Transmission device and transmission system

Abstract

To provide a transmission device and a transmission system capable of suppressing the reduction of transmission quality even when the number of wavelengths of a wavelength-multiplexed optical signal fluctuates at high speed.SOLUTION: The transmission device includes a signal power detection unit for detecting the signal power of a wavelength-multiplexed optical signal transmitted to a transmission line into which excitation light is input from a Raman amplifier, a variable optical attenuator for attenuating the wavelength-multiplexed optical signal, and a control unit for decreasing the attenuation of the variable optical attenuator in accordance with an increase in the signal power.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a transmission device and a transmission system. [Background technology]

[0002] A Raman amplifier can amplify, with a low noise level, a high data rate optical signal modulated by a multi-level modulation method such as 8QAM (Quadrature Amplitude Modulation). For example, Patent Document 1 describes a method for detecting the reception level of a Raman-amplified optical signal and adjusting the loss amount of a variable attenuator that attenuates the optical signal based on the detection result. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-25510 A Summary of the Invention [Problem to be solved by the invention]

[0004] The gain of Raman amplification depends on the number of wavelengths (number of channels) contained in a wavelength-multiplexed optical signal. Therefore, for example, in a wavelength-multiplexed optical transmission system, when the number of wavelengths in a wavelength-multiplexed optical signal fluctuates due to the addition or dropping of optical signals in wavelength units, the gain of Raman amplification fluctuates, and the received power of the wavelength-multiplexed optical signal varies depending on the number of wavelengths, which may result in a decrease in transmission quality.

[0005] In response to this, the variation in the received power can be reduced by adjusting the amount of attenuation of the wavelength-multiplexed optical signal in accordance with the results of monitoring the received power of the wavelength-multiplexed optical signal, as disclosed in Patent Document 1. However, due to the time required to transfer the results of monitoring the received power of the wavelength-multiplexed optical signal to a transmitting device, when the number of wavelengths of the wavelength-multiplexed optical signal fluctuates rapidly due to, for example, frequent switching of optical paths, it is difficult to adjust the amount of attenuation in accordance with the rapid fluctuation in the number of wavelengths.

[0006] Therefore, an object of the present invention is to provide a transmission device and a transmission system capable of suppressing degradation of transmission quality even if the number of wavelengths of a wavelength-multiplexed optical signal changes at high speed. [Means for solving the problem]

[0007] In one aspect, a transmission device includes a signal power detection unit that detects a signal power of a wavelength-multiplexed optical signal transmitted from a Raman amplifier to a transmission line to which pump light is input, and a variable optical attenuator that attenuates the wavelength-multiplexed optical signal. The attenuation amount is controlled based on the signal power detected by the signal power detection unit and the correlation between the signal power for each number of wavelengths included in the wavelength multiplexed optical signal and the attenuation amount of the variable optical attenuator. and a control unit.

[0008] In one aspect, another transmission device has an ASS detection unit that detects the amount of ASS light generated by a Raman amplifier that outputs pump light to a transmission path of a wavelength-multiplexed optical signal, a variable optical attenuator that attenuates the wavelength-multiplexed optical signal output to the transmission path, and a control unit that reduces the attenuation amount of the variable optical attenuator in response to a decrease in the amount of ASS light generated.

[0009] In one aspect, a transmission system includes a transmitting device that transmits a wavelength-multiplexed optical signal to a transmission line to which pump light is input from a Raman amplifier, and a receiving device that receives the wavelength-multiplexed optical signal from the transmitting device via the transmission line, the transmitting device including a signal power detection unit that detects the signal power of the wavelength-multiplexed optical signal transmitted to the transmission line, and a variable optical attenuator that attenuates the wavelength-multiplexed optical signal. The attenuation amount is controlled based on the signal power detected by the signal power detection unit and the correlation between the signal power for each number of wavelengths included in the wavelength multiplexed optical signal and the attenuation amount of the variable optical attenuator. and a control unit.

[0010] In one aspect, another transmission system includes a transmitting device that transmits a wavelength-multiplexed optical signal to a transmission line to which pump light is input from a Raman amplifier, and a receiving device that receives the wavelength-multiplexed optical signal from the transmitting device via the transmission line, and the transmitting device includes an ASS detection unit that detects the amount of ASS light generated by the Raman amplifier, a variable optical attenuator that attenuates the wavelength-multiplexed optical signal output to the transmission line, and a control unit that reduces the attenuation of the variable optical attenuator in response to a decrease in the amount of ASS light generated. Effect of the Invention

[0011] As one aspect, it is possible to suppress degradation of transmission quality even if the number of wavelengths in a wavelength-multiplexed optical signal changes at high speed. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram illustrating an example of a change in optical signal power with respect to a transmission distance in a transmission path between nodes. [Diagram 2] 11 is a diagram showing a change in power with respect to a transmission distance for each number of wavelengths of a wavelength-multiplexed optical signal. [Diagram 3] FIG. 1 is a configuration diagram showing a transmission system according to a first embodiment. [Figure 4] 6 is a flowchart showing an example of an operation of a control unit before the start of operation of the transmission system of the first embodiment. [Diagram 5] 6 is a flowchart showing an example of an operation of a control unit during operation of the transmission system of the first embodiment. [Figure 6] 11 is a diagram showing a change in power with respect to the transmission distance for each number of wavelengths of a wavelength-multiplexed optical signal when the control unit controls the amount of attenuation. FIG. [Figure 7] FIG. 13 is a diagram illustrating an example of the relationship between signal power and attenuation. [Figure 8] FIG. 11 is a configuration diagram showing a transmission system according to a second embodiment. [Figure 9] FIG. 11 is a diagram illustrating an example of the relationship between signal power and attenuation for each average input power. [Figure 10] FIG. 13 is a diagram showing a data table according to the third embodiment. [Figure 11] FIG. 1 is a diagram illustrating an example of the relationship between signal power and attenuation for each type of optical fiber. [Figure 12] FIG. 13 is a diagram showing a data table according to the fourth embodiment. [Figure 13] 1 is a diagram showing an example of the relationship between the number of wavelengths and Raman gain, and the relationship between the Raman gain and the amount of generated spontaneous Raman scattered light. [Figure 14] FIG. 13 is a configuration diagram showing a transmission system according to a fifth embodiment. [Figure 15]13 is a flowchart showing an example of an operation of a control unit before the start of operation of a transmission system according to a fifth embodiment. [Figure 16] 13 is a flowchart showing an example of an operation of a control unit during operation of the transmission system according to the fifth embodiment. [Figure 17] FIG. 13 is a configuration diagram showing a transmission system according to a sixth embodiment. [Figure 18] FIG. 23 is a diagram showing a data table according to the seventh embodiment. [Figure 19] FIG. 13 is a diagram showing a data table according to the eighth embodiment (part 1). [Figure 20] FIG. 23 is a diagram showing a data table according to the eighth embodiment (part 2). [Figure 21] FIG. 23 is a diagram showing a data table according to the eighth embodiment (part 2). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Example of Raman amplification) 1 is a diagram showing an example of the change in optical signal power (dBm) over the transmission distance (km) in a transmission path between nodes. The solid line shows the change in power of an optical signal amplified by a bidirectional distributed Raman amplifier and an EDFA (Erbium-Doped Fiber Amplifier), and the dotted line shows the change in power of an optical signal amplified only by an EDFA.

[0014] A bidirectional distributed Raman amplifier can amplify optical signals modulated by multi-level modulation methods such as 8QAM (Quadrature Amplitude Modulation) and 16QAM with a low noise factor (NF). At the input end Din of the transmission line, where the influence of the forward Raman amplifier is large, the power of the Raman-amplified optical signal is lower than when it is amplified by only EDFA, so degradation of the optical signal due to nonlinear optical effects is suppressed.

[0015] In addition, at the output end Dout of the transmission line where the influence of the backward Raman amplifier is large, the power of the Raman amplified optical signal is higher than when it is amplified by only EDFA, improving the OSNR (Optical Signal-to-Noise Ratio). Therefore, the transmission distance of the optical signal can be extended by using a bidirectional distributed Raman amplifier.

[0016] 2 is a diagram showing the change in power (dBm) versus transmission distance (km) for each number of wavelengths in a wavelength-multiplexed optical signal. Here, examples of the number of wavelengths are 1, 16, 32, 64, and 96. As can be seen by referring to graph G1a, the power is substantially the same at the input end Din of the transmission line regardless of the number of wavelengths, but the difference in power for each number of wavelengths increases closer to the output end Dout of the transmission line. The power is highest for 1 wavelength and lowest for 96 wavelengths.

[0017] Graph G1b shows the peak power value at peak position Dp in graph G1a for each number of wavelengths. The fewer the number of wavelengths, the greater the power. Therefore, when the number of wavelengths in the wavelength-multiplexed optical signal decreases, the power increases, resulting in greater degradation of the wavelength-multiplexed optical signal due to nonlinear optical effects.

