JP2968678B2 - Method for producing optical fiber and spinning furnace for producing optical fiber - Google Patents

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 an apparatus for manufacturing the same, and more particularly to a method for manufacturing an optical fiber in which the lateral pressure characteristics of the optical fiber are less likely to decrease even when the spinning speed of the optical fiber preform is increased. The present invention relates to a production method and a spinning furnace for producing an optical fiber.

[0002]

2. Description of the Related Art Generally, a spinning furnace as shown in FIG. 8 is used for producing an optical fiber, and reference numeral 1 in the figure denotes a spinning furnace. The spinning furnace 1 comprises a furnace core tube 3, a cylindrical heater 5 surrounding the outer periphery thereof, and an electrode 7 for supplying power to the heater 5, which are housed in a hollow cylindrical outer frame 9. The remaining voids in the outer frame 9 are filled with a heat insulating material 11 such as carbon fiber or ceramic. The heater 5 is attached to the outer frame 9 by fixing a fixing portion 5 a provided at a lower portion thereof 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 atmosphere of an inert gas such as argon to melt. Then, the optical fiber 15 was obtained by spinning at a rate of 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 to form a resin coating on the outer peripheral surface in order to make the optical fiber 15 resistant to lateral pressure and friction. It was a bare optical fiber.

[0003]

In such an optical fiber manufacturing method, it is desirable to perform high-speed melt-spinning for the purpose of improving the manufacturing efficiency and the like. 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 speed is low, and FIG. 9B shows the neck down shape of the optical fiber preform when the spinning speed is high. Symbols L ₁ and L ₂ indicate the length of the neck-down shape when the spinning line speed is low and high, respectively. However,
As described above, when the neck-down shape becomes longer, the outer diameter becomes 1
In order to manufacture an optical fiber having a constant width of 25 μm, the fluctuation amount of the spinning linear speed becomes large, and the temperature fluctuation on the surface of the optical fiber 15 when the fiber is passed through a resin coater becomes large. However, there is a disadvantage that the variation in the thickness of the resin coating becomes large, and the lateral pressure characteristics of the optical fiber deteriorate.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and prevents the neck-down shape of an optical fiber preform from becoming longer even when the spinning speed of the optical fiber preform is increased. An object of the present invention is to provide a method for producing an optical fiber and a spinning furnace for producing an optical fiber, which can improve characteristics.

[0005]

The method of manufacturing an optical fiber according to claim 1, wherein Means for Solving the Problems] is the tip of the optical fiber preform of the spinning reactor core
Heating in the tube, the tip of the optical fiber preform is inserted into the furnace tube.
The temperature (T ₀ ) at the position (E ₀ ) of the melted portion at the tip of the optical fiber preform when the neck down shape is formed by melting and the optical fiber preform is melt spun into an optical fiber. And below Xcm (where X ≧ 0)
And the difference (ΔT) between the temperature (T ₁ ) at the position (E ₁ ) in the furnace tube and the temperature (T ₁ ) is set to 25X ° C. or more and 50X ° C. or less. Further, the production of the optical fiber according to claim 2
A method for manufacturing an optical fiber according to claim 1, wherein the method comprises:
, Wherein X is 20 cm or less.
You. Further, a spinning furnace for producing an optical fiber according to claim 3 is:
A heating furnace surrounding the outer periphery of the furnace core tube, and a heat insulating material surrounding the furnace tube and the heating means; It is characterized by lack of material.
The spinning furnace for producing an optical fiber according to claim 4 is the spinning furnace for producing an optical fiber according to claim 3, in which the lower heat insulating material is replaced with the upper heat insulating material instead of lacking the lower heat insulating material. It is characterized by being at least one selected from metals, ceramics and heat-resistant plastics having a low heat insulating effect.

The present inventors have focused on the temperature of the spinning furnace in order to prevent the neck-down shape of the optical fiber preform from becoming long, and have conducted various studies and experiments. The inventors have found that lowering the temperature below the portion is effective in preventing the neck-down shape of the optical fiber preform from being lengthened, and completed the present invention.

