Temporal Talbot effect using an intensity-modulating frequency-shifting loop

We investigate an all-fibered frequency-shifting loop (FSL) that includes an electro-optic intensity modulator (EOM) and an optical amplifier, and is seeded by a continuous-wave laser. At variance with frequency-shifted feedback lasers that contain an acousto-optic frequency shifter (AOFS), the EOM creates at each round-trip two side-bands that recirculate inside the loop. We experimentally and theoretically investigate the time response of the FSL in the fractional Talbot condition. Experimental results show that the intensity-modulating FSL generates short pulses with a repetition rate multiplication. We observe pulses at repetition rates tunable between 5.867 MHz and 715.8 MHz. The system is also modeled by a simple linear interference model that takes the amplitude modulation function and loop delay into account. The model predicts the fractional Talbot property as in AOFS-based systems, but with an additional amplitude modulation of the pulse train, in good agreement with the experimental results. This experiment shows an alternative approach to AOFS loops, taking advantage of the inherent bandwidth and tunability of the EOM. This fractional Talbot laser may find applications in optical sampling, THz generation and ultrafast data processing systems.