JPH09124333A - Production of preform for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent crack formation in a preform for an optical fiber during its production or in the following process. SOLUTION: This is a method for producing a preform 4 for an optical fiber by ejecting a glass raw material from an accumulation burner 31, producing glass fine particles by flame hydrolysis and blowing them on a starting member 2 to accumulate. In the method, heating burners 32a, 32b are placed adjacently to the accumulation burner 31. These burners heat the accumulated areas 42 of the glass fine particles during the accumulation of the glass fine particles at a temperature the same as or higher than that of the accumulated area 41 which is heated by the accumulation burner 31 in terms of surface temperature.

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.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a glass fine particle deposit which is an optical fiber preform, a method described in Japanese Patent Laid-Open No. 3-83829 is known. That is,
A silicon compound such as silicon tetrachloride is oxidized and hydrolyzed in the flame from an oxyhydrogen flame burner on the outer periphery of a refractory carrier (bar-shaped starting member) such as quartz glass, carbon, and silicon carbide. By depositing as silica fine particles, and the carrier and the oxyhydrogen burner are relatively moved in parallel with each other in the axial direction of the carrier along with the deposition step, thereby forming a porous glass fine particle deposit, that is, an optical fiber preform. Therefore, by placing a heating burner adjacent to the above-mentioned oxyhydrogen flame burner and keeping the surface density of the glass particles in the glass particle deposit body constant, an attempt is made to prevent cracks in the deposit. It is a thing.

[0003]

However, the conventional technique for manufacturing an optical fiber preform has the following problems. In recent years, optical fiber preforms (deposits of glass particles) have been increased in diameter and diameter in order to improve productivity and reduce costs.
It is becoming longer, and when trying to manufacture such an optical fiber preform, heating by the burner at the end of the optical fiber preform is not sufficient, and when the optical fiber preform has a large diameter, The amount of heat around is insufficient. Even if an attempt is made to manufacture the optical fiber preform by increasing the heating power of each burner in order to solve the problem, there is still a problem that cracks occur at the end portion and the surface layer of the optical fiber preform.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method of manufacturing an optical fiber preform suitable for manufacturing a large-sized optical fiber preform. And

[0005]

That is, the present invention relates to a method for producing an optical fiber preform in which a glass raw material is ejected from a deposition burner and is sprayed and deposited on a starting member as glass particles by flame hydrolysis for deposition. A heating burner is arranged adjacent to the burner, and when glass fine particles are deposited,
It is characterized in that the surface temperature of the deposition surface of the glass particles heated by the heating burner is the same or higher than the surface temperature of the deposition surface heated by the deposition burner.

Further, according to the present invention, the surface temperature of the deposition surface heated by the heating burner is heated by the deposition burner by adjusting the supply amount of the fuel gas or the auxiliary gas supplied to the heating burner. It is characterized in that the same temperature or high temperature is applied to the deposition surface.

Further, according to the present invention, by using a heating burner having a larger diameter than that of the above-mentioned deposition burner, the surface temperature of the deposition surface heated by the heating burner is set to be higher than that of the deposition burner heated by the deposition burner. It is characterized in that the temperature is the same or high.

According to these inventions, the heating burner adjacent to the deposition burner sufficiently heats the deposition surface in advance before the deposition of the glass particles, so that the bulk density of the glass particles increases. Moreover, since the deposition surface of the glass fine particles is sufficiently hardened by the heating burner after the glass fine particles are deposited, cracks do not occur in the glass fine particle deposit body.

Further, according to the present invention, when the above-mentioned glass fine particles are deposited, the bulk density of the deposit formed by the deposition is set to 0.
It is characterized by being 6 to 1.2 g / cm ³ .

According to such an invention, since the deposited body of glass fine particles is baked and solidified, even if the deposited body has a large diameter, cracks do not occur in the deposited body. Further, bubbles are not mixed in the glass particle deposit body, and a good glass particle deposit body is formed.

Further, the present invention is characterized in that, when the above-mentioned glass fine particles are deposited, the bulk density of the deposit formed by the deposition is increased near the starting member at the initial stage of the deposition.

