Optical communication device, optical communication system, and optical power control method

Abstract

To suppress optical power deviation between channels and reduce optical power deviation within the band of each channel in WDM optical communication.SOLUTION: An optical communication device includes: an optical monitor that monitors a WDM signal in which signals of a plurality of channels are multiplexed; a processor that calculates a control value for controlling optical power of the WDM signal in frequency units narrower than the channel bandwidth of the WDM signal, based on a power spectrum detected by the optical monitor; and an optical power adjustment circuit that adjusts the optical power of the WDM signal in the frequency units narrower than the channel bandwidth based on the control value.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to an optical communication device, a communication system, and an optical power control method. [Background technology]

[0002] In wavelength division multiplexing (WDM) optical communication systems, 96-channel signal transmission has been put into practical use in both the 1550nm C-band and the 1590nm L-band. The bandwidth of the C-band and L-band is 4.8THz (approximately 40nm), and for 96 channels, both the channel spacing and channel bandwidth are 50GHz (approximately 0.4nm). With a channel spacing and channel bandwidth of 50GHz, signal transmission is performed at a bit rate of 100Gbps and a baud rate of 32GBaud. To prevent optical power deviations between channels, the optical power of each channel is controlled in advance by upstream optical communication equipment. This is because channels with low optical power have a lower optical signal-to-noise ratio (OSNR), degrading signal quality.

[0003] A WDM signal containing power-controlled signals from multiple channels passes through a post-amplifier, transmission line, relay (in-line) amplifier, pre-amplifier, etc. before being received by downstream optical communications equipment. The wavelength-dependent loss and stimulated Raman scattering of the transmission line, as well as the wavelength (frequency) characteristics of the gain of each amplifier, cause optical power deviations between channels in the received WDM signal. The optical communications equipment on the receiving side controls the optical power so that each channel reaches the target optical power, thereby reducing the optical power deviation between channels.

[0004] In recent years, the baud rate of signals has been increased to increase the bit rate per channel. For example, a 1.2 Tbps signal transmission would be 130 GBaud, and the use of a channel spacing and channel bandwidth of 150 GHz is being considered. [Prior art documents] [Non-patent literature]

[0005] [Patent Document 1] Patent Publication No. 2012-65060 [Patent Document 2] Patent Publication No. 2015-126487 Summary of the Invention [Problem to be solved by the invention]

[0006] In optical transmission with a channel spacing and channel bandwidth of 50 GHz, even if the optical power is controlled for each channel on the transmitting and receiving sides, optical power deviations may remain within the band of each channel. When the channel spacing and channel bandwidth are 150 GHz, the wider the bandwidth, the larger the optical power deviation within the band. The increase in the optical power deviation within the band results in a transmission penalty during reception and hinders the extension of the transmission distance. In one aspect, the present invention aims to suppress the optical power deviation between channels in WDM optical communications and reduce the optical power deviation within the band of each channel. [Means for solving the problem]

[0007] In an embodiment, the optical communication device comprises: an optical monitor for monitoring a WDM signal in which signals of a plurality of channels are multiplexed; a processor that calculates a control value for controlling the optical power of the WDM signal in frequency units narrower than the channel bandwidth of the WDM signal based on the power spectrum detected by the optical monitor; an optical power adjustment circuit that adjusts the optical power of the WDM signal in units of frequencies based on the control value; Equipped with. [Effects of the Invention]

[0008] In WDM optical communications, the optical power deviation between channels is suppressed, and the optical power deviation within the band of each channel is reduced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an optical communication system according to a first embodiment. [Figure 2] 1A and 1B are diagrams illustrating examples of channel spacing and bandwidth in WDM transmission. [Figure 3] FIG. 10 is a diagram showing the spectrum of a WDM signal after transmission. [Figure 4] FIG. 10 is a spectrum diagram showing an example of optical power control after transmission. [Figure 5] FIG. 2 is a functional block diagram of a processor of the optical communication device according to the first embodiment. [Figure 6] 4 is a flowchart of an optical power control method according to the first embodiment. [Figure 7] 1A and 1B are diagrams showing an optical power spectrum input to an optical monitor and an optical power spectrum for each channel detected by the optical monitor. [Figure 8] FIG. 10 is a diagram illustrating correction of a power spectrum detected by an optical monitor. [Figure 9] FIG. 10 is a diagram illustrating an example of dividing a channel bandwidth in the frequency direction based on a power spectrum after correction. [Figure 10] FIG. 10 is a diagram illustrating a calculation of the difference between the optical power of each divided subchannel and the target optical power. [Figure 11] FIG. 10 is a diagram illustrating updating of an attenuation value. [Figure 12] FIG. 4 is a diagram showing a spectrum after optical power control in the first embodiment. [Figure 13] FIG. 10 is a schematic diagram of an optical communication system using an optical communication device according to a second embodiment. [Figure 14] 10 is a flowchart of an optical communication method according to a second embodiment. [Figure 15] FIG. 10 is a schematic diagram of an optical communication system using an optical communication device according to a third embodiment. [Figure 16] 16 is a diagram illustrating the processing of the power spectrum in the upstream optical communication device of FIG. 15. FIG. [Figure 17] 16 is a diagram illustrating the processing of the power spectrum in the downstream optical communication device of FIG. 15. FIG. [Figure 18]16 is a diagram illustrating optical power control in the optical communication device on the downstream side of FIG. 15. [Figure 19] FIG. 10 is a schematic diagram of an optical communication system using an optical communication device according to a fourth embodiment. [Figure 20] 10 is a flowchart of a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] In this embodiment, the optical power deviation between channels is suppressed in WDM optical communications, and the in-band optical power deviation of each channel is reduced. To achieve this, the optical power is controlled in frequency units narrower than the channel bandwidth used in WDM optical communications systems. The optical power is controlled using the attenuation function of a wavelength selective switch (WSS), the variable attenuation function of a dynamic gain equalizer, and the output adjustment function of a wavelength blocker that can control the optical output over a variable bandwidth.

[0011] Conventionally, the power deviation between channels, which occurs in the optical transmission line or erbium-doped fiber amplifier (EDFA), is monitored by downstream optical communication equipment, and the attenuation of the WSS in the upstream optical communication equipment is controlled to keep the monitored value flat. However, for example, at a baud rate of 130 GBaud, the channel bandwidth expands to 150 GHz. When a Raman amplifier is used to amplify signals over such a wide wavelength range, ripple occurs according to the pump light wavelength, and the spectral tilt within the band becomes significant. Furthermore, even with the conventional 50 GHz bandwidth, the influence of the tilt within the channel band can become significant depending on the state of the transmission line.

[0012] Therefore, optical power is controlled in frequency units narrower than the channel bandwidth used in WDM optical communication systems. More specifically, an optical communication device detects the power spectrum of a WDM signal, which is a multiplexed WDM signal, and calculates a control value for adjusting the power level of the WDM signal in frequency units narrower than the channel bandwidth of the WDM signal based on the detected power spectrum. Based on this control value, the power level of the WDM signal is adjusted in frequency units narrower than the channel bandwidth. In the following description, frequency units narrower than the channel bandwidth are sometimes referred to as "subchannels" for convenience. However, please note that subchannels are not units of optical transmission but rather units of optical power control. For example, in a WDM signal with a channel bandwidth of 50 GHz, the optical power level of each channel is controlled in frequency units such as 25 GHz and 12.5 GHz. In the case of a channel bandwidth of 150 GHz, the optical power level of each channel is controlled in frequency units such as 50 GHz, 25 GHz, and 12.5 GHz. Hereinafter, identical components will be designated by the same reference numerals, and redundant explanations may be omitted.

