Harmonically Fourier Domain Mode-Locked Optoelectronic Oscillator

We experimentally demonstrate a harmonically Fourier domain mode-locked optoelectronic oscillator (FDML OEO). Harmonic Fourier domain mode locking operation is achieved when the cavity round-trip time is equal to integer multiples of the scanning period of the filter in the OEO loop. Compared with a fundamentally FDML OEO, frequency scanning microwave signals with increased tuning speed and large bandwidth can be easily generated by the proposed harmonically FDML OEO, which can find applications in spread-spectrum communication and modern radar systems. Up to fourth order, harmonic Fourier domain mode locking operation is achieved in the experiment. The time-bandwidth product of the harmonically FDML OEO is as large as tens of thousands. The maximum chirp rate of the generated X-band linearly chirped microwave waveform is 0.725 GHz/μs, which is four times higher than that of the fundamentally FDML OEO.