JP2818365B2 - Active optical fiber 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 active optical fiber coupler having a function of distributing and amplifying a high power signal light and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the development of the optical industry, an optical coupler having a function of equally distributing optical signals and merging a large number of optical signals has been used for optical fiber communication, optical signal processing, optical measurement, and the like.
It is widely used for optical sensors and the like.

Conventionally, as an optical coupler, an optical fiber type,
Optical waveguide type and the like are being studied. FIG. 8 shows a conventional example of an optical fiber type optical coupler (hereinafter referred to as an optical fiber coupler).

FIG. 8A shows a normal optical fiber (single mode optical fiber or multimode optical fiber).
FIG. 3 is an external view of a two-input two-output optical fiber coupler 14 configured using 15-1 and 15-2.

The optical fiber coupler 14 has a signal light (optical power Ps) Ls applied to an input end of one optical fiber 15-1.
Are incident, the output side optical fibers 15-3, 15-
4, a signal light (optical power Ps /
2-α, where α indicates excess loss) L ₀₁ and L ₀₂ are output.

The optical fiber coupler 14 bundles two optical fibers comprising a core and a clad in parallel, and heats the central portion of the optical fiber and stretches it in the longitudinal direction while heating the outer periphery thereof. From the center of the fusion-stretched portion to the tapered shape.

However, in this configuration, each distributed signal light is accompanied by a 3 dB branch loss and an excess loss α (absorption and scattering loss).

FIG. 8B is an external view of another conventional optical fiber coupler, which is proposed as an optical fiber coupler for compensating for the branch loss and excess loss α of the optical fiber coupler shown in FIG. 8A. It is a thing. That is, an optical fiber coupler 16 is formed by using an optical fiber doped with a rare earth element, and the same ordinary optical fiber as the optical fiber coupler 14 shown in FIG. An optical fiber coupler 14 using an optical fiber to which a rare earth element is not added is connected. That is, one optical fiber 15-1 of the optical fiber coupler 14
Signal light Ls is incident on the input end of the
-2, the pump light Le is incident on the input end of the -2, and the signal light Ls and the pump light Le are equally distributed and propagate in the rare-earth-doped optical fibers 17-1 and 17-2. The amplified signal lights L ₀₁ and L ₀₂ are obtained from the output ends of the added optical fibers 17-3 and 17-4. The degree of amplification in this case depends on the concentration of the rare earth element added in the optical fiber coupler 16 using the rare earth element-doped optical fiber,
It depends on the length of the optical fiber coupler, the optical power of the pump light Le, and the like.

Referring to FIG. 1B, the signal light Ls is directly applied to the input side optical fibers 17-1 and 17-2 of the optical fiber coupler 16 using the rare earth doped optical fiber.
The reason why the signal light Ls and the pump light Le are incident via the optical fiber coupler 14 using a normal optical fiber without inputting the pump light Le and the pump light Le is as follows.

When the signal light Ls is directly incident on the input side optical fiber 17-1 of the optical fiber coupler 16, the pumping light Le does not propagate to this portion, so that the signal light Ls passes through the fusion extending portion 16a. Immediately before the excitation light Le is mixed, the rare earth element causes significant attenuation. That is, useless attenuation of the signal light Ls is caused. When the pumping light Le is directly incident on the input end of the optical fiber 17-2, the signal light Ls does not propagate in the region up to the fusion-stretched portion 16a. Energy is not converted to light Ls. That is, useless attenuation of the excitation light Le is caused.

In order to prevent the signal light Ls and the pumping light Le from being wasted, and to increase the energy conversion efficiency of the pumping light Le into the signal light Ls, an optical fiber coupler 16 using a rare earth element-doped optical fiber is used. Before, the optical fiber coupler 14 using a normal optical fiber is connected, the signal light Ls and the pump light Le are appropriately mixed, and then input to the optical fiber coupler 16, so that the attenuation is reduced and the energy conversion is performed. Efficiency is improved.

[0012]

However, the conventional optical fiber coupler has the following problems.

(1) In the optical fiber coupler shown in FIG. 8A, each of the distributed signal lights has a branch loss of 3 dB and an excess loss α. Therefore, it is difficult to increase the values of N and M when realizing distribution of N inputs and N outputs or N inputs and M outputs (N and M are integers).

