JPH06308359A - Hermetically coated optical fiber and its production - Google Patents

Abstract

PURPOSE:To provide the hermetically coated optical fiber and the process for production of this optical fiber. CONSTITUTION:The thin-film coating layer of an optical fiber 8 having the thin-film coating layer possessing hermeticity on its surface has the bond of carbon-silicon. A preform 2 for the optical fiber is melted and spun by a furnace 1 kept at a high temp. to form a bare fiber 20 and this bare fiber 10 is immediately introduced into a reaction vessel 3 for hermetic coating and gaseous raw materials 4, 5 are introduced into this reaction vessel 3 to form the thin-film coating layer by a chemical vapor deposition method on the bare fiber 10, by which the optical fiber is produced. The thin-film coating layer having the bond of the carbon-silicon is formed by using a gaseous mixture composed of the gaseous carbon 4 and the gaseous silane 5 at this time. As a result, the hermeticity and fatigue characteristic are compatibly obtd.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art When a hermetic coating is applied to an optical fiber, the rate of penetration of substances such as water and hydrogen from the external environment can be slowed down as compared with a normal optical fiber. In particular, it is known that the penetration of water and hydrogen adversely affects the strength and optical transmission characteristics of the optical fiber, and the hermetic coating is very useful for improving these characteristics. Usually, a carbon film is used as the hermetic coating. It has chemical stability,
This is because it is excellent in terms of tissue fineness. Also,
As a coating method, by introducing the raw material gas into the reaction tube just below the drawing furnace, the raw material gas reacts due to the heat of the optical fiber, and a thermal chemical vapor deposition method for forming a carbon film on the fiber surface is used. Has been. Conventionally, as such a technique, a carbon film is coated by a thermal chemical vapor deposition method using a mixed gas of a hydrocarbon and a halogenated hydrocarbon as disclosed in JP-A-3-15349. The carbon-coated optical fiber obtained at this time has high hermetic properties and high fatigue properties.

[0003]

Conventionally, the hermetically coated optical fiber has been manufactured by the method as described above. Hermetic properties and fatigue properties are superior to those of the uncoated optical fiber, but it is known that mechanical strength is slightly weakened. Moreover, it was found that when the conditions were changed so that the strength was almost the same as that of the ordinary optical fiber, it was only hermetically equivalent to that of the ordinary optical fiber, despite the hermetic coating. Therefore, it is necessary to satisfy both properties of strength and hermeticity. The present invention addresses this problem, and is intended to provide a hermetically coated optical fiber having both hermetic properties and fatigue properties, and a method for producing the same.

[0004]

As a means for solving the above problems, the present invention provides an optical fiber having a hermetic thin film coating layer on its surface, wherein the hermetic thin film coating layer is carbon-based. Provided is a hermetically-coated optical fiber having a bond of silicon. Further, according to the present invention, an optical fiber preform is melted and spun in a furnace kept at a high temperature, and immediately after the bare fiber is formed, the bare fiber is introduced into a hermetic coating reaction vessel and a raw material gas is introduced into the reaction vessel. In the method for producing a hermetically coated optical fiber in which a thin film coating layer is formed on the bare fiber by a chemical vapor deposition method, a mixed gas of carbon-based gas and silane-based gas is used as the raw material gas to produce carbon-silicon. Provided is a method for manufacturing a hermetically coated optical fiber, which comprises forming a thin film coating layer having a bond. In the present invention, the raw material gas mixing ratio is particularly preferably such that the number of silicon atoms contained in the mixed gas does not exceed the number of carbon atoms, and the raw material gas is diluted with an inert gas. It is particularly preferable that

[0005]

The present invention will be described in detail with reference to FIG. When applying a hermetic coating, not only a carbon-based gas is used, but a silane-based gas is mixed and the gas is passed through a reaction vessel 3 into which a bare fiber drawn from an optical fiber preform 2 in a resistance furnace 1 is drawn. The fiber 10 is introduced and a hermetic coating is applied. The silane-based gas is supplied from a silane-based gas supply system 5, which is a system different from the carbon-based gas supply system 4,
The carbon-based gas and the silane-based gas are each diluted with an appropriate inert gas and then mixed at an arbitrary mixing ratio. This mixed gas reacts by the heat of the bare fiber 10 by the thermal chemical vapor deposition method (thermal CMD method), and the fiber is hermetically coated. At this time, the characteristics of the hermetic coating can be controlled by controlling the flow rate of each gas, the mixing ratio, and the fiber temperature. After the hermetic coating, an organic resin is applied with dice 6 and 7 and wound as a hermetic coat optical fiber 8 by a winding machine 9.

