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In this paper, we demonstrated a signed chromatic dispersion (CD) monitoring method of 10 GHz nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) and return-to-zero differential phase-shift keying (RZ-DPSK) signals by using asynchronous delay-tap sampling and an imperfect tuned delay interferometer. This method could monitor not only the value but also the polarity of residual CD. The demodulated signals show amplitude shoulders on the rising edge or the trailing edge with CD accumulation. Delay-tap sampling scatter plots could reflect this signal distortion by a unique characteristic and realize the signed CD monitoring. The monitoring range can be up to plusmn400 and plusmn720 ps/nm for NRZ-DPSK and RZ-DPSK signals, respectively. Simulation and experimental results are also proposed.