JP7024489B2 - Manufacturing method of base material for optical fiber - Google Patents

Description

The present invention relates to a method for manufacturing a base material for an optical fiber.

In Patent Document 1, a porous base material formed by depositing glass fine particles is dehydrated and transparently vitrified to produce a core member for an optical fiber base material, and the core member is stretched to obtain a desired core / clad ratio. A method for manufacturing an optical fiber base material to which a clad portion is added later is disclosed. In Patent Document 1, dehydration and transparency are performed from the lower end to the upper end of the optical fiber base material.
Patent Document 2 relates to a method for manufacturing an optical fiber base material, in which the soot base material is traversed twice or more and waits between each traverse in a step of traversing the soot base material for optical fiber in a heating furnace to dehydrate the soot base material. It is disclosed to provide a step.
Patent Document 3 relates to a method for vitrifying a porous soot body of an optical fiber base material, and controls the vitrification temperature of the electric heater according to the position of the porous soot body with respect to the vitrified region of the electric heater in the core tube. Is disclosed. Specifically, it is described that when the upper end side of the porous soot body is in the vitrification region of the electric heater, the vitrification temperature is lowered as compared with the case where the upper end side of the porous soot body is in the vitrification region.

Japanese Unexamined Patent Publication No. 2007-284302 Japanese Unexamined Patent Application Publication No. 2003-277094 Japanese Patent Application Laid-Open No. 2003-81657

As shown in the above Patent Documents 1 to 3, a method of making the temperature at the time of dehydration constant in the longitudinal direction of the optical fiber base material, raising the temperature on the upper end side, or lowering the traverse speed on the upper end side is known. However, in these methods, dehydration on the upper end side of the optical fiber base material is not sufficient, and transmission loss due to the OH group remaining on the upper end side increases, which may lead to a decrease in yield.

Therefore, an object of the present invention is to provide a method for manufacturing an optical fiber base material that can stably realize a low transmission loss over the entire length in the longitudinal direction of the optical fiber base material.

The method for producing a base material for an optical fiber according to one aspect of the present invention is as follows.
A method for producing a base material for an optical fiber, which is obtained by inserting a porous base material produced by depositing silica particles into a heating furnace and sequentially feeding the porous base material into a heating zone in the heating furnace to dehydrate and sinter. And
The porous base material includes a first region and a second region including the upper end portion of the porous base material in the longitudinal direction thereof.
The temperature of the heating zone is set lower when dehydrating the second region than when dehydrating the first region.

According to the above invention, it is possible to stably realize a low transmission loss over the entire length in the longitudinal direction of the base material for an optical fiber.

It is a figure which shows the manufacturing apparatus of the base material for an optical fiber. It is a figure explaining the structure of a porous base material. It is a figure explaining the improvement result of the base material for an optical fiber manufactured by the manufacturing method which concerns on this embodiment.

(Explanation of Embodiment of this invention)
First, embodiments of the present invention will be listed and described.
The method for producing a base material for an optical fiber according to one aspect of the present invention is as follows.
(1) A base material for an optical fiber that is dehydrated and sintered by inserting a porous base material produced by depositing silica particles into a heating furnace and sequentially feeding the porous base material into a heating zone in the heating furnace. It is a manufacturing method of
The porous base material includes a first region and a second region including the upper end portion of the porous base material in the longitudinal direction thereof.
The temperature of the heating zone is set lower when dehydrating the second region than when dehydrating the first region.
According to the above method, it is possible to stably realize a low transmission loss over the entire length in the longitudinal direction of the base material for an optical fiber.

(2) The temperature of the heating zone when dehydrating the first region may be in the range of 1200 ° C. or higher and 1300 ° C. or lower.
It is more preferable to apply the method of the present application in the case of dehydration in a temperature range where the porous base material shrinks at the time of dehydration as in the above range.

(3) The ratio of the outer diameter of the porous base material after dehydration to the outer diameter of the porous base material before dehydration in the second region may be larger than the ratio in the first region. ..
According to the above method, by suppressing the shrinkage after dehydration in the second region of the porous base material more than the shrinkage after dehydration in the first region, the upper end side can also be satisfactorily dehydrated.

(4) In the first region, the ratio of the outer diameter after dehydration to the outer diameter before dehydration is in the range of 0.85 times or more and 0.95 times or less, and in the second region, before dehydration. The ratio of the outer diameter after dehydration to the outer diameter may be in the range of 0.90 times or more and 1.00 times or less.
In order to satisfactorily dehydrate the upper end side of the porous base material, it is more preferable to set the shrinkage ratio within the above range.

