JPS62195607A - Splicing method for optical fiber - Google Patents

Abstract

PURPOSE:To obtain an optical fiber splicing method capable of reducing splicing loss by expanding a fiber melting area near a splicing point to reduce radiation loss. CONSTITUTION:Two pairs of electrode rods 5 are inclinedly arranged and a butting part of two optical fibers 3 to be fused and spliced is arranged on a space surrounded by the rods 5. A high voltage current power supply 7 is used as an electrostatic discharge circuit, two pairs of electrode rods 5 are alternately discharged by rectifiers 6 every half-wave of AC in each pair to expand the fiber fusing range, the butted optical fibers 3 are fused and spliced, and within the period the spliced part is kept at a high temperature, the optical fibers 3 are drawn so as to be thinned. Consequently, the fiber fusing range can be expanded and the length of the part thinned at the drawing of the splicing point can be expanded, so that both the radiation loss and splicing loss can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention in Industrial Application Field 9 relates to a method for fusion splicing optical fibers, and particularly to a method for splicing single mode optical fibers easily and with low loss.

2. Description of the Related Art The present inventors have proposed a splicing method that can be called a tensile diameter thinning splicing method for simply and low-loss fusion splicing of optical fibers (Japanese Patent Application No. 239985/1989). issue),
That is, it consists of two V-blocks 1. as shown in FIG. Optical fibers 3, 3 are placed in each of the V-grooves 2, 2 of 1, their ends are butted together without alignment, and fusion spliced by arc discharge heating using 1 pair of electrode rods 5, 5. Thereafter, while the splicing part is still hot, the optical fibers 3, 3 are pulled and tapered so that the diameter a° near the splicing point is smaller than the diameter a before being pulled, as shown in Figure 5. . After pulling.

The amount of axis deviation X of the core 4 before pulling (see Figure 4) is X・
(a'/a), but since the rate of decrease in the spot size, which indicates the spread of the optical field distribution, is smaller than that, the connection loss is improved. However, if the diameter of the connection point is made too small, the radiation loss increases and the connection loss actually increases, so a certain range exists.

Actually, a single mode optical fiber with an eccentricity of 2.3% was connected using this tensile thinning splicing method, and an LED with a wavelength of 1.3 gm was connected.
When the change in connection loss with respect to the change in the diameter of the connection point is measured using a light source, the results shown in FIG. 6 are obtained. In FIG. 6, the horizontal axis is the ratio of the diameter a° of the splicing point when the optical fiber is thinned by stretching to the initial diameter a of the optical fiber, and the vertical axis is the splicing loss. The circle mark is the average connection loss, 1
What was 0.52 dB at 00% becomes 0 at 60%.
．． This has been improved to 31 dB. However, more than a
When ゛ is decreased, the connection loss increases due to radiation loss at the connection point, and at 30% it becomes 0.95 dB.

Problems to be Solved by the Invention Incidentally, subsequent research has shown that the radiation loss at the connection point is determined not only by the diameter at the connection point but also by the length of the thinner part of the optical fiber (see L in Figure 5). It turns out that they are also related. In other words, if the diameter of the connection point is the same, the longer the tapered part is, the smaller the radiation loss will be. Therefore, they came up with the idea that by making the thinner part longer, the effect of radiation loss can be removed, and the connection loss can be improved by making the diameter of the connection point even smaller.

However, conventionally, as shown in Figure 4, an arc discharge is generated by a pair of electrodes to melt the optical fiber, and the length of the area where the fiber can be melted is L in Figure 5. Correspondingly, the area is determined by the shape of the electrodes, the distance between the electrodes, etc., but there is a limit to increasing L with a pair of electrodes. By the way, conventional general fusion splicers have only one pair of electrodes, and they all produce a similar fusion area. Therefore, when using a conventional fusion splicer, the fiber fusion area is It is not possible to reduce radiation loss by increasing the length.

An object of the present invention is to provide an optical fiber splicing method that can further reduce splicing loss by lengthening the fiber melting region near the splicing point in the tensile diameter thinning splicing method to reduce radiation loss.

Means for Solving the Problems According to the present invention, the ends of two optical fibers to be connected are brought together without alignment and fusion spliced, and then, while the spliced portion is still hot, In a method of connecting by pulling both ends, the diameter of the connection point is made smaller than the diameter before pulling, the above-mentioned fusion splicing process is performed, for example, by connecting at least two pairs of electrical discharges as shown in FIG. This is carried out by arc discharge using an electrode rod 5.

For example, as shown in FIG. 1, in order to fusion splice two butted optical fibers 3.
．． When arc discharge heating is performed using two pairs of electrode rods 5 arranged in parallel to 3.

