A self-starting method and device for a solid-state Kerr mode-locked laser based on resonant pump modulation feedback control

Abstract

The application discloses a self-starting method and device of a solid Kerr mode-locked laser based on resonant pumping modulation feedback control, belongs to the field of ultrafast lasers, and comprises the following steps: providing a solid laser resonant cavity; generating a reference electric signal with a frequency equal to the eigen-repetition frequency of the resonant cavity; superimposing a weak sinusoidal modulation signal with a frequency synchronized with the reference electric signal on the driving current of a pumping source to periodically modulate the gain of pumping light; dynamically adjusting the frequency and phase of the sinusoidal modulation signal through a phase-locked loop feedback control loop so that the sinusoidal modulation signal is accurately locked on the reference electric signal; and establishing a stable mode-locked pulse sequence by the synergistic effect of gain modulation and intracavity Kerr nonlinear effect. Through active gain modulation and closed-loop feedback control, the application realizes high-reliability self-starting and long-term stable operation of the solid Kerr mode-locked laser.

Description

Technical Field

[0001] This invention belongs to the field of ultrafast lasers, and particularly relates to a method and apparatus for self-starting a solid-state Kerr mode-locked laser based on resonant pump modulation feedback control. Background Technology

[0002] Solid-state lasers based on Kerr lens mode-locking are one of the main techniques for generating femtosecond pulses. Their mode-locking mechanism relies on the intensity-dependent nonlinear Kerr effect, generating self-focusing and interacting with the intracavity aperture to form an equivalent saturable absorption effect, thereby achieving pulse narrowing. However, the physical nature of this passive mode-locking method dictates that its initiation process requires an initial intensity fluctuation to "guide" it; therefore, mode-locking establishment is typically highly random and unstable. To overcome this difficulty, existing technologies mainly employ two schemes: one is to insert an electro-optic phase modulator into the resonant cavity and apply a radio frequency signal with a frequency close to the cavity repetition frequency during the initiation phase to actively trigger mode-locking; the other is to use a vibrating diaphragm saturable absorber, using mechanical vibration to initiate the mode-locking process.

[0003] However, the aforementioned existing solutions still have significant drawbacks in practical applications. For the intracavity-inserted modulator method, the device introduces additional losses, and manual intervention is usually required to shut down the modulation signal after mode-locking is initiated. The lack of an automatic monitoring and maintenance mechanism for the mode-locking state makes it impossible to guarantee the long-term stability of the system. For the vibrating diaphragm saturable absorber solution, it also lacks mode-locking state detection and feedback functions. Furthermore, as the laser's operating time increases, the thermal lensing effect of the gain medium changes, causing the resonant cavity parameters to drift. This results in a mismatch between the originally set vibration frequency and the actual repetition frequency of the cavity, thus affecting the stable maintenance of mode-locking and even leading to mode-locking loss. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a self-starting method for a solid-state Kerr mode-locked laser based on resonant pump modulation feedback control, comprising: A solid-state laser resonator is provided, the solid-state laser resonator comprising a gain medium and a pump source; Generate a reference electrical signal with a frequency equal to the intrinsic repetition frequency of the solid-state laser resonator; A weak sinusoidal modulation signal with a frequency synchronized with the reference electrical signal is superimposed on the driving current of the pump source to perform periodic gain modulation on the pump light. The frequency and phase of the sinusoidal modulation signal are dynamically adjusted through a phase-locked loop feedback control circuit, so that it accurately tracks and locks onto the reference electrical signal. By utilizing the synergistic effect of the gain modulation and the intracavity Kerr nonlinearity, a stable mode-locked pulse sequence is established and maintained in the solid-state laser resonant cavity.

[0005] Optionally, the step of generating the reference electrical signal further includes: generating the reference electrical signal by means of an active detection method or a passive calculation method through a frequency reference generation module; The active detection method involves using a high-speed photodetector to detect the pulse sequence output by the solid-state laser resonator and extracting the fundamental frequency repetition frequency signal from it; the passive calculation method involves calculating an approximate value of the intrinsic repetition frequency based on the physical parameters of the solid-state laser resonator and generating a reference signal of the approximate value by a frequency synthesizer.

