▎ 摘　　要

High-performance stable mode-locked fiber lasers (MLFLs) employing nano-composite polymer-graphene saturable absorber (SA) are demonstrated. The graphene layers were dispersed by two different dispersants including fluorinated MICA clay (MICA) and poly(oxyethylene)-segmented imide (POEM). Using the SA made by graphene dispersed in MICA with thickness and concentration product (TCP) of 36 (mu m*wt%), the MLFLs exhibited pulsewidth, 3-dB spectral bandwidth, and modulation depth (MD) of 393+/-14 fs, 6.6 nm, and 2.57%, respectively. By contrast, the graphene dispersed in POEM provides a TCP of 38 (mu m*wt%) to make the MLFLs deliver pulsewidth, 3-dB spectral bandwidth, and MD of 442+/-32 fs, 5.9 nm, and 1.70%, respectively. In comparison, the graphene SA dispersed by MICA performs a better MLFL pulse quality and uniformity than that dispersed by POEM. Both MLFLs with SAs fabricated by graphene/MICA and graphene/POEM reveal shortened pulsewidth and enhanced MD as the TCP increases. This observation indicates that the TCP and MD serve as key parameters for characterizing the MLFL pulsewidth. In this study, the nano-MICA dispersant is used for the first time to fabricate the graphene-polymer based SA film and has demonstrated highly stable and uniform ML pulse laser output. Judicious selection of dispersants for dispersing graphene in a homogeneous state is essential for enhancing the MLFL performance. This stable and uniform mode-locked pulse formation by employing the novel graphene-mediated SA has proven the high performance MLFLs that potentially applicable for a myriad of low-cost nano-devices.