The 1550 nm IR beam has the benefits of
being slightly less susceptible to atmospheric effects and safer for the human eye than
850 nm IR beam. However, the current state of transmitter and receiver technology
makes it less cost-effective.
Unlike RF wireless, FSO does not use sophisticated modulation techniques. FSO
systems, in general, use the same modulation techniques as fiber-optic systems do,
referred to as On-Off Keying (OOK) modulation, where the optical signal is turned ON
or OFF to transmit the ???1??? or ???0??? state of a bit in a digital datastream.
One of the key differentiations between the transmission technique of FSO and fiber
optics is the optical power transmitted. In fiber-optic systems, signals do not experience
significant loss as they travel from the transmitter to the receiver, as they do in the case
of FSO due to geometric spreading and atmospheric attenuation of the signals. In the
case of fiber optics, only a very small fraction of the transmitted light gets lost over a
comparable distance. On the contrary, in the case of FSO, only a very small fraction of
the transmitted light actually makes it to the receiver.
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