JPH03171020A - Hermetically coated optical fiber and production thereof - Google Patents

Abstract

PURPOSE:To improve the initial tensile strength of the optical fiber by providing a low-density hermetic coating of the density lower than the density of a high- density hermetic coating in addition to the high-density hermetic coating having good hydrogen resistance characteristic and fatigue resistance characteristic on the optical fiber. CONSTITUTION:This hermetically coated optical fiber 10 is provided with the high-density hermetic coating 9 on the surface of the optical fiber 3 and is provided with the low-density hermetic coating of the density lower than the density of the high-density hermetic coating 9 thereon. The low-density hermetic coating of the density lower than the density of the high-density hermetic coating is a relatively porous film and, therefore, the optical fiber withstands large elongation if the optical fiber is provided with the above-mentioned low-density hermetic coating in addition to the high-density hermetic coating having the good hydrogen resistance characteristic and fatigue resistance characteristic in such a manner. The initial tensile strength of the optical fiber is thus improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hermetic coated optical fiber and an apparatus for manufacturing the same.

[Conventional technology] Recently, a high-density hermetic coating made of an inorganic material is provided on the surface of an optical fiber, and H'2 from the outside to the inside of the optical fiber is
Hermetically coated optical fibers that prevent the intrusion of 0 and H2 have been proposed. In particular, carbon and carbon compounds are used as materials for the hermetic coating, and products with very good properties have been obtained.

FIG. 3 shows a conventional hermetic coated optical fiber manufacturing apparatus. By introducing the optical fiber base material l into a drawing furnace 2 and drawing it, an optical fiber 3 consisting of a core 3a and a cladding 3b is formed as shown in FIG.
This is introduced into the reactor 4. A heater 5 is arranged outside the reactor 4, and the heater 5 causes the reactor 4 to
A heating zone 6 is provided inside. A raw material gas inlet 7 for hermetic coating is provided at the lower part of the reactor 4, from which a raw material gas such as methane, ethane, ethylene, etc. is injected. Hydrocarbon gas such as acetylene, propane, butane, etc. is supplied into the reactor 4 together with an inert gas (for example, N2, etc.) added as necessary. An exhaust port 8 is provided at the top of the reactor 4 .

Carbon is formed at high density on the surface of the optical fiber 3 guided into the reactor 4 by the thermal decomposition of the raw material gas, and this causes a gas phase chemical reaction (hereinafter referred to as thermal CVD method). This deposits on the surface of the optical fiber 3 to form a high-density hermetic coating 9 made of carbon as shown in FIG. 4, resulting in a hermetically coated optical fiber 10. The hermetic coated optical fiber 10 passes through an outer diameter measuring device 11, the outer diameter is measured, and the drawing speed and feeding speed of the optical fiber base material 1 are adjusted based on the measured value, so that the outer diameter of the optical fiber 3 is kept constant. be restricted as follows.

In addition, when trying to form a hermetic coating made of SiC, Tic, add SicJ24,Sic to the hydrocarbon gas.
What is necessary is to add iH4, Tic, g4, etc.

The hermetically coated optical fiber 10 is then passed through an applicator 12 to form a plastic coating around its outer periphery. For example, an ultraviolet curable resin is applied onto the hermetically coated optical fiber 10 using an applicator 12, passed through a curing furnace 13 such as an ultraviolet irradiation furnace to be cured, and wound up using a winder t4.

As the resin applied by the applicator 12, a thermosetting resin or a thermoplastic resin can also be used. If a thermosetting resin is used, a heating furnace is used as the curing furnace 13.

As the hermetic coated optical fiber 10 manufactured by the thermal CVD method in this manner, one in which the high-density hermetic coating is a carbon film is well known. When this carbon film is made of hydrocarbon gas as a raw material, it becomes a very high-density film containing fine graphite crystals, that is, a high-density hermetic coating 9. In particular, the crystal planes on the surface of the optical fiber 3 are also aligned, so molecules such as hydrogen cannot pass through this film. Therefore, the hydrogen resistance of the optical fiber 3 is significantly improved.

Further, the high-density hermetic coating 9 made of a carbon film does not undergo fatigue fracture due to H20 unlike quartz glass, so its fatigue resistance is significantly improved.

