CN111048983B - Saturable absorber for optical fiber laser and preparation method thereof - Google Patents
Saturable absorber for optical fiber laser and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a saturable absorber for an optical fiber laser and a preparation method thereof, wherein the saturable absorber is a transmission type tapered structure saturable absorber and comprises a fiber core (101), a cladding (102), a coating layer (103) and a heterojunction layer which are sequentially coated from inside to outside. Layered graphene and Bi obtained by stripping liquid phase2Te3The solution is attached to the tapered region of the tapered single-mode fiber in a light absorption mode. Compared with the prior art, the invention has the advantages of high damage threshold, simple structure, capability of bearing high-power bidirectional transmission fiber laser and the like.
Description
Technical Field
The invention relates to the field of fiber lasers, in particular to a saturable absorber for a fiber laser and a preparation method thereof.
Background
In recent years, fiber lasers have become increasingly popular for domestic use. Such as material processing, laser marking, laser medicine, optical communication, scientific research, and the like. Compared with a solid laser, the optical fiber laser adopts the rare earth ion doped optical fiber as a gain medium and has a very high surface area-volume ratio, so that the heat dissipation efficiency is high, and the structure is simpler and more portable.
At present, low-dimensional nanomaterials for passive mode-locked fiber lasers are studied by many groups of subjects at home and abroad. These materials include zero-dimensional nanocrystals/quantum dots (Au nanoparticles, metal halide perovskite quantum dots and nanocrystals, PbS quantum dots, etc.), one-dimensional nanowires (Cu nanowires, carbon nanotubes, Bi nanowires, etc.)2S3Nanowires, etc.) and two-dimensional layered nanomaterials (graphene, molybdenum disulfide, topological insulators, black phosphorus, MXene, etc.).
In the field of ultrafast fiber laser, the two-color two-way mode-locked fiber laser is a research hotspot and has important application value in the fields of pump detection, nonlinear frequency conversion, coherent anti-Stokes Raman scattering spectroscopy, fiber optic gyroscope and the like. Compared with the active synchronous mode locking technology realized by utilizing electric feedback, the passive synchronous mode locking fiber laser has more compact structure and short response time. Current research on two-color, unidirectional mode-locked fiber lasers has been developed. However, due to the limitation of materials, no relevant report is found on the research of the three-color two-way mode-locked fiber laser which can be applied to the fiber optic gyroscope.
Patent CN 209200364U discloses a synchronous mode locking fiber laser of trichromatic, including three annular chamber, the pumping light that three pumping source produced advances an annular chamber through a wavelength division multiplexer coupling respectively, and absorbed by doping optic fibre respectively, the laser of arousing is at this annular intracavity unidirectional transmission, and export through the beam splitter, wherein, a saturable absorber is introduced respectively to two overlap regions that three annular chamber formed, through the wide spectrum response characteristic who utilizes saturable absorber, realize passive mode locking in the time to trichromatic optic fibre laser, and further adjust the optic fibre laser of two chromatic bands wherein through optic fibre time delay line accuracy, make trichromatic optic fibre laser mode locking reach the synchronization state. The laser uses a thin film material as a saturable absorber, and because the saturable absorber with high carrying capacity does not exist, only low-power unidirectional laser transmission can be carried out, namely, one bottleneck for improving the output power of the laser is the material of the saturable absorber.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a saturable absorber for an optical fiber laser, which has the advantages of high damage threshold, simple structure and high bearing power and can support a three-color bidirectional synchronous mode-locked optical fiber laser, and a preparation method thereof.
The purpose of the invention can be realized by the following technical scheme:
a saturable absorber for a fiber laser comprises a tapered single-mode fiber and a heterojunction layer coated outside the tapered single-mode fiber, wherein the diameter of the tapered single-mode fiber is 10-20 mu m, preferably 15 mu m, and the thickness of the heterojunction layer is 5-15 mu m, preferably 5 mu m.
Further, the heterojunction layer comprises a plurality of graphene layers and Bi which are distributed in a staggered mode2Te3And the graphene layer is attached to the tapered single-mode fiber.
