JP2001058842A - Production of optical fiber base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber base material which is produced by an OVD method, scarcely contains foreign matters, and gives a transparent glass base material that is scarcely broken and does scarcely cause the change of the diameter, when drawn. SOLUTION: This method for producing an optical fiber base material comprises maintaining the lowest surface temperature of a starting material 1 or the lowest surface temperature of the constant portion of a readily accumulated glass particle product 3 at >=150 deg.C, simultaneously relatively traversing a burner 7 or the starting material 1 to spray the flow 7a of glass particles on the starting material 1 or the readily accumulated glass particle product 3, thus laminating and accumulating the glass particles on the starting material 1. The glass particles are produced by supplying silicon tetrachloride, oxygen, hydrogen, and so on into the burner 7 and burning the materials.

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 manufactured by an OVD method (external method).

[0002]

2. Description of the Related Art In recent years, in the production of large optical fiber preforms, a so-called OVD method is used in which a core rod produced by a VAD method or the like is used as a starting material, and glass particles produced by flame hydrolysis are laminated and deposited around the core rod. (External method) is used. FIG. 1 is a longitudinal sectional view illustrating a manufacturing apparatus according to the OVD method, wherein 1 is a starting material, 2 is a support rod,
, A chuck; 5, a rotary drive mechanism; 6, a base; 7, a burner; 7a, a flow of glass fine particles; 8, a reaction vessel;

In this manufacturing apparatus, support rods 2 made of glass rods are connected to both ends of an elongated cylindrical starting material 1 mainly composed of quartz glass manufactured by a VAD method or the like, and the support rods 2 are connected. It is gripped by the chucks 4 arranged on both sides, and the whole of them is arranged in the reaction vessel 8. A rotation drive mechanism 5 is disposed on the base 6, and the rotation drive mechanism 5 rotates the chuck 4, the starting material 1 and the support bar 2 gripped by the chuck 4 around the main axis.

Further, silicon tetrachloride, oxygen, hydrogen and the like are supplied to the burner 7 and burned to generate glass fine particles.
With the burner 7 directed toward the starting material 1, a flow 7 a of glass fine particles is sprayed from the burner 7 onto the starting material 7. The burner or the starting material 1 is relatively reciprocated in the longitudinal direction of the starting material, that is, traversed by a driving mechanism (not shown).
In FIG. 1, the burner 7 is moved, but the starting material 1 may be moved.

The glass fine particles generated by the burner 7 are stacked and deposited around the starting material 1, and a glass fine particle deposit 3 is formed around the starting material 1. Since the outer diameter of the glass fine particle deposit 3 gradually increases due to the deposition of the glass fine particles, the burner 7 may be moved in a direction away from the main axis so that the distance between the burner 7 and the glass fine particle deposit 3 is not so close. is there. In addition, since corrosive gas such as hydrogen chloride is generated in flame hydrolysis, an exhaust hood 9 is provided in the reaction vessel 8 to exhaust unnecessary gas.

The porous optical fiber preform formed as described above is dehydrated and sintered into a transparent glass preform in the next step, and the transparent glass preform is drawn in a drawing furnace. Thus, an optical fiber is manufactured.

[0007] In the optical fiber preform manufacturing apparatus described above, foreign matter such as foreign matter that has invaded with the outside air, foreign matter formed by stripping silica powder or the like attached to the inner wall surface of the reaction vessel, etc., floats in the reaction vessel. These foreign substances may adhere to the starting material or the glass particle deposit being deposited, and may be taken into the glass particulate deposit to form an optical fiber preform containing the foreign substance. When a transparent glass preform is formed by using such an optical fiber preform, bubbles having foreign substances as nuclei are generated in the glass preform, and when the glass preform is drawn, problems such as disconnection and wire diameter variation occur. Sometimes.

[0008] Methods for dealing with such foreign matter are described in JP-A-5-11679 and JP-A-7-300333. In the method described in Japanese Patent Application Laid-Open No. 5-116979, an air curtain jet port is provided, and a clean gas flow is sprayed from the air curtain jet port toward a glass particle deposit being deposited, and foreign matter is deposited on the surface of the glass particle deposit. They are to be blown away so that they do not adhere. Further, in the method described in JP-A-7-30333, a heater is provided near an upper inner wall surface of a reaction vessel, and the inner wall surface of the reaction vessel is heated by the heater. This is to prevent adhesion.

[0009]

The present inventors have tried the methods described in JP-A-5-11697 and JP-A-7-30333, but have tried to obtain a transparent material obtained from an optical fiber preform. Sufficient results have not always been obtained for the purpose of preventing the glass base material from being broken by drawing or causing a change in the diameter of the optical fiber. In the method of spraying a clean gas, it is conceivable that even if the jetted gas stream is clean, foreign matter floating in the reaction vessel is involved before the gas stream reaches the glass fine particle deposit. Further, since the clean gas is blown onto the glass fine particle deposit being deposited, there is also a problem that it is difficult to prevent interference with the flow of the glass fine particles blown from the burner.

