JP3148196B2 - Method and apparatus for producing porous preform for optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for producing a porous preform for optical fibers. In particular, the present invention provides a light source in which a core and a clad can be uniformly deposited by a VAD (axis setting) method, and as a result, the cross-sectional shape is substantially circular and stable without deviation over the entire longitudinal direction of the porous base material. The present invention relates to a method and an apparatus for manufacturing a porous preform for an optical fiber, which can produce a porous preform for a fiber, and thus can provide a preform for an optical fiber having stable optical characteristics over the entire region in the longitudinal direction.

[0002]

2. Description of the Related Art In the production of a porous preform for an optical fiber by the VAD method, an O ₂ gas, an H ₂ gas, an inert gas, and a glass raw material gas (a core material burner) are respectively provided to a core burner and a clad burner. Includes SiCl ₄ and GeC
material gas l _4, etc., SiCl ₄ in the cladding burner
And the like, and the glass material gas is hydrolyzed in an oxyhydrogen flame of each burner to produce SiO ₂ , GeO ₂
And the like. Then, the generated glass fine particles are deposited and deposited on the tip of the rotating rod-shaped member,
Manufactures a porous preform for an optical fiber having a core-clad structure. Thereafter, the porous preform is dehydrated and melted and vitrified to obtain a transparent optical fiber preform. And
An optical fiber is obtained by melt-drawing and spinning the optical fiber base material.

In such a VAD method, in order to stabilize the optical characteristics (for example, refractive index distribution, etc.) of a preform for an optical fiber in the longitudinal direction (axial direction), the tip portion of a porous preform being formed. It is required that the porous base material be manufactured while maintaining a constant spatial positional relationship between the deposition surface and the burner flame. This is because this spatial positional relationship affects the surface temperature distribution at the tip of the porous preform and the chemical reaction state near the deposition surface, and therefore, maintaining the spatial positional relationship constant is the refraction of the optical fiber preform. This is because it is a very important factor for stabilizing the rate distribution.

[0004] In the production by the VAD method,
Since the rod-shaped member and the porous preform for optical fiber deposited and grown on the tip end are rotating, vibration due to rotation, that is, torsional vibration, flexural vibration and whirling caused by eccentricity of the shaft and deviation of the center of gravity. Vibration, and vibration caused by the bearing, occur. In a normal case, since the spatial positional relationship changes randomly, these vibrations hardly affect the formation of the refractive index distribution of the optical fiber base material.

However, when an integer multiple or a fraction of the natural frequency of the vibration is very close to the fluctuation frequency of the rotational load or the rotational output, a resonance state occurs. When this resonance state is reached, the spatial positional relationship between the deposition surface of the porous base material tip and the burner flame changes periodically, and the deposition state selectively changes in the circumferential direction of the porous base material tip. As a result, uniform deposition becomes difficult. As a result, the cross-sectional shape of the tip portion of the porous base material becomes non-circular. This non-circular state continues until the resonance stops, and the refractive index distribution of the optical fiber preform manufactured during that time becomes abnormal, and the quality deteriorates.

In order to prevent such a resonance state, generally, the number of revolutions (rotation cycle) and the integral frequency of the natural frequency of the rotating shaft do not coincide with each other. However, in the VAD method, the natural frequency of the rotating shaft changes along with the deposition and growth of the porous preform for an optical fiber, so that it is difficult to solve this general method. Therefore, in the related art, in the case of the resonance state, the optical fiber preform grows, the natural frequency changes, and it has to be left until the resonance state is released. However, the refractive index distribution of the optical fiber preform at the portion manufactured in this resonance state has changed, and the quality of this portion remains problematic. Further, when the resonance state is severe, it may not be possible to continue manufacturing.

For this reason, in the VAD method, the mechanical accuracy of a porous base material pulling device or the like has been improved so as not to cause resonance, the eccentricity and the displacement of the center of gravity during rotation have been eliminated, and the rotational load and the like have been reduced. Attempts have been made to eliminate the fluctuations in the rotational output itself, but this involves relentless effort. Also, even if the porous base material pulling device is adjusted with high precision, the effect of increasing the weight of the porous base material or the temperature on the mechanical accuracy is large, and it is extremely difficult to design in consideration of this. Because of the difficulty, there is a limit in the method based on the improvement of machine precision.

