JP3066444B2 - Manufacturing method of 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 a method of manufacturing an optical fiber coupler in which a plurality of optical fibers are fused and drawn to each other, and these optical fibers are optically coupled to each other. The present invention relates to a method for manufacturing an optical fiber coupler.

[0002]

2. Description of the Related Art FIG. 6A shows the wavelength dependence of the branching ratio of an optical fiber coupler produced by a conventional fusion drawing method. This is an optical fiber coupler having a relatively narrow bandwidth. In this case, a certain wavelength, in this example, 1.35 μm and the branching ratio is 0, that is, all the light from one optical fiber propagates to the other optical fiber. There are situations where

On the other hand, the wavelength dependence of the branching ratio of a broadband optical fiber coupler is as shown in FIG. 6B, for example. In this case, there is no wavelength at which the minimum branching ratio becomes 0,
The minimum branching ratio is about 40%. This is a broadband optical fiber coupler having the most general performance, and has a branching ratio of about 5 at both 1.3 μm and 1.55 μm.
It is 0%.

[0004] As a method for producing a wide-band optical fiber coupler in which the minimum branching ratio does not become zero, an international publication number WO
The method disclosed in Japanese Patent Application No. 87/00934 makes a difference between the propagation constants of two optical fibers used. However, simply making a difference between the propagation constants of these two optical fibers does not make it possible to produce a desired broadband optical fiber coupler. It is not necessary to simply set the minimum branching ratio of the optical fiber coupler to 0, but in a typical broadband optical fiber coupler as shown in FIG. 6B, the minimum branching ratio needs to be about 40%. It is.
Even if the minimum branching ratio is larger or smaller than 40%, a broadband optical fiber coupler having the desired performance cannot be realized. There is an extremely strong correlation between the difference between the propagation constants of the two optical fibers and the minimum branching ratio, and the difference between the propagation constants of the two optical fibers used must be managed with extremely high precision.

[0005]

In order to obtain the difference in propagation constant from the difference in the core diameter of the optical fiber, in order to control the minimum branching ratio within a range of ± 5% with respect to a desired value, it is necessary to set the core diameter to the desired value. It has been analyzed by the inventor that differences must be controlled within an accuracy of approximately ± 0.01 μm. It is considered very difficult to manage the difference in the diameter of the core of the optical fiber with such high accuracy not only at present but also in the near future.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the necessity of accurately managing the difference in the propagation constant of an optical fiber. Therefore, it is necessary to process the optical fiber so that the difference in core diameter is within an accuracy of ± 0.01 μm. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a broadband optical fiber coupler which can manufacture a wideband optical fiber coupler very easily.

[0007]

According to the present invention, at least two closely spaced optical fibers having different propagation constants are provided.
Is heated by applying the first heating temperature to the middle part,
The first tension is applied for fusing and stretching, and the fused optical fiber is drawn.
Measure the minimum branching ratio of Iva.

If the measured value is less than a predetermined value,
The fused portion is applied at a second heating temperature lower than the first heating temperature.
Heat and apply a second tension to both ends such that the fused part does not stretch.
In addition, the minimum branching ratio is increased. Also, the measured value is the specified value
In the above case, the third heating temperature lower than the first heating temperature
The fusion zone is heated at a temperature of
Apply a third tension that is close to both ends to reduce the minimum branching ratio.
Make it smaller.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an apparatus for manufacturing an optical fiber coupler used in the manufacturing method of the present invention will be described with reference to FIG. This is similar to a conventional optical fiber coupler manufacturing apparatus. 2
The optical fibers 11 and 12 are brought close to each other and both ends are held by clamps 13 and 14. One clamp 14 is fixed, and the other clamp 13 is a stretching clamp, which can be driven by a motor 15 to move in a direction away from the fixed clamp 14 along the longitudinal direction of the optical fibers 11 and 12, That is, the optical fiber 1
A tension can be applied to 1,12.

At an intermediate portion between the clamps 13 and 14,
In a state where the exposed cladding portions of the optical fibers 11 and 12 are in contact with each other, the optical fibers 11 and 12 can be fused by heating by the burners 16 and 17 as heating means. Since the fusion section 26 is performed over a certain range, the burners 16 and 17 are held by the moving stage 18 and can be moved within a certain range along the longitudinal direction of the optical fibers 11 and 12. Thus, the optical fiber 1
Heat the claddings 1 and 12 in contact with each other,
Further, a stress is applied to the optical fibers 11 and 12 by the stretching machine, that is, the clamp 13 and the motor 15 so that the optical fibers 11 and 12 are stretched. 1
1 and 12 are optically coupled to each other.