In addition, the method of heating the inner wall surface of the reaction vessel has a problem that it is difficult to completely eliminate the adhesion of silica powder to the inner wall surface. There is a problem that adhesion to the surface of the glass fine particle deposit cannot be prevented. Then, the present inventor studied other methods, and as a result, found a method of manufacturing the optical fiber preform of the present invention.

[0011]

SUMMARY OF THE INVENTION A method of manufacturing an optical fiber preform according to the present invention is a method of manufacturing an optical fiber preform in which glass fine particles generated by flame hydrolysis are deposited in a layer around an elongated cylindrical starting material. A method wherein the starting material or the glass particle deposit already deposited on the starting material has a surface minimum temperature of a stationary part of 150 ° C. or more, preferably 150 ° C. to 800 ° C.
While maintaining the above, either the burner or the starting material is relatively reciprocated in the longitudinal direction of the starting material, and the glass fine particles generated by the burner are sprayed on the starting material or the already deposited glass fine particle deposit, Glass particles are laminated and deposited on the periphery of the starting material.

As a result, the minimum surface temperature of the starting material or the glass fine particle deposit being deposited thereon is 150 ° C.
Since the temperature is maintained at a temperature of at least 150 ° C., preferably 150 ° C. to 800 ° C., it is possible to suppress the adhesion of floating foreign substances to their surfaces due to the thermophoresis effect. Further, the glass base material obtained by making the optical fiber base material transparent has extremely few defects such as disconnection or wire diameter fluctuation at the time of drawing, and is of good quality.

The stationary part of the glass particle deposit is a part that can be commercialized except for the parts that cannot be commercialized at both ends in the longitudinal direction, and the minimum surface temperature is the temperature of each part of the surface of the stationary part. It means the lowest temperature. The surface temperature is usually measured by a radiation thermometer such as a thermo tracer.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of manufacturing an optical fiber preform according to the present invention, the same apparatus as the apparatus shown in FIG. 1 can be used as a manufacturing apparatus. Further, as the starting material 1, a core rod which is an elongated cylindrical body mainly composed of quartz glass manufactured by a VAD method or the like and whose refractive index changes in a radial direction is used. Depending on the type of optical fiber preform, a pure quartz rod may be used as the starting material 1. Further, silicon tetrachloride, oxygen, and hydrogen are supplied to the burner 7 and burned to generate glass fine particles by flame hydrolysis. The burner 7 may be supplied with another additive material serving as a dopant, if necessary.

Then, the burner 7 is relatively reciprocated, that is, traversed in the longitudinal direction of the starting material 1. It is also possible to fix the burner and traverse the starting material. If the traverse speed is increased, high-temperature glass particles and a flame are sprayed on the surface of the already-deposited glass particle deposit, and then the high-temperature glass particles and the flame are again deposited on the glass-particle deposit. Since the time until spraying on the surface of the body is shortened, the minimum surface temperature of the glass fine particle deposit can be kept high. FIG. 2 shows the result of examining the relationship between the traverse speed and the minimum surface temperature of the glass particle deposit at the 100th turn of the traverse while keeping the conditions other than the traverse speed of the burner constant. The temperature will also be higher.

Of course, the minimum surface temperature of the glass particle deposit is determined not only by the traverse speed but also by the spindle speed, the heat capacity of the glass particle deposit, the gas flow rates of oxygen and hydrogen supplied to the burner, etc. If the other requirements such as the heat capacity of the glass particle deposit, the gas flow rate of the oxygen supplied to the burner, and the hydrogen gas flow rate are the same, increasing the burner traverse speed can raise the minimum surface temperature of the glass particle deposit. I can do it.

Then, the minimum temperature of the surface of the starting material 1 or the stationary part (producable part) of the glass particle deposit 3 being deposited is set to 150 ° C. or more, preferably 150 ° C. to 800 ° C.
While maintaining the temperature at ° C., laminating and depositing glass fine particles thereon, as described in the section of the next example, to reduce the amount of foreign matter in the transparent glass preform obtained from the optical fiber preform. Disconnection and wire diameter fluctuation in the glass base material drawing step can be almost zero. In addition, even if the outer diameter of the glass fine particle deposit increases and the minimum surface temperature tends to decrease, if the traverse speed is increased according to the increase in the number of layers of the glass fine particle deposit, the glass fine particle deposition can be easily performed. The minimum body surface temperature can be maintained at 150 ° C. or higher.

The reason why the upper limit of the minimum surface temperature is preferably 800 ° C. is as follows. Dehydrate the optical fiber preform made by depositing glass particles,
In removing OH and impurities, if the bulk density of the glass fine particle deposit is too high, OH and impurities cannot be sufficiently removed. Further, the minimum surface temperature and the bulk density of the glass particle deposit are closely related, and the higher the minimum surface temperature, the higher the bulk density. Therefore, in order to make the bulk density an appropriate value, it is desirable that the minimum surface temperature be 800 ° C. or less.

