Performance analysis in the equivalent photoconductive time-domain sampling of high-speed THz communication signals

In recent years, the photoconductive antenna (PCA) has been widely utilized for terahertz (THz) signal sampling and analysis due to its broadband response and ultrafast temporal resolution. When illuminated by ultrashort optical pulses from the mode-locked laser (MLL), PCAs exhibit transient photoconductivity, enabling high-speed THz signal sampling and analysis in the optical domain, which has been successfully applied to THz frequency measurement and THz communication signal analysis. However, the impact of noise interference, particularly time jitter and phase noise, on PCA-based THz signal sampling remains insufficiently explored. In this paper, a theoretical analysis of the time jitter and phase noise interference and effects on the sampling of on-off keying (OOK) and quadrature phase-shift keying (QPSK) signals is presented, followed by numerical simulations. To eliminate sampling errors caused by time jitter, the MLL repetition frequency is locked to an external reference source using a locking module while phase noise interference is compensated through the Viterbi and Viterbi algorithm. The effectiveness of the methods is validated through numerical simulations and experimental verification. The findings of this study provide valuable insights into optimizing PCA-based THz communication sampling systems, contributing to the advancement of broadband THz signal analysis.