Based on the single-periodic and multi-periodic oscillation states of an optically injected semiconductor laser,a scheme for the generation of an ultra-broadband microwave frequency comb through the cascaded optical injection of semiconductor lasers is proposed.In this scheme,the optical frequency comb produced from a slave laser with continuous-wave injection is injected into another one,to generate a microwave frequency comb with much wider bandwidth due to the optical injection effect of laser.The numeri...