Furthermore, the tapered single-mode optical fiber comprises a fiber core, and a cladding and a coating which are sequentially wrapped on the outer layer of the fiber core, wherein the cladding material comprises quartz, the thickness of the cladding is 2-3 μm, preferably 2.5 μm, the coating material is resin with the refractive index lower than 1.50, the coating material comprises acrylic resin, polymethyl methacrylate or polyallyl diglycol carbonate resin, and the thickness of the coating material is 2-3 μm, preferably 2.5 μm.
Actually, the single-mode optical fiber is a commercially available product, and originally also comprises a fiber core, and a cladding and a coating layer which are sequentially wrapped on the outer layer of the fiber core, wherein the thickness of the cladding is 50-60 μm, the thickness of the coating layer is 55-65 μm, the total diameter is 230-260 μm, and 245 μm is preferred.
As the single-mode optical fiber is tapered, the thickness of the cladding layer is gradually changed from 50-60 mu m to 2-3 mu m, and the thickness of the coating layer is gradually changed from 50-60 mu m to 2-3 mu m. And the section with the smallest middle diameter is called the beam waist, and the subsequent preparation work is performed around the small section of beam waist region of the tapered single-mode fiber.
A preparation method of the saturable absorber for the fiber laser comprises the following steps:
(1) after the single mode fiber is tapered, the single mode fiber is caused to have a middle beam waist to form the tapered single mode fiber;
(2) obtaining a layered graphene solution and Bi by liquid phase exfoliation2Te3A solution;
(3) firstly fixing the tapered single-mode optical fiber, then introducing laser into the tapered single-mode optical fiber, dripping graphene solution in the waist area of the tapered single-mode optical fiber, finally removing the laser, and heating and evaporating the graphene solution to realize the coating of the graphene layer;
(4) continuing to introduce the laser into the tapered single-mode fiber, and introducing Bi2Te3Dropping the solution in the waist region of the tapered single-mode optical fiber, removing the laser, and adding Bi2Te3Evaporation of the solution to obtain Bi2Te3Coating the layer;
(5) repeating the step (3) or (4) to carry out a plurality of graphene layers or Bi2Te3And coating the layer to obtain the saturable absorber for the fiber laser.
Further, the layered graphene solution and Bi2Te3The concentration of the solution is 0.5-2mg/mL, and the heating temperature is 40-80 ℃, preferably 50 ℃; the laser wavelength is 976-1550nm, and the power is 10-50mW, preferably 20 mW; when the laser is de-energized, the transmittance of the laser in the tapered single-mode fiber is reduced by 5-10%, the diameter of the single-mode fiber is 230-260 μm, preferably 245 μm, and the single-mode fiber comprises SMF-28e single-mode fiber or HI 1060 single-mode fiber.
The liquid phase stripping method for preparing graphene needs to overcome van der waals force between graphene layers, and the method for dispersing graphene in liquid is a direct and effective way for reducing van der waals force, so that the liquid phase stripping method has the possibility of realizing industrialization. The liquid phase stripping process is generally divided into 3 steps: (1) dispersing graphite in a solvent, (2) assisting stripping by means of ultrasonic waves, microwaves, shearing force, thermal stress, electrochemistry and the like, and (3) centrifugally separating to obtain a graphene dispersion liquid. The liquid phase stripping method for preparing graphene can be divided into two categories, including direct liquid phase stripping and auxiliary agent assisted liquid phase stripping, wherein the direct liquid phase stripping is to stably disperse graphene in a solvent through the interaction between the solvent and graphene lamellae, and the auxiliary agent assisted stripping is to stably disperse graphene in the solvent through the interaction between the solvent and the lamellae.
