Calibration method, device and system for inter-channel crosstalk of coherent transceiver

Abstract

The invention discloses a method, a device and a system for calibrating crosstalk between channels of a coherent transceiver, and relates to the technical field of optical communication. The method comprises the following steps: a coherent transmitter loads generated auxiliary calibration signals on four channels of the coherent transmitter and sends the auxiliary calibration signals to a coherent receiver; wherein the generated auxiliary calibration signal is a multi-carrier frequency signal of which the channels are mutually orthogonal and the sub-carrier frequency amplitude is increased along with the increase of the frequency; the coherent transmitter receives the crosstalk calibration issued by the coherent receiver, performs frequency-dependent crosstalk compensation based on the crosstalk calibration, and sends the compensated calibration service signal to the coherent receiver; wherein the crosstalk calibration is a crosstalk value obtained by performing frequency-dependent crosstalk measurement based on crosstalk angle reconstruction by the coherent receiver according to the auxiliary calibration signal. The technical problems that an existing inter-channel crosstalk calibration technology is high in complexity, poor in precision and not suitable for coherent optical modules of different rates and modulation formats can be solved, and actual application requirements are met.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a method, device and system for calibrating crosstalk between channels of a coherent transceiver. Background Art

[0002] Driven by the rapid deployment of bandwidth-intensive applications such as AI (Artificial Intelligence), 5G, and the Internet of Things, optical coherent transmission is entering the era of single-wavelength channel Tbps (Tera bit per second). With the breakthrough of advanced indium phosphide / thin-film lithium niobate material technology and corresponding integrated packaging technology, current high-speed coherent transceivers can achieve bandwidths of up to 70 to 100 GHz and support 400 Gbps to Tbps high-speed signal modulation and demodulation. However, although integrated packaging helps alleviate the connection loss between discrete components and helps increase the overall module bandwidth, the reduction of optical / circuit routing distance and the compactness of module size will also introduce crosstalk between adjacent channels of the DP-IQ (Dual Polarization-Inphase and Quadrature) branch of the coherent transceiver. That is, the energy of this channel leaks and superimposes on the adjacent channel, destroying the original orthogonal characteristics of the four channels of DP-IQ modulation and causing crosstalk. In addition, since the RF signal loss along the transmission line is frequency-dependent, the inter-channel interference also exhibits frequency-dependent characteristics. As bandwidth increases, the channel crosstalk of large-bandwidth chips may even increase from -40dB to -15dB. This frequency-related crosstalk is difficult to compensate using traditional DSP (Digital Signal Processing) technology. Therefore, in order to improve the performance of high-speed optical transmission, it is necessary to use a large-range, high-sensitivity channel crosstalk calibration for high-speed coherent optical transceivers.

[0003] At present, vector instruments such as vector network analyzers are widely used in intensity modulation direct detection systems to correct the crosstalk intensity between adjacent wavelength channels, but they are not applicable to coherent transceivers with phase modulation and demodulation, and are expensive. In recent years, some researchers have proposed using a generalized linear MIMO (Multiple Input Multiple Output) equalizer in the DSP chip of the coherent transceiver itself to compensate for the crosstalk between DP-IQ channels. This solution avoids the use of high-cost instruments, but the complexity is more than twice that of traditional MIMO equalizers. In addition, the compensation performance of the generalized MIMO equalizer solution depends to a large extent on the convergence accuracy of the equalizer. Under the combined effect of severe DP-IQ crosstalk or severe frequency-related crosstalk or other transceiver damage, the equalizer performance may be greatly reduced, resulting in inaccurate compensation for crosstalk between channels.

[0004] In addition, there have been some studies on the calibration of frequency-correlated damage of coherent transceivers, such as channel delay and channel bandwidth response, using multi-tone signals, and such solutions have the characteristics of low complexity and high precision. However, since channel crosstalk easily interacts with frequency offset phase noise in the optical fiber transmission system, the energy of multi-tone signals is repeatedly aliased between DP-IQ branches, which brings difficulties to the demodulation and crosstalk calibration of multi-tone signals. Therefore, there is no relevant multi-tone modulation and demodulation solution that can solve the channel crosstalk calibration caused by channel energy leakage. At the same time, the existing calibration schemes based on multi-tone signals for other damages besides crosstalk usually adopt the multi-tone signal design with equal power at each frequency point. There may be a loss of accuracy in the calibration of high-frequency crosstalk, so it is not suitable for the calibration of modules with different bandwidths and modulation formats. Summary of the invention

[0005] The purpose of the present invention is to provide a method, device and system for calibrating crosstalk between channels of a coherent transceiver, which are used to perform high-precision measurement and compensation of frequency-related crosstalk between adjacent channels of a coherent transceiver, solve the technical problems of high complexity, poor accuracy and inapplicability to coherent optical modules of different rates and modulation formats in existing crosstalk calibration technologies, and meet practical application needs.

[0006] To achieve the above objectives, in a first aspect, an embodiment of the present invention provides a method for calibrating crosstalk between channels of a coherent transceiver, the method comprising:

[0007] The coherent transmitter loads the generated auxiliary calibration signal onto the four channels of the coherent transmitter and transmits it to the coherent receiver; wherein the generated auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with the increase of frequency;

[0008] The coherent transmitter receives the crosstalk calibration sent by the coherent receiver, performs frequency-related crosstalk compensation based on the crosstalk calibration, and sends the compensated calibration service signal to the coherent receiver; wherein the crosstalk calibration is the crosstalk value obtained by the coherent receiver through frequency-related crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal.

[0009] In combination with the first aspect, in one implementation, the generation of the auxiliary calibration signal includes:

[0010] Generate four multi-carrier signals with a mutually orthogonal relationship; obtain the modulation information of the optical module of the coherent transmitter, including the modulation order, the modulation baud rate and the sampling rate; set the calibration bandwidth according to the modulation baud rate; set the total number of sub-carriers of the multi-carrier signal according to the modulation order; set the sub-carrier interval according to the calibration bandwidth and the total number of sub-carriers; set the amplitude of each sub-carrier according to the modulation baud rate, the total number of sub-carriers and the sampling rate.

