JPH10242556A - Er-doped optical fiber amplifier for wavelength multiplex transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of waveform distortion by eliminating the possibility of the induction of a nonlinear phenomenon even when the multiplexing number of wavelengths increases by adjusting the effective core diameter of an Er-doped optical fiber to a specific value or larger and constituting an optical fiber amplifier so that the zero dispersion wavelength may become a wavelength on the outside of a specific wavelength band. SOLUTION: In an Er-doped optical fiber which is used for constituting an Er-doped optical fiber amplifier for wavelength multiplex transmission, seven cores (having refractive indexes of nw ) 10 to which both Er and Al are added are formed in a clad 8 and an intermediate layer (having a refractive index Ni ) 9 is provided on the outer periphery of each core 10. Each core has a diameter D and the interval between each core is S. Fig. (b) shows the refractive index distribution in the optical fiber. The relative refractive-index difference between each core 10 and clad (having a refractive index nc ) 8 (or the intermediate layer 9) is expressed as Δn. Then the effective core diameter of the optical fiber at 1.55μm is adjusted to >=9μm and the zero dispersion wavelength is adjusted to a wavelength longer than 1.53-1.56μm by appropriately setting the values of the Δn, D, and S.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier for wavelength division multiplexing transmission, and more particularly, to a non-linear phenomenon that is not induced even when the number of wavelength division multiplexing is increased, thereby suppressing waveform distortion.
The present invention relates to an optical fiber amplifier for wavelength division multiplexing transmission that realizes flat gain characteristics over a predetermined wide wavelength band.

[0002]

2. Description of the Related Art In recent years, Er, P
Optical fiber amplifiers doped with rare earth elements of r and Nd have come to practical levels. In particular, since an optical fiber amplifier doped with Er has a high gain and a high saturation output in the 1.55 μm band, application to various systems is considered. Among them, application to high-speed, large-capacity, long-distance transmission systems and optical CATV systems by wavelength multiplex transmission using signal waves of several to several tens of waves in a wavelength band of 1.53 μm to 1.56 μm has attracted attention. ing.

FIG. 8 shows a conventional Er-doped optical fiber amplifier for wavelength division multiplexing transmission. This Er-doped optical fiber amplifier for wavelength division multiplexing transmission comprises a WDM coupler 4a, 4b disposed at both ends of an Er-doped optical fiber 1 having a predetermined length, and an excitation light source 3
a and 3b are combined, and an optical isolator 2a is arranged on the input side of the WDM coupler 4a, and an optical isolator 2b is arranged on the output side of the WDM coupler 4b.

In the Er-doped optical fiber amplifier for wavelength multiplexing transmission, the wavelength-multiplexed signal light 5a enters the WDM coupler 4a from the optical fiber 14a through the optical isolator 2a provided on the input side, where the pump light source 3a And then enter the Er-doped optical fiber 1 connected thereto as the signal light 5b and the excitation light 6b. Most of the pump light 6b is absorbed in the Er-doped optical fiber 1 to form a population inversion state, amplify the signal light 5b, and is transmitted to the output side as the signal light 5c. On the other hand, the pumping light 6c from the pumping light source 3b propagates as the pumping light 6d through the WDM coupler 4b in the direction opposite to the propagation direction of the signal light 5c, and is mostly absorbed in the Er-doped optical fiber 1 to amplify the signal light 5b. To be the signal light 5c. The amplified signal light 5c passes through the WDM coupler 4b and the optical isolator 2b and is output from the optical fiber 14b as the signal light 5d.

FIGS. 9 and 10 show Er used in FIG.
1 shows an additive optical fiber 1; The Er-doped optical fiber shown in FIG.
Iva 1 has a core 7 to which Er and Al are co-added, and
Step type refractive index component consisting of cladding 8 provided on the circumference
It is a cloth optical fiber, and the diameter D of the core 7 is high gain, high
In order to achieve efficiency and high saturation output characteristics,
is there. FIG. 9B shows the refractive index n of the core 7._wAnd cladding 8
Refractive index n _cAnd the relative refractive index difference Δn. This Δn is
Those having a range of 1.5% to 2.2% are used.

The Er-doped optical fiber 1 shown in FIG.
And a core (diameter D) 7 co-doped with Al, an intermediate layer 9 provided on the outer periphery thereof, and a clad 8 provided on the outer periphery thereof. It is selected from the range of several μm to 10 μm. FIG. 10B shows the relative refractive index differences Δn1, Δn2, and Δn3 of the refractive index n _w of the core 7, the refractive index n _i of the intermediate layer 9, and the refractive index n _c of the clad 8, and Δn1 is 1.5. % Is selected, and Δn2 is 0.7%
The degree is selected, and Δn3 is selected from the range of 2.0% to 2.4%.

