Tapered fiber based on reSse quantum dots as saturable absorber and preparation method and application thereof

Abstract

The present application relates to the technical field of fiber lasers, and particularly relates to a conical fiber saturable absorber based on selenium-sulfurized rhenium quantum dots and a preparation method and application thereof. The present application discloses a conical fiber saturable absorber based on selenium-sulfurized rhenium quantum dots, which comprises selenium-sulfurized rhenium quantum dots and a conical fiber, wherein the selenium-sulfurized rhenium quantum dots are deposited on a conical region of the conical fiber; in the present application, the selenium-sulfurized rhenium belongs to a triclinic system, has unique asymmetric surface characteristics and excellent nonlinear optical response, and the quantum dot form of the selenium-sulfurized rhenium has a carrier limiting effect, so that the state density is more concentrated; the conical fiber saturable absorber is made of the selenium-sulfurized rhenium quantum dots, the mode-locked pulse sequence generated by the fiber laser has higher stability, and stable ultrashort pulse output can be realized at a low starting threshold and high power.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and in particular to a tapered fiber saturable absorber based on ReSSe quantum dots, its preparation method, and its application. Background Technology

[0002] Compared to traditional long-pulse and continuous-wave lasers, ultrafast lasers, with their ultra-narrow pulse width and excellent beam quality, possess superior performance advantages and significant market potential, making them widely favored in numerous application fields such as national defense, industrial manufacturing, medical devices, and fiber optic communications. Especially in recent years, the rapid development of China's semiconductor industry has placed higher demands on the pulse width, operating time, and stable output of lasers. Therefore, mode-locked ultrashort-pulse fiber lasers, with their simple structure and stable performance, have received increasing attention.

[0003] Mode-locking technology enables the conversion of continuous wave output to ultrashort pulses, a key technology for generating ultrafast lasers. Based on modulation principles, mode-locking technology can be broadly classified into active mode-locking and passive mode-locking. Active mode-locking involves providing a modulation carrier wave to the laser's internal components via a modulator, thereby periodically altering the gain and loss of each longitudinal mode and achieving phase locking. Currently, acousto-optic modulators and electro-optic modulators are commonly used. Passive mode-locking, on the other hand, utilizes the saturable absorption properties of materials or the nonlinear effects of the optical path to lock the longitudinal modes. When longitudinal modes of different amplitudes pass through a saturable absorber, the smaller amplitude mode is suppressed, further widening the amplitude ratio of the various longitudinal modes. After multiple oscillations, side-mode suppression and phase locking between longitudinal modes are achieved, ultimately resulting in a periodic pulse sequence and mode-locked output. Compared to active mode-locking modulators, passive mode-locking modulators offer advantages such as smaller size and higher responsivity, making them a research hotspot in both scientific and commercial fields in recent years.

[0004] In existing passively mode-locked fiber lasers, the saturable absorbers mostly employ two-dimensional nanosheet materials such as graphene, black phosphorus, and transition metal sulfides. While these two-dimensional nanosheet materials have been successfully modulated into ultrashort pulses in fiber lasers due to their unique photoelectric properties and nonlinear optical response, their poor carrier confinement and low surface area-to-volume ratio have led to problems in current passive mode-locking technologies for fiber lasers, including excessively high start-up thresholds, poor heat accumulation resistance, and excessively low damage thresholds. Summary of the Invention

[0005] In view of this, the present invention provides a tapered fiber saturable absorber based on ReSSe quantum dots, its preparation method and application. The tapered fiber saturable absorber based on ReSSe quantum dots is used in a passively mode-locked fiber laser, which can achieve stable ultrashort pulse output at low start-up threshold and high power.

[0006] The first aspect of the present invention provides a tapered optical fiber saturable absorber based on rhenium selenide sulfide quantum dots, comprising: rhenium selenide sulfide (ReSSe) quantum dots and tapered optical fiber;

[0007] The rhenium selenide quantum dots are located in the tapered region of the tapered optical fiber.

[0008] A second aspect of this invention provides a method for preparing a tapered optical fiber saturable absorber based on ReSSe quantum dots, comprising the following steps:

[0009] The rhenium selenide quantum dots are dropped onto the tapered region of the tapered optical fiber, photodeposited, and then dried to obtain a tapered optical fiber SA based on ReSSe quantum dots.

