Signal processing device and transmission device

Abstract

To provide a signal processing apparatus and a transmission device that can reduce an error in measurement of power of signal light from a predetermined channel.SOLUTION: A signal processing apparatus has: a first conversion unit that converts an electric filed signal indicating an electric field component of signal light from a predetermined channel received in a reception band wider than the frequency interval between rays of signal light from a plurality of channels in wavelength multiplex signal light from a signal in a time domain into a signal in a frequency domain; a filter unit that transmits an electric field signal in the frequency domain with a transmission band narrower than the reception band; a second conversion unit that converts the electric field signal transmitted by the filter unit from a signal in the frequency domain into a signal in the time domain; an amplitude measurement unit that measures a first amplitude of the electric field signal input from the first conversion unit to the filter unit, and a second amplitude of the electric field signal input from the filter unit to the second conversion unit; and a notification unit that reports the first and second amplitudes used for correction of an error in the measurement of power to a power measurement device that measures the power of the signal light from the predetermined channel.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a signal processing device and a transmission device.

Background Art

[0002] For example, Patent Document 1 discloses a technique for measuring the power of signal light of a predetermined channel among signal lights of a plurality of channels included in wavelength-division multiplexed signal light transmitted by digital coherent optical transmission, based on the gain of an amplifier that amplifies an electrical signal photoelectrically converted from the signal light.

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There is a variable baud rate digital coherent optical receiver that can select an appropriate baud rate according to the transmission distance and transmission capacity of signal light from a plurality of baud rates. This type of digital coherent optical receiver is provided with optical components and electrical components corresponding to the reception band of signal light of the maximum selectable baud rate.

[0005] When a baud rate less than the maximum baud rate is selected, the frequency band of the received signal light becomes narrower than the reception band. In this case, since the digital coherent optical receiver includes not only the optical signal of a predetermined channel to be received but also the components of the signal light of adjacent channels, there is a possibility that an error occurs in the measured value of the power of the signal light of the predetermined channel.

[0006] Therefore, an object of the present invention is to provide a signal processing device and a transmission device capable of reducing the measurement error of the power of signal light of a predetermined channel.

Means for Solving the Problems

[0007] In one aspect, a signal processing apparatus includes: a first conversion unit that converts an electric field signal indicating an electric field component of signal light of a predetermined channel received in a reception band wider than a frequency interval between signal lights of a plurality of channels included in wavelength-division multiplexed signal light, from a signal in the time domain to a signal in the frequency domain; a filter unit that transmits the electric field signal converted to the signal in the frequency domain through a transmission band narrower than the reception band; a second conversion unit that converts the electric field signal transmitted through the filter unit from the signal in the frequency domain to the signal in the time domain; an amplitude measurement unit that measures a first amplitude of the electric field signal input from the first conversion unit to the filter unit and a second amplitude of the electric field signal input from the filter unit to the second conversion unit, respectively; and a notification unit that notifies a power measurement device for measuring the power of the signal light of the predetermined channel, of the first amplitude and the second amplitude used for correction of a measurement error of the power of the signal light of the predetermined channel.

[0008] In one aspect, a transmission apparatus includes: a light receiving unit that receives signal light of a predetermined channel in a reception band wider than a frequency interval between signal lights of a plurality of channels included in wavelength-division multiplexed signal light, and outputs an electric field signal indicating an electric field component of the signal light of the predetermined channel; a power measurement unit that measures the power of the signal light of the predetermined channel; a first conversion unit that converts the electric field signal from a signal in the time domain to a signal in the frequency domain; a filter unit that transmits the electric field signal converted to the signal in the frequency domain through a transmission band narrower than the reception band; a second conversion unit that converts the electric field signal transmitted through the filter unit from the signal in the frequency domain to the signal in the time domain; an amplitude measurement unit that measures a first amplitude of the electric field signal input from the first conversion unit to the filter unit and a second amplitude of the electric field signal input from the filter unit to the second conversion unit, respectively; and a notification unit that notifies the first amplitude and the second amplitude to the power measurement unit, wherein the power measurement unit corrects a measurement error of the power of the signal light of the predetermined channel based on a ratio of the first amplitude and the second amplitude.

Advantages of the Invention

[0009] As one aspect, it is possible to reduce the measurement error of the power of the signal light of a predetermined channel.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0011] (Configuration of the Wavelength Multiplexing Device and the Transponder) FIG. 1 is a configuration diagram showing an example of a wavelength division multiplexing (WDM) device 8 and a transponder 7. The WDM device 8 is provided at a node of an optical network and transmits and receives wavelength multiplexed signal light to and from other nodes. The wavelength multiplexed signal light includes a plurality of signal lights having different frequencies. The frequency interval between each signal light is constant, and a channel in the optical network is assigned to each signal light according to the frequency.

[0012] The WDM device 8 includes a preamplifier 80, a demultiplexer 81, a postamplifier 82, and a multiplexer 83. The preamplifier 80 receives wavelength-division multiplexed signal light from a transmission path 90 such as an optical fiber between other nodes. The preamplifier 80 is, for example, an EDFA (Erbium Doped Fiber Amplifier), which amplifies the wavelength-division multiplexed signal light.

[0013] The demultiplexer 81 receives the wavelength-division multiplexed signal light from the preamplifier 80. The demultiplexer 81 demultiplexes the wavelength-division multiplexed signal light toward the wavelength-division multiplexed signal light transponder 7 and other transponders (not shown).

[0014] Also, the multiplexer 83 receives signal light from the transponder 7 and other transponders. The multiplexer 83 multiplexes the signal light to generate wavelength-division multiplexed signal light. The wavelength-division multiplexed signal light is input from the multiplexer 83 to the postamplifier 82. The postamplifier 82 is, for example, an EDFA, which amplifies the wavelength-division multiplexed signal light and outputs it to a transmission path 91 such as an optical fiber between other nodes.

[0015] The transponder 7 is connected to the WDM device 8 via an optical fiber or the like. The transponder 7 includes a power measurement unit 1, a signal processing circuit 2, a front-end unit 3, a variable optical attenuator (VOA) 40, a local light source 41, an attenuation control unit 42, an analog-to-digital converter (ADC) 43, and a client signal transmission unit 44. Further, the transponder 7 includes a driver 50, a transmission light source 51, an optical modulator (MD) 52, and a client signal reception unit 53. Note that the transponder 7 is an example of a transmission device.

