurement time point is obtained, and the temperature difference is calculated. It is preferable to perform the control based on this. As a specific control method of the synthesis burner 25, for example, there is a method of changing the flow rate of the fuel gas supplied to the synthesis burner 25. Further, there is a method of changing the position and the distance of the synthesis burner 25 with respect to the porous glass base material 1. Alternatively, any other control method of the heating condition may be used as long as the surface heating temperature can be adjusted.

The uniformity of the outer diameter and the like in the longitudinal direction of the optical fiber preform obtained by using the manufacturing method according to the embodiment shown in FIGS. 1 and 2 will be further described with specific examples.

In this embodiment, a core rod 10 having a diameter of 10 mm and a length of 500 mm is used as a starting rod for sooting. The core rod 10 is rotated by a support mechanism 21 at a rotation speed of 40 rpm, and the core rod 10 is formed by the OVD method (FIG. 1). A glass porous layer 11 was deposited on the outer periphery of the substrate 10.
Further, the traverse speed of the synthesis burner 25 is set to 200 mm.
/ Min, the traverse distance with a 400 mm, the composition and flow rate of the gas used in the flame from the synthesis burner 25, in the initial setting at the time of initiation of synthesis, 40 l of H ₂
/ M (slm, standard 1 / m), O ₂ 70 l / m,
SiCl ₄ was set at 1.5 l / m.

When the synthetic glass burner 25 is traversed and the porous glass base material 1 is heated by the flame, as shown in FIG.
By setting _{0 to} P ₄ , the surface heating temperature of the heating portion A on the deposition surface of the glass porous layer 11 was measured. Here, the temperature measurement points P _{1 to} P _{4 are} arranged around the temperature measurement point (heating center point) P _{0 at} the center of the heating portion A at an interval of 5 mm in the traverse direction.
Was placed.

Regarding the measurement time interval of the surface heating temperature,
Every 10 mm of traverse of the burner 25 for synthesis (time interval 3
Every second). Further, the highest temperature among the surface temperatures measured at the temperature measurement points P _{0 to} P ₄ is defined as the surface heating temperature of the heating portion A at the time of the measurement, and the surface heating temperature, a preset reference temperature, Was calculated. And
On the basis of the sign and the magnitude of the obtained temperature difference, the flow rate of H ₂ , which is the fuel gas of the synthesis burner 25, is sequentially changed from the initial setting of 40 l / m, and the heating conditions by the flame (the glass porous layer 11 (Synthesis conditions).

Specifically, if the measured surface heating temperature is lower than the reference temperature, H
_{(2) The} flow rate was increased, and conversely, if the surface heating temperature was higher than the reference temperature, control was performed to decrease the H ₂ flow rate according to the temperature difference. The flow rates of O ₂ and SiCl ₄ were fixed at the initial settings described above.

The porous glass composite preform 1 produced by the above method was heated and sintered in a sintering furnace to make it transparent, thereby obtaining a transparent glass preform. At this time, the variation in the outer diameter of the preform in the longitudinal direction was reduced, and an optical fiber preform having good longitudinal uniformity was obtained. The outer diameter and length of the base material after sintering were 52 mm on average and 3 mm, respectively.
00 mm.

The fluctuation width of the surface heating temperature of the deposition surface depends on the measurement time interval of the surface heating temperature (the burner 25 for synthesis).
Control time interval) and the change amount of the H ₂ flow rate with respect to the temperature difference amount in the control of the synthesizing burner 25.
For example, when only the measurement time interval was changed under the above-described conditions, the variation in the surface heating temperature exceeded ± 50 ° C. when the measurement time interval exceeded every traverse 50 mm.

H ₂ for measurement time interval and temperature difference
FIG. 3 shows the result of obtaining the magnitude of the outer diameter variation of the base material for some variation ranges of the surface heating temperature by changing the two conditions of the change amount of the flow rate. Here, the horizontal axis indicates the fluctuation width of the surface heating temperature on the deposition surface of the glass porous layer 11 measured by the method described above, and the vertical axis indicates the outer diameter fluctuation in the longitudinal direction of the sintered transparent glass base material. Is shown.

