A spatiotemporal pure even-order dispersion soliton fiber laser and a method for generating the same

Abstract

This invention discloses a spatiotemporally pure high even-order dispersion soliton fiber laser and its generation method, belonging to the field of communication technology. It comprises a pump source, a wavelength division multiplexer, a few-mode erbium-ytterbium co-doped fiber, a first photonic lantern, a spectral pulse shaper, a second photonic lantern, a few-mode fiber beam splitter, and a saturable absorber connected sequentially to form a ring optical path. The first photonic lantern decomposes the multimode beam into multiple single-mode beams. The spectral pulse shaper independently applies a phase mask to each single-mode beam, introducing pure high even-order dispersion and compensating for low-order dispersion. The second photonic lantern multiplexes the modulated single-mode beams back into a multimode beam. This invention achieves independent and precise dispersion control of different transverse modes by spatially decoupling the multimode optical field. For the first time, it generates stable soliton pulses dominated by pure high even-order dispersion in a spatiotemporally mode-locked fiber laser, significantly improving pulse energy carrying capacity and providing a new solution for the development of high-energy ultrafast light sources.

Description

Technical Field

[0001] This invention belongs to the field of communication technology, specifically relating to a spatiotemporally pure high even-order dispersive soliton fiber laser and its generation method. Background Technology

[0002] Fiber mode-locked lasers have revolutionized many fields, including microscopic imaging, microfabrication, high-resolution spectroscopy, and time-frequency measurement. Single-mode fiber, with its cost-effectiveness, high reliability, and low loss, offers a simple method for realizing fiber mode-locked lasers. However, with the ever-increasing demand for high-energy lasers and the pursuit of greater data capacity in fiber optic communications, single-mode fiber is facing unprecedented challenges. Furthermore, the formation of traditional optical solitons relies on balancing negative second-order dispersion and Kerr nonlinearity, with pulse energy inversely proportional to pulse duration, which severely limits the generation of high peak power ultrashort pulses. Therefore, to overcome the bottleneck of pulse energy being limited by transverse mode constraints and soliton area, spatiotemporal high even-order dispersion soliton fiber laser technology has emerged.

[0003] Although experimental and theoretical work has demonstrated that the interaction between high even-order dispersion and Kerr nonlinearity in conventional mode-locked lasers can support the formation of high even-order dispersive solitons, exhibiting advantages in overcoming second-order dispersion dependence and energy limitations, the synergistic application of high even-order dispersive solitons and spatiotemporal mode-locking still faces fundamental challenges. Current dispersion management techniques mainly rely on spectral pulse shapers or custom-designed microstructured fibers to apply a global dispersion distribution to the beam. However, in multimode systems, the complex spatiotemporal dynamics within the multimode fiber result in different modes having different group velocities, accompanied by strong intermode crosstalk. The inherent spatial overlap of different modes makes it impossible to independently control mode-locking of specific modes using these methods, directly leading to difficulties in precisely controlling the high even-order dispersion of specific modes in multimode cavities.

[0004] Therefore, to date, research on high even-order dispersive solitons has been mainly limited to single-mode systems, and a new spatiotemporal mode-locking control mechanism is urgently needed to achieve stable output of high-energy solitons based on high even-order dispersion. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a spatiotemporally pure high even-order dispersive soliton fiber laser and its generation method. The aim is to achieve independent and precise dispersion control of different transverse modes by spatially decoupling the multimode optical field, generating stable soliton pulses dominated by pure high even-order dispersion for the first time in a spatiotemporally mode-locked fiber laser. These soliton pulses exhibit excellent energy scaling characteristics, enabling higher peak power to be supported within the same pulse duration. This invention not only experimentally verifies the formation mechanism of pure high even-order dispersive solitons in complex spatiotemporal systems but also opens up new pathways for the development of next-generation high-energy, multidimensional ultrafast light sources.

