JPH03113403A - Method for connecting optical fiber with high strength - Google Patents

Abstract

PURPOSE:To improve the tensile rupture strength of a junction part by deviating the butting parts of optical fibers in a >=0.05mm to <=0.1mm range from the axial line of electrodes. CONSTITUTION:The butting end parts of the optical fibers 1, 1' from which the coatings are removed by chemicals are arranged with the deviation by a height (h) from the axial line connecting the electrodes 2, 2' and the butting parts of the optical fibers 1, 1' are fusion-spliced in this state by the arc discharge heat generated between the electrodes 2 and 2'. The heating temp. of the optical fibers at the time of the fusion splicing and the luminance (light emitting intensity) of the optical fibers correspond to each other, the temp. distribution of the optical fiber surface is smoother when the height (h) is deviated by 0.1mm. Thus, the heating temp. range in the axial direction is made wide and gentle, the thermal strains at the fusion splicing point is released and the strength of the junction part is greatly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for fusion splicing fibers with high strength.

[Prior Art] For optical lines extending over several hundred to several thousand kilometers, such as submarine optical cables, it is desirable that the length of a single optical cable be as long as possible. This is because if optical cables of several tens of kilometers were connected one by one, the number of cable connection steps would increase, which would easily cause problems in terms of reliability. Therefore, recently the connection interval, that is, the relay interval, has been reduced to 1
The trend is to increase the distance to about 00kI11. However, it is difficult to industrially obtain a long optical fiber that satisfies the required tensile strength over its entire length, so it is necessary to prepare a long optical fiber in which several tens of kilometers of optical fibers are connected. This will be prepared and converted into a cable.

FIG. 2 is an explanatory diagram showing a conventional optical fiber fusion splicing method. In the figure, 1 and 1' are a pair of optical fibers extending perpendicularly to the paper surface, and since optical fiber 1' is actually hidden in the shadow of optical fiber 1, it is shown by a broken line for convenience. . Further, 2.2゛ is a pair of electrodes. In the conventional optical fiber fusion splicing method, first the optical fiber 1.
The abutting portion of 1" is located on the axis connecting the electrodes 2 and 2', and then an arc discharge is generated between the electrodes 2 and 2', and the heat is used to fuse and connect the electrodes.

[Problems to be Solved by the Invention] However, in the conventional optical fiber fusion splicing method, the strength of the fusion valley splice decreases to about 600 g, which is about one-tenth of the optical fiber core strength. When a long optical fiber having such a connection part with low connection strength is made into a cable, there is a problem that the connection part with low strength is broken during the cable production process or cable installation work.

The reasons why the strength of the connection part decreases are: 1. The connection part is rapidly cooled from the arc discharge temperature (1600 to 1800°C) to room temperature, resulting in large thermal strain; 2. Glass vapor evaporated by heating near the connection part. For example, it may deposit and adhere to the surface, making it easier for cracks to form. The results of the tensile rupture test show that many ruptures occur particularly at positions lll1ffi away from the connection point.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a high-strength flexible cable that will not break during the cable-making process or cable installation work even when a long optical fiber having a connection part is made into a cable. An object of the present invention is to provide a high-strength optical fiber splicing method that can obtain a bonded splice.

[Means for Solving the Problems] The gist of the present invention is to abut the ends of l pairs of optical fibers to be connected to each other, place the abutted portions between a pair of electrodes, and perform discharge heating of the electrodes to achieve the above-mentioned In the method of fusion splicing the butt portions of optical fibers, the butt portions of the optical fibers are shifted from the axis of the electrode by a range of 0.05 mm or more and 0.1 mm or less, thereby increasing the tensile breaking strength of the spliced portion. can be significantly improved compared to conventional methods.

[Example) Examples of the present invention will be described below.

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and explanations of the same symbols as those in FIG. 2 will be omitted. To explain the procedure of the fusion splicing method of this embodiment, first, the butt ends of the optical fibers 1, 1-, whose coatings have been removed using chemicals, are shifted by a height h from the axis connecting the electrodes 2, 2'. In this state, the abutting portions of the optical fibers 1, 1' are fused and spliced by arc discharge heat generated between the electrodes 2, 2'.

Next, the heating state of the optical fiber when the height h is changed will be explained.

