Generation Of Orbital Angular Momentum Beams By Metasurface

Orbital angular momentum(OAM)beams refer to a kind of beams with helical phase-front.A phase exp(il?)can always be found in the field expression of OAM beams,which depends on the azimuthal angle ? and integer l.Therefore,it endows OAM beams some special characteristics,such as spirally wavefronts,phase singularities,and ring-like intensities,so OAM beams can also be called vortex beams or hollow beams.Owing to these charming properties,OAM beams bring novel applications in micro-manipulation,communication,biophysics and optical data storage.The generation of OAM beams has received a great deal of attention.Unfortunately,the usual methods to produce OAM beams are restricted to limited conversion efficiency and single polarization.A new approach is proposed to enable a beam to carry OAM by using metasurfaces.The metasurfaces have high conversion efficiency and can manipulate the polarization of light accurately.OAM beams with any desired homogeneous polarization can be obtained by our scheme.The main works we do in this thesis are as follows:1.We introduce the theory related to the OAM beams and metasurfaces.The origins and application status of OAM beams are summarized,and then several usualgenerating methods of the OAM beams are introduced.We also give a introduction of the research progresses and applications of metasurfaces.2.A new approach is proposed to enable a circularly polarized beam to carry OAM and manipulate the OAM of vortex beams by using metasurfaces.The method to produce OAM beams and manipulate the OAM of vortex beams using metasurfaces is studied theoretically in this thesis,and further experiments verify the theoretical results.The experimental results are highly consistent with the theory.3.We present a simple and effective method to generate OAM beams with any homogeneous polarization.We introduce the concepts of vector beams,Then the method of producing vector beams by metasurfaces is introduced in detail,and the vector beams we have obtained are used to generate OAM beams with arbitrary homogeneous polarization.