JPH0826776A - Production of hermetically coated optical fiber - Google Patents

Abstract

PURPOSE:To detect the defective part of a hermetic coating and to assure the quality of the coating over the entire length by subjecting the hermetic coating to a hydrogen treatment right after formation of the hermetic coating in a drawing stage and making light of a prescribed wavelength thereon from its one end right after taking up on a reel, then inspecting the coating. CONSTITUTION:A reactor 2 for the hermetic coating is installed right under a drawing furnace 1 for melt spinning a preform to a bare fiber. Gaseous raw materials are introduced into this reactor and the coating layer of a thin layer is applied on the bare fiber by a chemical vapor deposition method. A hydrogen treatment vessel 7 is installed right under the reactor and a gaseous mixture composed of hydrogen and inert gas is introduced therein to execute the hydrogen treatment. The fiber is cooled in an atmosphere contg. the hydrogen in a cooler 12 right after the hydrogen treatment at need. Further, the fiber is passed through a resin coating device 13 and a curing furnace 14, by which the synthetic resin coating is formed thereon. The hermetically coated optical fiber 15 is taken up on the reel. The light of the prescribed wavelength is made incident on the taken-up optical fiber from its one end and thereafter, backward scattering is detected, by which the hermetic coating layer is inspected and the defective part is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hermetically coated optical fiber which is coated with a hermetic coating of carbon or the like. And a manufacturing method capable of providing a hermetically coated optical fiber.

[0002]

2. Description of the Related Art At present, optical fibers for communication are widely used because of their low loss and quartz as a main component. However, the silica-based optical fiber has a problem to be noted in terms of long-term reliability. One of them is the problem of increased transmission loss of signal light due to the penetration of hydrogen into the glass. Small molecules such as hydrogen can easily diffuse in the quartz glass and reach the core. It is known that when hydrogen invades, light is absorbed by itself to increase loss, or hydrogen (H ₂ ) reacts with glass to generate an OH group, which causes increase in loss.
As a method of solving these problems, carbon, metal,
A so-called hermetically-coated optical fiber in which a thin film of TiC or the like is coated on the surface of a quartz fiber is drawing attention. Among these, in particular, the carbon-coated optical fiber coated with carbon has a hydrogen barrier property due to the denseness of the coating film structure,
It is excellent in chemical stability, mechanical strength and manufacturing method, and is the mainstream of hermetically coated optical fibers. As a method for producing a carbon-coated optical fiber, it is known that a CVD method in which a raw material gas is chemically reacted and deposited on the fiber surface is advantageous in terms of film forming speed and film quality. Conventionally, such a technique is disclosed in, for example, Japanese Patent Publication No. 60-25351, U.S. Pat.
There is a manufacturing apparatus as shown in the specification No. 5 or EPA 0,308,143. As described above, the reaction vessel is generally of a type having a seal gas inlet, a raw material gas inlet, and an exhaust gas outlet from above, and the high-temperature spun fiber is thermally heated between these source gas inlet and outlet. A hermetic coat is applied by a chemical reaction, and then a synthetic resin coating is further formed on the outer periphery.

[0003]

