A saturable absorber based on tantalum nitride quantum dots, its preparation method, and a mode-locked fiber laser.

Abstract

This application belongs to the field of saturable absorbers, and particularly relates to a saturable absorber based on tantalum nitride quantum dots, its preparation method, and a mode-locked fiber laser. The tantalum nitride quantum dots in the saturable absorber provided by this application, as topological half-metals, exhibit excellent optical properties and saturation intensity. When a laser beam passes through the tantalum nitride quantum dots on the saturable absorber, the laser can quickly reach saturation, enabling the output of ultrafast lasers with a repetition frequency and stable laser mode-locking signal. This solves the technical problem of low performance in existing saturable absorbers based on two-dimensional materials.

Description

Technical Field

[0001] This application belongs to the field of saturable absorbers, and particularly relates to a saturable absorber based on tantalum nitride quantum dots, its preparation method, and a mode-locked fiber laser. Background Technology

[0002] Saturable absorbers are one of the key components in fiber lasers for generating laser pulses. Current saturable absorbers include artificial saturable absorbers such as nonlinear ring mirrors and nonlinear polarization evolution mirrors, as well as non-artificial "real" saturable absorbers such as semiconductor saturable absorber mirrors and low-dimensional materials.

[0003] The difficulty and cost of fabricating semiconductor saturable absorbers in saturable absorbers limit their widespread application in fiber lasers. Low-dimensional materials, on the other hand, are widely used in fiber lasers due to their photoelectric properties. However, the performance of current two-dimensional saturable absorber materials is not high. For example, graphene has a small light absorption coefficient and modulation depth, black phosphorus has low stability at room temperature, and the indirect band gap of transition metal sulfides is not conducive to internal photon transitions. As a result, the performance of saturable absorbers based on two-dimensional materials such as graphene is relatively low. Summary of the Invention

[0004] In view of this, this application provides a saturable absorber based on tantalum nitride quantum dots, a preparation method thereof, and a mode-locked fiber laser, to solve the technical problem of low performance of saturable absorbers based on two-dimensional materials in the prior art.

[0005] The first aspect of this application provides a saturable absorber based on tantalum nitride quantum dots, including tantalum nitride quantum dots and a tapered optical fiber;

[0006] The tapered optical fiber is loaded with the tantalum nitride quantum dots.

[0007] Preferably, the particle size of the tantalum nitride quantum dots is 1–5 nm.

[0008] The second aspect of this application provides a method for preparing a saturable absorber based on tantalum nitride quantum dots, comprising the steps of: dropping a tantalum nitride quantum dot solution onto a tapered optical fiber, and obtaining a saturable absorber based on tantalum nitride quantum dots after deposition.

[0009] Preferably, the step of dropping a tantalum nitride quantum dot solution onto a tapered optical fiber and depositing it to obtain a saturable absorber based on tantalum nitride quantum dots specifically includes:

[0010] Step S1: Place the tapered optical fiber on a constant temperature heating table for preheating to obtain a preheated tapered optical fiber;

[0011] Step S2: Drop a tantalum nitride quantum dot solution onto the tapered region of a tapered optical fiber. Pass a 1550nm continuous wave laser through the other end of the tapered optical fiber. Under the action of the optical gradient force of the evanescent field, the tantalum nitride quantum dots surround the tapered region of the tapered optical fiber, thus obtaining a saturable absorber based on tantalum nitride quantum dots.

[0012] It should be noted that, to ensure the deposition effect, a much larger amount of dispersion solution than is required to meet the requirements for cone deposition should be added. The optical power was monitored by the power meter and decreased as the deposition process continued. After adding an excessive amount of dispersion solution and waiting for a short period of time, it was found that the optical power remained basically unchanged, indicating that enough tantalum nitride quantum dot material had been deposited in the tapered fiber and it was not advisable to add more dispersion solution. Therefore, the addition operation needs to be carried out by adjusting the appropriate volume of dispersion solution between 0.2 and 2 ml according to the concentration of quantum dots in the dispersion solution.

