Mitigation of Rayleigh Backscattering inWavelength Division Multiplexing PassiveOptical Network Based on WS-ASKModulation

A novel integration scheme from time-division-multiplex passive optical network (TDMPON) to wavelength-division-multiplex PON (WDM-PON) using differential Quadreture phase-shift keying (DQPSK) for the downstream signal and wavelength-shifted amplitude-shift keying (WS-ASK) for the upstream signal is illustrated. The migration scheme does not change the existing fiber infrastructure. An optical filter is preinstalled at the optical networking unit (ONU) to select the desirable downstream wavelength for the WDM-PON and simultaneously demodulate the downstream DQPSK signal. Signal remodulation is used to generate the upstream signal by reusing the downstream wavelength. In the ONU, by wavelength shifting the upstream optical spectrum with respect to the downstream optical spectrum, the Rayleigh backscattering (RB) interference beat noise affecting the upstream signal can be significantly mitigated. The optimum bandwidth for the downstream DQPSK demodulation is analyzed.