All-polarisation-maintaining modified figure-of-8 fibre laser as a source of soliton molecules

The conditions are identified, under which a figure-of-eight all-polarisation-maintaining fibre laser with two independently pumped active media, each in one of the two cavity loops, generates soliton molecules with adjustable number of solitons in the molecule. The soliton count in the molecule may be reproducibly set between 2 and 6 by adjustment of the ratio of the pump powers of the active media. The average duration of the autocorrelation function of a single soliton is 11.6 ps, the repetition rate of the pulse train is 14.19 MHz, and its average spectral width is 10 nm. An analysis of the map of the mode-locked regimes set by different ratios of the pump source powers has shown that there exist two separate areas, one corresponding to generation of noise-like pulses and the other, to generation of soliton molecules. We believe that our findings will extend the application area of soliton molecules and will further bring a new insight into understanding of soliton molecule formation inside fibre cavities. (letter)