JP2002293565A - Method for producing optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber preform having less fluctuation of outer diameter in the longitudinal direction and targeted amount of glass piled up as a whole. SOLUTION: Assuming the starting rod outer diameter as a first variable, the optical fiber preform outer diameter as a second variable, and a variable representing the completion timing of glass fine particles pile up process as a third variable, a relationship among the three variables is obtained in advance, the starting rod and the burner are relatively moved based on the relationship, glass fine particles are piled up until the completion timing and the preform is made transparent. As the third variable, the traverse rate, the pile up time of the glass particle or the weight of piled up glass particles may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical fiber preform by the OVD method, and more particularly to a method in which a variation in outer diameter in the longitudinal direction is reduced and a target amount of glass is deposited as a whole without reducing the deposition rate. The present invention relates to a method for obtaining an optical fiber preform.

[0002]

2. Description of the Related Art In a method for manufacturing an optical fiber preform by the OVD method, a plurality of burners for synthesizing glass fine particles are arranged at regular intervals to form a burner row in order to manufacture a large optical fiber preform at a high speed. And the burner row are opposed to each other so that the axis of the starting rod and the burner row are parallel to each other, and one or both of them are moved (traversed) in the axial direction so that the starting rod is relatively reciprocated. Japanese Patent Laid-Open No. 3-228 discloses a method of depositing glass fine particles thereon to form a glass fine particle deposit and then vitrifying the glass fine particles to obtain an optical fiber preform.
No. 845.

In this method, a method of reciprocating motion is devised in order to reduce the variation in the outer diameter of the glass fine particle deposit in the longitudinal direction. Each time the starting rod and the row of burners are relatively reciprocated, the turning point of the reciprocating motion is moved, and after the turning point is moved to a predetermined position, the turning point is moved in the opposite direction to return to the initial start position. In this way, the turning point of the reciprocating motion, which causes the deposition time to be longer, is dispersed throughout the deposited body, the deposition amount of the glass fine particles is made equal in the longitudinal direction, and the outer diameter variation is reduced. In this specification, the number of reciprocating motions until the start position of the reciprocating motion returns to the initial position is referred to as “average number of turns”.

[0004] In this method, it is important to determine the schedule for depositing the glass particles so that the turning points are uniformly distributed over the entire length of the glass particle deposit. The amount of glass particles attached is continuously measured with a weight detector, etc., and when the measured value is close to the target weight, the deposition of the glass particles is completed at an integral multiple of the averaged number of turns, and the target weight is obtained. Determine the schedule. JP-A-3-
Japanese Patent No. 228845 does not disclose a method for determining a target weight.

As a method of reducing the outer diameter variation, the outer diameter variation of the entire deposit is measured using a CCD camera and a central information processing device capable of monitoring the entire glass particulate deposit, and the entire length of the deposit can be traversed independently. Japanese Patent Application Laid-Open No. H10-158025 proposes a method of reducing the variation in outer diameter by supplementing the accumulation of glass particles in a portion having a smaller outer diameter by using an auxiliary glass synthetic burner smaller than the main burner.

In addition, the weight of the glass particle deposit is measured during the deposition process, and an increase in the weight is predicted based on the data, and the speed in the last traverse is set so as to obtain a target amount of the glass particle deposit. Is determined by JP-A-4-2
Japanese Patent Application Laid-Open No. 3-54129 discloses that the speed or the supply amount of the glass raw material in the last traverse is determined in the same manner. JP-A-4-260633 and JP-A-3-5
Japanese Patent No. 4129 does not disclose a method of determining a target weight in consideration of glass particles deposited on a tapered portion. Further, in Japanese Patent Application Laid-Open No. Hei 2-137743, the outer diameter and weight of the glass fine particle deposit are measured during the deposition process, and the length of the deposit is regarded as the sum of the moving distance of the burner and the length of the tapered portion. A method is disclosed in which the weight per unit length of the body is calculated, and when this weight reaches a desired value, the deposition of the fine glass particles is stopped. Here, no method is disclosed for determining the target weight in consideration of the glass particles deposited on the tapered portion. Further, the shape of the tapered portion and the difference in bulk density between the effective portion and the tapered portion are not considered.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an optical fiber preform having a smaller outer diameter variation in the longitudinal direction and having a target amount of glass deposited as a whole. I do.

