Design Of Tunable Metasurface Made Of Single Crystal Silicon

The metasurface optics which is based on micro-nano preparation technology is small in size,and can be more widely applied.The metasurface is formed by periodically arranging artificially prepared sub-wavelength basic structural units,which can regulate the phase,amplitude and polarization of incident electromagnetic waves.In the early studies,metal-based plasmonic metasurfaces were the main research direction,and can be applied in many aspects.However,metals have higher ohmic losses in the visible and infrared,so researchers are increasingly turning their attention to the dielectric metasurface.Dielectric materials are widely used in metasurfaces because they have minimal loss in the visible and infrared regions,high refractive index,and are compatible with CMOS technology.Further,by using certain properties of the metasurface material,the dimension of the metasurface control can be increased,so that the metasurface can better control the electromagnetic wave,and the metasurface is called an tunable metasurface.Therefore,the use of dielectric materials to prepare an tunable metasurface can achieve optoelectronic chips which have low ohmic losses and are capable of achieving multiple dimensional control of visible light.Based on the principle of electromagnetic induction transparency(EIT)resonance,the metasurface of single crystal silicon dielectric in the visible region is designed.The experimental materials in this paper are single crystal silicon,which has mature preparation technology and low loss in visible light.The designed metasurface is simulated by the simulation software based on the finite element method,and the metasurface with EIT resonance phenomenon is obtained.Since the key to metasurface performance depends on its sub-wavelength basic structural unit,the influence of the geometric parameters of the metasurface basic structural unit on the metasurface can be studied.Due to the small gap of the designed metasurface,the preparation process is very difficult,and the dielectric metasurface is obtained after repeated experiments.An optical path for measuring transmittance and reflectivity is then designed and built,and the dielectric metasurface is measured based on this optical path.The transmission window can be seen in the transmission spectrum.According to the resonance generation principle,the experiment of the incident light angle transformation is further designed to verify that the EIT resonance phenomenon occurs on the metasurface at the corresponding wavelength of the transmission window.Further extending the dielectric metasurface of the single crystal silicon to the tunable dielectric metasurface.In this paper,two schemes are used to realize the tunable metasurface in the light region.One is to combine the dielectric metasurface with the flexible PDMS substrate to design a mechanically tunable metasurface.Through the simulation,the transmission and reflection spectra of the mechanically tunable metasurface after each stretching are calculated.According to the simulation results,the maximum deformation of the mechanically tunable superstructure surface is 133%,the maximum rate of change of transmittance(or reflectance)is 80%,which can be applied to mechanically regulated optical switches.Another solution is to design a thermally tunable metasurface using the refractive index of the semiconductor material as a function of temperature.Through simulating,the influence of temperature on the thermally tunable metasurface is obtained,and the feasibility of the thermally tunable metasurface is verified.The maximum change rate of transmittance or reflectivity measured in the experiment is 75%.This metasurface can be used for a thermo-optic switch or the like.