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

Abstract

To estimate nonlinear SNR with high accuracy.SOLUTION: An optical power control device 100 includes a control unit 140 that acquires a received waveform of a WDM optical signal transmitted between transmission devices 110 via a transmission line 130, calculates a power profile in the distance direction of the transmission line 130 on the basis of the received waveform, and calculates a nonlinear SNR of the transmission line 130 on the basis of the power profile. The control unit 140 compensates for variations in the calculated nonlinear SNR, calculates a control amount for controlling the input power to the transmission line 130, and outputs the control amount to the transmission device 110.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical power control device, an optical power control method, and an optical transmission system. [Background technology]

[0002] Wavelength Division Multiplexing (WDM) has been put to practical use to provide high-capacity optical communications. WDM allows optical signals to be transmitted using multiple wavelength channels, and by multiplexing a large number of wavelength channels, high-capacity optical communications can be realized.

[0003] The transmission characteristics of WDM signals depend on the wavelength. If the transmission characteristics vary depending on the wavelength, the transmission distance and the number of wavelengths will be limited. Therefore, in the past, designs and adjustments were made to suppress the variations in optical power and optical signal-to-noise ratio (OSNR).

[0004] In recent years, the bandwidth of WDM transmission systems has expanded, and for example, multi-band (C+L band) WDM transmission systems have been proposed that transmit optical signals using the C and L bands simultaneously. When the transmitted wavelength band is expanded from only the C band to C+L bands, etc., even if the variation in OSNR due to wavelength is suppressed, the wavelength characteristics of GSNR (nonlinear noise + OSNR) may not be uniform. GSNR is an abbreviation for Generalized SNR.

[0005] The following are prior art techniques related to optical power control for improving the transmission characteristics of optical signals. For example, in an optical amplifier device that combines Raman amplifiers, there is a technique for adjusting the operation of each Raman amplifier based on information related to each Raman pump light power and the OSNR of the optical amplification, thereby preventing deterioration of the OSNR of the output optical signal (see, for example, Patent Document 1 below). Also, in an optical amplifier device that combines Raman amplifiers, there is a technique for performing pre-emphasis on a transmission power profile based on a function of the OSNR deviation and nonlinear phase shift deviation of each span, thereby determining the power deviation for each channel (see, for example, Patent Document 2 below). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2002 / 021203 [Patent Document 2] US Patent Application Publication No. 2014 / 0147113 Summary of the Invention [Problem to be solved by the invention]

[0007] In the conventional patent documents 1 and 2, only the linear noise of Raman amplification is considered, and the nonlinear noise of GSNR is not considered. Therefore, the GSNR cannot be made uniform in the wavelength direction when multibanding is performed.

[0008] As a countermeasure, for example, it is possible to apply control to equalize the GSNR in the wavelength direction by estimating the SNR for nonlinear noise (nonlinear SNR, nonlinear noise amount) and adjusting the optical power of each wavelength. As will be described later in detail, it is possible to hold the nonlinear SNR for each wavelength in a table and estimate the nonlinear SNR by correcting it according to the fiber input power of the optical amplifier, including the effect of stimulated Raman scattering (SRS). However, the power profile of the signal in the fiber varies greatly depending on the loss profile of the pump light wavelength, which causes the nonlinear SNR to vary and makes it difficult to control the GSNR accurately. It is also possible to measure the power profile of the optical signal wavelength or the pump light wavelength using an OTDR (Optical Time Domain Reflectometer), but the pump light or optical signal may get in the way and make it impossible to measure the power profile itself. As such, the conventional technology was unable to estimate the nonlinear SNR accurately. Furthermore, the inability to estimate the nonlinear SNR accurately made it impossible to improve the GSNR of each band in multi-band transmission.

[0009] In one aspect, the present invention has an object to accurately estimate a nonlinear SNR. [Means for solving the problem]

[0010] According to one aspect of the present invention, an optical power control device is provided with a control unit that acquires a received waveform of a WDM optical signal transmitted between transmission devices via a transmission line, calculates a power profile in the distance direction of the transmission line based on the received waveform, and calculates a nonlinear SNR of the transmission line based on the power profile. Effect of the Invention

[0011] Advantageous Effects of Invention According to one aspect of the present invention, an effect is achieved in that a nonlinear SNR can be estimated with high accuracy. [Brief description of the drawings]

[0012] [Figure 1]FIG. 1 is a diagram illustrating an optical transmission system including an optical power control device according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating the uniformity of the wavelength characteristics of the GSNR. [Figure 3A] FIG. 3A is a flowchart showing an example of a conventional nonlinear SNR estimation. [Figure 3B] FIG. 3B is a diagram illustrating the challenges of GSNR estimation according to the prior art. [Figure 4] FIG. 4 is a chart showing the power profile for each type of Raman amplification. [Diagram 5] FIG. 5 is a flowchart illustrating an example of a calculation process of a nonlinear SNR according to the embodiment. [Figure 6A] FIG. 6A is a chart for explaining the details of calculation of the nonlinear effective length by acquiring a power profile. (Part 1) [Figure 6B] FIG. 6B is a diagram for explaining the details of the calculation of the nonlinear effective length by acquiring the power profile. (Part 2) [Figure 7] FIG. 7 is a diagram illustrating an example of a hardware configuration of a control unit of the optical power control device. [Figure 8] FIG. 8 is a flowchart illustrating an example of GSNR control according to the embodiment. [Figure 9A] FIG. 9A is a chart showing examples of power profiles by shape. (Part 1) [Figure 9B] FIG. 9B is a chart showing examples of power profiles by shape. (Part 2) [Figure 10] FIG. 10 is a flowchart showing another example of a conventional estimation of a nonlinear SNR. [Figure 11] FIG. 11 is a diagram showing an example of a table for calculating the nonlinear noise coefficient. [Figure 12] FIG. 12 is a diagram illustrating an optical transmission system including another configuration example of the optical power control device according to the embodiment. [Figure 13] FIG. 13 is a comparison diagram of each example of optical power control. [Figure 14A]14A is a flowchart showing a GSNR control example 1 according to an optical power control device of another configuration example. (Part 1) [Figure 14B] 14B is a flowchart showing a GSNR control example 1 according to another configuration example of the optical power control device (part 2). [Figure 15A] 15A is a flowchart showing a second example of GSNR control performed by an optical power control device according to another example of the configuration. (Part 1) [Figure 15B] 15B is a flowchart showing a second example of GSNR control performed by an optical power control device according to another example of the configuration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the disclosed optical power control device, optical power control method, and optical transmission system will be described in detail with reference to the accompanying drawings.

[0014] (Configuration Example of Optical Power Control Device According to the Embodiment) 1 is a diagram showing an optical transmission system including an optical power control device according to an embodiment. The optical transmission system includes a plurality of transmission devices #1 to #4 (nodes) 110 that transmit WDM signals, transmission paths 130 between each of the transmission devices 110, and an optical power control device 100 that controls the transmission state of each of the transmission devices 110, mainly the optical power.

[0015] The WDM signals are in different bands, for example, the C-band and the L-band. The optical power control device 100 is, for example, a function of a network controller (NWC) that manages and controls the transmission devices #1 to #4 (110). The transmission path 130 is, for example, an optical fiber. The multiple transmission devices #1 to #4 (nodes) 110 are, for example, ROADMs (Reconfigurable Optical Add / Drop Multiplexers) that can drop and add WDM signals by wavelength, optical repeaters, etc.

[0016] In the system example of Fig. 1, a transmitter (Tx) 101 is provided in transmission device #1 (110), a receiver (Rx) 102 is provided in transmission device #4 (110), and optical signals are transmitted between these transmission devices #1 to #4 (nodes) 110. The system example of Fig. 1 also shows a connection example in which the optical power control device 100 controls the optical power between a pair of transmission devices #2 to #3 (110) corresponding to a certain section (one span). The optical power control device 100 can similarly perform optical power control by connecting to a pair of transmission devices 110 corresponding to another span.

[0017] The transmission device 110 includes, from the input side of an optical signal, a wavelength selective switch (WSS) 121, an optical power monitor 122, an optical amplifier (optical amp) 123, a variable optical attenuator (VOA) 124, an optical branching unit 125, and an optical multiplexing unit 126. WSS stands for Wavelength Selective Switch, and VOA stands for Variable Optical Attenuator.

[0018] The optical power monitor 122 detects the optical power of the optical signal branched by the optical branching unit 125. The optical amplifier 123 is, for example, an EDFA (Erbium Doped Fiber Amplifier).