[0016] The client signal receiving unit 53 receives client signals from a client network such as a LAN (Local Area Network). Examples of client signals include, but are not limited to, Ethernet (registered trademark, the same applies hereinafter) signals. The client signal receiving unit 53 converts the client signal from an optical signal to an electrical signal and outputs it to the signal processing circuit 2. Note that the client signal receiving unit 53 is realized by an optical-electric converter and an integrated circuit such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specified Integrated Circuit).

[0017] Also, a client signal is input from the signal processing circuit 2 to the client signal transmitting unit 44. The client signal transmitting unit 44 converts the client signal from an electrical signal to an optical signal and transmits it to the client network. Note that the client signal transmitting unit 44 is realized by an electro-optical converter and an integrated circuit such as an FPGA or an ASIC.

[0018] The signal processing circuit 2 includes a transmission processing unit 20 and a reception processing unit 21. The signal processing circuit 2 is realized, for example, by a DSP (Digital Signal Processor), but is not limited thereto, and is realized by an integrated circuit such as an FPGA or an ASIC. Note that the signal processing circuit 2 is an example of a signal processing device.

[0019] The signal processing circuit 2 can select an appropriate baud rate according to the transmission distance and transmission capacity of the signal light of a predetermined channel CHi from a plurality of baud rates according to the instructions of a monitoring and control device (not shown). The transmission processing unit 20 and the reception processing unit 21 perform the transmission processing and reception processing of the signal light respectively according to the selected baud rate.

[0020] The transmission processing unit 20 generates a symbol signal by mapping symbols corresponding to a multi - value modulation method such as 16QAM (Quadrature Amplitude Modulation) to the client signal. Further, the transmission processing unit 20 may perform an encoding process such as FEC (Forward Error Correction) on the client signal. The transmission processing unit 20 converts the symbol signal from a digital signal to an analog signal and outputs it to the driver 50. The driver 50 converts the symbol signal into a drive signal for optical modulation and outputs it to the optical modulator 52.

[0021] A drive signal is input to the optical modulator 52 from the driver 50, and transmission light TO is input from the transmission light source 51. The transmission light source 51 is realized by, for example, a laser diode. The optical modulator 52 includes, for example, a Mach - Zehnder interferometer and optically modulates the transmission light TO based on the drive signal. The optically modulated transmission light is input from the optical modulator 52 to the multiplexer 83 as signal light.

[0022] Also, the signal light of a predetermined channel CHi demultiplexed by the demultiplexer 81 is input to the VOA 40. The attenuation control unit 42 controls the attenuation amount of the VOA 40 based on the VOA control voltage so that the power of the signal light does not exceed the upper limit value. The VOA 40 attenuates the signal light by an attenuation amount according to the VOA control voltage instructed by the attenuation control unit 42. The signal light is input from the VOA 40 to the front - end unit 3. Note that the VOA control voltage is an example of a control voltage.

[0023] The front - end unit 3 detects the signal light by the local oscillation light LO input from the local light source 41. The local light source 41 is realized by, for example, a laser diode. The center frequency of the local oscillation light LO coincides with the center frequency of the signal light.

[0024] Further, the front-end unit 3 photoelectrically converts the signal light after detection into an electrical signal. The electrical signal is an electric field signal indicating the electric field component of the signal light. The front-end unit 3 amplifies the electric field signal and outputs it to the reception processing unit 21. At this time, the front-end unit 3 notifies the power measurement unit 1 via the ADC 43 of each monitor value of the gain when the electric field signal is amplified and the amplitude of the amplified electric field signal. The ADC 43 converts a signal indicating the amplitude and the gain from an analog signal into a digital signal.

[0025] The power measurement unit 1 is an example of a power measurement device and measures the power of the signal light of a predetermined channel CHi. The power measurement unit 1 calculates the power based on the gain notified from the front-end unit 3, and corrects the power based on the amplitude notified from the front-end unit 3 when the gain satisfies a predetermined condition.

[0026] Further, the power measurement unit 1 acquires the VOA control voltage of the VOA 40 from the attenuation control unit 42. The power measurement unit 1 corrects the power based on the VOA control voltage when the VOA control voltage satisfies a predetermined condition.

[0027] Also, as described above, since the reception processing unit 21 performs reception processing at a variable baud rate, the front-end unit 3 and the reception processing unit 21 have a reception band corresponding to the selectable maximum baud rate. Therefore, when the signal processing circuit 2 selects a baud rate less than the maximum baud rate, the frequency band of the signal light of the received predetermined channel CHi becomes narrower than the reception band. In this case, since the digital coherent optical receiver includes not only the optical signal of the predetermined channel CHi to be received but also the signal light components of the adjacent channels CH(i + 1) and CH(i - 1), there is a possibility that an error will occur in the measured value of the power of the signal light of the predetermined channel CHi.

[0028] Therefore, the power measurement unit 1 corrects the measurement error of the power corresponding to the signal components of the adjacent channels CH(i + 1) and CH(i - 1) included in the electric field signal by communicating with the reception processing unit 21. The details of the power measurement method and the correction method will be described later.

[0029] (Configuration of the Front-End Unit) FIG. 2 is a configuration diagram showing an example of the front-end unit 3. The front-end unit 3 includes polarization beam splitters (PBSs) 30, 31, 90-degree optical hybrid circuits 32, 33, balanced photodiodes (PDs) 34a to 34d, and transimpedance amplifiers (hereinafter referred to as "TIAs") 35a to 35d. Note that the front-end unit 3 is an example of a light-receiving unit that outputs an electric field signal indicating the electric field component of the signal light of a predetermined channel CHi.

[0030] The front-end unit 3 also includes variable gain amplifiers 36a to 36d, automatic gain controllers (AGCs) 37a to 37d, and a monitor unit 38. In this example, although polarization multiplexed signal light having an X polarization component and a Y polarization component is cited as the signal light, the present invention is not limited thereto.

[0031] The signal light is input from the VOA 40 to the PBS 30. The PBS 30 separates the burst optical signal into an X polarization component and a Y polarization component and outputs them to the 90-degree optical hybrid circuits 32, 33, respectively. On the other hand, local oscillation light LO from the local light source 41 is input to the other PBS 31. The PBS 31 separates the local oscillation light LO into an X polarization component and a Y polarization component and outputs them to the 90-degree optical hybrid circuits 32, 33, respectively.

[0032] The 90-degree optical hybrid circuit 32 has a waveguide for interfering the X polarization component of the signal light and the X polarization component of the local oscillation light LO, and detects the X polarization component of the signal light. The 90-degree optical hybrid circuit 32 outputs optical components corresponding to the amplitudes and phases of the in-phase component and the quadrature phase component to the PDs 34a, 34b, respectively, as detection results.

