Application of hierarchical modulation to optical access network

Hierarchical modulation is a technology for point-to-multipoint architectures that can simultaneously transmit multiple independent signals using a single wavelength/frequency. This paper reviews the principle of hierarchical modulation and introduces some application examples. For this interesting technology, we have proposed its use for coexistence of different generation passive optical networks (PONs). The validity of combining hierarchical modulation with star quadrature amplitude modulation (QAM) format in migrating the conventional 10G/channel class PON to the future digital coherent PON is shown.