[0019] Further, in each transmission device 110, a forward Raman amplifier (Fwd Raman) 127 is disposed on the output side to the transmission line 130, and a backward Raman amplifier (Bwd Raman) 128 is disposed on the input side from the transmission line 130. The forward Raman amplifier 127 outputs pump light for forward pumping to the transmission line 130 via the optical multiplexer 126a. The forward Raman amplifier 127 may include, for example, an i-pump and secondary pump light. The backward Raman amplifier 128 outputs pump light for backward pumping to the transmission line 130 via the optical multiplexer 126b. The transmission device 110 arbitrarily combines forward pumping and backward pumping, and optically amplifies the optical signal in the transmission line 130 by using these pump lights.

[0020] The transmission device 110 also includes, as functions related to optical power control, a monitor information transmitter 131, a control information receiver 132, and a received waveform transmitter 133. The monitor information transmitter 131 transmits the optical power detected by the optical power monitor 122 to the optical power control device 100. The control information receiver 132 receives control information output by the optical power control device 100 and controls the attenuation (ATT value) of the WSS 121. The received waveform transmitter 133 transmits the received waveform of the wavelength to be controlled, which is received by the receiver (Rx) 102 of the transmission device #4 (110) at the end of the transmission line 130, to the optical power control device 100.

[0021] In the optical power control device 100, a control unit 140 controls the optical power of the transmission devices #1 to #4 (110). The control unit 140 includes a received waveform receiving unit 141, a power profile calculating unit 142, a monitor information receiving unit 143, a nonlinear SNR calculating unit 144, a linear SNR calculating unit 145, a GSNR calculating unit 146, a WSS ATT amount calculating unit 147, and a control information transmitting unit 148.

[0022] The received waveform receiving unit 141 receives the received waveform of the wavelength to be controlled, which is transmitted by the receiving unit (Rx) 102 of the terminal transmission device #4 (110). The power profile calculating unit 142 calculates a power profile, which is the distribution of the optical power of the optical signal in the longitudinal (distance) direction of the transmission line 130, using the received waveform of the wavelength to be controlled. The calculated power profile is stored in a storage unit such as a memory of the optical power control device 100.

[0023] The monitor information receiver 143 acquires the fiber input channel power to be controlled, which is obtained by the optical power monitor 122 and transmitted by the monitor information transmitter 131 of the transmission device #2 (110) on the transmitting side of the span section (#2 to #3) to be subjected to optical power control. The monitor information receiver 143 also acquires the optical input power of the optical amplifier 123, which is obtained by the optical power monitor 122 and transmitted by the monitor information transmitter 131 of the transmission device #3 (110) on the receiving side of the span section to be subjected to optical power control.

[0024] The nonlinear SNR calculation unit 144 calculates the nonlinear SNR of the span section (#2 to #3) using a predetermined calculation formula based on the power profile calculated by the power profile calculation unit 142 and the fiber input channel power of the transmission device #2 (110). The linear SNR calculation unit 145 calculates the linear SNR of the span section (#2 to #3) using a predetermined calculation formula based on the input power and noise figure (NF) of the optical amplifier 123 of the transmission device #3 (110). These calculated nonlinear SNRs and nonlinear SNRs are stored in the storage unit of the optical power control device 100.

[0025] The GSNR calculation unit 146 calculates the GSNR of the span section (#2 to #3) based on the nonlinear SNR calculated by the nonlinear SNR calculation unit 144 and the linear SNR calculated by the linear SNR calculation unit 145. The calculated GSNR is stored in a storage unit of the optical power control device 100.

[0026] The WSS ATT amount calculation unit 147 calculates the ATT value (ch ATT value) for each channel of the WSS 121 of the transmission device #2 (110) from the difference from a predetermined target GSNR (for example, the average value of the GSNRs of all WDM signals obtained from design) that is a control target. The calculated ch ATT value is stored in the storage unit of the optical power control device 100. The control information transmission unit 148 transmits the calculated ch ATT value to the transmission device #2 (control information reception unit 132) on the transmitting side of the span section (#2 to #3).

[0027] In the embodiment, the optical power control device 100 has a nonlinear SNR calculation unit 144, which calculates the nonlinear SNR of the span section. The nonlinear SNR calculation unit 144 in the embodiment corrects the nonlinear SNR (nonlinear noise amount) using power profile estimation. Although details will be described later, a reference nonlinear SNR is estimated using a value stored in a table for each wavelength and the fiber input power value. Then, correction is performed using the nonlinear effective length corresponding to the reference nonlinear SNR and the nonlinear effective length obtained from the power profile estimation to calculate the nonlinear SNR. This makes it possible to correct the nonlinear SNR using the power profile, and improve the accuracy of the nonlinear SNR.

[0028] (Conventional technology and its problems) Here, we will explain the conventional technology and its problems. Figure 2 is an explanatory diagram of the equalization of GSNR wavelength characteristics. In optical transmission in the C band and L band, (a) shows no GSNR control, and (b) shows GSNR control, with the horizontal axis showing the wavelength and the vertical axis showing the optical power and GSNR.

[0029] If the transmission performance varies depending on the wavelength, the transmission distance and the number of wavelengths will be limited, so conventionally, designs and adjustments have been made to suppress the variations in optical power and OSNR. When the transmission wavelength band is expanded from only the C band to the C+L band, as shown in Figure 2(a), the problem arose that the wavelength characteristics C1 and C2 of the GSNR (nonlinear noise + OSNR) are not uniform, even if the variation in OSNR due to wavelength is suppressed.

[0030] For this reason, as shown in FIG. 2(b), it is possible to apply control that estimates the SNR for linear noise and adjusts the optical power of each wavelength to equalize the wavelength characteristics C1 and C2 of the GSNR in the wavelength direction.

[0031] Conventionally, in power control that takes into account fiber loss and lamp loss between a pair of transmission equipment, the receiving transmission equipment (node ​​B) transfers the OSNR or linear SNR and optical power measured by an OCM (optical channel monitor) or OTDR to the transmitting transmission equipment (node ​​A). The transmitting transmission equipment then calculates the GSNR and controls the WSS and optical amplifier.

[0032] Nonlinear noise is proportional to the cube of the optical power, and is expressed by the following formula (1): (η: proportionality constant)

[0033]

number

[0034] If the channel bandwidth is constant, the nonlinear noise per unit bandwidth (e.g., 12.5 GHz) can be expressed by the following formula (2): (η d ; proportionality constant, CH ;channel bandwidth)

[0035]

number

[0036] Therefore, the nonlinear SNR is expressed by the following equation (3). (P CH(A) / B CH is the fiber input power per unit bandwidth)

[0037]

number

[0038] Furthermore, the GSNR is calculated from the linear SNR and the following equation (4).

[0039]

number

[0040] Specifically, the fiber input power per unit bandwidth at the central wavelength is measured by the OCM at node A, and the nonlinear SNR is calculated. The linear SNR value measured at node B is then transferred to node A, where the GSNR is calculated.

[0041] Here, we will explain a method for estimating the nonlinear SNR when forward Raman is applied, there is lamp loss, and there is no information on the optical power for each wavelength from an OTDR or the like. In this case, the nonlinear SNR is stored in a table in advance for each wavelength. Then, using a reference value and the fiber input power value, it is possible to estimate the nonlinear SNR by correcting according to the fiber input power, including the effect of tilt due to SRS. Here, differences in the fiber loss coefficient are not taken into account, and a fixed value of 0.2 dB / km is used, for example. The nonlinear SNR is calculated, for example, by the following formula (5), taking into account the signal bandwidth from the nonlinear noise coefficient.

[0042] Nonlinear noise factor [mW / GHz] -2 = Nonlinear noise coefficient slope × (fiber input power – fiber input power reference value) + nonlinear noise coefficient reference value … (5)

[0043] The above nonlinear noise coefficient slope and nonlinear noise coefficient reference value are stored in a table, and the fiber input power is set to a predetermined value [dBm / 50GHz]. The term nonlinear noise coefficient slope x (fiber input power - fiber input power reference value) is corrected according to the fiber input power, including the effect of SRS. Also, convert from the nonlinear noise coefficient to nonlinear SNR.

[0044] 3A is a flowchart showing an example of a conventional estimation method of nonlinear SNR. First, node A measures the optical amplifier input power per unit bandwidth at the center wavelength by OCM (step S301). Then, node A calculates the fiber input power by taking into account the gain of the optical amplifier and the amplifier tilt control (step S302).

[0045] Next, node A estimates the nonlinear SNR based on the table value and the fiber input power, taking into account the effect of tilt due to SRS (step S303).However, conventionally, it has not been possible to estimate the nonlinear SNR with high accuracy.

[0046] FIG. 3B is a diagram explaining the problems of GSNR estimation by the conventional technology. FIG. 3B(a) shows an example of the wavelength arrangement of the optical signal and the pump light, where the horizontal axis indicates the wavelength and the vertical axis indicates the amount of attenuation (loss coefficient). For example, when an S-band (1460-1530 nm) signal is optically amplified by forward Raman, the pump light needs to be arranged in the band of 1360-1430 nm. In addition, in the forward Raman amplifier, there is a problem of RIN (relative intensity noise of the pump light), so it is necessary to use an i-pump with a wide spectrum. On the other hand, it is known that optical fibers have a water peak at 1383 nm, and the amount of the water peak varies widely. It is also known that the amount of loss of the water peak deteriorates over time.

