On-Chip Optical Vortex Generation and Topological Charge Control by Methods of Wave Vector Manipulation

Optical vortices (OVs) have received much attention in recent years and are widely explored in communication applications. The on-chip vortex emitter/modulator is preferred when it comes to photonic integration and chip-scale communication. However, the existing emitters/modulators suffer from either narrow bandwidths or extensibility problems, which actually degrade their ability to improve communication capacity. Here, we propose a metasurface OV emitter based on wave vector synthesis for vortex generation and modulation. A thorough theoretical analysis of the OV generation by two approximate methods was carried out, which suggests the superiority of Wave Vector method over Phase method. Afterwards, the wave vector manipulation implemented by Phase gradient metasurfaces was studied for controlling the topological charges of generated OVs. Finite element method simulations showed that, in the topological charge range of -6 to 6 and the wavelength range of 1.45 mu m to 1.55 mu m, the effective vortex emission efficiency of the proposed emitter is around 45%. The on-chip vortex generation and control by wave vector manipulation is a very promising technology for high-capacity inter-chip optical communication.