JP2879266B2 - Broadband optical fiber coupler - 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 branching / combining device used for branching an optical signal in an optical communication system and the like, and more particularly to a broadband optical fiber coupler having a small branching ratio with respect to wavelength. is there.

[0002]

2. Description of the Related Art To perform large-capacity communication in an optical communication system, a wavelength multiplexing communication system has been proposed in which transmission and reception are performed using light of a plurality of wavelengths. By the way, when transmitting light of multiple wavelengths in the same optical fiber transmission line,
The branching ratio of the optical branching / combining device used in the branching or coupling part of the transmission line must not change due to the difference in wavelength. Therefore, for such an optical communication system, a broadband optical fiber coupler with little wavelength dependence has been proposed.

Conventionally, as shown in FIG. 5 (a), this type of broadband optical fiber coupler has an optical fiber 8 which has been previously drawn by heating (pre-drawing) to reduce its diameter.
In many cases, the optical fiber 80 is aligned with the optical fiber 80 which is not heated and stretched, and then, as shown in FIG. 2B, the two are heated and fused at the pre-stretched portion and then stretched again.

In this way, the two optical fibers 80 and 81 are asymmetrically coupled to each other, resulting in incomplete coupling, and a large branching ratio due to a change in wavelength as in a general symmetric fiber coupler. There is no change, the change in the branching ratio becomes flat, and a wider band is realized.

[0005]

However, the above-mentioned conventional broadband optical fiber coupler has the following disadvantages.

Although the flatness of the branching ratio with respect to wavelength increases,
The periodicity cannot be reduced.

In the case of a broadband optical fiber coupler as shown in FIG. 5, it is difficult to produce optical fibers having different diameters under the same conditions, the number of steps is increased, and reproducibility and yield are poor.

When two optical fibers having different outer diameters are brought into contact with each other and fused and drawn, the two optical fibers 80 and 81 are shown in FIG. 5A because the pre-drawn portion of the optical fiber 81 is tapered. When they are brought into contact with each other as described above, a gap is created between them, making the fusion difficult,
The optical fiber 81 on the pre-stretched side is liable to be deformed such as bending due to a heating effect at the time of fusion-stretching, thereby causing deterioration such as excessive loss.

The present invention has been made in view of the above points, and has a lower wavelength dependence of the branching ratio than before, enables stable fusion-stretching, improves reproducibility, yields, and reduces loss. It is an object to provide a type optical fiber coupler.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to fix one side of a heated portion of two optical fibers 2 and 3 simultaneously and extend the other side simultaneously, or By stretching both sides of the heated portions of the optical fibers 2 and 3 at different stretching speeds at the same time, the asymmetric tapered stretching portions 4 and 5 having the same shape are provided in the two optical fibers 2 and 3 and the direction of one optical fiber 3 is changed. Were changed in the opposite direction, and the stretched portions 4 and 5 of both optical fibers 2 and 3 were heat-fused and stretched and joined to form the broadband optical fiber coupler 1.

[0011]

The broadband optical fiber coupler 1 as described above
In the fused portion of the two optical fibers 2 and 3, the cross-sectional diameters of the two optical fibers 2 and 3 are different for each cross-section where the optical fibers 2 and 3 are cut, and the mode field diameter is different. That is, the propagation constant of each part of the fusion part differs. For this reason, this coupling portion becomes an incomplete coupling, the wavelength dependence of the branching ratio is flattened, and a wider band can be achieved.

Further, in the broadband optical fiber coupler 1, a pre-stretching operation is performed in advance, and further stretching is performed after fusion, so that a fused portion having a long tapered region is formed, thereby extending the wavelength cycle of the branching ratio fluctuation. , Flat characteristics with respect to wavelength change. It also contributes to lower loss.

When the above-mentioned broadband optical fiber coupler 1 is manufactured, the pre-stretch amount and the tapered shape of the two optical fibers 2 and 3 can be reproduced with high accuracy, so that reproducibility, reliability and yield can be increased, and productivity can be improved. improves.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, an asymmetric tapered extending portion having the same shape is provided on both optical fibers by simultaneously stretching both two equal optical fibers in advance by a predetermined method.
Change the direction of one optical fiber in the opposite direction and align,
After intersecting at the two extending portions, the intersecting portion is fused and re-stretched to join the optical fiber coupler, thereby broadening the bandwidth of the optical fiber coupler.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an external view showing a broadband optical fiber coupler 1 according to the present invention. 2A and 2B are cross-sectional views of the broadband optical fiber coupler 1. FIG. 2A is a cross-sectional view taken along line A of FIG. 1, FIG. 2B is a cross-sectional view taken along line B of FIG. 1, and FIG. FIG. 1D is a cross-sectional view on line C of FIG. 1, FIG. 1D is a cross-sectional view on line D of FIG. 1, and FIG.

As shown in FIG. 1, this broadband optical fiber coupler 1 has two optical fibers 2 of the same shape.
3 is formed by fusion-spreading. However, since the method of the fusion-stretching has a feature, as shown in FIG. The optical fibers 2 and 3 have different cross-sectional diameters.

FIG. 3 is a view showing a manufacturing process of the broadband optical fiber coupler 1 according to the present invention.

First, as shown in FIG. 1A, two optical fibers 2 and 3 in a state where the protective coating is removed and the clad is exposed are prepared, and these optical fibers 2 and 3 are aligned on a jig. Grasp both ends. Here, these two optical fibers 2 and 3 are the same, and the diameter and material of the core and the clad are the same.

Next, as shown in FIG. 1A, one end (left side in FIG. 1) of both optical fibers 2 and 3 is fixed to a predetermined fixing member 50.

