An electro-controlled saturable absorber device based on a gold nanometer thin film, a preparation method thereof, and an application thereof

Abstract

The present invention discloses an electrically tunable saturable absorber device based on a gold nanometer thin film, a preparation method thereof, and an application thereof, belonging to the technical field of lasers. The electrically tunable saturable absorber device includes an optical fiber substrate, a gold nanometer thin film, a metal wire electrode, and an adjustable DC power supply. The gold nanometer thin film is deposited on the optical fiber substrate by physical vapor deposition technology to form a saturable absorber device. The gold nanometer thin film is connected to the adjustable DC power supply through the metal wire electrode to form a loop. By applying a voltage to the gold nanometer thin film through the DC power supply, the purpose of dynamically regulating the linear loss and the nonlinear saturable absorption property of the device is realized. When a DC voltage is applied to the gold nanometer thin film, due to the Joule heat effect, the temperature of the gold nanometer thin film increases with the increase of the voltage, resulting in changes in the electron-phonon scattering probability and the dielectric constant in the gold nanometer thin film, thereby modulating the surface plasmon resonance absorption characteristics of the gold nanometer thin film, as well as the linear loss and saturable absorption property parameters of the device. When the electrically tunable saturable absorber is used as a modulation device in a mode-locked fiber laser, by applying a DC voltage to the electrically tunable saturable absorber, the working wavelength and pulse width of the mode-locked laser can be adjusted in real time, and the switching of the laser working state can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of lasers, and particularly relates to an electrically tunable saturable absorber device based on a gold nanometer thin film, a preparation method thereof, and an application thereof. Background Art

[0002] Passively mode-locked fiber lasers have the characteristics of narrow pulse width, high peak power, good beam quality, and compact structure, and are widely used in the fields of material processing, precision measurement, biomedicine, national defense security, etc. The saturable absorber is the core device for realizing passively mode-locked lasers, and its saturable absorption property directly affects the output parameters of the mode-locked laser. Adjusting the performance parameters of the saturable absorber device (such as linear loss, modulation depth, and saturation intensity) is one of the key technologies for realizing the wavelength modulation of the mode-locked laser, the pulse width adjustment, and even the switching of the laser working state. At present, many new applications require precise customization of the time-domain and frequency-domain characteristics of ultrashort pulsed lasers, but the existing designs of passively mode-locked fiber lasers still cannot meet this requirement.

[0003] Commonly used saturable absorbers mainly include semiconductor saturable absorption mirrors, and nanomaterial saturable absorbers such as carbon nanotubes, graphene, topological insulators, and gold nanorods. Breakthroughs have been made in passively mode-locked fiber lasers based on these saturable absorbers. However, for these saturable absorber devices with conventional designs, the characteristic parameters such as linear loss, modulation depth, and saturation intensity are usually fixed. After being placed in the laser cavity, although mode-locked laser output can be achieved, it is only equivalent to a passive "static" device, and the obtained mode-locked laser output parameters are limited, and the output parameters of the mode-locked laser cannot be precisely controlled. In this regard, designing and fabricating a saturable absorber device with flexible optical property regulation will be beneficial to realizing the flexible regulation of the mode-locked laser output parameters, which is also an important step in the engineering and industrialization of saturable absorbers.

[0004] The gold nanometer thin film has unique surface plasmon resonance characteristics, thus showing excellent optical properties, and is considered to be a saturable absorber with great potential. In addition, the gold nanometer thin film also has excellent electrical characteristics, which makes it possible to develop an electrically tunable saturable absorber device based on the gold nanometer thin film. Summary of the Invention

[0005] In view of the deficiency that the saturable absorption property of existing saturable absorber devices cannot be dynamically regulated, the present invention provides an electrically tunable saturable absorber device based on a gold nanometer thin film, a preparation method thereof, and an application thereof. The electrically controlled saturable absorber device includes a gold nanometer thin film, a D-shaped optical fiber substrate, metal wire electrodes, and an adjustable DC power supply. By applying a DC voltage to the gold nanometer thin film, due to the Joule heat effect, the temperature of the gold nanometer thin film increases with the increase of the voltage, resulting in changes in the electron-phonon scattering probability and dielectric constant in the gold nanometer thin film, thereby modulating the surface plasmon resonance absorption characteristics of the gold nanometer thin film, as well as the linear loss and saturable absorption property parameters of the device. When the electrically tunable saturable absorber is used as a modulation device in a mode-locked fiber laser, by applying a DC voltage to the electrically tunable saturable absorber, the working wavelength and pulse width of the mode-locked laser can be adjusted in real time, and the switching of the laser working state can be realized.

