Real-time frequency offset compensation method for coherent optical communication system

Abstract

The invention belongs to the technical field of coherent optical communication, and particularly relates to a real-time frequency offset compensation method for a coherent optical communication system. Comprising the following steps: generating residual optical carriers at a transmitting end by adjusting bias voltage of an IQ modulator; receiving a signal at a receiving end, processing the received signal to obtain a frequency offset between an information source and the local oscillator laser, feeding back the frequency offset, adjusting the output frequency of the local oscillator laser to carry out frequency offset compensation, and carrying out continuous iteration to realize frequency locking of the laser; when a received signal is processed, the signal is sampled through an ADC (Analog to Digital Converter) with a low sampling rate, an FFT (Fast Fourier Transform) is combined with a Chirp-z algorithm to obtain a fine frequency offset value, then the frequency offset value is converted into a controlled variable by a PID (Proportion Integration Differentiation) algorithm, and the controlled variable is converted into an analog voltage through a DAC (Digital to Analog Converter), so that the frequency of a local oscillator laser is adjusted; the method is low in complexity, is suitable for all coherent optical communication systems, lays a foundation for the coherent optical communication system with the single baud rate, and can effectively reduce the communication cost and power consumption.

Description

Technical Field

[0001] The present application relates to the field of coherent optical communication technology, and more specifically, to a real-time frequency offset compensation method for a coherent optical communication system. Background Art

[0002] With technological breakthroughs in cloud computing and large-scale AI models, information interconnection between intelligent computing centers is becoming increasingly frequent, and the demand for computing power is rapidly increasing. Due to its advantages of high bandwidth and long transmission distance, coherent optical communication technology has gradually become the preferred technology for information transmission between intelligent computing centers. To achieve reduced power consumption and improved transmission efficiency, coherent optical communication systems with single-baud-rate sampling are becoming an effective solution for efficient system operation.

[0003] Because lasers are susceptible to external environmental temperature and vibration noise, the frequency of the light emitted by the laser can drift, resulting in a frequency deviation between the source laser and the local oscillator (LO) laser, which in turn causes the received signal spectrum to shift. In actual communication systems, an anti-aliasing filter (AAF) is usually passed before the analog-to-digital converter (ADC) samples to prevent spectrum aliasing. However, for single-baud rate systems, due to the bandwidth limitations of the AAF, spectrum shifting can lead to loss of valid signals, seriously affecting communication quality. Therefore, real-time locking of the laser frequency, compensating for frequency deviation, and ensuring consistency between the transmitted and received frequencies are key to improving system performance.

[0004] Real-time adjustment of the laser output frequency is mostly achieved by using an optical phase-locked loop to phase-lock the laser. In coherent optical communication systems, the presence of modulation information makes accurate estimation of the laser frequency deviation extremely challenging. Traditional Costas phase-locked loops often use BPSK systems, which directly eliminate the modulation information through a multiplier to estimate the frequency deviation. However, when applied to higher-order modulation formats, due to the presence of multiple phase and amplitude states, the modulation information is complex, and traditional multiplier phase detectors are difficult to directly eliminate the modulation information, so a more complex phase detection design is required. For QAM signals, a fourth-power frequency deviation estimation algorithm based on QPSK is often used. However, this algorithm requires a high sampling rate for the receiving end digital-to-analog converter (DAC), and the estimation accuracy depends on the number of Fourier transform (FFT) points. In order to achieve a certain accuracy, a large number of FFT points are required, and the computational complexity is high. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing frequency offset estimation technology in that the sampling rate of the receiving end is high and the calculation is complex, and to provide a real-time frequency offset compensation method for a coherent optical communication system, which effectively reduces the sampling rate requirements and the calculation complexity of the receiving end.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] Provided is a real-time frequency offset compensation method for a coherent optical communication system, comprising:

[0008] At the transmitter, digital signal processing (DSP) is performed on the raw data. The IQ modulator modulates the DSP-processed data. By adjusting the bias voltage of the IQ modulator and controlling the operating point of the IQ modulator, a residual optical carrier is generated to generate the transmitter signal.

