JP3423221B2 - Method and apparatus for manufacturing 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 an optical fiber manufacturing method and a manufacturing apparatus for reducing bending of an optical fiber.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a conventional optical fiber manufacturing apparatus, in which reference numeral 1 is a spinning furnace. In this spinning furnace 1, an optical fiber glass base material 2 is rotatably and axially movably mounted, and a lower end of the optical fiber glass base material 2 is melt-spun in an inert gas atmosphere. is there. A cooling device 3 is provided below the spinning furnace 1. The cooling device 3 allows the bare optical fiber 4 spun in the spinning furnace 1 to pass through and cools the bare optical fiber 4 with a cooling gas. A coating device 5 is provided below the cooling device 3. This coating device 5 is
A synthetic resin is applied to the outer peripheral surface of the bare optical fiber 4. Then, in the spinning furnace 1, the bare optical fiber 4 melt-spun in an inert gas atmosphere is immediately cooled by the cooling device 3.
And then cooled to about 50 ° C. and then sent to the coating device 5 to apply the synthetic resin to the outer peripheral surface and then cured.
It is an optical fiber strand.

In the production of such an optical fiber element wire, in the spinning furnace 1, the bare optical fiber 4 immediately after being spun is accompanied by a layer of an inert gas from the spinning furnace 1 around it, It runs toward the cooling device 3 while cooling itself. At this time, when the traveling speed of the bare optical fiber 4 is slow (for example, 100 m / min), the temperature decreases to 1300 ° C. or less near the softening temperature in the spinning furnace or directly under the spinning furnace,
It is further cooled while it is uniformly wrapped in an inert gas.
However, when the running speed of the bare optical fiber 4 is high (for example, 1000 m / min or more), the temperature of the bare optical fiber 4 when it goes out of the spinning furnace 1 is higher than 1300 ° C. In such a high temperature state, contact with the outside air causes the layer of inert gas with high thermal conductivity formed around the bare optical fiber 4 in the spinning furnace to be destroyed, resulting in a circle of the bare optical fiber 4. When the uniform temperature distribution in the circumferential direction collapses, the optical fiber bare wire 4 may be bent.

The reason why the above-mentioned bending occurs is that when the bare optical fiber has a low viscosity at 1300 ° C. or higher, it is exposed to an uneven temperature distribution in the circumferential direction of the bare optical fiber, causing a cooling difference, that is, a stress difference. This is because, when receiving the stress, it cannot bend against the stress difference and bends.

The bending of the optical fiber as described above is determined by measuring the radius of curvature of the optical fiber. Normally, there is no problem if the radius of curvature is about 10 m, but if the radius of curvature is 2 m or less, there will be a practical problem, and it will be difficult to connect the optical fiber to another optical fiber, and the connection loss will increase. In particular, when a multi-core tape core wire using such an optical fiber is collectively connected, misalignment occurs, and connection loss becomes a serious problem.

Although a method of sealing the space between the spinning furnace and the cooling device to prevent contact with the outside air by some method, SiO ₂ sublimated and vaporized in the spinning furnace is used in the spinning furnace. In some cases, it solidified at the bottom and came into contact with the running bare optical fiber to cause a decrease in strength.

[0007]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an inert gas layer having a high thermal conductivity, which is formed around a bare optical fiber in a spinning furnace, with a bare optical fiber.
It is to prevent the bare optical fiber from being bent so as not to be broken by coming into contact with the outside air before being cooled to 300 ° C. or less.

Further, Si0 sublimated and vaporized in the spinning furnace
₂ is to prevent the strength of the optical fiber from decreasing by preventing it from solidifying in the lower part of the spinning furnace and coming into contact with the running bare optical fiber.

[0009]

The object is to provide an enclosing tube between the spinning furnace and the cooling device, and increase the spinning speed in the gap between the upper end of the enclosing tube and the lower end of the spinning furnace. The gap between the lower end of the enclosure and the upper end of the cooling device is adjusted to 1 mm to 100 mm so as to be small, and is set to 1 mm to 5 mm regardless of the spinning speed, or the spinning furnace and the cooling device are separated. An optical fiber bare wire enclosure is provided therebetween, and a gap is provided between the enclosure and the lower end of the spinning furnace and the upper end of the cooling device, and the enclosure and the lower end of the spinning furnace and the A gap is provided between the upper end of the cooling device, and the gap between the upper end of the enclosure and the lower end of the spinning furnace is adjustable between 1 mm and 100 mm according to the spinning speed. And the gap between the cooling device and the upper end of the cooling device is 1 mm to 5 m. It is solved by it.

