JP3006476B2 - Multi-core fiber, optical amplifier using the same, optical amplification repeater and optical amplification distributor using the optical amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-core fiber requiring flatness of gain wavelength characteristics, an optical amplifier using the same, an optical amplifier repeater using the optical amplifier, and an optical amplifier distributor. is there.

[0002]

2. Description of the Related Art In recent years, optical fiber amplifiers in which a rare earth element such as Er (erbium), Pr (praseodymium), or Nd (neodymium) is added to the core of an optical fiber have reached a practical level. In particular, since an optical fiber amplifier doped with Er has a high gain and a high saturation output in a 1.55 μm band, application to various systems is considered. Among them, 1.53μm to 1.56μ
High-speed, large-capacity, long-distance transmission and optical CATV (Cable Televis) by wavelength multiplex transmission using several or more wavelengths of signal light in the m wavelength band
Attention has been focused on application to ion) systems. When the Er-doped optical fiber amplifier is applied to such a system, the gain of the Er-doped optical fiber amplifier in the above-mentioned used wavelength band is flat in order to suppress deterioration of the optical S / N characteristics and crosstalk characteristics. This is very important.

In order to achieve such a high gain and flattening, the present inventors have previously described an Er-doped multi-core fiber as shown in FIG. 16, and FIG. 17 using this Er-doped multi-core fiber. An optical amplifier is proposed. First, the Er-doped multi-core fiber 37 used
Is the primary cladding layer 32, as shown in FIG.
A plurality of glass rods 34 (seven in the figure) having cores 31 _{-1 to} 31 _-7 co-doped with a rare earth element (for example, Er) and Al (aluminum), The structure is such that the periphery of the rod 34 is covered with a clad 33. By using such an optical fiber, it is possible to achieve high gain and flatten the wavelength characteristic of gain.

There are two reasons for this achievement. First, the first reason is that the Er-doped multi-core fiber can have a sufficiently high Al doping concentration as compared with a conventional core having one Er-doped fiber. The second reason is that when the power of the pumping light in the core is reduced in the conventional optical fiber, the gain peak near the wavelength of 1.535 μm decreases, and the gain-wavelength characteristic becomes gradually flat, As the power is further reduced, the wavelength becomes 1.53.
The gain in the short wavelength region on the μm side is reduced, and the gain in the long wavelength region on the 1.56 μm side is increased. In other words, the gain-wavelength characteristic rises to the right from the short wavelength to the long wavelength. It has been found that the gain becomes extremely low when it is used, and it cannot be used as an optical amplifier. However, this Er-doped multi-core fiber uses the principle positively. That is, as shown in the figure, the core diameter D and the core interval d are optimized so that the pump light and the signal light propagate almost uniformly in the respective cores 31 _{-1 to} 31 _-7 to which Er is added. For example, although the amplification gain of the signal light propagating through each of the cores 31 _{-1 to} 31 _-7 becomes low, the wavelength characteristic thereof becomes almost flat, and the signal light propagates through a desired length. Utilizes the fact that the signals amplified inside each of the cores 31 _{-1 to} 31 _-7 are superimposed, and the wavelength characteristic of the gain becomes almost flat.

Next, a description will be given of the configuration of the optical amplifier shown in FIG. 17 based on the above-described principle and the results of evaluating the wavelength characteristics of the gain for the configuration. Er-doped multi-core fiber 3
7 has a core interval d of 1.3 μm and a core diameter of about 2 μm.
m, the cladding diameter is 125 μm, the relative refractive index difference Δ between the core and the cladding is 1.45%, and the mode field diameter is about 8.8.
μm, the addition amount of Er and Al in each core is 400 pp
m, 8500 ppm, and a fiber length of about 45 m were used. Isolators 35a and 35b for preventing light from propagating in the opposite direction are connected to both ends of the Er-doped multi-core fiber 37, and a WDM is provided inside each of them.
(Wavelength Division Multiplexing)
Couplers 36a and 36b are provided. Signal light S ₁ is inputted to the isolator 35a, isolator 35b
Signal light S ₂ amplified from is output.

Optical fibers 39a, 39b connected to the pumping semiconductor lasers 38a, 38b are coupled to the WDM couplers 36a, 36b, respectively, and pumping lights 40a, 40b generated by the pumping semiconductor lasers 38a, 38b. Can be propagated to the Er-doped multi-core fiber 37. The signal light S passes through the isolator 35a.
_{When 1} is incident, a short-wavelength laser light is generated by the pumping semiconductor laser 38a, and this laser light is incident on the Er-doped multi-core fiber 37 via the WDM coupler 36a. Is excited, and an amplifying action by stimulated emission occurs. Amplified optical signal S ₂ is output from the Er-doped multi-core fiber 37 to the outside through the isolator 35b. Similarly, the laser light generated by the pumping semiconductor laser 38b is incident on the Er-doped multi-core fiber 37 from behind,
Optical amplification is performed according to the above principle. Here, the excitation light is applied from the front and back, but may be one of the front and the rear.

Here, the wavelength of the pump light 40a, 40b is 0.98 μm, and the power of the pump light 40a is 70 μm.
The excitation light power of the excitation light 40b was 80 mW. These values are determined from the fact that the wavelength characteristic of the gain is suitable for flattening. FIG. 18 shows the measured wavelength characteristics of the gain in the configuration of FIG. That is, the signal light power Sp is -37 dB, -27 dB,-
It is the result of measuring the wavelength characteristic of each gain in each case of 17 dB and -9 dB. As is clear from FIG. 18, the gain is flattened over a wide wavelength range.

FIG. 19 shows an Er-doped multi-core fiber 37.
The relationship between the core interval d and the bandwidth when the gain is reduced by 1 dB from the maximum value (hereinafter referred to as “1 dB bandwidth”) is experimentally obtained and plotted, and as in FIG. The optical power Sp is used as a parameter. When the core interval d is 0, this is the characteristic of a conventional Er-doped optical fiber amplifier (a so-called single-core structure). FIG.
As is clear from FIG. 5, the Er-doped multi-core fiber amplifier shows that the wavelength characteristic of the gain becomes flatter, and that as the core interval d increases, the 1 dB bandwidth increases.

[0009]

However, according to the conventional Er-doped multi-core fiber amplifier, a flat wavelength characteristic can be obtained when the gain is below a certain level, but 40 dB.
In the high gain region before and after, satisfactory results were not obtained for the wavelength characteristics of the gain. Therefore, the present invention is a multi-core fiber that can obtain sufficient flat characteristics even at high gain,
It is an object of the present invention to provide an optical amplifier using the same, an optical amplifier repeater and an optical amplifier distributor using the optical amplifier.

