A wavelength-switchable intelligent mode-locked fiber laser system and its control method

Abstract

The present application relates to the field of laser control technology, and discloses a wavelength-switchable intelligent mode-locked fiber laser system and its control method. The system includes: a pump source, a neodymium-doped fiber excitation unit, a spatial light modulation unit, an optical coupling unit, a first adjustment unit, and a second adjustment unit; the neodymium-doped fiber excitation unit is connected to the spatial light modulation unit, the neodymium-doped fiber excitation unit is connected to the pump source, and the neodymium-doped fiber excitation unit is connected to the first adjustment unit; the optical coupling unit is connected to the spatial light modulation unit, the optical coupling unit is connected to the first adjustment unit, and the optical coupling unit is connected to the second adjustment unit; the second adjustment unit is connected to the first adjustment unit. The laser cavity loop can be iteratively adjusted so that the mode-locked state of the laser cavity loop reaches the desired preset mode-locked state, solving the problem that the existing neodymium-doped fiber laser technology only operates in the 0.9μm band or the 1.06μm band, resulting in serious limitations in the application field.

Description

Technical Field

[0001] The present application relates to the field of laser control technology, and in particular, to a wavelength-switchable intelligent mode-locked fiber laser system and a control method thereof. Background Art

[0002] At present, neodymium-doped quartz optical fiber combines the excellent thermal and mechanical properties of quartz glass with the rich absorption and emission spectra of neodymium ions, and is widely used in two-photon imaging, obtaining pure blue light, micro-nano processing and other fields.

[0003] Research on existing neodymium-doped fiber pulsed lasers has found that most operate solely in the 0.9μm or 1.06μm bands, severely limiting their application areas. Furthermore, due to the numerous mode-locked regions in mode-locked lasers, achieving a stable single-pulse mode-locked state has long been a challenging problem. Summary of the Invention

[0004] The present application provides a wavelength-switchable intelligent mode-locked fiber laser system and a control method thereof to solve one or more technical problems existing in the prior art and at least provide a beneficial option or create conditions.

[0005] Other features and advantages of the present application will become apparent from the following detailed description, or may be learned in part by practice of the present application.

[0006] According to one aspect of an embodiment of the present application, a wavelength-switchable intelligent mode-locked fiber laser system is proposed, which includes: a pump source, a neodymium-doped fiber excitation unit, a spatial light modulation unit, an optical coupling unit, a first adjustment unit, and a second adjustment unit; the output end of the neodymium-doped fiber excitation unit is connected to the input end of the spatial light modulation unit, the first input end of the neodymium-doped fiber excitation unit is connected to the pump source, and the second input end of the neodymium-doped fiber excitation unit is connected to the output end of the first adjustment unit; the input end of the optical coupling unit is connected to the output end of the spatial light modulation unit, the first output end of the optical coupling unit is connected to the input end of the first adjustment unit, and the second output end of the optical coupling unit is connected to the input end of the second adjustment unit; the output end of the second adjustment unit is connected to the first adjustment unit;

[0007] Wherein, the neodymium-doped fiber excitation unit receives the pump light emitted by the pump source, amplifies the pump light to obtain a gain light wave, and inputs the gain light wave into the spatial light modulation unit; the spatial light modulation unit modulates the gain light wave to form a stable light pulse; the light pulse is input into the optical coupling unit for coupling to obtain a coupled light pulse, and the coupled light pulse is respectively input into the first adjustment unit and the second adjustment unit, so that the second adjustment unit outputs the target control parameter of the first adjustment unit, so that the first adjustment unit outputs according to the target control parameter, so that the mode-locked state of the laser cavity loop formed by the neodymium-doped fiber excitation unit, the spatial light modulation unit, the optical coupling unit and the first adjustment unit reaches a preset mode-locked state.

[0008] In one embodiment of the present application, based on the aforementioned scheme, the neodymium-doped fiber excitation unit includes a beam combiner and a neodymium-doped fiber, the input end of the beam combiner is respectively connected to the output end of the pump source and the first adjustment unit, and the neodymium-doped fiber is arranged between the beam combiner and the spatial light modulation unit; wherein, the beam combiner is used to combine the optical signal emitted by the pump source and the optical signal emitted by the first adjustment unit to obtain pump light, and excite and amplify through the neodymium-doped fiber to obtain the gain light wave, and input the gain light wave into the spatial light modulation unit.

[0009] In one embodiment of the present application, based on the aforementioned scheme, the spatial light modulation unit includes a first collimator, a second collimator, a half-wave plate, a quarter-wave plate and a polarization beam splitter prism; the input end of the first collimator is connected to the neodymium-doped optical fiber, and the output end of the first collimator is connected to the half-wave plate; the half-wave plate, the quarter-wave plate and the polarization beam splitter prism are arranged in sequence, the polarizer beam splitter prism is connected to the input end of the second collimator, and the output end of the second collimator is connected to the input end of the optical coupling unit.

[0010] In one embodiment of the present application, based on the aforementioned scheme, the optical coupling unit includes a first single-mode optical fiber, a polarization-independent isolator, and a first coupler; the input end of the polarization-independent isolator and the output end of the second collimator are connected through the first single-mode optical fiber, and the output end of the polarization-independent isolator is connected to the input end of the first coupler; the first output end of the first coupler is connected to the input end of the first adjustment unit, and the second output end of the first coupler is connected to the input end of the second adjustment unit.

[0011] In one embodiment of the present application, based on the aforementioned solution, the first adjustment unit includes a second single-mode optical fiber, an electric polarization controller, and a third single-mode optical fiber; the input end of the second single-mode optical fiber is connected to the first output end of the first coupler, the output end of the second single-mode optical fiber is connected to the electric polarization controller, and the electric polarization controller is further connected to the output end of the second adjustment unit and the input end of the third single-mode optical fiber, and the output end of the third single-mode optical fiber is connected to the input end of the combiner;

[0012] The polarization state of the light wave output by the first adjustment unit can be adjusted by adjusting the voltage parameters applied to the electric polarization controller, so that the beam combiner outputs the target pump light according to the light pulse parameters and the light signal parameters emitted by the pump source, and the laser cavity circuit reaches the preset mode-locked state through the spatial light modulation unit and the optical coupling unit.

[0013] In one embodiment of the present application, based on the aforementioned solution, the second adjustment unit includes a second coupler, a portable spectrometer, a photodetector, a data acquisition card, an analysis unit, and a digital-to-analog converter, wherein the input end of the second coupler is connected to the second output end of the first coupler, the first output end of the second coupler is connected to the portable spectrometer, and the second output end of the second coupler is connected to the photodetector; the data acquisition card is connected to the photodetector and the analysis unit respectively; the portable spectrometer is connected to the analysis unit, and the digital-to-analog converter is connected to the analysis unit;

[0014] The portable spectrometer is used to identify the spectral parameters of the coupled light pulses, the data acquisition card is used to collect the coupled light pulses detected by the photodetector and convert them into electrical signals, and input the electrical signals into the analysis unit so that the analysis unit can identify the waveform of the coupled light pulses; the analysis unit is used to determine the target voltage parameters required to achieve the preset mode-locked state based on the spectral parameters and the waveform, and convert the target voltage parameters in the form of digital signals into target voltage analog signals in the form of analog signals, so that the electric polarization controller can adjust its own voltage parameters according to the target voltage analog signals to output the adjusted light signal to the beam combiner, so that the beam combiner can perform cyclic laser modulation according to the adjusted light signal and the light signal emitted by the pump source until the laser cavity loop reaches the preset mode-locked state.

[0015] According to one aspect of an embodiment of the present application, a control method for a wavelength-switchable intelligent mode-locked fiber laser system is proposed. The method is executed in an analysis unit of the wavelength-switchable intelligent mode-locked fiber laser system as described in the above embodiment, and the method includes:

[0016] receiving spectral parameters sent by a portable spectrometer, wherein the spectral parameters are obtained by the portable spectrometer identifying the optical pulses output by the coupler;

[0017] receiving a waveform sent by a data acquisition card, wherein the waveform is obtained by detecting the light pulse output by the coupler by a photoelectric detector;

[0018] determining whether the optical pulse output by the coupler reaches a preset mode-locked state according to the spectral parameters and the waveform;

[0019] If the optical pulse output by the coupler does not reach the preset mode-locked state, determining a target control parameter of the first adjustment unit according to the spectral parameter and the waveform;

[0020] The target control parameter is sent to a digital-to-analog converter, so that the digital-to-analog converter converts the target control parameter in the form of a digital signal into a target voltage analog signal in the form of an analog signal, so that the digital-to-analog converter inputs the target voltage analog signal to the first adjustment unit, so that the first adjustment unit cyclically modulates the optical signal according to the target voltage analog signal until the laser cavity loop of the wavelength-switchable intelligent mode-locked fiber laser system reaches the preset mode-locked state.

[0021] Beneficial effects of this application:

[0022] The pump source of the present application can output a corresponding driving current to the Nd-doped fiber excitation unit based on the required power, thereby outputting corresponding pump light, so that the Nd-doped fiber excitation unit can amplify the pump light to obtain a gain light wave, which is then input into the spatial light modulation unit. The spatial light modulation unit is used to modulate the polarization state of the gain light wave, thereby forming a stable light pulse, which is then input into the optical coupling unit for coupling to obtain a coupled light pulse.

[0023] The coupled light pulses are respectively inputted into the first regulating unit and the second regulating unit so that the second regulating unit outputs the target control parameters of the first regulating unit, and the first regulating unit performs output according to the target control parameters, so that the mode-locked state of the laser cavity loop formed by the neodymium-doped fiber excitation unit, the spatial light modulation unit, the optical coupling unit and the first regulating unit reaches a preset mode-locked state.

[0024] Therefore, the output parameters of the first adjustment unit can be controlled by the second adjustment unit, so that the first adjustment unit can search for the mode-locked states of different bands under the target control parameters, that is, search for the preset mode-locked state and output it cyclically to the neodymium-doped fiber excitation unit through the first adjustment unit, that is, iterative adjustment of the laser cavity loop, and finally the mode-locked state of the laser cavity loop reaches the required mode-locked state, which solves the problem that most of the existing technologies only work in the 0.9μm band or the 1.06μm band, resulting in severely limited application fields.

[0025] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are incorporated into and constitute a part of the specification, illustrating embodiments consistent with the present application and, together with the specification, explaining the principles of the present application. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can derive other drawings based on these drawings without inventive effort. In the drawings:

[0027] Figure 1 A schematic diagram of a wavelength-switchable intelligent mode-locked fiber laser system provided in an embodiment of the present application;

[0028] Figure 2 An overall schematic diagram of a wavelength-switchable intelligent mode-locked fiber laser system provided in an embodiment of the present application;

[0029] Figure 3 The energy level structure diagram of neodymium ions provided in the embodiments of the present application;

[0030] Figure 4 Spectrum diagram of neodymium-doped quartz glass and neodymium-doped optical fiber provided in the embodiments of the present application;

[0031] Figure 5 This is a genetic algorithm logic diagram of a control method for a wavelength-switchable intelligent mode-locked fiber laser system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0032] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this application will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art.

[0033] In addition, described feature, structure or characteristic can be combined in one or more embodiments in any suitable manner.In the following description, many specific details are provided so as to provide a full understanding of the embodiments of the present application. However, it will be appreciated by those skilled in the art that the technical scheme of the present application can be put into practice without one or more of the specific details, or other methods, components, devices, steps etc. can be adopted. In other cases, known methods, devices, implementations or operations are not shown or described in detail to avoid blurring the various aspects of the application.

[0034] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically separate entities. That is, these functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or micro-controller node devices.

[0035] The flowcharts shown in the accompanying drawings are for illustrative purposes only and do not necessarily include all contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps may be decomposed, while others may be combined or partially combined. Therefore, the actual execution order may vary depending on the actual situation.

[0036] It should be noted that the term "plurality" used in this document refers to two or more. "And / or" describes a relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B together, or B alone. The character " / " generally indicates an "or" relationship between the associated objects.

[0037] Neodymium-doped fiber is an important laser material, and its energy level structure is crucial to understanding the working principle of neodymium-doped fiber mode-locked laser. Figure 3 As shown. Usually, the 808nm and 888nm bands correspond to the two main absorption peaks of neodymium ions. Neodymium ions have three emission lines corresponding to the central wavelengths of 0.9μm, 1.06μm and 1.34μm. 4 F 3 / 2 The radiative transition of neodymium ions to 4 I 11 / 2

[0038] When the energy level is 1060nm, a laser with a wavelength of 1060nm will be generated. Usually, the laser gain of 1060nm is the strongest. This is because it belongs to a four-level system. The lower energy level of the transition is not the ground state, which makes it easier to achieve particle number inversion. 4 I 9 / 2When the energy level is high, a laser with a wavelength of 920nm will be generated. It belongs to a three-level system. Compared with the four-level system, the transition is much weaker. This is due to Stark splitting. 4 I 9 / 2 Split into 4 sub-levels, the particle first jumps to the higher energy level of the sub-level, and then jumps to the lowest sub-level without radiation. 4 I 13 / 2 When the excited state energy level is high, laser in the 1340nm band will be generated. Since the excited state energy level has a strong effect of absorbing signal light, it is difficult to form laser oscillation in this band.

[0039] Figure 4 (a) shows the absorption spectrum of neodymium-doped quartz glass. Multiple absorption peaks exist within the 300-1200nm spectral range, with the dominant absorption peak occurring at 590nm. 590nm dye lasers were initially used as pump sources for 900nm neodymium-doped lasers. However, short-wavelength pumping suffers from large quantum losses, excessive heat generation, and low theoretical efficiency. With the rapid development of near-infrared semiconductor lasers, 808nm semiconductor lasers have gradually become the ideal pump source for neodymium-doped lasers. Figure 4 (b) shows the emission spectrum of the neodymium-doped fiber. The emission peaks are mainly concentrated at 0.9μm and 1.06μm, and the proportion at 1.3μm is very small and can be ignored. The emission near 0.9μm covers a spectral width of 850nm-950nm, so it has good wavelength tunability. However, 1.0μm is a four-level structure with a low laser threshold, which makes the ASE of 1.06μm have a greater impact on the 0.9μm laser, and is an important factor limiting the output energy of the 0.9μm laser. Therefore, how to ensure the stable operation of the neodymium-doped fiber in the three-level (0.9μm) or four-level mode (1.06μm) and effectively suppress the competition from other energy levels is a key problem to be solved by neodymium-doped fiber lasers. The present invention utilizes a cone-shaped coiling method, wrapping a neodymium-doped gain fiber from bottom to top around a truncated cone with a diameter of 15 cm at the bottom and 8 cm at the top. This effectively suppresses laser emission at 1.06 μm, ensuring that the excitation intensities of the three-level and four-level modes are similar. Finally, by utilizing nonlinear polarization rotation (NPR) technology and adjusting the polarization state of the laser within the cavity and the power of the pump source, single-pulse mode-locking in the 0.9 μm and 1.06 μm bands, as well as dual-wavelength mode-locking in the 0.9 μm and 1.06 μm bands, can be achieved in the pulsed fiber laser system.

[0040] The following is a detailed description of the implementation details of the technical solution of the embodiment of the present application:

[0041] According to one aspect of the embodiments of the present application, a wavelength-switchable intelligent mode-locked fiber laser system is provided. Figure 1 A specific schematic diagram of a wavelength-switchable intelligent mode-locked fiber laser system provided in an embodiment of the present application, Figure 2 This is an overall block diagram of the wavelength-switchable intelligent mode-locked fiber laser system provided in an embodiment of the present application. The following is a detailed introduction to the wavelength-switchable intelligent mode-locked fiber laser system:

[0042] A wavelength-switchable intelligent mode-locked fiber laser system includes: a pump source, a neodymium-doped fiber excitation unit, a spatial light modulation unit, an optical coupling unit, a first adjustment unit, and a second adjustment unit; the output end of the neodymium-doped fiber excitation unit is connected to the input end of the spatial light modulation unit, the first input end of the neodymium-doped fiber excitation unit is connected to the pump source, and the second input end of the neodymium-doped fiber excitation unit is connected to the output end of the first adjustment unit; the input end of the optical coupling unit is connected to the output end of the spatial light modulation unit, the first output end of the optical coupling unit is connected to the input end of the first adjustment unit, and the second output end of the optical coupling unit is connected to the input end of the second adjustment unit; and the output end of the second adjustment unit is connected to the first adjustment unit.

[0043] Wherein, the neodymium-doped fiber excitation unit receives the pump light emitted by the pump source, amplifies the pump light to obtain a gain light wave, and inputs the gain light wave into the spatial light modulation unit; the spatial light modulation unit modulates the gain light wave to form a stable light pulse; the light pulse is input into the optical coupling unit for coupling to obtain a coupled light pulse, and the coupled light pulse is respectively input into the first adjustment unit and the second adjustment unit, so that the second adjustment unit outputs the target control parameter of the first adjustment unit, so that the first adjustment unit outputs according to the target control parameter, so that the mode-locked state of the laser cavity loop formed by the neodymium-doped fiber excitation unit, the spatial light modulation unit, the optical coupling unit and the first adjustment unit reaches a preset mode-locked state.

[0044] Specifically, the pump source can be an 808nm pump source. The pump source of the present application can output a corresponding driving current to the neodymium-doped fiber excitation unit based on the required power, thereby outputting corresponding pump light, so that the neodymium-doped fiber excitation unit can amplify the pump light to obtain a gain light wave, which is input into the spatial light modulation unit. The spatial light modulation unit is used to modulate the polarization state of the gain light wave to form a stable light pulse, and then input the light pulse into the optical coupling unit for coupling to obtain a coupled light pulse.

[0045] The coupled light pulses are respectively inputted into the first regulating unit and the second regulating unit so that the second regulating unit outputs the target control parameters of the first regulating unit, and the first regulating unit performs output according to the target control parameters, so that the mode-locked state of the laser cavity loop formed by the neodymium-doped fiber excitation unit, the spatial light modulation unit, the optical coupling unit and the first regulating unit reaches a preset mode-locked state.

[0046] Therefore, the output parameters of the first adjustment unit can be controlled by the second adjustment unit, so that the first adjustment unit can search for the mode-locked states of different bands under the target control parameters, that is, search for the preset mode-locked state and output it cyclically to the neodymium-doped fiber excitation unit through the first adjustment unit, that is, iterative adjustment of the laser cavity loop, and finally the mode-locked state of the laser cavity loop reaches the required mode-locked state, which solves the problem that most of the existing technologies work in a single 0.9μm band or a small amount work in the 1.06μm band, and the application fields are severely limited.

[0047] In one embodiment of the present application, the neodymium-doped fiber excitation unit includes a beam combiner and a neodymium-doped fiber, the input end of the beam combiner is respectively connected to the output end of the pump source and the first adjustment unit, and the neodymium-doped fiber is arranged between the beam combiner and the spatial light modulation unit; wherein, the beam combiner is used to combine the optical signal emitted by the pump source and the optical signal emitted by the first adjustment unit to obtain pump light, and excite and amplify through the neodymium-doped fiber to obtain the gain light wave, and input the gain light wave into the spatial light modulation unit.

[0048] Specifically, the 808nm pump source is combined through the combiner to achieve wave combining and excite the neodymium-doped fiber, thereby inverting the number of particles in the neodymium-doped fiber, and finally obtaining a gain with a central wavelength of 920nm or a gain of 1064nm. The driving current of the 808nm pump source can be set and the target control parameters of the first adjustment unit can be adjusted. After multiple rounds of iterative cycles, the required 920nm single-wavelength mode-locking or 1064nm single-wavelength mode-locking can be obtained, and dual-wavelength mode-locking can be achieved simultaneously in the 920nm and 1064nm bands.

[0049] Furthermore, the spatial light modulation unit includes a first collimator, a second collimator, a half-wave plate, a quarter-wave plate and a polarization beam splitter prism; the input end of the first collimator is connected to the neodymium-doped optical fiber, and the output end of the first collimator is connected to the half-wave plate; the half-wave plate, the quarter-wave plate and the polarization beam splitter prism are arranged in sequence, the polarizer beam splitter prism is connected to the input end of the second collimator, and the output end of the second collimator is connected to the input end of the optical coupling unit.

[0050] Specifically, the quarter-wave plate (λ / 4) is used to convert elliptically polarized light into linearly polarized light; the half-wave plate (λ / 2) is used to adjust the polarization state of linearly polarized light; the polarization beam splitter (PBS) allows light of a specific polarization state to pass through; the 980nm polarization-independent isolator ensures unidirectional transmission of 0.9μm and 1.06μm light waves in the laser cavity loop; the spatial light modulation unit and the optical coupling unit provide a mode-locking mechanism for the laser system to enable the formation of stable transmission light pulses in the laser. The first collimator can be specifically Figure 1 The collimator 1 in the embodiment of the present invention can be specifically Figure 1 Collimator 2 in.

[0051] In one embodiment of the present application, the optical coupling unit includes a first single-mode optical fiber, a polarization-independent isolator and a first coupler; the input end of the polarization-independent isolator and the output end of the second collimator are connected through the first single-mode optical fiber, and the output end of the polarization-independent isolator is connected to the input end of the first coupler; the first output end of the first coupler is connected to the input end of the first adjustment unit, and the second output end of the first coupler is connected to the input end of the second adjustment unit.

[0052] Specifically, the first single-mode optical fiber can be specifically Figure 1 The single-mode optical fiber 1 in the polarization-independent isolator can be specifically Figure 1 The 980nm polarization-independent isolator and the first coupler can be specifically Figure 1 Coupler 1 in.

[0053] In one embodiment of the present application, the first adjustment unit includes a second single-mode optical fiber, an electric polarization controller, and a third single-mode optical fiber; the input end of the second single-mode optical fiber is connected to the first output end of the first coupler, the output end of the second single-mode optical fiber is connected to the electric polarization controller, the electric polarization controller is further connected to the output end of the second adjustment unit and the input end of the third single-mode optical fiber, and the output end of the third single-mode optical fiber is connected to the input end of the combiner;

[0054] The polarization state of the light wave output by the first adjustment unit can be adjusted by adjusting the voltage parameters applied to the electric polarization controller, so that the beam combiner outputs the target pump light according to the light pulse parameters and the light signal parameters emitted by the pump source, and the laser cavity circuit reaches the preset mode-locked state through the spatial light modulation unit and the optical coupling unit.

[0055] Specifically, the second single-mode optical fiber can be specifically Figure 1 The single-mode optical fiber 2 in the embodiment of the present invention, the third single-mode optical fiber can be specifically Figure 1In the single-mode optical fiber 3, the electric polarization controller can be specifically Figure 1 The EPC in the laser cavity can adjust the polarization state of the light wave in the laser cavity loop through the electric polarization controller (EPC). It has a three-loop DC voltage control. That is, the target control parameter has three voltage parameters to control the electric polarization controller, and then adjust the polarization state of the light wave in the laser cavity loop, that is, the mode-locked state in the laser.

[0056] In one embodiment of the present application, the second adjustment unit includes a second coupler, a portable spectrometer, a photodetector, a data acquisition card, an analysis unit, and a digital-to-analog converter, wherein the input end of the second coupler is connected to the second output end of the first coupler, the first output end of the second coupler is connected to the portable spectrometer, and the second output end of the second coupler is connected to the photodetector; the data acquisition card is connected to the photodetector and the analysis unit respectively; the portable spectrometer is connected to the analysis unit, and the digital-to-analog converter is connected to the analysis unit;

[0057] The portable spectrometer is used to identify the spectral parameters of the coupled light pulses, the data acquisition card is used to collect the coupled light pulses detected by the photodetector and convert them into electrical signals, and input the electrical signals into the analysis unit so that the analysis unit can identify the waveform of the coupled light pulses; the analysis unit is used to determine the target voltage parameters required to achieve the preset mode-locked state based on the spectral parameters and the waveform, and convert the target voltage parameters in the form of digital signals into target voltage analog signals in the form of analog signals, so that the electric polarization controller can adjust its own voltage parameters according to the target voltage analog signals to output the adjusted light signal to the beam combiner, so that the beam combiner can perform cyclic laser modulation according to the adjusted light signal and the light signal emitted by the pump source until the laser cavity loop reaches the preset mode-locked state.

[0058] Specifically, the first adjustment unit is a device in the laser cavity loop inside the laser, while the second adjustment unit is a device outside the laser cavity. The analysis unit included therein can be a terminal device such as a personal computer or a personal mobile phone that can perform analysis and processing. The second coupler can be specifically Figure 1 The coupler 2 in the photodetector can be specifically Figure 1 The PD in the digital-to-analog converter can be specifically Figure 1 The DAC in the

[0059] Furthermore, the coupler 1 outputs part of the laser cavity loop's light outside the laser cavity through the first coupler's second output port 2, while the first coupler's first output port 1 continues to receive light pulses from the laser cavity loop and input them into the EPC for regulation. Coupler 2 splits the laser into two beams, each used to detect different characteristics of the laser (the coupled light pulse).

[0060] The photodetector (PD) converts light pulses into electrical signals, and the high-speed data acquisition card converts analog signals into digital signals for further processing and analysis. The portable spectrometer decomposes complex light into spectral curves; the digital-to-analog converter (DAC) converts digital signals into analog signals. The personal computer serves as the main control center, responsible for running the genetic algorithm (GA), processing and transmitting spectral data and pulse sequence data (pulse sequence data is collected by the data acquisition card), and controlling the digital-to-analog converter (DAC) to output a specific three-ring voltage (i.e., the target voltage parameter or target voltage analog signal described in the embodiments of this application).

[0061] In summary, the principle of the entire wavelength-switchable intelligent mode-locked fiber laser system is explained in detail:

[0062] like Figure 1As shown, single-mode fiber 1, single-mode fiber 2, and single-mode fiber 3 are connected to various devices to form a ring resonator (i.e., the laser cavity loop described in this application); neodymium-doped fiber serves as a gain medium; a 980nm polarization-independent isolator simultaneously ensures unidirectional transmission of 0.9μm and 1.06μm optical pulses. An 808nm pump source serves as an external pump source; a quarter-wave plate (λ / 4), a half-wave plate (λ / 2), a polarization beam splitter prism (PBS), and a 980nm polarization-independent isolator are used to form a polarization-dependent isolator, and the laser cavity loop forms a mode-locked pulse by relying on nonlinear polarization rotation (NPR) technology. By adjusting the input power and polarization state of the 808nm pump source, the laser (laser cavity loop) can be made to operate in a mode-locked state in different wavelength bands (such as 0.9μm, 1.06μm, etc.). Finally, a portable spectrometer was used to receive the spectrum output by the laser (laser cavity loop) and the pulse waveforms acquired by a high-speed acquisition card to identify and determine the mode-locked state of different bands. A personal computer was used to control the waveforms of the acquired spectrum and pulse sequence. A fitness function was constructed based on this, and a genetic algorithm (GA) was used to adjust the three DAC voltages (target control parameters) applied to the electric polarization controller and the drive current of the 808nm pump to search for the mode-locked state of the set band. Furthermore, single-pulse mode-locking in the 0.9μm and 1.06μm bands and dual-wavelength mode-locking in the 0.9μm and 1.06μm bands were achieved in a single laser cavity.

[0063] According to one aspect of an embodiment of the present application, a control method for a wavelength-switchable intelligent mode-locked fiber laser system is provided. The method is executed in an analysis unit of the wavelength-switchable intelligent mode-locked fiber laser system as described in the above embodiment, and the method includes the following steps:

[0064] S1, receiving spectral parameters sent by a portable spectrometer, where the spectral parameters are obtained by the portable spectrometer identifying light pulses output by a coupler;

[0065] S2, receiving the waveform sent by the data acquisition card, wherein the waveform is obtained by detecting the light pulse output by the coupler by the photodetector;

[0066] S3, judging whether the optical pulse output by the coupler reaches a preset mode-locked state according to the spectral parameters and the waveform;

[0067] S4, if the optical pulse output by the coupler does not reach the preset mode-locked state, determining a target control parameter of the first adjustment unit according to the spectral parameter and the waveform;

[0068] S5, sending the target control parameter to the digital-to-analog converter, so that the digital-to-analog converter converts the target control parameter in the form of a digital signal into a target voltage analog signal in the form of an analog signal, so that the digital-to-analog converter inputs the target voltage analog signal to the first adjustment unit, so that the first adjustment unit cyclically modulates the optical signal according to the target voltage analog signal until the laser cavity loop of the wavelength-switchable intelligent mode-locked fiber laser system reaches the preset mode-locked state.

[0069] Specifically, by receiving the spectral parameters sent by the portable spectrometer and the waveform sent by the data acquisition card, it can be determined whether the light pulse output by the coupler has reached the preset mode-locked state. The preset mode-locked state can be set according to needs. If the light pulse output by the coupler has not reached the preset mode-locked state, then the target control parameters of the first adjustment unit, that is, the three DAC voltages mentioned above, are determined, and the EPC can be controlled to output the corresponding light wave. By adjusting the output power of the pump source, the beam combiner can receive the light wave emitted by the pump source and the light wave adjusted by the EPC, and then combine the two input light waves for the next round of iterative cycles. By continuously performing self-adjustment and analysis through the personal computer (analysis unit), until the preset mode-locked state is reached in the laser cavity after multiple rounds of iterative cycles, the technical limitations of the single mode-locked state in the prior art are solved in turn.

[0070] In a genetic algorithm (GA), potential solutions to an optimization problem are defined as individuals, with a set of individuals forming a population. In this paper, the three control voltages of an electronic polarization controller (EPC) are used as the genes of the individuals. By simulating the genetic processes of biological evolution, such as selection, crossover, and mutation, the individuals in the population evolve with each generation, their fitness continuously improving, and they gradually converge toward the optimal solution in the mode-locking parameter space.

[0071] The electrically controlled polarization controller (EPC) is used as the core tuning device of the laser cavity, supplemented by the current regulation of the pump source. The spectral characteristic data collected by the portable spectrometer, the number of pulses collected by the high-speed data acquisition card, and the flatness of the pulse sequence on a large time scale are used as the fitness evaluation function for determining the mode locking. For example, Figure 5 As shown, the specific process is as follows:

[0072] 1. Initialization: First, the desired mode-locking wavelength is set (i.e., the target mode-locking wavelength in the preset mode-locking state). Next, an initial population of individuals with genes is randomly generated. In this application, an individual is a lasing state associated with a nonlinear transfer function defined by three control voltages applied to the EPC; therefore, these voltages are defined as the genes of the individual. The process begins with a set of individuals or "populations" (constituting the first generation), each of which contains a set of randomly assigned genes.

[0073] Second, each individual gene is applied to an electronic polarizer (EPC) via a digital-to-analog converter (DAC), and its corresponding fitness value is recorded using an evaluation function. A portable spectrometer and a high-speed data acquisition card record the data output by the laser and input it into a computer.

[0074] 3. Use a computer to calculate and record the fitness value of each individual through the evaluation function.

[0075] Fourth, based on the fitness of individuals in the population, a "roulette wheel" method is used to select individuals from the population. Individuals with higher fitness are more likely to be selected, ensuring that excellent genes have a greater chance of being passed on to the next generation.

[0076] Fifth, the selected individuals are then subjected to a crossover process, recombining portions of the genes of the two parent individuals to generate new offspring individuals. During each crossover, multiple crossover points are randomly selected from the genetic codes of the two parent individuals. The gene segments between these crossover points are exchanged to generate two new offspring individuals. This method effectively increases population diversity and prevents the algorithm from prematurely falling into local optima.

[0077] Sixth, the newly generated offspring individuals are mutated. By randomly flipping some of their genes, randomness is introduced to improve the population's comprehensive exploration capabilities. The mutation probability is determined by the maximum fitness value in the current iteration. When the fitness value is low, the system increases the mutation probability to promote convergence to unexplored parameter regions; when the fitness value is high, the mutation probability is reduced to ensure search stability. The mutation operation ensures a thorough and comprehensive exploration of the search space, preventing the algorithm from prematurely converging on a local suboptimal solution. If the optimal fitness value of the population remains unchanged for multiple times, the current of the 808nm pump source is adjusted to increase search diversity and prevent the algorithm from prematurely convergence.

[0078] 7. Determine whether the optimal fitness value has reached the set value. If so, exit the algorithm; otherwise, enter the next cycle. To prevent the optimal solution from being destroyed during crossover or mutation, the present invention employs an elite retention strategy. In each generation of genetic operations, the two individuals with the highest fitness are directly retained for the next generation, ensuring that these outstanding individuals are not eliminated. This elite retention strategy effectively accelerates the algorithm's convergence process while ensuring its stability during the search process.

[0079] In summary, 1. The neodymium-doped optical fiber of the present application adopts a conical winding method, in which the neodymium-doped gain optical fiber is wound from bottom to top on a truncated cone with a bottom diameter of 15 cm and a top diameter of 8 cm. This can effectively suppress the 1.06 μm laser emission, making the excitation intensity of the three-level mode and the four-level mode similar, creating conditions for achieving multi-wavelength mode locking.

[0080] 2. A dual-wavelength switchable intelligent mode-locked pulse fiber laser system in an embodiment of the present application can intelligently and quickly output 920nm or 1064nm mode-locked pulses individually or simultaneously, solving the problems of high cost, complex system, and difficult adjustment caused by the need for multiple lasers in previous two-photon imaging. This solution has important application value in multi-photon imaging.

[0081] In the description of this application, it should be noted that the terms "upper", "lower", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application; unless otherwise clearly specified and limited, the terms "install", "connect", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediary medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0082] The apparatus includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or apparatus; in the absence of further limitations, an element defined by the phrase "comprising a..." does not preclude the presence of other identical elements in the process, method, article or apparatus that includes the element.

[0083] The above description is only a specific implementation method of the present application, which is convenient for those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined in this document can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown in this document, but will conform to the widest scope consistent with the principles and novel features of the application in this document.

Claims

1. A wavelength-switchable intelligent mode-locked fiber laser system, characterized in that: include: A pump source, a neodymium-doped fiber excitation unit, a spatial light modulation unit, an optical coupling unit, a first adjustment unit and a second adjustment unit; The output end of the Nd-doped fiber excitation unit is connected to the input end of the spatial light modulation unit, the first input end of the Nd-doped fiber excitation unit is connected to the pump source, and the second input end of the Nd-doped fiber excitation unit is connected to the output end of the first adjustment unit; the input end of the optical coupling unit is connected to the output end of the spatial light modulation unit, the first output end of the optical coupling unit is connected to the input end of the first adjustment unit, and the second output end of the optical coupling unit is connected to the input end of the second adjustment unit; the output end of the second adjustment unit is connected to the first adjustment unit; The neodymium-doped fiber excitation unit receives the pump light emitted by the pump source, amplifies the pump light to obtain a gain light wave, and inputs the gain light wave into the spatial light modulation unit; the spatial light modulation unit modulates the gain light wave to form a stable light pulse; The light pulse is input into the optical coupling unit for coupling to obtain a coupled light pulse, and the coupled light pulse is respectively input into the first adjustment unit and the second adjustment unit so that the second adjustment unit outputs the target control parameter of the first adjustment unit, so that the first adjustment unit outputs according to the target control parameter, so that the mode-locked state of the laser cavity loop formed by the neodymium-doped fiber excitation unit, the spatial light modulation unit, the optical coupling unit and the first adjustment unit reaches a preset mode-locked state.

2. The wavelength-switchable intelligent mode-locked fiber laser system according to claim 1, characterized in that: The neodymium-doped fiber excitation unit includes a beam combiner and a neodymium-doped fiber, the input end of the beam combiner is respectively connected to the output end of the pump source and the first adjustment unit, and the neodymium-doped fiber is arranged between the beam combiner and the spatial light modulation unit; wherein, the beam combiner is used to combine the optical signal emitted by the pump source and the optical signal emitted by the first adjustment unit to obtain pump light, and excite and amplify through the neodymium-doped fiber to obtain the gain light wave, and input the gain light wave into the spatial light modulation unit.

3. The wavelength-switchable intelligent mode-locked fiber laser system according to claim 2, characterized in that: The spatial light modulation unit includes a first collimator, a second collimator, a half-wave plate, a quarter-wave plate and a polarization beam splitter prism; the input end of the first collimator is connected to the neodymium-doped optical fiber, and the output end of the first collimator is connected to the half-wave plate; the half-wave plate, the quarter-wave plate and the polarization beam splitter prism are arranged in sequence, the polarization beam splitter prism is connected to the input end of the second collimator, and the output end of the second collimator is connected to the input end of the optical coupling unit.

4. The wavelength-switchable intelligent mode-locked fiber laser system according to claim 3, characterized in that: The optical coupling unit includes a first single-mode optical fiber, a polarization-independent isolator, and a first coupler; the input end of the polarization-independent isolator and the output end of the second collimator are connected via the first single-mode optical fiber, and the output end of the polarization-independent isolator is connected to the input end of the first coupler; the first output end of the first coupler is connected to the input end of the first adjustment unit, and the second output end of the first coupler is connected to the input end of the second adjustment unit.

5. The wavelength-switchable intelligent mode-locked fiber laser system according to claim 4, characterized in that: The first adjustment unit includes a second single-mode optical fiber, an electric polarization controller, and a third single-mode optical fiber; the input end of the second single-mode optical fiber is connected to the first output end of the first coupler, the output end of the second single-mode optical fiber is connected to the electric polarization controller, the electric polarization controller is also connected to the output end of the second adjustment unit and the input end of the third single-mode optical fiber, and the output end of the third single-mode optical fiber is connected to the input end of the combiner; The polarization state of the light wave output by the first adjustment unit can be adjusted by adjusting the voltage parameters applied to the electric polarization controller, so that the beam combiner outputs the target pump light according to the light pulse parameters and the light signal parameters emitted by the pump source, and the laser cavity circuit reaches the preset mode-locked state through the spatial light modulation unit and the optical coupling unit.

6. The wavelength-switchable intelligent mode-locked fiber laser system according to claim 5, characterized in that: The second adjustment unit includes a second coupler, a portable spectrometer, a photodetector, a data acquisition card, an analysis unit, and a digital-to-analog converter, wherein the input end of the second coupler is connected to the second output end of the first coupler, the first output end of the second coupler is connected to the portable spectrometer, and the second output end of the second coupler is connected to the photodetector; the data acquisition card is connected to the photodetector and the analysis unit respectively; the portable spectrometer is connected to the analysis unit, and the digital-to-analog converter is connected to the analysis unit; The portable spectrometer is used to identify the spectral parameters of the coupled light pulses, the data acquisition card is used to collect the coupled light pulses detected by the photodetector and convert them into electrical signals, and input the electrical signals into the analysis unit so that the analysis unit can identify the waveform of the coupled light pulses; the analysis unit is used to determine the target voltage parameters required to achieve the preset mode-locked state based on the spectral parameters and the waveform, and convert the target voltage parameters in the form of digital signals into target voltage analog signals in the form of analog signals, so that the electric polarization controller can adjust its own voltage parameters according to the target voltage analog signals to output the adjusted light signal to the beam combiner, so that the beam combiner can perform cyclic laser modulation according to the adjusted light signal and the light signal emitted by the pump source until the laser cavity loop reaches the preset mode-locked state.

7. A control method for a wavelength-switchable intelligent mode-locked fiber laser system, characterized in that: The method is performed in an analysis unit of the wavelength-switchable intelligent mode-locked fiber laser system according to any one of claims 1 to 6, and the method comprises: receiving spectral parameters sent by a portable spectrometer, wherein the spectral parameters are obtained by the portable spectrometer identifying the optical pulses output by the coupler; receiving a waveform sent by a data acquisition card, wherein the waveform is obtained by detecting the light pulse output by the coupler by a photoelectric detector; determining whether the optical pulse output by the coupler reaches a preset mode-locked state according to the spectral parameters and the waveform; If the optical pulse output by the coupler does not reach the preset mode-locked state, determining a target control parameter of the first adjustment unit according to the spectral parameter and the waveform; The target control parameter is sent to a digital-to-analog converter, so that the digital-to-analog converter converts the target control parameter in the form of a digital signal into a target voltage analog signal in the form of an analog signal, so that the digital-to-analog converter inputs the target voltage analog signal to the first adjustment unit, so that the first adjustment unit cyclically modulates the optical signal according to the target voltage analog signal until the laser cavity loop of the wavelength-switchable intelligent mode-locked fiber laser system reaches the preset mode-locked state.

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