The fiber melting region becomes longer. For example, if the length of the fiber melting area by a pair of electrode rods 5 is D, and the distance between adjacent electrode rods 5 is D, then the fiber melting area is 1
It is twice as 2D as in the case of a pair. In reality, the temperature at the ends of one fiber melting region is lower than that at the center, so in order to heat the fiber uniformly, the spacing between the electrode rods 5 is made slightly smaller than D, and the two electrode rods are arranged in a bidirectional manner. It is desirable that the melted regions overlap.

Therefore, the fiber melting area becomes larger, and the length of the thinner part when the connection point is pulled can be increased.
Radiation losses can be reduced and splice losses can be made lower.

Embodiment In FIG. 2, two pairs of electrode rods 5 are arranged at an angle, between which the abutting portions of two optical fibers 3.3 to be fusion spliced are arranged. Here, the electrode rods 5 were tilted as shown in the figure, the distance between a pair of opposing electrode rods 5 was 3.5 mm, and the interval (at the tips) of two adjacent pairs of electrode rods 5 was 1 mm. This is due to the following reason. That is, the distance between a pair of opposing electrode rods in a conventional fusion splicer is approximately 1.5 mm, and the fiber fusion area at this time has been found to be approximately 0.6 mm through experiments. When expanded to 3.5mm, the fiber melting area is approximately 1.2mm.
Therefore, it is sufficient to set the distance between the opposing ones to 3.5 mm and the interval between adjacent ones to 1 mm, but since the electrode rods 5 usually have a diameter of 1 mm, they should be placed in parallel with an interval of 1 mm. Since it is not possible to arrange the electrode rods 5, they are tilted as described above, and the distance between the two pairs of adjacent electrode rods 5 (the tips thereof) is 1 mm, so that the fiber melting area is about 1.2 mm.

As a discharge circuit, as shown in FIG. 2, a high-voltage AC power source 7 is used, and a rectifier 6 causes the two pairs of electrode rods 5 to alternately discharge each other in half-wave AC. This is to prevent when one power source 7 supplies voltage to both of the two pairs of electrode rods 5 at the same time, if one of the pairs starts discharging, the voltage will drop and the other will stop discharging. be.

After the fiber fusion region has been lengthened in this way and the butted optical fibers 3.3 have been fused and spliced, the optical fibers 3.3 are pulled and thinned while the spliced portion is still hot. The connection loss in this case was measured under the same conditions as in the case of FIG. That is, a single mode optical fiber with an eccentricity of 2.3% is connected using this method, and an LE with a wavelength of 1.3 g and m is connected.
When the change in connection loss with respect to the change in the diameter of the connection point was measured using a D light source, the results shown in FIG. 3 were obtained. The horizontal and vertical axes of FIG. 3 are the same as those of FIG. 6. In Figure 6, when a'/a is 60% or less, the connection loss increases due to radiation loss, whereas in Figure 3, the loss is lowest around 50%, with an average connection loss of 0.22 dB.
,! - Average splice loss at 60% of Figure 6: 0.31
It can be seen that there is an improvement of 0.08 dB compared to dB.

Note that it is possible to further widen the fiber melting area by making the distance between a pair of opposing electrodes larger than 3.5 mm or by increasing the number of electrode rods, but the distance between the opposing electrodes If the area is widened, a higher voltage power source is required, and the discharge state becomes unstable, making it impossible to obtain a constant fiber melting area. In addition, when increasing the number of electrode rods, a circuit for sequentially discharging each electrode pair is required, and the discharging circuit becomes complicated, which is difficult to realize in practice.

Effects of the Invention According to the present invention, it is possible to further improve the tensile diameter thinning connection method that enables low-loss connection without core alignment. That is, in this connection method, the number of electrodes for arc discharge is increased from the conventional one pair to at least two pairs, thereby widening the arc area and lengthening the fiber melting area.
The length of the tapered portion of the optical fiber can be increased, and an increase in splice loss due to radiation loss can be reduced.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an overview of the present invention, Fig. 2 is a schematic diagram of an embodiment of the invention, Fig. 3 is a graph showing measurement results of connection loss versus diameter reduction rate in the same embodiment, and Fig. 4 is a schematic diagram showing an overview of the present invention. 5 and 5 are schematic diagrams of the conventional example, and FIG. 6 is a graph showing the measurement results of splice loss versus diameter reduction rate in the conventional example. l...V block 2...V groove 3...optical fiber 4...core 5...electrode rod
6... Rectifier 7... High voltage AC power supply

Claims (1)

[Claims] (1) A first process in which the ends of two optical fibers to be connected are butted together without alignment, placed in at least two pairs of discharge electrodes, and fused and spliced by arc discharge heating, and the connection part is heated to a high temperature. By applying a tensile force to both ends while
The diameter of the connection point is 80% to 3 of the diameter before applying tension.
and a second step of thinning to 0%.