Generation Of Vector Vortex Beam Based On Reflective SLM And Analysis Of OAM Characteristics

The vector vortex beam with both anisotropic polarization and phase distribution is generated by jointly adjusting the optical field parameters such as phase and polarization state.It is a new type of structured beam with different polarization states on the same cross section of vortex beams.Due to the unique polarization phase characteristics and simultaneously carrying the orbital angular momentum(OAM),vector vortex beam has unique application potential in optical communication,optical micromanipulation and many other fields.Therefore,with the continuous deepening of application requirements,vector vortex beam generation systems with arbitrary polarization and phase modes are the foundation for the practical application of vector vortex beams.Thesis is based on the efficient generation of vector vortex light using a reflective spatial light modulator(SLM)and theoretical and experimental research on the OAM characteristics of the beam.The main work is as follows:(1)According to the working characteristics of reflective SLM and transmissive SLM,vortex beams generated by two different SLMs loaded with the same CGH were studied.Research has found that diffraction effect occurs after transmission SLM modulation,and the hollow light spots distributed on the left and right sides of the zero order diffraction light spot are respectively positive and negative first order diffraction light.As the topological charge gradually increases,the size of the dark empty light spot also increases,and the brightness of the light spot gradually decreases.By using reflective SLM to load the computed hologram,an ideal hollow light spot can be obtained,indicating that the utilization rate of light energy is weaker for transmissive SLM than for reflective SLM.(2)Through calculation and simulation,pure phase diagrams with different topological charges and polarization orders were obtained.According to the superposition principle of orthogonal left-right circular polarization vortices,an optical path system for generating arbitrary state vector vortex beams is designed based on reflective SLM,and an experimental optical path is built.By changing the phase distribution of the left-right component loaded on the spatial light modulator,the intensity distribution of the cylindrical vector beam obtained experimentally is consistent with the theoretical analysis.On this basis,by adjusting the topological charge value and changing the loaded phase information,arbitrary state vector vortex beams with different topological charges and polarization orders are generated.(3)The OAM theory is utilized to perform numerical calculations and analysis of the OAM density characteristics of the longitudinal component field of a vector vortex beam generated through construction of left-right circularly polarized vortices.The study investigates how the OAM density of the longitudinal component field is affected by the vector vortex beams topological charge and polarization order.Additionally,the OAM spectral characteristics of the vector vortex beams are analyzed through experiments involving the beam’s passage through a rotating ground glass.It is found that The OAM density distribution of the longitudinal component exhibits a hollow distribution,where the topological charges of the left and right spin components correspond to the negative and positive is attributions of the OAM density on the outer and inner layers,respectively.As the rotational speed of the ground glass of the rotating target increases,the homogenization effect on the speckle also increases,resulting in a dispersed OAM spectrum distribution,as seen in the experiment.The research results in this can provide some reference for the application of vector vortex beam in the field of space target detection and optical communication.