JPS6278126A - Production of optical fiber and apparatus therefor - Google Patents

Abstract

PURPOSE:To obtain optical fibers having little defects and causing slight deterioration in characteristic on exposure to radiation and in hydrogen atmosphere, by drawing a preform into a fiber of a constant wire diameter and heat-treating the fiber before coating with a resin. CONSTITUTION:The heated and softened tip of a preform 1 is drawn into a wire under a constant tension while moving the preform 1 in the direction of a heating and melting furnace 4 by a moving device 3 and formed into a fiber 2 of a constnat wire diameter, which is then introduced into a heat-treating furnace 10 and annealed to remove defects therefrom. The resultant fiber 2 is then introduced into a coating unit 5 and subjected to resin coating. Thereby, the fiber 2 is heat-treated before the resin coating and defects of the optical fiber 2 can be removed without causing deterioration in the synthetic resin. When the temperature on the side of the heating and melting furnace 4 is in creased and the temperature on the outlet side is decreased, the annealing effect can be further improved.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to improvements in optical fiber manufacturing methods and equipment, and more specifically to the improvement of optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more particularly, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment, and more specifically, to improve optical fiber manufacturing methods and equipment. The present invention relates to a manufacturing method and apparatus. However, optical fiber manufacturing usually includes both the preform manufacturing process and the process of drawing the obtained preform, but in this specification, it refers to drawing the preform to make an optical fiber. It shall be used only in the processes that involve.

<Conventional Technology> Optical fibers are smaller, lighter, lighter, have lower transmission loss, and are capable of high-bandwidth transmission than copper wire cables, so they are gradually being incorporated into communication lines in place of conventional copper wire cables.

However, it is known that the transmission loss of optical fibers increases when exposed to gamma rays or in a hydrogen atmosphere. Furthermore, it is known that this transmission loss is caused by defects in glass or quartz, and the fewer defects there are, the lower the transmission loss will be.

A typical defect occurring in an optical fiber is an <E' center based on oxygen vacancies, and this defect is induced by drawing the optical fiber or by exposure to radiation. When an E° center occurs, an absorption peak appears around 0.2μ, and transmission loss occurs in the wavelength range of 0.5 to 0.8μ.

On the occurrence and disappearance of E' centers in optical fibers, in the Proceedings of the National Conference of the Institute of Electronics and Communication Engineers, published by the Institute of Electronics and Communication Engineers, 1182.1183, Hinino, Hanabusa, and Sansui state that E' centers occur at high temperatures. reported that it is fixed during the wire drawing and quenching process and can be eliminated by heat treatment.

As shown in FIG. 2, the conventional optical fiber manufacturing method lowers a preform l fixed to a moving device 3 at a constant speed.
The tip of the preform 1 was heated and softened in a heating furnace 4 and drawn into a fiber 2, passed through a coating unit 5 and a capstan 6, and wound up with a winding device 7 at a constant tension. By the capstan 6 wire diameter measuring device 9, wire diameter control circuit 8 and winding device 7 in FIG.

It constitutes a means for winding the fiber 2 with a constant tension,
The wire diameter of the fiber 2 is compared with a set value in the wire diameter control circuit 8 using the output signal of the wire diameter measuring device 9, and the difference signal is sent to the capstan 6 as a control signal to control the tension applied to the fiber 2. The wire was wound to have a constant wire diameter.

(Problems to be Solved by the Invention) However, in an attempt to use the conventional optical fiber manufacturing method or apparatus shown in FIG. When the temperature is raised (for example, 200° C. or higher), there is a problem in that the synthetic resin deteriorates.

Furthermore, since the optical fibers are heat-treated at high temperatures, the optical fibers that do not contain one synthetic resin are extremely easily damaged, and the damaged optical fibers have the disadvantage of breaking even when a slight external force is applied.

The present invention has been made to eliminate the drawbacks of such optical fiber manufacturing methods, and aims to provide an optical fiber manufacturing method and apparatus that has fewer defects and exhibits less characteristic deterioration even under radiation exposure or hydrogen atmosphere. That is.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the optical fiber manufacturing method of the present invention draws the tip of the heat-softened preform with constant tension while moving the preform toward the melting and heating furnace. A method for manufacturing an optical fiber in which the fiber is formed into a fiber having a constant diameter, the fiber is coated with a resin, and then wound, the fiber being drawn to a constant diameter is heat treated before being coated with the resin. It is something.

The optical fiber manufacturing equipment also includes a preform transfer means that holds the preform and moves it in a fixed direction, a heating melting furnace disposed in the preform transfer direction, and a tip of the preform that is heated and softened by the melting heating furnace. In an optical fiber manufacturing device, the drawn fiber is connected between the melting furnace and the coating unit. It is characterized by being equipped with a heat treatment furnace.

(Function) With such a configuration, according to the optical fiber manufacturing method or apparatus of the present invention, the fiber drawn from the tip of the heated and softened preform is subjected to seven anneals in a processing furnace before being coated with resin. Since defects are removed and then resin coating is applied, there is no problem of resin deterioration, and it is possible to manufacture an optical fiber with little characteristic deterioration even when used under radiation exposure or hydrogen atmosphere.

<Example> Next, an example of the optical fiber manufacturing apparatus according to the present invention will be described, and a method for manufacturing the optical fiber will also be described.

FIG. 1 shows a schematic diagram of an optical fiber manufacturing plant according to an embodiment, in which 3 is a moving device, 4 is a melting furnace, 5 is a synthetic resin coating unit, 6 is a capstan, 7 is a winding device, and 8 is the wire diameter control circuit.

