JP2002305342A - Exciting light source for raman amplifier and raman amplifier using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Raman amplifier having an arbitrary wavelength characteristic superior in flatness and an arbitrary amplification gain only by independently changing the light intensity of a short wavelength side group and the light intensity of a long wavelength side group. SOLUTION: In an exciting light source for Raman amplification, a plurality of exciting light beams for Raman-amplifying signal light inputted to a light transmission line in the light transmission line are outputted. The exciting light source for Raman amplification is divided into the light source of a shot wavelength side and the light source of a long wavelength side, whose oscillation wavelengths differ. They synthesize and output a plurality of oscillation light beams outputted from the light source of the short wavelength side and the oscillation light of the long wavelength side, collectively control a plurality of oscillation light beams outputted from the light source of the short wavelength side or oscillation light outputted from the light source of the long wavelength side, and adjust output light intensity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pumping light source for Raman amplification for amplifying signal light in an optical transmission line such as an optical fiber by utilizing a stimulated Raman scattering phenomenon, and a Raman amplifier using the same.

[0002]

2. Description of the Related Art Generally, in a Raman amplification system, as shown in FIG. 9, when an optical signal 2 output from an optical transmitting station 1 is guided to an optical receiving station 4 via an optical transmission line 3 such as an optical fiber. An optical amplifying device 5 is arranged between the optical transmission lines 3 or at an end thereof so that the optical signal 2 attenuated in the optical transmission line 3 has an optical signal level required for reception by the optical receiving station 4. It is configured to optically amplify a signal. This configuration example shows an example of a backward-pumped Raman amplification system in which the optical amplifier 5 is disposed at the rear end of the optical transmission line 3. Of course, the optical amplifier 5 is provided at the front end or both ends of the optical transmission line 3. Sometimes (may be).

[0003] The optical transmitting station 1 converts electrical information to be transmitted into light and outputs it to the optical transmission line 3. The electric signal is converted to an optical signal by directly applying the electric signal to a semiconductor laser device or the like serving as a signal light source, or by modulating the light oscillated from the signal light source through an external modulator after the signal light source. 3 is output.

[0004] The optical receiving station 4 converts the optical signal 2 propagating through the optical transmission line 3 into an electrical signal using a photoelectric converter such as a photodiode, and demodulates information transmitted from the optical transmitting station 1. Read information.

[0005] As shown in FIG.
Oscillation light from the excitation light source 7 is input into the Raman amplification medium 31 via the optical coupler 6 from the end of the Raman amplification medium 31 which is a part of the optical transmission line 3, and Raman scattering is generated in the Raman amplification medium 31. The optical signal 2 is generated and Raman-amplified. The wavelength of the oscillation light is usually selected to be shorter by about 20 to 200 nm than the wavelength of the optical signal 2 emitted from the optical transmitting station 1.

The Raman gain due to the Raman amplification in the Raman amplification medium 31 can perform a wide range of optical amplification, but cannot amplify a wide signal band uniformly, and the amplification gain has a wavelength characteristic. I have. Therefore, in order to uniformly Raman-amplify a wide signal band, the intensity of oscillation light is adjusted using a plurality of pump light sources having different wavelengths so that the gain is uniform in the signal light band.

As described above, the amplification gain characteristics of the optical signal can be adjusted so as to have a constant gain over the entire signal band by adjusting each of the plurality of pumping lights. Conventionally, when changing the gain to another value, the light intensity of the oscillating light output from each light source is individually adjusted again for all the light sources.

[0008]

However, as described above, in the method of adjusting the intensity of the oscillating light of a plurality of light sources, the gain of a specific signal band is adjusted even if one of the plurality of light sources is adjusted. However, the gain of a wider signal band including the specific signal band also changed, and it was not easy to adjust the gain to a desired value.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to achieve a desired gain with a small adjustment.

The inventor has proposed that the oscillation wavelength λ1 = 1423.516 nm,
λ2 = 1430.990 nm, λ3 = 1438.543 nm, λ4 = 1460.265
nm semiconductor LD, and the respective excitation intensities were 248.0, 170.0, 128.0, 264.5 mW as shown in (1) of Table 1.
As a result of the adjustment so as to be as shown in FIG.
A flat gain of 25 dB was obtained within the signal band of 530-1560 nm.

