JPH04301804A - Method for fusion splicing carbon-coated optical fibers - Google Patents

Abstract

PURPOSE:To prevent burning of the carbon coating layer at the time of fusion splicing the carbon-coated optical fibers. CONSTITUTION:The fusion-splicing device is set in a tightly enclosed cover 7, an inert gas is introduced into its inside to reduce an oxygen concentration to <0.5 volume %, and then fusion-splicing of the carbon-coated optical fibers is carried out. At that time, the optical fibers are spliced without burning the carbon coating layer, thus permitting the spliced fiber to have good breaking strength and to prevent occurrences of lowering of mechanical strength and increase of absorption loss due to diffusion of steam and hydrogen into the optical fibers.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for splicing optical fibers having a carbon coating layer by fusion splicing.

0002

2. Description of the Related Art Generally, as an optical fiber, a silica glass-based optical fiber coated with an organic material such as a synthetic resin is used. The purpose of this coating with an organic material is to prevent the glass optical fiber from being scratched by dust, dirt, foreign matter, etc. in the external environment colliding with it, and thereby preventing the optical fiber from deteriorating its breaking strength. However, this organic material coating cannot prevent water vapor in the external environment and hydrogen molecules with smaller molecular diameters from diffusing into the optical fiber. When moisture adheres to the optical fiber under stress, a fatigue phenomenon occurs and the mechanical strength decreases over time. Furthermore, as hydrogen diffuses into the glass of the optical fiber, absorption loss due to the molecular vibration of hydrogen molecules increases, and it also reacts with P2O5, GeO2, B2O3, etc. contained as dopants in the optical fiber. There is a problem in that OH groups are generated and absorption loss due to these OH groups increases.

In order to prevent these problems, a carbon coating layer 2 is formed on the surface of a silica glass optical fiber 1 consisting of a core 1a and a cladding 1b, as shown in FIG. 2, and a resin coating layer 3 made of an organic material is further applied thereon. A carbon coated optical fiber 4 has been proposed. The carbon coating layer 2 on the circumference of the optical fiber 1 is generally formed by chemical vapor deposition (CVD).

[0004] In addition, with the demand for long-distance transmission in optical communications, long optical fibers have become unsuitable, but since the length of optical fibers is finite, it is necessary to install them over a finite length. It must be used by connecting two optical fibers. There are various methods for this connection, such as the connector method and fusion splicing, but the fusion splicing method is generally used as a permanent splicing method, in which the end faces of optical fibers are brought together and melted by arc discharge, etc. ing.

[0005]

[Problems to be Solved by the Invention] However, when this fusion splicing method is applied to the carbon coated optical fiber 4, the resin coating layer 3 at the ends of the carbon coated optical fiber 4 is removed and the ends are connected to each other. The carbon coating layer 2 burns and disappears during the process of being heated by this discharge, leaving the optical fiber 1 of the fusion spliced portion exposed. Since the carbon coating layer 2 is burned in this manner and the exposed optical fiber 1 is sufficiently heated, moisture in the external environment is likely to adhere thereto. If water adheres to the optical fiber 1 or if it is exposed to a hydrogen atmosphere, the breaking strength of the connection will decrease.
Alternatively, there were problems such as increased transmission loss. Also,
There was a risk that the carbon coating layer 2 would burn during fusion splicing and the burnt residue would damage the optical fiber 1.

[0006] Therefore, a method has been proposed in which a carbon recoating layer is formed on the fusion spliced portion of the carbon-coated optical fiber 4 by a thermal CVD method, a plasma CVD method, a carbon-containing gas flame method, or the like. However, it is difficult to form a carbon re-coating layer with a width of about 5 mm on the fusion splice, and there is also the problem that the carbon coating layer 2 is damaged when forming this re-coating layer.

The present invention has been made in view of the above-mentioned circumstances, and it provides a carbon-coated optical fiber 4 without adversely affecting the carbon coating layer and without deteriorating the breaking strength.
It is an object of the present invention to provide a fusion splicing method for carbon coated optical fibers 4 that can connect these fibers.

[0008]

[Means for Solving the Problems] The fusion splicing method of carbon coated optical fiber 4 of the present invention has an oxygen concentration of 0.5v.
ol. The solution to the above problem was to carry out fusion splicing under an inert gas atmosphere of less than 1%.

[0009] Here, the oxygen concentration is set to 0.5 vol. % is defined as less than 0.5 vol.% when the oxygen concentration is 0.5 vol. % or more, the carbon coating layer 2 will burn, albeit slightly, during fusion, so this is to prevent this. Further, as the inert gas, N2, Ar, He, etc. can be used.

[0010] This invention will be explained in detail below. FIG. 1 shows an example of an apparatus suitably used to carry out the method of fusion splicing carbon-coated optical fibers 4 of the present invention.