The saturable absorber is a transmission type tapering structure saturable absorber. graphene/Bi2Te3The graphene heterojunction saturable absorber is laminated graphene and Bi obtained by a liquid phase stripping method2Te3The solution is attached to the tapered region of the tapered single-mode fiber in a light absorption mode. The tapered single-mode fiber is obtained by melting and stretching the single-mode fiber on a tapering machine. The tapered structure has larger specific surface area, and when the output power is increased, the power per unit area cannot be increased too muchAnd thus has better durability, plus graphene/Bi2Te3The graphene heterojunction can further improve the damage threshold of the optical fiber, so that the output power of the laser is improved, and the durability of the saturable absorber is improved.
A three-colour bi-directionally synchronous mode-locked fibre laser comprising a saturable absorber as described above, the laser comprising first, second and third ring cavities connected by single-mode fibre, characterised by a plurality of saturable absorbers located in the region of overlap of the first and second ring cavities and in the region of overlap of the second and third ring cavities.
Further, the first ring cavity comprises a first main pump source, a first wavelength division multiplexer, a Yb optical fiber, a second front wavelength division multiplexer, a saturable absorber, a second rear wavelength division multiplexer, a first beam splitter and a first optical fiber delay line which are connected in sequence;
the second annular cavity comprises a first secondary pumping source, a third wavelength division multiplexer, an Er optical fiber, a second front wavelength division multiplexer, a saturable absorber, a second rear wavelength division multiplexer, a second beam splitter, a fourth middle wavelength division multiplexer, a saturable absorber and a fourth front wavelength division multiplexer which are sequentially connected;
the third annular cavity comprises a second pumping source, a fourth rear wavelength division multiplexer, a Tm optical fiber, a second optical fiber delay line, a third beam splitter, a fourth middle wavelength division multiplexer, a saturated absorber and a fourth front wavelength division multiplexer which are connected in sequence;
the second front wavelength division multiplexer, the second rear wavelength division multiplexer and the saturable absorber are positioned in an overlapping region of the first annular cavity and the second annular cavity;
the fourth front wavelength division multiplexer, the fourth middle wavelength division multiplexer and the saturable absorber are positioned in an overlapping area of the second annular cavity and the third annular cavity.
Furthermore, the pump light generated by the first main pump source is coupled into the first ring cavity through the first wavelength division multiplexer, is absorbed by the Yb optical fiber, and the excited laser is transmitted in the first ring cavity in a bidirectional manner and is output simultaneously in the clockwise direction and the anticlockwise direction through the first beam splitter;
the pump light generated by the first secondary pump source is coupled into the second annular cavity through the third wavelength division multiplexer, is absorbed by the Er fiber, and the excited laser is transmitted in the second annular cavity in a two-way manner and is output simultaneously in the clockwise direction and the anticlockwise direction through the second beam splitter;
the pump light generated by the second pump source is coupled into a third annular cavity through a fourth rear wavelength division multiplexer, is absorbed by the Tm optical fiber, and the excited laser is transmitted in the third annular cavity in a two-way manner and is output simultaneously in the clockwise direction and the anticlockwise direction through a third beam splitter;
the first main pump source, the first auxiliary pump source and the second pump source generate pump light with different wavelengths, and the first optical fiber time delay line and the second optical fiber time delay line respectively control the time delay of laser generated by the first annular cavity and the time delay of laser generated by the third annular cavity, so that three-color optical fiber laser synchronous mode locking is realized.
Furthermore, the first main pump source, the first auxiliary pump source and the second pump source are all continuous laser diodes with single-mode tail fiber output.
Furthermore, the central wavelength of the first main pump source and the first auxiliary pump source is 976nm, and the central wavelength of the second pump source is 1550 nm.
Further, the maximum adjusting range of the first optical fiber delay line and the second optical fiber delay line is 300 ps.
Furthermore, the Yb fiber, the Er fiber and the Tm fiber are all single-clad doped fibers.
Further, the first beam splitter, the second beam splitter and the third beam splitter are all bidirectional output beam splitters.