[0033] The 90-degree optical hybrid circuit 33 has a waveguide for interfering the Y-polarized wave component of the signal light and the Y-polarized wave component of the local oscillation light LO, and detects the Y-polarized wave component of the signal light. The 90-degree optical hybrid circuit 33 outputs, as detection results, optical components corresponding to the amplitudes and phases of the in-phase component and the quadrature phase component to PD34c and 34d, respectively. Note that each optical component includes light of the positive phase and the reverse phase.

[0034] In this way, the 90-degree optical hybrid circuits 32 and 33 detect the signal light of the predetermined channel CHi by the local oscillation light LO. Therefore, the front-end unit 3 can detect and receive the signal light of the predetermined channel CHi from the wavelength-division multiplexed signal light in which the signal lights of a plurality of channels are wavelength-division multiplexed according to the center frequency of the local oscillation light LO.

[0035] PD34a to 34d convert the optical components input from the 90-degree optical hybrid circuits 32 and 33 into electrical analog signals. PD34a to 34d output the analog signals to TIA35a to 35d, respectively. Note that each analog signal is a differential signal.

[0036] TIA35a to 35d amplify the analog signals and convert them from current signals to voltage signals. TIA35a to 35d output the converted analog signals to variable gain amplifiers 36a to 36d, respectively.

[0037] The variable gain amplifiers 36a to 36d amplify the analog signals based on variable gains controlled by AGC37a to 37d, respectively. The variable gain amplifier 36a outputs the analog signal to the reception processing unit 21 as an electric field signal XI indicating the electric field of the in-phase component of the X polarization of the signal light. The variable gain amplifier 36b outputs the analog signal to the reception processing unit 21 as an electric field signal XQ indicating the electric field of the quadrature phase component of the X polarization of the signal light.

[0038] The variable gain amplifier 36c outputs the analog signal to the reception processing unit 21 as an electric field signal YI indicating the electric field of the in-phase component of the Y polarization of the signal light. The variable gain amplifier 36d outputs the analog signal to the reception processing unit 21 as an electric field signal YQ indicating the electric field of the quadrature phase component of the Y polarization of the signal light.

[0039] AGC37a to 37d detect the respective amplitudes of the electric field signals XI, XQ, YI, and YQ output from the variable gain amplifiers 36a to 36d. AGC37a to 37d respectively control the gains of the variable gain amplifiers 36a to 36d so that the respective amplitudes of the electric field signals XI, XQ, YI, and YQ become the target values. Thereby, the respective amplitudes of the electric field signals XI, XQ, YI, and YQ become substantially the same. Here, the target value of the amplitude is determined according to, for example, the signal input specification of the reception processing unit 21. Note that the variable gain amplifiers 36a to 36d are an example of amplifiers that amplify the electric field signals XI, XQ, YI, and YQ so that the amplitudes of the electric field signals XI, XQ, YI, and YQ become a predetermined value.

[0040] The monitor unit 38 collects the gains of the variable gain amplifiers 36a to 36d and the amplitudes (peak indicators) detected by the variable gain amplifiers 36a to 36d from the respective variable gain amplifiers 36a to 36d. Note that the gain and amplitude collected by the monitor unit 38 are respectively referred to as "gain monitor value" and "amplitude monitor value". The monitor unit 38 notifies the power measurement unit 1 of the amplitude monitor value and the gain monitor value. Note that the monitor unit 38 is realized by, for example, an analog circuit that converts the amplitude and gain into a DC voltage, or a digital integrated circuit such as an FPGA or an ASIC.

[0041] (Example of power measurement) FIG. 3 is a diagram showing an example of the relationship between the power of the signal light and the amplitude monitor value (PI(V)) and the gain monitor value (GA(V)) of the electric field signals XI, XQ, YI, and YQ. Reference numeral G1a indicates the change in the amplitude monitor value of the electric field signals XI, XQ, YI, and YQ with respect to the power of the signal light when the attenuation amount of the VOA 40 is not considered. Further, reference numeral G1b indicates the change in the gain monitor value of the variable gain amplifiers 36a to 36d with respect to the power of the signal light when the attenuation amount of the VOA 40 is not considered.

[0042] Within the control range (AGC operation range) of AGC37a to 37d, the amplitude becomes the target value. Also, the gain decreases as the power increases.

[0043] P GA=f GA (V GA ) ···(1)

[0044] In the AGC operation range, the power measurement unit 1 calculates the power P GA based on, for example, the gain monitor value V GA by the above formula (1). Here, the function f GA (V GA ) is determined from the relationship between the gain monitor value V GA and the power P GA obtained from, for example, actual measurement or simulation.

[0045] Outside the control range (gain saturation range) of the AGCs 37a to 37d, the gain becomes a constant saturation value. Also, the amplitude decreases as the power decreases. Here, the power measurement unit 1 discriminates between the AGC operation range and the gain saturation range based on the comparison result between the gain monitor value V GA and a predetermined threshold value Vth.

[0046] P PI =f PI (V PI ) ···(2)

[0047] In the gain saturation range (V GA >Vth), the power measurement unit 1 calculates the correction value P PI of the power P GA based on, for example, the amplitude monitor value V PI by the above formula (2). Here, the function f PI (V PI ) is determined from the relationship between the amplitude monitor value V PI and the correction value P GA of the power P PI obtained from, for example, actual measurement or simulation. Note that in the AGC operation range (V GA ≤Vth), the correction value P PI is 0.

[0048] P = P GA + P PI ···(3)

[0049] Therefore, as shown in the above formula (3), the power measurement unit 1 calculates the power P calculated from the gain GA and the correction value P PI based on the amplitude monitor value V PI as the sum of the power P.

[0050] FIG. 4 is a diagram showing another example of the relationship between the power of the signal light and the amplitude monitor values (PI(V)) and gain monitor values (GA(V)) of the electric field signals XI, XQ, YI, and YQ. The symbol G2a indicates the change in the amplitude monitor values of the electric field signals XI, XQ, YI, and YQ with respect to the power of the signal light when the attenuation amount of the VOA 40 is taken into account. The symbol G2b indicates the change in the gain monitor values of the variable gain amplifiers 36a to 36d with respect to the power of the signal light when the attenuation amount of the VOA 40 is taken into account.

