Investigation Of Orbital Angular Momentum Beam Generation And Manipulation Based On Geometric Metasurface

Light with orbital angular momentum(OAM),commonly named vortex beam,is a peculiar type of beam which has doughnut-like intensity distribution and helically structured wavefront.The phase term of the vortex beam can be expressed as exp(il?),where ? is the azimuthal angle and l is the value of the OAM beam or the topological charge of the vortex beam,which can be any positive or negative value.Each photon of the vortex beam has certain orbital anular momentum of l?.The special characterizes of OAM have attracted a great deal of interests from many applications,such as optical communications,optical micromanipulation and optical detection.For instance,the infinite value of the topological charge can be used to encode the information,which can improve the information capacity and security.The orbital angular momentum and doughnut intensity profile of the vortex beam can be employed to spin and capture the particles.The vortex beams are conventionally controlled using spiral phase plate,spatial light modulators,computer generated holograms,or cylindrical mode converter.However,these generators often suffer from several drawbacks,such as the bulky size,curved surfaces and complex system.Such drawbacks are inimical to the development of the vortex beam in the area of the microelectronic integration.In recent years,an artificial material-metasurface has attracted great attentions due to its unprecedented functionalities of manipulating the amplitude,polarization and phase of the light at the two dimensional and planer surface.Thus the vortex beam can be controlled by the metasurface.In this dissertation,we investigate the generation and detection of the vortex beam based on the geometric metasurface that is based on a Pancharatnam-Berry phase change principle.The main works and results in this dissertation are listed as follows:1.A metasurface that can realize the generation and detection of the vortex beam is proposed.The two metasurfaces which can realize the generation and detection of OAM beam are integrated in different area.In order to obtain an appropriate integrated method,we investigate the behaviors of the various integrated method.The method that reference beam surrounds the OAM beam is choosed as the appropriate way.To realize the metasurface,the elliptical nanohole is selected as the components of the metasurface.Varying the major axis orientations of elliptical nanohole can obtain the phase shift of cross-polarization transmission light from 0 to 2? for circularly polarization light illumination.The elliptical nanoholes are hexagonally placed to reduce the interference generated by the adjacent elements.The elliptical nanoholes are arranged according to the phase profile of the OAM and reference beam.The characteristics of the metasurface are experimentally confirmed by the custom-built microscope test system.2.The phase and amplitude controlled vortex beam array based on the metasurface is proposed to overcome the drawbacks,such as bulky size,unequal energy in different diffraction orders and the interference of the high order lights,lie in the present generators.The effects of the phase and amplitude modulations in the generation of the beam array is analysed.The high quality beam array will be obtained with simultaneous phase and amplitude control.Simultaneously,the phase and amplitude changes of the cross-polarized components with the change of the orientation of the two type rectangle nanohole are analysed.Due to the subwavelength size of the metasurface,the high order diffraction light can be eliminated.The designed metasurfaces are finally measured using the microscope test system.The uniformity of the beam array with phase and two level amplitude modulations is about 0.14 in the experiment.The experimental result is near to the theoretical result of 0.1 and better than the phase modulation results of 0.46.3.The two wavelength modulated three-dimensional volumetric OAM beam based on the metasurface is proposed.According to the resonance characteristic of the silicon nanorod,the super unit cell composed by two nanorods with different size on the glass substrate can realize the wavelength selection and phase modulation is obtained.The nanorods with different size can realize different wavelength modulations.According to the point source algorithm,the three-dimensional volumetric OAM beam is realized.The numerical simulation results agree well with the desire results.