Optical transmission system and control method for optical transmission system

Abstract

The present invention provides an optical transmission system with a small gain variation in broadband and a control method therefor. Provided is an optical transmission system including a pair of end stations that transmit and receive wavelength division multiplexed (WDM) signal light to and from each other, an optical fiber through which the wavelength division multiplexed signal light transmitted and received by the pair of end stations propagates, and at least one repeater inserted in the optical fiber. The repeater includes an optical amplifier that divides the wavelength division multiplexed signal light into multiple subbands including signal beams in multiple wavelength bands, amplifies the multiple subbands with the corresponding optical amplification units, and then multiplexes the amplified subbands, the multiple subbands obtained by the division including a first subband on a relatively shorter wavelength side and a second subband on a relatively longer wavelength side. There are also included: a monitoring unit that monitors the output power of a channel with the longest wavelength in the first subband and the output power of a channel with the shortest wavelength in the second subband, the channels being received by a receiving end station in the pair of end stations; and a control unit that transmits a control signal to a transmitting end station, which transmits the wavelength division multiplexed signal light, so that a gap between the output power of the channel with the longest wavelength in the first subband and the output power of the channel with the shortest wavelength in the second subband is reduced.

Description

Technical Field

[0001] The present invention relates to an optical transmission system and the like, and particularly to an optical transmission system and the like using an optical fiber as a transmission line.

Background Art

[0002] An optical transmission system using an optical fiber as a transmission line is known. In this optical transmission system, wavelength bands such as the C-band (Conventional Band) and the L-band (Long Wave Band) are used as optical communication wavelength bands in consideration of transmission losses of the optical fiber. Here, the wavelength band of the C-band is 1530 nm to 1565 nm, and the wavelength band of the L-band is 1565 nm to 1625 nm. The wavelength band of the C-band has a high light transmittance of the optical fiber. In other words, the wavelength band of the C-band has a low transmission loss of the optical fiber. Therefore, the wavelength band of the C-band is suitable for long-distance transmission.

[0003] Such an optical transmission system is configured to include, for example, a pair of terminal stations that perform transmission and reception, an optical fiber as a transmission line connecting the pair of terminal stations, and a plurality of repeaters that relay the optical fiber. Each of the plurality of repeaters includes an optical amplification unit that amplifies signal light that attenuates as it propagates through a long-distance optical fiber. As this optical amplification unit, an erbium-doped fiber amplifier in which erbium (Er) ions, which are an example of rare earth ions, are added to the optical fiber as an impurity is used.

[0004] An erbium-doped fiber amplifier generally has a gain characteristic such that, in the wavelength band of the signal light to be amplified, the gain of the signal light with a longer wavelength is larger and the gain of the signal light with a shorter wavelength is smaller. In a repeater inserted into an optical fiber, considering this tendency of the amplification characteristic, the gain of the erbium-doped fiber amplifier is adjusted so that the output level of the signal light with a shorter wavelength among the wavelength bands of the input signal light to be amplified exceeds a predetermined level. Then, an equalizer connected to the next stage of the erbium-doped fiber amplifier cuts the portion exceeding the predetermined level, thereby performing equalization processing to equalize the output levels in each channel of the wavelength band of the signal light amplified by one erbium-doped fiber amplifier. The portion cut by the equalization processing of this equalizer does not contribute to optical transmission by the optical fiber and thus becomes an energy loss. An optical transmission system capable of reducing this energy loss is desired.

[0005] Patent Document 1 relates to a method for amplifying wavelength-division multiplexing (WDM) signal light. In this Patent Document 1, a method for amplifying wavelength-division multiplexing signal light is proposed, in which the wavelength-division multiplexing signal light is split into signal lights of a plurality of wavelength bands by a demultiplexer, the signal lights of each split wavelength band are amplified by an optical amplification unit corresponding to each, and then the amplified signal lights of each wavelength band are multiplexed by a multiplexer. Further, in Patent Document 1, a part of the signal light of each wavelength band amplified by the optical amplification unit is branched, the power of the branched light is measured, and the gain of the optical amplification unit is individually adjusted based on the measurement result, so that the wavelength deviation of the optical output levels generated by the optical amplification unit respectively is designed to be within a preset range.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] Here, consider the optical amplification section included in the repeater of the optical transmission system and the energy loss due to the equalization process of the equalizer. For example, consider the energy loss due to the equalization process of the equalizer in the case of applying a configuration in which wavelength-division multiplexed signal light is split into signal lights in a plurality of wavelength bands by a wavelength division device, the signal lights in each of the split wavelength bands are amplified by an optical amplification section corresponding to each, and then the amplified signal lights in each wavelength band are multiplexed by a multiplexing device (FIG. 13B).

[0008] When such a configuration is adopted, compared with the case where the wavelength-division multiplexed signal light is directly amplified by one optical amplification section as shown in FIG. 13A, the width of the wavelength band of the signal light in the wavelength band amplified by each optical amplification section becomes narrower. As a result, the difference between the gain of the signal light with a long wavelength and the gain of the signal light with a short wavelength becomes smaller in the wavelength band of the signal light amplified by each optical amplification section. As a result, even if the gain of the optical amplification section is adjusted so that the output level of the signal light with a short wavelength in the wavelength band of the signal light input and amplified by each optical amplification section exceeds a predetermined level, the portion exceeding the predetermined level becomes smaller. Thereby, even when an equalization process is performed to cut the portion exceeding the predetermined level and equalize the output levels of the channels in the wavelength band of the signal light amplified by the optical amplification section, the portion to be cut becomes smaller, and it is expected that the energy loss due to the equalization process of the equalizer becomes smaller.

[0009] By the way, consider new problems of a configuration in which wavelength-division multiplexed signal light is split into signal lights in a plurality of wavelength bands by a wavelength division device, the signal lights in each of the split wavelength bands are amplified by an optical amplification section corresponding to each, and then the amplified signal lights in each wavelength band are multiplexed by a multiplexing device as proposed in Patent Document 1.

[0010] Energy loss due to gain variation resulting from optical amplification of broadband wavelength-division multiplexed signal light is expected to be reduced by adopting a configuration in which, as proposed in Patent Document 1, the wavelength-division multiplexed signal light is split by a wavelength division device into signal lights in a plurality of wavelength bands, the signal lights in each of the split wavelength bands are amplified by optical amplifiers corresponding to each of them, and then the amplified signal lights in each wavelength band are multiplexed by a multiplexing device.

[0011] In the case of a configuration in which the signal lights in each of the split wavelength bands are amplified by optical amplifiers corresponding to each of them, when the output of the excitation light decreases due to the secular deterioration of the excitation light source of the optical amplifier, a gap in the output intensity occurs at the boundary between the sub-bands of the received signal (Fig. 14).

[0012] Since the standard deviation variation of the output intensity due to secular deterioration is about 0.03 dB per amplifier within the allowable range, the gap needs to be suppressed within 0.03 dB. Therefore, it becomes an issue to fill the gap in the output intensity caused by secular deterioration.

[0013] An object of the present invention is to provide an optical transmission system with a wide bandwidth and small gain variation, and a control method therefor, in view of the above-described problems.

Means for Solving the Problems

[0014] To achieve the above object, an optical transmission system according to the present invention is an optical transmission system including a pair of terminal stations that transmit and receive wavelength-division multiplexed (WDM) signal lights to and from each other, an optical fiber that propagates the wavelength-division multiplexed signal lights transmitted and received by the pair of terminal stations, and at least one repeater inserted into the optical fiber, the repeater includes an optical amplifier that divides the wavelength-division multiplexed signal light into a plurality of sub-bands including signal lights in a plurality of wavelength bands, amplifies the plurality of divided sub-bands by a plurality of corresponding optical amplifiers, and then multiplexes the amplified plurality of sub-bands, the plurality of divided sub-bands include a first sub-band on the relatively short-wavelength side and a second sub-band on the relatively long-wavelength side, received by the receiving-side terminal station among the pair of terminal stations, A monitor unit that monitors the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band; A control unit that transmits a control signal to the transmitting end station that transmits the wavelength-division multiplexed signal light so that the gap between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band becomes smaller.

