JP2866487B2 - Optical fiber coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coupler used for an optical fiber communication system, an optical fiber sensor, an optical measurement, and the like. More specifically, the present invention can be used in a wide wavelength band and is inexpensive. To an optical fiber coupler which can be manufactured with high reproducibility.

[0002]

2. Description of the Related Art A conventional low-loss optical fiber coupler is shown in FIG.
Shown in This holds multiple optical fibers 101 in parallel,
It is produced by heat-sealing a part thereof and further stretching it until a predetermined branching ratio is obtained. This conventional example has a drawback that it is not suitable for wavelength division multiplexing communication or the like because the branching ratio has a large wavelength dependence. FIG. 6 shows the wavelength characteristics of the branching ratio of this optical fiber coupler. The wavelength is shown on the horizontal axis and the branching ratio is shown on the vertical axis, and it can be seen that there is a difference in the branching ratio when the wavelength is different. With a wavelength of 1.3 μm and a branching ratio of 0.5,
As the wavelength increases, the branching ratio increases, and as the wavelength decreases, the branching ratio decreases.

FIG. 7 shows a second example of a conventional optical fiber coupler.
Shown in This is by DBMortimore by Electronics L
Wavelength-Flatt in etters Vol.21, No.17, pp742,1985
Published as enedFused Couplers. In this method, one of the two optical fibers 102 is heated and drawn in advance, and optical fibers having slightly different outer diameters are twisted and brought into close contact with each other, and then heated and fused and drawn. Thereby, the wavelength dependence of the branching ratio can be reduced.

In addition, as disclosed in Japanese Patent Application Laid-Open No. 2-236507, there is a type in which optical fibers having different outer diameters are fused and drawn to realize incomplete coupling,
As disclosed in Japanese Patent Application Laid-Open No. 2-167506, there has been developed a type in which optical fibers having different refractive indices of a core are fused and drawn to realize incomplete coupling.

[0005]

However, an optical fiber coupler with reduced wavelength dependency requires an extra step of extending one optical fiber in advance,
Not only is the process complicated, but the instability in the process has caused variations in product characteristics. In addition, since the optical fibers need to be twisted in order to make the optical fibers adhere to each other at the time of fabrication, unnecessary bending of the optical fibers occurs, causing loss. Further, in the case of using a different optical fiber, the matching of the optical fiber coupler with the transmission optical fiber, which is an advantage of the optical fiber coupler, is lost, so that reflection and loss at the connection portion cannot be avoided.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, according to the present invention, when fabricating a light coupling portion, a coating of an intermediate portion of a plurality of optical fibers is removed, and the optical fiber is made of a material having a different refractive index. After aligning the optical fiber with each of the two alignment members, and heat-fusing the optical fiber and the alignment member integrally,
The integrated portion was heated and stretched to form a joint.

[0007]

When the refractive indices of the two alignment members are different from each other, the coupling at the fusion-stretched portion becomes incomplete and the wavelength dependence of the branching ratio can be reduced. Thus, an optical fiber coupler that can be used in a wide wavelength band can be manufactured with good reproducibility. In addition, since the same optical fiber as the transmission optical fiber can be used as the optical fiber itself, its matching is not lost.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to FIGS. FIG. 1 shows an embodiment of the optical fiber coupler according to the present invention. First, two optical fibers 1 and 2 are prepared, and a coating on an intermediate portion thereof is partially removed. On the other hand, the alignment members 3 and 4 having substantially the same refractive index as the clad and having slightly different refractive indices are provided with half-shaped receiving grooves 8 and 9 having such a shape that there is no gap when the optical fibers 1 and 2 are sandwiched. The optical fibers 1, which are engraved on the contact surfaces 13, 14 and whose coating is removed on the receiving grooves 8, 9,
2 are sandwiched, and fixed so that the combination does not come off. Next, the alignment members 3 and 4 and the two optical fibers 1 and 2 are brought into contact with the contact surfaces 13 and 14 of the alignment members 3 and 4 and heated and fused together to form a fused portion. create.
At this time, the alignment members 3 and 4 and the claddings 11 and 12 of the two optical fibers 1 and 2 are integrated. Here, the cladding of the optical fibers 1 and 2 is indicated by reference numerals 11 and 12, and the core is 2
These are indicated by 1 and 22, respectively. Then, the optical fiber 1,
From one of the two terminals, substantially monochromatic light is made incident, the emitted light is monitored from the two terminals on the opposite side, and the alignment member 3 is heated while heating the fused portion until a desired branching ratio is obtained. Stretching is performed every four. The alignment members 3 and 4 have slightly different refractive indexes. For example, if the claddings 11 and 21 of the optical fibers 1 and 2 are made of quartz, one of the alignment members is made of quartz, and the other is made of Ge. Doping with a slightly higher refractive index is used.