In order to measure the optical coupling state, light is incident on one end of one optical fiber 11 from a light source 19, the amount of the light emitted from the other end of the optical fiber 11, and the other light on the other end. The amount of light emitted from the fiber 12 is detected by the photodetectors 21 and 22, respectively, and the branch ratio is measured by the branch ratio measuring device 23 from the outputs of the photodetectors 21 and 22. The measurement result is given to the controller 24 and the controller 2
Reference numeral 4 controls the motor 15 and the moving stage 18 so that a desired branching ratio is obtained. The branching ratio indicates, for example, the ratio of the output light amount of the same optical fiber 11 to the incident light amount of the optical fiber 11, that is, the ratio of the detection output of the photodetector 21 in%. That is, as the coupling between the optical fibers 11 and 12 becomes stronger, the branching ratio becomes smaller.

Next, an embodiment according to the present invention will be described with reference to FIG. As shown in FIG. 2A, in this embodiment, first, two optical fibers 11 and 12 having different propagation constants are prepared. The difference between the propagation constants of the optical fibers 11 and 12 may be an appropriate value, that is, an arbitrary value. In general, an optical fiber generally manufactured has a different propagation constant depending on a manufacturer or a production lot. I have. Accordingly, two commercially available optical fibers may be simply taken out and prepared. For example, FIG.
The difference in propagation constant required for a typical broadband optical fiber coupler as shown in FIG. ¹ needs to be about 0.4 cm ⁻¹ , whereas according to the present invention, the difference in propagation constant is There may be a difference of about one digit, that is, about 0.04 cm ^{-1 to} 4.0 cm ^-1 , and in some cases, 0.04 cm ^-1 or less, 4.0 cm ^-1.
The difference between the above propagation constants may be used.

The difference between the propagation constants of the optical fibers 11 and 12 can be obtained by using any two of the commercially available optical fibers as described above. Is stretched, and the difference between the propagation constants is provided between the two optical fibers by using this and the unstretched one. Alternatively, the two optical fibers 11 and 12 are stretched together, but the difference in propagation constant is provided by making the stretching amounts different. Alternatively, the outer diameter of each of the two optical fibers is made different by etching the clad portion, that is, without etching one, only the other is etched, or both are etched. Fibers 11 and 12 are provided with a difference in propagation constant.

Next, as shown in FIG.
In a state where the clad portions in the intermediate portions of the optical fibers ₁ and 12 are brought into contact with each other, the portions are heated by the burners 16 and 17 and a tension F1 is applied to the optical fibers 11 and 12 to fuse the optical fibers 11 and 12 together. Stretch. In this way, the clad portions of the fused portions 26 of the optical fibers 11 and 12 become thinner and the core portions also become thinner, and the two core portions approach each other to optically couple the optical fibers 11 and 12 with each other. In other words, the light that has propagated from one optical fiber 11 branches off and propagates to the other optical fiber 12 at the fusion portion 26.

The optical coupling between the optical fibers 11 and 12 may be arbitrary, that is, the optical fibers 11 and 12 may be merely optically coupled, and the degree of coupling may be arbitrary. Therefore, it may be performed under the same conditions as the fusion stretching performed in the production of the conventional optical fiber coupler. Further, as described above, when the optical fibers 11 and 12 are thinned by, for example, etching the cladding portion thereof, the two optical fibers 11 and 12 are brought into contact with each other and are simply fused to each other without any particular drawing. The optical fibers 11 and 12 are optically coupled.

Next, as shown in FIG. 2C, in the optical fibers 11 and 12 capable of optical coupling shown in FIG. 2B, the coupling state of the optical fibers 11 and 12, that is, the branching ratio is measured and the branching ratio is measured. Is processed so that the optical fiber 11 and 12 are in a predetermined state, that is, the heating temperature is changed or the stretching force is changed to F for the step of optically coupling the fused portion 26. It changes from ₁ to F _2,
Alternatively, by performing both of them, the coupling state of the optical fibers 11 and 12 is changed so that the processing is performed so that the minimum branching ratio in the fusion spliced portion 26 becomes a target value.