[0015] A control method for an optical transmission system includes a pair of end stations that transmit and receive wavelength-division multiplexed (WDM) signal lights to and from each other, an optical fiber that propagates the wavelength-division multiplexed signal light transmitted and received by the pair of end stations, and at least one repeater inserted into the optical fiber. The repeater divides the wavelength-division multiplexed signal light into a plurality of sub-bands including signal lights in a plurality of wavelength bands, amplifies the divided plurality of sub-bands with corresponding plurality of optical amplification units, and then multiplexes the amplified plurality of sub-bands. The plurality of divided sub-bands include a first sub-band on the relatively short-wavelength side and a second sub-band on the relatively long-wavelength side. Of the pair of end stations, the receiving end station receives Monitor the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band. Transmit a control signal to the transmitting end station that transmits the wavelength-division multiplexed signal light so that the gap between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band becomes smaller.

Advantages of the Invention

[0016] The present invention can provide an optical transmission system with a wide bandwidth and small gain variation, and a control method thereof.

Brief Description of the Drawings

[0017]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 2C

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 6

Figure 7A

Figure 7B

Figure 7C

Figure 8

Figure 9

Figure 10

Figure 11A

Figure 11B

Figure 12

Figure 13A

Figure 13B

Figure 14

Embodiments for Carrying Out the Invention

[0018] Before explaining the specific embodiments of the present invention, embodiments based on the upper concept of the present invention will be explained. FIG. 1A is a block diagram for explaining an optical transmission system according to an embodiment of the upper concept of the present invention. FIG. 1B is a block diagram for explaining the configuration of the repeater in FIG. 1A. The optical transmission system in FIG. 1A is, for example, a system including a terrestrial terminal station and an optical fiber that propagates wavelength-division multiplexed signal light between these terminal stations. A submarine cable system or the like using a submarine cable as this optical fiber is assumed.

[0019] The optical transmission system in FIG. 1A includes terminal stations 102A and 102B as an example of a pair of terminal stations that transmit and receive wavelength-division multiplexed (WDM) signal lights to and from each other, an optical fiber 101 that propagates the wavelength-division multiplexed signal lights transmitted and received by these terminal stations 102A and 102B, and at least one repeater 103 inserted into this optical fiber 101. As shown in FIG. 1B, the repeater 103 in FIG. 1A includes a demultiplexer 104 and a plurality of optical amplification units 105 1 ~105m (Here, m is an integer of 2 or more), and a multiplexer 106 are included.

[0020] The demultiplexer 104 divides the wavelength-division multiplexed signal light input to the repeater 103 into a plurality of sub-bands each including signal light in a plurality of wavelength bands. The plurality of optical amplification units 105 1 ~105 m amplify the wavelength-division multiplexed signal light divided into the plurality of sub-bands respectively. The plurality of optical amplification units 105 1 ~105 m are optical amplifiers represented by an EDFA (erbium-doped fiber amplifier), and are optical amplifiers that amplify and output an optical signal with excitation light. The multiplexer 106 multiplexes and outputs the wavelength-division multiplexed signal light amplified by each optical amplification unit 105 1 ~105 m and outputs it.

[0021] In the optical transmission system of FIG. 1A, the plurality of sub-bands include at least a first sub-band on the relatively short-wavelength side and a second sub-band on the relatively long-wavelength side.

[0022] The optical transmission system of FIG. 1A further includes a monitor unit 108 that monitors the output power of the channel with the longest wavelength among the first sub-bands received by the receiving-side terminal station of the pair of terminal stations, and the output power of the channel with the shortest wavelength among the second sub-bands.

[0023] The optical transmission system of FIG. 1A further includes a control unit 109 that transmits a control signal to the transmitting-side terminal station that transmits the wavelength-division multiplexed signal light so that the gap between the output power of the channel with the longest wavelength among the first sub-bands and the output power of the channel with the shortest wavelength among the second sub-bands becomes smaller.

[0024] In the optical transmission system of FIG. 1A, the monitor unit 108 monitors the output power of the channel with the longest wavelength among the first sub-bands on the relatively short-wavelength side, and monitors the output power of the channel with the shortest wavelength among the second sub-bands on the relatively long-wavelength side.

[0025] Furthermore, the control unit 109 transmits a control signal so that the gap between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band becomes smaller. The control signal for reducing this gap is transmitted to the transmitting end station that transmits the wavelength-division multiplexed signal light.

[0026] By this control signal, the transmitting end station changes its state regarding the transmission of the wavelength-division multiplexed (WDM) signal light. As a result, the gap between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band becomes smaller. Due to the optical amplification for each divided sub-band, by reducing the gap in the amplification characteristics, the energy loss due to the equalization process can be reduced. As a result, an optical transmission system with improved energy utilization efficiency can be realized, and the performance of the optical transmission system can be maintained.

[0027] In the optical transmission system of FIG. 1A, even when a time-dependent change occurs in the optical amplifier or the like included in the repeater 103 after the operation starts, by controlling to reduce the gap between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band, the variation in the amplification characteristics of the optical amplifier included in the repeater 103 can be reduced, an optical transmission system with improved energy utilization efficiency can be realized, and the performance of the optical transmission system can be maintained. Hereinafter, a more specific optical transmission system and its control method will be described.

[0028] 〔First Embodiment〕 The optical transmission system according to the first embodiment of the present invention and its control method will be described. FIG. 2A is a block diagram for explaining the optical transmission system according to the first embodiment of the present invention. FIG. 2B is a block diagram for explaining the configuration and amplification characteristics of the repeater in FIG. 2A. FIG. 2C is a graph for explaining the basic principle regarding the amplification characteristics of the optical amplifier. FIG. 4 is a graph for explaining the amplification characteristics of the optical amplification unit included in FIG. 2B.

[0029] The optical transmission system in FIG. 2A includes a terminal station 12A (transmitting terminal station Tx) that transmits wavelength-division multiplexed (WDM) signal light, a terminal station 12B (receiving terminal station Rx) that receives the wavelength-division multiplexed signal light, and an optical fiber 11 that propagates the wavelength-division multiplexed signal light transmitted and received by the terminal stations 12A and 12B. Further, the optical transmission system in FIG. 2A includes at least one repeater 13 inserted into the optical fiber 11. In FIG. 2A, the case where seven repeaters 13 are inserted into the optical fiber 11 is shown as an example.

[0030] As shown in FIG. 2B, the repeater 13 in FIG. 2A includes a demultiplexer 14, a plurality of optical amplification units 15 1 ~15 m (where m is an integer of 2 or more), and a multiplexer 16. The demultiplexer 14 divides the wavelength-division multiplexed signal light input to the repeater 13 into a plurality of sub-bands including signal lights in a plurality of wavelength bands. The plurality of optical amplification units 15 1 ~15 m amplify the wavelength-division multiplexed signal light divided into the plurality of sub-bands respectively. The plurality of optical amplification units 15 1 ~15 m are optical amplifiers represented by an EDFA (erbium-doped fiber amplifier), which are optical amplifiers that amplify and output an optical signal by excitation light. The multiplexer 16 multiplexes and outputs the wavelength-division multiplexed signal light amplified by each optical amplification unit 15 1 ~15 m .

[0031] In the optical transmission system in FIG. 2A, the plurality of sub-bands include at least a first sub-band on the relatively short-wavelength side and a second sub-band on the relatively long-wavelength side.

[0032] The optical transmission system of FIG. 2A further includes an output gap monitor 21 that monitors the output power of the channel with the longest wavelength among the first sub-bands received by the receiving end station Rx and the output power of the channel with the shortest wavelength among the second sub-bands.

