A semi-metallic phase molybdenum ditelluride film, a saturable absorber, a pulsed fiber laser and preparation and application thereof

Abstract

The application belongs to the technical field of passively mode-locked fiber lasers, and particularly relates to a semi-metallic phase molybdenum ditelluride film, a saturable absorber, a pulsed fiber laser and preparation and application thereof. The semi-metallic phase molybdenum ditelluride film is prepared by a magnetron sputtering method combined with a CVD method, and has the advantages of simple process, low cost and easy operation. The prepared semi-metallic phase molybdenum ditelluride film is uniform in steps, large in area, nanometer in size and stable in quality, is not easy to be oxidized, has good stability and the significant advantages of two-dimensional transition metal chalcogenides, can obtain ultrafast laser with large modulation depth and narrow pulse width, can be used for laser mode-locking for a long time, and the mode-locked laser based on the film material as a device has very stable performance and can be applied to the field of lasers.

Description

Technical Field

[0001] The present invention belongs to the technical field of passive mode-locked fiber lasers, and in particular relates to a semi-metallic phase molybdenum ditelluride film, a saturable absorber, a pulsed fiber laser, and preparation and application thereof. Background Art

[0002] With the development of scientific research, people's requirements and abilities for observing and understanding the world are getting higher and higher. Fiber lasers have the potential to revolutionize many fields and are widely used due to their ability to produce high-quality and coherent laser beams, low energy loss during operation, long-term stability, and small size and light weight that facilitate flexible movement.

[0003] Saturable absorbers can be used in lasers to generate ultrafast lasers. In recent years, two-dimensional materials have shown excellent properties in light, electricity, force, and magnetism, leading to their application as saturable absorbers. On this basis, two-dimensional transition metal dichalcogenides (TMDs) are also being developed and utilized. Their material properties are closely related to their bonding method and structure. Different phases of TMDs have huge differences in physical properties. Therefore, mastering the controllable synthesis of different phases of TMDs and studying the differences in their physical properties is a challenging and important task.

[0004] MoTe2 has two different phases, 2H and 1T'. 1T'-MoTe2 is a metallic material with a monoclinic structure and in-plane anisotropy. Moreover, the carrier mobility of 1T'-MoTe2 is very high, reaching 4000 cm 2 / (s·V), suitable for polarization-sensitive detectors, polarized surface plasmons, and nonlinear optical devices. However, thin layers of 1T'-MoTe2 are unstable in air, where oxidation, doping, and defects can affect their quality. Therefore, the preparation of large-scale, nanometer-sized, and stable 1T'-MoTe2 on a substrate is a forward-looking task. At the same time, there are no reports in the prior art of testing 1T'-MoTe2 as a saturable absorber in lasers to explore its application in lasers. Summary of the Invention

[0005] In order to overcome the deficiencies and shortcomings of the prior art, the primary purpose of the present invention is to provide a method for preparing a semi-metallic phase molybdenum ditelluride (1T'-MoTe2) thin film. The method adopts a combination of magnetron sputtering and CVD to prepare a semi-metallic phase molybdenum ditelluride thin film. The process is simple, low-cost and easy to operate.

[0006] Another object of the present invention is to provide a semi-metallic phase molybdenum ditelluride thin film prepared by the above-mentioned preparation method. The thin film has uniform step-by-step structure, large area, nanometer size and stable quality, and its thickness can be precisely controlled by process parameters (such as sputtering time). When placed in a ring fiber laser system, it can serve as a saturable absorber to generate ultrashort pulse lasers.

[0007] Another object of the present invention is to provide a saturable absorber based on the semi-metallic phase molybdenum ditelluride thin film.

[0008] A fourth object of the present invention is to provide a pulsed fiber laser.