[0008]

Means for Solving the Problems In order to solve this problem, the present inventors have conducted various studies and arrived at the following inventions. The outer diameter of the starting rod is the first variable, the outer diameter of the optical fiber preform (outer diameter of the sintered body) is the second variable, and the variable representing the end timing of the glass fine particle deposition process is the third variable. The starting rod and the burner are relatively moved on the basis of this relation, and the glass fine particles are deposited on the starting rod until the end timing, and are made transparent.

In one embodiment of the present invention, the starting rod may be extended to an outer diameter determined by a desired outer diameter of the optical fiber preform and a J magnification. The outer diameter of the reform may be determined. Note that J
The magnification refers to “the ratio of the cladding outer diameter to the starting rod outer diameter in the optical fiber preform”.

According to another aspect of the present invention, there is provided a method of relatively moving a starting rod containing a core and a burner to deposit glass particles on the starting rod. There is a method in which a speed is determined, and the starting rod and the burner are moved relative to each other a predetermined number of times at the speed to deposit glass particles. In this method, the predetermined number of relative movements between the starting rod and the burner varies with the type of the burner, the interval between the burners, the input amount of the raw material, and the outer diameter of the glass fine particle deposit due to restrictions other than the J attaching process. It is appropriately determined in consideration of these conditions in the process.

According to still another aspect of the present invention, there is provided a method of relatively moving a starting rod containing a core and a burner to deposit fine glass particles on the starting rod, wherein the starting rod diameter is changed. Determine a traverse speed that can make the base material diameter after transparent vitrification the same or almost the same, and perform the relative movement of the starting rod and the burner a predetermined number of times at the speed to deposit glass particles, At that time, there is a method characterized in that the diameter ratio is adjusted by changing the diameter of the starting rod. According to this method, the traverse speed is controlled in accordance with the diameter of the starting rod to perform glass particle deposition, and the glass diameter (sintered body outer diameter) of the obtained glass particle deposited body after sintering and transparency is made constant. Possible glass particle deposition step. In this case, the traverse speed is applied to control the glass particle deposition stop time.

According to an aspect of these inventions, the turning point of the reciprocating motion may be moved from the initial position by a fixed distance in a fixed direction, and after being moved by a predetermined distance, the turning point may be moved by a fixed distance to the initial position in the opposite direction. Good. The traverse speed may be constant from the start to the end of the deposition of the fine glass particles, or may be a speed at which the target J magnification can be realized from the middle. If the traverse speed is changed, a change in the surface temperature of the glass fine particle deposit in a time series before and after the change (change rate of the surface temperature with time) changes. Therefore, the flow rate of the flammable gas supplied to the burner is changed so that the change of the surface temperature of the glass fine particle deposit in the time series occurring when the speed of the traverse is changed is the same (the glass fine particles before and after the change of the traverse speed) (The rate of change over time of the surface temperature of the deposited body may be the same).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the relationship between the outer diameter of a starting rod, the outer diameter of an optical fiber preform, and the timing of terminating the deposition of glass particles is experimentally determined in advance. Then, at the time of manufacturing, the timing to terminate the deposition is determined using the outer diameter of the optical fiber preform, the outer diameter of the starting rod, and this relationship.

More specifically, glass particles are deposited by changing the outer diameter of the starting rod and the timing at which the deposition is completed, for example, the glass particle deposition time, and the outer diameter of the optical fiber preform is determined. Then, for example, data represented by the curved surface 21 in FIG. 2 is obtained. A function suitable for expressing this data is searched for, and a specific function form is obtained by the least square method. As a function, it may be approximated as a function of three variables, for example, R is the rod diameter, S is the outer diameter of the optical fiber preform, and C is the timing at which deposition ends,

[Equation 1] S = k ₁ × R × Exp (k ₂ × C) It is approximated by an exponential relationship such as (Equation 1).

