JP3392292B2 - Optical fiber coupler - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an optical fiber coupler capable of reducing reflection at an unnecessary port of the optical fiber coupler and increasing the return loss. 2. Description of the Related Art FIG. 6 shows an example of a conventional optical fiber type coupler. The optical fiber type coupler removes the coating layer 12 of the optical fiber 11 from the glass fiber 13
And a plurality of glass fibers 13 are fused and drawn. The portion where the glass fibers 13 are fused and drawn becomes the light branching / coupling portion 14 for coupling light. In the light branching / coupling portion 14, the fiber diameter (cladding diameter) is larger than that of the ordinary glass fiber 13.
Is thinner. Therefore, in an optical fiber coupler,
Reinforcing is performed by fixing the light branching / coupling portion 14 to a reinforcing device 15 such as a storage case. Reinforcer 15
Various adhesives 16 such as an epoxy-based adhesive are generally used for fixing to the substrate. In the optical fiber coupler manufactured in this way, the number of used optical fiber wires 1 × 2 ports is formed. For example, as shown in FIG. 6, a 2 × 2 optical fiber type coupler manufactured using two optical fiber strands 1 has a total of four ports 1, port 2, port 3, and port 4. By the way, when the optical fiber coupler is used as an optical branching coupler, not all the ports may be needed. In that case, the number of ports is reduced by cutting off the unnecessary ports. For example, cutting one port 4 of a 2 × 2 optical fiber coupler to process it into a 1 × 2 optical fiber coupler is the most common example. The unnecessary port 4 is generally cut at a position close to the stiffener 15 so that the unnecessary port 4 after cutting does not become an obstacle. However, when the unnecessary port 4 is cut, there is a problem that light is reflected on the cut surface and the amount of return loss of the optical fiber coupler is reduced. Of the unnecessary port 4 is reduced by covering the unnecessary port 4 with a transparent resin 17 having a refractive index close to that of glass. Here, the return loss, when the light enters from one port 1 refers to come light loss emitted and reflected to the same port 1, the incident light intensity to port 1 P _1, from port 2 Assuming that the intensity of the reflected light coming out is P ₂ , the return loss is P ₁ /
P ₂ , P ₁ -P _{2 for} dB display. However, even if the cut surface of the unnecessary port 4 is covered with the transparent resin 17, the antireflection effect is insufficient.
For example, when the cut surface of the unnecessary port 4 is covered with a transparent resin 17 having a refractive index close to that of glass, light from the outside of the optical fiber coupler enters the optical branching / coupling portion 14 from the unnecessary port 4 through the transparent resin 17. There was a fear that it would. If a foreign matter that reflects light adheres to the surface of the transparent resin 17, light emitted from the cut surface of the unnecessary port 4 is reflected by the foreign matter and returns to the unnecessary port 4 again. There is a fear that the return loss of the sample may decrease. Further, when the transparent resin 17 covers not only the end of the unnecessary port 4 but also a part of the other port 3 on the same side as the unnecessary port 4, the transparent resin 17 is transparent by an external force applied to the other port 3. The resin 17 is likely to be deformed, and the unnecessary port 4 and the transparent resin 17 are likely to peel off. Then, when the cut surface of the unnecessary port 4 and the transparent resin 17 are separated, the light emitted from the unnecessary port 4 is reflected on the separated surface and returns to the unnecessary port 4 again. As a result, the return loss of the optical fiber coupler is reduced. There was also a risk of falling. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to sufficiently and surely reduce reflection at an unnecessary port of an optical fiber type coupler so that a large return loss can be stably obtained. It is to make. According to the present invention, at least one port of an optical fiber type coupler is cut, and a cut surface of the port and a port adjacent to the port are cut off.
Part of the port to be covered is integrally covered with transparent resin,
The optical fiber coupler is characterized in that the transparent resin is covered with an opaque resin having a Young's modulus of 1 to 3 MPa. Hereinafter, the present invention will be described in detail.
FIG. 1 is a plan view showing one embodiment of the optical fiber type coupler of the present invention. The optical fiber coupler according to the present embodiment has an optical branching / coupling portion 14 formed by fusing and stretching two optical fibers.
Are stored in the reinforcing device 15, two ports 1 and 2 extend from one end of the reinforcing device 15, and a port 3 extends from the other end.
