Bit Error Rate Determination Of A Free Space Laser Communication System Using Adaptive Optics

Recent experiments performed at UNC Charlotte indicate a reduction in the bit-error rate for a laser communication system with the implementation of higher order adaptive optics in a free-space communication link. Using a commercially available atmospheric turbulence phase plate, both our adaptive optics system and the free-space laser communication system were characterized in performance as a function of the turbulence applied. The atmospheric turbulence phase plate was characterized and shown to have four distinct regions of turbulence representing D/r[subscript]0 values of 0.8, 1.4, 1.5, & 2.3 with a 2mm diameter beam. The adaptive optics system incorporated in the free-space laser communication system was shown to consistently improve the Strehl ratio of the turbulent beam for each of the turbulent regions of the phase plate for static turbulence. For dynamic turbulence it was shown that the adaptive optics system could keep up with each turbulent region until a D/r[subscript]0 value of 1.5 and a velocity of 0.4 beam diameters/sec. The bit-error rate of the free-space laser communication showed improvement over the uncorrected aberrations with the adaptive optics system in operation for each turbulent region of the atmospheric turbulence phase plate. The most marked improvement was the decrease of bit-error rate by a factor of 43 for turbulence corresponding to a D/r[subscript]0 value of 0.8.