[0010] Preferably, the method for preparing the rhenium selenide quantum dots includes the following steps:

[0011] Step 1: Mix powdered rhenium selenide sulfide with ethanol, and then dissolve it by ultrasonication to obtain a suspension;

[0012] Step 2: Centrifuge the suspension to obtain the rhenium selenide quantum dots.

[0013] In the prior art, rhenium selenide quantum dots can be prepared by methods other than the liquid phase exfoliation method used in this invention, such as hydrothermal method, calcination method, microwave method and electrochemical method. However, the liquid phase exfoliation method used in this invention is simple to operate, has a large output and low energy consumption compared to other methods, and is suitable for large-scale preparation.

[0014] Preferably, the frequency of the ultrasound is 20-40 kHz and the power is 300-400 W.

[0015] More preferably, the ultrasonic frequency of the present invention is 40 kHz and the power is 400 W. The liquid-phase exfoliation method of the present invention requires suitable reaction conditions to effectively prepare rhenium selenide quantum dots. If the ultrasonic frequency or power is insufficient, not only will the dispersion effect of rhenium selenide be poor, and the rhenium selenide nanomaterials cannot be broken into quantum dots with a diameter of less than 10 nm by vibration; it may even fail to break the van der Waals force connections between the layers of rhenium selenide, resulting in the rhenium selenide nanomaterials stacking in a nanobulk morphology.

[0016] Specifically, the ultrasonic temperature of the present invention is maintained at around 30°C. This can prevent problems such as material oxidation caused by excessively high temperature, and also prevent the anhydrous ethanol solvent from evaporating due to excessively high temperature.

[0017] Preferably, the centrifugation rate is 10,000 to 12,000 r / min, and the centrifugation time is 10 to 15 min.

[0018] Preferably, the tapered optical fiber is prepared by a forward fused taper system;

[0019] The tapered optical fiber has a tapered region with a length of 9 mm and a minimum diameter of 9 μm.

[0020] Preferably, before obtaining the ReSSe quantum dot-based tapered optical fiber saturable absorber after drying, the process further includes: dripping a UV adhesive with a low refractive index onto the tapered region and then curing it with a UV light source.

[0021] The third aspect of this invention provides an application of a tapered fiber saturable absorber based on ReSSe quantum dots in the fabrication of a passively mode-locked laser.

[0022] The fourth aspect of the present invention provides a mode-locked fiber laser, comprising: the above-described tapered fiber saturable absorber based on ReSSe quantum dots or the tapered fiber saturable absorber based on ReSSe quantum dots prepared by the above-described preparation method, a laser pump source, a wavelength division multiplexer, a gain fiber, a polarization-independent isolator, a single-mode fiber, an output coupler, and a polarization controller.

[0023] The laser pump source, the first input terminal of the wavelength division multiplexer, the polarization-independent isolator, the ReSSe quantum dot-based tapered fiber saturable absorber, the output coupler, the polarization controller, and the gain fiber are sequentially connected through the single-mode transmission fiber.

[0024] The gain fiber is connected to the second input terminal of the wavelength division multiplexer through the single-mode transmission fiber to form a ring resonant cavity.

[0025] Preferably, the gain fiber is an erbium-doped fiber with a length of 10 cm, the wavelength of the laser pump source is 980 nm, and the operating wavelength of the wavelength division multiplexer is 980 / 1550 nm.

[0026] As can be seen from the above technical solutions, the present invention has the following advantages:

[0027] This invention provides a tapered fiber saturable absorber based on ReSSe quantum dots, comprising: rhenium selenide sulfide quantum dots and a tapered fiber; the rhenium selenide sulfide quantum dots are located in the tapered region of the tapered fiber. In this scheme, ReSSe belongs to the triclinic system and has high anisotropy in optical and electrical properties. By using ReSSe quantum dots to fabricate the tapered fiber saturable absorber, the resulting tapered fiber saturable absorber exhibits higher stability in mode-locked fiber lasers, enabling stable ultrashort pulse output at low start-up thresholds and high power. Attached Figure Description

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

[0029] Figure 1 This is a schematic diagram of the structure of a mode-locked fiber laser provided by the present invention;

[0030] Figure 2 This is a transmission electron microscope image of rhenium selenide quantum dots provided in Embodiment 1 of the present invention;

[0031] Figure 3 The mode-locked pulse sequence of the mode-locked fiber laser provided in Example 3;

[0032] Figure 4 The broadband spectrum of the mode-locked fiber laser provided in Example 3;

[0033] Figure 5 The fundamental frequency signal-to-noise ratio of the mode-locked fiber laser provided in Example 3;

[0034] Figure 6 This is a test diagram of the saturated absorption performance of the saturable absorber provided in Example 3;

[0035] Figure 7 This is a graph showing the relationship between laser output power and pump power in Example 3.