The difference (ΔT) between the temperature (T ₀ ) of the melted portion at the tip of the optical fiber preform and the temperature (T ₁ ) below X cm (where X ≧ 0) is 25 ° C. or more and 50 ×
The range of the manufacturing condition of not more 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 (the position here is 0 cm) and an arbitrary position below this, and the vertical axis (ΔT) is The temperature (T ₀ ) of the melted portion at the tip of the fiber preform and Xc
The difference (ΔT) from the temperature (T ₁ ) at a position below m (where X ≧ 0). The equation representing the straight line A is ΔT = 50X
And the equation representing the straight line b is ΔT = 25X. In FIG.
As shown, X is preferably in the range of 20 cm or less.
No.

[0008] The range of manufacturing conditions for manufacturing an optical fiber by melt-spinning an optical fiber preform is a region A surrounded by the above-mentioned straight line a and the vertical axis (ΔT), that is, the melting of the tip of the optical fiber preform. Temperature (T ₀ ) and Xc
The difference (ΔT) from the temperature (T ₁ ) below m is 50X ° C
When the temperature exceeds the above range, the diameter of the fiber becomes unstable due to a rapid temperature change, and the fluctuation in the diameter becomes large, and the durability of a manufacturing apparatus used for manufacturing an optical fiber is reduced. 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 _{0 If} the difference (ΔT) from ₁ ) is less than 25 ° C., the optical fiber preform is likely to melt, and the effect of shortening the neck-down shape becomes insufficient.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a spinning furnace for producing an optical fiber and a method for producing an optical fiber according to the present invention will be described below in detail. FIG. 2 shows an example of the spinning furnace of the embodiment. The difference between this spinning furnace 1 and the spinning furnace 1 shown in FIG.
By removing the heat insulating material 11 located below the fixing portion 5a of the heater 5 and forming a gap 17 in the lower part of the outer frame 9, the temperature of the central portion E ₀ of the spinning furnace 1 and the position X cm below this temperature the difference between the temperature of the E ₁ is a point that was set at 50X ° C. less than 25X ° C.. FIG. 3 shows the relationship between the position in the spinning furnace and the temperature. In FIG. 3, the curve is a relationship between the position in the spinning furnace 1 and the temperature shown in FIG. 2, and the curve is shown in FIG. 8 where the heat insulating material 11 located below the fixing portion 5a of the heater 5 is not removed. 4 shows the relationship between the position in the furnace in the spinning furnace 1 and the temperature. As can be seen from FIG. 3, the spinning furnace 1 shown in FIG.
The temperature of the downward lower than the center portion E ₀ compared with spinning furnace 1 of Figure 8 that the heat insulating material 11 is not removed.

The production of an optical fiber using the spinning furnace 1 as shown in FIG. 2 involves the following steps. First, the optical fiber preform 13 is inserted into the furnace core tube 3 and then heated and melted at a high temperature in an inert gas atmosphere such as argon.
The optical fiber 1 is spun at ~ 1500 m / min.
Get 5. Here, when obtaining the optical fiber 15 by an optical fiber preform 13 was melt-spun, the temperature of the position E ₁ of the drawing furnace 1 is low 25X ° C. or higher 50X ° C. less than the temperature of the center portion E _0, spinning 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 13 a at the tip of the optical fiber preform 13 located at the center E ₀ of the spinning furnace 1.
₀ ) and lower than 25X ° C and lower than 50X ° C. In this case, even if the spinning speed is increased to about 300 m / min or more, the neck-down shape of the optical fiber preform 13 does not become longer than before, and becomes very compact.

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

In order to make the optical fiber 15 thus obtained resistant to lateral pressure and friction,
Further, a resin coating is formed on the outer peripheral surface of the optical fiber 15 by passing the resin through a resin coater (not shown) provided below the spinning furnace 1 to obtain an optical fiber. 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 speed can be small, and the temperature fluctuation of the surface of the optical fiber 15 when the fiber is passed 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 a method for manufacturing an optical fiber, even if the spinning speed of the optical fiber preform is increased, the neck-down shape of the optical fiber preform can be prevented from being lengthened. The resulting variation in thickness of the resin coating can be prevented from increasing, and thus an optical fiber having excellent lateral pressure characteristics can be obtained.

