Picosecond 1.3-μm bismuth fibre laser mode-locked by a nonlinear loop mirror

The influence of the concentration of bismuth active centres (BACs) in phosphosilicate fibres on their optical parameters, including gain coefficient and non-saturable losses, has been studied. A range of BAC concentrations optimal for designing ultrashort-pulse (USP) lasers was chosen based on the obtained results. The optimised fibre was used to fabricate an all-fibre 1.3-μm USP laser mode-locked by a nonlinear loop mirror, which emits 11.3-ps pulses with an energy of 1.65 nJ and a repetition rate of 3.6 MHz. A bismuth fibre amplifier made it possible to increase the pulse energy to 8.3 nJ. After compression in a diffraction grating compressor, the pulse duration decreased to 530 fs.