Method for calibrating crosstalk between channels of coherent transmitter and receiver, apparatus, and system

Abstract

The present invention relates to the technical field of optical communication. Disclosed are a method for calibrating crosstalk between channels of a coherent transmitter and receiver, an apparatus, and a system. The method comprises: a coherent transmitter loads generated auxiliary calibration signals on four channels of the coherent transmitter and sends same to a coherent receiver, the generated auxiliary calibration signals being multi-carrier signals which are orthogonal to one another between channels and the subcarrier frequency amplitudes of which increase as frequency increases; and the coherent transmitter receives crosstalk calibration issued by the coherent receiver, performs frequency-dependent crosstalk compensation on the basis of the crosstalk calibration, and sends a compensated calibration service signal to the coherent receiver, the crosstalk calibration being a crosstalk value obtained by the coherent receiver performing crosstalk angle reconstruction-based frequency-dependent crosstalk measurement on the basis of the auxiliary calibration signals. The present invention can solve the technical problems that the existing inter-channel crosstalk calibration technology has high complexity and poor accuracy and cannot be applied to coherent optical modules having different rates and modulation formats, and meets actual application requirements.

Description

Method, device and system for calibrating inter-channel crosstalk of coherent transceiver TECHNICAL FIELD

[0001] The present application relates to the field of optical communication technology, in particular to a method, device and system for calibrating inter-channel crosstalk of a coherent transceiver. BACKGROUND

[0002] With the rapid deployment and promotion 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, the current high-speed coherent transceiver can achieve a bandwidth of up to 70-100GHz or more, and support 400Gbps to Tbps high-speed signal modulation and demodulation. However, although integrated packaging helps to alleviate the connection loss between discrete components and helps to increase the overall module bandwidth, the reduction of optical / electrical circuit trace distance and the compactness of the module size 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 the current channel leaks and is superimposed on the adjacent channel, which destroys the original orthogonal characteristics of the four-channel DP-IQ modulation and causes crosstalk. In addition, since the radio frequency signal loss along the transmission line is frequency-dependent, the inter-channel interference also exhibits frequency-dependent characteristics. With the increase of bandwidth, the inter-channel crosstalk of large bandwidth chips may even increase from -40dB to -15dB. Such frequency-dependent crosstalk is difficult to compensate for by traditional DSP (Digital Signal Processing) technology. Therefore, in order to improve the performance of high-speed optical transmission, a large range and high sensitivity inter-channel crosstalk calibration is needed 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 cannot be applied to phase modulation demodulation coherent transceivers, and the cost is high. 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 the DP-IQ channels. This solution avoids the use of high-cost instruments, but the complexity is more than twice that of the traditional MIMO equalizer. And the compensation performance of the generalized MIMO equalizer depends largely on the convergence accuracy of the equalizer. In the presence of severe DP-IQ crosstalk or severe frequency-dependent crosstalk or other transceiver impairments, the performance of the equalizer may be greatly reduced, resulting in inaccurate compensation of the crosstalk between the channels.

[0004] In addition, there have been some studies on the calibration of frequency-dependent impairments of coherent transceivers, such as channel delay, channel bandwidth response, etc. using multi-tone signals, and such schemes have the characteristics of low complexity and high accuracy, but due to the mutual influence of channel crosstalk and frequency offset phase noise in fiber transmission systems, the energy of the multi-tone signal is overlapped multiple times between the DP-IQ branches, making it difficult to demodulate the multi-tone signal and calibrate the crosstalk. Therefore, there is no related multi-tone modulation and demodulation scheme that can solve the channel crosstalk calibration caused by channel energy leakage. At the same time, the existing multi-tone signal-based calibration schemes for impairments other than crosstalk usually use multi-tone signals with equal power at each frequency point, which may have precision loss in the calibration of high-frequency crosstalk, and thus are not suitable for calibration of modules with different bandwidths and modulation formats. SUMMARY

[0005] The present application aims to provide a coherent transceiver inter-channel crosstalk calibration method, device and system for high-precision measurement and compensation of frequency-dependent crosstalk between adjacent channels of a coherent transceiver, solving the technical problems of high complexity, poor precision and inability to be applied to different rate and modulation format coherent optical modules of existing inter-channel crosstalk calibration techniques, and meeting the actual application requirements.

[0006] To achieve the above purpose, in a first aspect, the embodiments of the present application provide a coherent transceiver inter-channel crosstalk calibration method, which comprises:

[0007] 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 that is orthogonal to each other between channels and has a sub-carrier frequency amplitude that increases with frequency.

[0008] The coherent transmitter receives the crosstalk calibration sent 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 the coherent receiver performing frequency-dependent crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal.

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

[0010] Four mutually orthogonal multi-carrier signals are generated; optical module modulation information of the coherent transmitter is obtained, including modulation order, modulation baud rate and sampling rate; a calibration bandwidth is set according to the modulation baud rate; the total number of sub-carrier frequencies of the multi-carrier signal is set according to the modulation order; a sub-carrier frequency interval is set according to the calibration bandwidth and the total number of sub-carrier frequencies; and the amplitude of each sub-carrier frequency is set according to the modulation baud rate, the total number of sub-carrier frequencies and the sampling rate.

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

[0012] In combination with the first aspect, in an implementation, the coherent transmitter performs frequency-dependent crosstalk compensation using a preset static MIMO equalizer; the preset static MIMO equalizer is provided with two groups, respectively used for crosstalk compensation of X polarization and Y polarization; each group of static MIMO equalizers is a 2x2 real number MIMO equalizer, the equalizer coefficient is obtained from the crosstalk calibration sent by the coherent receiver, and the compensation depth is adaptively adjusted according to the modulation baud rate and the modulation format, and the compensation depth is reduced for high-order modulation and high-baud signals.

