Compensation of Emulated Atmospheric Disturbance and Tracking of a Moving Object by a Real-Time Digital Phase Conjugate Mirror Using a Liquid Crystal Spatial Light Modulator

We developed a fast-response digital phase conjugate mirror using a 700 Hz high-speed liquid crystal spatial light modulator and a high-speed camera. The total delay from signal light acquisition to phase conjugate light generation was 9.7 ms at 1246 × 1024 and 5.9 ms at 640 × 512. The tracking experiment performed on a target moving at a constant distance perpendicular to the optical axis, produced an error of 2 %. Furthermore, a heated soldering iron, used to compensate for artificially generated air disturbance, showed that beam wandering and intensity fluctuations were reduced by 86 % and 55 %, respectively, compared to a phase conjugate mirror with added delay. Phase conjugate light irradiation of a continuously moving target at a maximum speed of 0.9 mm/s was also performed. This study shows that real-time digital phase conjugate mirrors can correct wavefront distortion caused by air fluctuation, which is a major challenge in long-distance wireless optical transmission in the turbulent atmosphere, without complicated control, and prevent beam quality degradation in the presence of atmospheric disturbance.