[0018] Moreover, graph G1c shows the power at the output end Dout of the transmission line in graph G1a for each number of wavelengths. Here too, the smaller the number of wavelengths at the output end Dout of the transmission line, the greater the power.

[0019] As described above, the gain of a Raman amplifier (Raman gain) depends on the number of wavelengths. Therefore, as the wavelength division multiplexed optical signal transmits over many spans, the power of the optical signal at the final receiving node may not be within the normal receivable range due to accumulated changes in Raman gain.

[0020] (First embodiment) 3 is a configuration diagram showing a transmission system 9 of a first embodiment. The transmission system 9 includes a transmitting device 1 that transmits a wavelength-multiplexed optical signal to a transmission line 90, and a receiving device 2 that receives the wavelength-multiplexed optical signal from the transmitting device 1 via the transmission line 90.

[0021] The sending device 1 and the receiving device 2 wavelength-multiplex (add) a new optical signal to the wavelength-multiplexed optical signal and drop (drop) an optical signal from the wavelength-multiplexed optical signal. The sending device 1 is an example of a transmission device, and the receiving device 2 is an example of an opposing device that faces the sending device 1 via a transmission path 90.

[0022] The transmitting device 1 includes a control unit 10, a memory 11, an OSC (Optical Supervisory Channel) receiving unit 12, a wavelength selective switch (WSS: Wavelength Selective Switch) unit 14, a tap 15, a variable optical attenuator 16, and a WDM (Wavelength Divisional Multiplexing) coupler 17. The transmitting device 1 also includes a preamplifier 130, a postamplifier 131, a signal power detection unit 18, and a forward pumping light source 19.

[0023] A wavelength-multiplexed optical signal is input to the preamplifier 130 from a previous adjacent node (not shown). The preamplifier 130 is an EDFA, and amplifies the wavelength-multiplexed optical signal and outputs it to the WSS unit 14.

[0024] The WSS unit 14 includes a wavelength selective switch, an optical coupler, an optical splitter, etc., and is optically connected to a plurality of optical transceivers (transponders) (not shown). The WSS unit 14 wavelength-multiplexes (adds) new optical signals from the optical transceivers to a wavelength multiplexed optical signal in accordance with settings from a network monitoring device (not shown), and also demultiplexes (drops) optical signals from the wavelength multiplexed optical signal and outputs them to the optical transceivers.

[0025] In this way, the number of wavelengths in the wavelength-multiplexed optical signal increases or decreases in response to adding or dropping by the WSS unit 14. The WSS unit 14 outputs to the tap 15 the wavelength-multiplexed optical signal to which the optical signal has been added or dropped.

[0026] The tap 15 is, for example, an optical splitter, and branches and outputs the wavelength-multiplexed optical signal to the post-amplifier 131 and the signal power detector 18. The signal power detector 18 includes, for example, a photodiode, and detects the power of the wavelength-multiplexed optical signal (hereinafter, signal power) output to the transmission line 90, and outputs the detected value to the controller 10. The post-amplifier 131 is an EDFA, and amplifies the wavelength-multiplexed optical signal and outputs it to the variable optical attenuator 16.

[0027] The variable optical attenuator 16 attenuates the wavelength-multiplexed optical signal by the attenuation amount set by the control unit 10. In this way, the control unit 10 adjusts the power of the wavelength-multiplexed optical signal to an appropriate value so that the transmission quality of the transmission system 9 satisfies the required level. The wavelength-multiplexed optical signal is input from the variable optical attenuator 16 to the WDM coupler 17.

[0028] The WDM coupler 17 is optically connected to a forward pumping light source 19. The forward pumping light source 19 is a laser diode, and outputs forward pumping light Ef to the WDM coupler 17. The wavelength-multiplexed optical signal is multiplexed with the forward pumping light Ef in the WDM coupler 17 and transmitted to a transmission path 90. Since the forward pumping light Ef is output from the forward pumping light source 19 to the transmission path 90 of the wavelength-multiplexed optical signal in this manner, the wavelength-multiplexed optical signal is Raman amplified.

[0029] The wavelength-multiplexed optical signal is input to the receiving device 2 through a transmission line 90 .

[0030] The receiver 2 includes a reception power detector 20, an OSC transmitter 21, a WDM coupler 22, a tap 23, a preamplifier 24, a WSS unit 25, a postamplifier 26, and a backward pumping light source 27. The WDM coupler 22 is optically connected to the backward pumping light source 27.

[0031] The backward pumping light source 27 is a laser diode, and outputs backward pumping light Eb to the transmission line 90 via the tap 22. The backward pumping light Eb flows through the transmission line 90 in the opposite direction to the wavelength-multiplexed optical signal. This causes the wavelength-multiplexed optical signal to be Raman amplified.

[0032] The forward pumping light source 19 and the backward pumping light source 27 are bidirectional distributed Raman amplifiers. However, the transmission system 9 may have only one of the forward pumping light source 19 and the backward pumping light source 27, and even in this case, Raman amplification of the wavelength multiplexed optical signal is possible. Note that the forward pumping light source 19 and the backward pumping light source 27 are examples of Raman amplifiers, and the forward pumping light and the backward pumping light are examples of pumping light.

[0033] The wavelength-multiplexed optical signal is input to the tap 23 from the WDM coupler 22. The tap 23 is, for example, an optical splitter, and splits the wavelength-multiplexed optical signal and outputs it to the preamplifier 24 and the reception power detection unit 20. The reception power detection unit 20 includes, for example, a photodiode, and detects the power of the wavelength-multiplexed optical signal received by the receiver 2 (hereinafter, reception power), and outputs it to the OSC transmission unit 21. The preamplifier 24 is an EDFA, and amplifies the wavelength-multiplexed optical signal and outputs it to the WSS unit 25.

[0034] The WSS unit 25 includes a wavelength selective switch, an optical coupler, an optical splitter, etc., and is optically connected to a plurality of optical transmitters and receivers (transponders) (not shown). Like the WSS unit 14 of the transmitting device 1, the WSS unit 25 wavelength-multiplexes new optical signals from the optical transmitters and receivers into a wavelength-multiplexed optical signal in accordance with settings from a network monitoring device (not shown), and also demultiplexes the optical signal from the wavelength-multiplexed optical signal and outputs the demultiplexed optical signal to the optical transmitter and receiver. The WSS unit 25 outputs the wavelength-multiplexed optical signal obtained by adding or dropping the optical signal to a post-amplifier 26. The post-amplifier 26 is an EDFA, and amplifies the wavelength-multiplexed optical signal and outputs it to another device.

[0035] The OSC transmitter 21 can communicate with the OSC receiver 12 of the transmitter 1 via an OSC communication line. The OSC transmitter 21 includes a logic circuit, a laser diode, and the like, and transmits power information indicating the reception power of the wavelength multiplexed optical signal to the OSC receiver 12, for example, when the transmission system 9 is started up, that is, before operation begins. Note that the receiver 2 may communicate with the transmitter 1 via, for example, a network monitoring device instead of the OSC.

[0036] The OSC receiving unit 12 includes a logic circuit, a photodiode, etc., and receives power information from the OSC transmitting unit 21 via the OSC. The OSC receiving unit 12 outputs the power information to the control unit 10. As a result, the control unit 10 obtains the reception power of the wavelength multiplexed optical signal from the receiving device 2. Note that the OSC transmitting unit 21 is an example of a notification unit that notifies the control unit 10 of the reception power.

[0037] The control unit 10 is, for example, a CPU (Central Processing Unit) circuit, and executes a series of processes according to a program. Note that the control unit 10 is not limited to a CPU circuit, and may be a circuit configured with hardware such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specified Integrated Circuit).

[0038] Before the transmission system 9 starts operating, the control unit 10 generates a data table 110 to be stored in the memory 11. In the data table 110, a correlation between the number of wavelengths of a wavelength-multiplexed optical signal, the signal power, and the amount of attenuation of the variable optical attenuator 16 when the reception power of the wavelength-multiplexed optical signal is a target value is registered. Here, the number of wavelengths of the wavelength-multiplexed optical signal is registered in advance from a network management device or the like before the signal power and the amount of attenuation. The data table 110 is an example of correlation data, and the memory 11 is an example of a storage unit that stores the data table 110.

[0039] Before the transmission system 9 starts operating, the control unit 10 controls the light emission of the light source device 91 optically connected to the transmitting device 1, and measures the signal power and attenuation for each wavelength number in the data table 110. The light source device 91 includes a light source of a plurality of wavelengths, an optical coupler, and the like, and generates a wavelength-multiplexed optical signal by wavelength-multiplexing light for the number of wavelengths set by the control unit 10. The wavelength-multiplexed optical signal is input from the light source device 91 to the WSS unit 14 and output to the tap 15.

[0040] Therefore, before the transmission system 9 starts operating, even when a wavelength-multiplexed optical signal of a main signal is not input from a previous adjacent node (not shown) to the WSS unit 14, the control unit 10 can measure the signal power and the amount of attenuation of the wavelength-multiplexed optical signal from the light source device 91. The light source device 91 may be implemented within the transmission device 1.

