An intelligent mode-locked fiber laser based on nonlinear polarization interference and a control method thereof

Abstract

This application provides an intelligent mode-locked fiber laser based on nonlinear polarization interference and its control method, belonging to the field of fiber laser and intelligent control technology. The application includes: scanning a waveplate, setting the angle corresponding to the maximum power as the mechanical zero point, and establishing a correspondence between angle and power; using the mechanical zero point as a reference and the correspondence between angle and power, scanning the waveplate with a first-step scanning length, marking states that meet the spectral width condition and exhibit a comb-like structure as mode-locking candidate points; using the mode-locking candidate points as the center, scanning with a second-step scanning length, determining mode-locking when the spectral bandwidth reaches a threshold and the power standard deviation is less than a stability threshold, recording the current power standard deviation as the reference fluctuation value, and recording the corresponding angle as the target mode-locked operating point; monitoring output parameters, calculating the power standard deviation and comparing it with the reference fluctuation value, and triggering a local search to restore mode-locking when the deviation exceeds the allowable range. This application can achieve automatic tuning of the intracavity polarization state and phase shift.

Description

Technical Field

[0001] This application relates to the field of fiber lasers and their intelligent control technology, and in particular to an intelligent mode-locked fiber laser based on nonlinear polarization interference and its control method. Background Technology

[0002] In related technologies, the mode-locking window of fully polarization-maintaining fiber lasers based on nonlinear polarization interference (NPI) is extremely narrow, typically requiring manual and repeated adjustments of the half-wave plate (HWP) and eighth-wave plate (EWP) angles to achieve mode-locked output. This manual adjustment method is inefficient, has poor repeatability, and cannot achieve self-starting. Furthermore, when environmental conditions such as temperature and vibration change, the laser is prone to disengagement and cannot automatically recover, requiring further manual intervention. Simultaneously, traditional fiber lasers use discrete component connections, resulting in numerous fusion splices, high insertion loss, and long cavity lengths, limiting the improvement of repetition frequency and the compactness of the system.

[0003] In summary, the technical problems existing in the relevant technologies need to be improved. Summary of the Invention

[0004] The main objective of this application is to propose an intelligent mode-locked fiber laser based on nonlinear polarization interference and its control method, which can realize automatic mode-locking start-up, long-term stable maintenance and automatic unlocking recovery of the fully polarization-maintaining fiber laser, with high environmental stability and unattended operation capability, thereby improving the engineering practicality of ultrafast fiber lasers.

[0005] To achieve the above objectives, one aspect of this application proposes a smart mode-locked fiber laser control method based on nonlinear polarization interference, the method comprising the following steps: In continuous wave mode, scan the waveplate, fix one of the half-wave plate or one-eighth waveplate, scan the other plate, set the angle corresponding to the maximum power value as the mechanical zero point, and establish the correspondence between angle and power. Using the mechanical zero point as a reference and referring to the relationship between angle and power, the state that meets the spectral width condition and has a comb-like structure is marked as a mode-locking candidate point using the first step long scanning waveplate; Centered on the candidate mode-lock point, scan with the second step size, calculate the spectral bandwidth and the power standard deviation within the preset time window. When the spectral bandwidth reaches the threshold and the power standard deviation is less than the stable threshold, mode-lock is determined. Record the current power standard deviation as the benchmark fluctuation value and record the corresponding angle as the target mode-lock working point. Monitor output parameters, calculate power standard deviation and compare it with the benchmark fluctuation value. When the deviation exceeds the allowable range, trigger a local search to restore mode lock.

[0006] In some embodiments, the step of scanning waveplates in continuous wave mode, fixing one half-wave plate or one-eighth waveplate, scanning the other plate, setting the angle corresponding to the maximum power as the mechanical zero point, and establishing the correspondence between angle and power includes: The eighth-wave plate is fixed, and the half-wave plate is driven to rotate within a preset range with a specific step size. The average power curve of the polarization beam splitter output port is recorded at each angular position. The position of the maximum value of the average power is found, the corresponding half-wave plate angle is recorded, and the angle is set as the mechanical zero point of the half-wave plate in the FPGA. A fixed half-wave plate is used to scan an eighth-wave plate with a specific step size, and the position with the maximum power is set as the mechanical zero point of the eighth-wave plate. After calibration, an angle-power lookup table is established in the FPGA to obtain the correspondence between angle and power.

[0007] In some embodiments, the step of using the mechanical zero point as a reference, referring to the angle-power correspondence, and using a first-step long-scan waveplate to mark states that satisfy the spectral width condition and exhibit a comb-like structure as mode-locking candidate points includes: Based on the mechanical zero point and referring to the relationship between angle and power, the search range of the half-wave plate and the eighth-wave plate are set to a preset range relative to the mechanical zero point, and a two-dimensional grid scan is performed with a preset first step length. For each set of angles, first wait for the cavity to stabilize, then read the optical power meter value. If the power is less than the preset threshold, it is determined to be a non-operating point and the spectral measurement is skipped. When the power exceeds the preset threshold, the spectral analyzer is triggered to sample and calculate the 10 dB spectral bandwidth and the 3 dB spectral bandwidth. When the spectral width increases significantly and exceeds the preset range, and comb-like feature structures appear at the spectral edge, the current state parameter is marked as a mode-locking candidate point.

[0008] In some embodiments, the step of scanning with a second step size, centered on a mode-lock candidate point, calculating the spectral bandwidth and the power standard deviation within a preset time window, determining mode-locking when the spectral bandwidth reaches a threshold and the power standard deviation is less than a stable threshold, recording the current power standard deviation as the baseline fluctuation value, and recording the corresponding angle as the target mode-locking operating point includes: For the mode-locked candidate points, the search range of the half-wave plate and the eighth-wave plate are narrowed to a preset range, the step size is reduced to a preset range, the 10 dB spectral bandwidth and the 3 dB spectral bandwidth are calculated, and the power fluctuation is statistically analyzed to calculate the standard deviation of the power within a preset time window. When both the 10 dB spectral bandwidth and the 3 dB spectral bandwidth reach or exceed the preset width threshold, and the power standard deviation is less than the preset stable mode-locking threshold, it is determined that stable mode-locking has been achieved, and angle scanning is stopped. Record the current power standard deviation as the baseline fluctuation value, and store the current angle and the corresponding 10 dB spectral bandwidth, 3 dB spectral bandwidth, and output power parameters in non-volatile memory as the target mode-locked operating point.

[0009] In some embodiments, the monitoring output parameters, calculating the power standard deviation and comparing it with the benchmark fluctuation value, and triggering a local search to restore mode-locking when the deviation exceeds the allowable range, include: The output power is monitored at a preset period, the power standard deviation within a preset time window is calculated, and the power standard deviation is compared with the recorded benchmark fluctuation value. When the power standard deviation exceeds a preset percentage threshold of the reference fluctuation value, or when the 10 dB spectral bandwidth decreases by more than a preset threshold, it is determined that the target mode-locked operating point has been deviated from, and local relocking is triggered. Increase pump power; The search is performed within a preset range of the target mold-locking working point using a third step size smaller than the second step size; For each set of search angles, calculate the 10 dB spectral bandwidth, the 3 dB spectral bandwidth, and the power standard deviation within the preset time window; When both the 10 dB spectral bandwidth and the 3 dB spectral bandwidth reach the preset width threshold, and the power standard deviation is less than the preset stability threshold, it is determined that mode-locked output should be restored, the current angle should be updated to the target mode-locked operating point, and the search should be stopped. If no angle that meets the conditions is found within the preset number of iterations, the process returns to the step of using the mechanical zero point as a reference, referring to the relationship between angle and power, and marking the state that meets the spectral width condition and has a comb-like structure as a mode-locking candidate point using the first step long scanning waveplate, and repeats until mode-locked output is restored.