The Er-doped optical fiber 1 shown in FIGS. 9 and 10
Has an effective core diameter of about 5 μm to 8 μm. The effective core diameter is obtained from the effective core area, and the effective core area is obtained from the following equation.

[0008]

(Equation 1)

Here, A is an effective core area, k is a proportional coefficient (（0.96), and MFD is a mode field diameter.

[0010]

However, the conventional Er-doped optical fiber amplifier for wavelength division multiplex transmission has the following problems. (1) When the number of multiplexed wavelengths increases to 8, 16, 32..., The light energy density propagating in the Er—Al co-doped core 7 becomes extremely high. Since the core diameter is as small as about 5 μm, waveform distortion is caused by induction of a nonlinear phenomenon. (2) When the effective core diameter is set to a large value of 9 μm or more, a decrease in gain, a decrease in saturation output, a deterioration in flatness of gain wavelength characteristics, and the like are caused. (3) As the number of multiplexed wavelengths increases, the power of signal light propagating in the core 7 increases, so that the gain deviation due to polarization dependence depending on hole burning increases. For this reason, in a system in which optical fiber amplifiers are connected in cascade with 10 and 20 stages, this gain deviation can be reduced from several dB to 1 stage.
It becomes large near 0 dB, which causes a system problem. (4) When performing wavelength division multiplexing transmission using a wavelength band of 1.53 μm to 1.56 μm, the chromatic dispersion characteristics in this wavelength band should be made as flat as possible or have a large negative dispersion value. Is desirable, but it cannot be realized.

On the other hand, the inventor has used an optical fiber having seven cores in which Er and Al are co-doped to obtain 1.55 μm.
We have proposed an Er-doped multi-core fiber amplifier that achieves a mode field diameter (MFD) of about 10 μm at a wavelength of m, thereby improving the coupling efficiency with a single-mode optical fiber. However, even with the Er-doped optical multi-core fiber amplifier, when the number of multiplexed wavelengths increases, problems such as generation of waveform distortion due to induction of the nonlinear phenomenon described above cannot be solved.

Accordingly, an object of the present invention is to provide an Er-doped optical fiber amplifier for wavelength-division multiplexing transmission, which does not cause a nonlinear phenomenon even if the number of wavelength-division multiplexes increases, thereby suppressing the occurrence of waveform distortion. To provide. It is another object of the present invention to provide an Er-doped optical fiber amplifier for wavelength division multiplexing transmission having a flat gain characteristic in a wavelength band of 1.53 μm to 1.56 μm.

It is another object of the present invention to provide an Er-doped optical fiber amplifier for wavelength division multiplexing transmission in which characteristics such as gain characteristics and saturation output characteristics can be easily controlled. Another object of the present invention is to reduce the deviation of the gain due to the polarization dependence depending on the hole burning even when the number of wavelength multiplexing increases. It is an object of the present invention to provide an Er-doped optical fiber amplifier for wavelength division multiplexing transmission in which the deviation of the optical signal / noise is suppressed so as not to decrease the optical signal / noise ratio.

Another object of the present invention is to provide a wavelength multiplex transmission Er for facilitating connection between optical fibers and reducing connection loss.
It is an object of the present invention to provide an additional optical fiber amplifier. Another object of the present invention is to provide an Er-doped optical fiber amplifier for wavelength division multiplexing transmission capable of transmitting a large amount of information at high speed over a long distance.

[0015]

In order to achieve the above object, the present invention provides the following Er-doped optical fiber amplifier for wavelength division multiplexing transmission. According to a first feature of the present invention, Er
Er provided with cladding outside the core co-doped with Al
A wavelength-division multiplexing transmission Er-doped optical fiber amplifier for amplifying the signal light by propagating a plurality of signal lights wavelength-multiplexed on the addition optical fiber and a pump light having a wavelength different from the wavelength of the signal light; The added optical fiber has a wavelength of 1.
The effective core diameter calculated from the effective area at 55 μm is 9
μm or more, the zero dispersion wavelength is from 1.53 μm to 1.56
Provided is an Er-doped optical fiber amplifier for wavelength multiplex transmission configured to have a wavelength other than the wavelength band of μm.

[0016] According to a second aspect of the present invention, the core, the clad at least three wavelength division multiplexing transmission Er doped optical fiber amplifier constituted by a core having a large consisting refractive index than the refractive index n _c of I will provide a. According to a third aspect of the present invention, the at least three cores, the wavelength multiplexing transmission Er structure being coated respectively by an intermediate layer having a small consisting refractive index n _i than the refractive index n _c of the cladding Provided is an doped optical fiber amplifier.

