Harmonic time-space mode-locked fiber laser based on Mmyshev mechanism

Abstract

The invention relates to the technical field of fiber lasers, in particular to a Mmyshev mechanism-based harmonic space-time mode-locked fiber laser. According to the technical scheme, the Mmyshev mechanism-based harmonic space-time mode-locked fiber laser comprises a first support arm and a second support arm, the first support arm is formed by sequentially connecting a first pumping source, a first beam combiner, a first gain optical fiber, a polarization dependent isolator, a first polarization controller and a first band-pass filter; and the second support arm is formed by sequentially connecting a second pumping source, a second beam combiner, a second gain optical fiber, a cladding pumping stripper, a polarization independent isolator, a multimode optical fiber output coupler, a second polarization controller and a wavelength adjustable band-pass filter. Mode locking is realized through spectrum broadening caused by self-phase modulation and bias spectrum filtering, and stable space-time mode-locked pulse output is obtained by combining a multimode optical fiber output coupler.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber lasers, and in particular to a harmonic spatiotemporal mode-locked optical fiber laser based on a Mamyshev mechanism. Background Art

[0002] Ultrashort pulse fiber lasers have important applications in micromachining, optical measurement, biomedical imaging, scientific research and other fields. Among them, harmonic mode-locked fiber lasers have the advantages of high output pulse repetition frequency and narrow pulse width, and can be widely used in optical communications, optical frequency combs, terahertz waves and other fields. However, the current research on harmonic mode-locked fiber lasers is mainly focused on single-mode structures, and their strong nonlinear effects limit the generation of high pulse energy. The development of space-time mode-locked fiber lasers provides a promising way to achieve higher pulse energy output in high repetition rate pulse laser systems. At present, there are only two reports on the research of harmonic space-time mode-locked fiber lasers. One is the harmonic mode-locked space-time dissipative soliton light pulses obtained in ytterbium-doped fiber lasers with free space structure. The volume is large, and the energy of its basic repetition frequency space-time mode-locked dissipative soliton pulses is 4.9 nanojoules; the other is an all-fiber erbium-doped space-time mode-locked fiber laser, whose basic repetition frequency space-time mode-locked pulse output power is 21.7 milliwatts, and the corresponding pulse energy is only 1.82 nanojoules. Both use nonlinear polarization rotation technology as saturable absorbers, which have disadvantages such as environmental sensitivity and anti-saturation absorption. In comparison, the modulation depth of the harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism is higher, and there is no anti-saturation absorption, which is more conducive to obtaining high-energy pulses.

[0003] However, due to the non-resonant cavity characteristics of the Mamyshev mechanism mode-locked fiber laser, it is difficult to self-start the mode-locking. Therefore, in order to meet the needs of practical applications, it is urgent to design a simple structure, high repetition frequency, self-starting harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism. This laser is not limited by the working wavelength of the gain fiber and can output spatiotemporal harmonic mode-locked optical pulses in different bands.

[0004] The patent with publication number CN114188805A discloses a space-time mode-locked fiber laser with an all-fiber structure, including a pump source 1, an isolator 2, a wavelength division multiplexer 3, an erbium-doped fiber 4, a step-index multimode fiber 5, a multimode output coupler 6, a single-mode output coupler 7, a saturable absorber 8, a polarization controller 9, and a polarization-independent isolator 10, which are fused in sequence. The problem to be solved is that the common space-time mode-locked fiber laser usually includes a partial spatial optical path and has a relatively complex structure, which is not conducive to the miniaturization of the laser.