[0010] To achieve the above objectives, another aspect of the embodiments of this application proposes an intelligent mode-locked fiber laser based on nonlinear polarization interference for executing the control method described above. The intelligent mode-locked fiber laser includes a linear cavity optical section and an intelligent detection and control section. The linear cavity optical section includes a pump source, a wavelength division multiplexing collimator, a polarization-maintaining erbium-doped fiber, a polarization-maintaining single-mode fiber, a Faraday mirror, and a free-space polarization and phase-shifting unit. The Faraday mirror is used to introduce a non-reciprocal phase shift. The free-space polarization and phase-shifting unit includes a polarization beam splitter, a half-wave plate, an eighth-wave plate, a Faraday rotator, and a high-reflectivity mirror. The free-space polarization and phase-shifting unit and the fiber arm together form a nonlinear polarization interference structure. The intelligent detection and control section includes a measurement module, a control and calculation module, and an electric polarization rotator; the measurement module includes an optical power meter and a spectrum analyzer; the control and calculation module includes an FPGA control board; the electric polarization rotator carries and drives the half-wave plate and the eighth-wave plate to rotate.

[0011] In some embodiments, the wavelength division multiplexing collimator integrates a wavelength division multiplexer, a gradient refractive index lens, a filter, and a glass sleeve. The pump end is connected to the pump light source, and the signal end is fused to the polarization-maintaining erbium-doped fiber to form a fusion interface in the optical path.

[0012] In some embodiments, the measurement module further includes a polarization-maintaining fiber coupler connected to the laser output port of the polarization beam splitter, used to divide the output light into a working output branch and a monitoring branch according to a preset ratio; the monitoring branch is respectively connected to the optical power meter and the spectrum analyzer; The electric polarization rotator is a multi-channel precision drive rotation device. Each channel carries and fixes a half-wave plate or an eighth-wave plate for step adjustment and repeated positioning. The angle adjustment is controlled by an FPGA.

[0013] In some embodiments, the polarization axes of the polarization-maintaining erbium-doped fiber and the polarization-maintaining single-mode fiber are aligned and fused together. In the free-space polarization and phase-shifting unit, the Faraday rotator and the Faraday mirror together constitute a nonlinear polarization interference structure; the optical axes of the half-wave plate and the eighth-wave plate maintain a preset angular relationship with the polarization axis of the polarization beam splitter in the initial state.

[0014] In some embodiments, the FPGA of the control and calculation module has a built-in angle-power lookup table for pre-setting the sampling frequency to collect spectral data, calculating the 10 dB spectral bandwidth and the 3 dB spectral bandwidth, outputting pulse signals to control the electric polarization rotator, and communicating with the host computer through a communication interface.

[0015] To achieve the above objectives, another aspect of this application provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method described above.

[0016] To achieve the above objectives, another aspect of the embodiments of this application proposes a computer-readable storage medium storing a computer program that, when executed by a processor, implements the methods described above.

[0017] To achieve the above objectives, another aspect of the embodiments of this application proposes a computer program product, including a computer program that, when executed by a processor, implements the aforementioned method.

[0018] This application provides at least the following beneficial effects: It offers a smart mode-locked fiber laser control method based on nonlinear polarization interference, a smart mode-locked fiber laser, electronic equipment, storage medium, and program product. The application includes: scanning a waveplate, setting the angle corresponding to the maximum power value as the mechanical zero point, and establishing a relationship between angle and power; using the mechanical zero point as a reference and the angle-power relationship as a reference, scanning the waveplate with a first-step scanning length, marking states that meet the spectral width condition and exhibit a comb-like structure as mode-locking candidate points; using the mode-locking candidate points as the center, scanning with a second-step scanning length, determining mode-locking when the spectral bandwidth reaches a threshold and the power standard deviation is less than a stable threshold, recording the current power standard deviation as a reference fluctuation value, and recording the corresponding angle as the target mode-locked operating point; monitoring output parameters, calculating the power standard deviation and comparing it with the reference fluctuation value, and triggering a local search to restore mode-locking when the deviation exceeds the allowable range. This application enables automatic tuning of the intracavity polarization state and phase shift. Attached Figure Description

[0019] Figure 1 This is a flowchart of a smart mode-locked fiber laser control method based on nonlinear polarization interference provided in an embodiment of this application; Figure 2 This is a schematic diagram of the optical cavity structure and its connection method with the intelligent control unit provided in the embodiments of this application; Figure 3 This is an automatic mold-locking flowchart provided in the embodiments of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0022] Before providing a detailed description of the embodiments of this application, some of the nouns and terms involved in the embodiments of this application will be explained first. The nouns and terms involved in the embodiments of this application are subject to the following interpretations.

[0023] 1) NPI (Nonlinear Polarization Interferometer): This is a fiber-based linear cavity structure, typically composed of polarization-maintaining fiber, polarization beam splitter (PBS), Faraday rotator (FR), and Faraday mirror (FM). This structure achieves stable interference mode-locking by introducing a non-reciprocal phase shift, offering advantages such as compact structure, high environmental stability, and strong disturbance resistance.

[0024] 2) Fully polarization-maintaining NPI laser: refers to an ultrafast fiber laser built on polarization-maintaining fiber and NPI structure. It has a fixed intracavity polarization state and high environmental robustness, but the mode-locking window is extremely narrow, and mode-locking is generally achieved by manually adjusting the waveplate.

[0025] 3) PBS (Polarizing Beam Splitter): A device used to separate or synthesize beams with different polarization states. In this invention, it is used to construct a linear cavity interference structure.

[0026] 4) FR (Faraday Rotator): A device that uses the magneto-optical effect to generate a fixed angle of non-reciprocal polarization rotation. It is often combined with FM to construct nonlinear polarization interference structures.

[0027] 5) FM (Faraday Mirror): An optical device that can reflect incident light and introduce non-reciprocal polarization rotation, used to form nonlinear polarization interference units.

[0028] 6) HWP (Half-Wave Plate): A waveplate used to adjust the direction of linear polarization. The polarization state of light is changed by rotating the angle of the waveplate.

[0029] 7) EWP (Eighth-Wave Plate): A waveplate used to introduce phase delay, enabling finer polarization and phase shift control.

[0030] 8) MPR (Motorized Polarizer Rotator): Drives a waveplate to rotate via a motor to achieve automatic and precise adjustment of the polarization state, used in the intelligent mode-locking structure of this invention.

[0031] 9) WDM-collimator: A combination device that integrates a wavelength division multiplexer, a gradient refractive index lens, and a filter, used for pump / signal beam combining and beam collimation.

[0032] 10) PM-EDF (Polarization Maintaining Erbium-Doped Fiber): A polarization-maintaining fiber that provides amplification gain and is used to achieve laser amplification in a specific wavelength band.

