JPH06317723A - Device for light distribution - Google Patents

Abstract

PURPOSE:To provide a device for light distribution capable of distributing the signal light with a low deviation in distribution and at a high gain while lessening the generation of reflected light. CONSTITUTION:An optical fiber 8 of a high specific refractive index difference DELTA1 added with Er is connected to the output side of an optical fiber 7 having a high specific refractive index difference DELTA1. A 1Xn waveguide type star coupler 12 of the high specific refractive index difference DELTA1 is connected to the output side of the optical fiber 8. Optical fibers 9 of the high specific refractive index difference DELTA1 is connected to the respective output sides of the 1Xn waveguide type star coupler 12. The signal light 4 and exciting light 5 are propagated from the input side of the optical fiber 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical distribution device for evenly distributing (n ≧ 2) n signals while amplifying an optical signal.

[0002]

2. Description of the Related Art Recently, with the advent of optical fiber amplifiers,
The feasibility of opticalizing video distribution services has increased. To achieve this, an optical star coupler is required in addition to the optical fiber amplifier. FIG. 13 shows a conventional example of the above optical fiber device. This is composed of 19 single mode fibers 1-1 to 1-19, a waveguide type 19 × 19 star coupler 2 and Er-doped optical fibers 3-1 to 3-19. Single mode fiber 1-1 to 1-18
To the single-mode fiber 1-19, and pumping light having a wavelength of 0.98 μm is input to the single-mode fibers 1 to 19 to propagate through the respective single-mode fibers. Input to each input terminal. Then, by propagating in the waveguide type 19 × 19 star coupler 2, the respective signal light and pumping light are mixed, and the Er-doped light connected to the respective output ends of the waveguide type 19 × 19 star coupler. It is input into the fibers 3-1 to 3-19. The signal light and the pumping light propagate through the respective Er-doped optical fibers 3-1 to 3-19, whereby the signal light is amplified. As a result, the distribution loss in the waveguide type 19 × 19 star coupler,
Excess loss, loss in single-mode fiber and Er-doped optical fiber can be compensated by amplification phenomenon (Herman M. Presby and C. Ra.
ndy Giles, “Amplified Inte
grated Star Couplers with
Zero Loss ”, IEEE Photonic
s Technology Letters, Vol.
3, No. 8, August 1991, pp. 724
~ 726).

[0003]