After that, as shown in Tables (2) to (5), all the pumping intensities were reduced to 80%, 60%, 40%, and 20%, respectively, and the gain of the signal band was measured. 7 were obtained as indicated by solid lines in FIG. Although these solid lines maintain flatness to the extent that there is a gain in the signal band,
The gain on the long wavelength side changes a little more than the gain on the short wavelength side, and has a downward-sloping gain.

[0012]

[Table 1]

Further, while maintaining the excitation intensity of the semiconductor LD of 1460.265 nm at 100%, the wavelengths of 1423.516 nm and 143
The excitation light intensities of the three semiconductor LDs of 0.990 nm and 1438.543 nm were set to 80%, 60%, and 40%, respectively, as shown in (6) to (9) of Table 2.
When the gain of the signal band was measured by reducing the gain to 20%, the values as shown by the solid lines in (6) to (9) of FIG. 6 were obtained. This solid line indicates that the gain on the short wavelength side of the signal band changes greatly with respect to the gain on the long wavelength side, and that the flatness of the gain is good.

[0014]

[Table 2]

Further, the present inventor has shown the oscillation intensity of the 1460.265 nm semiconductor LD arranged on the long wavelength side while maintaining the oscillation intensity of the three semiconductor LDs arranged on the short wavelength side at 100%. As shown in 2 (10) to (13), 80
When the gain of the signal band was measured by reducing the gain to%, 60%, 40%, and 20%, values as indicated by the dotted lines in (10) to (13) of FIG. 6 were obtained. This dotted line indicates that the gain on the short wavelength side of the signal band changes slightly with respect to the gain on the long wavelength side, and that the gain has good flatness.

Thus, the present inventor has found that when the pumping wavelength optimized so that the gain characteristic becomes flat in a certain signal band is divided into a short wavelength side group A and a long wavelength side group B. The following findings were obtained.

(A) If the pump powers of the A group and the B group are respectively reduced at the same rate, the Raman gain decreases with a right-down tilt. (B) The pump power of the A group is maintained at 100%. If the pumping power of group B is reduced at the same rate in the state where the pumping is performed, the Raman gain characteristic decreases with a right-down tilt. (C) The pumping of group A while the pumping power of group B is maintained at 100%. If all the powers are reduced at the same rate, the Raman gain will decrease with a downward tilt.

Although not shown, the group A and the group B
When the pumping power of the group is increased, (D) If the pumping power of the group A and the pumping power of the group B are respectively increased at the same rate, the Raman gain rises with a right-up tilt. (E) The pumping of the group A 100% power
When the pump power of group B is increased at the same rate while holding at the same value, the Raman gain characteristic rises with a tilt that rises to the right.
If the pumping power of group A is increased at the same rate while maintaining the percentage, the Raman gain rises with a tilt rising to the left.

When optical fibers having different amplification factors are used as shown in (14) to (18) of Table 3, even if the same pumping power is used, gain characteristics having different characteristics are obtained as shown in FIG. can get. That is, (G) when an optical fiber having a large Raman gain coefficient is used, the Raman gain characteristic increases in level with a right-up tilt,
(H) When an optical fiber having a small Raman gain coefficient is used, the level of the Raman gain characteristic decreases with a right-down tilt.

[0020]

[Table 3]

Thus, it has been found that by combining the techniques (A) to (H), a gain flatness can be maintained to some extent, and a Raman amplifier having an arbitrary gain level and tilt can be easily designed. .

The present invention has been made in view of the above point, and the excitation wavelength is divided into two, a short wavelength side and a long wavelength side.
By adjusting each of them arbitrarily, one having an arbitrary gain characteristic is obtained.

According to a first aspect of the present invention, there is provided a pumping light source for Raman amplification for outputting a plurality of pumping lights for Raman-amplifying signal light incident on the optical transmission line in the optical transmission line, wherein the pumping light source for Raman amplification is: Oscillation wavelengths are divided into different short-wavelength light sources and long-wavelength light sources, and a plurality of oscillation lights output from the short-wavelength light sources and long-wavelength oscillation lights are combined and output. A plurality of oscillating lights output from a light source on the short wavelength side or oscillating lights output from a light source on the long wavelength side are collectively controlled to adjust the output light intensity.