[0006] The present invention is realized through the following technical solutions:

[0007] In a first aspect, the present invention provides an electrically tunable saturable absorber device based on a gold nanometer thin film, including an optical fiber substrate, a gold nanometer thin film, metal wire electrodes, and an adjustable DC power supply; the gold nanometer thin film is deposited on the optical fiber substrate by physical vapor deposition technology to form a saturable absorber device, and the gold nanometer thin film is connected to the adjustable DC power supply through the metal wire electrodes to form a circuit, and a voltage is applied to the gold nanometer thin film through the DC power supply, thereby achieving the purpose of dynamically regulating the linear loss and nonlinear saturable absorption property of the saturable absorber device.

[0008] Further, the optical fiber substrate includes a D-shaped optical fiber or a tapered optical fiber; the optical fiber matrix is a silica optical fiber or a fluoride optical fiber.

[0009] Further, the thickness of the gold nanometer thin film is 3-50 nm.

[0010] In a second aspect, the present invention also provides a preparation method for an electrically tunable saturable absorber device based on a gold nanometer thin film, specifically including the following steps:

[0011] Step 1: Ultrasonically clean the optical fiber substrate;

[0012] Step 2: Deposit a copper thin film as a seed layer on the optical fiber substrate by physical vapor deposition technology;

[0013] Step 3: Deposit a gold thin film on the optical fiber substrate on which the copper thin film has been deposited by physical vapor deposition technology to obtain a gold nanometer thin film on the optical fiber substrate;

[0014] Step 4: Fix the metal wire electrodes at both ends of the gold nanometer thin film by using conductive silver glue.

[0015] Step Five: Connect the metal wire electrode to a DC power supply to form a closed loop, and obtain the electro-optically tunable saturable absorber device based on the gold nanofilms.

[0016] Further, in Step Two, the thickness of the evaporated copper thin film is 1 - 5 nm.

[0017] Further, the physical vapor deposition technology includes vacuum thermal evaporation, magnetron sputtering, or vacuum ion plating.

[0018] In a third aspect, the present invention also provides an application of the electro-optically tunable saturable absorber device based on the gold nanofilms in the preparation of mode-locked fiber lasers.

[0019] Further, the mode-locked fiber laser includes an electro-optically tunable saturable absorber device based on the gold nanofilms and a fiber laser resonator. A DC voltage is applied to the electro-optically tunable saturable absorber device based on the gold thin films through a DC power supply. Due to the Joule heat effect, the temperature of the gold nanofilms increases with the increase of the power supply voltage, which causes an increase in the electron-phonon scattering probability of the gold nanofilms and a change in their dielectric constant, thereby resulting in changes in the linear loss and the nonlinear saturable absorption properties of the above-mentioned gold nanofilms saturable absorber device; in the fiber laser, the gold nanofilms saturable absorber acts as a passive mode-locking device, and its linear loss and nonlinear saturable absorption properties can be adjusted in real time under electro-optic control, thereby modulating the operating wavelength, pulse width of the mode-locked laser, and switching the working state of the laser.

[0020] Further, the gain fiber of the fiber laser resonator is one of ytterbium (Yb)-doped fiber, erbium (Er)-doped fiber, thulium (Tm)-doped fiber, or holmium (Ho)-doped fiber.

[0021] Further, the fiber laser resonator is a linear cavity or a ring cavity.

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

[0023] 1. A kind of electro-optically tunable saturable absorber device based on gold nanofilms of the present invention uses a copper thin film as a seed layer, which not only increases the adhesion of the above-mentioned target gold nanofilm layer, but also can improve the surface roughness of the above-mentioned target gold nanofilm, and further reduces the linear loss of the device; uses a D-shaped optical fiber or a tapered optical fiber as the gold nanofilm substrate, and utilizes the interaction between the optical fiber evanescent field and the above-mentioned gold nanofilm to increase the damage threshold of the saturable absorber device; and the electro-optically tunable saturable absorber device prepared by integrating metal wire electrodes on the above-mentioned optical fiber substrate still maintains an all-fiber structure, which is convenient to be integrated into modern optoelectronic devices for electro-optically modulated optical modulation; applying a DC voltage to the above-mentioned gold nanofilm by using a DC power supply to generate Joule heat, which can regulate the electron-phonon scattering and dielectric constant of the gold nanofilm, and further achieve the purpose of dynamically regulating the linear loss and saturable absorption property parameters (modulation depth and saturation intensity) of the gold nanofilm saturable absorber device;

