Saturable absorber and preparation method thereof and ring cavity fiber laser

Abstract

The present invention relates to the technical field of saturable absorbers, and in particular to a saturable absorber based on tin oxide nanoparticles, a preparation method thereof, and a ring cavity fiber laser. The ring cavity fiber laser is composed of a pump source and a ring laser resonant cavity. The ring laser resonant cavity is composed of a wavelength division multiplexer, an erbium-doped optical fiber, a polarization light isolator, a saturable absorber, a polarization controller, and an optical splitter connected in sequence. The pump source is connected to the input end of the wavelength division multiplexer. The saturable absorber is a saturable absorber based on a mixture of tin oxide nanoparticles and a film-forming agent, or a saturable absorber based on tin oxide nanoparticles deposited on the surface of a tapered optical fiber, a D-type optical fiber, or a cladding-corroded optical fiber, or a saturable absorber based on tin oxide nanoparticles filled in the air hole cladding of a photonic crystal optical fiber. The present invention can provide a new solution for the development of ultrashort pulse fiber lasers.

Description

Technical Field

[0001] The invention relates to the technical field of saturable absorbers, and in particular to a saturable absorber based on tin oxide nanoparticles, a preparation method thereof, and a ring cavity fiber laser. Background Art

[0002] Ultrashort pulse fiber lasers have significant advantages such as low laser threshold, good output beam quality, high conversion efficiency, compact size, and convenient system integration. They are widely used in medical, national defense, scientific research, material processing and other fields. Mode locking and Q switching are two technologies for realizing pulsed lasers. Compared with mode locking technology, Q switching technology can obtain higher output power and pulse energy, and realize high-energy pulsed lasers. Q switching can be active or passive. Active Q switching usually relies on modulation devices, while passive Q switching uses saturable absorbers to realize pulsed lasers. In recent years, many scholars have explored saturable absorbers many times. For example, carbon-based materials, transition metal dihalides, transition metal carbonitrides, topological insulating structures, and metal-organic frameworks.

[0003] Carbon-based materials have poor dispersibility in aqueous solutions, the preparation method of transition metal dihalide compounds is slightly complicated and has a low optical damage threshold, the modulation depth of topological insulating structures is low and is limited by broadband light response, and transition metal carbonitrides and metal-organic frameworks are limited in their widespread application due to their complex structures. Summary of the invention

[0004] In view of the above problems, the present invention proposes a saturable absorber based on tin oxide nanoparticles and a preparation method thereof and a ring cavity fiber laser, which provide a new solution for the development of ultrashort pulse fiber lasers.

[0005] In a first aspect, the saturable absorber proposed by the present invention is a saturable absorber made by mixing tin oxide nanoparticles and a film-forming agent.

[0006] The method for preparing the saturable absorber comprises the following steps:

[0007] S1: Preparation of tin oxide nanoparticles by solvothermal method;

[0008] S2: Tin oxide nanoparticles are mixed with a film-forming agent to form a thin film to obtain a saturable absorber.

[0009] Preferably, step S1 specifically includes the following steps:

[0010] S11: tin chloride pentahydrate powder, ethylenediamine and oleic acid are respectively placed in a reaction kettle and fully mixed at room temperature using a magnetic mixer;

[0011] S12: heating the mixture in an oven at 180° C. for 10 hours, and centrifuging after natural cooling;

[0012] S13: washing the oleic acid with anhydrous ethanol and removing impurities with deionized water, and drying to obtain a tin hydroxide xerogel;

[0013] S14: placing the tin hydroxide xerogel in a muffle furnace, heating it at 600° C. for five minutes, and grinding it after natural cooling to obtain tin oxide nanoparticles.

[0014] In a second aspect, the saturable absorber provided by the present invention is a saturable absorber based on tin oxide nanoparticles deposited on the surface of a tapered optical fiber, a D-type optical fiber, or a cladding-etched optical fiber.

