Pulse repetition frequency doubling in the regeneratively mode-locked fibre ring lasers

We demonstrate the pulse repetition frequency doubling in the regeneratively mode-locked fibre ring laser by exploiting the nonlinearity in the intra-cavity Mach-Zehnder intensity modulator. Optical pulses at a repetition rate of 4 GHz from the 2 GHz drive electronics are successfully generated. The resulting 4 GHz optical pulses exhibit a low amplitude noise of 0.9% and a total pulse-to-pulse timing jitter of 1.7 ps showing that the pulses are highly stable.