According to this invention, since the deposited body of the glass fine particles becomes strong in the vicinity of the starting member where cracks are likely to occur, the occurrence of cracks is prevented in advance.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same elements are denoted by the same reference numerals, and the description is omitted.

FIG. 1 is an explanatory view of the manufacturing process of the optical fiber preform. First, prior to the description of the method for manufacturing the optical fiber preform, the manufacturing apparatus 1 for the optical fiber preform will be described.
In FIG. 1, a drive mechanism (not shown) is installed in the sealed reaction container, and a rod-shaped starting member 2 attached to this drive mechanism rotates about an axis (rotates about its axis).
In addition, the structure is such that it reciprocates in the axial direction. As this drive mechanism, a known one is adopted. The starting member 2 is a member for depositing glass fine particles on the outer periphery, and, for example, a member in which a support member 22 is connected to both ends of a glass rod member 21 having a clad arranged around an axially arranged core is adopted. It

On the other hand, as shown in FIG. 1, a deposition burner 31 and heating burners 32a and 32b are disposed near the center of the starting member 2 attached to the drive mechanism, and the outer periphery of the starting member 2 is arranged. It is possible to spray flames or fine glass particles toward. That is, the deposition burner 31 has S
A glass raw material gas such as iCl _4, a fuel gas such as H ₂ and a combustion supporting gas such as O ₂ can be supplied in set amounts, respectively, and by supplying these gases, the deposition burner 31 produces a flame of a predetermined thermal power. A predetermined amount of glass particles can be ejected. The supply of each gas is
Any known means and technique may be used. Further, the heating burner 32 can be supplied with a set amount of a fuel gas such as H ₂ and a supporting gas such as O ₂ respectively, and by supplying these gases, the burners 32 and 33 generate a predetermined thermal power. A flame can be emitted.

A deposition burner 31, a heating burner 32a,
The arrangement of 32b is such that the burners 32a, 31 and 32b are arranged side by side along the reciprocating movement direction of the starting member 2 and the deposition burner 31 is arranged between the heating burners 32a and 32b. When the glass burner 31 sprays and deposits glass particles on the starting member 2 or the deposit 4, the deposition surface before the deposition is preheated by either the heating burner 32a or 32b, and the deposition surface after the deposition is performed. Is further heated by the other heating burner 32B or 32a.

In the manufacturing apparatus 1 described above, the starting member 2 reciprocates with respect to the fixed burners 31 and 32. However, the starting member 2 and the burners 31 and 3 are provided.
2 has a structure in which it reciprocates relatively along the axial direction of the starting member 2, each burner 31, 3 with respect to the starting member 2.
2 may reciprocate.

Next, a method of manufacturing the optical fiber preform will be described.

In FIG. 1, after the starting member 2 having a core and a clad is attached to a driving mechanism (not shown), the driving mechanism 2 is operated to rotate the starting member 2 axially, and
The burners 31 and 32 are reciprocated along the axial direction thereof. On the other hand, a glass raw material is ejected together with a flame from the deposition burner 31 and is sprayed and deposited as fine glass particles on the outer periphery of the starting member 2 by flame hydrolysis, and flames are emitted from the heating burners 32a and 32b arranged on both sides thereof. To be jetted to the outer periphery of the starting member 2.

At this time, the amounts of the fuel gas and the auxiliary gas supplied to the burners 31, 32a, 32b are adjusted so that the deposition member 41 or the deposition surface 41 of the deposition body 4 heated by the flame of the deposition burner 31 is heated. Burner 3 for the surface temperature T _D of
The surface temperature T _S of the deposition surface 42 heated by the flames 2a and 32b is set to the same temperature or high temperature. Their surface temperature is T
_By setting _S ≧ T _D , since the deposition surface 41 onto which the glass particles are sprayed is preheated to a high temperature by the heating burners 32a or 32b, the bulk density of the glass particles is increased, and the glass particles are increased. Will be efficiently deposited on the starting member 2 or the deposit 4. Further, after the glass particles are deposited, the deposition surface 41 of the glass particles is heated by the heating burner 32.
b or 32a, which is further heated and baked to be solidified.
It is possible to make the bulk density on the deposition surface of (6) as high as about 0.6 to 1.2 g / cm ³ . Therefore, the glass fine particles forming the deposit 4 are firmly bonded to each other, and a good deposit 4 without cracks can be obtained. Also,
Since the deposit 4 has a high bulk density, the deposit 4
A long optical fiber can be formed from the (optical fiber base material).