[0047] Figure 3B(b) shows the design of the loss coefficient of the pumping light wavelength and the actual power profile. If the optical amplifier input power is monitored and controlled to a specified power, it is possible to control the pumping light power so that the ON / OFF gain becomes the target value. However, the power profile of the signal in the fiber varies greatly depending on the loss profile of the pumping light wavelength, which causes the nonlinear SNR to vary and affects the accuracy of GSNR control.

[0048] As shown in the power profile in Figure 3B(b), even if the fiber input power at 0 km is the same, if the nonlinear SNR is different, the characteristics of the loss coefficient P2 of the actual pumping light wavelength will differ from the characteristics of the loss coefficient P1 of the pumping light wavelength used in the design, resulting in variation in the nonlinear SNR.

[0049] As a countermeasure to this, it is conceivable to measure the power profile of the optical signal wavelength or the pumping light wavelength with an OTDR. However, the pumping light or optical signal gets in the way and makes it impossible to perform the measurement with an OTDR.

[0050] (Overview of Nonlinear SNR Correction Using Power Profile According to the Embodiment) The control unit 140 of the optical power control device 100 according to the embodiment corrects the nonlinear SNR using the power profile. The control unit 140 corrects the nonlinear SNR by using a reference standard value of each parameter obtained in advance by simulation or transmission experiment: nonlinear SNR ref , P 0,ref , L eff,ref , γ ref is used to approximately calculate the value using the following formula (6).

[0051] Nonlinear SNR(P 0,Leff ,γ) = nonlinear SNR ref -2×(P 0 -P 0,ref )-2×10log(L eff / L eff,ref )-2×10log(γ / γ ref ) [dB in receive band]…(6) (P 0 : Fiber input power [dBm], L eff : nonlinear effective length [km], γ: nonlinear coefficient

[0052] In addition, the nonlinear effective length L eff is shown in the following equation (7). L eff =∫[0~L]|P(z) / P 0 |dz …(7) (P(z): optical power at point z [W], P 0 : fiber input power [W], L: fiber length [km])

[0053] The nonlinear coefficient is expressed by the following equation (8). Nonlinear coefficient: γ = (n 2 ω 0 ) / (cA eff )=(n 2 2πf) / (cA eff )=2πcn 2 / (A eff / λ) …(8)

[0054] FIG. 4 is a chart showing power profiles for different Raman amplifications. If the values ​​of the fiber input power, nonlinear effective length, and nonlinear coefficient of the actual system are known, the nonlinear SNR can be corrected. The control unit 140 calculates the nonlinear effective length L from the power profile estimation result. eff The accuracy of the nonlinear SNR is improved by calculating the above. The control unit 140 uses the power profile estimation results for each Raman amplification type (BR: backward pumping, FR+BR: forward pumping+backward pumping, w / o R: no Raman amplification) of the system shown in FIG.

[0055] (Calculation of Nonlinear SNR Using Power Profile According to the Embodiment) The control unit 140 of the optical power control device 100 estimates the reference nonlinear SNR using the value stored in the table for each wavelength and the fiber input power value. Then, the control unit 140 performs correction using the nonlinear effective length corresponding to the reference nonlinear SNR and the nonlinear effective length obtained from the power profile estimation, and calculates the nonlinear SNR. Specifically, it is expressed by the following formula (9).

[0056] Nonlinear SNR [dB] = Nonlinear SNR ref -2×10log(L eff / L eff,ref ) …(9)

[0057] Among the above items, nonlinear SNR ref is estimated using the same method as before. eff is the nonlinear effective length obtained from the power profile estimation (PPE), L eff,ref is the nonlinear SNR ref The linear SNR can be easily calculated from the noise of the optical amplifier at the receiving node using the same method as in the past.

[0058] 5 is a flowchart showing an example of a calculation process of a nonlinear SNR according to the embodiment. The process shown in FIG. 5 is executed by the control unit 140, for example, a CPU, of the optical power control device 100. First, the control unit 140 acquires a power profile of a wavelength to be controlled, and calculates a nonlinear effective length (step S501).

[0059] Next, the control unit 140 measures the optical amplifier input power at the OCM of node A (the transmission device 110 on the sending side), and calculates the fiber input power taking into account the gain of the optical amplifier and the amplifier tilt control (step S502).

[0060] Next, the control unit 140 estimates a nonlinear SNR to be a reference based on the table value (power profile) and the fiber input power while taking into account the effect of the SRS tilt (step S503).

[0061] Then, the control unit 140 corrects the nonlinear SNR using the nonlinear SNR serving as a reference, the corresponding nonlinear effective length, and the nonlinear effective length calculated from the PPE (step S504).

[0062] 6A and 6B are diagrams for explaining the details of calculation of the nonlinear effective length by acquiring a power profile. The control unit 140 acquires the power profile of the wavelength to be controlled in FIG. 5 and calculates the nonlinear effective length L eff The process (step S501) for calculating (the above formula (7)) will be described in detail.

[0063] The control unit 140 obtains the power profile shown in Fig. 6A by calculating the power in 1 km increments, for example, using the waveform received by the termination transmission device #4 (110). The horizontal axis of Fig. 6A is the distance from the transmission device #1 (110) on the transmitting side, and the vertical axis is the power. The control unit calculates both the design value (Reference) P1 of the PPE and the actual measured value P2.

[0064] 6B shows the nonlinear effective length, with the horizontal axis representing distance and the vertical axis representing power. The control unit 140 converts the logarithm into an antilogarithm (mW) representation and integrates the power in 1-km increments to calculate the design nonlinear effective length L1 and the actual nonlinear effective length L2.

[0065] (Example of nonlinear SNR calculation) The nonlinear SNR is calculated, for example, by the following formula (10). SNR NLI =Ps / P NLI =Ps / (ηΔ fB ×Ps 3 ) =1 / (ηΔ fB ×Ps 2 ) =1 / (Kγ 2 L eff 2 Δf B Ps 2 ) …(10) (Ps: Fiber input power [dBm], ηΔ fB : Nonlinear noise = Kγ 2 L eff 2 Δf B , K: coefficient determined by dispersion, fiber length, loss, etc., γ: nonlinear coefficient, L eff : Nonlinear effective length, Δf B : signal bandwidth)

[0066] (Example of nonlinear SNR correction using reference nonlinear SNR) The correction of the nonlinear SNR using the reference nonlinear SNR will be explained below. The ratio of the nonlinear SNR to the reference nonlinear SNR is expressed by the following formula (11). SNR NLI / SNR NLI,ref =(1 / (Kγ 2 L eff 2 Δf B ×Ps 2 )) / (1 / (Kγ ref 2 L eff, ref 2 Δf B ×Ps ref2 )) =1 / (γ / γ ref ) 2 ×(L eff / L eff,ref ) 2 ×(Ps / Ps ref ) 2 …(11)

[0067] When converted to logarithm, it is expressed by the following equation (12). SNR NLI -SNR NLI,ref =-2×(Ps-Ps ref )-2×10log(L eff / L eff,ref )-2×10log(γ / γ ref ) [dB]…(12)

[0068] If the fiber input power and the nonlinear coefficient are the same, it is expressed by the following formula (13): Formula (13) is the same as the above formula (9). SNR NLI =SNR NLI,ref -2×10log(L eff / L eff,ref ) [dB]…(13) In this way, the control unit 140 can correct the nonlinear SNR by calculating the nonlinear effective length from the power profile.

[0069] (Example of hardware configuration of control unit) 7 is a diagram showing an example of a hardware configuration of a control unit of the optical power control device 100. The control unit 140 of the optical power control device 100 shown in FIG.

[0070] For example, the control unit 140 includes a processor 701 such as a CPU (Central Processing Unit), a memory 702, a network IF 703, a recording medium IF 704, and a recording medium 705. The components are connected to each other via a bus 710.

[0071] Here, the processor 701 is a control unit that controls the entire control unit 140. The processor 701 may have multiple cores. The memory 702 has, for example, a read only memory (ROM), a random access memory (RAM), and a flash ROM. Specifically, for example, the flash ROM stores a control program, the ROM stores an application program, and the RAM is used as a work area for the processor 701. The program stored in the memory 702 is loaded into the processor 701, causing the processor 701 to execute the coded process.

[0072] The network IF 703 manages the interface between the network NW and the inside of the device, and controls the input and output of information between the device and the outside.

[0073] The recording medium IF 704 controls reading / writing of data from / to the recording medium 705 under the control of the processor 701. The recording medium 705 stores the data written under the control of the recording medium IF 704.