[0013] The second aspect, the embodiment of the present application also provides a kind of calibration method of coherent transceiver inter-channel crosstalk, which comprises:

[0014] The coherent receiver receives the auxiliary calibration signal sent by the coherent transmitter on four channels; wherein the auxiliary calibration signal is a multi-carrier signal that is mutually orthogonal between channels and has sub-carrier frequency amplitude increasing with frequency.

[0015] 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; wherein the crosstalk calibration is used by the transmitter to perform frequency-dependent crosstalk compensation based on the crosstalk calibration.

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

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

[0018] By introducing a frequency-dependent phase extraction factor α(fn), the preprocessed auxiliary calibration signal is reconstructed into a crosstalk-free signal; where α(fn) is used to extract inter-channel crosstalk and phase deviation caused by laser phase rotation, and to reconstruct a crosstalk-free signal accordingly.

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

[0020] Obtain the phase extraction factor corresponding to the intensity extremum 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;

[0021] The α values ​​at the nth frequency points (n=2, ..., N) are sequentially... max (fn), minus α at the first frequency point max (f1) calculates the crosstalk angle of the subcarrier signal at the nth frequency point, and calculates the corresponding crosstalk value based on the crosstalk angle.

[0022] In conjunction with the second aspect, in one implementation, during the equalization and demodulation of the calibration service signal by the coherent receiver, a 2×2 complex MIMO equalizer is used for polarization demultiplexing equalization.

[0023] Thirdly, embodiments of the present invention also provide a coherent transmitter based on the method in the first aspect embodiment, the coherent transmitter including an auxiliary calibration signal transmission unit and a calibration service signal transmission unit;

[0024] The auxiliary calibration signal transmission unit is used to: load the generated auxiliary calibration signal onto the four channels of the coherent transmitter and transmit it to the coherent receiver; wherein, the generated auxiliary calibration signal is a multi-carrier signal that is mutually orthogonal between channels and whose sub-carrier frequency amplitude increases with frequency.

[0025] The calibration service signal transmission unit is used to: receive 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, the embodiments of the present application further provide a coherent receiver based on the method in the second aspect, which comprises a crosstalk calibration unit and a service signal demodulation unit.

[0027] The crosstalk calibration unit is configured to receive an auxiliary calibration signal sent by the coherent transmitter on four channels, the auxiliary calibration signal being a multi-carrier signal with inter-channel orthogonality and sub-carrier frequency amplitude increasing with frequency, and to perform frequency-dependent crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal to obtain crosstalk calibration and send the crosstalk calibration to the coherent transmitter, wherein the crosstalk calibration is used by the coherent transmitter to perform frequency-dependent crosstalk compensation.

[0028] The service signal demodulation unit is configured to receive the calibrated service signal after crosstalk compensation by the coherent transmitter and to perform equalization demodulation on the calibrated service signal.

[0029] In a fifth aspect, the embodiments of the present application further provide a crosstalk calibration system between channels of a coherent transceiver, which comprises the coherent transmitter in the third aspect and the coherent receiver in the fourth aspect.

[0030] The technical solutions provided by the embodiments of the present application have the following beneficial effects:

[0031] In the embodiments, the coherent transmitter generates an auxiliary calibration signal, which is a multi-carrier signal with inter-channel orthogonality and sub-carrier frequency amplitude increasing with frequency, and can be applied to different application scenarios of channel crosstalk measurement of different coherent optical modules. Meanwhile, frequency-dependent crosstalk measurement based on crosstalk angle reconstruction is performed in the coherent receiver, which can realize wide-range, high-precision and low-complexity measurement and calibration of frequency-dependent crosstalk between adjacent channels of the coherent transceiver. Finally, low-complexity frequency-dependent crosstalk compensation is performed in the coherent transmitter based on the measurement and calibration, so as to realize the calibration of the frequency-dependent crosstalk between channels, thereby solving the technical problems of high complexity, poor precision and inapplicability to different rate and modulation format coherent optical modules of the existing channel crosstalk calibration technology, and meeting the actual application requirements. BRIEF DESCRIPTION OF DRAWINGS

[0032] FIG. 1 is a flowchart of a first embodiment of a crosstalk calibration method of a coherent transceiver according to the present application;

[0033] FIG. 2 is a specific flowchart of generating an auxiliary calibration signal according to the present application;

[0034] FIG. 3 is a schematic diagram of a multi-carrier signal spectrum in different scenarios in an example;

[0035] FIG. 4 is a schematic diagram of crosstalk compensation for X polarization by using the crosstalk compensation method of the present embodiment in an example;

[0036] Figure 5 is a flow diagram of a second embodiment of the method for calibrating inter-channel crosstalk of a coherent transceiver according to the present application;

[0037] Figure 6 is a detailed flow diagram of the method for measuring crosstalk according to the present application;

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

[0039] Figure 8 is a diagram of the method for performing regular equalization demodulation on the received signal in a coherent receiver according to the present application;

[0040] Figure 9 is a diagram of the method for compensating crosstalk by using a generalized MIMO equalizer in a coherent receiver according to the prior art;

[0041] Figure 10 is a flow diagram of the method for calibrating inter-channel crosstalk of a coherent transceiver according to the present application in an example;

[0042] Figure 11 is a diagram of the spectrum of a multi-carrier signal in different transmission processes in an example;

[0043] Figure 12 is a diagram of the architecture of an embodiment of the system for calibrating inter-channel crosstalk of a coherent transceiver according to the present application. DETAILED DESCRIPTION

[0044] In order to make the technical problems, technical solutions and advantages of the present application clearer, the technical solutions of the present application 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 do not limit the embodiments of the present application to the following specific steps, values, conditions, data, sequences, etc. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0046] Embodiment One

[0047] The embodiment of the present application provides a method for calibrating inter-channel crosstalk of a coherent transceiver. Referring to Figure 1, Figure 1 is a flow diagram of a first embodiment of the method for calibrating inter-channel crosstalk of a coherent transceiver according to the present application. As shown in Figure 1, the method for calibrating inter-channel crosstalk 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 which is orthogonal to each other between channels and the amplitude of the sub-carrier frequency increases with the frequency;

[0049] Step A2, the coherent transmitter receives the crosstalk calibration issued by the coherent receiver, compensates the frequency-dependent crosstalk 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 the coherent receiver according to the auxiliary calibration signal and frequency-dependent crosstalk measurement based on crosstalk angle reconstruction.

