Binary wavefront control in the focal plane for improved fiber coupling in air-to-air laser communication

摘要

This paper investigates binary wavefront control in the focal plane to compensate for atmospheric turbulence in fiber-coupled free-space laser communication (LaserCom) systems. Traditional approaches to turbulence compensation (i.e., adaptive optics) modify optical phase in the pupil plane to improve the focal plane image or increase energy on target in the far field. For high-energy laser applications, focal plane phase modulation is problematic due to high power densities and device damage thresholds. However, LaserCom systems aim to use minimal power for reasons such as eye safety and covert communication. Thus, focal plane wavefront control is a reasonable approach for this application. Numerical results show that in an air-to-air scenario, binary phase modulation provides mean fiber coupling efficiency nearly identical to that resulting from ideal least-squares adaptive optics, but without the requirement for direct wavefront sensing. The binary phase commands are derived from a single imaging camera and an assumption about the nature of spot breakup. The use of binary wavefront control suggests that existing ferro-electric spatial light modulator technology may support real-time correction. Coupling efficiency results are also compared to those for the Strehl ratio, highlighting the importance of metric-driven design.