Further, in the embodiment, the temperature (T ₀ ) of the molten portion 13 a at the tip of the optical fiber preform 13 is reduced by removing the heat insulating material 11 located below the fixing portion 5 a of the heater 5. Temperature below Xcm (T ₁ )
The example described above has a difference between 25X ° C and 50X ° C. However, the cooling pipe to which the cold water is supplied is wound around the outer periphery of the furnace core tube 3 below the fixing portion 5a of the heater 5, and the gap 17 is formed. Metal, ceramics,
The same can be achieved by filling a heat insulating material such as heat-resistant plastic.

A specific example will be described below. (Example) First, a spinning furnace 1 similar to FIG. 2 was prepared. In the 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 at a lower portion in 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 . Then, an optical fiber preform 13 having an outer diameter of 50 mm and a length of 60 cm.
Is inserted into the furnace core tube 3 of the spinning furnace 1, heated and melted in an argon gas atmosphere at a high temperature, and then the optical fiber preform 13 is spun in the longitudinal direction of the optical fiber at a spinning speed of 100 m / m.
Min, 500 m / min, 1000 m / min and 1500 m / min by spinning 1000 km at a time.
A single-mode optical fiber 15 of 25 μm was obtained. Here, the optical fiber preform 13 is melt-spun to form an optical fiber 15.
When obtaining the optical fiber 1 is located in position E ₁ of the drawing furnace 1
5 (T ₁ ) is also the temperature (T ₀ ) of the melted portion 13 a at the tip of the optical fiber preform 13 located at the center E ₀ of the spinning furnace 1.
It was lower by 400 ° C. Further, the obtained optical fiber 15 is inserted into a resin coater provided below the spinning furnace 1 and filled with a urethane acrylate UV resin, to form a resin coating on the outer peripheral surface of the optical fiber 15, and to form an outer diameter 25.
An optical fiber of 0 μm was obtained.

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

(Test Example 1) The neck down shape of the optical fiber preform when the spinning linear speed was 100 m / min and 1500 m / min in the above-described example and comparative example was examined. The neck down shape here was measured using a laser outer diameter measuring device. FIG. 4 shows the results. 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 speed is 100 m / min. The curve is the relationship between the diameter of the preform and the position of the optical fiber preform in the spinning furnace, and the curve is the relation between the diameter of the preform in the spinning furnace and the position of the optical fiber preform in the spinning furnace. FIG. 4B shows that the spinning linear speed is 1500.
4 is a graph showing the relationship between the diameter of the optical fiber preform at m / min and the position of the optical fiber preform in the spinning furnace, and the curve is 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.

FIG. 4 shows that the spinning speed 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 does not extend very much to the lower part in the spinning furnace, and the neck-down shape is 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 bottom and has a long neck-down shape. It is almost the same as the case of the spinning line speed of 100 m / min, and it can be seen that the neck down shape is short.

Test Example 2 Each of the optical fibers obtained at each spinning speed in each of the above Examples and Comparative Examples was 1
The a / b of the cut surface at the time of cutting at 00 locations was calculated by microscopic observation as shown in FIG. Reference numeral 19 in FIG.
Is an optical fiber, a is the thickness (μm) of the thinnest portion, and b is the thickness (μm) of the thickest portion.
m). FIG. 6 shows the result of examining the relationship between the spinning linear speed (m / min) and a / b. In FIG. 6, ○ indicates the average value of a / b of the optical fiber at each spinning speed in Example, and ● indicates the average value of a / b of the optical fiber at each spinning speed in Comparative Example. is there.

As is apparent from the results shown in FIG. 6, when the spinning speed is as low as 100 m / min, the a / b values of the optical fiber of the embodiment and the comparative example are not so different. Since the respective a / b values are also small, variations in the thickness of the resin coating are small. Spinning speed is 500m / min, 1000m / min,
As the speed is increased to 1500 m / min, the a / b value of the optical fiber of the comparative example is increased, and the thickness of the resin coating varies greatly. 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) Each of the optical fiber strands obtained at each spinning speed in Examples and Comparative Examples was 1
A 100-km optical fiber strand was sampled at a distance of 100 km, and a tension winding test was performed at a winding tension of 350 g to examine a change in transmission loss before and after the tension winding. FIG. 7 shows the result. FIG.
Is a graph showing the relationship between each spinning linear speed and the loss increment, in which ○ is the average value of the loss increment of the optical fiber obtained in the example, and ● is the light obtained in the comparative example. This is the average value of the loss increment of the fiber strand.

