Complete theoretical analysis of actively mode-locked fiber ring laser with external optical modulation of a semiconductor optical amplifier

We present a complete and extensive study of an actively mode-locked ring laser that uses a semiconductor optical amplifier (SOA) acting both as gain medium and mode-locker controlled by an external optical signal, including self-phase modulation (SPM) due to the SOA gain saturation by the recirculating mode-locked pulses and the associated imposed chirp. The operation of the different cavity elements is separately modelled and combined to obtain the self-consistent equation of mode-locking. The role of the critical parameters on the formation of the mode-locked pulses, which include the SOA linewidth enhancement factor, small signal gain and carrier lifetime, the external driving pulse width and energy and the bandwidth of the filter, as well as the simultaneous effect of SPM and dispersion is thoroughly investigated in order to specify the conditions that are required to obtain output pulses of short width and high energy. The adopted theoretical approach and the outcome of the simulation can form the basis for analyzing, evaluating and improving the performance of more complex, non-trivial implementations that exploit this ring laser platform and which are expected to find application in all-optical networks.