[0010]

To achieve the above object, the present invention provides a multi-core fiber comprising a plurality of cores doped with a rare earth element covered with a cladding layer having a predetermined refractive index. , The plurality of cores are disposed at a central portion, have a first core having a first refractive index higher than the predetermined refractive index, and a first core disposed outside the first core, The second core has a second refractive index higher than the refractive index.

[0011] According to this configuration, by reducing the refractive index of the first core with respect to the second core, the power propagating in the first core is reduced, and the power in the first core and the second core are reduced. And the power propagating in the core becomes equal, and the power imbalance is eliminated. As a result, the flat characteristic of the gain wavelength characteristic can be improved. The first and second cores are doped with Al in addition to the rare earth element, and the cladding layer is provided on a primary cladding layer covering the first and second cores and on the outside of the primary cladding layer. It can be constituted by a secondary cladding layer.

According to this configuration, in addition to the rare earth element, A
By adding l, the absorption and scattering loss can be minimized and the refractive index can be adjusted with Al. Further, by dividing the optical fiber into the primary clad layer and the secondary clad layer, the relative refractive index difference Δ can be increased, and a highly efficient (= high gain) optical fiber for an optical amplifier can be obtained.

The primary clad layer can have a smaller refractive index than the secondary clad layer. According to this configuration, it is suitable for manufacturing an optical fiber in which the refractive index of the primary clad layer is different from the refractive index of the secondary clad layer, and it is possible to obtain an optical fiber for a high efficiency (= high gain) optical amplifier. it can.

The first and second cores are made of SiO.
₂ based glass, SiO ₂ -GeO ₂ based glass or S,
Al is at least 5000 ppm and Er is at least 200 ppm in the iO ₂ —GeO ₂ —P ₂ O ₅ system glass.
An added configuration can be adopted. According to this configuration,
When the rare earth element and Al are co-added, the absorption and scattering loss can be minimized, but the adjustment of the refractive index is made by Al.
Can only be done with However, GeO ₂ or P in the SiO ₂
By adding ₂ O ₅ , the relative refractive index difference Δ can be increased, and a highly efficient (= high gain) optical fiber for an optical amplifier can be obtained.

[0015] An object of the present invention is to provide a multi-core fiber constituted by covering a plurality of cores to which a rare earth element is added with a cladding layer, wherein the plurality of cores are arranged at the center of the plurality of cores. The present invention is also achieved by a multi-fiber constituted by a core having a second core and a second core which is arranged outside the first core and contains a rare earth element in an amount larger than the rare earth element addition amount of the first core.

According to this structure, the amount of the rare earth element added to the first core is made smaller than the amount of the second core added, so that the signal light power, the pump light power, The amplification degree determined by the addition amount of Er can be made substantially equal to the amplification degree determined by the signal light power, pumping light power, and the addition amount of Er propagating through the surrounding second core. As a result, the wavelength characteristic of the gain can be flattened.

Preferably, the first and second cores are added so that the rare earth element is distributed in a radial direction. According to this configuration, the rare earth element is added in a shape close to the distribution of the signal light power and the pump light power propagating in each core, and a high gain can be obtained. The first core may be configured to be larger than the refractive index of the cladding layer and smaller than the refractive index of the second core.

According to this configuration, in addition to the effect of adjusting the amount of Er added, the power propagating in the first core is reduced by reducing the refractive index of the first core with respect to the second core. As a result, the power propagating in the first and second cores becomes equal, and the power imbalance is eliminated. As a result, the flat characteristic of the gain wavelength characteristic can be improved. The first and second cores are doped with Al in addition to the rare earth element, and the cladding layer is provided on a primary cladding layer covering the first and second cores and on the outside of the primary cladding layer. It can be constituted by a secondary cladding layer.

According to this configuration, in addition to the rare earth element, A
By adding l, the absorption and scattering loss can be minimized and the refractive index can be adjusted with Al. Further, by dividing the optical fiber into the primary clad layer and the secondary clad layer, the relative refractive index difference Δ can be increased, and a highly efficient (= high gain) optical fiber for an optical amplifier can be obtained. The primary clad layer may be configured to have a smaller refractive index than the secondary clad layer.

According to this configuration, it is suitable for manufacturing an optical fiber in which the refractive index of the primary clad layer and the refractive index of the secondary clad layer are different, and high efficiency (= high gain)
Can be obtained. The first and second cores are made of SiO ₂ glass, SiO ₂ -G
eO ₂ based glass or SiO ₂ -GeO ₂ -P ₂ O,
_At least 5000 ppm of Al and E
It can be configured such that at least 200 ppm of r is added.

According to this configuration, when a rare earth element and Al are co-added, the absorption and scattering loss can be minimized, but the refractive index can be adjusted only with Al. However, by adding GeO ₂ or P ₂ O ₅ to SiO ₂ , the relative refractive index difference Δ can be increased, and a highly efficient (= high gain) optical fiber for an optical amplifier can be obtained. Further, an object of the present invention is to cover a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index, wherein the plurality of cores are arranged at a central portion, and A first core having a first refractive index greater than the first refractive index; and a second core disposed outside the first core and having a second refractive index greater than the first refractive index. And a W provided on an input side, an output side, or both sides of the multi-core fiber.
Achieved by an optical amplifier using a multi-core fiber including a DM circuit, an excitation light source for supplying excitation light to the WDM circuit, and an isolator provided between the WDM circuit and an input terminal or an output terminal. Is done.

According to this configuration, the rare-earth-doped multi-core fiber in consideration of the refractive index of the core is excellent in the flat characteristic of the wavelength characteristic of the gain. By combining this with the WDM circuit, the laser light for excitation is converted into the rare-earth-doped multi-core fiber. Can be injected, which allows optical amplification to take place. As a result, it is possible to increase the gain while securing the flat characteristic of the wavelength characteristic of the gain. Further, the above objectives are:
A plurality of cores to which the rare earth element is added are covered with a cladding layer having a predetermined refractive index, and the plurality of cores are a first core disposed at a central portion of the plurality of cores, and A multi-core fiber disposed outside the first core and including a second core containing a rare earth element in an amount larger than the rare earth element addition amount of the first core, and an input side and an output side of the multi core fiber Or a WDM circuit provided on both sides, an excitation light source for supplying excitation light to the WDM circuit, and an isolator provided between the WDM circuit and an input terminal or an output terminal. This is also achieved by an optical amplifier.

According to this configuration, the rare-earth-doped multi-core fiber in which the amount of the rare-earth element added to the second core is larger than that of the first core has excellent flatness of the wavelength characteristic of the gain, and this is combined with the WDM circuit. Excitation laser light can be injected into the rare-earth-doped multi-core fiber, thereby enabling optical amplification. As a result, it is possible to increase the gain while securing the flat characteristic of the wavelength characteristic of the gain. The pump light in the optical amplifier is 0.98
A wavelength in the μm band or the 1.48 μm band can be used.