[0005] The patent with publication number CN114188809B discloses a high-energy all-fiber time-space mode-locked laser and its control method and application. The high-energy all-fiber time-space mode-locked laser includes: a multi-mode pump source for exciting the laser working material; a wavelength division multiplexer for coupling the pump light and the signal light into the same optical fiber; an ytterbium-doped few-mode gain fiber for generating a one-micrometer-band laser through the gain material excited by the light emitted by the pump source; a 7:3 output coupler for dividing the light in the optical fiber ring cavity into two beams, one beam is output for observation, and the other beam continues to enter the cavity. The multimode pump source is connected to the wavelength division multiplexer through a gradient refractive index multimode fiber, the wavelength division multiplexer is fused with the ytterbium-doped few-mode gain fiber, the ytterbium-doped few-mode gain fiber is fused with the 7:3 output coupler, the 7:3 output coupler is fused with the polarization-sensitive isolator, and the polarization-sensitive isolator is fused with the wavelength division multiplexer. The above patent uses nonlinear polarization rotation technology and nonlinear multimode interference technology with strict restrictions on the length of multimode optical fiber as saturated absorbers. Both are sensitive to the environment and do not solve the problem of difficulty in obtaining stable harmonic mode locking. Here, we use the spectrum broadening and bias filtering effects in the Mamyshev oscillator, combined with a multimode fiber coupler, to achieve the self-starting generation of stable spatiotemporal harmonic mode-locked pulses. Summary of the invention

[0006] The present invention proposes a harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism, uses a polarization-sensitive device to generate initial pulsation, and combines spectrum broadening caused by self-phase modulation and bias spectrum filtering to achieve mode-locked self-starting, thereby solving the problem in the prior art that the Mamyshev oscillator is a non-resonant cavity, which makes it difficult to self-start the mode-locked state.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] A harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism comprises a first arm and a second arm, wherein two ends of the first arm are connected to two ends of the second arm;

[0009] The first arm is composed of a first pump source, a first beam combiner, a first gain fiber, a polarization-dependent isolator, a first polarization controller and a first bandpass filter connected in sequence;

[0010] The second arm is composed of a second pump source, a second beam combiner, a second gain fiber, a cladding pump stripper, a polarization-independent isolator, a multimode fiber output coupler, a second polarization controller, and a wavelength-tunable bandpass filter, which are connected in sequence.

[0011] Furthermore, an end of the first bandpass filter opposite to the first polarization controller is connected to the second beam combiner, and an end of the first beam combiner opposite to the first gain fiber is connected to the wavelength tunable bandpass filter.

[0012] Furthermore, the first polarization controller and the polarization-dependent isolator form a polarization-sensitive device for generating initial pulsation.

[0013] Furthermore, the first bandpass filter and the wavelength tunable bandpass filter form a bias filtering effect.

[0014] Furthermore, the first gain fiber and the second gain fiber are doped fibers.

[0015] Furthermore, the first gain fiber and the second gain fiber are ytterbium-doped fibers.

[0016] Furthermore, the first gain fiber and the second gain fiber are erbium-doped fibers.

[0017] Furthermore, the first gain fiber and the second gain fiber are thulium-doped fibers.

[0018] Furthermore, the first gain fiber and the second gain fiber are multi-mode gain fibers.

[0019] Furthermore, the first gain fiber and the second gain fiber are few-mode gain fibers.

[0020] Furthermore, the first beam combiner has a pigtail, one port of the first beam combiner pigtail is fused to the wavelength tunable bandpass filter, and the other port is fused to the first gain fiber, for coupling the pump light into the gain fiber.

[0021] Furthermore, the first combiner pigtail uses an optical fiber that matches the first gain optical fiber, and the other end uses an optical fiber that matches the wavelength tunable bandpass filter.

[0022] Furthermore, the first gain optical fiber is a double-clad gain optical fiber, and the core diameter of the first gain optical fiber is 10 microns.

[0023] Furthermore, the polarization-dependent isolator has a pigtail, one port of the polarization-dependent isolator pigtail is fused to the first gain fiber, and the other port is fused to the first polarization controller. The first polarization controller and the polarization-dependent isolator form a polarization-sensitive device to generate initial pulsation, and the core diameter of the first arm polarization-dependent isolator pigtail is 6 microns.

[0024] Furthermore, the first polarization controller pigtail is a 1060-XP optical fiber, one end of which is fused to the polarization-dependent isolator pigtail, and the other end of which is fused to the first bandpass filter.