FIG. 2 shows a cross-sectional view in an alignment step before fusion stretching. The alignment members 3 and 4 are provided with half-shaped receiving grooves 8 and 9 having a shape such that there is no gap between the optical fibers 1 and 2 when the optical fibers 1 and 2 are sandwiched therebetween. In this example, assuming that the outer diameter of the optical fiber is 125 μm, the receiving grooves 8 and 9 are U-shaped grooves 8 and 9 having a width of 125 μm and a depth of 125 μm.
To form The optical fibers 1 and 2 are mounted in the grooves 8 and 9 and the contact surfaces 13 and 14 are aligned and heated in parallel with the contact surfaces 13 and 14 so that the alignment members 3 and 4 and the optical fibers 1 and
2 can be fused together.

FIG. 3 is a cross-sectional view showing a state after fusion stretching. The alignment members 3 and 4 are claddings 11 of the optical fibers 1 and 2,
12 and optical fibers 1 and 2 near the joint.
Since the refractive indices of the alignment members 3 and 4 surrounding each other are different, asymmetry occurs in the distribution of electromagnetic waves, and imperfect coupling becomes possible. If the fusion stretching conditions are determined uniformly, the wavelength dependence of the branching ratio is determined with good reproducibility only by the refractive index of the alignment member.

FIG. 4 shows an example of the wavelength dependence of the branching ratio of the optical fiber coupler manufactured as described above. The horizontal axis shows the wavelength and the vertical axis shows the branching ratio, and it can be seen that there is not much difference in the branching ratio even if the wavelength is different. In this example, the branching ratio was 0.5 and 1.3 μm and 1.55 μm, respectively.
It is.

[0012]

According to the present invention, as described above, since the alignment member is used, the fusing step can be performed easily and in a short time.
The present invention eliminates the need to twist the optical fiber, thereby avoiding increased losses. In the present invention, the wavelength dependency of the branching ratio is determined with good reproducibility by appropriately selecting the refractive index of the alignment member, and the wavelength dependency can be controlled very easily.

Further, in the present invention, since the alignment member and the optical fiber are fused together, the strength of the tapered portion is high. Further, in the present invention, the receiving groove is provided in the alignment member, and since the cross-sectional shape after assembling integrally with the optical fiber is substantially circular, the deformation of the optical fiber during fusion drawing is small. Almost no unnecessary core deformation. For this reason, an increase in excess loss due to conversion of light propagating through the core to a radiation mode can be avoided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing how an optical fiber of an optical fiber coupler of the present invention is assembled with an alignment member.

FIG. 2 is a cross-sectional view of a main part of FIG.

FIG. 3 shows an optical fiber integrally heated and fused with an alignment member;
It is a longitudinal cross-sectional view of the principal part in the state where the integrated part was heat-stretched.

FIG. 4 is a characteristic diagram of a wavelength and a branching ratio according to the present invention.

FIG. 5 is a perspective view of a conventional optical fiber coupler.

FIG. 6 is a characteristic diagram showing a relationship between a wavelength and a branching ratio of a conventional optical fiber coupler.

FIG. 7 is a perspective view of a conventional twisted optical fiber coupler.

[Explanation of symbols]

 1, 2, optical fiber 3, 4, alignment member

Claims (1)

(57) [Claims] 1. An optical fiber comprising: a plurality of optical fibers; and an alignment member for closely aligning the optical fibers, wherein the closely aligned optical fibers and the alignment member are integrally heat-sealed, and the integrated heat-sealed portion is formed. In an optical fiber coupler formed by heating and stretching to form a coupling portion, the alignment member is composed of two members: an alignment member that covers at least one of the plurality of optical fibers, and an alignment member that covers the other optical fiber. Become
An optical fiber coupler, wherein both alignment members have different refractive indices.