JPH06298544A - Production of hermetically coated optical fiber - Google Patents

Abstract

PURPOSE:To provide a method for producing an optical fibers having conductive thin film with good film quality. CONSTITUTION:This method for producing a hermetically coated optical fiber is composed of the first step comprising drawing a preform 11 for optical fibers by a drawing furnace kept at high temperature and forming a raw optical fiber 12, the second step comprising introducing the raw optical fiber 12 into a furnace core pipe 32 provided in a thin film forming device and simultaneously introducing raw material glass into the furnace core pipe 32 and forming a carbon film by chemical vapor phase deposition method on the raw optical fiber 12, the third step comprising irradiating light from a direction making right angle to a shaft of optical fiber 13 on which carbon film is formed, measuring a transmitted light amount damped by absorption or scattering of light due to carbon film and simultaneously measuring electrical characteristics of the optical fiber 13 by an electrical characteristics-measuring device 5 and the fourth step comprising analyzing the measured result obtained by measuring transmitted light amount and the measured result obtained by measuring the electrical characteristics by a computer 10 and evaluating film quality of the carbon film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a hermetically coated optical fiber.

[0002]

2. Description of the Related Art A silica-based optical fiber, in the presence of water,
The reaction between water and glass promotes crack growth,
It may break. It is generally called fatigue property, and particularly in a high humidity heat environment, the fatigue property is deteriorated. Also,
It is well known that, in an H ₂ atmosphere, H ₂ penetrates into glass and causes absorption loss in the communication wavelength band. Although the outer circumference of the optical fiber is coated with a resin, generally, these resins allow water and H ₂ to pass through easily, and therefore are not a solution to the above problems.

[0003] Here, a submarine cable is considered as an environment in which it is likely to come into contact with water and H ₂ , but in such a case, due to the above problems, a cable structure in which water does not enter and H ₂ is less likely to occur. Material must be used.
Hermetically coated optical fibers are drawing attention as a method for fundamentally solving these problems. The hermetically-coated optical fiber has a glass surface coated with a hermetic layer that prevents water and H ₂ from penetrating, and can slow down the penetration rate of water, hydrogen, and the like from the external environment as compared with a normal optical fiber. Inorganic materials such as metals and carbon materials are generally used as hermetic coating materials. Among the inorganic materials, coating with carbon is particularly excellent in terms of chemical stability, structure denseness, and the like.

As the coating method, the following methods are known to be particularly excellent in terms of film formation rate and film quality. Immediately after the optical fiber strand is drawn from the preform (base material) by the drawing furnace,
This is a chemical vapor deposition method (CVD method) in which an optical fiber is drawn into a reaction tube provided directly below a drawing furnace and a raw material gas is introduced to deposit a carbon film or the like on the fiber surface. The reason why the carbon film or the like is deposited on the surface of the fiber by this method is that the raw material gas reacts with the heat of the optical fiber.

In the above-mentioned method, it is necessary to inspect the characteristics of the deposited film, that is, to know whether or not it has a uniform and sufficient film thickness and film quality. The following techniques have been disclosed as techniques for inspecting the characteristics of this film. First, as shown in Japanese Patent Laid-Open No. 3-245005, light is applied from a direction perpendicular to the side surface of the optical fiber,
This is a method of measuring the thickness of the carbon film from the intensity of the transmitted light (hereinafter referred to as the first conventional example). Secondly, as disclosed in Japanese Patent Laid-Open No. 3-131550,
This is a method of measuring an eddy current generated when a carbon-coated optical fiber is introduced into a high frequency magnetic field and measuring the impedance of the film from the output value (hereinafter referred to as a second conventional example).

[0006]

Since the hermetic property of the hermetic coat of the optical fiber mainly depends on the quality of the carbon film deposited on the surface, it is necessary to measure the film quality in the process of manufacturing the optical fiber. That is, even if the film thickness is large, if the denseness of the carbon layer is inferior, water and H ₂ easily enter, and conversely,
Even if the carbon layer is dense, if the film thickness is thin, the characteristics will still be inferior. Therefore, it is necessary to evaluate the film quality by matching the film thickness and the denseness of the carbon layer.