Here, as shown in FIG. 2, the length of the optical fiber obtained from the deposit 4 is constant when the length of the deposit 4 (axial dimension of the deposit 4) is constant. It is determined by the diameter and its bulk density, and the higher the bulk density of the deposit 4, the longer the optical fiber can be made. Therefore, the deposit 4
The average bulk density of is preferably set to 0.4~1.2g / cm ^3, and more preferably to further 0.6~1.0g / cm ^3. That is, when the bulk density is 0.4 g / cm ³ or less, the deposited body 4 (optical fiber preform) is easily cracked at the time of glass particle deposition or sinter transparentization, and even if a large deposited body 4 is formed, a fiber of a predetermined length is not formed. This is because it is difficult to obtain, and when it is 1.2 g / cm ³ or more, bubbles remain inside the deposited body 4 when the deposited body 4 is sintered and made transparent. Further, if it is set to 0.6 to 1.0 g / cm ³ , those problems can be surely avoided.

When the glass particles are sprayed onto the deposit 4 and heated, the above-mentioned heating burners 32a and 32b are used.
It is preferable to use a burner having a diameter larger than that of the deposition burner 31. By doing so, the heating burner 32
When a large flame is ejected from a and 32b and the deposition body 4 is deposited and has a large diameter, the heating area can be made large and the decrease in the surface temperature can be suppressed, which is very effective.

Although the deposit 4 is formed around the starting member 2 by spraying the glass particles, it is preferable to increase the bulk density of the deposit 4 at the initial stage of deposition. That is, cracks are likely to occur near the starting member 2, and by increasing the bulk density of the deposit 4 at the initial stage of deposition, the deposit 4 near the starting member 2 becomes solid and cracks are prevented from occurring. Will be done. The bulk density can be increased by slowing down the moving speed of the starting member 2 and increasing the heat power of the burners 31 and 32.

Then, for the surface temperature T _D of the deposition surface 41 by the deposition burner 31 of the deposition body 4, the heating burner 32
While keeping the surface temperature T _S of the deposition surface 42 due to a and 32b at the same temperature or high temperature, the reciprocating movement of the starting member 2 is repeated a predetermined number of times, and when the deposition body 4 reaches the required diameter by the deposition of the glass particles, The manufacturing of the deposit 4 is completed.

As described above, the heating burner 32 is provided adjacent to the deposition burner 31, and the temperature of the deposition surface 42 heated by the heating burner 32 is lower than the temperature of the deposition surface 41 of the temperature deposition burner 31. By setting the temperature to the same temperature or high temperature, when the glass particles are deposited, the glass particles are hardened and deposited in a state of high bulk density, and cracks are prevented from being generated in the deposit 4.

In this manufacturing method, the starting member 2 is reciprocally moved with respect to the fixed burners 31 and 32. However, the starting member 2 and the burners 31 and 32 are axially connected to the starting member 2. The respective burners 31, 32 may be reciprocated with respect to the starting member 2 by relatively reciprocating along the direction.

Next, a concrete example of manufacturing the deposit 4 by the above-described manufacturing method will be described.

In FIG. 1, the diameter is 20 mm and the length is 120.
A quartz glass rod including a 0 mm core and a clad is used as a glass rod 21, and a support member 22 is connected to both ends of the quartz glass rod to form a starting member 2 having a total length of 2500 mm, which is attached to a drive mechanism. Then, the driving mechanism is operated to axially rotate the starting member 2 at 30 rpm and reciprocate along the axial direction. The reciprocating movement is 50 mm / min in the first 5 rounds of deposition.
After that, the speed of reciprocating movement was accelerated by 10 mm / min for each reciprocation and increased to 200 mm / min to a constant speed. Thus, by slowing the reciprocating movement in the initial stage of the deposition, the bulk density of the deposit 4 in the vicinity of the starting member 2 is increased, and the deposit 4 is less likely to be cracked.

