Saturable absorber containing graphene-Ga composite layer and preparation method thereof

Abstract

The invention discloses a saturable absorber containing a graphene-Ga composite layer. The saturable absorber comprises a GaAs substrate, an AlGaAs / GaAs Bragg reflection layer, a GaAs / InGaAs buffer layer, a quantum dot absorption layer, an InGaAs cover layer, a GaAs cover layer and a graphene-Ga grid layer which are stacked in sequence, the graphene-Ga grid layer is of a lattice structure, and the aperture of a graphene round hole is 10-100 nm, more preferably 16-90 nm; the graphene-Ga grid layer is obtained by adopting laser annealing to cause mutual mixing of graphene and Ga elements. The saturable absorber can enhance the interaction between light and substances, and the preparation method improves the modulation depth of the QD-SESAM and improves the modulation range and stability by using the light absorption capability of the graphene nanometer grid. The laser prepared by using the saturable absorber has better application in the fields of biological science, processing and manufacturing, optical communication, nondestructive testing, scientific research and the like.

Description

Technical Field

[0001] The present application relates to a graphene-Ga composite saturable absorber and a preparation method thereof, and belongs to the field of optical materials. Background Art

[0002] Ultrafast lasers are lasers with pulse widths in the picosecond or femtosecond range. With the rapid development of laser technology, ultrafast lasers have found widespread applications in materials processing, medical treatment, lidar, and communications. In the field of materials processing, laser processing of metal materials using the thermal effect of lasers, such as cutting, drilling, and heat treatment, has been widely used in industry. Saturable absorbers are important components in ultrafast lasers and play a key role in controlling the stability and performance of ultrafast lasers. Common optical saturable absorbers include organic dyes, color filters, ion-doped crystals, semiconductor saturable absorber mirrors (SESAMs), and recently emerging two-dimensional materials such as carbon nanotubes, graphene, and transition metal sulfides.

[0003] A semiconductor saturable absorber mirror (SESAM) is a saturable absorber mirror (SAM) manufactured using semiconductor materials and processes. Currently, SESAMs are the most widely used mode-locked devices and play a key role in ultrafast laser systems. Different application scenarios require different SESAM characteristics. However, the vast majority of applications seek to obtain high-power, narrow-pulse femtosecond lasers while also achieving high repetition rate output. This requires the SESAM to achieve both low saturation flux and high modulation depth.

[0004] Zero-dimensional quantum dot materials are material systems in which carrier motion is constrained in all three dimensions. The energy of carrier motion in all three dimensions is quantized, resulting in a higher density of states than quantum wells. Because the size of quantum dots in these materials is comparable to the de Broglie wavelength of electrons in all three dimensions, the carriers within them are subject to three-dimensional quantum confinement, resulting in novel physical properties. This allows quantum dot semiconductor saturated absorber mirrors (QD-SESAMs) to achieve lower saturation flux than quantum well semiconductor saturable absorber mirrors (QW-SESAMs).

[0005] Due to its ultrafast carrier dynamics, graphene can achieve extremely fast optical responses in the picosecond to femtosecond range. Its absorption spectrum spans the ultraviolet to near-infrared spectral range, making it widely used in laser technology, ultrafast electronics, information and communications technology, and other fields. Compared to graphene, graphene nanogrid structures exhibit stronger nonlinear absorption effects due to the structure and shape of their internal pores, which affect the transmission and localization of photons. Furthermore, graphene is a zero-bandgap material. Microfabrication techniques, typically used to process graphene into nanostructures with a periodicity of several to tens of nanometers, effectively open its bandgap, thereby reducing carrier mobility and increasing its nonlinear absorption properties, achieving higher saturation absorption characteristics. Furthermore, opening the graphene bandgap shifts the wavelength of its transition toward longer wavelengths, meaning that this material can be used in applications such as wide-bandwidth tunable optical modulators and optical switches, improving the modulation range and performance. The band gap opening can also cause graphene to exhibit a weak passivation effect, which can be used to achieve passive mode-locking modulation to obtain stable, high-degree-of-freedom laser output. However, the preparation of graphene nanogrids is difficult and usually requires ultra-high-precision lithography technology, so their application in various optical devices is still relatively rare.

[0006] Nanoparticle self-assembly is a simple and effective method for preparing periodic ordered micro-nanostructures. It uses the electrostatic effect and solvent effect on the surface of nanoparticles to make disordered nanoparticles spontaneously form a layer of self-assembled microspheres on a two-dimensional plane. In the processing of periodic micro-nanostructures, it can be used as a mask pattern for etching and deposition coating.

