Abstract-An improvement in the accuracy of the sinusoidal interference method used to extract bit-error rates (BERs) that cannot be easily measured with conventional laboratory equipment is proposed. This technique is then used to estimate the very low BER performance of a multiple-wavelength photonic switching node for a 16-wavelength packet payload. The switching node contribution to the estimated BER is determined to be no worse than 4 10 18 from an extrapolated -factor of 8.6.Index Terms-Bit-error rate (BER), packet switching, photonic switching systems, wavelength-division multiplexing (WDM).