[0011] In combination with the first aspect, in one embodiment, when the coherent transmitter performs frequency-related crosstalk compensation, the following method is adopted: the crosstalk compensation coefficient is obtained by the crosstalk calibration sent by the coherent receiver, and the compensation depth is adaptively adjusted according to the modulation baud rate and modulation format, and the compensation depth is reduced for high-order modulation and high baud signals.

[0012] In combination with the first aspect, in one implementation, the coherent transmitter uses a preset static MIMO equalizer to perform frequency-related crosstalk compensation; the preset static MIMO equalizer is provided with two groups, which are used for crosstalk compensation of X polarization and Y polarization respectively; each group of static MIMO equalizers is a 2×2 real MIMO equalizer, and the equalizer coefficients are obtained according to the crosstalk calibration sent by the coherent receiver, and the compensation depth is adaptively adjusted according to the modulation baud rate and modulation format, and the compensation depth is reduced for high-order modulation and high-baud signals.

[0013] In a second aspect, an embodiment of the present invention further provides a method for calibrating crosstalk between channels of a coherent transceiver, the method comprising:

[0014] The coherent receiver receives the auxiliary calibration signal sent by the coherent transmitter loaded on four channels; wherein the auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with the increase of frequency;

[0015] The coherent receiver performs frequency-related crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal, obtains crosstalk calibration, and sends it to the coherent transmitter; wherein the crosstalk calibration is used for the transmitter to perform frequency-related crosstalk compensation based on the crosstalk calibration;

[0016] The coherent receiver receives the calibration service signal after the coherent transmitter performs crosstalk compensation, and performs equalization and demodulation on the calibration service signal.

[0017] In combination with the second aspect, in one implementation, the coherent receiver performs frequency-dependent crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal to obtain crosstalk calibration, including:

[0018] By introducing the frequency-dependent phase extraction factor α(fn), the preprocessed auxiliary calibration signal is reconstructed into a crosstalk-free signal; wherein α(fn) is used to extract the phase deviation caused by the crosstalk between channels and the phase rotation of the laser, and thereby reconstruct the crosstalk-free signal;

[0019] Select n=1,…N frequency points, scan α(fn) in the range of [0,2π], and obtain the intensity curve of the subcarrier signal at the nth frequency point of the reconstructed signal; wherein N is the total number of subcarriers of the multi-carrier signal;

[0020] Get the phase extraction factor corresponding to the intensity extreme point, denoted as α max (fn), and the α max (fn) is the sum of the crosstalk angle and the laser phase at this frequency, where the laser phase is a constant;

[0021] Sequentially change the α at the n=2,…N frequency points max (fn), minus α at the first frequency max (f1), calculating and obtaining a crosstalk angle of a sub-carrier frequency signal at an nth frequency point, and obtaining a corresponding crosstalk value according to the crosstalk angle.

[0022] In conjunction with the second aspect, in one implementation, when the coherent receiver performs equalization demodulation on the calibration service signal, a 2×2 complex MIMO equalizer is used to perform polarization demultiplexing equalization.

[0023] In a third aspect, an embodiment of the present invention further provides a coherent transmitter based on the method in the embodiment of the first aspect, the coherent transmitter comprising an auxiliary calibration signal sending unit and a calibration service signal sending unit;

[0024] The auxiliary calibration signal sending unit is used to: load the generated auxiliary calibration signal on the four channels of the coherent transmitter and send it to the coherent receiver; wherein the generated auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with the increase of frequency;

[0025] The calibration service signal sending unit is used to: receive the crosstalk calibration sent by the coherent receiver, perform frequency-related crosstalk compensation based on the crosstalk calibration, and send the compensated calibration service signal to the coherent receiver; wherein the crosstalk calibration is the crosstalk value obtained by the coherent receiver through frequency-related crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal.

[0026] In a fourth aspect, an embodiment of the present invention further provides a coherent receiver based on the method in the embodiment of the second aspect, the coherent receiver comprising a crosstalk calibration unit and a service signal demodulation unit;

[0027] The crosstalk calibration unit is used to: receive an auxiliary calibration signal sent by a coherent transmitter loaded on four channels, wherein the auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with the increase of frequency; and, according to the auxiliary calibration signal, perform frequency-related crosstalk measurement based on crosstalk angle reconstruction to obtain crosstalk calibration, and send it to the coherent transmitter; wherein the crosstalk calibration is used for the transmitter to perform frequency-related crosstalk compensation based on the crosstalk calibration;

[0028] The service signal demodulation unit is used to receive the calibration service signal after the coherent transmitter performs crosstalk compensation, and perform equalization demodulation on the calibration service signal.

[0029] In a fifth aspect, an embodiment of the present invention further provides a system for calibrating crosstalk between channels of a coherent transceiver, the system comprising a coherent transmitter as in an embodiment of the third aspect and a coherent receiver as in an embodiment of the fourth aspect.

[0030] The beneficial effects brought by the technical solution provided in the embodiments of the present application include:

[0031] In this embodiment, an auxiliary calibration signal is generated in the coherent transmitter. The auxiliary calibration signal is a multi-carrier signal that is orthogonal between channels and whose subcarrier amplitude increases with increasing frequency. It can be applied to the application scenario of channel crosstalk measurement of different coherent optical modules. At the same time, frequency-related crosstalk measurement based on crosstalk angle reconstruction will be performed in the coherent receiver, which can realize large-scale, high-precision, and low-complexity measurement and calibration of frequency-related crosstalk between adjacent channels of the coherent transceiver. Finally, low-complexity frequency-related crosstalk compensation will be performed in the coherent transmitter based on measurement calibration to realize the calibration of frequency-related crosstalk between channels, thereby solving the technical problems of high complexity, poor precision, and inapplicability to coherent optical modules of different rates and modulation formats in the existing channel crosstalk calibration technology, and meeting the actual application needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of a flow chart of a first embodiment of a method for calibrating crosstalk between channels of a coherent transceiver according to the present application;

[0033] Figure 2 A schematic diagram of the specific process of generating auxiliary calibration signals for this application;

[0034] Figure 3 A schematic diagram of a multi-carrier signal spectrum in different scenarios in an example;

[0035] Figure 4A schematic diagram of an example of using the crosstalk compensation method of this embodiment to perform crosstalk compensation on X polarization;

