Spatial And In-plane Light Field Manipulation Based On Metasurface

The optical properties of metasurface are related to the geometric parameters of the sub-wave length unit cell,such as size,direction,etc.Due to the excellent ability to control the amplitude,phase and polarization of the incident light,metasurface has become an important means to realize complex optical field modulation.People can realize various light field manipulation by adjusting the geometric parameters of structural unit of metasurface.Many optical components based on metasurface have made breakthroughs.In this paper,the spatial and in-plane beam control is studied.The beam deflector at the visible light and the surface plasmon polaritons directional coupler with wavelength-selectivity are designed.The main research contents are as follows:1.According to geometric phase and the principle of beam deflection,the rotation angle of each nanoantenna is determined by the deflection angle and the incident wavelength.We get the arrangement of nanoantennas if we want to deflect the beam when circular polarized light is incident.We choose TiO2 as antenna material for its high performance in the visible light band.We analyze the main factors affecting the deflection efficiency and conclude that the polarization conversion efficiency of the element structure needs to be improved in order to achieve high-efficiency beam deflection.Therefore,we determine three sizes for different wavelengths by calculating the polarization conversion efficiencies of different cell sizes.Based on the cell with high polarization conversion efficiency,beam deflectors for different angle and different wavelength is designed.The phase distribution of near electric field and far-field transmitted power distributions as the functions of angle are calculated by FDTD,and the results agree with each other.The deflector shows good performances of low loss,small size and easy integration,which has great application potential in the integration of optical elements.2.We theoretically analyze the SPP excited by the nanoaperture and derive the field interference results of the SPP excited by the nanoaperture array.Through the analysis of the formula,it was concluded that in order to make the coupler wavelength-selective,the period of nanoaperture array must meet certain requirements.The parameters of a single nanoaperture are optimized in order to improve the coupling efficiency.The wavelength-selective couplers are simulated and demonstrated them in experiment.When the incident light with different wavelengths(450 nm,550 nm and 650 nm)is illuminated on the coupler respectively,only the incident light with certain wavelength can launch strong SPP wave.The experimental results are in good agreement with the simulation results and show that our couplers realize wavelength-selectivity.Therefore,our couplers have great application potential in nanophotonics integrated systems and other optical integrated systems.