A saturable absorber and its application in a laser

Abstract

The application discloses application of two-dimensional transition metal boride in a saturable absorber and a laser, and the two-dimensional transition metal boride is Mo 4 / 3 B 2‑x T z The application builds a fiber laser based on two-dimensional Mo 4 / 3 B 2‑x T z , optimizes Mo 4 / 3 B 2‑ x T z saturable absorber and a cavity structure of the fiber laser, and after adjusting pump power and a polarization state in the cavity, self-starting of ultrashort and high-repetition-rate mode-locked pulses is realized.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and more particularly to a saturable absorber and its application in lasers. Background Technology

[0002] In the field of ultrafast lasers, passive mode-locking based on saturable absorbers overcomes the stringent requirements of Kerr lens mode-locking on the resonant cavity design at the edge of the stable region, while also allowing for convenient self-starting, making it one of the ideal methods for generating picosecond and femtosecond seed sources. To date, semiconductor saturable absorber mirrors (SESAMs) are the only commercially available saturable absorber material. However, SESAM fabrication requires complex and expensive molecular beam epitaxy equipment. Furthermore, high-quality ultrafast laser generation using SESAM saturable absorbers has not yet been achieved in the mid-infrared band. Therefore, the search for excellent saturable absorber materials that can be easily mass-produced has been a continuous pursuit for researchers in the fields of nonlinear optics and materials science. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, one of the objectives of this invention is to provide an application of two-dimensional transition metal borides in saturable absorbers.

[0004] The second objective of this invention is to provide a saturable absorbent.

[0005] The third objective of this invention is to provide an all-fiber mode-locked laser.

[0006] One of the objectives of this invention is achieved through the following technical solution:

[0007] Application of a two-dimensional transition metal boride in a saturable absorber, wherein the two-dimensional transition metal boride is a layered Mo. 4 / 3 B 2-x T z T z It is a surface functional group, usually -O, OH or -F; x is 0 to 0.5, z is 2 to 3.

[0008] As a preferred embodiment of the present invention, for the

[110] plane of the two-dimensional transition metal boride, Mo 4 / 3 B 2- x T z The spacing between adjacent lattice fringes is 0.2–0.3 nm, preferably 0.268 nm.

[0009] As a preferred embodiment of the present invention, Mo 4 / 3 B 2-x T z The thickness of the sheet is 2-3 nm, preferably 2.5 nm.

[0010] This invention also provides a method for preparing two-dimensional transition metal borides, comprising the following steps:

[0011] Right (Mo 2 / 3 Y 1 / 3 Selective etching of 2AlB2 was performed, primarily using hydrofluoric acid. After stirring at room temperature, the suspension was filtered and then suspended in deionized water. This step was repeated several times to achieve the etching effect. The solid was then air-dried at room temperature. The etching powder was dissolved in tetrabutylammonium hydroxide (TBAOH) for a stripping process called embedding, followed by centrifugation to remove the precipitate. Residual TBAOH was removed with deionized water, and this process was repeated several times. Finally, the material system was separated into monolayers and few-layers of Mo using deionized water while shaking. 4 / 3 B 2-x T z (Layered structure).

[0012] The two-dimensional transition metal borides described in this invention are based on the paper "Two-dimensional Mo 4 / 3 B 2-x The novel material (two-dimensional transition metal borides) described in this paper was prepared using the method described in the paper. The paper was published in Science 373(6556), 801-805. This invention applies the novel material (two-dimensional transition metal borides) described in the paper to a new technical field, discovering its promising application prospects in femtosecond lasers.

[0013] The second objective of this invention is achieved by the following technical solution:

[0014] A saturable absorber comprising an optical fiber and a two-dimensional transition metal boride deposited on the optical fiber, wherein the two-dimensional transition metal boride is any one of the two-dimensional transition metal borides described in the present invention.

[0015] As a preferred embodiment of the present invention, the optical fiber is a micro / nano optical fiber.

[0016] The third objective of this invention is achieved by the following technical solution:

[0017] An all-fiber mode-locked laser, comprising the saturable absorber described in any one of the second objectives.

[0018] As a preferred embodiment of the present invention, the all-fiber mode-locked laser includes a pump source, a wavelength division multiplexer, a single-mode fiber, a gain fiber, a dispersion compensation fiber, a polarization-independent isolator, a fiber coupler, the saturable absorber described in the second objective, and a polarization controller, connected in sequence.