According to this structure, the wavelength in the 0.98 μm band contributes to obtaining an amplifier having a lower noise figure and a flat gain wavelength characteristic, and the wavelength in the 1.48 μm band is highly reliable. Contribute to obtain high gain. Further, the above-described object of the present invention is configured by covering a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index,
A plurality of cores disposed at a central portion and having a first refractive index greater than the predetermined refractive index; and a first core disposed outside the first core and having a first refractive index. A multi-core fiber composed of a second core having a larger second refractive index, a WDM circuit provided on the input side, output side, or both sides of the multi-core fiber, and supplying pump light to the WDM circuit A light source for pumping, an isolator provided between the WDM circuit and an input terminal or an output terminal, and a dispersion-shifted fiber connected to the input side, output side, or both sides of the optical amplifier of the multi-core fiber. This is achieved by the optical amplification repeater having the configuration provided.

According to this structure, the mode field diameters of the dispersion-shifted fiber and the rare-earth-doped multi-core fiber are very close to each other while achieving a high gain while securing the flatness of the gain wavelength characteristic. , An optical amplification repeater that can perform transmission with low connection loss can be obtained. Further, the above object is achieved by covering a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index, and the plurality of cores are arranged at a central portion of the plurality of cores. A multi-core fiber including a first core, a second core disposed outside the first core, and including a rare earth element in an amount larger than a rare earth element addition amount of the first core; A WDM circuit provided on the input side, output side, or both sides of the fiber, and an excitation light source for supplying excitation light to the WDM circuit;
An optical amplification repeater having a configuration including an isolator provided between the WDM circuit and an input terminal or an output terminal, and a dispersion-shifted fiber connected to an input side, an output side, or both sides of the optical amplifier of the multi-core fiber. Achieved by

According to this structure, the mode field diameters of the dispersion-shifted fiber and the rare-earth-doped multi-core fiber are very close to each other while achieving high gain while securing the flat characteristic of the wavelength characteristic of the gain. , An optical amplification repeater that can perform transmission with low connection loss can be obtained. Further, in the optical amplification repeater, it is possible to adopt a configuration in which a dispersion compensation device is connected in the middle of the dispersion shift fiber.

According to this configuration, the dispersion value of the fiber, which becomes a problem when transmitting high-speed, large-capacity information to a longer distance, is compensated by the dispersion compensation device.
Therefore, a large amount of information can be transmitted at a high speed to a distant place while securing flat characteristics and high gain of the wavelength characteristic of the gain. In the optical amplification repeater, an optical multiplexing / demultiplexing circuit can be provided on the input side, output side, or both sides.

According to this configuration, wavelength multiplexing can be performed by the optical multiplexing / demultiplexing circuit, and long-distance transmission becomes possible by passing the wavelength-multiplexed signal light through the rare earth-doped multicore fiber and the dispersion shift fiber. Further, an object of the present invention is to cover a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index, wherein the plurality of cores are arranged at a central portion, and A first core having a first refractive index greater than the refractive index of
A multi-core fiber, which is disposed outside the first core and has a second core having a second refractive index larger than the first refractive index, and an input side, an output side, or A WDM circuit provided on both sides, an excitation light source for supplying excitation light to the WDM circuit,
An optical amplifier provided with an isolator provided between the WDM circuit and an input terminal or an output terminal; and an optical amplifier provided on the output side of the optical amplifier and amplifying an optical signal output from the optical amplifier. This is also achieved by a multi-core fiber optical amplifying / distributing device having a configuration in which an optical star coupler that distributes and outputs wavelengths is provided.

According to this structure, the amplified signal light is distributed by the optical star coupler while securing the flat characteristic of the gain wavelength characteristic by the optical amplification using the rare-earth-doped multi-core fiber, and is wavelength-multiplexed to a plurality of subscribers. It is possible to transmit the converted information signal almost uniformly and with extremely low S / N and crosstalk characteristic deterioration. Further, the object of the present invention is to cover a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index, and the plurality of cores are provided at a central portion of the plurality of cores. A multi-core fiber comprising a first core arranged, and a second core arranged outside the first core and containing a rare earth element in an amount larger than the rare earth element addition amount of the first core; A WDM circuit provided on the input side, output side, or both sides of the multi-core fiber,
An excitation light source for supplying excitation light to the WDM circuit; an optical amplifier including an isolator provided between the WDM circuit and an input terminal or an output terminal; and an optical amplifier provided on an output side of the optical amplifier. The present invention is also achieved by an optical amplification and distribution device having a configuration including an optical star coupler that distributes and outputs the amplified optical signal output from the optical amplifier to a plurality of different wavelengths.

According to this configuration, the signal light amplified by the optical amplification using the rare earth-doped multi-core fiber while securing the flat characteristic of the wavelength characteristic of the gain is distributed by the optical star coupler, and wavelength multiplexed to a plurality of subscribers. It is possible to transmit the converted information signal almost uniformly and with extremely low S / N and crosstalk characteristic deterioration.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. 1A and 1B show a first embodiment of an Er-doped multi-core fiber according to the present invention, wherein FIG. 1A is a sectional view, and FIG. 1B is a sectional view taken along line AA ′, BB ′, and FIG.
The refractive index distribution in each section of CC 'is shown.

Before describing the configuration of the multi-core fiber according to the present invention, the process of inventing the multi-core fiber having the configuration according to the present invention will be described. Theoretical analysis of the power distribution in each core in a state where 1 m of light propagated in the Er-doped multi-core fiber when 0.98 μm of pump light and 1.55 μm of signal light were made incident on the Er-doped multi-core fiber, FIG. 14 (in the figure, (a) is a sectional view of the fiber, (b) is a wavelength of 0.98 μm)
(Indicates the core spacing d-power input / output characteristics at m.)
And FIG. 15 (showing the core spacing d-power incidence / emission characteristics at a wavelength of 1.55 μm). In each case, the relationship between the power ratio and the core interval is shown, the horizontal axis represents the interval d between each core, and the vertical axis represents the ratio between the power incident on each core and the output power.

According to the theoretical analysis of the inventors, the AA axis, the BB axis, and the C-axis in FIGS.
Since the C axis is symmetric, the power ratio of each of the peripheral portions becomes equal. Therefore, FIGS. 14 and 15 plot the minimum value and the maximum value of the power ratio in the core at the center and the power ratio in the core at the periphery, respectively. First, FIG.
Explaining No. 4, there is a large difference between the minimum value and the maximum value of the power ratio between the central part and the peripheral part when the core interval d is small for the pumping light having a wavelength of 0.98 μm. That is, the excitation light propagates in each core with large vibration, and a large power imbalance occurs between the power in the core in the center and the power in the core in the peripheral part. However, when the core interval d is gradually increased, the power imbalance decreases, and when the core interval d is in the range of 1.3 to 1.5 μm, the power in the cores at the center and the peripheral portions is approximated. It turned out to be.