[0009] A fifth object of the present invention is to provide applications of the semi-metallic phase molybdenum ditelluride thin film, saturable absorber, and pulsed fiber laser.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] A method for preparing a semi-metallic phase molybdenum ditelluride thin film comprises the following steps:

[0012] (1) Sputtering of molybdenum (Mo) thin film: Mo polycrystalline block is used as target material, and Mo thin film is prepared on SiO2 / Si substrate by magnetron sputtering method to obtain SiO2 / Si substrate coated with Mo thin film; after sputtering is completed, the SiO2 / Si substrate coated with Mo thin film is removed after the temperature in the chamber is cooled to below 30-35°C (to avoid oxidation);

[0013] (2) Preparation of semi-metallic phase molybdenum ditelluride thin film: Tellurium powder (Te), SiO2 / Si substrate coated with Mo thin film and NaCl particles are placed in a double-temperature zone tubular furnace, wherein tellurium powder (Te) is placed in the upper temperature zone of the double-temperature zone tubular furnace, and SiO2 / Si substrate coated with Mo thin film and NaCl particles are placed in the lower temperature zone of the double-temperature zone tubular furnace. The temperature of the upper temperature zone is set to 580-600°C, and the temperature of the lower temperature zone is set to 650-700°C. Under the protection of nitrogen-hydrogen mixed gas, the upper and lower temperature zones are kept warm for 35-40 minutes for tellurization treatment, and then cooled naturally to obtain SiO2 / Si substrate carrying semi-metallic phase molybdenum ditelluride (1T'-MoTe2) thin film;

[0014] (3) Stripping of the semi-metallic molybdenum ditelluride film: uniformly spin-coating the solvent on the surface of the semi-metallic molybdenum ditelluride film obtained in step (2) and drying it, then immersing the SiO2 / Si substrate in an etching solution for etching, and washing and soaking the etched SiO2 / Si substrate in water until the semi-metallic molybdenum ditelluride film is separated from the SiO2 / Si substrate, thereby obtaining a semi-metallic molybdenum ditelluride (1T'-MoTe2) film;

[0015] The conditions for the magnetron sputtering in step (1) are preferably: a magnetron sputtering temperature of 100 to 120° C., a sputtering time of 8 to 10 minutes, and a radio frequency power of 70 to 80 W;

[0016] The conditions of the magnetron sputtering in step (1) are further preferably: magnetron sputtering temperature 100° C., sputtering time 810 min, and RF power 80 W;

[0017] The mass ratio of tellurium powder (Te) to sodium chloride in step (2) is 10:1;

[0018] The H2 content in the nitrogen-hydrogen mixed gas described in step (2) is preferably 4% (volume percentage), and the flow rate of the nitrogen-hydrogen mixed gas is preferably 30 sccm;

[0019] The heating rate of the upper temperature zone and the lower temperature zone in step (2) is preferably 20°C / min;

[0020] The temperatures of the upper temperature zone and the lower temperature zone in step (2) are preferably 580° C. and 650° C., respectively;

[0021] The holding time in step (2) is preferably 40 min;

[0022] The solvent in step (3) is preferably at least one of polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA) and polydimethylsiloxane (PDMS);

[0023] The spin coating conditions in step (3) are preferably 3000-4000 rpm for 60-90 s;

[0024] The drying conditions described in step (3) are preferably heating on a heating table at 100-120° C. for 20-30 minutes to dry the solvent;

[0025] The etching solution in step (3) is preferably BOE, wherein the HF content is 4% (volume percentage);

[0026] The etching conditions described in step (3) are preferably to immerse the SiO2 / Si substrate in the etching solution and let it stand for 1 to 2 minutes;

[0027] The film in step (3) is preferably cut into 8×8 mm;

[0028] A semi-metallic phase molybdenum ditelluride thin film is prepared by the above preparation method;

[0029] A saturable absorber based on the semi-metallic phase molybdenum ditelluride thin film, comprising the semi-metallic phase molybdenum ditelluride thin film;

[0030] The method for preparing the saturable absorber based on the semi-metallic phase molybdenum ditelluride thin film comprises the following steps:

[0031] A glass slide B is placed next to the glass slide A carrying the tapered optical fiber, and the semi-metallic molybdenum ditelluride thin film is spread on the glass slide B. Water is then added to wet the semi-metallic 1T'-MoTe2 thin film, and the film is transferred to the tapered optical fiber using water as a carrier. The film is then dried to obtain a saturable absorber based on the semi-metallic molybdenum ditelluride thin film.