[0019] As a preferred embodiment of the present invention, for the all-fiber mode-locked laser, the pump source, wavelength division multiplexer, single-mode fiber, gain fiber, dispersion compensation fiber, polarization-independent isolator, fiber coupler, saturable absorber as described in the second objective, and polarization controller are connected in sequence to form a ring fiber resonant cavity structure.

[0020] In a preferred embodiment of the present invention, for the all-fiber mode-locked laser, the pump source is connected to the pump end of the wavelength division multiplexer to input pump light into the fiber resonator. The common end of the wavelength division multiplexer is connected to one end of the gain fiber, and the other end of the gain fiber is connected to the input end of the polarization-independent isolator. The output end of the polarization-independent isolator is connected to the input end of a fiber coupler with a coupling ratio of 10:90. 10% of the output end of the fiber coupler is used to output optical signals, and 90% of the output end of the fiber coupler is connected to one end of the saturable absorber. The other end of the saturable absorber is connected to the input end of the polarization controller, and the output end of the polarization controller is connected to the signal end of the wavelength division multiplexer.

[0021] As a preferred embodiment of the present invention, the gain fiber is a ytterbium-doped fiber, an erbium-doped fiber, or a thulium-doped fiber, preferably an erbium-doped fiber.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The two-dimensional Mo provided by the present invention 4 / 3 B 2-x T z It possesses the following characteristics: broadband saturable absorption from visible light to mid-infrared, strong nonlinear optical response, and small laser threshold, which means that two-dimensional Mo... 4 / 3 B 2-x T z As a passive mode-locked device, it has broad application prospects and can be used to generate ultrafast pulses.

[0024] (2) This invention constructs a two-dimensional Mo 4 / 3 B 2-x T z Fiber lasers and optimized Mo 4 / 3 B 2-x T z By adjusting the pump power and intracavity polarization state, the cavity structure of the saturable absorber and fiber laser enables self-starting of ultrashort and high repetition rate mode-locked pulses. Attached Figure Description

[0025] Figure 1 The (Mo) provided in Embodiment 1 of the present invention 2 / 3 Y 1 / 3 SEM image of AlB2 powder;

[0026] Figure 2 The (Mo) provided in Embodiment 1 of the present invention 2 / 3 Y 1 / 3 Elemental mapping diagram of AlB2 powder;

[0027] Figure 3 The few-layer Mo provided in Embodiment 1 of the present invention 4 / 3 B 2-x T z SEM image;

[0028] Figure 4 The few-layer Mo provided in Embodiment 1 of the present invention 4 / 3 B 2-x T z Element mapping graph;

[0029] Figure 5 The few-layer Mo provided in Embodiment 1 of the present invention 4 / 3 B2-xT z TEM image;

[0030] Figure 6 The Mo provided in Embodiment 1 of the present invention 4 / 3 B 2-x T z High-resolution TEM image, with inset showing the SAED pattern (scale bar: 2 nm-1).

[0031] Figure 7 The Mo provided in Embodiment 1 of the present invention 4 / 3 B 2-x T z The AFM diagram, with the inset being a height profile diagram;

[0032] Figure 8 The XRD pattern provided in Embodiment 1 of the present invention;

[0033] Figure 9 This is the full-scan XPS spectrum provided in Embodiment 1 of the present invention;

[0034] Figure 10 The (Mo) provided in Embodiment 1 of the present invention 2 / 3 Y 1 / 3 )2AlB2 powder and few-layer Mo 4 / 3 B 2-x T z High-resolution scan and fitting results of Mo 3d;

[0035] Figure 11 The (Mo) provided in Embodiment 1 of the present invention 2 / 3 Y 1 / 3 )2AlB2 powder and Mo 4 / 3 B 2-xT z High-resolution XPS scan of peak fitting in the B1s region of nanosheets;

[0036] Figure 12 This is the linear optical absorption spectrum provided in Embodiment 1 of the present invention;

[0037] Figure 13 The Mo provided in Embodiment 2 of the present invention 4 / 3 B 2-x T z Z-Scan results of the pores in the nanosheets at 475 nm;

[0038] Figure 14 The Mo provided in Embodiment 2 of the present invention 4 / 3 B 2-x T z Z-Scan results of the pores in the nanosheets at 800 nm;

