Feasibility Study on a Scheme for Coexistence of DSP-Based PON and 10-Gbps/λ PON Using Hierarchical Star QAM Format

This paper presents a downlink scheme that permits the coexistence, on a passive optical network branch, of future DSP-based optical network units (ONUs) that can receive advanced modulation signals and legacy ONUs that can receive only on-off keying (OOK) signals. In the proposed scheme, the two types of signals, advanced modulation signals and OOK signals, are multiplexed by using a hierarchical star quadrature amplitude modulation (QAM) format and transmitted simultaneously on a single carrier. The design criteria and the feasibility of the proposal are discussed. The coexistence of 10G-class ONUs and DSP-based ONUs using hierarchical star 8-QAM format is numerically analyzed and experimentally evaluated. The results confirm that a 10-Gbps OOK signal and 30-Gbps star 8-QAM signal can be received with 30.5-dB loss budget by an APD and intradyne detector with DSP, respectively. The ability of the proposed approach to expand the coverage area is also introduced.