[0006] Optionally, the step of superimposing a weak sinusoidal modulation signal onto the pump source drive current further includes: using a modulation signal application module to linearly superimpose an AC modulation current and a DC bias current to jointly drive the pump source, wherein the amplitude of the AC modulation current is less than 5% of the amplitude of the DC bias current.

[0007] Optionally, the phase-locked loop feedback control loop includes a phase detector, a loop filter, and a voltage-controlled oscillator; The phase detector receives the reference electrical signal and the feedback signal from the voltage-controlled oscillator, and outputs an error voltage that is proportional to the phase difference between the two. The loop filter filters the error voltage to generate a smooth control voltage. The voltage-controlled oscillator generates the sinusoidal modulation signal according to the control voltage, and outputs it to the modulation signal application module and the phase detector respectively, forming a closed-loop control.

[0008] Optionally, the loop filter is a proportional-integral controller.

[0009] Optionally, after the mode-locked pulse sequence is established, a state monitoring and mode discrimination module automatically determines the mode-locked state and adjusts the modulation depth of the sinusoidal modulation signal according to the determination result.

[0010] Optionally, the step of automatically determining the mode-locking state further includes: using a high-speed photodetector to monitor the radio frequency power spectrum of the output pulse, and when a peak with a signal-to-noise ratio exceeding a preset threshold is detected at the intrinsic repetition frequency, it is determined that the mode-locking has been stably established.

[0011] Optionally, the step of adjusting the modulation depth includes: after confirming mode-locking, gradually reducing the modulation depth of the sinusoidal modulation signal to zero or a preset maintenance level using a digitally controlled attenuator; The step of adjusting the modulation depth includes: after confirming mode-locking, maintaining a preset weak modulation depth to enhance the anti-interference capability of the mode-locked pulse sequence.

[0012] To address the aforementioned technical problems, this invention also provides a self-starting device for a solid-state Kerr mode-locked laser based on resonant pump modulation feedback control, comprising: A solid-state laser resonator, which includes a gain medium and a pump source; A frequency reference generation module is used to generate a reference electrical signal with a frequency equal to the intrinsic repetition frequency of the solid-state laser resonator. A modulation signal application module, connected to the pump source, is used to superimpose a sinusoidal modulation signal onto the drive current of the pump source; A phase-locked loop feedback control module is connected to the frequency reference generation module and the modulation signal application module respectively, and is used to precisely lock the frequency and phase of the sinusoidal modulation signal onto the reference electrical signal; The state monitoring and mode discrimination module is connected to the output of the solid-state laser resonator and is used to monitor the mode-locking state and adjust the output of the modulation signal application module accordingly.

[0013] On the other hand, the present invention also provides an electronic device including a memory, a processor, and a computing program stored in the memory and executable on the processor, wherein the processor implements the method when executing the computing program.

[0014] On the other hand, the present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects: This invention achieves highly reliable self-starting and intelligent stable operation of a solid-state Kerr mode-locked laser by introducing resonant pump modulation and phase-locked loop (PLL) feedback control. Compared to existing technologies that rely on random disturbances or manual intervention, this invention actively "seeds" pulses during the startup phase by precisely locking the gain modulation to the cavity's intrinsic frequency, completely eliminating the randomness of mode-locking and achieving 100% reliable and rapid startup. Simultaneously, this invention integrates a state monitoring and mode discrimination module, which can evaluate the mode-locking state in real time and automatically adjust the modulation depth. This avoids the impact of modulation on long-term pulse quality and maintains weak modulation to enhance the system's anti-interference capability. Furthermore, the closed-loop control of the PLL ensures that the modulation frequency dynamically tracks cavity length drift caused by thermal effects and other factors, maintaining precise synchronization with the actual repetition frequency of the resonant cavity. This guarantees the long-term stability of the mode-locked pulse sequence, making it particularly suitable for unattended or demanding stability applications. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the system structure according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the method flow according to an embodiment of the present invention; The components include: 1. A first high-reflectivity mirror coated with a broadband dielectric film; 2. A first plano-concave lens; 3. A second plano-concave lens; 4. A first chirped mirror; 5. A pump source; 6. A second high-reflectivity mirror coated with a broadband dielectric film; 7. A second plano-concave lens; 8. A second chirped mirror; 9. An output mirror; 10. A first plano-convex lens; 11. A second plano-convex lens; 12. A Tee or adder; 13. A VCO; 14. An LF; 15. A bandpass filter; 16. A PD; and 17. A DDS or VCXO. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0019] Example 1 This embodiment provides a method and apparatus for self-starting a solid-state Kerr mode-locked laser based on resonant pump modulation feedback control, including: A solid-state laser resonator is provided, the solid-state laser resonator comprising a gain medium and a pump source; Generate a reference electrical signal with a frequency equal to the intrinsic repetition frequency of the solid-state laser resonator; A weak sinusoidal modulation signal with a frequency synchronized with the reference electrical signal is superimposed on the driving current of the pump source to perform periodic gain modulation on the pump light. The frequency and phase of the sinusoidal modulation signal are dynamically adjusted through a phase-locked loop feedback control circuit, so that it accurately tracks and locks onto the reference electrical signal. By utilizing the synergistic effect of the gain modulation and the intracavity Kerr nonlinearity, a stable mode-locked pulse sequence is established and maintained in the solid-state laser resonant cavity.

[0020] Specifically, it includes: This embodiment provides a self-starting device for a solid-state Kerr mode-locked laser based on resonant pump modulation feedback control. Its basic structure includes a laser cavity structure and a resonant pump modulation feedback control system.

[0021] The laser cavity structure adopts a standard X-type or Z-type folded cavity solid-state laser resonator. Its core components include: a first high-reflection mirror 1 coated with a broadband dielectric film, a first plano-concave lens 2, a second plano-concave lens 3, a first chirped mirror 4, a pump source 5, a second high-reflection mirror 6 coated with a broadband dielectric film, a second plano-concave lens 7, a second chirped mirror 8, an output mirror 9, a first plano-convex lens 10, a second plano-convex lens 11, a gain medium 18, and a hard or soft aperture for introducing losses. The pump light emitted from the pump source 5 is focused by the first plano-convex lens 10 and the second plano-convex lens 11 and then incident on the gain medium 18, which is a Brewster-angle-cut Kerr dielectric crystal.

[0022] The resonant pump modulation feedback control system mainly consists of a frequency reference generation module, a phase detection and feedback control module, a modulation signal application module, and a state monitoring module. Its core principle lies in directly modulating the pump source, i.e., using a feedback control circuit to apply a frequency equal to the cavity repetition frequency f to the drive current of the pump source 5 during startup. rep The weak sinusoidal modulation of the resonance utilizes the synergistic effect of this gain modulation and Kerr nonlinearity to actively seed pulses, thereby reliably initiating mode-locking.

[0023] Specifically, the frequency reference generation module is used to generate a highly stable frequency equal to the cavity fundamental frequency repetition frequency f. rep The reference electrical signal serves as the frequency reference for the entire system. There are two implementation methods: Method 1 is active detection, which involves setting up a high-speed photodetector 16, the output of which is connected to the input of a bandpass filter 15, with the output of the bandpass filter 15 serving as the frequency reference signal output. Method 2 is passive calculation, which involves setting up a direct digital frequency synthesizer or a voltage-controlled crystal oscillator 17, the output of which is directly used as the frequency reference signal output. Method 2 can be used initially, and then switched to Method 1 after mode-locking is established.

[0024] The modulation signal application module is used to superimpose the controlled modulation signal onto the drive current of the pump source. Its core component is a Tee or adder 12. The output of the voltage-controlled oscillator 13 is connected to the first input of the Tee or adder 12, the DC drive current source of the pump source 5 is connected to the second input of the Tee or adder 12, and the output of the Tee or adder 12 is connected to the drive current input of the pump source 5. This achieves the linear superposition of the DC bias current and the AC modulation signal to jointly drive the pump source 5. The modulation amplitude should be much smaller than the DC bias current, typically set to 1% to 5% of the DC bias current, to ensure that sufficient gain modulation is provided without disrupting the normal operation of the pump laser or introducing excessive noise.

[0025] The phase detection and feedback control module, as the core of the phase-locked loop, compares the phase of the modulation signal with the phase of the cavity repetition frequency signal, generates an error signal, and dynamically adjusts the modulation frequency f through a feedback loop. mod and phase φ, so that it is consistent with f rep Precise synchronization. This module includes a phase detector (not separately labeled in the diagram), a loop filter 14, and a voltage-controlled oscillator 13, which together form a complete phase-locked loop. The output of the frequency reference generation module comes from the bandpass filter 15 or DDS / VCXO 17 and is connected to the first input of the phase detector. The output of the voltage-controlled oscillator 13 is connected to the second input of the phase detector and the first input of the Tee or adder 12, and its output is also fed back to the phase detector to form a closed loop. The output of the phase detector is connected to the input of the loop filter 14, and the output of the loop filter 14 is connected to the control input of the voltage-controlled oscillator 13. The phase detector receives a reference signal f from the frequency reference generation module. rep and the feedback signal f from the voltage-controlled oscillator mod The loop filter 14 typically employs a proportional-integral controller to filter and integrate the error voltage, generating a smooth control voltage that determines the phase-locked loop's capture range, tracking speed, and stability. The output frequency f of the voltage-controlled oscillator 13 is... mod It is linearly controlled by the control voltage.

[0026] The state monitoring and mode discrimination module is used to automatically determine the mode-locking state and optimize or disable modulation after mode-locking is established to avoid negative impacts of modulation on long-term pulse stability. This module includes the high-speed photodetector 16, which is located at the laser output end and is used to monitor the radio frequency power spectrum of the output pulse. When a signal is detected at frequency f... repWhen a spike with an extremely high signal-to-noise ratio appears, it is determined that mode-locking has been stably established. The output of the high-speed photodetector 16 is also connected to a microprocessor or state discrimination circuit (not shown in the diagram) to execute subsequent control strategies.

[0027] This embodiment also includes an intelligent control unit, which can execute two control strategies after confirming mode-locking: Strategy A is attenuation modulation, which gradually reduces the modulation depth to an extremely low sustaining level or zero through a digitally controlled attenuator; Strategy B is sustaining modulation, which maintains a weak modulation to enhance the anti-interference capability of mode-locking.

[0028] The workflow of this embodiment is as follows: First, the system is powered on and initialized by applying a DC bias current slightly higher than the laser threshold to pump source 5. At the same time, the frequency reference generation module starts working, using a passive calculation method or attempting to capture any weak pulse signals that may exist.

[0029] Secondly, the search and capture process is initiated, the phase-locked loop starts working, and the voltage-controlled oscillator 13 outputs a frequency f. mod The scan is driven by the control voltage output from loop filter 14. When f mod The true repetition frequency f of the approximation cavity rep At that time, the phase-locked loop enters the capture range and quickly sets f mod Locked in f rep Up, and maintain phase synchronization.

[0030] The process then enters the resonant modulation and pulse shaping stage. At this time, the Tee or adder 12 superimposes the sinusoidal modulation signal output from the voltage-controlled oscillator 13 with the DC bias current to drive the pump source 5, so that the frequency and phase of the pump light gain are periodically modulated by precisely matched modulation. This modulation works synergistically with the Kerr nonlinear effect in the cavity, preferentially amplifying the noise fluctuations corresponding to the modulation peak, quickly "seeding" and establishing a stable mode-locked pulse sequence.

[0031] Finally, the system enters the stable operation phase. After the high-speed photodetector 16 in the status monitoring module detects a stable mode-locked signal, it adjusts the modulation depth according to the preset strategy, and the system enters a long-term stable operation state.

[0032] On the other hand, this embodiment also provides an electronic device, including a memory, a processor, and a computing program stored in the memory and executable on the processor, wherein the processor implements the method when executing the computing program.

[0033] On the other hand, this embodiment also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method.

[0034] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A self-starting method for a solid-state Kerr mode-locked laser based on resonant pump modulation feedback control, characterized in that, include: A solid-state laser resonator is provided, the solid-state laser resonator comprising a gain medium and a pump source; Generate a reference electrical signal with a frequency equal to the intrinsic repetition frequency of the solid-state laser resonator; A weak sinusoidal modulation signal with a frequency synchronized with the reference electrical signal is superimposed on the driving current of the pump source to perform periodic gain modulation on the pump light. The frequency and phase of the sinusoidal modulation signal are dynamically adjusted through a phase-locked loop feedback control circuit, so that it accurately tracks and locks onto the reference electrical signal. By utilizing the synergistic effect of the gain modulation and the intracavity Kerr nonlinearity, a stable mode-locked pulse sequence is established and maintained in the solid-state laser resonant cavity.

2. The method according to claim 1, characterized in that, The step of generating the reference electrical signal further includes: generating the reference electrical signal by means of an active detection method or a passive calculation method through a frequency reference generation module; The active detection method involves using a high-speed photodetector to detect the pulse sequence output by the solid-state laser resonator and extracting the fundamental frequency repetition frequency signal from it; the passive calculation method involves calculating an approximate value of the intrinsic repetition frequency based on the physical parameters of the solid-state laser resonator and generating a reference signal of the approximate value by a frequency synthesizer.

3. The method of claim 1, wherein, The step of superimposing a weak sinusoidal modulation signal onto the pump source drive current further includes: using a modulation signal application module to linearly superimpose an AC modulation current and a DC bias current to jointly drive the pump source, wherein the amplitude of the AC modulation current is less than 5% of the amplitude of the DC bias current.

4. The method of claim 1, wherein, The phase-locked loop feedback control circuit includes a phase detector, a loop filter, and a voltage-controlled oscillator; The phase detector receives the reference electrical signal and the feedback signal from the voltage-controlled oscillator, and outputs an error voltage that is proportional to the phase difference between the two. The loop filter filters the error voltage to generate a smooth control voltage. The voltage-controlled oscillator generates the sinusoidal modulation signal according to the control voltage, and outputs it to the modulation signal application module and the phase detector respectively, forming a closed-loop control.

5. The method of claim 4, wherein, The loop filter is a proportional-integral controller.

6. The method of claim 1, wherein, After the mode-locked pulse sequence is established, a state monitoring and mode discrimination module automatically determines the mode-locked state and adjusts the modulation depth of the sinusoidal modulation signal based on the determination result.

7. The method of claim 6, wherein, The step of automatically determining the mode-lock state further includes: using a high-speed photodetector to monitor the radio frequency power spectrum of the output pulse, and when a peak with a signal-to-noise ratio exceeding a preset threshold is detected at the intrinsic repetition frequency, it is determined that the mode-lock has been stably established.

8. The method of claim 6, wherein, The step of adjusting the modulation depth includes: after confirming mode-locking, gradually reducing the modulation depth of the sinusoidal modulation signal to zero or a preset maintenance level using a digitally controlled attenuator; The step of adjusting the modulation depth includes: after confirming mode-locking, maintaining a preset weak modulation depth to enhance the anti-interference capability of the mode-locked pulse sequence.

9. A self-starting device for a solid-state Kerr mode-locked laser based on resonant pump modulation feedback control for implementing the method of any one of claims 1-8, characterized in that, include: A solid-state laser resonator, which includes a gain medium and a pump source; A frequency reference generation module is used to generate a reference electrical signal with a frequency equal to the intrinsic repetition frequency of the solid-state laser resonator. A modulation signal application module, connected to the pump source, is used to superimpose a sinusoidal modulation signal onto the drive current of the pump source; A phase-locked loop feedback control module is connected to the frequency reference generation module and the modulation signal application module respectively, and is used to precisely lock the frequency and phase of the sinusoidal modulation signal onto the reference electrical signal; The state monitoring and mode discrimination module is connected to the output of the solid-state laser resonator and is used to monitor the mode-locking state and adjust the output of the modulation signal application module accordingly.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the method of any one of claims 1-8.

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