Measuring device, transmitting device, receiving device, measuring method, receiving method, and program

Abstract

To provide a measuring device that can measure the characteristics of a coherent receiver separately from the characteristics of a transmitter, without the need to measure the characteristics of the transmitter in advance. [Solution] The measuring device according to the present disclosure comprises: a conversion unit that converts a single-sideband signal affected by the transmission characteristics of a transmitter into a first electrical signal; a receiving unit that coherently receives the single-sideband signal; and a measuring unit that uses a second electrical signal generated by coherently receiving the first electrical signal to determine the transmission characteristics and the receiving characteristics of the receiving unit.

Description

[Technical Field]

[0001] This disclosure relates to measuring devices, transmitting devices, receiving devices, measuring methods, transmitting methods, receiving methods, and programs. [Background technology]

[0002] In recent years, the increase in internet traffic has created a demand for the construction of high-speed and high-capacity optical transmission systems. To achieve high-speed and high-capacity communication in optical transmission systems, multi-level modulation schemes such as high symbol rates and high-order quadrature amplitude modulation (QAM) are used. However, high symbol rate and high-order multi-level modulated signals are vulnerable to signal waveform distortion that occurs within the transmitter and receiver. To achieve high-speed and high-capacity communication, it is necessary to compensate for signal waveform distortion.

[0003] Generally, distortion in signal waveforms can be compensated using a fixed filter whose coefficient is the inverse characteristic of the frequency response of the transceiver. This method requires that the frequency characteristics of the transceiver be measured in advance. Non-patent document 1 discloses a method for measuring the frequency characteristics of the transceiver at high speed and with high resolution, using a known orthogonal frequency-division multiplexing (OFDM) signal.

[0004] Furthermore, Non-Patent Document 2 discloses the configuration of a receiving device that receives DSB (Double SideBand) signals in a CADD (Carrier-Assisted Differential Detection) configuration. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Honglin Ji, et al., “Single-shot Characterization of Frequency-resolved Imbalance in Coherent Transceivers Based on Inter-channel Response Ratio,” Journal of Lightwave Technology, vol. 41, no. 11, p. 3603-3611 (2023) [Non-Patent Document 2] Jingchi Li, et al., “Silicon Photonic Carrier-Assisted Differential Detection Receiver With High Electrical Spectral Efficiency for Short-Reach Interconnects” JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL.41, NO.3, FEBRUARY 1, 2023 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] When compensating the frequency characteristics of a coherent receiver using the method described in Non-Patent Document 1, it is first necessary to measure and compensate the frequency characteristics of the transmitter. Then, the frequency characteristics of the receiver are measured by transmitting and receiving a known OFDM signal using the transmitter with the calibrated frequency characteristics and the coherent receiver whose frequency characteristics are to be compensated. Therefore, the method described in Non-Patent Document 1 has the problem that it is not possible to measure the characteristics of the receiver based on a signal whose frequency characteristics in the transmitter have not been compensated.

[0007] The purpose of this disclosure is to provide a measuring device, transmitting device, receiving device, measuring method, transmitting method, receiving method, and program that can measure the frequency characteristics of a coherent receiver separately from the frequency characteristics of a transmitter without the need to measure the frequency characteristics of the transmitter in advance. [Means for solving the problem]

[0008] The measuring device according to this disclosure comprises: a conversion unit that converts a single-sideband signal affected by the frequency characteristics of a transmitter (hereinafter referred to as "transmission characteristics") into a first electrical signal; a receiving unit that coherently receives the single-sideband signal; and a measuring unit that uses the first electrical signal and a second electrical signal generated by the coherent reception to determine the transmission characteristics and the frequency characteristics of the receiving unit (hereinafter referred to as "receiving characteristics").

[0009] The transmitting device according to this disclosure includes a first electrical signal converted from a single-sideband signal affected by the transmitting characteristics of the transmitter, and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal. The compensation unit performs compensation processing of the transmitting signal using the inverse characteristics of the transmitting characteristics among the transmitting characteristics and the receiving characteristics of the receiving unit, which are identified using these two sets of characteristics. The communication unit transmits the transmitting signal to a receiving device having the receiving unit.

[0010] The receiving device according to this disclosure comprises a receiving unit that coherently receives a signal compensated using the transmission characteristics, which are identified using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of a transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal; and a signal processing unit that performs compensation processing on the received signal obtained as a result of the coherent reception using the inverse characteristics of the reception characteristics.

[0011] The measurement method according to this disclosure converts a single-sideband signal affected by the transmission characteristics of the transmitter into a first electrical signal, coherently receives the single-sideband signal, and uses the first electrical signal and a second electrical signal generated by the coherent reception to determine the transmission characteristics and the receiving characteristics of the receiver.

[0012] The transmission method according to this disclosure performs compensation processing on the transmission signal using the inverse characteristics of the transmission characteristics, which are identified using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, and the receiving characteristics of the receiving unit, and transmits the transmission signal to a receiving device having the receiving unit.

[0013] The receiving method according to this disclosure coherently receives a transmitted signal compensated using the transmission characteristics, and performs compensation processing on the received signal obtained as a result of the coherent reception using the inverse characteristics of the reception characteristics.

