JPH05246738A - Production of coated optical fiber - Google Patents

Abstract

PURPOSE:To produce a coated optical fiber while fixing the coating diameter without increasing the fluctuation of the outer diameter of the optical fiber. CONSTITUTION:An optical fiber preform 1 is heated and drawn from the lower end and made into an optical fiber 2 which is coated with a resin to produce a coated optical fiber 3. In this case, the temp. of the optical fiber 2 is controlled in an optical fiber cooling cylinder 6 by using gaseous helium to adjust the coating diameter while regulating the concn. of the gaseous helium in the cylinder 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of adjusting a coating diameter when a resin is coated on an optical fiber drawn from an optical fiber preform.

[0002]

2. Description of the Related Art An optical fiber core wire is manufactured by applying a resin coating to an optical fiber obtained by drawing a heat-melted optical fiber preform immediately after drawing and immediately after drawing. It is normal. This coating functions to protect the strength of the optical fiber made of glass and to protect the transmission characteristics against external force. The coating diameter (coating thickness) is designed so that this function is optimal, and it is important to control this diameter in manufacturing the optical fiber core wire. On the other hand, the optical fiber needs to be drawn at a high speed for cost reduction. At this time, the coating diameter is affected by the temperature of the optical fiber glass, and it is known that the coating diameter becomes smaller as the optical fiber becomes hot with high-speed drawing. In order to avoid this, for example, JP-A-55-1047
As disclosed in Japanese Patent Laid-Open No. 0-202, there is known a method in which the temperature of an optical fiber to be coated is cooled using a low-temperature gas and the temperature of the optical fiber is controlled by the gas flow rate to adjust the coating diameter. ..

[0003]

However, in the above method, when the flow rate of the helium gas is increased in order to keep the coating diameter constant, the vibration of the optical fiber becomes large, which causes a slight change in the drawing conditions. However, there has been a problem that the fluctuation of the outer diameter of the optical fiber becomes large.

[0004]

SUMMARY OF THE INVENTION The present invention provides a method for manufacturing an optical fiber core wire which solves the above problems, in which an optical fiber preform is heated, and an optical fiber drawn from the lower end of the optical fiber core is made of resin. When manufacturing an optical fiber core wire by applying a coating, the temperature of the optical fiber is controlled by using helium gas in the optical fiber cooling cylinder, and a method for manufacturing an optical fiber core wire in which the coating diameter is adjusted, the optical fiber It is characterized in that the concentration of helium gas in the cooling cylinder is adjusted.

[0005]

The present invention pays attention to the phenomenon that the heat transfer coefficient of the cooling gas containing helium depends on the helium concentration, the heat transfer coefficient increases as the helium concentration increases, and the heat transfer coefficient decreases as the helium concentration decreases. However, this phenomenon is utilized for cooling the optical fiber. That is, as mentioned above,
By adjusting the helium gas concentration in the optical fiber cooling tube, the temperature of the optical fiber is adjusted while keeping the cooling gas flow rate constant, and the coating diameter is controlled without increasing the fluctuation of the optical fiber outer diameter. You can

