Atomic-layer craphene as a saturable absorber for ultrafast pulsed lasers

Abstract

The optical conductance of monolayer graphene is defined solely by the fine structure constant, α= e2/hc (where e is the electron charge, h is Dirac's constant and c is the speed of light). The absorbance has been predicted to be independent of frequency. In principle, the interband optical absorption in zero-gap graphene could be saturated readily under strong excitation dueto Pauli blocking. Here, use of atomic layer graphene as saturable absorber in a mode-locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band is demonstrated. The modulation depth can be tuned in a wide range from 66.5% to 6.2% by varying the graphene thickness. These results suggest that ultrathin graphene films are potentially useful as optical elements in fiber lasers. Graphene as a laser mode locker can have many merits such as lower saturation intensity, ultrafast recovery time, tunable modulation depth, and wideband tunability. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.