[0014] The program relating to this disclosure is a program that causes a computer to perform the following actions: convert a single-sideband signal affected by the transmission characteristics of a transmitter into a first electrical signal, coherently receive the single-sideband signal, and use the first electrical signal and a second electrical signal generated by the coherent reception to determine the transmission characteristics and the receiving characteristics of a receiver. [Effects of the Invention]

[0015] This disclosure provides a measuring device, a transmitting device, a receiving device, a measuring method, a transmitting method, a receiving method, and a program that enable the measurement of coherent receiver characteristics separately from transmitter characteristics without the need to measure transmitter characteristics in advance. [Brief explanation of the drawing]

[0016] [Figure 1]FIG. 1 shows a configuration example of a measurement device. [Figure 2] FIG. 2 shows the processing flow of a measurement method executed in the measurement device. [Figure 3] FIG. 3 shows a configuration example of a communication system. [Figure 4] FIG. 4 shows a configuration example of a transmitter. [Figure 5] FIG. 5 shows a configuration example of an optical fiber transmission line. [Figure 6] FIG. 6 shows a configuration example of a receiver. [Figure 7] FIG. 7 shows the signal transmission processing flow in the transmitter. [Figure 8] FIG. 8 shows the signal reception processing flow executed in the receiver. [Figure 9] FIG. 9 is a block diagram showing configuration examples of the measurement device, the transmitter, and the receiver.

MODE FOR CARRYING OUT THE INVENTION

[0017] (Embodiment 1) Using FIG. 1, a configuration example of the measurement device 10 will be described. The measurement device 10 may be a computer device that operates by a processor executing a program stored in a memory.

[0018] The measurement device 10 includes a conversion unit 11, a reception unit 12, and a measurement unit 13. The conversion unit 11, the reception unit 12, and the measurement unit 13 may be software or modules whose processing is executed by a processor executing a program stored in a memory. Or, the conversion unit 11, the reception unit 12, and the measurement unit 13 may be hardware such as a circuit or a chip.

[0019] The conversion unit 11 may be used as means for converting an optical signal into an electrical signal or an electrical signal into an optical signal. The reception unit 12 may be used as means for receiving a signal. The measurement unit 13 may be used as means for measuring, for example, the characteristics of a signal transmitter or receiver.

[0020] The conversion unit 11 converts a single-sideband signal (SSB), which is affected by the transmitter's transmission characteristics, into a first electrical signal. The transmitter modulates, for example, the intensity or phase of the carrier wave, which is an optical signal. Furthermore, the transmitter transmits the modulated signal to the measuring device 10.

[0021] The transmission characteristics may include, for example, at least one of the following: frequency characteristics, amplitude characteristics, phase characteristics, etc. The transmission characteristics may also include characteristics relating to the optical transmission path between the transmitter and the measuring device 10. Furthermore, "characteristics" may be rephrased as "performance."

[0022] A single-sideband signal is a signal that has only one component, either the upper sideband or the lower sideband. The upper sideband may be a frequency band higher than the carrier frequency band, and the lower sideband may be a frequency band lower than the carrier frequency band. The conversion unit 11 converts the single-sideband signal, which is an optical signal, into an electrical signal.

[0023] The receiving unit 12 receives the single-sideband signal in a CADD configuration. Receiving in a CADD configuration can also be described as coherent reception, or more specifically, self-coherent reception. The single-sideband signal to be received is the same as the single-sideband signal that is converted into an electrical signal in the conversion unit 11. In other words, the measuring device 10 copies or branches the single-sideband signal received from the transmitter. The conversion unit 11 and the receiving unit 12 receive the copied or branched single-sideband signal. The receiving unit 12 may perform self-coherent reception using multiple single-sideband signals obtained by copying or otherwise modifying the received single-sideband signal. Specifically, the receiving unit 12 may perform self-coherent reception by interfering with multiple single-sideband signals.

[0024] The receiving unit 12 extracts or detects a desired information component contained in the single-sideband signal. The desired information component may be a signal component that is already known in the transmitter and measuring device 10, such as a pilot signal. Furthermore, the receiving unit 12 converts the detected information component into a second electrical signal. The second electrical signal is subject to the receiving characteristics of the receiving unit 12 because receiving processing is performed in the receiving unit 12. The receiving characteristics may include at least one of the following: characteristics related to frequency, characteristics related to amplitude, characteristics related to phase, etc.

[0025] The measurement unit 13 uses the first electrical signal and the second electrical signal to determine the transmission characteristics of the transmitter and the reception characteristics of the receiver. The measurement unit 13 may determine the transmission characteristics and reception characteristics by, for example, performing calculations using the first electrical signal and the second electrical signal. The calculations using the first electrical signal and the second electrical signal may, for example, be calculations relating to a composite signal generated by adding or multiplying the first electrical signal and the second electrical signal.

[0026] Figure 2 shows the processing flow of the measurement method performed in the measuring device 10. First, the conversion unit 11 converts the single-sideband signal, which is affected by the transmission characteristics of the transmitter, into a first electrical signal (S11). Next, the receiving unit 12 receives the single-sideband signal in a self-coherent manner (S12). Next, the measurement unit 13 uses the first electrical signal and the second electrical signal generated by the self-coherent reception to determine the transmission characteristics and the receiving characteristics of the receiving unit (S13).

[0027] As described above, the measuring device 10 performs measurements or calculations using a single-sideband signal that is not affected by the receiving characteristics (and is only affected by the transmitting characteristics) and a single-sideband signal that is affected by both the transmitting and receiving characteristics. This allows the measuring device 10 to identify the transmitting characteristics of the transmitter and the receiving characteristics of the receiving unit 12 included in the measuring device 10. As a result, the measuring device 10 can identify the transmitting characteristics of the transmitter and the receiving characteristics of the receiving unit 12 without having to measure the transmitting characteristics of the transmitter beforehand.