[0009] At the receiving end, the local oscillator optical signal generated by the distributed feedback semiconductor laser is mixed with the transmitting end signal. After passing through a balanced photodetector, the in-phase component and quadrature component of the modulated signal are obtained respectively. The received in-phase component and quadrature component signals are processed to obtain the frequency deviation between the source laser and the local oscillator laser. Feedback is given based on the frequency deviation to adjust the output frequency of the local oscillator laser and perform frequency deviation compensation. Continuous iterations are carried out to ultimately achieve frequency locking of the laser.

[0010] The present invention provides a real-time frequency offset compensation method for coherent optical communication systems. Combining residual carrier modulation with an optical phase-locked loop (OPL) technique, the method processes the beat frequency signals of the source laser and the local oscillator laser to obtain the frequency offset value, performing feedback adjustment to achieve frequency locking of the laser. This method can be used in all coherent optical communication systems and all modulation formats, significantly reducing the system's sampling rate requirements and the complexity of the receiving-end DSP algorithm, thereby reducing power consumption and costs. Furthermore, this method lays the foundation for single-baud-rate coherent communication.

[0011] Furthermore, processing the received in-phase component and quadrature component signals includes:

[0012] S1. Use a low sampling rate analog-to-digital converter (ADC) to sample the in-phase signal and the quadrature signal separately;

[0013] S2. Combining the collected in-phase signal and quadrature signal into a complex signal;

[0014] S3. Perform a 64-point FFT operation on the complex signal to obtain a spectrum value; modulo each spectrum value and search for the maximum value in the spectrum value after modulo, and obtain the frequency corresponding to the maximum value as a coarse frequency offset estimate;

[0015] S4. Perform a 32-point chirp z transform (Chirp-z) operation on the frequency obtained in step S3 to refine the spectrum, search for the maximum spectrum value, and obtain the frequency corresponding to the maximum spectrum value as the final frequency deviation estimate;

[0016] S5. Use the proportional-integral (PI) algorithm to determine the control voltage corresponding to the final frequency deviation. Feed this control voltage back to the local oscillator laser to adjust the output frequency of the local oscillator laser and compensate for the frequency deviation.

[0017] S6. Repeat steps S1 to S5 until the frequencies of the source laser and the local oscillator laser are locked.

[0018] Furthermore, step S4 includes:

[0019] S41. Fix the starting point position as A and perform equal-interval sampling on the points on the z-transform unit circle. The sampling points are expressed as:

[0020] z k =AW -k ,k=0,1,…,M-1

[0021] Where A represents the starting point phase, that is, the left end point of the peak range detected by FFT, and the parameter W is expressed as j represents an imaginary number, φ0 represents an equal angle;

[0022] S42. k Substitute the following formula:

[0023]

[0024] Where N represents the total number of chirp-z points, and n represents an integer from 0 to N-1; Then X(z k ) is obtained by the convolution of g(n) and h(n), and then the convolution form is converted into a spectrum Multiply them together and finally get the result X(z k ), X(z k The frequency corresponding to the peak value of ) is the final frequency offset estimation value.

[0025] Furthermore, in step S5, an incremental proportional-integral-derivative (PID) algorithm is used. The incremental PID algorithm formula is as follows:

[0026] u(k)=u(k-1)+Δu(k)

[0027] =u(k-1)+K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-2)]

[0028] In the formula, e(k), e(k-1), and e(k-2) are the current, last, and last error values respectively, and K P ,K i ,K dare the coefficients of the proportional term, integral term, and differential term, respectively; u(k) and u(k-1) are the control quantities of the current and previous states, respectively; wherein the error value is the final frequency deviation value calculated in step S4, and the control quantity is the control voltage of the laser.

[0029] The present invention also provides a real-time frequency offset compensation system for a coherent optical communication system, comprising:

[0030] Transmitter DSP processing module:

[0031] It is used to perform DSP processing on the original data, modulate the DSP-processed data through the IQ modulator, and control the operating point of the IQ modulator by adjusting the bias voltage of the IQ modulator to generate a residual optical carrier and generate the transmitting end signal;

[0032] DSP processing module at the receiving end:

[0033] Mixing processing module: used to mix the local oscillator optical signal generated by the distributed feedback semiconductor laser with the transmitter signal, and obtain the in-phase component and orthogonal component of the modulated signal after passing through the balanced photodetector;

[0034] Signal processing module: It is used to receive the in-phase component and quadrature component signals from the mixing processing module, and process the received signals to obtain the frequency deviation between the source laser and the local oscillator laser. It provides feedback on the frequency deviation, adjusts the output frequency of the local oscillator laser, compensates for the frequency deviation, and iterates continuously to finally achieve frequency locking of the laser.

