The Study Of Light Emission Manipulation In Active Resonant Metasurfaces

Electromagnetic metamaterials and metasurfaces have been widely studied due to their unique and novel response characteristics in microwave,terahertz and optical frequencies.The reason is that,compared with natural materials,the electromagnetic response of metamaterials and metasurfaces not only depends on the physical and chemical composition of the material itself,but also depends on the structural design and specific arrangement.Through proper design and arrangement,metamaterials and metasurfaces can control the amplitude,phase and polarization of electromagnetic waves almost arbitrarily.Compared with the three dimensional metamaterials,the two dimensional metasurfaces have a higher integration degree and a simpler fabrication process.Metasurfaces can be divided into gradient metasurfaces and resonant metasurfaces by their functionality.Taking the optical frequency as an example,gradient metasurfaces are mainly used to flexibly control the wavefront of propagating beams,while resonant metasurfaces are mainly used to confine and enhance local light fields at sub-wavelength scale.In particular,the combination of resonant metasurfaces and active luminescent materials can not only improve the luminescence intensity and reduce the lasing threshold by local field enhancement,but also control the radiation characteristics of the light emission to a certain extent,for example,directional emission,polarization engineered emission,vortex beam generation,so as to realize novel light-emitting devices like ultra-flat,multi-functional LEDs and lasers.In this thesis,a series of theoretical research and experimental exploration are carried out on the resonant metasurface made by active luminescent materials.Based on luminescent materials such as silicon-based Ge quantum dots and GaAs-based InAs quantum dots,by using Mie resonance and the induced multipole interactions in nanoscale structures,it is able to form Fano resonance,toroidal dipole resonance and anapole mode,BIC mode,Kerker effect,array effect and so on,further realizing high Q resonances with specific far-field radiation control.The details of the research are summarized as follows:(1)An asymmetry-induced Fano resonance modified Ge quantum dots emission metasurface is theoretically proposed and experimentally studied.Starting from the nanodisk,the Fano resonance is excited by introducing an air hole to break the symmetry of the structure.The experimental Q factor of the Fano resonance is ?1946,which is much high in this research field.Attributed to the Fano resonance,the spontaneous emission of Ge quantum dots is promoted,and the emission direction is modified,resulting in 1472 times enhancement of photoluminescence signal.At the same time,the asymmetric distribution of the electromagnetic field of the resonance also has certain control on the polarization characteristics of the luminescence.By moving the air holes in a controlled way,different resonance modes can achieve spectral overlap,showing the ability to further modifying the near-and far-field characteristics of the light emission.(2)A metasurface that simultaneously supports both magnetic and electric toroidal dipole resonances in the near-infrared region is proposed.Starting from the nanodisk,by introducing an air gap in the diameter direction,strong magnetic and electric toroidal dipole resonance can be excited in the structure under certain polarized light.Two orders of Ge quantum dots luminescence enhancement is experimentally achieved by using the excited toroidal dipole resonances.The reason is that,the light field is strongly concentrated by the toroidal dipole resonances,which improves the spontaneous emission,and the array effect of the structure improves the extraction and collection efficiency.In addition,the change of gap width can also control the polarization characteristics of the light emission to a certain extent.By modifying the air-gap-witdh distribution in the plane,it may be able to achieve light emitting devices with specific polarization states.(3)The nano-fabrication technologies of nanostructures made by Si-based Ge quantum dots material and GaAs-based InAs quantum dots material are explored and optimized.The MBE technology of silicon based embedded self-assembled Ge quantum dots is studied,the luminescence of the grown Ge quantum dots is improved to an advanced level.For GaAs-based InAs quantum dots luminescent material,wet etching and high temperature oxidation processes are explored to improve the refractive index difference between the active layer where the metasurface is located and the substrate layer below.The fabrication technique to realize large area and uniform resonant metasurface structure is studied and modified.(4)A BIC light-emitting metasurface with symmetry-controlled mode excitation is designed and experimentally studied.Starting from the tetragonal lattice arranged 2D circular hole metasurface,the symmetry properties of the eigenmodes caused by the symmetry feature of the structure are analyzed,and the formation of BIC modes in the structure caused by the symmetry mismatch is explained.By introducing weak symmetry-perturbation,one of the BIC modes is excited,and the degree of asymmetry is used to further adjust the Q factor of the mode.Based on GaAs-based InAs quantum dot luminescent material,this symmetry-perturbation controlled BIC mode is used to realize the generation of stimulated radiation beam under continuous laser pumping.Compared with the pulsed laser pumping method in related researches,the device performance has been improved.In addition,the Q factor variation caused by the array effect is also observed and analyzed.