JPH0210401B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber branch circuit used in optical communications using optical fibers and a method for manufacturing the same.

1A and 2A are cross-sectional views showing the general structure of optical fibers, and FIGS. 1B and 2B show their refractive index distributions, respectively. FIG. 1 shows an optical fiber called a graded type, in which the refractive index within the core 1 changes in the radial direction, and FIG. 2 shows an optical fiber called a step type, in which the refractive index within the core 1 does not change. The core 1 is surrounded by a cladding 2, which is further covered with a glass jacket 3 on the outside. If the core diameter is 2a, the cladding thickness is t, and the outer diameter is d, then d=2(a+t),
There are also optical fibers that do not have a glass jacket 3.

The optical fiber 4 thus constructed is covered with a coating layer 5, as shown in FIG. 3, and the entire optical fiber is called a cored optical fiber. The coating layer 5 consists of a primary coating, usually called a primary coating, and a secondary coating of nylon, polyethylene, etc. on the outside, and is an optical fiber with a cushion layer between the primary coating and the secondary coating. There is also a cord.

In order to form an optical communication network using such optical fibers, an optical fiber branching circuit is essential. Traditionally, fiber optic branch circuits
It was manufactured according to the steps shown in the figure. The glass jacket and cladding are removed by a predetermined length at the ends of the two optical fibers to be joined to expose the core 6. exposed 2
The book cores 6 are aligned parallel to each other and in close contact with each other, as shown in FIG. 4A. When this is heated from the surroundings as symbolized by arrow 7 and at the same time a tensile force is applied as shown by arrow 8, the two cores are fused to each other as shown in Figure 1B, and at the same time they are tapered. is formed. The fused core is cut at a point where its cross section gradually becomes smaller and becomes substantially equal to the cross section of a single core, and the cross section is cut while heating again, as symbolically shown by arrow 9 in FIG. 4C. The core 10 of another optical fiber is fused to the core 10 of another optical fiber.

This method has disadvantages in that it is difficult to bring the cores of two optical fibers into close contact with each other in parallel, and it is also difficult to create a branch circuit that branches one optical fiber into three or more fibers.

Therefore, an object of the present invention is to provide a method for manufacturing an optical fiber branch circuit that makes it possible to easily manufacture an optical fiber branch circuit that branches from one fiber to two or more fibers.

In order to achieve the above object, a method for manufacturing an optical fiber branch circuit according to the present invention involves removing the cladding at one end of a plurality of quartz optical fibers by etching to expose the cores and combining them into one. A process of penetrating the inside of a pipe made of high-purity quartz glass with an inner diameter that allows the quartz optical fiber to pass through, and heating the pipe from the outside while evacuating the inside of the pipe. At the same time, the tips of the optical fibers that have penetrated into the pipe are integrated, and a tensile force is applied to the integrated tips to form a tapered shape, and the molten core formed into a tapered shape by the above steps is cutting the pipe having the tapered molten core at the center at a point where the cross section of the pipe is substantially equal to one optical fiber; The gist of the method is to include a step of fusing one optical fiber.

The present invention will be explained in more detail below using examples with reference to the accompanying drawings, but it is understood that the present invention is not limited thereto and that various modifications and improvements can be made within the framework of the present invention. It is.

FIG. 5 shows, in cross-sectional or perspective view, the steps of a method for manufacturing an optical fiber branch circuit according to the present invention. Figure 5A
As shown in FIG. 2, a predetermined length of the cladding 2 and glass jacket 3 are removed by etching at the ends of the optical fibers to be joined, and the core 1 is exposed. Hydrofluoric acid is usually used as the etching agent. Next, as shown in FIG. 5B, two optical fibers 4 with exposed cores are passed through a pipe 11 made of glass, and heated from the outside of the pipe as shown symbolically at 7. , and simultaneously applies a tensile force in the axial direction as shown by arrow 8. The two cores are fused together and integrated into a tapered shape. At this time, the glass pipe 11 also tapers outside the core (FIG. 5C).
The integrated core is hereinafter referred to as a molten core. The tapered molten core is cut at a point where the diameter is substantially equal to the core diameter of the unprocessed optical fiber, ie, 2a. Then the fourth
Similar to the process shown in FIG.
Figure D).

In the branch part of the optical fiber branch circuit manufactured by the process explained above, the core diameter gradually increases from 2a and is branched into two optical fibers with a core diameter of 2a, so that light is transmitted to the outside. It is possible to create a branch circuit that is less likely to be radiated, that is, has less insertion loss.