[0025] Furthermore, the first bandpass filter has a pigtail, one port of the first bandpass filter pigtail is fused to the first polarization controller, and the other port is fused to the second combiner pigtail, which is used to transmit the spectrally filtered laser beam to the second arm for further amplification.

[0026] Furthermore, the second arm is provided with a second combiner pigtail, one port of which is fused to the first bandpass filter, and the other port of which is fused to the second gain fiber, for coupling the pump light into the second gain fiber.

[0027] Furthermore, the second combiner pigtail uses an optical fiber that matches the second gain optical fiber, and the other end uses an optical fiber that matches the first bandpass filter.

[0028] Furthermore, the second gain optical fiber is a double-clad gain optical fiber, and the core diameter of the second gain optical fiber is 10 microns.

[0029] Furthermore, the pigtails at both ends of the cladding pump stripper are double-clad passive optical fibers, which are used to absorb the pump light that is not completely absorbed by the gain optical fiber.

[0030] Furthermore, the polarization-independent isolator has a pigtail, one end of the pigtail is fused to the cladding pump stripper, and the other end is fused to the multimode fiber output coupler, and the core diameter of the pigtail is 10 microns.

[0031] Furthermore, the pigtail of the multimode optical fiber output coupler 12 is a multimode gradient refractive index optical fiber, and the core diameter of the pigtail of the multimode optical fiber output coupler is 50 microns.

[0032] Furthermore, the second polarization controller is connected to the multimode optical fiber output coupler and the wavelength tunable bandpass filter, and the core diameter of the polarization controller pigtail is 6 microns in order to achieve a spatial filtering effect.

[0033] Furthermore, the wavelength tunable bandpass filter is connected to the second polarization controller and the first beam combiner.

[0034] This laser is not limited by the operating wavelength of the gain fiber and can output time-space harmonic mode-locked optical pulses in different bands.

[0035] The positive effects of the present invention are: based on the Mamyshev mechanism harmonic time-space mode-locked fiber laser, the spectrum broadening caused by self-phase modulation and bias spectrum filtering are used to achieve mode-locked self-starting. Compared with the traditional mode-locked mechanism, it breaks the technical bottleneck of excessive nonlinear accumulation leading to pulse splitting and thus limiting pulse energy; and the two arms in the laser are each other's amplification arms, which can further increase the pulse energy. The few-mode gain fiber and multimode fiber output coupler in the laser expand the time-domain mode-locked pulse to simultaneous locking in the time domain and space domain, providing technical support for exploring the pulse dynamics characteristics and promoting the practical application of lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of the structure of a harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism provided in an embodiment of the present invention;

[0037] Figure 2 This is the mode-locked pulse spectrum of the harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism;

[0038] Figure 3 Output pulse sequence for harmonic spatiotemporal mode-locked fiber laser based on Mamyshev mechanism;

[0039] Figure 4 Measured spectrum of the output of a harmonic spatiotemporally mode-locked fiber laser based on the Mamyshev mechanism Figure 1 ;

[0040] Figure 5 Measured spectrum of the output of a harmonic spatiotemporally mode-locked fiber laser based on the Mamyshev mechanism Figure 2 ;

[0041] Figure 6 The pulse autocorrelation trace measured for the output of the harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism;

[0042] Figure 7 The beam profile measured at the multimode fiber output coupler of the harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism;

[0043] In the figure: 1. first pump source; 2. first beam combiner; 3. first gain fiber; 4. polarization-dependent isolator; 5. first polarization controller; 6. first bandpass filter; 7. second pump source; 8. second beam combiner; 9. second gain fiber; 10. cladding pump stripper; 11. polarization-independent isolator; 12. multimode fiber output coupler; 13. second polarization controller; 14. wavelength-tunable bandpass filter. DETAILED DESCRIPTION