[0024] 2. Applying the electro-optically tunable saturable absorber device based on gold nanofilms to a mode-locked laser as a mode-locking device with electro-optically tunable property parameters, by applying a DC voltage to the above-mentioned saturable absorber device to adjust its linear loss and nonlinear saturable absorption property parameters, the working wavelength, pulse width, output power and pulse working state of the mode-locked laser can be flexibly adjusted;

[0025] 3. The method of the present invention is simple to operate and highly flexible, and only by changing the DC voltage applied to the above-mentioned gold nanofilm saturable absorber, the state switching between mode-locked laser and Q-switched mode-locked laser can be achieved. The Q-switched mode-locked laser has higher pulse energy than the traditional mode-locked laser and has important application prospects in the fields of supercontinuum generation and industrial processing. Flexibly switching the working state of laser pulses has high value in increasing the functions of lasers and expanding their applicability;

[0026] 4. The voltage-regulated gold nanofilm device and method prepared by the present invention can also be applied to other optoelectronic devices for dynamic optical modulation, which is of great significance for optimizing the overall performance parameters of devices and systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally denoted by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to actual scale.

[0028] Figure 1 It is a schematic structural diagram of the electro-optically tunable saturable absorber device based on gold nanofilms of the present invention;

[0029] Figure 2 Atomic force microscope photograph of the gold nanometer thin film of the present invention;

[0030] Figure 3 Relationship curve between the temperature of the gold nanometer thin film of the present invention and the applied DC voltage;

[0031] Figure 4 Linear absorption curve of the electro-optically tunable saturable absorber device based on the gold nanometer thin film of the present invention under different voltages;

[0032] Figure 5 Linear loss at a wavelength of 2 μm of the electro-optically tunable saturable absorber device based on the gold nanometer thin film of the present invention under different voltages;

[0033] Figure 6 Saturable absorption curve of the electro-optically tunable saturable absorber device based on the gold nanometer thin film of the present invention under different voltages and relationship curve of the modulation depth and saturation intensity of the electro-optically tunable saturable absorber device varying with voltage;

[0034] Among them, (a) is the saturable absorption curve of the electro-optically tunable saturable absorber device based on the gold nanometer thin film of the present invention under different voltages;

[0035] (b) is the relationship between the modulation depth and saturation intensity of the electro-optically tunable saturable absorber device of the present invention varying with voltage;

[0036] Figure 7 Schematic diagram of the thulium-doped fiber laser resonator structure based on the electro-optically tunable saturable absorber device of the present invention;

[0037] Figure 8 Output spectrum diagram of mode-locked laser and relationship curve of the center wavelength of mode-locked laser varying with voltage of the present invention under different voltages;

[0038] Among them, (a) is the output spectrum diagram of mode-locked laser of the present invention under different voltages;

[0039] (b) is the relationship curve of the center wavelength of mode-locked laser of the present invention varying with voltage;

[0040] Figure 9 Autocorrelation curve of mode-locked laser and corresponding pulse width of the present invention under different voltages;

[0041] Figure 10 Laser output spectrum diagram when the applied voltage is 7 V and 8 V of the present invention;

[0042] Figure 11 Continuous mode-locked laser pulse sequence and Q-switched mode-locked laser pulse sequence of the present invention;

[0043] Among them, (a) is the continuous mode-locked laser pulse sequence of the present invention;

[0044] (b) is the Q - switched mode - locked laser pulse sequence of the present invention;

[0045] Figure 12 is the curve of the pulse width and repetition frequency of the Q - switched mode - locked laser of the present invention varying with the applied voltage;

[0046] Figure 13 is the curve of the output power of the pulsed laser of the present invention varying with the applied voltage;

[0047] In the figure: 1. Electrically - tunable saturable absorber based on gold - nanofilms, 11. Quartz glass, 12. Conductive silver paste, 13. Gold - nanofilms, 14. High - temperature tape, 15. D - type optical fiber, 16. Silver - wire electrode, 17. DC power supply, 2. Ordinary single - mode quartz optical fiber, 3. Polarization controller, 4. Isolator, 5. Thulium - doped fiber, 6. 1570 / 1980 nm wavelength - division multiplexer, 7. 1570 nm fiber laser, 8. 9:1 output coupler. Specific embodiments

[0048] To clearly and completely describe the technical solutions and their specific working processes of the present invention, in combination with the accompanying drawings of the specification, the specific embodiments of the present invention are as follows:

[0049] Example 1: Preparation of an electrically - tunable saturable absorber device based on gold - nanofilms.