[0033] 11) PM-SMF (Polarization Maintaining Single Mode Fiber): A polarization-maintaining fiber used for dispersion compensation and optical path extension to ensure stable polarization state within the cavity.

[0034] 12) 10-dB spectral bandwidth (BW10): refers to the spectral width at which the spectral amplitude decreases by 10 dB, and is an important criterion for mode-locking pulse width and spectral broadening. In this invention, it is used as a feature for automatic mode-locking determination.

[0035] 13) 3-dB spectral bandwidth (BW3): refers to the spectral width at which the spectral amplitude decreases by 3 dB, and is an important criterion for mode-locking pulse width and spectral broadening. In this invention, it is used as a feature for automatic mode-locking determination.

[0036] In related technologies, the "intelligent automatic mode-locking" capability has not yet been effectively introduced into the full polarization-maintaining NPI architecture to achieve an ultrafast fiber laser system that combines a full polarization-maintaining high-stability structure with automatic and fast mode-locking and automatic optimization of the operating point. The problems of narrow mode-locking window, reliance on manual experience in the debugging process, and difficulty in long-term stable operation still need to be further solved.

[0037] This invention addresses the narrow mode-locking window and complete reliance on manual fine-tuning of fully polarization-maintaining (NPI) lasers. While NPI fiber lasers possess excellent environmental stability and compact structure, the coupling relationships between intracavity equivalent phase bias, nonlinear effects, and gain distribution are complex, resulting in an extremely narrow parameter window for stable mode-locking. Existing NPI structures largely rely on fixed polarization-maintaining fiber fusion splices and a small number of free-space waveplate combinations to set the phase and polarization, lacking effective automatic search and optimization methods. In practical applications, operators need to perform small-step, repeated manual fine-tuning of components such as half-wave plates and 1 / 8-wave plates, combining various characterization methods such as spectral analysis, autocorrelation, and power analysis for judgment. The debugging process is time-consuming, and the results depend on personal experience. Once there are slight changes in the environment or device state, readjustment is often required, making it difficult to meet the engineering application requirements of "one-click start" and "plug and play."

[0038] In other words, intelligent automatic mode-locking and fully polarization-maintaining NPI architecture have not yet been effectively integrated. Fully polarization-maintaining NPI architectures with high environmental stability almost entirely remain at the level of manual adjustment or fixed polarization structures. No solution has yet been found that, while maintaining the compactness and high stability of the fully polarization-maintaining NPI structure, introduces adaptable adjustable polarization / phase-shifting units and intelligent search algorithms to achieve automatic tuning of key degrees of freedom within the cavity, thereby enabling rapid and reliable entry into and maintenance of mode-locking within a limited number of iterations.

[0039] In view of this, this application provides an intelligent mode-locked fiber laser based on nonlinear polarization interference and its control method. While maintaining the advantages of compact structure and high environmental robustness of fully polarization-maintaining NPI fiber lasers, this solution provides a mode-locked fiber laser system capable of intelligent automatic tuning of intracavity polarization state and phase. This allows it to quickly and autonomously achieve mode-locking within a narrow parameter window without complex manual fine-tuning, and maintain stable output during long-term operation. Thus, it combines a "fully polarization-maintaining high-stability structure" and "intelligent automatic mode-locking capability," making it suitable for engineering, modular, and mass production applications.

[0040] Figure 1 This is an optional flowchart of a smart mode-locked fiber laser control method based on nonlinear polarization interference provided in an embodiment of this application. Figure 1 The method may include, but is not limited to, steps S101 to S104.

[0041] Step S101: Scan the waveplate in continuous wave state, fix one of the half-wave plate or one-eighth waveplate, scan the other plate, set the angle corresponding to the maximum power value as the mechanical zero point, and establish the correspondence between angle and power. Step S102: Using the mechanical zero point as a reference and the correspondence between the angle and the power, the state that meets the spectral width condition and has a comb-like structure is marked as a mode-locking candidate point using the long scanning waveplate from the first step. Step S103: Using the candidate mode-lock point as the center, scan with the second step length to calculate the spectral bandwidth and the power standard deviation within the preset time window. When the spectral bandwidth reaches the threshold and the power standard deviation is less than the stable threshold, mode-lock is determined. The current power standard deviation is recorded as the reference fluctuation value, and the corresponding angle is recorded as the target mode-lock working point. Step S104: Monitor output parameters, calculate power standard deviation and compare it with the benchmark fluctuation value. When the deviation exceeds the allowable range, trigger a local search to restore mode lock.

[0042] In steps S101 to S104 of this embodiment, by fixing one waveplate, scanning another, and recording the angle corresponding to the maximum power, the mechanical zero point of the waveplate is automatically calibrated, and a lookup table of the correspondence between angle and power is established, providing a reference for subsequent precise searching. By using the mechanical zero point as a reference and performing a two-dimensional grid scan with a large step size, the angle space is quickly traversed, and states that meet the spectral width condition and have a comb-like structure are marked as mode-locking candidate points, significantly narrowing the range of subsequent fine-grained searches. By using the mode-locking candidate points as the center and performing fine scanning with a small step size, and calculating the spectral bandwidth and the power standard deviation within a preset time window, the stable mode-locking state is accurately determined, and the current power standard deviation is recorded as the reference fluctuation value, providing a quantitative basis for subsequent state monitoring. By monitoring the output parameters in real time, calculating the real-time power standard deviation, and comparing it with the reference fluctuation value, the mode-locking state is quantitatively monitored. When the deviation exceeds the allowable range, a local search is automatically triggered, achieving automatic mode-locking recovery.

[0043] In some embodiments, step S101 may include, but is not limited to, steps S111 to S112: Step S111: Fix the 1 / 8 wave plate and drive the half-wave plate to rotate within a preset range with a specific step size. Record the average power curve of the polarization beam splitter output port at each angular position, find the position of the maximum value of the average power, record the corresponding half-wave plate angle, and set the angle as the mechanical zero point of the half-wave plate in the FPGA. Step S112: Fix the half-wave plate, scan the eighth-wave plate with a specific step size, and set the position with the maximum power as the mechanical zero point of the eighth-wave plate; after calibration, establish an angle-power lookup table in the FPGA to obtain the correspondence between angle and power.

[0044] In steps S111 to S112 of this embodiment, by fixing the 1 / 8 waveplate stationary and driving the half-waveplate to rotate within a preset range while recording the output power corresponding to each angle, the automatic calibration of the mechanical zero point of the half-waveplate is performed. This achieves precise determination of the alignment position between the half-waveplate and the incident polarization axis, establishing a unified coordinate reference for subsequent angle control of the half-waveplate. By fixing the calibrated half-waveplate, driving the 1 / 8 waveplate to rotate, and recording the maximum power, the automatic calibration of the mechanical zero point of the 1 / 8 waveplate is performed. A complete angle-power lookup table is established in the FPGA, unifying the zero-point coordinate systems of the two waveplates and providing a complete reference for subsequent two-dimensional angle searches.

