JPS6026058B2 - Optical fiber coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION '1' Field of Application of the Invention The present invention relates to a method of coating an optical fiber with a polymer in a uniform film thickness.

■Prior Art Conventionally, low-loss optical fibers have been mainly produced by gas-phase chemical reaction methods.

The optical fiber preform (1 in FIG. 1) manufactured by this gas phase chemical reaction method contains many air bubbles and has many scratches on its surface. Therefore, the mechanical strength of the fiber obtained by drawing such a preform is low, and the outer peripheral surface of the optical fiber is coated with a polymer after or simultaneously with drawing for reinforcement and subsequent protection. The present inventor also studied these conventional methods.
First, as shown in FIG. 1, a method of coating the wire with a polymer at the same time as drawing the wire was investigated. In FIG. 1, a preform 1 is fed at a constant speed into a furnace core tube 2 heated by a heating source 3, the lower end of the heated and melted preform is pulled out and attached to a drum 6, and an optical fiber 12 is connected to a motor controller 8. While being wound up by the driven drum 6,
FIG. 2 is a schematic diagram of an apparatus that detects the wire diameter d of the optical fiber with a detector 4, measures it with a wire diameter measuring device 5, and then coats the outer peripheral surface of the optical fiber with a polymer 10 through a polymer coating tank 9 and a heating device 11. . If there is a change in the diameter of the optical fiber, the output of the wire diameter measurement bag counterfeit 5 is input to the control circuit 7, and the output signal of the control circuit is fed back to the motor controller 8 to change the rotation speed of the drum 6 to measure the wire diameter. control. However, as a result of conducting various experiments using this device, it was found that there were the following problems. That is, when there is a fluctuation in the preform melting temperature due to fluctuations in the thickness of the optical fiber preform or disturbances, fluctuations in the thickness of the optical fiber occur. Then, the rotational speed of the drum 6 is changed by the wire diameter control mechanism, and the winding speed is changed to perform wire wrapping control. This wire diameter control keeps the wire diameter of the optical fiber constant, but due to changes in the winding speed, the optical fiber coating tank 9
The passing speed of the coating changed, and the coating thickness varied. Also,
As the coating continues, the coating agent 10 is consumed and its liquid level gradually decreases, so the pressure to push out the coating agent 10 from the nozzle at the bottom of the coating tank 9 decreases, and the coating film thickness gradually decreases. became. In FIG. 2, the line flea d of the optical fiber thread 12 drawn by the apparatus shown in FIG. 1 is detected by the detector 4,
As a result of measurement by the measuring device 5, the coated optical fiber 1
3 shows the results of measuring the line 3 with the detector 4' and the measuring device 5'. In this process, a preform with an outer diameter of 8 skins is sent to a heating source with 7 rails/skin, the drawing temperature is 1950o○, the bran diameter of the optical fiber is set to 130 mounds, and the polymer agent is polyfluorinated in dimethylformamide solution. A solution containing pini-1'dene is used. As shown in FIG. 2, the wire diameter of the fiber wire is 130±lAm due to the wire diameter regulation, but the wire diameter of the coated optical fiber varies. If the thickness of the coating is non-uniform in this way, the reinforcing effect of the coating will be reduced and the transmission characteristics will also be adversely affected. '31 OBJECTS OF THE INVENTION It is an object of the present invention to solve the problems of the above-mentioned conventional methods and to uniformly coat the outer circumferential surface of an optical fiber with a polymer.

'41 General description of the invention The present invention provides that the outlet part of a polymer coating tank is formed of an elastic material, and that the inner diameter of the outlet part can be freely changed by applying external pressure to the mouth part and deforming it. Using a polymer-coated tank that can be This is a coating method that obtains an optical fiber with a uniform coating thickness by changing the inner diameter of the fiber.

