JP3073573B2 - Connection method of carbon coated optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fusion splicing of a carbon coated optical fiber, and more particularly to coating of a spliced portion.

[0002]

2. Description of the Related Art A carbon-coated optical fiber is an optical fiber in which the glass surface is covered with a carbon layer formed by a pyrolysis method or the like. The optical fiber has excellent characteristics that can prevent a decrease and an increase in loss due to hydrogen intrusion, and can improve long-term reliability of the optical fiber.
When such a carbon-coated optical fiber is fusion-spliced, in order to avoid mixing of impurities such as carbon into the fusion-bonded portion, a method is generally adopted in which the carbon layer at the connection portion is removed in advance by oxidation or the like and then fused. It is a target. In this case, it is necessary to apply a carbon coating to the connection portion to suppress the adsorption of water on the glass surface. As a preventive measure, C0 ₂ connecting section by laser heating (typically 5 to 20 mm) only locally, again carbon coating by a sealed container to reduction shaped evaporation introducing a material gas such as hydrocarbon (CVD method) Attempts have been made to do so.

[0003] On the other hand, a method of coating an optical fiber with a metal to prevent water from adsorbing to the glass surface and to suppress a decrease in strength has been conventionally performed. As a method for coating a metal on the surface of an optical fiber, a dipping method, a physical vapor deposition method (PV
D method) and CVD method. Among them, many studies have been made on the point that the PVD method can relatively easily form a uniform thin film. For example, as shown in JP-A-62-143848, after coating a metal with PVD, Attempts have been made to cause recrystallization and densification by heating.

[0004]

In the above prior art, the reason for using a CO ₂ laser is that an ordinary optical fiber is coated with an organic resin, and connection is made after removing this resin. This is because the resin is weak to heat, and it is necessary to locally heat only the connection portion. However, there is a problem that not only equipment such as the use of a sealed container is large-scale and expensive, but also it is difficult to obtain reproducibility because it is necessary to control a chemical reaction. or,
The thin film formed by the PVD method tends to have a fine grain or columnar particle structure, so that there is a problem that simply heating does not always form a sufficiently dense film.

[0005]

SUMMARY OF THE INVENTION The present invention provides a method for connecting a carbon-coated optical fiber which solves the above-mentioned problems, and has a feature as shown in FIGS. After removing the end carbon and performing the fusion splicing, and forming the metal coating 3 on the removed joint 2,
This is a method in which the metal coating is firstly heated and then secondarily heated.

Here, if the means for primary heating and secondary heating is infrared heating, high-frequency induction heating or laser light heating, it is preferable because only the metal coating can be locally heated.

The primary heating temperature is 0.1 to 1.0 times the melting point (absolute temperature) of the coating metal, preferably 0.3 to 0.6.
It is effective that the secondary heating temperature is at least 50 ° C. or higher than the primary heating temperature.

As a metal coating method, an electroless plating method, a sputtering method, a vacuum evaporation method, or a plasma CVD method is preferable for realizing the present invention because it can coat only the vicinity of the connection portion.

[0009]

The method such as electroless plating and sputtering can form a metal thin film at a relatively low temperature with a relatively simple apparatus. Therefore, there is almost no damage to the organic resin on both sides of the connection portion. This metal thin film is formed in a range of 0.1 to 1 times the melting point (absolute temperature) of the metal, preferably 0.1 to 1 times.
The recrystallization is performed by heating at a temperature of 3 times or more and 0.6 times or less (this temperature range has a high recrystallization progress rate). Recrystallization (1
The crystal grain size immediately after (secondary recrystallization) is generally small, and becomes larger by heating at a higher temperature for a long time. Therefore, heating is performed at a higher temperature to cause secondary recrystallization (coarsening). By such a heat treatment, a dense metal thin film having a large grain size, that is, a small grain boundary area, and having almost no grain boundary gap can be formed.

The heating time varies depending on the metal to be coated and the thickness of the coating, but in the case of primary recrystallization, the heating time is 30 seconds or more.
In the case of the next recrystallization, the time is preferably 10 minutes or more. The thickness of the metal to be coated may be arbitrarily set depending on the purpose. Au, Ag, Ni,
W, Mo, Zn, Sn, Cd, Pb, Pt, Mg, ln
However, in practice, it is desirable to use a noble metal having a melting point as low as possible.

What is important here is the heating method.
Without affecting both sides of the resin, as a method of heating only the coating portion after connection, intensive heating by infrared lamp, heating by high frequency induction, C0 ₂ but the heating method by laser or the like can be considered, condensing the infrared Among this The heating method is preferable because it is simple and the apparatus is inexpensive.

