A signal remodulation scheme of 10-Gb/s differential phase-shift keying (DPSK) downstream and 10-Gb/s on-off keying (OOK) upstream using a semiconductor optical amplifier (SOA) and a Mach-Zehnder intensity modulator (MZ-IM) at the optical networking unit (ONU) side for wavelength division multiplexed passive optical network (WDM PON) is proposed. Simulation results indicate that error-free operation can be achieved in a 20-km transmission, and the receiver sensitivity of return-to-zero differential phase-shift keying (RZ-DPSK) is higher than nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) in the proposed scheme.