However, in the first conventional example, only the thickness of the carbon film can be measured, and in the second conventional example,
Only the electrical properties of the carbon film, mainly the conductivity, could be measured. Therefore, since the film quality cannot be measured by the conventional method, it is not possible to show the uniformity of the carbon film over the entire optical fiber. That is, it can be said that the conventional method could not sufficiently inspect the characteristics of the film deposited on the optical fiber.

This means, for example, with respect to the method according to the first conventional example, even if the measured value of the transmitted light amount is constant, the hydrogen resistance characteristic at the time of performing the hydrogen test shows the change as shown in FIG. It is obvious from the fact that a good correlation between the measured value of the amount of transmitted light and the hydrogen resistance property cannot be obtained. It can also be seen from the fact that the method according to the second conventional example could not obtain a good correlation between the measured eddy current and the hydrogen resistance property.

Therefore, an object of the present invention is to provide a method of manufacturing an optical fiber which solves the above problems.

[0010]

In order to solve the above-mentioned problems, the present invention is to melt an optical fiber preform by a drawing furnace kept at a high temperature and spin it to form an optical fiber strand. The first step is to introduce the optical fiber strand into the reaction vessel for hermetic coating provided in the thin film forming apparatus, introduce the raw material gas into the reaction vessel, and perform chemical vapor deposition on the optical fiber strand. The second step of forming a thin film coating layer made of a conductive material and irradiating light from a direction intersecting the axis of the optical fiber having the thin film coating layer formed thereon, the light is absorbed or scattered by the thin film coating layer. Third step of measuring the amount of transmitted light that is attenuated as a result, and measuring the electrical characteristics of the optical fiber with an electrical characteristic measuring device, the measurement result of the transmitted light amount, and the measurement result of measuring the electrical characteristics. The analyzes by the arithmetic processing unit and having a fourth step of evaluating the quality of the thin film coating. It is desirable that the thin film coating layer contains carbon.

Even if the electrical characteristic measuring apparatus is an apparatus which introduces an optical fiber into a high frequency magnetic field and measures an eddy current generated in the thin film coating layer, the electrical characteristic measuring apparatus has an electromagnetic wave waveguide. However, an apparatus for introducing an optical fiber into the electromagnetic wave waveguide and measuring the dielectric loss of the electromagnetic wave caused by the thin film coating layer may be used.

Further, it is desirable that the measurement result of the amount of transmitted light and the measurement result of the electrical characteristics are analyzed by an arithmetic processing unit, and the arithmetic processing unit controls the thin film forming apparatus for forming the thin film coating layer.

Further, the thin film forming apparatus controls the fiber temperature adjusting means for adjusting the temperature of the optical fiber strand near the inlet of the reaction tube, and the gas composition of the raw material gas introduced into the reaction tube. A second controller for controlling the gas flow rate of the raw material gas introduced into the reaction tube, a third controller for controlling the valve for controlling the gas flow rate of the raw material gas, and a fourth controller for controlling the heating device for controlling the gas temperature in the reaction tube. Therefore, the arithmetic processing unit preferably controls at least one of the first controller to the fourth controller by analyzing the measurement result of the transmitted light amount and the measurement result of the electrical characteristic.

The amount of transmitted light and the electrical characteristic may be measured before coating the optical fiber having the thin film coating layer with the organic resin film.

[0015]

According to the above-mentioned method, the optical fiber having the thin film coating layer formed thereon is measured not only for the amount of transmitted light but also for the electrical characteristics, and these measurement results are sent online to the arithmetic processing unit. It is captured. These measurement results are processed by the arithmetic processing unit on the basis of the values recorded in advance in the arithmetic processing unit as data of good film quality, and the film quality is evaluated. Based on this evaluation of film quality,
By operating the thin film forming apparatus, a thin film coating layer having good film quality can be formed. It is considered that there is a relationship between the film thickness obtained by measuring the amount of transmitted light and the electric resistance value (impedance) obtained by measuring the electrical characteristics as shown in the following formula. It is because it is being done.

[0016]

[Equation 1]

That is, the film quality of the thin film coating layer is evaluated by the arithmetic processing unit based on the above formula, and the thin film forming apparatus is operated while monitoring the result to form the thin film coating layer. Layers can be formed.