According to a second aspect of the present invention, in the first aspect, the driving currents of the plurality of light sources divided on the short wavelength side are collectively controlled to adjust the output light intensity on the short wavelength side. And

According to a third aspect of the present invention, in the first aspect, after the lights oscillated from the plurality of light sources split on the short wavelength side are combined, the lights are collectively controlled by an optical attenuator to output light on the short wavelength side. The strength is adjusted.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the intensity of the oscillation light on the short wavelength side and the intensity of the oscillation light on the long wavelength side are simultaneously adjusted. .

According to a fifth aspect of the present invention, in the fourth aspect, the intensity of the oscillation light on the short wavelength side and the intensity of the oscillation light on the long wavelength side are set to one.
It is characterized by being changed at a ratio of 0.81.

According to a sixth aspect of the present invention, in the fourth aspect, the intensity of the oscillation light on the short wavelength side and the intensity of the oscillation light on the long wavelength side are set to one.
It is characterized by changing at a ratio of 1.40.

According to a seventh aspect of the present invention, in the fourth aspect, the intensity of the oscillation light on the short wavelength side and the intensity of the oscillation light on the long wavelength side are set to one.
It is characterized by being changed at a ratio of 1.92.

An eighth aspect of the present invention provides an optical transmitting station that emits a signal light, an optical receiving station that receives the signal light, an optical transmission line that propagates the signal light from the optical transmitting station to the optical receiving station, A Raman amplifier comprising: a Raman amplification pumping light source for introducing pumping light into a transmission line to cause Raman scattering in the optical transmission line to Raman-amplify the signal light; -7.

[0031]

FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, reference numerals 31, 6, and 7 denote a Raman amplification medium such as a quartz optical fiber, an optical coupler for coupling pump light and signal light so as to be integrated in the Raman amplification medium, respectively, as in FIG. And a Raman amplification excitation light source.
Further, 71 · 71 is a semiconductor laser device having an oscillation wavelength of 1423.516 nm, 72 is a semiconductor laser device having an oscillation wavelength of 1430.990 nm,
73 is a semiconductor laser device having an oscillation wavelength of 1438.543 nm;
Reference numeral 74 denotes a semiconductor laser device having an oscillation wavelength of 1460.265 nm.
Numerals 75 and 76 denote polarization combiners, 77, 78 and 79 denote wavelength optical multiplexers for coupling two lights, respectively.
0 is an optical isolator. 81 is a semiconductor laser element 7
This is a current controller capable of supplying a drive current to each of the elements 1 to 74 and controlling the current value.

The light from the semiconductor laser elements 71 is combined in a polarization combiner 75 such that the respective polarization planes are different from each other by 90 degrees and output. Similarly, the light from the semiconductor laser elements 74 and 74 is combined and outputted in the polarization combiner 76 so that the polarization planes thereof are different from each other by 90 degrees. The semiconductor laser element 71 synthesized by the polarization synthesizer 75
The light from 71 and the light from the semiconductor laser element 72 are combined by a wavelength optical multiplexer 77. The light from the semiconductor laser elements 74 and 74 and the light from the semiconductor laser element 73 combined by the polarization combiner 76 are combined by a wavelength optical multiplexer 78. The respective lights output from the wavelength optical multiplexers 77 and 78 are combined by the wavelength optical multiplexer 79, and guided to the Raman amplification medium 31 through the isolator 80 and the optical coupler 6.

The Raman amplifying medium 31 has 44 pseudo input signals within a wavelength of 1527.994 to 1562.233 nm, which are almost uniformly dispersed, and is introduced from the input terminal with a magnitude of about -15 dBm / ch. The semiconductor laser elements 71 and the semiconductor laser elements 74 and 74 are adjusted by the current controller 81 so that the light intensity oscillated from each element becomes the same.

In the above state, each of the semiconductor laser elements 71 to 74
Was adjusted by the current controller 81, an optical spectrum analyzer (not shown) was attached to the output terminal, and the current was adjusted so that the amplification was about 25 dB and the gain was flat over the entire signal wavelength band. At this time, the light intensities of the semiconductor laser elements 71 to 74 were 248, 170, 128, and 264.5 mW, respectively, as shown in Table 4 (the light intensity output from the single semiconductor laser elements 71 and 74 was 1 / 2). The amplification value at this time is in the range of 24.74 to 25.30 dB, and is almost flat as shown in FIG. In the present invention, for convenience, this value is referred to as excitation power 1
Defined as 00%.

