JPH09132438A - Partially hermetic coating method for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for partially applying a carbon hermetic coating on an optical fiber which obviates the formation of the reaction products and unreacted residues generated by cracking of a varnish layer at the time of initial reaction of reformation of a carbon film, improves the deposition state of the carbon film of this part and improves a fatigue characteristic, initial strength, etc. SOLUTION: The carbon film 12 is removed from the hermetically coated optical fiber which is provided with the carbon film 12 on the outer periphery of the optical fiber 11 and is provided with the varnish coating layer 14 on its outer periphery. The carbon film 19 is formed again on the optical fiber 11 of the part where this carbon film 12 is removed. At this time, the varnish coating layers 14 on both sides of the part where the carbon film 12 is removed are removed to the prescribed length and thereafter, the optical fiber 11 is irradiation with a laser beam, by which the temp. is elevated. A gaseous raw material 18 is brought into contact with this part, by which the carbon film 19 is formed again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for partially applying a carbon hermetic coating to an optical fiber.

[0002]

2. Description of the Related Art A general silica glass optical fiber is
For connector connection and fusion splicing, remove the coating and
Powder processing is performed. For this reason, these terminal processing
By simply contacting various jigs for connection to the surface of the optical fiber
Small cracks are likely to occur. Crush the surface of the optical fiber.
If there is a crack, moisture in the environment surrounding the optical fiber (especially H
_Two) Invades the tip of this crack,
To significantly reduce the strength of the optical fiber.
Labor phenomenon). Therefore, prevent such fatigue phenomenon and prevent
To improve long-term reliability of fiber strength,
Form a carbon hermetic coating that is impermeable to moisture
Methods have been developed.

One of the methods for producing a hermetically coated optical fiber is to bring a hydrocarbon-based raw material gas into contact with an optical fiber immediately after drawing and thermally decompose the hydrocarbon-based raw material gas to utilize the residual heat of the optical fiber. There is a method of forming a carbon film of about 500 Å on the surface of the optical fiber. Since this carbon film almost completely prevents H ₂ from penetrating, the hydrogen resistance of the optical fiber is remarkably improved.

Further, since at the same time carbon film suppressing of H ₂ O penetration does not occur stress corrosion caused in H ₂ O found in quartz glass, fatigue properties are also markedly improved. Further, it is possible to manufacture a hermetically coated optical fiber having an initial strength equal to or higher than that of a normal optical fiber. When these highly reliable hermetically coated optical fibers are fusion-spliced together, the carbon film on the surface is oxidized and disappeared by the discharge heat during fusion at the fusion-spliced part, leaving the optical fiber surface exposed. I will end up. If left in this state, the fusion spliced part will
Compared to other parts, the reliability of strength, fatigue characteristics, etc. is significantly impaired.

As a partial carbon film reforming method for such a carbon film disappearing portion, (1) an optical fiber is heated by irradiation with a carbon dioxide gas laser or the like, and a hydrocarbon-based raw material gas is supplied around the irradiated portion of the optical fiber. A thermal CVD method for coating a carbon film. (2) A plasma method in which plasma is generated around the optical fiber, and a hydrocarbon-based source gas is supplied into it to activate the source molecules and coat the carbon film. And so on. The present invention relates to the thermal CVD of (1) above.
It concerns the improvement of the law.

[0006]

In order to fusion splice the hermetically coated optical fiber, the UV resin coating layer formed on the outer periphery of the hermetically coated optical fiber is first removed by a predetermined length. Then, a varnish coat layer is formed by applying a protective varnish to the resin coating layer-removed portion to prevent scratches on the optical fiber that occur when the varnish coater is attached to the fusion machine. The optical fiber that has been subjected to such pretreatment is set in a fusion splicer and spliced. The carbon film at the fusion-bonded portion disappears due to the discharge heat of the discharge arc together with the varnish coat layer. However, the varnish coat layer is present at a portion separated by several mm or more from both ends of the fusion spliced portion.

The fusion-bonded portion containing the varnish coat layer at a portion separated by several mm or more at both ends is set in a container that blocks the flow of the outside air, and the raw material gas is introduced by the above-mentioned thermal CVD method to introduce a carbon film. The carbon film is reformed while overcoating several mm on both ends including the disappeared portion. However, in the initial stage of the thermal decomposition reaction of the raw material gas, reaction products and unreacted residues due to the decomposition of the varnish coat layer occur simultaneously with the formation of the carbon film. For this reason, the deposited state of the carbon small piece plates constituting the reformed carbon film becomes disordered, and uneven coating occurs in the longitudinal direction. In particular, the effect is remarkable in the overcoat part of several mm on both sides of the part where the carbon film disappears. Furthermore, this has a detrimental effect on the reformed carbon film. As a result, H ₂ O molecules easily reach the surface of the optical fiber through the gaps between the carbon small piece plates, which causes deterioration of fatigue characteristics. In addition, the carbon small pieces that are randomly deposited tend to cause cracks between the small pieces, which causes a decrease in initial strength.

