Dielectric Resonators Based Optical Metasurfaces Devices

Optical metasurfaces device is one of the hot research fields of micro-nano optics.It is emerging as a powerful building block for exploring the potential applications in sensing,imaging,holography and photodetection.And resonators are(avoid the superlative grammer)components of optical metasurfaces devices.With resonators,phase retardations are independent with thickness,thus flexible control of light can be realized within sub-wavelength propagating distance.With the developing of nanofabrication techniques,the fabrication quality of resonators has been improved significantly,providing more applications of optical metasurfaces.However,several crucial problems are also emerging.Conventional plasmonic resonator metasurfaces always have very low work efficiency because of ohmic loss,and the common used silicon material also experiences similar problems in visible light.So it's still a problem to improve the operation efficiency of metasurfaces in the visible region.Besides,the optical characteristics of most metasurfaces are static once they are fabricated with given sets of dimensions,it is highly desirable to find a simple way to control the resonances of nanostructures.Furthermore,highprecision processing equipment and much time cost are needed during fabrication of visible light metasufaces,it's important to find a new mechanism to eliminate the preparation difficulty and keep the performance.Finally,combining with new materials,composite metasurfaces also need research beyond conventional wavefront control aspect.Aiming at solving the above problems,this dissertation focuses on the dielectric resonators based optical metasurfaces devices.The study is divided into two aspects: for composed materials,from silicon with loss to Ti O2 without loss,and finally perovskite with gain,for the research of light modulation,from simple spectra modulation to wavefront phase-control,and finally laser modulation.One method to realize reconfigurable metasurfaces is also concluded.The main contents of the dissertation are summarized as follows:Firstly,the Fano resonance properties in optical structures are investigated.Midinfrared silicon-based Fano metasurfaces are utilized to realize high-Q resonances.With the coupling between silicon-based resonators,the Q factor can reach as high as 1839,the shift of the resonance change per refractive-index-unit equals to 1200 nm/RIU,leading to a figure-of-merit of 185.Based on random-phase approximation,detection of the thickness of graphene was done with numerical simulations and the corresponding figure-of-merit(FOM)is as large as 6.5.Secondly,high-quality Ti O2 films were prepared,whose real part of refractive index is around 2.2 at 632 nm and the imaginary part of refractive index is negligibly small.Ti O2 resonators based metasurfaces were designed theoretically.With coupling effect between electric dipole resonance and magnetic dipole resonance,high reflection narrow-band peaks emerge at designed wavelengths,corresponding to bright,distinct colors.In experiments,the maximal reflectance was as high as 64% with full width at half maximum(FWHM)around 30 nm and it proved to be angle and polarization independent.Pixel size tests indicate a resolution around 16,000 dpi can be achieved.Thus bright,high contrast,and high resolution colorful images were presented.Thirdly,real-time tunable colors with microfluidic reconfigurable all-dielectric metasurfaces were demonstrated.Simulation results demonstrate that with environment refractive index increasing,the structure colors for metasurfaces red shift.With the injection of water,DMSO,and CS2,the reflection peaks shift to longer wavelengths,consistent with the numerical results.Ti O2 metasurfaces also have the capability of the erasion of encoded information and the transition time is as small as 16 ms.Fourthly,Ti O2 metasurface with aspect ratio around 1-1.5 was designed and good enough to produce phase changes covering-? to ? with high reflection efficiency.Based on generalized Snell's law,anomalous reflection Ti O2 metasurfaces were designed with angle equal to 8°,theoretical efficiency equal to 80%,experimental efficiency equal to 49%.According to the Gerchberg-Saxton algorithm,a hologram was designed,in experiment the absolute conversion efficiencies for red,green,and blue hologram were 36.7%,24.5%,and 13.9%,respectively.Lastly,with one-step solution processed precipitation method,CH3NH3 Pb Br3 perovskite nanoribbons were synthesized and integrated with gold gratings.Both of our numerical calculations and the corresponding experiments show that the light can be well trapped within an air slot as small as ~ 400 nm.Consequently,a nanolaser array with density ~ 1250/mm has been experimentally realized.In summary,this dissertation provides the experimental and theoretical basis for studying optical metasurfaces devices.Based on the studies on graphene thickness detection,high resolution color printings,reconfigurable color printings,visible light full-phase modulation and high density laser array,this research shall also pave a new route of optical metasurfaces on sensing,imaging,light switch,hologram and biomedical sciences.