The conventional light distribution device has the following problems. (1) In the waveguide type 19 × 19 star coupler, an optical distribution deviation inevitably occurs when an optical signal is distributed. Normal,
This light distribution deviation becomes larger as the number of input and output ports increases, and is a deviation in the range of about ± 0.2 db to ± 2 db. This deviation is amplified and expanded in each _Er- doped optical fiber to be in the range of ± 2 db to ± 10 db. (2) 19 single mode fibers are waveguide type 19
They must be respectively connected to the input terminals of the × 19 star coupler, and the deviation of the connection loss cannot be ignored, not to mention the increase of the connection loss at these connection portions. It is also difficult to reduce costs. (3) In order to increase the gain of the _Er- doped optical fiber, the relative refractive index difference Δ ₁ between the core and the cladding is usually set to a high value of 1% to several%, but the single mode fiber The waveguide type 19 × 19 star coupler has a relative refractive index difference Δ ₂
And Δ ₃ is 0. Set to a few percent. This is because normally there is a match between Δ ₂ and Δ _3, and it is difficult to match because Δ ₁ is a particularly high value. Therefore, a mismatch in relative refractive index difference occurs between the waveguide type 19 × 19 star coupler and the Er-doped optical fiber, and reflection loss from this portion occurs. Further, since there is a large difference between the core diameter of the Er-doped optical fiber and the core shape of the waveguide type 19 × 19 star coupler, the connection loss due to this is large. As described above, a loss compensation type optical distribution device with a low distribution deviation and a small amount of reflected light has not yet been realized.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the drawbacks of the prior art, and provides an optical distribution device capable of distributing a signal light with a low distribution deviation, a small amount of reflected light, and a high gain. it is the purpose of the first invention, connects the optical fiber B having a high specific refractive index difference delta ₁ with the addition of rare earth elements on the output side of the optical fiber a having a high relative refractive index difference delta ₁ without the addition of rare earth elements Then, a 1 × n waveguide type star coupler C is connected to the output side of the optical fiber B, and an optical fiber D to which a rare earth element is not added is connected to each output side of the 1 × n waveguide type star coupler C. With Star Coupler C
Also, the relative refractive index difference between the optical fiber D and the optical fiber A and the optical fiber B is set to the same high relative refractive index difference Δ _1, and the signal light and the excitation light are propagated from the input side of the optical fiber A. According to this configuration, all the optical components to be connected, the optical fiber A, the optical fiber B, the star coupler C, and the optical fiber D are configured so that the relative refractive index differences have the same value Δ _1. No reflected light is generated at the connection point. Therefore, the signal light and the pumping light can be efficiently propagated, and an optical transmission system that performs amplification with high gain can be realized. Also, after amplifying the signal light in advance, 1
Since the signal light is divided into n by the × n waveguide type star coupler C, the distribution deviation can be suppressed small. Furthermore, in an optical transmission system that performs amplification with high gain, the generation of a slight amount of reflected light causes instability of the light source of the signal light and the excitation light (oscillation wavelength variation, emission output variation, etc.), but with the configuration of the present invention, There is no such fear. Further, since the optical components have the same relative refractive index difference, designing and manufacturing are facilitated, and cost reduction can be achieved. Further, conventionally, an optical isolator having a high isolation characteristic had to be inserted so that the reflected light from the optical component connecting portion did not return to the input side, which was very expensive, but in the present invention, Since it is not necessary to use an optical isolator having such high isolation characteristics, cost reduction can be expected by this amount. 2nd invention is 1xn in 1st invention.
The value of the relative refractive index difference between the waveguide type star coupler C and the optical fiber D connected to its output side is much lower than Δ _1.
The optical distribution is set to ₂ and the output side of the optical fiber B having a high relative refractive index difference Δ ₁ to which a rare earth element is added is adapted to expand the core by thermal diffusion and reduce the value of the relative refractive index difference to Δ _2. Device. With this configuration, the effect of preventing reflected light as in the first invention is not remarkable. However, since reflected light is not generated between the optical fiber A on which the rare earth element is not added and the optical fiber B on which the rare earth element is added on the input side, it is difficult to induce instability of the light source. Is the same as. The fact that the relative refractive index difference of the input side optical fiber A is high has an advantage that the coupling efficiency with the signal light and the pump light semiconductor laser can be increased. Reason for the value of the relative refractive index difference of the optical fiber D of the output side is low as delta ₂ is, delta ₂ is a value which is used for general purposes, from the viewpoint of improving compatibility with other optical components Is. A third invention is the same as the first invention, wherein the optical fiber B having a high relative refractive index difference Δ ₁ to which the rare earth element is added has only one core in the clad, but instead, the rare earth element is contained in the clad. It is a device for light distribution using a so-called rare earth element-doped multi-core fiber having a high relative refractive index difference Δ ₁ having a plurality of doped cores. That is, the optical distribution device is usually aimed at cost reduction by increasing the distribution number n as much as possible, but for that purpose, the rare earth element-doped optical fiber must be capable of high power amplification. Therefore, in the third aspect of the invention, so-called rare earth element-added multi-core fiber having a plurality of cores to which rare earth elements are added is provided in the clad to realize high power amplification. A fourth invention is the same as the second invention,
Optical fiber B with high relative refractive index difference Δ ₁ containing rare earth element
Instead of using, a rare-earth element-doped multi-core fiber with a high relative refractive index difference Δ ₁ is used, and the output side of the rare-earth element-doped multi-core fiber is expanded by thermal diffusion and the value of the relative refractive index difference is set to Δ ₂ . This is intended to reduce the reflected light at the connection portion with the 1 × n waveguide type star coupler C.

[0005]

