Method and apparatus for determining performance of coherent transmitter, and system, device and medium

Abstract

The present disclosure belongs to the technical field of coherent communications. Provided are a method and apparatus for determining the performance of a coherent transmitter, and a system, a device and a medium. The method comprises: acquiring a multi-path digital signal carried in a dual-polarization optical signal from a coherent transmitter; performing a noise search on the basis of the multi-path digital signal, so as to obtain a first power of additive white Gaussian noise that is added for the multi-path digital signal under a bit error rate threshold value; acquiring a second power of additive white Gaussian noise that is added for an ideal signal under the bit error rate threshold value, wherein the ideal signal is an undistorted signal determined on the basis of the multi-path digital signal; and then, on the basis of the first power and the second power, determining the performance of the coherent transmitter. By using the solution of the present disclosure, the performance of a coherent transmitter is measured on the basis of a bit error rate as a constraint, such that the performance of the coherent transmitter can be accurately measured.

Description

Method, apparatus, system, device and medium for determining performance of a coherent transmitter

[0001] The present disclosure claims priority to Chinese patent applications with application number 202311292193.8 filed on September 28, 2023, and invention name “Method, apparatus, system, device and medium for determining the performance of a coherent transmitter” and application number 202410941831.2 filed on July 12, 2024, and invention name “Method, apparatus, system, device and medium for determining the performance of a coherent transmitter”, the entire contents of which are incorporated by reference into the present disclosure. Technical Field

[0002] The present disclosure relates to the field of coherent communication technology, and in particular to a method, apparatus, system, device, and medium for determining the performance of a coherent transmitter. Background Art

[0003] In high-speed dense wavelength-division multiplexing (DWDM) systems, coherent transmitters are used to transmit signals. The performance of coherent transmitters directly affects whether the DWDM system can transmit data normally. Therefore, the performance of coherent transmitters needs to be determined.

[0004] Currently, the industry uses error vector magnitude (EVM) to measure coherent transmitter performance. When the coherent transmitter's degradation comes solely from additive white Gaussian noise (AWGN), EVM can accurately measure the performance of the coherent transmitter. However, coherent transmitters often experience other interference that can cause degradation, such as inter-symbol interference (ISI) and laser phase noise. Therefore, using EVM to measure coherent transmitter performance can be inaccurate.

[0005] Summary of the Invention

[0006] The present disclosure provides a method, apparatus, system, device, and medium for determining the performance of a coherent transmitter, which can improve the accuracy of determining the performance of a coherent transmitter. The technical solution is as follows:

[0007] In a first aspect, the present disclosure provides a method for determining the performance of a coherent transmitter, the method comprising: obtaining a multi-channel digital signal carried by a dual-polarized optical signal from the coherent transmitter, wherein the multi-channel digital signal is a dual-polarized co-directional and orthogonal signal, performing a noise search based on the multi-channel digital signal to obtain a first power of additive white Gaussian noise added to the multi-channel digital signal under a bit error rate threshold, obtaining a second power of additive white Gaussian noise added to an ideal signal under the bit error rate threshold, wherein the ideal signal is an undistorted signal determined based on the multi-channel digital signal, and determining the performance of the coherent transmitter based on the first power and the second power.

[0008] In the scheme shown in the present disclosure, when determining the performance of the coherent transmitter, under the bit error rate threshold, the greater the power of the additive white Gaussian noise added to the multi-channel digital signals, the less damage the signal transmitted by the coherent transmitter. Conversely, the smaller the power of the additive white Gaussian noise added to the multi-channel digital signals, the greater the damage the signal transmitted by the coherent transmitter. This is equivalent to using the bit error rate to directly measure the performance of the coherent transmitter.

[0009] In an optional manner, determining the performance of the coherent transmitter based on the first power and the second power includes: determining the performance of the coherent transmitter based on the first power, the second power and noise at the front end of a coherent receiver.

[0010] In the solution shown in the present disclosure, the noise of the front end of the coherent receiver is also taken into consideration, eliminating the influence of the noise of the front end of the coherent receiver on the performance of the determined coherent transmitter, so as to accurately evaluate the performance of the coherent transmitter.

[0011] In an optional manner, the noise search is performed based on the multi-channel digital signal to obtain the first power of the additive white Gaussian noise added to the multi-channel digital signal under a bit error rate threshold, including: performing pulse shaping and matched filtering on the multi-channel digital signal to obtain a matched filtered signal, and performing a noise search based on the matched filtered signal to obtain the first power of the additive white Gaussian noise added to the matched filtered signal under a bit error rate threshold.

[0012] In the solution shown in the present disclosure, before performing noise search, pulse shaping and filtering processing is performed on multiple digital signals, which can suppress noise and make the performance of the coherent transmitter determined more accurately.

[0013] In an optional manner, the noise search is performed based on the matched filtered signal to obtain a first power of additive white Gaussian noise added to the matched filtered signal under a bit error rate threshold, including: adding additive white Gaussian noise to the matched filtered signal to obtain a signal after adding additive white Gaussian noise, performing equalization processing on the signal after adding additive white Gaussian noise to obtain an equalized signal, and determining, based on the equalized signal, the first power of additive white Gaussian noise added to the matched filtered signal under a bit error rate threshold.

[0014] In an optional manner, before pulse shaping and matched filtering are performed on the multi-channel digital signals, low-pass filtering is performed on the multi-channel digital signals according to the bandwidth of the coherent receiver front end, so as to simulate the bandwidth limitation of the coherent receiver front end.

[0015] In an optional manner, obtaining the multi-channel digital signal carried by the dual-polarized optical signal from the coherent transmitter includes: obtaining the multi-channel analog signal carried by the dual-polarized optical signal from the coherent transmitter, and subjecting the multi-channel analog signal to low-pass filtering to obtain the low-pass filtered analog signal, wherein the bandwidth for the low-pass filtering is determined based on the bandwidth of the front end of the coherent receiver, and performing analog-to-digital conversion on the low-pass filtered analog signal to obtain the multi-channel digital signal.

[0016] In the solution shown in the present disclosure, after obtaining the multi-channel analog signals carried by the dual-polarization signal from the coherent transmitter, the multi-channel analog signals are low-pass filtered according to the bandwidth of the coherent receiver front end, and then converted into multi-channel digital signals by analog-to-digital conversion, which can simulate the bandwidth limitation of the coherent receiver front end.

[0017] In an optional manner, the performance of the coherent transmitter is determined based on the first power, the second power and the noise of the coherent receiver front end, including: according to the formula Determine the transmitter constellation closure cost (TCC), where TCC is the transmitter constellation closure cost. is the first power, is the second power, is the power of the noise at the front end of the coherent receiver, and the transmitter constellation closure cost is used to characterize the performance of the coherent transmitter.

[0018] In the solution shown in the present disclosure, when calculating the performance of the coherent transmitter, the residual noise that can be added to the multi-channel digital signals when the bit error rate threshold is reached is taken into account, and the performance of the coherent transmitter can be evaluated by the residual noise.

[0019] In an optional manner, the method further includes: determining the power of the multi-channel digital signal and the power of the matched filtered signal, and determining the performance of the coherent transmitter based on the first power, the second power and the noise of the coherent receiver front end, including: according to the formula Determine the transmitter constellation closure cost, where TCC is the transmitter constellation closure cost, is the first power, is the second power, is the power of the noise at the front end of the coherent receiver, punfiltered is the power of the multi-channel digital signal, p filtered is the power of the matched filtered signal, and the transmitter constellation closure cost is used to characterize the performance of the coherent transmitter.

[0020] In the solution shown in the present disclosure, when calculating the performance of the coherent transmitter, not only the residual noise that can be added by the multi-channel digital signals when the bit error rate threshold is reached is considered, but also the ratio of the power of the unfiltered signal to the power of the filtered signal is considered. When the ratio is large, it means that the damage to the received signal is relatively large. Conversely, when the ratio is small, it means that the damage to the received signal is relatively small. The bandwidth of the signal transmitted by the coherent transmitter is evaluated by using this ratio. It can be seen that not only the residual noise but also the bandwidth of the signal transmitted by the coherent transmitter is considered, which can more accurately evaluate the performance of the coherent transmitter.

[0021] In an optional manner, under the bit error rate threshold, the dual-polarization optical signal includes at least 1×10 5 Thus, with enough symbols, the performance of the coherent transmitter can be accurately determined.

[0022] In an optional manner, the performance of the coherent transmitter is determined based on the first power, the second power and the noise of the front end of the coherent receiver, including: determining the first sensitivity cost of the coherent transmitter under the bit error rate threshold based on the first power, the second power and the noise of the front end of the coherent receiver; the method also includes: performing a noise search based on the multi-channel digital signal to obtain a third power of the additive white Gaussian noise added to the multi-channel digital signal under at least one target bit error rate; obtaining a fourth power of the additive white Gaussian noise added to the ideal signal under the at least one target bit error rate; for the first target bit error rate of the at least one target bit error rate, determining the second sensitivity cost of the coherent transmitter under the first target bit error rate based on the third power and fourth power corresponding to the first target bit error rate and the noise of the front end of the coherent receiver; determining the target performance of the coherent transmitter based on the first sensitivity cost of the coherent transmitter and the second sensitivity cost of the coherent transmitter under the at least one target bit error rate.

