Mid-Infrared Polarization Devices Based On The Dielectric Metasurface

Metasurfaces are composed of the subwavelength structures,which can be used to manipulate the phase,amplitude,and polarization of the transmitted and reflected electromagnetic waves.Compared to conventional optical elements,which rely on long propagation distances,these devices facilitate strong light-matter interaction on a subwavelength scale,allowing abrupt changes of phase.In recent years,there has been great interest in controlling electromagnetic wave by metasurfaces.Due to its advantage of simple geometries,low losses and very promising for integration on a photonic chip,metasurfaces have great advantage in practical application.To date,a majority of the studies based on dielectric metasurface have been focused on the visible light and communication wavebands.Mid-infrared is significant in biological field,medical and military,which hold great potential for metasurface operating in mid-IR.In this paper,we design a variety of polarization devices base on the dielectric metasurface working in mid-infrared(mid-IR)range and we use finite difference time-domain(FDTD)method to emulate its diffraction characteristics.The content of this paper is as follows:(1)We propose double-phase modulating method and achieve modulated two polarization state at the same time.Three polarization devices-polarization beam splitters,beam deflectors,and dual-focus lenses-are designed in the mid-infrared based on dielectric metasurface.All-dielectric arrays made of silicon nanostructures have been used for its low absorption loss in the designed frequency.The phase accumulation is achieved through geometric optimization.(2)We design a mid-infrared polarization generator.There are three double-polarization focusing lenses based on the double-phase modulating method for the generator,which can generate six different polarization states of transmitted light and focus on corresponding positions.Through the optimization of the unit cell,the parabolic phase distribution required for focusing is achieved.We verify the function of the metasurface with different polarized light.(3)A mid-infrared reflective filter based on the dielectric metasurface is realized.Here,we choose cylindrical unit cell as the resonator.Metasurfaces with different unit sizes could generate high reflection peaks at designed wavelengths which is useful for wavelength selectivity.We analysis the influence of the structural parameters,the polarization of the incident light and the incident angle for on the reflection peaks,and then summarizes the method of wavelength regulation.