JPH0692661A - Apparatus for producing jacket tube for optical fiber - Google Patents

Abstract

PURPOSE:To provide an apparatus for producing a high-quality jacket tube free from contamination and crystal and useful for the production of an optical fiber having low transmission loss and high core diameter flexibility. CONSTITUTION:This production apparatus is provided with a holding means to hold a mold 2 and/or an electric furnace 1 in horizontal or vertical posture, a means to retreat the electric furnace 1 from the circumference of the mold 2 after preheating the mold 2, a means 3 for pouring molten glass 4 into a vertically held preheated mold 2 through a pouring port 2A placed immediately above the mold and a means for tilting the mold 2 from the vertical state B to the horizontal state D by rotating the mold with a rotating means 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for manufacturing an optical fiber jacket tube, and more particularly to an optical fiber for a multi-component glass used for jacket drawing or jacket drawing of a base material of an optical fiber for controlling a core diameter. The present invention relates to an apparatus for manufacturing a fiber jacket tube.

[0002]

2. Description of the Related Art As a manufacturing apparatus capable of controlling the core diameter of an optical fiber, it has a rod-in-tube method or a core-clad structure in which a core base material is coated with a jacket tube having the same composition as that of a clad and is drawn. A jacket stretching method in which a base material is coated with a jacket tube and then stretched (Japanese Patent Application Laid-Open No. HEI 4)
No. 31333) and the jacket wire drawing method have been applied.

Further, as a jacket tube manufacturing apparatus applied to the above method, the raw material is mainly melted in a crucible like a commercially available oxide glass tube, and the glass melt is lowered from a hole in the bottom of the crucible. A hollow glass tube is obtained by using a die provided on the central axis of the crucible while allowing the glass tube to flow out.

On the other hand, a multi-component glass characterized by a low melting point,
In particular, as a manufacturing device for fibers of fluoride glass,
A method has been used in which a molten glass raw material is poured into a hollow mold to form a glass rod by making a hole in the center of the glass rod to form a pipe.

[0005]

By the way, one of the loss factors of an optical fiber is a scattering loss, which is mainly due to microcrystals which are easily formed in the optical fiber.
In particular, in the rod-in-tube method in which the core base material is directly coated with a cladding tube to form a fiber, the scratches and dust on the surface of the core base material or on the inner surface of one of the jacket tubes remain at the core-clad interface and scatter. It becomes a factor.
In addition, such scratches and dust serve as crystal nuclei to grow crystals by heat treatment during drawing and drawing, thereby increasing the loss value.

Furthermore, even when a jacket tube is coated on a base material having a core / clad structure, the optical output of the single-mode optical fiber spreads to several times the core diameter, and the scratches, dust, and the like have loss values. It becomes a factor of increase.

Therefore, as a means for removing these scratches and dust, a flame polishing method has been used in which oxide glass, particularly quartz glass, is washed with hydrofluoric acid and then heated to near the melting point using an oxyhydrogen flame. And by such a process, 0.2
Scratches and dust can be removed by the time the dB / km and loss thresholds are reached. However, in the case of fluoride glass, which is expected to have a low loss exceeding that of the quartz system, when the glass is heated by using the same flame polishing method as the above-mentioned quartz glass system, the glass is likely to crystallize, and particularly such a crystallized on the glass surface. Therefore, there is a problem that the above-mentioned flame polishing method cannot be applied.

As another means, there is a method of etching using an aqueous solution of zirconium oxychloride / hydrochloric acid, but this does not lead to complete removal of scratches, but rather tends to increase the loss value.

Therefore, as an apparatus for producing a jacket tube in which the inner wall is not damaged, a glass melt is poured into a cylindrical hollow mold, and the mold is rotated at high speed to produce a hollow cylindrical pipe by centrifugal force. Rotational casting method (DC Tranet. Al, Electr
on. Lett. vol. 18, P.I. 59, (198
According to 2)), a jacket pipe having a relatively smooth inner wall has been manufactured.