[0023] In the solution shown in the present disclosure, the target performance is the comprehensive performance of the coherent transmitter. Using multiple bit error rates, multiple sensitivity costs can be determined. Using multiple sensitivity costs to determine the performance of the coherent transmitter can more accurately measure the performance of the coherent transmitter.

[0024] In an optional manner, the performance of the coherent transmitter is determined based on the first power, the second power and the noise of the coherent receiver front end, including: determining the transmitter constellation closure cost of the coherent transmitter based on the first power, the second power and the noise of the coherent receiver front end; the method also includes: obtaining the bit error rate of the multi-channel digital signal under at least one virtual noise signal-to-noise ratio; and determining the target performance of the coherent transmitter based on the obtained bit error rate and the transmitter constellation closure cost.

[0025] In the solution shown in the present disclosure, the performance of the coherent transmitter is determined using the virtual noise signal-to-noise ratio and the transmitter constellation closure cost, which is equivalent to multi-dimensional evaluation of the performance of the coherent transmitter and can more accurately measure the performance of the coherent transmitter.

[0026] In an optional manner, the performance of the coherent transmitter is determined based on the first power and the second power, including: determining a first relative virtual noise signal-to-noise ratio of the coherent transmitter under the bit error rate threshold based on the first power and the second power; the method also includes: performing a noise search based on the multi-channel digital signal to obtain a third power of additive white Gaussian noise added to the multi-channel digital signal under at least one target bit error rate; obtaining a fourth power of additive white Gaussian noise added to the ideal signal under the at least one target bit error rate; for a first target bit error rate among the at least one target bit error rate, determining a second relative virtual noise signal-to-noise ratio of the coherent transmitter under the first target bit error rate based on the third power and fourth power corresponding to the first target bit error rate; and determining the target performance of the coherent transmitter based on the first relative virtual noise signal-to-noise ratio of the coherent transmitter and the second relative virtual noise signal-to-noise ratio of the coherent transmitter under the at least one target bit error rate.

[0027] In the solution shown in the present disclosure, the target performance is the comprehensive performance of the coherent transmitter. Using multiple bit error rates, multiple relative virtual noise signal-to-noise ratios can be directly determined. Using multiple relative virtual noise signal-to-noise ratios to determine the performance of the coherent transmitter can more accurately measure the performance of the coherent transmitter.

[0028] In a second aspect, the present disclosure provides a method for determining the performance of a coherent transmitter, the method comprising: obtaining multiple digital signals carried by a dual-polarized optical signal from the coherent transmitter, wherein the multiple digital signals are dual-polarized co-directional and orthogonal signals; obtaining a bit error rate of the multiple digital signals under at least one virtual noise signal-to-noise ratio; and determining the performance of the coherent transmitter based on the obtained bit error rate.

[0029] In the solution shown in the present disclosure, starting from the virtual noise signal-to-noise ratio, the bit error rate is measured and the performance of the coherent transmitter can also be determined.

[0030] In a third aspect, the present disclosure provides an apparatus for determining coherent transmitter performance, the apparatus having the functionality of implementing the first aspect and its optional implementations. The apparatus includes at least one module configured to implement the method for determining coherent transmitter performance provided in the first aspect and its optional implementations.

[0031] In some embodiments, the modules in the apparatus for determining the performance of a coherent transmitter are implemented by software, and the modules in the apparatus are program modules. In other embodiments, the modules in the apparatus are implemented by hardware or firmware.

[0032] In a fourth aspect, the present disclosure provides an apparatus for determining coherent transmitter performance, the apparatus having the function of implementing the second aspect above. The apparatus includes at least one module, the at least one module being configured to implement the method for determining coherent transmitter performance provided in the second aspect above.

[0033] In some embodiments, the modules in the apparatus for determining the performance of a coherent transmitter are implemented by software, and the modules in the apparatus are program modules. In other embodiments, the modules in the apparatus are implemented by hardware or firmware.

[0034] In a fifth aspect, the present disclosure provides a computing device, comprising a processor and a memory, wherein: computer instructions are stored in the memory, and the processor executes the computer instructions to implement the method for determining the performance of a coherent transmitter in the first aspect and its optional implementation, or the method for determining the performance of a coherent transmitter in the second aspect.

[0035] In a sixth aspect, the present disclosure provides a computer-readable storage medium storing computer instructions. When the computer instructions in the computer-readable storage medium are executed by a computing device, the computing device executes the method for determining the performance of a coherent transmitter in the first aspect and its optional implementation, or the method for determining the performance of a coherent transmitter in the second aspect.

[0036] In the seventh aspect, the present disclosure provides a computer program product comprising instructions, which, when executed on a computing device, enables the computing device to execute the method for determining the performance of a coherent transmitter in the first aspect and its optional implementation, or the method for determining the performance of a coherent transmitter in the second aspect.

[0037] In an eighth aspect, the present disclosure provides a system for determining the performance of a coherent transmitter, the system comprising a coherent receiving device and a device for determining the performance of a coherent transmitter as described in the fourth aspect and its optional implementation, or comprising a coherent receiving device and a device for determining the performance of a coherent transmitter as described in the fourth aspect.

[0038] The coherent receiving device is used to coherently receive the dual-polarization optical signal from the coherent transmitter to obtain the multi-channel analog signal included in the dual-polarization optical signal, and output the multi-channel analog signal to the device, wherein the multi-channel analog signal becomes a multi-channel digital signal after analog-to-digital conversion.

[0039] In a ninth aspect, the present disclosure provides a communication system comprising a coherent transmitter and a coherent receiving device for transmitting dual-polarized optical signals and a device for determining the performance of the coherent transmitter as described in the fourth aspect and its optional implementation method, or a device for determining the performance of the coherent transmitter as described in the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG1 is a schematic diagram of a system architecture of a communication system provided by an exemplary embodiment of the present disclosure;

[0041] FIG2 is a schematic diagram of a system architecture for determining the performance of a coherent transmitter provided by an exemplary embodiment of the present disclosure;

[0042] FIG3 is a schematic diagram of a method flow for determining the performance of a coherent transmitter provided by an exemplary embodiment of the present disclosure;

[0043] FIG4 is a flow chart of determining the performance of a coherent transmitter according to an exemplary embodiment of the present disclosure;

[0044] FIG5 is a flow chart of determining the performance of a coherent transmitter provided by another exemplary embodiment of the present disclosure;

[0045] FIG6 is a schematic diagram showing the correspondence between a virtual noise signal-to-noise ratio and a bit error rate provided by an exemplary embodiment of the present disclosure;

[0046] FIG7 is a schematic diagram of virtual noise signal-to-noise ratio and bit error rate interpolation provided by an exemplary embodiment of the present disclosure;

[0047] FIG8 is a schematic diagram of using a virtual noise signal-to-noise ratio to measure the performance of a coherent transmitter according to an exemplary embodiment of the present disclosure;

[0048] FIG9 is a schematic diagram of simulation of bit error rate and optical signal-to-noise ratio (OSNR) provided by an exemplary embodiment of the present disclosure;

[0049] FIG10 is a schematic diagram of a symbol number simulation provided by an exemplary embodiment of the present disclosure;

[0050] FIG11 is a schematic diagram of the structure of a computing device provided by an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0051] In order to make the objectives, technical solutions and advantages of the present disclosure more clear, the embodiments of the present disclosure will be further described in detail below with reference to the accompanying drawings.

[0052] For high-speed DWDM systems, an accurate metric needs to be defined to evaluate the performance of coherent transmitters, which can also be considered as evaluating the quality of coherent transmitters. The bit error rate (BER) is a direct indicator of coherent transmitter performance. However, due to the low BER threshold, the number of bits required to transmit to calculate the bit error rate exceeded the buffer depth of the real-time sampling oscilloscope. Performance measurement relies on indirect performance indicators such as EVM or signal-to-noise ratio (SNR). EVM uses the root mean square (RMS) of the constellation diagram error as the standard deviation of AWGN to approximate the bit error rate. When the degradation of the coherent transmitter comes only from AWGN, measuring the performance of the coherent transmitter based on EVM is accurate. However, high-speed coherent transmitters are subject to various non-AWGN impairments, such as in-phase quadrature (IQ) imbalance, IQ skew, transmitter bandwidth limitations, and modulator nonlinearities. IQ imbalance refers to unequal proportions between the I and Q signals, while IQ skew refers to the time offset between the I and Q signals at each polarization state. While some improved EVM analysis methods exist for specific impairments, considering all possible impairments simultaneously makes EVM corrections extremely complex, defeating the original purpose of using EVM for simplicity.

