The Research On Vortex Beams Generation Method Based On The Annular Core Fiber

Vortex beams have more advantages than traditional polarized beam in particle trapping,metal cutting and other application fields.Therefore,the research on vortex beams generation method is necessary.The passive generation method based on optical waveguide receives concern.This method follows two ways.One is two LP₁₁ modes interference superposition generating vortex beams.The second is to achieve mode selection that degenerate mode can be distinguished with effective refractive index increasing between guide modes.In this thesis,based on the optical fiber mode theory and the polarization selection property of metal layer,the following works have been done:?A?A method for generating vortex beam based on the wall of waveguide type fiber has been studied.The method uses the principle that increasing the effective refractive index between modes makes degenerate modes be distinguished.First,analyze the relationship between different mode and fiber index,radius,core thickness,while analyze the difference effective refractive index between TM₀₁ mode and degenerate mode.Secondly,optimizing the fiber structure parameters to obtain a fiber both to meet guide mode cut-off to TM₀₁ mode and the TM₀₁ mode separated from other modes.Finally,demonstrate this fiber can generate vortex beam,and the beam is polarization maintaining in a symmetrical circular waveguide.?B?A novel method for generating vortex beam based on the inner wall of waveguide type fiber has been proposed.The method utilizes the transmission characteristics of metallic coating waveguide and the polarization-selective effect of the metal layer.First,simulate the mode distribution of this fiber in which between the inner wall and the air hole is coated with a layer of metallic silver.The electric vortex of guide mode is radial direction and the metallic coated fiber can be polarization selection.Then,design and build the vortex beam generating apparatus.Ultimately,experiment achieves and detects the generation of vortex beam.