As another solution, a method has been proposed in which the rotational speed is changed only when the resonance state is reached to escape from the vibration state. However, with the recent increase in the size of the porous preform for optical fibers and the length of the rod-shaped member, the range of change in the natural frequency of the rotating shaft is widened and the number of times of resonance increases. Since the change in the natural frequency of the material varies depending on the deposition rate and shape, and the factors of the vibration are not constant, it is difficult to completely prevent the resonance state by this method.

In Japanese Patent Application Laid-Open No. Hei 6-247737,
If severe vibration occurs due to resonance, detecting this will change the rotation speed to converge the vibration, and if it returns to the original rotation speed after deviating from the resonance, manufacturing may fail halfway. It is reported that the vibration state can be minimized without any vibration.

[0010] However, in the case of the above-mentioned method in which the vibration is converged and the production of the porous preform is continued, even if the state in which the production is impossible can be avoided, the obtained porous preform for the optical fiber is converted into the optical fiber preform. When a material is used, a change in the refractive index distribution occurs at a portion where resonance occurs even in a short time and violent vibration occurs. Therefore, the porous base material having such a portion has a problem that the deterioration of quality is inevitable.

Therefore, it is conceivable to avoid the resonance state by predicting a portion that will be in a resonance state in advance and changing the rotation speed in advance. However, as described above, there are cases where all resonance states cannot be avoided because the resonance site is not constant. Furthermore, the influence of the change in the rotation speed itself on the refractive index distribution of the optical fiber preform cannot be neglected, and a method that does not require changing manufacturing conditions such as the rotation speed in the middle is desired. I was

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to uniformly deposit glass fine particles on a porous preform regardless of the occurrence of resonance during the production of the porous preform for optical fibers. It is an object of the present invention to provide a method and an apparatus for manufacturing a porous preform for an optical fiber which can be used as a preform for an optical fiber in which the change in the longitudinal (axial) direction of the refractive index distribution can be minimized. And

[0013]

The inventor of the present invention has conducted intensive studies to achieve the above object, and as a result, has found that the static deflection δ
It is found that if is set to a specific value or less, it is possible to substantially uniformly deposit glass fine particles, and therefore, it is possible to produce a porous base material having a substantially circular cross section over the entire region in the longitudinal direction. Was completed.

That is, the invention described in claim 1 of the present invention provides:
At least a glass raw material gas, a combustible gas, and a combustible gas are supplied to each of the core burner and the clad burner, and the glass raw material is hydrolyzed in the oxyhydrogen flame of the burner to generate glass fine particles. In the method of manufacturing a porous preform for an optical fiber having a core-cladding structure by continuously depositing the obtained glass fine particles from the tip of a rotating rod-shaped member in the axial direction thereof, the amount of static deflection δ of the rod-shaped member is expressed by a / This is a method for producing a porous preform for an optical fiber of 15 or less (where a represents the outer diameter of the deposition surface at the tip of the porous preform for an optical fiber being formed).

As described above, the static deflection amount δ of the rod-shaped member is expressed by a
By setting the ratio to / 15 or less, the amplitude of the rod-shaped member can be reduced even in the case of resonance, so that the periodic change in the spatial positional relationship between the deposition surface and each deposition burner is suppressed, and Can be produced uniformly.

Further, according to the present invention, at least one of a second moment of area I of the rod-shaped member, a load W applied to the rod-shaped member, a length L of the rod-shaped member, and a longitudinal elastic modulus E of the rod-shaped member is provided. Is adjusted to make the amount of static deflection δ of the rod-shaped member a / 15 or less. Thus, the second moment of area I, the load W, the length L, or the modulus of longitudinal elasticity E of the rod-shaped member is obtained.
By adjusting the amount of static deflection δ of the rod-shaped member to a
/ 15 or less. As a result, even in the resonance state, the amplitude of the rod-shaped member can be reduced, so that the glass particles can be uniformly deposited.