[0032] The tapered optical fiber is preferably prepared by a flame tapered method;

[0033] The specific operation of the flame taper method is preferably:

[0034] The cladding in the middle of the single-mode optical fiber is removed, and the optical fiber is fixed on a tapered fiber drawing machine. When the flame directly heats the exposed optical core, the two ends of the optical fiber are moved and fixed, so that the optical core part is gradually elongated, and finally a tapered optical fiber with a tapered area diameter of 10μm is obtained;

[0035] Application of the semi-metallic phase molybdenum ditelluride thin film and the saturable absorber based on the semi-metallic phase molybdenum ditelluride thin film in the field of lasers;

[0036] A pulsed fiber laser comprises two parts: a pump light source and a resonant cavity; wherein the resonant cavity is connected to the pump light source; the resonant cavity comprises the semi-metallic phase molybdenum ditelluride thin film or the saturable absorber based on the semi-metallic phase molybdenum ditelluride thin film;

[0037] When the resonant cavity includes the semi-metallic molybdenum ditelluride thin film, the semi-metallic molybdenum ditelluride thin film is located on the end face of the single-mode optical fiber connector, and the wavelength division multiplexer, erbium-doped gain fiber, optical isolator, single-mode optical fiber, optical fiber coupler and polarization controller are connected in sequence to form a ring resonant cavity;

[0038] When the resonant cavity includes the above-mentioned saturable absorber based on the semi-metallic phase molybdenum ditelluride thin film, the wavelength division multiplexer, erbium-doped gain fiber, optical isolator, single-mode fiber, fiber coupler, polarization controller and the saturable absorber based on the semi-metallic phase molybdenum ditelluride thin film are sequentially connected to form a ring resonant cavity;

[0039] The fiber optic coupler is a 90:10 optical output coupler;

[0040] The wavelength of the pump light source is preferably 980 nm;

[0041] The central wavelength of the wavelength division multiplexer is preferably 1550 nm;

[0042] The pulse fiber laser may be an ultrashort pulse fiber laser;

[0043] The present invention has the following advantages and effects compared to the prior art:

[0044] (1) The present invention combines magnetron sputtering with CVD to prepare a semi-metallic phase molybdenum ditelluride (1T'-MoTe2) thin film. The method is simple in process, has stable quality, and the film thickness can be precisely controlled by process parameters (such as sputtering time). In addition, the present invention facilitates the formation of a 1T'-MoTe2 thin film by controlling the addition of sodium chloride. Tellurium (Te) is a metalloid whose melting point decreases when sodium chloride is present. When the melting point of Te decreases, selecting a reaction temperature higher than existing experimental parameters can volatilize a large amount of Te, resulting in the generation of many Te vacancy defects, thereby stably generating a semi-metallic phase 1T'-MoTe2.

[0045] (2) The 1T'-MoTe2 thin film prepared by the present invention is uniformly distributed, has a large area, is nano-sized and stable, is not easily oxidized, has good stability and the significant advantages of two-dimensional transition metal chalcogenides, can obtain ultrafast lasers with large modulation depth and narrow pulse width, can be used for laser mode locking for a long time, and the performance of the mode-locked laser obtained as a device based on this thin film material is very stable.

[0046] (3) When in use, in addition to transferring to the tapered optical fiber, the present invention can also choose to transfer the 1T'-MoTe2 film to the end face of the optical fiber connector. This operation is convenient, and the entire laser optical path system runs inside the optical fiber and is not affected by the external environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a low-magnification TEM image of the 1T'-MoTe2 thin film prepared in Example 1.

[0048] Figure 2 These are high-resolution transmission electron microscopy (HRTEM), fast Fourier transform (upper right), and high-resolution lattice fringe (lower right) images of the 1T'-MoTe2 thin film prepared in Example 1.

[0049] Figure 3 These are atomic force microscope characterization images of the 1T'-MoTe2 film prepared in Example 1 (left picture) and the 2H-MoTe2 film prepared in Comparative Example 1 (right picture).

[0050] Figure 4 These are Raman optical micrographs of the 1T'-MoTe2 thin film prepared in Example 1 (left picture) and the 2H-MoTe2 thin film prepared in Comparative Example 1 (right picture).

[0051] Figure 5 Schematic diagram of the structure of the ring cavity mode-locked pulse fiber laser of Application Example 2.

[0052] Figure 6 1 is a pulse sequence diagram of the ring cavity mode-locked pulse fiber laser of Application Example 2.

[0053] Figure 7 This is a spectrum diagram of the ring cavity mode-locked pulsed fiber laser of Application Example 2.