[0050] It can be understood that in the embodiment, the coherent transmitter generates an auxiliary calibration signal, which is a multi-carrier signal with inter-channel orthogonality and sub-carrier amplitude increasing with frequency. Unlike the prior art, the difference between the amplitude of the high-frequency carrier signal and the amplitude of the low-frequency carrier signal increases with the modulation order and modulation bit rate, which can be applied to different channel crosstalk measurement application scenarios of coherent optical modules.

[0051] Further, as an optional embodiment, referring to FIG. 2, in step A1 of the embodiment, the generation of the auxiliary calibration signal includes:

[0052] S201, generating four multi-carrier signals with mutual orthogonal relationship, the expression of the multi-carrier signal is formula (1) and the sub-carrier frequency contained in the multi-carrier signal satisfies formula (2);

[0053] In formula (1), n represents the nth sub-carrier, Amp ab (n) is the amplitude of the nth sub-carrier on the ab branch, f ab (n) is the frequency of the nth sub-carrier, n≤N, N is the total number of sub-carriers, a∈[X, Y], b∈[I, Q]; f ab (n)=F ab +nf base (2).

[0054] In formula (2), F ab is the initial frequency of the sub-carrier closest to the zero frequency point, f base is the sub-carrier interval.

[0055] It can be understood that in the embodiment, four multi-carrier signals with mutual orthogonal relationship will be generated, such as S XI , S XQ , S YI , S YQ . The four multi-carrier signals will be input into the four input ports TXI, TXQ, TYI and TYQ of the coherent transmitter. According to the design of the embodiment, corresponding to the four branches TXI, TXQ, TYI and TYQ, F XI , F YI , F XQ , FYQ They are equal to 0 and f respectively base / 4、f base / 2、3f base / 4 shows that the sub-carrier frequencies contained in the four multi-carrier signals are not equal, and they have the characteristics of being mutually orthogonal and non-overlapping.

[0056] S202. Obtain the current optical module modulation information of the coherent transmitter, including the modulation order M and the modulation baud rate f. baud and sampling rate f DAC It is understandable that the modulation order M corresponds to the modulation format M-QAM (Quadrature Amplitude Modulation).

[0057] S203, According to the modulation baud rate f baud Set calibration bandwidth f cal In practical applications, the calibration bandwidth f can usually be limited. cal =1.1f baud .

[0058] S204. Set the total number of sub-carrier frequencies N of the multi-carrier signal according to the modulation order M. It is understood that the higher the modulation order, the more sensitive it is to crosstalk. In order to ensure measurement accuracy, this embodiment is designed to select fewer sub-carrier frequencies for crosstalk measurement in order 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 set according to the modulation order M. The specific setting formula is: N=256 / log2(M) (3);

[0059] S205, according to the calibration bandwidth f cal And the total number of subcarrier frequencies N and the subcarrier frequency spacing f are set. base Similarly, since the total number of sub-carrier frequencies N of a multi-carrier signal is set according to the modulation order M, for a fixed calibration bandwidth, the sub-carrier frequency spacing f of the multi-carrier signal... base It is also set according to the modulation order M, and the specific setting formula is: f base =f cal / N=1.1f baud log2(M) / 256 (4).

[0060] S206, According to the modulation baud rate f baud Total number of subcarriers N and sampling rate f DAC Set the amplitude Amp of each subcarrier frequency ab(n) It can be understood that, due to the fact that inter-channel crosstalk often occurs at high frequencies, and the device loses a lot of energy at high frequencies, it is necessary to further design the amplitudes of the sub-carrier frequencies in the multi-carrier frequency signal to increase the strength of the multi-carrier frequency signal at high frequencies, so as to obtain a higher signal-to-noise ratio. In a specific application, the amplitudes of the sub-carrier frequencies in the multi-carrier frequency signal can be set as follows: Amp ab (n) = 1 + 4nf baud / N / f DAC (5).

[0061] After the above steps, the generation of the auxiliary calibration signal (i.e., the multi-carrier frequency signal with sub-carrier frequencies orthogonal to each other and the amplitudes of the sub-carrier frequencies increasing with frequency) is completed. Moreover, according to the above generation method, a multi-carrier frequency signal with sub-carrier frequencies whose amplitudes vary with frequency can be designed, which is suitable for different application scenarios of channel crosstalk measurement of coherent optical modules with different rates and modulation formats.

[0062] For example, it is assumed that, in scenario A, 16QAM format modulation is used and the modulation rate is 45 Gbaud; in scenario B, QPSK format modulation is used and the modulation rate is 90 Gbaud. Then, according to the above generation method, different multi-carrier frequency signals in the two scenarios can be designed, and the corresponding parameters are shown in Table 1, and the spectrum of the multi-carrier frequency signal is shown in FIG. 3:

[0063] Table 1

[0064] From the design examples of the multi-carrier frequency signals in the above two scenarios, it can be seen that: (1) scenario A uses 16QAM modulation, and scenario B uses QPSK modulation. Scenario A has a higher modulation format than scenario B, is more sensitive to crosstalk, and has fewer sub-carrier frequencies in the designed multi-carrier frequency signal, which can improve the signal-to-noise ratio of each sub-carrier frequency and ensure the measurement accuracy; (2) scenario A uses a 45 Gbaud modulation rate, and scenario B uses a 90 Gbaud modulation rate. Scenario B has a higher modulation rate than scenario A, and the higher the baud rate, the more serious the loss of high-frequency bandwidth of the device. Therefore, more sub-carrier frequencies located at high frequencies are amplified in the designed multi-carrier frequency signal to improve the signal-to-noise ratio at high frequencies and ensure the measurement accuracy at high frequencies.

