JP2004104473A - Optical amplification repeater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distributed constant-type optical amplification repeater suppressing deterioration of transmission quality by an increase of loss due to a physical fault such as optical fiber cable disconnection. <P>SOLUTION: The optical amplification repeater of a double line bidirectional optical transmission system is provided with a first excitation light source outputting first excitation light corresponding to first signal light, a second excitation light source outputting second excitation light corresponding to second signal light, a control means controlling output intensity of the first and second excitation light sources, a light synthesizing/branching means outputting first light signal excitation light obtained by synthesizing/branching first excitation light and second excitation light at a branching ratio a:b (a>b) and second light signal excitation light obtained by synthesizing/branching them at the branching ratio b:a, a first optical amplification means amplifying signal light in a first direction based on first light signal excitation light and a second optical amplification means amplifying signal light in a second direction based on second light signal excitation light. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical amplification repeater to which a distributed constant type optical amplification technique using an optical fiber as a transmission line and an amplification medium is applied.
[0002]
[Prior art]
In a conventional optical communication system, an amplifier using an erbium-doped optical fiber (hereinafter, referred to as “EDF”: Erbium Doped Fiber) has been generally adopted. This EDF amplifier repeater has an amplification band characteristic of 40 nm of 1530 to 1570 nm which is called C band, but the optical fiber is lengthened and the amplification band is shifted to a longer wavelength side, so that it is called 1570 to 1610 nm which is called L band. Even when a long-wavelength EDF amplifier repeater having an amplification characteristic of 40 nm is used together, the amplification bandwidth is limited to 80 nm, which is a major factor that limits the expansion of the transmission capacity of the optical communication system.
[0003]
Also, when the C-band and L-band EDF amplifying repeaters are used together, an optical coupler for multiplexing / demultiplexing different wavelength bands is required. However, the loss of the multiplexing optical coupler is caused by the input signal level to the repeater. And the noise figure is equivalently degraded. In an optical communication system having a relatively short relay distance such as a terrestrial system, the influence of noise figure degradation is small. However, in an optical communication system having a very long relay distance (for example, transoceanic distance) such as an optical submarine cable system, noise is reduced. Due to the deterioration of the signal-to-noise ratio (hereinafter referred to as “SNR”) due to the exponential deterioration, the communication quality may be significantly reduced and the communication may be disabled.
[0004]
As a method for solving such a problem, development of a Raman amplifier using stimulated Raman scattering phenomenon, which is a nonlinear effect of an optical fiber, has been actively performed in recent years. Raman amplification is a phenomenon in which light amplification is possible by using light having a short wavelength of about 100 nm and high light intensity with respect to the wavelength of signal light as excitation light.
[0005]
In this Raman amplification, signal light of an arbitrary wavelength can be selectively amplified by setting the pumping light wavelength, and it is easy to broaden the signal wavelength. In addition, since the Raman amplifier can use the optical fiber itself, which is the transmission line, as an amplifying medium, it can amplify in a distributed manner in the longitudinal direction, and can reduce the SNR degradation as compared with a lumped EDF amplifier repeater. It also has the advantage of suppressing power and enabling long-distance transmission.
[0006]
Therefore, there is a great advantage in applying the Raman amplifier as a repeater in an optical submarine cable system in which the characteristics of the transmission line fiber are stable, as compared with a terrestrial system in which the dispersion of the transmission characteristics of the optical fiber is relatively large.
[0007]
On the other hand, in an optical submarine cable system, a repeater or an optical fiber cable laid on the sea floor cannot be easily repaired, so that the repeater is required to have a reduced number of parts and high reliability.
[0008]
FIG. 4 is a configuration diagram of a conventional optical amplifying repeater for an optical submarine cable system (for example, see Patent Document 1).
In FIG. 4, 11a and 11b are EDFs, 2a and 2b are pump light sources, 5a and 5b are WDM couplers for multiplexing pump light and signal light, 7 is a control circuit for the pump light sources 2a and 2b, and 9 is a control circuit 7. A power supply circuit for supplying electric power, 6a and 6b are isolators, 12a and 12b are optical filters, 8 is a power supply line, and 10 is an output light P2a and P2b of two excitation light sources 2a and 2b, which are multiplexed / demultiplexed and equalized. Or an optical multiplexer / demultiplexer that excites the first and second EDFs 11a and 11b with two pumping lights P10a and P10b that are demultiplexed at different rates.
