JPH063554A - Wide-band coupler and its production - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide a broadband coupler that can be easily manufactured at low cost and a manufacturing method thereof. [Structure] A broadband coupler in which two optical fibers are fused and stretched to form a tapered optical coupling region 3,
The optical coupling region 3 is a broadband coupler in which a small width in the axial direction of the optical fiber is heated at the time of fusion and / or drawing to shorten the coupling length of light. The two fiber clads 2 are closely aligned, and a pair of burners are reciprocally moved in the axial direction of the optical fiber with a swing width of about 1 mm or less to heat and fuse the fiber clads 2 and the fused fiber clads 2
Is a method for producing a broadband coupler in which heating and stretching are stopped at the time when the optical coupling region 3 is obtained by stretching the film to obtain a desired branching ratio.

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, etc., and in particular, it has a substantially uniform branching ratio over a wide wavelength range of 1.31 .mu.m to 1.55 .mu.m with reduced wavelength dependence. The present invention relates to a so-called broadband coupler and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, a broadband coupler in which the wavelength dependence of the branching ratio is reduced is generally distributed coupling, which uses incomplete coupling due to a difference in propagation constant. This broadband coupler is manufactured by allowing two optical fibers to have a propagation constant difference, and fusion-drawing the optical fibers. Therefore, for example, in a method called a pre-stretching method, two identical optical fibers are used and one of the optical fibers is heated and stretched at an intermediate portion in advance to have a smaller diameter, and the portion having the smaller diameter is used as another optical fiber. The fiber is fused and stretched. In the thus-prepared wide-band coupler, the taper shape of the drawn region is different between the one optical fiber and the other optical fiber, and the two optical fibers propagate due to the difference in the taper shape. The constants will be slightly different. The number of optical fibers to be used is not limited to two, and may be more than that. In that case, at least one optical fiber is preheated and stretched by preheating and other optical fibers are used. The taper shape formed by fusion-spreading with the fiber may be different.

Further, as a conventional example of a wideband coupler manufactured with a difference in propagation constant, USP 4,798,436.
There is. In this patent, in order to have a propagation constant difference between the optical fibers forming the broadband coupler, a method of making the taper shapes of the optical fibers different as described above, a method of using optical fibers having different core diameters, and a refractive index distribution Methods using different optical fibers are described.

[0004]

However, in the case where the above-mentioned pre-stretching method is used to provide a difference in the propagation constant, it is necessary to control the difference in the diameter of the optical fiber on the order of several microns. In addition, in order to perform fusion drawing, it is necessary to closely adhere a region having a reduced diameter along the other optical fiber. Since these controls and operations on the order of micron are slightly different depending on the manufacturing conditions, the manufactured products have a poor yield and become expensive. Further, it is a problem that many manufacturing steps such as a pre-stretching step, a pre-stretching region adhesion step, a fusion bonding 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. However, this optical fiber coupler only allows a plurality of optical fibers to be closely adhered and fusion-stretched. Since the optical fiber coupler can be manufactured by the adhesion step, the fusion step, and the stretching step, it is possible to manufacture an inexpensive optical fiber coupler with few manufacturing steps.

Further, in the case of using the optical fibers having different core diameters or the case of using the optical fibers having different refractive index distributions, the pre-drawing step and the adhesion step of the pre-drawing region are not required, and therefore USP 4,392,712 is required. Although it can be manufactured by a small number of manufacturing steps similar to the optical fiber coupler described in (1), it becomes 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 a broadband coupler which can be easily manufactured at low cost and a method for manufacturing the same, in order to solve the above-mentioned problems of the prior art.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention provides a broadband coupler manufactured by bringing a plurality of optical fibers into close contact with each other, fusing and stretching, and a manufacturing method thereof. The heating width during fusion and / or stretching is made as narrow as possible to shorten the optical coupling length in the optical coupling region.

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

Further, in the case of producing one that can be used as a broadband coupler at a wavelength of 1.31 μm to 1.55 μm, the heating width during fusion and / or stretching is about 1
It may be set to mm or less.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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, in which 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 μm is used, two of these optical fibers, with the fiber coating 1 in between are removed. The exposed fiber clad 2 is closely aligned. Two fiber clads 2 closely aligned are heated and fused in a minute area of the optical fiber by a pair of burners (not shown). The burner heats the fiber clad while reciprocating in the axial direction of the optical fiber, and this minute range (heating range) means the swing width of the burner in the axial direction of the optical fiber. The fusion-bonded fiber clad 2 is stretched while being heated in a minute range. The heating and stretching are stopped when the optical coupling region 3 having the desired branching ratio is formed.