[0041] Prior to measuring the signal power and the amount of attenuation, the control unit 10 determines a target value for the reception power of the wavelength-multiplexed optical signal. As an example, the control unit 10 sets the reception power when the number of wavelengths included in the wavelength-multiplexed optical signal is maximum as the target value. At this time, the control unit 10 sets the maximum number of wavelengths in the light source device 91 and sets the amount of attenuation of the variable optical attenuator 16 to 0. After setting the number of wavelengths and the amount of attenuation, the control unit 10 obtains the reception power detected by the reception power detection unit 20 from the power information and sets it to the target value.

[0042] Thereafter, the control unit 10 adjusts the amount of attenuation according to a change in signal power according to the number of wavelengths included in the wavelength multiplexed optical signal so that the received power becomes a target value. In adjusting the amount of attenuation, the control unit 10 acquires the signal power from the signal power detection unit 18 and the received power from the received power detection unit 20 every time the control unit 10 sets the number of wavelengths already registered in the data table 110 to the light source device 91. The control unit 10 adjusts the amount of attenuation so that the received power becomes a target value, and registers the signal power and the amount of attenuation at the time of completion of the adjustment in the data table 110.

[0043] Furthermore, during operation of the transmission system 9, the control unit 10 stops the light emission of the light source device 91, and determines the amount of attenuation from the signal power of the wavelength-multiplexed optical signal from the adjacent node based on the data table 110. For example, the control unit 10 searches for an amount of attenuation corresponding to a signal power that is closest to the signal power detected by the signal power detection unit 18 among the signal powers registered in the data table 110, and sets the amount of attenuation in the variable optical attenuator 16.

[0044] In the data table 110, the greater the number of wavelengths, the greater the signal power, and the greater the signal power, the smaller the attenuation. For example, when the number of wavelengths is 1, the signal power is 0.01 (mW) and the attenuation is 2.52 (dB). When the number of wavelengths is 96, the signal power is 0.96 (mW) and the attenuation is 0 (dB).

[0045] 2, the greater the number of wavelengths, the smaller the Raman gain and the smaller the received power. Therefore, the control unit 10 can average the received power that varies depending on the number of wavelengths by reducing the amount of attenuation as the signal power increases depending on the number of wavelengths, according to the data table 110. This allows the control unit 10 to set the received power to a constant target value regardless of the number of wavelengths of the wavelength-multiplexed optical signal.

[0046] In this way, the control unit 10 reduces the amount of attenuation of the variable optical attenuator 16 in response to an increase in the signal power. Here, the data table 110 is not necessarily required, and the control unit 10 can calculate the amount of attenuation for setting the reception power to a target value from the signal power according to, for example, a preset calculation formula. Therefore, the control unit 10 can appropriately control the amount of attenuation without acquiring the reception power from the receiving device 2 during transmission of the wavelength multiplexed signal light.

[0047] Therefore, the transmitting device 1 can suppress deterioration of the transmission quality even if the number of wavelengths of the wavelength-multiplexed optical signal changes at high speed.

[0048] In this example, the control unit 10 determines the amount of attenuation during operation of the transmission system 9 based on the data table 110 generated before the start of operation, so that not only is it not necessary to obtain the reception power from the receiving device 2, but an appropriate amount of attenuation can be easily determined.

[0049] 4 is a flowchart showing an example of the operation of the control unit 10 before the start of operation of the transmission system 9 of the first embodiment. In order to determine a target value of the reception power, the control unit 10 sets the attenuation amount of the variable optical attenuator 16 to 0 (dBm) (step St1), and sets the maximum number of wavelengths in the light source device 91 among the numbers of wavelengths in the data table 110 (step St2).

[0050] Next, the control unit 10 causes the light source device 91 to start emitting light (step St3). As a result, a wavelength multiplexed optical signal with the maximum number of wavelengths is output from the light source device 91 to the WSS unit 14.

[0051] Next, the control unit 10 acquires the reception power from the power information received via the OSC (step St4). At this time, the control unit 10 sets the acquired reception power to the target value Po. In this way, the control unit 10 sets the reception power when the number of wavelengths included in the wavelength multiplexed optical signal is maximum as the target value, so that the reception power can be controlled based on the lowest Raman gain during operation of the transmission system 9. Note that the control unit 10 is not limited to this and may set the reception power according to another number of wavelengths as the target value.

[0052] Next, the control unit 10 selects the number of wavelengths from the data table 110 and sets it in the light source device 91 (step St5). As a result, a wavelength-multiplexed optical signal with the set number of wavelengths is output from the light source device 91 to the WSS unit 14. Note that the order of selecting the number of wavelengths in the data table 110 is not limited.

[0053] Next, the control unit 10 adjusts the amount of attenuation (step St6) and obtains the reception power from the power information received via the OSC (step St7). At this time, the control unit 10 increases or decreases the amount of attenuation, for example, in predetermined increments.

[0054] Next, the control unit 10 compares the reception power with the target value Po (step St8). At this time, the control unit 10 judges whether the reception power is substantially the same as the target value Po. For example, if the reception power is within a predetermined range including the target value Po, the control unit 10 judges that the reception power is substantially the same as the target value Po, and if the reception power is outside the predetermined range, the control unit 10 judges that the reception power is different from the target value Po.

[0055] If the received power is different from the target value Po (No in step St8), the process from step St6 onward is executed again. If the received power is substantially the same as the target value Po (Yes in step St8), the control unit 10 acquires the signal power from the signal power detection unit 18 (step St9).

[0056] Next, the control unit 10 registers the signal power and the amount of attenuation in the data table 110 (step St10). As a result, the correlation between the signal power and the amount of attenuation when the reception power becomes the target value is registered in the data table 110.

[0057] Next, the control unit 10 judges whether or not all the wavelength numbers registered in the data table 110 have been selected (step St11). If there are unselected wavelength numbers (No in step St11), the unselected wavelength numbers are selected (step St5), and the processes from step St6 onwards are executed again.

[0058] Moreover, if all the wavelength numbers have been selected (Yes in step St11), the control unit 10 stops the light emission of the light source device 91 (step St12). In this manner, the operation of the control unit 10 before the start of operation of the transmission system 9 is performed.

[0059] 5 is a flowchart showing an example of the operation of the control unit 10 during operation of the transmission system 9 of the first embodiment. This operation is repeatedly executed during operation of the transmission system 9. The control unit 10 acquires signal power from the signal power detection unit 18 (step St21).

[0060] Next, the control unit 10 refers to the data table 110 based on the signal power (step St22). At this time, the control unit 10 searches for a value of the signal power in the data table 110 that is closest to the signal power acquired from the signal power detection unit 18, for example.

[0061] Next, the control unit 10 determines the amount of attenuation from the signal power based on the data table 110 (step St23). At this time, the control unit 10 determines the amount of attenuation corresponding to the signal power searched from the data table 110 as the amount of attenuation (control value) of the variable optical attenuator 16.

[0062] Next, the control unit 10 sets the determined amount of attenuation in the variable optical attenuator 16 (step St24). This controls the reception power to the target value Po. In this manner, the control unit 10 operates while the transmission system 9 is in operation.

[0063] 6 is a diagram showing changes in power (dBm) versus transmission distance (km) for each number of wavelengths of a wavelength-multiplexed optical signal when the control unit 10 controls the amount of attenuation. The power at the input end Din of the transmission line 90 differs for each number of wavelengths, but the power at the output end Dout of the transmission line 90, i.e., the received power, is controlled to a target value Po regardless of the number of wavelengths. This improves the transmission quality of the wavelength-multiplexed optical signal.

[0064] In this example, the data table 110 includes combinations of signal power and attenuation, and therefore can be easily generated from the measurement results of the signal power and attenuation. However, the control unit 10 is not limited to this, and may calculate the coefficients of a formula showing the correlation between the signal power and the attenuation, store them in the memory 11, and calculate the attenuation according to the formula.

[0065] 7 is a diagram showing an example of the relationship between signal power (mW) and attenuation (dB). The signal power and attenuation registered in the data table 110 in the above example are plotted on the graph (see circles). The control unit 10 approximates the signal power and attenuation of the above measurement results to a straight line of a linear function shown by the dotted line.

[0066] Attenuation = A × signal power + B (1)

[0067] For example, before the transmission system 9 starts operating, the control unit 10 fits the relationship between the signal power and the attenuation amount obtained from the measurement results to the above formula (1). In the example of Fig. 7, the control unit 10 calculates the coefficient A = -2.63 and the coefficient B = 2.43 by fitting the linear function shown by the dotted line to formula (1).

[0068] The control unit 10 stores the coefficient A=-2.63 and the coefficient B=2.43 in the memory 11. Here, the coefficients A and B are an example of correlation data regarding the correlation between the signal power and the amount of attenuation.