[0015] The method for preparing the saturable absorber comprises the following steps:

[0016] S1: Preparation of tin oxide nanoparticles by solvothermal method;

[0017] S2: Depositing tin oxide nanoparticles on the surface of a tapered optical fiber, a D-type optical fiber, or a cladding-etched optical fiber to produce a saturable absorber.

[0018] Preferably, step S1 specifically includes the following steps:

[0019] S11: tin chloride pentahydrate powder, ethylenediamine and oleic acid are respectively placed in a reaction kettle and fully mixed at room temperature using a magnetic mixer;

[0020] S12: heating the mixture in an oven at 180° C. for 10 hours, and centrifuging after natural cooling;

[0021] S13: washing the oleic acid with anhydrous ethanol and removing impurities with deionized water, and drying to obtain a tin hydroxide xerogel;

[0022] S14: placing the tin hydroxide xerogel in a muffle furnace, heating it at 600° C., and grinding it to obtain tin oxide nanoparticles.

[0023] In a third aspect, the saturable absorber proposed by the present invention is a saturable absorber based on tin oxide nanoparticles filled in the air hole cladding of a photonic crystal optical fiber.

[0024] The method for preparing the saturable absorber comprises the following steps:

[0025] S1: Preparation of tin oxide nanoparticles by solvothermal method;

[0026] S2: Mixing tin oxide nanoparticles with deionized water, filling the mixed solution into the air hole cladding of a photonic crystal fiber and drying the mixed solution to prepare a saturable absorber.

[0027] Preferably, step S1 specifically includes the following steps:

[0028] S11: tin chloride pentahydrate powder, ethylenediamine and oleic acid are respectively placed in a reaction kettle and fully mixed at room temperature using a magnetic mixer;

[0029] S12: heating the mixture in an oven at 180° C. for 10 hours, and centrifuging after natural cooling;

[0030] S13: washing the oleic acid with anhydrous ethanol and removing impurities with deionized water, and drying to obtain a tin hydroxide xerogel;

[0031] S14: placing the tin hydroxide xerogel in a muffle furnace, heating it at 600° C., and grinding it to obtain tin oxide nanoparticles.

[0032] In a fourth aspect, the present invention further proposes a ring cavity fiber laser, comprising a pump source and a ring laser resonant cavity, the ring laser resonant cavity comprising a wavelength division multiplexer, an erbium-doped optical fiber, a polarization light isolator, a polarization controller and an optical splitter, and also comprising the above-mentioned saturable absorber, the output end of the pump source is connected to the pump end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to one end of the erbium-doped optical fiber, the other end of the erbium-doped optical fiber is connected to the input end of the polarization light isolator, the output end of the polarization light isolator is connected to one end of the saturable absorber, the other end of the saturable absorber is connected to one end of the polarization controller, and the other end of the polarization controller is connected to the optical splitter.

[0033] Compared with the prior art, the present invention can achieve the following technical effects:

[0034] 1. Tin oxide nanoparticles have high electron mobility and good chemical and thermal stability.

[0035] 2. Tin oxide nanoparticles have a wide band gap, high exciton binding energy, low resistivity and high transmittance, as well as excellent electrical, optical, catalytic and sensing properties.

[0036] 3. The film made by mixing tin oxide nanoparticles and film-forming agents has an obvious saturable absorption effect, is simple to prepare, and has good stability.

[0037] 4. The saturable absorber made by depositing tin oxide nanoparticles on the surface of tapered optical fiber, D-type optical fiber or cladding-etched optical fiber improves the interaction intensity between light and material through the evanescent field effect on the optical fiber surface, greatly improving the damage threshold of the saturable absorber.

[0038] 5. The saturable absorber filled with tin oxide nanoparticles in the air hole cladding of the photonic crystal fiber has ultra-weak interaction, which avoids the generation of high-order harmonics due to excessive interaction, thereby achieving high-power output.

[0039] 6. The prepared saturable absorber is embedded in the constructed fiber laser, and the generated pulsed laser has good stability and repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 3 is a scanning electron microscope image of tin oxide nanoparticles provided according to Example 1 of the present invention.

[0041] Figure 2 This is a transmission electron microscope image of tin oxide nanoparticles provided according to Example 1 of the present invention.