【Example】

(Embodiment 1) FIG. 1 shows a first embodiment of the light distribution device of the present invention. This shows a device configuration example for amplifying the signal light 4 indicated by an arrow and then distributing the signal light 7. In this configuration, the relative refractive index difference of the Er-doped single mode fiber 8 is set to a high value Δ ₁ , and the other optical components, the single mode fiber 7, the waveguide type 1 × 7 star coupler 12, the single mode fiber 9-1. The relative refractive index difference of ~ 9-7 is also set to Δ ₁ . This eliminates the reflected light from each connection. Signal light 4 from the input side of single mode fiber 7
Is entered. In addition, the pumping light source 1 is also transmitted via the optical demultiplexer 11.
The pumping light 5 from 0 is also coupled into the single mode fiber 7 and transmitted together with the signal light 4 into the Er-doped single mode fiber 8. For example, the wavelength of the excitation light 5 is 0.9
When 8 μm or 1.48 μm is used, electrons are excited to a high level, and the signal light incident in this state is amplified by stimulated emission, and is converted into seven amplified signal lights by the waveguide type 1 × 7 star coupler 12. It is distributed and transmitted to the respective single mode fibers 9-1 to 9-7. The distribution deviation amount of the amplified signal light outputs 6-1 to 6-7 depends on the distribution deviation amount of the waveguide type 1 × 7 star coupler 12. That is, unlike the conventional case, the distribution deviation amount is not further amplified and increased. The waveguide type 1 × 7 star coupler 12 is not limited to this, and the distribution number n may be a value of 2 or more. For example, the value may be 100 or more, and the number of distributions can be increased by connecting a plurality of waveguide type 1 × n star couplers in a cascade. A fiber type star coupler may be used instead of the waveguide type star coupler 12. (Embodiment 2) FIG. 2 shows a second embodiment of the light distributing device of the present invention. This is a waveguide type 1 × 7 star coupler 14 and single mode fibers 15-1 to 15-1.
The relative refractive index difference of 5-7 is set to a value Δ ₂ much lower than Δ ₁ , and the Er-doped single mode fiber 8 and the waveguide type 1 ×
In order to suppress the reflected light at the connection portion with the 7-star coupler 14, the output side of the Er-doped single mode fiber 8 is devised to expand the core and reduce the value of the relative refractive index difference to Δ ₂ by thermal diffusion. Has been done. (It will be referred to as a mode field diameter control region 13.) Δ ₂ is, for example,
For values of Δ ₁ of 1 to several percent, 0. A value of several% is set. The reason why the relative refractive index difference between the single mode fibers 15-1 to 15-7 is set to a low value Δ ₂ is that Δ ₂ is a value that is generally used, and the single mode fiber 15-1
This is because the compatibility with optical components (for example, optical demultiplexer, optical coupler, etc.) connected after ˜15 to 7 is taken into consideration. (Embodiment 3) FIG. 3 shows a third embodiment of the light distribution device of the present invention. This is instead of the Er-doped single mode fiber 8 of FIG. 1, the difference high relative refractive index delta ₁
This is the case of using the Er-doped multi-core fiber 17 of. This Er-doped multi-core fiber 17 is shown in FIGS.
As shown in FIG. 1, by using a plurality of cores to which Er is added in the clad, a high gain and a high power amplification are realized. Er-doped multi-core fiber 1
The input side of 7 is provided with a tapered portion 16 so that the signal light and the pumping light are uniformly excited in the respective cores. (Embodiment 4) FIG. 4 shows a fourth embodiment of the light distribution device of the present invention. This configuration is a waveguide type 1x
7 Star coupler 14 and single mode fiber 15-1
The relative refractive index difference between ˜15 and 7 is Δ _2, and the mode field diameter control region 13 is provided on the output side of the Er-doped multicore fiber 17. 5 to 11, 18 is a clad, 19 is a core to which a rare earth element is added, 20 is a group diameter of a plurality of cores, 21 is an intermediate layer, 2
Reference numeral 2 is a first cladding, and 23 is a buffer layer. That is, FIG. 5 shows a case where 21 cores are included in the clad 18, and the group diameter of the 21 cores is preferably selected to be substantially equal to the core diameter of the single mode fiber 7. FIG. 6 shows a case where nine cores are included in the clad. In FIG. 7, a large-diameter core 19-1 is arranged at the center of the clad 18, and small-diameter cores 19-2 to 19-19 are arranged around it.
-13 is arranged. FIG. 8 shows a case where the cores 19-1 to 19-13 are integrated. Figure 9
Is a structure in which the outer periphery of each core is covered with the intermediate layer 21. Here, the refractive index of the intermediate layer 21 is selected to be lower than the refractive index of the core. FIG. 10 shows the first clad 2 inside the clad 18 (which becomes the second clad in this case).
21 cores are arranged in 2 and the first clad 22
Is covered with the buffer layer 23. The refractive index of this buffer layer 23 is also selected to be lower than that of the core. Figure 11
Shows an example of the arrangement of cores within the core group diameter 20, and shows an example in the case where the number of cores is 7 to 361. (Embodiment 5) FIG. 12 shows a fifth embodiment of the light distribution device of the present invention.
FIG. This is between the single mode fiber 7 and the Er-doped single mode fiber 8,
The optical isolators 24-1, 24 are provided between the Er-doped single mode fiber 8 and the waveguide type 1 × 7 star coupler 12.
This is an example in which the H.-2 is inserted. The insertion of this optical isolator has the effect of sufficiently suppressing the reflected light and eliminating the instability of the pump light and signal light sources. However, the isolation characteristics of the optical isolators 24-1 and 242 do not have to be those having the conventional high isolation characteristics. The present invention is not limited to the above embodiment. First, as the rare earth element, in addition to Er, Nd, Pr, Yb, Sm,
A material containing at least one rare earth element such as Tm, Ho and Ce can be used. Further, the optical fiber may be a multimode fiber other than the single mode fiber. Further, an optical filter (not shown) for separating the excitation light may be inserted after the Er-doped single mode fiber 8 (or the multi-core fiber 17).
Further, the Er-doped single mode fiber (or multi-core fiber) may be connected in a cascade.