[0028] (Embodiment 2) Figure 3 shows an example of a communication system configuration. The communication system shown in Figure 3 includes a transmitter 20, an optical fiber transmission line 40, and a receiver 30. The transmitter 20 and the receiver 30 are interconnected by the optical fiber transmission line 40.

[0029] Figure 4 shows an example configuration of the transmitter 20. The transmitter 20 may be a computer device that operates by a processor executing a program stored in memory. The transmitter 20 has an OFDM signal generation unit 21, a DAC (Digital Analog Converter) 22, an LD (Laser Diode) 23, an optical modulation unit 24, an encoding unit 25, and a compensation unit 26. The OFDM signal generation unit 21, DAC 22, LD 23, optical modulation unit 24, encoding unit 25, and compensation unit 26 may be software or modules whose processing is performed by a processor executing a program stored in memory. Alternatively, the OFDM signal generation unit 21, DAC 22, LD 23, optical modulation unit 24, encoding unit 25, and compensation unit 26 may be hardware such as circuits or chips.

[0030] The OFDM signal generation unit 21 may be used as a means for generating an OFDM signal. The optical modulation unit 24 may be used as a means for modulating an optical signal. The encoding unit 25 may be used as a means for encoding data. The compensation unit 26 may be used as a means for compensating for distortions and the like in the data.

[0031] The OFDM signal generation unit 21 generates a known OFDM signal by performing digital signal processing. The known OFDM signal may be, for example, data that is expected to be received by the receiver 30. In other words, the known OFDM signal may be a signal that is recognized as a predetermined signal in both the transmitter 20 and the receiver 30. The known OFDM signal is used to measure the characteristics of the transmitter 20 and the receiver 30.

[0032] The OFDM signal generation unit 21 performs serial and parallel conversion on pilot data and assigns the converted data to each subcarrier. Furthermore, the OFDM signal generation unit 21 modulates the assigned data on each subcarrier. The OFDM signal generation unit 21 converts the modulated signal into time-domain data by performing an inverse fast Fourier transform (IFFT) and parallel and serial conversion. If the chromatic dispersion of the transmission line is significant, the distortion caused by chromatic dispersion is reduced by adding a copy of itself (cyclic prefix) to the time-domain data.

[0033] The encoding unit 25 encodes the data. The data may be so-called user data, such as image data or text data, or it may be control data used to control communication. The encoding unit 25 outputs four signals: in-phase (I) components of X polarization and Y polarization, and quadrature (Q) components.

[0034] The compensation unit 26 pre-compensates for the characteristics of the devices within the transmitter 20 for the four encoded signal sequences. The transmission characteristics of the transmitter 20 are compensated by a fixed filter whose coefficients are the inverse characteristics of the transmitter 20 calculated in the receiver 30. The transmission characteristics compensated by the fixed filter may be, for example, frequency characteristics.

[0035] The DAC22 converts the four compensated signal sequences and the known OFDM signal generated by the OFDM signal generation unit 21 into analog electrical signals. The DAC22 inputs the converted analog electrical signals to the optical modulator 24. An electrical amplifier may be placed between the DAC22 and the optical modulator 24, and the optical modulator 24 may receive analog electrical signals whose amplitude has been amplified by the electrical amplifier.

[0036] LD23 outputs CW (Continuous Wave) light. Optical modulator 24 modulates the CW light output from LD23 according to four analog electrical signals input from DAC22 to generate polarization-multiplexed optical signals such as polarization-multiplexed QAM signals. Furthermore, optical modulation unit 24 modulates the CW light output from LD23 according to an analog electrical signal of a known OFDM signal input from DAC22 to generate a known optical OFDM signal. Optical modulator 24 includes, for example, a Mach-Zehnder (MZ) modulator. Optical modulator 24 sends the generated polarization-multiplexed optical signals and optical OFDM signals to the transmission line 40.

[0037] Figure 5 shows an example configuration of an optical fiber transmission line 40. The optical fiber transmission line 40 transmits polarization-multiplexed optical signals and optical OFDM signals received from the transmitter 20 to the receiver 30. The optical fiber transmission line 40 includes an optical fiber 41 and an optical amplifier 42. The optical fiber 41 guides the optical signal transmitted from the transmitter 20. The optical amplifier 42 amplifies the optical signal and compensates for propagation loss in the optical fiber 41. The optical amplifier 42 is configured, for example, as an erbium-doped fiber amplifier (EDFA). The optical fiber transmission line 40 may include multiple optical amplifiers 42.

[0038] Figure 6 shows an example configuration of the receiver 30. The receiver 30 corresponds to the measuring device 10 in Figure 1. The receiver 30 may also be a computer device that operates by a processor executing a program stored in memory. The receiver 30 has the following components: a branching unit 31, a delay unit 32, a PD (Photodiode) 33, an ADC (Analog Digital Converter) 34, a coherent receiving unit 35, an LD 36, an ADC 37, a measuring unit 38, a digital signal processing unit 301, and a decoding unit 302. The branching unit 31 includes branching unit 31_1 and branching unit 31_2. Each component constituting the receiver 30 may be software or a module whose processing is executed by a processor executing a program stored in memory. Alternatively, each component constituting the receiver 30 may be hardware such as a circuit or a chip.

