We report a new optical performance monitoring technique based on the amplitude and phase histograms of the optical signal. The amplitude and phase histograms are obtained by using an intradyne receiver and the asynchronous delay-tap sampling method. From these histograms, we can evaluate the amplitude and phase Q-factors of the optical signal regardless of its modulation format. In addition, by using these Q-factors, we can estimate the bit-error rate (BER) of the monitoring signal. (C) 2009 Optical Society of America