[0013] First Embodiment FIG. 1 is a schematic diagram of an optical communication system 1 according to a first embodiment. The optical communication system 1 includes a first optical communication device 10-1, a second optical communication device 10-2, and an optical transmission path 6 connecting the optical communication devices 10-1 and 10-2. A repeater amplifier 5 is inserted in the optical transmission path 6. The optical communication devices 10-1 and 10-2 are, for example, reconfigurable optical add / drop multiplexers (ROADMs), and are denoted as "ROADM device 1" and "ROADM device 2," respectively, in the drawing. For convenience of illustration, only the configuration of the transmitting side of the optical communication device 10-1 is shown, but the optical communication devices 10-1 and 10-2 have the same configuration.

[0014] In the first embodiment, the receiving optical communication device 10-2 monitors the output of the receiving WSS and controls the optical power of each channel in frequency units narrower than the channel bandwidth based on the monitoring results. The optical communication device 10-2 includes a preamplifier 101, a receiving WSS 11, an optical splitter (denoted as "SPL" in the figure) 12, an optical monitor 13, and a processor 15. The optical monitor 13 is an optical channel monitor capable of monitoring optical power and wavelength in real time, and is denoted as "OCM" in the figure. The optical communication device 10-2 also includes a transmitting WSS 16, an optical splitter 17, an optical monitor 18, and a postamplifier 102. The optical communication device 10-1 also includes a transmitting WSS 16, an optical splitter 17, an optical monitor 18, and a postamplifier 102 as its transmitting side configuration.

[0015] Transceivers 105-1, 105-2, ..., 105-n (represented as "Transceiver Tx λ1," "Transceiver Tx λ2," and "Transceiver Tx λn," respectively) that handle signals of different wavelengths λ1, λ2, ..., λn are connected to optical communication device 10-1. The optical signals output from each transceiver 105-1, 105-2, ..., 105-n are multiplexed by multiplexer 104. The multiplexed optical signal is input to transmitting WSS 16, where it is multiplexed with the optical signal from path A along with the optical signal from path B.

[0016] The WDM signal output from the transmitting WSS 16 is split by the optical splitter 17 and input to the postamplifier 102 and the optical monitor 18. The optical monitor 18 monitors the optical power for each channel (i.e., wavelength) and feeds back the monitoring results to the transmitting WSS 16. In the figure, solid arrows indicate optical signal lines, and dotted arrows indicate electrical signal lines. The transmitting WSS 16 has an attenuation function and controls the optical power of each channel based on the monitoring results so that the optical power of each channel reaches a target value.

[0017] The post-amplifier 102 amplifies the power-adjusted WDM signal and transmits it to the optical transmission line 6. The repeater amplifier 5 amplifies the WDM signal that has been attenuated in the optical transmission line 6. The WDM signal that has propagated through the optical transmission line 6 is received by the optical communication device 10-2.

[0018] A preamplifier 101 in the downstream optical communication device 10-2 amplifies the WDM signal attenuated in the optical transmission line 6. The postamplifier 102, preamplifier 101, and repeater amplifier 5 may be Raman amplifiers or EDFAs. The output of the preamplifier 101 is input to a receiving WSS 11. In the receiving WSS 11, a portion of the WDM signal is output to path C, and another portion of the WDM signal is distributed by a demultiplexer 103 to multiple transceiver receivers 105a, 105b, and 105c (represented as "Transceiver Rx λa," "Transceiver Rx λb," and "Transceiver Rx λc," respectively). The remaining portion of the WDM signal is input to an optical splitter 12.

[0019] The output of the optical splitter 12 is connected to the input of the optical monitor 13 and the input of the transmitting WSS 16. The optical monitor 13 monitors the optical power for each channel (wavelength). The monitoring results are input to the processor 15. Based on the monitoring results, the processor 15 determines a control value for the optical power of each channel in frequency units narrower than the channel bandwidth. The control values ​​are sent from the processor 15 to the receiving WSS 11. The control value may be, for example, the amount of attenuation of the receiving WSS 11, the amount of optical loss compensation, or the output level control value of the receiving WSS 11. Based on the control value, the receiving WSS 11 adjusts the optical power level of the input WDM signal in frequency units narrower than the channel bandwidth, thereby bringing the optical power of the input WDM signal closer to a target value.

[0020] The WDM signal, whose optical power has been controlled by the receiving WSS 11 in frequency units narrower than the channel bandwidth, is sent in the respective directions, such as to path C, the demultiplexer 103, and the transmitting WSS 16. The WDM signal input to the transmitting WSS 16 is multiplexed with transmission signals of other wavelengths and output to the downstream optical transmission path 6. The operation and configuration of the transmitting side of the optical communication device 10-2 are the same as those of the transmitting side of the optical communication device 10-1, as described above. The attenuation functions of the receiving WSS 11 and the transmitting WSS 16 are realized by microprocessors and voltage generation circuits provided within the WSSs.

[0021] Figure 2 shows examples of channel spacing and channel bandwidth in WDM transmission. Figure 2(A) shows the signal spectrum when the channel spacing and channel bandwidth are 50 GHz. Figure 2(B) shows the signal spectrum when the channel spacing and channel bandwidth are 150 GHz. At both the 50 GHz and 150 GHz channel bandwidths, the signal spectrum is not a perfect square wave but has a trapezoidal spectral shape. If the 150 GHz bandwidth is divided into, for example, three parts in the frequency direction, the central subchannel will have a rectangular waveform and a higher spectral density than the subchannels at the ends. This improves the spectral density compared to 50 GHz signal transmission. The 50 GHz channel bandwidth in Figure 2(A) may also be divided into multiple frequency regions. For example, it may be divided into four frequency regions and the optical power may be controlled in 12.5 GHz frequency increments.

[0022] Figure 3 shows the spectrum after transmission of a WDM signal. Figure 3 (A) shows the spectrum after transmission of a signal with a channel bandwidth of 50 GHz, and (B) shows the spectrum after transmission of a signal with a channel bandwidth of 150 GHz. Due to the effects of wavelength-dependent loss in the optical transmission line, stimulated Raman scattering, and the frequency characteristics of amplifier gain, optical power deviations occur between channels at both 50 GHz and 150 GHz. Furthermore, in-band optical power deviations occur in each channel. In-band optical power deviations represent the difference between the minimum and maximum power levels within that channel band, or the magnitude of the deviation from a reference value.

[0023] At 150 GHz, the wider the bandwidth, the larger the deviation in in-band optical power becomes. To reduce this deviation in in-band optical power, in this embodiment, optical power is controlled for each narrow frequency range in frequency units narrower than the channel bandwidth. As one example, the attenuation function of the receiving WSS 11 is used to control optical power in frequency units narrower than the channel bandwidth.

[0024] FIG. 4 is a spectrum diagram showing an example of optical power control after transmission. To facilitate understanding of the optical power control of the embodiment, we will first explain optical power control when the channel bandwidth is not divided. That is, this is the case where the channel bandwidth and the frequency unit of the optical power control are the same. FIG. 4(A) shows the optical power spectrum of the WDM signal output from the preamplifier 101 of the optical communication device 10-2. As described above, due to the influence of the optical transmission path 6, optical power deviation occurs between channels, and in-band optical power deviation occurs in each channel. This optical power spectrum is input to the receiving WSS 11.

