Effects of Crosstalk Caused by Finite Extinction Ratio in Optical Time-Division Demultiplexer for PADC

Optical time-division demultiplexing photonic analog-to-digital converters (PADCs) represent a compelling paradigm for breaking the bandwidth-resolution trade-off of conventional electronic ADCs, yet inter-channel crosstalk induced by the finite extinction ratio of demultiplexing modulators imposes critical limitations on channel response flatness. Prior investigations have generally ascribed periodic response ripples exclusively to backend bandwidths narrower than half the total sampling rate, while the distortion behavior under wider bandwidths remains inadequately clarified. In this numerical work, we establish a full-link numerical model of a two-channel time-division demultiplexing PADC operating at a total sampling rate of 10 GS/s and systematically characterize crosstalk-induced frequency responses under four representative backend bandwidths (2.5, 5, 7.5, and 10 GHz) with an extinction ratio of 10 dB. Results demonstrate that prominent 10 GHz periodic ripples persist in the channel response even when the backend bandwidth exceeds half the sampling rate. The underlying spectral mechanism is elucidated: demultiplexed comb lines follow a 10 GHz periodic strength distribution, and sampling-generated sidebands inherit the amplitude of their parent comb teeth; the superposition of strong and weak sidebands within the passband governs the ripple magnitude. These findings furnish fundamental insights into crosstalk physics and deliver actionable guidance for device selection and system-level optimization in high-performance PADC implementations.