Studies On Generation And Detection Technology Of Multi-phase Singularity Optical Vortices

Vortex beam,also known as “optical vortices”,is a light field with special phase structure.The particularity of vortex beam is that it has central isolated singularity and helical phase wavefront.The light intensity at the phase singularity is 0,and the phase at the beam center is uncertain,so its intensity presents a hollow ring distribution.Compared with other light fields,the most significant feature of optical vortices is that they carry orbital angular momentum(OAM).Therefore,optical vortices carrying OAM have important application value in particle control,high resolution imaging,chiral material processing,optical communication and other aspects.In order to realize the simultaneous manipulation of multiple particles,researchers focus on the vortex array.By coaxial superposition of two or more vortex beams,vortex arrays with different distribution characteristics of singularities can be formed.In order to regulate the properties of space waveguide arrays formed when periodic lattice light fields are illuminated to photorefractive crystals or atomic media,it is necessary to generate two dimensions(2D)optical lattice with different periodic structures.A two-dimensional optical lattice can be formed by off-axis interference of three or more beams.The common feature of these beams is that they all have phase singularities,and there are abundant physical phenomena near the singularities,which attract more and more scholars’ attention.Taking the interference between Laguerre Gaussian(LG0l)vortex beam as the starting point,this paper studies the generation and detection technology of optical vortices with multi-phase singularities.The main research contents are as follows:1.Generation of vortex beam and detection of its topological charge.The modulation principle of spiral phase plate(SPP)is analyzed theoretically.In the experiment,LG0 l vortex beams with different topological charges(TCs)are generated based on SPP,and the TCs of vortex beams generated in the experiment are preliminarily judged by inclined lens.In the experiment,the off-axis interference of two plane wave LG0 l beams and the coaxial interference of two LG0 l beams with different wavefront curvature radius are realized by Mach Zehnder interferometer(MZI),and the interference patterns with fork fringes and spiral fringes are obtained respectively.Combined with theoretical analysis and experimental verification,the relationship between TCs,tilt angle,azimuth,phase difference,curvature radius of two component vortex beam and interference pattern is summarized.The TCs of vortex beams based on interferometry broadens people’s understanding of the off-axis and coaxial interference characteristics of two vortex beams.By referring to the interference pattern,the azimuth relationship between the TCs of unknown vortex and the two beams can be judged more accurately.2.Generation and detection of multi-singularity optical vortex array.Vortex array are generated when two LG0 l vortex beams carrying different TCs are coaxially superimposed.Using analytical,numerical,and experimental techniques,the effects of TCs,relative power and beam waists of two component beams on the number,sign and distribution of singularities in the composite vortex beams are studied.Optical experiments based on the nested MZI verify the numerical results and theoretical analysis.The net TCs of the composite vortex beam depend on the beam waists and TCs of two component beams,and the radial position of new single vortices in the periphery relates to the relative power.The “vortex dipole” and “singularities splitting” phenomena are observed and analyzed.This study provides a thorough study on the composite vortex beam,and may find potential applications in particle manipulation,optical communication,etc.3.Generation and detection of 2D optical lattices.A theoretical model of 2D optical lattices generated by off-axis interference among three beams was established.In the experiment,based on nested MZI,2D optical lattices were generated by off-axis interference of three planar vortex beams at a certain angle.By controlling the tilt angle and azimuth angle between the three coherent beams,the structural morphology of 2D optical lattices can be controlled,and a single vortex with periodic distribution exists between the optical grids.By changing the TCs of three coherent beams,2D optical lattices with point defects and edge dislocations in the center are generated.