[0025] Figure 4(B) shows the attenuation value set in the receiving WSS 11. The attenuation value is determined by the processor 15 based on the optical power monitoring results for each channel obtained by the optical monitor 13. The amount of attenuation varies for each channel due to the influence of the wavelength-dependent loss of the optical transmission line 6 and the frequency characteristics of the amplifier gain. By applying the attenuation shown in Figure 4(B) to the power spectrum shown in Figure 4(A), the power spectrum shown in Figure 4(C) is obtained. In this power spectrum, the optical power deviation between channels is suppressed, resulting in a spectral shape close to the target optical power, but in-band optical power deviation remains for each channel. This in-band deviation becomes more pronounced as the channel bandwidth becomes wider. Below, we will explain a specific configuration and method for reducing in-band optical power deviation.

[0026] 5 is a functional block diagram of the processor 15 of the optical communication device 10. The optical communication device 10 is applied to both the optical communication devices 10-1 and 10-2 in FIG. 1. The processor 15 has, as its functional blocks, an optical power reading unit 151, an optical power correction unit 152, a difference calculation unit 153, a difference determination unit 154, an attenuation (denoted as "ATT" in the figure) setting value calculation unit 155, an attenuation reading unit 156, and an attenuation setting unit 157. The "difference" in the difference calculation unit 153 and the difference determination unit 154 is the difference between the optical power of the frequency unit (referred to as a "subchannel" for convenience) to be subjected to optical power control and the target optical power, and is represented by ΔP(λ).

[0027] The transmitted WDM signal is input to the input port of the receiver WSS 11. The receiver WSS 11 has an attenuation function with frequency intervals narrower than the channel bandwidth. For example, if the channel bandwidth is 150 GHz, attenuation is possible at intervals narrower than 150 GHz, such as 50 GHz, 25 GHz, 12.5 GHz, and 6.25 GHz. In this example, optical power is controlled using the attenuation function of the receiver WSS 11, but instead of a WSS, other devices capable of power control in variable frequency units, such as a dynamic gain equalizer or wavelength blocker, may also be used.

[0028] A portion of the output of the receiving WSS 11 is split by the optical splitter 12 and input to the optical monitor 13. The other portion of the output of the receiving WSS 11 is sent to an output port. The optical monitor 13 detects the optical power for each channel (wavelength).

[0029] The optical power reading unit 151 of the processor 15 reads the optical power for each channel from the optical monitor 13. The optical power read by the optical power reading unit 151 is not identical to the optical power spectrum of the WDM signal input to the optical monitor 13, but represents the average optical power of each channel detected by the optical monitor 13. The optical power correcting unit 152 corrects the read power spectrum to estimate or restore the optical power spectrum input to the optical monitor 13. Details of this spectrum correction will be described later.

[0030] Based on the corrected power spectrum, the difference calculation unit 153 calculates the difference between the power level of the received WDM signal and the target optical power for each subchannel, which is a control unit narrower than the channel bandwidth. The target optical power is determined based on the results of a prior measurement of the optical transmission line 6, and is set to be flat within the channel band and flat between channels, for example, as shown by "target optical power" in Fig. 4(C).

[0031] The difference determination unit 154 determines whether the difference calculated for each frequency unit falls within the allowable range. If the optical power difference is within the allowable range, it means that the deviation from the target optical power for that subchannel is within the allowable range and the attenuation value set for the corresponding frequency band of the receiving WSS 11 is appropriate.

[0032] If the difference exceeds the allowable range, the attenuation reading unit 156 reads the current attenuation value of the subchannel to be controlled from the receiving WSS 11 in order to update the current attenuation value. The read attenuation value is supplied to the attenuation setting value calculation unit 155. The attenuation setting value calculation unit 155 calculates a new attenuation setting value based on the current attenuation value of the subchannel to be controlled and the difference ΔP(λ) calculated by the difference calculation unit 153. The calculated attenuation setting value is set by the attenuation setting unit 157 to the corresponding subchannel of the receiving WSS 11. As a result, the attenuation value of the receiving WSS 11 is updated to an appropriate value with a resolution finer than the channel bandwidth.

[0033] FIG. 6 is a flowchart of the optical power control method of the first embodiment executed by the processor 15. The processor 15 reads the optical power of each channel from the optical monitor 13 (S11). FIG. 7 shows the optical power spectrum input to the optical monitor 13 and the optical power spectrum detected by the optical monitor 13. Here, WDM transmission with a channel bandwidth of 150 GHz is assumed. In FIG. 7(A), the optical power spectrum input to the optical monitor 13 shows optical power deviations between channels, as well as in-band optical power deviations in each channel. In FIG. 7(B), the optical power of each channel detected by the optical monitor 13 shows optical power deviations between channels, but does not show in-band optical power deviations for each channel. This is because the optical monitor 13 detects the optical power of each channel as the average optical power of that channel.

[0034] Returning to FIG. 6, the processor 15 corrects the power spectrum detected by the optical monitor 13 (S12). This correction estimates the optical power spectrum when input to the optical monitor 13. FIG. 8 shows an example of power spectrum correction. In this example, the power spectrum acquired from the optical monitor 13 is corrected in the frequency direction by linear interpolation, and the optical power spectrum input to the optical monitor 13 is estimated. The power level after correction is indicated by Litrp. If the power levels of wavelengths λ1 and λ3 are P(λ1) and P(λ2), respectively, the linear interpolation can be expressed, for example, by equation (1).

[0035]

number

[0036] Returning to Fig. 6, the processor 15 calculates the difference ΔP(λ) between the corrected optical power and the target optical power in frequency units narrower than the channel bandwidth (S13). As described above, the target optical power is a power level that is flat within the channel band and flat between channels. Fig. 9 shows an example of dividing the channel bandwidth in the frequency direction based on the corrected power spectrum. The division into frequency units narrower than the channel bandwidth may be performed prior to the difference calculation by the difference calculation unit 153, or may be performed simultaneously with the difference calculation.

[0037] In the example of Figure 9, the 150 GHz bandwidth of each channel is divided into three in the frequency direction. Each channel is divided into three sub-channels with a bandwidth of 50 GHz, and an optical power Pdiv is obtained for each divided sub-channel. The center wavelengths of the three sub-channels of the λ1 channel are λ1-Δλ, λ1, and λ1+Δλ, respectively. The center wavelengths of the three sub-channels of the λ2 channel are λ2-Δλ, λ2, and λ2+Δλ, respectively. The λ3 channel is similarly divided in the frequency (wavelength) direction. Δλ corresponds to the sub-channel spacing of 50 GHz, which is equivalent to a wavelength spacing of approximately 0.4 nm in the 1550 nm band.

[0038] Since the difference ΔP(λ) between the corrected optical power and the target optical power is calculated in frequency units narrower than the channel bandwidth, the power spectrum in FIG. 8 has the same effect as if it had been corrected in frequency units narrower than the channel bandwidth.

[0039] FIG. 10 shows the calculation of the difference between the optical power for each subchannel and the target optical power Ptrg. As described above, the target optical power Ptrg is determined in advance based on measurements of the transmission path. Furthermore, the optical power spectrum input to the optical monitor 13 is estimated from the detection results of the optical monitor 13, and the optical power Pdiv for each subchannel is estimated based on the corrected power spectrum. This allows the difference ΔP(λi) between the optical power Pdiv and the target optical power Ptrg to be calculated in frequency units narrower than the channel bandwidth. Here, "i" represents the subchannel number. In the example of FIG. 10, if the number of channels in the WDM system is N, i is an integer between 1 and 3×N. If the subchannel number i is omitted, the difference ΔP(λ) calculated for each subchannel, i.e., in frequency units narrower than the channel bandwidth, is expressed by Equation (2).