[0050] It should be noted that in Example 1 of the present invention, only one preferred embodiment of the above - mentioned electrically - tunable saturable absorber device based on gold - nanofilms is listed. The fiber substrate is a D - type quartz fiber, and the combination of gold - nanofilms and the tapered - fiber substrate is also included in the embodiments of the present invention.

[0051] Figure 1 is the structural schematic diagram of the electrically - tunable saturable absorber device based on gold - nanofilms of the present invention. The electrically - tunable saturable absorber device 1 includes quartz glass 11, conductive silver paste 12, gold - nanofilms 13, high - temperature tape 14, D - type optical fiber 15, metal - wire electrode 16, and DC power supply 17.

[0052] The gold - nanofilms are deposited on the D - type fiber substrate by physical vapor deposition. The specific steps are as follows:

[0053] Step 1 - 1: Place the side - polished area of the D - type optical fiber 15 in a beaker, add acetone to the beaker, ultrasonically clean for 10 minutes, pour out the acetone, add absolute ethanol, ultrasonically clean for 10 minutes, pour out the absolute ethanol, add deionized water, ultrasonically clean for 10 minutes, and then take out the D - type optical fiber and place it in a vacuum drying oven to dry at 60 °C for 3 hours. The purpose of cleaning the D - type optical fiber is to ensure the cleanliness of the side - polished plane of the D - type optical fiber, which is beneficial to improving the quality of the evaporated gold - nanofilms.

[0054] Step 1-2: First, use a vacuum thermal evaporation coating instrument to deposit a 1-nm-thick copper nanometer film on the above-mentioned D-shaped optical fiber's horizontal plane as a seed layer. During deposition, the vacuum degree is 1×10 -3 Pa, and the deposition rate is Using this copper film as a seed layer can increase the adhesion of the subsequently deposited gold nanometer film and reduce the surface roughness of the gold nanometer film.

[0055] Step 1-3: Use a vacuum thermal evaporation coating instrument to deposit a 15-nm-thick gold film 13 on the above-mentioned D-shaped optical fiber plane where the copper nanometer film has been deposited. The vacuum degree is 1×10 -3 Pa, and the deposition rate is

[0056] Step 1-4: Place two silver wires 16 at both ends of the D-shaped region of the above-mentioned D-shaped optical fiber after depositing the gold nanometer film, and drop conductive silver glue 12. Wait for it to dry naturally in the air. The total resistance between the two electrodes is measured to be about 96 Ω. Then, connect the above-mentioned silver wires 16 to a DC power supply 17 to form a closed loop.

[0057] Figure 2 is the atomic force microscope photo of the above-prepared gold nanometer film. It can be analyzed by the atomic force microscope that the root-mean-square surface roughness of the above-prepared gold nanometer film is about 0.9 nm. The obtained high-quality gold nanometer film benefits from the cleaning of the optical fiber substrate before evaporation and the use of the copper film as a seed layer.

[0058] Example 2: Use electrical regulation to achieve modulation of the saturable absorption property parameters of the device.

[0059] Apply a DC voltage to the gold nanometer film prepared in Example 1 using a DC regulated power supply. Due to the Joule heat effect, the temperature of the gold nanometer film increases as the voltage rises. As Figure 3 shown, when the power supply voltage increases from 0 V to 8 V, the temperature of the gold nanometer film rises from 28.6 °C to 51.3 °C. The increase in the temperature of the gold nanometer film enhances its electron-phonon scattering, increases the optical damping coefficient, and further changes its dielectric constant, resulting in a change in its surface plasmon absorption characteristics, and further leading to changes in the linear loss of the gold nanometer film saturable absorber device and the nonlinear saturable absorption property parameters.

[0060] Figure 4 is the absorption spectrum of the electrically regulated saturable absorber device based on the gold nanometer film under different power supply voltages. Near 2 μm, as the applied voltage increases, the absorption of the saturable absorber device gradually decreases.

[0061] Figure 5Relationship curve between the linear loss of the electro-optically tunable saturable absorber device based on a gold nanofilms at a wavelength of 2 μm and the applied DC voltage. As the voltage increases from 0 V to 10 V, the linear loss of the saturable absorber device decreases from 7.35 dB to 4.22 dB.

