ABSTRACT
Receivers convert optical inputs back into electrical inputs. A photodiode converts the electrical signal into a current signal. Because the received optical signal and resulting electrical current have small amplitudes, the receiver will usually contain one or more amplification stages. A receiver is generally designed to be used with a particular transmitter. A receiver consists of a photodiode, bias resistor, and low–noise preamp. A complete receiver system may incorporate a number of support functions. One of the most common is clock recovery. The photodiode converts the optical signal directly into electrical current, using the reverse of the physical process in the light emitting diode. There are two types of photodiode structures: the PIN and APD. The APD photodiode, with its more complex structure, amplifies the signal current within the photodiode itself. The two heavily doped layers produce junction breakdown at relatively low voltages.
