Light spot-adjustable space-time mode-locked fiber laser based on intracavity phase modulation

Abstract

The invention discloses a light spot-adjustable space-time mode-locked fiber laser based on intracavity phase modulation, which comprises a multimode fiber ring cavity, and is characterized in that an intracavity dynamic phase modulation system is arranged in the multimode fiber ring cavity and is used for applying phase modulation to a light field in the multimode fiber ring cavity; the system further comprises a feedback control unit, and the feedback control unit collects light spots output by the multimode optical fiber annular cavity, obtains a mode decomposition result and a time domain mode locking result of the output light spots, and takes the mode decomposition result and the time domain mode locking result of the output light spots as target functions. And an optimization algorithm is operated to generate a phase control signal of the intracavity dynamic phase modulation system, and closed-loop control is formed until a target light field of which the light spot mode and the time domain mode locking stability both meet target requirements is obtained. According to the invention, mode-locked pulses of various light field structures can be flexibly generated.

Description

Technical Field

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

[0002] As the core light source in the field of ultrafast photonics, the traditional single-mode fiber mode-locked laser can generate ultrashort pulses in the femtosecond scale in the time domain and equally spaced optical frequency combs in the frequency domain, with both high peak power and broad spectral characteristics, and has important applications in frontier fields such as precision spectroscopy measurement, high-capacity optical communication, and micro-nano processing. However, its small mode field area and strong nonlinear effect limit the improvement of pulse energy (usually <50 nJ), making it difficult to meet the requirements of applications such as high-power processing and multi-channel communication. In contrast, by introducing spatial degrees of freedom to construct a high-dimensional nonlinear system, multimode fiber lasers have a larger mode field area and more mode capacity, can withstand higher pulse energy and support parallel transmission of multiple optical signals. In 2017, the Wise research group at Cornell University first reported in Science the realization of synchronous locking of multiple transverse modes and longitudinal modes in a multimode fiber laser, forming a multimode pulse sequence that is stable in the time domain and coherent in space, namely spatiotemporal mode-locking (STML). Spatiotemporal mode-locked fiber lasers not only provide an ideal platform for studying basic physical problems such as spatiotemporal optical field dynamics and multimode soliton molecules, but also show potential in application scenarios such as super-resolution imaging of scattering media, multi-focus parallel processing, and multi-dimensional optical frequency combs.

[0003] In recent years, significant progress has been made in spatio-temporal mode-locked fiber lasers. However, for currently realized spatio-temporal mode-locked fiber lasers, the output multimode interference spots are complex and uncontrollable, resulting in the difficulty of effectively utilizing the spatio-temporal coherence of mode-locked pulses, which limits their extended applications in special fields such as laser lithography, super-resolution imaging, optical sensing, fiber communication, and optical tweezers. In terms of mode field modulation methods, the beam self-cleaning effect provides an important way for the mode field modulation of spatio-temporal mode-locked fiber lasers. However, this method depends on specific fiber parameters, pump conditions, etc., and can only generate a nearly single-mode optical field, unable to meet the requirements for special modes in scenarios such as laser lithography, super-resolution imaging, optical sensing, fiber communication, and optical tweezers. In addition, although optical elements such as q-wave plates, mode converters, and metasurfaces have been integrated into fiber lasers to generate laser optical fields with specific structures, they usually can only modulate and generate fixed modes, lacking flexibility, and the dynamic modulation mechanism in spatio-temporal mode-locked multimode systems is still unclear. It is worth noting that the method of inserting a Spatial Light Modulator (SLM) into the laser cavity has opened up a new idea for the mode field modulation of spatio-temporal mode-locked fiber lasers. The research group of Wei Xiaoming at South China University of Technology placed the spatial light modulator in a multimode laser cavity and modulated the phase in the laser cavity by changing the phase on the spatial light modulator, and almost single-mode output was generated in the continuous wave state using a genetic algorithm. This work provides an important inspiration for the dynamic modulation of spatio-temporal mode-locked optical fields, but this work has not demonstrated the ability to generate arbitrary output beam profiles in the mode-locked state. Due to the essential differences in the nonlinear dynamic characteristics between the continuous wave and the spatio-temporal mode-locked fiber laser system, combined with the strong interaction of mode competition and spatio-temporal coupling effects in the multimode system, how to achieve real-time dynamic modulation in the mode-locked state still faces major challenges. Summary of the Invention