[0006] This invention is achieved through the following technical solution:

[0007] A spatiotemporally pure high even-order dispersive soliton fiber laser includes a pump source 1, a wavelength division multiplexer 2, a few-mode erbium-ytterbium co-doped fiber 3, a first photonic lantern 4, a spectral pulse shaper 5, a second photonic lantern 6, a few-mode fiber beam splitter 7, and a saturable absorber 8. The wavelength division multiplexer 2, the few-mode erbium-ytterbium co-doped fiber 3, the first photonic lantern 4, the spectral pulse shaper 5, the second photonic lantern 6, the few-mode fiber beam splitter 7, and the saturable absorber 8 are sequentially connected by optical fibers to form a ring optical path. The pump source 1 is connected to the wavelength division multiplexer 2 to provide pump light to the ring resonant cavity. The few-mode fiber beam splitter 7 has an A port and a B port, with the A port connected to the saturable absorber 8 and the B port serving as the total output of the laser.

[0008] The first photonic lantern 4 is used to spatially decompose the multimode beam from the few-mode erbium-ytterbium co-doped fiber 3 into multiple independent single-mode beams. The spectral pulse shaper 5 has multiple input ports and multiple output ports, which are respectively connected to multiple single-mode outputs of the first photonic lantern 4 and multiple single-mode inputs of the second photonic lantern 6. It is used to independently apply a preset phase mask to each spatially separated single-mode beam to introduce pure high even-order dispersion of the target order, while compensating for its low-order dispersion. The second photonic lantern 6 is used to re-multiplex the multiple single-mode beams after independent phase masking into a multimode beam and couple it back into the ring optical path.

[0009] Furthermore, the pump source 1 outputs 915nm pump light.

[0010] Furthermore, the few-mode erbium-ytterbium co-doped fiber 3 adopts a double-clad fiber structure, with a gain range of 1530~1570nm and a fiber length of 1.5m.

[0011] Furthermore, both the first photon lantern 4 and the second photon lantern 6 are mode-selective photon lanterns, supporting LP. 01 LP 11 LP 21 and LP02 Four modes.

[0012] Furthermore, the few-mode fiber beam splitter 7 has a 1×2 structure and a splitting ratio of 2:8.

[0013] Furthermore, the saturable absorber 8 is an artificial saturable absorber with nonlinear polarization rotation, which includes two polarization controllers and a polarization-dependent isolator, and can be controlled via LP. 01 LP 11 LP 21 and LP 02 model.

[0014] Furthermore, the polarization controller and polarization-dependent isolator in the few-mode fiber beam splitter 7 and the saturable absorber 8 are all made of few-mode fiber that supports multimode transmission, wherein the core and cladding diameters of the few-mode fiber are 18.5 μm and 125 μm, respectively.

[0015] Furthermore, the target order of pure even-order dispersion includes pure fourth-order dispersion, pure sixth-order dispersion, or pure eighth-order dispersion; the low-order dispersion includes second-order dispersion and third-order dispersion.

[0016] On the other hand, the present invention also provides a method for generating spatiotemporally pure high even-order dispersive solitons based on a spatiotemporally pure high even-order dispersive soliton fiber laser, comprising the following steps:

[0017] S1. The pump light emitted from the pump source is coupled into the ring resonant cavity via a wavelength division multiplexer, which excites the gain fiber to generate a multimode optical field.

[0018] S2. The multimode light field enters the first photon lantern and is spatially decomposed into multiple independent single-mode beams.

[0019] S3. The multiple independent single-mode beams are input to the transverse mode control module, and the single-mode beams are input to the corresponding channels of the spectral pulse shaper. By applying an independent phase mask to each channel, pure high even-order dispersion of the target order is introduced into each single-mode beam, while its low-order dispersion is compensated at the same time, to obtain multiple single-mode beams after dispersion control. By inserting compensation fibers of different lengths into the multiple single-mode beam paths, the group velocity mismatch between the modes is compensated to achieve synchronization of the modes in the time domain.

[0020] S4. Multiple single-mode beams after dispersion modulation are input into the second photonic lantern, re-multiplexed into a multimode beam, and then input into a few-mode fiber beam splitter. The beam is output from the A port of the few-mode fiber beam splitter to the saturable absorber, and then re-enters the loop through the B port of the wavelength division multiplexer for oscillation. At the same time, the generated beam is output as a mode-locked pulse from the B port of the few-mode fiber beam splitter.