[0042] Figure 3 3 is a nonlinear transmission curve diagram of tin oxide nanoparticles provided according to Example 1 of the present invention.

[0043] Figure 4 is a structural diagram of a ring cavity fiber laser provided according to Example 1 of the present invention.

[0044] Figure 5a This is an output spectrum diagram of the tin oxide nanoparticle film provided in Example 1 of the present invention used as a saturable absorber in a ring cavity fiber laser at 1.5 μm.

[0045] Figure 5b This is a single pulse shape diagram of the tin oxide nanoparticle film provided in Example 1 of the present invention used as a saturable absorber in a ring cavity fiber laser at 1.5 μm.

[0046] Figure 5c This is a pulse sequence diagram of the tin oxide nanoparticle film provided in Example 1 of the present invention used as a saturable absorber in a ring cavity fiber laser at 1.5 μm.

[0047] Figure 6a This is an output spectrum diagram of the tin oxide nanoparticles deposited on a D-type optical fiber as a saturable absorber used in a ring cavity fiber laser at 1.5 μm according to Example 2 of the present invention.

[0048] Figure 6b This is a single pulse shape diagram of the tin oxide nanoparticles deposited on the D-type optical fiber provided by Example 2 of the present invention as a saturable absorber used in a ring cavity fiber laser at 1.5 μm.

[0049] Figure 6c This is a pulse sequence diagram of tin oxide nanoparticles deposited on a D-type optical fiber as a saturable absorber used in a ring cavity fiber laser at 1.5 μm according to Example 2 of the present invention.

[0050] Reference numerals: pump source 1 , wavelength division multiplexer 2 , erbium-doped optical fiber 3 , polarization light isolator 4 , saturable absorber 5 , polarization controller 6 , optical splitter 7 , pulse light output terminal 8 . DETAILED DESCRIPTION

[0051] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0052] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0053] The present invention proposes three saturable absorbers. The first saturable absorber is a saturable absorber based on a mixture of tin oxide nanoparticles and a film-forming agent. The second saturable absorber is a saturable absorber based on tin oxide nanoparticles deposited on the surface of a tapered optical fiber, a D-type optical fiber, or a cladding-etched optical fiber. The third saturable absorber is a saturable absorber based on tin oxide nanoparticles filled in the air hole cladding of a photonic crystal optical fiber.

[0054] A first method for preparing a saturable absorber comprises the following steps:

[0055] S1. Preparation of tin oxide nanoparticles using a solvothermal method.

[0056] Step S1 specifically includes the following steps:

[0057] S11, tin chloride pentahydrate powder, ethylenediamine and oleic acid were respectively placed in a reaction kettle and fully mixed using a magnetic mixer at room temperature.

[0058] S12, placing the mixture in an oven and heating it at 180° C. for 10 hours, and centrifuging it after natural cooling.

[0059] S13, washing the oleic acid with anhydrous ethanol and removing impurities with deionized water, and obtaining the tin hydroxide xerogel after drying.

[0060] S14. Put the tin hydroxide dry gel into a muffle furnace, heat it at 600° C. for five minutes, and grind it after natural cooling to obtain tin oxide nanoparticles.

[0061] S2. Mixing tin oxide nanoparticles with a film-forming agent to form a thin film to obtain a saturable absorber.

[0062] Film formers include, but are not limited to, sodium carboxymethylcellulose, polyvinyl alcohol, polymethyl methacrylate, polydimethylsiloxane, and the like.

[0063] The second method for preparing a saturable absorber comprises the following steps:

[0064] S1. Preparation of tin oxide nanoparticles using a solvothermal method.

[0065] S2. Depositing tin oxide nanoparticles on the surface of a tapered optical fiber, a D-type optical fiber, or a cladding-etched optical fiber to obtain a saturable absorber.

[0066] A third method for preparing a saturable absorber comprises the following steps:

[0067] S1. Preparation of tin oxide nanoparticles using a solvothermal method.