Further, according to a third aspect of the present invention, at least a part of the rod-like member is made hollow and / or at least a part of the rod-like member is made of ceramic, so that the amount of static deflection δ of the rod-like member is reduced by a. / 15 or less. As described above, by increasing the second moment of area by hollowing out at least a part of the rod-shaped member, or by reducing the weight of the rod-shaped member by using a ceramic material, the amount of static deflection δ of the rod-shaped member can be reduced by a / It can be 15 or less.

According to a fourth aspect of the present invention, there is provided an optical fiber having at least a rod-shaped member attached to a rotating mechanism and a core burner and a clad burner capable of depositing glass fine particles at the tip of the rod-shaped member. In the manufacturing apparatus of the porous base material, the rod-shaped member is always a / 1 during the operation.
5 (where a represents the outer diameter of the deposition surface at the tip of the porous preform for optical fiber being formed). This is an apparatus for producing a porous preform for optical fiber having a static deflection δ of not more than 5.

As described above, the amplitude of the rod-shaped member can be reduced even when the rod-shaped member is in a resonance state during operation because the static deflection δ of the rod-shaped member is always less than a / 15 during operation. This makes it possible to reduce the change in the spatial positional relationship between the base material deposition surface and the burner.
Therefore, with a manufacturing apparatus using such a rod-shaped member,
It is possible to manufacture a porous base material in which glass fine particles are uniformly deposited over the entire region in the longitudinal direction.

According to a fifth aspect of the present invention, the rod-shaped member is adjusted by adjusting at least one of the second moment of area I, the load W, the length L of the rod-shaped member, or the modulus of longitudinal elasticity E of the rod-shaped member. Is an apparatus for producing the optical fiber porous preform having a static deflection δ of a / 15 or less.

As described above, if the amount of static deflection δ of the rod-shaped member is always a / 15 or less during the operation, it is possible to manufacture a porous base material in which glass fine particles are uniformly deposited over the entire region in the longitudinal direction. . A device having such a static deflection amount δ can be specifically configured by adjusting the second moment of area I, the load W, the length L, the modulus of longitudinal elasticity E, and the like of the rod-shaped member.

Further, in the invention according to claim 6, at least a part of the rod-shaped member is made hollow and / or at least a part thereof is made of ceramic, so that the rod-shaped member is a / 1.
An apparatus for producing a porous preform for an optical fiber having a static deflection δ of 5 or less.

As described above, at least a part of the rod-shaped member is hollowed to increase the second moment of area, or a part of the rod-shaped member is made of ceramic to reduce the weight, so that the rod-shaped member can be constantly operated during operation. It is possible to configure an apparatus capable of maintaining the deflection amount δ at a / 15 or less. By using a manufacturing apparatus using such a rod-like member, the amplitude of the rod-like member can be reduced even during the operation, even if a resonance state occurs, and therefore, glass fine particles are uniformly deposited over the entire area in the longitudinal direction. A porous base material can be manufactured.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments. Here, FIG. 1 is a schematic configuration diagram of an apparatus for manufacturing a porous preform for an optical fiber by the VAD method. In the method for producing a porous preform for an optical fiber of the present invention, a VAD method or the like can be particularly preferably used. Specifically, at least a glass raw material gas, a combustible gas, and a combustible gas are supplied to each of the core burner and the clad burner,
A porous base material is obtained by forming a core and a clad, respectively.
The burner is, for example, a quartz burner.

Examples of the glass raw material gas include silicon halide compounds such as SiCl ₄ . Incidentally, a dopant may be included in order to impart a desired refractive index or the like to the optical fiber preform. As the dopant, for example, GeCl ₄
And the like. Further, the glass raw material gas may be supplied together with the carrier gas. Examples of the carrier gas include an inert gas such as Ar and N ₂ . Examples of the combustible gas and the combustible gas include H ₂ gas and O ₂ gas, respectively.