According to the present invention, the heat of the drawn bare fiber itself reacts with the mixed gas of the carbon-based gas and the silane-based gas, which is a raw material, and in addition to the carbon-carbon bond, the carbon-silicon bond. A hermetic coating is formed which has a structure with. Here, as the carbon-based gas in the raw material gas, for example, hydrocarbons such as ethylene, acetylene and chloroform, and halogen carbon hydrocarbons are used. Further, as the silane-based gas, SiH ₄ , SiHCl ₃ , SiCl
_A compound consisting of silicon, hydrogen, halogen, etc. such as ₄ is used. It is desirable that these raw materials are gases, but they may be liquids. This is because it is possible to vaporize using an appropriate inert gas. Among the compounds having a carbon-silicon bond, the silicon carbide produced in this system has two types of structures, a sphalerite type and a wurtzite type, both of which have a dense structure and a high structure. Since it has high strength, by coating a film having this structure, it is possible to manufacture a hermetically coated optical fiber having excellent strength and hermeticity.

Regarding the raw material composition ratio, it is preferable to adjust the mixing ratio of the raw material gases so that the silicon-silicon bond does not occur. Specifically, it is particularly preferable that the number of silicon atoms contained in the mixed gas does not exceed the number of carbon atoms. As a suitable mixing ratio, 1 to 2 silicon atoms are preferable to 10 carbon atoms. When the number of silicon atoms exceeds the number of carbon atoms, silicon-silicon bonds are locally formed, which causes deterioration of strength and hermeticity. This is because the silicon crystal has a structure with a lot of gaps and the hermetic coating property is deteriorated. The inter-bond distances are carbon-carbon bond 1.42Å, silicon-carbon bond 1.89Å, and silicon-silicon bond 2.35Å. Further, the raw material is preferably diluted with a suitable inert gas. This is because when it is diluted to a certain extent, the reaction for breaking the Si—O—Si bond on the fiber surface does not occur, cracks do not occur, and the strength of the glass itself does not decrease and the fiber strength does not deteriorate. It is impossible to completely prevent the reaction with the glass surface, but it is possible to reduce the frequency of occurrence by reducing the concentration of the raw material gas,
Strength deterioration can be suppressed. The degree of dilution is such that the concentration of the raw material gas is in the range of 10 to 50%. A particularly preferable range is 25 to 35%. The thickness of the hermetic coat layer of the present invention is not particularly limited, but usually about 30 to 50 μm is sufficiently effective.

[0008]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. The initial strength in the following Examples and Comparative Examples is as follows: the optical fiber is pulled at a constant speed of 300 mm / min until it is broken,
The 50% value of the breaking probability obtained from the Weibull plot of the value at the time of breaking. In the hydrogen test, an optical fiber was placed in a furnace kept at 80 ° C., 1 atm of hydrogen was blown into the furnace, and the optical fiber was allowed to stand for 20 hours, and then the optical transmission loss of the optical fiber at a wavelength of 1.24 μm was measured. .

COMPARATIVE EXAMPLE 1 Using the apparatus shown in FIG.
A carbon coated optical fiber was manufactured. At this time, drawing was performed using only a carbon-based gas as a raw material gas. As carbon-based gas, ethylene and chloroform are 100
Flowing ml / min, 150ml / min, drawing speed is 200m
/ Min. Regarding the characteristics of this carbon-coated optical fiber, the initial strength showed a reasonable value of 5.8 kg, while the loss increase at the wavelength of _1.24 μm after the hydrogen test at 80 ° C. for 1 atm for 20 hours was Δα _1.24 0.21 dB / km
And it was pretty bad.

