This diploma thesis first handles the general issues concerning free space optics in the atmosphere, which will then discuss the components and adjustments modification RONJA in laboratory. The aim is to simplify the control of laboratory FSO with programming compensation for HyperTerminal and provide external simulation influences on the FSO measurements in non-standard situations such as fog. It was created RONJA terminal with just cursor control to communicate with the serial port, ping, and FTP protocol. In the last part of this work were measured by an abnormal situation on the optical link RONJA.