[0004] Aiming at the technical problems existing in the prior art, the present invention proposes a spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation. The present invention realizes the intelligent mode field modulation of the spatio-temporal 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: On the one hand, the present invention provides a spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation, which includes a multimode fiber ring cavity. An intracavity dynamic phase modulation system is arranged in the multimode fiber ring cavity for applying phase modulation to the optical field in the multimode fiber ring cavity. The spatio-temporal mode-locked fiber laser further includes a feedback control unit. The feedback control unit collects the output spot of the multimode fiber ring cavity, obtains the mode decomposition result and the time-domain mode-locking result of the output spot, takes the mode decomposition result and the time-domain mode-locking result of the output spot as the objective function, runs an optimization algorithm to generate a phase control signal for the intracavity dynamic phase modulation system, forms a closed-loop control, and until a target optical field is obtained where both the spot mode and the time-domain mode-locking stability meet the target requirements.

[0006] Further, the multimode fiber ring cavity includes a pump source, a beam 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 beam combiner. The input end of the gain multimode fiber is connected to the output end of the beam combiner. The pump light output by the pump source is coupled into the gain multimode fiber through the beam 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, and a laser cavity loop is formed through the spatial optical path arranged between the output end of the passive multimode fiber and the input end of the beam combiner, and the light output from the passive multimode fiber to free space is coupled back into the gain multimode fiber.

[0007] Further, the intracavity dynamic phase modulation system includes a spatial light modulator. The spatial light modulator is arranged in the spatial optical path between the output end of the passive multimode fiber and the input end of the beam combiner. The spatial light modulator is used to apply phase modulation to the intracavity optical field in the laser cavity loop to regulate the output optical field of the spatio-temporal mode-locked fiber laser.

[0008] Further, the spatial optical path between the output end of the passive multimode fiber and the input end of the beam combiner is sequentially provided with a first lens, a first quarter-wave plate, a first half-wave plate, a polarization beam splitter, a second lens, a first beam splitter, a band-pass filter, a second half-wave plate, a spatial light modulator, an isolator, a third lens, more than one mirror, a second quarter-wave plate, and a fourth lens.

[0009] Further, the feedback control unit includes a second beam splitter, a near-infrared camera, a collimator, a single-mode 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. The second beam splitter outputs the received spot in two paths: One path is detected and received by the near-infrared camera. The near-infrared camera transmits the detected spot image to the computer for mode decomposition to obtain the mode decomposition result of the output spot; Another path is coupled to a single-mode fiber through a collimator for dispersion Fourier transform. 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 result of the output light spot.

[0010] Further, the computer uses the mode decomposition result and the time-domain mode-locking stability result of the output light spot as objective functions, and uses a genetic algorithm to find the optimal phase diagram and feedback control the spatial light modulator.

[0011] Compared with the prior art, the technical effects of the present invention are as follows: In view of the current domestic and foreign research status of spatio-temporal mode-locking and the demand for its mode field regulation, the present invention innovatively designs a spatio-temporal mode-locking fiber laser with adjustable light spots based on intracavity phase modulation. Adopting a multi-mode fiber ring cavity structure, integrating a high-precision spatial light modulator and an intelligent feedback control system, dynamically optimizing the phase parameters through an optimization algorithm, and realizing high-purity regulation of the output light spot mode and improvement of mode-locking stability. The laser can flexibly generate mode-locked pulses with various optical field structures, providing a high-performance intelligent light source for precision machining, optical communication and nonlinear optical research.

[0012] In the prior art, the mechanical deformation is combined with an intelligent algorithm to regulate the mode field distribution, which has the following limitations: the mechanical regulation has a slow response speed (>500 ms), cannot realize dynamic mode switching, and the mechanical deformation is easily interfered by environmental vibration; the time-domain mode-locking stability index is not quantified, and the pulse quality is uncontrollable; the geometric deformation of the fiber will introduce additional losses. The present invention directly regulates the intracavity light field phase distribution through a spatial light modulator (SLM), realizes high-purity regulation of the light spot mode through feedback control, and combines multi-objective optimization of a genetic algorithm to realize millisecond-level switching of the light spot mode (such as LP01, LP11, ring, etc.) and collaborative control of mode-locking stability without changing the physical structure of the fiber. Description of the Drawings

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on the structures shown in these drawings without creative efforts.