[0054] Figure 8 3 is a pulse width diagram of the ring cavity mode-locked pulse fiber laser of Application Example 2.

[0055] Figure 9 This is a radio frequency spectrum diagram of the ring cavity mode-locked pulsed fiber laser of Application Example 2.

[0056] Figure 10 3 is a graph showing the relationship between the output power and pump power of the ring cavity mode-locked pulse fiber laser according to the second embodiment.

[0057] Figure 11 This is a comparison chart of the output spectra of the ring cavity mode-locked pulsed fiber laser of Application Example 2 for 5 consecutive days.

[0058] Figure 12 This is a schematic diagram of the connection method between the 1T'-MoTe2 film and the single-mode optical fiber in Application Example 3. A: The red arrow indicates the placement position of the 1T'-MoTe2 film. B: The structure after the 1T'-MoTe2 film and the single-mode optical fiber are connected through a flange. DETAILED DESCRIPTION

[0059] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0060] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0061] Example 1

[0062] (1) Sputtering of Mo thin film: Mo polycrystalline block was used as target material, and Mo thin film was prepared on SiO2 / Si substrate by magnetron sputtering method. The specific process parameters were: vacuum to 10 -5 mbar, the magnetron sputtering temperature was 100°C, the sputtering time was 8 minutes, and the RF power was 80W. After the sputtering was completed, nitrogen was introduced as a protective gas, and the SiO2 / Si substrate coated with the Mo film was removed after the chamber temperature cooled to below 30°C.

[0063] (2) Preparation of 1T'-MoTe2 thin film: a quartz boat carrying 200 mg of tellurium powder (Te) was placed in the upper temperature zone of a dual-zone tube furnace, and the temperature was set to 580 °C; a quartz boat carrying the SiO2 / Si substrate coated with the Mo film obtained in step (1) and 20 mg of NaCl particles was placed in the lower temperature zone of the dual-zone tube furnace, and the temperature was set to 650 °C, wherein the sodium chloride particles were placed next to the substrate and away from the tellurium powder; under the protection of a nitrogen-hydrogen mixed gas (4% H2) with a flow rate of 30 sccm, the upper temperature zone and the lower temperature zone were heated at a heating rate of 20 °C / min respectively, and after reaching the set temperature, the upper temperature zone and the lower temperature zone were kept warm for 40 minutes for tellurization treatment; finally, the temperature was naturally cooled to room temperature to obtain a SiO2 / Si substrate carrying a semi-metallic phase molybdenum ditelluride (1T'-MoTe2) thin film;

[0064] (3) Stripping of 1T'-MoTe2 film: polymethyl methacrylate (PMMA) solvent was added dropwise to the surface of the semi-metallic phase molybdenum ditelluride (1T'-MoTe2) film prepared in step (2), and then spin-coated at 4000 rpm for 60 seconds, and then heated on a heating table at 120°C for 20 minutes to dry the solvent; then the SiO2 / Si substrate was immersed in the etching solution BOE (containing 4% HF) and allowed to stand for 2 minutes for etching; the etched SiO2 / Si substrate was placed in deionized water, washed and soaked several times until the 1T'-MoTe2 film was separated from the SiO2 / Si substrate, and then the 1T'-MoTe2 film was cut into 8×8 mm specifications.

[0065] Example 2

[0066] (1) Sputtering of molybdenum (Mo) thin film: the specific method is the same as that of Example 1;

[0067] (2) Preparation of MoTe2 thin film: The difference from Example 1 is that the temperature of the upper temperature zone is 600°C, the temperature of the lower temperature zone is 700°C, and the holding time is 35 minutes. Other operations are the same as in Example 1;

[0068] (3) Stripping of MoTe2 thin film: same as Example 1.

[0069] Example 3

[0070] (1) Sputtering of molybdenum (Mo) thin film: the specific method is the same as that of Example 1;

[0071] (2) Preparation of MoTe2 thin film: The difference from Example 1 is that the temperature of the upper temperature zone is 580°C, the temperature of the lower temperature zone is 660°C, and the holding time is 40 min. Other operations are the same as in Example 1;

[0072] (3) Stripping of MoTe2 thin film: same as Example 1.