[0053] With the development of high-performance forward error correction (FEC) technology, the bit error rate threshold can now operate at the 1E-2 level. Furthermore, the increasing buffer depth of real-time oscilloscopes (such as those supporting 10 megasamples) has made it possible to directly measure the performance of coherent transmitters by measuring the bit error rate. Based on this, the present disclosure provides a method for measuring the performance of coherent transmitters based on the bit error rate.

[0054] For ease of understanding, the system architecture of the communication system is described below.

[0055] Figure 1 exemplifies a system architecture for a communication system. This system architecture includes a coherent transmitter 11 and a system 12 for determining the performance of the coherent transmitter. The coherent transmitter 11 and the system 12 are connected via an optical fiber. The coherent transmitter 11 is the coherent transmitter to be tested and is configured to transmit a dual-polarized optical signal. The system 12 is configured to receive the dual-polarized optical signal transmitted by the coherent transmitter 11 and determine the performance of the coherent transmitter 11 based on the dual-polarized optical signal.

[0056] The coherent transmitter 11 is a high-speed coherent transmitter, such as a coherent transmitter with a bandwidth of 400G. The coherent transmitter 11 includes a DSP, a digital-to-analog converter (DAC), an optical signal providing component, a first in-phase / quadrature modulator, a second in-phase / quadrature modulator, and a polarization beam combiner (PBC). When transmitting an optical signal, the electrical signal of the test signal enters the DAC through the DSP. The DAC performs digital-to-analog conversion on it and converts it into an analog signal. The analog signal is converted into a four-channel analog signal through serial-to-parallel conversion, where the test signal is a signal sequence of a fixed length. The test signal is random and can simulate the data transmitted in a real optical transmission scenario. The optical signal providing component includes a laser and a polarization beam splitter. The laser transmits an optical signal, which passes through the polarization beam splitter and becomes an x-polarized and y-polarized optical signal, where the x-polarization and y-polarization are perpendicular. The first in-phase / quadrature modulator includes two modulators and a π / 2 phase shifter, and the second in-phase / quadrature modulator includes two modulators and a π / 2 phase shifter. The two modulators in the first in-phase / quadrature modulator modulate the two analog signals onto the x-polarized optical signal, respectively, to obtain two modulated polarized optical signals. One of the signals passes through a π / 2 phase shifter, shifting its phase by π / 2, making it orthogonal to the other signal. The signals ultimately output an x-polarized co-directional signal and a quadrature signal, denoted as Ix1 and Qx1. The two modulators in the second in-phase / quadrature modulator modulate the two analog signals onto the y-polarized optical signal, respectively, to obtain two modulated polarized optical signals. One of the signals passes through a π / 2 phase shifter, shifting its phase by π / 2, making it orthogonal to the other signal. The signals ultimately output a y-polarized co-directional signal and a quadrature signal, denoted as Iy1 and Qy1. The two polarized co-directional and quadrature signals are then combined into a dual-polarized optical signal by a polarization combiner and transmitted to system 12 via an optical fiber. The length of the optical fiber is set according to actual test requirements.

[0057] The system 12 includes a coherent receiving device 121 and a determining device 122. The coherent receiving device 121 is configured to obtain four analog signals carried by the dual-polarized optical signals from the coherent transmitter 11. The determining device 122 is configured to determine the performance of the coherent transmitter 11 based on the four analog signals.

[0058] Referring to Figure 2, the coherent receiving device 121 includes a polarization beam splitter, a local oscillator light providing component, a first 90-degree hybrid, a second 90-degree hybrid, and four pairs of detectors, each pair including two detectors. The polarization beam splitter splits the dual-polarization optical signal from the coherent transmitter 11 into an x-polarized optical signal and a y-polarized optical signal. The local oscillator light providing component includes a laser and a polarization beam splitter. The laser emits a local oscillator light signal, which passes through the polarization beam splitter and is converted into x-polarized and y-polarized local oscillator light signals. The x-polarized local oscillator light signal and the x-polarized light signal enter the first 90-degree hybrid for mixing, outputting four optical signals. The relative phase differences of the four optical signals are 0 degrees, 90 degrees, 180 degrees, and 270 degrees. Among the four optical signals, the optical signals with a phase difference of 0 degrees and 180 degrees enter a pair of detectors to generate one electrical signal, and the optical signals with a phase difference of 90 degrees and 270 degrees enter another pair of detectors to generate one electrical signal. The y-polarized local oscillator optical signal and the y-polarized optical signal enter the second 90-degree mixer for mixing, outputting four optical signals with relative phase differences of 0, 90, 180, and 270 degrees. The optical signals with a phase difference of 0 and 180 degrees enter a pair of detectors, generating one electrical signal. The optical signals with a phase difference of 90 and 270 degrees enter another pair of detectors, generating one electrical signal. In this manner, the coherent receiving device 121 outputs the four electrical signals to the determining device 122.

[0059] The determining device 122 is a real-time oscilloscope or computing device with digital signal processing capabilities, and the computing device is a server or terminal device. The determining device 122 includes an analog-to-digital conversion module and a digital signal processing module. The analog-to-digital conversion module is used to perform analog-to-digital conversion on the four electrical signals from the coherent receiving device 121, converting them into four digital signals. For example, the analog-to-digital conversion module includes four analog-to-digital conversion units, and the four analog-to-digital conversion units convert the four electrical signals into four digital signals, respectively. The four digital signals are four real-number digital signals. The digital signal processing module is used to determine the performance of the coherent transmitter 11 based on the four digital signals. The four digital signals include a co-directional signal of x polarization, a co-directional signal of y polarization, an orthogonal signal of x polarization, and an orthogonal signal of y polarization, respectively represented as Ix, Iy, Qx, and Qy. The four digital signals can also be referred to as four field component signals. Alternatively, the digital signal processing module converts the four digital signals into two complex digital signals, one of which is an x-polarized co-directional signal and an orthogonal signal, and the other is a y-polarized co-directional signal and an orthogonal signal. The process of determining the performance of the coherent transmitter 11 by the determination device 122 is described in conjunction with FIG3.

[0060] FIG3 provides a method flow for determining the performance of a coherent transmitter 11 (hereinafter described as a coherent transmitter), see steps 301 to 304 .

[0061] Step 301: Acquire a multi-channel digital signal carried by a dual-polarization optical signal from the coherent transmitter, wherein the multi-channel digital signal is a dual-polarization co-directional and orthogonal signal.

[0062] In this embodiment, as described above, the analog-to-digital conversion module performs analog-to-digital conversion on the four electrical signals from the coherent receiving device 121, converting them into four digital signals. The four digital signals are four real digital signals. Alternatively, the digital signal processing module combines the four digital signals into two complex digital signals. In this way, the obtained multi-channel digital signal includes four real digital signals or two complex digital signals.

[0063] Step 302 : Perform a noise search based on the multi-channel digital signal to obtain a first power of additive white Gaussian noise added to the multi-channel digital signal at a bit error rate threshold.

[0064] The bit error rate threshold is the decision threshold for forward error correction. It refers to the maximum bit error rate at which a coherent receiver can correctly decode a dual-polarization optical signal transmitted by a coherent transmitter. The bit error rate threshold is related to the coherent transmitter's transmission bandwidth, process technology, optical signal transmission power, and transmission distance.

[0065] In this embodiment, when the digital signal processing module performs noise search based on the multiple digital signals and determines the bit error rate as the bit error rate threshold, the power of the additive white Gaussian noise added to the multiple digital signals is called the first power.

[0066] When performing noise search, the same additive white Gaussian noise is added to each digital signal, and then the comprehensive bit error rate of multiple digital signals is calculated uniformly. The first power is the power of the additive white Gaussian noise added to each digital signal.

[0067] Step 303: Obtain a second power of additive white Gaussian noise added to the ideal signal at the bit error rate threshold.

[0068] The ideal signal is an undistorted digital signal determined based on multiple digital signals.

[0069] In this embodiment, the digital signal processing module adds additive white Gaussian noise to the ideal signal so that the bit error rate reaches the bit error rate threshold. The power of the additive white Gaussian noise added to the ideal signal when the bit error rate is the bit error rate threshold is determined, which is called the second power.

[0070] The method for obtaining the second power here is similar to the method for obtaining the first power, and will not be repeated here.

[0071] Step 304: Determine the performance of the coherent transmitter according to the first power and the second power.

[0072] In one implementation of step 304, the performance of the coherent transmitter is determined based on the first power, the second power, and the noise of the coherent receiver front end.

[0073] The coherent receiver front end is used to convert the received dual-polarization optical signal into an electrical signal. The noise of the coherent receiver front end is determined based on empirical values. For example, the noise is the common noise of the front end of a first-generation coherent receiver used to receive the dual-polarization optical signal transmitted by the coherent transmitter under test.