[0013] Preferably, in step S1, the heating temperature of the constant temperature heating table is 60°C.

[0014] Preferably, in step S2, the power of the continuous wave laser is 10 to 30 mW.

[0015] It should be noted that setting the heating temperature of the constant-temperature heating stage is beneficial for solvent evaporation. The incident light power during the tapered fiber deposition process will have a certain impact on the final deposition effect. When the input power is below 10mW, the output power remains basically unchanged, indicating that deposition has not occurred. Higher optical deposition power results in more material deposition and a greater modulation depth of the saturable absorber. When the incident light power exceeds approximately 30mW, excessive material deposition may occur, exceeding the tapered fiber's tolerance threshold, leading to a significant reduction in transmittance and a sharp drop in output light power to nanowatts. Therefore, the deposition operation requires adjusting the continuous-wave laser power between 10 and 30mW according to the tantalum nitride quantum dot concentration.

[0016] Preferably, the method for preparing the tantalum nitride quantum dots includes the following steps:

[0017] Step S12: Mix tantalum nitride and organic solvent, sonicate, and let stand to obtain an organic solution of tantalum nitride;

[0018] Step S22: Take the upper layer of the organic solution of tantalum nitride, mix it with the organic solvent, centrifuge, discard the upper layer of solution to obtain tantalum nitride quantum dots.

[0019] Preferably, in step S12, the mass-to-volume ratio of tantalum nitride to organic solvent is 1-10 g: 10-100 mL.

[0020] Preferably, in steps S12 and S22, the organic solvent is selected from ethanol.

[0021] Preferably, in step S12, the power of the ultrasound is 300-500W and the duration is 4-8h.

[0022] Preferably, in step S12, the settling time is 6 to 18 hours.

[0023] Preferably, in step S22, the centrifugation speed is 8000-12000 rpm and the time is 1-20 min.

[0024] A third aspect of this application provides a mode-locked fiber laser, including a laser pump source, a wavelength division multiplexer, an erbium-doped gain fiber, a polarization-independent isolator, a polarization controller, an output coupler, a saturable absorber based on tantalum nitride quantum dots, and a single-mode fiber.

[0025] The wavelength division multiplexer includes a first input terminal and a second input terminal;

[0026] The laser pump source, the first input terminal of the wavelength division multiplexer, the erbium-doped gain fiber, the polarization-independent isolator, the polarization controller, the output coupler, the saturable absorber based on tantalum nitride quantum dots, the single-mode fiber, and the second input terminal of the wavelength division multiplexer are sequentially connected to form a ring laser resonant cavity.

[0027] In summary, this application provides a saturable absorber based on tantalum nitride quantum dots, its preparation method, and a mode-locked fiber laser. The saturable absorber is prepared by dropwise deposition of a tantalum nitride quantum dot solution prepared by liquid-phase exfoliation onto a tapered optical fiber. In the saturable absorber, the tantalum nitride quantum dots, as a topological half-metal, have bulk energy bands with topological properties that intersect near the Fermi surface, forming a gapless electronic state. This makes it a saturable absorber material with excellent optical properties and saturation intensity. When a laser passes through the tantalum nitride quantum dots on the saturable absorber, the laser can quickly reach saturation, enabling the output of ultrafast lasers with high repetition rates and stable laser mode-locking signals. This solves the technical problem of low performance of saturable absorbers based on two-dimensional materials in the prior art. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is an atomic structure diagram of the tantalum nitride quantum dots prepared by the preparation method described in Example 2 of this application;

[0030] Figure 2The X-ray diffraction pattern of tantalum nitride quantum dots prepared by the preparation method described in Example 2 of this application;

[0031] Figure 3 The Raman spectrum of tantalum nitride quantum dots prepared by the preparation method described in Example 2 of this application;

[0032] Figure 4 This is a transmission electron microscope image of tantalum nitride quantum dots prepared by the preparation method described in Example 2 of this application;

[0033] Figure 5 An atomic force microscope image of tantalum nitride quantum dots prepared by the preparation method described in Example 2 of this application;

[0034] Figure 6 for Figure 5 The height diagram of quantum dots in the atomic force microscope image shown;

[0035] Figure 7 The optical properties of the tantalum nitride quantum dots prepared by the preparation method described in Example 2 of this application are shown in the test image.