[0035] Furthermore, the signal processing module includes:

[0036] Sampling unit: used to use a low sampling rate analog-to-digital converter ADC to sample the in-phase signal and the quadrature signal respectively, and combine the collected in-phase signal and the quadrature signal into a complex signal;

[0037] Coarse frequency offset estimation unit: used to perform a 64-point FFT operation on the complex signal to obtain the spectrum value, and then modulo each spectrum value, search for the maximum value among the modulo spectrum values, and obtain the frequency corresponding to the maximum value as the coarse frequency offset estimate;

[0038] Fine frequency offset estimation unit: This unit performs a 32-point Chirp-z operation on the frequency obtained by the coarse frequency offset estimation unit to refine the spectrum, search for the maximum value of the spectrum, and obtain the frequency corresponding to the maximum value as the final frequency offset estimate.

[0039] Frequency offset compensation unit: Uses a proportional-integral algorithm to obtain the control voltage corresponding to the final frequency offset estimate, feeds the control voltage back to the local oscillator laser, adjusts the output frequency of the local oscillator laser, and performs frequency offset compensation;

[0040] Iteration unit: used to continuously iterate the processing of the sampling unit, coarse frequency offset estimation unit, fine frequency offset estimation unit, and frequency offset compensation unit until the frequency of the source laser and the local oscillator laser are locked.

[0041] Furthermore, the fine frequency offset estimation unit includes the following processing when performing frequency offset estimation:

[0042] The starting point is fixed at A, and the points on the z-transform unit circle are sampled at equal intervals. The sampling points are expressed as:

[0043] z k =AW -k ,k=0,1,…,M-1

[0044] Where A represents the starting point phase, that is, the left end point of the peak range detected by FFT, and the parameter W is expressed as j represents an imaginary number, φ0 represents an equal angle;

[0045] z k Substitute the following formula:

[0046]

[0047] Where N represents the total number of chirp-z points, and n represents an integer from 0 to N-1; Then X(z k ) is obtained by the convolution of g(n) and h(n), and then the convolution form is converted into a spectrum Multiply them together and finally get the result X(z k ), X(z k The frequency corresponding to the peak value of ) is the final frequency offset estimation value.

[0048] Furthermore, the frequency offset compensation unit includes the following processing when performing frequency offset compensation:

[0049] The incremental PID algorithm is used. The incremental PID algorithm formula is as follows:

[0050] u(k)=u(k-1)+Δu(k)

[0051] =u(k-1)+K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-2)]

[0052] In the formula, e(k), e(k-1), and e(k-2) are the current, last, and last error values respectively, and K P ,K i ,K dare the coefficients of the proportional term, integral term, and differential term, respectively; u(k) and u(k-1) are the control quantities of the current and previous states, respectively; among them, the error value is the final frequency deviation value calculated in the fine frequency deviation estimation unit, and the control quantity is the control voltage of the laser.

[0053] The present invention also provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, wherein the processor implements the steps of the above method when executing the computer program.

[0054] The present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of the above-described method when executed by a processor.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] The present invention provides a real-time frequency offset compensation method for coherent optical communication systems. Combining residual carrier modulation and optical phase-locked loop technology, the method processes the beat frequency signals of the source laser and the local oscillator laser, obtains the frequency offset value, and then performs feedback adjustment to achieve frequency locking of the laser. This method can be used in all coherent optical communication systems and all modulation formats, and can significantly reduce the system's sampling rate requirements for the DAC and the complexity of the receiving-end DSP algorithm, thereby reducing power consumption and costs. Through precise frequency detection and feedback control mechanisms, the present invention ensures frequency synchronization between the source laser and the local oscillator laser, effectively avoiding signal loss caused by spectrum shifting, and laying the foundation for the implementation of single-baud-rate communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is a system framework diagram for real-time frequency offset compensation for coherent optical communication according to the present invention;

[0058] Figure 2 Flowchart of the Chirp-z algorithm used in the present invention;