On the other hand, the deposition burner 31 having a diameter of 45 mm is used, and SiCl ₄ is used as a glass raw material in an amount of ₆ l / mi.
n, H ₂ as a fuel gas and O ₂ as a supporting gas at a rate of 60 l / min were supplied to the deposition burner 31. Then, SiCl ₄ ejected from the deposition burner 31 is flame-hydrolyzed and becomes fine particles of SiO ₂ which adhere to the outer periphery of the starting member 2 and are deposited. The heating burner 32a, 32b is used as the diameter 60mm respectively, as a fuel gas H ₂ to 12
0 l / min, O ₂ as an auxiliary gas 70 l / min
Is supplied to each of the heating burners 32a and 32b at a ratio of 10 to preheat the deposition surface 41 before the deposition of the glass particles,
Further, after the deposition, the deposition body 4 was further heated and solidified.

As shown in FIG. 3, the surface temperatures of the deposition surfaces 41 and 42 of the deposition body 4 in the deposition process of the glass particles are set to a high temperature at the initial stage of the deposition, and then the deposition surface by the deposition burner 31 is set. The surface temperature of 41 is about 850
C., the surface temperature of the deposition surface 42 by the heating burner 32 was kept constant at about 1000.degree. At that time, as the diameter of the deposit 4 increases, the amount of heat per unit area becomes insufficient and the surface temperature tends to decrease. However, the supply amount of the fuel gas (H ₂ ) and the combustion supporting gas (O ₂ ) is The surface temperature was made constant by adjusting the increase.

In this way, the deposit 4 (starting member 2)
And the relative reciprocating movement of each burner 31, 32 is repeated,
Glass particles are deposited to a diameter of 160 mm and a length of 12
A deposit 4 having a size of 00 mm and an average bulk density of 1.0 g / cm ³ was obtained. This deposited body 4 was placed in a heating furnace having a core tube, and kept under reduced pressure of 200 pa at 1100 ° C. for 2 hours,
It was heated to 1600 ° C. to make it transparent by sintering. The transparent optical fiber preform was good without bubbles. An optical fiber of about 1000 km can be obtained from this base material.

Next, another embodiment according to the present invention will be described. In the manufacturing apparatus 1 described above, a structure is provided in which a plurality of burner groups including the deposition burner 31 and the heating burners 32a and 32b are provided, and the starting member 2
The deposit 4 may be formed by heating the starting member 2 while depositing and depositing fine glass particles. For example, as shown in FIGS. 4 and 5, two sets of burner groups 3 are arranged around the starting member 2.
0 and 50 are provided, and glass particles and a flame are sprayed from the respective burner groups 30 and 50 toward the starting member 2 to form the deposit 4. The burner groups 30 and 50 are configured by arranging the deposition burners and the heating burners side by side as described above, and are directed to the starting member 2 as shown in FIG. The burner groups 30, 50 are arranged at a predetermined angle θ in the circumferential direction of the deposit 4 with the starting member 2 as the center, and the burner groups 30, 50 are arranged.
The glass particles can be sprayed onto the deposit 4 in a narrow range. Therefore, in the production of the deposited body 4, the end portion of the deposited body 4 having a tapered shape becomes small, and the effective length of the optical fiber preform (the length excluding the tapered end portion)
Can be large. The angle θ formed by the burner group 30 and the burner group 50 is preferably set to about 60 ° in order to avoid flame interference between the burner groups.

Further, as shown in FIG. 4, the deposition burner 31 of the burner group 30 and the heating burner 52a or 52b of the burner group 50 are opposed to each other, and the deposition burner 5 of the burner group 50 is opposed.
1 and the heating burners 32a or 32b of the burner group 30 are opposed to each other, and the burner groups 30 and 50 are preferably arranged so that the deposition burners 31 and 51 do not face each other. With this arrangement, the deposition surfaces 41, 61 of the deposition burners 31, 51 of the respective burner groups 30, 50 are preheated by the heating burners of the other burner group, so that the glass fine particles have a higher bulk density. Will be deposited at.