[0074] In this embodiment, the digital signal processing module determines a transmitter constellation closure cost based on the first power, the second power, and the noise at the coherent receiver front end. The transmitter constellation closure cost is used to characterize the performance of the coherent transmitter. A smaller transmitter constellation closure cost indicates better coherent transmitter performance, while a larger transmitter constellation closure cost indicates worse coherent transmitter performance. The transmitter constellation closure cost is used to indicate the quality of the constellation, which is generated based on the dual-polarization optical signal from the coherent transmitter. The quality of the constellation includes the degree of openness or closeness of the constellation points, which can also be referred to as the degree of discreteness.

[0075] In another implementation of step 304, the first power and the second power are used to directly determine the performance of the coherent transmitter. Exemplarily, the performance of the coherent transmitter can be determined using the relative virtual noise signal-to-noise ratio of the signal. Under the bit error rate threshold, the relative virtual noise signal-to-noise ratio is the difference between the first virtual noise signal-to-noise ratio and the second virtual noise signal-to-noise ratio. The first virtual noise signal-to-noise ratio is the virtual noise signal-to-noise ratio of the multiple digital signals under the bit error rate threshold. The second virtual noise signal-to-noise ratio is the virtual noise signal-to-noise ratio of the ideal signal under the bit error rate threshold. When the signal power has been normalized, the virtual noise signal-to-noise ratio is determined by the inverse of the power of the additive white Gaussian noise added to the signal, see formula (1). The ideal signal is an undistorted signal determined based on the multiple digital signals.

[0076] In formula (1), SNR is the virtual noise signal-to-noise ratio, σ 2 is the power of the additive white Gaussian noise added to the signal.

[0077] Thus, for each target bit error rate, the relative virtual noise signal-to-noise ratio is expressed as formula (2).

[0078] In formula (2), △SNR is the relative virtual noise signal-to-noise ratio, σ 2 TUT is the first power, σ 2 ideal The second power.

[0079] Then, it is determined whether the relative virtual noise signal-to-noise ratio is greater than a specified threshold corresponding to the bit error threshold. If so, it is determined that the performance of the coherent transmitter does not meet the standard; otherwise, it is determined that the performance of the coherent transmitter meets the standard.

[0080] In an optional manner, the digital signal processing module can be logically divided into multiple parts. The following describes the process of determining the performance of a coherent transmitter in conjunction with the division method of the digital signal processing module. Figure 4 provides a block diagram of the process, corresponding to the following steps 401 to 405. Referring to Figure 4, the digital signal processing module includes a low-pass filter (LPF), a pulse shaping filter (PSF), a noise search unit, a reference equalizer, a measurement unit, and a calculation unit. Figure 4 uses four real digital signals as an example for illustration. The method of evaluating the performance of a coherent transmitter based on two complex digital signals is similar and will not be repeated in detail in the present embodiment.

[0081] Step 401: A low-pass filter performs low-pass filtering on the multi-channel real digital signals.

[0082] The bandwidth of the low-pass filter is determined based on the bandwidth of the coherent receiver front end and is used to simulate the bandwidth limitation of the coherent receiver front end. Exemplarily, the bandwidth of the low-pass filter is equal to the bandwidth of the coherent receiver front end, which is determined based on empirical values. For example, the bandwidth of the coherent receiver front end is the common bandwidth of the front end of a first-generation coherent receiver, which is used to receive the optical signal transmitted by the coherent transmitter under test. The low-pass filter can be a Gaussian filter with a 3dB bandwidth of Bd / 2, where Bd is the symbol rate of the dual-polarization signal.

[0083] In this embodiment, the digital signal processing module receives four real digital signals from the analog-to-digital conversion module, and the low-pass filter performs low-pass filtering on the four real digital signals to obtain four low-pass filtered signals. For example, the low-pass filter has four channels for low-pass filtering, and the four channels respectively perform low-pass filtering on the four real digital signals to obtain four low-pass filtered signals.

[0084] It should be noted that the bandwidth of the coherent receiving device used to test the performance of the coherent transmitter is generally large and will not limit the signal. Therefore, a low-pass filter is introduced here to simulate the bandwidth limitation of the coherent receiver front end to subsequently determine the performance of the coherent transmitter under this coherent receiver front end.

[0085] Step 402: A pulse shaping filter performs pulse shaping and matched filtering on the low-pass filtered signal to obtain a matched filtered signal.

[0086] In this embodiment, the pulse shaping filter performs pulse shaping on the four low-pass filtered signals to obtain four pulse-shaped signals. The four pulse-shaped signals are then filtered to perform matched filtering to obtain four matched filtered signals. For example, the pulse shaping filter may have four channels for pulse shaping filtering, and the four channels perform pulse shaping and matched filtering on the four low-pass filtered signals to obtain four matched filtered signals.

[0087] Optionally, the pulse shaping filter is a root raised cosine (RRC) filter, and a roll-off factor of the RRC filter is 0.1.

[0088] In step 403, a noise search unit adds additive white Gaussian noise (AWGN) to the matched filtered signal to obtain an AWGGN-added signal. A reference equalizer performs equalization on the AWGGN-added signal to obtain an equalized signal. Based on the equalized signal, the noise search unit determines a first power of the AWGGN to be added to the matched filtered signal at a bit error rate threshold, and obtains a second power of the AWGGN to be added to the ideal signal at the bit error rate threshold.

[0089] The reference equalizer may be a feed forward equalizer (FFE), for example, a 13-tap FFE with a T / 2 interval, where T is a symbol period.

[0090] In this embodiment, the noise search unit outputs the matched filtered signal to the reference equalizer. The reference equalizer performs equalization damage processing on the matched filtered signal to obtain a balanced signal. The balanced signal is a recovered symbol sequence. The noise search unit uses the recovered symbol sequence to calculate the bit error rate and determines whether the bit error rate reaches the bit error rate threshold. If the bit error rate threshold is reached, the power of the additive white Gaussian noise is determined to be 0. If the bit error rate threshold is not reached, additive white Gaussian noise is added to the matched filtered signal to obtain a signal after the additive white Gaussian noise is added. The reference equalizer performs equalization processing on the signal after the additive white Gaussian noise is added to obtain a balanced signal. The balanced signal is a recovered symbol sequence. The noise search unit uses the recovered symbol sequence to calculate the bit error rate and determines whether the bit error rate reaches the bit error rate threshold. If the bit error rate threshold is reached, the power of the currently added additive white Gaussian noise is obtained. If the bit error rate threshold is not reached, the additive white Gaussian noise is continued to be added until the bit error rate reaches the bit error rate threshold, and the power of the currently added additive white Gaussian noise is obtained. For simplicity of description, the power of the added additive white Gaussian noise is referred to as the first power.

[0091] And the noise search unit obtains the ideal signal, such as the sequence of the ideal signal can be the sequence of the test signal mentioned above. The power of the ideal signal is the same as the power of the four-way real digital signal after passing through the low-pass filter, the pulse shaping filter and the reference equalizer. The noise search unit determines the power of the additive white Gaussian noise added when the ideal signal reaches the bit error rate threshold. For example, the noise search unit directly uses the formula to calculate the power of the added additive white Gaussian noise. For another example, the noise search unit performs a noise search on the ideal signal to obtain the power of the added additive white Gaussian noise. The noise search process is the same as the process of performing a noise search on the signal after matched filtering. In order to simplify the description, the power of the additive white Gaussian noise added here is referred to as the second power.

[0092] In step 404 , the measuring unit determines the power of the four-channel real digital signal and the power of the matched filtered signal.

[0093] In this embodiment, the measurement unit calculates the power of the four-way real digital signal before entering the low-pass filter, and the power of the four-way real digital signal is equal to the sum of the power of the four-way real digital signal, which is expressed as punfiltered. And the measurement unit calculates the power of the signal after matched filtering, which is expressed as p filtered , which is the sum of the powers of the four real digital signals after passing through the low-pass filter and the pulse shaping filter.

[0094] Step 405: The calculation unit determines the performance of the coherent transmitter according to the first power, the second power, and the noise of the front end of the coherent receiver.

[0095] In this embodiment, the digital signal processing module determines the performance of the coherent transmitter using equation (1).

[0096] Where, in formula (3), TCC is the transmitter constellation closure cost, is the first power, is the second power, The power of the noise at the front end of the coherent receiver is determined based on an empirical value. For example, the noise is the common noise at the front end of a first-generation coherent receiver, which is used to receive the optical signal transmitted by the coherent transmitter to be tested.

[0097] In formula (3), the transmitter constellation closure cost is used to reflect the performance of the coherent transmitter. The smaller the transmitter constellation closure cost, the greater the power of the additive white Gaussian noise added to the matched filtered signal when the bit error rate threshold is reached, which means that the noise of the optical signal received by the coherent receiver is relatively low, and thus the performance of the coherent transmitter is better. Conversely, the larger the transmitter constellation closure cost, the smaller the power of the additive white Gaussian noise added to the matched filtered signal when the bit error rate threshold is reached, which means that the noise of the optical signal received by the coherent receiver is relatively high, and thus the performance of the coherent transmitter is worse.