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is an explanatory view of a manufacturing apparatus used in an embodiment of a method for manufacturing an optical fiber core wire according to the present invention, and FIG. 2 is a perspective view of a cooling cylinder used in the manufacturing apparatus. In the figure, 1 is an optical fiber base material, 2 is an optical fiber, 3 is an optical fiber core wire, 4 is a heating furnace, 5 is an optical fiber outer diameter measuring instrument, 6 is a cooling tube, 7 is a coating die, and 8 is a UV lamp. , 9
Is a coating outer diameter measuring instrument. As shown in FIG. 2, the cooling cylinder 6 is provided with a helium gas inlet 11 at its lower end and a gas outlet 13 whose upper end can be adjusted with a shutter 12 at its upper end. Reference numeral 14 is a lever for adjusting the opening of the shutter, and 15 is an oximeter used for calculating the helium concentration. When the opening degree of the shutter 12 is increased, the amount of invasion of outside air increases, the helium concentration decreases, and the cooling efficiency also decreases. Further, when the opening degree of the shutter 12 is reduced, the amount of outside air entering decreases, the helium concentration increases, and the cooling efficiency also increases. In this apparatus, the coating diameter is measured by a laser coating outer diameter measuring device 9, and this is hooded back to the opening degree of the shutter 12 of the cooling cylinder 6. That is,
When the coating diameter is small, the shutter opening is reduced to increase the helium concentration and the temperature of the optical fiber is lowered.When the coating diameter is large, the shutter opening is increased to reduce the helium concentration. Increase fiber temperature. The relationship between the helium concentration in the cooling cylinder 6 and the optical fiber temperature and the relationship between the shutter opening (diameter of the opening) and the helium concentration are shown in FIGS. 3 and 4. Using the above device, a drawing speed of 40
An optical fiber having an outer diameter of 125 μm was obtained at 0 m / min, and this was coated with an ultraviolet curable resin to manufacture an optical fiber core wire having a coating diameter of 250 μm. Helium gas was passed at 5 l / min to cool the optical fiber. In practice, the optical fiber outer diameter is controlled to 125 μm, so that the drawing speed is 380 to
It was necessary to vary within the range of 420 m / min. The result is that the outer diameter of the optical fiber is 125 μm ± 0.3 μm,
The coating diameter could be controlled to 250 μm ± 3 μm.
Further, the optical fiber hardly oscillated during cooling. Next, as a comparative example, an optical fiber core wire was manufactured using the apparatus shown in FIG. In this apparatus, the coating diameter was measured by a laser coating outer diameter measuring device 9, and the result was fed back to the flow rate of the helium gas used for cooling. That is, when the coating diameter is small, the flow rate is increased. The drawing conditions were the same as in the above example. As a result, it was possible to control the coating diameter to 250 μm ± 3 μm by varying the drawing speed in the range of 380 to 420 m / min. However, on the high speed side, the optical fiber shakes due to helium gas, and the outer diameter of the optical fiber is 125 μm ± 1.0.
.mu.m, which is a large variation compared with the above-mentioned example.

[0007]

As described above, according to the present invention, when an optical fiber preform is heated and an optical fiber drawn from the lower end thereof is coated with a resin to produce an optical fiber core wire, In the manufacturing method of the optical fiber core wire, in which the temperature of the optical fiber is controlled by using helium gas in the optical fiber cooling cylinder, and the coating diameter is adjusted, in order to adjust the concentration of helium gas in the optical fiber cooling cylinder, the optical fiber Without increasing the fluctuation of the outer diameter of the optical fiber due to the fluctuation of
There is an excellent effect that the coating diameter can be kept constant.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a manufacturing apparatus used in an embodiment of a method for manufacturing an optical fiber according to the present invention.

FIG. 2 is a perspective view of a cooling cylinder used in the manufacturing apparatus.

FIG. 3 is a diagram showing a relationship between a helium concentration in a cooling cylinder and an optical fiber temperature.

FIG. 4 is a diagram showing a relationship between a shutter opening degree of a cooling cylinder and helium concentration.

FIG. 5 is an explanatory diagram of a conventional optical fiber core wire manufacturing apparatus used in a comparative example.

[Explanation of symbols]

 1 Optical Fiber Base Material 2 Optical Fiber 3 Optical Fiber Core 4 Heating Furnace 5 Optical Fiber Outer Diameter Measuring Instrument 6 Cooling Tube 7 Coating Die 8 UV Lamp 9 Coating Outer Diameter Measuring Instrument 11 Helium Gas Inlet 12 Shutter 13 Outlet 14 Lever 15 Oxygen meter

Claims (1)

[Claims] 1. When manufacturing an optical fiber core wire by heating an optical fiber preform and applying a resin coating to the optical fiber drawn from the lower end thereof, the temperature of the optical fiber is kept in an optical fiber cooling tube. Control with helium gas,
In the manufacturing method of the optical fiber core wire for adjusting the coating diameter,
A method for manufacturing an optical fiber core wire, which comprises adjusting the concentration of helium gas in an optical fiber cooling cylinder.