Research On Beam Polarization Based On Metasurface

Metasurface refers to a two-dimensional artificial structure whose characteristic size is smaller than the wavelength(that is,the sub-wavelength size),which can effectively control the state of the beam.When traditional optical components control the incident beam,they are relatively bulky and are not suitable for integration applications.However,the super-surface with sub-wavelength structure is beneficial to the integration and miniaturization of components.From the perspective of metasurfaces,we construct a multi-layer unit and construct a polarization rotator to realize the wideband application of beam polarization.Multi-polarized beams are generated at the same time to realize the polarization conversion of the incident beam.The working bandwidth is a very important indicator in the design and application of metasurfaces.The application of metasurfaces is often limited by the electromagnetic response bandwidth of the structure.Therefore,we propose to achieve a wide-band adjustment of the beam.One is to start with a single-layer slot structure unit for design simulation,and then extend to the design simulation of a multi-layer slot structure unit,and use the design idea of multi-order resonance to achieve its broadband working performance.The structural unit works in the X-band,with a center frequency of 10 GHz and a bandwidth of 1GHz.When the polarized wave in the x direction is incident,the multilayer structure has a good transmission effect for the polarized electromagnetic wave in the x direction,and exhibits passband characteristics.The multilayer structure is almost completely suppressed against y-axis polarized electromagnetic waves,and exhibits stop band characteristics.For incident circularly polarized waves,the transmitted cross-polarized wave conversion coefficient is basically close to 0.5,that is,the transmitted cross-polarized wave is about 25% of the total energy of the incident wave,because the multilayer structure does not use the interlayer Magnetic coupling improves the conversion efficiency of cross-polarization,so the simulation results are basically in agreement with the theoretical limit.The second is that we designed a rotator that rotates the polarization direction to rotate the incident linearly polarized wave to any polarization direction.The device is a three-layer grid structure,and its rotation comes from multi-wave interference between the grids.The polarization rotation direction we want can be obtained by changing the relative rotation angle between the grids.Since the device has a sub-wavelength structure,the phase of the beam polarization of different frequencies does not change much when the beam is rotated,so the rotation is a broadband effect.When we reduce the thickness of the grid or the interval between grids,the bandwidth of efficient polarization conversion increases but the frequency band will increase.The device works in the X-band,with an index bandwidth of 1GHz and a center frequency of10 GHz,which meets the index requirements.The combination of simultaneous generation of multiple polarization beams with metasurfaces has always been the focus of research.In terms of the metasurface effectively controlling the polarization characteristics of the electromagnetic beam,the beam polarization conversion generated by the P-B phase theory is limited,that is,by rotating the P-B phase element,the imposed phase of the left-hand circular polarization generated by it is 2?,The resulting right-handed circular polarization has an imposed phase of-2?.Since the phases of the left-handed circular polarization and the right-handed circular polarization generated by the regulation of the beam based on the P-B phase theory have a strong correlation,the combination of polarization states cannot be generated arbitrarily.In order to break through the limitation of P-B phase theory on the generation of multiple beams by unit devices,we construct small resonant units based on the theory of geometrically scaled phases.The unit resonant structure is an L device.When a polarized wave in the x direction is incident,the reflected beam is circularly polarized.By changing the size of the L structure,we can obtain circularly polarized beams with different additional phases.Mirroring the L structure,we get a circularly polarized beam of opposite chirality.We choose eight resonant small units as a sequence unit,arrange the small units in different orders,can generate multiple polarization beam combinations at the same time,breaking through the P-B phase unit device can not generate circularly polarized waves and linearly polarized waves at the same time limit.