[0014] Figure 1 It is a schematic structural diagram of a spatio-temporal mode-locking fiber laser with adjustable light spots based on intracavity phase modulation; Figure 2 It is a flow chart for using a genetic algorithm to find the optimal phase diagram and feedback control the spatial light modulator; Markings in the figure: 1. Pump source; 2. Beam combiner; 3. Gain multimode fiber; 4. Passive multimode fiber; 5. First lens; 6. First quarter-wave plate; 7. First half-wave plate; 8. Polarizing beam splitter; 9. Second lens; 10. First beam splitter; 11. Band-pass filter; 12. Second half-wave plate; 13. Spatial light modulator; 14. Isolator; 15. Third lens; 16. Mirror; 17. Second quarter-wave plate; 18. Fourth lens; 19. Second beam splitter; 20. Near-infrared camera; 21. Collimator; 22. Single-mode fiber; 23. Photoelectric detector; 24. High-speed oscilloscope; 25. Computer. Detailed implementation manners

[0015] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0016] In one embodiment, a spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation is provided, including a multimode fiber ring cavity, and an intracavity dynamic phase modulation system is arranged in the multimode fiber ring cavity for applying phase modulation to the optical field in the multimode fiber ring cavity. It is characterized in that it further includes a feedback control unit. The feedback control unit collects the output spot of the multimode fiber ring cavity and obtains the mode decomposition result and the 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 the objective function, runs an optimization algorithm to generate a phase control signal for the intracavity dynamic phase modulation system, forms a closed-loop control, until a target optical field with both the spot mode and the time-domain mode-locking stability meeting the target requirements is obtained.

[0017] Referring to Figure 1 , in this embodiment, a spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation is provided. 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 an optical path in free space arranged 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 into 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, and a laser cavity loop is formed through the optical path in free space arranged 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 into the gain multimode fiber 3. The pump source 1 uses a multimode laser diode.

[0018] The intracavity dynamic phase modulation system includes a spatial light modulator 13, which is arranged in the spatial optical path between the output end of the passive multimode fiber 4 and the input end of the beam combiner 2. The spatial light modulator 13 is used to apply phase modulation to the intracavity optical field in the laser cavity loop to regulate the output optical field of the spatio-temporal mode-locked fiber laser.

[0019] Specifically, 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 band-pass filter 11, a second half-wave plate 12, a spatial light modulator 13, an isolator 14, a third lens 15, more than one reflector 16, a second quarter-wave plate 17, and a fourth lens 18 are sequentially arranged in the spatial optical path between the output end of the passive multimode fiber and the input end of the beam combiner. A first quarter-wave plate 6, a second quarter-wave plate 17, a second half-wave plate 12, and a polarization beam splitter 8 are sequentially arranged in the laser cavity loop. By adjusting the wave plate angle, the nonlinear polarization rotation effect is induced to form an equivalent saturable absorber to assist mode locking. The combination of more than one reflector 16 is used to change the transmission direction and path of the light beam, flexibly adjust the spatial coupling condition, ensure the efficient transmission of the optical signal between different optical elements, and improve the overall performance of the laser. In the present invention, one function of the polarization beam splitter 8 is to output part of the light for observation, and the other function is to form a nonlinear polarization effect-assisted mode locking with the first quarter-wave plate 6, the second quarter-wave plate 17, and the second half-wave plate 12.

[0020] The intracavity dynamic phase modulation system described above consists of a first lens 5 and a second lens 9 for magnifying 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 optical field, and the temperature of the spatial light modulator is controlled by a dynamic temperature control module (±0.1 °C) to suppress the thermally induced phase drift at high power and ensure the phase stability loaded by the spatial light modulator, so as to regulate the output optical field of the laser. The first lens 5 and the second lens 9 are used to magnify the light spot to ensure that the light spot can sense 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.

