Dispersion-tuned mode-locked optoelectronic oscillator

A dispersion-tuned mode-locked optoelectronic oscillator (OEO) is demonstrated for the first time, to the best of our knowledge. A flat and highly chirped microwave photonic filter with a large bandwidth within the OEO, which is essential for dispersion tuning, is realized by employing a sliced amplified spontaneous emission (ASE) source and a 1.1 km dispersion-compensating fiber (DCF). A recirculating loop is used to form a comb filter that ensures single-mode oscillation in the free-running state and maintains the sidemode suppression ratio under harmonic mode-locking. As the modulation frequency is swept from 10.3122 MHz to 10.3042 MHz, corresponding to approximately 58-order harmonic mode-locking and matched to the comb-filter period, the OEO output frequency exhibits discrete tuning from 4.08 GHz to 5.08 GHz, with a total of four distinct frequency steps. This work opens up a new approach to frequency control in OEOs.