When depositing glass particles by the method disclosed in Japanese Patent Application Laid-Open No. 3-228845, the number of reciprocating movements of the starting rod and the burner is determined in advance to be an integral multiple of the averaged number of turns. The traverse speed can also be used as a manufacturing parameter that gives the timing to terminate. Since the traverse speed can be changed mechanically, accurately and continuously, the amount of glass particles deposited can be adjusted accurately and continuously.

The outer diameter of the optical fiber preform may be determined by multiplying the outer diameter of the starting rod by a constant value and multiplying it by a target J magnification. In this case, since the starting rod can be manufactured in a fixed manner, the accuracy of the starting rod diameter can be easily controlled, and the yield can be improved. On the other hand, since the outer diameter of the optical fiber preform has a preferable value determined by the convenience of the subsequent process, the outer diameter of the starting rod may be determined from the preferable value and the target J magnification.

In the following, the present invention will be compared with other methods. (1) Method of terminating glass particle deposition with a predetermined number of turns: In this method, the number of turns is a discrete amount, so that the amount of deposition cannot be continuously adjusted. In particular, when this method is applied to the glass fine particle deposition method disclosed in JP-A-3-228845, the glass fine particle deposition is stopped at the averaged number of turns that is closest to the target J magnification. It is impossible to finely adjust the amount of deposition. On the other hand, in the present invention, the end timing is determined by using the relationship between the starting rod outer diameter, the optical fiber preform outer diameter, and the timing of terminating the deposition represented by a continuous amount, which is obtained in advance. , The amount of deposition can be finely adjusted.

(2) JP-A-3-228845, JP-A-2-137743, JP-A-4-260633
Method described in Japanese Unexamined Patent Application Publication No. 3-54129 and Japanese Patent Application Laid-Open No. 3-54129: The estimation of the weight of the glass fine particle deposit which is tapered at both ends of the starting rod and becomes an ineffective portion is inaccurate. A method for solving this is not disclosed in any of the publications. Therefore, in these methods, the J magnification or the outer diameter of the deposit may deviate from the design value due to an error in the weight of the ineffective portion. On the other hand, in the present invention, since the end timing is determined using the relationship between the starting rod outer diameter, the optical fiber preform outer diameter, and the timing at which the deposition ends, the end timing is determined in advance. Are offset, and the outer diameter or J magnification of the deposit can be made almost as designed. Note that Japanese Patent Laid-Open No. 4-2
In the method described in Japanese Patent No. 60633 and Japanese Patent Application Laid-Open No. 3-54129, only the final traverse speed is changed, so that it is necessary to change the traverse speed very widely. Further, when measuring the outer diameter of the glass fine particle deposit as disclosed in Japanese Patent Application Laid-Open No. 2-137743 to determine the timing for terminating the glass fine particle deposition, an outer diameter measuring device is required, and equipment cost is reduced. Is high. Furthermore, the accuracy of the outer diameter measuring device is not always good,
If the sediment swings or shakes, there is a problem that correct measurement cannot be performed.

(3) The method disclosed in JP-A-10-158025: Since the auxiliary glass synthetic burner is smaller than the main burner,
This lowers the deposition efficiency of the glass particle deposition. In addition, it is necessary to install an operation mechanism of the auxiliary glass composite burner. If the operation mechanism is installed outside the muffle, it is necessary to make a large hole in the muffle, and there is a possibility that air bubbles may be generated in the optical fiber preform due to foreign matter entering from outside the muffle. Even if the operating mechanism is installed in the muffle, the foreign matter generated by the operating mechanism is mixed with the glass particle deposit,
Bubbles may be generated. According to the present invention, an optical fiber preform can be manufactured without lowering the deposition rate, and it is possible to prevent foreign matters from being mixed into the optical fiber preform.