[0033] The optical transmission system of FIG. 2A further includes a loading control device 22 that transmits a control signal to the transmitting end station Tx on the transmission side so that the gap between the output power of the channel with the longest wavelength among the first sub-bands and the output power of the channel with the shortest wavelength among the second sub-bands becomes smaller.

[0034] In the optical transmission system of FIG. 2A, the output gap monitor 21 monitors the output power of the channel with the longest wavelength among the first sub-bands on the relatively short-wavelength side and also monitors the output power of the channel with the shortest wavelength among the second sub-bands on the relatively long-wavelength side.

[0035] Furthermore, the loading control device 22 transmits a control signal so that the gap between the output power of the channel with the longest wavelength among the first sub-bands and the output power of the channel with the shortest wavelength among the second sub-bands becomes smaller. The control signal for reducing this gap is transmitted to the transmitting end station Tx on the transmission side.

[0036] By this control signal, the transmitting end station Tx on the transmission side changes its state regarding the transmission of the wavelength-division multiplexed signal light. As a result, the gap between the output power of the channel with the longest wavelength among the first sub-bands and the output power of the channel with the shortest wavelength among the second sub-bands becomes smaller. In this way, due to the optical amplification for each divided sub-band, by reducing the gap in the amplification characteristics, the energy loss due to the equalization process can be reduced. As a result, an optical transmission system with improved energy utilization efficiency can be realized, and the performance of the optical transmission system can be maintained.

[0037] FIG. 3 is a block diagram for explaining a more specific configuration of the optical transmission system of FIG. 2A. The optical transmission system of FIG. 3 includes the terminal stations 12A (transmitting terminal station Tx) and 12B (receiving terminal station Rx) shown in FIG. 2A, and an optical fiber 11 that propagates wavelength-division multiplexed signal light, and further includes a network management system 30. The network management system 30 oversees the entire optical transmission system of FIG. 2A, and particularly in this embodiment, shows a configuration for controlling the loading control device 22 based on the output of the output gap monitor 21. Note that in FIG. 3, illustration of the repeater 13 inserted into the optical fiber 11 is omitted.

[0038] In the optical transmission system of FIG. 3, the transmitting terminal station Tx is configured to include a configuration for wavelength-division multiplexing the transmitted signal light and dummy light related to loading, and a loading control device 22. The transmitting terminal station Tx includes a multiplexer 121 that wavelength-division multiplexes the signal lights (Sig.1 to Sig.K-1) of channels #1 to #K-1, and a multiplexer 122 that wavelength-division multiplexes the signal lights (Sig.K to Sig.N) of channels #K to #N. Here, N and K are integers that satisfy, for example, N>K≧2. Also, for the sake of convenience in explanation here, it is assumed that the channel numbers of channels #1 to #N are assigned in order from the side with the shorter wavelength to the side with the longer wavelength. The transmitting terminal station Tx further includes a multiplexer 123 that wavelength-division multiplexes the dummy lights (Rod.1 to Rod.n) of #1 to #n, a multiplexing means 124 that multiplexes the outputs of the multiplexers 121, 122, and 123, and a loading control device 22 that controls the multiplexer 123 according to the input control signal. The loading control device 22 instructs the multiplexer 123 to output or stop the dummy lights of #1 to #n, or to attenuate the optical power of the dummy lights of #1 to #n, according to the input control signal.

[0039] In the optical transmission system of FIG. 3, the receiving end station Rx on the receiving side is configured to include a configuration for demultiplexing the received signal light and dummy light related to loading, and an output gap monitor 21. The receiving end station Rx on the receiving side includes a demultiplexing means 125 for demultiplexing the wavelength-division multiplexed signal light propagated through the optical fiber 11, a demultiplexing section 126 for demultiplexing the signal light (Sig.1 to Sig.K-1) of channels #1 to #K-1, and a demultiplexing section 127 for demultiplexing the signal light (Sig.K to Sig.N) of channels #K to #N. Further, the receiving end station Rx on the receiving side includes a demultiplexing section 128 for demultiplexing into dummy lights #1 to #n, and an output gap monitor 21.

[0040] The output gap monitor 21 monitors the output power of the signal light (Sig.K-1) of channel #K-1 output by the demultiplexing section 126 and the output power of the signal light (Sig.K) of channel #K output by the demultiplexing section 127. The output gap monitor 21 monitors, for example, the gap amount between the output power of the signal light (Sig.K-1) of channel #K-1 and the output power of the signal light (Sig.K) of channel #K. Here, the signal light (Sig.K-1) of channel #K-1 corresponds to the channel with the longest wavelength in the first sub-band, and the signal light (Sig.K) of channel #K corresponds to the channel with the shortest wavelength in the second sub-band.

[0041] The transmitting end station Tx on the transmitting side includes a multiplexing section 123 for multiplexing dummy lights #1 to #n (Rod.1 to Rod.n), a multiplexing means 124 for multiplexing the outputs of the multiplexing sections 121, 122, and 123, and a loading control device 22 for controlling the multiplexing section 123 according to the input control signal.

[0042] The loading control device 22 instructs the multiplexing section 123 to output or stop the dummy lights #1 to #n (Rod.1 to Rod.n) of the multiplexing section 123 or to attenuate the dummy lights according to the input control signal. Thereby, the loading control device 22 controls the loading amount in the optical transmission system.

[0043] (Operation of the Embodiment) Next, the operation of the optical transmission system of the present embodiment will be described. In the optical transmission system shown in FIGS. 2A and 3, the wavelength division multiplexing (WDM) signal light transmitted by the terminal station 12A propagates through the optical fiber 11 and is received by the terminal station 12B. The wavelength division multiplexing signal light that attenuates while propagating through the long-distance optical fiber 11 is amplified by the repeater 13 inserted into the optical fiber 11, and a predetermined level of gain is maintained. In the repeater 13, the wavelength division multiplexing signal light is divided into a plurality of sub-bands including signal lights in a plurality of wavelength bands. In the repeater 13 of FIG. 2B, a demultiplexer 14 is provided as a means for dividing the wavelength division multiplexing signal light, and the wavelength division multiplexing signal light is divided into a plurality of sub-bands by the demultiplexer 14. The plurality of sub-bands are, for example, the first to m-th sub-bands (where m is an integer of 2 or more). In the optical amplifier, the wavelength division multiplexing signal light is amplified in the form of an optical signal by the introduction of the pump light. As shown in FIG. 2C as a characteristic of the optical amplifier, even if the introduced pump light is the same, the amplification amount tends to be larger for a narrow-band input signal and smaller for a wide-band input signal.

[0044] In the repeater 13, after amplifying the plurality of divided sub-bands by the optical amplification units 15 1 ~15 m corresponding to each of them, the amplified plurality of sub-bands are multiplexed by the multiplexer 16. After the optical transmission system starts operation, it is assumed that changes in characteristics (aging changes) occur over time.

[0045] The optical transmission system of the present embodiment, particularly the plurality of optical amplification units 15 1 ~15 mIt is intended to address the change over time in the amplification characteristics. For example, assume a case where a plurality of sub-bands are divided into a first sub-band on the relatively short-wavelength side and a second sub-band on the relatively long-wavelength side. The first sub-band is, for example, a sub-band that includes the signal lights (Sig.1 to Sig.K-1) of channels #1 to #K-1, and the second sub-band is, for example, a sub-band that includes the signal lights (Sig.K to Sig.N) of channels #K to #N. In this case, in the repeater 13, the signal lights (Sig.1 to Sig.K-1) of channels #1 to #K-1 are amplified by the optical amplification unit 15 1 and the signal lights (Sig.K to Sig.N) of channels #K to #N are amplified by the optical amplification unit 15 2 and multiplexed by the multiplexer 16.