[0045] In some embodiments, step S102 may include, but is not limited to, steps S201 to S204: Step S201: Using the mechanical zero point as a reference and referring to the correspondence between angle and power, set the search range of the half-wave plate and the eighth-wave plate to a preset range relative to the mechanical zero point, and perform a two-dimensional grid scan with a preset first step length. Step S202: For each set of angles, first wait for the cavity to stabilize, then read the optical power meter value. If the power is less than the preset threshold, it is determined to be a non-operating point and the spectral measurement is skipped. Step S203: When the power is greater than the preset threshold, the spectrometer is triggered to sample and the 10 dB spectral bandwidth and 3 dB spectral bandwidth are calculated. Step S204: When the spectral width increases significantly and exceeds the preset range, and is accompanied by the appearance of comb-like feature structures at the spectral edge, the current state parameter is marked as a mode-locking candidate point.

[0046] In steps S201 to S204 of this embodiment, a rapid traversal of the mode-locking parameter space is performed by using the mechanical zero point as a reference, referencing an angle-power lookup table, and scanning a two-dimensional grid with a large step size. This achieves coverage of a wide range of angle combinations within a limited time, narrowing down the candidate region for subsequent fine-tuning searches. Rapid screening of the working state is performed by waiting for the cavity to stabilize, reading the optical power meter value, and comparing it with a preset threshold. This eliminates invalid angle combinations and avoids invalid spectral measurements, significantly improving search efficiency. Spectroscopic quantification of the mode-locking characteristics is performed by triggering the spectrometer to sample and calculate the 10 dB and 3 dB spectral bandwidths. This transforms the abstract mode-locking state into a calculable and comparable numerical indicator, providing an objective basis for determining mode-locking candidate points.

[0047] In some embodiments, step S103 may include, but is not limited to, steps S301 to S303: Step S301: For the mode-locked candidate points, the search range of the half-wave plate and the eighth-wave plate is narrowed to a preset range, the step size is reduced to a preset range, the 10 dB spectral bandwidth and the 3 dB spectral bandwidth are calculated, and the power fluctuation is statistically analyzed to calculate the standard deviation of the power within the preset time window. Step S302: When both the 10 dB spectral bandwidth and the 3 dB spectral bandwidth reach or exceed the preset width threshold and the power standard deviation is less than the preset stable mode-locking threshold, it is determined that stable mode-locking has been obtained and the angle scanning is stopped. Step S303: Record the current power standard deviation as the reference fluctuation value, and store the current angle and the corresponding 10 dB spectral bandwidth, 3 dB spectral bandwidth and output power parameters into the non-volatile memory as the target mode-locked operating point.

[0048] In steps S301 to S303 of the embodiments of this application, a refined scan is performed by narrowing the search range and reducing the step size, while simultaneously calculating the spectral bandwidth and power standard deviation. This enables refined detection of the mode-locking candidate region, achieving a multi-dimensional quantitative evaluation of the mode-locking state and providing comprehensive data support for accurate mode-locking determination. By simultaneously satisfying the spectral bandwidth threshold condition and the power standard deviation threshold condition, a composite criterion for determining the stable mode-locking state is executed, achieving high-confidence identification of the mode-locking state and avoiding misjudging continuous wave, self-excited oscillation, or noise-like states as stable mode-locking. By recording the current power standard deviation as a benchmark fluctuation value and storing the angle, spectral bandwidth, and power parameters in non-volatile memory, a complete record of the mode-locking operating point is executed. This provides a traceable and comparable quantitative benchmark for the subsequent mode-locking maintenance stage, making the judgment of "deviation from the target state" verifiable.

[0049] In some embodiments, step S104 may include, but is not limited to, steps S401 to S407: Step S401: Monitor the output power at a preset period, calculate the power standard deviation within a preset time window, and compare the power standard deviation with the recorded benchmark fluctuation value; Step S402: When the power standard deviation exceeds a preset proportional threshold of the reference fluctuation value, or the 10 dB spectral bandwidth decreases by more than a preset threshold, it is determined that the target mode-locked operating point has been deviated from, and local relocking is triggered. Step S403: Increase pump power; Step S404: Search within the preset range of the target mold-locking working point with a third step length smaller than the second step length; Step S405: For each set of search angles, calculate the 10 dB spectral bandwidth, the 3 dB spectral bandwidth, and the power standard deviation within the preset time window. Step S406: When both the 10 dB spectral bandwidth and the 3 dB spectral bandwidth reach the preset width threshold and the power standard deviation is less than the preset stability threshold, it is determined that mode-locked output is restored, the current angle is updated to the target mode-locked operating point and the search is stopped. Step S407: If no angle that meets the conditions is found within the preset number of iterations, the process returns to the step of marking the state that meets the spectral width condition and has a comb-like structure as a mode-locking candidate point, based on the mechanical zero point and the correspondence between the angle and the power, using the long scanning waveplate of the first step, until the mode-locked output is restored.

[0050] In steps S401 to S407 of the embodiments of this application, the closed-loop maintenance and multi-level automatic recovery of the mode-locked state are performed through seven coordinated steps: real-time monitoring of quantization status, detection of unlocking by multi-parameter intelligent criteria, increasing pump power to expand the attraction domain, local fine search for rapid positioning, ensuring recovery quality by the same criteria, dynamically updating the operating point to adapt to changes, and backing up to coarse search as a fallback. This achieves full automation from daily maintenance to abnormal recovery, enabling the laser to operate stably for a long time under environmental disturbances, and automatically recovering from occasional unlocking events within hundreds of milliseconds to several seconds, truly achieving the intelligent mode-locking goal of "self-starting + self-maintaining".

[0051] This application also provides an intelligent mode-locked fiber laser based on nonlinear polarization interference for performing the control method described above. The intelligent mode-locked fiber laser includes a linear cavity optical part and an intelligent detection and control part. The linear cavity optics section includes a pump source, a wavelength division multiplexing collimator, polarization-maintaining erbium-doped fiber, polarization-maintaining single-mode fiber, a Faraday mirror, and a free-space polarization and phase-shifting unit. The Faraday mirror is used to introduce non-reciprocal phase shift. The free-space polarization and phase-shifting unit includes a polarization beam splitter, a half-wave plate, an eighth-wave plate, a Faraday rotator, and a high-reflectivity mirror. The free-space polarization and phase-shifting unit and the fiber arm together form a nonlinear polarization interference structure. The intelligent detection and control section includes a measurement module, a control and computing module, and an electric polarization rotator; the measurement module includes an optical power meter and a spectrum analyzer; the control and computing module includes an FPGA control board; and the electric polarization rotator carries and drives the rotation of the half-wave plate and the eighth-wave plate.

[0052] In some embodiments, the wavelength division multiplexing collimator integrates a wavelength division multiplexer, a gradient refractive index lens, a filter, and a glass sleeve. The pump end is connected to the pump light source, and the signal end is fused to a polarization-maintaining erbium-doped fiber to form a fusion interface in the optical path.

[0053] In some embodiments, the measurement module further includes a polarization-maintaining fiber coupler connected to the laser output port of the polarization beam splitter, used to divide the output light into a working output branch and a monitoring branch according to a preset ratio; the monitoring branch is connected to an optical power meter and a spectrum analyzer respectively. The electric polarization rotator is a multi-channel precision driven rotation device. Each channel carries and fixes a half-wave plate or an eighth-wave plate for step adjustment and repeated positioning. The angle adjustment is controlled by an FPGA.

[0054] In some embodiments, the polarization axes of the polarization-maintaining erbium-doped fiber and the polarization-maintaining single-mode fiber are aligned and fused together. In the free-space polarization and phase-shifting unit, the Faraday rotator and the Faraday mirror together constitute a nonlinear polarization interference structure; the optical axes of the half-wave plate and the eighth-wave plate maintain a preset angular relationship with the polarization axis of the polarization beam splitter in the initial state.

[0055] In some embodiments, the FPGA of the control and calculation module has a built-in angle-power lookup table for pre-setting the sampling frequency to collect spectral data, calculating the 10 dB spectral bandwidth and the 3 dB spectral bandwidth, outputting pulse signals to control the electric polarization rotator, and communicating with the host computer through the communication interface.

[0056] I. As an optional implementation, the intelligent automatic mode-locked polarization-maintaining fiber laser (intelligent mode-locked fiber laser) of this invention includes a linear cavity optical section and an intelligent detection and control section connected thereto, wherein: 1.1 The linear cavity optical component includes: Pump light source: used to provide pump energy at a preset wavelength; Wavelength division multiplexing collimator (WDM-collimator): It integrates a wavelength division multiplexer, a gradient refractive index lens (G-lens), a filter, and a glass sleeve. The pump light is injected through the wavelength division end, and the signal end is fused with polarization-maintaining erbium-doped fiber. The gradient lens is used to achieve beam collimation, and the filter provides unidirectional isolation. This integrated structure realizes pump / signal beam combining and free space coupling, forming a single fusion interface only at the fusion point, thereby reducing insertion loss and shortening the cavity length. Erbium-doped polarization-maintaining fiber (PM-EDF): fused to the signal end of the WDM-collimator to provide amplification gain; Polarization-maintaining single-mode fiber (PM-SMF): Serial with polarization-maintaining erbium-doped fiber to compensate for dispersion and extend cavity length; Faraday mirror (FM): Connected to the end of a polarization-maintaining single-mode fiber, it is used to introduce a non-reciprocal phase shift during round-trip propagation to achieve nonlinear polarization interference; Free-space polarization and phase shifting unit: Located between the output of the WDM-collimator and the reflector, it includes a polarization beam splitter (PBS), a half-wave plate (HWP), an eighth-wave plate (EWP), a Faraday rotator (FR), and a high-reflectivity mirror (M1). One end of the PBS serves as the laser output port, and the other end, together with the HWP, FR, EWP, and M1, forms a free-space arm, which, together with the fiber arm, forms a nonlinear polarization interference structure to achieve the polarization selection and phase offset required for mode locking.

[0057] 1.2 The intelligent detection and control section includes: Measurement module: includes an optical power meter and a spectrum analyzer, used to collect the average power and real-time spectral information of the laser output, respectively; Control and computation module: including field programmable gate array (FPGA) control board and power supply circuit, used to receive signals from the measurement module and perform real-time calculations, status discrimination and search strategy updates; Motorized Polarizer Rotator (MPR): Installed in the free-space polarization and phase-shifting unit, it carries and drives the rotation of HWP and EWP; the MPR is controlled by FPGA, which can achieve high-resolution angular resolution and finely programmable adjustment of the equivalent polarization state and phase in the cavity.

[0058] The above components together constitute a fully polarization-maintaining linear cavity: a portion of the light is split from the output port of the PBS as laser output, and the other portion propagates back and forth through the free space arm and fiber arm. The coherent superposition and intensity selection required for nonlinear polarization interference mode-locking are achieved through the non-reciprocal interference structure formed by the PBS, FR and FM. The WDM-collimator is responsible for pump injection and signal coupling, ensuring that the cavity is compact, has low loss and high repetition frequency.

[0059] 1.3 Intelligent Automatic Mold Closing Method: The present invention also provides an intelligent automatic mold-locking method based on the above-mentioned device, comprising the following steps: a) Initial calibration steps: In continuous wave operation mode, fix one of the HWP or EWP, scan the other within a certain range, and measure the average power at the PBS output port. The position where the waveplate is aligned with the incident polarization axis is determined by the angle corresponding to the maximum power, and this position is set as the mechanical zero point of MPR; Repeat the above process to calibrate the two waveplates and establish the correspondence between the HWP and EWP angles and the output power.

[0060] b) Coarse search steps: Starting from the initial angle near the maximum power, a two-dimensional combined scan of HWP and EWP is performed with a preset large step size. For each set of angles, the FPGA collects data from the optical power meter and spectrometer, calculates the full spectrum width, center wavelength and frequency comb fringe characteristics, and eliminates states that are obviously continuous waves or self-excited oscillations, retaining only candidate points with increased spectral width and comb-like structure. In the coarse search stage, most angle combinations are quickly traversed to narrow down the parameter region that may enter mode-locking.

[0061] c) Spectral width-guided adaptive fine-search steps: Within the candidate region, the FPGA automatically reduces the step angle to perform a detailed scan of the HWP and EWP. Simultaneously, it calculates parameters such as the 10 dB spectral bandwidth and 3 dB spectral bandwidth, and distinguishes between various soliton mode-locking modes, including noise-like mode-locking, based on preset spectral width thresholds and power stability criteria. When the 10 dB bandwidth significantly increases and the 3 dB bandwidth and output power meet the stability conditions, the system is determined to have entered the mode-locked operating range. Further fine-tuning with smaller step sizes is then employed within this range to obtain a wider spectral bandwidth and better pulse characteristics.

[0062] d) Mold maintenance and automatic relocking procedures: After obtaining the mode-locked operating point, the FPGA records the corresponding HWP, EWP angles, and key spectral parameters as the target state. During normal operation, the output power and spectral characteristics are continuously monitored. When deviations from the target state are detected (e.g., decreased spectral width or the appearance of noise), a local search is automatically triggered, adjusting the MPR angle within a small range near the target to achieve rapid relocking. Through the above closed-loop control, the fully polarization-maintaining NPI cavity can maintain stable mode-locked output for a long time even with environmental disturbances. Through the above structure and method, this invention, while maintaining the high environmental stability and compact structure of the fully polarization-maintaining NPI architecture, introduces a high-precision electric polarization rotator and intelligent search algorithm, achieving automatic tuning of the intracavity polarization state and phase shift. Self-starting mode-locking can be completed and stable operation maintained within a finite number of iterations.

[0063] II. The solutions of the embodiments of the present invention will be described in detail and explained with reference to specific application examples: 2.1 Optical cavity structure: like Figure 2 As shown, the optical cavity in this embodiment employs a laser with a fully polarization-maintaining nonlinear polarization interference (PM-NPI) structure and a specific operating wavelength, comprising the following components: 1. Pump light source: A semiconductor laser diode specifically designed for erbium-doped fiber is selected as the energy excitation source. Its output power is continuously adjustable through the driving power supply and has high output stability.

[0064] 2. Wavelength Division Multiplexing Collimator (WDM-collimator): This solution employs an integrated wavelength division multiplexing collimation component as the core coupling architecture. It integrates collimation elements, optical filtering elements, and encapsulation sleeves. The pump input is connected to a pump source pigtail with adjustable and stable output characteristics, and the signal output is fused to a polarization-maintaining gain fiber. The internal spatial coupling structure achieves beam combining and collimation of the pump and signal light. This integrated structure forms only a single fusion interface in the optical path, which significantly optimizes the physical length of the cavity while suppressing system insertion loss.

[0065] 3. Polarization-maintaining erbium-doped fiber (PM-EDF): A polarization-maintaining gain fiber adapted to the signal band is selected, and one end of it is fused with the pigtail of the integrated wavelength division multiplexing collimation component through polarization axis alignment. The required amplification gain is provided through the preset fiber length.

[0066] 4. Polarization-maintaining single-mode fiber (PM-SMF): A pre-set length of polarization-maintaining single-mode fiber is connected in series after the polarization-maintaining gain fiber to adjust the intracavity dispersion distribution and set the total length of the resonant cavity in order to achieve the target pulse repetition frequency; the polarization axes of all polarization-maintaining single-mode fibers are aligned and fused with the polarization axis of the preceding polarization-maintaining gain fiber to maintain the full polarization-maintaining characteristics of the entire system.

[0067] 5. Faraday Mirror (FM): A non-reciprocal reflection component is connected to the end of the polarization-maintaining single-mode fiber. By introducing a non-reciprocal polarization rotation at a preset angle and returning the optical signal into the cavity, the nonlinear polarization interference characteristics in the fiber optic link are constructed.

[0068] 6. Free-space polarization and phase shift unit: This unit is located on the free space side of the integrated beam combining and collimating assembly. Along the optical path, it sequentially includes a polarization beam splitter (PBS), a half-wave plate (HWP) mounted on the adjustment device (MPR), a non-reciprocal rotation element (FR), an eighth-wave plate (EWP) mounted on the adjustment device (MPR), and a high-reflectivity mirror (M1). The PBS is used for polarization mode separation. One end of the PBS serves as the laser output port. The transmitted light enters the free space arm formed by the wave plate and the mirror and returns along the original path. It works with the return light from the fiber optic link to construct an interference structure. The optical axes of each phase delay element and the polarization axis of the PBS maintain a preset angular relationship in the initial state.

[0069] 7. Electrodynamic polarization rotator (MPR): This embodiment employs a multi-channel precision drive rotation device as an electric polarization rotator (MPR), with each channel carrying and fixing either the HWP or EWP. This rotation device features high-resolution step adjustment capability and high repeatability positioning accuracy, and can receive logic control signals from the control unit, thereby enabling independent and automated programmable adjustment of the angles of each waveplate.

[0070] 8. Output coupling and monitoring port: The reflective end of the PBS serves as the main laser output port, which is connected to the subsequent measurement module via a polarization-maintaining fiber optic pigtail. To enable online signal monitoring, the output end is further connected to a polarization-maintaining fiber optic coupler, which divides the optical signal into a working output branch and a monitoring branch according to a preset ratio.

[0071] 2.2 Intelligent Detection and Control Unit: a) Measurement module: Monitoring branch: The monitoring end is connected to the power detection module and the spectrum analysis module respectively via polarization-maintaining pigtails.

[0072] Power detection module: Used to acquire the average power value of the optical signal in real time.

[0073] Spectral Analysis Module: Performs spectral analysis on optical signals within a preset scanning range and interacts with the control unit in real time via a communication interface; the system control software can acquire the current spectral profile and multiple performance parameters, including specific bandwidth and center wavelength.

[0074] b) Control and computation module: The control and computing module uses an integrated FPGA, which is responsible for high-speed I / O, MPR pulse control and real-time mode-locking criterion calculation, and can communicate with the host computer.

[0075] After each spectral measurement is completed, the FPGA reads the data from the spectral analyzer and performs calculations.

[0076] 10 dB spectral bandwidth BW10; 3 dB spectral bandwidth BW3.

[0077] c) Control interface: The FPGA outputs two sets of pulses to drive the stepper motors of the HWP and EWP respectively; it also provides an enable signal to control the power-on state of the MPR. The system is equipped with an emergency stop button and a host computer command interface, which can be switched to manual control mode when needed.

[0078] 2.3 Initial calibration steps: After the initial setup or maintenance of the device, the zero point of the MPR angle needs to be calibrated: 1. Turn off the intelligent search function and set the pump power to a specific value to make the laser work in continuous light output mode.

[0079] 2. Lock the EWP angle stationary, and drive the HWP to rotate within a certain range in specific steps. For each angular position, record the average power curve of the PBS output port.

[0080] 3. Locate the position of the maximum average power and record the corresponding HWP angle as . And set this angle as the mechanical zero point of HWP in the FPGA.

[0081] 4. With HWP fixed as Under these conditions, the location of maximum power is recorded by scanning the EWP with the same time interval. And set it as the mechanical zero point of the EWP.

[0082] 5. After calibration, an angle-power lookup table is created in the FPGA to provide a reference for subsequent searches.

[0083] 2.4 Coarse Search and Model-Lock Capture: After calibration, an automatic coarse-search process for mode locking is executed, such as... Figure 3 As shown: 1. Increase the pump power to provide sufficient gain within the cavity to support mode locking.

[0084] 2. The FPGA sets the search range of HWP and EWP to a certain range relative to the mechanical zero point, with a large step size, and adopts a two-dimensional grid scanning method.

[0085] 3. For each set of angles : Wait for the cavity to reach steady state; Read the optical power meter value; if the power is less than the threshold... If the value is not specified, it is considered a non-operating point, and the spectral measurement is skipped. When power is greater than At that time, the spectrometer is triggered to sample and calculate BW10 and BW3.

[0086] 4. The FPGA classifies scan points according to the following rules: Continuous wave state determination: When the specific bandwidth parameters of the spectrum are all below the preset threshold, the system determines that it is in continuous wave output state.

[0087] Mode-lock candidate point determination: When the spectral width increases significantly and exceeds the preset range, and is accompanied by obvious comb-like feature structures at the spectral edge, the system marks the current state parameter as a mode-lock candidate position.

[0088] After the coarse search is completed, several points with the largest BW10 are selected from all "mode-locking candidate points" as the centers for the next stage of fine search. This process is usually completed within a few seconds to a dozen seconds, avoiding blind scanning of the entire angular space.

[0089] 2.5 Spectral Width-Guided Fine-Scale Search and Optimization: Based on the coarse search, the system performs a fine search near the candidate points to capture the true stable mode-locked state: 1. For each candidate point This narrows the search range for HWP1 and EWP1, and reduces the step size.

[0090] 2. During the detailed search process, in addition to calculating BW10 and BW3, the FPGA also performs statistical analysis on power fluctuations and calculates the standard deviation of power within a certain time window. .

[0091] 3. Stable mode locking is determined when a set of angles meets the following conditions: The specific bandwidth parameters BW10 and BW3 of the spectrum both reach or exceed the preset width thresholds to ensure that the pulse has sufficient spectral broadening. Power stability assessment: The real-time monitored average output power fluctuation is within a preset minimum error range, ensuring stable system energy output; Spectral stability determination: The spectral profile does not drift significantly during the observation period, and the fluctuation amplitude of its center wavelength remains within the preset accuracy range.

[0092] 4. Once the above conditions are met, the FPGA immediately stops angle scanning and sets the current angle... The corresponding parameters such as BW10, BW3, and output power are stored in non-volatile memory as the "target mode-locked operating point".

[0093] 2.6 Mold Locking Maintenance and Automatic Relocking: After the system enters mode-locking, the following strategies are used to ensure long-term stable operation: 1. The control unit (FPGA) periodically collects specific bandwidth indicators and output power of the spectrum at a preset cycle, and compares them with the reference value of the mode-locked target point in real time.

[0094] 2. When any indicator deviates beyond the preset allowable range, such as when the spectral bandwidth or output power decreases beyond the preset threshold, the system determines that a lockout has occurred or there is a lockout trend. 3. Once a lockout is detected, the FPGA triggers a "local relock mode": First, slightly increase the pump power to expand the mold-locking attraction area; Then A small-scale search is performed within the vicinity with a small step size, and the same criteria as the fine search are used to find the lock point again; If a new mode-locking point is found within the limited number of iterations, the target operating point parameters are updated and normal operation is restored. First, the pump power is increased appropriately to expand the mode-locking attraction domain. Then, a small-range search is performed near the original operating position with small steps, and a preset criterion is used to find the mode-locking point again. If a new modulator-locked point is found within the limited number of iterations, the target working point parameters are updated and normal operation resumes; if the local search fails, the initial search procedure is returned to search for a global modulator-locked point again.

[0095] 4. In actual testing, the laser of this embodiment can achieve stable mode-locked output for several hours under conditions of desktop vibration and slow fluctuations in room temperature. Occasional unlocking events usually recover automatically through local relocking mode within hundreds of milliseconds to several seconds, without manual intervention.

[0096] III. The beneficial effects of this invention are: 3.1 Significantly improves environmental stability and engineering reliability.

[0097] Employing a polarization-preserving nonlinear polarization interference (PM-NPI) structure, a polarization beam splitter, a Faraday rotator, and a Faraday mirror are introduced to form a non-reciprocal phase bias, making the mode-locking condition insensitive to external disturbances such as temperature and vibration, and enabling long-term stable output of ultrashort pulses.

[0098] 3.2 Achieve automatic and rapid mode-locking within a narrow mode-locking window. By precisely adjusting the angles of the half-wave plate (HWP) and the eighth-wave plate (EWP) using an electric polarization rotator, combined with an intelligent algorithm that integrates coarse and fine search, and a mode-locking criterion based on power and a 10 dB spectral bandwidth, a stable operating point can be automatically found and locked within a limited number of iterations. This eliminates the need for repeated fine-tuning by experimenters, significantly reducing setup time and improving repeatability.

[0099] 3.3 Compact structure and high system integration. The use of a wavelength division multiplexing collimator to achieve pump beam combining and fiber-free space coupling reduces the number of devices and fusion splices. The cavity length is short and the loss is low, which can achieve a high repetition frequency and good beam quality. At the same time, compared with intelligent mode-locking systems that rely on long-distance dispersive fibers and complex measurement links, the present invention has a simple structure, is easy to modularly package and mass-produce.

[0100] 3.4 It possesses automatic relocking and self-recovery capabilities. During operation, the output power and spectral characteristics are monitored in real time. When the operating point drift causes unlocking, the control unit can automatically trigger a local search and restore to the recorded optimal angle, realizing intelligent locking mode of "self-starting + self-maintaining", which is beneficial for long-term unattended operation and practical engineering applications.

[0101] Key points and protection points of this invention: 1. The construction method of the polarization-preserving nonlinear polarization interference (PM-NPI) structure and its non-reciprocal phase shift mechanism for mode locking; 2. Introducing and using an electrically driven polarization rotator (MPR) as an adjustable polarization / phase unit in an NPI cavity; 3. Intelligent automatic mode-locking method based on spectral bandwidth and power analysis (coarse search + fine search + re-locking mechanism).

[0102] This application also provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the above-described method.

[0103] It is understood that the content of the above method embodiments is applicable to this device embodiment. The specific functions implemented by this device embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0104] Another embodiment of the hardware structure of the electronic device, the electronic device including: The processor can be implemented using a general-purpose CPU (Central Processing Unit), microprocessor, application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to achieve the technical solutions provided in the embodiments of this application. The memory can be implemented in the form of read-only memory (ROM), static storage device, dynamic storage device, or random access memory (RAM). The memory can store the operating system and other applications. When the technical solutions provided in the embodiments of this specification are implemented through software or firmware, the relevant program code is stored in the memory and called by the processor to execute the methods described in the embodiments of this application. Input / output interfaces are used to implement information input and output; The communication interface is used to enable communication and interaction between this device and other devices. Communication can be achieved through wired means (such as USB, Ethernet cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.). A bus is used to transfer information between various components of a device, such as processors, memory, input / output interfaces, and communication interfaces. The processor, memory, input / output interfaces, and communication interfaces communicate with each other within the device via a bus.

[0105] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method.

[0106] It is understood that the content of the above method embodiments is applicable to this storage medium embodiment. The specific functions implemented in this storage medium embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0107] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the above-described method.

[0108] It is understood that the content of the above method embodiments is applicable to the embodiments of this program product. The specific functions implemented by the embodiments of this program product are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0109] Memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. Furthermore, memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, memory may optionally include memory remotely located relative to the processor, and these remote memories can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0110] This application provides a control method, intelligent mode-locked fiber laser, electronic device, storage medium, and program product based on nonlinear polarization interference. It ensures high environmental stability through a fully polarization-maintaining nonlinear polarization interference structure, achieves automatic and precise adjustment of waveplate angles through an electric polarization rotator, rapidly locates the mode-locked operating point through a two-level search algorithm combining coarse and fine search, maintains the mode-locked state long-term by real-time monitoring of output power and spectral characteristics and comparing with a reference fluctuation value, automatically restores mode-locked output upon delocking through a local relocking mechanism, and reduces the number of components and fusion points to lower insertion loss and shorten cavity length through a wavelength division multiplexing collimator. This achieves the intelligent goals of automatic mode-locking startup, long-term stable maintenance, automatic delocking recovery, compact structure, high integration, and unattended operation of the fully polarization-maintaining fiber laser.

[0111] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0112] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0113] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0114] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0115] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0116] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0117] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0118] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0119] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0120] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes multiple instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned storage medium includes various media capable of storing programs, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0121] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A method for controlling a nonlinear polarization interference-based smart mode-locked fiber laser, characterized in that, The method includes the following steps: In continuous wave mode, scan the waveplate, fix one of the half-wave plate or one-eighth waveplate, scan the other plate, set the angle corresponding to the maximum power value as the mechanical zero point, and establish the correspondence between angle and power. Using the mechanical zero point as a reference and referring to the relationship between angle and power, the state that meets the spectral width condition and has a comb-like structure is marked as a mode-locking candidate point using the first step long scanning waveplate. Centered on the candidate mode-lock point, scan with the second step size, calculate the spectral bandwidth and the power standard deviation within the preset time window. When the spectral bandwidth reaches the threshold and the power standard deviation is less than the stable threshold, mode-lock is determined. Record the current power standard deviation as the benchmark fluctuation value and record the corresponding angle as the target mode-lock working point. Monitor output parameters, calculate power standard deviation and compare it with the benchmark fluctuation value. When the deviation exceeds the allowable range, trigger a local search to restore mode lock.

2. The method of claim 1, wherein, The step of scanning waveplates in continuous wave mode, fixing one half-wave plate or one-eighth waveplate, scanning the other plate, setting the angle corresponding to the maximum power as the mechanical zero point, and establishing the correspondence between angle and power includes: The eighth-wave plate is fixed, and the half-wave plate is driven to rotate within a preset range with a specific step size. The average power curve of the polarization beam splitter output port is recorded at each angular position. The position of the maximum value of the average power is found, the corresponding half-wave plate angle is recorded, and the angle is set as the mechanical zero point of the half-wave plate in the FPGA. A fixed half-wave plate is used to scan an eighth-wave plate with a specific step size, and the position with the maximum power is set as the mechanical zero point of the eighth-wave plate. After calibration, an angle-power lookup table is established in the FPGA to obtain the correspondence between angle and power.

3. The method of claim 1, wherein, The step of using the mechanical zero point as a reference, referring to the angle-power correspondence, and using a first-step long-scan waveplate to mark states that meet the spectral width condition and exhibit a comb-like structure as mode-locking candidate points includes: Based on the mechanical zero point and referring to the relationship between angle and power, the search range of the half-wave plate and the eighth-wave plate are set to a preset range relative to the mechanical zero point, and a two-dimensional grid scan is performed with a preset first step length. For each set of angles, first wait for the cavity to stabilize, then read the optical power meter value. If the power is less than the preset threshold, it is determined to be a non-operating point and the spectral measurement is skipped. When the power exceeds the preset threshold, the spectrometer is triggered to sample and calculate the 10 dB spectral bandwidth and the 3 dB spectral bandwidth. When the spectral width increases significantly and exceeds the preset range, and comb-like feature structures appear at the spectral edge, the current state parameter is marked as a mode-locking candidate point.

4. The method according to claim 1, characterized in that, The process involves using a candidate mode-lock point as the center, scanning with a second step size, calculating the spectral bandwidth and the power standard deviation within a preset time window, determining mode-lock when the spectral bandwidth reaches a threshold and the power standard deviation is less than a stable threshold, recording the current power standard deviation as the baseline fluctuation value, and recording the corresponding angle as the target mode-lock operating point. This includes: For the mode-locked candidate points, the search range of the half-wave plate and the eighth-wave plate are narrowed to a preset range, the step size is reduced to a preset range, the 10 dB spectral bandwidth and the 3 dB spectral bandwidth are calculated, and the power fluctuation is statistically analyzed to calculate the standard deviation of the power within a preset time window. When both the 10 dB spectral bandwidth and the 3 dB spectral bandwidth reach or exceed the preset width threshold, and the power standard deviation is less than the preset stable mode-locking threshold, it is determined that stable mode-locking has been achieved, and angle scanning is stopped. Record the current power standard deviation as the baseline fluctuation value, and store the current angle and the corresponding 10 dB spectral bandwidth, 3 dB spectral bandwidth, and output power parameters in non-volatile memory as the target mode-locked operating point.

5. The method according to claim 1, characterized in that, The monitoring output parameters are used to calculate the power standard deviation and compare it with the benchmark fluctuation value. When the deviation exceeds the allowable range, a local search is triggered to restore mode-locking, including: The output power is monitored at a preset period, the power standard deviation within a preset time window is calculated, and the power standard deviation is compared with the recorded benchmark fluctuation value. When the power standard deviation exceeds a preset percentage threshold of the reference fluctuation value, or when the 10 dB spectral bandwidth decreases by more than a preset threshold, it is determined that the target mode-locked operating point has been deviated from, and local relocking is triggered. Increase pump power; The search is performed within a preset range of the target mold-locking working point using a third step size smaller than the second step size; For each set of search angles, calculate the 10 dB spectral bandwidth, the 3 dB spectral bandwidth, and the power standard deviation within the preset time window; When both the 10 dB spectral bandwidth and the 3 dB spectral bandwidth reach the preset width threshold, and the power standard deviation is less than the preset stability threshold, it is determined that mode-locked output should be restored, the current angle should be updated to the target mode-locked operating point, and the search should be stopped. If no angle that meets the conditions is found within the preset number of iterations, the process returns to the step of using the mechanical zero point as a reference, referring to the relationship between angle and power, and marking the state that meets the spectral width condition and has a comb-like structure as a mode-locking candidate point using the first step long scanning waveplate, and repeats until mode-locked output is restored.

6. A smart mode-locked fiber laser based on nonlinear polarization interference, used to execute the control method as described in any one of claims 1 to 5, characterized in that, The intelligent mode-locked fiber laser includes a linear cavity optical section and an intelligent detection and control section; The linear cavity optical section includes a pump source, a wavelength division multiplexing collimator, a polarization-maintaining erbium-doped fiber, a polarization-maintaining single-mode fiber, a Faraday mirror, and a free-space polarization and phase-shifting unit. The Faraday mirror is used to introduce a non-reciprocal phase shift. The free-space polarization and phase-shifting unit includes a polarization beam splitter, a half-wave plate, an eighth-wave plate, a Faraday rotator, and a high-reflectivity mirror. The free-space polarization and phase-shifting unit and the fiber arm together form a nonlinear polarization interference structure. The intelligent detection and control section includes a measurement module, a control and calculation module, and an electric polarization rotator; the measurement module includes an optical power meter and a spectrum analyzer; the control and calculation module includes an FPGA control board; the electric polarization rotator carries and drives the half-wave plate and the eighth-wave plate to rotate.

7. The intelligent mode-locked fiber laser according to claim 6, characterized in that, The wavelength division multiplexing collimator integrates a wavelength division multiplexer, a gradient refractive index lens, a filter, and a glass sleeve. The pump end is connected to the pump light source, and the signal end is fused to the polarization-maintaining erbium-doped fiber to form a fusion interface in the optical path.

8. The intelligent mode-locked fiber laser according to claim 6, characterized in that, The measurement module also includes a polarization-maintaining fiber coupler connected to the laser output port of the polarization beam splitter, used to divide the output light into a working output branch and a monitoring branch according to a preset ratio; the monitoring branch is respectively connected to the optical power meter and the spectrum analyzer. The electric polarization rotator is a multi-channel precision drive rotation device. Each channel carries and fixes a half-wave plate or an eighth-wave plate for step adjustment and repeated positioning. The angle adjustment is controlled by an FPGA.

9. The intelligent mode-locked fiber laser according to claim 6, characterized in that, The polarization-maintaining erbium-doped fiber and the polarization-maintaining single-mode fiber are fused together with their polarization axes aligned. In the free-space polarization and phase-shifting unit, the Faraday rotator and the Faraday mirror together constitute a nonlinear polarization interference structure; the optical axes of the half-wave plate and the eighth-wave plate maintain a preset angular relationship with the polarization axis of the polarization beam splitter in the initial state.

10. The intelligent mode-locked fiber laser according to claim 6, characterized in that, The FPGA-built angle-power lookup table of the control and calculation module is used to preset the sampling frequency to collect spectral data, calculate the 10 dB spectral bandwidth and the 3 dB spectral bandwidth, output pulse signals to control the electric polarization rotator, and communicate with the host computer through the communication interface.

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