Q-switched mode-locked Er-doped fiber laser with few-layer germanene nanosheets

Abstract

Germanene (Ge) has a Dirac-type electronic structure similar to that of graphene and has excellent nonlinear saturable absorption properties, which has attracted extensive research. In this paper, few-layer Ge nanosheets were prepared and characterized in detail. Its nonlinear modulation depth was measured to be 8.5%, and the saturation intensity was 0.12 GW/cm 2 . Ge nanosheets are used as a saturable absorber (SA) in an Er-doped fiber laser (EDFL) to obtain a stable Qswitched mode-locking (QML) pulse. As the pump power (Ppump) increases from 64.2 mW to 204 mW, the repetition frequency (RF) and pulse width of the Q-switched (QS) envelope increase from 46.2 KHz to 109 KHz and decrease from 4.4 μs to 2.25 μs, respectively. The mode-locked pulse has a RF of 30.2 MHz with a center wavelength of 1559.6 nm. The QML pulses obtain a maximum output power of 2.278 mW and a maximum pulse energy of 20.9 nJ when the Ppump is 204 mW. Our study proves that Ge, as a high-energy light pulse absorbing material, can be used in the field of ultrafast laser.