[0098] Alternatively, the digital signal processing module determines the performance of the coherent transmitter using equation (2).

[0099] Where, in formula (4), TCC is the transmitter constellation closure cost, is the first power, is the second power, is the power of the noise at the front end of the coherent receiver. The power of the noise at the front end of the coherent receiver is determined based on the empirical value. punfiltered is the power of the four-way real digital signal. filtered is the power of the signal after matched filtering.

[0100] In formula (4), the closure cost of the transmitter constellation is reflected by two parts, one part is the added additive white Gaussian noise, and the other part is the bandwidth of the signal transmitted by the coherent transmitter. When considering the added additive white Gaussian noise, when the bit error rate threshold is reached, the greater the power of the additive white Gaussian noise added to the matched filtered signal, the less noise the optical signal received by the coherent receiver, and thus the better the performance of the coherent transmitter. Conversely, when the bit error rate threshold is reached, the smaller the power of the additive white Gaussian noise added to the matched filtered signal, the greater the noise of the optical signal received by the coherent receiver, and thus the worse the performance of the coherent transmitter. When considering the bandwidth of the signal transmitted by the coherent transmitter, It represents the ratio of the power of the four-way real digital signal to the power after low-pass filtering, pulse shaping, and matched filtering. The larger the ratio, the greater the loss after low-pass filtering, pulse shaping, and matched filtering. Conversely, the smaller the ratio, the smaller the loss, indicating that the bandwidth of the signal transmitted by the coherent transmitter is more appropriate. Therefore, this ratio can be used to constrain the bandwidth of the signal transmitted by the coherent transmitter. In this way, when measuring the performance of the coherent transmitter, the smaller the cost of the transmitter constellation diagram closure, the better the performance of the coherent transmitter. Conversely, the larger the cost of the transmitter constellation diagram closure, the worse the performance of the coherent transmitter. The determination method of formula (4) not only considers the additive white Gaussian noise, but also takes into account the bandwidth of the signal transmitted by the coherent transmitter, so it can more accurately determine the performance of the coherent transmitter.

[0101] It should be noted that when using formula (3) to calculate the transmitter constellation closure cost, step 404 is not necessary. In addition, when the low-pass filter is not used, p filtered is the power of the matched filtered signal without low-pass filtering.

[0102] It should also be noted that in the above step 405, the noise of the front end of the coherent receiver is used when determining the closure cost of the transmitter constellation diagram. The reason is that the signal received by the coherent receiving device already contains the noise of the front end of the coherent receiver. In order to eliminate the influence of this part of the noise, the power of the noise of the front end of the coherent receiver is added to the denominator, so that only the damage and noise of the coherent transmitter are retained, thereby making the performance of the determined coherent transmitter accurate.

[0103] In the block diagram shown in FIG4 , the low-pass filter performs low-pass filtering on a digital signal. In another optional manner, the low-pass filter may also perform low-pass filtering on an analog signal. The processing of the low-pass filtering is as follows:

[0104] The analog-to-digital conversion module includes a low-pass filter and an analog-to-digital conversion unit. After receiving the four analog signals from the detector, the low-pass filter performs low-pass filtering on the four analog signals to produce four low-pass filtered analog signals. The analog-to-digital conversion unit performs analog-to-digital conversion on the four low-pass filtered analog signals to produce four real digital signals. See Figure 5 for a flowchart of the digital signal processing module determining the closure cost of the transmitter constellation diagram in this case. These four real digital signals are input into a pulse shaping filter for subsequent processing. This subsequent processing is identical to the process in the block diagram shown in Figure 4, except that punfiltered represents the power of the four real digital signals before passing through the pulse shaping filter.

[0105] In an optional approach, in order to accurately determine the performance of the coherent transmitter, a certain number of symbols need to be measured. When the bit error rate threshold is equal to 1E-2, at least 1×10 5 symbols, that is, the dual-polarization optical signal includes at least 1×10 5 For example, when the bit error rate threshold is equal to 1E-2, approximately 3×10 5 Since the current oscilloscope has an increased buffer depth, it is easy to achieve a sampling rate of 3×10 5 symbols.

[0106] Alternatively, in order to accurately determine the performance of the coherent transmitter, when the bit error rate threshold is equal to 1E-2, each constellation point in the constellation diagram after decoding the dual-polarization optical signal is approximately 2×10 4 symbols.

[0107] In the process described in Figure 3 above, the bit error rate threshold is considered. To more comprehensively measure the performance of a coherent transmitter, the performance margin and the bit error floor performance can be considered, rather than just the bit error rate threshold. The performance margin refers to the amount of headroom reserved for the coherent transmitter's performance to account for uncertainties and provide fault tolerance to ensure reliability. The bit error rate gradually decreases as the signal-to-noise ratio increases. The point at which it stops decreasing is called the bit error floor. Therefore, in addition to considering the forward error correction decision threshold as the bit error rate threshold, a wider range of bit error rates can be considered to obtain a set of measurement results at different bit error rates.

[0108] Here, at least one target bit error rate is taken into consideration as an example. The number and value of the at least one target bit error rate are set according to actual needs or empirical values. For example, the at least one target bit error rate includes 3 bit error rates. The target bit error rate can be less than the bit error rate threshold or greater than the bit error rate threshold. Here, the target bit error rate is less than the bit error rate threshold as an example for explanation.

[0109] When the sensitivity cost is TCC, for the bit error rate threshold, the TCC of the coherent transmitter is determined using formula (3) and formula (4), which is called the first sensitivity cost. For each target bit error rate, a noise search is performed on the multi-channel digital signal to obtain the power of the additive white Gaussian noise added to the multi-channel digital signal at the target bit error rate, which is called the third power. In this way, for at least one target bit error rate, at least one third power can be obtained. And for each target bit error rate, the power of the additive white Gaussian noise added to the ideal signal is obtained, which is called the fourth power. In this way, for at least one target bit error rate, at least one fourth power can be obtained. Then for each target bit error rate, according to formula (3) and formula (4), the TCC of the coherent transmitter corresponding to the target bit error rate is determined, which is called the second sensitivity cost, σ 2 TUT is the third power, σ 2 ideal The fourth power.

[0110] When the sensitivity cost is the relative virtual noise signal-to-noise ratio, for a certain bit error rate, the relative virtual noise signal-to-noise ratio is the difference between the first virtual noise signal-to-noise ratio and the second virtual noise signal-to-noise ratio. The first virtual noise signal-to-noise ratio is the virtual noise signal-to-noise ratio of the multi-channel digital signal at the target bit error rate, and the second virtual noise signal-to-noise ratio is the virtual noise signal-to-noise ratio of the ideal signal at the target bit error rate. When the signal power has been normalized, the virtual noise signal-to-noise ratio is determined by the inverse of the power of the additive white Gaussian noise added to the signal, see formula (1). For the bit error rate threshold, the relative virtual noise signal-to-noise ratio of the coherent transmitter is determined using formula (2), which is called the first sensitivity cost. For each target bit error rate, the relative virtual noise signal-to-noise ratio of the coherent transmitter is determined using formula (2), which is called the second sensitivity cost, except that σ 2 TUT is the third power, σ 2 ideal The fourth power.

[0111] Alternatively, there is a conversion relationship between each relative virtual noise signal-to-noise ratio and TCC. The conversion relationship is shown in formula (5).

[0112] In formula (5), ΔSNR is the relative virtual noise signal-to-noise ratio, and TCC can be obtained according to formula (3) or formula (4) in the previous article. When calculating ΔSNR, it can be calculated using formula (2) or formula (5).

[0113] Considering the noise of the front end of the coherent receiver in practice In a certain range, it can be ignored. It is also within a certain range and close to 1, so formula (5) can be converted to formula (2).

[0114] Both the bit error rate threshold and the target bit error rate are bit error rates, and both correspond to a sensitivity penalty for the coherent transmitter. After obtaining the sensitivity penalty corresponding to each bit error rate, for each bit error rate, it can be determined whether the sensitivity penalty corresponding to the bit error rate exceeds a first threshold. The first threshold is a specified threshold corresponding to the bit error rate, which can be set according to actual needs. If the sensitivity penalty corresponding to at least one bit error rate exceeds the specified threshold, the coherent transmitter is determined to be substandard. Otherwise, the coherent transmitter is determined to be meeting the performance standard.

[0115] For example, as shown in Table 1, a corresponding relationship table between the bit error rate and the specified threshold required by TCC is provided when the sensitivity cost is TCC.

[0116] Table 1

[0117] As shown in Table 2, a corresponding relationship table of the bit error rate and the corresponding specified threshold is provided when the sensitivity cost is the relative virtual noise signal-to-noise ratio.

