Study of nonlinear optical properties of Bi2Te3-Graphene longitudinal heterostructures and their application to fibre lasers

Abstract

Two-dimensional (2D) materials present numerous advantages as saturable absorbers in passive mode-locked lasers, including rapid response times, high saturation intensities, and excellent controllability. However, individual 2D materials often fall short of meeting the performance requirements for optical applications. To address this limitation, improved heterostructures combining different 2D materials are essential to mitigate the shortcomings of single materials and enhance overall performance. In this study, we investigated a van der Waals heterostructure saturable absorber (SA) composed of graphene (GR) and bismuth telluride (Bi₂Te₃), integrated with an organic thin film, through both simulation and experimental methods. The Bi₂Te₃-GR vertical heterostructure (BG-VHS) SA achieves fundamental mode locking (FML) with a pulse duration of 390 fs and harmonic mode locking (HML) with a repetition frequency of 1.406 GHz in an erbium-doped fibre (EDF) ring cavity. We measured the optical absorption intensity and modulation depth of the VHS SA and compared these results with those of the saturable absorbers composed solely of Bi₂Te₃ or GR. Our findings were further analyzed and interpreted through simulations focusing on carrier mobility and band gap variations. The composite structure exhibited favorable properties such as saturable absorption, indicating its strong potential for applications in saturable absorbers and mode-locked pulsed lasers.