[0021] S5. By adjusting the phase mask of the spectral pulse shaper, the circulating light pulses in the cavity are made to form stable spatiotemporally pure high even-order dispersion solitons under the combined effect of pure high even-order dispersion and nonlinear effects.

[0022] The working principle of the spatiotemporally pure high even-order dispersive soliton fiber laser of the present invention is as follows:

[0023] This invention employs a multi-channel silicon-based liquid crystal programmable spectral pulse shaper to independently apply precise arbitrary phase masks to each mode, thereby introducing high even-order artificial dispersion into each mode and simultaneously compensating for second-order and third-order dispersion. Its schematic diagram is shown in Figure 2. In the spectral pulse shaper, each channel uses a Fourier transform structure composed of a grating and a curved mirror to unfold the temporal pulse dispersion into a spatially distributed spectrum. A silicon-based liquid crystal array phase screen is used to apply phase modulation of the corresponding dispersion to each spectral frequency component, and then the beam is combined and output via an inverse Fourier transform, achieving precise management of the dispersion of each mode and providing reliable assurance for dynamic compensation of mode-dependent dispersion in multimode optical systems. The phase distribution loaded on the phase screen can be represented by equation (1).

[0024] (1)

[0025] Where Φ P This represents the phase loaded in the p-th mode, where ω and ω0 are the angular frequency and the center angular frequency, respectively. This represents the nth order dispersion of the p-th mode in the first fiber segment. This represents the nth order dispersion of the p-th mode in the second fiber segment. L represents the nth order dispersion of the p-th mode in the third fiber segment, and L1 and L2 represent the lengths of the gain fiber and the passive fiber, respectively. 3,p This represents the length of the compensation fiber for the p-th mode. This configuration ensures that the low-order dispersions of all modes are completely canceled during each round trip within the cavity, so that pulse propagation is dominated only by high even-order dispersions of uniform intensity.

[0026] This invention employs a transverse mode control module to individually control the dispersion of each mode in a spatiotemporally mode-locked laser, as shown in the schematic diagram. Figure 1The transverse mode control module is shown in the diagram. To address the limitations of inter-mode crosstalk on precise dispersion management, a custom-cascaded photonic lantern is used as a mode demultiplexer / multiplexer to achieve physical separation of the multimode optical field within the cavity. The multimode beam is first spatially decomposed into independent transverse mode channels by the first photonic lantern, and then these separated modes are coupled to different input ports of a silicon-based liquid crystal programmable spectral pulse shaper. After applying a precise arbitrary phase mask to each independent mode by the spectral pulse shaper, a compensation fiber of a specific length is inserted into the optical path to precisely adjust the group velocity mismatch between modes. This design effectively reduces inter-mode loss, achieves temporal overlap and synchronization between different modes, and the spectral pulse shaping is completed directly within the fiber laser cavity.

[0027] This invention utilizes a nonlinear polarization rotation effect to prepare a saturable absorber, such as... Figure 3 As shown, this module contains two polarization controllers and one polarization-dependent isolator. This design not only ensures unidirectional circulation, but also ensures that when light passes through the polarization controllers and polarization-dependent isolator inside the cavity, the strong light component has lower loss due to the polarization rotation and better matching with the transmission axis of the polarizer, while the weak light component has greater loss. This forms an equivalent saturable absorption mechanism within the resonant cavity, allowing the high-peak pulse to be preferentially amplified and gradually formed into a stable ultrashort pulse, thus achieving passive mode-locked operation of the laser.

[0028] Compared with the prior art, the advantages of the present invention are as follows:

[0029] 1. The spatiotemporal pure high even-order dispersive soliton fiber laser of the present invention achieves experimental output of pure high even-order dispersive solitons for the first time in a spatiotemporal mode-locked fiber laser. Addressing the technical bottleneck of spatial mode overlap in standard multimode fibers, which prevents independent dispersion control, this invention effectively solves the problem of flexibly controlling the dispersion characteristics of different temporal modes in complex multimode systems by spatially decoupling the modes before phase shaping.