[0046] This wavelength-division multiplexed signal light propagates through the optical fiber 11 and is received at the terminal station 12B. At the terminal station 12B, the wavelength-division multiplexed signal light is demultiplexed by the demultiplexing means 125, the demultiplexing section 126, and the demultiplexing section 127. The output gap monitor 21 monitors the output power of the signal light (Sig.K-1) of channel #K-1, which is the channel with the longest wavelength among the first sub-bands, and the output power of the signal light (Sig.K) of channel #K, which is the channel with the shortest wavelength among the second sub-bands. When there is a gap between the output power of the signal light (Sig.K-1) of channel #K-1 and the output power of the signal light (Sig.K) of channel #K, which is the channel with the shortest wavelength among the second sub-bands, control is performed so that this gap becomes smaller. In FIG. 2A, when there is a gap between the output power of the signal light (Sig.K-1) of channel #K-1 and the output power of the signal light (Sig.K) of channel #K, which is the channel with the shortest wavelength among the second sub-bands, a control signal is transmitted to the transmitting terminal station 12A that transmits the wavelength-division multiplexed signal light. In FIG. 2A, the output gap monitor 21 transmits a control signal to the loading control device 22, and in FIG. 3, the output gap monitor 21 transmits the monitoring result to the network management system 30, and the network management system 30 transmits a control signal to the loading control device 22 based on this monitoring result.

[0047] In the loading control device 22, the output or stop of the dummy lights (Rod.1 to Rod.n) #1 to #n, or the attenuation of the dummy lights is instructed. Since the optical amplifier has an amplification characteristic as shown in FIG. 2C, by instructing the loading control device 22 to change the output of the dummy light from stop to output, from output to stop, or from output to attenuation, the optical amplification section 15 of the repeater 13 1 , 15 2 of the gain can be individually changed from the terminal station 12A.

[0048] (Effect of the Embodiment) In the optical transmission systems of FIGS. 2A and 3, the output gap monitor 21 monitors the output power of the signal light (Sig.K-1) of channel #K-1, which is the channel with the longest wavelength among the first sub-bands on the relatively short-wavelength side, and monitors the output power of the signal light (Sig.K) of channel #K, which is the channel with the shortest wavelength among the second sub-bands on the relatively long-wavelength side. Further, the output gap monitor 21 in FIG. 2A and the network management system 30 in FIG. 3 transmit a control signal so that the gap between the output power of the signal light (Sig.K-1) of channel #K-1 and the output power of the signal light (Sig.K) of channel #K becomes smaller. Such a control signal that reduces this gap is transmitted to the transmitting end station 12A (transmitting end station Tx) on the transmitting side that transmits the wavelength-division multiplexed signal light. In particular, this control signal is transmitted to the loading control device 22 of the transmitting end station 12A on the transmitting side that transmits the wavelength-division multiplexed signal light.

[0049] By this control signal, the transmitting end station changes its state regarding the transmission of the wavelength-division multiplexed (WDM) signal light. As a result, the gap between the output power of the signal light (Sig.K-1) of channel #K-1 and the output power of the signal light (Sig.K) of channel #K becomes smaller. In this way, due to the optical amplification for each divided sub-band, by reducing the gap in the amplification characteristics, the energy loss due to the equalization process can be reduced. As a result, an optical transmission system with improved energy utilization efficiency can be realized, and the performance of the optical transmission system can be maintained.

[0050] In the optical transmission systems of FIGS. 2A and 3, even when time-dependent changes occur in the optical amplification unit 15 1 ~15 m included in the repeater 13 after the operation starts, by control to reduce the gap between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band, the optical amplification unit 15 1 ~15 mA optical transmission system is realized that reduces the variation in amplification characteristics and improves the energy utilization efficiency, and the performance of the optical transmission system can be maintained.

[0051] Hereinafter, the specific content of the control will be described in order. Here, the gap between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band is reduced.

[0052] 〔Second Embodiment〕 The optical transmission system and its control method according to the second embodiment of the present invention will be described. FIG. 5A is a graph for explaining the control method of the optical transmission system according to the second embodiment of the present invention. FIGS. 7A to 7C are graphs for explaining the control method of the optical transmission system according to the second embodiment of the present invention. This embodiment is an embodiment using the configuration of the optical transmission system shown in FIGS. 2A and 3 described above, and is characterized by the operation of the optical transmission system and the control method of the optical transmission system. In this embodiment, as the configuration of the optical transmission system shown in FIGS. 2A and 3 described above is used, the description of the configuration will be omitted.

[0053] In this specification, in the optical transmission system of the embodiment, the "frequency band used for the transmission of the wavelength-division multiplexed signal light" is referred to as the "used band", and the "entire C band" (wavelength band: 1530 nm to 1565 nm) is referred to as the "Full C band". As shown in FIG. 4, the Full C band includes a plurality of sub-bands (the first sub-band, the second sub-band) used for the transmission of the wavelength-division multiplexed signal light, and also includes a band shorter in wavelength than the first sub-band on the shorter wavelength side and a band longer in wavelength than the second sub-band on the longer wavelength side.

[0054] An optical transmission system is designed to include a plurality of channels used at the start of operation, as well as a plurality of channels (dark channels) that are in an unused state at the start of operation assuming future enhancements. Considering the amplification characteristics of the amplifier section of the repeater shown in FIG. 2C, control is performed such as outputting dummy light to the channels in the unused state. Then, after the start of operation, changes such as supplying signal light and stopping the dummy light are made to the channels in the unused state.

[0055] In FIG. 5A, a state is shown where dummy light is output in a band having a wavelength shorter than that of the first sub-band and in a band having a wavelength shorter than that of the second sub-band in the Full C band.

[0056] In the optical transmission system and its control method of the present embodiment, similar to the above-described embodiment, the output power of the channel having the longest wavelength among the first sub-bands on the relatively short-wavelength side is monitored, and the output power of the channel having the shortest wavelength among the second sub-bands on the relatively long-wavelength side is monitored. Further, a control signal is transmitted so that the gap between the output power of the channel having the longest wavelength in the first sub-band and the output power of the channel having the shortest wavelength in the second sub-band becomes small.

[0057] As this control signal, in the optical transmission system and its control method of the present embodiment, as shown by the two arrows in FIG. 7A, control for changing the loading amount is assumed. More specifically, for example, as in the change from the state shown in FIG. 7A to the state shown in FIG. 7B, it is control for decreasing the loading amount of wavelengths longer than the second sub-band. This control for decreasing the loading amount of wavelengths longer than the second sub-band is, for example, control by the loading control device 22 in FIG. 3, and is realized by the loading control device 22 stopping one or more pieces of dummy light having wavelengths longer than the second sub-band. As understood from the amplification characteristics shown in FIG. 2C, as the band of the input signal becomes narrower, the amplification amount of the optical amplification section increases, and the gain of the optical amplification section rises. As a result, the output power of each signal light of the wavelength multiplexed signal light in the second sub-band increases, and the gap between the output power of the channel having the longest wavelength in the first sub-band and the output power of the channel having the shortest wavelength in the second sub-band can be reduced.

[0058] By the control by the loading control device 22, by stopping one or more pieces of dummy light having wavelengths longer than the second sub-band, the above-described output power gap can be reduced. In this control for reducing the output power gap by stopping the dummy light having a wavelength longer than the second sub-band, it is control for stopping the dummy light in the output state, and the control can be performed until all the dummy lights are stopped.

[0059] When the control for stopping the dummy light having a wavelength longer than the second sub-band cannot reduce the output power gap either, for example, as in the change from the state shown in FIG. 7B to the state shown in FIG. 7C, control for increasing the loading amount of wavelengths shorter than the first sub-band may be performed. This control for increasing the loading amount of wavelengths shorter than the first sub-band is, for example, control by the loading control device 22 in FIG. 3, and is realized by the loading control device 22 adding and outputting one or more pieces of dummy light having wavelengths shorter than the first sub-band.