FIG. 15 shows the same tendency with respect to the signal light having a wavelength of 1.55 μm, and the core interval d for distributing the pump light and the signal light almost equally in each core and propagating the same. The optimum was found to be in the range of 1.3-1.5 μm. However, as can be seen from the above results, there is still an imbalance in the power propagating in the core at the center and in the core at the periphery, and as shown in FIG. 18, the flatness of the gain wavelength characteristic deteriorates. It is thought to be the cause.

Accordingly, in the present invention, FIGS.
The refractive index (n _WC ) of the central core is lower than the refractive index (n _wo ) of the peripheral core so that the power propagating in the central core and the peripheral core in 5 is more equal. Value so that the power propagating in the core at the center is reduced. This makes it possible to make the power propagating in the core at the center substantially equal to the power propagating in the core at the peripheral portion, thereby improving the flatness of the gain wavelength characteristic.

Next, an embodiment of the present invention embodying the above idea will be described with reference to FIG. Core 1
a to 1 g are covered with the primary cladding layer 2. Er and Al are co-added to the cores 1a to 1g. Then, one core 1a to 1g (core 1g = first
The other six cores (cores 1a to 1f = second core) are integrally bundled so as to surround this core. These cores 1a to 1g are further covered with a secondary cladding layer 3. Assuming that the refractive index of the secondary cladding layer 3 is n _C , the refractive indexes of the cores 1 a to 1 f are set to n _WO and the refractive index of the central core 1 g is set to n _WC . That is, the refractive index n _{WO of the} cores 1 a to 1 g is compared with the refractive index n _C of the secondary cladding layer 3.
Is set so that n _WO > n _C, and the refractive index n _WO of the cores 1a to 1g with respect to the refractive index n _WC of the core 1g is n _WC <
n _WO . The refractive index n _P of the primary cladding layer 2 is set to n _C = n _P with respect to the refractive index n _C of the secondary cladding layer 3.

FIG. 1 (b) is a view showing A- in FIG. 1 (a).
The refractive index distribution in each section of A ', BB', and CC 'is shown. The refractive index n _WC of the central core 1 g is set to be lower than the refractive index n _WO of the surrounding cores 1 a to 1 g, and the signal light (wavelength 1.53
The power amount of the pump light (0.95 μm band or 1.48 μm band) is suppressed as compared with the value in the case of FIG. 14 so that the power amount of the light in the cores 1 a to 1 g is substantially reduced. Since the equal distribution can be achieved, the wavelength characteristic of the gain can be further flattened.

The core material of the Er-doped multi-core fiber having the structure shown in FIG. 1 is SiO ₂ —GeO ₂ —Al ₂
It is obtained by adding Er to O ₃ . The primary clad layer 2 and the secondary clad layer 3 use SiO ₂ . Specifically, the outer diameter of the secondary cladding layer 3 is 125 μm, the outer diameter of the cores 1a to 1g is about 1.9 μm, and the core interval between the cores 1a to 1g is about 1.3 μm.
m, the refractive index n _WC of the central core 1 g is 1.478, the core 1
The refractive indexes n _{WO of a} to 1f are 1.4795, the refractive index n _P of the primary cladding layer 2 and the refractive index n _C of the secondary cladding layer 3 are 1.458, and Er and A in the cores 1 a to 1 g.
1 was added to 400 ppm and 8,500 ppm, respectively. The interval between the cores 1a to 1g of about 1.3 μm was controlled by the thickness of the primary clad layer 2.

Then, the gain characteristic and the 1 dB bandwidth characteristic were measured by the configuration shown in FIG. As a result, the results shown in FIGS. 2 and 3 were obtained. 2 and 3
As is clear from FIG. 5, the small signal input (Sp = −37 dB)
The wavelength characteristic of the gain at the time of m) is flattened. That is, conventionally, the 1 dB bandwidth (the bandwidth in which the gain is reduced by 1 dB) is about 15 nm, but according to the present invention, it is about 2 nm.
It could be enlarged to 2 nm. In addition, cores 1a to 1g
When the addition amount of Al was set to 17,000 ppm, the 1 dB bandwidth at the time of inputting the small signal could be expanded to about 26 nm.

FIG. 4 shows a second embodiment of the Er-doped multi-core fiber according to the present invention, wherein FIG.
(B) shows AA ', BB', and C in FIG.
The refractive index distribution in each section of -C 'is shown. FIG.
Is the refractive index n _C of the secondary cladding layer 3 with respect to the refractive index n _P of the primary cladding layer 2, and n _C = n _P
In contrast, in this configuration, the refractive index n _P of the primary cladding layer 2 and the refractive index n _C of the secondary cladding layer 3 in FIG. 1 are set to different values (n _C > n _P ). For example, when the refractive index n _C of the secondary cladding layer 3 is set to 1.458, the refractive index n _P of the primary cladding layer 2 is set to 1.448 by adding fluorine. According to this setting, the relative refractive index difference delta _O refractive index n _P of the refractive index n _WO and the primary cladding layer 2 of the core 1 a - 1 f 2.15%, the refractive index of the core 1 g n _WC and the primary cladding layer 2 it can be the refractive index n _P of the relative refractive index difference delta _C and 2.03% increases the relative refractive index difference than the fiber of Figure 1. As a result, the confinement of the signal light and the pump light in each core can be enhanced. As a result, the gain could be increased by about 2 dB as compared with the configuration of FIG. 1, and the 1 dB bandwidth could be obtained at the same value as the fiber of the configuration of FIG.

The core material of the Er-doped multi-core fiber having the structure shown in FIG. 4 is SiO ₂ —GeO ₂ —Al ₂
It is obtained by adding Er to O ₃ . The primary clad layer 2 is made of SiO ₂ with F added,
SiO ₂ is used for the secondary cladding layer 3. 5A and 5B show a third embodiment of the Er-doped multi-core fiber according to the present invention, wherein FIG. 5A is a sectional view, and FIG. 5B is a sectional view taken along lines AA ', BB' and C- in FIG. The refractive index distribution in each section of C 'is shown.