Compared with the prior art, the invention has the following advantages:
(1) graphene with high thermal conductivity and high carrier migration rate and topological insulator Bi with higher modulation depth2Te3The graphene/topological insulator/graphene heterojunction is formed by compounding, compared with a single materialHas higher optical damage threshold, can effectively improve the output power and the optical conversion efficiency of laser, and further utilizes graphene/Bi2Te3The wide-spectrum response characteristic of the graphene heterojunction is that when the ultra-short pulse laser passes through the conical region, the effect of a transverse evanescent field between the laser and the heterojunction is utilized to realize the simultaneous passive mode locking of three-color optical fiber laser;
(2) meanwhile, the saturable absorber adopts a tapered structure, so that the specific surface area is larger, when the output power is increased, the power in unit area cannot be increased too much, and the heat effect is greatly reduced, so that the saturable absorber has better durability and helps to increase the output power of the fiber laser;
(3) the optical fiber lasers in different wave bands are accurately adjusted through the two optical fiber time delay lines, so that the mode locking of the three-color optical fiber lasers can reach a synchronous state; in addition, a bidirectional beam splitter is adopted to realize bidirectional output of three-color mode-locked laser;
(4) adopts graphene/Bi2Te3The graphene heterojunction is used as a saturable absorber, and the existing two-color one-way synchronous passive mode-locked fiber laser is expanded to a three-color two-way synchronous passive mode-locked fiber laser; compared with an active mode locking technology realized by utilizing electric feedback, the passive mode locking fiber laser is simpler in structure and short in response time.
Drawings
FIG. 1 is a schematic sectional view of a saturable absorber in an example;
FIG. 2 is a schematic diagram of a laser according to an embodiment;
the reference numbers in the figures indicate: a first main pump source 1001, a first auxiliary pump source 1002, a second pump source 2, a first wavelength division multiplexer 3, a second front wavelength division multiplexer 4001, a second rear wavelength division multiplexer 4002, a third wavelength division multiplexer 5, a fourth front wavelength division multiplexer 6001, a fourth middle wavelength division multiplexer 6002, a fourth rear wavelength division multiplexer 6003, a Yb fiber 7, an Er fiber 8, a Tm fiber 9, a saturated absorber 10, a fiber core 101, a cladding 102, a coating layer 103, a graphene layer 104, and a Bi2Te3 Layer 105, first fiber delay line 11, second fiber delay line 12, first beam splitter 13, second beam splitter 14, third beam splitter 15,SMF-28e single mode fiber 16, HI 1060 single mode fiber 17.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Example 1
A preparation method of a saturable absorber for an optical fiber laser comprises the following steps:
(1) after the SMF-28e single-mode fiber 16 or the HI 1060 single-mode fiber 17 with the fiber core 101 coated with the cladding 102 and the coating layer 103 is tapered, the single-mode fiber is enabled to have a middle beam waist, and the tapered single-mode fiber is obtained; the diameter of each of the SMF-28e single mode fiber 16 and the HI 1060 type single mode fiber 17 was 245 μm;
(2) obtaining a layered graphene solution and Bi by liquid phase exfoliation2Te3A solution; layered graphene solution and Bi2Te3The concentration of the solution is about 1 mg/mL;
(3) firstly fixing the tapered single-mode fiber, then introducing laser into the tapered single-mode fiber, dripping graphene solution in the waist area of the tapered single-mode fiber, finally removing the laser, and heating and evaporating the graphene solution to realize the coating of the graphene layer 104; wherein the laser wavelength is 976nm, the power is 20mW, and when the laser is removed, the transmittance of the laser in the tapered single-mode fiber is reduced by 5%;
(4) continuing to introduce the laser into the tapered single-mode fiber, and introducing Bi2Te3Dropping the solution in the waist region of the tapered single-mode optical fiber, removing the laser, and adding Bi2Te3Evaporation of the solution to obtain Bi2Te3Coating of layer 105; wherein the laser wavelength is 1550nm, and the power is 20 mW; when de-excitation is removed, the transmittance of laser in the tapered single-mode fiber is reduced by 10%;
(5) and (5) repeating the step (3), and then coating the graphene layer 104 to obtain the saturable absorber for the optical fiber laser.