In the manufacture of hermetically coated optical fibers, ensuring the uniformity of the hermetically coated layer over the entire length has long been a concern. That is, it is a problem of a method of detecting a coating defective portion. On the other hand, various methods have been proposed. For example, as described in US Pat. No. 5,057,781, a method of monitoring the coating state of a coating layer by measuring an electrical parameter using the conductivity of a carbon layer, and US Pat. There is known a method of optically detecting the thickness of the coating layer using a laser beam or the like as described in the specification No. 226 and inspecting a defective portion. However, all of the conventional monitoring methods are indirect evaluation methods such as the conductivity and thickness of carbon, and although macro defective parts such as the presence or absence of coating and the thickness can be reliably detected by this method, the hydrogen blocking property or It was very difficult to reliably capture microscopic characteristic changes such as the ease of diffusion. On the other hand, as a method of detecting a defective portion of the hermetic coat over the entire length offline, as disclosed in Japanese Patent Laid-Open No. 64029/1992, a hermetically coated optical fiber after being hermetically coated and further coated with a synthetic resin is subjected to a hydrogen atmosphere. A method has been proposed in which a coating state of a coating layer is detected by placing it inside, injecting an optical pulse having an absorption wavelength of hydrogen from one end, and observing the scattered echo on the incident side. According to this method, it is possible to detect the defective coating portion positionally in the lengthwise direction, but the hydrogen treatment takes about 1 to 24 hours, for example. This is because the diffusion rate of hydrogen is controlled by the hydrogen partial pressure in the atmosphere and the temperature of the atmosphere. However, when the hydrogen treatment is performed after coating the synthetic resin, the heat resistant temperature of the resin (about 10
This is because it takes a long time because the treatment temperature cannot be raised above 0 ° C). The present invention is intended to solve the problems of the conventional method, to reliably detect a hermetic coating defect portion, and to provide a hermetically coated optical fiber in which the quality of coating over the entire length is guaranteed, and to provide a manufacturing method. .

[0004]

As a means for solving the above-mentioned problems, the present invention is to melt an optical fiber preform in a drawing furnace in a drawing furnace to spin it into a bare fiber, and then form the bare fiber. While introducing into the reaction vessel,
In the method for producing a hermetically coated optical fiber by introducing a raw material gas into the reaction vessel and applying a thin coating layer on the bare fiber by a chemical vapor deposition method, hydrogen is produced immediately after the hermetic coating is formed in the drawing step. Hydrogen treatment has been performed by passing through an atmosphere containing, and at the end of the drawing step, the hermetically coated optical fiber is wound on a reel, and light having a predetermined wavelength is incident from one end of the hermetically coated coil. By detecting the backscattered light, the quality state of the hermetic coat layer can be inspected in a positional manner in the fiber length direction. In a particularly preferred embodiment of the present invention, the optical fiber is cooled at the same time as or immediately after the hydrogen treatment of passing through the atmosphere containing hydrogen, and the synthetic resin is coated on the hermetic coat. In addition, according to the result of the above inspection, a hermetic coat coating state defective portion is detected, and screening is performed to remove the defective portion.Furthermore, the loss wavelength characteristic of the hermetic coated optical fiber after the screening is measured, and loss due to hydrogen intrusion is measured. It is another particularly preferable embodiment of the present invention that the quality of the overall hermetic coat layer is determined by obtaining the average value of the increase amount in the lengthwise direction. In the present invention, the atmosphere containing hydrogen is at least one of He, Ar and N _2.
Those containing seeds are particularly preferred. The predetermined wavelength of the present invention is 1.24 ± 0.1 μm or 1.39 ±
0.1 μm can be mentioned. Examples of the material for the hermetic coating in the present invention include carbon, ceramics or nitrides of silicon, ceramics such as carbides or nitrides of titanium, aluminum, nickel,
Examples thereof include metals such as copper, tin, lead and indium, and alloys thereof, with carbon coating being particularly preferred.

[0005]

In the present invention, an optical fiber preform is melted and spun in a drawing furnace to form a bare fiber, and then the bare fiber is introduced into a reaction vessel and a source gas is introduced into the reaction vessel. In a method for producing a hermetically coated optical fiber in which a thin coating layer is formed on the bare fiber by a chemical vapor deposition method, immediately after the hermetic coating of carbon or the like is applied, about 3
At a high temperature of 00 ° C. or higher, hydrogen is passed through an atmosphere containing hydrogen, and the optical fiber is cooled at the same time as or immediately after the hydrogen treatment to suppress the release of hydrogen due to the back diffusion, and then the light is continuously emitted. A synthetic resin is coated on the fiber.
The coated fiber is wound on a regular reel. From one end of this wound fiber, a predetermined wavelength of light, for example, a wavelength band such as 1.24 μm or 1.39 μm, which is an absorption band by hydrogen or OH group, greatly changes, and the S / N ratio at the time of detection By injecting light of a large wavelength and detecting the backscattered light (B / S waveform), the defective coating portion in the length direction is inspected. After removing the defective coating, measure the loss-wavelength characteristics, determine the total amount of loss increase due to hydrogen intrusion, and inspect the quality of the entire hermetic coating layer to ensure a full-length guarantee. You can

