JPH04295809A - Production of wide-band optical fiber coupler - Google Patents

Abstract

PURPOSE:To allow stretching without twisting a prestretched optical fiber around an unstretched optical fiber by heating and prestretching the 1st optical fiber and heating and fusing this fiber in parallel with the 2nd optical fiber, then stretching the fibers. CONSTITUTION:The 1st optical fiber 1 prestretched by heating and the unstretched optical fiber 2 are paralleled and the part near the stretching part of the unstretched part of the optical fiber 1 is brought into tight contact with the optical fiber 2. Tension is not applied to the two fibers 1, 2 or the tension as small as not to stretch the fibers is applied thereto and the prestretched part including the unstretched part of the fiber 1 is heated in this state. The heating is executed by moving a heating source 3 back and forth in a fusing region. The part where the nonstretched parts are in tight contact with each other melts first and a fused part is formed. The fused part, then, spreads to the prestretched part and the spacing part is melted as well. All of the prestretched parts are thus fused to the optical fiber 2. The region forming a coupler part is heated and stretched after fusing, by which the optical fiber coupler having desired characteristics is produced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical fiber coupler for branching and combining optical power used in optical communications and the like.

0002

2. Description of the Related Art An optical fiber coupler is made by twisting a plurality of optical fibers together several times, heating the twisted portion, and stretching it to form a tapered portion. It has low loss, good temperature stability, is mechanically strong, and is easy to manufacture, so it is suitable for constructing optical fiber communication networks. However, in such an optical fiber coupler, the branching ratio has wavelength dependence. For example, an optical fiber coupler manufactured to have a branching ratio of 50% at a wavelength of 1.3 μm has a branching ratio of 80% or more at a wavelength of 1.55 μm, and that value is also affected by the drawing state, so the individual This varies depending on the optical fiber coupler, and is not suitable for use with multiple wavelengths or as a high-band coupler.

[0003] In order to provide broadband characteristics to an optical fiber coupler, an optical fiber coupler has been proposed in which the propagation constant of some optical fibers is different from that of other optical fibers in a coupler made up of a plurality of optical fibers. .

[0004] The optical fiber coupler described in Japanese Patent Publication No. 63-501527 is, for example, a 2×2 port coupler in which two fibers have slightly different propagation constants measured at a given wavelength in the coupling region. It is manufactured by melting optical fibers. The difference in propagation constant can be determined by using two optical fibers with different diameters, using optical fibers with different profiles, or
This is achieved by making one of two identical optical fibers thinner than the other. A high-bandwidth optical fiber coupler is manufactured by twisting these two optical fibers together, melting them, and drawing them.

However, the method of using optical fibers of different diameters not only has problems in preparing the optical fibers, but also has problems in connecting the coupler and the optical fiber of the transmission line. Furthermore, since two optical fibers are twisted together, it is difficult to make the characteristics uniform, and there are problems of deterioration of reliability and non-reproducibility of loss. The method of using optical fibers of the same diameter does not solve the problem of connection with the optical fibers of the transmission line, but it does not solve the problem of twisting them together.

FIG. 2 is an explanatory diagram of a method of manufacturing an optical fiber coupler using optical fibers having the same diameter as described above. (A) As shown in the figure, a part of one optical fiber is stretched in the optical axis direction while being heated with a torch such as an oxyhydrogen flame.
An optical fiber 1 having a tapered portion n with a narrowed diameter is manufactured. This stretching process will be referred to as preliminary stretching.

This pre-stretched optical fiber 1 is melt-stretched together with an unstretched optical fiber of the same diameter, but since the stretched tapered part n is thinner than the unstretched part, as shown in FIG. As shown, even if the optical fibers 2 are placed parallel to each other and in close contact with each other, a gap g is created between the two optical fibers at the tapered portion. Leave this as it is 2
When the optical fiber 1 is heated and stretched, a stretching force is also applied to the optical fiber 1, so the tapered part n cannot easily contact the optical fiber 2 side, and the tapered part n can form a coupler. part cannot be formed. In addition, even if bonding is possible, there is no guarantee that a uniform fused portion will always be formed, so it is not possible to produce an optical fiber coupler with good reproducibility.

Therefore, conventionally, in order to bring the tapered portion n into close contact with the unstretched optical fiber 2, as shown in FIG. The material was wound at a gentle angle over half a turn or several turns, and then melt-stretched.

In such a conventional method, the twisting shape, twisting length, pressing force, etc. when twisting the pre-drawn optical fiber 1 are likely to fluctuate, and the subsequent melt-drawing process also causes variations in loss. This tends to cause problems in reproducibility, and the stress applied to the optical fiber during twisting deteriorates reliability, which has become a manufacturing problem.

0010

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems.
The object of the present invention is to realize a method for manufacturing a broadband optical fiber coupler that can be manufactured by stretching the optical fiber coupler.

[0011]

Means for Solving the Problems The present invention provides a method for manufacturing a broadband optical fiber coupler in which a first optical fiber is heated and pre-stretched, and the first optical fiber is drawn in parallel with a second optical fiber.
The method is characterized in that a pre-stretched portion including an unstretched portion of the optical fiber is heated and fused to a second optical fiber, and then stretched.

[0012] There may be a plurality of first optical fibers and/or second optical fibers.

[0013]

[Operation] The case of a 2×2 port optical fiber coupler will be explained. A heated and pre-stretched first optical fiber and an unstretched second optical fiber are placed in parallel, and at least the unstretched portion of the first optical fiber near the stretched portion is
Bring it into close contact with the second optical fiber. At this time, no tension is applied to both optical fibers, or a small tension that does not lead to stretching is applied to both optical fibers, including the unstretched portion of the first optical fiber,
Heat the pre-stretching section. Heating is accomplished by moving a heating source back and forth across the fusion region. The part of the non-stretched part that is in close contact melts first, and a fused part can be formed. As the heating progresses, the fused portion spreads to the pre-stretched portion, and the gap portion opened by the stretching is also fused to the second optical fiber, so that the entire pre-stretched portion is fused to the second optical fiber. The reason why the fused area spreads to the pre-stretched area is thought to be that the fused area of the glass softened and melted by heating progresses to the adjacent non-fused area due to surface tension, and eventually the heating Fusion is performed over the entire area.

[0014] By doing so, both optical fibers can be easily melted without applying stress from the outside, so that external factors causing variations in characteristics can be minimized.

After fusing, an optical fiber coupler with desired characteristics can be produced by heating and stretching the region where the coupler portion is to be formed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram of an embodiment of the method for manufacturing a broadband optical fiber coupler according to the present invention. In the figure, 1 is a first optical fiber, 2 is a second optical fiber, and 3 is a heating source. As the heat source 3, an oxyhydrogen flame torch was used.

First, as shown in Figure (A), the first optical fiber 1 is pre-stretched by applying a stretching force while heating it over the length L1 as a heating region using the heating source 3. The figure (B) shows a state in which preliminary stretching has been completed, and the length L1 of the heated region becomes L2 after being stretched. In this example, the length of the heating region L1 is 1500 μm,
By stretching this on both sides at a stretching speed of 145 μm/sec for about 2 seconds, the length L2 of the pre-stretched part is about 20
It became 00 μm.

The figure (C) shows the welding process. A pre-stretched optical fiber 1 and an unstretched optical fiber 2 are arranged in parallel and brought into close contact. The unstretched portion of the pre-stretched optical fiber 1 is brought into close contact with the optical fiber 2, but the pre-stretched portion of the optical fiber 1 is not necessarily brought into close contact with the optical fiber 2. Here, heating is performed over a length of L3 centering on the pre-stretched part. At this time, substantially no tension is applied to the two optical fibers. The heating section 3 is reciprocated by a length L3, and in this example, L3 is set to 4500 .mu.m, and the heating section 3 is reciprocated at a speed of 2500 .mu.m/sec for about 10 seconds. As a result, optical fibers 1 and 2
was melted and fused from the unstretched portion, and the fused region gradually expanded, and as shown in FIG. Note that the figure does not show the positional relationship between the heating section 3 and the two optical fibers;
Heating may be performed from an appropriate direction depending on the arrangement of the optical fibers 1 and 2.

Next, while heating the fused portion, a stretching force is applied to the fused portion to stretch it. In the drawing process, optical power of a certain wavelength is input from one end of one optical fiber, and the branching ratio is monitored using the other end of the optical fiber and a photodetector connected to the other end of the other optical fiber. Stretch while stretching. Then, when the branching ratio reaches a predetermined value, for example, 50%, the stretching is stopped, and as shown in (E) the optical fiber coupler section is made up of two tapered parts with different propagation constants. can be made. L4 is the length of the tapered portion formed by stretching. An optical fiber coupler can be manufactured by fixing this to a suitable protective member.

In the above explanation, the relationship between the length L2 of the pre-stretched region and the length L3 of the heated stretching region is set as follows: L2 = 2000 μm L3 = 4500 μm, so that L3 is sufficiently larger than L2. It is. However, since the heating region needs to be melted from the unstretched part of the pre-stretched optical fiber, L
2 and L3 may be substantially the same. In any case, the condition is that the relationship L2 < L3 is satisfied.

[0021] Since the band characteristics also depend on the preliminary stretching process, it is necessary to adjust the amount of stretching in the preliminary stretching process. Although the amount of preliminary stretching can be determined depending on the design, optical power may be introduced from one end and preliminary stretching may be performed while monitoring the output light from the other end. The measurement may be carried out while alternately switching the input and output ends, and in any case, the amount of preliminary stretching may be determined while measuring the amount of loss during preliminary stretching based on the amount of loss confirmed experimentally. can.

Although it is assumed that a single mode optical fiber is used as the optical fiber described above, the present invention is not limited to this. Further, the number of the first and/or second optical fibers is not limited to one, but may be two or more. In that case, in the fusion process, it is sufficient to sequentially fusion one optical fiber or a predetermined number of optical fibers at a time, and it is not necessary to fusion all the optical fibers at once. The heating method is not limited to a torch flame, and any suitable heating source such as a laser can be used.

[0023]

As is clear from the above description, according to the present invention, a pre-stretched first optical fiber can be stretched without being twisted onto an unstretched second optical fiber, thereby improving reliability. This has the effect of making it possible to manufacture a broadband optical fiber coupler with high performance and good reproducibility of characteristics.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the method for manufacturing a broadband optical fiber coupler of the present invention.

FIG. 2 is an explanatory diagram of an example of a conventional manufacturing method of a broadband optical fiber coupler.

[Explanation of symbols]

1 First optical fiber 2 Second optical fiber 3 Heating source

Claims (1)

[Claims] Claims: 1. A first optical fiber is heated and pre-stretched so as to be parallel to a second optical fiber, and the pre-stretched portion including the non-stretched portion of the first optical fiber is heated and fused to the second optical fiber. 1. A method for producing a broadband optical fiber coupler, which comprises stretching the optical fiber coupler after attaching the fiber.