Further, if the thin film forming apparatus is directly controlled by the arithmetic processing unit, the thin film forming apparatus can be operated more precisely and quickly, so that a thin film coating layer having a better film quality can be formed. become.

If the amount of transmitted light and the electrical characteristics are measured before coating the resin film on the optical fiber on which the thin film coating layer is formed, the resin film is opaque. However, the amount of transmitted light of the thin film coating layer can be measured without being affected by this, and even if the resin film has conductivity, it is independent of the electrical properties of the thin film coating layer. The property can be measured.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

First, a manufacturing apparatus used in the method for manufacturing an optical fiber according to the present invention will be described. As shown in FIG. 1, first, an optical fiber preform (hereinafter, simply referred to as a base material) 11 is inserted into a core tube 22 of a drawing furnace 21, and a tip portion of the base material 11 is a drawing furnace. The optical fiber element wire 12 is produced by drawing the wire while being heated and melted by the heating device 23 provided in.

The optical fiber element wire 12 is inserted into a core tube 32 of a thermal CVD furnace 31 which is a thin film forming apparatus. Core tube 3
A reaction gas introduction port 33 is provided on the upper part of 2, and the reaction gas is supplied from this reaction gas introduction port 33 and is thermally decomposed by a heating device 34 provided in the core tube 32,
A carbon film is deposited on the surface of the optical fiber element wire 12, and a conductive thin film which is a thin film coating layer made of a carbon film is formed on the surface of the optical fiber element wire 12. At this time, the temperature of the optical fiber element wire 12 is adjusted by moving the thermal CVD furnace 31 up and down by a thermal CVD furnace vertical movement device (not shown). That is, the carbon film is vapor-deposited on the surface by utilizing the temperature of the optical fiber element wire 12 itself.
The temperature of the optical fiber strand 12 can also be adjusted by using a heating device. The waste gas after the reaction is discharged from the exhaust port 35 provided in the lower portion of the core tube 32. At this time, in this embodiment, ethylene is used as the reaction gas. The substance used as the reaction gas may be a substance other than the above, for example, methane, benzene, or the like. In particular, the material of the conductive thin film is not particularly limited as long as it can form a solid conductive airtight layer on the surface of the optical fiber and does not adversely affect the optical fiber. The forming device can also be selected as an appropriate type depending on its material. The carbon referred to here includes amorphous (non-crystalline) carbon and fine crystalline carbon. The optical fiber 13 whose surface is coated with a conductive thin film passes through the transmittance measuring device 4 after exiting the thermal CVD furnace 31.

As shown in FIG. 2, the transmittance measuring device 4 is provided with an LED 41 which is a light source, and the light emitted from the LED 41 becomes a parallel light beam α ₁ by the collimator lens 42. The parallel light beam α ₁ is adapted to be incident perpendicularly to the optical fiber 13. Although the parallel constraint α ₁ is orthogonal to the optical fiber 13 in this embodiment, it may be incident in a slightly oblique direction. Light flux alpha ₂ refracted transmitted enters the out optical fiber 13 of the parallel light beam alpha ₁ is parallel light alpha ₃ by the first imaging lens 43
Is converted to. The first imaging lens 43 is provided so that the optical fiber 13 is at the position where the first imaging lens 43 is in focus. The parallel light α ₃ is introduced into the second imaging lens 44, passes through the second imaging lens 44, and then passes through the second imaging lens 44.
The light is condensed by the photodetector 46 provided at the light condensing point. On the other hand, the light flux that does not pass through the optical fiber is the first imaging lens 4
After passing through 3, the light becomes focused light α _{4 and} is shielded by the shielding plate 45 provided at the converging point. In addition, in order to guide most of the parallel light 4 to the second imaging lens 44, the shield plate 45 is used.
Must be set to a necessary and sufficient size. Photodetector 4 provided in the transmittance measuring device 4
The output signal from 6 is the computer 1 as shown in FIG.
Input to 0.