[0039] Figure 15 The Mo provided in Embodiment 2 of the present invention 4 / 3 B 2-x T z Z-Scan results of the pores in the nanosheets at 1200 nm;

[0040] Figure 16 The Mo provided in Embodiment 2 of the present invention 4 / 3 B 2-x T z Z-Scan results of the openings in the nanosheets at 1550 nm;

[0041] Figure 17 The Mo provided in Embodiment 2 of the present invention 4 / 3 B 2-x T z Z-Scan results of the pores in the nanosheets at 1800 nm;

[0042] Figure 18 This is a structural diagram of the fiber laser provided in Embodiment 3 of the present invention;

[0043] Figure 19 The spectrum provided in Embodiment 3 of the present invention;

[0044] Figure 20 This is a pulse sequence diagram of the laser provided in Embodiment 3 of the present invention at different time scales;

[0045] Figure 21 This is the autocorrelation trajectory diagram of the laser provided in Embodiment 3 of the present invention;

[0046] Figure 22 This is the radio frequency spectrum diagram of the laser provided in Embodiment 3 of the present invention. Detailed Implementation

[0047] The present invention will now be further described with reference to the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments. Unless otherwise specified, the raw materials, equipment, etc., used in the following embodiments can all be obtained by purchase.

[0048] The embodiments of this invention are mainly divided into three progressively layered parts. First, the preparation, morphology, and composition characterization of two-dimensional transition metal borides; second, the investigation of the saturable absorption characteristics of two-dimensional transition metal borides; and third, the exploration of their potential applications in fiber optic exciters.

[0049] Example 1: Preparation, morphology, and composition characterization of two-dimensional transition metal borides

[0050] A method for preparing two-dimensional transition metal borides, based on the paper "Two-dimensional Mo 4 / 3 B 2-x "Withordered metal vacancies obtained by chemical exfoliation. Science 373(6556), 801-805." The preparation includes the following steps:

[0051] Right (Mo 2 / 3 Y 1 / 3 Selective etching was performed using 2AlB2 (purchased from Beijing Beike 2D Materials Co., Ltd.). The etching process primarily involved stirring in 10 ml of 48% hydrofluoric acid at room temperature for 24 hours. The suspension was then filtered and suspended in deionized water. This step was repeated three times to achieve the desired etching effect. The solid was then air-dried at room temperature for 24 hours. 0.4 g of etching powder was dissolved in 4 mL of tetrabutylammonium hydroxide (TBAOH) for a stripping process called embedding. The mixture was then centrifuged at 6000 rpm for 10 minutes to remove the precipitate. Residual TBAOH was removed with deionized water, and this process was repeated five times. Finally, the material was separated into monolayers and few-layers of Mo using deionized water while the material system was agitated. 4 / 3 B 2-x T z (Layered structure).

[0052] Get raw materials (Mo 2 / 3 Y 1 / 3 )2AlB2 and the two-dimensional transition metal boride Mo obtained in Example 1 4 / 3 B 2-x T z The relevant characterization was performed, and the specific results are shown below.

[0053] Figure 1 For raw materials (Mo) 2 / 3 Y 1 / 3 SEM image of 2AlB2 powder. From the image, it can be seen that the blocky (Mo) 2 / 3 Y 1 / 3 )2AlB2 exhibits a non-layered structure.

[0054] Figure 2 for (Mo 2 / 3 Y 1 / 3 Energy dispersive X-ray spectroscopy (EDS) mapping of AlB2 powder, showing the elements B, Mo, Al and Y.

[0055] Figure 3 The Mo provided in Embodiment 1 of the present invention 4 / 3 B 2-x T z SEM image. Mo 4 / 3 B 2-x T z It is achieved through selective etching (Mo) in hydrofluoric acid solution. 2 / 3 Y 1 / 3 It was prepared from Y and Al atoms in 2AlB2. Figure 3 It can be seen that, after etching, Mo with a multilayer structure can be obtained. 4 / 3 B 2-x T z .

[0056] Figure 4 The Mo provided in Embodiment 1 of the present invention 4 / 3 B 2-x T z The elemental mapping diagram shows the presence of O, F, Mo, and B elements, indicating that Al elements have been successfully removed. Multilayer Mo 4 / 3 B 2-x T z It is peeled into a few-layer material by further stratification in tetrabutylammonium hydroxide (TBAOH).