The prepared saturable absorber for the fiber laser comprises a tapered single-mode fiber and a heterojunction layer coated outside the tapered single-mode fiber, wherein the diameter of the tapered single-mode fiber is about 15 mu m, and the thickness of the heterojunction layer is about 5 mu m, as shown in figure 1.
Wherein the heterojunction layer is graphene layer 104 and Bi distributed in a staggered way2Te3Layer 105 and graphene layer 104, graphene layer 104 and the tapered single mode optical fiber are laminated. The tapered single-mode fiber comprises a fiber core 101, a cladding layer 102 and a coating layer 103, wherein the cladding layer 102 and the coating layer 103 are sequentially wrapped on the outer layer of the fiber core 101, the cladding layer 102 is made of quartz and 2.5 mu m thick, and the coating layer 103 is made of acrylic resin and 2.5 mu m thick.
graphene/Bi2Te3The graphene heterojunction saturable absorber is laminated graphene and Bi obtained by a liquid phase stripping method2Te3The solution is attached to the tapered region of the tapered single-mode fiber in a light absorption mode. The tapered single-mode optical fiber is obtained by melting and stretching the single-mode optical fiber on a tapering machine. The tapered structure has larger specific surface area, when the output power is increased, the power in unit area cannot be increased too much, the heat effect is greatly reduced, and therefore the tapered structure has better durability, and in addition, the graphene/Bi2Te3The graphene heterojunction can further improve the damage threshold of the optical fiber, so that the output power of the laser is improved, and the durability of the saturable absorber is improved.
The saturated absorber is placed in a three-color bidirectional synchronous mode-locked fiber laser, as shown in fig. 2, the laser comprises a first main pump source 1001, a first auxiliary pump source 1002, a second pump source 2, a first wavelength division multiplexer 3, a second front wavelength division multiplexer 4001, a second rear wavelength division multiplexer 4002, a third wavelength division multiplexer 5, a fourth front wavelength division multiplexer 6001, a fourth middle wavelength division multiplexer 6002, a fourth rear wavelength division multiplexer 6003, a Yb optical fiber 7, an Er optical fiber 8, a Tm optical fiber 9, a first optical fiber delay line 11, a second optical fiber delay line 12, a first beam splitter 13, a second beam splitter 14, a third beam splitter 15, and two saturated absorbers 10;
the first ring cavity formed by connecting single-mode fibers comprises a first main pump source 1001, a first wavelength division multiplexer 3, a Yb fiber 7, a second front wavelength division multiplexer 4001, a saturated absorber 10, a second rear wavelength division multiplexer 4002, a first beam splitter 13 and a first fiber delay line 11 which are connected in sequence;
the second annular cavity formed by connecting the single-mode fibers comprises a first secondary pumping source 1002, a third wavelength division multiplexer 5, an Er fiber 8, a second front wavelength division multiplexer 4001, a saturable absorber 10, a second rear wavelength division multiplexer 4002, a second beam splitter 14, a fourth middle wavelength division multiplexer 6002, a saturable absorber 10 and a fourth front wavelength division multiplexer 6001 which are connected in sequence;
the third ring cavity formed by connecting single-mode fibers comprises a second pumping source 2, a fourth rear wavelength division multiplexer 6003, a Tm fiber 9, a second fiber delay line 12, a third beam splitter 15, a fourth middle wavelength division multiplexer 6002, a saturable absorber 10 and a fourth front wavelength division multiplexer 6001 which are connected in sequence;
the second front wavelength division multiplexer 4001, the second rear wavelength division multiplexer 4002 and the saturable absorber 10 are located in an overlapping region of the first ring cavity and the second ring cavity; the fourth front wavelength division multiplexer 6001, the fourth middle wavelength division multiplexer 6002 and the saturable absorber 10 are located at an overlapping region of the second and third ring cavities.
