Study Of The Regulation And Evolution Mechanism Of Optical Singularities

In coherent light fields,singularities are often divided into two categories:phase singularity in scalar field;vector singularities and polarization singularities in vector fields.These two types of singularities are respectively related to phase and polarization properties,and often act as "skeletons" of the light field.In recent years,through the study of the fine topology structure of the light fields it has been found that singular beams have many unique properties in areas such as optical capture,information transmission,optical encoding,high-density storage,high-resolution imaging and so on,exhibiting a wide range of application prospects.The distribution,morphology,transmission and scattering properties,generation and measurement methods of singularities have become research hotspots of the discipline.This paper focuses on related issues theoretically and experimentally.First of all,a theoretical study of the shape,topological charge,mathematical characterization and discriminant methods of singular points under paraxial approximation is taken.Then based on the surface plasmon polaritons generated by the incident light on the surface of the sub wavelength metal structure,an annular apecture array structure is constructed,which can enhance the extraordinary optical transmission phenomenon.Since near-field diffraction does not meet paraxial approximation conditions,theoretical results of the singularities are generalized to non-paraxial approximation conditions.The distribution of the light field in the near-field diffraction pattern of the structure and locate the singularities in the light field is calculated by using the non-approximate finite-difference time-domain method.Moreover,the annihilation process of polarization singularities is obtained by calculating light field distributions under different diffraction distances.In order to achieve modulation and measurement of vector and polarization singularities,firstly a series of high-order and hybrid-order Poincare spheres are constructed using a pair of circularly polarized beams with vortex as the base.These spheres can be used to characterize so called full Poincare beams.Then an experimental method to modulate and mearsure a full Poincare beam with arbitrary parameters based on superposition of a pair of lights with orthogonal polarization state is proposed.A phase retarder is also used in the system.In addition to vector singularities and conventional bright C-points,we also succeed in modulating dark C-points with arbitrary topological charges.The experimental results then are used in reverse to derive the correlation between the parameters of the orthogonal polarized base lights and the characteristics of singularities in the modulation field.Subsequently,the widely used scalar Laguerre-Gaussian beams get vectorized to get vector Laguerre-Gaussian beams which belong to the class of full Poincare beams and study the characteristics of light field formed by the superposition of two such beams in free space propagation.The type and stability of various types of singularities in coaxial and non-coaxial superposition fields are analyzed in detail.Numerical simulation methods are used to show the process of generation,annihilation and transmission processes of them.Mathematical derivation formulas are given for the spatial distribution of various kinds of singularities as well.To further improve the encoding and information transmission quality of scalar singular light beams,a study in their scattering properties is taken.Througlh experiments it is proved that the average size of the speckle can be characterized by an autocorrelation dimension,which is related to the topological charge and intensity distribution of the beam.In order to quantitatively eliminate the interference of scattering,the scattering process is described in the form of a random complex matrix using discretization algorithm.Combined with optical weighing measurements,an experimental method is constructed for measuring such optical transmission matrices.Subsequently,an experimental setup is built,and the spatial transmission matrices of random scattering media with different particle sizes was successfully measured using full-field phase-shifting interferometry method.Further,according to the measured transmission matrix,the wavefront of the incident scalar vortex light is successfully reconstructed using time reversal method with a phase conjugate operator.The influence of particle size of random scattering medium on reconstruction results is analyzed.The verification of the validity of the generation and measurement of transmission matrix has been completed as well.The research work in this paper can provide a certain theoretical basis and experimental support for future research on the potential applications of singular optics.