Investigation on the saturable absorption characteristics of GeNS and its application to harmonic mode‐locked modulation

Abstract The high‐quality germanene nanosheets (GeNS) were fabricated by a liquid‐phase exfoliated technique and used as the saturable absorber (SA) to generate the harmonic mode‐locked (HML) pulses in an Er‐doped fiber laser. The investigation on the nonlinear absorption effect of the GeNS was carried out systemically in this work. On the basis of the GeNS SA, the third‐ and fourth‐order HML pulses with repetition rates of 5.275 and 7.031 MHz were achieved, corresponding to the minimum pulse width of 3.04 and 3.21 ps, respectively. The research reveals that the GeNS has great capability for ultrafast pulses modulation and can be used as an outstanding nonlinear optical device to expand its applications in nonlinear optics.