JPH07187701A - Production of optical fiber and spinning furnace for producing optical fiber - Google Patents

Abstract

PURPOSE:To prevent the neck down shape of a preform of a optical fiber from becoming longer even by raising the spinning linear velocity of the preform of the optical fiber by specifying difference in temperature at a molten part of the tip of the preform of the optical fiber and temperature at a position lower than the part. CONSTITUTION:First, a preform 13 of an optical fiber is inserted into a core tube 3 of a furnace, heated in an inert gas atmosphere such as argon to a high temperature, melted and the preform 13 of the optical fiber is spun in the longer direction of the optical fiber at 100-1,500m/minute to give an optical fiber 15. In obtaining the optical fiber 15 by subjecting the preform 13 of the optical fiber to melt spinning, the temperature at a position E1 of a spinning furnace 1 is 25-50 deg.CX deg.C (X>=0) lower than that at a central part E0. Therefore, the temperature (T1) of the optical fiber 15 positioned located at the position E1 of the spinning furnace 1 is also 25-50 deg.CX deg.C lower than the temperature (T0) at a molten part 13a of the tip of the preform 13 of the optical fiber. By making the temperature, different the neck down shape of the preform 13 of the optical fiber does not become longer than that of a conventional method even if the spinning linear velocity is increased to a high speed of >=300m/minute and the spinning furnace is made compact.

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 and a manufacturing apparatus therefor, and more particularly to a method for manufacturing an optical fiber in which the lateral pressure characteristic of the optical fiber is less likely to deteriorate even when the spinning linear velocity of the optical fiber base material is increased. The present invention relates to a manufacturing method and a spinning furnace for manufacturing an optical fiber.

[0002]

2. Description of the Related Art Generally, a spinning furnace as shown in FIG. 8 is used for manufacturing an optical fiber, and reference numeral 1 in the drawing is a spinning furnace. The spinning furnace 1 comprises a core tube 3, a cylindrical heater 5 surrounding the outer circumference of the core tube 3, and an electrode 7 for supplying electric power to the heater 5, which are housed in a hollow columnar outer frame 9. The remaining voids in the outer frame 9 are filled with a heat insulating material 11 such as carbon fiber or ceramics. Further, the heater 5 is attached to the outer frame 9 by fixing the fixing portion 5a provided in the lower portion to the electrode 7 and further fixing the electrode 7 to the outer frame 9. In order to manufacture an optical fiber using the spinning furnace 1 having such a configuration, the optical fiber preform 13 is inserted into the furnace core tube 3 and then heated at a high temperature in an inert gas atmosphere such as argon and melted. Then, the optical fiber 15 was obtained by spinning at 100 to 600 m / min in the longitudinal direction of the optical fiber. The optical fiber 15 is further passed through a resin coater (not shown) provided below the spinning furnace 1 in order to make it strong against lateral pressure and friction, so that a resin coating is formed on the outer peripheral surface. It was used as an optical fiber strand.

[0003]

By the way, in such a method for producing an optical fiber, it is desirable to melt-spin at a high speed for the purpose of increasing the production efficiency. It is known that the neck-down shape, which is the molten portion of the base material 13, also becomes long. FIG. 9A shows the neck-down shape of the optical fiber preform when the spinning linear velocity is low, and FIG. 9B shows the neck-down shape of the optical fiber preform when the spinning linear velocity is high. Reference symbols L ₁ and L ₂ respectively indicate the length of the neck-down shape when the spinning linear velocity is low and high. However,
If the neck-down shape becomes longer as described above, the outer diameter becomes 1
Since the optical fiber having a constant thickness of 25 μm is manufactured, the variation in the spinning linear velocity becomes large, and the temperature variation on the surface of the optical fiber 15 when passing through the resin coater becomes large. There is a drawback in that the thickness variation of the resin coating becomes large and the lateral pressure characteristic of the optical fiber deteriorates.

The present invention has been made in view of the above circumstances, and prevents the neck-down shape of the optical fiber preform from becoming long even if the spinning linear velocity of the optical fiber preform is increased, and the lateral pressure of the optical fiber is reduced. An object of the present invention is to provide an optical fiber manufacturing method capable of improving characteristics and a spinning furnace for manufacturing the optical fiber.