[0059] Figure 3 1 is a block diagram of the PID algorithm used in the present invention;

[0060] Figure 4 It is a structural block diagram of the simulation system in the present invention;

[0061] Figure 5 The power spectrum of the beat frequency signal processed in the present invention; (a) is the power spectrum obtained by 64-point FFT of the received signal; (b) is the power spectrum obtained by 32-point Chirp-z transform within the range of the spectrum peak point;

[0062] Figure 6The block diagram of the Simulink simulation system built in the present invention;

[0063] Figure 7 This is a result diagram of the frequency offset compensation process implemented using Simulink simulation in the present invention. DETAILED DESCRIPTION

[0064] The present invention will be further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only and are schematic, not actual, representations. They should not be construed as limiting the present invention. To better illustrate the embodiments of the present invention, some components in the drawings may be omitted, enlarged, or reduced in size, and do not represent the actual dimensions of the products. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted from the drawings.

[0065] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "up", "down", "left", "right", etc. indicate directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0066] Example 1

[0067] This embodiment is a first embodiment of a real-time frequency offset compensation method for a coherent optical communication system. Figure 1 FIG. 1 is a system framework diagram of the frequency offset compensation method provided by the present invention, which combines residual carrier modulation at the transmitting end and an optical phase-locked loop at the receiving end to perform frequency offset compensation.

[0068] The following steps are involved:

[0069] At the transmitter, the original data is processed by DSP, and the IQ modulator modulates the DSP-processed data. By adjusting the bias voltage of the IQ modulator and controlling the operating point of the IQ modulator, a residual optical carrier is generated to generate the transmitter signal.

[0070] At the receiving end, the local oscillator optical signal generated by the distributed feedback semiconductor laser is mixed with the transmitting end signal through a 90° optical mixer. After passing through a balanced photodetector, the in-phase component and quadrature component of the modulated signal are respectively obtained. The received in-phase component and quadrature component signals are processed to obtain the frequency offset between the source laser and the local oscillator laser. Feedback is provided for the frequency offset, and the output frequency of the local oscillator laser is adjusted to compensate for the frequency offset. Continuous iteration is carried out to ultimately achieve frequency locking of the laser.

[0071] In this embodiment, if Figure 1 As shown, the 90° optical mixer and the balanced detector are equivalent to the phase detector of an optical phase-locked loop, and the local oscillator laser is equivalent to an optical voltage-controlled oscillator. The entire system can achieve closed-loop real-time compensation for frequency deviation.

[0072] In this embodiment, processing the received in-phase component and quadrature component signals includes:

[0073] Step 1: Use a low sampling rate analog-to-digital converter (ADC) to sample the in-phase signal and the quadrature signal separately; combine the collected in-phase signal and the quadrature signal into a complex signal;

[0074] Step 2: Obtain a coarse frequency offset estimate.

[0075] Use FFT to obtain a coarse frequency offset estimate. A 64-point FFT is performed on the complex signal to obtain its spectrum. Each spectrum value is modulo-ed and the maximum value is searched for. The frequency corresponding to the maximum value is obtained as the coarse frequency offset estimate. To reduce computational complexity, the number of FFT points is reduced. To improve accuracy, further estimation is required.

[0076] Step 3: Obtain the final frequency offset estimate.

[0077] The final frequency offset estimate is obtained using the Chirp-z algorithm. Chirp-z is a method that can perform dense sampling along a spiral line in a specific frequency band, thereby more accurately analyzing narrowband signals. In step 2, the approximate range of the signal spectrum peak was obtained, that is, the ±1 / 2 spectral resolution where the maximum modulus value after FFT is located. At this time, the Chirp-z algorithm is used to refine the spectrum within the peak range. The algorithm process is as follows: First, the starting point position is fixed to A, and this range on the z-transform unit circle is sampled at equal intervals. These sampling points can be expressed as:

[0078] z k =AW -k ,k=0,1,…,M-1

[0079] Where A represents the starting point phase, that is, the left end point of the peak range detected by FFT, and the parameter W is expressed as j represents an imaginary number, φ0 represents an equal angle;

[0080] z k Substitute the following formula:

[0081]

[0082] Where N represents the total number of chirp-z points, and n represents an integer from 0 to N-1; Then X(z k ) is obtained by the convolution of g(n) and h(n), and then the convolution form is converted into a spectrum Multiplication, the algorithm flow is as follows Figure 2 As shown, the final result after spectrum refinement is X(z k ), X(z k The frequency corresponding to the peak value of ) is the final frequency offset estimation value.

[0083] Step 4: Get the feedback voltage.

[0084] The final feedback voltage is obtained using the PI algorithm. After obtaining the estimated value of the frequency deviation using the Chirp-z algorithm, it needs to be converted into the corresponding voltage of the laser. The PID control algorithm is a widely used feedback control algorithm used to adjust and optimize the output of the controlled object in automatic control systems. In this embodiment, it can be used to optimize the frequency output of the local oscillator laser. Figure 4 The block diagram of the working principle of the position PID algorithm is shown. The integral term is proportional to the error signal and can be used to quickly eliminate errors; the integral term is proportional to the integral of the error signal and can be used to eliminate static errors; the differential term is proportional to the rate of change of the error signal and can be used to predict the error change trend and improve system stability. The position structure is simple and easy to implement, but there is a continuous accumulation of error terms. Once the current error value is wrong, it will increase the instability of the system. In this embodiment, the incremental PID algorithm is used. The incremental PID algorithm formula is as follows:

[0085] u(k)=u(k-1)+Δu(k)

[0086] =u(k-1)+K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-2)]

[0087] In the formula, e(k), e(k-1), and e(k-2) are the current, last, and last error values respectively, and K P ,K i ,K d are the coefficients of proportional term, integral term and differential term respectively, u(k) and u(k-1) are the control quantities of the current and previous states respectively; as long as KP ,K i ,K d The control increment can be calculated using the error signals of the first three times, and the current control amount can be obtained by adding the control amount of the previous state. In this embodiment, the error value is the final frequency deviation value calculated in step 3, and the control amount is the control voltage of the laser.

[0088] After the control voltage is obtained, it is fed back to the local oscillator laser to adjust the laser output frequency.

[0089] In summary, the present embodiment provides a real-time frequency offset compensation method for a coherent optical communication system, comprising: generating a residual optical carrier at the transmitting end by adjusting the bias voltage of the IQ modulator; receiving a signal at the receiving end, processing the received signal, obtaining the frequency offset between the signal source and the local oscillator laser, providing feedback on the frequency offset, adjusting the output frequency of the local oscillator laser to compensate for the frequency offset, and continuously iterating to achieve frequency locking of the laser; when processing the received signal, sampling the signal through a low sampling rate ADC, using FFT combined with the Chirp-z algorithm to obtain a fine frequency offset value, and then using the PID algorithm to convert the frequency offset value into a control quantity, and converting it into an analog voltage through a DAC, thereby adjusting the frequency of the local oscillator laser; the method provided in the present embodiment has low complexity, is applicable to all coherent optical communication systems, and lays the foundation for single-baud rate coherent optical communication systems, which can effectively reduce communication costs and power consumption.

[0090] Step 5: Iteration.

[0091] Repeat steps 1 to 4 above until the frequencies of the source laser and the local oscillator laser are locked.

[0092] In this embodiment, the effects of the present invention are further verified by using specific examples. Figure 4 This is a block diagram of the simulation system structure of the present invention, implemented jointly using Matlab and VPI TransmissionMaker (VPI). The transmitter signal is first processed in Matlab, with the transmission rate set to 50 GBaud, the data modulation format to 16QAM, and dual-polarization transmission. A complete coherent optical system is implemented in VPI, and the beat frequency signal after fiber transmission is obtained and then transferred to Matlab for digital signal processing. Frequency regulation of the local oscillator laser and bias voltage adjustment of the IQ modulator are both implemented in VPI.

[0093] The above beat frequency signal is sampled at a sampling rate of 2.5GSa / s. Figure 5A comparison of the power spectral density after FFT and the power spectral density after Chirp-z is given. Here, this embodiment performs a 64-point FFT on the received signal and a 32-point Chirp-z on the signal within the peak range. It can be seen that the spectrum peak position is more accurate after the Chirp-z transform.

[0094] In addition, in order to simulate the dynamic effect of frequency offset compensation and verify the effectiveness of this method, the entire coherent optical communication system is simulated by Simulink in this embodiment. Figure 6 The system includes a coherent optical communication transmitter, a fiber channel, and a receiver. The receiver includes an ADC, a frequency offset estimation module, and an incremental PID algorithm. The simulation parameters are set to be consistent with those in the VPI. The control variable obtained by the incremental PID is fed back to the local oscillator laser. Through continuous iteration, the convergence process of the local oscillator laser frequency is verified.

[0095] Figure 7 for Figure 6 The simulation results of the Simulink simulation system are shown in Figure 2. The solid and dashed lines represent the time-varying variations of the laser frequency offset and control voltage, respectively. It can be seen that when the initial frequency offset is 1 GHz, the control voltage stabilizes after 4 microseconds after adjustment using this method. Simultaneously, the laser frequency offset converges to the MHz range, achieving frequency locking between the master and slave lasers.

[0096] Example 2

[0097] This embodiment is an embodiment of a real-time frequency offset compensation system for a coherent optical communication system. This embodiment is similar to the first embodiment and includes:

[0098] Transmitter DSP processing module:

[0099] It is used to perform DSP processing on the original data, modulate the DSP-processed data through the IQ modulator, and control the operating point of the IQ modulator by adjusting the bias voltage of the IQ modulator to generate a residual optical carrier and generate the transmitting end signal;

[0100] DSP processing module at the receiving end:

[0101] Mixing processing module: used to mix the local oscillator optical signal generated by the distributed feedback semiconductor laser with the transmitter signal, and obtain the in-phase component and orthogonal component of the modulated signal after passing through the balanced photodetector;

[0102] Signal processing module: It is used to receive the in-phase component and quadrature component signals from the mixing processing module, and process the received signals to obtain the frequency deviation between the source laser and the local oscillator laser. It provides feedback on the frequency deviation, adjusts the output frequency of the local oscillator laser, compensates for the frequency deviation, and iterates continuously to finally achieve frequency locking of the laser.

[0103] In this embodiment, the signal processing module includes:

[0104] Sampling unit: used to use a low sampling rate analog-to-digital converter ADC to sample the in-phase signal and the quadrature signal respectively, and combine the collected in-phase signal and the quadrature signal into a complex signal;

[0105] Coarse frequency offset estimation unit: used to perform a 64-point FFT operation on the complex signal to obtain the spectrum value, and then modulo each spectrum value, search for the maximum value among the modulo spectrum values, and obtain the frequency corresponding to the maximum value as the coarse frequency offset estimate;

[0106] Fine frequency offset estimation unit: This unit performs a 32-point Chirp-z operation on the frequency obtained by the coarse frequency offset estimation unit to refine the spectrum, search for the maximum value of the spectrum, and obtain the frequency corresponding to the maximum value as the final frequency offset estimate.

[0107] Frequency offset compensation unit: Uses a proportional-integral algorithm to obtain the control voltage corresponding to the final frequency offset estimate, feeds the control voltage back to the local oscillator laser, adjusts the output frequency of the local oscillator laser, and performs frequency offset compensation;

[0108] Iteration unit: used to continuously iterate the processing of the sampling unit, coarse frequency offset estimation unit, fine frequency offset estimation unit, and frequency offset compensation unit until the frequency of the source laser and the local oscillator laser are locked.

[0109] In this embodiment, the fine frequency offset estimation unit includes the following processing when performing frequency offset estimation:

[0110] The starting point is fixed at A, and the points on the z-transform unit circle are sampled at equal intervals. The sampling points are expressed as:

[0111] z k =AW -k ,k=0,1,…,M-1

[0112] Where A represents the starting point phase, that is, the left end point of the peak range detected by FFT, and the parameter W is expressed as j represents an imaginary number, φ0 represents an equal angle;

[0113] z k Substitute the following formula:

[0114]

[0115] Where N represents the total number of chirp-z points, and n represents an integer from 0 to N-1; Then X(z k ) is obtained by the convolution of g(n) and h(n), and then the convolution form is converted into a spectrum Multiply them together and finally get the result X(z k ), X(z k The frequency corresponding to the peak value of ) is the final frequency offset estimation value.