[0030] 2. This invention combines a spatiotemporal mode-locking mechanism with a pure high-even-order dispersive soliton mechanism, fully leveraging the advantages of spatial degrees of freedom and significantly improving pulse energy, with an energy carrying capacity far exceeding that of traditional single-mode lasers. This breakthrough provides an efficient solution for generating high peak power optical frequency combs, and is particularly suitable for energy-saving light source applications in future space-division multiplexing systems.

[0031] 3. The laser cavity design proposed in this invention has good versatility and can be extended to platforms such as multimode solid-state lasers and integrated photonic circuits, opening up new paths for the generation of customized spatiotemporal structure beams, and can be further extended to research directions such as higher-order dispersion control and vortex beam synthesis. Attached Figure Description

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0033] Figure 1 This is a schematic diagram of the spatiotemporal pure high even-order dispersive soliton fiber laser of the present invention;

[0034] In the diagram: 1. Pump source; 2. Wavelength division multiplexer; 3. Few-mode erbium-ytterbium co-doped fiber; 4. First photonic lantern; 5. Spectral pulse shaper; 6. Second photonic lantern; 7. Few-mode fiber beam splitter; 8. Saturable absorber.

[0035] Figure 2 This is a schematic diagram of the internal optical path and working principle of the programmable spectral pulse shaper of the present invention;

[0036] Figure 3 This is a schematic diagram of the saturable absorber structure based on the nonlinear polarization rotation effect of the present invention;

[0037] Figure 4 The dominant dispersion coefficient is set to β. k =-0.96ps k Schematic diagram of spectral characterization and sideband analysis of a single-mode pure high even-order dispersive soliton;

[0038] The left column shows the normalized experimental spectra of four different transmission modes, corresponding to pure fourth-order a, sixth-order b, and eighth-order c, respectively; df corresponds to the quantitative analysis of the Kelly lateral band position.

[0039] Figure 5 The dominant dispersion coefficient is set to β. k =-1.44ps k Schematic diagram of spectral characterization and sideband analysis of a single-mode pure high even-order dispersive soliton;

[0040] The left column shows the normalized experimental spectra of four different transmission modes, corresponding to pure fourth-order a, sixth-order b, and eighth-order c, respectively; df corresponds to the quantitative analysis of the Kelly lateral band position.

[0041] Figure 6 The dominant dispersion coefficient is set to β. k =-1.96ps k Schematic diagram of spectral characterization and sideband analysis of a single-mode pure high even-order dispersive soliton;

[0042] The left column shows the normalized experimental spectra of four different transmission modes, corresponding to pure fourth-order a, sixth-order b, and eighth-order c, respectively; df corresponds to the quantitative analysis of the Kelly lateral band position.

[0043] Figure 7 A schematic diagram of the spectral characterization and sideband analysis of spatiotemporally pure high even-order dispersive solitons;

[0044] The left column shows the normalized experimental spectra under three dispersion parameters, corresponding to pure fourth-order a, sixth-order b, and eighth-order c, respectively; df corresponds to the quantitative analysis of the Kelly fringe position.

[0045] Figure 8 This is a schematic diagram representing the demultiplexing of a pure sixth-order spacetime soliton, with the dominant dispersion coefficient set as β6 = -1.44 ps. 6 ;

[0046] Among them, a is a schematic diagram of the experimental setup for mode demultiplexing and time synchronization verification; b is the radio frequency spectrum of each demultiplexed time mode and the total spatiotemporal state; c is a comparison of the independent time mode spectrum and the total spatiotemporal mode-locked spectrum; d is a quantitative analysis of the corresponding sideband positions. Detailed Implementation

[0047] To clearly and completely describe the technical solution and its specific working process of the present invention, the specific embodiments of the present invention are as follows, in conjunction with the accompanying drawings:

