Fig. 1. Main types of for UAV. (a) Fixed-wing UAV; (b) tilt-wing UAV; (c) unmanned helicopter; (d) multicopter

Fig. 2. Illustration of for UAV 5G and beyond 5G wireless optical network architecture^[15]

Fig. 3. Optical wireless communication between UAVs and ground vehicle. (a) A team of micro unmanned aerial and ground vehicles deployed to a disaster area; (b) connectivity cone C with its parameters^[19]

Fig. 4. BER measurement of the optical wireless link for UAVs (Terminal 1) and GCSs (Terminal 2)^[24]. (a) From terminal 1 to terminal 2; (b) from terminal 2 to terminal 1

Fig. 5. A typical A2A FSO link^[28]

Fig. 6. UAV swarm^[31]. (a) Exchanging data with surveillance plane; (b) ring architecture; (c) star architecture; (d) meshed architecture

Fig. 7. Modular wireless optical elements and 10-module flat receiver array under test^[32]

Fig. 8. Illustrations of the optical uplink, optical downlink and the Doppler effects between UAV and satellite^[36]

Fig. 9. Laser communication scenarios from HAPs^[36]