[0068] S2. Mixing tin oxide nanoparticles with deionized water, and filling the mixed solution into the air hole cladding of the photonic crystal optical fiber and drying the mixed solution to obtain a saturable absorber.

[0069] The present invention also proposes a ring cavity fiber laser, comprising a pump source and a ring laser resonant cavity, the ring laser resonant cavity comprising a wavelength division multiplexer, an erbium-doped optical fiber, a polarization light isolator, a polarization controller and an optical splitter, and also comprising any one of the above three saturable absorbers, the output end of the pump source is connected to the pump end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to one end of the erbium-doped optical fiber, the other end of the erbium-doped optical fiber is connected to the input end of the polarization light isolator, the output end of the polarization light isolator is connected to one end of the saturable absorber, the other end of the saturable absorber is connected to one end of the polarization controller, and the other end of the polarization controller is connected to the optical splitter.

[0070] Example 1: Using a saturable absorber made by mixing tin oxide nanoparticles and sodium carboxymethyl cellulose powder and using it for Q-switched laser output at 1.5 μm;

[0071] 1. Sample preparation process

[0072] Tin oxide nanoparticles with an average particle size of 40 nm were prepared by a solvothermal method.

[0073] Specifically, 1 part of tin chloride pentahydrate powder is put into a reactor, ethylenediamine and oleic acid are added in a ratio of 6:1, mixed with a magnetic mixer at room temperature, put into an oven, heated at 180°C for 10 hours, centrifuged after natural cooling, then washed with anhydrous ethanol to remove oleic acid, other impurities are washed with deionized water, and dried to obtain tin hydroxide xerogel, which is then placed in a muffle furnace and calcined at 600°C, and ground after natural cooling to prepare tin oxide nanoparticles. The scanning electron microscope and transmission electron microscope images of tin oxide nanoparticles are shown in Figure 2. Figure 1 and Figure 2 shown.

[0074] Sodium carboxymethyl cellulose powder and deionized water are mixed at a molar ratio of 8 to 25:1, stirred at 60-80°C for 24 hours, the solution is colorless and transparent, and no precipitate is precipitated after standing for 5-7 hours, thus forming a sodium carboxymethyl cellulose aqueous solution. The prepared tin oxide nanoparticles are mixed with a sodium carboxymethyl cellulose aqueous solution at a mass ratio of 1:0.5 to 16, ultrasonically dispersed at 70-90°C for 2 to 5 hours, and the dispersed solution is spin-coated on a flat glass slide surface, and naturally dried in a vacuum sealed container until a film is formed, and the film is the prepared saturable absorber.

[0075] The nonlinear absorption of the prepared films was tested, such as Figure 3 shown.

[0076] 2. Fiber laser testing

[0077] like Figure 4 As shown in the figure, it is a ring cavity fiber laser operating in the 1.5μm band, where 1 is a 980 nm semiconductor laser, which serves as a pump source; 2 is a 980nm / 1560nm wavelength division multiplexer; 3 is an erbium-doped quartz fiber (erbium-doped fiber for short), which serves as a gain medium for laser generation; 4 is a 1560nm polarization light isolator, which ensures the unidirectional operation of the laser in the ring laser resonant cavity to avoid damage to the device; 5 is a saturable absorber, which generates pulse light; 6 is a polarization controller, which is used to adjust the polarization state of the ring laser resonant cavity; 7 is a 1560nm 10dB optical splitter, which is used to branch and export the generated pulse light; 8 is a pulse light output end, which is connected to a spectrometer and an oscilloscope respectively for spectrum and pulse testing.

[0078] The joints of each component in the entire ring cavity fiber laser are connected by single-mode fiber SMF-28, and then welded by a fiber welding machine of Fujikura Co., Ltd. of Japan. The pump light is guided into the ring laser resonant cavity through a wavelength division multiplexer 2 working at 980 / 1560nm. A 20cm long erbium-doped fiber 3 is inserted into the cavity as a gain medium. The 1560nm polarized light isolator 4 is mainly used to ensure unidirectional transmission of light. The tin oxide nanoparticle film as a saturable absorber 5 is placed in the fiber ferrule, and the polarization state of the cavity is adjusted by a polarization controller 6. The output laser passes through a 10dB optical splitter 7 to output 10% of the light through the pulse light output end 8 to a spectrometer or oscilloscope to observe the pulse shape or pulse sequence.