After passing through the transmittance measuring device 4, the optical fiber 13 passes through the detection coil 51 provided in the eddy current measuring device 5. The detection coil 51 is hollow,
In this embodiment, the inner diameter of the coil is 500 μm, and the center of the detection coil and the center of the optical fiber are highly accurately centered so that the optical fiber 13 passing therethrough does not come into contact with the detection coil 51. Further, the eddy current measuring device 5 is provided with a reference coil 52, and the reference coil 52
Is an air-core coil of the same shape and size as the detection coil 51, and has the same characteristics at least with respect to the AC impedance. The detection coil 51 and the reference coil 52 are
In this embodiment, a high frequency current is supplied from a high frequency power source 53 having a frequency of 200 MHz, and the output of the AC bridge 54 is connected to a signal processing device 55. The output signal from the signal processing device 55 is input to the computer 10. The high frequency power supply 53, the AC bridge 54, and the signal processing device 55 are all elements that make up the eddy current measuring device.

Optical fiber 13 passing through the detection coil 51
Then, the contour is measured by the contour measuring device 6. Subsequently, a flexible resin is coated on the die 7a, and a hard resin is coated on the flexible resin in the die 7b. Then, in the curing furnace 8, U
It is cured by V irradiation or heating. The optical fiber 14 thus completed is wound around a drum (not shown) via the capstan 9.

In the manufacturing apparatus according to this embodiment, the amount of transmitted light and the electrical characteristics are measured before coating the optical fiber on which the conductive thin film is formed with the resin film. Therefore, even if the resin film is opaque, the amount of transmitted light of the conductive thin film can be measured without being affected by this, and even if the resin film has conductivity, this The electrical property of the conductive thin film can be measured independently of the above. Therefore, if the resin film further applied on the conductive thin film is transparent, the position where the transmittance measuring device 4 is installed is, for example, after the resin film is formed, regardless of the position of the above embodiment. It may be a position.
If the resin film is non-conductive, the position where the eddy current measuring device 5 is installed may be, for example, a position after the resin film is formed, regardless of the position in the above embodiment. Needless to say.

Next, the operation of the apparatus of the above embodiment and the manufacturing method according to the embodiment will be described.

In FIG. 1, the base material 1 in the drawing furnace 21 is
1 is drawn to make an optical fiber strand 12. The optical fiber wire 12 is heated by the heating device 34 in the furnace core tube 32 of the thermal CVD furnace 31, the surface thereof is contacted with the reaction gas to be thermally decomposed, and the surface of the optical fiber wire 12 is electrically conductive such as carbon. A substance is deposited and a thin film is formed. The coating conditions were an ethylene flow rate of 100 ml / min, chloroform of 200 ml / min, and a drawing speed of 200 m / min.

When the optical fiber 13 whose surface is coated with a conductive thin film as described above passes through the transmittance measuring device 4, the transmittance measuring device 4 measures the amount of transmitted light. That is, as described above, the light emitted from the light source 41 is converted into the parallel light beam α ₁ by the collimator lens 42, but the parallel light beam incident on the optical fiber 13 is refracted and transmitted to the first condensing lens 43. Will be introduced to. The light flux α ₂ introduced into the condenser lens 43 becomes parallel light α ₃ , which is further introduced into the second imaging lens 44, condensed, and taken into the photodetector 46. The photodetector 46 detects the amount of transmitted light and sends it as an output signal to the computer 10 to be captured. The parallel light flux α _{1 that} has not entered the optical fiber 13 is condensed by the first imaging lens 43 and is shielded by the shielding plate 45, so that the second imaging lens 44 and the photodetector 46. Will be blocked.

The computer 10 measures the film thickness of the conductive thin film based on the amount of transmitted light. This is processed in the computer 10 as follows. It is known that the amount of transmitted light and the film thickness of the conductive thin film have a unique relationship. Therefore, the thickness of the conductive thin film is obtained in advance by an electric resistance method or the like, and a calibration curve of this thickness and the amount of transmitted light measured using a device similar to the transmittance measuring device 4 is obtained. The data is input as data to the film, and the film thickness of the conductive thin film is obtained from the relationship between this data and the amount of transmitted light obtained by the apparatus of this embodiment.

