Cascaded MZM High Extinction Ratio Optical Signal Generation System, Control Method, Chip and Terminal

Abstract

The present invention discloses a cascaded MZM high extinction ratio optical signal generation system and a control method. The generation system includes: a laser, at least two stages of MZM modulators connected in series, a PPM electrical signal input device, a voltage driver, and a phase shifter. For each MZM modulator, a photodetector PD, an analog-to-digital converter ADC, a controller, and a digital-to-analog converter DAC are provided. The control method includes: obtaining the optimal peak-to-peak value of the PPM input electrical signal for each stage of MZM modulator based on the optimal peak-to-peak value acquisition method of the PPM input electrical signal; for the first stage of MZM modulator, controlling the output optical power of the MZM modulator to be minimum, and obtaining the optimal bias voltage of the first stage of MZM modulator based on the optimal bias voltage tracking method; for the Nth stage of MZM modulator, controlling the output optical power of the MZM modulator to be maximum, and obtaining the optimal bias voltage of the Nth stage of MZM modulator based on the optimal bias voltage tracking method.

Description

Technical Field

[0001] The present invention relates to the technical fields of deep space optical communication, detection and modulation, and particularly relates to a cascaded MZM high extinction ratio optical signal generation system, a control method, a chip and a terminal. Background Art

[0002] In recent years, with the continuous enhancement of scientific detection capabilities and the popularization of advanced detection equipment, the bandwidth demand for deep space communication has increased rapidly. Compared with microwave communication, space optical communication using laser as the carrier gradually occupies a dominant position in the field of deep space optical communication due to its advantages such as high energy efficiency, long transmission distance, and large bandwidth. The deep space laser communication link is a typical photon-starved channel. Pulse position modulation (PPM) has the characteristics of high energy efficiency and high detection sensitivity of single-photon detectors when the average power is limited, making the single-photon communication system based on PPM combined with single-photon detectors (such as SNSPD, SPAD, etc.) the preferred system for deep space detection. However, although single-photon detectors have extremely high detection sensitivity, their tolerance to noise photons is extremely low. Therefore, to improve the signal detection of single-photon detectors and reduce the interference caused by noise photons, the deep space laser communication system has relatively high requirements for the extinction ratio of the optical signal at the transmitting end.

[0003] Currently, an external modulation technology based on a cascaded Mach-Zehnder Modulator (MZM) is usually used to achieve the modulation of a high extinction ratio optical signal at the transmitting end. However, the cascaded MZM faces the following problems when generating a high extinction ratio optical signal: one is environmental factors, such as temperature, humidity, and mechanical stress, which will cause phase drift of the MZM, thereby reducing the quality of the optical signal output at the transmitting end; the other is that the peak-to-peak voltage of the MZM directly affects the performance of the system. Although some methods for compensating the phase drift of the MZM have been proposed in the prior art, most of them only consider the fixed operating point of the MZM and do not propose how to optimize the extinction ratio at the transmitting end. Moreover, the prior art does not consider the optimized measurement of the peak-to-peak value of the input signal, making it difficult to meet the requirements of the deep space laser communication system for improving the extinction ratio performance.

[0004] In summary, the prior art has the defect of not comprehensively considering the bias voltage tracking of the MZM and the optimized measurement of the peak-to-peak value of the input signal, making it difficult to achieve the purpose of optimizing the performance of the high extinction ratio modulation signal while tracking and controlling the bias voltage of the MZM. Summary of the Invention

[0005] In a first aspect, the present invention provides a control method for a cascaded MZM high extinction ratio optical signal generation system, where the optical signal generation system includes at least two stages of MZM modulators connected in series; the control method includes the following steps:

[0006] Based on the method for obtaining the optimal peak-to-peak value of the PPM input electrical signal, obtain the optimal peak-to-peak value of the PPM input electrical signal for each stage of the MZM modulator;

[0007] For the first-stage MZM modulator, control the output optical power of the MZM modulator to be minimized, and based on the optimal bias voltage tracking method, obtain the optimal bias voltage of the first-stage MZM modulator;

[0008] For the Nth-stage MZM modulator, control the output optical power of the MZM modulator to be maximized, and based on the optimal bias voltage tracking method, obtain the optimal bias voltage of the Nth-stage MZM modulator.

[0009] As a possible implementation, for each stage of the MZM modulator, the method for obtaining the optimal peak-to-peak value of the PPM input electrical signal includes the following steps:

[0010] S10. Initialize the random points, where the random points include the peak-to-peak value of the PPM input electrical signal and the bias voltage;

[0011] S11. Initialize the number of iterations and configure the maximum number of loops;

[0012] S12. Determine whether the current number of iterations is less than the maximum number of loops. If so, execute S13;

[0013] S13. Configure the initial step voltage; record the current average optical power value; update the peak-to-peak value of the PPM input electrical signal to the sum of the input electrical signal peak-to-peak value in the previous cycle and the step voltage; calculate the difference between the current average optical power value and the average optical power value saved in the previous cycle, and configure the average optical power threshold; repeatedly determine the relationship between the difference and the average optical power threshold until the difference is less than or equal to the average optical power threshold, and then execute S14;

[0014] S14. Configure the initial step voltage; record the current average optical power value; update the bias voltage to the sum of the bias voltage in the previous cycle and the step voltage; calculate the difference between the current average optical power value and the average optical power value saved in the previous cycle, and configure the average optical power threshold; repeatedly determine the relationship between the difference and the average optical power threshold until the difference is less than or equal to the average optical power threshold, and then execute S15;

[0015] S15. Update the number of iterations, and continue to execute S12 - S14 until the number of iterations is equal to the maximum number of loops to obtain the optimal peak-to-peak value.

[0016] As a possible implementation, in S13, repeatedly determining the relationship between the difference and the average optical power threshold includes the following steps:

[0017] S130. Determine whether the difference is greater than the average optical power threshold. If so, execute S131;

[0018] S131. Update the partial derivative of the average optical power for this cycle;

[0019] S132. Save the current average optical power value;

[0020] S133. Update the step voltage based on the partial derivative of the average optical power in the previous cycle and the empirical value;

[0021] S134. Update the peak-to-peak value of the PPM input electrical signal to the sum of the peak-to-peak value of the PPM input electrical signal in the previous cycle and the step voltage;

[0022] S135. Loop through S130 to S134 until the difference is less than or equal to the average optical power threshold.

[0023] As a possible implementation, in S14, loop to judge the relationship between the difference and the average optical power threshold, including the following steps:

[0024] S140. Judge whether the difference is greater than the average optical power threshold. If so, execute S141;

[0025] S141. Update the partial derivative of the average optical power for this cycle;

[0026] S142. Save the current average optical power value;

[0027] S143. Update the step voltage based on the partial derivative of the average optical power in the previous cycle and the empirical value;

[0028] S144. Update the bias voltage to the sum of the bias voltage in the previous cycle and the step voltage;

[0029] S145. Loop through S140 to S144 until the difference is less than or equal to the average optical power threshold.

[0030] As a possible implementation, the average optical power P avg is expressed as:

[0031]

[0032] In the formula, P avg is a function of, expressed as V bias represents the bias voltage, V gg represents the peak-to-peak voltage of the PPM electrical signal, M represents M time slots of the PPM optical signal, α represents the loss factor, β represents the leakage factor, and P in represents the input optical power.

[0033] As a possible implementation, the optimal bias voltage tracking method takes the waiting control interval time as the cycle period, and updates the optimal bias voltage cyclically. Within one cycle period, the optimal bias voltage tracking method specifically includes the following steps:

[0034] S20. Save the current average optical power;

[0035] S21. Save the average optical power after increasing the step voltage;

[0036] S22. Save the average optical power after decreasing the step voltage;

[0037] S23. Compare the three voltage values corresponding to the average optical power values obtained in S20 - S21;

[0038] S24. Obtain the optimal bias voltage based on the comparison result.

[0039] As a possible implementation, S24 specifically includes: when the voltage value corresponding to the average optical power after increasing the step voltage is the largest, the optimal bias voltage is updated to the sum of the previous optimal bias voltage and the step value;

[0040] when the voltage value corresponding to the average optical power after decreasing the step voltage is the largest, the optimal bias voltage is updated to the difference between the previous optimal bias voltage and the step value;

[0041] when the voltage value corresponding to the current average optical power is the largest, keep the previous optimal bias voltage unchanged.

[0042] In a second aspect, the present invention provides a cascaded MZM high extinction ratio signal generation system, including:

[0043] A laser, for emitting an optical signal with a fixed frequency;

[0044] At least two - stage MZM modulators connected in series. The first - stage MZM modulator receives the optical signal emitted by the laser and outputs the first - modulated optical signal. The subsequent - stage MZM modulators receive the modulated optical signals emitted by the previous - stage MZM modulators, and the last - stage MZM modulator outputs the final modulated optical signal;

[0045] A PPM electrical signal inputter, for emitting a PPM electrical signal;

[0046] A voltage driver, for adjusting the peak - to - peak voltage of the PPM electrical signal;

[0047] A phase shifter, for adjusting the phase of the PPM electrical signal entering different MZM modulators;

[0048] For each MZM modulator, a photodetector PD, an analog - to - digital converter ADC, a controller, and a digital - to - analog converter DAC are provided;

[0049] The cascaded MZM high extinction ratio optical signal generation system obtains the optimal peak-to-peak value of the PPM input electrical signal of each stage of the MZM modulator and tracks the optimal bias voltage by using the control method provided in the first aspect.

[0050] In a third aspect, the present invention provides a chip, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the control method of the cascaded MZM high extinction ratio optical signal generation system provided in the first aspect.

[0051] In a fourth aspect, the present invention provides a terminal, including a processor and a communication interface coupled to the processor. The processor is used to run a computer program or instruction to implement the control method of the cascaded MZM high extinction ratio optical signal generation system provided in the first aspect.

[0052] Compared with the prior art, the beneficial effects produced by the present invention are as follows:

[0053] 1. The signal quality and anti-interference ability of the deep space laser communication system are improved. By introducing the MZM control method combining optimal peak-to-peak value measurement and bias voltage tracking, the adaptive compensation of the MZM phase drift can be realized within a wider working range, effectively improving the extinction ratio of the output optical signal; experimental results show that after adopting the method provided by the present invention, the extinction ratio of the system output optical signal can be increased by about 6 dB, greatly improving the signal quality and enhancing the anti-interference ability of the system.

[0054] 2. The environmental adaptability and robustness of the deep space laser communication system are enhanced. Aiming at the problem that the MZM modulator is prone to phase drift due to the influence of factors such as temperature and humidity in the actual application scenario, the bias voltage tracking method proposed by the present invention can adaptively track environmental changes and realize the dynamic optimization control of the MZM bias voltage; long-term continuous operation experiments show that the method provided by the present invention can effectively suppress the influence of phase drift on the system performance, ensure the stability of the extinction ratio of the output optical signal, and improve the environmental adaptability and robustness of the system.

[0055] 3. The working life of the deep space laser communication equipment is extended. By introducing the optimal peak-to-peak voltage measurement method, the present invention can optimize the peak-to-peak value of the MZM input signal, avoiding the problems of MZM performance degradation and life reduction caused by excessive driving voltage. At the same time, the adaptive control of the bias voltage tracking method reduces the fluctuation of the bias voltage and the risk of performance attenuation caused by MZM phase drift, which helps to extend the working life of the equipment and improve the reliability of the system.

[0056] 4. Reduced the operation and maintenance costs of the laser communication system. Thanks to the adaptability and robustness of the MZM control method, the present invention can reduce the need for manual intervention and equipment maintenance, thus reducing the operation and maintenance costs of the system. The optimized bias voltage control and stable extinction ratio output also reduce the risk of equipment failure and communication interruption, improve the availability and maintainability of the system, and further reduce the operation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0058] Figure 1 is a flowchart of the method for obtaining the optimal peak-to-peak value of the PPM input electrical signal in the embodiment of the present invention;

[0059] Figure 2 is a flowchart of the optimal bias voltage tracking method in the embodiment of the present invention;

[0060] Figure 3 is a schematic diagram of the cascaded MZM high extinction ratio signal generation system in the embodiment of the present invention;

[0061] Figure 4 is a graph showing the relationship between different bias voltages and the extinction ratio when the peak-to-peak voltage is 4V in the embodiment of the present invention;

[0062] Figure 5 is a graph showing the relationship between the peak-to-peak voltage and the output extinction ratio in the embodiment of the present invention;

[0063] Figure 6 is a comparison graph of the extinction ratio experimental results of the first-stage MZM modulator with and without using the optimal bias voltage tracking method in the embodiment of the present invention;

[0064] Figure 7 is a comparison graph of the extinction ratio experimental results of the cascaded MZM modulator with and without using the optimal bias voltage tracking method in the embodiment of the present invention;

[0065] Figure 8 is a graph showing the relationship between the average optical power and the symbol error rate under different extinction ratios in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0066] For the convenience of clearly describing the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, terms such as "first" and "second" are used to distinguish identical or similar items with basically the same functions and roles. For example, the first threshold and the second threshold are only used to distinguish different thresholds, and do not limit their sequence. Those skilled in the art can understand that terms such as "first" and "second" do not limit the quantity and execution order, and terms such as "first" and "second" do not necessarily limit them to be different.

[0067] It should be noted that in the present invention, words such as "exemplary" or "for example" are used to represent examples, illustrations or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the present invention should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Exactly speaking, using words such as "exemplary" or "for example" aims to present relevant concepts in a specific manner.

[0068] In the present invention, "at least one" means one or more, and "a plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone, where A and B can be singular or plural. The character " / " generally represents that the associated objects before and after are in an "or" relationship. The following at least one (item) or its similar expression refers to any combination of these items, including any combination of single item (item) or plural items (items). For example, at least one (item) of a, b or c can represent: a, b, c, the combination of a and b, the combination of a and c, the combination of b and c, or the combination of a, b and c, where a, b and c can be single or multiple.

[0069] In order to achieve the modulation of high extinction ratio optical signals at the transmitting end, the external modulation technology based on cascaded MZM has become one of the research focuses in deep space laser communication. However, cascaded MZM faces the following problems when generating high extinction ratio optical signals: one is environmental factors, such as temperature, humidity and mechanical stress, etc., which will cause phase drift of MZM, and then lead to a decrease in the quality of the optical signals output at the transmitting end; the other is that the peak-to-peak voltage of MZM directly affects the performance of the system.

[0070] Some methods for compensating the phase drift of MZM have been proposed in the prior art. A certain Patent One discloses an automatic bias control device and its automatic bias control method for a cascaded Mach-Zehnder modulator (MZM). The control device includes a laser, a cascaded MZM, a splitter, a photodetector, and a bias voltage control module. A pilot signal is output from the bias voltage control module and enters the first MZM. After being modulated by the cascaded MZM, it is converted into an electrical signal through the splitter and the photodetector and enters the bias voltage control module. In the module, it is amplified, low-pass filtered, and then converted into a digital signal and enters the MCU for fast Fourier transform (FFT) to obtain the ratio of the second-order and first-order components of the pilot signal. The pilot method is used to stabilize the operating point of the first MZM, and the DC component detection method is used to stabilize the second MZM. By analyzing the characteristics of the transfer function of the cascaded MZM, this invention comprehensively utilizes the pilot method and the DC component detection method to achieve the bias voltage control of any point of the two cascaded MZMs successively within one processing cycle.

[0071] A certain Patent Two discloses a method for controlling the bias point of an MZM in an optical link containing an EDFA. A laser is used to input into the MZM, a VOA is used to simulate the insertion loss of the optoelectronic conversion circuit, a PD and a spectrum analyzer are used to monitor the spectrum of the signal. Utilizing the response characteristics of the EDFA, without increasing the system complexity, the method is simple and the cost is controllable; the bias voltage of the MZM is set to make the MZM operate at the linear point and the carrier suppression point, the pilot frequency is adjusted to change the phase response of the EDFA to the pilot frequency, reducing or not increasing the in-band intermodulation signal introduced by the bias point control signal, thereby improving or maintaining the spurious-free dynamic range of the system; promoting the application of the pilot bias point control method in practical engineering. Compared with the power method, the MZM can be more accurately and stably controlled at the set operating point, especially the linear point and the carrier suppression point.

[0072] A certain Patent Three discloses a method and device for controlling the operating point of an MZM modulator, which adaptively adjusts the operating voltage of the MZM modulator to make the modulator operate at the optimal linear operating point. The device includes an MEM modulator, a coupler, an optical filter, an optical detector, a processor, and an amplifier connected in sequence to form a closed-loop circuit; when an optical carrier signal and an actual communication signal are input into the MZM modulator simultaneously, the optical power signal at the output end of the MEM modulator is successively converted into a voltage signal Vx through the coupler, the optical filter, and the optical detector; after receiving the voltage signal Vx, the processor compares the voltage signal Vx with the voltage value V in the voltage optical power meter, and through correction, makes Vx equal to the closer linear operating point V; the processor amplifies the voltage signal V through the amplifier and controls the MZM modulator to operate at the linear operating point.

[0073] It can be seen that although some methods for compensating the phase drift of the MZM have been proposed in the prior art, they mainly focus on controlling at specific operating points (such as the linear point), with a limited scope of application. Moreover, they do not combine the peak-to-peak value of the input electrical signal, so it is impossible to optimize the performance of the high extinction ratio optical modulation signal while implementing the bias voltage control, and it is difficult to meet the requirements of the deep space laser communication system for improving the extinction ratio performance.

[0074] An embodiment of the present invention provides a cascaded MZM high extinction ratio optical signal generation system, a control method, a chip and a terminal, so as to achieve the purpose of optimizing the performance of the high extinction ratio modulation signal while tracking and controlling the bias voltage of the MZM.

[0075] In a first aspect, the present invention provides a control method for a cascaded MZM high extinction ratio optical signal generation system. The optical signal generation system includes at least two stages of MZM modulators connected in series. The control method includes the following steps:

[0076] S1. Based on the optimal peak-to-peak value acquisition method of the PPM input electrical signal, obtain the optimal peak-to-peak value of the PPM input electrical signal of each stage of the MZM modulator;

[0077] See Figure 1 , as a possible implementation manner, for each stage of the MZM modulator, the optimal peak-to-peak value acquisition method of the PPM input electrical signal includes the following sub-steps:

[0078] S10. Initialize a random point, where the random point includes the peak-to-peak value of the PPM input electrical signal and the bias voltage;

[0079] S11. Initialize the number of iterations and configure the maximum number of loops;

[0080] S12. Determine whether the current number of iterations is less than the maximum number of loops. If it is less, execute S13;

[0081] S13. Configure the initial step voltage; record the current average optical power value; update the peak-to-peak value of the PPM input electrical signal to the sum of the input electrical signal peak-to-peak value of the previous cycle and the step voltage; calculate the difference between the current average optical power value and the average optical power value saved in the previous cycle, configure the average optical power threshold; loop to judge the relationship between the difference and the average optical power threshold until the difference is less than or equal to the average optical power threshold, and then execute S14;

[0082] As a possible implementation manner, the loop in S13 to judge the relationship between the difference and the average optical power threshold includes the following sub-steps:

[0083] S130. Determine whether the difference is greater than the average optical power threshold. If it is, execute S131;

[0084] S131. Update the average optical power partial derivative of this cycle;

[0085] S132. Save the current average optical power value;

[0086] S133. Update the step voltage according to the average optical power partial derivative and the empirical value of the previous cycle;

[0087] S134. Update the peak-to-peak value of the PPM input electrical signal to the sum of the peak-to-peak value of the PPM input electrical signal of the previous cycle and the step voltage;

[0088] S135. Loop through S130 to S134 until the difference is less than or equal to the average optical power threshold value.

[0089] S14. Configure the initial step voltage; record the current average optical power value; update the bias voltage to the sum of the bias voltage of the previous cycle and the step voltage; calculate the difference between the current average optical power and the average optical power saved in the previous cycle, configure the average optical power threshold value; loop to judge the relationship between the difference and the average optical power threshold value until the difference is less than or equal to the average optical power threshold value, and execute S15;

[0090] As a possible implementation, the loop in S14 to judge the relationship between the difference and the average optical power threshold value includes the following sub-steps:

[0091] S140. Judge whether the difference is greater than the average optical power threshold value. If so, execute S141;

[0092] S141. Update the average optical power partial derivative of this cycle;

[0093] S142. Save the current average optical power value;

[0094] S143. Update the step voltage according to the average optical power partial derivative and the empirical value of the previous cycle;

[0095] S144. Update the bias voltage to the sum of the bias voltage of the previous cycle and the step voltage;

[0096] S145. Loop through S140 to S144 until the difference is less than or equal to the average optical power threshold value.

[0097] S15. Update the iteration times, and continue to execute S12 to S14 until the iteration times is equal to the maximum number of cycles to obtain the optimal peak-to-peak value.

[0098] As a possible implementation, the average optical power P avg is expressed as:

[0099]

[0100] In the formula, P avg is The function, denoted as V bias represents the bias voltage, V gg represents the peak-to-peak voltage of the PPM electrical signal, M represents M time slots of the PPM optical signal, α represents the loss factor, β represents the leakage factor, P in represents the input optical power.

[0101] S2. For the first-stage MZM modulator, control the output optical power of the MZM modulator to be the minimum, and based on the optimal bias voltage tracking method, obtain the optimal bias voltage of the first-stage MZM modulator;

[0102] As a possible implementation, refer to Figure 2 , the optimal bias voltage tracking method takes the waiting control interval time as the cycle period, and cyclically updates the optimal bias voltage. Within one cycle period, the optimal bias voltage tracking method specifically includes the following sub-steps:

[0103] S20. Save the current average optical power;

[0104] S21. Save the average optical power after increasing the step voltage;

[0105] S22. Save the average optical power after decreasing the step voltage;

[0106] S23. Compare the three voltage values corresponding to the average optical power obtained in S20 - S21;

[0107] S24. Obtain the optimal bias voltage based on the comparison result.

[0108] As a possible implementation, S24 specifically includes: when the voltage value corresponding to the average optical power after increasing the step voltage is the largest, update the optimal bias voltage to the sum of the previous optimal bias voltage and the step value;

[0109] when the voltage value corresponding to the average optical power after decreasing the step voltage is the largest, update the optimal bias voltage to the difference between the previous optimal bias voltage and the step value;

[0110] when the voltage value corresponding to the current average optical power is the largest, keep the previous optimal bias voltage unchanged.

[0111] S3. For the Nth-stage MZM modulator, control the output optical power of the MZM modulator to be the maximum, and based on the optimal bias voltage tracking method, obtain the optimal bias voltage of the Nth-stage MZM modulator.

[0112] To facilitate the understanding of the control method of the cascaded MZM high extinction ratio optical signal generation system provided by the embodiments of the present invention, the following will be elaborated in detail with specific examples. It should be understood that the following examples are only for explanatory purposes and are not specifically limited.

[0113] The laser emits an optical signal with a fixed frequency, which is split by an optical splitter in the MZM modulator. The splitting ratio can be between 0.1% and 1%, such as 0.1%, 0.3%, 0.5%, 0.7%, 0.8%, 0.9%, 1%. The output of the photodetector PD is a PPM optical signal. The analog-to-digital converter ADC receives the PPM optical signal output by the photodetector PD and converts it into a digital signal for transmission to the controller. The controller receives the digital signal of the PPM optical signal converted by the analog-to-digital converter ADC, and then adjusts it through the digital-to-analog converter DAC and outputs it to the bias voltage of the MZM.

[0114] In the PPM optical signal, one symbol consists of M time slots and only one time slot carries the optical signal. This time slot is called the signal time slot, and the remaining time slots are called non-signal time slots. The signal time slot is selected from the M time slots with equal probability.

[0115] The PPM electrical signal is emitted by the PPM electrical signal inputter and includes signal time slots and non-signal time slots. The voltage value of the signal time slot is denoted as V max , and the voltage value of the non-signal time slot is denoted as V min ; The peak-to-peak voltage of the PPM electrical signal is denoted as V gg , then: V gg = V max - V min .

[0116] The optical power P 1 of the signal time slot is expressed as:

[0117]

[0118] In the formula, α represents the loss factor, β represents the leakage factor, and P in represents the input optical power.

[0119] The optical power of the non-signal time slot is expressed as:

[0120]

[0121] In the formula, α represents the loss factor, β represents the leakage factor, P in represents the input optical power, and V bias represents the bias voltage.

[0122] The extinction ratio is defined as the optical power ratio between the signal time slot and the non-signal time slot, denoted as ε, and ε = P 1 / P 0Indicate;

[0123] Use And To simplify the expression, let V π Represent the half-wave voltage of the modulator. Then the extinction ratio ε of the PPM optical signal output from the MZM modulator is expressed as:

[0124]

[0125] Therefore, the extinction ratio ε can be regarded as And A function of, and when the condition k ∈ Z and k ∈ Z are satisfied, the maximum value of ε is reached. Z represents the set of integers.

[0126] For the M-PPM optical signal, the duty cycle of the signal time slot is 1 / M. The average optical power P of the PPM optical signal avg Is expressed as:

[0127]

[0128] P avg Is A function of, expressed as The points (π + 2kπ, π + 2kπ), where k ∈ Z, are a series of "saddle points" of this function. P 01 Is the optical power of the non-signal time slot of the first-stage MZM modulator, and P 11 Is the optical power of the signal time slot of the first-stage MZM modulator;

[0129] The peak-to-peak voltage of the PPM input electrical signal is relatively stable and remains unchanged for a period of time. Therefore, it is only necessary to measure the peak-to-peak voltage V gg Once before the system starts running, without the need for continuous tracking, and only re-evaluated and adjusted when the control method starts.

[0130] See Figure 1 To obtain the method for the optimal peak-to-peak voltage of the PPM input electrical signal, it specifically includes:

[0131] S10. Initialize random points, including the peak-to-peak Of the PPM input electrical signal

[0132] S11. Initialize the iteration count i = 0, and configure the maximum number of loops as k;

[0133] S12. Judge the size of the current iteration count i and the maximum number of loops k. If i is less than k, then execute S13;

[0134] S13. Configure the initial step voltage VΔ = 0.1; Record the current average optical power value Update the peak-to-peak value of the PPM input electrical signal to the sum of the peak-to-peak value of the input electrical signal in the previous cycle and the step voltage: Calculate the current average optical power value And the average optical power value saved in the previous cycle Of the difference, configure the average optical power threshold Loop to judge the relationship between the difference and the average optical power threshold Until the difference is less than or equal to the average optical power threshold, execute S14.;

[0135] As a possible implementation, loop to judge the relationship between the difference and the average optical power threshold, including the following steps:

[0136] S130. If Then execute S131;

[0137] S131. Update the average optical power partial derivative of this cycle:

[0138] S132. Save the current average optical power value:

[0139] S133. Update the step voltage according to the average optical power partial derivative of the previous cycle and the empirical value: μ represents the learning rate, Represents the average optical power partial derivative caused by the peak-to-peak value of the electrical signal in this cycle;

[0140] S134. Update the peak-to-peak value of the PPM input electrical signal to the sum of the peak-to-peak value of the PPM input electrical signal in the previous cycle and the step voltage:

[0141] S135. Loop to execute S130~S134 until the difference is less than or equal to the average optical power threshold Execute S14.

[0142] S14. Configure the initial step voltage V Δ = 0.1; Record the current average optical power value Update the bias voltage to the sum of the bias voltage in the previous cycle and the step voltage: Calculate the current average optical power And the average optical power saved in the previous cycle Of the difference, configure the average optical power threshold Loop to judge the relationship between the difference and the average optical power threshold until the difference is less than or equal to the average optical power threshold value, and then execute S15;

[0143] As a possible implementation, continuously judge the relationship between the difference and the average optical power threshold value, including the following steps:

[0144] S140. If: then execute S141;

[0145] S141. Update the average optical power partial derivative of this cycle:

[0146] S142. Save the current average optical power value:

[0147] S143. Update the stepping voltage according to the average optical power partial derivative of the previous cycle and the empirical value: μ represents the learning rate, represents the average optical power partial derivative caused by the bias voltage in this cycle;

[0148] S144. Update the bias voltage to the sum of the bias voltage of the previous cycle and the stepping voltage:

[0149] S145. Continuously execute S140 - S144 until the difference is less than or equal to the average optical power threshold value and then execute S15.

[0150] S15. Update the iteration number, and continue to execute S12 - S14 until the iteration number i is equal to the maximum loop number k to obtain the optimal peak - to - peak value.

[0151] After obtaining the optimal peak - to - peak value, further track the optimal bias voltage. Substitute the average optical power P avg into the expression of the extinction ratio ε, and get:

[0152]

[0153] It can be seen that as the average optical power P avg decreases, the extinction ratio ε monotonically increases. Therefore, as long as the average optical power P avg is kept minimum, it is possible to stably track the phase drift of the MZM and keep the bias voltage of the MZM at the optimal point.

[0154] The optimal bias voltage tracking method takes the waiting control interval time as the cycle period, and continuously updates the optimal bias voltage. Within one cycle period, the optimal bias voltage tracking method specifically includes the following steps:

[0155] S20. Save the current average optical power

[0156] S21. Save the average optical power after increasing the step voltage

[0157] S22. Save the average optical power after decreasing the step voltage

[0158] S23. Compare the three voltage values corresponding to the average optical powers obtained in S20 to S21;

[0159] S24. Obtain the optimal bias voltage based on the comparison result, specifically including: when the voltage value corresponding to the average optical power after increasing the step voltage is the largest, the optimal bias voltage is updated to the sum of the previous optimal bias voltage and the step value: V bias →V bias +V step ; when the voltage value corresponding to the average optical power after decreasing the step voltage is the largest, the optimal bias voltage is updated to the difference between the previous optimal bias voltage and the step value: V bias →V bias -V step ; when the voltage value corresponding to the current average optical power is the largest, keep the previous optimal bias voltage unchanged: V bias →V bias .

[0160] When using a multi-stage MZM, as long as the electrical signal of the first-stage MZM is converted into a constant voltage signal, the optimal peak-to-peak value acquisition method can be applied to all cascaded MZMs. However, the optimal bias voltage tracking method will change. For the first-stage MZM modulator, by controlling the output optical power of the MZM modulator to be the minimum, the optimal bias voltage of the first-stage MZM modulator can be obtained. For the second-stage or more-stage MZM modulators, by controlling the output optical power of the MZM modulator to be the maximum, the optimal bias voltage of the multi-stage MZM modulators can be obtained.

[0161] Taking the second-stage MZM modulator as an example, the extinction ratio at the output end of the second-stage MZM is expressed as:

[0162]

[0163] where P 21 represents the optical power of the signal time slot of the second-stage MZM modulator, P 20 represents the optical power of the non-signal time slot of the second-stage MZM modulator, β 1 represents the first-stage leakage factor, β 2 represents the second-stage leakage factor,

[0164] The average optical power P at the output of the second - stage MZM avg2 is expressed as:

[0165]

[0166] where ε 1 represents the power distribution coefficient from the first - stage MZM to the photodetector, M represents the number of time slots, and α 1 represents the first - stage loss factor, and α 2 represents the second - stage loss factor.

[0167] At being the optimal value, the derivative of ε 2 with respect to P avg2 is obtained. Rewrite ε 2 as:

[0168]

[0169] where γ represents the splitting coefficient of the photodetector and is expressed as:

[0170]

[0171] Generally, the leakage factor of the MZM is usually between 0.1% and 1%, satisfying Therefore, ε 2 exhibits a monotonically decreasing behavior with respect to P avg2 .

[0172] To evaluate the performance of the optimal bias voltage tracking method for tracking the optimal bias voltage during long - term operation, an experimental system is built. When the peak - to - peak voltage is 4V, the relationship between different bias voltages and the extinction ratio is shown in Figure 4 ; the relationship between the peak - to - peak voltage and the output extinction ratio is shown in Figure 5 . The extinction ratio performance of the sub - method for tracking the optimal bias voltage of the first - stage MZM modulator within 60 minutes is statistically analyzed, and the results are shown in Figure 6 . It can be seen that for a fixed bias voltage and peak - to - peak voltage, the output extinction ratio of the MZM without the optimization method decreases by about 6dB within 60 minutes. In contrast, for the MZM with the optimal bias voltage tracking method, the output extinction ratio remains stable at about 16.5dB, with a fluctuation range of ±0.5dB.

[0173] For a multi - stage MZM, taking the maximum value of the optical power as the basis for determining the optimal bias voltage, based on the experimental system, the output extinction ratio of the cascaded MZM within 60 minutes is tested, and the results are shown in Figure 7, at the beginning of the experiment, the optimal bias voltage and the optimal peak-to-peak value are determined using the method of the present invention. For the second-stage MZM, since the control of the second-stage MZM is more susceptible to noise, the extinction ratio (dB) of the output of the two-stage MZM is not the superposition of the extinction ratios of the two-stage MZM. At the same time, if the MZM bias voltage tracking method is not used, although the phase shift occurs in the second stage, the extinction ratio decreases by about 4 dB, which is less than the decrease in the extinction ratio of the first-stage MZM. This is because although the phase shift occurs in the second stage, the power of the non-signal time slot does not change much.

[0174] Taking practical applications as an example, Figure 8 the relationship between the average optical power and the symbol error rate at different extinction ratios is described, and the change of the symbol error rate at different extinction ratios is simulated. It can be seen from the figure that the higher the extinction ratio, the lower the average optical power required by the system.

[0175] In a second aspect, the present invention provides a cascaded MZM high extinction ratio signal generation system, see Figure 3 , including:

[0176] A laser for emitting an optical signal with a fixed frequency;

[0177] As an example, the laser is connected to the MZM modulator through an optical fiber link.

[0178] At least two cascaded MZM modulators. The first MZM modulator in the series receives the optical signal emitted by the laser and outputs the first-modulated optical signal. The subsequent MZM modulators receive the modulated optical signals emitted by the previous MZM modulators, and the last MZM modulator outputs the final modulated optical signal;

[0179] A PPM electrical signal inputter for emitting PPM electrical signals;

[0180] A voltage driver for adjusting the peak-to-peak voltage of the PPM electrical signal;

[0181] A phase shifter for adjusting the phase of the PPM electrical signal entering different MZM modulators;

[0182] For each MZM modulator, a photodetector PD, an analog-to-digital converter ADC, a controller, and a digital-to-analog converter DAC are provided;

[0183] As an example, the output of each MZM modulator is connected to the analog-to-digital converter ADC, the analog-to-digital converter ADC is connected to the controller, the controller is connected to the digital-to-analog converter DAC, and the digital-to-analog converter DAC is then connected to the corresponding MZM modulator. The photodetector includes a PIN photodiode and a transimpedance amplifier TIA.

[0184] The cascaded MZM high extinction ratio optical signal generation system obtains the optimal peak-to-peak value of the PPM input electrical signal for each stage of the MZM modulator and tracks the optimal bias voltage by using the control method provided in the first aspect. In a third aspect, the present invention provides a chip, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the control method of the cascaded MZM high extinction ratio optical signal generation system provided in the first aspect.

[0185] In a fourth aspect, the present invention provides a terminal, including a processor and a communication interface coupled to the processor. The processor is used to run a computer program or instruction to implement the control method of the cascaded MZM high extinction ratio optical signal generation system provided in the first aspect.

[0186] Compared with the prior art, the present invention has the following technical effects:

[0187] 1. It improves the signal quality and anti-interference ability of the deep space laser communication system. By introducing the MZM control method combining optimal peak-to-peak value measurement and bias voltage tracking, the adaptive compensation of the MZM phase drift can be realized within a wider working range, effectively improving the extinction ratio of the output optical signal. Experimental results show that after adopting the method provided by the present invention, the extinction ratio of the system output optical signal can be increased by about 6 dB, greatly improving the signal quality and enhancing the anti-interference ability of the system.

[0188] 2. It enhances the environmental adaptability and robustness of the deep space laser communication system. Aiming at the problem that the MZM modulator is prone to phase drift due to factors such as temperature and humidity in the actual application scenario, the bias voltage tracking method proposed by the present invention can adaptively track environmental changes and realize the dynamic optimization control of the MZM bias voltage. Long-term continuous operation experiments show that the method provided by the present invention can effectively suppress the influence of phase drift on the system performance, ensure the stability of the extinction ratio of the output optical signal, and improve the environmental adaptability and robustness of the system.

[0189] 3. It extends the working life of the deep space laser communication equipment. By introducing the optimal peak-to-peak voltage measurement method, the present invention can optimize the peak-to-peak value of the MZM input signal, avoiding the problems of MZM performance degradation and life reduction caused by excessive driving voltage. At the same time, the adaptive control of the bias voltage tracking method reduces the fluctuation of the bias voltage and the risk of performance attenuation caused by MZM phase drift, which helps to extend the working life of the equipment and improve the reliability of the system.

[0190] 4. Reduced the operation and maintenance costs of the laser communication system. Benefiting from the adaptability and robustness of the MZM control method, the present invention can reduce the need for manual intervention and equipment maintenance, thereby reducing the operation and maintenance costs of the system. The optimized bias voltage control and stable extinction ratio output also reduce the risk of equipment failure and communication interruption, improve the availability and maintainability of the system, and further reduce the operation and maintenance costs.

Claims

1. A control method for a cascaded MZM high extinction ratio optical signal generation system, characterized in that: The optical signal generation system comprises at least two stages of MZM modulators connected in series; the control method comprises the following steps: Based on the optimal peak-to-peak value acquisition method of the PPM input electrical signal, the optimal peak-to-peak value of the PPM input electrical signal of each level of the MZM modulator is obtained; specifically including: S10. Initializing random points, the random points include the peak-to-peak value of the PPM input electrical signal and the bias voltage; S11. Initializing the number of iterations and configuring the maximum number of cycles; S12. Determining whether the current number of iterations is less than the maximum number of cycles, if less, executing S13; S13. Configuring the initial step voltage; recording the current average optical power value; updating the peak-to-peak value of the PPM input electrical signal to the sum of the peak-to-peak value of the input electrical signal and the step voltage in the previous cycle; calculating the difference between the current average optical power value and the average optical power value saved in the previous cycle , configure the average optical power threshold value; cyclically determine the relationship between the difference and the average optical power threshold value until the difference is less than or equal to the average optical power threshold value, and execute S14; S14. Configure the initial step voltage; record the current average optical power value; update the bias voltage to the sum of the bias voltage and the step voltage of the previous cycle; calculate the difference between the current average optical power value and the average optical power value saved in the previous cycle, and configure the average optical power threshold value; cyclically determine the relationship between the difference and the average optical power threshold value until the difference is less than or equal to the average optical power threshold value, and execute S15; S15. Update the number of iterations, and continue to execute S12~S14 until the number of iterations is equal to the maximum number of cycles to obtain the optimal peak-to-peak value; For the first-stage MZM modulator, controlling the output optical power of the first-stage MZM modulator to be minimum, and obtaining the optimal bias voltage of the first-stage MZM modulator based on the optimal bias voltage tracking method; For the N-th level MZM modulator, the output optical power of the N-th level MZM modulator is controlled to be maximum, and based on the optimal bias voltage tracking method, the optimal bias voltage of the N-th level MZM modulator is obtained.

2. The control method of the cascaded MZM high extinction ratio optical signal generation system according to claim 1, characterized in that: In S13, the relationship between the difference value and the average optical power threshold value is cyclically determined, including the following steps: S130. Determine whether the difference is greater than the average optical power threshold, if so, execute S131; S131. Update the partial derivative of the average optical power of this cycle; S132. Save the current average optical power value; S133. Update the step voltage according to the partial derivative of the average optical power of the previous cycle and the empirical value; S134. Update the peak-to-peak value of the PPM input electrical signal to the sum of the peak-to-peak value of the PPM input electrical signal of the previous cycle and the step voltage; S135. Execute S130 to S134 in a loop until the difference is less than or equal to the average optical power threshold.

3. The control method of the cascaded MZM high extinction ratio optical signal generation system according to claim 1, characterized in that: In S14, the relationship between the difference value and the average optical power threshold value is cyclically determined, including the following steps: S140. Determine whether the difference is greater than the average optical power threshold, if so, execute S141; S141. Update the partial derivative of the average optical power of this cycle; S142. Save the current average optical power value; S143. Update the step voltage according to the partial derivative of the average optical power of the previous cycle and the empirical value; S144. Update the bias voltage to the sum of the bias voltage of the previous cycle and the step voltage; S145. Execute S140 to S144 in a loop until the difference is less than or equal to the average optical power threshold.

4. The control method of the cascaded MZM high extinction ratio optical signal generation system according to claim 1, characterized in that: Average optical power P avg It is expressed as: Where P avg yes The function is expressed as V bias Represents the bias voltage, V min Indicates the voltage value of the non-signal time slot, V gg represents the peak-to-peak voltage of the PPM electrical signal, M represents the M time slots of the PPM optical signal, and P 11 is the optical power of the first-stage MZM modulator signal time slot, α represents the loss factor, β represents the leakage factor, P in Indicates the input optical power; P 01 is the optical power of the non-signal time slot of the first-stage MZM modulator; V π is a half-wave voltage.

5. The control method of the cascaded MZM high extinction ratio optical signal generation system according to claim 1, characterized in that: The optimal bias voltage tracking method takes the waiting control interval time as a cycle period and cyclically updates the optimal bias voltage. In one cycle period, the optimal bias voltage tracking method specifically includes the following steps: S20. Save the current average optical power; S21. Save the average optical power after increasing the step voltage; S22. Save the average optical power after reducing the step voltage; S23. Compare the three voltage values ​​corresponding to the average optical power obtained in S20 to S22; S24. Obtain an optimal bias voltage based on the comparison result.

6. The control method of the cascaded MZM high extinction ratio optical signal generation system according to claim 5, characterized in that: S24 specifically includes: when the voltage value corresponding to the average value of the optical power after the step voltage is increased is the largest, the optimal bias voltage is updated to the sum of the optimal bias voltage at the previous moment and the step value; When the voltage value corresponding to the average optical power value is the largest after reducing the step voltage, the optimal bias voltage is updated to the difference between the optimal bias voltage at the previous moment and the step value; When the voltage value corresponding to the current average optical power value is the largest, the optimal bias voltage at the previous moment is kept unchanged.

7. A cascaded MZM high extinction ratio signal generation system, characterized in that: include: Laser, used to transmit light signals of fixed frequency; At least two stages of MZM modulators are connected in series, the first MZM modulator receives the optical signal emitted by the laser and outputs the optical signal after the first modulation, the second MZM modulator receives the modulated optical signal emitted by the first MZM modulator, and the last MZM modulator outputs the final modulated optical signal; A PPM electrical signal input device, used for transmitting a PPM electrical signal; A voltage driver, used to adjust the peak-to-peak voltage of the PPM electrical signal; A phase shifter, used to adjust the phase of the PPM electrical signal entering different MZM modulators; Each level of the MZM modulator is provided with a photodetector PD, an analog-to-digital converter ADC, a controller and a digital-to-analog converter DAC; The cascaded MZM high extinction ratio optical signal generation system adopts the control method described in any one of claims 1 to 6 to obtain the optimal peak-to-peak value of the PPM input electrical signal of each stage of the MZM modulator and track the optimal bias voltage.

8. A chip comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the control method of the cascaded MZM high extinction ratio optical signal generating system as described in any one of claims 1 to 6 is implemented.

9. A terminal, characterized in that: It comprises a processor and a communication interface coupled to the processor, wherein the processor is used to run a computer program or instruction to implement the control method of the cascaded MZM high extinction ratio optical signal generation system according to any one of claims 1 to 6.

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