[0048] Example 1

[0049] like Figure 1 As shown, this embodiment provides a spatiotemporally pure high even-order dispersive soliton fiber laser, including: a pump source 1, a wavelength division multiplexer 2, a few-mode erbium-ytterbium co-doped fiber 3, a first photonic lantern 4, a spectral pulse shaper 5, a second photonic lantern 6, a few-mode fiber beam splitter 7, and a saturable absorber 8; wherein, the output end of the pump source 1 is connected to the A port of the wavelength division multiplexer 2, the output port of the wavelength division multiplexer 2 is connected to one end of the few-mode erbium-ytterbium co-doped fiber 3, and the other end of the few-mode erbium-ytterbium co-doped fiber 3 is connected to the few-mode port of the first photonic lantern 4. The connection is as follows: multiple single-mode output ports of the first photonic lantern 4 are connected to the corresponding input ports of the spectral pulse shaper 5 via single-mode optical fibers; multiple output ports of the spectral pulse shaper 5 are connected to multiple single-mode input ports of the second photonic lantern 6; the few-mode port of the second photonic lantern 6 is connected to the input end of the few-mode fiber beam splitter 7; the A port of the few-mode fiber beam splitter 7 is connected to the input end of the saturable absorber 8, and the output end of the saturable absorber 8 is then connected to the B port of the echo division multiplexer 2, thereby forming a complete ring cavity. The B port of the few-mode fiber beam splitter 7 serves as the total output end of the laser, used to output the generated spatiotemporal soliton pulses.

[0050] In this embodiment, the pump source 1 is a multimode pump source from SkyEra Laser, with a center wavelength of 915nm and a maximum output power of 5W;

[0051] The few-mode erbium-ytterbium co-doped fiber 3 adopts a double-clad fiber structure, with a fiber length of 1.5m, a core diameter of 12.0μm, and a gain range of 1530-1570nm.

[0052] The first photon lantern 4 and the second photon lantern 6 are mode-selective photon lanterns that can support LP. 01 LP 11 LP 21 and LP 02 Four modes are used for mode reuse and demultiplexing;

[0053] like Figure 2 As shown, the spectral pulse shaper 5 employs a multi-channel silicon-based liquid crystal programmable spectral pulse shaper, which independently applies precise arbitrary phase masks to each mode, thereby introducing high even-order artificial dispersion into each mode and simultaneously compensating for second-order and third-order dispersion. Specifically, in the spectral pulse shaper, each channel expands the time-domain pulse dispersion into a spatially distributed spectrum through a Fourier transform structure composed of a grating and a curved mirror; the phase modulation of the corresponding dispersion is applied to each spectral frequency component using a silicon-based liquid crystal array phase screen, and then the beam is combined and output through inverse Fourier transform, realizing precise management of the dispersion of each mode and providing reliable protection for the dynamic compensation of mode-dependent dispersion in a multimode optical system. The phase distribution loaded on the phase screen can be represented by equation (1).

[0054] (1)

[0055] Where, Φ P This represents the phase loaded in the p-th mode, where ω and ω0 are the angular frequency and the center angular frequency, respectively. This represents the nth order dispersion of the p-th mode in the first fiber segment. This represents the nth order dispersion of the p-th mode in the second fiber segment. L represents the nth order dispersion of the p-th mode in the third fiber segment, and L1 and L2 represent the lengths of the gain fiber and the passive fiber, respectively. 3,p This represents the length of the compensation fiber for the p-th mode. This configuration ensures that the low-order dispersions of all modes are completely canceled during each round trip within the cavity, so that pulse propagation is dominated only by high even-order dispersions of uniform intensity.

[0056] The few-mode fiber beam splitter 7 adopts a 1×2 structure with a splitting ratio of 2:8, meaning that 20% of the energy is used for output and 80% of the energy remains in the cavity to continue oscillating.

[0057] like Figure 3 As shown, the saturable absorber 8 is an artificial saturable absorber based on the nonlinear polarization rotation (NPR) effect, consisting of two cascaded polarization controllers and a polarization-dependent isolator, and can be controlled via LP. 01 LP11 LP 21 and LP 02 This design not only ensures unidirectional circulation, but also ensures that when light passes through the polarization controller and polarization-dependent isolator set in the cavity, the strong light component has lower loss due to the polarization rotation and better matching with the transmission axis of the polarizer, while the weak light component has greater loss. This forms an equivalent saturable absorption mechanism in the resonant cavity, allowing the high peak pulse to be preferentially amplified and gradually formed into a stable ultrashort pulse, thus realizing the passive mode-locked operation of the laser.