[0073] Comparative Example 1: No sodium chloride particles added

[0074] (1) Sputtering of molybdenum (Mo) thin film: the specific method is the same as that of Example 1;

[0075] (2) Preparation of MoTe2 thin film: A quartz boat carrying 200 mg of tellurium powder (Te) was placed in the upper temperature zone of a dual-zone tubular furnace, and the temperature was set to 580°C; a quartz boat carrying the SiO2 / Si substrate coated with Mo thin film obtained in step (1) was placed in the lower temperature zone of the dual-zone tubular furnace, and the temperature was set to 650°C; under the protection of a nitrogen-hydrogen mixed gas (4% H2) with a flow rate of 30 sccm, the upper temperature zone and the lower temperature zone were heated at a heating rate of 20°C / min respectively. After reaching the set temperature, the upper temperature zone and the lower temperature zone were kept warm for 40 minutes for tellurization treatment; finally, the temperature was naturally cooled to room temperature to finally generate a 2H-MoTe2 thin film.

[0076] (3) Stripping of 2H-MoTe2 thin film: The specific method is the same as Example 1.

[0077] Comparative Example 2

[0078] (1) Sputtering of molybdenum (Mo) thin film: the specific method is the same as that of Example 1;

[0079] (2) Preparation of MoTe2 thin film: The difference from Example 1 is that the temperature of the upper temperature zone is 560°C and the temperature of the lower temperature zone is 630°C. Other operations are the same as in Example 1;

[0080] (3) Stripping of MoTe2 thin film: same as Example 1.

[0081] Comparative Example 3

[0082] (1) Sputtering of molybdenum (Mo) thin film: the specific method is the same as that of Example 1;

[0083] (2) Preparation of MoTe2 thin film: The difference from Example 1 is that the holding time is 25 min, and the other operations are the same as Example 1;

[0084] (3) Stripping of MoTe2 thin film: same as Example 1.

[0085] Effect embodiment

[0086] (1) Transmission electron microscopy and analysis

[0087] The 1T'-MoTe2 film prepared in Example 1 was sampled and transferred to a copper mesh for microscopic morphology observation and structural confirmation. Figure 1 This is a TEM image of the 1T'-MoTe2 thin film prepared in Example 1 observed at a low magnification. It can be seen from the image that Example 1 successfully generated a large-area polycrystalline continuous thin film.

[0088] Figure 2 This is a TEM image of the 1T'-MoTe2 thin film prepared in Example 1 observed at high magnification. The fast Fourier transform pattern in the upper right corner is a monoclinic structure, and the lattice spacing shown in the high-resolution lattice fringe image in the lower right corner corresponds to the (002) crystal plane of 1T'-MoTe2, indicating that the present invention has successfully prepared stable 1T'-MoTe2.

[0089] (2) Atomic force microscopy

[0090] The thickness of the 1T'-MoTe2 film prepared in Example 1 and the 2H-MoTe2 film prepared in Comparative Example 1 were measured by atomic force microscopy. Figure 3 ,from Figure 3 It can be seen that the thickness of 1T'-MoTe2 film is thinner.

[0091] (3) Raman optical microscopy

[0092] The morphologies of the 1T'-MoTe2 film prepared in Example 1 and the 2H-MoTe2 film prepared in Comparative Example 1 were observed under a Raman optical lens. Figure 4 It can be observed that although both films have achieved large-area growth, the surface of the 1T'-MoTe2 film in the left figure is flatter and more continuous, and no other impurities are generated.

[0093] In addition, although Comparative Examples 2 and 3 also obtained 1T'-MoTe2 thin films, it can be seen with the naked eye that the thin films generated on the substrate are not continuous and are not suitable for pulsed fiber lasers, indicating that the temperatures and holding time in the upper and lower temperature zones will also affect the morphology and properties of the 1T'-MoTe2 thin films.