Optical fiber 1 which has passed through the transmittance measuring device 4.
3 further passes through the hollow portion of the detection coil 51 of the eddy current measuring device 5, but at this time, an eddy current is generated in the conductive thin film on the surface of the optical fiber 13. This is because the conductor fiber surface is placed in the magnetic field created in the detection coil 51. At the same time, this eddy current also creates a magnetic field, which in turn acts on the detection coil 51 to change its apparent AC impedance. On the other hand, since the impedance of the reference coil 52 does not change because it is an air core, while observing the difference in AC impedance of the detection coil 51 and the reference coil 52 with the AC bridge 54,
By operating the AC bridge 54 so that the difference becomes zero, the amount of change in impedance generated in the detection coil 51 can be detected as the operation amount of the AC bridge 54. That is, since the strength of the eddy current is caused by the change amount of the AC impedance, the eddy current value can be detected as the operation amount of the AC bridge. The amount of change in impedance is sent to the computer 10 as an output signal, input, and recorded.

In this eddy current measurement, in order to generate a sufficiently strong eddy current under a constant high frequency current, the coil filling rate ν of the detection coil should be as large as possible (close to 1).
There is a need to. The coil filling factor ν is the ratio of the fiber cross-sectional area to the hollow cross-sectional area of the coil.
Is defined by

Ν = (d _f / d _c ) ² (1) Here, d _f represents the outer diameter of the optical fiber, and d _c represents the inner diameter of the detection coil. If the value of ν is small, a highly sensitive AC bridge or the like is required, and the gain of the amplifier has to be increased, which makes it difficult to handle a high frequency as described later. By the way, when the outer diameter of the optical fiber is 125 μm, the inner diameter of the detection coil is preferably 500 μm or less. Therefore, the outer diameter is 250 μm
It can be said that the practical range of the inner diameter of the detection coil is 1 mm or less in the manufacturing apparatus for manufacturing the optical fiber to the extent.

On the other hand, the high frequency power source 53 used for eddy current measurement
The frequency f is determined by the electric conductivity σ and the magnetic permeability μ of the conductive thin film so that the penetration depth δ of the eddy current in the thin film becomes an appropriate value. Here, the penetration depth δ of the eddy current is expressed by the following equation (2).

Δ = 1 / √πfσμ (2) It is desirable that δ be sufficiently larger than the thickness of the conductive thin film of the optical fiber and smaller than the outer diameter of the optical fiber. When the constant of the carbon film is put into the equation (2) and the outer diameter of the optical fiber is 100 μm, f is 250M.
Although it becomes more than Hz, this is 44 in the case of the copper wire of the same thickness.
The difference is clear when compared to 0 KHz. By the way, in the case of the carbon film, the outer diameter of the optical fiber of 80 μm is 390 MHz or more, and the outer diameter of 200 μm is 60 MH.
z or more. From this, it can be said that in the case of a carbon film, the practical range of this frequency is 10 MHz or higher.

The computer 10 calculates the state of film quality based on the amount of change in film thickness and impedance recorded above. The computer 10 is preset with a range of values obtained from equation (3) described below when the film quality is good. Therefore, when the value obtained by the calculation deviates from the preset range, feedback is applied to the thin film forming apparatus so that the film quality becomes constant. This is the heat C (not shown) that moves the thermal CVD furnace 31 up and down to adjust the temperature of the optical fiber strand 12.
VD furnace vertical movement device, heating device 34 for adjusting the temperature of the gas in the core tube 32, a valve (not shown) for adjusting the flow rate of the raw material gas, and a control device (not shown) for controlling the composition of the gas. Is. Further details regarding this point will be described below.

It is the film thickness and the bonding state of carbon atoms, that is, the film quality, that determines the hydrogen resistance of the carbon film. It is generally considered that the film quality has the relationship of the following expression (3) between the film thickness and the impedance.

[0038]

[Equation 2]

Then, as a result of combining the film thickness obtained by the transmittance measuring device and the impedance obtained by the eddy current measuring device, a very good correlation with the film quality could be obtained. The results measured at this time are as shown below.