[0065] In addition, it can be understood that, in the embodiment, the coherent transmitter performs frequency-dependent crosstalk compensation based on the crosstalk calibration issued by the coherent receiver. Unlike the prior art, the crosstalk compensation method adopted in the embodiment is that the crosstalk compensation coefficient is obtained from the measured frequency-dependent crosstalk value (i.e., the crosstalk calibration issued 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 PAPR (Peak to Average Ratio) increase and signal-to-noise ratio decrease of the transmitted signal caused by counter compensation, and effectively improving the crosstalk compensation effect.

[0066] Further, as an optional implementation, in step A2 of the embodiment, the coherent transmitter performs frequency-dependent crosstalk compensation based on the crosstalk calibration, including: performing frequency-dependent crosstalk compensation on the service signal by using a preset static MIMO equalizer, the preset static MIMO equalizer being provided with two groups of static MIMO equalizers for X polarization and Y polarization crosstalk compensation respectively; each group of static MIMO equalizers being a 2x2 real number MIMO equalizer, and the equalizer coefficient being obtained according to the crosstalk calibration issued by the coherent receiver; and the compensation depth being adaptively adjusted according to the modulation baud rate and modulation format, and the compensation depth being reduced for high-order modulation and high baud signals.

[0067] Exemplarily, referring to FIG. 4, FIG. 4 is a schematic diagram of crosstalk compensation for X polarization by using the crosstalk compensation method of the embodiment. As shown in FIG. 4, the preset static MIMO equalizer is arranged after the static filter equalizer of the coherent transmitter DSP, that is, after the service signal is subjected to QAM modulation, up-sampling, and subjected to frequency offset shaping, inter-channel time delay compensation, dispersion pre-compensation, and other conventional DSP processing in the static equalizer, the service signal is subjected to frequency-dependent crosstalk compensation by the preset static MIMO equalizer, and then enters the iFFT module and the resampling module. As shown in FIG. 4, the preset static MIMO equalizer is composed of a 2x2 real number MIMO equalizer, and the equalizer coefficient is obtained according to the crosstalk calibration (i.e., the measured frequency-dependent crosstalk angle) issued by the coherent receiver. Specifically, the calculation formulas are shown in formulas (6) and (7): TXI_c(f) = TXI(f)Cos(β2(f))-ATXQ(f)Sin(β1(f)) (6); TXQ_c(f) = TXQ(f)Cos(β1(f))-ATXI(f)Sin(β2(f)) (7);

[0068] TXI_c(f), TXQ_c(f) are the I and Q channel signals of the coherent transmitter which are compensated according to the crosstalk calibration value, TXI(f), TXQ(f) are the original I and Q channel signals of the coherent transmitter which are not compensated, (f) represents that the compensation is processed in the frequency domain, β1(f) is the frequency-dependent crosstalk angle value of the Q channel to the I channel sent by the coherent receiver, β2(f) is the frequency-dependent crosstalk angle value of the I channel to the Q channel sent by the coherent receiver; TXQ(f)Sin(β1(f)) is the Q channel to I channel crosstalk signal calculated according to the crosstalk calibration angle value, TXI(f)Cos(β2(f)) represents the I channel signal crosstalk to the Q channel signal, and according to the energy conservation, the transmitted signal of each frequency point on the I channel, TXI(f)Sin(β2(f)) is the I channel to Q channel crosstalk signal calculated according to the crosstalk calibration angle value, TXQ(f)Cos(β1(f)) represents the Q channel signal crosstalk to the I channel signal, and according to the energy conservation, the transmitted signal of each frequency point on the Q channel, A is a compensation depth coefficient, and its expression is: A=f DAC / (2f baud ) / (log2(M) / 2)=f DAC / f baud / log2(M) (8)。

[0069] The preset static MIMO equalizer adopts the calculation of formula (6) and formula (7) to realize the compensation of the frequency-dependent crosstalk between channels, and adopts formula (8) to design the compensation depth of the channel crosstalk, to adaptively adjust the compensation depth and reduce the compensation depth for high-order modulation and high baud signals, so as to solve the problems of PAPR rising and signal-to-noise ratio reduction of the transmitted signal caused by counter compensation, and effectively improve the crosstalk compensation effect.

[0070] Embodiment two

[0071] Based on the same inventive concept, the application also provides a calibration method for crosstalk between channels of a coherent transceiver. Referring to FIG. 5, FIG. 5 is a flowchart of a second embodiment of the calibration method for crosstalk between channels of a coherent transceiver. As shown in FIG. 5, the calibration method for crosstalk between channels of a coherent transceiver comprises the following steps:

[0072] Step B1, the coherent receiver receives an auxiliary calibration signal sent by the coherent transmitter on four channels; the auxiliary calibration signal is a multi-carrier signal which is orthogonal to each other between channels and whose sub-carrier amplitude increases with frequency.

[0073] Step B2, the coherent receiver performs frequency-dependent crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal to obtain a crosstalk calibration and sends the crosstalk calibration to the coherent transmitter; the crosstalk calibration is used for the coherent transmitter to perform frequency-dependent crosstalk compensation based on the crosstalk calibration.

[0074] Step B3, the coherent receiver receives the calibration service signal after the coherent transmitter performs the crosstalk compensation, and performs equalization demodulation on the calibration service signal.