[0060] (Effects of Embodiment) According to the optical transmission system and its control method of the present embodiment, due to the optical amplification for each sub-band divided in the same manner as in the above-described embodiment, the gap in the amplification characteristics becomes smaller, so that the energy loss due to the equalization process can be reduced. As a result, an optical transmission system with improved energy utilization efficiency can be realized, and the performance of the optical transmission system can be maintained.

[0061] Furthermore, according to the present embodiment, by controlling to reduce the loading amount at wavelengths longer than the second sub-band on the long wavelength side, the gap in the output power is reduced. Since the loading amount at wavelengths longer than the second sub-band is reduced by a method such as stopping the dummy light, the power consumption related to the dummy light can be reduced, and an optical transmission system with further improved energy utilization efficiency can be realized, and the performance of the optical transmission system can be maintained.

[0062] In addition, in the present embodiment, in addition to controlling to reduce the loading amount at wavelengths longer than the second sub-band on the long wavelength side, by combining control to increase the loading amount at wavelengths shorter than the first sub-band on the short wavelength side, the gap in the output power can be made smaller.

[0063] FIG. 6 is a graph for explaining the effects according to the embodiment of the present invention. The horizontal axis represents the wavelength, and the vertical axis represents the relative spectral intensity. When the output of the excitation light source of the optical amplification unit is 100%, the optical transmission system is designed so that there is no gap (GAP) between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band. When the output of the excitation light source of the optical amplification unit decreases from 100% to 82%, there is a gap (GAP) of about 0.4 dB in the output waveform after passing through the equalizer between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band, as shown in FIG. 6.

[0064] On the other hand, in the case of the control such as in the present embodiment that reduces the loading amount of wavelengths longer than the second sub-band, in the case illustrated in FIG. 6, the gap (GAP) can be filled by reducing the loading wavelengths by four waves. In other words, the gap (GAP) can be filled by stopping a total of four waves of dummy lights L44, L43, L42, and L41 on the longer wavelength side than the second sub-band. Also, in the case illustrated in FIG. 6, it is understood that by stopping the dummy lights L40, L39, L38, L37, and L36 on the longer wavelength side, the relative spectral intensity of the second sub-band on the longer wavelength side increases.

[0065] 〔Third Embodiment〕 Next, an optical transmission system and its control method according to the third embodiment of the present invention will be described. FIG. 8 is a graph for explaining the control method of the optical transmission system according to the third embodiment of the present invention. This embodiment is an embodiment that uses the configuration of the optical transmission system shown in FIGS. 2A and 3 described above, similar to the second embodiment, and is characterized by the operation of the optical transmission system and the control method of the optical transmission system. In this embodiment, since the configuration of the optical transmission system shown in FIGS. 2A and 3 described above is used, the description of the configuration will be omitted.

[0066] In an optical transmission system, as described above, it is designed to include a plurality of channels used at the start of operation and also a plurality of channels (dark channels) that are in an unused state at the start of operation assuming future enhancements. After the start of operation, changes such as supplying signal light and stopping dummy light are made in the channels that are in an unused state. When converting the channels in the unused state to the used state in this way, it is assumed that it becomes difficult to perform control to reduce the gap with the output power by control such as reducing the loading amount of wavelengths longer than the second sub-band as in the second embodiment described above.

[0067] In other words, as the optical transmission system is operated for many years, the used band in FIG. 8 gradually approaches the Full C band, the loading amount itself decreases, and it is assumed that it becomes difficult to control the loading amount only within the Full C band to reduce the gap with the output power.

[0068] In this embodiment, as shown in FIG. 8, by controlling to increase the loading amount at a wavelength shorter than the first sub-band on the short-wavelength side, the bandwidth of the input signal becomes wider with respect to the optical amplification of the first sub-band, so that the amplification amount of the optical amplification unit decreases, and the gain of the optical amplification unit in the first sub-band decreases. As a result, the gap with the output power can be reduced.

[0069] Note that in this embodiment, the control to increase the loading amount at a wavelength shorter than the first sub-band on the short-wavelength side shows adding the loading amount to a wavelength band shorter than the Full C band as shown in FIG. 8. By adding loading to a band outside the Full C band in this way, the bandwidth of the input signal becomes wider with respect to the optical amplification of the first sub-band, so that the amplification amount of the optical amplification unit can be reduced, and the gain of the optical amplification unit in the first sub-band can be decreased.

[0070] (Effect of the embodiment) According to the optical transmission system and its control method of this embodiment, due to the optical amplification for each sub-band classified in the same manner as in the above-described embodiment, the gap in amplification characteristics is reduced, so that the energy loss due to equalization processing can be reduced. As a result, an optical transmission system with improved energy utilization efficiency can be realized, and the performance of the optical transmission system can be maintained.

[0071] Furthermore, in the present embodiment, by controlling to increase the loading amount at wavelengths shorter than the first sub-band on the short-wavelength side, the gap in output power can be made smaller. In this case, in the present embodiment, additional loading is performed outside the Full C band. Specifically, by adding a loading amount in a wavelength band shorter than the Full C band, the amplification amount of the optical amplification unit regarding the optical amplification of the first sub-band can be reduced, and the gain of the optical amplification unit of the first sub-band can be decreased. As a result, the gap in output power can be made smaller.

[0072] 〔Fourth Embodiment〕 Next, an optical transmission system and its control method according to the fourth embodiment of the present invention will be described. FIG. 9 is a graph for explaining the control method of the optical transmission system according to the fourth embodiment of the present invention. This embodiment is an embodiment that uses the configuration of the optical transmission system shown in FIGS. 2A and 3 described above, similar to the second and third embodiments, and is characterized by the operation of the optical transmission system and the control method of the optical transmission system. In this embodiment, since the configuration of the optical transmission system shown in FIGS. 2A and 3 described above is used, the description of the configuration will be omitted.

[0073] In the above-described second and third embodiments, it has been described that the gap in output power can be made smaller by controlling the loading amount at wavelengths longer than the plurality of divided sub-bands or by controlling the loading amount at wavelengths shorter than the plurality of divided sub-bands. However, the control of the loading amount according to the embodiments of the present invention is not limited to these. For example, it is also conceivable to reduce the gap in output power by controlling the loading amount in the band between the first sub-band and the second sub-band.

[0074] In this embodiment, the used band is divided into a first sub-band in a shorter wavelength band and a second sub-band in a longer wavelength band. And in this embodiment, as shown in FIG. 9, the loading amount in the band between the first sub-band and the second sub-band is controlled.

[0075] Monitor the output power of the channel with the longest wavelength among the first sub-bands on the relatively short-wavelength side, and monitor it together with the output power of the channel with the shortest wavelength among the second sub-bands on the relatively long-wavelength side. Then, transmit a control signal so that the gap between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band becomes smaller.

[0076] For example, among the loading amounts of the bands between the first sub-band and the second sub-band, by controlling to reduce the loading amount of the band closer to the second sub-band, the output power of each signal light of the wavelength-division multiplexed signal light in the second sub-band can be increased. Also, among the loading amounts of the bands between the first sub-band and the second sub-band, by controlling to increase the loading amount of the band closer to the first sub-band, the output power of each signal light of the wavelength-division multiplexed signal light in the first sub-band can be decreased. By controlling the loading amount of the band between the first sub-band and the second sub-band in this way, the gap with the output power can be made smaller.

[0077] (Effect of Embodiment) According to the optical transmission system and its control method of the present embodiment, due to the optical amplification for each sub-band classified in the same manner as in the above-described embodiment, the gap in amplification characteristics becomes smaller, so that the energy loss due to equalization processing can be reduced. As a result, an optical transmission system with improved energy utilization efficiency can be realized, and the performance of the optical transmission system can be maintained.

[0078] Furthermore, in the present embodiment, by controlling the loading amount of the band between the first sub-band and the second sub-band, the gap in output power can be made even smaller.