[0021] The settings of the pump source 1, the beam 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 the actual situation and requirements.

[0022] In a specific embodiment, the pump source 1 uses a multimode 976 nm laser diode with a maximum power of 27 W. The gain multimode fiber 3 uses 0.5 m of ytterbium-doped multimode fiber, and the passive multimode fiber 4 uses 1.5 m of passive multimode fiber. The gain multimode fiber 3 is pumped by a multimode 976 nm laser diode with a maximum power of 27W. In order to excite more high-order modes in the cavity, the fusion splicing between the output end of the gain multimode fiber 3 and the input end of the passive multimode fiber 4 is not core-to-core fusion splicing, but misalignment fusion splicing. Specifically, misalignment fusion splicing is adopted between the output end of the gain multimode fiber and the input end of the passive multimode fiber, where the misalignment fusion splicing is the misalignment fusion splicing with the core axis of the output end of the gain multimode fiber offset from the core axis of the input end of the passive multimode fiber by a set value. The set value is not limited, for example, it can be selected within the range of 0.2D - 0.5D, and D is the smaller core diameter of the core diameter of the output end of the gain multimode fiber and the core diameter of the input end of the passive multimode fiber. The center wavelength of the band-pass filter 11 is 1060 nm and the bandwidth is 3 nm, which suppresses spectral broadening and compresses pulses to ensure the realization of mode locking. In addition, an isolator 14 is used to ensure the unidirectional propagation of the laser in the cavity.

[0023] As Figure 1 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 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: One path is detected and received by the near-infrared camera 20, and the near-infrared camera 20 transmits the detected light spot image to the computer for mode decomposition to obtain the mode decomposition result of the output light spot; The other path is coupled to the single-mode fiber through the collimator for dispersion Fourier transform. The high-speed oscilloscope captures the spectrum in real time and transmits the captured spectral real-time evolution data to the computer for time-domain mode-locking stability analysis and laser dynamics evolution analysis research to obtain the time-domain mode-locking stability result of the output light spot.

[0024] The computer uses the mode decomposition result and the time-domain mode-locking stability result of the output light spot as the objective function, and uses the genetic algorithm to find the optimal phase diagram and feedback control the spatial light modulator. As Figure 2 shown, this process specifically includes: (1) Turn on the pump source and adjust the intracavity parameters to make the spatio-temporal mode-locked fiber laser in the spatio-temporal mode-locked state; (2) Randomly generate multiple phase diagrams and load them on the spatial light modulator as all individuals in the first generation of the genetic algorithm; (3)The spatial light modulator respectively loads the phase diagrams corresponding to each individual in 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 result of the output light spot and the time-domain mode-locking stability result, 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 objective requirements: If the requirements are not met, among all individuals in the current generation, select all individuals whose objective function rankings are before the set serial number, and perform interleaving and mutation on the phase diagrams corresponding to the selected individuals to generate the next-generation individuals, and return to step (3) to start a new round of iteration; If the requirements are met, end the iteration and set the phase diagram of the spatial light modulator to the phase diagram with the best objective function.

[0025] In summary, the computer 25 uses the genetic algorithm to find the optimal phase diagram and feedback control the spatial light modulator 13 to form a closed-loop control. The algorithm takes the mode purity and mode-locking stability as the dual objective functions, dynamically adjusts the priorities of the mode-locking stability and the mode purity, and breaks through the static regulation limit. The individual genes in the genetic algorithm are encoded as the phase diagrams loaded on the spatial light modulator. The algorithm takes the mode purity and mode-locking stability as the dual objective functions. If the set objective requirements are: the proportion of the LP11 mode > 95%, and the signal-to-noise ratio of the radio frequency spectrum of the mode-locking pulse > 60 dB, then continuously update the phase diagram through the optimization algorithm until the mode decomposition result of the output light spot and the time-domain mode-locking stability result meet the requirements of the proportion of the LP11 mode > 95%, and the signal-to-noise ratio of the radio frequency spectrum of the mode-locking pulse > 60 dB, then end the iteration and set the phase diagram of the spatial light modulator to the phase diagram with the best objective function. The present invention sets the mode proportion and phase of the intracavity light field to obtain the target light field, realizes the high-purity regulation of the output light spot mode and the improvement of the mode-locking stability. The laser can flexibly generate mode-locking pulses with various light field structures.

