JP3101958B2 - Broadband coupler and method of manufacturing the same - 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 optical communication, optical measurement, and the like, and more particularly, to an optical fiber coupler having a substantially uniform branching ratio at a wide wavelength of, for example, 1.31 .mu.m to 1.55 .mu.m by reducing the wavelength dependency. And a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a broadband coupler in which the wavelength dependency of a branching ratio is reduced generally uses distributed coupling and incomplete coupling due to a difference in propagation constant. This broadband coupler is manufactured by fusing and stretching the optical fibers with a propagation constant difference between the two optical fibers. For this purpose, for example, in a method called a pre-drawing method, two identical optical fibers are used, and one optical fiber is previously heated and stretched at an intermediate portion thereof to reduce the diameter, and the portion having the reduced diameter is replaced with another optical fiber. The fiber is fused and drawn. The broadband coupler produced by pre-stretching in this way has a tapered shape in the stretched region of one optical fiber and that of the other optical fiber different from each other. The constants will be slightly different. The number of optical fibers to be used is not limited to two, and may be more. In such a case, at least one optical fiber is pre-drawn and pre-drawn, and the other What is necessary is just to make the taper shape formed by fusion-drawing with the fiber different.

[0003] As a conventional example of a broadband coupler manufactured with a difference in propagation constant, US Pat.
There is. In this patent, in order to provide a difference in propagation constant between optical fibers constituting a broadband coupler, a method of changing the taper shape of the optical fiber as described above, a method of using an optical fiber having a different core diameter, a refractive index distribution, And the like using different optical fibers.

[0004]

However, in the case of providing a propagation constant difference by the pre-drawing method, it is necessary to control the difference in diameter of the optical fiber on the order of several microns. Further, in order to carry out the fusion-stretching, a region whose diameter has been reduced in advance must be brought into close contact with the other optical fiber. Since these controls and operations on the order of microns are subtly different depending on the manufacturing conditions, the manufactured ones have a low yield and are expensive. Furthermore, there is a problem that many manufacturing steps such as a pre-stretching step, a contact step of a pre-stretched region, a fusion step, and a stretching step are required. For example, US
P4, 392, 712 describes an optical fiber coupler (narrow band coupler) used only for a specific wavelength. Since the optical fiber coupler can be manufactured through the adhesion step, the fusion step, and the stretching step, an inexpensive optical fiber coupler can be manufactured with fewer manufacturing steps.

In the case of using optical fibers having different core diameters or optical fibers having different refractive index distributions, the pre-stretching step and the step of closely adhering to the pre-stretched region are not required, and US Pat. Although the optical fiber coupler can be manufactured by the same small number of manufacturing steps as the optical fiber coupler described above, it is expensive because optical fibers having different core diameters and special optical fibers having a refractive index distribution are used.

An object of the present invention is to provide an inexpensive and easy-to-manufacture broadband coupler and a method of manufacturing the same to solve the above-mentioned problems of the prior art.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems in the prior art, the present invention relates to a broadband coupler produced by bringing a plurality of optical fibers into close contact with each other and fusing and stretching the same, and a method for producing the same. The heating width at the time of fusion and / or stretching is reduced as much as possible to shorten the optical coupling length in the optical coupling region.

In the optical fiber coupler manufactured according to this configuration, the wavelength dependence of the degree of coupling is reduced by shortening the optical coupling length in the optical coupling region. Therefore, it is possible to obtain and manufacture a broadband coupler having a small change in the branching ratio over a wide wavelength range without having a propagation constant difference between a plurality of optical fibers unlike the conventional broadband coupler.

In the case of manufacturing a coupler which can be used as a broadband coupler at a wavelength of 1.31 μm to 1.55 μm, the heating width at the time of fusion and / or stretching is set to about 1 mm.
mm or less.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic perspective view of a broadband coupler according to an embodiment of the present invention, wherein 1 is a fiber coating, 2 is a fiber cladding, and 3 is a tapered optical coupling region which is an extension.