[0074] In addition to the above-mentioned components, the control unit 703 may be capable of connecting, for example, an input device, a display, and the like via an IF.

[0075] The processor 701 shown in Fig. 7 can realize each function of the optical power control of the optical power control device 100 shown in Fig. 1 by executing a program. For example, the functions of the power profile calculation unit 142, the nonlinear SNR calculation unit 144, the linear SNR calculation unit 145, the GSNR calculation unit 146, and the WSS ATT amount control unit 147 can be realized. In addition, the function of a storage unit in which information on the power profile calculated by the power profile calculation unit 142 is stored can be realized by using the memory 702 and the recording medium 705 shown in Fig. 7.

[0076] 1, for example, the functions of the received waveform receiver 141, the monitor information receiver 143, and the control information transmitter 148 can be realized via the network IF 703 shown in Fig. 7. The network NW between the optical power control device 100 and each transmission device 110 is, for example, Ethernet (registered trademark) or the like, and transmits and receives information via electrical signals.

[0077] The control unit 140 having the hardware configuration shown in FIG. 7 is also mounted on each transmission device 110 and controls each transmission device 110.

[0078] (GSNR control example) Fig. 8 is a flowchart showing an example of GSNR control according to the embodiment. A processing example in the case of controlling fiber input channel power between transmission devices #2 and #3 (110) corresponding to the span to be controlled shown in Fig. 1 will be described. The processing shown in Fig. 8 is mainly controlled by the control unit 140 of the optical power control device 100 shown in Fig. 1. The thick frame in Fig. 8 indicates the processing executed by the control unit 140 of the optical power control device 100.

[0079] First, the transmission device #4 (110) at the end of the transmission line 130 acquires the received waveform of the wavelength to be controlled and transmits the received waveform information to the optical power control device 100 (step S801). Then, the optical power control device 100 (control unit 140) calculates a power profile using the received waveform (step S802).

[0080] Next, the transmission device #2 (110) acquires the fiber input channel power to be controlled by the optical power monitor and transmits it to the optical power control device 100 (step S803). Then, the optical power control device 100 calculates the nonlinear SNR from the calculated power profile and the fiber input channel power (step S804).

[0081] Next, the transmission device #3 (110) obtains the optical input power of the optical amplifier by the optical power monitor and transmits it to the optical power control device 100 (step S805). Then, the optical power control device 100 calculates the linear SNR using the optical input power of the optical amplifier and the NF (step S806).

[0082] Next, the optical power control device 100 calculates the GSNR from the nonlinear SNR and the linear SNR (step S807). Next, the optical power control device 100 calculates the ch ATT value of the WSS 121 of the transmission device #2 (110) from the difference between the calculated GSNR and the target GSNR (average value) (step S808). Then, the optical power control device 100 transmits the calculated ch ATT value of the WSS to the transmission device #2 (110) (step S809). Then, the WSS 121 of the transmission device #2 (110) sets the received ch ATT value (step S810), and the above process ends.

[0083] (First Modification of the Embodiment: Derivation of Target GSNR) A modified example of the above-mentioned embodiment will be described. First, an example of derivation of the target GSNR in GSNR control will be described. In the above description, the target GSNR in GSNR control is the average value of the GSNRs of all WDM signals obtained from the design. However, the actual average value of GSNR may differ from the design value. For this reason, the GSNR of the wavelength in operation may be calculated using the nonlinear SNR obtained from the power profile, and the target GSNR value may be corrected using the calculated value.

[0084] (Modification 2 of the embodiment: Speeding up power profile acquisition) Next, we will explain how to speed up the acquisition of a power profile used in GSNR control. For example, by making the step granularity of the power profile estimation coarser, the number of calculation points can be reduced and the speed can be increased. In order to calculate the amount of nonlinear noise, it is necessary to know the integral value of the power in the distance direction, not the power profile shape, so there is a possibility that the step granularity can be made coarse.

[0085] In addition, it is possible to limit the variance values ​​at the start and end points of the power profile estimation, reduce the number of calculation points, and increase the speed. Since nonlinear noise only affects areas close to the fiber input end (e.g., 0 to 40 km), it is highly likely that calculations will not be necessary for areas far from the fiber input end (e.g., 40 to 80 km).

[0086] (Comparison between conventional method and embodiment) Next, a comparison is made between the conventional method and the embodiment. For example, as explained with reference to FIG. 3B and the like, it is possible to set a target gain of forward-pumped Raman (FWD Raman) from the fiber type and span loss, and set it to the pump light power stored in a table. In this case, the nonlinear SNR is estimated from information on the wavelength, gain, and fiber input power, and the nonlinear noise coefficient parameters stored in the table. However, in a case where the span loss measurable by OTDR or OCM and the ON / OFF gain of FWD Raman are the same and only the shape of the power profile is different, a difference occurs in the nonlinear SNR.

[0087] In contrast, in the embodiment, the power profile is actually measured and the nonlinear SNR is calculated from the measurement result, so that the difference in the power profile shape can be corrected.

[0088] 9A and 9B are diagrams showing examples of power profiles by shape. The horizontal axis of Fig. 9A and Fig. 9B is distance, and the vertical axis is relative power. Case 1 shows the power profile by the conventional method, and Case 2 shows the power profile of the embodiment.

[0089] Here, in FIG. 9B, in the design (corresponding to case 1), the amount of nonlinear noise at the Raman gain with a loss coefficient of 0.28 dB / km in the pumping light wavelength band is calculated taking into account the span loss and fiber input power. In reality (corresponding to case 2), the loss coefficient of the pumping light wavelength band is 0.38 dB / km, the Raman gain is different from the design, and the loss coefficient of the main signal wavelength band is different in the first half (0.25 dB / km) and the second half (0.283 dB / km) of the span compared to the design. However, the ON / OFF gain of the FWD Raman is the same, and the span loss is also under the same conditions. Therefore, in the conventional method, although it is controlled by the same parameters as the design (case 1), the shape of the actual power profile (case 2) is different, and a difference occurs in the amount of nonlinear noise.

[0090] Here, the amplification degree of FWD Raman is expressed by the following formula (14).

[0091]

number

[0092] For the loss coefficient of the pumping wavelength, if the value used in the design is 0.28 dB / km and the actual value is 0.38 dB / km, only the loss coefficient of the fiber will change in the above formula (14). When the loss coefficient is 0.28 dB / km, the gain is 7 dB, whereas when the loss coefficient is 0.38 dB / km, it is 5.15 dB, resulting in a difference of about 1.85 dB.

[0093] If case 1 is a condition where the design values ​​are stored in a table using the conventional method, then in case 2, which is the actual case, the amount of nonlinear noise differs from case 1 by 3.2 dB.

[0094] The GSNR calculated by conventional GSNR control is 23.9 dB when the linear SNR is 26 dB and the nonlinear SNR is 28 dB. When the amount of nonlinear noise is 3.2 dB smaller, the linear SNR is 26 dB and the nonlinear SNR is 31.2 dB, so the GSNR is 24.9 dB, and in case 2 (conventional method), an error of 1.0 dB occurs per span. Therefore, according to the embodiment, it is possible to improve the GSNR by 1.0 dB compared to the conventional method.

[0095] (Additional Notes: Other existing issues) In the above explanation of the conventional technology, we have described a method for estimating a nonlinear SNR when forward Raman (FWD Raman) is applied, there is a lamp loss, and there is no information on the optical power for each wavelength from an OTDR, etc. Here, we will also explain the issues with the method for estimating a nonlinear SNR when forward Raman is applied, there is a lamp loss, and there is information on the optical power for each wavelength from an OTDR, etc.

[0096] In this way, when OTDR information can be used, the nonlinear SNR is stored in a table in advance for each wavelength. Then, using a reference value and the fiber input power value, the nonlinear SNR can be estimated by correcting according to the fiber input power, including the effect of tilt due to SRS. Here, differences in the fiber loss coefficient are not taken into account, and a fixed value of, for example, 0.2 dB / km is used. The nonlinear SNR is calculated from the nonlinear noise coefficient and the signal bandwidth using the above formula (5).

[0097] Here, when the position and amount of lamp loss can be determined by OTDR, it becomes necessary to correct the nonlinear noise coefficient slope in the above formula (5) according to the position and amount of lamp loss.

[0098] Fig. 10 is a flowchart showing another example of estimating a nonlinear SNR according to the related art. Steps S1001, S1002, and S1004 in the process shown in Fig. 10 are the same as steps S301, S302, and S304 in the process shown in Fig. 3. First, node A measures the optical amplifier input power per unit bandwidth at the center wavelength by OCM (step S1001). Then, node A calculates the fiber input power taking into account the gain of the optical amplifier and the amplifier tilt control (step S1002).

