JPH04138404A - Optical fiber coupler and arraying member for optical fiber coupler - Google Patents

Abstract

PURPOSE:To attain imperfect coupling and to lessen the dependency of a branching ratio on wavelengths by integrally heating and fusing members for arraying the optical fibers held in parallel and filling the spacing therebetween, then stretching these members under heating, thereby producing tapered parts and imparting asymmetry to the waveguide structure of the two cores at the time of producing the light coupling part. CONSTITUTION:The protective coatings of two pieces of the optical fibers 1, 2 are partly removed and the fibers are held parallel. The parts where the coatings are removed are pinched by the arraying members 3 made of dielectrics having nearly the same refractive index as the refractive index of the clads and are tentatively fastened to prevent the disengagement of this combination. The arraying members 3 made of the dielectrics and two pieces of the optical fibers 1, 2 are integrally heated and fused to form the fused part and to integrate the arraying members 3 made of the dielectrics and the clads 4, 5 of two pieces of the optical fibers 1, 2. The outside shape of the arraying members 3 made of the dielectrics and the optical fibers taken therein are offcentered. The optical fiber coupler exhibits the imperfect coupling in this way and the dependency of the branching ratio on the wavelengths is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an optical fiber coupler and an alignment member for the optical fiber coupler used in optical fiber communications and the like. In particular, the present invention relates to an optical fiber coupler and an alignment member for the optical fiber coupler that has low loss and reduced wavelength dependence of the branching ratio.

"Prior Art" A conventional low-loss optical fiber coupler is shown in FIG. This is produced by holding two or more optical fibers 101 in parallel, heating and fusing a portion, and further drawing until a predetermined branching ratio is obtained. This conventional example had the disadvantage that the branching ratio was highly wavelength dependent, making it unsuitable for wavelength division multiplexing communications. FIG. 6 shows the wavelength characteristics of the branching ratio of this optical fiber coupler. The horizontal axis shows the wavelength and the vertical axis shows the branching ratio, and it can be seen that if the wavelength is different, there is a difference in the branching ratio. When the wavelength is 1.3μ, the branching ratio is 0.5, and as the wavelength becomes larger, the branching ratio increases, and as the wavelength becomes smaller, the branching ratio becomes smaller.

A second example of a conventional optical fiber coupler is shown in FIG.
This is selected by B, Mortimore.
ronics Letters Vol, 21. No,
17. Wavelength in pp, 742.1985
-Flattened Fused Couplers
It is published under the title. This is two optical fibers 10
One of the two optical fibers is heated and stretched in advance, and the optical fibers, which have slightly different external shapes, are twisted and brought into close contact with each other, heated, and fused and stretched. Thereby, the wavelength dependence of the branching ratio can be reduced.

[Problems to be Solved by the Invention] However, the optical fiber coupler with reduced wavelength dependence requires an extra step of drawing one optical fiber in advance, making the process complicated. Moreover, instability in the process caused variations in product properties.

Furthermore, since it is necessary to twist the optical fibers to each other in order to bring them into close contact with each other during fabrication, unnecessary bending occurs in the optical fibers, causing loss.

[Means for Solving the Problem] In view of the above circumstances, the present invention aligns optical fibers held in parallel when producing an optical coupling part, and integrally heats a member for filling the gap.・By fusing and heating and stretching to create a tapered part, and by making the waveguide structure of the two cores asymmetric, we achieved incomplete coupling.
The present invention provides an optical fiber coupler with reduced wavelength dependence of branching ratio.

"Embodiment" An embodiment of the optical fiber coupler according to the present invention is shown in FIG.

First, two optical fibers 2 are prepared, their protective coatings are partially removed, and they are held in parallel.

Then, the coating removal portion is sandwiched between alignment members 3 made of a dielectric material having almost the same refractive index as the cladding, and temporary fixing is performed to prevent the combination from coming apart.

The dielectric alignment member 3 and the two optical fibers 2 are heated and fused together to form a fused portion. At this time, the dielectric alignment member 3 and the claddings 4 and 5 of the two optical fibers 2 are integrated. The cladding of the optical fiber 2 is designated by reference numeral 45, and the cores are designated by 6 and 7, respectively.

Thereafter, substantially monochromatic light is inputted from one terminal 1a of the optical fiber 2, and the emitted light is monitored from the two terminals 1b and 2b on the opposite side, until the desired branching ratio is obtained. While heating the optical fiber 2, the stage holding the optical fiber 2 is moved to perform stretching.

FIG. 2 shows a cross-sectional view in the alignment step before fusion stretching. The dielectric alignment member 3 has a half-split receiving groove 8 shaped so that there is no gap when the optical fiber 2 is inserted.
- 9 is provided so as to be biased toward the contact surface 11. Therefore, the alignment member 3 and the optical fiber 2 can be integrally fused together.

FIG. 3 is a sectional view showing the state after fusion stretching.

Since the dielectric alignment member 3 uses the same material as the claddings 4 and 5 of the optical fiber 2, the alignment member 3 and the cladding 4
・5 is integrated.

The optical fiber coupler manufactured in this manner can reduce the wavelength dependence of its branching ratio. The reason for this will be explained next.