In FIGS. 1 and 4, SiO ₂ -GeO
_Although the configuration of the Er-doped multi-core fiber using _2- Al ₂ O ₃ as the main material of the core has been described, FIG.
The configuration of the Er-doped multi-core fiber using _2- Al ₂ O ₃ as the main material of the core will be described. 1g of core at the center
Is made of a material obtained by adding Er to SiO ₂ —Al ₂ O ₃ . The amount of Al ₂ O ₃ is being as much added 5 to 6% (up to 60,000 ppm). Core 1a
1 to 1f are for adjusting the refractive index to SiO ₂ —Al ₂ O ₃ added with Er (Al ₂ O ₃ is added in substantially the same amount as 1 g of the core) in order to make the refractive index larger than 1 g of the core at the center. As a material to which a small amount of GeO ₂ or P ₂ O ₅ is added. It should be noted that P ₁ O
₅ may be added. Since the upper limit of the achievable refractive index of SiO ₂ —Al ₂ O ₃ glass is about 1.478, the relative refractive index difference Δ cannot be made too large. When it is desired to increase the relative refractive index difference Δ, as shown in FIG. 6, the primary clad layer 2 may be formed using SiO ₂ to which fluorine is added, and the refractive index of the primary clad layer 2 may be reduced.

The characteristic of the multi-core fiber having the structure shown in FIG. 5 is that Al ₂ O ₃ is added to each core as much as possible, and GeO ₂ or P ₂ O is added to the surrounding cores 1 a to 1 f.
By adding ₅ and making the refractive index larger than that of the core 1g at the center, flattening of the wavelength characteristic of the gain can be realized over a wider band. Further, by adding P ₂ O ₅ to each core, it is possible to provide an auxiliary role for more and more uniform addition of Er, as well as to achieve higher gain and higher gain. It is also effective for flattening wavelength characteristics.

FIG. 6 shows a fourth embodiment of the Er-doped multi-core fiber according to the present invention, wherein FIG.
(B) shows AA ', BB', C in FIG.
The refractive index distribution in each section of -C 'is shown. FIG.
The multi-core fiber of the structure shown in FIG. 1 is obtained by integrating cores 1a to 1g each having a primary clad layer 2 formed thereon, and the periphery thereof is covered with an intermediate layer 100 in a cylindrical shape. It is configured to be covered with the secondary cladding layer 3. As the material of the intermediate layer 100, SiO ₂ to which F is added can be used, and its diameter is 10 to 1
A range of 00 μm is preferred.

According to the configuration of FIG. 6, the same refractive index distribution as that of the configuration of FIG. 4 can be provided, and the effect of confining each of the signal light and the pump light in the core by increasing the relative refractive index difference is provided. Can be higher. In the configurations of FIGS. 1, 4, 5, and 6, the refractive index distribution in the cores 1a to 1g is stepped as shown in FIG. Instead, they may have a gentle distribution in the radial direction. Similarly, the refractive index in the primary cladding layer 2 and the intermediate layer 100 may have a distribution other than the step shape.

FIGS. 7 and 8 show an example of the Er-added concentration distribution on each of the cross sections AA ', BB' and CC 'in FIGS. 1, 4, 5 and 6A. FIG. As described above, the Er addition concentration in the cores 1a to 1f may also have a step shape as shown in FIG. 7 or a gentle distribution in the radial direction as shown in FIG. In the first to fourth embodiments described above, the power propagating through the central core 1g is reduced by making the refractive index of the central core 1g lower than that of the surrounding cores 1a to 1f. , The wavelength characteristic of the gain is flattened over a wide band by making the power substantially equal to the power propagating in the surrounding cores 1a to 1f. However, regardless of this means, as shown in FIGS. The signal light power propagating through the center core 1g even when only the means for reducing the amount of Er added to the center core 1g to be smaller than the Er addition amounts of the surrounding cores 1a to 1f is used,
Amplification degree determined by the excitation light power and the amount of Er added,
The wavelength characteristics of the gain can be flattened by making the signal light power and pumping light power propagating through the surrounding cores 1a to 1f substantially equal to the amplification degree determined by the added amount of Er.

Means for configuring the refractive index of the central core 1g to be lower than the refractive indexes of the peripheral cores 1a to 1f, and the amount of Er added to the central core 1g is determined by adjusting the amount of Er added to the peripheral cores 1a to 1f. Means for constituting less than the amount of Er added to 1f may be combined.
This is convenient for flattening the wavelength characteristic of the gain. That is, the refractive index of the central core 1g is made lower than the refractive indices of the surrounding cores 1a to 1f to suppress the signal light power and the pumping light power propagating through the central core 1g.
g, the amount of Er added to the surrounding cores 1a to 1f is made smaller than the amount of Er added to the surrounding cores 1a to 1f, so that the amplification degree is slightly suppressed. The degree can be made uniform. By combining both means in this way, it is possible to have more flexibility in designing an Er-doped multi-core fiber.

For example, in order to obtain desired characteristics, the degree of decrease in the refractive index of the central core 1g and the degree of decrease in the amount of added Er can be considered in various combinations, and the degree of decrease in the refractive index is small. In this case, the degree of decrease in the amount of Er added may be increased, and when the degree of decrease in the refractive index is large, the degree of decrease in the amount of Er added may be decreased.

FIG. 9 is a connection diagram showing a first embodiment of an optical amplifier using an Er-doped multi-core fiber according to the present invention. Lenses 5a and 5b are provided at both ends of the Er-doped multi-core fiber 4, and WDM circuits 6a and 6b are provided facing each of the lenses 5a and 5b. The lenses 7a and 7b are located at symmetrical angular positions with respect to the lenses 5a and 5b with respect to the vertical line to the WDM circuits 6a and 6b.
Are arranged. Further, lenses 9a and 9b are disposed outside the WDM circuits 6a and 6b via isolators 8a and 8b having a bulk structure.
Facing the input side fiber 10a and the output side fiber 1
0b is provided. Optical fibers 11a and 11b are disposed facing the lenses 7a and 7b, and the ends of the optical fibers 11a and 11b are respectively provided with semiconductor lasers 12a and 12b for generating excitation light 13a and 13b. Each is arranged. Then, the optical fiber 10a is the signal light S ₁ is the incident signal light S ₂ amplified from the optical fiber 10b is output. Each lens is used for converting non-parallel light into parallel light.

Here, the WDM circuits 6a and 6b are composed of interference film filters in which low refractive index layers and high refractive index layers of SiO ₂ and TiO ₂ films are alternately formed on a glass substrate, and transmit signal light. And a circuit having a characteristic of reflecting the excitation light. The reason why the fiber type structure is not used for the isolators 8a and 8b and the WDM circuits 6a and 6b is as follows.
Since the relative refractive index difference Δ of the Er-doped multi-core fiber 4 is large, if a fiber-type structure is used, a mode field matching circuit must be provided, and loss due to this is avoided.