According to a fourth aspect of the present invention, the at least three cores, the intermediate layer, and the cladding comprise:
Relative refractive index difference of the refractive index n _c of the cladding and the refractive index of the core, and the refractive index of the refractive index and the middle layer of the core n
Provided is an Er-doped optical fiber amplifier for wavelength division multiplexing transmission, wherein the relative refractive index difference of _i is in the range of 1% to 2.5%.

According to a fifth aspect of the present invention, the core has a predetermined diameter, a central core having a refractive index n _w greater than a refractive index n _{c of the} cladding, and a refractive index n _w.
Wherein provided on the outside of the central core is constituted by the cladding outer core having a large consisting refractive index n _r than the refractive index n _c of via an intermediate layer of a predetermined width having more small consisting refractive index n _i To provide an Er-doped optical fiber amplifier for wavelength multiplex transmission.

According to a sixth aspect of the present invention, the outer core is provided between the outer core and the clad, and the refractive index n _i is provided.
The present invention provides an Er-doped optical fiber amplifier for wavelength division multiplexing transmission having a configuration covered by another intermediate layer. According to a seventh aspect of the present invention, the central core, the intermediate layer, the outer core, the other intermediate layer, and the clad have a relative refractive index difference between the refractive index n _w and the refractive index n _c , relative refractive index difference of the refractive index n _r and the refractive index n _c, the relative refractive index difference of the refractive index n _w and the refractive index n _i, and the relative refractive index of the refractive index n _r and the refractive index n _i An Er-doped optical fiber amplifier for wavelength division multiplexing transmission is provided wherein the differences are each in the range of 1% to 2.5%.

According to an eighth aspect of the present invention, the core comprises a first core located at a center having a refractive index n _w greater than a refractive index n _{c of the} cladding; located outside, to provide a second configuration wavelength multiplexing transmission Er doped optical fiber amplifier from the core having a large consisting refractive index n _r than the refractive index n _w. According to a ninth feature of the present invention, wavelength multiplexing is performed from an input optical fiber to a Er-doped optical fiber having a clad provided outside a core doped with Er and Al via a first optical component such as an isolator. Amplifying the signal light by injecting a plurality of signal lights and injecting pump light having a wavelength different from the wavelength of the signal light into the Er-doped optical fiber via a second optical component such as a WDM coupler. In the Er-doped optical fiber amplifier for wavelength-division multiplexing that outputs the amplified signal light from the Er-doped optical fiber to a transmission line via an output optical fiber, the Er-doped optical fiber has a wavelength of 1.55 μm. The effective core diameter determined from the effective core area is 9 μm or more,
The zero-dispersion wavelength is configured to be a wavelength other than the wavelength band of 1.53 μm to 1.56 μm, and the input optical fiber and the output optical fiber have an effective core diameter of 9 μm or more obtained from an effective cross-sectional area. And an Er-doped optical fiber amplifier for wavelength division multiplexing transmission.

According to a tenth feature of the present invention, the first
Also, the present invention provides an Er-doped optical fiber amplifier for wavelength division multiplexing transmission including an optical component having a dispersion compensation function. Here, the optical component having the dispersion compensation function is, for example, a dispersion compensation fiber, a fiber grading with an optical circulator, or the like. According to the Er-doped optical fiber amplifier for wavelength division multiplexing transmission of the present invention, the effective core diameter at the wavelength of 1.55 μm is set to 9 μm or more and the wavelength outside the wavelength band of 1.53 μm to 1.56 μm from the zero dispersion wavelength. , The number of wavelength multiplexing is 8, 16 waves,
Even if it increases like 32 waves, non-linear phenomena hardly occur and waveform distortion is not caused. Moreover, even when the effective core diameter is 9 μm or more, the wavelength is 1.53 μm to 1.56 μm.
Gain characteristics can be realized over the entire wavelength band. Further, even if the number of multiplexed wavelengths increases, the power of the signal light is distributed and propagated in each core, so that the deviation of the gain due to polarization dependency depending on hole burning is extremely small. As a result, even when 10-stage and 20-stage optical fiber amplifiers are connected in cascade, the gain deviation can be suppressed to a small value, and a system in which the deterioration of the optical signal / noise is small can be constructed. Furthermore, the effective core diameter of the fiber type components (optical isolators, WDM filters, etc.) used for the optical fiber amplifier and the input / output optical fiber is set to 9 μm.
As described above, the connection loss between these fibers can be reduced, and the connection becomes easy. Also,
It is possible to expect effects such as suppression of non-linear phenomena.

