Coherent dual-frequency microwave signal generation based on self-injection-locked optoelectronic oscillator

In this paper, we propose and experimentally demonstrate an approach to generate a coherent dual-frequency microwave signal based on a self-injection-locked optoelectronic oscillator (OEO). In this scheme, an electrical bandpass filter (BPF)with two passbands is used to select two oscillation modes for the final output. The key point of this scheme lies in that an electrical mixer is employed to generate the injected low-frequency signal. By passing the two initial oscillation modes through the mixer, a beating signal centered at the difference frequency between the two oscillation modes can be obtained and further injected into the OEO cavity to lock the phase relationship between the two frequency components. In such a case, a dual-frequency microwave signal with high coherence can be generated by this self-injection-locked OEO, without the assistance of any external source. A proof-of-concept experiment is carried out to demonstrate the feasibility of the proposed scheme, where a coherent dual-frequency microwave signal with frequencies of 10 GHzand10.1 GHz is obtained. The sidemode suppression ratio (SMSR) and the phase noise of the generated dual-frequency microwave signal are 38 dB and -130 dBc/Hz@10 kHz, respectively. In addition, the coherence of the generated dual frequency microwave signal is also verified.