WDM-PON Using Differential-Phase-Shift-Keying Remodulation of Dark Return-to-Zero Downstream Channel for Upstream

We evaluate the use of differential-phase-shift-keying modulation format in the remodulation of a downstream dark return-to-zero (DRZ) channel for the transport of upstream data in a wavelength-division-multiplexing passive optical network. To reduce complexity and costs of the optical networking unit (ONU) transceiver, we propose a system which does not have precise half-bit-delayed time control at ONU. The use of DRZ modulation format allows for a high extinction-ratio for the downstream data without the trade-off in the upstream data quality normally present with the use of conventional RZ modulation format for downstream data transmission. The 10-Gb/s bit-error-rate measurements were performed both for downstream and upstream signals.