Example 1 Using the apparatus shown in FIG. 1 as in Comparative Example 1, a hermetically coated optical fiber was manufactured according to the present invention by using a silane-based gas in addition to a carbon-based gas as a raw material gas. . Ethylene 1 as carbon-based gas
00 ml / min, chloroform 130 ml / min, and silane-based gas of 20 ml / min of silicon tetrachloride were flown, and drawing was performed at a drawing speed of 200 m / min. The characteristics of this hermetically coated optical fiber are as follows: initial strength 6.0 kg, 80 ° C, 1a
The loss increase Δα _1.24 at the wavelength of _1.24 μm after the hydrogen test for 20 hours at tm was 0.04 dB / km, and it was possible to obtain a hermetically coated optical fiber excellent in both strength and hydrogen resistance. After removing the organic resin of the optical fiber to form a fiber having only the hermetic coat layer, the electron spin resonance spectrum (ESR) of the fiber was measured, and the spectrum shown in FIG. 2 was obtained. The small peak is the signal of the standard sample and the large peak in the center is the signal obtained from the fiber according to this example, which has the same spectrum as SiC and the coating of this fiber contains SiC bonds. It indicates that It should be noted that no spectrum can be seen in this region in the fiber that is not hermetically coated.

[Embodiment 2] As in Embodiment 1, the apparatus of FIG. 1 is used, but the source gas is diluted to 1/3 of that in Embodiment 3 with helium, and the other conditions are exactly the same as in Embodiment 3. To produce a hermetically coated optical fiber. That is, changing only the concentration without changing the amount of raw material gas introduced into the reaction tube, 300 ml of ethylene: helium (1: 2) mixed gas
/ Min, mixed gas of chloroform: helium (1: 2) 15
0 ml / min, silicon tetrachloride: helium (1: 2) 60 m
Flowed at 1 / min. Also in this example, the number of silicon atoms does not exceed the number of carbon atoms. The characteristics of the hermetically coated optical fiber obtained at this time were that the initial strength was 5.9 kg, 80 ° C,
A loss increase Δα _1.24 at a wavelength of _1.24 μm after a hydrogen test at 1 atm for 20 hours was 0.03 dB / km, and a hermetic coated optical fiber excellent in both characteristics could be obtained.

[0012]

As described above, the hermetically coated optical fiber produced by mixing not only the carbon-based gas but also the silane-based gas as the hermetic coating gas is excellent in initial strength and hermeticity. , Does not cause long-term deterioration in strength. Furthermore, since water vapor and hydroxyl groups do not enter the bare fiber, the transmission characteristics can be maintained in a good state. Therefore, the optical fiber obtained by the present invention is very suitable for use in a state where stress is applied in an atmosphere of water or hydrogen, such as a state where it is used as a submarine cable.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a method for producing a hermetically coated optical fiber of the present invention.

FIG. 2 is an electron spin resonance (E) of the hermetically-coated optical fiber of the present invention manufactured in Example 1 of the present invention.
(SR) spectrum diagram.

[Explanation of symbols]

1 resistance furnace, 2 optical fiber base material, 3 reaction vessel, 4 carbon-based gas supply device, 5 silane-based gas supply device, 6 dice, 7 dice, 8 hermetic coat optical fiber, 9 winder,
10 Bare fiber.

Claims (4)

[Claims] 1. An optical fiber having a hermetic thin-film coating layer on its surface, wherein the hermetic thin-film coating layer has a carbon-silicon bond. fiber. 2. Immediately after melting and spinning an optical fiber preform in a furnace kept at a high temperature to form a bare fiber, the bare fiber is introduced into a hermetic coating reaction vessel and a raw material gas is introduced into the reaction vessel. In the method for producing a hermetically coated optical fiber, wherein a thin film coating layer is formed on the bare fiber by a chemical vapor deposition method by introducing,
A method for producing a hermetically coated optical fiber, comprising forming a thin film coating layer having a carbon-silicon bond by using a mixed gas of a carbon-based gas and a silane-based gas as the raw material gas. 3. The method for producing a hermetically coated optical fiber according to claim 2, wherein the raw material gas mixing ratio is such that the number of silicon atoms contained in the mixed gas does not exceed the number of carbon atoms. 4. The method for producing a hermetically coated optical fiber according to claim 2, wherein the raw material gas is diluted with an inert gas.