As described above, the wavelength division multiplexing transmission E of the present invention
The r-doped optical fiber amplifier has an effective core diameter of 9 μm or more obtained from an effective core area at a wavelength of 1.55 μm,
And whether the zero dispersion wavelength is shorter than 1.53 μm,
By specifying the optical fiber structure so as to have a wavelength longer than 1.56 μm, the signal spectrum can be expanded due to the self-phase modulation effect and the cross-phase modulation effect, and the waveform deterioration due to dispersion can be suppressed. Interference noise due to mixing can also be suppressed. Therefore, the wavelength 1.5
Eight signal lights in a wavelength band of 3 μm to 1.56 μm,
Even if multiplexed transmission is performed such as 6 waves, 32 waves,..., Each signal light is amplified at a substantially uniform amplification degree, and the amount of noise added to each signal light is reduced to be substantially uniform. Value can be suppressed.

[0023]

FIG. 1 (a) shows a configuration of an Er-doped optical fiber for realizing an Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to the present invention. In this Er-doped optical fiber, seven cores (refractive index n _W ) 10 in which Er and Al are co-doped are formed in a cladding 8, and an intermediate layer (refractive index n _i ) 9 is formed on the outer periphery of each core 10. Is provided. The diameter of each core 10 is D, and the interval between each core 10 is S. FIG. 1 (a)
FIG. 1B shows the distribution of the refractive index of the first embodiment, and the cladding (refractive index n _c ) 8 has SiO 2.
₂ is used, SiO ₂ is also used for the intermediate layer 9, and each core 10 is made of SiO ₂ —GeO in which Er and Al are co-added.
_Second glass is used. The relative refractive index difference between each core 10 and the cladding 8 (or the intermediate layer 9) is represented by Δn. In this configuration, by setting the values of Δn, D, and S appropriately, the effective core diameter at 1.55 μm is set to 9 μm or more, and the zero dispersion wavelength is set to 1.53 μm to 1.5 μm.
The wavelength is other than 6 μm. As specific examples, for example, D = 1.88 μm, S = 1.24 μm, Δn = 1.
When set to 5%, the effective core diameter is 9.88 μm and the zero dispersion wavelength is 1415 nm. D = 2.35 μ
When m, S = 1.55 μm, and Δn = 1.5%,
The effective core diameter is 9.27 μm and the zero dispersion wavelength is 1455n
m. However, in each case, the outer diameter of the cladding 8 is 125 μm. In the configuration of FIG.
(C) shows the refractive index distribution of the second embodiment, wherein the cladding (refractive index n _c ) 8 is made of SiO ₂ glass in which fluorine is added toward the inside of the cladding, and the intermediate layer 9 is made of fluorine. Er and A were added to each core 10 using the added SiO _2.
codoped been SiO ₂ -GeO ₂ glass of l. Here, the distribution in which the refractive index in the clad 8 decreases from the outside to the inside is that the core 10 covered with the intermediate layer 9 doped with fluorine and doped with Er and Al.
Were each inserted into SiO ₂ tube was added F-containing, the tube near the outside of the tube is heated from the outside by the oxyhydrogen burner in the process of the solid rods of the SiO ₂ tube was added the F-containing F This is because the element evaporates and goes out. As described above, when the refractive index distribution is provided in the cladding 8, there is a feature that the bending loss can be reduced while the effective core diameter is kept large. The relative refractive index difference between each core 10 and the cladding 8 is Δn1, the relative refractive index difference between the outermost cladding 8 and the intermediate layer 9 is Δn2, and the relative refractive index difference between each core 10 and the intermediate layer 9. Is Δn3. In this configuration, by appropriately setting the values of Δn1 to Δn3, D and S, the effective core diameter at 1.55 μm is made 9 μm or more, and the zero dispersion wavelength is set at 1.53 μm.
The wavelength is other than μm to 1.56 μm. As a specific example, for example, when D = 1.3 μm and S = 1.38 μm, the effective core diameter is 9.6 μm, and the zero dispersion wavelength is 14 μm.
95 nm. D = 1.2 μm, S = 1.25
Assuming μm, the effective core diameter is 10.2 μm and the zero dispersion wavelength is 1470 nm. These results have been found for the first time by the present inventors from various experimental results. However, in each case, the outer diameter of the cladding 8 is 125 μm. When these Er-doped optical fibers are used in the optical fiber amplifier of FIG. 8, the signal light and the pump light are distributed almost evenly in each core 10 and propagated, and have a high gain at the output side and a wide wavelength range ( (1530 to 1560 nm), an almost flat gain is obtained. Further, since the effective core diameter is 9 μm or more, even if signal light having different wavelengths of eight or more channels is wavelength-division multiplex-transmitted in the Er-doped optical fiber, it is possible to suppress the occurrence of waveform distortion due to the non-linear phenomenon. Furthermore, since the zero dispersion wavelength is also set to a wavelength other than the wavelength of 1.53 μm to 1.56 μm, it is possible to suppress the addition of interference noise due to four-wave mixing. In general, when multi-channel wavelength multiplexed signal light is transmitted, such as eight channels, the signal light increases, polarization dependence due to hole burning occurs, and the amplified gain fluctuates. In the embodiment, since the signal light is distributed and transmitted in each core 10, the polarization dependence due to hole burning is greatly reduced, and a very stable gain can be obtained.

