The Propagation Characteristic Of The Helical Structured Laser Beam And Its Application In Optical Communication

Light beams with special structure of helix play an important role in in both classical and quantum fields,such as optical communication,data storage,microscopy imaging,materials processing,optical measurement,and astronomy.The helical structure is divided into phase and intensity type.Vortices are well known for their helical phase structure,and their photons carry orbital angular momentum.This thesis studies the motion of single vortex and double vortices in circular Airy beam,and discusses the interaction and mutual evolution process of double vortices in this self-focusing beam.Higher-order Bessel beam is the exact solution of the Helmholtz equation.The photon has orbital angular momentum and has a helical phase.This thesis discusses the transmission characteristics of Bessel beam of different orders.With the superposition of high-order Bessel beams,high-order Bessel beam and plane wave,high-order Bessel beam and circular Airy beam respectively,light intensities with different helical structures are constructed,and the relationships between their periods and various parameters are calculated.Finally,a new encoding/decoding method for optical communication is proposed by using the periodicity of the spiral structure,and this hexadecimal communication mode is realized in experiments.The specific chapters of this thesis are arranged as follows:The first chapter introduces the research background and significance of helical structure beams with phase-type and intensity-type,as well as the research status at home and abroad.It gives the main theoretical basis of the beam transmission involved and clarifies the main research content,innovation points and the arrangement of each chapter.In the second chapter,the propagation dynamics of the circular Airy beam load with vortices is studied.The tailoring effect of the loading distance between two vortices on the focus of the circular Airy beam is observed experimentally,and the interaction between these two vortices during propagation is discussed.The modulation mechanism of the light intensity in the focal plane is studied.Chapter 3 discusses the transmission dynamics of Bessel beam loaded with different parameters,and demonstrates that the superposition of high-order Bessel beam and Gaussian beam,and the superposition of high-order Bessel beams to generate spiral beam intensity,the periodic interval of the spiral intensity structure is calculated.Chapter 4 constructs a light beam with both a ring structure and a helical structure by the superposition of high-order Bessel beam and circular Airy beam.The period changing with distance is theoretically studied,the beginning position of the light intensity structure transformation is calculated,and the self-healing properties of the beam are discussed.Chapter five proposes a new idea of hexadecimal encoding/decoding using the periodic braiding characteristic of beam,and the method is successfully implemented in the laboratory.The communication security of this method is discussed.Chapter 6 summarizes the research content of this paper and looks forward to future work.