[0026] Matters not covered in this invention are well-known technologies.

[0027] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, 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, it should be considered as the scope described in this specification.

[0028] The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

[0029] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation, comprising a multimode fiber ring cavity, wherein an intracavity dynamic phase modulation system is arranged in the multimode fiber ring cavity for applying phase modulation to the optical field in the multimode fiber ring cavity; characterized in that, It further includes a feedback control unit. The feedback control unit collects the output light spot of the multimode fiber loop cavity, obtains the mode decomposition result and the time-domain mode locking result of the output light spot, takes the mode decomposition result and the time-domain mode locking result of the output light spot as the objective function, runs an optimization algorithm to generate the phase control signal of the intracavity dynamic phase modulation system, forms a closed-loop control, until the target optical field with the spot mode and the time-domain mode locking stability both meeting the target requirements is obtained.

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

3. The spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation according to claim 2, wherein Misalignment splicing is adopted between the output end of the gain multimode fiber and the input end of the passive multimode fiber, and the misalignment splicing is misalignment splicing with the core axis of the output end of the gain multimode fiber offset by a set value from the core axis of the input end of the passive multimode fiber.

4. The spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation according to claim 2 or 3, wherein The intracavity dynamic phase modulation system includes a spatial light modulator. The spatial light modulator is arranged in the spatial optical path between the output end of the passive multimode fiber and the input end of the beam combiner. The spatial light modulator is used to apply phase modulation to the intracavity optical field in the laser cavity loop to regulate the output optical field of the spatio-temporal 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 the thermally induced phase drift at high power and ensure the phase stability loaded by the spatial light modulator.

5. The spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation according to claim 4, characterized in that, The spatial optical path between the output end of the passive multimode fiber and the input end of the beam combiner is successively provided with a first lens, a first quarter-wave plate, a first half-wave plate, a polarization beam splitter, a second lens, a first beam splitter, a band-pass filter, a second half-wave plate, a spatial light modulator, an isolator, a third lens, more than one reflector, a second quarter-wave plate, and a fourth lens.

6. The spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation according to claim 5, characterized in that, The first quarter-wave plate, the second quarter-wave plate, the second half-wave plate, and the polarization beam splitter form an equivalent saturable absorber by adjusting the wave plate angle to induce the nonlinear polarization rotation effect and assist in mode locking.

7. The spatio-temporal mode-locked fiber laser with adjustable spot 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 spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation according to claim 5 or 6 or 7, characterized in that, The feedback control unit includes a second beam splitter, a near-infrared camera, a collimator, a single-mode 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. The second beam splitter outputs the received light spot in two paths: One path is detected and received by the near-infrared camera. The near-infrared camera transmits the detected light spot image to the computer for mode decomposition to obtain the mode decomposition result of the output light spot. Another path is coupled to a single-mode fiber through a collimator for dispersion Fourier transform. 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 result of the output light spot.

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

10. The spatio-temporal mode-locked fiber laser with adjustable spot based on intracavity phase modulation according to claim 9, wherein Using a genetic algorithm to find the optimal phase diagram and feedback control the spatial light modulator includes: (1) Turn on the pump source and adjust the intracavity parameters to make the spatio-temporal mode-locked fiber laser in the spatio-temporal mode-locked state; (2) Randomly generate multiple phase diagrams and load them on the spatial light modulator as all individuals in the first generation of the genetic algorithm; (3) The spatial light modulator respectively loads the phase diagram corresponding to each individual in the current generation, and obtains the objective function corresponding to each individual. The objective function includes the mode decomposition result and time-domain mode-locking stability result of the output light spot; (4) Sort the objective functions of all individuals in the current generation according to the mode decomposition result and time-domain mode-locking stability result of the output light spot, 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 objective requirements: If it does not meet the requirements, among all individuals in the current generation, select all individuals whose objective function ranking is before the set serial number, and perform interleaving and mutation on the phase diagrams 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 it meets the requirements, end the iteration and set the phase diagram of the spatial light modulator to the phase diagram with the best objective function.

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