[0039] When measuring the transmission characteristics of the transmitter 20 and the reception characteristics of the receiver 30, the optical OFDM signal transmitted from the transmitter 20 is received at the branching unit 31. The polarization-multiplexed optical signal transmitted from the transmitter 20 is received at the coherent receiver 35. When measuring the transmission and reception characteristics, for example, the optical fiber transmission line 40 may be connected to a port connected to the branching unit 31 in advance. When performing normal data transmission, for example, the optical fiber transmission line 40 may be connected to a port connected to the coherent receiver 35 in advance. Alternatively, the receiver 30 may be provided with a switch or the like that allows the output destination of the optical signal received from the optical fiber transmission line 40 to be changed depending on whether the transmission and reception characteristics are being measured or normal data transmission is being performed. Furthermore, the receiver 30 may be provided with a switch or the like that allows the LD36 not to be used when measuring the transmission and reception characteristics, but to be used when performing normal data transmission.

[0040] Here, we will describe a configuration for measuring the transmission characteristics of the transmitter 20 and the reception characteristics of the receiver 30 in the receiver 30. The reception characteristics of the receiver 30 may also refer to the reception characteristics of the coherent receiver 35. Below, we will describe a CADD (Carrier-Assisted Differential Detection) configuration as a configuration for measuring the transmission characteristics and reception characteristics.

[0041] The branching unit 31_1 branches the optical OFDM signal received via the optical fiber transmission line 40. The branching unit 31_1 outputs the optical OFDM signal to the delay unit 32 and the coherent receiving unit 35. The branching unit 31_1 may be, for example, a coupler with a branching ratio of 50:50. Similarly, the branching unit 31_2 may also be a coupler with a branching ratio of 50:50, just like the branching unit 31_1. The branching ratio of the couplers is not limited to 50:50 and may be other values.

[0042] The delay unit 32 delays one of the optical OFDM signals that was branched in the branching unit 31_1. The delay unit 32 may be, for example, an optical delay line. The branching unit 31_2 branches the optical OFDM signal that was delayed in the delay unit 32. The branching unit 31_2 outputs the optical OFDM signal to the PD 33 and the coherent receiver 35.

[0043] PD33 converts the optical signal input from branching section 31_2 into an electrical signal. PD33 outputs the electrical signal to ADC34. ADC34 samples the electrical signal input from PD33 and converts the electrical signal into a digital signal. ADC34 outputs the converted digital signal to measurement section 38.

[0044] The coherent receiver 35 performs coherent detection using the optical OFDM signal input from branch 31_1 and the optical OFDM signal input from branch 31_2, specifically, self-coherent detection or self-coherent reception. Coherent detection may also involve detecting two series of electrical signals corresponding to the I component and Q component by interfering the optical OFDM signal with a delayed optical OFDM signal.

[0045] The coherent receiver 35 outputs the electrical signal to the ADC 37. The ADC 37 samples the electrical signal input from the coherent receiver 35 and converts the electrical signal into a digital signal. The ADC 37 outputs the converted digital signal to the measurement unit 38.

[0046] ADC34 and ADC37 may convert the electrical signals amplified using an electrical amplifier into digital signals.

[0047] The measurement unit 38 receives digital signals output from ADC 34 and ADC 37. ADC 37 outputs a digital signal converted from two electrical signals, the I component and the Q component, to the measurement unit 38. The measurement unit 38 demodulates the OFDM signal from the three input digital signals. Furthermore, the measurement unit 38 calculates the error between the OFDM signal generated in the transmitter 20 and the demodulated OFDM signal, thereby separately measuring the transmission characteristics of the transmitter 20 and the reception characteristics of the coherent receiver 42. Separate measurement may mean measuring the transmission characteristics and reception characteristics individually. In other words, separate measurement may mean identifying transmission and reception characteristics such that they do not have a dependency relationship with each other.

[0048] Here, a method for separately measuring the transmission characteristics of the transmitter 20 and the reception characteristics of the coherent receiver 35 in the measurement unit 38 will be described. The measurement unit 38 may measure the frequency characteristics of the transmitter 20 and receiver 30, for example, when the transmitter 20 and receiver 30 are shipped from the factory, or during pre-operation testing of the optical fiber system using the transmitter 20 and receiver 30. In the following description, a method for measuring frequency characteristics as transmission characteristics and reception characteristics will be described.

[0049] First, the receiver 30 receives the optical signal E(n) transmitted from the transmitter 20. The optical signal E(n) consists of an optical carrier C and an OFDM signal s(n), and is expressed as E(n) = C + s(n). Here, the OFDM signal s(n) is an odd-interleaved OFDM signal, which has values ​​only in odd-numbered subcarriers. The odd-interleaved OFDM signal s(n) is expressed as shown in equation (1) below.

[0050] TIFF2026105138000002.tif14150

[0051] N is the number of subcarriers, including even subcarriers that do not have data, d k is the data symbol of the k-th odd subcarrier. Also, s(n) is a single-sideband (SSB) signal that has no value in the negative frequency region.

[0052] The optical signal E(n) is branched at branching section 31_1. One optical signal is input to coherent receiver 35, and the other optical signal is delayed at delay section 32. The delayed optical signal is branched at branching section 31_2. One optical signal is input to PD33, and the other optical signal is input to coherent receiver 35. Subsequently, the electrical signal I0 output from ADC34 and the two series of electrical signals I1 and I2, corresponding to the I and Q components output from ADC37, are expressed as shown in equation (2) below.