[0035]

[Table 4]

Next, the semiconductor laser device 71
As shown in Table 4, the short-wavelength side semiconductor laser elements 71 to 73 are collectively controlled by the current controller 81 to increase the light intensity to a light intensity of 140%.
The light intensity from the semiconductor laser element 74 was increased to 113%. The semiconductor laser elements 71 to 7 at that time
The light intensity of No. 4 was 384.6, 238, 179.2, and 343.85 mW, respectively (the light intensity output from the single semiconductor laser elements 71 and 74 was 1/2). The amplification value at this time is 30.01
And is within a range of 30.77 dB, and is almost flat as shown in FIG.

Next, similarly, the semiconductor laser device 71
As shown in Table 4, the semiconductor laser devices 71 to 73 on the short wavelength side are collectively controlled by the current controller 81 to reduce the light intensity to 60%. The strength was reduced to 84%. At this time, the light intensity of the semiconductor laser elements 71 to 74 is 14
9.4, 102, 76.8, 211.6 mW (the light intensity output from the single semiconductor laser elements 71 and 74 is 1 /
2). The amplification value at this time is in the range of 17.36 to 17.76 dB, and is almost flat as shown in FIG.

Next, the semiconductor laser device 71
As shown in Table 4, the semiconductor laser devices 71 to 73 on the short wavelength side are collectively controlled by the current controller 81 to reduce the light intensity to 31.2%. Was reduced to 60%. The light intensity of the semiconductor laser devices 71 to 74 at that time was 77.688, 53.04, 39.936, and 158.7 mW, respectively (the light intensity output from the single semiconductor laser devices 71 and 74 was 1/2). At this time, the amplification value is in the range of 10.44 to 10.73 dB, and is almost flat as shown in FIG.

Table 5 shows that the driving current on the short wavelength band side and the driving current on the long wavelength side are collectively controlled, and the light intensity from each semiconductor laser device is further changed to a value other than the above four examples. The light intensity when a substantially flat gain is obtained over a range of 100% is shown by the ratio based on the above 100%. FIG. 3 is a graph showing the measured values. The change rate of the semiconductor laser elements 71 to 73 with respect to the change rate of the semiconductor laser element 74 is plotted on the vertical axis (Y axis), and the gain characteristic is plotted on the horizontal axis (X axis). ). This graph was in excellent agreement with the curve of Y = 0.0006X ² + 0.0129X + 0.3202.

[0040]

[Table 5]

Therefore, when trying to obtain an arbitrary Raman amplification gain α using the optical component according to the present embodiment, the above X
Only by adjusting the light intensity of both wavelengths while setting the light intensity ratio of the short wavelength side group to the long wavelength side light intensity so that it becomes the same as the Y value obtained by substituting α into the value of Thus, an arbitrary flat gain characteristic can be obtained.

FIG. 4 is a block diagram showing another embodiment of the present invention. In FIG. 4, 82 and 83 are optical attenuators,
A controller 84 controls the amount of attenuation. Other components are the same as those in FIG.

The light from the semiconductor laser elements 71 is combined in a polarization combiner 75 such that the respective polarization planes are different from each other by 90 degrees and output. Similarly, the light from the semiconductor laser elements 74 and 74 is also combined and output in the polarization combiner 76 such that the polarization planes thereof are different from each other by 90 degrees. The semiconductor laser element 71 synthesized by the polarization synthesizer 75
The light from 71 and the light from the semiconductor laser element 72 are combined by the wavelength multiplexer 77. The light from the semiconductor laser elements 71, 72 and 72 and the light from the semiconductor laser element 73 synthesized by the wavelength multiplexer 77 are combined with the wavelength multiplexer 78.
Are synthesized by Wavelength multiplexer 78 and polarization combiner 76
Are attenuated by optical attenuators 82 and 83, respectively, and then combined by a wavelength multiplexer 79.
The light is guided to the optical coupler 6 via the isolator 80 and to the Raman amplification medium 31.

The effect obtained in the above state is the same as that of the embodiment shown in FIG.

In the above embodiment, the case where the number of light sources on the short wavelength side is three and the case where the number of light sources on the long wavelength side is one has been described. However, the present invention can be applied even when each light source is other than this. it can. However, a plurality of light sources on the short wavelength side are required.

In the above embodiment, the case where a flat gain distribution is obtained has been described. However, by adjusting the rate of increase / decrease of the drive current of the semiconductor laser device on the short wavelength side and the drive current on the long wavelength side, an arbitrary gain profile can be obtained. It is also possible to have a slope.

