Research Of The Coherent Optical Communication System With Wavefront Sensorless

Coherent optical communication has attracted widespread attention due to its high detection sensitivity,multiple modulation methods and large communication capacity.Due to the randomness of the atmospheric turbulence,the wavefront of the signal beam is distorted after transmitted through the atmospheric turbulence,and the mixing efficiency of coherent communication system is reduced.Adaptive optics can effectively compensate the wavefront aberrations of the signal beam and keep the communication link stable.Therefore,the study of adaptive optics has important theoretical significance and practical value.In this paper,the wavefront sensorless adaptive optics technology is used to correct the distortion wavefront in coherent communication system.The main work included:1.Based on the structure and principle of wavefront sensorless adaptive optics system,the peak-to-valley value,root mean square value,far-field spot strehl ratio(SR)and mixing efficiency of coherent optical communication system were derived.Based on the theory of laser atmospheric propagation and Fresnel diffraction principle,combined with Hill spectrum model,the change of laser spot after laser beam propagating through atmospheric turbulence was investigated.2.Using the SR of the far field spot as the objective function of the system,the ability of the wavefront sensorless adaptive optics based on stochastic parallel gradient descent(SPGD)algorithm under different turbulence intensities to correct the wavefronts distortion was analyzed,and the influence of different algorithm parameters on system performance was discussed.3.Developed an adaptive optical experimental platform with wavefront sensorless.Using the light gray value detected by the charge coupled device(CCD)camera as the objective function of the system,and verified the correcting ability of the SPGD algorithm for the signal wavefront distortion at different turbulence intensities.4.The coherent optical communication experiment system based on wavefront sensorless adaptive optics technology was developed.The optical power coupled into a single-mode fiber was used as the objective function of the system,and the optical correction ability of the SPGD algorithm for the signal wavefront distortion after transmitting 600 m and transmitting 1300 m were verified respectively.The experimental results demonstrate that the objective function of the system after signal wavefront aberration corrected by adaptive optics(the mean gray value of 100 pixels at the center of the spot detected by the CCD camera)was increased from 119.8,84.6 and 35.7 to 246.6,249.1 and 245.7 respectively.In the field experiment of 600 m and 1300 m,the optical power value coupled into single mode fibers was increased from-36.32 dBm and-43.68 dBm to-10 dBm and-27.1 dBm respectively.It shows that the adaptive optics technology with wavefornt sensorless can effectively compensate the influence of atmospheric turbulence on signal beam and improve the coupling power of single mode fiber in coherent optical communication system.