[0079] The experimental results are as follows Figure 5a-5c As shown in the figure, the Q-switching center of the input power of 76mW is located at 1568nm, and the corresponding pulse repetition frequency is 36.15kHz. The single pulse time width is 10.7µs. The increase in input power causes the repetition frequency to increase and the time width to decrease, which is a typical characteristic of passive Q-switched lasers.

[0080] Example 2: A saturable absorber prepared by depositing synthesized tin oxide nanoparticles on a D-type optical fiber and used for Q-switched laser output at 1.5 μm;

[0081] 1. Sample preparation process

[0082] The preparation method of tin oxide nanoparticles is the same as that of Example 1, so it will not be repeated here.

[0083] The prepared tin oxide nanoparticles are mixed with deionized water in a mass ratio of 1:0.5-16, and ultrasonically dispersed at 70-90°C for 2-5 hours. The dispersed tin oxide nanoparticles are dropped on the D-type cross-section of the D-type optical fiber, and naturally dried in a vacuum-sealed container. The D-type optical fiber with deposited tin oxide nanoparticles is the prepared saturable absorber.

[0084] 2. Fiber laser testing

[0085] like Figure 4 As shown, the difference from Example 1 is that the saturable absorber 5 is different. In Example 2, the D-type optical fiber deposited with tin oxide nanoparticles as the saturable absorber 5 is connected to the optical fiber ferrule. The output laser passes through a 10dB optical splitter 7 and 10% of the light is output through the pulse light output terminal 8 to a spectrometer or oscilloscope to observe the pulse shape or pulse sequence.

[0086] The experimental results are as follows Figure 6a-6c As shown in the figure, the Q-switching center of the input power of 405mW is located at 1532nm, and the corresponding pulse repetition frequency is 26.6kHz. The single pulse time width is 4.08µs. The increase in input power causes the repetition frequency to increase and the time width to decrease, which is a typical characteristic of passive Q-switched lasers.

[0087] The saturable absorber based on tin oxide nanoparticles is more stable than the saturable absorber based on stannous oxide nanoparticles because stannous oxide is easily converted into tin oxide when heated. Therefore, tin oxide nanoparticles have higher stability under the action of laser thermal effect.

[0088] The saturable absorber based on tin oxide nanoparticles is more controllable than the saturable absorber based on indium tin oxide nanoparticles. Indium, the main component of indium tin oxide, is expensive and has the characteristics of optical transparency, and the controllability of optical saturable absorption characteristics is low. Tin oxide has good conductivity and high density, and has high temperature resistance, high temperature load softening point and excellent corrosion resistance, making it an ideal saturable absorber material.

[0089] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0090] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A saturable absorber, characterized in that: It is a saturable absorber based on a mixture of tin oxide nanoparticles and a film-forming agent; The method for preparing the saturable absorber comprises the following steps: S1: preparing tin oxide nanoparticles by a solvothermal method; wherein step S1 specifically comprises the following steps: S11: tin chloride pentahydrate powder, ethylenediamine and oleic acid are respectively placed in a reaction kettle and fully mixed at room temperature using a magnetic mixer; S12: heating the mixture in an oven at 180° C. for 10 hours, and centrifuging after natural cooling; S13: washing the oleic acid with anhydrous ethanol and removing impurities with deionized water, and drying to obtain a tin hydroxide xerogel; S14: placing the tin hydroxide xerogel in a muffle furnace, heating at 600° C. for five minutes, and grinding after natural cooling to obtain tin oxide nanoparticles; S2: Mixing the tin oxide nanoparticles with a film-forming agent to form a film to prepare a saturable absorber; wherein, sodium carboxymethyl cellulose powder and deionized water are mixed at a molar ratio of 8-25:1, stirred at 60-80°C for 24 hours, the solution is colorless and transparent, and no precipitate is precipitated after standing for 5-7 hours, thereby forming a sodium carboxymethyl cellulose aqueous solution; the tin oxide nanoparticles and the sodium carboxymethyl cellulose aqueous solution are mixed at a mass ratio of 1:0.5-16, ultrasonically dispersed at 70-90°C for 2-5 hours, spin-coated the dispersed solution on a flat glass slide surface, and naturally dried in a vacuum-sealed container until a film is formed, and the film is the prepared saturable absorber.