Next, as shown in FIG. 2B, predetermined portions of the two optical fibers 2 and 3 are simultaneously heated and softened by a heating source, and then the other side (the right side in FIG. 2) of the two optical fibers 2 and 3 is moved. At the same time, the same length is stretched and the diameter is reduced (pre-stretching), and stretching portions 4 and 5 are provided respectively. As described above, since the extending portions 4 and 5 are provided at the same time, both the extending portions 4 and 5 have the same shape and can be reproduced with high accuracy. Further, since the stretching portions 4 and 5 are formed by changing the pulling speed of both ends (in the above embodiment, the pulling speed of both ends is changed by fixing one end side), the taper of the stretching portions 4 and 5 is changed. Is different between the left and right sides a and b, and the taper has a left-right asymmetric shape.

Next, as shown in FIG. 3C, the direction (input / output direction) of one optical fiber 3 is changed to the opposite direction (reverse direction).
And the positions of the extending portions 4 and 5 of the two optical fibers 2 and 3 are aligned. If the optical fibers 2 and 3 are aligned in this manner, the extending portions 4 and 5 of the two optical fibers 2 and 3 are asymmetric, so that the opposing portions of the extending portions 4 and 5 have different core and cladding diameters.

Next, as shown in FIG. 2D, the upper and lower positions of the optical fibers 2 and 3 on one side (the right side in the figure) are exchanged around the extending portions 4 and 5, and the extending portions 4 and 5 are exchanged. The part of 5 is set to the intersection state. With such an intersection, there is no gap between the tapered extending portions 4 and 5, and the following fusion is facilitated.

Next, as shown in FIG. 3E, in this state, the stretched portions 4 and 5 are heated by a heating source and fused.
In this state, the optical fibers 2 and 3 are simultaneously redrawn at the same speed from both sides, and the drawing is stopped at the required branching ratio. Thereby, the broadband optical fiber coupler 1 shown in FIG. 1 is completed.

By manufacturing as described above, the cross-sectional diameter of the two optical fibers 2 and 3 differs at each cross-section where the two optical fibers 2 and 3 are fused, as shown in FIG. , The mode field diameters are different. That is, the propagation constant of each part of the fusion part differs. For this reason, this coupling portion becomes an incomplete coupling, the wavelength dependence of the branching ratio is flattened, and a wider band can be achieved.

FIG. 4 is a diagram showing the relationship between the branching ratio and the wavelength of the broadband optical fiber coupler 1 according to the above embodiment and the conventional broadband optical fiber coupler shown in FIG. As shown in the figure, the wavelength characteristic of the broadband optical fiber coupler 1 according to the above embodiment has a lower wavelength dependence of the branching ratio than the wavelength characteristic of the conventional broadband optical fiber coupler shown in FIG.

In the present invention, a pre-stretching operation is performed in advance, and further stretching is performed after the fusion, so that a fused portion having a long tapered region is formed. On the other hand, it has flat characteristics. It also contributes to lower loss.

When the above-mentioned broadband optical fiber coupler 1 is manufactured, since the pre-stretching amount and the crossing amount of the two optical fibers 2 and 3 can be reproduced with high accuracy, the broadband optical fiber coupler 1 having high reproducibility and reliability is provided. it can.

Further, since the two optical fibers 2 and 3 are fused in an intersecting manner, there is no gap between the tapered stretching portions 4 and 5, and the adhesion between the two is improved, so that easy and stable fusion stretching can be performed.

The heating source used in the above embodiment is preferably an acid / hydrogen flame or a similar high-temperature flame with oxygen addition.

In the above embodiment, one side of both optical fibers 2 and 3 is fixed and only the other side is stretched. Instead, both sides of the heated portion of both optical fibers 2 and 3 are made different in stretching speed. It may be stretched. Even in this case, the stretched portion has an asymmetric tapered shape.

[0032]

As described in detail above, the broadband optical fiber coupler according to the present invention has the following excellent effects.

[0033] A broadband optical fiber coupler can be realized in which the wavelength dependence of the branching ratio is lower than that of a conventional broadband optical fiber coupler.

The wavelength cycle of the branching ratio fluctuation is extended, and the characteristic becomes flat with respect to the wavelength change.

Due to its structure, reproducibility can be achieved with a simple manufacturing process.
A highly reliable and low-loss broadband optical fiber coupler can be provided, the yield can be increased, and the cost can be reduced by improving productivity.

[Brief description of the drawings]

FIG. 1 is an external view showing a broadband optical fiber coupler 1 according to one embodiment of the present invention.

FIGS. 2A and 2B are cross-sectional views of the broadband optical fiber coupler 1; FIG. 2A is a cross-sectional view on line A in FIG. 1; FIG. 2B is a cross-sectional view on line B in FIG. 1; 1, (d) is a cross-sectional view along line D in FIG. 1, and (e) is a cross-sectional view along line E in FIG.

FIG. 3 is a view showing a manufacturing process of the broadband optical fiber coupler 1 according to the present invention.

FIG. 4 is a diagram showing the relationship between the branching ratio and the wavelength of the broadband optical fiber coupler 1 and the conventional broadband optical fiber coupler shown in FIG.

FIG. 5 is a diagram illustrating a method of manufacturing a conventional broadband optical fiber coupler.

[Explanation of symbols]

 1 Broadband optical fiber coupler 2, 3 Optical fiber 4, 5 Extension

Claims (1)

(57) [Claims] 1. A heating section of two optical fibers, one side of which is simultaneously fixed and the other side is simultaneously stretched, or
Along the both sides of the portion to be heated of the optical fiber at the same time by extending the stretching speed is different by providing an asymmetric tapered stretching portion of the same shape in both optical fibers,
Change the direction of one optical fiber in the opposite direction and align,
A broadband optical fiber coupler, wherein the stretched portions of both optical fibers are connected by heat fusion and stretched.