Actively mode-locked optoelectronic oscillator for microwave pulse generation

Abstract

The optoelectronic oscillator (OEO) is the most widely investigated microwave photonic hybrid system for the generation of microwave signal with high frequency and low phase noise. It has been considered a reasonable and promising solution for obtaining pure microwave signal. Generally, a conventional OEO is used for the generation of only continuous microwave signal owing to the long mode building time of the oscillation cavity, leading to limited application areas. Here, the concept of actively mode-locking in fiber laser is introduced into the OEO, in which an external microwave signal with the frequency integral multiple of the free spectral range of OEO is injected to achieve a mode-locked condition. In this case, an OEO that can directly generate pulsed microwave signal with adjustable central frequency and time duration is demonstrated. Furthermore, by changing the frequency of the injection signal, harmonic mode locking with different orders can be easily achieved, while supermodes are confined. The proposed OEO has great potential in applications such as radars, communications and metrology.