And an unnecessary port 4 is extended. Unnecessary port 4
At a position close to the stiffener 15, it is preferably cut obliquely with respect to the optical fiber length direction. The optical fiber coupler according to the present invention is largely different from the conventional optical fiber coupler in that the cut surface of the unnecessary port 4 is covered with a transparent resin 20 and the transparent resin 20 is made of an opaque resin 21. It is a point covered with. The transparent resin 20 has a transmittance of light of at least 80% in a wavelength band used by the optical fiber coupler, and has a refractive index close to that of the glass constituting the optical fiber. Used. For example, when the optical fiber coupler is made of quartz glass, the transparent resin 20
Is preferably about 1.45 to 1.50. As the transparent resin 20, an ultraviolet curable resin is particularly preferable in terms of workability. For example, an ultraviolet curable acrylic resin, an ultraviolet curable silicone resin, an ultraviolet curable urethane resin, or the like is suitably used. In addition, a thermosetting epoxy resin, a thermosetting acrylic resin, a thermosetting silicone resin, a two-component curable epoxy resin, a two-component curable acrylic resin, a two-component curable silicone resin, or the like can also be preferably used. The transparent resin 20 has at least an unnecessary port 4
In the present embodiment, it is provided so as to cover the end of the unnecessary port 4 and a part of another port 1 adjacent thereto. The thickness of the transparent resin 20 on the cut surface of the unnecessary port 4 is preferably thinner from the viewpoint of making the optical fiber coupler compact. However, if it is too thin, the amount of return loss is reduced, and favorable reflection characteristics are obtained. I can't. Therefore, the thickness of the transparent resin 20 is
Distance a from the cut surface of the above to the end of the transparent resin 20 is 1 to
It is preferable to set it to about 3 mm. The opaque resin 21 is a resin in which the attenuation of light in the wavelength band used by the optical fiber coupler and the light outside the optical fiber coupler are both 30 dB. Preferably, the unnecessary port 4 and the port adjacent thereto are used. 3 is made of a resin having an appropriate elasticity to cover and protect. For example, silicone resin, urethane resin, vinyl chloride resin, chloroprene rubber and the like can be suitably used. The opaque resin may be white or may be colored appropriately, such as black, but if the resin has a large scattering, the return loss will be reduced as described later. It is desirable to use a resin that has low scattering (high absorption) with respect to light in the used wavelength band. The Young's modulus of the opaque resin 21 is preferably about 1 to 3 MPa. The opaque resin 21 is at least transparent resin 20
, And is preferably provided adjacent to the stiffener 15. In this embodiment, the opaque resin 21 is used.
Is provided so as to cover the transparent resin 20 and the unnecessary port 4 and the portion of the port 3 adjacent to the unnecessary port 4 adjacent to the reinforcing device 15. Since it is preferable that the thickness of the opaque resin 21 is thinner in terms of making the optical fiber coupler compact,
It is preferable to form the optical fiber as thin as possible as long as a suitable amount of light attenuation is obtained and the stress applied to the optical fiber (port 3) can be preferably reduced. In such an optical fiber coupler, the optical branching / coupling portion 14 is formed by, for example, a well-known fusion-stretching method, the unnecessary port 4 is cut, and then fixed to the reinforcing device 15. After applying the transparent resin 20 so as to cover the cut surface and curing the resin, an opaque resin 21 is applied so as to cover the transparent resin 20 and cured. In the optical fiber type coupler of this embodiment, since the cut surface of the unnecessary port 4 is covered with the transparent resin 20 and this transparent resin 20 is covered with the opaque resin 21, 4 is diffused in the transparent resin 20 and then scattered and absorbed in the opaque resin 21, so that the amount of light returning to the unnecessary port 4 again becomes sufficiently small, and large reflection occurs. The amount of attenuation is obtained. Further, since the transparent resin 20 is covered with the opaque resin 21, external light passes through the transparent resin 20 and enters the unnecessary port 4, or a foreign substance adheres to the surface of the transparent resin 21, thereby causing the optical fiber coupler to fail. There is no possibility that the return loss is reduced. Even if foreign matter adheres to the surface of the opaque resin 21, since the resin 21 has a low light transmittance, the light emitted from the unnecessary port is not reflected by the foreign matter on the surface and returns to the unnecessary port 4 again. Further, the external force applied to the other port 3 extending on the same side as the unnecessary port 4 is reduced by the opaque resin 21, so that the deformation of the transparent resin 20 can be small, and the cut surface of the unnecessary port 4 can be cut. And the transparent resin 20 are hardly peeled off. Therefore, port 3 on the same side as unnecessary port 4
When an external force is applied to the optical fiber coupler, it is possible to prevent the return loss of the optical fiber coupler from decreasing. Further, in this embodiment, since the opaque resin 21 is provided adjacent to the stiffener 15, external force applied to another port 3 extending on the same side as the unnecessary port 4 can be effectively reduced. . Example 1 An optical fiber coupler shown in FIG. 1 was manufactured. First, using two optical fiber strands, fusion-stretching is performed by a well-known method to form a light-branch-coupling portion.
A 0% broadband coupler was made. After cutting one of the four ports (unnecessary ports) of the coupler, it was fixed to the reinforcing device with an epoxy-based adhesive. Next, a UV-curable acrylic resin having a refractive index of 1.49 was applied to the cut position of the unnecessary port. The thickness of the transparent resin was such that the distance a from the cut surface of the unnecessary port after curing of the transparent resin to the end of the transparent resin was 1 mm. After curing the transparent resin, a white silicone resin was applied so as to completely cover the transparent resin and was cured. In producing this optical fiber coupler, the return loss was measured after cutting the unnecessary port, before applying the transparent resin, after curing the transparent resin, before applying the opaque resin, and after curing the opaque resin. The measurement of the return loss was performed for each of the four optical fiber coupler samples, and the measurement wavelength was 1550 nm. The results are shown in the graph of FIG. (Example 2) In Example 1, the thickness of the transparent resin was changed so that the distance a from the cut surface of the unnecessary port after curing of the transparent resin to the end of the transparent resin was 3 mm. An optical fiber coupler was produced in the same manner. Also, when manufacturing this optical fiber type coupler, the above-mentioned Example 1 was used.