Pump light generated by the first main pump source 1001 is coupled into the first ring cavity through the first wavelength division multiplexer 3, is absorbed by the Yb optical fiber, and excited laser is transmitted in the first ring cavity in a bidirectional manner and is output simultaneously in both clockwise and counterclockwise directions through the first beam splitter 13;
the pump light generated by the first secondary pump source 1002 is coupled into the second annular cavity through the third wavelength division multiplexer 5, absorbed by the Er fiber, and the excited laser is transmitted in the second annular cavity in two directions and is output simultaneously in both clockwise and counterclockwise directions through the second beam splitter 14;
pump light generated by the second pump source 2 is coupled into the third ring cavity through the fourth rear wavelength division multiplexer 6003, is absorbed by the Tm fiber, and the excited laser is transmitted in the third ring cavity in two directions and is output simultaneously in both clockwise and counterclockwise directions through the third beam splitter 15;
the first main pump source 1001, the first auxiliary pump source 1002 and the second pump source 2 generate pump light with different wavelengths, and the first optical fiber delay line 11 and the second optical fiber delay line 12 respectively control the time delay of laser generated by the first ring cavity and the time delay of laser generated by the third ring cavity, so that three-color optical fiber laser synchronous mode locking is realized.
The first main pump source 1001, the first auxiliary pump source 1002 and the second pump source 2 are all continuous laser diodes with single-mode pigtail output. The central wavelengths of the first main pump source 1001, the first auxiliary pump source 1002 and the second pump source 2 are 976nm and 1550nm respectively, the two laser diodes are packaged on the butterfly-shaped driving power supply, the heat dissipation mode is air cooling, and the maximum pump light power is 1W.
The maximum tuning range of the first fiber delay line 11 and the second fiber delay line 12 is 300 ps. The Yb optical fiber 7, the Er optical fiber 8 and the Tm optical fiber 9 are single-cladding doped optical fibers, and the lengths of the single-cladding doped optical fibers are about 1 m. The first beam splitter 13, the second beam splitter 14 and the third beam splitter 15 are all bidirectional output beam splitters, and are used for bidirectional output of laser in different wave bands, and the output rates are all 20%.
When the laser pumping device works, the first main pumping source 1001 and the first auxiliary pumping source 1002 generate pump light of 976nm, the pump light is coupled into a first annular cavity through the first wavelength division multiplexer 3, laser is transmitted in the first annular cavity in a two-way mode, and finally the pump light is output out of the cavity through the first beam splitter 13; the first main pump source 1001 and the first auxiliary pump source 1002 generate pump light of 976nm, the pump light is coupled into the second annular cavity through the third wavelength division multiplexer 5, laser is transmitted in the second annular cavity in a two-way mode, and finally the pump light is output out of the cavity through the second beam splitter 14; the second pump source 2 generates pump light of 1550nm, the pump light is coupled into the third annular cavity through the fourth rear wavelength division multiplexer 6003, the laser light is transmitted in the third annular cavity in a two-way mode, and finally the pump light is output out of the cavity through the third beam splitter 15.
Wherein, the working wavelength of the first wavelength division multiplexer 3 is 976/1060nm, the working wavelengths of the second front wavelength division multiplexer 4001 and the second rear wavelength division multiplexer 4002 are 1064/1550nm, the working wavelength of the third wavelength division multiplexer 5 is 976/1550nm, and the working wavelengths of the fourth front wavelength division multiplexer 6001, the fourth middle wavelength division multiplexer 6002 and the fourth rear wavelength division multiplexer 6003 are 1550/1900 nm; the working wavelength of the first beam splitter 13 is 1 μm, the working wavelength of the second beam splitter 14 is 1.55 μm, and the working wavelength of the third beam splitter 15 is 1.9 μm; the operating wavelength of the first optical fiber delay line 11 is 1 μm, and the operating wavelength of the second optical fiber delay line 12 is 1.9 μm.
Meanwhile, the first optical fiber delay line 11 can precisely adjust the time delay of the optical fiber laser with the wavelength of 1 μm, and the second optical fiber delay line 12 can precisely adjust the time delay of the optical fiber laser with the wavelength of 1.9 μm. The maximum adjustment range of the first optical fiber delay line 11 and the second optical fiber delay line 12 is 300 picoseconds.