[0075] It can be understood that in the embodiment, the coherent receiver performs frequency-dependent crosstalk measurement based on crosstalk angle reconstruction on the four-way received signals loaded with the auxiliary calibration signal in the digital domain, so as to obtain crosstalk calibration. This crosstalk measurement based on crosstalk angle reconstruction is a frequency-dependent crosstalk measurement method using crosstalk-free signal reconstruction plus frequency-point-by-frequency-point crosstalk angle search, which can realize wide-range, high-precision and low-complexity calibration of frequency-dependent crosstalk between IQ channels of the coherent transceiver.

[0076] Further, referring to FIG. 6, as an optional embodiment, in step B2 of the embodiment, the coherent receiver performs frequency-dependent crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal to obtain crosstalk calibration, comprising:

[0077] S601, a crosstalk-free signal is reconstructed by introducing a frequency-dependent phase extraction factor a(fn); wherein a(fn) is used to extract the phase deviation caused by inter-channel crosstalk and laser phase rotation, and the crosstalk-free signal is reconstructed based on the phase deviation.

[0078] It can be understood that after the auxiliary calibration signal is transmitted to the coherent receiver through the optical fiber link, the coherent receiver will perform detection, and four-way radio frequency signals RXI, RXQ, RYI and RYQ are obtained from the four input ports respectively. The received signals will be preprocessed, such as frequency offset estimation and frequency offset compensation, in the digital signal processing (DSP) module.

[0079] For example, taking the channel crosstalk between RXI and RXQ as an example, before performing 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-way signals after preprocessing can be represented as:

[0080] Wherein, μ(f), γ(f) represent the frequency-dependent crosstalk of the coherent transmitter and the coherent receiver respectively, and the inter-channel crosstalk at different fn points is considered as rotation angles μ(f), γ(f) according to the law of conservation of energy; θ represents the azimuth angle introduced by the laser phase rotation. represents the amplitude phase frequency response of the transmission channel when there is a laser frequency offset in the non-homologous coherent optical communication system.

[0081] As shown in equation (9), due to the transceiver crosstalk and the laser phase rotation effect, the RXI and RXQ signals of the coherent receiver will contain the TXI and TXQ signals of the coherent transmitter at the same time, and the two are mixed with each other. Based on the power conservation formula of the frequency-dependent crosstalk, the transceiver crosstalk rotation angle and the laser phase are combined into one term in the model, and it is difficult to separate the crosstalk independently.

[0082] In order to solve the problem that the crosstalk is difficult to separate from the laser phase and measure independently, the embodiment particularly introduces a frequency-dependent phase extraction factor α(fn) for extracting the phase deviation caused by the inter-channel crosstalk and the laser phase rotation, and reconstructs the crosstalk-free signal based on the same. Exemplarily, the reconstructed crosstalk-free signal can be written as equation (10):

[0083] Since the transmission 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 transmission signals TXI and TXQ, and does not contain the cross terms of the two. Wherein, M I and M Q are functions of α(fn), θ, μ(f), γ(f).

[0084] S602, select the n-th frequency point, scan α(fn) in the range of [0, 2π], and obtain the intensity curve of the sub-carrier signal at the n-th frequency point of the reconstructed signal.

[0085] Specifically, in actual application, the phase extraction factor α(fn) is scanned in the range of [0, 2π] with the fixed frequency point fn, and the intensity curve corresponding to the n-th sub-carrier signal can be obtained as shown in equation (11):

[0086] 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 of the frequency point, wherein the laser phase is a constant.

[0087] It can be understood that when Amp_Rx(α(fn)) in equation (11) takes the maximum, the M I and M Q of the n-th sub-carrier signal at the frequency point fn reach the intensity extreme point, as shown in equation (12):

[0088] At this intensity extreme point, the corresponding phase extraction factor α max (fn) is obtained, and the α max(fn) and the phase deviation caused by inter-channel crosstalk and laser phase rotation satisfies the relationship of equation (13): 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).

[0089] S604, sequentially subtract α max (fn) on the n = 2, … N frequency points from α max (f1) on the first frequency point to eliminate the influence of the laser phase constant, and calculate the crosstalk angle of the sub-carrier frequency signal on the n frequency point, and calculate the corresponding crosstalk value according to the crosstalk angle.

[0090] It can be understood that in actual application, the phase azimuth angle θ introduced by the laser in equation (13) can be regarded as a constant within the measurement time, and is recovered by the equalizer in the receiver DSP, so the phase extraction factor α max1 (f1) and α max2 (f1) at the first frequency f1 can be regarded as reference values, and the phase extraction factors α max1 (fn) and α max2 (fn) at other sub-carrier frequencies can be subtracted from the reference values to obtain the crosstalk angles β1, β2 at different frequencies. The specific calculation formulas are shown in equations (14) and (15): β1(f1) = α max1 (f1), β2(f1) = α max2 (f1) (14); β1(fn) = α max1 (fn) - α max1 (f1), β2(fn) = α max2 (fn) - α max2 (f1) (15).

[0091] Referring to FIG. 7, FIG. 7 is a schematic diagram of the relationship between α max (fn) and crosstalk at different frequency point intensity extreme points. As shown in FIG. 7, when there is no frequency-dependent crosstalk on the n frequency point, the α max (fn) corresponding to the extreme point of the intensity curve calculated in step S603 coincides with α max (f1) at the first frequency point, when there is frequency-dependent crosstalk on the n frequency point, the α max (fn) corresponding to the extreme point of the intensity curve calculated in step S603 does not coincide with α max (f1) at the first frequency point, and the angle difference is the crosstalk angle.

[0092] Then, the crosstalk value can be calculated according to the obtained crosstalk angle, so as to realize the frequency-dependent crosstalk calibration in the full bandwidth range. Exemplarily, the crosstalk value calculation formula is as follows: XT TRx_IQ (fn) = Sin(β1(fn)) / Cos(β2(fn)) (16); XT TRx_QI (fn) = Sin(β2(fn)) / Cos(β1(fn)) (17);

[0093] Wherein, XT TRx_IQ (fn) represents the crosstalk value of the XQ channel to the XI channel, XT TRx_QI (fn) represents the crosstalk value of the XI channel to the XQ channel.