[0099] Next, node A corrects the nonlinear noise coefficient slope using the position and amount of lamp loss obtained from the OTDR (step S1003). Then, node A estimates the nonlinear SNR based on the table value and the fiber input power, taking into account the effect of tilt due to SRS (step S1004).

[0100] However, it is difficult to derive a correction formula for correcting the value of the nonlinear noise coefficient slope according to the position and amount of lamp loss. For this reason, for example, a method is considered in which correction values ​​of the nonlinear noise coefficient slope are derived in advance by simulation or the like for several combinations of the position and amount of lamp loss, stored in a table, and the values ​​are used for interpolation.

[0101] (Issues in creating nonlinear noise coefficient tables) Fig. 11 is a diagram showing an example of a table for calculating a nonlinear noise coefficient. For example, the nonlinear noise coefficient may be calculated by combining a nonlinear noise base table 1101 shown in Fig. 11(a) with a nonlinear noise coefficient slope correction table 1102 shown in Fig. 11(b).

[0102] A nonlinear noise coefficient slope and a nonlinear noise coefficient reference value are set for each optical frequency in a nonlinear noise base table 1101 shown in Fig. 11(a). A nonlinear noise coefficient slope correction value for each distance (position) is set in a nonlinear noise coefficient slope correction table 1102 shown in Fig. 11(b), and node A uses the correction value to interpolate the slope.

[0103] However, there is a problem that interpolation is difficult because there are two variables, the position and amount of lamp loss. In addition, creating the above table itself increases the amount of work required to create a database. To create a nonlinear noise table, possible combinations include the position and amount of lamp loss, FWD Raman gain, wavelength, and fiber type.

[0104] In this case, for example, there are 20 types of lamp loss positions up to 20 km in 1 km increments, 6 types of lamp loss amounts up to 3 dB in 0.5 dB increments, and 6 types of FWD Raman gains. Also, there are 90 types of wavelengths at 100 GHz intervals in the C+L band, and 6 types of fiber types, such as SMF (Single Mode Fiber), DSF (Dispersion Shifted Fiber), and ELEAF (NZ-DSF). Combining these, it would take time to create a database of 388,800 = 20 x 6 x 6 x 90 x 6 ≒ 400,000 combinations, and it is not realistic to keep all of these in a database.

[0105] In this way, by correcting the nonlinear SNR using power profile estimation as in the embodiment, compared to the conventional technology in which nonlinear noise coefficients are tabulated, it is possible to reduce the labor required for creating the database and the processing load.

[0106] (Another Configuration Example of the Optical Power Control Device of the Embodiment) Fig. 12 is a diagram showing an optical transmission system including another example of the configuration of the optical power control device according to the embodiment. In Fig. 12, the same components as those in Fig. 1 are denoted by the same reference numerals. The control unit 140 of the optical power control device 100 in Fig. 1 is provided with a WSS ATT amount calculation unit 147. In contrast, the control unit 1201 of the optical power control device 1200 in the other example of the configuration shown in Fig. 12 is different in that it is provided with an average power attenuation amount calculation unit 1202 and a pre-emphasis amount calculation unit 1203 instead of the WSS ATT amount calculation unit 147.

[0107] The control unit 140 of the optical power control device 100 described in Fig. 1 controls only the WSS 121 of the transmission device 110. In contrast, a control unit 1201 of an optical power control device 1200 of another configuration example shown in Fig. 12 controls the WSS 121, optical amplifier 123, and VOA 124 of the transmission device 110.

[0108] In the optical power control device 1200, a control unit 1201 controls the optical power of the transmission devices #1 to #4 (110). The control unit 1201 includes a received waveform receiving unit 141, a power profile calculating unit 142, a monitor information receiving unit 143, a nonlinear SNR calculating unit 144, a linear SNR calculating unit 145, a GSNR calculating unit 146, a control information transmitting unit 148, an average power attenuation calculating unit 1202, and a pre-emphasis amount calculating unit 1203.

[0109] In addition, the configuration of each transmission device 110 shown in FIG. 12 is the same as that in FIG. 1, but the control information receiving unit 132 receives control information output by the optical power control device 1200 and controls the average power attenuation of the VOA 124, the gain and tilt amount of the optical amplifier 123, and the attenuation amount (ATT value) of the WSS 121.

[0110] The received waveform receiving unit 141 receives the received waveform of the wavelength to be controlled that is output by the receiving unit (Rx) 102 and transmitted by the received waveform transmitting unit 133 of the terminal transmission device #4 (110). The power profile calculating unit 142 calculates a power profile, which is the distribution of the optical power of the optical signal in the longitudinal (distance) direction of the transmission line 130, using the received waveform of the wavelength to be controlled. The calculated power profile is stored in a storage unit such as a memory of the optical power control device 1200.

[0111] The monitor information receiver 143 acquires the fiber input channel power to be controlled, which is obtained by the optical power monitor 122 and transmitted by the monitor information transmitter 131 of the transmission device #2 (110) on the transmitting side of the span section (#2 to #3) to be subjected to optical power control. The monitor information receiver 143 also acquires the optical input power of the optical amplifier 123, which is obtained by the optical power monitor 122 and transmitted by the monitor information transmitter 131 of the transmission device #3 (110) on the receiving side of the span section to be subjected to optical power control.

[0112] The nonlinear SNR calculation unit 144 calculates the nonlinear SNR of the span section (#2 to #3) using a predetermined calculation formula based on the power profile calculated by the power profile calculation unit 142 and the fiber input channel power of the transmission device #2 (110). The linear SNR calculation unit 145 calculates the linear SNR of the span section (#2 to #3) using a predetermined calculation formula based on the input power and noise figure (NF) of the optical amplifier 123 of the transmission device #3 (110). These calculated nonlinear SNR and linear SNR are stored in the storage unit of the optical power control device 1200.

[0113] The GSNR calculation unit 146 calculates the GSNR of the span section (#2 to #3) based on the nonlinear SNR calculated by the nonlinear SNR calculation unit 144 and the linear SNR calculated by the linear SNR calculation unit 145. The calculated GSNR is stored in a storage unit of the optical power control device 1200.

[0114] The average power attenuation calculation unit 1202 and the pre-emphasis amount calculation unit 1203 calculate the average power attenuation and the pre-emphasis amount of the transmission device #2 (110) from the difference with a predetermined target GSNR (for example, the average value of GSNRs of all WDM signals obtained from design) as a control target, and calculate the gain and tilt amount of the optical amplifier 123 and the attenuation amount (ATT value) of the WSS 121 for each channel from the calculated pre-emphasis amount. The calculated average power attenuation amount of the VOA 124, the gain and tilt amount of the optical amplifier 123, and the attenuation amount (ATT value) of the WSS 121 are stored in the storage unit of the optical power control device 1200. The control information transmission unit 148 transmits the calculated average power attenuation amount of the VOA 124, the gain and tilt amount of the optical amplifier 123, and the attenuation amount (ATT value) of the WSS 121 for each channel to the transmission device #2 (control information reception unit 132) on the transmission side of the span section (#2 to #3).

[0115] When the forward Raman pumping is started by the forward Raman amplifier (Fwd Raman) 127, the transmission device 110 monitors the optical power using an optical power monitor (PD) provided in the preamplifier (optical amplifier 123) or the like, and adjusts the power of the Raman pumping light so as to achieve a predetermined gain.

[0116] FIG. 13 is a comparison diagram of each example of optical power control. In FIG. 13(a) to (c), the horizontal axis is wavelength, and the vertical axis is optical power, and the characteristics of the transmission device #2 (110) that is the target of optical power control are shown. FIG. 13(a) shows the control state of the transmission device #2 (110) by the control unit 140 of the optical power control device 100 shown in FIG. 1. The control unit 140 of the optical power control device 100 shown in FIG. 1 controls only the WSS 121 of the transmission device #2 (110), and the power is controlled on a channel-by-channel basis in each band (e.g., C-band, L-band). However, in order to suppress the input power reduction and OSNR deterioration of the optical amplifier 123 provided in the rear stage of the WSS 121 of the transmission device #2 (110), it is desirable to reduce the average ATT value of the WSS 121, and in that case, the amount of pre-emphasis that can be adjusted by the WSS 121 is limited.

[0117] 13(b) shows a state assuming control of the optical amplifier 123 and WSS 121 of the transmission device #2 (110). In this case, the amount of pre-emphasis of each band is sufficient, but there is no average power control, and optical power control of each band is required to deal with NF degradation.

[0118] Fig. 13(c) shows the control state of the transmission device #2 (110) by the control unit 1201 of the optical power control device 1200 of the other configuration example shown in Fig. 12. By controlling the gain and tilt amount of the optical amplifier 123 of the transmission device #2 (110), the attenuation amount for each channel of the WSS 121, and the average power attenuation amount of the VOA 124 based on the calculation of the average power attenuation amount and the pre-emphasis amount by the optical power control device 1200, it becomes possible to sufficiently control both the average power control of each band and the pre-emphasis control. Note that the average power control of each band can also be performed by the optical amplifier 123, but since control by the optical amplifier 123 involves NF degradation, it is preferable to control it by the VOA 124 on the output side.