[0118] Table 2

[0119] Figure 6 also provides a plot of the virtual noise signal-to-noise ratio (SNR) versus bit error rate (BER). As shown in Figure 6, Curve 1 represents the SNR versus BER curve for an ideal signal. Curve 2, Curve 1, the BER threshold, and the target BER minimum in Table 2 form a region. If the coherent transmitter's sensitivity penalty falls within this region, the performance meets the standard; otherwise, it fails to meet the standard. For example, circles represent coherent transmitters that meet the performance standard, while squares and ovals represent coherent transmitters that fail to meet the performance standard. Furthermore, this region, shaped like a waterfall, is also called the waterfall template region.

[0120] In another optional method, when there are multiple bit error rates, considering that the more bit error rates there are, the more calculations are required. Therefore, in order to improve the calculation efficiency, an interpolation method can be used to calculate the first sensitivity cost corresponding to each bit error rate. The processing method is:

[0121] When calculating the sensitivity penalty of a coherent transmitter in a single pass, noise is gradually added to the signal according to a certain step size. Each time the step size is adjusted, a set of sensitivity penalties and bit error rates is obtained. By interpolating multiple sets of sensitivity penalties and bit error rates, the sensitivity penalties at various bit error rates can be obtained. This improves computational efficiency. Figure 7 shows a schematic diagram of interpolating the relative virtual noise signal-to-noise ratio at various bit error rates. Figure 7 shows two coherent transmitters and an ideal coherent transmitter, with a circle indicating one coherent transmitter and a square indicating the other.

[0122] In another optional approach, considering that a single constraint may be inaccurate, the virtual noise signal-to-noise ratio and TCC may be used for simultaneous constraint.

[0123] The formula for the virtual noise signal-to-noise ratio is shown in formula (1). Using formula (1), the power of the additive white Gaussian noise added to the multi-channel digital signal can be determined. Then, the additive white Gaussian noise of this power is added to each digital signal in the multi-channel digital signal to calculate the bit error rate of the multi-channel digital signal. In this way, using at least one virtual noise signal-to-noise ratio, at least one bit error rate can be obtained, and the virtual noise signal-to-noise ratio corresponds to the bit error.

[0124] The TCC of the coherent transmitter is determined using one or more bit error rates. If multiple bit error rates are used, multiple TCCs can be calculated. See the TCC calculation process described above. When using a single bit error rate, the bit error rate can be a bit error rate threshold. When using multiple bit error rates, the multiple bit error rates include the bit error rate threshold and at least one target bit error rate. The following uses a single bit error rate as an example.

[0125] Then, for each virtual noise signal-to-noise ratio, the ratio of the bit error rate corresponding to the virtual noise signal-to-noise ratio to the bit error rate threshold is calculated to determine whether the ratio is greater than the bit error rate ratio corresponding to the virtual noise signal-to-noise ratio. Furthermore, a determination is made as to whether the TCC corresponding to the bit error rate threshold is greater than a specified threshold corresponding to the bit error rate threshold. If no ratio is greater than the corresponding bit error rate ratio, and no TCC corresponding to the bit error rate threshold is greater than the specified threshold corresponding to the bit error rate threshold, the coherent transmitter is determined to have met the performance standard. Otherwise, the coherent transmitter is determined to have failed to meet the performance standard.

[0126] For example, as shown in Tables 3 and 4, both the bit error rate threshold and the relative virtual noise signal-to-noise ratio are used as constraints. Table 3 uses the bit error rate threshold as a constraint, while Table 4 uses the relative virtual noise signal-to-noise ratio as a constraint, uses the forward error correction judgment threshold as the bit error rate threshold, and uses two virtual noise signal-to-noise ratios.

[0127] Table 3

[0128] Table 4

[0129] Figure 8 provides the coordinate points of the virtual noise SNR and BER in Table 4.

[0130] In another optional approach, the performance of the coherent transmitter can be determined using only the contents of Table 4. For example, for each virtual noise signal-to-noise ratio, the above method is used to calculate the bit error rate of the multi-channel digital signal at each virtual noise signal-to-noise ratio. Then, for each specified virtual noise signal-to-noise ratio, the ratio of the bit error rate corresponding to the virtual noise signal-to-noise ratio to the bit error rate threshold is calculated, and a determination is made as to whether the ratio is greater than the bit error rate ratio corresponding to the virtual noise signal-to-noise ratio. If no ratio is greater than the corresponding bit error rate ratio, the coherent transmitter is determined to meet the performance standard; otherwise, the coherent transmitter is determined to fail to meet the performance standard.

[0131] In this way, since there is no need to adjust the power of the additive white Gaussian noise one by one, the calculation process can be simplified and computing resources can be saved.

[0132] In an optional manner, at a target bit error rate, the dual-polarization optical signal includes at least 1×10 5 symbols.

[0133] In an optional manner, the analog-to-digital conversion module acquires multiple digital signals, the digital signal processing module determines the power, and the power and other information are used to determine the performance of the coherent transmitter.

[0134] It should be noted that the above are all based on thresholds to judge the performance of the coherent transmitter. In practice, you can also first draw the waterfall template area shown in Figure 6, and then determine whether it falls within the waterfall template area. If it does, it is determined that the performance of the coherent transmitter meets the standard. Otherwise, it is determined that the performance of the coherent transmitter does not meet the standard. The further it deviates from the waterfall template area, the worse the performance of the coherent transmitter.

[0135] In addition, in the embodiment of the present disclosure, no noise may be added to the signal, and the EVM may be obtained by measuring the recovered signal, and the EVM may be used as auxiliary information for judging the performance of the coherent transmitter.

[0136] In order to better illustrate the effect of using a bit error rate threshold to determine the performance of a coherent transmitter in the embodiment of the present disclosure, the effect of the embodiment of the present disclosure is illustrated below with simulation results.

[0137] Using 112GBd probabilistic constellation shaping (PCS)-16 quadrature amplitude modulation (QAM) back-to-back (BTB) transmission as an example, the accuracy of the EVM method and the bit error rate method (the method used in this disclosure to determine the performance of a coherent transmitter) are compared. Figure 9 shows the bit error rate and optical signal-to-noise ratio curves for four cases measured using the EVM method and the bit error rate method, with the horizontal axis showing the optical signal-to-noise ratio in dB and the vertical axis showing the bit error rate. The first case is that there is only additive white Gaussian noise in the coherent transmitter, corresponding to curves i and j, curve i is the EVM method, and curve j is the bit error rate method. The second case is that the bandwidth of the signal transmitted by the coherent transmitter is 67 GHz, the resolution of the analog-to-digital converter is 4 bits (bit), and the linewidth of the laser in the coherent transmitter is 0 kHz, corresponding to curves e and curve f, curve e is the EVM method, and curve f is the bit error rate method. The third case is that the bandwidth of the signal transmitted by the coherent transmitter is 55 GHz, the resolution of the analog-to-digital converter is 4 bits, and the linewidth of the laser in the coherent transmitter is 0 kHz, corresponding to curves c and curve d, curve c is the EVM method, and curve d is the bit error rate method. The fourth case is that the bandwidth of the signal transmitted by the coherent transmitter is 55 GHz, the resolution of the analog-to-digital converter is 4 bits, and the linewidth of the laser in the coherent transmitter is 3 kHz, corresponding to curves a and curve b, curve a is the EVM method, and curve b is the bit error rate method. As shown in Figure 9, when the coherent transmitter is exposed only to additive white Gaussian noise, the EVM curve matches the bit error rate curve perfectly. When intersymbol interference (ISI) is present, the EVM method underestimates the actual bit error rate. As shown in Table 5, in some scenarios, the EVM method can achieve an error of up to 0.5 dB.

[0138] Table 5

[0139] Table 5 shows that, when the presence of additive white Gaussian noise (AWGN) is not exclusive, the optical signal-to-noise ratio (OSNR) calculated using the BER method is lower than that calculated using the EVM method to achieve the same BER. This indicates that the EVM method requires a higher OSNR to achieve this BER, suggesting that the EVM method overestimates the noise. When the presence of additive white Gaussian noise is not exclusive, the coherent transmitter power penalty calculated using the BER method is lower than that calculated using the EVM method to achieve the same BER. This indicates that the EVM method requires a higher power penalty to achieve this BER, suggesting that the power penalty is overestimated. Therefore, using the BER method can reduce the optical output power of the coherent transmitter.

[0140] In an embodiment of the present disclosure, a simulation diagram of the measurement error of the bit error rate method and the number of measured symbols is also provided, see Figure 10. In Figure 10, the horizontal axis is the number of symbols, and the vertical axis is the measurement error. Figure 10 is the measurement error of dual-polarization (DP)-16QAM and PCS-shaped DP-16QAM when the bit error rate threshold is IE-2. Figure 10 provides curves of the measurement errors of three symbols, namely curve 1, curve 2 and curve 3. Curve 1 corresponds to each symbol including 4.0 bits, curve 2 corresponds to each symbol including 3.5 bits, and curve 3 corresponds to each symbol including 3.0 bits. It can be seen from Figure 10 that when the number of measured symbols exceeds 1×10 7 When , the measurement errors of the three symbols are close.

[0141] In addition, when obtaining the simulation results of Figure 10, constellation diagrams of three symbols are also obtained. When the symbol includes 4.0 bits, the constellation points in the constellation diagram are evenly distributed. When the symbol includes 3.5 bits or 3.0 bits, the constellation points in the constellation diagram are unevenly distributed. The number of symbols at the middle constellation points is large, and the number of symbols at the edge is small, which is not shown in Figure 10.

[0142] In an embodiment of the present disclosure, a computing device 100 is also provided. As shown in FIG11 , computing device 100 includes a bus 102, a processor 104, a memory 106, and a communication interface 108. Processor 104, memory 106, and communication interface 108 communicate with each other via bus 102. Computing device 100 may be a server or a terminal device. It should be understood that the present disclosure does not limit the number of processors and memories in computing device 100.

[0143] Bus 102 may be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, among others. Buses may be classified as address buses, data buses, control buses, and the like. For ease of illustration, FIG11 shows only one bus line, but this does not imply a single bus or type of bus. Bus 102 may include a path for transmitting information between various components of computing device 100 (e.g., memory 106, processor 104, and communication interface 108).

[0144] The processor 104 may include any one or more processors such as a central processing unit (CPU), a graphics processing unit (GPU), a microprocessor (MP), or a digital signal processor (DSP).

[0145] The memory 106 may include volatile memory, such as random access memory (RAM). The memory 106 may also include non-volatile memory, such as read-only memory (ROM), flash memory, hard disk drive (HDD), or solid state drive (SSD).

[0146] The memory 106 stores executable computer instructions, and the processor 104 executes the executable computer instructions to implement the functions of the analog-to-digital conversion module and the digital signal processing module.

[0147] The communication interface 108 uses a transceiver module such as, but not limited to, a network interface card or a transceiver to implement communication between the computing device 100 and other devices or a communication network.

[0148] In an embodiment of the present disclosure, a computer program product is further provided. The computer program product includes computer instructions stored in a computer-readable storage medium. A processor of a computing device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the computing device to execute the process from steps 301 to 304.

[0149] Those skilled in the art will appreciate that the various method steps and units described in conjunction with the embodiments disclosed in this disclosure can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the steps and components of each embodiment have been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this disclosure.

[0150] In the several embodiments provided in the present disclosure, it should be understood that the disclosed system architecture, device and method can be implemented in other ways. For example, the device embodiment described above is schematic. For example, the division of the module is a logical function division. There may be other division methods in actual implementation. For example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or modules, or it can be an electrical, mechanical or other form of connection.

[0151] The modules described as separate components may or may not be physically separate, and the components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the objectives of the embodiments of the present disclosure.

[0152] In addition, the modules in the various embodiments of the present disclosure may be integrated into a single processing module, or each module may exist physically separately, or two or more modules may be integrated into a single module. The integrated modules may be implemented in the form of hardware or software modules.

[0153] If the integrated module is implemented in the form of a software functional module and used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present disclosure is essentially or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method in each embodiment of the present disclosure. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a ROM, a RAM, a magnetic disk, or an optical disk.

[0154] In the present disclosure, the words such as the term "first" and "second" are used to distinguish between identical or similar items having substantially the same effects and functions. It should be understood that there is no logical or temporal dependency between the "first" and "second", nor is the quantity and execution order limited. It should also be understood that although the following description uses the terms "first" and "second" etc. to describe various elements, these elements should not be limited by the terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of various examples, the first power can be referred to as the second power, and similarly, the second power can be referred to as the first power. Both the first power and the second power can be powers, and in some cases, can be separate and different powers.

[0155] The above description is merely an exemplary embodiment of the present disclosure, but the scope of protection of the present disclosure is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present disclosure, and such modifications or substitutions should be included in the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure should be based on the scope of protection of the claims.

Claims

1. A method for determining the performance of a coherent transmitter, characterized in that, The method includes: Obtaining multiple digital signals carried by a dual-polarization optical signal from the coherent transmitter, where the multiple digital signals are dual-polarization in-phase and quadrature signals; Performing noise search based on the multiple digital signals to obtain a first power of additive white Gaussian noise added to the multiple digital signals at a bit error rate threshold; Obtaining a second power of additive white Gaussian noise added to an ideal signal at the bit error rate threshold, where the ideal signal is an undistorted signal determined according to the multiple digital signals; Determining the performance of the coherent transmitter according to the first power and the second power.

2. The method according to claim 1, wherein The determining the performance of the coherent transmitter according to the first power and the second power includes: Determining the performance of the coherent transmitter according to the first power, the second power, and the noise at the front end of the coherent receiver.

3. The method according to claim 2, wherein The performing noise search based on the multiple digital signals to obtain a first power of additive white Gaussian noise added to the multiple digital signals at a bit error rate threshold includes: Performing pulse shaping and matched filtering on the multiple digital signals to obtain a signal after matched filtering; Performing noise search based on the signal after matched filtering to obtain a first power of additive white Gaussian noise added to the signal after matched filtering at the bit error rate threshold.

4. The method according to claim 3, wherein The performing noise search based on the signal after matched filtering to obtain a first power of additive white Gaussian noise added to the signal after matched filtering at the bit error rate threshold includes: Adding additive white Gaussian noise to the signal after matched filtering to obtain a signal after adding additive white Gaussian noise; Performing equalization processing on the signal after adding additive white Gaussian noise to obtain a signal after equalization processing; Determining a first power of additive white Gaussian noise added to the signal after matched filtering at the bit error rate threshold according to the signal after equalization processing.

5. The method according to claim 4, wherein Before performing pulse shaping and matched filtering on the multiple digital signals, it further includes: Performing low-pass filtering on the multiple digital signals, where the bandwidth for performing low-pass filtering is determined according to the bandwidth of the front end of the coherent receiver.

6. The method according to any one of claims 1 to 4, characterized in that, The obtaining multiple digital signals carried by a dual-polarization optical signal from the coherent transmitter includes: Obtaining multiple analog signals carried by a dual-polarization optical signal from the coherent transmitter; Performing low-pass filtering on the multiple analog signals to obtain a low-pass filtered analog signal, where the bandwidth for performing low-pass filtering is determined according to the bandwidth of the front end of the coherent receiver; Performing analog-to-digital conversion on the low-pass filtered analog signal to obtain the multiple digital signals.

7. The method according to any one of claims 2 to 5, characterized in that, The determining the performance of the coherent transmitter according to the first power, the second power, and the noise at the front end of the coherent receiver includes: According to the formula Determine the transmitter constellation closure cost, where TCC is the transmitter constellation closure cost, is the first power, is the second power, For the power of the noise at the front end of the coherent receiver, the transmitter constellation closure cost is used to characterize the performance of the coherent transmitter.

8. The method according to any one of claims 3 to 5, characterized in that The method further includes: Determining the power of the multiple digital signals and the power of the signal after matched filtering; Determining the performance of the coherent transmitter according to the first power, the second power, and the noise of the coherent receiver front end includes: According to the formula Determine the transmitter constellation closure cost, where TCC is the transmitter constellation closure cost, For the first power, For the second power, is the power of the noise at the front end of the coherent receiver, punfiltered is the power of the multiplexed digital signals, p filtered is the power of the signal after the matched filtering, and the transmitter constellation closure cost is used to characterize the performance of the coherent transmitter.

9. The method according to any one of claims 1 to 8, characterized in that At the bit error rate threshold, the dual-polarization optical signal includes at least 1×10 5 symbols.

10. The method according to claim 2, wherein Determining the performance of the coherent transmitter according to the first power, the second power, and the noise of the coherent receiver front end includes: Determining a first sensitivity penalty of the coherent transmitter at the bit error rate threshold according to the first power, the second power, and the noise of the coherent receiver front end; The method further includes: Performing noise search according to the multiplex digital signals to obtain a third power of additive white Gaussian noise added to the multiplex digital signals at at least one target bit error rate; Obtaining a fourth power of additive white Gaussian noise added to the ideal signal at the at least one target bit error rate; For a first target bit error rate among the at least one target bit error rates, determining a second sensitivity penalty of the coherent transmitter at the first target bit error rate according to the third power and the fourth power corresponding to the first target bit error rate and the noise of the coherent receiver front end; Determining the target performance of the coherent transmitter according to the first sensitivity penalty of the coherent transmitter and the second sensitivity penalty of the coherent transmitter at the at least one target bit error rate.

11. The method according to any one of claims 2 to 5, 7, 8 and 10, characterized in that Determining the performance of the coherent transmitter according to the first power, the second power, and the noise of the coherent receiver front end includes: Determining a transmitter constellation closure penalty of the coherent transmitter according to the first power, the second power, and the noise of the coherent receiver front end; The method further includes: Obtaining the bit error rate of the multiplex digital signals at at least one virtual noise signal-to-noise ratio; Determining the target performance of the coherent transmitter according to the obtained bit error rate and the transmitter constellation closure penalty.