FIG. 2A shows Er for wavelength division multiplexing transmission according to the present invention.
Er-doped optical fiber that realizes doped optical fiber amplifier
Another configuration is shown. This Er-doped optical fiber is composed of Er and Al.
Co-doped SiO_Two-GeO_TwoStraight made of glass
A first core having a diameter D (refractive index n _w11) and its outer periphery
To the first intermediate layer (refractive index n_i) Cover with 9a. This middle layer
The width of 9a is S, and its outer periphery is co-doped with Er and Al.
SiO_Two-GeO_TwoSecond glass of width W made of base glass
A (refractive index n_w) 12 and outside of its second core 12
Around the second intermediate layer having a width S (refractive index n_i) 9b is provided,
A cladding (refractive index nc) is provided on the outer periphery of the second intermediate layer 9b.
8 are provided. In the configuration of FIG.
(B) shows the refractive index distribution of the third embodiment. here
And the first and second intermediate layers 9a and 9b are made of SiO._TwoMoth
And Δn is 1.5% and S is 0.5 μm to 1.3.
μm, and D and W are set to 2.4 μm or less. FIG.
(C) shows the refractive index distribution of the fourth embodiment. here
The first and second intermediate layers 9a and 9b are doped with fluorine.
SiO_TwoGlass, Δn1 is 1.5%, Δn2
0.7%, and D and W are 2.4 μm or less, preferably,
Set to 1.2 μm or less. This Er-doped optical fiber
When the optical fiber amplifier of FIG. 8 is used, the addition of Er of FIG.
Almost the same effects as those of the optical fiber can be obtained. signal
Light and pump light are distributed between the first core 11 and the second core 12
Be transmitted. The degree of this distribution is
Depends on diameter D, width W of second core 12, and core spacing S
I do. With this configuration, the wavelength at 1.55 μm
The effective core diameter is 9 μm or more, and the zero dispersion wavelength is 1.53 μm.
m to 1.56 μm, and the core 11
And the degree of distribution of signal light and pump light into the core 12
It can be uniform.

FIG. 3A shows Er for wavelength division multiplexing transmission according to the present invention.
2 shows another configuration of the Er-doped optical fiber for realizing the doped optical fiber amplifier, which has the same configuration as that of FIG.
The refractive index distributions according to the fifth and sixth embodiments of FIGS. 3B and 3C are different from the refractive index distributions of FIGS. 2B and 2C. In FIGS. 3B and 3C, Er and A
The index n _w of the co-doped first core 11 is slightly lower than the index n _r of the second core 12, and the signal propagating in the first core 11 and the second core 12. The powers of the light and the excitation light are almost equalized. Relative refractive index Δn, Δ
n ′, Δn1, Δn1 ′, Δn2, Δn3 are as illustrated. Thereby, the first core 11 and the second core 1
When the refractive indices of the two are made equal, the signal light and the pump light are prevented from being strongly excited and propagated toward the first core 11. Since the signal light and the pump light are substantially evenly distributed in the first core 11 and the second core 12, the saturation output of the Er-doped optical fiber amplifier for wavelength division multiplexing transmission can be increased.

FIG. 4A is a diagram illustrating Er for wavelength division multiplexing transmission according to the present invention.
FIG. 4 shows another configuration of the Er-doped optical fiber for realizing the doped optical fiber amplifier, and has the same configuration as that of FIGS. 2A and 3A, but FIGS. 26 shows a refractive index distribution according to the seventh and eighth embodiments, which are different from the first embodiment. The relative refractive indices Δn, Δn′Δn1 to Δn4 forming the refractive index distribution are as shown in the drawing.
By this refractive index distribution, the first core (refractive index n _w ) 1
The powers of the signal light and the pump light propagating in the first and second cores (refractive index n _w ) 12 can be made substantially equal. The refractive index distribution, to enhance the confinement factor of the signal light and the pumping light of a refractive index n _i2 of the intermediate layer 9b lower than the refractive index n _i1 of the intermediate layer 9a to the second core 12. Thereby, the first
The power distribution of the signal light and the pump light to the core 11 and the second core 12 can be made substantially uniform. This also contributes to increasing the effective core diameter, which is effective in suppressing nonlinear phenomena and reducing polarization-dependent gain deviation.