[0094] Further, referring to FIG. 8, as an optional embodiment, in step B3 of the embodiment, a 2x2 complex MIMO equalizer is used for polarization demultiplexing equalization in the equalization and demodulation process of the coherent receiver, which is different from the inter-channel crosstalk compensation generalized equalizer of the prior art coherent receiver, and has the characteristics of lower complexity.

[0095] Specifically, referring to FIG. 8, in the coherent receiver DSP of the embodiment, a conventional DSP is used to equalize and demodulate the received signal, that is, after clock recovery, frequency offset recovery, and static equalization, only a 2x2 complex MIMO equalizer is used for polarization demultiplexing equalization, so only 4 complex equalizers (equivalent to 8 real equalizers) are needed to realize signal demodulation, plus the 8 static real equalizers (two polarizations, each polarization has a 2x2 real MIMO equalizer) of the coherent transmitter, a total of 16 real equalizers. Although the generalized equalizer can also realize inter-channel crosstalk compensation, the received signal and its conjugate signal (conj() represents conjugate) need to be input to a 4x4 complex MIMO equalizer for processing in the coherent receiver, as shown in FIG. 9, so the complexity is higher, 16 complex equalizers are needed, equivalent to 32 real equalizers, which is twice the complexity of the present scheme. The complexity comparison between the crosstalk compensation scheme of the embodiment and the generalized MIMO equalizer crosstalk compensation scheme is shown in Table 2 below.

[0096] Table 2

[0097] In order to better understand the calibration method of the inter-channel crosstalk of the coherent transceiver in the present application, the specific content of the calibration method of the present application will be illustrated below in combination with the contents of embodiments one and two and the accompanying drawings.

[0098] Referring to FIG. 10, a calibration method of inter-channel crosstalk of a coherent transceiver specifically includes the following processes:

[0099] Step S101, an auxiliary calibration signal is generated in the coherent transmitter, which is a multi-carrier signal with inter-channel mutual orthogonality and sub-carrier amplitude increasing with frequency, to calibrate the inter-channel crosstalk of optical modules with different rates and modulation formats. The spectrum of the auxiliary calibration signal is shown in Figure 11-(a). The generation process of the specific auxiliary calibration signal is described in the corresponding content of Embodiment I, which will not be described here.

[0100] Step S102, the coherent transmitter loads the generated auxiliary calibration signal on the XI, XQ, YI and YQ channels of the coherent transmitter, and performs photoelectric modulation to obtain a frequency-domain orthogonal multi-carrier signal at the output of the coherent transmitter. The spectrum of the multi-carrier signal is shown in Figure 11-(b). As shown in Figure 11-(b), due to the influence of device bandwidth, the high-frequency power of the original multi-carrier signal with increasing sub-carrier amplitude (power) with frequency may be attenuated, and the power is attenuated to the same power of each frequency point in the example shown in the figure; at the same time, due to inter-channel crosstalk, the originally orthogonal sub-carrier components between channels are leaked to adjacent channels.

[0101] Step S103, the output multi-carrier signal is transmitted in the fiber link, and the spectrum of the multi-carrier signal is shown in Figure 11-(c). Due to the influence of polarization rotation and laser phase noise, the originally orthogonal sub-carrier components between channels are further leaked to adjacent channels and overlap with the inter-channel crosstalk of the transmitter, which is difficult to directly extract and measure.

[0102] Step S104, the coherent receiver coherently detects the polarization multiplexed QAM signal transmitted, and obtains XI, XQ, YI and YQ four-channel multi-carrier signals (i.e. four-channel digital domain received signals) through an analog-to-digital converter. The spectrum of the multi-carrier signal is shown in Figure 11-(d). Due to the influence of inter-channel crosstalk of the receiver, the originally orthogonal sub-carrier components between channels are further leaked to adjacent channels and overlap with the inter-channel crosstalk of the transmitting end and the crosstalk caused by polarization rotation, which is difficult to directly extract and measure.

[0103] 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 deliver it to the coherent transmitter. In this step, by using the crosstalk measurement method based on crosstalk angle reconstruction, wide-range, high-precision and low-complexity measurement and calibration of frequency-dependent crosstalk between IQ channels of the coherent transmitter and receiver can be realized. The specific process of frequency-dependent crosstalk measurement based on crosstalk angle reconstruction is described in the corresponding content of Embodiment II, which will not be described here.

[0104] Step S106, the coherent transmitter receives the crosstalk calibration sent by the coherent receiver, compensates the frequency-dependent crosstalk 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 compensates the frequency-dependent crosstalk based on the crosstalk calibration to realize the calibration of the frequency-dependent crosstalk between channels. For details of the crosstalk compensation process, refer to the description of the corresponding content in Embodiment 1, which will not be described here.

[0105] Step S107, after receiving the crosstalk-compensated calibration service signal, the coherent receiver performs regular equalization demodulation on the calibration service signal.

[0106] Embodiment three

[0107] Based on the same inventive concept, the present embodiment also provides a coherent transmitter based on the calibration method of Embodiment 1. As shown in FIG. 12, the coherent transmitter comprises an auxiliary calibration signal sending unit and a calibration service signal sending unit.

[0108] The auxiliary calibration signal sending unit is configured to load the generated auxiliary calibration signal on the four-channel coherent transmitter and send it to the coherent receiver. The generated auxiliary calibration signal is a multi-carrier signal with inter-channel mutual orthogonality and increasing sub-carrier amplitude with frequency.

