Transmission ends if signal is blocked
A natural security feature of Free-Space Optics (FSO) is the need for there to be an uninterrupted signal between the transmitting/receiving units for the communication to be effective. If the signal becomes blocked for any reason, including by an unauthorized detector, the transmission will automatically end. With Free Space Optics (FSO) there is also an absence of what are termed side lobes, which is energy that is lost to the sides and back of the signal. This lost energy carries the same signal as the main transmission and can be picked up by someone other than the intended target.
A system and method of free-space optical satellite communications includes a ground station and transceiver for transmitting and receiving an optical communications signal. Adaptive optics at the ground station are operative with the transceiver for determining the shape of any distortions in the wavefront of the optical communications signal and compensating at the ground station for the distortions. A satellite includes a transceiver for transmitting and receiving the optical communications signal and includes adaptive optics for determining the shape of any distortions in the waveform of the optical communications signal and compensating at the satellite for the distortions. 
Paper: A survey of FSO networks
Paper: Investigation of suitability of RF signal transmission over FSO links