JP2002139754A - Pump module for Raman amplification, Raman amplifier, and optical communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a raman amplifier in which deterioration of transfer quality of signal light can be suppressed even if any light source out of plural light sources is broken down. SOLUTION: Light of center wavelength λ1-λ6 outputted from light sources 111-116 in an excitation module 10 for raman amplification is synthesized, made excitation light for raman amplification, this excitation light for raman amplification is supplied to an optical fiber 30 for raman amplification through a synthesis module 40. Signal light of multi-wavelength inputted to an input end 1a is transmitted in the optical fiber 30 for raman amplification after passing through an light isolator 20, and raman amplification is performed. The signal light of multi-wavelength raman-amplified is outputted from an output end 1b through the synthesis module 40. Difference (λ2n-λ2n-1) of center wavelength λ2n-1, λ2n of output light from light sources 112n-1, 112n in the excitation module 10 for raman amplification is 6 nm or less (n=1, 2, 3).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Raman amplifier for Raman amplifying signal light, a Raman amplification pump module for outputting pump light for Raman amplifying the signal light, and an optical communication system including the Raman amplifier. It is about.

[0002]

2. Description of the Related Art A Raman amplifier supplies pump light for Raman amplification to an optical waveguide (optical fiber) and Raman amplifies signal light propagating through the optical fiber. For example, the wavelength of the signal light is in the 1.55 μm band, and the wavelength of the pump light is around 1.45 μm. When Raman-amplifying multi-wavelength signal light, it is important that the gain of Raman amplification is flat in the signal light wavelength band including the multi-wavelength. In order to flatten the gain, it is conceivable to use a gain equalizer having a loss spectrum having the same shape as the gain spectrum shape of the Raman amplification, and the Raman amplification pump light has a plurality of peak wavelengths. It is possible to have. The latter case is preferable in that the excitation light energy can be used effectively without causing a loss to the signal light.

[0003] For example, the document "Y. Emori, et al.," 100 n
m bandwidth flat gain Raman amplifiers pumped and
gain-equalized by 12-wavelenth-channel WDM high po
In the Raman amplifier described in werlaser diodes ", OFC'99, PD19 (1999)", in order to flatten the gain of Raman amplification in a signal light wavelength band of 100 nm, light of 12 different wavelengths is combined. This is used as the excitation light for Raman amplification. Further, the light of each wavelength is obtained by polarization-combining the lights output from the two semiconductor laser light sources and having mutually orthogonal polarization states. In this document, the wavelength interval of the 12-wavelength light is 7.5 nm or 15 n.
m. Further, in the Raman amplifier disclosed in Japanese Patent Application Laid-Open No. 2000-98433, the center wavelength interval of light output from each of a plurality of light sources is set from the viewpoint of efficiency and gain flattening when combining lights of a plurality of wavelengths. The wavelength is set to 6 nm or more and 35 nm or less, and these lights are combined to form excitation light.

[0004]

However, in the above prior art, when any one of the plurality of light sources fails, the flatness of the gain of the Raman amplification is impaired and the transmission quality of the signal light deteriorates. In addition, when polarization combining is performed, the transmission quality of signal light is further deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and it is possible to suppress the deterioration of the transmission quality of signal light even when one of a plurality of light sources fails. An object of the present invention is to provide a Raman amplifier that can be used, a pump module for Raman amplification that outputs pump light for Raman amplification in the Raman amplifier, and an optical communication system including the Raman amplifier.

[0006]

A Raman amplification pump module according to the present invention is a Raman amplification pump module that outputs pump light for Raman amplification of signal light propagating through an optical waveguide, and has a center wavelength. Excitation light generation means including a plurality of light sources that output different lights from each other, and multiplexing means that multiplexes a plurality of lights output from the excitation light generation means and outputs the multiplexed light as excitation light, among the plurality of light sources The difference between the center wavelengths of the two lights output from any two light sources is less than 6 nm. Further, the Raman amplifier according to the present invention includes an optical waveguide that propagates the signal light and Raman-amplifies the signal light by supplying the pump light, and the Raman amplifier according to the present invention that supplies the pump light to the optical waveguide. And an amplification excitation module. Also,
An optical communication system according to the present invention is an optical communication system that performs optical communication by propagating signal light, and includes the Raman amplifier according to the present invention for Raman-amplifying the signal light.

