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

Abstract

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 2^nd to 44^th 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.