Optical networks with only a portion of their nodes capable of supporting multicast are called sparse splitting optical networks.In consideration of network performance and cost

optical networks are usually configured in a sparse light-splitting state.The multicast routing in these networks mainly aims at requesting to find appropriate light-trees or light-forests for the multipoint transmission of multicast traffic.This paper focuses on analyzing and summarizing the multicast routing mechanism and the relevant algorithms in current sparse splitting optical networks on the basis of integrated classification and forecasting the future work.