Next, a first embodiment of the present invention will be described. Here, the traverse speed is adjusted so that the deposition amount of the glass fine particles is set to a desired value. As an example, it is assumed that the number of reciprocating motions to stop the deposition of glass particles is 10 turns, and the distance traversed in one turn is 100 mm. 10 in total
Traversed 00 mm. Traverse speed 200, 500, 1
Change the glass particle size to 000 mm / min to carry out glass particle deposition. That is, the glass fine particle deposition is performed by changing the glass fine particle deposition time to 5, 2, or 1 minute. This change in the glass particle deposition time appears as a change in the thickness of the glass particles deposited in one traverse. In the case of 1000 mm / min, the thickness of the glass fine particles is about half as compared with the case of 500 mm / min. However, since the time until the end of the deposition of the glass particles is also halved, the deposition amount per time does not decrease. Next, the preform thus obtained is sintered, and the J magnification is measured.
The relationship between the traverse speed and the J magnification is shown in FIG. If the curve 2 is approximated by an appropriate function such as a straight line or a quadratic function, a relational expression between the traverse speed and the J magnification is obtained.
The traverse speed suitable for the desired J magnification can be calculated from the equation. In this embodiment, the dimensions of the starting rod and the number of relative movements of the burner depend on the type of burner,
It is determined separately in advance, taking into account the burner interval, the amount of raw materials to be charged, and restrictions in equipment and post-processing. By changing the traverse speed in this way, it is possible to freely change the glass particle deposition time when the number of traverse turns is determined, and adjust the glass particle deposition amount.

In this embodiment, since the relationship between the traverse speed and the J magnification is experimentally obtained, the influence of the ineffective portion has already been considered. Also, the traverse speed is mechanically controlled and very accurate. Since the amount of glass particles deposited during a predetermined number of traverses is adjusted by the traverse speed, fine control is possible.

In the first embodiment, the outer diameter of the optical fiber preform is adjusted by changing the traverse speed for a starting rod having the same diameter. However, there is also a demand for adjusting the J magnification by adjusting the outer diameter of the optical fiber preform to the size of the equipment in the process after the deposition of the glass fine particles and changing the outer diameter of the starting rod.

The second embodiment of the present invention responds to such a demand, and performs glass particle deposition by setting the traverse speed according to the outer diameter of the starting rod, and sets the outer diameter of the optical fiber preform to a desired value. Is a way to Again,
The traverse speed is used to adjust the timing of terminating the glass particle deposition. More specifically, the total traverse distance between the glass rod and the burner is determined by determining the number of turns until the glass particle deposition stops,
By changing the traverse speed, the time until the deposition of the glass particles is changed. The following describes what happens when the starting rod outer diameter changes.

FIG. 4 shows the relationship between the traverse speed and the outer diameter of the optical fiber preform when the outer diameter of the starting rod is 40 mm and 20 mm, where the number of turns until the deposition of the glass particles is stopped is the same. The straight line in FIG. 4 shows the relationship between the traverse speed and the outer diameter of the optical fiber preform with the outer diameter of the starting rod as a parameter.When the relationship between these three quantities is shown in three dimensions, the plane in FIG. It becomes 51.

The flat surface 51 defines the outer diameter of the optical fiber preform.
Assuming that S, traverse speed is T, and starting rod outer diameter is R, it can be approximately expressed using the coefficients a, b, and c as follows:

[Equation 2] T = a × R + b × S + c (Equation 2)

The coefficients a, b, and c in Equation 2 can be determined based on several experimental data. Therefore, by substituting the starting rod outer diameter calculated from the desired optical fiber preform outer diameter and the target J magnification into Equation 2, the traverse speed can be obtained. By considering the plane 51 of FIG. 5, it is possible to determine the traverse speed for keeping the glass diameter after sintering and clarification constant when the outer diameter of the starting rod is changed, which is the adjustment of the glass fine particle deposition time. Means that only the traverse speed is possible as in the first embodiment.