[0006]

Since the optical distribution device of the present invention is a system that amplifies the signal light and then distributes it, the distribution deviation can be suppressed to a small value. Further, the generation of reflected light is small and the signal light can be distributed with high gain. Particularly, according to the first aspect of the present invention, by making all the relative refractive index differences of the respective optical components equal, it is possible to eliminate the generation of reflected light from the connection point, and to propagate the signal light and the excitation light efficiently. Therefore, it is possible to realize an optical transmission system that performs high-gain amplification. Further, since all the optical components have the same relative refractive index difference, designing and manufacturing are facilitated, and a significant cost reduction is possible. Further, since the reflected light is extremely small, it is possible to realize a stable light distribution device simply by inserting an inexpensive optical isolator. In the second invention, by reducing the relative refractive index difference of the optical fiber on the output side, it is possible to improve the compatibility with the optical component to be connected later.
In addition, since the relative refractive index difference between the input side optical fiber and the rare earth element-doped optical fiber connected to it is the same high relative refractive index difference, no reflected light is generated and the light source becomes unstable. Is similar to the first invention in that it is difficult to attract. Further, in particular, according to the third and fourth aspects of the invention, by using a rare earth element-doped multi-core fiber instead of the rare earth element-doped optical fiber, it is possible to realize high power amplification and multi-distribution with high gain.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of a light distribution device of the present invention.

FIG. 2 is a configuration diagram of a second embodiment of a light distribution device of the present invention.

FIG. 3 is a configuration diagram of a third embodiment of a light distribution device of the present invention.

FIG. 4 is a configuration diagram of a fourth embodiment of a light distribution device of the present invention.

FIG. 5A is an Er-doped multicore fiber used in the light distribution device of the present invention. (B) is a cross-sectional view showing an example in which an Er-doped multicore fiber has 21 cores.

FIG. 6 is a cross-sectional view of an example in which an Er-doped multicore fiber has 9 cores.

FIG. 7 is a cross-sectional view of an example in which an Er-doped multi-core fiber has a large-diameter core in the center and a small-diameter core around the core.

FIG. 8 is a cross-sectional view of an example in which an Er-doped multicore fiber has a core in which a core in a central portion and cores arranged around the core are integrated.

FIG. 9 is a cross-sectional view of an example in which an Er-doped multicore fiber has a core whose outer periphery is covered with an intermediate layer.

FIG. 10 is a cross-sectional view of an example of an Er-doped multicore fiber having 21 cores in a first cladding covered with a buffer layer.

11A to 11J are cross-sectional views of an example of an Er-doped multicore fiber in which 7 to 361 cores are arranged within a group diameter 20 of a plurality of cores.

FIG. 12 is a configuration diagram of a fifth embodiment of a light distribution device of the present invention.

FIG. 13 is a block diagram of a conventional optical fiber device.

[Explanation of symbols]

 17 Er-doped multi-core fiber 18 Clad 19 Core 20 Group diameter of a plurality of cores 21 Intermediate layer 22 First clad 23 Buffer layer

Claims (4)

[Claims] 1. A high relative refractive index difference Δ without adding a rare earth element.
The rare earth element high ratio connect the optical fiber B having a refractive index difference delta ₁ added to the output side of the _first optical fiber A, the optical fiber B
1 × n waveguide type star coupler C is connected to the output side of each of the star couplers C, optical fibers D to which no rare earth element is added are connected to each output side of the star coupler C, and the relative refraction of the star coupler C and the optical fiber D is connected. The optical fiber A,
An optical distribution device having the same high relative refractive index difference Δ ₁ as the optical fiber B and propagating signal light and pumping light from the input side of the optical fiber A. 2. The optical distribution device according to claim 1, wherein the relative refractive index difference between the 1 × n waveguide star coupler C and the optical fiber D connected to the output side thereof is much lower than Δ _1. By setting the value Δ ₂ and expanding the core on the output side of the optical fiber B having a high relative refractive index difference Δ ₁ to which a rare earth element is added, and reducing the relative refractive index difference value to Δ ₂ , Characterized light distribution device. 3. The optical distribution device according to claim 1, wherein, instead of the optical fiber B having a high relative refractive index difference Δ ₁ containing a rare earth element, a high core having a plurality of cores containing a rare earth element is provided in a cladding. An optical distribution device characterized by using a rare earth element-doped multicore fiber having a relative refractive index difference Δ ₁ . 4. The optical distribution device according to claim 2, wherein the optical fiber B having a high relative refractive index difference Δ ₁ containing a rare earth element is replaced with a plurality of cores containing a rare earth element in the cladding. Using a rare earth element-doped multicore fiber having a relative refractive index difference Δ ₁ , the output side of the rare earth element-doped multicore fiber is characterized in that the value of the core expansion and the relative refractive index difference is reduced to Δ ₂ by thermal diffusion. Optical distribution device.