What is the term optical wireless communication? According to my point of view, in optical communication there msut be a medium so the refractive index should be capable of keeping the wave inside the medium. Can you explain it?
There's no reason why optical communication needs to be fibre optic.
Sending Morse code using an Aldis lamp is a form of wireless optical communication. For computers, IrDA was an early protocol, using infra-red LEDs to communicate between laptop computers and peripherals. More recently, LiFi has been put forward as a way to communicate around an office space - the computers and routers flicker bright LEDs at a rate too high for the human eye to percieve.