Since the heating temperature of the optical fiber during fusion splicing corresponds to the brightness (emission intensity) of the optical fiber, the spliced portion was monitored with a brightness meter to observe the heating state of the optical fiber. FIG. 3 is an explanatory diagram showing the brightness distribution in the axial direction of the optical fiber during fusion splicing, where the horizontal axis shows the width of the brightness distribution of the optical fiber, and the vertical axis shows the brightness intensity. Curve A shows the brightness distribution when the height is h-0°1ml11, and curve B
shows the brightness distribution at the height h-0. Note that in order to match the peak brightness values, measurements were performed with different discharge current values. As is clear from the figure, curve A is wider and gentler than curve B, and this means that curve A, that is, height h, is 0.1 +
It is shown that the temperature distribution on the optical fiber surface becomes gentler when shifted by nm.

FIG. 4 is an explanatory diagram showing the relationship between the height h and the brightness peak value when the discharge current value is constant, where the horizontal axis shows the height h1 and the vertical axis shows the brightness. Note that the brightness is H when the width of the brightness distribution is D and the peak value of brightness is H, as in Figure 3.
/D (%). As is clear from the figure,
The brightness H/D is maximum at height h=o, and as the height h increases, the brightness H/D decreases. Therefore, when the height h > Oam, if the discharge current value is adjusted so that the brightness is the same as that at the height ho, the heating in the axial direction of the optical fiber can be achieved as shown in Figure 3. The temperature range can be widened and moderated.

This means that thermal strain at the optical fiber fusion splicing point is alleviated.

Next, the optimum conditions for the height h will be explained. FIG. 5 is an explanatory diagram showing the relationship between height h and tensile breaking strength, in which the breaking load of the optical fiber fusion spliced portion was measured and this was plotted on Weibull probability paper. The horizontal axis shows the failure load, and the vertical axis shows the cumulative failure probability. If the cumulative failure probability is 50%,
Height h-0゜h-0, 05mm, h-0, 1m
The breaking load for l11 is 2.3 kgr and 3 kgr, respectively.
．． 2 kgr and 3.7 kgr, and the tensile strength at break improves as the height h increases. In this way the height h
As mentioned above, the tensile strength at break increases as the value increases because the temperature distribution on the surface of the optical fiber becomes gentle during fusion splicing, which greatly reduces thermal strain near the fusion splicing point. It is thought that this was due to an accident. Note that high-strength connections must have a tensile strength at break of 2.1 kgf or more with a high probability, and other deterioration factors must be considered, so they usually have an average strength of 3.0 kgf. It is necessary to secure about Okgf.

Therefore, the height h must be h≧0.05a+i or more. In addition, if the height h is too large, the optical fiber will not be heated sufficiently, and the life of the electrode will be shortened due to the increased arc discharge energy. 15a+i, preferably h≦061■.

[Effects of the Invention] As explained below, according to the present invention, the following remarkable effects can be achieved.

(1) Since the heating temperature range in the axial direction of the optical fiber can be widened and moderated, thermal strain at the optical fiber fusion splicing point can be alleviated and the strength of the spliced portion can be significantly improved.

(2) Since the heating temperature range in the axial direction of the optical fiber is wide and the connection point is not overheated, glass particles evaporated by heating do not adhere to the vicinity of the connection point, increasing the strength of the connection point. can be significantly improved.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram showing a conventional example, Fig. 3 is an explanatory diagram showing the luminance distribution in the axial direction of the optical fiber during fusion splicing, and Fig. 4 is an explanatory diagram showing an example of the present invention. The figure is an explanatory diagram showing the relationship between misalignment height h and brightness peak value when the discharge current value is constant, and FIG. 5 is an explanatory diagram showing the relationship between misalignment height h and tensile breaking strength. . ... Optical fiber μ 2. ···electrode. Applicant Hitachi Cable stock brightness distribution convergence = D

Claims (1)

[Claims] (1) In a method of abutting the ends of a pair of optical fibers to be connected to each other, placing the abutting portion between a pair of electrodes, and fusion splicing the abutting portions of the optical fibers by electric discharge heating of the electrodes. , the abutting portion of the optical fiber is 0.05 mm or more and 0.1 m from the axis of the electrode.
A high-strength optical fiber connection method characterized by shifting within a range of less than m.