As the gas flow rate, for example, the raw material gas 200
３００300 cc / min, flammable gas 1-10 cc / min, and combustible gas 5-15 cc / min. Glass particles are generated by hydrolyzing the glass raw material in the oxyhydrogen flame of each burner. That is, an oxyhydrogen flame is formed by the combustible gas and the auxiliary gas, and a glass raw material such as silicon halide is hydrolyzed by introducing a glass raw material gas into the flame, and silicon oxide (ie, glass fine particles)
Generate

The generated glass particles are continuously deposited in the axial direction from the tip of the rotating rod-shaped member. Specifically, first, generated glass fine particles are sprayed from the core burner and the clad burner onto the tip of the rotating rod-shaped member. At this time, the directions and positions of the core burner and the clad burner are adjusted so that the clad is formed on the periphery of the core. Then, while continuously rotating the rod-shaped member, the rod-shaped member is pulled up in the axial direction, and glass particles are continuously sprayed on a new deposition surface to form a porous base material in the axial direction. The rotation speed of the rod-shaped member is, for example, 10 to 50 rpm. The pulling speed of the rod-shaped member is, for example, 0.5 to 1.5 mm / min.

In the manufacturing method of the present invention, during the deposition of the glass fine particles, the static deflection amount δ of the rod-shaped member is set to a /
15 or less. Thus, by suppressing the amount of static deflection δ of the rod-shaped member, the amplitude of the rod-shaped member can be reduced even in a resonance state, and the spatial positional relationship between the deposition surface of the porous base material and the burner can be reduced. The change can be reduced. As a result, the glass fine particles can be uniformly deposited, and a porous base material of stable quality having a substantially circular cross section and no deviation can be manufactured over the entire region in the longitudinal direction. The above a is the outer diameter of the deposition surface at the tip of the porous base material. In the VAD method, it is the same as the core diameter, for example. Specifically, a is 30 to 60 mm.

Hereinafter, the amount of static deflection δ of the rod-like member during the operation is always
Is set to a / 15 or less. The amount of static deflection δ of the rod-shaped member varies depending on the shape, structure, material, and the like of the rod-shaped member, but is also variously affected by the gripping state and the load state of the rod-shaped member. For example, as shown in FIG.
In the VAD method, the rod-shaped member 2 has an upper end portion gripped and a lower end portion is a free end, and glass fine particles are adhered and deposited on the end portion to produce the porous preform 1 for an optical fiber. In such a case, since the static deflection amount δ of the rod-shaped member 2 can be applied to “one-end support, concentrated load”, δ =
WL ³ / (3EI) [where W is the load applied to the rod-shaped member (that is, the weight of the porous preform for optical fiber at that time), L
Is the length of the bar, E is the longitudinal modulus of the bar, and I
Represents the second moment of area of the rod-shaped member. ].

Therefore, as a method for suppressing the static deflection amount δ of the rod-shaped member, for example, the length L of the rod-shaped member is shortened,
The rod-shaped member may be made of a material having a large modulus of longitudinal elasticity E. Incidentally, the load W is the weight of the porous preform for optical fiber to be manufactured, and there is a limit in reducing this from the viewpoint of productivity. The length L is, for example, 1 to 5 m. Examples of the material having a large longitudinal elastic modulus E include stainless steel and ceramic.

As described above, the length L and the longitudinal elastic modulus E may be adjusted. However, considering that the static deflection δ can be effectively reduced and the implementation is easy, the cross-sectional secondary It is preferable to increase the moment I. When the rod-shaped member is a solid cylinder, I = πd ⁴
/ 64 (where d is the diameter of the rod-shaped member). Therefore, a large second moment of area can be obtained if the cross-sectional shape has a large diameter. In addition, in the case of the same weight, there is an effect that the second moment of area I can be made larger in the hollow than in the solid cylinder regardless of the material. Accordingly, a cross-sectional shape having a large second moment of area I includes a hollow shape having a large diameter. Specifically, a circular tube (hollow cylinder) is preferable as the hollow rod-shaped member because it is easily available.

The amount of static deflection δ of the porous preform is proportional to the load W (that is, the weight of the porous preform being formed) according to the above equation. That is, during the production of the porous base material, the static deflection amount δ continues to increase. Therefore, when adjusting the static deflection δ by the above various factors, in consideration of this in advance, the static deflection δ of the rod-shaped member is adjusted so that the static deflection δ does not exceed a / 15 at the end of the operation. Need to be kept.

Further, the weight of the rod-shaped member must be taken into consideration. That is, since there is a limit in the manufacturing accuracy of the rod-shaped member and the mounting accuracy to the rotating mechanism, the rod-shaped member is generally eccentric and the center of gravity is shifted. When the rod-shaped member is rotated in such a state, the deflection amount further increases due to the weight of the rod-shaped member or the like. Therefore, it is preferable that the rod-shaped member used is made of a lightweight material. Such materials include
Examples include stainless steel and ceramic.

