A free space optics (or optical wireless) system can be thought of as a "radio"
system that uses infrared "light" instead of radio waves, or as
an optical communications system that transmits laser beams point-to-point
through the air, instead of along a fiber optics cable.
Unlike radio and microwave systems, no spectrum licensing or frequency coordination
with other users is required, interference from or to other systems or equipment
is not a concern, and the point-to-point laser signal is extremely difficult
to intercept, and therefore secure. Data rates comparable to fiber transmission
can be carried with very low error rates, while the extremely narrow laser
beam widths ensure that it is possible to co-locate multiple tranceivers without
risk of mutual interference in a given location.
Freedom from licensing and regulation translates into ease, speed and low
cost of deployment. Since optical wireless transceivers can transmit and receive
through windows, it is possible to mount them inside buildings, reducing the
need to compete for roof space, simplifying wiring and cabling, and permitting
the equipment to operate in a very favorable environment. The only essential
requirement is line of sight between the two ends of the link.