[0069] Attenuation = -2.63 × signal power + 2.43 (2)

[0070] After the transmission system 9 starts operating, the control unit 10 reads out the coefficients A and B from the memory 11 and substitutes them into the equation (1) to generate the above equation (2). During the operation of the transmission system 9, the control unit 10 calculates the amount of attenuation from the signal power using the equation (2).

[0071] In this way, the control unit 10 determines the amount of attenuation based on the signal power and the coefficients A and B. Therefore, the control unit 10 can calculate the amount of attenuation with higher accuracy than when using the data table 110. Note that the formula used by the control unit 10 is not limited to a linear function, and may be another formula such as a quadratic function.

[0072] As described above, before the transmission system 9 starts operating, the control unit 10 controls the attenuation amount of the variable optical attenuator 16 in accordance with the change in signal power according to the number of wavelengths so that the reception power of the wavelength-multiplexed optical signal becomes the target value, and generates the data table 110 or the coefficients A and B of formula (1) based on the signal power and the attenuation amount when the reception power becomes the target value by controlling the attenuation amount. Furthermore, after generating the data table 110 or the coefficients A and B, the control unit 10 determines the attenuation amount based on the data table 110 or the coefficients A and B from the signal power during operation of the transmission system 9.

[0073] Therefore, the control unit 10 does not need to acquire the reception power from the receiving device 2 to determine the amount of attenuation during operation of the transmission system 9. Therefore, the transmitting device 1 can control the reception power to a target value so as to follow high-speed fluctuations in the number of wavelengths of the wavelength-multiplexed optical signal, and can suppress deterioration of the transmission quality.

[0074] In this example, the control unit 10 generates the data table 110 or the coefficients A and B using the transmission system 9 and stores them in the memory 11, but is not limited to this. The data table 110 or the coefficients A and B may be stored in advance in the memory 11 based on experimental results and simulation results based on design values ​​of the transmission system 9. In this case, the control unit 10 uses the data table 110 or the coefficients A and B stored in the memory 11, and therefore the same effect as above can be obtained.

[0075] Furthermore, the signal power detector 18 in this example detects the power of the wavelength-multiplexed optical signal between the WSS unit 14 and the postamplifier 131 as the signal power, but is not limited to this. For example, the signal power detector 18 may detect the signal power between the postamplifier 131 and the variable optical attenuator 16. Even in this case, the signal power changes depending on the number of wavelengths of the wavelength-multiplexed optical signal, so that the same effect as above can be obtained.

[0076] (Second Example) In the first embodiment, the memory 11 stores a data table 110 relating to the correlation between the signal power and the amount of attenuation, but is not limited to this. As in the following example, the memory 11 may store a data table relating to the correlation between the signal power, the amount of attenuation, and the average value per wavelength of the input power at the input end of the transmission line 90 (hereinafter referred to as the average input power) when the reception power becomes a target value.

[0077] Fig. 8 is a configuration diagram showing a transmission system 9a of the second embodiment. In Fig. 8, components common to Fig. 3 are given the same reference numerals, and the description thereof will be omitted.

[0078] The transmission system 9a includes a transmitter 1a that transmits a wavelength-multiplexed optical signal to a transmission line 90, and a receiver 2 that receives the wavelength-multiplexed optical signal from the transmitter 1a via the transmission line 90. A tap 92 that branches the wavelength-multiplexed optical signal to the transmitter 1 and the receiver 2 is provided at the input end of the transmission line 90.

[0079] The transmitting device 1a includes a control unit 10a, a memory 11, an OSC receiving unit 12, a WSS unit 14, a tap 15, a variable optical attenuator 16, and a WDM coupler 17. The transmitting device 1a also includes a preamplifier 130, a postamplifier 131, a signal power detecting unit 18, an input power detecting unit 18a, and a forward pumping light source 19.

[0080] The input power detection unit 18a is optically connected to the tap 92. The input power detection unit 18a includes a photodiode and detects the input power of the wavelength multiplexed optical signal at the input end of the transmission line 90. The control unit 10a obtains the detection value of the input power from the input power detection unit 18a and calculates the average input power per wavelength by averaging the detection value by the number of wavelengths. Here, one wavelength refers to a wavelength assigned to one channel of the wavelength multiplexed optical transmission. Similarly to the first embodiment, the control unit 10a obtains the signal power from the signal power detection unit 18 and obtains the reception power from the receiving device 2 via the OSC.

[0081] The control unit 10a is, for example, a CPU circuit, and executes a series of processes according to a program. Note that the control unit 10a is not limited to a CPU circuit, and may be, for example, a circuit configured with hardware such as an FPGA or an ASIC.

[0082] Before the transmission system 9a starts operating, the control unit 10a generates a data table 110a from the measurement results of the signal power and the amount of attenuation for each average input power (dBm / ch) in the same manner as in the first embodiment. At this time, the control unit 10a calculates the average input power by averaging the input power detected by the input power detection unit 18a by the number of wavelengths set in the light source device 91.

[0083] In the data table 110a, combinations of signal power and attenuation according to the number of wavelengths for each average input power are registered. Examples of average input power include, but are not limited to, 0 (dBm / ch), -4 (dBm / ch), and -8 (dBm / ch). Note that the data table 110a is an example of correlation data.

[0084] During operation of the transmission system 9a, the control unit 10a determines the amount of attenuation of the variable optical attenuator 16 from the signal power and the average input power based on the data table 110. That is, the control unit 10a determines the amount of attenuation from the correlation between the signal power and the amount of attenuation according to the average input power.

[0085] At this time, the control unit 10a calculates the average input power by averaging the input power detected by the input power detection unit 18a over the number of wavelengths set by, for example, a network monitoring device, etc. Therefore, the control unit 10a can set an appropriate attenuation amount in the variable optical attenuator 16 according to the average input power.

[0086] Furthermore, the control unit 10a may generate the coefficients A and B in the above equation (1) for each average input power, instead of using the data table 110a.

[0087] 9 is a diagram showing an example of the relationship between the signal power and the attenuation for each average input power. In the graph, the signal power and the attenuation registered in the data table 110a in the above example are plotted with individual symbols (see the symbol Na) for each average input power.

[0088] The control unit 10a approximates the signal power and attenuation of the above-mentioned measurement results for each average input power to a straight line of a linear function shown by a dotted line. The straight line L1a shows the characteristics when the average input power is 0 (dBm / ch), the straight line L1b shows the characteristics when the average input power is -4 (dBm / ch), and the straight line L1c shows the characteristics when the average input power is -8 (dBm / ch).

[0089] For example, before the transmission system 9a starts operation, the control unit 10a fits the relationship between the signal power and the amount of attenuation measured to the above formula (1). The control unit 10a calculates the coefficients A and B of each of the straight lines L1a, L1b, and L1c, and stores them in the memory 11. Here, the coefficients A and B are an example of correlation data regarding the correlation between the signal power and the amount of attenuation.

[0090] After the transmission system 9a starts operating, the control unit 10a reads out the coefficients A and B corresponding to the average input power from the memory 11 and substitutes them into the equation (1) to generate a linear function equation such as the equation (2). During the operation of the transmission system 9a, the control unit 10a calculates the amount of attenuation from the signal power using the equation.

[0091] In this way, the control unit 10a determines the amount of attenuation based on the coefficients A and B corresponding to the average input power from the signal power. Therefore, the control unit 10a can calculate the amount of attenuation with higher accuracy than when using the data table 110a. Note that the formula used by the control unit 10a is not limited to a linear function, and may be another formula such as a quadratic function.

[0092] (Third Example) A data table relating to the correlation between signal power, attenuation, and the type of transmission path 90 may be stored in the memory 11. In this example, the type of optical fiber is given as an example of the type of transmission path 90. The types of optical fiber include, but are not limited to, SMF (Single Mode optical Fiber), DSF (Dispersion Shifted optical Fiber), and ExtCORE. The transmission system of this example has the same configuration as that of the first embodiment.

[0093] 10 is a diagram showing a data table 110c of the third embodiment. In the data table 110c, the signal power, the amount of attenuation, and the type of optical fiber when the reception power becomes a target value are registered. That is, the data table 110c shows the correlation between the signal power, the amount of attenuation, and the type of optical fiber. The data table 110c is an example of correlation data.

[0094] Before the transmission system 9 starts operating, the control unit 10 generates a data table 110c for each type of optical fiber from the measurement results of the signal power and the amount of attenuation in the same manner as in the first embodiment. In the data table 110c, combinations of the signal power and the amount of attenuation according to the number of wavelengths for each type of optical fiber are registered.

[0095] The control unit 10 determines the amount of attenuation of the variable optical attenuator 16 based on the data table 110c from the signal power and the type of optical fiber during operation of the transmission system 9. That is, the control unit 10 determines the amount of attenuation from the correlation between the signal power and the amount of attenuation according to the type of optical fiber.

[0096] At this time, the control unit 10 receives a notification of the type of optical fiber of the transmission line 90 from, for example, a network monitoring device. Therefore, the control unit 10 can set an appropriate attenuation amount in the variable optical attenuator 16 according to the type of optical fiber.

