Research On The Asymmetric Transmission And Electromagnetically Induced Transparency-like Based On Metasurfaces

The interaction between electromagnetic waves and matter will cause many scattering phenomena,including transmission,reflection,absorption,etc.This thesis is mainly focused on the control of transmission responses by using metasurfaces,which includes the asymmetric transmission and electromagnetically induced transparency-like(EIT-like)effect.Asymmetric transmission means that when electromagnetic wave incident on a medium forwardly and backwardly,it exhibits different transmission responses;while EIT-like is a quantum-like effect,which can be described that a narrow-band peak appears at an original broadband absorption peak.Traditional asymmetric transmission and EIT devices are bulky and inefficient,which limits their applications.The emergence of metasurfaces(two-dimensional metamaterials)provides an alternative to break through the limitations of traditional optoelectronic devices.This is mainly because metasurfaces are composed of two-dimensional planar subwavelength structures,and their design is flexible,so they have unique ability to manipulate electromagnetic waves.Asymmetric transmission and EIT-like devices based on metasurfaces can avoid the need for additional auxiliary systems in traditional nonreciprocal devices and slow-optical devices,and they have important significance for promoting the integration and miniaturization of asymmetric transmission and EIT-like devices.In addition,these devices have a wide range of applications in signal processing,one-way transmission,sensing,and so on.This thesis mainly focuses on the control of transmission response of electromagnetic waves,and mainly conducts in-depth research on asymmetric transmission and EIT-like effect.(1)We designed a kind of asymmetric transmission device composed of dielectric-metal metasurface.The simulation results show that under the forward incidence of x-polarized light,the working wavelength at 922 nm corresponds to a resonant peak with a transmittance of 0.70.In contrast,when the light is incident from the opposite direction,a resonant valley with transmittance as low as 0.07 appears at the same wavelength.Thus,an asymmetric transmission window with excellent performance is produced at the operation wavelength.In addition,due to the device is of rotational symmetry,its function of asymmetric transmission is effective for any linearly polarized light and circularly polarized light.Moreover,the device can also achieve unidirectional1:2(one beam of light is divided equally into two beams)and 1:4(one beam of light is divided equally into four beams)optical beam splitting function for linearly polarized light and circularly polarized light,respectively.In addition,based on the principle of Babinet complementarity,we designed and fabricated a kind of Z-shaped complementary chiral metasurface,which can simultaneously achieve dual-band asymmetric transmission both for linearly polarized wave and circularly polarized wave.The research reveals that the chiral characteristics of the device and the near-field coupling within the complementary structures have an important impact on the asymmetric transmission performance.This work provides a new idea for the design of asymmetric transmission metasurface.(2)We demonstrated a metasurface,which can realize multiple transparency windows.Based on Fano formula and electromagnetic mode coupling theory,we analyze the resonance type and formation mechanism of each transparent window in detail.The research results show that the three transparent windows correspond to different resonance types,which are Fano resonance,EIT-like resonance and Lorentz resonance,respectively.The experimental test results further verify the relevant conclusions.Different resonance types have different electromagnetic response characteristics,so the metasurface is expected to be used in different applications.Moreover,we designed and fabricated another kind of metasurface,which can simultaneously realize EIT-like and EIR-like(Electromagnetic Induced Reflectance-like)effects.We analyzed the formation mechanisms of these two windows deeply by using electromagnetic mode coupling theory and electromagnetic multipole decomposition method.Then we discussed the group delay and refractive index sensing performance of the device at the EIT-like and EIR-like windows,and the metasurface samples have been tested experimentally.The test results are in good agreement with the simulation ones.It should be pointed that EIT-like effect is applicable to transmission space,and EIR-like effect is applicable to reflection space.This proposed metasurface may further expand the application fields of metasurfaces.(3)We proposed a metasurface,which can realize asymmetric EIT-like effect.We employed the transfer matrix method and mode coupling theory to reveal the formation mechanism of the asymmetric EIT-like effect.Compared with the previously reported metasurfaces that can only achieve asymmetric transmission or EIT-like effect alone,the designed metasurface can achieve these two functions simultaneously.And the experimental results are in good agreement with the simulation ones.Such a metasurface is expected to be applied in unidirectional filtering,sensing and optical switches.