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A scheme for the mitigation of Rayleigh backscattering (RB) in hybrid passive optical networks (PON) is presented. Semiconductor optical amplifiers (SOA) of the optical network units (ONU) are advantageously used as nonlinear elements, exploiting Four-Wave Mixing (FWM) between the downstream signals to create a spectrally displaced optical upstream carrier. The proposed technique is experimentally proven in a long reach and high split PON, and the suppression of the pumps and further FWM products, obtained via a modified filtering scheme inside the PON, is analyzed. Full-duplex transmission at 10/2.5 Gb/s is demonstrated, showing that upstream transmission is possible despite low optical signal-to-RB ratios (OSRR) of ~ 12 dB.