JPH07104140A - Optical fiber coupler - Google Patents

Abstract

PURPOSE:To provide the optical fiber coupler which suppresses the bending loss according to local bending of optical fibers and has high reliability for long-term use. CONSTITUTION:This optical fiber coupler 1 has a fusion stretched part 6 and leads extending from the fusion stretched part 6. The leads are composed of a clad exposing part and a coating material remaining part 4. The leads are fixed to a protective case 2 by maintaining the state of arranging the leads near the boundary between the clad exposing part and the coating material remaining part 4 on the extension line of a curve formed by the part near the lead branching point 7 where the lead is branched or the coating material on the clad exposing part side of the coating material remaining part 4 of the leads is formed successively thinner toward the clad exposing part and is fixed to the protective case 2. As a result, the length of the optical fibers is shortened. In addition, the excellent optical characteristics are obtd. and the high reliability is maintained for the long-term use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fusion-stretching type optical fiber coupler having excellent optical characteristics, which is used in the fields of optical communication and optical measurement.

[0002]

2. Description of the Related Art Conventionally, a fusion-spreading type optical fiber coupler is one in which a plurality of optical fibers are, for example, spliced, fused, and stretched to form a fusion-stretched portion. It is used as a component that splits the light propagating through the optical fiber, or conversely enters from multiple optical fiber terminals and joins the propagating light, and is used for optical communication and optical measurement using optical fibers as a transmission medium. .

This fusion-stretching type optical fiber coupler is
As shown in FIG. 5, the coupler body is fixed on the base material called the protective case 2 using the adhesive 8 and is housed. The coupler body is composed of the fusion splicing portion 6
And the non-fusion-bonded stretched portion, and the non-fusion-bonded stretched portion is composed of the clad exposed portion and the coating material residual portion 4. The protective case 2 is often made of quartz glass or ceramics and has a cylindrical outer shape.

The following is a method for manufacturing the optical fiber coupler. First, a plurality of optical fibers 3a and 3b are prepared, a part of the coating material is removed to form a clad exposed portion, and then the clad exposed portions are spliced to each other, and the spliced portion is oxyhydrogen flame. While heating with
Fusing and stretching are performed to form the fusion stretching part 6.

Then, the fusion-bonded stretched portion 6 of the coupler body is housed in the protective case 2, and the non-fusion-stretched stretch including both ends of the protective case 2 and the boundary between the exposed cladding portion of the coupler body and the coating material residual portion 4. The part is fixed by the adhesive 8.

However, in the conventional manufacturing method, when the two optical fibers 3a and 3b are juxtaposed, the cladding exposed portions are inevitably separated from each other due to the thickness of the coating material. Therefore, when forming the fusion-bonded stretched portion 6, clamping pressure is applied to the vicinity of both ends of the exposed cladding portion in order to reduce the distance between the exposed cladding portions. Therefore, from the position where the clamping pressure is applied, the covering material is applied. A local bend was generated in the portion up to the residual portion 4. Hereinafter, the portion where this bending has occurred is referred to as the lead branch portion 5, and the starting point of the bending is referred to as the lead branch point 7.

Such local bending causes optical distortion, increases bending loss, and if the bending state continues for a long period of time, a tensile force is internally applied to the outer circumference of the lead branch portion 5. Since the pressing force is applied to the circumference over time, the probability of breakage of the optical fiber coupler increases. By the way, a radius of curvature is known as an index indicating the degree of bending. It is said that the larger the radius of curvature, the lower the fracture probability, and conversely, the smaller the radius of curvature, the higher the fracture probability. In order to suppress the breakage probability of the optical fiber coupler to withstand long-term use, in the case of a single-mode optical fiber for communication used for manufacturing the optical fiber coupler, the radius of curvature of the lead branching portion 5 should be about 30 mm or more. Has been preferred.

However, in the case of an optical fiber having a coating diameter of 250 μm, in order to make the radius of curvature of the lead branch 5 about 30 mm, the length of the lead branch 5 needs to be about 5 mm. Then, the length of the left and right lead branch portions 5 aligned with respect to the entire coupler body is 10 mm, which is a problem when downsizing the optical fiber coupler.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of these circumstances and has excellent optical characteristics and leads formed in a protective case without increasing the length of lead branch portions. It is an object of the present invention to provide an optical fiber coupler having a large bending radius of curvature.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to have a fusion splicing portion formed by fusing and stretching a plurality of optical fibers, and a lead extending from the fusion splicing portion, the lead being the clad exposed portion. An optical fiber coupler composed of a coating material residual portion and a lead near the boundary between the clad exposed portion and the coating material residual portion on an extension line of a curve formed by the vicinity of the lead branch point where the lead is branched. Hold the placed state,
This can be solved by fixing the leads to the protective case, or by making the coating material on the exposed cladding portion side of the coating material remaining portion of the lead thinner toward the exposed cladding portion and fixing the leads to the protective case. .

[0011]

According to the optical fiber coupler of the present invention, the radius of curvature of the lead bend generated in the protective case can be increased without increasing the length of the lead branch portion.

[0012]

The present invention will be described in detail with reference to the drawings. FIG. 1 shows an example of an optical fiber coupler 1 of the present invention. The optical fiber coupler 1 has a structure in which a fusion-spreading type coupler main body is fixed and housed in a protective case 2 with an adhesive 8. The coupler body is
It is composed of a fusion-bonded stretched portion 6 and a non-fusion-bonded stretched portion, and the non-fusion-bonded stretched portion is composed of a clad exposed portion and a coating material residual portion 4. In addition, a lead branch portion 5 having a bend is present in the exposed clad portion. The lead branching portion 5 is gradually separated from the lead branching point 7 while drawing a gentle curve in a portion from a position where a pressure is applied to the exposed clad portion to the coating material residual portion 4. Further, the base end portion of the coating material remaining portion 4 on the cladding exposed portion side is present on the extension line of the curve formed by the vicinity of the lead branch point 7.

The protective case 2 is composed of an accommodating portion and a lid portion, which are joined together by an adhesive, laser welding or the like, and have a cylindrical outer shape. The main material of the protective case 2 is the fusion-bonded extension portion 6 of the coupler body.
Since it is the purpose of protecting the glass, it is preferable that it has excellent earthquake resistance, heat resistance, and waterproofness, and quartz glass, ceramics with a low coefficient of thermal expansion, synthetic resin, Invar alloy, etc. are especially used because of compatibility with optical fibers. Has been done.

The coupler body and the protective case 2 are fixed by the non-fusion extending portion including the boundary between the exposed clad portion and the coating material residual portion 4 and the portions up to both ends of the protective case 2.
The lead branch portion 5 and the covering material residual portion 4 are provided on the fixing portion.
The base end portion of the clad exposed portion side is included and is fixed in a bent state. Therefore, a gap is formed in the vicinity of both ends of the protective case 2 of the covering material residual portion 4.

Next, a method for manufacturing the optical fiber coupler 1 of the present invention will be described. First, two optical fibers 3a and 3b
Is prepared, a part of the covering material is removed, and the exposed clad portion is formed. Next, the optical fibers 3a and 3b are arranged in parallel so that the exposed cladding portions are parallel and the coating material residual portions 4 are in contact with each other. At this time, since the clad exposed portions are separated from each other by the thickness of the covering material, in order to reduce the distance, a clamping pressure is applied to the vicinity of both ends of the clad exposed portion to join the clad exposed portions. Then, while heating the central portion of the spliced portion with an oxyhydrogen flame, fusion bonding,
It is stretched to form the fusion-bonded stretched portion 6. Since the fusion-bonded stretched portion 6 has a small diameter due to the stretching, it is easily affected by the outside. Therefore, in order to protect this, the fusion extending portion 6 is housed in the protective case 2.

Next, the coupler body and the protective case 2 are
Fix with adhesive 8. By the way, when the two optical fibers 3a and 3b are arranged side by side, the lead branch portion 5 is bent due to the thickness of the covering material. Therefore, the lead in the vicinity of the boundary between the exposed clad portion and the remaining coating material portion 4 is overlapped on the extension line of the curve formed by the vicinity of the lead branch point 7, and this state is held so that the coupler body and the protective case 2 are separated. Fix it.

The fixing portion is a range from the both ends of the protective case 2 to the non-fusion extending portion including the boundary between the exposed clad portion and the coating material residual portion 4, and the lead branch portion 5 and the curved coating material residual portion 4. To be included. Further, the type of the adhesive 8 is desired to have a low linear expansion coefficient because the optical fibers 3a and 3b are mainly composed of quartz glass, and a curing shrinkage rate is small. Therefore, an epoxy-based or acrylic-based resin that satisfies this condition is preferable.

In the optical fiber coupler 1 manufactured in this manner, the lead near the boundary between the exposed cladding portion and the coating material remaining portion 4 is placed on the extension line of the curve formed by the lead branch point 7 and near the lead, so that the lead Since the length of the branching portion 5 can be shortened and the curvature radius of the bending of the lead generated in the protective case 2 can be made equal, the optical distortion due to the bending can be suppressed and the optical fiber coupler 1 can be used for a long period of time. Credibility is maintained.

FIG. 2 shows another example of the optical fiber coupler 1 of the present invention, which is different from the previous example.
The coating material residual portion 4 is in contact with it. In this example, the coating diameter is successively reduced in order to increase the radius of curvature. Therefore, the coating material on the exposed clad portion side is thinned by a method such as softening by heat, physical removal, or chemical removal by chemicals.

As shown in FIG. 3, the coating material is adjusted so that it becomes thinner as the exposed clad portion becomes closer, so that the two optical fibers 3c and 3d are parallel to each other at the exposed clad portion. In addition, when the coating material residual portions 4 are arranged in parallel so that they are in contact with each other, the gap between the clad exposed portions, which inevitably occurs due to the thickness of the coating material, is smaller than that of the conventional one. Even if clamping pressure is applied, the degree of bending is small and the radius of curvature is large.

Further, as shown in FIG. 4, the first example and the second example
Using the above example together, a fusion splicing type coupler body is manufactured using the optical fibers 3c and 3d in which the coating material on the cladding exposed portion side of the coating material residual portion 4 is successively thinned toward the cladding exposed portion. It is also possible to fix the coupler body to the protective case 2 such that the lead near the boundary between the exposed clad portion and the coating material remaining portion 4 is overlapped on the extension line of the curve formed near the lead branch point 7. .

(Embodiment 1) Hereinafter, the effects of the present invention will be clarified by showing concrete examples. First, the optical fibers 3a and 3a each having a core diameter of 8 μm, a clad diameter of 125 μm, and a coating diameter of 250 μm.
Two b were prepared, and a part of each coating material was removed.
Then, the optical fibers 3a and 3b are juxtaposed so that the clad exposed portions are parallel to each other and the coating material residual portions 4 are in contact with each other, and then a narrow pressure is applied from both ends of the clad exposed portions to the clad exposed portion from the central portion by about 2 mm. Then, the exposed clad portion was attached. Next, the central portion of the exposed clad portion was heated with an oxyhydrogen flame, further fused and stretched to manufacture a coupler body.

Next, the coupler main body is housed in the protective case 2, and on the extended line of the curve formed by the vicinity of the lead branch point 7,
Leads near the boundary between the exposed clad portion and the remaining coating material portion 4 were stacked. The range of the lead is within the range that can be accommodated in the protective case 2, and the length is preferably 4 to 6 mm. Next, the gap between the protective cases 2 was filled with the adhesive 8 to fix the coupler body and the protective case 2.

Further, an epoxy resin is used as the adhesive 8, the fixing portion includes the lead branch portion 5, and the coating material remains on the lead branch portion 5 and the clad exposed portion side up to both ends of the protective case 2. The part 4 was fixed while being held in a bent state. The protective case 2 has a length of 35 mm and a width of 2 m.
The glass used had a size of m and a height of 2 mm. In this example, the lead branch 5 of the optical fiber coupler 1 had a length of 2 mm and a radius of curvature of 32 mm.

(Example 2) As in Example 1, two optical fibers 3c and 3d from which a part of the coating material was removed were prepared.
Then, the coating material at the base end portion of the coating material remaining portion 4 on the clad exposed portion side has a thickness of 6 mm over 1.5 mm so that the coating material becomes thinner toward the exposed clad portion.
It was thinned by thermocompression bonding so as to have a thickness of 2.5 to 20 μm.

Next, the optical fibers 3c and 3d are juxtaposed so that the cladding exposed portions are parallel and the coating material residual portions 4 are in contact with each other, and the cladding exposed from both ends of the cladding exposed portion is about 1.5 mm from the central portion. Apply clamping pressure to the part,
The exposed clad portion was attached. Then, the central part of the exposed clad is heated with an oxyhydrogen flame, and further fused and stretched,
The coupler body was manufactured.

Then, the coupler body is housed in the protective case 2, and the gap between the protective cases 2 is filled with the adhesive 8.
The coupler body and the protective case 2 were fixed. Further, the type of adhesive 8, the position of the fixed portion, the type and size of the protective case 2 were the same as in Example 1. The length of the lead branch portion 5 of the optical fiber coupler 1 in this example is 1.5 mm,
The radius of curvature was 100 mm. When the insertion loss was examined to examine the optical characteristics, it was 0.1 dB or less.

(Conventional example) manufactured by a conventional manufacturing method,
The lead branch 5 of the optical fiber coupler had a length of 5 mm and a radius of curvature of 33 mm.

Now, the results of Examples 1 and 2 will be described in comparison with the results of the conventional example. First, in Example 1, although the length of the lead branch portion 5 was shortened by 3 mm as compared with the conventional example, the same radius of curvature was obtained.
The length of the lead branch part 5 is 3 before and after the fusion splicing part.
Since the radius can be shortened by mm, the radius of curvature of the lead branch portion 5 is the same and the length of the coupler can be shortened by 6 mm as compared with the conventional example. That is, the miniaturization is achieved while maintaining the same reliability as the conventional example.

On the other hand, in Example 2, although the length of the lead branch portion 5 was shortened by 3.5 mm as compared with the conventional example, the radius of curvature about 3 times was obtained. Since the length of the lead branch portion 5 can be shortened by 3.5 mm before and after the fusion splicing portion, respectively, even though the radius of curvature of the lead branch portion 5 is about three times that of the conventional example, the coupler. Is 7mm long
I was able to shorten it. In other words, miniaturization was achieved while maintaining reliability exceeding that of the conventional example.

[0031]

As described above, the optical fiber coupler of the present invention has a fusion splicing part formed by fusing and stretching a plurality of optical fibers, and a lead extending from the fusion splicing part. An optical fiber coupler in which the lead is composed of a clad exposed portion and a coating material residual portion, and the clad exposed portion and the coating material residual portion are provided on an extension line of a curve formed in the vicinity of a lead branch point where the lead is branched. Hold the lead in the vicinity of the boundary and fix the lead to the protective case, or reduce the coating material on the exposed clad portion of the lead coating material remaining portion gradually toward the exposed cladding portion. And since the lead is fixed to the protective case,
Even if the length of the lead branch part is shortened, the radius of curvature of the lead bending generated in the protective case can be made equal or more, so that optical distortion due to bending is unlikely to occur and it is suitable for long-term use. It is possible to manufacture a highly reliable optical fiber coupler that is equivalent to or better than the conventional case.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an optical fiber coupler of the present invention.

FIG. 2 is a schematic configuration diagram showing an embodiment of an optical fiber coupler of the present invention.

FIG. 3 is a schematic configuration diagram showing an embodiment of an optical fiber used in the optical fiber coupler of the present invention.

FIG. 4 is a schematic configuration diagram showing an embodiment of an optical fiber coupler of the present invention.

FIG. 5 is a schematic configuration diagram showing an example of a conventional optical fiber coupler.

[Explanation of symbols]

1 ... Optical fiber coupler, 2 ... Protective case, 3a ・ 3b ・
3c and 3d ... Optical fiber, 5 ... Lead branch portion, 6 ... Fusion extension portion, 7 ... Lead branch point

Claims (2)

[Claims] 1. A fusion splicing section formed by fusing and stretching a plurality of optical fibers, and a lead extending from the fusion splicing section, wherein the lead comprises a clad exposed portion and a coating material residual portion. In the optical fiber coupler, the lead is branched, on the extension line of the curve formed by the vicinity of the branch point of the lead, holding the state of placing the lead near the boundary between the clad exposed portion and the coating material residual portion, An optical fiber coupler in which the leads are fixed to a protective case. 2. A fusion splicing part formed by fusing and stretching a plurality of optical fibers, and a lead extending from the fusion splicing part, wherein the lead comprises a clad exposed part and a coating material residual part. An optical fiber coupler, wherein the coating material on the cladding exposed portion side of the coating material remaining portion of the lead is sequentially thinned toward the exposed cladding portion, and the lead is fixed to a protective case. Fiber coupler.