Study On Propagation Through Atmospheric Turbulence And Adaptive Optics Of OAM Beams

OAMτOrbital angular momentumυbeams, known as optical vortices, are attractingmore and more attentions due to their characteristics of helical wavefront and doughnutintensity distribution. OAM beams have been applied in many field, such as opticalmanipulation, quantum information technology, remote sensing, and optical communication.This thesis focuses on the propagation through atmospheric turbulence and adaptive opticsof OAM beams. The main contents of this thesis are as follows:1. In order to study the propagation of the OAM beam through atmospheric turbulence,scalar diffraction theory is used. We simulate the diffraction of OAM beams by usingMatlab, and verify the accuracy of diffraction calculation.2. Kolmogorov turbulence theory and phasescreen theory are described. The powerspectrum method is used to generate phasescreen for the simulation of atmosphericturbulence. The simulation results show the distortion of OAM beams. The OAM spectratheory is also studied to illustrate the distorted OAM beams. It was found that propagatingin weak turbulence and moderate turbulence, OAM beams can keep a relatively high purityand in strong turbulence, OAM beams suffer a heavy damage.3. The adaptive optics is studied to improve the quality of distorted OAM beams afterpropagating in atmospheric turbulence. A scheme based on GS algorithm is proposed. Inthis scheme, a Gaussian probe beam which progagates through the atmospheric turbulencetogether with OAM beams is used to detect the distorted wavefront, then we get a correctedphase which can amend the wavefront of OAM beams. In weak turbulence and moderateturbulence, the proposed scheme works well and improve the quality of OAM beamseffectively, but in strong turbulence, the intensity and phase of OAM beams after correctingare still very tanglesome. Besides, we put forward a method involve withperiod-gradually-changing grating to measure the OAM beams, and use this grating todetect OAM states after correction. The results fit well with the analysis of OAM spectra.