[Problems to be Solved by the Invention] However, by coating the fiber with the high-density hermetic coating 9 made of a carbon film, the initial tensile strength of the fiber itself is approximately 4 to 5 kg, which is higher than that of conventional optical fibers without the high-density hermetic coating 9. Fiber (initial tensile strength is approximately 6 kg)
In comparison, the initial tensile strength appears to have deteriorated. this is,
In the case of a high-density hermetic coating 9, fine inter-crystal defects tend to become the starting point of cracks, and the high-density hermetic coating 9 has a small elongation. The micro cracks on the surface are enlarged,
It is presumed that this is because it leads to breakage.

In actual use of optical fibers, it is essential that they have high strength when handling them during construction work such as splicing. Therefore, there has been a demand for a hermetic coated optical fiber 10 that has both hydrogen resistance, fatigue properties, and required initial tensile strength. However, such a product could not be obtained by conventional methods simply by changing the coating material.

An object of the present invention is to provide a hermetically coated optical fiber having hydrogen resistance, fatigue resistance, and required initial tensile strength, and an apparatus for manufacturing the same.

[Means for Solving the Problems] The means of the present invention for achieving the above object are as follows.

The hermetic coated optical fiber according to the invention described in claim (1) is characterized in that the surface of the optical fiber is coated with a high-density hermetic coating and a low-density hermetic coating with a lower density.

The invention according to claim (2) provides a hermetic-coated optical fiber manufacturing apparatus for manufacturing a hermetic-coated optical fiber by passing an optical fiber drawn from an optical fiber preform into a reaction furnace and providing a hermetic coating thereon. A first raw material gas inlet for introducing raw material gas for high-density hermetic coating is provided on one longitudinal side of the reactor, and a first raw material gas inlet for introducing raw material gas for low-density hermetic coating is provided on the other longitudinal side of the reactor. The reactor is characterized in that a second raw material gas inlet is provided for introducing the reactor, and an exhaust port is provided approximately in the center of the reactor in the longitudinal direction.

[Function] As claimed in claim (1), when an optical fiber is provided with a low-density hermetic coating having a lower density than the high-density hermetic coating in addition to a high-density hermetic coating with good hydrogen resistance and fatigue resistance, Because the low-density hermetic coating is a relatively porous film, it can withstand large elongations and improve the initial tensile strength of the optical fiber.

Therefore, the hermetically coated optical fiber of the present invention has the required initial tensile strength in addition to hydrogen resistance and fatigue resistance.

According to claim (2), both a high-density hermetic coating and a low-density hermetic coating can be formed in a common reactor. In this case, the hermetic layer made of the raw material gas supplied on the upstream side becomes the lower layer, and the hermetic coating made of the raw material gas supplied on the downstream side is coated thereon.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings. Note that parts corresponding to those in FIGS. 3 and 4 described above are designated by the same reference numerals.

FIG. 1 shows a hermetic coated optical fiber 1 according to the present invention.
0 shows an example of 0. The hermetic coated optical fiber 10 of this embodiment has a structure in which a high-density hermetic coating 9 is provided on the surface of the optical fiber 3, and a low-density hermetic coating 15 having a lower density than the high-density hermetic coating 9 is provided thereon. It has become.

With this structure, the high-density hermetic coating 9 has hydrogen resistance and fatigue resistance, and the low-density hermetic coating 15 has the required initial tensile strength to withstand large elongation, so that the hydrogen resistance and fatigue resistance are improved. and the required initial tensile strength.

FIG. 2 shows an example of a manufacturing apparatus for manufacturing the hermetically coated optical fiber as shown in FIG.

In this embodiment, a first raw material gas inlet 7a is used to introduce the raw material gas for the high-density hermetic coating 9 into the upper end side of the reactor 4.
A second source gas inlet 7 is provided for introducing the source gas for the low-density hermetic coating 15 into the lower end side of the reactor 4.
b, and an exhaust port 8 is provided at approximately the center of the reactor 4 in the vertical direction.

When the hermetic coated optical fiber 10 is manufactured using such a reactor 4, the high-density hermetic coating 9 is applied to the surface of the optical fiber 3 in the upper half of the reactor 4 by thermal CV.
A low-density hermetic coating 1 is formed on the surface of the high-density hermetic coating 9 in the lower half of the reactor 4.
5 is formed by thermal CVD method.