[0057] Figure 5 The few-layer Mo provided in Embodiment 1 of the present invention 4 / 3 B2-xT z The transmission electron microscope (TEM) image shows transparent thin sheets, revealing their ultrathin structure.

[0058] Figure 6 The Mo provided in Embodiment 1 of the present invention 4 / 3 B 2-x T zThe image is a high-resolution transmission electron microscope (HRTEM) image, with the inset showing the SAED pattern (scale bar: 2 nm⁻¹). The image clearly shows lattice fringes with a spacing of 0.268 nm, corresponding to the

[110] plane. Figure 6 The illustration shows the measured selected-area electron diffraction (SAED) pattern.

[0059] To further determine the stripped Mo 4 / 3 B 2-x T z The thickness of the nanosheets was determined by spin-coating the sample onto a Si / SiO2 substrate for atomic force microscopy (AFM) characterization. Figure 7 As shown, Mo 4 / 3 B 2-x T z It exhibits a sheet-like structure. Figure 7 The inset plot (height profile plot) shows the height distribution of the sections marked with horizontal lines, from which it can be seen that Mo 4 / 3 B 2-x T z The nanosheets are approximately 2.5 nm thick.

[0060] Figure 8 The image shows the X-ray diffraction (XRD) pattern provided in Embodiment 1 of the present invention. The pattern corresponds to orthorhombic and hexagonal symmetric structures, exhibiting alternating serrated arrangements along the crystallographic direction. This is confirmed by the increased interlayer distance after acid etching, as evidenced by the downward shift of peak values ​​in the XRD. In Mo... 4 / 3 B 2-x T z It can be observed in The large d value, while in (Mo 2 / 3Y 1 / 3 Only )2AlB2 precursor After the atomic chains are arranged along

[100] and

[010] , each molybdenum chain is surrounded by hexagonal boron atoms, which is consistent with Mo 1.33 C is similar.

[0061] To further confirm the composition, full-resolution XPS spectroscopy was used to analyze (Mo) 2 / 3 Y 1 / 3 )2AlB2 and Mo 4 / 3 B 2-x T z Tests were conducted. (For example...) Figure 9 As shown, the full-scan spectrum indicates that the Al layer was successfully etched, while the presence of F elements may be caused by HF acid.

[0062] Figure 10 The (Mo) provided in Embodiment 1 of the present invention 2 / 3 Y 1 / 3)2AlB2 powder and few-layer Mo 4 / 3 B 2-x T z The figure shows the high-resolution scanning and fitting results of Mo 3d. The figure demonstrates that the high-resolution spectrum of the Mo 3d region has been well fitted. In Mo... 4 / 3 B 2-x T z In the figure, the peaks at ~230 and 232 eV refer to Mo-BT. z The substance, while other peaks can be specified as Mo. +4 Mo +5 and Mo +6 The oxidation state is due to surface oxidation.

[0063] Figure 11 The (Mo) provided in Embodiment 1 of the present invention 2 / 3 Y 1 / 3 )2AlB2 powder and Mo 4 / 3 B 2-x T z High-resolution XPS scan of the peak fit in the B1s region of the nanosheet. The figure shows the effect of selective etching (Mo). 2 / 3 Y 1 / 3 After 2AlB2, Mo 4 / 3 B 2-x T z The oxidation state is more pronounced in it.

[0064] This invention utilizes ultraviolet-visible-infrared spectroscopy to study few-layer Mo. 4 / 3 B 2-x T z The linear optical properties, such as Figure 12 As shown, few-layered Mo 4 / 3 B 2-x T z It exhibits ultrawideband absorption characteristics from 400 to 2500 nm, demonstrating the two-dimensional Mo 4 / 3 B 2-x T z It has great application potential in visible light to mid-infrared photonic devices.

[0065] Example 2: Investigation into the saturable absorption characteristics of two-dimensional transition metal borides

[0066] Exploring the nonlinear optical properties of nanomaterials is of great significance for fabricating high-performance photonic devices based on nanomaterials.

[0067] To explore the Mo obtained in Example 1 4 / 3 B 2-x T zThe nonlinear optical properties of nanosheets were studied in Example 2 of this invention using an open-aperture Z-scan system. The laser source of this system consisted of a titanium-sapphire oscillator and an optical parametric amplifier, which facilitated the study of Mo... 4 / 3 B 2-x T z The nonlinear optical response of nanosheets at various laser wavelengths has become possible.

