From all perspectives,
the receive optics in FSO systems serve the same purpose as antennas do in RF wireless
systems??”they collect the signal. The receive optics are characterized by two key parameters:
the receive aperture and the field of view (FoV). A simple form of receive optics is
illustrated in Figure 9.3.
Receive Aperture Receive aperture is the diameter of the receiver through which
the received signal is collected. It is, therefore, a key factor in determining the amount
of light collected by the receiver. A receiver with twice the receive aperture can collect
Optical Wireless Mesh Networks 241
four times the amount of light. A larger aperture also has the benefit of mitigating the
effect of atmospheric scintillation due to averaging over a greater area of the receiver.
However, as in the case of transmitter optics, the downside of using a large aperture is
the size, weight, and cost of the system.
Unlike transmitter optics where multiple transmit beams can be used to transmit
more power, using multiple receive optics to increase the amount of received signal
collected is not always efficient because of the challenges in combining the signals
received from multiple receivers.
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