[0097] Moreover, the control unit 10 may generate the coefficients A and B in the above formula (1) for each type of optical fiber, instead of the data table 110c.

[0098] 11 is a diagram showing an example of the relationship between signal power and attenuation for each type of optical fiber. In the graph, the signal power and attenuation registered in the data table 110c in the above example are plotted with individual symbols (see symbol Nb) for each type of optical fiber.

[0099] The control unit 10 approximates the signal power and attenuation of the above-mentioned measurement results for each type of optical fiber to a straight line of a linear function shown by a dotted line. The straight line L2a shows the characteristics when the type of optical fiber is DSF, the straight line L2b shows the characteristics when the type of optical fiber is SMF, and the straight line L2c shows the characteristics when the type of optical fiber is ExtCORE.

[0100] For example, before the transmission system 9 starts operating, the control unit 10 fits the relationship between the signal power and the amount of attenuation measured to the above formula (1). The control unit 10 calculates the coefficients A and B of each of the straight lines L2a, L2b, and L2c, and stores them in the memory 11. Here, the coefficients A and B are an example of correlation data regarding the correlation between the signal power and the amount of attenuation.

[0101] After the transmission system 9 starts operating, the control unit 10 reads out coefficients A and B corresponding to the type of optical fiber from the memory 11 and substitutes them into equation (1) to generate a linear function formula such as equation (2). During operation of the transmission system 9, the control unit 10 calculates the amount of attenuation from the signal power using the formula.

[0102] In this way, the control unit 10 determines the amount of attenuation based on the signal power and the coefficients A and B according to the type of optical fiber. Therefore, the control unit 10 can calculate the amount of attenuation with higher accuracy than when the data table 110c is used.

[0103] (Fourth Example) A data table relating to the correlation between signal power, attenuation, average input power, and type of optical fiber may be stored in the memory 11. In this example, the average input power is calculated in the same manner as in the third embodiment, and the type of optical fiber is the same as in the third embodiment. Also, the transmission system of this example has the same configuration as in the second embodiment.

[0104] 12 is a diagram showing a data table 110d of the fourth embodiment. The data table 110d registers the signal power, attenuation, average input power, and type of optical fiber when the received power is the target value. That is, the data table 110c shows the correlation between the signal power, attenuation, average input power, and type of optical fiber.

[0105] Before the transmission system 9a starts operation, the control unit 10a generates a data table 110d from the measurement results of the signal power and the amount of attenuation for each average input power and type of optical fiber by the same method as in the first embodiment. The data table 110d registers combinations of the signal power and the amount of attenuation according to the number of wavelengths for each average input power and type of optical fiber. The data table 110d is an example of correlation data.

[0106] During operation of the transmission system 9a, the control unit 10a determines the amount of attenuation of the variable optical attenuator 16 based on the signal power, the average input power, and the type of optical fiber on the basis of the data table 110c. That is, the control unit 10a determines the amount of attenuation based on the correlation between the signal power and the amount of attenuation according to the average input power and the type of optical fiber.

[0107] At this time, the control unit 10a receives a notification of the type of optical fiber of the transmission line 90 from, for example, a network monitoring device. Therefore, the control unit 10a can set, in the variable optical attenuator 16, not only the average input power but also an appropriate attenuation amount according to the type of optical fiber.

[0108] Furthermore, the control unit 10a may generate a formula showing the correlation between the signal power, the average input power, the type of optical fiber, and the amount of attenuation by the same method as described above before the transmission system 9a starts operating. In this case, the control unit 10a may store coefficients of the formula in the memory 11 and read them out during the operation of the transmission system 9a to use them to determine the amount of attenuation.

[0109] (Fifth Example) In the first to fourth embodiments, the input power is used to determine the attenuation amount, but this is not limited to this. In this embodiment, the amount (dBm) of amplified spontaneous Raman scattering (ASS) light (hereinafter referred to as ASS amount) is used instead of the input power. Spontaneous Raman scattering is noise light that accompanies Raman amplification.

[0110] 13 is a diagram showing an example of the relationship between the number of wavelengths and the Raman gain (dB), and the relationship between the Raman gain (dB) and the amount of spontaneous Raman scattering light (ASS amount) (dBm). Graph G2a shows the relationship between the number of wavelengths and the Raman gain. As described above, the Raman gain decreases linearly as the number of wavelengths increases.

[0111] Graph G2b shows the relationship between Raman gain and the amount of ASS. As the Raman gain increases, the amount of ASS increases linearly. Therefore, the higher the Raman gain, the greater the amount of ASS. Therefore, by detecting the amount of ASS, it is possible to detect the change in Raman gain associated with the change in the number of wavelengths.

[0112] Fig. 14 is a configuration diagram showing a transmission system 9b of the fifth embodiment. In Fig. 14, components common to Fig. 3 are given the same reference numerals, and descriptions thereof will be omitted.

[0113] The transmission system 9b includes a transmitting device 1c that transmits a wavelength multiplexed optical signal to a transmission line 90, and a receiving device 2 that receives the wavelength multiplexed optical signal from the transmitting device 1c via the transmission line 90. The transmitting device 1c includes a control unit 10c, a memory 11, an OSC receiving unit 12, a WSS unit 14, a tap 15c, a variable optical attenuator 16, and a WDM coupler 17. The transmitting device 1c also includes a preamplifier 130, a postamplifier 131, an ASS detecting unit 18c, and a forward pumping light source 19.

[0114] The tap 15c is, for example, a WDM coupler, and is optically connected between the variable optical attenuator 16 and the WDM coupler 17. The tap 15c guides the ASS light input from the forward pumping light source 19 via the WDM coupler 17 to the ASS detection unit 18c. In addition, the tap 15c guides the wavelength-multiplexed optical signal input from the variable optical attenuator 16 to the WDM coupler 17.

[0115] The ASS detector 18c includes, for example, a photodiode, detects the amount of ASS, and outputs the detected value to the controller 10c. The ASS detector 18c is an example of an ASS light detector that detects the amount of ASS light generated by the forward pumping light source 19.

[0116] The control unit 10c is, for example, a CPU circuit, and executes a series of processes according to a program. Note that the control unit 10c is not limited to a CPU circuit, and may be, for example, a circuit configured with hardware such as an FPGA or an ASIC.

[0117] Before the transmission system 9b starts operating, the control unit 10c generates a data table 110e to be stored in the memory 11. The data table 110e registers the correlation between the number of wavelengths of the wavelength-multiplexed optical signal, the amount of ASS, and the amount of attenuation of the variable optical attenuator 16 when the reception power of the wavelength-multiplexed optical signal is a target value. The data table 110e is an example of correlation data regarding the correlation between the amount of ASS and the amount of attenuation when the reception power of the wavelength-multiplexed optical signal is a target value.

[0118] Before the transmission system 9b starts operating, the control unit 10c controls the light emission of the light source device 91 and sets the number of wavelengths, and measures the amount of ASS and the amount of attenuation for each number of wavelengths in the data table 110e, as in the first embodiment. Prior to the measurement, the control unit 10c sets the reception power when the number of wavelengths included in the wavelength multiplexed optical signal is maximum, as an example.

[0119] Thereafter, the control unit 10c adjusts the amount of attenuation according to a change in the amount of ASS according to the number of wavelengths included in the wavelength multiplexed optical signal so that the received power becomes a target value. In adjusting the amount of attenuation, the control unit 10c acquires the amount of ASS from the ASS detection unit 18c and acquires the received power from the received power detection unit 20 every time the control unit 10c sets the number of wavelengths already registered in the data table 110e to the light source device 91. The control unit 10c adjusts the amount of attenuation so that the received power becomes a target value, and registers the amount of ASS and the amount of attenuation at the time of completion of the adjustment in the data table 110e.

[0120] Furthermore, during operation of the transmission system 9b, the control unit 10c stops the light emission of the light source device 91 and determines the amount of attenuation based on the amount of ASS and the data table 110e. For example, the control unit 10c searches for an attenuation amount corresponding to an ASS amount that is closest to the amount of ASS detected by the ASS detection unit 18c among the amounts of ASS registered in the data table 110e, and sets the attenuation amount in the variable optical attenuator 16.

[0121] In the data table 110e, the greater the number of wavelengths, the smaller the ASS amount, and the greater the ASS amount, the smaller the attenuation amount. For example, when the number of wavelengths is 1, the ASS amount is -29.24 (dBm) and the attenuation amount is 2.52 (dB). Also, when the number of wavelengths is 96, the ASS amount is -30.30 (dBm) and the attenuation amount is 0 (dB).

[0122] As described above, the greater the number of wavelengths, the smaller the Raman gain and the smaller the amount of ASS. Therefore, the control unit 10c can average the reception power that changes according to the number of wavelengths by reducing the amount of attenuation as the amount of ASS decreases according to the number of wavelengths in accordance with the data table 110. This allows the control unit 10 to set the reception power to a constant target value regardless of the number of wavelengths of the wavelength-multiplexed optical signal.

