Photonic frequency-octupling scheme for stable microwaves generation based on two incoherent optical sources

In this paper, a real-time frequency-octupling photonic generator scheme that can realize stable microwave signal generation by using two incoherent optical sources without the support of phase-locked loops is successfully demonstrated, which proves that the improved feed-forward modulation is a feasible method for reducing phase noise. The principle of the proposed generator is illustrated by theory, simulation, and experiment. A 16GHz stable microwave signal with a bandwidth less than 0.2MHz is generated by using a 2GHz driving signal, and a 64GHz optical millimeter wave signal is obtained by using an 8GHz driving signal. Furthermore, a purity 320GHz terahertz wave signal is obtained by simulation based on the same principle and setup. The results show that the terahertz signal has good transmission characteristic and fine eye diagram in the 40.5km fiber link. In addition, to enhance the flexibility and feasibility of the generator, the feasible range of the modulation index and a signal enhancement method are also explored.