Another embodiment in which the deposit 4 is manufactured by the above manufacturing method will be described.

In FIG. 4, the diameter is 25 mm and the length is 120.
A quartz glass rod including a 0 mm core and a clad is used as a glass rod 21, and a support member 22 is connected to both ends of the quartz glass rod to form a starting member 2 having a total length of 2500 mm, as in the above-described embodiment. The starting member 2 is attached to the drive mechanism to operate the drive mechanism,
The starting member 2 is axially rotated at pm and is reciprocally moved along the axial direction. The reciprocating movement is 5 at the beginning of deposition.
In the reciprocation, 50 mm / min, and thereafter, the reciprocating speed is accelerated by 10 mm / min for each reciprocation,
The speed was increased to 200 mm / min to keep the speed constant.

On the other hand, in FIGS. 4 and 5, the burner group 30
The deposition burner 31 used in the above has a diameter of 45 mm, and SiCl ₄ is 6 l / min as a glass material, H ₂ is 100 l / min as a fuel gas, and O ₂ is 60 l / min as a combustion supporting gas. 31 was supplied. Further, the deposition burner 5 in the burner group 50
1 has a diameter of 65 mm and uses Si as a glass raw material.
Cl ₄ 10 l / min, H ₂ 150 as fuel gas
O ₂ as an auxiliary gas was supplied to the deposition burner 31 at a rate of 90 l / min. Then, SiCl ₄ ejected from each of the deposition burners 31 and 51.
Is flame-hydrolyzed and becomes SiO2 glass fine particles which adhere to and accumulate on the outer periphery of the starting member 2.

The heating burners 32a and 32b in the burner group 30 each have a diameter of 60 mm, and H ₂ is 120 l / min as a fuel gas and O ₂ is 70 l / min as a combustion supporting gas for heating. Burner 3
It was supplied to each of 2a and 32b. Also, burner group 5
As the heating burners 52a and 52b in No. 0, those having a diameter of 80 mm were used, and H ₂ was 120 l / min as the fuel gas and O ₂ was 70 l / m as the combustion supporting gas.
It was supplied to each in the ratio of in. By these heating burners 32 and 52, the deposition surface 4 before the deposition of the glass particles is performed.
1, 1 and 61 are preliminarily warmed, and the deposition body 4 is baked and solidified by further heating after the deposition.

In the manufacturing process of such a stack 4,
While adjusting the supply amount of each gas, the surface temperature of the deposition surface 42 by the heating burner 32 is kept equal to or higher than the surface temperature of the deposition surface 41 by the deposition burner 31. The surface temperature of the deposition surface 62 formed by the heating burner 52 was maintained at the same temperature or higher than the surface temperature of the deposition surface 61 formed by the burner 51. When the diameter of the deposited body 4 reaches 150 mm, the supply amount of each gas to the deposition burner 31 and the heating burners 32a and 32b of the burner group 30 is made constant, and the deposition burner 51 of the burner group 50 is supplied. Burner group 5 with each gas supply constant
No. 0 heating burners 52a and 52b are supplied with increasing amounts of each gas so that the surface temperature of the deposition surface 62 of the heating burners 52a and 52b is 900 to 1000 ° C., and the surface of the deposition surface 61 of the deposition burner 51 is Temperature is 800-900
° C.

In this way, the deposit 4 (starting member 2)
By repeating relative reciprocating movement between the burner groups 30 and 50 and depositing glass particles, a deposit 4 having a diameter of 220 mm, a length of 1200 mm and an average bulk density of 0.85 g / cm ³ was obtained. This deposit 4 was a good one without any cracks. When this deposited body 4 was heated in the heating furnace in the same manner as described above to be sintered and made transparent, a transparent glass base material having no bubbles was obtained. It is possible to obtain an optical fiber of about 1500 km from this base material.

Next, a comparative example for comparison with the manufacturing method in each of the above-described embodiments will be described.