(Details of Embodiment of the present invention)
A specific example of the method for manufacturing the base material for an optical fiber according to the embodiment of the present invention will be described below with reference to the drawings.
It should be noted that the present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

FIG. 1 shows an example of a heating device used in a method for manufacturing a base material for an optical fiber.
As shown in FIG. 1, the heating device 1 includes a heating furnace 2 for heat-treating the porous base material 10 which is an object to be heated. The heating furnace 2 has a core tube 21 into which the porous base material 10 is inserted. Below the core tube 21, a gas introduction section 22 for introducing an inert gas such as helium gas or a corrosive gas such as chlorine or fluoride gas is provided in the core tube 21. An exhaust unit 23 for discharging unnecessary gas from the core pipe 21 is provided in the upper part of the core pipe 21.

A heater 24 arranged concentrically with the core tube 21 is provided on the outer periphery of the core tube 21. The heater 24 is designed to heat around the heating zone 25 inside the core tube 21. Therefore, the heat treatment of the porous base material 10 is mainly performed in the heating zone 25. A thermometer 26 for measuring the temperature of the heating zone 25 heated by the heater 24 is provided in the vicinity of the heater 24.

Further, the heating device 1 includes a heating control unit 3 that controls the operation of each unit. The heating control unit 3 is electrically connected to the heater 24 and the thermometer 26. The heating control unit 3 controls the output of the heater 24 so that the temperature of the heating zone 25 becomes a predetermined temperature based on, for example, the temperature of the heating zone 25 measured by the thermometer 26.

Further, the heating device 1 includes a traverse mechanism 4 for traversing the position of the porous base material 10 in the core tube 21 in the longitudinal direction. The traverse mechanism 4 is electrically connected to the heating control unit 3. In order for the porous base material 10 suspended by the seed rod 41 to pass through the heating zone 25 in the core tube 21, the traverse mechanism 4 follows the control of the heating control unit 3 in the vertical direction indicated by arrows 42a and 42b. Traverse.

Further, the heating device 1 includes a displacement sensor 5 that measures the distance to the porous base material 10. The displacement sensor 5 calculates the displacement of the outer diameter of the porous base material 10 based on the measured distance. The displacement sensor 5 is electrically connected to the heating control unit 3. The displacement data calculated by the displacement sensor 5 is transmitted to the heating control unit 3.

FIG. 2 shows an example of the porous base material 10 inserted into the core tube 21. The porous base material 10 is a base material synthesized by depositing silica (quartz) particles by, for example, a VAD method or an OVD method. The porous base material 10 is dehydrated and sintered in the core tube 21 to become a transparent base material for optical fibers (core base material).

As shown in FIG. 2, the porous base material 10 has a second region 11 provided on the side (upper side) connected to the seed rod 41 in the longitudinal direction (vertical direction of FIG. 2) and a second region. It has a first region 12 continuously provided in the second region below the second region.

The second region 11 is an upper end portion (a region where the diameter is changing) from the upper end 13 which is the deposition start point of the porous base material 10 to the position 14 where the diameter of the porous base material 10 is stable. 11a and the first to some extent section region 11b of the stationary portion having a stable diameter are included.

The first region 12 includes a stationary region 12a which is a stationary portion continuous with the section region 11b, and a lower end portion 12b whose diameter changes in the region continuous with the stationary region 12a.

The size of the porous base material 10 is preferably such that the diameter of the stationary portion is 180 mm or more.

Next, a method of manufacturing a base material for an optical fiber manufactured by using the heating device 1 will be described.
A predetermined amount of inert gas and corrosive gas are introduced from the gas introduction unit 22, and unnecessary gas is discharged from the exhaust unit 23 so that the pressure in the core tube 21 becomes lower than the atmospheric pressure. To control. Further, the heater 24 is heated to raise the temperature inside the core tube 21.

The entire porous base material 10 is dehydrated by sequentially feeding the porous base material 10 into the heating zone 25 while traversing the porous base material 10 in the vertical direction by the traverse mechanism 4.

The temperature of the heating zone 25 during the dehydration treatment is set to a predetermined temperature for each part of the porous base material 10 which is the object to be heated. The temperature of the heating zone 25 when dehydrating the second region 11 of the porous base material 10 is set to be lower than the temperature of the heating zone 25 when dehydrating the first region 12. For example, the temperature of the heating zone 25 when dehydrating the first region 12 is set to be within the range of 1200 ° C. or higher and 1300 ° C. or lower. Further, the temperature of the heating zone 25 when dehydrating the second region 11 is set to be in the range of, for example, 1140 ° C to 1200 ° C.