2. A saturable absorber, characterized in that: It is a saturable absorber based on tin oxide nanoparticles deposited on the surface of tapered fiber or D-type fiber or cladding-etched fiber; The method for preparing the saturable absorber comprises the following steps: S1: preparing tin oxide nanoparticles by a solvothermal method; wherein step S1 specifically comprises the following steps: S11: tin chloride pentahydrate powder, ethylenediamine and oleic acid are respectively placed in a reaction kettle and fully mixed at room temperature using a magnetic mixer; S12: heating the mixture in an oven at 180° C. for 10 hours, and centrifuging after natural cooling; S13: washing the oleic acid with anhydrous ethanol and removing impurities with deionized water, and drying to obtain a tin hydroxide xerogel; S14: placing the tin hydroxide xerogel in a muffle furnace, heating at 600° C. for five minutes, and grinding after natural cooling to obtain tin oxide nanoparticles; S2: Depositing the tin oxide nanoparticles on the surface of a tapered optical fiber, a D-type optical fiber or a cladding-etched optical fiber to obtain a saturable absorber; wherein the tin oxide nanoparticles are mixed with deionized water in a mass ratio of 1:0.5-16, and ultrasonically dispersed at 70-90°C for 2-5 hours, and the dispersed tin oxide nanoparticles are dropped on the D-type section of the D-type optical fiber, and dried naturally in a vacuum-sealed container. The D-type optical fiber on which the tin oxide nanoparticles are deposited is the obtained saturable absorber.

3. A saturable absorber, characterized in that: It is a saturable absorber based on tin oxide nanoparticles filled in the air hole cladding of photonic crystal fiber; The method for preparing the saturable absorber comprises the following steps: S1: preparing tin oxide nanoparticles by a solvothermal method; wherein step S1 specifically comprises the following steps: S11: tin chloride pentahydrate powder, ethylenediamine and oleic acid are respectively placed in a reaction kettle and fully mixed at room temperature using a magnetic mixer; S12: heating the mixture in an oven at 180° C. for 10 hours, and centrifuging after natural cooling; S13: washing the oleic acid with anhydrous ethanol and removing impurities with deionized water, and drying to obtain a tin hydroxide xerogel; S14: placing the tin hydroxide xerogel in a muffle furnace, heating at 600° C. for five minutes, and grinding after natural cooling to obtain tin oxide nanoparticles; S2: Mixing the tin oxide nanoparticles with deionized water, and filling the mixed solution into the air hole cladding of a photonic crystal fiber and drying it to obtain a saturable absorber; wherein the tin oxide nanoparticles and deionized water are mixed at a mass ratio of 1:0.5-16, ultrasonically dispersed at 70-90°C for 2-5 hours, and the dispersed tin oxide nanoparticles are filled into the air hole cladding of the photonic crystal fiber. The photonic crystal fiber filled with the tin oxide nanoparticles is the obtained saturable absorber.

4. A ring cavity fiber laser, comprising a pump source and a ring laser resonant cavity, wherein the ring laser resonant cavity comprises a wavelength division multiplexer, an erbium-doped fiber, a polarization isolator, a polarization controller and an optical splitter, characterized in that: It also includes a saturable absorber as described in any one of claims 1 to 3, the output end of the pump source is connected to the pump end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to one end of the erbium-doped optical fiber, the other end of the erbium-doped optical fiber is connected to the input end of the polarization light isolator, the output end of the polarization light isolator is connected to one end of the saturable absorber, the other end of the saturable absorber is connected to one end of the polarization controller, and the other end of the polarization controller is connected to the optical splitter.

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