The above parameters (outer diameter of the starting rod, outer diameter of the optical fiber preform, and traverse speed) can be accurately controlled because they can all be measured accurately and have high accuracy. Further, even after the formula is once obtained and the production is started based on the formula, the formula 2 can be made more accurate by using the outer diameter of the product or the like as new data. Although FIG. 5 illustrates the plane 51 in the three-dimensional space, a function suitable for the plane may be selected even when the plane is not a plane.

In the present invention, the least squares method can be used to derive the coefficients. However, it is not limited to this. Further, in the above description, the traverse speed is used as a variable representing the end timing of the glass fine particle deposition step. However, the present invention is not limited to this, and the glass fine particle deposition time itself may be used. Body weight or the like may be used.

In the third embodiment of the present invention, the change in the surface temperature of the glass fine particle deposit that occurs during the deposition of the glass fine particles is adjusted. FIG. 6 is a graph showing the change in surface temperature during the three traverse rate deposition processes (A, B, C). Surface temperatures are generally in the range of 500-850 ° C. As shown in FIG. 6, not only does the surface temperature change during the deposition of a series of glass particles, but the manner in which it varies varies for each deposition process (A, B, C) with altered traverse speed. When the surface temperature changes, the bulk density of the deposit changes. A change in the bulk density results in a change in the refractive index when a dopant is added during sintering and transparency. Even when the traverse speed is changed, it is preferable that the temporal change of the surface temperature does not change and the refractive index becomes equal in each optical fiber preform. Therefore, as temporal change of the surface temperature is the same in each stack, adjusted flammable gas such as H ₂ or CH ₄ is supplied to the burner.

In the case of the method disclosed in Japanese Patent Application Laid-Open No. Hei 3-228845, there is a problem that it is difficult to set the number of reciprocating movements at the target J magnification to an integral multiple of the averaging turn. The fourth embodiment has been made to solve such a problem. A case where the number of averaged turns is 40 will be described. In the present embodiment, the number of reciprocating movements that becomes the target J magnification is
First of all, it is decided to be 1600 turns, which is the 40th averaged number of turns. Then, under these conditions, the deposition amount of the glass particles is adjusted at the traverse speed. For example, considering three traverse speeds of traverse speeds of B mm / min and B ± C mm / min, they differ in the deposition time of glass fine particles and in the amount of glass fine particles deposited. Comparing the deposition amounts of the three, [when B + C mm / min] <[when B mm / min]
<[When B−C mm / min]. In this way, it is possible to adjust the deposition amount of the glass particles.

In the first to fourth embodiments, a rod traverse speed or a burner traverse speed suitable for the target J magnification is selected, and this speed is maintained from the start to the end of the deposition of the fine glass particles. By the way, in a situation in which no glass particles are deposited on the starting rod, such as immediately after the start of the deposition of the glass particles, the deposition efficiency of the glass particles is poor because the target is small. In such a case, the traverse speed is kept constant until the diameter of the glass fine particle deposit becomes large to some extent, and after entering the stable region where the diameter of the deposit becomes large, the traverse speed is reduced to a speed at which the desired J magnification can be achieved. It is also preferable to do so.

Therefore, in the fifth embodiment, the traverse speed is set to a predetermined value until a certain traverse turn of glass particle deposition, and the traverse speed after that turn is set to a speed capable of realizing the target J magnification. The term "up to a certain traverse turn" as used herein means up to a turn at which the outer diameter of the glass particle deposit increases to such an extent that the outer diameter of the glass particle deposit increases and the efficiency of deposition of the glass particles does not change even when the traverse speed is changed. . In the case of this embodiment, even when first determining the relationship between the starting rod outer diameter, the outer diameter of the optical fiber preform and the timing of terminating the deposition of the glass particles, up to a certain traverse turn,
The traverse speed is set to a predetermined value. In this method, in addition to the effect of stabilizing the deposition of the glass particles as described above, the slope of the graph of the traverse speed and the J magnification becomes gentle,
The effect of improving the controllability of the magnification can be obtained.