[0036] Figure 5 A schematic flow chart of a second embodiment of a method for calibrating crosstalk between channels of a coherent transceiver according to the present application;

[0037] Figure 6 A schematic diagram of the specific process of crosstalk measurement for this application;

[0038] Figure 7 α is the intensity extreme point corresponding to different frequency points max Schematic diagram of the relationship between (fn) and crosstalk;

[0039] Figure 8 A schematic diagram of performing conventional equalization and demodulation on a received signal in a coherent receiver according to the present application;

[0040] Fig. 9 A schematic diagram of the prior art using a generalized MIMO equalizer in a coherent receiver to perform crosstalk compensation;

[0041] Fig.10 It is a flowchart of a method for calibrating crosstalk between channels of a coherent transceiver using the present application in an example;

[0042] Fig.11 A schematic diagram of the spectrum of a multi-carrier signal in different transmission processes in an example;

[0043] Fig.12 FIG. 1 is a schematic diagram of the architecture of an embodiment of a system for calibrating crosstalk between coherent transceiver channels of the present application. DETAILED DESCRIPTION

[0044] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] However, it should be noted that the examples to be introduced below are only some specific examples, and are not intended to limit the embodiments of the present invention to the following specific steps, values, conditions, data, sequences, etc. All other embodiments obtained by ordinary technicians in this field without creative work based on the embodiments in this application are within the scope of protection of this application.

[0046] Embodiment 1

[0047] The present application embodiment provides a method for calibrating crosstalk between channels of a coherent transceiver. Figure 1 , Figure 1 FIG. 1 is a flow chart of a first embodiment of a method for calibrating crosstalk between channels of a coherent transceiver of the present application. Figure 1As shown, a method for calibrating crosstalk between channels of a coherent transceiver includes:

[0048] Step A1, the coherent transmitter loads the generated auxiliary calibration signal on the four channels of the coherent transmitter and sends it to the coherent receiver; wherein the generated auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with the increase of frequency;

[0049] Step A2, the coherent transmitter receives the crosstalk calibration sent by the coherent receiver, performs frequency-related crosstalk compensation based on the crosstalk calibration, and sends the compensated calibration service signal to the coherent receiver; wherein the crosstalk calibration is the crosstalk value obtained by the coherent receiver through frequency-related crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal.

[0050] It can be understood that in this embodiment, an auxiliary calibration signal is generated in the coherent transmitter, and the auxiliary calibration signal is a multi-carrier signal with orthogonal channels and sub-carrier amplitudes increasing with increasing frequency. Different from the prior art, the difference between the amplitude of the high-frequency carrier signal and the amplitude of the low-frequency carrier signal in the multi-carrier signal increases with the increase of the modulation order and the modulation baud rate, which can be applied to the application scenario of channel crosstalk measurement of different coherent optical modules.

[0051] Further, see Figure 2 As shown, as an optional implementation, in step A1 of this embodiment, the generation of the auxiliary calibration signal includes:

[0052] S201, generating four multi-carrier frequency signals having a mutually orthogonal relationship, wherein the expression of the multi-carrier frequency signal is formula (1) and the sub-carrier frequencies contained in the multi-carrier frequency signal satisfy formula (2);

[0053]

[0054] In formula (1), n ​​represents the nth subcarrier frequency, Amp ab (n) is the amplitude of the nth subcarrier frequency on the ab branch, f ab (n) is the frequency of the nth subcarrier, n≤N, N is the total number of subcarriers, a∈[X, Y], b∈[I, Q];

[0055] f ab (n) = F ab + nf base (2);

[0056] In formula (2), F ab is the initial frequency of the subcarrier closest to the zero frequency point, f base is the sub-carrier frequency spacing.

[0057] It can be understood that in this embodiment, four multi-carrier frequency signals with a mutually orthogonal relationship are generated, such as S XI , S XQ , S YI , S YQ The four-channel multi-carrier signal will be input into the four input ports TXI, TXQ, TYI, and TYQ of the coherent transmitter respectively. According to the design of this embodiment, corresponding to the four branches of TXI, TXQ, TYI, and TYQ, F XI 、F YI 、F XQ 、F YQ are equal to 0 and f respectively base / 4, f base / 2, 3f base / 4, it can be seen that the sub-carrier frequencies contained in the four-way multi-carrier signal are not equal to each other, and have the characteristics of being orthogonal and non-overlapping.

[0058] S202, obtaining the optical module modulation information of the current coherent transmitter, including the modulation order M, the modulation baud rate f baud And the sampling rate f DAC It can be understood that the modulation format corresponding to the modulation order M is M-QAM (Quadrature Amplitude Modulation).

[0059] S203, according to the modulation baud rate f baud Set the calibration bandwidth f cal In practical applications, the calibration bandwidth f can usually be limited cal =1.1f baud .

[0060] S204, setting the total number of sub-carrier frequencies N of the multi-carrier signal according to the modulation order M. It can be understood that the higher the modulation order, the more sensitive the crosstalk is. To ensure the measurement accuracy, this embodiment is designed to select a smaller number of sub-carrier frequencies for crosstalk measurement to improve the signal-to-noise ratio of each sub-carrier frequency. Therefore, the total number of sub-carrier frequencies N of the multi-carrier signal is designed to be set as the modulation order M changes. The specific setting formula is:

[0061] N = 256 / log2(M) (3);

[0062] S205, according to the calibration bandwidth f cal and the total number of subcarrier frequencies N to set the subcarrier frequency spacing f base Similarly, since the total number of sub-carrier frequencies N of the multi-carrier signal is set as the modulation order M changes, for a fixed calibration bandwidth, the sub-carrier frequency spacing f of the multi-carrier signal is base It is also set with the change of modulation order M. The specific setting formula is:

[0063] f base = f cal / N=1.1f baud log2(M) / 256 (4).

[0064] S206, according to the modulation baud rate f baud , the total number of subcarrier frequencies N and the sampling rate f DAC Set the amplitude of each sub-carrier frequency Amp ab (n). It is understandable that, since crosstalk between channels often occurs in the high frequency part and the high frequency energy loss of the device is serious, it is necessary to further design the amplitude of each sub-carrier in the multi-carrier to increase the strength of the multi-carrier signal at high frequency to obtain a higher signal-to-noise ratio. In specific applications, the amplitude of each sub-carrier in the multi-carrier signal can be set as follows:

[0065] Amp ab (n) = 1 + 4nf baud / N / f DAC (5).