[0053] Formula (2) TIFF2026105138000003.tif9150 TIFF2026105138000004.tif10150 TIFF2026105138000005.tif10150

[0054] s τ is the OFDM signal delayed by the optical delay line, Re[·] represents the real part of the signal, and Im[·] represents the imaginary part of the signal.

[0055] The measuring unit 38 first measures equation (2) and

[0056] TIFF2026105138000006.tif6150

[0057] Using this, we obtain equation (3) below.

[0058] TIFF2026105138000007.tif11150 TIFF2026105138000008.tif10150

[0059] In equation (3), TIFF2026105138000009.tif6150 is an example of signal-signal beat interference (SSBI), which negatively impacts signal quality. Using equation (1), Each of the TIFF2026105138000010.tif6150 files can be represented as shown in the following formula (4).

[0060] Formula (4) TIFF2026105138000011.tif15150 TIFF2026105138000012.tif15150

[0061] d τ,k is the delayed k-th data symbol. In equation (4), since 2k1-2k2 is an even number, TIFF2026105138000013.tif6150 has values ​​in even subcarriers. Therefore, s(n), which has values ​​only in odd subcarriers, can avoid the negative effects of SSBI.

[0062] Next, the measurement unit 38 performs a Fourier transform on the calculated R. R may be used as a value obtained by combining electrical signals. The Fourier transform of R with respect to equation (3) is calculated as shown in equation (5) below.

[0063] TIFF2026105138000014.tif10150

[0064] Here, F[·] represents the Fourier transform, and S(ω) represents the Fourier transform of s(n). Ignoring the influence of SSBI, S(ω) is given by the following equation.

[0065] TIFF2026105138000015.tif11150

[0066] As described above, the measurement unit 38 demodulates the OFDM signal from the electrical signals that are the outputs of ADC 34 and ADC 37.

[0067] Subsequently, a method for measuring the characteristics of the coherent reception unit 35 from the demodulated OFDM signal will be described. In the following description, the characteristics of the transmitter 20 are h T (n), the characteristics of the optical fiber transmission line 40 are h C (n), and the characteristics of the coherent reception unit 35 are h R (n). Also, the characteristics of the transmitter 20 in the frequency domain are H T (ω), the characteristics of the optical fiber transmission line 40 are H C (ω), and the characteristics of the coherent reception unit 35 are H R (ω). "×" represents the convolution operation.

[0068] The characteristics of the transmitter 20 and the optical fiber transmission line 40 affect the entire OFDM signal received by the receiver 30. On the other hand, the characteristics of the coherent reception unit 35 do not affect the signal received at PD 33. The influence of the frequency characteristics on the signal is represented by the convolution operation in the time domain. Therefore, the two series of signals I'0 output from ADC 34 and I'1 and I'2 corresponding to the I component and Q component output from ADC 37 are represented by the following equation (6).

[0069] Equation (6) TIFF2026105138000016.tif9150 TIFF2026105138000017.tif10150 TIFF2026105138000018.tif10150

[0070] The measuring unit 38 is

[0071] TIFF2026105138000019.tif6150

[0072] Using equation (6), we obtain the following equation.

[0073] TIFF2026105138000020.tif25155

[0074] When R' is Fourier transformed, the following equation is obtained.

[0075] TIFF2026105138000021.tif6150 TIFF2026105138000022.tif6150

[0076] If we ignore the effect of SSBI and rearrange the above equation, we get the following equation.

[0077] TIFF2026105138000023.tif11150

[0078] s(n) is an SSB signal, and when ω < 0, S(ω) = 0. Therefore, rearranging the above equation, we obtain the following equation.

[0079] TIFF2026105138000024.tif6150 TIFF2026105138000025.tif6150

[0080] In the above formula, the characteristic H of the transmitter 20 T (ω), Characteristics of optical fiber transmission line 40 H C (ω) and the characteristics of the coherent receiver 35 H R By moving (ω) to the left side and rearranging, we obtain equations (7) and (8) below.

[0081] TIFF2026105138000026.tif12150 TIFF2026105138000027.tif11150

[0082] Let A(ω) be the right-hand side of equation (7) and B(ω) be the right-hand side of equation (8). Then the characteristics of the transmitter 20, the optical fiber transmission line 40, and the coherent receiver 35 are given by the following equations (9) and (10).

[0083] TIFF2026105138000028.tif9150 TIFF2026105138000029.tif11150

[0084] Here, equations (7) and (8) show that A(ω) and B(ω) are calculated from the data symbols of a known OFDM signal and the electrical signal received by the receiver 30. As a result, equation (10) shows that the characteristics of the coherent receiver 35 can be measured separately from the characteristics of the transmitter 20. Furthermore, if the characteristics of the optical fiber transmission line 40 are negligible, equation (9) shows that the characteristics of the transmitter 20 can be measured. The case where the characteristics of the optical fiber transmission line 40 are negligible means that the influence of the characteristics of the optical fiber transmission line 40 is small enough to be negligible, or the characteristics of the optical fiber transmission line 40 may be predetermined.

[0085] Next, the configuration for processing the polarization-multiplexed optical signal in the receiver 30 will be described. The polarization-multiplexed optical signal transmitted via the optical fiber transmission line 40 is input to the coherent receiver 35.

[0086] The coherent receiver 35 performs coherent detection on the polarization-multiplexed optical signal using the CW light output from the LD 36. The coherent receiver 35 is configured as a polarization diversity type coherent receiver. By performing coherent detection on the polarization-multiplexed optical signal, the coherent receiver 35 outputs four series of electrical signals corresponding to the I and Q components of the X and Y polarizations. These four series of electrical signals are input to the ADC 37.

