Multi-actuator lens systems for turbulence correction in free-space optical communications

Abstract: The implementation of efficient free-space channels is fundamental for both classical and quantum Free-Space Optical (FSO) communication. This can be challenging for fibre-coupled receivers, due to the time variant inhomogeneity of the refractive index that can cause strong fluctuations in the power coupled into the Single-Mode Fiber (SMF), and requires the use of Adaptive Optics (AO) systems to correct the atmospheric induced aberrations. In this work, we present two adaptive optic systems, one using a Fast-Steering Prism (FSP) for the correction of tip-tilt and a second one based on a Multi-Actuator deformable Lens (MAL), capable of correcting up to the third order of Zernike's polynomials. We test both systems at telecom wavelength both with artificial turbulence in the laboratory and on a free-space channel, demonstrating their effectiveness in increasing the fibre coupling efficiency.