ABSTRACT
Optical communications is a very old form of data transfer. Line-of-sight primitive digital systems have
included lighting bon fires on mountain tops to send a simple one-bit message, smoke signals to send a
multiple-bit message, and ship-to-ship broad-incoherent-beam transmission of Morse-code messages.
The inventions of the low-loss optical fiber1 and the high-speed semiconductor laser2 have caused an
explosion in the transmission capacity of optical systems.3 We will discuss in this chapter the technologies
behind sophisticated optical systems, some of which can transmitO10 trillion (10!1012) digital bits of
information per second across transpacific distances.4 In addition to higher capacity, tethered systems
have lower loss and higher security than untethered systems. We will therefore focus on the discussion of
fiber-based transmission systems.