The signal light S ₁ entering the input side fiber 10a is sent to the Er-doped multi-core fiber 4 via the lens 9a, the isolator 8a and the WDM circuit 6a. 1
Excitation light 13a is provided from 2a. The excitation light 13a incident on the Er-doped multi-core fiber 4 excites a certain energy level of ions, and an amplifying action by stimulated emission occurs. Here amplified optical signal S _2, the lens 5b from Er-doped multi-core fiber 4, WDM circuit 6b, is sent via the isolator 8b sequentially to the output fiber 10b. Similarly, the pumping light 13b generated by the pumping semiconductor laser 12b is
Is incident from the rear, and performs optical amplification according to the above-described principle. Here, the excitation light is applied from both front and rear directions, but may be applied from either the front side or the rear side.

At both ends of the Er-doped multi-core fiber 4, isolators 8a and 8b for preventing light from propagating in the opposite direction are connected.
M couplers 6a and 6b are provided. Isolator 8
The a signal light S ₁ is inputted, the signal light S ₂ amplified from isolator 8b is output. FIG. 10 shows a second optical amplifier using an Er-doped multi-core fiber according to the present invention.
It is a connection diagram showing an embodiment.

The optical amplifier of FIG. 10 is different from the configuration of FIG.
It is characterized in that the arrangement of the DM couplers 6a and 6b and the isolators 8a and 8b are interchanged. The other configuration is as shown in FIG. In this case, it is necessary to use the isolator 8a having a characteristic of transmitting the signal light and the pump light in the right direction in the drawing. That is, a broadband isolator that can transmit not only the signal light wavelength band (1.53 to 1.56 μm) but also the excitation light wavelength band (0.98 μm band or 1.48 μm band) is used. .

As shown in FIG. 10, the isolators 8a and 8b
At the subsequent stage of the WDM couplers 6a and 6b,
Since not only the signal light reflected from the Er-doped multi-core fiber 4 side but also the pumping light can be blocked, the operation of the light source on the signal light side and the operation of the pumping semiconductor laser 12a can be stably maintained. Further, the pumping light 13b from the pumping semiconductor laser 12b propagates in the Er-doped multi-core fiber 4, is reflected by the isolator 8a, and returns to
Since the light propagates through the r-doped multi-core fiber 4, the pump light can more efficiently contribute to the amplification, and as a result, a higher gain can be achieved.

FIG. 11 is a connection diagram showing an example of the configuration of an optical amplifier / distributor configured using the optical amplifier shown in FIG. The amplification and distribution device is configured by connecting the optical star coupler 14 to the optical amplifier shown in FIG. That is, by connecting the optical star coupler 14 to the output side fiber 10b in FIG. 8, a plurality of signal output lights 15 obtained by distributing the amplified optical signal can be obtained.

The input to the optical star coupler 14 is N (N:
In (1) and (2), the output having M (M: ≧ 2) is used, and one of the inputs is connected to the output side fiber 10b. Here, N is “2” and M is “16”, but N may be 1, and M is “4”, “8”, “32”,
"64" or the like. Further, for the optical star coupler 14, any of a fiber type structure and a waveguide type structure can be used.

The mode field diameter of the output fiber 10b and the input fiber of the optical star coupler 14 is set to Er.
If the mode field diameter of the doped multi-core fiber is set to be substantially equal, the amplified and distributed output light 15 can be extracted from the output side of the optical star coupler 14 with lower loss and no reflected light. FIG. 12 is a connection diagram illustrating a configuration example of an optical amplification repeater configured using the optical amplifier illustrated in FIG.

As shown in FIG. 12, a plurality of dispersion-shifted fibers 16a, 16b, and 16c having the same specifications are used.
Between them, Er-doped multi-core fiber amplifiers 17a and 17b having the configuration shown in FIG. 9 are arranged. Further, the optical amplifier 1 is connected to the output side of the dispersion shift fiber 16c.
7c is provided. The output side of the optical multiplexing / demultiplexing circuit 18a is connected to the input side of the dispersion shift fiber 16a, and the optical multiplexing / demultiplexing circuit 18b is connected to the output end of the optical amplifier 17c.
Are connected to the input port 20b. Further, the optical multiplexing / demultiplexing circuit 18a has an input port 20a, and wavelengths λ _{1 to} λ ₈
Is input. Further, the optical multiplexing / demultiplexing circuit 18b has an output port 19b, and each of the amplified optical signals having the wavelengths λ _{1 to} λ ₈ is individually output.

In the configuration shown in FIG. 12, the wavelengths λ _{1 to} λ ₈
Is input to the optical multiplexing / demultiplexing circuit 18a, the optical signals wavelength-multiplexed by the optical multiplexing / demultiplexing circuit 18a are transmitted through the dispersion shift fibers 16a, 16b, 16c to the optical amplifiers 17a, 17a.
The light is sequentially supplied to 17b and 17c, and optical amplification is performed. Finally, each wavelength (wavelength λ) is
_{1 to} λ ₈ ) and output. At this time, since the wavelength characteristics of the gain of the optical amplifiers 17a, 17b, and 17c at the time of inputting a small signal are flat over a wide band as described above, more information is carried on the optical signal of each wavelength and a longer distance is obtained. Can be transmitted. Further, the S / N and optical crosstalk characteristics of each channel at the output port 19b can be maintained at high performance.

Further, the dispersion shift fibers 16a, 16
By setting the mode field diameters of the optical amplifiers b and 16c and the optical amplifiers 17a, 17b and 17c close to each other, low reflection,
A low-loss optical transmission system can be configured. That is, high-speed, large-capacity information can be transmitted over a long distance with a low-noise figure. In FIG. 12, the number of multiplexed wavelengths is eight, but this is not a limitation. For example, “16”, “32”, “64”,
The number of channels such as “128” can be used. Further, the number of the dispersion-shifted fibers and the number of the optical amplifiers are each three, but may be arbitrary.

FIG. 13 is a connection diagram showing another example of the configuration of the optical amplification repeater. The amplifying repeater shown here has a configuration using a fiber-type or waveguide-type dispersion compensation device 21 instead of the optical amplifier 17c in the configuration of FIG. If high-capacity information is to be transmitted at high speed over a long distance in the configuration of FIG. 12, the dispersion characteristics of the fiber become a problem.
To solve this problem, a dispersion compensation device 21 is provided.

In each of the above embodiments, an example in which Er is added to the cores 1a to 1g has been described.
Instead of this, Pr (praseodymium), Nd, Yb (ytterbium), Sm (samarium), Ce (cerium)
And the like can be used. Further, at least two of the above rare earth elements can be added.

The main material of the cores 1a to 1g is SiO 2
₂ system (Ge on SiO _2, P, Al, Ti, B, obtained by adding at least one additive for the refractive index control such as F), a fluoride-based, using either a multi-component material Can be. Further, the primary cladding layer 2 and the secondary cladding layer 3 are made of SiO ₂ or the above-mentioned SiO _2.
2 system, it is possible to use fluoride-based, any material of the multi-component system.

