JP2596837B2 - Manufacturing method and manufacturing apparatus for aluminum coated optical fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for manufacturing an aluminum-coated optical fiber in which a glass optical fiber is coated with aluminum on its outer periphery.

(Background and Problems of the Invention) An aluminum-coated optical fiber in which both a core and a clad layer are made of glass such as silica glass and coated with aluminum directly above aluminum has excellent heat resistance, and hydrogen is a glass optical fiber. Since these materials can be prevented from diffusing into the inside, and have no translucency, and have excellent static fatigue characteristics, their use in applications utilizing these characteristics is increasing.

The coating of the aluminum on the glass optical fiber is performed in the same process as the drawing of the glass optical fiber.For example, the molten aluminum is guided into the molten aluminum through an entrance die of the glass optical fiber immediately after drawing from the preform member, and the molten aluminum is drawn into the glass. This is done by coagulating around the optical fiber and drawing it through an exit die. Part of the aluminum layer solidified around the glass optical fiber is redissolved by the heat of the molten aluminum while the fiber moves through the molten aluminum and reaches the exit die. If the balance is not achieved, a so-called one-sided coating occurs, as shown in FIG. 3, in which the aluminum coating 5 is formed only on a part of the periphery of the glass optical fiber 3 instead of the entire peripheral surface.

At the start of the work of drawing the glass optical fiber and coating with aluminum, so-called tapping work, it is normal for one-sided coating to occur, and after increasing the drawing speed of the optical fiber from the low speed at the time of tapping work to the speed at the time of steady operation. After a while, solidification and remelting are balanced, and an aluminum-coated optical fiber having good appearance in which aluminum is coated on the entire circumference of the glass optical fiber can be obtained. When this state is reached, winding of the product is started.

Conventionally, winding was started after visually confirming that the state of the single-sided coating had been eliminated and that an aluminum coating covering the entire circumference of the glass optical fiber had been obtained.
The outer diameter of the aluminum-coated optical fiber is extremely thin, about 170 to 1200 μm, and it travels at a relatively high speed of about 30 to 200 m / min. It is extremely difficult to visually determine whether or not the aluminum coating is formed on the entire circumference of the fiber, and the judgment is liable to be erroneous. Even after entering the stable operation state in which a good appearance aluminum coating covering the entire circumference of the glass optical fiber is obtained, one-sided coating may not occur due to fluctuations in conditions for any reason, such as a rise in the temperature of the molten aluminum. In such a case, relying on visual monitoring of the one-sided coating not only requires a large amount of labor, but also has a problem in terms of quality assurance.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method and an apparatus for manufacturing an aluminum-coated optical fiber that can easily and reliably detect the presence or absence of a one-sided coating during the manufacturing process of the aluminum-coated optical fiber.

(Constitution of the Invention) The production method of the present invention relates to a method for producing an aluminum-coated optical fiber in which a glass optical fiber is introduced into molten aluminum below immediately after drawing and the aluminum is coated around the glass optical fiber. It is characterized by detecting the presence or absence of leakage light from the aluminum-coated fiber immediately after being drawn downward, the manufacturing apparatus of the present invention is provided with a drawing furnace for drawing glass optical fiber downward, and provided therebelow. In an aluminum-coated optical fiber manufacturing device comprising a molten aluminum coating device and a take-off device provided further below,
A light-detecting optical fiber and a light-detecting optical fiber in which the light-entering tip is positioned just below the exit of the molten aluminum-coated device for pulling out the aluminum-coated optical fiber so as to face the drawn aluminum-coated optical fiber. And a photodetector connected to the other end of the photodetector.

(Operation) Since the present invention is configured as described above, if the aluminum-coated optical fiber drawn downward from the molten aluminum coating device has a single-sided coat, that is, a portion not coated with aluminum, the optical fiber is pulled out from the molten aluminum coating device. Leakage light from the aluminum-coated fiber immediately after it enters the light-receiving tip of the optical fiber for light detection, is detected by the photodetector, and the presence or absence of one-sided coating can be detected during the manufacturing process of the aluminum-coated optical fiber. .