Specifically, the change in the outer diameter of the porous base material 10 before and after dehydration in the first region 12 and the second region 11 is set to have the following relationship.
The outer diameter of the porous base material 10 before dehydration in the first region 12 is R1, the outer diameter after dehydration is r1, and the outer diameter of the porous base material 10 before dehydration in the second region 11 is R2, dehydrated. When the latter outer diameter is r2, (r2 / R2) is set to be larger than (r1 / R1).

For example, in the first region 12, the ratio r1 / R1 of the outer diameter r1 after dehydration to the outer diameter R1 before dehydration is set to be in the range of 0.85 times or more and 0.95 times or less. In the second region 11, the ratio r2 / R2 of the outer diameter r2 after dehydration to the outer diameter R2 before dehydration is set to be in the range of 0.90 times or more and 1.00 times or less.
That is, each temperature of the heating zone 25 is set so that the shrinkage after dehydration in the second region 11 can be suppressed more than the shrinkage after dehydration in the first region 12.

The temperature of the heating zone 25 is adjusted by controlling the output of the heater 24. While measuring the temperature of the heating zone 25 with the thermometer 26, the output of the heater 24 is controlled by the heating control unit 3 so that the temperature of the heating zone 25 becomes the preset heating temperature. In the traverse of the porous base material 10, when the temperature of the heating zone 25 is shifted from the temperature at which the first region 12 is dehydrated to the temperature at which the second region 11 is dehydrated, for example, in a stepped shape (inclined shape). The output of the heater 24 is controlled so that the temperature changes (decreases). Similarly, when the temperature of the heating zone 25 is shifted from the temperature at which the second region 11 is dehydrated to the temperature at which the first region 12 is dehydrated, the temperature is controlled to change (rise) in a stepwise manner.

The displacement of the outer diameter of the porous base material 10 during the treatment, that is, the shrinkage rate of the porous base material 10, is measured by the displacement sensor 5 and transmitted from the displacement sensor 5 to the heating control unit 3. The heating control unit 3 may adjust the output control of the heater 24, the control of the traverse speed of the traverse mechanism 4, and the like based on the received displacement data.

The porous base material 10 dehydrated in this way is subsequently subjected to a sintering treatment to become a transparent base material for an optical fiber.

By the way, conventionally, a base material for an optical fiber having a large outer diameter (for example, 180 mm or more) (hereinafter referred to as a large core) is compared with a material having a normal thickness (for example, 150 mm) (hereinafter referred to as a normal core). , The transmission loss due to the OH group loss (remaining OH group) tended to be high. In particular, the transmission loss on the seeded portion side (upper end side) of the base material for optical fiber is high, and it has been desired to investigate the cause and improve it.

When the present inventor investigated the cause of this, it was found that when manufactured by the conventional manufacturing method, the large core shrinks more before and after dehydration than the normal core. It was also found that in the large core, the porous base material was generally dehydrated at a higher temperature than in the normal core. When the porous base material is dehydrated at a high heating temperature, the surface layer of the porous base material shrinks and hardens due to the high heat, and as a result, water accumulates inside the porous base material and goes to the outside. It was found that one of the causes of OH group loss is that it is not discharged and dehydration is insufficient.

For example, when the porous base material for a large core is dehydrated by a conventional manufacturing method, the porous base material after dehydration (shown by the solid line 51) is before dehydration, as shown in FIG. 3 (a). It is shrunk as compared with the porous base material (indicated by the broken line 52), and the amount of shrinkage is particularly large in the second region 11 on the upper end side. As shown by the polygonal line 71 in FIG. 3C, the shrinkage ratio was 77.6% on average in the first region 12 of the porous base material and 67.3% on average in the second region 11. .. The "shrinkage rate" of the porous base material before and after the dehydration treatment is assumed to be R when the outer diameter of the porous base material before dehydration is R and r when the outer diameter of the porous base material after dehydration is r. It is calculated by the rate (%) = r / R × 100. The dehydration temperature was 1280 ° C., which is shown by the polygonal line 61 in FIG. 3 (b). The dehydration temperature of the core is usually about 1210 ° C.

Therefore, first, the present inventor paid attention to the dehydration temperature, and as shown in the broken line 62 in FIG. 3 (b), the dehydration temperature was reduced to 1220 ° C. to perform the dehydration treatment of the large core. As a result, the shrinkage rate averaged 86.9% in the first region 12 and 80.4% in the second region 11 of the porous base material, as shown by the polygonal line 72 in FIG. 3 (c). I was able to improve.

Next, in order to further suppress the shrinkage in the second region 11, the dehydration temperature of the second region 11 was further reduced as shown by the polygonal line 63 in FIG. 3 (b). In the polygonal line 63, the dehydration temperature (1220 ° C.) is gradually lowered from the end of the first region 12 toward the second region 11, and is maintained constant when the temperature reaches 1160 ° C. As a result of the dehydration treatment at the dehydration temperature changed in this way, as shown by the polygonal line 73 in FIG. 3 (c), the shrinkage can be further suppressed in the second region 11 of the porous base material. did it. As a result, the total shrinkage of the large core could be suppressed to the same level as the total shrinkage of the normal core (contract rate average 91.8%) shown in the polygonal line 74 in FIG. 3 (c).
As a result, the defect rate due to OH group loss on the basis of the number of base materials for optical fibers could be reduced from the conventional 16.3% to 5.2%.

As described above, according to the method for manufacturing the base material for optical fiber of this example, the temperature of the heating zone 25 when dehydrating the second region 11 is the temperature of the heating zone 25 when dehydrating the first region 12. It is controlled to be lower than. Therefore, shrinkage can be suppressed over the entire length of the optical fiber base material in the longitudinal direction during dehydration, and stable and low transmission loss can be realized.

Further, according to the present manufacturing method, the temperature of the heating zone 25 when dehydrating the first region 12 is controlled to be within the range of 1200 ° C. or higher and 1300 ° C. or lower. It is more preferable to apply this production method when dehydration is performed in a temperature range in which the porous base material 10 shrinks during dehydration. This manufacturing method is suitable for dehydrating a porous base material 10 having a large diameter of, for example, 180 mm or more.

Further, according to the present manufacturing method, the ratio of the outer diameter of the porous base material 10 before and after dehydration in the second region 11 is controlled to be larger than the ratio of the outer diameter before and after dehydration in the first region 12. Has been done. In this way, by suppressing the shrinkage after dehydration in the second region 11 of the porous base material 10 more than the shrinkage after dehydration in the first region 12, the upper end side of the porous base material 10 is also satisfactorily dehydrated. can do. For example, in the first region 12, the ratio of the outer diameter before and after dehydration is in the range of 0.85 times or more and 0.95 times or less, and in the second region 11, the ratio of the outer diameter is 0.90 times or more and 1.00 times. By setting the range to twice or less, the upper end side of the porous base material 10 can be satisfactorily dehydrated.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. Further, the number, position, shape and the like of the constituent members described above are not limited to the above-described embodiment, and can be changed to a number, position, shape and the like suitable for carrying out the present invention.

1: Heating device 2: Heating reactor 3: Heating control unit 4: Traverse mechanism 5: Displacement sensor 10: Porous base material 11: Second region 12: First region 11a: Upper end 11b: Section region 12a: Steady Area 21: Core tube 24: Heater 25: Heating zone

Claims (3)

A method for producing a base material for an optical fiber, which is obtained by inserting a porous base material produced by depositing silica particles into a heating furnace and sequentially feeding the porous base material into a heating zone in the heating furnace to dehydrate and sinter. And
The porous base material includes a first region and a second region including the upper end portion of the porous base material in the longitudinal direction thereof.
The temperature of the heating zone is set lower when dehydrating the second region than when dehydrating the first region.
In the traverse of the porous base material, when the temperature of the heating zone is shifted from the temperature at which the first region is dehydrated to the temperature at which the second region is dehydrated, the temperature is lowered in an inclined manner. The temperature of the heating zone is controlled
In the traverse of the porous base material, when the temperature of the heating zone is shifted from the temperature at which the second region is dehydrated to the temperature at which the first region is dehydrated, the temperature is increased in an inclined manner. By controlling the temperature of the heating zone,
The second region includes a region in which the dehydration temperature is maintained constant.
The ratio of the outer diameter of the porous base material after dehydration to the outer diameter of the porous base material before dehydration in the second region is larger than the ratio in the first region, the base material for optical fiber. Manufacturing method. The method for producing an optical fiber base material according to claim 1, wherein the temperature of the heating zone when dehydrating the first region is within the range of 1200 ° C. or higher and 1300 ° C. or lower. In the first region, the ratio of the outer diameter after dehydration to the outer diameter before dehydration is in the range of 0.85 times or more and 0.95 times or less, and in the second region, the outer diameter before dehydration. The method for producing a base material for an optical fiber according to claim 1 or 2 , wherein the ratio of the outer diameter after dehydration to the above is in the range of 0.90 times or more and 1.00 times or less.

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