[0051] In the control ranges (AGC·VOA operation ranges) of the AGCs 37a to 37d and the VOA 40, the amplitude becomes the target value. Also, since the power is suppressed to the upper limit value by the VOA 40, the gain becomes a predetermined value.

[0052] L VOA =f VOA (V VOA ) ···(4)

[0053] In the AGC·VOA operation range, the power measurement unit 1 calculates the correction value L VOA of the power loss based on the VOA control voltage V VOA of the VOA 40, for example, according to the above formula (4). Here, the function f VOA (V VOA ) is determined from the relationship between the VOA control voltage V VOA obtained from, for example, actual measurement or simulation, and the attenuation amount of the light passing through the VOA.

[0054] P = P GA + P PI + L VOA ···(5)

[0055] Therefore, as shown in the above formula (5), the power measurement unit 1 calculates the power P calculated from the gain monitor value V GA ​GA and the correction value P based on the amplitude monitor value V PI and the correction value L based on the VOA control voltage V PI and calculate the power P as the sum thereof. Note that the power measurement unit 1 may calculate the power P from one gain monitor value V VOA and the amplitude monitor value V of the electric field signals XI, XQ, YI, YQ, or may calculate the power P from the average gain monitor value V VOA and the amplitude monitor value V of the electric field signals XI, XQ, YI, YQ. GA and the amplitude monitor value V PI Furthermore, as described above, the power measurement unit 1 further communicates with the reception processing unit 21 to correct the measurement error of the power corresponding to the signal components of the adjacent channels CH(i + 1), CH(i - 1) included in the electric field signal. The details of the correction method will be described below. GA and the amplitude monitor value V PI from which the power P may be calculated.

[0056] Also, as described above, the power measurement unit 1 further communicates with the reception processing unit 21 to correct the measurement error of the power corresponding to the signal components of the adjacent channels CH(i + 1), CH(i - 1) included in the electric field signal. The details of the correction method will be described below.

[0057] (Spectrum of wavelength-division multiplexed signal light) FIG. 5 is a diagram showing an example of the spectrum of wavelength-division multiplexed signal light. In FIG. 5, the horizontal axis represents the frequency (GHz), and the vertical axis represents the power (dBm) of the signal light. Reference numeral G3a indicates the spectrum when the bandwidth of the signal light of each channel CH(i - 2) to CH(i + 2) is narrower than the reception bandwidth B Wr of the transponder 7.

[0058] As an example, assume that the interval between the center frequencies Fi - 2 to Fi + 2 of each signal light is 50 (GHz), and the reception bandwidth B Wr is 75 (GHz). That is, each signal light is arranged on the frequency axis at a grid interval of 50 (GHz), and the signal processing circuit 2 selects a baud rate of 50 (GHz) according to the frequency interval of the signal light. Further, the transponder 7 has a reception bandwidth B Wr capable of receiving signal light with a grid interval of 75 (GHz) wider than the frequency interval of the signal light.

[0059] Therefore, the received band BWr includes not only the optical signal of a predetermined channel CHi but also the components of the signal lights of adjacent channels CH(i + 1) and CH(i - 1) (see the shaded part). Therefore, when the power measurement unit 1 calculates the power P according to the above formulas (1) to (5), there is a possibility of measurement error.

[0060] Also, the code G3b shows the spectrum when the bands of the signal lights of each channel CH(i - 2) to CH(i + 2) match the received band BWr of the transponder 7. As an example, assume that the interval between the center frequencies Fi - 2 to Fi + 2 of each signal light is 75 (GHz) and the received band BWr is 75 (GHz). That is, each signal light is arranged on the frequency axis at a grid interval of 75 (GHz), and the signal processing circuit 2 selects a baud rate of 75 (GHz) according to the frequency interval of the signal lights.

[0061] In this case, the received band BWr includes only the optical signal of the predetermined channel CHi and does not include the components of the signal lights of adjacent channels CH(i + 1) and CH(i - 1). Therefore, even if the power measurement unit 1 calculates the power P according to the above formulas (1) to (5), it can measure the power with high precision.

[0062] Therefore, as shown by the code G3a, when the electric field signals XI, XQ, YI, YQ indicating the electric field components of the signal light of the predetermined channel CHi received in the received band BWr wider than the frequency interval of each signal light are input to the reception processing unit 21, the power measurement unit 1 determines based on the baud rate selected by the reception processing unit 21. In this case, the power measurement unit 1 corrects the measurement error of the power corresponding to the signal components of the adjacent channels CH(i + 1) and CH(i - 1) included in the electric field signal by communicating with the reception processing unit 21.

[0063] (Configuration of reception processing unit) FIG. 6 is a configuration diagram showing an example of the reception processing unit 21. The reception processing unit 21 includes analog-to-digital converters (ADCs) 210a to 210d, a fast Fourier transform (FFT) unit 211, a filter unit 212, and an inverse fast Fourier transform (IFFT) unit 213. The reception processing unit 21 further includes an adaptive equalizer 214, a demodulation unit 216, an error correction unit 215, a client processing unit 200, an amplitude monitor unit 217, a setting control unit 218, and a communication processing unit 219.

[0064] The ADCs 210a to 210d convert the electric field signals XI, XQ, YI, and YQ input from the front-end unit 3 from analog signals to digital signals, respectively. The electric field signals XI, XQ, YI, and YQ are input from the ADCs 210a to 210d to the FFT unit 211.

[0065] The FFT unit 211, which is an example of a first conversion unit, converts the electric field signals XI, XQ, YI, and YQ from time-domain signals to frequency-domain signals. The electric field signals XI, XQ, YI, and YQ are input from the FFT unit 211 to the filter unit 212.

[0066] The filter unit 212 is, for example, a frequency domain equalizer (FDE) that performs equalization by multiplying the inverse characteristic of the transfer function of the transmission path 90 in the frequency domain, and is also used as a filter. The setting control unit 218 performs filter setting for the filter unit 212. The filter unit 212 sets tap coefficients that determine, for example, the shape of the passband of the filter unit 212 based on the filter setting.

[0067] The filter unit 212 filters the electric field signals XI, XQ, YI, and YQ according to the passband. The filter unit 212 shapes the waveforms of the electric field signals XI, XQ, YI, and YQ to flatten them. The electric field signals XI, XQ, YI, and YQ are input from the filter unit 212 to the IFFT unit 213.

[0068] The IFFT unit 213 is an example of a second conversion unit, and converts the electric field signals XI, XQ, YI, and YQ transmitted by the filter unit 212 from the signals in the frequency domain to the signals in the time domain. The electric field signals XI, XQ, YI, and YQ are input from the IFFT unit 213 to the adaptive equalizer 214.