As described above, for example, at least a part of the rod-shaped member is hollowed to have a large second moment of area, and / or the weight of the rod-shaped member is reduced by using ceramic or the like for at least part of the rod-shaped member. Static deflection δ
And the amplitude of the rod-shaped member can be effectively suppressed. As a result, a change in the spatial positional relationship between the deposition surface of the porous base material and the burner can be reduced, and a high-quality porous base material having glass fine particles uniformly deposited thereon can be manufactured.

As described above, the static deflection amount δ of the rod-shaped member is set to a / 15
Although the following method has been specifically described, in the present invention, any other method may be used as long as the static deflection amount δ of the rod-shaped member can be set to a / 15 or less. According to the production method of the present invention, it is possible to produce a porous preform for an optical fiber having a substantially circular cross section, in which glass particles are uniformly deposited without bias.

Further, in order to produce a preform for an optical fiber, the porous preform produced by the production method of the present invention may be melted and vitrified according to a conventional method. Molten vitrification is, for example, 1
This is performed by heating to 500 ° C. or higher. At that time, if necessary, the glass may be melted and vitrified in an atmosphere of a halogen compound such as chlorine gas to simultaneously perform dehydration.

Further, in order to manufacture an optical fiber, an ordinary method may be used. For example, the optical fiber preform obtained as described above is heated and melted at 2100 ° C. or more in an electric furnace or the like.
It may be performed by drawing and spinning to a desired diameter. By using the porous preform manufactured by the manufacturing method of the present invention, it is possible to obtain an optical fiber having stable optical characteristics such as a refractive index distribution over the entire region in the longitudinal direction.

The apparatus for manufacturing a porous preform for an optical fiber according to the present invention has at least a rotating mechanism, a rod-shaped member, a core burner, and a clad burner. The rotation mechanism is for rotating a rod-shaped member, and is, for example, a rotation motor. Further, it is preferable that the rotating mechanism can lift the rod-shaped member in the axial direction. By pulling up the rod-shaped member in the axial direction as the glass fine particles are deposited, the glass fine particles can be continuously sprayed onto the tip end of the deposition surface without changing the position and the direction of the burner.

The manufacturing apparatus according to the present invention is characterized in that the bar-shaped member attached to the rotating mechanism always has a static deflection δ of not more than a / 15 during operation. Thereby, even when the resonance state occurs during the formation of the porous base material, the amplitude of the rod-shaped member can be reduced. Therefore, there is almost no change in the spatial positional relationship between the deposition surface and each deposition burner,
Therefore, a porous preform for an optical fiber in which glass fine particles are uniformly deposited can be manufactured. As a result, a preform for an optical fiber having a stable refractive index distribution can be manufactured from such a porous preform.

As described above in connection with the manufacturing method of the present invention, the rod-shaped member having a static deflection δ of not more than a / 15 includes the second moment of area I, load W, length L, longitudinal elasticity of the rod-shaped member. A rod-shaped member in which the amount of static deflection δ is adjusted to a / 15 or less by various factors such as the coefficient E and its own weight.

Specifically, as such a rod-shaped member,
As described in the production method of the present invention, for example, at least a part of the rod-shaped member is hollow to have a large second moment of area, and / or the rod-shaped member is lightened by using ceramic or the like for at least a part of the rod-shaped member. Is mentioned.

As described above, when adjusting the amount of static deflection δ by the above-described various factors, it is necessary to pay attention to the fact that the amount of static deflection δ also keeps increasing because the load W always increases during operation. That is, the amount of static deflection δ at the end of the operation is a / 15
It is necessary to adjust the static deflection amount δ so as not to exceed. By adjusting the amount of static deflection δ in this way, it is possible to configure a device in which the rod-shaped member always has a static deflection δ of a / 15 or less during operation. As a result,
The deflection of the rod-shaped member can be reduced, and the glass fine particles can be uniformly deposited. Therefore, it is possible to manufacture a high-quality porous preform for optical fibers in which glass fine particles are uniformly deposited over the entire length and the cross section is substantially circular and stable. It is preferable to attach a target member made of quartz or the like to the tip of the rod-shaped member in order to facilitate attachment of glass fine particles and to separate the manufactured porous base material from the rod-shaped member.

