JPH0618743A - Optical branch coupler - Google Patents

Abstract

PURPOSE:To obtain an optical branch coupler capable of shortening a stretching length, increasing the strength and also having a wide band. CONSTITUTION:Optical fibers 10 and 20 provided with core enlargement parts 30 and 40 are prepared, and the coupler is produced by welding and stretching the core enlargement parts 30 and 40 of the optical fibers 10 and 20 each other. Since the core enlargement parts 30 and 40 of the optical fibers 10 and 20 are welded and stretched, the coupling of both parts is started earlier, so that a stretching distance to the position having a necessary branching ratio is shortened in accordance with the starting of the coupling, and a narrow diameter part can be thickened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical branching / coupling device used for branching / coupling, demultiplexing or multiplexing of light in an optical communication network.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 7A, a fiber fusion splicing type optical branching / coupling device has a cladding 8 of optical fibers 80 and 85 from which two (or many) protective coatings have been removed.
The clads 81 and 86 were manufactured by aligning and grasping the clads 81 and 86, heating and fusing the clads 81 and 86 locally, and then stretching the clad 81 and 86 as shown in FIG.

By this extension, each optical fiber 8
The diameters of the cores 83 and 87, which are the optical waveguide portions of 0 and 85, are gradually reduced, the mode field diameter of the guided light is increased, and the distance between the cores 83 and 87 is shortened.
Bonding occurs between 87. That is, sinusoidal periodic coupling of the guided light is performed. It can be simply expressed as a sine function by a mode coupling equation.

[0004]

However, in the case of a single-mode fiber having a smaller core diameter than the cladding diameter, such as a single-mode fiber, the extension length is set to be long in order to reach the core diameter and the inter-core distance for initiating coupling. It is necessary to increase the length L ₂ of the tapered portion, which causes the connecting portion 84
The diameter D _{2 of the} becomes smaller. This caused the following problems.

Since the length L ₂ of the tapered portion is long and the diameter D ₂ of the connecting portion 84 is small, the strength is weak.

Since the length L ₂ of the tapered portion is long,
The mounting portion also becomes long, and the component size becomes large.

It cannot be said that the reliability against breakage is sufficient.

[0008] In order to bond them, the stretching length must be long, and it takes time to manufacture.

The present invention has been made in view of the above points, and an object of the present invention is to provide an optical branching / coupling device capable of shortening the stretching length and increasing the strength.

[0010]

In order to solve the above problems, the present invention uses a core-expanding fiber as at least one of the two optical fibers to be used, and manufactures these optical fibers by heat fusion fusion drawing. To be done. In the core expanding fiber used here, in order to increase the refractive index of the core as compared with that of the clad, a predetermined portion of the optical fiber is heat-treated at a high temperature to diffuse the dopant (eg, germanium Ge) added to the core to the clad portion. It is obtained by doing.

[0011]

Since the expanded core portion of the optical fiber is fusion-stretched, the coupling is started early and the stretching distance to the required branching ratio is shortened. Further, since the film is stretched for a short time, the thin portion can be made thick.

Also, the length of the tapered portion is shortened (especially 1
If it is 0 mm or less), the wavelength dependence of the branching ratio is reduced and the band can be widened.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. [First Embodiment] FIG. 1 is a diagram showing a method of manufacturing an optical branching / coupling device according to a first embodiment of the present invention. In order to manufacture this optical branching / coupling device, first, as shown in FIG. 3A, two optical fibers 10 and 20 (single mode) of the same structure having the core expanding portions 30 and 40 are aligned and shown. The gripping means does not grip.

In order to provide the core expansion portion 30 (40) in the optical fiber 10 (20), the optical fiber wire may be heated by a gas burner or an electric furnace for a time of 1000 to 1500 ° C. Thereby, the core 13 (23)
The dopant (germanium Ge) added to is diffused into the cladding 11 (21), the high refractive index portion spreads to the cladding 11 (21), and as a result, the optical waveguide portion spreads,
The mode field diameter is expanded, which is equivalent to the state in which the core 13 (23) is expanded. In this way, the mode field diameter can be increased by about 2 to 5 times while maintaining the single mode of the normal single mode optical fiber.