FIG. 5A shows Er for wavelength division multiplexing transmission according to the present invention.
5 shows another configuration of the Er-doped optical fiber optical fiber for realizing the doped optical fiber amplifier, which has the same configuration as FIGS. 2 (a), 3 (a) and 4 (a), but FIG. 5 (b).
(C) is the ninth and first embodiments different from the above-described embodiment.
0 shows a refractive index distribution as an embodiment. Δn, Δn ′, Δn ″, Δn that form this refractive index distribution
1, Δn1 ′, Δn2, and Δn3 are as illustrated. As is clear from this refractive index distribution, the power of the signal light and the pumping light does not concentrate on the first core (refractive index n _w ) 11, and the first core 11 and the second core (refractive index n _r ) are eliminated. ) 12 equally distributed. As a result, the same effects as in the fifth to eighth embodiments can be obtained.

FIG. 6A shows Er for wavelength division multiplexing transmission according to the present invention.
Er-doped optical fiber that realizes doped optical fiber amplifier
Another configuration is shown. This Er-doped optical fiber is substantially centered.
SiO co-doped with Er and Al_Two-GeO_TwoSystem glass
Of the first core 11 (diameter D₁, Refractive index n_wHas 11)
And the outer periphery of the SiO.sub.2 where Er and Al are not co-added.
_Two-GeO_TwoSecond core 11 (based on diameter D_TwoSuccumb
Folding ratio n_r) 13 and a cladding (refractive index n
_c8) is provided. FIG. 6B shows a refractive index distribution,
The relative refractive index difference between the first core 11 and the clad 8 is Δn3,
The relative refractive index difference between the first core 11 and the second core 13 is Δn
1. The relative refractive index difference between the second core 13 and the clad 8 is Δn
Let it be 2. Here, Δn3 is 1% or less and Δn2 is 0.5
% Or less, D ₁/ D_TwoIs set to 0.5 or less, the wavelength
The effective core diameter at 1.55 μm is 9 μm or more, and
Zero dispersion wavelength out of 1.53 μm to 1.56 μm
Wavelength.

FIG. 7A shows Er for wavelength division multiplexing transmission according to the present invention.
1 shows another configuration of an Er-doped optical fiber for realizing an doped optical fiber amplifier, and FIG.
The configuration is the same as that of FIG. The core 10 is a central core 10
a and the outer core 10b, and FIGS. 7B and 7C show the refractive index n _w of the center core 10a and the refractive index n _{r of the} outer core 10b.
Shown is a smaller configuration. Therefore, FIG.
In addition to the effect of the Er-doped optical fiber described above, the concentration of power of signal light and pump light on the central core 10a can be suppressed, and the effect of uniform distribution of power can be further improved.

Next, the Er-doped optical fiber shown in FIGS.
To implement an Er-doped optical fiber amplifier for wavelength division multiplexing transmission
The resulting configuration will be described with reference to FIG. In FIG.
Input optical fiber 14a, output optical fiber 14b, WDM
Optical fibers constituting the couplers 4a and 4b, and
Optical fibers constituting optical isolators 2a and 2b;
And the effective core diameter at a wavelength of 1.55 μm is 9 μm or less.
Above, where the zero dispersion wavelength is longer than 1560 nm
Is used. Naturally, Er-doped light
The fiber 1 is shown in FIG. 1 to FIG. This
With such a configuration, light with an effective core diameter of 9 μm or more
Fiber and optical components.
Therefore, the occurrence of nonlinear phenomena in optical fiber amplifiers is almost
Performs high-quality optical amplification with no waveform distortion
be able to. Also, fluctuations in gain due to polarization dependence are suppressed.
available. Furthermore, connection loss and reflection loss between optical components are reduced.
can do. 1 to 7 Er-doped optical fiber
The concentration of Er added in the core is 50 ppm
Is preferably in the range of 1,000 ppm, and the concentration of Al is
The range of 1,000 ppm to 60,000 ppm is preferred.
New The concentrations of Er and Al in each core are the same.
No need to be. Further, the composition of the core is SiO 2 _Two-Ge
O_TwoIn addition to system glass, SiO_Two-GeO_Two−P_TwoO_Fivesystem
Glass, SiO _Two−P_TwoO_FiveBase glass, these glasses
To which fluorine is added, or the like can be used.