[0010]

According to the optical fiber manufacturing method of the present invention,
By making the space between the spinning furnace and the cooling device non-sealed, the SiO ₂ sublimated and vaporized in the spinning furnace is solidified in the lower part of the spinning furnace and directly under the spinning furnace to contact the running bare optical fiber. Can be prevented. 13 more bare optical fibers
When the bare optical fiber has a low viscosity at 1300 ° C. or higher by not destroying the inert gas layer formed in the spinning furnace around the bare optical fiber until cooled to 00 ° C. or lower. , Exposed to a non-uniform temperature distribution in the circumferential direction of the bare optical fiber, receiving a cooling difference, that is, a stress difference,
It is possible to prevent bending without being able to withstand the stress difference.

In the optical fiber manufacturing apparatus according to the second aspect of the present invention, an enclosing tube for the bare optical fiber is provided between the spinning furnace and the cooling device, and the upper gap and the lower gap of the enclosing tube are set. , Keep the layer of inert gas (eg, helium gas) with high thermal conductivity formed around the bare optical fiber in the spinning furnace as completely as possible, so that the bare optical fiber is circumferentially uniform It can be cooled to a high temperature, and it is possible to prevent SiO ₂ sublimated and vaporized in the spinning furnace from solidifying below the spinning furnace and directly below the spinning furnace.

In the optical fiber manufacturing apparatus according to the fourth aspect, a clean air unit is provided between the spinning furnace and the cooling device, and clean air is blown to the bare optical fiber in a direction perpendicular to the running direction. As a result, the temperature of the bare optical fiber is made uniform to a desired temperature (1300 ° C.) or lower before the inert gas layer with high thermal conductivity formed around the bare optical fiber in the spinning furnace is destroyed. Can be cooled.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
FIG. 1 shows an example of the optical fiber manufacturing apparatus of the present invention. In the figure, reference numeral 1 is a spinning furnace. This spinning furnace 1
The optical fiber glass base material 2 is rotatably and axially movably attached to the inside thereof, and the lower end of the optical fiber glass base material 2 is melt-spun. A cooling device 3 is provided below the spinning furnace 1. This cooling device 3
Is for passing the bare optical fiber 4 spun in the spinning furnace 1 and cooling the bare optical fiber 4 with a cooling gas. A coating device 5 is provided below the cooling device 3. This coating device 5 applies a synthetic resin to the outer peripheral surface of the bare optical fiber 4.

An envelope 6 for the bare optical fiber 4 is provided between the spinning furnace 1 and the cooling device 3.

The spinning furnace 1 has a built-in heater 7 for heating the tip of the optical fiber preform 2 obtained by the VAD method or the like, and He gas is provided between the optical fiber preform 2 and the heater 7. A gas flow path 1a for flowing an inert gas such as is formed. The cooling device 3 is provided with a cooling path 3a for passing the bare optical fiber 4 spun in the spinning furnace 1 and cooling the bare optical fiber 4 with a cooling gas.

The enclosure 6 has a passage hole formed in the center thereof for allowing the bare optical fiber 4 to pass therethrough. The diameter of this passage hole should be set in consideration of the inner diameter of the lower shutter (not shown) attached to the lower portion of the spinning furnace 1, and is equal to or larger than the inner diameter of the lower shutter. To do. Further, the gap between the upper end of the surrounding cylinder 6 and the lower end of the spinning furnace 1 is adjusted so as to become smaller as the spinning speed becomes faster, and is adjusted to approximately 100 mm to 1 mm. Enclosure 6
The gap between the lower end of the cooling device and the upper end of the cooling device 3 is about 1 to 5 mm, preferably about 1 mm regardless of the spinning speed. As described above, the degree of opening of the enclosing tube 6 is such that the diameter of the passage hole and the upper gap between the upper end of the enclosing tube 6 and the lower end of the spinning furnace 1, and the lower end of the lower end of the enclosing tube 6 and the upper end of the cooling device 3. It is defined by the gap.

In order to adjust the degree of opening defined in this way according to manufacturing conditions such as spinning speed, several types of enclosures are prepared in advance, and will be described below each time the manufacturing lot changes. As described above, a suitable enclosure is set in the optical fiber manufacturing apparatus. For example, spinning speed 500m
When the spinning speed is 1500 m / min, the upper gap is 85 mm or less, and when the spinning speed is 1500 m / min, the upper gap is 35 mm or less. When the above relationship when the spinning speed is 2000 m / min or less is expressed by an equation, the upper gap (mm) ≦ −0.05x + 11
0 (x indicates a spinning speed (m / min)), and the upper gap is reduced as the spinning speed increases. On the other hand, the lower gap is set to about 1 to 5 mm, preferably about 1 mm regardless of the spinning speed.

