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WDM passive optical network with subcarrier transmission and baseband detection scheme for laser-free optical network units

We demonstrate a new scheme to achieve source-free optical network units (ONUs) in a wavelength-division-multiplexed passive optical network. The scheme utilizes subcarrier downlink transmission that enables penalty-free remodulation of the downstream signal for upstream transmission. The downstream data can be recovered at baseband either using an optical or electrical technique. In the optical scheme, the downstream signal is passed through a delay interferometer (DI) at the ONUs. A single variety of the DI is applicable to all ONUs that eliminates location-specific devices. Alternatively, the baseband data can be detected using a high-speed photodiode, a dc block, and a rectifier without any optical filter or phase locked loop for down-conversion. The upstream data is also detected at baseband without any modification to conventional receivers. We present experimental and simulation results for the scheme at 2-Gb/s downstream and upstream transmission over 20 km of fiber