[0044] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] in, Figures 2 to 7 This is a diagram of the output results of the harmonic space-time mode-locked fiber laser based on the Mamyshev mechanism. Figure 2 It is a mode-locked pulse spectrum diagram of the harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism of the present application when the pump power is 2.06 watts and 2.09 watts, with a central wavelength of 1046.29 nanometers and a 3dB bandwidth of 32.44 nanometers. Figure 3 is the output pulse train with a pulse interval of 11.055 nanoseconds, corresponding to the 14th-order harmonic mode locking, and its output power is 63.5 milliwatts. Figure 4 and Figure 5 This is the measured spectrum diagram. The signal-to-noise ratio is about 50 dB. It can be seen that it is in a stable mode-locked state. Figure 6 is the measured pulse autocorrelation trace, with a pulse width of 13.49 picoseconds. Figure 7 is the beam profile measured at the output coupler of a multimode fiber.

[0046] Example 1

[0047] Combination Figures 1 to 7 As shown, a harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism includes a first arm and a second arm, and two ends of the first arm are connected to two ends of the second arm;

[0048] The first arm is composed of a first pump source 1, a first beam combiner 2, a first gain fiber 3, a polarization-dependent isolator 4, a first polarization controller 5 and a first bandpass filter 6 connected in sequence;

[0049] The second arm is composed of a second pump source 7, a second beam combiner 8, a second gain fiber 9, a cladding pump stripper 10, a polarization-independent isolator 11, a multimode fiber output coupler 12, a second polarization controller 13, and a wavelength-tunable bandpass filter 14, which are connected in sequence.

[0050] The end of the first bandpass filter 6 opposite to the first polarization controller 5 is connected to the second beam combiner 8 , and the end of the first beam combiner 2 opposite to the first gain fiber 3 is connected to the wavelength tunable bandpass filter 14 .

[0051] The first gain optical fiber 3 and the second gain optical fiber 9 are both double-clad gain optical fibers.

[0052] In this embodiment, for the first arm, the first pump source 1 emits pump light, the first beam combiner 2 couples the pump light into the first gain fiber 3, the double-clad first gain fiber 3 absorbs the pump light, a population inversion occurs, a signal light is generated and amplified, the signal light is transmitted unidirectionally through the polarization-dependent isolator 4, and the signal light then changes its polarization state through the first polarization controller 5, wherein the polarization-dependent isolator 4 and the first polarization controller 5 constitute a polarization-sensitive device to form a laser beam, and the laser beam then passes through the first bandpass filter 6 for filtering. The bandwidth of the first bandpass filter 6 is 6.8 nanometers.

[0053] The filtered laser beam then enters the second arm. For the second arm, the second pump source 7 emits pump light. The second beam combiner 8 couples the pump light and the laser beam generated by the first arm into the second gain fiber 9. The second gain fiber 9 absorbs the pump light, forming a population inversion, and continues to amplify the laser beam generated by the first arm. After passing through the cladding pump stripper 10, the unpumped cladding light is absorbed and stripped out of the laser cavity. The laser beam is transmitted unidirectionally through the polarization-independent isolator 11, and then passes through the multimode fiber output coupler 12 to excite a multimode laser beam, realizing spatiotemporal mode locking. The multimode laser beam that returns to the cavity through the multimode fiber coupler 12 passes through the second polarization controller 13 and is converted into a single-mode laser beam. Then the single-mode laser beam passes through the wavelength-tunable bandpass filter 14, and finally forms a complete cavity cycle.

[0054] This laser is not limited by the operating wavelength of the gain fiber and can output time-space harmonic mode-locked optical pulses in different bands.

[0055] The self-start of mode locking is achieved through spectrum broadening and bias spectrum filtering caused by self-phase modulation; the pulse in the laser undergoes two amplifications to further increase the pulse energy. The gain fiber and multimode fiber output coupler in the laser expand the time-domain mode-locked pulse to lock it simultaneously in the time domain and space domain, and each component is reasonably designed and optimized to achieve stable time-space mode-locked laser output.

[0056] Example 2

[0057] Combination Figures 1 to 7 As shown, the difference between this embodiment and embodiment 1 is that:

[0058] The first polarization controller 5 and the polarization-dependent isolator 4 constitute a polarization-sensitive device.

