Laser diodes offer their own sets of benefits. For one, laser generates a much narrower
band of optical spectrum, making it easier to eliminate background light at the
receiver by using a narrowband optical filter, a benefit that will be discussed in more
detail in Section Receive Field of View (FoV). In general, more optical power can be
238 Chapter 9
generated using laser diodes than can be done with LEDs. Lasers also have optical
properties that make them more suitable for very long-range FSO systems.
Passive Fiber Coupled Systems Unlike active systems, passive systems do not contain
any active electro-optical components as part of the communication subsystem.
Passive Fiber Coupled Systems (PFCS) are designed to directly couple optical signals
coming out of a fiber-optic cable to its transmission optics without electrically regenerating
the signals. Similarly, they are designed to collect and inject the received optical
signal directly into the fiber-optic cable without electrically regenerating it. In its simplest
comparative description, PFCS can be thought of as serving the same purpose as
the directional antenna in RF wireless.
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