However, in the process using this apparatus, in order to inject the glass melt in a state in which the preheated mold is tilted and taken out in an electric furnace set upright, the first melt melt is injected. Will adhere to a part of the inner wall of the mold, solidify, and be reheated by the subsequent melt injection. Therefore, this reheating causes the glass adhering to a part of the inner wall of the mold to crystallize, and there will be crystals that affect a part of the jacket tube produced for that purpose, so that a crystal-free material cannot be obtained over the entire tube. There was a drawback.

Further, since fluoride glass easily reacts with moisture in the air to generate an OH group which causes absorption loss, a rotational glass is kept in an inert gas atmosphere in a glove box (closed vessel). A casting device is installed to inject the glass melt and rotate the mold.

However, in the case of this example, since the mold is rotated at a high speed, the dust generated from the driving unit enters the mold through the melt injection port of the mold and contaminates the inner wall of the jacket tube. Then, there is a defect that such a contaminant becomes a crystal generation nucleus and crystals are generated by heating during jacket stretching and jacket drawing to increase the scattering loss value.

Furthermore, since the mold containing the glass melt is rotated at a high speed in the rotation casting device, even if an attempt is made to produce a pipe having a small inner diameter by containing a large amount of the glass melt, the mold melts. There is a drawback that a jacket tube having an inner diameter smaller than that of the injection port cannot be manufactured because the glass melt flows out of the liquid injection port and is scattered.

An object of the present invention is to solve the above-mentioned drawbacks and to obtain a high-quality jacket tube which is free from contamination and crystals, which is involved in the manufacture of an optical fiber having a low loss and capable of freely controlling the core diameter. Is to provide a manufacturing apparatus of.

[0015]

In order to achieve the above object, the present invention uses a centrifugal force by injecting a glass melt into a cylindrical mold and rotating the mold while keeping it preheated. In an apparatus for manufacturing an optical fiber jacket tube capable of forming a hollow glass jacket tube, holding means for holding the mold and / or an electric furnace for preheating the mold horizontally or vertically, and the electric furnace for holding the mold. While holding the retreating means for retreating from around the mold after preheating and the mold after retreating the electric furnace,
Injection means for injecting the glass melt from an injection port directly above the mouth of the mold is narrowed, rotating means for rotating the mold in which the glass melt is injected, and the vertical means while rotating the mold. And a tilting means for tilting from a state to the horizontal state.

Further, in a preferred form of the present invention, in addition to the above-mentioned means, the mold is characterized in that the injection port is closed by a lid member after the glass melt is injected.

[0017]

According to the present invention, the mold and / or the electric furnace are preheated by the holding means in a horizontal or vertical state, and then the electric furnace is retracted from around the mold by the retracting means. With the heated mold kept vertical, the glass melt is injected directly above the injection port. Then, after closing the injection port of the mold after the injection, preferably by directly closing the lid with the lid, while rotating the mold by the rotating means, tilt it horizontally by the tilting means and rotate the glass melt around the mold by centrifugal force. It is possible to obtain a jacket tube which is evenly dispersed on the wall and has a smooth inner and outer surface and is free of dust and crystals.

[0018]

Embodiments of the present invention will be described in detail and specifically below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. here,
1 is an electric furnace for preheating, 2 is a crucible 3 to a glass melt 4
, 5 is a lid that can seal the melt injection port 2A of the mold 2, and 6 is a mold that holds the mold 2 rotatably,
The motor itself is also a motor for driving the mold rotation that can be tilted up and down together with the mold 2. The electric furnace 1 is configured to be separable in the radial direction, for example, in order to allow the mold 2 to move in the direction indicated by the arrow A in the figure, while the mold 2 is also described later. In the case of this example, the jacket tube 7 formed by molding is formed so as to be vertically separable into three parts.