[0119] 14A and 14B are flowcharts showing a GSNR control example 1 of an optical power control device of another configuration example. A control example in which fiber input channel power between transmission devices #2 and #3 (110) corresponding to the span to be controlled shown in FIG. 12 is controlled will be described. The following processing is mainly controlled by the control unit 1201 of the optical power control device 1200 shown in FIG. 12. The thick frames in FIG. 8 indicate processing executed by the control unit 1201 of the optical power control device 1200.

[0120] 14A, the transmission device #4 (110) at the end of the transmission line 130 acquires the received waveform of the wavelength to be controlled and transmits the received waveform information to the optical power control device 1200 (step S1401). Then, the optical power control device 1200 (control unit 1201) calculates a power profile using the received waveform (step S1402).

[0121] Next, the transmission device #2 (110) acquires the fiber input channel power to be controlled by the optical power monitor and transmits it to the optical power control device 1200 (step S1403). Then, the optical power control device 1200 calculates the nonlinear SNR from the calculated power profile and the fiber input channel power (step S1404).

[0122] Next, the transmission device #3 (110) acquires the optical input power of the optical amplifier using the optical power monitor, and transmits it to the optical power control device 1200 (step S1405). Then, the optical power control device 1200 calculates the linear SNR using the optical input power of the optical amplifier and the NF (step S1406).

[0123] Next, the optical power control device 1200 calculates the GSNR from the nonlinear SNR and the linear SNR (step S1407). Next, the optical power control device 1200 calculates the average power attenuation and the amount of pre-emphasis of the transmission device #2 (110) from the difference between the calculated GSNR and the target GSNR (average value) (step S1408). Then, the optical power control device 1200 transmits the calculated attenuation (average power attenuation) of the VOA 124 to the transmission device #2 (110) (step S1409). Then, the optical power control device 1200 sets the average power attenuation received by the VOA 124 of the transmission device #2 (110) (step S1410).

[0124] 14B, the optical power control device 1200 calculates the gain and tilt amount of the optical amplifier 123 and the ch ATT value of the WSS 121 from the calculated pre-emphasis amount of the transmission device #2 (110) (step S1411). Then, the optical power control device 1200 transmits the calculated gain and tilt amount of the optical amplifier 123 and the ch ATT value of the WSS 121 to the transmission device #2 (110) (step S1412). As a result, the optical amplifier A123 of the transmission device #2 (110) sets the received gain and tilt amount, and the WSS 121 sets the ch ATT value (step S1413), and the above process ends.

[0125] 15A and 15B are flowcharts showing a GSNR control example 2 of an optical power control device with another configuration example. In the control example 1 described in Fig. 14A and Fig. 14B, serial (sequential execution) control by the control unit 1201 of the optical power control device 1200 is described. In the control example 2 in Fig. 15A and Fig. 15B, parallel (parallel execution) control by the control unit 1201 of the optical power control device 1200 is described.

[0126] The processes from step S1501 to step S1507 shown in Fig. 15A are the same as steps S1401 to S1407 shown in Fig. 14A. First, as shown in Fig. 15A, the transmission device #4 (110) at the end of the transmission line 130 acquires a received waveform of a wavelength to be controlled, and transmits information on the received waveform to the optical power control device 1200 (step S1501). Then, the optical power control device 1200 (control unit 1201) calculates a power profile using the received waveform (step S1502).

[0127] Next, the transmission device #2 (110) acquires the fiber input channel power to be controlled by the optical power monitor and transmits it to the optical power control device 1200 (step S1503). Then, the optical power control device 1200 calculates the nonlinear SNR from the calculated power profile and the fiber input channel power (step S1504).

[0128] Next, the transmission device #3 (110) acquires the optical input power of the optical amplifier using the optical power monitor, and transmits it to the optical power control device 1200 (step S1505). Then, the optical power control device 1200 calculates the linear SNR using the optical input power of the optical amplifier and the NF (step S1506).

[0129] Next, the optical power control device 1200 calculates the GSNR from the nonlinear SNR and the linear SNR (step S1507).

[0130] 15B, the optical power control device 1200 calculates the average power attenuation amount and the pre-emphasis amount of the transmission device #2 (110) from the difference between the calculated GSNR and the target GSNR (average value) (step S1508). Then, the optical power control device 1200 controls the VOA 124 from step S1509 onwards and the optical amplifier 123 and WSS 121 from step S1511 onwards in parallel with respect to the following processing.

[0131] For example, the optical power control device 1200 transmits the calculated attenuation (average power attenuation) of the VOA 124 to the transmission device #2 (110) (step S1509). Then, the optical power control device 1200 sets the average power attenuation received by the VOA 124 of the transmission device #2 (110) (step S1510).

[0132] In parallel with the process of step S1509, the optical power control device 1200 calculates the gain and tilt amount of the optical amplifier 123 and the ch ATT value of the WSS 121 from the calculated pre-emphasis amount of the transmission device #2 (110) (step S1511). Then, the optical power control device 1200 transmits the calculated gain and tilt amount of the optical amplifier 123 and the ch ATT value of the WSS 121 to the transmission device #2 (110) (step S1512). As a result, the optical amplifier A123 of the transmission device #2 (110) sets the received gain and tilt amount, and the WSS 121 sets the ch ATT value (step S1513). When the processes of steps S1510 and S1513 are completed, the above series of processes is terminated.

[0133] The optical power control device according to the embodiment described above includes a control unit that acquires a received waveform of a WDM optical signal transmitted between transmission devices via a transmission line, calculates a power profile in the distance direction of the transmission line based on the received waveform, and calculates a nonlinear SNR of the transmission line based on the power profile. This makes it possible to estimate the nonlinear SNR with high accuracy.

[0134] In addition, in the optical power control device according to the embodiment, the control unit may be configured to compensate for the variation in the calculated nonlinear SNR, calculate a control amount for controlling the input power to the transmission line, and output the control amount to the transmission device. This makes it possible to appropriately control the input power to the transmission device based on the accurately estimated nonlinear SNR.

[0135] In addition, in the optical power control device according to the embodiment, the control unit may calculate a linear SNR of the transmission line based on the optical power of the transmission line, calculate a GSNR variation based on the nonlinear SNR variation and the linear SNR, and calculate a control amount for compensating for the GSNR variation as the control amount. This makes it possible to improve the GSNR of each band in multiband transmission using the accurately estimated nonlinear SNR.

[0136] In addition, the optical power control device of the embodiment may be configured such that the control unit calculates a nonlinear effective length based on the power profile of the wavelength to be controlled, calculates a nonlinear SNR of the span based on the optical amplifier input power detected by the transmission device of the pair of transmission devices corresponding to the desired span to be controlled and the power profile, calculates a linear SNR of the span based on the optical amplifier input power detected by the reception device of the pair of transmission devices corresponding to the span to be controlled and the noise figure of the optical amplifier, calculates a GSNR based on the nonlinear SNR and the linear SNR, calculates an attenuation amount for each channel of the transmission device of the transmission side based on the difference from the target GSNR to be controlled, and outputs the attenuation amount for each channel to the transmission device of the transmission side as a control amount. This makes it possible to appropriately control the optical power between the pair of transmission devices corresponding to the span to be controlled, and by performing similar optical power control for each span on the transmission path, it becomes possible to optimize the optical power in the entire section and uniform the GSNR.

[0137] In addition, in the optical power control device of the embodiment, the control unit may calculate a nonlinear effective length based on a power profile of the wavelength to be controlled, calculate a nonlinear SNR of the span based on the optical amplifier input power detected at a transmitting transmission device of a pair of transmission devices corresponding to the span to be controlled and the power profile, calculate a linear SNR of the span based on the optical amplifier input power detected at a receiving transmission device of the pair of transmission devices corresponding to the span to be controlled and the noise figure of the optical amplifier, calculate a GSNR based on the nonlinear SNR and the linear SNR, calculate an average power attenuation and a pre-emphasis amount of the transmitting transmission device based on a difference from the target GSNR that is a control target, calculate a gain and tilt amount of the optical amplifier of the transmission device and an attenuation amount for each channel of the WSS from the calculated pre-emphasis amount, and output the average power attenuation for the VOA of the transmitting transmission device, the gain and tilt amount for the optical amplifier, and the attenuation amount for each channel of the WSS as control amounts. In this way, by controlling the VOA, optical amplifier, and WSS of the transmission equipment, it is possible to sufficiently control the average power and pre-emphasis control for each band while suppressing NF degradation, and it becomes possible to more appropriately control the optical power between a pair of transmission equipment corresponding to the span to be controlled. By performing similar optical power control for each span on the transmission path, it is possible to optimize the optical power over the entire section and equalize the GSNR.