'51 Example Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 3 shows a cross-sectional view of a polymer coating tank according to the present invention.
This polymer coating tank consists of an inner cylinder 14 and an outer cylinder 15, and the upper parts of the inner cylinder 14 and the outer cylinder 15 are closed by a wall 16.
At the bottom, there is a wall 17 around the inner cylinder 14 with a gap. A material with high speed, in this example, a rubber film 1 is filled in this gap.
8 and let gas flow in from the gas inlet 19. Gas flows out through small holes 20. At this time, if the inflowing gas flow rate is larger than the outflowing gas flow rate, the inner cylinder 14 and the outer cylinder 1
The gas pressure in the space between 5 increases, and the rubber membrane 18 deforms.
As shown in FIG. 3b, the inner diameter of the outlet of the polymer coating tank changes. If the amount of gas inflow is increased, the internal pressure will increase and the inner diameter of the outlet will become smaller. If the amount of gas inflow is reduced, the internal pressure will decrease and the inner diameter of the outlet will increase. FIG. 4 shows a schematic diagram of a method of coating an optical fiber using the above polymer coating tank. When the optical fiber 12 has a bran or flea fluctuation, the wire diameter d is detected by the detector 4, the output of the wire flea measuring device 5 is input to the control circuit 7, and this output signal is fed back to the motor controller 8 to control the drum 6. By changing the number of revolutions of the wire, the winding speed is changed and the wire diameter is controlled so that the desired wire diameter 4 is obtained. At this time, the optical fiber coating tank 2
Since the speed at which the particles pass through 1 changes, variations occur in the coating film thickness. Therefore, in the present invention, the wire diameter of the coated optical fiber 13 is detected by a detector 4' and measured by a wire diameter measuring device 5'. The line detection amount Vd' of this coated optical fiber
is input to the gas flow rate control circuit 22. At this time, a signal Vr corresponding to the diameter of the coated optical fiber is input to the gas flow rate control circuit 22. Gas flow control circuit 22
Vd' and Vr are compared and amplified, and if Vr≠Vd,
Vm is generated at the output of the gas flow rate control circuit 22. The output signal Vm of the gas flow rate control circuit 22 is supplied to the gas valve drive motor 2.
4 and drives the gas valve 25. By changing the gas flow rate flowing into the polymer coating tank 21, the pressure applied to the rubber membrane 18 is controlled, and by changing the inner diameter of the exit part (nozzle) of the polymer coating tank 21, the thickness of the coating film is made uniform. to control. In the case of Vr>Vd', the amount of gas sulfur is reduced, the pressure inside the polymer coating tank is lowered, and the inner diameter of the outlet part is increased, and if Vr<Vd'
In this case, the pressure inside the polymer coating tank is increased by increasing the amount of gas inflow, and the inner diameter of the outlet portion is reduced. In this example, a preform with an outer diameter of 8 ribs is used.
Feed it to the heating source at the speed of a rib/kite, and the drawing temperature was 195 pi.
Then, the wire thickness of the optical fiber was set to 130 mm, and a solution of polyvinylidene fluoride dissolved in dimethylformamide solution was used as the polymer coating material 10, and the coating thickness was set to 10 mm, that is, the coating thickness was set to 10 mm. The diameter of the optical fiber was set to 150 mm. FIG. 5 shows the measurement results of the wire curvature d of the optical fiber strand and the measurement results of the wire curvature ′ of the optical fiber coated according to the present invention. As is clear from the figure, according to the present invention, it became possible to uniformly coat the film with a coating thickness loAm. FIG. 6a shows an embodiment of a cross-sectional view of a polymer coating tank that facilitates the attachment of a rubber membrane.

This polymer coating tank consists of a tapered inner cylinder 26 and a tapered outer cylinder 27. The upper parts of the inner cylinder 26 and the outer cylinder 27 are closed by a wall 28, and there is a gap between the lower part of the inner cylinder 26 and the outer cylinder 27. Turn the pipe-shaped rubber membrane 29 over as shown in FIG.
, rings 30 and 31 having the same taper as the outer cylinder 27 are driven in, and a rubber membrane 29 is fixed. [6] Summary As explained above, according to the present invention, fluctuations in the coating film thickness caused by changes in the passage speed of the optical fiber through the polymer coating tank due to line density control, and decreases in the liquid level due to the use of polymer agent. The variation in coating film thickness caused by the decrease in the amount of polymer extruded due to By controlling the coating thickness by changing the coating thickness, it has become possible to obtain an optical fiber coated with a uniform thickness.

As a result, there is a great effect on improving the quality of the optical fiber.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional coating method, FIG. 2 is a diagram showing line variations of an optical fiber coated by a conventional coating method, and FIG. 3 is a diagram showing a polymer coating tank according to the present invention. Figure 4 is a schematic diagram showing the coating method according to the present invention, Figure 5 is a diagram showing the line variation of the optical fiber coated according to the present invention, and Figure 6 is a diagram showing the implementation of a polymer coating tank that facilitates fixation of the rubber film. It is a figure which shows an example. Figure 3: Many diagrams; Figure 4: Many diagrams; Figure 4: Many diagrams;

Claims (1)

[Claims] 1. Putting an optical fiber into a coating tank filled with polymer,
In the method of coating the outer peripheral surface of an optical fiber with a polymer by pulling out the optical fiber from an outlet portion formed in the coating tank, the outlet portion is formed of an elastic material, and the fiber is drawn out from the outlet portion formed in the coating tank. A method for coating an optical fiber, comprising: providing a space; and controlling the inner diameter of the outlet by deforming the outlet by gas pressure applied to the space. 2. A method for coating an optical fiber according to claim 1, characterized in that the gas pressure applied to the space is controlled in accordance with the coating density of the fiber pulled out from the coating tank. 3. The method for coating an optical fiber according to claim 1, wherein the coating tank has a space formed by a double cylindrical tube. 4. The method for coating an optical fiber according to claim 3, wherein the outlet portion is formed by turning over a pipe-shaped rubber membrane and fixing it in the coating tank. 5. The method for coating an optical fiber according to claim 3, wherein the coating tank is configured in a tapered shape.