In the manufacturing apparatus of the present invention, the core burner is arranged at the tip of the rod-shaped member so as to be oriented so that glass particles are deposited. Then, the burners for cladding are arranged so as to be oriented so that glass particles are deposited on the periphery of the core formed by the burner for core. Thereby, a porous preform having a core-clad structure is manufactured. The core burner and the clad burner are made of, for example, quartz. In addition, the manufacturing apparatus of the present invention can include various apparatuses usually used in the VAD method and the like, for example, an exhaust unit, a gas rectifying plate, and the like. With the apparatus for manufacturing a porous preform for optical fibers of the present invention, it is possible to produce a porous preform for optical fibers having a substantially circular cross-section on which glass fine particles are uniformly and uniformly deposited.

[0044]

The present invention will be specifically described below with reference to examples. (Example 1) A porous preform 1 was produced by using an apparatus for producing a porous preform for optical fibers by the VAD method shown in FIG. That is, the rod-shaped member 2 was attached to a rotary motor (not shown) capable of moving up and down. As the rod member 2, a stainless steel hollow cylinder (length L = 400 cm, inner diameter 7 cm, outer diameter 11c)
m, the longitudinal elastic modulus E = 1.96 × 10 ⁶ kg / cm ² ). The target member 3 made of quartz was attached to the tip of the rod-shaped member 2.

Accordingly, the amount of static deflection δ of the rod-like member is expressed as follows by the following formula. That is, the length L
= 400, Young's modulus E = 1.96 × 10 ^6, and the second moment ^{_{I = π (d 2 4 -d}} 1 4) / 64 = π (11
^From 4−7 ⁴ ) /64=600.8, the static deflection amount δ = W
L ³ / (3EI) = W × 400 ³ /(3×1.96×1
0 ⁶ × 600.8) = become 0.018W (cm).

On the other hand, the core burner 4 made of quartz was oriented so as to deposit glass fine particles on the tip of the rod-shaped member 2. In addition, the quartz clad burner 5 was arranged so as to be oriented such that glass particles were deposited around the core formed by the burner 4.

The rod-shaped member 2 is rotated about 30 rpm by the rotation motor.
m, and while pulling up at a speed of about 0.9 mm / min, a core and a clad are deposited from the burners 4 and 5, respectively.
Was manufactured. The burner 4 has a glass source gas of SiCl ₄ at 250 cc / min and GeCl ₄ at 35 c / min.
c / min, H ₂ was supplied at a flow rate of 5 L / min as a combustible gas, O ₂ was supplied at a flow rate of 12 L / min as an auxiliary gas, and Ar was supplied at a flow rate of 3 L / min as an inert gas. Also burner 5
Are 3 L / min of SiCl ₄ as a glass raw material gas, 50 L / min of H ₂ as a flammable gas, and O as a combustible gas.
₂ at 30 L / min, and 15 L /
Min flow rate.

The deflection of the rod-shaped member 2 during the production of the porous preform was extremely small, and the deflection at the tip of the porous preform was also small. Even in the case of the resonance state, the swing was extremely small similarly. As described above, a porous preform 1 for an optical fiber having a weight W of 8.3 kg and a tip outer diameter a of 4.5 cm was produced. The porous base material 1 had glass particles deposited uniformly over its entire length and had a substantially circular cross section. Therefore, the maximum static deflection amount δ of the porous preform 1 is 0.0
18W = 0.018 x 8.3 = 0.1494 (cm). On the other hand, a / 15 = 4.5 / 15 = 0.3.
Therefore, the static deflection δ <a / 15 is satisfied.

As is clear from the above results, by setting the static deflection δ of the rod-shaped member to a / 15 or less at all times during the operation, the amplitude of the rod-shaped member can be maintained even when a resonance occurs during the formation of the porous base material. Can be reduced. Therefore, a change in the spatial positional relationship between the deposition surface and each deposition burner can be almost eliminated, and glass fine particles can be deposited uniformly. As a result, it is possible to manufacture a stable high-quality porous preform for an optical fiber having a substantially circular cross section in which glass fine particles are uniformly deposited over the entire length in the longitudinal direction.