The return loss was measured in the same manner as described above. The results are shown in the graph of FIG. Example 3 An optical fiber coupler was prepared in the same manner as in Example 1 except that a black silicone resin was used instead of the white silicone resin. Also, when manufacturing this optical fiber type coupler, the above-mentioned Example 1 was used.
The return loss was measured in the same manner as described above. The results are shown in the graph of FIG. Example 4 In Example 3, the thickness of the transparent resin was changed so that the distance a from the cut surface of the unnecessary port after curing of the transparent resin to the end of the transparent resin was 3 mm. An optical fiber coupler was produced in the same manner. Also, when manufacturing this optical fiber type coupler, the above-mentioned Example 1 was used.
The return loss was measured in the same manner as described above. The results are shown in the graph of FIG. As shown in these graphs, in the sample of Example 1 in which a white silicone resin was used as the opaque resin and the thickness of the transparent resin was 1 mm, the amount of return loss was reduced by applying the opaque resin. However, this is because the scattering in the white silicone resin is larger than the scattering in the black silicone resin, and the light scattered at the interface between the transparent resin and the opaque resin slightly returns to the original fiber. In Example 2 in which the thickness of the transparent resin was 3 mm, the light was sufficiently diffused in the transparent resin, so that the light scattered at the resin interface and returned to the optical fiber was sufficiently small, and the return loss did not decrease. . On the other hand, in the case of using black silicone (Examples 3 and 4), since the scattering in the black silicone resin is small, even if the thickness of the transparent resin is 1 mm, the light returning to the optical fiber is sufficiently small, and the return loss does not decrease. . When using either white silicone or black silicone, a practically sufficient return loss of 55 dB or more can be obtained, but the use of black silicone with low scattering reduces the thickness of the transparent resin. A good return loss can be obtained in a thinner state, which is more preferable. Also, when another resin with large scattering was applied to the resin surface in a state where only the transparent silicone was applied without applying the opaque silicone, the return loss was reduced to about 40 dB. In the case where the opaque resin was white or black, no decrease in the return loss due to the application of another resin having large scattering was observed. From these results, in the optical fiber type coupler of the above embodiment in which the cut surface of the unnecessary port is covered with the transparent resin and the opaque resin, the surface of the transparent resin is protected by the opaque resin, and all of them have a good quality of 55 dB or more. It was confirmed that the return loss was stably obtained. In this embodiment, both the transparent resin and the opaque resin are formed so as to integrally cover the cut surface of the unnecessary port and a part of the port adjacent thereto. When the and other ports are separated from each other, a transparent resin and an opaque resin may be formed so as to cover only the cut surface of the unnecessary port. As described above, in the optical fiber coupler of the present invention, at least one port is cut, and the cut surface of the port is covered with a transparent resin . It is characterized by being covered with an opaque resin having a Young's modulus of 1 to 3 MPa . Therefore, since the light emitted from the cut surface of the port is diffused in the transparent resin and then scattered and absorbed in the opaque resin, the amount of light returning from the cut surface of the port into the port becomes sufficiently small . A large return loss can be obtained. In addition, since the transparent resin is covered with the opaque resin, the external light enters the cut port through the transparent resin, or the foreign matter adheres to the surface of the transparent resin, and the return loss of the optical fiber coupler is reduced. There is no danger of lowering.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view showing an embodiment of an optical fiber type coupler of the present invention. FIG. 2 is a graph showing a result of measuring a return loss in an example according to the present invention. FIG. 3 is a graph showing a result of measuring a return loss in an example according to the present invention. FIG. 4 is a graph showing a result of measuring a return loss in an example according to the present invention. FIG. 5 is a graph showing the result of measuring the return loss in the example according to the present invention. FIG. 6 is a plan view showing an example of a conventional optical fiber coupler. [Description of Signs] 1, 2, 3 ... ports, 4 ... unnecessary ports, 20 ... transparent resin, 21 ... opaque resin.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Ryozo Yamauchi 1440 Mutsuzaki, Sakura City, Chiba Prefecture Inside Fujikura Sakura Factory (56) References JP-A-7-333461 (JP, A) (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/287 G02B 6/10

Claims (1)

(57) [Claim 1] At least one port of an optical fiber type coupler is cut, and a cut surface of the port and a port adjacent to the port are cut off.
Ports that are in contact with each other are integrally covered with transparent resin.
Ri, and the transparent resin, the optical fiber coupler being characterized in that it is covered with an opaque resin having a Young's modulus 1 to 3 MPa.