[0058] The polarization controller and polarization-dependent isolator in the few-mode fiber beam splitter 7 and the saturable absorber 8 are all made of few-mode fiber that supports multimode transmission, wherein the core and cladding diameters of the few-mode fiber are 18.5 μm and 125 μm, respectively.

[0059] In this embodiment, the total fiber length within the cavity is 8.3m, and the delays of each mode group within the cavity are 0, 4.4, 10.67, and 18 ps / m, respectively. Based on the fiber length and parameters, each meter of single-mode fiber can compensate for a delay of 4.829 ns. Therefore, at the demultiplexed single-mode end of the first photonic lantern 4, respectively at LP 01 Add 2.7cm fiber optic cable and LP cable to the splitter. 11 Add 2.1cm fiber optic cable and LP cable to the splitter. 21 A 1.1cm fiber was added to the splitter to balance the intermodal dispersion.

[0060] In this embodiment, the dispersion parameter of the single-mode fiber is 17 ps (nm•km). -1 For few-mode fibers, corresponding to LP 01 LP 11 LP 21 and LP 02 The dispersion parameters of the modes are 21.9, 22.5, 22.0, and 21.8 ps (nm•km). -1 Therefore, the intrinsic net cavity second-order dispersion values ​​for these modes are calculated to be −0.1773, −0.1816, −0.1778, and −0.1761 ps². To compensate for the intracavity dispersion, the second-order and third-order dispersion values ​​applied through the spatial light modulator are set to 0.1826 ps² and -0.00012 ps³, respectively, where the third-order dispersion value is derived from the reference. Ultimately, the net cavity second-order dispersion remains at a slightly positive value (LP). 01 LP 11 LP 21 and LP 02 The values ​​were 0.0053, 0.001, 0.0048 and 0.0065 ps², respectively, to effectively suppress the formation of conventional solitons.

[0061] In this embodiment, the mode-locked spectrum of the output light pulse is measured using a spectrometer with a resolution of 0.1 nm. After the light pulse is photoelectrically converted using a multimode photodetector, the time-domain sequence of the mode-locked light pulse is measured using an oscilloscope.

[0062] With the above settings, the laser in this embodiment can operate stably. By adjusting the phase mask applied by the programmable spectral pulse shaper, the dispersion order of the dominant soliton formation can be flexibly controlled. Using the system described above, the output of spatiotemporally pure high even-order dispersive solitons was achieved through selective excitation of specific modes, and the discrete Kelly sidebands appearing in the spectrum were quantitatively analyzed. The results are as follows: Figures 4-6 As shown, the spectral profiles of all excited individual modes exhibit significant evolutionary characteristics—the spectral morphology changes markedly as the dominant dispersion order k increases from 4th to 8th. Due to the combined effects of the inherent spatial properties of the gain medium and transmission loss, significant differences in steady-state output energy were observed among the different modes.

[0063] To completely eliminate the influence of the traditional second-order soliton mechanism and verify that the generated spacetime wave envelope is indeed controlled by specific high even-order dispersion, phase-matching verification was performed on the output spectra dominated by pure fourth-order dispersion, sixth-order dispersion, and eighth-order dispersion. Figure 7 As shown, all spectra exhibit a distinctive flat-top profile and steep edges, accompanied by discrete Kelly bands. Quantitative analysis reveals that each dispersion order maintains a strict linear relationship with the sideband exponent. Comparing the spectral characteristics of spatiotemporally pure high even-order dispersive solitons with those of single-mode pure high even-order dispersive solitons, the spectra of spatiotemporally high even-order dispersive solitons exhibit two significant features: significant suppression of sidebands and a marked central asymmetry in the spectral profile.

