Abstract
Abstract Vortex field in photonic metamaterials has been revealed in recent years, which provides an extra degree of freedom to control the behavior of electromagnetic waves, such as the unidirectional propagation in topological metamaterials and orbital angular momentum multiplexing in optical fibers. Achieving topologically protected unidirectionality needs an external source either with a vortex index of m = ±1 (i.e. 2πm phase winding around phase singularity) or with a spin index of ±1 (i.e. right- or left-handed circular polarization). However, it is still an open question on the relationship between higher-order (|m | > 1) vortex field and topological metamaterials. Here, we study the excitation of valley bulk states by a source with a higher-order vortex index in Kagome photonic crystals. The selection rule for the excitation of valley bulk states is derived and can be applied to predict the selective excitation of valley bulk states by a source with a higher-order vortex index. Interestingly, we find that the Fourier spectrum and the averaged Fourier spectrum of the Ez component enable us to identify the vortex index of the source. Besides, it is shown that the unidirectional edge states can be excited by a source with a vortex index of 1 or 2 in a straight or 120° detour waveguide. Our work paves the way for the demonstration of the selection rule and may have potential applications in optical mode identification.
Highlights
Topological insulators are electronic materials featuring an insulating bulk but conducting edge or surface states [1, 2]
Vortex field in photonic metamaterials has been revealed in recent years, which provides an extra degree of freedom to control the behavior of electromagnetic waves, such as the unidirectional propagation in topological metamaterials and orbital angular momentum multiplexing in optical fibers
It has been theoretically demonstrated that valley photonic crystals (PCs) (VPC) can be applied to emulate the quantum valley Hall effect and hosts robust edge states that are immune to sharp bending [24, 25]
Summary
Topological insulators are electronic materials featuring an insulating bulk but conducting edge or surface states [1, 2]. As the analogues of topological insulators in electronic systems, photonic topological insulators (PTIs) support topologically protected edge states, which enable the realization of the robust propagation of electromagnetic waves against sharp bend and disorder [3,4,5,6,7,8]. Different from the spin of light that is limited to s = ±1, the vortex index of the phase vortex can be higher and be any integer up to infinity in principle (e.g. m = ±2, ±3) It is still unknown whether the vortex states in PCs can be selectively excited by a source with a higher-order vortex index. We study the excitation of valley bulk states by a source with a higher-order vortex index and. Our results pave the way for studying the relationship between higher-order vortexes and topological metamaterials
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