In the manufacturing apparatus 1 shown in FIG. 1, similarly to the above, the starting member 2 is axially rotated and reciprocally moved to eject the glass particles together with the flame from the deposition burner 31 and the flame from the heating burner 32. While ejecting, glass particles are deposited and deposited on the outer periphery of the starting member 2,
The deposit 4 is formed. At that time, as shown in FIG.
As the deposition of glass particles on the deposit 4 progresses, the supply amount of each gas is adjusted so that the deposition burner 32 heats the deposition burner 32 against the surface temperature of the deposition burner 31.
The deposit 4 was manufactured so that the surface temperature of 2 was lowered.

Then, the glass particulate deposit 4 has a diameter of 1
Around 35 mm, a crack was generated starting from the end of the deposit 4.

[0043]

As described above, according to the present invention, the following effects can be obtained. That is, since the deposition surface is sufficiently warmed in advance before the deposition of the glass particles by the heating burner adjacent to the deposition burner, the efficiency of the glass particle adhesion can be improved. In addition, since the deposition surface is sufficiently baked and solidified by the heating burner even after deposition, the bulk density becomes high, and it is used as an optical fiber preform (deposit of glass fine particles) at the time of manufacturing or at the time of sintering and transparency after manufacturing. No cracks will occur.

When the glass particles are deposited, the bulk density of the deposit formed by the deposition is 0.6 to 1.2 g /
If it is cm ³ , the deposited body of fine glass particles is sufficiently hardened, and even if the deposited body has a large diameter, cracks do not occur in the deposited body and bubbles are mixed into the deposited body. Nothing. Therefore, a good optical fiber preform can be obtained, which is particularly effective for forming a large-sized optical fiber preform.

Further, when the glass fine particles are deposited, if the bulk density of the deposit is increased in the vicinity of the starting member at the initial stage of deposition, the deposit of glass particles becomes strong in the vicinity of the starting member where cracks are likely to occur. Therefore, it is possible to prevent the occurrence of cracks.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a manufacturing process of an optical fiber preform.

FIG. 2 is a chart showing a diameter of a deposited body (optical fiber preform) and an optical fiber formation length obtained from the deposited body.

FIG. 3 is a table showing the surface temperature of the deposit during the production of the deposit.

FIG. 4 is an explanatory diagram of a manufacturing process of an optical fiber preform.

FIG. 5 is an explanatory diagram of a manufacturing process of an optical fiber preform.

FIG. 6 is a chart showing the surface temperature of the deposit during the production of the deposit according to the comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber preform manufacturing apparatus, 2 ... Starting member, 31 ... Deposition burner, 32a, 32b ... Heating burner, 4 ... Deposition body (optical fiber preform),

Claims (5)

[Claims] 1. A method for producing an optical fiber preform in which a glass raw material is ejected from a deposition burner, and is made into glass particles by flame hydrolysis and is sprayed and deposited on a starting member, wherein heating is performed adjacent to the deposition burner. And a surface temperature on the deposition surface of the glass particles heated by the heating burner is the same as the surface temperature of the deposition surface heated by the deposition burner. Alternatively, the method for producing an optical fiber preform is characterized in that the temperature is high. 2. The deposition temperature of the deposition surface heated by the heating burner is adjusted by adjusting the supply amount of the fuel gas or the supporting gas supplied to the heating burner. The method for producing an optical fiber preform according to claim 1, wherein the temperature is the same as or higher than that of the surface. 3. By using a heating burner having a larger diameter than that of the deposition burner, the surface temperature of the deposition surface heated by the heating burner is the same as that of the deposition surface heated by the deposition burner. Alternatively, the temperature is set to a high temperature, and the method for manufacturing an optical fiber preform according to claim 1. 4. When depositing the glass fine particles, the bulk density of the deposit formed by the deposition is 0.6 to 1.2 g /
The method for producing an optical fiber preform according to claim 1, wherein the optical fiber preform has a size of cm ³ . 5. When depositing the glass fine particles, the bulk density of a deposit formed by the deposit is increased in the vicinity of the starting member at the initial stage of deposition. The method for producing an optical fiber preform according to 1.