[0007] CN109167245A discloses a method for preparing a laser saturable absorber, comprising the following steps: 1) dispersing a two-dimensional nanomaterial in a dispersion liquid and subjecting it to ultrasonic treatment to obtain a two-dimensional nanomaterial dispersion liquid; 2) placing porous glass in the two-dimensional nanomaterial dispersion liquid and subjecting it to screening and adsorption under ultrasonic conditions to form a composite of the porous glass and the two-dimensional nanomaterial; 3) removing the composite of the porous glass and the two-dimensional nanomaterial and drying it; 4) annealing the dried composite of the porous glass and the two-dimensional nanomaterial; and 5) cutting and polishing the annealed composite of the porous glass and the two-dimensional nanomaterial to obtain a saturable absorber. The saturable absorber has a wide spectrum, a high damage threshold, and a long service life.

[0008] CN115755245A discloses a saturable absorber, its preparation method, and saturable absorber device. The saturable absorber comprises graphene and composite nanosheets supported on graphite. The composite nanosheets include Bi2Te3 nanosheets and annular Sb2Te3 nanosheets surrounding the Bi2Te3 nanosheets and forming a heterojunction therewith. A Bi2Te3 / Sb2Te3 lateral heterojunction is formed at the interface between the Bi2Te3 nanosheets and the annular Sb2Te3 nanosheets, facilitating rapid charge transfer and electron-hole pair recombination, effectively shortening relaxation time and achieving rapid saturation absorption. Furthermore, the composite nanosheets are combined with graphene, leveraging graphene's high thermal conductivity, strong oxidation resistance, and ability to form large films. This effectively mitigates the shortcomings of two-dimensional layered materials, such as susceptibility to air oxidation and agglomeration, thereby improving the stability of the saturable absorber. Summary of the Invention

[0009] The present invention prepares a graphene nanomesh with controllable size and period on the surface of a QD-SESAM using a simple and easy combination of self-assembly and etching to form a van der Waals heterostructure. Laser annealing is then used to induce intermixing of graphene and Ga elements, resulting in a saturable absorber with better interface bonding. The saturable absorber in the present invention can enhance the interaction between light and matter. The preparation method utilizes the light absorption capacity of the graphene nanomesh to increase the modulation depth of the QD-SESAM, thereby improving the modulatable range and stability to achieve a narrower pulse laser. Lasers prepared using the saturable absorber described in the present invention have better applications in fields such as biological sciences, processing and manufacturing, optical communications, nondestructive testing, and scientific research.

[0010] The present invention discloses a saturable absorber comprising a graphene-Ga composite layer, comprising a GaAs substrate, an AlGaAs / GaAs Bragg reflection layer, a GaAs / InGaAs buffer layer, a quantum dot absorption layer, an InGaAs cap layer, a GaAs cap layer, and a graphene-Ga mesh layer, which are stacked in sequence. The graphene-Ga mesh layer is a lattice structure, and the diameter of the graphene circular holes is 10-100 nm, more preferably 16-90 nm. The graphene-Ga mesh layer is obtained by intermixing graphene and Ga elements by laser annealing.

[0011] The layers are grown sequentially by MBE or MOCVD.

[0012] The thickness of the AlGaAs / GaAs Bragg reflection layer, GaAs / InGaAs buffer layer, one period InAs quantum dot absorption layer, InGaAs cap layer, and GaAs cap layer is 100-300nm; the graphene-Ga nanomesh layer uses a single layer of graphene, and its thickness is 0.2-0.5nm, more preferably 0.34nm.

[0013] A method for preparing a saturable absorber comprising a graphene-Ga composite layer comprises the following steps: (1) sequentially growing an AlGaAs / GaAs Bragg reflection layer, a GaAs / InGaAs buffer layer, a periodic InAs quantum dot absorption layer, an InGaAs cap layer, and a GaAs cap layer on a GaAs substrate; (2) transferring a single layer of graphene onto the material layer prepared in the previous step; (3) laying a layer of microspheres on the surface of the graphene; (4) etching the graphene by dry etching; (5) removing PS (polystyrene) microspheres by immersion in an organic solution; and (6) annealing the graphene by laser.

[0014] The growth of each composite layer in step (1) is achieved using MBE or MOCVD.

[0015] In step (3), the self-assembly method is used to achieve the tiling of PS microspheres, and the average particle size of the PS microspheres is 20-100 nm, preferably 40-70 nm.

[0016] In step (4), RIE etching equipment is used, O2 is used as the etching gas, the flow rate is 30-100 sccm, the power is 100-300 W, and the etching time is 5-30 s.

[0017] The organic solvent in step (5) is acetone.

[0018] In step (6), a femtosecond laser is used with an emission wavelength of 740 nm, a pulse width of 130 fs, and a repetition frequency of 76 MHz.

[0019] The invention also discloses the application of the nano-grid graphene saturable absorber in an ultrafast laser.