The most important feature of the present invention resides in that during the drawing, hydrogen treatment is carried out for inspecting the quality of the hermetically coated state while the fiber temperature is high. If there is insufficient coverage in the coating, hydrogen will penetrate into the fiber from that location, and the absorption loss due to hydrogen will increase at this location. The diffusion coefficient of gas in a solid is generally expressed by the equation 1.

## EQU1 ## D = A.exp ^{(-E / RT)} However, in the equation 1, D: diffusion coefficient, A: constant, E: activation energy, R: gas constant, T: temperature. Number 1
As shown in, the diffusion coefficient D increases as the temperature (T) increases. For example, the diffusion coefficient of hydrogen in quartz glass is
It is about 7 × 10 ^-10 [cm ² / s] at a temperature of 100 ° C, but 5
It becomes about 1 × 10 ⁻⁶ [cm ² / s] at 00 ° C., which is about 1500 times. If the temperature is high as described above, the hydrogen treatment can be performed in a short time. It is also effective to cool the fiber immediately after the hydrogen treatment. This is because by lowering the temperature of the fiber, hydrogen that has once penetrated is suppressed from being diffused back into the atmosphere, and the state of H ₂ having penetrated is maintained to improve the measurement accuracy. As described above, during the drawing online, the hermetic coating and the hydrogen treatment necessary for judging the quality of the hermetic coating layer are performed at the same time as the hermetic coating. Therefore, it is possible to efficiently and surely inspect the coating state in an extremely short time as compared with the conventional method, and it is possible to manufacture a hermetically coated optical fiber with a guaranteed full length with high productivity.

FIG. 1 is a schematic cross-sectional view showing one specific example showing a realization means for performing on-line hydrogen treatment immediately after hermetic coating during drawing. The hermetic coat reaction vessel 2 may be any of those known in the technical field of this type. A hermetic coating reaction vessel 2 is installed immediately below the drawing furnace 1, and an inert seal gas such as nitrogen, He, or Ar is introduced from an upper seal gas introduction pipe 3 to maintain the atmosphere inside the reaction vessel 2. . When carbon is coated as a hermetic coat layer, a raw material gas such as acetylene and hydrocarbons such as ethylene and a halogen-containing gas are mixed and introduced from the raw material gas introduction pipe 4. The reaction waste is discharged to the outside through the exhaust pipe 5, and the seal gas is introduced through the lower seal gas introduction pipe 6 to seal the lower part of the reaction vessel.

Immediately below that, the hydrogen treatment which is the feature of the present invention.
Install container 7. In the examples described below,
Then, use a transparent quartz tube with an inner diameter of 10 mm and a length of 100 mm.
However, it does not substantially react with hydrogen, heat resistance and safety and health
Materials without problems such as metals, alloys, ceramics, etc.
The thing can be selected arbitrarily. The size is drawn
It is appropriately determined according to the speed and the like. From hydrogen gas introduction pipe 8
Hydrogen and He, Ar, N ₂Mixed with an inert diluent gas such as
Then, the mixed gas is introduced. The amount of hydrogen and the dilution gas
The type and temperature of gas depend on the intended hydrogen treatment conditions.
It can be decided as appropriate.