[0064] To further verify whether the pulses obtained in the experiment represent true spacetime locked modes (rather than incoherent superposition of different time modes), a pure sixth-order dispersive soliton (net dispersion of -1.44 ps) was selected. 6 ) to perform mode demultiplexing characteristic analysis. This is achieved by building a mode demultiplexing system (such as... Figure 8 As shown in (a), the output beam was separated into four independent time modes. The time-domain traces recorded by the oscilloscope showed that all separated modes exhibited periodic, stable pulse sequences. To confirm whether these modes were strictly locked, the radio frequency spectrum of each mode component was measured (…). Figure 8 (b). The results show that all time modes and spatiotemporal outputs share a common fundamental frequency repetition rate of 24.95 MHz. This confirms that all modes achieve precise synchronization in the time domain, forming stable spatiotemporal pure high even-order dispersive solitons.

[0065] In summary, this embodiment establishes a spatiotemporally pure high even-order dispersive soliton fiber laser. By employing transverse mode-splitting control technology, it overcomes the challenge of mode-specific dispersion management and achieves experimental output of pure high even-order dispersive solitons for the first time in a spatiotemporally mode-locked fiber laser. This highlights the unique advantages of combining spatiotemporal mode-locking with the pure high even-order dispersive soliton mechanism, significantly increasing pulse energy through spatial degrees of freedom. Its energy carrying capacity far exceeds that of traditional single-mode lasers, providing an efficient solution for generating high peak power optical frequency combs.

[0066] Example 2

[0067] This embodiment provides a method for generating spatiotemporally pure high even-order dispersive solitons based on the laser described in Embodiment 1, including the following steps:

[0068] Step S1: Turn on pump source 1. The 915nm pump light emitted by it is coupled into the ring resonant cavity through wavelength division multiplexer 2, which excites the few-mode erbium-ytterbium co-doped fiber 3 to generate an amplified multimode optical field.

[0069] In step S2, the multimode light field sequentially enters the first photon lantern 4 and is spatially decomposed into LP. 01 LP 11 LP 21 and LP 02 Four independent single-mode beams.

[0070] In step S3, the four single-mode beams are input to the four independent channels of the spectral pulse shaper. Different phase masks are designed and loaded for each channel using host computer software; for example, a net dispersion of -1.44 ps is introduced for all channels. 6 The pure sixth-order dispersion is eliminated, while the second- and third-order dispersions are precisely compensated to zero. Simultaneously, based on the group delay difference of each mode, a pre-set length of compensation fiber is inserted into the corresponding single-mode beam path to ensure that the optical pulses of each mode are approximately aligned in the time domain.

[0071] Step S4: After independent dispersion modulation, the four single-mode beams output from the compensation fiber enter the second photonic lantern, are multiplexed into a single multimode beam, and coupled back into the loop optical path. This multimode beam, after passing through a few-mode fiber beam splitter, has 80% of its energy enter the saturable absorber. Under the effect of nonlinear polarization rotation, pulse narrowing and mode-locking are achieved, and the beam continues to circulate within the cavity via a wavelength division multiplexer. The remaining 20% ​​of the energy is output from port B of the few-mode fiber beam splitter.

[0072] Step S5: By adjusting the phase mask and pump power of the spectral pulse shaper, the circulating light pulse in the cavity forms a stable spatiotemporal pure high even-order dispersion soliton under the combined effect of pure high even-order dispersion and nonlinear effects.

[0073] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0074] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0075] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A spatiotemporally pure high even-order dispersive soliton fiber laser, characterized in that, The system includes a pump source (1), a wavelength division multiplexer (2), a few-mode erbium-ytterbium co-doped fiber (3), a first photonic lantern (4), a spectral pulse shaper (5), a second photonic lantern (6), a few-mode fiber beam splitter (7), and a saturable absorber (8). The wavelength division multiplexer (2), the few-mode erbium-ytterbium co-doped fiber (3), the first photonic lantern (4), the spectral pulse shaper (5), the second photonic lantern (6), the few-mode fiber beam splitter (7), and the saturable absorber (8) are connected sequentially by optical fibers to form a ring optical path. The pump source (1) is connected to the wavelength division multiplexer (2) to provide pump light to the ring resonant cavity. The few-mode fiber beam splitter (7) has an A port and a B port. Its A port is connected to the saturable absorber (8), and its B port serves as the total output of the laser. The first photonic lantern (4) is used to spatially decompose the multimode beam from the few-mode erbium-ytterbium co-doped fiber (3) into multiple independent single-mode beams; the spectral pulse shaper (5) has multiple input ports and multiple output ports, which are respectively connected to multiple single-mode outputs of the first photonic lantern (4) and multiple single-mode inputs of the second photonic lantern (6), and are used to independently apply a preset phase mask to each single-mode beam after spatial separation, so as to introduce pure high even-order dispersion of the target order, and at the same time compensate for its low-order dispersion; the second photonic lantern (6) is used to reuse the multiple single-mode beams after independent phase masking into a multimode beam and couple them back into the ring optical path.

