Nonlinear optical properties of anisotropic two-dimensional layered materials for ultrafast photonics

The discovery of graphene has intrigued the significant interest in exploring and developing the two-dimensional layered materials (2DI,Ms) for the photonics application in recent years. Unlike the isotropic graphene, a number of 2DLMs possess the in-plane anisotropic crystal structure with low symmetry, enabling a new degree of freedom for achieving the novel polarization-dependent and versatile ultrafast photonic devices. In this review article, we focus on the typical anisotropic 2DLMs including BP, ReS2, ReSe2, SnS, and SnSe and summarize the recent development of these anisotropic 2DLMs in the pulsed laser and the optical switch applications. First, we introduce the fabrication methods as well as the material characterization of the anisotropic 2DLMs by analyzing the polarized Raman configuration. Second, we discuss the anisotropic nonlinear optical properties of the anisotropic 2DLMs and concentrate on the anisotropic nonlinear absorption response. Next, we sum up state of the art of the anisotropic 2DLMs in the application of pulse lasers and optical switches. This review ends with perspectives on the challenge and outlook of the anisotropic 2DLMs for ultrafast photonics applications.