CVD graphene-based low pump threshold bidirectional mode-locked fibre laser

A passively mode-locked femtosecond erbium-doped bidirectional fibre laser with low pump threshold using chemical vapour deposition grown graphene saturable absorbers is demonstrated. Two synchronised and counter-propagating soliton output pulse trains with a repetition rate of similar to 10.38 MHz and pulse widths of 660 and 860 fs are obtained simultaneously from the fibre laser. Simultaneous mode locking of the fibre laser has been realised with a threshold pump power of 56 mW from a single-pump laser diode, indicating an similar to 62% reduction in pump threshold compared to previous results.