[0009]
When a rare earth-doped optical fiber typified by the EDFs 11a and 11b is used as an amplifying medium, when the pumping light is not supplied, the EDF becomes an optical signal absorbing medium and the signal light is interrupted. Is adopted, the intensity of the pump light P10a, P10b does not become zero at the same time even if one of the pump light sources 2a, 2b fails. As a result, the gain of the EDF is reduced, but it is possible to avoid the occurrence of a normal and fatal system failure of the optical signal.
[0010]
Further, by designing the control circuit 7 so that the output of the other pumping light source 2a or 2b can be increased when one of the pumping light sources 2a or 2b fails, the intensity of the pumping light P10a or P10b is set to be equal to that before the failure. It is also possible to set them at substantially the same level.
[0011]
Here, the second optical multiplexer / demultiplexer 10 has two input ports and two output ports, and an optical signal incident from one of the input ports is equally distributed to the two output ports. The above-mentioned conventional document suggests that the branching ratio of the optical signal of the second optical multiplexer / demultiplexer 10 is not limited to an equal value, and that the same effect can be obtained even with an arbitrary branching ratio.
Specifically, when the branching ratio of the second optical multiplexer / demultiplexer 10 is 40:60, for example, even if one of the pumping light sources 2a fails, the pumping light is reduced by only 60% compared to before the failure. As described above, the EDF does not serve as an optical signal absorbing medium as described above.
[0012]
However, when the branching ratio of the second optical multiplexer / demultiplexer 10 is 99: 1, if one of the pumping light sources 2a fails, the pumping light is reduced by only 1% as compared to before the failure, but P10b is the value before the failure. Is reduced by 99% as compared with the optical amplifier repeater of FIG. 5 having no redundant configuration, and the above-mentioned effect cannot be obtained. This indicates that the branching ratio of the second optical multiplexer / demultiplexer 10 is not arbitrarily set, but is limited to a branching ratio of 50:50 and its vicinity. This is apparent from the fact that the above-mentioned conventional document has a description "usually called" 3 dB coupler "".
[0013]
FIG. 6 is a characteristic diagram of the amplification gain of the EDF amplification repeater. The dependency of the gain of the EDF amplifier repeater on the input light intensity has a self-healing effect. The amplification gain is almost constant in a region where the input light intensity is small, but the gain is saturated as the input light intensity increases. Therefore, when the EDF amplification repeater is operated in the saturation region of the amplification gain, the change in the output light intensity is suppressed with respect to the change in the input light intensity, and the output light intensity can be stabilized. Therefore, fluctuations in transmission path loss of optical fiber cables and output fluctuations caused by an increase in loss that occurs when repairing optical fiber cables that have suffered a physical failure such as cable disconnection are suppressed, and the output of the repeater is kept constant. Quality can be stabilized.
[0014]
[Patent Document 1]
Patent No. 2669483 (paragraphs [0018] to [0024], FIG. 1)
[0015]
[Problems to be solved by the invention]
As described above, by applying the redundant configuration of the pump light source to the Raman amplifier, it is possible to suppress the performance deterioration due to the failure of the pump light source and to enhance the reliability of the optical communication system. However, when a distributed constant Raman amplifier using the transmission line optical fiber cable itself as an amplifying medium is applied as a repeater, the influence of a physical obstacle such as an optical fiber cable disconnection causes the following problems.
[0016]
FIG. 7 is a configuration diagram of a conventional Raman amplification repeater employing a redundant configuration. In FIG. 7, reference numerals 1a, 1b, 1c and 1d denote optical fiber cables used as transmission lines and Raman amplification media, 2a, 2b, 2c and 2d denote excitation light sources, 3a and 3b denote the excitation light sources 2a and 2b, and 2c and 2d, respectively. 5a, 5b are WDM couplers for multiplexing / demultiplexing signal light and Raman pumping light, 6a, 6b are optical isolators, and 7 is the pumping light sources 2a, 2b, 2c, 2d. , A power supply cable for supplying power to the control circuit 7 from the power supply line 8, and a power supply circuit 10 for multiplexing the pumping light P3a and P3b from the optical multiplexers 3a and 3b. , Optical multiplexing / demultiplexing that is equally split into a line pumping light P4a in a first direction (hereinafter referred to as “upward direction”) and a line pumping light P4b in a second direction (hereinafter “downward direction”). It is a vessel.
[0017]
When the intensity of the pumping light from the pumping light sources 2a, 2b, 2c, and 2d is 100 mW in the normal state, the pumping light P3a and P3b are each 200 mW by the optical multiplexer 3a. For the sake of simplicity, it is assumed in the following description that there is no loss in each optical component.
[0018]
The pump lights P3a and P3b are further multiplexed by the second optical multiplexer / demultiplexer 10, and then demultiplexed. As a result, the pumping lights P5a and P5b sent out to the upstream optical fiber cable 1a and the downstream optical fiber cable 1c are each 200 mW.
[0019]
Here, consider a case where a disconnection failure of the optical fiber cable has occurred.
In the Raman amplification repeater, the upstream optical fiber cable 1a on the input side and the downstream optical fiber cable 1d on the output side are housed in the same cable bundle. If a disconnection occurs immediately near the left splicer in the figure during Raman amplification, the input optical fiber 1a is disconnected in the upward direction, and the output optical fiber 1d is disconnected in the downward direction. Here, when the broken optical fiber cable is repaired, the loss increases, and only the signal light intensity decreases in the downward direction (optical fiber cable 1d), but the signal light intensity decreases in the upward direction (optical fiber cable 1a). At the same time as the decrease, the intensity of the excitation light decreases. As a result, the transmission quality of the signal in the upstream direction is significantly degraded as compared with the transmission quality in the downstream direction.
[0020]
On the other hand, by increasing the intensity of the pumping light from the pumping light sources 2a, 2b, 2c, and 2d, it is possible to recover the transmission quality degradation of the upstream signal. For example, when the generated loss is 3 dB, the intensity of the excitation light input to the optical fiber cable 1a can be returned to the same level as before the disconnection by doubling the output of all the excitation light sources.
[0021]
However, in this case, even in the optical fiber cable 1c on the downstream signal input side where the intensity of the excitation light does not decrease, the intensity of the excitation light is doubled as compared to before the disconnection. As a result, the signal light intensity is significantly increased in the optical fiber cable 1c, and non-linear optical effects such as cross-phase modulation, four-wave mixing, and stimulated Brillouin scattering, which are particularly problematic in wavelength division multiplexing transmission, occur, and the downstream signal Transmission quality deteriorates.
[0022]
The present invention has been made in order to solve the above-described problems, and has a distributed constant type optical amplifying repeater that suppresses transmission quality deterioration due to an increase in loss due to a physical failure such as a broken optical fiber cable. The purpose is to get.
[0023]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, an optical amplifying repeater according to the present invention is an optical amplifying repeater of a two-wire bidirectional optical transmission system, wherein a first pump corresponding to a first signal light is provided. A first pumping light source that outputs light, a second pumping light source that outputs a second pumping light corresponding to the second signal light, and an output intensity of the first and second pumping light sources, respectively. A control means, a first optical signal pump light obtained by multiplexing and demultiplexing the first pump light and the second pump light at a branch ratio a: b (where a> b), and a branch ratio b: a Optical multiplexing / demultiplexing means for outputting the second optical signal excitation light multiplexed / demultiplexed in the first optical amplification means for amplifying the signal light in the first direction based on the first optical signal excitation light And second optical amplification means for amplifying the signal light in the second direction based on the second optical signal pump light.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a configuration diagram of the Raman amplification repeater according to the first embodiment. In FIG. 1, reference numerals 1a, 1b, 1c, and 1d denote optical fiber cables used as transmission lines and Raman amplification media, 2a, 2b, 2c, and 2d denote excitation light sources, 3a and 3b denote the excitation light sources 2a and 2b, and 2c, respectively. An optical multiplexer 4 for multiplexing the pumping light from 2d multiplexes the pumping light P3a from the optical multiplexer 3a and the pumping light P3b from the optical multiplexer 3b, and forms an uplink line at a predetermined branching ratio. Multiplexer / demultiplexer for outputting pumping light P5a for downstream and pumping light P5b for downlink communication, 5a and 5b are WDM couplers for multiplexing / demultiplexing signal light and Raman pumping light, 6a and 6b are optical isolators, and 7 is the optical isolator. A control circuit for controlling the excitation light sources 2a, 2b, 2c, 2d, 8 is a power supply cable, 9 is a power supply circuit for supplying power from the power supply line 8 to the control circuit 7, and 10 is a power supply circuit from the optical multiplexers 3a, 3b. Excitation light P a, the multiplexes P3b, a demultiplexer for equally branching the excitation light P4b for upstream line for excitation light P4a and downstream lines.
