JPS6161646B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for fusion splicing optical fibers,
In particular, it relates to a high-strength optical fiber fusion splicing method.

Background of the Technology The method of fusion splicing optical fibers involves abutting optical fibers whose coatings have been removed, and heating and melting the abutted ends of both optical fibers by electric discharge to fusion splice them. ing.

Prior Art and Problems Figure 1 shows a model of the settings when connecting optical fibers. Reference numerals 1 and 1' denote optical fibers connected to each other from which the coating has been removed, 2 and 2' respectively the core wires of the optical fibers, and ε the mutual spacing between the optical fibers 1 and 1'. FIG. 2 is a chronological model showing the steps of a conventional optical fiber fusion splicing method. T ₁ indicates the start of discharging, and T ₂ indicates the end of discharging. In the conventional optical fiber fusion splicing method, the optical fibers 1 and 1' whose core wires 2 and 2' have been removed are butted against each other, and a preliminary discharge is performed for a time t2.
(for about 0.2 seconds), for example, move one optical fiber 1 opposite to the other optical fiber 1' (time t3), and connect both optical fibers 1 and 1' in a molten state by heating the main discharge. The ends are glued together, and then the optical fiber 1 is further pushed in (time t3'). After that, at the time of T2, the complete discharge is stopped and the optical fiber 1,
1' fusion splice is completed. The total discharge time t1 in this case is approximately 5 seconds. According to the conventional fusion splicing method described above, the splicing strength is about 0.6 kg at most, which is very low and has the disadvantage of causing breakage.

Purpose of the Invention In order to overcome the conventional drawbacks, the present invention is characterized by adding a step of further pushing the optical fiber even after the heating by discharge is stopped when fusion splicing the optical fiber. An object of the present invention is to provide an optical fiber fusion splicing method that increases splicing strength approximately twice as much as that of the conventional method.

Embodiments of the Invention FIG. 3 is a diagram showing a chronological model of the steps of the optical fiber fusion splicing method according to the present invention. The same symbols as in FIG. 2 indicate the same contents. As shown in FIG. 3, the present invention is characterized in that, in conventional optical fiber fusion splicing, the optical fiber 1 is further pushed in by about 5 μm (time t3'') after the time T2 when all discharge is stopped.The present invention It was confirmed that the strength of the fusion splice was approximately 1.2 kg, which is approximately twice as strong as that of the conventional method.The present invention has been developed to reduce the thermal distortion of the optical fiber caused by local heating caused by electrical discharge by heating the optical fiber. By further pushing in after stopping the discharge, compressive stress is applied to the optical fiber connection and removed.The amount of pushing in of the optical fiber after stopping the discharge is determined to prevent cracks caused by thermal strain on the surface of the optical fiber. Since applying compressive stress is effective in preventing the growth of the crack, the optimal value of the amount of optical fiber pushing in the second step of the present invention is determined experimentally.In other words, the optical fiber surface is 1800℃~2000℃ during discharge
The cracks are thought to grow due to the thermal stress caused by the temperature difference between the fused splice and the rest of the optical fiber due to the electrical discharge that occurs during this time, as it is rapidly cooled down from a high temperature of ℃ in a few seconds. It is experimentally estimated that the fiber connection does not break at the center of the discharge, but occurs concentrated at a location 1 mm to 2 mm away from the center. According to the present invention, the second pushing of the optical fiber after the complete discharging is stopped is performed by further pushing the optical fiber, which causes shortening due to the shortening phenomenon caused by the temperature cooling that occurs during the cooling process of the optical fiber after the discharging is stopped. This leads to the effect of canceling out the thermal strain of. The pushing amount shown earlier in the present invention is approximately 5μ.
A fusion splicing strength of about 1.2 Kg was obtained at m, but in other examples, substantially the same fusion splicing strength was confirmed when the pushing amount was 5 μm to 20 μm.

Note that if the second pushing amount is further increased, the connection loss of the optical fiber tends to increase, so it is not preferable to simply increase the pushing amount.
When the indentation amount was 50 μm or more, the optical fiber tended to curve and crack growth due to bending stress was observed. That is, the amount of second pushing of the optical fiber according to the present invention is preferably in the range of about 5 μm to 20 μm, although it also depends on the discharge conditions.
The second pushing amount of the optical fiber according to this example is the amount of shrinkage when the discharge part is cooled from 2000°C to 25°C, assuming that the discharge acts on 1 mm of the optical fiber, when the optical fiber is made of quartz glass. Approximately 10μm
It was confirmed that the calculated result was almost the same as the calculated example.

Furthermore, the present invention is applied to a method in which the coating of an optical fiber is chemically removed using, for example, H ₂ SO ₄ , and the bare optical fiber is fusion-spliced by clamping the coating in a non-contact state. According to the example, it is possible to prevent scratches that occur on the optical fiber surface when the coating is removed, as well as scratches that occur due to contact with other objects, such as V-grooves, and a high-strength fusion splice with an average weight of approximately 2.5 kg has been confirmed. It was done.

Furthermore, the heat supply method for fusion heating of the present invention is not limited to electric discharge, and any method such as a CO ₂ laser or a gas flame such as an oxyhydrogen flame can be applied. In the embodiments described above, it is effective for the total discharge time t1 to be about 1 second for a single mode optical fiber. In addition, although the example shows an example in which the second push is performed after the full discharge has stopped (T ₂ ), the same effect can be obtained even if the second push is started immediately before the full discharge has stopped (T ₂ ). The results were obtained.

Effects of the Invention As explained above, when fusion splicing optical fibers, the strength of the fusion splicing of optical fibers can be increased by approximately 100% compared to the conventional method by adding a step of further pushing the optical fiber after or just before the stop of all discharge according to the present invention. The strength can be improved to twice as high, and the effect is remarkable.

[Brief explanation of the drawing]

Figure 1 shows a model of the settings when connecting optical fibers, Figure 2 shows a chronological model of the steps of a conventional optical fiber fusion splicing method, and Figure 3 The figure is a chronological model of the steps of the optical fiber fusion splicing method of the present invention. 1, 1'...Optical fiber, 2, 2'...Optical fiber core wire, ε...Optical fiber connection end face spacing, T1...
... At the start of discharge, T2 ... At the end of full discharge, t1 ... Total discharge time, t2 ... Preliminary discharge time, t3 ... Optical fiber movement time, t3' ... Pushing time, t3'' ... Second
times push time.

Claims (1)

[Scope of Claims] 1. After removing the coating of the optical fibers, abutting the connection ends of the bare optical fibers against each other, and heating the connection ends of the bare optical fibers by preliminary discharge, one of the optical fibers is is moved opposite to the other optical fiber, the two optical fibers in a molten state are bonded together by the heating of the main discharge, and the one optical fiber is further pushed into the other optical fiber, and then the entire discharge is stopped. In the optical fiber fusion splicing method, the one optical fiber bonded in the molten state is pushed into the other optical fiber, and the one optical fiber is further pushed into the other optical fiber after or immediately before the stop of the entire discharge. An optical fiber fusion splicing method characterized by: