Reduction‐controlled graphene oxide saturable absorbers and its effect on ultrashort Er‐doped fibre laser

Abstract

The authors controlled the reduction of three graphene oxide (GO) saturable absorber (SA) thin films by controlling the exposure time under a solar simulator and afterwards, incorporated them into an Er-doped fibre laser in order to investigate their effect on ultrashort pulse. The authors also hypothesized that the controlled reduction would result in a controlled absorption, and ultimately, a controlled modulation depth. A larger modulation depth would lead to stronger pulse shaping and shorter pulse duration. Sample A was left unreduced, whereas samples B and C were exposed for 15 and 30 min, respectively. Afterwards, their modulation depths were measured using twin-detector method and determined to be 0.69%, 1.2% and 1.94%, respectively. When used as an SA in an Er-doped fibre laser, the result showed pulse duration shortening; from 670 to 520 fs, as well as spectral broadening; from 4.22 to 6.73 nm. In addition, we also observed changes in repetition rate, output power and time-bandwidth product (TBP). The result of this paper shows the feasibility of controlling the modulation depth of a GO SA and conclusively shows the effect of modulation depth on ultrashort pulse.