Example 2 A solid stainless steel cylinder (length L = 200 cm, outer diameter 5 cm, modulus of longitudinal elasticity E = 1.96 × 10 ⁶ kg / cm ² ) was used as the rod-shaped member 2, Porous optical fiber preform 1 in the same manner as in Example 1.
Was manufactured.

Therefore, the amount of static deflection δ of the rod 2 is
It is expressed as follows by the following formula. That is, the length L = 200, a longitudinal elastic modulus E = 1.96 × 10 ^6, and the second moment ^{I = πd 4/64 = π} × 5 4/64 =
From 30.68, the static deflection amount δ = WL ³ / (3EI) =
W × 200 ³ /(3×1.96×10 ⁶ × 30.68)
= 0.044 W (cm).

The deflection of the rod-shaped member 2 during the production of the porous base material was extremely small, and the deflection at the tip of the porous base material was also small. Even in the case of the resonance state, the swing was extremely small similarly. As described above, a porous preform 1 for an optical fiber having a weight W = 4.5 kg and a tip outer diameter a = 3 cm was manufactured. The porous base material 1 had glass particles deposited uniformly over its entire length and had a substantially circular cross section. Therefore, the maximum static deflection amount δ of the porous base material 1 is 0.04.
4W = 0.044 × 4.5 = 0.198 (cm). On the other hand, a / 15 = 3/15 = 0.2. Therefore, the static deflection δ <a / 15 is satisfied.

As is apparent from the above results, by setting the static deflection δ of the rod-shaped member to a / 15 or less during the operation, the amplitude of the rod-shaped member can be maintained even when a resonance occurs during the formation of the porous base material. Can be reduced. Therefore, a change in the spatial positional relationship between the deposition surface and each deposition burner can be almost eliminated, and glass fine particles can be deposited uniformly. As a result, it is possible to manufacture a stable high-quality porous preform for an optical fiber having a substantially circular cross section in which glass fine particles are uniformly deposited over the entire length in the longitudinal direction.

Comparative Example 1 Except that a solid cylinder made of stainless steel (length L = 250 cm, outer diameter 4.8 cm, modulus of longitudinal elasticity E = 1.96 × 10 ⁶ kg / cm ² ) was used as the rod-shaped member 2. Tried to produce several optical fiber preforms 1 in the same manner as in Example 1.

Therefore, the amount of static deflection δ of the rod-shaped member 2 is
It is expressed as follows by the following formula. That is, the length L = 250, a longitudinal elastic modulus E = 1.96 × 10 ^6, and the second moment I = πd ⁴ /64=π×4.8 ^4/6
4 = 26.06, the static deflection amount δ = WL ³ / (3E
I) = W × 250 ³ /(3×1.96×10 ⁶ × 26.
06) = 0.102 W (cm).

The deflection of the rod-shaped member during the production of the porous preform was large, and the deflection at the tip of the porous preform was also large. In particular, the swing in the case of the resonance was extremely large. For this reason, under these conditions, half of the porous preform 1 was excessively vibrated in the resonance state, and could not be manufactured.

On the other hand, even if the production could be continued, the shape of the tip of the porous preform 1 in the resonance state was not uniform in the circumferential direction. When the resonance state subsided, the shape of the base metal tip became uniform and recovered. However, during the manufacture of the base metal, a resonance state occurred several times, and each time the base metal tip became non-uniform. When the quality of the porous base material was examined, the quality was deteriorated at the portion where resonance occurred, and the porous base material itself was defective.

The obtained porous base material 1 has a weight W =
It was 5.8 kg and the tip outer diameter a = 3.5 cm. Therefore, the maximum static deflection amount δ of the porous preform 1 is 0.1
02W = 0.102 × 5.8 = 0.5916 (cm). On the other hand, a / 15 = 3.5 / 15 = about 0.23. Therefore, the static deflection amount δ> a / 15.

