avalanche photo diode (fiber optics) (APD)

An avalanche photodiode (APD) is a sensitive photodiode for converting light signals into electrical signals as used in optical network detectors.

The avalanche photodiode works with the photoelectric effect and multiplies the photon current by exploiting the avalanche effect. It is thus functionally equivalent to a photomultiplier. The APD photodiode operates in the negatively biased characteristic region, multiplying the photon current and by multiplication. The gain factor is about 100 and increases with negative bias. As the negative bias increases, hole-electron pairs are generated by absorbed photons. The avalanche effect occurs when the hole-electron pairs have absorbed sufficient energy and collide with the ions, holes and electrons.

In the APD diode, avalanche carrier multiplication (avalanche effect) results in higher sensitivity than other photodiodes or PIN diodes. It can also handle significantly higher data rates (up to 1 Gbit/s). Avalanche photodiodes have their spectral sensitivity up to wavelengths of 1,550 nm.