In the jacket tube manufacturing apparatus thus constructed, first, as shown on the right side of FIG. 1, the electric furnace 1 and the mold 2 are laid down substantially horizontally to preheat the mold 2. Then, if preheated to a predetermined temperature, the electric furnace 1 is separated so as not to hinder the raising operation shown by the arrow A of the mold 2, and then the preheated mold 2 is separated into the glass melt 4 Up to the injection position (B).
Then, the glass melt 4 kept in a molten state in the crucible 3 is injected from the melt injection port 2A of the mold 2 as shown in the figure, and then the injection port 2A is closed by the lid 5 and the motor 6 is used. While rotating at high speed, the closed mold 2 is tilted to the horizontal position shown in (D) as shown by arrow C. Even at this position (D), the mold 6 is continuously rotated at a high speed by the motor 6 around its axis, and the glass melt 4 is evenly diffused toward the inner surface of the mold by its centrifugal force, thereby forming a hollow jacket. The tube 7 can be formed. Therefore, after this, after cooling, the mold may be divided and the solidified jacket tube may be taken out.

An example of manufacturing a jacket tube made of fluoride glass for forming a multi-component optical fiber using the jacket tube manufacturing apparatus will be described below.

Production Experimental Example 1 Composition was 47.5% ZrF ₄ -23.5% BaF ₂ -2.
_{5% LaF 3 -2% YF 3} -4.5% AlF 3 -20%
A total amount of 98 g of fluoride was weighed so as to be NaF (mol fraction%), and this was put in a gold crucible 3 together with 20 g of NH ₄ F.HF, and 400 ° C. in an argon gas atmosphere.
1.5 hours at 850 ° C after heating and fluorination
After being held for a period of time to be melted, the temperature was lowered to 700 ° C. and kept. Next, with respect to the apparatus shown in FIG. 1 housed in the glove box, after the inside of the box was sufficiently replaced with nitrogen gas, the brass cylindrical hollow mold 2 heated to 200 ° C. in the electric furnace 1 was electrically operated. The furnace 1 was opened and it was made to stand upright in the state shown in (B). And the injection port 2A on the upper part of this mold 2
Then, the glass melt 4 is injected at the above temperature, the melt injection port 2A of the mold 2 is immediately closed and sealed by the lid 5, and the mold 2 is laid horizontally while rotating it at 2000 rpm by the mold rotation motor 6. After being kept for 3 minutes, it was gradually cooled to room temperature.

Thus, the outer diameter is 15 mmφ, the inner diameter is 7 mmφ,
A cylindrical jacket tube 7 of fluoride glass having a length of 140 mm and a bottom at the bottom was obtained, and another jacket tube was manufactured in the same manner.

The whole of the fluoride jacket tube was observed in detail with a microscope. No scratches, dust, etc. were observed on the inner wall, no crystals were found in the glass, and especially the inner wall of the tube was smooth. It was

Furthermore, apart from the above, the core composition is 4
9% ZrF ₄ -25% BaF ₂ -3.5% LaF ₃ -2
% YF ₃ -2.5% AlF ₃ -18% LiF (mol fraction%), clad composition 47.5% ZrF ₄ -23.5%
BaF ₂ -2.5% LaF ₃ -2% YF ₃ -4.5% A
lF ₃ Suction the preform outer diameter 7mmφ having a core-clad structure consisting of -20% NaF (molar fraction%)
It was produced by the casting method (see Japanese Patent Laid-Open No. 63-11535). The surface of this base material was polished, further etched in a zirconium oxychloride / hydrochloric acid aqueous solution and sufficiently dried, and then inserted into the cylindrical fluoride glass tube (jacket tube) described above. Then, while the jacket tube was decompressed using a vacuum pump, it was zone-heated from the outside to be softened, and while stretching the base material and the jacket tube while changing the stretching speed, the core diameter was stretched to be constant (above, See JP-A-4-31333). The outer shape of the base material stretched in a tapered shape is 6.8 mm.
It was polished to a constant level, etched with a zirconium oxychloride / hydrochloric acid aqueous solution, and sufficiently dried. This base material was inserted into the other jacket tube described above, the outside of this jacket tube was covered with a Teflon FEP pipe, and the jacket was drawn by zone heating while depressurizing the inside of the tube.