Next, as shown in FIG. 2B, the portions of the expanded core portions 30 and 40 of both optical fibers 10 and 20 are fusion-bonded and stretched, and when the stretching is stopped at a predetermined branching ratio, this light is emitted. The branch coupler is completed.

Here, the mode field diameters of the core expanding portions 30 and 40 are wider than the mode field diameters of the other ordinary cores 13 and 23, and the waveguide light in that portion is further extended by a slight extension. The mode field spreads, and the coupling starts between the cores 13 and 23 adjacent to each other earlier, and the light moves. That is, as compared with the conventional optical branching / coupling device shown in FIG. 7, the extension length required for coupling both optical fibers 10 and 20 can be short.

On the other hand, as in the case of an optical multiplexer / demultiplexer,
When it is necessary to match the 0 and 1 peaks of the branching ratio between the used wavelengths, it is necessary to stretch for a necessary number of beats (stretching-branching period PL), but in the case of the present embodiment, the coupling is performed as described above. Since it rises quickly, it can be finished in a short stretch accordingly.

Therefore, the length L ₁ of the tapered portion of the optical branching coupler shown in FIG. ₁ and the diameter D ₁ of the coupling portion 50, and the length L of the tapered portion of the conventional optical branching coupler shown in FIG. _{When 2} is compared with the diameter D ₂ of the connecting portion 84, L ₁ <L ₂ D ₁ > D ₂ is obtained.

FIG. 2 is a diagram showing the extension length-branching ratio characteristics of the optical branching / coupling device according to the above embodiment. As shown in the figure,
It can be seen that the binding is started earlier in this embodiment.

FIGS. 3A and 3B are comparisons of the mode field diameters of the core expansion portions 30 and 40 of the optical fibers 10 and 20 and the mode field diameter of a normal optical fiber, respectively. It can be seen that although the diameter is different, the light intensity does not change.

[Second Embodiment] By the way, in order to manufacture a conventional optical branching / coupling device, a gas burner is used as a heating source, and a predetermined portion of the aligned and held optical fibers is heat-fused while swinging the gas burner back and forth and left and right. It was stretched. When the optical branching / coupling device is manufactured in this manner, the length (L _{2 in} FIG. 7) of the taper-shaped portion, which is the fusion-spreading portion, becomes long, and its central portion becomes substantially linear. In this case, a branching ratio close to perfect coupling can be obtained as the coupling. However, although complete coupling between optical fibers is a necessary characteristic when it is used as an optical multiplexer / demultiplexer, the ordinary branching characteristic cannot be broadened because the branching ratio changes due to wavelength fluctuation.

For this reason, the inventors of the present application shortened the length of the fused portion as much as possible and stretched it to shorten the coupling portion length and flatten the wavelength characteristic in order to widen the band of the optical branching / coupling device. As a result, it has been found that the length of the tapered portion is short in appearance (L is 10 mm or less) and the taper angle is steep, and various measures have been taken for that purpose.

FIG. 4 is a diagram showing a method of manufacturing an optical branching / coupling device having a short tapered portion. First, as shown in FIG. 3A, two optical fibers 10 and 20 (single mode) having the same structure and having core expansion portions 30 and 40 (see FIG. 1) are aligned and gripped by a gripping means (not shown).

Next, as shown in FIG. 2B, gas burners 60 and 6 are arranged from the right and left sides of the aligned optical fibers 10 and 20, respectively.
5 is brought closer, the tip of the flame is applied, and heat fusion is locally applied.

After fusing, as shown in FIG. 7C, the gas burners 60 and 65 are brought closer to each other and stretched, and stopped at the required branching ratio. However, the length L of the tapered portion
Must be 10 mm or less.

In the above fusion-drawing step, the gas burners 60 and 65, which are the heat sources, are stopped without moving in the left-right direction (the drawing direction of the optical fiber). As a result, the spread of the flame can be reduced, a short and steep taper shape can be obtained, and a short optical coupling portion can be obtained.