[0036] Figure 8 This is a schematic diagram of the mode-locked fiber laser structure described in Embodiment 3 of this application;

[0037] Figure 9 This is a pulse sequence diagram of the mode-locked fiber laser described in Embodiment 3 of this application;

[0038] Figure 10 This is a broadband spectrum diagram of the mode-locked fiber laser described in Embodiment 3 of this application;

[0039] Figure 11 This is the fundamental frequency diagram of the mode-locked fiber laser described in Embodiment 3 of this application;

[0040] Figure 12 This is the spectrum of the mode-locked fiber laser described in Embodiment 3 of this application;

[0041] Figure 13 This is a graph showing the spectrum of the mode-locked fiber laser described in Embodiment 3 of this application as a function of time.

[0042] Figure 14 This is a graph showing the relationship between the optical path output power and the pump power of the mode-locked fiber laser described in Embodiment 3 of this application.

[0043] Figure 15 The pulse width diagram of a single pulse of the mode-locked fiber laser described in Embodiment 3 of this application;

[0044] Figure 4 a is a transmission electron microscope image of tantalum nitride quantum dots. Figure 4 b is a high-resolution transmission electron microscope image of tantalum nitride quantum dots;

[0045] Figure 6 a is Figure 5 The height diagram of the four groups of tantalum nitride quantum dots in the atomic force microscope image shown. Figure 6 b is Figure 5 The height distribution statistics of four groups of tantalum nitride quantum dots in the atomic force microscope image shown;

[0046] Figure 7 a is a schematic diagram of a dual-arm balanced detector used for testing the optical properties of tantalum nitride quantum dots. Figure 7 b is the saturable absorption curve of tantalum nitride quantum dots obtained by testing with a dual-arm balanced detector. Detailed Implementation

[0047] This application provides a saturable absorber based on tantalum nitride quantum dots, its preparation method, and a mode-locked fiber laser, which solves the technical problem of low performance of saturable absorbers based on two-dimensional materials in the prior art.

[0048] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0049] Example 1

[0050] In view of the low performance of existing two-dimensional saturable absorbers, Embodiment 1 of this application provides a saturable absorber based on tantalum nitride quantum dots, which consists of a tapered optical fiber and tantalum nitride quantum dots loaded thereon. As a topological half-metal, tantalum nitride quantum dots have bulk energy bands that cross near the Fermi surface, forming gapless electronic states. They are saturable absorber materials with excellent optical properties and saturation intensity. When a laser passes through the tantalum nitride quantum dots on the saturable absorber, the laser can reach saturation quickly, and an ultrafast laser with a repetition frequency can be output. The laser mode-locking signal is stable, thereby overcoming the technical problem of low performance of current two-dimensional saturable absorbers.

[0051] For tapered optical fibers, tapered optical fibers are obtained using a tapering method commonly used in this field. During tapering, the outer film of the portion of the single-mode optical fiber that needs to be tapered is first stripped off, and then the fiber is placed on a tapering machine of a forward fusion tapering system for tapering preparation.

[0052] Example 2

[0053] Example 2 of this application provides a method for preparing a saturable absorber based on tantalum nitride quantum dots as described in Example 1. The preparation method includes first preparing tantalum nitride quantum dots and then preparing a saturable absorber based on tantalum nitride quantum dots.

