Adaptive Compensation Method Without A Wave-Front Sensor Of Free Space Optics Communication

Free Space Optical-communication is research hotspot and frontier in communication because of its high capacity, high rate, strong confidentiality and so on. The transmission media of FSO is atmosphere, so atmosphere turbulence will have an effect on the system. In order to weaken the communication performance degradation caused by turbulence, adaptive compensation method of FSO system through turbulence is researched, effective method of improve FSO communication performance is explored, which is significative of functionization and engineering on FSO.Improvement on FSO communication performance by applied Adaptive Optics without a wave-front sensor is researched, which is based on Adaptive Optics technology principle and transmission characteristic through atmospheric turbulence. Principles and system models for adaptive optics technique without a wave-front sensor are discussed, emphasis on principles of three algorithms in aberrant wave-front correction, that is differential evolution(DE) algorithm, stochastic parallel gradient descent(SPGD) algorithm and simulated annealing(SA) algorithm. Through correction of phase with different fluctuation variance by the three algorithm, good performance on aberrant wavefront correction. Effect of atmospheric channel on laser transmission is simulated, different strength turbulent phase screen based on power spectrum method and Fourier transform and Zernike polynomial method have been generated under Kolmogorov spectral model, and discussion on far-field intensity through turbulence has been given out. Adaptive optics technique without a wave-front sensor dispense with a wave-front sensor and unconstrained by scintillation effect, it is applied in FSO system to compensate aberrated wave-front caused by turbulence. Numerical simulation on application of adaptive optics technique without a wave-front sensor to FSO system has been obtained based on DE, SPGD and SA algorithms.Effect of parameters in DE, SPGD and SA algorithm on convergence rate and extremum are discussed respectively, Suitable range have been given based on performance function after correction. Adjust suitable parameter of three algorithm, variation of bit error rate(BER) and scintillation index have been analyzed based on receiver intensity before andafter algorithm correction in different turbulence intensity. Results show that adaptive optics technique without a wave-front sensor based on these three algorithms can improve FSO receiver intensity and coupling efficiency, BER can be reduced below 610- under the ratio of noise to ideal intensity is 0.008, but intensity fluctuation cannot be weakened. Through comparison of three algorithm on correction speed and result, DE algorithm has the best correction in strong turbulence, but it also needs the most iterations, the correction result of SA is better than SPGD algorithm, the iterations SA needs is more. So in practical application, systemic needs such as convergence rate, correction result and so on should be considered to select suitable algorithm.