According to the Raman amplification pump module, the Raman amplifier or the optical communication system, lights having different center wavelengths output from a plurality of light sources included in the pump light generating means are multiplexed by the multiplexing means. The excitation light is supplied to an optical waveguide (preferably an optical fiber). And
The signal light propagating through the optical waveguide is Raman-amplified in the optical waveguide. In particular, in the present invention, since the difference between the center wavelengths of two lights output from any two of the plurality of light sources is less than 6 nm, when one of the two light sources fails, By increasing the output power of the other light source, fluctuations in the gain of the Raman amplification of the signal light in the optical fiber for Raman amplification can be suppressed to be small, and deterioration in the transmission quality of the signal light in the optical communication system can be suppressed. Can be.

In the Raman amplification pumping module according to the present invention, the pumping light generator outputs 2N (N is an integer of 1 or more) lights having different center wavelengths. The difference between the center wavelengths of the 2n-1st light and the 2nth light (n is an integer of 1 or more and N or less) is less than 6 nm. In this case, 2
Even if any of the N light sources fails, the Raman amplification device is increased by increasing the output power of another light source whose output light has a difference in center wavelength of less than 6 nm from the failed light source. , The fluctuation of the gain of the Raman amplification of the signal light in the optical communication system can be suppressed small, and the deterioration of the transmission quality of the signal light in the optical communication system can be suppressed.

Further, in the Raman amplification pump module according to the present invention, the pump light generating means polarization-combines and outputs any one of the plurality of lights. In this case, the power of the pumping light for Raman amplification can be increased.

Further, the Raman amplification pumping module according to the present invention is characterized in that the pumping module further comprises a depolarizer for setting the pumping light to a non-polarized state. Further, in the Raman amplification pump module according to the present invention, the multiplexing means is characterized in that two lights having a difference of the center wavelengths of less than 6 nm are inputted and multiplexed in mutually orthogonal polarization states. In these cases, a stable Raman amplification operation can be obtained.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

First, a description will be given of how the present invention was conceived. FIG. 1 is a diagram illustrating a Raman gain spectrum in a dispersion-shifted optical fiber. In this figure,
Raman gain spectrum A shows a Raman gain spectrum when supplying excitation light having a center wavelength lambda _A to the optical fiber. Raman gain spectrum B shows the Raman gain spectrum when supplying excitation light having a center wavelength lambda _B to the optical fiber. The Raman gain spectrum C has a center wavelength λ _A
3 shows a Raman gain spectrum when the pump light of FIG. 1 and the pump light of the center wavelength λ _B are supplied to the optical fiber. Each of the Raman gain spectra A to C shows peak values equal to each other. As can be seen from this figure, the Raman gain spectrum when two lights (wavelengths λ _A , λ _B ) having different center wavelengths are multiplexed to generate Raman amplification pump light is such that only one of the lights is Raman amplified. As compared with the Raman gain spectrum when the pumping light is used for amplification, it is flat near the peak.

FIG. 2 shows a Raman gain spectrum obtained when two lights (wavelengths λ _A , λ _B ) having different center wavelengths are multiplexed to generate Raman amplification pump light, and only one of the two lights is subjected to Raman amplification. FIG. 9 is a diagram illustrating a difference ΔG from a Raman gain spectrum when the pump light is used for amplification. In this figure, the difference Δλ (= λ _B −λ _A ) between the center wavelengths of the two lights is 1 nm, 6n
The cases of m, 7 nm and 10 nm are shown. As can be seen from this figure, the center wavelength difference Δλ is 10 nm or less in a gain range where the difference from the peak gain value in the Raman gain spectrum when only one of the lights is the pumping light for Raman amplification is 1 dB or less. If so, the absolute value of the gain difference ΔG is 0.3 dB or less, and if the center wavelength difference Δλ is less than 6 nm, the absolute value of the gain difference ΔG is 0.2 dB or less. That is, when one of the two light sources having different center wavelengths of the output light fails and the light output only from the other light source is forced to be the Raman amplification pump light, Center wavelength difference Δλ
Is less than 6 nm, the fluctuation of the gain can be suppressed to 0.2 dB or less, and the deterioration of the transmission quality of the signal light can be suppressed. The present invention has been made based on the above findings of the present inventor.

Next, embodiments of the Raman amplification pump module and the Raman amplifier according to the present invention will be described. FIG. 3 is a configuration diagram of the Raman amplifier 1 according to the present embodiment. FIG. 4 is a configuration diagram of the Raman amplification excitation module 10 according to the present embodiment. The Raman amplifier 1 includes an optical isolator 20, an optical fiber for Raman amplification 30, and a multiplexing module 40 in this order from the input end 1a to the output end 1b.
Is connected to a Raman amplification excitation module 10.
The Raman amplification excitation module 10 includes six light sources 11 ₁
To 11 including ₆ and a wavelength combiner 12.