[0087] The ADC37 samples the four electrical signals output from the coherent receiver 35 and converts the electrical signals into digital signals. Furthermore, the ADC37 outputs the converted digital signals to the digital signal processing unit 301.

[0088] The digital signal processing unit 301 performs digital signal processing on the four electrical signals sampled by the ADC 37 and demodulates the digital signals. The digital signal processing unit 301 may also be called a digital signal processing circuit. The digital signal processing unit 301 may include an adaptive equalization filter. The adaptive equalization filter compensates for various distortions contained in the digital signals.

[0089] Furthermore, the digital signal processing unit 301 may include a fixed filter, a 2x2 strictly linear (SL) MIMO equalizer, and a carrier phase compensation filter. The fixed filter may compensate for signal distortion caused by chromatic dispersion. In addition, the fixed filter may compensate for distortions with gradual fluctuations, such as signal distortion caused by the transmission characteristics of the transmitter 20, the transmission line characteristics of the optical fiber transmission line 40, and the reception characteristics of the coherent receiver 42. The 2x2 SL MIMO equalizer compensates for signal distortion caused by polarization state fluctuations and dispersion of polarization modes. The carrier phase compensation filter compensates for signal distortion caused by frequency offset and phase offset between the carrier of the transmitted optical signal and the local oscillator light on the receiving side.

[0090] Here, in the fixed filter included in the digital signal processing unit 301, the coefficients of the fixed filter may be the inverse characteristics of the coherent receiver 35 specified by equation (10). Furthermore, a case in which a fixed filter is used in the compensation unit 26 of the transmitter 20 and the characteristics of the optical fiber transmission line 40 can be ignored will be described. In this case, the coefficients of the fixed filter used in the compensation unit 26 of the transmitter 20 may be the inverse characteristics of the transmitter 20 specified by equation (9). The inverse characteristics of the transmitter 20 are given by the following equation (11), and the inverse characteristics of the coherent receiver 35 are given by the following equation (12).

[0091] TIFF2026105138000030.tif11150 TIFF2026105138000031.tif10150

[0092] Figure 7 shows the signal transmission process flow in the transmitter 20. First, the transmitter 20 performs compensation processing of the transmitted signal using the inverse characteristics of the transmitted characteristics, which are the transmission characteristics identified in the receiver 30 and the reception characteristics of the coherent receiver 35 (S21). The transmitted characteristics are identified in the receiver 30 using a first electrical signal converted from a single-sideband signal affected by the characteristics of the transmitter 20 and a second electrical signal output from the coherent receiver 35, which coherently receives the single-sideband signal. The compensation processing of the transmitted signal may be performed, for example, in a fixed filter of the compensation unit 26.

[0093] Next, the transmitter 20 transmits the transmission signal to the receiver 30 having a coherent receiving unit 35 (S22). Specifically, the transmitter 20 may transmit the transmission signal as a polarization-multiplexed optical signal from the optical modulation unit 24 to the receiver 30 via the optical fiber transmission line 40.

[0094] Figure 8 shows the flow of signal reception processing performed in receiver 30. First, the coherent receiver 35 coherently receives the transmitted signal, which has been compensated using the transmission characteristics of transmitter 20. The transmission characteristics are identified by separating them from the reception characteristics using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of transmitter 20, and a second electrical signal output from the coherent receiver 35 that coherently receives the single-sideband signal.

[0095] Next, the receiver 30 performs compensation processing on the received signal obtained as a result of coherent reception using the inverse characteristics of the receiving characteristics of the coherent receiving unit 35 (S32). The compensation processing may be performed, for example, in the digital signal processing unit 301.

[0096] As described above, the receiver 30 can use the optical OFDM signal transmitted from the transmitter 20 to determine the transmission characteristics of the transmitter 20 and the reception characteristics of the coherent receiver 35 included in the receiver 30.

[0097] Figure 9 is a block diagram showing an example configuration of a measuring device 10, a transmitter 20, and a receiver 30 (hereinafter referred to as the measuring device 10, etc.). Referring to Figure 9, the measuring device 10, etc. includes a network interface 1201, a processor 1202, and a memory 1203. The network interface 1201 may be used to communicate with a network node. The network interface 1201 may include, for example, a network interface card (NIC) compliant with the IEEE 802.3 series. IEEE stands for Institute of Electrical and Electronics Engineers.

[0098] The processor 1202 reads and executes software (computer programs) from the memory 1203 to perform processing on the measuring device 10, etc., as described using a flowchart. The processor 1202 may be, for example, an MPU (Micro Processor Unit) or a CPU (Central Processing Unit). The processor 1202 may include multiple processors.

[0099] Memory 1203 is composed of a combination of volatile and non-volatile memory. Memory 1203 may also include storage located away from the processor 1202. In this case, the processor 1202 may access memory 1203 via an I / O (Input / Output) interface, which is not shown.

[0100] In the example shown in Figure 9, memory 1203 is used to store a group of software modules. The processor 1202 can read these software modules from memory 1203 and execute them to perform processing on the measuring device 10, etc.

[0101] As explained with reference to Figure 9, each processor in the measuring device 10, etc., executes one or more programs that include a set of instructions for causing the computer to perform the algorithm described in the diagram.