As is apparent from the results shown in FIG. 7, the loss of the optical fiber obtained in the comparative example becomes considerably large as the spinning line speed increases, and the optical fiber obtained at 1500 m / min. The line has about four times the loss increment compared to that obtained at 500 m / min, indicating poor lateral pressure characteristics. On the other hand, the optical fiber obtained in the example was not so large even when the spinning speed was high, and the loss increment at 1500 m / min was about 1/3 of that of the comparative example. It turns out that the characteristics are excellent.

[0022]

As described above, the method of manufacturing an optical fiber according to the first or second aspect of the present invention provides a method for manufacturing a fiber at a tip portion of an optical fiber preform which has a temperature (T ₀ ) lower than Xcm. The difference (ΔT) from the position temperature (T ₁ ) is 25X ° C or more and 50X ° C.
By setting the following, it is possible to prevent the neck-down shape of the optical fiber preform from being lengthened even when the spinning linear speed of the optical fiber preform is increased, so that the fluctuation amount of the spinning linear speed can be small, and as a result, Since the temperature fluctuation of the surface of the optical fiber when the fiber is passed through the resin coater is also small, it is possible to prevent the variation in the thickness of the resin coating formed on the optical fiber from becoming large, and therefore, the optical fiber having excellent lateral pressure characteristics. Can be obtained. The spinning furnace according to claim 3 is
Due to the lack of the lower heat insulating material, when producing an optical fiber using this spinning furnace, the difference 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 below this temperature is calculated. The temperature can be set to 25X ° C or more and 50X ° C or less, and an optical fiber having excellent lateral pressure characteristics can be manufactured.
The spinning furnace according to claim 4 is the spinning furnace according to claim 2, in which the lower heat insulating material is replaced with the lower heat insulating material, and the lower heat insulating material has a lower heat insulating effect than the upper heat insulating material. By using one or more selected from plastics, the same operation and effect as the spinning furnace according to claim 2 can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram of a spinning furnace according to an embodiment.

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

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

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

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

FIG. 7 is a graph showing the relationship between spinning linear speed and 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 speed is low, and FIG. 9B shows a neck down shape of the optical fiber preform when the spinning speed is high.

[Explanation of symbols]

1 ... spinning furnace, 3 ... furnace core tube, 5 ... heater, 9 ... outer frame,
11: heat insulating material, 13: optical fiber preform, 13a: molten portion at the tip, 15: optical fiber, 17: gap, E _0.
..Central portion, E ₁ position, T ₀ temperature, T ₁ temperature, ΔT
···difference.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C03B 37/00-37/16

Claims (4)

(57) [Claims] 1. A core tube of a spinning furnace having a tip of an optical fiber preform.
And the tip of the optical fiber preform is melted into the furnace tube.
A temperature (T ₀ ) at the position (E ₀ ) of the melted portion at the tip of the optical fiber preform when the neck down shape is formed by melting and the optical fiber preform is melt spun into an optical fiber. And below Xcm (where X ≧ 0)
And a difference (ΔT) between a temperature (T ₁ ) at a position (E ₁ ) in the furnace tube and a temperature (T ₁ ) of 25 ° C. or more and 50 ° C. or less. 2. The method according to claim 1, wherein X is 20 cm or less.
The method for producing an optical fiber according to claim 1, wherein 3. A spinning furnace for producing an optical fiber, comprising: a furnace core tube, a heating means surrounding the outer periphery of the furnace core tube, and a heat insulating material surrounding the furnace core tube and the heating means, for melt-spinning an optical fiber preform. 2. The spinning furnace for producing an optical fiber according to claim 1, wherein a lower heat insulating material is missing . 4. The spinning furnace for producing an optical fiber according to claim 3, wherein the lower heat insulating material has a lower heat insulating effect than the upper heat insulating material in place of the lack of the lower heat insulating material. A spinning furnace for producing an optical fiber, wherein the spinning furnace is at least one member selected from the group consisting of: