Low-repetition-frequency fiber laser active coherent phase locking method based on laser waveform self-reference optimization algorithm

Abstract

The invention discloses a low-repetition-frequency fiber laser active coherent phase locking method based on a laser waveform self-reference optimization algorithm, and the method comprises the steps: firstly, carrying out the time domain nonlinear zooming processing of a coherent combined photoelectric signal through extracting the light intensity fluctuation characteristics of a full-period single-path pulse laser; the pulse intrinsic intensity fluctuation is effectively eliminated, the phase noise modulation characteristics are completely reserved, and a pseudo-continuous signal representing the real phase deviation is generated; a phase mismatch control signal is obtained based on bilateral symmetry phase disturbance operation, two laser phases are corrected through closed-loop feedback, and coherent combination output efficiency optimization is achieved. The method solves the problems that a traditional active phase locking method cannot effectively distinguish phase noise and pulse fluctuation under the condition of low repetition frequency, and phase noise information is lost due to the fact that a filtering algorithm is directly applied, and the threshold preset requirement is avoided through a waveform self-reference mechanism. The adaptability to different waveforms and repetition frequency parameters in coherent combination is improved, and high-precision phase locking control is achieved under the low repetition frequency condition (smaller than or equal to 5 kHz).

Description

Technical Field

[0001] This invention relates to the field of fiber laser coherent synthesis technology, specifically to a low repetition rate fiber laser active coherent phase-locked loop method based on a laser waveform self-reference optimization algorithm. Background Technology

[0002] Low repetition rate (less than 5 kHz, typical noise cutoff frequency) pulsed fiber lasers, due to their large pulse intervals, can accumulate higher single-pulse energy at the same average power compared to high repetition rate lasers. They are widely used in fields requiring high single-pulse energy, such as remote sensing, advanced manufacturing, and healthcare. However, the potential for increasing laser power is limited by physical factors such as nonlinear and thermal effects. Fiber laser coherent combining technology can significantly increase output power while maintaining high beam quality. Compared to passive phase-controlled coherent combining, active phase control can achieve higher combined power.

[0003] Currently, several mature schemes exist for active phase control in continuous-wave laser systems. However, when phase-locked systems are applied to pulsed lasers, traditional phase-locked methods face challenges. Due to the inherent intensity fluctuations of pulses, it is difficult to distinguish between the inherent intensity changes of the pulse and the intensity fluctuations caused by phase noise. Therefore, traditional phase control mechanisms based on synthesized intensity fluctuations as the phase-locking criterion are adversely affected. Filtering methods provide a solution for coherent synthesis in pulsed fiber lasers. These methods involve adding a low-pass filter with an appropriate cutoff frequency after the photoelectric conversion device to filter out intensity fluctuations caused by pulse time-domain waveform fluctuations, and then performing phase control according to the coherent synthesis method for continuous-wave lasers. However, this method is only effective under relatively high repetition frequencies. Under low repetition frequencies, the phase noise spectrum overlaps with the repetition frequency, and the filtering process eliminates key phase noise information, causing the phase-locked control signal to become inaccurate.

[0004] When the repetition frequency is less than or equal to the phase noise cutoff frequency, the adverse effects of pulses on phase-locked loops can be eliminated by chopping pulse fluctuations in the time domain. CN113125120A discloses a low repetition rate fiber laser coherent synthesis method based on multi-jitter method. Through a self-designed window filtering algorithm, it effectively filters out pulse signal noise doped in the phase noise, and uses a multi-jitter phase-locked loop algorithm to achieve coherent synthesis of lasers with a repetition frequency of 10kHz. Active phase control can also be achieved by using continuous laser as a probe. The continuous optical probe method uses devices such as acousto-optic modulators to chop off pulsed lasers, retaining only the continuous portion between pulses, and uses the phase information contained in the continuous laser to correct the phase difference of the pulsed laser in real time. CN103346470A discloses a pulse-pumped low repetition rate fiber laser coherent synthesis system. The signal generator provides a modulation signal to the intensity modulator to chop off the intensity of the pulsed portion, retaining only the continuous signal light between pulses for phase control. However, the control signal waveform used to choke the pulse in the above method needs to be designed with threshold or characteristic conditions for a specific system to achieve separation of the continuous part and the pulse part, resulting in poor adaptability to different complex laser waveforms. On the other hand, the phase information of the pulse part is ignored. If the pulse width is wide or the waveform is complex, the information of the continuous part can be greatly reduced.

[0005] Therefore, there is an urgent need to develop a novel low-repetition-frequency phase-locked loop (PLL) method that can avoid the loss of phase information and circumvent preset condition limitations, and has the ability to adaptively suppress pulse waveform fluctuations, so as to achieve stable PLL control in low-repetition-frequency pulsed laser coherent synthesis scenarios. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and solve the problem that traditional phase-locked loop (PLL) methods are unable to handle coherent synthesis of low-repetition-frequency pulsed fiber lasers. Under low repetition-frequency conditions, the inherent intensity fluctuation frequency of the pulse overlaps with the ambient noise frequency, making it difficult for traditional methods to distinguish between phase noise and inherent pulse fluctuations. Directly applying filtering methods results in the loss of key noise information after filtering due to the overlap of phase noise and repetition frequency, thus degrading the PLL effect. While continuous optical probe methods can utilize the continuous portion between pulses for feedback control of the low-repetition-frequency coherent synthesis system, they require preset waveform separation conditions, limiting their applicability, and the pulse information is ignored. This invention provides an active coherent PLL method for low-repetition-frequency fiber lasers based on a laser waveform self-reference optimization algorithm. This method eliminates the influence of pulse intensity fluctuations on PLL without requiring preset thresholds and fully preserves phase noise information, achieving adaptive suppression of pulse waveform fluctuations and enabling stable PLL under different pulse waveforms and repetition frequency parameters.

[0007] The method of this invention is achieved through the following technical solution:

[0008] This invention discloses a low-repetition-rate fiber laser active coherent phase-locked loop method based on a laser waveform self-reference optimization algorithm. First, the intensity fluctuation signal of a single-pulse laser is acquired, and a pulse waveform self-reference model is constructed based on this signal. Then, positive and negative phase perturbations are applied to the multi-laser signal arms, and photoelectric conversion is performed on the coherently synthesized output beam. Next, the synthesized photoelectric signal obtained by conversion is nonlinearly scaled using the established self-reference waveform to suppress the inherent intensity fluctuations of the pulse and generate a pseudo-continuous signal. Finally, the phase error is extracted based on this pseudo-continuous signal, and a control signal is generated. This feedback control signal is applied to the signal arm optical path to complete closed-loop phase correction.

[0009] This invention discloses a low-repetition-rate fiber laser active coherent phase-locking method based on a laser waveform self-reference optimization algorithm. It is based on a pulsed fiber laser coherent synthesis hardware system, which includes a low-repetition-rate pulsed laser seed source, a polarization-preserving fiber coupler, a phase adjustment unit, a fiber gain amplification link, a pigtail collimation component, a light-blocking gate, a spatial polarization combining cube, a high-reflectivity lens, a photoelectric conversion device, a self-reference sequence analog-to-digital sampler, and an active coherent phase-locking operation module.

[0010] This invention discloses a low-repetition-rate fiber laser active coherent phase-locking method based on a laser waveform self-reference optimization algorithm, the basic implementation process of which is as follows:

[0011] Step 1: Extraction of intensity fluctuation features of a single-pulse laser throughout its entire cycle. The temporal amplitude characteristics of a single-pulse laser are captured using a photoelectric conversion device, and the voltage distribution at multiple sampling points within the pulse period is recorded to obtain discrete characteristic data of the inherent intensity fluctuations of the laser pulse.

[0012] A low-repetition-rate pulsed laser seed source is powered on. The laser beam is transmitted to a polarization-maintaining fiber coupler and split into two equal-intensity paths: a reference arm and a signal arm. A light-blocking gate is placed at the exit port of the reference arm's pigtail collimation assembly, allowing the photoelectric signal of the single-pulse laser to be incident on the photoelectric conversion device. The voltage values ​​at N sampling points within one pulse cycle are collected by a self-reference sequence analog-to-digital sampler. The voltage values ​​at N sampling points are represented as:

[0013] V ref (n), n=1,2,…,N (11)

[0014] Step 2: Self-reference waveform modeling without preset thresholds. Discrete voltage sample values ​​are integrated into a discrete sequence of self-reference signals to form a standard intrinsic model of the pulse waveform, achieving threshold-independent adaptive waveform representation.

[0015] The active coherent phase-locked loop (PLL) module will process the voltage values ​​V from multiple sampling points. ref (n) can be combined in time order to form a discrete sequence of self-reference signals, represented as:

[0016] S ref (n)=[V ref (1),V ref (2),...V ref (n)] (12)

[0017] Step 3: Apply bilateral symmetric phase perturbation. Using the optical path without the phase adjustment unit as the reference arm and the optical path with the phase adjustment unit as the signal arm, apply symmetric phase perturbation to the signal arm.

[0018] The active coherent phase-locked loop (PLL) module controls the phase modulation unit to apply positive and negative phase perturbations to the laser signal arm, respectively. The time-domain expressions of the signal arm with added positive and negative perturbations are as follows:

[0019]

[0020] In the formula, Γ k (t) represents the amplitude-time term of the laser in the signal arm, and ω represents the laser angular frequency. The initial phase of the laser. The phase noise time term of the laser in the signal arm. The phase perturbation applied.

[0021] Step 4: Photoelectric conversion of the coherent synthesized interferometric field. The superposition state of the two laser synthesized interferometric fields is converted into an electrical signal using a photoelectric conversion device, and the output is a discrete sequence of the original interferometric synthesized signal containing phase noise.

[0022] The photoelectric conversion device performs photoelectric conversion on the output beam after coherent combination of two laser beams. The time-domain expression of the coherently combined signal is as follows:

[0023]

[0024] The synthesized electrical signal output by photoelectric conversion is proportional to the square of the time-domain amplitude. After analog-to-digital conversion, the discrete sequence V of the synthesized signal... c (t) is represented as:

[0025]

[0026] Step 5: Reconstruction of the pseudo-continuous signal after phase noise decoupling. Based on the discrete sequence of the self-reference signal, a time-domain nonlinear scaling operation is performed on the discrete sequence of the original interferometric synthesized signal to generate a discrete sequence of pseudo-continuous signal, eliminating pulse eigenin intensity fluctuations while fully preserving the phase noise modulation characteristics.

[0027] The active coherent phase-locked loop (PLL) module uses the established self-reference signal discrete sequence S ref (n), for the discrete sequence of the synthesized signal V c(t) Perform a sampling-point scaling operation to generate a pseudo-continuous discrete sequence V. p (t), thereby eliminating the inherent intensity fluctuations of the pulse while retaining the intensity fluctuation characteristics caused by phase noise. The pseudo-continuous signal discrete sequence is represented as:

[0028]

[0029] Step Six: Generation of Perturbation Response Feedback Signal. Based on the voltage difference between the pseudo-continuous signal sampling points at the time of the bilateral perturbation, the phase mismatch control signal is calculated for real-time phase difference correction.

[0030] The active coherent phase-locked loop (PLL) module calculates the phase control signal based on the discrete sequence of the pseudo-continuous signal, and subtracts the voltage values ​​of the pseudo-continuous signal sampling points obtained at time t during a positive phase disturbance and time t+1 during a negative phase disturbance.

[0031] △J=V p (t+1)-V p (t) (18)

[0032] The control signal is obtained by scaling the difference:

[0033]

[0034] Step 7: Dynamic Phase Mismatch Closed-Loop Correction. The phase mismatch control signal is injected into the signal arm optical path through the phase adjustment unit to actively compensate for phase noise, ultimately optimizing the output efficiency of the coherent synthesized beam.

[0035] The active coherent phase-locked loop (PLL) module controls the phase modulation unit to apply a phase control signal to the signal arm optical path, completing phase compensation and ultimately increasing the power of the coherently synthesized output beam. The time-domain representation of the signal arm to which the phase control signal is applied is as follows:

[0036]

[0037] Compared with existing technologies, the method of this invention avoids the phase noise loss problem caused by traditional filtering methods through a laser waveform self-reference mechanism, reduces the requirement for preset characteristic conditions, realizes low repetition frequency coherent synthesis phase-locked loop, and has strong adaptability to different pulse waveforms and repetition frequency parameters under low repetition frequency conditions.

[0038] Invention Effects

[0039] 1. The present invention discloses a low repetition frequency fiber laser active coherent phase-locked loop method based on a laser waveform self-reference optimization algorithm. By constructing a self-reference waveform from the extracted pulse intensity, the interference of inherent pulse intensity fluctuations on the phase-locked loop control signal can be suppressed, while retaining the fluctuation characteristics caused by full-cycle phase noise.

[0040] 2. The present invention discloses a low repetition frequency fiber laser active coherent phase-locked loop method based on a laser waveform self-reference optimization algorithm. When used for low repetition frequency coherent synthesis, it does not require preset separation thresholds or waveform characteristic conditions for pulse / continuous parts, thus enhancing the adaptability of the phase-locked loop system to diverse waveforms in low repetition frequency coherent synthesis.

[0041] 3. The present invention discloses a low repetition frequency fiber laser active coherent phase-locking method based on laser waveform self-reference optimization algorithm, which integrates waveform self-reference mechanism and bilateral perturbation optimization mechanism. For the first time, it achieves low repetition frequency pulse laser active phase-locking coherent synthesis with pulse repetition frequency (5kHz) and ambient noise frequency (main energy concentrated within 5kHz) on the same order of magnitude without preset threshold. Attached Figure Description

[0042] The above and other features and advantages of the present invention will become clearer from the accompanying drawings and from a detailed description of specific embodiments thereof.

[0043] in:

[0044] Figure 1 This is a schematic diagram of an embodiment of the present invention.

[0045] Figure 2 This is a flowchart of a low-repetition-frequency fiber laser active coherent phase-locked loop method based on a laser waveform self-reference optimization algorithm, as described in this invention.

[0046] Figure 3 This is a time-domain intensity diagram of the coherent synthesis signal of the two low-repetition-frequency lasers before phase-locked loop.

[0047] Figure 4 This is a time-frequency domain intensity diagram of the simulated environmental phase noise.

[0048] Figure (a) shows the phase noise time-domain intensity, and Figure (b) shows the phase noise frequency-domain intensity.

[0049] Figure 5 The time-domain intensity diagram of the pseudo-continuous signal coherently synthesized from two low-repetition-frequency lasers before phase-locked loop.

[0050] Figure 6 The figure shows the change in coherent synthesis efficiency of two low-repetition-frequency lasers during phase-locked loop (PLL) process.

[0051] Figure 7 This is a time-domain intensity diagram of the coherent composite signal of two low-repetition-frequency lasers after phase-locking. Detailed Implementation

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] See Figure 1 As shown, the present invention provides a low repetition rate fiber laser active coherent phase-locked loop method based on a laser waveform self-reference optimization algorithm. It is based on a pulsed fiber laser coherent synthesis hardware system, which includes a low repetition rate pulsed laser seed source 1, a polarization-preserving fiber coupler 2, a phase adjustment unit 3, fiber gain amplification links A4 and B5, a pigtail collimation assembly A6 and B7, a light-blocking gate 8, a spatial polarization combining cube 9, a high reflectivity lens 10, a photoelectric conversion device 11, a self-reference sequence analog-to-digital sampler 12, and an active coherent phase-locked loop operation module 13.

[0054] A low-repetition-rate fiber laser active coherent phase-locked loop method based on a laser waveform self-reference optimization algorithm, the specific steps of which include:

[0055] Step 1: Power on the low-repetition-rate pulsed laser seed source 1. After the laser beam is transmitted to the polarization-maintaining fiber coupler 2, it is split into two paths of equal intensity, namely the reference arm and the signal arm. Place the light-blocking gate 8 at the outlet of the reference arm pigtail collimation assembly B7, so that the photoelectric signal of the single-path pulsed laser is incident on the photoelectric conversion device 11. The voltage values ​​of N sampling points within one pulse period are collected by the self-reference sequence analog-to-digital sampler 12. The voltage values ​​of the N sampling points are represented as follows.

[0056] V ref (n), n=1,2,…,N (21)

[0057] Step 2: The active coherent phase-locked loop (PLL) module 13 processes the voltage values ​​V from multiple sampling points. ref (n) can be combined in time order to form a discrete sequence of self-reference signals, represented as:

[0058] S ref (n)=[V ref (1),V ref (2),...V ref (n)] (22)

[0059] Step 3: The active coherent phase-locked loop (PLL) module 13 controls the phase modulation unit 3 to apply positive and negative phase perturbations to the signal arm laser, respectively. The time-domain expressions of the signal arm with added positive and negative perturbations are as follows:

[0060]

[0061] In the formula, Γ k (t) represents the amplitude-time term of the laser in the signal arm, and ω represents the laser angular frequency. The initial phase of the laser. The phase noise time term of the laser in the signal arm. The phase perturbation applied. Figure 3 The time-frequency domain intensity plot of the phase noise in the simulated environment is displayed. Figure 3 (a) is the time-domain intensity diagram of environmental phase noise. Figure 3 (b) is the frequency domain intensity diagram of environmental phase noise. Figure 3 (b) The illustration shows that most of the phase noise energy is concentrated in the low-frequency part (≤5kHz).

[0062] Step 4: The photoelectric conversion device 11 performs photoelectric conversion on the output beam after coherent combination of the two lasers to obtain the time-domain intensity diagram of the two coherently combined signals, as shown below. Figure 4 As shown, the pulse light intensity is unstable due to phase noise. The time-domain expression of the two coherently synthesized signals is:

[0063]

[0064] The synthesized electrical signal output by photoelectric conversion is proportional to the square of the time-domain amplitude. After analog-to-digital conversion, the discrete sequence V of the synthesized signal... c (t) is represented as:

[0065]

[0066] Step 5: The active coherent phase-locked loop (PLL) module 13 uses the established self-reference signal discrete sequence S ref (n), for the discrete sequence of the synthesized signal V c (t) Perform a sampling-point scaling operation to generate a pseudo-continuous discrete sequence V. p (t) Time-domain intensity plot as shown Figure 5 As shown, this eliminates the inherent intensity fluctuations of the pulse while preserving the intensity fluctuation characteristics caused by phase noise. Figure 5 This demonstrates that nonlinear scaling eliminates light intensity fluctuations caused by pulse waveforms. The discrete sequence of the pseudo-continuous signal is represented as:

[0067]

[0068] Step Six: The active coherent phase-locked loop (PLL) module 13 calculates the phase control signal based on the discrete sequence of the pseudo-continuous signal, and calculates the difference between the voltage values ​​of the pseudo-continuous signal sampling points obtained at time t during positive phase disturbance and time t+1 during negative phase disturbance.

[0069] △J=V p (t+1)-V p(t) (28)

[0070] The control signal is obtained by scaling the difference:

[0071]

[0072] Step 7: The active coherent phase-locked loop (PLL) module 13 controls the phase modulation unit 3 to apply a phase control signal to the signal arm optical path, completing phase compensation and ultimately increasing the power of the coherently synthesized output beam. The time-domain representation of the signal arm to which the phase control signal is applied is as follows:

[0073]

[0074] The efficiency of the reference arm and signal arm combination is as follows: Figure 6 As shown, after phase-locked control based on the laser waveform self-reference optimization algorithm, the synthesized light intensity tends to stabilize, reaching 0.991Imax, and the phase-locked residual is 0.0185λ. The time-domain intensity diagram of the synthesized signal from the two lasers is shown below. Figure 7 As shown, this demonstrates that a coherently synthesized pulsed laser output with stable light intensity was achieved after phase locking.

[0075] The embodiments of the present invention have been described in detail above through examples, but the content described is only an exemplary embodiment of the present invention and should not be considered as limiting the scope of implementation of the present invention. The protection scope of the present invention is defined by the claims. Any technical solutions designed by those skilled in the art using the technical solutions described in the embodiments of the present invention, or designed by those skilled in the art under the inspiration of the technical solutions of the embodiments of the present invention, within the substance and protection scope of the present invention, to achieve the above-mentioned technical effects, or any equivalent changes and improvements made to the scope of the application, should still fall within the patent protection scope of the present invention.

Claims

1. A low-repetition-rate fiber pulsed laser active coherent phase-locked loop method based on a laser waveform self-reference optimization algorithm, characterized in that, for fiber pulsed lasers with a repetition frequency not exceeding a typical 5kHz phase noise, the method is designed for such lasers. Includes the following steps: Step 1: Extraction of intensity fluctuation features of a single-pulse laser throughout its entire cycle. The temporal amplitude characteristics of a single-pulse laser are captured using a photoelectric conversion device, and the voltage distribution at multiple sampling points within the pulse period is recorded to obtain discrete characteristic data of the inherent intensity fluctuations of the laser pulse. Step 2: Self-reference waveform modeling without preset thresholds. Discrete voltage sample values ​​are integrated into a discrete sequence of self-reference signals to form an intrinsic model of the pulse waveform, achieving threshold-independent adaptive waveform representation. Step 3: Apply bilateral symmetric phase perturbation. Using the optical path without the phase adjustment unit as the reference arm and the optical path with the phase adjustment unit as the signal arm, apply symmetric phase perturbation to the signal arm. Step 4: Photoelectric conversion of the coherent synthesized interferometric field. The superposition state of the two laser synthesized interferometric fields is converted into an electrical signal using a photoelectric conversion device, and the output is a discrete sequence of the original interferometric synthesized signal containing phase noise. Step 5: Reconstruction of the pseudo-continuous signal after phase noise decoupling. Based on the discrete sequence of the self-reference signal, a time-domain nonlinear scaling operation is performed on the discrete sequence of the original interferometric synthesized signal to generate a discrete sequence of pseudo-continuous signal, eliminating pulse eigenin intensity fluctuations while fully preserving the phase noise modulation characteristics. Step Six: Generation of Perturbation Response Feedback Signal. Based on the voltage difference between the pseudo-continuous signal sampling points at the time of the bilateral perturbation, the phase mismatch control signal is calculated for real-time phase difference correction. Step 7: Dynamic Phase Mismatch Closed-Loop Correction. The phase mismatch control signal is injected into the signal arm optical path through the phase adjustment unit to actively compensate for phase noise, ultimately optimizing the output efficiency of the coherent synthesized beam.

2. The method for low repetition rate fiber laser active coherent phase-locked loop based on a laser waveform self-reference optimization algorithm according to claim 1, characterized in that, The implementation method of step one is as follows: A low-repetition-rate pulsed laser seed source is powered on. The laser beam is transmitted to a polarization-maintaining fiber coupler and split into two equal-intensity paths: a reference arm and a signal arm. A light-blocking gate is placed at the exit port of the reference arm's pigtail collimation assembly, allowing the photoelectric signal of the single-pulse laser to be incident on the photoelectric conversion device. The voltage values ​​at N sampling points within one pulse cycle are collected by a self-reference sequence analog-to-digital sampler. The voltage values ​​at N sampling points are represented as: V ref (n),n=1,2,…,N (1) 3. The method for low repetition rate fiber laser active coherent phase-locked loop based on a laser waveform self-reference optimization algorithm according to claim 1, characterized in that, The implementation method of step two is as follows: The active coherent phase-locked loop (PLL) module will process the voltage values ​​V from multiple sampling points. ref (n) can be combined in time order to form a discrete sequence of self-reference signals, represented as: S ref (n)=[V ref (1),V ref (2),...V ref (n)] (2) 4. The method for low repetition rate fiber laser active coherent phase-locked loop based on laser waveform self-reference optimization algorithm according to claim 1, characterized in that, The implementation method of step three is as follows: The active coherent phase-locked loop (PLL) module controls the phase modulation unit to apply positive and negative phase perturbations to the laser signal arm, respectively. The time-domain expressions of the signal arm with added positive and negative perturbations are as follows: In the formula, Γ k (t) represents the amplitude-time term of the laser in the signal arm, and ω represents the laser angular frequency. The initial phase of the laser. The phase noise time term of the laser in the signal arm. The phase perturbation applied.

5. The method for low repetition rate fiber laser active coherent phase-locked loop based on laser waveform self-reference optimization algorithm according to claim 1, characterized in that, The implementation method of step four is as follows: The photoelectric conversion device performs photoelectric conversion on the output beam after coherent combination of two laser beams. The time-domain expression of the coherently combined signal is as follows: The synthesized electrical signal output by photoelectric conversion is proportional to the square of the time-domain amplitude. After analog-to-digital conversion, the discrete sequence V of the synthesized signal... c (t) is represented as:

6. The method for low repetition rate fiber laser active coherent phase-locked loop based on laser waveform self-reference optimization algorithm according to claim 1, characterized in that, The method for implementing step five is as follows: The active coherent phase-locked loop (PLL) module uses the established self-reference signal discrete sequence S ref (n), for the discrete sequence of the synthesized signal V c (t) Perform a sampling-point scaling operation to generate a pseudo-continuous discrete sequence V. p (t), thereby eliminating the inherent intensity fluctuations of the pulse while retaining the intensity fluctuation characteristics caused by phase noise. The pseudo-continuous signal discrete sequence is represented as:

7. The method for active coherent phase-locked loop of low repetition frequency fiber laser based on laser waveform self-reference optimization algorithm according to claim 1, characterized in that, The calculation method for step six is ​​as follows: The active coherent phase-locked loop (PLL) module calculates the phase control signal based on the discrete sequence of the pseudo-continuous signal, and calculates the difference between the voltages of the pseudo-continuous signal sampling points obtained at time t during a positive phase disturbance and time t+1 during a negative phase disturbance: △J=V p (t+1)-V p (t) (8) The control signal is obtained by scaling the difference:

8. The method for low repetition rate fiber laser active coherent phase-locked loop based on laser waveform self-reference optimization algorithm according to claim 1, characterized in that, The implementation method of step seven is as follows: The active coherent phase-locked loop (PLL) module controls the phase modulation unit to apply a phase control signal to the signal arm optical path, completing phase compensation and ultimately increasing the power of the coherently synthesized output beam. The time-domain representation of the signal arm to which the phase control signal is applied is as follows:

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