(2) In the optical fiber coupler shown in FIG. 8B, the entire length of the optical fiber coupler becomes longer and the overall size becomes larger. In addition, since the signal light Ls and the pump light Le are attenuated due to the excess loss α in the optical fiber coupler 14 in the preceding stage, the amplified signal lights L ₀₁ and L _{02 are} amplified.
Does not have a very large value. Further, since an extra optical fiber coupler is provided, it is difficult to reduce the cost. Also, the bandwidth characteristic of the optical fiber coupler is 2
Since the two optical fiber couplers 14 and 16 are connected in a cascade, the width becomes smaller by that amount. The most serious problem is that the linearity of the input / output characteristics of the optical fiber coupler is poor, so that when a high-power signal light enters the optical fiber 15-1, the amplification characteristics are saturated, and the optical fiber 17-3 , 1
That is, the signal lights L ₀₁ and L ₀₂ extracted from 7-4 are also saturated.

The causes are as follows: 1) The power of the pump light Le is attenuated and the optical fiber 17-1
That sufficient optical power is not supplied to the optical fibers 17-1 to 17-4, that the efficiency of confining the pump light Le in the optical fibers 17-1 to 17-4 is low, and that 3) the optical fibers 17-1 to 17-17. -4 cannot increase the amount of the rare earth element added to the core (this is because
If a large amount of rare earth element is added, the rare earth element may be contained in a granular form, or may be contained in close proximity to each other.
This is to cause concentration quenching and reduce gain efficiency. ) Etc.

SUMMARY OF THE INVENTION An object of the present invention is to provide an active optical fiber coupler which can solve the above-mentioned problems, and which can realize high-power signal light distribution at a small size and at low cost, and a method of manufacturing the same.

[0017]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for manufacturing a semiconductor device, comprising the steps of: providing a central portion of at least two optical fibers arranged in parallel; In an active type optical fiber coupler that is tapered toward both ends, an optical fiber in which a rare earth element is not added in the core is used from the input side of the optical fiber to the fusion-extended portion, and light is transmitted from the fusion-extended portion. On the output side of the fiber, an optical fiber having a plurality of cores in the cladding and adding a rare earth element in each core is used.

In the optical fiber coupler of the present invention, a part of the optical fiber to which the rare earth element is added may be included in the fusion-stretched portion.

In the optical fiber coupler of the present invention, the relative refractive index difference of the optical fiber doped with the rare earth element may be different from the relative refractive index difference of the optical fiber doped with the rare earth element.

In the optical fiber coupler of the present invention, the signal light may enter one optical fiber on the input side and the excitation light may enter the other optical fiber.

The optical fiber coupler of the present invention uses Er, Nd, Yb, Pr, Tm, Sm, Ce, H as a rare earth element.
A material containing at least one of o and Eu may be used.

In the optical fiber coupler of the present invention, at least one of the at least two optical fibers arranged in parallel may have different structural parameters.

In the optical fiber coupler of the present invention, at least one of the at least two optical fibers arranged in parallel may have a different amount of rare earth element in the core.

According to the present invention, an end face of an optical fiber in which a rare earth element is not added in a core and an end face of an optical fiber having a plurality of cores in a clad and in which each core is doped with a rare earth element are provided. Prepare at least two fusion spliced parts, align the position of each fusion spliced part and arrange them in parallel,
The optical fiber that does not contain a rare earth element is stretched while being fused near the position of the fusion spliced portion of the optical fibers arranged in parallel, and is formed into a tapered shape that spreads from the center toward both ends. It is a processed fiber.

[0025]

According to the above construction, the pump light propagating in the optical fiber having a plurality of cores in the clad and having each core doped with a rare-earth element emits light power into the core as it propagates. Since the confinement is increased, the energy is efficiently converted, and as a result, the signal light that has been amplified with high power is equally distributed to the output terminals. Moreover, the size of the entire optical fiber coupler is reduced by half, and the size can be reduced, as compared with a conventional optical fiber coupler in which a normal optical fiber coupler and an optical fiber coupler doped with a rare earth element are connected. Further, since there is no unnecessary propagation loss, the optical power of the distributed signal light can be increased.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a schematic view showing an embodiment of an active type optical fiber coupler according to the present invention, and shows a two-input two-output optical fiber coupler.