12. The method according to claim 1, wherein Determining the performance of the coherent transmitter according to the first power and the second power includes: Determining a first relative virtual noise signal-to-noise ratio of the coherent transmitter at the bit error rate threshold according to the first power and the second power; The method further includes: Performing noise search according to the multiplex digital signals to obtain a third power of additive white Gaussian noise added to the multiplex digital signals at at least one target bit error rate; Obtaining a fourth power of additive white Gaussian noise added to the ideal signal at the at least one target bit error rate; For a first target bit error rate among the at least one target bit error rates, determining a second relative virtual noise signal-to-noise ratio of the coherent transmitter at the first target bit error rate according to the third power and the fourth power corresponding to the first target bit error rate; Determining the target performance of the coherent transmitter according to the first relative virtual noise signal-to-noise ratio of the coherent transmitter and the second relative virtual noise signal-to-noise ratio of the coherent transmitter at the at least one target bit error rate.

13. A method for determining the performance of a coherent transmitter, characterized in that, The method includes: Obtaining multiplex digital signals carried by a dual-polarization optical signal from the coherent transmitter, where the multiplex digital signals are dual-polarization in-phase and quadrature signals; Obtaining the bit error rate of the multiplex digital signals at at least one virtual noise signal-to-noise ratio; Determine the performance of the coherent transmitter according to the obtained bit error rate.

14. A device for determining the performance of a coherent transmitter, characterized in that, The device includes an analog-to-digital conversion module and a digital signal processing module; The analog-to-digital conversion module is configured to: obtain multiplexed digital signals carried by a dual-polarization optical signal from the coherent transmitter; The digital signal processing module is configured to: Perform noise search according to the multiplexed digital signals to obtain a first power of additive white Gaussian noise added to the multiplexed digital signals at a bit error rate threshold; Obtain a second power of additive white Gaussian noise added to an ideal signal at the bit error rate threshold, where the ideal signal is an undistorted signal determined according to the multiplexed digital signals; Determine the performance of the coherent transmitter according to the first power and the second power.

15. The method according to claim 14, wherein The digital signal processing module is configured to: Determine the performance of the coherent transmitter according to the first power, the second power, and the noise at the front end of the coherent receiver.

16. The device according to claim 15, characterized in that, The digital signal processing module is configured to: perform pulse shaping and matched filtering on the multiplexed digital signals to obtain a signal after matched filtering; Perform noise search according to the signal after matched filtering to obtain a first power of additive white Gaussian noise added to the multiplexed digital signals at a bit error rate threshold.

17. The device according to claim 16, characterized in that, The digital signal processing module is configured to: Add additive white Gaussian noise to the signal after matched filtering to obtain a signal after adding additive white Gaussian noise; Perform equalization processing on the signal after adding additive white Gaussian noise to obtain a signal after equalization processing; Determine a first power of additive white Gaussian noise added to the signal after matched filtering at a bit error rate threshold according to the signal after equalization processing.

18. The device according to claim 17, characterized in that, The digital signal processing module is further configured to: Before performing pulse shaping and matched filtering on the multiplexed digital signals, perform low-pass filtering on the multiplexed digital signals, where the bandwidth for performing low-pass filtering is determined according to the bandwidth at the front end of the coherent receiver.

19. The device according to any one of claims 14 to 18, characterized in that The analog-to-digital conversion module is configured to: Obtain multiplexed analog signals carried by a dual-polarization optical signal from the coherent transmitter; Perform low-pass filtering on the multiplexed analog signals to obtain low-pass filtered analog signals, where the bandwidth for performing low-pass filtering is determined according to the bandwidth at the front end of the coherent receiver; Perform analog-to-digital conversion on the low-pass filtered analog signals to obtain multiplexed digital signals.

20. The device according to any one of claims 15 to 18, characterized in that The digital signal processing module is configured to: According to the formula Determine the transmitter constellation closure cost, where TCC is the transmitter constellation closure cost, is the first power, for the second power For the power of the noise at the front end of the coherent receiver, the transmitter constellation closure cost is used to characterize the performance of the coherent transmitter.

21. The device according to any one of claims 16 to 18, characterized in that The digital signal processing module is further configured to: Determine the power of the multiplexed digital signals and the power of the signal after matched filtering; The digital signal processing module is configured to: According to the formula Determine the transmitter constellation closure cost, where TCC is the transmitter constellation closure cost, is the first power, is the second power, is the power of the noise of the coherent receiver front end, punfiltered is the power of the multiplexed digital signals, p filtered is the power of the signal after the matched filtering, and the transmitter constellation closure cost is used to characterize the performance of the coherent transmitter.

22. The device according to any one of claims 14 to 21, characterized in that At the bit error rate threshold, the dual-polarization optical signal includes at least 1×10 5 symbols.

23. The device according to claim 15, characterized in that The digital signal processing module is configured to: Determine the first sensitivity cost of the coherent transmitter at the bit error rate threshold according to the first power, the second power, and the noise at the front end of the coherent receiver Machine; The digital signal processing module is further configured to: Perform noise search based on the multiplexed digital signals to obtain a third power of the additive white Gaussian noise added to the multiplexed digital signals at at least one target bit error rate; Obtain a fourth power of the additive white Gaussian noise added to the ideal signal at the at least one target bit error rate; For a first target bit error rate among the at least one target bit error rates, determine a second sensitivity cost of the coherent transmitter at the first target bit error rate according to the third power and the fourth power corresponding to the first target bit error rate and the noise of the coherent receiver front end; Determine the target performance of the coherent transmitter according to the first sensitivity cost of the coherent transmitter and the second sensitivity cost of the coherent transmitter at the at least one target bit error rate; 24. The device according to any one of claims 15 to 18, 20, 21 and 23, characterized in that, The determining the performance of the coherent transmitter according to the first power, the second power and the noise of the coherent receiver front end includes: Determine a transmitter constellation closure cost of the coherent transmitter according to the first power, the second power and the noise of the coherent receiver front end; The digital signal processing module is further configured to: Obtain the bit error rate of the multiplexed digital signals at at least one virtual noise signal-to-noise ratio; Determine the target performance of the coherent transmitter according to the obtained bit error rate and the transmitter constellation closure cost; 25. The device according to claim 14, characterized in that, The digital signal processing module is configured to: Determine a first relative virtual noise signal-to-noise ratio of the coherent transmitter at the bit error rate threshold according to the first power and the second power; The digital signal processing module is further configured to: Perform noise search based on the multiplexed digital signals to obtain a third power of the additive white Gaussian noise added to the multiplexed digital signals at at least one target bit error rate; Obtain a fourth power of the additive white Gaussian noise added to the ideal signal at the at least one target bit error rate; For a first target bit error rate among the at least one target bit error rates, determine a second relative virtual noise signal-to-noise ratio of the coherent transmitter at the first target bit error rate according to the third power and the fourth power corresponding to the first target bit error rate; Determine the target performance of the coherent transmitter according to the first relative virtual noise signal-to-noise ratio of the coherent transmitter and the second relative virtual noise signal-to-noise ratio of the coherent transmitter at the at least one target bit error rate; 26. A device for determining the performance of a coherent transmitter, characterized in that, The device includes an analog-to-digital conversion module and a digital signal processing module; The analog-to-digital conversion module is configured to: obtain multiplexed digital signals carried by a dual-polarization optical signal from the coherent transmitter, where the multiplexed digital signals are dual-polarization in-phase and quadrature signals; The digital signal processing module is configured to: Obtain the bit error rate of the multiplexed digital signals at at least one virtual noise signal-to-noise ratio; Determine the performance of the coherent transmitter according to the obtained bit error rate; 27. A system for determining the performance of a coherent transmitter, characterized in that, The system includes a coherent receiving device and the device according to any one of claims 14 to 25; or, the system includes a coherent receiving device and the device according to claim 26; The coherent receiving device is configured to coherently receive a dual-polarization optical signal from the coherent transmitter to obtain multiple analog signals, and output the multiple analog signals to the device according to any one of claims 14 to 25, or the device according to claim 26, wherein the multiple analog signals are converted into multiple digital signals after analog-to-digital conversion.

28. A communication system, characterized in that, The communication system includes a coherent transmitter for transmitting a dual-polarization optical signal and the system according to claim 27.

29. A computing device, characterized in that, The computing device includes a processor and a memory, wherein: Computer instructions are stored in the memory; The processor executes the computer instructions to cause the computing device to execute the method according to any one of claims 1 to 12, and the method according to claim 13. Method, the method according to claim 13.

30. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions, and when the computer instructions in the computer-readable storage medium are executed by a computing device, the computing device is caused to execute the method according to any one of claims 1 to 12, or the method according to claim 13.

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