The Research Of Beam Centroid Detection Technology Of Space Optical Communication System Based On Orbit Angular Momentum

Optical Vortex (OV) is a kind of optical beams with spiral wavefront structure, which has unlimited eigen-states corresponding to different azimuthal index. Since the eigen-state is orthogonal to each other, the vortex beams could carry infinite bits of information. With above features, Optical Vortex beams can be applied to space optical communication to improve communication capacity.Nevertheless, Optical Vortex beam communication needs extremely high alignment accuracy. Any azimuthal or axial offset would reduce the receiving power and degrade the performance of communication system. Therefore, we must solve the problem of misalign of beam and the aperture adaptation before we applied the vortex beam to the space optical communication system. In this paper, an improved algorithm was proposed by studying the centroid detection algorithm of vortex beam, and the performance of the algorithm is analyzed. The main work and results are as follows:Firstly, we built the model of space optical communication based on orbit angular momentum and analyzed the ATP (Acquiring, Pointing, Tracking) system and the influence of atmospheric turbulence on ATP system and vortex beam.Secondly, a modified centroid detection algorithm for beam centroid was proposed for the core algorithm of the offset correction. Moreover, we evaluated and summarized the performance of the algorithm when the Laguerre-Gaussian(LG) beam transmitting in the free space and the atmosphere turbulence. The simulation experiments show that the new algorithm, compared with the centroid algorithm, has 2 orders of magnitude higher in computing accuracy and 3-4 orders of magnitude higher in stability. However, the computing time has increased by about 1.5 times compared with the centroid algorithm.Thirdly, the adaptation of the width of optical beam and the aperture of receiving system was studied. And a schematic of beam width control was designed. The simulation experiment shows that the schematic can meet the requirement of aperture adaptation and improve the performance of modified algorithm.