Experimental Study On Eigenmode Method Correction Of Beam Distortion

In free space optical communication(FSOC),it is inevitable to be affected by atmospheric turbulence effect in the process of transmission,which makes the signal wavefront distorted.In order to improve the communication quality of FSOC system,adaptive optics technology has been widely studied,among which the mode based wavefront sensorless adaptive optics(WSAO)has great application potential due to its fast correction speed.This paper mainly studies the WSAO technology based on deformable mirror eigenmodes method was used to correct the distorted spot in FSOC system.The main work of this paper is as follows:1.The power spectrum inversion method based on hill spectrum is used to simulate the atmospheric turbulence with different intensities,and the distortion spot under the influence of atmospheric turbulence with different intensities is simulated and analyzed;The components and working principle of WSAO system are introduced,the expression of common beam quality evaluation index is deduced.2.According to the actuator influence function of 69 element high-speed deformable mirror,the corresponding 69 order deformable mirror eigenmodes is derived;and the system simulation model was established by combining Fresnel diffraction and multi-phase screen transmission principle;Analyze the best value of mode bias in different cases;The ability of the proposed method to correct the distorted spot was studied by using strehl ratio as the evaluation index;The system performance is analyzed with the fast convergence ratio of the system as the index;And the numerical simulation of various correction algorithms is carried out,and the differences between them are analyzed and compared.3.Build indoor and outdoor experimental systems to verify the practicability of the system.The indoor experiment results discover that the proposed method can increase the strehl ratio of the system from 0.11,0.32,and 0.56 to 0.57,0.71,and 0.88,respectively;The outdoor experiment results confirm that the proposed method can correct the wavefront distortion caused by dynamic atmospheric turbulence,and the strehl ratio of the system can be maintained at about 0.85.The results show that the wavefront sensorless adaptive optics technology based on deformable mirror eigenmodes method can effectively correct the wavefront distortion caused by atmospheric turbulence in FSOC system,and the convergence speed of the algorithm is fast,which has obvious effect in practical application.