Controlling the multiplication factor of avalanche photodiodes in optical receivers.

摘要

In avalanche photodiodes (APD), noise increases above a temperature-dependent value more rapidly than the multiplication factor, so that the signal-to-noise ratio deteriorates, possibly leading to a rise in the bit error rate in the transmission of digital signals, while the bandwidth also decreases as the multiplication factor rises. The multiplication factor is dependent on the bias voltage of the avalanche photodiode, so that it is appropriate to control the multiplication factor by controlling the bias voltage or bias current. A low-amplitude audio-frequency signal is added to the bias current or bias voltage and the attenuation of the signal determined by the avalanche photodiode and compared with a standard value. Deviations from the standard value manifest themselves in a reference signal of unspecified magnitude, which is used to re-adjust the bias current or bias voltage.