[0102] In the examples described above, the program includes a set of instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more of the functions described in the embodiments. The program may be stored on a non-temporary computer-readable medium or a physical storage medium. Examples, but not limited to, include RAM (random-access memory), ROM (read-only memory), flash memory, SSD (solid-state drive), or other memory technologies, CD-ROM, DVD (digital versatile disc), Blu-ray® disc, or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage, or other magnetic storage devices. The program may be transmitted over a temporary computer-readable medium or a communication medium. Examples, but not limited to, include, a temporary computer-readable medium or a communication medium that includes an electrical, optical, acoustic, or other form of propagating signal.

[0103] Although the present disclosure has been described above with reference to embodiments, the present disclosure is not limited to the embodiments described above. Various modifications to the structure and details of the present disclosure can be made as can be understood by those skilled in the art within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0104] Each drawing is merely illustrative to illustrate one or more embodiments. Each drawing may be associated with one or more other embodiments rather than with only one specific embodiment. As those skilled in the art will understand, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings, for example, to create embodiments not explicitly shown or described. Not all features or steps shown in any one drawing to illustrate an exemplary embodiment are necessarily required, and some features or steps may be omitted. The order of steps shown in any of the drawings may be changed as appropriate.

[0105] Some or all of the above embodiments may also be described as follows, but are not limited to the following: (Note 1) A conversion unit that converts a single-sideband signal affected by the transmitter's transmission characteristics into a first electrical signal, A receiving unit that coherently receives the aforementioned single-sideband signal, A measuring device comprising: a measuring unit that determines the transmission characteristics and the reception characteristics of the receiving unit using the first electrical signal and the second electrical signal generated by the coherent reception. (Note 2) A delay unit that delays the timing of signal output, A first branching unit outputs the aforementioned single-sideband signal to the receiving unit as a first single-sideband signal, and outputs the aforementioned single-sideband signal to the delay unit as a second single-sideband signal, The measuring apparatus according to Appendix 1, further comprising: a second branching unit that outputs the second single-sideband signal to the conversion unit as a third single-sideband signal; and a second branching unit that outputs the second single-sideband signal to the receiving unit as a fourth single-sideband signal. (Note 3) The aforementioned single-sideband signal is an OFDM (orthogonal frequency-division multiplexing) signal having a complex-modulated I (in-phase) component and a Q (quadrature) component. The measuring device according to Appendix 1 or 2, wherein the receiving unit outputs an I component electrical signal corresponding to the I component and a Q component electrical signal corresponding to the Q component. (Note 4) The aforementioned measuring unit is The measuring apparatus described in Appendix 3, which separates and calculates the transmission characteristics and reception characteristics by performing a Fourier transform on a composite signal generated based on the first electrical signal, the I component electrical signal, and the Q component electrical signal. (Note 5) The aforementioned measuring unit is Generate the composite signal of equation (1), TIFF2026105138000032.tif6150I'0: First electrical signal I'1: I component electrical signal I'2: Q component electrical signal By performing a Fourier transform on equation (1), we derive equations (2) and (3). TIFF2026105138000033.tif6150 TIFF2026105138000034.tif6150H T (ω): Transmitter frequency characteristics H C (ω): Frequency characteristics of the transmission path between the transmitter and the measuring device H R (ω): Frequency characteristics of the receiver Based on equations (2) and (3) above, equations (4) and (5) are calculated. TIFF2026105138000035.tif9150 The measuring device described in Appendix 4 of TIFF2026105138000036.tif11150. (Note 6) The receiving unit is The transmitted signal generated using the inverse characteristics of the aforementioned transmission characteristics is coherently received. The measuring apparatus according to any one of the appendices 1 to 5, further comprising a signal processing unit that performs compensation processing on the received signal obtained as a result of the coherent reception using the inverse characteristics of the reception characteristics. (Note 7) A compensation unit that performs compensation processing on the transmitted signal using the inverse characteristics of the transmitted characteristics, among the transmitted characteristics and the receiving characteristics of the receiving unit, which are identified using a first electrical signal converted from a single-sideband signal affected by the transmitting characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, A transmitting device comprising: a communication unit that transmits the transmission signal to a receiving device having the receiving unit. (Note 8) Among the transmission characteristics and receiving characteristics of the receiving unit identified using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, the receiving unit coherently receives a transmitted signal compensated using the transmission characteristics, A receiving device comprising: a signal processing unit that performs compensation processing on the received signal obtained as a result of the coherent reception using the inverse characteristics of the reception characteristics. (Note 9) The single-sideband signal, affected by the transmitter's transmission characteristics, is converted into a first electrical signal. The aforementioned single-sideband signal is received coherently, A measurement method for determining the transmission characteristics and the reception characteristics of a receiver using the first electrical signal and the second electrical signal generated by the coherent reception. (Note 10) Compensation processing for the transmitted signal is performed using the inverse characteristics of the transmitted characteristics, among the transmitted characteristics and the receiving characteristics of the receiving unit, which are identified using a first electrical signal converted from a single-sideband signal affected by the transmitting characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal. A transmission method for transmitting the transmission signal to a receiving device having the receiving unit. (Note 11) Of the transmission characteristics and receiving characteristics of the receiving unit identified using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, the transmission characteristics and receiving characteristics of the receiving unit identified using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, the transmitted signal compensated using the transmission characteristics is coherently received, A receiving method comprising performing compensation processing on the received signal obtained as a result of the coherent reception using the inverse characteristics of the receiving characteristics. (Note 12) The single-sideband signal, affected by the transmitter's transmission characteristics, is converted into a first electrical signal. The aforementioned single-sideband signal is received coherently, A program that causes a computer to determine the transmission characteristics and the receiver characteristics of a receiver using the first electrical signal and the second electrical signal generated by the coherent reception. (Note 13) Compensation processing for the transmitted signal is performed using the inverse characteristics of the transmitted characteristics, among the transmitted characteristics and the receiving characteristics of the receiving unit, which are identified using a first electrical signal converted from a single-sideband signal affected by the transmitting characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal. A program that causes a computer to transmit the aforementioned transmission signal to a receiving device having the aforementioned receiving unit. (Note 14) Of the transmission characteristics and receiving characteristics of the receiving unit identified using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, the transmission characteristics and receiving characteristics of the receiving unit identified using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, the transmitted signal compensated using the transmission characteristics is coherently received, A program that causes a computer to perform compensation processing on the received signal obtained as a result of the coherent reception, using the inverse characteristics of the reception characteristics.