[0036] Figure 1 In the diagram, 1 is the laser pump source, 2 is the wavelength division multiplexer, 3 is the gain fiber, 4 is the polarization-independent isolator, 5 is the saturable absorber, 6 is the output coupler, and 7 is the polarization controller. Detailed Implementation

[0037] Using optical materials with saturable absorption properties (i.e., saturable absorbers, hereinafter referred to as SA) as passive mode-locked modulation devices in laser cavities is an effective method for obtaining pulsed lasers. Currently, mode-locked fiber lasers, as stable and efficient short-pulse sources, have low timing jitter and high repetition rates, and are widely used in fields such as communications, precision materials processing, medical imaging, and biomedicine. However, the existing technology uses two-dimensional material black phosphorus as a saturable absorber material, and the application of this saturable absorber material in mode-locked fiber lasers still suffers from poor stability.

[0038] In view of this, the present invention provides a tapered optical fiber SA based on ReSSe quantum dots, its preparation method and application, to solve the problem of poor stability of saturable absorber materials in mode-locked fiber lasers in the prior art.

[0039] like Figure 1 As shown, this invention uses ReSSe quantum dots to fabricate tapered optical fibers (SA), and uses the fabricated tapered optical fibers (SA) in a mode-locked fiber laser, thereby giving the mode-locked fiber laser higher stability.

[0040] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "fixing," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; or they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0041] In the description of this application, it should be noted that the tapered optical fiber in this application is prepared by a forward fused fiber tapering system. The thinnest part in the middle of the tapered optical fiber is called the waist (tapered region), and the part between the waist and the un-tapered optical fiber is called the transition region.

[0042] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] Example 1

[0044] This embodiment provides a rhenium selenide sulfide quantum dot. The ReSSe quantum dots are prepared using a high-performance liquid phase exfoliation (LPE) method. The preparation steps are as follows:

[0045] Step 1: Place 0.8g of powdered rhenium selenide in 80ml of ethanol. Place the ethanol solution containing rhenium selenide in an ultrasonic machine for ultrasonic exfoliation and dissolution for 9 hours. The ultrasonic device frequency is 40kHz, the power is 400W, and the temperature is maintained at 30℃ to avoid powder degradation, so as to obtain a suspension.

[0046] Step 2: Centrifuge the above suspension at a speed of 12000 r / min for 15 min to obtain rhenium selenide quantum dots.

[0047] This invention employs a liquid-phase exfoliation method to prepare rhenium selenide quantum dots. The preparation conditions are simple, conducted at room temperature to reduce energy consumption and byproduct formation, and the solvent used is green and pollution-free. This invention overcomes the shortcomings of existing rhenium disulfide quantum dot and preparation methods. Existing methods require ultrasonic vibration of raw materials in an ice bath, resulting in high energy consumption. Furthermore, they require N-methylpyrrolidone, anhydrous ethanol, and ultrapure water for initial dispersion, washing, and redispersion, making it difficult to avoid intermediate product formation. In terms of preparation results, existing rhenium disulfide quantum dots exhibit inconsistent morphology and size, extremely uneven spatial distribution, and some quantum dots have aggregated. Additionally, the particle diameter is mainly between 20 and 40 nm, indicating excessively large particle size.

[0048] Furthermore, the rhenium selenide-sulfide quantum dot dispersion of this embodiment was characterized by transmission electron microscopy, such as... Figure 2 As shown, from Figure 2 It can be observed that the rhenium selenide quantum dots have smooth morphology, similar size and uniform distribution, and have a higher volume surface area ratio.

[0049] Example 2

[0050] This embodiment provides a tapered optical fiber saturable absorber based on rhenium selenide quantum dots, the preparation method of which includes the following steps:

[0051] (1) Taking advantage of the reshaping properties of glass optical fiber in the high-temperature molten state, a tapered optical fiber is prepared using a forward molten fiber tapering machine. The system can change parameters to control the length of the tapered optical fiber and the waist diameter of the tapered region. The length and minimum diameter of the prepared tapered region are controlled at about 9 mm and 9 μm, respectively.