Light source 11₁~ 11₆Each is preferably half
It is a conductor laser light source. Light source 11_{2n -1}In the output light from
Heart wavelength λ_2n-1And the light source 11_2nCenter wavelength λ of output light from
_2nDifference (λ_2n−λ_2n-1) Is less than 6 nm (n =
1, 2, 3). The light source 11_2nOutput light center wave
Long λ_2nAnd the light source 11_{2n + 1}Center wavelength λ of output light from_{2n +1}
Difference (λ_{2n + 1}−λ_2n) May be 6 nm or more
(N = 1, 2). For example, the light source 11₁In the output light from
Heart wavelength λ₁Is 1430 nm and the light source 11_TwoOutput from
Center wavelength of light λ_TwoIs 1433 nm and the light source 11_ThreeFrom
Output light center wavelength λ_ThreeIs 1450 nm and light source 1
1_FourCenter wavelength λ of output light from_FourIs 1453 nm,
Light source 11_FiveCenter wavelength λ of output light from_FiveIs 1465nm
Yes, and light source 11₆Center wavelength λ of output light from₆Is 1
468 nm.

The wavelength multiplexing device 12, a light having a central wavelength lambda ₁ to [lambda] ₆ outputted from the light source 11 ₁ to 11 ₆ multiplexes, multiplexing module that this combined as excitation light for Raman amplification Output to 40. FIG. 5 is a diagram illustrating a spectrum of Raman amplification pump light output from the Raman amplification pump module 10 according to the present embodiment.

The optical isolator 20 transmits light arriving from the input end 1a toward the Raman amplification optical fiber 30, but does not transmit light in the reverse direction. The Raman amplification optical fiber 30 propagates the signal light input from the optical isolator 20 and also Raman amplifies the signal light by supplying the Raman amplification pump light from the multiplexing module 40. The multiplexing module 40 outputs the signal light output from the Raman amplification optical fiber 30 toward the output end 1b, and Raman amplifies the Raman amplification pump light output from the Raman amplification pump module 10. And output to the optical fiber 30 for use.

[0018] In the Raman amplifier 1 and Raman amplification pumping module 10, light having a center wavelength lambda ₁ to [lambda] ₆ outputted from the light source 11 ₁ to 11 ₆ are multiplexed by the wavelength multiplexing device 12 excitation for Raman amplification The Raman amplification pumping light is supplied to the Raman amplification optical fiber 30 via the multiplexing module 40. The multi-wavelength signal light of the 1.55 μm band input to the input terminal 1a is
After passing through 0, the light propagates through the Raman amplification optical fiber 30 and is subjected to Raman amplification during this propagation. The Raman-amplified multi-wavelength signal light passes through the multiplexing module 40 and is output from the output terminal 1b.

In this embodiment, the difference between the center wavelengths λ _2n-1 and λ _2n of the output light from the light sources 11 _2n-1 and 11 _2n (λ _2n −
λ _2n-1 ) is less than 6 nm (n = 1, 2, 3). Thus, for example, when the center wavelength of the output light of the six light sources 11 ₁ to 11 ₆ is the light source 11 ₁ fails is lambda _1, the difference in central wavelength of the output light and lambda ₂ (lambda ₁ 6 nm by increasing the light source 11 _{and second} output power is less), the variation in the gain of Raman amplification of the signal light in the Raman amplification optical fiber 30 can be suppressed to 0.2dB or less, the transmission quality of signal light Deterioration can be suppressed.

FIG. 6 shows the Raman amplification excitation according to this embodiment.
It is a figure which shows the 1st modification of a starting module. This Raman
The amplification excitation module 10A includes eight light sources 11₁₁, 1
1₁₂, 11_{twenty one}, 11_{twenty two}, 11_Three~ 11₆, Polarization combiner 13
₁, 13_Two, And a wavelength synthesizer 12. Light source 11₁₁You
And 11₁₂Are the same center wavelength λ₁(For example, 1430n
m) and outputs linearly polarized light.
You. Polarization synthesizer 13₁Is the light source 11₁₁, 11₁₂Output from
Center wavelength λ₁Is polarized and combined to produce a wavelength combiner 12.
Output to Light source 11_{twenty one}And 11_{twenty two}Is the same center wave
Long λ_Two(For example, 1433 nm) and linearly polarized light.
It is to output things. Polarization synthesizer 13_TwoIs the light source
11_{twenty one}, 11_{twenty two}Center wavelength λ output from_TwoPolarized light
The signals are synthesized and output to the wavelength synthesizer 12. Wavelength synthesizer 12
Is a polarization synthesizer 13₁, 13_TwoCenter wavelength λ output from
₁, Λ_TwoLight and light source 11_Three~ 11₆Output from
Center wavelength λ_Three~ Λ₆And multiplex the light
The excitation light is used for Raman amplification. Polarization synthesis in this way
The center wavelength included in the pump light for Raman amplification
λ ₁, Λ_TwoLight power can be increased.

