We outline our recent experimental studies on free-space optical (FSO) communications enabled by directly modulated quantum cascade lasers (DM-QCL) operating in the mid-wave infrared (MWIR, 3-5 μm) and long-wave infrared (LWIR, 8-12 μm) regions. Our research compares the performance of unipolar quantum optoelectronic (UQO) devices, including the QCL, and various detector types, such as quantum cascade detectors (QCD) and quantum well-infrared photodetectors (QWIP), each with distinct characteristics. In the last section, we get into the FSO experimental setup and reported results in the atmospheric windows.