(Example) If this is described in detail with reference to the drawings, FIG. 1 is an explanatory view for explaining an example of a production method and a production apparatus of the present invention, 1 is a preform base material of a silica glass optical fiber, 2 is a drawing electric furnace. The quartz glass optical fiber 3 is drawn downward from the tip of the preform heated to about 2200 ° C. by the electric furnace 2 and drawn. The drawn quartz glass optical fiber 3 passes through the inlet die 43 of the molten aluminum coating device 4 provided below the electric furnace 2 while cooling naturally, and the molten aluminum 42 melted in the melting crucible 41. Will be introduced. The temperature of the quartz glass optical fiber entering the entrance die 43 is usually about 40 to 100 ° C., and the molten aluminum 42 solidifies around the introduced quartz glass optical fiber 3. A part of the solidified layer is redissolved by the heat of the molten aluminum while the optical fiber reaches the exit die 44. However, the aluminum coated optical fiber 6 having an aluminum coating layer solidified and adhered around the silica glass optical fiber is used as the exit die. Pulled down from 44. The drawn aluminum coated optical fiber 6 is picked up by a pulling device 7 provided below the molten aluminum coating device, and is wound on a winding reel 9 via a dancer roll 8. Reference numeral 11 denotes a light detecting optical fiber, and a light incident end portion 12 of the aluminum coated optical fiber 6 drawn out of the exit diamond 44 at the exit side of the exit die 44 of the molten aluminum coating apparatus 4, preferably directly below the exit die. The photodetector 13 is connected to the other end of the optical fiber 11 for photodetection. A light detection unit 10 comprising such a light detection optical fiber 11, its light incident tip 12 and a light detector 13.
3 is provided (only one set is illustrated in FIG. 1), and the light-entering front end of each unit is provided so as to surround the aluminum-coated optical fiber 6 drawn out from the exit die 44. Any leakage light from any part on the peripheral surface can be detected.

It is desirable that a light-shielding hood be attached to the light-receiving end portion 12 of the optical detection optical fiber 11 such that light other than light leaking from the aluminum-coated optical fiber in a single-side coated state is prevented from entering as much as possible. Further, it is preferable to increase the light input efficiency by using a lens. FIG. 2 shows a vertical cross-sectional view of such a light incident tip. In the figure, 11 is a light detection optical fiber cord, 101 is a ferrule for gripping the tip 100 of the core wire, 102 is a tip case, which is integrally connected by the light detection optical fiber cord 11 and a mold part 104. ing. 105 is a condenser lens. A hood 106 is screwed to the flange surface 103 of the case 102 with a screw 108, and a mounting flange 107 is provided at the tip of the hood 106.

The optical fiber 11 for light detection may be a single-core optical fiber or a multiple-core optical fiber, but the core diameter is 250 to
A single fiber with a large diameter of m is preferred.

As the photodetector 13, a pin photodiode, an avalanche photodiode, a germanium photodiode, a silicon blue cell, or the like is used. As will be described later, the leakage of light from the aluminum-coated optical fiber 6 drawn out from the exit die 44 of the molten aluminum-coating device 4 by the photodetector 13 indicates that the aluminum-coated optical fiber is partially covered with aluminum. Indicates that there is an uncoated portion, that is, there is a one-sided coat. The photodetector 13 includes one or more photodetectors of the photodetection unit provided around the aluminum-coated optical fiber 6 drawn out from the exit die 44.
When all of 13 no longer detect the leakage light from the aluminum-coated optical fiber 6, an alarm is issued or a control signal is issued to start an automatic control mechanism that starts winding (at the start of operation), or a photodetector. When any of 13 detects leakage light from the aluminum-coated optical fiber 6, an alarm is issued and recorded on the recorder (during normal operation).
A signal processing circuit or a control circuit for processing the photodetection signal of the photodetector 13 can also be connected. The manufacturing method of the present invention can be applied not only to the case where the glass optical fiber is drawn from the preform base material by an electric furnace but also to the case where the glass optical fiber is drawn by a crucible method.