[0054] The steps for preparing tantalum nitride quantum dots include: first, placing 5g of tantalum nitride powder in 50ml of ethanol solvent, then placing the ethanol solvent containing tantalum nitride in an ultrasonic machine for a period of time and then removing it and letting it stand; wherein, the ultrasonic machine power is 400W, the ultrasonic duration is 6 hours, and the standing time is 12 hours.

[0055] After standing, 15 ml of the supernatant was mixed with 15 ml of ethanol solvent, and centrifuged at 10,000 rpm for 15 min. The supernatant was then removed to obtain the tantalum nitride quantum dot solution. The atomic structure of the tantalum nitride quantum dots is as follows: Figure 1 As shown, the X-ray diffraction of tantalum nitride quantum dots is as follows: Figure 2 As shown, the Raman spectrum of tantalum nitride quantum dots is as follows: Figure 3 As shown, the morphology of tantalum nitride quantum dots is as follows: Figure 4-5 As shown, the height dimension of the tantalum nitride quantum dot is as follows: Figure 6 As shown.

[0056] The steps for preparing a saturable absorber based on tantalum nitride quantum dots include: dropping 2 mL of tantalum nitride quantum dot solution onto a tapered optical fiber, and depositing the saturable absorber based on tantalum nitride quantum dots; wherein, the tantalum nitride quantum dot solution is dropped onto the tapered optical fiber, and a 1550 nm continuous wave laser is introduced on one side. Under the action of the optical gradient force of the evanescent field, the tantalum nitride quantum dots surround the tapered region of the tapered optical fiber. After the dispersion is completely dried, the tantalum nitride quantum dots are deposited on the tapered optical fiber to obtain a saturable absorber based on tantalum nitride quantum dots. During the preparation process, in order to ensure that the anhydrous ethanol in the tantalum nitride quantum dot solution evaporates as soon as possible, the tapered optical fiber should be preheated, and the entire deposition operation should be carried out on a constant temperature heating stage at 60°C, and the continuous wave laser should be controlled between 10 and 30 mW.

[0057] Example 3

[0058] Embodiment 3 of this application provides a mode-locked fiber laser, the structure of which is as follows: Figure 8 As shown, the system comprises a laser pump source 1, a wavelength division multiplexer 2, an erbium-doped gain fiber 3, a polarization-independent isolator 4, a polarization controller 5, an output coupler 6, a saturable absorber based on tantalum nitride quantum dots 7, and a single-mode fiber 8; wherein, the wavelength division multiplexer 2 includes a first input terminal and a second input terminal; the output coupler 6 includes a 75% output terminal and a 25% output terminal; the saturable absorber based on tantalum nitride quantum dots 7 is the saturable absorber based on tantalum nitride quantum dots described in Example 1 or 2.

[0059] The mode-locked fiber laser structure consists of a laser pump source 1, the first input terminal of a wavelength division multiplexer 2, an erbium-doped gain fiber 3, a polarization-independent isolator 4, a polarization controller 5, the 75% output terminal of an output coupler 6, a saturable absorber based on tantalum nitride quantum dots 7, and a single-mode fiber 8 connected in sequence. The single-mode fiber 8 is connected to the second input terminal of the wavelength division multiplexer 2 to form a ring resonant cavity. The ring resonant cavity is mainly composed of single-mode fiber with EDF parameters: Liekk, Er110-4 / 125, and a dispersion coefficient of approximately -15 ps / ( The laser beam (nm·km) is connected by fiber fusion splicing, with a cavity length of approximately 20 meters. In the ring resonant cavity, the laser pump source provides energy to the resonant cavity in pulsed or continuous form. Erbium-doped gain fiber serves as the gain medium. A wavelength division multiplexer is used to couple the pump light (980nm) and the excitation light (1550nm) from the erbium-doped fiber. An output coupler keeps 75% of the laser energy circulating inside the cavity, while 25% of the energy is output outside the cavity for detection. A polarization controller is used to adjust the polarization state and loss of the entire optical path. A polarization-independent isolator ensures that the entire laser operates unidirectionally within the cavity.