[0068] Prepared few-layer Mo 4 / 3 B 2-x T z -IPA solution was deposited on a clean 170 μm borosilicate glass substrate and then integrated into the Z-Scan system for nonlinear optical characterization. Figure 13-17 The nonlinear absorption data measured at 475 nm, 800 nm, 1200 nm, 1550 nm, and 1800 nm and their corresponding fitted curves are shown. It can be seen that the normalized transmittance has a significant bulge near Z=0, indicating that Mo... 4 / 3 B 2-x T z It exhibits a significant saturable absorption phenomenon. The mechanism of this phenomenon is that the energy of the excited photon is greater than that of the prepared Mo. 4 / 3 B 2-x T z The band gap, and Mo 4 / 3 B 2-x T z The conduction band is filled with electrons generated under such strong photon energy, which will lead to Pauli blockade and then saturation absorption.

[0069] To quantitatively analyze Mo 4 / 3 B 2-x T z The nonlinear optical properties of the material are determined, and the Z-Scan data will be fitted by a nonlinear absorption model. 4 / 3 B 2-x T z The total absorption (α) can be described as

[0070] α=α0+α NL

[0071] Where α0 and α NL =βI represents the linear and nonlinear absorption components, respectively. I represents the incident laser intensity. β is the nonlinear absorption coefficient, which can be obtained by fitting Z-Scan data using the following equation.

[0072]

[0073] in It is the focused laser intensity, L effThe effective thickness of the sample is represented by z0, which is the Rayleigh range. Through simple calculation and fitting, the maximum value of β in the range of 475–1800 nm was obtained. The β value at 800 nm is -0.32 cm / GW. Under the same laser conditions, its absolute value is significantly higher than that of graphene, BP, and MOF, and approximates that of MXenes. The higher the absolute value of β, the stronger the Mo... 4 / 3B 2-x T z The stronger the nonlinear interaction between the laser and the incident laser.

[0074] Table 1 Mo at different wavelengths 4 / 3 B 2-x T z Nonlinear optical parameters of nanosheets

[0075] λ(nm) β(cm / GW) <![CDATA[I sat (GW / cm 2 )]]> ΔT(%) <![CDATA[ΔT ns (%)]]> 475 -0.1 15.25 43.5 41.72 800 -0.32 23.18 24.83 23.75 1200 -0.12 3.39 31.7 29.92 1550 -0.11 11.97 50.25 48.85 1800 -0.03 33.91 18.54 17.24

[0076] For passively mode-locked lasers, modulation depth and saturation intensity are the most important parameters of a saturable absorber. To evaluate Mo... 4 / 3 B 2-x T z Modulation depth (ΔT) and saturation intensity (I) sat ) and its application potential in ultrashort pulse lasers, experimental data on the variation of normalized transmittance with input peak intensity were extracted from Z-Scan data ( Figure 13-17 (The illustration) and fitted by the following formula:

[0077]

[0078] Where ΔT ns It is a non-saturated loss. As shown in Table 1, Mo is obtained through fitting. 4 / 3 B 2-x T z I at different wavelengths sat ΔT and ΔT ns The values ​​of Mo are shown in Table 1. 4 / 3 B 2-x T z I sat A smaller value is advantageous for generating pulsed lasers with lower incident light intensity, which means that Mo... 4 / 3 B 2-x T z It is very suitable as a saturable absorber for passive laser systems.

[0079] In summary, the Mo obtained in Example 1 4 / 3 B 2-x T z It possesses the following characteristics: broadband saturable absorption from visible light to mid-infrared, strong nonlinear optical response, and small laser threshold, which means that two-dimensional Mo...4 / 3 B 2-x T z As a passive mode-locked device, it has broad application prospects and can be used to generate ultrafast pulses.

[0080] Example 3: Application of two-dimensional transition metal borides in fiber optic exciters

[0081] Embodiment 3 of the present invention achieves a Mo-based resonant cavity by designing and optimizing the resonant cavity. 4 / 3 B 2-x T z Mode-locked laser pulse output. The specific solution is as follows.

[0082] Embodiment 3 of the present invention provides a saturable absorber comprising an optical fiber (e.g., a micro / nano fiber) and a two-dimensional transition metal boride Mo deposited on the optical fiber. 4 / 3 B 2-x T z Specifically, Mo 4 / 3 B 2-x T z Nanosheet dispersions are deposited onto micro / nano optical fibers (~15 μm) to fabricate a saturated absorber based on two-dimensional transition metal boride optical fibers.