[0025]
Next, the operation of the Raman amplification repeater according to the first embodiment configured as described above will be described.
Each of the pump light sources 2a to 2d outputs pump light at an optical output of 100 mW. 3a combines the pumping light sources 2a and 2b and outputs a combined pumping light P3a. Similarly, 3b combines the pump light sources 2c and 2d and outputs a combined pump light P3b.
[0026]
The optical multiplexer / demultiplexer 4 receives the combined pumping light P3a, branches the upstream pumping light P5a and the downstream pumping light P5b at a branching ratio P5a: P5b = 80: 20, and outputs the branched light. The optical multiplexer / demultiplexer 4 receives the combined pump light P3b, branches the upstream line pump light P5a and the downstream line pump light P5b at a branching ratio P5a: P5b = 20: 80, and outputs the branched light.
[0027]
The uplink pump light P5a is input to the WDM coupler 5a and combined with the optical signal output from the optical fiber cable 1a. The amplified optical signal passes through the optical isolator 6a and is output to the optical fiber cable 1b on the upstream output side.
Similarly, the downstream line pump light P5b is combined with the optical signal input to the WDM coupler 5b and output from the optical fiber cable 1c. The amplified optical signal is output to the optical fiber cable 1d on the downstream output side via the optical isolator 6b.
[0028]
When the Raman amplification repeater is operating normally, the control circuit 7 instructs each of the pumping light sources 2a to 2d to output pumping light at a preset light intensity (100 mW in the above example). I do. In this case, the optical intensities of the uplink line pump light P5a and the downlink line pump light P5b are each 200 mW.
[0029]
Next, in the vicinity of the Raman amplification repeater of the upstream optical fiber cable 1a and the downstream optical fiber cable 1d, a disconnection failure of the optical fiber cable occurs. Consider a case where the signal light intensity decreases in the (optical fiber cable 1d) and the pump light intensity decreases simultaneously with the signal light intensity in the upstream direction (optical fiber cable 1a). Here, it is assumed that the amount of increase in loss of each signal light and pump light accompanying the restoration is 3 dB.
[0030]
The receiving station of the optical communication system measures the loss increase (3 dB) of each signal light and pump light accompanying the restoration of the optical fiber cable. In order to compensate for the loss increase of the uplink line pumping light P5a, the receiving station sends the pumping light intensity of the pumping light sources 2a and 2b corresponding to the upstream direction to the control circuit 7 of the Raman amplification repeater, A control command for increasing the power from 100 mW to 200 mW is transmitted using a control cable (not shown in FIG. 1).
[0031]
The control circuit 7 increases the excitation light intensity of the excitation light sources 2a, 2b according to the control command. In this case, the intensity of the combined excitation light P3a is 400 mW, and the intensity of the combined excitation light P3b is 200 mW.
[0032]
The optical multiplexer / demultiplexer 4 receives the combined pumping lights P3a and P3a, and branches the pumping light P5a for the uplink line and the pumping light P5b for the downlink line according to the above-described branching ratio.
That is, the upstream line pump light P5a is a total of 360 mW of 320 mW (= 400 mW × 0.8) from the combined pump light P3a and 40 mW (= 200 mW × 0.2) from the combined pump light P3b. On the other hand, the downlink line pump light P5b is 240 mW, which is the sum of 80 mW (= 400 mW × 0.2) from the combined pump light P3a and 160 mW (= 200 mW × 0.8) from the combined pump light P3b.