[0052] (2) The prepared tapered optical fiber was fixed on a glass slide. The ReSSe quantum dot dispersion prepared in Example 1 was dropped into the tapered region of the tapered optical fiber. A continuous wave laser was passed through one side of the tapered optical fiber. The ReSSe quantum dots diffused and surrounded the tapered region of the tapered optical fiber under the action of the optical gradient force provided by the evanescent wave. After the solvent of the ReSSe quantum dot dispersion dried, it was observed under a microscope that the ReSSe quantum dots were directly deposited in the tapered region. After repeating this step several times, a saturable absorber with ReSSe quantum dots deposited in the tapered optical fiber was prepared.

[0053] (3) To ensure that SA does not easily deteriorate, a UV adhesive with a low refractive index is dropped onto the conical area and then cured with a UV light source.

[0054] The rhenium selenide sulfide prepared in this invention belongs to the triclinic system and has unique asymmetric surface characteristics and excellent nonlinear optical response. The quantum dot morphology of rhenium selenide sulfide restricts the charge carriers, resulting in a more concentrated density of states. Using rhenium selenide sulfide quantum dots to fabricate tapered fiber saturable absorbers for use in fiber lasers produces mode-locked pulse sequences with higher stability.

[0055] Example 3

[0056] This embodiment provides an application example of a tapered fiber saturable absorber based on rhenium selenide quantum dots, and provides a mode-locked fiber laser, the structure of which is as follows: Figure 1 As shown, Pump Source is the laser pump source, WDM is the wavelength division multiplexer, EDF is the erbium-doped fiber, PI-ISO is the polarization-independent isolator, OC is the output coupler, PC is the polarization controller, and SA is the saturable absorber.

[0057] Please see Figure 1 A mode-locked fiber laser includes: a tapered fiber SA 5 based on ReSSe quantum dots prepared in Example 2, a laser pump source 1, a wavelength division multiplexer 2, a gain fiber 3, a polarization-independent isolator 4, an output coupler 6, and a polarization controller 7.

[0058] The wavelength division multiplexer includes a first input terminal and a second input terminal. The laser pump source 1, the first input terminal of the wavelength division multiplexer 2, the polarization-independent isolator 4, the tapered fiber SA based on ReSSe quantum dots 5, the output coupler 6, the polarization controller 7, and the gain fiber 3 are connected in sequence. The gain fiber 3 is connected to the second input terminal of the wavelength division multiplexer 2 to form a ring resonant cavity.

[0059] Specifically, the connection can be made via single-mode optical fiber.

[0060] In this implementation, a mode-locked fiber laser is composed of tapered fiber SA based on ReSSe quantum dots, which has the advantages of high stability, high damage threshold and low loss.

[0061] Furthermore, the fiber pulsed laser in this embodiment adopts a ring cavity structure.

[0062] Furthermore, erbium-doped fiber is selected for gain fiber 3.

[0063] Furthermore, the wavelength of the laser pump source is 975–980 nm, and the center wavelength of the wavelength division multiplexer is 980 nm / 1550 nm (the operating wavelength of the wavelength division multiplexer is 980 nm and / or 1550 nm).

[0064] Furthermore, the output coupler has a beam splitting ratio of 90:10, with 90% of the output connected to a ReSSe quantum dot-based tapered fiber SA, and the other 10% of the output used to connect to relevant instruments to measure the laser output characteristics of the fiber laser.

[0065] This embodiment also provides performance testing of the mode-locked fiber laser, and the results are as follows: Figures 3 to 7 As shown.

[0066] Figure 3 This is a pulse sequence diagram of the mode-locked fiber laser based on a tapered fiber SA using ReSSe QD (rhenium selenide quantum dots) in this embodiment. Figure 2 It can be seen that the intensity of the visible pulse sequence is stable and the pulse interval is 44.2 ns, indicating that the mode-locked pulse in the annular cavity operates in a stable state.

[0067] Figure 4 For the broadband radio frequency spectrum of mode-locked fiber lasers, from Figure 4 It can be seen that the amplitude fluctuation is small when recorded in the frequency range of 100MHz to 600MHz, and the radio frequency interval and the pulse sequence interval time are mutually corroborated. Figure 5 For the fundamental frequency spectrum of a mode-locked fiber laser, from Figure 5 It can be seen that the signal-to-noise ratio at the fundamental frequency of 22.76MHz is as high as 58dB, which together indicate that the mode-locked pulse sequence output is stable.