This device has discharge electrodes 5, 5 and a V-groove (
It is generally composed of a discharge section (not shown) and a cover 7 that accommodates the discharge section and is formed so as to keep the interior airtight. Subsequently, a pair of discharge electrode rods 6, 6 facing each other are formed on the discharge electrodes 5, 5, and the V
The grooves hold the two carbon-coated optical fibers 4 and align their axes, and the discharge electrode rods 6, 6 are perpendicular to the longitudinal direction of the two optical fibers fixed to the V-groove. It is located in Further, the cover 7 is
An air outlet 8, an inert gas inlet 9, and a gas leak port 10 are provided, and are made of acrylic resin or the like.

[0012] Fusion splicing of carbon coated optical fibers using such a device is carried out as follows. The carbon-coated optical fiber 4 used here has a carbon coating layer 2 formed on the circumference of a silica glass optical fiber 1, and a resin coating layer 3 further formed on the circumference. First, this carbon-coated optical fiber 4 is cut into a desired length using a well-known method. Next, the end of the carbon-coated optical fiber 4 is immersed in a dichloromethane solution to remove this portion of the resin coating layer 3. Two carbon-coated optical fibers 4 from which the resin coating layer 3 at the end portions have been removed are fixed in the V-groove portion with their end surfaces abutted against each other, and the tips of the opposing discharge electrode rods 6, 6 are aligned with the carbon-coated optical fibers. The discharge electrode rods 6, 6 are arranged so as to be located near the abutting portions of the electrodes 4. Next, after evacuating the inside of the cover 7 from the air outlet 8, an inert gas is introduced into the cover 7 from the inert gas inlet 9 to reduce the oxygen concentration to 0.5.
vol. Adjust to less than %. Here, the oxygen concentration can be confirmed by installing an oxygen concentration meter inside the cover 7. Next, a voltage is applied to the discharge electrodes 5, 5 to cause discharge from the discharge electrode rods 6, 6, and the carbon coated optical fiber 4 is fused and spliced. Furthermore, after completing the fusion splicing,
Inert gas is exhausted and recovered from the gas leak port 10.

(Example 1) Fusion splicing of carbon-coated optical fibers 4 was performed using the above-mentioned apparatus. As the carbon-coated optical fiber 4, a carbon coating layer 2 with a thickness of 0.05 μm is formed on the circumference of the optical fiber 1 with an outer diameter of 125 μm, and a UV-curable urethane acrylate resin coating layer 3 is further formed on the circumference. A material having an outer diameter of 250 μm was used. First, the carbon-coated optical fiber 4 was cut with a fiber cutter, and the end portion was immersed in a dichloromethane solution to remove the resin coating layer 3 over a 1.5 cm region from the end surface. In this way, the resin coating layer 3 at the end portion was removed, and the two carbon coated optical fibers 4 with the carbon coating layer 2 exposed were each fixed in the V groove. The inside of the cover 7 is evacuated, and then N2 gas is introduced into the cover 7 to reduce the oxygen concentration inside the cover 7 to 0.05.
vol. %. Here, the flow rate of N2 gas is 2 l
/min. A voltage was applied to the discharge electrodes 5, 5 to generate a discharge, and the carbon coated optical fiber 4 was fusion spliced.

At the splicing portion of the carbon-coated optical fiber 4 fusion-spliced in this way, the carbon coating layer 2
No combustion or removal was observed. Furthermore, a tensile test was conducted on the fusion spliced portion of the carbon coated optical fiber 4 obtained here, and its breaking strength was investigated. Span length 300mm
A tensile test was conducted on 420 carbon-coated optical fibers at a strain rate of 30 mm/min. As a result, the breaking strength at a breakage probability of 50% was 1.53 kg.

(Example 2) Fusion splicing of carbon-coated optical fibers 4 was performed using the above-mentioned apparatus. Optical fiber 1 with an outer diameter of 125 μm as carbon coated optical fiber 4
A carbon coating layer 2 with a thickness of 0.02 μm was formed on the periphery of the carbon coating layer 2, and a UV-curable urethane acrylate resin coating layer 3 was further formed on the periphery of the carbon coating layer 2, and the outer diameter was 250 μm. First, the carbon-coated optical fiber 4 was cut with a fiber cutter, and the end portion was immersed in a dichloromethane solution to remove the resin coating layer 3 over a 1.5 cm region from the end surface. In this way, the resin coating layer 3 at the end portion was removed, and the two carbon coated optical fibers 4 with the carbon coating layer 2 exposed were each fixed in the V groove. The inside of the cover 7 is evacuated, and then He gas is introduced into the cover 7 to reduce the oxygen concentration in the cover 7 to 0.4 vo.
l. %. Here, the flow rate of He gas is 1l/m
It was set as in. A voltage was applied to the discharge electrodes 5, 5 to generate a discharge, and the carbon coated optical fiber 4 was fusion spliced.