When the swing width of the burner for heating the fiber clad 2 was set to about 1 mm or less, a wideband coupler having a branching ratio substantially equal at wavelengths of 1.31 μm and 1.55 μm was formed.

Next, FIG. 2 shows the heating range (running width of the burner).
In the experimental example showing the relationship between the branching ratio and the
The graph which shows the branching ratio of m, (b) is a graph which shows the branching ratio of 1 mm of heating ranges. From the same figure (b), heating range 1
It can be seen that, in mm, the branching ratios are substantially equal at wavelengths of 1.31 μm and 1.55 μm, and a broadband coupler that can be used in a wide wavelength band of 1.31 μm to 1.55 μm can be manufactured.

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

As described above, according to one embodiment of the present invention,
Without using the pre-stretching method that has been conventionally used, two commercially available optical fibers having the same diameter and refractive index are used, and these are closely adhered to each other so that the heating width during fusion and stretching is about 1 mm or less. A wide band coupler can be easily realized only by this.

Although the heating width (running width of the burner) is set to about 1 mm or less at the time of fusing and stretching in the above embodiment, the present invention is not limited to this. That is, by making the heating width during the fusion process and / or the stretching process as narrow as possible, the produced coupler can be used in a substantially wide wavelength range of about 1.31 μm to 1.55 μm as in the above embodiment. Those that are included in the present invention are included in the present invention.

Further, although the burner is reciprocally moved in the above embodiment, the present invention is not limited to this, and the heating width in the fusing step and / or the stretching step can be made as narrow as possible. Good.

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

[0019]

As described above, the present invention is not a wideband coupler obtained by providing a difference in propagation constant between optical fibers, so that 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 fiber pretreatment steps such as pre-drawing. Further, there is no need to use a manufacturing jig dedicated to the broadband coupler. Therefore, a wideband coupler can be easily manufactured with a small number of steps, which dramatically improves the yield and contributes to a significant reduction in price.

[Brief description of drawings]

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

2A and 2B are graphs showing a relationship between a heating range and a branching ratio for explaining an embodiment of the present invention, FIG. 2A is a graph showing a branching ratio in a heating range of 4 mm, and FIG. 2B is a branching ratio in a heating range of 1 mm. It is a graph shown.

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

[Explanation of symbols] 1 fiber coating 2 fiber cladding 3 optical coupling region

Claims (7)

[Claims] 1. A method of manufacturing a wideband coupler in which a tapered optical coupling region is formed by fusing and stretching a part of a plurality of closely adhered optical fibers, and a contact step of closely contacting the plurality of optical fibers. And a fusion step of fusing a part of the closely attached optical fibers, and a stretching step of stretching the fused optical fibers until a desired branching ratio is obtained, A method for manufacturing a broadband coupler, wherein a plurality of optical fibers are heated in the axial direction by a minute width in the fusion process and the drawing process. 2. A method of manufacturing a broadband coupler in which a taper-shaped optical coupling region is formed by fusing and stretching a part of a plurality of optical fibers that have been in close contact with each other, and a step of closely contacting the plurality of optical fibers with each other. And a fusing step of fusing by heating only a minute width in the axial direction of the plurality of closely adhered optical fibers, and until the desired branching ratio of the fused plurality of optical fibers is obtained. A method for producing a broadband coupler, comprising a stretching step of stretching. 3. A method of manufacturing a wideband coupler in which a tapered optical coupling region is formed by fusing and stretching a part of a plurality of optical fibers that have been brought into close contact with each other, and a step of bringing the plurality of optical fibers into close contact with each other. A fusing step of heating and fusing a part of the plurality of closely adhered optical fibers, and a desired width while heating a minute width in the axial direction of the plurality of fused optical fibers. A method for producing a broadband coupler, comprising a stretching step of stretching until a branching ratio is obtained. 4. The method of manufacturing a broadband coupler according to claim 1, wherein the minute width is a swing width for reciprocating the heating means in the axial direction of the optical fiber. 5. The method of manufacturing a wideband coupler according to claim 4, wherein the swing width is about 1 mm or less. 6. A broadband coupler in which a plurality of optical fibers are fused and stretched to form a tapered optical coupling region, wherein the optical coupling region is minute in the axial direction of the optical fiber during fusion and / or stretching. A broadband coupler characterized in that its optical coupling length is shortened by being heated by the width. 7. The wideband coupler according to claim 6, wherein the minute width is about 1 mm or less.