A circuit for detecting optical failures in a passive optical network (PON) wherein digital burst data transmitted by an optical transmitter is monitored by a photodiode, includes a power determination unit coupled to the photodiode for providing measurements of an output optical power of a high logic level and a low logic level of the digital burst data during ON times of the optical transmitter and for providing a measurement of an output optical power during OFF times of the optical transmitter. A logic unit coupled to the power determination unit is responsive to the measurements for generating control and calibration signals. Such a circuit may be used for detecting rogue optical network unit (ONU) failure or eye safety hazards in a passive optical network (PON) wherein digital burst data transmitted by an optical transmitter is monitored by a photodiode.