FIG. 7 is a diagram showing a second modification of the Raman amplification excitation module according to the present embodiment. This Raman amplification excitation module 10B is a depolarizer 14 in addition to the Raman amplification excitation module 10 shown in FIG.
Is provided. The depolarizer 14 sets the Raman amplification pumping light output from the wavelength synthesizer 12 in a non-polarized state, and supplies this to the Raman amplification optical fiber 30 via the multiplexing module 40. By providing the depolarizer 14 in this manner, a stable Raman amplification operation can be obtained. The depolarizer may be provided between each light source 11 and the wavelength combiner 12. In this case, one depolarizer may be provided for one light source 11, or one depolarizer may be provided after multiplexing the lights output from the plurality of light sources 11.

FIG. 8 is a diagram showing a third modification of the Raman amplification excitation module according to the present embodiment. This Raman amplification pumping module 10C is such that the wavelength synthesizer 12 in the Raman amplification pumping module 10 shown in FIG. 4 is a polarization maintaining type. The semiconductor laser light source suitably used as the light source 11 outputs linearly polarized light. Therefore, the polarization maintaining wavelength synthesizer 12 includes the light sources 11 ₁ and 11 _2.
The lights having the center wavelengths λ ₁ and λ ₂ (the difference between the two is less than 6 nm) output from the light sources are input and multiplexed as orthogonal polarization states, and the center wavelengths λ ₃ output from the light sources 11 ₃ and 11 ₄ are combined. , Λ ₄
Multiplexes enter the light as polarization states orthogonal to each other (the difference therebetween is less than 6nm), The light source 11 _5, 11 central wavelength lambda ₅ to be outputted from the _6, lambda ₆ (difference between the two 6nm Less than)
Are input as orthogonal polarization states and multiplexed. By doing so, a stable Raman amplification operation can be obtained.

FIG. 9 is a configuration diagram of the optical communication system 100 according to the present embodiment. This optical communication system 100
Relay stations 131 and 1 between transmitting station 110 and receiving station 120
32, an optical fiber transmission line 141 is laid between the transmitting station 110 and the relay station 131, and the relay station 13
An optical fiber transmission line 142 is laid between the relay station 132 and the relay station 132, and an optical fiber transmission line 143 is laid between the relay station 132 and the receiving station 120. The relay stations 131 and 132 are provided with the above-described Raman amplifier 1 according to the present embodiment.

In the optical communication system 100, the transmitting station 1
The multi-wavelength signal light transmitted from the optical fiber 10 propagates through the optical fiber transmission line 141 and the Raman amplifier 1 in the relay station 131.
, Propagates through the optical fiber transmission line 142, is Raman amplified by the Raman amplifier 1 in the relay station 132, further propagates through the optical fiber transmission line 143, reaches the receiving station 120, and In, the signal light of each wavelength is demultiplexed and received. This optical communication system 10
0, the signal light is Raman-amplified by the Raman amplifier 1 according to the above-described embodiment, so that if any one of the plurality of light sources included in the Raman amplifier 1 fails, the failed light source 6n difference in center wavelength of output light
By increasing the output power of the other light source less than m, the variation in the gain of the Raman amplification of the signal light in the Raman amplification device 1 can be suppressed to 0.2 dB or less, and the transmission quality of the signal light deteriorates. Can be suppressed.

It is to be noted that the Raman amplifier 1 is not provided in the repeaters 141 and 142, but the Raman amplification excitation module 10 according to the present embodiment is provided in the repeaters 141 and 142, and the Raman amplifiers in the repeaters 141 and 142 are provided. The Raman amplification pump light output from the amplification pump module 10 may be supplied to the optical fiber transmission lines 141 and 142. In this case, the optical fiber transmission lines 141 and 142 are used as Raman amplification optical fibers.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, the number of central wavelengths of light that is multiplexed and output from the Raman amplification pumping module may be more than six.

[0027]

As described above in detail, according to the present invention, lights having different center wavelengths output from a plurality of light sources are multiplexed by multiplexing means and supplied to the optical waveguide as excitation light. You. Then, the signal light propagating through the optical waveguide is Raman-amplified in the optical waveguide. In particular, in the present invention, since the difference between the center wavelengths of two lights output from any two of the plurality of light sources is less than 6 nm, when one of the two light sources fails, By increasing the output power of the other light source, fluctuations in the gain of the Raman amplification of the signal light in the optical fiber for Raman amplification can be suppressed to be small, and deterioration in the transmission quality of the signal light in the optical communication system can be suppressed. Can be.

