Simplex-based wavefront control for the mitigation of dynamic distortions caused by atmospheric turbulence

Laser communication systems operating in the atmosphere require certain power and beam quality to establish and maintain a reliable communication link. Although such systems utilize the most advanced materials and technologies, their performance is adversely affected by optical turbulence, often posing a serious problem, even for short-range links. Atmospheric effects change optical properties of the propagation channel, causing signal fades, beam wander and scintillations. A common method of mitigating turbulence effects suggests dynamic wavefront control. In this paper the proposed technique is based on correction of the distorted beam using an electrically addressed programmable spatial light modulator (SLM). The phase profile that we impose on the distorted laser beam is described using Zernike formalism to calculate the wavefront OPD function. The Nelder-Mead simplex optimization algorithm is used as a correction procedure that provides fast results, required for real-time operation. In general, calculation of the required phase profile for an SLM with large number of pixels could be highly computationally intensive. Coupling modulator inputs to the first several Zernike coefficients allows significant reduction of the dimension of the optimization problem. The algorithm is tested in the simulation environment and its ability to compensate dynamic distortions is assessed. The results show that both dimension of the input space and the initial conditions affect the speed and convergence to a particular minimum. Recommendations for improving the system performance are also presented.