[0069] The adaptive equalizer 214 adaptively compensates for the degradation of the signal light that changes with time in the transmission line 90 with respect to the electric field signals XI, XQ, YI, and YQ. The main factors of this degradation include, mainly, polarization mode dispersion (PMD) and the like. The electric field signals XI, XQ, YI, and YQ are input from the adaptive equalizer 214 to the demodulation unit 216.

[0070] The demodulation unit 216 demodulates the electric field signals XI, XQ, YI, and YQ by compensating for the frequency difference and the phase difference between the signal light and the local oscillation light LO with respect to the electric field signals XI, XQ, YI, and YQ. The electric field signals XI, XQ, YI, and YQ are output from the demodulation unit 216 to the error correction unit 215.

[0071] The error correction unit 215 performs reproduction and error correction of the data signal by performing, for example, FEC decoding processing on the electric field signals XI, XQ, YI, and YQ. The data signal is input from the error correction unit 215 to the client processing unit 200.

[0072] The client processing unit 200 demaps the data signal mapped to a frame such as OTN. Thereby, the data signal is converted into the original client signal. The client signal is output to the client signal transmission unit 44.

[0073] The communication processing unit 219 receives a baud rate instruction signal from a monitoring and control device (not shown). The communication processing unit 219 notifies the baud rate setting control unit 218 of the baud rate. The baud rate setting control unit 218 sets the baud rate for the entire signal processing circuit 2.

[0074] The setting control unit 218 notifies the baud rate to the power measurement unit 1. The power measurement unit 1 determines whether correction for removing the signal components of the adjacent channels CH(i - 1) and CH(i + 1) from the power of the signal light is necessary based on the baud rate. When the power measurement unit 1 determines that correction is necessary, it instructs the setting control unit 218 to execute band limitation for narrowing the transmission band of the filter unit 212.

[0075] The setting control unit 218 narrows the transmission band of the filter unit 212 to be narrower than the reception band BWr in accordance with the band limitation instruction. Thereby, the signal components of the adjacent channels CH(i - 1) and CH(i + 1) are removed from the electric field signals XI, XQ, YI, and YQ.

[0076] FIG. 7 is a diagram showing an example of the change in the signal spectrum due to band limitation. Although only one sideband of the signal is shown in FIG. 7, signal processing such as inverse fast Fourier transform is performed on both sidebands.

[0077] Reference symbol G4a indicates the spectrum of the reception band B Wr of the transponder 7. The horizontal axis indicates frequency (GHz), and the vertical axis indicates gain (dB). In the reception band B Wr, a band of -3 (dB) is provided for 40 (GHz) in accordance with a grid of 75 (GHz) (64 (Gbd)) as an example.

[0078] Reference symbol G4b indicates the signal spectrum of the electric field signals XI, XQ, YI, and YQ before transmission by the filter unit 212. The horizontal axis indicates frequency (GHz), and the vertical axis indicates amplitude (dB). The dotted line indicates the reception band B Wr. The electric field signals XI, XQ, YI, and YQ correspond to the signal light of a grid of 50 (GHz) (32 (Gbd)) as an example. The signal spectrum includes the signal component of a predetermined channel CHi and the signal component of the adjacent channel CH(i + 1).

[0079] Symbol G4c indicates the shape of the transmission band of the filter unit 212. The horizontal axis indicates the frequency (GHz), and the vertical axis indicates the gain (dB). The setting control unit 218 sets the filter unit 212 so that a transmission band is formed to remove signal components of 30 (GHz) or higher, for example, from the electric field signals XI, XQ, YI, and YQ. The setting control unit 218 sets the filter coefficients of the filter unit 212 so that a transmission band having a frequency band of 30 (GHz) is formed for a gain of -10 (dB) as an example. The dotted line indicates the shape of the transmission band when band limiting is not performed and coincides with the reception band BWr. As a result, the transmission band of the filter unit 212 has a bandwidth corresponding to the frequency interval (50 (GHz)) of the signal light.

[0080] Symbol G4d indicates the signal spectra of the electric field signals XI, XQ, YI, and YQ after transmission by the filter unit 212. The horizontal axis indicates the frequency (GHz), and the vertical axis indicates the amplitude (dB). The dotted line indicates the shape of the transmission band. The filter unit 212 removes the signal components of the adjacent channel CH(i + 1) from the electric field signals XI, XQ, YI, and YQ. For this reason, the electric field signals XI, XQ, YI, and YQ substantially contain only the signal components of a predetermined channel CHi.

[0081] In this way, the filter unit 212 transmits the electric field signals XI, XQ, YI, and YQ through a transmission band corresponding to the frequency interval of the signal light. For this reason, the filter unit 212 can effectively remove the signal components of the adjacent channel CH(i + 1) from the electric field signals XI, XQ, YI, and YQ.

[0082] Referring to FIG. 6 again, the amplitude monitor unit 217 is an example of an amplitude measurement unit, and measures the amplitude Va of the electric field signals XI, XQ, YI, and YQ (refer to symbol A) input from the FFT unit 211 to the filter unit 212 and the amplitude Vb of the electric field signals XI, XQ, YI, and YQ (refer to symbol B) input from the filter unit 212 to the IFFT unit 213, respectively. That is, the amplitude monitor unit 217 measures the amplitudes Va and Vb of the electric field signals XI, XQ, YI, and YQ before and after the filter unit 212.

[0083] Here, the amplitude monitor unit 217 may measure any of the amplitudes Va and Vb of the electric field signals XI, XQ, YI, and YQ, or may measure the average amplitudes Va and Vb of the electric field signals XI, XQ, YI, and YQ. The amplitude Va is the amplitude before being transmitted by the filter unit 212, and the amplitude Vb is the amplitude after being transmitted by the filter unit 212. Note that the amplitude Va is an example of the first amplitude, and the amplitude Vb is an example of the second amplitude.

[0084] The amplitude monitor unit 217 notifies the setting control unit 218 of the amplitudes Va and Vb. At this time, the amplitude monitor unit 217 may calculate and notify the root mean square (RMS) of each of the amplitudes Va and Vb. Thereby, the setting control unit 218 can obtain the time average of the amplitudes Va and Vb.

[0085] After the execution of the band limitation of the filter unit 212, the setting control unit 218 notifies the power measurement unit 1 of the amplitudes Va and Vb. The power measurement unit 1 uses the amplitudes Va and Vb for correcting the measurement error of the power of the signal light. Note that the setting control unit 218 is an example of the notification unit.

