Multichannel Polarization-Controllable Superpositions of Orbital Angular Momentum States

Abstract

An efficient approach to generate multiple orbital angular momentum (OAM) states and arbitrarily control their superpositions was reported. OAM states with different topological charges are realized in four separate channels using a single plasmonic metasurface consisting of space-variant arrays of gold nanoantennas without any additional optical elements. fabricate the designed metasurface, a standard electron-beam lithography (EBL) and lift-off process were used. First, the gold background layer (150 nm) and the SiO2 spacer (85 nm) were deposited onto a silicon substrate by using an electron beam evaporator. Then, the positive polymethyl methacrylate (PMMA) resist film was spin coated onto the SiO2 spacer layer and baked at 180 °C for 5 min. Then, the nanostructures were defined on the PMMA film by EBL. Prior to gold deposition, a titanium layer of 3 nm was deposited on the silicon dioxide (SiO2) layer for adhesion purposes. After that, a 30 nm gold film was deposited on the sample via electron beam evaporation. Finally, the metasurface structure was achieved by a subsequent lift-off procedure. Arbitrary manipulation of OAM superpositions in four channels is observed by controlling the polarization state of the incident light.