A New Remodulation Scheme for WDM-PONs With Enhanced Tolerance to Chromatic Dispersion and Remodulation Misalignment

We investigate the use of differential phase-shift keying (DPSK) with a reduced modulation depth (RMD) as the downstream modulation format to enhance the tolerance to both chromatic dispersion and remodulation timing misalignment. Despite the RMD, in each optical network unit the demodulated DPSK signal from the destructive port of the delay-interferometer still maintains a high extinction ratio (ER), whereas the signal from the constructive port has a very low ER and can be readily remodulated by the upstream signal. Error-free operation at 10 Gb/s was achieved in a 20-km-reach experiment without dispersion compensation and remodulation synchronization.