[0066] After the above steps, the generation of the auxiliary calibration signal (i.e., a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with the frequency) is completed. In addition, according to the above generation method, a multi-carrier signal in which the sub-carrier amplitude changes with the frequency can be designed, which is suitable for the application scenario of channel crosstalk measurement of coherent optical modules with different rates and modulation formats.

[0067] For example, assuming that 16QAM format modulation is used in scenario A and the modulation rate is 45Gbaud; QPSK format modulation is used in scenario B and the modulation rate is 90Gbaud. Then, according to the above generation method, different multi-carrier frequency signals can be designed for the two scenarios. The corresponding related parameters are shown in Table 1 below, and the spectrum of the multi-carrier frequency signal is as follows: Figure 3 As shown:

[0068] Table 1

[0069]

[0070] From the multi-carrier signal design examples in the above two scenarios, we can see that: (1) Scenario A uses 16QAM modulation, and Scenario B uses QPSK modulation. Scenario A has a higher modulation format than Scenario B and is more sensitive to crosstalk. Designing a multi-carrier signal with a smaller number of carrier frequencies N can improve the signal-to-noise ratio of each carrier frequency and ensure measurement accuracy. (2) Scenario A uses a 45Gbaud modulation rate, and Scenario B uses a 90Gbaud modulation rate. Scenario B has a higher modulation rate than Scenario A. The higher the baud rate, the more serious the high-frequency bandwidth loss of the device. The design obtains that the carrier signal at the high frequency is amplified more, thereby improving the high-frequency signal-to-noise ratio and ensuring high-frequency measurement accuracy.

[0071] In addition, it can be understood that in this embodiment, after receiving the crosstalk calibration sent by the coherent receiver, the coherent transmitter will perform frequency-related crosstalk compensation based on the crosstalk calibration. Different from the prior art, the crosstalk compensation method adopted in this embodiment is: the crosstalk compensation coefficient is obtained by measuring the frequency-related crosstalk value (i.e., the crosstalk calibration sent by the coherent receiver), and the compensation depth can be adaptively adjusted according to the modulation rate and modulation format of the coherent optical module, and the compensation depth is reduced for high-order modulation and high-baud signals, thereby solving the problem of increased PAPR (Peak to Average Ratio) and reduced signal-to-noise ratio of the transmitted signal caused by anti-compensation, and effectively improving the crosstalk compensation effect.

[0072] Further, as an optional implementation, in step A2 of this embodiment, the coherent transmitter performs frequency-related crosstalk compensation based on crosstalk calibration, including: using a preset static MIMO equalizer to perform frequency-related crosstalk compensation on the service signal, the preset static MIMO equalizer is provided with two groups, which are used for crosstalk compensation of X polarization and Y polarization respectively; each group of static MIMO equalizers is a 2×2 real MIMO equalizer, and the equalizer coefficients are obtained according to the crosstalk calibration sent by the coherent receiver; and the compensation depth is adaptively adjusted according to the modulation baud rate and modulation format, and the compensation depth is reduced for high-order modulation and high baud signals.

[0073] For example, see Figure 4 As shown, Figure 4 FIG. 4 is a schematic diagram of performing crosstalk compensation on X polarization using the crosstalk compensation method of this embodiment. Figure 4 As shown in , the preset static MIMO equalizer is set after the static filter equalizer of the coherent transmitter DSP, that is, after the service signal is QAM modulated and up-sampled in the coherent transmitter, and undergoes frequency deviation shaping, inter-channel delay compensation, dispersion pre-compensation and other conventional DSP processing in the static equalizer, it will pass through the preset static MIMO equalizer to perform frequency-related crosstalk compensation, and then enter the iFFT module and resampling module. Figure 4 As shown, the preset static MIMO equalizer consists of a 2×2 real MIMO equalizer, and the equalizer coefficients are obtained according to the crosstalk calibration sent by the coherent receiver (i.e., the measured frequency-related crosstalk angle). Specifically, the calculation formulas are shown in equations (6) and (7):

[0074] TXI_c(f)=TXI(f)Cos(β2(f))-ATXQ(f)Sin(β1(f)) (6);

[0075] TXQ_c(f)=TXQ(f)Cos(β1(f))-ATXI(f)Sin(β2(f)) (7);

[0076] Wherein, TXI_c(f) and TXQ_c(f) are the service signals to be transmitted in the I-channel and Q-channel channels of the coherent transmitter that are compensated according to the crosstalk calibration value, TXI(f) and TXQ(f) are the original service signals to be transmitted in the I-channel and Q-channel channels of the coherent transmitter that are not compensated, (f) represents that the compensation is processed in the frequency domain, β1(f) is the crosstalk angle value related to the frequency of the Q-channel to the I-channel sent by the coherent receiver, and β2(f) is the crosstalk angle value related to the frequency of the I-channel to the Q-channel sent by the coherent receiver; TXQ(f)Sin(β1( f)) is the Q-to-I crosstalk signal calculated based on the crosstalk calibration angle value, TXI(f)Cos(β2(f)) represents the transmitted signal of each frequency point on I-channel after the I-channel signal crosstalks to the Q-channel signal according to the energy conservation, TXI(f)Sin(β2(f)) is the I-to-Q crosstalk signal calculated based on the crosstalk calibration angle value, TXQ(f)Cos(β1(f)) represents the transmitted signal of each frequency point on Q-channel after the Q-channel signal crosstalks to the I-channel signal according to the energy conservation, A is the compensation depth coefficient, and its expression is:

[0077] A=f DAC / (2f baud ) / (log2(M) / 2)=f DAC / f baud / log2(M) (8).

[0078] The preset static MIMO equalizer uses calculations such as equations (6) and (7) to achieve frequency-related crosstalk compensation between channels; and equation (8) is used to design the channel crosstalk compensation depth, adaptively adjust the compensation depth, and reduce the compensation depth for high-order modulation and high-baud signals, thereby solving the problem of increased PAPR and reduced signal-to-noise ratio of the transmitted signal caused by anti-compensation, and effectively improving the crosstalk compensation effect.