In particular, if the high-density hermetic coating 9 and the low-density hermetic coating 15 are formed continuously in the same reactor 4,
A gradual layer change occurs at the boundary between the two, resulting in two coatings 9
, 10 is improved, and the bonding strength between both the coatings 9 and 15 can be increased.

In addition, when both hermetic coatings are provided in the same reactor 4, the inner hermetic coating that was coated first has a high temperature, which helps the reaction of the next hermetic coating, speeding up the reaction, and improving synthesis efficiency. .

In addition, a second raw material gas inlet 7b for introducing raw material gas for the low-density hermetic coating 15 is provided on the upper side of the reactor 4,
A first raw material gas inlet 7a for introducing raw material gas for the high-density hermetic coating 9 can also be provided on the lower side of the reactor 4. In this way, it is possible to obtain a hermetically coated optical fiber 10 having a structure in which the low-density hermetic coating 5 exists on the surface of the optical fiber 3, and the high-density hermetic coating 9 exists on the outside thereof.

The low-density hermetic coating 15 can be formed as a substantially poor quality carbon film by using a halogen compound as a main raw material or by adding a hydrocarbon gas to the halogen compound. This is because the presence of large halogen molecules during the reaction suppresses crystal growth and tends to result in a film with a relatively porous, non-quality structure.

Such a low-density hermetic coating 15 can withstand large elongations and does not reduce the tensile strength of the optical fiber 3. However, since this low-density hermetic coating 15 does not have a sufficiently dense structure, hydrogen molecules permeate to some extent.

However, by combining with the high-density hermetic coating 9, the properties of both coatings 9.15 can be combined. In particular, it is most effective to provide the low-density hermetic coating 15, which is a layer with high strength and resistance to elongation, on the outside at the interface with the resin, which is likely to be the starting point of fracture and where microcracks are likely to occur. Of course, even if the low-density hermetic coating 15 is first provided on the surface of the optical fiber 3, it is still effective because delamination at the interface with the optical fiber 3 is less likely to occur.

In addition, on the surface of the high-density hermetic coating 9, Sic, T
A low density hermetic coating 15 of a material with higher fracture toughness than carbon, such as iC, can also be provided.

Film thickness: Strength by electron microscope: Tensile test with a length of 10 m, tensile strength 5%/min,
n=19 Fatigue properties: Two thread length: 40an, tensile speed: 0. 5, 1. 0. 5. 0. 10.
50%/mim, n40 hydrogen resistance: H2 1at
m, loss increase of 1.24 μ after treatment at 75°C for 24 hours Film thickness: Strength by electron microscope: Tensile test with 10 m length, tensile strength 5%/min,
n・19 fatigue properties: length 40an, tensile speed 0. 5, 1. 0, 5. 0, 10.
50%/min, n=lo Hydrogen resistance: H2 1a
+m. Loss increase of 1.24 μ after treatment at 75° C. for 24 hours Tables 1-a and 1-b show the experimental conditions and fiber characteristics of the comparative example and the example.

Comparative Example 1 is an example of a carbon-coated fiber produced using only acetylene gas as a raw material. When the structure of the obtained carbon film was investigated by Raman spectroscopy and electron beam diffraction, it was found that the carbon was oriented on the fiber surface and contained graphite.

Such a membrane is dense and does not allow H2 molecules to pass through, so no increased loss was observed in the fiber after hydrogen treatment. However, the tensile strength is quite low at 4.5 kg. In Comparative Example 2, chlorine was added to the raw material gas, and in this reaction, chlorine suppresses the reaction and prevents the growth of crystals such as graphite, resulting in a network-like non-quality structure. Since such a weakly bonded carbon film can withstand the elongation of the glass fiber, and therefore fracture begins from the glass surface, the optical fiber exhibited high strength comparable to that of the conventional non-coated fiber shown in Comparative Example 3. However, since the structure has many gaps, a certain amount of H2 molecules will pass through. However, compared to non-coated fibers, the hydrogen resistance is much improved.

