JPS61120106A - Connecting method of single-mode optical fiber - Google Patents

Abstract

PURPOSE:To make a connection with low loss and high strength in a short time by forming a gently tapered connection part while connecting two single- mode optical fibers by welding. CONSTITUTION:Two single-mode optical fibers 1 and 2 to be connected together are set opposite each other and both their end surfaces are fused by heating and connected together by welding. Then, the optical fibers 1 and 2 are drawn away from the connection part 25 until the connection part 25 has necessary thickness; while the optical fiber 2 is fixed and the other optical fiber 1 is drawn, discharge electrodes 23A and 23B are moved simultaneously in such a direction that the optical fiber 1 is drawn, thereby forming a taper 27 at the side of the optical fiber 1. Then, the discharge electrodes 23A and 23B are returned to the center of the connection part and while the optical fiber 1 is fixed and the optical fiber 2 is drawn, the discharge electrodes 23A and 23B are moved in the drawing direction at the same time to form a taper 28 at the side of the optical fiber 2, thereby connecting the both together.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for splicing and splicing single mode optical fibers.

[Prior art] Single-mode optical fibers have a small field distribution of a mode propagating in the fiber (hereinafter referred to as a propagation mode spot size or simply spot size), which is as small as a few gm. Large losses are likely to occur due to axis deviation due to deviation of the core or eccentricity of the core.
It was a problem.

As a method to solve this problem, what has generally been put into practical use is to detect the axis of the core with some kind of monitor device, align the axis, and then connect the core so that no axis misalignment occurs. However, this type of connection device requires a high-precision fine movement mechanism and a complicated monitoring device.
This method has disadvantages in that the equipment cost is extremely high and the connection time is several times longer than in the case of multimode optical fiber.

On the other hand, methods have been proposed to connect single mode optical fibers with low loss without core alignment.

Among them, the shaft-fixed tapered fusion splicing method is a method that has the possibility of achieving the lowest loss connection. This method will be explained with reference to FIGS. 1(A) to (D). Figure 1 (
As shown in A), the two single mode optical fibers 1 and 2 to be connected are brought together at the center of the opposing discharge electrodes 3A and 3B, and a discharge arc 4 is generated between the discharge electrodes 3A and 3B. Melt by heating.

Next, as shown in FIG. 1(B), one or both of the optical fibers 1 and 2 is pushed in the direction of the arrow to fuse the molten end faces.

Thereafter, as shown in FIG. 1C, while heating again, both optical fibers 1 and 2 are pulled around the connecting portion 5 to form a tapered shape B constricted at the connecting point.

Ultimately, the shape shown in Fig. 1 (D) is formed, but when such a tapered shape B is used, the core shape at the connecting portion 5 is reduced in proportion to the outer diameter, and the propagation The spot size of the mode is increased by the connection portion 5. Furthermore, since the amount of axial misalignment at the connection point also decreases in proportion to the outer diameter, there is an advantage that connection loss due to axial misalignment becomes extremely small. = However, this method was not developed as a practical method because of the following problems.

The first problem is that in order to achieve low loss in the tapered shape 8 in FIG. No.

For this purpose, the change numerator of the diameter in the longitudinal direction of the fiber must be approximately γ = 2L/CD-d)≧40, where d is the diameter at the connection part 5, and D is the diameter of the optical fiber 1.2. It is the outer diameter.

However, 1.
If the steps in Figures 1 (A) to (C) are carried out, L will be only 0.5 or less because the fiber melting area is narrow, and if D = 125 JLm and dm40 JLm, it will be about γ-12. As a result, the propagation loss at the tapered portion became extremely large, making it impossible to realize a low-loss connection.

Therefore, in order to widen the heating melting region of the optical fiber and lengthen L of the tapered part, the steps shown in FIGS. 2(A) and (B) are as follows.
The following methods can be considered. That is, as shown in FIG. 2(A), the discharge electrode 13A is wide in the axial direction of the optical fiber.
and 13B are arranged facing each other to form a wide discharge arc 14, thereby expanding the melting area.

In this method, as shown in FIG. 2(B), during fusion splicing of the fiber end faces before forming the tapered shape, the fused region does not widen, so the end face shape changes drastically during fusion splicing. There is a problem in that the core tends to undergo large deformation, and therefore a low-loss connection cannot be made.

Therefore, in order to solve these problems, it is necessary to separately install a tapered shape processing device, which is not only uneconomical, but also when moving the connection part to that device.
This has not been realized until now because there is a risk that the connection part may break.

The second problem is that since the shape of the RA connection part is tapered and thin, the strength of the connection part is extremely weak. This is especially true when twisting of the core wire that occurs when processing extra length of the connection core is applied to the connection section, or when the fiber protrudes from the core sheath due to temperature changes, causing longitudinal compressive stress at the connection section. If this happens, there is a very high probability that the optical fiber connection will break, which has been the biggest drawback of conventional connection methods.