In the configuration of the optical amplifier shown in FIG. 8, before or after the optical isolators 2a and 2b, or in the WDM
By providing a dispersion compensating fiber before or after the couplers 4a and 4b to compensate for dispersion of the wavelength division multiplexed signal light, higher quality transmission amplification can be performed. Further, instead of the optical isolator 2a, a three-terminal optical circulator is used to input signal light from one of the three terminals, and a fiber grating is inserted into the second terminal. May be reflected to perform dispersion compensation and output from the third port, and thereafter, the signal light may be incident on the Er-doped optical fiber 1 to amplify the dispersion-compensated signal light. A three-terminal optical circulator is used in place of the optical isolator 2b, and the signal light of each wavelength amplified by the Er-doped optical fiber 1 is input to the first terminal, and then the above-mentioned fiber grating is provided at the second output terminal. Here, the respective signal lights may be subjected to dispersion compensation, reflected, and output from the third terminal.

[0032]

As described above, according to the Er-doped optical fiber amplifier for wavelength division multiplexing transmission of the present invention, the following effects can be obtained. (1) The diameter of the effective core at a wavelength of 1.55 μm is 9 μm
In addition, the zero dispersion wavelength is set to 1.53 μm to 1.
Since the wavelength is outside the range of 56 μm, the wavelength multiplexing number is 8
Even if it increases like waves, 16 waves, 32 waves, 64 waves ...
There is no danger of inducing a nonlinear phenomenon, and the occurrence of waveform distortion due to the phenomenon is not suppressed. (2) The effective core diameter at a wavelength of 1.55 μm is 9 μm or more, and the zero dispersion wavelength is 1.53 μm to 1.5 μm.
Even when the wavelength is out of the range of 6 μm, the power distribution of the signal light in the core is made uniform, so that the wavelength is reduced from 1.53 μm to 1.5 μm.
Flat gain characteristics can be realized over a wide wavelength range of 6 μm. (3) Since the structural parameters of the Er-doped optical fiber are increased, characteristics such as gain characteristics and saturation output characteristics can be easily controlled. (4) The number of multiplexed wavelengths is 8, 16, 32, 64, etc.
Even when the power increases, the power of the signal light is distributed and propagated in each core, so that a deviation in gain due to polarization dependence depending on hole burning can be suppressed. Therefore, even if the Er-doped optical fiber amplifiers are connected in cascade with 10 or 20 stages, the deviation of the gain can be suppressed to a small value, and a system with a small deterioration of the optical signal / noise ratio can be constructed. (5) Since the effective core diameter of the fiber-type components (optical isolators, WDM filters, etc.) and the input / output optical fibers used for the Er-doped optical fiber amplifier is 9 μm or more,
Connection loss between these optical fibers can be reduced, connection can be easily performed, and induction of a nonlinear phenomenon can be suppressed. (6) Based on the effects described above, it is possible to configure an Er-doped optical fiber amplifier for wavelength division multiplexing transmission capable of transmitting large-capacity information at high speed over a long distance.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view illustrating a configuration of an Er-doped optical fiber that realizes an Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to first and second embodiments of the present invention. (B) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 1st Embodiment. (C) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 2nd Embodiment.

FIG. 2A is a cross-sectional view showing a configuration of an Er-doped optical fiber for realizing an Er-doped optical fiber amplifier for wavelength division multiplexing transmission in the third and fourth embodiments of the present invention. (B) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 3rd Embodiment. (C) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 4th Embodiment.

FIG. 3A is a cross-sectional view showing a configuration of an Er-doped optical fiber that realizes an Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to fifth and sixth embodiments of the present invention. (B) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 5th Embodiment. (C) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 6th Embodiment.

FIG. 4A is a sectional view showing a configuration of an Er-doped optical fiber for realizing an Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to the seventh and eighth embodiments of the present invention. (B) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 7th Embodiment. (C) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 8th Embodiment.

FIG. 5A is a cross-sectional view showing a configuration of an Er-doped optical fiber for realizing an Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to ninth and tenth embodiments of the present invention. (B) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 9th Embodiment. (C) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 10th Embodiment.

FIG. 6 (a) Er for realizing an Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to an eleventh embodiment of the present invention.
Sectional drawing which shows the structure of an addition optical fiber. (B) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 11th Embodiment.

FIG. 7A is a sectional view showing a configuration of an Er-doped optical fiber for realizing an Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to twelfth and thirteenth embodiments of the present invention. (B) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 12th Embodiment. (C) Explanatory drawing which shows the refractive index distribution of the Er-doped optical fiber in 13th Embodiment.

FIG. 8 is an explanatory diagram showing an Er-doped optical fiber amplifier for wavelength multiplex transmission according to the related art and the present invention.