Hydrogen treatment conditions are mainly determined by the hydrogen concentration, gas temperature, fiber temperature and treatment time. For example, when the hermetic properties are severely demanded, hard hydroprocessing conditions are required to guarantee the quality. When performing the hardest hydrogen treatment, 100% hydrogen gas is heated and introduced to make the treatment vessel length as long as possible. Further, if the required performance is not so severe, if the hard hydrogen treatment is carried out, the hermetic layer will be impregnated with hydrogen, which may deteriorate the characteristics. Therefore, it is desirable to keep the conditions under necessary and sufficient conditions. Therefore, when performing mild hydrogen treatment, a method of diluting with an inert gas such as He and introducing a mixed gas having a hydrogen concentration of several volume% at room temperature is adopted. Since hydrogen and He easily take away the heat of the fiber, if the hydrogen or He is introduced into the hydrogen reaction container 7 at room temperature or after cooling, the fiber can be cooled at the same time. On the other hand, Ar and N ₂ are less likely to absorb heat than He, so that it is preferable to use these gases as the diluent gas when it is not desired to lower the temperature of the fiber. In any case, hydrogen or an inert gas that does not react with the hermetic coat layer is used as the diluent gas.

As described above, the concentration of hydrogen and the type of diluent gas may be arbitrarily selected according to desired processing conditions. The temperature and processing time of the fiber are mainly factors that depend on the drawing speed, and at the same time, they are also hermetic coating conditions, so that the degree of freedom in selection may be limited. After determining the conditions such as the treatment time, it is desirable to determine the hydrogen concentration and the type of the diluent gas according to the conditions.

The hydrogen-containing atmosphere is discharged from the exhaust pipe 9,
A fresh gas is always allowed to flow in the hydrogen treatment container 7. Further, in order to prevent the hydrogen-containing atmosphere from leaking to the outside, a seal gas such as He is introduced into the seal gas introducing pipe 10.

The cooler 12 is used as necessary and supplies He gas inside. When the temperature of the hermetically-coated fiber after leaving the hydrogen treatment container 7 is as low as about 150 ° C. or lower, it is sent to the next synthetic resin coating step without using a cooler. If cooling is required, cooler 1
2 is passed, but it is preferable to supply He gas into the cooler 12 for the above reason.

A coated hermetically coated optical fiber 15 which is a product obtained by forming a synthetic resin coating through a resin coating device 13 and a curing furnace 14 is wound on a reel, and a normal OTDR is formed.
(Optical Time Domain Refr
backscattering (B)
ack Scattering (abbreviated as BS) waveform is measured. A specific method of measurement is described in, for example, JP-A-4-64
No. 029, etc.

If there is a portion where hydrogen penetrates into the glass from the defective coating portion, it is detected as a waveform step, as shown in the example of the observation result of FIG. In FIG. 2, the horizontal axis represents the distance (km) from the incident end, and the vertical axis represents the backscattered light intensity. Hereinafter, the same applies to FIGS. 4, 6 and 7. In order to remove the defective point thus inspected, a good portion is rewound on a reel, and the defective portion is removed when it is fed out, so that screening is performed.

FIG. 3 is a loss-wavelength characteristic diagram of a fiber which is subjected to only hydrogen treatment without performing hermetic coating. The vertical axis represents the difference value of the loss when the hydrogen treatment was performed and when the hydrogen treatment was not performed [(loss value after the hydrogen treatment)-(loss value when the hydrogen treatment was not performed)]. Drawing speed is 300m
/ Min, the hydrogen concentration of the hydrogen-containing gas was 10%, and N ₂ was used as the diluting gas. The mixed gas was maintained at 30 ° C. and introduced at a flow rate of 2 liter / min. As shown in FIG. 3, remarkably peaks are observed at the absorption wavelength of hydrogen molecules of 1.24 μm and the absorption wavelength of OH groups of 1.39 μm. From this, the wavelength bands of 1.24 μm and 1.39 μm are the S / N ratio [in this case, as the measurement wavelength for detecting that the hermetic coat has a defective portion and hydrogen has penetrated into the glass. (Loss value after hydrogen treatment) /
(Loss value without hydrogen treatment)].

