Actively Mode-Locked Optoelectronic Oscillator with Independently-Tunable Pulse Width and Repetition Frequency

A method for independently tuning the pulse width and the repetition frequency of the microwave pulse train generated by an actively mode-locked optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The innovation of this scheme is that the driving signal applied to the mode-locking device is not a conventional sinusoidal signal, but an amplitude-modulated signal. In such a case, with an appropriate setting of the loop gain, microwave pulse is generated only at the maximum amplitude of the driving waveform. Consequently, the carrier frequency of the driving signal regulates the pulse width, and its amplitude modulation frequency controls the repetition frequency. An experiment is carried out to verify the feasibility of the proposed method. In the experiment, three microwave pulse trains with a fixed repetition frequency of 179.64 kHz and pulse widths from 510 ns to 125 ns are generated. In addition, two microwave pulse trains with an identical pulse width of 125 ns and repetition frequencies of 359.28 kHz and 718.56 kHz are generated. This scheme greatly enhances the controllability of the mode-locked pulse train from an OEO, and also paves a way to generate ultra-short microwave pulses.