FIG. 9A is a cross-sectional view showing a conventional Er-doped optical fiber. (B) Explanatory drawing which shows the refractive index distribution of the conventional Er-doped optical fiber.

FIG. 10A is a sectional view showing a conventional Er-doped optical fiber. (B) Explanatory drawing which shows the refractive index distribution of the conventional Er-doped optical fiber.

[Explanation of symbols]

 Reference Signs List 1 Er-doped optical fiber 2a, 2b Optical isolator 3a, 3b Pump light source 4a, 4b WDM coupler 5a, 5b, 5c, 5d Signal light 6a, 6b, 6c, 6d Pump light 7, 10, 11, 12 Er-Al co-doped Core 8 Clad 9, 9a, 9b Intermediate layer 14a Input optical fiber 14b Output optical fiber

Claims (10)

[Claims] 1. A multi-wavelength signal light wavelength-division multiplexed on an Er-doped optical fiber having a cladding provided outside a core co-doped with Er and Al, and pump light having a wavelength different from the wavelength of the signal light are propagated. To amplify the signal light.
In the r-doped optical fiber amplifier, the Er-doped optical fiber has an effective core diameter of 9 μm or more obtained from an effective cross-sectional area at a wavelength of 1.55 μm, and a zero-dispersion wavelength other than the wavelength band of 1.53 μm to 1.56 μm. An Er-doped optical fiber amplifier for wavelength division multiplexing transmission, characterized in that: 2. The Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to claim 1, wherein said core comprises at least three cores having a refractive index larger than the refractive index n _{c of} said cladding. 3. The at least three cores include
Refractive index n_cSmaller refractive index n _iIn the middle layer with
3. The wave according to claim 2, wherein the waves are respectively coated.
Er-doped optical fiber amplifier for long multiplex transmission. 4. The at least three cores, the intermediate layer,
And the cladding, the relative refractive index difference of the refractive index n _c of the cladding and the refractive index of the core, and the relative refractive index difference of the refractive index n _i of the refractive index and the intermediate layer of said core, respectively 1
4. The method according to claim 3, wherein the ratio is in the range of 2.5% to 2.5%.
An Er-doped optical fiber amplifier for wavelength multiplexing transmission as described in the above. Wherein said core has a predetermined diameter, a central core having a large consisting refractive index n _w than the refractive index n _c of the cladding, the refractive index n _i made smaller than the refractive index n _w provided outside the central core via the intermediate layer having a predetermined width having the wavelength multiplexing of claims 1, wherein configuration by an outer core having a large consisting refractive index n _r than the refractive index n _c of the cladding Er-doped optical fiber amplifier for transmission. 6. The Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to claim 5, wherein said outer core is provided between said cladding and said intermediate layer and is covered with another intermediate layer of said refractive index n _i. . 7. The relative refractive index difference between the refractive index n _w and the refractive index n _c , the refractive index n _r , the central core, the intermediate layer, the outer core, the other intermediate layer, and the clad.
The relative refractive index difference of the refractive index n _c, the relative refractive index difference of the refractive index n _w and the refractive index n _i, and the relative refractive index difference of the refractive index n _r and the refractive index n _i, respectively and, 1% to 2.5
7. The Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to claim 6, wherein the optical fiber amplifier is configured to be in the range of%. 8. A first core located at a center having a refractive index n _W greater than a refractive index n _{c of the} cladding, and a core located outside the first core and having a refractive index of n. n _w is composed of the second core having an above atmospheric consisting refractive index n _r claims 1 wavelength multiplexing transmission Er doped optical fiber amplifier according. 9. A multi-wavelength signal light multiplexed from an input optical fiber to a Er-doped optical fiber having a cladding provided outside a core co-doped with Er and Al via a first optical component such as an isolator. And the pump light having a wavelength different from the wavelength of the signal light is incident on the Er-doped optical fiber via a second optical component such as a WDM coupler to amplify the signal light, and the amplified signal light is amplified. An Er-doped optical fiber amplifier for wavelength division multiplexing transmission, which outputs the signal light from the Er-doped optical fiber to a transmission line via an output optical fiber, wherein the Er-doped optical fiber has an effective core area at a wavelength of 1.55 μm. The effective core diameter is 9 μm or more, and the zero dispersion wavelength is set to a wavelength other than the wavelength band of 1.53 μm to 1.56 μm. The output optical fiber is configured so that an effective core diameter determined from an effective area is 9 μm or more.
r-doped optical fiber amplifier. 10. An Er-doped optical fiber amplifier for wavelength division multiplexing transmission according to claim 9, wherein said first and second optical components include an optical component having a dispersion compensation function.