[0094] Application Example 1 Preparation of a saturable absorber based on 1T'-MoTe2 thin film

[0095] (1) Preparation of tapered optical fiber: Remove the cladding in the middle of the single-mode optical fiber and fix the optical fiber on the tapered machine. When the flame directly heats the exposed optical core, move the two ends of the optical fiber to gradually elongate the optical core. Finally, a tapered optical fiber with a tapered area diameter of 10 μm is obtained. The tapered optical fiber is fixed on a glass slide A with tape ( Figure 5 );

[0096] (2) Place a clean glass slide B next to the glass slide A carrying the tapered optical fiber prepared in step (1), and spread the 1T'-MoTe2 film cut out in Example 1 on the glass slide B. Then, use a rubber-tipped dropper to drip a few drops of deionized water between the two glass slides to wet part of the 1T'-MoTe2 film. Use water as a carrier to transfer the film to the tapered optical fiber. After drying at room temperature, a saturable absorber based on the 1T'-MoTe2 film is obtained, which can be put into use. Application Example 2 Preparation of Ring Cavity Mode-Locked Pulsed Fiber Laser

[0097] This embodiment provides a pulsed fiber laser, which adopts a ring cavity structure, including a pump light source and a resonant cavity, and uses a fiber fusion machine according to Figure 5 A pump light source 1, a wavelength division multiplexer 2, an erbium-doped gain fiber 3, an optical isolator 4, a single-mode fiber 5, a fiber coupler 6, a polarization controller 7, and a saturable absorber 8 based on a 1T'-MoTe2 thin film prepared in Example 1 are connected in this order. At the same time, a spectrum analyzer is connected to the output port of the coupler to record the signal spectrum, and an oscilloscope is connected to output a pulse sequence diagram. The wavelength of the pump light source is 980 nm, the central wavelength of the wavelength division multiplexer is 1550 nm, and the fiber coupler is a 90:10 optical output coupler.

[0098] Figure 6 This is a pulse sequence diagram of the ring cavity mode-locked pulse fiber laser of this application embodiment. It can be seen from the figure that when the pump power is 150mW, the pulse interval is 46.45ns, and it can be concluded that the pulse signal has good stability.

[0099] Figure 7 This is a spectrum diagram of the ring cavity mode-locked pulsed fiber laser of this application embodiment. The figure shows that when the pump power is 150mW, the bandwidth is 5.96nm and the central wavelength is at 1576nm, indicating a traditional soliton mode-locked state.

[0100] Figure 8 This is the pulse width diagram of the ring cavity mode-locked pulse fiber laser of this application embodiment. It can be seen from the figure that when the pump power is 150mW, the measured pulse width is 828fs. 2 The experimental data obtained by function fitting showed that the actual pulse width was about 538fs.

[0101] Figure 9 This is the radio frequency spectrum diagram of the ring cavity mode-locked pulsed fiber laser of this application embodiment. It can be seen from the figure that when the pump power is 150mW, the basic repetition frequency is 22MHz, and the corresponding signal-to-noise ratio is about 62dB.

[0102] Figure 10This is a graph showing the relationship between the output power and pump power of the ring cavity mode-locked pulse fiber laser of this application embodiment. It can be seen from the graph that a stable mode-locked pulse signal is present when the pump power ranges from 50 mW to 380 mW. The corresponding output power increases from 45 mW to 380 mW, and the output efficiency is 1.6%. When the pump power continues to increase beyond 380 mW, the mode-locked pulse signal becomes unstable.

[0103] Figure 11 This is a comparison chart of the output spectra of the ring cavity mode-locked pulsed fiber laser (pump power of 150 mW) of Application Example 2 for 5 consecutive days. It can be seen from the figure that the output spectra are highly similar, indicating that the laser can work normally for several consecutive days and has good stability.

[0104] Application Example 3 Preparation of Ring Cavity Mode-Locked Pulsed Fiber Laser

[0105] This embodiment provides a pulsed fiber laser, including a pump light source and a resonant cavity. A fiber fusion splicer is used to sequentially connect the pump light source 1, a wavelength division multiplexer 2, an erbium-doped gain fiber 3, an optical isolator 4, a single-mode fiber 5, a fiber coupler 6, and a polarization controller 7. Unlike Application Example 2, the 1T'-MoTe2 thin film prepared in Example 1 is directly arranged on the end faces of two single-mode optical fibers and connected and fixed by flanges, thereby forming a complete single-mode optical fiber 5 ( Figure 12 ); at the same time, the output port of the coupler is connected to an optical spectrum analyzer to record the signal spectrum, and to an oscilloscope to output a pulse sequence diagram; the wavelength of the pump light source is 980 nm, the central wavelength of the wavelength division multiplexer is 1550 nm, and the fiber coupler is a 90:10 optical output coupler.