[0040]

number

[0041] Returning to FIG. 6, the processor 15 determines for each subchannel whether the difference ΔP(λ) for that subchannel is within the allowable range (S14). If the difference ΔP(λ) is not within the allowable range (NO in S14), the attenuation value currently set for that subchannel is inappropriate, and so the attenuation value is updated. Specifically, the attenuation value ATT(λ) of the subchannel to be controlled, set in the receiving WSS 11, is read into the processor 15 (S15), and a new attenuation setting value ATTset(λ) to be set for that subchannel is calculated (S16). The calculated attenuation value ATTset(λ) is set for the corresponding subchannel of the receiving WSS 11 (S17).

[0042] Once the attenuation of the subchannel to be controlled has been updated, the processor 15 determines whether there are any other subchannels (S18). If there are any other subchannels (YES in S18), the process returns to step S13 and repeats steps S13 to S17. If the difference ΔP(λ) of the subchannel to be controlled is within the allowable range (YES in S14) in step S14, the attenuation value is not updated, and a determination is made in step S18 as to whether there are any other subchannels to be controlled. If there are no other subchannels (NO in S18), the process ends. Instead of controlling the subchannels sequentially, they may be controlled in parallel at once. The control flow in FIG. 6 can be performed periodically or irregularly during service.

[0043] FIG. 11 shows the updating of attenuation values. (A) of FIG. 11 shows the current setting values. (B) of FIG. 11 shows the setting values ​​after updating. In the example of (A) of FIG. 11, the same attenuation value is set for all subchannels, but different attenuation values ​​may be set by measuring the state of the transmission path in advance when the optical communication device 10 starts service. In (B) of FIG. 11, for each subchannel, the difference ΔP(λi) between the optical power of the divided subchannel and the target optical power is added to the current attenuation value to set a new attenuation value.

[0044] When the sub-channel number i is omitted, the updated attenuation setting value ATTset(λ) is expressed by equation (3).

[0045]

number

[0046] Fig. 12 shows the spectrum after optical power control in the first embodiment. Fig. 12(A) shows the spectrum after optical power control when each channel is divided into three in the frequency direction when the channel bandwidth is 150 GHz, and Fig. 12(B) shows the spectrum when each channel is divided into six in the frequency direction.

[0047] Referring to Figure 12(A), the in-band optical power deviation is significantly improved compared to Figure 3(B) when the 150 GHz channel bandwidth is not divided in the frequency direction. Furthermore, the in-band optical power deviation is reduced even compared to Figure 3(A) when the 50 GHz channel bandwidth is not divided in the frequency direction. Referring to Figure 12(B), the in-band optical power deviation is further reduced by setting the frequency unit for optical power control to 25 GHz. This reduces both the optical power deviation between channels and the optical power deviation within the channel band in WDM transmission, enabling optical communications with minimal degradation in signal quality.

[0048] Second Embodiment 13 is a schematic diagram of an optical communication system 2 using optical communication devices 20-1 and 20-2 according to the second embodiment. In the second embodiment, optical power is controlled on the transmitting side in frequency units narrower than the channel bandwidth so that the wavelength characteristics of the output power of the preamplifier 101 on the receiving side become flat. ROADM devices are used as an example of the optical communication devices 20-1 and 20-2.

[0049] The optical communication system 2 includes a first optical communication device 20-1, a second optical communication device 20-2, and an optical transmission line 6 connecting the optical communication devices 20-1 and 20-2. An in-line amplifier may be inserted in the optical transmission line 6. The optical communication devices 20-1 and 20-2 are, for example, ROADM devices. As in FIG. 1, solid arrows indicate optical signal lines, and dotted arrows indicate electrical signal lines.

[0050] The optical communication device 20-1 includes a transmitting WSS 26, a postamplifier 102, an optical supervisory channel (OSC) processing unit 23, an OSC filter 21, and a processor 25-1 as components of its transmitting section, while the optical communication device 20-2 includes an OSC filter 22, an OSC processing unit 24, a preamplifier 101, an optical splitter 29, an optical monitor 13, and a processor 25-2 as components of its receiving section.

[0051] For convenience of illustration, only a portion of the configuration of the receiving section of optical communication device 20-2 is depicted as the configuration of the receiving section of optical communication device 20-1, and only a portion of the configuration of the transmitting section of optical communication device 20-1 is depicted as the configuration of the transmitting section of optical communication device 20-2. In reality, optical communication devices 20-1 and 20-2 have the same configuration, and optical communication device 20-1 has the same configuration as the receiving section of optical communication device 20-2 as the configuration of its receiving section, and optical communication device 20-2 has the same configuration as the transmitting section of optical communication device 20-1 as the configuration of its transmitting section. Processors 25-1 and 25-2 may be shared between the transmitting section and the receiving section.

[0052] The WDM signal transmitted from the optical communication device 20-1 to the optical transmission line 6 is received by the optical communication device 20-2. A portion of the WDM signal that passes through the OSC filter 22 and is amplified by the preamplifier 101 is split by the optical splitter 29, and the optical power of each channel is detected by the optical monitor 13. As shown in FIG. 7A, the optical power spectrum output from the preamplifier 101 contains an in-band optical power deviation as well as an inter-channel optical power deviation. On the other hand, as shown in FIG. 7B, the optical power detected for each channel by the optical monitor 13 has lost the in-band optical power deviation. The power information of each channel detected by the optical monitor 13 is input to the processor 25-2.

[0053] The processor 25-2 has a received optical power reading unit 261 and a received power forwarding unit 262. The received optical power reading unit 261 reads the optical power of each channel detected by the optical monitor 13. The received power forwarding unit 262 forwards the read optical power of each channel to the OSC processing unit 23 in the upstream transmission unit. The OSC processing unit 23 incorporates the forwarded optical power information into monitoring information. The monitoring information is converted into an optical signal and transmitted to the optical transmission line 8 via the OSC filter 21. When the optical communication device 20-1 receives the OSC from the optical transmission line 8, the OSC filter 22 extracts the OSC, and the OSC processing unit 24 converts it into an electrical signal and demodulates it. The demodulated OSC signal is input to the processor 25-1.

[0054] The processor 25-1 has, as its functional blocks, an optical power correction unit 252, a difference calculation unit 253, a difference determination unit 254, an attenuation (denoted as "ATT" in the figure) setting value calculation unit 255, an attenuation reading unit 256, an attenuation setting unit 257, and a reception power acquisition unit 258.

[0055] The received optical power acquisition unit 258 acquires the received optical power of the optical communication device 20-1 from the input OSC signal, specifically, the optical power at the output stage of the preamplifier 101. The optical power correction unit 252 corrects the power spectrum of the received light monitored by the optical communication device 20-2 in the same way as in the first embodiment, and estimates or restores the optical power spectrum input to the optical monitor 13.

[0056] Based on the corrected power spectrum, the difference calculation unit 253 calculates the difference between the power level of the received light at the optical communication device 20-2 and the target optical power for each frequency unit (subchannel) narrower than the channel bandwidth. The target optical power is a power level that is set in advance so that it is flat within the channel band and flat between channels. The difference determination unit 254 determines whether the difference calculated for each predetermined frequency unit is within an allowable range. If the optical power difference is within an allowable range, it means that the deviation from the target optical power for that subchannel is within an allowable range and that the attenuation value set for the corresponding frequency band of the transmitting WSS 26 is appropriate.

[0057] If the difference exceeds the allowable range, the attenuation reading unit 256 reads the current attenuation value of the subchannel to be controlled from the transmitting WSS 26 in order to update the current attenuation value. The read attenuation value is supplied to the attenuation setting value calculation unit 255. The attenuation setting value calculation unit 255 calculates a new attenuation setting value based on the current attenuation value of the subchannel to be controlled and the difference ΔP(λ) calculated by the difference calculation unit 153. The calculated attenuation setting value is set for the corresponding subchannel of the transmitting WSS 26 by the attenuation setting unit 257. As a result, the attenuation value of the transmitting WSS 26 is updated to an appropriate value with a resolution finer than the channel bandwidth.