By doing so, the solidified S
Prevention of bending of the optical fiber because it is possible to simultaneously achieve the prevention of adhesion of iO ₂ to the bare optical fiber, efficient cooling of the bare optical fiber, and nondestruction of the inert gas layer around the bare optical fiber. And the prevention of strength reduction can be realized.

The bend of the optical fiber is determined by measuring the radius of curvature. According to the present invention, an optical fiber having a maximum radius of curvature of about 5 times that of the prior art and a radius of curvature of about 10 m can be obtained. The strength of the optical fiber is determined by measuring the number of breaks in a proof test (strain rate 0.8%, strip length 10,000 km). According to the present invention, the number of breaks is at least about 1/10 of that of the prior art, and an optical fiber having a break of 2-3 times can be obtained.

The shape of the enclosure may be an ordinary cylindrical shape, but it is preferable to prevent the temperature rise of the enclosure by making a double cylinder into which the circulating water for cooling flows in the outer cylinder. good. Further, the shape of the surrounding cylinder is not limited to the cylindrical shape described above, and may be a square shape. The material of the enclosure 6 may be a metal such as aluminum, iron, stainless steel, brass, copper, a ceramic such as silicon nitride, or a polymer material such as Teflon.

FIG. 2 shows another example of the optical fiber manufacturing apparatus of the present invention. 1 is different from FIG. 1 in that instead of the enclosure 6, a clean air unit 8 is provided between the spinning furnace 1 and the cooling device 3 so that clean air can be blown to the bare optical fiber in a direction perpendicular to the running direction. That is what I did. The wind speed of the clean air blown to the bare optical fiber can be adjusted within a range of 0.1 m / s or less. By doing so, solidified SiO
₍₂ ) Adhesion prevention to bare optical fiber, efficient cooling of bare optical fiber and non-destruction of the inert gas layer around bare optical fiber can be achieved at the same time. It is possible to prevent reduction in strength.

A method of manufacturing an optical fiber according to claim 1 or 2 , which is a superordinate concept of the optical fiber manufacturing apparatus shown in FIGS. 1 and 2, will be described below. The temperature range of 1300 ° C. or lower described in claim 1 or 2 is calculated from the temperature characteristic of viscosity of the optical fiber, and is an important technical element of the optical fiber manufacturing method of the present invention. When the bare optical fiber has a low viscosity above 1300 ° C, it is exposed to a non-uniform temperature distribution in the circumferential direction of the bare optical fiber, receives a cooling difference, that is, a stress difference, and cannot withstand the stress difference. In order to prevent the phenomenon of bending without being generated, the state in which the bare optical fiber is cooled to 1300 ° C. or lower and the inert gas layer is not yet destroyed,
It needs to be created on the pass line from the lower end of the spinning furnace 1 to the inside of the cooling device 3. To this end, there are three methods: efficient cooling of bare optical fiber to 1300 ° C. or lower, non-destruction of an inert gas layer around the bare optical fiber, and prevention of solidified SiO ₂ from adhering to the bare optical fiber. It is necessary to achieve both of them at the same time, and the manufacturing apparatus according to claims 3 and 4 is effective as means for realizing this.

From the above, the technical idea of the method for producing an optical fiber according to the first or second aspect is that the SiO ₂ sublimated and vaporized in the spinning furnace is maintained in the lower portion of the spinning furnace and the spinning by maintaining the non-sealing property. Even if it solidifies right under the furnace, it can escape to the outside because it is not hermetically sealed, so it is possible to prevent contact with the bare optical fiber while it is running, and prevent the strength of the optical fiber from decreasing. 1300 ℃ bare optical fiber
When the bare optical fiber has a low viscosity at 1300 ° C. or higher, it is possible to prevent the optical fiber layer formed in the spinning furnace from being destroyed around the bare optical fiber until it is cooled to the following temperature. It is possible to prevent a bare fiber from being exposed to a non-uniform temperature distribution in the circumferential direction and receiving a cooling difference, that is, a stress difference, and bending without being able to withstand the stress difference.

[0024]

EXAMPLES The present invention will be described in detail below with reference to examples. FIG. 3 shows an enlarged view from the lower end of the spinning furnace 1 to the cooling device 3. In the first embodiment, the optical fiber preform 2 having a diameter of 81 mm is spun in a spinning furnace 1 in a He gas atmosphere to a bare optical fiber 4 having a diameter of 125 μm (d1) and a spinning speed of 1
00m / min, 300m / min, 500m / min, 1000m
/ Min, 1500 m / min, and 2000 m / min. The inner diameter (d2) of the enclosure 6 at this time is 50 m
m, and the outer diameter was 60 mm. Further, the gap (l1) between the lower end of the spinning furnace 1 and the upper end of the enclosure 6 is 10 mm, and the enclosure 6 is
The gap (12) between the lower end of the cooling device and the upper end of the cooling device 3 was 1 mm. The solid line in FIG. 4 shows the measurement result of the radius of curvature of the optical fiber strand manufactured under such conditions.

