A fiber-optic receiver is a device that takes a signal in the form of light, usually from a fiber-optic cable, and converts it to an electrical form. The signal is then usually sent to an electrical receiver, and the electrical signal is then translated back to its original form, which is often data, audio or video. Receivers are usually combined with several other devices to transport the signals in a fiber-optic network.
The key component of the fiber-optic receiver is the photodetector, which transforms the light signals to electrical ones. In most modern fiber-optic receivers, the photodetector is a semiconductor photodiode. This photo diode is a very small device that is typically built into the electrical circuitry of the receiver. It forms an integrated package that provides amplification of the signals, as well as connections for the supply of power. Fiber-optic receivers generally come in three different photo diodes: positive-intrinsic-negative (PIN) photo diodes, positive-negative (PN) junctions, and avalanche photo diodes (APDs).
It is important that the fiber-optic receiver be able to accurately regenerate and decode the encoded stream of data over the entire range of power levels from the optical signal. Equally as important is the capability to take the encoded/decoded signals and move them over the entire bandwidth of the network. This allows for less degradation of the signal across the network.
Typically, a fiber-optic receiver is paired with a transimpedance amplifier and a limiting amplifier. The function of the transimpedance amplifier is to amplify the optic signal from the photodiode into a relatively larger amplitude electrical signal, which helps to take care of any distortion or attenuation that the signal has gone through while passing through the network. A limiting amplifier protects the components from input overdrive. There may also be more processing done to the signal, such as clock recovery from data (CDR), which is performed by a built-in control system known as a phase-locked loop.
A fiber-optic receiver may also be a transmitter or transceiver, meaning it includes both receiver and transmitter functions. Regardless if it is a fiber-optic receiver, transmitter, transceiver, or all three, it will have both optical and electrical elements. It may also be paired with a fiber-optic regenerator which can further boost the signal if it has to travel over a long distance. Even though most receivers have signal regeneration capabilities, the extra boost is often needed in very large networks, such as metropolitan area networks (MANs).