This optical fiber coupler 1 is composed of ordinary optical fibers 4-1 and 4- in which a core is not doped with a rare earth element.
2 and an optical fiber having a plurality of cores in a cladding and having each core doped with a rare earth element (hereinafter, this optical fiber is referred to as a rare earth element-doped multi-core fiber) 5 -1, 5-2.

The tapered fiber portions 4 and 5 are
-1, 4-2 and the optical fibers 5-1 and 5-2 are fusion-bonded and have a fusion-stretched portion 2 formed by stretching in the longitudinal direction. A stretch taper portion 3 is formed by the fusion-stretched portion 2 and the tapered portions of both tapered fiber portions 4 and 5.

Optical fibers 4-1 and 4-2 having no core added to the core are connected to the input side of the extension taper section 3, and the rare-earth element-added multi-core fiber 5-2 is connected to the output side of the extension taper section 3. 1, 5-2 are connected.

With this configuration, the signal light Ls incident on the optical fibers 4-1 and 4-2, respectively, is
The pumping light Le propagates in the cores of the optical fibers 4-1 and 4-2, respectively, and propagates through the input side of the extension taper section 3 and the inside of the fusion extension section 2, thereby being divided into two equal parts. Rare earth element-doped multi-core fiber 5 at the output side
-1, 5-2 and propagate each.

The excitation light Le is absorbed by the rare-earth element, thereby raising the energy level, forming a population inversion state, and amplifying the signal light Ls.

Here, the pumping light Le propagating in the tapered fiber portion 5 using the rare-earth element-doped multi-core fibers 5-1 and 5-2 becomes more confined to the optical power in the core as it propagates. The signal light L ₀₁ , L _{02, which} is efficiently converted in energy and amplified as a result, is output from the output ends of the rare earth element-doped multi-core fibers 5-1 and 5-2, respectively.

This configuration is characterized in that the pump light Le and the signal light Ls propagating in the tapered fiber portion 5 are hardly reflected on the input side. This is because even if the reflected light attempts to travel inside the elongated taper portion 3, the total reflection angle increases, so that the light enters the radiation mode and is emitted to the outside,
This is because it is almost attenuated. The reason for using the tapered fiber portion 5 using the rare earth element-doped multi-core fibers 5-1 and 5-2 on the output side of the drawing taper portion 3 is that the rare earth element-doped multi-core fibers 5-1 and 5-
2 of the specific refractive index difference delta _1, is so as to achieve a high gain characteristic is set larger than the relative refractive index difference delta ₂ of the normal optical fiber 4-1 and 4-2 without added rare earth elements That's why.

If the relative refractive index difference Δ ₁ and the relative refractive index difference Δ ₂ are different, the reflection at the connection point of two types of optical fibers having the relative refractive index difference Δ ₁ and the relative refractive index difference Δ ₂ is obtained. Always occurs. However, if the connection point is included in the elongated tapered portion 3, the reflected light is attenuated for the above-described reason.
Conversely, if the above-mentioned connection point is not in the stretched tapered portion 3, for example, on the output end side of the unstretched portion, the reflected light generated therefrom returns to the input side with almost no attenuation. This causes a problem of destabilizing a light source (not shown) such as a semiconductor laser provided on the input side.

In the configuration of the present embodiment, the size can be reduced to half since there is no need to use an optical fiber coupler using a normal optical fiber as in the conventional example shown in FIG. . Further, since there is no unnecessary propagation loss (propagation loss in the optical fiber coupler), the optical power Ps of the distributed signal light Ls can be increased. Optical fibers 4-1 and 4
-2, 5-1 and 5-2 can be made of quartz-based, phosphate-based or fluoride-based glass, and Ge, P, Al, B, F, Ti, Zn, N
It is sufficient that at least one kind of additive for controlling the refractive index, such as b, Ta, Na, K, Li, or Zr, is contained. The rare earth elements added to the cores of the rare earth element-doped multi-core fibers 5-1 and 5-2 include Er, Nd, Yb, Pr, and T.
m, Sm, Ce, Ho, Eu, and the like can be used. Since various rare earth elements can be used in this way, active optical fiber couplers in various wavelength bands can be realized. For example, if Nd or Pr is used, the 1.3 μm band is
The common amplification in the 1.5 μm band can be realized by using the element, and the 1.3 μm band and the 1.5 μm band can be realized by using both elements.

