JPH0585781A - Production of carbon coated optical fiber - Google Patents

Abstract

PURPOSE:To produce a carbon coated optical fiber having a uniform film thickness and excellent hydrogen resistance within a wide range of spinning rate from low rate to high rate. CONSTITUTION:A naked optical fiber 1 is allowed to run in a carbon coating reaction tube 4, where gaseous starting materials are brought into a reaction to form a carbon coating film on the surface of the optical fiber 1 by a thermochemical vapor growth method. At this time, relative change in thickness of the carbon coating film is measured and the position of the reaction tube 4 is varied in the longitudinal directions of the optical fiber 1 in accordance with the measured value to control conditions in film formation.

Description

Detailed Description of the Invention

[0001]

This invention relates to hydrogen resistance in a wide range of spinning speed from low speed to high speed by spinning while monitoring the relative change in the film thickness of the carbon coating formed on the surface of an optical fiber. The present invention relates to a method for producing a carbon-coated core wire capable of coating a carbon coat having an excellent uniform thickness.

[0002]

2. Description of the Related Art Conventionally, a method for producing a carbon coated core wire utilizes the residual heat of an optical fiber bare wire melted in a spinning furnace to guide the bare optical fiber to a carbon coated reaction tube, where the bare optical fiber is used. A carbon gas is formed by reacting the raw material gas on the surface of the wire by a thermochemical vapor deposition reaction, a carbon coated core wire is made, laser light is irradiated to this, and the transmittance of the laser light is measured. There is a method of feeding back the raw material supply system based on the measured value to change the concentration and flow rate of the supply raw material gas to adjust the thickness of the carbon coating. Also, heat is applied using a heating furnace to decompose the raw material gas, a carbon coating is formed on the surface of the bare optical fiber, a carbon coated core wire is made, and similarly the transmittance of the laser light is measured. There is a method of adjusting the film thickness of the carbon coating by changing the temperature of the heating furnace based on the above. There is also a method of using these two methods in combination. On the other hand, in the spinning of bare optical fibers, the outer diameter of the base material of an optical fiber is not always constant in the longitudinal direction, so the rate of insertion of the base material into the spinning furnace is constant, and the spinning speed is varied to change the fiber diameter. A method of keeping the outer diameter constant is adopted. The rate of change of spinning speed at this time is about ± 10%.

Therefore, in these methods, when the spinning speed changes, the arrival time of the bare optical fiber to the carbon-coated reaction tube changes, so the rate of temperature decrease on the bare optical fiber surface varies depending on the spinning speed. The temperature of the surface of the bare optical fiber that comes into contact with the raw material gas in the carbon-coated reaction tube changes. In the thermal chemical vapor deposition method, the surface temperature of the bare optical fiber when the source gas reacts is important, and in the above methods, the change in temperature of the bare optical fiber causes a nonuniform carbon film thickness. Cause. The hydrogen resistance of the carbon coating formed on the surface of the bare optical fiber largely changes depending on this film thickness. Further, in these methods, there is a delay of several seconds to several tens of seconds until the temperature of the bare optical fiber surface changes when reacting with the raw material gas after feedback is applied. It has a drawback that it cannot be applied to form a film.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to increase the temperature of a bare optical fiber that directly controls the thermochemical vapor deposition reaction immediately after feedback is applied, thereby achieving high-speed spinning. Another object is to provide a method capable of forming a carbon film having a uniform film thickness.

[0005]

When a carbon coating is formed on the surface of a bare optical fiber by a thermochemical vapor deposition method, the carbon along the length direction of the surface of the optical fiber on which the carbon coating is formed is formed. Measure the relative change in the film thickness of the coating,
This is solved by changing the position of the carbon-coated reaction tube in the longitudinal direction of the optical fiber based on the measured value to control the conditions for forming the carbon coating.

[0006]

The function of measuring the variation of the film thickness of the carbon coating and changing the position of the carbon coating reaction tube by this allows control without delay.

The present invention will be described in detail below. FIG. 1 shows an example of a manufacturing apparatus preferably used in the manufacturing method of the present invention. In the figure, reference numeral 1 is a bare optical fiber, and the bare optical fiber 1 is obtained by spinning an optical fiber preform 2 in a spinning furnace 3 and is a carbon coated reaction tube provided below the spinning furnace 3. 4, and a carbon film is formed on the surface thereof. Here, a bare carbon fiber having a carbon coating formed on its surface is referred to as a carbon coated core wire. Further, below the carbon coat reaction tube 4, there is provided a laser film thickness monitor 5 which evaluates the film thickness of the carbon coating by irradiating the carbon coat core wire with laser light.

The laser film thickness monitor 5 irradiates the carbon coated core wire with laser light, measures the amount of transmission of this laser light, and measures the film thickness, which is an index representing the hydrogen resistance of the carbon coating, from this measured value. The measurement device is provided as a measurement point below the carbon coat reaction tube 4 on the running path of the carbon coat core wire. The carbon coat reaction tube 4 and the laser film thickness monitor 5 are connected via a controller 6 and a motor 7, and the laser film thickness monitor 5
The measured value of the film thickness of the carbon coating obtained in step 1 is sent to the controller 6, which feeds it back to the carbon coating reaction tube 4, and the carbon coating reaction tube 4 is moved by the motor 7 along the longitudinal direction of the optical fiber. It is designed to move up and down.

