Therefore, systems
with larger beamwidths can maintain the same level of eye safety while transmitting
more total power than systems with smaller beamwidths. For example, an FSO
system can transmit four times as much power as one with half its transmit beamwidth
while maintaining the same level of eye safety.
Another benefit of using a wider beamwidth is in reducing the effect of atmospheric
scintillation. Scintillation is an atmospheric phenomenon commonly observed as the
twinkling of stars or distant light sources. Scintillation produces a similar effect on
FSO systems, causing fluctuation in optical signals over long propagation distances.
Wider beams can reduce the overall signal fluctuation caused by scintillation because
of the averaging effect over a greater area. Scintillation will be discussed in more detail
later in separate section on this subject.
Both of the benefits derived from larger transmit beamwidths can also be achieved
by FSO systems using multiple transmitters. For example, an FSO system that uses
four transmit beams of 1-in diameter can achieve the same transmit power level and
the same safely level as a system using a single 2-in diameter transmit beam.
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