The film thickness obtained from the transmittance measuring device is shown in FIG.
In addition, the impedance obtained from the eddy current measuring device was as shown in FIG. In FIG. 3, the vertical axis represents the film thickness, and the horizontal axis represents the drawn length of the optical fiber. The unit in FIG. 3 is nm on the vertical axis and km on the horizontal axis. In FIG. 4, the vertical axis represents impedance, and the horizontal axis represents the length of the optical fiber drawn. In the unit of FIG. 4, the vertical axis represents kΩ / cm and the horizontal axis represents km. From these results and the above formula (3), the results as shown in FIG. 5 were obtained regarding the film quality of the conductive thin film of the optical fiber obtained by the manufacturing method according to this example. From FIG. 3 and FIG. 4, the film quality and the impedance both fluctuate in the horizontal axis direction, but since the manufacturing apparatus is controlled by feeding back the computer 10 as described above, the film quality of FIG. The results show that it is stable.

At this time, with respect to the optical fiber,
A hydrogen test was performed under the conditions of atm and 40 hours, and the hydrogen resistance was measured. At the beginning of pulling, Δα _1.24 = 0.035 dB / k
m, and the end of pull was Δα _1.24 = 0.038 dB / km. From this, it was found that the hydrogen resistance was stable from the beginning to the end of pulling. Also,
If Δα _1.24 ≦ 0.1 dB / km is defined as a good product,
The yield of the optical fiber manufactured by this method was 90%, and very excellent results could be obtained.

That is, as described above, according to this embodiment, a hermetically coated optical fiber having a stable film quality can be manufactured, and the yield can be remarkably improved. That is, since the manufacturing apparatus is controlled based on the information about the film quality related to the hermetic property, which is the most important property of the hermetic coating, a highly reliable hermetic coated optical fiber can be manufactured.

In this embodiment, the temperature of the inlet of the core tube 32 and the core tube 3 are controlled by the computer 10.
Although the gas temperature, the flow rate of the raw material gas and the gas composition in 2 are controlled, this control may be performed manually. That is, even if the film thickness and the impedance are monitored manually and appropriately controlled, a conductive thin film having stable hydrogen resistance can be formed as in the case of controlling by a computer.

A comparative experiment was conducted to clarify the effect of the present invention, which will be described below.

As a first comparative example, the eddy current measuring device 5 of the device according to the present invention was not used, but only the transmittance measuring device 4 was used, and the conductive thin film of the optical fiber was formed while monitoring this. . The other conditions are the same as in the present invention.
The film thickness measured by the transmittance measuring device 4 was 50 ± 5 nm. As a result of measuring this with a scanning electron microscope (SEM), the drawing start was 50 nm, and after drawing about 80 km, it was 48 nm, so that it was substantially in agreement with the previous measurement result. However, for hydrogen resistance, the same hydrogen test as above was performed, but at the beginning, Δα _1.24 = 0.17 dB.
/ km was Δα _1.24 = 0.0 at the end of pulling
It became 3 dB / km, and a film with good film quality could not be obtained only by monitoring the transmittance measuring device 4.

As a second comparative example, the conductive thin film of the optical fiber was formed by monitoring only the eddy current measuring device 5 without using the transmittance measuring device 4 of the device according to the present invention. . The other conditions are the same as in the present invention.
The output value at this time was 0.5 ± 0.1V. This will also have been subjected to the same hydrogen test and above, the pull start, had a Δα _1.24 = 0.19dB / km is than end pull, it becomes a Δα _1.24 = 0.04dB / km, Only by monitoring the eddy current measuring device 5, a film having good film quality could not be obtained. Also, Δα _1.24 ≦ 0.1
When dB / km was defined as a good product, the yield of the optical fiber manufactured by this method was 60%.

[0047]

As described above in detail, according to the present invention, the amount of transmitted light and the electrical characteristics of the optical fiber on which the thin film coating layer is formed are measured. It is sent online to the processing unit and captured. Then, the film quality is evaluated from the values recorded in advance in the arithmetic processing device as the data of the good film quality and these results. With this evaluation, by feeding back these results to the thin film forming apparatus, the thin film forming apparatus is operated and the thin film coating layer is formed on the optical fiber, so that the thin film coating layer with good film quality is formed. .
Therefore, a thin film coating layer having more stable characteristics can be formed, and the yield can be further improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a manufacturing apparatus used in a method for manufacturing an optical fiber according to an embodiment.