[0033]

(Embodiment 1) As shown in FIG. 1, a plurality of glass synthesis burners 2 are arranged at regular intervals in opposition to a starting rod 1 installed in a container 4, and a rotating starting rod 1 and the burner Row 2 was relatively reciprocated to produce a glass particulate deposit. In the present embodiment, as shown in FIG.
Using four glass synthetic burners 71 arranged at an interval of 00 mm, these burners are combined with the length +1 of the effective portion 73 of the starting rod 72.
An experiment to measure the outer diameter of the optical fiber preform was performed by changing the outer diameter of the starting rod and the deposition time of the glass particles by reciprocating 000 mm. Each burner was supplied with an equal amount of SiCl ₄ 74 as each burner was facing the active portion of the starting rod. In this example, the speed of the traverse of the rod was 740 mm / min. Table 1 shows the results.

[0034]

[Table 1]

When the relationship between the three variables is approximated by (time) = a × S ² + b × S + c × R, and a, b, and c are obtained by the least squares method, this relationship is expressed as (time ) = 0.04554 × S ² −1.7403 × S−2.632 × R. The correlation coefficient between the value obtained from the relational expression and the experimental value was 0.98, and the functional expression could approximate the experimental result with an accuracy of ± 1%. Next, glass particles were deposited on a starting rod having an outer diameter of 36 mmφ so that the outer diameter of the optical fiber preform was 130 mmφ. The deposition time was 449 minutes as calculated from the relational expression. The obtained preform outer diameter was 131 mmφ, and the deviation from the target value was 0.8%. The deviation from the target value may be ± 2% or less, and ±
It is more preferably at most 1%, more preferably at most ± 0.5%.

(Embodiment 2) As shown in FIG. 7, four glass composite burners 71 arranged at intervals of 200 mm were used, and these burners were combined with the length of the effective portion 73 of the starting rod 72 +1000 mm.
The glass particle was deposited by reciprocating. Target J magnification of 3.0
And how to determine the end timing of glass fine particle deposition, (1) predetermined weight, (2) predetermined number of turns, (3) predetermined glass fine particle outer diameter, (4) of the method of the present invention There were four types. Where (1)
Is a conventional method, and calculates the deposition of glass particles to be deposited from the outer diameter of the deposit, the outer diameter of the starting rod, and the J magnification, and multiplies the volume by the bulk density to obtain the weight of the glass particles to be deposited. Is calculated in advance, and the deposition of the glass particles is stopped when the glass particles of the weight are deposited on the starting rod. In (4), the number of turns until the stop was 1600 turns, and the manufacturing parameter for determining the end timing was the traverse speed. The traverse speed in (1) to (3) was 800 mm / min, and the traverse speed in (4) was 740 mm / min. | Measured J magnification-Target J magnification |
変 動 The fluctuation rates defined by the target J magnification × 100 were 1.5%, 1.3%, 2%, and 1% for (1) to (4), respectively. (1)
In the case of (1), in addition to the problem of estimating the weight of the ineffective portion, it is considered that the weight measurement becomes unstable due to the rod traverse, and the fluctuation rate is increased. In the case of (3), it is considered that there is an error due to the difference in bulk density of each layer and an outer diameter measurement error due to the fact that the deposit as the measurement object moves on the rod traverse.

(Embodiment 3) As shown in FIG. 7, four glass composite burners 71 arranged at intervals of 200 mm were used, and these burners were combined with the length of the effective portion 73 of the starting rod 72 +1000 mm.
Reciprocate and change the starting rod outer diameter and traverse speed 1600
An experiment was performed to measure the outer diameter of an optical fiber preform by depositing glass particles in turns. Table 2 shows the obtained results.
Shown in

[0038]

[Table 2]

The results of this experiment were approximated by a plane, and the coefficients were determined by the least squares method.