[0033]
As a result, 180 mW of excitation light is supplied to the optical fiber cable 1a in consideration of a loss increase of 3 dB due to restoration of the optical cable disconnection. On the other hand, the pump light of 240 mW is supplied to the optical fiber cable 1c, and the distribution of the pump light in the up / down direction is in a state close to a normal state.
[0034]
FIG. 2 shows the transmission quality by the branching ratio of the first optical multiplexer / demultiplexer 4 in the Raman amplification repeater when the optical fiber immediately near the input end in the upstream direction is disconnected and the loss increases by 3 dB due to the repair. FIG. 6 is a characteristic diagram showing how a Q value, which is one index of the above, and the signal light output intensity change.
Here, FIG. 2 shows that the total optical cable length of the optical communication system is 12,000 km, the repeater interval is 50 km (of which 35 km is the positive dispersion fiber with a large effective core area on the repeater output side, and 15 km is the effective core cutoff on the repeater input side). Negative dispersion fiber having a small area), the output intensity of the pump light source is 100 mW, the sum of losses of the optical components between the optical fiber cables 1a and 1c and the pump light source is 1 dB, the Raman gain is 12.3 dB, and the per channel This is the result of a simulation operation assuming that the transmission level of the signal light is -5.8 dBm.
[0035]
As shown in FIG. 2, the Q value which was 13.1 dB at the time of normal operation is degraded to 12.8 dB due to a loss increase of 3 dB. Here, after the relaying process is performed by the three repeaters, the three repeaters downstream of the loss increase point so that the signal light output intensity in the upstream direction recovers to the optical signal intensity before the disconnection restoration point. Is performed, the Q value of the optical signal after the relay processing is restored to 13.0 dB.
[0036]
As described above, by changing the pumping light intensity in the upward direction, the Q value in the downward direction can be recovered to almost constant regardless of the branching ratio of the first optical multiplexer / demultiplexer 4. However, as in the case of the conventional Raman amplification repeater shown in FIG. 7 described above, when the intensities of the uplink line pump light and the downlink line pump light are the same (the splitting ratio of the first optical multiplexer / demultiplexer 4). Is 50:50), the optical signal output intensity in the downstream direction increases by 2.5 dB.
The increase in the optical signal strength in the opposite direction (downward direction when a disconnection failure occurs immediately near the input end in the upward direction) is determined when the branching ratio of the first optical multiplexer / demultiplexer 4 is 60:40. 1.8 dB, 1.2 dB for 70:30, and 0.8 dB for 80:20.
[0037]
In general, when performing long-distance optical transmission by wavelength division multiplexing, transmission quality is significantly degraded by nonlinear optical effects such as four-wave mixing, cross-phase modulation, or stimulated Brillouin scattering caused by high signal light intensity. An increase in light intensity is not preferred.
[0038]
As described above, according to the Raman amplification repeater of the first embodiment, the splitting ratio of the first optical multiplexer / demultiplexer 4 is not equal, and the ratio of the pump light from the corresponding pump light sources 2a and 2b is smaller. By selecting the pump light sources to be larger than the other pump light sources 2c and 2d, in an optical communication system having a very long transmission distance and a large number of repeaters to be inserted, such as an optical submarine cable system, the optical fiber cable It is possible to appropriately compensate for the deterioration of the communication quality (Q value) due to the increase in the loss that occurs at the time of repairing the objective failure, and also suppress the deterioration of the transmission quality due to the increase in the output intensity of the optical signal.
[0039]
In the first embodiment, the case where the branching ratio of the first optical multiplexer / demultiplexer 4 is 80:20 (20:80 in the facing direction) is described. However, the branching ratio is 60:40 to 90:80. Within the range of 10, an appropriate value is set based on preliminary experiments and computer simulations, and an appropriate branching ratio is changed by changing the set value of the Raman gain and the transmission level of the optical signal.
[0040]
Embodiment 2 FIG.
In the first embodiment, in a Raman amplification repeater using an optical fiber cable as a Raman amplification medium, the outputs of a plurality of pumping light sources are subjected to multiplexing / demultiplexing processing by using an optical multiplexer / demultiplexer having a non-uniform branching ratio. In the second embodiment, an optical multiplexer / demultiplexer in which the branching ratio is not uniform is used in an EDF amplifying repeater that uses an EDF cable as a transmission line medium on the input side.