[0060] Experimental Example 1

[0061] The experimental examples in this application involve spectral analysis, morphology testing, and optical performance testing of the tantalum nitride quantum dots obtained in Example 2. The results are as follows: Figure 2-6 As shown, the mode-locked fiber laser characteristics of the described Example 3 were tested. The saturable absorber was obtained by depositing tantalum nitride quantum dots described in Example 2 onto a tapered optical fiber. The results are as follows. Figure 9-15 As shown.

[0062] The results of X-ray diffraction and Raman spectroscopy tests on tantalum nitride quantum dots are as follows: Figure 2-3 As shown, from Figure 2-3 It can be seen that the product obtained by the preparation method described in Example 2 of this application is tantalum nitride. Figure 4-6 The morphology images shown by transmission electron microscopy and atomic force microscopy confirm that the product is tantalum nitride quantum dots with a height size of 1 to 3 nm. Most of the tantalum nitride quantum dots have a height size of less than 2 nm. The preparation method provided in Example 2 of this application can prepare tantalum nitride quantum dots.

[0063] The optical properties of tantalum nitride quantum dots were tested using a dual-arm balanced detector, such as... Figure 7As shown in Figure a, the system consists of a light source, attenuator, coupler, and two identical power meters A1 and A2. The laser beam is split into two beams by the coupler. One beam passes through a tantalum nitride quantum dot loss circuit before entering power meter A1 for measurement, while the other beam directly enters power meter A2 for measurement. The saturable absorption curve of the material can be obtained by processing and analyzing the data measured by the two power meters. The specific data processing steps are as follows: a 50:50 coupler is used to build a dual-arm balanced detector for convenient data processing; T = P1 / P2 (T is the transmittance, P1 and P2 are the power values ​​measured by power meters a and b, respectively); each transmittance corresponds to a light field intensity, I = P2 / S (I is the light field intensity, S is the fiber core area); processing the above data yields a scatter plot, which can be fitted with formula 1 to obtain the saturable absorption curve (T is the transmittance, α is the attenuator, α is the attenuator). NS The loss is nonlinear and saturable, ΔT is the modulation depth, and I is the optical field intensity. sat (Saturated light intensity).

[0064]

[0065] The optical properties of tantalum nitride quantum dots, such as Figure 7 As shown in b, the basic parameters of tantalum nitride quantum dots, which are saturable absorbers, can be obtained, including saturation intensity, modulation depth, and unsaturation loss. By comparing with other two-dimensional materials, it is found that tantalum nitride quantum dots have lower saturation intensity and are a saturable absorber material with superior performance.

[0066] The mode-locked laser characteristics of a mode-locked fiber laser at a pump power of 100mW are as follows: Figure 9-15 As shown, Figure 9 The diagram shows the pulse sequence of a mode-locked fiber laser, indicating that the mode-locked pulses operate very stably with a pulse interval of approximately 46.8 ns. Figure 10 The broadband spectrum of the mode-locked fiber laser in the 600MHz range shows a relatively flat sequence, further illustrating the stability of the mode-locked signal. Figure 11 Based on the fundamental frequency spectrum of the mode-locked fiber laser, the signal-to-noise ratio of the laser is approximately 56.27 dB. Figure 12 The image shows the spectrum of the mode-locked signal of a mode-locked fiber laser. The center wavelength is approximately 1566.92 nm and the full width at half maximum (FWHM) is approximately 5.69 nm. Figure 13 The spectrum of the mode-locked fiber laser changes over time. It can be clearly seen that the shape and intensity of the spectrum do not change significantly within 0-80 minutes, further demonstrating the stability of the mode-locked signal. Figure 14 The relationship between the optical output power and pump power of a mode-locked fiber laser is shown. When the pump power increases from 50mW to 300mW, the output power also changes from 0.5mW to 5.5mW, with a corresponding slope efficiency of 1.92%. Figure 15The autocorrelation curve of the autocorrelation unit of the mode-locked fiber laser shows that the pulse width of the output single pulse is 1.54 × 713 fs.