[0047]

According to the present invention, as described above, only the light intensity of the short-wavelength side group and the light intensity of the long-wavelength side group are changed independently, and any wavelength characteristic and any amplification gain excellent in flatness can be obtained. There is an excellent effect that a Raman amplifier having

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a Raman gain profile in an example of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a pump power change rate on a short wavelength side and a Raman gain with respect to a change rate of pump power on a long wavelength side.

FIG. 4 is a configuration diagram showing another embodiment of the present invention.

FIG. 5 is a characteristic diagram showing a relationship between a signal wavelength and a Raman amplification gain when a Raman gain coefficient of an optical fiber changes.

FIG. 6 is a characteristic diagram showing a relationship between a signal wavelength and a Raman amplification gain when a pump power supplied to an optical fiber changes.

FIG. 7 is a characteristic diagram showing a relationship between a signal wavelength and a Raman amplification gain depending on a difference in pump power supplied to an optical fiber.

FIG. 8 is a configuration diagram illustrating a general Raman amplifier.

FIG. 9 is a configuration diagram showing a general backward-pumped Raman amplification system.

[Explanation of symbols]

 1: Optical transmitting station 2: Optical signal 3: Optical transmission line 31: Raman amplification medium 4: Optical receiving station 5: Optical amplifier 6: Optical coupler 7: Pump light source 71: Semiconductor laser device with oscillation wavelength of 1423.516 nm 72: Oscillation Semiconductor laser device having a wavelength of 1430.990 nm 73: Semiconductor laser device having an oscillation wavelength of 1438.543 nm 74: Semiconductor laser device having an oscillation wavelength of 1460.265 nm 75, 76: Polarization combiner 77, 78, 79: Wavelength optical multiplexer 80: Optical isolator 81 : Current controller 82, 83: Optical attenuator 84: Optical attenuator controller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2K002 AA02 AB30 BA01 CA15 DA10 GA10 HA24 5F072 AB07 AK06 HH04 HH05 JJ20 MM01 MM07 PP07 QQ07 YY17 5K002 AA06 BA02 BA04 BA05 BA13 CA13 FA01

Claims (8)

[Claims] 1. A Raman amplification pumping light source for outputting a plurality of pumping lights for Raman-amplifying signal light input into an optical transmission line in the optical transmission line, wherein the Raman amplification pumping light sources have oscillation wavelengths mutually. It is divided into two light sources, one on the short wavelength side and the other on the long wavelength side, and combines and outputs a plurality of oscillating lights output from the short wavelength light source and the oscillating light on the long wavelength side. Collectively controlling a plurality of oscillating lights output from a light source or an oscillating light output from a long wavelength side light source,
A pump light source for Raman amplification, wherein the output light intensity is adjusted. 2. The Raman amplification device according to claim 1, wherein the driving currents of the plurality of light sources divided on the short wavelength side are collectively controlled to adjust the output light intensity on the short wavelength side. Excitation light source. 3. After synthesizing light oscillated from a plurality of light sources split on the short wavelength side, collectively controlling the light by an optical attenuator,
2. The pump light source for Raman amplification according to claim 1, wherein the output light intensity on the short wavelength side is adjusted. 4. The pump for Raman amplification according to claim 1, wherein the intensity of the oscillation light on the short wavelength side and the intensity of the oscillation light on the long wavelength side are simultaneously adjusted. light source. 5. The pump light source for Raman amplification according to claim 4, wherein the intensity of the oscillation light on the short wavelength side and the intensity of the oscillation light on the long wavelength side are changed at a ratio of 1: 0.81. 6. The Raman amplification pump light source according to claim 4, wherein the intensity of the oscillation light on the short wavelength side and the intensity of the oscillation light on the long wavelength side are changed at a ratio of 1: 1.40. 7. The pump light source for Raman amplification according to claim 4, wherein the intensity of the oscillation light on the short wavelength side and the intensity of the oscillation light on the long wavelength side are changed at a ratio of 1: 1.2. 8. An optical transmitting station that emits a signal light, an optical receiving station that receives the signal light, an optical transmission line that propagates the signal light from the optical transmitting station to the optical receiving station, and a pump in the optical transmission line. A Raman amplification pumping light source comprising: a Raman amplification pumping light source that introduces light to cause Raman scattering in an optical transmission line to Raman-amplify the signal light;
A Raman amplifier comprising any one of the above items 7 to 7.