[0005]

According to a first aspect of the present invention, there is provided a method for manufacturing an optical fiber, wherein when the optical fiber preform is melt-spun to form an optical fiber, the temperature (T ₀ ) and the temperature (T ₁ ) at a position lower by X cm (where X ≧ 0) than this, the difference (ΔT) is 25 × ° C. or more 50
It is characterized in that the temperature is X ° C. or less. A spinning furnace for producing an optical fiber according to claim 2 (hereinafter abbreviated as a spinning furnace).
Is characterized by a lack of lower insulation. Further, in the spinning furnace according to claim 3, in the spinning furnace according to claim 2, a cooling pipe, to which cold water is supplied, is wound around the outer periphery of the lower part of the furnace core tube in place of the lack of the lower heat insulating material. It is characterized by being. Further, the spinning furnace according to claim 4 is the spinning furnace according to claim 2, in which the lower heat insulating material is replaced by a metal, ceramics, or the like having a lower heat insulating effect than the upper heat insulating material. It is characterized by being one or more selected from heat resistant plastics.

The present inventors have paid attention to the temperature of the temperature inside the spinning furnace in order to prevent the neck-down shape of the optical fiber preform from becoming long, and as a result of various studies and experiments, the center of the heater It has been clarified that lowering the temperature below the portion is effective in preventing the neck-down shape of the optical fiber preform from becoming long, and has completed the present invention.

The difference (ΔT) between the temperature (T ₀ ) of the molten portion at the tip of the optical fiber preform and the temperature (T ₁ ) at a position X cm (where X ≧ 0) below it is 25X ° C. or more and 50X or more.
The range of manufacturing conditions that is equal to or lower than ° C is the range of the region B surrounded by the straight line a and the straight line b in the graph shown in FIG.
In FIG. 1, the horizontal axis (X) is the distance (cm) between the position of the tip of the optical fiber preform (where the position is 0 cm) and an arbitrary position below this, and the vertical axis (ΔT) is The temperature (T ₀ ) of the molten portion at the tip of the fiber preform and Xc from this
It is the difference (ΔT) from the temperature (T ₁ ) at a position below m (where X ≧ 0). Also, the equation expressing the straight line a is ΔT = 50X
And the equation expressing the straight line B is ΔT = 25X.

The range of manufacturing conditions for manufacturing the optical fiber by melt spinning the optical fiber preform is a region A surrounded by the straight line a and the vertical axis (ΔT), that is, the melting of the tip of the optical fiber preform. Part temperature (T ₀ ) and Xc from this
The difference (ΔT) from the temperature (T ₁ ) at the position m below is 50X ° C.
If it exceeds, the diameter of the fiber becomes unstable due to a rapid temperature change, and the diameter variation becomes large, and the durability of the manufacturing apparatus used for manufacturing the optical fiber deteriorates. On the other hand, the range of the manufacturing conditions is a region C surrounded by the straight line B and the horizontal axis (X), that is, the temperature (T ₀ ) of the molten portion at the tip of the optical fiber preform and the temperature (T _This is because if the difference (ΔT) from ₁ ) is less than 25 × ° C., the optical fiber preform easily melts, and the effect of shortening the neck-down shape becomes insufficient.

[0009]

EXAMPLES Examples of the spinning furnace for producing an optical fiber and the method for producing an optical fiber according to the present invention will be described in detail below. FIG. 2 shows an example of the spinning furnace of the embodiment. The spinning furnace 1 is different from the spinning furnace 1 shown in FIG.
By removing the heat insulating material 11 located below the fixed portion 5a of the heater 5 and forming the gap 17 in the lower portion of the outer frame 9, the temperature of the central portion E ₀ of the spinning furnace 1 and the position X cm below the temperature. The difference from the temperature of E ₁ is 25X ° C or more and 50X ° C or less. FIG. 3 shows the relationship between the position in the spinning furnace and the temperature. In FIG. 3, a curve is the relationship between the position and temperature in the spinning furnace 1 shown in FIG. 2, and the curve is shown in FIG. 8 in which the heat insulating material 11 located below the fixing portion 5a of the heater 5 is not removed. 3 shows the relationship between the position inside the spinning furnace 1 and the temperature. As can be seen from FIG. 3, the spinning furnace 1 shown in FIG.
Has a lower temperature below the central portion E _{0 as} compared with the spinning furnace 1 of FIG. 8 in which the heat insulating material 11 is not removed.