[0106] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a semi-metallic phase molybdenum ditelluride thin film, characterized in that The following steps are included: (1) Sputtering of molybdenum thin film: Mo polycrystalline block is used as target material, and Mo thin film is prepared on SiO2 / Si substrate by magnetron sputtering method to obtain SiO2 / Si substrate coated with Mo thin film; after sputtering is completed, the SiO2 / Si substrate coated with Mo thin film is taken out after the temperature in the chamber cools down to below 30-35°C; (2) Preparation of semi-metallic phase molybdenum ditelluride thin film: Tellurium powder, SiO2 / Si substrate coated with Mo thin film and NaCl particles are placed in a double-temperature zone tubular furnace, wherein the tellurium powder is placed in the upper temperature zone of the double-temperature zone tubular furnace, and the SiO2 / Si substrate coated with Mo thin film and NaCl particles are placed in the lower temperature zone of the double-temperature zone tubular furnace. The temperature of the upper temperature zone is set to 580-600°C, and the temperature of the lower temperature zone is set to 650-700°C. Under the protection of nitrogen-hydrogen mixed gas, the upper and lower temperature zones are kept warm for 35-40 minutes for tellurization treatment, and then cooled naturally to obtain SiO2 / Si substrate carrying semi-metallic phase molybdenum ditelluride thin film; (3) Stripping of the semi-metallic phase MoTe film: The solvent is evenly spin-coated on the surface of the semi-metallic phase MoTe film prepared in step (2) and dried. The SiO2 / Si substrate is then immersed in an etching solution for etching. The etched SiO2 / Si substrate is washed and soaked in water until the semi-metallic phase MoTe film is separated from the SiO2 / Si substrate, thereby obtaining a semi-metallic phase MoTe film.

2. The method for preparing a semi-metallic phase molybdenum ditelluride thin film according to claim 1, wherein: The conditions of the magnetron sputtering described in step (1) are: magnetron sputtering temperature 100-120° C., sputtering time 8-10 min, and RF power 70-80 W.

3. The method for preparing a semi-metallic phase molybdenum ditelluride thin film according to claim 1, wherein: The mass ratio of tellurium powder to sodium chloride in step (2) is 10:

1.

4. The method for preparing a semi-metallic phase molybdenum ditelluride thin film according to claim 1, wherein: The heating rate of the upper temperature zone and the lower temperature zone described in step (2) is 20°C / min.

5. The method for preparing a semi-metallic phase molybdenum ditelluride thin film according to claim 1, wherein: The temperatures of the upper temperature zone and the lower temperature zone in step (2) are 580°C and 650°C respectively; The holding time in step (2) is 40 minutes.

6. A semi-metallic phase molybdenum ditelluride film, characterized in that It is prepared by the preparation method according to any one of claims 1 to 5.

7. A saturable absorber based on a semi-metallic phase molybdenum ditelluride thin film, characterized in that The semi-metallic phase molybdenum ditelluride thin film comprises the semi-metallic phase molybdenum ditelluride thin film according to claim 6.

8. The method for preparing a saturable absorber based on a semi-metallic phase molybdenum ditelluride thin film according to claim 7, characterized in that The following steps are included: A glass slide B is placed next to the glass slide A carrying the tapered optical fiber, and the semi-metallic phase molybdenum ditelluride thin film described in claim 6 is spread on the glass slide B. Then, water is added to wet the semi-metallic phase 1T'-MoTe2 thin film, and the film is transferred to the tapered optical fiber using water as a carrier. After drying, a saturable absorber based on the above-mentioned semi-metallic phase molybdenum ditelluride thin film is obtained.

9. Use of the semi-metallic molybdenum ditelluride thin film according to claim 6 or the saturable absorber based on the semi-metallic molybdenum ditelluride thin film according to claim 7 in the field of lasers.

10. A pulsed fiber laser, characterized in that It includes two major parts: a pump light source and a resonant cavity; wherein the resonant cavity is connected to the pump light source; the resonant cavity includes the semi-metallic phase molybdenum ditelluride thin film according to claim 6 or the saturable absorber based on the semi-metallic phase molybdenum ditelluride thin film according to claim 7.

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