Examples 1 and 2 are examples in which both of the above-mentioned favorable characteristics were attempted to be combined. In Example 1, acetylene gas was introduced from the top of the reactor, and chlorine-added acetylene gas was flowed from the bottom. In Example 2, carbon tetrachloride is introduced from below as a source gas using an argon carrier. In both cases, a film with good hydrogen resistance is first formed on the surface of the optical fiber, and a high-strength film is synthesized on top of that, resulting in high fiber strength and at the same time improved fatigue properties and hydrogen resistance. There is.

Examples 3 and 4 show cases in which high-toughness SiC and TiC are combined as a low-density hermetic coating 15 on a high-density hermetic coating 9. Its strength is better than carbon, but its fatigue properties are slightly lower. However, the carbon layer as the high-density hermetic coating 9 is effective in terms of hydrogen resistance, and has a sufficient function as a hermetic coating.

In Example 5, acetylene gas was introduced from the lower part of the reactor, and chlorine-added acetylene gas was flowed from above. In this case, a low-density hermetic coating made of a non-quality film with good stretch is formed on the fiber surface, and a high-density hermetic coating that does not allow hydrogen to permeate is synthesized thereon.

Therefore, the alignment between the optical fiber and the low-density hermetic coating is good, and there is no decrease in strength due to peeling at the interface.

However, since fractures from the surface of the high-density hermetic coating remained, the improvement in strength was 5.0 kgf.

However, the hydrogen resistance has been sufficiently improved.

[Effects of the Invention] As explained above, according to the hermetic coated optical fiber and the manufacturing apparatus thereof according to the present invention, the following effects can be obtained.

In claim (1), in addition to the high-density hermetic coating having good hydrogen resistance and fatigue resistance, the optical fiber is provided with a low-density hermetic coating having a lower density than the high-density hermetic coating. Since the coating is a relatively porous film, it can withstand large elongations and improve the initial tensile strength of the optical fiber.

Therefore, the hermetic structure of the present invention. The thick-coated optical fiber has the advantage of having the required initial tensile strength in addition to hydrogen resistance and fatigue resistance.

According to claim (2), there is an advantage that a high-density hermetic coating and a low-density hermetic coating can be formed together in the same reactor. Furthermore, if a high-density hermetic coating and a low-density hermetic coating are continuously formed in the same reactor, both can be formed continuously,
A gradual layer change occurs at the boundary between the two, improving the consistency between the two and increasing the bonding strength between the two. Furthermore, when both hermetic coatings are provided in the same reactor, the inner hermetic coating that was coated first has the advantage of helping the reaction of the next hermetic coating, speeding up the reaction, and improving synthesis efficiency. There is.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of an embodiment of a hermetic-coated optical fiber according to the present invention, and FIG. 2 is a longitudinal sectional view showing a schematic structure of an embodiment of a hermetic-coated optical fiber manufacturing apparatus according to the present invention. 3 is a vertical cross-sectional view showing a schematic configuration of a conventional hermetic-coated optical fiber manufacturing apparatus, and FIG. 4 is an enlarged cross-sectional view of the conventional hermetic-coated optical fiber. 1... Optical fiber base material, 2... Drawing furnace, 3...
Optical fiber, 4... Reactor, 5... Heater, 6...
-Heating zone, 7a...first raw material gas inlet, 7b
...Second source gas inlet, 8...Exhaust port, 9...
- High-density hermetic coating, 10...hermetic coating optical fiber. Figure 1

Claims (2)

[Claims] (1) A hermetic-coated optical fiber characterized in that the surface of the optical fiber is coated with a high-density hermetic coating and a low-density hermetic coating with a lower density. (2) In a hermetic-coated optical fiber manufacturing apparatus that manufactures a hermetic-coated optical fiber by passing an optical fiber drawn from an optical fiber preform into a reactor and providing a hermetic coating, one side in the longitudinal direction of the reactor is provided with a first raw material gas inlet for introducing the raw material gas for the high-density hermetic coating, and a second raw material gas inlet for introducing the raw material gas for the low-density hermetic coating is provided on the other longitudinal side of the reactor. An apparatus for manufacturing a hermetic coated optical fiber, characterized in that an inlet is provided, and an exhaust port is provided approximately in the center of the reactor in the longitudinal direction.