Thus, the length is 1 km, the outer diameter is 125 μm,
With a core diameter of 10.3 mm and a relative refractive index difference of 0.61%,
A single mode optical fiber with a cutoff of 2.2 μm was obtained. As a result of observing the cross section of this optical fiber with a microscope, no crystal formation or disorder was observed at the jacket interface and it was smooth. The transmission loss characteristic of this optical fiber is shown in FIG.
As shown in this figure, the minimum loss value is 1.5 dB / km at a wavelength of 2.55 μm, and by using the jacket tube obtained in this example, a low loss single tube can be obtained regardless of two jacket tubes. A mode optical fiber could be manufactured.

FIG. 3 shows a second embodiment according to the present invention.
In this example, preheating can be performed by the electric furnace 1 at this position while holding the mold 2 in the upright state shown in (B).
Therefore, after the mold 2 was preheated by the electric furnace 1 so as to surround the mold 2 at the position (B), the electric furnace 1 was moved and retracted from the position (B) as shown by an arrow A'in this figure, and was collapsed. It can be in a state. In the case of this example, the mold driving motor 6 and the mold 2 rotatably held by the motor 6 are used.
It suffices that both are movable from the position (B) to the position (D) in the direction of arrow C while being rotated, and it is not necessary to move in the direction of arrow A as shown in FIG.

Using the jacket tube manufacturing apparatus constructed as described above, the glass is placed in the mold 2 which is kept upright by using the gold crucible 3 prepared by the same procedure as described in the manufacturing experiment example 1 above. Although the melt 4 was injected, in this case, the preheating of the mold 2 was performed by keeping the electric furnace 1 at the position (B). The subsequent procedure was carried out according to Production Experimental Example 1.

The jacket tube 7 thus obtained had the same shape and dimensions as those in the above-mentioned Production Experimental Example 1, and the entire tube was observed with a microscope, but no scratches, dust or other crystals were observed on the inner wall. A jacket tube equivalent to that of Experimental Example 1 could be manufactured. Using this jacket tube, an optical fiber was manufactured by the same method as in Experimental Example 1 and the transmission loss characteristics were measured, but it was the same as in FIG.

FIG. 4 shows a third embodiment according to the present invention.
In this example, the electric furnace 1 which is kept upright around the mold 2 at the position (B) is movable in the horizontal direction.
8 is a moving table having the moving rail 8A, 9 is a support rod for vertically supporting the electric furnace 1, 10 is a fixing screw for fixing the supporting rod 9 to the moving rail 8A, and the electric furnace 1 is a mold. 2 is moved from the position after preheating (B) to the position shown in the figure as shown by the arrow E, but in order to prevent it from interfering with the mold 2, the electric furnace 1 itself is moved along the longitudinal direction. It is configured to be divided into two open parts. The rest of the configuration is the same as in the above-described embodiments, so the description thereof is omitted.

A manufacturing experiment was carried out using the jacket tube manufacturing apparatus thus configured. In the case of this example, the preheating of the mold 2 by the electric furnace 1 at the position (B) is the same as in the case of the experimental example carried out for the second embodiment.
Further, the transmission loss characteristic of the optical fiber manufactured by using the obtained jacket tube was measured, and the same result as shown in FIG. 2 was obtained.

FIG. 5 shows a fourth embodiment according to the present invention.
In this example, the electric furnace 1 is movable from a position (B) in which the mold 2 is held in the upright state along the support rod 9 in a direct upward direction as shown by an arrow F. Support rod 9
It is a fixing screw for fixing to. Note that the other basic configurations are the same as those of the embodiments described above.