[0062] Figure 6 (a) shows the saturable absorption curves of the electro-optically tunable saturable absorber device based on a gold nanofilms in the 2-μm wavelength band under different voltages. The parameters of the laser used for testing are: central wavelength: 1965 nm, repetition frequency: 21.4 MHz, pulse width: 1 ps. The solid lines in the figure are the theoretical fitting curves. Figure 6 (b) shows the relationships between the modulation depth and saturation intensity of the electro-optically tunable saturable absorber device based on a gold nanofilms obtained by fitting and the applied voltage. As the applied voltage increases from 0 V to 10 V, the modulation depth of the above-mentioned electro-optically tunable saturable absorber device based on a gold nanofilms decreases from 17.6% to 13.3%, and the saturation intensity increases from 0.29 MW / cm 2 increases to 0.5 MW / cm 2 . This is because the temperature of the gold nanofilms increases with the increase of the applied voltage, resulting in enhanced electron-phonon scattering and reduced linear absorption coefficient in the gold nanofilms. Therefore, the modulation depth decreases (proportional to the linear absorption coefficient), and the saturation intensity increases (inversely proportional to the product of the absorption coefficient and relaxation time).

[0063] Example 3: A tunable mode-locked fiber laser in the 2-μm wavelength band based on an electro-optically tunable saturable absorber device.

[0064] Figure 7 is a schematic diagram of the structure of a tunable mode-locked laser ring cavity in the 2-μm wavelength band. The pump source is a fiber laser 7 with a working wavelength of 1570 nm. The pump source is coupled into the laser resonator through a 1570 / 1980 nm wavelength division multiplexer 6. The gain fiber 5 is a 40-cm-long thulium-doped silica fiber, and its absorption coefficient for 1570-nm light is 340 dB / m. A 2-μm wavelength optical isolator 4 is connected after the gain fiber to ensure unidirectional operation of the laser in the cavity. The function of the polarization controller 3 is to adjust the polarization state in the cavity. The above-mentioned electro-optically tunable saturable absorber device 1 based on a gold nanofilms is connected into the laser ring cavity as a modulation device. A 9:1 output optical coupler 8 is used to output 10% of the light out of the cavity for detection, and the remaining light continues to circulate in the cavity. Except for the gain fiber 5 in the laser resonator, the pigtails of the other devices are all ordinary single-mode silica fibers 2.

[0065] When the power of the pump source 7 is increased to 850 mW, mode-locked laser self-starting can be achieved. Keeping the current pump power and polarization state unchanged, increasing the voltage of the DC power supply 17, when the applied voltage changes within 0 to 7 V, the laser remains in the mode-locked state, and its central wavelength gradually redshifts, as shown in Figure 8As shown in (a). When the applied voltage increases from 0V to 7V, the central wavelength of the mode-locked laser redshifts from 1964.9nm to 1991.5nm, as Figure 8 shown in (b). This is because as the voltage increases, the loss curve of the electro-optically tunable saturable absorber changes accordingly, resulting in the change of the operating wavelength of the mode-locked laser.

[0066] Figure 9 Figure shows the autocorrelation curves of the mode-locked laser corresponding to different voltages measured by an autocorrelator. Using the Sech 2 function for fitting, the pulse width of the mode-locked laser at each voltage can be obtained. When the applied voltage increases from 0V to 7V, the pulse width of the mode-locked laser decreases from 482fs to 375fs.

[0067] When the applied voltage varies from 0 to 7V, the laser always maintains a stable mode-locked state. Continuing to increase the voltage applied to the electro-optically tunable saturable absorber can achieve the switching of the pulse operating state from mode-locking to Q-switched mode-locking. When the voltage increases to 8V, the laser pulse changes from the continuous mode-locked state to the Q-switched mode-locked state, as Figure 10 shown. The output spectrum of the laser changes from a typical soliton profile with Kelly sidebands to a bell-shaped profile. When the applied voltage is switched between 7V and 8V, the switching between the continuous mode-locked and Q-switched mode-locked states can be achieved.

[0068] Figure 11 (a) shows the pulse train of the continuous mode-locked laser. The time domain interval of the mode-locked pulses is 40.3ns, corresponding to a repetition frequency of the mode-locked laser of 24.8MHz. Figure 11 (b) shows the pulse train of the Q-switched mode-locked laser. The time domain interval of each Q-switched envelope is about 9μs, corresponding to a repetition frequency of the Q-switched mode-locked laser of 111kHz. Each Q-switched envelope of the Q-switched mode-locked laser contains a large number of ultrashort mode-locked pulses. Compared with the continuous mode-locked laser, the Q-switched mode-locked laser has a higher single-pulse energy, making it have important application prospects in the fields of supercontinuum generation, nonlinear frequency conversion, and ultra-precision machining.