The time delay of the 1-micron-waveband ultrashort pulse laser in the first annular cavity is adjusted through the first optical fiber time delay line 11, the time delay of the 1.9-micron-waveband ultrashort pulse laser in the third annular cavity is adjusted through the second optical fiber time delay line 12, so that the pulse repetition frequencies of the three-color lasers of 1 micron, 1.55 microns and 1.9 microns are consistent, and synchronous mode locking of the three-waveband optical fiber lasers of 1 micron, 1.55 microns and 1.9 microns is achieved.
The three-color synchronous mode-locking optical fiber laser cavity is of an all-fiber structure, and has no space light part, so that the structure is more compact. The Polarization Controller (PC) is not added in the cavity, and the self-starting process of the laser can be realized by properly bending the single-mode optical fiber in the cavity or applying certain stress to the optical fiber.
Example 2
The difference from the embodiment 1In the step (1), the diameter of the single-mode optical fiber is 230 μm; in the step (2), the concentration of the layered graphene solution is 0.5mg/mL, and Bi is2Te3The concentration of the solution is 2 mg/mL; the laser power in the step (3) is 10 mW; the laser power in the step (4) is 50 mW.
Referring to fig. 2, the diameter of the tapered single-mode fiber is 10 μm, and the thickness of the heterojunction layer is 5 μm. The cladding 102 has a thickness of 2 μm, and the coating layer 103 is made of polyallyldiglycol carbonate resin and has a thickness of 3 μm.
Example 3
The difference from example 1 is that in the preparation method step (1), the diameter of the single-mode optical fiber is 260 μm; in the step (2), the concentration of the layered graphene solution is 2mg/mL, and Bi is2Te3The concentration of the solution is 0.5 mg/mL; the laser power in the step (3) is 50 mW; the laser power in the step (4) is 10 mW.
The prepared saturable absorber for the fiber laser has the diameter of 20 mu m and the thickness of the heterojunction layer of 15 mu m, and is shown in figure 2. The thickness of the cladding 102 was 3 μm, and the material of the coating layer 103 was polyallyldiglycol carbonate resin, which was 2 μm thick.
The above disclosure is only three specific embodiments of the present application, but the present application is not limited thereto, and any variations that can be made by those skilled in the art are intended to fall within the scope of the present application.
Claims (8)
1. A three-color bidirectional synchronous mode-locked fiber laser comprises a first ring cavity, a second ring cavity and a third ring cavity which are connected by single-mode fibers, and is characterized by further comprising a plurality of saturable absorbers (10) for the fiber laser, wherein the saturable absorbers (10) are positioned in an overlapping region of the first ring cavity and the second ring cavity and an overlapping region of the second ring cavity and the third ring cavity;
the saturable absorber (10) comprises a tapered single-mode fiber and a heterojunction layer coated outside the tapered single-mode fiber, the diameter of the tapered single-mode fiber is 10-20 mu m, the thickness of the heterojunction layer is 5-15 mu m, and the heterojunction layer is heterogeneousThe junction layer comprises a plurality of graphene layers (104) which are distributed in a staggered way and Bi2Te3And a layer (105), wherein the graphene layer (104) is attached to the tapered single mode fiber, and the graphene layer (104) is at least two layers.
2. The three-color bidirectional synchronous mode-locked fiber laser according to claim 1, wherein the tapered single-mode fiber comprises a core (101), and a cladding (102) and a coating (103) which are sequentially wrapped on the outer layer of the core (101), the cladding (102) comprises quartz and has a thickness of 2-3 μm, and the coating (103) comprises a resin with a refractive index lower than 1.50, such as acrylic resin, polymethyl methacrylate or polyallyl diglycol carbonate resin, and has a thickness of 2-3 μm.