[0079] 〔Fifth Embodiment〕 Next, a optical transmission system and its control method according to the fifth embodiment of the present invention will be described. This embodiment is an embodiment that uses the configuration of the optical transmission system shown in FIGS. 2A and 3 described above, similar to the second to fourth embodiments, and is characterized by the operation of the optical transmission system and the control method of the optical transmission system. In this embodiment, since the configuration of the optical transmission system shown in FIGS. 2A and 3 described above is used, the description of the configuration will be omitted.

[0080] In this embodiment, in addition to controlling the loading amount such as output and stop of dummy light in a specific band as in the second to fourth embodiments described above, the transmission waveform of the transmitting-side terminal station is also controlled. FIG. 10 is a graph for explaining the control method of the optical transmission system according to the fifth embodiment of the present invention.

[0081] In the optical transmission system of this embodiment, at the terminal station 12A (transmitting-side terminal station Tx), the output power of the wavelength-division multiplexed signal light and the dummy light is increased for the Full C band. In FIG. 10, a state is shown in which dummy light is output in a band having a wavelength shorter than that of the first sub-band in the Full C band, and dummy light is also output in a band having a wavelength shorter than that of the second sub-band. In FIG. 10, the output power of the dummy light is also increased.

[0082] In the optical transmission system and its control method of this embodiment, similar to the above-described embodiments, the output power of the channel having the longest wavelength in the first sub-band on the relatively short-wavelength side is monitored, and the output power of the channel having the shortest wavelength in the second sub-band on the relatively long-wavelength side is monitored. Further, a control signal is transmitted so that the gap between the output power of the channel having the longest wavelength in the first sub-band and the output power of the channel having the shortest wavelength in the second sub-band becomes small.

[0083] In the optical transmission system and its control method of this embodiment, as shown by the arrow in FIG. 10, control for changing the loading amount is assumed. More specifically, it is control for reducing the loading amount of wavelengths longer than the second sub-band. As control for reducing the loading amount, control is performed to attenuate the output power of dummy light having a wavelength longer than the second sub-band. By this control, the amplification amount of the optical amplification unit for the second sub-band increases, and the gain of the optical amplification unit rises. As a result, the output power of each signal light of the wavelength-division multiplexed signal light in the second sub-band increases, and the gap between the output power of the channel having the longest wavelength in the first sub-band and the output power of the channel having the shortest wavelength in the second sub-band can be reduced.

[0084] FIG. 11A is a graph for explaining the amplification characteristics of an optical amplifier by the optical transmission system according to the fifth embodiment of the present invention. The horizontal axis indicates the wavelength, and the vertical axis indicates the relative spectral intensity. The optical transmission system is designed so that no gap (GAP) occurs between the output power of the channel having the longest wavelength in the first sub-band and the output power of the channel having the shortest wavelength in the second sub-band when the output of the excitation light source of the optical amplification unit is 100%. When the output of the excitation light source of the optical amplification unit decreases from 100% to 82%, a gap (GAP) of about 0.4 dB occurs in the output waveform after passing through the equalizer between the output power of the channel having the longest wavelength in the first sub-band and the output power of the channel having the shortest wavelength in the second sub-band, as shown in FIG. 11A.

[0085] On the other hand, by control such as that of this embodiment for reducing the loading amount of wavelengths longer than the second sub-band, specifically, control for attenuating dummy light having a wavelength longer than the second sub-band, in the case illustrated in FIG. 11A, the gap (GAP) can be filled by controlling to attenuate 8 waves of the dummy light.

[0086] FIG. 11B is a graph for explaining the amplification characteristics of an optical amplifier in an optical transmission system according to the fifth embodiment of the present invention. The attenuation applied to the loading wavelength at the terminal station 12A (the transmitting terminal station Tx) is output while maintaining the original wavelength characteristics. Therefore, in a plurality of serially connected repeaters 13, the same input waveform as that of the optical amplification unit of the first-stage repeater 13 is incident on the optical amplification unit of the subsequent-stage repeater 13. Thus, if control is performed to attenuate the dummy light at the terminal station 12A (the transmitting terminal station Tx), the input signals to the plurality of serially connected repeaters 13 can be controlled collectively. In other words, each stage of the plurality of serially connected repeaters 13 can amplify light while filling the gaps.

[0087] (Effect of the embodiment) According to the optical transmission system and its control method of the present embodiment, due to the optical amplification for each sub-band classified in the same manner as in the above-described embodiment, the gap in the amplification characteristics becomes smaller, so that the energy loss due to the equalization process can be reduced. As a result, an optical transmission system with improved energy utilization efficiency can be realized, and the performance of the optical transmission system can be maintained.

[0088] Furthermore, in the present embodiment, by performing control to reduce the loading amount of wavelengths longer than the second sub-band, specifically, control to attenuate the dummy light of wavelengths longer than the second sub-band, the gap in the output power can be reduced.

[0089] The control of the loading amount according to the second to fourth embodiments described above and the control of the loading amount according to the fifth embodiment can be used in combination. For example, the control for stopping the dummy light having a wavelength longer than that of the second sub-band as in the second embodiment and the control for attenuating the dummy light having a wavelength longer than that of the second sub-band as in this embodiment can be used in combination. The control for stopping the dummy light having a wavelength longer than that of the second sub-band as in the second embodiment corresponds to coarse adjustment. In other words, the control for reducing the number of loading lines having a wavelength longer than that of the second sub-band corresponds to coarse adjustment. The control for attenuating the dummy light having a wavelength longer than that of the second sub-band as in this embodiment corresponds to fine adjustment.

[0090] By using in combination the control for attenuating the dummy light having a wavelength longer than that of the second sub-band as in this embodiment, it becomes possible to adjust the intermediate gap amount (fine adjustment) with respect to the adjustment of the discrete gap amounts (coarse adjustment) shown in FIG. 6.

[0091] 〔Sixth Embodiment〕 Next, an optical transmission system and its control method according to the sixth embodiment of the present invention will be described. This embodiment is an embodiment using the configuration of the optical transmission system shown in FIGS. 2A and 3 described above, similar to the second to fourth embodiments, and is characterized by the operation of the optical transmission system and the control method of the optical transmission system. In this embodiment, since the configuration of the optical transmission system shown in FIGS. 2A and 3 described above is used, the description of the configuration will be omitted.

[0092] In this embodiment, similar to the fifth embodiment described above, the transmission waveform of the transmitting end station is also controlled. FIG. 12 is a graph for explaining the control method of the optical transmission system according to the sixth embodiment of the present invention.

[0093] In the optical transmission system of this embodiment, similar to the fifth embodiment, at the terminal station 12A (the terminal station Tx on the transmission side), the output powers of the wavelength-division multiplexed signal light and the dummy light for the Full C band are increased. In FIG. 12, among the Full C band, dummy light is output in a band having a wavelength shorter than that of the first sub-band, and a state where dummy light is output in a band having a wavelength shorter than that of the second sub-band is shown. In FIG. 12, the output power of the dummy light is also in an increased state.

[0094] In the optical transmission system of this embodiment and its control method, similar to the above-described embodiments, the output power of the channel having the longest wavelength among the first sub-bands on the relatively short-wavelength side is monitored, and the output power of the channel having the shortest wavelength among the second sub-bands on the relatively long-wavelength side is monitored. Further, a control signal is transmitted so that the gap between the output power of the channel having the longest wavelength among the first sub-bands and the output power of the channel having the shortest wavelength among the second sub-bands becomes smaller.

[0095] In the optical transmission system of this embodiment and its control method, as shown by the arrow in FIG. 12, it is assumed that the wavelength-division multiplexed signal light of the second sub-band is attenuated and the loading amount is changed. More specifically, in addition to the control for reducing the loading amount having a wavelength longer than that of the second sub-band as in the fifth embodiment, among the wavelength-division multiplexed signal light transmitted by the terminal station 12A (the terminal station Tx on the transmission side), control is performed to globally attenuate the wavelength-division multiplexed signal light of the second sub-band on the longer wavelength side. By this control, the amplification amount of the optical amplification unit for the second sub-band increases, and the gain of the optical amplification unit rises. As a result, the output power of each signal light of the wavelength-division multiplexed signal light of the second sub-band increases, and the gap between the output power of the channel having the longest wavelength among the first sub-bands and the output power of the channel having the shortest wavelength among the second sub-bands can be reduced.