[0086] (Correction of Power Based on Amplitude of Electric Field Signal) The power measurement unit 1 corrects the power calculated by the above formulas (1) to (5) based on the ratio of the amplitudes Va and Vb.

[0087] L FEQ = 10 log(Vb / Va) ···(6) G = f FEQ (L FEQ ) ···(7)

[0088] The power measurement unit 1 calculates the voltage loss L FEQ (dB) of the electric field signals XI, XQ, YI, and YQ generated in the filter unit 212 according to the above formula (6). The voltage loss L FEQ corresponds to the power of the signal component removed by the filter unit 212.

[0089] Therefore, the power measurement unit 1, for example, calculates the voltage loss L FEQBased on this, a correction value G is calculated. Here, the function f FEQ (L FEQ ) is determined from the relationship between the voltage loss L FEQ and the power P GA obtained from, for example, actual measurements or simulations. Note that the setting control unit 218 may calculate the voltage loss L FEQ and notify the power measurement unit 1 of it.

[0090] FIG. 8 is a diagram showing an example of the relationship between the voltage loss L FEQ (dB) and the correction value G (dB) of the power P GA . The correction value G gradually increases as the voltage loss L FEQ increases. The function f FEQ (L FEQ ) can be, for example, a quadratic function of the voltage loss L FEQ .

[0091] P = P GA + G ···(8) P = P GA + P PI + G ···(9) P = P GA + L VOA + G ···(10) P = P GA + P PI + L VOA + G ···(11)

[0092] As shown in the above equations (8) to (11), the power measurement unit 1 calculates the power P by adding the correction value G to the power P GA calculated from the gain monitor value V GA .

[0093] In this way, the setting control unit 218 notifies the power measurement unit 1 of the amplitudes Va and Vb. The power measurement unit 1 corrects the measurement error of the power of the signal light of the predetermined channel CHi based on the ratio of the amplitudes Va and Vb. Therefore, the transponder 7 can reduce the measurement error of the power of the signal light of the predetermined channel CHi.

[0094] (Configuration of the Power Measurement Unit) FIG. 9 is a configuration diagram showing an example of the power measurement unit 1. The power measurement unit 1 includes a CPU (Central Processing Unit) 10, a ROM (Read Only Memory) 11, a RAM (Random Access Memory) 12, a storage memory 13, a communication port 14, and a hardware interface unit (HW-IF) 15. The CPU 10 is connected to the ROM 11, the RAM 12, the storage memory 13, the communication port 14, and the HW-IF 15 via a bus 19 so that signals can be input and output to and from each other.

[0095] The ROM 11 stores a program for driving the CPU 10. The RAM 12 functions as a working memory of the CPU 10. The communication port 14 processes communication, for example, between the CPU 10 and the reception processing unit 21 and the attenuation control unit 42. The HW-IF 15 processes communication between the CPU 10 and the front-end unit 3. Note that the communication port 14 and the HW-IF 15 are realized by an integrated circuit such as an FPGA or an ASIC, for example.

[0096] When the CPU 10 reads a program from the ROM 11, as functions, it forms a measurement control unit 100, a calculation unit 101, a PI correction unit 102, a VOA correction unit 103, and a power correction unit 104. Note that the measurement control unit 100, the calculation unit 101, the PI correction unit 102, the VOA correction unit 103, and the power correction unit 104 may be realized by an integrated circuit such as an FPGA or an ASIC instead of the CPU 10.

[0097] The storage memory 13 stores parameter information 130 and baud rate information 131. The parameter information 130 is various parameters such as coefficients and threshold values used in the functions of the above formulas (1), (2), (4), and (7), for example. The baud rate information 131 is the baud rate set by the setting control unit 218.

[0098] The measurement control unit 100 instructs the calculation unit 101, the PI correction unit 102, the VOA correction unit 103, and the power correction unit 104 to perform various operations according to the sequence defined in the program. The measurement control unit 100 reads the gain monitor value V GA and the amplitude monitor value V PI from the front-end unit 3, and reads the VOA control voltage V VOA of the VOA 40 from the attenuation control unit 42. Also, the measurement control unit 100 reads the currently selected baud rate from the setting control unit 218 and stores it in the storage memory 13 as baud rate information 131. The measurement control unit 100 instructs the calculation unit 101 to calculate the power P GA based on the gain monitor value V GA .

[0099] The calculation unit 101 calculates the power P GA according to the above formula (1) in accordance with the instruction of the measurement control unit 100. At this time, the calculation unit 101 obtains the gain monitor value V GA from the measurement control unit 100, and obtains the coefficient of the function f GA (V GA ) from the parameter information 130. The calculation unit 101 outputs the power P GA to the measurement control unit 100.

[0100] The measurement control unit 100 compares the gain monitor value V GA with the threshold value Vth. If V GA > Vth holds, it is determined that the actual power of the signal light is within the gain saturation range, and the PI correction unit 102 is instructed to calculate the correction value P PI based on the amplitude monitor value V PI .

[0101] The PI correction unit 102 calculates the correction value P PI according to the above formula (2) in accordance with the instruction of the measurement control unit 100. At this time, the PI correction unit 102 obtains the amplitude monitor value V PI from the measurement control unit 100, and obtains the coefficient of the function f PI (V PI ) from the parameter information 130. The PI correction unit 102 outputs the correction value P PI to the measurement control unit 100.

[0102] The measurement control unit 100 compares the VOA control voltage V VOA with the threshold value Ath, and when V VOA > Ath holds, it determines that the power of the signal light is within the AGC·VOA operation range, and instructs the VOA correction unit 103 to calculate the correction value L VOA based on the VOA control voltage V VOA .

[0103] The VOA correction unit 103 calculates the correction value L VOA in accordance with the above formula (4) according to the instruction of the measurement control unit 100. At this time, the VOA correction unit 103 acquires the VOA control voltage V VOA from the measurement control unit 100, and acquires the coefficient of the function f VOA (V VOA ) from the parameter information 130. The VOA correction unit 103 outputs the correction value L VOA to the measurement control unit 100.

[0104] The measurement control unit 100 compares the baud rate with the threshold value THr, and when the baud rate < THr holds, it determines that the power P GA calculated by the calculation unit 101 includes the power of the signal components of the adjacent channels CH(i - 1) and CH(i + 1), and instructs the power correction unit 104 to calculate the correction value G based on the voltage loss L FEQ .