[0138] In addition, the optical power control device of the embodiment may be configured such that the control unit calculates the nonlinear effective length based on the power profile of the wavelength to be controlled, calculates the input power to the transmission line based on the optical amplifier input power detected in the transmitting transmission device of the pair of transmission devices corresponding to the desired span to be controlled and the gain and tilt of the optical amplifier, estimates the reference nonlinear SNR based on the value stored in the table for each wavelength, the input power to the transmission line, and stimulated Raman scattering, and calculates the nonlinear SNR by correcting the reference nonlinear SNR based on the calculated nonlinear effective length and the nonlinear effective length corresponding to the reference nonlinear SNR. In this way, the nonlinear effective length is calculated based on the power profile of the wavelength to be controlled, thereby making it possible to accurately estimate the nonlinear SNR.

[0139] In addition, the optical power control device according to the embodiment may be configured such that the control unit acquires a received waveform of an optical signal received by a transmission device at the end of the transmission line, and calculates the received power for each predetermined distance based on the received waveform, thereby calculating the power profile. This makes it possible to easily calculate the power profile of the transmission line.

[0140] In addition, in the optical power control device according to the embodiment, the control unit may calculate a reference power profile based on design values ​​and an actual power profile based on actual measurements, convert each of the reference power profile and the actual power profile from log units to antilog units of optical power, calculate the reference and actual nonlinear effective lengths by integrating the optical power for each predetermined distance, and correct the nonlinear SNR variation based on the reference and actual nonlinear effective lengths. In this way, by using the reference power profile and the actual power profile, the nonlinear SNR variation can be estimated with high accuracy.

[0141] In addition, in the optical power control device according to the embodiment, the control unit may set the average value of the GSNRs for all wavelengths of the optical signal as the target GSNR based on a design value, which allows the nonlinear SNR and GSNR to be easily estimated with high accuracy.

[0142] In addition, the optical power control device according to the embodiment may be configured such that the control unit calculates the GSNR of the optical signal actually in operation based on the nonlinear SNR obtained from the power profile, and corrects the target GSNR value using the calculated GSNR. This makes it possible to handle cases where the actual GSNR differs from the design value, and to accurately estimate the nonlinear SNR and GSNR.

[0143] In addition, the optical power control device of the embodiment may be configured such that the control unit calculates the power profile based on the received waveform for a short distance portion from the start of the transmission line that affects the nonlinear SNR roughly for a predetermined distance, or from the start of the transmission line to the predetermined distance. This makes it possible to speed up the acquisition of the power profile used for GSNR control and reduce the processing load.

[0144] Also, an optical transmission system according to an embodiment includes a plurality of transmission devices connected to each other via a transmission line and transmitting and receiving a WDM optical signal transmitted via the transmission line, and a control unit that acquires a received waveform of the WDM optical signal received by any of the plurality of transmission devices, calculates a power profile in the distance direction of the transmission line based on the received waveform, and calculates a nonlinear SNR of the transmission line based on the power profile. Also, the control unit controls the input power to the transmission line based on the nonlinear SNR. This makes it possible to accurately estimate the nonlinear SNR of the transmission line of the optical transmission system, and to appropriately control the input power of each transmission device based on the estimated nonlinear SNR.

[0145] In addition, in the optical transmission system according to the embodiment, the control unit may control the input power to the transmission line based on the nonlinear SNR and the linear SNR. This makes it possible to appropriately control the optical power between the transmission devices, and to optimize the optical power in the entire section. Furthermore, the control unit may calculate the GSNR based on the nonlinear SNR and the linear SNR, and control the input power to the transmission line based on the GSNR. This makes it possible to optimize the optical power in the entire section, and to equalize the GSNR.

[0146] The optical transmission system according to the embodiment may also include a forward Raman amplifier that amplifies from the front of the transmission line. The forward Raman amplifier may also include an i-pump and secondary pumping light. In this way, even when the optical transmission device performs forward Raman amplification, the nonlinear SNR of the transmission line can be accurately estimated based on the actual power profile without being affected by the pumping light, and the input power of each transmission device can be appropriately controlled.

[0147] The following supplementary notes are further disclosed regarding the above-described embodiment.

[0148] (Appendix 1) Obtain the received waveform of the WDM optical signal transmitted between transmission devices via the transmission line, Calculating a power profile in a distance direction of the transmission path based on the received waveform; An optical power control device comprising: a control unit that calculates a nonlinear SNR of the transmission line based on the power profile.

[0149] (Additional Note 2) The control unit is Compensating for the calculated nonlinear SNR variation and calculating a control amount for controlling the input power to the transmission line; outputting the control amount to the transmission device; 2. An optical power control device according to claim 1,

[0150] (Additional Note 3) The control unit is Calculating a linear SNR of the transmission line based on the optical power of the transmission line; Calculating a variance in a generalized SNR (GSNR) based on the variance in the nonlinear SNR and the linear SNR; A control amount for compensating for the GSNR variation is calculated as the control amount. 2. An optical power control device according to claim 1,

[0151] (Additional Note 4) The control unit is Calculating a nonlinear effective length based on the power profile of the wavelength to be controlled; Calculating a nonlinear SNR of the span based on an optical amplifier input power detected by a transmitting transmission device of the pair of transmission devices corresponding to the span to be controlled and the power profile; Calculating a linear SNR of the span based on an optical amplifier input power detected by a receiving transmission device of the pair of transmission devices corresponding to the span to be controlled and a noise figure of the optical amplifier; Calculating the GSNR based on the nonlinear SNR and the linear SNR; Calculating an attenuation amount for each channel of the transmission device on the transmitting side based on a difference from a target GSNR that is a control target; outputting the attenuation amount for each channel to the transmission device on the transmitting side as the control amount; 4. An optical power control device according to claim 3,

[0152] (Additional Note 5) The control unit is Calculating a nonlinear effective length based on the power profile of the wavelength to be controlled; Calculating a nonlinear SNR of the span based on an optical amplifier input power detected by a transmitting transmission device of the pair of transmission devices corresponding to the span to be controlled and the power profile; Calculating a linear SNR of the span based on an optical amplifier input power detected by a receiving transmission device of the pair of transmission devices corresponding to the span to be controlled and a noise figure of the optical amplifier; Calculating the GSNR based on the nonlinear SNR and the linear SNR; Calculating an average power attenuation amount and a pre-emphasis amount of the transmission device on the transmitting side based on a difference from the target GSNR that is the control target; Calculating the gain and tilt of an optical amplifier of the transmission device and the attenuation of each channel of a WSS (Wavelength Selective Switch) from the calculated amount of pre-emphasis; outputting, as the control amounts, the average power attenuation amount for a VOA (Variable Optical Attenuator) of the transmission device on the transmitting side, the gain and tilt amount for the optical amplifier, and the attenuation amount for each channel for the WSS; 4. An optical power control device according to claim 3,

[0153] (Additional Note 6) The control unit is Calculating a nonlinear effective length based on the power profile of the wavelength to be controlled; Calculating an input power to the transmission line based on an optical amplifier input power detected by a transmission device on a transmitting side of the pair of transmission devices corresponding to a desired span to be controlled and a gain and tilt of the optical amplifier; A reference nonlinear SNR is estimated based on a value stored in a table for each wavelength, the input power to the transmission line, and stimulated Raman scattering; calculating the nonlinear SNR by correcting the reference nonlinear SNR based on the calculated nonlinear effective length and a nonlinear effective length corresponding to the reference nonlinear SNR; 5. An optical power control device according to claim 4,

[0154] (Supplementary Note 7) The control unit is acquiring a waveform of the optical signal received by the transmission device at the end of the transmission path; calculating the power profile by calculating the reception power for each predetermined distance based on the reception waveform; 7. An optical power control device according to claim 6,

[0155] (Additional Note 8) The control unit is Calculating a reference power profile based on a design value and an actual power profile based on an actual measurement, converting each of the reference power profile and the measured power profile from log units to antilog units of optical power; calculating the reference and actual measured nonlinear effective lengths by integrating the optical power for each of the predetermined distances; correcting the variation in the nonlinear SNR based on the reference and the actually measured nonlinear effective length; 6. An optical power control device according to claim 5,

[0156] (Additional Note 9) The control unit is 5. The optical power control device according to claim 4, wherein the target GSNR is set to an average value of GSNR for all wavelengths of the optical signal based on a design value.

[0157] (Additional Note 10) The control unit is An optical power control device as described in Appendix 4, characterized in that a GSNR of the optical signal actually being operated is calculated based on the nonlinear SNR obtained from the power profile, and the calculated GSNR is used to correct the value of the target GSNR.