Regarding the manufacturing procedure by the manufacturing apparatus of the jacket tube thus constructed, after preheating the mold 2, the injection of the glass melt 4 from the crucible 3 pulling up the electric furnace 1 in the direction of the arrow F is not hindered. Other than the above, it is the same as described above, and the characteristics of the jacket tube manufactured as an experiment using the manufacturing apparatus according to this example, and the characteristics of the optical fiber manufactured using the jacket tube, It was possible to maintain the same results as those obtained in the above-mentioned manufacturing experiment example 1.

Other Manufacturing Experiment Examples A total of 100 g of raw materials having the same composition as in the production of the jacket tube of Manufacturing Experiment Example 1 was weighed and held in the metal crucible 3 together with 20 g of NH ₄ F.HF, and the same as in Experiment Example 1. Melted Subsequent casting operations were also performed following Experimental Example 1,
A jacket tube having an inner diameter of 5 mmφ was obtained. Further, the inner diameter of the tube manufactured by the above procedure was 3 mmφ, with the total amount of raw materials having the same composition being 102 g.

[0035]

As described above, according to the present invention, holding means for holding the mold and / or the electric furnace for preheating the mold horizontally or vertically, and the electric furnace for preheating the mold. After that, the retracting means for retracting from around the mold and the mold after the electric furnace is retracted are kept vertical, and the glass melt is injected from the injection port directly above where the mouth of the mold is narrowed. Injecting means, a rotating means for rotating the mold into which the glass melt has been injected, and a tilting means for tilting the mold from the vertical state to the horizontal state while rotating the mold are used. When pouring into the mold, the melt did not come into contact with a part of the inner wall of the mold, and the melt was filled in order from the bottom, and a high-quality jacket tube with suppressed crystal formation over the entire jacket tube was obtained. . Further, according to the present invention, a good quality jacket tube can be provided without being contaminated in the tube due to dust or scratches, which can contribute to the production of a long optical fiber with low loss.

Furthermore, by controlling the amount of the glass melt, it is possible to manufacture a jacket tube whose inner diameter can be freely set by this apparatus.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of a jacket pipe manufacturing apparatus according to a first embodiment of the present invention together with its operation.

FIG. 2 is a characteristic curve diagram showing transmission loss of a fluoride single mode optical fiber by a jacket tube manufactured by using the first embodiment.

FIG. 3 is a diagram showing the configuration of a jacket pipe manufacturing apparatus according to a second embodiment of the present invention together with its operation.

FIG. 4 is a diagram showing the configuration of a jacket pipe manufacturing apparatus according to a third embodiment of the present invention together with its operation.

FIG. 5 is a diagram showing the construction of a jacket pipe manufacturing apparatus according to a fourth embodiment of the present invention together with its operation.

[Explanation of symbols]

 1 Electric Furnace 2 Mold 2A Injection Port 3 Crucible 4 Glass Melt 5 Lid 6 Motor (for Mold Rotation) Motor 7 Jacket Tube 8 Moving Stand 9 Support Rod 10 Fixing Screw

Claims (2)

[Claims] 1. An optical fiber jacket tube capable of forming a hollow glass jacket tube by centrifugal force by pouring a glass melt into a cylindrical mold and rotating the mold while keeping the mold preheated. In the manufacturing apparatus of, the holding means for holding the mold and / or the electric furnace for preheating the mold horizontally or vertically, and the retreating means for retracting the electric furnace from around the mold after preheating the mold, An injection means for injecting the glass melt from an injection port directly above where the mouth of the mold is narrowed while keeping the mold vertical after the electric furnace is retracted, and the glass melt was injected. An optical fiber jacket tube, comprising: rotating means for rotating the mold; and tilting means for tilting the mold from the vertical state to the horizontal state while rotating the mold. Forming apparatus. 2. The apparatus for manufacturing an optical fiber jacket tube according to claim 1, wherein the casting port is closed by a lid member after the casting of the glass melt.