| The electromagnetic metasurface is an artificially engineered optical material which has functions or properties that the natural material does not have.Due to its amplitude and phase modulation capabilities,metasurface has received extensive attention in the field of optics in recent years.Compared with plasmonic metasurface composed of metal materials,all-dielectric metasurface composed of dielectric materials has a lower absorption rate of light,leading to the higher energy utilization efficiency.All-dielectric metasurface can realize optical field modulation through Mie resonance.However,most of the current metasurface designs are still static.Once the design is fixed,the properties of the metasurface cannot be changed.Therefore,how to design dynamic metasurface has become a research focus.The Mie resonance of alldielectric metasurface is affected by the ambient medium around the metasurface,thus the dynamic modulation of the optical field can be achieved by modulate the properties of the ambient medium.As an electro-optical material,liquid crystal can be used as the ambient medium and controlled by electric field.Therefore,it is an important method for realizing the dynamic metasurface.The research focuses on properties of the dynamic metasurface based on liquid crystal modulation.Metasurfaces for the light propagating in the plane and large-area spatial light modulation are designed respectively with physical field simulation methods.Furthermore,device fabrication and experiments are carried out to test the metasurface for spatial light modulation.The main contents of this research are as follows:1.A design of the dynamic metasurface waveguide based on liquid crystal modulation for light propagating in the plane is proposed.The metasurface waveguide is composed of a onedimensional array of all-dielectric nanostructures arranged in a chain immersed in liquid crystal.At a wavelength of 1550 nm,it can dynamically modulate the intensity and phase of transmitted light.The physical modeling and simulation of this structure are carried out.It is proved that the transmittance of the metasurface waveguide can be changed between 1.0% and 75.2% by liquid crystal modulation.In addition,a Mach-Zehnder interferometer is designed based on this structure,and its phase modulation capability is verified by the variation of the light intensity at the two output ends.It is proved by simulation that the light intensity of the two output ends can vary dynamically with liquid crystal modulation.Finally,by introducing a tapered coupler,the energy efficiency of the device is improved.2.A design of the dynamic metasurface based on liquid crystal modulation for spatial light that can be fabricated in a large area is proposed.The metasurface can be fabricated in a large area that cannot be achieved by photolithography through LB film and ALD coating.The metasurface consists of an array of PS sphere nanostructures coated with a Ti O2 shell.Through physical modeling and simulation,it is verified that with liquid crystal modulation,the reflection peak shifts by about 9nm.In addition,optimization is carried out through simulation,and the parameters suitable for the experiment are determined.3.Aiming at the design of the dynamic metasurface based on liquid crystal modulation for spatial light,the corresponding devices are fabricated and their reflectance spectra are tested.The test results show that with liquid crystal modulation,the reflection peak of the metasurface shifts by about 10 nm,which verifies the principle of the design,but at the same time,the test results also show that the performance of the actual device is worse than expected.The difference between the experimental results and the simulation results is analyzed,especially the influence of disorder.It is proved that the disorder of metasurface is an important factor affecting the reflection peak width.It is provided that a theoretical and experimental reference for the research on characteristics of dynamic metasurface based on liquid crystal modulation.Particularly,an innovative design theory is proposed for the metasurface in the field of optical computing of integrated optics and large-area spatial light modulation. |
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