[0016]

The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. Example 1 A hermetically coated optical fiber having the configuration shown in FIG. 1 was manufactured according to the present invention. Drawing speed is 300m / m
In, 100 cc / min of ethylene and 150 cc / mi of chloroform as source gas for hermetic coating
It was introduced into the reaction vessel at a flow rate of n to form a carbon coating having a thickness of about 40 nm (nanometer) in the reaction vessel 2. N ₂ was used as the seal gas above and below the reaction vessel, and the flow rate was 3 liters / min. At this time, when the fiber temperature immediately below the reaction vessel was measured, it was about 600 ° C. The gas introduced into the hydrogen treatment container 7 is
A mixed gas of hydrogen and Ar with a hydrogen concentration of 40% is
It was heated to 0 ° C. and introduced at a flow rate of 3 l / min.
He is flowed from the seal gas introduction pipe 10 at the lower part of the hydrogen treatment container at a flow rate of 5 liters / min, and He is flown to the cooler 12 by flowing He.
At 10 liters / min to cool the fiber,
The release of hydrogen that once entered the fiber was suppressed. At this time, the temperature of the hermetically coated fiber immediately below the cooler was about 60 ° C. About 10k under the above conditions
At the time of drawing 3 km on the way and 7 k
At the time of drawing the m-line, the supply of the raw material gas for the carbon coating was stopped, and a defective coating portion was intentionally created. After winding this fiber, 1.39 as a light source
Using a wavelength of ± 0.1 μm, enter from the drawing start end,
The measurement was performed by the OTDR method. As shown in FIG. 4, the obtained waveform had two steps, which coincided with the point at which the supply of the raw material gas was stopped. Next, this fiber was rewound, and a portion including a defective portion was taken out for each 1 km centering on a point of 3 km and a point of 7 km, and loss-wavelength characteristics of the normal portion and the defective portion were measured.
FIG. 5 shows the measurement results. In FIG. 5, (a) is a waveform of a normal portion, (b) is a waveform of a defective portion, and (c) is a waveform of a reference sample when neither carbon coating nor hydrogen treatment was applied. The waveform (a) of the normal part is the same as the waveform (c) of the reference sample that was not treated with hydrogen, and it was confirmed that the carbon coating layer effectively blocks hydrogen. On the other hand, in the waveform (b) of the sample containing the defective portion, the peak of absorption by hydrogen was observed. Thus the defective part
Screening was performed by removing (b), and the average loss increase due to hydrogen from the waveform chart of the loss-wavelength characteristics of the good part (a) (Fig. 5) was less than 0.01 dB / km. Was judged.

[Embodiment 2] Similar to Embodiment 1, a coating defect portion is intentionally formed, and after winding this carbon-coated fiber, 1.24 μm ± 0.1 μm as a light source.
Was measured by the OTDR method. As shown in FIG. 6, the obtained waveform has two steps,
The defective part could be detected.

[Embodiment 3] Carbon coating was performed under the same conditions as in Embodiment 1, and hydrogen 1 was placed in the hydrogen treatment container 7.
Heating 00% gas to 200 ℃, 2 liter / min
Was introduced at a flow rate of. The defective coating portion was measured in the same manner as in Example 1, and was measured by the OTDR method using a wavelength of 1.39 μm ± 0.1 μm. In the obtained waveform, three steps were detected, as shown in FIG. 3km and 7k
The two parts of m were the parts where the defective part was intentionally created, and the size of the step was also large, but the step at the point of 8 km was small, and the carbon coat thickness of this part was about 20.
nm and half of the normal area. This example shows a newly discovered defective portion under hard hydrogen treatment conditions, which was not detected under hydrogen treatment conditions of hydrogen 10%, He 90%, and room temperature. This part is judged to be within the good range when the environment in which it is used is not severe, but it is an example where it is judged to be a defective part when it is used in a field where the required characteristics are severe. As described above, it is necessary to set the hydrogen treatment condition according to the required characteristic specifications, and the present invention can deal with it.

[0019]

As described above, according to the method of the present invention, since hydrogen treatment is performed during drawing, it is possible to directly and efficiently inspect the hermetic coating state over the entire length in an extremely short time. It is very effective when used as a means for guaranteeing the full length of a hermetically coated optical fiber.

