Chapter 9 - 2D materials in nonlinear optics

Abstract

Since the rise of 2D materials revealing a variety of striking nonlinear optical (NLO) phenomena, optical signal processing (OSP) applications based on the NLO properties of low-dimensional nanomaterials, such as on-chip light source, optical holography, optical switch, and optical neural network, have been further developed. Compared to the bulk material, due to 2D materials consist of only a single layer of atoms and lack of the shielding effect, so the interaction between the electron and holes is significantly enhanced and the nonlinear susceptibilities 〖(χ〗^((n)), n≥2) are also increased by several orders of magnitude. In addition, different 2D materials have different electronic band structures that allow existing 2D materials to cover a broadband of electromagnetic spectrum from the ultraviolet to microwave ranges. Unlike traditional bulk materials such as silicon, germanium, and III-V compound semiconductors, 2D materials have many unique electrical, optical, thermal, and mechanical properties. The optoelectronic properties can be modulated through the extremely large surface-to-volume ratios of 2D materials. Their surface is naturally passivated without dangling bonds and is easier to combine with different micro–nano structures such as optical waveguides and cavities. In this chapter, we summarize the NLO properties of typical 2D materials, including graphene, black phosphorus, topological insulators, transition metal chalcogenides, and hexagonal boron nitride, which will play an important role in OSP.