[0105] The power correction unit 104 calculates the voltage loss L FEQ and the correction value G respectively in accordance with the above formulas (6) and (7) according to the instruction of the measurement control unit 100. At this time, the power correction unit 104 acquires the amplitudes Va and Vb from the measurement control unit 100, and acquires the coefficient of the function f FEQ (L FEQ ) from the parameter information 130. The power correction unit 104 outputs the correction value G to the measurement control unit 100.

[0106] The measurement control unit 100 calculates the power P of the measurement result according to any one of the above formulas (8) to (11). When the measurement control unit 100 calculates only the correction value G, it uses formula (8), and the correction value PPI , When only G is calculated, using Equation (9), the correction value L VOA , When only G is calculated, Equation (10) is used. Further, the measurement control unit 100 calculates all correction values P PI , L VOA , When G is calculated, Equation (11) is used.

[0107] (Operation of Power Measurement Unit) Figure 10 is a flowchart showing an example of the operation of the power measurement unit 1. This operation is executed, for example, when the power measurement unit 1 receives a power measurement instruction from a monitoring control device (not shown).

[0108] First, the measurement control unit 100 reads the gain monitor value V GA and the amplitude monitor value V PI from the front end unit 3 (step St1). Next, the calculation unit 101 calculates the power P GA of the signal light of the predetermined channel CHi based on the gain monitor value V GA according to the above Equation (1). Thereby, the calculation unit 101 can measure from the electric field signals XI, XQ, YI, YQ after detection of the signal light without using an external photodiode or the like.

[0109] Next, the measurement control unit 100 compares the gain monitor value V GA with the threshold value Vth (step St3). When V GA > Vth is satisfied (Yes in step St3), the PI correction unit 102 calculates the correction value P PI of the power P GA based on the amplitude monitor value V PI according to the above Equation (2) (step St4). The power measurement unit 1 corrects the measurement error of the power of the signal light of the predetermined channel based on the amplitude monitor value V PI of the electric field signals XI, XQ, YI, YQ. Therefore, as described above, the power measurement unit 1 can measure the power with high accuracy even when the power of the signal light is within the gain saturation range.

[0110] Also, V GAWhen ≦Vth holds (No in step St3), the power of the signal light is within the AGC operation range or the AGC·VOA operation range, and correction of the measurement error based on the amplitude monitor value V PI is not necessary, so the operation in step St4 is not executed. The threshold value Vth is determined from the characteristics in FIG. 3 obtained by, for example, experiments or simulations.

[0111] Next, the measurement control unit 100 reads the VOA control voltage V VOA of the VOA 40 from the attenuation control unit 42 (step St5). Next, the measurement control unit 100 compares the VOA control voltage V VOA with the threshold value Ath (step St6).

[0112] V VOA When >Ath holds (Yes in step St6), the VOA correction unit 103 calculates the correction value L VOA of the power loss based on the VOA control voltage V VOA of the VOA 40 according to the above formula (4) (step St7). The power measurement unit 1 corrects the measurement error of the power of the signal light of the predetermined channel CHi based on the VOA control voltage V VOA of the VOA 40. Therefore, as described above, the power measurement unit 1 can measure the power with high accuracy even when the power of the signal light is within the AGC·VOA operation range.

[0113] Also, when V VOA ≦Ath holds (No in step St6), the power of the signal light is outside the AGC·VOA operation range, and correction of the measurement error based on the VOA control voltage V VOA is not necessary, so the operation in step St7 is not executed. The threshold value Ath is determined from the characteristics in FIG. 4 obtained by, for example, experiments or simulations.

[0114] Next, the measurement control unit 100 reads the baud rate of the transponder 7 from the setting control unit 218 (step St8). Next, the measurement control unit 100 compares the baud rate with the threshold value THr (step St9). When the baud rate < THr is satisfied (Yes in step St9), the measurement control unit 100 instructs the setting control unit 218 to perform band limitation of the filter unit 212 (step St10). As a result, since the transmission band of the filter unit 212 becomes narrower than the reception band, the signal components of the adjacent channels CH(i - 1) and CH(i + 1) included in the electric field signals XI, XQ, YI, and YQ are reduced.

[0115] Next, the measurement control unit 100 reads the amplitudes Va and Vb of the electric field signals XI, XQ, YI, and YQ at the front stage and the rear stage of the filter unit 212 from the setting control unit 218 (step St11).

[0116] Next, the power correction unit calculates the correction value G from the amplitudes Va and Vb according to the above formulas (6) and (7) (step St12). The power measurement unit 1 corrects the measurement error of the power of the signal light of the predetermined channel CHi based on the ratio of the amplitudes Va and Vb as described above. As a result, the measurement error of the power of the signal light of the predetermined channel CHi is reduced.

[0117] Also, when the baud rate ≥ THr is satisfied (No in step St9), the measurement control unit 100 determines that the band of the signal light is substantially the same as the reception band and correction by the amplitudes Va and Vb is unnecessary, and does not execute steps St10 to St12.

[0118] Next, the measurement control unit 100 calculates the power (measured power) P of the measurement result according to any one of the above formulas (8) to (11) (step St13). The power P is notified to, for example, a monitoring control device (not shown). In this way, the power measurement unit 1 operates.

[0119] The above-described embodiments are preferred examples of the present invention. However, the present invention is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

[0120] In addition, the following supplementary notes are disclosed regarding the above description. (Supplementary Note 1) Among the signal lights of a plurality of channels included in the wavelength-division multiplexed signal light, a first conversion unit that converts an electric field signal indicating an electric field component of the signal light of a predetermined channel received in a reception band wider than the frequency interval between the signal lights of the plurality of channels from a signal in the time domain to a signal in the frequency domain; A filter unit that transmits the electric field signal converted into a signal in the frequency domain through a transmission band narrower than the reception band; A second conversion unit that converts the electric field signal transmitted by the filter unit from a signal in the frequency domain to a signal in the time domain; An amplitude measurement unit that measures a first amplitude of the electric field signal input from the first conversion unit to the filter unit and a second amplitude of the electric field signal input from the filter unit to the second conversion unit, respectively; A signal processing apparatus, comprising: a power measurement apparatus that measures the power of the signal light of the predetermined channel; and a notification unit that notifies the power measurement apparatus of the first amplitude and the second amplitude used for correcting a measurement error of the power of the signal light of the predetermined channel. (Supplementary Note 2) The signal processing apparatus according to Supplementary Note 1, wherein the filter unit transmits the electric field signal through the transmission band corresponding to the frequency interval. (Supplementary Note 3) The amplitude measurement unit calculates a root mean square of each of the first amplitude and the second amplitude, The signal processing apparatus according to Supplementary Note 1 or 2, wherein the notification unit notifies the power measurement apparatus of the root mean square of each of the first amplitude and the second amplitude. (Supplementary Note 4) Among the signal lights of a plurality of channels included in the wavelength-division multiplexed signal light, a light receiving unit that receives the signal light of a predetermined channel in a reception band wider than the frequency interval between the signal lights of the plurality of channels and outputs an electric field signal indicating an electric field component of the signal light of the predetermined channel; A power measurement unit that measures the power of the signal light of the predetermined channel; A first conversion unit that converts the electric field signal from a signal in the time domain to a signal in the frequency domain; A filter unit that transmits the electric field signal converted into a signal in the frequency domain through a transmission band narrower than the reception band; A second conversion unit that converts the electric field signal transmitted by the filter unit from a signal in the frequency domain to a signal in the time domain; An amplitude measurement unit that measures a first amplitude of the electric field signal input from the first conversion unit to the filter unit and a second amplitude of the electric field signal input from the filter unit to the second conversion unit, respectively; A notification unit that notifies the power measurement unit of the first amplitude and the second amplitude; The power measurement unit corrects a measurement error of the power of the signal light in the predetermined channel based on a ratio of the first amplitude and the second amplitude. A transmission device characterized by this. (Supplementary Note 5) The transmission device according to Supplementary Note 4, wherein the filter unit transmits the electric field signal through the transmission band corresponding to the frequency interval. (Supplementary Note 6) The amplitude measurement unit calculates the root mean square of each of the first amplitude and the second amplitude, The notification unit notifies the power measurement device of the root mean square of each of the first amplitude and the second amplitude. The transmission device according to Supplementary Note 4 or 5, characterized by this. (Supplementary Note 7) The light receiving unit has an amplifier that amplifies the electric field signal so that the amplitude of the electric field signal becomes a predetermined value, The power measurement unit calculates the power of the signal light in the predetermined channel based on the gain of the amplifier. The transmission device according to any one of Supplementary Notes 4 to 6, characterized by this. (Supplementary Note 8) The power measurement unit acquires the amplitude after amplification of the electric field signal from the light receiving unit, and corrects a measurement error of the power of the signal light in the predetermined channel based on the amplitude of the electric field signal. The transmission device according to Supplementary Note 7, characterized by this. (Supplementary Note 9) A variable optical attenuator that attenuates the power of the signal light in the predetermined channel input to the light receiving unit by an attenuation amount according to a control voltage, The power measurement unit corrects a measurement error of the power of the signal light in the predetermined channel based on the control voltage. The transmission device according to any one of Claims 4 to 8, characterized by this.

Explanation of Signs

[0121] 1 Power measurement unit 2 Signal processing circuit 3 Front-end unit 7 Transponder 8 Wavelength division multiplexing device 21 Reception processing unit 34a~34d Photodiode 36a~36d Variable gain amplifier 40 Variable optical attenuator 41 Local light source 42 Attenuation control unit 211 Fast Fourier transform unit 212 Filter unit 213 Inverse fast Fourier transform unit 217 Amplitude monitor unit 218 Setting control unit

Claims

1. Among the optical signals of a plurality of channels included in the wavelength-division multiplexed optical signal, a first conversion unit that converts an electric field signal indicating an electric field component of the optical signal of a predetermined channel received in a reception band wider than the frequency interval between the optical signals of the plurality of channels from a signal in the time domain to a signal in the frequency domain; A filter unit that transmits the electric field signal converted into a signal in the frequency domain through a transmission band narrower than the reception band; A second conversion unit that converts the electric field signal transmitted by the filter unit from a signal in the frequency domain to a signal in the time domain; An amplitude measurement unit that measures a first amplitude of the electric field signal input from the first conversion unit to the filter unit and a second amplitude of the electric field signal input from the filter unit to the second conversion unit, respectively; A signal processing apparatus, comprising: a power measurement apparatus that measures the power of the optical signal of the predetermined channel; and a notification unit that notifies the power measurement apparatus of the first amplitude and the second amplitude used for correcting a measurement error of the power of the optical signal of the predetermined channel.

2. The signal processing apparatus according to claim 1, wherein the filter unit transmits the electric field signal through the transmission band corresponding to the frequency interval.

3. The amplitude measurement unit calculates a root mean square of each of the first amplitude and the second amplitude; The signal processing apparatus according to claim 1 or 2, wherein the notification unit notifies the power measurement apparatus of the root mean square of each of the first amplitude and the second amplitude.

4. A light receiving unit that receives the optical signal of a predetermined channel among the optical signals of a plurality of channels included in the wavelength-division multiplexed optical signal in a reception band wider than the frequency interval between the optical signals of the plurality of channels, and outputs an electric field signal indicating an electric field component of the optical signal of the predetermined channel; A power measurement unit that measures the power of the optical signal of the predetermined channel; A first conversion unit that converts the electric field signal from a signal in the time domain to a signal in the frequency domain; A filter unit that transmits the electric field signal converted into a signal in the frequency domain through a transmission band narrower than the reception band; A second conversion unit that converts the electric field signal transmitted by the filter unit from a signal in the frequency domain to a signal in the time domain; An amplitude measurement unit that measures a first amplitude of the electric field signal input from the first conversion unit to the filter unit and a second amplitude of the electric field signal input from the filter unit to the second conversion unit, respectively; A notification unit that notifies the first amplitude and the second amplitude to the power measurement unit. The transmission device is characterized in that the power measurement unit corrects a measurement error of the power of the signal light of the predetermined channel based on a ratio between the first amplitude and the second amplitude.

5. The light receiving unit includes an amplifier that amplifies the electric field signal so that an amplitude of the electric field signal becomes a predetermined value. The transmission device according to claim 4, wherein the power measurement unit calculates the power of the signal light of the predetermined channel based on a gain of the amplifier.

6. The transmission device according to claim 5, wherein the power measurement unit acquires an amplitude of the amplified electric field signal from the light receiving unit, and corrects a measurement error of the power of the signal light of the predetermined channel based on the amplitude of the electric field signal.

7. The light receiving unit includes a variable optical attenuator that attenuates the power of the signal light of the predetermined channel input thereto by an attenuation amount according to a control voltage. The transmission device according to any one of claims 4 to 6, wherein the power measurement unit corrects a measurement error of the power of the signal light of the predetermined channel based on the control voltage.

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