Generation of In-Plane Light Beam with Orbital Angular Momentum with an Asymmetrical Plasmonic Waveguide

Based on silicon plasmonic waveguide with asymmetrical metal and dielectric coatings, we show that in-plane light beam with orbital angular momentum (OAM) in its axis field component could be generated by forming a pi/2 phase difference between two fundamental modes of the asymmetrical waveguide. At the same time, the transverse field components contain a spin angular momentum due to the polarization rotation in the asymmetrical waveguide. The whole structure is ultracompact with a footprint less than < 3 x 0.5 x 0.5 mu m. The proposed method to generate OAM beam in a waveguide would be interesting for on-chip integrated optical tweezers, information processing, etc.