Coherent Control Of Polarization Conversion In Metamaterials

Metamaterials,as a type of artificial composite materials,have specific properties that can not be obtained from natural materials.These properties can be achieved by designing sub-wavelength electromagnetic cells.It is a new research direction in the cross-discipline,and provides a new method and a new idea for optical devices,signal transmission and processing.At present,the storage and processing of optical information rely on electronics.If all-optical signal processing is used,the bit rate will be improved.In this thesis,the optical controlled metamaterials are studied,and the standing wave formed by coherent light is used to dynamically control the metamaterials,so as to realize the optical information processing.In this thesis,the polarization conversion characteristics of two kinds of metamaterials can be controlled by different forms of coherent incident light in the near-infrared band.The details are as follows:An S-shaped all dielectric metamaterial is designed,which has a polarization conversion effect illuminated by a single beam.It has a polarization conversion efficiency of 25% in both transmission and reflection directions.When the metamaterial is placed in the energy standing wave formed by two beams of coherent light of the same polarization state,the polarization conversion realized by the linearly polarized light excitation can be dynamically controlled.When the metamaterials are located at the electric or magnetic nodes of the energy standing wave,the polarization conversion will be strengthened or weakened respectively.Because the response of the metamaterials to the incident light of cross polarization state is similar,the polarization standing wave can be formed by two beams of orthogonal polarization coherent light,and the polarization state in the two output directions can be adjusted.This all dielectric polarization converter has no absorption,and the polarization conversion efficiency can reach 100%.It can be used for the conversion of polarized light to different polarization states,and the phase difference between two beams can be changed to simply adjust the polarization conversion of metamaterials.A phase gradient metasurface is designed.The structure unit of this metasurface is V-shaped metal antenna.It can produce a beam of co-polarized light with normal angle and a beam of cross-polarized light with anomalous angle.By using the energy standing wave to adjust the metasurface,we can simply modulate the intensity of the cross polarized output light through the phase difference,and will not make the beam distortion or reorientation at this anomalous angle.The intensity of the output light can be controlled by changing the phase difference between the two coherent beams transmitted in the opposite direction.The normal light of co-polarization and the anomalous light of cross polarization can be turned on or off coherently when the phase difference is different.If the phase gradient metasurface is placed in the polarization standing wave,the output light intensity of the metamaterial in the two radiation directions is constant in the coherent control process,but its polarization state can be dynamically controlled.When the phase difference is changed,the polarization state at the anomalous angle corresponds to the polarization state of the excitation light,which can change between linear polarization and circular polarization.The coherent control of metal metasurface can provide a good solution for wavefront shaping,multi-channel signal modulation and sensing.