Proposal of Inverse Pulse Position Modulation for Downstream Signal in Remodulation PON With PolSK-Modulated Multicast Overlay

Inverse pulse position modulation (PPM) is proposed for downstream data modulation in an optical network unit-source-free wavelength-division-multiplexed passive optical network, while optical amplitude shift keying (ASK) modulation is used for upstream data remodulation. In such a PON, polarization shift keying (PolSK) modulation overlay can be supported on the downstream signals for multicasting services. Our experimental results show that the inverse PPM optical ASK modulation for downstream data has small channel crosstalk with PolSK multicast data and ASK-remodulated upstream data. Compared with the approaches based on the Manchester code or inverse return-to-zero code, the proposed scheme based on inverse PPM has a better power margin, indicating a longer transmission distance and a higher tolerance to link loss.