[0058] The transmitting WSS 26 of the optical communication device 20-1 transmits a WDM signal that has been spectrally shaped in advance to the optical transmission line 6. The WDM signal received by the optical communication device 20-2 and amplified by the preamplifier 101 has flat wavelength characteristics within the channel band, and the deviation between channels is reduced. By flattening the wavelength characteristics of the output power of the preamplifier 101, the end-to-end OSNR is improved. In addition, demodulation errors of optical signals dropped by the optical communication device 20-2 are reduced.

[0059] 14 is a flowchart of the optical power control method of the second embodiment. The control flow (S21 to S28) of the section labeled "ROADM-1" is executed by the processor 25-1 of the optical communication device 20-1. The processing flow (S31, S32, S33) of the section labeled "ROADM-2" is executed by the optical communication device 20-2.

[0060] The processor 25-2 of the optical communication device 20-2 reads the received optical power spectrum output from the preamplifier 101 and detected by the optical monitor 13 (S31), and transfers the optical power of each channel to the OSC processing unit 23 (S32). The optical communication device 20-2 transmits the optical power spectrum of each channel to the source optical communication device 20-1 using OSC (S33).

[0061] The processor 25-1 of the optical communication device 20-1 acquires optical power information of the receiving-side WDM signal received by the OSC (S21). This receiving-side optical power information represents the optical power of each channel output from the preamplifier 101 of the optical communication device 20-2 and detected by the optical monitor 13. The processor 25-1 corrects the optical power with respect to wavelength (frequency) (S22). The optical power correction may be linear interpolation as described in the first embodiment, or curved interpolation. Based on the corrected optical power spectrum, the processor 25-1 calculates the difference ΔP(λ) from the target optical power in frequency units narrower than the channel bandwidth (or channel spacing) (S23). The target optical power is an optical power set to flatten the wavelength characteristics of power within the channel band and suppress deviations between channels.

[0062] The processor 25-1 determines whether the difference ΔP(λ) is within the allowable range for each frequency unit (subchannel) narrower than the channel bandwidth (S24). If the difference ΔP(λ) is not within the allowable range (NO in S24), the attenuation value set for the frequency corresponding to that subchannel is inappropriate, and so the attenuation value is updated. Specifically, the attenuation value ATT(λ) of the subchannel to be controlled, set in the transmitting WSS 26, is read into the processor 15 (S25), a new attenuation setting value ATTset(λ) to be set for that subchannel is calculated (S26), and the new attenuation value ATTset(λ) is set (S27).

[0063] Once the attenuation value of the subchannel to be controlled is updated, processor 25-1 performs similar control on the other subchannels. When optical power control for all subchannels is completed, the current control process ends. Instead of controlling the subchannels sequentially, they may be controlled in parallel at once. The control flow in Figure 14 can be performed periodically or irregularly during service.

[0064] Third Embodiment 15 is a schematic diagram of an optical communication system 3 using optical communication devices 30-1 and 30-2 according to the third embodiment. ROADM devices are used as an example of the optical communication devices 30-1 and 30-2. In the third embodiment, optical power is controlled using an upstream signal spectrum that has not yet been affected by the optical transmission line 6 or amplifiers, and the power spectrum of the signal light received downstream from the optical transmission line 6. As in the first and second embodiments, the optical power of the received WDM signal is controlled in frequency units narrower than the channel bandwidth.

[0065] Both the power spectrum of the upstream WDM signal not yet affected by the optical transmission line 6 and the power spectrum of the downstream WDM signal received via the optical transmission line 6 are detected with high resolution, at frequency intervals sufficiently narrower than the attenuation resolution of the WSS. The WDM signal not yet affected by the optical transmission line 6 is a WDM signal added inside the optical communication device 30-1 and not yet passing through the optical transmission line 6. The attenuation resolution of the WSS is 50 GHz, 25 GHz, 12.5 GHz, 6.25 GHz, etc., and the power spectrum is detected with a higher resolution. The upstream power spectrum detected with high resolution is integrated in the frequency direction to match the control interval of the WSS and sent to the downstream optical communication device via the OSC. Similarly, the downstream power spectrum detected with high resolution is integrated in the frequency direction to match the control interval of the WSS. Based on the integrated upstream signal spectrum and downstream power spectrum, the optical power is controlled in frequency units narrower than the channel bandwidth.

[0066] The optical communication devices 30-1 and 30-2 are connected by an optical transmission line 6. A repeater amplifier 5 is inserted in the optical transmission line 6. The upstream optical communication device 30-1 has a processor 35-1, a transmitting WSS 36, an optical splitter 37, an optical monitor 38, a multiplexer 104, a post-amplifier 102, and an OSC processing unit 107.

[0067] Transceivers 105-1, 105-2, and 105-3 (collectively referred to as "transceiver 105up") that handle signals of different wavelengths are connected to optical communication device 30-1. In FIG. 15, the transmitting side configuration of optical communication device 30-1 is shown with the transmitting circuits Tx of each transceiver 105-1, 105-2, and 105-3 connected. Optical signals output from transceiver 105up are multiplexed by multiplexer 104. The multiplexed optical signal is input to transmitting WSS 16 and multiplexed with optical signals from path A and path B.

[0068] A portion of the output of the transmitting WSS 36 is split by the optical splitter 37 and input to the optical monitor 38. The optical monitor 38 detects the power spectrum of channels of the input WSS signal that are not affected by the frequency characteristics of the optical transmission line 6 or the amplifier gain, at frequency intervals that are sufficiently narrower than the attenuation interval of the transmitting WSS 36. The signals from paths A and B have already been affected by the optical transmission line 6, etc., but the WDM signal output from the transceiver 105up and multiplexed by the multiplexer 104 is an untransmitted signal that is not affected by the optical transmission line 6 or the amplifier.

[0069] If the resolution of the attenuation function of the transmitting WSS 36 is 25 GHz, the optical monitor 38 detects the optical power of the untransmitted channels multiplexed by the multiplexer 104 at a frequency interval finer than 25 GHz with high resolution. Detecting the power at a resolution higher than the resolution of the attenuation function has the same effect as correcting the power spectrum detected by the optical monitor 38. The detected power spectrum is input to the processor 35-1.

[0070] The data processing unit 351 of the processor 35-1 integrates the power spectrum detected by the optical monitor 38 in the frequency direction so as to match the control interval (for example, the frequency interval of attenuation) of the WSS. The signal spectrum integrated in the frequency direction is converted into an optical signal by the OSC processing unit 107 and transmitted to the optical transmission line 6.

[0071] The optical communication device 30-2 has a receiving WSS 31, an optical splitter 32, an optical monitor 33, a processor 35-2, and an OSC processing unit 106. The optical communication device 30-2 also has, as its transmitting side configuration, a transmitting WSS 36, an optical splitter 37, an optical monitor 38, a multiplexer 104, a post-amplifier 102, and an OSC processing unit 107. The configuration and functions of these components are the same as those of the transmitting side of the optical communication device 30-1. The data processing unit 351 of the processor 35-2 may also have the function of the data processing unit 351 of the processor 35-1.

[0072] The OSC signal received by the optical communication device 30-2 is converted into an electrical signal by the OSC processing unit 106 and input to the data processing unit 351 of the processor 35-2. The WDM signal received by the optical communication device 30-2 is amplified by the preamplifier 101 and input to the receiving WSS 31. In the receiving WSS 31, a portion of the WDM signal is output to path C, and another portion of the WDM signal is distributed by the demultiplexer 103 to multiple transceiver receivers 105a, 105b, and 105c. The remaining portion of the WDM signal is input to the optical splitter 32.

[0073] The output of the optical splitter 32 is connected to the input of the optical monitor 33 and the input of the transmitting WSS 36. The optical monitor 33 detects the input optical power spectrum at a frequency interval narrower than the frequency interval of the attenuation of the receiving WSS 31. The detection result is input to the data processing unit 351 of the processor 35-2. The data processing unit 351 integrates the high-resolution power spectrum acquired from the optical monitor 33 in the frequency direction to match the frequency interval of the attenuation of the receiving WSS 31. As a result, the frequency interval of the upstream signal spectrum acquired from the OSC 106 matches the frequency interval of the power spectrum detected by the optical monitor 33.

[0074] The data processing unit 351 compares the power spectrum of the transmission signal sent by the optical communication device 30-1 via OSC with the power spectrum of the reception signal monitored by the optical communication device 30-2, and supplies the comparison result to the control processing unit 352 as a control amount for the reception WSS 31. The control processing unit 352 controls the attenuation value of the reception WSS 31 in accordance with the control amount. The control amount or the attenuation value is determined so that the reception signal power spectrum approaches the transmission signal power spectrum. In addition, the control amount or the attenuation value is determined so that the deviation between the channels of the reception signal power spectrum is minimized.

[0075] If the optical power for each channel (wavelength λi) in the upstream optical communication device 30-1 is Pλi, the optical power for each wavelength λi monitored by the receiving optical communication device 30-2 is P'λi, and the number j of the sub-channel into which the channel bandwidth is divided is 1 or 2, the attenuation value Ajλi for each sub-channel at each wavelength can be expressed, for example, as follows: A1λ1=P'1λ1-P1λ1 A2λ1=P'2λ1-P2λ1 ... A1λ2=P'1λ2-P1λ2 A2λ2=P'2λ2-P2λ2 ... A1λ3=P'1λ3-P1λ3 A2λ3=P'2λ3-P2λ3.

[0076] Using as a reference the power spectrum of a WDM signal that is not affected by the transmission line, etc., i.e., a WDM signal that has been added inside the optical communication device 30-1 and has not yet passed through the optical transmission line 6, the optical power is controlled in frequency units narrower than the channel bandwidth so as to compensate for the effects of the optical transmission line 6. This achieves more precise power control, and sufficiently reduces both the optical power deviation between channels and the optical power deviation within the channel band.

[0077] Fig. 16 shows the processing of power spectra in the optical communication device 30-1. Fig. 16(A) shows the power spectrum of the signal light input to the optical monitor 38 that is not affected by the optical transmission line 6. In other words, it is the power spectrum of the optical signal multiplexed by the multiplexer 104.

[0078] 16B shows the optical power of each channel detected by the optical monitor 38. The optical monitor 38 detects the input optical power at frequency intervals that are much finer than the attenuation control interval of the transmitting WSS 36. However, the average power is detected for each frequency interval. In this state, this does not match the control interval of the WSS.

[0079] 16(C) shows the power spectrum integrated in the frequency direction by the data processing unit 351. The integration in the frequency direction is a process for matching the optical power control interval of the downstream optical communication device 30-2, for example, the attenuation control interval of the receiving WSS 31. The signal spectrum in FIG. 16(C) is sent to the optical communication device 30-2 using OSC.

[0080] Fig. 17 shows the processing of power spectra in the optical communication device 30-2. Fig. 17(A) shows the power spectrum of the WDM signal input to the optical monitor 33. Due to the influence of wavelength-dependent loss in the optical transmission line 6, stimulated Raman scattering, and the wavelength characteristics of the amplifier gain, power deviations occur between channels, and also within the channel band.

[0081] 17B shows the optical power of each channel detected by the optical monitor 33. The optical monitor 33 detects the optical power of the input WDM signal at frequency intervals that are much finer than the attenuation control interval of the receiving WSS 31. However, the average power is detected for each frequency interval. In this state, this does not match the control interval of the receiving WSS 31.

[0082] 17C shows the power spectrum integrated in the frequency direction by the data processing unit 351. The integration in the frequency direction is a process of matching the detection result of the optical monitor 33 with the attenuation control interval of the receiving WSS 31.

[0083] Fig. 18 shows optical power control in the optical communication device 30-2. Fig. 18(A) shows the power spectrum integrated in the frequency direction on the downstream side, i.e., in the optical communication device 30-2. This power spectrum is the power spectrum shown in Fig. 17(C). Each channel is divided into, for example, eight frequency bands j (j is an integer from 1 to 8) in accordance with the control interval of the receiving WSS 31. In this example, the attenuation control interval of the receiving WSS 31 is 18.76 GHz. The integrated power in frequency band j of each channel is represented by P'jλn, where n is the channel number.

[0084] (B) in Figure 18 shows the spectrum of a signal sent from the upstream side, i.e., from optical communication device 30-1. This signal spectrum corresponds to the power spectrum in (C) in Figure 16. In this signal spectrum, each channel is also divided into eight frequency bands j. The integrated power of frequency band j of each channel is represented by Pjλn.

[0085] (C) in FIG. 18 shows the comparison result (difference, power ratio, etc.) between (A) and (B) in FIG. 18. The comparison result becomes the control value (for example, attenuation value) of the receiving WSS 31. The control value is represented by Ajλn. When the difference is used as the comparison result, the control value is Ajλn=P'jλn - P'jλn When the power ratio is used as the comparison result, the control value is calculated as follows: Ajλn=P'jλn / P'jλn It is also possible to use an appropriate function other than the difference or power ratio to calculate the control value.

[0086] This configuration and method allows the optical power to be controlled at control intervals narrower than the channel bandwidth, thereby reducing both the optical power deviation between channels and the optical power deviation within the channel band.

[0087] <Fourth embodiment> 19 is a schematic diagram of an optical communication system 4 using optical communication devices 40-1 and 40-2 according to the fourth embodiment. In the fourth embodiment, the results of monitoring the optical power spectrum on the receiving side are fed back to the optical communication device that is the source of transmission, and the optical power is controlled on the transmitting side in frequency units narrower than the channel bandwidth, thereby reducing the in-band optical power deviation on the receiving side. The optical communication device on the transmitting side determines wavelength dependency for each predetermined frequency unit and controls the optical power based on the in-band optical power deviation on the receiving side.

[0088] The optical communication system 4 includes a first optical communication device 40-1, a second optical communication device 40-2, and optical transmission lines 6 and 8 connecting the optical communication devices 40-1 and 40-2. In-line amplifiers may be inserted in the optical transmission lines 6 and 8. The optical communication devices 40-1 and 40-2 are, for example, ROADM devices. As in FIGS. 1, 13, and 15, solid arrows indicate optical signal lines, and dotted arrows indicate electrical signal lines.

[0089] The optical communication device 40-1 includes a transmitting WSS 46, an optical splitter 47, an optical monitor 48, a postamplifier 102, an OSC processor 43, an OSC filter 41, and a processor 45-1 as components of its transmitting section. The optical communication device 40-2 includes an OSC filter 42, an OSC processor 44, a preamplifier 101, an optical splitter 49, an optical monitor 43, and a processor 45-2 as components of its receiving section.

