JPH04100007A - Manufacture of fiber fusion-spliced type optical directional coupler - Google Patents

Abstract

PURPOSE:To easily manufacture the fiber fusion-spliced type optical directional coupler which has an intermediate core layer by connecting the clads of optical fibers, which are increased in refractive index by heating the optical fibers under reduced pressure and vaporizing dopants nearby the clad surface, and drawing the fusion-spliced part. CONSTITUTION:When an optical fibers is heated under the reduced pressure almost up to its fusion point, dopants nearby the clad surface are vaporized to increase the refractive index nearby the clad surface. This optical fiber is only coupled with another optical fiber by a normal fusion splicing and drawing process to easily manufacture the fiber fusion-spliced type optical coupler which has an intermediate core layer.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for manufacturing a fiber fusion type optical directional coupler, and in particular, an intermediate core having a higher refractive index than a cladding portion between two cores. The present invention relates to a method of manufacturing a fiber fusion type optical directional coupler provided with a layer.

[Conventional technology]

Conventionally, one of the methods of branching and combining optical signals in optical fibers is
One example is a fiber fusion type optical directional coupler.

This fiber fusion type optical directional coupler removes the coatings of multiple optical fibers, leaving only the core and cladding, and then attaches these claddings closely parallel to each other at a predetermined distance, and heats the closely attached part to generate both beams. It was formed by fusing fibers together and stretching the fused portion.

By the way, in this type of fiber fusion type optical directional coupler, in order to shorten the coupling length of the fibers, an intermediate core layer having a higher refractive index than the cladding part is provided between the cores of the optical fibers to be fused. There is.

FIG. 5 is a diagram showing a conventional manufacturing method of this type of fiber fusion type optical directional coupler.

First, as shown in FIG. 5A, two optical fibers 80.85 are prepared with their coatings peeled off to expose their claddings 81.86.

Next, as shown in FIG. 8B, both claddings 81 and 86 are side-polished by a predetermined length.

Next, as shown in FIG. 4(c), high refractive index layers 82 and 87 are deposited on each polished side surface.

And as shown in the same figure (d), high refractive index layer 82.87
By welding them together and then stretching them, a fiber fusion type optical directional coupler with the high refractive index layers 82 and 87 as the intermediate core layer is completed.

Next, FIG. 6 is a diagram showing a method of manufacturing a fiber fusion type optical directional coupler having an intermediate core layer having another structure.

As shown in FIG. 9(a), the core 9 in the cladding 92 is
An intermediate core layer 9 consisting of a ring-shaped high refractive index layer around 4
An optical fiber 90 provided with a core 96 and an optical fiber 95 having a normal core 96 and a clad 97 are prepared.

Then, as shown in FIG. 9B, the cladding 92 of the optical fiber 90 and the cladding 97 of the optical fiber 95 are brought into contact at a predetermined distance and fused to be integrated. Then, by stretching this integrally fixed portion, an intermediate core layer 9 is formed between the core 94 and the core 96.
A fiber fusion type optical directional coupler comprising 3 is completed.

[Problem to be solved by the invention]

However, in the manufacturing method of the fiber fused optical directional coupler shown in FIG. 5, the thin cladding 81.86
The step of polishing the side surfaces of the measuring refractive index layer 82.87 is not easy, and it is difficult to align both sides of the measuring refractive index layer 82.87 so that the surfaces of the measuring refractive index layer 82.87 come into good contact when welding the measuring refractive index layer 82.87. Furthermore, there is a problem in that it is not easy to deposit the high refractive index layer 82.87 only on the polished side surface portion of the cladding 81.86.

On the other hand, in the method for manufacturing the fiber fusion type optical directional coupler shown in FIG.
It is necessary to manufacture a special optical fiber 90 having the following characteristics, and there is a problem in that the cost thereof is higher than that of a normal optical fiber.

The present invention has been made in view of the above points, and provides a fiber fusion type optical directional coupler that can easily produce a fiber fusion type optical directional coupler having an intermediate core layer without using an optical fiber with a special structure. An object of the present invention is to provide a method for manufacturing an optical directional coupler.

[Means to solve the problem]

In order to solve the above problems, the method for manufacturing a fiber fusion type optical directional coupler according to the present invention lowers the refractive index of the cladding surrounding the core by doping a predetermined material with a dopant material. a step of heating the optical fiber under reduced pressure to near its melting point to evaporate dopants near the cladding surface to increase the refractive index near the cladding surface; It was constructed by the steps of bringing the claddings of a plurality of optical fibers, including optical fibers with a high refractive index in the vicinity, into contact with each other and fusing the contact portions, and stretching the fused portion.

[Effect]

As described above, according to the present invention, by heating the optical fiber under reduced pressure to near its melting point, the dopant near the cladding surface can be evaporated and the refractive index near the cladding surface can be increased.

