Study Of Generation And Transmission Characteristics Of Polarization Singularity Light Field

With the continuous development of optical technology,the properties such as wavelength,intensity,and phase of light have been deeply researched and widely used.Polarization,another natural property of light,has also attracted increasingly attention in recent decades.The polarization property carries abundant information,including not only the information of the light source,but also the information scattered by different objects during propagation.As a means to sense and explore the physical world,it has great application prospects.At present,the use of polarization properties of light has made significant progress in the fields of physics,chemistry and biological sciences,and provides important sensing,diagnostic,analysis and metrology tools in many fields of application.However,at present,there are few studies on the distribution of the polarization state of the optical field,and the abundant polarization information in the optical field hasn't be effectively utilized yet.To solve these problems,it is an important step to clearly understand the regular distribution of the polarization state of light field.In this thesis,polarization singularity,one of the polarization distribution laws of light field,is analyzed,and the generation and transmission characteristics of the polarization singularity field are studied.The polarization singularity of a light field refers to in the light field whose polarization states vary with spatial position,the distribution of the polarization ellipses around the circular polarization and the linear polarization follows a certain rule,and the circular and linear polarization in the field are polarization singularities.In this thesis,the method of obtaining a polarization singularity light field by using superimposing two orthogonally polarized beams under the condition of paraxial approximation are mainly investigated.Two cases of the orthogonal polarizations are researched.One is the orthogonally linearly polarized system,and the other is the orthogonally circularly polarized system.In orthogonally linearly polarized system,several boundary lines with special properties of the polarization state distribution in the polarization singularity field are selected,and are used to analyze the amplitude and phase distribution trends of the two components.Using the analysis results in reverse,a method for generating a polarization singularity is proposed by modulating the amplitude and phase of a single component.This method was found not only to obtain the desired polarization singularity mode but also has free space to modulate the polarization states distruibutions.Based on this method,the structure of the light field when the two polarization singularity modes are cross-coupled is analyzed,and the periodic arrangement of the cross-coupled structures,that is,the polarization singularity array is also numerically simulated.On the other hand,in orthogonally circularly polarized system,the relationship between the polarization ellipse parameters of the composite light field and the amplitude ratio and phase difference of the two components is analyzed.It is found that the azimuth of the polarization ellipse in the composite field is half the phase difference between the two components,and the ellipticity is equal to their amplitude ratio,and the effect of the amplitude ratio on the polarization states is emphatically analyzed.With this analysis conclusion,two components with different amplitude distributions and phase difference as vortex phases are used to obtain a polarization singularity field,and the hybrid singular light field obtained when one component is a double vortex beam is researched,and the influence of parameters such as amplitude distribution and vortex distance of the double vortex beam on the topological structure of the synthesized light field is studied,and for the first time such a rule is obtained:the amplitude of the double vortex beam will not change the topological structure of the synthesized light field,but may introduce a circularly polarized point without singularity;while the limti value of the parameter of the vortex distance will affect the topological structure.Also in orthogonally circularly polarized system,two novel light fields with high attention in recent yeas,Bessel beams and circular Airy beams,are used to generate a polarization singularity field,and its transmission characteristics are studied with fast Fourier transform method.Due to the self-healing property of Bessel beams,the polarization singularity field based on Bessel beams also has a self-healing prapagation characteristic,and the recovery of the topological structure of the polarization state of synthesized field is faster than the restore of the intensity of the components.To the polarization singularity field based on the circular Airy beam,it is found that the structure of polarization singularity is destroyed at the beginning of the propagation in free space,while it recovers after a certain transmission distance,and then the polarization ellipses of the entire light field rotate.The transmission characteristic is attributed to the autofocusing of circular Airy beams after analyzing.This thesis provides a theoretical basis for the application research of polarization singularity light field.