Since the amount of the rare earth element to be added depends on the degree of amplification of the signal light, it is preferable that the amount of the rare earth element be as large as possible without increasing the concentration quenching. The rare-earth-element-doped multi-core fibers 5-1 and 5-2 used in the optical fiber coupler 1 of the present embodiment have a structure including, for example, 21 cores 21 to which a rare-earth element is added in a clad 22 as shown in FIG. Have. However, the number of cores is not limited to this. As described above, in order to increase the amplification degree, the relative refractive index difference delta ₁ between the core 21 and the cladding 22 is selected from the range of about 0.5% to 5%. By the way, ordinary optical fibers 4-1 and 4-2 to which no rare earth element is added.
The relative refractive index difference delta ₂ between the optical fiber is about 0.2% to 0.4
% Range. Thus, the ratio difference in refractive index delta ₁ and the relative refractive index difference delta ₂ it can be seen that the range is different.

Further, the rare-earth element-doped multi-core fibers 5-1 and 5-2 in the present embodiment are not limited to the multi-core fibers as shown in FIG. For example, the number of cores is two or more, and the core diameter is about 0.1μ.
m to several μm, and the core shape may be circular, elliptical, polygonal, or the like. Further, a structure in which a low refractive index layer is provided on the outer periphery of the core group or between the cores may be used.

FIG. 3 is a schematic diagram showing another embodiment of the active type optical fiber coupler of the present invention.

The optical fiber coupler of this embodiment is also of a two-input two-output type. As in the embodiment shown in FIG. 1, the input side of the extension taper section 3 is constituted by optical fibers 4-1 and 4-2 in which the core is not doped with a rare earth element.
Output side of the multi-core fiber 5-
1, 5-2 are connected. However, the difference from the optical fiber coupler shown in FIG. 1 is that most of the fusion-spread portion 2a has an optical fiber in which a core is not doped with a rare earth element.
1, 4-2 are included, but a part thereof also includes the rare-earth element-doped multi-core fibers 5-1 and 5-2.

As described above, when the fused and drawn portion 2a includes the rare-earth element-added multi-core fibers 5-1 and 5-2, the signal light in the fused and drawn portion 2a involves some loss.
It is a very small value, because it connecting point of the two optical fibers are drawn while being heated during the fusing draw even with a relative refractive index difference delta ₁ and the relative refractive index difference delta ₂ from,
Rare earth element-doped multi-core fiber 5 near the connection point
Since the relative refractive index difference delta ₁ of 1,5-2 decreases by heating, approaches the relative refractive index difference delta _2, it is possible to reduce the amount of light reflected here. In addition, since there is a connection point in a region where the diameter of each optical fiber is small, it is easy to couple two types of optical fibers.

FIG. 4 is a diagram showing a method of manufacturing an active optical fiber coupler according to the present invention. The description will be made in the case of a two-input two-output optical fiber coupler.

First, as shown in FIG. 3A, a so-called ordinary optical fiber 6 in which a rare earth element is not added in a core, and a rare earth element-doped multi-core fiber 7 in which a rare earth element is added in a core. (Here, the number of cores is set to four for convenience) is prepared, and the end faces of the two optical fibers 6 and 7 described above are opposed to each other and butted.

Then, as shown in FIG. 4B, the portions where the end faces of the optical fibers 6 and 7 are joined to each other are fusion-spliced by an arc fusion device 18 utilizing arc discharge. And an optical fiber in which the rare-earth element-doped multi-core fiber 7 is integrated.

Next, as shown in FIG. 3C, two integrated optical fibers of the ordinary optical fiber 6-1 (6-2) and the rare earth element-doped multi-core fiber 7-1 (7-2) are used. Arrange in parallel contact. Then, a heating source (in this case, a burner that emits a flame 9 is used, but an arc fusion device or the like may be used instead) outside the two optical fiber bundles arranged side by side. The heating source 8 is disposed at a position away from the fusion splicing surface 19 by a distance L toward the normal optical fibers 6-1 and 6-2. The value of this distance L is several mm to several tens m.
m. When the value of the distance L is large,
The optical fiber coupler 1 shown in FIG. 1 can be made,
Conversely, when the value of the distance L is small, the optical fiber coupler shown in FIG. 2 can be manufactured.