[0123] In this way, the control unit 10c reduces the amount of attenuation of the variable optical attenuator 16 in response to a decrease in the amount of ASS. Here, the data table 110e is not necessarily required, and the control unit 10c can calculate the amount of attenuation for setting the reception power to a target value from the amount of ASS according to, for example, a preset calculation formula. Therefore, the control unit 10c can appropriately control the amount of attenuation without acquiring the reception power from the receiving device 2 during transmission of the wavelength multiplexed signal light.

[0124] Therefore, the transmitting device 1 can suppress deterioration of the transmission quality even if the number of wavelengths of the wavelength-multiplexed optical signal changes at high speed.

[0125] In this example, the control unit 10c acquires the reception power from the receiving device 2 to determine the amount of attenuation based on the data table 110e during operation of the transmission system 9b. Need Therefore, the appropriate amount of attenuation can be easily determined without any need for a calculation.

[0126] Fig. 15 is a flow chart showing an example of the operation of the control unit 10c before the start of operation of the transmission system 9b of the fifth embodiment. In Fig. 15, the same processes as those in Fig. 4 are denoted by the same reference numerals, and the description thereof will be omitted.

[0127] If the reception power is substantially the same as the target value Po (Yes in step St8), the control unit 10c acquires the ASS amount from the ASS detection unit 18c (step St9a). Next, the control unit 10c registers the ASS amount and the attenuation amount in the data table 110e (step St10a). As a result, the correlation between the ASS amount and the attenuation amount is registered in the data table 110e. In this manner, the operation of the control unit 10c before the start of operation of the transmission system 9b is performed.

[0128] 16 is a flow chart showing an example of the operation of the control unit 10 during operation of the transmission system 9b of the fifth embodiment. This operation is repeatedly executed during operation of the transmission system 9b.

[0129] The control unit 10c acquires the ASS amount from the ASS detection unit 18c (step St21a). Next, the control unit 10c refers to the data table 110e based on the ASS amount (step St22a). At this time, the control unit 10c searches for, for example, the ASS amount in the data table 110e, which is closest to the ASS amount acquired from the ASS detection unit 18c.

[0130] Next, the control unit 10c determines the amount of attenuation based on the amount of ASS based on the data table 110e (step St23a). At this time, the control unit 10c determines the amount of attenuation corresponding to the amount of ASS searched from the data table 110e as the amount of attenuation (control value) of the variable optical attenuator 16.

[0131] Next, the control unit 10c sets the determined amount of attenuation in the variable optical attenuator 16 (step St24a). This controls the reception power to the target value Po. In this manner, the control unit 10c operates while the transmission system 9b is in operation.

[0132] As described above, the control unit 10c controls the attenuation amount of the variable optical attenuator 16 according to the change in the ASS amount according to the number of wavelengths so that the reception power of the wavelength-multiplexed optical signal becomes the target value before the transmission system 9b starts operating, and generates the data table 110e based on the signal power and the attenuation amount when the reception power becomes the target value by controlling the attenuation amount. Furthermore, after generating the data table 110e, the control unit 10c determines the attenuation amount based on the data table 110e from the ASS amount during the operation of the transmission system 9b.

[0133] Therefore, the control unit 10c does not need to acquire the reception power from the receiving device 2 to determine the amount of attenuation during operation of the transmission system 9b. Therefore, the transmitting device 1c can control the reception power to a target value so as to follow high-speed fluctuations in the number of wavelengths of the wavelength-multiplexed optical signal, and can suppress deterioration of the transmission quality.

[0134] In this example, the control unit 10c uses the transmission system 9b to generate the data table 110e and stores it in the memory 11, but this is not limiting. The data table 110e may be stored in advance in the memory 11 based on experimental results and simulation results based on design values ​​of the transmission system 9b. In this case, the control unit 10c uses the data table 110e stored in the memory 11, and therefore the same effect as above can be obtained.

[0135] Furthermore, the control unit 10c may generate a formula showing the correlation between the amount of ASS and the amount of attenuation by the same method as described above before the transmission system 9b starts operating. In this case, the control unit 10c stores coefficients of the formula in the memory 11 and reads them out during the operation of the transmission system 9b to use them to determine the amount of attenuation.

[0136] (Sixth Example) In the fifth embodiment, a data table 110e relating to the correlation between the amount of ASS and the amount of attenuation is stored in the memory 11, but is not limited to this. As in the following example, a data table relating to the correlation between the amount of ASS, the amount of attenuation, and the average input power when the reception power becomes a target value, similar to the second embodiment, may be stored in the memory 11.

[0137] Fig. 17 is a configuration diagram showing a transmission system 9c of Example 6. In Fig. 17, components common to Fig. 8 and Fig. 16 are given the same reference numerals, and descriptions thereof will be omitted.

[0138] The transmission system 9c includes a transmitter 1d that transmits a wavelength-multiplexed optical signal to a transmission line 90, and a receiver 2 that receives the wavelength-multiplexed optical signal from the transmitter 1d via the transmission line 90. A tap 92 is provided at the input end of the transmission line 90.

[0139] The transmitting device 1d includes a control unit 10d, a memory 11, an OSC receiving unit 12, a WSS unit 14, a tap 15, a variable optical attenuator 16, and a WDM coupler 17. The transmitting device 1a includes a preamplifier 130, a postamplifier 131, an ASS detecting unit 18c, an input power detecting unit 18a, and a forward pumping light source 19.

[0140] The control unit 10d is, for example, a CPU circuit, and executes a series of processes according to a program. Note that the control unit 10d is not limited to a CPU circuit, and may be, for example, a circuit configured with hardware such as an FPGA or an ASIC.

[0141] The control unit 10d obtains the detection value of the ASS amount from the ASS detection unit 18c as in the fifth embodiment, obtains the detection value of the input power from the input power detection unit 18a as in the second embodiment, and calculates the average input power per wavelength by averaging the detection values ​​by the number of wavelengths. The control unit 10d also obtains power information on the received power from the receiving device 2 via the OSC.

[0142] Before the transmission system 9c starts operating, the control unit 10d generates a data table 110f from the measurement results of the ASS amount and the attenuation amount for each average input power (dBm / ch) by the same method as in the fifth embodiment. At this time, the control unit 10a calculates the average input power by averaging the input power detected by the input power detection unit 18a by the number of wavelengths set in the light source device 91.

[0143] In the data table 110f, a combination of the ASS amount and the attenuation amount according to the number of wavelengths for each average input power is registered. Examples of the average input power include, but are not limited to, 0 (dBm / ch), -4 (dBm / ch), and -8 (dBm / ch). The ASS amount corresponding to each number of wavelengths in the data table 110f varies depending on the average input power. The data table 110f is an example of correlation data regarding the correlation between the ASS amount and the attenuation amount when the reception power of the wavelength multiplexed optical signal becomes a target value.

[0144] The control unit 10d determines the amount of attenuation of the variable optical attenuator 16 based on the amount of ASS and the average input power on the basis of the data table 110f during operation of the transmission system 9c. That is, the control unit 10d determines the amount of attenuation based on the correlation between the amount of ASS and the amount of attenuation according to the average input power.

[0145] At this time, the control unit 10d calculates the average input power by averaging the input power detected by the input power detection unit 18a over the number of wavelengths set by, for example, a network monitoring device, etc. Therefore, the control unit 10d can set an appropriate attenuation amount in the variable optical attenuator 16 according to the average input power.

[0146] Furthermore, the control unit 10d may generate a formula showing the correlation between the amount of ASS, the average input power, and the amount of attenuation by the same method as described above before the transmission system 9c starts operating. In this case, the control unit 10d stores coefficients of the formula in the memory 11 and reads them out during the operation of the transmission system 9c to use them to determine the amount of attenuation.

[0147] (Seventh Example) A data table regarding the correlation between the amount of ASS, the amount of attenuation, and the type of the transmission path 90 may be stored in the memory 11. As an example of the type of the transmission path 90, the type of optical fiber is given as in the third embodiment. Also, the transmission system of this embodiment has the same configuration as the fifth embodiment.

[0148] 18 is a diagram showing a data table 110g of the seventh embodiment. The data table 110g registers the ASS amount, the attenuation amount, and the type of optical fiber when the reception power becomes the target value. That is, the data table 110g shows the correlation between the ASS amount, the attenuation amount, and the type of optical fiber. The data table 110g is an example of correlation data.

[0149] Before the transmission system 9b starts operation, the control unit 10c generates a data table 110g from the measurement results of the ASS amount and the attenuation amount for each type of optical fiber by the same method as in the fifth embodiment. The data table 110g registers combinations of the ASS amount and the attenuation amount according to the number of wavelengths for each type of optical fiber. The ASS amount corresponding to each number of wavelengths in the data table 110g differs depending on the type of optical fiber.