[0083] Next, in Embodiment 3 of the present invention, a two-dimensional transition metal boride Mo is included. 4 / 3 B 2-x T z The saturable absorber is used in all-fiber mode-locked lasers.

[0084] Specifically, such as Figure 18 As shown, an all-fiber mode-locked laser based on a saturable absorber of a two-dimensional transition metal boride fiber includes, in sequence, a pump source 10, a wavelength division multiplexer 11, a single-mode fiber, a gain fiber 12, a dispersion compensation fiber, a polarization-independent isolator 13, a fiber coupler 14, and a two-dimensional transition metal boride-based Mo... 4 / 3 B 2-x T z The optical fiber has a saturable absorber 15 and a polarization controller 16.

[0085] like Figure 18 As shown, the pump light generated by the pump source 10 is coupled into the cavity of the fiber laser through the wavelength division multiplexer 11, and then passes through the single-mode fiber, gain fiber 12, dispersion compensation fiber and polarization-independent optical isolator 13 in sequence to ensure unidirectional transmission of the light. After passing through the fiber coupler 14, the saturable absorber 15 based on the two-dimensional transition metal boride fiber and the polarization controller 16, it enters the wavelength division multiplexer 11 again. The wavelength division multiplexer 11 completes the fiber loop, and the pulsed laser is output by the fiber coupler 14 (output coupler).

[0086] As a further embodiment of the present invention, in the all-fiber mode-locked laser, the pump source is connected to the pump end of a wavelength division multiplexer to input pump light into the fiber resonant cavity. The common end of the wavelength division multiplexer is connected to one end of the gain fiber, and the other end of the gain fiber is connected to the input end of a polarization-independent isolator. The output end of the polarization-independent isolator is connected to the input end of a fiber coupler with a coupling ratio of 10:90. 10% of the fiber coupler output is used to output the optical signal, and 90% of the fiber coupler output is connected to one end of a saturable absorber. The other end of the saturable absorber is connected to the input end of a polarization controller, and the output end of the polarization controller is connected to the signal end of the wavelength division multiplexer. The all-fiber mode-locked laser device provided in this embodiment, by employing the above-described specific connection sequence and setting the output ratio of the coupler, enables more stable output pulse performance of the entire ring cavity structure.

[0087] As a further embodiment of the present invention, the gain fiber can be ytterbium-doped fiber, erbium-doped fiber or thulium-doped fiber, preferably erbium-doped fiber.

[0088] Embodiment 3 of the present invention constructs a two-dimensional Mo 4 / 3 B 2-x T z Fiber lasers and optimized Mo 4 / 3 B 2-x T z The cavity structure of a saturable absorber and a fiber laser. After adjusting the pump power and intracavity polarization state, ultrashort and high-repetition-rate mode-locked pulses achieve self-starting. In one embodiment of the invention, the pump source outputs a pump light with a center wavelength of 980 nm and a pump power of 100-450 mW.

[0089] Typical mold-locking states are as follows: Figure 18 As shown.

[0090] The pulses generated by the all-fiber mode-locked laser provided in Embodiment 3 of this invention were recorded using a 1GHz high-speed oscilloscope, showing a fundamental repetition rate of 11.39MHz, which is well matched with the cavity length. No fluctuations were observed in the pulse sequence within the scanning range, demonstrating the stable operation of the mode-locked fiber laser. The mode-locked spectrum of the pulses was concentrated in the range of ~1562.5nm, with a 3dB bandwidth of ~4.86nm.

[0091] like Figure 19 As shown, the clear and distinct Kelly fringe in the spectrum is a typical feature of soliton fiber lasers with net anomalous dispersion, indicating that mode-locked pulses can be shaped into optical soliton pulses.

[0092] Figure 20 The corresponding pulse sequences of the laser system at different time scales are shown. The measured pulse spacing of 87.7 ns corresponds to the cavity length of the laser resonator, further proving that the generation of these laser pulses originates from a mode-locking mechanism. Figure 20 The illustration shows the graphical oscilloscope trajectory of the laser system's pulse sequence over a long timescale, where consistent pulse intensity demonstrates the stability of the mode-locked pulses over a large span. The autocorrelation trajectory of the laser was recorded using an autocorrelation meter and Sech. 2 The actual pulse width obtained by fitting is ~582.3fs.