Further, at this time, a steeper taper shape can be obtained when the flame diameter is smaller. According to the experiments conducted by the inventor of the present application, it was necessary to set the gas blowing nozzle diameter of the gas burners 60 and 65 to 0.3 mm or less in order to reduce the length of the tapered portion to 10 mm or less. As a means to obtain a small flame diameter equivalent to this, as shown in FIG.
The diameter of the flame of the gas burners 60, 65 to be used may be reduced by installing a throttle pinhole plate 66 having a pinhole 67 in the flames of the gas burners 60, 65. Oxygen was added to the gas used to increase the temperature.

FIG. 6 shows the wavelength-branching ratio characteristic depending on the length L of the tapered portion. As shown in the figure, it can be seen that the shorter the length L of the tapered portion, the flatter the wavelength-branch ratio characteristic becomes, and particularly when L = 10 mm or less, it can be seen that a good broadband is realized. .

That is, if the tapered portion of the fusion splicing portion is shortened (10 mm or less) as in the second embodiment, the band of the optical branching / coupling device can be widened in addition to the effect produced in the first embodiment. That effect will also occur.

Although the embodiment according to the present invention has been described above, the present invention is not limited to this, and the following modifications can be made. The optical branching / coupling device configured in the present invention is not limited to two branches, but may be configured to be multi-branching by using a large number of optical fibers.

The core expansion part may be provided only on one optical fiber to be coupled, or the diameters of the core expansion parts provided on both optical fibers to be coupled may be different. in this case,
Since the propagation constants of the propagating light are different, incomplete coupling occurs and a wider band is possible.

Gas burners 60, 6 used in the second embodiment
Although the number of 5 is two, it may be one, or a large number may be used if necessary.

[0033]

As described in detail above, the optical branching / coupling device according to the present invention has the following excellent effects. Since the expanded core portion of the optical fiber was fusion-stretched, the coupling started quickly, and the stretching distance to the required branching ratio was short,
Therefore, it can be manufactured in a short time and the working efficiency is improved.

Due to the short stretching, the length of the taper-shaped portion of the fusion-stretched portion can be shortened, so that the small diameter portion can be thickened,
Increased mechanical strength. Therefore, reliability against breakage is improved.

Since the stretched length is short, the components can be mounted and configured more compactly than the conventional one.

Shorten the length of the tapered portion (especially 10
mm or less), the wavelength dependence of the branching ratio is reduced and a wider band can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a method of manufacturing an optical branching / coupling device according to a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a drawing length-branching ratio characteristic of the optical branching / coupling device according to the first exemplary embodiment of the present invention.

FIG. 3 is a view showing the core expansion portions 30, 40 of the optical fibers 10, 20.
FIG. 3 is a diagram in which the mode field diameter of (1) and the mode field diameter of a normal optical fiber are compared.

FIG. 4 is a diagram showing a method of manufacturing the optical branching / coupling device according to the second example.

FIG. 5 is a view showing how to use the gas burners 60 and 65.

FIG. 6 is a diagram showing wavelength-branching ratio characteristics according to the length L of the tapered portion.

FIG. 7 is a diagram showing a manufacturing process of a conventional optical branching / coupling device.

[Explanation of symbols]

 10,20 Optical fiber 30,40 Core expansion part 50 Coupling part 60,65 Gas burner

Claims (3)

[Claims] 1. A fiber fusion-spreading type optical branching / coupling unit that aligns two or more optical fibers and locally heat-melts and stretches the periphery thereof to provide a coupling section for splitting / coupling light. In the container, at least one of the optical fibers is an optical fiber having a core portion enlarged by heat treatment at a high temperature, and the core enlarged portion of the optical fiber is fusion-stretched and the portion is used as a coupling portion. Optical branching coupler. 2. The optical branching / coupling device according to claim 1, wherein the length of the portion narrowed into a tapered shape by the heat fusion drawing is 10 mm or less. 3. At least one of which has a core expansion portion 2.
Aligning a book or more optical fibers, and locally heating and fusing the periphery of the expanded core of the optical fiber with a heating source that is fixed or stationary with respect to the drawing direction and is squeezed into a tapered shape. And a step of stretching the portion so that the length of the portion is 10 mm or less.