[0096] (Effect of the embodiment) According to the optical transmission system and its control method of the present embodiment, due to the optical amplification for each sub-band divided in the same manner as in the above-described embodiment, the gap in the amplification characteristics becomes smaller, so that the energy loss due to the equalization process can be reduced. As a result, an optical transmission system with improved energy utilization efficiency can be realized, and the performance of the optical transmission system can be maintained.

[0097] Furthermore, in the present embodiment, similar to the fifth embodiment, control is performed to reduce the loading amount of wavelengths longer than the second sub-band, specifically, control to attenuate dummy light having a wavelength longer than the second sub-band, whereby the gap in the output power can be reduced.

[0098] Furthermore, in the present embodiment, control is performed to overall attenuate the wavelength-division multiplexed signal light in the second sub-band on the longer wavelength side among the wavelength-division multiplexed signal light transmitted by the terminal station 12A (the transmitting terminal station Tx). By not only adjusting the loading amount of wavelengths longer than the second sub-band but also overall adjusting the input signal intensity of the second sub-band, the amplification amount of the optical amplification unit for the second sub-band increases, and the gain of the optical amplification unit rises. As a result, the gap in the output power can be made smaller.

[0099] Note that in the present embodiment as well, it can be used in combination with the control of the loading amount according to the second to fourth embodiments described above. For example, control to stop dummy light having a wavelength longer than the second sub-band as in the second embodiment and control to overall attenuate the wavelength-division multiplexed signal light of the second sub-band as in the present embodiment can be used in combination. By using in combination control to overall attenuate the wavelength-division multiplexed signal light of the second sub-band as in the present embodiment, adjustment of the intermediate gap amount (fine adjustment) can be performed with respect to the adjustment of the jumpy gap amount (coarse adjustment) shown in FIG. 6.

[0100] 〔Other Embodiments〕 As described above, the preferred embodiments of the present invention have been explained, but the present invention is not limited thereto. FIG. 5B is a graph for explaining a modification of the control method of the optical transmission system according to the second embodiment of the present invention. For example, in the second embodiment described above, if it is determined that the change over time is large for the second sub-band on the longer wavelength side among the plurality of sub-bands, the used band is shifted toward the shorter wavelength side of the Full C band from the start of operation of the optical transmission system, and a design in which the loading is provided on the longer wavelength side can also be considered. In FIG. 5A, loading is provided on the shorter wavelength side of the first sub-band and on the longer wavelength side of the second sub-band, whereas in FIG. 5B, loading is provided only on the longer wavelength side of the second sub-band. When it is determined that the change over time is large for the second sub-band, control such as providing loading only on the longer wavelength side of the second sub-band and gradually reducing the loading amount can be considered. If it is determined that the change over time is large for the second sub-band on the longer wavelength side in this way, by designing with the used band shifted toward the shorter wavelength side of the Full C band, it is possible to solve the problem that the amount of loading that can be reduced runs out. Even in long-term operation, it is possible to maintain a margin for reducing the gap in output power.

[0101] Among the plurality of optical amplification units 15 in the above-described repeater 13 1 ~15 m Two or more SC-EDFAs (Single Core-Erbium doped Optical Fiber Amplifiers) can be used. Also, among the plurality of optical amplification units 15 in the above-described repeater 13 1 ~15 m One or more core-individually excited MC-EDFAs (Multi-Core-Erbium doped Optical Fiber Amplifiers) can be used. Also, among the plurality of optical amplification units 15 in the above-described repeater 13 1 ~15 mOne or more hybrid MC-EDFAs that combine clad collective excitation and core individual excitation can be used. As for two or more SC-EDFAs, one or more core individual excitation type MC-EDFAs, and one or more hybrid MC-EDFAs that combine clad collective excitation and core individual excitation, existing technologies can be applied to the present invention. For example, in FIG. 8 of Patent Document 2, an optical amplifier using a plurality of single-core optical fibers has been proposed. Each of these plurality of single-core optical fibers has a configuration including a single core doped with rare earth ions and a clad surrounding this single core. Also, in FIGS. 4 and 6 of Patent Document 2, optical amplifiers using multi-core optical fibers have been proposed. This multi-core optical fiber has a configuration including a plurality of cores doped with rare earth ions and a clad surrounding these plurality of cores. Needless to say, various modifications are possible within the scope of the invention described in the claims, and these are also included in the scope of the present invention.

