▎ 摘　　要

A stable passive Q-switched thulium-doped fibre laser (TDFL) operating at the 1900 nm region is demonstrated by using a multi-layer graphene film-based saturable absorber (SA). The graphene is synthesised by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulphate aqueous solution. Graphene flakes obtained from the process are mixed with polyethylene oxide as the host polymer to produce free standing composite thin film which acts as a passive Q-switcher in the TDFL ring cavity. At 793 nm pump power of 186 mW, the TDFL generates an optical pulse train with a repetition rate of 7.5 kHz, pulse width of 19.7 mu s and a pulse energy of 66.6 nJ. A higher performance Q-switched TDFL could be achieved with the optimisation of the graphene SA and the laser cavity.