Topological photonics aims to utilize topological photonic bands and corresponding edge modes to implement robust light manipulation. Importantly, topological photonics provide an ideal platform to study nonlinear interactions. In this talk, I will review some recent results regarding nonlinear interactions of one-way edge-modes in frequency mixing processes in topological photonic nanostructures. More specifically, I will discuss the band topology of 2D photonic crystals with hexagonal symmetry and demonstrate that SHG and THG can be implemented via one-way edge modes. Moreover, I will demonstrate that more exotic phenomena, such as slow-light enhancement of nonlinear interactions and harmonic generation upon interaction of backward-propagating edge modes can also be realized. Finally, FWM of topological plasmon modes of graphene plasmonic crystals and SHG upon interaction of valley-Hall topological modes of all-dielectric photonic crystals will be discussed.
Topologically protected plasmonic states with wide topological band gaps provide unprecedented robustness against disorder-induced backscattering. In this study, we design a graphene bi-layer metasurface that possesses valley-Hall topological plasmonic modes in a nontrivial bandgap. In particular, the breaking of mirror symmetry of two graphene layers is achieved via a horizontal shift of the hole lattice of the top layer, which leads to topologically protected edge modes in the nontrivial bandgap. The corresponding band dispersion of the topological edge modes shows unidirectional propagation features. Moreover, we have designed a sensitive molecular sensor based on such graphene bi-layer metasurfaces, using the fact that the chemical potential of graphene varies upon adsorption of gas molecules. This effect leads to a marked variation of the transmission of the topological mode, and thus a sensing device with large sensitivity can be realized.
We investigate topological photonic crystals specially designed such that the frequency band gaps appear around ω0, 2ω0, 3ω0 and, more importantly, each band gap contains exactly one unidirectional edge mode. These one-way edge modes are then utilized to implement key nonlinear frequency mixing processes, such as second- and third-harmonic generation.
We present several approaches for orders-of-magnitude enhancement of optical nonlinearities in specially engineered
nanostructures containing graphene and other 2D materials and illustrate how they apply to second- and third-harmonic
generation in such 2D-3D photonic heteromaterials. Applications to active photonic devices, such as nonlinear optical
gratings, are discussed as well.
Peculiar physical properties of graphene offer remarkable potential for advanced photonics, particularly in the area of nonlinear optics at deep-subwavelength scale. In this article, we use a theoretical and computational analysis to demonstrate an efficient mechanism for enhancing the third-harmonic generation in graphene diffraction gratings. By taking advantage of the relation between the resonance wavelength of localized surface-plasmon polaritons of graphene ribbons and disks their specific geometry, we can engineer the spectral response of graphene gratings so as strong plasmonic resonances exist at both the fundamental frequency and third-harmonic (TH). As a result of this dual resonance mechanism for optical near-field enhancement, the intensity of the TH can be increased greatly.