[Equation 3] T = 11.68 x R-9.22 x S + 1783.82 (Equation 3)

Next, glass particles were deposited on a starting rod having an outer diameter of 40 mm so that the outer diameter of the optical fiber preform was 145 mm. The burner traverse speed is given by Equation 3.
Was calculated to be 913.7 mm / min. The outer diameter of the obtained preform is 1465 mm, and the deviation from the target value is about 1%.
Met.

EXAMPLE 4 As shown in FIG. 8, four glass composite burners arranged at intervals of 200 mm were used, and the amplitude of the reciprocating motion of the burners was set to approximately 38 mm as the burner interval.
Deposition of glass particles was performed on a starting rod having a diameter. The amount of shift of the turning position in each reciprocation was set to 10 mm, and the dispersion of the turning position in the entire glass fine particle deposit was completed in 40 reciprocations. How to determine the end timing of the deposition of the glass fine particles is also performed in the same manner as in Example 2 (1) to (4), and in (4), the number of turns to stop is 1600 turns, and the traverse speed is 740 mm / min. . As a result, the fluctuation rate and outer diameter fluctuation in each case were as shown in Table 3.

[0042]

[Table 3]

The fluctuation rates of (1) to (3) were worse than in Example 2. This is because the traverse was stopped when the outer diameter of the deposit reached a value corresponding to the target J magnification, and the deposition of the glass fine particles was stopped while dispersing the traverse turning position over the entire deposit. This indicates that the fluctuation rate became worse because the outer diameter fluctuation became worse. On the other hand, the fluctuation rate of (4) was 1.3%. This is a result of the fact that the J-diameter adjustment can be performed without changing the number of stop turns, so that fluctuations in the outer diameter are kept small. However, in this traverse method, the outer diameter fluctuation is slightly larger than the data of the J magnification adjustment based on the traverse speed in Example 1 because the glass particles are deposited in such a manner that the four burners share the effective portion. Therefore, the fluctuation rate is slightly worse.

Example 5 As shown in FIG. 7, four glass composite burners 71 arranged at intervals of 200 mm were used, and these burners were combined with the length of the effective portion 73 of the starting rod 72 +1000 mm.
The glass particles were reciprocated to deposit glass fine particles. At that time, the number of turns to stop the deposition of glass particles is fixed at 1600 turns,
The traverse speed was changed to 703, 803, and 983 mm / min, and the J magnification and the bulk density of the glass fine particle deposit were measured. J magnification is
As shown by the dashed line in FIG. 9, there was a substantially linear relationship with the traverse speed. Further, the bulk density of the glass fine particle deposit was 0.5 to 0.7 g / cm ³ .

(Embodiment 6) In the three cases of Embodiment 5, the traverse speed up to 1200 turns is fixed at 803 mm / min, and the traverse speed after 1200 turns is 703, 803, 98.
Glass particles were deposited at a rate of 3 mm / min. The relationship between the traverse speed after 1200 turns and the J magnification is shown in FIG. When the traverse speed of the present embodiment is 703 mm / min, the traverse speed up to 1200 turns is 803 mm / min, which is higher than that of the fifth embodiment, and the J magnification is smaller. On the other hand, in the case of 983 mm / min, the traverse speed up to 1200 turns is 803 mm / min, which is lower than that of Example 5, and the J magnification is large. It can be seen that the slope of the approximate straight line is gentler in the case of the sixth embodiment, and that the J magnification controllability is high.

[0046] In Example 7 Example 5, only the flow rate of H ₂ supplied to the burner so that the time rate of change of the surface temperature of the glass particle deposited body is constant by adjusting was performed soot glass deposit . As a result, the bulk density is 0.6 to 0.65 g.
/ Cm ³ . The variation in the bulk density was determined in Example 5
It is smaller than the glass particle deposit obtained in the above. It is considered effective to use a deposit manufactured by the present method when a dopant is added in a sintering / clearing step or the like.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of an apparatus used in the present invention.