At the branch portion of the branch circuit described above, there is a possibility that an air layer remains between the pipe and the molten core.
Since the refractive index of the core is higher than that of air, there is no problem with transmission characteristics, but there is a problem with reliability.

FIGS. 6 and 7 illustrate an embodiment of the method of fabricating an optical fiber circuit according to the present invention in which the air layer is removed. In the embodiment shown in FIG. 6, the pipe 11 and the optical fiber 4 are fixed at one end of the pipe by an airtight sealing part 12 using glass solder or epoxy adhesive, or by heating and melting. be done. As in the previous example, the core 1 is heated from the outside of the pipe 11 as symbolized by the arrow 7, and a tensile force is applied in the direction of the arrow 13, and at the same time a vacuum is drawn. In the embodiment shown in FIG. 7, a vacuum protrusion 14 is provided on the pipe 11.
are provided, sealing portions 12 are provided at both ends of the pipe 11, and a tensile force is applied in the direction of arrow 8 and through the evacuation protrusion 14 in the direction of arrow 15. The vacuum protrusion 14 is removed after processing. By these methods, it is possible to produce a solid tapered branching optical fiber as shown in FIG. 8, which does not contain the air layer described in the previous embodiment. When fabricated using this method, since it does not contain an air layer, it is possible to have an outer diameter of d and a core diameter of 2a, and when the optical fiber comes in contact with air, cruds on the surface of the optical fiber grow. As a result, reduction in mechanical strength and breakage can be prevented, greatly improving reliability.

Although the optical fiber to be processed into a tapered shape has been described above as a fiber in which only the core remains by etching, as shown in FIG. Optical fibers with only layer 5 removed, but with both the cladding and the glass jacket remaining, can be used as well. When such an optical fiber is used, instead of the molten core in the previously described embodiments, what may also be called a fused optical fiber is formed, in which the branching channels are separated to a certain extent, so that the separation is possible. This has the effect of improving isolation.

In addition, although the optical fiber branching circuit for branching into two optical fibers has been described above, a multi-optical fiber branching circuit can also be created by inserting a large number of optical fibers into a pipe. It is possible. For example, to make an optical fiber branch circuit for branching into seven optical fibers, as shown in FIG. All you have to do is perform the following operations.

As is clear from the above description, according to the present invention, since no polishing is used, optical fiber branch circuits can be manufactured at low cost, and since there is no precision work such as axis alignment, mass production is possible and reliability is high. Not only
It has the advantage that a branch circuit to three or more optical fibers can be easily produced.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views and refractive index distribution diagrams of two types of optical fibers, Figure 3 is a cross-sectional view of an optical fiber core, and Figure 4 shows the steps of a conventional optical fiber branch circuit manufacturing method. The perspective view and FIG. 5 are diagrams showing the steps of the optical fiber branch circuit manufacturing method according to the present invention.
A is a cross-sectional view; B, C, and D are perspective views; FIGS. 6 and 7 are perspective views showing methods for fabricating fiber optic branch circuits according to two different embodiments of the present invention; and FIG. FIG. 7 is a cross-sectional view of a fused optical fiber obtained by the method shown in FIG. 9; FIG. The figure is a sectional view showing a part of the process of manufacturing a branch circuit for three or more optical fibers according to the present invention. 1, 6, 10...Core, 2...Clad, 3...
...Glass jacket, 4...Optical fiber, 5...
...Coating layer, 7,9,18...Arrow indicating heating, 8...Arrow indicating applying tensile force,
11...Glass pipe, 12...Sealing part, 13
. . . Arrow indicating applying a tensile force at the same time as evacuation, 14 . . . Protrusion for evacuation, 15 . . . Arrow indicating evacuation.

Claims (1)

[Claims] 1 Remove the cladding at one end of a plurality of quartz optical fibers by etching to expose the core and combine them into a high-purity fiber having an inner diameter that allows the plurality of quartz optical fibers to pass through. A process of penetrating the inside of a pipe made of quartz glass,
A process of evacuating the inside of the pipe and heating it from the outside, simultaneously integrating the pipe and the tip of the optical fiber penetrating into the pipe, and applying a tensile force to the integrated tip to form a tapered shape. and a pipe having a molten core formed in a tapered shape in the center at a place where the cross section of the pipe having a molten core formed in a tapered shape in the center by the above process is substantially equal to one optical fiber. a process of cutting;
A method for producing an optical fiber branch circuit, comprising the step of fusing another optical fiber to the cross section obtained in the above step.