The second embodiment is different from the first embodiment in that the transmission path medium on the input side is an EDF cable, and other configurations are the same. The description is omitted by attaching the reference numerals.
[0041]
FIG. 3 is a configuration diagram of the EDF amplification repeater according to the second embodiment. In FIG. 3, reference numerals 13a and 13b denote EDF cables used as transmission line media on the input side.
[0042]
Next, the operation of the EDF amplifying repeater according to the second embodiment configured as described above will be described.
Each of the pump light sources 2a to 2d outputs pump light at an optical output of 100 mW. 3a combines the pumping light sources 2a and 2b and outputs a combined pumping light P3a. Similarly, 3b combines the pump light sources 2c and 2d and outputs a combined pump light P3b.
[0043]
The optical multiplexer / demultiplexer 4 receives the combined pumping light P3a, branches the upstream pumping light P5a and the downstream pumping light P5b at a branching ratio P5a: P5b = 80: 20, and outputs the branched light. The optical multiplexer / demultiplexer 4 receives the combined pumping light P3b, branches the upstream-line pumping light P5a and the downstream-line pumping light P5b at a branching ratio P5a: P5b = 20: 80, and outputs the resultant.
[0044]
When the EDF amplifying repeater is operating normally, the control circuit 7 instructs each of the pumping light sources 2a to 2d to output pumping light at a preset light intensity (100 mW in the above example). I do. In this case, the optical intensities of the uplink line pump light P5a and the downlink line pump light P5b are each 200 mW.
[0045]
Next, in the vicinity of the EDF amplifier repeater of the upstream EDF cable 13a and the downstream optical fiber cable 1d, a disconnection failure of the optical fiber cable occurs. Consider a case where the signal light intensity decreases in the optical fiber cable 1d), and in the upward direction (EDF cable 13a), the excitation light intensity simultaneously decreases with the signal light intensity. Here, it is assumed that the amount of increase in loss of each signal light and pump light accompanying the restoration is 3 dB.
[0046]
The control circuit 7 increases the pumping light intensity of the pumping light sources 2a, 2b corresponding to the upstream direction from 100 mW to 200 mW in order to compensate for the loss increase of the upstream line pumping light P5a estimated as described above. In this case, the intensity of the combined excitation light P3a is 400 mW, and the intensity of the combined excitation light P3b is 200 mW.
[0047]
The optical multiplexer / demultiplexer 4 receives the combined pumping lights P3a and P3a, and branches the pumping light P5a for the uplink line and the pumping light P5b for the downlink line according to the above-described branching ratio.
That is, the upstream line pump light P5a is a total of 360 mW of 320 mW (= 400 mW × 0.8) from the combined pump light P3a and 40 mW (= 200 mW × 0.2) from the combined pump light P3b. On the other hand, the downlink line pump light P5b is 240 mW, which is the sum of 80 mW (= 400 mW × 0.2) from the combined pump light P3a and 160 mW (= 200 mW × 0.8) from the combined pump light P3b.
[0048]
As a result, 180 mW of excitation light is supplied to the EDF cable 13a. On the other hand, the pump light of 240 mW is supplied to the optical fiber cable 1c, and the distribution of the pump light in the up / down direction is in a state close to a normal state.
[0049]
As described above, the branching ratio of the first optical multiplexer / demultiplexer 4 is selected so as to be unequal and the ratio of the pumping light from the corresponding pumping light sources 2a and 2b is larger than that of the other pumping light sources 2c and 2d. Therefore, in an optical communication system having a very long transmission distance and a large number of inserted repeaters, such as an optical submarine cable system, the communication quality due to an increase in loss occurring at the time of repairing a physical failure of the optical fiber cable ( While appropriately compensating for the deterioration of the Q value, it is possible to suppress the deterioration of the transmission quality due to the increase in the output intensity of the optical signal.
[0050]
In the second embodiment, the case where the branching ratio of the first optical multiplexer / demultiplexer 4 is 80:20 (20:80 in the facing direction) is described, but the branching ratio is 60:40 to 90:20. An appropriate value is set within the range of 10 based on preliminary experiments and computer simulations, and an appropriate branching ratio is changed by changing the transmission level of the optical signal.
