Patent ID: 7112777

Claim:
A method for protecting an avalanche photodiode (APD) of an optical receiver from overload optical signals, comprising: providing a feedback control loop for controlling a gain of the photodiode by measuring an optical power incident the photodiode, and computing and applying an optimal gain setting in accordance with changes in the measured optical power; using the measured optical power to detect a potential overload state in which the photodiode is susceptible to optical overload; controlling the feedback control loop so that if the potential overload state is detected, the feedback control loop is preempted and a predetermined safe gain setting is applied to the photodiode by a bias control circuit that modulates a reverse bias voltage across a depletion region of the APD; and determining that the measured optical power indicates that the photodiode is susceptible to overload when the measured optical power falls below a threshold that is associated with a loss of signal condition during which no signal is received at the photodiode.