9 is a wire diameter measuring device, and IO is a heat treatment furnace.

The difference between the optical fiber manufacturing device shown in FIG. 1 and the conventional optical fiber manufacturing device shown in FIG. 2 is that the device shown in FIG. In contrast to the structure in which the fiber 2 formed by drawing is drawn directly to the synthetic resin coating unit 5, the apparatus shown in FIG. - The foot is passed through a heat treatment furnace 1O to be annealed (L) to remove defects before being introduced into the coating unit 5.

The preform l used in manufacturing an optical fiber with this apparatus had a pure silica core and a fluorine-doped cladding. The heating temperature of the heat treatment furnace 10 was set to 400° C., the length of the fiber in the heat treatment furnace was approximately 2 m, and the optical fiber obtained at a drawing speed of 30 m/sin was designated as A.

Further, optical fiber B was produced under the same conditions as above except that the heat treatment furnace IO was not used.

Then, 105R/h is added to the above two types of optical fibers A and B.
After being irradiated with γ-rays for 1 hour, we measured the loss increase at 0.851L, and found that optical fiber A had a layer thickness of 8 dB/layer, while optical fiber B had a layer thickness of 10 dB/layer, indicating that heat treatment is not necessary. It was found that there were fewer defects and less deterioration of characteristics.

The heat treatment furnace lO of the apparatus shown in Fig. 1 has no temperature gradient and is uniform.
Although the example is given for a furnace, for example, a heat treatment furnace lO
The inlet side (melting heating furnace side) is set to about 1800°C, the outlet side (coating unit 5 side) is set to about 500°C, and the heater is set so that there is a linear temperature gradient distribution from the inlet side to the outlet side in the middle. When placed in the furnace body, even greater effects can be obtained. Of course, it goes without saying that it is better to find and apply the optimum temperature gradient conditions.

Furthermore, if the distance between the heat treatment furnace 1O and the coating unit 5 is narrow, it is preferable to cool the fiber 2 by blowing cooling nitrogen there, because coating becomes easier.

The reason why the heat treatment furnace is given the above-mentioned temperature gradient is that when the annealing temperature is high, the thermal equilibrium state is quickly approached, but the number of defects in the thermal equilibrium state is large.

However, when the annealing temperature is low, the number of defects in the thermal equilibrium state is small, but it is slow to approach the thermal equilibrium state.Therefore, even if the drawing speed and the length of the fiber in the heat treatment furnace are constant, at a high temperature on the melting furnace side, This is because by creating a temperature gradient such that the coating unit side is at a low temperature, the annealing conditions can be optimized.

It is expressed as the defect density n (violet) at the position of the fiber. However, 1: the position in the heat treatment furnace. : the value of X from the melting heating furnace of the heat treatment furnace, the value of X from the coating unit of the xez heat treatment furnace value.

nQ: fiber defect density in XQ, E: activation energy for defect generation, Ed: activation energy for defect disappearance.

N: sum of densities of defects and defect precursors, T: temperature at position X of the fiber, k: Portzmann's constant, C: proportionality constant.

However, since n is included in the right-hand side of the above equation, it cannot be easily determined, but n can be expressed as a function of X and T(ri).

Therefore, T(x) such that n (!e) is minimum
If we give , then that is the optimal temperature distribution.

<Effects of the Invention> As is clear from the above description, according to the optical fiber manufacturing method or apparatus according to the present invention, it is possible to anneal an optical fiber and remove defects in the fiber without causing deterioration of the synthetic resin. I can do it.

It is possible to manufacture an optical fiber with less characteristic deterioration when exposed to radiation or under a hydrogen atmosphere.

In particular, if a temperature gradient is provided in the heat treatment furnace so that the temperature is higher on the melting furnace side and lower on the coating unit side, the 7-neel effect of the optical fiber can be made even more effective.

Further, the annealing temperature of the heat treatment furnace can be selected to be any temperature from room temperature to near the melting furnace temperature. Since the annealing time is determined by the length of the fiber in the heat treatment furnace and the drawing speed, it can be set to a desired value.

Further, although the length of the heat treatment furnace is usually about 1 to 5 m, continuous treatment is possible, so the productivity of optical fibers is also good.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical fiber manufacturing apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a conventional optical fiber manufacturing apparatus. In the drawings, l... Preform, 2... Fiber, 3... Moving device, 4... Melting heating furnace, 5... Coating unit, 6... Capstan, 7... Winding removing device, 8... wire diameter control circuit, 9... wire diameter measuring device, 10... heat treatment furnace.

Claims (3)

[Claims] (1) While moving the preform toward the melting and heating furnace, the tip of the heated and softened preform is drawn with a constant tension to form a fiber with a constant diameter, and the fiber is coated with resin and then wound into an optical fiber. A method for manufacturing an optical fiber, characterized in that the fiber drawn to a constant diameter is heat treated before being coated with a resin. (2) A preform transfer means that holds the preform and moves it in a fixed direction, a melting heating furnace arranged in the direction of transferring the preform, and a preform tip heated and softened by the melting heating furnace with a constant tension. In an optical fiber manufacturing apparatus comprising a winding means for drawing a fiber of a certain diameter and a coating unit for coating the drawn fiber with a resin, a heat treatment furnace for the drawn fiber is provided between the melting heating furnace and the coating unit. An optical fiber manufacturing device characterized by: (3) The optical fiber manufacturing apparatus according to claim (2), wherein the heat treatment furnace has a temperature gradient such that the melting furnace side is heated to a high temperature and the coating unit side is heated to a low temperature.