[0150] The control unit 10c determines the amount of attenuation of the variable optical attenuator 16 based on the amount of ASS and the type of optical fiber on the basis of the data table 110g during operation of the transmission system 9b. That is, the control unit 10c determines the amount of attenuation based on the correlation between the amount of ASS and the amount of attenuation according to the type of optical fiber.

[0151] At this time, the control unit 10c receives a notification of the type of optical fiber of the transmission line 90 from, for example, a network monitoring device. Therefore, the control unit 10c can set an appropriate attenuation amount in the variable optical attenuator 16 according to the type of the optical fiber.

[0152] Furthermore, the control unit 10c may generate a formula indicating the correlation between the amount of ASS, the type of optical fiber, and the amount of attenuation by the same method as described above before the transmission system 9b starts operating. In this case, the control unit 10c stores coefficients of the formula in the memory 11 and reads them out during the operation of the transmission system 9b to use them to determine the amount of attenuation.

[0153] (Eighth Example) A data table relating to the correlation between the amount of ASS, the amount of attenuation, the average input power, and the type of optical fiber may be stored in the memory 11. In this example, the average input power is calculated in the same manner as in the second embodiment, and the type of optical fiber is the same as in the third embodiment. Also, the transmission system of this example has the same configuration as in the sixth embodiment.

[0154] 19, 20, and 21 are diagrams showing data tables 110h-1 to 110h-3 according to the eighth embodiment. The data tables 110h-1 to 110h-3 are stored in the memory 11 as one data table, but for convenience, they are shown divided into three tables.

[0155] Data table 110h-1 shows the correlation between the amount of ASS and the amount of attenuation for each average input power when the type of optical fiber is SMF. Data table 110h-2 shows the correlation between the amount of ASS and the amount of attenuation for each average input power when the type of optical fiber is DSF. Data table 110h-3 shows the correlation between the amount of ASS and the amount of attenuation for each average input power when the type of optical fiber is ExtCORE.

[0156] The data tables 110h-1 to 110h-3 register the ASS amount, attenuation amount, average input power, and type of optical fiber when the reception power reaches the target value. That is, the data tables 110h-1 to 110h-3 indicate the correlation between the ASS amount, attenuation amount, average input power, and type of optical fiber.

[0157] Before the transmission system 9c starts operation, the control unit 10d generates data tables 110h-1 to 110h-3 from the measurement results of the ASS amount and the attenuation amount for each average input power and type of optical fiber using a method similar to that of the fifth embodiment. The data tables 110h-1 to 110h-3 register combinations of the ASS amount and the attenuation amount according to the number of wavelengths for each average input power and type of optical fiber. The data tables 110h-1 to 110h-3 are examples of correlation data.

[0158] The control unit 10d determines the amount of attenuation of the variable optical attenuator 16 based on the amount of ASS, the average input power, and the type of optical fiber, based on the data tables 110h-1 to 110h-3 during operation of the transmission system 9c. That is, the control unit 10d determines the amount of attenuation based on the correlation between the amount of ASS and the amount of attenuation according to the average input power and the type of optical fiber.

[0159] At this time, the control unit 10d receives a notification of the type of optical fiber of the transmission line 90 from, for example, a network monitoring device. Therefore, the control unit 10d can set, in the variable optical attenuator 16, not only the average input power but also an appropriate attenuation amount according to the type of optical fiber.

[0160] Furthermore, the control unit 10d may generate a formula showing the correlation between the amount of ASS, the average input power, the type of optical fiber, and the amount of attenuation by the same method as described above before the transmission system 9c starts operating. In this case, the control unit 10d may store coefficients of the formula in the memory 11 and read them out during the operation of the transmission system 9c to use them to determine the amount of attenuation.

[0161] The above-described embodiment is a preferred example of the present invention, but the present invention is not limited to this embodiment and can be modified in various ways without departing from the scope of the present invention.

[0162] In addition, the following supplementary notes are provided in relation to the above description. (Supplementary Note 1) A signal power detection unit that detects the signal power of a wavelength-multiplexed optical signal transmitted from a Raman amplifier to a transmission line to which pump light is input; a variable optical attenuator for attenuating the wavelength-multiplexed optical signal; a control unit that reduces an amount of attenuation of the variable optical attenuator in response to an increase in the signal power. (Additional Note 2) A storage unit is provided for storing correlation data regarding a correlation between the signal power and the attenuation amount when a reception power of the wavelength multiplexed optical signal received by a counterpart device via the transmission path becomes a target value, 2. The transmission device according to claim 1, wherein the control unit determines the amount of attenuation of the variable optical attenuator based on the correlation data from the signal power. (Supplementary Note 3) The transmission device according to Supplementary Note 2, wherein the correlation data includes a combination of the signal power and the amount of attenuation. (Supplementary Note 4) The transmission device according to Supplementary Note 2, wherein the correlation data includes coefficients of a formula indicating a correlation between the signal power and the amount of attenuation. (Supplementary Note 5) The transmission device according to any one of Supplementary Notes 2 to 4, wherein the control unit sets the receiving power when the number of wavelengths included in the wavelength-multiplexed optical signal is maximum to the target value. (Additional Note 6) An input power detector for detecting an input power of the wavelength multiplexed optical signal at an input end of the transmission line, The correlation data relates to a correlation between the signal power, the attenuation, and an average value of the input power per wavelength when the reception power becomes the target value, The transmission device according to any one of claims 2 to 5, wherein the control unit calculates the average value from the input power, and determines the attenuation amount of the variable optical attenuator based on the correlation data from the signal power and the average value. (Supplementary Note 7) The correlation data relates to a correlation among the signal power, the amount of attenuation, the average value, and the type of the transmission path when the reception power becomes the target value, The transmission device according to claim 6, wherein the control unit determines the amount of attenuation of the variable optical attenuator based on the correlation data from the signal power, the input power, and the type of the transmission path. (Additional Note 8) The correlation data relates to a correlation between the signal power, the amount of attenuation, and the type of the transmission path when the reception power becomes the target value, 6. The transmission device according to claim 2, wherein the control unit determines the amount of attenuation of the variable optical attenuator based on the correlation data from the signal power and the type of the transmission path. (Appendix 9) An ASS detector that detects the amount of ASS light generated by a Raman amplifier that outputs pump light to a transmission line of a wavelength-multiplexed optical signal; a variable optical attenuator that attenuates the wavelength-multiplexed optical signal output to the transmission line; a control unit that reduces an amount of attenuation of the variable optical attenuator in response to a reduction in the amount of generated ASS light. (Appendix 10) a storage unit that stores correlation data regarding a correlation between the amount of ASS light generated and the amount of attenuation when a reception power of the wavelength multiplexed optical signal received by a counterpart device via the transmission path reaches a target value, The transmission device according to claim 9, wherein the control unit determines the amount of attenuation of the variable optical attenuator based on the correlation data from the amount of ASS light generated. (Supplementary Note 11) The transmission device according to Supplementary Note 10, wherein the correlation data includes a combination of the amount of ASS light generated and the amount of attenuation. (Supplementary Note 12) The transmission device according to Supplementary Note 10 or 11, wherein the control unit sets the reception power to the target value when the number of wavelengths included in the wavelength-multiplexed optical signal is maximum. (Additional Note 13) An input power detector for detecting an input power of the wavelength multiplexed optical signal at an input end of the transmission line, The correlation data relates to a correlation between the amount of ASS light generated, the amount of attenuation, and the average value of the input power per wavelength when the reception power becomes the target value, The transmission device according to any one of appendices 10 to 12, characterized in that the control unit calculates the average value from the input power, and determines the attenuation amount of the variable optical attenuator based on the correlation data from the amount of ASS light generated and the average value. (Supplementary Note 14) The correlation data relates to a correlation among the amount of ASS light generated, the amount of attenuation, the average value, and the type of the transmission line when the reception power becomes the target value, The transmission device described in Appendix 13, characterized in that the control unit determines the attenuation amount of the variable optical attenuator based on the correlation data from the amount of ASS light generated, the input power, and the type of the transmission path. (Supplementary Note 15) The correlation data relates to a correlation among the amount of ASS light generated, the amount of attenuation, and the type of the transmission line when the reception power becomes the target value, The transmission device according to any one of appendices 10 to 12, characterized in that the control unit determines the amount of attenuation of the variable optical attenuator based on the correlation data from the amount of ASS light generated and the type of the transmission path. (Supplementary Note 16) A transmitter for transmitting a wavelength-multiplexed optical signal to a transmission line to which pump light is input from a Raman amplifier; a receiving device for receiving the wavelength multiplexed optical signal from the transmitting device via the transmission line, The transmitting device a signal power detection unit that detects the signal power of the wavelength multiplexed optical signal transmitted to the transmission line; a variable optical attenuator for attenuating the wavelength-multiplexed optical signal; a control unit that reduces an amount of attenuation of the variable optical attenuator in response to an increase in the signal power. (Additional Note 17) The transmitting device has a storage unit that stores correlation data regarding a correlation between the signal power and the attenuation amount, The receiving device includes: a reception power detection unit for detecting a reception power of the wavelength multiplexed optical signal; a notification unit that notifies the control unit of the reception power; The control unit is controlling the amount of attenuation according to a change in the signal power corresponding to the number of wavelengths included in the wavelength-multiplexed optical signal so that the reception power becomes the target value; generating the correlation data based on the signal power and the amount of attenuation when the reception power reaches the target value by the control; 17. The transmission system according to claim 16, further comprising: determining the attenuation amount of the variable optical attenuator based on the correlation data from the signal power after the correlation data is generated. (Supplementary Note 18) A transmitter for transmitting a wavelength-multiplexed optical signal to a transmission line to which pump light is input from a Raman amplifier; a receiving device for receiving the wavelength multiplexed optical signal from the transmitting device via the transmission line, The transmitting device an ASS detector for detecting an amount of ASS light generated by the Raman amplifier; a variable optical attenuator that attenuates the wavelength-multiplexed optical signal output to the transmission line; a control unit that reduces an amount of attenuation of the variable optical attenuator in response to a reduction in the amount of generated ASS light. (Supplementary Note 19) The transmitting device has a storage unit that stores correlation data regarding a correlation between the amount of ASS light generated and the amount of attenuation, The receiving device includes: a reception power detection unit for detecting a reception power of the wavelength multiplexed optical signal; a notification unit that notifies the control unit of the reception power; The control unit is controlling the amount of attenuation according to a change in the amount of ASS light generated according to the number of wavelengths included in the wavelength multiplexed optical signal so that the reception power becomes a target value; generating the correlation data based on the amount of ASS light generated and the amount of attenuation when the reception power reaches the target value by the control; 19. The transmission system according to claim 18, wherein after the correlation data is generated, the attenuation amount of the variable optical attenuator is determined based on the correlation data from the amount of ASS light generated. [Explanation of symbols]

