Coherent dual-frequency signal generation in an optoelectronic oscillator

Coherent dual-frequency microwave signal generation using an optoelectronic oscillator (OEO) is presented and demonstrated. In the proposed OEO, a dual-band bandpass filter (DB-BPF) is utilized to select two oscillation modes. An external signal is injected into the OEO loop with its frequency equaling the frequency interval of the two oscillation modes. Owing to the modulation nonlinearity of the Mach-Zehnder modulator, the two oscillation frequencies interact with the injection frequency. When the phase and gain conditions are satisfied within the loop, injection locking between the two oscillation signals will be established, and their phases will be synchronized. The effect of gain competition in the OEO loop, which leads to single-frequency oscillation, is suppressed. An experiment is carried out, and two frequencies, of 16.083 GHz and 9.998 GHz, are generated at the same time. The phase noise values are -140.1 and -141.0 dBc/Hz @ 10 kHz, respectively. The coherence between the generated signals and sidemode suppression performance are evaluated.