2. The spatiotemporally pure high even-order dispersive soliton fiber laser as described in claim 1, characterized in that, The pump source (1) outputs 915nm pump light.

3. A spatiotemporally pure high even-order dispersive soliton fiber laser as described in claim 1, characterized in that, The few-mode erbium-ytterbium co-doped fiber (3) adopts a double-clad fiber structure, with a gain range of 1530~1570nm and a fiber length of 1.5m.

4. A spatiotemporally pure high even-order dispersive soliton fiber laser as described in claim 1, characterized in that, Both the first photon lantern (4) and the second photon lantern (6) are mode-selectable photon lanterns that support LP. 01 LP 11 LP 21 and LP 02 Four modes.

5. A spatiotemporally pure high even-order dispersive soliton fiber laser as described in claim 1, characterized in that, The few-mode fiber beam splitter (7) has a 1×2 structure and a splitting ratio of 2:

8.

6. A spatiotemporally pure high even-order dispersive soliton fiber laser as described in claim 1, characterized in that, The saturable absorber (8) is an artificial saturable absorber with nonlinear polarization rotation, comprising two polarization controllers and a polarization-dependent isolator, which can be controlled by LP. 01 LP 11 LP 21 and LP 02 model.

7. A spatiotemporally pure high even-order dispersive soliton fiber laser as described in claim 1, characterized in that, The polarization controller and polarization-dependent isolator in the few-mode fiber bundle splitter (7) and saturable absorber (8) are all made of few-mode fiber that supports multimode transmission, wherein the core and cladding diameters of the few-mode fiber are 18.5 μm and 125 μm, respectively.

8. A spatiotemporally pure high even-order dispersive soliton fiber laser as described in claim 1, characterized in that, The target order of pure even-order dispersion includes pure fourth-order dispersion, pure sixth-order dispersion, or pure eighth-order dispersion; the low-order dispersion includes second-order dispersion and third-order dispersion.

9. The method for generating spatiotemporally pure high even-order dispersive solitons in a fiber laser with spatiotemporally pure high even-order dispersive solitons as described in claim 1, characterized in that, Includes the following steps: S1. The pump light emitted from the pump source is coupled into the ring resonant cavity via a wavelength division multiplexer, which excites the gain fiber to generate a multimode optical field. S2. The multimode light field enters the first photon lantern and is spatially decomposed into multiple independent single-mode beams. S3. Input the multiple independent single-mode beams into the transverse mode control module respectively. The single-mode beams are input into the corresponding channels of the spectral pulse shaper. By applying an independent phase mask to each channel, pure high even-order dispersion of the target order is introduced into each single-mode beam, while compensating for its low-order dispersion, to obtain multiple single-mode beams after dispersion control. By inserting compensation fibers of different lengths into multiple single-mode beam paths, the group velocity mismatch between modes is compensated, thereby achieving synchronization of modes in the time domain. S4. Multiple single-mode beams after dispersion modulation are input into the second photonic lantern, re-multiplexed into a multimode beam, and then input into a few-mode fiber beam splitter. The beam is output from the A port of the few-mode fiber beam splitter to the saturable absorber, and then re-enters the loop through the B port of the wavelength division multiplexer for oscillation. At the same time, the generated beam is output as a mode-locked pulse from the B port of the few-mode fiber beam splitter. S5. By adjusting the phase mask of the spectral pulse shaper, the circulating light pulses in the cavity are made to form stable spatiotemporally pure high even-order dispersion solitons under the combined effect of pure high even-order dispersion and nonlinear effects.

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