[0090] For convenience of illustration, only a portion of the configuration of the receiving section of optical communication device 40-2 is depicted as the configuration of the receiving section of optical communication device 40-1, and only a portion of the configuration of the transmitting section of optical communication device 40-1 is depicted as the configuration of the transmitting section of optical communication device 40-2. In reality, optical communication devices 40-1 and 40-2 have the same configuration, and the receiving section of optical communication device 40-1 has the same configuration as the receiving section of optical communication device 40-2. The transmitting section of optical communication device 40-2 has the same configuration as the transmitting section of optical communication device 40-1. Processors 45-1 and 45-2 may be shared between the transmitting section and the receiving section.

[0091] The WDM signal and OSC signal transmitted from optical communication device 40-1 to optical transmission line 6 are received by optical communication device 40-2. The OSC signal is extracted by OSC filter 42 and processed by OSC processing unit 44. The WDM signal is amplified by preamplifier 101 and input to optical splitter 49. A portion of the WDM signal is split by optical splitter 49, and the optical power of each channel is detected by optical monitor 43. The optical power spectrum input to optical monitor 43 contains an in-band optical power deviation as well as an inter-channel optical power deviation, as shown in FIG. 7A. However, in the power spectrum detected by optical monitor 43, the in-band optical power deviation is lost, as shown in FIG. 7B.

[0092] The processor 45-2 has a received optical power reading unit 461 and a received power forwarding unit 462. The received optical power reading unit 461 reads the power spectrum detected by the optical monitor 43. The received power forwarding unit 462 forwards the read power spectrum as power spectrum information to the OSC processing unit 43 in the upstream transmission unit. The OSC processing unit 43 incorporates the forwarded power spectrum information into monitoring information. The monitoring information is converted into an optical signal and transmitted to the optical transmission line 8 via the OSC filter 41. When the optical communication device 40-1 receives the OSC from the optical transmission line 8, the OSC filter 42 extracts the OSC and the OSC processing unit 44 converts it into an electrical signal.

[0093] The processor 45-1 has, as its functional blocks, a transmission light power reading unit 451, a wavelength dependency calculation unit 452, a wavelength dependency correction unit 453, a wavelength dependency determination unit 454, an attenuation setting value calculation unit 455, an attenuation reading unit 456, an attenuation setting unit 457, and a reception light power acquisition unit 458.

[0094] The transmission optical power reading unit 451 reads the power spectrum of the transmission WDM signal detected by the optical monitor 48. The power spectrum of the transmission WDM signal detected by the optical monitor 48 is in the state shown in FIG. 7B. This power spectrum is defined as the transmission optical power Ptransmit(λn), where n is the channel number. The wavelength dependency calculation unit 452 receives the transmission optical power Ptransmit(λn) from the transmission optical power reading unit 451. Meanwhile, the reception optical power acquisition unit 458 acquires the reception optical power Preceive(λn) from the OSC processing unit 44 and inputs it to the wavelength dependency calculation unit 452.

[0095] The wavelength dependency calculation unit 452 calculates the wavelength dependency WDL(λn) using equation (4) based on the transmitted optical power Ptransmit(λn) and the received optical power Preceive(λn).

[0096]

number

[0097] The wavelength dependence calculated by the wavelength dependence calculation unit 452 is acquired for each channel and does not reflect the deviation within the channel band. Therefore, the wavelength dependence correction unit 453 corrects the wavelength dependence WDL(λn) in the frequency direction. When the wavelength dependence WDL(Ln) is corrected by linear interpolation as in the power correction in FIG. 8, the corrected wavelength dependence WDL(Ln) is expressed by Equation (5). WDL(λ)=aλ+b (5) Here, a and b are constants, and a indicates the slope of the wavelength dependency.

[0098] The wavelength dependency determination unit 454 determines whether the wavelength dependency is within an allowable range in frequency units narrower than the channel bandwidth based on the wavelength dependency after correction. Since the allowability of the wavelength dependency after correction is determined in frequency units narrower than the channel bandwidth, the correction by the wavelength dependency correction unit 453 has the same effect as correction in frequency units narrower than the channel bandwidth.

[0099] If the wavelength dependency is not within the allowable range, the attenuation value set for that subchannel is inappropriate, so the attenuation set value calculation unit 455 updates the current attenuation set value ATTset(λ). Specifically, the attenuation reading unit 456 reads the attenuation value ATT(λi) currently set for the corresponding subchannel of the transmitting WSS 46, and calculates a new attenuation set value ATTTset(λi) using equation (6). ATTset(λi)=ATT(λi)-WDL(λi) (6) Here, i is the subchannel number. If a WDM signal includes n channel signals and the channel bandwidth of each channel is divided into m parts in the frequency direction, i is an integer between 1 and m×n.

[0100] The newly calculated attenuation setting value ATTTset(λi) is set in the corresponding frequency domain of the transmitting WSS 46 by the attenuation setting unit 457. Although the above expressions (4), (5), and (6) are expressed as functions of wavelength, they may also be written as functions of frequency f based on the relationship c=λ×f, where c is the speed of light and f is the frequency.

[0101] 20 is a flowchart of the optical power control method of the fourth embodiment. The main part of this control flow is executed by the processor 45-1 of the optical communication device 40-1. The processor 45-1 reads the transmission optical power of each channel from the optical monitor 48 (S41). Meanwhile, the processor 45-2 of the optical communication device 20-2 reads the received optical power spectrum detected by the optical monitor 43 (S51) and transfers the received optical power spectrum to the OSC processing unit 43 (S52). The optical communication device 40-2 notifies the source optical communication device 40-1 of the received optical power spectrum information using OSC.

[0102] The processor 45-1 of the optical communication device 40-1 acquires received optical power spectrum information from the OSC processing unit 44 (S42) and calculates wavelength dependency for each channel from the transmitted optical power and received power (S43). Because the calculated wavelength dependency does not reflect the state within the channel band, the wavelength dependency is corrected (S44). This correction estimates the tilt within the channel band, achieving the same effect as correcting wavelength dependency at frequency intervals narrower than the channel bandwidth.

[0103] The processor 45-1 determines whether the wavelength-dependent WDL(λ) is within the allowable range for each frequency unit narrower than the channel bandwidth (S45). If the wavelength-dependent WDL(λ) of the frequency unit to be controlled, i.e., the subchannel, is not within the allowable range (NO in S45), the processor 45-1 reads the corresponding attenuation value ATT(λi) of the transmitting WSS 46 (S46) and calculates a new attenuation setting value ATTset(λ) (S47). The new attenuation setting value ATT,set(λi) is set for the corresponding frequency band of the transmitting WSS 46 (S48). When appropriate attenuation values ​​have been set for all subchannels of the transmitting WSS 45, the process ends. This control flow can be performed periodically or irregularly during service.

[0104] The wavelength dependency is corrected in frequency units narrower than the channel bandwidth, and the attenuation setting value is controlled based on the corrected wavelength dependency, thereby suppressing the optical power deviation between channels and reducing the optical power deviation within the channel band. That is, the effect shown in FIG. 12 can be obtained. As mentioned above, optical power control may be performed using other devices with power adjustment functions, such as a dynamic gain equalizer or wavelength blocker, instead of the attenuation function of the transmitting WSS 46. Furthermore, the 150 GHz channel bandwidth may be divided into four or more parts in the frequency direction to control the optical power with higher resolution.

