We propose two novel wavelength-division-multiplexed passive-optical-network (WDM-PON) architectures where subcarriers are employed to transmit downstream data and optical carriers are reused for upstream transmission. Architecture I is designed for the situation where two short distribution fibers are available between the remote node (RN) and each optical network unit (ONU), whereas Architecture II is devised for the case where there is only one distribution fiber between the RN and each ONU. Both architectures use only one interferometric filter located at the RN to simultaneously separate all downlink optical carriers and subcarriers, leading to a considerable cost reduction in the implementation of the WDM-PONs. Separated optical carriers are then reused and injected into reflective semiconductor optical amplifiers as the uplink light sources, which eliminates the necessity of specific wavelength sources at the ONUs. The downstream subcarrier signals are directly detected using baseband receivers. Two multichannel upstream and downstream transmission experiments are carried out at 1.25 Gb/s using the proposed schemes. The impact of optical carrier-to-subcarrier ratio of downlink signal, Rayleigh-backscattering noise, and wavelength mismatch between laser source and filter on system performance is also investigated.
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