Investigations of the nonlinear optical properties of ZrGeTe 4 nanosheets and their application in ultrafast photonics

The new ternary anisotropic semiconductor ZrGeTe 4 has excellent potential to be a photonic device or a mode-locked device. However, its nonlinear optical (NLO) characteristics in ultrafast fiber lasers have not been demonstrated. Here, high-quality ZrGeTe 4 nanosheets (NSs) were prepared via the liquid phase exfoliation (LPE) method and characterized systematically. The NLO characteristics were measured at 1550 nm with a saturation intensity of 24.5 MW cm −2 and a modulation depth of 5.6%. The nonlinear absorption coefficient and nonlinear refractive index coefficient of the ZrGeTe 4 films measured using OA and CA Z-scan techniques were −1.08 × 10 3 cm GW −1 and −2.59 × 10 −3 cm 2 GW −1 , respectively. For the first time, ZrGeTe 4 NSs were applied as a saturable absorber (SA) for the soliton mode-locking pulse modulation in an Er-doped fiber laser (EDFL). Conventional soliton mode-locking (CS-ML) pulses and harmonic mode-locking (HML) pulses were all successfully realized. The shortest pulse duration of 1.74 ps for the CS-ML pulse was generated with a fundamental frequency of 11.754 MHz. The HML pulses with orders from 2 nd to 44 th were also observed, with the highest pulse repetition frequency of 517.2 MHz. The research results indicate that ZrGeTe 4 NSs have excellent NLO properties for high repetition rate ultrafast laser modulation, enabling them with high application potential in ultrafast nonlinear photonics.