[0067] The above experiments confirm that when a laser passes through a saturable absorber based on tantalum nitride quantum dots in a mode-locked fiber laser, the tantalum nitride quantum dots, as a topological half-metal, have bulk energy bands with topological properties that intersect near the Fermi surface, forming a gapless electronic state. This makes them a saturable absorber material with excellent optical properties and saturation intensity. When the laser passes through the tantalum nitride quantum dots on the saturable absorber, the laser can reach saturation quickly, enabling the output of ultrafast lasers with high repetition rates. The laser mode-locked signal is stable, and the performance is superior to other saturable absorbers based on two-dimensional materials.

[0068] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A mode-locked fiber laser, characterized in that, This includes laser pump sources, wavelength division multiplexers, erbium-doped gain fibers, polarization-independent isolators, polarization controllers, output couplers, saturable absorbers based on tantalum nitride quantum dots, and single-mode fibers; The wavelength division multiplexer includes a first input terminal and a second input terminal; The laser pump source, the first input terminal of the wavelength division multiplexer, the erbium-doped gain fiber, the polarization-independent isolator, the polarization controller, the output coupler, the saturable absorber based on tantalum nitride quantum dots, the single-mode fiber, and the second input terminal of the wavelength division multiplexer are sequentially connected to form a ring laser resonant cavity. The saturable absorber based on tantalum nitride quantum dots includes tantalum nitride quantum dots and a tapered optical fiber; The tapered optical fiber loads the tantalum nitride quantum dots; The tantalum nitride quantum dots have a particle size of 1~5nm.

2. A mode-locked fiber laser according to claim 1, characterized in that, The method for preparing the saturable absorber based on tantalum nitride quantum dots includes the following steps: dropping a tantalum nitride quantum dot solution onto a tapered optical fiber, and obtaining a saturable absorber based on tantalum nitride quantum dots after deposition.

3. A mode-locked fiber laser according to claim 2, characterized in that, The process of dropping a tantalum nitride quantum dot solution onto a tapered optical fiber and depositing it to obtain a saturable absorber based on tantalum nitride quantum dots specifically includes: Step S1: Place the tapered optical fiber on a constant temperature heating table for preheating to obtain a preheated tapered optical fiber; Step S2: Drop a tantalum nitride quantum dot solution onto the tapered region of a tapered optical fiber. Pass a 1550nm continuous wave laser through the other end of the tapered optical fiber. Under the action of the optical gradient force of the evanescent field, the tantalum nitride quantum dots surround the tapered region of the tapered optical fiber, thus obtaining a saturable absorber based on tantalum nitride quantum dots.

4. A mode-locked fiber laser according to claim 3, characterized in that, In step S1, the heating temperature of the constant temperature heating table is 60°C; In step S2, the power of the continuous wave laser is 10~30 mW.

5. A mode-locked fiber laser according to claim 2, characterized in that, The method for preparing the tantalum nitride quantum dots includes the following steps: Step S12: Mix tantalum nitride and organic solvent, sonicate, and let stand to obtain an organic solution of tantalum nitride; Step S22: Take the upper layer of the organic solution of tantalum nitride, mix it with the organic solvent, centrifuge, discard the upper layer of solution to obtain tantalum nitride quantum dots.

6. A mode-locked fiber laser according to claim 5, characterized in that, In step S12, the power of the ultrasound is 300~500W, and the duration is 4~8h; The settling time is 6 to 18 hours.

7. A mode-locked fiber laser according to claim 5, characterized in that, In step S22, the centrifugation speed is 8000~12000 rpm and the time is 1~20 min.

8. A mode-locked fiber laser according to claim 5, characterized in that, In step S12, the mass-to-volume ratio of tantalum nitride to organic solvent is 1~10g:10~100mL.

Images