3. The three-color bi-directional synchronous mode-locked fiber laser according to claim 1, wherein the preparation method of the saturable absorber (10) comprises the following steps:
(1) after the single mode fiber is tapered, the single mode fiber is caused to have a middle beam waist to form the tapered single mode fiber;
(2) obtaining a layered graphene solution and Bi by liquid phase exfoliation2Te3A solution;
(3) firstly fixing the tapered single-mode fiber, then introducing laser into the tapered single-mode fiber, dripping graphene solution in the waist area of the tapered single-mode fiber, finally removing the laser, and heating and evaporating the graphene solution to realize the coating of the graphene layer (104);
(4) continuing to introduce the laser into the tapered single-mode fiber, and introducing Bi2Te3Dropping the solution in the waist region of the tapered single-mode optical fiber, removing the laser, and adding Bi2Te3Evaporation of the solution to obtain Bi2Te3Coating of the layer (105);
(5) repeating the step (3) or (4) to carry out the multilayer graphene layer (104) or Bi2Te3Coating of the layer (105) yields a saturable absorber (10).
4. The tristimulus pair of claim 3The mode-locked fiber laser is characterized in that the layered graphene solution and Bi are used2Te3The concentration of the solution is 0.5-2mg/mL, and the heating temperature is 40-80 ℃; the laser wavelength is 976-1550nm, and the power is 10-50 mW; when the laser is deenergized, the transmittance of the laser in the tapered single-mode fiber is reduced by 5-10%, the diameter of the single-mode fiber is 230-260 mu m, and the single-mode fiber comprises SMF-28e single-mode fiber or HI 1060 single-mode fiber.
5. The three-color bidirectional synchronous mode-locked fiber laser according to claim 1, wherein the first ring cavity comprises a first main pump source (1001), a first wavelength division multiplexer (3), a Yb fiber (7), a second front wavelength division multiplexer (4001), a first saturated absorber (10), a second rear wavelength division multiplexer (4002), a first beam splitter (13) and a first fiber delay line (11) which are connected in sequence;
the second annular cavity comprises a first secondary pumping source (1002), a third wavelength division multiplexer (5), an Er fiber (8), a second front wavelength division multiplexer (4001), a first saturable absorber (10), a second rear wavelength division multiplexer (4002), a second beam splitter (14), a fourth middle wavelength division multiplexer (6002), a second saturable absorber (10) and a fourth front wavelength division multiplexer (6001) which are connected in sequence;
the third annular cavity comprises a second pumping source (2), a fourth rear wavelength division multiplexer (6003), a Tm optical fiber (9), a second optical fiber delay line (12), a third beam splitter (15), a fourth intermediate wavelength division multiplexer (6002), a second saturated absorber (10) and a fourth front wavelength division multiplexer (6001) which are connected in sequence;
the second front wavelength division multiplexer (4001), the second rear wavelength division multiplexer (4002) and the first saturable absorber (10) are positioned in the overlapping area of the first ring cavity and the second ring cavity;
the fourth front wavelength division multiplexer (6001), the fourth middle wavelength division multiplexer (6002) and the second saturable absorber (10) are located in an overlapping region of the second annular cavity and the third annular cavity.
6. The three-color bi-directional synchronous mode-locked fiber laser according to claim 5, wherein the first main pump source (1001), the first sub pump source (1002) and the second pump source (2) are all continuous laser diodes with single-mode pigtail output; the central wavelength of the first main pump source (1001) and the first auxiliary pump source (1002) is 976nm, and the central wavelength of the second pump source (2) is 1550 nm.
7. The three-color bi-directional synchronous mode-locked fiber laser according to claim 5, wherein the maximum adjustment range of the first fiber delay line (11) and the second fiber delay line (12) is 300 ps; the Yb optical fiber (7), the Er optical fiber (8) and the Tm optical fiber (9) are all single-cladding doped optical fibers.
8. The three-color bidirectional synchronous mode-locked fiber laser according to claim 5, wherein the first beam splitter (13), the second beam splitter (14) and the third beam splitter (15) are all bidirectional output beam splitters.
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