This broadband coupler is manufactured in the following steps. Cladding diameter φ125 μm, mode field diameter φ10
A normal single mode fiber of .mu.m is used, two of which are stripped of the fiber coating 1 in between. The exposed fiber clad 2 is closely aligned. The two fiber clads 2 closely aligned are heated and fused in a small area of the optical fiber by one or one burner (not shown). The burner heats the fiber clad while reciprocating in the axial direction of the optical fiber, and this minute range (heating range) refers to the swing width of the burner in the optical fiber axial direction. The fused fiber clad 2 is stretched while being heated in a minute area. The heating and stretching are stopped when the optical coupling region 3 having a desired branching ratio is formed.

The burner for heating the fiber clad 2 was manufactured so that the swing width was about 1 mm or less. As a result, a broadband coupler having substantially the same branching ratio at 1.31 μm and 1.55 μm was obtained.

Next, FIG. 2 shows a heating range (run-out width of a burner).
And (a) shows a heating range of 4 m.
7A is a graph showing a branching ratio of m, and FIG. 7B is a graph showing a branching ratio of a heating range of 1 mm. As shown in FIG.
It can be seen that a broadband coupler that can be used in a wide wavelength band from 1.31 μm to 1.55 μm can be manufactured in which the branching ratios are substantially equal between 1.31 μm and 1.55 μm.

FIG. 3 is a graph showing a difference in the branching ratio between the wavelengths of 1.31 μm and 1.55 μm with respect to the swing width of the burner. As the swing width decreases, the wavelengths of 1.31 μm and 1.55 μm increase.
It can be seen that the branching ratio difference of μm becomes small. From this graph, in order to make the branching ratio at both wavelengths, for example, 50 ± 5%, it is necessary to make the branching ratio difference between both wavelengths within 10%. Therefore, if the swing width of the burner is limited to 1 mm or less. It turns out to be good.

As described above, according to one embodiment of the present invention,
Without using the conventional pre-drawing method, two commercially available optical fibers having the same diameter and the same refractive index are used, and they are brought into close contact with each other to reduce the heating width at the time of fusion and drawing to about 1 mm or less. Only by doing so, a broadband coupler can be easily realized.

In the above embodiment, the heating width (running width of the burner) is set to about 1 mm or less at the time of fusing and stretching, but the present invention is not limited to this. That is, by making the heating width at the time of the fusion step and / or the stretching step as narrow as possible, the manufactured coupler can be used at a substantially wide wavelength of about 1.31 μm to 1.55 μm as in the above embodiment. The present invention is included in the present invention.

In the above-described embodiment, the burner is reciprocated. However, the present invention is not limited to this, as long as the heating width during the fusion step and / or the stretching step can be reduced as much as possible. Good.

Furthermore, in the above embodiment, two optical fibers are used, but it is obvious that the present invention is not limited to this.

[0019]

As described above, since the present invention is not a broadband coupler obtained by providing a propagation constant difference between optical fibers, a special optical fiber having a different core diameter or a different refractive index distribution is used. There is no need, or there is no need to perform a fiber pretreatment step such as pre-drawing. Further, it is not necessary to use a manufacturing jig dedicated to the broadband coupler. Therefore, the broadband coupler can be manufactured easily and with a small number of steps, so that the yield is remarkably improved and the cost is significantly reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view of a broadband coupler according to an embodiment of the present invention.

FIGS. 2A and 2B are graphs showing a relationship between a heating range and a branching ratio for explaining an embodiment of the present invention, wherein FIG. 2A is a graph showing a branching ratio of a heating range of 4 mm, and FIG. It is a graph shown.

FIG. 3 is a graph illustrating a difference between a branching ratio of 1.31 μm and a wavelength of 1.55 μm with respect to a swing width of a burner for explaining an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fiber coating 2 Fiber clad 3 Optical coupling area

Claims (2)

(57) [Claims] 1. A method of manufacturing a broadband coupler in which a tapered optical coupling region is formed by fusing and extending a part of a plurality of optical fibers that are brought into close contact with each other. And, a fusion step of fusing a part of the plurality of optical fibers adhered, and a stretching step of stretching the fused optical fibers until a desired branching ratio is obtained, Fusion process and / or
1mm than the plurality of optical fibers in the axial direction or the stretching step
Method of manufacturing a broadband coupler characterized that you heated by the width of the bottom. 2. A broadband coupler in which a plurality of optical fibers are fused and drawn to form a tapered optical coupling region, wherein the optical coupling region extends in the axial direction of the optical fiber during fusion and / or extension. A broadband coupler characterized by being heated by a width of 1 mm or less .