[Object of the Invention] Therefore, an object of the present invention is to provide a single mode optical fiber splicing method that solves these drawbacks and can perform low-loss, high-strength splicing in a short time. be.

Another object of the present invention is to provide a method for splicing single-mode optical fibers, which can easily reinforce the spliced portion and establish a high-strength splice in a short time.

[Structure of the Invention] In order to achieve such an object, in a first embodiment of the present invention, two single mode optical fibers to be connected are faced to each other,
Both end faces of these optical fibers are heated and melted and fusion spliced.
Then, while heating and melting the connecting portion, the optical fibers are pulled in a direction away from each other around the connecting portion, thereby making the connecting portion thin and tapered.
After fusion splicing two single-mode optical fibers to be spliced, the two single-mode optical fibers are pulled in a direction away from each other to make the spliced part the required thickness, and the first single-mode fiber is spliced. Fix one end of the optical fiber.

While pulling the other single mode optical fiber, the heating and melting region is simultaneously moved in the pulling direction of the other single mode optical fiber to form a taper on the other single mode optical fiber side. Next, heating is performed. After moving the melted area back to the center of the connection.

While fixing the other single mode optical fiber and pulling one single mode optical fiber, the heated and melted region is simultaneously moved in the direction in which the one optical fiber is pulled, thereby forming a taper on the side of the one optical fiber. and connect.

Here, it is preferable to change the heating temperature when fusion splicing one single mode optical fiber and when processing the splicing portion into a tapered shape.

In the second embodiment of the present invention, two hazy-mode optical fibers to be connected are faced to each other, and both end surfaces of the optical fibers are heated and melted to perform fusion splicing, and the connecting portion is heated and melted. A process of processing into a tapered part, a process of adding reinforcing material to two single mode optical fibers including the tapered part, and a process of adding reinforcing material to the two single mode optical fibers at the ends or outside of the tapered part. It has a step of fusing and integrating the materials.

[Example] The present invention will be described below with reference to the drawings.

One embodiment of the present invention will be explained with reference to FIGS. 3(A,) to (G). First, as shown in FIG. 3(A), two single mode optical fibers 1 and 2 to be connected are connected. to face each other. A discharge arc 24 is formed between the discharge electrodes 23A and 23B, which are arranged opposite to each other across the opposing ends of these fibers 1 and 2.
is generated, the fiber end face is melted by the discharge heating, and in this state, both fibers 1 and 2 are pushed in the direction of the arrow and fusion spliced as shown in FIG. 3(B).

Next, to make the connecting portion 25 thin and tapered.

$3 r! ! J(C) ノ, J-Uni, 7 y 4A1
Pull the tapered parts 2 away from each other as shown by the arrows, and thin the connecting part 25 to the required outer diameter.
form 8. In this state, since the shape of the tapered portion 26 changes rapidly with respect to the longitudinal direction of the optical fibers 1 and 2, the loss of the propagation mode in the tapered portion 26 is large, making it impractical.

Therefore, as shown in FIG. 3(D), one of the optical fibers 2 is fixed, and the other optical fiber 1 is pulled in a direction in which the other optical fiber 2 is also moved away, and at the same time,
Discharge electrodes 23A and 23B are moved in the direction of optical fiber 1. Thereby, a gentle taper shape 27 can be formed on the other optical fiber 1 side according to the moving speed, tensile force, and heating temperature of the discharge electrodes 23A and 23B.

Note that during such taper processing, since no temperature is required during fusion splicing of the fiber end faces, it is effective for control to lower the heating temperature by changing the discharge current.

Next, in order to form a gentle taper on one of the optical fibers, as shown in FIG. 3(E), the discharge electrode 23A is
and 23B to the side of one optical fiber 2, the other optical fiber l is fixed, and one optical fiber 2
While pulling the discharge electrode 2, as shown in Fig. 3 (1))
3A and 23B are also moved in the direction in which one of the optical fibers 2 is pulled. As a result, as shown in FIG.
form 8. Figure 3 (G) is connected! 25 shows the completion state of the taper process at step 25.

By the above processing, the tapers 27 and 28 extending in the axial direction from the connecting portion 25 are tapered! j:L can be made long, and the shape change γ of the core in the longitudinal direction can be reduced to y = 2L/(
D-d) ≧40, thereby realizing a low-loss optical fiber connection.

Here, the discharge electrodes 23A and 23B used melt only the vicinity of the end surfaces of the optical fibers 1 and 2, and the connecting portion 25
The change in the core shape is made as small as possible in the discharge electrode, and the present invention also has the advantage that it is possible to perform mechanical machining using this discharge electrode.

A tapered connection that satisfies the above formula has low loss, but
On the other hand, it has the disadvantage of being weak in terms of strength due to its thin outer diameter.

FIGS. 4(A) to 4(D) show other embodiments of the present invention which solve this weak strength defect, and FIG. 3(A)
After performing the taper processing as shown in (G), for example, a V-shaped reinforcing glass groove 30 is attached to the tapered portions 27 and 28, as shown in FIGS. 4(A) and (B).
The reinforcing glass V-groove 30 and the optical fibers 1 and 2 are fused together at the outside of these tapered portions 27 and 28 by discharge heating using discharge electrodes 23A and 23B.

Note that this fused portion does not necessarily include the tapered portions 27 and 28.
Of course, the tapered part is not limited to the outer part, but may be fused at the end of the tapered part, or may extend from the end to the inner side.

FIG. 4(C) shows how the reinforcing glass V-groove 30 is fused to the optical fibers 1 and 2 and deformed as shown by reference numeral 30' due to this discharge heating, and FIG. 4(D) shows this deformation. The state in which fusion reinforcement is completed using the reinforcing glass member 30' is shown.

In this example, when the reinforcing material 30 is fused to the optical fibers 1 and 2, the discharge electrode 23A used for fusion splicing the optical fibers is
Moreover, by incorporating a large number of reinforcing materials 30 into the main body of the connecting device and automatically supplying them to the connecting position shown in FIG. 3(G), this series of steps can be automated. It is possible.

Furthermore, according to this embodiment, the strength of the connection part is considerably strengthened, so when reinforcing the entire connection part including the core wire part, conventional reinforcement methods such as heat shrink tube reinforcement method can be used as is. Can be used.

[Effects] As explained above, according to the present invention, two single mode optical fibers are fusion spliced using a discharge heating mechanism that enables low-loss splicing, and at the same time, a gently tapered splice is made. Since it is possible to form a section, extremely low-loss connections can be realized. Moreover, according to the present invention, T
There are many advantages, such as simplifying the construction of the I-connection device, facilitating maintenance of the electrodes, and design of the high-voltage circuit.

Furthermore, by attaching reinforcing material to the connection part that has been thinly processed into a gently tapered shape, and reinforcing both ends of the gently tapered part by welding, we can create a connection that is even stronger than conventional fusion splices. This has the advantage of allowing highly reliable connections to be achieved.

The present invention can be realized only by the axis alignment method in the past.
A low-loss, high-strength connection can be achieved using an extremely simple shaft-fixed connection, reducing the cost of the connection device to approximately 115% compared to the conventional method, and reducing the connection time to approximately 1/4 of the conventional method.
It can be shortened to

[Brief explanation of the drawing]

Figures 1 (A) to (D) are explanatory diagrams of the process of the conventional fixed shaft taper type fusion splicing method. Figures 2 (A) and CB) are the conventional fixed shaft taper type with expanded discharge heating area. 3(A) to (G) are explanatory diagrams of sequential steps in one embodiment of the present invention. FIG. 3 is an explanatory diagram of an example in which fusion reinforcement is applied. 1.2...Single mode optical fiber to be connected, 23A
, 23B...Discharge electrode for heating/heating, 24...Discharge arc, 25...Connection part, 28...Tapered part. 27, 28... gentle taper portion, 30... glass V groove for reinforcement. 30'...Deformed reinforcing glass member.

Claims (1)

[Claims] 1) Two single-mode optical fibers to be connected are faced to each other, and both end surfaces of the optical fibers are heated and melted to be fusion-spliced, and then, while the spliced portion is heated and melted, After the two single mode optical fibers to be connected are fusion-spliced, in a method of connecting the optical fibers by pulling the optical fibers away from each other around the connection part to make the connection part thin and tapered. , the two single mode optical fibers are pulled away from each other to make the connection part a predetermined thickness, then one of the single mode optical fibers is fixed, and the other single mode optical fiber is While pulling, simultaneously move the heating and melting region in the pulling direction of the other single mode optical fiber to form a taper on the other single mode optical fiber side, and then move the heating and melting region to the connecting portion. the other single mode optical fiber is fixed, and while pulling the one single mode optical fiber, the heated melting region is simultaneously moved in the direction in which the one single mode optical fiber is pulled. A method for connecting single mode optical fibers, characterized in that the single mode optical fibers are connected by forming a taper on the side of the single mode optical fiber. 2) According to claim 1, the heating temperature is changed when fusion splicing the two single mode optical fibers and when processing the splicing portion into a tapered shape. How to connect single mode optical fiber. 3) A step of fusion splicing two single mode optical fibers to be connected by heating and melting both end surfaces of the optical fibers, and a step of heating and melting the spliced portion to form a tapered shape. , adding a reinforcing material to the two single mode optical fibers including the tapered portion; and adding a reinforcing material to the two single mode optical fibers at the ends or outside of the tapered portion. A method for connecting single mode optical fibers, which is characterized by fusing and integrating single mode optical fibers.