[0116] In this embodiment, the frequency offset compensation unit includes the following processing when performing frequency offset compensation:

[0117] The incremental PID algorithm is used. The incremental PID algorithm formula is as follows:

[0118] u(k)=u(k-1)+Δu(k)

[0119] =u(k-1)+K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-2)]

[0120] In the formula, e(k), e(k-1), and e(k-2) are the current, last, and last error values respectively, and K P ,K i ,K d are the coefficients of the proportional term, integral term, and differential term, respectively; u(k) and u(k-1) are the control quantities of the current and previous states, respectively; among them, the error value is the final frequency deviation value calculated in the fine frequency deviation estimation unit, and the control quantity is the control voltage of the laser.

[0121] Example 3

[0122] This embodiment provides a computer device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. When the processor executes the computer program, the steps of the method in embodiment 1 are implemented.

[0123] Example 4

[0124] This embodiment provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of the method of embodiment 1 when executed by a processor.

[0125] In the specific contents of the above-mentioned specific implementation methods, the various technical features can be combined in any non-contradictory manner. In order to make the description concise, not all possible combinations of the above-mentioned technical features are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0126] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A real-time frequency offset compensation method for a coherent optical communication system, characterized in that: include: At the transmitter, the original data is digitally processed, and the IQ modulator modulates the processed data. By adjusting the bias voltage of the IQ modulator and controlling the operating point of the IQ modulator, a residual optical carrier is generated to generate the transmitter signal. At the receiving end, the local oscillator optical signal generated by the distributed feedback semiconductor laser is mixed with the transmitting end signal. After passing through a balanced photodetector, the in-phase component and quadrature component of the modulated signal are obtained respectively. The received in-phase component and quadrature component signals are processed to obtain the frequency deviation between the source laser and the local oscillator laser. Feedback is given based on the frequency deviation to adjust the output frequency of the local oscillator laser and perform frequency deviation compensation. Continuous iterations are carried out to ultimately achieve frequency locking of the laser.

2. The real-time frequency offset compensation method for a coherent optical communication system according to claim 1, wherein: Processing the received in-phase component and quadrature component signals includes: S1. Use a low sampling rate analog-to-digital converter (ADC) to sample the in-phase signal and the quadrature signal separately; S2. Combining the collected in-phase signal and quadrature signal into a complex signal; S3. Perform a 64-point Fourier transform on the complex signal to obtain a spectrum value, modulo each spectrum value, and search for the maximum value in the spectrum value after modulo, and obtain the frequency corresponding to the maximum value as a coarse frequency offset estimate; S4. Perform a 32-point linear frequency modulation z-transform operation on the frequency obtained in step S3 to refine the spectrum, search for the maximum spectrum value, and obtain the frequency corresponding to the maximum spectrum value as the final frequency deviation estimate; S5. Use the proportional-integral algorithm to determine the control voltage corresponding to the final frequency deviation. Feed this control voltage back to the local oscillator laser to adjust the output frequency of the local oscillator laser and compensate for the frequency deviation. S6. Repeat steps S1 to S5 until the frequencies of the source laser and the local oscillator laser are locked.

3. The real-time frequency offset compensation method for a coherent optical communication system according to claim 2, wherein: Step S4 includes: S41. Fix the starting point at A and perform equal-interval sampling on the z-transform unit circle. The sampling points are expressed as: z k =AW -k ,k=0,1,…,M-1 Where A represents the starting point phase, i.e. the left end point of the peak range detected by Fourier transform, and the parameter W is expressed as j represents an imaginary number, φ0 represents an equal angle; S42. k Substitute the following formula: Where N is the total number of points of the linear frequency modulation z-transform, and n is an integer from 0 to N-1; Then X(z k ) is obtained by the convolution of g(n) and h(n), and then the convolution form is converted into a spectrum Multiply them together and finally get the result X(z k ), X(z k The frequency corresponding to the peak value of ) is the final frequency offset estimation value.

4. The real-time frequency offset compensation method for a coherent optical communication system according to claim 3, wherein: In step S5, an incremental proportional-integral-differential algorithm is used. The incremental proportional-integral-differential algorithm formula is as follows: u(k)=u(k-1)+Δu(k) =u(k-1)+K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-2)] In the formula, e(k), e(k-1), and e(k-2) are the current, last, and last error values respectively, and K P ,K i ,K d are the coefficients of the proportional term, integral term, and differential term, respectively; u(k) and u(k-1) are the control quantities of the current and previous states, respectively; wherein the error value is the final frequency deviation value calculated in step S4, and the control quantity is the control voltage of the laser.

5. A real-time frequency offset compensation system for a coherent optical communication system, characterized in that: include: Transmitter digital signal processing module: It is used to perform digital signal processing on the original data, modulate the digital signal processed data through the IQ modulator, and control the operating point of the IQ modulator by adjusting the bias voltage of the IQ modulator to generate a residual optical carrier and generate a transmitting end signal; Receiver digital signal processing module: Mixing processing module: used to mix the local oscillator optical signal generated by the distributed feedback semiconductor laser with the transmitter signal, and obtain the in-phase component and orthogonal component of the modulated signal after passing through the balanced photodetector; Signal processing module: It is used to receive the in-phase component and quadrature component signals from the mixing processing module, and process the received signals to obtain the frequency deviation between the source laser and the local oscillator laser. It provides feedback on the frequency deviation, adjusts the output frequency of the local oscillator laser, compensates for the frequency deviation, and iterates continuously to finally achieve frequency locking of the laser.

6. The real-time frequency offset compensation system for a coherent optical communication system according to claim 5, characterized in that: The signal processing module includes: Sampling unit: used to use a low sampling rate analog-to-digital converter ADC to sample the in-phase signal and the quadrature signal respectively, and combine the collected in-phase signal and the quadrature signal into a complex signal; Coarse frequency offset estimation unit: used to perform a 64-point Fourier transform on the complex signal to obtain spectrum values, modulo each spectrum value, search for the maximum value among the moduloed spectrum values, and obtain the frequency corresponding to the maximum value as the coarse frequency offset estimate; Fine frequency offset estimation unit: This unit performs a 32-point linear frequency modulation z-transform on the frequency obtained by the coarse frequency offset estimation unit, refines the spectrum, searches for the maximum value of the spectrum, and obtains the frequency corresponding to the maximum value as the final frequency offset estimate. Frequency offset compensation unit: Uses a proportional-integral algorithm to obtain the control voltage corresponding to the final frequency offset estimate, feeds the control voltage back to the local oscillator laser, adjusts the output frequency of the local oscillator laser, and performs frequency offset compensation; Iteration unit: used to continuously iterate the processing of the sampling unit, coarse frequency offset estimation unit, fine frequency offset estimation unit, and frequency offset compensation unit until the frequency of the source laser and the local oscillator laser are locked.

7. The real-time frequency offset compensation system for a coherent optical communication system according to claim 6, characterized in that: When performing frequency offset estimation, the fine frequency offset estimation unit includes the following processing steps: The starting point is fixed at A, and the points on the z-transform unit circle are sampled at equal intervals. The sampling points are expressed as: z k =AW -k ,k=0,1,…,M-1 Where A represents the starting point phase, i.e. the left end point of the peak range detected by Fourier transform, and the parameter W is expressed as j represents an imaginary number, φ0 represents an equal angle; z k Substitute the following formula: Where N is the total number of points of the linear frequency modulation z-transform, and n is an integer from 0 to N-1; Then X(z k ) is obtained by the convolution of g(n) and h(n), and then the convolution form is converted into a spectrum Multiply them together and finally get the result X(z k ), X(z k The frequency corresponding to the peak value of ) is the final frequency offset estimation value.

8. The real-time frequency offset compensation system for a coherent optical communication system according to claim 6, wherein: When the frequency offset compensation unit performs frequency offset compensation, the following processing steps are included: The incremental proportional-integral-differential algorithm is used. The incremental proportional-integral-differential algorithm formula is as follows: u(k)=u(k-1)+Δu(k) =u(k-1)+K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-2)] In the formula, e(k), e(k-1), and e(k-2) are the current, last, and last error values respectively, and K P ,K i ,K d are the coefficients of the proportional term, integral term, and differential term, respectively; u(k) and u(k-1) are the control quantities of the current and previous states, respectively; among them, the error value is the final frequency deviation value calculated in the fine frequency deviation estimation unit, and the control quantity is the control voltage of the laser.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 4 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

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