[0068] Figure 6 The graph shows the saturable absorption performance of the tapered fiber SA based on ReSSe quantum dots. Figure 6 It can be seen that the unsaturated loss ans of the tapered fiber SA based on ReSSe quantum dots is only 26.3%, indicating that the tapered fiber SA based on ReSSe quantum dots has low loss.

[0069] Figure 7 The graph shows the relationship between laser output power and pump power. Figure 7It can be seen that when the pump power is increased from 40mW to 360mW, the mode-locked laser can always generate a stable pulse output, indicating that the mode-locked fiber laser prepared in this embodiment has a low start-up threshold and a high damage threshold.

[0070] In summary, the mode-locked fiber laser fabricated using a tapered fiber saturable absorber based on rhenium selenide quantum dots in this embodiment has the following advantages: The ReSSe used in this embodiment belongs to the triclinic system, with unique asymmetric surface characteristics and excellent nonlinear optical response. The fabricated ReSSe quantum dots are two-dimensional quantum dots (QDs), and exhibit unique electronic and optical properties due to their quantum confinement and edge effects. At the same time, the high surface area ratio of quantum dot materials greatly alleviates the thermal accumulation effect in the laser, making it easier for the tapered fiber saturable absorber fabricated with ReSSe quantum dots to obtain a stable and strong mode-locked signal in a saturable absorber fiber laser. This also improves the stability and damage threshold of the mode-locked fiber laser and reduces losses.

[0071] The foregoing has provided a detailed description of a tapered optical fiber saturable absorber based on ReSSe quantum dots, its preparation method, and its applications. For those skilled in the art, based on the ideas of the embodiments of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A mode-locked fiber laser, characterized by, The application relates to a selenium-sulfur-rhenium quantum dot-based tapered fiber saturable absorber, a laser pumping source, a wavelength division multiplexer, a gain fiber, a polarization-independent isolator, an output coupler and a polarization controller. The laser pumping source, the first input end of the wavelength division multiplexer, the polarization-independent isolator, the selenium-sulfur-rhenium quantum dot-based tapered fiber saturable absorber, the output coupler, the polarization controller and the gain fiber are sequentially connected. The gain fiber is connected with the second input end of the wavelength division multiplexer to form a ring resonant cavity. The selenium-sulfur-rhenium quantum dot-based tapered fiber saturable absorber comprises selenium-sulfur-rhenium quantum dots and a tapered fiber; the selenium-sulfur-rhenium quantum dots are located in a tapered region of the tapered fiber.

2. The mode-locked fiber laser of claim 1, wherein, The selenium-sulfur-rhenium quantum dot-based tapered fiber saturable absorber is prepared by the following steps: The selenium-sulfur-rhenium quantum dots are added dropwise in the tapered region of the tapered fiber, and then dried after photodeposition to obtain the selenium-sulfur-rhenium quantum dot-based tapered fiber saturable absorber.

3. The mode-locked fiber laser of claim 1, wherein, The preparation method of the selenium-sulfur-rhenium quantum dots comprises the following steps: Step 1: mixing powdered selenium-sulfur-rhenium and ethanol, and then performing ultrasonic dissolution to obtain a suspension; Step 2: performing centrifugal treatment on the suspension to obtain the selenium-sulfur-rhenium quantum dots.

4. The mode-locked fiber laser of claim 3, wherein, The frequency of the ultrasonic is 20-40 KHz, and the power is 300-400 W.

5. The mode-locked fiber laser of claim 3, wherein, The rate of the centrifugal treatment is 10000-12000 r / min, and the time length of the centrifugal treatment is 10-15 min.

6. The mode-locked fiber laser of claim 2, wherein, The tapered fiber is prepared by a fiber tapering system. The length of the tapered region of the tapered fiber is 9 mm, and the minimum diameter of the tapered region is 9 mu m.

7. The mode-locked fiber laser of claim 2, wherein, After drying, the selenium-sulfur-rhenium quantum dot-based tapered fiber saturable absorber is obtained, and then a UV adhesive with a low refractive index is added dropwise in the tapered region, and then cured by a UV light source.

8. The mode-locked fiber laser of claim 1, wherein, The gain fiber is an erbium-doped fiber with a length of 10 cm, the wavelength of the laser pumping source is 975-980 nm, and the working wavelength of the wavelength division multiplexer is 980 / 1550 nm.

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