Example 1 For example, in FIG. 2B, in order to optically couple the optical fibers 11 and 12, the heating temperature and tension at the time of fusion drawing in the conventional method of manufacturing an optical fiber coupler were applied as they were. When the branching ratio in the combined state was measured,
The state shown in FIG. 3A was obtained. That is, light having a wavelength of 1.55 μm incident on one end of the optical fiber 11 is
1 was about 24% of the incident light from the other end. The minimum branching ratio at this time is about 10%, that is, only about 10% of the light incident on the optical fiber 11 is emitted from the other end of the optical fiber 11, and the remaining 90% is It was in a state of branching to the 12 side. Therefore, in order for the branching ratio to be 50% at the wavelengths of 1.3 μm and 1.55 μm, it is necessary to set the minimum branching ratio to about 40% in the middle of these wavelengths.

Therefore, in the process of FIG. 2C, the heating temperature for the optical fibers 11, 12 is lowered while the stretching stress on the optical fibers 11, 12 in the process of FIG. 2B is kept constant, so that the drawing is not performed. By doing so, the interval between the cores in the fusion portion 26 is increased. That is, as shown in FIG. 2D, the optical fibers 11 and 12 are covered with a jacket 27 on their core wires, and the cladding is exposed on both sides of the fusion spliced portion 26. Wearing part 2
6 is considerably thicker. This optical fiber 1
1 and 12 are clamps 1 with their jackets 27 in contact.
3 and 14, and a tension is applied to the fusion portion 26, but the fusion portion 2 is located at a distance d ₁ between the centers of the cores of the optical fibers 11 and 12 in the clamps 13 and 14.
6, the distance d ₂ between the cores is quite small, and the clamp 1
From the positions 3 and 14, the cores are gradually approaching each other. For this reason, when the stresses F _{1 that} are stretched by the clamps 13 and 14 are applied to the optical fibers 11 and 12, both the slack cores act so as to be stretched, and the cores in the fusion portion 26 have a distance d ₂ between them. There acts force F ₃ to be large.

Therefore, when the optical fibers 11 and 12 are tensioned in this manner in a state where the heating temperature for the fusion portion 26 is lowered and the fusion portion 26 is not so softened, the fusion portion 26 becomes without stretching acts to distance d ₂ of the core is released, the optical coupling is reduced between the two cores, thus splitting ratio increases with this time. Then, the light emitted from the optical fiber 11 is observed, and as shown in FIG. 4A, when the branching ratio at the wavelength of 1.55 μm becomes 56%, heating and application of tension are stopped. At this time, at approximately 1.3 μm and 1.55 μm, the branching ratio is about 50%, that is, the minimum branching ratio is about 40%.
%.

As means for weakening the heating temperature in the second step (FIG. 2B), the gas flow rate to the burners 16 and 17 is restricted, or the burners 16 and 1 are connected from the fusion portion 26.
In the case where heating is performed by increasing the distance of each of the heaters 7 or heating by electric heating, the heating temperature of the fusion bonding portion 26 is reduced by reducing the current to the electric heater. Alternatively, the electric heater is similarly connected to the fusion portion 26.
The heating temperature in the fusion section 26 can be reduced by separating the heating section from the heating section.

Example 2 Optical fibers having different propagation constants were prepared in the same manner as in Example 1, and they were fused and drawn. The branching ratio was measured.
That is, when the second step (FIG. 2B) was completed, the branching ratio became 75% at a wavelength of 1.55 μm as shown in FIG. 3B. That is, in this case, unlike the above-described example 1, the minimum branch ratio is considerably larger than the target value. Therefore, in this case, the branch ratio is reduced in the next third step (FIG. 2C). There is a need.

For this reason, the stretching stress was reduced to about 1/6 compared with the case of the second step (FIG. 2B), and the heating temperature for the fused portion 26 was lowered. As described above, when the stretching stress becomes considerably small, the distance between the clamps 13 and 14 becomes slightly short, and the heating temperature for the fusion portion 26 is also low.
The two cores act more slackly than in the second step, and the two cores approach each other at the fusion portion 26. Therefore, the outgoing light of the other end with respect to the incident light of the optical fiber 11 decreases, that is, the branching ratio increases. When the branching ratio at a wavelength of 1.55 μm drops to about 50% as shown in FIG. 4B,
The heating and the application of the stretching stress were stopped. At this time, the minimum value of the branching ratio was about 40%, and the intended broadband optical fiber coupler was obtained.

Example 3 The optical fibers 11 and 12 are arbitrarily selected and combined,
In the step (FIG. 2B), fusion bonding and stretching were performed and optically coupled in the same manner as in Example 1. At this time, the branch ratio is the same as in the case of Example 1 shown in FIG.
It became as shown in. That is, the minimum branching ratio was about 10%, and the amount of light input to the optical fiber 11 was branched to the optical fiber 12 too much.

