Controllable microwave pulse generation in actively mode-locked optoelectronic oscillator based on electro-optic dual-drive Mach-Zehnder modulator

We present and demonstrate what we believe to be a novel approach to realizing controllable microwave pulse generation based on an actively mode-locked optoelectronic oscillator (AML-OEO) employing an electro-optic dual-drive Mach-Zehnder modulator (DDMZM). One radio-frequency (RF) port of the DDMZM is utilized to achieve feedback of the microwave pulse signal self-oscillated from the AML-OEO cavity, and the other RF port of the DDMZM is injected by an external low-frequency signal to realize mode locking. Through adjusting the direct-current (DC) bias voltage applied to the DDMZM, the gain distribution curve of the AML-OEO cavity varies accordingly, leading to the generation of microwave pulse trains with switchable repetition rates or definable pulse positions. Numerical simulation and experiment are performed to verify the feasibility of the proposed approach. The results show that microwave pulse trains with repetition rates identical to the free spectral range (FSR) of the cavity and half of the FSR are generated by tuning the applied DC bias voltage. Besides, microwave pulses with definable temporal positions are generated under a fixed repetition rate.