In this thesis, we explore advanced techniques to mitigate the effects of atmospheric turbulence in Free-Space Optical (FSO) communication systems. The focus is on the application of Mode Division Multiplexing (MDM) techniques in the receiver apparatus of FSO systems. After presenting the theoretical foundations and reviewing the state of the art of MDM-supported receivers FSO systems, we experimentally characterize an innovative solution based on Multi-Plane Light Converter (MPLC). We then evaluate its performance compared both to a photonic lantern approach and to conventional single mode fiber solution. The study demonstrates the potential of MPLC to enhance mode separation and reduce modal crosstalk, both of which are critical in improving signal robustness under turbulent propagation conditions.