Investigations of the nonlinear optical properties of ZrGeTe4 nanosheets and their application in ultrafast photonics

The new ternary anisotropic semiconductor ZrGeTe4 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 ZrGeTe4 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 ZrGeTe4 films measured using OA and CA Z-scan techniques were −1.08 × 103 cm GW−1 and −2.59 × 10−3 cm2 GW−1, respectively. For the first time, ZrGeTe4 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 2nd to 44th were also observed, with the highest pulse repetition frequency of 517.2 MHz. The research results indicate that ZrGeTe4 NSs have excellent NLO properties for high repetition rate ultrafast laser modulation, enabling them with high application potential in ultrafast nonlinear photonics.