[0069] Figure 12 Figure shows the curves of the pulse width and repetition frequency of the Q-switched mode-locked laser varying with the applied voltage. When the applied voltage increases from 8V to 10V, the pulse width of the Q-switched envelope of the Q-switched mode-locked laser decreases from 2.56μs to 2.48μs, and the repetition frequency of the Q-switched envelope increases from 111kHz to 118.5kHz, which are typical characteristics of Q-switched lasers.

[0070] Figure 13 Figure shows the curve of the output power of the pulsed laser varying with the applied voltage. When the applied voltage increases from 0V to 10V, the output power of the pulsed laser increases from 16.36mW to 24.55mW.

[0071] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0072] In addition, it should be noted that, in the case of no conflict, the various specific technical features described in the above specific embodiments can be combined in any appropriate manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination manners.

[0073] Furthermore, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. An electrically controllable saturable absorber device based on gold nanofilm, characterized in that: It includes an optical fiber substrate, a gold nanofilm, a metal wire electrode and an adjustable DC power supply; the gold nanofilm is evaporated on the optical fiber substrate by physical vapor deposition technology to form a saturable absorber device, the gold nanofilm is connected to the adjustable DC power supply through the metal wire electrode to form a loop, and a voltage is applied to the gold nanofilm through the DC power supply, thereby achieving the purpose of dynamically regulating the linear loss and nonlinear saturable absorption properties of the saturable absorber device; The optical fiber substrate includes a D-type optical fiber or a tapered optical fiber; the optical fiber matrix is ​​a quartz optical fiber or a fluoride optical fiber; The thickness of the gold nanofilm is 3 to 50 nm; The electrically regulated saturable absorber device based on gold nanofilm is prepared by the following method, which specifically comprises the following steps: Step 1: Ultrasonic cleaning of the optical fiber substrate; Step 2: using physical vapor deposition technology to deposit a copper film on the optical fiber substrate as a seed layer; Step 3: using physical vapor deposition technology to evaporate a gold film on the optical fiber substrate on which the copper film has been evaporated, to obtain the gold nanofilm on the optical fiber substrate; Step 4: Use conductive silver glue to fix the metal wire electrodes to the two ends of the gold nanofilm; Step 5: Connect the metal wire electrode to a direct current power supply to form a closed loop, thereby obtaining the electrically regulated saturable absorber device based on the gold nanofilm.

2. The electrically controllable saturable absorber device based on gold nanofilm according to claim 1, characterized in that: In step 2, the thickness of the evaporated copper film is 1 to 5 nm.

3. The electrically controllable saturable absorber device based on gold nanofilm according to claim 1, characterized in that: The physical vapor deposition technology includes vacuum thermal evaporation, magnetron sputtering or vacuum ion plating.

4. The use of an electrically controllable saturable absorber device based on a gold nanofilm in the preparation of a mode-locked fiber laser as claimed in claim 1, characterized in that: The mode-locked fiber laser comprises an electrically controllable saturable absorber device based on a gold nanofilm and a fiber laser resonant cavity. A DC voltage is applied to the electrically controllable saturable absorber device based on the gold film through a DC power supply. Due to the Joule heating effect, the temperature of the gold nanofilm increases with the increase of the power supply voltage, causing an increase in the electron-phonon scattering probability in the gold nanofilm and a change in its dielectric constant, thereby causing changes in the linear loss and nonlinear saturable absorption properties of the above-mentioned gold nanofilm saturable absorber device; in the fiber laser, the gold nanofilm saturable absorber acts as a passive mode-locked device, and can adjust its own linear loss and nonlinear saturable absorption properties in real time under electrical control, thereby modulating the working wavelength and pulse width of the mode-locked laser and switching the laser working state.

5. The use of an electrically controllable saturable absorber device based on a gold nanofilm in the preparation of a mode-locked fiber laser as claimed in claim 4, characterized in that: The gain fiber of the fiber laser resonant cavity is one of ytterbium-doped Yb fiber, Er-doped Er fiber, thulium-doped Tm fiber or holmium-doped Ho fiber.

6. The use of an electrically controllable saturable absorber device based on a gold nanofilm in the preparation of a mode-locked fiber laser as claimed in claim 4, characterized in that: The optical fiber laser resonant cavity is a linear cavity or a ring cavity.

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