FIG. 2 is an explanatory diagram showing a transmittance measuring device of the manufacturing apparatus according to the present embodiment.

FIG. 3 is an explanatory diagram showing a change in film thickness measured by the transmittance measuring apparatus according to the present embodiment.

FIG. 4 is an explanatory diagram showing a change in impedance obtained from an eddy current value measured by the eddy current measuring device according to the present embodiment.

FIG. 5 is an explanatory diagram showing a change in film quality based on a value obtained from a correlation between a change in film thickness and a change in impedance.

FIG. 6 is an explanatory diagram showing changes in measured values in a hydrogen experiment regarding an optical fiber obtained from an apparatus according to a conventional example.

[Explanation of symbols]

11 ... Optical fiber preform, 12 ... Optical fiber element wire, 13 ... Optical fiber coated with conductive thin film, 21 ...
Drawing furnace, 22 ... Reactor tube, 31 ... Thermal CVD furnace, 32 ... Reactor tube, 4 ... Transmittance measuring device, 5 ... Eddy current measuring device, 10 ...
Computer.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Katsuya Nagayama 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Ryo Inoue, Taya-cho, Sakae-ku, Yokohama, Kanagawa Sumitomo Electric Ki Industry Co., Ltd. Yokohama Works (72) Inventor Toshio Tsuzuka, Tani-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries Co., Ltd. Yokohama Works (72) Inventor Nobuyuki Yoshizawa 1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo No. Japan Telegraph and Telephone Corporation

Claims (7)

[Claims] 1. A first step of forming an optical fiber element wire by melting the optical fiber preform by a drawing furnace kept at a high temperature and spinning to form an optical fiber element wire, and forming a thin film of the optical fiber element wire. Introducing into the reaction vessel for hermetic coating provided in the apparatus, introducing the raw material gas into the reaction vessel, to form a thin film coating layer made of a conductive substance on the optical fiber strand by a chemical vapor deposition method. Step 2 and irradiating light from a direction intersecting the axis of the optical fiber on which the thin film coating layer is formed, and measuring the amount of transmitted light that is absorbed or scattered by the thin film coating layer and attenuated, A third step of measuring an electrical characteristic of the optical fiber by an electrical characteristic measuring device, a measurement result of measuring the transmitted light amount, and a measurement result of measuring the electrical characteristic. And a fourth step of evaluating the film quality of the thin film coating layer by analyzing according to the above method. 2. The method for producing a hermetically coated optical fiber according to claim 1, wherein the thin film coating layer contains carbon. 3. The electrical characteristic measuring device is a device for introducing the optical fiber into a high frequency magnetic field and measuring an eddy current generated in the thin film coating layer.
A method for manufacturing the hermetically coated optical fiber according to 1. 4. The device for measuring electrical characteristics has an electromagnetic wave waveguide, and a device for introducing the optical fiber into the electromagnetic wave waveguide to measure the dielectric loss of the electromagnetic wave caused by the thin film coating layer. The method for producing a hermetically coated optical fiber according to claim 1, wherein 5. The arithmetic processing device analyzes the measurement result of the amount of transmitted light and the measurement result of the electrical characteristics, and the arithmetic processing device controls the thin film forming device for forming a thin film coating layer. The method for manufacturing a hermetically coated optical fiber according to claim 1, wherein the hermetically coated optical fiber is manufactured. 6. The thin film forming apparatus comprises: a first controller for controlling a fiber temperature adjusting means for adjusting the temperature of an optical fiber strand near the entrance of the reaction tube; and a source gas gas introduced into the reaction tube. A second controller for controlling the composition, a third controller for controlling a valve for adjusting the gas flow rate of the raw material gas introduced into the reaction tube, and a fourth controller for controlling a heating device for adjusting the gas temperature in the reaction tube. The controller has at least one of the first to fourth controllers by analyzing the measurement result of the transmitted light amount and the measurement result of the electrical characteristic. The method for producing a hermetically coated optical fiber according to claim 1, wherein the method is controlled. 7. An optical fiber having a thin film coating layer formed thereon,
Further, before coating the resin film, the measurement of the transmitted light amount,
The method for producing a hermetically coated optical fiber according to claim 1, wherein the electrical characteristic is measured.