[0064]

As described above, the present invention includes a first core and a second core disposed near the first core, wherein the first core is smaller than the second core. By setting the refractive index, the power of each core can be balanced, and the wavelength characteristic of the gain can be flattened over a wide band.

Further, if each of the core and the second core is covered with a primary clad layer and the outer periphery thereof is covered with a secondary clad layer, the refractive index n _P of the primary clad layer and the secondary clad layer This is suitable for producing a fiber having a different refractive index n _C , and a highly efficient (= high gain) optical fiber for an optical amplifier can be obtained.

Further, a first electrode disposed at the center of the clad is provided.
By making the added amount of the rare earth element of the core less than the added amount of the rare earth element of the second core disposed around,
Amplification determined by the amount of signal light power, pumping light power, and Er added to the first core, and amplification determined by the amount of signal light power, pumping light power, and Er added to the surrounding second core. Can be made approximately equal. Therefore, the gain wavelength characteristic can be flattened.

Further, the present invention provides a rare earth-doped multi-core fiber having improved flatness of gain wavelength characteristics, and a WD.
Since the optical amplifier is configured in combination with the M circuit, high gain can be achieved while securing flatness of the gain wavelength characteristic. Further, when the rare earth element is added, by making the refractive index of the first core smaller than the refractive index of the second core, the signal light power and the pump light propagating in each of the first core and the second core are reduced. The power and the degree of amplification determined by the rare earth element can be made substantially equal.

Further, according to the present invention, by adding a dispersion-shifted fiber to an optical amplifier using a rare-earth-doped multi-core fiber, the mode-field diameters of the dispersion-shifted fiber and the rare-earth-doped multi-core fiber can be made very close. In addition, transmission of an information signal can be performed with low connection loss. In addition, the present invention can perform wavelength multiplexing by adding a dispersion shift fiber and an optical multiplexing / demultiplexing circuit. If this wavelength multiplexed signal light is passed through each fiber, flatness of gain wavelength characteristics and high gain can be maintained. It is possible to obtain an optical amplification repeater capable of long-distance transmission while transmitting.

Further, since the present invention has a configuration in which the dispersion compensating device is connected to the dispersion-shifted fiber, the dispersion value of the fiber, which becomes a problem when transmitting high-speed, large-capacity information to a longer distance, is: Compensated by the dispersion compensation device. Therefore, it is possible to obtain an optical amplifying repeater capable of transmitting a large amount of information at a high speed to a distant place while securing flat characteristics and high gain of the wavelength characteristic of the gain.

Further, according to the present invention, the optical amplifier using the rare earth-doped multi-core fiber is provided with an optical star coupler to distribute and output the amplified optical signal to a plurality of different wavelengths. The amplified signal light is distributed by an optical star coupler while securing the flat characteristic of the wavelength characteristic of the gain by the optical amplification, and the information signals wavelength-multiplexed to a plurality of subscribers are almost equally distributed and the S / N ratio is increased. It is possible to obtain an optical amplifying / distributing apparatus capable of transmitting the signal with extremely low deterioration and deterioration of the crosstalk characteristic.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of a multi-core fiber according to the present invention.

FIG. 2 is a wavelength-gain characteristic diagram in the multi-core fiber of FIG.

FIG. 3 is a diagram showing a core interval in the multi-core fiber of FIG. 1;
It is a bandwidth characteristic figure.

FIGS. 4A and 4B show a second embodiment of an Er-doped multi-core fiber according to the present invention, wherein FIG. 4A is a cross-sectional view, and FIG. 3 shows the refractive index distribution in each section.

5A and 5B show a third embodiment of the Er-doped multi-core fiber according to the present invention, wherein FIG. 5A is a sectional view, and FIG. 5B is a sectional view taken along AA ′, BB ′, and CC ′ in FIG. 3 shows the refractive index distribution in each section.

6A and 6B show a fourth embodiment of the Er-doped multi-core fiber according to the present invention, wherein FIG. 6A is a sectional view, and FIG. 6B is a sectional view taken along line AA ′, BB ′ and CC ′ in FIG. 3 shows the refractive index distribution in each section.

FIG. 7 is a distribution characteristic diagram showing an example of a distribution (step-like distribution) of an Er added concentration in a core according to the present invention.

FIG. 8 is a distribution characteristic diagram showing another example of the distribution (gradual distribution in the radial direction) of the Er addition concentration in the core according to the present invention.

FIG. 9 is a connection diagram showing a first embodiment of an optical amplifier using an Er-doped multi-core fiber according to the present invention.

FIG. 10 is a connection diagram showing a second embodiment of the optical amplifier using the Er-doped multi-core fiber according to the present invention.

11 is a connection diagram illustrating a configuration example of an optical amplification and distribution device configured using the optical amplifier illustrated in FIG. 9;

FIG. 12 is a connection diagram illustrating a configuration example of an optical amplification repeater configured using the optical amplifier illustrated in FIG. 9;

FIG. 13 is a connection diagram illustrating another configuration example of the optical amplification repeater.

FIG. 14 is a graph of the d-power incidence / emission characteristics between cores at a wavelength of 0.98 μm.

FIG. 15 is a graph showing a d-power incidence / emission characteristic between cores at a wavelength of 1.55 μm.

FIG. 16 is a sectional view showing an example of a conventional Er-doped multi-core fiber.

FIG. 17 is a connection diagram showing an optical amplifier using the Er-doped multi-core fiber shown in FIG.

18 is a wavelength-gain characteristic diagram obtained by measuring the wavelength characteristic of the gain in the Er-doped multi-core fiber having the configuration of FIG.

FIG. 19 is a characteristic diagram illustrating a relationship between a core interval d of a multi-core fiber and a 1 dB bandwidth of an optical amplifier.

