To use fiber optic cables for communications, electrical signals must be converted to light, transmitted, received, and converted back from light to electrical signals. This requires optical sources and detectors that can operate at the data rates of the communications system.

There are two main categories of optical signal sources—light emitting diodes and infrared laser diodes.

Light emitting diodes (LEDs) are the lower-cost, lower-performance source. They’re used in applications where lower data rates and/or shorter distances are acceptable. Infrared laser diodes operate at much higher speeds, dissipate higher power levels, and require temperature compensation or control to maintain specified performance levels. They are also more costly.

Signal detectors also fall into two main categories—PIN photodiodes and avalanche photodiodes.

Similar to sources, the two types provide much different cost/performance ratios. PIN photodiodes are more commonly used, especially in less stringent applications. Avalanche photodiodes, on the other hand, are very sensitive and can be used where longer distances and higher data rates are involved.