In this case, the minimum branching ratio must be increased in the third step (FIG. 2C). For this reason, the heating temperature is set lower than in the second step, and the temperature in that case is lowered. Stretching is also made higher than in the case of Thereby to towards the percentage size of the core of the optical fibers 11 and 12 becomes smaller core distance d ₂ than the ratio becomes smaller at the fused portion 26 is reduced. In other words, the stretching is performed so that the interval between the cores with respect to the diameter of the core is increased.
The branching ratio was measured in this manner, and the heating and stretching were stopped when the branching ratio reached about 48% at the state shown in FIG. 6B, that is, 1.55 μm. At this time, the minimum branching ratio is 46%
It was about.

In any of the above cases, the optical fibers 11 and 12 are fused and optically coupled to each other in the second step, but the third step may be performed continuously. That is, both steps are continuously performed while measuring the branching ratio. In the above description, the control of the stress on the optical fiber, that is, the pulling force, can be performed not only by the motor as described above, but also by a weight, a magnetic force, or the like.

FIG. 5 shows a graph obtained by an experiment corresponding to the control of the branching ratio in Examples 1 and 2. In FIG. 5, the abscissa indicates the so-called aspect ratio of the fused portion 26 to its length. If this aspect ratio is small, the distance between the cores is closer, and the amount of light that branches to the other party is larger,
The branching ratio decreases, and conversely, if the aspect ratio is large, the spacing between the cores is large, the amount of branching to the other party is small, and the branching ratio increases.

The stress applied to the optical fiber in the third step of Example 1 is increased to a certain level, but the heating temperature is lowered so that tension is applied to both optical fibers to such an extent that stretching is not performed so as to increase the distance between the cores. In this case, it can be seen that as the time elapses, the branching ratio increases as shown in the figure, that is, the interval between the cores increases. on the other hand,
By reducing the tension on the optical fiber in the third step of Example 2, a slack occurs between the clamps 13 and 14 corresponding to the tension applied to the optical fiber up to that time, and both optical fiber cores of the fusion portion 26 are formed. Approach with time. In FIG. 5, 1, 2, 3, 4, and 5 are indicated by numbers without a circle, and it can be seen that the branching ratio decreases with time and the interval between the cores increases.

In the above description, two optical fibers are fused to form an optical fiber coupler. However, three or more optical fibers may be similarly fused to form a broadband optical fiber by a similar method.

[0029]

As described above, according to the present invention, it is not necessary to precisely control the difference between the propagation constants of the optical fibers used, that is, it is not necessary to precisely control the core diameter ratio. If an existing optical fiber is used, there is usually a difference in the propagation constant due to variations between them, so using that, the optical fiber is first fused and simply optically coupled, and the branching ratio is measured. It is sufficient to control the fused portion so as to obtain the desired minimum branching ratio in accordance with the above, and a broadband optical fiber coupler can be manufactured very easily as compared with the prior art.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of an optical fiber coupler manufacturing apparatus used in the method of the present invention.

FIG. 2 is a diagram showing steps of a method for manufacturing an optical fiber coupler according to the present invention.

FIG. 3 is a diagram showing the wavelength dependence of the coupling state after each second step in Examples 1 and 2.

FIG. 4 is a diagram showing the wavelength dependence of a state in which the third step is completed in Examples 2 and 3 and a broadband optical fiber coupler is obtained.

FIG. 5 is a view showing experimental results for explaining that the branching ratio can be controlled by the processing in the third step in Examples 1 and 2.

6A is a diagram showing the wavelength dependence of the branching ratio of a conventional narrowband optical fiber coupler, and FIG. 6B is a diagram showing the wavelength dependence of the branching ratio of a wideband optical fiber coupler.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/28-6/293

Claims (1)

(57) [Claims] At least two or more different propagation constants
Apply the first heating temperature to the middle part
To apply heat and apply the first tension to both ends for fusing and stretching.
A step of measuring the extent, the minimum branching ratio of the fused optical fiber
And when the measured value is equal to or less than a predetermined value, the first heating temperature
Heating the fused portion at a second heating temperature lower than
A second tension is applied to both ends to such an extent that the fused portion does not extend.
Increasing the minimum branching ratio, and if the measured value is equal to or greater than a predetermined value, the first heating temperature
Heating the fused portion at a lower third heating temperature,
A third tension that is close to the core interval due to a decrease in temperature
And reducing the minimum branching ratio by adding to the two ends described above .