Third-order Nonlinear Optical Properties And Applications Of Layered Natural Van Der Waals Heterostructure

Nonlinear optical devices are important optical information processing functional devices,which play an indispensable role in the fields of optical communications,optical sensing,biomedicine,industrial processing,and national defense.With the application requirements of broadband ultra-fast optoelectronic devices,the exploration of nonlinear optical materials with high chemical and mechanical stability,wide band operation,ultra-fast response time,high modulation depth,high damage threshold,low cost and other excellent properties has become a research hotspot in the field of nonlinear optics and optoelectronics.Accurate fabrication of semiconductor heterostructures is the starting point of semiconductor devices and the cornerstone of modern elect ronics and optoelectronics.The layered van der Waals heterostructure can stack materials with different properties together like building blocks by virtue of weak van der Waals force,which not only retains the excellent physical and chemical properties o f single-layer materials,but also has flexible customizability,bringing dawn to the design and manufacture of new optoelectronic devices.At present,most van der Waals heterostructures can be realized by mechanical exfoliation and manual stacking methods,but the yield is limited and adsorbents are easily introduced.Based on chemical epitaxial growth or physical vapor deposition methods,the synthesis of van der Waals heterostructures can be accurately controlled on a large scale,but the preparation pr ocess needs to be fine controlled.Natural van der Waals heterostructures are layered materials that exist stably in nature,and high-quality,stable performance two-dimensional van der Waals heterostructures can be directly obtained by mechanical exfoliation and other methods.At present,researchers have found that sulfur minerals such as franckeite are natural van der Waals heterostructures.However,its optical properties and applications are rarely studied.In this thesis,focusing on the application requirements of broadband ultra-fast nonlinear optical materials,few-layer franckeite was prepared experimentally,and it was verified that layered franckeite is a naturally occurring van der Waals heterostructure formed by alternately stacking Sn S 2-like and Pb S-like layers,with a narrow band gap(<0.7 e V)and p-type doping characteristics.At the same time,the broadband third-order nonlinear response capability and ultra-fast dynamic characteristics of layered franckeite were proved experimentally,and its potential applications in pulsed laser generation,phase modulator,photodiode and other functional optoelectronic devices were verified.The main tasks include:(1)The broadband nonlinear optical properties and ultra-fast response capabilities of few-layer franckeite were studied,and the influence of different excitation conditions and material parameters on its broadband nonlinear optical properties was obtained.The few-layer franckeite nanosheets were prepared by liquid phase exfoliation method.The optical properties of franckeite nanosheets were analyzed,and it was proved that the natural van der Waals heterostructures were formed by alternately stacking Sn S2-like and Pb S-like layers.DFT energy band structure analysis showed that franckeite was a type II heterostructure and p-type doped semiconductor,and exhibited a smaller band gap than Sn S2-like and Pb S-like monolayers.The nonlinear optical test results showed that the layered franckeite have the characteristics of broadband saturable absorption and self-defocusing.The calculated nonlinear absorption coefficient of the layered franckeite was?10^-9 W·m^-1,and the nonlinear refractive index was?10^-15 m²·W^-1.The study of ultra-fast carrier dynamics showed that the layered franckeite has two ultrafast relaxation times of?16 ps and?300 ps,indicating its application potential in nonlinear optical devices and ultrafast optoelectronic devices.(2)Based on the optical properties of broadband saturable absorption of layered franckeite,the stable ultrafast mode-locked laser output in 1?m and 1.5?m band and Q-switched laser output in?3?m band were obtained.Combined with the broadband saturable absorption and ultra-fast carrier dynamics characteristics of layered franckeite,the ultra-fast fiber lasers with pulse duration of 292 ps at 1?m and 798 fs at 1.5?m were successfully obtained by optimizing Yb³⁺doped and Er³⁺doped fiber lasers,respectively.In addition,based on the layered franckeite saturable absorber,a Q-switched fluoride fiber laser output with a pulse width of 920 ns was obtained in the mid-infrared band,further confirming the broadband nonlinear optical modulation ability of the layered franckeite.(3)The broadband optical Kerr effect of layered franckeite was studied,and its nonlinear optical modulation potential in all-optical devices such as photodiodes was demonstrated.The unidirectional transmission function of photonic diodes based on layered franckeite was demonstrated by cascading layered franckeite and C60 materials with opposite nonlinear optical behavior in the optical path,and a nonlinear passive all-optical diode with non-reciprocity factor of 2 d B was obtained experimentally.Based on the light control light technology,the functions of optical modulator and optical switcher based on layered franckeite were demonstrated successfully,which proved the application potential of natural van der Waals hetero structure in nonlinear optoelectronic devices.