[0019]

EXAMPLE Using a core rod having a step-shaped refractive index distribution with a diameter of 10 mm as a starting material, glass tetragonal particles produced by supplying silicon tetrachloride, oxygen and hydrogen from a burner and burning them are sprayed around the starting material. Glass fine particles were laminated and deposited to form a glass fine particle deposit, thereby producing a porous optical fiber preform. The outer diameter of the optical fiber preform was 100 mm. Experiments were performed on five cases with various traverse speeds of the burner and the number of revolutions of the main shaft of the starting material at that time. It was as follows.

The traverse speed of the burner was constant for Cases 1 to 4, and for Case 5, the traverse speed was increased in three stages according to the number of traverses. In addition, since the lowering of the minimum surface temperature increases as the outer diameter of the glass fine particle deposit increases, the supply amount of oxygen and hydrogen to the burner is gradually increased so that the minimum surface temperature of the glass fine particle deposit is always constant. I tried to be.
In case 5, the traverse speed is increased in three stages to compensate for a decrease in the minimum surface temperature due to an increase in the outer diameter of the glass fine particle deposit. Since the surface minimum temperature slightly changes with the passage of time, Table 1 shows the surface minimum temperature in that range.

Further, the optical fiber preform thus manufactured was dehydrated and sintered to be transparent, and a transparent glass preform was obtained. When the transparent glass base material was visually observed, the number of foreign substances in the glass base material was as shown in Table 1. In addition, when an optical fiber was manufactured by drawing using a glass preform using a drawing furnace, the frequency of occurrence of disconnection at the time of drawing and the frequency of occurrence of variation in the diameter of the optical fiber obtained by drawing were as shown in Table 1. Met. The optical fiber has a diameter of 125 ± 1 μm.
Those out of the range were regarded as the occurrence of wire diameter fluctuation.

[0022]

[Table 1]

According to the results shown in Table 1, when the minimum surface temperature of the glass fine particle deposit increases, the number of foreign substances in the glass base material after the transparency decreases, and the frequency of occurrence of disconnection during drawing,
Wire diameter variation is also reduced. Then, when the surface minimum temperature of the glass fine particle deposit becomes 150 ° C. or more, the number of foreign substances in the glass base material becomes 2 or less, and the disconnection frequency and wire diameter variation during drawing become almost zero.

According to the result of Case 5 in which the traverse speed is increased along with the number of traverses, even if the traverse speed at the initial stage of lamination is considerably low at 200 mm / min, the traverse speed at the end of lamination is increased to 1000 mm / min. The minimum surface temperature of the glass fine particle deposit can be maintained at 150 ° C. or higher, foreign matter in the glass base material can be reduced to zero, and disconnection and wire diameter variation during drawing can be reduced to zero.

[0025]

According to the method for manufacturing an optical fiber preform of the present invention, the glass fine particles generated by the burner are kept while keeping the minimum temperature of the surface of the stationary part of the starting material or the already deposited glass fine particle deposit at 150 ° C. or higher. By spraying them, a fine glass particle deposit is formed on the periphery of the starting material, so that foreign substances are suppressed from adhering to the surface of the starting material or the fine glass particle deposit being deposited. Foreign matter is less likely to be taken into the glass particle deposit.

As a result, the glass base material obtained by making the optical fiber base material transparent has less foreign matter, bubbles, etc., and less occurrence of abnormalities such as disconnection and wire diameter fluctuation in the drawing process using the same. . Keeping the optical fiber preform at a high temperature during the deposition of the glass microparticles also leads to a reduction in stress in the optical fiber preform, and has the effect of preventing cracks in the optical fiber preform.

Further, by increasing the traverse speed of the burner in accordance with the number of layers of the deposited glass fine particles, the traverse speed at the beginning of the deposition is low, but the traverse speed at the end of the deposition is only increased. The minimum surface temperature of a certain glass fine particle deposit can be maintained at 150 ° C. or higher, and efficient production can be achieved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating an optical fiber preform manufacturing apparatus according to an OVD method.

FIG. 2 is a graph showing an example of a relationship between a traverse speed and a minimum surface temperature of a glass fine particle deposit.

[Explanation of symbols]

 1: Starting material 2: Support rod 3: Glass fine particle deposit 4: Chuck 5: Rotary drive mechanism 6: Base 7: Burner 7a: Flow of glass fine particles 8: Reaction vessel 9: Exhaust hood

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Motonobu Nakamura 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Masaaki Hirano 1-Tagamachi, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo 4G021 EA03 EB02 EB06 EB14 EB26

Claims (2)

[Claims] 1. A method for producing an optical fiber preform in which glass fine particles generated by flame hydrolysis are deposited in a layer around an elongated cylindrical starting material, wherein said starting material or glass fine particles already deposited thereon Either the burner or the starting material is relatively reciprocated in the longitudinal direction of the starting material while maintaining the surface minimum temperature of the stationary portion of the deposit at 150 ° C. or higher, and the glass fine particles generated by the burner are discharged from the starting material. A method for producing an optical fiber preform, comprising spraying onto a material or an already deposited glass fine particle deposit, and laminating and depositing glass fine particles around the starting material. 2. The light according to claim 1, wherein the moving speed of the burner or the starting material in the longitudinal direction is increased in accordance with an increase in the number of layers of the glass fine particles to be stacked and deposited. Manufacturing method of fiber preform.