From this graph, it can be seen that by suppressing the fluctuation range of the surface heating temperature to ± 50 ° C. or less, the fluctuation of the outer diameter in the longitudinal direction can be made within 1.5 mm.
At this time, an optical fiber preform having a sufficiently stable outer diameter to be supplied to the drawing step is obtained.

Further, in addition to the change in the outer diameter of the base material, the thickness of the layer added to the core rod 10, that is, the layer obtained by sintering the porous glass layer 11, is a thickness ratio to the core rod 10. The magnification is preferably uniform in the longitudinal direction in order to stabilize the characteristics of the optical fiber. FIG. 4 shows the result of similarly determining the dependency of the external heating magnification on the fluctuation range of the surface heating temperature. Here, the horizontal axis indicates the variation width of the surface heating temperature on the deposition surface, and the vertical axis indicates the variation of the external magnification in the longitudinal direction of the sintered transparent glass base material.

From this graph, it can be seen that by suppressing the fluctuation range of the surface heating temperature to ± 50 ° C. or less, the fluctuation of the external magnification can be suppressed to within 1%. The effect of the change in the external magnification on the optical fiber depends on the refractive index distribution in the core rod 10, but in general, a change within 1% is sufficient for almost all types of optical fibers. Characteristic stability in the longitudinal direction can be obtained.

In the synthesis method in which the burner is traversed in the axial direction to deposit the glass fine particle layer, the method of measuring the temperature of the glass fine particle layer and adjusting the heating conditions is described in Japanese Patent Application Laid-Open No. Hei 2-243530 and Japanese Patent Laid-Open No. 2-243530. Kaihei 2-
No. 307838. However, these production methods aim at adjusting the bulk density of the fine particle layer formed between the traverses for a plurality of times, and therefore, the temperature of the glass fine particle layer is set at a fixed temperature such as an end thereof. Measured only at measurement points. Therefore, although it is possible to adjust the synthesizing conditions for each traverse, it is not possible to adjust the synthesizing conditions in the traverse, and it is not possible to adjust the uniformity in the longitudinal direction of the obtained porous glass base material. Not improved.

On the other hand, in the above-described method for manufacturing an optical fiber preform, the surface heating temperature is measured for a heated portion on the glass porous layer which is moved together with the traverse of the burner for synthesis, and based on the measurement result. This is for adjusting the synthesizing conditions by the synthesizing burner. This makes it possible to adjust the synthesis conditions in the traverse, and to improve the uniformity of the obtained porous glass base material in the longitudinal direction.

The method for manufacturing an optical fiber preform according to the present invention is not limited to the above-described embodiments and examples, and various modifications are possible. For example, the limit temperature range for the fluctuation range of the surface heating temperature is not limited to ± 50 ° C. described above, and a different temperature range may be appropriately set in each manufacturing process.

The setting of the plurality of temperature measurement points is not limited to the heating center point P ₀ of the heating portion A being arranged only in the direction along the longitudinal direction, but to the heating center point P ₀ as the center. They may be arranged in a dimensional array (matrix). Alternatively, the conditions such as the traverse speed and required uniformity of accuracy may be a temperature measuring point only one point of the heating center point P _0. In addition, for the surface heating temperature when there are a plurality of temperature measurement points, in addition to the method of setting the maximum temperature of each surface temperature, various temperature determination methods such as a method of obtaining an average temperature of the surface temperature at each temperature measurement point. Can be used.

Although the starting rod is a core rod in the above embodiment, a rod formed with a part of the core and the clad may be used as the starting rod. For the movement (traverse) of the burner 25 for glass synthesis with respect to the starting rod, the burner 25 for synthesis is fixed.
A method in which the starting rod (porous glass base material) is moved and reciprocated with respect to the synthesis burner 25 may be used. Also,
The support shaft of the base material is not limited to the above-described lateral direction,
It may be in the vertical direction.