[0079] Embodiment 2

[0080] Based on the same inventive concept, an embodiment of the present invention also provides a method for calibrating crosstalk between channels of a coherent transceiver. Figure 5 , Figure 5 FIG. 2 is a flow chart of a second embodiment of a method for calibrating crosstalk between channels of a coherent transceiver according to the present application. Figure 5 As shown, a method for calibrating crosstalk between channels of a coherent transceiver includes:

[0081] Step B1, a coherent receiver receives an auxiliary calibration signal sent by a coherent transmitter loaded on four channels; the auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with increasing frequency;

[0082] Step B2: the coherent receiver performs frequency-dependent crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal, obtains crosstalk calibration, and sends it to the coherent transmitter; the crosstalk calibration is used by the transmitter to perform frequency-dependent crosstalk compensation based on the crosstalk calibration;

[0083] Step B3: The coherent receiver receives the calibration service signal after the coherent transmitter performs crosstalk compensation, and performs equalization demodulation on the calibration service signal.

[0084] It can be understood that in this embodiment, the coherent receiver performs frequency-related crosstalk measurement based on crosstalk angle reconstruction on the four received signals loaded with auxiliary calibration signals in the digital domain, thereby obtaining crosstalk calibration. This crosstalk measurement based on crosstalk angle reconstruction is a frequency-related crosstalk measurement method that uses crosstalk-free signal reconstruction plus frequency-point crosstalk angle search, which can achieve large-scale, high-precision, and low-complexity calibration of frequency-related crosstalk between IQ channels of a coherent transceiver.

[0085] Further, see Figure 6 As shown, as an optional implementation manner, in step B2 of this embodiment, the coherent receiver performs frequency-dependent crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal to obtain crosstalk calibration, including:

[0086] S601. Reconstruct the crosstalk-free signal of the preprocessed auxiliary calibration signal by introducing a frequency-related phase extraction factor α(fn); wherein α(fn) is used to extract the phase deviation caused by the crosstalk between channels and the laser phase rotation, and thereby reconstruct the crosstalk-free signal.

[0087] It can be understood that after the auxiliary calibration signal is transmitted to the coherent receiver via the optical fiber link, the coherent receiver will perform detection and obtain four RF signals RXI, RXQ, RYI, and RYQ from four input ports respectively; and will perform pre-processing such as frequency offset estimation and frequency offset compensation on the received signal in the digital signal processing DSP module.

[0088] For example, taking the channel crosstalk between RXI and RXQ as an example, before the crosstalk measurement, the coherent receiver first performs frequency offset estimation and frequency offset compensation preprocessing on RXI and RXQ. Considering the residual laser phase noise effect and the amplitude frequency response of the transceiver, the two preprocessed signals can be expressed as:

[0089]

[0090] Among them, μ(f) and γ(f) represent the frequency-related crosstalk of the coherent transmitter and the coherent receiver, respectively. According to the law of conservation of energy, the inter-channel crosstalk at different fn frequencies is regarded as the rotation angles μ(f) and γ(f); θ represents the azimuth angle introduced by the laser phase rotation. It represents the amplitude-phase-frequency response of the transmission channel in a non-coherent optical communication system when there is a laser frequency offset.

[0091] As shown in formula (9), due to the transceiver channel crosstalk and laser phase rotation effect, the RXI and RXQ signals of the coherent receiver will simultaneously contain the TXI and TXQ transmission signals of the coherent transmitter, and the two are mixed with each other. Based on the power conservation formula of frequency-dependent crosstalk, the transceiver crosstalk rotation angle and the laser phase are combined into one item in the model, making it difficult to separate the crosstalk independently.

[0092] In order to solve the problem that crosstalk is difficult to separate from the laser phase and measure separately, this embodiment specifically introduces a frequency-related phase extraction factor α(fn) to extract the phase deviation caused by the crosstalk between channels and the laser phase rotation, and reconstruct the crosstalk-free signal. For example, the reconstructed crosstalk-free signal can be written as formula (10):

[0093]

[0094] Since the transmit signals TXI and TXQ are orthogonal to each other in the frequency domain, as shown in the lower part of equation (10), the reconstructed crosstalk-free signal is further written as a function of the transmit end signals TXI and TXQ, and does not contain the cross terms between the two. I and M Q are functions of α(fn), θ, μ(f), and γ(f).

[0095] S602 , selecting n=1, . . . N frequency points, scanning α(fn) in the range of [0, 2π], and obtaining a strength curve of the subcarrier frequency signal at the nth frequency point of the reconstructed signal.

[0096] Specifically, in practical applications, the frequency point fn is fixed, and the phase extraction factor α(fn) is scanned in the range of [0,2π] to obtain the intensity curve corresponding to the nth subcarrier signal as shown in formula (11):

[0097]

[0098] S603, obtain the phase extraction factor corresponding to the intensity extreme point, denoted as α max (fn); and the α max (fn) is the sum of the crosstalk angle and the laser phase at that frequency, where the laser phase is a constant.

[0099] It can be understood that when Amp_Rx(α(fn)) in equation (11) is maximized, the M corresponding to the nth subcarrier signal at frequency point fn is I and M Q Reach the extreme value of strength, as shown in formula (12):

[0100]

[0101] At this intensity extreme point, the corresponding phase extraction factor α is obtained max (fn), the α max The phase deviation caused by (fn) and the crosstalk between channels and the laser phase rotation satisfies the relationship (13):

[0102] α max1 (fn) = θ + γ (f XI,n )+μ(f XI,n ), α max2 (fn) = θ + γ (f XQ,n )+μ(f XQ,n ) (13).

[0103] S604, sequentially adjust the α at the n=2,…Nth frequency points max (fn), minus α at the first frequency max (f1), eliminate the influence of the laser phase constant, calculate the crosstalk angle of the sub-carrier signal at the nth frequency point, and calculate the corresponding crosstalk value based on the crosstalk angle.