As shown in FIG. 2, by shifting the center of the outer shape of the dielectric alignment member 3 and the positions of the half-split receiving grooves 8 and 9 for receiving and aligning the two optical fibers 2,
Even in the waist portion 10 after fusion stretching, the claddings 4 and 5 can be made to exist asymmetrically with respect to the cores 6 and 7.

In the waist portion 10, the diameter of the cores 6 and 7 is quite small, and the light energy seeps into the claddings 4 and 5 and is transmitted, so the electromagnetic field of the light also affects the external shape of the claddings 4 and 5. receive. For this reason, core 6 and 7
However, if the claddings 4 and 5 exist asymmetrically, the shapes of the electromagnetic fields of the two cores 6 and 7 are different, and incomplete coupling is realized. Incomplete coupling refers to a state in which the energy of light does not transfer completely when two waveguides that are not exactly the same perform distributed coupling.In this case, by creating an appropriate asymmetry, it is possible to The wavelength dependence of the branching ratio can be reduced. As shown in FIG. 4, it is shown that the branching ratio hardly changes even if the wavelength changes.

"Effects of the Invention" Since the present invention uses an alignment member, the fusion process can be performed easily and in a short time, and since there is no need to twist the optical fiber, an increase in loss can be avoided.

In the present invention, since the outer shape of the dielectric alignment member and the optical fiber taken therein are eccentric, the manufactured optical fiber coupler exhibits incomplete coupling, and the wavelength dependence of the branching ratio is reduced. Further, since the degree of eccentricity is determined by the shape of the dielectric alignment member, the wavelength dependence of the branching ratio can be easily controlled with good reproducibility.

Furthermore, as can be seen by comparing FIG. 4, which shows the relationship between wavelength and branching ratio, and FIG. 6, which shows the conventional relationship between wavelength and branching ratio, the present invention improves the wavelength dependence of the branching ratio. Optical fiber couplers with reduced fiber density can be manufactured with high yield.

Furthermore, in the present invention, since the dielectric alignment member and the optical fiber are integrally fused, the strength of the tapered portion is high. In addition, the alignment member has a groove, and the cross-sectional shape after it is assembled integrally with the optical fiber is approximately circular, so there is less deformation of the optical fiber during fusion, and unnecessary cores are eliminated. There is almost no deformation. Therefore, it is possible to avoid an increase in excessive loss due to conversion of light propagating through the waveguide into a radiation mode.

The present invention has mutually abutting surfaces composed of two members,
In order to hold a plurality of optical fibers by bringing both abutting surfaces into contact with each other, a half-shaped receiving groove in the axial direction for holding the optical fibers in parallel is cut on both abutting surfaces. Since it is provided eccentrically on the contact surface, it is suitable for manufacturing an optical fiber coupler that has less wavelength dependence.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing how to assemble the optical fibers of the optical fiber coupler of the present invention with the alignment member, Fig. 2 is a vertical sectional view of the main part of Fig. FIG. 4 is a characteristic diagram of the wavelength and branching ratio of the present invention, and FIG. FIG. 6 is a perspective view of a conventional optical fiber coupler, FIG. 6 is a characteristic diagram showing the relationship between wavelength and branching ratio of the conventional technology, and FIG. 7 is a perspective view of a conventional optical fiber coupler in a twisted state. ■・2... Optical fiber 3... Alignment member 4, 5... Optical fiber cladding 6, 7... Optical fiber core 8, 9... Half-split receiving groove 11... Applicant on the side: Kyocera Co., Ltd. Agent Yoshiteru Takagi Procedural amendment (indication of own ship 1゜2゜3゜4゜ incident) 1990 Patent application No. 2r2tGS'' Name of invention Optical fiber coupler Relationship with the case of a person who corrects the alignment member of an optical fiber coupler Patent applicant address: 22 people, 5, Kamimachi, Higashino Kitai, Yamashina-ku, Kyoto City
Name (663) Kyocera Co., Ltd. Representative Ito
Kensuke

Claims (3)

[Claims] (1) Consists of two or more optical fibers and an alignment member that aligns them and fills gaps between the fibers, and the alignment member is made of a material that has approximately the same refractive index as the cladding of the optical fiber. Or, an optical fiber made of substantially the same material as the cladding of the optical fiber, in which the optical fiber and the alignment member are integrally heated and fused, and the integrated part is heated and stretched to form a tapered part. An optical fiber coupler, wherein the optical fiber is located at an eccentric position in an integrated fusion part. (2) The alignment member has an axial half-shaped receiving groove that holds the optical fibers in parallel, and in order to minimize the deformation of the optical fibers due to surface tension during fusion, it is in close contact with the optical fibers and The half-shaped receiving groove is formed so that the cross-sectional shape after integrally assembling the fiber is approximately circular, and the half-shaped receiving groove is located at an eccentric position in the fused part where the optical fiber is integrated. 2. The optical fiber coupler according to claim 1, wherein the optical fiber coupler is provided eccentrically on the member. (3) Consists of two members, each having abutting surfaces, and holding optical fibers parallel to both abutting surfaces so that a plurality of optical fibers can be held by abutting both abutting surfaces. 1. An alignment member for an optical fiber coupler, characterized in that a half-shaped receiving groove is carved in the axial direction, and the receiving groove is eccentrically provided on a contact surface.