At the splicing portion of the carbon-coated optical fiber 4 fusion-spliced in this way, the carbon coating layer 2
No combustion or removal was observed. Furthermore, a tensile test was conducted on the fusion spliced portion of the carbon coated optical fiber 4 obtained here, and its breaking strength was investigated. A tensile test was conducted under the same conditions as in Example 1, and the breaking strength at a probability of breakage of 50% was 2.07 kg.

(Comparative Example 1) Fusion splicing of carbon-coated optical fibers 4 was performed using the above-mentioned apparatus. As the carbon-coated optical fiber 4, a carbon coating layer 2 with a thickness of 0.05 μm is formed on the circumference of an optical fiber with an outer diameter of 125 μm, and a UV-curable urethane acrylate resin coating layer 3 is further formed on the circumference. A material with an outer diameter of 250 μm obtained in this manner was used. First, the carbon-coated optical fiber 4 was cut with a fiber cutter, and the end portion was immersed in a dichloromethane solution to remove the resin coating layer 3 over a 1.5 cm region from the end surface. In this way, the resin coating layer 3 at the end portion was removed, and the two carbon coated optical fibers 4 with the carbon coating layer 2 exposed were each fixed in the V groove. The inside of the cover 7 is evacuated, and then N2 gas is introduced into the cover 7 to reduce the oxygen concentration in the cover 7 to 0.5 vo.
l. %. Here, the flow rate of N2 gas is 0.4
It was set as 1/min. A voltage was applied to the discharge electrodes 5, 5 to generate a discharge, and the carbon coated optical fiber 4 was fusion spliced.

At the splicing portion of the carbon-coated optical fiber 4 fusion-spliced in this way, the carbon coating layer 2
It was observed that approximately 1 mm of the material had been burned and removed. Furthermore, a tensile test was conducted on the fusion spliced portion of the carbon coated optical fiber 4 obtained here, and its breaking strength was investigated. As a result of a tensile test conducted under the same conditions as Example 1,
The breaking strength at a breakage probability of 50% was 0.87 kg.

(Comparative Example 2) In the above device, the cover 7 was removed and the carbon-coated optical fiber 4 was exposed in the atmosphere.
A fusion splice was performed. As the carbon-coated optical fiber 4, a layer with a thickness of 0 is placed on the circumference of an optical fiber with an outer diameter of 125 μm.
．． A material having an outer diameter of 250 μm obtained by forming a carbon coating layer 2 of 0.05 μm and further forming a UV-curable urethane acrylate resin coating layer 3 on the periphery thereof was used. first,
The carbon-coated optical fiber 4 was cut with a fiber cutter, and the end portion was immersed in a dichloromethane solution to remove the resin coating layer 3 from the end surface over a distance of 1.5 cm. In this way, the resin coating layer 3 at the end portion was removed, and the two carbon coated optical fibers 4 with the carbon coating layer 2 exposed were each fixed in the V groove. A voltage was applied to the discharge electrode to generate a discharge, and the carbon coated optical fiber 4 was fusion spliced.

At the splicing portion of the carbon-coated optical fiber 4 fusion-spliced in this way, the carbon coating layer 2
It was observed that about 5 mm of the material had been burned and removed. Furthermore, a tensile test was conducted on the fusion spliced portion of the carbon coated optical fiber 4 obtained here, and its breaking strength was investigated. As a result of a tensile test conducted under the same conditions as Example 1,
The breaking strength at a breakage probability of 50% was 0.72 kg.

[0021]

Effects of the Invention As explained above, the carbon coated optical fiber fusion splicing method of the present invention has an oxygen concentration of 0.5.
vol. % in an inert gas atmosphere. Therefore, it is possible to prevent the carbon coating layer from burning due to fusion splicing, and to make a connection with good breaking strength. Then, it is possible to prevent a decrease in mechanical strength and an increase in absorption loss due to the diffusion of water vapor and hydrogen molecules into the optical fiber, and obtain a carbon-coated optical fiber that has excellent quality and can be lengthened by fusion splicing. be able to.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a device used in the fusion splicing method of the present invention.

FIG. 2 is a perspective view of a carbon coated optical fiber.

[Explanation of symbols]

1... Optical fiber, 2... Carbon coating layer, 4... Carbon coated optical fiber

Claims (1)

[Claims] 1. A method of splicing carbon-coated optical fibers having a carbon coating layer on the periphery of the optical fibers by fusion bonding, the method comprising: an oxygen concentration of 0.5 vol. A fusion splicing method for carbon-coated optical fibers, characterized in that fusion splicing is performed in an inert gas atmosphere of less than 1%.