Electromagnetic Wave Manipulation And Functional Devices Based On Polarization-Dependent Metasurfaces

Electromagnetic metasurfaces are planar optical elements that is composed of phase shifters made by subwavelength resonant antennas.Compared to traditional optical components,electromagnetic metasurfaces exploit the abrupt phase changes associated with scattered light from resonant antennas to control the amplitude,phase,and polarization of light beams within subwavelength scale.By finely controlling the shape,size,direction,and arrangement of the antenna unit,metasurfaces can arbitrarily control light propagation,which present a new avenue for achieving miniaturization,multifunction and integrated optical devices.Although the studies on the electromagnetic wave manipulation by using metasurfaces have already made great achievements,further researches are necessary on asymmetric transmission,metalens,electromagnetically induced transparency-like(EIT-like)and multifunctional devices.Polarization state is one of the basic characteristic parameters of electromagnetic waves,and polarization devices based on metasurfaces have wide application potential in the fields of detection,communication,etc.In the thesis,we have made theoretical and experimental studies onpolarizationdependent electromagnetic metasurfaces.We have designed and fabricated several different polarization-dependent metasurfaces to manipulate the beam,phase and polarization of electromagnetic waves,which can carry out asymmetric transmission,focusing,beam deflection,electromagnetically induced transparency-like(EIT-like)and multifunctional functions.The main research contents and results are summarized as following:(1)Asymmetric transmission is characterized by the high contrast between forward transmission(front-side incidence)and backward transmission(back-side incidence),which has great application potential in optical networks and integrated optical systems.We propose and design two kinds of polarization-dependent asymmetric transmission devices.We first design asymmetric transmission device based on unidirectionally excited surface plasmon polariton(SPP).Owing to the unidirectional excitation of SPPs by the metasurface,forward incident light has much higher transmission than the backward one.It is worth noting that the asymmetrical transmission device is only suitable for x-polarized waves.In order to obtain asymmetric transmission for both linearly and circularly polarized waves,we also design and fabricate asymmetric transmission device based on chiral metarsurfaces.Experimental results show that it can realize asymmetric transmission not only for linearly polarized waves,but also for circularly polarized waves.(2)To circumvent the design difficulties associated with the metasurfaces based on effective propagation phase and Pancharatnam-Berry phase,a polarization-controllable reflective metalens is designed and manufactured.Experimental results show that,for a righthanded circularly polarized wave of 12 GHz,the metalens works in focusing state with a short focal length of 18.6 cm;while for the left-handed circularly polarized wave at the same frequency,it can work in focusing state with a long focal length of 38.9 cm.This metalens with polarization-dependent focal points has the potential to be used in polarizationdependent imaging,detection,and display,etc.(3)To solve the dilemma between limited functions and complicated design in multifunctional metasurfaces,we propose a polarization-switchable and wavelengthcontrollable multi-functional metasurface.Compared to the above-mentioned polarizationcontrollable metalens,it can work as a flat focusing lens for y-polarized incident light or as an SPP coupler for x-polarized incident light.More importantly,by tuning the wavelength of x-polarized incident beams,it can also control the confinement region of the excited SPP waves.In addition,in order to integrate more functions,a polarization-dependent asymmetric multifunctional metasurface is also proposed.The research results show that the metasurfacer carries out different functions for different polarized waves when they are incident from different directions.(4)Dynamical manipulation of EIT-like effect in metasurfaces has the potential to be applied for slow light,enhanced nonlinear effects,optical storage,etc.However,previously reported methods require an external stimulus or complex metasurface structures,and the number of transparent windows cannot be adjusted.In this regard,we design and manufacture a polarization-controllable EIT-like metasurface based on bright-dark mode coupling.By changing the polarization state of the incident light,not only the intensity and frequency of the EIT-like window,but also the number of transparent windows can be adjusted.In addition,by employing both bright-dark mode coupling and bright-bright mode coupling,we further broaden and manufacture the EIT-like metasurface working in optical communication band.Experimental results show that the peak wavelength of the EIT-like window excited by x-polarized waves is located at 1462 nm;and the peak wavelength of the EIT-like window excited by y-polarized waves is located at 1395 nm.We believe this kind of metasurface has the potential to be used in dual-frequency filters,sensors,and optical switches.