To manufacture an optical fiber using the spinning furnace 1 as shown in FIG. 2, the following steps are performed. First, the optical fiber preform 13 is inserted into the furnace core tube 3 and then heated at a high temperature in an atmosphere of an inert gas such as argon to be melted. Then, the optical fiber preform 13 is heated to 100 in the longitudinal direction of the optical fiber.
Optical fiber 1 by spinning at ~ 1500 m / min
Get 5. Here, when the optical fiber preform 13 is melt-spun to obtain the optical fiber 15, the temperature of the position E ₁ of the spinning furnace 1 is lower than the temperature of the central portion E ₀ by 25X ° C or more and 50X ° C or less, and thus spinning is performed. The temperature (T ₁ ) of the optical fiber 15 located at the position E ₁ of the furnace 1 is also the temperature (T ₁ ) of the molten portion 13a at the tip of the optical fiber preform 13 located at the central portion E ₀ of the spinning furnace 1.
₀ ) and 25X ° C or more and 50X ° C or less. By doing so, the neck-down shape of the optical fiber preform 13 does not become longer than the conventional one, and becomes very compact even if the spinning linear velocity becomes high at about 300 m / min or more.

The temperature (T ₁ ) of the optical fiber 15 located at the position E ₁ of the spinning furnace 1 is the temperature (T ₀₎ of the molten portion 13a at the tip of the optical fiber preform 13 located at the central portion E ₀ of the spinning furnace 1. ) Is less than 25X ° C, the optical fiber preform 13 is easily melted, and the effect of shortening the neck-down shape is insufficient. On the other hand, when it is more than 50X ° C, the temperature in the spinning furnace 1 is low. Too much, the fiber diameter becomes unstable due to a sudden temperature change, and the diameter fluctuation becomes large.
This is because there is a risk that the durability of the heat insulating material constituting the spinning furnace and the carbon parts such as the heater and the muffle may deteriorate.

Then, in order to make the optical fiber 15 thus obtained strong against lateral pressure and friction,
Further, the resin coating is formed on the outer peripheral surface of the optical fiber 15 by passing through a resin coater (not shown) provided below the spinning furnace 1 to form an optical fiber strand. Here, when the optical fiber 15 is passed through the resin coater, the optical fiber preform 1
Since the neck-down shape of No. 3 is compact, the fluctuation amount of the spinning linear velocity is small, and thus the temperature fluctuation of the surface of the optical fiber 15 when passing through the resin coater is also small. Variations in the thickness of the resin coating formed on the fiber 15 are also reduced. According to such an optical fiber manufacturing method, it is possible to prevent the neck-down shape of the optical fiber preform from becoming long even if the spinning linear velocity of the optical fiber preform is increased, so that the neck-down shape becomes long. It is possible to prevent the resulting variation in the thickness of the resin coating from increasing, and thus it is possible to obtain an optical fiber having excellent lateral pressure characteristics.

Further, in the embodiment, by removing the heat insulating material 11 located below the fixing portion 5a of the heater 5, the temperature (T ₀ ) of the molten portion 13a at the tip of the optical fiber preform 13 and the temperature Temperature at the position below Xcm (T ₁ )
Although the difference between the temperature and the temperature is set to 25X ° C or more and 50X ° C or less, the cooling pipe to which the cold water is supplied is wound around the outer periphery of the furnace core pipe 3 below the fixing portion 5a of the heater 5, and the gap 17 Has a low heat insulation effect on metals, ceramics,
The same can be done by filling a heat insulating material such as heat resistant plastic.

A specific example will be shown below. (Example) First, a spinning furnace 1 similar to that shown in FIG. 2 was prepared. In this spinning furnace 1, the heat insulating material 11 located below the fixing portion 5a of the heater 5 is removed to form a gap 17 in the lower portion of the outer frame 9, and a position E ₁ 12 cm below the central portion E _0.
Was 450 ° C. lower than the temperature of the central portion E ₀ . The optical fiber preform 13 having an outer diameter of 50 mm and a length of 60 cm
After being inserted into the core tube 3 of the spinning furnace 1 and heated at a high temperature in an argon gas atmosphere to melt, the optical fiber preform 13 is spun at a linear velocity of 100 m / m in the longitudinal direction of the optical fiber.
Min., 500 m / min, 1000 m / min, 1500 m / min.
A 25 μm single mode optical fiber 15 was obtained. Here, the optical fiber preform 13 is melt-spun to produce the optical fiber 15
To obtain the optical fiber 1 located at the position E ₁ of the spinning furnace 1.
The temperature 5 (T ₁ ) is also the temperature (T ₀ ) of the melted portion 13a at the tip of the optical fiber preform 13 located in the central portion E ₀ of the spinning furnace 1.
It was 400 ° C lower than that. Further, the obtained optical fiber 15 is inserted into a resin coater filled with a urethane acrylate UV resin provided below the spinning furnace 1 to form a resin coating on the outer peripheral surface of the optical fiber 15, and an outer diameter of 25
An optical fiber strand of 0 μm was obtained.