[0104] It can be understood that in practical applications, since the phase azimuth angle θ introduced by the laser in equation (13) can be regarded as a constant within the measurement time and is restored by the equalizer in the DSP of the receiver, the phase extraction factor α at the first frequency point f1 can be max1 (f1), α max2 (f1) is regarded as a reference value, and the phase extraction factor α at other subcarrier frequencies is used max1 (fn), α max2 Subtracting the reference value from (fn) can obtain the crosstalk angles β1 and β2 at different frequencies. The specific calculation formulas are shown in equations (14) and (15):

[0105] β1(f1) = α max1 (f1), β2(f1) = α max2 (f1) (14);

[0106] β1(fn) = α max1 (fn)-α max1 (f1), β2(fn) = α max2 (fn)-α max2 (f1) (15).

[0107] See also Figure 7 As shown, Figure 7 α is the intensity extreme point corresponding to different frequency points max Schematic diagram of the relationship between (fn) and crosstalk. Figure 7 As shown in FIG. 1 , when there is no frequency-dependent crosstalk at the nth frequency point, the α corresponding to the extreme point of the intensity curve calculated in step S603 is max (fn) and α at the first frequency point max (f1) overlaps, when there is frequency-dependent crosstalk at the nth frequency point, the α corresponding to the extreme point of the intensity curve calculated in step S603 max (fn) and α at the first frequency point max (f1) do not overlap, and the angle of difference is the crosstalk angle.

[0108] Afterwards, the corresponding crosstalk value can be calculated by the obtained crosstalk angle, thereby realizing frequency-dependent crosstalk calibration within the full bandwidth. For example, the crosstalk value calculation formula is as follows:

[0109] XT TRx_IQ (fn)=Sin(β1(fn) / Cos(β2(fn)) (16);

[0110] XT TRx_QI (fn)=Sin(β2(fn)) / Cos(β1(fn)) (17);

[0111] Among them, XT TRx_IQ (fn) represents the crosstalk value of XQ channel to XI channel, XT TRx_QI (fn) represents the crosstalk value of the XI channel to the XQ channel.

[0112] Further, see Figure 8 As shown, as an optional implementation, in step B3 of this embodiment, during the equalization demodulation process of the coherent receiver, a 2×2 complex MIMO equalizer is used to perform polarization demultiplexing equalization, which is different from the inter-channel crosstalk compensation generalized equalizer of the coherent receiver in the prior art and has the characteristic of lower complexity.

[0113] Specifically, see Figure 8 As shown, in the coherent receiver DSP, this embodiment uses a conventional DSP to perform equalization and demodulation on the received signal, that is, different from the generalized equalizer for inter-channel crosstalk compensation at the receiving end, only one 2×2 complex MIMO equalizer is used for polarization demultiplexing equalization after clock recovery, frequency offset recovery, and static equalization. Therefore, only 4 complex equalizers (equivalent to 8 real equalizers) are needed to realize signal demodulation, plus the 8 static real equalizers of the coherent transmitter (two polarizations, one 2×2 real MIMO equalizer for each polarization), a total of 16 real equalizers. Although the generalized equalizer can also realize inter-channel crosstalk compensation, it is necessary to input the received signal and its conjugate signal (conj() represents conjugation) into the 4×4 complex MIMO equalizer for processing in the coherent receiver, as shown in FIG. Fig. 9 As shown, the complexity is relatively high, requiring 16 complex equalizers, equivalent to 32 real equalizers, which is twice as complex as the present solution. The complexity comparison between the crosstalk compensation solution of the present embodiment and the crosstalk compensation solution of the generalized MIMO equalizer is shown in Table 2 below.

[0114] Table 2

[0115]

[0116] In order to better understand the calibration method of the coherent transceiver channel crosstalk in the present invention, the specific contents of the calibration method of the present invention are described below with reference to the contents of the first and second embodiments and the accompanying drawings.

[0117] See also Fig.10 As shown, a method for calibrating crosstalk between channels of a coherent transceiver specifically includes the following process:

[0118] Step S101, generating an auxiliary calibration signal in a coherent transmitter, the auxiliary calibration signal is a multi-carrier signal with orthogonal channels and sub-carrier amplitude increasing with increasing frequency, so as to be applicable to the crosstalk calibration between channels of optical modules with different rates and modulation formats, and its spectrum is as follows: Fig.11 The specific process of generating the auxiliary calibration signal is as described in the corresponding content of the first embodiment, which will not be repeated here.

[0119] Step S102: The coherent transmitter loads the generated auxiliary calibration signal onto the four channels XI, XQ, YI, and YQ of the coherent transmitter, performs photoelectric modulation, and obtains a frequency domain orthogonal multi-carrier signal at the output of the coherent transmitter, whose spectrum is as follows: Fig.11 -(b). Fig.11 -(b), due to the influence of the device bandwidth, the high-frequency power of the multi-carrier signal, whose sub-carrier amplitude (power) increases with the increase of frequency, may be attenuated. The example in the figure shows that the power is attenuated until the power of each frequency point is the same; at the same time, due to the crosstalk between channels, the sub-carrier components that were originally orthogonal between channels leak into the adjacent channels.

[0120] Step S103: The output multi-carrier signal is transmitted in an optical fiber link. The spectrum of the signal is affected by optical fiber effects such as polarization rotation. Fig.11 As shown in (c), due to the influence of polarization rotation and laser phase noise, the sub-carrier components that were originally orthogonal between channels further leak into adjacent channels and overlap with the channel crosstalk of the transmitter, making it difficult to directly extract and measure.

[0121] Step S104: The coherent receiver performs coherent detection on the transmitted polarization multiplexed QAM signal, and obtains four-channel multi-carrier frequency signals (i.e., four-channel digital domain received signals) of XI, XQ, YI, and YQ through an analog-to-digital converter. The spectrum thereof is as follows: Fig.11 As shown in (d), due to the crosstalk between receiver channels, the subcarrier components that were originally orthogonal between channels are further leaked to adjacent channels and overlap with the crosstalk between channels and the crosstalk caused by the phase rotation of the optical field at the transmitter, making it difficult to directly extract and measure.

[0122] Step S105: The coherent receiver performs frequency-dependent crosstalk measurement based on crosstalk angle reconstruction on the four-channel multi-carrier signal to obtain crosstalk calibration, and sends it to the coherent transmitter. In this step, by adopting the crosstalk measurement method based on crosstalk angle reconstruction, a large-scale, high-precision, low-complexity measurement and calibration of frequency-dependent crosstalk between IQ channels of the coherent transceiver can be achieved. The specific frequency-dependent crosstalk measurement process based on crosstalk angle reconstruction is described in the corresponding content of Example 2, which will not be repeated here.