[0059] The first bandpass filter 6 and the wavelength tunable bandpass filter 14 form a bias filtering effect.

[0060] In this embodiment, high power is achieved through double-clad gain fiber; initial pulses and bias filtering effects are generated through polarization-sensitive devices, and stable spatiotemporal mode locking is achieved through multimode fiber.

[0061] Through the rational design of each device and the optimized layout of the resonant cavity structure, high repetition rate stable spatiotemporal mode locking can be achieved simultaneously.

[0062] The first arm of the spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism is also provided with a pigtail of the first beam combiner 2, one end of the pigtail of the first beam combiner 2 is fused with a wavelength-tunable bandpass filter 14, and the other end is fused with the first gain fiber 3, which is used to couple the pump light into the first gain fiber 3. In the first arm, the pigtail of one end of the first beam combiner 2 uses an optical fiber that matches the gain fiber, which is used to couple the pump light into the first gain fiber 3. The first beam combiner 2 and the second beam combiner 8 are both 980 / 1030 nanometer beam combiners.

[0063] The first gain fiber 3 has high gain, and when the pump provides energy, a population inversion occurs, which can realize the function of high power output, absorb pump light, generate signal light, and amplify the signal light. The gain fiber realizes high power.

[0064] The first gain fiber 3 is a double-clad gain fiber with a core diameter of 10 microns. The first gain fiber 3 and the second gain fiber 9 are positive dispersion fibers with lengths of 4.1 meters and 5.6 meters. The entire Mamyshev mechanism-based harmonic time-space mode-locked fiber laser cavity length is about 30.8 meters.

[0065] A polarization-dependent isolator 4 pigtail is also provided in the first arm of the Mamyshev mechanism mode-locked fiber laser. One end of the polarization-dependent isolator 4 pigtail is fused to the first gain fiber 3, and the other end is fused to the first polarization controller 5, which is used to make the laser beam in the cavity unidirectionally transmitted. The first polarization controller 5 is used to change the polarization state of the laser beam.

[0066] The core diameters of the pigtails of the polarization-dependent isolator 4 and the first polarization controller 5 are both 6 microns.

[0067] One port of the first polarization controller 5 of the first arm is connected to the first bandpass filter 6 , and the other port is connected to the polarization-dependent isolator 4 , wherein the central wavelength of the first bandpass filter 6 is 1030 nanometers and the bandwidth is 6.8 nanometers.

[0068] Example 3

[0069] Combination Figures 1 to 7 As shown, the difference between this embodiment and embodiment 2 is that:

[0070] After passing through the first bandpass filter 6, the laser beam reaches the second arm and first passes through the second combiner 8. One end of the second combiner 8 is connected to the first bandpass filter 6, and the other end is connected to the second gain fiber 9. The pump light is coupled to the second gain fiber 9 through the second pump source 7 through the second combiner 8. The pigtail at one end of the second combiner 8 is a 6-micron core diameter single-clad fiber that matches the first bandpass filter 6, and the pigtail at the other end is a 10-micron core diameter double-clad fiber that matches the second gain fiber 9.

[0071] The laser beam passes through the second gain optical fiber 9 and then passes through the cladding pump stripper 10. The core diameters of the two ports of the cladding pump stripper 10 are both 10 microns, which are used to absorb the unpumped cladding light.

[0072] The laser beam then enters the polarization-independent isolator 11 . The core diameters of both ends of the pigtail of the polarization-independent isolator 11 are 10-micron double-clad optical fibers, ensuring unidirectional transmission of the laser beam.

[0073] A multimode fiber output coupler 12 is also provided in the second arm. One end of the pigtail of the multimode fiber output coupler 12 is fused to the polarization-independent isolator 11, and the other end is fused to the second polarization controller 13, which is used to couple and output the multimode laser beam. The pigtail of the multimode fiber output coupler 12 adopts a multimode gradient refractive index transmission fiber, and the core diameter of the pigtail of the multimode fiber output coupler 12 is 50 microns. The coupling ratio of the multimode fiber output coupler 12 is 20:80, and 20% is used as the output port. The multimode fiber output coupler 12 is a 1×2 type. The first polarization controller 5 and the second polarization controller 13 are composed of a half-wave plate and a quarter-wave plate.