[0052]

The method for manufacturing an optical fiber preform according to the present invention has the following effects as described in detail above. That is, in the synthesis method in which the glass synthesis burner is moved in the longitudinal direction with respect to the porous glass base material (starting rod) to deposit a glass porous layer on the outer circumference of the starting rod, The surface heating temperature for the heating site on the deposition surface of the glass porous layer due to the flame of
Measure at each point during the synthesis. Then, based on the result, the heating condition by the synthesis burner is controlled so that the fluctuation range of the surface heating temperature becomes a predetermined temperature range (for example, ± 50 ° C.) or less, and the synthesis condition of the glass porous layer is adjusted. I do.

As a result, the occurrence of non-uniformity such as the outer diameter of the porous glass layer due to the difference in the heating temperature at each portion in the longitudinal direction is suppressed, and the uniformity of the optical fiber preform in the longitudinal direction is improved. . At this time, the drawing process of the optical fiber preform can be performed under favorable conditions, and the characteristics of the optical fiber after drawing can be stabilized. In particular, in the above-described manufacturing method, since a separate repairing step is not required after the synthesis of the porous glass layer, the manufacturing process is simplified and the manufacturing cost is reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical fiber preform manufacturing apparatus used in an embodiment of an optical fiber preform manufacturing method.

FIG. 2 is a schematic diagram showing an embodiment of measurement of a surface heating temperature using a plurality of temperature measurement points.

FIG. 3 is a graph showing a correlation between a fluctuation range of a surface heating temperature and a fluctuation of an outer diameter of a base material.

FIG. 4 is a graph showing a correlation between a fluctuation width of a surface heating temperature and a fluctuation of an external magnification.

[Explanation of symbols]

1 ... porous glass preform, 10 ... core rod, 11 ... glass porous layer, A ... heating site, P ₀ to P ₄ ... temperature measuring point, 20 ... base material supporting device 21 ... supporting mechanism, 25 ... glass synthesis Burner, 26: traverse device, 27: radiation thermometer, 28: burner control unit.

Claims (7)

[Claims] 1. A method for manufacturing an optical fiber preform, wherein a glass synthesis burner is moved within a predetermined range in a longitudinal direction with respect to a starting rod to synthesize a glass porous layer on an outer periphery of the starting rod. During the movement of the burner for glass synthesis within the predetermined range, while measuring the surface heating temperature of the glass porous layer at a heating site being heated by a flame from the burner for glass synthesis, A method for manufacturing an optical fiber preform, wherein the heating condition of the glass porous layer is controlled such that a fluctuation width of the surface heating temperature is equal to or less than a predetermined temperature width with respect to a set reference temperature. 2. The method according to claim 1, wherein the predetermined temperature range is ± 50 ° C. 3. The method of measuring the surface heating temperature at predetermined measurement time intervals, and based on a difference between the surface heating temperature measured at each measurement time point and the reference temperature, measuring the surface heating temperature of the glass porous layer. The method for producing an optical fiber preform according to claim 1, wherein the heating condition is controlled. 4. The optical fiber preform according to claim 1, wherein a heating condition of said glass porous layer is controlled by changing a flow rate of a fuel gas supplied to said glass synthesizing burner. Manufacturing method. 5. A plurality of temperature measurement points respectively set at predetermined positions with respect to the heating site are set on the glass porous layer, and the surface temperature measured at each of the temperature measurement points is calculated based on the surface temperature. The method for producing an optical fiber preform according to claim 1, wherein the surface heating temperature is determined. 6. The method of manufacturing an optical fiber preform according to claim 5, wherein the surface heating temperature is determined from a maximum temperature of the surface temperature measured at each of the plurality of temperature measurement points. 7. The method of manufacturing an optical fiber preform according to claim 5, wherein the surface heating temperature is determined from an average of the surface temperatures measured at each of the plurality of temperature measurement points.