[0123] Step S106, the coherent transmitter receives the crosstalk calibration sent by the coherent receiver, performs frequency-related crosstalk compensation based on the crosstalk calibration, and sends the compensated calibration service signal to the coherent receiver. In this step, after receiving the crosstalk calibration sent by the coherent receiver, the coherent transmitter performs frequency-related crosstalk compensation based on the crosstalk calibration to calibrate the frequency-related crosstalk between channels. The specific crosstalk compensation process is described in the corresponding content of Example 1, which will not be repeated here.

[0124] Step S107: After receiving the calibration service signal after crosstalk compensation, the coherent receiver performs conventional equalization demodulation on the calibration service signal.

[0125] Embodiment 3

[0126] Based on the same inventive concept, an embodiment of the present invention further provides a coherent transmitter based on the calibration method of the above embodiment 1. Fig.12 As shown, the coherent transmitter includes: an auxiliary calibration signal sending unit and a calibration service signal sending unit.

[0127] Among them, the auxiliary calibration signal sending unit is used to: load the generated auxiliary calibration signal on the four channels of the coherent transmitter and send it to the coherent receiver; wherein the generated auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with increasing frequency.

[0128] The calibration service signal sending unit is used to: receive the crosstalk calibration sent by the coherent receiver, perform frequency-related crosstalk compensation based on the crosstalk calibration, and send the compensated calibration service signal to the coherent receiver; wherein the crosstalk calibration is the crosstalk value obtained by the coherent receiver through frequency-related crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal.

[0129] It should also be noted that the various variations and other specific examples in the aforementioned coherent transceiver channel crosstalk calibration method embodiment are also applicable to the coherent transmitter of this embodiment. Through the detailed description of the aforementioned method, those skilled in the art can clearly understand the implementation method of the coherent transmitter in this embodiment, so for the sake of brevity of the specification, it will not be described in detail here.

[0130] Embodiment 4

[0131] Based on the same inventive concept, the embodiment of the present invention further provides a coherent receiver based on the calibration method of the above-mentioned embodiment 2. Fig.12 As shown, the coherent receiver includes: a crosstalk calibration unit and a service signal demodulation unit.

[0132] Among them, the crosstalk calibration unit is used to: receive the auxiliary calibration signal sent by the coherent transmitter loaded on the four channels, the auxiliary calibration signal is a multi-carrier signal with mutually orthogonal channels and the sub-carrier amplitude increasing with the increase of frequency; and, according to the auxiliary calibration signal, perform frequency-related crosstalk measurement based on crosstalk angle reconstruction to obtain crosstalk calibration, and send it to the coherent transmitter; wherein, the crosstalk calibration is used for the transmitter to perform frequency-related crosstalk compensation based on the crosstalk calibration.

[0133] The service signal demodulation unit is used to receive the calibration service signal after the coherent transmitter performs crosstalk compensation, and perform equalization demodulation on the calibration service signal.

[0134] It should also be noted that the various variations and other specific examples in the aforementioned coherent transceiver channel crosstalk calibration method embodiment are also applicable to the coherent receiver of this embodiment. Through the detailed description of the aforementioned method, those skilled in the art can clearly understand the implementation method of the coherent receiver in this embodiment. Therefore, for the sake of brevity of the specification, it will not be described in detail here.

[0135] Embodiment 5

[0136] See also Fig.12 As shown, based on the same inventive concept, an embodiment of the present invention further provides a calibration system for crosstalk between channels of a coherent transceiver, and the calibration system includes the coherent transmitter of the above-mentioned embodiment three and the coherent receiver of the above-mentioned embodiment four.

[0137] Note: The serial numbers of the above embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0138] The terms "including" and "having" and any variations thereof in the specification and claims of the present application and the above drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units that are inherent to these processes, methods, products or devices.

[0139] In the description of the embodiments of the present application, "exemplary", "for example" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary", "for example" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary", "for example" or "for example" is intended to present related concepts in a specific way.

[0140] The advantages, strengths, effects, etc. mentioned in the embodiments of the present invention are only examples, not limitations, and it cannot be considered that these advantages, strengths, effects, etc. must be possessed by each embodiment of the present invention. In addition, the above specific details disclosed in the embodiments of the present invention are only for the purpose of illustration and facilitating understanding, not limitation, and the above details do not limit the embodiments of the present invention to be implemented by adopting the above specific details.

[0141] The block diagrams of the devices, apparatuses, equipment, and systems involved in the embodiments of the present invention are only illustrative examples, and are not intended to require or imply that they must be connected, arranged, and configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these devices, apparatuses, equipment, and systems can be connected, arranged, and configured in any manner. The words "or" and "and" used in the embodiments of the present invention refer to the words "and / or" and can be used interchangeably therewith, unless the context clearly indicates otherwise. The words "such as" used in the embodiments of the present invention refer to the phrase "such as but not limited to" and can be used interchangeably therewith. The terms "first", "second", and "third" are described to distinguish different objects, etc., and do not represent a sequence, nor do they limit "first", "second", and "third" to be different types.

[0142] Each operation in the embodiment of the present invention may be performed by any appropriate means capable of performing the corresponding functions, which may include various hardware and / or software components and / or modules, including but not limited to hardware circuits or processors.

[0143] The method of the embodiment of the present invention includes one or more actions for implementing the above-mentioned method. The method and / or action can be interchangeable with each other without departing from the scope of the claims. In other words, unless a specific order of actions is specified, the order and / or use of specific actions can be modified without departing from the scope of the claims.

[0144] Various changes, substitutions and modifications of the techniques described herein may be made by those skilled in the art without departing from the teachings defined by the appended claims. In addition, the scope of the claims of the present disclosure is not limited to the specific aspects of the processes, machines, manufactures, components of events, means, methods and actions described above. Currently existing or later to be developed processes, machines, manufactures, components of events, means, methods or actions that perform substantially the same functions or achieve substantially the same results as the corresponding aspects described herein may be utilized. Thus, the appended claims include such processes, machines, manufactures, components of events, means, methods or actions within their scope.