[0074] The laser beam reaches the second polarization controller 13 after passing through the multimode optical fiber output coupler 12. The core diameters of the pigtail fibers at both ends of the second polarization controller 13 are both 6 microns, in order to achieve the functions of spatial filtering and changing the polarization state.

[0075] The tail fibers at both ends of the wavelength tunable bandpass filter 14 are both 6 microns, in order to match the tail fibers of the second polarization controller 13 and the first combiner 2. In addition, the first bandpass filter 6 and the wavelength tunable bandpass filter 14 form a bias filtering effect, which plays an important role in the mode locking based on the Mamyshev mechanism. The bandwidth of the wavelength tunable bandpass filter 14 is 0.85 nanometers. The adjustable range is from 1020 nanometers to 1100 nanometers.

[0076] This embodiment uses gain fiber and multimode transmission fiber to increase the output power of the laser; this application only needs to simply fuse the pigtails of each device and adjust the wavelength tunable bandpass filter to the appropriate central wavelength, and increase the pump power to achieve various functions required for mode locking. The first pump source 1 and the second pump source 7 are multimode pump sources with pigtail outputs, with a central wavelength of 976 nanometers and a maximum output power of 9 watts.

[0077] This embodiment effectively realizes stable spatiotemporal mode locking through the ingenious combination and optimized design of polarization sensitive devices, multimode optical fibers and filters.

[0078] In some embodiments, the polarization-dependent isolator 4 and the polarization-independent isolator 11 have the function of ensuring unidirectional transmission of signal light; wherein the polarization-dependent isolator 4 combined with the first polarization controller 5 plays the function of generating initial pulsation of the polarization-sensitive device.

[0079] When the laser beam is transmitted from the multimode optical fiber output coupler 12 pigtail to the second polarization controller 13 pigtail, due to the difference in specifications of the multimode optical fiber output coupler 12 pigtail and the second polarization controller 13 pigtail, a spatial filtering effect is generated at the fusion point of the two pigtails, thereby achieving a spatial filtering effect on the laser beam.

[0080] This embodiment cleverly implements the spatial filtering function through the effective combination of multi-mode optical fiber and single-mode (few-mode) optical fiber.

[0081] In some embodiments, the polarization-dependent isolator 4 and the polarization controller 5 together constitute a polarization-sensitive device to generate the initial pulsation.

[0082] The above-mentioned harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism uses gain fiber and a filter structure based on the fiber itself to achieve spatial filtering and spectral filtering, and combines the mode-locking device to achieve spatiotemporal mode-locking, and the gain fiber achieves high power. After adjusting the central wavelength of the tunable filter to 1034.5 nanometers and increasing the pump power to 2.06 watts and 2.09 watts, the self-starting operation of the harmonic spatiotemporal mode-locked fiber laser based on the Mamyshev mechanism can be achieved.

[0083] In addition, in this embodiment, the first gain fiber 3 and the second gain fiber 9 are doped fibers, which are the core part of the fiber laser; the pump light is used to provide energy to the rare earth elements in the doped fiber, so that the rare earth elements in the doped fiber can achieve population inversion. The rare earth elements in the doped fiber can be of various types, such as ytterbium (Yb), erbium (Er), thulium (Tm), and praseodymium (Pr). According to the different doped elements, signal light output of different bands can be achieved.

[0084] The first gain optical fiber 3 and the second gain optical fiber 9 are ytterbium-doped optical fibers. The emission peak of the ytterbium-doped optical fiber is located near 1 micron and can be used in the field of laser processing.

[0085] The first gain optical fiber 3 and the second gain optical fiber 9 are erbium-doped optical fibers. The emission peak of the erbium-doped optical fibers is located in the communication band and can be used in the field of optical communications.