FIG. 2 shows a starting rod outer diameter according to an embodiment of the present invention;
4 is a graph showing a relationship between a deposition time and an outer diameter of an optical fiber preform.

FIG. 3 is a graph showing a relationship between a traverse speed and a J magnification according to the present invention.

FIG. 4 is a graph showing the relationship between the traverse speed and the outer diameter of the optical fiber preform when the number of reciprocation of the burner is set to a constant value.

FIG. 5 is a graph showing a relationship between a traverse speed, a starting rod outer diameter, and an optical fiber preform outer diameter.

FIG. 6 is a graph showing the relationship between the glass particle deposition time and the surface temperature of the glass particle deposit.

FIG. 7 is a view schematically showing a traverse of a rod in a glass particle depositing step of Example 1.

FIG. 8 is a view schematically showing a traverse of a rod in a glass particle depositing step of Example 4.

FIG. 9 is a graph showing the relationship between traverse speed and J magnification in Examples 5 and 6.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshio Yokoyama 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Motonobu Nakamura 1-Tagachi-cho, Sakae-ku, Yokohama, Kanagawa Prefecture Sumitomo Electric Industry Co., Ltd. Yokohama Works F-term (reference) 4G021 BA00 EA03 EB06 EB14 EB26

Claims (9)

[Claims] 1. An external diameter of a starting rod is set as a first variable, an external diameter of an optical fiber preform is set as a second variable, and a variable representing an end timing of a glass fine particle deposition step is set as a third variable. A method for producing an optical fiber preform, wherein a relation between the starting rod and the burner is relatively moved based on this relation, and glass particles are deposited on the starting rod until the end timing and are made transparent. 2. The starting rod is stretched to an outer diameter determined by a desired optical fiber preform outer diameter and a ratio (J magnification) of a cladding outer diameter to a starting rod outer diameter in the optical fiber preform. A method for manufacturing an optical fiber preform. 3. The method of manufacturing an optical fiber preform according to claim 1, wherein an outer diameter of the optical fiber preform is determined by an outer diameter of the starting rod and a J magnification. 4. A method for relatively moving a starting rod containing a core and a burner to deposit glass particles on said starting rod, wherein a speed of a traverse capable of achieving a target J magnification is determined. And performing a relative movement of the starting rod and the burner a predetermined number of times to deposit glass fine particles. 5. A method of relatively moving a starting rod containing a core and a burner to deposit fine glass particles on the starting rod, wherein the base material after vitrification is transparent even if the starting rod diameter is changed. A traverse speed that allows the diameter to be substantially the same is determined, and the soot is deposited by performing a relative motion of the starting rod and the burner a predetermined number of times at the speed, and at this time, the diameter of the starting rod is changed by changing the starting rod diameter. A method for producing an optical fiber preform, comprising adjusting a ratio. 6. A method of adjusting a flow rate of flammable gas to be supplied to a burner so that a change in a surface temperature of a glass fine particle deposit in a time series occurring when a speed of a rod traverse or a burner traverse is changed is equalized. The method for producing an optical fiber preform according to claim 4 or 5, wherein: 7. A method in which the turning position of the rod traverse or the burner traverse is moved in a fixed direction at regular intervals, and the direction in which the turning position is shifted by a predetermined interval is reversed, and the rod traverse or burner traverse is shifted to the first position. The method for producing an optical fiber preform according to any one of claims 4 to 6, wherein: 8. The rod traverse speed or burner traverse speed which is suitable for the target J magnification is selected, and the selected speed is set from the start to the end of the application of the glass fine particles. A method for manufacturing an optical fiber preform. 9. A method in which the speed of the rod traverser or the burner traverse is set to a predetermined value until a certain traverse turn for attaching the glass particles, and the traverse speed after that turn is set to a speed capable of realizing the target J magnification. The method for producing an optical fiber preform according to any one of claims 4 to 8, wherein: