JPH0735946A - Optical fiber coupler - Google Patents

Abstract

PURPOSE:To provide the optical fiber coupler having excellent vibration resistance characteristics. CONSTITUTION:Resins 5 having <=1kg/mm<2> Young's modulus are applied to parts nearer a fusion stretched part 7 than fixing parts 4A, 4B at the time of fixing a coupler body 2 to a reinforcing device 3. As a result, the optical fiber coupler 1 having the excellent vibration resistance characteristics and the stable optical characteristics is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fusion splicing type optical fiber coupler, and more particularly to an optical fiber coupler having a structure excellent in vibration resistance.

[0002]

2. Description of the Related Art Conventionally, fusion-stretched optical fiber couplers are
A plurality of optical fibers are spliced, fused, and stretched to form a fused stretched portion. Light propagating in one optical fiber is branched, or conversely, it is incident from a plurality of optical fiber terminals. , Is used as a component for joining propagating light, and is used for optical communication using an optical fiber as a transmission medium and optical measurement.

This fusion-stretched optical fiber coupler is shown in FIG.
As shown in FIG. 2, the coupler body 2 is fixed on the base material called the reinforcing device 3 by using an adhesive, and the vicinity 4A of the outlet of the reinforcing device 3 from the accommodation portion 3A and the coupler. The main body 2 is fixed at the boundary 4B between the portion where the coating remains and the portion where the coating does not remain. In this structure, the positions and the numbers of the fixed portions 4A and 4B are appropriately selected depending on the use of the optical fiber coupler, the material of the coupler body 2 and the material of the reinforcing device 3.

By the way, in the fusion-stretched optical fiber coupler, the fusion-stretched portion 7 is thinly stretched. Therefore, when the incident light propagates through the fusion extension part 7, the light is confined to the core to a small extent, and as a result, the light energy reaches the surface of the clad glass. Therefore, the fusion-stretched portion 7 is in an air-clad state, and it is not preferable that a substance other than air comes into contact with it.
Fixing with an adhesive at the fusion-bonding stretched portion 7 is impossible. Therefore, in most of the fusion-stretched optical fiber couplers, the portion other than the fusion-stretched portion 7 is fixed with an adhesive.

However, in the fixing method using the above-mentioned adhesive, when vibration is applied to the optical fiber coupler, the fixed portion 4B becomes the fixed end 4C, and the fusion extending portion 7 of the coupler body 2 is used.
Shows a string-like behavior, and resonates at a specific vibration frequency as shown in FIG. At such vibration frequency,
Since the coupler body 2 exhibits a very sharp resonance characteristic, the fusion spliced portion 7 is deformed, which in turn weakens the mechanical strength of the fusion spliced portion 7 and may cause fatal damage such as breakage. There was a problem.

In order to avoid the above-mentioned resonance phenomenon, it is possible to shift the resonance frequency to a very high frequency. As means therefor, the tension when fixing the coupler body 2 to the housing portion 3A of the reinforcing device 3 is increased, the diameter of the fusion extending portion 7 of the coupler body 2 is reduced, and the distance between the fixing portions by the adhesive is shortened. , And the like.

However, the first method is not desirable from the viewpoint of the life of the coupler body 2 because glass is a brittle material. Regarding the second method, the shape of the fusion splicing portion 7 is determined from the required optical characteristics of the optical fiber coupler, and it is difficult to arbitrarily determine the size of the diameter of the fusion splicing portion 7. is there. Further, as described above, also in the third method, it is impossible to bring the adhesive, which is a foreign matter, close to the fusion-bonded stretched portion 7 until it comes into contact. For these reasons, there is a limit in any of the above methods.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of these circumstances, and an object thereof is to provide an optical fiber coupler which prevents adverse effects due to external vibration and is excellent in vibration resistance. Has an aim.

[0009]

This object can be solved by applying a resin having a Young's modulus lower than that of an adhesive for fixing the coupler body and the reinforcing device to a portion closer to the fusion stretched portion than the fixed portion. . In particular, the Young's modulus of the resin is 1
It is preferably not more than kg / mm ² .

[0010]

By applying a resin having a Young's modulus lower than that of the adhesive to the portion closer to the fusion stretched portion than the portion fixed by the adhesive, the resin absorbs vibration from the outside, and the coupler body caused thereby Avoid resonance.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the drawings. 1 and 2 show an example of the optical fiber coupler 1 of the present invention. Optical fiber coupler 1 of this embodiment
Is roughly composed of a coupler body 2 and a stiffener 3 that houses the coupler body 2. The coupler body 2 is manufactured by bringing a plurality of optical fibers 6, 6 into contact in parallel, fusing and stretching the contact portions while heating the contact portions, and the fusion extending portion 7 and the non-fusion extending portion 8 It consists of Since the fusion-bonded stretched portion 7 is stretched, it has a smaller diameter than the non-fusion-bonded stretched portion 8.

The reinforcing device 3 is composed of an accommodating portion 3A and a lid portion 3B, which are joined by an adhesive or laser welding. As shown in FIG. 2, the accommodating portion 3A of the reinforcing device 3 has a prismatic shape, and has a groove-shaped recess 3C having a quadrangular cross section in the longitudinal direction. This recess 3C
Accommodates the coupler body 2, and the shape of the recess 3C is
In addition to the rectangular cross section as shown in FIG. 2, the cross section may be semicircular. In addition to the prismatic shape,
It may be cylindrical. As a material for forming the reinforcing device 3, a material having excellent vibration resistance, heat resistance, and waterproofness is preferable because the purpose is to protect the coupler body 2, and in particular, silica glass is preferable because of compatibility with the optical fibers 6 and 6. Metals having a low coefficient of thermal expansion are used. Also, the recess 3
C is set so that the center of the coupler body 2 and the center of the reinforcing device 3 coincide with each other in order to minimize the influence of external force when the coupler body 2 is housed.

Next, the coupler bodies 2 are bonded to each other by filling the gaps in the recesses 3C of the reinforcing device 3 with the adhesive 4. As shown in FIG. 1 and FIG. 2, here, by the adhesive 4, the vicinity 4A of the outlet of the accommodation portion 3A of the reinforcing device 3
And the portions where the coating is removed by the fusion stretching method and the boundary portions 4B of the remaining portions are fixed respectively, but the fixed portions 4A and 4B are not particularly limited, and It suffices that the coated portions 5A and 5B of the resin 5 other than the adhesion / stretching section 7 remain in the non-fusing / stretching section 8. As the type of the adhesive 4, since the material of the optical fibers 6, 6 is mainly quartz glass, optical transparency is required, and epoxy type, acrylate type and silicone rubber type are preferable.

On the other hand, a resin 5 having a Young's modulus lower than that of the adhesive 4 is applied to a portion adjacent to the fixed portion 4B and close to the fusion extending portion 7. Since this resin 5 is not intended to fix the coupler body 2 and the housing portion 3A of the reinforcing device 3, the coupler body 2 and the reinforcing device 3 are applied at the coated portions 5A and 5B.
It is not necessary that the housing portion 3A is fixed. Further, it is preferable that the distance between the coated portions 5A and 5B of the resin 5 is as short as possible, but for the reason described above, it may be arbitrarily set within a range of about 0.5 to 10 mm so as not to come into contact with the fusion stretched portion 7. You can As the resin 5, an ultraviolet-curable silicone acrylate resin having a Young's modulus of 1 kg / mm ² or less is preferably used. The Young's modulus of 1 kg / mm ² or less is preferable because the resin 5 has good vibration absorption characteristics.
Other than the above, the resin 5 may be any of those that satisfy the above conditions, such as a thermosetting type, a room temperature curing type, and a liquid silicone rubber.

In such an optical fiber coupler 1, since the resin 5 is applied to a portion closer to the fusion extending portion 7 than the fixed portion 4B, this resin 5 absorbs vibration from the outside, and as a result, The resonance of the coupler body 2 is avoided,
The vibration resistance will be improved.

The effects of the present invention will be clarified below by showing concrete examples. (Example) The coupler body 2 was fused by using two single mode fibers having a coating diameter of 250 μm, a cladding diameter of 125 μm, a core diameter of about 10 μm, a mode field diameter of 9.8 μm, and a secondary mode cutoff wavelength of 1.25 μm. It was produced by the stretching method. The optical characteristics of the coupler body 2 are an operating wavelength of 1.3 μm, a branching ratio of 1: 1 and an insertion loss of 0.15 dB.

The coupler body 2 is accommodated in the accommodating portion 3A of the reinforcing device 3.
It was housed in the concave portion 3C, and the gap between the coupler main body 2 and the concave portion 3C was filled with the adhesive 4 to bond them to each other. That is, the area around the outlet 4A from the accommodation portion 3A of the reinforcing device 3 and the location of the boundary 4B between the portion where the coating was removed and the remaining portion were firmly fixed. As the adhesive 4, a modified acrylate adhesive having a Young's modulus of about 300 kg / mm ² was used.
Further, in the coupler body 2, about 10 g of tension was applied to the fusion-bonded stretched portion 7.

Next, the fixed portion 4 in the coupler body 2
Adjacent to B, the non-fusion stretched portion 8 near the fusion stretched portion 7
Then, a UV-curable silicone acrylate resin having a Young's modulus of about 0.2 kg / mm ² was applied. The coating amount was about 2 mm as the length of the coating portions 5A and 5B.

This optical fiber coupler 1 was installed in a vibration tester, and a sine wave with a vibration acceleration of 10 G was applied in a direction perpendicular to the planes containing the fiber axes of the two optical fibers 6, 6. The vibration frequency was changed from 0.25 octave per minute to a range of 10 Hz to 3000 Hz. Further, the incident light power and the emitted light power at each oscillation frequency were measured to obtain the insertion loss (dB), and the results are shown in FIG.

(Comparative Example) A vibration test was conducted in the same manner as in the above-described example except that the resin 5 was not applied. The results are shown in Fig. 5.

Now, the results of Example 1 will be described in comparison with Comparative Example. First, in FIG. 5, a fairly sharp resonance waveform was observed at a vibration frequency of about 1800 Hz. It is expected that the fusion splicing extension 7 of the optical fiber coupler is likely to undergo a large deformation at this resonance point. On the other hand, in FIG. 3, the resonance waveform at about 1800 Hz as seen in FIG. The reason why the resonance point is slightly shifted to a higher frequency here is presumed to be that the distance between the fixed portions of the fusion-stretched portion is shortened by the application of the resin 5.

[0022]

As described above, in the optical fiber coupler of the present invention, when the fusion splicing type coupler body is fixed to the reinforcing device with the adhesive, the portion closer to the fusion splicing portion than the fixed portion is fixed. , Young's modulus is 1kg / mm ² or less, so the resin absorbs the vibration from the outside.
The resonance of the coupler body is avoided, the vibration resistance is improved, and higher mechanical reliability can be obtained as compared with the case where no resin is applied. Furthermore, since the tension of the fusion-bonded stretched portion of the coupler body is the same as that of the conventional one, the effect of loosening does not occur.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of an optical fiber coupler of the present invention.

FIG. 2 is a perspective view showing an embodiment of the optical fiber coupler of the present invention.

FIG. 3 is a graph showing the relationship between vibration frequency and insertion loss in the optical fiber coupler of the present invention.

FIG. 4 is a perspective view showing an example of a conventional optical fiber coupler.

FIG. 5 is a graph showing the relationship between vibration frequency and insertion loss in a conventional optical fiber coupler.

[Explanation of symbols]

1 ... Optical fiber coupler, 2 ... Coupler body, 3 ... Reinforcer,
4 ... Adhesive, 5 ... Resin

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichiro Shishikura 1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Co., Ltd.Sakura Factory (72) Inventor Hirohisa Fujimoto 1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Sakura Factory, Ltd.

Claims (2)

[Claims] 1. A resin having a Young's modulus lower than that of the adhesive is applied to a portion closer to the fusion-stretched portion than the fixed portion when the fusion-stretched coupler body is fixed to a reinforcing device with an adhesive. An optical fiber coupler characterized in that 2. The optical fiber coupler according to claim 1, wherein the Young's modulus of the resin is 1 kg / mm ² or less.