As is apparent from the above results, when the static deflection δ of the rod-shaped member exceeds a / 15 during the operation, the deflection of the rod-shaped member and the porous base material in the resonance state becomes extremely large, and therefore, The periodic change in the spatial positional relationship between the metal and the deposition burner becomes extremely large. As a result, a defective optical fiber porous preform having an unstable quality in which the production becomes impossible or the glass fine particles are unevenly deposited is produced. As a result, an optical fiber preform having unstable optical characteristics is produced.

Although the present invention has been described in detail, the present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

[0061]

According to the present invention, the amount of static deflection δ of the rod-shaped member is
Is set to a / 15 or less, the amplitude of the rod-shaped member can be reduced even when a resonance state occurs during manufacturing. Therefore, the amount of change in the spatial positional relationship between the glass particle deposition surface and each deposition burner can be reduced,
Glass particles can be uniformly deposited. As a result, it is possible to manufacture an excellent porous preform for an optical fiber having a stable quality with a substantially circular cross section in the longitudinal direction. By using such a porous preform for optical fibers, a preform for optical fibers having excellent optical characteristics such as a refractive index distribution can be manufactured in a longitudinal direction.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an apparatus for manufacturing a porous preform for an optical fiber by a VAD method.

[Explanation of symbols]

1: porous base material for optical fiber, 2: rod-shaped member, 3:
Target member, 4: core burner, 5: clad burner, a: outer diameter (core diameter) of the deposition surface at the tip of the porous base material.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Fumio Saito 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Gunma Plant (72) Inventor Dai Inoue 2--13 Isobe, Annaka-shi, Gunma No. 1 Shin-Etsu Chemical Industry Co., Ltd.Precision Functional Materials Laboratory (72) Inventor Hideo Hirasawa 2-13-1, Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Chemical Co., Ltd.Precision Functional Materials Research Laboratory (56) References Special JP-A-7-215725 (JP, A) JP-A-7-187699 (JP, A) JP-A-7-109142 (JP, A) JP-A-6-345476 (JP, A) (58) Int.Cl. ⁷ , DB name) C03B 37/018

Claims (6)

(57) [Claims] A burner gas for a core, a burner gas for a clad, and a burner gas for a clad.
And supplying a combustion-supporting gas, and hydrolyzing the glass raw material in an oxyhydrogen flame of a burner to generate glass fine particles, and continuously generate the generated glass fine particles from the tip of a rotating rod-shaped member in the axial direction thereof. In the method for producing a porous preform for an optical fiber having a core-cladding structure by depositing, the static deflection amount δ of the rod-shaped member is set to a / 15 (where a is the tip of the porous preform for the optical fiber being formed. A method for producing a porous preform for an optical fiber, characterized in that: 2. Adjusting at least one of the second moment of area I of the rod-shaped member, the load W applied to the rod-shaped member, the length L of the rod-shaped member, or the longitudinal elastic modulus E of the rod-shaped member, The method for producing a porous preform for an optical fiber according to claim 1, wherein the static deflection amount δ is set to a / 15 or less. 3. At least a part of the rod-shaped member is made hollow,
And / or by making at least part of the rod-shaped member made of ceramic, the static deflection amount δ of the rod-shaped member can be reduced to a / 15.
The method for producing a porous preform for an optical fiber according to claim 1 or 2, wherein: 4. An apparatus for producing a porous preform for an optical fiber, comprising at least a rod-shaped member attached to a rotating mechanism, and a core burner and a clad burner capable of depositing glass fine particles at the tip of the rod-shaped member. During operation, the rod-shaped member always has a static deflection δ of not more than a / 15 (where a represents the outer diameter of the deposition surface at the tip of the porous preform for optical fiber being formed). Equipment for manufacturing porous preforms for optical fibers. 5. The rod-shaped member is adjusted to a / 15 by adjusting at least one of the second moment of area I, the load W, the length L of the rod-shaped member, or the modulus of longitudinal elasticity E of the rod-shaped member.
5. The apparatus according to claim 4, wherein the amount of static deflection is as follows.
An apparatus for producing a porous preform for an optical fiber according to the above. 6. A rod-shaped member having at least a part thereof hollow,
The porous preform for an optical fiber according to claim 4 or 5, wherein the rod-shaped member has a static deflection δ of not more than a / 15 by at least part of being made of ceramic. Manufacturing equipment.