[0020] Beneficial technical effects of the present application: The saturable absorber in the present invention can enhance the interaction between light and matter. The preparation method utilizes the light absorption ability of the graphene nanogrid to improve the QD-SESAM modulation depth, improve the modulatable range and stability, and can be used to manufacture narrower wavelength pulsed lasers. The lasers prepared using the saturable absorber described in the present invention have better applications in the fields of biological sciences, processing and manufacturing, optical communications, non-destructive testing, and scientific research. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 : Top view of lattice-structured nanogrid graphene saturable absorber;

[0022] Figure 2: Cross-section of a nano-mesh graphene saturable absorber, where: 1GaAs substrate, 2AlGaAs / GaAs Bragg reflection layer, 3GaAs / InGaAs buffer layer, 4 quantum dot absorption layer, 5InGaAs cap layer, 6GaAs cap layer, 7graphene-Ga mesh layer;

[0023] Figure 3 : Example 1 reflection spectrum test chart;

[0024] Figure 4 : The raman spectrum of Example 1;

[0025] Figure 5 : Schematic diagram of embodiment 1. DETAILED DESCRIPTION

[0026] Example 1:

[0027] (1) Using MBE or MOCVD, an AlGaAs / GaAs Bragg reflection layer, a GaAs / InGaAs buffer layer, a periodic InAs quantum dot absorption layer, an InGaAs cap layer, and a GaAs cap layer are grown on a GaAs substrate in sequence; (2) a single layer of graphene is transferred onto the material layer prepared in the previous step; (3) a layer of PS microspheres with a diameter of 20-100 nm is laid flat on the graphene surface by self-assembly; (4) the graphene is etched by dry etching using RIE etching equipment, O2 as the etching gas, a flow rate of 30-100 sccm, a power of 100-300 W, and an etching time of 5-30 s; (5) the PS microspheres are removed by immersion in acetone solution; (6) the graphene is annealed using a laser, and the parameters of the Ti femtosecond laser are: 740 nm emission wavelength, 130 fs pulse width, and 76 MHz repetition frequency.

[0028] Example 2:

[0029] (1) Using MBE or MOCVD to grow AlGaAs / GaAs Bragg reflection layer, GaAs / InGaAs buffer layer, multi-period InAs quantum dot absorption layer, InGaAs cap layer, and GaAs cap layer on GaAs substrate in sequence; (2) transferring single-layer graphene to the material layer prepared in the previous step; (3) using self-assembly method to lay a layer of 20-100 nm silica microspheres on the graphene surface; (4) using dry etching, using RIE etching equipment, O2 as etching gas, flow rate 30-100 sccm, power 100-300 W, and etching time 5-30 s; (5) using BOE solution to soak and remove silica microspheres; (6) using laser annealing, the Ti femtosecond laser parameters are: 740 nm emission wavelength, 130 fs pulse width, 76 MHz repetition frequency.

[0030] The above contents are merely examples and explanations of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the present invention, they should all fall within the scope of protection of the present invention.

Claims

1. A saturable absorber comprising a graphene-Ga composite layer, comprising a GaAs substrate, an AlGaAs / GaAs Bragg reflection layer, a GaAs / InGaAs buffer layer, a quantum dot absorption layer, an InGaAs cap layer, a GaAs cap layer, and a graphene-Ga mesh layer stacked in sequence; the graphene-Ga mesh layer having a lattice structure, wherein the diameter of the graphene circular holes is 10-100 nm, more preferably 16-90 nm; and the graphene-Ga mesh layer is obtained by laser annealing to induce intermixing of graphene and Ga elements.

2. The saturable absorber according to claim 1, wherein The layers are grown sequentially by MBE or MOCVD.

3. The saturable absorber according to claim 1, wherein The thickness of the AlGaAs / GaAs Bragg reflection layer, the GaAs / InGaAs buffer layer, a period of InAs quantum dot absorption layer, the InGaAs cap layer and the GaAs cap layer is 100-300 nm.

4. The method for preparing a saturable absorber comprising a graphene-Ga composite layer according to claim 1, comprising the following steps: (1) On a GaAs substrate, an AlGaAs / GaAs Bragg reflection layer, a GaAs / InGaAs buffer layer, a periodic InAs quantum dot absorption layer, an InGaAs cap layer, and a GaAs cap layer are sequentially grown; (2) a single layer of graphene is transferred onto the material layer prepared in the previous step; (3) a layer of microspheres is laid flat on the graphene surface; (4) the graphene is etched using dry etching; (5) the PS microspheres are removed by immersion in an organic solution; and (6) the graphene is annealed using a laser.

5. The method according to claim 4, wherein The growth of each composite layer in step (1) is achieved using MBE or MO CVD.

6. The method according to claim 4, wherein In step (3), the self-assembly method is used to achieve the tiling of PS microspheres, and the average particle size of the PS microspheres is 20-100 nm, preferably 40-70 nm.

7. The method according to claim 4, wherein In step (4), RIE etching equipment is used, O2 is used as the etching gas, the flow rate is 30-100 sccm, the power is 100-300 W, and the etching time is 5-30 s.

8. The method according to claim 4, wherein The organic solvent in step (5) is acetone.

9. The method according to claim 4, wherein In step (6), a femtosecond laser is used with an emission wavelength of 740 nm, a pulse width of 130 fs, and a repetition frequency of 76 MHz.

10. Use of the nanomesh graphene saturable absorber according to claims 1 to 3 in ultrafast lasers.

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