[0105] Although the above embodiments have been described based on specific configuration examples, the present disclosure is not limited to the above embodiments. The power control method of the embodiments can also be applied to control power deviations within or between channels with a 50 GHz bandwidth. In the embodiments, the attenuation function of a WSS is used as an optical power adjustment circuit that adjusts the optical power level in frequency units narrower than the channel bandwidth. However, other power adjustment circuits, such as a dynamic gain equalizer or a wavelength blocker, may be used instead of the WSS function. In the third embodiment, instead of controlling the optical power by the optical communication device 30-2, the optical power may be controlled by the optical communication device 30-1. In this case, the optical power monitored with high resolution by the optical communication device 30-2 may be integrated by the optical communication device 30-2 or by the optical communication device 30-1. To reduce the amount of OSC information, the power spectrum information integrated by the optical communication device 30-2 may be sent to the optical communication device 30-1. In the fourth embodiment, instead of controlling the optical power by the optical communication device 40-1, the optical power may be controlled by the optical communication device 40-2. In this case, the optical communication device 40-1 simply notifies the optical communication device 40-2 of the transmission power spectrum information via OSC. Instead of correcting the power spectrum detected by the optical monitor in the first, second, and fourth embodiments, the power spectrum input to the optical monitor may be detected with high resolution and integrated in the frequency direction, as in the third embodiment. The formula for calculating the control value is not limited to the calculations exemplified in the above embodiments, and an appropriate function may be used. In any case, the power of the WDM signal is controlled in frequency units narrower than the channel bandwidth, so that it is possible to reduce both the optical power deviation between channels and the optical power deviation within the channel band. [Explanation of symbols]

[0106] 1, 2, 3, 4 Optical communication system 6, 8 Optical transmission line 10-1, 10-2, 20-1, 20-2, 30-1, 30-2, 40-1, 40-2 Optical communication device 11, 31 Receiver WSS (optical power adjustment circuit) 13, 18, 28, 33, 38, 43, 48 Optical monitor 15, 25-1, 25-2, 35-1, 35-2, 45-1, 45-2 processors 16, 26, 36, 46 Transmit WSS (optical power adjustment circuit) 23, 24, 43, 44, 106, 107 OSC processing section 101 Preamp 102 Post-amplifier 103 Duplexer 104 Multiplexer

Claims

1. an optical monitor for monitoring a WDM signal in which signals of a plurality of channels are multiplexed; a processor that calculates a control value for controlling the optical power of the WDM signal in frequency units narrower than the channel bandwidth of the WDM signal based on the power spectrum detected by the optical monitor; an optical power adjustment circuit that adjusts the optical power of the WDM signal in units of frequencies based on the control value; Equipped with An optical communication device, wherein each of the frequency units has a bandwidth obtained by dividing each of the plurality of channels, and does not include two of the plurality of channels.

2. the processor calculates a control value for controlling the optical power so as to reduce the optical power deviation within the channel band; 2. The optical communication device according to claim 1.

3. the processor calculates a control value for controlling optical power so as to reduce the optical power deviation between channels of the WDM signal and the optical power deviation within the band of each channel; 2. The optical communication device according to claim 1.

4. An optical monitor for monitoring a WDM signal in which signals of multiple channels are multiplexed; a processor that calculates a control value for controlling the optical power of the WDM signal in frequency units narrower than the channel bandwidth of the WDM signal based on the power spectrum detected by the optical monitor; an optical power adjustment circuit that adjusts the optical power of the WDM signal in units of frequencies based on the control value; Equipped with the processor corrects the power spectrum detected by the optical monitor, and calculates the control value in the frequency unit narrower than the channel bandwidth based on the corrected power spectrum. Optical communication equipment.

5. the processor compares an optical power level of the power spectrum with a target optical power level in the frequency unit narrower than the channel bandwidth based on the corrected power spectrum, and calculates the control value based on a comparison result.

5. The optical communication device according to claim 4.

6. An optical monitor for monitoring a WDM signal in which signals of multiple channels are multiplexed; a processor that calculates a control value for controlling the optical power of the WDM signal in frequency units narrower than the channel bandwidth of the WDM signal based on the power spectrum detected by the optical monitor; an optical power adjustment circuit that adjusts the optical power of the WDM signal in units of frequencies based on the control value; Equipped with the processor calculates the wavelength dependency of the WDM signal based on the power spectrum detected by the optical monitor and received power spectrum information received from a downstream optical communication device, and calculates the control value in frequency units based on the wavelength dependency. Optical communication equipment.

7. the processor corrects the wavelength dependency in a frequency direction and calculates the control value based on the wavelength dependency after the correction.

7. The optical communication device according to claim 6.

8. An optical monitor for monitoring a WDM signal in which signals of multiple channels are multiplexed; a processor that calculates a control value for controlling the optical power of the WDM signal in frequency units narrower than the channel bandwidth of the WDM signal based on the power spectrum detected by the optical monitor; an optical power adjustment circuit that adjusts the optical power of the WDM signal in units of frequencies based on the control value; Equipped with the processor calculates the control value in the frequency unit narrower than the channel bandwidth based on the power spectrum detected by the optical monitor and power spectrum information of an untransmitted WDM signal received from an upstream optical communication device that has been added by the upstream optical communication device and has not yet passed through an optical transmission line. Optical communication equipment.

9. the optical monitor detects the power spectrum at frequency intervals narrower than a channel bandwidth; 9. The optical communication device according to claim 8.

10. the optical monitor detects a first power spectrum of the WDM signal at a frequency interval narrower than the frequency unit that is a control interval of the optical power adjustment circuit; the processor integrates the first power spectrum in a frequency direction to generate a second power spectrum aligned with the frequency unit, and calculates the control value in the frequency unit narrower than the channel bandwidth based on the generated second power spectrum and the power spectrum information received from the upstream optical communication device.

9. The optical communication device according to claim 8.

11. the processor calculates a control value for controlling optical power so that the power spectrum detected by the optical monitor approaches power spectrum information of the untransmitted WDM signal.

9. The optical communication device according to claim 8.

12. the processor calculates the control value for controlling optical power so as to minimize the optical power deviation between channels of the received WDM signal; The optical communication device according to claim 11.

13. a first optical communication device; a second optical communication device; an optical transmission line connecting the first optical communication device and the second optical communication device; Equipped with the first optical communication device or the second optical communication device corrects the power spectrum of the WDM signal received by the second optical communication device from the first optical communication device via the optical transmission path in frequency units narrower than the channel bandwidth of the WDM signal, and controls the optical power level of the WDM signal in frequency units based on the corrected power spectrum. Optical communication system.

14. a first optical communication device; a second optical communication device; an optical transmission line connecting the first optical communication device and the second optical communication device; Equipped with the first optical communication device or the second optical communication device calculates the wavelength dependency of the WDM signal based on a transmission power spectrum of the WDM signal transmitted to the optical transmission line and a reception power spectrum of the WDM signal received from the optical transmission line, corrects the wavelength dependency in the frequency direction in frequency units narrower than the channel bandwidth of the WDM signal, and adjusts the optical power level of the WDM signal in frequency units based on the corrected wavelength dependency. Optical communication system.

15. a first optical communication device; a second optical communication device; an optical transmission line connecting the first optical communication device and the second optical communication device; Equipped with the first optical communication device or the second optical communication device adjusts the optical power level of the WDM signal at frequency intervals narrower than the channel bandwidth of the WDM signal based on a first power spectrum of the WDM signal that has been added by the first optical communication device and has not yet passed through the optical transmission line, and a second power spectrum of the WDM signal that has passed through the optical transmission line and been received by the second optical communication device. Optical communication system.

16. The optical communication device acquires the power spectrum of a WDM signal in which signals of multiple channels are multiplexed, calculating a control value for adjusting the power level of the WDM signal in frequency units narrower than the channel bandwidth of the WDM signal based on the power spectrum; adjusting the power level of the WDM signal in units of the frequency based on the control value; An optical power control method, wherein the frequency unit has a bandwidth obtained by dividing each of the plurality of channels and does not include two of the plurality of channels.

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