[0086] The first gain fiber 3 and the second gain fiber 9 are thulium-doped fibers, the emission peak of which is located near 2 microns, and can be used in the field of medical surgery.

[0087] The first gain fiber 3 and the second gain fiber 9 are multi-mode gain fibers. Multi-mode gain fibers can support more modes and are more helpful in achieving high-energy pulse output.

[0088] The first gain fiber 3 and the second gain fiber 9 are few-mode gain fibers. Few-mode gain fibers can support fewer modes and are more conducive to achieving spatiotemporal mode locking.

[0089] The above-mentioned embodiments are described in a relatively detailed and specific manner, expressing the preferred embodiments of the present invention, and are only used to illustrate the technical ideas and features of the present invention. The purpose is to enable technicians in this field to understand the contents of the present invention and implement them accordingly, but are not limited to the present invention. The patent scope of the present invention cannot be limited only by this embodiment, that is, any equivalent changes or modifications made to the spirit disclosed by the present invention, for researchers or technicians in this field, without departing from the structure of the present invention, local improvements within the system and changes and conversions between subsystems, etc., are still within the patent scope of the present invention.

Claims

1. Harmonic spatiotemporal mode-locked fiber laser based on Mamyshev mechanism, characterized by: It comprises a first arm and a second arm, wherein two ends of the first arm are connected to two ends of the second arm; The first arm is composed of a first pump source (1), a first beam combiner (2), a first gain optical fiber (3), a polarization-dependent isolator (4), a first polarization controller (5) and a first bandpass filter (6) connected in sequence; The second arm is composed of a second pump source (7), a second beam combiner (8), a second gain fiber (9), a cladding pump stripper (10), a polarization-independent isolator (11), a multimode fiber output coupler (12), a second polarization controller (13), and a wavelength-tunable bandpass filter (14), which are connected in sequence.

2. The Mamyshev mechanism-based harmonic time-space mode-locked fiber laser according to claim 1, characterized in that: The end of the first bandpass filter (6) opposite to the first polarization controller (5) is connected to the second beam combiner (8), and the end of the first beam combiner (2) opposite to the first gain optical fiber (3) is connected to the wavelength tunable bandpass filter (14).

3. The Mamyshev mechanism-based harmonic time-space mode-locked fiber laser according to claim 1 or 2, characterized in that: The first polarization controller (5) and the polarization-dependent isolator (4) form a polarization-sensitive device.

4. The harmonic time-space mode-locked fiber laser based on the Mamyshev mechanism according to claim 3, characterized in that: The first bandpass filter (6) and the wavelength tunable bandpass filter (14) form a bias filtering effect.

5. The harmonic time-space mode-locked fiber laser based on the Mamyshev mechanism according to claim 1, characterized in that: The first gain optical fiber (3) and the second gain optical fiber (9) are doped optical fibers.

6. The harmonic time-space mode-locked fiber laser based on the Mamyshev mechanism according to claim 5, characterized in that: The first gain optical fiber (3) and the second gain optical fiber (9) are ytterbium-doped optical fibers.

7. The harmonic time-space mode-locked fiber laser based on the Mamyshev mechanism according to claim 5, characterized in that: The first gain optical fiber (3) and the second gain optical fiber (9) are erbium-doped optical fibers.

8. The harmonic time-space mode-locked fiber laser based on the Mamyshev mechanism according to claim 5, characterized in that: The first gain optical fiber (3) and the second gain optical fiber (9) are thulium-doped optical fibers.

9. The harmonic time-space mode-locked fiber laser based on the Mamyshev mechanism according to any one of claims 5 to 8, characterized in that: The first gain optical fiber (3) and the second gain optical fiber (9) are multi-mode gain optical fibers.

10. The Mamyshev mechanism-based harmonic time-space mode-locked fiber laser according to any one of claims 5 to 8, characterized in that: The first gain optical fiber (3) and the second gain optical fiber (9) are few-mode gain optical fibers.

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