[0163] 1, 1a, 1c, 1d Transmitting device 2. Receiving device 9, 9a, 9b, 9c Transmission Systems 10, 10a, 10c, 10d Control section 11. Memory 12 OSC receiver 14,25 WSS Department 16 Variable Optical Attenuator 18 Signal power detector 18a Input power detector 18c ASS detector 19 Forward excitation light source 20 Reception power detection section 21 OSC Transmitter 27 Backward excitation light source 90 Transmission Line 110,110a,110c~110g Data Table 110h-1~110h-3 Data Table

Claims

1. a signal power detection unit that detects the signal power of a wavelength-multiplexed optical signal transmitted from a Raman amplifier to a transmission line to which pump light is input; a variable optical attenuator for attenuating the wavelength-multiplexed optical signal; a control unit that controls the amount of attenuation based on the signal power detected by the signal power detection unit and a correlation between the signal power for each number of wavelengths included in the wavelength multiplexed optical signal and the amount of attenuation of the variable optical attenuator.

2. a signal power detection unit that detects the signal power of a wavelength-multiplexed optical signal transmitted from a Raman amplifier to a transmission line to which pump light is input; a variable optical attenuator for attenuating the wavelength-multiplexed optical signal; a control unit that reduces an attenuation amount of the variable optical attenuator in response to an increase in the signal power, a control unit that determines the amount of attenuation of the variable optical attenuator based on the signal power detected by the signal power detection unit and a correlation between the signal power of the wavelength-multiplexed optical signal and the amount of attenuation, the correlation corresponding to a target value of the received power of the wavelength-multiplexed optical signal received by an opposing device via the transmission path.

3. a storage unit that stores correlation data regarding a correlation between the signal power and the attenuation amount when a reception power of the wavelength multiplexed optical signal received by an opposing device via the transmission line becomes a target value, 2. The transmission device according to claim 1, wherein the control unit determines the amount of attenuation of the variable optical attenuator based on the correlation data from the signal power.

4. 4. The transmission device according to claim 3, wherein the correlation data includes coefficients of a mathematical expression that indicates a correlation between the signal power and the amount of attenuation.

5. 4. The transmission device according to claim 3, wherein the control unit sets the reception power to the target value when the number of wavelengths included in the wavelength-multiplexed optical signal is maximum.

6. an input power detection unit that detects the input power of the wavelength multiplexed optical signal at an input end of the transmission line, the correlation is a relationship between the signal power, the attenuation, and an average value per wavelength of the input power; 6. The transmission device according to claim 1, wherein the control unit calculates the average value from the input power, and determines the amount of attenuation of the variable optical attenuator based on the correlation between the signal power and the average value.

7. The correlation is a relationship among the signal power, the amount of attenuation, the average value, and the type of the transmission path, 7. The transmission device according to claim 6, wherein the control unit determines the amount of attenuation of the variable optical attenuator based on the correlation between the signal power, the input power, and the type of the transmission line.

8. The correlation is a relationship between the signal power, the amount of attenuation, and the type of the transmission path, 6. The transmission device according to claim 1, wherein the control unit determines the amount of attenuation of the variable optical attenuator based on the correlation between the signal power and the type of the transmission line.

9. an ASS detector that detects the amount of ASS light generated by a Raman amplifier that outputs pump light to a transmission line of a wavelength-multiplexed optical signal; a variable optical attenuator that attenuates the wavelength-multiplexed optical signal output to the transmission line; a control unit that reduces an amount of attenuation of the variable optical attenuator in response to a reduction in the amount of generated ASS light.

10. a storage unit configured to store correlation data regarding a correlation between the amount of ASS light generated and the amount of attenuation when a reception power of the wavelength multiplexed optical signal received by a counterpart device via the transmission path reaches a target value, 10. The transmission device according to claim 9, wherein the control unit determines the amount of attenuation of the variable optical attenuator based on the correlation data from the amount of generated ASS light.

11. a transmitting device for transmitting a wavelength multiplexed optical signal to a transmission line to which pump light is input from a Raman amplifier; a receiving device for receiving the wavelength multiplexed optical signal from the transmitting device via the transmission line, The transmitting device a signal power detection unit that detects the signal power of the wavelength multiplexed optical signal transmitted to the transmission line; a variable optical attenuator for attenuating the wavelength-multiplexed optical signal; a control unit that controls the amount of attenuation based on the signal power detected by the signal power detection unit and a correlation between the signal power for each number of wavelengths included in the wavelength-multiplexed optical signal and the amount of attenuation of the variable optical attenuator.

12. the transmitting device has a storage unit that stores correlation data regarding the correlation; The receiving device includes: a reception power detection unit for detecting a reception power of the wavelength multiplexed optical signal; a notification unit that notifies the control unit of the reception power; The control unit is controlling the amount of attenuation according to a change in the signal power corresponding to the number of wavelengths included in the wavelength multiplexed optical signal so that the reception power becomes a target value; generating the correlation data based on the signal power and the amount of attenuation when the reception power reaches the target value by the control; 12. The transmission system according to claim 11, wherein after the correlation data is generated, the attenuation amount of the variable optical attenuator is determined based on the correlation data from the signal power.

13. a transmitting device for transmitting a wavelength multiplexed optical signal to a transmission line to which pump light is input from a Raman amplifier; a receiving device for receiving the wavelength multiplexed optical signal from the transmitting device via the transmission line, The transmitting device a signal power detection unit that detects the signal power of the wavelength multiplexed optical signal transmitted to the transmission line; a variable optical attenuator for attenuating the wavelength-multiplexed optical signal; a control unit that reduces an attenuation amount of the variable optical attenuator in response to an increase in the signal power, a control unit that determines the amount of attenuation of the variable optical attenuator based on the signal power detected by the signal power detection unit and a correlation between the signal power of the wavelength-multiplexed optical signal and the amount of attenuation, the correlation corresponding to a target value of the reception power of the wavelength-multiplexed optical signal received by the receiving device.

14. a transmitting device for transmitting a wavelength multiplexed optical signal to a transmission line to which pump light is input from a Raman amplifier; a receiving device for receiving the wavelength multiplexed optical signal from the transmitting device via the transmission line, The transmitting device an ASS detector for detecting an amount of ASS light generated by the Raman amplifier; a variable optical attenuator that attenuates the wavelength-multiplexed optical signal output to the transmission line; a control unit that reduces an amount of attenuation of the variable optical attenuator in response to a reduction in the amount of generated ASS light.

15. the transmitting device has a storage unit configured to store correlation data regarding a correlation between the amount of ASS light generated and the amount of attenuation, The receiving device includes: a reception power detection unit for detecting a reception power of the wavelength multiplexed optical signal; a notification unit that notifies the control unit of the reception power; The control unit is controlling the amount of attenuation according to a change in the amount of ASS light generated according to the number of wavelengths included in the wavelength multiplexed optical signal so that the reception power becomes a target value; generating the correlation data based on the amount of ASS light generated and the amount of attenuation when the reception power reaches the target value by the control; 15. The transmission system according to claim 14, wherein after the correlation data is generated, the amount of attenuation of the variable optical attenuator is determined based on the correlation data from the amount of ASS light generated.

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