[Explanation of symbols]

 1a, 1b, 1c, 1d, 1e, 1f Surrounding core 1g Core 2 Primary cladding layer 3 Secondary cladding layer 4 Er-doped multi-core fiber 6a, 6b WDM circuit 8a, 8b Isolator 12a, 12b Semiconductor laser for excitation 13a, 13b Excitation light 14 Optical star coupler 16a, 16b, 16c Dispersion shift fiber 17a, 17b Optical amplifier 18a, 18b Optical multiplexing / demultiplexing circuit 21 Dispersion compensation device 100 Intermediate layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-37385 (JP, A) JP-A-9-5538 (JP, A) JP-A-9-265021 (JP, A) JP-A-5-205 299733 (JP, A) Patent 2816097 (JP, B2) IEICE Technical Report, VOL. 95 (415) (1995) 7-12 (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/00-6/54 H01S 3/10

Claims (19)

(57) [Claims] 1. A multi-core fiber configured by covering a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index, wherein the plurality of cores are arranged at the center of the plurality of cores. A first core having a first refractive index larger than the predetermined refractive index; and a second core disposed outside the first core and having a second refractive index larger than the first refractive index. A multi-core fiber comprising a second core. 2. The first and second cores are doped with Al in addition to a rare earth element, wherein the cladding layer is a primary cladding layer covering the first and second cores, and a cladding layer of the primary cladding layer. 2. The multi-core fiber according to claim 1, comprising a secondary cladding layer provided on the outside. 3. The multi-core fiber according to claim 2, wherein the primary clad layer has a smaller refractive index than the secondary clad layer. 4. The first and second cores are made of SiO.
_TwoGlass, SiO _Two-GeO_TwoSystem glass or S
iO_Two-GeO_Two−P_TwoO_FiveWhen Al is low in system glass
5000 ppm, and Er is at least 200 ppm
The mulch according to claim 2, wherein the mulch is added.
Core fiber. 5. A multi-core fiber configured by covering a plurality of cores to which a rare earth element is added with a cladding layer, wherein the plurality of cores include a first core disposed at the center of the plurality of cores. A multi-core fiber comprising a second core disposed outside the first core and containing a rare earth element in an amount larger than the rare earth element addition amount of the first core. 6. The multi-core fiber according to claim 5, wherein the first core and the second core are added so that the rare earth element is distributed in each core in a radial direction. 7. The multi-core fiber according to claim 5, wherein the first core has a refractive index larger than a refractive index of the cladding layer and smaller than a refractive index of the second core. 8. The first and second cores are doped with Al in addition to a rare earth element. The clad layer is a primary clad layer covering the first and second cores, and a clad layer of the primary clad layer. The multi-core fiber according to claim 5, comprising a secondary cladding layer provided outside. 9. The multi-core fiber according to claim 5, wherein said primary clad layer has a smaller refractive index than said secondary clad layer. 10. The first and second cores are made of SiO ₂
Glass, SiO ₂ —GeO ₂ glass, or Si
O ₂ -GeO ₂ -P ₂ O ₅ based glass in Al is at least 5000 ppm, and the multi-core fiber according to claim 5, wherein Er is characterized in that it is at least 200ppm added. 11. A plurality of cores to which a rare earth element is added, which are covered with a cladding layer having a predetermined refractive index,
The plurality of cores are disposed at a center of the plurality of cores, a first core having a first refractive index greater than the predetermined refractive index, and a first core disposed outside the first core, A multi-core fiber including a second core having a second refractive index larger than the first refractive index; a WDM circuit provided on an input side, an output side, or both sides of the multi-core fiber; and the WDM circuit. An optical amplifier using a multi-core fiber, comprising: a pumping light source for supplying pumping light to the WDM circuit; and an isolator provided between the WDM circuit and an input terminal or an output terminal. 12. A plurality of cores to which a rare earth element is added, which are covered with a cladding layer having a predetermined refractive index,
A plurality of cores, a first core disposed at a central portion of the plurality of cores, and a first core disposed outside the first core;
A multi-core fiber composed of a second core containing a rare earth element in an amount larger than the rare earth element addition amount of the first core; and a WDM circuit provided on the input side, the output side, or both sides of the multi-core fiber. An optical amplifier using a multi-core fiber, comprising: an excitation light source for supplying excitation light to the WDM circuit; and an isolator provided between the WDM circuit and an input terminal or an output terminal. . 13. The pump light according to claim 1, wherein the wavelength of the excitation light is 0.98 μm band or 1.48 μm band.
13. An optical amplifier using the multi-core fiber according to 1 or 12. 14. A plurality of cores to which a rare earth element is added are covered with a cladding layer having a predetermined refractive index,
The plurality of cores are disposed at a center of the plurality of cores, a first core having a first refractive index greater than the predetermined refractive index, and a first core disposed outside the first core, A multi-core fiber including a second core having a second refractive index larger than the first refractive index; a WDM circuit provided on an input side, an output side, or both sides of the multi-core fiber; and the WDM circuit. A pumping light source for supplying pumping light, an isolator provided between the WDM circuit and an input end or an output end, and an input side and an output side of the optical amplifier of the multi-core fiber.
An optical amplifying repeater using a multi-core fiber, comprising: a dispersion-shifted fiber connected to both sides. 15. A plurality of cores to which a rare earth element is added, which are covered with a cladding layer having a predetermined refractive index,
A plurality of cores, a first core disposed at a center of the plurality of cores, and a first core disposed outside the first core;
A multi-core fiber composed of a second core containing a rare earth element in an amount larger than the rare earth element addition amount of the first core; and An excitation light source for supplying excitation light to the WDM circuit; an isolator provided between the WDM circuit and an input end or an output end; and an input side and an output side of an optical amplifier of the multi-core fiber.
An optical amplifying repeater using a multi-core fiber, comprising: a dispersion-shifted fiber connected to both sides. 16. The optical amplification repeater using a multi-core fiber according to claim 14, wherein a dispersion compensating device is connected to the dispersion-shifted fiber. 17. An optical multiplexing / demultiplexing circuit is provided on an input side, an output side, or both sides of a device.
Or an optical amplifying repeater using the multi-core fiber according to 16. 18. A structure comprising a plurality of cores to which a rare earth element is added covered with a cladding layer having a predetermined refractive index,
The plurality of cores are disposed at a center of the plurality of cores, a first core having a first refractive index greater than the predetermined refractive index, and a first core disposed outside the first core, A multi-core fiber composed of a second core having a second refractive index larger than the first refractive index, and W provided on the input side, output side, or both sides of the multi-core fiber
A DM circuit, an excitation light source for supplying excitation light to the WDM circuit, an optical amplifier including an isolator provided between the WDM circuit and an input terminal or an output terminal, and an output side of the optical amplifier. And an optical star coupler for distributing and outputting the amplified optical signal output from the optical amplifier to a plurality of different wavelengths. 19. A method comprising: coating a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index;
A plurality of cores, a first core disposed at a central portion of the plurality of cores, and a first core disposed outside the first core;
A multi-core fiber composed of a second core containing a rare earth element in an amount larger than the rare earth element addition amount of the first core, and WDM circuits provided on the input side, the output side, or both sides of the multi-core fiber; An excitation light source for supplying excitation light to the WDM circuit, an optical amplifier including an isolator provided between the WDM circuit and an input terminal or an output terminal, and an optical amplifier provided on an output side of the optical amplifier. And an optical star coupler that distributes and outputs the amplified optical signal output from the optical amplifier to a plurality of different wavelengths.