(Comparative Example) An optical fiber strand was obtained in the same manner as in the above Example except that the spinning furnace 1 located below the fixing portion 5a of the heater 5 and in which the heat insulating material 11 was not removed was used.

(Test Example 1) The neck-down shape of the optical fiber preform was examined in the above Examples and Comparative Examples when the spinning linear speeds were 100 m / min and 1500 m / min. The neck-down shape here was measured using a laser outer diameter measuring device. The result is shown in FIG. FIG. 4A is a graph showing the relationship between the diameter of the optical fiber preform and the position of the optical fiber preform in the spinning furnace when the spinning linear velocity is 100 m / min, and the curve is the optical fiber of the example. It is the relationship between the preform diameter and the position of the optical fiber preform in the spinning furnace, and the curve is the relationship between the optical fiber preform diameter of the comparative example and the position of the optical fiber preform in the spinning furnace. Further, in FIG. 4B, the spinning linear velocity is 1500.
It is a graph showing the relationship between the optical fiber preform diameter at m / min and the position of the optical fiber preform in the spinning furnace, and the curves are the optical fiber preform diameter of the example and the optical fiber preform in the spinning furnace. The curve is the relationship between the diameter of the optical fiber preform of the comparative example and the position of the optical fiber preform in the spinning furnace.

As is apparent from FIG. 4, the spinning linear velocity is 100 m.
At a low speed of / min, the melted portion at the tip of the optical fiber preforms of Examples and Comparative Examples did not extend much to the lower part in the spinning furnace, and the neck-down shape was short. Spinning speed is 150
At a high speed of 0 m / min, the melted portion at the tip of the optical fiber preform of the comparative example extends considerably to the lower portion and has a long neck-down shape. It can be seen that the neck-down shape is short, which is almost the same as the spinning linear speed of 100 m / min.

(Test Example 2) In each of the above Examples and Comparative Examples, one optical fiber was obtained at each spinning linear velocity.
The a / b of the cut surface at the time of cutting at 00 points was calculated by microscopic observation as shown in FIG. Reference numeral 19 in FIG.
Is the optical fiber strand, a is the thickness of the thinnest part (μm), and b is the thickness of the thickest part (μm).
m). Then, the result of examining the relationship between the spinning linear velocity (m / min) and a / b is shown in FIG. In FIG. 6, ◯ is the average value of a / b of the optical fiber strand at each spinning linear velocity of the example, and ● is the average value of a / b of the optical fiber strand at each spinning linear velocity of the comparative example. is there.

As is clear from the results shown in FIG. 6, when the spinning linear velocity is as low as 100 m / min, there is not much difference in a / b value between the optical fiber strands of the example and the comparative example, and Since the respective a / b values are also small, there is little variation in the thickness of the resin coating. Spinning line speed is 500m / min, 1000m / min,
The a / b value with the optical fiber strand of the comparative example increases as the speed increases to 1500 m / min, and the variation in the thickness of the resin coating is large. Compared with this, a of the optical fiber strand of the example It can be seen that the / b value is not so large and the variation in the thickness of the resin coating is small.

Test Example 3 From the optical fiber strands obtained at each spinning linear velocity in Examples and Comparative Examples, 1
A sample of 100 optical fiber strands of km was sampled and a tension winding test with a winding tension of 350 g was performed to examine the change in transmission loss before and after the tension winding. The result is shown in FIG. 7. Figure 7
Is a graph showing the relationship between each spinning linear velocity and loss increment, in the figure ○ is the average value of the loss increment of the optical fiber strand obtained in the example, ● ● is the light obtained in the comparative example It is the average value of the loss increment of the fiber strand.

As is clear from the results shown in FIG. 7, in the optical fiber obtained in the comparative example, the loss increment becomes considerably large as the spinning linear velocity becomes high, and the optical fiber element obtained at 1500 m / min. The line has a loss increment of about 4 times that obtained at 500 m / min, indicating that the lateral pressure characteristic is poor. On the other hand, the optical fibers obtained in the examples did not increase so much even when the spinning linear velocity became high, and the loss increment at 1500 m / min was about 1/3 of that in the comparative example, and the lateral pressure It turns out that the characteristics are excellent.

[0022]

As described above, in the method of manufacturing an optical fiber according to the first aspect of the invention, the temperature (T ₀ ) of the fused portion at the tip of the optical fiber preform and the temperature (T ₁ ) at a position X cm below it. By setting the difference (ΔT) from 25 × ° C. to 50 × ° C. inclusive, it is possible to prevent the neck-down shape of the optical fiber preform from becoming long even if the spinning linear velocity of the optical fiber preform is high. The speed fluctuation amount is small, so that the temperature fluctuation of the optical fiber surface when the optical fiber is passed through the resin coater is also small, so that the variation in the thickness of the resin coating formed on the optical fiber becomes large. Therefore, an optical fiber having excellent lateral pressure characteristics can be obtained. Further, since the spinning furnace according to claim 2 lacks the lower heat insulating material, when the optical fiber is manufactured using this spinning furnace, the temperature T ₀ of the molten portion at the tip of the optical fiber preform and The difference from the temperature T _{1 at} a position Xcm below is 2
It is possible to set the temperature to 5X ° C or more and 50X ° C or less, and it is possible to manufacture an optical fiber having excellent lateral pressure characteristics. Further, the spinning furnace according to claim 3 is the spinning furnace according to claim 2, wherein a cooling pipe to which cold water is supplied is wound around the outer periphery of the lower part of the furnace core tube in place of the lack of the heat insulating material in the lower part. As a result, the same operational effect as that of the spinning furnace according to the second aspect is achieved. The spinning furnace according to claim 4 is the spinning furnace according to claim 2, wherein the lower heat insulating material is replaced by a metal, ceramics, or the like having a lower heat insulating effect than the upper heat insulating material as the lower heat insulating material. By using at least one selected from heat-resistant plastics, the same operational effect as the spinning furnace according to claim 2 is achieved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between X (cm) and ΔT (° C.).

FIG. 2 is a schematic configuration diagram of a spinning furnace of an example.

FIG. 3 is a graph showing the relationship between the position in the spinning furnace and the temperature.

FIG. 4A is a graph showing the relationship between the optical fiber preform diameter and the position of the optical fiber preform in the spinning furnace in Examples and Comparative Examples when the spinning linear velocity is 100 m / min. (B)
6 is a graph showing the relationship between the diameter of the optical fiber preform and the position of the optical fiber preform in the spinning furnace in Examples and Comparative Examples when the spinning linear velocity is 1500 m / min.

FIG. 5 is a diagram for explaining a method of calculating a / b.

FIG. 6 is a graph showing the relationship between the spinning linear velocity (m / min) and a / b.

FIG. 7 is a graph showing the relationship between the spinning linear velocity and the loss increment.

FIG. 8 is a schematic configuration diagram showing an example of a conventional spinning furnace.

9A shows a neck-down shape of the optical fiber preform when the spinning linear velocity is low, and FIG. 9B shows a neck-down shape of the optical fiber preform when the spinning linear velocity is high.

[Explanation of symbols]

1 ... Spinning furnace, 3 ... Furnace core tube, 5 ... Heater, 9 ... Outer frame,
11 ... Insulation material, 13 ... Optical fiber base material, 13a ... Molten portion at the tip, 15 ... Optical fiber, 17 ... Gap, E _0.
... central, E ₁ · · · position, T ₀ · · · temperature, T ₁ · · · Temperature, [Delta] T
···difference.

Claims (4)

[Claims] 1. When the optical fiber preform is melt-spun to form an optical fiber, the temperature (T ₀ ) of the melted portion at the tip of the optical fiber preform and a position lower than Xcm (where X ≧ 0) Difference (ΔT) from temperature (T ₁ ) is 25X ° C or more and 50X
A method of manufacturing an optical fiber, characterized in that the temperature is below ℃. 2. A spinning furnace for producing an optical fiber, comprising a furnace core tube, a heating means surrounding the outer circumference of the furnace core tube, and a heat insulating material surrounding the furnace core tube and the heating means, and melt-spinning an optical fiber preform. In the spinning furnace for manufacturing an optical fiber, the heat insulating material at the bottom is lacking. 3. The spinning furnace for producing an optical fiber according to claim 2, wherein a cooling pipe, to which cold water is supplied, is wound around the outer periphery of the lower part of the furnace core tube instead of lacking the lower heat insulating material. A spinning furnace for producing an optical fiber. 4. The spinning furnace for producing an optical fiber according to claim 2, wherein the lower heat insulating material has a lower heat insulating effect than that of the upper heat insulating material instead of lacking the lower heat insulating material. A spinning furnace for producing an optical fiber, which is one or more kinds selected from plastics.