Next, a flame is generated in the burner of the heating source 8,
While heating and melting the optical fiber bundle, the optical fiber bundle is moved in the direction of the arrows P ₁ and P ₂ (or only in the direction of the arrow P ₁ or the arrow P ₂
Direction only).

As shown in FIG. 5D, the active optical fiber coupler 1 is obtained by processing the optical fiber bundle into a tapered shape from the center to both ends.

FIG. 5 is a schematic diagram showing still another embodiment of the active type optical fiber coupler of the present invention.

This is an example of a three-input / three-output type optical fiber coupler, in which ordinary cores 4-1, 4-2, and 4-3 in which a core is not doped with a rare earth element, and cores in which a rare earth element is added. Doped rare earth doped multi-core fiber 5-
After fusion-splicing each of the optical fibers 1, 5-2 and 5-3 by the method shown in FIG. 4, three optical fibers are bundled, and the central portion thereof is fused and stretched while being heated by a heating source. It is formed.

The signal light Ls is made incident on two input optical fibers (for example, optical fibers 4-1 and 4-2), and the pump light L
e is incident on any one of the remaining input optical fibers, for example, the optical fiber 4-3. As a result, the amplified signal lights L ₀₁ , L ₀₂ , and L ₀₃ are output to the output optical fibers 5-1, 5-2, and 5-3, respectively. With such a configuration, it is possible to output equally distributed signal light,
Optical fiber 4-1 and optical fiber 5-1, optical fiber 4-
2 and the optical fiber 5-2, and the structural parameters of the optical fiber 4-3 and the optical fiber 5-3 (for example, core diameter, cladding diameter,
If the relative refractive index difference between the core and the clad is made different, it becomes asymmetric, the wavelength dependency is reduced, and a wide-band optical fiber coupler can be realized.

Also, the optical fibers 5-1, 5-2, 5-3
The degree of amplification is different by changing the amount of the rare earth element added in the cores of the optical fibers 5-1 and 5-2.
The signal lights L ₀₁ , L _{01 having} different optical powers from the output terminal 5-3
₀₂ and _L03 can be output. That is, the distribution ratio can be controlled by the amount of the rare earth element added.
This is suitable when used as an optical tap circuit for an optical tap type system.

FIG. 6 is a schematic diagram showing a modification of the active type optical fiber coupler shown in FIG.

As in the case of the optical fiber coupler shown in FIG.
An optical fiber in which the core is not doped with a rare earth element
1, 4-2, 4-3 and the optical fibers 5-1, 5-2, 5-3 having the core doped with a rare earth element are fusion-spliced, and then three optical fibers are bundled. It is formed by fusing and stretching while heating the vicinity of the center by a heating source. The difference from the optical fiber coupler shown in FIG. 5 is that most of the fusion-spread portion 2c is formed of optical fibers 4-1, 4-2, and 4-3 in which the core is not doped with a rare earth element. A part thereof includes the rare earth element-doped multi-core fibers 5-1, 5-2, and 5-3.
The reason is the same as in the case of the optical fiber coupler shown in FIG.

FIG. 7 is a view showing still another modification of the active type optical fiber coupler of the present invention.

This is a two-input, four-output type optical fiber coupler. At both output ends of the optical fiber coupler 1 shown in FIG. 1, an optical fiber 5-3 doped with a rare earth element in a core is provided.
Optical fiber coupler 20-
1 and 20-2.

The signal light L is applied to the input end of the input optical fiber 4-1.
s is made incident, and the excitation light Le is made incident on the input end of the input optical fiber 4-2. The signal light Ls and the pumping light Le are distributed by the active type optical fiber coupler 1, respectively, and the pumping light Le is efficiently converted into energy by the signal light Ls, and the output ends of the optical fibers 5-1 and 5-2 are amplified. The obtained signal light and the remaining pump light are obtained. After the optical fibers 5-1 and 5-2, an optical fiber coupler 20- using a multi-core or single-core rare earth element-doped optical fiber 5-3 to 5-10 is used.
1 and 20-2 are connected, the signal light Ls is further distributed and amplified by these optical fiber couplers 20-1 and 20-2, and output optical fibers 5-7 to 5-10 are connected to the output optical fibers 5-7 to 5-10. Each further amplified signal light is output.