For this reason, this optical fiber and another optical fiber (whether the other optical fiber is the above-mentioned optical fiber with a high refractive index on the cladding surface or a normal optical fiber) are bonded together using a normal fusion and drawing process. A fiber fusion type optical directional coupler having an intermediate core layer can be easily manufactured by simply combining the two.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings.

1 to 4 are diagrams for explaining the manufacturing method of the fiber fusion type optical directional coupler according to this embodiment, and FIG. 1(a), FIG. 2(a), and FIG. Figure (a), Figure 4 (a)
) are side sectional views showing the state of the optical fiber in each manufacturing process, Figure 1 (b), Figure 2 (b), Figure 3 (b).
) and FIG. 4(b) are diagrams showing the state of the refractive index n of the optical fiber in each manufacturing process.

First, as shown in FIG. 1, an optical fiber 1 having a normal structure in which a core 2 is surrounded by a cladding 3 is prepared.

In this embodiment, pure quartz (5iOz) is used as the material constituting the core 2, and pure quartz doped with fluorine (5iOa + F) is used as the material constituting the cladding 3.

Here, as shown in FIG. 6(b), when pure quartz is doped with fluorine, its refractive index is lower than that of pure quartz.

Note that as the doping material (dopant), for example, poron (B) may be used in addition to fluorine. In other words, any substance may be used as long as the refractive index of the predetermined material is reduced by doping it with some substance.

Next, this optical fiber 1 is heated to around its melting point under reduced pressure.

As a result, as shown in Figure 2, the fluorine in the peripheral area of the cladding 3 evaporates from its surface, the amount of fluorine doped in the peripheral area decreases, and the refractive index of the peripheral area initially changes. The refractive index of the cladding 3 is higher than that of the cladding 3.

Note that the reason why the heating step is performed under reduced pressure is to promote evaporation of fluorine from the surface of the cladding 3.

Next, two optical fibers 1 with a high refractive index around the cladding 3 are prepared as described above, and these optical fibers 1,
The claddings 3 of 1 are brought into contact with each other at a predetermined distance, and the two are fused together as shown in FIG.

Next, as shown in FIG. 4, a portion with a high refractive index (portion indicated by a dotted line) on the outer periphery of this fused portion is removed by etching.

As a result, an intermediate core layer 4 having a high refractive index can be provided between the two cores 2, 2.

Then, by heating and stretching the fused portion, a fiber fused optical directional coupler is completed.

Although one embodiment of the method for manufacturing a fiber fusion type optical directional coupler according to the present invention has been described in detail above, the present invention is not limited to this, and various modifications such as the following are possible. be.

(2) In the above embodiment, the high refractive index portion on the outer periphery of the 1.1fi optical fiber fused portion was removed by etching, but in some cases, this portion may be left without being etched.

■In the above embodiment, both of the two optical fibers to be fused were heated to increase the refractive index of the outer circumference, but in the present invention, only one of the optical fibers is heated. The refractive index of the outer periphery may be increased by heating the optical fiber, and a normal optical fiber may be fused thereto. In this case as well, the intermediate core layer 4 can be formed between both cores.

■Although the above embodiment shows an example in which two optical fibers are fused together, the method for manufacturing a fiber fusion type optical directional coupler according to the present invention is not limited to this, and three or more optical fibers are fused together. Needless to say, it may also be used for fusion bonding.

〔Effect of the invention〕

As described above in detail, the method for manufacturing a fiber fusion type optical directional coupler according to the present invention has the following excellent effects.

(1) Complicated processes such as polishing the side surfaces of the optical fiber are not required, and the intermediate core layer can be formed simply by heating the optical fiber and then performing the normal fusion drawing process, so this type of fiber fusion type Manufacturing of the optical directional coupler becomes easy.

(2) Since the intermediate core layer can be formed simply by heating the optical fiber without vapor deposition, the conditions for forming the intermediate core layer are simplified and easy.

(3) Furthermore, unlike conventional optical fibers, there is no need to use a special optical fiber having a ring-shaped intermediate core layer inside the cladding, and the manufacturing cost thereof can be reduced.

[Brief explanation of the drawing]

1 to 4 are diagrams for explaining the manufacturing method of a fiber fusion type optical directional coupler according to this embodiment, and FIG. 5 is a fiber fusion type optical directional coupler having an intermediate core layer. FIG. 6 is a diagram showing a method of manufacturing a fiber fusion type optical directional coupler having an intermediate core layer having another structure. In the figure, 1... Optical fiber, 2... Core, 3... Clarad, 4... Intermediate core layer.

Claims (1)

[Claims] An optical fiber is provided in which the cladding surrounding the core is made of a material whose refractive index is lowered by doping a predetermined material with a dopant material, and the optical fiber is heated under reduced pressure near its melting point. heating to evaporate the dopant near the cladding surface to increase the refractive index near the cladding surface, and connecting the claddings of a plurality of optical fibers including an optical fiber having a high refractive index at least near the cladding surface. 1. A method for manufacturing a fiber fusion type optical directional coupler, comprising: a step of contacting the contact portions and fusing the contact portion; and a step of stretching the fused portion.