[0051]
In the second embodiment, the EDF cable is used as the transmission medium on the input side of the EDF amplification repeater. However, the present invention is not limited to such a configuration, and the optical fiber to which other rare earth elements such as thulium and praseodymium are attached. It is naturally possible to obtain the same effect by using a fiber.
[0052]
【The invention's effect】
As described above, according to the present invention, in an optical communication system having a very long transmission distance and a large number of inserted repeaters, such as an optical submarine cable system, when repairing a physical failure of an optical fiber cable, It is possible to appropriately compensate for the deterioration of the communication quality (Q value) due to the increase in the loss and to suppress the deterioration of the transmission quality due to the increase in the output intensity of the optical signal.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a Raman amplification repeater according to Embodiment 1 of the present invention.
FIG. 2 is a characteristic diagram showing a relationship between a branching ratio, transmission quality (Q value), and signal light output intensity of the optical multiplexer / demultiplexer according to the first embodiment of the present invention.
FIG. 3 is a configuration diagram of an EDF amplification repeater according to a second embodiment of the present invention.
FIG. 4 is a configuration diagram of a conventional EDF amplifying repeater having a redundant configuration.
FIG. 5 is a configuration diagram of a conventional EDF amplifying repeater without a redundant configuration.
FIG. 6 is an explanatory diagram showing a self-healing effect of the EDF amplification repeater.
FIG. 7 is a configuration diagram of a conventional Raman amplification repeater having a redundant configuration.
[Explanation of symbols]
1a, 1b, 1c, 1d Optical fiber cable 2a, 2b, 2c, 2d Pump light source 3a, 3b Optical multiplexer 4 First optical multiplexer / demultiplexer 5a, 5b WDM coupler 6a, 6b Optical isolator 7 Control circuit 8 Feeding cable 9 Power supply circuit 10 Second optical multiplexer / demultiplexer 11a, 11b EDF
12a, 12b Optical filter 13a, 13b EDF cable

Claims (6)

An optical amplification repeater for a two-wire bidirectional optical transmission system,
A first pumping light source that outputs a first pumping light corresponding to the first signal light,
A second pumping light source that outputs a second pumping light corresponding to the second signal light,
Control means for controlling the output intensity of the first and second excitation light sources,
A first optical signal pumping light obtained by multiplexing / demultiplexing the first pumping light and the second pumping light at a branching ratio a: b (where a> b), and a multiplexing / demultiplexing at a branching ratio b: a Optical multiplexing / demultiplexing means for outputting the pumping light for the second optical signal,
First optical amplification means for amplifying the signal light in the first direction based on the first optical signal excitation light,
An optical amplifying repeater comprising: a second optical amplifier that amplifies the signal light in the second direction based on the second optical signal pump light. 2. The optical amplifying repeater according to claim 1, wherein the optical multiplexing / demultiplexing unit is set to have a branching ratio a: b = 60: 40 to 90:10. The optical amplifying repeater according to claim 1, wherein the optical multiplexing / demultiplexing means is set to have a branching ratio a: b = 80: 20. The control means is configured to determine the output intensity of the first and second optical signals based on the loss increase amount of the first or second optical signal, wherein 3. The optical amplifying repeater according to any one of 3. The first and second pump light sources output pump light having a predetermined wavelength for stimulated Raman amplification of the signal light,
The first and second optical amplifying means transmit the signal light and input it to the optical amplifying repeater, and the signal light based on the corresponding first optical signal pumping light or second optical signal pumping light, respectively. The optical amplifying repeater according to any one of claims 1 to 4, further comprising an optical fiber cable for performing Raman amplification processing on the optical fiber. The first and second optical amplifying means transmit the signal light and input it to the optical amplifying repeater, and the signal light based on the corresponding first optical signal pumping light or second optical signal pumping light, respectively. Having a rare earth doped optical fiber cable for amplifying the
The optical amplification repeater according to any one of claims 1 to 4, wherein the first and second pumping light sources are configured to output pumping light of a predetermined wavelength for pumping the rare-earth-doped optical fiber. vessel.

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