Research On The Influence Of Optical Spatial Distribution On Mixing Efficiency

Compared with traditional free-space optical communication,coherent detection has high sensitivity and has the advantages of long communication distance and flexible modulation mode,and has gradually become the research focus of many scholars.The research on the influencing factors of the mixing efficiency of the coherent detection system can provide a basis for the improvement of the performance of the coherent detection system.This dissertation mainly studies the mixing performance of different combination models when the signal beam and the local oscillator beam have different spatial distributions,and the performance of the vortex optical coherent detection system under oblique transmission.The work included is as follows:1.Elaborated the basic principle of coherent detection,the mixing efficiency of different combination models is analyzed theoretically when the signal beam is Uniform,Gaussian distribution and vortex beam,and the local oscillator beam is Gaussian,Airy,and Uniform distribution;discussed the signal When the beam is Uniform distribution and the local oscillator beam is Gaussian distribution,factors such as primary phase difference,spot size,and Gaussian beam waist radius affect the mixing efficiency.2.When the signal beam is a vortex beam,by changing the topological charge of the local oscillator beam,the coherent demultiplexing of the vortex beam can be realized at the receiving end.The coherent demultiplexing performance of the vortex beam multiplexing is studied.The effects of topological charge numbers,altitude,and transmission distance on the performance of the vortex optical multiplexing communication system are analyzed.3.Set up a beams path to conduct experimental research on the influence of vortex optical coherent detection,verify the feasibility of the vortex optical coherent detection,and prove that under the same transmission distance,with the increase of the topological charge between the signal beam and the local beam,the coherence gain gradually decreases.Corresponding to the theoretical calculation results.Studies have shown that the spatial distribution of the signal beam and local oscillator beam will affect the heterodyne mixing efficiency.As the structural constant of the atmospheric refractive index increases,the mixing efficiency decreases gradually.When both the signal beam and the local oscillator beam are Uniform distribution,the suppression effect on atmospheric turbulence is the best,and the influence of turbulence is the least.The wavefront distortion caused by atmospheric turbulence will destroy the orthogonality between the signal beam of different topological charges and the local oscillator beam wavefront;the same set of adaptive optics systems is used to correct the signal beam wavefront of the uplink and downlink,and the comparison and analysis According to the changes of wavefront distortion pre-correction and post-coherence gain,it is found that the post-correction effect of the downlink is better than the pre-correction effect of the uplink,which lays a theoretical foundation for multi-channel vortex optical multiplexing transmission.