| As a new type of micro-nano photonic device,metasurfaces can achieve powerful electromagnetic control in ultra-thin interfaces with deep sub-wavelength thickness,including complete control of amplitude,phase and polarization,typically arbitrary based on generalized Snell’s law wavefront(phase)control.In principle,the metasurfaces constructed by periodic units of anisotropic nano-antennas or resonators can produce a phase shift covering the entire range from 0 to 2π in the cross-polarized scattered wave,and simultaneously maintain the amplitude uniformity,then they have the only superiority in light wave control.However,most of the metasurfaces available are static in performance and their properties are fixed upon fabrication.So actively tuning or tailoring the amplitude,phase and polarization and designing optical devices with smaller volume,higher integration,better performance are highly desirable for many occasions especially the integrated photonic devices or systems.The main research content of this subject is to realize the analysis of tunable devices based on the sub-wavelength metasurface structure,and explore the ability to control electromagnetic waves from multiple aspects such as unit design,theoretical calculation,numerical simulation,and functional application.It aims to provide new ideas and implementation methods for the future development of supersurfaces in the direction of reconfigurability,multi-function and integration.The related work can be concluded as follows:(1)Switch type metalens.Using the refractive index changes of phase change materials,the generalized Snell ’ s law and the Pancharatnam-Berry(PB)phase principle,in a wide spectral range between 2.8 μm and 3.8 μm,the reflective beam focuses with a cross-polarization efficiency of 80% in the amorphous state,but defocuses in the crystalline state with zero cross-polarization,i.e.the ‘on’ and‘off’ states of the metalens.(2)Zoom type metalens.Both device architectures what we designed show tunable focal length from 4.4 μm to 4.8 μm(MI)and 3.4 μm and 3.6 μm(MIM)respectively upon phase transition between the amorphous and crystalline states.(3)Reconfigurable holographic metasurface.Utilizing the principle of GS algorithm and geometric phase coding,the reconfigurable effect of "open" or "close" the reconstructed image with high efficiency and high image quality in the broadband range is realized.Further,we explained the reason for the high efficiency of the reflective metasurface device broadband,and then simulated and analyzed the holographic algorithm and the number of iterations on the holographic imaging quality,providing some new ideas for the design of metasurface holography. |