[0102] Some or all of the above embodiments can be described as follows in the appended notes, but are not limited thereto. (Appended Note 1) An optical transmission system including a pair of terminal stations that transmit and receive wavelength-division multiplexed (WDM) signal lights to and from each other, an optical fiber that propagates the wavelength-division multiplexed signal lights transmitted and received by the pair of terminal stations, and at least one repeater inserted into the optical fiber, The repeater includes an optical amplifier that divides the wavelength-division multiplexed signal light into a plurality of sub-bands including signal lights in a plurality of wavelength bands, amplifies the divided plurality of sub-bands with a plurality of corresponding optical amplification units, and then multiplexes the amplified plurality of sub-bands, The divided plurality of sub-bands include a first sub-band on the relatively short-wavelength side and a second sub-band on the relatively long-wavelength side, A monitor unit that monitors the output power of the channel with the longest wavelength among the first sub-bands received by the receiving-side terminal station of the pair of terminal stations and the output power of the channel with the shortest wavelength among the second sub-bands received by the receiving-side terminal station of the pair of terminal stations, A control unit that transmits a control signal to a transmitting-end station that transmits the wavelength-division multiplexed signal light, such that a gap between the output power of the channel with the longest wavelength among the first sub-bands monitored by the monitor unit and the output power of the channel with the shortest wavelength among the second sub-bands monitored by the monitor unit is reduced. Optical transmission system. (Appendix 2) The control signal instructs the transmitting-end station to change the loading amount. The optical transmission system according to Appendix 1. (Appendix 3) The control signal instructs the transmitting-end station to reduce the loading amount of wavelengths longer than the second sub-band. The optical transmission system according to Appendix 2. (Appendix 4) The control signal instructs the transmitting-end station to reduce the loading amount of wavelengths longer than the second sub-band. When reducing the loading amount of this long wavelength does not sufficiently reduce the gap, the control signal further instructs the transmitting-end station to increase the loading amount of wavelengths shorter than the first sub-band. The optical transmission system according to Appendix 3. (Appendix 5) The control signal instructs the transmitting-end station to reduce the power of dummy light with wavelengths longer than the second sub-band. The optical transmission system according to Appendix 2. (Appendix 6) The control signal instructs the transmitting-end station to reduce the power of the signal light in the wavelength band divided into the second sub-band. The optical transmission system according to Appendix 5. (Appendix 7) The control signal instructs the transmitting-end station to increase the loading amount of wavelengths shorter than the first sub-band. The optical transmission system according to Appendix 2. (Appendix 8) The control signal instructs the transmitting end station to change the loading amount of the bandwidth between the first sub-band and the second sub-band. The optical transmission system according to Appendix 2. (Appendix 9) The transmitting end station generates the wavelength-division multiplexed signal light by wavelength-division multiplexing the signal light and the dummy light. The control of the loading amount is performed by increasing or decreasing the channels of the dummy light at the transmitting end station. The optical transmission system according to any one of Appendices 2 to 8. (Appendix 10) By shifting the channel with the shortest wavelength among the plurality of sub-bands toward the shorter wavelength side of the used band, A larger loading amount of the wavelength longer than the second sub-band is ensured. The optical transmission system according to Appendix 3. (Appendix 11) The plurality of optical amplifying units are two or more single-core impurity-added optical fiber amplifiers. The optical transmission system according to any one of Appendices 1 to 10. (Appendix 12) The plurality of optical amplifying units are one or more multi-core impurity-added optical fiber amplifiers. The optical transmission system according to any one of Appendices 1 to 10. (Appendix 13) The plurality of optical amplifying units are one or more hybrid multi-core impurity-added optical fiber amplifiers that use both clad collective excitation and core individual excitation. The optical transmission system according to any one of Appendices 1 to 10. (Appendix 14) A control method for an optical transmission system including a pair of end stations that transmit and receive wavelength-division multiplexed (WDM) signal lights to and from each other, an optical fiber that propagates the wavelength-division multiplexed signal lights transmitted and received by the pair of end stations, and at least one repeater inserted into the optical fiber. The repeater divides the wavelength-division multiplexed signal light into a plurality of sub-bands including signal lights in a plurality of wavelength bands, amplifies the divided plurality of sub-bands with a corresponding plurality of optical amplifying units, and then multiplexes the amplified plurality of sub-bands. The plurality of sub-bands divided as described above include a first sub-band on the relatively short-wavelength side and a second sub-band on the relatively long-wavelength side. Of the pair of end stations, the received signal of the receiving end station Monitor the output power of the channel with the longest wavelength among the first sub-bands and the output power of the channel with the shortest wavelength among the second sub-bands. Transmit a control signal to the transmitting end station that transmits the wavelength-division multiplexed signal light so that the gap between the output power of the channel with the longest wavelength among the first sub-bands and the output power of the channel with the shortest wavelength among the second sub-bands becomes smaller. A method for controlling an optical transmission system. (Appendix 15) The control signal instructs the transmitting end station to change the loading amount. The method for controlling an optical transmission system according to Appendix 14. (Appendix 16) The control signal instructs the transmitting end station to reduce the loading amount of wavelengths longer than the second sub-band. The method for controlling an optical transmission system according to Appendix 15. (Appendix 17) The control signal instructs the transmitting end station to reduce the loading amount of wavelengths longer than the second sub-band. When reducing the loading amount of this long wavelength does not sufficiently reduce the gap, further instruct the transmitting end station to increase the loading amount of wavelengths shorter than the first sub-band. The method for controlling an optical transmission system according to Appendix 16. (Appendix 18) The control signal instructs the transmitting end station to reduce the power of the dummy light of wavelengths longer than the second sub-band. The method for controlling an optical transmission system according to Appendix 15. (Appendix 19) The control signal instructs the transmitting end station to reduce the power of the signal light in the wavelength band divided into the second sub-band. The control method of the optical transmission system described in Supplementary Note 18. (Supplementary Note 20) The control signal instructs the terminal station on the transmission side to increase the loading amount of a wavelength shorter than that of the first sub-band. The control method of the optical transmission system described in Supplementary Note 15. (Supplementary Note 21) The control signal instructs the terminal station on the transmission side to change the loading amount of the band between the first sub-band and the second sub-band. The control method of the optical transmission system described in Supplementary Note 15. (Supplementary Note 22) The terminal station on the transmission side generates the wavelength-division multiplexed signal light by wavelength-division multiplexing the signal light and the dummy light. The control of the loading amount is performed by increasing or decreasing the channels of the dummy light at the terminal station on the transmission side. The control method of the optical transmission system according to any one of Supplementary Notes 15 to 21. (Supplementary Note 23) By shifting the channel with the shortest wavelength among the plurality of sub-bands toward the shorter wavelength side of the wavelength of the used band, a larger loading amount of a wavelength longer than that of the second sub-band is ensured. The control method of the optical transmission system described in Supplementary Note 16.

Explanation of Signs

[0103] 11, optical fiber 12A, 12B, 102A, 102B terminal stations 13, 103 repeaters 14, 104 demultiplexers 15 1 ~15 m 、105 1 ~105 m optical amplification unit 16, 106 multiplexers 121, 121, 123 multiplexing parts 124 multiplexing means 125 demultiplexing means 126, 127, 128 demultiplexing parts 21 output gap monitor 22 Loading control device 30 Network management system 108 Monitor section 109 Control section

Claims

1. An optical transmission system including a pair of terminal stations that transmit and receive wavelength-division multiplexed (WDM) signal lights to and from each other, an optical fiber that propagates the wavelength-division multiplexed signal lights transmitted and received by the pair of terminal stations, and at least one repeater that relays the optical fiber, wherein the repeater includes an optical amplifier that divides the wavelength-division multiplexed signal light into a plurality of sub-bands including signal lights in a plurality of wavelength bands, amplifies the divided plurality of sub-bands with a plurality of corresponding optical amplification units, and then multiplexes the amplified plurality of sub-bands, the divided plurality of sub-bands include a first sub-band on the relatively short-wavelength side and a second sub-band on the relatively long-wavelength side, a monitor unit that monitors the output power of the channel with the longest wavelength among the first sub-bands received by the receiving-side terminal station of the pair of terminal stations and the output power of the channel with the shortest wavelength among the second sub-bands received by the receiving-side terminal station of the pair of terminal stations, and a control unit that transmits a control signal to the transmitting-side terminal station that transmits the wavelength-division multiplexed signal light so that the gap between the output power of the channel with the longest wavelength among the first sub-bands monitored by the monitor unit and the output power of the channel with the shortest wavelength among the second sub-bands monitored by the monitor unit becomes small. Optical transmission system.

2. The control signal is for instructing the transmitting-side terminal station to change the loading amount. The optical transmission system according to Claim 1.

3. The control signal is for instructing the transmitting-side terminal station to reduce the loading amount of wavelengths longer than the second sub-band. The optical transmission system according to Claim 2.

4. The control signal further instructs the transmitting-side terminal station to increase the loading amount of wavelengths shorter than the first sub-band. The optical transmission system according to Claim 3.

5. The control signal is for instructing the transmitting-side terminal station to reduce the power of dummy light having a wavelength longer than the second sub-band. The optical transmission system according to Claim 2.

6. The control signal is for instructing the transmitting-side terminal station to reduce the power of the signal light in the wavelength band divided into the second sub-band. The optical transmission system according to Claim 5.

7. The control signal instructs the end station on the transmission side to increase the loading amount of wavelengths shorter than the first sub-band. The optical transmission system according to claim 2.

8. The control signal instructs the end station on the transmission side to change the loading amount of the band between the first sub-band and the second sub-band. The optical transmission system according to claim 2.

9. The end station on the transmission side generates the wavelength-division multiplexed signal light by wavelength-division multiplexing the signal light and the dummy light. The control of the loading amount is performed by increasing or decreasing the channels of the dummy light at the end station on the transmission side. The optical transmission system according to any one of claims 2 to 8.

10. A control method for an optical transmission system including a pair of end stations that transmit and receive wavelength-division multiplexed (WDM) signal lights to and from each other, an optical fiber that propagates the wavelength-division multiplexed signal lights transmitted and received by the pair of end stations, and at least one repeater inserted into the optical fiber. The repeater divides the wavelength-division multiplexed signal light into a plurality of sub-bands including signal lights in a plurality of wavelength bands, amplifies the plurality of divided sub-bands with a plurality of corresponding optical amplification units, and then multiplexes the amplified plurality of sub-bands. The plurality of divided sub-bands include a first sub-band on the relatively short-wavelength side and a second sub-band on the relatively long-wavelength side. Received by the receiving-side end station among the pair of end stations. Monitor the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band. Transmit a control signal to the end station on the transmission side that transmits the wavelength-division multiplexed signal light so that the gap between the output power of the channel with the longest wavelength in the first sub-band and the output power of the channel with the shortest wavelength in the second sub-band becomes smaller. A control method for an optical transmission system.

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