The present invention solves the above-mentioned problems and eliminates the generation of reaction products and unreacted residues due to the decomposition of the protective varnish layer generated at the initial stage of the reaction when the carbon film is reformed. It is an object of the present invention to provide a method for partially applying a hermetic coating to an optical fiber in which the deposited state of the carbon film thus obtained is improved, and as a result, fatigue characteristics, initial strength and the like are improved.

[0009]

The present invention has the following means to solve the above problems.

According to the first aspect of the present invention, a varnish coat layer is applied to a portion where carbon film disappearance is predicted in a hermetically coated optical fiber having a carbon film on the outer periphery of the optical fiber and its periphery, and then the carbon film and the varnish coat layer are provided. In the partially hermetic coating method of the optical fiber to re-form a carbon film on the partially disappeared optical fiber, after removing a predetermined length of the varnish coat layer on both sides of the part where the carbon film and the varnish coat layer have disappeared, The optical fiber from which the carbon film has been removed is irradiated with laser light to raise the temperature, and then a raw material gas is brought into contact with the optical fiber to re-form the carbon film by a thermal CVD method.

According to a second aspect of the present invention, the varnish coat layer on both sides of the optical fiber from which the carbon film has disappeared is removed by a predetermined length by irradiating a laser beam having an output lower than that of the laser beam for reforming the carbon film. It is characterized by doing.

[0012]

According to the partially hermetic coating method of the optical fiber of the first aspect of the present invention, the portion where the carbon film and the varnish coat layer disappear when the carbon film is re-formed on the optical fiber where the carbon film disappears. Since the varnish coat layer on both sides of the varnish coat is removed by a predetermined length, the reaction product and unreacted residue are not generated due to the decomposition of the varnish coat layer by the irradiation of laser light in the initial reaction of the formation of the carbon film, The deposition state of the carbon small piece plate is improved.

That is, since the reaction product and the unreacted residue are not generated due to the decomposition of the varnish coat layer,
Recycled carbon strips at the fusion splice deposit horizontally or near horizontally to the substrate. It is difficult to deposit carbon strips having other random orientations in the atmosphere where the CVD reaction is occurring. Therefore, the orientation of the carbon small piece plate constituting the carbon film is improved, and the fatigue characteristics, initial strength, etc. are remarkably improved.

According to the partially hermetic coating method of the optical fiber of the second aspect of the present invention, the varnish coat layer on both sides of the optical fiber where the carbon film has disappeared is removed by a predetermined length when the carbon film is re-formed. Since the varnish coat layer is thermally decomposed and volatilized without being decomposed by combustion, a reaction product and an unreacted residue are not generated. Further, since the high-power laser beam is not applied to the portion of the optical fiber where the carbon film has disappeared, the optical fiber is not exposed to the laser beam and damaged.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. (Embodiment 1) FIGS. 1 to 4 show an embodiment of a method for partially hermetically coating an optical fiber according to the present invention. 1 to 4, reference numeral 10 is a hermetically coated optical fiber. The hermetically coated optical fiber 10 has an outer diameter of 12
A carbon film coating 12 and a UV resin coating layer 13 are sequentially provided on the outer periphery of a 5 μm silica optical fiber 11.

The end of the hermetically coated optical fiber 10 is dipped in a trichlene solution for about 1 to 2 minutes and U at the tip thereof is immersed.
The carbon film 12 is exposed by removing the V resin film layer by, for example, about 15 mm. After immersing the exposed portion of the carbon film 12 in a urethane insulating varnish diluting solution, a urethane insulating varnish is applied so as to prevent unevenness, and the urethane insulating varnish is dried with a heat gun. This operation is repeated about 3 times to form the varnish coat layer 14 of about 50 μm in FIG.
It is formed as shown in (a). Subsequently, the ends of the hermetically coated optical fibers 10 having the two varnish coat layers 14 formed thereon are set facing each other to a fusion splicer (not shown), and preliminary discharge and fusion discharge are performed to perform hermetic coating. The end faces of the optical fiber 10 are fusion-spliced as shown in FIG.