The pumping light generating means outputs 2N (N is an integer of 1 or more) lights having different center wavelengths, and among the 2N lights, the (2n-1) th light and the (2n) th light (n
It is preferable that the difference between the central wavelengths of the respective lights is less than 6 nm. In this case, even if any of the 2N light sources fails, By increasing the output power of another light source having a difference of the center wavelength of the output light from the failed light source of less than 6 nm, it is possible to reduce the fluctuation of the gain of the Raman amplification of the signal light in the Raman amplification device. As a result, it is possible to suppress deterioration of signal light transmission quality in the optical communication system.

In the case where the pumping light generating means polarization-combines and outputs any one of the plurality of lights, the power of the pumping light for Raman amplification can be increased. Also,
When further provided with a depolarizer that sets the excitation light to a non-polarized state, or when the multiplexing unit multiplexes two lights having a center wavelength difference of less than 6 nm by inputting them as mutually orthogonal polarized states, A stable Raman amplification operation can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a Raman gain spectrum in a dispersion-shifted optical fiber.

FIG. 2 is a diagram illustrating a Raman gain spectrum when two lights having different center wavelengths are combined to generate Raman amplification pump light and a Raman gain when only one of the lights is used as Raman amplification pump light. It is a figure which shows the difference with a spectrum.

FIG. 3 is a configuration diagram of a Raman amplifier according to the present embodiment.

FIG. 4 is a configuration diagram of a Raman amplification excitation module according to the present embodiment.

FIG. 5 is a diagram illustrating a spectrum of Raman amplification pump light output from the Raman amplification pump module according to the present embodiment.

FIG. 6 is a diagram showing a first modified example of the Raman amplification excitation module according to the present embodiment.

FIG. 7 is a diagram showing a second modified example of the Raman amplification excitation module according to the present embodiment.

FIG. 8 is a diagram showing a third modification of the Raman amplification excitation module according to the embodiment.

FIG. 9 is a configuration diagram of an optical communication system according to the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Raman amplifier, 1a ... input terminal, 1b ... output terminal, 10
... Raman amplification pump module, 11 ... Light source, 12 ... Wavelength combiner, 13 ... Polarization combiner, 14 ... Depolarizer, 2
0 ... optical isolator, 30 ... optical fiber for Raman amplification,
40: multiplexing module, 100: optical communication system, 11
0: transmitting station, 120: receiving station, 131, 132: relay station, 141 to 143: optical fiber transmission line.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masayuki Nishimura 1-chome Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa F-term (reference) in Yokohama Works, Sumitomo Electric Industries, Ltd. 2K002 AA02 AB30 BA01 DA10 GA05 HA23 5F072 AK06 JJ05 JJ09 PP07 QQ07 YY17 5K002 AA06 BA05 BA13 CA13 EA03 FA01

Claims (7)

[Claims] 1. A pumping module for Raman amplification for outputting pumping light for Raman-amplifying signal light propagating through an optical waveguide, comprising: a plurality of light sources for outputting light having different center wavelengths. And multiplexing means for multiplexing a plurality of lights output from the excitation light generating means and outputting the multiplexed light as the excitation light, wherein two lights output from any two light sources among the plurality of light sources A Raman amplification excitation module, wherein the difference of the center wavelengths is less than 6 nm. 2. The pumping light generating means outputs 2N (N is an integer of 1 or more) lights having different center wavelengths, wherein 2n-1st light and 2n-th light (n The difference between the center wavelengths of the respective lights is less than 6 nm.
The excitation module for Raman amplification according to the above. 3. The Raman amplification pumping module according to claim 1, wherein said pumping light generating means polarization-combines and outputs any one of the plurality of lights. 4. The pump module for Raman amplification according to claim 1, further comprising a depolarizer for setting the pump light to a non-polarized state. 5. The Raman amplifying device according to claim 1, wherein said multiplexing means inputs and multiplexes the two lights having a center wavelength difference of less than 6 nm as polarization states orthogonal to each other. Excitation module. 6. The pump for Raman amplification according to claim 1, wherein the optical waveguide propagates the signal light and Raman-amplifies the signal light by supplying the pump light, and supplies the pump light to the optical waveguide. A Raman amplifier comprising a module. 7. An optical communication system for performing optical communication by propagating signal light, comprising: the Raman amplifier according to claim 6 for Raman-amplifying the signal light.