[0106] Some or all of the elements (e.g., configuration and function) described in Appendices 2 to 6 that are dependent on Appendice 1 may also be dependent on Appendices 9 and 12 in the same manner as those described in Appendices 2 to 6. Some or all of the elements described in any appendice may be applicable to various hardware, software, recording means, systems, and methods for recording software. [Explanation of Symbols]

[0107] 10 Measuring device 11 Conversion section 12 Receiver 13 Measuring part 20 Transmitters 21 OFDM signal generation section 22 DAC 23 LD 24 Optical Modulation Section 25 Encoding section 26 Compensation Department 30 receivers 31 Branching point 32 Delay section 33 PD 34 ADC 35 Coherent Receiver 36 LD 37 ADC 38 Measuring part 40 Optical fiber transmission lines 41 Optical Fiber 42 Optical Amplifier 301 Digital Signal Processing Unit 302 Decoding Unit

Claims

1. A conversion unit that converts a single-sideband signal affected by the transmitter's transmission characteristics into a first electrical signal, A receiving unit that coherently receives the aforementioned single-sideband signal, A measuring device comprising: a measuring unit that determines the transmission characteristics and the reception characteristics of the receiving unit using the first electrical signal and the second electrical signal generated by the coherent reception.

2. A delay unit that delays the timing of signal output, A first branching unit outputs the aforementioned single-sideband signal to the receiving unit as a first single-sideband signal, and outputs the aforementioned single-sideband signal to the delay unit as a second single-sideband signal, The measuring device according to claim 1, further comprising: a second branching unit that outputs the second single-sideband signal to the conversion unit as a third single-sideband signal and outputs the second single-sideband signal to the receiving unit as a fourth single-sideband signal.

3. The aforementioned single-sideband signal is an OFDM (orthogonal frequency-division multiplexing) signal having a complex-modulated I (in-phase) component and a Q (quadrature) component. The measuring device according to claim 1 or 2, wherein the receiving unit outputs an I-component electrical signal corresponding to the I-component and a Q-component electrical signal corresponding to the Q-component.

4. The aforementioned measuring unit is The measuring device according to claim 3, wherein the transmission characteristics and reception characteristics are separated and calculated by performing a Fourier transform on a composite signal generated based on the first electrical signal, the I component electrical signal, and the Q component electrical signal.

5. The aforementioned measuring unit is Generate the composite signal of equation (1), I' ０ : First electrical signal I' １ : I component electrical signal I' ２ : Q component electrical signal By performing a Fourier transform on equation (1), we derive equations (2) and (3). H Ｔ (ω): Transmitter frequency characteristics H C (ω): Frequency characteristics of the transmission path between the transmitter and the measuring device H Ｒ (ω): Frequency characteristics of the receiver Based on equations (2) and (3) above, equations (4) and (5) are calculated. The measuring device according to claim 4.

6. A compensation unit that performs compensation processing on the transmitted signal using the inverse characteristics of the transmitted characteristics, among the transmitted characteristics and the receiving characteristics of the receiving unit, which are identified using a first electrical signal converted from a single-sideband signal affected by the transmitting characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, A transmitting device comprising: a communication unit that transmits the transmission signal to a receiving device having the receiving unit.

7. Of the transmission characteristics and receiving characteristics of the receiving unit identified using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, the receiving unit coherently receives a transmitted signal compensated using the transmission characteristics, A receiving device comprising: a signal processing unit that performs compensation processing on the received signal obtained as a result of the coherent reception using the inverse characteristics of the reception characteristics.

8. The single-sideband signal, affected by the transmitter's transmission characteristics, is converted into a first electrical signal. The aforementioned single-sideband signal is received coherently, A measurement method for determining the transmission characteristics and the reception characteristics of a receiver using the first electrical signal and the second electrical signal generated by the coherent reception.

9. Of the transmission characteristics and receiving characteristics of the receiving unit identified using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, the transmission characteristics and receiving characteristics of the receiving unit identified using a first electrical signal converted from a single-sideband signal affected by the transmission characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal, the transmitted signal compensated using the transmission characteristics is coherently received, A receiving method comprising performing compensation processing on the received signal obtained as a result of the coherent reception using the inverse characteristics of the receiving characteristics.

10. Compensation processing for the transmitted signal is performed using the inverse characteristics of the transmitted characteristics, among the transmitted characteristics and the receiving characteristics of the receiving unit, which are identified using a first electrical signal converted from a single-sideband signal affected by the transmitting characteristics of the transmitter and a second electrical signal output from a receiving unit that coherently receives the single-sideband signal. A program that causes a computer to transmit the aforementioned transmission signal to a receiving device having the aforementioned receiving unit.

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