The varnish coat layer 14 and the carbon film coating 12 disappear about 4 to 5 mm around the periphery including the fusion splicing portion 15 due to the discharge at the time of fusion, and the silica-based optical fiber 11 is removed.
Is exposed. The optical fiber 11 including the exposed fusion spliced portion 15 is dipped in a sulfuric hydrofluoric acid solution, etched for about 3 minutes, washed with acetone, dried, and set in a carbon film reforming apparatus (not shown). The exposed optical fiber 11 including the fusion splicing portion 15 of the hermetically coated optical fiber 10 set in the carbon film reforming apparatus is shown in FIG.
As shown in (1), the hermetically coated optical fiber 10 is scanned in the longitudinal direction while irradiating a laser beam having an output of 2/3, which is lower than a predetermined laser used for reforming the carbon film, and the carbon film 12 is discharged by fusion. Figure 2 from the time it disappears
As shown in (c), the varnish coat layer 14 was thermally decomposed and removed by about 1 to 2 mm on both sides to expose the carbon film 12.

Thereafter, as shown in FIG. 4, the optical fiber 11 including the vanish coat layer disappearing portion 16 and the exposed fusion splicing portion 15 is irradiated with a laser having a predetermined output when the carbon film is reformed, and the raw material gas is irradiated. Raw material gas 1 from the inlet pipe 17A
8 was introduced to reform the carbon film 19, and the optical fiber 11 was partially provided with the hermetic coating 20 as shown in FIG. In FIG. 4, 17B shows an exhaust pipe. Table 1 shows the characteristics of the hermetically coated optical fiber 10A having the hermetic coating 20 of the fusion splicing portion 15 obtained in the above-mentioned embodiment.

(Embodiment 2) Pretreatment and fusion splicing are performed in the same manner as in Embodiment 1, and the optical fiber 11 including the fusion splicing portion 15 is provided.
Was immersed in a sulfuric hydrofluoric acid solution, etched for about 3 minutes in the same manner as in Example 1, and then set in an apparatus for regenerating a carbon film.
As shown in FIG. 3, the exposed optical fiber 11 including the fusion splicing portion 15 of the hermetically coated optical fiber 10 set in the carbon film forming apparatus is used as a laser at the output of 3/5 of the laser used for reforming the carbon film From the time when the hermetically coated optical fiber 10 is scanned in the longitudinal direction while irradiating light and the coating 12 of the carbon film disappears due to the discharge at the time of fusion, as shown in FIG. The varnish coat layer 14 was thermally decomposed and removed to expose the carbon film 12. Then, the same treatment as in Example 1 was performed to re-form the carbon film 19A, and the optical fiber 11 was partially provided with the hermetic coating 20A as shown in FIG. Table 1 shows the characteristics of the hermetically coated optical fiber 10B having the hermetically coated 20A of the fusion spliced portion 15 obtained in the above-mentioned embodiment.

(Embodiment 3) Pretreatment and fusion splicing are performed in the same manner as in Embodiment 1, and the optical fiber 11 including the fusion splicing portion 15 is provided.
Was immersed in a sulfuric hydrofluoric acid solution and etched for about 3 minutes in the same manner as in Example 1, and then set in a carbon film reforming apparatus. As shown in FIG. 3, the exposed optical fiber 11 including the fusion splicing portion 15 of the hermetically coated optical fiber 10 set in the carbon film forming apparatus is provided with a predetermined one when the carbon film is re-formed.
The carbon film 1 is obtained by scanning the hermetically coated optical fiber 10 twice in the longitudinal direction while irradiating the laser beam with an output of 1/2.
As shown in FIG. 2C, the varnish coat layer 14 was thermally decomposed and removed to remove the carbon film 12 from the time when 2 disappeared due to the electric discharge during fusion bonding. After that, the same treatment as in Example 1 was performed to re-form the carbon film 19B, and the optical fiber 11 was partially provided with the hermetic coating 20B as shown in FIG. Table 1 shows the characteristics of the hermetically coated optical fiber 10C having the hermetically coated 20B of the fusion spliced portion 15 obtained in the above-mentioned embodiment.