The present invention relates to a method in which, when an aluminum-coated optical fiber drawn downward from a molten aluminum coating device has a single-sided coating, that is, a portion not coated with aluminum, the aluminum-coated optical fiber immediately after being drawn from the molten aluminum coating device is used. It is based on what the inventors of the present invention have found that leaked light can be observed. The reason why the leakage light is observed is considered as follows. For example, since the temperature when drawing a silica glass optical fiber from a preform preform is a high temperature of about 2200 ° C., the tip of the preform in the electric furnace and the glass optical fiber near the tip are in a red-hot state. The emitted red light propagates through the core and cladding layers of the drawn glass optical fiber. Since the distance from the lower end of the electric furnace to the outlet of the molten aluminum coating device is usually a short distance of 3 m or less, immediately after being pulled out from the outlet of the molten aluminum coating device, particularly immediately below the molten aluminum coating device, the glass optical fiber It is considered that the leakage of the core propagation light and the leakage of the cladding layer propagation light may occur. When the outer periphery of the glass optical fiber is coated with aluminum, of course, light is not leaked from the optical fiber because it is blocked by the aluminum coating, but a part of the periphery of the glass optical fiber is coated with aluminum. It is considered that there is a missing part, and the leaked light leaks from this part and is observed. Therefore, as described above, the light incident end of the optical fiber for light detection is provided on the exit side of the molten aluminum coating apparatus, preferably immediately below the exit, so as to face the aluminum coated optical fiber to be drawn out.
If the aluminum-coated optical fiber has a single-sided coating and there is a portion that is not coated with aluminum, light leaking from the portion that is not coated with aluminum enters the light-receiving end of the optical fiber for light detection. Then, the presence or absence of a one-sided coating can be detected during the manufacturing process of the aluminum-coated optical fiber by the detection by the photodetector.

(Effects of the Invention) As described above, according to the manufacturing method and the manufacturing apparatus of the present invention, the presence or absence of a one-sided coating can be easily and reliably detected during the manufacturing process of manufacturing an aluminum-coated optical fiber. Therefore, at the start of the production of an aluminum-coated optical fiber, that is, at the time of tapping work, it is accurately detected whether or not the state of one-side coating is continuing and whether or not the entire circumference of the glass optical fiber is coated with the aluminum coating. This makes it possible to accurately determine when to start winding the product, and also to automatically start winding. Further, when a one-sided coat occurs for some reason after entering the steady operation state, it is possible to reliably detect the occurrence of the one-sided coat and to issue a warning to take measures to eliminate the one-sided coat. Further, by recording the occurrence of a one-sided coat on a recorder, the presence or absence of a one-sided coat on a product and the place where the one-sided coat is located can be easily known, and the benefit in quality control is great.

[Brief description of the drawings]

FIG. 1 is an explanatory view for explaining a manufacturing method and a manufacturing apparatus of the present invention, FIG. 2 is a longitudinal sectional view of an example of a light incident tip portion of an optical fiber for light detection in the present invention, and FIG. It is a cross-sectional view of the optical fiber shown. (Explanation of symbols) 1: Preform base material, 2: Drawing electric furnace, 3: Glass optical fiber drawn, 4 : Molten aluminum coating device, 41: Aluminum melting crucible, 42: Molten aluminum coating, 6: Aluminum coating Optical fiber, 7: take-up device, 8: dancer roll, 9: take-up reel, 10 : light detection unit, 11: optical fiber for light detection, 12:
Light incident tip, 13: Photodetector, 100: Optical fiber core end, 1
01: Ferrule, 105: Condensing lens, 106: Hood.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Tanaka 4-3-3 Ikejiri, Itami-shi, Hyogo Pref.

Claims (2)

(57) [Claims] In a method of manufacturing an aluminum-coated optical fiber for guiding a glass optical fiber into a molten aluminum below immediately after drawing and coating aluminum around the glass optical fiber, the glass optical fiber immediately after being drawn downward from the molten aluminum is provided. A method for producing an aluminum-coated optical fiber, comprising detecting the presence or absence of light leaked from the aluminum-coated fiber. 2. An aluminum coated optical fiber manufacturing apparatus comprising: a drawing furnace for drawing a glass optical fiber downward; a molten aluminum coating apparatus provided below the furnace; and a drawing apparatus provided further below the drawn furnace. Immediately below the outlet of the molten aluminum coating device that pulls the optical fiber downward, a light detection optical fiber whose light incident tip is positioned so as to face the drawn aluminum coated optical fiber, and a light detection optical fiber. An apparatus for manufacturing an aluminum-coated optical fiber, comprising: a photodetector connected to the other end.