[0109] The calibration service signal sending unit is configured to receive the crosstalk calibration sent by the coherent receiver, compensate the frequency-dependent crosstalk based on the crosstalk calibration, and send the compensated calibration service signal to the coherent receiver. The crosstalk calibration is the crosstalk value obtained by the coherent receiver based on the frequency-dependent crosstalk measurement of the crosstalk angle reconstruction of the auxiliary calibration signal.

[0110] In addition, it should be noted that the various variations and other specific examples of the aforementioned calibration method of inter-channel crosstalk of the coherent transceiver are also applicable to the coherent transmitter of the present 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 the present embodiment. Therefore, in order to make the description concise, the detailed description will not be repeated here.

[0111] Embodiment four

[0112] Based on the same inventive concept, the present embodiment also provides a coherent receiver based on the calibration method of Embodiment 2. As shown in FIG. 12, the coherent receiver comprises a crosstalk calibration unit and a service signal demodulation unit.

[0113] The crosstalk calibration unit is configured to receive an auxiliary calibration signal sent by the coherent transmitter and loaded on four channels, the auxiliary calibration signal being a multi-carrier signal with inter-channel mutual orthogonality and sub-carrier amplitudes increasing with frequency; and perform frequency-dependent crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal to obtain crosstalk calibration and send the crosstalk calibration to the coherent transmitter; and the crosstalk calibration is used by the coherent transmitter to perform frequency-dependent crosstalk compensation.

[0114] The service signal demodulation unit is configured to receive the calibrated service signal after crosstalk compensation by the coherent transmitter and perform equalization demodulation on the calibrated service signal.

[0115] It should also be noted that the various changes and other specific examples of the foregoing method for calibrating inter-channel crosstalk of a coherent transceiver are also applicable to the coherent receiver of the present embodiment, and the implementation method of the coherent receiver in the present embodiment can be clearly understood by the foregoing detailed description of the method. Therefore, for the sake of brevity of the description, the implementation method of the coherent receiver in the present embodiment will not be described in detail.

[0116] Embodiment five

[0117] Referring to FIG. 12, based on the same inventive concept, the present embodiment also provides a calibration system for inter-channel crosstalk of a coherent transceiver, which comprises the coherent transmitter of the foregoing embodiment three and the coherent receiver of the foregoing embodiment four.

[0118] Note: The serial numbers of the foregoing embodiments of the present application are only for description, and do not represent the advantages or disadvantages of the embodiments.

[0119] The terms “comprising” and “having” and any variations thereof in the specification and claims of the present application and the foregoing drawings are intended to cover non-exclusive inclusion. 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 can optionally further comprise steps or units not listed, or can optionally further comprise other steps or units inherent to the process, method, product or device.

[0120] In the description of the embodiments of the present application, “exemplary”, “for example”, “for instance” or the like are used to represent an example, illustration or description. Any embodiment or design scheme described as “exemplary”, “for example” or “for instance” in the embodiments of the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the words “exemplary”, “for example” or “for instance” are intended to present the relevant concept in a specific manner.

[0121] The advantages, benefits, and effects mentioned in the embodiments of the present application are only examples, and are not limiting. The advantages, benefits, and effects are not necessarily required for each of the embodiments of the present application. In addition, the above-described specific details of the embodiments of the present application are only for the purpose of illustration and understanding, and are not limiting. The above-described specific details are not required for the embodiments of the present application to be implemented.

[0122] The block diagrams of the devices, apparatuses, equipment, systems involved in the embodiments of the present application are only illustrative examples, and are not intended to require or imply that the connections, arrangements, configurations are as shown in the block diagrams. As those skilled in the art will recognize, the devices, apparatuses, equipment, systems can be connected, arranged, configured in any manner. The words "or" and "and" used in the embodiments of the present application refer to the words "and / or", and can be used interchangeably. The word "such as" used in the embodiments of the present application refers to the phrase "such as but not limited to", and can be used interchangeably. The terms "first", "second", and "third" and the like are used to distinguish different objects, and do not represent the order of sequence, nor limit the "first", "second", and "third" to be different types.

[0123] Each operation in the embodiments of the present application can be performed by any appropriate means capable of performing the corresponding function. The means can include various hardware and / or software components and / or modules, including but not limited to hardware circuitry or processors.

[0124] The method of the embodiments of the present application includes one or more acts for implementing the above-described method. The method and / or acts can be interchanged with each other without departing from the scope of the claims. In other words, the order and / or use of the specific acts can be modified without departing from the scope of the claims, unless a specific order of acts is specified.

[0125] Those skilled in the art can make various changes, replacements, and modifications to the technology described herein 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 above-described specific aspects of processes, machines, manufactures, compositions of matter, means, methods, and acts. Processes, machines, manufactures, compositions of matter, means, methods, or acts currently existing or to be developed in the future that perform substantially the same function or achieve substantially the same result as the corresponding aspects described herein can be utilized. Thus, the appended claims encompass such processes, machines, manufactures, compositions of matter, means, methods, or acts within their scope.

[0126] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other aspects without departing from the scope of the application. Thus, the present application is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0127] The above description has been presented to enable any person skilled in the art to make or use the application. Numerous modifications to the aspects described herein will be readily apparent to those skilled in the art, and the principles defined herein can be applied to other aspects without departing from the scope of the application. Thus, the present application is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method of calibration of inter-transceiver-path crosstalk in a coherent transceiver, characterized in that, The method comprises: The coherent transmitter loads the generated auxiliary calibration signal on the four-way channel of the coherent transmitter to send to the coherent receiver; wherein the generated auxiliary calibration signal is a multi-carrier signal which is mutually orthogonal between channels and whose sub-carrier frequency amplitude increases with 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 the coherent receiver based on the auxiliary calibration signal and frequency-dependent crosstalk measurement based on crosstalk angle reconstruction.