(Comparative Example) For comparison, pretreatment and fusion splicing were performed in the same manner as in Example 1, and the optical fiber 11 including the fusion splicing portion 15 was dipped in a sulfuric hydrofluoric acid solution to obtain Example 1. Similarly, after etching for about 3 minutes, the optical fiber 11 including the fusion splicing portion 15 was immediately set to a carbon film by setting in a carbon film reforming apparatus, except for the step shown in FIG. While irradiating with a predetermined laser output at the time of reforming as shown in FIG.
Was introduced to re-form the carbon film 19C as shown in FIG. 6 to partially provide the optical fiber 11 with the hermetic coating 30. Table 1 shows the characteristics of the hermetically coated optical fiber 40 having the hermetic coating 30 of the fusion splicing portion 15 obtained in the above comparative example.

[0022]

[Table 1] Note) About property measurement method Tensile strength: Tensile test with 40 cm length, Tensile speed: 5% / min, Number of samples = 50 Dynamic fatigue coefficient: 40 cm length, Tensile speed: O.5,1.0,5,10,50 % / Min, sample number = 20.

According to Table 1 showing the characteristics of Examples 1 to 3 and Comparative Example, the 50% tensile strength value and the dynamic fatigue coefficient are as follows:
It can be seen that Examples 1 to 3 are remarkably superior to the Comparative Example. In addition, when the appearance was observed with a scanning electron microscope, the one obtained in the comparative example had fine pits on the carbon film surface, and the carbon film was disturbed on both sides of the carbon film reforming part, and the surface was partially Some of them had cracks. However, in Examples 1 to 3, there was no such disorder of the carbon film, and a uniform film was formed.

[0024]

As described above, according to the partially hermetic coating method for an optical fiber of claim 1 of the present invention, when the carbon film is re-formed on the optical fiber from which the carbon film has disappeared, the carbon film Since the varnish coat layer on both sides of the part where the varnish coat layer has disappeared is removed by a predetermined length, the reaction product generated by the decomposition of the varnish coat layer by the irradiation of the laser beam during the initial reaction when forming the carbon film, The reaction residue does not occur, the deposition state of the carbon small piece plate in that portion is improved, and the fatigue characteristics, initial strength, etc. are remarkably improved.

According to the partially hermetic coating method of the optical fiber of the second aspect of the present invention, the varnish coat layer on both sides of the optical fiber where the carbon film has disappeared is removed by a predetermined length when the carbon film is re-formed. Since the varnish coat layer is thermally decomposed and volatilized without being decomposed by combustion, a reaction product and an unreacted residue are not generated. In addition, since the high-power laser beam is not applied to the portion of the optical fiber where the carbon film has disappeared, the optical fiber is not exposed to the laser beam and damaged.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a hermetically coated optical fiber used in the present invention.

FIG. 2 is an explanatory view showing an example of steps of the method for partially hermetically coating an optical fiber according to the present invention.

FIG. 3 is an explanatory view showing a part of the steps of the method for partially hermetically coating an optical fiber according to the present invention.

FIG. 4 is an explanatory view showing another part of the steps of the method for partially hermetically coating an optical fiber according to the present invention.

FIG. 5 is an explanatory view showing a part of the steps of a comparative example of the partial hermetic coating method for an optical fiber.

FIG. 6 is an explanatory diagram showing another part of the process of the comparative example of the partial hermetic coating method for an optical fiber.

[Description of Reference Signs] 10 Hermetically-coated optical fiber 11 Optical fiber 12 Carbon film coating 13 UV resin coating layer 14 Varnish coat layer 15 Fusion splicing portion 16 Varnish coat layer disappearing portion 18 Raw material gas 19 Reforming carbon film 19A Reforming Carbon film to be formed 19B Carbon film to be reformed 20 Hermetic coating 20A Hermetic coating 20B Hermetic coating

Claims (2)

[Claims] 1. A carbon film and a varnish coat layer partially disappeared after a varnish coat layer was applied to a portion where the carbon film disappearance was predicted in a hermetically coated optical fiber having a carbon film on the outer circumference of the optical fiber and its periphery. In a partial hermetic coating method of an optical fiber for reforming a carbon film on an optical fiber, after removing a predetermined length of the varnish coat layer on both sides of the part where the carbon film and the varnish coat layer have disappeared, the carbon film is removed. A laser beam is applied to the optical fiber to raise its temperature, and then a raw material gas is brought into contact with the optical fiber to re-form a carbon film by a thermal CVD method. 2. The removal of a predetermined length of the varnish coat layer on both sides of the optical fiber from which the carbon film has disappeared is performed by irradiating a laser beam having a lower output than the laser beam used for reforming the carbon film. A method of partially hermetically coating an optical fiber according to claim 1.