[0012]

【Example】

(Embodiment 1) FIG. 1 is a cross-sectional view of a carbon-coated optical fiber in which a connecting portion is provided with a metal coating. The carbon coating at the end of the carbon-coated optical fiber 1 was removed, and the surface of the fusion spliced connection 2 was coated with copper as a coating metal 3 to a thickness of about 1 μm by electroless plating.
The electroless plating method is a method in which metal ions are reduced and deposited on the surface of an object to form a thin film of metal, and has the advantage that no external power source is required and non-conductive materials can be used as an object. . This metal-coated portion was heated by an apparatus as shown in FIG. Note that the apparatus shown in FIG. 2 is an example, and does not limit the method. Window 1 in chamber 11
2. A purge gas introduction pipe 14, an exhaust pipe 15, a seal member / fiber holding member 13, and a light shielding material 16 are respectively attached. Stainless steel was used for the chamber 11, quartz glass was used for the window material 12, and rubber such as Viton was used for the seal member 13. He, A from the purge gas introduction pipe 14
An inert gas such as r or N ₂ is introduced to keep the inside of the chamber in an oxygen-free atmosphere. This is to prevent oxidation of carbon. Of course, for this purpose, the inside of the chamber can be kept at a vacuum by pulling from the exhaust pipe 15 with a vacuum pump (not shown). The infrared lamp 10 is condensed by a mirror 17 (usually plated with gold) and focused on the coated metal part so as not to heat the resin 4 and the carbon coated part 1 on both sides of the connection part 2 at about 200 ° C. Heated for 1 minute and then at about 600 ° C. for about 30 minutes. Shading material 1 just in case
6 was installed. A device (not shown) for cooling the resin portion by water cooling or the like may be additionally provided.

Microscopic observation and X before and after heating
As a result of examining the structure by line diffraction, it was confirmed that the crystal grain size was increased and the orientation was increased. In order to protect the connection part, it was molded with a synthetic resin 5 as shown in FIG.
In order to confirm the water resistance, strain rate: 1% / min, 10% / min, 50% in an atmosphere of 23 ° C. and 50% humidity.
As a result of performing a tensile test at four levels of / min and 100% / min and examining dynamic fatigue characteristics, as shown in FIG. 4, a parameter “n” indicating a resistance to fatigue is 150 or more.
No accelerated fatigue phenomenon due to moisture adsorption on the glass surface was observed, confirming that the glass had excellent water resistance. On the other hand, those having no coating on the connection portion had n = 25, which was equivalent to a normal fiber without carbon coating.

The following various fibers were wound around metal rods having various diameters of 5 mm to 30 mm and immersed in warm water at 60 ° C., and the n value was measured. N = 18 to 24 without coating, n = 35 to 4 with coating applied to the connection and not heated
0, n = 50 to 60 when the connection portion was coated and only the primary heating was performed, and n ≧ 50 when the connection portion was coated and the primary heating and the secondary heating were performed as in the present invention. 100
And confirmed that it is better than others.

Example 2 A coating was applied to a thickness of about 1 μm by sputtering using aluminum as a coating metal. The sputtering is 10 ^-2 to 10 ^-3 [P
a] with Ar ions under low pressure. This was heated with an infrared lamp to about 230 ° C. for 1 minute and further at 500 ° C. for 1 hour as in Example 1. As a result of performing the same evaluation as in Example 1, formation of a dense metal film having excellent water resistance was also confirmed in this case.

[0016]

By connecting a carbon coated optical fiber according to the method of the present invention, a dense metal coating can be formed on the connecting portion, and a highly reliable optical fiber can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical fiber connected by the method of the present invention.

FIG. 2 is an explanatory diagram of a specific example of a heating method according to the present invention.

FIG. 3 is another sectional view of an optical fiber connected by the method of the present invention.

FIG. 4 is a diagram showing an example of a tensile breaking strength test result with respect to a strain rate.

[Explanation of symbols]

 1: Carbon coated optical fiber 2: Optical fiber connecting part 3: Metal coating film 4: Resin coated optical fiber 5: Resin mold 10: Infrared lamp 11: Chamber 12: Window 13: Seal and fiber holding part 14: Purge gas inlet pipe 15: Exhaust pipe 16: Light shielding material 17: Mirror

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Isamu Fujita 1-chome, Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Nobuyuki Yoshizawa 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan (56) References JP-A-62-143848 (JP, A) JP-A-2-195304 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6 /twenty four

Claims (5)

(57) [Claims] An optical fiber coated with carbon is removed from the end portion by removing carbon and fusion-spliced. After forming a metal film on the removed connection portion, the metal film is firstly heated and subsequently subjected to secondary heating. A method for connecting a carbon-coated optical fiber. 2. The carbon according to claim 1, wherein the means for the primary heating and the secondary heating is infrared heating, high-frequency induction heating or laser beam heating, and only the portion of the metal coating is locally heated. How to connect coated optical fiber. 3. The method according to claim 1, wherein the primary heating temperature is 0.1 to 1.0 times, preferably 0.3 to 0.6 times, the melting point (absolute temperature) of the coating metal. Connection method of carbon coated optical fiber. 4. The method for connecting a carbon-coated optical fiber according to claim 1, wherein the secondary heating temperature is at least 50 ° C. or higher than the primary heating temperature. 5. The method for connecting a carbon coated optical fiber according to claim 1, wherein the metal coating method is an electroless plating method, a sputtering method, a vacuum deposition method, or a plasma CVD method.