2. The method of calibration of inter-path crosstalk of a coherent transceiver of claim 1, wherein, The generation of the auxiliary calibration signal comprises: Generating a four-way multi-carrier signal with mutual orthogonality; Obtaining the modulation information of the optical module of the coherent transmitter, including the modulation order, the modulation baud rate and the sampling rate; Setting 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; Setting the sub-carrier frequency interval according to the calibration bandwidth and the total number of sub-carrier frequencies; Setting the amplitude of each sub-carrier frequency according to the modulation baud rate, the total number of sub-carrier frequencies and the sampling rate.

3. The method of calibration of inter-path crosstalk of a coherent transceiver of claim 1, wherein, When the coherent transmitter performs frequency-dependent crosstalk compensation, the following method is used: the crosstalk compensation coefficient is obtained from the crosstalk calibration issued by the coherent receiver, and the compensation depth is adaptively adjusted according to the modulation baud rate and the modulation format, and the compensation depth is reduced for high-order modulation and high-baud signals.

4. The method of calibration of inter-path crosstalk of a coherent transceiver of claim 3, wherein: The coherent transmitter uses a preset static MIMO equalizer to perform frequency-dependent crosstalk compensation; the preset static MIMO equalizer is provided with two groups, respectively used for crosstalk compensation of X polarization and Y polarization; Each group of static MIMO equalizers is a 2x2 real number MIMO equalizer, and the equalizer coefficient is obtained from the crosstalk calibration issued by the coherent receiver, and the compensation depth is adaptively adjusted according to the modulation baud rate and the modulation format, and the compensation depth is reduced for high-order modulation and high-baud signals.

5. A method of calibration of inter-transceiver path crosstalk in a coherent transceiver, characterized in that, The method comprises: The coherent receiver receives the auxiliary calibration signal sent by the coherent transmitter on the four-way channel; wherein the auxiliary calibration signal is a multi-carrier signal which is mutually orthogonal between channels and whose sub-carrier frequency amplitude increases with frequency; The coherent receiver performs frequency-dependent crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal, obtains crosstalk calibration, and issues it to the coherent transmitter; wherein the crosstalk calibration is used by the transmitter to perform frequency-dependent crosstalk compensation based on the crosstalk calibration; The coherent receiver receives the calibration service signal after crosstalk compensation by the coherent transmitter, and performs equalization demodulation on the calibration service signal.

6. The method of calibration of inter-path crosstalk of a coherent transceiver of claim 5, wherein, The coherent receiver performs frequency-dependent crosstalk measurement based on crosstalk angle reconstruction according to the auxiliary calibration signal to obtain crosstalk calibration, comprising: A phase extraction factor α(fn) related to frequency is introduced to reconstruct a crosstalk-free signal from the preprocessed auxiliary calibration signal; wherein α(fn) is used to extract the phase deviation caused by inter-channel crosstalk and laser phase rotation, and to reconstruct a crosstalk-free signal therefrom; Selecting the n th =1,…N frequency points, scanning α (fn) in the range of [0, 2π], and obtaining the intensity curve of the sub-carrier frequency signal of the reconstructed signal at the n th frequency point; wherein N is the total number of sub-carrier frequencies of the multi-carrier frequency signal; A phase extraction factor corresponding to the intensity extreme point is obtained, denoted as α max (fn), and the α max (fn) is the sum of the crosstalk angle and the laser phase of the frequency point, wherein the laser phase is a constant; successively subtracting α(fn) on the nth = 2,...N frequency point from α(f1) on the first frequency point max successively subtracting α(fn) on the nth = 2,...N frequency point from α(f1) on the first frequency point max computing the crosstalk angle of the sub-carrier signal on the nth frequency point according to the crosstalk angle, and computing the corresponding crosstalk value according to the crosstalk angle.

7. The method of calibration of inter-path crosstalk of a coherent transceiver of claim 5, wherein: In the process of equalizing and demodulating the calibration service signal by the coherent receiver, a 2*2 complex MIMO equalizer is used for polarization demultiplexing equalization.

8. A coherent transmitter based on the method of any one of claims 1 to 4, characterized by: The coherent transmitter comprises an auxiliary calibration signal issuing unit and a calibration service signal issuing unit; The auxiliary calibration signal issuing unit is configured to load the generated auxiliary calibration signal on the four channels of the coherent transmitter and send the auxiliary calibration signal to the coherent receiver; wherein the generated auxiliary calibration signal is a multi-carrier frequency signal which is orthogonal among channels and whose sub-carrier frequency amplitude increases with frequency. The calibration service signal issuing unit is configured to receive the crosstalk calibration issued by the coherent receiver, perform frequency-dependent crosstalk compensation based on the crosstalk calibration, and send the compensated calibration service signal to the coherent receiver; wherein the crosstalk calibration is a crosstalk value obtained by the coherent receiver based on the auxiliary calibration signal and frequency-dependent crosstalk measurement based on crosstalk angle reconstruction.

9. A coherent receiver based on the method of any one of claims 5 to 7, characterized by: The coherent receiver comprises a crosstalk calibration unit and a service signal demodulation unit. The crosstalk calibration unit is configured to receive the auxiliary calibration signal sent by the coherent transmitter on the four channels, wherein the auxiliary calibration signal is a multi-carrier frequency signal which is orthogonal among channels and whose sub-carrier frequency amplitude increases with frequency; and perform frequency-dependent crosstalk measurement based on crosstalk angle reconstruction based on the auxiliary calibration signal, obtain the crosstalk calibration, and issue the crosstalk calibration to the coherent transmitter; wherein the crosstalk calibration is used by the transmitter to perform frequency-dependent crosstalk compensation based on the crosstalk calibration. The service signal demodulation unit is configured to receive the calibration service signal compensated by the coherent transmitter, and perform equalization and demodulation on the calibration service signal.

10. A calibration system for inter-channel crosstalk in a coherent transceiver, characterized in that: The system comprises the coherent transmitter according to claim 8 and the coherent receiver according to claim 9.

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