A novel large scale all optical star coupler is presented. This star coupler can provide not only a great number of ports for very large scale bidirectional WDM network systems in future, but also the WDM star networks composed of this star coupler have the great flexibility of networking. Its capacities can be expanded conveniently and smoothly on line. At the same time, it also can be adapted in unidirectional WDM network systems used extensively now.