Therefore, if the combination of the optical fiber couplers shown in FIG. 7 is further increased, a two-input N-output (N ≧ 4) optical fiber coupler can be realized.

[0058]

In summary, according to the present invention, the following excellent effects are exhibited.

Excitation light propagating in an optical fiber having a plurality of cores in the cladding and doped with a rare earth element in each core has a stronger optical power confinement in the core as it propagates. The energy is efficiently converted, and as a result, the signal light that has been amplified with high power is equally distributed to the output terminals. In addition, since it is not necessary to use a normal optical fiber coupler, the size of the entire optical fiber coupler is reduced to half, and the size and cost can be reduced. Further, since there is no unnecessary propagation loss, the optical power of the distributed signal light can be increased.

[Brief description of the drawings]

FIG. 1 is a schematic view of one embodiment of an active optical fiber coupler of the present invention.

FIG. 2 is a structural diagram of an optical fiber used in the active type optical fiber coupler shown in FIG.

FIG. 3 is a schematic diagram showing another embodiment of the active type optical fiber coupler of the present invention.

FIG. 4 is a diagram illustrating a method for manufacturing an active optical fiber coupler of the present invention.

FIG. 5 is a diagram showing a schematic diagram of still another embodiment of the active optical fiber coupler of the present invention.

FIG. 6 is a schematic diagram showing a modification of the active optical fiber coupler shown in FIG.

FIG. 7 is a view showing still another modification of the active optical fiber coupler of the present invention.

FIG. 8 (a) is a sectional view of a structure 2 using a normal optical fiber.
FIG. 2 is an external view of an optical fiber coupler having two inputs and two outputs.
(B) is an external view of another conventional example of an optical fiber coupler.

[Explanation of symbols]

2 Fused and stretched parts 4-1 and 4-2 (No rare earth element added in core) Optical fiber 5-1 and 5-2 (Multiple cores in clad and rare earth in each core) Optical fiber doped with elements

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-123323 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 6/28 G02F 1/135 H01S 3 / 07

Claims (8)

(57) [Claims] 1. An active type optical fiber coupler in which a central portion of at least two optical fibers arranged in parallel is fused to each other, extended in a longitudinal direction, and expanded in a tapered shape from the central portion toward both ends. In the above, an optical fiber in which a rare earth element is not added is used in the core from the input side of the optical fiber to the fusion-spread section, and a plurality of cores are provided in the clad from the fusion-split section to the output side of the optical fiber. An active type optical fiber coupler, wherein each core has an optical fiber doped with a rare earth element. 2. The active type optical fiber coupler according to claim 1, wherein the optical fiber doped with the rare earth element is partially included in the fusion-spliced portion. 3. The optical fiber according to claim 1, wherein the relative refractive index difference of the optical fiber doped with the rare earth element is different from the relative refractive index difference of the optical fiber doped with the rare earth element. The active optical fiber coupler according to claim 2. 4. The apparatus according to claim 1, wherein the signal light enters one of the optical fibers on the input side and the pump light enters the other optical fiber. An active type optical fiber coupler according to any one of the preceding claims. 5. The method according to claim 1, wherein the rare earth element is Er, Nd, Y.
4. The active optical fiber coupler according to claim 1, wherein at least one of b, Pr, Tm, Sm, Ce, Ho, and Eu is used. 6. The optical fiber according to claim 1, wherein at least one of the at least two optical fibers arranged in parallel has a different structural parameter.
The active-type optical fiber coupler according to any one of the preceding claims. 7. The device according to claim 1, wherein at least one of the at least two optical fibers arranged in parallel has a different amount of rare earth element added in the core.
The active type optical fiber coupler according to any one of claims 1 to 3. 8. An end face of an optical fiber in which a rare earth element is not added in a core, and a plurality of cores in a clad,
In addition, at least two fusion-spliced optical fiber end faces to which the rare earth elements are added in each core are prepared, and the positions of the fusion spliced portions are aligned and arranged in parallel contact with each other. The optical fiber that does not contain rare earth elements is stretched while being fused near the position of the fusion spliced part of the placed optical fiber, and processed into a tapered shape that spreads from the center to both ends A method for manufacturing an active type optical fiber coupler, characterized in that: