Temporally and spatially mode-locked fiber laser with adjustable spot size based on intracavity phase modulation

Abstract

The present invention discloses a spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation. The laser comprises a multimode fiber ring cavity, within which is disposed an intracavity dynamic phase modulation system for applying phase modulation to the light field within the multimode fiber ring cavity. The laser also comprises a feedback control unit that collects the output spot of the multimode fiber ring cavity and obtains the mode decomposition results and time-domain mode-locking results of the output spot. The feedback control unit uses these mode decomposition results and time-domain mode-locking results as objective functions, runs an optimization algorithm to generate a phase control signal for the intracavity dynamic phase modulation system, and forms a closed-loop control until a target light field is obtained, with both the spot pattern and time-domain mode-locking stability meeting target requirements. The present invention can flexibly generate mode-locked pulses of various light field structures.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of optical fiber lasers, in particular to a spatiotemporal mode-locked optical fiber laser with adjustable light spot based on intracavity phase modulation. Background Art

[0002] Traditional single-mode fiber mode-locked lasers, core light sources in ultrafast photonics, can generate ultrashort pulses on the order of femtoseconds in the time domain and equally spaced optical frequency combs in the frequency domain. These lasers combine high peak power with a broad spectrum, finding important applications in cutting-edge fields such as precision spectral measurement, high-capacity optical communications, and micro-nanofabrication. However, their small mode area and strong nonlinear effects limit pulse energy expansion (typically <50 nJ), making them difficult to meet the demands of applications such as high-power processing and multi-channel communications. In contrast, multimode fiber lasers, by introducing spatial degrees of freedom to construct high-dimensional nonlinear systems, offer larger mode areas and greater mode capacity, enabling higher pulse energies and supporting the parallel transmission of multiple optical signals. In 2017, the Wise group at Cornell University reported in Science for the first time the synchronous locking of multiple transverse and longitudinal modes in a multimode fiber laser, resulting in a temporally stable and spatially coherent multimode pulse train, known as spatiotemporal mode-locking (STML). Spatiotemporally mode-locked fiber lasers not only provide an ideal platform for studying fundamental physical problems such as spatiotemporal light field dynamics and multimode soliton molecules, but also demonstrate potential in application scenarios such as super-resolution imaging of scattering media, multi-focus parallel processing, and multidimensional optical frequency combs.

[0003] In recent years, significant progress has been made in spatiotemporally mode-locked fiber lasers. However, the multimode interference patterns currently achieved in spatiotemporally mode-locked fiber lasers are complex and uncontrollable, making it difficult to effectively utilize the spatiotemporal coherence of the mode-locked pulses. This limits their expanded application in specialized fields such as laser lithography, super-resolution imaging, optical sensing, fiber-optic communications, and optical tweezers. In terms of mode field control methods, the beam self-cleaning effect provides an important approach for mode field control in spatiotemporally mode-locked fiber lasers. However, this method relies on specific fiber parameters and pumping conditions and can only generate near-single-mode light fields, which cannot meet the demand for specialized modes in scenarios such as laser lithography, super-resolution imaging, optical sensing, fiber-optic communications, and optical tweezers. Furthermore, although optical elements such as q-plates, mode converters, and metasurfaces have been integrated into fiber lasers to generate laser light fields with specific structures, they are generally only capable of producing fixed modes, lacking flexibility, and the dynamic control mechanism in spatiotemporally mode-locked multimode systems remains unclear. It is worth noting that the method of inserting a spatial light modulator (SLM) into the laser cavity has opened up new ideas for the mode field control of spatiotemporally mode-locked fiber lasers. Wei Xiaoming's research group at South China University of Technology placed the SLM in a multimode laser cavity, modulated the phase in the laser cavity by changing the phase on the SLM, and used a genetic algorithm to produce an almost single-mode output in the continuous wave state. This work provides important insights for the dynamic control of spatiotemporally mode-locked light fields, but the work has not yet demonstrated the ability to generate arbitrary output beam profiles in the mode-locked state. Due to the essential differences in the nonlinear dynamic characteristics of continuous wave and spatiotemporally mode-locked fiber laser systems, coupled with the strong interaction between mode competition and spatiotemporal coupling effects in multimode systems, how to achieve real-time dynamic control in the mode-locked state still faces major challenges. Summary of the Invention

[0004] In response to the technical problems existing in the prior art, the present invention proposes a spatiotemporally mode-locked fiber laser with adjustable light spot based on intracavity phase modulation. The present invention realizes intelligent mode field control of the spatiotemporally mode-locked fiber laser through intracavity phase modulation and algorithm feedback.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] In one aspect, the present invention provides a spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation, comprising a multimode fiber ring cavity, wherein an intracavity dynamic phase modulation system is disposed within the multimode fiber ring cavity for applying phase modulation to the light field within the multimode fiber ring cavity. The spatiotemporally mode-locked fiber laser also includes a feedback control unit that collects the output spot of the multimode fiber ring cavity and obtains a mode decomposition result and a time-domain mode-locking result of the output spot. The feedback control unit uses the mode decomposition result and the time-domain mode-locking result as objective functions, runs an optimization algorithm to generate a phase control signal for the intracavity dynamic phase modulation system, and forms a closed-loop control until a target light field is obtained in which both the spot pattern and the time-domain mode-locking stability meet the target requirements.

[0007] Furthermore, the multimode fiber ring cavity includes a pump source, a combiner, a gain multimode fiber, a passive multimode fiber, and a spatial optical path arranged between the output end of the passive multimode fiber and the input end of the combiner. The input end of the gain multimode fiber is connected to the output end of the combiner. The pump light output by the pump source is coupled to the gain multimode fiber through the combiner. The output end of the gain multimode fiber is connected to the input end of the passive multimode fiber. The output end of the passive multimode fiber outputs a light beam to free space. A laser cavity loop is formed by the spatial optical path arranged between the output end of the passive multimode fiber and the input end of the combiner, and the light output from the passive multimode fiber to the free space is coupled back to the gain multimode fiber.

[0008] Furthermore, the intracavity dynamic phase modulation system includes a spatial light modulator, which is arranged in the spatial light path between the output end of the passive multimode optical fiber and the input end of the combiner. The spatial light modulator is used to apply phase modulation to the intracavity light field in the laser cavity loop to regulate the output light field of the spatiotemporally mode-locked fiber laser.

[0009] Furthermore, the spatial optical path between the output end of the passive multimode optical fiber and the input end of the combiner is sequentially provided with a first lens, a first 1 / 4 wave plate, a first 1 / 2 wave plate, a polarization beam splitter, a second lens, a first beam splitter, a bandpass filter, a second 1 / 2 wave plate, a spatial light modulator, an isolator, a third lens, one or more reflectors, a second 1 / 4 wave plate, and a fourth lens.

[0010] Furthermore, the feedback control unit includes a second beam splitter, a near-infrared camera, a collimator, a single-mode optical fiber, a photodetector, a high-speed oscilloscope, and a computer. The second beam splitter is arranged on the reflected light path of the first beam splitter, and the second beam splitter outputs the received light spot in two paths:

[0011] One route is detected and received by a near-infrared camera, which transmits the detected light spot image to a computer for pattern decomposition to obtain the pattern decomposition result of the output light spot;

[0012] The other path is coupled to a single-mode optical fiber through a collimator for dispersion Fourier change. The spectrum is captured in real time by a high-speed oscilloscope and the captured spectrum data is transmitted to a computer for time-domain mode-locking stability analysis to obtain the time-domain mode-locking stability results of the output light spot.

[0013] Furthermore, the computer uses the mode decomposition result of the output light spot and the time-domain mode-locking stability result as the objective function, uses the genetic algorithm to find the optimal phase diagram and feedback-controls the spatial light modulator.

[0014] Compared with the prior art, the technical effects of the present invention are:

[0015] In response to the current state of research on spatiotemporal mode-locking (SML) both domestically and internationally and the demand for its mode field control, this paper innovatively designs a tunable SML fiber laser based on intracavity phase modulation. Employing a multimode fiber ring cavity structure, it integrates a high-precision spatial light modulator (SLM) and an intelligent feedback control system. Dynamically optimizing phase parameters through an optimization algorithm achieves high-purity control of the output SML pattern and enhances mode-locking stability. This laser can flexibly generate mode-locked pulses in a variety of light field structures, providing a high-performance intelligent light source for precision machining, optical communications, and nonlinear optics research.

[0016] Existing technologies that use mechanical deformation combined with intelligent algorithms to control mode field distribution have the following limitations: slow mechanical control response speed (>500ms), inability to achieve dynamic mode switching, and susceptibility to environmental vibration interference; unquantified time-domain mode-locking stability indicators, resulting in uncontrollable pulse quality; and fiber geometric deformation introduces additional losses. This invention directly controls the intracavity light field phase distribution through a spatial light modulator (SLM), achieving high-purity control of the spot pattern through feedback control. Combined with a genetic algorithm for multi-objective optimization, this method achieves millisecond-level switching of spot patterns (such as LP01, LP11, and ring) and coordinated control of mode-locking stability without changing the fiber's physical structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0018] Figure 1 This is a schematic diagram of the structure of a spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation;

[0019] Figure 2 Flowchart for finding the optimal phase diagram and feedback control of the spatial light modulator using genetic algorithm;

[0020] Markings in the figure: 1. Pump source; 2. Beam combiner; 3. Gain multimode fiber; 4. Passive multimode fiber; 5. First lens; 6. First 1 / 4 wave plate; 7. First 1 / 2 wave plate; 8. Polarization beam splitter; 9. Second lens; 10. First beam splitter; 11. Bandpass filter; 12. Second 1 / 2 wave plate; 13. Spatial light modulator; 14. Isolator; 15. Third lens; 16. Reflector; 17. Second 1 / 4 wave plate; 18. Fourth lens; 19. Second beam splitter; 20. Near-infrared camera; 21. Collimator; 22. Single-mode fiber; 23. Photodetector; 24. High-speed oscilloscope; 25. Computer. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] In one embodiment, a spatiotemporally locked fiber laser with adjustable spot based on intracavity phase modulation is provided, comprising a multimode fiber ring cavity, wherein an intracavity dynamic phase modulation system is provided in the multimode fiber ring cavity for applying phase modulation to the light field in the multimode fiber ring cavity; the laser is characterized in that it further comprises a feedback control unit, which collects the output spot of the multimode fiber ring cavity and obtains a mode decomposition result and a time-domain mode-locking result of the output spot, uses the mode decomposition result and the time-domain mode-locking result of the output spot as objective functions, runs an optimization algorithm to generate a phase control signal for the intracavity dynamic phase modulation system, and forms a closed-loop control until a target light field is obtained in which both the spot pattern and the time-domain mode-locking stability meet the target requirements.

[0023] Reference Figure 1 This embodiment provides a spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation. Its multimode fiber ring cavity includes a pump source 1, a beam combiner 2, a gain multimode fiber 3, a passive multimode fiber 4, and a spatial optical path disposed between the output end of the passive multimode fiber 4 and the input end of the beam combiner 2. The input end of the gain multimode fiber 3 is connected to the output end of the beam combiner 2. The pump light output by the pump source 1 is coupled to the gain multimode fiber 3 through the beam combiner 2. The output end of the gain multimode fiber 3 is connected to the input end of the passive multimode fiber 4. The output end of the passive multimode fiber 4 outputs a light beam to free space. A laser cavity loop is formed by the spatial optical path disposed between the output end of the passive multimode fiber 4 and the input end of the beam combiner 2, and the light output from the passive multimode fiber 4 to free space is coupled back to the gain multimode fiber 3. The pump source 1 is a multimode laser diode.

[0024] The intracavity dynamic phase modulation system includes a spatial light modulator 13, which is arranged in the spatial light path between the output end of the passive multimode optical fiber 4 and the input end of the combiner 2. The spatial light modulator 13 is used to apply phase modulation to the intracavity light field in the laser cavity loop to regulate the output light field of the spatiotemporally mode-locked fiber laser.

[0025] Specifically, the spatial optical path between the output end of the passive multimode optical fiber and the input end of the beam combiner is sequentially provided with a first lens 5, a first quarter-wave plate 6, a first half-wave plate 7, a polarization beam splitter 8, a second lens 9, a first beam splitter 10, a bandpass filter 11, a second half-wave plate 12, a spatial light modulator 13, an isolator 14, a third lens 15, one or more reflectors 16, a second quarter-wave plate 17, and a fourth lens 18. The first quarter-wave plate 6, the second quarter-wave plate 17, the second half-wave plate 12, and the polarization beam splitter 8 are sequentially provided within the laser cavity loop. By adjusting the wave plate angles, a nonlinear polarization rotation effect is induced, forming an equivalent saturable absorber to assist in mode locking. By utilizing a combination of one or more reflectors 16, the propagation direction and path of the light beam are changed, and the spatial coupling conditions are flexibly adjusted, ensuring efficient transmission of the optical signal between different optical components and improving the overall performance of the laser. In the present invention, the polarization beam splitter 8 has one function of outputting part of the light for observation, and another function of forming a nonlinear polarization effect auxiliary mode locking together with the first 1 / 4 wave plate 6, the second 1 / 4 wave plate 17, and the second 1 / 2 wave plate 12.

[0026] The intracavity dynamic phase modulation system consists of a first lens 5 and a second lens 9 for amplifying the light spot, a third lens 15 and a fourth lens 18 for reducing the light spot, and a spatial light modulator 13. The spatial light modulator 13 is used to apply phase modulation to the intracavity light field. The dynamic temperature control module (±0.1°C) controls the temperature of the spatial light modulator to suppress thermally induced phase drift at high power levels, ensuring phase stability of the spatial light modulator, and thus regulating the output light field of the laser. The first lens 5 and the second lens 9 are used to amplify the light spot to ensure that the light spot experiences a sufficiently large spatial phase modulation. When the light beam is recoupled back into the multimode gain fiber, the third lens 15 and the fourth lens 18 are used to restore its original characteristics.

[0027] The settings of the pump source 1, the combiner 2, the gain multimode fiber 3, the passive multimode fiber 4, etc., including but not limited to the fiber length setting, fiber selection, pump parameter setting, etc., can be reasonably selected and designed by those skilled in the art according to actual conditions and needs.

[0028] In one specific embodiment, the pump source 1 utilizes a multimode 976nm laser diode with a maximum power of 27W, the gain multimode fiber 3 utilizes a 0.5m ytterbium-doped multimode fiber, and the passive multimode fiber 4 utilizes a 1.5m passive multimode fiber. The gain multimode fiber 3 is pumped by a multimode 976nm laser diode with a maximum power of 27W. To excite more high-order modes in the cavity, the splice between the output end of the gain multimode fiber 3 and the input end of the passive multimode fiber 4 is not a core-to-core splice, but rather an offset splice. Specifically, the offset splice is performed between the output end of the gain multimode fiber and the input end of the passive multimode fiber, where the cores of the output end of the gain multimode fiber and the input end of the passive multimode fiber are offset by a set value. The set value is not limited and can be selected within the range of 0.2D-0.5D, where D is the smaller of the core diameters of the output end of the gain multimode fiber and the input end of the passive multimode fiber. The bandpass filter 11 has a central wavelength of 1060 nm and a bandwidth of 3 nm, which suppresses spectral broadening and compresses the pulse to ensure the realization of mode locking. In addition, an isolator 14 is used to ensure unidirectional propagation of the laser light in the cavity.

[0029] like Figure 1 As shown, the feedback control unit in this embodiment includes a second beam splitter 19, a near-infrared camera 20, a collimator 21, a single-mode optical fiber 22, a photodetector 23, a high-speed oscilloscope 24 and a computer 25. The second beam splitter 19 is arranged on the reflected light path of the first beam splitter 10, and the second beam splitter 19 outputs the received light spot in two paths:

[0030] One route is detected and received by the near-infrared camera 20, which transmits the detected light spot image to the computer for pattern decomposition to obtain the pattern decomposition result of the output light spot;

[0031] The other path is coupled to a single-mode optical fiber through a collimator for dispersion Fourier change. The spectrum is captured in real time by a high-speed oscilloscope, and the captured spectrum real-time evolution data is transmitted to a computer for time-domain mode-locking stability analysis and laser dynamic evolution analysis research to obtain the time-domain mode-locking stability results of the output light spot.

[0032] The computer uses the mode decomposition results of the output light spot and the time domain mode locking stability results as the objective function, uses the genetic algorithm to find the optimal phase diagram and feedback control the spatial light modulator. Figure 2 As shown, the process specifically includes:

[0033] (1) Turn on the pump source and adjust the intracavity parameters to put the spatiotemporal mode-locked fiber laser into a spatiotemporal mode-locked state;

[0034] (2) Randomly generate multiple phase images and load them onto the spatial light modulator as all individuals in the first generation of the genetic algorithm;

[0035] (3) The spatial light modulator loads the phase map corresponding to each individual of the current generation and obtains the objective function corresponding to each individual. The objective function includes the mode decomposition result of the output light spot and the time domain mode locking stability result;

[0036] (4) Sort the objective functions of all individuals in the current generation according to the mode decomposition results of the output light spot and the time domain mode-locking stability results, obtain the individual with the best objective function in the current generation, and evaluate whether the objective function of the individual with the best objective function meets the target requirements:

[0037] If the requirements are not met, then among all individuals in the current generation, select all individuals whose objective function ranking is before the set sequence number, and interleave and mutate the phase graphs corresponding to the selected individuals to generate the next generation of individuals, and return to step (3) to start a new round of iteration;

[0038] If the requirements are met, the iteration ends and the phase map of the spatial light modulator is set to a phase map with the best objective function.

[0039] In summary, computer 25 uses a genetic algorithm to find the optimal phase diagram and feedback-control the spatial light modulator 13, forming a closed-loop control. The algorithm uses mode purity and mode-locking stability as dual objective functions, dynamically adjusting the priority of mode-locking stability and mode purity, thus breaking through the limitations of static control. The individual genes in the genetic algorithm are encoded as phase diagrams loaded onto the spatial light modulator. The algorithm uses mode purity and mode-locking stability as dual objective functions. For example, if the target requirements are set as: LP11 mode ratio > 95% and mode-locked pulse RF spectrum signal-to-noise ratio > 60 dB, the optimization algorithm continuously updates the phase diagram until the mode decomposition results and time-domain mode-locking stability results of the output light spot meet the requirements of LP11 mode ratio > 95% and mode-locked pulse RF spectrum signal-to-noise ratio > 60 dB. The iteration ends, and the phase diagram of the spatial light modulator is set to the phase diagram that meets the optimal objective function. This method of setting the mode ratio and phase of the intracavity light field to obtain the target light field achieves high-purity control of the output light spot mode and improved mode-locking stability. This laser can flexibly generate mode-locked pulses with various light field structures.

[0040] Matters not covered by the present invention are known technologies.

[0041] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0042] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and such modifications and improvements are intended to fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

[0043] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation, comprising a multimode fiber ring cavity, wherein an intracavity dynamic phase modulation system is provided in the multimode fiber ring cavity for applying phase modulation to the light field in the multimode fiber ring cavity; characterized in that: The system also includes a feedback control unit, which collects the output light spot of the multimode fiber ring cavity and obtains the mode decomposition result and time-domain mode locking result of the output light spot. The mode decomposition result and time-domain mode locking stability result of the output light spot are used as the objective function, and an optimization algorithm is run to generate a phase control signal of the intra-cavity dynamic phase modulation system to form a closed-loop control until a target light field is obtained in which the mode decomposition result of the output light spot and the time-domain mode locking stability result both meet the target requirements. The iteration is then terminated, and the phase diagram of the spatial light modulator is set to a phase diagram with the optimal objective function, wherein the mode decomposition result of the output light spot is the purity of the target mode, and the time-domain mode locking stability result is the radio frequency spectrum signal-to-noise ratio of the mode-locked pulse.

2. The spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation according to claim 1, characterized in that: The multimode fiber ring cavity includes a pump source, a combiner, a gain multimode fiber, a passive multimode fiber, and a spatial optical path arranged between the output end of the passive multimode fiber and the input end of the combiner. The input end of the gain multimode fiber is connected to the output end of the combiner. The pump light output by the pump source is coupled to the gain multimode fiber through the combiner. The output end of the gain multimode fiber is connected to the input end of the passive multimode fiber. The output end of the passive multimode fiber outputs a light beam to free space. A laser cavity loop is formed by the spatial optical path arranged between the output end of the passive multimode fiber and the input end of the combiner, and the light output from the passive multimode fiber to the free space is coupled back to the gain multimode fiber.

3. The spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation according to claim 2, characterized in that: The output end of the gain multimode optical fiber and the input end of the passive multimode optical fiber are staggered and fused, wherein the staggered fusion is a staggered fusion of the core axial offset of the output end of the gain multimode optical fiber and the input end of the passive multimode optical fiber by a set value.

4. The spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation according to claim 2 or 3, characterized in that: The intracavity dynamic phase modulation system includes a spatial light modulator, which is arranged in the spatial light path between the output end of the passive multimode optical fiber and the input end of the beam combiner. The spatial light modulator is used to apply phase modulation to the intracavity light field in the laser cavity loop to regulate the output light field of the spatiotemporally mode-locked fiber laser. At the same time, the temperature of the spatial light modulator is controlled by a dynamic temperature control module to suppress thermally induced phase drift under high power and ensure the phase stability of the spatial light modulator loading.

5. The spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation according to claim 4, characterized in that: The spatial light path between the output end of the passive multimode optical fiber and the input end of the beam combiner is sequentially provided with a first lens, a first 1 / 4 wave plate, a first 1 / 2 wave plate, a polarization beam splitter, a second lens, a first beam splitter, a bandpass filter, a second 1 / 2 wave plate, a spatial light modulator, an isolator, a third lens, one or more reflectors, a second 1 / 4 wave plate, and a fourth lens.

6. The spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation according to claim 5, characterized in that: The first 1 / 4 wave plate, the second 1 / 4 wave plate, the second 1 / 2 wave plate and the polarization beam splitter induce a nonlinear polarization rotation effect by adjusting the wave plate angles, forming an equivalent saturable absorber to assist in mode locking.

7. The spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation according to claim 5, characterized in that: The first lens and the second lens are used to magnify the light spot; the third lens and the fourth lens are used to reduce the light spot.

8. The spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation according to claim 5, 6 or 7, characterized in that: The feedback control unit includes a second beam splitter, a near-infrared camera, a collimator, a single-mode optical fiber, a photodetector, a high-speed oscilloscope, and a computer. The second beam splitter is arranged on the reflected light path of the first beam splitter and outputs the received light spot in two paths: One route is detected and received by a near-infrared camera, which transmits the detected light spot image to a computer for pattern decomposition to obtain the pattern decomposition result of the output light spot; The other path is coupled to a single-mode optical fiber through a collimator for dispersion Fourier change. The spectrum is captured in real time by a high-speed oscilloscope and the captured spectrum data is transmitted to a computer for time-domain mode-locking stability analysis to obtain the time-domain mode-locking stability results of the output light spot.

9. The spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation according to claim 8, characterized in that: The computer uses the mode decomposition result of the output light spot and the time domain mode locking stability result as the objective function, uses the genetic algorithm to find the optimal phase diagram and feedback control the spatial light modulator.

10. The spatiotemporally mode-locked fiber laser with adjustable spot size based on intracavity phase modulation according to claim 9, characterized in that: Genetic algorithms are used to find the optimal phase diagram and feedback control the spatial light modulator, including: (1) Turn on the pump source and adjust the intracavity parameters to put the spatiotemporal mode-locked fiber laser into a spatiotemporal mode-locked state; (2) Randomly generate multiple phase images and load them onto the spatial light modulator as all individuals in the first generation of the genetic algorithm; (3) The spatial light modulator loads the phase map corresponding to each individual of the current generation and obtains the objective function corresponding to each individual. The objective function includes the mode decomposition result of the output light spot and the time domain mode locking stability result; (4) Sort the objective functions of all individuals in the current generation according to the mode decomposition results of the output light spot and the time domain mode-locking stability results, obtain the individual with the best objective function in the current generation, and evaluate whether the objective function of the individual with the best objective function meets the target requirements: If the requirements are not met, then among all individuals in the current generation, select all individuals whose objective function ranking is before the set sequence number, and interleave and mutate the phase graphs corresponding to the selected individuals to generate the next generation of individuals, and return to step (3) to start a new round of iteration; If the requirements are met, the iteration ends and the phase map of the spatial light modulator is set to a phase map with the best objective function.

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