[0158] (Additional Note 11) The control unit is Calculating the power profile based on a received waveform for a short distance portion from the start point of the transmission line to a predetermined distance, the short distance being roughly calculated, or the nonlinear SNR being affected. 8. An optical power control device according to claim 7,

[0159] (Appendix 12) An optical power control method for controlling optical power of a transmission device, comprising: Acquiring a received waveform of a WDM optical signal transmitted between the transmission devices via a transmission line; Calculating a power profile in a distance direction of the transmission path based on the received waveform; Calculating a nonlinear SNR of the transmission path based on the power profile. 23. A method for controlling optical power comprising:

[0160] (Appendix 13) A plurality of transmission devices connected to each other via a transmission line, transmitting and receiving a WDM optical signal transmitted via the transmission line; a control unit that acquires a received waveform of the WDM optical signal received by any one of the plurality of transmission devices, calculates a power profile in a distance direction of the transmission line based on the received waveform, and calculates a nonlinear SNR of the transmission line based on the power profile; An optical transmission system comprising:

[0161] (Supplementary Note 14) The optical transmission system according to Supplementary Note 13, wherein the control unit controls the input power to the transmission path based on the nonlinear SNR.

[0162] (Supplementary Note 15) The optical transmission system according to Supplementary Note 13, wherein the control unit controls the input power to the transmission path based on the nonlinear SNR and the linear SNR.

[0163] (Supplementary Note 16) The optical transmission system according to Supplementary Note 13, wherein the control unit calculates a GSNR based on the nonlinear SNR and the linear SNR, and controls the input power to the transmission path based on the GSNR.

[0164] (Supplementary Note 17) The optical transmission system according to any one of Supplementary Notes 13 to 16, further comprising a forward Raman amplifier that amplifies from the front of the transmission line.

[0165] (Supplementary Note 18) The optical transmission system according to Supplementary Note 17, wherein the forward Raman amplifier comprises an i-pump and a secondary pumping light. [Explanation of symbols]

[0166] 100,1200 Optical power control device 110 Transmission equipment (node) 121 WSS 122 Optical Power Monitor 123 Optical Amplifier 124 VOA 127 Forward Raman amplifier 128 Backward Raman amplifier 130 Transmission Line 131 Monitor information transmission unit 132 Control information receiver 133 Received Waveform Transmitter 140,1201 Control section 141 Received waveform receiver 142 Power profile calculation unit 143 Monitor information receiver 144 Nonlinear SNR calculation unit 145 Linear SNR calculation unit 146 GSNR Calculation Unit 147 WSS ATT amount control section 148 Control information transmission unit 701 Processor 702 Memory 705 Recording media 1101 Nonlinear noise basic table 1102 Nonlinear noise coefficient slope correction table 1202 Average power attenuation calculation unit 1203 Pre-emphasis amount calculation section NW Network

Claims

1. Acquire a received waveform of a WDM optical signal transmitted between transmission devices via a transmission line; Calculating a power profile in a distance direction of the transmission path based on the received waveform; An optical power control device comprising: a control unit that calculates a nonlinear SNR of the transmission line based on the power profile.

2. The control unit is Compensating for the nonlinear SNR variation and calculating a control amount for controlling an input power to the transmission line; outputting the control amount to the transmission device; 2. The optical power control device according to claim 1.

3. The control unit is Calculating a linear SNR of the transmission line based on the optical power of the transmission line; Calculating a variation in a generalized SNR (GSNR) based on the variation in the nonlinear SNR and the linear SNR; A control amount for compensating for the GSNR variation is calculated as the control amount.

2. The optical power control device according to claim 1.

4. The control unit is Calculating a nonlinear effective length based on the power profile of the wavelength to be controlled; Calculating a nonlinear SNR of the span based on an optical amplifier input power detected by a transmission device on a transmitting side of the pair of transmission devices corresponding to the span to be controlled and the power profile; Calculating a linear SNR of the span based on an optical amplifier input power detected by a receiving transmission device of the pair of transmission devices corresponding to the span to be controlled and a noise figure of the optical amplifier; Calculating the GSNR based on the nonlinear SNR and the linear SNR; Calculating an attenuation amount for each channel of the transmission device on the transmitting side based on a difference from a target GSNR that is a control target; outputting the attenuation amount for each channel to the transmission device on the transmitting side as the control amount; 4. The optical power control device according to claim 3.

5. The control unit is Calculating a nonlinear effective length based on the power profile of the wavelength to be controlled; Calculating a nonlinear SNR of the span based on an optical amplifier input power detected by a transmission device on a transmitting side of the pair of transmission devices corresponding to the span to be controlled and the power profile; Calculating a linear SNR of the span based on an optical amplifier input power detected by a receiving transmission device of the pair of transmission devices corresponding to the span to be controlled and a noise figure of the optical amplifier; Calculating the GSNR based on the nonlinear SNR and the linear SNR; Calculating an average power attenuation amount and a pre-emphasis amount of the transmission device on a transmitting side based on a difference between the target GSNR as the control target and the average power attenuation amount and a pre-emphasis amount of the transmission device on a transmitting side; Calculating the gain and tilt of an optical amplifier of the transmission device and the attenuation of a WSS (Wavelength Selective Switch) for each channel from the calculated amount of pre-emphasis; outputting, as the control amounts, the average power attenuation amount for a VOA (Variable Optical Attenuator) of the transmission device on the transmitting side, the gain and tilt amount for the optical amplifier, and the attenuation amount for each channel for the WSS; 4. The optical power control device according to claim 3.

6. The control unit is Calculating a nonlinear effective length based on the power profile of the wavelength to be controlled; Calculating an input power to the transmission line based on an optical amplifier input power detected by a transmission device on a transmitting side of the pair of transmission devices corresponding to a desired span to be controlled and a gain and tilt of the optical amplifier; A reference nonlinear SNR is estimated based on a value stored in a table for each wavelength, the input power to the transmission line, and stimulated Raman scattering; calculating the nonlinear SNR by correcting the reference nonlinear SNR based on the calculated nonlinear effective length and a nonlinear effective length corresponding to the reference nonlinear SNR; 5. An optical power control device according to claim 4.

7. The control unit is acquiring a waveform of the optical signal received by the transmission device at the end of the transmission path; calculating the power profile by calculating the reception power for each predetermined distance based on the reception waveform; 7. An optical power control device according to claim 6.

8. The control unit is Calculating a reference power profile based on a design value and an actual power profile based on an actual measurement, converting each of the reference power profile and the measured power profile from log units to antilog units of optical power; calculating the reference and actual measured nonlinear effective lengths by integrating the optical power for each of the predetermined distances; correcting the variation in the nonlinear SNR based on the reference and the actually measured nonlinear effective length; 6. An optical power control device according to claim 5.

9. The control unit is 5. The optical power control apparatus according to claim 4, wherein an average value of GSNR for all wavelengths of the optical signal is set as the target GSNR based on a design value.

10. The control unit is 5. The optical power control device according to claim 4, further comprising: a GSNR of the optical signal actually being operated being calculated based on the nonlinear SNR obtained from the power profile; and a value of the target GSNR being corrected using the calculated GSNR.

11. The control unit is The power profile is calculated based on a received waveform for a short distance portion from a start point of the transmission line to a predetermined distance, the short distance being roughly calculated, or the nonlinear SNR is affected.

8. An optical power control device according to claim 7.

12. 1. An optical power control method for controlling optical power of a transmission device, comprising: Acquiring a received waveform of a WDM optical signal transmitted between the transmission devices via a transmission line; Calculating a power profile in a distance direction of the transmission path based on the received waveform; Calculating a nonlinear SNR of the transmission path based on the power profile.

23. A method for controlling optical power comprising:

13. A plurality of transmission devices connected to each other via transmission lines, transmitting and receiving WDM optical signals transmitted via the transmission lines; a control unit that acquires a received waveform of the WDM optical signal received by any one of the plurality of transmission devices, calculates a power profile in a distance direction of the transmission line based on the received waveform, and calculates a nonlinear SNR of the transmission line based on the power profile; An optical transmission system comprising:

14. 14. The optical transmission system according to claim 13, wherein the control unit controls an input power to the transmission line based on the nonlinear SNR.

15. 14. The optical transmission system according to claim 13, wherein the control unit controls an input power to the transmission line based on the nonlinear SNR and the linear SNR.

16. 14. The optical transmission system according to claim 13, wherein the control unit calculates a GSNR based on the nonlinear SNR and the linear SNR, and controls an input power to the transmission line based on the GSNR.

17. 17. The optical transmission system according to claim 13, further comprising a forward Raman amplifier that amplifies the signal from the front of the transmission line.

18. 18. The optical transmission system according to claim 17, wherein the forward Raman amplifier comprises an i-pump and a secondary pump light.

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