[0093] like Figure 21 As shown, the calculated time-bandwidth product is approximately 0.347, very close to the theoretical transformation limit (0.315), indicating only a very small pulse chirp. The mode-locked pulse operates in a highly stable state, through... Figure 22 The radio frequency spectrum shows that the signal-to-noise ratio of the laser is approximately ~68.3dB.

[0094] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. The application of a two-dimensional transition metal boride in a saturable absorber, characterized in that, The two-dimensional transition metal boride is a layered Mo. 4 / 3 B 2-x T z T z Surface functional groups, -O, OH, or -F; x is 0~0.5, z is 2~3; Mo 4 / 3 B 2-x T z The thickness of the sheet is 2-3 nm; The method for preparing the two-dimensional transition metal boride includes the following steps: (Mo 2 / 3 Y 1 / 3 Selective etching of 2AlB2 was performed, primarily using 10 ml of 48% hydrofluoric acid, stirred at room temperature for 24 h, the suspension was filtered, and then suspended in deionized water. This step was repeated three times to achieve the etching effect. The solid was then air-dried at room temperature for 24 hours. 0.4 g of etching powder was dissolved in 4 mL of tetrabutylammonium hydroxide for a stripping process called embedding, followed by centrifugation at 6000 rpm for 10 minutes to remove precipitates. Residual tetrabutylammonium hydroxide was removed with deionized water, and this process was repeated five times. Finally, the material was separated into monolayers and few-layers of Mo using deionized water while shaking the material system. 4 / 3 B 2-x T z .

2. The application of the two-dimensional transition metal borides as described in claim 1 in saturable absorbers, characterized in that, For the [110] face, Mo 4 / 3 B 2-x T z The spacing between adjacent lattice fringes is 0.2~0.3 nm.

3. The application of the two-dimensional transition metal borides as described in claim 1 in saturable absorbers, characterized in that, For the [110] face, Mo 4 / 3 B 2-x T z The spacing between adjacent lattice fringes is 0.268 nm.

4. The application of the two-dimensional transition metal borides as described in claim 1 in saturable absorbers, characterized in that, Mo 4 / 3 B 2-x T z The thickness of the sheet is 2.5 nm.

5. A saturable absorber, characterized in that, The saturable absorber includes an optical fiber and a two-dimensional transition metal boride deposited on the optical fiber, wherein the two-dimensional transition metal boride is the two-dimensional transition metal boride according to any one of claims 1 to 3.

6. The saturable absorber as described in claim 5, characterized in that, The optical fiber is a micro / nano optical fiber.

7. An all-fiber mode-locked laser, characterized in that, Includes the saturable absorber as described in claim 5 or 6.

8. The all-fiber mode-locked laser as described in claim 7, characterized in that, It includes a pump source, a wavelength division multiplexer, a single-mode fiber, a gain fiber, a dispersion compensation fiber, a polarization-independent isolator, a fiber coupler, a saturable absorber as described in claim 7, and a polarization controller, connected in sequence.

9. The all-fiber mode-locked laser as described in claim 8, characterized in that, The pump source, wavelength division multiplexer, single-mode fiber, gain fiber, dispersion compensation fiber, polarization-independent isolator, fiber coupler, saturable absorber as described in claim 7, and polarization controller are connected in sequence to form a ring fiber resonant cavity structure.

10. The all-fiber mode-locked laser as described in claim 9, characterized in that, The pump source is connected to the pump end of the wavelength division multiplexer to input pump light into the fiber resonator. The common end of the wavelength division multiplexer is connected to one end of the gain fiber, and the other end of the gain fiber is connected to the input end of the polarization-independent isolator. The output end of the polarization-independent isolator is connected to the input end of a fiber coupler with a coupling ratio of 10:

90. 10% of the output end of the fiber coupler is used to output optical signals, and 90% of the output end of the fiber coupler is connected to one end of the saturable absorber. The other end of the saturable absorber is connected to the input end of the polarization controller, and the output end of the polarization controller is connected to the signal end of the wavelength division multiplexer.

11. The all-fiber mode-locked laser as described in claim 8, characterized in that, The gain fiber is a ytterbium-doped fiber, an erbium-doped fiber, or a thulium-doped fiber.

12. The all-fiber mode-locked laser as described in claim 8, characterized in that, The gain fiber is an erbium-doped fiber.

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