[Brief description of drawings]

FIG. 1 is a schematic sectional view illustrating an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the distance from the incident end and the backscattered light intensity, which is used when detecting a defective coating portion in the method of the present invention.

FIG. 3 is a loss-wavelength characteristic diagram of an optical fiber when only hydrogen treatment is performed without performing hermetic coating.

FIG. 4 is an OTD of a hermetically coated optical fiber in which a coating defect is intentionally formed in Example 1 of the present invention.
It is a wave form diagram which shows R measurement result.

FIG. 5 shows the loss-wavelength characteristics of the normal state coating portion and the defective portion of the hermetically coated optical fiber prepared in Example 1 of the present invention in comparison with a reference sample which is neither hermetically coated nor hydrogenated. It is a figure.

FIG. 6 is an OTD of a hermetically coated optical fiber in which a defective coating is intentionally formed in Example 2 of the present invention.
It is a wave form diagram which shows R measurement result.

FIG. 7 is a waveform diagram showing an OTDR measurement result of a hermetically coated optical fiber that has been subjected to severe hydrogen treatment in Example 3 of the present invention.

[Explanation of symbols]

1 drawing furnace, 2 reaction vessel for hermetic coating, 3 upper seal gas introducing pipe,
4 source gas introduction pipes, 5 exhaust pipes,
6 Lower seal gas introduction pipe, 7 Hydrogen treatment container, 8 Hydrogen-containing gas introduction pipe, 9
Exhaust pipe, 10 Seal gas introduction pipe 11, Outer diameter measuring device, 12 Cooler,
13 resin coating device, 14 curing furnace,
15 Hermetically coated fiber.

Front page continued (72) Inventor Hiroki Ishikawa 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Motonobu Nakamura 1-taya-cho, Sakae-ku, Yokohama, Kanagawa Sumitomo Electric Industries Yokohama Works Co., Ltd.

Claims (7)

[Claims] 1. A preform for an optical fiber is melted and spun in a drawing furnace in a drawing step to form a bare fiber, and then the bare fiber is introduced into a reaction vessel and a raw material gas is introduced into the reaction vessel. In the method for producing a hermetically coated optical fiber by applying a thin coating layer on the bare fiber by a chemical vapor deposition method, in the drawing step, hydrogen is passed through an atmosphere containing hydrogen immediately after the hermetic coating is formed. After the treatment, the hermetically coated optical fiber is wound on a reel at the end of the drawing step, light of a predetermined wavelength is incident from one end of the wound hermetically coated optical fiber, and the backscattered light is detected. The optical quality of the hermetic coat layer is characterized by inspecting the quality of the hermetic coat layer in a positional manner in the fiber length direction. Manufacturing method of ba. 2. The method for producing a hermetically coated optical fiber according to claim 1, wherein the optical fiber is cooled at the same time as or immediately after the hydrogen treatment of passing through the atmosphere containing hydrogen. 3. The method for producing a hermetically coated optical fiber according to claim 1, wherein the atmosphere containing hydrogen contains at least one of He, Ar and N ₂ . 4. The predetermined wavelength is 1.24 ± 0.1 μm
Or 1.39 ± 0.1 μm, The method for producing a hermetically coated optical fiber according to any one of claims 1 to 3. 5. The hermetic coat light according to claim 1, wherein a hermetic coat covering state defective portion is detected according to the result of the inspection, and screening is performed to remove the defective portion. Fiber manufacturing method. 6. The quality of the overall hermetic coat layer is determined by measuring the loss wavelength characteristic of the hermetically coated optical fiber after the screening and obtaining the average value of the amount of loss increase due to hydrogen penetration in the lengthwise direction. The method for manufacturing a hermetically coated optical fiber according to any one of claims 1 to 5, which is characterized in that. 7. The method for producing a hermetically coated optical fiber according to claim 1, wherein the hermetic coating is a carbon coating.