The following steps are used to manufacture a carbon-coated core wire using the manufacturing apparatus as shown in FIG. First, the optical fiber preform 2 is prepared, installed in the spinning furnace 3, and
The bare optical fiber 1 is sent into the carbon-coated reaction tube 4 by melt-spinning at 100 to 600 m / min. In the carbon coat reaction tube 4, a raw material gas such as dichloroethane reacts by a thermochemical vapor deposition reaction to form a carbon coating on the surface of the bare optical fiber 1 and a carbon coated core wire is obtained.
This carbon coated core wire is then sent to a laser film thickness monitor 5 for measuring the film thickness of this carbon coated core wire, and this film thickness is measured. Since the laser light transmission amount varies depending on the film thickness of the carbon coated core wire, a carbon coated core wire having a sufficient film thickness is preliminarily run in the laser film thickness monitor 5 so that the relationship between the laser light transmission amount and the film thickness. If you check
The film thickness is obtained by the amount of transmission measured in the laser film thickness monitor 5. Therefore, if the output signal from the monitor 5 is sent to the controller 6 as a control signal, the controller 6 operates the motor 7 based on this signal to move the carbon coat reaction tube 4 upward or in the longitudinal direction of the carbon coat core wire. Move it down.

When the spinning linear velocity becomes slow and the film thickness starts to become thin, the laser beam transmission amount increases, and the transmission amount measured here is sent to the controller 6 as a control signal. The controller 6 receiving the control signal is the carbon coating reaction tube 4
When a drive signal is sent to the motor 7 to move the
The carbon-coated reaction tube 4 moves upward, and the raw material gas is decomposed at the high temperature portion of the surface of the bare fiber wire and reacts with the bare optical fiber, so that the efficiency of the thermochemical vapor deposition reaction increases and the film thickness increases. ..

Further, when the spinning linear velocity becomes faster and the film thickness becomes thicker, the laser light transmission amount decreases, and the transmission amount measured here is sent to the controller 6 as a control signal. Upon receiving the control signal, the controller 6 sends a drive signal to the motor 7 so as to move the carbon coated reaction tube 4 downward, and the carbon coated reaction tube 4 moves downward, where the temperature of the surface of the bare fiber wire is low. Since the raw material gas is decomposed and reacts with the bare optical fiber, the efficiency of the thermochemical vapor deposition reaction becomes low and the film thickness becomes thin. The film thickness is preferably 0.03 μm or more and less than 0.1 μm from the viewpoint of reducing optical fiber transmission loss due to hydrogen permeation and improving mechanical strength. Although laser light was used as the device for measuring the film thickness here, it is not necessarily limited to this, and a method of irradiating electromagnetic waves on the carbon coated core wire to measure the dielectric constant or the electrical resistance value of the carbon coated core wire can be measured. There is also a method of measuring by edge method.

In this way, the thickness of the carbon coating is monitored to detect the defective portion of the carbon coating, and this is fed back to move the position of the carbon coating reaction tube 4 upward or along the longitudinal direction of the optical fiber. By moving it downward, it becomes possible to manufacture a carbon-coated core wire in which a carbon coating film having a uniform film thickness is formed in the longitudinal direction. Further, since the carbon coat reaction tube 4 is movable, the surface temperature of the bare fiber wire when reacting with the raw material gas that directly controls the thermochemical vapor deposition reaction can be instantly changed, and the time from the feedback can be changed. Is very small, and the higher the spinning speed, the less the time delay. Therefore, it becomes possible to manufacture a carbon-coated core wire in high-speed spinning.

[0013]

As described above, the method for producing a carbon coated core wire of the present invention measures the relative change in the thickness of the carbon coating along the length direction of the optical fiber on which the carbon coating is formed, Based on this measurement value, the position of the carbon coating reaction tube is changed in the longitudinal direction of the optical fiber to control the conditions for forming the carbon coating, so that the water resistance is always constant over a wide range of spinning speed from low speed to high speed. It is possible to manufacture a carbon-coated core wire having excellent characteristics and a uniform film thickness.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a manufacturing apparatus preferably used for carrying out the method for manufacturing a carbon-coated core wire of the present invention.

[Explanation of symbols]

 1 ... Bare optical fiber, 4 ... Carbon coated reaction tube

Claims (1)

[Claims] 1. When a bare optical fiber is run in a carbon coated reaction tube and a raw material gas is reacted in the reaction tube by a thermochemical vapor deposition method to form a carbon coating on the bare optical fiber surface. The relative change of the film thickness of the carbon coating along the length direction of the optical fiber surface on which the carbon coating is formed is measured, and the position of the carbon coated reaction tube is changed in the longitudinal direction of the optical fiber based on this measurement value. A method for producing a carbon-coated core wire, which comprises controlling the conditions for forming the carbon coating.