In the second embodiment, by the method shown in FIG.
The preform 2 for an optical fiber having a diameter of 81 mm was formed into a bare optical fiber 4 having a diameter of 125 μm in a spinning furnace 1 in a He gas atmosphere.
It was drawn at a spinning speed of 1500 m / min. The wind speed of the clean air from the clean air unit 8 at this time is 0.02 m / s, 0.
05m / s, 0.1m / s, 0.2m / s, 0.3m /
Seven different types were manufactured so as to obtain s, 0.4 m / s, and 0.5 m / s. The measurement result of the radius of curvature of the optical fiber strand manufactured under such conditions is shown by a solid line in FIG. As can be seen from FIG. 5, when the wind velocity of clean air on the pass line is 0.1 m / s or less, an optical fiber element wire having a radius of curvature of about 10 m can be obtained.

In this comparative example, a diameter of 8 is obtained by the method shown in FIG.
In a spinning furnace 1 in a He gas atmosphere, a 1 mm optical fiber base material 2 is spun on an optical fiber bare wire 4 having a diameter of 125 μm at a spinning speed of 100 m / min, 300 m / min, 500 m / min, 100
Drawing was performed at 6 types of 0 m / min, 1500 m / min, and 2000 m / min. The result of measurement of the radius of curvature of the optical fiber strand manufactured under such conditions is shown by the broken line in FIG.

[0027]

As described above, the effect of the present invention is that the bending of the optical fiber and the decrease in strength can be prevented even when the spinning speed is increased. This makes it possible to keep the splice loss small even when a large number of tape core wires are collectively connected.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a method and an apparatus for manufacturing an optical fiber according to claims 1 and 2 of the present invention.

FIG. 2 is a sectional view of an example (Embodiment 2) of the optical fiber manufacturing method and manufacturing apparatus according to claims 1 and 3 of the present invention.

FIG. 3 is a sectional view of an example (Example 1) of the method and apparatus for manufacturing an optical fiber according to claims 1 and 2 of the present invention.

FIG. 4 is a table showing measurement results of radius of curvature of Example 1 and Comparative Example.

FIG. 5 is a chart showing a measurement result of a radius of curvature of Example 2.

FIG. 6 is a cross-sectional view of a conventional optical fiber manufacturing method and manufacturing apparatus (comparative example).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Spinning furnace, 1a ... Gas flow path, 2 ... Optical fiber glass base material, 3 ... Cooling device, 3a ... Cooling path, 4 ... Optical fiber bare wire, 5 ... Coating device, 6 ... Enclosure, 7 ... Heater , 8 ... Clean air unit

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Claims (2)

(57) [Claims] 1. A glass preform for optical fibers is melt-spun in an inert gas atmosphere in a spinning furnace, the spun optical fiber is guided to a cooling device to be cooled, and then the cooled optical fiber is cooled. In an optical fiber manufacturing method in which a coating is provided on an outer peripheral surface, an enclosing tube is provided between the spinning furnace and the cooling device, and a gap between an upper end of the enclosing tube and a lower end of the spinning furnace is increased to increase a spinning speed. The gap between the lower end of the enclosure and the upper end of the cooling device is adjusted to 1 mm to 100 mm so that the gap becomes 1 mm to 5 mm regardless of the spinning speed, and the optical fiber is cooled to 1300 ° C. or lower. Until done
A method for producing an optical fiber, characterized in that the optical fiber is cooled so as not to destroy an inert gas layer formed in the spinning furnace around the optical fiber. 2. A spinning furnace for melt-spinning an optical fiber glass preform in an inert gas atmosphere, a cooling device for passing the optical fiber spun in the spinning furnace to cool the optical fiber, and these spinning devices. An optical fiber enclosure is provided between the furnace and the cooling device, and the enclosure is provided with a gap between the enclosure and the lower end of the spinning furnace and the upper end of the cooling device. The gap between the upper end of the cylinder and the lower end of the spinning furnace is 1 m depending on the spinning speed.
The optical fiber manufacturing apparatus is adjustable between m and 100 mm, and the gap between the lower end of the enclosure and the upper end of the cooling device is 1 mm to 5 mm.