[0145] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present invention. Therefore, the present invention is not intended to be limited to the aspects shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

[0146] The above description has been given for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments of the present invention to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions and sub-combinations thereof. And the content not described in detail in this specification belongs to the prior art known to those skilled in the art.

Claims

1. A method for calibrating crosstalk between coherent transceiver channels, characterized in that: The method includes: The coherent transmitter loads the generated auxiliary calibration signal onto the four channels of the coherent transmitter and transmits it to the coherent receiver; wherein the generated auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with the increase of frequency; The coherent transmitter receives the crosstalk calibration sent by the coherent receiver, performs frequency-related crosstalk compensation based on the crosstalk calibration, and sends the compensated calibration service signal to the coherent receiver; wherein the crosstalk calibration is the crosstalk value obtained by the coherent receiver through frequency-related crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal.

2. The method for calibrating crosstalk between channels of a coherent transceiver as claimed in claim 1, characterized in that: The generation of the auxiliary calibration signal comprises: Generate four multi-carrier frequency signals with mutually orthogonal relationship; Obtain the optical module modulation information of the coherent transmitter, including the modulation order, modulation baud rate and sampling rate; Set the calibration bandwidth according to the modulation baud rate; Setting the total number of sub-carrier frequencies of the multi-carrier signal according to the modulation order; Set the subcarrier frequency interval according to the calibration bandwidth and the total number of subcarrier frequencies; The amplitude of each subcarrier is set according to the modulation baud rate, the total number of subcarriers and the sampling rate.

3. The method for calibrating crosstalk between channels of a coherent transceiver as claimed in claim 1, characterized in that: When the coherent transmitter performs frequency-related crosstalk compensation, the following method is adopted: the crosstalk compensation coefficient is obtained by the crosstalk calibration sent by the coherent receiver, and the compensation depth is adaptively adjusted according to the modulation baud rate and modulation format, and the compensation depth is reduced for high-order modulation and high baud signals.

4. The method for calibrating crosstalk between channels of a coherent transceiver as claimed in claim 3, characterized in that: The coherent transmitter uses a preset static MIMO equalizer to perform frequency-related crosstalk compensation; the preset static MIMO equalizer is provided with two groups, which are used for crosstalk compensation of X polarization and Y polarization respectively; Each static MIMO equalizer is a 2×2 real MIMO equalizer. The equalizer coefficients are obtained according to the crosstalk calibration sent by the coherent receiver, and the compensation depth is adaptively adjusted according to the modulation baud rate and modulation format, and the compensation depth is reduced for high-order modulation and high-baud signals.

5. A method for calibrating crosstalk between coherent transceiver channels, characterized in that: The method includes: The coherent receiver receives the auxiliary calibration signal sent by the coherent transmitter loaded on four channels; wherein the auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with the increase of frequency; The coherent receiver performs frequency-related crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal, obtains crosstalk calibration, and sends it to the coherent transmitter; wherein the crosstalk calibration is used for the transmitter to perform frequency-related crosstalk compensation based on the crosstalk calibration; The coherent receiver receives the calibration service signal after the coherent transmitter performs crosstalk compensation, and performs equalization and demodulation on the calibration service signal.

6. The method for calibrating crosstalk between channels of a coherent transceiver as claimed in claim 5, characterized in that: The coherent receiver performs frequency-related crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal to obtain crosstalk calibration, including: By introducing the frequency-dependent phase extraction factor α(fn), the preprocessed auxiliary calibration signal is reconstructed into a crosstalk-free signal; wherein α(fn) is used to extract the phase deviation caused by the crosstalk between channels and the phase rotation of the laser, and thereby reconstruct the crosstalk-free signal; Select n=1,…N frequency points, scan α(fn) in the range of [0,2π], and obtain the intensity curve of the subcarrier signal at the nth frequency point of the reconstructed signal; wherein N is the total number of subcarriers of the multi-carrier signal; Get the phase extraction factor corresponding to the intensity extreme point, denoted as α max (fn), and the α max (fn) is the sum of the crosstalk angle and the laser phase at this frequency, where the laser phase is a constant; Sequentially change the α at the n=2,…N frequency points max (fn), minus α at the first frequency max (f1), calculating and obtaining a crosstalk angle of a sub-carrier frequency signal at an nth frequency point, and obtaining a corresponding crosstalk value according to the crosstalk angle.

7. The method for calibrating crosstalk between channels of a coherent transceiver as claimed in claim 5, characterized in that: When the coherent receiver performs equalization and demodulation on the calibration service signal, a 2×2 complex MIMO equalizer is used to perform polarization demultiplexing equalization.

8. A coherent transmitter based on the method according to any one of claims 1 to 4, characterized in that: The coherent transmitter includes an auxiliary calibration signal sending unit and a calibration service signal sending unit; The auxiliary calibration signal sending unit is used to: load the generated auxiliary calibration signal on the four channels of the coherent transmitter and send it to the coherent receiver; wherein the generated auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with the increase of frequency; The calibration service signal sending unit is used to: receive the crosstalk calibration sent by the coherent receiver, perform frequency-related crosstalk compensation based on the crosstalk calibration, and send the compensated calibration service signal to the coherent receiver; wherein the crosstalk calibration is the crosstalk value obtained by the coherent receiver through frequency-related crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal.

9. A coherent receiver based on the method according to any one of claims 5 to 7, characterized in that: The coherent receiver includes a crosstalk calibration unit and a service signal demodulation unit; The crosstalk calibration unit is used to: receive an auxiliary calibration signal sent by a coherent transmitter loaded on four channels, wherein the auxiliary calibration signal is a multi-carrier signal in which the channels are mutually orthogonal and the sub-carrier amplitude increases with the increase of frequency; and, according to the auxiliary calibration signal, perform frequency-related crosstalk measurement based on crosstalk angle reconstruction to obtain crosstalk calibration, and send it to the coherent transmitter; wherein the crosstalk calibration is used for the transmitter to perform frequency-related crosstalk compensation based on the crosstalk calibration; The service signal demodulation unit is used to receive the calibration service signal after the coherent transmitter performs crosstalk compensation, and perform equalization demodulation on the calibration service signal.

10. A calibration system for crosstalk between coherent transceiver channels, characterized in that: The system comprises the coherent transmitter as claimed in claim 8 and the coherent receiver as claimed in claim 9.

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